bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural determination of the capsular polysaccharide of Streptococcuspneumoniae type-19 (19F)
Authors: Jennings Harold J. , Rosell Karl-Gunnar , Carlo Dennis J.
Published: May 2006

The structure of the Pneumococcus type-19 (19F) capsular polysaccharide has been reinvestigated using nmr spectroscopy. It is composed of residues of 2-acetamido-2-deoxy-D-mannose, D-glucose, L-rhamnose, and phosphate in the molar ratio of 1:1:1:1. The polysaccharide is linear and is composed of the above components in a repeating unit of the following structure:→ 4)-β-D-ManNAcp-(1 → 4)-α-D-Glcp-(1→ 2)-α-L-Rhap-(1-PO4−)→.
Novel molybdenum and tungsten carbonyl compounds containing the bidentate chelating thiomethoxymethyl group and tridentate chelating gallate ligands: crystal and molecular structures of [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe) and [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe)
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis and physical properties of novel molybdenum and tungsten carbonyl compounds containing the bidentate chelating thiomethoxymethyl group and tridentate chelating gallate ligands are described. Crystals of [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe) are triclinic, a = 8.144(1), b = 9.150(1), c = 13.731(1) Å, α = 96.155(6), β = 98.83(1), γ = 108.73(1) °, Z = 2, space group [Formula: see text] and crystals of [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe) are monoclinic, a = 8.1754(7), b = 15.074(1), c = 16.708(1) Å, β = 94.365(6) °, Z = 4, space group P21/c. The structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to final R values of 0.021 and 0.033 for 3679 and 4362 reflections with I ≥ 3σ(I) respectively. The Mo atoms in both structures are best described as heptacoordinate with bidentate η2-CH2SMe ligands. Important bond lengths (corrected for libration) are: Mo—S, 2.4750(6), Mo—C(S), 2.202(3), Mo—O, 2.248(2), Mo—N(pyrazolyl), 2.192(2), Mo—N(amino), 2.394(2), Mo—C(O), 1.903(3) and 1.957(3), Ga—O, 1.912(2), Ga—N, 2.020(2), and Ga—C, 1.962(4) and 1.969(4) Å for [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe); corresponding distances for [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Mo(CO)2(η2-CH2SMe) are 2.4906(8), 2.211(3), 2.263(2), 2.205(2), 2.403(3), 1.906(3), 1.958(3), 1.918(2), 2.014(3), 1.963(4), and 1.966(4) Å.
Cyclisation during an attempted Meyer–Schuster rearrangement
Authors: Cachia Paul , Darby Nicholas , Mak Thomas C. W. , Money Thomas , Trotter James
Published: May 2006

The structure of a tricyclic diketone produced during Meyer–Schuster rearrangement has been established by chemical and X-ray crystallographic evidence.
The reaction of malondiamides with disulfur dichloride: a reinvestigation
Authors: Kutney Gerald W. , Still Ian W. J.
Published: May 2006

The reactions of a series of N,N′-dialkyl and N,N′-diaryl malondiamides with disulfur dichloride have been reinvestigated. The claim, made almost 60 years ago. that the products of this reaction are dithioketones R2CS2, is shown to be unfounded. The structures of these products are shown to be the symmetrically substituted 1,2,4,5-tetrathianes, 8a–e.
Indirect determination of the protonation constants pKa(B/BH+) of substituted pyrazoles and indazoles from electrochemical results on the corresponding pentacyanoferrates complexes
Authors: Brisset Jean-Louis , Ilimbi Victor
Published: May 2006

A linear correlation is found between the oxidation potentials of the pentacyano (L) ferrates(II) complexes, where L refers to various substituted pyrazoles and indazoles, and the protonation constants of the heterocyclic base L. This correlation allows the pKa(L/LH+) of very weak bases in these series be estimated.
Electrophilic cleavage of cyclopropanes. III. The reaction of molecular bromine with tetracyclo[3.2.0.02,7.04,6]heptane1,2
Authors: Garratt Dennis G.
Published: May 2006

The ionic addition of molecular bromine to tetracyclo[3.2.0.02,7•04,6]heptane (quadricyclene) has been investigated in a variety of solvent Systems. Depending upon the nature of the solvent, three or more of six dibromo and five solvent-incorporated adducts are isolable. A mechanism involving a series of ion-pairs and competitive edge-on vs. corner (end-on) attack is proposed.
The synthesis of oligoribonucleotides VI. The synthesis of a hexadecamer by a block condensation approach
Authors: Ogilvie Kelvin K. , Nemer Mona J.
Published: May 2006

The synthesis of the 5′-monomethoxytrityl-2′-tert-butyldimethylsilyl-3′-levulinylribonucleosides 4 of the four major bases involved in the phosphite procedure for the synthesis of oligoribonucleotides is described along with the 2′,3′-isomeric derivatives 6. This report describes a total protection system for nucleotide units which allows for the block condensation procedure to be used for the synthesis of long chains. The procedure is illustrated by the synthesis of a hexadecauridylic acid.
Cation mobilities in liquid and supercritical C1–C4 hydrocarbons
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

The relationship between ion mobility and liquid viscosity is commonly expressed as μ [Formula: see text] η−m. In hydrocarbons the value of m tends to be near 1.0 at η > 5 mP, m > 1.0 at ~5 < η < 1 mP, and m < 1.0 at η < 0.5 mP. Thus there is a maximum in a plot of μη against η−1 and Walden's rule (m = 1.0) is only a rough approximation. The decrease of μη as the critical region is approached is accompanied by an increase in the ratio of diffusion coefficients Dmolec/Dion. Ion mobilities in the liquids well below their normal boiling points are chiefly controlled by the fluidity. At higher temperatures and concomitant lower liquid densities and viscosities μη first increases, due to an increasing ion mean free path, then decreases as the critical region is approached, due to the increasing liquid compressibility and consequent electrostriction about the ion.
The mild rhodium(I), and phase transfer catalyzed, dehydrogenation of benzylic alcohols
Authors: Alper Howard , Hachem Khaled , Gambarotta Sandro
Published: May 2006

Benzylic alcohols can be dehydrogenated to carbonyl compounds by phase transfer catalyzed reaction (8 M NaOH, benzene, and PhCH2N(C2H5)3+Cl− as the catalyst) in the presence of catalytic amounts of chlorodicarbonylrhodium(I) dimer. Evidence is presented for the intermediacy of ortho-metalated complexes in these reactions.
Homoenolization of 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione. Rearrangement to 1,3,3-trimethylbicyclo[2.2.1]octane-2,5-dione via a novel β-homoenolate switch
Authors: Werstiuk Nick Henry , Yeroushalmi Shahin
Published: May 2006

Treatment of 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione (1) with K+ŌtBu in t-BuOH at 175 °C results in rearrangement to 1,3,3-trimethylbicyclo[2.2.2]octane-2,5-dione (3a) vai a novel β-homoenolate switch.
Homoenolization of 1,3,3-trimethylbicyclo[2.2.2]octane-2,5-dione. Unusually rapid H–D exchange of a bridgehead methyl
Authors: Werstiuk Nick Henry , Yeroushalmi Shahin
Published: May 2006

The title compound 2a undergoes unusually rapid H–D exchange at the bridgehead methyl at a rate 5300 times faster than exchange of the bridgehead methyl of 1,3,3-trimethylbicyclo[2.2.1]heptan-2-one (fenchone). From the isotopic composition of partially deuterated 2a, we deduce that exchange occurs via an isomer, in equilibrium with 2a, which contains an active methylene derived from the bridgehead methyl.
Preparation and X-ray crystal structure of (4bα,6β,9β,9aα,10α,13α)-4b,5,6,7,8,9,9a,10,11,12,13,14-dodecahydro-4b-phenyl-6,9:10,13-dimethanodicyclohepta[a,c]naphthalene
Authors: Harris Alan Richard , Mills Keith , Martin-Smith Michael , Murray-Rust Peter , Murray-Rust Judith
Published: May 2006

The novel hexacyclic title hydrocarbon, formed by an unusual oxidative dimerization of 3-phenylbicyclo[3,2,1]oct-2-ene, has been isolated and its structure elucidated by means of X-ray crystallography. The trivial name 4b-phenylmariontetraene is proposed for the hydrocarbon. Crystals are orthorhombic, Pbca; a = 21.87(2), b = 10.57(2), c = 17.41(2) Å from diffractometer measurements (Mo [Formula: see text] radiation). V = 4024.2 Å3, Z = 8, Dc = 1.21 Mg m−3, F(000) = 1584, μ = 0.34 cm−3. The structure was solved by direct phasing methods with MULTAN 78 and was refined by weighted full-matrix least-squares procedures to R = 0.046 for 2287 observed reflexions.
The synthesis of daunosaminyl ε-rhodomycinone, daunosaminyl 10-epi-ε-rhodomycinone, daunosaminyl ε-pyrromycinone, and 10-descarbomethoxy-ε-pyrromycin
Authors: Essery John M. , Doyle Terrence W.
Published: May 2006

The epimerisation at C10 of ε-rhodomycinone by aqueous alkali treatment of its 6,7-acetonide is described. Daunosaminyl ε-rhodomycinone and daunosaminyl 10-epi-ε-rhodomycinone were prepared and compared with regard to their antibacterial properties. Daunosaminyl ε-pyrromycinone and 10-descarbomethoxy-ε-pyrromycin were synthesized and their antitumor properties were compared with some naturally occurring glycosides of ε-pyrromycinone.
Chemical shift correlated two-dimensional nmr spectroscopy and its application to solving the proton nmr spectra of oligoribonucleotides
Authors: Bain Alex D. , Bell Russell A. , Everett Jeremy R. , Hughes Donald W.
Published: May 2006

An alternative two-dimensional nmr pulse sequence, (90°–t1/2–90°–t1/2–FID),correlates the chemical shifts of coupled nuclei. The application of this technique to the solution of the complicated proton nmr spectra of oligoribonucleotides is discussed.
Quantitative prediction of stereochemistry in the reduction of cyclohexanones by sodium borohydride
Authors: Murugan R.
Published: May 2006

An extremely simple method is presented for quantitatively predicting the stereochemical product ratio in the reduction of alkylcyclohexanones by sodium borohydride. Accurate predictions are made except in the cases of highly hindered ketones.
Oxidation of substituted aromatic compounds by peroxydisulphate. Homolytic benzylation and oxidative coupling reaction
Authors: Clerici Angelo , Porta Ombretta
Published: May 2006

Under the same experimental conditions 4-methoxytoluene brings about homolytic benzylation of isoquinoline while 3,4- dimethoxytoluene gives a coupling reaction. Proton loss by the radical cation [Formula: see text] in the former case and its electrophilic attack to the starting aromatic in the latter account for these experimental findings.
Studies on nucleation phenomena occurring in aqueous solutions supersaturated with calcium sulfate. III. The cation:anion ratio
Authors: Keller Douglas M. , Massey Ronald E. , Hileman Jr. O. E.
Published: May 2006

Nucleation rates from solutions of calcium sulfate dihydrate were measured at constant supersaturation but at varying cation:anion ratios. Induction times were also measured. The values of each were found to be dependent on the Ca:SO4 ratio. The results of empirical modeling studies are reported. These suggest that ion pair formation has an impact on the nucleation event beyond that of ion removal.
Kinetic deuterium isotope effects and kinetic solvent isotope effects for the solvolyses in water and in water + acetonitrile mixtures related to a series of substituted benzyl nitrates
Authors: Ahsan Mohammed , Robertson Ross Elmore , Blandamer Michael Jesse , Scott John Marshall William
Published: May 2006

In aqueous solution, the α-deuterium isotope effects in the solvolyses of benzyl nitrates derivatives depend on the nature of the substituent in the benzene ring. In addition, the isotope effect for some derivatives depends on mole fraction of added acetonitrile while for others the isotope effect is insensitive to solvent composition. However, the kinetic solvent isotope effects for para-methyl and meta-trifluoromethyl derivatives remain unchanged when acetonitrile is added. These observations are accounted for in terms of a model which describes the solvolytic reaction as a two-stage process and contrasts the relative importance of bond-making and bond-breaking.
Rates of OH radical reactions. VII. Reactions of OH and OD radicals with n-C4H10, n-C4D10, H2 and D2, and of OH with neo-C5H12 at 297 K
Authors: Paraskevopoulos George , Nip Wing S.
Published: May 2006

Absolute rate constants of hydrogen and deuterium atom abstraction by OH and OD radicals from n-C4H10, n-C4D10, H2 and D2, and by OH radicals from neo-C5H12 have been measured at room temperature in the gas phase using the flash photolysis-resonance absorption technique. The rate constants in units of cm3 mol−1 s−1 were found to be:[Formula: see text]The quoted errors are the 95% confidence limits. A kinetic isotope effect was observed when hydrogen was replaced by deuterium in the paraffin and H2, whereas there was no significant effect when OH was replaced by OD.
Kinetic studies of the reactions of 2,4,6-trinitrotoluene and 2,4,6-trinitrotoluene-d3 with ion-paired KOBut and free tert-butoxide ion in tert-butanol
Authors: Norris Albert R.
Published: May 2006

The reactions of 2,4,6-trinitrotoluene (TNT) and TNT-d3 (deuterated methyl group) with tetra-n-butylammonium tert-butoxide and with potassium tert-butoxide (KOBut), in the absence and presence of the crown ethers 18-crown-6, and dicyclohexyl-18-crown-6, have been studied kinetically in tert-butanol at 30.0 °C. Evidence is presented to support the suggestion that, at ratios of crown ether to base > 1, the reactive base species is free tert-butoxide ion and that this rapidly reacts with TNT or TNT-d3 to form, in each case, a mixture of σ-complex and purple anion. Specific rate constants for the reactions of free tert-butoxide ion and ion-paired KOBut with TNT and TNT-d3 to form both σ-complex and purple anion are compared.
Mass spectrometry of diamantane and some adamantane derivatives
Authors: Waltman Robert J. , Ling A. Campbell
Published: May 2006

The mass spectrometric fragmentation of adamantane, adamantane-d6, diamantane, 1- and 2-adamantanol, and 3,5,7-trimethyl-1-adamantanol has been re-examined, and new data for diamantane and 3,5,7-trimethyl-1-adamantanol are presented in more detail. Metastable peak data have been used to support potential fragmentation pathways. Simple statistical considerations applied to peak intensity data seem to indicate that ionization occurs at the primary bridgehead in both adamantane and diamantane, and that loss of a primary hydrogen is favored over loss of a secondary hydrogen atom.
Photocycloaddition of 2-methyl-1,4-naphthoquinone to enol esters. A photochemical approach to benzofuran derivatives
Authors: Liu Hsing-Jang , Chan Wing Hong
Published: May 2006

Naphthoquinone 1 undergoes facile photocycloaddition with vinyl acetate and isopropenyl acetate to give cyclobutane derivatives in excellent yields. The photocycloaddition reactions were found to be completely regioselective; in the case of vinyl acetate, a mixture of epimeric acetates 2 and 3 was obtained and in the case of isopropenyl acetate, a single adduct 7 was formed. Treatment of the photoadducts with dilute sulfuric acid resulted in skeletal rearrangement giving naphthofurans 4 and 8.
Spin–lattice relaxation in MBBA and MBBA – carbon tetrachloride mixtures
Authors: Heldman Margaret A. , Gilson D. F. R.
Published: May 2006

The spin–lattice relaxation time has been measured at 33 MHz as a function of temperature for the liquid crystal MBBA and mixtures with carbon tetrachloride. The behaviour of T1, close to the nematic–isotropic transition can be explained if the correct order fluctuation dependence is included. Diffusion constants calculated from fits to the self-diffusion contribution to relaxation are in agreement with existing results.
Crown ether catalysis of decarboxylation and decarbalkoxylation of β-keto acids and malonates: a synthetic application
Authors: Hunter Duncan H. , Patel Vijay , Perry Richard A.
Published: May 2006

The effect of 18-crown-6 ether on the decarboxylation rates of the sodium and potassium salts of 3-camphorcarboxylic acid 1 and of 1-carbomethoxy-1-carboxycyclohexane 2 was studied. For 2 the K-18C6 salt reacted ca. 104 times faster than the parent acid. This remarkable difference in reactivity was used in developing a one-pot, two-step procedure for decarbalkoxylation of malonic esters. This procedure was then applied to a range of malonates, β-keto esters, and an α-cyano ester. The effect of 15C5, other cations, and good nucleophiles was also studied.
3-Aminotropane-3-carboxylic acids. Preparation and properties
Authors: Trigo Gregorio G. , Avendaño Carmen , Santos Emilia , Christensen Halvor N. , Handlogten Mary E.
Published: May 2006

The two isomers of 3-aminotropane-3-carboxylic acid have been prepared by hydrolysis of the two α- and β-tropane-3-spiro-5′-hydantoins whose configurations were determined by X-ray crystallography and 13C nmr. The [Formula: see text] values of these amino acids and the hydrolysis rates of their N-formyl derivatives have been determined to study the influence of the amino group in an axial or equatorial position. The biological transport – inhibitory action of the two tropane amino acids has also been compared.
Aromatization and microbial hydroxylation of 3-18O-testosterone
Authors: Holland Herbert L. , Taylor Gregg J.
Published: May 2006

3-18O-Testosterone (1) is transformed to estradiol (4) by human placental microsomes, and to the 6β- and 11α-hydroxy derivatives 2 and 3 by Rhizopusarrhizus, without significant loss of label. Neither process is therefore one which involves reversible Schiff base formation at C-3 at any stage.
Mechanistic study of the reaction of vitamin B12s with 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane
Authors: Nome Faruk , Zanette Dino
Published: May 2006

The reaction of vitamin B12s with 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane results in the formation of trans-4,4′-dichlorostilbene in a two-step process. In the first step, there is a nucleophilic attack by the cobalt(I) at C-1 resulting in the displacement of chloride ion and formation of an alkyl cobalamin with a chlorine atom on the α-carbon. The second step is a cobalt chloride α-elimination which proceeds through a carbenoid type intermediate that readily rearranges to the product.
The reduction of aryl trifluoromethyl ketones by sodium borohydride. The hydride transfer process
Authors: Stewart Ross , Teo K. C.
Published: May 2006

The rates of reduction of 17 aryl trifluoromethyl ketones by sodium borohydride in 2-propanol have been measured. The rho (ρ) value is +3.12, excluding the 4-amino and 4-dimethylamino groups, which both lower the rate to a greater extent than their σ values predict. The close correspondence between substituent effects for hydride addition in the methyl and trifluoromethyl series (excluding the amino groups) suggests that normal substituent effects are to be expected for oxidation processes involving hydride removal in trifluoromethyl compounds. The present results are consistent with the oxidation of aryl trifluoromethyl carbinols by permanganate taking place by hydrogen atom abstraction. The effect of substituents on the rate of reduction of the trifluoromethyl ketones is almost identical to that on the equilibrium constant for formation of the ketone hydrates. The application of the reactivity–selectivity principle to the reduction reaction is also considered. Reduction of the 4-ethyl compound has ΔH≠ = 2.7 kcal mol−1 and ΔS≠ = −38 cal deg−1 mol−1
Nuclear analogs of β-lactam antibiotics. XIII. Structure activity relationships in the isocephalosporin series
Authors: Doyle Terrence W. , Douglas James L. , Belleau Bernard , Conway Terry T. , Ferrari C. F. , Horning Donald E. , Lim Gary , Luh Bing-Yu , Martel Alain , Menard Marcel , Morris L. R. , Misiek Martin
Published: May 2006

The general synthetic scheme to nuclear analogs of cephalosporins described in previous papers of this series is reviewed and the synthesis of a series of sidechain derivatives is given. Thus, systems of the following type were formed: carbacephems (A), 2-isocephems (B), N-2-isocephems (C), and O-2-isocephems (D). The invitro microbiological activity of these compounds (with appropriate side-chains attached) is given, with comparison to analogous cephalosporins. Systems of type A, B, and C were only prepared with a 3-H or CH3 substituent and had modest antibacterial activity. The O-2-isocephems (D) were prepared with a wide variety of sidechains at 3 and 7 and were found to have biological activity quite comparable to the cephalosporins. A more detailed biological examination (both invitro and invivo) of the O-2-isocephem analog (19i) of cephalothin was made.
Reactions of phthalans with dienophiles. II. Synthesis of naphthalenes and dihydronaphthalenes by reaction of ethyl maleate and maleic anhydride with 1,1-diethoxyphthalan
Authors: Contreras Luis , MacLean David B.
Published: May 2006

The reactions of 1,1-diethoxyphthalan with diethyl maleate and with maleic anhydride have been studied. The reaction with diethyl maleate in a sealed tube gave a mixture of diethyl 1-hydroxynaphthalene-2,3-dicarboxylate and its O-ethyl derivative. The same reactants at atmospheric pressure gave the ethoxy ester above along with a mixture of isomeric diethyl 1,2-dihydro-1-hydroxy-4-ethoxynaphthalene-2,3-dicarboxylates. The reaction with maleic anhydride gave only diethyl-1-ethoxynaphthalene-2,3-dicarboxylic acid anhydride. These reactions provide further insight into the mechanism of the reaction of phthalans with dienophiles.
Facile cleavage of some 2-acetamido-2-deoxy-β-D-gluco- and galactopyranosides using aqueous HF
Authors: Jennings Harold J. , Lugowski Czeslaw
Published: May 2006

Treatment of pneumococcal C-substance (PnC) with 48% aqueous HF resulted in not only the intended removal of all the phosphate esters but also in the highly specific hydrolysis of the glycosidic bond between the 2-acetamido-2-deoxy-β-D-galactopyranose and ribitol residues. Some of the structural features associated with this facile hydrolysis were elucidated from studies on the treatment of model methyl glycosides and oligosaccharides with the same reagent. These studies indicate that an increase in the rate of hydrolysis is associated with glycosides of 2-acetamidohexapyranoses having a trans diequatorial disposition of the aglycon and 2-acetamido groups. These studies also indicate that the nature of the aglycon is also a contributing factor, because although simple alkoxy and terminal open-chain glycitols are readily cleaved from glycosides satisfying the above criteria, hydrolysis does not occur where the aglycon is another cyclized sugar moiety. Thus chitotriose can only be degraded to chitobiose using this reagent following the reduction of its terminal reducing moiety.
Pillaromycin-A: structural and synthetic studies related to the sugar moiety, pillarose
Authors: Fraser-Reid Bert , Walker David Louis
Published: May 2006

The photo-induced alkylation of enone 6 with ethylene glycol gave an adduct from which the α-D-threo (16) and α-D-erythro (17) modifications of structure 2 have been elaborated. It was thereby shown that 2 is not the structure of pillarose. Addition of vinyl magnesium bromide to the ketone 24b gave a slight excess of one allylic alcohol, 25, which upon treatment with osmium tetroxide and hydrogen peroxide gave directly the α,α′-ketodiol 3a. The epimer of the latter 33b was available via carboxymethylenation of ketone 24b, reduction of ester, and hydroxylation. Benzoylation of these epimers gave 3b and 33c respectively and it was concluded that the former, methyl 2,3,6-trideoxy-4-C-[oxo(benzoyloxymethyl)methyl]-α-D-threo-hexopyranoside, 3b, is the enantiomer of the "methyl 8-O-benzoyl pillaroside" obtained from the antibiotic pillaromycin A.
Evaluation of thermodynamic functions relative to cavity formation in liquids: uses and misuses of Scaled Particle Theory
Authors: Morel-Desrosiers Nicole , Morel Jean-Pierre
Published: May 2006

The Scaled Particle Theory (SPT) is probably the most powerful theory presently available, that enables the calculation of the thermodynamic functions relative to the formation of cavities in liquids. We give the general relationship between the enthalpy of vaporization and the enthalpy of formation of a molecular cavity in a pure normal liquid; the good agreement with the experimental data constitutes one of the strongest arguments justifying the application of SPT to real liquids. However, we show that SPT can lead to uncertain cavity terms if the molecular diameters of the studied liquids are not well-known. We compare, on the other hand, the cavity terms (G and H) calculated from Sinanoglu's theory, since this theory has been used to that end recently, with those obtained from SPT.
Etude de l'adsorption de surfactants ioniques et non ioniques sur de la matière végétale carbonisée
Authors: Perineau Francis , Gaset Antoine
Published: May 2006

The aim of this investigation was to assess the possible use of sulfuric lignins for the purification of industrial liquid wastes. The adsorption of anionic (SDS), cationic (CPC), and non-ionic (NPPO) surfactants on charred plant material was carried out under various pH and temperature conditions. Ionic and hydrophobic interactions are involved in the adsorption process. The analysis of the adsorption kinetics in aqueous and alcoholic media allowed the mode of adsorption to be characterized. The plot of the surfactant uptake against the square root of time led to the determination of the mode of diffusion. The effect of the chain length of alkylsulfates on their adsorption corroborated the involvement of hydrophobic interactions and could be correlated with the values of their cmc.
Hydrogen bonding solvent effect on the basicity of primary amines CH3NH2, C2H5NH2, and CF3CH2NH2
Authors: Lau Yan K. , Kebarle P.
Published: May 2006

The equilibria RNH3+(H2O)n−1 + H2O = RNH3+(H2O)n were measured for R = CH3, C2H5, and CF3CH2 from n = 1 to n = 3 with a pulsed electron beam high ion source pressure mass spectrometer. The proton and hydrate transfer equilibria CH3NH3+(H2O)n + C2H5NH2 = CH3NH2 + C2H5NH3+(H2O)n were measured for n = 0 to n = 3. These data allow the evaluation of ΔH0 and ΔG0 for the reactions: R0NH3+(H2O)n + RNH3+ = R0NH3+ + RNH3+(H2O)n. ΔH0 = δΔH00,n(RNH3+), ΔG = δΔG00,n(RNH3+). These data are compared with δΔE0,3 (STO-3G) evaluated by Hehre and Taft. In general good agreement is observed at n = 3. The δΔH00,3(RNH3+) ≈ δΔE0,3(RNH3+) are also found close to the ion hydration free energy difference in aqueous solutions.
Ouverture de dichlorocyclopropanes en présence d'un nucléophile interne. Absence de participation intramoléculaire. Réarrangement concerté en chlorures allyliques
Authors: Chiche Laurent , Christol Henri , Coste Jacques , Pietrasanta Francine , Plénat Françoise
Published: May 2006

It is shown that a conveniently placed internal nucleophile (carboxyl group) is not involved with the rearrangement of a dichlorocyclopropane into an allylic chloride. This result appears to support a concerted mechanism of a σs2 + σa2 type for this rearrangement. In the products obtained, the allylic chloride may undergo displacement either by solvent (H2O), leading to alcohols, or by the internal carboxyl group, leading to a lactone. [Journal translation]
The conversion of sweroside to secologanin
Authors: Hamilton Raymond G. , McLean Stewart
Published: May 2006

A chemical route from sweroside (2a) to secologanin (1a) has been established. The lactone ring of sweroside tetraacetate (2b) was opened by trimethylsilyl iodide. The unstable iodo carboxylic acid 3 (R = H; X = I) was then formed and immediately converted to its methyl ester. The iodo function was displaced by formate, and the formate was selectively methanolized under neutral conditions. The resulting alcohol 3 (R = Me; X = OH) was oxidized by pyridinium chlorochromate to the aldehyde, secologanin tetraacetate (1b). With care, the conversion from the sweroside series to the secologanin series can be carried out in excellent yield. Secologanin can readily be recovered from its tetraacetate.
Thione photochemistry. Dual pathways in aralkyl thione cyclizations
Authors: Basu S. , Couture Axel , Ho Kam W. , Hoshino Mikio , Mayo Paul De , Suau R.
Published: May 2006

It is shown that aralkyl thiones, which possess an oxygen atom at the δ position in the side chain, can therefore not undergo the preferred δ insertion, and insert at the γ and ε positions. Although ε insertion occurs only from the 1(π,π*) state, γ abstraction (followed by cyclization or cleavage) occurs from both 1(π,π*) and 3(n,π*) states. The quantum yields of photocyclization of 2c, 2d, and 2g change little with solvent polarity, which suggests that a thione–ether charge transfer interaction contributes little to the cyclization. Fluorescence and product quenching studies are reported which support this.
Synthesis of some bicyclo[2.2.2]oct-5-en-2-ones and bicyclo[2.2.2]octan-2-ones. Rearrangements accompanying oxidative decarboxylation with lead tetraacetate
Authors: Yates Peter , Langford Gordon E.
Published: May 2006

1-Methoxy-2-methyl-1,4-cyclohexadiene (3), 2-methoxy-1-methyl-1,3-cyclohexadiene (2), and 2-methoxy-1,5,5-trimethyl-1,3-cyclohexadiene (14) on heating with maleic anhydride give 1-methoxy-endo-7-methylbicyclo[2.2.2]oct-5-ene-syn-2,3-dicarboxylic acid anhydride (7) and its 6-methoxy-1-methyl (16a) and 6-methoxy-1,8,8-trimethyl (16b) analogues, respectively. On hydrolysis 16a and 16b give the corresponding keto dicarboxylic acids, 18a and 18b, via keto anhydrides 17a and 17b. Treatment of 18b with lead tetraacetate gives 1,8,8-trimethylbicyclo[2.2.2]oct-5-en-2-one (19) together with products in which rearrangement to a bicyclo[3.2.1]octane system has occurred. Treatment of 17b with bis(triphenylphosphino)nickel dicarbonyl gives only 19; similar treatment of 17a gives 1-methylbicyclo[2.2.2]oct-5-en-2-one (1). Reaction of bicyclo[2.2.2]octane-2,3-dione (27) with methyllithium gives 3-hydroxy-3-methylbicyclo[2.2.2]octan-2-one (28), its dimer 31, and a diol 30. Treatment of 5-exo-acetoxy-1, 5-endo-dimethyl-6-oxobicyclo[2.2.2]octane-anti-2,3-dicarboxylic acid (37) with lead tetraacetate gives 3-endo-acetoxy-1,3-exo-dimethyl-bicyclo[2.2.2]oct-5-en-2-one (33) as a minor product; the major product is derived by rearrangement to a bicyclo[3.2.1]octane system. It is proposed that this rearrangement, like that of 18b, involves oxidative decarboxylation of a single carboxylic acid group to give a carbonium ion that undergoes rearrangement via a 1,2-acyl migration.
Betylates. 2. The formation and high reactivity of alkyl [0]betylates
Authors: King James Frederick , Lee Teresa Mee-Ling
Published: May 2006

Unhindered primary alkyl N,N-dimethylsulfamates (1) react with methyl fluorosulfate to give the corresponding alkyl fluorosulfates (3) and the betaine, [Formula: see text] (4), evidently by way of the intermediate alkyl [0]betylate fluorosulfate (2); with certain other alkyl esters (1) products of substitution, elimination, and rearrangement are formed. The reaction not only provides a potentially useful route to simple alkyl fluorosulfates, but serves to demonstrate the powerful nucleofugality of the [0]betylate group. To obtain a method for predicting the reactivity of [0]betylates, we have compared substituent parameters with rate constants in four series of nucleophilic displacements involving esters of the general structure ROSO2Z; correlation (of log k) with σ* is mediocre but a new parameter, [Formula: see text] with a "15% resonance" contribution as defined by Swain and Lupton, gives good to excellent agreement in the four reaction series. Evidence is presented for formation of the 7-norbornyl cation via the [0]betylate from 7-norbornyl N,N-dimethylsulfamate and methyl fluorosulfate. Comparison with what is known of the reactivities of 7-norbornyl p-toluenesulfonate and trifluoromethanesulfonate esters serves to confirm that [0]betylates are among the most nucleofugal functions of which a derivative has been fully characterized.
Bulk optical properties of phthalocyanine pigment particles
Authors: Loutfy Rafik O.
Published: May 2006

The optical absorption spectra of small particles of α-, β-, and x-form of metal-free phthalocyanine (H2Pc) and vanadyl phthalocyanine (VOPc) surrounded by a dielectric (polymers) have been studied. The true bulk absorption can be obtained by measuring the difference in transmittance of two films of identical composition but different thicknesses. This approach eliminates effectively light reflection losses. Comparison between the absorption spectra measured by direct vs. difference in transmittance revealed a number of differences: shift in the absorption frequencies, change in absorption intensities, and change in peak-to-valley ratio. These differences are due to light scattering which can be significantly minimized by using the differential transmittance method. The true peak absorption of x-H2Pc particles located at 770 and 615 nm had an absorption coefficient of 35.3 and 34.2 μm−1, respectively. The absorption minimum occurs at 477 nm. The peak-to-valley ratio was 27.The absorption spectra of VOPc particles did not correspond to any one polymorph, but are due to a mixture of two known polymorphs. Some discrepancies between the particle absorption of α-H2Pc or β-H2Pc and the corresponding evaporated film absorption were observed. These discrepancies are attributed to the spread in particle size and also to local agglomeration of the particles.
The addition of 2,4-dinitrobenzenesulphenyl chloride to 2-methylenebicyclo[2.2.1]hept-5-ene: the crystal structure of 1-chloromethyl-3-endo-(2′,4′-dinitrophenylthio)tricyclo[2.2.1.02,6]heptane, C14H13ClN2O4S
Authors: Przybylska Maria , Garratt Dennis G.
Published: May 2006

1-Chloromethyl-3-endo-(2′,4′-dinitrophenylthio)tricyclo[2.2.1.02,6]heptane, C14H13ClN2O4S, crystallizes in space group P21/a with unit cell dimensions a = 12.785(2), b = 10.653(1), c = 11.061(1) Å, β = 101.54(l)° Z = 4.The structure was solved from Patterson and Fourier maps. The parameters were refined by block-diagonal least-squares to a final R = 0.038 for 2063 observed reflections. The structural data provide unequivocal proof for our earlier ascertainment of configurational-specific exo attack upon the endocyclic double bond of 2-methylenebicyclo[2.2.1]hept-5-ene with homoallylic participation.The molecule is characterized by the presence of an interaction between oxygen of the 2-nitro group and a sulphur atom, and of a weak bifurcated hydrogen bond system involving [Formula: see text] bonds.
The Orton rearrangement in aprotic solvents. Part IV. An examination of the kinetics of the rearrangement of N-bromo-4-chloroacetanilide and N-bromoacetanilide catalyzed by trifluoroacetic acid and trifluoroacetic acid-d
Authors: Golding Peter David , Reddy Sethu , Scott John Marshall William , White Valerie Ann , Winter June Gertrude
Published: May 2006

The rates of rearrangement of N-bromo-4-chloroacetanilide to 2-bromo-4-chloroacetanilide catalyzed by trifluoroacetic acid and trifluoroacetic acid-d have been measured as a function of acid concentration in chlorobenzene at T = 323 K. Similar experiments have been carried out with N-bromoacetanilide and N-bromo-4-chloro-2,6-dideuterioacetanilide. A comprehensive analysis of the observed rates for each substrate as a function of acid concentration reveals that the rearrangements involve at least three mechanistic steps when trifluoroacetic acid is the catalyst. In contrast, the rate of rearrangement of N-bromoacetanilide catalyzed by trichloroacetic acid at T = 288 K appears to follow a limiting form of the same rate law. Earlier observations are assessed in the light of the proposed mechanism, and it is concluded that both present and past work can be satisfactorily rationalized in terms of an intramolecular migration of bromine.
Thermolysis of the tricyclic 1,2-dioxetanes 3,4:3,4-dipropano-, 3,4-pentano-3,4-propano-, and 3,4-butano-3,4-propano-1,2-dioxetane
Authors: Kopecky Karl R. , Lockwood Peter A. , Gomez Rodrigo Rico , Ding Jan-Yih
Published: May 2006

The title compounds have been isolated in crystalline form by cyclization of the corresponding bromo- or iodohydroperoxides. The activation parameters for thermolysis are, respectively (Ea, kcal/mol, ΔS≠, eu): 25.6 ± 0.6, 4 ± 2; 29.8 ± 0.4, 4 ± 2; 26.3 ± 0.5, 1 ± 2. The singlet [Formula: see text] and triplet [Formula: see text] excited state product yields produced on thermolysis of these compounds are, respectively: 0.011, 0.10; 0.0019, 0.18; 0.0013, 0.11. These yields are relative to a value of 0.31 for [Formula: see text] of tetramethyl-l,2-dioxetane. The cyclic 1,5-diones from thermolysis of the last two title compounds cyclized before isolation to give the bicyclic hydroxyketones.
Solvolysis of 9-(ortho-substituted benzyl)fluorene-9-trimethylammonium ions. The effect of steric crowding
Authors: Pradhan Jyotsna , Smith Peter James
Published: May 2006

The solvolytic reaction of several 9-(ortho-substituted benzyl)fluorene-9-trimethylammonium salts in ethanol at 57.3 °C has been found to give both the substitution and elimination products. The observed rate constant for alkene formation increases when both ortho positions have substituents, kobs(s−1) = 2.35 × 10−5 and 268 × 10−5 for 2-Me and 2,6-diMe compounds, respectively. As well, the magnitude of the observed hydrogen–deuterium isotope effect is dependent on ring substituents, kobsH/kobsD = 1.22 and 2.35 for 2-Me and 2,6-diMe substrates, respectively. The results are discussed in the light of steric acceleration favouring loss of the poor leaving group, which leads to only the second example of a trimethylammonium salt reacting via the E1 mechanism.
Isomérisation de l'ion phényl-2 oxétane protoné avant sa fragmentation en spectrométrie de masse
Authors: Audier Henri Edouard , Milliet Arielle , Mruzek Margaret , Denhez Jean Pierre , Dizabo Pierre , Schaal Catherine
Published: May 2006

Fragmentations of the phenyl-2 oxetane ion by chemical ionization mass spectrometry, and of some isomeric ions, have been studied using deuterated and 13C labelled compounds. The heterocyclic system of the protonated phenyl-2 oxetane ion is broken before fragmentation giving a hydroxylated carbocation which can isomerize by 1–2 or 1–3 hydride transfers. The protonated phenyl-3 propanal thus obtained eliminates a molecule of water and yields a protonated indene ion. The potential energy profile and the mechanism proposed are in agreement with the experimental results.
Crystal structures of racemic and optically active 4,4′-dimethyl-1,1′-binaphthyl
Authors: Pauptit Richard A. , Trotter James
Published: May 2006

The structures of the title compounds were determined to aid in understanding spontaneous resolution in binaphthyl derivatives. Crystals of the racemate, C22H18, are monoclinic, C2/c, a = 13.225(8), b = 10.768(4), c = 11.572(7) Å, β = 114.04(2)°, Z = 4. The structure was solved by direct methods and refined to R = 0.074 for 886 reflections with I ≥ 3σ(I). The crystals of the optically active form are tetragonal, P41212 or P43212, a = 8.3031(8), c = 23.706(7) Å, Z = 4. This structure was also solved by direct methods and refined to R = 0.060 for 723 reflections with I ≥ 3σ(I).
Conformational dynamic investigation of 1,5-benzodioxepin and its dimethyl derivative by 1H and 13C nmr
Authors: Menard D. , St-Jacques M.
Published: May 2006

The conformational and dynamic properties of 1,5-dioxa-6,7-benzocycloheptene (2; 1,5-benzodioxepin) and its dimethyl derivative (7) have been investigated by dynamic 1H and 13C nmr methods. Analysis of the spectra at low temperatures (below coalescence) indicates that the most stable seven-membered ring conformations detected for solutions in CHF2Cl are a mixture of the chair (C, 80%) and the twist-boat (TB, 20%) for 2 and a mixture of TB (64%) and C (36%) for 7. Free energy barriers were determined for the chair inversion of 2 (6.5 kcal/mol) and 7 (7.5 kcal/mol) as well as for the twist-boat pseudorotation of 7 (6.8 kcal/mol). The conformational properties of these seven-membered heterocycles are discussed and compared to those known for 2,4-benzodioxepins.
Phosphorus-31 nuclear magnetic resonance studies of phosphido-bridged dinuclear complexes of palladium and platinum
Authors: Brandon James Bradley , Dixon Keith Roger
Published: May 2006

Proton decoupled 31P nmr spectra are reported for a series of dinuclear metal complexes containing bridging dialkyl- or diarylphosphido groups: [M2Cl2(μ-PR′2)2(PR3)2], M = Pd, R′ = Ph, R3 = Et3 or HPh2; M = Pd, R′ = Me, R3 = Et3, Ph3, or HMe2; M = Pt, R′ = Ph, R3 = Et3 or HPh2; and [M2(μ-PPh2)2(dppe)2]Cl2, M = Pd, or Pt, dppe = Ph2P(CH2)2PPh2. Detailed analysis and computer simulation of the spectra in the AA′XX′, AA′XX′M, AA′A″A′′′XX′, and AA′A′′A′′′XX′M spin systems leads to the following ranges and relative signs for coupling constants involving the bridging phosphorus atoms: 2J(R3P—cis PR′2), M = Pt, −1 to +5 Hz, M = Pd, +20 to +32 Hz; 2J(R3P—transPR′2), M = Pt, +291 to +396 Hz, M = Pd, +311 to +443 Hz; 2J(R2P—cis PR2), M = Pt, −162 to −208 Hz, M = Pd, −261 to −350 Hz (the assignment of negative signs to these couplings is not completely certain); 1J(Pt—PR2), trans to Cl, +2364 to +2635 Hz, trans to PR3, +1690 to +1992 Hz. Resonances due to the bridging phosphido groups occur at very high field (−267 to −322 ppm upfield of P(OCH3)3), in strong contrast to literature reports of phosphido bridges in palladium cluster complexes where the bridged metal atoms are linked by a metal–metal bond and the bridging phosphorus occurs +57 to +82 ppm downfield of P(OCH3)3.
Spectroscopic confirmation of orientational disorder of the cyanide groups in sodium cyanide dihydrate, NaCN•2H2O
Authors: Falk Michael
Published: May 2006

Occurrence of orientational disorder involving the CN groups in NaCN•2H2O, suggested by van Rij and Britton on the basis of a refinement of X-ray diffraction data, has been confirmed by the doubling of CN stretching fundamentals. The ratios of doublet band areas are consistent with the energy of the orientation [Formula: see text] being higher than that of the "normal" orientation, [Formula: see text] by 800 ± 300 cal mol−1.
The addition of simple aromatic hydrocarbons to condensed aromatic thiophenes promoted by aluminum chloride. Part II. Naphtho[1,2-b]thiophene
Authors: Clark Peter David , McKinnon David M.
Published: May 2006

The reaction of naphtho[1,2-b]thiophene with an aromatic hydrocarbon in the presence of aluminum chloride at 20 °C gave either a 3-aryl-2,3-dihydronaphtho[1,2-b]thiophene by addition to the 2,3-bond or 2,3-dihydronaphtho[1,2-b]thiophene as a result of hydride abstraction.Occasionally 2-aryl-2,3-dihydronaphtho[1,2-b]thiophenes were obtained. At higher temperatures 2-arylnaphtho[1,2-b]thiophenes and 2,3-dihydronaphtho[1,2-b]thiophene were isolated. Attempts are made to rationalize the formation of these products in terms of protonation of naphtho[1,2-b]thiophene by moist aluminum chloride and reaction of the resulting electrophile with an aromatic substrate.
Synthesis and complexation of the novel tridentate anionic organogallate ligands, [Me2Ga(N2C5H7)(OCH2CH2SR)]− (R = Et or Ph)
Authors: Chong Kenneth S. , Storr Alan
Published: May 2006

The synthesis and complexation of the novel tridentate chelating anionic organogallate ligands [Me2Ga(N2C5H7)(OCH2CH2SR)]− (R = Et or Ph) have been investigated. A variety of octahedral molybdenum, tungsten, and manganese carbonyl compounds have been studied in which the organogallate ligand (R = Et) is in the fac coordination mode. In addition tetrahedral "Cu•PPh3" and "Ni(NO)" complexes have been characterized which display fluxional behaviour in solution. The dearth of derivatives available using the ligand where R = Ph is attributed to steric factors.
Le potentiel chimique d'excès dans des systèmes binaires: acides dicarboxyliques –acides monocarboxyliques ou esters. L'énergie libre d'interéchange entre groupes aliphatiques et carboxyliques
Authors: Berchiesi Gianfrancesco , Gioia-Lobbia Giancarlo , Vitali Giovanni , Berchiesi Maria A.
Published: May 2006

We report experimental data concerning the solid–liquid and liquid–liquid equilibrium temperatures for some binary systems composed of ethyl hexadecanoate and some bicarboxylic aliphatic acids. The crystallization curves of these systems and of others, previously published only in a graphical form, are used in order to obtain the excess chemical potential of the bicarboxylic acid along its crystallization curve. This thermodynamic quantity is compared with that calculated from the theory of group interaction, by means of the areas of the contact surfaces and of three interchange energy parameters.
Lewis acid promoted reactions of ethyl cyanoformate. Reaction with 2,5-dimethylfuran
Authors: McCulloch Archibald W. , McInnes A. Gavin , Smith Donald G.
Published: May 2006

Aluminum chloride promoted reaction of 2,5-dimethylfuran with ethyl cyanoformate affords, depending on the experimental conditions, cis and trans ethyl 5-cyano-2,5-dimethyl-2,5-dihydrofuran-2-carboxylates, 3 and 4, ethyl 2,5-dimethylfuran-3-carboxylate 5, 4,8-dicyano-1,2,4,8-tetramethyl-3,9-dioxatricyclo-[5.2.1.02,6]decane 6, and ethyl 3-(2,5-dimethyl-3-furyl)-5-cyano-2,5-dimethyltetrahydrofuran-2-carboxylate 7. Structures were elucidated from spectral evidence and chemical transformations.
An 129I Mössbauer study of organotin iodides
Authors: Jones C. H. W. , Dombsky M.
Published: May 2006

Iodine-129 Mössbauer data for SnI4, MeSnI3, Me2SnI2, Me3SnI, Me3SnI2−, Me3SnI.py, and Me2SnI2.2py are reported. The data are compared with available nqr data for the corresponding chlorides and bromides. The Mössbauer data are interpreted as evidence that MeSnI3, Me2SnI2, and Me3SnI are distorted from tetrahedral geometry in the solid state. The applicability of the additive model in interpreting 119Sn quadrupole splittings in these compounds is commented on.
Orthophosphoric acid: calculation of concentration quotients for the first ionization equilbrium at 25.0 °C
Authors: Gamble Donald S.
Published: May 2006

Equilibrium concentration quotients, K1, have been calculated for the first ionization step of orthophosphoric acid at 25.0 °C. Literature information for γHCl in mixed orthophosphate–chloride solutions has made it possible to use the published electrochemical data of Bates and Nims for this purpose. K1 is found to be a function of two independent variables for orthophosphate concentrations from 9 × 10−2 m down to at least 1.0 × 10−2 m. K1 is described in terms of total orthophosphate concentration CT and the degree of ionization, α1. Linear multiple regression analysis was used to produce the empirical equation K1 = K1* + A0CT1/2 − βα1CT1/2, in which K1* is an experimental constant not identified with the thermodynamic equilibrium constant, [Formula: see text].
Membrane transport systems. II. Transport of alkali metal ions against their concentration gradients
Authors: Fyles Thomas M. , Malik-Diemer Virginia A. , Whitfield Dennis M.
Published: May 2006

An artificial membrane system based on a series of macrocyclic polyether carriers (crown ethers) is described. Under the influence of a proton gradient the carriers move alkali metal ions from basic to acidic solution through a chloroform membrane phase. Transport occurs against the concentration gradient of the transported ion as a result of a coupled counterflow of protons. Different transport behaviors are observed depending upon the metal ion concentration. At high metal ion concentration the amount transported is a linear function of time; at lower metal ion concentration the amount transported is a complex function of time which may be described as the result of a pair of consecutive first order processes. Effects of metal ion, carrier, and proton concentration on transport rate are considered. The rate increases with increasing metal ion or carrier concentration but is essentially independent of the pH of either aqueous phase. Increased lipophilicity of the carrier also results in a rate increase. Carriers derived from 18-crown-6 transport potassium selectively and all ions more rapidly than 15-crown-5 derivatives which are, however, selective for sodium. The overall efficiency of the system is discussed in terms of competing "leak" reactions, either of cations from the basic phase or of anions from the acidic phase.