CAIE A-Level Chemistry 37.4.5 Identifying O–H and N–H with D₂O

Practise using signal loss after D₂O exchange to identify labile O–H, N–H and carboxylic-acid protons.

Exam points

compare spectra before and after shaking with D2O and assign any disappearing signal to an exchangeable proton
count OH, NH and COOH protons in the structure when predicting how many hydrogens lose 1H signals
predict no change only when the molecule contains no proton that can exchange with deuterium under the test

[Maximum number: 1]

Amino acids are molecules that contain $-\mathrm{NH}_{2}$ and -COOH functional groups.
Glycine, $\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}$ , is the simplest stable amino acid.

Compound V is another amino acid.

The proton $\left({ }^{1} \mathrm{H}\right)$ NMR spectrum of V shows hydrogen atoms in five different environments, a , b , c, d and e, as shown in Fig. 6.2.

Fig. 6.2

Table 6.1

Complete Table 6.3 by placing a tick ( $\checkmark$ ) to indicate any protons whose peaks are still present in the proton $\left({ }^{1} \mathrm{H}\right)$ NMR spectrum of V taken in $\mathrm{D}_{2} \mathrm{O}$ .

Table 6.3

proton & a & b & c & d & e

present in $\mathrm{D}_{2} \mathrm{O}$ & & & & &

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37.4.5—O-H and N-H proton exchange with D2O question 1