1
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Vu K, Pandian J, Zhang B, Annas C, Parker AJ, Mancini JS, Wang EB, Saldana-Greco D, Nelson ES, Springsted G, Lischka H, Plasser F, Parish CA. Multireference Averaged Quadratic Coupled Cluster (MR-AQCC) Study of the Geometries and Energies for ortho-, meta- and para-Benzyne. J Phys Chem A 2024. [PMID: 39240216 DOI: 10.1021/acs.jpca.4c04099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2024]
Abstract
The diradical benzyne isomers are excellent prototypes for evaluating the ability of an electronic structure method to describe static and dynamic correlation. The benzyne isomers are also interesting molecules with which to study the fundamentals of through-space and through-bond diradical coupling that is important in so many electronic device applications. In the current study, we utilize the multireference methods MC-SCF, MR-CISD, MR-CISD+Q, and MR-AQCC with an (8,8) complete active space that includes the σ, σ*, π and π* orbitals, to characterize the electronic structure of ortho-, meta- and para-benzyne. We also determine the adiabatic and vertical singlet-triplet splittings for these isomers. MR-AQCC and MR-CISD+Q produced energy gaps in good agreement with previously obtained experimental values. Geometries, orbital energies and unpaired electron densities show significant through-space coupling in the o- and m-benzynes, while p-benzyne shows through-bond coupling, explaining the dramatically different singlet-triplet gaps between the three isomers.
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Affiliation(s)
- Khanh Vu
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Joshua Pandian
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Boyi Zhang
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Christina Annas
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Anna J Parker
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - John S Mancini
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Evan B Wang
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Diomedes Saldana-Greco
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Emily S Nelson
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Greg Springsted
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Hans Lischka
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
| | - Felix Plasser
- Department of Chemistry, Loughborough University, Ashby Road, Loughborough LE11 3TU, Leicestershire, U.K
| | - Carol A Parish
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
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2
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Hu H, Zhang B, Luxon A, Scott T, Wang B, Parish CA. An Extended Multireference Study of the Singlet and Triplet States of the 9,10-didehydroanthracene Diradical. J Phys Chem A 2018; 122:3688-3696. [DOI: 10.1021/acs.jpca.8b01233] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hui Hu
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Boyi Zhang
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Adam Luxon
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Thais Scott
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
| | - Baoshan Wang
- College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei Province 430072, P.R. China
| | - Carol A. Parish
- Department of Chemistry, Gottwald Center for the Sciences, University of Richmond, Richmond, Virginia 23173, United States
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3
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Yang Y, Peng D, Davidson ER, Yang W. Singlet–Triplet Energy Gaps for Diradicals from Particle–Particle Random Phase Approximation. J Phys Chem A 2015; 119:4923-32. [DOI: 10.1021/jp512727a] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
| | | | - Ernest R. Davidson
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Weitao Yang
- Key
Laboratory of Theoretical Chemistry of Environment, Ministry of Education,
School of Chemistry and Environment, South China Normal University, Guangzhou 510006, China
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Wittrig AM, Archibold EF, Sheng H, Nash JJ, Kenttämaa HI. Polar Effects Control the Gas-phase Reactivity of Charged para-Benzyne Analogs. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 377:39-43. [PMID: 25838787 PMCID: PMC4378589 DOI: 10.1016/j.ijms.2014.04.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The gas-phase reactivity of charged para-benzynes is entirely unexplored as they and/or their precursors tend to undergo ring-opening upon their generation. We report here a gas-phase reactivity study of two such benzynes, the 2,5-didehydropyridinium and 5,8-didehydroisoquinolinium cations, generated in a modified dual-linear quadrupole ion trap (DLQIT) mass spectrometer. Both biradicals were found to form diagnostic products with organic molecules, indicating the presence of two radical sites. As opposed to earlier predictions that the singlet-triplet (S-T) splitting controls the radical reactivity of such species, the 2,5-didehydropyridinium cation reacts much faster in spite of its larger S-T splitting. Calculated vertical electron affinities of the radical sites of the para-benzynes, a parameter related to the polarity of the transition states of their reactions, appears to be the most important reactivity controlling factor.
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Affiliation(s)
- Ashley M. Wittrig
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Enada F. Archibold
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Huaming Sheng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - John J. Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Hilkka I. Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
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5
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Ramos-Cordoba E, Salvador P. Diradical character from the local spin analysis. Phys Chem Chem Phys 2014; 16:9565-71. [DOI: 10.1039/c4cp00939h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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6
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Kirkpatrick LM, Vinueza NR, Jankiewicz BJ, Gallardo VA, Archibold EF, Nash JJ, Kenttämaa HI. Experimental and computational studies on the formation of three para-benzyne analogues in the gas phase. Chemistry 2013; 19:9022-33. [PMID: 23703949 DOI: 10.1002/chem.201203264] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Revised: 02/26/2013] [Indexed: 11/11/2022]
Abstract
Experimental and computational studies on the formation of three gaseous, positively-charged para-benzyne analogues in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer are reported. The structures of the cations were examined by isolating them and allowing them to react with various neutral reagents whose reactions with aromatic carbon-centered σ-type mono- and biradicals are well understood. Cleavage of two iodine-carbon bonds in N-deuterated 1,4-diiodoisoquinolinium cation by collision-activated dissociation (CAD) produced a long-lived cation that showed nonradical reactivity, which was unexpected for a para-benzyne. However, the reactivity closely resembles that of an isomeric enediyne, N-deuterated 2-ethynylbenzonitrilium cation. A theoretical study on possible rearrangement reactions occurring during CAD revealed that the cation formed upon the first iodine atom loss undergoes ring-opening before the second iodine atom loss to form an enediyne instead of a para-benzyne. Similar results were obtained for the 5,8-didehydroisoquinolinium cation and the 2,5-didehydropyridinium cation. The findings for the 5,8-didehydroisoquinolinium cation are in contradiction with an earlier report on this cation. The cation described in the literature was regenerated by using the literature method and demonstrated to be the isomeric 5,7-didehydro-isoquinolinium cation and not the expected 5,8-isomer.
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Affiliation(s)
- Lindsey M Kirkpatrick
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA
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7
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Ramos-Cordoba E, Matito E, Salvador P, Mayer I. Local spins: improved Hilbert-space analysis. Phys Chem Chem Phys 2012; 14:15291-8. [DOI: 10.1039/c2cp42513k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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8
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Dong H, Chen BZ, Huang MB, Lindh R. The bergman cyclizations of the enediyne and its N-substituted analogs using multiconfigurational second-order perturbation theory. J Comput Chem 2011; 33:537-49. [DOI: 10.1002/jcc.22889] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 09/15/2011] [Accepted: 10/18/2011] [Indexed: 11/06/2022]
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9
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Epifanovsky E, Krylov AI. Direct location of the minimum point on intersection seams of potential energy surfaces with equation-of-motion coupled-cluster methods. Mol Phys 2010. [DOI: 10.1080/00268970701549397] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Abstract
There is experimental evidence that intermediate ortho-benzynes can be made by intramolecular [2 + 4] cycloaddition of a 1,3-diyne with an alkyne. Computations by several groups support a concerted mechanism for the cycloaddition of butadiyne with acetylene. High temperature benzyne cycloreversion has also been demonstrated experimentally; this may in fact be a common reaction in hydrocarbon fuel combustion. Following leads from earlier pyrolysis experiments, herein we predict that cycloaddition of benzyne with butadiyne can proceed by a stepwise mechanism to 2,3-naphthyne. However, a slightly lower energy path leads to a benzocyclobutadiene. ortho-Benzyne can be generated by solution-phase and solid-phase reaction in a microwave reactor. We have developed the method of microwave flash pyrolysis (MFP) for high temperature solid-phase microwave reactions. MFP reaction of phthalic anhydride, a classic benzyne precursor, results in a typical suite of products expected from a relatively high concentration of benzyne.
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Polukhtine A, Karpov G, Pandithavidana DR, Kuzmin A, Popik VV. Photochemical Triggering of the Bergman and Myers - Saito Cyclizations. Aust J Chem 2010. [DOI: 10.1071/ch10185] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Two strategies for the photochemical generation of reactive enediyne compounds and their subsequent cycloaromatization to p-benzyne or α,3-didehydrotoluene derivatives are discussed in this account. The first method employs a photo-Wolff reaction of stable 11- or 12-membered ring precursor enediynes containing the 2-diazo-1,3-diketone moiety. Irradiation of these compounds results in ring contraction and the formation of two isomeric enediynes possessing an enolized β-ketoester fragment. One of the isomers undergoes the conventional Bergman cyclization, whereas the other isomerizes into the enyne-allene tautomer, which rapidly cyclizes via a Myers–Saito mechanism. The second strategy consists of replacing the triple bond in a cyclic enediyne or enyne-allene structure with a cyclopropenone group, rendering them thermally stable. Photolysis of cyclopropenones results in efficient decarbonylation and the regeneration of a triple bond, restoring the enediyne π-system. The generation of reactive enediynes by non-resonant two-photon excitation using wavelengths within a ‘phototherapeutic window’ was also demonstrated. Photogenerated enediynes show significant nuclease activity, efficiently inducing single-strand dDNA cleavage.
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Pandithavidana DR, Poloukhtine A, Popik VV. Photochemical generation and reversible cycloaromatization of a nine-membered ring cyclic enediyne. J Am Chem Soc 2009; 131:351-6. [PMID: 19053819 DOI: 10.1021/ja8077076] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Irradiation of the nine-membered ring enediyne precursor, which has one of its triple bonds masked as cyclopropenone, efficiently (Phi = 0.34) generates the reactive 4,5-benzocyclonona-2,6-diynol. The latter rapidly equilibrates with the corresponding 1,4-didehydronaphthalene diradical and then undergoes rate-limiting hydrogen abstraction to produce the ultimate product of the Bergman cyclization, benz[f]indanol.
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13
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Wang EB, Parish CA, Lischka H. An extended multireference study of the electronic states of para-benzyne. J Chem Phys 2008; 129:044306. [DOI: 10.1063/1.2955744] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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14
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The S1 states of o-, m-, and p-benzyne studied using multiconfiguration second-order perturbation theory. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.10.095] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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15
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Tandem coupling reactions of benzynes and 1,3-diones: a novel synthesis of 2,2-diphenyl-1,3-diones. Tetrahedron Lett 2007. [DOI: 10.1016/j.tetlet.2007.09.092] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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16
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Nash JJ, Kenttämaa HI, Cramer CJ. Quantum chemical characterization of the vertical electron affinities of didehydroquinolinium and didehydroisoquinolinium cations. J Phys Chem A 2007; 110:10309-15. [PMID: 16928123 DOI: 10.1021/jp062857+] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Vertical electron affinities (EA) are predicted for the lowest energy singlet states of the 21 didehydroquinolinium cation isomers and the 21 didehydroisoquinolinium cation isomers, as well as the doublet states of the seven dehydroquinolinium cation isomers, the seven dehydroisoquinolinium cation isomers, the seven N-methyldehydroquinolinium cations, and the seven N-methyldehydroisoquinolinium cations, by using density functional theory. For the monoradicals, the calculated EA of the radical site depends only on the distance from the (formally charged) nitrogen atom, and is reduced by 0.14-0.24 eV when the NH+ group is replaced with an NCH3+ group. Nearly all of the calculated EAs for the ortho biradicals are lower (by 0.04-0.72 eV) than those for either of the corresponding monoradicals. For the meta biradicals, the calculated EAs lie either between the EAs of the corresponding monoradicals or higher (by 0.07-0.58 eV), and they are extremely sensitive to the separation (distance) between the two dehydrocarbon atoms. For the biradicals that do not have either an ortho or meta relationship the calculated EAs are all higher (by 0.02-1.93 eV) than those for either of the corresponding monoradicals. The EAs are examined to gain insight into the nature of inductive/field and resonance effects that influence the electrophilicity of the radical site(s), which is a major factor controlling the reactivity of these types of (bi)radicals.
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Affiliation(s)
- John J Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
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17
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Nash JJ, Nizzi KE, Adeuya A, Yurkovich MJ, Cramer CJ, Kenttämaa HI. Demonstration of Tunable Reactivity for meta-Benzynes. J Am Chem Soc 2005; 127:5760-1. [PMID: 15839653 DOI: 10.1021/ja0449473] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A combined computational and experimental study on the gas-phase structures and reactivities of charged 1,3-didehydroarenes (meta-benzynes) demonstrates that the reactivity of such biradicals can be "tuned" by using appropriate substituents. Substituents that destabilize a specific zwitterionic resonance structure can change the reactivity of the biradical from mildly carbocationic to radical-like. These substituent effects are not the result of changes in the singlet-triplet gaps of the biradicals, but rather reflect changes in the potential energy surfaces for the dehydrocarbon separation.
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Affiliation(s)
- John J Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
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18
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Hernández-Trujillo J, García-Cruz I, Martínez-Magadán JM. Topological analysis of the electron density and of the electron localization function of pyrene and its radicals. Chem Phys 2005. [DOI: 10.1016/j.chemphys.2004.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Nath M, Pink M, Zaleski JM. Controlling Both Ground- and Excited-State Thermal Barriers to Bergman Cyclization with Alkyne Termini Substitution. J Am Chem Soc 2004; 127:478-9. [PMID: 15643844 DOI: 10.1021/ja045979t] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The cross-coupling reaction of 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with corresponding organostannanes in the presence of a Pd0 catalyst in THF at reflux temperature yields free base 2,3-dialkynylporphyrins 1a,c-e. The subsequent deprotection of trimethylsilyl group of 1a with TBAF in THF under aqueous conditions produces the 2,3-diethynyl-5,10,15,20-tetraphenylporphyrins 1b in 87% yield. Compounds 1a-d undergo zinc insertion upon treatment with Zn(OAc)2.2H2O in CHCl3/MeOH to give zinc(II) 2,3-dialkynyl-5,10,15,20-tetraphenylporphyrins (2a-d) in 70-92% yields. Thermal Bergman cyclization of 1a-e and 2a-d was studied in chlorobenzene and approximately 35-fold 1,4-cyclohexadiene at 120-210 degrees C. Compounds 1b and 2b with R = H react at lower temperature (120 degrees C) and produce cyclized products 3b and 4b in higher yields (65-70%) than their propyl, isopropyl, and phenyl analogues, with R = Ph being the most stable. Continuing in this trend, the -TMS derivatives 1a and 2a exhibit no reactivity even after heating at 190 degrees C in chlorobenzene/CHD for 24 h. Photolysis (at lambda >/= 395 nm) of 1b and 2b at 10 degrees C leads the formation of isolable picenoporphyrin products in 15 and 35% yields, respectively, in 72 h, whereas these compounds are stable in solution under same reaction conditions at 25 degrees C in the dark. Unlike thermolysis at 125 degrees C, which did not yield Bergman cyclized product for R = Ph, photolysis generated very small amounts of picenoporphyrin products (3c: 5%; 4c: 8% based on 1H NMR) as well as a mixture of reduced porphyrin products that were not separable. Thus, trends in the barrier to Bergman cyclization in the excited state exhibit the same trend as those observed in the ground state as a function of R-group. Finally, photolysis of 2b at 10 degrees C with lambda >/= 515 or 590 nm in benzene/iPrOH (4:1, 72 h) produces 4b in 15 and 6% isolated yields, indicating that conjugation of the enediyne unit into the porphyrin electronic transitions leads to sufficient distortion to generate photoproduct even with long wavelength excitation.
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Affiliation(s)
- Mahendra Nath
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA
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Tichy SE, Nelson ED, Amegayibor FS, Kenttämaa HI. Gas-Phase Reactivity of Charged π-Type Biradicals. J Am Chem Soc 2004; 126:12957-67. [PMID: 15469293 DOI: 10.1021/ja049534g] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Four pi,pi-biradicals, 2,6-dimethylenepyridinium and the novel isomers N-(3-methylenephenyl)-3-methylenepyridinium, N-phenyl-3,5-dimethylenepyridinium, and N-(3,5-dimethylenephenyl)pyridinium ions, were generated and structurally characterized in a Fourier transform ion cyclotron resonance mass spectrometer. Their gas-phase reactivity toward various reagents was compared to that of the corresponding monoradicals, 2-methylenepyridinium, N-phenyl-3-methylenepyridinium, and N-(3-methylenephenyl)pyridinium ions. The biradicals reactivity was found to reflect their predicted multiplicity. The 2,6-dimethylenepyridinium ion, the only biradical in this study predicted to have a closed-shell singlet ground state, reacts significantly faster than the other biradicals, which are predicted to have triplet ground states. In fact, this biradical reacts at a higher rate than the analogous monoradical, which suggests that to avoid the costly uncoupling of its unpaired electrons, the biradical favors ionic mechanisms over barriered radical pathways. In contrast, the second-order reaction rate constants of the isomeric biradicals with triplet ground states are well approximated by those of the analogous monoradicals, although the final reaction products are sometimes different. This difference arises from rapid radical-radical recombination of the initial monoradical reaction products. The overall reactivity toward the hydrogen-atom donors benzeneselenol and tributylgermanium hydride is significantly greater for the radicals with the charged site in the same ring system as the radical site. This finding indicates that polar effects play an important role in controlling the reactivity of pi,pi-biradicals, just as has been demonstrated for sigma,sigma-biradicals.
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Affiliation(s)
- Shane E Tichy
- Contribution from the Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, USA
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21
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Liu H, Zhang X, Wang C, Guo W, Wu Y, Yang S. Effects of Aromatic Substitutions on the Photoreactions in Mg•+(C6HnF2X4-n) (X = F, CH3) Complexes: Formation and Decomposition of Benzyne Radical Cations. J Phys Chem A 2004. [DOI: 10.1021/jp037535+] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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22
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Maurin P, Ibrahim-Ouali M, Parrain JL, Santelli M. Structure of substituted o-benzynes and their cycloaddition to ketene dialkyl acetals. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s0166-1280(03)00412-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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23
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Clark AE, Davidson ER. p-Benzyne derivatives that have exceptionally small singlet-triplet gaps and even a triplet ground state. J Org Chem 2003; 68:3387-96. [PMID: 12713336 DOI: 10.1021/jo026824b] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In an effort to find a p-benzyne (1,4-didehydrobenzene) derivative with a triplet ground state, we have investigated tetrasubstitution by -F, -NH(2), -CH(3), and -NO(2) groups. These were predicted to reduce the singlet-triplet gap, but none led to a triplet ground state because of unexpected destabilization of one of the radical orbitals. This effect is likely the result of rehybridization of the substituted C atom, which has been observed for substituted benzene and perturbs the side sigma and sigma* orbital energies of the phenyl ring. The role of substituent rotation on the energy difference between the two nominally singly occupied orbitals (S and A) was then investigated. The energy of the A radical orbital was found to be much more sensitive to perturbations within the sigma C[bond]C framework than the S MO. Consequently, we believe that rehybridization of the ring carbons destabilizes the A radical orbital and can lead to large singlet-triplet splittings. To test this hypothesis, calculations on a p-benzyne with 2,6 substitution by oxygen were performed. Interestingly, a triplet ground state was predicted. Yet, examination of the geometry and wave function showed that 2,6-quinone p-benzyne is a very twisted molecule with a C3-C4-C5 allene linkage and a C1 triplet carbene center.
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Affiliation(s)
- Aurora E Clark
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA
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Mohler DL, Gray Coonce J, Predecki D. Photoinduced DNA cleavage by benzenediradical equivalents. 1,3- and 1,4-bis(dicarbonylcyclopentadienyliron)benzene. Bioorg Med Chem Lett 2003; 13:1377-9. [PMID: 12657286 DOI: 10.1016/s0960-894x(03)00097-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Upon photolysis, diiron complexes 1,4- and 1,3-Fp(2)C(6)H(4) (1 and 2) linearize plasmid DNA at ratios as low as 1.5 and 3.0 molecules/bp DNA, respectively. Additionally, single-strand cleavage was observed at ratios higher than 0.05 and 0.19 molecules/bp DNA for 1 and 2, respectively. Radical scavenging studies and metal radical control experiments implicate carbon-centered radicals as participants in the cleavage pathway.
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Affiliation(s)
- Debra L Mohler
- Department of Chemistry, Emory University, Atlanta, GA 30322, USA.
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Clark AE, Davidson ER. Local Spin III: Wave Function Analysis along a Reaction Coordinate, H Atom Abstraction, and Addition Processes of Benzyne. J Phys Chem A 2002. [DOI: 10.1021/jp020992q] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Aurora E. Clark
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102
| | - Ernest R. Davidson
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102
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