Interpretation of Infra red spectra

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Transcript of Interpretation of Infra red spectra

  • 1. Presented by Y. Narayudu(Pharm. Analysis & Q.A)

2. Featuresof an ideal IR Spectrum Informationcould be obtained. Requirements Generalfor the interpretationrules of interpretation Illustration 3. Absorption(Band) spectrum Spectrum between percent transmittance (% T) and wave number () Wave number () represents frequency () of lR absorption Two regions of absorption: FGR (4000-1500 cm-1): Identification of groups FPR (1500-400 cm-1): Molecular fingerprint (Spectral matching) Nature (Intensity and Shape) of spectral bands: Strong (s), medium (m), weak (w); Broad and Narrow 4. IR is most useful in providing information about the presence or absence of specific functional groups (FGR)IR can provide a molecular fingerprint that can be used for the identification of samples (FPR) 5. The spectrum must be adequately resolved and of adequate intensity. The spectrum should be of a pure compound. The spectrophotometer should be calibrated so that the bands are observed at their proper frequencies or wavelength. The method of sample handling must be specified. If a solvent is employed, the solvent concentration, and the cell thickness should be indicated. 6. Source of Data Literature(Books, Journals, Spectral library) CorrelationTables CorrelationCharts Reference WebSpectra (IP, BP etc.)Database 7. O-H3400cm-1CC2150cm-1N-H3400cm-1C=O1715cm-1C-H3000cm-1C=C1650cm-1CN2250cm-1C-O1100cm-110 8. Typical Infrared Absorption Regions WAVELENGTH (m) 2.54O-HC-H56.1C=OC NN-H5.5C C X=C=YVery few bands(C,O,N,S) 4000250020006.5C-Cl C-O C=C C-N C-C N=O N=O * C=N1800 1650FREQUENCY (cm-1)15.41550650 9. BASE VALUES -1 (+/- 10 cm )O-H N-H C-H3600 3400 3000C N C C2250 2150C=O C=C1715 1650C O~1100These are the minimum number of values to memorize.large range 10. Lookif carbonyl group is present?...... The C=O gives strong absorption in the region 1820-1660 cm-1 IfC=O is present, check for the presence of following group..... 11. Acids (OH)a broad band near 3400-2400 cm -1Amides(N- medium absorption near 3400 cm-1 & some times H) double dips with equivalent halves Ester(C-O) strong absorption near 1300-1000 cm-1. Anhydride s (c-o) Aldehyde (C-H)Gives two C-O absorption near 1810-1760 cm-1Ketones (C-R)If none of the above is present, conforms the presence of ketonesshow two weak absorption near 2850 and 2750 cm-1. 12. If C=O is absent, Alcohols and Phenols: Check for O-H, show broad absorption near 3400-3300 cm-1. confirm this by finding C-O near 1300-1000cm-1. Amines: N-H stretch, show medium absorption near 3400 cm-1 (1O 2 bands, 2O-1 band) Ethers: C-O near 1300-1000cm-1,and also absence of O-H near 3400cm-1 13. Double bonds and / or Aromatic ring: C=C is a weak absorption near 1650 cm-1 Medium to strong absorption 1600-1450 cm-1 Aromatic C-H occurs to left of the 3000 cm-1 Aliphatic C-H occurs to right of 3000 cm-1Triple bonds: CN medium, sharp absorption near 2250 cm-1CC weak sharp absorption near 2150 cm-1 14. Nitrogroups two absorptions at 1600-1530 cm-1 & 1390-1300 cm-1 Hydrocarbons None of the preceding is found Major absorptions are in C-H region near 3000 cm-1 Very simple spectrum 15. Illustrations Taking example of drugs