# Why do elimination reactions compete with substitution reactions when alkyl halides react with a nucleophile?

Oct 19, 2015

Not always!

#### Explanation:

Elimination reactions compete with substitution reactions because both reaction mechanisms favour the same conditions: Alkyl halide and a nucleophile.

Under some conditions, the elimination reactions cannot compete with substitution reactions because they cannot occur and vice versa.

Example on No Elimination reaction:

The acetate $C {H}_{3} C O {O}^{-}$ is a strong nucleophile and a weak base, therefore, the substitution ${S}_{N 1}$ will occur at a very fast rate and consume all the alkyl halide before any elimination product is formed.

Example on No substitution reaction:

The tert-butoxide ${\left(C {H}_{3}\right)}_{3} C {O}^{-}$ is a strong bulky base and a weak nucleophile. The elimination will occur at a very fast rate and consume the alkyl halide before any substitution product is formed.