摘要:

The125Te Mössbauer spectra of a number of hexahalotellurates have been measured and no significant effects of the size or symmetry of the cation on the Mössbauer parameters were observed. The mixed hexahalotellurates, M2TeX4Y2(X, Y = Cl, Br, or I), do not exhibit a quadrupole splitting, Δ, and the trends in δ with variation in X and Y are discussed. The pentahalotellurates MTeCl5, MTeBr5, and MTeBr4Cl also yield single line spectra and this is interpreted as evidence of intermolecular bridging. The tetrahaloaryltellurates MArTeX4and MArTeX3Y (X, Y = Cl, Br, or I) have been studied and the trends in Δ with variation X and Y are consistent with an additive model. The trends in δ are more complex.

ISSN:0008-4042    

DOI:10.1139/v81-131

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The129I Mössbauer spectra of PhTeI,p-EtOPhTeI2−,p-EtOPhTeI4−, Ph3TeI, (Me2TeI2)2•Ph2Hg, and Na2HgI4have been measured and the data interpreted in terms of the bonding to tellurium in these compounds and ions. Evidence is presented that PhTeI is polymeric. The129I coupling constants inp-EtOPhTeI2−andp-EtOPhTeI4−are very similar and are the same as those observed in other compounds containing linear I—Te—I linkages, lending support to the use of an additive model in interpreting125Te quadrupole splittings. The compound Ph3TeI is best formulated as an ionic species. The compound formed on reaction of α-Me2TeI2with Ph2Hg is concluded to be (Me2PhTe+)2HgI42−.

ISSN:0008-4042    

DOI:10.1139/v81-132

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Kinetic parameters (Eaand ΔS≠) for the thermolysis of 3-methyl-1-p-tolyltriazene (1) in tetrachloroethylene have been determined. The near-zero value for ΔS≠suggests a transition state with minimal stretching of the N—N bonds in tautomers1aor1b. The activation energy (Ea = 29.2 kcal/mol) and ΔS≠for the decomposition of1are very similar to those of the azoarylalkanes (Ar—N=N—R), suggesting a similar mechanism of degradation. The major products of the thermolysis of1arep-toluidine,N-methyl-p-toluidine, andp-chlorotoluene, which are rationalized in terms of homolytic breakdown of both tautomers.

ISSN:0008-4042    

DOI:10.1139/v81-133

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The reaction of benzeneselenenyl chloride with twenty-two propargyl alcohols in methylene chloride solution is reported. Products of both Markownikoff and anti-Markownikoff regiochemistry are formed in anantistereospecific manner. The regioselectivity or specificity is found to be very dependent upon the nature of the substituents geminal to the alcoholic moiety. In general the presence of bulky substituents geminal to the alcoholic moiety tend to favour formation of the anti-Markownikoff adduct under conditions of kinetic control. The Markownikoff adducts are found to be favoured thermodynamically.

ISSN:0008-4042    

DOI:10.1139/v81-134

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Reaction of permethylated glycopyranosiduronic acids with lead tetraacetate furnishes epimeric 5-acetoxypentopyranosides as products of oxidative decarboxylation. Glycoside cleavage then occurs on treatment with sodium borohydride which affords the corresponding pentitols with exposure of aglyconic hydroxyl groups. The reaction sequence has been performed with permethylated derivatives of methyl β-melibiosiduronic acid, methyl β-gentiobiosiduronic acid, gum arabic, leiocarpan A,Sterculia urensgum, and citrus pectic acid. The scope of the reaction sequence in polysaccharide studies is discussed.

ISSN:0008-4042    

DOI:10.1139/v81-135

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The synthesis of 3,3-disubstituted iso-oxapenams is described.

ISSN:0008-4042    

DOI:10.1139/v81-136

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A systematic study of the anodic oxidation of β-ketocarboxylate anions in aqueous or hydroorganic solvents allows to distinguish the factors directing this reaction. Thus, it is possible by the appropriate choice of reaction medium and the structure of the starting ion to synthesize products such as γ diketones, ethylenic ketones and ketoamides.The mode of formation of these last two classes of compound involves an α-ketocarbonium ion which is usually difficult to obtain. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v81-137

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The electronic absorption spectra of 3,3-dimethylbutane-2-thione and 3-methylbutane-2-thione in the gas phase have been measured and the observed transitions assigned with the aid ofabinitioand semi-empirical calculations. In the quartz ultraviolet region four transitions are observed. A strong, broad, structureless band is assigned to the π → π* transition and three weaker, narrower bands are assigned to Rydberg n → 4s, n → 4pyand n → 4pztransitions on sulfur.

ISSN:0008-4042    

DOI:10.1139/v81-138

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A theoretical study has been made of the effect of changing acidity on the rate of aqueous prototropic reactions. These processes, typified by ketone enolization, are catalyzed by general acids and bases and their log rate–pH profiles may take a number of different shapes. In the absence of buffer catalysis there are four reaction paths available to a substrate Z: ZH+ + HO−, Z + HO−, ZH+ + H2O, and Z + H2O. Equations have been derived that express the contributions each of these paths makes to the observed rate in terms of the experimental catalytic constants, the proton activating factor (paf), the deprotonating factor (dpf), and the basicity of the substrate as expressed byKZH+. For ideal systems the relative rates of the kinetically equivalent paths Z + H2O and ZH+ + HO−(though one does not know which is the larger) is given by the quantitywhere, andare the experimental catalytic constants. It is argued in the case of the real substrate acetone that (a) this quantity underestimates the rate difference, and (b) the more important path is Z + H2O. Wherepafis available from rate data determined in buffers an unequivocal choice can be made between the kinetically equivalent paths, providedpafis a constant for the particular substrate.

ISSN:0008-4042    

DOI:10.1139/v81-139

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Resonance Raman spectra have been obtained for a deuterated crystal violet [p(CH3)2N•C6D4]3C+Cl−, as a dilute aqueous solution. The assignment of some of the strong features seen in the spectra of crystal violet and deuterated crystal violet is discussed.

ISSN:0008-4042    

DOI:10.1139/v81-140

出版商:NRC Research Press    

年代:1981

数据来源: NRC