Dynamics of 1,2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes

Albu, Titus V.; Lynch, Benjamin J.; Truhlar, Donald G.; Goren, Alan C.; Hrovat, David A.; Borden, Weston Thatcher; Moss, Robert A.

doi:10.1021/jp020544i

Cited by 47 publications

(78 citation statements)

References 133 publications

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“…, 84 values that are close to those that he had previously published. 83 Clearly, there was and there still is a major disagreement between the results of Don's calculations and Bob's experiments because, to date, neither Don, nor Bob, nor I have been able to think of a way to reconcile the conflicting results.…”

supporting

confidence: 90%

“…Don agreed, and several months later he sent me the first draft of a comprehensive manuscript on 1,2-shifts in carbenes. 84 The manuscript reflected a huge amount of very careful work that Don and his co-workers had put into calculations on these reactions. They had calculated rate constants for four different types of carbene 1,2-shifts, each at several different levels of theory and with inclusion of both solvent effects and corrections for tunneling.…”

Section: Don Truhlar Does More Calculations Bob Moss Does More Expermentioning

confidence: 99%

“…These calculations found that, at the temperatures at which Bob Moss had measured the rate constants for ring expansion of 26 to 27, tunneling contributes very little to the rate of reaction. 84 When I informed Bob of Don's computational results, Bob was concerned that they might indicate that there was a problem with his experiments. Therefore, Bob repeated his experiments and obtained E a = 5.1 ( 1.1 kcal/mol and log A = 9.2 ( 0.9 s…”

Section: Don Truhlar Does More Calculations Bob Moss Does More Expermentioning

confidence: 99%

“…Alan calculated ΔH q = 14.7 kcal/mol and ΔS q = À2.7 eu at the (10/10)CASPT2/cc-pVTZ//(10/10)CASSCF/6-31G* level of theory. 84 Bob Moss and his co-workers had measured ΔH q = 3.6 kcal/mol and ΔS q = À22.5 eu for this reaction. 83 There is obviously a significant difference between the calculated and observed activation parameters for the rearrangement of 26 to 27.…”

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confidence: 97%

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

Borden

2011

J. Org. Chem.

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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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supporting

confidence: 90%

Section: Don Truhlar Does More Calculations Bob Moss Does More Expermentioning

confidence: 99%

Section: Don Truhlar Does More Calculations Bob Moss Does More Expermentioning

confidence: 99%

mentioning

confidence: 97%

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

Borden

2011

J. Org. Chem.

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“…For the second criterion, the ratio A H /A D was 0.28 (A H = 97.9, A D = 344.2), much less than 0.7, which implies tunneling. This suggestion is supported by ample precedent for tunneling in 1,2-H shifts, particularly in carbenes (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27), and also in cyclopentadienes (14). The barriers in these reactions vary from ca.…”

Section: Methodsmentioning

confidence: 91%

Evidence for tunneling in base-catalyzed isomerization of glyceraldehyde to dihydroxyacetone by hydride shift under formose conditions

Cheng

Doubleday

Breslow

2015

Proc. Natl. Acad. Sci. U.S.A.

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Hydrogen atom transfer reactions between the aldose and ketose are key mechanistic features in formose chemistry by which formaldehyde is converted to higher sugars under credible prebiotic conditions. For one of these transformations, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the deuterium kinetic isotope effect associated with the hydrogen transfer during the isomerization of glyceraldehyde to the corresponding dihydroxyacetone. To do this, we developed a quantitative HPLC assay that allowed us to measure the apparent large intrinsic kinetic isotope effect. From the Arrhenius plot of the kinetic isotope effect, the ratio of the preexponential factors A H /A D was 0.28 and the difference in activation energies E a(D) − E a(H) was 9.1 kJ·mol −1 . All these results imply a significant quantum-mechanical tunneling component in the isomerization mechanism. This is supported by multidimensional tunneling calculations using POLYRATE with small curvature tunneling.formose reaction | quantum tunneling | hydride shift | prebiotic reactions W e have described a new mechanism for the formose reaction ( Fig. 1) (1), essentially the same as we had proposed earlier (2) except that the isomerizations of aldose to ketose and the reversal involve a hydride shift rather than an enolization (3-7). Our evidence came from the finding that 2-deuteroglyceraldehyde was converted to 1-deuterodihydroxyacetone under conditions of the formose reaction, with catalysis by Ca 2+ at pH 12. In 2001 Nagorski and Richard had reported an extensive study of the interconversion of glyceraldehyde and dihydroxyacetone by either enolization or hydride shift and had seen that with Zn 2+ the hydride shift mechanism was the exclusive process, by a mechanism closely related to our more recent one (8). We also showed that the isomerization of the ketose erythrulose to the aldose aldotetrose in D 2 O did not lead to deuterium incorporation, as it would have in an enolization process, so it also uses the hydride shift mechanism (1). The first study of the formose reaction in D 2 O was performed by Benner, who saw that no deuterium was incorporated in the intermediates; for some reason he did not invoke hydride shift mechanisms (6).It should be mentioned that we saw that the presence of formaldehyde in the formose reaction in D 2 O led to trapping of any enols formed; without formaldehyde, as in our previous study, there is subsequent deuterium incorporation in dihydroxyacetone, but not significant in glyceraldehyde. We saw that the glyceraldehyde was present almost entirely as its hydrate, a gem diol, but dihydroxyacetone was present mainly as the ketone. This reverses the normally accepted enolization relative rates. Materials and MethodsIn a hydride shift the distance traveled by the proton is small, comparable to the range of its wave character, so we have investigated the possibility that there is a quantum-mechanical tunneling process involved (9). We find that there is indeed tunnelin...

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Variational Transition State Theory in the Treatment of Hydrogen Transfer Reactions

Truhlar¹,

Garrett²

2006

Hydrogen‐Transfer Reactions

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Dynamics of 1,2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes

Cited by 47 publications

References 133 publications

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

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

Evidence for tunneling in base-catalyzed isomerization of glyceraldehyde to dihydroxyacetone by hydride shift under formose conditions

Variational Transition State Theory in the Treatment of Hydrogen Transfer Reactions

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