National Medicines Institute Laboratory of Theoretical Methods and Computation, 30/34 Chelmska, 00-725 Warsaw, Poland.
Phys Chem Chem Phys. 2013 Mar 7;15(9):3286-93. doi: 10.1039/c2cp43426a. Epub 2013 Jan 29.
The ring-current aromaticity of the bicalicene molecule arises, in spite of the 16 π carbon perimeter, from strong local diatropic circulations on the two pentagonal rings, as shown by current-density maps computed at the ipsocentric RHF/6-311G** and DFT/6-311G** levels of theory. Conjugated-circuit models cannot capture this pattern of circulation as it arises from 'ionic' contributions in a valence-bond picture. Canonical molecular-orbital analysis reveals a cancellation of paratropic and diatropic frontier-orbital contributions, which explains the difficulties that Hückel-based models have in producing qualitatively correct current-density maps for this molecule. Other measures of aromaticity reflect, to different extents, the dominance of the 'tetraionic' contribution to the aromaticity of this species.
双环烯分子的环电流芳香性，尽管具有 16π 个碳外围，但其源于两个五边形环上的强局部顺磁环流，这一点通过在等心 RHF/6-311G和 DFT/6-311G理论水平上计算的电流密度图得到了证实。共轭电路模型无法捕捉到这种环流模式，因为它源于价键图中的“离子”贡献。典型分子轨道分析揭示了反磁和顺磁前线轨道贡献的抵消，这解释了基于休克尔模型在为这种分子生成定性正确的电流密度图方面所遇到的困难。其他芳香性度量在不同程度上反映了该物种芳香性的“四离子”贡献的主导地位。
