Tunnelling control of chemical reactions – the organic chemist's perspective

Ley, David; Gerbig, Dennis; Schreiner, Peter R.

doi:10.1039/c2ob07170c

Cited by 158 publications

(205 citation statements)

References 89 publications

(94 reference statements)

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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: 66%

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: 66%

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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“…Moreover, Oba et al (2012) concluded that a tunnel effect is responsible for the H abstraction of H 2 by OH radicals resulting in the formation of water molecules in astrophysical conditions. The importance of the tunnel effect in chemistry is discussed in more than one review (Ley et al 2012;Schreiner et al 2011) as well as for its implication in the surface reactions happening in an astrochemical context (Hama & Watanabe 2013;Trixler 2013;Reboussin et al 2014). Our study demonstrates that H 2 can be a source of hydrogenation of CN radicals, but since we are using VUV to generate CN radicals, kinetic studies to confirm tunneling reaction are not possible.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Borget

Müller

Grote

et al. 2017

A&A

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Context. Molecular hydrogen (H 2 ) is the most abundant molecule of the interstellar medium (ISM) in gas phase and it has been assumed to exist in solid state or as coating on grains. Aims. Our goal is to show that solid H 2 can act as a hydrogenation agent, reacting with CN radicals to form HCN. Methods. In a H 2 matrix, we studied the hydrogenation of the CN radical generated from the vacuum ultraviolet photolysis (VUVphotolysis) of C 2 N 2 at 3.8 K. We modified the wavelengths and the host gas in order to be sure that CN radicals can abstract H from H 2 molecules. Results. HCN monomers, dimers, and oligomers have been characterised by Fourier transform infrared spectroscopy (FTIR). H 2 CN as well as CN radicals have also been clearly observed during the photolysis performed at 3.8 K.Conclusions. H 2 is a hydrogenation reagent towards CN radicals producing HCN. This type of reaction should be taken into account for the reactivity at low temperature in contaminated H 2 ice macro-particles (CHIMPs), H 2 flakes or in the first sublayers of grains where solid H 2 has accumulated.

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“…a) Electronic mail: jeremy.richardson@phys.chem.ethz.ch Quantum tunneling effects have been measured in atmospheric and astrochemistry, 7,8 as well as organic chemistry at low temperatures. 9 In some cases, they can change the mechanism for the reaction and hence the selectivity of the products. 10 On surfaces, one can directly observe tunneling events such as the hopping of atoms between sites 11 or the rearrangement of a molecular cluster.…”

Section: Introductionmentioning

confidence: 99%

Perspective: Ring-polymer instanton theory

Richardson

2018

The Journal of Chemical Physics

124

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Since the earliest explorations of quantum mechanics, it has been a topic of great interest that quantum tunneling allows particles to penetrate classically insurmountable barriers. Instanton theory provides a simple description of these processes in terms of dominant tunneling pathways. Using a ring-polymer discretization, an efficient computational method is obtained for applying this theory to compute reaction rates and tunneling splittings in molecular systems. Unlike other quantum-dynamics approaches, the method scales well with the number of degrees of freedom, and for many polyatomic systems, the method may provide the most accurate predictions which can be practically computed. Instanton theory thus has the capability to produce useful data for many fields of low-temperature chemistry including spectroscopy, atmospheric and astrochemistry, as well as surface science. There is however still room for improvement in the efficiency of the numerical algorithms, and new theories are under development for describing tunneling in nonadiabatic transitions.

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Tunnelling control of chemical reactions – the organic chemist's perspective

Cited by 158 publications

References 89 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

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Perspective: Ring-polymer instanton theory

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Tunnelling control of chemical reactions – the organic chemist's perspective

Cited by 158 publications

References 89 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

CN radical hydrogenation from solid H2 reactions, an alternative way of HCN formation in the interstellar medium

Perspective: Ring-polymer instanton theory

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CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium