Rate constants were measured for the reactions of 9-phenylanthracene (PA) and 9,10-diphenylanthracene (DPA) radical cations with a number of primary, secondary, and tertiary amines in acetonitrile using nanosecond laser flash photolysis (NLFP), Generation of the radical cations of PA and DPA (PA(.+) and DPA(.+)) was accomplished by 266- or 355-nm photoionization of the parent compound. Primary amines react with PA(.+) with second-order rate constants in the range 8 X 10(6) to 2 X 10(9) M(-1) s(-1), and rate constants for reaction of DPA(.+) with the same amines are 60-250 times lower. For both radical cations, Bronsted-type plots of log(k(amine)(RNH(2))) versus pK(a)(RNH(3)(+)) serve to illustrate that the rates of reaction with primary amines increase with increasing amine basicity and decrease as the steric requirement of the amine increases. Transient absorption studies complement the kinetic data and demonstrate that primary amines react with both radical cation species by nucleophilic addition to generate the expected radical intermediates. The observed difference in reactivity between PA(.+) and DPA(.+) with these nucleophiles can be accounted for by the lack of steric hindrance toward nucleophilic attack at the 10 position in the former. In acetonitrile/water (9:1) solution, rates of reaction with the primary amines are retarded compared to those in acetonitrile and the extent to which the rates are slowed is largest for the more basic amines. It is suggested that the rate differences observed in the mixed solvent system are a result of the equilibrium between free and hydrated amine. Interestingly, the reactivity patterns for the addition of primary amines to these radical cations parallel those observed in carbocation chemistry. Tertiary amines and anilines were found to react with both radical cation species with similar rate constants, exclusively by electron transfer, regenerating PA or DPA concomitant with formation of the radical cation of the corresponding amine. Rate constants for reaction with tertiary amines range from 1.5 X 10(9) M(-1) s(-1) to rates approaching the diffusion-controlled limit in this solvent (2 X 10(10) M(-1) s(-1)) and correlate with the oxidation potential of the amines. Secondary amines exhibit rate constants that do not reflect their basicity. For PA(.+), electron transfer occurs competitively with nucleophilic addition and, thus, the rate constants measured reflect the relative contribution from each of these two processes. Nucleophilic addition to DPA(.+) is in most cases slow enough that electron transfer dominates.