摘要:

AbstractThe kinetics of the Menshutkin reaction between triethylamine and iodoethane was studied at 313 K in seven primary and secondary alkanols. An accurate conductimetric method was employed to obtain second‐order rate constants at pressures of 0·1–200 MPa. Volumes and isothermal compressions of activation were calculated by different model‐based equations which are compared. Activation volumes at 0·1 MPa are in the range −26 to −33 cm3mol−1. Procedures for dissecting intra‐ and intermolecular contributions to the volume of activation are discussed. A clear dependence of model parameters on the solvent volumetric prope

ISSN:0894-3230    

DOI:10.1002/poc.610080202

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction of 2‐(p‐nitrophenyl)ethyl bromide with hydroxide ion was studied in oil‐in‐water (o/w) microemulsions at 50°C. The octane‐in‐water microemulsion systems were stabilized by chemodegradable cyclic acetal‐type cationic surfactants as [(2‐alky‐1,3‐dioxolan‐4‐yl)methyl]trimethylammonium bromides Ia–c (alkyl: a =n‐C9H19; b = C11H23; c = C13H27) and butan‐1‐ol as co‐surfactant. The rate constants were also determined in the corresponding aqueous micelles and in water. The hydrolytic lability of Ia–c in the microemulsion systems was achieved at 50°C by acid hydrolysis of the 1,3‐dioxolane ring. Systematic synthetic studies of the dehydrobromination were performed in order to develop a preparative approach for the product separation without unfavourable pro

ISSN:0894-3230    

DOI:10.1002/poc.610080203

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe hydrogen bond complexes between metyrapone [methyl‐1,2‐di(3‐pyridyl)propan‐1‐one] and hydroxylic proton donors (phenols, water) were investigated by infrared spectroscopy. The thermodynamic and spectroscopic data determined in carbon tetrachloride suggest that the nitrogen atom of the pyridine ring A [bonded to the C(CH3)2group] is the main hydrogen bond interaction site. The data are compared with di‐2‐pyridylglyoxal complexes where the hydrogen bonds are formed on the oxygen atom of the carbonyl function. In the solid adduct of metyrapone with HCl, protonation takes place on the two nitrogen atoms of the pyridine rings. The data from this work are compared with those from chemical oxidation, which leads predominantly to the formation of mono‐N‐oxide

ISSN:0894-3230    

DOI:10.1002/poc.610080204

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dependence of the amount of water bound to human serum albumin (HSA) suspended in water–dioxane mixtures vs the equilibrium water concentration in the liquid phase was determined by the Fisher method at 298 K. The Langmuir model was used in order to describe the isotherm of the sorption of water by HSA at low water concentrations in the solvent. The calculated equilibrium constant of water adsorption (3.8 ± 0.6 l mol−1) is in good agreement with the adsorption constant obtained earlier from calorimetric data. The comparison of the determined isotherm of water sorption by HSA with the reported enthalpies of suspension formation showed that at low water concentrations in the solvent, water sorption is the only process contributing to the heat effects of the formation of the ‘protein + liquid’ heterogeneous system. From this comparison, the enthalpy of water adsorption by HSA was evaluated as −11.9 ± 1.7 kJ mol−1. At higher water concentrations in the solvent the amount of water adsorbed by HSA increased considerably. This increase in the amount of water on HSA at water activities above 0.5 is assumed to be due to the enlargement of the protein

ISSN:0894-3230    

DOI:10.1002/poc.610080205

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractConformational preferences have been measured for 4‐X‐cyclohexenes (X = Br, Cl, CHO, COOH) in a series of solvents with increasing polarity. The conformational equilibrium exhibits a very weak solvent dependence. ΔGvaries at most by 0·25 kcal mol−1(1 kcal = 4·184 kJ) shifting from a non‐polar mixture (CS2–CDCI3) to highly polar (CD3)2SO. The reaction field theory was used to calculate the variation of ΔGwith solvent polarity. The calculated solvent shifts δΔGare small and in agreement with the values determined

ISSN:0894-3230    

DOI:10.1002/poc.610080206

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractX‐ray data on the crystal and molecular structure of bis(biphenyl‐2,2′‐diyl)allene, reveal a remarkably strong deviation from linearity (170·1°) of the allene unit of the molecule.Ab initiocalculations involving dimers of molecules yield good correlation with this geometry, showing that the non‐linearity is due to packing effects in

ISSN:0894-3230    

DOI:10.1002/poc.610080207

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of the reaction of 1,1,1‐trichloro‐4‐methoxy‐3‐penten‐2‐one with various aliphatic and aromatic amines was studied at 25°C in water, dimethyl sulphoxide, methanol, ethanol, chloroform, toluene and hexane. The formation of the corresponding 1,1,1‐trichloro‐4‐amino‐3‐penten‐2‐one is explained in terms of an ad

ISSN:0894-3230    

DOI:10.1002/poc.610080208

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe superaromaticity concept is examined and developed, taking into account what is known about aromaticity. Three new hardness indices indices are defined, and shown to be excellent parameters for characterizing superaromaticity. High superaromaticity indicates significant global annulenoid conjugation relative to local benzenoid conjugation in circularly annealed benzenoid molecules. Kekulene, coronene and corannulene tetraanion all are predicted to be superaromatic. The prediction for the corannulene tetraanion strongly supports the “annulene‐within‐an‐annulene” structure derived from

ISSN:0894-3230    

DOI:10.1002/poc.610080209

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractTitration calorimetric data show a dramatic change from endo‐ to exothermic deaggregation when pentanol–hexadecyltrimethylammonium bromide (CTAB) mixed solutions are injected into an aqueous solution containing pentanol. The results are interpreted in terms of a change in the structures of the aggregates in solution from simple CTAB micelles to mixed amphiphilic microheterogeneities when pentanol is ad

ISSN:0894-3230    

DOI:10.1002/poc.610080210

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetic study of the reaction of 1‐pyrrolidino‐2,4‐dinitrobenzene, 1‐piperidino‐2,4‐dinitrobenzene and 1‐morpholino‐2,4‐dinitrobenzene with NaOH in the presence and absence of the amine leaving group was carried out in aqueous solutions at 25°C, giving 2,4‐dinitrophenol as the only product. A mechanism involving the formation of σ complexes by addition of HO−or the amine to the unsubstituted positions of the aromatic ring is proposed. These complexes were found to react faster than

ISSN:0894-3230    

DOI:10.1002/poc.610080211

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY