COMBINATION OF EMPIRICAL FORCE-FIELD AND EXTENDED HUCKEL MOLECULAR-ORBITAL CALCULATIONS AS A COMPUTATIONAL APPROACH TO CONFORMATIONAL-ANALYSIS

A combined empirical force field (EFF)-extended Hückel molecular orbital (EHMO) approach to conformational analysis has been developed. This hybrid approach involves a full relaxation EFF calculation of conformer structures, followed by a single EH calculation on each structure. The new method appears to represent a useful adjunct to existing EFF calculations, especially in application to relative conformer energies of arene derivatives. Constitutional isomerism cannot be handled by the EFF-EHMO approach. Our results indicate that, contrary to previous notions, the EHMO method tends to underestimate conventional steric effects. © 1979, American Chemical Society. All rights reserved.