? Values of N-substituted azoles

Abstract

The cp coefficients of azoles and their benzo-derivatives have been determined by i.r. and n.m.r. spectroscopy, based on the study of the NH2 bands arising from 1 -p-aminophenylazoles.KAUFFMANN suggested that ' azoles containing more than one N atom bound by way of an N atom correspond to halogen and other good negative leaving groups.' In this work we have attempted to make quantitative comparison on this basis by determining the C T ~ coefficients of N-substituted azoles.Two examples of good correlation between spectroscopic properties and Hammett (r coefficients exist for the aniline series. In the first case,2 the physical property which is measured is the symmetrical or antisymmetrical stretching vibration of the NH2 group determined in carbon disulphide [equations (l)] ; the v,(NH~) == -1.92 + 28.470, (Y 0.979) vas(NH2) = -3.30 + 40.310, (r 0-968)} (l) second3 is the proton chemical shift of the NH, group in dimethyl sulphoxide (DMSO). Thus we have prepared a series of l-@-aminophenylazoles in order to study their i.r. and n.m.r. behaviour and to determine their oP coefficients by these two independent methods. 8(NH2)= 290.6 + 79.27~ (urn and op) (Y 0.997) (2) EXPERIMENTALThe fifteen compounds studied were prepared by reduction of the corresponding fi-nitrophenyl derivatives (Table 1) by the following procedure. A mixture of 1-pnitrophenylazole (0.01 mol), stannous chloride (10 g), and concentrated hydrochloric acid (1 2 g) was heated until a clear solution was obtained. A dilute sodium hydroxide solution was added (basic pH) and the 1-9-aminophenylazole was extracted either with chloroform or with ethyl acetate. Yields were ca. 90%.All n.m.r. spectra were recorded a t 31.5' on a Varian A60 spectrometer. Solutions in anhydrous CaH,]DMSO were 0-2-0.4~ (we were able to verify that in some cases, in this range of concentration, the NH, chemical shifts were independent of the concentration). Measurements are given in Hz a t 60 MHz and are accurate to &Om5 Hz.1.r. spectra were measured using 1 0 -3 ~ solutions in CCl, with a Perkin-Elmer 225 spectrometer equipped with 1 cm cells (scan width, 5 cm-l per cm of paper; scan speed, 30 s per cm-1). In contrast to literature data,a we found that CS, is not a suitable solvent because it reacts with anilines to yield dithiocarbamic acids; 4 for this reason experiments were carried out in CCl, in spite of possible amine-CC1, interactions.2 The vas(NH) and v,(NH) values were

The Structure ofN‐phenyl‐pyrazoles and Indazoles: Mononitro, Dinitro, and Trinitro Derivatives

“…In a paper reporting many basicity values, p K a , of pyrazoles, there are data for 4‐nitro, 2,4‐dinitro, and 2,4,6‐trinitro‐pyrazoles 3 (−0.65), 36 (1.50), 4 (−1.40), 56 (0.55), and 7 (approximately −2.0) among other derivatives . We have determined for a large set of compounds, including several of this review, log π (4‐nitrophenylpyrazoles) and Hammett's σ values (4‐aminophenylpyrazoles and indazoles obtained by reduction of the corresponding 4‐nitrophenyl derivatives) .…”

“…We have published 40 papers on the title topic between 1959 and 2013; this set continues to be the only systematic study of these compounds . Our publications deal with most of these structures: 1 ; 3 ; 4 ; 5 ; 7 ; 9 ; 10 ; 11 ; 13 ; 14 ; and 15 .…”

The organic chemistry of poly(1H-pyrazol-1-yl)methanes

“…N-Substituted azoles can be considered as pseudohalogens [174,175] since they are also good leaving groups and they undergo analogous reactions. The reaction depicted in Scheme 12 is reversible and the 1-pyrazolyl residues of 1 can be replaced by other nucleophiles, including other pyrazoles [165].…”

A theoretical and experimental study of the NMR spectra of 4,5,6,7-tetrafluorobenzazoles with special stress on PCM calculations of chemical shifts

“…In our group, we have devoted several papers to fluorinated heterocycles, with one to seven F atoms (Fig. ): a imidazoles, b pyrazoles, c indazoles, d benzimidazoles, e benzothiazoles and f benzodiazepinones . Highly or super‐fluorinated derivatives are of considerable interest for multiple purposes …”