Looking for classes? Ksquare Career Institute, Bengaluru →
Which of the following compounds is most basic?
A
- 
B
- 
C
- 
D
- 
Detailed Solution
Basicity depends on how available the lone pair on nitrogen is for accepting a proton.
In benzylamine the $-NH_2$ group is attached to an $sp^3$ carbon ($-CH_2-$), not directly to the ring, so the lone pair is not delocalised into the benzene ring; it behaves like an aliphatic primary amine.
In aniline the lone pair is delocalised into the ring by resonance, which lowers its basicity.
In p-nitroaniline the electron-withdrawing $-NO_2$ group withdraws the lone pair further, making it even less basic than aniline.
In acetanilide the lone pair is delocalised onto the carbonyl oxygen of the $-COCH_3$ group as well, so it is almost non-basic.
Order of basicity: benzylamine > aniline > p-nitroaniline > acetanilide. Hence benzylamine is the most basic.
In benzylamine the $-NH_2$ group is attached to an $sp^3$ carbon ($-CH_2-$), not directly to the ring, so the lone pair is not delocalised into the benzene ring; it behaves like an aliphatic primary amine.
In aniline the lone pair is delocalised into the ring by resonance, which lowers its basicity.
In p-nitroaniline the electron-withdrawing $-NO_2$ group withdraws the lone pair further, making it even less basic than aniline.
In acetanilide the lone pair is delocalised onto the carbonyl oxygen of the $-COCH_3$ group as well, so it is almost non-basic.
Order of basicity: benzylamine > aniline > p-nitroaniline > acetanilide. Hence benzylamine is the most basic.