Cyclooctatetraene dianion—an artifact?

Abstract

Cyclooctatetraene in its dianionic form (COT(2-)) is considered to be partially or fully aromatic due to the fact that, unlike its neutral counterpart, it adopts planar structure with CC bonds equalized. However, some authors report that this dianion is neither planar nor aromatic. Thus, we performed a detailed analysis of the COT(2-) case. The influence of several technical parameters on the result of calculations on COT(2-) was investigated. It appears from our analysis that the use of some specific level of approximation may lead to very misleading results in which the COT ring occurs in its neutral structure, in fact being neither planar nor aromatic. Additionally, our results may suggest that COT(2-) dianion is rather an artificial structure (being the result of specific basis set description) and should not occur in experimental conditions.

The Laplacian of Electron Density versus NICSzzScan: Measuring Magnetic Aromaticity among Molecules with Different Atom Types

“…This effect particularly contaminates the NICS values when the constituent atoms of the systems under study are of different types, i.e., different nuclear charges, electronegativities, and atomic radii. The recently introduced electron density versus NICS zz scan approach could improve the conventional NICS scan methodology among similar molecules with different ring sizes; however, the issue for molecules with remarkable differences in electron density distribution remained unsolved (doubly charged anions must be considered cautiously as they are prone to auto electron detachment) …”

EL: the new aromaticity measure based on one-electron density function

“…Thus, the same could be expected in the case of EL use. However, the use of large basis sets with diffuse and polarization functions, wherever possible, is always recommended, since small basis sets may sometimes give artificial results [66]. 4.…”

Influence of fluoro and cyano substituents in the aromatic and antiaromatic characteristics of cyclooctatetraene

“…[18][19][20][21] Additionally, the properties of COT's hetero-derivatives as well as those of its dianion have also been explored in the literature. 11,[22][23][24][25] Besides, the reactivity of metallic derivatives of COT with carbon monoxide has been additionally explored at theoretical level. 26 In the present study, we have focused in the effect that the systematic substitution of a hydrogen atom by a fluorine atom or a cyano group will have in the aromaticity/antiaromaticity of COT.…”