Ab initio calculations of the singlet-triplet energy difference in phenylnitrene

Hrovat, David A.; Waali, Edward E.; Borden, Weston Thatcher

doi:10.1021/ja00048a052

Cited by 123 publications

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“…The energy difference between 3 A 2 and 1 A 1 was calculated to be ca. 30 kcal/mol, 45,46,50 about the same size as the singlet-triplet splitting in H 3 CN. 43 The much lower energy singlet state was the open-shell 1 A 2 state.…”

Section: Nitrenes -Hn H 3 Cn and Phnmentioning

confidence: 83%

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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.

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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Section: Nitrenes -Hn H 3 Cn and Phnmentioning

confidence: 83%

“…The clue to the answer was found in the bond lengths computed for the three low-lying states of PhN. 46 One set of the calculated bond lengths is reproduced in Fig. 6.…”

Section: Nitrenes -Hn H 3 Cn and Phnmentioning

confidence: 99%

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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“…The heat capacity was assumed to be similar to the triplet state, and the entropy was corrected by -R ln3 to account for the lack of electronic degeneracy in the singlet CH 2 CHN(s). The singlettriplet energy gap was assumed to be 15 kcal mol -1 , similar to that in phenyl nitrene [44].…”

Section: Computational Methodologymentioning

confidence: 99%

Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

Lucassen

Zhang

Warkentin

et al. 2012

Combustion and Flame

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Laminar premixed flames of the two smallest isomeric amines, dimethylamine and ethylamine, were investigated under one-dimensional low-pressure (40 mbar) conditions with the aim to elucidate pathways that may contribute to fuel-nitrogen conversion in the combustion of biomass. For this, identical flames of both fuels diluted with 25% Ar were 2 studied for three different stoichiometries (Φ=0.8, 1.0, and 1.3) using in situ molecular-beam mass spectrometry (MBMS). Quantitative mole fractions of reactants, products and numerous stable and reactive intermediates were determined by electron ionization (EI) MBMS with high mass resolution to separate overlapping features from species with different heavy elements by exact mass. Species assignment was assisted by using single-photon vacuum- We attempted to analyze the major pathways in the two flames with a detailed combustion model developed for this purpose. For this, thermochemical values for a number of intermediates had to be determined from quantum chemistry calculations. Also, specific sets of reactions were incorporated for the two fuels. While many trends seen in the experiments can be successfully reproduced by the simulations, additional efforts may be needed to reliably describe the fuel-nitrogen chemistry in the combustion of biomass-related model fuels with amine functions.

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“…73 However, calculations performed independently by Fritz Schaefer's group 70a and by my own 40 found that in PhN the lowest singlet state has the same orbital occupancy as the triplet. One nonbonding electron occupies the 2p x AO on nitrogen, which lies in the plane of the benzene ring, and the other nonbonding electron occupies the 2p y AO on nitrogen, which is aligned with the π orbitals of the benzene ring.…”

Section: Phenylcarbene and Phenylnitrenementioning

confidence: 96%

“…The results of calculations, intended only to compute the singletÀtriplet energy gap in PhN, 40,70 turned out, serendipitously, In singlet PhCH both nonbonding electrons occupy the same hybridized AO on the carbene carbon. 73 However, calculations performed independently by Fritz Schaefer's group 70a and by my own 40 found that in PhN the lowest singlet state has the same orbital occupancy as the triplet.…”

Section: Phenylcarbene and Phenylnitrenementioning

confidence: 99%

With a Little Help from My Friends: Forty Years of Fruitful Chemical Collaborations

Borden

2011

J. Org. Chem.

Self Cite

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A former colleague of mine at the University of Washington once told me, only half-jokingly, "You do a lot of collaborative research, and I think the reason for its success is that you are brave enough to choose as your collaborators people who are better chemists than you." Looking back over the past 40 years of my career, I have, indeed, had an unusually large number of research collaborations, and they have, in fact, been successful, largely because my collaborators have all been talented chemists who had expertise that I lacked.These collaborations have come about in several ways. In some cases, an experimentalist has asked my research group to perform calculations. On other occasions, I have sought collaborators outside of my own research group when I needed help, usually experimental but sometimes computational, in testing a prediction. I have also had research collaborations begin when I was on sabbatical or when Professors from other universities spent sabbaticals in my research group, usually with the goal of learning how to do electronic structure calculations.This Perspective allows me to thank at least a few of my many collaborators over the past 40 years by recounting how their contributions made it possible for me to do research that I probably would not have been able to do on my own. This Perspective also gives me the opportunity to give some examples of the synergism between theory and experiments in my research and to acknowledge the important role that serendipity has played throughout my career, but particularly in the collaborative projects that are the focus of this Perspective. I have been lucky in having had puzzling experimental and computational results brought to my attention at times when I had the knowledge and/or computational resources that were necessary in order to explain those results. I have also been very fortunate in knowing experimentalists and theoreticians who were willing to collaborate with me on experiments and calculations that were of interest to me, but which I could not have readily done on my own.Serendipity has also played a different kind of role in my research. When I have been working on finding the solution to a specific problem, my research has frequently led me to the solution of a problem of much broader scope. I attribute my good fortune, at least in part, to my compulsive habit of persistently asking myself the question, "Why is that?" when I am presented with an experimental or computational result that I do not understand.I have divided this Perspective into eight major sections, each of which describes a different area of my research during the past 40 years, in which collaborations have played an important role. Rather than reading this Perspective in its entirety, some readers may prefer to be selective and peruse just a few of the eight sections. The sections cover my collaborative research on (1) hydrocarbons containing unsaturatively 1,3-bridged cyclobutane rings, (2) the use of orbital topology for predicting the ground states of diradicals, (3)...

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Ab initio calculations of the singlet-triplet energy difference in phenylnitrene

Cited by 123 publications

References 0 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

Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

With a Little Help from My Friends: Forty Years of Fruitful Chemical Collaborations

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