Akinori Hasegawa

Matrix interactions for radical cations: Theoretical and experimental results for the trichlorofluoromethane matrix illustrated by 19F coupling for Me2Se+ radical cations

Abstract A range of radical cations generated in trichlorofluoromethane by exposure to ionizing radiation from adducts with one solvent molecule, the ESR spectra exhibiting hyperfine coupling either to 35 Cl or to 19 F. A theoretical explanation for this dichotomy is proposed, which is supported by comparison between Me 2 S + and Me 2 Se + cations.

Radical Anions in Disordered Matrices

In this chapter we are concerned with the radical anions which were derived from guest molecules in disordered matrices by radiolysis or photolysis at low temperature and detected mainly by ESR spectroscopy. The matrix isolation technique in ESR studies has facilitated the selective detection of the highly reactive ionic radicals primarily formed from guest molecules by electron-gain or electron-loss, using suitable matrices.

Static and dynamic structures of halogenated dimethyl ether radical cations: An EPR and MO study

The EPR spectra of the radical cations of CH3OCH2F and CH3OCH2Cl generated in CF3CCl3 matrices by ionizing radiation at 77 K were fully analyzed with the help of their selectively deuterated compounds. The spectra were analyzed in terms of hyperfine coupling constants (hfcc) to the 1H nuclei in the CH3 and CH2X (Xu2006=u2006F, Cl) groups. Based on the EPR results combined with ab initio and DFT MO calculations, the conformation of the cations was determined; the halogen atom preferentially occupies a position in the molecular C–O–C plane which is perpendicular to the unpaired electron orbital of the central oxygen and the C–O–C–Cl framework has a geometry corresponding to a cis conformation. The temperature-dependent EPR spectra for CH3OCH2Cl+ in CF3CCl3 nobserved between 50 K and 100 K were analyzed in terms of a three-site chemical exchange model among the three protons, caused by CH3 group rotation. The observed activation energy for the rotation, 3.3u2006±u20060.5 kJ mol−1, is in reasonable agreement with the value calculated for the potential barrier of the rotation.

EPR spectra and structure of bis-chlorinated dimethyl ether radical cation, CH2ClOCH2Cl+

The EPR spectrum of the CH2ClOCH2Cl+ radical cation, generated by ionizing radiation in a halocarbon matrix at 77 K, consists of a major septet due to two equivalent Cl nuclei and an additional triplet due to two protons in the terminal CH2Cl groups. This assignment was confirmed using CD2ClOCD2Cl+. Theoretical calculations were performed to obtain the optimized geometries and theoretical hyperfine coupling constants (hfcc) for CH2ClOCH2Cl+ using density functional theory (DFT). The results suggested Structures I (with Cs symmetry) and II (with C2 symmetry), where the two Cl, two C and one oxygen atoms make a five-membered ring and the unpaired electron is largely and equally shared by the two Cl nuclei. A reasonable magnitude in the proton coupling was obtained only for Structure nI, having an energy lower than that of Structure II. The results were compared with those in our previous study on Cl(CH2)3Cl+, giving similar EPR spectra. For Cl(CH2)3Cl+, a geometry corresponding to Structure II was suggested from the proton coupling calculated by the CNDO/2 method. In this study, we reexamined the calculation by the DFT method and reached the conclusion that Cl(CH2)3Cl+ preferred a structure corresponding to Structure I.