The relative stability of some C4H4F+ and C4H4Cl+ isomers investigated by ab initio quantum chemical methods. Are cyclic halogenophenium ions aromatic?

Abstract

Molecules with the general formulae C₄H₄F⁺, C₄H₄Cl⁺, and C₄H₄O have been investigated by applying ab initio quantum chemical methods. The relative stability and the geometries of a number of isomers were obtained from the calculations. Of special interest are the cyclic fluorophenium and chlorophenium ions. These two structures represent local but not global minima of their respective potential energy surfaces. Populational analysis and the structural parameters show that these cyclic ions are not aromatic. These findings are discussed in connection with previous results from solution chemistry.