苯酚的一些衍生物电子结构的量子化学研究

QUANTUM CHEMICAL STUDIES ON THE CHARGE DISTRIBUTION OF SOME PHENOL DERIVATIVES

采用MNDO法计算了苯酚和它的一些衍生物的最稳定的几何构型(用能量梯度法优化得到)的电荷分布,探讨了羟基、甲酰基等取代基对电荷分布的影响.计算结果表明,在这类化合物中绝对值最大的负的净电荷总是出现在羟基的邻位,适当配置羟基、甲酰基等取代基的位置可使苯环上的某些点(如羟基的邻位)上的净电荷变得更负.1个基团是“拉电子基团”或是“推电子基团”不能准确说明取代基对电荷分布的影响,必须从取代基在分子体系中的诱导、共轭效应等方面进行具体分析,并藉助量子化学计算,才能获得准确的定量结果.

The electronic structures of phenol and some of its derivatives are studied by means of MNDO method. The influence of substituting groups (-CHO, -OH, etc.) on the charge distribution of the benzene ring is investigated. The results indicate that the atom with the greatest negative charge always comes at the ortho-position of the hydroxy group. -CHO substituted at proper positions of phenols usually possesses greater negative electron densities on one or more sites on the benzene ring. The calculated results also show that the substitution effect or a substituting group can not be simply explained by electron donating or withdrawing. The charge distribution of the molecules is an overall effect of inductive and conjugative effects.