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Unexpected reversal of stability in strained systems containing one-electron bonds

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Abstract

Ring strain energy is a very well documented feature of neutral cycloalkanes, and influences their structural, thermochemical and reactivity properties. In this work, we apply density functional theory and high-level coupled cluster calculations to describe the geometry and relative stability of C6H12+˙ radical cations, whose cyclic isomers are prototypes of singly-charged cycloalkanes. Molecular ions with the mentioned stoichiometry were produced via electron impact experiments using a gaseous cyclohexane sample (20–2000 eV). From our calculations, in addition to structures that resemble linear and branched alkenes as well as distinct conformers of cyclohexane, we have found low-lying species containing three-, four- and five-membered rings with the presence of an elongated C–C bond. Remarkably, the stability trend of these ring-bearing radical cations is anomalous, and the three-membered species are up to 11.3 kcal mol−1 more stable than the six-membered chair structure. Generalized Valence Bond calculations and the Spin Coupled theory with N electrons and M orbitals were used in conjunction with the Generalized Product Function Energy Partitioning (GPF-EP) method and Interference Energy Analysis (IEA) to describe the chemical bonding in such moieties. Our results confirm that these elongated C–C motifs are one-electron sigma bonds. Our calculations also reveal the effects that drive thermochemical preference of strained systems over their strained-free isomers, and the origin of the unusual stability trend observed for cycloalkane radical cations.

Graphical abstract: Unexpected reversal of stability in strained systems containing one-electron bonds

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Publication details

The article was received on 06 Sep 2019, accepted on 31 Oct 2019 and first published on 31 Oct 2019


Article type: Paper
DOI: 10.1039/C9CP04964A
Phys. Chem. Chem. Phys., 2019, Advance Article

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    Unexpected reversal of stability in strained systems containing one-electron bonds

    F. Fantuzzi, W. Wolff, H. M. Quitián-Lara, H. M. Boechat-Roberty, G. Hilgers, B. Rudek and M. A. C. Nascimento, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C9CP04964A

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