α-单取代环十二酮构象转换的溶剂效应和温度效应

Effects of Solvent and Temperature on the Conformational Interconversion of α-Monosubstituted Cyclododecanones

利用1HNMR技术研究了α 单取代环十二酮的α 边外取代 [3 3 3 3 ] 2 酮构象 (A)和α 角顺取代 [3 3 3 3 ] 2 酮构象 (B)相互转换的溶剂效应和温度效应 .结果显示 ,一般情况下随着溶剂极性的增加 ,构象B的含量增加 ,这可以解释为构象B较构象A有较大的偶极矩 .当分子中的取代基能与羰基形成分子内氢键时 ,情况则相反 ,随着溶剂极性的增加 ,构象B的含量降低 ,这可以解释为构象B的分子内氢键的减弱 .结果还显示 。

The effects of the solvent and temperature on the interconversion between the α-side-exo-substituted[3333]-2-one (A) and α-corner-syn-substituted[3333]-2-one (B) conformations of the α-monosubstituted cyclododecanones have been studied by means of 1H NMR technology. The result shows that increasing the polarity of the solvent generally increases the population of the conformation B owing to the higher dipole moment of the conformation B than that of A. By contrast, in the case of the monosubstituted cyclododecanones with an intramolecular hydrogen bond between the substituent and the carbonyl group, increasing the polarity of the solvent decreases the population of the conformation B owing to the weakening of the intramolecular hydrogen bond. The result also shows that raising temperature is favourable to the interconversion of two conformations, achieving a new equilibrium.