What is "carbonium ion"

n. (context chemistry English) a carbenium ion or any carbocation

In chemistry, carbonium ion is any cation that has a pentavalent carbon atom, The name carbonium may also be used for the simplest member of the class, properly called methanium , where the five valences are filled with hydrogen atoms.

Doo Wan Boo and Yuan T. Lee (1995), "Infrared spectroscopy of the molecular hydrogen solvated carbonium ions, (n=1–6)". J. Chem. Phys. volume 103, page 520;

The next simplest carbonium ions after methanium have two carbons. Ethynium or protonated acetylene and ethenium are usually classified in other families. The ethanium ion has been studied as an extremely rarefied gas by infrared spectroscopy.

L. I. Yeh, J. M. Price, and Y. T. Lee (1989), "Infrared spectroscopy of the pentacoordinated carbonium ion ". Journal of the American Chemical Society, volume 111, pages 5591-5604.

In older literature the name "carbonium ion" was used for what is today called carbenium. The current definitions were proposed by the chemist George Andrew Olah in 1972. and are now widely accepted.

A stable carbonium ion is the complex penta(triphenylphosphine gold(I))methanium , produced by Schmidbauer and others.