Kiminori Ushida

Static distortion of 2E molecular cations of cyclobutane at 4.2 K giving 2B2 with C2v symmetry and its dynamic average at >77 K: ESR evidence

Etude par spectrometrie RPE de la distorsion de la structure du cation cyclobutane c-C 4 H 8 + qui est une espece presentant un effet Jahn Teller tres important

Temperature change of OD ESR and freon matrix ESR of the radical cations of 9,10-octalin and cyclohexene

Abstract The optical detection (OD) ESR and Freon matrix ESR spectra were observed for the radical cations of 9,10-octalin and cyclohexene from 77 to 300 K. The observed spectral change was attributed to ring inversion in both radical cations based on MO calculations and an analysis by the modified Bloch equation. The activation energy for the inversion of the radical cation of octalin was calculated as 18.8 kJ mol −1 .

Photoinduced ring-opening rearrangement of a radical cation of cyclobutane in CFCl3 at low temperature: ESR observation

Abstract ESR observation is described of a new type of reaction of alkane radical cations in solid matrices; the cyclobutane radical cation in CFCl 3 and in SF 6 suffers photoinduced ring opening followed by 1,3-hydride ion transfer to rearrange into the but-1-ene radical cation, which further photoisomerizes into the cis-but-2-ene radical cation. The results are compared with thermal ring opening reported for the cyclopropane radical cation to give the trimethylene radical cation CH 2 CH 2 CH 2 + in CFCl 2 CF 2 Cl. A possibility of hydride ion transfer to form CH 2 CH 2 CH 3 is discussed as an alternative interpretation of the spectrum assigned to the trimethylene radical cation.

Esr studies on the γ-irradiated acetone-CCl3F system

Abstract γ-irradiated acetone in polycrystalline CCl 3 F at 77 K has been studied by ESR to reveal that the acetone molecules tend to be oriented in CCl 3 F Matrix upon freezing the solution in ESR tubings. At higher concentrations both monomer and dimer radical cations of acetone are produced. The dimer cation is responsible for the optical absorption with λ max ≈ 740 nm.

Radical-cations of aldehydes and ketones generated by ionizing radiation: an electron spin resonance study

Exposure of dilute solutions of various aldehydes and ketones in trichlorofluoromethane to 60Co γ-rays at 77 K gave, in most cases, the corresponding cations, identified by e.s.r. spectroscopy. The acetaldehyde cation is characterized by a very large proton hyperfine coupling, the SOMO being the in-plane, formally non-bonding, p-orbital on oxygen. At 77 K there was a weak interaction with one chlorine atom of a solvent molecule, but this was lost reversibly on annealing to ca. 120 K. That the quartet splitting was due to chlorine rather than to the methyl protons as had been previously supposed was established by studying the (CD3CDO)+ cation. The acetone cation spectrum comprised a single asymmetric feature with no evidence of solvent interaction or hyperfine coupling to the γ-protons. In contrast, aldehyde and ketone cations with δ-protons showed hyperfine coupling in the 10–30 G range to conformationally selected protons. For methyl groups, one proton only is selected, the coupling being lost reversibly on annealing. These findings are semi-quantitatively supported by INDO calculations.

An ion—molecule reaction in γ-irradiated CCl4 solids containing acetals: production of the ·CCl3 radical as a sole paramagnetic species

Methylal, 1,3-dioxolane, and 1,3-dioxane, all having the O CH 2 O unit, have been found to induce the ion—molecule reaction CCl 4 + + O CH 2 O → ·CCl 3 + HCl + O CH O + in γ-irradiated solid CCl 4 at 77 K. ESR analysis of the system reveals that the sole paramagnetic species in the ·CCl 3 radical.