https://doi.org/10.1351/goldbook.B00737
A ![Not defined](/img/inline/B00737.png)
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. ![Not defined](/img/inline/B00737.png)
See also:
carbonium ion
, multi-centre bond
, neighbouring group participation