Carbonium Ions

molecular particles containing a triva-lent positively charged carbon atom. Carbonium ions are highly reactive and therefore unstable. They form on heterolytic cleavage of the C—X bond (the electron pair which effects this bond is removed with the X group):

For example, the action of strong acids on triphenyl carbinol yields a triphenylmethyl cation salt:

This carbonium ion is stable due to the distribution of the positive charge among several carbon atoms. Carbonium ions also form during the action of aprotic acids on halogen derivatives, for example

They also form during the addition of a proton or other cation to the multiple bond:

Carbonium ions readily interact with anions, with molecules containing an unshared electron pair or a multiple bond, and with other compounds, attacking areas with increased electron density. Carbonium ions are intermediate particles in many organic reactions of both theoretical and practical value (for example, alkylation and acylation according to the Friedel-Crafts reaction, reactions of electrophilic combination with olefins, iso-merization and cation polymerization of olefins, and pinacolic and retropinacolic, Dem’ianov, and Wagner-Meerwein rearrangements).