Competitive coupling of amide anion over menthyl propionate anion with aryl radical

A competitive coupling of amide anion over menthyl propionate anion with aryl radical in photo-SRN 1 mechanism was encountered. The reaction afforded N-aryl propionic amide in excellent yield. In contrast, the expected nucleophilic photo-S_RN 1 substitution originating from the carbanion was observed in the case of t-butyl propionate. According to the proposed mechanisms and MO correlation diagrams of the coupling step of nucleophiles with aryl radical, the interesting contrast is reasonably attributed to the variation in energy gap between x*C-O and x*Ar of (ArNu)+. Usually, the odd electron of (ArNu)+ is weightly populated at x*C-O, however, the diminished privilege of x*C-O in menthyl propionate promotes a dominant population of the odd electron at x*Ar, which leads to the fragmentation of (ArNu)+ into the starting carbanion and aryl radical.