N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
350
7 IR
Assignment
Range
Comments
≈1775–1705 Cyclic, ν ~ decreases with increasing ring size
O
≈1775
O
≈1750
O
≈1715
O
≈1705
Conjugated:
1700–1670
α,β-Unsaturated, often 2 bands (rotational
isomers)
1680–1640
α,β;γ,δ-Diunsaturated; α,β;α',β'-diunsaturated
1650–1600
C=C st
≈1695
al
O
≈1670
C
O
C
≈1675
ar
O
≈1690
Aryl ketones
≈1665
Diaryl ketones, with N or O in p-position:
down to ≈1600
α-Halogenated Shifted toward higher wavenumbers depending on dihedral
angle φ between C=O and C-hal; largest effect for φ = 0°, no
effect for φ = 90°
Maximal shifts: α-chloro
≈25
α-bromo
≈20
α,α-dichloro ≈45
α-iodo
≈0
α,α'-dichloro ≈45
α,α-difluoro ≈60
perfluoro
≈90
α-Diketones:
≈1720
Aliphatic
≈1775,
≈1760
Aliphatic 5-ring
≈1760,
≈1730
Aliphatic 6-ring
≈1675
Aliphatic enolized, C=C st: ≈1650
≈1680
Aromatic
≈1675
o-Quinones, with peri-OH: ≈1675, ≈1630
β-Diketones:
≈1720
Keto form, sometimes doublet