Abstract The nucleophilic aromatic substitution reactions of pentafluoronitrobenzene (PFNB) and 2,3,4,5-tetrafluoronitrobenzene with methanol are both reductively activated. However, the first one is sensitive to the presence of radical scavengers but the second is not. In addition, the kinetic behavior of both reactions in the absence of stimulation is very similar suggesting they are examples of second stage rate determining S NAr mechanism. Kinetic studies also show that no real photochemical stimulation exist in those reactions. The reported facts are not compatible with the previously proposed (for the reaction of PFNB with methanol) S RN2 mechanism. A new mechanistic rationale is discused.