The Tunnel Effect in Chemistry

Bell, R. P.; Roy, Robert J. Le

doi:10.1007/978-1-4899-2891-7

Cited by 932 publications

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“…In 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 tunneling accompanying thermal excitation on the way to the TS (Fig.…”

Section: Methodsmentioning

confidence: 97%

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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: 97%

“…E a values were obtained from the slopes in the plots of lnk vs. 1/T in Fig. 2 using the Arrhenius equation k = A exp(−E a /RT) (9). E a(H) was 35.4 kJ·mol −1 while E a(D) was 44.5 kJ·mol −1 , so the difference of 9.1 kJ·mol −1 is well in excess of 5.0 kJ·mol −1 , consistent with a tunneling process.…”

Section: Methodsmentioning

confidence: 99%

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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“…Because the de Broglie wavelength is inversely proportional to particle momentum, tunneling becomes noticeable in small masses and at low temperatures. The de Broglie wavelengths for hydrogen (H, 9.8-1.8 Å) and deuterium (D, 6.9-1.3 Å) at 10-300 K exceed the scale of the typical widths of activation barriers in chemical reactions (∼1 Å), which invalidates a purely classical description of their motion in chemistry (1,2). Hydrogen, including its ionic forms (H + and H − ), is present in water and most organic compounds, and kinetic measurements have established that tunneling occurs in reactions involving hydrogen in gas (1), liquid (1,3,4), and solid phases (4).…”

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confidence: 99%

“…The de Broglie wavelengths for hydrogen (H, 9.8-1.8 Å) and deuterium (D, 6.9-1.3 Å) at 10-300 K exceed the scale of the typical widths of activation barriers in chemical reactions (∼1 Å), which invalidates a purely classical description of their motion in chemistry (1,2). Hydrogen, including its ionic forms (H + and H − ), is present in water and most organic compounds, and kinetic measurements have established that tunneling occurs in reactions involving hydrogen in gas (1), liquid (1,3,4), and solid phases (4). Tunneling has also been recognized as a significant factor in reactions on surfaces and at interfaces; for example, proton transfer reactions at the air/water interface (5) and enzyme catalysis (3,6).…”

mentioning

confidence: 99%

“…This means different isotopes of a given element show very different tunneling behaviors, and larger kinetic isotope effects (KIEs) than those expected from semiclassical theory have been regarded as a reliable indicator of tunneling (1). However, chemical reactions involving tunneling on condensed phases are usually accompanied by other surface processes such as adsorption, diffusion, and desorption.…”

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Quantum tunneling observed without its characteristic large kinetic isotope effects

Hama

Ueta

Kouchi

et al. 2015

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

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Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (≳100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system. quantum tunneling | kinetic isotope effect | heterogeneous reactions | reaction dynamics | astrochemistry

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Ab initio studies on hydrogen-transfer tunneling for Cl + HCl abstraction hydrogen reaction

Cao

Song

1996

Int. J. Quantum Chem.

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mThis article presents a treatment scheme of the tunneling of hydrogen between two molecular centers ((3.'. Cl). The purpose is to calculate the tunneling probabilities of hydrogen atom transfer from the initial (the proceeding complex) to the final-state energy minima (the succeeding complex) in two anharmonic vibrational states (0 + 0 and gen atom or proton abstraction from small organic molecules by methyl radials in frozen matrices [7-111. This interest is stimulated by the observation of finite, temperature-independent rate constants at very low temperature. This phenomenon is interpreted as a manifestation of quantum mechanical tunneling through a potential energy barrier. The low-temperature experiments are often analyzed with the aid of corrections to transition-

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The Tunnel Effect in Chemistry

Cited by 932 publications

References 0 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

Quantum tunneling observed without its characteristic large kinetic isotope effects

Ab initio studies on hydrogen-transfer tunneling for Cl + HCl abstraction hydrogen reaction

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