bluuebunny/crossref_metadata_2025 huggingface dataset:
Volumetric studies on binary mixtures of some furan derivatives with benzene, chlorobenzene, and bromobenzene at 298.15 K
Authors: Naorem Homendra , Suri S. K.
Published: May 2006

Molar excess volumes for the binary mixtures of tetrahydrofuran, furan, furfural, and furfuryl alcohol with benzene, chlorobenzene, and bromobenzene have been calculated from precise experimental density data at 298.15 K over the entire composition range. The results have been discussed in light of unlike n–π interactions between the π-electron cloud of the aromatic ring and the oxygen atom of the heterocyclic ring. The substitution of a halogen atom in the aromatic ring activates the molecule for n–π interactions in tetrahydrofuran and furan solutions and deactivates the molecule in furfural and furfuryl alcohol solutions. Keywords: furan derivatives, binary mixtures, excess volumes, n–π interactions, π–π interactions.
A point-charge representation of nonbonding electron pairs: model derived from the ability of the hydrogen bond to act as a probe of electron density
Authors: Legon A. C. , Millen D. J.
Published: May 2006

A simple point-charge model is presented for some molecules B which assigns charges to atom centres and to nonbonding pairs, those for the latter placed at distances r along directions α as conventionally envisaged. The magnitude δ of the charge assigned to the nonbonding pairs is chosen so that the variation of the electrostatic interaction energy between B and HF with the angular position of HF agrees with that calculated on the basis of a more complete description (DMA) of the electrostatic charge distribution of B. The charges δ in the three molecules explored (B = H2O, H2CO, and H2S) prove to be only a few hundredths of an electron at distances r comparable with bond distances in B. Keywords: nonbonding pairs, point-charge model, hydrogen bond, Gillespie–Nyholm model, electron localization.
The preparation and X-ray crystal structure of Te(N3)3SbF6 containing the triazidotellurium(IV) cation, Te(N3)3+
Authors: Johnson James P. , MacLean Gregory K. , Passmore Jack , White Peter S.
Published: May 2006

The crystal structure of Te(N3)3SbF6 containing the first binary tellurium–nitrogen cation, triazidotellurium(IV) (Te(N3)3+), has been determined by X-ray crystallography. Single crystals of Te(N3)3SbF6 are monoclinic, space group P21/c with a = 9.201(6), b = 8.445(4), c = 13.582(7) Å, β = 100.36(5)°, Z = 4, final R1 = 0.036 for 1286 observed reflections. The structure consists of discrete Te(N3)3+ cations and distorted octahedral SbF6− anions, with some cation–anion interactions. The average Te—Nα—Nβ—Nγ bond distances in Te(N3)3+ are Te—Nα, 1.994(7); Nα—Nβ, 1.237(11); and Nβ—Nγ, 1.116(12) Å. The average bond angles about the Te, Nα, and Nβ atoms are 94.1(3)°, 116.5(6)°, and 173.7(9)°. Structural correlations with other TeX3+ species have yielded an estimate of the electronegativity of the N3− group to be 3.1 ± 0.1. Keywords: tetratellurium (2+) cation, triazidotellurium(IV) cation, electronegativity, azide.
Hexafluoro antimonates(V) of divalent metals, synthesis and properties
Authors: Cader M. S. R. , Aubke F.
Published: May 2006

Solvolysis of metal(II) fluorosulfates in liquid antimony(V) fluoride according to:[Formula: see text]with M = Sn, Ni, Pd, Cu, or Ag, is found to be a clean, efficient route to the hexafluoro antimonates of the corresponding metals. Two of the compounds reported here display unusual features: Pd(SbF6)2 is, like its fluorosulfate precursor, paramagnetic with the Pd2+ ion in a 3A2g ground state, and an analysis of the ligand field spectrum is presented; Ag(SbF6)2 is, unlike a recently reported paramagnetic, blue, valence isomer, diamagnetic and nearly white in color. Formulation as a mixed valency compound Ag(I)Ag(III)(SbF6)4 is suggested. Low temperature magnetic susceptibility measurements (where appropriate), Raman, and IR data are reported. The hexafluoro antimonates of Ni, Pd, and Cu show antiferromagnetic exchange at very low temperatures. Pd(SbF6)2 shows very weak ferromagnetism below 10 K. Keywords: fluoroantimonates of divalent metals, synthesis and solvolysis in SbF5, vibrational spectra, magnetic susceptibility measurements.
Preparation and characterization of diphenylbis(N,N-dialkyldithiocarbamato)tellurium (IV) and chlorodiphenyl(N,N-dialkyldithiocarbamato)tellurium(IV). Crystal structures of Ph2Te[S2CNMe2]2, Ph2TeCl[S2CNEt2], and Ph2TeCl[S2CN(i-Pr)2]
Authors: Bailey Jane H. E. , Drake John E. , Sarkar Anil B. , Wong Maria L. Y.
Published: May 2006

A number of dithiocarbamate derivatives Ph2Te[S2CNR2]2, where R = Me, Et, and Ph2TeCl[S2CNR2], where R = Me, Et, i-Pr, have been prepared and characterized initially by analysis and vibrational spectroscopy. Three crystal structures have been completed that allow for comparisons of the effect of the change in the nature of R and of the presence of a chlorine atom. The dithiocarbamate groups are monodentate (or anisobidentate) and the geometry about tellurium is consistently that of a distorted sawhorse structure. Examples of both inter- and intra-molecular Te … S interactions are observed as well as an intêrmolecular Te … Cl interaction. The crystal structures of Ph2Te[S2CNMe2]21, [Formula: see text]4 and Ph2TeCl[S2CN(i-Pr)2] 5 were determined. The cell parameters for 1 are a = 20.158(5) Å, b = 8.632(2) Å, c = 12.727(4) Å, β = 92.70(2)°, V = 2212(1) Å3, Z = 4, R = 0.0221, and Rw = 0.0243; for 4 are a = 11.198(4) Å, b = 13.974(4) Å, c = 13.812(5) Å, α = 99.56(2)°, β = 103.08(3)°, γ = 87.39(3)°, V = 2076(1) Å3, Z = 4, R = 0.0363, and Rw = 0.0398; and for 5 are a = 12.736(3) Å, b = 8.397(1) Å, c = 21.961(1) Å, β = 117.36(1)°, V = 2086(7) Å3, Z = 4, R = 0.0266, and Rw = 0.0312. NMR spectra are not simple and indicate that several species are present in solution. Keywords: structure, tellurium, chloro, diphenyl, dialkyldithiocarbamato.
An NMR study of the Lycopodium alkaloids, annotinine and annotine: verification of the annotine structure
Authors: Hughes Donald W. , Gerard Robert V. , MacLean David B.
Published: May 2006

The Lycopodium alkaloids, annotinine and annotine, were examined by 1H and 13C NMR spectroscopy. Proton spectra were assigned by the application of double-quantum filtered phase-sensitive COSY and nuclear Overhauser enhancement difference spectra. These and other data confirmed the structure previously assigned to annotine. The 13C chemical shifts were consistent with the structural data derived from the proton spectra. The NMR data showed a good correlation with structures determined from molecular mechanics (MMX) calculations. Keywords: Lycopodium alkaloids 1H and 13C NMR, annotinine, annotine, structure of Lycopodium alkaloids, NMR alkaloids.
Disproportionation of chlorine in hydrogen fluoride and related media
Authors: Gambardella Mario , Kongpricha Santad , Pitts James J. , Jache Albert W.
Published: May 2006

Chlorine can be made to disproportionate to chlorine monofluoride and chloride, taking advantage of Le Chatelier's principle in several different ways. It will disproportionate to form insoluble silver chloride and chlorine monofluoride when silver fluoride is present. It will disproportionate in a melt of alkali metal fluorides to form alkali metal chlorides and chlorine monofluoride. The alkali metal chlorides will react with hydrogen fluoride to regenerate the metal fluorides and hydrogen chloride. Chlorine will also disproportionate in hydrogen fluoride containing antimony pentafluoride to yield antimony pentafluoride adducts of chlorine monofluoride and of hydrogen chloride. These adducts are readily decomposed to yield the disproportionation products and the original antimony pentafluoride. Keywords: hydrogen fluoride, disproportionation, chlorine, waterlike, solvent system.
Polyfluoroaralkyl amines. Further studies on the reactivity of 4,5,6,7-tetrafluoroindole
Authors: Filler Robert , Woods Sarah M. , White William L.
Published: May 2006

4,5,6,7-Tetrafluoroindole 1 undergoes electrophilic formylation and aminoalkylation at C-3 to give compounds that can be readily converted to a variety of products, including the skatole, tryptamine, and tryptophan. 1 reacts with ethyl diazoacetate to yield 4,5,6,7-tetrafluoroethyl-3-indole acetate. The Grignard reagent of 1 offers a direct route to the versatile substituted acetonitrile 10 via C-3 alkylation with chloroacetonitrile. Keywords: tetrafluoroindole, tetrafluorotryptamine, tetrafluoroindolyl magnesium bromide, tetrafluorotryptophan.
"Through-space" spin–spin coupling between thallium and fluorine in fluorophenylthallium compounds
Authors: Pecksen Gerald Norman , White Raymond Frederick Martin
Published: May 2006

Thallium to fluorine spin–spin coupling constants have been measured for a number of fluoro- and trifluoro-methyl-substituted mono- and di-arylthallium derivatives. The results provide evidence of "through-space" coupling in the diaryl derivatives when the fluoro- or trifluoro-methyl group is ortho to the thallium atom. Keywords: thallium, fluorine, NMR, through-space coupling.
A nuclear magnetic resonance spectroscopic study of some tri-sulfide bridged ferrocenes
Authors: Butler Ian R. , Cullen William R.
Published: May 2006

The synthesis of some new [S3]-bridged aminoferrocenophanes is described. The 1H nuclear magnetic resonance spectra of these compounds are completely assigned and are discussed in terms of the stereochemistry of the tri-sulfide bridge. In addition 13C/1H correlation spectra of one of the derivatives are presented to illustrate the complete assignment of the 13C spectrum. Keywords: ferrocene derivatives, sulfur-bridged, synthesis, NMR, conformation.
The reactions of nitrosoarenes with cationic cyclohexadienyl complexes of iron tricarbonyl: an ESR study
Authors: Li Lijuan , Perrier Richard E. , Eaton Donald R. , McGlinchey Michael J.
Published: May 2006

The reactions of nitrosoarenes with the (cyclohexadienyl)Fe(CO)3 cation have been investigated by using electron spin resonance spectroscopy. The radicals produced are nitroxides of the type (OC)3Fe(C6H7)(Ar)N—O• but, in some cases, disproportionation and loss of the metal carbonyl fragment leads to the corresponding C6H5(Ar)N—O• radical. With bulky nitrosoarenes, such as C6Me5NO, isomers are observed in which the aryl ring rotation is slow on the ESR time scale. The analogous reactions with the cyclohexadienyl cation derived from the B ring of (ergosteryl acetate)Fe(CO)3 lead to initial attack not at one of the termini of the delocalized system but rather at the central carbon, i.e., at C-7. Subsequent hydrogen migration leads to the (5,7-diene)Fe(CO)3 complex bearing the arylnitroxide at the 7-position. The mechanisms of these reactions are discussed. Keywords: nitrosoarenes, iron cations, ESR.
Reaction of N,N′-dihydroxy-.N,N′-dimethylmethanediamine with phenylboronic acid and the crystal and molecular structure of N,N′-dihydroxy-N,N′-dimethylmethanediamine
Authors: Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of N,N′-dihydroxy-N,N′-dimethylmethanediamine with phenylboronic acid leads to the product 1,7-dimethyl-3,5-diphenyl-2,4,6-trioxa-7-aza-1-azonia-3-bora-5-boratabicyclo[3.3.0]octane rather than the expected product 1,5-dimethyl-3-phenyl-1,5-diaza-2,4-dioxa-3-boracyclohexane. The structure of N,N′-dihydroxy-N,N′-dimethylmethanediamine has been determined and is discussed in terms of its reaction with PhB(OH)2. Crystals of N,N′-dihydroxy-N,N′-dimethylmethanediamine are tetragonal, a = 8.5346(3), c = 8.4178(7) Å, Z = 4, space group P421c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.036 and Rw of 0.038 for 333 reflections with I ≥ 3σ(I). The structure consists of hydrogen-bonded dimers having exact [Formula: see text] symmetry. Keywords: N,N′-dihydroxy-N,N′-dimethylmethanediamine, crystal structure.
A Raman spectral study of the equilibria of zinc bromide complexes in DMSO solutions
Authors: Heumen Jeff Van , Ozeki Toru , Irish Donald E.
Published: May 2006

Using Raman spectroscopy, the stepwise formation of zinc bromide complexes in dimethylsulfoxide (DMSO) solution has been investigated. The presence of four different zinc bromide complexes is suggested and their Raman spectra have been extracted. The formation constant of each reaction has been estimated by the application of factor analysis to the spectra. The usual methods of factor analysis have been extended by the introduction of constraints imposed by the equilibria. Keywords: zinc bromide complexes, solvation in DMSO, Raman spectroscopy, factor analysis.
Enhanced polymerization of molybdate ions in the presence of antimonic acid
Authors: Kone M. , Courtin P. , Lemerle J.
Published: May 2006

Polymer compounds including both antimony and molybdenum were formed by mixing freshly prepared solutions of antimonic and molybdic acid. These acids were formed through an ion exchange process. When antimony is in excess, molybdenum is included in the high polymers having the ccp structure of β antimonic acid. When molybdic acid is in excess in the starting mixture, molybdenum-rich polymers with a larger molecular weight than molybdic acid were formed. In GPC experiments the behaviour of the compounds is related to their Mo and Sb content. The elution volume is only related to the molecular weight of the compound when Sb is the main component and imposes its structure. Keywords: molybdoantimonic acids, inorganic polymers, ultracentrifugation, GPC.
Structural studies of organoboron compounds. XXXVII. 8,8-Pentamethylene-6-phenyl-6,9-epoxy-5,7-dioxa-8-azonia-6-borata-6,7,8,9-tetrahydro-5H-benzocycloheptene
Authors: Kliegel Wolfgang , Motzkus Hans-Walter , Drückler Klaus , Rettig Steven J. , Trotter James
Published: May 2006

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 group P21/c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.039 and Rw = 0.047 for 2420 reflections with I ≥ 3σ(I). The compound has a bridged heterocyclic B,N-betaine structure with a PhB(OR)3 anionic 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.
Characterization of lignin residues derived from the alkaline hydrolysis of glycol lignin
Authors: Thring Ronald W. , Chornet Esteban , Bouchard Jean , Vidal Pierre F. , Overend Ralph P.
Published: May 2006

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−1 and 900–800 cm−1 regions 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.
Thermodynamic behaviour of molten metal oxychlorides. 1. The PbO–PbCl2 system
Authors: Hacetoglu A. , Flengas S. N.
Published: May 2006

Partial molar and integral molar properties of mixing for PbO–PbCl2 melts have been investigated by using solid electrolyte galvanic cells of the type: Ni–NiO | CaO–ZrO2 | PbO–PbCl2 | Pb. Thermodynamic properties, such as activities and partial molar enthalpies of mixing, calculated from the measured cell potentials show pronounced negative deviations from ideality. To explain this behaviour and to predict the concentration dependence of the thermodynamic properties of these solutions, a theoretical model based on a number of possible reaction mechanisms has been developed. It is shown that in a non-ideal solution, the activity of any component A+X− is given as[Formula: see text]equilibriumwhere [Formula: see text] and [Formula: see text] are respectively the cation and anion fractions in a solution that has reached the ionic composition representing a specific reaction mechanism at equilibrium. From the activity data, the limiting experimental conditions for removing the oxygen impurity from PbCl2 melts and for recovery of Pb and O2 by fused salt electrolysis have been established. Keywords: oxychlorides, activities, solution properties, PbO–PbCl2, EMF.
Structure of 2-methoxy-3,5-dinitropyridine
Authors: Punte G. , Rivero B. E. , Cerdeira S. , Nudelman N. S.
Published: May 2006

2-Methoxy-3,5-dinitropyridine, C6N3O5H5, crystallizes in the monoclinic system, space group P21/n, with cell parameters a = 7.496(5), b = 18.38(1), c = 6.068(2) Å, β = 77.18(4)°, V = 815(1) Å3, and four molecules per unit cell. Its structure was solved by direct methods and refined by least-squares procedures to a final R = 4.99%, Rw = 5.42%, for 753 observed independent reflections. The molecule is not planar, a rotation of the methoxy and 3-nitro groups out of the pyridine ring (7° and 16°, respectively) is observed. The methoxy group is located syn to the ring nitrogen atom to avoid repulsion with the 3-NO2 group and adopts a geometry different from the mean reported in the literature for methoxyaromatic groups. Geometrical parameters suggested by Domenicano and Murray-Rust and Norrestam and Schepper are used to analyze substituent effects on the pyridine shape and the possible causes of non-additivity of substituent effects are discussed. The relation of molecular conformation with reactivity of the title compound with amines is examined. Keywords: methoxy pyridine, substituted nitropyridines, crystal structure.
1,3,5-Trimethylbenzene(mesitylene) adducts with selected tin(II) compounds: the syntheses of Sn(SO3F)2•C9H12 and Sn(SbF6)2•2C9H12
Authors: Gin D. Y. , Cader M. S. R. , Sams J. R. , Aubke F.
Published: May 2006

Addition of 1,3,5-trimethylbenzene (mesitylene or mes) to the tin(II) salts, Sn(SO3F)2 and Sn(SbF6)2, results in the formation of adducts of the composition Sn(SO3F)2•mes and Sn(SbF6)2•2mes in very high yield. The adducts are characterized by chemical analysis and infrared spectra. The adduct formation is followed by 119Sn Mössbauer spectroscopy. It appears that only tin(II) compounds with large, weakly nucleophilic anions are capable of forming mesitylene adducts, while SnCl2, SnF2, and stannocene do not give any indication of adduct formation under similar conditions. Keywords: tin(II)–mesitylene complexes, synthesis, vibrational study, 119Mossbauer spectra.
Poly(vinyl acetate) as a template for polymerization of methacrylic acid
Authors: Tewari Neeta , Srivastava A. K.
Published: May 2006

The template polymerization (TP) of methacrylic acid (MAA) using polyvinyl acetate (PVAc) of [Formula: see text] 66 400 at 60 °C for 120 minutes in dimethyl formamide (DMF) has been studied dilatometrically to study the effect of template, and of the monomer and initiator (α-α′ azobisisobutyronitrile) concentrations upon the kinetics. Viscometric measurements showed that complexation between PVAc and PMAA was maximum when the template/polymer ratio was 1:1, and the time required for complete complexation was 7 minutes. The overall energy of activation was the same, i.e., 115 kJ/mol, in the presence and absence of template. The overall system follows mechanism II. Keywords: template polymerization, polyvinyl acetate, methacrylic acid, α,α′-azobisisobutyronitrile, relative rate of polymerization.
Conformational analysis of [3.3.3](1,3,5)cyclophane systems
Authors: Meno Tatsuya , Sako Katsuya , Suenaga Masahiko , Mouri Miyuki , Shinmyozu Teruo , Inazu Takahiko , Takemura Hiroyuki
Published: May 2006

2,2,11,11,20,20-Hexadeuterio[3.3.3](1,3,5)cyclophane 1-d6 and its precursor, [3.3.3](1,3,5)cyclophane-2,11,20-trione 2, were synthesized and their conformational behavior was examined by a variable temperature 1H NMR method; 1-d6 (ca. 1% CD2Cl2 solution) exists in a mixture of the conformer A (C3h) and the conformer B (Cs) in a 27:73 ratio at −70 °C with the energy barriers for the trimethylene bridge inversion processes [Formula: see text] being 12.4 kcal/mol (Tc = −7 °C, 270 MHz). Conformer B is more stable than A by 0.4 kcal/mol based on the populations of both conformers. In contrast to the conformational behavior of 1, inversion of the tricarbon bridges of 2 is not frozen even at −90 °C because of the increased flexibility of these tricarbon bridges. Keywords: conformational analysis, cyclophane, tri-n-butyltin deuteride.
Repulsive gauche conformational effect. Analysis of seven-membered rings containing endo and exo sulfur atoms
Authors: Dionne P. , ST-Jacques M.
Published: May 2006

The so-called repulsive gauche conformational effect associated with sulfur is investigated through a study of 3-methylthio-1,5-benzodioxepin (1) and 3-methylthio-1-benzoxepin (2), together with 3-fluoro- and 3-chloro-1,5-benzodithiepins (3 and 4), by 13C and 1H dynamic nuclear magnetic resonance methods. The results show that, while compounds 2, 3, and 4 exhibit a large amount of the Ce conformation, the TB form predominates for compound 1. Intramolecular stereoelectronic σ–σ* orbital interactions are analyzed, together with several other factors (steric, electrostatic, and solvation), to explain the observed conformational behaviour. Keywords: gauche effect, seven-membered rings, 1,5-benzodithiepins, variable temperature NMR, orbital interactions.
Substituted ferrocenecarboxylic acids and esters
Authors: Cullen W. R. , Wickenheiser E. B.
Published: May 2006

The synthesis of Fe(η-C5H5)(η-C5H3(CHMeNMe2)(COOH)-1,2), 3a, and its methyl and ethyl esters is described. Esterification of 3a by using RI in DMA affords Fe(η-C5H5)(η-C5H3(CHMeOH)(COOR)-1,2), R = Me, Et, with retention of configuration at the chiral center. The variable temperature 1H NMR spectrum of 3a reveals H-bonding between the two functional groups. Keywords: ferrocenecarboxylic acids and esters, NMR spectra, synthesis, hydrogen bonding.
Energetics of intra- and intermolecular bonds in ω-alkanediols. III. Thermochemical study of 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol at 298.15 K
Authors: Knauth P. , Sabbah R.
Published: May 2006

The enthalpies of combustion and sublimation or vaporization of the title compounds were determined on milligram samples and used to derive, at 298.15 K, the enthalpies of formation in the gaseous phase and the enthalpies of atomization. The previous conclusions drawn from the investigation of the lower ω-alkanediols were confirmed: the enthalpy of a hydrogen bond in solid ω-alkanediols amounts to 27 kJ mol−1 and the intramolecular C—C and C—OH bond enthalpies to 343.2 and 819.5 kJ mol−1, respectively. The enthalpies of fusion and the triple point temperatures of the ω-alkanediols [Formula: see text] are reported and discussed. Keywords: ω-alkanediols, enthalpies of formation, triple point temperatures, differential thermal analysis, calorimetry.
Synthesis of a biologically active isomer of frontalin and some new products from acylative decarboxylation of 3-methyltricarballylic acid
Authors: Strunz George M. , Yu Chao-Mei , Ya Li , White Peter S. , Dixon E. A.
Published: May 2006

2-Acetonyl-2-methylsuccinic anhydride, 3, the major product from base-catalysed reaction of 3-methyltricarballylic acid with acetic anhydride, was converted by simple manipulation of functional groups into 1,5-dimethyl-2,7-dioxabicyclo[3.2.1]octane. This bicyclic ketal (6) is isomeric with frontalin, 7, an aggregation pheromone for Dendroctonus bark beetles. It elicited electroantennogram responses in D. ponderosae and D. rufipennis. Besides 3 and the known compounds, 4 and 5, two new minor products, 8 and 9, were identified from base-catalysed acylative decarboxylation of 3-methyltricarballylic acid. Keywords: pheromone analogue, Dendroctonus, bark beetles.
The crystal and molecular structures of two isostructural complexes: [(H3O•18-crown-6)2(ZnCl4)] and [(H3O•18-crown-6)2(MnCl4)]
Authors: Chênevert Robert , Chamberland Daniel , Simard Michel , Brisse François
Published: May 2006

New macrocycle polyether 18-crown-6 complexes of stoichiometry [(H3O+•18-crown-6)2(MC42−)] have been synthesized for M = Zn and Mn. The two complexes are isostructural and crystallize in the monoclinic system, space group C2/c. The unit cell dimensions are as follows: a = 16.229(9), b = 11.535(3), c = 20.134(8) Å, β = 97.55(4)° and a = 16.255(6), b = 11.625(3), c = 20.122(8) Å, β = 96.54(3)° for the Zn and Mn complexes respectively. In both crystal structures (final Rw = 0.048 with 1817 reflections for Zn and Rw = 0.074 with 728 reflections for Mn), the crown ether molecule and the H3O+ cation to which it is hydrogen-bonded are disordered over two sites. The MCl42− anions, which have tetrahedral coordination, are on crystallographic twofold axes of rotation. The Mn—Cl and Zn—Cl distances average 2.270 and 2.361 Å respectively. The hydronium cation, H3O+, has pyramidal coordination. Of the two disordered crown ether molecules in the Zn and the Mn complexes, one has a slightly deformed (ttg)6 conformation while the other one may be described as having the distorted (ttg)5(ttc) conformation. These observations are in agreement with the infrared analyses of the complexes. Keywords: 18-crown-6 complexes, hydronium ion, ZnCl42−, MnCl42−, crystal structure.
A spiro-annulation approach to the zizaane sesquiterpenes
Authors: Burnell D. Jean , Wu Yong-Jin
Published: May 2006

4,4-Dimethyl-2-oxabicyclo[3.2.1]octan-3-one (10), obtained in two steps from norcamphor, was converted to 3-(1,1-dimethyl-2-oxopropyl)cyclopentanone (14), then selectively ketalized. The ketal function underwent Lewis acid catalysed spiro-annulation with 1,2-bis)trimethylsiloxy)cyclobutene (4) yielding 7-(1,1-dimethyl-2-oxopropyl)spiro[4.4]nonane-1,4-dione (21), and intramolecular titanium-induced ketone–ketone coupling and oxidation afforded (±)-isokhusimone (3) in an overall yield of 35% from norcamphor. In an alternative approach, the ethylene ketal of methyl 2-mefhyl-2-(3-oxocyclopentyl)propanoate (27) was prepared from 10. Spiro-annulation proceeded in good yield, but subsequent titanium-induced ketone–ester coupling failed to provide the desired tricyclic product, 7,7-dimefhyltricyclo[6.2.1.01,5]undecane-2,6-dione (30). Keywords: annulation, carbonyl coupling, isokhusimone, terpene.
Structure and conformation of 5-methoxymethyl-2′-deoxycytidine
Authors: Jia Zongchao , Tourigny Guy , Delbaere Louis T. J. , Stuart Allan L. , Gupta Sagar V.
Published: May 2006

The three-dimensional structure of the antiviral agent 5-methoxymethyl-2′-deoxycytidine (MMdCyd) was deduced by X-ray crystallographic analysis. MMdCyd crystallized in space group P21 with a = 7.9255(6) Å; b = 16.1505(15) Å, c = 10.1861(5) Å, β = 103.801(5)°, and Z = 4 (2 molecules per asymmetric unit); R = 0.044 (Rw = 0.046) for 2560 observed reflections with net I > 3σ(I). The furanose ring adopts the C(3′)-exo envelope conformation (3E) in molecule A and the C(2′)-endo envelope conformation (2E) in molecule B. In the sugar ring of both crystallographically independent molecules A and B, the side chain at C(5′) has the g+ conformation. This appears to be a preferred geometry required for antiherpes activity in 2′-deoxyribonucleosides. The glycosyl linkage is anti with χ = 213.7° for the A molecule and 222.2° for the B molecule. With respect to this anti conformation, the methoxy group at C(5) in molecules A and B exhibits different conformations; it is on the same side of the pyrimidine plane as the deoxyribofuranose ring oxygen (O4′) in molecule B and on the opposite side in molecule A. Keywords: antiherpes agent, conformation, 5-methoxymethyl-2′-deoxycytidine, crystal structure.
Enzymatically catalysed decarboxylation of β-carboxyaspartic acid (Asa)
Authors: Annett Robert G. , Hassamal Vanita M. , Fishpool Annette M. , Kosakarn Panadda , Cassamalli Allen , Allinson E. Tracey
Published: May 2006

A better synthetic route to β-carboxyaspartic acid (Asa) was achieved through condensation of sodium dibenzyl malonate and benzyl 2-bromoacetate as an alternative to two steps in the method of Koch etal. Catalytic hydrogenation at 5 atm pressure in a shaken stainless steel vessel removed protecting carbobenzyloxy groups. Asa was purified on a cation exchange column. An extract of E. coli was found to catalyse the decarboxylation of Asa in a doubly coupled assay designed to be specific for produced aspartic acid. Evidence for enzymatic decarboxylation includes complete loss of activity on boiling and progressive loss of activity on repeated freeze–thawing of the extract. Keywords: decarboxylation, β-carboxyaspartic acid, Asa decarboxylase.
A novel electrochemical method for benzoylation of aminoalcohols with methyl benzoates at room temperature
Authors: Arm Kenji , Tamura Shohei , Masumizu Tatsuya , Kawai Ken-Ichi , Nakajima Shoichi , Ueda Akira
Published: May 2006

A novel electrochemical method of benzoylating aminoalcohols 2 by use of methyl benzoates 1 at room temperature was developed. 2-Aminoethanols 2 (n = 0, R3 = H) and 3-aminopropanols 2 (n = 1, R3 = H) gave the corresponding benzamides 4, as a result of electrochemical transesterification followed by O,N-actyl migration. In contrast, o- and m-aminobenzylalcohols (7a and 7b) and trans-4-(aminomethyl)cyclohexanemethanol (8a) afforded the corresponding benzoic esters, since their acyl migration is hindered. A local anesthetic, procaine, was prepared by using this electrochemical reaction. A mechanism for electrochemical transesterification, which involves a formation of alcoholate anion by a one-electron reduction of alcohol, is presented. Keywords: amides, aminoalcohols, benzoylation, electrochemical, esters.
Conformational analysis of key disaccharide components of Brucella A and M antigens
Authors: Peters Thomas , Brisson Jean-Robert , Bundle David R.
Published: May 2006

The synthetic α 1,2 and α 1,3 disaccharide methyl glycosides of 4-amino-4,6-dideoxy-D-mannose 1–6 that constitute key structural elements of Brucella A and M antigens were analyzed by 1H and 13C nuclear magnetic resonance spectroscopy. A detailed conformational analysis was performed for the N-acetylated derivatives 1 and 4 as well as for the amino derivatives 2 and 5. Potential energy calculations using the GESA program established the global minima for the disaccharides 1, 2, 4, and 5, and mapped the energy surface as a function of the glycosidic torsion angles [Formula: see text] and ψ. Ensemble averaged nuclear Overhauser enhancements, weighted according to the Boltzmann distribution function, were derived for each of the four disaccharides. This procedure improved the fit between experimentally and theoretically derived nOe values, when compared to interpretations based on a single conformer model. The Brucella A and M antigens are homopolymers of 4-formamido-4,6-dideoxy-D-mannose and, as.N-formyl groups (saccharides 3, 6, and 8) are essential for the binding of these antigens to their respective antibodies, amide conformation was analyzed by examination of the vicinal proton–proton and proton–carbon coupling constants of the model monosaccharide 8. The conformational properties of the model compounds 1–8 were used to model the Brucella A and M polysaccharide antigens. Keywords: conformational analysis, disaccharide conformation, nuclear Overhauser measurements, molecular modeling, Brucella antigen.
Chemical synthesis of GDP-fucose analogs and their utilization by the Lewis *A(1 → 4) fucosyltransferase
Authors: Gokhale Uday B. , Hindsgaul Ole , Palcic Monica M.
Published: May 2006

Chemical syntheses are reported for GDP-fucose (5), GDP-3-deoxy-fucose (6), and GDP-arabinose (7), the demethyl analog of 5. All three sugar nucleotides were found to act as donor substrates for an α(1 → 4) fucosyltransferase isolated from human milk when *BDGal(1 → 3)*BDGlcNAc-O(CH2)8COOMe (1) was used as the acceptor. The rate of transfer of sugar residues to 1 was measured using a coupled spectrophotometric assay and was found to be 100% (5), 2.3% (6), and 5.9% (7). The product Lea-active oligosaccharide analogs were identified by both an enzyme-linked immunosorbent assay (ELISA) and by 1H NMR spectroscopy. Keywords: glycosyltransferase, oligosaccharide synthesis, sugar-nucleotide analog, ELISA assay, fucosyltransferase.
Molecular recognition of a human blood group determinant by a plant lectin
Authors: Delbaere Louis T. J. , Vandonselaar Margaret , Prasad Lata , Quail J. Wilson , Pearlstone Joyce R. , Carpenter Michael R. , Smillie Lawrence B. , Nikrad Pandurang V. , Spohr Ulrike , Lemieux Raymond U.
Published: May 2006

The lectin IV of Griffoniasimplicifolia (GS4) specifically binds the terminal tetrasaccharide unit of the Lewis b human blood group determinant (Leb). The single crystal X-ray analysis of the complex with Leb-OMe has demonstrated that the binding site on the lectin is a shallow depression with a negatively charged aspartate side chain at the bottom of the cavity. In addition to this aspartate, a serine and an asparagine side chain provide the polar groups that hydrogen bond to the three hydroxyl groups of Leb, which has been termed the key polar grouping for complex formation. A notable characteristic of the binding site is that five aromatic amino acid side chains (one Phe, two Tyr, and two Trp residues) surround these polar interactions and make van der Waals contacts with the tetrasaccharide. Thus, as predicted from previous solution binding studies, extensive nonpolar interactions are involved, which contribute importantly both to the specificity of the reaction and the stability of the noncovalent complex that is formed. These results represent the first structural example of the molecular recognition of a human blood group determinant by the receptor site of a protein. Extensive sequence homology exists between GS4 and the concanavalin A (Con A), pea, and favin lectins. The main hydrophilic groups of the carbohydrate-binding site of GS4 and Con A are aspartate, asparagine, and serine residues; the homology suggests that the serine is replaced by asparagine in the case of the pea and favin lectins. It appears probable that these two latter lectins possess very similar, if not identical, specificities. Keywords: lectin, carbohydrate, molecular recognition, binding.
The crystal and molecular structures of adamantanecarboxylic acid at 173 and 280 K
Authors: Bélanger-Gariépy Francine , Brisse François , Harvey Pierre D. , Gilson Denis F. R. , Butler Ian S.
Published: May 2006

The crystal structure of adamantanecarboxylic acid, tricyclo[3.3.1.13,7] decan-1-carboxylic acid C10H15COOH, has been determined by X-ray diffraction at two temperatures, 173 and 280 K. At both temperatures, the unit cells are triclinic, space group[Formula: see text], and each contains two molecules. At 173 K, a = 6.452(3), b = 6.681(2), c = 11.510(3) Å, α = 80.84(2)°, β = 87.22(3)°, γ = 74.11(3)°; V = 471.10 Å3, Dx = 1.271 g cm−3, [Formula: see text]. The structure was solved by direct-methods. The least-squares refinement, based on 1347 observed reflections converged to R = 0.0485 and Rw = 0.0415. At 280 K, a = 6.503(2), b = 6.849(2), c = 11.620(4) Å, α = 77.11(2)°, β = 85.77(2)°, γ = 76.34(2)°; V = 490.11 Å3, Dx = 1.221 g cm−3, [Formula: see text], R = 0.0874, and Rw = 0.0512 for 828 observed reflections. The low-temperature form is ordered while at room temperature the molecule is disordered. In the structure of the high-temperature phase, the adamantyl group takes two distinct orientations, in a 60:40 proportion, at about 14° from one another. The carboxylic group also has two orientations differing by about 170°. The geometry of the adamantane skeleton is not affected by the presence of the carboxylic group. The molecules form centrosymmetric dimers through hydrogen bonds of the [Formula: see text] type. The [Formula: see text] distances range between 2.616(11) and 2.752(15) Å. The order-disorder transition is interpreted using the Guthrie–McCullough approach. Keywords: adamantanecarboxylic acid, order–disorder transition, crystal structure.
Analysis of the kinetics of the thermal decomposition of pentafluoroethane
Authors: Aviyente Viktorya , Inel Yüksel
Published: May 2006

The thermal decomposition of pentafluoroethane has been studied experimentally over the temperature range 1180–1470 K under 3500 torr pressure by Tschuikow-Roux and co-workers (1). Although the principal process which occurred at around 1200 K was the elimination of hydrogen fluoride, the formation of radicals by carbon–carbon bond scission is suggested at around 1400 K. In this article the C2HF5 molecule has been submitted to a treatment in terms of the RRKM theory to test plausible activated complex models and to explain the formation of different products at different temperatures. The hydrogen fluoride elimination reaction is modeled after a four-membered ring for the activated complex whereas two different approaches (Gorin model and the criterion of minimum state density) have been used to explain the C—C bond rupture. In this work it is confirmed satisfactorily by calculation of the rate energy dependences for the different mechanisms that, at around 1200 K, the alkene (C2F4) is the dominant product; as the temperature approaches 1400 K carbon–carbon bond rupture becomes feasible. Keywords: RRKM, bond rupture, HF elimination, pyrolysis, rate coefficient.
Retinylidene Schiff bases in surfactant-solubilized water pools in heptane
Authors: Singh Anil K. , Sandorfy Camille , Fendler Janos H.
Published: May 2006

All-trans-retinal (1) was reacted with n-butylamine in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles in heptane to form all-trans-N-retinylidene–n-butylamine Schiff bases (2). The extent of protonation of 2 by 3-chloropropionic acid (CPA) to give 3 in AOT reverse micelles in heptane was found to depend on the ratio of [CPA] to [2], as well as on [H2O]/[AOT] (i.e., on the ω value). At any given [2] and ω values, increasing amounts of CPA increased the protonation and at any given constant [2] and [CPA], increasing ω values also increased the protonation. Over a period of 24 hours, there was only 4% decomposition of 2 in AOT reverse micelles in heptane at ω = 24. Conversely, in three hours, 23% of 3 decomposed in the same system. The trans to cis photoisomerization of 2 in heptane occurred at a much faster rate in the presence of AOT reverse micelles than in their absence. The appearance of carboxylate peaks (FTIR, 1400–1500 cm−1) indicated that the larger the AOT solubilized water pools, the greater the CPA dissociation. 1 also reacted with the α-NH2 group of l-lysine (4) in AOT reverse micelles in heptane to give the corresponding Schiff base 6. Protonation of 6 occurred either intramolecularly or by reaction with unreacted 4. These results were discussed in terms of rhodopsin protonations. Keywords: retinylidene Schiff bases, reverse micelles, protonation of Schiff bases, trans to cis photoisomerization.
Motion about the bond in benzyl OR (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3). Solvent and substituent dependence
Authors: Schaefer Ted , Cox Kerry J. , Morier Cherrie L. , Beaulieu Christian , Sebastian Rudy , Penner Glenn H.
Published: May 2006

The 1H nuclear magnetic resonance spectral parameters of benzyl alkyl ethers (CH3, CH2CH3, CH(CH3)2, and C(CH3)3) in CS2 and acetone-d6 solutions are obtained, as are those for the 3,5-dichloro derivatives (CH3, CH2CH3, and CH(CH3)3) in acetone-d6 solution. The long-range coupling constants between the methylene and para ring protons show that the apparent twofold barrier to rotation about the [Formula: see text] bond is solvent and ring-substituent dependent. The apparent twofold barrier ranges from a vanishing value for benzyl methyl ether in CS2 solution to as much as 4.6 kJ/mol for 3,5-dichlorobenzyl isopropyl ether in acetone-d6 solution. The data imply that, for the free molecules, the conformation of highest energy has the CH2—O bond in a plane perpendicular to that of the phenyl group. Molecular orbital computations with a minimal Gaussian basis set agree that, for benzyl methyl ether in the exo form (the methyl group pointing away from the phenyl moiety), this conformation is the least stable. However, geometry optimization procedures imply that the CH2—O bond is twisted out of the ring plane by 30.3° in the most stable geometry of the exo form. Such procedures for the (distorted) endo form locate another stable conformer, in which the CH2—O bond is twisted out of the phenyl plane by 45°, only 0.25 kJ/mol less stable than the most stable conformer of the exo form. These results, together with some computations for the tert-butyl derivative, are discussed in terms of the theoretical potentials for rotation about the [Formula: see text] bond. The approximate potential surface is rather flat compared to kT at ambient temperatures for the free molecules, consistent with its sensitivity to the medium and to ring substituents. Keywords: 1H NMR, benzyl alkyl ethers; long-range coupling constants in benzyl alkyl ethers; conformations, benzyl alkyl ethers; internal motion, benzyl alkyl ethers; MO computations on benzyl methyl ether.
Determination of the structure and absolute configuration of the glycerolphosphate-containing capsular polysaccharide of Pasteurellahaemolytica serotype T3 by high-resolution nuclear magnetic resonance spectroscopy
Authors: Richards James C. , Leitch Robert A.
Published: May 2006

The specific capsular polysaccharide antigen produced by Pasteurellahaemolytica serotype T3 was found to be a high molecular weight teichoic acid composed of equal molar amounts of D-galactose, glycerol, and phosphate and a nonstoichiometric amount of O-acetate. Structural analysis of the polymer employed a combination of one- and two-dimensional 1H and 13C nuclear magnetic resonance methods at high field. Homo- and heteronuclear chemical shift correlation techniques, together with J-resolved and nuclear Overhauser effect (nOe) difference experiments led to the unambiguous assignments of the 1H and 13C resonances corresponding to the D-galactose and glycerol structural units and established that the repeating unit of the polysaccharide antigen was composed of → 4)-α-D-Galp-(1 → 1)-L-glycerol-(3 → units joined by phosphate diester groups. The chirality of the glycerol moiety was established by conformational analysis of a 1-O-α-D-galactopyranosyl-S-glycerol fragment (2) obtained from the teichoic acid by depolymerization with HF, from which the stereochemistry of the glycerol methine carbon centre was related to that of the D-glycose from 1H–1H nOe and 3J values. The chirality was confirmed by gas–liquid chromatographic and mass spectral analysis of the (−)-camphanate ester of 2,3-di-O-methylglycerol derived from permethylated 2. The D-galactosyl residues are partially mono-O-acetylated at C-2 and C-3. Keywords: Pasteurellahaemolytica, capsular polysaccharide, NMR analysis.
Carbocationic polymerization in the gas phase: polymerization of acetylene induced by BF2+
Authors: Forte Leonard , Lien Min H. , Hopkinson Alan C. , Bohme Diethard K.
Published: May 2006

Gas-phase measurements for the primary reaction of BF2+ with acetylene and the ensuing higher-order reactions with acetylene have been performed at 296 ± 2 K in helium at 0.35 torr using the Selected-Ion Flow Tube (SIFT) technique. The primary reaction was observed to be rapid and to produce two species which both initiated rapid polymerization of acetylene. The major primary product, C2HBF+, was observed to initiate the sequential addition of four molecules of acetylene, most likely by termolecular association reactions. The first few steps in this polymerization were also followed using abinitio molecular orbital theory. The calculations and measurements provide structural, energetic, and kinetic information and, in combination, reveal several intrinsic features of the initial steps of the cationic polymerization of acetylene initiated by BF2+. Keywords: polymerization, acetylene, aromaticity.
On the electron transfer and hydrogen atom abstraction mechanism for 1-benzyl-1,4-dihydronicotinamide reduction of benzoquinones
Authors: Tanner Dennis D. , Kharrat Abdelmajid , Oumar-Mahamat H.
Published: May 2006

The reduction of p-benzoquinone (BQ) by 1-benzyl-1,4-dihydronicotinamide (BNAH) proceeds by a free-radical chain mechanism initiated by single electron transfer (SET). In dry deoxygenated acetonitrile, the chain, whose propagation steps contain a SET–hydrogen atom transfer sequence, could be inhibited by dinitrobenzene and initiated by di-tert-butylperoxyoxalate. The reduction does not follow second-order reaction kinetics. The fractional order of each reactant was found to be 0.80 and 1.36 for BNAH and BQ, respectively. The AG0 values for both the initiation and the propagation steps were evaluated electro-chemically (CV) and were found to be of a reasonable magnitude to sustain a free-radical chain process. Keywords: 1-benzyl-1,4-dihydronicotinamide, p-benzoquinone, free radical, reduction.
Thermodynamics of protonation of N,N-dimethylthioamides in aqueous sulfuric acid
Authors: Bagno Alessandro , Lucchini Vlttorio , Scorrano Glanfranco
Published: May 2006

The protonation (m* and [Formula: see text]) and thermodynamic (ΔG°, ΔH°, ΔS°) parameters of ionization of four thioamides RCSNMe2 (R = Me, Et, i-Pr, t-Bu) have been determined in aqueous sulfuric acid in the 25–60 °C temperature range with a UV technique. The title compounds are relatively strong bases; 100% protonation is reached in 47% H2SO4. Their solvation is lower than for primary thioamides and sulfides, as indicated by the higher values of m*, and close to the range of carbon bases. Base strengths are discussed in terms of the competition between internal and external stabilization. Keywords: basicity, protonation, solvation, thermodynamics, thioamides.
Kinetics and mechanism of the bromination of phenols in aqueous solution. Evidence of general base catalysis of bromine attack
Authors: Tee Oswald S. , Iyengar N. Rani
Published: May 2006

The reactions of bromine with phenol, 4-bromophenol, and 4-methylphenol (p-cresol) in aqueous solution are catalyzed by carboxylate anions, confirming the suggestions of earlier work. The results are consistent with deprotonation of the phenol hydroxyl group by a general base occurring at more or less the same time as electrophilic attack by molecular bromine. Possible origins of the general base catalysis are discussed. Combined with earlier results, the present findings suggest that a protonated cyclohexadienone is not a mandatory intermediate in phenol bromination; it can be avoided in both the formation of and enolization of the cyclohexadienone intermediate by general catalysis. Keywords: bromination, phenol, mechanism, catalysis, kinetics.
The reaction of (η5-cyclopentadienyl)dicarbonyliron(2-thienoyl) with acetylenes; a mechanistic study using proton nuclear magnetic resonance, and application in synthesis
Authors: Butler Ian R.
Published: May 2006

The thermal reactions of dicarbonyl-η5-cyclopentadienyl(2-thienoyl)iron with a series of substituted acetylenes to give indenones and cyclopentathiophenones have been reinvestigated. The results obtained support a reaction mechanism involving initial acetylene insertion followed by that of carbon monoxide, in contradiction to the previously reported results. The reaction products were identified and characterized primarily using 2D 1H nmr spectroscopy. Keywords: acetylene, carbon monoxide, iron, indenone, mechanism, thienyl.