Question

Which of the following compounds gives fastest reaction with HBr and why

(i) (CH3)3 COH

(ii) CH3 CH2 CH2OH

(iii) CH3 CHOH CH3

(iv) CH3 (CH3) CH CH2OH

Answer 1

Solution -
(ii) CH3CH2CH2OH -

CH3CH2CH2OH + HBr ---------------- CH3CH2Br + H2O
Because

For the reaction between alkyl halide and a nucleophile, following the S_N2 mechanism, the reactivity of alkyl halides is in the order: primary halide > secondary halide > tertiary halide.

If you consider the reactivity of alcohols with halogen acids to form alkyl halides, the reactivity of alcohols is in the order: tertiary alcohol > secondary alcohol > primary alcohol.