Aromaticity analysis of lithium cation/pi complexes of aromatic systems.
Aromaticity analysis of lithium cation/pi complexes of aromatic systems.
复制标题
芳香族体系的锂阳离子/π配合物的芳香性分析。
作者：
M. Güell;Jordi Poater;J. Luis;O. Mó;M. Yáñez;M. Solà
以芳香性指数的准离域指数（PDI）、芳香性波动指数（FLU）、芳香性指数的谐振子模型（HOMA）和非核依赖化学位移（NICS）为探针，讨论了一系列多环芳烃与锂离子络合时芳环局部芳香性的变化.在大多数情况下，基于电子的PDI和FLU指数的变化几乎是不相关的。因此，主要使用更敏感的HOMA和NICS描述符进行分析。这些指数表明，不同环的局部芳香特性的变化很小。一般来说，Li+与具有最大π电荷的环更有利地相互作用，但这些幅度之间没有相关性。与锂阳离子直接相互作用的环遭受轻微但显著的芳香性降低，而相邻环的局部芳香性的降低是轻微的。对于那些位于更远离直接连接到Li+的环的环，我们发现芳香性通常略有增加。尽管芳香性与Li+结合焓之间没有明确的相关性，但后者与直接与金属阳离子相互作用的环的芳香性变化之间存在粗略的相关性。
The changes in the local aromaticity of aromatic rings on complexation with lithium cation are discussed for a series of polycyclic aromatic hydrocarbons by using, as probes of aromaticity, the para-delocalization index (PDI), the aromatic fluctuation index (FLU), the harmonic oscillator model of aromaticity index (HOMA), and the nucleus-independent chemical shift (NICS). In most cases, changes in the electronically based PDI and FLU indices are almost irrelevant. For this reason, the analysis is carried out mainly with the more sensitive HOMA and NICS descriptors. These indices indicate that changes in the local aromatic character of the different rings are small. In general, Li+ interacts more favorably with the ring having the largest pi charge, but there is no correlation between these magnitudes. The ring directly interacting with the lithium cation suffers a slight but significant reduction of aromaticity, while the reduction of the local aromaticity of the adjacent rings is minor. For those rings located further away from the ring directly connected to Li+, we found generally a small increase in aromaticity. Although there is no clear correlation between aromaticity and Li+ binding enthalpies, there is a rough correlation between the latter and the change in the aromaticity of the ring directly interacting with the metal cation.