Department of Chemistry, North-Eastern Hill University, Shillong 793 022, India.
J Phys Chem A. 2010 Feb 25;114(7):2710-26. doi: 10.1021/jp911593y.
Two DFT methods are used to study the stability, singlet-triplet splitting, and geometry of all didehydrogenated quinolines and isoquinolines in their lowest lying singlet and triplet states. Here, the relative stability within an isomeric series is differentiated from the biradical stabilization energy, which pertains to the propensity for radical abstraction reactions. Analysis of relative stability orders for these hetarynes points to the influence of the basic hetaryne type (ortho, meta, peri, para, and other), the effects of bond alternation in the bicycle, and the position of the ring nitrogen atom with respect to the nearest radical center. Singlet hetaryne stability tends to follow the order ortho > meta > (para and peri) and the reverse order for the triplet species. Among ortho-hetarynes, the singlet state is stabilized, and the triplet state destabilized when the hetaryne bond is shorter, and vice versa. The effects of the nitrogen atom on the relative stability depend upon (a) the hetaryne spin state, (b) whether the nitrogen is adjacent to or one atom removed from a radical center, and (c) the distance between the heteroatom and the nearest radical center for hetarynes with more widely separated radical centers. The singlet-triplet splitting is, in most cases, more dependent upon singlet stability than triplet stability. The biradical stabilization energy does not, in general, correlate with relative stability but furnishes predictions concerning capacity for reactions like hydrogen atom abstraction. Geometries of the singlet hetarynes (notably the ortho- and meta-hetarynes) present greater departures from the parent hetarene structure than do the triplet geometries.
两种 DFT 方法被用于研究所有二氢化喹啉和异喹啉在其最低单重态和三重态中的稳定性、单重态三重态分裂和几何形状。这里，异构体系列内的相对稳定性与双自由基稳定化能区分开来，后者与自由基提取反应的倾向有关。对这些杂芳烃的相对稳定性顺序的分析表明，基本杂芳烃类型（邻位、间位、对位、并位和其他位置）、环中键交替的影响以及环氮原子相对于最近的自由基中心的位置都有影响。单重态杂芳烃的稳定性倾向于遵循邻位 > 间位 >（对位和并位）的顺序，而三重态物种则相反。在邻位杂芳烃中，当杂芳烃键更短时，单重态稳定，三重态不稳定，反之亦然。氮原子对相对稳定性的影响取决于(a)杂芳烃的自旋态，(b)氮原子是紧邻还是距离自由基中心一个原子，以及(c)对于具有更分离的自由基中心的杂芳烃，杂原子与最近的自由基中心之间的距离。在大多数情况下，单重态三重态分裂更多地取决于单重态稳定性而不是三重态稳定性。双自由基稳定化能通常与相对稳定性不相关，但可以预测像氢原子提取这样的反应的能力。单重态杂芳烃（特别是邻位和间位杂芳烃）的几何形状比三重态杂芳烃的几何形状更偏离母体杂芳烃的结构。
