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21.
New Schiff bases have been prepared by reacting 3-hydroxy-4-pyridine- carboxaldehyde with various amines. NMR spectroscopic methods provided clear evidence that the Schiff bases exist in the solid state and in solution as hydroxyimino tautomers with the E-configuration. A study of the stabilities of the tautomeric forms and the different conformers has been carried out using density functional calculations at the B3LYP/6-31G** level. 相似文献
22.
Claramunt RM Sanz D Torralba MP Elguero J Sanchez P Enjalbal C Martinez J Aubagnac JL 《European journal of mass spectrometry (Chichester, England)》2003,9(4):403-407
A series of aminotroponimine and aminotropone derivatives were studied by electrospray mass spectrometry. MS and MS/MS data were acquired according to automated procedures. In the case of mono- and di-halogenated compounds, their specific behavior upon collisionally-activated dissociation conditions provided rapid structural assignments through inexpensive isotopic labeling MS/MS experiments. 相似文献
23.
Dionisia Sanz Almudena Perona RosaM. Claramunt Elena Pinilla M.Rosario Torres Jos Elguero 《Helvetica chimica acta》2006,89(7):1290-1303
The new N‐salicylideneheteroarenamines 1 – 4 were prepared by reacting the biologically relevant 3‐hydroxy‐4‐pyridinecarboxaldehyde ( 5 ) with 1H‐imidazol‐1‐amine ( 6 ), 1H‐pyrazol‐1‐amine ( 7 ), 1H‐1,2,4‐triazol‐1‐amine ( 8 ), and 1H‐1,3,4‐triazol‐1‐amine ( 9 ). Solution 1H‐, 13C‐, and 15N‐NMR were used to establish that the hydroxyimino form A is the predominant tautomer. A combination of 13C‐ and 15N‐CPMAS‐NMR with X‐ray crystallographic studies confirms that the same form is present in the solid state. The stabilities and H‐bond geometries of the different forms, tautomers and rotamers, are discussed by using B3LYP/6‐31G** calculations. 相似文献
24.
The 243 coupling constants of eight N-R-pyrazoles [R=H, CH3, C6H5, COCH3, NH2, NO2, SO2CF3, Si(CH3)3] have been calculated and compared with 131 experimental values. The agreement is good and can be used to estimate new couplings. The whole collection has been statistically analyzed. 相似文献
25.
Christine Enjalbal Jean-Louis Aubagnac Swiatoslaw Trofimenko Rosa Claramunt Dionisia Sanz Jos Elguero 《Journal of heterocyclic chemistry》1998,35(6):1405-1412
The nature of the matrix used in Fast Atom Bombardment (FAB) mass spectrometry analyses of pyrazolo[1,2-a]pyrazoles was found to influence significantly their positive and negative ions mass spectra. Indeed the use of glycerol provided an abundant ion corresponding to the protonated molecule (M+H)+ whereas the meta-nitrobenzyl alcohol favored the formation of the radical ion M+°. Such results which are in accordance with the oxidoreduction properties of the matrices studied were also established in Frit-FAB mass spectrometry analyses of pyrazolo[1,2-a]pyrazoles. 相似文献
26.
Schiff bases of 3-hydroxypyridin-4-carboxaldehyde and L-alpha-amino esters as well as those derived from the structurally related amines lacking the ester function have been synthesised. In two cases a tetrahydro-1H-imidazo[4,5-c]pyridine was formed as a by-product. (1)H, (13)C, (15)N-NMR spectral data and density functional theory (DFT) calculations established the structure of all compounds. 相似文献
27.
An NMR and Computational Study of Azolo[a]pyrimidines with Special Emphasis on Pyrazolo[1,5‐a]pyrimidines
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Ranjana Aggarwal Virender Kumar Gulshan Singh Dionisia Sanz Rosa M. Claramunt Ibon Alkorta Goar Sánchez‐Sanz José Elguero 《Journal of heterocyclic chemistry》2015,52(2):336-345
The reaction of 3(5)‐amino‐5(3)‐hydrazinopyrazole, a bifunctional compound, with 3‐oxo‐3‐phenylpropanenitrile and two of its p‐substituted derivatives affords 2,5‐diaryl‐7‐aminopyrazolo[1,5‐a]pyrimidines. A mechanism for this unexpected reaction involving the formation of hydrazine is proposed. The position of the aryl substituents on the bicyclic ring has been established by the combined use of NMR and DFT calculations. Moreover, the chemical shifts have been calculated, and some general rules have been withdrawn. 相似文献
28.
Alkorta Ibon Claramunt Rosa M. Sanz Dionisia Elguero José Holzer Wolfgang 《Structural chemistry》2021,32(3):925-937
Structural Chemistry - This work reports the 13C chemical shifts of 49 iodopyrazoles and the 15N chemical shifts of 6 iodopyrazoles, most of them from the literature but a number of significant... 相似文献
29.
A theoretical and experimental NMR study of BODIPY 493/503: difluoro{2‐[1‐(3,5‐dimethyl‐2H‐pyrrol‐2‐ylidene‐N)ethyl]‐3,5‐dimethyl‐1H‐pyrrolato‐N}boron
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30.
Effect of Substituents on the Regioselectivity of the Reaction of α‐Tosyloxyketones with Thioureas in Acidic Medium: Access to 2‐Aminothiazoles and 2‐Imino‐2,3‐dihydrothiazoles
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Ranjana Aggarwal Rajiv Kumar Dionisia Sanz Rosa M. Claramunt 《Journal of heterocyclic chemistry》2014,51(3):598-603
Regioselective condensation of α‐tosyloxyacetophenones 1 and N‐substituted thioureas 2 in acidic medium to give regioisomers 2‐aminothiazoles I and 2‐imino‐2,3‐dihydrothiazoles II is largely influenced by the substituents present on 1 and 2 . A mechanism, supported by DFT calculations has been proposed to explain the observed regioselectively. 相似文献