JEE Chemistry 2023 Question with Solution

Given: Assertion about chlorination of glycine in presence of red phosphorus, and a Reason about molecules with $2$ chiral carbons.

Find: Which option correctly evaluates Assertion $A$ and Reason $R$.

For Assertion $A$, glycine is $\text{NH}_2\text{CH}_2\text{COOH}$. In the presence of chlorine and red phosphorus, $\alpha$-halogenation occurs to give:

In the product, the carbon attached to $\text{NH}_2$, $\text{Cl}$, $\text{H}$ and $\text{COOH}$ has four different groups, so it is a chiral carbon atom. Therefore, Assertion $A$ is true.

For Reason $R$, the statement 'a molecule with $2$ chiral carbons is always optically active' is false. A compound with two chiral centers can be optically inactive if it contains an internal plane of symmetry. Such compounds are called meso compounds.

Therefore, Reason $R$ is false.

Hence, Assertion $A$ is true but Reason $R$ is false. The correct option is C.

Given: Glycine undergoes chlorination in presence of red phosphorus.

Find: Whether the product contains a chiral carbon.

The starting amino acid is glycine, $\text{NH}_2\text{CH}_2\text{COOH}$. After substitution at the $\alpha$-carbon, the product becomes $\text{NH}_2\text{CHClCOOH}$. Now inspect the substituted carbon:

• it is attached to $\text{NH}_2$
• it is attached to $\text{Cl}$
• it is attached to $\text{H}$
• it is attached to $\text{COOH}$

Since all four attached groups are different, that carbon is chiral. This confirms the Assertion.