Instant Notes: Analytical Chemistry

E13 – NMRS: interpretation of proton and carbon-13 spectra 265

Cl OCH

CH 3

COOH

11 10 9 8 7 6

d (ppm)

543210

1

4

1

3

600 500 400 300

(Hz)

200 100 0

Fig. 5.^1 H spectrum of 2-(1,4-chlorophenoxy)propanoic acid.

The CH 3 resonance in 2-(4-chlorophenoxy)propanoic acid(Fig. 5) is well

upfield as it is not affected by an adjacent electronegative group. The CHproton

is deshielded by the oxygen, and the aromatic protons by the ring current effect.

The downfield COOHproton is strongly deshielded by the adjacent oxygen and

by H-bonding. The coupled CH 3 and CHprotons give an AX 3 quartet and

doublet, and the symmetry of the aromatic resonances is typical of a 1,4-disub-

stituted ring. The integral ratios are 1:4:1:3.

The CH 3 resonance of phenylethyl ethanoate (Fig. 6) is shifted downfield by

the deshielding effect of the ester group. The two CH 2 groups (methylenes)

couple to give A 2 X 2 triplets, the higher field one being the CH 2 adjacent to the

ring, the lower field being more strongly deshielded due to the oxygen. The five

ring protons are almost equally deshielded by the ring current and the integral

ratios are 5:2:2:3.