Properties of tetramethyleneethane (TME) as revealed by ion chemistry and ion photoelectron spectroscopy

Clifford, Eileen P.; Wenthold, Paul G.; Lineberger, W. C.; Ellison, G. Barney; Wang, Cun X.; Grabowski, Joseph J.; Vila, Fernando D.; Jordan, Kenneth D.

doi:10.1039/a707322d

Cited by 59 publications

(118 citation statements)

References 44 publications

(42 reference statements)

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“…51,52 The ability of the phenyl group to delocalize the nonbonding electron on nitrogen in the open-shell singlet state of PhN, thus confining this  electron to a region of space different from that occupied by the  electron of opposite spin, is responsible for all three of these calculated and observed properties of PhN. 51,52 The minimization of the Coulombic repulsion between electrons of opposite spin, by confining them to different regions of space, is also responsible a number of predictions and observations about non-Kekulé hydrocarbon diradicals These include (a) the difference between the planar geometry of triplet TMM and the preferred geometry of the singlet, which has one CH 2 group twisted out of conjugation, 1,28,29,87,88 (b) the triplet ground states calculated and found for non-Kekulé diradicals with non-disjoint NBMOs (e.g., TMM 1, 2, 28, 29, 80-83, 86, 98 and MBQDM 84,[96][97][98] ) and (c) the singlet ground states calculated and found for non-Kekulé diradicals with disjoint NBMOs (TME [105][106][107][108][109]115 and TMB 110,111,[122][123][124].…”

Section: Discussionmentioning

confidence: 99%

“…21. 115 Since the three-fold degeneracy of the triplet should make the band for the formation of this state three times as intense as the band for the formation of the singlet state, the NIPE spectrum in Figure 21 indicates that the ground state of TME is a singlet, with E ST = -3 kcal/mol.…”

Section: Two Disjoint Alternant-hydrocarbon Diradicals With Singlet mentioning

confidence: 99%

“…NIPE spectrum 115 of TME •-Reprinted with permission. TME •-is calculated to have a D 2d geometry; and the size of the singlet-triplet energy difference in TME, measured at what is presumably the D 2d geometry of TME •-, appears to be too large to make it likely that the triplet falls below the singlet at the D 2 equilibrium geometry of the triplet.…”

Section: Figure 21mentioning

confidence: 99%

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The synergy between qualitative theory, quantitative calculations, and direct experiments in understanding, calculating, and measuring the energy differences between the lowest singlet and triplet states of organic diradicals

Lineberger

Borden

2011

Phys. Chem. Chem. Phys.

105

107

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This Perspective describes research, carried out in the authors' labs over the past forty years, aimed at understanding, predicting, and measuring the singlet-triplet energy differences ( ST ) in diradicals. A theory for qualitatively predicting the ground states of diradicals and the use of Negative Ion Photoelectron Spectroscopy (NIPES) for measuring  ST are described. The application of this theory, ab initio calculations, and NIPES to the prediction and measurement of  ST in a wide variety of organic diradicals is detailed. Among the diradicals that are discussed in this Perspective are HN, CH 3 N, PhN, CH 2 , trimethylenemethane (TMM), oxyallyl (OXA), meta-benzoquinodimethane (MBQDM), meta-benzoquinone (MBQ), tetramethyleneethane (TME), 1,2,4,5-tetramethylenebenzene (TMB), and D 8h cyclooctateraene (COT). All of these diradicals have been studied in one and, in most cases, in both of the authors' laboratories. The studies of OXA and D 8h COT were, in fact, collaborations between the research groups of the authors. These two projects both took advantage of the ability of NIPES to provide information about transition states. Transition-state spectroscopy was used to measure the cabonyl stretching frequency in the singlet state of OXA and to establish that D 8h COT violates the strictest version of Hund's rule. However, in some cases, it is not qualitative theories but the results of high-level calculations that motivate experimentalists to test how quantitatively accurate the calculations are. In other cases calculations are performed to see how well they reproduce experimental results that have already been obtained. When the results of calculations and experiments are found to be at odds with each other, additional experiments and/or calculations almost inevitably follow.Investigations of the energy differences between the lowest singlet and triplet state (E ST ) of organic diradicals 1 have provided many illustrations of the above types of synergies. Qualitative theories have resulted in computational and/or experimental tests, and calculations and experiments have not only stimulated each other but, in some cases, also led to the development of qualitative theories.For example, in response to the results of experiments and calculations on cyclobutadiene and trimethylenemethane, one of the coauthors of this review (WTB) helped to develop a qualitative theory, which allows the qualitative prediction of the approximate size and sign of

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Section: Discussionmentioning

confidence: 99%

Section: Two Disjoint Alternant-hydrocarbon Diradicals With Singlet mentioning

confidence: 99%

Section: Figure 21mentioning

confidence: 99%

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The synergy between qualitative theory, quantitative calculations, and direct experiments in understanding, calculating, and measuring the energy differences between the lowest singlet and triplet states of organic diradicals

Lineberger

Borden

2011

Phys. Chem. Chem. Phys.

105

107

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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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“…These factors combine to generate activation barriers to proton transfer between carbon centers. Thus, even with a large thermodynamic driving force, the furanide (Δ acid H 298 =391.10±0.40 kcal mol -1 ) [65] reaction has a transition state barrier of 5 kcal mol -1 above the H-bonded complex inhibiting and slowing the reaction. Essentially the ion-dipole complex is trapped in either a H-bonded complex well or an anionic σ-adduct.…”

Section: Potential Energy Surface Of 135-triazine Reactionsmentioning

confidence: 99%

Gas Phase Reactions of 1,3,5-Triazine: Proton Transfer, Hydride Transfer, and Anionic σ-Adduct Formation

Garver

Yang

Kato

et al. 2011

J. Am. Soc. Mass Spectrom.

Self Cite

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The gas phase reactivity of 1,3,5-triazine with several oxyanions and carbanions, as well as amide, was evaluated using a flowing afterglow-selected ion flow tube mass spectrometer. Isotopic labeling, H/D exchange, and collision induced dissociation experiments were conducted to facilitate the interpretation of structures and fragmentation processes. A multi-step (→ HCN + HC 2 N 2 − → CN − + 2 HCN) and/or single-step (→ CN − + 2 HCN) ring-opening collision-induced fragmentation process appears to exist for 1,3,5-triazinide. In addition to proton and hydride transfer reactions, the data indicate a competitive nucleophilic aromatic addition pathway (S N Ar) over a wide range of relative gas phase acidities to form strong anionic σ-adducts (Meisenheimer complexes). The significant hydride acceptor properties and stability of the anionic σ-adducts are rationalized by extremely electrophilic carbon centers and symmetric charge delocalization at the electron-withdrawing nitrogen positions. The types of anion-arene binding motifs and their influence on reaction pathways are discussed.

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Properties of tetramethyleneethane (TME) as revealed by ion chemistry and ion photoelectron spectroscopy

Cited by 59 publications

References 44 publications

The synergy between qualitative theory, quantitative calculations, and direct experiments in understanding, calculating, and measuring the energy differences between the lowest singlet and triplet states of organic diradicals

The synergy between qualitative theory, quantitative calculations, and direct experiments in understanding, calculating, and measuring the energy differences between the lowest singlet and triplet states of organic diradicals

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

Gas Phase Reactions of 1,3,5-Triazine: Proton Transfer, Hydride Transfer, and Anionic σ-Adduct Formation

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