An organic compound [A](C₄H₁₁ N), shows optical activity and gives N₂ gas on treatment with HNO₂. The compound [A] reacts with PhSO₂Cl producing a compound which is soluble in KOH. The structure of A is :

Solution

Chemistry ma’am · 4 steps

The two tests say primary amine, and optical activity says chiral carbon. Only one option passes all three.

1. Nitrous acid test. A primary aliphatic amine reacts with HNO₂ to give an alcohol and N₂ gas. Secondary amines give an N-nitrosoamine instead, and tertiary amines give no N₂.
2. Hinsberg test. A primary amine gives PhSO₂NHR. Its N–H is acidic because of the sulfonyl group, so it dissolves in KOH. A secondary amine gives PhSO₂NR₂ with no N–H, which does not dissolve, and a tertiary amine does not react.

   Option	Type of amine	Chiral carbon?	Fits all clues?
   (a) CH₃CH₂CH₂NHCH₃	secondary	no	no
   (b) CH₃CH₂CH(NH₂)CH₃	primary	yes, C-2	yes
   (c) CH₃CH₂N(CH₃)₂	tertiary	no	no
   (d) CH₃CH₂CH₂CH₂NH₂	primary	no	no

3. Optical activity. In butan-2-amine, C-2 carries four different groups: H, CH₃, C₂H₅ and NH₂. That makes it a chiral carbon, so the compound is optically active.
4. So. A is butan-2-amine, option (b). It is a primary amine, so it releases N₂ and gives a KOH-soluble sulfonamide, and it has a chiral carbon.

The idea to keep. N₂ with HNO₂ and a Hinsberg product that dissolves in alkali both point to a primary amine. After that, look for a carbon with four different groups to explain the optical activity.

Answer from the NTA final answer key. Solution by PrepWiser.