Question

Write structures of different isomers corresponding to the molecular formula C₃H₉N. Write the IUPAC names of the isomers which will liberate nitrogen gas on treatment with nitrous acid.

Answer 1

The molecular formula C₃H₉N represents four isomers of aliphatic amines. This is as follows:

Primary amines:

(i) \[\ce{\underset{Propan-1-amine}{CH3CH2CH2NH2}}\]

(ii) \[\begin{array}{cc}
\ce{CH3 - CH - CH3}\\
|\phantom{..}\\
\phantom{..}\ce{\underset{Propan-2-amine}{NH2}}
\end{array}\]

Secondary amine:

(iii) \[\ce{\underset{N-Methylethanamine}{CH3 - NH - C2H5}}\]

Tertiary amine:

(iv) \[\begin{array}{cc}
\phantom{...}\ce{CH3}\\
|\\
\ce{\underset{N, N-Dimethylmethanarnine}{CH3 - N - CH3}}
\end{array}\]

Only primary amines react with HNO₂ to liberate N₂ gas.

\[\ce{\underset{Propan-1-amine}{CH3CH2CH2NH2} + HNO2 -> \underset{(major product)}{\underset{Propan-1-ol}{CH3CH2CH2OH}} + H2O + N2^}\]

\[\begin{array}{cc}
\phantom{.}\ce{CH3}\phantom{.......................}\ce{CH3}\phantom{.............................}\\
\phantom{..}\ce{\backslash}\phantom{..........................}\ce{\backslash}\phantom{..........................}\\
\ce{\underset{Propan-2-amine}{CH - NH2} + HNO2 -> \underset{(major product)}{\underset{Propan-2-ol}{CHOH}} + H2O + N2 ^}\\
/\phantom{..........................}/\phantom{..........................}\\
\phantom{.}\ce{CH3}\phantom{.......................}\ce{CH3}\phantom{..............................}\\
\end{array}\]