Features of molecular structure of small non-IPR fullerenes: the two isomers of C 50
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Features of molecular structure of small non‑IPR fullerenes: the two isomers of C50 Ayrat R. Khamatgalimov1 · Liana I. Yakupova2 · Valeri I. Kovalenko1 Received: 6 July 2020 / Accepted: 8 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Here for the first time, we applied approach developed earlier for higher fullerenes to investigate the features of molecular structures of non-IPR isomers 270 (D3) and 271 (D5h) of small fullerene C50. The bond distributions are presented as structural formulas. The instability of the studied isomers is caused by a significant local overstrain due to the excessive folding of pentagons in pentalene fragments, which typically are planar molecules. It is found that the chains of π-bonds are passing through some cycles like in the previously studied higher non-IPR fullerenes C 66 and C 68. Chemical shifts of the centers of the pentagons and hexagons (NICS(0)) are reported. It is shown that chlorine atoms in the exohedral derivative C 50Cl10 of isomer 271 (D5h) are attached to the indacene-like substructures confirming the preference of addition to π-delocalized hexagons in radical reactions. The identified features in the structures of smaller fullerene molecules can be predictive of the ability to be synthesized as derivatives and will assist in determination of their reactivity. Keywords Small fullerene · Structural formula · Substructure · Pentalene · Overstrain
1 Introduction An empirical rule of isolated pentagons (IPR), that appeared after the discovery of the molecular structures of first most stable fullerenes C 60, C70, etc., suggested that fullerene molecule in which all 12 pentagons are separated by hexagons has to be stable and conversely the molecule with some abutting pentagons is unstable [1, 2]. In fact, all fullerenes that were obtained, isolated and characterized during the first period after their discovery in 1985 were obeying IPR. Nevertheless, sometimes some of non-IPR fullerene Cn (n > 20) can be obtained in the form of endohedral or exohedral derivatives; in other words, molecules of such fullerenes can be stabilized to study them. However, basically, this is Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02675-z) contains supplementary material, which is available to authorized users. * Ayrat R. Khamatgalimov [email protected] 1
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences, Kazan, Russian Federation
Kazan National Research Technological University, Kazan, Russian Federation
2
a random unexpected luck. The unused potential of a huge amount of non-IPR fullerenes and the scanty proportion of IPR fullerenes obtained and used in practice is a paradox of the current situation in the field of research of fullerenes. It is obvious that only theoretical studies can (and not always) shed light on the molecular features of non-IPR fullerenes so far in connection with t
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