It turns out that in monooxygenase reactions, the job of FADH 2 is to reduce O 2 to peroxide in order to activate one of the oxygen atoms for insertion into the organic substrate. The mechanism for th...It turns out that in monooxygenase reactions, the job of FADH 2 is to reduce O 2 to peroxide in order to activate one of the oxygen atoms for insertion into the organic substrate. The mechanism for this step is though in most cases to involve single-electron chemistry and free radical intermediates – we will discuss the single-electron reactions of flavin in section 17.3C, and you will be invited to propose a mechanism for flavin hydroperoxide formation in problem P17.11.