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Feng E, Yu ZJ, Jiang H, Ma X, Nash JJ, Kenttämaa HI. Gas-Phase Reactivity of Phenylcarbyne Anions. J Am Chem Soc 2022; 144:8576-8590. [PMID: 35507319 DOI: 10.1021/jacs.1c13714] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gas-phase reactivities of the phenylcarbyne anion and its four derivatives were studied using a linear quadrupole ion trap mass spectrometer. The phenylcarbyne anions were calculated to have a triplet ground state (singlet-triplet splittings of 4-9 kcal mol-1), with the exception of the 4-cyanophenylcarbyne anion that has a singlet ground state (singlet-triplet splitting of -1.9 kcal mol-1). Only the phenylcarbyne anions with a triplet ground state react with acetone and dimethyl disulfide via radical mechanisms. On the other hand, only the phenylcarbyne anion with a singlet ground state abstracts H2O and H2C═C═O from acetic acid via electrophilic addition of the reagents to the anion. Finally, two hydroxy-substituted phenylcarbyne anions (with triplet ground states) partially tautomerize with the assistance of reagent molecules to the more stable distonic phenylcarbene anions. This occurs via abstraction of a proton from the reagent by the phenylcarbyne anion to generate a neutral (triplet) phenylcarbene and a reagent anion, which is followed by proton abstraction from the hydroxyl group of the neutral phenylcarbene by the reagent anion to generate the distonic phenylcarbene anion in an excited triplet state. Experiments performed on deuterated hydroxy-substituted phenylcarbyne anions verified the mechanism. The reactivities of the distonic phenylcarbene anions were found to be quite different from those of the phenylcarbyne anions. For example, they were found to abstract CH2 from acetonitrile, which is initiated by C-H insertion─typical singlet carbene reactivity.
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Affiliation(s)
- Erlu Feng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Zaikuan J Yu
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hanning Jiang
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Xin Ma
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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Ma X, Feng E, Jiang H, Boulos VM, Gao J, Nash JJ, Kenttämaa HI. Protonated Ground-State Singlet meta-Pyridynes React from an Excited Triplet State. J Org Chem 2021; 86:3249-3260. [PMID: 33555870 DOI: 10.1021/acs.joc.0c02594] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The gaseous 2,6-didehydropyridinium cation and its derivatives transfer a proton to reagents for which the reaction for their singlet ground states is too endothermic to be observed. These reactions occur from the lowest-energy excited triplet states, which has not been observed (or reported) for other meta-benzyne analogues. Quantum chemical calculations indicate that the (excited) triplet states are stronger Brønsted acids than their (ground) singlet states, likely due to unfavorable three-center, four-electron interactions in the singlet-state conjugate bases. The cations have substantially smaller (calculated) singlet-triplet (S-T) splittings (ranging from ca. -11 to -17 kcal mol-1) than other related meta-benzyne analogues (e.g., -23.4 kcal mol-1 for the 3,5-isomer). This is rationalized by the destabilization of the singlet states (relative to the triplet states) by reduced (spatial) overlap of the nonbonding molecular orbitals due to the presence of the nitrogen atom between the radical sites (making the ring more rigid). Both the singlet and triplet states are believed to be generated upon formation of these biradicals via energetic collisions due to their small S-T splittings. It appears that once the triplet states are formed, the rate of proton transfer is faster than the rate of intersystem crossing unless the biradicals contain heavy atoms.
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Affiliation(s)
- Xin Ma
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Erlu Feng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hanning Jiang
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Victoria M Boulos
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Jinshan Gao
- Department of Chemistry and Biochemistry, Center for Quantitative Obesity Research, Montclair State University, 1 Normal Avenue, Montclair, New Jersey 07043, United States
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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Ma X, Jin C, Wang D, Nash JJ, Kenttämaa HI. Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects. Chemistry 2019; 25:6355-6361. [PMID: 30811712 DOI: 10.1002/chem.201806106] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Revised: 02/24/2019] [Indexed: 01/22/2023]
Affiliation(s)
- Xin Ma
- Department of ChemistryPurdue University 560 Oval Drive West Lafayette Indiana 47907 USA
| | - Chunfen Jin
- Department of ChemistryPurdue University 560 Oval Drive West Lafayette Indiana 47907 USA
| | - Duanda Wang
- Department of ChemistryPurdue University 560 Oval Drive West Lafayette Indiana 47907 USA
| | - John J. Nash
- Department of ChemistryPurdue University 560 Oval Drive West Lafayette Indiana 47907 USA
| | - Hilkka I. Kenttämaa
- Department of ChemistryPurdue University 560 Oval Drive West Lafayette Indiana 47907 USA
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