The structure of a secondary vinylic carbocation. The cation. The cationic carbon atom is sp-hybridized and has a vacant p orbital perpendicular to the plane of the π bond orbitals. Only one R group is attached to the positively charged carbon rather than two, as in a secondary alkyl carbocation. The electrostatic potential map shows that the most positive (blue) regions coincide with lobes of the vacant p orbital and are perpendicular to the most negative(red) regions associated with the π bond.