Nonadditivity of Secondary Deuterium Isotope Effects on Basicity of Trimethylamine
作者:Charles L. Perrin、Yanmei Dong
DOI:10.1021/ja803084w
日期:2008.8.1
Secondary deuterium isotope effects (IEs) on basicities of isotopologues of trimethylamine have been accurately measured by an NMR titration method applicable to a mixture. Deuteration definitely increases the basicity, by approximately 0.021 in the Delta pK per D. The IE is attributed to the lowering of the CH stretching frequency and zero-point energy by delocalization of the nitrogen lone pair into
二次氘同位素效应 (IE) 对三甲胺同位素体的碱度的影响已通过适用于混合物的 NMR 滴定方法准确测量。氘化肯定会增加碱度,每 D 的 Delta pK 大约增加 0.021。IE 归因于通过氮孤对离域到 CH 反键轨道降低 CH 伸缩频率和零点能量。因为这取决于孤对和 CH 之间的二面角,进一步的结果是优先选择与孤对和 D gauche 反周的 H 构象。这导致预测的 IE 不可加性,这在实验中得到证实。发现每个氘的碱度降低随着氘的数量而增加。