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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopic, Kinetic, and Structural Properties of Rotamers of the 2-Vinylpyridinium Ylide of Phenylchlorocarbene
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Spectroscopic, Kinetic, and Structural Properties of Rotamers of the 2-Vinylpyridinium Ylide of Phenylchlorocarbene

机译：苯基氯卡宾的2-乙烯基吡啶鎓叶立德旋转体的光谱，动力学和结构性质

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摘要

The analysis of the time-resolved UV-vis absorption spectra of the 2-vinylpyridinium ylide of phenylchlorocarbene, measured by laser-flash photolysis, indicates the existence of two rotamers of this species. The absorption spectrum, rise time, and decay time of each rotamer were determined by a global analysis method. The kinetic analysis of the results indicates an interconversion between the rotamers and a large difference between their rates of cyclization. The observed rotamerism involves a rotation of the vinyl pyridine with respect to the carbene, the two rotamers being differentiated by the fact that the vinyl group faces either the chlorine or the phenyl groups of the carbene. Calculations of the absorption spectra and enthalpies of formation of numerous possible structures indicate that the 100-nm difference between the wavelengths of maximum absorption is well explained by a change in the tilt angle between the phenyl and the ylide planes from 35-40° for the "red-absorbing" ylide to 55-60° for the other. However, the calculated enthalpies of formation of the various structures being nearly the same, these calculations do not allow us to assign one specific structure to one or the other of the observed species.
机译：通过激光闪光光解法对苯基氯卡宾的2-乙烯基吡啶鎓叶立德的时间分辨紫外可见吸收光谱进行分析，结果表明该物种存在两个旋转异构体。通过整体分析方法确定每个旋转异构体的吸收光谱，上升时间和衰减时间。结果的动力学分析表明，旋转异构体之间相互转化，并且其环化速率之间存在较大差异。观察到的旋转异构体涉及乙烯基吡啶相对于卡宾的旋转，这两个旋转异构体的区别在于乙烯基面对卡宾的氯或苯基。吸收光谱的计算和许多可能结构的形成焓表明，最大吸收波长之间的100-nm差异可以很好地解释为，苯基和内酯平面之间的倾斜角从35-40°改变为另一个“吸收红”的叶利德达到55-60°。但是，计算得出的各种结构的形成焓几乎相同，这些计算不允许我们将一种特定的结构分配给所观察物种中的一种或另一种。

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