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Rodrigues R, Bou Debes D, Mendes M, Guerra P, Mestre G, Eden S, Cornetta LM, Ingólfsson O, da Silva FF. Experimental and Theoretical Study on Electron Ionization and Fragmentation of Propylene Oxide─the First Chiral Molecule Detected in the Interstellar Medium. J Phys Chem A 2024; 128:4795-4805. [PMID: 38860325 DOI: 10.1021/acs.jpca.4c02116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2024]
Abstract
Propylene oxide, CH3CHOCH2, is the first chiral molecule detected in space and the third C3 oxide detected toward the Sagittarius B2 (Sgr B2 (N)) molecular cloud, the others being propanal, CH3CH2CHO, and acetone, (CH3)2CO. With homochirality being ubiquitous in the building blocks of living matter, the formation and decay paths of propylene oxide in space are of specific interest. Motivated by the significant role of photo- and secondary electrons in astrochemistry, we have studied electron ionization and fragmentation of propylene oxide. Ion appearance energies are determined and compared to threshold values for the respective processes calculated at the G4MP2 level of theory, and potential reaction pathways are computed at the DFT level of theory. Electron ionization is found to destabilize propylene oxide, leading to barrierless opening of the C1-C2 bond of the epoxy ring, hydrogen transfer, and fragmentation over the methyl vinyl ether or rupture of the C2-O bond of the epoxy ring and fragmentation of the allyl alcohol cation as an intermediate, rather than direct bond ruptures.
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Affiliation(s)
- Rodrigo Rodrigues
- CEFITEC, Departamento de Física, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal
| | - Daniel Bou Debes
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K
| | - Mónica Mendes
- CEFITEC, Departamento de Física, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal
| | - Pedro Guerra
- CEFITEC, Departamento de Física, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal
| | - Gonçalo Mestre
- CEFITEC, Departamento de Física, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal
| | - Samuel Eden
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K
| | - Lucas M Cornetta
- Instituto de Física da Universidade de São Paulo, Universidade de São Paulo, São Paulo 05508-900, Brazil
| | - Oddur Ingólfsson
- Department of Chemistry and Science Institute, University of Iceland, Dunhagi 3, Reykjavik IS-107, Iceland
| | - F Ferreira da Silva
- CEFITEC, Departamento de Física, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica 2829-516, Portugal
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McAdoo DJ. Contributions of C3H6O+. ions with the oxygen on the middle carbon to gas phase ion chemistry. MASS SPECTROMETRY REVIEWS 2000; 19:38-61. [PMID: 10715831 DOI: 10.1002/(sici)1098-2787(2000)19:1<38::aid-mas2>3.0.co;2-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The numerous ways in which studies of C3H6O+. ions with the oxygen on the second carbon have added to our knowledge of gas phase ion chemistry are reviewed. The enol form of this ion (1) first attracted interest during early investigations of the mechanism of the McLafferty Rearrangement and later in characterizing the double McLafferty Rearrangement. Next, it was found that 1 isomerizes to the higher energy acetone ion (2). This discovery sparked studies of the relative stabilities of ionized and neutral enol and ketone species. It also led to the discovery that 1-->2 surmounts a substantial barrier, and that 2 dissociates faster than the excess energy deposited in it by the isomerization can become randomly distributed; i.e., dissociation following 1-->2 is nonergodic. This fact is manifested by a more abundant loss of the methyl formed by isomerization and a greater associated translational energy release. Propene oxide and methyl vinyl ether ions also appear to ionize to 2 and to dissociate nonergodically. Methane is eliminated from 2 through a methyl-acetyl ion complex. Characterization of this reaction by photoionization mass spectrometry, ab initio theory, and RRKM calculations helped to establish that complex-mediated alkane eliminations are generally confined to a region just above threshold. At higher energies, because attractions between ions and nonpolar neutrals are weak, simple dissociation is too fast for complex-mediated H-transfer to compete with it. Studies of the collision-induced dissociations of 2 demonstrate that the first electronically excited A state of 2 is very long-lived and efficiently releases its energy into translational energy when the ion collides with a neutral at low impact energies. Finally, ion-molecule reactions of 2 and acetone-containing ion clusters in the gas phase are described.
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Affiliation(s)
- DJ McAdoo
- Marine Biomedical Institute, University of Texas Medical Branch, Galveston 77555-1069, USA
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Polce MJ, Wesdemiotis C. Characterization of the C3H 6O (+·) ion from 2-methoxyethanol. Mixture analysis by dissociation and neutralization-reionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 1995; 6:1030-1036. [PMID: 24214049 DOI: 10.1016/1044-0305(95)00504-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/1995] [Revised: 06/13/1995] [Accepted: 06/14/1995] [Indexed: 06/02/2023]
Abstract
The C3H6O(+·) ion formed upon the dissociative ionization of 2-methoxyethanol is identified by a combination of several tandem mass spectrometry methods, including metastable ion (MI) characteristics, collisionally activated dissociation (CAD), and neutralization-reionization mass spectrometry (NRMS). The experimental data conclusively show that 2-methoxyethanol molecular ion, namely, HOCH2CH2OCH 3 (+·) , loses H2O to yield mainly the distonic radical ion ·CH2CH2OCH 2 (+) along with a smaller amount of ionized methyl vinyl ether, namely, CH2=CHOCH 3 (+·) . Ring-closed products, such as the oxetane or the propylene oxide ion are not observed. The proportion of ·CH2CH2OCH 2 (+) increases with decreasing internal energy of the 2-methoxyethanol ion, which indicates a lower critical energy for the pathway leading to this product than for the competitive generation of CH2=CHOCH 3 (+·) . The present study also uses MI, CAD, and NRMS data to assess the structure of the distonic ion(+) (CH3)CHOCH2· (ring-opened ionized propylene oxide) and evaluate its isomerization proclivity toward the methyl vinyl ether ion.
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Affiliation(s)
- M J Polce
- Department of Chemistry, The University of Akron, 44325-3601, Akron, Ohio
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Bowen RD, Wright AD, Derrick PJ. Unimolecular reactions of ionized methyl allyl ether. ACTA ACUST UNITED AC 1992. [DOI: 10.1002/oms.1210270812] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Martinez RI, Ganguli B. Kinetics and mechanism of the collision-activated dissociation of the acetone cation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 1992; 3:427-444. [PMID: 24243053 DOI: 10.1016/1044-0305(92)87070-f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/1991] [Revised: 11/07/1991] [Accepted: 11/07/1991] [Indexed: 06/02/2023]
Abstract
For center-of-mass collision energies Ecm = 1-60 eV, the major fragment ions for the collision-activated dissociation (CAD) of the acetone cation are the acetyl cation (m / z 43; absolute branching ratios of 0.96-0.60) and the methyl cation (m/ z 15; absolute branching ratios of 0.02-0.26); the absolute total cross-sections were 24-35) Å(2). The breakdown curves (viz, plots of the absolute branching ratios versus Ecm) show complex, complementary energy dependences for production of MeCO(+) and Me(+), indicating apparent closure of the Me(+) channel for Ecm > 30 eV. Our observations are consistent with a competition between three fast, primary (direct) reactions, each of which opens sequentially at its respective threshold energy (viz, reactions 8, 10, and 8'). [Formula: see text] [Formula: see text] [Formula: see text] That is, the breakdown curves for MeCO(+) and Me(+) (and other CAD fragments) are consistent with the interpretation by other authors that the collisional activation of the acetone cation involves electronic transitions, so that CAD occurs primarily from isolated electronic states (i.e., non-quasi-equilibrium theory (QET) behavior). For acetone we found a correspondence between the photoelectron-photoion-coincidence and CAD breakdown curves. This may indicate that collisional activation in non-QET systems corresponds to scattering angles that emphasize optically allowed transitions accessed by photoionization.
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Affiliation(s)
- R I Martinez
- Chemical Kinetics and Thermodynamics Division, National Institute of Standards and Technology, 20899, Gaithersburg, MD
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Hartke B, Manz J, Mathis J. Mode selective control of unimolecular dissociations: Survey, and model simulations for HDO → H+DO, D+HO. Chem Phys 1989. [DOI: 10.1016/0301-0104(89)90007-4] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Lifshitz C, Rejwan M, Levin I, Peres T. Unimolecular fragmentations of the nitromethane cation. ACTA ACUST UNITED AC 1988. [DOI: 10.1016/0168-1176(88)80104-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Bouchoux G, Djazi F, Hoppilliard Y, Jaudon P, Nouts N. Dissociation of positively charged aliphatic epoxides. II. [C5H10O]+˙ epoxides and α,β unsaturated ethers. ACTA ACUST UNITED AC 1988. [DOI: 10.1002/oms.1210230107] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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