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Bromomethane with aqueous NaOH

Short answer

Bromomethane reacts via SN2: hydroxide ion attacks the backside of carbon in a concerted step, displacing bromide and forming methanol with Walden inversion; rate = k[CH3Br][OH⁻].

How does the reaction of bromomethane occur with aqueous caustic soda?

Bromomethane (CH₃Br) is a methyl halide. Its carbon is even less hindered than that of a primary halide, so it reacts with aqueous NaOH by the SN2 mechanism to give methanol.

Mechanism: SN2 (one step, concerted).

HO⁻ + H₃C—Br  →  [HO···CH₃···Br]⁻‡  →  HO—CH₃ + Br⁻
                 (transition state)

        H                 H                  H
         \                |                 /
 HO⁻ +  H—C—Br  →  [HO····C····Br]⁻  →  HO—C—H  +  Br⁻
         /               / \                \
        H               H   H                H
 backside attack      transition state    inverted product

Overall: CH₃Br + NaOH(aq) → CH₃OH + NaBr

  • Rate = k[CH₃Br][OH⁻]: second order (bimolecular).
  • The nucleophile attacks from the side opposite to the leaving group; the three H atoms flip over like an umbrella in the wind (Walden inversion).
  • Reactivity order: CH₃X > 1° > 2° > 3° (steric hindrance).

✓ Answer checked by Claude Opus 5.5 (high effort)

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