Mass spectrometric investigation of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives (original) (raw)
Ab initio study of the effect of N-substituents on properties of pyrazoles
Tetrahedron, 1995
A series of fourteen derivatives of pyrazole have been calculated at the MP2-6-31G** level. The first thirteen are derivatives of the parent pyrazole with different substituents on the nitrogen N(1) and the last one is pyrazole N-oxide. The substituents have been selected to cover a wide range of electronic effects. The theoretical results are discussed in relation with geometries, energies, vibrational spectra, Bader analysis and tautomerism (in the case l-hydroxypyrazole/pyrazole N-oxide).
Monatshefte Fur Chemie, 2009
Abstract Stoichiometric ionization constants of some pyrazole carboxylic acids [4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-benzoyl-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1,5-diphenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid] were determined in ethanol–water mixtures of 50, 60, 70% ethanol (v/v) by a potentiometric titration method. Titrations were performed in an ionic strength of 0.10 M NaCl at 25.0 ± 0.1 °C using an Orion 960 automatic titrator under a nitrogen atmosphere. Using the potentiometric titration data, ionization constants were calculated in three different ways. The effects of structure and solvent on the acidity of pyrazole carboxylic acids are also discussed. Graphical abstract
Synthesis and Characterization of Some Compounds containing Pyrazole Moiety
Journal of University of Anbar for Pure Science
This study includes the preparation of some heterocyclic compounds compact of the Pyrazole, work is done in three steps. First step, treatment of acetophenone derivatives with DMF-DMA for the preparation of the first compound (2E)-1-(R phenyl)-3-(dimethylamino)prop-2-en-1-one , (R) is one of the derivatives used for acetophenone (R = Br, NH 2). The second step, treatment of benzaldehyde derivatives with hydrazine to prepare the second compound in the series (1E)-(R benzylidene) hydrazine, where (R) is one of the derivatives used for benzaldehyde to get the Shiff bases. And the third step, treatment of the first step products with the products of the second step. Each product from the first step gives us a series of Pyrazole compounds with its reaction with products of the second step interaction after the other. Thus, we can bring a number of compounds, the sum of the first step products multiplied by the products of the second step. The third-step reaction is a ring-blocking reaction to form a combined heterogeneous ring of Pyrazole. Finally, characterization these compounds with infrared spectra, NMR spectrum and mass spectrometry.
Electron ionization induced fragmentation of some oxadiazole and thiadiazole derivatives
Rapid Communications in Mass Spectrometry, 2004
The mass spectrometric behaviour under electron ionization of several 3,4-(alkyl/aryl)-disubstituted 1,2,4-oxadiazole-5(4H)-ones (1–13) and 1,2,4-thiadiazole-5(4H)-thiones (14–17), and that of 3-aryl-5-alkyl- or arylthio-1,2,4-thiadiazoles (18–24), was studied. These five-membered rings split similarly to the corresponding 1,2,4-thiadiazole-5(4H)-ones, although substitution has also a clear effect on the routes of fragmentation and the magnitude of secondary processes. In particular, the fragmentation of 1,2,4-oxadiazole-5(4H)-ones (1–6), which do not bear aromatic substituents, was, in addition to the ring ruptures, fairly complicated. The other compounds fragmented more systematically and relatively few unpredictable fragmentations occurred. Copyright © 2004 John Wiley & Sons, Ltd.
Collisional activation of protonated C-halogenopyrazoles
Chemical Physics Letters, 2001
Collisional activation of protonated 3-halogenopyrazoles (X±Pz, X Cl, Br and I) in the high or low translational energy regime induced an intense loss of X giving C 3 H 4 N Å 2 radical cations whose structure depends on the nature of the halogen. Protonated 3-I±Pz generated thus ionized pyrazole a, whereas protonated 3-Cl±Pz was a precursor of an isomeric species ascribed to a dehydropyrazolium distonic structure b. A mixture of C 3 H 4 N Å 2 ions was formed in protonated 3-Br±Pz. B3LYP/6-31G(d,p) computations con®rmed a regiospeci®c N 2 -protonation, and a low energy content of the distonic ions b or c (50 kJ mol À1 above a and lying in deep energy wells). Two competitive C±H and C±X bond cleavages were invoked to explain the contrasting behaviour of various protonated X±Pz under dehalogenation conditions. Ó
Electron impact mass spectrometry of some 6-substituted tetrazolo[1,5-c]pyrimidin-5(6H)-ones
Journal of Mass Spectrometry, 1993
The electron impact mass spectra of 6-methyltetrazolo[1,5-c]pyrimidin-5(6H)-one, its 7- and 8-methyl derivatives, three 8-halo derivatives and two related nucleosides are reported. On the basis of the high-resolution data and detected metastable ions, the fragmentation routes of their molecular ions are proposed. Coexistence of the tautomeric forms of the title compounds of cyclic (tetrazole) or linear (azide) structure can be suggested owing to the fragmentation pathways identified for the bases. Decomposition of the related nucleosides lies in the breaking of nucleoside bonds to produce the appropriate base and sugar fragments.
Journal of Physical Organic Chemistry, 1996
The gas-phase basicities of 3,4,5-tri-tert-butylpyrazole (I) and 1,3,4,5-tetra-tert-butyl-pyrazole (11) were measured by Fourier transform ion cyclotron resonance spectrometry. The x-ray molecular structures of 1-HCI (a monohydrate) and I1 were determined. A clear lack of planarity is present in the pyrazole rings because of the steric effects of the tert-butyl substituents. The CSp3 atom bonded to N-1, 12-3, C-4 and C-5 atoms deviates significantly from the pyrazole plane, as expected on the basis of semi-empirical AM1 calculations. In I-HCI, the molecules form dimers through symmetry centres in which the chlorine atom and the water molecules play an important role. The proton affinity (P A) is defined as GBs were determined from equilibrium protontransfer reactions conducted in a modified Bruker CMS-47 Fourier transform ion cyclotron resonance (FT-ICR)' mass spectrometer used in previous studies." Its high magnetic field strength (4.7 T) easily allows the PA (B) = AHH + (g).
Journal of Heterocyclic Chemistry, 1985
The mass spectral fragmentation patterns of ten 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles, I, obtained by electron impact have been studied. All the spectra analyzed contain molecular ions and the principal fragmentation routes take place either from the molecular ion, or from (M+-1) ion. Likewise, our investigation of the mass spectra of these compounds revealed interesting relationships between the substitution pattern in the framework of I and the fragmenation pathways.
Biological Mass Spectrometry, 1985
The mass spectrometric behaviour of methyl 0-acetyl-P-D-xylopyranosides has been studied using electron impact, methane and ammonia chemical ionization and collisional activation mass spectrometry. Based on this study the fragmentation of the compounds studied has been described. The structures of ions occurring after elimination of ketene in the fragmentation reactions of acetylated saccharides were studied by using the MNDO semi-empirical quantum chemical method. Calculated geometrical parameters (bond lengths, bond and torsional angles), distribution of net atomic charges and the difference in heat of formation (70 kJ mol-') between the keto and enol isomers of [CSH,O,]' ions studied predict that the enol structure is more stable thermodynamically than its corresponding keto isomer.