摘要:

The less polar component of the glycoside mixture extracted from the bulbs ofMuscaricomosumhas been completely characterized. This glycoside,5, possesses an α-L-rhamnopyranosyl(1→2)-β-D-glucopyranosyl(1→2)-α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl chain linked at the C-3 position of eucosterol1.

ISSN:0008-4042    

DOI:10.1139/v83-452

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The action of bromine(1)fluorosulfate on graphite has led to the synthesis of several novel intercalation compounds. The intercalation of bromine(1)fluorosulfate at room temperature results in a first stage compound, C12BrSO3F, while at higher temperatures (~110 °C) C20BrF(SO3F)2forms instead. Oxidation of C12BrSO3F with S2O6F2yields C16Br(SO3F)3and this reaction can be reversed by reacting the latter with an excess of Br2.Graphite trifluoromethylsulfate C12SO3CF3is formed in the solvolysis of C12BrSO3F with an excess of trifluoromethyl-sulfuric acid. First stage nature of these compounds has been confirmed by the X-ray identity period alongCaxis and, vibrational lattice mode in the Raman spectra. The use of19F nmr in identifying the chemical species in the inter-lamellar space has been demonstrated. The planar electrical conductivity of these compounds has been observed to be three to six times higher than that of graphite.

ISSN:0008-4042    

DOI:10.1139/v83-453

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The rates of hydrolysis of the following orthoesters, 6 or 7-substituted 1,1-diethoxy 3,4-dihydrobenzo-2-pyrans (R = 6-MeO, H, 7-MeO, 7-NO2and 6-NO2) were determined at 27 °C in water/dioxan (2:1 by volume). The catalytic rate constants as well as the Hammett ρ constants show that the rate-determining step is the formation of a cyclic carboxonium ion intermediate and constitute a kinetic piece of evidence for the determination of the nature of the reactive conformer in hydrolysis of 2,2-dialkoxy tetrahydropyran orthoesters.

ISSN:0008-4042    

DOI:10.1139/v83-454

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The rates of hydrolysis of 6-substituted 2,2-diethoxy 3,4-dihydro benzo-1-pyrans (X = MeO, Me, H and Cl) were determined at two temperatures in water/dioxane 2:1 by volume. The observed change of sign of the Hammett ρ constantsis characteristic of a phenolate leaving group, i.e. of the rate-determining cleavage of the endocyclic C—O bond in the systems here studied; these results clearly indicate a change in the nature of the reactive conformer in hydrolysis of 2,2-diethoxy tetrahydropyrans.

ISSN:0008-4042    

DOI:10.1139/v83-455

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

TheDL-γ-carboxyglutamic acid (Gla) reacts quantitatively with formaldehyde to give 4,4-dicarboxyproline and with other aldehydes to give the racemic diastereoisomers of the 5-substituted 4,4-dicarboxyprolines. The pH-dependent reaction rate and the stereochemical behaviour suggest an intramolecular Mannich mechanism.After heating at 100 °C for 30 min, the 4,4-dicarboxyproline and the 5-substituted 4,4-dicarboxyprolines lose a carboxyl group from C4 to give the racemic diastereoisomers of the cyclic analogs of glutamic acid.

ISSN:0008-4042    

DOI:10.1139/v83-456

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The reaction of (phenylazo) stilbene and copper(II) chloride wih some dienophiles produced benzaldehyde andN-(α-chlorobenzylidene)-N′-phenylhydrazine, instead of the expected (4+2)-cycloaddition products. By reaction of some (arylazo) alkenes and copper(II) chloride in acetone at 0 °C, the relativeN-(α-chlorobenzylidene)-N′-arylhydrazine derivatives were successfully obtained in high yields.

ISSN:0008-4042    

DOI:10.1139/v83-457

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

We report high resolution photoelectron spectra of both the valence bands and Tl 5dlevels of the thallium halides (TlX; X = Cl, Br, I) in the gas phase. A transition state Xα-SW calculation on TlCl agrees with previous valence band assignments, although our calculated orbital characters are quite different from those reported previously. The calculated spin–orbit splitting of the 22II state in TlI is in good agreement with the observed value of 0.83 eV. Line width variations are rationalized considering the increase in covalency from TlCl to TlI, and variations in the slope of the excited state potential curve.Ligand field splitting of the Tl 5dlevel has been resolved in all three compounds. The observed values of the non-cubic part of the crystal field (C20) are: −0.0210 eV (TlCl), −0.0233 eV (TlBr), and −0.0258 eV (TlI). The above trend is due to the increasing covalency from TlCl to TlI, with a concomitant increase in the Tl 6porbital population. CalculatedC20values are in good agreement with those observed. The configuration interaction structure in the Tl 5dregion is explained qualitatively using Xα-SW calculations of two-hole valence band energies in TlCl.

ISSN:0008-4042    

DOI:10.1139/v83-458

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Bond energies are derived from total (nuclear–electronic and nuclear–nuclear) potential energies involving the individual nuclei of a molecule. It appears that the carbon–carbon bond energies in ethane, ethylene, allene, acetylene, and benzene are in a ratio of 1:2:1.9:2.9:1.6. This result enables a rapid estimate of approximate atomization energies of unsaturated hydrocarbons from those of their corresponding saturated parent compounds and, more importantly, shows the links relating to one another the various classes of saturated and unsaturated hydrocarbons in a unifying fashion.

ISSN:0008-4042    

DOI:10.1139/v83-459

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

At 25 °C both molar volumesVand partial molal volumesin carbon tetrachloride of cyclohexane-d12and of acetone-d6are smaller thanVandof the corresponding protio compounds. However, bothVandof acetonitrile-d3are larger thanVandof acetonitrile-h3, and in solvent cyclohexaneof acetone-d6and of acetone-h6are approximately equal. Apparently deuteration has not only a steric effect, but (in polar compounds) a counter-balancing effect, which may be polar.

ISSN:0008-4042    

DOI:10.1139/v83-460

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

On peracetylation of methyl α- or β-D-glucopyranoside, there is a reversal in the order of the chemical shifts of the 6,6′-methylene protons, i.e., whereas the H-6Ssignal appears downfield of H-6Rin the spectra of the glucosides, their relative locations in the spectra of the tetraacetates are interchanged. Evidence is presented from comparative data for a wide range of regioselectively acetylatedD-glucose derivatives, showing that the reversal in chemical shifts of the methylene protons occurs only whenbothO-4 and O-6 are acetylated. Consequently, in the disaccharide series, shift reversal isnotobserved with glucose residues that are bonded glycosidically through O-4, whereas the reversal occurs when the linkage is through O-3. A conformational model offered to account for these effects suggests that the 4- and 6-O-acetyl substituents are oriented by means of a weak, mutual, interaction in such a way that the magnetic anisotropy of the carbonyl group of the 6-O-acetyl substituent can induce selective deshielding of H-6R. The comparable influences ofO-benzoyl andO-(4-nitro)benzoyl substituents on chemical shift are consistent with this proposal.D-Mannopyranosides exhibit characteristics analogous to those of theirD-glucoepimers, whereasD-galactopyranosides give a different, more complex, chemical shift pattern.

ISSN:0008-4042    

DOI:10.1139/v83-461

出版商:NRC Research Press    

年代:1983

数据来源: NRC