Typical Infrared Absorption Frequencies
Stretching Vibrations
Bending Vibrations
Functional Class
Range (cm-1)
Intensity
Assignment
Range (cm-1)
Intensity
Assignment
2850-3000
Strong
CH3, CH2 & CH
2 or 3 bands
1350-1470
1370-1390
720-725

medium
medium
weak

CH2& CH3 deformation
CH3 deformation
CH2 rocking
3020-3100
1630-1680
1900-2000
medium
variable
strong
=C-H & =CH2 (usually sharp)
C=C (symmetry reduces intensity)
C=C asymmetric stretch
880-995
780-850
675-730
strong
medium
medium
=C-H & =CH2
(out-of-plane bending)
cis-RCH=CHR
3300
2100-2250
strong
variable
C-H (usually sharp)
C≡C (symmetry reduces intensity)
600-700
strong
C-H deformation
3030
1600 & 1500
variable
medium-weak
C-H (may be several bands)
C=C (in ring) (2 bands) (3 if conjugated)
690-900
strong-medium
C-H bending &
ring puckering
3580-3650
3200-3550
970-1250
variable
strong
strong
O-H (free), usually sharp
O-H (H-bonded), usually broad
C-O
1330-1430
650-770
medium
variable-weak
O-H bending (in-plane)
O-H bend (out-of-plane)
3400-3500 (dil. soln.)
3300-3400 (dil. soln.)
1000-1250
weak
weak
medium
N-H (1°-amines), 2 bands
N-H (2°-amines)
C-N
1550-1650
660-900
medium-strong
variable
NH2 scissoring (1°-amines)
NH2 & N-H wagging
(shifts on H-bonding)

2690-2840(2 bands)
1720-1740
1710-1720
1690
1675
1745
1780

medium
strong
strong
strong
strong
strong
strong

C-H (aldehyde C-H)
C=O (saturated aldehyde)
C=O (saturated ketone)
aryl ketone
a, -unsaturation
cyclopentanone
cyclobutanone
1350-1360
1400-1450
1100
str
str
med
a-CH3 bending
a-CH2 bending
  C-C-C bending

2500-3300 (acids) overlap C-H
1705-1720 (acids)
1210-1320(acids)
1785-1815 ( acyl halides)
1750 & 1820 (anhydrides)
1040-1100
1735-1750 (esters)
1000-1300
1630-1695(amides)

strong
strong
medium-strong
strong
strong
strong
strong
strong
strong

O-H (very broad)
C=O (H-bonded)
O-C (sometimes 2-peaks)
C=O
C=O (2-bands)
O-C
C=O
O-C (2-bands)
C=O (amide I band)

1395-1440
1590-1650
1500-1560

med
med
med

C-O-H bending
N-H (1¡-amide) II band
N-H (2¡-amide) II band

Nitriles
Isocyanates,

Isothiocyanates,
Diimides,

Azides & Ketenes

2240-2260

2100-2270

med

med

C≡N (sharp)

-N=C=O, -N=C=S
-N=C=N-, -N3 , C=C=O