Question

Which one of the following is least able to behave as a Lewis base: CH3NH2, (CH3)2NH, (CH3)3N , or (CH3)3NH+?

Answer 1

Trimethylammonium ion, `[(H_3C)_3NH]^+`, is clearly least able to function as a Lewis Base; the nitrogen has been quaternized and is no longer available.

Explanation:

By definition, a Lewis Base is an electron pair donor, whereas a Bronsted base is a proton acceptor. Methylamine, `H_3CNH_2`, dimethylamine, `(H_3C)_2NH`, and trimethylamine, `(H_3C)_3N` are all Bronsted bases and Lewis bases by virtue of the lone electron pair on the nitrogen centre.