What is "carbenium ion"

n. (context chemistry English) any carbocation containing a tervalent carbon atom

A carbenium ion is a positive ion with the structure RR′R″C, that is, a chemical species with one trivalent carbon that bears a +1 electric charge.

In older literature the name carbonium ion was used for this class, but now it refers exclusively to another family of carbocations, the carbonium ions, where the charged carbon is pentavalent. The current definitions were proposed by the chemist George Andrew Olah in 1972, and are now widely accepted.

Carbenium ions are generally highly reactive due to having an incomplete octet of electrons; however, certain carbenium ions, such as the tropylium ion, are relatively stable due to the positive charge being delocalised between the carbon atoms.