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NUCLEAR MAGNETIC RESONANCE (NMR) SPECTROSCOPY
- 1. NMR SPECTROSCOPY Presented by: GUNTISHASHIKANTH DEPARTMENT OF PHARMACEUTICAL ANALYSIS UNIVERSITY COLLEGE OF TECHNOLOGY OSMANIA UNIVERSITY (UCT, OU)
- 2. NUCLEAR MAGNETIC RESONANCE(H1) • The radio frequency radiation (RFR) is used for NMR spectra. • The frequency is 107 Hz. • The energy of RFR is expressed by E= hv (planck constant). h= 6.624 × 10−27 v= 107 HZ E= 6.624 × 10−27 × 107 E=6.624 × 10−20 • The energy is not sufficient to induce either of excitation, vibration , rotation (depends on own state). • This energy is sufficient to effect the “nuclear spinning of an atom of a molecule” of sample. Or induce “flipping process” or effect the nuclear spinning either clock wise or anti clock wise.
- 3. We arenot creating the spinning we can change the direction of spin that is called induce flipping process. A case analytical study ,in which the presence of external magnetic field (EMF) and the absorption of Radiofrequency radiation (RFR) is called nuclear magnetic resonance. The possibility of NMR spectra is based in on the 3 conditions. 1.RFR 2.EMF 3.NUCLEAR SPINNING.
- 5. To calculateΔE value we need to have 2 0r more energy levels. In the sample protons & neutrons produce magnetic filed but very little /low so, energy not enough to RFR . EMF 50% energy+ sample have 50%...then net energy is 100%...it leads to formation of orbit those orbit is called as Precessional orbit. From the orbit release Precessional frequency . PF=RFR ABSORPTION TAKES PLACE
- 6. Absence ofexternal magnetic field , there is a average spin energy state hence RFR cannot absorbed in the presence of EMF , there is a clear difference between 2 spin energy state. Hence radio frequency radiation Can be absorbed . In the ground state , magnetic filed created by spinning nucleus is aligned with external magnetic field is called Precissional orbit with some energy is called pressional frequency. In the excited state, direction of spinning nuclei is anti –aligned with the direction of EMR .Hence it never produce pressional orbit . When the pressional frequency 100% is equal to the frequency of RFR(100%) then absorption takes Place.
- 7. S.NO MASS NOATOMIC NO SPIN QUANTUM NO ( I ) SPINNING 1 EVEN EVEN I = 0 NO SPIN 2 EVEN ODD I > 1 SPIN 3 ODD ODD / EVEN I > 0 SPIN
- 8. 1) 2nd conditionalways produce numerical value 1,2,3,4,5, etc.. Depends up on atomic weight. 2) 3rd condition always integral value 1/2 , 3/2, 5/2, 7/2, 9/2,etc..
- 9. NMR spectroscopy consistsof 4-steps: 1.Number of signals: it tells us how many kind or type of protons are present in molecule. 2.Intensity of signals: it tells us the number number of protons in each kind (hight of the peak). 3.position of signal : it tells us the environment of a proton in each kind . 4.Spin –spin splitting of signals: it tell us the environment pf proton with other adjacent proton. 1.number of signals: A set of proton with identical environment are called equivalent protons. A set of protons with different environment are called non-equivalent protons.
- 11. Examples:1 Chemically equivalentprotons are magnetically equivalent (absorption capacity same)hence which are NMR signal on the spectra . example: Benzene it gives as a 1 signal. Example2: Acetone gives 1 NMR signal Example 3: Ethanol gives 3 NMR signals
- 12. i. Alkene class: Always look for CIS and TRANS arrangement of hydrogen with respect to bulkier groups. Example: 1 Ethene gives 1NMR signal Example : 2 These particular Alkene class gives 4 NMR signals
- 13. ii. AROMATIC CLASS:- Always look for environment of a proton At Ortho , Meta , Para positions. EXAMPLE-1 Methyl benzene gives 4 NMR signals. EXAMPLE -2 Dimethyl benzene gives 2 NMR signals.
- 14. iii. Cycloalkanes:- Alwayslook for the environment of proton towards above the plane and below the plane. Example 1 methyl cyclopropane gives 4NMR signals. Some Examples like: 1) methyl cyclobutene it gives 6 NMR signals. 2) dimethyl cyclopropane it gives 2 NMR signals etc..
- 15. 2.Position of signals: Theabsorption signals are measured by chemical shift values. Chemicals shift is the difference between reference standard and sample NMR signal the chemical shift scale is range 0-10 delta (PPM). Example: chloroethane(CH3-CH2-Cl).
- 16. change inthe chemical shift value is due to 1. shielding effect 2. desheilding effect 1. Sheilding effect (up field effect): The influence of EMF on to a nucleus is less due to more number of circulating electrons(higher secondary induced magnetic field)hence it requires excess strength of EMF to create pressional orbit thus results in position Of NMR signal more towards up – field and the chemical shift values are lower. 2.Deshielding effect(Down field effect) The influence of EMF on to a nucleus is more due to less no of circulating electrons (low secondary magnetic Field). Hence it the normal strength of EMF is sufficient to produce pressional orbit. Thus result in position of NMR Signal more towards downfield and downfield and the chemical shift values are higher.
- 18. Factors effecting chemicalshift value: 1.Inductive effect: by introducing electron withdrawing groups(F ,Cl , Br , I) it gives desheilding effect . F > Cl > Br > I When proton is attached with any electronegative group atom then proton will desheilded and delta values will be increased . Example: CH3 F (4.26) > CH3 Cl (3.05) > CH3 Br (2.68) > CH3 I (2.16) > CH4 (0.23) delta values. 2.Hydrogen bonding: causes desheilding effect. 3.Space effect(inisotropic effect ): Exhibit either shielding or desheilding based on special arrangement of H – atoms in multiple bonded molecule. e.g.: alkynes (acetylene) alkenes (ethene) Acetylene: it is linear molecule Because of linearity nature whatever the proton around the hydrogen atom the direction is completely to opposite to the direction of EMF because of opposite direction it cause shielding effect & that shielding gives lower chemical Shift value (2-3 delta ).
- 19. Diamagnetic protons: whatever the shielding proton is opposite direction to EMF that is called Diamagnetic protons( diamagnetic protons are shielding protons).
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- 21. This isnot linear there by whatever the 2 0 _ IMF electrons around the protons is aligned with same direction with magnetic field created by EMF so it exhibit desheilding effect ( delta value is 4-6 ) such a protons called paramagnetic protons. chemical shift values: R – CH3 (methyl) 0.9 R - CH2 1.2 R - CH 1.8 CH2 2-3
- 23. 3.Intensity of signal More no of protons will have high intense NMR signal, less number of protons will have low intense NMR signals. CH3 - CH2 – Cl (chloro ethane)
- 24. 4.Spin – spinsplitting Interaction of set of protons with other adjacent non equivalent protons leads to split within a signal is called spin-spin splitting or spin spin coupling. Example: 1 CH3 – CH2 – Cl ( cholro ethane). CH3- CH-Cl , Cl – CH2- CH –Cl .
- 25. Example 2: CH3- CH-Cl2 (chloroethane)
- 26. Spin –spin splittingpossible in non –equivalent protons Rules: Rule1: equivalent protons do not undergo spin spin splitting process. Ex: benzene, acetone. Rule2: even through non equivalent protons are present there is no splitting. No splitting because adjacent protons are not present so ultimately no splitting. Rule3: N=n+1 N=number of peaks N= number of adjacent protons( non- equivalent). n=1 doublet (1:1) n=2 triplet (1:2:1) n=3 quartet (1:3:3:1)
- 27.
- 28. Coupling constant (J): Measure the distance existing between centres of 2 adjacent split within a multiplet. Coupling scale consist of 0 to 20 hz (j=0-20 hz). Coupling constant independent on the EMF but it depends on spatial arrangement of atoms based on the shape of molecule .
- 29. For geminalprotons the coupling constant value (2-18 hz). For vicinal protons the coupling constant value (0 -10 hz) . Based on the spatial arrangement of H atom j Gem > j vicinal
- 30. SOLVENTS USED INNMR SS TYPES OF SOLVENTS: 1. Carbon tetra chloride (CCl4) 2. Carbon disulphide (CS2) 3. Deuterochloroform (CDCl3) 4. Hexachloroacetone ((CCl3)2CO) 5. Deuterodimethyl sulfoxide (CH3)2SO 6. Deuterobenzene C6D6
- 31. Characteristics of solvents Solvent should Chemically inert Solvents should be magnetically isotropic It should be free from any hydrogen atom. Solvents should able to dissolve the molecules sample in a reasonable quantity. It should be pure and easily available. It should not interfere with any molecule in the sample. Solvent should be non-viscous in nature.
- 32. Solvent Requirement inNMR When selecting a solvent for running NMR analysis, typically deuterated solvent is used in order to minimize background signals and provide a lock signals to component for drifts in the magnetic field. NMR solvents are distinctly different from other spectroscopic solvent as the majority of hydrogen nuclei are replaced with deuterium so as to minimize the interference due to proton. Though deuterium atom has a nuclei spin, it does not operate on the same frequency as proton in the given magnetic filed. Therefore it serves the purpose of NMR spectroscopy.
- 33. Why Deuterated chloroformis used as solvent? Deuterated chloroform is a general purpose NMR solvent, as it is not very chemically reactive and unlikely to exchange its deuterium with its solute, and its low boiling point allows for easy sample recovery This is due to the very small amount of CHCl3 present in commercial CDCl3. The coupling constants for proton–deuterium splitting are very small. Even when H and D are on adjacent carbons, the H–D coupling is negligible. For this reason, deuterium substitution can be used to simplify NMR spectra and assign resonances.
- 34. Why Dimethyl Sulfoxideis used in NMR Due to its ability to dissolve a wide range of solvents, as well as its simple spectrum and high boiling point, DMSO is the most widely used deuterium solvent, especially in the discussion of NMR analysis. DMSO-d6 with unique features about its ability for researchers and craftsmen and due to the increasing development of the use of deuterated in various sciences of electronics and pharmaceutical industries, which obtains a valid alternative license in between
- 35. INSTRUMENTATION This instrumentconsists of nine major parts. They are discussed below: Sample holder – It is a glass tube which is 8.5 cm long and 0.3 cm in diameter. Magnetic coil – A magnetic coil produces a magnetic field whenever current flows through it. Permanent Magnet – This helps provide a uniform magnetic field at 60 – 100 MHz
- 36. Sweep generator– modifies the strength of an already applied magnetic field. Radiofrequency Transmitter – This produces a powerful but short pulse of radio waves. Radiofrequency – This receiver helps to detect radio frequency. RF Detector – It helps to determine the unabsorbed radio frequencies Recorder – It records the NMR signals that are received by the RF detector. Readout System – A computer that records data
- 37. WORKING OF NMRSPECTROSCOPY • Place the sample in the magnetic field. • Excite the nuclear sample in nuclear magnetic resonance with the help of radio waves to produce NMR signals. • These NMR signals are detected with sensitive radio receivers. • The resonance frequency of an atom in a molecule is changed by the intramolecular magnetic field surrounding it. • It describes the individual functional groups of a molecule and its electronic structure.
- 38. • Nuclear magneticresonance spectroscopy is a conclusive method of identifying monomolecular organic compounds. • This method provides a description of the reaction conditions, structure, chemical environment and dynamics of a molecule.
- 39. References: 1.Organic spectroscopy byWilliam kemp ( third edition). 2.Introduction to spectroscopy by Pavia ( 5th edition ). 3.Instrumental method of chemical analysis by G.R Chatwal. 4.Text book of pharmaceutical analysis by Dr . S. Ravi Sankar. 5.A text book of pharmaceutical analysis by G. Vidyasagar volume -1.