Nuclear Magnetic Resonance Spectroscopy: Theory and Applications
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OCH 3
OCH 3
OCH 3
OCH 3
OCH 3
OCH 3
a
b
c
b
c
Four peaks
a
a
b
b
c
c
Three peaks
a
a
a
a
Two peaks
b
b
d
7.3.1 Effect of Electronegativity
13 C chemical shift chart shows that effect of electronegative-substituent that cause
downfield shift in
1 H-NMR cause similar variation in
13 C-NMR. For e.g.
13 C-NMR
chemical shift values in 4-methyl pentanone is shown below:
H 3 C C
O H 2
C C
H
CH 3
CH 3
22.8
25.0
53.0
207.3
30.4
Though, a small shielding effect (upfield shift) of electronegative elements can
be seen on γ-carbon atom of skeleton [4, 5]:
H 3 C
H 2
C
H 2
C
H 2
C
H 2
C
H 2
C OH
61.9
32.8
25.8
32.0
22.8
14.8
a
ß
Y
7.3.2 Effect of Hybridization
State of hybridization of carbon has significant effect on
13 C-NMR similar to
1 HNMR signals and can be analyzed from the following table:
Hybridization state
δ-range (ppm)
sp 3 -carbon
0–60
sp 2 -carbon
80–200
sp-carbon
65–90