摘要:

Monofluorocyclopropane isomerises at 475 °C to give four products,cis-1-fluoropropene,trans-1-fluoropropene, 2-fluoropropene, and 3-fluoropropene; the ratios of product formation are not independent of pressure and it is shown that, using the Kassel representation, the individual fall-off curves correspond to values of the parameters = 9, 6, 4, and 4 respectively. It is shown that although conventional RRKM theory can account satisfactorily for the difference in fall-off behaviour between thecis- andtrans-1-propene yields, it cannot account for the pressure dependence of the formation of 2- and 3-fluoropropene; the latter behaviour is, however, easily understood in terms of the master-equation approach.

ISSN:0008-4042    

DOI:10.1139/v77-224

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Modifications are reported to a conventional gas-kinetics computer program which allow for the continuous addition of chemical species to the flowing gas. This is necessary in modelling the gas flows in a jet engine where air is continuously entrained with the burnt or burning gases, and it also facilitates the investigation of introducing chemical additives into a flowing reaction mixture.The program is used to compare, under the sameone-dimensionalmodelling approximations, the nitric-oxide emissions from a conventional jet engine and from a proposed lean-burning modification, and it is concluded that the lean-burning model has potential for reducing nitric-oxide emission by more than two orders of magnitude.

ISSN:0008-4042    

DOI:10.1139/v77-225

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Rate constants and associated activation parameters for dissociation of (NiSCN)+were measured kinetically in methanol and dimethylsulfoxide by stopped-flow spectrophotometry using copper(II) as the decomposing ion. The data along with previous results by others on dissociation of (NiSCN)+in water, acetonitrile, andN,N-dimethylformamide are discussed mechanistically by considering the effect of solvent donor properties on the activation enthalpy for the dissociation process. Rate constants for dissociation at a single temperature are not systematically related to the Gutmann donor number of the solvent, but the enthalpy of activation for the dissociation process shows a linear inverse relation to the donor number. Pathways for dissociation of (NiSCN)+in these solvents are accommodated within an Id-type mechanism.

ISSN:0008-4042    

DOI:10.1139/v77-226

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

An important matrix effect which can be correlated with the polarisability of radicals is observed for the73Ge coupling constant of Ġe(CH3)3radical

ISSN:0008-4042    

DOI:10.1139/v77-227

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

In order to determine the orientation of the isopropenyl group and confirm the stereochemistry at other chiral centers in lubimin (1) and hydroxylubimin (2), two antifungal sesquiterpenes, an X-ray structure analysis of2was carried out. Crystals of2are orthorhombic, space groupP212121,a = 6.190,b = 7.210,c = 63.082 Å,Z = 8. The structure was solved by direct methods and refined toR = 0.045. In both independent molecules the six-membered ring is chair-shaped with all four substituents equatorially oriented. The five-membered ring, attached by a spiro junction, is a half-chair with the isopropenyl substituent in an equatorial position. This side-chain istransto the methyl-bearing carbon in the six-membered ring.

ISSN:0008-4042    

DOI:10.1139/v77-228

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The thermal methyl-radical exchange reaction, CH4 + CD4 → CH3D + CD3H, has been studied in a static system at temperatures from 880 to 1103 K, with equimolar mixtures at a pressure of 440 Torr. The exchange occurs by a methyl-radical chain mechanism, propagated by the reactions CH3 + CD4 → CH3D + CD3, and CH3 + CD4 → CH3H + CD3. Values of an average rate constant for these reactions have been estimated;kx = 1.42 × 106 ℓmol−1s−1at 995 K. Comparison with shock tube data and photochemical measurements, at higher and lower temperatures respectively, indicates pronounced non-Arrhenius behaviou

ISSN:0008-4042    

DOI:10.1139/v77-229

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The intramolecular alkylation of a ketone by three epoxide stereoisomers of1has been studied. Although a variety of products are possiblea priori, intert-BuOH–H2O–KOH each reaction yields a preponderant product. The course of these reactions can be rationalized by considering the accessibility of both faces of the three possible enolates to the backside of each carbon of the epoxide group for the SN2 reaction.

ISSN:0008-4042    

DOI:10.1139/v77-230

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The two reversible base-catalyzed ketol rearrangementsandhave been proved to occur by intramolecular hydrogen (probably hydride) transfer. A combination of evidence including reduction studies,1Hmr data, and determination of absolute configuration has shown that both ketol pairs have the stereochemistry required for suprafacial hydride migration. In the course of this work, the anomalous sodium–1-propanol reduction of dione9has been reinvestigated.

ISSN:0008-4042    

DOI:10.1139/v77-231

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The initial reaction of cupric dialkyldithiophosphates and dialkyldithiocarbamates withtert-butyl hydroperoxide and α-cumyl hydroperoxide is a free radical chain process. Initiation is achieved by a redox reaction between the complex and the hydroperoxide to give alkoxy and alkylperoxy radicals. The alkoxy radicals then abstract a hydrogen from excess hydroperoxide to give alkylperoxy radicals. The cupric complexes are converted to copper sulphate by reaction with peroxy radicals while the hydroperoxide is reduced to alcohol. About 5 mol of hydroperoxide are decomposed by each mole of complex. The decomposition oftert-butyl hydroperoxide then stops whereas complete destruction of α-cumene hydroperoxide occurs by a heterogeneous ionic reaction.The kinetics of the initial reaction are second-order for both complexes. The dithiophosphate reaction is first-order in each reactant while the dithiocarbamate reaction is zero-order in the complex concentration and second-order in the hydroperoxide concentration. Simple kinetics, however, only hold for the initial rates of complex disappearance. Total dithiophosphate decomposition exhibits three stages, an initial fast reaction followed by an induction period and a rapid third stage. The concentration–time profile for dithiocarbamate decomposition is quite different and the overall rate of reaction in some instances increases as the complex concentration decreases.

ISSN:0008-4042    

DOI:10.1139/v77-232

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

2-Hydroxymethyl- and 2-acetoxymethylbenzimidazole, and theirC-4(7)-carboxy derivatives, have been synthesized and characterized for evaluation as chemical models of the Asp-His-Ser triad present at the active sites of several serine proteases. Preliminary studies of the 2-acetoxy compounds, which are analogues of the acyl enzymes, show that the rate of hydrolysis is augmented only 2.5 fold by the carboxylate group of the model charge relay system.

ISSN:0008-4042    

DOI:10.1139/v77-233

出版商:NRC Research Press    

年代:1977

数据来源: NRC