Semi-empirical and ab initio study of pericyclized naphthalene systems containing an eight-membered ring

Abstract

The conformational properties of peri-bridged naphthalenes in which the C-1 and C-8 atoms of the naphthalene ring are bonded by five atoms in a bridging chain Z [Z=(CH2)5, 1a; (CH2)2O(CH2)2, 1b; (CH2)2S(CH2)2, 1c; CH2OCH2OCH2, 1d; CH2SCH2SCH2, 1e; O(CH2)3O, 1f; S(CH2)3S, 1g] were studied by the Modified Neglect of Diatomic Overlap (MNDO) semi-empirical SCF MO method. Two minimum-energy conformations, namely chair and boat, with similar energies were found for 1a–c and 1e–g, which are separated by fairly low (3.5–6.2kcalmol−1) energy barriers. The barriers for chair-to-chair ring inversion in these compounds are 9.7–12.4kcalmol−1. For compound 1d, only the chair conformation was found to have the lowest energy; the twist and boat conformations are less stable by 1.1 and 1.4kcalmol−1, respectively. Ab initio STO-3G calculations were carried out for 1a.