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Zhang YR, Yuan DF, Wang LS. Probing the Electronic Structure and Spectroscopy of the Pyrrolyl and Imidazolyl Radicals using High-Resolution Photoelectron Imaging of Cryogenically-Cooled Anions. Phys Chem Chem Phys 2022; 24:6505-6514. [DOI: 10.1039/d2cp00189f] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
High-resolution photoelectron imaging and photodetachment spectroscopy of cryogenically-cooled pyrrolide and imidazolide anions are used to probe the electronic structure and spectroscopy of the pyrrolyl and imidazolyl radicals. The high-resolution data...
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2
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Lin L, Zhu J. Antiaromaticity-Promoted Radical Stability in α-Methyl Heterocyclics. J Org Chem 2021; 86:15558-15567. [PMID: 34632764 DOI: 10.1021/acs.joc.1c02050] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Aromaticity is a fundamental and important concept in chemistry, and usually, the enhancement of aromaticity brings additional thermodynamic stability to a compound. Moreover, since radicals can act as intermediates in chemical reactions, they have attracted considerable attention from both experimental and theoretical chemists for a long time. However, it remains unclear whether there is a relationship between the thermodynamic stability of cyclic planar radicals and their aromaticity. In this work, using various aromaticity indices including anisotropy of the induced current density analysis and nucleus-independent chemical shifts against the radical stabilization energy, we systematically investigated the relationship between aromaticity and the thermodynamic stability of α-methyl heterocyclics. Density functional theory calculations suggest that the stronger the antiaromaticity of the original form heterocyclics, the higher the thermodynamic stability of the corresponding radicals, which is in sharp contrast to the general knowledge that aromaticity brings compounds' thermodynamic stabilities. The principal interacting spin orbital analysis shows that the stronger the π-bond formed between the heterocyclics and the α-methyl carbon, the more spin density the radicals tend to be distributed on the heterocyclics. Thus, the strong π-bonding is one of the factors for improving the thermodynamic stability of radicals.
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Affiliation(s)
- Lu Lin
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Jun Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
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Johansen SL, Xu Z, Westerfield JH, Wannenmacher AC, Crabtree KN. Coupled Cluster Characterization of 1-, 2-, and 3-Pyrrolyl: Parameters for Vibrational and Rotational Spectroscopy. J Phys Chem A 2021; 125:1257-1268. [PMID: 33502858 DOI: 10.1021/acs.jpca.0c09833] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pyrrolyl (C4H4N) is a nitrogen-containing aromatic radical that is a derivative of pyrrole (C4H5N) and is an important intermediate in the combustion of biomass. It is also relevant for chemistry in Titan's atmosphere and may be present in the interstellar medium. The lowest-energy isomer, 1-pyrrolyl, has been involved in many experimental and theoretical studies of the N-H photodissociation of pyrrole, yet it has only been directly spectroscopically detected via electron paramagnetic resonance and through the photoelectron spectrum of the pyrrolide anion, yielding three vibrational frequencies. No direct measurements of 2- or 3-pyrrolyl have been made, and little information is known from theoretical calculations beyond their relative energies. Here, we present an ab initio quantum chemical characterization of the three pyrrolyl isomers at the CCSD(T) level of theory in their ground electronic states, with an emphasis on spectroscopic parameters relevant for vibrational and rotational spectroscopy. Equilibrium geometries were optimized at the CCSD(T)/cc-pwCVTZ level of theory, and the quadratic, cubic, and partial quartic force constants were evaluated at CCSD(T)/ANO0 for analysis using second-order vibrational perturbation theory to obtain harmonic and anharmonic vibrational frequencies. In addition, zero-point-corrected rotational constants, electronic spin-rotation tensors, and nuclear hyperfine tensors are calculated for rotational spectroscopy. Our computed structures and energies agree well with earlier density functional theory calculations, and spectroscopic parameters for 1-pyrrolyl are compared with the limited existing experimental data. Finally, we discuss strategies for detecting these radicals using rotational and vibrational spectroscopy on the basis of the calculated spectroscopic constants.
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Affiliation(s)
- Sommer L Johansen
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - Zhongxing Xu
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - J H Westerfield
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - Anna C Wannenmacher
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - Kyle N Crabtree
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
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4
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Thermal unimolecular reactivity pathways in dehydro‐diazines radicals. J PHYS ORG CHEM 2020. [DOI: 10.1002/poc.4152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Hendrix J, Bera PP, Lee TJ, Head-Gordon M. Cation, Anion, and Radical Isomers of C 4H 4N: Computational Characterization and Implications for Astrophysical and Planetary Environments. J Phys Chem A 2020; 124:2001-2013. [PMID: 32077700 DOI: 10.1021/acs.jpca.9b11305] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Nitrogen-containing ions and molecules in the gas phase have been detected in non-Earth environments such as dark molecular clouds and more recently in the atmosphere of Saturn's moon Titan. These molecules may serve as precursors to larger heterocyclic structures that provide the foundation of complex biological molecules. On Titan, molecules of m/z 66 have been detected by the Cassini mission, and species of the empirical formula C4H4N may contribute to this signature. We have characterized seven isomers of C4H4N in anionic, neutral radical, and cationic states using density functional theory. Structures were optimized using the range-separated hybrid ωB97X-V with the cc-pVTZ and aug-cc-pVTZ basis sets. Anionic and radical C4H4N favor cyclic structures with aromatic and quasi-aromatic electron arrangements, respectively. Interestingly, ionization from the radical surface to the cation induces significant changes in structural stability, and the global minimum for positively charged isomers is CH2CCHCNH+, a pseudo-linear species reminiscent of cyanoallene. Select formation pathways to these structures from Titan's existing or postulated gas-phase species, reactions that are also relevant for other astrophysical environments, are discussed. By characterizing C4H4N isomers, we have identified energetically stable anionic, radical, and cationic structures that may be present in Titan's atmosphere and dark molecular clouds.
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Affiliation(s)
- Josie Hendrix
- Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Partha P Bera
- NASA Ames Research Center, Moffett Field, Mountain View, California 94035, United States.,Bay Area Environmental Research Institute, Moffett Field, Mountain View, California 94952, United States
| | - Timothy J Lee
- NASA Ames Research Center, Moffett Field, Mountain View, California 94035, United States
| | - Martin Head-Gordon
- Department of Chemistry, University of California, Berkeley, California 94720, United States
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Rajamanickam S, Sah C, Mir BA, Ghosh S, Sethi G, Yadav V, Venkataramani S, Patel BK. Bu4NI-Catalyzed, Radical-Induced Regioselective N-Alkylations and Arylations of Tetrazoles Using Organic Peroxides/Peresters. J Org Chem 2020; 85:2118-2141. [DOI: 10.1021/acs.joc.9b02875] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Suresh Rajamanickam
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
| | - Chitranjan Sah
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, Manauli, SAS Nagar 140306, India
| | - Bilal Ahmad Mir
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
| | - Subhendu Ghosh
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
| | - Garima Sethi
- School of Chemical Sciences, Department of Chemistry, Central University of Haryana, Mahendragarh, Haryana 123031, India
| | - Vinita Yadav
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
| | - Sugumar Venkataramani
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, Manauli, SAS Nagar 140306, India
| | - Bhisma K. Patel
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
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Acke G, Van Damme S, Havenith RWA, Bultinck P. Quantifying the conceptual problems associated with the isotropic NICS through analyses of its underlying density. Phys Chem Chem Phys 2019; 21:3145-3153. [DOI: 10.1039/c8cp07343k] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Despite correlations with other aromaticity descriptors, the NICS is based on fields that have no features chemists associate with aromaticity.
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Affiliation(s)
- Guillaume Acke
- Ghent Quantum Chemistry Group
- Department of Chemistry
- B-9000 Ghent
- Belgium
| | - Sofie Van Damme
- Ghent Quantum Chemistry Group
- Department of Chemistry
- B-9000 Ghent
- Belgium
| | - Remco W. A. Havenith
- Theoretical Chemistry
- Zernike Institute for Advanced Materials and Stratingh Institute for Chemistry
- University of Groningen
- Groningen
- The Netherlands
| | - Patrick Bultinck
- Ghent Quantum Chemistry Group
- Department of Chemistry
- B-9000 Ghent
- Belgium
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