The [2H8]THF radical cation in CF3CCl3 and CFCl3. An EPR and ENDOR study

The structure and dynamics of the radical cation of deuteriated tetrahydrofuran ([2H8]THF) stabilized in the freon matrices CFCl3 and CF3CCl3 have been investigated by means of EPR and ENDOR spectroscopy. The EPR and ENDOR results of the rigid structure give two pairs of strongly interacting β-deuterium hf splittings [aD= 1.36 (2 D) and aD= 0.60 mT (2 D)] consistent with the protonated analogue [Kubodera et al., J. Phys. Chem., 1981, 85, 2583 (ref. 1)]. An additional hf splitting (0.9–1.1 mT) assigned to the matrix fluorine was resolved above ca. 110 K in CFCl3. The temperature dependent EPR lineshapes (77–145 K) involving the exchange between four coupled (I= 1) nuclei have been analysed. A two-site model explained qualitatively the alterating line-widths at intermediate temperatures and resulted in an activation energy of ca. 1.7 kcal mol–1 A non-perturbative approach adopting a four-site model to account for puckering motion was tested. The dynamics were also manifested as a reversible temperature effect for the ENDOR. The relative abundance of resonances due to an averaged (hf) structure become predominant as the temperature is increased.