A) Maleic acid
B) \[\text{-}\]amino acids
C) Lactic acid
D) Tartaric acid
Correct Answer: A
Solution :
Only those compounds exhibit optical isomerism, which have chiral centre and/or absence of symmetry elements. (Chiral carbon is the carbon all the four valencies of which are satisfied by four different groups.) \[\underset{\begin{align} & \,\,\,\,\,\,\,\text{maleic}\,\text{acid} \\ & \text{(no}\,\text{chiral}\,\text{centre,} \\ & \,\,\,\,\text{so,}\,\text{optically} \\ & \,\,\,\,\,\,\,\,\,\,\text{inactive} \\ \end{align}}{\mathop{\underset{\text{CHCOOH}}{\overset{\text{CHCOOH}}{\mathop{\text{ }\!\!|\!\!\text{ }\!\!|\!\!\text{ }}}}\,}}\,\] \[\underset{\begin{smallmatrix} \alpha \text{-amino}\,\text{acids} \\ \text{(one}\,\text{chiral}\,\text{centre}\, \\ \text{so,}\,\text{opticall}\,\text{active)} \end{smallmatrix}}{\mathop{\underset{\begin{smallmatrix} | \\ N{{H}_{2}} \end{smallmatrix}}{\mathop{\text{R}-\overset{\text{*}}{\mathop{\text{C}}}\,\text{H}-\text{COOH}}}\,}}\,\] \[\underset{\begin{smallmatrix} \,\,\,\,\,\,\,\text{lactic}\,\text{acid} \\ \text{(one}\,\text{chiral}\,\text{centre,} \\ \text{so}\,\,\text{optically}\,\text{active}\, \end{smallmatrix}}{\mathop{\text{C}{{\text{H}}_{\text{3}}}\overset{\text{*}}{\mathop{\text{C}}}\,\text{H(OH)COOH}}}\,\] \[\underset{\begin{smallmatrix} \,\,\,\,\,\,\,\text{tartaric}\,\text{acid} \\ \text{(two}\,\text{chiral}\,\text{carbon,} \\ \text{so}\,\text{optically}\,\text{active)}\, \end{smallmatrix}}{\mathop{\underset{\begin{smallmatrix} \text{ }\!\!|\!\!\text{ } \\ \text{*}\overset{{}}{\mathop{\text{C}}}\,\text{H(OH)COOH} \end{smallmatrix}}{\mathop{\text{*}\overset{{}}{\mathop{\text{C}}}\,\text{H(OH)COOH}}}\,}}\,\] Thus, maleic acid does not exhibit optical isomerism. Note If R = H, the a-amino acid is achiral.
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