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Karir G, Mendez-Vega E, Portela-Gonzalez A, Saraswat M, Sander W, Hemberger P. The elusive phenylethynyl radical and its cation: synthesis, electronic structure, and reactivity. Phys Chem Chem Phys 2024; 26:18256-18265. [PMID: 38904382 DOI: 10.1039/d4cp02129k] [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
Alkynyl radicals and cations are crucial reactive intermediates in chemistry, but often evade direct detection. Herein, we report the direct observation of the phenylethynyl radical (C6H5CC˙) and its cation (C6H5CC+), which are two of the most reactive intermediates in organic chemistry. The radical is generated via pyrolysis of (bromoethynyl)benzene at temperatures above 1500 K and is characterized by photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). Photoionization of the phenylethynyl radical yields the phenylethynyl cation, which has never been synthesized due to its extreme electrophilicity. Vibrationally-resolved ms-TPES assisted by ab initio calculations unveiled the complex electronic structure of the phenylethynyl cation, which appears at an adiabatic ionization energy (AIE) of 8.90 ± 0.05 eV and exhibits an uncommon triplet (3B1) ground state, while the closed-shell singlet (1A1) state lies just 2.8 kcal mol-1 (0.12 eV) higher in energy. The reactive phenylethynyl radical abstracts hydrogen to form ethynylbenzene (C6H5CCH) but also isomerizes via H-shift to the o-, m-, and p-ethynylphenyl isomers (C6H4CCH). These radicals are very reactive and undergo ring-opening followed by H-loss to form a mixture of C8H4 triynes, along with low yields of cyclic 3- and 4-ethynylbenzynes (C6H3CCH). At higher temperatures, dehydrogenation from the unbranched C8H4 triynes forms the linear tetraacetylene (C8H2), an astrochemically relevant polyyne.
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Affiliation(s)
- Ginny Karir
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Bochum 44780, Germany.
| | - Enrique Mendez-Vega
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Bochum 44780, Germany.
| | | | - Mayank Saraswat
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Bochum 44780, Germany.
| | - Wolfram Sander
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Bochum 44780, Germany.
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute (PSI), Villigen CH-5232, Switzerland.
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A Barrierless Pathway Accessing the C 9H 9 and C 9H 8 Potential Energy Surfaces via the Elementary Reaction of Benzene with 1-Propynyl. Sci Rep 2019; 9:17595. [PMID: 31772216 PMCID: PMC6879741 DOI: 10.1038/s41598-019-53987-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 11/07/2019] [Indexed: 11/16/2022] Open
Abstract
The crossed molecular beams reactions of the 1-propynyl radical (CH3CC; X2A1) with benzene (C6H6; X1A1g) and D6-benzene (C6D6; X1A1g) were conducted to explore the formation of C9H8 isomers under single-collision conditions. The underlying reaction mechanisms were unravelled through the combination of the experimental data with electronic structure and statistical RRKM calculations. These data suggest the formation of 1-phenyl-1-propyne (C6H5CCCH3) via the barrierless addition of 1-propynyl to benzene forming a low-lying doublet C9H9 intermediate that dissociates by hydrogen atom emission via a tight transition state. In accordance with our experiments, RRKM calculations predict that the thermodynamically most stable isomer – the polycyclic aromatic hydrocarbon (PAH) indene – is not formed via this reaction. With all barriers lying below the energy of the reactants, this reaction is viable in the cold interstellar medium where several methyl-substituted molecules have been detected. Its underlying mechanism therefore advances our understanding of how methyl-substituted hydrocarbons can be formed under extreme conditions such as those found in the molecular cloud TMC-1. Implications for the chemistry of the 1-propynyl radical in astrophysical environments are also discussed.
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Lucas M, Thomas AM, Kaiser RI, Bashkirov EK, Azyazov VN, Mebel AM. Combined Experimental and Computational Investigation of the Elementary Reaction of Ground State Atomic Carbon (C; 3Pj) with Pyridine (C5H5N; X1A1) via Ring Expansion and Ring Degradation Pathways. J Phys Chem A 2018. [DOI: 10.1021/acs.jpca.8b00756] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Michael Lucas
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | - Aaron M. Thomas
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | - Ralf I. Kaiser
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | | | | | - Alexander M. Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
- Samara University, Samara, 443086, Russia
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4
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Rezgui Y. Role of hydrogen enrichment on acetylene emission during benzene oxidation. KINETICS AND CATALYSIS 2017. [DOI: 10.1134/s0023158417030107] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Mebel AM, Landera A, Kaiser RI. Formation Mechanisms of Naphthalene and Indene: From the Interstellar Medium to Combustion Flames. J Phys Chem A 2017; 121:901-926. [DOI: 10.1021/acs.jpca.6b09735] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Alexander M. Mebel
- Department
of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Alexander Landera
- Chemical
Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Ralf I. Kaiser
- Department
of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
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Zeng T, Danovich D, Shaik S, Ananth N, Hoffmann R. Tuning the Ground State Symmetry of Acetylenyl Radicals. ACS CENTRAL SCIENCE 2015; 1:270-278. [PMID: 27162981 PMCID: PMC4827494 DOI: 10.1021/acscentsci.5b00187] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Indexed: 06/05/2023]
Abstract
The lowest excited state of the acetylenyl radical, HCC, is a (2)Π state, only 0.46 eV above the ground state, (2)Σ(+). The promotion of an electron from a π bond pair to a singly occupied σ hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of (2)Π and (2)Σ(+) states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply for substituted acetylenyl radicals, RCC. However, π-donor/acceptor substitution is effective in modifying the state energies. We are able to design molecules with (2)Π ground states (NaOCC, H2NCC ((2)A″), HCSi, FCSi, etc.) and vary the (2)Σ(+)-(2)Π energy gap over a 4 eV range. We find an inconsistency between bond order and bond dissociation energy measures of the bond strength in the Si-containing molecules; we provide an explanation through an analysis of the relevant potential energy curves.
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Affiliation(s)
- Tao Zeng
- Department
of Chemistry and Chemical Biology, Cornell
University, Ithaca, New York 14853, United
States
| | - David Danovich
- Institute
of Chemistry and The Lise Meitner-Minerva Center for Computational
Quantum Chemistry, Hebrew University of
Jerusalem, 91904 Jerusalem, Israel
| | - Sason Shaik
- Institute
of Chemistry and The Lise Meitner-Minerva Center for Computational
Quantum Chemistry, Hebrew University of
Jerusalem, 91904 Jerusalem, Israel
| | - Nandini Ananth
- Department
of Chemistry and Chemical Biology, Cornell
University, Ithaca, New York 14853, United
States
| | - Roald Hoffmann
- Department
of Chemistry and Chemical Biology, Cornell
University, Ithaca, New York 14853, United
States
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Parker DSN, Dangi BB, Balucani N, Stranges D, Mebel AM, Kaiser RI. Gas-phase synthesis of phenyl oxoborane (C6H5BO) via the reaction of boron monoxide with benzene. J Org Chem 2013; 78:11896-900. [PMID: 24191702 DOI: 10.1021/jo401942z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Organyl oxoboranes (RBO) are valuable reagents in organic synthesis due to their role in Suzuki coupling reactions. However, organyl oxoboranes (RBO) are only found in trimeric forms (RBO3) commonly known as boronic acids or boroxins; obtaining their monomers has proved a complex endeavor. Here, we demonstrate an oligomerization-free formation of organyl oxoborane (RBO) monomers in the gas phase by a radical substitution reaction under single-collision conditions in the gas phase. Using the cross molecular beams technique, phenyl oxoborane (C6H5BO) is formed through the reaction of boronyl radicals (BO) with benzene (C6H6). The reaction is indirect, initially forming a van der Waals complex that isomerizes below the energy of the reactants and eventually forming phenyl oxoborane by hydrogen emission in an overall exoergic radical-hydrogen atom exchange mechanism.
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Affiliation(s)
- Dorian S N Parker
- Department of Chemistry, University of Hawaii at Manoa , 2545 The Mall, Honolulu, Hawaii 96822-2275, United States
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Nguyen VS, Elsamra RMI, Peeters J, Carl SA, Nguyen MT. Experimental and theoretical study of the reaction of the ethynyl radical with nitrous oxide, C2H + N2O. Phys Chem Chem Phys 2012; 14:7456-70. [PMID: 22517118 DOI: 10.1039/c2cp40367f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Vinh Son Nguyen
- Department of Chemistry, University of Leuven, Leuven, Belgium
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Jamal A, Mebel AM. An ab initio/RRKM study of the reaction mechanism and product branching ratios of the reactions of ethynyl radical with 1,2-butadiene. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.10.064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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Swinnen S, Elsamra RM, Nguyen VS, Peeters J, Carl SA, Nguyen MT. Theoretical and experimental investigation of the C2H+SO2 reaction over the range T=295–800K. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.07.098] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block--the aromatic benzene molecule--has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C(6)H(6)) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C(2)H + H(2)CCHCHCH(2) → C(6)H(6) + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.
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