Answer to Question #54376 in Organic Chemistry for ravish

Question

Arrange the following in order of decreasing basic strength, justify your answer: alkanide anion , alkenide anion, alkynide anion.

Answer 1

The anions can be arranged in order of decreasing basic strength as follows:
Alkynide > alkenide > alkanide
The basic strength is defined by the capability of anion to use the electron lone pair (negative charge) in formation of new bond. The main reason of decreasing basic strength from alkynide to alkanide is stabilization of anion. This is conditioned by the s-character of hybridized orbitals which increases in the following order: alkynide(sp3) < alkenide(sp2) < alkanide(sp). As it known, s-orbital has spherical shape that provides efficient distribution of negative charge and stabilizes anion. Therefore, the alkynide is less stable, but is very basic, and the alkanide is very stable but is a very weak base.