Thermochemical studies of carbonyl reactions. 2. Steric effects in acetal and ketal hydrolysis
作者:Kenneth B. Wiberg、Robert R. Squires
DOI:10.1021/ja00405a030
日期:1981.7
series of alkyl-substituted dimethyl acetals is reported. These data are critially compared with the enthalpies of hydrolysis from an analogous set of aliphatic dimethyl ketals derived from 2-alkanones. The acetals exhibit a significantly attenuated range in their enthalpies of hydrolysis relative to that for ketal hydrolysis. The free energies of acetal formation in solution were modeled by measurements
报道了一系列烷基取代的二甲基缩醛的水解焓的量热测定。将这些数据与衍生自 2-烷酮的一组类似脂肪族二甲基缩酮的水解焓进行关键比较。与缩酮水解相比,缩醛的水解焓显着减小。溶液中缩醛形成的自由能通过中性甲醇中醛形成缩醛的相应自由能的测量来模拟。观察到的自由能差异与 Taft E/sub s/空间取代基常数标度具有令人满意的相关性,但相应的缩醛焓数据以复杂的方式变化。讨论了熵在确定各种其他系统中的动力学和平衡空间效应中的作用。对这些系统的初步分子力学计算表明键角弯曲在评估羰基扭转势中的重要性。发现许多化合物具有几种具有可比能量的构象。