Amino acids exhibit amphoteric behavior in aqueous solution due to the presence of both acidic (carboxyl group) and basic (amino group) groups, forming a dipolar ion or zwitterion. Naturally occurring a-amino acids, except glycine, are optically active due to the asymmetry of the a-carbon atom, existing in both ‘D’ and ‘L’ forms with most having L-configuration.
Explain the amphoteric behavior of amino acids in aqueous solution, and why are naturally occurring a-amino acids optically active?
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Amino acids exhibit amphoteric behavior in aqueous solution as they can act as both acids (donating a proton from the carboxyl group) and bases (accepting a proton by the amino group). This dual nature enables them to undergo zwitterion formation, with a positively charged amino group and a negatively charged carboxyl group in equilibrium. Regarding optical activity, naturally occurring α-amino acids are optically active due to their chiral nature. They possess a central carbon (α-carbon) bonded to four different substituents, creating a mirror-image isomerism. This asymmetry results in enantiomers, and the presence of chiral centers makes α-amino acids optically active.