Question

When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place:

\(CH_3-\underset{\underset{CH_3}{|}}{CH}-\underset{\underset{OH}{|}}{CH} -CH_3 \underset{}{\stackrel{HBr}{\longrightarrow}} \) \(CH_3- \underset{ \overset{|}{CH_3}}{\stackrel{\overset{Br}{|}}{C}} - CH_2 - CH_3 \)

Give a mechanism for this reaction.

(Hint: The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.

Answer 1

The mechanism of the given reaction involves the following steps:

Step 1: Protonation

Step 2: Formation of 2° carbocation by elimination of water molecule

Step 3: Rearrangement by the hydride-ion shift

Step 4: Nucleophilic attack