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

Abstract

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 [a_D= 1.36 (2 D) and a_D= 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.