Answer to Question #329598 in Organic Chemistry for Lipika

Question

With the help of two examples, compare the terms basicity and nucleophilicity.

Answer 1

Basicity means the ability to act as a base (to accept a proton).

Nucleophilicity means the ability of a species to act as a nucleophile (i. e. to interact with positive centers).

Example I:

HCl, HBr and HI are strong acids, which means that Cl^-, Br^- and I^- are weak bases.

However, Cl^-, Br^- and (especially) I^- are great nucleophiles and actively partake in S_N reactions.

Example II:

t-BuO^- is an exceptionally strong base, but because of the bulky methyl groups screening the electron pair on oxygen it is very hard for t-BuO^- to attack a positive center, which makes it a poor nucleophile. A proton, on the other hand, is a very small particle and basicity is not affected by steric hindrance.