Activation/driving force relationships for cyclopropylcarbinyl → homoallyl-type rearrangements of radical anions
Activation/driving force relationships for cyclopropylcarbinyl → homoallyl-type rearrangements of radical anions
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DOI：
10.1021/jp050193i
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发表时间：
2005-04-21
影响因子：
2.9
通讯作者：
Tanko, JM
中科院分区：
文献类型：
--
作者：
Chahma, M;Li, XZ;Tanko, JM
采用直接和间接电化学方法，计算了反式-1-苯甲酰基-2-苯基环丙烷、反式-1-苯甲酰基-2-乙烯基氯丙烷、2-亚甲基环丙基苯基酮、螺[蒽-9,1'-环丙-10-酮]的单电子还原衍生的自由基阴离子环丙烷开环的速率常数(k,,)，测定了3-环丙基环己-2-en-1-酮和3-(1-甲基环丙基)环己-2-en-1-酮。定性地，这些（以及其他含环丙基和环丁基的自由基阴离子）的开环速率常数可以基于自由基阴离子的热力学稳定性、环丙基上的取代基稳定二张力自由基阴离子的自由基部分的能力以及二张力自由基阴离子的烯醇化物部分的稳定性而合理化。基于这一概念，提出了估计开环 Delta G 度的热化学循环。对于简单的含环丙基的羰基阴离子，发现了 log(k(o)) 和 Delta G 度之间的合理相关性，并应用逐步离解电子转移理论使结果合理化。使用密度泛函理论 (UB3LYP/6-31+G*) 计算的活化能与测量的 log(k(o)) 具有相当好的相关性。一般来说，导出的 log(k(o)) 和 Delta G 度以及 log(k(o)) vs Ea 图为“校准曲线”提供了基础，以预测衍生自羰基化合物的自由基阴离子的开环速率常数。
By using direct and indirect electrochemical methods, rate constants (k,,) for cyclopropane ring opening of radical anions derived from the one-electron reduction of trans-1-benzoyl-2-phenylcyclopropane, trans-1-benzoyl-2-vinyleyclopropane, 2-methylenecyclopropyl phenyl ketone, spiro[anthracene-9,1'-cyclopropan-10-one], 3-cyclopropylcyclohex-2-en-1-one, and 3-(1-methylcyclopropyl)cyclohex-2-en-1-one were determined. Qualitatively, rate constants for ring opening of these (and other cyclopropyl- and cyclobutyl-containing radical anions) can be rationalized on the basis of the thermodynamic stability of the radical anion, the ability of substiments on the cyclopropyl group to stabilize the radical portion of the distonic radical anion, and the stability of the enolate portion of the distonic radical anion. On the basis of this notion, a thermochernical cycle for estimating Delta G degrees for ring opening was presented. For simple cyclopropyl-containg ketyl anions, a reasonable correlation between log(k(o)) and Delta G degrees was found, and stepwise dissociative electron transfer theory was applied to rationalize the results. Activation energies calculated with density functional theory (UB3LYP/ 6-31+G*) correlate reasonably well with measured log(k(o)). The derived log(k(o)) and Delta G degrees and log(k(o)) vs Ea plots provide the basis for a "calibration curve" to predict rate constants for ring opening of radical anions derived from carbonyl compounds, in general.