Kinetics and equilibrium constants for reactions of α-phenyl-substituted cyclopropylcarbinyl radicals
Kinetics and equilibrium constants for reactions of α-phenyl-substituted cyclopropylcarbinyl radicals
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DOI：
10.1021/ja991114h
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发表时间：
2000-04-05
影响因子：
15
通讯作者：
Newcomb, M
中科院分区：
文献类型：
--
作者：
Halgren, TA;Roberts, JD;Newcomb, M
用激光闪光光解法测定了4，4-二苯基-3-丁烯基（2）和反式-4-苯基-3-丁烯基（5）环化为1，1-二苯基环丙基原基（1）和1-苯基环丙基原基（4）的Arrhenius函数。分别在20 ℃时，环化速率常数为1.7 × 10（7）和5.4 × 10（6）s（-1）。用热化学数据和计算方法估算了这两个反应的平衡常数，计算了环丙基原基开环反应的Arrhenius函数。2和5的环化反应为强焓控制。在Et_3SnH存在下由相应的叔丁基过氧酯生成自由基1和2，由自由基1和2的H原子捕获得到二苯基环丙基甲烷和1，1-二苯基-1-丁烯，以及由2中的自由基部分加成到顺式苯基上形成的产物自由基衍生的4-苯基-1，2-二氢萘。从间接动力学研究中获得的速率常数为后者环化2和自由基1和2与Et 3SnH的反应。
Laser-flash photolysis methods were used to determine Arrhenius functions for cyclizations of the 4.4-diphenyl-3-butenyl (2) and trans-4-phenyl-3-butenyl (5) radicals to the 1,1-diphenylcyclopropylcarbinyl (1) and 1-phenylcyclopropylcarbinyl (4) radicals. respectively. At 20 degrees C, the cyclization rate constants are 1.7 x 10(7) and 5.4 x 10(6) s(-1). Equilibrium constants for the two processes were estimated and evaluated with thermochemical data and via computational methods, and Arrhenius functions for the ring-opening reactions of the cyclopropylcarbinyl radicals were calculated, The cyclization reactions of 2 and 5 are strongly enthalpy controlled. Production of radicals 1 and 2 from the corresponding tert-butylperoxy esters in the presence of Et3SnH gave diphenylcyclopropylmethane and 1.1-diphenyl-1-butene from H-atom trapping of radicals 1 and 2 and 4-phenyl-1,2-dihydronaphthalene which derives from the product radical formed by addition of the radical moiety in 2 to the cis-phenyl group. Rate constants for the latter cyclization of 2 and for reactions of radicals 1 and 2 with Et3SnH were obtained from the indirect kinetic studies.