Structural dependence of the singlet-triplet energy gap of the tetramethylene biradical

Doubleday, Charles; McIver, James; Page, Matthew A.

doi:10.1021/ja00312a017

Cited by 11 publications

(3 citation statements)

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“…It seems inappropriate to introduce the triplet states in calculations because of the singlet‐triplet transition being spin forbidden by direct absorption, but the triplet state can be populated from above by an excited singlet state 35, 36, which is possible for the present situation. As a matter of fact, Doubleday et al, 37 have introduced triplet state and the triplet‐singlet interaction to discuss the dissociation of tetramethylene diradical in their dynamical model of triplet‐derived tetramethylene derivatives. On the other hand, DFTB calculations used in the simulation is not spin‐polarized, the energy obtained does not correspond to that of a pure spin state, consequently involvement of triplet state together with singlet state will be helpful to interpreting the energy curve obtained by the simulation and comparing the simulation results with those of high‐level ab initio calculations.…”

Section: Resultsmentioning

confidence: 99%

“…However, at the latter intersection the second CC bond breaking does not emerge but the diradical may undergo ISC which will affect the distribution of photodissociation products. If the ISC rate is fast enough, transition between 1 3 A and 1 1 A can easily takes place, and the dissociation of the diradical into two ethylenes will proceed along the singlet ground state S 0 , as Doubleday et al have suggested 37. On the contrary, if the rate is very slow, the triplet diradical has a long lifetime and might be measured as an intermediate.…”

Section: Resultsmentioning

confidence: 99%

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Involvement of excited triplet state in the photodissociation of cyclobutane

Lei

Suo

et al. 2007

Int J of Quantum Chemistry

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The potential energy curves (PECs) of the ground state and the lowlying excited states for the photodissociation of cyclobutane have been calculated at the multi-reference configuration interaction with singlet and doublet excitation (MRCISD) and the multi-reference second order perturbation theory (MRPT2). Firstly, the PECs are constructed following a reaction path determined by semiclassical dynamics simulation, which suggests that the lowest triplet state of tetramethylene is involved in the photodissociation of cyclobutane. Then, the adiabatic PECs are calculated for the breaking processes of C1OC3 and C2OC4 bond respectively. The singlet-triplet PECs' intersections have been found in the two breaking COC bond processes. During the breaking process of the second C2OC4 bond, a local minimum has been found on the PEC of the lowest triplet state, which gives us some insight to reinterpret the experimental observed diradical intermediate as being trapped in its triplet state.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Involvement of excited triplet state in the photodissociation of cyclobutane

Lei

Suo

et al. 2007

Int J of Quantum Chemistry

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“…On the diradical mechanisms for [212] cycloaddition of ethylene, Doubleday, [37][38][39][40] Lindh and coworkers, 41 and Lischka and coworkers 42 reported that the ring closure of the diradical had little or no barrier when calculated at higher levels of theory, such as CISD, MRCI, MR-AQCC, and CASPT2. To compare the levels of theory used in this work with the best available calculations for the cycloaddition of ethylene, we recalculated the cyclization of ethylene at the same level of theory used in this work, CASPT2 (4, .…”

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confidence: 99%

Computational studies on the dimers and the thermal dimerization of norbornadiene

Yang

Kim

2007

J Comput Chem

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In this study, 14 norbornadiene (NBD) dimers and the thermal dimerization mechanism were studied using the hybrid density functional theory (B3LYP) and the second-order multiconfigurational perturbation theory (CASPT2). In the process of dimerization, the biradical stationary points were located using the unrestricted, broken-spin, symmetry approach. The pathways were divided into eight parts to aid the analysis of their mechanisms. Our results indicated that the process for the formation of the cage-like heptacyclo[6.6.0.0.260.3130.411059.01014] tetradecane (HCTD, D14) is highly exothermic (92.15 kcal/mol), indicating that D14 is the most stable NBD dimer. However, the formation of D14 is very difficult to achieve kinetically because of a higher barrier in the thermal dimerization. On the contrary, the formation of exo-cis-exo (D5) is kinetically favorable, but thermodynamically unfavorable at higher temperature. Therefore, the combination of both thermodynamic and kinetic factors indicated that the formation of exo-exo (D9), which resembles the product of the pseudo-Diels-Alder addition, is most likely in the NBD dimerization.

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