58
3 Combination Tables
3.4 Aromatic Hydrocarbons
Assignment
Range
Comments
ar C
ar CH
al C–C ar
120–150 ppm
110–130 ppm
10–60 ppm
Same ranges for polycyclic aromatic hydrocarbons
H–C ar
6.5–7.5 ppm
In polycyclic aromatic hydrocarbons
up to ≈9 ppm
Coupling constants: 3 J ortho ≈7 Hz
4 J meta ≈2 Hz
5 J para <1 Hz
CH 3 –C ar
CH 2 –C ar
CH–C ar
≈2.3 ppm
≈2.6 ppm
≈2.9 ppm
Often line broadening due to long-range
coupling with aromatic protons
ar C–H st
3080–3030 cm -1 Often multiple bands, weak
comb
2000–1650 cm -1 Very weak
ar C–C st
≈1600 cm -1
≈1500 cm -1
≈1450 cm -1
Of variable intensity, sometimes not all bands
observable
ar C–H δ oop
960–650 cm -1 Strong, frequently multiple bands
Molecular ion
Strong, often base peak
Fragments
m/z 39, 50–53,
63–65, 75–78,
[M-26] +· , [M-39] +
Often doubly charged fragment ions
Benzylic cleavage
CH 1-3
m/z 91 (90, 92)
Other typical fragments
m/z 127
+ .
m/z 152
+
m/z 165
Rearrangements
R
R
R H
X
- X C H =CH 2
R
R
R H
+ .
+ .
13 C
1 H
IR
MS