Question

The correct order of basic strength is :
A. ${C_6}{H_5}N{H_2}$ $>$ $C{H_3}N{H_2}$ $>$ $N{H_3}$
B. $C{H_3}N{H_2}$ $>$ ${C_6}{H_5}N{H_2}$ $>$ $N{H_3}$
C. $C{H_3}N{H_2}$ $>$ $N{H_3}$ $>$ ${C_6}{H_5}N{H_2}$
D. $N{H_3}$ $=$ $C{H_3}N{H_2}$ $=$ ${C_6}{H_5}N{H_2}$

Answer 1

Basic strength directly depends on the availability of lone pairs for ${H^ + }$ Factors which affect the basicity are: Steric effects, Inductive effect and Solvation effect.

Complete step by step answer:
Amines are aliphatic and aromatic derivatives of ammonia. Amines, like ammonia, are weak bases .This basicity is due to the unshared electron pair on the nitrogen atom.
Order of basic strength in amines is decided by the availability of lone pairs present on the nitrogen. Nitrogen atom in amine is the electron donor, because it has a total $7\,{e^ - }$ .
To check the order of basicity, we have to check the availability of lone pairs on nitrogen, how easily it is available for attack of an electrophile.
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair.
For better understanding let us recall them one by one:
Steric effect: Any effect on a molecule, a reaction, etc. due to the size of atoms or groups. Common steric effects include steric hindrance and van der Waals repulsion.
Inductive effect: The effect on electron density in one portion of a molecule due to electron-withdrawing or electron-donating groups elsewhere in the molecule.
Solvation is an interaction of a solute with the solvent, which leads to stabilization of the solute species in the solution. In the solvated state, an ion in a solution is surrounded or complexed by solvent molecules. It is not considered in this question
In $N{H_3}$the lone pair of nitrogen is available in it.
In $C{H_3}N{H_2}$, lone pairs of nitrogen are available and also inductive effects of methyl group, so electron density is more than $N{H_3}$.
In ${C_6}{H_5}N{H_2}$the lone pair of benzene is taking part in resonance with the benzene ring, so it is least available.
Correct order : $C{H_3}N{H_2}$ $>$ $N{H_3}$ $>$ ${C_6}{H_5}N{H_2}$

Note: Resonance is a way of describing bonding in certain molecules or ions by the combination of several contributing structures into a resonance hybrid in valence bond theory.