Non-classical ions differ from traditional cations in their electronic structure: though chemical bonds are typically depicted as the sharing of electrons between two atoms, stable non-classical ions can contain three or more atoms that share a single pair of electrons. In 1939, Thomas Nevell and others attempted to elucidate the mechanism for transforming camphene hydrochloride into isobornyl chloride. In one of the proposed reaction mechanisms depicted in the paper, the positive charge of an intermediate cation was not assigned to a single atom but rather to the structure as a whole. This was later cited by opponents of the non-classical description as the first time that a non-classical ion was invoked. However, the term "non-classical ion" did not explicitly appear in the chemistry literature until over a decade later, when it was used to label delocalized bonding in a pyramidal, butyl cation.
The term synartetic ion was also invoked to describe delocalized bonding in stable carbocations before the term non-classical ion was in widespread use. The first users of this term commented on the striking similarity between bonding in these types of cations and bonding in borohydrides.