Instant Notes: Analytical Chemistry

268 Section E – Spectrometric techniques

d (ppm)

190180170160150140130120110100 90 80 70 60 50 40 30 20 10 0

H 3 C

H 3 C

CH CH C

OH CH 3

CH 3

CH 2 OH

c

c

d

g

e f

a

b g f

d

e

b

c

a

CDCI 3

Fig. 10.^13 C spectrum of 2,2,4-trimethyl-1,3-pentanediol.

d (ppm)

190180170160150140130120110100 90 80 70 60 50 40 30 20 10 0

O

HO CH

NH 2

C

CH 3

Fig. 9.^13 C spectrum of alanine.

Some examples of carbon-13 spectra with their resonances assigned are

shown in Figures 9- 11.

The three carbons show a very wide range of chemical shifts. The lowest field

resonance corresponds to the carbonyl carbon, which is highly deshielded by

the double-bonded oxygen. The nitrogen deshields the CHcarbon much less,

and the CH 3 carbon is the least deshielded of the three.

The carbon-13 resonances of this fully saturated compound (Fig. 10) are all

found between 0 and 90 d/ppm. The two carbons directly bonded to oxygens are

deshielded significantly more than the CHcarbon, which in turn is more

deshielded than the CH 3 carbons.