孤对键弱化效应研究

在H_2O_2、N_2H_4、F_2分子中,O—O、N—N、F—F键的键长分别是0.148、0.148、0.144nm,虽比C_2H_6分子中的C—C键(0.154nm)短,但其σ键键能分别是146、160、155kJ/mol,却比C—C键能(365 kJ/mol)小约2.5倍,通常称这类原子的单键键能的反常现象为“孤对键弱化效应”。传统观点认为,半径很小的N、O、F等在化合时必须相当接近才能键合,孤对电子的排斥作用阻止了其相互接近,削弱了键能,降低了键的稳定性。显然,将这种削弱效应考虑为原子间效应是不合理的。本文用键参数图解法对“孤对键弱化效应”提出了合理的解释。

Studies on the Effect of the Lone Pair Bond Weakening

The traditional explanation on the effect of lone pair bond weakening, as the result of inter-electronic repulsions between lone pair electrons on bonding atoms, become void when we compare bond energies of the hydrogen halides, because there are certainly no lone pair electrons on the hydrogen atom to repel the lone pair electrons of the fluorine. In this paper, the reasonable explanation on the effects of lone pair bond weakening by using graphic method of bond parameters is presented. It is considered that the weakening effect is a prime shielding result of lone pair electrons intervening between the bonding electrons and nucleus, rather than the interelectronic repulsions between lone pair electrons on separate atoms.