Question

The correct increasing order of basic strength of the following amines/compounds is:
(I) \(C_6H_5NH_2\) (Aniline)
(II) \(NH_3\) (Ammonia)
(III) \(C_6H_5CH_2NH_2\) (Benzylamine)
(IV) \(C_2H_5NH_2\) (Ethylamine)
(V) \((C_2H_5)_2NH\) (Diethylamine)

• A. \(C_6H_5NH_2 < NH_3 < C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_2NH\)
• B. \(NH_3 < C_6H_5NH_2 < C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_2NH\)
• C. \(C_6H_5CH_2NH_2 < C_6H_5NH_2 < NH_3 < C_2H_5NH_2 < (C_2H_5)_2NH\)
• D. \(C_2H_5NH_2 < (C_2H_5)_2NH < C_6H_5NH_2 < NH_3\)

Hint:

Aromatic amines are weaker bases because resonance delocalizes the lone pair on nitrogen. Aliphatic amines are stronger due to the \(+I\) effect of alkyl groups.

Answer 1

The Correct Option is A

The basic strength of amines is determined by the availability of the lone pair of electrons on the nitrogen atom for donation. The factors affecting the basicity include the inductive effect, steric hindrance, and resonance. Let's analyze each compound:

1. \(C_6H_5NH_2\ (Aniline)\): Aniline is the least basic among the given compounds. The lone pair of nitrogen is involved in resonance with the benzene ring, making it less available for donation.
2. \(NH_3\ (Ammonia)\): Ammonia is a simple compound with a lone pair on nitrogen that is slightly more available compared to aniline.
3. \(C_6H_5CH_2NH_2\ (Benzylamine)\): Benzylamine has its lone pair on nitrogen, which is not conjugated with the aromatic ring like in aniline, making it more basic than both ammonia and aniline.
4. \(C_2H_5NH_2\ (Ethylamine)\): The ethyl group has a +I (inductive) effect, increasing the electron density on the nitrogen atom, making ethylamine more basic than benzylamine.
5. \((C_2H_5)_2NH\ (Diethylamine)\): Diethylamine has two ethyl groups providing an even stronger +I effect, resulting in the highest basicity among the given compounds.

The correct increasing order of basic strength for these compounds is:

\(C_6H_5NH_2 < NH_3 < C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_2NH\)

This order is primarily due to the inductive effect and resonance effects, influencing the electron availability on the nitrogen atom for bonding with protons.