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) $$\underset{\mathrm{Propan}\text{-}1\text{-}\mathrm{amine}}{\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{CH}{\phantom{A}}_2\mathrm{NH}{\phantom{A}}_2}$$

(ii) $$\begin{array}{c}\mathrm{CH}{\phantom{A}}_3-\mathrm{CH}-\mathrm{CH}{\phantom{A}}_3\\ |\phantom{..}\\ \phantom{..}\underset{\mathrm{Propan}\text{-}2\text{-}\mathrm{amine}}{\mathrm{NH}{\phantom{A}}_2}\end{array}$$

Secondary amine:

(iii) $$\underset{\mathrm{N}-\mathrm{Methylethanamine}}{\mathrm{CH}{\phantom{A}}_3-\mathrm{NH}-\mathrm{C}{\phantom{A}}_2\mathrm{H}{\phantom{A}}_5}$$

Tertiary amine:

(iv) $$\begin{array}{c}\phantom{...}\mathrm{CH}{\phantom{A}}_3\\ |\\ \underset{\mathrm{N},\mathrm{N}-\mathrm{Dimethylmethanarnine}}{\mathrm{CH}{\phantom{A}}_3-\mathrm{N}-\mathrm{CH}{\phantom{A}}_3}\end{array}$$

Only primary amines react with HNO₂ to liberate N₂ gas.

$$\underset{\mathrm{Propan}\text{-}1\text{-}\mathrm{amine}}{\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{CH}{\phantom{A}}_2\mathrm{NH}{\phantom{A}}_2}+\mathrm{HNO}{\phantom{A}}_2⟶\underset{(\mathrm{major}\mathrm{product})}{\underset{\mathrm{Propan}\text{-}1\text{-}\mathrm{ol}}{\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{CH}{\phantom{A}}_2\mathrm{OH}}}+\mathrm{H}{\phantom{A}}_2\mathrm{O}+\mathrm{N}{\phantom{A}}_2$$

$$\begin{array}{c}\phantom{.}\mathrm{CH}{\phantom{A}}_3\phantom{.......................}\mathrm{CH}{\phantom{A}}_3\phantom{.............................}\\ \phantom{..}\mathrm{\setminus }\phantom{..........................}\mathrm{\setminus }\phantom{..........................}\\ \underset{\mathrm{Propan}\text{-}2\text{-}\mathrm{amine}}{\mathrm{CH}-\mathrm{NH}{\phantom{A}}_2}+\mathrm{HNO}{\phantom{A}}_2⟶\underset{(\mathrm{major}\mathrm{product})}{\underset{\mathrm{Propan}\text{-}2\text{-}\mathrm{ol}}{\mathrm{CHOH}}}+\mathrm{H}{\phantom{A}}_2\mathrm{O}+\mathrm{N}{\phantom{A}}_2\uparrow \\ /\phantom{..........................}/\phantom{..........................}\\ \phantom{.}\mathrm{CH}{\phantom{A}}_3\phantom{.......................}\mathrm{CH}{\phantom{A}}_3\phantom{..............................}\end{array}$$