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Saha PK, Mallick A, Turley AT, Bismillah AN, Danos A, Monkman AP, Avestro AJ, Yufit DS, McGonigal PR. Rupturing aromaticity by periphery overcrowding. Nat Chem 2023; 15:516-525. [PMID: 36879076 PMCID: PMC10070187 DOI: 10.1038/s41557-023-01149-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 01/26/2023] [Indexed: 03/08/2023]
Abstract
The balance between strain relief and aromatic stabilization dictates the form and function of non-planar π-aromatics. Overcrowded systems are known to undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. In this study we incremented the strain energy of an aromatic system beyond its aromatic stabilization energy, causing it to rearrange and its aromaticity to be ruptured. We noted that increasing the steric bulk around the periphery of π-extended tropylium rings leads them to deviate from planarity to form contorted conformations in which aromatic stabilization and strain are close in energy. Under increasing strain, the aromatic π-electron delocalization of the system is broken, leading to the formation of a non-aromatic, bicyclic analogue referred to as 'Dewar tropylium'. The aromatic and non-aromatic isomers have been found to exist in rapid equilibrium with one another. This investigation demarcates the extent of steric deformation tolerated by an aromatic carbocycle and thus provides direct experimental insights into the fundamental nature of aromaticity.
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Affiliation(s)
| | | | | | | | - Andrew Danos
- Department of Physics, Durham University, Durham, UK
| | | | | | | | - Paul R McGonigal
- Department of Chemistry, Durham University, Durham, UK.
- Department of Chemistry, University of York, York, UK.
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Affiliation(s)
- Susannah C. Coote
- Department of Chemistry; Lancaster University; Bailrigg Lancaster LA1 4YB UK
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Hogeveen H, Gaasbeek CJ. Photochemically induced conversion of tropylium ion into 7-norbornadienyl ion: (Short communication). ACTA ACUST UNITED AC 2010. [DOI: 10.1002/recl.19700891010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Li H, Ren K, Neckers DC. Photochemical reactions of substituted cyclopropenium salts. J Org Chem 2001; 66:8556-62. [PMID: 11735538 DOI: 10.1021/jo0108562] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Photochemical reactions of triphenylcyclopropenium tetrakis(pentafluorophenyl)gallate (TPCPGa) and diphenyl-(2-methoxy-1-naphthyl)-cyclopropenium tetrakis(pentafluorophenyl)gallate (DPMNCPGa) (Chart 1) have been investigated in acetonitrile. Traces of water were required for the photochemical reactions to proceed. The disappearance of both TPCPGa and DPMNCPGa obeys zero-order kinetics with rate constants (k) having a linear dependence on the concentration of water. Electron-transfer from water to the cyclopropenium cation is proposed as the primary process in the formation of the cyclopropenyl radical. The latter dimerizes leading to the photoproducts.
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Affiliation(s)
- H Li
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
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Li H, Ren K, Zhang W, Malpert JH, Neckers DC. A Novel Initiation System for the Cationic Polymerization of Glycidyl Phenyl Ether: Triphenylcyclopropenium Tetrakis(pentafluorophenyl)gallate/Cyclohexanone. Macromolecules 2001. [DOI: 10.1021/ma001912o] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Huiying Li
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Spectra Group Limited, Inc., 1722 Indian Wood Circle, Suite H, Maumee, Ohio 43537
| | - Kangtai Ren
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Spectra Group Limited, Inc., 1722 Indian Wood Circle, Suite H, Maumee, Ohio 43537
| | - Wenqin Zhang
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Spectra Group Limited, Inc., 1722 Indian Wood Circle, Suite H, Maumee, Ohio 43537
| | - John H. Malpert
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Spectra Group Limited, Inc., 1722 Indian Wood Circle, Suite H, Maumee, Ohio 43537
| | - Douglas C. Neckers
- Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Spectra Group Limited, Inc., 1722 Indian Wood Circle, Suite H, Maumee, Ohio 43537
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Bedlek JM, Valentino MR, Boyd MK. Substituent effects on carbocation photophysics: 9-arylxanthyl and 9-arylthioxanthyl carbocations. J Photochem Photobiol A Chem 1996. [DOI: 10.1016/1010-6030(95)04187-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Valentino MR, Boyd MK. Ether quenching of singlet excited 9-arylxanthyl cations. J Photochem Photobiol A Chem 1995. [DOI: 10.1016/1010-6030(95)04033-c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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9
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Product studies of electron transfer from dimethoxybenzene and trimethoxybenzene to photoexcited xanthenium cations in S1 in aqueous acid solution. J Photochem Photobiol A Chem 1993. [DOI: 10.1016/1010-6030(93)80172-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Sustmann R, Brandes D, Lange F, Nüchter U. Rearrangements of free radicals, XI. Sigmatropic and electrocyclic reactions of bicyclo[3.2.0]heptadienyl radicals, 3-Quadricyclanyl radicals, and 7-norbornadienyl radical. ACTA ACUST UNITED AC 1985. [DOI: 10.1002/cber.19851180907] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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The Photochemistry of Carbonium Ions. ADVANCES IN PHYSICAL ORGANIC CHEMISTRY 1973. [DOI: 10.1016/s0065-3160(08)60245-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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Dürr H. Photochemie kleiner Ringe, IX1) Direkte oderin situ-Photodimerisierung von Triphenyl-cyclopropen. European J Org Chem 1969. [DOI: 10.1002/jlac.19697230112] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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