摘要:

AbstractFirst and second thermodynamic dissociation constants of glycine at five temperatures from 278.15K to 318.15K in {14.926 mass% urea + water} mixed solvent have been determined from preciseemfmeasurements of hydrogen‐silver chloride electrodes in two cells, (A) and (B), without liquid junction, by the new method of polynomial approximation proposed on the basis of Pitzer's electrolytic solution theory in our previous papers, as compared with traditional extrapolation on the basis of the extended Debye‐Hückel equation. The results obtained from both methods are in agreement within experimental error. The thermodynamic quantitiesΔG°,ΔH°,ΔS° andΔCp° were derived from the dependence of pK° values on temperature, and pK1= 367.60 (K / T) − 0.3973 + 3.108 × 10−2(T / K), whereas pK2, = 2028.77 (K / T) + 2.8791 – 2.110 × 10−3(T / K). The results have been discussed in terms of the solute‐solvent interaction and have been compared with those results in water an

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090601

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThree new heterobimetallic acetylene complexes CpNiCo (CO)3(PPh3) (PhC2C4H4‐R‐p) [R = H (2), Br (3), COCH2(4)] have been synthesized in suitable yield (31–47%) via the reaction of (PhC2C3H4‐R‐p)CO2(CO)5PPh2with nickelcene inn‐octane. The complex CpNiCo(CO)3(Ph2C3) (1) has also been obtained in 12% by the reaction of (Ph2C2) Co2(CO)4with nickelcene. The complexes have been characterized by elemental analysis, IR and1H NMR. Electrochemical study of redox couples of these complexes was presented by using cyclic voltammetry on Pt electrodes in acetone. At room temperature, all complexes underwent electrochemically reversible or guasi‐reversible oneelectron oxidation or reduction to the stable radicals. The radical anions of the complexes could be easily detected by ESR methodin situelectrolysis in the THF solution. The isotropic parameters,CO=2.20mT,= 2.052 for the radical anion of complex 1,CO= 2.20 mT,P = 1.42 mT,=2.057 for the radical anion of complex 2, might indicate that NiCoC2framework is a delocalized unit and the ligand obitals in the complex have more contribution to the LUMO o

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090602

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper reports the determination of stability constants for complexes of Pb(II) with Gly, Ala, Asp and Gly‐Gly using both micro‐pH‐metric titrations and the application of convolution‐de‐convolution cyclic voltammetry at 25°C andI= 0.10 mol·dm−3(KNO3). Stability constants were calculated from pH‐metric data using the SUPERQUAD computer program and cyclic voltammograms were collected, stored and manipulated using the E G and G CONDECON 300 software. A′ considerably larger ligand: metal ratio (e.g.50:1) was possible using voltammetry. Under these conditions, hydroxy complex formation was minimised and the formation of bis‐complexes optimised. Computer based calculations were carried out on PC‐compatible microcomputers fitted with mathematics coprocessors. Evaluation of results from the two techniques suggests that stability constants for the species [PbL2] are reliable when calculated from voltammetry while those for [PbL]are more reliable when determined b

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090603

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractA new highly sensitive method for determination of trace silver in waste water with 9,10‐dimethylacridinium fluorosulfonate (DAFA)‐K2S2O8system was suggested. In the basic aqueous solution, trace of silver (I) showed strongly catalytic effect on the chemiluminescence system with the presence of 2,2′‐bipyridine. The range of the linear relationship between light intensity and concentration of silver (I) is 1.0 × 103mol / L to 6.0 × 103mol / L. The detection limit is 8.0 × 103mol / L, and the RSD for 5.0 × 103mol / L Ag (I) is 6.5% (n=13). In the existence of potassium fluoride, the selectivity is higher. Combining the treatment with nitric acid, the method is applied to determine some environmental waste water and the results are similar to atomic absorption s

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090604

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractKinetic studies of the singlet oxygenation of the title compounds were performed according to Monroe's method. The reaction rate increases with temperature decreasing, leading to a negative activation enthalpy and a large negative activation entropy. These data are interpreted as the evidence for the intermediacy of an exciplex. The solvent effect on the reaction rate suggests that the “dioxetane” path involves a transition state or an intermediate with significant zwitterionic character. The electronic effect of the substituent is obvious, with electron‐withdrawing substituent retarding the reaction and electron‐donating substituent increasing the reaction rate. However, steric bulkiness at the 6‐position does not play an important role in the reac

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090605

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction between cyclodextrins (CDs) and 1,3‐di(1‐naphthyl)propane (1) in aqueous methanol (V:V=1:1) has been investigated by means of fluorescence emission and UV absorption. Fluorescence enhancement and absorption spectra reveal that β‐ or γ‐CD can form inclusion complexes with 1, buta‐CD cannot. One of these complexes is identified as ground state complex (2:1),i.e.the eclipsed conformer of 1 is included. Molecule 1 can be driven out of the CD cavity by sodium dodecylsulfate (SDS) molecule, but cannot by cetyltrimethylammonium bromide (CTAB) or sodium cetylsulfate (SCS) molecules due to their alkyl ch

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090606

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate constants (k) of the homo‐cycloaddition reactions of five substituted α,β,β‐trifluorostyrenes (TFS's),i.e. p‐nitrotrifluorostyrene (4),p‐cyanotrifluorostyrene (5),p‐carbomethoxytri‐fluorostyrene (6),p‐carboxytrifluorostyrene (7) andp‐carbamyltrifluorostyrene (8), have been measured in the temperature range of 110–160°C. Thes̀mbpolar substituent parameters of these TFS's calculated from10F NMR chemical shifts are: NO2, 0.86; CN, 0.86; CO3CH3, 0.40; CO2H, 0.31; CONH2, 0.10. The spin delocalization substituent parameters σT˙of NO2, CN, CO2CH3, CO2H and CONH2are 0.32, 0.38, 0.31, 0.37 and 0.37 respectively. Thus all these electron‐pair attracting groups are also very

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090607

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThe reaction of silyl enol ethers (1a‐1e) with perfluoroalkyl iodides (2f–2k) initiated with sodium dithionite was studied. α‐Perfluoroalkyl ketones (3) were synthesized in excellent yield by this method.α, β‐Unsaturated fluorinated ketones (4) were obtained easily by dehydrofluorination of the α‐perfluoroalkyl ketones. A radical mechanism

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090608

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractA new and efficient method for the synthesis of potential antiviral agents Carba‐ACV (3) and Carba‐DHPG (4) is described. The synthesis makes the use ofN‐acetylguanine to condense with the corresponding tosylates (16) and (11) under the catalysis of dibenzo‐18‐C‐6, resulting in the desired coupling products (17) and (12) in good yield and in the case of Carba‐DHPG with high reg

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090609

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractA novel 1,6‐asymmetric induction has been observed in the iodolactonization of γ, delta;‐unsaturated amides. The optically active γ‐butyrolactone was synthesized by employing iodolactonization reaction as a k

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090610

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY