Fulvenes, fulvalenes, and azulene:: Are they aromatic chameleons?
Fulvenes, fulvalenes, and azulene:: Are they aromatic chameleons?
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DOI：
10.1021/ja045729c
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发表时间：
2004-11-03
影响因子：
15
通讯作者：
Ottosson, H
中科院分区：
文献类型：
--
作者：
Möllerstedt, H;Piqueras, MC;Ottosson, H
On the basis of the theory of Baird on reversal of Hückel's rule for aromaticity and antiaromaticity of annulenes when going from the electronic ground state (S0) to the lowest ππ* triplet state (T1) (J. Am.Chem. Soc.1972,94, 4941), we argue that fulvenes, fulvalenes, and azulene are “aromatic chameleons”. The dipole moments of fulvenes in T1should be of comparable magnitude to those of S0, but due to the reversal of Hückel's aromaticity rule in T1, their dipole should be in the opposite direction. Thereby, they are capable of adopting some aromaticity in both the T1and S0states as they adapt their dipolar resonance structures. The same applies to fulvalenes and azulene in their lowest quintet states (Q1) when compared to S0. Our hypothesis on chameleon behavior is supported by quantum chemical OLYP, CASSCF, and CASPT2 calculations of dipole moments, π-orbital populations, and energies.
