摘要:

The enhancement of the (C + 1)/Cratio in the fast atom bombardment mass spectra of seven pyridinium cations has been measured. No dependence of the enhancement on the cation reduction potential could be identified. TheN-methyl pyridinium cation, which showed no enchancement under matrix-free conditions, exhibited an increase in the (C + 1)/Cratio with decreasing concentration. This concentration dependence was eliminated when the bombardment energy was reduced from 9 to 5 keV. Possible mechanisms for the concentration dependence and the variation with bombardment energy are proposed.Keywords: fast atom bombardment, reduction, pyridinium salts.

ISSN:0008-4042    

DOI:10.1139/v89-030

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The behavior of theendoandexoisomers of 7,7-dimethyltricyclo[3.2.2.02,4]nonan-6-one (9,17) under strongly basic conditions (t-BuO−/t-BuOH/185 °C) has been examined. In both cases rearrangement to the corresponding 8,8-dimethyl-tricyclo[4.2.1.02,4]nonan-7-one (11,18) was found, with theexoisomer reacting approximately 8 times faster. Experiments intert-butyl alcohol-O-d1were carried out to determine the specific sites, the relative rates, and the stereochemistry of deuterium incorporation in the initial ketones. Although H/D exchange occurs most readily at the cyclopropyl methylene carbon in theendoisomer, none of the rearrangement product expected to arise via γ-enolate formation was observed. The results for these ketones are compared with our earlier observations in the related [2.2.2], [3.2.1.0], and [3.3.1.0] systems.Keywords: homoenolization, tricyclic ketones, H/D exchange.

ISSN:0008-4042    

DOI:10.1139/v89-031

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Debromination of the title dienone (1), formed during the bromination of 5-methylsalicylic acid (2), is strongly catalyzed by α-cyclodextrin (CD). The bromination of2is also catalyzed by CD. The extent of the catalysis of the debromination of1is independent of pH in the range pH 3–5 and it tends to saturate at high [Br−] and high [CD]. Analysis of the [Br−] dependence data in the presence of1 mM CD yields a value of 0.68 M for the dissociation constant of the CD•Br−complex. Also, from the dependence of the rate of debromination on [CD], the anion of the dienone1(i.e.,1−) forms a complex with CD with aKdof 15 mM, which appears to react with Br−at a rate 170 times faster than does free1−. However, the catalysis is more likely due to the reaction of free dienone, reacting as1, with the CD•Br−complex, which is 3400 times more reactive than uncomplexed Br−. The combined effect of the internal catalysis by the carboxyl group of1and the external catalysis by CD is an overall rate enhancement of 12 million.Keywords: catalysis, cocatalysis, cyclodextrin, debromination, intramolecular.

ISSN:0008-4042    

DOI:10.1139/v89-032

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The crystal and molecular structure of the title compound has been determined from three-dimensional X-ray intensity data. The crystals are orthorhombic with space groupPbcm,a = 8.877(4),b = 9.813(2),c = 6.545(2) Å,Z = 4. The structure has been refined toR = 0.029 andRw = 0.035. The molecules are present in the thione form as planar molecules with only intermolecular interactions. Bond lengths and angles suggest that the electron density is more localized in the N—N—C—S ring fragment. Theoretical calculations (MNDO method) were also carried out on the compound both in the thione and its thiol tautomeric forms. Some comparisons are made between several properties (formation enthalpies, proton affinities, molecular electrostatic potentials, atomic charges) of both tautomers. The results indicate some important differences in reactivity between both forms.Keywords: crystal structure, molecular structure, electronic structure, 1-H-3-methyl-4-amine-5-thione-1,2,4-triazol.

ISSN:0008-4042    

DOI:10.1139/v89-033

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Substantial differences are founded between the absorption properties of two Rhodesian chrysotile samples (−1 and −2), which are, in most chemical and structural aspects, highly similar. The phenanthrene and CO2amounts adsorbed are much less important on chrysotile-2 than on chrysotile-1. This indicates that chrysotile-2 has fewer basic surface sites. DTA and XRD results show that dry grinding and leaching produce a breakdown of the chrysotile structure, yield amorphous silica, and lower the temperature of the dehydroxylation peak. The dehydroxylation peaks of chrysotile-1 and -2 are really doublets. As the low-temperature component of the dehydroxylation peak is greater in chrysotile-2 than in chrysotile-1, the chrysotile-2 contains more ground and (or) leached fibers than chrysotile-1 and consequently shows weaker absorption properties.Keywords: chrysotile, leaching, phenanthrene adsorption.

ISSN:0008-4042    

DOI:10.1139/v89-034

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The new diterpenes canariquinone (9), rosmaquinone (10), and 11-acetoxycarnosic acid (6), together with the already known 7-ethoxyrosmanol (1), 7-methoxyrosmanol (2), and rosmanol (3), were isolated from the flowers ofSalviacanariensis. The structure of the new substances was established by a combination of chemical and spectroscopic means. Reaction of galdosol (4), isolated from the aerial part of the same plant, with diazomethane, unexpectedly gave the new homoditerpenes15and16, the structures of which were determined by spectroscopic methods. A mechanism accounting for the formation of these substances is suggested.Keywords: abietane diterpenes,Salvia, Labiatae, antibiotic activity, galdosol reactivity.

ISSN:0008-4042    

DOI:10.1139/v89-035

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The photocyclization of enaminones was extended to aryl enaminones bearing a substituent on the aromatic moiety. This reaction was studied in order to achieve the synthesis of indole alkaloid synthons. Trials of regioselectivity control were made by using groups with enhanced steric hindrance. The reactivity of secondary enaminones was tested, and the ratio of C-alkylation to N-alkylation was shown to be dependent on the nature of the aromatic substituent. During this work, new hexahydrocarbazolones were synthesized, with substituents on the A ring or the modified C ring.Keywords: photocyclization, aryl enaminones, indole alkaloids, hexahydrocarbazolones-4, cyclopenta[b]indoles.

ISSN:0008-4042    

DOI:10.1139/v89-036

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

We report a new synthesis of 3-nitroveratrole, based on the directed lithiation of veratrole, and photochemical substitutions of both 3-nitroveratrole ando-nitroanisole with several nucleophiles. Both aromatic substrates undergo photocyanationmetato the nitro group. With hydroxide ion, 3-nitroveratrole reactsmetato the nitro group, but 2-nitroanisole undergoes replacement of either substituent, the proportion of reaction at each site depending upon the OH−concentration. 3-Nitroveratrole undergoes an inefficient reaction with butylamine at each methoxy group; this reaction is apparently second order in amine. The reaction betweeno-nitroanisole and diethylamine results only in photohydrolysis.Keywords: photosubstitution, nucleophilic, 3-nitroveratrole,o-nitroanisole.

ISSN:0008-4042    

DOI:10.1139/v89-037

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

An acidity scale for excited state protonation kinetics in 20% ethanol:80% aqueous sulfuric has been developed using 1-cyano-naphthalene as a fluorescent indicator. The utility of this new scale is demonstrated using the proton quenching of fluorescence of a variety of chromophores. These include 1- and 2-cyanonaphthalenes, 1- and 2-methoxynaphthalenes, benzyl alcohols, toluenes, and 2-vinylnaphthalene.Keywords: acidity scale, fluorescence quenching, excited state basicity.

ISSN:0008-4042    

DOI:10.1139/v89-038

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The phase diagram ofp-phenylenediamine – benzoic acid system, determined by the thaw–melt method, shows the formation of two eutectics and a 1:1 addition compound. The linear velocity of crystallization of pure components, eutectics and addition compound, determined by measuring the movement of growth front in a capillary, suggests that crystallization data obey the Hillig–Turnbull equation. Using experimental values of heats of fusion, entropy of fusion and excess thermodynamic functions were calculated and the results are explained on the basis of cluster formation in the melts. X-ray diffraction data infer that these eutectics are not simply the mechanical mixture of the two components and there is preferential ordering of atomic planes during their formation. The infrared spectral studies suggest the formation of intermolecular hydrogen bonding between the components forming the molecular complex.Keywords: organic eutectics, growth kinetics, phase diagram, thermochemistry, X-ray diffraction studies.

ISSN:0008-4042    

DOI:10.1139/v89-039

出版商:NRC Research Press    

年代:1989

数据来源: NRC