The C=O stretching frequency
aldehydes and ketones
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
Aliphatic Aldehyde
100
90
% Transmittance
80
70
60
50
H-C=O
Impurity peak,
probably O-H
40
30
1730 cm-1
20
10
4000
3500
3000
2500
2000
Wavenumbers, cm
1500
1000
500
-1
Figure IR-14. Butanal, neat liquid, thin film: CH3CH2CH2CHO
Aliphatic Ketone
100
% Transmittance
80
60
40
20
1715 cm-1
0
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumbers, cm
Figure IR-35. 5-Hexene-2-one, neat liquid: CH2=CH2CH2CH2COCH3
The C=O stretching frequency
esters
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
Aliphatic Ester
100
% Transmittance
80
60
40
20
Top: CHCl3 vs CHCl3
Bottom: 2.5 % v/v un CHCl3
1720 cm-1
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers, cm-1
Figure IR-33. Methyl acetate in 0.1 mm NaCl cells: CH3CO2CH3
CCl4
neat
1746 cm-1
1748 cm-1
100
% Transmittance
80
60
40
20
Top: CHCl3 vs CHCl3
Bottom: 2.5 % v/v un CHCl3
1720 cm-1
0
4000
3500
3000
2500
2000
-1
Wavenumbers, cm
1500
1000
500
Aliphatic Ester
The effect of phase on IR frequencies
120
% Transmittance
100
vapor: 106 °C
80
60
40
liquid film
20
0
4000
3500
3000
2500
2000
1500
1000
Wavenumber, cm-1
Figure IR-34. Vapor and liquid spectra of ethyl n-hexanoate:
CH3CH2CH2CH2CH2CO2CH2CH3
The C=O stretching frequency
aliphatic acids
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
120
% Transmittance
100
vapor: 134 °C
80
Aliphatic Acid
60
40
liquid film
20
0
4000
3500
3000
2500
2000
1500
1000
W avenumber, cm -1
Figure IR-26. The liquid,
vapor and CCl4 soln
spectra of hexanoic acid:
1710 cm-1
CH3(CH2)4 CO2H
The C=O stretching frequency
aliphatic amides
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
Amide I 
1662 cm-1
KBr
pellet
Amide II; 1634 cm-1
Secondary Amide
100
90
% Transmittance
80
70
60
50
40
30
Amide I
20
Amide II
10
4000
3500
3000
2500
2000
1500
1000
500
Wavnumbers, cm-1
Figure IR-21. N-Methyl acetamide, neat liquid; thin film:
CH3CONHCH3
Tertiary Amide
100
% Transmittance
80
60
40
20
No amide II band
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers, cm -1
Figure IR-23. N,N-Dimethylacetamide, neat liquid; thin film:
CH3CON(CH3)2
The C=O stretching frequency
anhydrides
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
Anhydrides
100
% Transmittance
80
60
40
20
0
4500
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm-1
Figure IR-36. Propionic anhydride, neat liquid:
CH3CH2CO2COCH2CH3
The C=O stretching frequency
carboxylates
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
1560 cm-1
1410 cm-1
The C=C bond stretch
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
100
% Transmittance
80
60
HC=C
stretches
C=C
stretch
40
20
(CH2)4
rocking
CH3,CH2 symmetric
and asymmetric stretches
CH3,CH2
bending
vibrations out of plane
H wag of vinyl
group 900, 1000 cm-1)
0
4000
3500
3000
2500
2000
1500
1000
Wavenumbers, cm-1
Figure IR-9. 1-Heptene; neat sample, thin film:
H2C=CH-CH2CH2CH2CH2CH3
500
The C=C bond stretch when next to a heteroatom
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
100
% Transmittance
80
60
40
20
0
4000
3500
3000
2500
2000
1500
1000
Wavenumbers, cm -1
CH3O
O
500
OCH3
Figure IR-40. 2,5-Dimethoxy2,5-dihydrofuran, neat liquid:
100
% Transmittance
80
60
40
20
1610 cm-1
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers, cm-1
O
Figure IR-41. 2,3-Dihydrofuran, neat liquid:
1652 cm-1
The cumulative C=C bond stretch
1958 cm-1
The NO2 stretching frequency
A summary of the principle infrared bands and their assignments.
R is an aliphatic group.
C=O
C=C
aldehydes
ketones
esters
carboxylic acids
amides (Amide I)
(Amide II)
(Amide II)
amide
anhydrides
carboxylates
olefins
-NO2 nitro groups
R(C=O)H
R(C=O)R
R(CO2)R
RCO2H
RCONH2, RCONHR
RCONH2
RCONHR
RCONR2
R(CO2CO)R
R(CO2)-, M+
R2C=CR2
R2C=CH2
R2C=C(OR)R
RNO2
1740-1720
1730-1710
1750-1735
1720-1680
1670-1640
1650-1620
1550
1650-1620
1820, 1750
1600, 1400
1680-1640
1600-1675
1600-1630
1550, 1370
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S(sh)
S, S(sh)
S,S(sh)
W(sh)
M(sh)
S(sh)
S,S(sh)
14
35
33, 34
26,27,30
19, 21
19, 21
19, 21
23
36
42
10, 39, 40
9, 35
41
28
1556
cm-1
1367 cm-1
+ ON
O
O
+
N
O -
120
% Transmittance
100
80
60
40
20
symmetric and asymmetric
-NO2 stretch
1510
0
4000
3500
3000
2500
2000
and 1320 cm-1
1500
Wavenumbers, cm-1
4-Chloro-2-nitrophenol, KBr pellet:
1000
500
Aromatic Rings
Ring breathing motions
1600-1585
1500-1400
Both often appear as doublets
100
% Transmittance
80
60
carbon-carbon
triple bond stretch
40
20
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers, cm-1
H
90
% Transmittance
80
70
60
overtones of
the benzene
ring
50
40
30
20
4000
3500
3000
2500
2000
Wavenumbers, cm-1
Benzene, neat, thin film:
1500
1000
500