CC bond cleavages of radical cations of 2-substituted benzothiazoline derivatives were investigated to determine the parameters controlling the fragmentation rate constants. In spite of the low oxidation potentials of the compounds, fragmentation rate constants greater than 1 × 106 s1 could be achieved through weakening of the fragmenting bond by substituents that stabilize the radical fragment and exert steric crowding. A quantitative assessment of the relative roles of radical stabilization vs. steric effects to weaken the fragmenting CC bond was achieved through DFT calculations. The calculated activation enthalpies matched reasonably well with the experimentally determined values. A thermokinetic analysis revealed that the fragmentations of benzothiazoline radical cations have relatively large intrinsic kinetic barriers, ascribed to the delocalized nature of the product radical and cation fragments. Interestingly, the same factors that lead to the large intrinsic barriers led, simultaneously, to large thermodynamic driving forces for the fragmentations, which should lead to lower activation barriers. These effects oppose each other kinetically and provide important insight into the design of fast radical ion fragmentation reactions.Key words: benzothiazoline, radical cation, fragmentation, steric effects, DFT.
2-取代苯并噻唑啉衍生物的自由基阳离子的C-C键裂解进行了研究,以确定控制裂解速率常数的参数。尽管化合物的氧化电位较低,但通过通过取代基使裂解键变弱,从而稳定自由基片段并施加立体阻碍,可以实现大于1×10^6 s^-1的裂解速率常数。通过密度泛函理论(DFT)计算,对自由基稳定与立体效应相对作用于使裂解的C-C键变弱的定量评估取得了成功。计算得到的活化焓与实验测定值相当吻合。热动力学分析显示,苯并噻唑啉自由基阳离子的裂解具有相对较大的固有动力学壁垒,归因于产物自由基和阳离子片段的离域性质。有趣的是,导致大固有壁垒的因素同时导致了裂解的大热力学驱动力,这应该导致较低的活化壁垒。这些效应在动力学上相互对立,并为设计快速自由基离子裂解反应提供了重要见解。关键词:苯并噻唑啉,自由基阳离子,裂解,立体效应,DFT。