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Protonation of alcohols to give oxonium ions

Description: Addition of a strong acid to an alcohol leads to the formation of its conjugate acid (called an “oxonium ion”).

Notes: This reaction is the first step in many reactions that form carbocations, such as the SN1 and E1 reactions, as OH2(+) is an excellent leaving group. Typical acids for this reaction are HCl, HBr, HI, and H2SO4.



Mechanism: The reaction is a simple acid base reaction with the alcohol attacking the acid (Step 1, arrows A and B).