Faculty of Science, University of Kragujevac, P. O. Box 60, 34000 Kragujevac, Serbia.
Phys Chem Chem Phys. 2012 Oct 28;14(40):14067-78. doi: 10.1039/c2cp41472d. Epub 2012 Sep 19.
In this paper, a detailed study of the local aromaticity in a series of cyclopenta-fused linear polyacenes (acenaphthylene derivatives) was performed using several different criteria of aromaticity. Namely, the energy effect (ef), bond resonance energy (BRE), harmonic oscillator model of aromaticity (HOMA) index, multi centre delocalization indices (MCI), electron density at ring critical points ρ(r(C)), nucleus independent chemical shifts (NICS) and ring current maps were employed. All these methods agree that the extent of aromaticity of the five-membered ring in the acenaphthylene molecule is quite small. On the other hand, it was shown that the aromatic character of the five-membered rings depends on the size of the polyacenic part and on the position of the five-membered ring along the polyacenic part of the given acenaphthylene derivatives. According to energetic, electron delocalization and geometrical indices, the aromatic character of the pentagons in some higher acenaphthylene congeners is of the same order of magnitude as the aromatic character of some hexagons in the respective molecules. Ring current maps revealed the existence of a weak paratropic (antiaromatic) circulation in the five-membered rings which, in the case of higher members of the homolog series, becomes weaker. In contrast, the NICS indices showed a significant antiaromatic character of the five-membered rings in higher members of the acenaphthylene series.
本文使用多种不同的芳香性标准，对一系列并五苯稠合的线性多环芳烃（苊烯衍生物）中的局部芳香性进行了详细研究。具体来说，我们使用了能量效应（ef）、键共振能（BRE）、芳香性哈莫尔模型（HOMA）指数、多中心离域指数（MCI）、环临界点电子密度 ρ(r(C))、核独立化学位移（NICS）和环电流图等方法。所有这些方法都表明，苊烯分子中五元环的芳香性程度相当小。另一方面，研究结果表明，五元环的芳香特征取决于多环芳烃部分的大小以及五元环在给定苊烯衍生物的多环芳烃部分中的位置。根据能量、电子离域和几何指数，某些较高苊烯同系物中五元环的芳香性与相应分子中某些六元环的芳香性处于同一数量级。环电流图揭示了五元环中存在较弱的反芳香（反芳香性）环流，而在同系物系列的较高成员中，这种环流变得更弱。相比之下，NICS 指数表明，在苊烯系列的较高成员中，五元环具有显著的反芳香性。
