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991.
The ionization and solution enthalpies of o-methoxybenzoic acid have been measured in H2O-DMSO mixtures. In the same solutions, the ΔG0 values for the ionization process have been determined by potentiometric measurements. A study of the ortho effects by means of a linear combination of the ordinary polar, proximity polar, and steric effects was also performed. The CH3O group seems to undergo a partial steric inhibition of resonance. Finally, the proton transfer process from the ortho derivative to benzoic acid, compared with the same process in the gaseous phase, is presented. 相似文献
992.
F W Wang 《Macromolecules》1976,9(1):97-101
An equation for the translational diffusion coefficient of block copolymers in dilute solution has been obtained by modifying Zimm's equation for homopolymers to take into account the existence of dissimilar segments in block copolymers. Illustrative calculations for homopolymers and block copolymers have been made and the results for homopolymers have been compared with experiments and with the calculations of Yamakawa and Fujii. A procedure has been proposed to determine the molecular weight of a block copolymer from measurements of its limiting viscosity number and its sedimentation coefficient or translational diffusion coefficient. 相似文献
993.
Fluorescence of the Xe2 continuum between 1460 and 1800 Å has been observed during excitation of Xe2 molecules with CO fourth positive bands from a microwave discharge lamp. Fluorescence spectra at different Xe and added gas pressures show that in collisions with Xe or Kr atoms, the excited Xe2 diatoms are efficiently relaxed to low vibrational levels of the 1Σu+ and 3Σu+ potentials without being quenched noticeably. With Kr the rate constant for relaxation out of the primarily excited high vibrational levels is found to be about 3×10?11 cm3 molecule?1 s?1. 相似文献
994.
I. A. Ol'shevskaya V. Ya. Pochinok L. F. Avramenko 《Chemistry of Heterocyclic Compounds》1971,4(5):649-651
5-Azido-2-methylbenzthiazole, 6-azido-1, 2-dimethyl-, and 5-azido-2-methyl-1-phenylbenzimidazoles were prepared. By the reactions of these azides with alkyl halides the quaternary slats based on the cyanine dyes were obtained. 相似文献
995.
W. F. Kinard 《Journal of Radioanalytical and Nuclear Chemistry》1993,171(1):153-157
A large fraction of the potential graduate students in chemistry come from undergraduate colleges. The exposure of these students to the field of nuclear and radiochemistry is limited by the fact that few professionals actively involved in the field teach at these schools. There is also increasing competition for the limited number of chemistry students by other chemical specializations. Innovative approaches such as a short course to introduce students to nuclear and radiochemistry and some of the needs for undergraduate teaching are discussed. 相似文献
996.
F. De Meester J. M. Frre J. L. Piette P. Jacquemin L. Grooters G. Llabres S. Defays 《Journal of heterocyclic chemistry》1992,29(2):535-541
In an attempt to rationalize a synthesis of penicillin analogs modified at C(3), we have isolated the 3R(β)-carbinolamide derivative 4a. The trityl substituent on N(6′) seems to be responsible for the inversion of configuration which occurs at C(3) during the acid hydrolysis of the isocyanate intermediate. An hydrogen bond is formed on the β-face of the bell-shaped bicyclic skeleton between the N(6′)-nitrogen lone pair and the C(3) hydroxyl group. On standing, the carbinolamide analog slowly isomerizes to its expanded bicyclic isomer 4b , but the starting material may be easily recovered by treatment with acid. The postulated intermediate during isomerization, i.e., the open aldehyde form, does not accumulate. Substitutions of the hydroxyl group at C(3) lead to a variety of compounds with the biologically active 3S(α) configuration. These may be used to study the importance of the carboxyl group of penicillins in their interaction with β-lactamases at the molecular level. 相似文献
997.
Various oxazolidines were prepared from ephedrine. It was shown that their formation is not general, the reaction is not always stereoselective and can lead to isomerization of the double bond of α,β-unsaturated aldehydes. Some of these oxazolidines were used in stereoselective preparation of β-alkyl aldehydes. 相似文献
998.
Dimethyl α-bromo-o-benzenediacetate ( 1 ) condensed with hydrazine and acetylhydrazine to give respectively 1-carbomethoxy-2-amino-1,4-dihydro-3-(2H)isoquinolinone (2) and its N-acetyl derivative ( 9 ). Replacement of the bromine atom of 1 with the N-1-methylhydrazino ( 3 ) and the N-1-phenylhydrazino ( 5 ) groups occurred by allowing 1 to react respectively with methylhydrazine and phenylhydrazine. In the latter case alkylation by 1 at the N-2 also occurred which led to the formation of the 2-phenylaminoisoquinolinone ( 8 ). Derivatives 3 and 5 smoothly cyclized to the 1-earbomethoxy-5(H)-1,2,3,4-tetrahydro-2,3-benzodiazepin-4-ones 4 and 6 . A series of derivatives of 2 were also pharmacologically tested as antiinflammatory and CNS depressant agents. 相似文献
999.
Copolymers of 1,2,2,2-tetrachloroethyl esters of unsaturated acids and halogenated N-phenyl maleimides with styrene were pyrolyzed; volatile products were analyzed with a mass spectrometer combined with a gas chromatograph. Hydrogen halide and carbon dioxide in the volatile products were determined during the thermal decomposition of copolymers in glass ampoules; the acyl chloride groups were determined in the residues. The thermal decomposition of copolymers of tetrachloroethyl esters with styrene sets in at ca. 230° by the release of chloral from the copolymer and splitting of some of the CCl bonds in the copolymer. The decomposition of copolymers of styrene with halogenated N-phenyl maleimides starts above 300° by depolymerization of the polystyrene chain sections and by splitting of some of the carbon-halogen bonds. At 310 and 500° for copolymers of tetrachloroethyl esters and at 500° for halogenated N-phenyl maleimides, there is radical dehydrohalogenation of the copolymers, with depolymerization of polystyrene blocks and splitting of carbon-carbon bonds in the main chain. 相似文献
1000.
F. Benoit 《Journal of mass spectrometry : JMS》1972,6(12):1377-1382
The effect of substituents on the activation energy for primary dissociation processes in the molecular ions of mono- and para and meta di-substituted benzenes has been examined. Where the daughter ion retains the substituent group, variation of the energy of activation derives from a combination of the effects of substituents on the ionisation potential of the molecular ion and the appearance potential of the daughter ion. An equation relating the energy of activation for the fragmentation of the molecular ion of a mono-substituted benzene to that of related para and meta di-substituted benzenes is presented. 相似文献