摘要:

The spectral displacement technique with phenolphthalein as the chromophore has been used to obtain 1:1 equilibrium binding constants (K2) for a homologous series of hydrocarbon (hc) (CnH2n+1COONa,n = 5–13) and fluorocarbon (fc) anionic surfactants (CnF2n+1COONa,n = 3–8) with β-cyclodextrin (β-CD). The magnitude ofK2increases as the alkyl chain length increases in each homologous series.K2values in the ranges of 102–105 M−1and 101–104 M−1were obtained for the β-CD–fc and for the β-CD–hc surfactant complexes, respectively. The different binding affinity of β-CD with hc and fc surfactants is discussed in terms of such physicochemical properties of the guest species as hydrophobicity, geometrical size, conformational effects, molecular polarizability, and solvation of the head group.Keywords: spectral displacement, phenolphthalein, cyclodextrin, surfactant, binding constant.

ISSN:0008-4042    

DOI:10.1139/v97-111

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The electronic absorption spectra ofN-sulfinylaniline and some of its derivatives were investigated using different solvents. The spectral behavior of the molecules indicated their planarity and that the NSO group is a strong electron acceptor. All the observed bands correspond to delocalized π → π* transitions;n → π* transition were not observed as discrete bands. Ab initio molecular orbital calculations were performed using four different basis sets. The results showed that the NSO group is nonlinear, the molecules studied are planar, and thesynconformer is more stable than theanticonformer.Keywords:N-sulfinylanilines, spectra and theoretical treatment.

ISSN:0008-4042    

DOI:10.1139/v97-112

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

New syntheses are described of 5-hydroxypentane-2,3-dione (7) (i.e., laurencione) and of 3-amino-1-hydroxypropan-2-one (3-amino-1-hydroxyacetone) (5) hydrochloride, putative precursors of the C5unit, C-2′,2,3,4,4′, and of the C3N unit, N-1,C-6,5,5′, respectively, of pyridoxine (6).Keywords: 3-amino-1-hydroxyacetone, 3-amino-1-hydroxypropanone, 5-hydroxypentane-2,3-dione, laurencione, vitamin B6.

ISSN:0008-4042    

DOI:10.1139/v97-113

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The reactions of nickelocene with pyrazoles in benzene solution have resulted in the isolation of either dimeric compounds, [CpNi(μ-pz′)]2, (room temperature conditions) or trimetallic complexes, [CpNi(μ-pz″)2]2Ni, (elevated temperature conditions). Both dimeric and trimetallic species were obtained as red crystalline materials and X-ray structural investigations are reported for representative samples of each type. Structural features are interpreted and compared with similar, previously reported, nickel pyrazolate structures. Crystals of [CpNi(3,5-diMepz)]2(C20H24N4Ni2),1, are orthorhombic,a = 15.204(1),b = 17.967(2),c = 6.9786(9) Å,Z = 4, space groupAma2; those of [CpNi(4-NO2-3,5-diMepz)]2(C20H22N6Ni2O2),5, are orthorhombic,a = 17.145(3),b = 17.738(1),c = 7.006(1) Å,Z = 4, space groupP212121; those of [CpNi(3,5-F6diMepz)]2(C20H12F12N4Ni2),6, are orthorhombic,a = 18.7134(8),b = 15.619(2),c = 7.7263(9) Å,Z = 4, space groupPnma; those of [CpNi(3,5-diMepz)2]2Ni (C30H38N8Ni3),7, are triclinic,a = 10.078(2),b = 16.134(2),c = 9.992(1) Å, α = 91.586(10)°, β = 111.050(9)°, γ = 86.95(1)°,Z = 2, space group; and those of [CpNi(4-Cl-3,5-diMepz)2]2Ni (C30H34Cl4N8Ni3),10, are monoclinic,a = 10.2201(7),b = 16.174(1),c = 10.7207(9) Å, β = 108.193(5)°,Z = 2, space groupP21/a. The structures were solved by direct (dimetallic species) or Patterson (trimetallic complexes) methods and were refined by full-matrix least-squares procedures toR = 0.035, 0.032, 0.058, 0.032, and 0.033 (Rw = 0.021, 0.026, 0.053, 0.028, and 0.032) for 1157, 1894, 1642, 4499, and 2113 reflections withI ≥ 3σ(F2), respectively.Keywords: crystal structures, nickel, nickelocene, pyrazolates, cyclopentadienyl.

ISSN:0008-4042    

DOI:10.1139/v97-114

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

3-Alkyl-2-hydroxyindolines, conveniently prepared from 2-hydroxyindolenines and a Grignard reagent, cyclize in the aprotic solvent tetrahydrofuran to afford tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles, while in the protic solvent methanol the chemoselectivity changed to give dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles. The steric effect of the alkyl group on the reactivity of 3-alkyl-2-hydroxyindolines is discussed for both processes. The ring transformation of tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles into dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles via γ-lactone imines is also discussed.Keywords: furo[2,3-b]indoles, α-cyano-γ-lactones, chemoselectivity, ring transformation, β-enamino esters.

ISSN:0008-4042    

DOI:10.1139/v97-115

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Ester-substituted allyltetracarbonyliron cations react with cycloalkylidene-type silyl enol ethers, silyl ketene acetals, and β-keto-esters to give 1,6-dicarbonyl compounds containing a newly formed quaternary centre. Selected condensation products are converted by enolate chemistry into spirocyclic [4.4], [4.5], and [4.6] systems. Acyloin and other reductive cyclization reactions are employed to convert the condensation products into spirocyclic [4.5], [5.5], and [5.6] systems.Keywords: allyliron complexes, umpolung synthesis, 1,6-dicarbonyls, spirocycle synthesis.

ISSN:0008-4042    

DOI:10.1139/v97-116

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient speciesassigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λmax = 312 nm), and reactivity toward methanol (kMeOH = (3.6 ± 0.1) × 109 M−1s−1;kH/kD = 1.3 ± 0.1), ethanol (kEtOH = (2.41 ± 0.06) × 109 M−1s−1),tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1s−1;kH/kD = 1.5 ± 0.1), and oxygen. Experiments using isooctane and acetonitrile as solvent are also described. In acetonitrile, the lifetime of the silene is shortened considerably compared to hydrocarbon solvents, presumably due to quenching by adventitious water. In isooctane, under conditions of low excitation intensity, the siladiene decays with clean pseudo-first-order kinetics and a maximum lifetime of ~ 5 μs at 23 °C. The decay rate constant varies only slightly with temperature over the 20–60 °C range, leading to Arrhenius activation parameters ofEa = 0.5 ± 0.2 kcal/mol and logA = 5.7 ± 0.2. While steady state irradiation experiments suggest that in the absence of silene traps the predominant fate of the silabutadiene is thermal ring closure to regenerate the precursor, it is concluded that the rate constants and activation parameters for decay of the siladiene measured by flash photolysis represent a composite of those due to thermal electrocyclic ring closure (withEa > ~3 kcal/mol) and reaction with adventitious quenchers (probably water, withEa < 0). The measured Arrhenius parameters for reaction of the siladiene with methanol in isooctane (Ea = −2.6 ± 0.3 kcal/mol and logA = 7.6 ± 0.3) are consistent with this proposal. The potential and limitations of the use of 193-nm laser excitation for flash photolysis studies in solution are discussed.Keywords: far-UV, silene, flash photolysis, kinetics, electrocyclic.

ISSN:0008-4042    

DOI:10.1139/v97-117

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Dialkylstannylene acetals derived from a number of different carbohydrates having bothcis- andtrans-1,2-diols free were reacted with diacyl chlorides and disulfonyl chlorides in the presence of tertiary amines at room temperature to give symmetrical non-glycosidically linked disaccharides with excellent regioselectivity and in excellent yield. The regioselectivity obtained was the same as that previously found in acylation reactions of the same substrates. In one case, a symmetric non-glycosidically linked diasaccharide was also obtained in excellent yield. For methyl 4,6-O-benzylidene-α-D-glucopyranoside, a 16-membered ring macrocyclic tetralactone was obtained in 50% yield by altering the reaction stoichiometry and performing the reaction at 80 °C.Keywords: carbohydrates, clusters, non-glycosidically linked oligosaccharides, disaccharides, trisaccharides.

ISSN:0008-4042    

DOI:10.1139/v97-118

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The CH + CH4reaction has been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to second and fourth orders with the 6-31G(d,p) and 6-311++G(2d,p) basis sets. An energetically feasible insertion reaction path has been found in the potential energy surface that confirms the experimental proposal for the mechanism of the CH + CH4reaction. The feature of the mechanism for the CH + CH4insertion reaction is found to be different from the feature of the mechanisms for the CH + NH3, CH + H2O, and CH + HF insertion reactions, but somewhat similar to that for the CH2 + CH4insertion reaction. Energetic results for the CH + CH4reactions are in agreement with experiment.Keywords: CH radical, methane, reaction mechanism.

ISSN:0008-4042    

DOI:10.1139/v97-119

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The aqueous reactions of hydroxylamine andN-methylhydroxylamine with vanadate have been studied. Ligand, vanadium, and proton stoichiometries of the products have been obtained as have their formation constants. At lower ligand concentrations the predominant complex contains a single hydroxamido ligand and this has been assigned a five-coordinate, tetrahedral-like structure where the hydroxamido group is coordinated in a side-on fashion. Four bishydroxamido products were observed. These four complexes consisted of two distinct groups of two isomeric complexes each and have been assigned six-coordinate (tetrahedral-like) and seven-coordinate (trigonal bipyramidal-like) geometries. For theN-methylhydroxamido ligand, 10 bisligand products in 2 groups of 5 isomers each were observed. The additional products over the hydroxylamine situation arise from the relative orientations of the ligand methyl groups. For both ligands, the monoligand products carried a single negative charge and did not have a pKa, within the range of about 6–10. The bisligand products did not carry a charge under neutral conditions. The tetrahedral bisligand products could be protonated under acidic conditions (pKa ~ 6.6) but could not be deprotonated. In contrast, the trigonal bipyramidal products were not protonated under acidic conditions but could give up a proton under basic conditions (pKa ~ 7.4) to form anionic complexes. The relative orientations of the ligands and also the number of methyl groups and their relative orientations in the complex have a significant influence on the51V chemical shifts. One additional complex was observed to form and was assigned to an ester-like product formed by reaction at the hydroxyl group.Keywords: vanadate, complexes, hydroxylamine, methylhydroxylamine, peroxovanadate.

ISSN:0008-4042    

DOI:10.1139/v97-120

出版商:NRC Research Press    

年代:1997

数据来源: NRC