摘要:

The Diels–Alder reactivity of various 2H-thiopyrans bearing electron-donating substituents has been investigated. The approximate order of reactivity among the 2H-thiopyrans studied was 4,6-disubstituted5-substituted > 4-substituted, 3,5-disubstituted3-substituted. Good yields of predominantlyendoadducts are obtained with reactive dienophiles. With less reactive dienophiles, reactions are much slower and yields are attenuated due to the competing thermal decomposition of the dienes under the reaction conditions. The adducts obtained are equivalent (via desulfurization) to those from unreactivecis-substituted dienes.Keywords: Diels–Alder, 2H-thiopyran.

ISSN:0008-4042    

DOI:10.1139/v91-220

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The di-, tri-, and hexavacant lacunary tungstoarsenates α-[HAs2W16O59]11−, α-[As2W15O56]12−, and α-[H2As2W12O48]12−were prepared by controlled alkaline degradation of the Dawson-type anion α-[As2W18O62]6−. The relationships between all these anions and the two α-[As2W17O61]10−isomers were established. The mixed saturated derivatives α-[As2VxW18−xO62](6+x)−(x = 1,2,3) and α-[As2MoxW18−xO62]6−(x = 1, 3) were obtained by refilling the lacunas with vanadium and molybdenum respectively. The new mixed anion α2-[As2Mo2W15O61]10−was used concurrently with α-[HAs2WI6O59]11−to obtain α-[As2Mo2W16O62]6−; in both cases minor parts of α-[As2MoxW18−xO62]6−(x = 1 and 3) were obtained simultaneously. All species have been characterized by polarography and by IR spectrometry. Proposed structures, based on the similarity of the redox properties and syntheses processes to those of the corresponding Dawson-type lacunary and mixed tungstophosphates, were given for all these species. The structures of the "saturated" tungstovanado- and molybdotungstoarsenates were confirmed by183W solution NMR. In addition the183W solution NMR spectra of all these latter species are discussed in relation to those of the analogous phosphoric derivatives. Finally, the main differences with the corresponding tungstophosphoric anions lie in (i) the existence of [HAs2W16O59]11−, whose protonation satisfies Lipscomb's rule, (ii) the lack of a stable oligomer like [P8W48O184]40−, and (iii) the lower stability of the octadeca(molybdotungsto)diarsenates.Keywords: heteropolyanions, tungstoarsenate, molybdotungstoarsenate, tungstovanadoarsenate,l83W NMR.

ISSN:0008-4042    

DOI:10.1139/v91-221

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Carbonyl ylides2, generated by thermolysis of alkoxyoxadiazolines1in chloroform, react with chloroform to form ketals (3) of 1,1,1-trichloropropanone. The isotope effect at 80 °C, determined by analysis of products from thermolysis of1in mixed solvent (CHCl3/CDCl3, both in large excess) was estimated to bekH/kD = 5. A mechanism involving concerted C—Cl and C—H bond formation between the ylide C atoms and the Cl and H atoms of chloroform is proposed. The ketals of 1,1,1-trichloropropanone are the first to be reported.Keywords: carbonyl ylide, reaction with chloroform; chloroform, reaction with carbonyl ylides; ketals, of 1,1,1-trichloropropanone; 1,1,1-trichloropropanone, ketals of.

ISSN:0008-4042    

DOI:10.1139/v91-222

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

CuO–Al2O3catalysts containing various amounts of copper oxide have been prepared by precipitation. The phase changes were studied by X-ray diffraction. The results obtained revealed that the thermal treatment of solid CuO–Al2O3at 700 °C produced only crystalline CuO. Heating to 900 °C led to the formation of copper alumina spinel together with unreacted CuO and γ-Al2O3. The spinel content was found to increase with increasing copper content. Nitrogen adsorption–desorption isotherms on the calcined samples have been measured. Surface areas have been calculated and the pore structure analysed. The textural properties of the system were found to depend on both the copper content and the calcination temperature.Keywords: CuO, Al2O3catalysts, structure, surface area, pore structure.

ISSN:0008-4042    

DOI:10.1139/v91-223

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The tensammograms of several sets of cationic polyacrylamide copolymers are discussed and compared. Tensammograms are not affected by molecular weight, but plots of capacitive current at a chosen potential versus charge density give regular curves.Keywords: tensammetry, cationic, polyacrylamide, charge density.

ISSN:0008-4042    

DOI:10.1139/v91-224

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Infrared spectra are reported for binary complexes between perfluoro-tert-butanol as proton donor and nitromethane and acetone as bases. The complexes have been investigated in low temperature solutions and in cryogenic matrices. The spectra have been evaluated in terms of frequency shifts (ΔVOH), half widths (FWHH) and anharmonicities (κ) caused by the hydrogen bonding of these complexes. The influence of the environment (solvents and solid matrices) as well as temperature on the spectra of the complexes has also been studied and is discussed in detail.Keywords: hydrogen bonding, temperature effects, solutions, matrix.

ISSN:0008-4042    

DOI:10.1139/v91-225

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The adsorption of hydroxyproline (HPRO) on mercury in aqueous solutions of 10−2 M KClO4has been determined from electrocapillary and capacity measurements. Comparison of the results obtained for HPRO with those reported for proline (PRO) shows that the presence of a hydroxyl group in the molecule has a small effect on the adsorption process. The respective values for adsorption parameters are −7 and −5 μC cm−2for the charges of maximum adsorption, −13.0 and −10.4 kj mol−1for the standard Gibbs energies of adsorption at zero charge, and −1.28 and +0.6 for the α parameter in the Frumkin isotherms. According to the analysis carried out for the normal component of the dipole moment of HPRO, −0.8 D, the more probable orientation of this aminoacid adsorbed on mercury is with the pyrrolidine ring parallel to the electrode surface resting the OH group away from the surface.Keywords: adsorption, double layer, aminoacids, hydroxyproline.

ISSN:0008-4042    

DOI:10.1139/v91-226

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The photochemistry of RDX was studied in argon matrices at 10 K and examined by FTIR spectroscopy. The spectra and kinetics of product growth indicate that there are two decomposition pathways:[I]        RDX → 4NO + 2CH2O + N2+ CH2→ 4NO + 2CO + N2+CH4+ H2[II]        RDX → N2O + [O3+ N2] or [N2O3] + CO2+ C2H2+N2+ 2H2The mechanism II nitrogen products can easily be rationalized for the chair configuration of RDX with axial NO2groups adjacent (Cssymmetry). When considering the carbon products of II, it may be necessary to postulate intermolecular reactions. Our studies gave no evidence for the symmetric triple fission path, which leads to N2O and CH2O, nor for the NO2stripping mechanism reported for the gas-phase thermal reactions, which leads to the formation of NO2and HCN. Rather, our findings were more consistent with the known condensed phase products. The production of CH4, C2H2, N2O3, and O3are unique to the matrix study.Keywords: RDX, photochemistry, argon matrices.

ISSN:0008-4042    

DOI:10.1139/v91-227

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The absorption and fluorescence spectral properties of 2-(3′-hydroxyphenyl)-, 2-(4′-hydroxyphenyl)-, and 2-(3′,4′-dihydroxyphenyl)-, and 2-(4′-hydroxy-3′-methoxyphenyl), 2-(3′-hydroxy-4′-methoxyphenyl)-, and 2-(3′-methoxyphenyl)benzothiazoles have been studied in a number of solvents of varying polarity. The ionization constants (pKa) for various prototropic reactions of these molecules in bothS0andS1states are determined. The effect of substitution on the spectral properties and on the pKavalues are discussed. The molecules have been found to undergo biprotonic phototautomerism in dilute acid solutions. On the basis of the fluorimetric titration behaviour of the molecules (except 2-(3′-methoxyphenyl)benzothiazole), the existence of monocation–zwitterion equilibrium in theS1state is proposed. PPP-SCF-MO-CI method has been used to calculate charge densities on the heteroatoms.Keywords: spectra, proton transfer.

ISSN:0008-4042    

DOI:10.1139/v91-228

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The Taylor dispersion (peak-broadening) technique is used to measure the ternary mutual diffusion coefficients of the mixed salt solutions MgCl2 + MgSO4 + H2O and Na2SO4 + MgSO4 + H2O at 25 °C. The dispersion of the solutes is followed by differential refractometry. A simple least-squares procedure is developed to calculate the ternary diffusion coefficients from the refractive index profiles. The coefficients are measured at 0.04, 0.20, or 0.40 mol dm−3total salt for the molar salt ratios 1:3, 1:1, or 3:1. The measured diffusion coefficients are compared with the limiting values for the completely dissociated salts.Keywords: mixed salt solutions, multicomponent diffusion, Taylor dispersion, ternary diffusion coefficients.

ISSN:0008-4042    

DOI:10.1139/v91-229

出版商:NRC Research Press    

年代:1991

数据来源: NRC