Molecular Rearrangements: Part 1. Pericyclic Reactions

Armstrong, S. K.

doi:10.1002/9780470669587.ch13

Cited by 1 publication

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References 84 publications

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“…Theoretical studies found some exceptions where the Cope rearrangement of substituted 6 can be stepwise going through a diradicaloid intermediate with a rather short R around 1.6 Å . Nevertheless, compared with the transition states 7 - 9 , the intermediate 5 is considered to be unusual as it is stabilized by the 2e/4c π−π bonding due to the through-space π−π overlap (Scheme ). Note that the previous investigations at the B3LYP level should be deemed as semiquantitative, in that the reaction barrier height from the reactant 3 to the intermediate 5 is 4.6 kcal/mol, while the experimental measurement using dynamic NMR found a larger value of 9 (±1) kcal/mol …”

Section: Resultsmentioning

confidence: 99%

Cyclo-biphenalenyl Biradicaloid Molecular Materials: Conformation, Tautomerization, Magnetism, and Thermochromism

et al. 2010

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Phenalenyl and its derivatives have recently attracted a great deal of interest as a result of a two-electron multicenter (2e/mc) π−π bonding between two π-stacked phenalenyl units. The 2e/mc bonded π-dimers are close in energy to the σ-dimers of phenalenyl and therefore fickle properties may emerge from bond fluctuation, yielding “smart” π-functional materials. Here, we examine the valence tautomerization of two cyclo-biphenalenyl biradicaloid molecular materials with chair and boat conformations by spin-restricted (R) and unrestricted (U) DFT using the M06 and B3LYP functionals. We found that the chair conformation involves a 2e/4c π−π bonded structure, whereas the boat conformation involves a 2e/12c π−π bonded structure on their potential energy surfaces. The global minimum for the chair conformation is the σ-bonded structure, whereas it is the π−π bonded structure for the boat conformation. The chair conformation exhibits a stepwise [3,3]-sigmatropic rearrangement, and calculations predict a negligible paramagnetic susceptibility near room temperature. In comparison, the paramagnetism of the boat conformation should be observable by SQUID and ESR. According to the energy differences of the respective σ- and π-dimers of the two conformations and the UV−vis calculations, the color of the chair conformation is expected to become darker, whereas that of the boat conformation should become lighter with increasing temperature.

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Section: Resultsmentioning

confidence: 99%