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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Modern Molecular Mechanics and ab Initio Calculations on Benzylic and Cyclic Delocalized Cations
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Modern Molecular Mechanics and ab Initio Calculations on Benzylic and Cyclic Delocalized Cations

机译：现代分子力学和对苯甲酸和环状离域阳离子的从头算计算

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Calculations of optimized force field (MMP2 extended to carbocations) and ab initio (MP2/6-31G~*) geometries as well as π-electron densities of various benzyl and cyclic delocalized cations agree well. The MMP2 heats of formation reproduce the available experimental values. MMP2 π-resonance energies are consistent with those obtained by isodesmic equations from experimental and ab initio data. When carbon π-charges are lower than 0.2, the influence of phenyl substituents is attenuated. Thus, the triphenylmethyl cation resonance stabilization value (-41.6 kcal/mol average for each phenyl ring) is much less than that of the benzyl cation (-76.4 kcal/mol) and the benzhydryl cation (average stabilization value of -51.4 kcal/mol). MMP2 aromatic stabilization energy estimates of the benzyl and tropylium cations as well as benzene agree well with the assessments of aromaticity by the nucleus independent chemical shift (NICS) criterion, which is based on the magnetic shieldings computed at ring centers. The MMP2 method allows quantitative evaluations of homoconjugative interactions. The stabilization in the homotropylium cation due to 1,7 homoconjugative overlap is estimated to be quite appreciable, -13.4 kcal/mol.
机译：优化的力场（MMP2扩展到碳正离子）和从头算（MP2 / 6-31G〜*）几何形状以及各种苄基和环状离域阳离子的π电子密度的计算结果非常吻合。 MMP2的地层热可复制可用的实验值。 MMP2π共振能量与从实验数据和从头算数据通过等渗方程获得的能量一致。当碳π电荷低于0.2时，苯基取代基的影响减弱。因此，三苯甲基阳离子共振稳定值（每个苯环平均为-41.6 kcal / mol）比苄基阳离子（-76.4 kcal / mol）和二苯甲基阳离子（平均稳定值-51.4 kcal / mol）小得多。 ）。对MMP2的苄基和对yl阳离子以及苯的芳香族稳定能估计值与基于核独立化学位移（NICS）准则的芳香性评估非常吻合，该准则基于环中心计算的磁屏蔽。 MMP2方法可对同共轭相互作用进行定量评估。据估计，由于1,7个共轭重叠，导致在同向阳离子阳离子中的稳定性非常可观，为-13.4 kcal / mol。

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