CATION RADICAL NUCLEOPHILE COMBINATION REACTIONS - REACTIONS OF NITROGEN-CENTERED NUCLEOPHILES WITH CATION RADICALS DERIVED FROM ANTHRACENES

Cation radicals derived from anthracene and 9-substituted anthracenes react with pyridine and substituted pyridines to form pyridinium salts. 9-Nitro- and 9-cyano-substituted cation radicals were observed to be about 10(2) times as reactive as unsubstituted anthracene (AH) cation radicals while the 9-phenylanthracene (PAH) cation radical was found to be from 2 to 7 times less reactive than AH*+. The reactivities of the nitrogen-centered nucleophiles were observed to depend upon both electronic and steric factors. The mechanism of the reactions involves nucleophilic attack by the nitrogen lone pair at the 10-position of the cation radical. The reaction are accompanied by a change in hybridization, sp2 to sp3, at the anthracene 10-position, giving rise to inverse deuterium kinetic isotope effects ranging from 0.7 to 0.8 when the 10-position is substituted with deuterium. An electron-transfer mechanism for the substitution reactions was ruled out on the basis of energetic considerations.