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

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.

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

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)₅ COOH 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.
Keywords： quantum computation charge distribution functional group electrostatic interaction