bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of N-3′-furylbenzamide with some dienophiles
Authors: Bridson John N.
Published: May 2006

N-3′-Furylbenzamide gives a conventional Diels–Alder adduct with maleic anhydride but with dimethyl maleate and methyl acrylate further reactions take place at the enamide grouping of the initially formed adducts. Compounds have been isolated in which molecules of an alcohol, used as solvent, or the starting furan have added to the double bond of the 1:1 adducts. In the first case unstable alkoxyamides are formed; in the second stable 2:1 adducts result from a novel uncatalysed addition to the double bond of the enamide. The stereochemistry of these and related compounds is discussed.
Kinetic isotope effect and tunnelling in the proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent
Authors: Jarczewski Arnold , Pruszynski Przemyslaw , Leffek Kenneth T.
Published: May 2006

The proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent shows a large primary deuterium isotope effect, kH/kD = 24.3 at 0 °C and 16.9 at 20 °C. The enthalpy of activation difference (ΔHD≠ − ΔHH≠) = 2.6 ± 0.4 kcal mol−1 and the entropy of activation difference (ΔSD≠ − ΔSH≠) = 3.4 ± 1.3 cal mol−1 K−1. This isotope effect, when fitted to Bell's equation, indicates that there is a considerable contribution to this reaction from tunnelling of the proton through the potential energy barrier.
Volumes, expansivities, enthalpies of solution, and conductivities of K+ and of Bu4N+ 1-adamantylcarboxylates in H2O and in D2O
Authors: Morel-Desrosiers Nicole , Morel Jean-Pierre
Published: May 2006

The standard molar volumes, the standard molar enthalpies of solution, and the limiting conductivities have been determined for potassium and tetrabutylammonium adamantylcarboxylates in water and heavy water, at 298.15 K. The temperature dependence of the volume and of the conductivity of the potassium salt has also been studied. The results are compared with those relative to potassium acetate. The change of the methyl group for the adamantyl one does not follow the behaviour normally expected for the transfer of hydrophobic solutes from water to heavy water.
A shock-tube study of ammonia pyrolysis
Authors: Dove John E. , Nip Wing S.
Published: May 2006

The pyrolysis of NH3 was studied behind reflected shock waves at temperatures 2500–3000 K, using mass spectrometric analysis of dynamically sampled gas. The initial mixtures contained 0.14% to 6% NH3, with Kr as diluent, at total gas concentrations of about 2 × 10−6 mol cm−3. Concentration profiles of NH3, NH2, NH, and N2 were measured. It was found that the apparent rate coefficient for overall removal of NH3 is increased by increasing the initial NH3 concentration, but is decreased by addition of H2. Addition of H2 also suppressed NH, but left the NH2 concentration relatively unchanged. A close correlation was found between NH2 concentration and N2 formation rate, indicating that NH2 participates in the reaction which produces N2.The experimental results are consistent with a chain mechanism in which NH3 is removed by unimolecular decomposition and by attack by H, NH, and NH2. Computer analysis yields a rate constant of 1.2 × 1016 exp (−91 000 cal mol−1/RT) cm3 mol−1 s−1 for the unimolecular process.
Evidence for the existence of complex ions in mixed solutions of indium trichloride and ammonium chloride
Authors: Campbell Alan N.
Published: May 2006

The conductances, densities, and viscosities of concentrated solutions of ammonium chloride in water, at 25 °C, have been determined with good agreement with existing conductance data. The same data have been obtained for mixed solutions of indium trichloride and ammonium chloride. The fact that the conductance is always much less than the sum of the individual conductances, in some cases less than that of indium chloride alone, points to the existence of a complex in solution.
A total synthesis of (−)-khusimone
Authors: Liu Hsing-Jang , Chan Wing Hong
Published: May 2006

A total synthesis of (−)-khusimone (1), an odoriferous norsesquiterpenoid ketone, has been achieved in 16 steps from the ammonium salt of l-10-camphorsulfonic acid.
Chemical and microbiological remote functionalisation of (+)- and (−)-bornyl acetate
Authors: Allen Malcolm S. , Darby Nicholas , Salisbury Phillip , Sigurdson Elin R. , Money Thomas
Published: May 2006

Chemical oxidation of (−)-bornyl acetate provides a mixture of 3-, 5-, and 6-oxobornyl acetate, whereas microbiological hydroxylation with cultures of Helminthosporiumsativum gives a mixture of 2,3-, 2,6-, and 2,5-bornanediols. In each case the reaction occurs preferentially at the C(5) position. Microbiological hydroxylation of (+)-bornyl acetate with H. sativum occurs almost exclusively at the C(5) position. Regiospecific hydroxylation of (+)- or (−)-bornyl acetate with cultures of Fusariumculmorum also occurs at the C(5) position but without concomitant hydrolysis of the acetoxy group.
The effect of tetra-n-butylammonium bromide on the proton magnetic resonance of 1-X-2,4-dinitrobenzenes
Authors: McLaughlin D. R. , Reinheimer J. D.
Published: May 2006

The chemical shifts of the ring protons of 1-X-2,4-dinitrobenzenes are changed with the addition of tetrabutylammonium bromide. In general, the chemical shift of proton 3 decreases with salt addition, that of proton 5 may increase or decrease, while that of proton 6 increases. Where X is an oxygen containing group, the changes are somewhat more pronounced.
Structure et réactivité des benzoxazoles: étude par résonance magnétique nucléaire du carbone-13
Authors: Llinares Jeanine , Galy Jean-Pierre , Faure Robert , Vincent Emile-Jean , Elguero José
Published: May 2006

Thirty-four benzoxazoles, oxazole, and 10 o-aminophenols have been studied by 13C nmr spectroscopy. All the signals have been attributed from substituent effects. The structure of products obtained by nitration of benzoxazole have been determined by 13C nmr. The shifts induced by substitution at the 2 position have been discussed as a function of an empirical model using the structural parameters F, R, and Q*. Azido–tetrazole equilibria (N3 in position 2) and prototropic tautomerism (NH2, OH, and SH in position 2) have been also discussed. The chemical shifts and coupling constants of oxazole and unsubstituted benzoxazole have been compared.
Temperature dependence of rate constants for reaction of oxygen atoms, O(3P), with allene and 1,3-butadiene
Authors: Nip W. S. , Singleton D. L. , Cvetanović R. J.
Published: May 2006

Rate constants were determined for the reactions of O(3P) atoms with allene and with 1,3-butadiene by a phase shift technique in which oxygen atoms were generated by modulated mercury photosensitized decomposition of nitrous oxide and monitored by the chemiluminescence from their reaction with NO. Over the temperature interval 297–574 K, the Arrhenius equation for the O(3P) + allene reaction is k1A = (2.99 ± 0.41) × 10−11 exp [(−941 ± 54)/T] cm3 molecule−1 s−1, where the indicated uncertainties are 95% confidence limits. At 299 and 488 K, the rate constant for O(3P) + 1,3-butadiene is essentially the same, within 10%, with an average value of 2.07 × 10−11 cm3 molecule−1 s−1.
The reaction products of N-alkylquinoxalines with 7,7,8,8-tetracyanoquinodimethane
Authors: Keller Heimo Jürgen , Nöthe Dietrich , Werner Manfred
Published: May 2006

Simple (1:1) and complex (2:3) TCNQ salts of the N-ethylquinoxalinium (NEQ) and N-methylquinoxalinium (NMQ) cations were prepared and characterized. In contradiction to earlier claims it was found that the 1:1 NMQ-TCNQ compound is not highly conducting but is a semiconductor. The triclinic crystals with unit cell dimensions a = 4.79, b = 10.46, c = 7.60 Å, α = 93.49, β = 110.92, γ = 82.69° show triplet exciton lines in the epr spectra indicating the occurrence of dimerized radicals in this solid. The high dc conductivity of the simple salt as reported earlier can only be attributed to a complex salt.
Studies on the adsorption and the association of cytidine sulphate at the dropping mercury electrode with phase-sensitive ac-polarography
Authors: Temerk Yassein M.
Published: May 2006

The adsorption and association of cytidine sulphate have been studied by using phase-sensitive ac-polarography in acidic buffer solution (pH 3.24) at the dropping mercury electrode. At low bulk concentrations, adsorbed molecules of cytidine sulphate at maximal adsorption potential (−0.7 V) are orientated in 'dilute' adsorption layer planar to the electrode surface where the interaction of π-electrons with interface favours adsorption. At bulk concentrations above a threshold value (6.6 × 10−3 M), the stacking interactions between vertically oriented molecules lead to association and formation of a compact layer; and a pit is observed. The concentration dependence of the ac-capacity current at a maximal adsorption potential (−0.7 V) shows a two-step Frumkin isotherm due to association of the adsorbed molecules. The adsorption parameters are computed and discussed.
Kinetics of ion exchange of some complex cations on chromium ferrocyanide gel
Authors: Saraswat Ishwari P. , Srivastava Suresh K. , Sharma Ashok K.
Published: May 2006

The parameters effective diffusion coefficients, activation energies, and entropies of activation are reported for the exchange of the ammine-complex cations of cobalt, viz. [Co(NH3)6]3+ and[Co(en)3]3+ (en = enthylenediamine) on chromium ferrocyanide gel in the H form. The values of these constants throw significant light on the possible structural changes in the exchanger framework caused by the introduction of these large size complex cations. Kinetic measurements have been made as the function of particle size of the exchanger, temperature, and solution concentration of the exchanging ions. The slow step governing the rate of exchange is diffusion of ions through the exchanger particles.
The adsorption of tri-n-butylphosphate at the n-dodecane–water interface
Authors: Sagert Norman H. , Lee Woon , Quinn Michael J.
Published: May 2006

The adsorption of tri-n-butylphosphate (TBP) from n-dodecane to the n-dodecane–water interface has been studied as a function of TBP mole fraction up to 2.7 × 10−4 in the n-dodecane, and as a function of temperature from 293.15 K to 308.15 K. Free energies of adsorption were calculated from the results at low TBP mole fractions, where the surface pressures were linear with mole fraction. They were in the range −36.1 to −35.6 kJ/mol. The enthalpy of adsorption, determined from the variation of the free energies of adsorption with temperature, was −45.4 kJ/mol.Several equations of state based on two-dimensional gas laws were applied to the results. The Schofield–Rideal equation described the results adequately but the simpler Volmer equation was inadequate especially at lower temperatures. Deviations from the Volmer equation were in the direction of higher surface pressure. A simple version of the two-dimensional solution model equation of state was not helpful.
The reaction of methylene radicals with methyl isocyanide
Authors: Glionna Marsha T. J. , Pritchard Huw O.
Published: May 2006

An exploratory study has been made of the gas-phase reactions of methylene radicals, generated by the photolysis of ketene near 3000 Å, with methyl, ethyl, and allyl isocyanides at room temperature.With methyl isocyanide, the principal product at low pressure is ethyl cyanide, together with a few percent of methyl cyanide; ethyl isocyanide is also formed, increasingly so as the total pressure is increased. Reaction appears to take place through a vibrationally excited ethyl isocyanide intermediate, and approximate rate constants for each reaction pathway are derived. Isotopic studies suggest that the methylene radicals insert in the H3C—NC bond of the methyl isocyanide.
Reactions of the tetrasulfur pentanitride(-1) ion with halogens: synthesis, spectroscopic characterization, and crystal structure of pentasulfur hexanitride
Authors: Chivers T. , Proctor J.
Published: May 2006

Pentasulfur hexanitride, S5N6, has been prepared in good yield by the reaction of [n-Bu4N+][S4N5−] with bromine (or iodine) in methylene chloride at 0 °C. In contrast, the tetrasulfur pentanitride(−1) ion reacts smoothly with chlorine to give S4N5Cl, while the reaction with sulfuryl chloride produces S4N5Cl and S5N6 and the reaction with thionyl chloride produces a mixture of S3N2O, S3N2O2, S4N4, and S5N6. Pentasulfur hexanitride is an air-sensitive, explosive, yellow-orange solid which sublimes at ca. 45 °C/10−2 Torr without significant decomposition. It has been characterised by infrared, Raman, uv–visible, and mass spectra and by a single crystal X-ray structure determination. The crystals are monoclinic and belong to the space group C2/c, a = 8.787(2), b = 11.190(2), c = 7.427(2) Å, β = 106.46(2)°, V = 700.3(5) Å3, Z = 4, Dc = 2.317 g cm−3. The refined structure (Rw = 0.040) has twofold symmetry and resembles a basket in which an —N=S=N— unit (d(S—N) = 1.54 Å) is the handle which bridges an S4N4 cradle via S—N single bonds (d(S—N) = 1.70 Å). The introduction of this bridge widens one of the [Formula: see text] transannular separations in S4N4 to 3.94 Å while the other is shortened to 2.43 Å. Thus, the S4N4 cradle can be viewed as two five-membered rings fused at the S—S bond.
Vapour pressure and calorimetric data for the solution of sulfur dioxide in aprotic solvents
Authors: Benoit Robert L. , Milanova Etela
Published: May 2006

Vapour–liquid equilibrium data for dilute sulfur dioxide solutions in sixteen solvents were derived from total vapour pressure measurements at 25 °C. The SO2 enthalpies of solution at infinite dilution ΔH0 were determined at 25 °C by direct calorimetry. The solvents used belong to the aprotic class. The ΔH0 values (kcal mol−1) are for the non-polar solvents, isooctane (−3.5), cyclohexane (−3.5), n-heptane (−3.8), benzene (−5.8), and for the polar solvents, 1,2-dichloroethane (−5.5), nitromethane (−6.2), nitrobenzene (−6.3), acetonitrile (−6.7), ethyl acetate (−7.1), sulfolane (−7.3), propylene carbonate (−7.5), trimethyl phosphate (−8.9), tetrahydrofuran (−9.4), dimethylformamide (−10.9), pyridine (−11.6), dimethylsulfoxide (−13.0). Out of three correlation methods which we tested to account for our data in non-polar solvents, the Hildebrand solubility parameter treatment gives the best results. The SO2 enthalpies of solution, ΔH0, in the polar solvents are discussed in terms of solvent basicity. There is a good correlation between the ΔH0 values, which relate to the basicity of the bulk solvent, and the solvent 'donor number' which is a molecular basicity parameter.
The crystal and molecular structure of cis-dichloro(2,2′-o-phenylenebisbenzothiazole)copper(II)
Authors: Ball Richard G. , Trotter James
Published: May 2006

The molecular structure of cis-dichloro(2,2′-o-phenylenebisbenzothiazole)copper(II) has been determined by single crystal X-ray diffractometry. The crystal is monoclinic, P21/n, a = 8.408(1), b = 15.819(1), c = 14.229(2) Å, β = 93.19(1)°, and Z = 4. The structure has been refined by full-matrix least-squares techniques on F, using 3316 unique reflections for which F2 > 3σ(F2), to a final agreement factor of 0.028. The complex adopts an approximately square planar coordination geometry with the Cu bound to two cis Cl atoms and the N atoms of the chelating benzothiazole ligand. The mean Cu—N and Cu—Cl distances are 2.016(6) and 2.217(6) Å, respectively.
Synthesis of long-chain coumarines and 2H-chromenes. Spectral and monolayer properties
Authors: Pommier H. P. , Baril J. , Gruda I. , Leblanc R. M.
Published: May 2006

Several coumarines and 2H-chromenes containing one or two long-chain substituents were synthesized and their spectroscopic properties (uv, nmr) were investigated. All compounds were studied at the air–water interface. Five of them give a monolayer which is characterized by the pressure–area isotherm. An interpretation of the isotherms is discussed in relation to the molecular structure.
The thermal chemistry of vinyldiazo compounds as a method for the generation of vinylmethylenes
Authors: Pincock James A. , Murray Kim P.
Published: May 2006

The thermal chemistry of a series of substituted 1-aryl-3-methyl-2-phenyl-1-diazobut-2-enes has been examined. These vinyldiazo compounds react in two parallel pathways: cyclization to a 3-aryl-5,5-dimethyl-4-phenyl-5H-pyrazole or loss of nitrogen and cyclization to a 1-aryl-2-phenyl-3,3-dimethylcyclopropene presumably by a vinylmethylene intermediate. The kinetics of these processes reveal quite different substituent effects. The relation of these results to the stability of the vinylmethylene produced and to the singlet photochemistry of cyclopropene derivatives is discussed.
Stereoselective synthesis of β-substituted α,β-unsaturated esters by dialkylcuprate coupling to the enol phosphate of β-keto esters
Authors: Sum Fuk-Wah , Weiler Larry
Published: May 2006

The anions from β-keto esters or β-diketones were reacted with diethyl phosphorochloridate to yield the corresponding enol phosphates. These enol phosphates were coupled with dialkylcuprates to produce the β-substituted α,β-unsaturated esters or ketones in good yield. Starting from acyclic β-keto esters this sequence was used to stereoselectively generate tri- and tetrasubstituted olefins.
Synthesis of exo- and endo-brevicomin and frontalin
Authors: Sum Phaik-Eng , Weiler Larry
Published: May 2006

The dianion of methyl acetoacetate is alkylated at the γ-carbon with homoallylic bromides. The resulting alkenes are epoxidized and then cyclized with a Lewis acid to produce esters of 6,8-dioxabicyclo[3.2.1]octane. These esters can be hydrolyzed and decarboxylated in a novel reaction. This methodology has been applied to a stereospecific synthesis of the title compounds. In addition, one of the intermediates in the exo-brevicomin synthesis can be resolved to provide the natural (+)-pheromone.
Strong hydrogen bonding in oxime solvates of tetra-n-butylammonium fluoride
Authors: Clark James H.
Published: May 2006

Four stable, crystalline oxime solvates of tetra-n-butylammonium fluoride have been prepared, characterised, and studied by 1H, 13C, and 19F nmr, infrared, and ultraviolet spectroscopy. All of the complexes crystallise from solution as the disolvates, Bu4NF(oxime)2. The spectroscopic changes accompanying solvate formation are interpreted on the basis of strong hydrogen bonding between the fluoride anion and the oxime hydroxyl.
Gas-phase proton-transfer reactions of the hydronium ion at 298 K
Authors: Mackay Gervase I. , Tanner Scott D. , Hopkinson Alan C. , Bohme Diethard K.
Published: May 2006

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.
A convergent route to phthalideisoquinoline alkaloids via directed metalation of tertiary benzamides
Authors: Silva S. O. De , Ahmad I. , Snieckus V.
Published: May 2006

Diastereomeric phthalideisoquinolines 8 and 9 have been synthesized by a route involving an amine-induced bromohomophthalic anhydride – phthalide-α-carboxamide rearrangement, 3 + 4 → 6, as the key step. This rearrangement has been applied to the synthesis of the methoxylated phthalide-α-carboxamide 18 which has been converted into the dehydrophthalide 19 thereby achieving a formal synthesis of the phthalideisoquinoline alkaloids cordrastine I (1a) and cordrastine II (1b). The key intermediate in this sequence, 3,4-dimethoxyhomophthalic acid (15), has been efficiently prepared in two steps via directed lithiation of 2,3-dimethoxy-N,N-diethylbenzamide (13).
Splendidine, a new oxoaporphine alkaloid from Abutarufescens Aublet
Authors: Skiles Jerry W. , Saa Jose M. , Cava Michael P.
Published: May 2006

The oxoaporphine alkaloids lysicamine, homomoschatoline, imenine, and splendidine have been isolated from Abutarufescens Aublet (=Abutasplendida Krukoff and Moldenke). Splendidine has been shown to be 1,2,4-trimethoxy-7H-dibenzo[de,g]quinolin-7-one (1) by total synthesis.
An approach to the synthesis of quadrigemine-A
Authors: Battey P. K. , Crookes D. L. , Smith G. F.
Published: May 2006

Two syntheses of N-{2-[1′-benzyl-3′-(indole-7″-yl)oxindol-3′-yl]ethyl}-N-methylacetamide (6), a possible intermediate in a synthesis of quadrigemine-A, are described. The more efficient of the two syntheses gives an overall yield of 12% in 11 steps from tryptamine.
Unimolecular reactions of N2O and CO2 at high pressure
Authors: Yau Andrew W. , Pritchard Huw O.
Published: May 2006

An apriori calculation in the framework of the theory of radiationless transitions is presented for the non-adiabatic spin-forbidden reactions of N2O and CO2. The calculation is two-dimensional, incorporating the two stretching degrees of freedom, and the microscopic reaction process is formulated using the relative coordinate system of Rosen as modified by Beswick and Jortner. All microscopic parameters required for the calculation are derived from spectroscopic data; no adjustable parameter is included. For each reaction, a purely theoretical reaction probability function k(E) is synthesised and used to derive a theoretical Arrhenius expression for the infinite-pressure reaction rate. The calculated high-pressure unimolecular dissociation rates for both reactions are in reasonable agreement with experiment. High-pressure recombination rate coefficients are also presented for CO2; they exhibit positive activation energies which increase from 0.5 kcal/mol at room temperature to 8 kcal/mol at 5000 K.
Five-coordinate iron(II) porphyrins derived from meso-α,β,γ,δ tetraphenylporphin: synthesis, characterization, and coordinating properties
Authors: Momenteau Michel , Loock Bernard , Bisagni Emile , Rougee Michel
Published: May 2006

Meso-α,β,γ,δ, tetraphenylporphin derivatives bearing acrylic (cis and trans isomers) and propionic side chains with a terminal imidazole group have been synthesized. Intermediate compounds obtained during their preparation were characterized by visible spectroscopy and nmr. In non-coordinating solvents (benzene or toluene), the iron(III) complexes of these compounds do not show intramolecular coordination of the terminal base on the metal ion. The reduced forms of the compounds have been obtained from ferric forms by heterogeneous reduction with aqueous dithionite and exhibit optical spectra characteristic of five-coordinate ferrous complexes. The nitrogenous bases and carbon monoxide affinities of the latter have been measured and the results indicate that the 'transinfluence' exerted by the terminal imidazole does not depend greatly on the nature and the structure of the covalent side chain. In contrast the stability of the five-coordinate compounds depends on the side chain (trans acrylic < propionic < cis acrylic) as suggested by the values reported for the replacement constants of the terminal imidazole by 4-cyanopyridine in unsymmetrical six-coordinate derivatives. The stability of these compounds towards oxidation is also reported.
Use of XαSW calculations for parametrising the CNDO method for the heavier elements. II. Tests for the elements aluminium to sulphur
Authors: Head J. D. , Mitchell K. A. R.
Published: May 2006

In Part I (Mol. Phys. 35, 1681 (1978)) we used results from the Xα scattered wave (XαSW) method for guiding the parametrisation of the complete neglect of differential overlap (CNDO) method for clusters of silver, and we proposed the extension of this approach to other heavier elements for which CNDO schemes are not well developed. The main purpose of the present paper is to test this approach for the elements aluminium to sulphur for which more information is available. XαSW calculations have been made for the molecular clusters Al7, Si5H12, and P4, and comparisons made with experiment and with other calculations where possible. The charge distributions and transition-state energies, along with information obtained previously for S8 by Salahub et al., have been used to derive new parameters (designated CNDO/HM) for the elements aluminium to sulphur essentially following the procedure in Part I. Calculations using these parameters have then been tested against an XαSW calculation made here for an Al10 cluster (which simulates the (111) surface of aluminium), and against other calculations made previously for P8, P4S3, SiH4, PH3, H2S, and SO2. Comparisons are also made with results from the CNDO/2 scheme. Generally the CNDO/HM procedure seems at least as successful as CNDO/2.
Synthesis of some alkoxyfluorophosphoranes and alkoxyfluorophosphines and characterization by 1H, 19F, and 31P nuclear magnetic resonance spectroscopy
Authors: Janzen Alexander F. , Kruczynski Leonard J.
Published: May 2006

The preparation of phosphoranes C6H5PF2HOR by the oxidative addition of alcohols to C6H5PF2, followed by elimination of HF to give phosphines C6H5PFOR (R = CH3, CH2CH3, CH2CF3, CH(CF3)2, CH(CF3)C6H5, C(CH3)3), is described. All products were characterized by 1H, 19F, and 31P nmr spectroscopy. The 31P nmr spectrum of C6H5PFOCH(CF3)C6H5 confirms the presence of diastereomers. Rapid ligand exchange in phosphoranes C6H5PF2HOR occurs upon addition of a base such as pyridine.
Pyrrolidine- and piperidine-alkanoic acid hydrochlorides. Synthesis by hydrogenation of pyrrolyl ester and pyridine-alkanoic acid hydrochlorides
Authors: Tsui Sooi-Kay , Wood James Douglas
Published: May 2006

2-Pyrrolidylacetic acid and β-(2-pyrrolidyl)propionic acid hydrochloride have been prepared by hydrogenation of ethyl 2-pyrrolylacetate and diethyl 2-pyrrolylmethylenemalonate respectively, over rhodium on alumina in HCl solution, followed by acidic hydrolysis. Similarly, 1-methylnipecotic acid, 1-methylisonipecotic acid, 2- and 3-piperidine-acetic acid, and 3-piperidine-propionic acid hydrochlorides have been prepared by hydrogenation of the corresponding pyridine-alkanoic acid hydrochlorides over platinum oxide, rhodium on alumina, or palladium on carbon in water.
Temperature and concentration dependence of fluidity of mixed hydrated melts of calcium- and nickel(II)-nitrates
Authors: Islam Nurul , Ali Anwar
Published: May 2006

The non-Arrhenius temperature dependence of fluidity, [Formula: see text], of molten mixtures of calcium nitrate tetrahydrate and nickel(II) nitrate hexahydrate has been explained in terms of equations based upon the Vogel–Tammann–Fulcher (VTF) and the configurational entropy (CEM) models. The role of the relevant parameters in understanding the successive variations in their behaviour with concentration has been examined. The concentration dependence of fluidity has been explained satisfactorily by an isoenergetic equation. In addition to the linear dependence of the pre-exponential terms of the VTF and the Doolittle equations on the ideal glass-transition temperature, T0, and the molar intrinsic volume, V0, respectively, linear interdependence of the two thermodynamic parameters, T0 on V0, has been found. Linear dependence of the corrected activation energy, Ecor, on the V0 and the T0 values have been demonstrated in the system under investigation.
Ion association and charge-transfer excitation between N-heterocyclic cations and cyanoiron complexes
Authors: Toma Henrique E.
Published: May 2006

N-Heterocyclic cations form with substituted pentacyanoferrates a series of outer-sphere complexes of general formula Fe(CN)5L//N-Het, suitable for systematic studies in aqueous solution. The equilibrium constants for the association of dipositive cations (e.g. N,N′-dimethyl-4,4-bipyridyl, or paraquat ion) and monopositive cations (e.g. N-methylpyrazinium) with the hexacyanoferrate(II) anion are typically in the range of 30–40 M−1and 10–13 M−1. The optical charge-transfer energies depend on the nature of the N-heterocyclic acceptor, and on the binding properties of the ligand L as they modify the ionization potentials of the Fe(CN)5Ln− complexes. A linear correlation between the optical charge-transfer energies and ΔE0 was found, with a slope (ΔEop/ΔG0) of 1.03 ± 0.03. The results were interpreted on the light of Hush's theory for intervalence transitions, with the aid of the equation Eop = 2(ΔG11* + ΔG22*) + ΔG120, which correlates the optical energy (Eop) for electron-transfer with the intrinsic barriers (ΔG11* + ΔG22*) of the donor and acceptor ions, and the free energy change (ΔG120) for the process.
Pyrolysis of trifluoroacetaldehyde, initiated by di-tertiary-butyl peroxide decomposition
Authors: Loucks Leon F. , Liu Michael T. H. , Hooper David G.
Published: May 2006

The thermal decomposition of 95:5 mixtures of trifluoroacetaldehyde (TFA) and di-tert-butyl peroxide (DTBP) has been studied at 100 Torr over the temperature range of 390 to 440 K. The major decomposition products included CO, CF3H, CH3COCH3, and CH4 while C2F6, CF3CHOHCH3, CF3CH3, CF3COCH3, C2H6, (CF3)2CHOH, and H2 were also found. In addition to the usual reactions for TFA thermal decomposition, reactions of methyl radicals with TFA to form isopropoxyl radicals were found. The alcohol products result from H atom abstraction reactions of the isopropoxyl radicals while CF3COCH3 is a decomposition product. Arrhenius parameters for several reactions were determined: for DTBP decomposition, log k = 15.82 − 37.73/2.303RT; for H abstraction from TFA by CH3, log k = 8.30 − 7.37/2.303RT; for H abstraction from TFA by CF3, log k = 8.98 − 8.61/2.303RT. Consideration has also been given to several rate constant ratios for the formation and decomposition of isopropoxyl radicals.A study of the reaction order for the formation of CF3H, C2F6, and CH4 showed that the orders were 3/2, 1, and 1 respectively for these three products. A reaction mechanism involving 14 individual steps is proposed to explain the reaction products and the observed orders of reaction.
The ultraviolet photoelectron spectra of C6F5X compounds, X = (F, Cl, Br, I, H, CH3)
Authors: Trudell Barry C. , Price S. James W.
Published: May 2006

This work provides a study of the 1a2uπ, 2e2gσ, and 1e1gπ levels of a series of C6F5X compounds (X = F, Cl, Br, I, H, CH3) using ultraviolet photoelectron spectroscopy or more simply PES. The three levels are assigned from the PES spectra using the perfluoro effect. A correlation between the energies of these levels and the energies predicted by CNDO/2 and INDO is presented.
Reply to comment: Ultrasonic velocities for deuterium oxide – water mixtures at 298.15 K
Authors: Kiyohara Osamu , Halpin Carl J. , Benson George C.
Published: May 2006

The calculations of excess sound velocities in D2O–H2O mixtures by Ernst and Glinski are discussed and new results are presented.
Carbon-13 nuclear magnetic resonance studies of the cholesteryl ester – phosphatidylcholine system
Authors: Cushley Robert J. , Forrest Bruce J.
Published: May 2006

Using difference spectroscopy, 13C spin–lattice relaxation measurements on 40% egg phosphatidylcholine multilamellar liposomes (containing 25 mol% cholesteryl palmitate)–60% D2O indicate the ester contributes negligibly to the microviscosity of the acyl chains in the bilayers.At 37 °C, spin–spin and spin–lattice relaxation measurements have been obtained for 25 mol% cholesteryl linoleate in both egg phosphatidylcholine and dipalmitoyl phosphatidylcholine multilayers and indicate: (a) T1 values of the linoleate ester chain are 0.5 times those of the lecithin chain carbons, and (b) T2* = 16 ± 6 ms for all discernable linoleate carbons. At 52 °C, cholesteryl ring carbons C5 and C6 yield T2* values of 23 and 20 ms, respectively. These studies suggest the esters reside in an environment whose "fluidity" approaches that found in very low density lipoprotein (VLDL).
Cyclization of cysteinylglycine sulfoxides under Pummerer reaction conditions
Authors: Wolfe Saul , Kazmaier Peter Michael , Auksi Hillar
Published: May 2006

A number of sulfoxides derived from 3-benzylthiopropionic acid, S-benzylcysteine, and S-phenylcystelne have been synthesized and exposed to typical Pummerer reaction conditions. Cyclization of the S-benzyl sulfoxides to six-membered or seven-membered heterocyclic rings (1,3-thiazin-4-ones and 1,3,6-oxathiazepines) is observed only in acetic anhydride solvent and only after conversion of the carboxyl group to an amide or peptide. Cyclization of S-phenylcysteinyl amides to β-lactams could not be achieved. The thiazolidine isomers of the six- and seven-membered rings have been synthesized and found not to be intermediates in the acetic anhydride reactions. The thiazolidines do rearrange to the six- and (or) seven-membered rings in anhydrous trifluoroacetic acid solvent. S-Benzylphthalimidocysteinylglycine sulfoxide, a 3:2 mixture of epimers at sulfur, affords a 3:2 mixture of isomeric thiazinones. A mechanism for these cyclizations is proposed, and it is suggested that the configuration at sulfur controls the configuration at the new asymmetric centre in the product.
Osmotic and activity coefficients of lithium chloride in water from 50 to 150 °C
Authors: Campbell Alan N. , Bhatnagar Om N.
Published: May 2006

The activity coefficients of lithium chloride in aqueous solution at temperatures of 50, 75, 100, 125, and 150 °C and concentrations varying from 0.5 to 3 m have been determined. The method used was the application of the Gibbs–Duhem theorem, i.e., the activity of the solvent water was the quantity actually determined. The experimental determination was that of the vapour pressure of the solution using a differential manometer. At all temperatures the activity coefficient passes through a minimum and then increases progressively.
Structure of a new crystalline modification of dithiocyanato(triphenylphosphine)mercury(II)
Authors: Makhija Ramesh C. , Rivest Roland , Beauchamp André L.
Published: May 2006

Crystals of the β-form of the title compound are monoclinic, space group P21/c, a = 21.071(5), b = 17.716(5), c = 11.285(3) Å, β = 101.66(5)° and Z = 8. The structure was refined on 2741 independent observed reflections to an R factor of 0.042.The crystals consist of two types of infinite chains with backbones of thiocyanate-bridged mercury atoms. In chain 1, mercury shows the same (3 + 2) coordination as observed in the α-form. It is bound to P of triphenylphosphine (Hg—P = 2.429(4) Å) and two S-bonded thiocyanate ligands (Hg—S = 2.491(5), 2.519(5) Å) in the equatorial plane of a distorted trigonal bipyramid. The axial positions are occupied by weakly-bonded N atoms from adjacent units (Hg—N = 2.74(1), 2.89(1) Å). Chain 2 contains four-coordinated mercury with an approximate tetrahedral geometry. A bridging SCN group links successive Hg atoms in the chain by moderately strong Hg—S (2.648(5) Å) and Hg—N (2.40(1) Å) bonds. The coordination sphere also includes phosphorus (Hg—P = 2.432(4) Å) and a unidentate S-bonded thiocyanate group (Hg—S = 2.454(5) Å). The chains are held together by normal van der Waals contacts.
The structure and fragmentation of protonated carboxylic acids in the gas phase
Authors: Middlemiss Nora E. , Harrison Alex. G.
Published: May 2006

Gaseous protonated acids fragment in the first drift region of a double focussing mass spectrometer to yield the corresponding acylium ion and water. The metastable peaks for this fragmentation reaction have been recorded for the protonated acids from acetic to valeric and the kinetic energy release distributions evaluated from the metastable peak shapes. The protonated acids were produced by dissociative ionization of the ethyl, propyl, and butyl esters. The results provide evidence for two structures for gaseous protonated acids. Fragmentation of the hydroxyl protonated structure, a minor contributor to the metastable peak intensity, shows a low kinetic energy release (T(most probable) = 0.02 eV) as would be expected for a simple bond fission reaction. Fragmentation of the carbonyl protonated acid, which represents the major part of the metastable peak, is accompanied by a muchlarger kinetic energy release (T(most probable) = 0.30 to 0.43 eV). This result is interpreted in terms of an activation barrier for fragmentation of the carbonyl protonated acid which is considerably greater than the reaction endothermicity, with the excess energy being partitioned between internal energy and kinetic energy of the fragments. The results indicate that the addition of the acylium ion to water in the gas phase to produce the carbonyl protonated acid has an activation energy barrier.
Relation entre structure et réactivité dans les réactions d'addition nucléophile sur les dérivés carbonylés: influence des interactions diaxiales-1,3 sur la réactivité de cyclanones et cyclanols stériquement encombrés
Authors: Boyer Bernard , Lamaty Gérard , Moreau Claude , Geneste Patrick
Published: May 2006

The rate constants for the addition of sodium borohydride to the sterically hindered cyclic ketones, 3,3,5-trimethylcyclohexanone (2), 3,3,5,5-tetramethylcyclohexanone (3), bicyclo[3,2,1]-3-octanone (4), tricyclo[5,2,1,03,8]-3-decanone (5), tricyclo[5,3,1,03,8]-5-undecanone (6) and bicyclo[3,3,1]-3-nonanone (7) have been determined at 25 °C in a 50/50 by volume mixture of water and dioxane. The values demonstrate energies due to 1,3-diaxial interactions that arise on passing from the initial to the transition states. The measured energies of activation represent almost the total conformational energy corresponding to these interactions, suggesting a late transition state.Comparison of the rates of reduction of these ketones where the carbon atom at the site of attack passes from sp2 to sp3 hybridisation, with the rates of chromic acid oxidation of the corresponding alcohols showing therefore the opposite change in hybridisation, indicates that the magnitude of the 1,3-diaxial interactions can serve to determine the position of the transition state along the reaction coordinate.The observed differences in reactivity can also contribute to the elucidation of conformational problems. [Journal translation]
The transannular electrophilic reaction of alkenyl nitroso compounds and the stereochemistry of nitrosyl chloride addition
Authors: Chow Yuan L. , Pillay K. Somasekharan , Richard Hervé
Published: May 2006

Nitrosyl chloride reacted with 1,5-cyclooctadiene and trans,trans,trans-1,5,9-cyclododecatriene in methylene chloride by the cis-addition to give chloronitroso alkenes with cis and threo (trans) configuration, respectively. These enantiomorphic C-nitroso compounds were isolated as a single compound for the former, and a mixture for the latter, of dl and (or) meso dimers, the presence of which was readily monitored by 13C nmr spectroscopy. The former can assume a conformation to place the π-bonds of the nitroso and olefinic groups in interacting vicinity and undergo an acid catalyzed intramolecular electrophilic cyclization to give bicyclic hydroxylamines which are readily air oxidized to the corresponding nitroxide radicals. Rearrangement in acetic anhydride – methylene chloride afforded good yields of the stable bicyclic hydroxyl-amine acetates which served as precursors to generate the corresponding nitroxides under mild conditions. Photoaddition of N-nitrosopiperidine to 1,5-cyclooctadiene also partly afforded the cis-aminonitroso adduct which underwent the intramolecular addition to give hydroxylamines. The threo(trans)-chloronitroso alkenes failed to cyclize in similar fashion under comparable conditions. Nitrosylchloride added exclusively to the trans-double bond of trans,cis-1,5-cyclo- decadiene without regiospecificity but was believed to follow the stereospecific cis-addition; this chloronitroso compound also underwent the acid catalyzed transannular reaction to give similar hydroxylamines that were not isolated in pure states.
An isokinetic relationship in the oxidation of acetals by ozone. Evidence for rotation before the oxidation of acyclic acetals
Authors: Taillefer Roland J. , Thomas Shirley E. , Nadeau Yves , Beierbeck Helmut
Published: May 2006

Second order rate constants for the oxidation by ozone of several acyclic acetals of heptaldehyde were determined at several temperatures. An isokinetic relationship is shown to exist for this series of reactions and the isokinetic temperature was found to be below the experimental temperature range, a domain of temperatures where reactivity is dominated by entropy factors. These results are contrasted with those obtained for cyclic acetals of heptaldehyde, where the isokinetic temperature falls above the working temperatures, a domain of temperatures where reactivity depends mainly on enthalpy factors. These results are interpreted in terms of a conformational change before oxidation in the acyclic acetals.
Artificial carbohydrate antigens: the synthesis of the tetrasaccharide repeating unit of Shigella flexneri O antigen
Authors: Josephson Staffan , Bundle David R.
Published: May 2006

The synthesis of a tetrasaccharide glycoside, 8-methoxycarbonyloctyl O-2-acetamido-2-deoxy-β-D-glucopyranosyl-(1 → 2)-O-α-L-rhamnopyranosyl-(1 → 2)-O-α-L-rhamnopyranosyl-(1 → 3)-α-L-rhamnopyranoside, representing the repeating unit of the Shigella flexneri serogroup Y O antigen is reported, together with that of a component trisaccharide. Both oligosaccharide glycosides are functionalised to permit covalent attachment to immunogenic carriers and solid matrices. A key intermediate used to establish α-1,2-rhamnopyranoside linkages was 2-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranosyl chloride (1), which was obtained in quantitative yield from 3,4-di-O-benzyl-1,2-O-(methoxyethylidene)-β-L-rhamnopyranose. Thus 8-methoxycarbonyloctyl 3,4-di-O-benzyl-α-L-rhamnopyranoside (2) prepared from the rhamnopyranosyl chloride 1 was used in a second Koenigs–Knorr reaction to provide an α-1,2-linked disaccharide. The disaccharide is in turn glycosylated at the C-2′ position with tri-O-acetyl-2-deoxy-2-phthalimido-D-glucopyranosyl bromide to provide the trisaccharide glycoside, 8-methoxycarbonyloctyl O-2-acetamido-2-deoxy-β-D-glucopyranosyl-(1 → 2)-O-α-L-rhamnopyranosyl-(1 → 2)-α-L-rhamnopyranoside. Application of the same reaction sequence to a rhamnopyranoside selectively blocked with benzoate esters at C-2 and C-4 gave the S. flexneri tetrasaccharide repeating unit. The success of this strategy was dependent upon the ability to use selective transesterification conditions, which permit removal of O acetate groups whilst leaving benzoate esters intact.
The preparation and Raman spectra of SeBr3AsF6, SeBr3SbF6, TeBr3AsF6, and normal coordinate analyses of the tribromosulphur(IV), tribromoselenium(IV), and tribromotellurium(IV) cations
Authors: Brooks W. V. F. , Passmore Jack , Richardson E. Keith
Published: May 2006

SeBr3AsF6 and TeBr3AsF6 were prepared from the elements and an excess of bromine and arsenic pentafluoride, as well as from Se4(AsF6)2 and Te4(AsF6)2 with excess bromine. SeBr3SbF6 was prepared from Se4(SbF6)2 and bromine, and TeBr3AsF6 from tellurium tetrabromide and arsenic pentafluoride. Br3AsF6 was found to oxidize arsenic trifluoride and sulphur dioxide to arsenic pentafluoride and SO2BrF respectively. Reaction pathways to the tribromochalcogen cations are discussed. Raman spectra of the tribromochalcogen salts were obtained. Assignments were confirmed, and force constants derived from normal coordinate analyses and compared with those derived for SBr3+, PBr3, AsBr3, and SbBr3.
Studies on trifluoromethanesulfonic acid. Part 2. Conductivities of solutions of metal trifluoromethanesulfonates and other bases in trifluoromethanesulfonic acid
Authors: Russell David G. , Senior John B.
Published: May 2006

Electrical conductivity measurements are reported for solutions in trifluoromethanesulfonic acid of a number of simple and complex bases, including univalent and divalent metal trifluoromethanesulfonates. The univalent metal salts, water, aniline, and acetic acid behave as fully dissociated bases, while the alkaline earth metal salts show considerable ion association. The trifluoromethanesulfonate anion appears to have an abnormally high mobility, as compared to the metal cations, and is believed to conduct by a proton-transfer mechanism. Dissociation constants for some weak organic bases and association constants for strontium and barium trifluoromethanesulfonates are estimated. Sulfuric acid behaves as a weak electrolyte, while sulfur trioxide is effectively a non-electrolyte. The conductivities of potassium nitrate and potassium dihydrogenphosphate are consistent with the formation of the nitryl cation and the phosphate acidium ion, respectively.
Transfer free energies of alkali metal chlorides and of some individual ions in glycerol and water mixtures
Authors: Basumullick Indra N. , Kundu Kiron K.
Published: May 2006

Staqndard free energies of transfer, ΔGt0, of alkali metal chlorides from water to aqueous mixtures of 10, 30, 50, and 70 wt.% glycerol have been determined from emf measurements of the double cell comprising Ag AgCl and K(Hg) electrodes at 25°C. These values were divided into individual ion contributions by use of tetraphenyl arsonium tetraphenyl boride (Ph4AsBPh4) assumption, the required ΔGt0 values of the reference electrolyte (Ph4AsPh4B), obtained by measuring solubilities of KBPh4, Ph4AsPi, and KPi (Pi = picrate) in the solvents. The solvation behaviour of the involved ions, as dictated by their respective ΔGt0(i) values, in this as well as in systems of other similar co-solvents like ethanol, ethylene glycol, and urea, suggests that it is determined by one or several effects of acid-base, Born-type, and dispersion interactions. Moreover, comparable stability of PH4B, particularly in aqueous glycerol and urea, suggests that "specific interactions" are possibly responsible for the well_known folding-unfolding phenomenon of native conformation of proteins in presence of co-solvents.
Cell surface carbohydrates for targeting studies
Authors: Ponpipom M. M. , Bugianesi R. L. , Shen T. Y.
Published: May 2006

Syntheses of a series of glycolipids with 6-(5-cholesten-3β-yloxy)-1-thiohexane as the aglycon and the following carbohydrates as surface determinants are described: D-glucose, D-mannose, D-galactose, 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose, L-fucose, L-arabinose, D-xylose, N-acetyl-D-neuraminic acid, lactose, and cellobiose. These 6-(5-cholesten-3β-yloxy)hexyl 1-thioglycopyranosides have been incorporated into phospholipid vesicles for invivo tissue distribution studies.
Binuclear and mononuclear nickel(II) and zinc(II) complexes of the tetradentate ligand 1,4-di(2′-pyridyl)aminophthalazine
Authors: Doull James Alfred , Thompson Laurence Kenneth
Published: May 2006

Previous studies with the title ligand, PAP, have shown a predominance of binuclear complexes with cobalt and copper in which the ligand-to-metal ratio is 1:2. The nickel complexes produced are more varied in composition; e.g., 1:2 binuclear systems [PAPNi2X(OH)(H2O)4]X2 (X = Cl, Br); 1:1 binuclear systems [PAP2Ni2(H2O)4]X4 (X = Cl, Br), [PAP2Ni2(NCS)3]NCS, [PAP2Ni2(OH)I2]I•2H2O, [PAP2Ni2(OH)(H2O)2]X3 (X = ClO4, BF4, I); and 2:1 mononuclear systems [(PAPH)2Ni(H2O)2]X4 (X = I, BF4). Zinc forms both mononuclear, [PAPZnX2]•H2O (X = Br, I), and a 1:1 binuclear system, [PAP2Zn2Cl4]. Triple bridges are suggested between the nickel atoms in all binuclear systems involving bridging hydroxy groups. Weak antiferromagnetic exchange is observed (−J < 10 cm−1) in two binuclear nickel complexes, which is enhanced in the presence of a hydroxy bridge. Spin–spin coupling is assumed to occur via a superexchange mechanism. In all cases nickel appears to be six-coordinate while for the zinc complexes both four- and six-coordination are observed.