Article abstract of DOI:10.1139/v97-150

The ionization of a series of 7-(4′-X anilino) 4-nitrobenzofurazans (4H) (X = NO₂, CN, CO₂Me, F, H, Me, OMe) to give the conjugate amide anions 4^- has been studied by ¹H and ¹³C NMR in Me₂SO-d₆. Concomitantly, their acidity (pK_a) has been measured spectrophotometrically in a H₂O-Me₂SO mixture with a molar fraction N_Me2SO = 0,509. Although the measured pK_a values for the whole series of compounds 4H lie in a relatively narrow range (6.40, X = NO₂/7.98, X = OMe), they reveal that each derivative is about 3 times more acidic than the similarly X-substituted 2,4,6-trinitrodiphenylamines. These results, together with an analysis of substituent effects on the proton and carbon chemical shifts (δ_Hi et δ_Ci) and the related deprotonation parameters (Δδ), which are specially significant for H₆, C₄, C₆, and C₇, emphasize the very strong electron-withdrawing character of the 4-nitrobenzofurazanyl moiety. In addition, the observation of nice linear correlations of the type δ_Hi(Ci) = f(pK_ai) has enabled us to control and sometimes to firmly assign the various chemical shifts.

Full text of DOI:10.1139/v97-150

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