Question

Which compound can exist in a dipolar (zwitterion) structure?
(A) \[{C_6}{H_5}C{H_2}CH(N = C{H_2})COOH\]
(B) \[{(C{H_3})_2}CHCH(N{H_2})COOH\]
(C) \[{C_6}{H_5}CONHC{H_2}COOH\]
(D) \[HOOCC{H_2}C{H_2}COCOOH\]

Answer 1

Hint: Zwitterions are basically molecules with two sets of functional groups. The condition to be followed is that one of these functional groups needs to be positively charged, while the other functional group needs to be negatively charged. Also, the net charge on the molecule must be zero.

Complete Step-by-Step Solution:
To determine which of the given molecules is a zwitterion, we need to understand the molecular structures of these molecules and also understand the type of functional groups present on these molecules. Another condition to be followed is that both these functional groups must be present on the same carbon atom.
\[{C_6}{H_5}C{H_2}CH(N = C{H_2})COOH\]

The functional groups present in this compound are secondary amine and carboxylic acids. Amine is a positive functional group and carboxylic acid is a negative functional group. But both these functional groups are not present on the same carbon atom.

\[{(C{H_3})_2}CHCH(N{H_2})COOH\]

The functional groups present in this compound are amine and carboxylic acid. Amine is a positive functional group and carboxylic acid is a negative functional group. And both these functional groups are present on the same carbon atom.

\[{C_6}{H_5}CONHC{H_2}COOH\]

The functional groups present in this compound are amide and carboxylic acid. Amide is a negative functional group and carboxylic acid is also a negative functional group.

\[HOOCC{H_2}C{H_2}COCOOH\]

The functional groups present in this compound are carbonyl and carboxylic acid. Carbonyl is a negative functional group and carboxylic acid is also a negative functional group.

Hence, Option C is the correct option.

Note: Amino Acids have both the amine functional group and carboxylic acid functional group. Both of these are present on the same carbon atom. Hence all amino acids are by default zwitterions.