THEORETICAL DEFINITION OF SIZE OF ELECTRON PAIRS AND ITS STEREOCHEMICAL IMPLICATIONS
THEORETICAL DEFINITION OF SIZE OF ELECTRON PAIRS AND ITS STEREOCHEMICAL IMPLICATIONS
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DOI：
10.1021/ja00782a007
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发表时间：
1973-01-01
影响因子：
15
通讯作者：
CSIZMADI.IG
中科院分区：
文献类型：
--
作者：
ROBB, MA;HAINES, WJ;CSIZMADI.IG
提出了如下定义，将电子对(即定域双电子基团)“大小”的半经典概念与两个量子力学算符的期望值联系起来，这两个算符对应于定域分子轨道电荷分布的一阶和二阶矩。出于化学解释的目的，“局域”电子对的“大小”可以用半径球的体积来表示，该半径球等于与该电子对有关的电子距该电子对电荷中心(质心)的距离的均方根。立体化学是由电荷质心的几何位置和以质心为原点计算的二阶矩的非球形分量给出的。结果表明，上述定义适用于非经验和半经验分子轨道计算。给出了NH_4~+、NH_3、NH_2~-、NH_2~-、NH_3~-和C=0的数值结果。然后将上述定义推广到任何官能团的大小和其电子电荷分布的方向性。作为例子，给出了FCH2-OH的FCH2和OH基团随旋转角的变化情况。
The following definition is proposed which relates the semiclassical concept of the “size” of an electron pair (ie, localized two-electron group) to the expectation values of two quantum mechanical operators corresponding to the first and second moments of the electronic charge distribution of localized molecularorbitals. The “size” of a “localized” electron pair can be represented, for the purposes of chemical interpretation, by the volume of a sphere of radius equal to the root mean square of the distance of an electron associated with the pair from the center of charge (centroid) of the pair. The stereochemistry is given by the geometrical position of the centroid of charge and by the nonspherical components of the second moment calculated with the origin at the centroid. It is illustrated that the above definition is applicable to nonempirical and semiempirical molecular orbital calculations. Some numerical results are given for NH4+, NH3, NH2~, NH2-, N3_, and C= 0. The above definition is then ex-tended to give the size of any functional group andthe directional properties of its electronic charge distribution. An application to the FCH2 and OH groups of FCH2-OH as a function of rotational angle is presented as an example.