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

2.  Features
of an ideal IR Spectrum
 Information
could be obtained….
 Requirements
 General
for the interpretation…
rules of interpretation
 Illustration

3.  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

7. 
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)

8. 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.


9. Source of Data
 Literature
(Books, Journals, Spectral library)
 Correlation
Tables
 Correlation
Charts
 Reference
 Web
Spectra (IP, BP etc.)
Database

10. 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

12. Typical Infrared Absorption
Regions
WAVELENGTH (µm)
2.5
4
O-H
C-H
5
6.1
C=O
C N
N-H
5.5
C C
X=C=Y
Very
few
bands
(C,O,N,S)
4000
2500
2000
6.5
C-Cl
C-O
C=C
C-N
C-C
N=O N=O *
C=N
1800 1650
FREQUENCY (cm-1)
15.4
1550
650

15. BASE VALUES
-1
(+/- 10 cm )
O-H
N-H
C-H
3600
3400
3000
C N
C C
2250
2150
C=O
C=C
1715
1650
C O
~1100
These are
the minimum
number of
values to
memorize.
large range

16.  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.....

17. Acids (OH)
a broad band near 3400-2400 cm -1
Amides(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-1
Ketones
(C-R)
If none of the above is present, conforms the presence
of ketones
show two weak absorption near 2850 and 2750 cm-1.

18. 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

19. 
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

20.  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

21. Illustrations
Taking example of drugs