Isomerization pathways from the norbornadiene to the cycloheptatriene radical cation by opening a bridgehead-methylene bond: a theoretical investigation

Norberg, Daniel; Larsson, Per-Erik; Salhi-Benachenhou, Nessima

doi:10.1039/b612791f

Cited by 9 publications

(5 citation statements)

References 34 publications

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“…The ring closure to 3 , which is 14.0 kcal/mol more stable than 2 , proceeds with a low activation energy, 1.8 kcal/mol, thereafter followed by ring expansion to 4 , with a barrier of 8.2 kcal/mol. As we previously noted, 4 is found to be only slightly more stable than 3 (−0.8 kcal/mol), a result that is also consistent with the recent G3//B3LYP computational study of Choe.…”

Section: Resultssupporting

confidence: 91%

Rearrangement and Hydrogen Scrambling Pathways of the Toluene Radical Cation: A Computational Study

2008

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A computational study is undertaken to provide a unified picture for various rearrangement reactions and hydrogen scrambling pathways of the toluene radical cation (1). The geometries are optimized with the BHandHLYP density functional, and the energies are computed with the ab initio CCSD(T) method, in conjunction with the 6-311+G(d,p) basis set. In particular, four channels have been located, which may account for hydrogen scrambling, as they are found to have overall barriers lower than the observed threshold for hydrogen dissociation. These are a stepwise norcaradiene walk involved in the Hoffman mechanism, a rearrangement of 1 to the methylenecyclohexadiene radical cation (5) by successive [1,2]-H shifts via isotoluene radical cations, a series of [1,2]-H shifts in the cycloheptatriene radical cation (4), and a concerted norcaradiene walk. In addition, we have also investigated other pathways such as the suggested Dewar-Landman mechanism, which proceeds through 5, via two consecutive [1,2]-H shifts. This pathway is, however, found to be inactive as it involves too high reaction barriers. Moreover, a novel rearrangement pathway that connects 5 to the norcaradiene radical cation (3) has also been located in this work.

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Section: Resultssupporting

confidence: 91%

Rearrangement and Hydrogen Scrambling Pathways of the Toluene Radical Cation: A Computational Study

2008

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“…As was the case in the first step of the synthesis, the main challenge at this point was one of purification. DDQ is known to rupture bicyclic structures, 22 and one would expect this phenomenon here as well. Initial attempts at purification by standard chromatography were not successful, as many byproducts coeluted with the norbornadiene in a narrow yellowcolored band.…”

Section: ■ Results and Discussionsupporting

confidence: 90%

Substituted Diarylnorbornadienes and Quadricyclanes: Synthesis, Photochemical Properties, and Effect of Substituent on the Kinetic Stability of Quadricyclanes

et al. 2017

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In this Article, we present a new method for the synthesis of diarylnorbornadiene derivatives. Through the use of a two-step procedure consisting of a tandem alkene insertion-Suzuki coupling reaction followed by a DDQ dehydrogenation, we have been able to synthesize derivatives with a wide variety of substituents. We also present the results of UV-visible spectroscopy studies and kinetics experiments that show the effect of substituent on light absorption properties of the norbornadienes as well as the kinetic stability of the quadricyclanes that result from their photochemical conversion. While substitution on the aromatic rings had comparatively little effect on quadricyclane lability, substitution at a bridgehead position with a methyl group produced a quadricyclane that thermally reverted to the norbornadiene at a rate that was significantly slower than that for the quadricyclane without the methyl substituent. From the results of the kinetics experiments, we determined that the reversion of the quadricyclanes occurs via a free radical mechanism with very little contribution from polar effects. This observation led us to speculate as to whether our data may form the basis for a free radical substituent constant, σ•, analogous to the traditional Hammett σ parameter.

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“…The B3LYP method has proven highly successful for calculating proton hyperfine coupling constants ( 1 H hfccs) of organic radicals. [22][23][24][25] Therefore, we used this method for computing the 1 H hfccs, atomic charges, spin densities, and dipole moments of the MP2 structures. The atomic charges were computed by fitting the charges to the electrostatic potential according to the Merz-Singh-Kollman (MK) scheme 26 using default atomic radii for all atoms.…”

Section: Computational Detailsmentioning

confidence: 99%

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

Norberg

Salhi-Benachenhou

2007

J Comput Chem

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The stepwise and concerted pathways for the McLafferty rearrangement of the radical cations of butanal (Bu(+)) and 3-fluorobutanal (3F-Bu(+)) are investigated with density functional theory (DFT) and ab initio methods in conjunction with the 6-311+G(d,p) basis set. A concerted transition structure (TS) for Bu(+), (H), is located with a Gibbs barrier height of 37.7 kcal/mol as computed with CCSD(T)//BHandHLYP. Three pathways for the stepwise rearrangement of Bu(+) have been located, which are all found to involve different complexes. The barrier height for the H(gamma) transfer is found to be 2.2 kcal/mol, while the two most favorable TSs for the C(alpha)-C(beta) cleavage are located 8.9 and 9.2 kcal/mol higher. The energies of the 3F-Bu(+) system have been calculated with the promising hybrid meta-GGA MPWKCIS1K functional of DFT. Interestingly, the fluorine substitution yields a barrier height of only 20.5 kcal/mol for the concerted TS, (3F-H). A smaller computed dipole moment, 12.1 D, for (3F-H) compared with 103.2 D for (H) might explain the stabilization of the substituted TS. The H(gamma) transfer, with a barrier height of 4.9 kcal/mol, is found to be rate-determining for the stepwise McLafferty rearrangement of 3F-Bu(+), in contrast to the unsubstituted case. By inspection of the spin and charge distributions of the stationary points, it is noted that the bond cleavages in the concerted rearrangements are mainly of heterolytic nature, while those in the stepwise channels are found to be homolytic.

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Isomerization pathways from the norbornadiene to the cycloheptatriene radical cation by opening a bridgehead-methylene bond: a theoretical investigation

Cited by 9 publications

References 34 publications

Rearrangement and Hydrogen Scrambling Pathways of the Toluene Radical Cation: A Computational Study

Rearrangement and Hydrogen Scrambling Pathways of the Toluene Radical Cation: A Computational Study

Substituted Diarylnorbornadienes and Quadricyclanes: Synthesis, Photochemical Properties, and Effect of Substituent on the Kinetic Stability of Quadricyclanes

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

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