Substituent effects on the aromaticity of carbocyclic five-membered rings.
Substituent effects on the aromaticity of carbocyclic five-membered rings.
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DOI：
10.1039/b917343a
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发表时间：
2010-01
期刊：
影响因子：
--
通讯作者：
M. Alonso;B. Herradón
中科院分区：
文献类型：
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作者：
M. Alonso;B. Herradón
分析了取代基性质、取代基数目和位置对阴离子、环戊二烯和阳离子衍生物芳香性/反芳香性的影响。取代的芳香性/反芳香性的衍生物已被测量使用能量，磁性和结构的标准，考虑到芳香性的多维特征。此外，所有化合物的欧几里得距离值（d（j））已使用先前开发的神经网络进行了估计。结果表明，d（j）作为芳香度的标度，克服了ASE、Lambda、NICS和HOMA指数描述取代基效应引起的环戊二烯环芳香度变化的局限性。此外，它表明，神经网络是有用的工具，建立结构-性能关系。结果表明，无论取代基的电子性质如何，取代后环戊二烯环和阴离子环的芳香度大部分降低。给电子基团，特别是羟基，使碳负离子不稳定的程度比接受电子的更大。另一方面，所有的取代基强烈降低的反芳香性的双阳离子。这些结果可用于设计具有降低的不稳定性的新的阳离子配体和具有改进的稳定性和反应性的新的阳离子配体。
The influence of the substituent nature, as well as the number and position of the substituents, on the aromaticity/antiaromaticity of a comprehensive set of derivatives of cyclopentadienyl anion, cyclopentadiene and cyclopentadienyl cation has been analyzed. The aromaticity/antiaromaticity of substituted cyclopentadienyl derivatives has been measured using energetic, magnetic and structural criteria to take into account the multidimensional character of aromaticity. Furthermore, the Euclidean distance values (d(j)) for all compounds have been estimated using the neural network developed previously. It has been demonstrated that the d(j) as a scale of aromaticity overcomes the particular limitations of the ASE, Lambda, NICS and HOMA indices to describe the changes in the aromaticity of cyclopentadiene ring due to substituent effects. Additionally, it is shown that neural networks are useful tools for establishing structure-property relationships. The results indicate that mostly the aromaticity of cyclopentadiene ring and cyclopentadienyl anion ring decrease upon substitution irrespective of the electronic character of the substituent. The electron-donating groups, especially hydroxyl groups, destabilize carbanion to a larger extent than electron-accepting ones. On the other hand, all the substituents reduce strongly the antiaromaticity of the cyclopentadienyl cation. These results can be useful for the design of new cationic ligands with lowered instability and new cyclopentadienyl ligands with improved stability and reactivity.