494
M. Rashid et al.
Fig. 21 13 C-NMR chemical shifts (δ-values) of compounds with functional groups
200 ppm and therefore spread upto 20 times larger range than
1 H-NMR (0–12 ppm).
Nature of distribution of chemical shift is similar to
1 H-NMR (Fig. 21).
7.3 Factors Affecting 13 C-NMR Chemical-Shift
Presence of equivalent carbons in
13 C-spectra give information about carbon-skeleton
of molecule i.e. presence of non-equivalent set of carbons in a molecule and hence
presence of symmetry in organic molecule [22]. For e.g. number of peaks of
13 CNMR (proton-decoupled) can be depicted on the basis of symmetry point of view:
a
a
a
a
a
a
a
CH 3
a
b
c
b
a
d
e
CH 3
a
b
c
b
a
d
e
a
b
b
a
a
b
b
a
c
c
a
a
a
a
a
a
b
b
one
three
five
five
two
eight
O
a
b
c
d
e
f
g h
Substitution pattern of the aromatic ring (o-, m- and p- substitution) can be
depicted on the basis of
13 C-NMR: