IR Exercise
Match the following 10 compounds with the 10 spectra on the following pages. Label the major diagnostic
peaks on each spectrum to receive full credit.
1-butanol
HOCH2CH2CH2CH3
CH2OH
benzyl alcohol
N-methylcyclohexylamine
aniline
NHCH3
NH2
O
2-pentanone H3C C CH2CH2CH3
O
C
acetophenone
ethyl acetate
1-hexene
pentane
H 3C
O
C
O
CH3
CH2CH3
CH2=CHCH2CH2CH2CH3
CH3CH2CH2CH2CH3
butyraldehyde H3CH2CH2C
O
C
H
Reference
Some IR Stretching Frequencies
3400-3250 cm-1
N–H (1˚, 2˚ amines)
1680-1640 cm-1
C=C (alkenes)
3500-3200 cm-1
O–H (alcohols)
1600-1585 cm-1
C–C (aromatics)
3100-3000 cm-1
C–H (alkenes, aromatics)
1500-1400 cm-1
C–C (aromatics)
3000-2850 cm-1
C–H (alkanes)
1335-1250 cm-1
C–N ( aromatic amines)
2830-2695 cm-1
C–H (aldehydes)
1250-1020 cm-1
C–N (aliphatic amines)
1750-1665 cm-1
C=O (see discussion on back)
1300-1050 cm-1
C–O (alcohols, esters)
Carbonyl Stretching Frequencies
The exact position of the carbonyl band in the 1760-1665 cm-1 range is determined by the constituents
neighboring the carbonyl group. Some examples are:
range
1750-1735 cm-1
type of carbonyl
examples
saturated aliphatic esters
O
C
R
1740-1720 cm-1
1730-1715 cm-1
saturated aliphatic aldehydes
R
O
C
O
H
!,"-unsaturated esters
R'
"R
saturated aliphatic
ketones
1715 cm-1
1710-1665 cm-1
R'
R
O
C
O
C
O
C
OR
OR
R'
!,"-unsaturated alde-
hydes and ketones
R'
"R
O
C
R'
H
"R
O
C
O
C
H
O
C
R
R
Another way of looking at the correlation between wavenumber and functional group stretch:
C
H
O
4400
C
C
H
H
C C
O
H
H
C
H (or R)
H (or R)
O
C
C
C
O
N
}
increasing band intensity
N
}
H (or R)
4000 3750 3500 3250 3000 2750 2500 2250 2000 1750 1500 1250 1000 750
450 cm
1
2
3
4
5
6
A
7
8
9
A
10