Conformational analysis of substituted 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene: comparison of 1H NMR, molecular mechanics and semiempirical methods

✍ Scribed by Parviz Rashidi-Ranjbar; Jamshid Najafpour; Farideh Piri

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 80 KB
• Volume: 11
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(1998110)11:11<781::aid-poc31>3.0.co;2-r

✦ Synopsis

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 DG o values obtained from 1 H NMR spectra are compared with the DE steric and DG values calculated by molecular mechanics and semiempirical quantum mechanics methods respectively. The experimental DG o values are reproduced better by the DE steric 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 DG o 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, transdimethyl ester 2e and trans-bis-hydroxymethyl 2f searched by molecular mechanics is not reproduced completely by semiempirical methods.