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3 Combination Tables
3.10 Carbonyl Compounds
3.10.1 Aldehydes
Assignment
Range
Comments
CHO
al C–(CHO)
al C–(C–CHO)
190–205 ppm
30–70 ppm
5–50 ppm
Coupling constant 1 J CH ≈ 170 Hz
Coupling constant 2 J CH ≈ 25 Hz
Shift with respect to C–(C–CH 3 ) ≈-10 ppm
(C)=C–(CHO)
C=(C–CHO)
ar C–(CHO)
110–160 ppm
110–160 ppm
120–150 ppm
H–(C=O)
9.0–10.5 ppm
al CH–(CHO)
2.0–2.5 ppm
3 J HH 0–3 Hz
(CH)=CH(CHO) 5.5–7.0 ppm
3 J HH ≈8 Hz
CH=(CH–CHO) 5.5–7.0 ppm
ar CH–(C–CHO) 7.2–8.0 ppm
Shift with respect to CH–(C–H):
ortho ≈+0.6 ppm
meta ≈+0.2 ppm
para ≈+0.3 ppm
comb
2900–2700 cm -1 Two weak bands
C=O
1765–1645 cm -1 Aliphatic: ≈1730 cm -1
Conjugated: ≈1690 cm -1
Molecular ion
Aliphatic: moderate
Aromatic: strong
Fragments
[M-1] +
[M-29] +
For aliphatic aldehydes, only significant up
to C 7
Rearrangements
m/z 44
[M-44] +·
Aliphatic aldehydes
O
H
H
R
- RCH =CH 2
OH
H
+ .
+ .
n π*
270–310 nm (log ε ≈1) Saturated aldehydes
≥207 nm (log ε ≈4)
α,β-Unsaturated aldehydes
≥250 nm (log ε >3)
Aromatic aldehydes
13 C
1 H
IR
MS
UV