A) Glycine
B) Valine
C) Leucine
D) Isoleucine
Correct Answer: A
Solution :
Amino acids are colourless crystalline, water soluble and aminated organic acids formed of C, H, 0, N and some times 'S'. General formula of amino acid \[\text{NH}_{\text{3}}^{\text{+}}\text{-}\underset{\begin{smallmatrix} \text{ }\!\!|\!\!\text{ } \\ \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix} \text{R} \\ \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,\text{-CO}{{\text{O}}^{\text{-}}}\] \[R=\text{ }H.C{{H}_{3,}}{{C}_{2}}{{H}_{7,}}{{C}_{3}}{{H}_{11}}\]etc, Glycine is the simplest and smallest amino acid. A compound show optical activity, when a chiral carbon or asymmetrical carbon (i.e., carbon which attached to four different groups or atoms) is present. Because chiral carbon is absent in glycine. So, it does not show optical activity. \[\text{Glycine}\xrightarrow[{}]{{}}\text{NH}_{\text{3}}^{\text{+}}\text{-}\underset{\begin{smallmatrix} \text{ }\!\!|\!\!\text{ } \\ \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix} \text{R} \\ \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,\text{-CO}{{\text{O}}^{\text{-}}}\] Other amino acids contain atleast single asymmetric carbon atoms, so they show optical activity e.g., Valine, Icucine and isoleucine.
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