Question

What is steric effect? N, N-dimethy1 aniline is a weaker base than 2,6-dimethyl N, N - dimethyl aniline. Explain.

Answer 1

In both of them lone is participating in resonance(mesomeric effect).

But in N,N dimethyl aniline there is +I effect of the two methyl group, but due to the presence of methyl groups there is also a steric hindrance but inductive effect dominates .Hence , N,N dimethyl aniline is more basic than aniline.

TRICKS

See whether lone pair is participating in resonance or not , if yes then basicity decreases because availability of donation of lone pair decreases as they are delocalised.(#more is the resonance less basic is the amine.)

As the +I effect increases electron density over nitrogen atom increase .Hence donation tendency increases, basic nature increases.(#Basic nature is proportional to +I effect).