Question

Why is aniline a stronger base than para methyl alinine?

Answer 1

Answer:

hii mahima

Explanation:

As expected from Inductive(/hypercojugative) as well as ortho effect the basicity order should be: ortho-toluidine>para-toluidine>meta-toluidine. But,

experimental order is: para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69)>ortho-toluidine(Pka=4.39).

The order of basicity is explained by two opposing effects :

i) inductive effect

ii) Stability of the conjugate base

. Here 2nd factor is more significant for ortho-toluidine & 1st factor is important for para-toluidine. For ortho-toluidine the conjugate base [o-MeC6H4NH3+] is destabilized by

steric interaction

between -NH3+ & -Me(at ortho). This desatabilization is absent with para-toluidine & meta-toluidine.Tha's why basicity of:

ortho-toluidine(Pka=4.39)<

para & meta isomer

.On the other hand,in meta toluidine only +I of Me is operative whereas in para-toludine both hypercojugative & +I of Me is operative, that's why basicity of:

para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69).