摘要:

Reversed-phase ion-interaction chromatography has been used to study the separation of Cu(I), Ag(I), Ni(II), Au(I), Co(III), Fe(III), and Fe(II) cyano complexes on silica and carbon-based reversed-phases with UV detection at 215 nm. Separation of the metal-cyanide complexes was affected by a number of experimental factors including the nature and concentration of the organic modifier, nature and concentration of the ion-pairing reagent, pH, and ionic strength of the mobile phase. Differences between the elution order of metallo-cyanides observed in the present work and in other investigations under similar experimental conditions are explained by a difference in the ionic strength of the mobile phase. Finally, this technique is used to analyze metal-cyanide complexes in a gold mill solution.

ISSN:0008-4042    

DOI:10.1139/v94-041

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A simple and precise potentiometric titration method has been developed for the determination of milligram quantities of alkyl ketene dimer (AKD) in non-aqueous solvents. It involves the addition of chloroform solutions of AKD to an excess of an organic base followed by the titration of excess base with perchloric acid in glacial acetic acid. The method was used to determine non-reacted AKD extracted from hand-sheets: our results agreed with those obtained by capillary gas chromatography. The method was also used to monitor the stability of AKD formulations. Wood resin components and stearone, a hydrolysis product of AKD, do not interfere.

ISSN:0008-4042    

DOI:10.1139/v94-042

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Structural features, configurational stability, and chiroptical properties of the nonplanar amide group in α-lactams were investigated by means of ab initio (6-31 + G*) molecular orbital calculations on (1R)-aziridinone1, (1R)-1-methylaziridinone2, (1R,3R)-3-methylaziridinone3, (1R,3R)-1,3-dimethylaziridinone4a, itscisdiastereomer (1S,3R)-1,3-dimethylaziridinone4b, and (1R,3R)-3-tert-butyl-1-methylaziridinone5, and by experimental CD spectra of 1-tert-butyl- and 1-(1′-adamantyl)-substituted 3(R)-3-tert-butylaziridinones6and7. The nitrogen inversion barriers of4aand4bare 2.8 and 1.6 kcal mol−1, respectively. The lowest excited singlet state of all of the aziridinones is a valence state (thenO–πCO* transition); the second is a Rydberg state (thenN–3stransition). The signs of the first and second Cotton effects in the CD spectra of the compounds6and7coincide with the calculated ones for1and2and thetransisomers3,4a, and5. According to the calculated and experimental data for aziridinones1–7as well as to the well-known data for other nonplanar amides, the sign of the first Cotton effects is determined by the intrinsic chirality of the nonplanar amide chromophore and obeys a spiral rule. For cases where the chromophore has the conformation around the N—C(O) bond, which is close to the antiperiplanar, a reverse octant rule is proposed.

ISSN:0008-4042    

DOI:10.1139/v94-043

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Using lethality to brine shrimp, activity-directed fractionation of extracts ofAsiminaparviflora(Michx.) Dunal. (Annonaceae) has led to the isolation of two new and four known acetogenins (1–6). Compound1, parvifloracin, is the first nonadjacent bistetrahydrofuran acetogenin with 35 carbons. Compound2, parviflorin, is an unusual adjacent bistetrahydrofuran acetogenin with 35 carbons. Bullatacin (3), molvizarin (4), annonacin (5), and goniothalamicin (6) are also reported for the first time from this plant. Brine shrimp lethality test data and comparative cytotoxicities of1–6against three human solid tumor cell lines are presented.

ISSN:0008-4042    

DOI:10.1139/v94-044

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The platinum(IV) complex, [CpPt(CH3)2(COCH3)], was examimed by IR spectroscopy in the gas phase and found to exist as an equilibrium mixture of two rotational conformers. The equilibrium was examined as a function of temperature by using gas phase IR and the energy difference between the rotamers was determined. Molecular modelling studies were also carried out and are consistent with a model in which the conformers correspond to different rotational positions of the acetyl group.

ISSN:0008-4042    

DOI:10.1139/v94-045

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Abinitiostudies up to the MP2/6-31G* level were performed on the geometry and energy of S42+. Eleven different structures were considered. In the RHF/6-31G* method, the square structure is the most stable, followed by thetrans-planarC2hstructure. S42+(square) is 105.9 kcal/mol less stable than 2S22+. Minimum energy paths were calculated for the reaction 2S2+ → S42+, both inC2vandD2hsymmetry. Using RHF/6-31G*, the transition state lies about 50 kcal/mol above the energy of square planar S42+. Using CASSCF or MP2 methods this energy can be significantly lowered (to about 33 kcal/mol in MP2/6-31G*). Calculated vibrational frequencies for the square structure are also given and compared with experimental values.

ISSN:0008-4042    

DOI:10.1139/v94-046

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Experimental excess molar enthalpieshEat 298.15 K and normal atmospheric pressure were obtained for the binary mixtures 1,2-dichloropropane + (2-propanone, 2-butanone, or 2-pentanone), 1,3-dichloropropane + (2-butanone or 2-pentanone), 1,4-dichlorobutane + (2-butanone or 2-pentanone) using a Calvet microcalorimeter. ThehEvalues for all the mixtures were negative. The experimental results used to test the capability of the interaction parameters of two versions of the UNIFAC group-contribution model to predict the proximity effect in these kind of mixtures.

ISSN:0008-4042    

DOI:10.1139/v94-047

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) is described as an excellent solvent for those Diels–Alder reactions in which Lewis-acid-sensitive reagents are used, leading to high yields with good regio- andendo/exoselectivities under very mild conditions.

ISSN:0008-4042    

DOI:10.1139/v94-048

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Several acyclic α-chlorosulfoxides have been shown to undergo a γ-dehydrochlorination upon treatment with LDA. The proposed immediate products of γ-dehydrochlorination, thiirane-S-oxides, are unstable under the basic conditions and react further with the LDA; the isolated products are usuallyE-alkenes and (or)E-vinyl sulfoxides. Some of the proposed intermediate thiirane-S-oxides, compounds6,7,8, and18, were synthesized independently and treated with one equivalent of LDA in order to mimic the second step of the overall dehydrochlorination/ring opening sequence. The products obtained from the reactions of compounds6and18compared favourably with those products which were believed to arise from certain conformations of α-chlorosulfoxides1kBand1e, respectively. The addition of one equivalent of LDA to1kAafforded a mixture containing thiirane-S-oxide8, which is proposed as the immediate product of γ-dehydrochlorination of1kA. The configurations of1kBand1hAwere both shown to bethreoby X-ray crystallographic studies. Those conformations which are preferred for the dehydrochlorination possess a geometry where the sulfinyl oxygen isantito any of the substituents of the ring carbons.

ISSN:0008-4042    

DOI:10.1139/v94-049

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In an effort to probe the compatibility of the 2-(trimethylsilyl)ethyl sulfur moiety with standard organosulfur transformations, several 2-(trimethylsilyl)ethanethiol derivatives have been prepared in excellent yield. Thus 2-(trimethylsilyl)ethanethiol (1) and 2-(trimethylsilyl)ethyl disulfide (4) and its corresponding thiosulfinate9and thiosulfonate10have been synthesized. One method of formation of4involves the breakdown of a 1-(trimethylsilyl)ethyl unit while the 2-(trimethylsilyl)ethyl fragment survives. Oxidation of4or9to10did not proceed efficiently with common reagents, but proceeded well with an iodine/water system. 2-(Trimethylsilyl)ethyl sulfide (11a) and its oxides (13,14) were also prepared in good yield. Sulfoxide13and 2-(trimethylsilyl)ethyltert-butyl sulfoxide15were shown to be good precursors to 2-(trimethylsilyl)ethanesulfinyl chloride (16). (Trimethylsilyl)methyl sulfine reacted with16in an inefficient manner to give thiosulfonates10,19, and20. 2-(Trimethylsilyl)ethanesulfenyl chloride could be generated and captured by addition across cyclohexene. The reaction of thiosulfinate9with several thiosilanes is an excellent method for the synthesis of 2-(trimethylsilyl)ethyl containing mixed disulfides.

ISSN:0008-4042    

DOI:10.1139/v94-050

出版商:NRC Research Press    

年代:1994

数据来源: NRC