bridged carbocation
A @[email protected] (real or hypothetical) in which there are two (or more) carbon atoms that could in alternative @[email protected] be designated as @[email protected] but which is instead represented by a structure in which a group (a hydrogen atom or a hydrocarbon residue, possibly with substituents in non-involved positions) bridges these potential carbenium centres. One may distinguish 'electron-sufficient bridged carbocations' and 'electron-deficient bridged carbocations'. Examples of the former are phenyl-bridged ions (for which the @[email protected] 'phenonium ion' has been used), such as (A). These ions are straightforwardly classified as @[email protected] The latter type of ion necessarily involves three-centre bonding. Structures (C) and (D) contain five-coordinate carbon atoms. The 'hydrogen-bridged @[email protected]' (B) contains a two-coordinate hydrogen atom. @[email protected], which includes [email protected]@ for hydrogen and five- but also higher @[email protected] for carbon is generally observed in bridged carbocations.
See also:
carbonium ion
multi-centre bond
neighbouring group participation
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1090 [Terms] [Paper]