摘要:

For thecis–anti–cisisomer of dicyclohexano-13-crown-4 ether, disorder has been detected in the crystal structure, with two conformations being present in the ratio of ca. 3:2. Crystal structures for two Li+complexes of thecis–syn–cisisomer have also been determined. Representative13C solid phase NMR spectra are presented and discussed for these systems and the related dibenzo substituted compounds.Keywords: crown ethers, solids, NMR, conformation.

ISSN:0008-4042    

DOI:10.1139/v90-011

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The synthesis and structural characterization of representative and novel pyrazagaboles, boron- and gallium-containing compounds with a central six-membered heterocyclic B—(N—N)2—Ga ring feature, are detailed. Crystals of dimethylgallium-bis(μ-pyrazolyl)dimethylboron are orthorhombic,a = 7.6135(5),b = 16.2917(5),c = 22.331(1) Å,Z = 8, space groupPbca, and those of hydroxy(methyl)galliumbis(μ-pyrazolyl)dimethylboron are orthorhombic,a = 7.6197(3),b = 16.2184(7),c = 22.190(1) Å,Z = 8, space groupPbca. Both structures were solved by conventional heavy atom methods and were refined by full-matrix least-squares procedures toR = 0.054 and 0.040 for 1243 and 1272 reflections withI ≥ 1.5 and 3σ(I), respectively. The crystal structures are isomorphous and both feature six-membered B—(N—N)2—Ga rings having highly asymmetric boat conformations, unlike those observed for the majority of the homobinuclear analogs previously reported. The mean Ga—N and B—N distances in the two compounds are 1.977 and 1.61 Å.Keywords: pyrazagaboles, pyrazolyl-bridged heterocycles, crystal structures, synthesis of pyrazagaboles.

ISSN:0008-4042    

DOI:10.1139/v90-012

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Condensation of equimolar amounts of salicylaldehyde,N-hydroxypiperidine, and phenylboronic acid yields the title compound. Crystals of 8,8-pentamethylene-6-phenyl-6,9-epoxy-5,7-dioxa-8-azonia-6-borata-6,7,8,9-tetrahydro-5H-benzocycloheptene are monoclinic,a = 12.773(1),b = 11.9600(7),c = 10.6411(6) Å, β = 103.786(7)°,Z = 4, space groupP21/c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures toR = 0.039 andRw = 0.047 for 2420 reflections withI ≥ 3σ(I). The compound has a bridged heterocyclic B,N-betaine structure with a PhB(OR)3anionic centre. Bond lengths (corrected for libration) include: B—O(aryl C) = 1.481(2), B—O(alkyl C) = 1.488(2), B—O(N) = 1.539(2), and B—C = 1.591(2) Å.Keywords: organoboron, boron compounds, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v90-013

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Reaction of oxybis(diphenylborane) with the condensation product of salicylohydroxamic acid and cyclopentanone gives the title compound in good yield. Crystals of 2,2-diphenyl-4,4-tetramethylene-1,3,5-trioxa-3a-azonia-2-borata-2,3,4,5-tetrahydro-1H-cyclopenta[a]naphthalene are monoclinic,a = 12.521(1),b = 12.409(1),c = 12.975(1) Å, β = 93.784(8)°,Z = 4, space groupP21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures toR = 0.043 andRw = 0.044 for 1502 reflections withI ≥ 2σ(I). The molecule has a typical diphenylboron hydroxamate structure featuring a five-membered COBON chelate ring. TheO,O-chelating ligand is weakly bound to the diphenylboron moiety. Bond lengths (corrected for libration) include: (N)O—B = 1.558(4), (C=)O—B = 1.578(4), and C—B = 1.589(5) and 1.603(5) Å.Keywords: crystal structure, boron compound, organoboron compound.

ISSN:0008-4042    

DOI:10.1139/v90-014

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Volumetric and enthalpic effects have been measured at 308.15 K for pyridine (A) + aniline,o-toluidine, formamide, orN,N-dimethylformamide (B) mixtures and the same have been rationalized by graph–theoretical arguments to suggest that while aniline in the pure state exists as an equilibrium mixture of monomers and dimers,o-toluidine exists mainly as dimers. This analysis has further yielded information about the state of association in formamide andN,N-dimethylformamide that is consistent with the existing views on their nature of association. This analysis has further yielded information about the molecular entities in these mixtures that has been supported by their infrared spectral studies. The energetics of the various interactions that result in the formation of these A + B mixtures have also been investigated and the results have been rationalized by graph–theoretical arguments.Keywords: topological, association, solvation, energetics, volumetric, enthalpic effects.

ISSN:0008-4042    

DOI:10.1139/v90-015

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

An iodimetric technique has been developed to quantitatively analyze the oxidants present in organic solutions. Addition of excess tetrabutylammonium iodide and excess glacial acetic acid results in the formation of tetrabutylammonium triiodide, whose concentration can be measured spectrophotometrically at 295 or 365 nm. Application of this technique to the determination of the final oxidation state of manganese in permanganate reactions in methylene chloride solutions is described. The equilibrium constant for formation of tetrabutylammonium triiodide in methylene chloride has been measured:K = (3.48 ± 0.12) × 104at 25.0 °C.Keywords: iodimetric determinations, manganese oxidation states, methylene chloride, quaternary ammonium permanganate, quaternary ammonium triiodide.

ISSN:0008-4042    

DOI:10.1139/v90-016

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Lignin residues from the alkaline hydrolysis of solvolytic lignin have been characterized by elemental analysis, size exclusion chromatography, Fourier transform infrared spectroscopy,13C NMR, and for methoxyl content. All lignin residues were found to have higher carbon and lower oxygen contents than the original glycol lignin. Methoxyl contents decreased with increasing severity of treatment. All treated lignins have lower molecular weights than the original, which is indicative of the extensive depolymerization of glycol lignin by alkaline hydrolysis. The appearance of new bands in the 3050–2800 cm−1and 900–800 cm−1regions in the infrared spectra along with increasing absorption intensity under more severe conditions demonstrates that, despite the tendency to depolymerization, new carbon–carbon bonds are formed due to repolymerization reactions.13C NMR revealed that extensive cleavage of the side chains and β-O-4 interunit linkages had occurred during alkaline hydrolysis and that the new bonds formed due to condensation reactions at higher severities are of the methine, methylene, methyl and carboxyl types.Keywords: residual lignins, alkaline hydrolysis, characterization.

ISSN:0008-4042    

DOI:10.1139/v90-017

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The vibrational spectra have been measured for 2-methylthietane over the range 100–1600 cm−1(Raman) and 400–3200 cm−1(solution and vapour phase infrared).Abinitiocalculations at the 3-21G and 6-31G* levels indicate that both the axial and equatorial conformers represent minima on the ring inversion potential surface, the latter suggesting the equatorial species to be more stable by 191 cm−1. Vibrational force fields were evaluated for each of the two conformers and scaled using factors previously optimized for thietane and 2-methyloxetane. All of the major experimental features were readily assigned to the equatorial species, and most transitions expected for the axial species were also located. Calculated absorption intensities, although not accurate in an absolute sense, proved useful in predicting the relative intensities for corresponding axial and equatorial transitions.Keywords: 2-methylthietane, vibrational spectra,abinitioforce fields, vibrational assignment, conformations.

ISSN:0008-4042    

DOI:10.1139/v90-018

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Solutions of bis(fluorosulfuryl)peroxides, S2O6F2, in fluorosulfuric acid, HSO3F, are synthetically very useful. The nature of the solvent (HSO3F)–solute (S2O6F2or SO3F•) interaction is probed by Raman,1H and19F NMR, and ESR spectroscopy, the latter focussing on the radical SO3F•formed by the dissociation of S2O6F2. Both S2O6F2and SO3F•behave as very weak bases in HSO3F. Proton transfer between solvent and solute and SO3F exchanges are suggested on the basis of NMR and ESR measurements. The symmetry and electronic structure of the SO3F•radical are altered in HSO3F solution. Agisovalue of 1.97267 is obtained. The radical appears to be formed on dissolution of S2O6F2at room temperature and persists down to 183 K. The solvent–solute interaction depends on the acid strength of the protonic solvent and addition of the base KSO3F to HSO3F leads to a loss of solubility and the separation of S2O6F2as a second phase.Keywords: solution study in HSO3F of weak bases, Raman spectrum, ESR study in HSO3F.

ISSN:0008-4042    

DOI:10.1139/v90-019

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The tricarbonyl anions of Cr, Mo, and W incorporating unsymmetrical tridentate chelating pyrazolyl gallate ligands, [Me2Ga(N2C5H7)(OCH2CH2X)]M(CO)3−, have been isolated as their crystalline Et4N+salts.1H nmr and solution infrared studies indicate that the octahedral anions display a facial arrangement of the gallate ligand and the three carbonyl groups. This stereochemistry has been proven definitively for the tungsten complex with X = NMe2by an X-ray structure determination (see below). Fluxional behavior for the anions ind6-acetone solution has been demonstrated by variable temperature1H nmr studies and is compared to similar behavior displayed by the neutral molybdenum "allyl" complex, [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η3-C4H7). Crystals of tetraethylammonium [dimethyl(3,5-dimethylpyrazol-1-yl)(2-N,N-dimethylaminoethoxy)gallato-N2,N3,O]tricarbonyltungstate are orthorhombic,a = 11.312(9),b = 33.111(9),c = 7.445(6) Å,Z = 4, space groupP212121. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures toR = 0.033 andRw = 0.034 for 2508 reflections withI ≥ 3σ(I). The [Me2Ga(N2C5H7)(OCH2CH2NMe2)]W(CO)3−anion hasfac-octahedral coordination geometry with W—O = 2.228(7), W—N(pyrazolyl) = 2.299(8), W—N(amine) = 2.37(1), and W—CO = 1.91 (1)–1.92(1) Å.Keywords: pyrazolyl-gallate complexes, fluxional behavior of Ga–W complexes, crystal structure of Ga–W complex, gallate–tungsten complexes.

ISSN:0008-4042    

DOI:10.1139/v90-020

出版商:NRC Research Press    

年代:1990

数据来源: NRC