Electrostatic effects on the photoreactions of nitrophenyl ethers with nucleophiles

Abstract

Nucleophilic aromatic photosubstitutions of 1,2-dialkoxy-4-nitrobenzenes by oxygen nucleophiles such as water or alcohols in basic media and in air equilibrated solutions, lead to low yields of substitution, following the "polar" S N Ar * mechanism. Photoreduction of the nitro group is the exclusive process in an inert atmosphere. By using Topologically Controlled Coulombic Interactions (TCCI), the photosubstitution process becomes predominant, allowing the SET mechanism for S N Ar * reactions to occur. This is due, on one hand, to the reduced tendency of the radical anion to be oxidized, and on the other hand, to the removal of electronic density from the nitro group in the radial anion which lowers the rate of proton transfer from the nucleophile radical cation.