Carbon (13C) has a much broader chemical shift range.
One important difference is that the aromatic and alkene regions
overlap to a significant extent. We now see all the carbons,
though quaternary carbons (having no hydrogens) are usually quite weak;
the proton decoupling process gives rise to an enhancement that
quaternary carbons do not experience.
The reference point (0 ppm) is also the chemical shift of carbon in
tetramethylsilane,
(CH3)4Si.
Here is a table of typical 13C chemical shifts:
Chemical Environment of
the Carbon
|
200+
|
180
|
160
|
140
|
120
|
100
|
80
|
60
|
40
|
20
|
0
|
Alkane CH-CR3
|
|
|
|
|
|
|
|
|
10-50
|
Allylic, Benzylic, ketone
=C-CH, Ph-CH, CH-C=O
|
|
|
|
|
|
|
|
|
40-55
|
|
|
Alkyne C=C-H
|
|
|
|
|
|
|
70-110
|
|
|
|
|
Alkyl halide CH-X
|
|
|
|
|
|
|
|
55-80
|
|
|
|
Ether/alcohol/ester CH-O
|
|
|
|
|
|
|
60-80 Acetals:
90-100
|
|
|
|
Nitriles, RC=N
|
|
|
|
|
|
110-120
|
|
|
|
|
|
Alkene =C-H
|
|
|
|
120-160
|
|
|
|
|
|
|
Aromatic Ph-H
|
|
|
125-170
|
|
|
|
|
|
|
Aldehyde, Ketone RC(=O)-H
|
>200
|
|
|
|
|
|
|
|
|
|
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Carboxylic Acid RCO2H
and derivatives (esters, acid chlorides, amides, anhydrides)
|
|
165-190
|
|
|
|
|
|
|
|
|
|
200+
|
180
|
160
|
140
|
120
|
100
|
80
|
60
|
40
|
20
|
0
|
Some examples
Spectrum
|
Structure & Notes
|
tBuOH.jdx
|
Note the 1:1:1 triplet at 77 ppm: this is CDCl3 solvent. The carbon couples to the deuterium (spin = 1) and creates this pattern.
|
trimethylpentene.jdx |
|
ochlorobenzoic.jdx
|
It is possible to predict which carbon is which based on additive substituent effects on each carbon. Those of you in CH 362 are learning how to do that.
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|