Effect of meta electron-donating groups on the electronic structure of substituted phenyl nitrenium ions.
Effect of meta electron-donating groups on the electronic structure of substituted phenyl nitrenium ions.
复制标题
间位给电子基团对取代苯基氮离子电子结构的影响。
DOI：
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发表时间：
2004
影响因子：
15
通讯作者：
C. Cramer
中科院分区：
文献类型：
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作者：
A. Winter;D. Falvey;C. Cramer
采用密度泛函理论（UB 3LYP/6- 31 G（d，p））研究了21个间位取代苯基氮鎓离子单重态-三重态能隙的取代基效应.结果发现，强给电子取代基稳定的三重态相对于单重态。具有足够强的Meta电子供体（例如，m，m ′-二氨基苯基氮离子），预测三重态为基态。平衡几何形状，Kohn-Sham轨道分布，和Mulliken自旋密度的三重态的这一系列的氮离子的分析导致的结论是，有两种空间上不同类型的低能量三重态。简单的芳基氮鎓离子如苯基氮鎓离子以及具有吸电子或弱供Meta取代基的那些离子具有最低能量的三重态，其本质上是n，pi。也就是说，一个单占据分子轨道与苯环平面正交，另一个共面。这些n，pi三联体通常以大的ArNH键角为特征（约100 °）。130-132度）和垂直于苯环平面的NH键。相反，Meta给体芳基氮鎓离子具有最低能量的三重态，最好描述为pi，pi。也就是说，两个单占据分子轨道都与芳环正交。这样的π，π状态的特征在于与苯环共面的NH键，并且具有更尖锐的ArNH键角（约100 °）。110-111度）。这些三重态氮鎓离子的电子结构类似于间苯醌二甲烷衍生物。
Density functional theory (UB3LYP/6-31G(d,p)) was used to determine substituent effects on the singlet-triplet-state energy gap for 21 meta-substituted phenylnitrenium ions. It was found that strongly electron-donating substituents stabilize the triplet state relative to the singlet state. With sufficiently strong meta electron donors (e.g., m,m'-diaminophenylnitrenium ion) the triplet is predicted to be the ground state. Analysis of equilibrium geometries, Kohn-Sham orbital distributions, and Mulliken spin densities for the triplet states of this series of nitrenium ions leads to the conclusion that there are two spatially distinct types of low-energy triplet states. Simple arylnitrenium ions such as phenylnitrenium ions as well as those having electron-withdrawing or weakly donating meta substituents have lowest-energy triplet states that are n,pi in nature. That is, one singly occupied molecular orbital is orthogonal to the plane of the phenyl ring and one is coplanar. These n,pi triplets are generally characterized by large ArNH bond angles (ca. 130-132 degrees ) and an NH bond that is perpendicular to the plane of the phenyl ring. In contrast, meta donor arylnitrenium ions have a lowest-energy triplet state best described as pi,pi. That is, both singly occupied molecular orbitals are orthogonal to the aromatic ring. Such pi,pi states are characterized by NH bonds that are coplanar with the phenyl ring and have ArNH bond angles that are more acute (ca. 110-111 degrees ). These triplet nitrenium ions have electronic structures analogous to those of meta-benzoquinodimethane derivatives.