# Why do tertiary halides react faster in SN1 mechanism but are slow to reactivity in an SN2 mechanism?

Oct 11, 2016

Well, ${S}_{N} 2$ processes are essentially bond-making reactions,......

#### Explanation:

.......whereas ${S}_{N} 1$ processes are essentially bond-breaking reactions., and of course, are only dependent on the concentration of the electrophile.

A bond making process at a tertiary carbon centre, for instance, is unlikely to be kinetically favoured, given the shrubbery around the ${3}^{\circ}$ carbon.

On the other hand, this same shrubbery is likely to favour bond-breaking kinetically, and tend to stabilize a ${3}^{\circ}$ carbocation, which is conceived to be an intermediate in an ${S}_{N} 1$ process :

${R}_{1} {R}_{2} {R}_{3} C - X \rightarrow {R}_{1} {R}_{2} {R}_{3} {C}^{+} + {X}^{-}$

Hydrocarbyl substitution at carbon thus stabilizes the carbocation kinetically and thermodynamically, and favour unimolecular nucleophilic substitution.