Editing Carbocation (section)

==== Non-classical carbenium ions ====
Non-classical carbenium ions feature also σ delocalization (3c2e bonds) in their bonding but have the general formula CR<sub>3</sub><sup>+</sup> (R = alkyl or H).  Thus, in principle, one can propose non-bridged, classical structures for these cations, as well as a bridged non-classical structure.  Because of the subtle differences in the expected behavior of a non-classical carbenium ions compared to the alternative hypothesis of two rapidly equilibrating classical structures, a lively and often acrimonious debate took place over several decades regarding the merits of each model. For a detailed history of this dispute, see the article on the [[2-Norbornyl cation|2-norbornyl cation]]. Currently, there is overwhelming evidence that, at least in some cases (notably the extremely well-studied 2-norbornyl cation), the equilibrium structure of a carbenium ion is non-classical, although even minor changes in structure could result in a classical structure being favored.