摘要:

A pyrazoline ring is used as a masking, a stereodirecting, and a latent formyl group in the synthesis of 7-amino-4-formyl cephems from 6H-1,3-thiazines.Keywords: thiazine, cephem, pyrazoline, benzeneseleninic anhydride.

ISSN:0008-4042    

DOI:10.1139/v89-169

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The synthesis of two new series of polyoxygenated macrocyclic derivatives,1and2, was realised. All these compounds have a 1,4-benzodioxinic moiety and are related to crown ethers, benzocrown ethers, and lariat ethers. The complexing properties of sodium and potassium ions were studied using potentiometry in methanol; results thus obtained are compared to data, previously reported in the literature, for classical polyoxygenated macrocyclic compounds.Keywords: polyoxygenated macrocycles, 1,4-benzodioxin, lariat ethers, sodium and potassium complexes, solvent methanol.

ISSN:0008-4042    

DOI:10.1139/v89-170

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

2-Chloromethyl-1-methylimidazole undergoes a pH-dependent aqueous hydrolysis with the neutral substrate being the reactive species, and the imidazole-protonated form (pKa = 5.7) unreactive. Addition of sodium chloride retards the hydrolysis, evidence that there is a free carbenium ion intermediate (the common ion effect). The rate constant ratioKcl/Kwfor the reactions of this cation with the added chloride and with the solvent is 7.4 M−1. Further evidence for a free cation is the observation of the 2-azidomethyl product when the hydrolysis is carried out with sodium azide present, but with no change in the rate constant. The Kaz/Kwratio as determined by product analysis is 1.1 × 102 M−1With the assumption thatkazrepresents a diffusion-controlled reaction and has a value of 7 × 109 M−1 s−1, the rate constant kwfor the reaction of the cation with solvent is 6 × 107 s−1. A comparison with azide–water selectivity ratios reported for other cations shows that the imidazole-stabilized primary cation of this study is relatively long-lived. A possible explanation for this is given, in terms of the extensive resonance delocalization of the positive charge in this cation.Keywords: solvolysis, carbenium ion, heterocycle.

ISSN:0008-4042    

DOI:10.1139/v89-171

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

1-Chloromethyl-3,5-dimethylpyrazole hydrochloride readily undergoes nucleophilic displacement with O-, N-, or S-nu-cleophiles. 1-Phenylthiomethyl-3,5-dimethylpyrazole can be lithiated at the CH2group and reacted with alkyl halides and carbonyl compounds. Desulfurization of the products affords a novel method of preparing N-substituted pyrazoles.Keywords: pyrazole, lithiation, chloromethylazoles, desulfurization.

ISSN:0008-4042    

DOI:10.1139/v89-172

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Molecular orbital computations with the basis set 6-31G are reported for seven values of θ, the torsion angle about thebond in anisole. All bond angles and lengths are optimized but the atoms of the phenyl group are constrained to a plane. The relative energies are fit by V(θ)/kJ mol−1 = 7.78(5) sin2θ + 2.41(5) sin22θ − 0.54(5) sin23θ, where θ is zero when the heavy-atom skeleton is planar. Computations with the basis set 6-31G*(5D) for three values of θ can be reproduced by V(θ)/kJ mol−1 = 6.07 sin2θ + 2.68 sin22θ. These results are compared with experimental gas phase data from the literature. The analysis of the1H nuclear magnetic resonance spectrum of anisole-α-13C in aCS2/C6D12/TMS solvent mixture yields a value of6J(1H,13C), the long-range spin-spin coupling constant between the13C nucleus in the methyl group andtheparaproton. Because this coupling constant is proportional to sin2θ, it is shown, together with previous dynamic nmr measurements, that the barrier to rotation about thebond in solution cannot be purely twofold. The internal potential must also contain a fourfold term of the same sign as that of the twofold component. If the V2/V4ratio given by the various molecular orbital computations holds in solution, then V2is 15.0 ± 2.0 kJ/mol and V4is 5.6 ± 2.2 kj/mol. The apparent doubling of the internal barrier in solution is perhaps unprecedented for such a simple molecule.Keywords: anisole, internal barrier in solution, anisole-α-13C,1H NMR, conformational behaviour, MO computations.

ISSN:0008-4042    

DOI:10.1139/v89-173

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

We have made new measurements of the enthalpies of adding cyclohexane to mixtures of chloroform + triethylamine + cyclohexane at 25 °C. The results of these measurements have been analysed in terms of the ideal associated solution model to obtain ΔHθfor the dissociation of the chloroform-triethylamine complex. Our value of ΔHθis in excellent agreement with a published value that was obtained from results of measurements on binary mixtures of chloroform + triethylamine. This agreement indicates that it is usefully accurate to treat mixtures of chloroform + triethylamine + cyclohexane as ideal mixtures of chloroform, triethylamine, cyclohexane, and chloroform-triethylamine complex. This result has important implications for studies of associated systems dissolved in "inert" solvents and helps to provide a connection between complex formation in dilute solutions and in binary systems (A + B, no solvent).Keywords: ideal associated solution model, chloroform, triethylamine, inert solvent, hydrogen bonded complex.

ISSN:0008-4042    

DOI:10.1139/v89-174

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The synthesis and magnetic data of four copper(II) complexes obtained from squaric acid and bipyridyl or imidazole as ligand are described. Cu(C4O4)(imidazole)2•2H2O (compoundI) is made of chains of squarato-1,3-bridged Cu(II) ions. The compound crystallizes in the monoclinic system, space groupP21/n, and lattice parametersa = 7.455(2) Å,b = 8.196(2) Å,c = 11.235(2) Å and β = 100.55(2)°.RF = 0.067 for 1076 observed reflections. [Cu2(bipyridyl)2(C4O4)(H2O)4](C4O4H)2-4H2O (compound II) is a C4O4H−salt of a squarato-1,3 bridged centrosymmetric Cu(II) dimeric cation. The compound crystallizes in the triclinic system, space groupP-1and lattice parametersa = 9.021(2) Å,b = 9.017(2) Å,c = 12.581(4) Å, α = 98.58(2)°,β = 106.81(2)°, and γ = 106.03(2)°.RF = 0.038 for 2376 reflections. Each copper atom is pentacoordinated in a distorted square-based pyramidal and is linked by two nitrogen atoms of the bipyridyl, one oxygen atom of the squarato bridge, and one oxygen atom of a water molecule in the plane and one water molecule out of plane. [Cu2(bipyridyl)2(C4O4) (H2O)2Br2] (compoundIII) is a squarato-1,3 bridged copper(II) dimer. The compound crystallizes in the monoclinic system, space groupP21/n, and lattice parametersa = 10.480(4) Å,b = 8.503(1) Å,c = 14.590(2) Å, and β = 99.75(2)°.RF = 0.048 for 1423 reflections. Each copper atom is pentacoordinated in a distorted square-based pyramidal and is linked by two nitrogen atoms of the bipyridyl, one oxygen atom of the squarato bridge and one oxygen atom of a water molecule in the plane, and one bromine atom out of the plane.In complexesI,II, andIII, the magnetic susceptibility data could be best described by neglecting the exchange coupling. The magnetic data of [Cu(bipyridyl)(C4O4)•-4H2O]n(IV) are best explained in terms of an alternating Heisenberg ferrornagnet. The epr spectra ratify results obtained from magnetic and crystallographic measurements.Keywords: squaric acid, 3,4-dihydroxy-3-cyclobutene-1,2-dion, copper(II) dimers, copper(II) chains, magnetic properties.

ISSN:0008-4042    

DOI:10.1139/v89-175

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The photolysis of ethylene has been studied at pressures from 50 to 3000 Torr using a pulsed ArF excimer laser at 193.3 nm. Major products were acetylene,n-butane, 1-butene, ethane, and 1,3-butadiene, with smaller amounts of propane, propene, methane, and allene. Quantum yields varied with pressure and reaction time; the latter dependence is ascribed to secondary photolysis of butene and butadiene. The reaction products are accounted for by three primary processes:followed by reactions of H,and C2H5radicals. The vibrationally excited C2H3radical can decompose to H + C2H2or can be stabilized by collision. The pressure dependence of the quantum yields of the primary processes [1]–[3] is complex, and a photodissociation mechanism involving several intermediates and excited states of ethylene is presented to account for the present results and previous measurements at 185 nm.Keywords:ethylene, uv photolysis.

ISSN:0008-4042    

DOI:10.1139/v89-176

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The rearrangement of germacrone (1) to β-elemenone (2) is common during gas chromatographic (GC) analysis, with the conversion taking place in the injector port at temperatures above 250 °C as well as on the column. While production of2in the injector is evident from the gas chromatographic trace,2produced from1during its migration down the column is difficult to detect because of the diffuse nature of the chromatographic peak produced by this process. A mathematical model and kinetic parameters (A = (1.35 ± 0.03) × 10−3s−1;Ea = 137 ± 4 kJ mol−1) determined from the reaction in solution can be used to estimate the degree of conversion of 1 to2for chromatographic runs (including temperature-programmed analyses). The results of these calculations verify that substantial amounts of1are converted to2under conditions that are commonly used for the analysis. The method for modeling thermally induced rearrangements in nonisothermal processes represents the first approach to quantitatively assessing their importance in GC analyses of thermally labile substances.Keywords: kinetics, gas chromatography, thermal rearrangement, germacrone, β-elemenone.

ISSN:0008-4042    

DOI:10.1139/v89-177

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Laser-induced thermal modulation of electrical conductivity is a new photothermal method for the measurement of minute absorbance in sub-nanoliter liquid samples. In this paper, a model is presented for the technique. This model is based upon the interaction of a Gaussian laser beam with a cylindrical, homogeneous electrolytic resistor. Particularly simple results are produced if the laser beam spot size is much smaller than the diameter of the electrodes. The theory is verified with respect to the electrode spacing and to the laser power, spot size, and chopping frequency; the highest sensitivity occurs with low chopping frequency, high laser power, and small electrode spacing. The signal is independent of laser spot size, as long as the beam does not illuminate the electrode surface. The precision of the measurement is dominated by shot noise in the current flow through the electrolytic resistor. One point absorbance detection limits of 5.5 × 10−6measured across the 76-μm diameter electrode wires are obtained in aqueous solution with a 5- mW helium–neon laser. With this instrument, the difference in the absorbance of water and deuterated water is easily determined at 632.8 nm.Keywords: thermal modulation of electrical conductivity.

ISSN:0008-4042    

DOI:10.1139/v89-178

出版商:NRC Research Press    

年代:1989

数据来源: NRC