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Electron-donating Properties (electron-donating + property)
Selected AbstractsReaction of 4-benzylidene-2-methyl-5-oxazolone with amines, Part 2: Influence of substituents in para-position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kineticsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002B. Bet, akowska An influence of a structure of the amine (benzylamine, N -methyl-benzylamine, N -isopropyl-benzylamine, N -methyl-butylamine, N -ethyl-butylamine, sec -butylamine, and tert -butylamine) on a rate constant of the ring-opening reaction of 4-benzylidene-2-methyl-5-oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant , as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring-opening reaction was studied. The substituents (OH, OCH3, N(CH3)2, Cl, NO2) in para-position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring-opening reaction decreased with increase of the electron-donating properties of the substituent. A good correlation between the rate constants of the reaction of 4-(4,-substituted-benzylidene)-2-methyl-5-oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148,155, 2002; DOI 10.1002/kin.10039 [source] X-Ray Photoelectron Spectroscopy and Reactivity Studies of a Series of Ruthenium CatalystsCHEMCATCHEM, Issue 1 2009Katarzyna Jarzembska Abstract X-Ray photoelectron spectroscopy (XPS) was applied to six selected ruthenium precatalysts. The XPS data obtained were compared against reactivity and structural results. The XPS data confirmed some dependencies such as the electron-donor properties of the substituents at the ruthenium center. Additionally, the data combined with structural and reactivity results explain the differences between the character of Grubbs and Hoveyda catalysts. It was found that changing the PCy3 ligand to OiPr (PCy3=tricyclohexylphosphane, OiPr=isopropoxy) has a major influence on relative electron-donating properties of the N-heterocyclic carbene ligand (NHC) and PCy3 groups, which was supported by the relative charges on the Ru center for the examined compounds. Moreover, the turnover frequency (TOF) of a selected example reaction decreased when introducing a NHC group in the case of Grubbs catalysts, but increased in the case of Hoveyda-type catalysts. The XPS data also explained the relative activity values of some catalysts (higher reactivity of nitro-Hoveyda than Hoveyda second-generation catalysts). However, the binding energies do not predict TOFs. Sole examination of the XPS data does not provide a base for reaching unambiguous and binding conclusions as to the relative reactivity of all the investigated systems. [source] The Influence of Phosphane Ligands on the Versatility of Ruthenium,Indenylidene Complexes in MetathesisCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2010Julie Broggi Dr. Abstract The aim of the present study is to develop readily available and stable pre-catalysts that could be easily prepared on large scale from simple starting materials. Based on the hypothesis that substitution of classical PCy3 with phosphanes of varying electron-donating properties could be a straightforward manner to improve catalytic activity, a methodical study dealing with the effect of phosphane fine-tuning in ruthenium,indenylidene catalysts was performed. Challenged to establish how the electronic properties of para -substituted phosphane ligands translate into catalyst activity, the versatile behaviour of these new ruthenium,indenylidene complexes was investigated for a number of metathesis reactions. [source] Electron- and Energy-Transfer Properties of Hydrophilic CarotenoidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2007Hans-Richard Sliwka Abstract The antioxidant activities,expressed as the electron-donating properties,of five hydrophilic carotenoids (carotenoid surfactants) and three related hydrophobic carotenoids were investigated by flash photolysis. The electron-transfer rates of the carotenoids to the triplet state of the sensitizer 2-nitronaphthalene and the energy transfer rates of triplet 2-nitronaphthalene to the carotenoids were determined. The results demonstrate that the electron-donating effects of the hydrophilic and hydrophobic carotenoids were comparable when evaluated in acetonitrile. In the presence of water, however, electron transfer (i.e., antioxidant efficiency) was enhanced by a factor of four for the hydrophilic carotenoids. The increased hydrophilicity of carotenoids, therefore, could expand their antioxidant properties, thus facilitating their use as aqueous-phase radical scavengers. At the same time, it was shown that supramolecular assembly ("aggregation") of the amphiphilic carotenoids prevented electron transfer, thus deactivating the antioxidant function. Modulation of the biophysical properties of carotenoids through synthetic modification is capable of increasing the biological and medical utility of this natural class of predominantly hydrophobic antioxidant compound. [source] An Extremely Simple Dibenzopentalene Synthesis from 2-Bromo-1-ethynylbenzenes Using Nickel(0) Complexes: Construction of Its Derivatives with Various FunctionalitiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2009Takeshi Kawase Prof. Abstract Nice and easy: A very simple synthesis for dibenzopentalenes, which starts from 1-bromo-2-ethynylbenzenes, has been developed. It uses Ni0 complexes (see scheme), from which a relatively stable NiII complex as an important intermediate has been isolated. Dibenzopentalenes with various functional groups can be prepared by the procedure, and their electronic properties are consistent with theoretical calculations. An extremely simple dibenzopentalene synthesis from readily available 2-bromo-1-ethynylbenzenes using a nickel(0) complex is described. Although the yields are moderate, the formation of three CC bonds in a single process and the high availability of the starting materials are important advantages of this reaction. The corresponding aryl,nickel(II) complex as an important intermediate was isolated as relatively stable crystals, and the structure was confirmed by X-ray crystallographic analysis. The high stability of this complex should play a key role in this reaction. The reaction is applicable to the preparation of dibenzopentalenes bearing various functional groups. Their electronic properties are consistent with theoretical calculations. The cyclic voltammograms of these compounds reveal highly amphoteric redox properties. In particular, the electron-donating property of a tetramethoxy derivative is greater than that of oligothiophenes and dibenzodithiophenes and almost comparable to that of pentacene. [source] Dyeing and fastness properties of phthalimide-based alkali-clearable azo disperse dyes on poly(ethylene terephthalate)COLORATION TECHNOLOGY, Issue 6 2009Joonseok Koh The properties of a series of phthalimide-containing azo disperse dyes and azo dyes with N -methyl phthalimide moieties in their diazo component were investigated and compared when used to colour polyethylene terephthalate. The N -substitution of the phthalimide gave a hypsochromic effect on the colour change and better colour yields on poly(ethylene terephthalate) fabrics, probably because of the electron-donating property of the methyl group and the higher hydrophobicity of phthalimide-containing azo dyes compared with those containing phthalimide moieties. The results show that phthalimide-based azo disperse dyes have excellent dyeing fastness properties and that high wash fastness can be achieved using alkali clearance. This alternative clearance method is important for reducing the environmental impact of the dyeing process by replacing reductive clearing and, in particular, by removing the need for sodium hydrosulphite, which creates a high biological oxygen demand when released in conventional disperse dyeing effluent and which generates aromatic amines. [source] | ||||||||||