The radical cation of bicyclobutylidene

Morihashi, Kenji; Kometani, Hiroyuki; Takahashi, Ohgi; Togo, Hideo; Kikuchi, Osamu

doi:10.1039/c39890001473

Cited by 5 publications

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“…The available ESR experimental data of alkene cation radical in the chemical literature have been generated by three major techniques: namely, oxidation methods in liquid solutions, 9,15 chemisorption with solid state defects (or modified Lewis acid sites) on pretreated H-zeolites, 7,11 and photolysis or radiolysis of alkenes in various solid matrix isolation techniques at low temperatures. 8,10,[16][17][18][19][20][21][22][23][24][25][26] Some of the radiolysis ESR work have not been resolved and their assignments of the alkene cation radical conformations are ambiguous be-cause chemical active alkene cation radicals may have different chemical pathways even in the rigid zeolitic matrix as observed by this author and his co-workers. 7,11 The steady flow mixed system in combination with transitional metal ion oxidation in liquid solutions gives well-resolved ESR spectra of alkene cation radicals, 9 and aromatic radical cation dimer with intermolecular Jahn-Teller effect, 15 but they are limited to room temperature ranges experimentally.…”

Section: Resultsmentioning

confidence: 99%

“…The molecular and electronic structures of alkene radical cations have been widely investigated both in experimental studies [16][17][18][19][20][21][22][23][24][25][26][27][28] and theoretical calculations based on various molecular orbital calculations. [29][30][31][32][33][34][35][36][37][38][39][40] Much effort has been devoted to clarifying whether olefin radical cations are planar or twisted about the olefinic C-C central bond.…”

Section: Introductionmentioning

confidence: 99%

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A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Shih

2003

J Chinese Chemical Soc

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A large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called "hyperconjugation") are estimated to be small in compared with the total energy of the molecule.We used theories of both isotropic and anisotropic proton hyperfine interactions in the p-electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non-planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn-Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non-planar structures of the open-chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line-width effect of the four methyl groups observed in the 2,3-dimethyl-2-butene cation radicals also confirmed the positive sign of the electron-proton hyperfine constant of hyper-conjugation mechanism.A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the p electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Shih

2003

J Chinese Chemical Soc

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“…Some years later, a further bicyclobutylidene with six spiroannelated cyclopropane rings, 10,10′‐bis(trispiro[2.0.2.0.2.1]decylidene) ( 5 ), was reported by us to be readily oxidized to its radical cation by electrolysis in CH 2 Cl 2 (supporting salt n Bu 4 NClO 4 ) and to exhibit a well‐defined 1 H‐hyperfine pattern 6. On the other hand, because of the presence of acidic hydrogen atoms in the allylic 2,2′,4,4′‐positions and the high ionization energy of the parent bicyclobutylidene ( 2 a ), its radical cation had to be produced by γ irradiation of 2 a in a CFCl 3 matrix 7. There are six sorts of protons31 in the radical cations of bicyclobutylidene ( 2 a ) and its derivatives 2 b and 3 – 5 (see pertinent formulae): i) Eight β protons in the 2,2′,4,4′‐positions of the bicyclobutylidene core, present in 2 a .…”

Section: Resultsmentioning

confidence: 99%

“…The observed 1 H‐coupling constants are consistent with an effective D 2h symmetry, as previously pointed out for 2 a . + 7. The apparent planar geometry of 2 a , b .…”

Section: Resultsmentioning

confidence: 99%

“…For comparison, the unsymmetrically oligospirocyclopropanated bicyclobutylidenes 6 and 7 were also prepared and their spectroscopic properties studied along with those of 3 – 5 . The ESR spectral features of the radical cations of 3 – 5 were of particular interest in comparison to those of the radical cations of the parent bicyclobutylidene ( 2 a )7 and its 2,2,2′,2′,4,4,4′,4′‐octamethyl derivative 2 b ,8 because the coupling constants of the protons at the bicyclobutylidene core sensitively respond to the introduction of spiroannelated cyclopropane rings in the neighboring positions.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, Spectroscopic, and Structural Properties of Spirocyclopropanated Bicyclobutylidenes and Their Radical Cations

et al. 2001

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The spirocyclopropanated bicyclobutylidenes 3-7 have been prepared by McMurry coupling of the corresponding spirocyclopropanated cyclobutanone (3 and 5), Staudinger-Pfenniger reaction (4), oxidative coupling of a Wittig ylide (4) or Wittig olefination of perspirocyclopropanated cyclobutanone (6 and 7). The structure of the parent 2a and the perspirocyclopropanated bicyclobutylidene 5 was determined by X-ray crystallography which disclosed considerable steric congestion around the double bond. As a result 5 did undergo addition of dichlorocarbene, epoxidation with meta-chloroperbenzoic acid, and cyclopropanation with CH2I2/ZnEt2, but did not add the more bulky dibromocarbene. The reaction of 5 with tetracyanoethene proceeded smoothly, but led to a formal [3+2] cycloadduct across the proximal single bond of one of the inner cyclopropane rings. The consecutive spirocyclopropanation of bicyclobutylidene led to a bathochromic shift in the UV spectra of 12 and 17nm, respectively, for each pair of beta- and alpha-spirocyclopropane groups. In the He(I)-photoelectron spectra of these bicyclobutylidenes, the effect of spirocyclopropanation upon their pi-ionization energies (pi-IE,) was found to be almost additive, leading to a lowering of 0.05 eV per any additional beta-spirocyclopropane, and 0.28-0.22 eV per additional alpha-spirocyclopropane group; this indicates an increasing nucleophilicity of the double bonds in the order 1 < 4 < 3 < 5. Following the radical cations of the three symmetrical bicyclobutylidenes without (2a, b) and with six (5) spiroannelated cyclopropane rings, the radical cations of two symmetrical bicyclobutylidenes with two (4) and four (3) such rings were studied by ESR spectroscopy. Whereas 2b.+, 3.+, and 5.+ could be generated by electrolytic oxidation of the corresponding hydrocarbons in solution, the spectra of 2a.+ and 4.+, with unsubstituted 2,2',4,4'-positions, were observed upon radiolysis of their neutral precursors in a Freon matrix. On going from 2a.+ to 4.+, the coupling constant [aH] of the eight beta protons in the 2,2',4,4'-positions of bicyclobutylidene increases from 2.62 to 3.08 mT, and that of the four gamma protons in the 3,3'-positions changes from 0.27 to 0.049 to 0.401 mT on passing from 2a.+ via 2b.+ to 3.+. Computations by means of the density functional theory (DFT) at the B3LYP/6-311+G*//B3LYP/6-31G* level reproduce well the experimental hyperfine data.

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17.4.1 Radical cations of acyclic monoenes

Davies

2009

Phosphorus-Centered Radicals, Radicals Centered on Other Heteroatoms, Organic Radical Ions. Part 2

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The radical cation of bicyclobutylidene

Cited by 5 publications

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A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Synthesis, Spectroscopic, and Structural Properties of Spirocyclopropanated Bicyclobutylidenes and Their Radical Cations

17.4.1 Radical cations of acyclic monoenes

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