Instant Notes: Analytical Chemistry

series of steps, generally displayed above each resonance signal. The vertical

height of each step, in arbitrary units, gives the relative number of protons

associated with the signal. Integration of carbon-13 resonances is not sufficiently

reliable to be of value.

Proton spectra The interpretation of proton spectra depends on three features: chemical shifts,
multiplicities of resonancesand integrated peak areas. These are exemplified
in the spectrum of ethanol, C 2 H 5 OH, shown in Figure 2.
The following is a general approach to spectral interpretation, which should
be augmented by reference to chemical shift data, coupling constants and the
spectra of known compounds.

262 Section E – Spectrometric techniques

12 11 10 9 8 7 6

Chemical shift d (ppm)

543210

–COOH –OH

Ar–OH CH–Ar

CH–C=O

CH–Hal.

ArCH=O CH–O–

Ar–H CH–C=C

CH–N CH–C

HC=C

HC=O

HC C––––

C–O

CH–O

CH 2 –O

CH 3 –O

C–N

CH–N

CH 2 –N

CH 3 –N

C–Hal

CH–Hal

CH 2 –Hal

CH 3 –Hal

C–C

CH–C

CH 2 –C

C=O acid C=C alkene

C=O ketone

C=O quinone

C=C aromatic

C=O ester, amide C N C C

aldehyde

C=O ––– ––– CH 3 –C

200 160 120 80 40 0

Chemical shift d (ppm)

Fig. 1. Chemical shift charts for proton (a) and carbon-13 (b) spectra.

(a)

(b)