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Reazioni di interconversione di anello. Sintesi e reattività di Z-2,4-dinitrofenilidrazone del 5-ammino-3-benzoil-1,2,4-ossadiazolo
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Studies on azole-to-azole interconversions. Substituent effects on the ring degenerate equilibration between 3-aroylamino-5-methyl-1,2,4-oxadiazoles and 3-acetylamino-5-aryl-1,2,4-oxadiazoles
No full textCan the absence of solvation of neutral reagents by ionic liquids be responsible for the high reactivity in base-assisted intramolecular nucleophilic substitutions in these solvents?
No full text5-ammino-3-benzoil-1,2,4-ossadiazolo:sintesi di arilidrazoni e loro conversione in N[2-aril-5-fenil-2H-1,2,3-triazol-4-il]benzencarbossamidi
No full textAcid- and Base-Catalysis in the Mononuclear Rearrangement of Some (Z)-Arylhydrazones of 5-Amino-3-benzoyl-1,2,4-oxadiazole in Toluene: Effect of Substituents on the Course of Reaction
No full textThe reaction rates for the rearrangement of eleven(Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-kinto the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas4a-k in the presence of trichloroacetic acid or of piperidinehave been determined in toluene at 313.1 K. The results havebeen related to the effect of the aryl substituent by usingHammett and/or Ingold-Yukawa-Tsuno correlations andhave been compared with those previously collected in a proticpolar solvent (dioxane/water) as well as with those on theanalogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general differences of chemical reactivity between protic polar (or dipolar aprotic) and apolar solvents
Secondary steric effects in SNAr of thiophenes: A coordinate kinetic, thermodynamic, UV-VIS, crystallographic and ab initio study
No full textThe reactivity of some dinitro-benzene and -thiophene derivatives with piperidine and sodium benzenethiolate has been examined giving evidence that benzenes show large and thiophenes show small kinetic secondary steric effects, respectively. The acid dissociation reaction and the UV-VIS spectra of some nitrothiophenamines have also been studied. The crystal structure and the absolute conformation of 2-iodo-3,5-dinitrothiophene and of 2-iodo-4-methyl-3,5-dinitrothiophene have been determined. For different conformations of the analogous chlorodinitro derivatives in the thiophene and benzene series, ab initio energy calculations have been performed. The results collected show that steric strain among adjacent groups affects the benzene and thiophene compounds and the kinetic, thermodynamic and spectroscopic properties of the molecules examined differently. Differences in geometry of the two aromatic rings and then in rotation of nitro groups with respect to the rings themselves as well as differences along reaction coordinates (essentially depending on hybridation changes) are used to explain the above data
Spiro-Meisenheimer adducts in the thiophene series: interdependence of 13C NMR and thermodynamic data
No full textNew examples of specific-base catalysis in monunuclear rearrangements of heterocycles found via a designed modification of the side-chain structure
No full textTo select suitable candidates for the occurrence of specific-base-catalysis in MRH of (Z)-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole we have designed a modification of the side-chain structure by linking a strong electron-withdrawing system to the hydrazono group. Thus we have synthesized the (Z)-semicarbazone (3d), the (Z)-phenylsemicarbazone (3e), and the (Z)-acetylhydrazone (3f) of the above oxadiazole and examined their kinetic behavior in dioxane/water in a large range of proton concentrations (pS(+) 4.0-14.5). In all the pS(+) range examined only a base-catalyzed process has been evidenced (no uncatalysed path occurs). The behavior at the largest pS(+) values (the reactivity tends to a limiting rate constant) and that at variable concentrations of buffer have furnished clear evidence for the occurrence of a specific-base-catalysed process, thus reaching the target proposed and confirming the previsio
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