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Study of molecular structures for arylidene derivatives of 3R‐methylcyclohexanone by 1H NMR and molecular simulation
Abstract:Conformational states of the cyclohexanone ring were established for 3R‐methyl‐6‐(4‐phenylbenzylidene)cyclohexanone and several 2,6‐bis(4‐X‐benzylidene)‐3R‐methylcyclohexanones (X = Br, OCOCH3 and C6H5) by 1H NMR spectroscopy combined with molecular simulation using the semi‐empirical methods AM1 and PM3. The first compound studied contains only one arylidene group, and exists predominantly in a chair conformation of the cyclohexanone ring with an equatorial orientation of the methyl substituent in C6D6 and CDCl3 solutions at room temperature (22–23 °C). In contrast, the 2,6‐bis(arylidene) derivatives of 3R‐methylcyclohexanone preferentially adopt conformations with an axially oriented methyl group. The extent of twisting of enone fragments was also characterized for the compounds studied based on simulation results and comparison of chemical shifts for the arylidene protons of appropriate model compounds. Copyright © 2003 John Wiley & Sons, Ltd.
Keywords:NMR  1H NMR  3R‐methyl‐6‐(4‐phenylbenzylidene)cyclohexanone  2  6‐bis(arylidene)‐3R‐methylcyclohexanones  chemical shift  spin–  spin coupling  conformation  molecular modelling
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