Molecular mechanics of diastereoisomers with phenyl groups on neighbouring carbon atoms

Abstract

Results are summarized from systematic studies by the molecular mechanics method of the conformations of diastereoisomeric pairs of 1,2-disubstituted-1,2-diphenylethanes. An overall result in both series is the preference for conformations with the minimal number of synclinal interactions around the C(1)C(2) bond. Special attention is devoted to the performance of the MM2 force field with the 1,2-diarylethane system. With the readjustment of the V 1 parameter for the torsional unit C arC alC alC ar MM2 operates reasonably well in the case of substituents of a moderate size. For the 1,2,3-triphenylpropane system however, where phenyl groups participate in 1,3-parallel interactions, this force field fails completely. A further more substantial revision of the MM2 force field is necessary in order to achieve internal consistency between different energy contributions in such systems.