Which of the following alcohols is most reactive towards aqueous HBr ?

Step-by-step solution

The reaction of an alcohol with aqueous HBr proceeds via the formation of a carbocation intermediate. The reactivity of the alcohol depends directly on the stability of the intermediate carbocation formed after protonation and loss of a water molecule. For 1-phenyl-2-propanol, the intermediate is a secondary carbocation: C ₆ H ₅- CH ₂- C ⁺ H - CH ₃ . For 1-phenyl-1-propanol, the intermediate is a secondary benzylic carbocation: C ₆ H ₅- C ⁺ H - CH ₂- CH ₃ . This carbocation is highly stabilized by resonance with th