Synthesis and Structural Investigation of Some Electron-Rich Nitroaromatics

Abstract

2,4-Difluoro-, 2,4,6-trifluoro-, and 2,3,4,6,tetrafluoronitrobenzenes undergo nucleophilic aromatic substitution, once, twice, and three times with a variety of amine substituents with a high degree of regiochemical control to provide a range of electron-rich nitrobenzene derivatives. In these structures the nitro group proves a useful structural probe to reveal the varying extents of electron donation from the varying number of amino substituents onto the nitro group as revealed by accurate low temperature X-ray crystal structure analysis, thus increasing electron donation manifests in a decrease in the Ar–NO2 distance consistent with increased double bond character, while the N–O bond distance increases as the oxygens accept the electron density. The effect of delocalization of the aniline nitrogen lone pair onto the nitro group impacts on the geometry and hybridization of the nitrogen substituent and also impacts on the ability of the nitrogen lone pair electrons to participate in other competing electronic interactions, such as the nN–σ*C–S anomeric effect as demonstrated by the thiazolidine substituted derivatives 3c, 4c, and 6c.