The rate coefficients for the base-catalysed ring fission of a series of 2-phenyl-3-(2-, 3- or 4-substituted phenyl)cycloprop-2-en-1-ones to give the corresponding (E)-2,3-diphenylacrylic acids have been determined in water at 30.0 °C, as well as for the unsubstituted compound at 40.0, 50.0 and 60.0 °C. The effects of meta- and para-substituents on the rates have been correlated using the Hammett equation to give a reaction constant, ρ, equal to ca 1.2 at 30 °C. For the unsubstituted compound, the activation parameters have been calculated and the kinetic solvent isotope effect has been studied. The effects of ortho-substituents on the rates appear to be mainly polar, rather than steric, in origin. The evidence indicates a mechanistic pathway which proceeds by addition of hydroxide anion to the ketone, which is rate-determining. The adduct suffers ring fission to give the final product via a carbanionic intermediate.
一系列2-苯基-3-(2-, 3- 或 4-取代苯基)环丙烯酮在30.0°C的水中的碱催化环裂速率系数已确定,以及未取代化合物在40.0、50.0和60.0°C的速率系数。利用Hammett方程相关了对速率的间位和对位取代基的影响,得到在30°C时等于约1.2的反应常数ρ。对于未取代化合物,已计算了活化参数并研究了动力学溶剂同位素效应。取代基对速率的影响似乎主要是极性的,而不是立体的。证据表明,该机理途径通过氢氧根离子加成到酮中,这是决定速率的步骤。该加合物经历环裂,生成最终产物,通过一个碳负离子中间体。