AN AB-INITIO STUDY OF ANNULATION EFFECTS ON THE VALENCE ISOMERISM OF BENZENE

Annulation should tilt the benzene/Dewar-benzene equilibrium toward be nzenes the largest effective annulating ring being six-membered; MP2(f c)/6-31G//RHF/6-31G* methods are needed to reproduce experimental iso merization energies, but 6-31G calculations suffice td show trends for molecular design. [GRAPHICS] Smaller ''n'' should favor isomerization ; effective rings will have n less than or equal to 6. (C) 1997 Elsevi er Science B.V.