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.