摘要:

We have measured at 25 °C the enthalpies of solution of acetic, benzoic, and valeric acids and of their potassium salts in water –tert-butyl alcohol mixtures containing up to 40% by weight of organic cosolvent. We have also determined these quantities for phenol, aniline, and pyridine in the same mixtures and for acetic acid, aniline, and pyridine in water–DMSO, water–acetone, and water–urea in the zone rich in water. Using these data we have calculated the standard enthalpies of solution, the corresponding transfer quantities, and the enthalpies of solvation. When the enthalpies of solution are difficult or impossible to measure we have shown that the enthalpies of transfer can be calculated from judiciously selected transfer quantities obtained from experimental measurements. In this way we have worked out the enthalpies of transfer of potassium phenolate and of anilinium and pyridinium chlorides and bromides in the various mixtures. The enthalpies of solvation have been separated into enthalpies of formation of a cavity in the solvent and enthalpies of interaction. From these last quantities an attempt at interpretation in terms of solute and aqueous-organic media structures was made.Keywords: enthalpies, solution, solvation, acids–bases, aqueous-organic media.

ISSN:0008-4042    

DOI:10.1139/v90-101

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The 1,2-hydrogen migration of hydrogen peroxide has been investigated byabinitiomethods and the Intrinsic Reaction Coordinate (IRC) has been constructed. An analysis of the evolution of the electron distribution along the reaction path has shown that the shifting hydrogen behaves as a proton. This transferring proton polarizes the O—O bond of the hydrogen peroxide that becomes broken at the transition state. If a water molecule is allowed to participate in the reaction, the energy barrier is noticeably lowered, this water molecule acting as a bifunctional catalyst.Keywords: 1,2-hydrogen migration, hydrogen peroxide, proton transfer, bifunctional catalyst, Intrinsic Reaction Coordinate.

ISSN:0008-4042    

DOI:10.1139/v90-102

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

In the present work, 11 aromatic and nine aliphatic carboxylic acids, namely benzoic, 2-nitrobenzoic, 3-nitrobenzoic, 4-nitrobenzoic, 2,4-dinitrobenzoic, 3,5-dinitrobenzoic, 2-aminobenzoic, 3-aminobenzoic, 4-aminobenzoic,o-phthalic, salicylic, formic, acetic, monochloroacetic, dichloroacetic, trichloroacetic, propionic,n-butyric, caprylic, and myristic acids, were titrated conductimetrically and potentiometrically with triethylamine in acetonitrile solvent, under a nitrogen atmosphere, at 25 °C. Closer investigation of the conductimetric titration curves of these acids showed that the acidity of an acid, rather than the basicity of its conjugate base, plays a major part in the formation of homoconjugate ions, at least in acetonitrile solvent. If the acid is strong enough, there is a maximum before the experimental end point at about the half-neutralization point. To determine the minimum strength for an acid to show this maximum before the end point, all acids were also titrated potentiometrically. It was found that those acids which have half-neutralization potentials over −85 mV give a strong homoconjugation reaction and show a maximum before the experimental end point. Moreover, the acids that show maxima before the experimental end point in the conductimetric titration also show rather well-shaped potentiometric titration curves.Keywords: nonaqueous media, conductimetric titrations, potentiometric titrations, titration in acetonitrile, acidity and homoconjugation.

ISSN:0008-4042    

DOI:10.1139/v90-103

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Trifluoroacetic anhydride – sodium iodide mixture (TFAA-I) reacts with nitrones with the release of iodine. Since stoichiometrical amounts of iodine are formed with respect to starting nitrones, TFAA-I reagent can be used for analytical determination of nitrones. Two procedures for the determination of nitrones (on μ mole and on nmole scale) have been described.Keywords: nitrones determination, TFAA-I reagent.

ISSN:0008-4042    

DOI:10.1139/v90-104

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Reactions of compound Cl3W(μ-H)(μ-Me2S)2WCl2(Me2S),1, and salts of derived chloro anion [Cl3W(μ-H)(μ-Me2S)2WCl3]−,2, with bromide ion and with benzyl bromide are described.1was previously shown (1) to exist as a mixture ofmeso(C2v) andDL-pair (C1) of isomers, with theC2visomer being the more stable. Displacement of the terminal dimethyl sulfide ligand of1by bromide ion results in the formation of the analogous isomers of ion [Cl3W(μ-H)(μ-Me2S)2WCl2Br]−, with retention of stereochemistry. The1H NMR spectra of compounds in this series are uniquely informative as to the isomers present since the two environments of the methyl groups in the bridging dimethyl sulfide ligands (axial and equatorial) provide a probe for the ion stereochemistry. This is used to show that in reactions of2with benzyl bromide, after replacement of μ-H by Br, Br exchanges with terminal chlorides to give a mixture of isomers. Reactions of1with benzyl bromide are further complicated by the fact that both terminal dimethyl sulfide and μ-H are replaced by bromides which then redistribute over all possible terminal sites.Keywords: hydride, confacial bioctahedral complexes, tungsten, bromocarbons.

ISSN:0008-4042    

DOI:10.1139/v90-105

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The visible spectra of a series of merocyanines, derivatives of 4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine, have been investigated in a number of solvents and solvent mixtures. The effect of substituents on the solvatochromic behaviour of these compounds is described. All investigated merocyanines exhibited a strong negative solvatochromism. Inverse solvatochromism was observed in solvents of very low polarity for polar dyes, and in polar solvents for dyes containing hydrophobic substituents. This inversion of the solvatochromic behaviour is attributed to aggregation phenomena.Keywords: merocyanines, solvatochromism, betaine, aggregation.

ISSN:0008-4042    

DOI:10.1139/v90-106

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A series of compounds containing a cyclopropyl ring adjacent to the position of oxidation during fungal biotransformation has been prepared and subjected to enzymic oxidation usingMortierellaisabellinaorRhizopusarrhizus. Carbon hydroxylation and sulfoxidation reactions were observed, but in neither case did opening of the cyclopropyl ring occur. Both these reactions were subject to inhibition by carbon monoxide but not by cyanide ion, properties characteristic of cytochrome P-450 dependent mono-oxygenase enzymes. Hydroxylation at a cyclopropyl C—H bond has been studied by the use of phenylcyclopropane and phenylthiirane as substrates for the mono-oxygenase ofM.isabellina. The former was not oxidized, but the latter was converted to phenyl glyoxylic acid in moderate yield.Keywords: biotransformation, cyclopropanes, fungi, metabolism.

ISSN:0008-4042    

DOI:10.1139/v90-107

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

1,1-Dihalocyclopropane derivatives and furanones were synthesized from ±α- and β-ionones using CHCl3, NaOH, and triethylbenzyl ammonium chloride (TEBAC). 2D NMR and single-crystal X-ray analyses of the products are reported.Keywords: addition of 1,1-dihalocarbenes to ionones, phase transfer addition of 1,1-dihalo systems, formation of cyclopropanes.

ISSN:0008-4042    

DOI:10.1139/v90-108

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The synthesis of Fe(η-C5H5)(η-C5H3(CHMeNMe2)(COOH)-1,2),3a, and its methyl and ethyl esters is described. Esterification of3aby using RI in DMA affords Fe(η-C5H5)(η-C5H3(CHMeOH)(COOR)-1,2), R = Me, Et, with retention of configuration at the chiral center. The variable temperature1H NMR spectrum of3areveals H-bonding between the two functional groups.Keywords: ferrocenecarboxylic acids and esters, NMR spectra, synthesis, hydrogen bonding.

ISSN:0008-4042    

DOI:10.1139/v90-109

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Western Pacific Ocean spongeHymeniacidonsp. was found to contain a cyclo-octapeptide designated hymenistatin 1 (1) active against the P388 leukemia cell line (ED503.5 μg/mL). Structural determination was accomplished utilizing high field NMR (400 MHz) and mass spectral techniques (FAB MS/MS) followed by chiral gas chromatographic analysis to establish the absolute configuration (allS-amino acids).Keywords: cytostatic,Hymeniacidon, hymenistatin, cyclo-octapeptide, P388 leukemia.

ISSN:0008-4042    

DOI:10.1139/v90-110

出版商:NRC Research Press    

年代:1990

数据来源: NRC