The Structure of a Seven‐Bladed Propeller: C7Ph7+ is Not Planar

The first nondisordered structure of a free tropylium cation has been unequivocally determined by single‐crystal X‐ray diffraction. The solid‐state structure of the heptaphenylcycloheptatrienyl cation, C7Ph7+, in [C7Ph7+][CF3CO2−]⋅2 CF3CO2H reveals a severely crowded system in which the central ring is nonplanar, and the propeller blades (the peripheral phenyl substituents) are arranged in a slightly tilted fashion about the seven‐membered ring (right).