Question

The descending order of basic strength of the following amines is
(i) N-Methylbenzenamine (ii) N,N'-Dimethylbenzenamine (iii) Benzenamine (iv) Phenylmethanamine

• A. (i) $>$ (ii) $>$ (iv) $>$ (iii)
• B. (iv) $>$ (i) $>$ (ii) $>$ (iii)
• C. (iv) $>$ (ii) $>$ (i) $>$ (iii)
• D. (iv) $>$ (iii) $>$ (ii) $>$ (i)
• E. (i) $>$ (iv) $>$ (ii) $>$ (iii)

Hint:

Basicity trend: - Aliphatic amines $>$ aromatic amines - More alkyl groups $\Rightarrow$ higher basicity

Answer 1

The Correct Option is C

Concept: Basic strength of amines depends on availability of lone pair on nitrogen:
• Aliphatic amines $>$ aromatic amines (due to resonance in aromatic amines)
• Electron donating groups increase basicity

Step 1: Analyze each compound.

• (iv) Phenylmethanamine (benzylamine): behaves like aliphatic amine $\Rightarrow$ most basic
• (ii) N,N-dimethylbenzenamine: +I effect of two methyl groups increases basicity
• (i) N-methylbenzenamine: less +I effect than (ii)
• (iii) Benzenamine (aniline): least basic due to resonance

Step 2: Arrange order.
\[ (iv) > (ii) > (i) > (iii) \]