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

To solve this question, we must first discuss the different compounds formed by using amine groups. Then the nature of the basic character can be discussed on the basis of the molecular structures of the different compounds and a corresponding relation can be established.

Complete step by step answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
-We can observe that all the options have one common functional group present in their molecules. This functional group is known as amine and is denoted by the chemical formula $R - N{H_2}$ , where R could either be an alkyl group or an aryl group or just a hydrogen atom. The base compound from which this functional group is obtained is known as ammonia. The molecular formula for ammonia is $N{H_3}$ and the molecular structure for ammonia is:

-We can see that there are 3 sigma bonds and one lone pair of electrons present in the molecule of ammonia. This lone pair of electrons gives ammonia its basic character. The amine group is formed when one of the hydrogen atoms is removed from the molecule.
In order to derive a trend of basicity observed in amine compounds, we must consider the following factors:
1.Alkyl groups have the tendency to push electrons towards the more electronegative substituent present in the compound. In a compound with amine, the nitrogen atom is usually the most electronegative substituent present. Hence, the alkyl groups tend to push electrons to nitrogen atoms, thereby increasing its basicity in comparison to ammonia.
2.When an amine group is attached to a benzene ring, it too becomes aromatic in nature. The different resonant structures of benzene would now include the amine group as well. This would decrease the possibility of the amine to have the delocalised electrons available all the time. This would in turn decrease the basicity of the compound in comparison to ammonia.
Hence, the order of basicity of the different amine groups can be given as:
Alkyl amines > ammonia > aryl amine
Hence, the order of the basic strength of the given compounds is $C{H_3}N{H_2} > N{H_3} > {C_6}{H_5}N{H_2}$

Hence, Option C is the correct option.

Note:
The stability of a compound would definitely increase if it is aromatic in nature, but the resonant structures cause delocalisation of electrons. This at times alters with the acidic and basic characters of the compound.