作者:Han Joong Koh、Kwang Lae Han、Hai Whang Lee、Ikchoon Lee
DOI:10.1021/jo000411y
日期:2000.7.1
studies of the reactions of substituted phenacyl bromides (YC6H4COCH2Br) with pyridines (XC5H4N) are carried out in acetonitrile at 45.0 degrees C. A biphasic Bronsted plot is obtained with a change in slope from a large (betaX approximately equals 0.65-0.80) to a small (betaX approximately 0.36-0.40) value at pKa = 3.2-3.6, which can be attributed to a change in the rate-determining step from breakdown
在45.0摄氏度下于乙腈中进行了取代的苯甲酰溴(YC6H4COCH2Br)与吡啶(XC5H4N)反应的动力学研究。获得了双相布朗斯台德图,其斜率从大(βX约等于0.65-0.80)变化为pKa = 3.2-3.6时有一个很小的值(betaX大约为0.36-0.40),这可以归因于随着吡啶亲核试剂的碱度增加,从分解到反应路径中四面体中间体形成的速率确定步骤发生变化。吡啶比苯胺具有更快的速率以及交叉相互作用常数rhyXY从大的正(rhoXY = +1.4)到小的正的(rhoXY大约+0.1)值的变化支持了该机制。Hammett rhoX的大小很大(= -5.5至-6。9)具有吸电子取代基的吡啶值和pi受体p-CH3CO和p-CN的正偏差与吡啶离子形成平衡的值非常相似。激活参数也符合所提出的机制。