Tetramethyleneethane, a ground-state triplet

Dowd, Paul; Chang, Wonghil; Paik, Yi Hyon

doi:10.1021/ja00283a051

Cited by 94 publications

(54 citation statements)

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“…These results, however, conflict with the ESR experiment, 128 which indicates a D 2d triplet conformation. Both the lowest energy singlet and triplet have D 2 symmetry; the angle is 58.0 ∘ for the singlet and 59.0 ∘ for the triplet.…”

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confidence: 73%

“…Dowd,128 in 1986, prepared TME by photolysis of 4,5-bis(methylene)-3,4,5,6-tetrahydropyridazine 35 in a methyltetrahydrofuran glass at 10 K. The ESR spectrum The following year, Borden 129 reported computations of TME at three geometries: D 2h , D 2d , and D 2 . Dowd,128 in 1986, prepared TME by photolysis of 4,5-bis(methylene)-3,4,5,6-tetrahydropyridazine 35 in a methyltetrahydrofuran glass at 10 K. The ESR spectrum The following year, Borden 129 reported computations of TME at three geometries: D 2h , D 2d , and D 2 .…”

Section: Is Tme a Ground-state Singlet Or Triplet?mentioning

confidence: 99%

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Diradicals and Carbenes

Bachrach

2014

Computational Organic Chemistry

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Reactive intermediates play a critical role in the chemist's understanding of many reaction mechanisms. 1 Given their often fleeting appearance, experimental observation, let alone acquiring any property data on them, can be a great challenge. It is not, therefore, surprising that computational chemistry has been a strong partner with experiment in gaining knowledge of a broad spectrum of reactive intermediates.In this chapter, we focus on the class of reactive intermediates that bear at least two unpaired electrons: diradicals and carbenes. The exact definition of a diradical is somewhat in the eye of the beholder. Salem and Rowland 2 provided perhaps the most general, yet effective, definition-a diradical is a molecule that has two degenerate or nearly degenerate orbitals occupied by two electrons. With this definition, carbenes can be considered as a subcategory of diradicals. In a carbene, the two degenerate molecular orbitals are localized about a single carbon atom.The chemistry of radicals has been described many times. 3 -6 Likewise, the chemistry of diradicals and carbenes has been the subject of many reviews. 7 -16 Two issues will guide our presentation in this chapter. First and foremost, we discuss examples of diradicals and carbenes, where computational chemistry has greatly aided in understanding the properties, structure, and chemistry of these intermediates. A theme that will emerge here is the strong collaborative relationship between experimental and computational chemists that greatly aided in resolving the controversies and discrepancies that arose in trying to understand these unusual species. The second aspect of this chapter is that computational studies of diradicals and (especially) carbenes helped to establish the discipline of computational chemistry. In fact, the first example we discuss in this chapter is the nature of methylene, which is the topic that many claim to have single handedly won over skeptics to the advantages and power of computational chemistry.Following the section on methylene, we present the chemistry of phenylcarbene and phenylnitrene and describe how computational chemistry helped detail why these two closely related molecules behave so differently. A discussion of tetramethyleneethane (TME) and oxyallyl diradicals explores how theories of apparently simple molecules may be quite complicated. Next, we discuss the chemistry of Computational Organic Chemistry, Second Edition. Steven M. Bachrach

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confidence: 73%

Section: Is Tme a Ground-state Singlet Or Triplet?mentioning

confidence: 99%

Diradicals and Carbenes

Bachrach

2014

Computational Organic Chemistry

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“…(B) Description of various structural forms of TME emerging from the torsion of the central carbon-carbon bond nearly degenerate (obey the Ovchinnikov's rule) that are responsible for the diradical character and hence obtaining a definite order of the singlet and triplet states of TME is not easy task. [102][103][104][105][106][107][108][109][110][111][112][113] Despite various works on TME, determination of the shape of twisting potential for the lowest energy singlet and triplet states is a challenging task as the system easily twists around the central C C bond and various methods encountered give an unbalanced account of the intricate interplay of different correlation effects in the two low-lying electronic states. Note that the singlet and triplet energy surfaces could cross one another as the twisting angle is varied.…”

Section: Tetramethyleneethanementioning

confidence: 99%

Multireference perturbation theory with improved virtual orbitals for radicals: More degeneracies, more problems

Ray

Manna

Ghosh

et al. 2018

Int J of Quantum Chemistry

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IVO‐SSMRPT is an affordable and accurate type of state‐specific multireference perturbation (SSMRPT) theory that adds dynamic correlation energy to improved virtual orbital (IVO) complete active space configuration interaction (CASCI) wave functions using a single‐root parametrization of multi‐root Hilbert‐space ansatz. We applied it to many chemically important di‐ and tri‐radicals to analyze the geometries and electronic properties of spectroscopic interest for both closed‐ and open‐shell singlet‐ and nonsinglet ground as well as excited states. We observed that IVO‐SSMRPT identifies optimized geometries, splitting between multiplets and frequencies for several radicals that are similar to those displayed by current generation state‐of‐the‐art methods but with admiringly decreased computational effort. This study illustrates the importance of having an accurate treatment of both nondynamical and dynamical correlation effects when examining multiradical species. Chemically and spectroscopically relevant answers can be obtained using our computationally tractable method. Our method will be a serviceable avenue for portraying open‐shell interactions in other radicals.

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“…[9] However, using gas-phase negative ion photoelectron spectroscopy, Clifford et al [8] found that the singlet state of TME is about 2 kcal mol À1 below the triplet state. Experimental data reported by Iwamura, [10] based on EPR and superconducting quantum interference device measurements, unambiguously evidenced that the ground state for TME is singlet which is nearly degenerate (within a few cal mol À1 ) with 3 [TME].…”

Section: Introductionmentioning

confidence: 99%

Ab Initio Multireference Investigation of Disjoint Diradicals: Singlet versus Triplet Ground States

2011

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We present improved virtual orbital (IVO) complete active space (CAS) configuration interaction (IVO-CASCI) and IVO-CASCI-based multireference Møller-Plesset perturbation theory (MRMPPT) calculations with an aim to elucidate the electronic structure of tetramethyleneethane (TME) in its lowest singlet and triplet state and to quantify their order and extent of splitting. The potential surfaces of singlet and triplet states for the twisting of TME are also studied. We found that the triplet state is higher in energy than the singlet one in the whole range of twisting angles with the energy gap minimum at a twisting angle of about 45°. Harmonic vibrational frequencies of TME have also been calculated for both the states. We also report the ground to first excited triplet state transition energies. Our results are analyzed with respect to the results available in the literature to illustrate the efficacy of our methods employed. We also demonstrate that the spin character of the ground state of disjoint, TME-like diradicals can be manipulated by using appropriate selection of annulenic spacer to separate the allyl groups of TME.

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Tetramethyleneethane, a ground-state triplet

Cited by 94 publications

References 0 publications

Diradicals and Carbenes

Diradicals and Carbenes

Multireference perturbation theory with improved virtual orbitals for radicals: More degeneracies, more problems

Ab Initio Multireference Investigation of Disjoint Diradicals: Singlet versus Triplet Ground States

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