Proton affinity of the stable free radical 2,2,6,6-tetramethyl-l-piperidinyloxy measured by the kinetic method

Abstract

Proton-bound dimers can be generated between the stable free radical, 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO), and various reference compounds in a chemical ionization source. The individual mass-selected dimers dissociate upon collision to yield the protonated monomers as the only product ions. From their relative abundances the kinetic method yields a value of 209.5 ± 1.0 kcal mol −1 for the proton affinity of the TEMPO radical. The proton affinity is compared to that of m-methylphenoxyl and other oxy radicals.