Ab initio study of atropisomers of some derivatives of 1,8-disubstituted biphenylenes and naphthalenes

Ab initio calculation at HF/6-31G* and MP2/6-31G* levels of theory for geometry optimization of some syn- and anti-1,8-diaryl and heteroaryl biphenylenes are reported. The rotational energy barriers, heat of formation and Gibbs energy are determined for the conversion of the anti (syn) to the syn (anti) isomers at 25 degrees C in the gas phase and in chloroform as solvent. The models are chosen as isomers of biphenylene (as scaffold) with alpha-naphthyl, beta-naphthyl, pyridine and pyrimidine as modules. Results obtained show that (at equilibrium) for all atropisomers the anti- is highly favored over the syn-isomer. Moreover, the ground state structures show that the modules are not parallel to each other but are tilted away in order to increase separation and there by minimize electrostatic repulsion. (c) 2006 Elsevier B.V. All rights reserved.