Question

Identify the most basic compound from the following: Primary amines, Secondary amines, Aromatic amines and aliphatic amines.

Answer 1

Hint : Amines compounds are basic in nature. They are basic in nature due to the presence of nitrogen atoms in the amine group. The basicity of the amines depend on the lone pair of electrons of nitrogen. Higher the electronic effect on the lone pair of nitrogen more will be its basicity.

Complete Step By Step Answer:
Amines act as a Lewis base because of the presence of lone pairs of electrons on the nitrogen atom. Therefore when a ${H^ + }$ ion approaches amines, nitrogen donates its lone pair to the ion. Thus it acts like a Lewis base. The availability of lone pairs on the amine group makes it basic in nature.
Therefore aliphatic amines are more basic than aromatic amines. This is because the lone pair present on nitrogen atoms in aromatic amines will take part in resonance of the ring. Thus the availability of lone pairs is less in aromatic amines. But in aliphatic amines no such resonance takes place. Thus we can say that aliphatic amines are more basic than the aromatic amines.
Further, for aliphatic amines, primary amines and tertiary amines are less basic than secondary amines. This is because when ${H^ + }$ ion approaches the tertiary amine, it experiences a steric hindrance due to alkyl groups. Thus the basicity of tertiary mines becomes less. Also for primary amine, due to less inductive effect, the protonation of amines becomes less efficient. Thus secondary amines are the most basic amines among all the compounds.

Note :
Steric Hindrance takes place when the compound becomes bulky in nature. Thus when an atom approaches it , then it experiences a hindrance. The lone pair in aromatic amines is delocalised, hence the availability of lone pair electrons reduces which reduces its basicity.