摘要
在水分子间可以形成氢键的事实早为化学家所熟知,然而对于水分子间氢键的性质到现在还未得到较深入的了解.大多数学者倾向于静电引力的看法.很多作者利用简单的静电模型(把水分子看成是偶极子或用其他点电荷模型)计算了水分子间氢键的键能,大致都得到与实验相近的数值.
It is well known that hydrogen bond may be formed between water molecules. Many scientists are inclined to the opinion that the origin of hydrogen bond is due mainly to the electrostatic force. Some authors calculated the energy of hydrogen bond by various simple H_2O models (as point dipole or other point charge models). But obviously these models are too crude for our purpose of calculation of the bond energy. The aim of this paper is to calculate the energy of hydrogen bond by means of a H_2O model obtained from quantum mechanical point of view. Each water molecule is considered to be composed of four bonds: 2 lone-pair bonds with S character 0.2944 and 2 OH bonds with S character 0.2056, the angle between 2 OH bonds is 105°, between 2 lone-pair bonds is 114°40′ and that between a OH bond and a lone-pair bond is 109°11′; hence the H_2O model is approximately tetrahedral. In the course of calculation, the interaction energy between two bonds are evaluated according to the approximate formula proposed by Tang (1954). In his formulae the interaction energy between 2 electron clouds (or between a point charge and an electron cloud) is expressed as an infinite series in terms of R (distance) and Tn'S (2 moments of elec- tron clouds). The energy of hydrogen bond is the sum of the interaction energy between 16 pairs of bonds of the 2 H_2O molecules. The calculated value is-4.8 and-5.6 Kcal/mole, (2 different spacial arrangements of 2 H_2O molecules) which agree satisfactorily with the experimental value-4.5 Kcal./mole. From the result thus obtained we may see that: The lone-pair electrons of water molecule play an important role in the hydrogen bond formation. Since the lone-pair electrons are distributed in localized parts of the H_2O molecule and protrude out in particular directions from the oxygen nucleus, distribution of electronic charge in water molecule is thus asymmetrical, and the lone-pair electrons provide region of negative charge, while the rest of the H_2O molecule is then in deficit of negative
出处
《北京师范大学学报（自然科学版）》
CAS
1956年第1期85-97,共13页
Journal of Beijing Normal University(Natural Science)
