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Classical and distonic radical cations: A valence bond approach

机译：经典和distonic自由基阳离子：价键方法

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摘要

The conventional radical cations arising from the ionization of CH3CH2X (X=F, OH, NH2, Cl, SH, PH2), and their distonic isomers, CH2CH2XH center dot+, were studied by means of standard Moller-Plesset and G2 methods, and by an ab initio valence bond method. Among the conventional structures, two distinct states are considered. In the so-called c' states, the impaired electron is in an orbital that lies in the plane of the heavy atoms, while the C states have their impaired electron in an orbital lying out of the plane. It is shown that c '' states are, as a rule, more stable than the C states, by up to approximately 20 kJmol(-1) depending on the nature of X, owing to a stabilizing interplay of resonating structures. While the geometries of the C states are rather similar to those of the neutral molecules, some of the c' states display very different geometries, characterized by elongated C-C bonds, particularly when X=F or, to a lesser extent, when X-OH or Cl. These peculiar geometric features are rationalized by the valence bond analysis, which reveals that the C-C bond in these species is better viewed as a two-center, one-electron bond. The distonic radical cations are generally more stable than the conventional ones (by 20-100 kJmol(-1)), except for the less electronegative X groups of the series, namely X=SH and PH2. In these two cases, together with X=NH2, the radical cation displays a classical distonic structure, as regards the geometry and electronic state. On the other hand, considerable C-X elongation is found for X-F or Cl. In these last cases, the valence bond analysis shows that the radical cation is better viewed as an ion-molecule complex between an ionized ethylene and a neutral HX molecule. The electronic structure of the distonic radical cation with X=OH lies between the two previous limiting descriptions.
机译：通过标准的Moller-Plesset和G2方法研究了CH3CH2X（X = F，OH，NH2，Cl，SH，PH2）的电离产生的常规自由基阳离子及其二元异构体CH2CH2XH中心点+。从头价键法。在常规结构中，考虑了两种不同的状态。在所谓的c'态中，受损的电子位于重原子平面内的轨道中，而C态的受损电子位于平面外的轨道中。结果表明，由于共振结构的稳定相互作用，通常C态比C态更稳定，取决于X的性质，其稳定性最高可达约20 kJmol（-1）。尽管C态的几何形状与中性分子的几何形状非常相似，但某些c'态却表现出非常不同的几何形状，其特征是拉长的CC键，特别是当X = F或较小程度的X-OH时或Cl。这些特殊的几何特征通过价键分析得到合理化，这表明这些物种中的C-C键最好视为两中心单电子键。除二元自由基阳离子系列的负电性较小的X基团（即X = SH和PH2）外，它们通常比常规阳离子更稳定（提高20-100 kJmol（-1））。在这两种情况下，就几何形状和电子状态而言，自由基阳离子与X = NH2一起显示出经典的扭曲结构。另一方面，发现X-F或Cl具有相当大的C-X伸长率。在这些最后的情况下，价键分析表明，自由基阳离子更好地被视为离子化的乙烯与中性HX分子之间的离子分子复合物。 X = OH的二烯基自由基阳离子的电子结构位于两个先前的限制描述之间。

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