Conformational equilibrium and intramolecular hydrogen bond of 4 ' X and 4X substituted 2 '(OH)chalcones

By using the AM1 method on 4X and 4'X substituted 2'(OH)chalcones (X = H, O H, F, Cl, CH3, CH3O, N(CH3)(2), and NO2), certain currently unclear structu ral characteristics, conformational equilibria, intramolecular hydrogen bon ds and UV spectroscopic properties had been clarified. The compounds studie d have non-planar structures. The 2'(OH),4'Xchalcones only present the tran s-s-cis conformation. trans-s-cis and trans-s-trans conformers of 2'(OH),4X -chalcones have a comparable thermodynamic stability. For these chalcones, a conformational equilibrium at 298 K exists, with 91% of the trans-s-cis f orm. The proposal of analyzing the intramolecular hydrogen bond of 2'(OH),4 X-chalcones as an intramolecular proton-transfer reaction, is acceptable be cause the results and theoretical prediction of this study agree well with available UV spectroscopic experimental data. (C) 1999 Elsevier Science B.V . All rights reserved.