e) 2-hydroxypropanoic acid exhibits optical isomerism. i) What is isomerism? ii) Give the structures of the optical isomers.

The structural formula is $\mathrm{CH_3CH(OH)COOH}$.

The carbon atom at position 2 (alpha carbon) is attached to four different groups: $\mathrm{-H}$, $\mathrm{-OH}$, $\mathrm{-CH_3}$, $\mathrm{-COOH}$.

This chiral center results in optical isomerism.

(i) Optical isomerism

The two enantiomers in Fischer projection (vertical bonds going into the page, horizontal coming out):

First enantiomer:

$$\begin{array}{c} \mathrm{COOH} \\ \, \\ \mathrm{H-C-OH} \\ \, \\ \mathrm{CH_3} \end{array}$$

Second enantiomer (mirror image):

$$\begin{array}{c} \mathrm{COOH} \\ \, \\ \mathrm{HO-C-H} \\ \, \\ \mathrm{CH_3} \end{array}$$

These are non-superimposable mirror images.

(ii) Structures as shown above.

optical isomerism