Question

Assertion: Due to ortho effect basic nature of aniline decreases.
Reason: It is due to steric hindrance because of solvation of cation.
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
(C) Assertion is correct but Reason is incorrect
(D) Both Assertion and Reason are incorrect.

Answer 1

Hint : Ortho effect is referred to as a set of steric hindrance produced in a compound having ring structure. It is caused when a substituent is present at the ortho position of that ring compound. Anilinium ion is produced on protonation of aniline which inhibits the solvation due to steric hindrance.

Complete Step By Step Answer:
When aniline acts as a base, it forms anilinium ion, ${C_6}{H_5}NH_3^ +$ by protonation. The protonation further changes the hybridization of nitrogen in the amino group from $s{p^2}$ to $s{p^3}$ which results in change of the planarity of the amino group by making it non planar. But it can be stabilised by solvation. However, if there is any substituent group present at the ortho position then, it inhibits the solvation. It is inhibited because of the steric hindrance between the ortho substituted group and the hydrogen atom of the amino group which results in making the conjugate acid more stable due to change in planarity of the benzene ring. There is also some electronegativity repulsion at ortho position. Hence, there is a reduction in basicity of substituted aniline.
Hence, option A is correct that Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Note :
Steric hindrance can be understood as the congestion caused by the presence of two or more molecules in a given arrangement. Steric hindrance can change the way a compound reacts with another compound. It can also change the shape of a molecule. Anilinium ion is a meta-activator or ortho/para deactivator and produces substantial amounts of meta products during nitration even though the ortho/para directivity of $- \ddot N{H_2}$ group.