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Tautomerism and hydrogen bonding in reaction products from 4-aminopent-3-en-2-one and diazonium ions
No full textThe azo-coupling products have been prepared from 4-aminopent-3-en-2-one and 4-chloro- or 4-nitrobenzenediazonium ion.
Structure of the products obtained was studied by means of multinuclear NMR spectroscopy in CDCl3 solutions and X-ray
diffraction in solid state. Both products are predominantly present as azo forms in both the solution and the solid state, the azo
form content being higher in solid state. The substituent effect on azo-hydrazone tautomeric equilibrium of the substances is
more significant in solution than in solid state
Solution and solid state structure and tautomerism of azo coupled enaminone derivatives of benzoylacetone
No full textThe reaction of 4-substituted benzenediazonium tetrafluoroborates with 3-amino-1-phenylbut-2-en-1-one, 4-amino-4-phenylbut-3-en-2-one and their N-aryl derivatives 1a-1g has been used to prepare the respective azo coupling products i.e. compounds 2-5 from enaminone 1a, compounds 6-9 from enaminone 1c, compound 10 from enaminone 1d, compound 11 from enaminone 1e, compounds 12, 13 from enaminone 1f, compounds 14, 15 from enaminone 1b and compound 16 from enaminone 1g. Tautomerism of the azo coupling products prepared has been investigated in CDCl3 solutions by means of H-1, C-13 and N-15 NMR spectra. Crystal structures of selected products have also been investigated by means of X-ray diffraction
An NMR and X-ray study of the structure of the azo coupling product of 4-dimethylaminopent-3-en-2-one and benzenediazonium-tetrafluoroborate
No full text4-Dimethylaminopent-3-en-2-one reacts with two molecules of benzenediazonium-tetrafluoroborate to give compound 1. The structure of this compound was determined by means of X-ray analysis of its crystal and 1H, 13C and 15N NMR spectra of its solution in CDCl3. The molecule of this compound contains one azo group and one hydrazone group. The substance exists, both in crystal form and in solutions of concentrations above 0.1
mol-1, in the form of a dimer, in which the pair of molecules are bound by two hydrogen bonds N–H ... N. On diluting the
solution, the dimers decompose, the two forms being in an equilibrium that is rapid on the NMR time scale
Synthesis, NMR and X-ray characterisation of 6-substituted 4-amino-5-aryldiazenyl-1-arylpyridazinium salts
No full textA new simple method has been used to prepare 6-substituted 4-(subst. amino)-5-aryldiazenyl-l-arylpyridazinium salts from N-methyl- or N-aryl-3-amino-l-phenylbut-2-en-l-ones and 4-aminopent-3-en-2-ones and substituted benzenediazonium tetrafluoroborates or hexafluorophosphates. The structure of selected derivatives was studied by means of N-15 NMR spectra and X-ray
Novel 5-(4-substituted-phenyldiazenyl)-1,3,2 lambda(4)-oxazaborines and their rearrangement to 1,2,4,3 lambda(4)-triazaborines
No full textThe reaction of substituted benzenediazonium tetraphenylborates with the beta-enaminones derived from pentane-2,4-dione, 1-phenylbutane-1,3-dione, and 1,4-diphenylbutane-1,3-dione with a primary or secondary (N-methyl, N-phenyl) amino group in CH2Cl2 gives 5-(substituted-phenyldiazenyl)-2,2-diphenyl-4,6-disubstituted- 1,3,2 lambda(4)-oxazaborines or 5-(substituted-phenyldiazenyl)-2,2-diphenyl-3,4,6-trisubstituted-1,3,2 lambda(4)- oxazaborines, respectively. The reaction intermediate of these compounds has been identified, and a mechanism for the reaction has been suggested. Substituted 1,3,2 lambda(4)-oxazaborines gradually rearrange into 1,2,4,3 lambda(4)-triazaborines at temperatures above 100 degrees C
Structure and base catalysed cyclization of methyl (2,6-disubstituted-4-nitrophenylsulphanyl)ethanoates
No full textThe conformation of side chain –SCH2COOCH3 in title compounds in crystal agrees with the reactivity of these compounds
in base catalysed ring closure in solution. In the 2,4-dinitro derivative, the side chain is oriented towards the unsubstituted
ortho-position of benzene ring, in the case of the 2-methoxycarbonyl derivative towards this substituent
Formation of pyridazinium salts by azo coupling of N-substituted 3-amino-1-phenylbut-2-en-1-ones and diazonium salts
No full textTreatment of 3-(2,4-dimethoxyphenylamino)- and 3-methylamino-1-phenylbut-2-en-1-ones with some benzenediazonium tetrafluoroborates gives, besides the usual azo coupling products [i.e., 3-(substituted imino)-1-phenylbutane-1,2-di-ones 2- (4-substituted phenylhydrazones) and 2-(4-methoxy-phenyldiazenyl)-3-methylamino-1-phenylbut-2-en-1-one, respectively], the previously unreported 1,4,5,6-tetrasubstituted pyridazinium tetrafluoroborates. The pyridazinium salts have been identified by X-ray analysis and by their H-1, C-13, N-15, B-11 and F-19 NMR spectra. Their formation is most probably the result of nucleophilic attack on the carbonyl carbon by the nitrogen of the hydrazone group and subsequent dehydration
Structure and tautomerism of azo coupling products from N-alkylenaminones derived from acetylacetone and benzoylacetone in solid phase and in solution
No full textA series of azo coupling products have been prepared by reaction of substituted benzenediazonium tetrafluoroborates with N-alkyl 4-aminopent-3-en-2-ones or 3-amino-1-phenylbut- 2-en-1-ones. The structure and tautomerism of the reaction products were studied by means of single-crystal X-ray study and by NMR spectroscopy in deuteriochloroform solution. The azo coupling products obtained from 4-methylaminopent-3-en-2-ones (3a-i) exist in CDCl3 solution as E/Z isomer mixtures with the Z isomer strongly predominating. The major isomer is a mixture of enamino - azo and imino - hydrazo tautomers with the former predominating. The proportion of the azo form depends on substitution of the benzene ring of the diazonium salt and decreases in the order of MeO > Me > Br > NO2. The position of tautomeric equilibrium is practically unaffected by switching from 4-methylaminopent-3-en-2-ones to 3-methylamino-1-phenylbut- 2-en-1-ones. In the solid phase, the azo form always predominates; substitution of diazonium salt and at N3 nitrogen does not significantly affect the position of the tautomeric equilibrium. The azo coupling products always exist in the form of a single Z isomer. All determined structures, in the solid state, consist of a mixture of the two tautomeric forms, amino - diazenyl and imino - hydrazone, in ratios ranging from 82/18 to 91/9%. The weighed superimposition of both the hydrogen-bonded N1=N2 - C1=C2 - N3H/HN1 - N2=C1 - C2=N3 heterodienic fragments, however, do not allow to clarify the effects of the para-substituents at the N1-phenyl ring both on the N1 center dot center dot center dot N3 hydrogen-bond distances and on the bond lengths in the heterodienic systems within the series 3a - c, f and 4a - c, e, f
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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