carbocationes

Carbocationes are positively charged carbon-centered ions characterized by an electron-deficient carbon atom bearing an empty p orbital. In the dominant Lewis structure, the carbon is sp2-hybridized, three sigma bonds to surrounding substituents, and no lone pairs, giving a planar geometry and a formal +1 charge. The term is the Latin plural form of carbocation; in English texts “carbocations” is standard.

Stability of carbocationes grows with substitution and with resonance. Tertiary carbocations are more stable than secondary and primary due to hyperconjugation. If the positive charge is adjacent to a pi system (allylic or benzylic positions) or heteroatom with lone pairs, resonance or hyperconjugation further stabilizes the species. Inductive effects and solvent can modify stability; polar protic media often stabilize carbocations via solvation of the developing charge.

Carbocationes are common reactive intermediates in many reactions, notably SN1 and E1 processes, where a leaving group departs to form the carbocation, followed by nucleophilic capture or proton elimination. They can rearrange rapidly through hydride or alkyl shifts to reach more stable cations. In highly stabilized environments, such as in superacids or with extensive resonance, longer-lived carbocations can be observed or trapped using nucleophiles or isotopic labeling.

Classical carbocationes include tert-butyl, cyclopentyl, and benzyl/allyl cations; nonclassical or bridged carbocations have been proposed in some systems. Carbocation chemistry is central to organic synthesis, rearrangement chemistry, and reaction mechanism studies.