Chemistry of the t-butoxyl radical: Evidence that most hydrogen abstractions from carbon are entropy-controlled
Chemistry of the t-butoxyl radical: Evidence that most hydrogen abstractions from carbon are entropy-controlled
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DOI：
10.1021/ja0493493
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发表时间：
2004-06-23
影响因子：
15
通讯作者：
Tanko, JM
中科院分区：
文献类型：
--
作者：
Finn, M;Friedline, R;Tanko, JM
叔丁氧基自由基（（BuO.）Bu-t）的几种烃和叔胺在溶液中的报告。结合文献中已有的数据，对所有可用数据的分析表明，大多数氢提取（从碳）通过（BuO.）-但t是熵控制的（即，TDeltaS（双匕首）> DeltaH（双匕首），在室温下的溶液中）。对于C-H键离解能（BDES）> 92 kcal/mol的底物，夺氢活化能随着BDES的降低而降低，雅阁Evans-Polanyi方程，α近似为0.3。对于C-H BDE的底物，其活化能在79至92 kcal/mol范围内，C-H BDE的活化能变化不大。讨论了作为活性氧中心自由基的化学模型。
Absolute rate constants and Arrhenius parameters for hydrogen abstractions (from carbon) by the t-butoxyl radical ((BuO.)-Bu-t) are reported for several hydrocarbons and tertiary amines in solution. Combined with data already in the literature, an analysis of all the available data reveals that most hydrogen abstractions (from carbon) by (BuO.)-Bu-t are entropy controlled (i.e., TDeltaS(double dagger) > DeltaH(double dagger), in solution at room temperature). For substrates with C-H bond dissociation energies (BDES) > 92 kcal/mol, the activation energy for hydrogen abstraction decreases with decreasing BIDE in accord with the Evans-Polanyi equation, with alpha approximate to 0.3. For substrates with C-H BDEs in the range from 79 to 92 kcal/mol, the activation energy does not vary significantly with C-H BDE The implications of these results in the context of the use of (BuO.)-Bu-t as a chemical model for reactive oxygen-centered radicals is discussed.