Question

The correct sequence of base strengths in aqueous solution is

• A. ${(CH_3)_2NH > CH_3NH_2 > (CH_3)_3N}$
• B. ${(CH3)3N > (CH3)2 NH > CH3NH2}$
• C. ${ (CH3)3N > CH3 NH2 = (CH3 )2 NH}$
• D. ${(CH3)2N H > (CH3 )3 N > CH3 NH2}$

Answer 1

The Correct Option is A

It is expected that the basic nature of amines should be in order tertiary > secondary > primary but the observed order in the case of lower members is found to be as secondary > Primary > tetriary. This anomalous behaviour of tetriary amines is due to steric factors i.e crowding of alkyl groups cover nitrogen atom from all sides thus makes the approach and bonding by a proton relatively difficult which results the maximum steric strain in tetiary amines. The electrons are there but the path is blocked, resulting the reduction in basicity.
Thus the correct order is ${R_2NH > RNH_2 > R_3 N}$