Computational Support for Tunneling in Thermal [1,7]-Hydrogen Shift Reactions

Ba, Hess

doi:10.1021/jo010622i

Cited by 18 publications

(19 citation statements)

References 12 publications

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“…Transition state theory 24 (TST) calculations carried out by Hess 22 on Tri at 60 • C led to a KIE of 3.9, which is almost half the experimental value. TST ignores quantum effects, but since the [1,7]-hydrogen shift is a hydrogen transfer reaction, 25 Hess indicated that the discrepancy between both KIEs may be due to quantum mechanical tunneling.…”

Section: Introductionmentioning

confidence: 91%

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Tunneling and Conformational Flexibility Play Critical Roles in the Isomerization Mechanism of Vitamin D

Meana-Pañeda

Fernández‐Ramos

2011

J. Am. Chem. Soc.

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The thermal isomerization reaction converting previtamin D to vitamin D is an intramolecular [1,7]-sigmatropic hydrogen shift with antarafacial stereochemistry. We have studied the dynamics of this reaction by means of the variational transition-state theory with multidimensional corrections for tunneling in both gas-phase and n-hexane environments. Two issues that may have important effects on the dynamics were analyzed in depth, i.e., the conformations of previtamin D and the quantum effects associated with the hydrogen-transfer reaction. Of the large number of conformers of previtamin D that were located, there are 16 that have the right disposition to react. The transition-state structures associated with these reaction paths are very close in energy, so all of them should be taken into account for an accurate calculation of both the thermal rate constants and the kinetic isotope effects. This issue is particularly important because the contribution of each of the reaction paths to the total thermal rate constant is quite sensitive to the environment. The dynamics results confirm that tunneling plays an important role and that model systems that were considered previously to study the hydrogen shift reaction cannot mimic the complexity introduced by the flexibility of the rings of previtamin D. Finally, the characterization of the conformers of both previtamin D and vitamin D allowed the calculation of the thermal equilibrium constants of the isomerization process.

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Section: Introductionmentioning

confidence: 91%

“…The similarity between the experimental data indicates that Tri could be a good theoretical model to study the isomerization reaction. 22,23 Scheme 3…”

Section: Introductionmentioning

confidence: 99%

Tunneling and Conformational Flexibility Play Critical Roles in the Isomerization Mechanism of Vitamin D

Meana-Pañeda

Fernández‐Ramos

2011

J. Am. Chem. Soc.

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“…81 The B3LYP/6-31G* calculations give activation energies similar to experiment though consistently slightly higher. The calculated primary kinetic isotope effects are substantially smaller than those obtained by experiment, also as expected in systems in which tunnelling occurs.…”

Section: [17] Sigmatropic Rearrangementsmentioning

confidence: 64%

6 Reaction mechanisms : Part (ii) Pericyclic reactions

Morgan

2002

Annu. Rep. Prog. Chem., Sect. B: Org. Chem.

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“…On the other hand, for an effective hydride migration a collinear TS with C 2v symmetry cannot be excluded 11. Recently, density functional calculations have been performed by Hess for the thermal [1,7]‐H shift in 1,3,5‐heptatrienes 12. The geometric results of these calculations are in good correspondence with our former 3‐21G/CI‐MP2 calculations of the in‐plane C 2v TS for the [1,5]‐H shift in cis ‐1,3‐pentadiene 4, vide supra.…”

Section: Resultsmentioning

confidence: 99%

Critical evaluation of the bond order concept with application to thermal hydrogen shifts

Buck¹

2003

Int J of Quantum Chemistry

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ABSTRACT:Since Coulson introduced the concept of bond order into the molecular orbital theory its significance has been proven as an important tool for the discussion and calculation of bond strength and bond length. On studying simple -conjugated odd-and even-membered carbonOhydrogen systems in an open and cyclic geometry, it could be shown that the use of the concept of bond order with respect to bond length in geometric representations for ground or transition states must be handled with caution. This has been concluded from a theoretical study of Okajima and Imafuku on chlorine and hydrogen thermal shifts in (cyclo)pentadiene and cycloheptatriene compounds. The results of their calculations and our previous calculations on the [1,5]-H shift in cis-1,3-pentadiene following a suprafacial transition state compared with a shift of the migrating hydrogen in the plane of the carbon skeleton ask for a critical evaluation. The impact on the result of the systems under investigation and on the results of others will be disclosed.

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Computational Support for Tunneling in Thermal [1,7]-Hydrogen Shift Reactions

Cited by 18 publications

References 12 publications

Tunneling and Conformational Flexibility Play Critical Roles in the Isomerization Mechanism of Vitamin D

Tunneling and Conformational Flexibility Play Critical Roles in the Isomerization Mechanism of Vitamin D

6 Reaction mechanisms : Part (ii) Pericyclic reactions

Critical evaluation of the bond order concept with application to thermal hydrogen shifts

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