Write structures of different isomers corresponding to the molecular formula, C₃H₉N. Write IUPAC names of the isomers which will liberate nitrogen gas on treatment with nitrous acid.
The molecular formula C₃H₉N corresponds to four structural isomers:
1. Primary Amines:
- CH₃-CH₂-CH₂-NH₂ (Propan-1-amine)
- CH₃-CH(NH₂)-CH₃ (Propan-2-amine)
2. Secondary Amine:
- CH₃-CH₂-NH-CH₃ (N-Methylethanamine)
3. Tertiary Amine:
- (CH₃)₃N (N,N-Dimethylmethanamine)
Isomers liberating nitrogen gas with nitrous acid: The two primary amines — Propan-1-amine and Propan-2-amine — will liberate nitrogen gas on treatment with nitrous acid. This is because aliphatic primary amines react with nitrous acid to form alcohols with the evolution of nitrogen gas.
Explanation
The question tests understanding of structural isomerism in amines and their characteristic reactions. C₃H₉N has 4 isomers: 2 primary, 1 secondary, and 1 tertiary amine. Primary aliphatic amines react with HNO₂ to form diazonium salts which decompose to give N₂ gas and alcohols. Secondary and tertiary amines do not liberate N₂ gas with nitrous acid.
Solution Steps
Step 1: Determine the degree of unsaturation for C₃H₉N (saturated compounds)
Step 2: Identify all possible primary amine structures (2 isomers)
Step 3: Identify secondary amine structure (1 isomer)
Step 4: Identify tertiary amine structure (1 isomer)
Step 5: Apply knowledge that primary amines react with HNO₂ to liberate N₂ gas