Factors affecting the stability and equilibria of free radicals. XIII. N-alkoxy- and N-aralkoxypicrylamines and ESR spectra of the corresponding capto-dative persistent aminyls

Reactions of 2,2‐Diphenyl‐1‐picrylhydrazyl (DPPH) with Two Syringylic Phenols or One Aroxide Derivative

“…[56][57][58][59][60] In addition, it has been shown that the steric properties of the picryl group also contribute to the stability of DPPH. [61,62] Convincing experimental evidence for the push-pull (capto-dative [63] or merostabilizing [64] ) effect was provided by the identification of high rotation barriers around the N-bonds of congeneric sulfonyl-hydrazyls.…”

N-Alkoxy-3,5-dinitro-4-aminobenzoic acid derivatives with controlled physico-chemical properties

“…N-Alkoxy-polynitroaniline derivatives (Ar-NH-OR) are organic compounds with very interesting physico-chemical properties, from which the following two are well known: (i) by oxidation, they easily generate free N-alkoxyaminyl (or aminoxyl) radicals (Ar-N • -OR) [1][2][3][4][5][6], which may react with other stable free radicals such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) and its congeners, leading to the blue-colored betaines [7,8], and (ii) their high acidity [9][10][11][12] leads in a presence of an organic or inorganic base to the corresponding anions (RO-N --Ar), also with very intense colors, red, blue, or blue-violet [9,11]. These anions have been involved as partners in supramolecular hydrophobic complexes with alkaline cations and crown ethers [9,11,13,14], and as nucleophiles in the synthesis of N-methyl or N-aryl derivatives [9,11].…”

QSPR study on pKa values of N-methoxy-polynitroaniline derivatives

“…In recent years, we reported the synthesis and properties of N-methoxy-polynitroanilines 1 with various substituents [3][4][5][6][7][8][9][10][11][12][13][14]. These compounds are acidic, and their pK a values have been reported [7,[12][13][14].…”

“…Other interesting properties of compounds 1 are: (i) oxidation affording persistent free radicals (N-aryl-N-alkoxyaminyls), which are probable intermediates in the disproportionation (self-nitration) of N-methoxy-dinitroaniline derivatives affording picryl derivatives [3][4][5][6][7][8]10]; (ii) enhancement of their acid-basic properties in the presence of crown ethers [11,15,16]; (iii) their reaction with the stable free radical 2,2-diphenyl-1-picrylhidrazyl leading to new, intensely coloured, betaionic compounds, which present reversible chromogenic and redox properties [11,17].…”