Single-electron transfer and hydrogen atom transfer pathways have been proposed to account for the cytochrome P450-catalyzed a-carbon oxidations of amines. With the aid of electrochemistry-electrospray ionization mass spectrometry, the electrochemical potentials required for the one-electron oxidations of N-methyl- and selected N-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridinyl derivatives and the chemical fates of the resulting aminyl radical cations have been investigated. Comparison of the results of these studies with those observed in the corresponding enzyme catalyzed oxidations suggests that aminyl radical cations are not obligatory intermediates in the cytochrome P450-catalyzed a-carbon oxidations of this class of substrates.