Structure of radicals produced by γ-radiolysis. Part 5. Radicals derived from some aliphatic alkene molecules

Linder, Ron E.; Winters, Dwight; Ling, A. Campbell

doi:10.1139/v76-201

Cited by 21 publications

(4 citation statements)

References 3 publications

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“…This is reminiscent of the 14.4 G splitting observed for the spectra of neutral allyl radicals obtained from olefins in Freon matrices, , where the small difference of ca. 0.8 G between the α-couplings from unsubstituted exo - and endo -1,3-hydrogens is typically not resolved.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic and Computational Studies on the Rearrangement of Ionized [1.1.1]Propellane and Some of its Valence Isomers: The Key Role of Vibronic Coupling

et al. 2010

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, generated by radiolytic oxidation of the parent compound in argon and Freon matrices at low temperatures, undergoes a spontaneous rearrangement to form the distonic 1,1-dimethyleneallene (or 2-vinylideneallyl) radical cation 3•+ consisting of an allyl radical substituted at the 2-position by a vinyl cation. In similar matrix studies, it is found that the isomeric dimethylenecyclopropane radical cation 2•+ also rearranges to 3 •+ . The unusual molecular and electronic structure of 3•+ has been established by the results of ESR, UV-vis, and IR spectroscopic measurements in conjunction with detailed theoretical calculations. Also of particular interest is an NIR photoinduced reaction by which 3 •+ is cleanly converted to the vinylidenecyclopropane radical cation 4•+ , a process that can be represented in terms of a single electron transfer from the allyl radical to the vinyl cation followed by allyl cation cyclization. The specificity of this photochemical reaction provides additional strong chemical evidence for the structure of 3•+ . Theoretical calculations reveal the decisive role of vibronic coupling in shaping the potential energy surfaces on which the observed ring-opening reactions take place. Thus vibronic interaction in 1•+ mixes the 2 A 1 ′ ground state, characterized by its "non-bonding" 3a 1 ′ SOMO, with the 2 E′′ first excited state resulting in the destabilization of a lateral C-C bond and the initial formation of the methylenebicyclobutyl radical cation 5•+ . The further rearrangement of 5 •+ to 3 •+ occurs via 2 •+ and proceeds through two additional lateral C-C bond cleavages characterized by transition states of extremely low energy, thereby explaining the absence of identifiable intermediates along the reaction pathway. In these consecutive ring-opening rearrangements, the "non-bonding" bridgehead C-C bond in 1•+ is conserved and ultimately transformed into a normal bond characterized by a shorter C-C bond length. This work provides strong support for the Heilbronner-Wiberg interpretation of the vibrational structure in the photoelectron spectrum of 1 in terms of vibronic coupling.

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Section: Resultsmentioning

confidence: 99%

Spectroscopic and Computational Studies on the Rearrangement of Ionized [1.1.1]Propellane and Some of its Valence Isomers: The Key Role of Vibronic Coupling

et al. 2010

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“…9). This signal consisted of an apparent six-line spectrum with a hyperfine coupling of approximately 1.7 G. The line shape and hyperfine coupling were clearly inconsistent with a signal arising from the dimethylallyl radical 13 (26). However, the four hydrogens of the methylene groups and the aldehydic hydrogen of the radical 12 would be expected to couple to the free radical to produce the observed spectrum.…”

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confidence: 92%

A formal [1,3] sigmatropic reaction involving free radical intermediates: a mechanistic investigation

Bates¹,

Ramaswamy²

1985

Can. J. Chem.

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. 63, 745 (1985).The quantitative isornerization of 2,2-bis(ethylthi0)-3,3-dimethylpent-4-en to 2.2-bis(ethy1thio)-5-methylhex-4-enal was studied over the temperature range 130-170°C. An investigation of the generality and specific mechanism of this formal [I ,3] sigmatropic shift was conducted with six related compounds. The rearrangements were found to obey first-order kinetics, and on the basis of significant positive entropies of activation (52-106 J deg-I mol-I), crossover and trapping experiments, and the lack of a solvent effect (decane vs. DMF), an intermolecular, free-radical chain pathway has been proposed for the isomerization. During the rearrangement of several of the compounds esr signals were observed that were consistent with the presence of the proposed free-radical intermediates. These esr signals have been computer simulated. GORDON S. BATES et S. RAMASWAMY. Can. J . Chem. 63, 745 (1985).OpCrant a des tempCratures allant de 130 170°C, on a CtudiC I'isomCrization quantitative du bis(Cthylthi0)-2,2 dimethyl-3,3 pentkne-4 al en bis(Cthy1thio)-2,2 mCthyl-5 hexknc-4 al. Utilisant six composCs apparent&, on a dCterminC la gCnCralitC et le mCcanisme spCcifique de cette transposition qui est, d'un point de vue formel, du type sigrnatropique [I ,3]. On a trouvC que la cinCtique de ces transpositions est du premier ordre et, sur la base d'entropies d'activation qui sont assez positives (52-106 J deg-' mol-I), d'expkriences d'echanges et de piegeages ainsi que sur Ic fait qu'il n'y a pratiquement pas d'effet de solvant (dCcane vs. DMF), on suggkre que cettc isomCrisation sc produit par le biais d'un proccssus radicalaire intermolCculaire. Au cours des transpositions de plusieurs cornposCs, on a pu observer des signaux de rpe qui sont en accord avec la presence des interrnkdiaires radicalaires proposCs. Utilisant un ordinateur, on a simule ces signaux de rpc.[Traduit par le journal]Although the chemical literature contains many examples of [1,3] alkyl shifts in cyclic systems, their occurrence in acyclic analogues is relatively rare (1). Cookson and Kemp (2) have reported a benzyl migration in the thermal conversion of 3,3-dicyano-2-methyl-4-phenylpent-1 -ene to 1,l-dicyano-2-methyl-4-phenylpent-1-ene which occurs with retention of configuration. Baldwin et al. have evidence for the presence of a radical pathway in the [1,3] sigmatropic rearrangements of a number of systems (3). More recently, Ollis and coworkers (4) have reported rearrangements of various dimethylaminobutenes that again can formally be regarded as [1,3] alkyl shifts. These authors speculate that, although a stereoselective transformation involving a concerted pathway is a likely possibility in the case of several of the compounds, a process involving a weakly interacting radical pair is not unlikely.We recently observed2 a high yielding3 thermal rearrangement of 2,2-bis(ethylthi0)-3,3-dimethylpent-4-enal 1 into compound 2. This rearrangement, which is an example of a [1,3] carbon-carbon shift in an acyclic system, should be favoured si...

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“…Because of its unique reactivity of taking part in a series of free radical reactions, NO attracts interest among theoretical physicists and chemists, and reaction mechanisms of a variety of free radicals like CH 3 O 2 [2], OBrO [3], CH 3 S [4], C 2 (a 3 Π u ) [5], NCS [6], CH 3 [7,8], H 2 [9], XCO (X=H,F,Cl) [10], and NH(D) [11] with NO have been reported. C 3 H 5 , which is isomeric with allyl and glyceryl, plays an important role in combustion processes, photochemistry and interstellar chemistry [12,13]. C 3 H 5 • has three isomers: allyl, 1-propenyl, and 2-propenyl.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

Cheng

Zhao

et al. 2008

Chinese Journal of Chemical Physics

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The reaction system of 1-propenyl radical with NO is an ideal model for studying the intermolecular and intramolecular reactions of complex organic free radicals containing C=C double bonds. On the basis of the full optimization of all species with the Gaussian 98 package at the B3LYP/6-311++G * * level, the reaction mechanism was elucidated extensively using the vibrational mode analysis. There are seven reaction pathways and five sets of small molecule end products: CH 2 O+CH 3 CN, CH 2 CHCN+H 2 O, CH 3 CHO+HCN, CH 3 CHO+HNC, and CH 3 CCH+HNO. The channel of C 3 H 5 •+NO→ IM1→TS1→IM2→TS2→IM3→TS3→CH 3 CHO+HCN is thermodynamically most favorable.

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Structure of radicals produced by γ-radiolysis. Part 5. Radicals derived from some aliphatic alkene molecules

Cited by 21 publications

References 3 publications

Spectroscopic and Computational Studies on the Rearrangement of Ionized [1.1.1]Propellane and Some of its Valence Isomers: The Key Role of Vibronic Coupling

Spectroscopic and Computational Studies on the Rearrangement of Ionized [1.1.1]Propellane and Some of its Valence Isomers: The Key Role of Vibronic Coupling

A formal [1,3] sigmatropic reaction involving free radical intermediates: a mechanistic investigation

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

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