Question

When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place:
`CH_(3)-underset(CH_(3))underset("| ")("C ")H-underset(OH)underset("| ")("C")H-CH_(3)overset(HBr)rarr CH_(3)-overset(Br)overset("| ")underset(CH_(3))underset("| ")("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

Protonation of the given alcohol followed by loss of water gives a `2^(@)` carbocation (I), which being unstable rearranges by 1,2-hydride shift to form the more stable `3^(@)` carbocation (II). Nucleophilic attack by Br ion on this carbocation (II) gives the final product.