N
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
311
7.2 Alkenes
311
Assignment
Range
Comments
Subranges: C=C
C=C–C=O
C=C–OR
C=C–O–C=O
CH=CH 2 1005–985
920–900
(overtone at
1850–1800)
≈980
≈960
≈810
≈960
≈815
≈950
≈870
C=CH 2
900–880
(overtone at
1850–1780)
≈940
≈810
≈795
H
H
990–960
≈975
≈960
≈950
H
H
725–675
≈820
H
840–800
≈820
C=C st
1690–1635
Of variable intensity,
absent with symmetric substitution,
strong for N–C=C and O–C=C
Subranges:
1650–1635
CH=CH 2
1660–1640
C=CH 2
1690–1665
H
H
Weak
1665–1635
H
H
1690–1660
H Weak, often absent
1690–1650
Weak, often absent
Beyond normal range:
down to
≈1590
C=C–X with X: O, N, S; of higher intensity; in
vinyl ethers often doublet due to rotational
isomers