Chemistry Department, College of Sciences, Shahid Chamran University, Ahvaz, Iran.
Phys Chem Chem Phys. 2010 May 14;12(18):4742-9. doi: 10.1039/b916509f. Epub 2010 Mar 16.
Based on the local Shannon entropy concept in information theory, a new measure of aromaticity is introduced. This index, which describes the probability of electronic charge distribution between atoms in a given ring, is called Shannon aromaticity (SA). Using B3LYP method and different basis sets (6-31G**, 6-31+G** and 6-311++G**), the SA values of some five-membered heterocycles, C(4)H(4)X, are calculated. Significant linear correlations are observed between the evaluated SAs and some other criteria of aromaticity such as ASE, Lambda and NICS indices. According to the obtained relationships, the range of 0.003 < SA < 0.005 is chosen as the boundary of aromaticity/antiaromaticity. Using B3LYP/6-31+G** level of theory, the Shannon aromaticities for a series of mono-substituted benzene derivatives are calculated and analyzed. It is found that the least standard deviation between the aromaticities and the best linear correlation with the Hammett substituent constants are observed for the new index in comparison with the other indices. Also the values of the new index are evaluated for some substituted penta- and heptafulvenes, which successfully predict the order of aromaticity in these compounds. Applying this index to some non-benzonoids, linear and angular polyacenes also give satisfactory results and prove to be quite suitable for determining the local aromaticity of different rings in polyaromatic hydrocarbons.
基于信息论中的局部香农熵概念，引入了一种新的芳香度度量。该指数描述了给定环中原子之间电子电荷分布的概率，称为香农芳香度（SA）。使用 B3LYP 方法和不同的基组（6-31G**、6-31+G和 6-311++G），计算了一些五元杂环，C(4)H(4)X 的 SA 值。评估的 SAs 与芳香度的其他一些标准（如 ASE、Lambda 和 NICS 指数）之间观察到显著的线性相关性。根据获得的关系，选择 0.003<SA<0.005 的范围作为芳香性/反芳香性的边界。使用 B3LYP/6-31+G**理论水平，计算并分析了一系列单取代苯衍生物的香农芳香度。与其他指数相比，该新指数在芳香性方面具有最小的标准偏差和与哈米特取代常数的最佳线性相关性。此外，还评估了一些取代的五元和七元富烯的新指数的值，成功预测了这些化合物的芳香性顺序。将该指数应用于一些非苯并类化合物，线性和角形多环芳烃也给出了令人满意的结果，并证明非常适合确定多环芳烃中不同环的局部芳香性。
