摘要:

A theoretical model based on a diffusional process is proposed for a better understanding of the migration phenomenon of mobile hydrogen species. The validity of the model is tested by theoretical simulation of the various parameters. The model is compared with kinetic experimental results of solid 4-ten-butylphenol hydrogenation.

ISSN:1058-725X    

DOI:10.1080/10587259208032122

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A kinetic model for the radiation induced oxidation of isotactic polypropylene film (38μ thick) has been developed which allows determination of the concentration profiles, rate constants and diffusion coefficients. The match with the experimental data is consistent with a distribution of reactivity that changes during the course of the reaction giving rise to time dependent fat? constants according to the Plonka's equation (k=ko(a-1). This equation can be rationalized within the framework of the random walk models under the assumption of temporal, geometric or energetic disorder. The origin and the characteristics of the reactivity distribution have been investigated by an ESR spectroscopy study of the degree of order and the molecular dynamics of the intermediate peroxy radicals.

ISSN:1058-725X    

DOI:10.1080/10587259208032123

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The selective spin labelling of polypropylene films for monitoring the molecular dynamics at the oxidation sites has been obtained by reacting 3-chloroformyl-2,2,5,5-tetramethylpyrroline-1-oxy1 with the OH groups formed in the photo oxidation. The line shape changes of the ESR spectrum of the spin label, detected as a function of the temperature, have been interpreted in terms of a very anisotropic motion with fast rotation about a molecular axis oriented approximately along the N-O bond; also evidence of the presence of two different populations of nitroxides with different mobilities has been obtained. The use of sulphonyl radicals as novel probes for molecular motion in polymers has also been tested.

ISSN:1058-725X    

DOI:10.1080/10587259208032124

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Threetrans-syn- 3,3′-diary1-2,2′-biindenyl-idene-1,1′-diones (2a-c) showed sharp photochromic phenomena in their crystalline forms. By exposure to sunlight,2a-cwere converted to stable biradicals (3a-c). AlthoughN,N′-dimethyl indigo (6) has an almost planar structure,6in its 1:1 inclusion crystal with the host 1,1,6,6-tetrapheny1-2,4-hexadiyne-1,6-diol (7) was found to have a twisted structure of dihedral angle 42.6° between the two rings.

ISSN:1058-725X    

DOI:10.1080/10587259208032125

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A new polycyclic nitramine, hexanitroisowunzitane (HNIW), has physical properties which differ from monocyclic nitramines. One unique property of HNIW is the formation of inclusion sites in the a-polymorph which can trap solvents or other impurities, forming clathrate complexes. Trapped solvents such as methanol and H2O have been observed directly by crystal structures of α-HNIW. Free radicals such as (i) nitric oxide and nitrogen dioxide, (ii) nitroxides, (iii) radical pairs, and (iv) ionic or non-ionic paramagnetic fragments can be formed in crystalline nitramines by photolytic and thermal decomposition. In a previous EPR (electron paramagnetic resonance) study, trapped NO2radicals have been analyzed in a single crystal of HNIW at 77 K before (I) and after (II) annealing an HNIW crystal at 298 K. In this study, the formation of a free radical product fromthermal decompositionof HNIW is reported. The radical is detected in the temperature range from 403–443 K by heating HNIW in sulfolane (b.p. 558 K) or deuterated dimethylsulfoxide (b.p. 458 K). The radical product is suggested to form from the parent fragment after NO2dissociates.

ISSN:1058-725X    

DOI:10.1080/10587259208032126

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A chiral dimethoxycarbonylethyl group in a cobaloxime complex with pyridine as an axial base ligand revealed crystalline-state racemization by X-ray exposure or visible light, whereas those of complexes with (S)- and (R)-phenylethylamines and propylamine showed no change. Such differences can be explained by the size of the reaction cavity for the dimethoqcarbonylethyl group and the packing mode of the groups in each crystal.

ISSN:1058-725X    

DOI:10.1080/10587259208032127

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In crystalline state racemization of cobaloxime complexes, the reaction rate and the reaction cavity, a void space around a reactive group, depend linearly on temperature. The change of the unit cell dimensions did not reveal the true rate when the cavity was large enough. The Arrhenius plot indicated that the activation energy for the crystalline state racemization is 5–9 kJmol−1.

ISSN:1058-725X    

DOI:10.1080/10587259208032128

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Etherification reaction of secondary alcohols proceeded more efficiently in the solid state than in solution. The etherification of two different alcohols in their 1:1 co-crystal gave unsymmetrical ethers selectively.

ISSN:1058-725X    

DOI:10.1080/10587259208032129

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Mn and Zn derivatives of 4-ethenyl benzoic acid (eba) were prepared as part of our investigations on the crystal chemistry and solid state reactivity of metal complexes of unsaturated mono and dicarboxylic acids. The complexes were synthetized by reaction in water of the appropriate stoichiometric amounts of the metal mrbonate and eba. After filtration, the clear solutions were allowed to evaporate slowly at room temperature to yield crystalline materials. The compounds, hefore and after exposure to heat or gamma radiation, were characterized by FT-IR and by x-ray diffraction methods. The results are presented in this paper.

ISSN:1058-725X    

DOI:10.1080/10587259208032130

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

PVA membranes containing nucleic acid analogs were prepared. Separation of nucleosides and dinucleotides were studied using these membranes. In the case of PVA membranes containing thymine base, selective diffusion of adenosine, which is the complementary Watson-Crick base pair of thymine, was observed. This may be caused by specific base-base interaction between thymine and adenine.

ISSN:1058-725X    

DOI:10.1080/10587259208032131

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor