After this initial discovery and following optimization to improve the reaction generality, 21 the rAP-(hetero)arene reduction was successfully applied to variety of (hetero)arenes that are challenging to be reduced under known reduction conditions (Figure ). The relationship between the reduction potential of the target (hetero)arene motif and the functional groups present is a predictor of reaction outcome. Thus, the method works if (hetero)arene is more reactive (i.e. reduction potential is more positive) than other surrounding functional groups. Accordingly, reduction of electron-deficient heteroarenes has the widest functional group tolerance including epoxide, nitrile, carbamate, alkyne and even alkyl chloride as well as aryl halides (16-22). Particularly, rAP is uniquely suited to differentiate multiple arenes in one molecule based on the electronic character of the arenes, as illustrated in the reduction of 23. Chemical Birch reduction does not have such precise chemoselectivity, resulting in the mixture of all possible reduction products 24-26 despite quenching the reaction before full consumption of 23. When there are redox-active functional groups that can compete with (hetero)arene reduction, it is difficult to selectively reduce (hetero)arenes as shown in the reduction of 27-31. In general, DC electrolysis under the optimized conditions leads to little or no desired product formation.