Which of the following alcohols undergoes acid-catalysed dehydration through a carbocation the fastest under the same conditions?

Aethanol
B2-methylpropan-2-ol
Cbutan-2-ol
Dbutan-1-ol

Answer: B

The rate-determining step is formation of the carbocation. 2-Methylpropan-2-ol gives the tertiary cation, butan-2-ol a secondary one, and the other two would need primary cations. Rate:

3^{\circ} > 2^{\circ} > 1^{\circ}

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