摘要:

A study of the prewave of the Ni2+- nicotine system was carried out under the experimental conditions when the influence of electroreduction of nicotine is negligible. The kinetics of Ni(II) reduction in nicotine media on the dropping mercury electrode were studied by direct current Tast polarography (DCTP) via the determination of the Koutecky's parameter, χ and the influence of different variables was analyzed. An electrochemical study of the prewave was also made by using various polarographic techniques. Values of χ depend on the nicotine concentration, pH, ionic strength (ψ-effect), and on the nature of the supporting electrolyte. The &agr;nproduct (χ = transfer coefficient,n= number of electrons) and the stoichometric number,v, were determined. The prewave is interpreted as a surface reaction, the main features of the mechanism being its catalytic nature. The discharge is a two electron step and reaction between species of opposite charge is rate-determining.Key words: catalytic, prewave, polarography, nickel(II), nicotine.

ISSN:0008-4042    

DOI:10.1139/v00-048

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Various 2,3-disubstituted norbornadienes that can hardly be made by the traditional Diels-Alder method were synthesized by double lithium halide exchange of 2,3-dibromonorbornadiene in moderate to good yields.Key words: 2,3-disubstituted norbornadienes, Diels-Alder reaction, lithium halide exchange.

ISSN:0008-4042    

DOI:10.1139/v00-047

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Indium(III) iodide forms a 1:1 adduct with 9-xanthenone, of quasi-tetrahedral structure; triclinic,a= 10.805(4),b= 11.494(4),c= 7.493 (2) Å,&agr; = 104.12(3), &bgr; = 106.35(3), &ggr; = 91.165(3)°,V= 860.8(5) Å3,Z= 2, space groupP1-. With 9-fluorenone, the adduct has 1:2 stoichiometry, and approximatelyD3hsymmetry in the InI3O2kernel; the structure is triclinic,a=11.212(2),b= 16.504(3),c= 7.537(2) Å, &agr; = 94.57(2), &bgr; = 109.05(1), &ggr; = 91.165(15)°,V= 1312.6(4) Å3,Z= 2, space groupP1-. The solid structures, and the solution chemistry, are compared with those of related neutral derivatives of indium(III) halides.Key words: Indium(III) iodide, solution chemistry, crystal structures, ad

ISSN:0008-4042    

DOI:10.1139/v00-049

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The synthesis ofN-(4-acetamidobutyl)-N-((Z)-4-hydroxy-3-methyl-2-butenyl) guanidine confirmed this as the structure of the natural product hydroxysmirnovine.Key words: hydroxysmirnovine, synthesis, naturally occurring guanidines.

ISSN:0008-4042    

DOI:10.1139/v00-053

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Synthesis has been carried out of 15 examples of anionic diphenylboron complexes of arylpyruvic acids, and the structures of the compounds have been determined from spectroscopic data and from X-ray analysis of one of the compounds. Crystals of5jare monoclinic,P21/n,a= 9.5566(10),b= 15.961(3),c= 16.6382(6) Å, beta = 99.3239(10)°, andZ= 4, at 180 K. The structure was solved by direct methods and refined by full-matrix least-squares procedures toR(F2) = 0.056 for 6662 CCD data.5jcontains a triethylammonium cation and an anion containing a planar five-membered OBOCC ring, with cation and anion linked by an N-H···O hydrogen bond. Spectroscopic data and bond distances establish that the pyruvate ligand is the enol-tautomeric stat

ISSN:0008-4042    

DOI:10.1139/v00-052

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A practical method for large scale synthesis of 1-arylnaphthalene and 1-aryl-1,2-dihydronaphthalene lignans is described. The method makes use of the classic Stobbe condensation followed by regioselective reactions that provide access to both the common and retrolactone lignans, e.g.,2and3. A total of 25 compounds, many of which are known natural products, were prepared and their antiviral activity against human cytomegalovirus measured.Key words: lignan, Stobbe, arylnaphthalene, antiviral.

ISSN:0008-4042    

DOI:10.1139/v00-059

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Homodesmotic reactions were designed to study substituent effects on stability of oxiranes, oxirenes, and dioxiranes. Good or fair correlation between their homodesmotic stabilization energies and Taft's dual-substituent-parameters has been found. Oxiranes are stabilized by &sgr;-donating and &pgr;-donating substituents but destabilized by &sgr;-accepting and &pgr;-accepting substituents. The &pgr;-effects on oxiranes are comparable to &sgr;-effects for &pgr;-acceptor substituents and are much stronger than &sgr;-effects for &pgr;-donor substituents. Oxirenes are stabilized by &sgr;-donating, &pgr;-donating, and &pgr;-accepting substituents but destabilized by &sgr;-accepting substituents. The &pgr;-effects on oxirenes are stronger than &sgr;-effects. Oxirenes with strong &pgr;-donor substituents such as F, OH, and NH2, or strong &sgr;-donor substituents such as Li and Na are neither real molecules nor transition states. Dioxiranes are stabilized by &sgr;-donating and &pgr;-donating substituents but destabilized by &sgr;-accepting and &pgr;-accepting substituents. The &pgr;-effects on dioxiranes are stronger than &sgr;-effects for &pgr;-donor substituents, but weaker than &sgr;-effects for &pgr;-acceptor substituentsKey words: oxirane, oxirene, dioxirane, homodesmotic reaction, substituent effect.

ISSN:0008-4042    

DOI:10.1139/v00-064

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Addition ofcis-cyclooctene (coe) to K2PtCl4givestrans-[PtCl2(coe)]2(1), which reacts with excess coe to givetrans-PtCl2(coe)2(2). Compound2was characterized by an X-ray diffraction study and crystals were found to be triclinic,a= 5.7838(5),b= 7.4347(6),c= 9.9972(9) Å, &agr; = 83.924(1), &bgr; = 87.844(2), &ggr; = 73.546(1)°,Z= 1, with space groupP1-. Addition of 4-vinylpyridine (4vp) to1gavetrans-PtCl2(4vp)2(5) which was also characterized by an X-ray diffraction study. Crystals of5were monoclinic,a= 8.2255(6),b= 12.8254(10),c= 6.9624(5) Å, &bgr; = 98.8230(10)°,Z= 2, with space groupP21/c. Although alkenylamines react with1to give a mixture of products, addition of one equivalent of apve (H2NCH2CH2CH2OCH&bgr;CH2) to1cleanly afforded the organometallic producttrans-PtCl2(coe)(thmo) (thmo = tetrahydro-2-methyl-1,3-oxazine) arising from a metal-catalyzed intramolecular hydroamination of the starting alkenylamine. Initial investigations into the functionalization of metal complexes containing pendant alkene groups have shown that catecholborane can be added in some cases, using a rhodium catalyst, to give the corresponding organoboronate ester platinum compounds.Key words: alkenylamines, alkenylpyridines, hydroamination, hydroboration, plati

ISSN:0008-4042    

DOI:10.1139/v00-060

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Three 2-deoxy-&agr;-D-glucopyranosyl pyridinium tetrafluoroborates were tested for their binding affinity to a range of &agr;-glucosidases and &agr;-mannosidases. The &agr;-isoquinolinium salt (11) binds approximately 275-fold more tightly to yeast &agr;-glucosidase than does the isomeric quinolinium salt (12). In addition, compound11binds to the yeast enzyme approximately two-fold tighter than the corresponding glucopyranosyl isoquinolinium salt (9). The (kcat/khyd) values for the yeast &agr;-glucosidase-catalyzed reactions of11and9are 1.6 × 105and 2.0 × 109, respectively, when compared to the spontaneous uncatalyzed reactions. Thus, the interaction of the 2-OH group in compound9with the yeast enzyme's active site generates a relative transition state stabilization of about 23.5 kJ mol-1. For both compounds11and12, the observed rate accelerations for the yeast &agr;-glucosidase-catalyzed hydrolysis, relative to the spontaneous reaction in solution, (kcat/khyd) are identical within experimental error.Key words: glycosidase, inhibitor, 2-deoxyglucose, pyridinium, catalysi

ISSN:0008-4042    

DOI:10.1139/v00-061

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

N,N'-bis-(2,6-diisopropylphenyl)trifluoroacetamidine has been prepared for the first time from 2,6-diisopropylaniline and the trifluoroacylation reagent TFAP via the imidoylchloride. The crystal structure of the amidine was determined, indicating that it crystallizes in theZ-antitautomer, in contrast to the nonfluorinated analogue, which isE-antiin the solid state. In solution, as indicated by NMR spectroscopy, it exists in two isomeric forms. The amidine reacts with Mo(CO)6to produce a coordination complex with Mo(CO)3in which the ligand is also in theZ-antigeometry, the metal is η6-coordinated to the imino-2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards the metal, as determined by a single-crystal X-ray structure. Unlike the analogous nonfluorinated acetamidine, there is no indication of an intermediate in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)5unit, which we now attribute to the predominant geometry of the ligand, both in the solid state and in solution, beingZ-anti. The high steric bulk of this superamidine ligand apparently prevents the formation of a metal-metal bonded Mo2(amidinate)4as observed previously in a redox reaction betweenN,N'-diphenylbenzamidine and Mo(CO)6under similar thermal reaction conditions.Key words: trifluoromethyl, superamidine, amidine, molybdenum, carbonyl, coordination.

ISSN:0008-4042    

DOI:10.1139/v00-063

出版商:NRC Research Press    

年代:2000

数据来源: NRC