20671-17-4

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• 99-87-6 4-methylisopropylbenzene 
• 775305-82-3 Methyl 2-(methoxycarbonyl)-2,3-dimethyl-3-(4-methylphenyl)butanoate 

Relevant academic research and scientific papers

Evidence for significant through-space and through-bond electronic coupling in the 1,4-diphenylcyclohexane-1,4-diyl radical cation gained by absorption spectroscopy and DFT calculations

Photoinduced single-electron-transfer promoted oxidation of 2,5-diphenyl-l,5-hexadiene by using N-methylquinolinium tetrafluoroborate/ biphenyl co-sensitization takes place with the formation of an intense electronic absorption band at 476 nm, which is attributed to the 1,4-diphenylcyclohexane-1,4-diyl radical cation. The absorption maximum (λob) of this transient occurs at a longer wavelength than is expected for either the cumyl radical or the cumyl cation components. Substitution at the para positions of the phenyl groups in this radical cation by CH3O, CH3, F, Cl, and Br leads to an increasingly larger redshift of λob. A comparison of the ρ value, which was obtained from a Hammett plot of the electronic transition energies of the radical cations versus σ+, with that for the cumyl cation shows that the substituent effects on the transition energies for the 1,4-diarylcyclohexane-1,4-diyl radical cations are approximately one half of the substituent effects on the transition energies of the cumyl cation. The observed substitu_ent-induced redshifts of λob and the reduced sensitivity of λob to substituent changes are in accordance with the proposal that significant through-space and -bond electronic interactions exist between the cumyl radical and the cumyl cation moieties of the 1,4-diphenylcyclohexane-1,4-diyl radical cation. This proposal gains strong support from the results of density functional theory (DFT) calculations. Moreover, the results of time-dependent DFT calculations indicate that the absorption band at 476 nm for the 1,4-diphenylcyclohexane-1,4-diyl radical cation corresponds to a SOMO-3-SOMO transition.

Substituent Effects on the C-C Bond Strength, 19. Geminal Substituent Effects, 10. Radical Stabilization Enthalpies of α,α-Bis(methoxycarbonyl)alkyl and Tris(methoxycarbonyl)methyl Radicals

Heats of formation ΔH0f(g) were determined from enthalpies of combustion ΔH0f(c) and enthalpies of vaporization ΔH0vap or sublimation ΔH0sub for the eight substituted methanetricarboxylates 2a-h.From these data and from previously determined enthalpies of formation ΔH0f of substituted malonic esters new thermochemical group increments were derived.From these increments and from the recently published improved increments for carboxylic acid esters the gem. interaction enthalpies of two and three COOR groups were calculated.The radical stabilization enthalpies RSE of α,α-bis(methoxycarbonyl)alkyl (18.2 kJ mol-1, 1a) and tris(methoxycarbonyl)methyl radicals (5.2 kJ mol-1, 1b) were derived from kinetic data obtained by means of our previously developed protocol.They were corrected for the gem. interaction energies of the ester groups in the ground state and are satisfactorily explained by an additive stabilizing effect for the ester substituents and by dipolar substituent interactions in the radicals.The dipolar energies were taken from MM2 calculations. - Keywords: Enthalpies of formation / Geminal substituents, energetic interaction of / Bond cleavage, C-C, kinetics of / Radicals, stabilization of / Increments, thermochemical, of esters

Absorption Spectra and Photochemical Rearrangements of Alkyl- and Dialkylbenzene Cations in Solid Argon

Matrix photoionization of alkyl- and dialkylbenzenes produced and trapped the parent radical cations.Irradiation in the visible parent cation absorption induced α-H transfer to the cation ring to give substituted methylenecyclohexadiene cations.The ease of 1,3-hydrogen transfer in these experiments suggests that this may be an important rearrangement in gaseous alkylbenzene cations.Subsequent ultraviolet photolysis of these samples produced substituted styrene cations.