Weaver M N, Janicki S Z, Petillo P A
Roger Adams Laboratory, Department of Chemistry, University of Illinois, 600 S. Matthews Avenue, Urbana, Illinois 61801, USA.
J Org Chem. 2001 Feb 23;66(4):1138-45. doi: 10.1021/jo0011742.
The geometries of a series of substituted arenediazonium cations (p-NO2, p-CN, p-Cl, p-F, p-H, m-CH3, p-CH3, p-OH, p-OCH3, p-NH2) and the corresponding diazenyl radicals were optimized at the HF/6-31G, MP2/6-31G, B3LYP/6-31G, B3LYP/TZP, B3PW91/TZP, and CASSCF/6-31G levels of theory. Inner-sphere reorganization energies for the single electron-transfer reaction between the species were computed from the optimized geometries according to the NCG method and compared to experimental values determined by Doyle et al. All levels of theory predicted a CNN bond angle of 180 degrees in the cation. A bent neutral diazenyl radical was predicted at all levels of theory excepting B3LYP/TZP and B3PW91/TZP for the p-Cl-substituted compound. Inner-sphere reorganization energies determined at the HF, MP2, and CASSCF levels of theory correlated poorly with both experimental results and calculated geometries. Density functional methods correlated best with the experimental values, with B3LYP/6-31G yielding the most promising results, although the ROHF/6-31G survey also showed some promise. B3LYP/6-31G calculations correctly predicted the order of the inner-sphere reorganization energies for the series, excluding the halogen-substituted compounds, with values ranging from 42.8 kcal x mol(-1) for the p-NO2-substituted species to 55.1 kcal x mol(-1) for NH2. The magnitudes of these energies were lower than the experimental by a factor of 2. For the specific cases examined, the closed-shell cation geometries showed the expected geometry about the CNN bond, with variations in the CN and NN bond lengths correlating with the electron-donating/withdrawing capacity of the substituent. As predicted by Doyle et al., a large geometry change was observed upon reduction. The neutral diazenyl radicals showed a nominal CNN bond angle of 120 degrees and variations in the CN and NN bond lengths also correlated with the electron-donating/withdrawing capacity of the substituent. Changes in theta(CNN) and r(CN) both correlated well with calculated lambda(inner). The key parameters influencing inner-sphere reorganization energy were the CN and NN bond lengths and the CNN bond angle. This influence is explained qualitatively via resonance models produced from NRT analysis and is related to the amount of CN double bond character. Based on these observations, B3LYP/6-31G calculations are clearly the most amenable for calculating inner-sphere reorganization energies for the single electron-transfer reaction between cation/neutral arenediazonium ion couples.
在HF/6 - 31G、MP2/6 - 31G、B3LYP/6 - 31G、B3LYP/TZP、B3PW91/TZP和CASSCF/6 - 31G理论水平下，对一系列取代芳基重氮阳离子（对硝基、对氰基、对氯、对氟、对氢、间甲基、对甲基、对羟基、对甲氧基、对氨基）及其相应的重氮自由基的几何结构进行了优化。根据NCG方法，从优化后的几何结构计算出这些物种之间单电子转移反应的内球重组能，并与Doyle等人测定的实验值进行比较。所有理论水平都预测阳离子中的CNN键角为180度。除了对氯取代化合物的B3LYP/TZP和B3PW91/TZP水平外，所有理论水平都预测中性重氮自由基呈弯曲状。在HF、MP2和CASSCF理论水平下测定的内球重组能与实验结果和计算出的几何结构相关性都很差。密度泛函方法与实验值的相关性最好，其中B3LYP/6 - 31G给出了最有希望的结果，尽管ROHF/6 - 31G的研究也显示出一定的前景。B3LYP/6 - 31G计算正确地预测了该系列（不包括卤素取代化合物）内球重组能的顺序，对硝基取代物种的值为42.8 kcal·mol⁻¹，氨基取代物种的值为55.1 kcal·mol⁻¹。这些能量的大小比实验值低2倍。对于所研究的特定情况，闭壳阳离子几何结构显示出围绕CNN键的预期几何形状，CN和NN键长的变化与取代基的给电子/吸电子能力相关。正如Doyle等人所预测的，还原时观察到了较大的几何结构变化。中性重氮自由基的标称CNN键角为120度，CN和NN键长的变化也与取代基的给电子/吸电子能力相关。θ(CNN)和r(CN)的变化与计算出的λ(内)都有很好的相关性。影响内球重组能的关键参数是CN和NN键长以及CNN键角。这种影响通过NRT分析产生的共振模型进行了定性解释，并且与CN双键特征的量有关。基于这些观察结果，B3LYP/6 - 31G计算显然最适合计算阳离子/中性芳基重氮离子对之间单电子转移反应的内球重组能。
