Karbokationin

A carbocation (karbokationi) is a positively charged carbon-containing species, typically represented as R3C+. It is electron-poor and highly reactive, usually adopting an sp2-hybridized, planar geometry with an empty p orbital.

Stability increases with alkyl substitution due to hyperconjugation and inductive effects; tertiary > secondary > primary > methyl. Resonance with adjacent pi bonds or lone-pair-bearing atoms leads to extra stabilization, as in allylic and benzylic carbocations. Nonclassical carbocations involve bridged structures and delocalization; their existence has historically been debated.

Carbocations are key intermediates in many reactions, notably SN1 and E1, where a leaving group departs to generate a carbocation that is then trapped by a nucleophile or base. They can undergo rearrangements such as hydride or alkyl shifts, often to form more stable cations. Solvent polarity and temperature influence their lifetimes and reaction pathways; polar protic solvents stabilize carbocations via solvation.

Common examples include the tert-butyl cation, allyl cation, and benzyl cation. The study of carbocations combines kinetic, mechanistic, and theoretical approaches, and understanding their behavior informs synthetic planning and reaction design.