Photochemical isomerization of cyclobutene radical cation to 1,3-butadiene radical cation. A "nonelectrocyclic" ring-opening reaction?

Aebischer, Jean-Nicolas; Bally, Thomas; Roth, K.; Haselbach, Edwin; Gerson, Fabian; Qin, Xue-Zhi

doi:10.1021/ja00202a035

Cited by 50 publications

(28 citation statements)

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“…[3] Matrix isolation studies showed that for the analogous ring opening of the cyclobutene radical cation 1 · + , the reaction proceeds directly to the s-trans-1,3-butadiene 3 · + , without forming the s-cis isomer first. [11] As shown in Figure 2, this is due to the lack of correlation between the electronic states of 1 · + , which has a 2 B 1 ground state, and 2 · + , which has a 2 A 2 ground state. Consequently, there is no symmetrypreserving pathway for the radical cation to form 2 · + .…”

Section: The Conservation Of Orbital Symmetrymentioning

confidence: 99%

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

Donoghue¹,

Wiest²

2006

Chemistry A European J

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Electron transfer is the simplest reaction possible, yet it has a profound impact on the structure and reactivity of organic compounds. These changes allow a new look at some of the fundamental concepts that are used to explain organic chemistry, such as symmetry, aromaticity, and bonding. The results from high-level electronic structure calculations are used to analyze the mechanistic differences in the pericyclic reactions of simple hydrocarbons and their radical cation counterparts. The importance of state symmetry correlation, Jahn-Teller distortions, delocalization, and fractional bonding for the reaction pathways of hydrocarbon radical cations is discussed.

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Section: The Conservation Of Orbital Symmetrymentioning

confidence: 99%

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

Donoghue¹,

Wiest²

2006

Chemistry A European J

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“…[16] However, experimental studies did not produce conclusive evidence about the mechanism of the reaction. [15f,15g] In the matrix, the parent cyclobutene radical cation was observed to yield trans-butadiene, [17] and a product study of the substituted cis-3,4-diphenylcylobutene radical cation led the authors to conclude a conrotatory pathway. [15e] Measurement of activation energies gave contradictory results.…”

Section: Electrocyclic Reactions: the Ring-opening Of Cyclobutene Radmentioning

confidence: 99%

“…[17] Starting from the C 2v -symmetric cyclobutene radical cation, only a conrotatory pathway connects the ground states of cyclobutene 1 •؉ and trans-butadiene 2 •؉ . Any other symmetry-conserving pathway would result in an excited state.…”

Section: Electrocyclic Reactions: the Ring-opening Of Cyclobutene Radmentioning

confidence: 99%

Pericyclic Reactions of Radical Cations

Saettel¹,

Oxgaard²,

Wiest³

2001

Eur. J. Org. Chem.

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“…, it is noteworthy that the b-protons of the two Me substituents at C(1) and C(6) have slightly different coupling constants. Such a finding is often encountered with formally equivalent b-protons of radical cations in Freon matrices [6] [7] [14] and points to small deviations from planarity caused by the solid medium. A passable reference for the diene 4d .…”

Section: Scheme 2 Schemementioning

confidence: 88%

Influence of Ring Annelation on the Mode Selectivity of the Ionized Diazabicycloheptenes and Corresponding Housanes: An ESR and ENDOR Study

Gerson

Şahin

2001

HCA

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Dedicated to Professor Edgar Heilbronner on the occasion of his 80th birthdayThe tricyclic azoalkanes, (1a,4a,4aa,7aa)-4,4a,5,6,7,7a-hexahydro-1,4,8,8-tetramethyl-1,4-methano-1H-cyclopenta[d]pyridazine (1c), (1a,4a,4aa,6aa)-4,4a,5,6,6a-pentahydro-1,4,7,7-tetramethyl-1,4-methano-1H-cyclobuta[d]pyridazine (1d), (1a,4a,4aa,6aa)-4,4a,6a-trihydro-1,4,7,7-tetramethyl-1,4-methano-1H-cyclobuta[d]-pyridazine (1e), and (1a,4a,4aa,5aa)-4,4a,5,5a-tetrahydro-1,4,6,6-tetramethyl-1,4-methano-1H-cyclopropa[d]-pyridazine (1f), as well as the corresponding housanes, the 2,3,3,4-tetramethyl-substituted tricyclo[3.3.0.0 2,4 ]octane (2c), tricyclo[3.2.0.0 2,4 ]heptane (2d), and tricyclo[3.2.0.0 2,4 ]hept-6-ene (2e), were subjected to g-irradiation in Freon matrices. The reaction products were identified with the use of ESR and, in part, ENDOR spectroscopy. As expected, the strain on the C-framework increases on going from the cyclopentane-annelated azoalkanes and housanes (1c and 2c) to those annelated by cyclobutane (1d and 2d), by cyclobutene (1e and 2e), and by cyclopropane (1f). Accordingly, the products obtained from 1c and 2c in all three Freons used, CFCl 3 , CF 3 CCl 3 , and CF 2 ClCFCl 2 , were the radical cations 3c . and 2c . of 2,3,4,4-tetramethylbicyclo[3.3.0]oct-2-ene and 2,3,3,4-tetramethylbicyclo[3.3.0]octane-2,4-diyl, respectively. In CFCl 3 and CF 3 CCl 3 matrices, 1d and 2d yielded analogous products, namely the radical cations 3d . and 2d . of 2,3,4,4-tetramethylbicyclo[3.2.0]hept-2-ene and 2,3,3,4-tetramethylbicyclo[3.2.0]heptane-2,4-diyl. The radical cations 3c . and 3d . and 2c . and 2d . correspond to their non-annelated counterparts 3a . and 3b . , and 2a . and 2b . generated previously under the same conditions from 2,3-diazabicyclo[2.2.1]hept-2-ene (1a) and bicyclo[2.1.0]pentane (2a), as well as from their 1,4-dimethyl derivatives (1b and 2b). However, in a CF 2 ClCFCl 2 matrix, both 1d and 2d gave the radical cation 4d . of 2,3,3,4-tetramethylcyclohepta-1,4-diene. Starting from 1e and 2e, the radical cations 4e . and 4e' . of the isomeric 1,2,7,7-and 1,6,7,7-tetramethylcyclohepta-1,3,5-trienes appeared as the corresponding products, while 1f was converted into the radical cation 4f . of 1,5,6,6-tetramethylcyclohexa-1,4-diene which readily lost a proton to yield the corresponding cyclohexadienyl radical 4f . . Reaction mechanisms leading to the pertinent radical cations are discussed.Introduction. ± In a previous work, ionization of 2,3-diazabicyclo[2.2.1]hept-2-ene (1a) and the corresponding bicyclo[2.1.0]pentane (housane; 2a), as well as of their 1,4-dimethyl derivatives 1b and 2b, respectively, was carried out by g-irradiation in Freon matrices, and the resulting radical cations were studied by ESR spectroscopy [1]. Whereas the azoalkanes 1a and 1b yielded the radical cations of cyclopentene (3a) and its 1,3-dimethyl derivative 3b, respectively, cyclopentane-1,3-diyl radical cations were obtained by starting from the corresponding housanes 2a and 2b (Scheme 1).Despite a considerable weakening of the cent...

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Photochemical isomerization of cyclobutene radical cation to 1,3-butadiene radical cation. A "nonelectrocyclic" ring-opening reaction?

Cited by 50 publications

References 0 publications

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

Pericyclic Reactions of Radical Cations

Influence of Ring Annelation on the Mode Selectivity of the Ionized Diazabicycloheptenes and Corresponding Housanes: An ESR and ENDOR Study

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