A largegem-dimethyl effect in the cyclization ofω-phenylhydantoic acids: computational modeling of thegem-dimethyl effect on the acid- or base-catalyzed cyclization of hydantoic acids and esters
作者:P. M. Ivanov、I. G. Pojarlieff、I. B. Blagoeva、C. Jaime、V. T. Angelova、A. H. Koedjikov
DOI:10.1002/poc.748
日期:2004.5
The rates of the cyclization of methyl-substituted 5-phenylhydantoic acids were measured in acid solutions. A particularly strong gem-dimethyl effect (GDME) was observed with the N-methyl compounds amounting to an acceleration of six powers of ten for the 2,2,3-trimethyl derivative. The variations in the free energies of activation for the cyclization of hydantoic acids and esters were modeled by the
在酸溶液中测量甲基取代的5-苯基乙内酰脲酸的环化速率。观察到特别强的宝石-二甲基效应(GDME),其中N-甲基化合物对2,2,3-三甲基衍生物的加速度为十的六次幂。通过四面体中间体的应变能和由MM3力场计算的反应物的应变能,模拟了用于乙二酸和酯环化的活化自由能的变化。中性四面体中间体Ť 0是用于涉及酸催化和带负电荷的中间反应系列Ť -用于碱催化。对于完整系列的N-甲基取代的底物的酸催化环化,获得了与实验GDME的非常吻合的结果,显示出加速是由于反应物的应变增加所致。有T的结果-紧密平行,表明GDME的损失在碱催化下观察2,2,3- trimethylhydantoate酯不是由于在分子内应变Ť - 。线性相关性(斜率1.22,r 排除了重度偏离的母体酸的数据时,获得了针对5-苯基乙二酸的反应系列的自由能变化对应变能的曲线图(= 0.934)。在酯和酸的反应系列之间获得了优异的LFER。观察