Mass spectrometric investigation of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives (original) (raw)
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Trends for Pyrazole Fragmentation Determined by Gas Chromatography Coupled with Mass Spectrometry
Gas Chromatography - Derivatization, Sample Preparation, Application [Working Title], 2018
In this chapter, we present a review on pyrazole fragmentation by gas chromatography coupled with mass spectrometry, in order to evaluate the substituent effect on pyrazole fragmentation. Our objective was to present a comprehensive study on the fragmentation pattern of substituted pyrazoles, contribute to the systematization of knowledge, and offer support to researchers in the characterization of pyrazoles via a comprehensive and versatile technique such as gas chromatography coupled with mass spectrometry. The pyrazole fragmentation showed two important processes: (i) expulsion of HCN from [M] +• and [M-H] + and (ii) the loss of N 2 from [M-H] +. Substituents such as D, Me, Br, Cl, and Ph did not influence these two processes; however, the presence of nitro, acetyl, oxime, diphenyl, or methyl and nitro in the ortho-position transforms the two processes into secondary fragmentation or results in their absence in the fragmentation of the said pyrazoles.
Electron‐impact induced fragmentation of spiro‐1‐pyrazolines
Rapid Communications in Mass Spectrometry, 1992
The positive‐ion electron impact mass spectra of twelve spiro‐1‐pyrazolines have been recorded as 70 eV electron energy and the dat analyzed to elucidate their fragmentation pathways. None of these compounds gave abundant molecular ions (M+) due to the instability of the pyrazoline ring. The first step in the decomposition of M+ ions is the elimination of a nitrogen molecule followed by a rearrangement resulting in the formation of the cation radical [M–28]+, the decomposition of which is discussed in detail. The proposed fragmentation pathways and their mechanisms are supported by high‐resolution data, linked‐scan measurements at constant B/E and collision‐induced dissociation‐mass‐analyzed ion kinetic energy spectra.
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