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Ben-Eliyahu Y, Kozuch S. Quantum tunnelling effect in the cis- trans isomerization of uranyl tetrahydroxide. Dalton Trans 2024; 53:16271-16279. [PMID: 39308316 DOI: 10.1039/d4dt02071e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/09/2024]
Abstract
The role of quantum tunnelling (QT) in the proton transfer kinetics of the uranyl tetrahydroxide (UTH, [UO2(OH)4]2-) cis to trans isomerization was computationally studied under three possible reaction pathways. The first pathway involved a direct proton transfer from the hydroxide ligand to the oxo atom. In the other two pathways, one or two water molecules were added to the second sphere. The first H2O, bound by hydrogen bonds to the ligands, acts as a bridge enabling a proton shuttling, a concerted hopping of a proton from the hydroxide to the oxo atom similar to the Grotthuss mechanism. In the third pathway, the second water molecule does not participate in the H-transfer chain, but works as an anchor for the first water molecule, limiting its movement and therefore enhancing the QT. Since experimentally the reaction occurs in water, the first two pathways (no water or one H2O) serve only as models of the gas phase behaviour, while the third pathway will always be thermodynamically and kinetically preferred. The effects were investigated in the gas phase as well as in a continuum aqueous model, including the H/D Kinetic Isotope Effect (KIE). The results indicate that at very low temperatures, QT is the only mechanism that permits the reaction kinetics, consistent with the large computed KIE. At higher temperatures, thermally activated tunnelling competes with the classical crossing over the potential barrier.
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Affiliation(s)
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel.
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2
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Rodríguez SJ, Kozuch S. Heavy-atom tunnelling in benzene isomers: how many tricyclic species are truly stable? Chem Sci 2024:d4sc05109b. [PMID: 39345775 PMCID: PMC11428002 DOI: 10.1039/d4sc05109b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2024] [Accepted: 09/02/2024] [Indexed: 10/01/2024] Open
Abstract
The variety of possible benzene isomers may provide a fundamental basis for understanding structural and reactivity patterns in organic chemistry. However, the vast majority of these isomers remain unsynthesized, while most of the experimentally known species are only moderately stable. Consequently, there is a high probability that the theoretically proposed isomers would also be barely metastable, a factor that must be taken into account if their creation in the laboratory is sought. In this work, we studied the kinetic stability of all 73 hypothetical tricyclic benzene isomers, especially focusing on their nuclear quantum effects. With this in mind, we evaluated which species are theoretically possible to synthesize, detect, and isolate. Our computations predict that 26% of the previously deemed stable molecules are completely unsynthesizable due to their intrinsic quantum tunnelling instability pushing for their unimolecular decomposition even close to the absolute zero. Five more systems would be detectable, but they will slowly and inevitably degrade, while seven more supposedly stable systems will break apart in barrierless mechanisms.
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Affiliation(s)
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev Beer-Sheva 841051 Israel
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Guo W, Kong WY, Tantillo DJ. Revisiting a classic carbocation - DFT, coupled-cluster, and ab initio molecular dynamics computations on barbaralyl cation formation and rearrangements. Chem Sci 2024; 15:d4sc04829f. [PMID: 39268206 PMCID: PMC11385376 DOI: 10.1039/d4sc04829f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2024] [Accepted: 08/26/2024] [Indexed: 09/15/2024] Open
Abstract
Density functional theory computations were used to model the formation and rearrangement of the barbaralyl cation (C9H+ 9). Two highly delocalized minima were located for C9H+ 9, one of C s symmetry and the other of D 3h symmetry, with the former having lower energy. Quantum chemistry-based NMR predictions affirm that the lower energy structure is the best match with experimental spectra. Partial scrambling was found to proceed through a C 2 symmetric transition structure associated with a barrier of only 2.3 kcal mol-1. The full scrambling was found to involve a C 2v symmetric transition structure associated with a 5.0 kcal mol-1 barrier. Ab initio molecular dynamics simulations initiated from the D 3h C9H+ 9 structure revealed its connection to six minima, due to the six-fold symmetry of the potential energy surface. The effects of tunneling and boron substitution on this complex reaction network were also examined.
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Affiliation(s)
- Wentao Guo
- Department of Chemistry, Univeristy of California Davis USA
| | - Wang-Yeuk Kong
- Department of Chemistry, Univeristy of California Davis USA
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Frenklach A, Amlani H, Kozuch S. Quantum Tunneling Instability in Pericyclic Reactions: The Cheletropic, Coarctate, and Ene Cases. Org Lett 2024; 26:5157-5161. [PMID: 38847371 DOI: 10.1021/acs.orglett.4c01635] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/22/2024]
Abstract
Some retro-pericyclic reactions, as a result of their high exothermicity and short trajectories, are the perfect ground for heavy atom tunneling molecular decompositions, also known as "quantum tunneling instability" (QTI). Considering this effect, in our first installment [Frenklach, A.; Amlani, H.; Kozuch, S. Quantum Tunneling Instability in Pericyclic Reactions. J. Am. Chem. Soc. 2024, 146 (17), 11823-11834, DOI: 10.1021/jacs.4c00608], we computed several retro-Diels-Alder reactions, predicting that many studied reactants cannot be isolated. Herein, we will explore the QTI of retro-cheletropic, coarctate, and ene exemplars, where again we hypothesize the impossibility to detect their reactants.
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Affiliation(s)
- Alexander Frenklach
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
| | - Hila Amlani
- 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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Frenklach A, Amlani H, Kozuch S. Quantum Tunneling Instability in Pericyclic Reactions. J Am Chem Soc 2024; 146:11823-11834. [PMID: 38634836 DOI: 10.1021/jacs.4c00608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2024]
Abstract
Several cycloreversion reactions of the retro-Diels-Alder type were computationally assessed to understand their quantum tunneling (QT) reactivity. N2, CO, and other leaving groups were considered based on their strong exothermicity, as it reduces their thermodynamic and kinetic stabilities. Our results indicate that for many of these reactions, it is essential to take into account their QT decomposition rate, which can massively weaken their molecular stability and shorten their half-lives even at deep cryogenic temperatures. In practical terms, this indicates that many supposedly stable molecules will actually be unsynthesizable or unisolable, and therefore trying to prepare or detect them would be a futile attempt. In addition, we discuss the importance of tunneling to correctly understand the enthalpy of activation and the collective atomic effect on the tunneling kinetic isotope effects to test if third-row atoms can tunnel in a chemical reaction. This project raises the question of the importance of in silico chemistry to guide in vitro chemistry, especially in cases where the latter cannot solve its own uncertainties.
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Affiliation(s)
- Alexander Frenklach
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
| | - Hila Amlani
- 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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Sedgi I, Kozuch S. Quantum tunneling instability of the mythical hexazine and pentazine. Chem Commun (Camb) 2024; 60:2038-2041. [PMID: 38284898 DOI: 10.1039/d3cc05840a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Through computational analysis we found that pentazine and hexazine, two hypothetical high-energy density materials, exhibit inherent instability due to quantum tunneling effects. This instability remains even near the absolute zero, and therefore they can be deemed as unsynthesizable. We propose substituents that could potentially stabilize pentazine, especially dimethylamine.
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Affiliation(s)
- Itzhak Sedgi
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel.
- Department of Analytical Chemistry, Nuclear Research Center Negev., P.O. Box 9001, Beer-Sheva, Israel
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel.
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Altalhi WAO, Chan B, O'Hair RAJ. Methide Affinity Scale: Key Thermodynamic Data Underpinning Catalysis, Organic Synthesis, and Organometallic and Polymer Chemistry. J Phys Chem A 2024; 128:977-988. [PMID: 38295100 DOI: 10.1021/acs.jpca.3c05974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2024]
Abstract
Methide transfer reactions play important roles in many areas of chemistry, including the Grignard reaction, in the transmetalation steps of metal-catalyzed cross-coupling reactions, and in the generation of cationic metal polymerization catalysts. Methide affinities (MAs) are the key thermodynamic quantity that underpin such reactions, and yet comprehensive methide affinity scales are poorly developed. Here, B3LYP-D3BJ/def2-TZVP calculations are used to calculate the energy changes (MAs) for cations (MeZ → Z+ + Me-), neutrals (MeY- → Y + Me-), and anions (MeX2- → X- + Me-) derived from permethyl species of all group s and p elements. The MAs range from 2525.8 for the singlet cation F+ to -820.4 kJ/mol for the tetramethylborate anion, Me4B-. The cations show the clearest trends: the MAs in all cases decrease going down the group, while moving across a period, the MAs increase from group 1 to group 2 and then decrease for group 3, remaining about the same or with a modest increase moving to group 4, and then continue to increase across a period to a maximum for the halogens (group 17). The anions and dianions are sensitive to hypervalency; those elements that cannot expand the octet have very unfavorable MAs (e.g., MA of Me4C requires the formation of Me5C- and of Me4B- requires the formation of Me5B2-). To address whether the anion MeY- and dianion MeZ2- are stable, the vertical detachment energies of the anions and dianions were calculated. All of the anions are thermodynamically stable with respect to electron loss, except for Me4N-, while the dianions are all thermodynamically unstable with respect to electron loss. The kinetic stability of the dianions with respect to methide and electron loss was also evaluated for the lowest MAs. The only dianions that might be kinetically stable and observable in the gas phase are Me4Ca2-, Me4Sr2-, and Me4Ba2-. The dianion CF3CaF32- is predicted to be both thermodynamically and kinetically stable in the gas phase.
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Affiliation(s)
- Weam A O Altalhi
- School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, Victoria 3010, Australia
- Department of Chemistry, Prince Sattam Bin Abdulaziz University, Hotat Bani Tamim 16511, Saudi Arabia
| | - Bun Chan
- Graduate School of Engineering, Nagasaki University, Bunkyo 1-14, Nagasaki 852-8521, Japan
- Computational Molecular Science Research Team, RIKEN Center for Computational Science, 7-1-26 minatojima-minami, Cyuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Richard A J O'Hair
- School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, Victoria 3010, Australia
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Nandi A, Tarannam N, Rodrigues Silva D, Fonseca Guerra C, Hamlin TA, Kozuch S. Boron Tunneling in the "Weak" Bond-Stretch Isomerization of N-B Lewis Adducts. Chemphyschem 2021; 22:1857-1862. [PMID: 34245098 DOI: 10.1002/cphc.202100505] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Indexed: 11/08/2022]
Abstract
Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a "long bond" geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a "short bond" structure (SB, a covalent dative bond). This behavior can be considered as a "weak" form of bond stretch isomerism. Our computations reveal that complexes RCN-BX3 (R=CH3 , FCH2 , BrCH2 , and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.
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Affiliation(s)
- Ashim Nandi
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 841051, Israel
| | - Naziha Tarannam
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 841051, Israel
| | - Daniela Rodrigues Silva
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The, Netherlands.,Departamento de Química, Instituto de Ciências Naturais, Universidade Federal de Lavras, 37200-900, Lavras-MG, Brazil
| | - Célia Fonseca Guerra
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The, Netherlands.,Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The, Netherlands
| | - Trevor A Hamlin
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The, Netherlands
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 841051, Israel
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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: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 12/15/2020] [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.
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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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11
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Cernuto A, Lopes A, Romanzin C, Cunha de Miranda B, Ascenzi D, Tosi P, Tonachini G, Maranzana A, Polášek M, Žabka J, Alcaraz C. Effects of collision energy and vibrational excitation of CH 3+ cations on its reactivity with hydrocarbons: But-2-yne CH 3CCCH 3 as reagent partner. J Chem Phys 2017; 147:154302. [PMID: 29055295 DOI: 10.1063/1.4990514] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The methyl carbocation is ubiquitous in gaseous environments, such as planetary ionospheres, cometary comae, and the interstellar medium, as well as combustion systems and plasma setups for technological applications. Here we report on a joint experimental and theoretical study on the mechanism of the reaction CH3+ + CH3CCCH3 (but-2-yne, also known as dimethylacetylene), by combining guided ion beam mass spectrometry experiments with ab initio calculations of the potential energy hypersurface. Such a reaction is relevant in understanding the chemical evolution of Saturn's largest satellite, Titan. Two complementary setups have been used: in one case, methyl cations are generated via electron ionization, while in the other case, direct vacuum ultraviolet photoionization with synchrotron radiation of methyl radicals is used to study internal energy effects on the reactivity. Absolute reactive cross sections have been measured as a function of collision energy, and product branching ratios have been derived. The two most abundant products result from electron and hydride transfer, occurring via direct and barrierless mechanisms, while other channels are initiated by the electrophilic addition of the methyl cation to the triple bond of but-2-yne. Among the minor channels, special relevance is placed on the formation of C5H7+, stemming from H2 loss from the addition complex. This is the only observed condensation product with the formation of new C-C bonds, and it might represent a viable pathway for the synthesis of complex organic species in astronomical environments and laboratory plasmas.
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Affiliation(s)
- Andrea Cernuto
- Department of Physics, University of Trento, Via Sommarive 14, Trento I-38123, Italy
| | - Allan Lopes
- Laboratoire de Chimie Physique, Bât. 350, UMR 8000, CNRS-Univ. Paris-Sud 11 and Paris Saclay, Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France
| | - Claire Romanzin
- Laboratoire de Chimie Physique, Bât. 350, UMR 8000, CNRS-Univ. Paris-Sud 11 and Paris Saclay, Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France
| | | | - Daniela Ascenzi
- Department of Physics, University of Trento, Via Sommarive 14, Trento I-38123, Italy
| | - Paolo Tosi
- Department of Physics, University of Trento, Via Sommarive 14, Trento I-38123, Italy
| | - Glauco Tonachini
- Department of Chemistry, University of Torino, Via Pietro Giuria, 7, Torino I-10125, Italy
| | - Andrea Maranzana
- Department of Chemistry, University of Torino, Via Pietro Giuria, 7, Torino I-10125, Italy
| | - Miroslav Polášek
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 3, 182 23 Prague 8, Czech Republic
| | - Jan Žabka
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 3, 182 23 Prague 8, Czech Republic
| | - Christian Alcaraz
- Laboratoire de Chimie Physique, Bât. 350, UMR 8000, CNRS-Univ. Paris-Sud 11 and Paris Saclay, Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France
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Meisner J, Markmeyer MN, Bohner MU, Kästner J. Comparison of classical reaction paths and tunneling paths studied with the semiclassical instanton theory. Phys Chem Chem Phys 2017; 19:23085-23094. [DOI: 10.1039/c7cp03722h] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Comparison of classical reaction paths and semiclassical instanton paths for a proton transfer reaction mechanism.
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Affiliation(s)
- Jan Meisner
- Institute for Theoretical Chemistry
- University of Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - Max N. Markmeyer
- Institute for Theoretical Chemistry
- University of Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - Matthias U. Bohner
- Institute for Theoretical Chemistry
- University of Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - Johannes Kästner
- Institute for Theoretical Chemistry
- University of Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
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Meisner J, Kästner J. Atom Tunneling in Chemistry. Angew Chem Int Ed Engl 2016; 55:5400-13. [DOI: 10.1002/anie.201511028] [Citation(s) in RCA: 140] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 01/08/2016] [Indexed: 01/01/2023]
Affiliation(s)
- Jan Meisner
- Institut für Theoretische Chemie Universität Stuttgart Pfaffenwaldring 55 70569 Stuttgart Germany
| | - Johannes Kästner
- Institut für Theoretische Chemie Universität Stuttgart Pfaffenwaldring 55 70569 Stuttgart Germany
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Affiliation(s)
- Jan Meisner
- Institut für Theoretische Chemie Universität Stuttgart Pfaffenwaldring 55 70569 Stuttgart Deutschland
| | - Johannes Kästner
- Institut für Theoretische Chemie Universität Stuttgart Pfaffenwaldring 55 70569 Stuttgart Deutschland
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Borden WT. Reactions that involve tunneling by carbon and the role that calculations have played in their study. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2015. [DOI: 10.1002/wcms.1235] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Weston Thatcher Borden
- Department of Chemistry and the Center for Advanced Scientific Computing and Modeling University of North Texas Denton TX USA
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