摘要:

AbstractChiral polymethine dyes constitute a particular class of conjugated π systems. Artificial chiral polymethine dyes were first synthesized by König and Langbein in 1928 in order to clarify the electronic structure of cyanine dyes; some natural dyes such as musca‐aurin I (from the toadstool fly agaric) and betanin (from the vegetable red beets) are known to be chiral pentamethinium cyanine dyes, the chirality of which stems fromL‐α‐amino acids as end‐groups. The reasons why chiral polymethine dyes are not only of historical interest but once again the subject of research are

ISSN:0894-3230    

DOI:10.1002/poc.610081202

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPeroxidation of linoleic acid was initiated by azobis(isobutyronitrile) intert‐butyl alcohol and inhibited by α‐tocopherol, β‐carotene and retinal, either alone or in combination. Significant antioxidant synergism and a novel mutual protection of α‐tocopherol and β‐carotene were found and the possible involvement of retinal in the process

ISSN:0894-3230    

DOI:10.1002/poc.610081203

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractUV spectra of 16p‐Y‐substituted phenylacetylenes (I‐Ys), ninep‐Y‐substituted acetophenones (2‐Ys) and sixp‐Y‐substituted‐p′‐methylsulphonylstilbenes (3‐Ys) were measured and correlated against spin‐delocalization substitutent constants (σ.) with confidence levels above 99·9%. UV spectra of five ethyl 3‐hydroxy‐3‐(p‐Y‐substituted‐phenyl)‐propanates (4‐Ys) and five 1‐(p‐Y‐substituted‐phenyl)‐3‐butyn‐1‐ols (5‐Ys) were also measured. Correlation analysis results are discussed. Some literature UV data wer

ISSN:0894-3230    

DOI:10.1002/poc.610081204

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe directionally weighted steric substituent constant Ωjkwas introduced to evaluate the anisotropic steric hindrance effect to the reaction centre. The correlation of the rates with a series of directionally weighted Ωjkis useful for characterizing the feature of steric effect. The difference between the hydrolyses of carboxylic esters and carboxamides was shown by this metho

ISSN:0894-3230    

DOI:10.1002/poc.610081205

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe photolysis and thermolysis of 7,8‐diaza‐3‐oxatricyclo[4.2.1.02,5]non‐7‐enes were studied. Photolysis showed a novel [4π + 2π + 2π]cycloreversion in a formal way, the first example in azoalkane chemistry. This cycloreversion was found to be sensitized by the benzophenone produced. In contrast, thermolysis showed the typical decomposition pattern of azoalkanes, extrusion of nitrogen and subsequent σ‐bond formation of the resulting biradical to afford the tr

ISSN:0894-3230    

DOI:10.1002/poc.610081206

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of the oxidation of leuco methylene blue and leuco thionine by somep‐benzoquinones were investigated spectrophotometrically by means of the stopped‐flow technique. Leuco methylene blue and leuco thionine were produced by photoreductions of methylene blue and thionine with triethylamine in ethanol in the drive syringe of the stopped‐flow apparatus and their solutions were used as such in the measurement of the oxidation rates. The kinetic isotope effect on the oxidation rate was observed. The results can be explained by the general mechanism with stepwise electron–proton–‐electro

ISSN:0894-3230    

DOI:10.1002/poc.610081207

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractBis(2,4‐dinitrophenyl ether)s of the water‐soluble polymer poly(ethylene glycol) (PEG) are low‐loading models for time‐release herbicide systems and may potentially hydrolyse in basic aqueous media according to a mechanistic menu that includes elimination, aliphatic and/or aromatic displacement, as well as anchimerically assisted displacement involving O‐6 of the plyether backbone. This paper study reports kinetic (second‐order rate constnts,k2, and activation parameters) and1H (400 MHz) NMR results (monitoring of the reaction in DMSO‐d6and D2O) for the alkaline hydrolysis of a series of these ethers (DNPEGs). DNPEGs with varying average molecular weights (MW) of the polymer backbone (DNPEG‐59, ‐1900 and ‐3200, where the numbers refer to the PEG MW) were studied, as were DNPEGs that differed only in the degree of end‐group substitution, namely DNPEG‐1900‐59 and ‐81 (where the final numbers refer to the percentage substitution). The1H NMR studies show significant aryl ring hydrogen–deuterium exchange in the hydroxide–DMSO‐d6and hydroxide–D2O systems examined, as well as a poly(ethylene glycol) alkoxide (PEG‐O−) C‐1 adduct in DMSO‐d6; the PEG‐O−is displaced in anSNAr fashion from DNPEG as a result of initial hydroxide attack at C‐1 of DNPEG. The kinetic and spectroscopic results are discussed in the context of previous kinetic studies of alkaline hydrolysis of alkyl 2,4‐dinitrophenyl ethers, recent1H NMR spectroscopic studies of electron‐deficient aryl ethers and the mechanism of hydrolysis in the DNPEG systems. The possible significance of these results for the development o

ISSN:0894-3230    

DOI:10.1002/poc.610081208

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAnalysis of temperature dependent equilibrium constant data for the complexation of α‐cyclodextrin with approximately 70 different substrates demonstrates the existence of a general compensation effect. Enthalpies (kJ mol−1) and entropies (J K−1mol−1) of complexation are related by ΔH= −5·70(±0·05) + [421·1(±1·2)]ΔS. A few substrates deviate from the general effect, possibly owing to reorganization of internal hydrogen bonding interactions. Complexation reactions involving β‐cyclodextrin are found to divide into two groups. Eleven small molecule or ion substrates undergo isoentropic complexations with ΔS= −5·7±2 J K−1mol−1. Fourteen larger substrate species exhibit a compensation effect with ΔH= −23·5(±0·2) + [634(±26)]ΔS. The compensation behavior of the two cyclodextrins is discussed in terms

ISSN:0894-3230    

DOI:10.1002/poc.610081209

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

ISSN:0894-3230    

DOI:10.1002/poc.610081201

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY