Monoaza-analogs † of trimethylenemethane. Isoelectronic similarities and differences

Li, Jiabo; Worthington, Sharon E.; Cramer, Christopher J.

doi:10.1039/a706267b

Cited by 18 publications

(18 citation statements)

References 55 publications

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“…In contrast to the 1 B 2 state, the 1 A 1 state with a closed-shell configuration was predicted to have a planar C 2v geometry in which one of the C-C bonds was shorter than those of the other two. These geometries obtained by PM3-CI calculations are qualitatively consistent with recent ab initio studies [17,21].…”

Section: Resultssupporting

confidence: 90%

“…Thus the essential character of TIM 3+ seems to be well described by the most left hand side in Figure 5(b) in which positive charges are delocalized on not only the nitrogen atoms and but also the carbon atom. Interestingly, IDMM + is predicted to have a singlet ground state [21]. This is explained using resonance structures in the right-most hand in Figure 5(c).…”

Section: Resultsmentioning

confidence: 90%

“…The spinpaired structures in which the positive charge is localized on carbon atoms are more stable than that of the biradical structure in the left hand side because the electronegativity of the nitrogen atom is higher than that of the carbon atoms. The summed group charges of the ground state of IDMM + are reported in [21]; amino group; +0.05, central carbon; +0.15, methylene group; +0.40. Thus the ground state of IDMM + is expected to be singlet.…”

Section: Resultsmentioning

confidence: 99%

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High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

Hatanaka

Shiba

2006

J. Comput. Chem. Jpn.

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High-spin stability of non-Kekulé-type molecule triiminiummethane ion (TIM 3+ ) is discussed using the semiempirical molecular orbital method. The triplet ground state 3 A 2 ' with a D 3h geometry is predicted to lie below the Jahn-Teller distorted singlet states similar to trimethylenemethane (TMM). The lowest singlet states 1 B 1 , 1 B 2 and 1 A 1 with C 2v geometries are nearly degenerate. The spin-density distribution of the 3 A 2 ' state is calculated and the origin of the spin alignment is discussed relating to the spin-polarization rule characteristic of high-spin organic molecules. The valence bond analysis on the spin states of TIM 3+ is also carried out.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

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High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

Hatanaka

Shiba

2006

J. Comput. Chem. Jpn.

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“…Molecule A is predicted to have a singlet ground state. (Calculations by Cramer and coworkers 104 have also found that substitution of NH 2 + for CH 2 in TMM changes the predicted ground state from a triplet to a singlet.) In B, where nitrogen substitution is made at a carbon that belongs to the more delocalized of the two MBQDM NBMOs in Fig.…”

Section: Predicted Effects Of Heteroatom Substitution At Ring Carbons...mentioning

confidence: 92%

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.

106

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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“…41,42 This work thus represented one of the first contributions towards our understanding of how heteroatomic substitution affects relative state energies in non-Kekulé systems, a subject that continues to be of interest and indeed is the primary topic of two papers contributed to this issue. 43,44 The embedding of TMM and TME into various ring systems was always of particular interest to Dowd. In 1991, he showed that simple Hückel theory predicted fivefold and sixfold orbital degeneracies for tris(cyclopentadienyl)trimethylenemethane and tetrakis(cyclopentadienyl)tetramethyleneethane, respectively.…”

Section: The Pittsburgh Yearsmentioning

confidence: 99%

Paul Dowd and diradicals

Cramer¹

1998

J. Chem. Soc., Perkin Trans. 2

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Monoaza-analogs † of trimethylenemethane. Isoelectronic similarities and differences

Cited by 18 publications

References 55 publications

High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

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

Paul Dowd and diradicals

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