摘要:

Ph4SbBr (P21/n,a = 12.282(2) Å,b = 10.656(1) Å,c = 16.156(1) Å, β = 104.92(7)°,Z = 4) crystallizes with the same space group as Ph4SbCl, but the two compounds are not isostructural. The structure of Ph4SbBr consists of layers of Ph4SbBr molecules with the Br atoms almost exactly in theplanes. The coordination figure of the Sb atom is a trigonal bipyramid (TBP) with Br in an axial position. The Sb—Br distance, 2.950(1) Å is the longest reported for Sb(V) to date. The Sb(V)—Hal bond lengths and the Ph4SbBr and Ph4SbCl structures are compared in detail. Analysis of a large sample of Ph4EX (E = P, As) structures and of all the available R4EX (E = Sb, Bi; R = Ph, Me) structures shows that the former are always ionic, R4E+X−, whereas in the latter the observed coordination figures represent R4EX trigonal bipyramids with various degrees of axial distortion. The inverse variation of the axial bond lengths (thetranseffect) in the TBP Sb compounds can be quantified as Sb—Cax ~ 2.4(Sb—X)−1/9to a very high degree of correlation. This and other geometric relationships show that there exists a limiting E—X bond length (~3.3 Å for E = Sb and ~3.5 Å for E = Bi when X is oxygen) at which the TBP coordination becomes unstable and changes over to a tetrahedral R4E. This change is accompanied by a rearrangement of the structure to an ionic R4E+X−solid (of high symmetry where permitted by the size and shape of the anion) withseparations no smaller than ~4 Å when E = Sb or Bi and X = O. The distribution of the CEC angles in the Ph4EX (E = P, As) sample is analyzed; the mean (uncorrected) P—C and As—C bond lengths in Ph4E+are found to be 1.789(11) and 1.902(12) Å, respectively.Keywords: crystal structure, organoantimony compounds, Ph4SbBr, pentacoordination, tetraphenylantimony bromide.

ISSN:0008-4042    

DOI:10.1139/v89-011

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The stereoselective synthesis ofcis- andtrans-F2TePh3Cl (phenyl substituents adopt amerarrangement) via 5-coordinate cations Ph3TeFCl+andis described.trans-F2TcPh3Cl isomerizes to the thermodynamically more stablecisisomer, andcis-F2TePh3Cl has non-equivalent fluorines which undergo stereoselective fluorine exchange, as confirmed by19F andl25Te nmr spectroscopy. These results are consistent with an intermolecular mechanism of isomerization and fluorine exchange involving Te—F bond cleavage.The coordination model of reaction mechanisms provides a unified description of stereochemical rearrangements, ligand exchange processes, and chemical reactions in these, and related, octahedral and trigonal bipyramidal compounds.Keywords: synthesis ofcis- andtrans-F2TcPh3Cl, isomerization of octahedral Te compounds, fluorine exchange incis-F2TePh3Cl, synthesis of Ph3TeF, coordination model of reaction mechanisms.

ISSN:0008-4042    

DOI:10.1139/v89-012

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Interconversion reactions among the solids SiO2(quartz and fused), γ-AlOOH (boehmite), CsAlSiO4, CsAlSi2O6(pollucite), and CsAlSi5O12, in contact with aqueous solutions at 200 °C, have been investigated. Results support earlier suggestions that CsAlSi5O12is not stable with respect to CsAlSi2O6 + SiO2. CsAlSiO4is only stable, if at all, when the activity product of dissolved Cs+and OH−, with respect to unit molality standard states, exceeds about 10−2. CsAlSi2O6is stable with respect to boehmite and quartz when the cesium hydroxide activity product exceeds 10−7.8±1.5. The significance of these results to the possible immobilization of radioactive cesium as a solid aluminosilicate is discussed. Based on a comparison with published estimates of enthalpies of formation, the following revised values are suggested:Keywords: cesium aluminosilicates, enthalpy of formation, hydrothermal reactions, pollucite, thermodynamic stability.

ISSN:0008-4042    

DOI:10.1139/v89-013

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The direct irradiation of 5-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (18) led to 6-cyanobenzocyclooctatetraene (17; Φ = 0.00075), 6-cyanobenzosemibullvalene (14; Φ = 0.0003), and 2-cyanonaphthalene (Φ = 0.00015). The triplet excited state of18, generated by sensitization with a variety of ketone sensitizers (e.g., Michler's ketone and acetophenone), showed no unimolecular reactivity. Compound 18 does not participate in Zimmerman di-π-methane rearrangement; the potential product from such a transformation, 8-cyanobenzosemibullvalene (19), was, however, isolated from direct (Corex filter; Φ = 0,0010) irradiation of the semibullvalene14. Deuterium labelling experiments suggest that14derives from a mechanism involving initial C4—C8 bonding of18, and that cyclooctatetraene17is probably formed by simple electrocyclic opening of the cyclobutene ring of18.Keywords: photochemistry, rearrangement mechanism, di-π-methane, semibullvalenes.

ISSN:0008-4042    

DOI:10.1139/v89-014

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

A least-square fitting method is given for exact evaluation of spin-Hamiltonian and line shape parameters from EPR powder spectra. The method is applicable to cases where the resonance fields can be analytically expressed or can only be obtained by diagonalization of Hamiltonian. It is also suitable for different line shapes and spin-Hamiltonians. The fitted spectra and corresponding refined parameters were obtained on FACOM-M340S computer with a Fortran 77 program.Keywords: spin-Hamiltonian, line shape parameters, electron paramagnetic resonance, calculated spectra, least squares fitting.

ISSN:0008-4042    

DOI:10.1139/v89-015

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Sulfur dioxide and (R)-N,N-dimethylaminoethylferrocene (I) react with an enthalpy of formation of 21.5 ± 1 kcal mol−1to give a complex with sulfur bonded to nitrogen. The SO2exchanges between adduct molecules by a dissociation mechanism. BF3reacts with the above amine to give an adduct and its partly hydrolyzed product, [(η5-C5H5)Fe(η5-C5H4—CH(CH3)N(CH3)2•BF(OH)2] (II).IIcrystallizes in the orthorhombic space groupP212121witha = 9.882(3),b = 10.625(5), andc = 13.988(13) Å andz = 4.Rf = 0.102 andRw = 0.104.Keywords:N,N-dimethylaminoethylferrocene complexes, X-ray structure, NMR exchange.

ISSN:0008-4042    

DOI:10.1139/v89-016

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Ion/molecule reactions of C2H3Cl+have been studied in a mixture of vinyl and ethyl chlorides. The ionic processes have been followed using two mass spectrometers; one is based on the ionic cyclotronic resonance (ICR) while the other is based on photo-ionization at high pressure. The results obtained on these two instruments are complementary and they indicate that the ion C2H3Cl+does not react directly with ethyl chloride. However, the ions C4H3Cl+and C4H6Cl+, which are formed following the decomposition of the excited ion-dimer of vinyl chloride, do react with ethyl chloride in a series of condensation reactions involving in each step an elimination of HCl or of Cl. In a mixture of the two chlorides, the most important ions are the C8H13+and C8H14+; at a pressure of 1 Tonr, their total intensity is equal to 50%.Keywords: ion/molecule reactions of C2H3Cl+, vinyl and ethyl chloride mixtures, mass spectrometry. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v89-017

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Iodine nitrate or bromine nitrate in acetonitrile or in chloroform react with a variety of phenolic substrates to form both halogenated and nitrated products. In the presence of strong complexing agents of halonium ions, no reaction occurs, while in the presence of pyridine or triethylamine, only halogenated phenols exhibiting a strongortho-directing effect of the phenolic function are produced.Keywords: phenols, iodine nitrate, bromine nitrate, halogenation, nitration.

ISSN:0008-4042    

DOI:10.1139/v89-018

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Syntheses are described for d(e4pT) (1) and d(Tpe4) (2), the O4-ethylated analogues of d(TpT) (3), and mass spectrometric (FAB),1H nuclear magnetic resonance (300 MHz), and circular dichroic data are provided for the three molecules. The [M –H]−ions as well as the aggregates [2M – H]−and, in the case of1, [3M – H]−, are easily detected by FAB mass spectrometry operating in the negative ion mode. In contrast with the modified nucleoside, e4dT, the two methylene protons of the O4-ethyl groups of1and2are nonequivalent in the NMR spectra, and their chemical shift difference decreases with increasing temperature. This chemical shift difference can be related to intramolecular base stacking. The vicinal coupling constants of the sugar rings reveal an unusual shift at low temperature towards the 3′-endoconformation of the e4p unit of1, but this shift is not noted for the pe4unit of2. O4-Alkylation of either unit of3effects a large reduction in the amplitude of the negative CD peak at 252 nm. The CD spectra of1and2are qualitatively similar to those of d(CpT) and d(TpC), respectively, and suggest that in some respects an O4-alkylated thymine base is "cytosine-like". The amplitudes of the positive CD peaks of1and3are reduced by 40% as the temperature is increased from 10 to 65 °C, indicating the presence of some base stacking at low temperatures. However, the CD spectrum of2shows a much smaller reduction (<10%).Keywords: O-alkylation, oligonucleotides, stereochemistry, NMR, mass spectrometry.

ISSN:0008-4042    

DOI:10.1139/v89-019

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Rate constants have been sought for the reaction of muonium (Mu) ando-positronium (Ps) with solutions of thirteen solutes containingthe groups. Values ofkrange from <105 M−1 s−1to 3 × 1010 M−1 s−1and show a variety of trends. For instance, Mu adds across the carbonyl group much faster than does H, but abstracts from an adjacent methyl group more slowly. Mu adds exceptionally efficiently to the thiocarbonyl group. Abstraction reactions are identified by large enhancements in reaction rates when localized in micelles. Ps behaves quite differently to the others in neither abstracting nor adding to these compounds, consistent with it not being a pseudo-isotope of hydrogen.Keywords: muonium, positronium, hydrogen, hydrated electrons, micelles.

ISSN:0008-4042    

DOI:10.1139/v89-020

出版商:NRC Research Press    

年代:1989

数据来源: NRC