Question

Question #898eb

Answer 1

I think you are asking, "Is the reaction: HCl + CH₃OH → CH₃Cl + H₂O an `S_N1` or an `S_N2`process?". If so, the answer is `S_N2`.

`S_N1` requires the formation of CH₃⁺. This is a highly unstable carbocation, so the reaction will not go `S_N1`.

The rate determining step in an `S_N2` reaction would be

Cl⁻ + CH₃-O⁺H₂ → [Cl•••CH₃•••OH₂]⁺ → Cl-CH₃ + OH₂

This is the favoured mechanism because:

1. It avoids formation of the methyl cation.
2. There is no steric hindrance to back-side attack by a nucleophile.
3. H₂O is an excellent leaving group.
4. Cl⁻ is a fairly good nucleophile.