Carbenium ion

A carbenium ion is a carbocation of the trivalent and classical type R3C+. A carbonium ion is a carbocation of the penta- or tetracoordinated nonclassical type such as an ion of the type R5C+. Carbonium ions appear as nonclassical carbocations such as the norbornyl cation These definitions have been proposed by the chemist George Andrew Olah in 1972 and now widely accepted. In older literature a carbocation of the type R3C+ may still be referred to as a carbonium ion.