Sequential cation-free radical mechanism

We proposed the sequential single-electron transfer mechanism for ethylene biosynthesis based on precedents of cyclopropylamine oxidations by enzymes such as cytochrome P450 (55, 40) and monoamine oxidase (59,40). A syllogism underlying this postulate is that the electrochemical oxidation of ACC must have a close mechanistic relationship to the enzymatic oxidation because each gives the same products with the same stereochemistry. This mechanism was modified slightly by theoretical considerations (5) (eq 10). Key intermediates are 1, the cyclopropylamine radical cation, and 2, the "half-opened radical." The presence of the latter species explains, by free rotation about the -CH2-CH2 bond, the loss of stereochemistry observed with deuterated substrates. It is further consistent with cyclopropylcarbinyl... 

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