5]Paracyclophane: molecular structure and implications for aromaticity

Abstract

Abstract The structure of [5]paracyclophane was optimized at the STO-3G SCF level. The dihedral angle φ, which is zero for benzene, is 22.4°. This value is significantly less than previously reported values obtained via molecular mechanics modeling techniques or MNDO calculations. Although our ab initio structure predicts a larger C-C bond alternation in the benzene ring (C-C bond lengths vary from 1.365 to 1.415 A), the smaller angle φ indicates that the title compound is more stable and probably possesses more “aromatic character” than previous theoretical studies concluded. A discussion concerning the ambiguity of “aromatic character” is presented.