Manassir Mohammad, Pakiari Ali H
Chemistry Department, College of Sciences, Shiraz University, Shiraz, 71454, Iran.
Chemistry Department, College of Sciences, Shiraz University, Shiraz, 71454, Iran.
J Mol Graph Model. 2022 Jan;110:108062. doi: 10.1016/j.jmgm.2021.108062. Epub 2021 Oct 30.
Based on the linear combination of atomic orbital-molecular orbital by the natural bond orbitals (NBO) theory, the attractive donor-acceptor superposition interaction between filled (Lewis-type) and vacant (non-Lewis-type) orbitals provide a general mechanism for quantal energy lowering. This interaction has a direct impact on the quantity of the second-order stabilization energy. Therefore, the valence non-Lewis density (VNLD) index, the electron density of unoccupied valence nonbonding and antibonding orbitals, is introduced as an approach to describe and measure aromaticity. This index is based on the frontier orbital concept. To investigate the validity of the proposed aromaticity index, we selected several test sets of organic and inorganic molecules such as different ring sizes in cyclic and heterocyclic hydrocarbons, and all-metal and semimetal clusters, and compared our findings with previous aromaticity analysis. According to the results, VNLD values are well correlated and anticipated the order of aromaticity with the formerly introduced criteria. Furthermore, VNLD reveals that the rings with π-sextet electrons localized in a ring are more aromatic than the other rings, thus, it is in line with Clar's rule. Our proposed aromaticity index has advantages such as, easy to obtain from NBO analysis, and does not require reference molecules which made it more applicable for realizing the aromaticity order in many organic and inorganic compounds.
基于自然键轨道（NBO）理论中原子轨道 - 分子轨道的线性组合，填充（Lewis型）和空（非Lewis型）轨道之间有吸引力的给体 - 受体叠加相互作用为量子能量降低提供了一种通用机制。这种相互作用对二阶稳定能的量有直接影响。因此，引入价非Lewis密度（VNLD）指数，即未占据价非键合和反键轨道的电子密度，作为描述和测量芳香性的一种方法。该指数基于前沿轨道概念。为了研究所提出的芳香性指数的有效性，我们选择了几个有机和无机分子的测试集，如环状和杂环烃中不同环大小的分子，以及全金属和半金属簇，并将我们的研究结果与先前的芳香性分析进行了比较。根据结果，VNLD值具有良好的相关性，并与先前引入的标准预测的芳香性顺序一致。此外，VNLD表明，π - 六重态电子定域在环中的环比其他环更具芳香性，因此，这与克拉尔规则一致。我们提出的芳香性指数具有易于从NBO分析中获得等优点，并且不需要参考分子，这使得它更适用于确定许多有机和无机化合物中的芳香性顺序。
