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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Through-Space Charge and Dipolar Effects in Substituted Ethanes and 1,1,1-Trifluoroethanes
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Through-Space Charge and Dipolar Effects in Substituted Ethanes and 1,1,1-Trifluoroethanes

机译：取代的乙烷和1,1,1-三氟乙烷的空间电荷和偶极效应

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The results of ab initio calculations with the 6-31+G~* basis set are reported on over sixty compounds of the type CZ_3CH_2X (Z = H, F) and on a few longer chain-substituted alkanes. Data for the eclipsed conformations with Z = H and both the staggered and eclipsed conformations with Z = F are presented. The charges on the atoms in these molecules are determined with the Atoms in Molecules (AIM) and Natural Population Analysis (NPA) methods of analysis. The charges on the fluorine atoms in the trifluoroethyl derivatives parallel those of the hydrogen atoms of the ethyl derivatives. A potential gradient model for charge variations is presented. In this model, the magnitude of the charge is dictated by a through-space electrostatic interaction that arises from the charges on the atoms of the CH_2X group. The length of the vectors from the atoms in the CH_2X group to the bond critical point of the C-Z (Z = H, F) bond and the angle this vector makes with the C-Z bond are critical parameters. The model is tested in systems in which the charge of the methylene carbon atom can be ignored, as well as more rigorously with inclusion of the charge of the methylene carbon atom. The potential gradient model accounts for a greater positive (negative) charge on the antiperiplanar atom than on the gauche ones (staggered conformer) and on the gauche compared to synperiplanar (eclipsed conformer) for positively (negatively) charged X. The model also gives a rationalization for the change in charge observed on the Z atoms when X = EH_(n~q) is replaced by X = EF_n~q. Comparisons of antiperiplanar and eclipsed conformers of CH_3CH_2X and CF_3CH_2X show that these conformational changes have little effect on the charges of the atoms in the methylene (CH_2X) fragment.
机译：用6-31 + G〜*基集从头计算的结果报道了六十多种CZ_3CH_2X类型的化合物（Z = H，F）和一些更长的链取代烷烃。给出了Z = H的月食构象以及Z = F的交错和月食构象的数据。这些分子中原子上的电荷是通过分子原子（AIM）和自然种群分析（NPA）分析方法确定的。三氟乙基衍生物中氟原子上的电荷与乙基衍生物的氢原子上的电荷平行。提出了一种用于电荷变化的电势梯度模型。在此模型中，电荷的大小由CH_2X基团原子上的电荷引起的贯穿空间的静电相互作用所决定。从CH_2X基团的原子到C-Z键的键临界点（Z = H，F）的向量的长度以及该向量与C-Z键的夹角是关键参数。该模型在可以忽略亚甲基碳原子的电荷的系统中进行了测试，并且在包含亚甲基碳原子的电荷的情况下也可以更严格地进行测试。相对于带正电（负）的X，与同平面（椭圆形的构象异构体）相比，电势梯度模型在反周面原子上的电（与负交错的构象异构体）和在薄纱上的原子相比，具有更大的正（负）电荷。该模型还给出了当X = EH_（n〜q）时，Z原子上观察到的电荷变化的合理化被X = EF_n〜q代替。比较CH_3CH_2X和CF_3CH_2X的反平面构型和蚀变构型，这些构象变化对亚甲基（CH_2X）片段中原子的电荷影响很小。

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