Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014 Helsinki, Finland.
J Phys Chem A. 2012 Oct 18;116(41):10257-68. doi: 10.1021/jp308121b. Epub 2012 Oct 8.
The effect of fluorine substitution on the aromaticity of polycyclic hydrocarbons (PAH) is investigated. Magnetically induced current densities, current pathways, and current strengths, which can be used to assess molecular aromaticity, are calculated using the gauge-including magnetically induced current method (GIMIC). The degree of aromaticity of the individual rings is compared to those obtained using calculated nucleus-independent chemical shifts at the ring centers (NICS(0) and NICS(0)(zz)). Calculations of explicitly integrated current strengths for selected bonds show that the aromatic character of the investigated polycyclic hydrocarbons is weakened upon fluorination. In contrast, the NICS(0) values for the fluorinated benzenes increase noteworthy upon fluorination, predicting a strong strengthening of the aromatic character of the arene rings. The integrated current strengths also yield explicit current pathways for the studied molecules. The current pathways of the investigated linear polyacenes, pyrene, anthanthrene, coronene, ovalene, and phenanthro-ovalene are not significantly affected by fluorination. NISC(0) and NICS(0)(zz) calculations provide contradictory degrees of aromaticity of the fused individual ring. Obtained NICS values do not correlate with the current strengths circling around the individual rings.
研究了氟取代对多环芳烃（PAH）芳香性的影响。使用包含磁场感应电流的方法（GIMIC）计算了可用于评估分子芳香性的磁诱导电流密度、电流路径和电流强度。将各个环的芳香度与通过计算环中心的核独立化学位移（NICS(0) 和 NICS(0)(zz)）获得的值进行了比较。对选定键的显式积分电流强度的计算表明，多环芳烃的芳香性在氟化后减弱。相比之下，氟化苯的 NICS(0) 值在氟化后显著增加，预测芳烃环的芳香性得到了强烈增强。积分电流强度还为研究的分子提供了明确的电流路径。所研究的线性多并苯、芘、蒽、并五苯、并六苯和菲并并六苯的电流路径不受氟化的显著影响。NISC(0) 和 NICS(0)(zz) 计算提供了融合的单个环的芳香度的矛盾程度。获得的 NICS 值与围绕各个环的电流强度不相关。
