The Interplay of Angle Strain and Aromaticity: Molecular and Electronic Structures of [0n]Paracyclophanes

The belt-like polyphenylenes, 0_n]paracyclophanes, (n = 5 and 6), have been investigated using semi-empirical, ab initio and DFT methods. The molecular structure, rotational barrier on twisting a single phenyl ring and the aromatic character within each ring as well as in the whole molecule have been evaluated. 0₅]Paracyclophane is predicted to have a quinonoid structure. In contrast, the equatorial pentaphenyl fragment found in C₇₀ as well as the hexagons of the less strained 0₆]paracyclophane have benzenoid character. Approximate band structures have been derived for larger cycles of 0_n] paracyclophanes.Electronic Supplementary Material available.