互变异构体
化学
平衡常数
电离
蒂奥-
哈米特方程
计算化学
线性
水溶液
热力学
物理化学
立体化学
有机化学
反应速率常数
动力学
离子
量子力学
物理
作者
M. I. Kabachnik,T.A. Mastrukova,А.Г. Шипов,T.A. Melent'yeva
出处
期刊:Tetrahedron
[Elsevier]
日期:1960-01-01
卷期号:9 (1-2): 10-28
被引量:124
标识
DOI:10.1016/0040-4020(60)80048-8
摘要
The applicability of the Hammett equation to the effective ionization constants of tautomeric substances has been investigated. The tautomeric equilibrium being shifted toward one of the forms, a good linear dependence of pKA on σ is observed. When at particular σ values the second tautomeric form makes its appearance in the equilibrium to a noticeable extent one observes the deviation from linearity. It is seen to run parallel to the increase of that form in the equilibrium. The tautomeric equilibrium constant is related to the deviations from linearity 'a' by a simple correlation KT = K1/K2 = 10a-1 Thus has been established the quantitative relationship between the ionization constants of particular forms, the effective ionization constants of tautomeric substances and the σ values. The relationships determined were used to investigate the thione—thiol tautomerism of thioorgano-phosphorus compounds. To this end the Hammett equation has been previously shown to be applicable to organo-phosphorus acids of the type RR′P(O)OH and RR′P(S)SH and the σ constants, characteristic of phosphorus compounds, have been determined. 25 phosphorus mono- thio- and 16 dithio-acids were synthesized, their ionization constants determined in aqueous 7 per cent and 80 per cent alcohol and the tautomeric equilibrium constants evaluated. For most phosphorus thio-acids the equilibrium has been shown to be shifted toward the thione form RR′P(S)OH, the second, or thiol form RR′P(O)SH appearing in noticeable amounts only with such substituents whose σ value is near to 0. This effect is stronger in the 7 per cent than in the 80 per cent alcohol.
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