Uploaded byBrajendraKumar56
67 views

ajajhsoaoqkwhsja81818272814473wloiwuwo928828282818sd.pdf

The document provides a comprehensive overview of haloalkanes and haloarenes, including their classifications, properties, preparation methods, and examples. It outlines different types of haloalkanes such as monohalides, dihalides, trihalides, and tetrahalides, along with preparation methods like halogenation and substitution reactions. Key concepts related to reactivity, structure, and specific reactions for the formation of various haloalkanes and haloarenes are also discussed.

Download to read offline
1. Haloalkanes and Haloarenes Haloalkanes Haloalkanes are the halogen deivatives of hydrocarbons. Classification of Haloalkanes Monohalides (R–X): Monohalides are monohalogen derivatives of alkanes which have a general formula Cn H2n+1 X and are known as alkyl halides. R–X may be of three types: 1. Primary R–CH2 X 2. Secondary R2 CHX 3. Tertiary R3 CX Dihalides (Cn H2n X2 ): Dihalides are the di-halogen derivatives of alkanes and are of geminal and vicinal types. Example (a) CH3 CHBr2 (Ethylidine dibromide), (b) BrCH2 CH2 Br (Ethylene dibromide) Trihalides (Cn H2n–1 X3 ) or haloforms: Trihalides are tri-halogen derivatives of alkanes and are represented by a general formula CHX3 (haloforms). Tetrahalides: Tetrahalides are tetra-halogen derivatives of alkanes and arerepresented by a general formula CX4 or CX2 Y2 . Aromatic Halogen Compounds When halogen atom is attached to aromatic hydrocarbons directly to the ring , the substance is known aryl halides. Their general formula is Ar—X. Haloalkanes and Haloarenes Concept Ladder In haloalkanes, the halogen atom is attached to the sp3 - hybridised carbon atom of an alkyl group whereas in haloarenes, the halogen atom is attached to sp2 - hybridized carbon atom of an aryl group. Definitions The monohalogen derivatives of alkanes are called alkyl halides or monohaloalkanes or simply haloalkanes. Concept Ladder Haloalkynes or Alkynyl halides are the halogen derivatives of alkynes. The monohalogen derivatives of alkynes have the general formula Cn H2n-3 X where X=F, Cl Br or I and n = 2, 3, 4....., etc.
2. Haloalkanes and Haloarenes (a) Mono Halogen Derivatives Examples (i) Chlorobenzene (ii) p-Bromotoluene (iii) Bromobenzene (iv) m-Bromotoluene (b) Side chain Halogen Derivatives Example (i) Benzyl chloride (ii) b-Phenylethyl bromide Allylic, Vinylic and Benzylic Halides (a) Allylic Halides Example (i) 3-Haloprop-1-ene (1°) (ii) 3-Halo-3-methylcyclohex-1-ene (3°) (b) Vinylic Halides (i) Chloroethene (ii) 1-Chloroprop-1-ene (c) Benzylic Halides (i) Benzyl halide (1°) (ii) A benzylic halide (3°)
3. Haloalkanes and Haloarenes Methods of preparation Halogenation of alkanes hv 2 R H X R X HX − +  → − + For example hv 4 2 3 2 2 3 4 or520 650K CH Cl CH Cl CH Cl CHCl CCl − +  → + + + 2 Cl ,hv 3 2 3 3 2 2 3 3 298K Propane 1 Chloropropane (45%) 2-Chloropropane (55%) CH — CH — CH CH — CH — CH — Cl CH — CHCl — CH −  → + 2 Cl ,hv 3 2 2 3 3 2 2 2 3 2 3 298 K Butane 2 Chlorobutane (72%) 1 Chlorobutane(28%) CH CH CH CH CH CH CH CH Cl CH CH — CHCl — CH − −  → + In general, the ease of subsitution of various hydrogens follows the sequence: Allylic > 3° > 2° > 1° > CH4 Reactivity order in halogens: F2 > Cl2 > Br2 > I2 Iodination is reversible, but it may be carried out in presence of an oxidising agent, such as, HIO3 , HNO3 , HgO, etc., which oxidises the HI as it is formed. hv 4 2 3 3 2 2 CH I CH I HI ; 5HI HIO 3I 3H O + + +  → +     Flourination: The best way to prepare alkyl fluorides is by halogen exchange. An alkyl chloride or bromide is heated in the presence of a metallic fluoride, such as AgF, Hg2 F2 , CoF3 or SbF3 to give alkyl fluorides. 3 3 Bromomethane Fluoromethane CH Br AgF CH F AgBr +  → + 3 2 2 2 3 2 2 2 2CH CH Cl Hg F 2CH CH F Hg Cl +  → + This reaction is called Swarts reaction. When the organic halide contains two or three halogen atoms at the same carbon, CoF3 or the more easily available SbF3 is used. For example, from Alcohols : Generally alkyl halides are prepared from alcohols by replacement of —OH group by an halogen ion. This is usually by using HX or PX5 . R – OH + X–  → R – X + OH– 3 2 3 3 3 2 3 3 2, 2 Dichloropropane 2,2 Difluoropropane 3CH CCl CH 2SbF 3CH CF CH 2SbCl − − +  → + Concept Ladder Vinylic and aryl hydrogen are so much unreactive that they do not participate in free radical halogenation. However, allylic and benzylic halides can be prepared from alkenes and arenes without any complication. Definitions Swarts' reaction is generally used to get alkyl fluorides from alkyl chlorides or alkyl bromides. This is done by heating of the alkyl chloride/bromide in the presence of the fluoride of some heavy metals (silver fluoride or mercurous fluoride for example).
4. Haloalkanes and Haloarenes (a) By the action of Halogen acids : R – OH + HX Catalyst  → R – X + H2 O (i) Using HCl : ( ) 2 2 anhy. ZnCl 3 2 3 2 2 anhy. ZnCl 3 3 3 3 2 CH CH OH HCl g CH CH Cl H O CH — CH— CH HCl CH — CH— CH H O | | Cl OH +   → + +   → + Anhydrous ZnCl2 helps in the cleavage of C–O bond. Being a Lewis acid, it co-ordinates with the oxygen atom of the alcohol. As a result, C–O bond weakens and ultimately breaks to form carbocations, which form chlorides. ( ) ( ) ( ) Room 3 3 2 temp 3 3 conc. CH C— OH HCl CH C — Cl H O +  → + Yield is improved when vapours of alcohol and HCl are passed over alumina at 350°C. (ii) Using HBr : Alkyl bromides are obtained by refluxing the alcohol with constant boiling in HBr (40%) in presence of a little conc. H2 SO4 2 4 H SO 3 2 3 2 2 Reflux 2 5 2 4 2 5 4 2 CH CH OH HBr CH CH Br H O C H OH KBr H SO C H Br KHSO H O +  → − + + +  → + + (iii) Using HI : Reflux 3 2 3 2 3 3 4 3 2 4 2 CH CH OH HI CH CHI H O CH OH KI H PO CH I KH PO H O ∆ +  → + + +  → + + (b) By the action of Phosphorus Halides: Phosphorus halides react with alcohols to form haloalkanes in excellent yield (80% or above). ROH + PX5  → R – X + POX3 + HX Here X can be either chlorine or bromine or iodine. 3ROH + PX3  → 3R – X + H3 PO3 Concept Ladder Order of reactivity of the halogen acids HI>HBr>HCl. Order of reactivity of Alcohols: R3 COH > R2 CHOH > RCH2 OH Concept Ladder In alkyl halide electro -negativity difference between the carbon and the halogen, the shared pair of electron lies closer to the halogen atom. As a result, the halogen carries a small negative charge, and carbon carries a small positive charge. So, C—X bond is always a polar covalent bond.
5. Haloalkanes and Haloarenes Since, PI3 and PBr3 are not very stable compounds, these are generally prepared in situ by the action of red phosphorus on bromine and iodine respectively. 2 2 P Br P I 4 2 3 P 6X 4PX ; R — OH R —Br; R — OH R I + + +  →  → → − This method gives good yield of primary alkyl halides but poor yields of secondary and tertiary alkyl halides. The method is generally useful for preparing lower alkyl bromides and iodides in laboratory. (c) By the action of Thionyl chloride : (Darzen’s method) Chloroalkanes are conveniently prepared by refluxing alcohol with thionyl chloride (SOCl2 ) in presence of pyridine (C5 H5 N). Pyridine 2 2 Reflux R — OH SOCl R — Cl SO HCl + → + ↑ + ↑ Thionyl chloride method is preferred over hydrogen chloride or phosphorus chloride method for the preparation of chloroalkanes since both the by-products (SO2 and HCl) in this reaction being gases escape, leaving behind chloroalkanes in almost pure state. 3. From Silver salt of fatty acids : This reaction is called as Borodine Hundsdiecker reaction and is a free radical reaction. This reaction gives the product with one carbon atom less than the fatty acid. The yield of the alkyl halide formation with this reactions is : 4 CCl ,Reflux 3 2 2 3 2 2 CH CH COOAg Br CH CH —Br CO AgBr + → + + primary > secondary > tertiary. Chloroalkanes can also be prepared by this method by using Cl2 instead of Br2 but the yields are poor. With I2 , silver salts give esters instead of iodoalkanes. 2 2 2 2RCO Ag I RCOOR CO 2AgI +  → + + Concept Ladder Iodoalkanes or alkyl iodides are prepared by refluxing a suitable alcohol with constant boiling hydriodic acid (57%). HI may also be generated in situ by the action of 95% phosphoric acid on KI. Previous Year’s Question The compound C7 H8 undergoes the following reactions : 2 2 3Cl / Br /Fe Zn/HCl 7 8 C H A B C ∆  →  →  → The product C is [NEET] (1) m-bromotoluene (2) o-bromotoluene (3)3-bromo-2,4,6-trichlorotoluene (4) p-bromotoluene.
6. Haloalkanes and Haloarenes 4. Halogen exchange reaction : Iodoalkanes are easily prepared from corresponding chloroalkanes or bromoalkanes by heating with sodium iodide in acetone or methanal. This reaction is called Frinkelstein Reaction. Acetone RCl NaI RI NaCl; X Cl or Br ∆ +   → + = Its a halide exchange reaction which involves a substitution of Cl/Br by I. The reaction was specially de signed to prepare iodo-alkanes which were not easily prepared using simple halogenation method. (Due to the reversibility of Iodination) Acetone R — X NaI R I NaX ; X Cl or Br +  → − + ↓ = Reaction is supposed to be based on principle of greater solubility of NaI in acetone as compared to NaCl or NaBr because of greater covalent character in NaI. That is why despite of being a weaker reagent than Cl- / Br- , I- still substitues them and the NaCl/NaBr formed precipitates out driving the equilibrium in forward direction. from Alkenes : Alkenes react with halogen acids to form haloalkanes. Order of reactivity : HI > HBr > HCl > HF. 2 3 RCH CH HX RCH— CH | X = +  → The unsymmetrical alkenes follows Markovnikov’s rule during addition forming secondary or tertiary alkyl halides predominantly. ( ) ( ) HBr HBr 3 3 2 2 3 2 2 Peroxide Peroxide CH — CH— CH CH CH CH CH CH CH Br | Br ←  =  → (c) Allylic halogenation :When alkenes (except Ethylene) are heated with Cl2 or Concept Ladder Peroxide effect is observed only for HBr. So HCl and HI when added to alkene give same product in presence of absence of peroxide. Previous Year’s Question The reaction of C6 H5 CH=CHCH3 with HBr produces [NEET] (1) C6 H5 CH2 CH2 CH2 Br (2) (3) 6 5 2 3 C H CHCH CH | Br (4) 6 5 2 3 C H CH CHCH | Br .
7. Haloalkanes and Haloarenes Br2 at a high temperature of about 773 K, the hydrogen atom at the allylic carbon (i.e., carbon next to the double bond) is substituted by a halogen atom. For example, ( ) 773K 3 2 2 2 2 3 Chloroprop 1 ene Allyl chloride CH — CH CH Cl Cl — CH — CH CH − − − = +  → = However, a more specific reagent for allylic bromination is N-bromosuccinimide (NBS). Allylic chlorination can also be carried out with sulphuryl chloride. 475, hv 3 2 2 2 2 2 2 Traces of peroxide CH — CH CH SO Cl Cl — CH — CH CH HCl SO = + → = + + Previous Year’s Question When chlorine is passed through propene at 400°C, which of the following is formed? [NEET] (1) PVC (2) Allyl chloride (3) Propyl chloride (4) 1, 2-Dichloroethane Definitions Reactions in which halogenation occurs at the allylic position of an alkene are called allylic halogenation reactions.
8. Haloalkanes and Haloarenes Physical properties of monohalides y Lower members of monohalides(CH3 X, C2 H5 X) are colourless gases while higher members are colourless liquid up to C18 , members are colourless solids. y Boiling point and density increase with increase in molecular weight. C4 H9 Cl C3 H7 Cl C2 H5 Cl CH3 Cl RI RBr RCl RF Likewise it happens in alkanes, branching also decrease B.P y Dipole moment: RCl RF RBr RI y Stability : RF RBr RCl RI y Solubility α 1 Mol. wt. In general: CH3 X C2 H5 X C3 H7 X C4 H9 X Concept Ladder CH3 Cl, CH3 Br, C2 H5 Cl, some chlorofluoromethanes are gases at room temperature. Higher chloro, bromo, iodo compounds are either liquids or solids. Many volatile halogen compounds have sweet smell. Haloalkanes are less soluble in water, why? Haloalkanes are polar molecules, neither they form H-bond with water nor can thye break the H-bonds already existing between water molecules. As a result, the solubility of haloalkanes in water in very low. Q.1 A.1 Rack your Brain n-Butyl bromide has higher boiling point than t-butyl bromide. Give reasons?
9. Haloalkanes and Haloarenes
10. Haloalkanes and Haloarenes Chemical Properties of Monohalides y Since the is polar, these are reactive compounds. y The reactivity order is as follows: R3 CX R2 CHX RCH2 X RI RBr RCl CH3 X C2 H5 HX C3 H7 X …. Nucleophilic substitution reactions: Alkyl halides undergo nucleophilic substitution reactions as follows: .. .. Strong Nucleophile R X R Z Z X +δ −δ − +  → − + This reactions occurs by either SN 1 or SN 2 mechanism. For example, y Aq.KOH R X R OH HX −  → − + y AgOH R X R OH AgX −  → − + y Alc.KCN R X R CN KX −  → − + R–CN is major product as KCN being ionic, provides CN– ions. Therefore, attack occurs from the carbon atom side. y AgCN R X R NC AgX −  → − + Major product is R–NC as AgCN being covalent cannot give CN– ions. Therefore, attack occurs from nitrogen atom to give R–NC. y 2 AgNO 2 Nitroalkane R X R NO AgX −  → − + y 2 KNO Alkylnitrite R X R O N O KX −  → − − = + y 3 NaN 3 Azides R X R N NaX −  → − + y R'COOAg R X R'COOH AgX −  → + y R'ONa R X R' O R NaX −  → − − + The above reaction is called williamson synthesis. Definitions Reaction in which a stronger nucleophile displaces a weaker nucleophile are called nucleophilic substitution reaction and the atom or group which departs with its bonding pair of electrons is called the leaving group. Concept Ladder Š Order of reactivity of haloalkanes: RI RBr RCl RF Š Order of leaving tendency : I­ - Br- Cl- F- Previous Year’s Question In a SN2 substitution reaction of the type DMF R —Br Cl R — Cl Br − − + → + which one of the following has the highest relative rate? [NEET] (1) 3 3 2 3 CH | CH — C — CH Br | CH (2) CH3 CH2 Br (3) CH3 CH2 CH2 Br (4) 3 2 3 CH — CH— CH Br | CH .
11. Haloalkanes and Haloarenes
12. Haloalkanes and Haloarenes
13. Haloalkanes and Haloarenes y 2 5 2 R'SNa C H OH/H O Thioether R X R' S R NaX −  → − − + y 2 Na S R X R S R 2NaX −  → − − + y 6 6 3 C H 6 5 Anhyd.AlCl R X C H R HX −  → − + The above reaction is called Friedel–Crafts reaction. 2 Moist Ag O R X R OH −  → − y 2 Ether Dry 2R X Ag O R O R 2AgX − +  → − − + y Alkyne R X NaC CR' R C C R' NaX − + ≡  → − ≡ − + 3 NH X R 2 HX HX R X R NH − − − −   → −   → Dehydrohalogenation It involves α, β-elimination following E1 and E2 mechanisms. y Here, α, β-elimination reaction takes place as follows: In case of tertiary and secondary halides, elimination dominates over substitution while in Primary-halides substitution is dominating. Low polarity of solvent, high temperature and strongness of base also favour elimination over substitution. Concept Ladder When elimination and substitution are competing reaction Rack your Brain Ethyl iodide undergoes SN 2 reaction faster than ethyl bromide? Previous Year’s Question Which of the following undergoes nucleophilic substitution exclusively by SN 1 mechanism? [AIPMT] (1) Ethyl chloride (2) Isopropyl chloride (3) Chlorobenzene (4) Benzyl chloride.
14. Haloalkanes and Haloarenes Br CH CH CH CH CH CH CH CH CH CH alc KOH Major 3 2 2 3 3 2 3 | . C CH CH CH CH CH Minor 3 2 2 2 Saytzeff’s Rule According to Saytzeff’s rule, removal of b-Hydrogen atom takes place from b-carbon atom having more number of alkyl groups, so that a more stable alkene is formed. e.g., In case of a fluoro-alkane or other secondary halide, with very strong base like (CH3 )3 COK or C2 H5 ONa, major product (Alkene) is according to Hoffmann’s Rule. According to it, b-Hydrogen atom is eliminated from b-Carbon atom with less H-atom or less acidic b-H-atom which means less stable alkene is major product. CH CH CH CH CH CH CH CH CH CH CH CH KOH Minor 3 2 3 3 3 2 2 3 | , M Major Minor F CH CH CH CH CH CH CH CH 3 2 3 3 3 3 3 | CH COK, CH CH CH CH X Major 2 2 3 Reaction with metals (a) Reaction with Na (Wurtz reaction) Dryether R X 2Na X R R R 2NaX − + + −  → − + (b) Reaction with Zn ( Frankland reaction) 2 R X Zn X R R R ZnX ∆ − + + −  → − + (c) Reaction with Mg Dryether Grignardreagent R X Mg R Mg X − +  → − − R may be —CH3 , —C2 H5 , —C6 H5 etc. Reactivity order for R–MgX is given as CH3 X C2 H5 X C3 H7 X R–I R–Br R–Cl Previous Year’s Question Elimination reaction of 2-bromopentane to form pent-2-ene is (A) b-Elimination reaction (B) Follows Zaitsev rule (C) Dehydrohalogenation reaction (D) Dehydration reaction [NEET] (1)  (A), (B), (C) (2) (A), (C), (D) (3) (B), (C), (D) (4) (A), (B), (D)
15. Haloalkanes and Haloarenes
16. Haloalkanes and Haloarenes (d) Reaction with lead sodium alloy 2 5 2 5 4 Tetraethyllead 4C H Br 4Pb(Na) (C H ) Pb 4NaBr 3Pb +  → + + y Tetraethyl lead (TEL) has anti-knocking properties used in petrol to avoid knocking. (e) Reaction with lithium Ether R X 2Li R Li LiX − +  → − + Reduction 4 LiAlH R X 2[H] R H Hx − +  → − + Heating effect 560 C 2 2 2 R CH CH R CH CH HX ° − −  → −= + Isomerination Dihalides Gem or geminal halide or alkylidene halides Methods of preparation of geminal halides 1. From aldehyde or ketone O Cl CH C H PCl CH C H PCl Cl Dichloroethane O Cl CH 3 5 3 5 3 || | | C C CH PCl CH C CH PCl Cl Dichloropropane || | | , 3 5 3 3 5 2 2 Concept Ladder Organic lead (tetraethyl lead; TEL) is used as an antiknock agentingasolineandjetfuels. TEL is absorbed rapidly from the skin as well as the lungs and gastrointestinal tract and is converted to triethyl lead in the body. This form of lead may be responsible for its toxic effects. Previous Year’s Question Grignard reagent is prepared by the reaction between [NEET] (1) magnesium and alkane (2) magnesium and aromatic hydrocarbon (3) zinc and alkyl halide (4) magnesium and alkyl halide.
17. Haloalkanes and Haloarenes 2. From alkyne Chemical properties of geminal halides (Alkylidene halides) These are less reactive than the alkyl halides due to the fact that the presence of one-X-atom (E.W.G) makes the replacement of other X-atom slightly difcult. 1. Reaction with alcoholic KOH 2. Reaction with aqueous KOH Here, R–CHO, R–CO–R are formed 3. Reaction with KCN 4. Reaction with Zn CH CH Br Zn CH CH ZnBr Br CH OH 3 2 2 3 | , Previous Year’s Question A compound of molecular formula C7 H16 shows optical isomerism, compound will be [NEET] (1)  2,3-dimethylpentane (2) 2,2-dimethylbutane (3) 2-methylhexane (4) none of these
18. Haloalkanes and Haloarenes Vic or vicinal dihalide or alkylene halides Methods of preparation of vicinal dihalides 1. From alkenes 2. From diols like glycol Chemical properties of vicinal dihalides: They are as reactive as alkyl halides. 1. Reaction with KOH 2. Reaction with KCN 3. Reaction with Zn Trihalides or Haloforms (CHX3 ) Chloroform (CHCl3 ) y Chloroform was discovered by Justus Von Liebig and named by Jean-Baptiste Dumas. y It has anesthetic nature which was discovered by James Young Simpson. Methods of preparation 1. From chloral 3 3 CCl CHO NaOH CHCl HCOONa ∆ +  → + Previous Year’s Question Industrial preparation of chloroform employs acetone and [AIPMT] (1)  phosgene (2) calcium hypochlorite (3) chlorine gas (4) sodium chloride Concept Ladder Geminal dihalides have both halide groups attached to the same carbon atom whereas vicinal dihalides have their two halide groups attached to two adjacent carbon atoms in the same compound.
19. Haloalkanes and Haloarenes 2. From ethyl alcohol or acetone Ethyl alcohol (C2 H5 OH) or acetone (CH3 COCH3 ) reacts with bleaching powder to give chloroform as follows: 2 2 2 2 2 2 2 2 2 [O] 3 2 3 2 3Cl 3 3 2 HCl 4Cl Ca(OH) 3 3 3 3 3 3 2 HCl 2moles CaOCl H O Ca(OH) Cl H O Cl HCl [O] CH CH OH CH CHO H O CH CHO CCl CHO H O CH COCH CCl COCH 2CHCl (CH COO) Ca − − +  → + +  → +  → +  → +  →  → + 3. From CCl4 2 Fe/H O 4 3 CCl 2[H] CHCl HCl + → + 4. From chloral hydrate y Chloral hydrate is stable because of intramolecular hydrogen bonding in it which has butterfly-like structure. 5. Haloform reaction (A) It is given by C=O having –COCH3 group. For example, Definitions The reaction of a methyl ketone with chlorine, bromine, or iodine in the presence of hydroxide ions to give a carboxylate ion and a haloform is the haloform reaction. Concept Ladder Bleaching powder is basic in nature. It gives calcium chloride, chlorine and water when bleaching powder reacts with hydrochloric acid. Rack your Brain What are the harmful effect of chloral in human body?
20. Haloalkanes and Haloarenes y Ethanal is the only aldehyde to show this reaction. For example, y CH3 CHO + 3I2 + 4NaOH  → CHI3 ↓ + HCOONa + 3NaX + 3H2 O y CH3 COCH3 + 3I2 + 4NaOH  → CHI3 ↓+ CH3 COONa + 3NaX + 3H2 O (B) Alcohol having group shows haloform reaction. For example, CH3 –CH2 –OH Shows For example, CH3 –CH2 –OH + 4I2 + 6NaOH  → CHI3 ↓ + HCOONa + 5NaX CHCl3 y Chloroform is a colourless liquid having a sweet smell. y It is also a good solvent for resins, fats, etc. y Its boiling point is 61°C. y Soluble in organic solvents as oils but insoluble in H2 O. CHBr3 y CHBr3 is a colourless liquid and its boiling point is 149.5°C. Previous Year’s Question An organic compound A(C4 H9 Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative then, A is [AIPMT] (1)  t-butyl chloride (2) s-butyl chloride (3) iso-butyl chloride (4) n-butyl chloride
21. Haloalkanes and Haloarenes CHI3 y Its melting point is 119°C. y It occurs as yellow, hexagonal plate like crystals. y It can be used as antiseptic (due to the liberation of free I2 ). Test of Purity of CHCl3 No precipitate is formed when chloroform reacts with silver nitrate. This is because, being covalent, CHCl3 cannot furnish Cl– ions. Chemical properties of chloroform (CHCl3 ) 1. Nitration CHCl3 + HO–NO2  → CCl3 .NO2 + H2 O Chloropicrin (insecticide) y It is used in the manufacture of tear gas, phenacyl chloride [C6 H5 COCH2 Cl]. 2. Reduction 2 6[H]Zn H O 3 4 CHCl CH 3HCl +  → + 2[H]Zn/HCl 3 2 2 CHCl CH Cl HCl  → + Zn 3 3 alc.HCl CHCl 4(H) CH Cl 2HCl +   → + 3. Oxidation hv 3 2 2 Phosgene (Poisonous) 1 CHCl O COCl HCl 2 +  → + y Chloroform is kept in dark, filled, tightly closed bottle with a small amount of C2 H5 OH (negative catalyst) to avoid oxidation or formation of phosgene. Ethyl alcohol (C2 H5 OH) converts phosgene into non-poisonous diethyl carbonate. Concept Ladder y CHCl3 is mainly used in the production of Freon refrigerant, R-22. y CHCl3 is also used as a solvent for fats, alkaloids, iodine etc. y CHCl3 causes dizziness, headache and fatigue. y Chronic chloroform exposure may damage liver and kidney. Rack your Brain Chloroform is no longer used as an anaesthetic agent. Why? Concept Ladder Iodoform is mainly used as an antiseptic, since it liberates free iodine. However it is not used now because of its bad smell.
22. Haloalkanes and Haloarenes 4. Reaction with hot Sodium Hydroxide 5. Reaction with hot Sodium Ethoxide 6. Carbylamine reaction: It is a test a primary amine. Here, the primary amine reacts with chloroform and base KOH, to give bad smelling isocyanide as follows: R–NH2 + CHCl3 + 3KOH  → R–NC + 3KCl + 3H2 O y Here, the reaction intermediate is: CCl2 , that is, dichlorocarbene. y If ethylamine is taken, product formed is ethyl isocyanide. C2 H5 NH2 + CHCl3 + 3KOH  → C2 H5 NC + 3KCl + 3H2 O y If aniline is taken, product formed is phenylisocyanide. C6 H5 NH2 + CHCl3 + 3KOH  → C6 H5 NC + 3KCl + 3H2 O 7. Reaction with Ag powder CHX3 + 6Ag + CHX3  → C2 H2 + 6AgX 8. Reimer–Tiemann reaction: Here reaction inter mediate is: CCl2 . 9. Reaction with acetone y Chloretone is used in hypnotic medicines. Previous Year’s Question Benzene reacts with n-propyl chloride in thepresence of anhydrous AlCl3 to give [AIPMT] (1)  3-propyl-1-chlorobenzene (2) n-propylbenzene (3) no reaction (4) isopropylbenzene
23. Haloalkanes and Haloarenes CCl4 or Pyrene (Carbon Tetra-Chloride) Tetrahedral structure, sp3 hybridization, bond angle 109° 28’ and μ is zero Methods of preparation 1. CH4 + 4Cl2 hv 4HCl −  →CCl4 2. CHCl3 + Cl2 hv  → CCl4 + HCl 3. CS2 + 2S2 Cl2  → CCl4 + 6S 4. C3 H8 + 9Cl2 70 100atm ∆ −  → CCl4 + C2 Cl6 + 8HCl Physical properties of pyrene y It is a colourless, non-flammable, poisonous liquid having a boiling point of 350 K. y Soluble in organic solvents as oils but insoluble in water and is a good solvent for fat, oil and wax. Chemical properties of pyrene 1. Reaction with steam 2 H O 4 2 500 Cunderhighpressure CCl COCl 2HCl °  → + 2. Hydrolysis 2 4 4 2 BoilingKOH 2H O CCl C(OH) CO ∆ ∆ −  →  → 3. Reaction with HF 5 SbF 4 2 2 Freon CCl 2HF CF Cl 2HCl +  → + y Freon-12 is used in air conditioners and refrigerators as a refrigerant. 4. Reaction with phenol Concept Ladder Carbon tetrachloride is released into the air, it goes in the upper atmosphere and depletes the ozone layer. Depletion of ozone layer increases the human exposure to ultraviolet radiations which may lead to increased skin cancer, eye diseases and disorders, and disruption of the immune system. Previous Year’s Question Phosgene is a common name for [AIPMT] (1)  phosphoryl chloride (2) thionyl chloride (3) carbon dioxide and phosphine (4) carbonyl chloride.
24. Haloalkanes and Haloarenes Uses of CCl4 : (i) Under Pyrene it is used as a fire extinguisher. (ii) Used as solvent for fats, oils, resins etc. Teflon (–CF2 –CF2 –)n y Teflon is a polymer of tetrafluoroethylene. y It is a chemically inert thermostatic plastic. y It is used for electrical insulation and in gasket materials. 3 SbF 800 C 3 2 2 2 HF HCl CHCl CHF Cl CF CF ° −  →  → = 2 2 2 2 n Tetrafluoroethylene Teflon nCF CF ( CF CF ) =  → − − − Chlorobenzene Methods of preparation From benzene can not be obtained by direct iodination as not only the reaction is reversible but also HI being a reductant can reduce into Benzene. But if strong oxidants like HNO3 , HgO are used the reaction is possible as they oxidise HI into I2 . can not be obtained as F is highly reactive and the reaction is violent also. Concept Ladder Teflon is the trading name for a commonly used polymer called Polytetrafluoroethylene. PTFE has unique and valuable qualities such as being chemical resistant, temperature resistant, low permeation and high corrosion resistant. Previous Year’s Question Whichofthefollowingcompounds undergoes nucleophilic substitution reaction most easily? [NEET] (1)  (2) (3) (4)
25. Haloalkanes and Haloarenes y Commercial method or Raschig method From alcohol From benzene diazonium chloride or Sand Mayer’s reaction Gatterman reaction Physical properties of Chlorobenzene y It is colourless liquid with pleasant odour and a boiling point of 132°C. y It is heavier than water and insoluble in it. Chemical properties of Chlorobenzene Due to benzene ring y The Cl– atom present in the ring deactivates the ring but it is o- and p- directing. The rate of electrophilic substitution is slower than that of benzene. Here due to resonance electron density increases at o, p positions but due to –I effect –X atom has a tendency to withdraw electrons from benzene ring. It means due to deactivation in ring rate of electrophillic substitution decreases. Previous Year’s Question The correct order of increasing reactivity of [AIPMT] C—X bond towards nucleophile in the following compounds is (1)  I II IV III (2) II III I IV (3) IV III I II (4) III II I IV Concept Ladder In haloarens and vinyl halides, the phenyl cation or the vinyl cation formed as a result of self ionization is not stabilized by resonance because the sp2 -hybridized orbital of carbon having the +ve charge is perpendicular to the p-orbital of the penyl ring or the vinyl group.
26. Haloalkanes and Haloarenes y Halogenation y Nitration y Sulphonation y Friedel Crafts alkylation y Acylation Here para product is major in all these cases. Previous Year’s Question Benzene reacts with n-propyl chloride in the presence of anhydrous AlCl3 to give [NEET] (1) 3-propyl-1-chlorobenzene (2) n-propylbenzene (3) no reaction (4) isopropylbenzene Rack your Brain The C—Cl bond length in chlorobenzene is shorter than C—Cl bond length in CH3 —Cl? Concept Ladder In Chlorobenzene, Cl is attached to a sp2 -hybrid carbon atom. has greater s-character and more electronegative therefore chlorobenzene has less tendency to release electrons towards the Cl atom.
27. Haloalkanes and Haloarenes Reactions due to chlorine y Reactivity of chlorine atom in chlorobenzene The reactivity of Cl– atom in chlorobenzene is very low than R–X because C–Cl bond in chlorobenzene acquires a double bond character and is resonance stabilized, so more energy is required to break a double bond than a single bond. In C –X while in 2 R — CH — X it means in haloarenes C–X bond length is shorten than in haloalkanes which is 169 and 177 PM respectively. It also decreases reactivity in haloarenes. Here is very less stable so SN1 reaction does not occur. The attack of electron rich Nucleophile is also inhibited by higher electron density at arenes. y Substitution by –OH group Previous Year’s Question Whichofthefollowingcompounds will undergo racemisation when solution of KOH hydrolyses? [NEET] (i) (ii) CH3 CH2 CH2 Cl (iii) 3 3 2 CH | H C — CH— CH Cl (iv) (1)  (i) and (ii) (2) (ii) and (iv) (3) (iii) and (iv) (4) (i) and (iv) Concept Ladder In haloarence presence of EWG such as —NO2 , —CN, etc. at o-and p-position (but not at m-position) w.r.t. the halogen greatly activates the halogen towards nucleophilic displacement.
28. Haloalkanes and Haloarenes When a strong E.W.G group like –NO2 is present at o, p position the substitution of –X becomes comparatively easier and reaction occurs. y Substitution by NH2 group This reaction proceeds with Benzyne Rack your Brain p-Chloronitrobenzene undergoes nucleophilic substitution faster than chlorobenzene. Explain giving the resonating structure as well? Previous Year’s Question Whichchloroderivativeofbenzene among the following would undergo hydrolysis most readily with aqueous sodium hydroxide to furnish the corresponding hydroxy derivative? [AIPMT] (1)  (2) (3) (4) C6 H5 Cl
29. Haloalkanes and Haloarenes y Substitution by CN group y Substitution by –OR group: y Reaction with magnesium y Wurtz Fittig reaction y Fittig reaction y Ullmann reaction y Reaction with chloral: Chloral on heating with chlorobenzene in presence of concentrated H2 SO4 gives DDT (p,p-dichlorodiphenyl trichloroethane). It is non-biodegradable as both Cl atoms are linked with benzene ring. Rack your Brain Haloarence are less reactive towardsnucleophilicsubstitution reactions?
30. Haloalkanes and Haloarenes Uses and Effects of Polyhalogen Compounds on Environment and Human Health Iodoform Freon y Freon is used as a coolant in A.C and refrigerators. However, now its use has been abandoned since it damages the ozone layer. DDT y DDT is an off-white crystalline powder and has been a popular pesticide. y It is highly toxic towards fish. y It is not metabolized very rapidly by animals; it is deposited and is stored in the fatty tissues. y Being non-biodegradable its residues accumulate in environment and are toxic to mammals etc. Carbon tetrachloride y Carbon tetrachloride or CCl4 is mainly used in the synthesis of chloroflouro carbons. y It may cause liver cancer in humans. y It may cause headache, vomiting and nerve damage. y It may lead to depletion of the ozone layer. Benzene Hexachloride (B.H.C): It is commonly called as Gammexene or γ-Lindane or 6,6,6 [C6 H6 Cl6 ]. It is a famous pesticide for killing of Thermites (white ants) from soil. Previous Year’s Question Trichloroacetaldehyde, CCl3 CHO reacts with chlorobenzene in presence of sulphuric acid and produces [NEET] (1) (2) (3) (4) )
31. Haloalkanes and Haloarenes Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does preparation of aryl iodides requires presence of an oxidising agent? Iodination reaction is reversible in nature. To carry out reaction in forward direction, HI formed during iodination is removed by oxidation. HIO4 is used as an oxidising agent. Q.2 A.2 Out of o-and p-dibromobenzene which one has higher melting point and why? p-Dibromobenzene has higher melting point (M.P.) than its o-isomer. It is due to symmetry of p-isomer which fits in crystal lattice better than o-isomer. Q.3 A.3 Which of the following compounds will have the highest melting point and why? II, due to symmetry of para-positions; it fits into crystal lattice better than other isomers. Q.4 A.4 Which of the following compounds would undergo SN 1 reaction faster and why? (B) Undergoes SN 1 reaction faster than (A) because in case of (B), the carbocation formed after the loss of Cl– is stabilised by resonance, whereas, no such stabilisation is possible in the carbocation obtained from (A). Q.5 A.5
32. Haloalkanes and Haloarenes Allyl chloride is hydrolysed more readily than n-propyl chloride. Why? Allyl chloride shows high reactivity as the carbocation formed by hydrolysis is stabilised by resonance while no such stabilisation of carbocation exists in the case of n-propyl chloride. Q.6 A.6 Arrange each set of compounds in order of increasing boiling points (i) Bromomethane, bromoform, chloromethane, dibromomethane. (ii) 1 – Chloropropane, isopropyl chloride, 1 – chlorobutane. (I) As molecular mass of compound increases, boiling point also increases. Therefore, correct order is: chloromethane bromomethane dibromomethane bromoform (ii) Of molecules having same mass, it is size of molecule that determines boiling point. Branched compounds are comparatively more compact and hence have less surface area when compared to their straight chain compounds and therefore lower boiling point. Order of boiling point : iso-propyl chloride 1-chloropropane 1-chlorobutane Q.7 A.7 A hydrocarbon C5 H10 does not react with chlorine in dark but gives a single monochloro compound C5H9Cl in bright sunlight. Identify the hydrocarbon. Hydrocarbon with molecular formula C5 H10 can either be a cycloalkane or an alkene. Since, compound does not react with Cl2 in dark, therefore it cannot be an alkene but must be a cycloalkane. Since, cycloalkane reacts with Cl2 in presence of bright sunlight to give a single monochloro compound, C5 H9 Cl, therefore, all ten hydrogen atoms of cycloalkanes must be equivalent. Thus, cycloalkane is cyclopentane. Q.8 A.8
33. Haloalkanes and Haloarenes A hydrocarbon C5 H10 does not react with chlorine in dark but gives a single monochloro compound C5 H9 Cl in bright sunlight. Identify the hydrocarbon. A number of structural isomers are possible for molecular formula C5 H10 . But, the given compound gives a single monochloro derivative when reacted with Cl2 in sunlight suggests that, all the H-atoms in the compound are equivalent. This is possible only if the compound is a cyclic alkane. therefore, the compound is Q.9 A.9 Which compound in each of the following pairs will react faster in SN2 reaction with OH– ? (i) CH3 Br or CH3 l (ii) (CH3 )3 CCI or CH3 Cl (i) Between CH3 I and CH3 Br, CH3 I will react faster via SN 2 mechanism. In SN 2 , C—X bond breaks and faster it breaks faster is the reaction. I– is a better leaving group. Owing to its large size, C—I bond breaks faster than C—Br bond and hence reaction proceeds at a higher rate. (ii) Order of reactivity in case of SN2 reaction depends upon minimal steric hindrance around carbon involved in C—X bond. Lesser will be the steric hindrance as felt by incoming nucleophile, and hence alkyl halide will be more reactive towards SN 2 reaction. Based on the above, CH3 Cl will react faster than (CH3 )3 CCl. Q.11 A.11 Which of the compounds will react faster in SN 1 reaction with the –OH ion? CH3 —CH2 —Cl or C6 H5 —CH2 —Cl C6 H5 —CH2 —Cl Q.10 A.10
34. Haloalkanes and Haloarenes Arrange the compounds of each set in order of reactivity towards SN 2 displacement : 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane SN 2 reaction proceeds via formation of transition state where carbon atom is surrounded by 5 other atoms (groups). Thus, for such a transition state to form, steric interactions have to be minimum. So, the most preffered substrates for SN 2 reactions are 1° alkyl halides followed by 2° and 3° alkyl halides. Order of reactivity for SN 2 reactions : 1° 2° 3° aryl halide. ( ) ( ) ( ) 3 2 2 3 2 3 3 2 3 3 2 2 1 Bromopentane 2 Bromopentane 3 2 Bromo 2 methylpentane Br Br | | H C— CH — CH Br CH — CH— CH — CH CH — C — CH — CH | CH − − − − − Q.12 A.12 Out of C6 H5 CH2 Cl and C6 H5 CHClC6 H5 , which is more easily hydrolysed by aqueous KOH? C6 H5 CHClC6 H5 is hydrolysed faster. (a) Hydrolysis of an alkyl halide is an example of nucleophilic substitution reaction. In case of aryl halides this follows the SN1 pathway i.e., via the formation of carbocation. (b) C6 H5 CH2 Cl or benzyl chloride gives (c) Out of I II, carbocation II is more stable. Reason is presence of two phenyl rings attached to carbon carrying positive charge. (d) As a result, delocalisation of +ve charge is greater and carbocation is more stable. Due to this, (II) is formed faster and corresponding halide is hydrolysed with greater ease as compared to benzyl chloride. Q.13 A.13
35. Haloalkanes and Haloarenes p-Dichlorobenzene has higher m.p. and solubility than those of o- and m-isomers. Discuss. The para-isomers have high melting points and solubility as compared to their ortho and meta isomers due to symmetry of para-isomers that fits into crystal lattice better than ortho and para isomers. Q.14 A.14 What happens when n-butyl chloride is treated with alcoholic KOH. al. KOH 3 2 2 2 3 2 2 n Butylchloride But 1 ene CH — CH — CH — CH — Cl CH — CH — CH CH − − −  → = The reaction is an example of b-hydrogen elimination brought about by C2 H5 O- Q.15 A.15 How can the following conversions be carried out: Propene to propan-1 -ol? HBr/ aq.KOH/ 3 2 3 2 2 3 2 2 peroxide Propene Propanol CH —HC CH CH — CH — CH Br CH — CH — CH — OH ∆ =  →  → Q.16 A.16 How can the following conversions be carried out: Ethanol to propanenitrile. 2 2 SOCl KCN/Et OH—H O 3 2 3 2 3 2 Ethanol Propanenitrile H C — CH OH H C — CH Cl CH — CH OH  →  → Q.17 A.17 Give the uses of freon 12, DDT, carbon tetrachloride and iodoform: Freon 12 (CCl2 F2 ) is (i) used in aerosol propellants (ii) refrigeration (iii) air-conditioning. Q.18 A.18 Give the uses of freon 12, DDT, carbon tetrachloride and iodoform: DDT (p, p’- dichlorodiphenyltrichloroethane) is (i) used as an insecticide, (ii) mainly used against mosquitoes. Q.19 A.19
36. Haloalkanes and Haloarenes alkyl halides, though polar, are immiscible with water. Explain why? Only those compounds which can form hydrogen bonds with water are miscible with it. Alkyl halides, though polar due to the presence of electronegative halogen atom, are immiscible since they cannot form hydrogen bonds. Q.20 A.20
37. Haloalkanes and Haloarenes Chapter Summary 1. CCl4 is used as a medicine for treatment against hookworms. 2. CF4 is freon-14, CF3 Cl is freon-13, CF2 Cl2 is freon-12 and CFCl3 is freon-11. 3. Perfluorocarbons have a general formula Cn F2n + 2 . C6 H14 + 14F2 2 573K,COF  → C6 F14 + 14HF 4. Halothane (CF3 CHClBr) is used as an inhalative anaesthetic agent. 5. Chloretone is a hypnotic or sleep-inducing drug. 6. Westron is tetrachloroethane 2 2 CHCl CHCl |         while Westrosol is trichloroethylene 2 CCl CHCl ||         7. The boiling point have the following order: alkyl iodides alkyl bromides alkyl chlorides alkyl fluorides R–I R–Br R–Cl R–F 8. The volatility has the following order: R–Cl R–Br R–I 9. Dipole moment has the following order: CH3 Cl CH3 F CH3 Br CH3 I 10. The order of the boiling points in a group of isomeric alkyl halides is primary secondary tertiary 11. The order of the densities of alkyl halides is R–I R–Br R–Cl R–F CH3 Cl CH2 Cl2 CHCl3 CCl4 12. The order of chemical reactivity of alkyl halides is RI RBr RCl 13. The order of reactivity of an alkyl halides is tertiary secondary primary This has been explained in terms of the inductive effect of alkyl groups, which increases the polarity of C–X bond and thereby making it more reactive. 14. It has been observed that presence of bulky groups in primary halides—inspite of higher positive ionization energy—causes steric hinderance and makes them less reactive towards SN2 mechanism. The reactivity follows the order CH3 X C2H5 X C3 H7 X. 15. Antiseptic action of CHI3 is due to the liberation free I2 . 16. Perfluoro carbons (PFCs) have a general formula Cn H2n+2 . C7 H16 +16F2 2 0 2 573K VapourphaseN C F ∆ → C7 F16 +16HF
38. Haloalkanes and Haloarenes Perfluoro heptane These are colourless, odourless, non polar stable, non-toxic, substanies. They are stable to U.V or other radiations so don’t deplete the U3 -layer. They can be used as lubricants, in medicines for skin care, medical diagnosis etc. 17. The halogen derivatives of the aromatic hydrocarbons in which the halogen atom is present in the side chain are called aryl alkyl halides or aralkyl halides. For example, Ar–CH2 –X. 18. Bond strength and stability decreases as R–F R–Cl R–Br R–I 19. The relative nucleophilicity order for SN1 Reaction: RS CN I R O OH − 20. The Leaving group tendency for SN2 Reaction: 3 6 5 3 3 6 4 3 3 3 3 2 2 p CF C H SO p CH C H SO I Br Cl H O F CH COO N R R O R N N H − − − − − + − − + − − − − − − 21. Decreasing order of Reactivity of Nucleophilic Substitution Reaction: 22. In Dorzen’s method R–Br and R–I can not be obtained as SOBr2 is un-stable and SOI2 does not exist.

More Related Content

PPTX
28.-HaloalkaneandHaloarene12_-Notes.pptx
bySadiyaFatima22
 
PDF
NEO_JEE_12_P1_CHE_H_Haloalkanes and Haloarenes_5_208.pdf
byRahulGupta29181
 
PPTX
10 haloalkanes and haloarenes.pptx
byviivekmaurya
 
PDF
NEO_JEE_12_P1_CHE_H_Haloalkanes and Haloarenes_5_208.pdf
byRahulGupta29181
 
PPTX
CBSE Class 12 Chemistry Chapter 10 (Haloalkanes and Haloarenes) | Homi Institute
byHomi Institute
 
PPTX
Haloalkanes and haloarenes.pptx
byArshiyaGusain
 
PDF
Haloalkanes in one Shot by Singh Sahab.pdf
byShyamRaghu
 
PPTX
Alkyl Halides.pptx
byMHAMZASHARIF1
 
28.-HaloalkaneandHaloarene12_-Notes.pptx
bySadiyaFatima22
 
NEO_JEE_12_P1_CHE_H_Haloalkanes and Haloarenes_5_208.pdf
byRahulGupta29181
 
10 haloalkanes and haloarenes.pptx
byviivekmaurya
 
NEO_JEE_12_P1_CHE_H_Haloalkanes and Haloarenes_5_208.pdf
byRahulGupta29181
 
CBSE Class 12 Chemistry Chapter 10 (Haloalkanes and Haloarenes) | Homi Institute
byHomi Institute
 
Haloalkanes and haloarenes.pptx
byArshiyaGusain
 
Haloalkanes in one Shot by Singh Sahab.pdf
byShyamRaghu
 
Alkyl Halides.pptx
byMHAMZASHARIF1
 

Similar to ajajhsoaoqkwhsja81818272814473wloiwuwo928828282818sd.pdf

PPTX
Haloalkanes and haloarenes
byVeenuGupta8
 
PPT
Chapter 8 Alkyl halides
byWong Hsiung
 
PPTX
Alkyl halide (haloalkane)
byDilip Ghimire
 
PPTX
Defination and reactions of Alkyl Halides
bynashranadeemkhan
 
PPT
HALOALKANES- STUDY OF ORGANIC CHEMISTRY PART 2
byAmazingWorld57
 
PDF
haloalkanes .pdf
byRenuha0130
 
PPT
class 12 chapter 10 haloalkanes and haloareans
byPoonam Bathija Pardasani
 
PPTX
Alkyl Halides
byXavier Chang
 
PPT
Aliphatic Compounds For class XI and Class XII
bySumanAdhikari78
 
PPTX
Haloalkanes and Haloareneres Chapter 1 organic chemistry
byAnnamariyapeter1
 
PDF
Organic reactions
byIvonneBustamante5
 
PPTX
HALOALKANES AND HALOARENES CHAPTER 1 ORGANIC CHEMISTRY CLASS 12
byAnnamariyapeter1
 
PDF
JEE-Hydrocarbons.pdf nhi papa ne big bazaar ke liye toh bahut
byragni991164
 
PPTX
Haloalkanes and Haloarenes Topic 2 Class XII By Kailash Bhatt
byKailashBhatt21
 
PPTX
Org.chem_Lecture_5_Haloderivatives.pptx
byssuser183732
 
PPTX
HALOALKANES & HALOARENES.pppppppppppppppppppppppptx
by13RohiniGuleria
 
PPTX
Nomenclature of Alkyl Halides and its reactions.pptx
bybaginareca
 
PPTX
Chapter 17 alkyl halides and amines
byHashim Ali
 
PPTX
Chapter 19 aldehydes and ketones
byHashim Ali
 
PPT
12 10th chapter heloalkane.ppt chapter heloalka
byamiyadavt2020
 
Haloalkanes and haloarenes
byVeenuGupta8
 
Chapter 8 Alkyl halides
byWong Hsiung
 
Alkyl halide (haloalkane)
byDilip Ghimire
 
Defination and reactions of Alkyl Halides
bynashranadeemkhan
 
HALOALKANES- STUDY OF ORGANIC CHEMISTRY PART 2
byAmazingWorld57
 
haloalkanes .pdf
byRenuha0130
 
class 12 chapter 10 haloalkanes and haloareans
byPoonam Bathija Pardasani
 
Alkyl Halides
byXavier Chang
 
Aliphatic Compounds For class XI and Class XII
bySumanAdhikari78
 
Haloalkanes and Haloareneres Chapter 1 organic chemistry
byAnnamariyapeter1
 
Organic reactions
byIvonneBustamante5
 
HALOALKANES AND HALOARENES CHAPTER 1 ORGANIC CHEMISTRY CLASS 12
byAnnamariyapeter1
 
JEE-Hydrocarbons.pdf nhi papa ne big bazaar ke liye toh bahut
byragni991164
 
Haloalkanes and Haloarenes Topic 2 Class XII By Kailash Bhatt
byKailashBhatt21
 
Org.chem_Lecture_5_Haloderivatives.pptx
byssuser183732
 
HALOALKANES & HALOARENES.pppppppppppppppppppppppptx
by13RohiniGuleria
 
Nomenclature of Alkyl Halides and its reactions.pptx
bybaginareca
 
Chapter 17 alkyl halides and amines
byHashim Ali
 
Chapter 19 aldehydes and ketones
byHashim Ali
 
12 10th chapter heloalkane.ppt chapter heloalka
byamiyadavt2020
 

Recently uploaded

PPTX
B. Tech Sem 1 Gravimetric Chemical Analysis - Copy.pptx
byShriNRPrasad
 
PPTX
LNG Basics by Choi SPE LNG Processes Introduction
byRobertWaters35
 
PPTX
Why Did The submarine Kursk Sink? What went wrong?
byBob Mayer
 
PPTX
Code Generation phase in Compiler Design
byProfMonikaShah
 
PPTX
Control system Basics, MODEL-BASED SYSTEM DESIGN, Easy understanding,
byBhagavathyP
 
PDF
Natural disaster resistant Building (earthquake and flood resistant)
byAshish Kumar
 
PPTX
CHAPTER 3_HYDROLOGIC STATISTICS AND FREQUENCY ANALYSIS.pptx
byp26335566
 
PPTX
MESSAGE AUTHENTICATION CODE in cryp.pptx
bysoundariya20
 
PDF
Drone Supported by modular optical systems
bymkevinfahlevi445
 
PDF
research material for reasearch scholers and main topics
byHariKrishna92507
 
PPTX
an overview to software engineering.pptx
by1111287
 
PDF
From Lab to Launch Building a Career Beyond Academia
byYunyao Li
 
PDF
Purpose-Driven Quality Intelligence - A QI Concept
byJohan Hoberg
 
PDF
Request for Information - #10547 CBTC
bymdrodriguez7
 
PDF
Evolution of MQ Messaging to Distributed Data Pipeline
byPeerapat Asoktummarungsri
 
PDF
Shell Chemicals Pipeline Magazine April 1989
byJohn Downs
 
PPTX
5G Technology & Future Communication Systems
bySakshiMarakana
 
PDF
asyad-shipping-esg-report0f7b3d1ec3f44f7c8cbea33ef21f4690.pdf
byJaszsingh
 
PPTX
Class 1 of Module 2 - Strings in Python Syllabus, VIT
byVijayanthVijay
 
PPTX
Mastering Asynchronous Communication with Queues.pptx
byAdalberto Toledo
 
B. Tech Sem 1 Gravimetric Chemical Analysis - Copy.pptx
byShriNRPrasad
 
LNG Basics by Choi SPE LNG Processes Introduction
byRobertWaters35
 
Why Did The submarine Kursk Sink? What went wrong?
byBob Mayer
 
Code Generation phase in Compiler Design
byProfMonikaShah
 
Control system Basics, MODEL-BASED SYSTEM DESIGN, Easy understanding,
byBhagavathyP
 
Natural disaster resistant Building (earthquake and flood resistant)
byAshish Kumar
 
CHAPTER 3_HYDROLOGIC STATISTICS AND FREQUENCY ANALYSIS.pptx
byp26335566
 
MESSAGE AUTHENTICATION CODE in cryp.pptx
bysoundariya20
 
Drone Supported by modular optical systems
bymkevinfahlevi445
 
research material for reasearch scholers and main topics
byHariKrishna92507
 
an overview to software engineering.pptx
by1111287
 
From Lab to Launch Building a Career Beyond Academia
byYunyao Li
 
Purpose-Driven Quality Intelligence - A QI Concept
byJohan Hoberg
 
Request for Information - #10547 CBTC
bymdrodriguez7
 
Evolution of MQ Messaging to Distributed Data Pipeline
byPeerapat Asoktummarungsri
 
Shell Chemicals Pipeline Magazine April 1989
byJohn Downs
 
5G Technology & Future Communication Systems
bySakshiMarakana
 
asyad-shipping-esg-report0f7b3d1ec3f44f7c8cbea33ef21f4690.pdf
byJaszsingh
 
Class 1 of Module 2 - Strings in Python Syllabus, VIT
byVijayanthVijay
 
Mastering Asynchronous Communication with Queues.pptx
byAdalberto Toledo
 

ajajhsoaoqkwhsja81818272814473wloiwuwo928828282818sd.pdf

  • 1.
    1. Haloalkanes and Haloarenes Haloalkanes Haloalkanes are thehalogen deivatives of hydrocarbons. Classification of Haloalkanes Monohalides (R–X): Monohalides are monohalogen derivatives of alkanes which have a general formula Cn H2n+1 X and are known as alkyl halides. R–X may be of three types: 1. Primary R–CH2 X 2. Secondary R2 CHX 3. Tertiary R3 CX Dihalides (Cn H2n X2 ): Dihalides are the di-halogen derivatives of alkanes and are of geminal and vicinal types. Example (a) CH3 CHBr2 (Ethylidine dibromide), (b) BrCH2 CH2 Br (Ethylene dibromide) Trihalides (Cn H2n–1 X3 ) or haloforms: Trihalides are tri-halogen derivatives of alkanes and are represented by a general formula CHX3 (haloforms). Tetrahalides: Tetrahalides are tetra-halogen derivatives of alkanes and arerepresented by a general formula CX4 or CX2 Y2 . Aromatic Halogen Compounds When halogen atom is attached to aromatic hydrocarbons directly to the ring , the substance is known aryl halides. Their general formula is Ar—X. Haloalkanes and Haloarenes Concept Ladder In haloalkanes, the halogen atom is attached to the sp3 - hybridised carbon atom of an alkyl group whereas in haloarenes, the halogen atom is attached to sp2 - hybridized carbon atom of an aryl group. Definitions The monohalogen derivatives of alkanes are called alkyl halides or monohaloalkanes or simply haloalkanes. Concept Ladder Haloalkynes or Alkynyl halides are the halogen derivatives of alkynes. The monohalogen derivatives of alkynes have the general formula Cn H2n-3 X where X=F, Cl Br or I and n = 2, 3, 4....., etc.
  • 2.
    2. Haloalkanes and Haloarenes (a) Mono HalogenDerivatives Examples (i) Chlorobenzene (ii) p-Bromotoluene (iii) Bromobenzene (iv) m-Bromotoluene (b) Side chain Halogen Derivatives Example (i) Benzyl chloride (ii) b-Phenylethyl bromide Allylic, Vinylic and Benzylic Halides (a) Allylic Halides Example (i) 3-Haloprop-1-ene (1°) (ii) 3-Halo-3-methylcyclohex-1-ene (3°) (b) Vinylic Halides (i) Chloroethene (ii) 1-Chloroprop-1-ene (c) Benzylic Halides (i) Benzyl halide (1°) (ii) A benzylic halide (3°)
  • 3.
    3. Haloalkanes and Haloarenes Methods of preparation Halogenationof alkanes hv 2 R H X R X HX − +  → − + For example hv 4 2 3 2 2 3 4 or520 650K CH Cl CH Cl CH Cl CHCl CCl − +  → + + + 2 Cl ,hv 3 2 3 3 2 2 3 3 298K Propane 1 Chloropropane (45%) 2-Chloropropane (55%) CH — CH — CH CH — CH — CH — Cl CH — CHCl — CH −  → + 2 Cl ,hv 3 2 2 3 3 2 2 2 3 2 3 298 K Butane 2 Chlorobutane (72%) 1 Chlorobutane(28%) CH CH CH CH CH CH CH CH Cl CH CH — CHCl — CH − −  → + In general, the ease of subsitution of various hydrogens follows the sequence: Allylic > 3° > 2° > 1° > CH4 Reactivity order in halogens: F2 > Cl2 > Br2 > I2 Iodination is reversible, but it may be carried out in presence of an oxidising agent, such as, HIO3 , HNO3 , HgO, etc., which oxidises the HI as it is formed. hv 4 2 3 3 2 2 CH I CH I HI ; 5HI HIO 3I 3H O + + +  → +     Flourination: The best way to prepare alkyl fluorides is by halogen exchange. An alkyl chloride or bromide is heated in the presence of a metallic fluoride, such as AgF, Hg2 F2 , CoF3 or SbF3 to give alkyl fluorides. 3 3 Bromomethane Fluoromethane CH Br AgF CH F AgBr +  → + 3 2 2 2 3 2 2 2 2CH CH Cl Hg F 2CH CH F Hg Cl +  → + This reaction is called Swarts reaction. When the organic halide contains two or three halogen atoms at the same carbon, CoF3 or the more easily available SbF3 is used. For example, from Alcohols : Generally alkyl halides are prepared from alcohols by replacement of —OH group by an halogen ion. This is usually by using HX or PX5 . R – OH + X–  → R – X + OH– 3 2 3 3 3 2 3 3 2, 2 Dichloropropane 2,2 Difluoropropane 3CH CCl CH 2SbF 3CH CF CH 2SbCl − − +  → + Concept Ladder Vinylic and aryl hydrogen are so much unreactive that they do not participate in free radical halogenation. However, allylic and benzylic halides can be prepared from alkenes and arenes without any complication. Definitions Swarts' reaction is generally used to get alkyl fluorides from alkyl chlorides or alkyl bromides. This is done by heating of the alkyl chloride/bromide in the presence of the fluoride of some heavy metals (silver fluoride or mercurous fluoride for example).
  • 4.
    4. Haloalkanes and Haloarenes (a) By theaction of Halogen acids : R – OH + HX Catalyst  → R – X + H2 O (i) Using HCl : ( ) 2 2 anhy. ZnCl 3 2 3 2 2 anhy. ZnCl 3 3 3 3 2 CH CH OH HCl g CH CH Cl H O CH — CH— CH HCl CH — CH— CH H O | | Cl OH +   → + +   → + Anhydrous ZnCl2 helps in the cleavage of C–O bond. Being a Lewis acid, it co-ordinates with the oxygen atom of the alcohol. As a result, C–O bond weakens and ultimately breaks to form carbocations, which form chlorides. ( ) ( ) ( ) Room 3 3 2 temp 3 3 conc. CH C— OH HCl CH C — Cl H O +  → + Yield is improved when vapours of alcohol and HCl are passed over alumina at 350°C. (ii) Using HBr : Alkyl bromides are obtained by refluxing the alcohol with constant boiling in HBr (40%) in presence of a little conc. H2 SO4 2 4 H SO 3 2 3 2 2 Reflux 2 5 2 4 2 5 4 2 CH CH OH HBr CH CH Br H O C H OH KBr H SO C H Br KHSO H O +  → − + + +  → + + (iii) Using HI : Reflux 3 2 3 2 3 3 4 3 2 4 2 CH CH OH HI CH CHI H O CH OH KI H PO CH I KH PO H O ∆ +  → + + +  → + + (b) By the action of Phosphorus Halides: Phosphorus halides react with alcohols to form haloalkanes in excellent yield (80% or above). ROH + PX5  → R – X + POX3 + HX Here X can be either chlorine or bromine or iodine. 3ROH + PX3  → 3R – X + H3 PO3 Concept Ladder Order of reactivity of the halogen acids HI>HBr>HCl. Order of reactivity of Alcohols: R3 COH > R2 CHOH > RCH2 OH Concept Ladder In alkyl halide electro -negativity difference between the carbon and the halogen, the shared pair of electron lies closer to the halogen atom. As a result, the halogen carries a small negative charge, and carbon carries a small positive charge. So, C—X bond is always a polar covalent bond.
  • 5.
    5. Haloalkanes and Haloarenes Since, PI3 and PBr3 arenot very stable compounds, these are generally prepared in situ by the action of red phosphorus on bromine and iodine respectively. 2 2 P Br P I 4 2 3 P 6X 4PX ; R — OH R —Br; R — OH R I + + +  →  → → − This method gives good yield of primary alkyl halides but poor yields of secondary and tertiary alkyl halides. The method is generally useful for preparing lower alkyl bromides and iodides in laboratory. (c) By the action of Thionyl chloride : (Darzen’s method) Chloroalkanes are conveniently prepared by refluxing alcohol with thionyl chloride (SOCl2 ) in presence of pyridine (C5 H5 N). Pyridine 2 2 Reflux R — OH SOCl R — Cl SO HCl + → + ↑ + ↑ Thionyl chloride method is preferred over hydrogen chloride or phosphorus chloride method for the preparation of chloroalkanes since both the by-products (SO2 and HCl) in this reaction being gases escape, leaving behind chloroalkanes in almost pure state. 3. From Silver salt of fatty acids : This reaction is called as Borodine Hundsdiecker reaction and is a free radical reaction. This reaction gives the product with one carbon atom less than the fatty acid. The yield of the alkyl halide formation with this reactions is : 4 CCl ,Reflux 3 2 2 3 2 2 CH CH COOAg Br CH CH —Br CO AgBr + → + + primary > secondary > tertiary. Chloroalkanes can also be prepared by this method by using Cl2 instead of Br2 but the yields are poor. With I2 , silver salts give esters instead of iodoalkanes. 2 2 2 2RCO Ag I RCOOR CO 2AgI +  → + + Concept Ladder Iodoalkanes or alkyl iodides are prepared by refluxing a suitable alcohol with constant boiling hydriodic acid (57%). HI may also be generated in situ by the action of 95% phosphoric acid on KI. Previous Year’s Question The compound C7 H8 undergoes the following reactions : 2 2 3Cl / Br /Fe Zn/HCl 7 8 C H A B C ∆  →  →  → The product C is [NEET] (1) m-bromotoluene (2) o-bromotoluene (3)3-bromo-2,4,6-trichlorotoluene (4) p-bromotoluene.
  • 6.
    6. Haloalkanes and Haloarenes 4. Halogen exchangereaction : Iodoalkanes are easily prepared from corresponding chloroalkanes or bromoalkanes by heating with sodium iodide in acetone or methanal. This reaction is called Frinkelstein Reaction. Acetone RCl NaI RI NaCl; X Cl or Br ∆ +   → + = Its a halide exchange reaction which involves a substitution of Cl/Br by I. The reaction was specially de signed to prepare iodo-alkanes which were not easily prepared using simple halogenation method. (Due to the reversibility of Iodination) Acetone R — X NaI R I NaX ; X Cl or Br +  → − + ↓ = Reaction is supposed to be based on principle of greater solubility of NaI in acetone as compared to NaCl or NaBr because of greater covalent character in NaI. That is why despite of being a weaker reagent than Cl- / Br- , I- still substitues them and the NaCl/NaBr formed precipitates out driving the equilibrium in forward direction. from Alkenes : Alkenes react with halogen acids to form haloalkanes. Order of reactivity : HI > HBr > HCl > HF. 2 3 RCH CH HX RCH— CH | X = +  → The unsymmetrical alkenes follows Markovnikov’s rule during addition forming secondary or tertiary alkyl halides predominantly. ( ) ( ) HBr HBr 3 3 2 2 3 2 2 Peroxide Peroxide CH — CH— CH CH CH CH CH CH CH Br | Br ←  =  → (c) Allylic halogenation :When alkenes (except Ethylene) are heated with Cl2 or Concept Ladder Peroxide effect is observed only for HBr. So HCl and HI when added to alkene give same product in presence of absence of peroxide. Previous Year’s Question The reaction of C6 H5 CH=CHCH3 with HBr produces [NEET] (1) C6 H5 CH2 CH2 CH2 Br (2) (3) 6 5 2 3 C H CHCH CH | Br (4) 6 5 2 3 C H CH CHCH | Br .
  • 7.
    7. Haloalkanes and Haloarenes Br2 at a hightemperature of about 773 K, the hydrogen atom at the allylic carbon (i.e., carbon next to the double bond) is substituted by a halogen atom. For example, ( ) 773K 3 2 2 2 2 3 Chloroprop 1 ene Allyl chloride CH — CH CH Cl Cl — CH — CH CH − − − = +  → = However, a more specific reagent for allylic bromination is N-bromosuccinimide (NBS). Allylic chlorination can also be carried out with sulphuryl chloride. 475, hv 3 2 2 2 2 2 2 Traces of peroxide CH — CH CH SO Cl Cl — CH — CH CH HCl SO = + → = + + Previous Year’s Question When chlorine is passed through propene at 400°C, which of the following is formed? [NEET] (1) PVC (2) Allyl chloride (3) Propyl chloride (4) 1, 2-Dichloroethane Definitions Reactions in which halogenation occurs at the allylic position of an alkene are called allylic halogenation reactions.
  • 8.
    8. Haloalkanes and Haloarenes Physical properties ofmonohalides y Lower members of monohalides(CH3 X, C2 H5 X) are colourless gases while higher members are colourless liquid up to C18 , members are colourless solids. y Boiling point and density increase with increase in molecular weight. C4 H9 Cl C3 H7 Cl C2 H5 Cl CH3 Cl RI RBr RCl RF Likewise it happens in alkanes, branching also decrease B.P y Dipole moment: RCl RF RBr RI y Stability : RF RBr RCl RI y Solubility α 1 Mol. wt. In general: CH3 X C2 H5 X C3 H7 X C4 H9 X Concept Ladder CH3 Cl, CH3 Br, C2 H5 Cl, some chlorofluoromethanes are gases at room temperature. Higher chloro, bromo, iodo compounds are either liquids or solids. Many volatile halogen compounds have sweet smell. Haloalkanes are less soluble in water, why? Haloalkanes are polar molecules, neither they form H-bond with water nor can thye break the H-bonds already existing between water molecules. As a result, the solubility of haloalkanes in water in very low. Q.1 A.1 Rack your Brain n-Butyl bromide has higher boiling point than t-butyl bromide. Give reasons?
  • 9.
  • 10.
    10. Haloalkanes and Haloarenes Chemical Properties ofMonohalides y Since the is polar, these are reactive compounds. y The reactivity order is as follows: R3 CX R2 CHX RCH2 X RI RBr RCl CH3 X C2 H5 HX C3 H7 X …. Nucleophilic substitution reactions: Alkyl halides undergo nucleophilic substitution reactions as follows: .. .. Strong Nucleophile R X R Z Z X +δ −δ − +  → − + This reactions occurs by either SN 1 or SN 2 mechanism. For example, y Aq.KOH R X R OH HX −  → − + y AgOH R X R OH AgX −  → − + y Alc.KCN R X R CN KX −  → − + R–CN is major product as KCN being ionic, provides CN– ions. Therefore, attack occurs from the carbon atom side. y AgCN R X R NC AgX −  → − + Major product is R–NC as AgCN being covalent cannot give CN– ions. Therefore, attack occurs from nitrogen atom to give R–NC. y 2 AgNO 2 Nitroalkane R X R NO AgX −  → − + y 2 KNO Alkylnitrite R X R O N O KX −  → − − = + y 3 NaN 3 Azides R X R N NaX −  → − + y R'COOAg R X R'COOH AgX −  → + y R'ONa R X R' O R NaX −  → − − + The above reaction is called williamson synthesis. Definitions Reaction in which a stronger nucleophile displaces a weaker nucleophile are called nucleophilic substitution reaction and the atom or group which departs with its bonding pair of electrons is called the leaving group. Concept Ladder Š Order of reactivity of haloalkanes: RI RBr RCl RF Š Order of leaving tendency : I­ - Br- Cl- F- Previous Year’s Question In a SN2 substitution reaction of the type DMF R —Br Cl R — Cl Br − − + → + which one of the following has the highest relative rate? [NEET] (1) 3 3 2 3 CH | CH — C — CH Br | CH (2) CH3 CH2 Br (3) CH3 CH2 CH2 Br (4) 3 2 3 CH — CH— CH Br | CH .
  • 11.
  • 12.
  • 13.
    13. Haloalkanes and Haloarenes y 2 5 2 R'SNa CH OH/H O Thioether R X R' S R NaX −  → − − + y 2 Na S R X R S R 2NaX −  → − − + y 6 6 3 C H 6 5 Anhyd.AlCl R X C H R HX −  → − + The above reaction is called Friedel–Crafts reaction. 2 Moist Ag O R X R OH −  → − y 2 Ether Dry 2R X Ag O R O R 2AgX − +  → − − + y Alkyne R X NaC CR' R C C R' NaX − + ≡  → − ≡ − + 3 NH X R 2 HX HX R X R NH − − − −   → −   → Dehydrohalogenation It involves α, β-elimination following E1 and E2 mechanisms. y Here, α, β-elimination reaction takes place as follows: In case of tertiary and secondary halides, elimination dominates over substitution while in Primary-halides substitution is dominating. Low polarity of solvent, high temperature and strongness of base also favour elimination over substitution. Concept Ladder When elimination and substitution are competing reaction Rack your Brain Ethyl iodide undergoes SN 2 reaction faster than ethyl bromide? Previous Year’s Question Which of the following undergoes nucleophilic substitution exclusively by SN 1 mechanism? [AIPMT] (1) Ethyl chloride (2) Isopropyl chloride (3) Chlorobenzene (4) Benzyl chloride.
  • 14.
    14. Haloalkanes and Haloarenes Br CH CH CHCH CH CH CH CH CH CH alc KOH Major 3 2 2 3 3 2 3 | . C CH CH CH CH CH Minor 3 2 2 2 Saytzeff’s Rule According to Saytzeff’s rule, removal of b-Hydrogen atom takes place from b-carbon atom having more number of alkyl groups, so that a more stable alkene is formed. e.g., In case of a fluoro-alkane or other secondary halide, with very strong base like (CH3 )3 COK or C2 H5 ONa, major product (Alkene) is according to Hoffmann’s Rule. According to it, b-Hydrogen atom is eliminated from b-Carbon atom with less H-atom or less acidic b-H-atom which means less stable alkene is major product. CH CH CH CH CH CH CH CH CH CH CH CH KOH Minor 3 2 3 3 3 2 2 3 | , M Major Minor F CH CH CH CH CH CH CH CH 3 2 3 3 3 3 3 | CH COK, CH CH CH CH X Major 2 2 3 Reaction with metals (a) Reaction with Na (Wurtz reaction) Dryether R X 2Na X R R R 2NaX − + + −  → − + (b) Reaction with Zn ( Frankland reaction) 2 R X Zn X R R R ZnX ∆ − + + −  → − + (c) Reaction with Mg Dryether Grignardreagent R X Mg R Mg X − +  → − − R may be —CH3 , —C2 H5 , —C6 H5 etc. Reactivity order for R–MgX is given as CH3 X C2 H5 X C3 H7 X R–I R–Br R–Cl Previous Year’s Question Elimination reaction of 2-bromopentane to form pent-2-ene is (A) b-Elimination reaction (B) Follows Zaitsev rule (C) Dehydrohalogenation reaction (D) Dehydration reaction [NEET] (1)  (A), (B), (C) (2) (A), (C), (D) (3) (B), (C), (D) (4) (A), (B), (D)
  • 15.
  • 16.
    16. Haloalkanes and Haloarenes (d) Reaction withlead sodium alloy 2 5 2 5 4 Tetraethyllead 4C H Br 4Pb(Na) (C H ) Pb 4NaBr 3Pb +  → + + y Tetraethyl lead (TEL) has anti-knocking properties used in petrol to avoid knocking. (e) Reaction with lithium Ether R X 2Li R Li LiX − +  → − + Reduction 4 LiAlH R X 2[H] R H Hx − +  → − + Heating effect 560 C 2 2 2 R CH CH R CH CH HX ° − −  → −= + Isomerination Dihalides Gem or geminal halide or alkylidene halides Methods of preparation of geminal halides 1. From aldehyde or ketone O Cl CH C H PCl CH C H PCl Cl Dichloroethane O Cl CH 3 5 3 5 3 || | | C C CH PCl CH C CH PCl Cl Dichloropropane || | | , 3 5 3 3 5 2 2 Concept Ladder Organic lead (tetraethyl lead; TEL) is used as an antiknock agentingasolineandjetfuels. TEL is absorbed rapidly from the skin as well as the lungs and gastrointestinal tract and is converted to triethyl lead in the body. This form of lead may be responsible for its toxic effects. Previous Year’s Question Grignard reagent is prepared by the reaction between [NEET] (1) magnesium and alkane (2) magnesium and aromatic hydrocarbon (3) zinc and alkyl halide (4) magnesium and alkyl halide.
  • 17.
    17. Haloalkanes and Haloarenes 2. From alkyne Chemicalproperties of geminal halides (Alkylidene halides) These are less reactive than the alkyl halides due to the fact that the presence of one-X-atom (E.W.G) makes the replacement of other X-atom slightly difcult. 1. Reaction with alcoholic KOH 2. Reaction with aqueous KOH Here, R–CHO, R–CO–R are formed 3. Reaction with KCN 4. Reaction with Zn CH CH Br Zn CH CH ZnBr Br CH OH 3 2 2 3 | , Previous Year’s Question A compound of molecular formula C7 H16 shows optical isomerism, compound will be [NEET] (1)  2,3-dimethylpentane (2) 2,2-dimethylbutane (3) 2-methylhexane (4) none of these
  • 18.
    18. Haloalkanes and Haloarenes Vic or vicinaldihalide or alkylene halides Methods of preparation of vicinal dihalides 1. From alkenes 2. From diols like glycol Chemical properties of vicinal dihalides: They are as reactive as alkyl halides. 1. Reaction with KOH 2. Reaction with KCN 3. Reaction with Zn Trihalides or Haloforms (CHX3 ) Chloroform (CHCl3 ) y Chloroform was discovered by Justus Von Liebig and named by Jean-Baptiste Dumas. y It has anesthetic nature which was discovered by James Young Simpson. Methods of preparation 1. From chloral 3 3 CCl CHO NaOH CHCl HCOONa ∆ +  → + Previous Year’s Question Industrial preparation of chloroform employs acetone and [AIPMT] (1)  phosgene (2) calcium hypochlorite (3) chlorine gas (4) sodium chloride Concept Ladder Geminal dihalides have both halide groups attached to the same carbon atom whereas vicinal dihalides have their two halide groups attached to two adjacent carbon atoms in the same compound.
  • 19.
    19. Haloalkanes and Haloarenes 2. From ethylalcohol or acetone Ethyl alcohol (C2 H5 OH) or acetone (CH3 COCH3 ) reacts with bleaching powder to give chloroform as follows: 2 2 2 2 2 2 2 2 2 [O] 3 2 3 2 3Cl 3 3 2 HCl 4Cl Ca(OH) 3 3 3 3 3 3 2 HCl 2moles CaOCl H O Ca(OH) Cl H O Cl HCl [O] CH CH OH CH CHO H O CH CHO CCl CHO H O CH COCH CCl COCH 2CHCl (CH COO) Ca − − +  → + +  → +  → +  → +  →  → + 3. From CCl4 2 Fe/H O 4 3 CCl 2[H] CHCl HCl + → + 4. From chloral hydrate y Chloral hydrate is stable because of intramolecular hydrogen bonding in it which has butterfly-like structure. 5. Haloform reaction (A) It is given by C=O having –COCH3 group. For example, Definitions The reaction of a methyl ketone with chlorine, bromine, or iodine in the presence of hydroxide ions to give a carboxylate ion and a haloform is the haloform reaction. Concept Ladder Bleaching powder is basic in nature. It gives calcium chloride, chlorine and water when bleaching powder reacts with hydrochloric acid. Rack your Brain What are the harmful effect of chloral in human body?
  • 20.
    20. Haloalkanes and Haloarenes y Ethanal isthe only aldehyde to show this reaction. For example, y CH3 CHO + 3I2 + 4NaOH  → CHI3 ↓ + HCOONa + 3NaX + 3H2 O y CH3 COCH3 + 3I2 + 4NaOH  → CHI3 ↓+ CH3 COONa + 3NaX + 3H2 O (B) Alcohol having group shows haloform reaction. For example, CH3 –CH2 –OH Shows For example, CH3 –CH2 –OH + 4I2 + 6NaOH  → CHI3 ↓ + HCOONa + 5NaX CHCl3 y Chloroform is a colourless liquid having a sweet smell. y It is also a good solvent for resins, fats, etc. y Its boiling point is 61°C. y Soluble in organic solvents as oils but insoluble in H2 O. CHBr3 y CHBr3 is a colourless liquid and its boiling point is 149.5°C. Previous Year’s Question An organic compound A(C4 H9 Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative then, A is [AIPMT] (1)  t-butyl chloride (2) s-butyl chloride (3) iso-butyl chloride (4) n-butyl chloride
  • 21.
    21. Haloalkanes and Haloarenes CHI3 y Its meltingpoint is 119°C. y It occurs as yellow, hexagonal plate like crystals. y It can be used as antiseptic (due to the liberation of free I2 ). Test of Purity of CHCl3 No precipitate is formed when chloroform reacts with silver nitrate. This is because, being covalent, CHCl3 cannot furnish Cl– ions. Chemical properties of chloroform (CHCl3 ) 1. Nitration CHCl3 + HO–NO2  → CCl3 .NO2 + H2 O Chloropicrin (insecticide) y It is used in the manufacture of tear gas, phenacyl chloride [C6 H5 COCH2 Cl]. 2. Reduction 2 6[H]Zn H O 3 4 CHCl CH 3HCl +  → + 2[H]Zn/HCl 3 2 2 CHCl CH Cl HCl  → + Zn 3 3 alc.HCl CHCl 4(H) CH Cl 2HCl +   → + 3. Oxidation hv 3 2 2 Phosgene (Poisonous) 1 CHCl O COCl HCl 2 +  → + y Chloroform is kept in dark, filled, tightly closed bottle with a small amount of C2 H5 OH (negative catalyst) to avoid oxidation or formation of phosgene. Ethyl alcohol (C2 H5 OH) converts phosgene into non-poisonous diethyl carbonate. Concept Ladder y CHCl3 is mainly used in the production of Freon refrigerant, R-22. y CHCl3 is also used as a solvent for fats, alkaloids, iodine etc. y CHCl3 causes dizziness, headache and fatigue. y Chronic chloroform exposure may damage liver and kidney. Rack your Brain Chloroform is no longer used as an anaesthetic agent. Why? Concept Ladder Iodoform is mainly used as an antiseptic, since it liberates free iodine. However it is not used now because of its bad smell.
  • 22.
    22. Haloalkanes and Haloarenes 4. Reaction withhot Sodium Hydroxide 5. Reaction with hot Sodium Ethoxide 6. Carbylamine reaction: It is a test a primary amine. Here, the primary amine reacts with chloroform and base KOH, to give bad smelling isocyanide as follows: R–NH2 + CHCl3 + 3KOH  → R–NC + 3KCl + 3H2 O y Here, the reaction intermediate is: CCl2 , that is, dichlorocarbene. y If ethylamine is taken, product formed is ethyl isocyanide. C2 H5 NH2 + CHCl3 + 3KOH  → C2 H5 NC + 3KCl + 3H2 O y If aniline is taken, product formed is phenylisocyanide. C6 H5 NH2 + CHCl3 + 3KOH  → C6 H5 NC + 3KCl + 3H2 O 7. Reaction with Ag powder CHX3 + 6Ag + CHX3  → C2 H2 + 6AgX 8. Reimer–Tiemann reaction: Here reaction inter mediate is: CCl2 . 9. Reaction with acetone y Chloretone is used in hypnotic medicines. Previous Year’s Question Benzene reacts with n-propyl chloride in thepresence of anhydrous AlCl3 to give [AIPMT] (1)  3-propyl-1-chlorobenzene (2) n-propylbenzene (3) no reaction (4) isopropylbenzene
  • 23.
    23. Haloalkanes and Haloarenes CCl4 or Pyrene (Carbon Tetra-Chloride) Tetrahedralstructure, sp3 hybridization, bond angle 109° 28’ and μ is zero Methods of preparation 1. CH4 + 4Cl2 hv 4HCl −  →CCl4 2. CHCl3 + Cl2 hv  → CCl4 + HCl 3. CS2 + 2S2 Cl2  → CCl4 + 6S 4. C3 H8 + 9Cl2 70 100atm ∆ −  → CCl4 + C2 Cl6 + 8HCl Physical properties of pyrene y It is a colourless, non-flammable, poisonous liquid having a boiling point of 350 K. y Soluble in organic solvents as oils but insoluble in water and is a good solvent for fat, oil and wax. Chemical properties of pyrene 1. Reaction with steam 2 H O 4 2 500 Cunderhighpressure CCl COCl 2HCl °  → + 2. Hydrolysis 2 4 4 2 BoilingKOH 2H O CCl C(OH) CO ∆ ∆ −  →  → 3. Reaction with HF 5 SbF 4 2 2 Freon CCl 2HF CF Cl 2HCl +  → + y Freon-12 is used in air conditioners and refrigerators as a refrigerant. 4. Reaction with phenol Concept Ladder Carbon tetrachloride is released into the air, it goes in the upper atmosphere and depletes the ozone layer. Depletion of ozone layer increases the human exposure to ultraviolet radiations which may lead to increased skin cancer, eye diseases and disorders, and disruption of the immune system. Previous Year’s Question Phosgene is a common name for [AIPMT] (1)  phosphoryl chloride (2) thionyl chloride (3) carbon dioxide and phosphine (4) carbonyl chloride.
  • 24.
    24. Haloalkanes and Haloarenes Uses of CCl4 : (i)Under Pyrene it is used as a fire extinguisher. (ii) Used as solvent for fats, oils, resins etc. Teflon (–CF2 –CF2 –)n y Teflon is a polymer of tetrafluoroethylene. y It is a chemically inert thermostatic plastic. y It is used for electrical insulation and in gasket materials. 3 SbF 800 C 3 2 2 2 HF HCl CHCl CHF Cl CF CF ° −  →  → = 2 2 2 2 n Tetrafluoroethylene Teflon nCF CF ( CF CF ) =  → − − − Chlorobenzene Methods of preparation From benzene can not be obtained by direct iodination as not only the reaction is reversible but also HI being a reductant can reduce into Benzene. But if strong oxidants like HNO3 , HgO are used the reaction is possible as they oxidise HI into I2 . can not be obtained as F is highly reactive and the reaction is violent also. Concept Ladder Teflon is the trading name for a commonly used polymer called Polytetrafluoroethylene. PTFE has unique and valuable qualities such as being chemical resistant, temperature resistant, low permeation and high corrosion resistant. Previous Year’s Question Whichofthefollowingcompounds undergoes nucleophilic substitution reaction most easily? [NEET] (1)  (2) (3) (4)
  • 25.
    25. Haloalkanes and Haloarenes y Commercial methodor Raschig method From alcohol From benzene diazonium chloride or Sand Mayer’s reaction Gatterman reaction Physical properties of Chlorobenzene y It is colourless liquid with pleasant odour and a boiling point of 132°C. y It is heavier than water and insoluble in it. Chemical properties of Chlorobenzene Due to benzene ring y The Cl– atom present in the ring deactivates the ring but it is o- and p- directing. The rate of electrophilic substitution is slower than that of benzene. Here due to resonance electron density increases at o, p positions but due to –I effect –X atom has a tendency to withdraw electrons from benzene ring. It means due to deactivation in ring rate of electrophillic substitution decreases. Previous Year’s Question The correct order of increasing reactivity of [AIPMT] C—X bond towards nucleophile in the following compounds is (1)  I II IV III (2) II III I IV (3) IV III I II (4) III II I IV Concept Ladder In haloarens and vinyl halides, the phenyl cation or the vinyl cation formed as a result of self ionization is not stabilized by resonance because the sp2 -hybridized orbital of carbon having the +ve charge is perpendicular to the p-orbital of the penyl ring or the vinyl group.
  • 26.
    26. Haloalkanes and Haloarenes y Halogenation y Nitration ySulphonation y Friedel Crafts alkylation y Acylation Here para product is major in all these cases. Previous Year’s Question Benzene reacts with n-propyl chloride in the presence of anhydrous AlCl3 to give [NEET] (1) 3-propyl-1-chlorobenzene (2) n-propylbenzene (3) no reaction (4) isopropylbenzene Rack your Brain The C—Cl bond length in chlorobenzene is shorter than C—Cl bond length in CH3 —Cl? Concept Ladder In Chlorobenzene, Cl is attached to a sp2 -hybrid carbon atom. has greater s-character and more electronegative therefore chlorobenzene has less tendency to release electrons towards the Cl atom.
  • 27.
    27. Haloalkanes and Haloarenes Reactions due tochlorine y Reactivity of chlorine atom in chlorobenzene The reactivity of Cl– atom in chlorobenzene is very low than R–X because C–Cl bond in chlorobenzene acquires a double bond character and is resonance stabilized, so more energy is required to break a double bond than a single bond. In C –X while in 2 R — CH — X it means in haloarenes C–X bond length is shorten than in haloalkanes which is 169 and 177 PM respectively. It also decreases reactivity in haloarenes. Here is very less stable so SN1 reaction does not occur. The attack of electron rich Nucleophile is also inhibited by higher electron density at arenes. y Substitution by –OH group Previous Year’s Question Whichofthefollowingcompounds will undergo racemisation when solution of KOH hydrolyses? [NEET] (i) (ii) CH3 CH2 CH2 Cl (iii) 3 3 2 CH | H C — CH— CH Cl (iv) (1)  (i) and (ii) (2) (ii) and (iv) (3) (iii) and (iv) (4) (i) and (iv) Concept Ladder In haloarence presence of EWG such as —NO2 , —CN, etc. at o-and p-position (but not at m-position) w.r.t. the halogen greatly activates the halogen towards nucleophilic displacement.
  • 28.
    28. Haloalkanes and Haloarenes When astrong E.W.G group like –NO2 is present at o, p position the substitution of –X becomes comparatively easier and reaction occurs. y Substitution by NH2 group This reaction proceeds with Benzyne Rack your Brain p-Chloronitrobenzene undergoes nucleophilic substitution faster than chlorobenzene. Explain giving the resonating structure as well? Previous Year’s Question Whichchloroderivativeofbenzene among the following would undergo hydrolysis most readily with aqueous sodium hydroxide to furnish the corresponding hydroxy derivative? [AIPMT] (1)  (2) (3) (4) C6 H5 Cl
  • 29.
    29. Haloalkanes and Haloarenes y Substitution byCN group y Substitution by –OR group: y Reaction with magnesium y Wurtz Fittig reaction y Fittig reaction y Ullmann reaction y Reaction with chloral: Chloral on heating with chlorobenzene in presence of concentrated H2 SO4 gives DDT (p,p-dichlorodiphenyl trichloroethane). It is non-biodegradable as both Cl atoms are linked with benzene ring. Rack your Brain Haloarence are less reactive towardsnucleophilicsubstitution reactions?
  • 30.
    30. Haloalkanes and Haloarenes Uses and Effectsof Polyhalogen Compounds on Environment and Human Health Iodoform Freon y Freon is used as a coolant in A.C and refrigerators. However, now its use has been abandoned since it damages the ozone layer. DDT y DDT is an off-white crystalline powder and has been a popular pesticide. y It is highly toxic towards fish. y It is not metabolized very rapidly by animals; it is deposited and is stored in the fatty tissues. y Being non-biodegradable its residues accumulate in environment and are toxic to mammals etc. Carbon tetrachloride y Carbon tetrachloride or CCl4 is mainly used in the synthesis of chloroflouro carbons. y It may cause liver cancer in humans. y It may cause headache, vomiting and nerve damage. y It may lead to depletion of the ozone layer. Benzene Hexachloride (B.H.C): It is commonly called as Gammexene or γ-Lindane or 6,6,6 [C6 H6 Cl6 ]. It is a famous pesticide for killing of Thermites (white ants) from soil. Previous Year’s Question Trichloroacetaldehyde, CCl3 CHO reacts with chlorobenzene in presence of sulphuric acid and produces [NEET] (1) (2) (3) (4) )
  • 31.
    31. Haloalkanes and Haloarenes Aryl chlorides andbromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does preparation of aryl iodides requires presence of an oxidising agent? Iodination reaction is reversible in nature. To carry out reaction in forward direction, HI formed during iodination is removed by oxidation. HIO4 is used as an oxidising agent. Q.2 A.2 Out of o-and p-dibromobenzene which one has higher melting point and why? p-Dibromobenzene has higher melting point (M.P.) than its o-isomer. It is due to symmetry of p-isomer which fits in crystal lattice better than o-isomer. Q.3 A.3 Which of the following compounds will have the highest melting point and why? II, due to symmetry of para-positions; it fits into crystal lattice better than other isomers. Q.4 A.4 Which of the following compounds would undergo SN 1 reaction faster and why? (B) Undergoes SN 1 reaction faster than (A) because in case of (B), the carbocation formed after the loss of Cl– is stabilised by resonance, whereas, no such stabilisation is possible in the carbocation obtained from (A). Q.5 A.5
  • 32.
    32. Haloalkanes and Haloarenes Allyl chloride ishydrolysed more readily than n-propyl chloride. Why? Allyl chloride shows high reactivity as the carbocation formed by hydrolysis is stabilised by resonance while no such stabilisation of carbocation exists in the case of n-propyl chloride. Q.6 A.6 Arrange each set of compounds in order of increasing boiling points (i) Bromomethane, bromoform, chloromethane, dibromomethane. (ii) 1 – Chloropropane, isopropyl chloride, 1 – chlorobutane. (I) As molecular mass of compound increases, boiling point also increases. Therefore, correct order is: chloromethane bromomethane dibromomethane bromoform (ii) Of molecules having same mass, it is size of molecule that determines boiling point. Branched compounds are comparatively more compact and hence have less surface area when compared to their straight chain compounds and therefore lower boiling point. Order of boiling point : iso-propyl chloride 1-chloropropane 1-chlorobutane Q.7 A.7 A hydrocarbon C5 H10 does not react with chlorine in dark but gives a single monochloro compound C5H9Cl in bright sunlight. Identify the hydrocarbon. Hydrocarbon with molecular formula C5 H10 can either be a cycloalkane or an alkene. Since, compound does not react with Cl2 in dark, therefore it cannot be an alkene but must be a cycloalkane. Since, cycloalkane reacts with Cl2 in presence of bright sunlight to give a single monochloro compound, C5 H9 Cl, therefore, all ten hydrogen atoms of cycloalkanes must be equivalent. Thus, cycloalkane is cyclopentane. Q.8 A.8
  • 33.
    33. Haloalkanes and Haloarenes A hydrocarbon C5 H10 doesnot react with chlorine in dark but gives a single monochloro compound C5 H9 Cl in bright sunlight. Identify the hydrocarbon. A number of structural isomers are possible for molecular formula C5 H10 . But, the given compound gives a single monochloro derivative when reacted with Cl2 in sunlight suggests that, all the H-atoms in the compound are equivalent. This is possible only if the compound is a cyclic alkane. therefore, the compound is Q.9 A.9 Which compound in each of the following pairs will react faster in SN2 reaction with OH– ? (i) CH3 Br or CH3 l (ii) (CH3 )3 CCI or CH3 Cl (i) Between CH3 I and CH3 Br, CH3 I will react faster via SN 2 mechanism. In SN 2 , C—X bond breaks and faster it breaks faster is the reaction. I– is a better leaving group. Owing to its large size, C—I bond breaks faster than C—Br bond and hence reaction proceeds at a higher rate. (ii) Order of reactivity in case of SN2 reaction depends upon minimal steric hindrance around carbon involved in C—X bond. Lesser will be the steric hindrance as felt by incoming nucleophile, and hence alkyl halide will be more reactive towards SN 2 reaction. Based on the above, CH3 Cl will react faster than (CH3 )3 CCl. Q.11 A.11 Which of the compounds will react faster in SN 1 reaction with the –OH ion? CH3 —CH2 —Cl or C6 H5 —CH2 —Cl C6 H5 —CH2 —Cl Q.10 A.10
  • 34.
    34. Haloalkanes and Haloarenes Arrange the compoundsof each set in order of reactivity towards SN 2 displacement : 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane SN 2 reaction proceeds via formation of transition state where carbon atom is surrounded by 5 other atoms (groups). Thus, for such a transition state to form, steric interactions have to be minimum. So, the most preffered substrates for SN 2 reactions are 1° alkyl halides followed by 2° and 3° alkyl halides. Order of reactivity for SN 2 reactions : 1° 2° 3° aryl halide. ( ) ( ) ( ) 3 2 2 3 2 3 3 2 3 3 2 2 1 Bromopentane 2 Bromopentane 3 2 Bromo 2 methylpentane Br Br | | H C— CH — CH Br CH — CH— CH — CH CH — C — CH — CH | CH − − − − − Q.12 A.12 Out of C6 H5 CH2 Cl and C6 H5 CHClC6 H5 , which is more easily hydrolysed by aqueous KOH? C6 H5 CHClC6 H5 is hydrolysed faster. (a) Hydrolysis of an alkyl halide is an example of nucleophilic substitution reaction. In case of aryl halides this follows the SN1 pathway i.e., via the formation of carbocation. (b) C6 H5 CH2 Cl or benzyl chloride gives (c) Out of I II, carbocation II is more stable. Reason is presence of two phenyl rings attached to carbon carrying positive charge. (d) As a result, delocalisation of +ve charge is greater and carbocation is more stable. Due to this, (II) is formed faster and corresponding halide is hydrolysed with greater ease as compared to benzyl chloride. Q.13 A.13
  • 35.
    35. Haloalkanes and Haloarenes p-Dichlorobenzene has higherm.p. and solubility than those of o- and m-isomers. Discuss. The para-isomers have high melting points and solubility as compared to their ortho and meta isomers due to symmetry of para-isomers that fits into crystal lattice better than ortho and para isomers. Q.14 A.14 What happens when n-butyl chloride is treated with alcoholic KOH. al. KOH 3 2 2 2 3 2 2 n Butylchloride But 1 ene CH — CH — CH — CH — Cl CH — CH — CH CH − − −  → = The reaction is an example of b-hydrogen elimination brought about by C2 H5 O- Q.15 A.15 How can the following conversions be carried out: Propene to propan-1 -ol? HBr/ aq.KOH/ 3 2 3 2 2 3 2 2 peroxide Propene Propanol CH —HC CH CH — CH — CH Br CH — CH — CH — OH ∆ =  →  → Q.16 A.16 How can the following conversions be carried out: Ethanol to propanenitrile. 2 2 SOCl KCN/Et OH—H O 3 2 3 2 3 2 Ethanol Propanenitrile H C — CH OH H C — CH Cl CH — CH OH  →  → Q.17 A.17 Give the uses of freon 12, DDT, carbon tetrachloride and iodoform: Freon 12 (CCl2 F2 ) is (i) used in aerosol propellants (ii) refrigeration (iii) air-conditioning. Q.18 A.18 Give the uses of freon 12, DDT, carbon tetrachloride and iodoform: DDT (p, p’- dichlorodiphenyltrichloroethane) is (i) used as an insecticide, (ii) mainly used against mosquitoes. Q.19 A.19
  • 36.
    36. Haloalkanes and Haloarenes alkyl halides, thoughpolar, are immiscible with water. Explain why? Only those compounds which can form hydrogen bonds with water are miscible with it. Alkyl halides, though polar due to the presence of electronegative halogen atom, are immiscible since they cannot form hydrogen bonds. Q.20 A.20
  • 37.
    37. Haloalkanes and Haloarenes Chapter Summary 1. CCl4 isused as a medicine for treatment against hookworms. 2. CF4 is freon-14, CF3 Cl is freon-13, CF2 Cl2 is freon-12 and CFCl3 is freon-11. 3. Perfluorocarbons have a general formula Cn F2n + 2 . C6 H14 + 14F2 2 573K,COF  → C6 F14 + 14HF 4. Halothane (CF3 CHClBr) is used as an inhalative anaesthetic agent. 5. Chloretone is a hypnotic or sleep-inducing drug. 6. Westron is tetrachloroethane 2 2 CHCl CHCl |         while Westrosol is trichloroethylene 2 CCl CHCl ||         7. The boiling point have the following order: alkyl iodides alkyl bromides alkyl chlorides alkyl fluorides R–I R–Br R–Cl R–F 8. The volatility has the following order: R–Cl R–Br R–I 9. Dipole moment has the following order: CH3 Cl CH3 F CH3 Br CH3 I 10. The order of the boiling points in a group of isomeric alkyl halides is primary secondary tertiary 11. The order of the densities of alkyl halides is R–I R–Br R–Cl R–F CH3 Cl CH2 Cl2 CHCl3 CCl4 12. The order of chemical reactivity of alkyl halides is RI RBr RCl 13. The order of reactivity of an alkyl halides is tertiary secondary primary This has been explained in terms of the inductive effect of alkyl groups, which increases the polarity of C–X bond and thereby making it more reactive. 14. It has been observed that presence of bulky groups in primary halides—inspite of higher positive ionization energy—causes steric hinderance and makes them less reactive towards SN2 mechanism. The reactivity follows the order CH3 X C2H5 X C3 H7 X. 15. Antiseptic action of CHI3 is due to the liberation free I2 . 16. Perfluoro carbons (PFCs) have a general formula Cn H2n+2 . C7 H16 +16F2 2 0 2 573K VapourphaseN C F ∆ → C7 F16 +16HF
  • 38.
    38. Haloalkanes and Haloarenes Perfluoro heptane Theseare colourless, odourless, non polar stable, non-toxic, substanies. They are stable to U.V or other radiations so don’t deplete the U3 -layer. They can be used as lubricants, in medicines for skin care, medical diagnosis etc. 17. The halogen derivatives of the aromatic hydrocarbons in which the halogen atom is present in the side chain are called aryl alkyl halides or aralkyl halides. For example, Ar–CH2 –X. 18. Bond strength and stability decreases as R–F R–Cl R–Br R–I 19. The relative nucleophilicity order for SN1 Reaction: RS CN I R O OH − 20. The Leaving group tendency for SN2 Reaction: 3 6 5 3 3 6 4 3 3 3 3 2 2 p CF C H SO p CH C H SO I Br Cl H O F CH COO N R R O R N N H − − − − − + − − + − − − − − − 21. Decreasing order of Reactivity of Nucleophilic Substitution Reaction: 22. In Dorzen’s method R–Br and R–I can not be obtained as SOBr2 is un-stable and SOI2 does not exist.