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 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.