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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electronic Structure and Noncovalent Interactions within Ion-Radical Complexes of N-(2-Furylmethyl)aniline Molecular Ions
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Electronic Structure and Noncovalent Interactions within Ion-Radical Complexes of N-(2-Furylmethyl)aniline Molecular Ions

机译：N-（2-呋喃甲基）苯胺分子离子的离子自由基配合物中的电子结构和非共价相互作用

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摘要

We investigate the electronic structure and noncovalent interactions within cationradical complexes that are relevant in the electron impact mass spectrometry of N-(2-furylmethyl)anilines, 4-RC6H4-NH-CH2-C4H3O with (R = -H, -OCH3, -CH3, -F, -Cl, -Br). In particular, we consider the reactive intermediates that precede the final products of two previously suggested dissociation pathways for these systems, i.e., (i) a direct cleavage of the NH-CH2 bond and (ii) an isomerization/fragmentation mechanism. The study is performed by means of correlated calculations (UCCSD and UMP2) together with density functionals (UM06 an UM06-2x) along with the triple-zeta quality basis set 6-311++G(2d,2p). In addition, we carried out a topological analysis of the electron density in accordance with the quantum theory of atoms in molecules (QTAIM) together with the examination of the noncovalent interaction (NCI) index. In contrast with previous studies based on the UB3LYP approximation, we could determine the transition states associated with both fragmentation pathways. The RiceRamspergerKasselMarcus theory, used to determine the relative importance of these dissociation mechanisms, indicates that whereas the direct cleavage and the isomerization/fragmentation reaction routes have similar constant rates at low energy, the former prevails when the energy of the system is increased. The QTAIM analysis reveals that the charge of the cationradical complex is mainly located on either a furfuryl (direct cleavage mechanism) or a pyrylium (isomerization/fragmentation pathway) ion and that these units interact with a neutral radical aniline moiety. The localization of the positive charge in either a furfuryl or pyrylium cation is in agreement with the preminecence of the m/z = 81 fragment in the mass spectrometry of N-(2-furylmethyl)anilines. Moreover, the QTAIM properties indicate that the a unpaired electron of the system is principally distributed over the nitrogen and the ortho and para carbon atoms with respect to the -NH group in the R-C6H4-NH unit. The investigation of the NCI index and the intermolecular bond critical points and bond paths gives an account of the NCIs linking the radical cation clusters under consideration. Finally, we found correlations which indicate that the concentration of the m/z = 81 fragment in a mass spectrum is reduced with the interaction energy of the radical complex from which it is originated. Altogether, this work shows how the combination of suitable electronic structure calculations along with post wave function analyses can yield important insights about the formation and properties of cationradical complexes relevant in mass spectrometry.
机译：我们研究了N-（2-呋喃甲基）苯胺，4-RC6H4-NH-CH2-C4H3O与（R = -H，-OCH3，-的N-（2-呋喃甲基）苯胺的电子碰撞质谱中相关的阳离子自由基配合物中的电子结构和非共价相互作用CH3，-F，-Cl，-Br）。特别地，我们认为在这些系统的两个先前提出的解离途径的最终产物之前的反应性中间体，即（i）NH-CH 2键的直接裂解和（ii）异构化/片段化机理。该研究是通过相关计算（UCCSD和UMP2）以及密度泛函（UM06和UM06-2x）以及三重Zeta质量基础集6-311 ++ G（2d，2p）进行的。此外，我们根据分子中原子的量子理论（QTAIM）进行了电子密度的拓扑分析，并检查了非共价相互作用（NCI）指数。与以前的基于UB3LYP近似的研究相反，我们可以确定与两个片段化途径相关的过渡态。 RiceRamspergerKasselMarcus理论用于确定这些离解机理的相对重要性，表明尽管在低能下直接裂解和异构化/片段化反应路线具有相似的恒定速率，但当系统能量增加时，前者占优势。 QTAIM分析表明，阳离子自由基络合物的电荷主要位于糠基（直接裂解机理）或吡啶鎓（异构化/片段化途径）离子上，并且这些单元与中性自由基苯胺部分相互作用。在N-（2-糠基甲基）苯胺质谱中，正电荷在糠基或吡啶鎓阳离子中的定位与m / z = 81片段的优势有关。此外，QTAIM性质表明，相对于R-C6H4-NH单元中的-NH基团，该系统的未配对电子主要分布在氮以及邻和对碳原子上。对NCI指数以及分子间键的临界点和键路径的研究给出了NCI连接所考虑的自由基阳离子簇的说明。最后，我们发现了相关性，这些相关性表明质谱中m / z = 81片段的浓度随自由基复合物的相互作用能而降低。总而言之，这项工作表明如何将合适的电子结构计算与波后功能分析结合起来，才能获得与质谱相关的阳离子自由基配合物的形成和性质的重要见解。

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