Alkyl bromide formation [HBr]

Alkyl bromide formation (HBr) Definition:

Treatment of tertiary alcohols with HBr leads to the formation of tertiary alkyl bromides.

Alkyl bromide formation (HBr) Explained:

When treated with HBr tertiary alcohols typically undergo a nucleophilic substitution reaction to generate an alkyl bromide and water. The reactivity of alcohols is totally opposite in S_N1 from S_N2 reactions. The most reactive is tertiary alcohol, and the least reactive is methanol. This reaction proceeds via a carbocation intermediate which can also undergo rearrangement.

STEP 1. Protonation of the alcoholic oxygen to make a better leaving group. This step is very fast and reversible.

STEP 2. Loss of the good leaving group by the cleavage of the C-O bond. The carbocation is formed. This is the rate-determining step.

STEP 3. Attack of the nucleophilic bromide ion on the electrophilic carbocation creates the alkyl bromide.