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Zhang J, Gao J, Wang H, Guan J, Xu G, Xing L, Truhlar DG, Wang Z. Less-Dominant Resonance Configuration of Propargyl Radical Leads to a Growth Mechanism for Polycyclic Aromatic Hydrocarbons that Preserves the Cyclopenta Ring. J Am Chem Soc 2025; 147:9283-9293. [PMID: 40043144 DOI: 10.1021/jacs.4c15155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2025]
Abstract
Understanding the growth of polycyclic aromatic hydrocarbons (PAHs) is essential for combustion, astrochemistry, and carbon-based nanomaterial synthesis. This study presents theory-guided experiments on radical-radical combination reactions of propargyl (•C3H3). The addition of •C3H3 to three cyclopenta-fused PAH radicals─1-indenyl (•1-C9H7), acenaphthenyl (•C12H9), and 4H-cyclopenta[def]phenanthrenyl (•C15H9)─revealed that the reaction between the dominant propyne-3-yl resonance configuration of •C3H3 and the three radicals consistently produces PAHs with all hexagonal rings, while the reaction between the less dominant allene-1-yl resonance configuration of •C3H3 and the three radicals selectively preserves the cyclopenta ring and forms a new hexagonal ring. Elusive intermediates and isomeric products were observed and identified by combining molecular beam-sampling synchrotron photoionization mass spectrometry with gas chromatography-mass spectrometry. The complementary results suggest a high selectivity of the allene-1-yl addition pathway, which is thermodynamically controlled. The findings presented here are based on a combination of experimental capabilities, and they provide new mechanisms and insights into the selective formation of bowl-shaped PAHs, serving as templates for fullerene and nanotube structures. The high selectivity of the allene-1-yl pathway provides a rational synthetic strategy for cyclopenta-fused PAHs, bearing barrierless and facile radical-radical reaction pathways in various environments, including high-temperature combustion, circumstellar envelopes, and cold molecular clouds.
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Affiliation(s)
- Jinyang Zhang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Jiao Gao
- School of Pharmacy, Anhui Medical College, Hefei, Anhui 230601, P. R. China
| | - Hong Wang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Jiwen Guan
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Guangxian Xu
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Lili Xing
- Energy and Power Engineering Institute, Henan University of Science and Technology, Luoyang, Henan 471003, P. R. China
| | - Donald G Truhlar
- Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States
| | - Zhandong Wang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
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2
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Yang Z, Fujioka K, Galimova GR, Medvedkov IA, Goettl SJ, Sun R, Mebel AM, Kaiser RI. Directed Gas-Phase Formation of Azulene (C 10H 8): Unraveling the Bottom-Up Chemistry of Saddle-Shaped Aromatics. ACS CENTRAL SCIENCE 2025; 11:322-330. [PMID: 40028355 PMCID: PMC11869134 DOI: 10.1021/acscentsci.4c01606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2024] [Revised: 01/09/2025] [Accepted: 01/24/2025] [Indexed: 03/05/2025]
Abstract
The azulene (C10H8) molecule, the simplest polycyclic aromatic hydrocarbon (PAH) carrying a fused seven- and five-membered ring, is regarded as a fundamental molecular building block of saddle-shaped carbonaceous nanostructures such as curved nanographenes in the interstellar medium. However, an understanding of the underlying gas-phase formation mechanisms of this nonbenzenoid 10π-Hückel aromatic molecule under low-temperature conditions is in its infancy. Here, by merging crossed molecular beam experiments with electronic structure calculations and molecular dynamics simulations, our investigations unravel an unconventional low-temperature, barrierless route to azulene via the reaction of the simplest organic radical, methylidyne (CH), with indene (C9H8) through ring expansion. This reaction might represent the initial step toward to the formation of saddle-shaped PAHs with seven-membered ring moieties in hydrocarbon-rich cold molecular clouds such as the Taurus Molecular Cloud-1 (TMC-1). These findings challenge conventional wisdom that molecular mass growth processes to nonplanar PAHs, especially those containing seven-membered rings, operate only at elevated pressure and high-temperature conditions, thus affording a versatile low-temperature route to contorted aromatics in our galaxy.
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Affiliation(s)
- Zhenghai Yang
- Department
of Chemistry, University of Hawai’i
at Manoa, Honolulu, Hawaii 96822, United States
| | - Kazuumi Fujioka
- Department
of Chemistry, University of Hawai’i
at Manoa, Honolulu, Hawaii 96822, United States
| | - Galiya R. Galimova
- Department
of Chemistry and Biochemistry, Florida International
University, Miami, Florida 33199, United States
| | - Iakov A. Medvedkov
- Department
of Chemistry, University of Hawai’i
at Manoa, Honolulu, Hawaii 96822, United States
| | - Shane J. Goettl
- Department
of Chemistry, University of Hawai’i
at Manoa, Honolulu, Hawaii 96822, United States
| | - Rui Sun
- 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
| | - Ralf I. Kaiser
- Department
of Chemistry, University of Hawai’i
at Manoa, Honolulu, Hawaii 96822, United States
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Yang Z, Medvedkov IA, Goettl SJ, Nikolayev AA, Mebel AM, Li X, Kaiser RI. Low-temperature gas-phase formation of cyclopentadiene and its role in the formation of aromatics in the interstellar medium. Proc Natl Acad Sci U S A 2024; 121:e2409933121. [PMID: 39661056 DOI: 10.1073/pnas.2409933121] [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: 05/17/2024] [Accepted: 11/02/2024] [Indexed: 12/12/2024] Open
Abstract
The cyclopentadiene (C5H6) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (C20H10), nanobowls (C40H10), and fullerenes (C60) in deep space. However, the underlying elementary gas-phase processes synthesizing cyclopentadiene from acyclic hydrocarbon precursors have remained elusive. Here, by merging crossed molecular beam experiments with rate coefficient calculations and comprehensive astrochemical modeling, we afford persuasive testimony on an unconventional low-temperature cyclization pathway to cyclopentadiene from acyclic precursors through the reaction of the simplest diatomic organic radical-methylidyne (CH)-with 1,3-butadiene (C4H6) representing main route to cyclopentadiene observed in TaurusMolecular Cloud. This facile route provides potential solution for the incorporation of the cyclopentadiene moiety in complex aromatic systems via bottom-up molecular mass growth processes and offers an entry point to the low-temperature chemistry in deep space leading eventually to nonplanar PAHs in our carbonaceous Universe.
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Affiliation(s)
- Zhenghai Yang
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822
| | - Iakov A Medvedkov
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822
| | - Shane J Goettl
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822
| | - Anatoliy A Nikolayev
- Laboratory of Combustion Physics and Chemistry, Samara National Research University, Samara 443086, Russia
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199
| | - Xiaohu Li
- Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, People's Republic of China
- Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, People's Republic of China
- Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822
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Schneiker A, Góbi S, Ragupathy G, Keresztes B, Bazsó G, Tarczay G. Investigating H-atom reactions in small PAHs with imperfect aromaticity: A combined experimental and computational study of indene (C9H8) and indane (C9H10). J Chem Phys 2024; 160:214303. [PMID: 38832739 DOI: 10.1063/5.0209722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Accepted: 05/20/2024] [Indexed: 06/05/2024] Open
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are widely recognized as catalysts for interstellar H2 formation. Extensive exploration into the catalytic potential of various PAHs has encompassed both theoretical investigations and experimental studies. In the present study, we focused on studying the reactivity of an imperfect aromatic molecule, indene (C9H8), and its hydrogenated counterpart, indane (C9H10), as potential catalysts for H2 formation within the interstellar medium. The reactions of these molecules with H atoms at 3.1 K were investigated experimentally using the para-H2 matrix isolation technique. Our experimental results demonstrate that both indene and indane are reactive toward H atoms. Indene can participate in H-atom-abstraction and H-atom-addition reactions, whereas indane primarily undergoes H-atom-abstraction reactions. The H-atom-abstraction reaction of indene results in the formation of the 1-indenyl radical (R1) (C9H7) and H2 molecule. Simultaneously, an H-atom-addition reaction forms the 1,2-dihydro-indene-3-yl radical (R2) (C9H9). Experiments also reveal that the H-atom-abstraction reaction of indane also produces the R2 radical. To the best of our knowledge, this study represents the first reporting of the infrared spectra of R1 and R2 radicals. The experimental results, combined with theoretical findings, suggest that indane and indene may play a role in the catalytic formation of interstellar H2. Furthermore, these results imply a quasi-equilibrium between the investigated molecules and the formed radicals via H-atom-addition and H-atom-abstraction reactions.
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Affiliation(s)
- A Schneiker
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- George Hevesy Doctoral School, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
| | - S Góbi
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
| | - G Ragupathy
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
| | - B Keresztes
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- George Hevesy Doctoral School, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
| | - G Bazsó
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
| | - G Tarczay
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
- Centre for Astrophysics and Space Science, ELTE Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary
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Abeysooriya DNKH, White NJ, Workman KT, Dupuy JA, Gichuhi WK. Cyanocyclopentadiene-Annulated Polycyclic Aromatic Radical Anions: Predicted Negative Ion Photoelectron Spectra and Singlet-Triplet Energies of Cyanoindene and Cyanofluorene Radical Anions. J Phys Chem A 2024. [PMID: 38437617 DOI: 10.1021/acs.jpca.3c08312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2024]
Abstract
Isomer-specific negative ion photoelectron spectra (NIPES) of cyanoindene (C9H7CN) and cyanofluorene (C14H9N), acquired through the computation of Franck-Condon (FC) factors that utilize harmonic vibrational frequencies and normal mode vectors derived from density functional theory (DFT) at the B3LYP/aug-cc-pVQZ and 6-311++G(2d,2p) basis sets, are reported. The adiabatic electron affinity (EA) values of the ground singlet (S0) and the lowest lying triplet (T1) states are used to predict site-specific S0-T1 energies (ΔEST). The vibrational spectra of the S0 and T1 states are typified by ring distortion and ring C-C stretching vibrational progressions. Among all the S0 isomers in C9H7CN, the 2-cyanoindene (2-C9H7CN) is found to be the most stable at an EA of 0.716 eV, with the least stable isomer being the 1-C9H7CN at an EA of 0.208 eV. In C14H9N, the most stable S0 isomer, 2-cyanofluorene (2-C14H9N), has an EA of 0.781 eV. The least stable S0 isomer in C14H9N is the 9-C14H9N, with an EA of 0.364 eV. The FC calculations are designed to mimic simulations that would be performed to aid in the analysis of experimental spectra obtained in NIPE spectroscopic techniques. The vibrational spectra, adiabatic EAs, and ΔEST values reported in this study are intended to act as a guide for future gas-phase ion spectroscopic experiments and astronomical searches, especially with regard to the hitherto largely unexplored C14H9N isomers.
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Affiliation(s)
- Dushmantha N Koku Hannadige Abeysooriya
- Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
- School of Environmental Studies, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
| | - Nolan J White
- Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
- Department of Chemical Engineering, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
| | - Kie T Workman
- Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
- Department of Chemical Engineering, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
| | - Jonathan A Dupuy
- Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
| | - Wilson K Gichuhi
- Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States
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