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Presented by
Y. Narayudu(Pharm. Analysis & Q.A)
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Features of an ideal IR Spectrum
Information could be obtained….
Requirements for the interpretation…
General rules of interpretation
Illustration
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Absorption (Band) spectrum Spectrum between percent transmittance (% T)
and wave number (ύ) Wave number (ύ) represents frequency (υ) 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
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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)
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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.
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Literature (Books, Journals, Spectral library)
Correlation Tables
Correlation Charts
Reference Spectra (IP, BP etc.)
Web Database
Source of Data
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O-H 3400cm-1 C≡C 2150cm-1
N-H 3400cm-1 C=O 1715cm-1
C-H 3000cm-1 C=C 1650cm-1
C≡N 2250cm-1 C-O 1100cm-1
10
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Typical Infrared AbsorptionTypical Infrared AbsorptionRegionsRegions
2.5 4 5 5.5 6.1 6.5 15.4
4000 2500 2000 1800 1650 1550 650
FREQUENCY (cm-1)
WAVELENGTH (m)
O-H C-H
N-H
C=O C=NVeryfewbands
C=C
C-ClC-O
C-NC-CX=C=Y
(C,O,N,S)
C N
C C
N=O N=O*
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BASE VALUESBASE VALUES(+/- 10 cm-1)
These arethe minimumnumber ofvalues tomemorize.
O-H 3600N-H 3400C-H 3000
C N 2250C C 2150
C=O 1715
C=C 1650
C O ~1100 large range
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Look if carbonyl group is present?...... The C=O gives strong absorption in the region 1820-1660 cm-1
If C=O is present, check for the presence of following group.....
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Acids (O-H)
a broad band near 3400-2400 cm-1
Amides(N-H)
medium absorption near 3400 cm-1 & some times double dips with equivalent halves
Ester(C-O)
strong absorption near 1300-1000 cm-1.
Anhydrides(c-o)
Gives two C-O absorption near 1810-1760 cm-1
Aldehyde (C-H)
show two weak absorption near 2850 and 2750 cm-1.
Ketones(C-R)
If none of the above is present, conforms the presence of ketones
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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
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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-1
Triple bonds: C≡N medium, sharp absorption near 2250 cm-1 C≡C weak sharp absorption near 2150 cm-1
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Nitro groups
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
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IllustrationsTaking example of drugs
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