Cyclobutadiene

Cyclobutadiene

Aromaticity

Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020

As for organic molecules, different studies in this area show that when the benzene is interacting with cyclobutadiene, its ring will adopt a shifted, parallel conformation, but when is interacting with another benzene ring will have a tilted T-shaped orientation, meaning that the aromaticity may be correlated with the tilt angle. A further research (Shee and Datta, 2015) came with the idea that the angular conformation is possible only for the interaction with an aromatic system, but is not possible for the interaction with an anti-aromatic system. To verify the validity of this idea, the interaction of benzene with ten systems of the form C4H4X (with X = BH, AlH, SiH2, CH2, O, S, PH, NH, SiH, CH−) was studied, by analyzing the obtained values for different index of aromaticity (Table 4.1).

Molecular magnetisabilities computed via finite fields: assessing alternatives to MP2 and revisiting magnetic exaltations in aromatic and antiaromatic species

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Journal Information

Published in Molecular Physics, 2021

Tim Stauch, Brad Ganoe, Jonathan Wong, Joonho Lee, Adam Rettig, Jiashu Liang, Jie Li, Evgeny Epifanovsky, Teresa Head-Gordon, Martin Head-Gordon

Moving on to 4 π electron systems, cyclobutadiene, being the classic anti-aromatic molecule, displays a large positive exaltation as expected. Likewise, also displays a very large positive exaltation. In contrast , when considering the 70 kcal/mol more stable and electronically more similar isomer, is predicted to be non-aromatic. For the group of molecules with two π electrons, all four molecules are predicted to be aromatic, with exaltations comparable to benzene and pyradine if normalised by π electron count.

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Aromaticity

Molecular magnetisabilities computed via finite fields: assessing alternatives to MP2 and revisiting magnetic exaltations in aromatic and antiaromatic species