Abstract
The 6-Mono- and trans-6,7-di-substituted derivatives of 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene exist in solution in two different conformations. The experimental ΔGo values obtained from 1H NMR spectra are compared with the ΔEsteric and ΔG values calculated by molecular mechanics and semiempirical quantum mechanics methods respectively. The experimental ΔGo values are reproduced better by the ΔEsteric values. The semiempirical methods predict the order of stability of the conformers correctly except for two cases in the PM3 and AM1 methods, but the estimated values are far from the experimental ones. The standard deviation between the experimental ΔGo values and those calculated by semiempirical methods is less for AM1 and MNDO and greater for PM3 and MINDO/3. The conformational space of the flexible side chains in monoacetoxy 1d, monohydroxy 1e, trans-diacid 2d, trans-dimethyl ester 2e and trans-bis-hydroxymethyl 2f searched by molecular mechanics is not reproduced completely by semiempirical methods. © 1998 John Wiley & Sons, Ltd.
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