1
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Guo W, Robinson EE, Thomson RJ, Tantillo DJ. Heavy Atom Quantum Mechanical Tunneling in Total Synthesis. Org Lett 2024. [PMID: 38809009 DOI: 10.1021/acs.orglett.4c01152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
Contributions from quantum mechanical tunneling to the rates of several radical coupling reactions between carbon sp2 centers used as key steps in natural product total syntheses were computed using density functional theory. Contributions ranging from ∼15-52% from tunneling were predicted at room temperature, thereby indicating that tunneling plays an important role in the rates of these reactions and should perhaps be considered when designing complex synthetic schemes.
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Affiliation(s)
- Wentao Guo
- Department of Chemistry, University of California - Davis, 1 Shields Ave, Davis, California 95616, United States
| | - Emily E Robinson
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Regan J Thomson
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Dean J Tantillo
- Department of Chemistry, University of California - Davis, 1 Shields Ave, Davis, California 95616, United States
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2
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Qiu G, Schreiner PR. The Intrinsic Barrier Width and Its Role in Chemical Reactivity. ACS CENTRAL SCIENCE 2023; 9:2129-2137. [PMID: 38033803 PMCID: PMC10683502 DOI: 10.1021/acscentsci.3c00926] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 09/29/2023] [Accepted: 10/12/2023] [Indexed: 12/02/2023]
Abstract
Chemical reactions are in virtually all cases understood and explained on the basis of depicting the molecular potential energy landscape, i.e., the change in atomic positions vs the free-energy change. With such landscapes, the features of the reaction barriers solely determine chemical reactivities. The Marcus dissection of the barrier height (activation energy) on such a potential into the thermodynamically independent (intrinsic) and the thermodynamically dependent (Bell-Evans-Polanyi) contributions successfully models the interplay of reaction rate and driving force. This has led to the well-known and ubiquitously used reactivity paradigm of "kinetic versus thermodynamic control". However, an analogous dissection concept regarding the barrier width is absent. Here we define and outline the concept of intrinsic barrier width and the driving force effect on the barrier width and report experimental as well as theoretical studies to demonstrate their distinct roles. We present the idea of changing the barrier widths of conformational isomerizations of some simple aromatic carboxylic acids as models and use quantum mechanical tunneling (QMT) half-lives as a read-out for these changes because QMT is particularly sensitive to barrier widths. We demonstrate the distinct roles of the intrinsic and the thermodynamic contributions of the barrier width on QMT half-lives. This sheds light on resolving conflicting trends in chemical reactivities where barrier widths are relevant and allows us to draw some important conclusions about the general relevance of barrier widths, their qualitative definition, and the consequences for more complete descriptions of chemical reactions.
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Affiliation(s)
- Guanqi Qiu
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392 Giessen, Germany
| | - Peter R. Schreiner
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392 Giessen, Germany
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3
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Prado Merini M, Schleif T, Sander W. Heavy-Atom Tunneling in Bicyclo[4.1.0]hepta-2,4,6-trienes. Angew Chem Int Ed Engl 2023; 62:e202309717. [PMID: 37698374 DOI: 10.1002/anie.202309717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Revised: 09/11/2023] [Accepted: 09/12/2023] [Indexed: 09/13/2023]
Abstract
Heavy-atom tunneling limits the lifetime and observability of bicyclo[4.1.0]hepta-2,4,6-triene, a key intermediate in the rearrangement of phenylcarbene. Bicyclo[4.1.0]hepta-2,4,6-triene had been proposed as the primary intermediate of the rearrangement of phenylcarbene, but despite many efforts evaded its characterization even in cryogenic matrices. By introducing fluorine substituents into the ortho-positions of the phenyl ring of phenylcarbene, the highly strained cyclopropene 1,5-difluorobicyclo[4.1.0]hepta-2,4,6-triene becomes stable enough to be characterized in argon matrices. However, even at 3 K this cyclopropene is only metastable and rearranges via heavy-atom tunneling to the corresponding cycloheptatetraene. Calculations suggest that fluorination is necessary to slow down the tunneling rearrangement of the bicycloheptatriene. The parent bicycloheptatriene rapidly rearranges via heavy-atom tunneling and therefore cannot be detected under matrix isolation conditions.
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Affiliation(s)
- Melania Prado Merini
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Universitätsstraße 150, 44801, Bochum, Germany
| | - Tim Schleif
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT 06520, USA
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Universitätsstraße 150, 44801, Bochum, Germany
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4
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Laconsay CJ, Tantillo DJ. Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes To Form Semibullvalene. J Org Chem 2023. [PMID: 37335974 DOI: 10.1021/acs.joc.3c00735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
We describe the various escape channels available to dirhodium carbene intermediates from cycloheptatrienyl diazo compounds located with density functional theory. An intramolecular cyclopropanation would, in principle, provide a new route to semibullvalenes (SBVs). A detailed exploration of the potential energy surface reveals that methylating carbon-7 suppresses a competing β-hydride migration pathway to heptafulvene products, giving SBV formation a reasonable chance. During our explorations, we additionally discovered unusual spirononatriene, spironorcaradiene, and metal-stabilized 9-barbaralyl cation structures as local minima.
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Affiliation(s)
- Croix J Laconsay
- Department of Chemistry, University of California─Davis, Davis, California 95616, United States
| | - Dean J Tantillo
- Department of Chemistry, University of California─Davis, Davis, California 95616, United States
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5
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Bernhardt B, Schauermann M, Solel E, Eckhardt AK, Schreiner PR. Equilibrating parent aminomercaptocarbene and CO 2 with 2-amino-2-thioxoacetic acid via heavy-atom quantum tunneling. Chem Sci 2022; 14:130-135. [PMID: 36605744 PMCID: PMC9769125 DOI: 10.1039/d2sc05388h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Accepted: 11/17/2022] [Indexed: 11/19/2022] Open
Abstract
The search for methods to bind CO2 and use it synthetically as a C1-building block under mild conditions is an ongoing endeavor of great urgency. The formation of heterocyclic carbene-carbon dioxide adducts occurs rapidly when the carbene is generated in solution in the presence of CO2. Here we demonstrate the reversible formation of a complex of the hitherto unreported aminomercaptocarbene (H2N-C̈-SH) with CO2 isolated in solid argon by photolysis of 2-amino-2-thioxoacetic acid. Remarkably, the complex disappears in the dark as deduced by time-dependent matrix infrared measurements, and equilibrates back to the covalently bound starting material. This kinetically excluded process below ca. 8 K is made possible through heavy-atom quantum mechanical tunneling, as also evident from density functional theory and ab initio computations at the CCSD(T)/cc-pVTZ level of theory. Our results provide insight into CO2 activation using a carbene and emphasize the role of quantum mechanical tunneling in organic processes, even involving heavy atoms.
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Affiliation(s)
- Bastian Bernhardt
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Markus Schauermann
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Ephrath Solel
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - André K. Eckhardt
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Peter R. Schreiner
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
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6
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Schleif T. Transformations of Strained Three-Membered Rings a Common, Yet Overlooked, Motif in Heavy-Atom Tunneling Reactions. Chemistry 2022; 28:e202201775. [PMID: 35762788 PMCID: PMC9804509 DOI: 10.1002/chem.202201775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Indexed: 01/05/2023]
Abstract
Quantum mechanical tunneling has long been recognized as an important phenomenon when considering transformations dominated by a lightweight hydrogen atom. Tunneling of heavier atoms like carbon, initially dismissed as negligible, has seen a quickly increasing number of computationally predicted and/or experimentally confirmed examples over the last decade, thus highlighting its importance for a wide variety of reactions. However, no common structural motif has been pointed out within these seemingly unconnected examples, strongly limiting the predictability of the impact of heavy-atom tunneling on a given reaction. This Concept article will provide this perspective and showcase how the recognition of the formation and cleavage of three-membered rings as common motif can inform the prediction of and research into heavy-atom tunneling reactions.
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Affiliation(s)
- Tim Schleif
- Lehrstuhl für Organische Chemie IIRuhr-Universität Bochum44780BochumGermany,Present address: Sterling Chemistry LaboratoryYale UniversityNew HavenCT 06520USA
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7
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Schleif T, Prado Merini M, Henkel S, Sander W. Solvation Effects on Quantum Tunneling Reactions. Acc Chem Res 2022; 55:2180-2190. [PMID: 35730754 DOI: 10.1021/acs.accounts.2c00151] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A decisive factor for obtaining high yields and selectivities in organic synthesis is the choice of the proper solvent. Solvent selection is often guided by the intuitive understanding of transition state-solvent interactions. However, quantum-mechanical tunneling can significantly contribute to chemical reactions, circumventing the transition state and thus depriving chemists of their intuitive handle on the reaction kinetics. In this Account, we aim to provide rationales for the effects of solvation on tunneling reactions derived from experiments performed in cryogenic matrices.The tunneling reactions analyzed here cover a broad range of prototypical organic transformations that are subject to strong solvation effects. Examples are the hydrogen tunneling probability for the cis-trans isomerization of formic acid which is strongly reduced upon formation of hydrogen-bonded complexes and the [1,2]H-shift in methylhydroxycarbene where a change in product selectivity is predicted upon interaction with hydrogen bond acceptors.Not only hydrogen but also heavy atom tunneling can exhibit strong solvent effects. The direction of the nearly degenerate valence tautomerization between benzene oxide and oxepin was found to reverse upon formation of a halogen or hydrogen bond with ICF3 or H2O. But even in the absence of strong noncovalent interactions such as hydrogen or halogen bonding, solvation can have a decisive effect on tunneling as evidenced by the Cope rearrangement of semibullvalenes via heavy-atom tunneling. Can quantum tunneling be catalyzed? The acceleration of the ring expansion of 1H-bicyclo[3.1.0.]-hexa-3,5-dien-2-one by complexation with Lewis acids provides a proof-of-concept for tunneling catalysis.Two concepts are central for the explanation and prediction of solvation effects on tunneling phenomena: a simple approach expands the Born-Oppenheimer approximation by separating nuclear degrees of freedom into intra- and intermolecular degrees. Intermolecular movements represent the slowest motions within molecular aggregates, thus effectively freezing the position of the solvent in relation to the reactant during the tunneling process. Another useful approach is to treat reactants and products by separate single-well potentials, where the intersection represents the transition state. Thus, stabilization of the reactants via solvation should result in an increase in barrier heights and widths which in turn lowers tunneling probabilities. These simple models can predict trends in tunneling kinetics and provide a rational basis for controlling tunneling reactions via solvation.
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Affiliation(s)
- Tim Schleif
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Melania Prado Merini
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Stefan Henkel
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, 44801 Bochum, Germany
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8
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Fausto R, Ildiz GO, Nunes CM. IR-induced and tunneling reactions in cryogenic matrices: the (incomplete) story of a successful endeavor. Chem Soc Rev 2022; 51:2853-2872. [PMID: 35302145 DOI: 10.1039/d1cs01026c] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In this article, IR-induced and tunneling-driven reactions observed in cryogenic matrices are described in a historical perspective, the entangling of the two types of processes being highlighted. The story of this still ongoing fascinating scientific endeavor is presented here following closely our own involvement in the field for more than 30 years, and thus focuses mostly on our work. It is, because of this reason, also an incomplete story. Nevertheless, it considers a large range of examples, from very selective IR-induced conformational isomerizations to IR-induced bond-breaking/bond-forming reactions and successful observations of rare heavy atom tunneling processes. As a whole, this article provides a rather general overview of the major progress achieved in the field.
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Affiliation(s)
- Rui Fausto
- CQC-IMS, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Gulce O Ildiz
- CQC-IMS, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal. .,Department of Physics, Faculty of Sciences and Letters, Istanbul Kultur University, 34158 Bakirkoy, Istanbul, Turkey
| | - Cláudio M Nunes
- CQC-IMS, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
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9
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Schleif T, Sander W. Photolysis and thermolysis of (iodomethyl)cyclopropane: Rapid ring opening of cyclopropylcarbinyl via heavy‐atom tunneling? J PHYS ORG CHEM 2021. [DOI: 10.1002/poc.4295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Tim Schleif
- Lehrstuhl für Organische Chemie II Ruhr‐Universität Bochum Bochum Germany
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie II Ruhr‐Universität Bochum Bochum Germany
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10
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Kozuch S, Schleif T, Karton A. Quantum mechanical tunnelling: the missing term to achieve sub-kJ mol -1 barrier heights. Phys Chem Chem Phys 2021; 23:10888-10898. [PMID: 33908522 DOI: 10.1039/d1cp01275d] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
To predict barrier heights at low temperatures, it is not enough to employ highly accurate electronic structure methods. We discuss the influence of quantum tunnelling on the comparison of experimental and theoretical activation parameters (Ea, ΔH‡, ΔG‡, or ΔS‡), since the slope-based experimental techniques to obtain them completely neglect the tunnelling component. The intramolecular degenerate rearrangement of four fluxional molecules (bullvalene, barbaralane, semibullvalene, and norbornadienylidene) were considered, systems that cover the range between fast deep tunneling and small but significant shallow tunnelling correction. The barriers were computed with the composite W3lite-F12 method at the CCSDT(Q)/CBS level, and the tunnelling contribution with small curvature tunnelling. While at room temperature the effect is small (∼1 kJ mol-1), at low temperatures it can be considerable (in the order of tens of kJ mol-1 at ∼80 K).
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Affiliation(s)
- Sebastian Kozuch
- Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, 841051, Israel.
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11
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Bernhardt B, Dressler F, Eckhardt AK, Becker J, Schreiner PR. Characterization of the Simplest Thiolimine: The Higher Energy Tautomer of Thioformamide. Chemistry 2021; 27:6732-6739. [PMID: 33496350 PMCID: PMC8252572 DOI: 10.1002/chem.202005188] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/21/2021] [Indexed: 12/21/2022]
Abstract
As sulfur‐containing organic molecules thioamides and their isomers are conceivable intermediates in prebiotic chemistry, for example, in the formation of amino acids and thiazoles and resemble viable candidates for detection in interstellar media. Here, we report the characterization of parent thioformamide in the solid state via single‐crystal X‐ray diffraction and its photochemical interconversion to its hitherto unreported higher energy tautomer thiolimine in inert argon and dinitrogen matrices. Upon photogeneration, four conformers of thiolimine form, whose ratio depends on the employed wavelength. One of these conformers interconverts due to quantum mechanical tunneling with a half‐life of 30–45 min in both matrix materials at 3 and 20 K. A spontaneous reverse reaction from thiolimine to thioformamide is not observed. To support our experimental findings, we explored the potential energy surface of the system at the AE‐CCSD(T)/aug‐cc‐pCVTZ level of theory and computed tunneling half‐lives with the CVT/SCT approach applying DFT methods.
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Affiliation(s)
- Bastian Bernhardt
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Friedemann Dressler
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - André K Eckhardt
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Jonathan Becker
- Institute of Inorganic and Analytical Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
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12
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Viegas LP, M. Nunes C, Fausto R. Spin-forbidden heavy-atom tunneling in the ring-closure of triplet cyclopentane-1,3-diyl. Phys Chem Chem Phys 2021; 23:5797-5803. [DOI: 10.1039/d1cp00076d] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The putative spin-forbidden heavy-atom tunneling process for the ring closure of cyclopentane-1,3-diyl at cryogenic temperatures is confirmed with calculations employing the weak-coupling formulation of nonadiabatic transition state theory.
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Affiliation(s)
- Luís P. Viegas
- University of Coimbra
- CQC
- Department of Chemistry
- 3004-535 Coimbra
- Portugal
| | - Cláudio M. Nunes
- University of Coimbra
- CQC
- Department of Chemistry
- 3004-535 Coimbra
- Portugal
| | - Rui Fausto
- University of Coimbra
- CQC
- Department of Chemistry
- 3004-535 Coimbra
- Portugal
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13
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Kirshenboim O, Frenklah A, Kozuch S. Switch chemistry at cryogenic conditions: quantum tunnelling under electric fields. Chem Sci 2020; 12:3179-3187. [PMID: 34164085 PMCID: PMC8179409 DOI: 10.1039/d0sc06295b] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
While the influence of intramolecular electric fields is a known feature in enzymes, the use of oriented external electric fields (EEF) to enhance or inhibit molecular reactivity is a promising topic still in its infancy. Herein we will explore computationally the effects that EEF can provoke in simple molecules close to the absolute zero, where quantum tunnelling (QT) is the sole mechanistic option. We studied three exemplary systems, each one with different reactivity features and known QT kinetics: π bond-shifting in pentalene, Cope rearrangement in semibullvalene, and cycloreversion of diazabicyclohexadiene. The kinetics of these cases depend both on the field strength and its direction, usually giving subtle but remarkable changes. However, for the cycloreversion, which suffers large changes on the dipole through the reaction, we also observed striking results. Between the effects caused by the EEF on the QT we observed an inversion of the Arrhenius equation, deactivation of the molecular fluxionality, and stabilization or instantaneous decomposition of the system. All these effects may well be achieved, literally, at the flick of a switch. Adding an external electric field to reactions driven by quantum mechanical tunneling brings a whole new dimension to the idea of switch chemistry.![]()
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Affiliation(s)
- Omer Kirshenboim
- Department of Chemistry, Ben-Gurion University of the Negev Beer-Sheva 841051 Israel
| | - Alexander Frenklah
- Department of Chemistry, Ben-Gurion University of the Negev Beer-Sheva 841051 Israel
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev Beer-Sheva 841051 Israel
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14
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Laconsay CJ, Mallick D, Shaik S. External Electric Fields Interrupt the Concerted Cope Rearrangement of Semibullvalene. J Org Chem 2020; 86:731-738. [PMID: 33280381 DOI: 10.1021/acs.joc.0c02322] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The topic of this paper is whether the mechanism of the degenerate Cope rearrangement of semibullvalene can be affected by the presence of electrostatic fields. Herein, we report that the shape of the energy surface, as demonstrated by an "interrupted" (stepwise) mechanism, is altered in the presence of a copper cation, Cu+. Natural bond-orbital and block-localized wave-function energy decomposition analyses suggest that orbital and electrostatic interactions play a major role in altering the shape of the energy surface. Applying additional external electric fields (EEFs) induces a significant change to the energy surface with Cu+ present but negligible effects in the absence of Cu+. These findings are consistent with recent studies that demonstrate that EEFs more readily stabilize/destabilize systems with larger, more polarizable, dipole moments.
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Affiliation(s)
- Croix J Laconsay
- Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.,Department of Chemistry, University of California-Davis, 1 Shields Avenue, Davis, California 95616, United States
| | - Dibyendu Mallick
- Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.,Department of Chemistry, Presidency University, Kolkata 700073, India
| | - Sason Shaik
- Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
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15
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Sarkar S, Chandra S, Suryaprasad B, Ramanathan N, Sundararajan K, Suresh A. Conformational topography of tris(2-methylbutyl) phosphate and the influence of methyl branching at the non-hyperconjugative carbon on the conformational landscape: insights from matrix isolation infrared spectroscopy and DFT computations. Phys Chem Chem Phys 2020; 22:24372-24392. [PMID: 33084659 DOI: 10.1039/d0cp03403g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The branching of a methyl group in a linear chain has a profound influence on the conformational morphology as it wields a strong control in reducing a large number of conformations. To unravel the effect of branching on the second non-hyperconjugative carbon atom on the conformational landscape, the conformations of tris(2-methylbutyl)phosphate (T2MBP) were studied using Density Functional Theory (DFT) computations and matrix isolation infrared spectroscopy. Experimentally, T2MBP along with N2/Ar/Kr/Xe gases was effusively expanded and deposited at a low temperature of 12 K, which was subsequently probed using infrared spectroscopy. The computations of all the conformations were accomplished using the B3LYP level of theory with the 6-311++G(d,p) basis set. A dimethyl(2-methylbutyl) phosphate (DM2MBP) prototype, a molecule containing a single 2-methylbutyl moiety, was examined for its conformations. Computations predicted 18 and 9 conformations each for the 'gauche' and 'trans' families, respectively, in which the third branched carbon completely influences the orientation of the fourth carbon, which simplifies the conformational problem of DM2MBP. Of the 18 and 9 bunches each in the 'gauche' and 'trans' families, only 7 and 3 conformations, respectively, became energetically important, which when extrapolated to T2MBP resulted in 343 and 147 conformational possibilities. The factor of degeneracy further reduced these numbers and a total of 168 conformations effectively contribute to the conformational composition of T2MBP in the gas phase. The role of stereo electronic and steric factors prevalent in the conformational clusters of T2MBP was unravelled respectively using natural bond orbital and non-covalent interaction analyses.
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Affiliation(s)
- Subramee Sarkar
- Homi Bhabha National Institute, Materials Chemistry and Metal Fuel Cycle Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu, India.
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16
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Schleif T, Prado Merini M, Sander W. The Mystery of the Benzene-Oxide/Oxepin Equilibrium-Heavy-Atom Tunneling Reversed by Solvent Interactions. Angew Chem Int Ed Engl 2020; 59:20318-20322. [PMID: 32816382 PMCID: PMC7702039 DOI: 10.1002/anie.202010452] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Indexed: 11/24/2022]
Abstract
The equilibrium between benzene oxide (1) and oxepin (2) is of large importance for understanding the degradation of benzene in biological systems and in the troposphere. Our studies reveal that at cryogenic temperatures, this equilibration is governed by rare heavy-atom tunneling. In solid argon at 3 K, 1 rearranges to 2 via tunneling with a rate constant of approximately 5.3×10-5 s-1 . Thus, in a nonpolar environment, 2 is slightly more stable than 1, in agreement with calculations at the CCSD(T) level of theory. However, if the argon is doped with 1 % of H2 O or CF3 I as typical hydrogen or halogen bond donors, respectively, weak complexes of 1 and 2 are formed, and now 2 is tunneling back to form 1. Thus, by forming non-covalent complexes, 1 becomes slightly more stable than 2 and the direction of the heavy-atom tunneling is reversed.
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Affiliation(s)
- Tim Schleif
- Lehrstuhl für Organische Chemie IIRuhr-Universität BochumUniversitätsstraße 15044801BochumGermany
| | - Melania Prado Merini
- Lehrstuhl für Organische Chemie IIRuhr-Universität BochumUniversitätsstraße 15044801BochumGermany
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie IIRuhr-Universität BochumUniversitätsstraße 15044801BochumGermany
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17
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Schleif T, Prado Merini M, Sander W. The Mystery of the Benzene‐Oxide/Oxepin Equilibrium—Heavy‐Atom Tunneling Reversed by Solvent Interactions. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202010452] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Tim Schleif
- Lehrstuhl für Organische Chemie II Ruhr-Universität Bochum Universitätsstraße 150 44801 Bochum Germany
| | - Melania Prado Merini
- Lehrstuhl für Organische Chemie II Ruhr-Universität Bochum Universitätsstraße 150 44801 Bochum Germany
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie II Ruhr-Universität Bochum Universitätsstraße 150 44801 Bochum Germany
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