carbocation

A carbocation is a molecule with a positive charge localized on a carbon atom. These are often short-lived intermediates in chemical reactions, though some can be stable enough for study. Carbocations are fundamental to understanding many organic reactions, including those important in industry and biochemistry.1

There are two main types:
* Classical carbocations: These have a trivalent carbon atom and a planar structure.1
* Nonclassical carbocations: These have a pentacoordinated carbon atom with a three-center bond.1

Carbocations are typically formed through the cleavage of a bond, removal of an electron, addition of a proton, or protonation of a bond. They are more stable in polar solvents and their stability increases with the number of alkyl groups attached to the positively charged carbon atom. Tertiary carbocations are more stable than secondary, which are more stable than primary. Benzyl cations are also relatively stable due to charge distribution within an aromatic ring. Carbocations react readily with electron-donor molecules called nucleophiles.1