Question

how will you explain that o Nitro arenes are less basic than o toluidine​

Answer 1

Explanation:

Ortho toluidine is aniline with an additional methyl group in ortho position. When the NH2 group in 0-toludine accepts a proton to form anilinium ion, you have -NH3+ and CH3 on adjacent carbons in 0-toluidine. These groups come close to each other giving rise to steric repulsions and hence the total energy of the structure increases, making it less stable. As a result the equilibrium is shifted to the left making it less basic.

NH2 group in o-toluidine on accepting a proton becomes -NH3+ which moves out of plane due to steric repulsions and hence the positive charge is not delocalized making the compound less stable. So the equilibrium is towards the left, making it less basic.

Answer 2

The basicity of o-toluidine is higher than that of o-nitroaniline. In o-toluidine, the methyl group enhances electron density, but in o-nitroaniline, the nitro group is an electron withdrawing group that reduces electron density. As a result, o-toluidine has a higher basicity than o-nitroanilin.

An aniline with an extra methyl group in the ortho position is called ortho toluidine. You get -NH3+ and CH3 on neighbouring carbons in 0-toluidine when the NH2 group takes a proton to generate anilinium ion. As these groups become closer to each other, steric repulsions form, increasing the overall energy of the structure and making it less stable. As a result, the balance has shifted to the left.