Reaction of Phenols with the 2,2-Diphenyl-1-picrylhydrazyl Radical. Kinetics and DFT Calculations Applied To Determine ArO-H Bond Dissociation Enthalpies and Reaction Mechanism
作者:Mario C. Foti、Carmelo Daquino、Iain D. Mackie、Gino A. DiLabio、K. U. Ingold
DOI:10.1021/jo8016555
日期:2008.12.5
strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO(2) groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) x 10(5) M(-1) s(-1)] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely
通过结合在非极性溶剂中的动力学测量和密度泛函理论(DFT),研究了由27种苯酚和两种不饱和烃类中的2,2-二苯基-1-吡啶并肼基(dpph(*))形成的形式H原子的抽象形式。计算得出的dpph(*)的最小能量结构表明,每个苯环上的邻H原子和吡咯环的o-NO(2)基团严重阻碍了其二价N的进入。苯酚的小Arrhenius指数前因数[范围(1.3-19)x 10(5)M(-1)s(-1)]归因于空间效应。的确,熵障占了大约。70%的自由能反应壁垒。然而,不同酚的速率差异主要是由于活化能E(a,1)(范围2至10 kcal / mol)的差异。在苯酚中 取代基和分子内氢键的电子效应对活化能和ArO-H BDEs具有很大的影响。E(a,1)与ArO-H BDE之间存在线性Evans-Polanyi关系:E(a,1)/ kcal x mol(-1)= 0.918 BDE(ArO-H)/ kcal x mol(-