The 1,2-hydrogen rearrangement of methylchlorocarbene: contribution of quantum mechanical tunneling

Dix, Edward J.; Herman, Michael S.; Goodman, Joshua L.

doi:10.1021/ja00075a094

Cited by 52 publications

(30 citation statements)

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“…Supporting this assignment, the σ → p absorption is predicted to appear at 556 nm in simulated heptanes by TD‐B3LYP/6‐311 + G(d) calculations at the PBEPBE/6‐311 + G(d) optimized geometry . From the directly monitored decay of the 544 nm absorption, we obtain k = 2.0 × 10 6 s −1 for the 1,2‐H shift rearrangement of MeCCl to vinyl chloride, Eqn , in good agreement with k = 1.4–3.0 × 10 6 s −1 determined for this reaction by the pyridine ylide method …”

Section: Alkylchlorocarbene Complexessupporting

confidence: 67%

“…decay of the 544 nm absorption, we obtain k = 2.0 × 10 6 s −1 for the 1,2-H shift rearrangement of MeCCl to vinyl chloride, Eqn 4, in good agreement with k = 1.4-3.0 × 10 6 s −1 determined for this reaction by the pyridine ylide method. [16,17,18] When MeCCl is generated from the diazirine by LFP in anisole, the carbene's σ → p absorption at 544 nm is replaced within 50 ns by two new absorptions at 520 and 368 nm (cf. Fig 3).…”

Section: Alkylchlorocarbene Complexesmentioning

confidence: 99%

“…We also did not find spectroscopic evidence for CCl 2 πcomplexation with mesitylene (23) or durene (24), even though calculations predicted that these complexes should be as enthalpically favorable as the CCl 2 -anisole complexes. [27] Possibly, the sensitivity of our UV dectector is reduced in the 300-350 nm spectral region (where the most intense absorptions of the CCl 2 complexes of 23 and 24 are expected), because of strong background absorption by dichlorodiazirine (17).…”

Section: Arylchlorocarbene Complexesmentioning

confidence: 99%

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Solvation and complexation of carbenes – a perspective

Moss

2011

J of Physical Organic Chem

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Complexes of several carbenes with aryl ethers are documented by laser flash photolysis with UV‐visible spectroscopic detection. The carbenes include methylchlorocarbene, benzylchlorocarbene, phenylchlorocarbene, p‐nitrophenylchlorocarbene, and dichlorocarbene, whereas the complexing ligands are anisole, various methylanisoles, dibenzo‐18‐crown‐6, dibenzofuran, 1,3‐dimethoxybenzene, and 1,3,5‐trimethoxybenzene. The carbene complexes are characterized both by spectroscopy and computation. Complexation retards the additions of the carbenes to olefins. The complexation of phenylchlorocarbene by 1,3,5‐trimethoxybenzene is shown to be an equilibrium process, and the pertinent thermodynamic parameters are obtained by experiment and computed from theory. Copyright © 2011 John Wiley & Sons, Ltd.

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Section: Alkylchlorocarbene Complexessupporting

confidence: 67%

Section: Alkylchlorocarbene Complexesmentioning

confidence: 99%

Section: Arylchlorocarbene Complexesmentioning

confidence: 99%

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Solvation and complexation of carbenes – a perspective

Moss

2011

J of Physical Organic 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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“…the one where the carbene has a r 2 electronic con®guration [6,17]. Tunnelling eects were not considered in the present work on the basis of two assumptions [7,8,16]. First, the experiments were carried out at 274 K and second, the shifts (especially for the substituted system) involved movements of several heavy atoms (see later).…”

Section: Regular Articlementioning

confidence: 99%

The influence of protecting the hydroxyl group of β-oxy-α-diazo carbonyl compounds in the competition between Wolff rearrangement and [1,2]-hydrogen shift. Density functional theory study and topological analysis of the charge density

Calvo-Losada

Sordo

Lopez‐Herrera

et al. 2000

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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The in¯uence of protecting the hydroxyl group of a b-oxy-a-diazo carbonyl compound on the competition between the Wol rearrangement (WR) and the [1,2]-hydrogen shift (HS) was investigated theoretically. Stationary points on the potential-energy surface were located with the B3LYP density functional and the 6-31G** basis set. For the basic system geometry optimisations at B3LYP/6-311+G** were performed to validate the reliability of the B3LYP/6-31G** calculations. Singlepoint energy calculations were carried out at the B3LYP/ 6-311+G** level on the B3LYP/6-31G**-optimised geometries. Further insight into the processes was achieved with the aid of the theory of``atoms in molecules'' of Bader. The calculated energy barriers qualitatively predicted the yields of HS and WR obtained experimentally. In order to rationalise the calculated energy barriers, it was necessary to take into account not only the electronegativity of the protective groups but also the alignment of the migrating groups with the depletion sites at the carbene centre. Further, when the hydroxyl group was not protected the existence of an intramolecular hydrogen bond played an important role in both HS and WR.

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The 1,2-hydrogen rearrangement of methylchlorocarbene: contribution of quantum mechanical tunneling

Abstract: The 1,2-hydrogen and carbon rearrangements of singlet alkylcarbenes to alkenes is a reaction of current theoretical and experimental interest.1 •2 Several recent experiments have focused on the temperature dependence of the rate constants for these

Cited by 52 publications

References 1 publication

Solvation and complexation of carbenes – a perspective

Solvation and complexation of carbenes – a perspective

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

The influence of protecting the hydroxyl group of β-oxy-α-diazo carbonyl compounds in the competition between Wolff rearrangement and [1,2]-hydrogen shift. Density functional theory study and topological analysis of the charge density

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