Classical ion
From Mass Spec Terms
A penta-coordinated carbonium ion (see Onium Ion) such as the norbornyl cation named non-classical by S. Winstein. The term derives from a cornerstone of the classical theory of structural chemistry since the time of Kekul???????????? in the 1860s that stated that carbon could bind at most four other atoms (tetra-coordination). Tri-coordinated carbenium ions (see Enium Ion) are consequently termed 'Classical Ions'.
