Wired Chemist

Characteristic Infrared Absorptions

C-H

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Alkanes	2962 - 2853	m - s
Alkenes	3090 - 3010	m
Alkynes	ca. 3300	s
Aromatics	ca. 3030	v
NCH₃, OCH₃	2850 - 2700	m
CHO	2900 - 2820 and 2775 - 2700	w - m

Bending Vibrations
Group	Range, cm^-1	Intensity*
CH	ca. 1340	w
CH₂	1485 - 1445	m
CH₃	1470 - 1430 and 1380 - 1370	s
C(CH₃)₂	1385 - 1380 and 1370 - 1365	s
C(CH₃)₃	1395 - 1385 and ca. 1365	s
Aromatics
5 adj H	750 and 700	v, s

O-H

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Free O-H	3650 - 3590	v, sh
H-bonded	3550 - 3200	b

Bending Vibrations
Group	Range, cm^-1	Intensity*
Alcohols	1430 - 1280	b, m
Phenols	1390 - 1310	m
Carboxylic acids	1440 - 1400	m

N-H

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Primary amine, free	3500 - 3300 and 3420 - 3250	m - s
Secondary amine	3500 - 3310	m

Bending Vibrations
Group	Range, cm^-1	Intensity*
	1650 - 1550	w - s

C=O

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Ketones, aldehydes, carboxylic acids	ca. 1750 - 1660	s
Acyl halides	1850 - 1750	s
Amides	ca. 1710 - 1620	s

C=N

Stretching Vibrations
Range, cm^-1	Intensity*
1690 - 1630	v

C≡N

Stretching Vibrations
Range, cm^-1	Intensity*
2260 - 2220	m

C=C

Stretching Vibrations
Range, cm^-1	Intensity*
1690 - 1560	w

C≡C

Stretching Vibrations
Range, cm^-1	Intensity*
2275 - 2100	w - m

C_ar-C_ar

	Range, cm^-1	Intensity*
Skeletal vibrations	ca. 1600	w - m
in aromatics	1580, 1500, 1450

C-O-C, C-O-H

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Esthers	ca. 1100
Esthers: aliphatic	1280 - 1220	s
Esthers: alkyl, aryl	1050 - 1000
Esters	1290 - 1180	b, s

Bending Vibrations
Group	Range, cm^-1	Intensity*
Alcohols	1430 - 1280	m
Phenols	1390 - 1310	m - s

C-X, X is a halogen

Stretching Vibrations
Group	Range, cm^-1	Intensity*
Fluorides	1400 - 1000	s
Chlorides	800 - 600	s
Bromides	625 - 400	s
Iodides	625 - 400	s

* v = variable; sh = sharp; b = broad; w = weak; m = medium; s = strong

Reference: R.M. Silverstein, G.C. Bassler, and T.C. Morrill, "Spectrometric Identification of Organic Compounds," 5th ed., Wiley, NY, 199l, pps. 158-164.