Carbocation

A carbocation whose positively charged carbon is bonded to three carbon substituents.

A carbocation whose positively charged carbon is bonded to two carbon substituents.

Migration of a neighboring C–H bonding pair onto an electron-deficient carbon, moving the carbocation site.

An oxocarbenium ion is a cationic species stabilized by adjacent oxygen donation, commonly represented by carbon-cation and oxonium resonance contributors. Reversible acetal opening can expose a locally planar carbon for attack from either face.

An oxocarbenium ion at the anomeric carbon of a cyclic glycosyl fragment. Positive charge is delocalized between that carbon and the ring oxygen. A counterion can remain nearby and influence which face a nucleophile approaches.