Mechanisms of the Thermal Isomerization about the C=N+ Bond of Some Iminium Salts

Article abstract of DOI:10.1021/jo00223a025

The thermal stereomutations of a series of N-aryl 3-arylpropenylidene iminium perchlorate salts have been examined.These salts crystallize as E,E isomers but isomerize thermally about the C=N bond in solution The rates of isomerization (8 <*> 9) were measured at 100 deg C in trifluoroacetic acid.A Hammett correlation of the rate constants indicated that two mechanisms operate in the system.The iminium salts with electron-withdrawing substituents react by a nucleophile-catalyzed mechanism, while those with electron-donating substituents isomerize by a protonation mechanism.This latter process was shown to involve protonation on nitrogen.