question_answer

  Account for the following : (i) Tertiary amines do not undergo acylation reaction, (ii) The basic strength of aliphatic amines in solution is in the order sec > tert > prim. (iii) Amines are more basic than comparable alcohols.

Answer:

                  (i) In tertiary amines there are no acidic hydrogen due to which it do not undergo acylation reaction. (ii) Basic strength in aqueous solution is determined by three factors - Inductive effect, solvation effect and steric factor. Inductive effect favours 3° amine, solvation effect favours 1° amine and steric factor favours 1° amine. So, over all basicity is : 2° > 3° > 1°. (iii) N being less electronegative than O gives lone pair of electron more easily than O atom. Therefore amines are more basic than alcohols. Basicity is decided by three factors : (i) Inductive effect. (ii) Solvation effect. (iii) Steric factor. Electron releasing group increases the electron density on nitrogen atom that increases its basic strength. So, the order is 3° > 2° > 1°. Now in aqueous solution 1° amine forms 3 hydrogen bond 2° amine forms two hydrogen bond and 3° amine forms one hydrogen so, the stability of ions by solvation and hence basicity should follows a trend 1° > 2° > 3° and due to steric reason 2° amine is more basic than 1°.