On the regioselectivity of the nucleophilic aromatic photosubstitutions of 4-nitroveratrole. A threefold mechanistic pathway

4-Nitroveratrole (NVT) is photosubstituted with primary amines, piperidine and hydroxide ion. Primary amines and hydroxide ion cause replacement of the methoxy group in meta position with respect to the nitro group whereas piperidine photosubstitutes the methoxy group in para to the nitro group. Photoreactions with piperidine and hydroxide ion involve attack of the amine upon a triplet excited state of NVT.Mechanistic evidences indicate that the reaction with hydroxide ion is probably a SN23Ar* process whereas the reaction with piperidine involves a radical ion pair formed via electron transfer from the amine to a triplet excited state. Photoreactions. with primary amines involve attack of the amine upon a singlet excited state of NVT (SN21Ar* process). These results are discussed and justified in the context of nucleophile ionization potential considerations and ground state donor-acceptor complex formation abilities. © 1988.