New benzene dimers: a benchmark theoretical investigation
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New benzene dimers: a benchmark theoretical investigation J. McNeely1 · A. Yu. Rogachev1 Received: 30 March 2020 / Accepted: 6 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A wide variety of methods have been used to study the retro-dimerization reactions of one cis-fused (1) and four new transfused benzene dimers (2–5). These methods, which included both single-reference and multi-reference approaches, were benchmarked against multi-reference Møller-Plesset perturbation theory of the second order (MRMP2) based on CASSCF(12,12) wavefunctions. Each of the single-reference approaches was found to be overestimating the activation barrier for retro-dimerization process. Interestingly, N-electron valence perturbation theory (NEVPT2) energies also diverged for these reactions from MRMP2 values. Canonical MP2 barriers were in better agreement with MRMP2 results than the NEVPT2 numbers, with mean unsigned deviations (MUD) of 5.4 kcal/mol and 6.6 kcal/mol, respectively. The behavior of each of the methods is discussed and compared with the application of the same methods to the standard pericyclic reaction set proposed by Houk et al. (J Phys Chem A 107:11445, 2003). The comparison between NEVPT2 and MRMP2 reaction barriers, when applied to the cycloadditions in the Houk set and the synchronous symmetry-allowed retro-dimerization of the benzene dimer 1, showed that these two methods give almost identical results for these reaction types (MUD of 0.5 kcal/mol). Keywords Benzene dimers · Benchmark calculations · Multireference methods · Perturbation theory · DFT · MRMP2
1 Introduction The [2 + 2] and [4 + 2] pericyclic reactions have a rigorous foundation in molecular orbital theory as described in the seminal work by Woodward and Hoffmann [1] and Fukui [2]. Cycloadditions, as with the other common classes of pericyclic reactions, are considered “allowed” or “forbidden” based on their conservation of orbital symmetry or lack thereof. For [4 + 2] cycloadditions, exemplified by Diels–Alder reaction [3], the process is “allowed” if the addition is suprafacial and disrotatory. In the case of [2 + 2] cycloaddition, the only “allowed” reaction is antarafacial one. This cycloaddition is rarely observed because it is usually characterized by significant steric hindrance in the transition state [1].
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02684-y) contains supplementary material, which is available to authorized users. * A. Yu. Rogachev [email protected]; [email protected] 1
Department Chemistry, Illinois Institute of Technology, Chicago, IL 60616, USA
There have been many theoretical investigations of the nature of both the “allowed” and “forbidden” [4 + 2] and [2 + 2] cycloadditions [4–16]. These studies have been complemented by a wide number of studies on other pericyclic reactions such as Cope rearrangements [17–27], 1,5-sigmatropic hydrogen shifts [28–34], and electrocyclic ring opening
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