The first implementation rAP into synthetic electrochemistry was set forth based on the following hypothesis: if the rate of polarity switching is faster than the rate of certain processes on an electrode, a slower subset of electrochemical processes might be suppressed (Figure ). Though this hypothesis was supported by early theoretical studies and rudimentary experiments, it was entirely unclear how useful or workable such a process would be in practice. Thus, compound 1 with multiple redox-active sites was designed to explore this hypothesis. Both oxidative C-H functionalization on the piperidine (Shono oxidation) and reduction of a carbonyl group on the phthalimide could occur depending on reaction conditions. Accordingly, reaction conditions were chosen such that they could potentially lead to either reductive or oxidative outcomes (non-sacrificial electrodes and slightly acidic conditions). Then, the electrolysis was compared between DC and rAP. Crude 1 H NMR analysis revealed that DC electrolysis led to random methoxy group incorporation resulting in a complex mixture of isomers. Presumably, C-H oxidation (Shono oxidation) occurred along with varying degrees of imide reduction, leading to this unselective and synthetically useless outcome. In stark contrast, rAP led to highly selective formation of 2 in 76% yield under otherwise identical conditions. Remarkably, the result was seemingly a clean carbonyl reduction, while methoxy group incorporation indicative of Shono oxidation was barely observable in the crude NMR. A follow-up experiment using a different rAP frequency indeed confirmed that Shono oxidation is progressively attenuated as rAP frequency increases, whereas carbonyl reduction was much less affected. Simplifying complex redox reactions using rAP unveiled various intriguing chemoselectivities that are barely recognized or unobservable otherwise. Figure illustrates such examples. One of the most surprising chemoselectivities was observed with phthalimide 3, in which selective deoxygenation of phthalimide proceeded without affecting an alkyl aldehyde (Figure ). This striking chemoselectivity was indeed unique to rAP as conventional DC electrolysis under the same reaction conditions led to extensive decomposition of 3. Conventional chemical reductants such as DIBAL and LiBH4 gave exclusive reduction of aldehyde, which is in good agreement with the common reactivity order. Another example is the reduction of imide 6, a versatile building block for PROTAC containing five carbonyl groups in addition to reductively labile azide group (Figure ). Again, rAP-based carbonyl reduction led to selective deoxygenation of a single carbonyl group, whereas DC electrolysis under the identical conditions led to complex mixtures. This powerful, yet chemoselective rAP-based reduction could be applied to reductive removal of Evans auxiliary to reveal an aldehyde (Figure ). Compound 9 is a particularly challenging case, since it has another reducible carbonyl group within the molecule. To avoid this chemoselectivity issue, a nine-step route was required involving three protecting group manipulations and five redox manipulations was required to construct 11. Instead, the rAPbased method cleanly generated intermediate 10 without overreduction or reducing the ester functionality. Simple basic work-up readily delivered the aldehyde 11. The corresponding DC electrolysis failed to convert 9 into 10, whereas common chemical reductants such as DIBAL and LiBH4 resulted in either undesired selectivity or overreduction. These case studies in Figure -3C illustrate intriguing or even perplexing chemoselectivities based on common chemist's intuition and basic undergraduate organic curriculum. However, it needs to be emphasized that this reactivity manifests from innate reactivity under single-electron transfer (SET) conditions. Indeed, these selectivities can be easily explained based on measured reduction potentials or calculated LUMO coefficients. 9 Thus, rAP is a synthetic tool to access "innate SET reactivity", which could be challenging to realize by DC electrolysis or canonical chemical reagents due to various side reactions or completely different reaction pathways. To conclude this section, the reduction of a tetrapeptide 12, the most complex substrate in this work, is instructive to demonstrate how the reactivity differentiation illustrated in Figure and SET-based chemoselectivity in Figure could be employed in the most demanding of contexts. Thus, the selective reduction occurs on a functional group that has the most positive reduction potential with a fast electrochemical response. Phthalimide is the only functionality that satisfies these criteria among numerous potential redox sites, affording 13 in 52% yield. Such precision is beyond the reach of conventional DC electrolysis if the same reaction conditions were employed and is obviously outside the reach of currently known chemical reagents.