Question

Which compound in the following pair will react faster in S_N2 reaction with OH⁻?

CH₂=CHBr or CH₂=CH-CH₂Br

Answer 1

CH₂=CH–CH₂Br (allyl bromide) reacts faster in an S_N2 reaction with OH⁻ than CH₂=CHBr (vinyl bromide) because S_N2 cannot proceed at a vinylic (sp²) carbon, while the allylic position is highly favorable for S_N2 due to sp³ hybridization and resonance stabilization.