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

Step-by-step solution

The reaction of alcohols with aqueous HBr proceeds via the formation of a carbocation intermediate ( S_ N 1 mechanism). The reactivity of the alcohol is directly proportional to the stability of the carbocation formed. Let us analyze the carbocations formed from the given alcohols: 1-Phenyl-2-propanol forms C₆H₅-CH₂-CH⁺-CH₃ , which is a secondary carbocation. 3-Phenyl-1-propanol forms C₆H₅-CH₂-CH₂-CH₂⁺ , which is a primary carbocation. 2-Phenyl-1-propanol forms C₆H₅-CH(CH₃)-CH₂⁺ , which is a primary carbocation. 1-