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Interpretation of organic compounds by IR, NMR and Mass Spectrometry
This document discusses various spectroscopy techniques for analyzing organic compounds, including infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry. It describes attenuated total reflectance (ATR)-IR spectroscopy and how it works. It also explains 2D NMR techniques like COSY spectroscopy and how they provide more structural information than 1D NMR. Finally, it discusses how mass spectrometry works and common fragmentation patterns seen in mass spectra for different functional groups like alkanes, cycloalkanes, and compounds containing isotopes.
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Interpretation of organic compounds by IR, NMR and Mass Spectrometry
- 1. Advanced Spectral Analysis Presented by:Ashitosh Panchal M Pharm Sem-II Pharmaceutical Chemistry Interpretation of Organic Compound by IR, NMR and Mass Spectrometry
- 2. Contents • ATR-IR • COSYTechnique • Mass fragmentation and it’s rule • Fragmentation of Alkanes • Isotopic Peaks
- 3. INFRARED SPECTROSCOPY • ATR-IR •Attenuated Total Reflectance • Sampling technique used in infrared spectroscopy. • Samples are examined directly in solid or liquid form
- 4. Principle of ATR •A beam of radiation entering a crystal will undergo total internal reflection when the angle of incidence at the interface between the sample and crystal is greater than critical angle. • This reflection forms the evanescent waves which extends into the sample.
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- 6. • Crystals usedin ATR cells are made from materials that have low solubility in water and a very high refractive index.
- 7. Types of ATRCell 1. Single-BounceATR Cell 2. Multiple-BounceATR Cell Figure. Single bounce ATR cell Fig. Multiple Bounce ATR Cell
- 8. Factors Affecting theSpectrum: • Refractive index of the ATR crystal and the sample. • Angle of incidence of the IR beam. • Critical angle • Wavelength of the IR radiation. • Number of reflections. • ATR crystal characteristics. • Depth of penetration.
- 9. •Depth of penetration: λ… wavelength of incident light in vacuum n1 … refractive index of ATR crystal (dense medium) n2 … refractive index of sample (rare medium) ϴ … angle of incidence
- 10. Interpretation of Methamphetamineby ATR-IR IUPAC Name : N-methyl-1-phenylpropan-2-amine Formula: C10H15N
- 11. • The fourprimary regions of IR Spectrum
- 12. Fig. ATR-IR Spectraof methamphetamine.
- 13. Wave number cm-1FunctionalGroup 747.44 C-H aromatic 1059.44 CH3 1453.54 CH2 1486.57 C=C aromatic 1603.15 N-H 2727.50 C-H
- 14. NMR Spectroscopy 2D NMR •2D NMR is a set of nuclear magnetic resonance spectroscopy methods which give data plotted in a space defined by two frequency axes rather than one. • 2D NMR spectra provide more information about a molecule than 1D NMR spectra.
- 15. Types of 2DNMR 1. COSY- Correlation Spectroscopy 2. NOESY- Nuclear Over Hauser Effect Spectroscopy 3. HETCOR- Heteronuclear Correlation 4. INADEQUATE- Incredible Natural Abundance Double Quantum Transfer Experiment.
- 16. •Correlation Spectroscopy (COSY ) •The first and most popular 2D NMR experiment is the homonuclear correlation spectroscopy (COSY) which is useful method for determining which signals arise from neighbouring proton’s. •Correlation appear when there is spin-spin coupling between proton’s, but where there is no coupling, no correlation is expected to be appear.
- 17. • In thesemethods, magnetization transfer occurs between nuclei of the same type, through J-coupling of nuclei connected by up to a few bonds.
- 18. • The two-dimensionalspectrum that results from the COSY experiment shows the frequencies for a single isotope, most commonly hydrogen (1H) along both axes. • Cosy spectra shows two types of peaks: A. Diagonal Peaks B. Cross Peaks
- 19.
- 20. Example of aCOSY NMR spectrum: Ethyl crotonate
- 21. 1H NMR spectraof acetylsalicylic acid
- 22. Chemical shift (ppm) No. Of hydrogen Positionof hydrogen 7-8.3 1H Aromatic H 2-2.7 3H R-CH3 carbonyl 10.5-12 1H R-COOH carbonyl 1H-1H COSY NMR spectrum of aspirin
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- 24. • Fragmentation ofthe molecular ion • When any molecule/sample is bombarded with electrons, the molecular ion is produced by loss of single electron with same mass of its molecular weight. Molecularion • These molecular ion or a radical cation undergoes fragmentation to break a bond between A and B to form a radical and a cation. • Only cations or fragments with positive charge is detected in MS.
- 25. Fragmentation of Alkanes( R-R ) • Fragmentation of straight chain alkane is observed by breaking of any C-C bond from molecular ion. • Alkanes gives following m/z fragments due to loose of group M-15 ( due to loss of -CH3 group ) M-29 ( due to loss of -CH2CH3 group ) M-43 ( due to loss of -CH2CH2CH3 group ) • Loss of largest substituent is more fevered due to stability. • Stability of cation:- Methyl < Primary < Secondary < Tertiary carbocation
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- 29. Mass fragmentation of2-methyl pentane
- 30. Fragmentation of Cycloalkanes •Loss of side chains if present, alpha cleavage. • Loss of ethylene or double bond fragment from ring. • Cleavage takes place by homolytic fission.
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- 33. Fragmentation of 1-MethylCyclopentane
- 34. Mass spectrum :1-methyl Cyclopentane
- 35. Isotopic Peaks • Mostelements occurs naturally as a mixture of isotopes. • The presence of significant amounts of heavier isotopes leads to small peaks that have masses that are higher than the parent ion peak. • M+1 : a peak that is one mass unit higher than M+. • M+2 : a peak that is two mass units higher than M+.
- 36. • In massspectrum of halogen multiple peaks occur due to different isotopes of halogen are called as isotopic Peak. • A compound with one chlorine atom gives a M+2 peak which is one third the intensity of the molecular ion peak (M+) due to the presence of molecular ion containing 37Cl isotope. • Cl has two isotopes 35Cl and 37Cl ( 3:1).
- 37. • Mass spectrumof Cl2
- 39. References: 1. https://en.m.wikipedia.org/wiki/Attenuated_total_reflectance 2. https://en.m.wikipedia.org/wiki/Two- dimensional_nuclear_magnetic_resonance_spectroscopy 3.https://en.m.wikipedia.org/wiki/Fragmentation_(mass_spectrometry)#:~:text= In%20mass%20spectrometry%2C%20fragmentation%20is,pattern%20in%20th e%20mass%20spectrum. 4.https://wiki.anton-paar.com/in-en/attenuated-total-reflectance-atr/