Question

Among the following the most basic compound is: -

(A) p-nitroaniline

(B) Acetanilide

(C) Aniline

(D) Benzylamine

Answer 1

Hint: The lone pair of electrons in some compounds are in conjugation with the benzene ring and thus are not available to react with other compounds, whereas in some compounds the lone pair of electrons are not in conjugation with the ring and are away from it and thus they are readily available to react and combine with other elements.

Complete Step By Step Answer:
(A) The structure of p-nitroaniline is as follows:

Here the $-NO_2$ group shows the -I effect as it is an electron withdrawing group and the electron withdrawing group increases the acidity of compounds. So (A) will be acidic in nature.

(B) The structure of acetanilide is as follows:

In this, the lone pair of electrons of Nitrogen are in conjugation with the aromatic system (i.e. the Benzene ring) and are not freely available for donation. So, it is less basic.

(C) The structure of aniline is as follows:

In aniline also, the lone pair of electrons on Nitrogen are in conjugation with the aromatic system. So, it is delocalized and is not available for donation. So, it is also less basic.

(D) The structure of benzylamine is as follows:

In benzylamine, the lone pair of electrons are not in conjugation or attached with the benzene ring and thus are free for donation to an electrophile (i.e. an electron deficient group) or to combine with other elements. So, the compound benzylamine is the most basic compound among the given options.
Hence, the correct answer is (D).

Note:
Carefully examine the structure of given compounds. All these four compounds have benzene rings in common and they only differ in the arrangement of other nitrogen and carbon groups. If the nitrogen group is attached with the benzene ring then the electrons are not free and thus the nature of the compound will be acidic, and if the nitrogen group is not directly linked with the benzene ring then electrons can move freely and react.