Carbocation
A carbocation (/ˌkɑːrbəˈkætaɪən, -boʊ-/) is an ion with a positively charged carbon atom. Among the simplest examples are methenium CH+
3, methanium CH+
5, and ethanium C
2H+
7. Some carbocations may have two or more positive charges, on the same carbon atom or on different atoms; such as the ethylene dication C
2H2+
4.
Until the early 1970s, all carbocations were called carbonium ions. In present-day chemistry, a carbocation is any positively charged carbon atom, classified in two main categories according to the valence of the charged carbon: three in the carbenium ions (protonated carbenes), and five or six in the carbonium ions (protonated alkanes, named by analogy to ammonium). This nomenclature was proposed by G. A. Olah. Carbocations are stabilized by the dispersion or delocalization of the positive charge
Definitions
Some university-level textbooks discuss carbocations as if they were only carbenium ions, or discuss carbocations with only a fleeting reference to the older terminology of carbonium ions or carbenium and carbonium ions. One textbook retains the older name of carbonium ion for carbenium ion to this day, and uses the phrase hypervalent carbenium ion for CH5+.
