Electronic and Steric Substituent Influences on the Conformational Equilibria of Cyclohexyl Esters: The Anomeric Effect Is Not Anomalous!
作者:Erich Kleinpeter、Ferdinando Taddei、Philipp Wacker
DOI:10.1002/chem.200390155
日期:2003.3.17
differences of the axial and equatorial conformers were evaluated with respect to the factors normally influencing conformational preference, namely, 1,3-diaxial steric interactions in the axial conformer and hyperconjugation. It was assessed that hyperconjugative interactions, sigma(C-C)/sigma(C-H) and sigma*(C-O), together with a steric effect--the destabilization of the equatorial conformer with increasing
R取代基的一系列羧酸RCO(2)H的环己基酯,其电负性和位阻的商数范围(R = Me,Et,iPr,tBu,CF(3),CH(2)制备了Cl,CHCl(2),CCl(3),CH(2)Br,CHBr(2)和CBr(3))。通过低温(1)H NMR光谱检查了CD(2)Cl(2)中它们的构象平衡,以研究酯官能度相对于环己烷环所采用的椅子构象的轴向或赤道取向。还从HF / 6-311G **,MP2 / 6-311G **和B3LYP / 6-31G **的水平计算了从头算和DFT几何优化的结构以及轴向和赤道构象的相对自由能。理论上,无论是在气相中还是在溶液中。在后一种情况下,使用了自洽的等价极化连续谱模型。仅通过在溶剂化分子的建模计算中包括电子相关性,才有可能在DeltaG度(计算值)和DeltaG度(exp)之间获得合理的相关性。相对于通常影响构象偏好的因素,即轴向构象体和超共轭中的1,3-双