Tunneling in the 1,5-Hydrogen Shift Reactions of 1,3-Cyclopentadiene and 5-Methyl-1,3-Cyclopentadiene

Shelton, G. Robert; Hrovat, David A.; Borden, Weston Thatcher

doi:10.1021/ja0664279

Cited by 51 publications

(56 citation statements)

References 23 publications

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“…The Kreevoy criteria are based on a collinear model of H-transfer. For application to a 1,2-H shift, the E a(D) −E a(H) criterion should be reduced to reflect the smaller loss of C-H/C-D zero point energy (ZPE) in the bent transition state (TS) (14). Nevertheless, the results reported here greatly exceed the Kreevoy criteria.…”

Section: Methodsmentioning

confidence: 76%

“…Red: experimental points ± 1 SD; black: computed by canonical variational transition state theory (CVT); blue: computed by CVT+SCT. (14). Because the current calculation underestimates the KIEs, this column is effectively a lower bound on the contribution of tunneling.…”

Section: Computational Results and Discussionmentioning

confidence: 92%

“…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%

“…The important criteria are: (i) an activation energy difference E a(D) −E a(H) > 5.0 kJ·mol −1 , and (ii) a ratio of Arrhenius pre-exponential factors A H /A D < 0.7. Borden and Singleton and coworkers have recently emphasized the importance of A factor ratios and isotopic differences in E a as experimental criteria for tunneling (14)(15)(16), although the numerical criteria depend on the type of reaction. The Kreevoy criteria are based on a collinear model of H-transfer.…”

Section: Methodsmentioning

confidence: 99%

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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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Section: Methodsmentioning

confidence: 76%

Section: Computational Results and Discussionmentioning

confidence: 92%

Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

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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“…The temperature dependencies of k H /k D are listed in Table 2 and shown in Figure 2. The values of k H /k D greater than 10 are generally taken to indicate a significant contribution of quantum tunneling in proton transfer reactions [69]. The temperature dependence of KIE can also determine the presence or absence of tunneling [70].…”

Section: Figurementioning

confidence: 99%

The tautomerization of H2NCH2C(OH)NH to H2NCH2CONH2 in the interstellar medium

Deng

et al. 2010

Sci. China Phys. Mech. Astron.

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The tautomerization of H 2 NCH 2 C(OH)NH to H 2 NCH 2 CONH 2 is an important step by way of Strecker synthesis for the production of glycine in the interstellar medium (ISM) with respect to the origin of amino acids on the early Earth. Our work indicates two mechanisms for the tautomerization to occur. k CVT/SCT (rate constant) is 45.6 s −1 at 50 K, obtained with the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT), to support one mechanism assisted by quantum tunneling in the ISM. Another mechanism is through the (H 2 O) 2 -coupled proton transfer. In the (H 2 O) 2 -coupled reaction, two H 2 O molecules act as a catalyst to reduce the barrier energy by 23.7 kcal mol −1 , and cooperatively let a proton pass a hydrogen-bonded bridge composed of H 2 NCH 2 C(OH)NH with (H 2 O) 2 . k TST is 8.08×10 −4 s −1 at 100 K, calculated with TST kinetics, to demonstrate the mechanism. Therefore, the tautomerization is feasible in the ISM. H 2 NCH 2 C(OH)NH and H 2 NCH 2 CONH 2 will be detected in the ISM and found in carbonaceous chondrites. The results present new evidence for the third theory on the origin of amino acids on the early Earth.

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Molecular Rearrangements: Part 1. Pericyclic Reactions

Armstrong¹

2007

Organic Reaction Mechanisms Series

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Tunneling in the 1,5-Hydrogen Shift Reactions of 1,3-Cyclopentadiene and 5-Methyl-1,3-Cyclopentadiene

Cited by 51 publications

References 23 publications

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

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

The tautomerization of H2NCH2C(OH)NH to H2NCH2CONH2 in the interstellar medium

Molecular Rearrangements: Part 1. Pericyclic Reactions

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