Electron paramagnetic resonance studies on the generation and solvation of n-heptafluoropropyl t-butyl nitroxide

Abstract

n-Heptafluoropropyl t-butyl nitroxide ( 3) has been generated by the use of the electron-transfer reaction of O-benzoyl-N-t-butylhydroxylamine ( 1) and heptafluorobutyryl peroxide ( 2) in CFCl 2CF 2Cl solution. Electron paramagnetic resonance (EPR) measurements of a N and a F β values for 3 in 25 solvents have been carried out at 25±2 °C. The a N values for 3 in 16 aprotic solvents (but not in t-BuOH and acetone) show a linear correlation with the cybotactic solvent parameters E T and Z (Kosower constant) i.e. a N = 3.60 × 10 −2 E T + 10.25 and a N = 1.56 × 10 −2 Z + 10.66. The physical significance for the slope, (slope x E T) or (slope x Z), and the extrapolated intercept on the a N axis is linked to the sensitivity of the nitroxide toward solvation, the magnitude of the overall solvation effect on the a N values and the intrinsic a N value of 3 in the ideal gaseous state, respectively. It is believed that the virtually constant value of a N (11.56–11.61 G) for 3 in alcohols and carboxylic acids is caused by H-bond formation between 3 and the solvents.