有机分子的结构与排列方式对原子电荷分布及静电作用的影响

Effect of the structure and the arrangement of organic molecules on the atomic charge and electrostatic interaction

对由两个相同的长直链分子(CH3(CH2)5—R(R=COOH,CH3,OH)、CH3(CH2)4—COOH))呈镜面对称分布组成的四种模型,及由两个CH3(CH2)5COOH分子平行分布组成的模型进行了量化计算,研究了分子间距、功能团、链长及排列方式对原子电荷分布及分子静电相互作用的影响.结果表明:1)分子中不同位置的亚甲基团(—CH2—)的C原子电荷各不相同.2)原子电荷不仅受到分子链长及功能团的影响,同时,当分子间距及排列方式发生改变时,原子电荷也发生改变;双分子模型较单分子模型的原子电荷变化较大.3)分子间静电作用由尾基功能团的极性决定,由强到弱为—COOH>—OH>—CH3,分子中其他原子对静电作用的贡献较小;分子链长的增加导致尾基功能团中电荷减少,从而使得分子间静电作用减弱.

The quantum computation method has been used to investigate the atomic charge and electrostatic interaction of five models： four of which are composed of two mirror-symmetrical long-chain organic molecules（CH3（CH2）5—R（R =COOH, CH3, OH） and CH3（CH2）4COOH）; and one is composed of two parallel CH3（CH2）5COOH molecules. Results show that：（1）The charge of the C atoms of the methylenes（—CH2—） in the molecules is different from each other;（2）the atomic charge is mainly determined by the chain-length and the functional group; meanwhile, it may change when the distance between molecules changes or the arrangement of the molecules changes. The atomic charge in the bimolecular models changes more than in the single molecule models;（3）the electrostatic interaction is mainly determined by the tail function groups： the interaction strength is —COOH—OH—CH3; while the other atoms have little contribution.Electrostatic interaction will decrease when the atomic charge of the tail functional groups decreases, which is caused by the increased chain-length.