论文部分内容阅读
有关无机含氧酸的强度问题,自L.Pauling提出两项经验规则之后,不少学者又相继探讨了计算pK值的各种经验公式。在这些公式中,有的虽然形式简单,但计算值与实测值偏差较大。例如,根据pK=8.0-n(9.0)+m(4.O)以及pK=7+5(m-n+2q)的经验式,许多含氧酸pK的计算值与实验值的偏差超过7,有的甚至超过15(如H_3IO_6,偏差17.45)。又如Gallais提出的AOH型和AO_m(OH)_n型的酸分别按pK=8.3+4.2(x_H-x_A)和pK=2+2.2(x_H-X_A)计算,其式中的电负性差值(x_H-x_A)一项与酸分子的实际情况亦不十分相符。因为Gallais等都未考虑到电负性以及由它表征的电荷密度分布情况的变化是决定含氧酸强度的一个十分重要的因素,所以存在偏差是可以理解的。徐光宪等在研究Pauling规则后,把氧原子与中心原子间形成的d-pπ配键数等因素考虑在内,
Concerning the strength of inorganic oxygen acids, many scholars have successively discussed various empirical formulas for calculating the pK value after two empirical rules have been proposed by L. Pauling. Some of these formulas, although simple in form, have large deviations from the measured values. For example, the calculated value of many oxoacids pK deviates from the experimental values by more than 7 according to the empirical formula of pK = 8.0-n (9.0) + m (4.0) and pK = 7 + 5 (m-n + 2q) , Some even more than 15 (such as H_3IO_6, deviation 17.45). Another example Gallais proposed AOH-type and AO_m (OH) _n-type acid pK = 8.3 +4.2 (x_H-x_A) and pK = 2 +2.2 (x_H-X_A) calculated in the formula of electronegativity difference (x_H-x_A) an acid molecule and the actual situation is not very consistent. Since Gallais et al. Do not take into account the electronegativity and the change in the charge density distribution characterized by it, it is a very important factor that determines the strength of oxyacid, it is understandable that there is a deviation. After studying Pauling’s rule, Xu Guangxian et al. Took into consideration the d-pπ bond number formed between the oxygen atom and the central atom,