3.10 Carbonyl Compounds
69
3.10.2 Ketones
Assignment
Range
Comments
C=O
al C–(C=O)
al C–(C–C=O)
195–220 ppm
25–70 ppm
5–50 ppm
Shift with respect to C–(C–CH 3 ) ≈-6 ppm
(C)=C–(C=O)
C=(C–C=O)
ar C–(C=O)
105–160 ppm
105–160 ppm
120–150 ppm
al CH–(C=O)
2.0–3.6 ppm
al CH–C(=O)–C al 2.0–2.6 ppm
al CH–C(=O)–C ar 2.5–3.6 ppm
CH=CH–(C=O) 5.5–7.0 ppm
ar CH–(C–C=O) 7.2–8.0 ppm
Shift with respect to CH–(C–H):
ortho ≈+0.6 ppm
meta ≈+0.1 ppm
para ≈+0.2 ppm
C=O st
1775–1650 cm -1 Aliphatic: ≈1715 cm -1
Cyclic: ring size ≥6: ≈1715 cm -1
ring size <6: ≥1750 cm -1
Conjugated: ≈1690–1665 cm -1
Molecular ion
Aliphatic: moderate
Aromatic: strong
Fragments
Ketone cleavages:
R 1
O
R 2
R 1 CO
+
, R 1
+
, R 2 CO
+
, R 2
+
+ .
Rearrangements
m/z 44
[M-44] +·
Aliphatic ketones
O
R 2
H
R 1
- R 1 CH=CH 2
OH
R 2
O
R 2
+ .
+ .
+ .
π π*
n π*
<200 nm (log ε 3–4)
Saturated ketones
250–300 nm (log ε 1–2) Saturated ketones
≥215 nm (log ε ≈4)
α,β-Unsaturated ketones
≥245 nm (log ε >3)
Aromatic ketones
13 C
1 H
IR
MS
UV