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El Hadki H, Gámez VG, Dalbouha S, Marakchi K, Kabbaj OK, Komiha N, Carvajal M, Senent Diez ML. Theoretical spectroscopic study of acetyl (CH 3CO), vinoxy (CH 2CHO), and 1-methylvinoxy (CH 3COCH 2) radicals. Barrierless formation processes of acetone in the gas phase. OPEN RESEARCH EUROPE 2022; 1:116. [PMID: 37645120 PMCID: PMC10445905 DOI: 10.12688/openreseurope.14073.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 03/10/2022] [Indexed: 08/31/2023]
Abstract
Background: Acetone is present in the earth´s atmosphere and extra-terrestrially. The knowledge of its chemical history in these environments represents a challenge with important implications for global tropospheric chemistry and astrochemistry. The results of a search for efficient barrierless pathways producing acetone from radicals in the gas phase are described in this paper. The spectroscopic properties of radicals needed for their experimental detection are provided. Methods: The reactants were acetone fragments of low stability and small species containing C, O and H atoms. Two exergonic bimolecular addition reactions involving the radicals CH 3, CH 3CO, and CH 3COCH 2, were found to be competitive according to the kinetic rates calculated at different temperatures. An extensive spectroscopic study of the radicals CH 3COCH 2 and CH 3CO, as well as the CH 2CHO isomer, was performed. Rovibrational parameters, anharmonic vibrational transitions, and excitations to the low-lying excited states are provided. For this purpose, RCCSD(T)-F12 and MRCI/CASSCF calculations were performed. In addition, since all the species presented non-rigid properties, a variational procedure of reduced dimensionality was employed to explore the far infrared region. Results: The internal rotation barriers were determined to be V 3=143.7 cm -1 (CH 3CO), V 2=3838.7 cm -1 (CH 2CHO) and V 3=161.4 cm -1 and V 2=2727.5 cm -1 (CH 3COCH 2).The splitting of the ground vibrational state due to the torsional barrier have been computed to be 2.997 cm -1, 0.0 cm -1, and 0.320 cm -1, for CH 3CO, CH 2CHO, and CH 3COCH 2, respectively. Conclusions: Two addition reactions, H+CH 3COCH 2 and CH 3+CH 3CO, could be considered barrierless formation processes of acetone after considering all the possible formation routes, starting from 58 selected reactants, which are fragments of the molecule. The spectroscopic study of the radicals involved in the formation processes present non-rigidity. The interconversion of their equilibrium geometries has important spectroscopic effects on CH 3CO and CH 3COCH 2, but is negligible for CH 2CHO.
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Affiliation(s)
- Hamza El Hadki
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Victoria Guadalupe Gámez
- Departamento de Química y Física Teóricas, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Madrid, 28006, Spain
| | - Samira Dalbouha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
- Equipe de recherche : Matériaux et Applications Environnementales, Laboratoire de Chimie Appliquée et Environnement, Département de chimie, Faculté des Sciences d’Agadir, Université Ibn Zohr, Agadir, B.P 8106, Morocco
| | - Khadija Marakchi
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Oum Keltoum Kabbaj
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Najia Komiha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, LS3MN2E/CERNE2D, Faculté des Sciences Rabat, Université Mohammed V, Rabat, BP1014, Morocco
| | - Miguel Carvajal
- Departamento de Ciencias Integradas, Centro de Estudios Avanzados en Física, Matemática y Computación; Unidad Asociada GIFMAN, CSIC-UHU, Universidad de Huelva, Huelva, 21071, Spain
- Instituto Universitario Carlos I de Física Teórica y Computacional, University of Granada, Granada, Spain
| | - Maria Luisa Senent Diez
- Departamento de Química y Física Teóricas, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Madrid, 28006, Spain
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Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol. MOLECULES (BASEL, SWITZERLAND) 2021; 27:molecules27010101. [PMID: 35011331 PMCID: PMC8746872 DOI: 10.3390/molecules27010101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/11/2021] [Accepted: 12/15/2021] [Indexed: 12/31/2022]
Abstract
Rotational microwave jet spectroscopy studies of the monoterpenol α-fenchol have so far failed to identify its second most stable torsional conformer, despite computational predictions that it is only very slightly higher in energy than the global minimum. Vibrational FTIR and Raman jet spectroscopy investigations reveal unusually complex OH and OD stretching spectra compared to other alcohols. Via modeling of the torsional states, observed spectral splittings are explained by delocalization of the hydroxy hydrogen atom through quantum tunneling between the two non-equivalent but accidentally near-degenerate conformers separated by a low and narrow barrier. The energy differences between the torsional states are determined to be only 16(1) and 7(1) cm-1hc for the protiated and deuterated alcohol, respectively, which further shrink to 9(1) and 3(1) cm-1hc upon OH or OD stretch excitation. Comparisons are made with the more strongly asymmetric monoterpenols borneol and isopinocampheol as well as with the symmetric, rapidly tunneling propargyl alcohol. In addition, the third-in contrast localized-torsional conformer and the most stable dimer are assigned for α-fenchol, as well as the two most stable dimers for propargyl alcohol.
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Medel R. Simple models for the quick estimation of ground state hydrogen tunneling splittings in alcohols and other compounds. Phys Chem Chem Phys 2021; 23:17591-17605. [PMID: 34369526 DOI: 10.1039/d1cp02115j] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Models for the quick estimation of energy splittings caused by coherent tunneling of hydrogen atoms are evaluated with available experimental data for alcohols and improvements are proposed. The discussed models are mathematically simple and require only results from routine quantum chemical computations, i.e. hybrid DFT calculation of the equilibrium geometry and the transition state within the harmonic approximation. A benchmark of experimental splittings spanning four orders of magnitude for 27 alcohol species is captured by three evaluated models with a mean symmetric deviation factor of 1.7, 1.5 and 1.4, respectively, i.e. the calculated values deviate on average by this factor in either direction. Limitations of the models are explored with alcohols featuring uncommon properties, such as an inverted conformational energy sequence, a very light molecular frame, an elevated torsional frequency, or a coupling with a second internal degree of freedom. If the splitting of either the protiated or deuterated form of an alcohol is already experimentally determined, the one of the second isotopolog can be estimated by three additional models with a mean symmetric deviation factor of 1.14, 1.19 and 1.15, respectively. It is shown that this can be achieved with a novel approach without any quantum chemical calculation by directly correlating experimental splittings of isotopologs across related species. This is also demonstrated for other classes of compounds with hydrogen tunneling, such as amines, thiols, and phenols. Furthermore, it is found that the isotope effect can even be anticipated without any further knowledge about the system solely from the size of either splitting with a mean symmetric deviation factor of 1.3. This is based on an extensive sample of 77 pairs of splittings spanning eight orders of magnitude for isotopologs of chemically diverse compounds.
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Affiliation(s)
- Robert Medel
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
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Large Amplitude Motions of Pyruvic Acid (CH 3-CO-COOH). Molecules 2021; 26:molecules26144269. [PMID: 34299546 PMCID: PMC8303138 DOI: 10.3390/molecules26144269] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 07/08/2021] [Accepted: 07/10/2021] [Indexed: 11/17/2022] Open
Abstract
Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the Cs point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406-986 cm-1 region and represent excitations of the ν24 (skeletal torsion) and the ν23 (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν23. The A1/E splitting of the ground vibrational state has been evaluated to be 0.024 cm-1 as it was expected given the high of the methyl torsional barrier (338 cm-1). A very good agreement with respect to previous experimental data concerning fundamental frequencies (νCAL - νEXP ~ 1 cm-1), and rotational parameters (B0CAL - B0EXP < 5 MHz), is obtained.
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Boussessi R, Senent ML. Computational analysis of the far infrared spectral region of various deuterated varieties of ethylene glycol. Phys Chem Chem Phys 2020; 22:23785-23794. [PMID: 33063802 DOI: 10.1039/d0cp03315d] [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 far infrared spectra of three deuterated isotopologues of ethylene glycol, CH2OD-CH2OD, CH2OD-CH2OH and CH2OH-CH2OD, where the latter two species differ in their intramolecular hydrogen-bonding arrangement, are studied using highly correlated ab initio methods, vibrational second order perturbation theory and a variational procedure of reduced dimensionality. New subroutines suitable for the study of large systems with more than two interacting large amplitude motions were implemented and applied. The molecular symmetry of ethylene glycol decays by the formation of weak intramolecular bonds producing very asymmetrical stable structures. Three internal rotations contribute to the formation of a very anisotropic potential energy surface and to the puzzling distribution of the rovibrational energy levels. The ground vibrational state rotational constants and the centrifugal distortion constants (S-reduction, Ir representation) corresponding to the aGg' (G1) and gGg' (G2) forms are provided for the studied isotopologues. The low-lying vibrational levels up to 550 cm-1 are obtained variationally for J = 0. Two series of sublevels of the ground vibrational state are obtained: eight components localized in G1 lying between 0.0 and 0.3 cm-1 and eight sublevels localized in G2 lying between 138.1 and 138.4 cm-1. The gap between both sets is lower in CH2OD-CH2OD and more dispersed in the monodeuterated variety.
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Affiliation(s)
- Rahma Boussessi
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Serrano 121, Madrid 28006, Spain.
| | - María Luisa Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Unidad Asociada GIFMAN, CSIC-UHU, Serrano 121, Madrid 28006, Spain.
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Yazidi O, Senent ML, Gámez V, Carvajal M, Al-Mogren MM. Ab initio spectroscopic characterization of the radical CH 3OCH 2 at low temperatures. J Chem Phys 2019; 150:194102. [PMID: 31117793 DOI: 10.1063/1.5095857] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Spectroscopic and structural properties of methoxymethyl radical (CH3OCH2, RDME) are determined using explicitly correlated ab initio methods. This radical of astrophysical and atmospheric relevance has not been fully characterized at low temperatures, which has delayed astrophysical research. We provide rovibrational parameters, excitations to the low energy electronic states, torsional and inversion barriers, and low vibrational energy levels. In the electronic ground state (X2A), which appears "clean" from nonadiabatic effects, the minimum energy structure is an asymmetric geometry whose rotational constants and dipole moment have been determined to be A0 = 46 718.67 MHz, B0 = 10 748.42 MHz, and C0 = 9272.51 MHz, and 1.432D (μA = 0.695D, µB = 1.215D, µC = 0.302D), respectively. A variational procedure has been applied to determine torsion-inversion energy levels. Each level splits into 3 subcomponents (A1/A2 and E) corresponding to the three methyl torsion minima. Although the potential energy surface presents 12 minima, at low temperatures, the infrared band shapes correspond to a surface with only three minima because the top of the inversion Vα barrier at α = 0° (109 cm-1) stands below the zero point vibrational energy and the CH2 torsional barrier is relatively high (∼2000 cm-1). The methyl torsion barrier was computed to be ∼500 cm-1 and produces a splitting of 0.01 cm-1 of the ground vibrational state.
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Affiliation(s)
- O Yazidi
- Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, Tunis 2092, Tunisia
| | - M L Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain and Unidad Asociada GIFMAN, CSIC-UHU, 21071 Huelva, Spain
| | - V Gámez
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain and Unidad Asociada GIFMAN, CSIC-UHU, 21071 Huelva, Spain
| | - M Carvajal
- Dpto. Ciencias Integradas, Centro de Estudios Avanzados en Física, Matemática y Computación, Facultad de Ciencias Experimentales, Universidad de Huelva, Unidad Asociada GIFMAN, CSIC-UHU, 21071 Huelva, Spain and Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, Granada, Spain
| | - M Mogren Al-Mogren
- Chemistry Department, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia
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Dalbouha S, Senent ML. Large amplitude vibrations of acetyl isocyanate, methyl cyanoformate, and acetyl cyanate. Phys Chem Chem Phys 2019; 21:3597-3605. [DOI: 10.1039/c8cp04490b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The far infrared region of three detectable molecules sharing the empirical formula C3H3O2N, acetyl isocyanate CH3CONCO (AISO), methyl cyanoformate NC–COOCH3 (MCN) and acetyl cyanate CH3COOCN (ACN), is explored using explicitly correlated coupled cluster ab initio methods and a variational procedure designed for non-rigid species and large amplitude motions.
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Affiliation(s)
- Samira Dalbouha
- Departamento de Química y Física Teóricas
- Instituto de Estructura de la Materia, CSIC
- 28006 Madrid
- Spain
| | - María L. Senent
- Departamento de Química y Física Teóricas
- Instituto de Estructura de la Materia, CSIC
- 28006 Madrid
- Spain
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