Non-classical Ion

In organic chemistry, a non-classical ion is a molecule with a positively charged carbon atom or atoms whose structure includes the sharing of two valence electrons by three atoms. They typically exhibit the delocalization of sigma bonds and the presence of hydrogen atoms as bridges between two carbon atoms.

The term non-classical ion was first used by John D. Roberts in 1951 in relation to the properties of cyclobutyl cations but the actual ions were first described by Saul Winstein in 1949 in order to explain the reactivity of certain norbornyl compounds.