MECHANISTIC STUDY OF THERMAL Z-E ISOMERIZATION OF AZOBENZENES BY HIGH-PRESSURE KINETICS
MECHANISTIC STUDY OF THERMAL Z-E ISOMERIZATION OF AZOBENZENES BY HIGH-PRESSURE KINETICS
复制标题
DOI：
10.1021/ja00382a026
复制
发表时间：
1982-01-01
影响因子：
15
通讯作者：
OKADA, T
中科院分区：
文献类型：
--
作者：
ASANO, T;YANO, T;OKADA, T
在不同的溶剂中测量了几种偶氮苯热ZE异构化的压力效应。4-二甲氨基-4 '-硝基偶氮苯的活化体积表明，在正己烷中的反应机理由反转转变为在苯等极性溶剂中的旋转。4-苯胺基-4 '-硝基偶氮苯在溶剂由苯变为丙酮时，反应机理也发生了同样的变化，而4-甲氧基-4'-硝基偶氮苯和未取代偶氮苯的反应机理随溶剂极性变化不大。重新测定了偶氮苯的活化焓，结果表明偶氮苯的偶极矩在活化步骤中降低了约40%，偶氮苯热ZE异构化反应机理的研究最近又重新引起了人们的兴趣。大多数新的研究是动力学的，1，3”7，但也进行了分子轨道计算1，8和热化学测量2 9。在大多数情况下，反转机制是可以接受的; 7，9在这条途径中，氮原子之间的双键保持完整，但其中一个经历了从sp2到sp的过渡态1的再杂交。然而，对于推拉取代偶氮苯，
Pressure effects for the thermal ZE isomerization of several azobenzenes were measured in various solvents. The activation volumes for 4-(dimethylamino)-4'-nitroazobenzene indicate that the reaction mechanismchanges from inversion in n-hexane to rotation in benzene and other relatively polar solvents. The same change in mechanism takes place in the case of 4-anilino-4'-nitroazobenzene when the solvent is changed from benzene to acetone; for 4-methoxy-4'-nitroazobenzene and unsubstituted azobenzene, the reaction mechanism does not change greatly with solvent polarity. The activation enthalpy for azobenzene was redetermined; the result suggests that the original dipolemoment is reduced by about 40% in the activation step.Interest in the mechanism of thermal ZE isomerizations of azobenzenes has recently revived. The majority of the new studies have been kinetic, 1, 3" 7 but molecular orbital calculations1, 8 and thermochemical measurements2 9have also been made. Theinversion mechanism is accepted for most cases; 7, 9 in this pathway, the double bond between the nitrogen atoms remains intact, but one of them undergoes rehybridization from sp2 to sp in the transition state 1. However, for push-pull substituted azobenzenes