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

Abstract

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 C_s 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 I, 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.