Illustrated Glossary of Organic Chemistry

Vinylic carbocation: A carbocation in which the carbon atom having the open octet and positive formal charge is part of a carbon-carbon double bond. The carbocation carbon has sp hybridization.

General vinylic carbocation structure.		The vinyl carbocation (a primary carbocation).

Acid-catalyzed hydration of phenylacetylene (a terminal alkyne) involves a vinylic carbocation intermediate. In the first mechanism step, the alkyne is protonated by hydronium ion (a strong acid) to produce a resonance-stabilized secondary vinylic carbocation (shown in red). This carbocation is also a benzylic carbocation.