Kinetic studies including the evaluation of deuterium kinetic isotope effects and Arrhenius activation energies implicate an addition-elimination mechanism for the proton transfer reaction between 9-methylanthracene radical cation and 2,6-lutidine in acetonitrile-Bu4NPF6, (0.1 M) and in dichloromethane-Bu4NPF6 (0.2 M). Isotopic substitution of D for H at the 10-position results in inverse deuterium kinetic isotope effects (k(H)/k(D)) equal to 0.83 due to nucleophilic attack on the radical cation by 2,6-lutidine. Primary k(H)/k(D) Of 3.5-5.9 were observed for D-3 substitution in the 9-methyl group. The addition-elimination mechanism involves unimolecular rearrangement of the initially formed adduct to give the product of proton transfer, 9-anthracenylmethyl radical. Oxidation of the latter followed by reaction with 2,6-lutidine affords N-(9-anthracenylmethyl)-2,6-lutidinium ion, which was isolated as the perchlorate salt. A comparison of kinetic data from reactions of both 9-methyl and 9,10-dimethylanthracene radical cations with pyridine and 2,6-lutidine results in the conclusion that in the absence of severe steric effects, radical cation-nucleophile combination is kinetically favored over direct proton transfer for these radical cations.