Nonclassical ion

They are characterized by delocalized three-center, two-electron bonds.

The more stable members are often bi- or polycyclic.

[2][3] Historically, nonclassical ions were invoked to explain unusually fast solvolyses of steroidal, norbornyl, and cyclopropyl halides.

As indicated first by low-temperature NMR spectroscopy and confirmed by X-ray crystallography,[1] it has a symmetric structure with an RCH2+ group bonded to an alkene group, stabilized by a bicyclic structure.

Solvolyses of cyclopropylcarbinyl, cyclobutyl, and homoallyl esters are also characterized by very large rates, and have been shown to occur via a common nonclassical ion structure in the form of a bicyclobutonium ion.

Structure of the 2-norbornyl cation, an iconic nonclassical ion. The structure was deduced from X-ray crystallography . C-C bond lengths not labeled are normal (ca. 1.5 Å). [ 1 ]