Preferred Label : bridged carbocation;
IUPAC definition : A carbocation (real or hypothetical) in which there are two (or more) carbon atoms
that could in alternative Lewis formulae be designated as carbenium centres 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 trivial name 'phenonium ion' has been used), such as (A). These
ions are straightforwardly classified as carbenium ions. The latter type of ion necessarily
involves three-centre bonding. Structures (C) and (D) contain five-coordinate carbon
atoms. The 'hydrogen-bridged carbocation' (B) contains a two-coordinate hydrogen atom.
hypercoordination, which includes two-coordination for hydrogen and five- but also
higher coordination for carbon is generally observed in bridged carbocations.;
Origin ID : B00737;
See also
A carbocation (real or hypothetical) in which there are two (or more) carbon atoms
that could in alternative Lewis formulae be designated as carbenium centres 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 trivial name 'phenonium ion' has been used), such as (A). These
ions are straightforwardly classified as carbenium ions. The latter type of ion necessarily
involves three-centre bonding. Structures (C) and (D) contain five-coordinate carbon
atoms. The 'hydrogen-bridged carbocation' (B) contains a two-coordinate hydrogen atom.
hypercoordination, which includes two-coordination for hydrogen and five- but also
higher coordination for carbon is generally observed in bridged carbocations.