bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotope effect studies of the decomposition of 2-propanol on hafnium(IV) oxide
Authors: Hoodless Ian M.
Published: May 2006

The catalytic decomposition of 2-propanol on hafnium dioxide has been investigated over the temperature range 355–397 °C by a micropulse reactor technique. The major reaction is one of dehydration to propene but dehydrogenation also occurs to a small extent. Isotope effect measurements with deuterio-2-propanols indicate that the rate-limiting step in dehydration involves cleavage of the β-carbon-hydrogen while in the dehydrogenation reaction it is cleavage of the α-carbon-hydrogen bond.
Studies of the rhenium-oxygen bond. III. The crystal and molecular structure of 1-oxo-6-ethoxo-2,4-dichloro-3,5-dipyridinerhenium(V)
Authors: Lock Colin James Lyne , Turner Graham
Published: May 2006

The crystal and molecular structure of the title compound has been examined by single crystal X-ray diffraction. The crystals are monoclinic with a = 28.045(10), b = 8.766(3), c = 12.376(5) Å, β = 91.14(3)°. The space group is C2/c and there are eight molecules per unit cell. A total of 5053 independent reflections, of which 2860 were observed, were examined on a Syntex [Formula: see text] diffractometer. The structure was refined by full matrix least squares to an R2 value of 0.0449. The ligands form a very rough octahedron around the rhenium atom with Re—Cl(1), 2.441(3); Re—Cl(2), 2.366(3), Re—O(1), 1.684(7); Re—O(2), 1.896(6); Re—N(1), 2.144(7); Re—N(2), 2.132(7) Å. The pyridine rings are a dominant factor in determining the details of the molecular structure.
Carbon monoxide activation by bromorhodate complexes; a catalyzed reduction of iron(III)
Authors: James Brian R. , Rosenberg George
Published: May 2006

Kinetics have been studied for the decomposition of Rh(CO)Br52− to cis-Rh(CO)2Br2− in aqueous HBr solutions at 60 °C under a carbon monoxide atmosphere. A hydrolysis step leads to formation of rhodium(I) which is stabilized as the dicarbonyl; this dicarbonyl then reacts with Rh(CO)Br52− in an autocatalytic process to give more Rh(CO)2Br2− via a mixed valence [RhI … Br … RhIII] bridged intermediate. Ferric ion may be reduced according to the net reaction:[Formula: see text]using the bromorhodate(III or I) complexes as catalyst, and the kinetics of this process are also reported.
13C nuclear magnetic resonance studies. 64. The 13C spectra of a variety of bicyclo[3.2.1]octanols
Authors: Stothers J. B. , Tan C. T.
Published: May 2006

The 13C nmr spectra of a series of 20 bicyclo[3.2.1]octanols and -octenols have been determined to examine the shielding effects of the hydroxyl group on the skeletal carbons in this ring system. For comparison, the previously unreported data for a few closely related alcohols in the [2.1.1], [2.2.1], and [3.2.2] systems were also collected. The utility of these substituent effects for configuraional and conformational assignments is discussed.
N-Methylamino acids in peptide synthesis. V. The synthesis of N-tert-butyloxycarbonyl, N-methylamino acids by N-methylation
Authors: Cheung S. T. , Benoiton N. Leo
Published: May 2006

The preparation of enantiomerically pure N-tert-butyloxycarbonyl,N-methylamino acids by N-methylation of the parent amino acid derivatives using sodium hydride and methyl iodide in tetrahydrofuran at room temperature is described for neutral amino acids including O-benzyl-protected threonine and tyrosine. Methylation of the O-benzylserine derivative under these conditions gives the N-methyldehydroalanine derivative. The β-elimination is completely suppressed, giving the corresponding N-methylserine derivative when the reaction is carried out at 5 °C. Other related data on N-methylation and N-methylamino acid derivatives are presented.
Velocity separation of isotopic mixtures in underexpanded supersonic beams
Authors: Redpath A. E. , Menzinger M.
Published: May 2006

The velocity distributions of the heavy components in CD4/CH4/He(H2) supersonic beams were measured by time-of-flight and the slippage with respect to the seeding gas was investigated as a function of nozzle pressure and temperature. The isotopic species attain different velocity distributions. Following a proposal by Anderson and Davidovits, isotope separation factors are calculated both for the present system and, by analogy, for 235UF6/238UF6/Ar(He,Xe).
The use of polymer supports in organic synthesis. VIII. Solid phase syntheses of insect sex attractants
Authors: Leznoff Clifford C. , Fyles Thomas M. , Weatherston J.
Published: May 2006

A 2% cross-linked divinylbenzene–styrene copolymer, incorporating trityl chloride groups, (1), was used in the synthesis of insect sex attractants of Lepidoptera by two independent routes. Polymer 1 reacted with the symmetrical diols 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol to give the monoblocked polymer-bound diols 5–7, respectively. Mesylation of 5–7 gave the polymer-bound monomesylates 8–10, which on coupling with 1-lithio-1-hexyne or 1-lithio-1-butyne gave the polymer-bound alkyne trityl ethers 18–20. Alkynols, obtained by hydrolysis from polymers 18-20, were selectively reduced and acetylated to give cis-7-dodecen-1-ol acetate (28), cis-9-tetradecen-1-ol acetate (29), and cis-11-tetradecen-1-ol acetate (30), the sex attractants of Trichoplusia ni (Hübner), Spodoptera frugiperda (J. E. Smith), and Argyrotaenia velutinana (Walker), respectively. Alternatively, polymer-bound 1,7-heptanediol (33), polymer-bound 1,9-nonanediol (34), and 7 were oxidized with the Sharpless reagent (CrO2Cl2/tert-butyl alcohol/pyridine) to give polymer-bound aldehydes 35–37, which on reaction with Wittig reagents and subsequent hydrolysis and acetylation gave 28, 29, and 10-tetradecen-1-ol acetate (47), the sex attractant of Archips semiferanus (Walker). A 'reverse' Wittig synthesis of 47 was achieved by the reaction of polymer 10 with molten triphenylphosphine followed by base and treatment with butyraldehyde. Subsequent cleavage and acetylation gave 47 in high yield and stereoselectivity containing greater than 91% of the cis isomer.
An electron spin resonance and CIDNP study of the structure and reactivity of some excited triplet biphenyl ketones
Authors: Vyas Harish M. , Wan Jeffrey K. S.
Published: May 2006

The correlation of structure and reactivity of some excited triplet biphenyl ketones was approached by a combined esr and CIDNP study. The low temperature esr study confirmed the assignment of the triplet π,π* as the lowest triplet state in these biphenyl ketones. An analysis of the zero-field energies suggests that these π,π* triplets have a structure with both the biphenyl and the carbonyl groups being coplanar. Consequently a substantial unpaired spin density may result at the carbonyl oxygen atom which could lead to abstraction reactions. The CIDNP results are consistent with the triplet photoreduction mechanism. The polarization is mainly due to the cage products and the polarization magnitude is therefore dependent upon the light intensity
Toward an understanding of rates of crystal nucleation from solution with a variable driving force
Authors: Massey Ronald E. , Hileman Jr O. E.
Published: May 2006

'Number-time' data obtained during studies on the nucleation from aqueous solution of CaSO4•2H2O (gypsum) using the droplet technique and a variable driving force are reported. Sulfate ion was generated, in situ, by the reaction between S2O82− and S2O32− in the presence of Ca2+. The rate of the reaction was determined from polarographic data. The stoichiometry and solubility of the precipitate in the aqueous matrix were determined.Problems which arise during analysis of 'number-time' data obtained from droplet experiments with a large spread in individual droplet volumes and a variable driving force using techniques suggested in the literature are commented upon. A new technique was developed and applied to the analysis of our data. The effects of a non-steady state rate of nucleation, variable lag times and a decreasing cation: anion ratio on the derived results are discussed.
The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp≠ for displacement of the nitrate ion in water
Authors: Koshy Kalavelil Matthew , Mohanty Rajani Kanta , Robertson Ross Elmore
Published: May 2006

Values of ΔCP≠ have been obtained for the hydrolysis of 1- and 2-adamantyl nitrate in water and of 1-adamantyl nitrate in 0.2 mol fraction ethanol–water and acetonitrile–water. The limiting value of ΔCP≠ for displacement of the NO3− ions in water is more negative than −130 cal mol−1 deg−1. Much less negative values in mixed solvents show that the large negative values obtained for hydrolysis in water derive in some manner from the structural properties of water. The mechanistic implications of these facts are discussed.
Sign reversal of geminal 13CH3—C—15N coupling in configurationally isomeric fragments
Authors: Buchanan Gerald W. , Dawson Brian A.
Published: May 2006

The signs of geminal 15N—C—13CH3 couplings in configurationally isomeric acetophenone oximes have been determined relative to those of the vicinal 15N—C—C—H interactions using an off resonance proton decoupling technique. In the Z-isomer where the nitrogen lone pair is cis to the coupled carbon, the coupling is large and negative, whereas in the E-isomer, the geminal 15N—C—13CH3 coupling is small and positive in sign.
Ab initio calculations on 4-substituted benzoic acids; a further theoretical investigation into the nature of substituent effects in aromatic derivatives
Authors: Mezey Paul G. , Reynolds William F.
Published: May 2006

Ab initio (STO-3G) molecular orbital calculations for 4-substituted benzoic acids and XCH3–HCO2H pairs are used to derive a theoretical field, TF and resonance, TR(BA), substituent scale. Comparison with previous calculations for 4-substituted styrenes shows that a common field scale can be used for different systems but that different resonance scales are necessary, depending upon the electronic nature of the probe group. The field effect primarily reflects the direct electrostatic interaction between the substituent and the carboxylic acid. However, there are also significant contributions due to field-induced polarization of the intervening phenyl π electron system. By contrast, the π polarization effect seems to be the dominant field effect in the case of non-interacting probes (such as carbon atomic charges or chemical shifts). A very close parallel is noted between substituent effects upon atomic charges and acid dissociation energies.
Solvent effects on thermodynamics and mechanism of dissociation of the monocomplex of nickel(II) with thiocyanate
Authors: Chattopadhyay Praphulla Kumar , Kratochvil Byron
Published: May 2006

Rate constants and associated activation parameters for dissociation of (NiSCN)+ were measured kinetically in methanol and dimethylsulfoxide by stopped-flow spectrophotometry using copper(II) as the decomposing ion. The data along with previous results by others on dissociation of (NiSCN)+ in water, acetonitrile, and N,N-dimethylformamide are discussed mechanistically by considering the effect of solvent donor properties on the activation enthalpy for the dissociation process. Rate constants for dissociation at a single temperature are not systematically related to the Gutmann donor number of the solvent, but the enthalpy of activation for the dissociation process shows a linear inverse relation to the donor number. Pathways for dissociation of (NiSCN)+ in these solvents are accommodated within an Id-type mechanism.
Matrix effect on the structure of Ġe(CH3)3
Authors: Bonazzola Lydia , Leray Nicole , Roncin Jacques
Published: May 2006

An important matrix effect which can be correlated with the polarisability of radicals is observed for the 73Ge coupling constant of Ġe(CH3)3 radical.
Metal complexes as antioxidants. IV. Reaction of cupric dialkyldithiophosphates and dialkyldithiocarbamates with alkyl hydroperoxides
Authors: Chenier Joseph Hector Bernard , Howard James Anthony , Tait John Charles
Published: May 2006

The initial reaction of cupric dialkyldithiophosphates and dialkyldithiocarbamates with tert-butyl hydroperoxide and α-cumyl hydroperoxide is a free radical chain process. Initiation is achieved by a redox reaction between the complex and the hydroperoxide to give alkoxy and alkylperoxy radicals. The alkoxy radicals then abstract a hydrogen from excess hydroperoxide to give alkylperoxy radicals. The cupric complexes are converted to copper sulphate by reaction with peroxy radicals while the hydroperoxide is reduced to alcohol. About 5 mol of hydroperoxide are decomposed by each mole of complex. The decomposition of tert-butyl hydroperoxide then stops whereas complete destruction of α-cumene hydroperoxide occurs by a heterogeneous ionic reaction.The kinetics of the initial reaction are second-order for both complexes. The dithiophosphate reaction is first-order in each reactant while the dithiocarbamate reaction is zero-order in the complex concentration and second-order in the hydroperoxide concentration. Simple kinetics, however, only hold for the initial rates of complex disappearance. Total dithiophosphate decomposition exhibits three stages, an initial fast reaction followed by an induction period and a rapid third stage. The concentration–time profile for dithiocarbamate decomposition is quite different and the overall rate of reaction in some instances increases as the complex concentration decreases.
Effects of very high dose-rates on solvated electron yields (Extended Abstract)
Authors: Karolczak Stefan , Walker David C.
Published: May 2006

not available
A semicontinuum model with a structured first solvation shell for excess electrons in liquid and glassy alkanes
Authors: Kimura Toyoaki , Fueki Kenji , Narayana P. A. , Kevan Larry
Published: May 2006

The microdipole model for excess electrons in alkanes seems inconsistent with recent electron spin echo data. We develop a new model for electron binding in alkanes based on a semi-continuum potential framework in which the electron-polarizability energy is dependent on molecular structure by considering the electron interaction with the polarizability of each C—C bond of the first solvation shell molecules rather than with point molecules. In addition we incorporate the effect of hydrogen–hydrogen repulsion between first solvation shell molecules. This model accounts well for the variety of experimental data known for localized electrons in 3-methylpentane glass at 77 K and for electron localization or nonlocalization in various liquid alkanes consistent with electron mobility data.
Density-, temperature-, and concentration-induced metal–nonmetal transitions in fluids
Authors: Hensel F.
Published: May 2006

A brief review is given of the continuous metal–nonmetal transition observed in different fluid systems, with special emphasis on recent work by the author and his colleagues. Selected results of abroad experimental survey of the electrical and magnetic properties of fluid binary semiconducting alloys, expanded fluid metals, and fluid selenium are reported. The results are discussed with special emphasis on their relationship to some theoretical areas of controversy, especially the importance of the amount of covalency and ionicity for the electrical and magnetic properties of semiconducting alloys, the role of chemical bond satisfaction in covalent selenium and tellurium for the temperature-induced nonmetal to metal transition, and some speculations concerning the importance of fluctuations and microscopic inhomogeneity for the metal–nonmetal transition in expanded fluid metals. It is concluded that no theory of the metal–nonmetal transition is available which is generally valid for all the fluid systems discussed. It is proposed that measurements of the structure factor and of thermodynamic data of the fluids are necessary to make it possible to formulate a theory which is tested experimentally. The first new results of the structure factor and the compressibility of fluid expanded rubidium are reported.
Substituent effects on the triplet–singlet energy separation in diphenylmethylene
Authors: Humphreys Robert W. R. , Arnold Donald R.
Published: May 2006

The electron paramagnetic resonance (epr) spectra of the diarylmethylenes: diphenylmethylene, p-cyanodiphenylmethylene, p-methoxydiphenylmethylene, p,p′-dimethoxydiphenylmethylene, p,p′-dicyanodiphenylmethylene, p-cyano-p′-methoxydiphenylmethylene, have been studied. The zero-field splitting parameters have been determined. The signal intensity as a function of temperature (ca. 4–20 K) indicates these methylenes are ground state triplet species.
Synthesis of 3,5-dihydroxy-2,2-dimethylchroman-4-one and its implications for the structure of the phytotoxin stemphylin
Authors: Starratt A. N. , Stoessl A.
Published: May 2006

3,5-Dihydroxy-2,2-dimethylchroman-4-one was prepared by an unambiguous synthesis. Its spectroscopic properties and those of its methyl ether are incompatible with its identity as the aglycone moiety of the fungal toxin stemphylin.
Thermal and photochemical reactivity of cyclopropene derivatives: a semi-empirical molecular orbital study
Authors: Pincock J. A. , Boyd R. J.
Published: May 2006

The MINDO/3 semi-empirical MO method has been used to study the conversion of cyclopropene to vinyl carbene. In particular, the surfaces of the ground state and the first excited singlet and triplet states have been calculated. Additional calculations, including geometry optimization, have been carried out on vinyl substituted cyclopropenes. In general, the results are consistent with the known thermal and photochemical reactivities of cyclopropenes and the results of the few abinitio calculations on these species.
Studies of the rearrangements of aminoalkylsilanes to alkylaminosilanes
Authors: Duff James M. , Brook Adrian G.
Published: May 2006

A wide variety of aminoalkylsilanes (R3SiCR2NHR′) are rearranged to the isomeric alkylaminosilanes (R3SiNR′CHR2) by traces of n-butyllithium. It is shown that an equilibrium exists between the isomeric amide ions (N−) and carbanions (C−) which are involved as intermediates in the rearrangement. The values of the equilibrium constants were determined for several systems and in one case the rates and activation parameters were obtained for both the forward and reverse directions. The overall kinetics were also investigated for several systems and kinetic parameters were obtained. In some cases anion isomerization was the rate-controlling step; in other cases the rate-controlling step was the proton transfer between the starting amine and the carbanion which leads to product.
On the induced decomposition of α-phenylethylhydroperoxide by peroxy radicals
Authors: Hajdu I. P. , Nemes I. , Gál D. , Rubaylo V. L. , Emanuel N. M.
Published: May 2006

The induced decomposition of α-phenylethylhydroperoxide (HROOH) has been investigated in three different systems: hydroperoxide + cyclohexene + AIBN + O2 (I); cyclohexene substituted by isooctane (II), and cyclohexene substituted by chlorobenzene (III). The decomposition products of the HROOH were in all cases acetophenone (RO) and methylphenylcarbinol (HROH).It was established that peroxy radicals induced the decomposition. The considerable material balance deficit in I is due to the addition of the peroxy radicals to cyclohexene the rate constant of which was estimated from the experimental data. No material balance deficit was observed with II. Experiments supported the assumption that both RO and HROH were formed simultaneously in the interaction between peroxy radicals and HROOH.The rate constant of the reaction HRO2• + HROOH → HROH + O2 + HRO• was measured as k = 1.03 × 109 exp (−13 100/RT). It is suggested that in the autoxidation of ethylbenzene the induced decomposition of HROOH is fast enough to be the main source of RO and HROH.
Oxygen-18 isotope effects in the liquid water–pyridine system as a probe of intermolecular forces
Authors: Betts Robert H. , Bron Jan , Buchannon Wayne D. , Wu Kwok-Ying D.
Published: May 2006

Oxygen-18 exchange between gaseous carbon dioxide and water in liquid water–pyridine mixtures is used as a probe for changes in intermolecular forces when the composition of the system is changed from pure water to pure pyridine. In agreement with results obtained previously by other methods, it is found that the interaction energy of an 'average' water molecule with the medium decreases when the mole fraction of pyridine is varied from zero to unity. The experimental results are related to the vapour pressure isotope effect, P(H218O)/P(H216O), of the binary mixtures. The utility of the Stern – Van Hook – Wolfsberg equation for vapour pressure isotope effects has been investigated. In addition, a plot of the equilibrium constant of the oxygen-18 exchange reaction vs. the mole fraction of pyridine presents no evidence of the formation of stoichiometric pyridine–water complexes.
Thermodynamics of complex formation in binary liquid mixtures: application to systems containing acetonitrile
Authors: Lorimer John W. , Jones David E.
Published: May 2006

Equations for enthalpies and volumes of mixing are derived from thermodynamic association theory for complex binary liquid mixtures containing self-associating species and binary complexes. The various species can interact through general non-specific interactions of the simple mixture type.The equations, along with equations for the excess Gibbs energy, are applied to experimental data on excess Gibbs energies, heats, and volumes of mixing for the three binary systems formed from acetonitrile, carbon tetrachloride, and chloroform. The data require a theoretical model that involves two types of self-association of acetonitrile, one type of self-association of chloroform and formation of a binary complex CH3CN•2CHCl3. Thermodynamic parameters for the various types of association and interaction are derived by constrained least-squares methods, and provide a unified picture of the thermodynamic properties of these mixtures.
The kinetics of the reaction of boric acid with salicylic acid
Authors: Queen Alan
Published: May 2006

Salicylic acid forms a 1:1 complex with boric acid, the reaction involving both the fully protonated ligand, and the salicylate ion. The kinetics of this reaction have been studied by the stopped-flow method. The stability constant for the reaction involving salicylate ion has been calculated from measurements of the absorbances of solutions at equilibrium and is the same as that obtained from the kinetic data. The kinetic results at pH values in the range 3.45–4.63 suggest that, when salicylic acid is the ligand, the complex is formed in two steps. A similar process may also occur with salicylate ions.
Behavior of hydrogen atoms in the fragmentation of CH3CD3
Authors: Suzuki Isao H. , Maeda Kogoro
Published: May 2006

The behavior of hydrogen atoms in the fragmentation of CH3CD3 has been studied by use of a monoenergetic electron beam. Ionization efficiency curves for ions (m/e 3, 4, 15 to 18, 26 to 33) from CH3CD3 have been measured over ranges of 12 to 30 eV near their appearance thresholds. Mass spectra over various ranges of m/e have been measured at several electron energies. It has been found that at least two processes participate in the formation of C2X4+ and CH3+(X = H or D) and the rates of these processes depend on the energy of electron beam. The formations of C2X2+ and X2+ are independent of the electron energy.
Conformational study of a series of 6-substituted 5,6,7,12-tetrahydrodibenzo[a,d]-cyclooctenes by nuclear magnetic resonance spectroscopy
Authors: Renaud Roger N. , Bovenkamp John W. , Fraser Robert R. , Roustan Jean-Louis A.
Published: May 2006

The conformational properties of seven 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctenes bearing substituents at C-6 have been studied using variable temperature proton nmr spectroscopy. The position of the equilibrium between boat-chair (BC) and twist-boat (TB) conformers has been measured in several solvents. In contrast to the unsubstituted dibenzocyclooctene, appreciable amounts of TB conformer are present when C-6 is substituted by alkyl, hydroxy, or cyano substituents. Measurements at different temperatures showed the TB form to possess the greater entropy. Barriers to the BC → TB interconversion were determined by coalescence studies, using both approximate and complete line shape methods. Barriers ranged from 10.1 kcal/mol for the 6-keto derivative to 16.7 kcal/mol for the 6-hydroxy-6-methyl derivative.
The acid-catalyzed hydrolysis of phosphinates. III. The mechanism of hydrolysis of methyl and benzyl dialkylphosphinates
Authors: Abbas Khamis A. , Cook Robert D.
Published: May 2006

The rates of the acid-catalyzed hydrolysis of methyl dimethyl-, diethyl-, diisopropyl-, and di-tert-butylphosphinate in D2SO4–D2O and of p-methoxybenzyl, p-chlaorobenzyl, p-nitrobenzyl, and benzyl diethylphosphinate in H2SO4 – 70% w/w DMSO-H2O have been studied. The bell-shaped pH-rate profiles, the Bunnett–Olsen Φ (0.91 to 1.28), Bunnett w (2.28 to 3.52) and w* (−0.94 to +0.17), and Yates-McClelland r (0.61 to 2.6) values, and the entropies of activation (−18 to −24 eu) all support an A2 mechanism for the methyl esters. The suggested mechanism for the benzyl esters is a unimolecular hydrolysis (Aa11). This conclusion is supported by the pH-rate profiles, the Φr values (−0.12 to −0.29) and the entropies of activation (−4 to −7 eu). The pKa's of the esters are also reported and they range between −2.4 to −3.3.
Failure of the scaling laws in the thermal explosion of methyl isocyanide
Authors: Collister John L. , Pritchard Huw O.
Published: May 2006

Thermal explosions of methyl isocyanide have been studied in spherical reaction vessels with volumes in the range 300–5000 ml. The normal inverse dependence of the explosion limit on the square of the radius appears to hold over limited ranges, e.g. from 300–1000 ml and from 2000–3000 ml, but the explosion limits at 1000 ml and 2000 ml are characterized by markedly different values of the critical parameter δc. Temperature measurements were made at and near the vessel walls, but they do not reveal any abnormalities which could be used to explain these results.An appendix reports measurements of the thermal conductivities of methyl cyanide and methyl isocyanide from 200–350 °C.
Partial tosylation of 1,5-anhydro-D-glucitol
Authors: Kondo Yôtaro , Yabuuchi Kazuyoshi , Hirano Shigehiro
Published: May 2006

Dimolar tosylation of 1,5-anhydro-D-glucitol (1) in pyridine yielded the 2,6-di-O-tosylate (6) (35%) as the major product, along with the tetra-O-tosylate (2) (1%), the 3,4,6-tri-O- (3) (1%), 2,4,6-tri-O- (4) (8%), and 2,3,6-tri-O-tosylate (5) (6%), and the 3,6-di-O- (7) (4%) and 4,6-di-O-tosylate (8) (6%). The order of the relative reactivity of the hydroxyl groups in 1 towards tosyl chloride was predicted as 6-OH > 2-OH > 4-OH > 3-OH.
Ammonium salts of benzoic acid and the crystal structure of ammonium hydrogen bisbenzoate
Authors: Oxton Ian A. , Cameron T. Stanley , Knop Osvald , McCulloch Archibald W.
Published: May 2006

The ir spectrum of the isotopically isolated NH3D+ ion was used to deduce the possible site symmetries of the NH4+ ion in ammonium benzoate, NH4PhCOO, and ammonium hydrogen bisbenzoate, NH4H(PhCOO)2. The NH4+ ion in both crystals is strongly hydrogen-bonded, one of the two isotopically isolated ND frequencies in ammonium benzoate being the lowest such frequency reported to date. The site symmetry C2 of NH4+ in NH4H(PhCOO)2 has been confirmed by determining the crystal structure of this compound. The [Formula: see text] bond in the dibenzoate ion, [Formula: see text] is short, 2.46(1) Å, and probably symmetric.
The effects of counter ion nature on the adsorption of nitrate ion at the mercury/solution interface
Authors: Fawcett W. Ronald , Sellan James B.
Published: May 2006

The adsorption of nitrate ion at mercury has been studied from two systems at constant ionic strength, namely, xM NaNO3 + (0.2 − x) M NaF and x M KNO3 + (0.2 − x) M KF. The surface excess due to adsorbed nitrate ions was determined from differential capacity data using a modified version of the Hurwitz–Parsons analysis which takes into consideration variation in ionic activity coefficients with solution composition. The amount of adsorbed nitrate ion at a given electrode charge density and bulk nitrate ion concentration is shown to depend markedly on both ionic strength and the nature of the counter ion at the outer Helmholtz plane; when the charge in the diffuse layer is positive, an increase in ionic strength results in more anion adsorption and vice versa. A change in the cation from Na+ to K+ also results in increased anion adsorption. The effects observed are discussed in terms of the Stern–Grahame–Levine model for ionic adsorption which is based on an electrostatic description of the charged interface with consideration of discreteness-of-charge effects.
The heterogeneous catalytic reaction between carbon monoxide and nitrous oxide over manganous oxide and cobalto-cobaltic oxide
Authors: Krupay Bordan Walter , Ross Robert Anderson
Published: May 2006

The catalytic reaction between carbon monoxide and nitrous oxide has been studied on MnO from 493 to 573 K and on Co3O4 from 383 to 493 K. The apparent activation energy on MnO was 130 ± 4 kJ mol−1, while for Co3O4, a change from 31 ± 4 to 105 ± 4 kJ mol−1 was observed at 450 K. The rate-controlling step for the catalytic reaction on MnO was associated with the surface reaction between carbon monoxide and nitrous oxide in a manner similar to that previously reported for NiO, while for Co3O4, the rate-determining step was related to the formation of an intermediate surface carbonate. The changes in EA may be a consequence of the surface reaction proceeding via a concerted redox reaction in the low temperature region and then to a stepwise mechanism at higher temperatures resulting from the presence of structurally and energetically different forms of the intermediate surface carbonate.
The radiation chemistry of nitrogen: primary neutral dissociative excitation yield and the isotopic exchange mechanism
Authors: Boyd A. W. , Miller O. A. , Willis C.
Published: May 2006

Measurements of the yield of NO2 in N2–NO mixtures give a neutral dissociative excitation yield of [Formula: see text] in good agreement with those derived from excitation cross-section measurements and from product yield measurement in the radiolysis of N2–O2 mixtures.The dependence of exchange yields in the radiolysis of 28N2–30N2 mixtures on pressure, O2 concentration, and dose-rate has been measured. The results are consistent with a significant contribution to these yields from the isotopic exchange reaction of N+ with N2. They also indicate that dose-rates of the order of >1022 eV g−1 s−1 are required for the N2+ ions to contribute to the exchange yield.
Complex fluoroanions in solution. VII. Replacement of fluoride by trifluoroacetate
Authors: Brownstein S.
Published: May 2006

Binary fluorides of groups III, IV, V, VI, and VII of the periodic table form complex fluoroanions with the trifluoroacetate ion. There is frequently disproportionation to yield species containing more than one trifluoroacetate group. Fluorine and trifluoroacetate exchange reactions are usually slow on the nmr time scale at −70 °C.
Transition layer model of the oxide–electrolyte interface
Authors: Dignam Michael J.
Published: May 2006

A model of the oxide–electrolyte interface is proposed which accounts both for the Nernstian behaviour of the oxide (glass) electrode and the anomalous capacitance values of some oxides defined in terms of the change in surface charge with pH. The essential feature of the model is the existence of a transition layer of atomic dimensions in thickness within which is established an equilibrium between oxide and aqueous ionic species. The Nernstian behaviour of the oxide (glass) electrode is independent of the model chosen for the oxide–electrolyte double layer but requires that the oxide be conducting; the capacitance of the system, of course, is dependent on the detailed structure of the interface.
Vapour pressures of aqueous solutions of (Ag,Tl,Cd)NO3 at 98.5 °C. II. Henry's law and excess free energy
Authors: Abraham Marie-Christine , Abraham Maurice , Sangster James Malcolm
Published: May 2006

Curves of the water activity coefficient γw have been obtained as a function of water mole fraction in the mixtures AgNO3 + TlNO3 + Cd(NO3)2 + H2O at 98.5 °C. It has been shown, in this study, from the BET equation itself and verified experimentally, that γw may pass through an extremum value for certain systems. The position of such an extremum near the fused salt end of the concentration scale can explain the appearance of a 'practical' Henry's law in a finite concentration range. The curves of the excess free energy of the system undergo rather unusual changes of shape as the cadmium content of the melt is varied.
The formation of hex-5-enopyranosides and their selective hydrolysis in methylated polysaccharides
Authors: Aspinall Gerald Oliver , Rosell Karl-Gunnar
Published: May 2006

The introduction of hex-5-enopyranoside residues into methylated acidic polysaccharides is effected by reduction of uronic acid residues, followed by reaction with triphenyl phosphite methiodide, and dehydroiodination. The selective hydrolysis of hex-5-enopyranosidic linkages with characterization of the 6-deoxyglycos-5-uloses thus formed and location of the aglyconic hydroxyl groups thus exposed has been demonstrated for methylated derivatives of birch xylan and gum arabic. The reaction sequence provides a new method for linkage analysis of acidic polysaccharides.
Etude polarographique de l'antimoine(III) et (V) dans le fluorure d'hydrogène anhydre et dans ses mélanges avec l'eau
Authors: Devynck Jacques , Tremillon Bernard , Menard Hugues , Comarmond Germain
Published: May 2006

The electrochemical behaviour of Sb(III) and Sb(V) in water–HF mixtures (2.5 to 50% HF) and in anhydrous HF is described. A Teflon capillary dropping mercury electrode is proposed for polarographie investigations in these fluorinated media. It is shown, by classical or puise polarography, that Sb(III) can be reduced to Sb(0), as in acidic non-fluorinated media. The electrochemical reaction becomes reversible by addition of Cl−, Br− or I−. Sb(V) is not electroactive in the various HF-media, except when it is introduced as the SbCl5. In this case, the two polarographie waves of Sb(V) disappear with time because of SbF6− formation. Analytical applications to the determination of Sb(III) in water–HF and in anhydrous HF are discussed.
Kinetics and mechanism of the base hydrolysis of some trans-dihalogeno(cyclam)rhodium(III) complexes
Authors: Chung H. L. , Bounsall E. J.
Published: May 2006

The base hydrolysis of trans-[Rh(cyclam)XY]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane; X− and Y− = Cl−, Br−, and I−) are studied in aqueous solution over a range of OH− concentration and at various temperatures. The kinetics are done at a constant ionic strength with excess of [OH−] (smallest ratio = 200:1) so that pseudo first order rate constants are obtained for all the determinations. All of the reactions proceed with complete retention of configuration, and no trans-to-cis isomerization is found. The kinetic trans effect of these complexes is I− > Br− > Cl− on a rate basis, but based on ΔH≠, I− > Br− = Cl−. These Rh(III) complexes exhibit kinetic class (b) character on the ΔH≠ basis. The results of the rate constants and the activation parameters are interpreted in ternis of an SN1CB mechanism. The behavior of these complexes is compared to that of the other analogous complexes.
X-Ray, Raman, infrared, and nuclear magnetic resonance studies of the crystal structure of ammonium tetrachloroaluminate, NH4AlCl4
Authors: Mairesse Gaëtan , Barbier Pierre , Wignacourt Jean-Pierre , Rubbens Annick , Wallart Francis
Published: May 2006

Ammonium tetrachloroaluminate crystallizes in the orthorhombic System a = 11.022(6) Å, b = 7.072(3) Å, c = 9.257(5) Å, Z = 4, space group Pnma. The structure was determined by direct methods from diffractometer data and refined by full-matrix least-squares procedures to final R and Rw values of 0.053 and 0.069 respectively, for 596 reflections with I > 2σ(I). Hydrogen atoms were not observed. Al—Cl bond lengths are similar to those of other alkaline chloroaluminate salts (Li+, Na+, NO+). The salt is isostructural with NH4ClO4.Crystals and polycrystalline samples of this compound have been studied by Raman scattering above 10 K, and infrared spectra of specimens of a polycrystalline sample have been recorded in Nujol and a fluorolube above 80 K. Both methods enabled us to observe the bands corresponding to the ν1(A2), ν3, and ν4(F2) vibration modes of the ammonium ion but the infrared spectra contain no band due to combination modes involving the librations of this ion. Nuclear magnetic second moment remains equal to 4 G2 over the range 298–80 K. These spectroscopic results, compared to those of other ammonium salts, indicate that the ammonium ion seems to be freely rotating.The four characteristic bands of the AlCl4− tetrahedral anion have been studied by Raman scattering in the 298–10 K temperature range.
The pyridinium–dihydropyridine system. I. Synthesis of a series of substituted pyridinium ions and their 1,4-dihydro reduction products and a determination of their stabilities in aqueous buffers
Authors: Norris Donald J. , Stewart Ross
Published: May 2006

not available
Propriétés hydrodynamiques des conformations ordonnées et desordonnées du poly(γ-L-glutamate de benzyle): dimensions et flexibilité de la chaîne
Authors: Ho-Duc Nga
Published: May 2006

Theoretically we can determine the disordered or ordered structure of polypeptides and their dimensions in dilute solutions from hydrodynamic properties. We have presently a wealth of theories for random coil chains and a limited but sufficient number of theories for ordered chains for interpreting experimental results.Viscosity data for seven poly(γ-benzyl-L-glutamate) samples in 1,2-dichloroethane at 25 °C are analyzed and the length per monomeric residue (h) is calculated according to the equivalent ellipsoid approach. The degree of flexibility or rigidity is characterized by calculating Ns, the number of monomer units in a rigid segment or a Kuhn statistical segment; the determination of Ns is made by applying Yamakawa and Fujii's equation modified by Vitovskaya and Tsvetkov.Values obtained for h assuming the solute molecule to be a rigid, stiff chain, range between 1.3 to 2 Å. One notices that the h value close to 1.5 Å is found for the three following molecular weights: 1.8 × 105, 1.7 × 105, and 1.5 × 105. They are, in fact, the samples having a length in good quantitative agreement with that of the rigid segment determined by the method of Vitovskaya and Tsvetkov. This rigid segment corresponds to a sample of 700 ± 100 monomer units.The analysis of the experimental data of poly(γ-benzyl-L-glutamate) in dichloroacetic acid indicates that, in addition to the formation of hydrogen bonds, other interactions between the polypeptide and the solvent are present.In summary, we may conclude that the study of the helix–coil transition using hydrodynamic measurements is judged satisfactory but the determination of characteristic dimensions used to describe exactly the conformation of the macromolecule is somewhat ambiguous. One major problem is the degree of flexibility encountered with high molecular weight chains. However, to get around this difficulty, we propose, according to our results, a method which consists in determining the number of monomer units within a rigid segment from the different values found for h and then the dimensions from the samples for which the chain length is in good agreement with that of a rigid segment thus determined.
The reactions of metal acetylacetonates with acids
Authors: Nixon A. J. C. , Eaton D. R.
Published: May 2006

The reactions of a number of metal acetylacetonates with trifluoroacetic acid have been investigated using nmr. The initial reaction involves protonation on the carbon atom of the ligand. In the case of the aluminum compound in coordinating solvents there is further reaction to give cationic complexes. The results are used to reinterpret the kinetics of ligand exchange for this compound. It is argued that, contrary to previous suggestions, the slow step is the breaking of the first metal oxygen bond to form a dangling ligand intermediate. A consequence of this conclusion is that intramolecular rearrangements of Al(III) β diketonates must proceed by twisting rather than by bond rupture mechanisms.
Pulse radiolysis: evidence for the reaction of HO2 with NO2 in aqueous solution
Authors: Sutton Harry Callender , Seddon William Arthur , Sopchyshyn Fred Charles
Published: May 2006

Nitroform is the major radiation induced species observed after the pulse radiolysis of acidic oxygen saturated solutions of tetranitromethane (TNM) and formic acid. It is formed in three stages, of which a major component at pH < 3 is first order with t1/2 = 49 s, independent of [TNM] and pH. Evidence is provided for the reactions[Formula: see text]in which k14 = 0.014 ± 0.002 s−1. The data support similar conclusions reached previously in rapid mixingexperiments (1) from which it was concluded that k3 = 4 × 109 dm3 mol−1 s−1.Analysis of the fastest component of nitroform production over the pH range 1–4 shows that the COOH radical reduces TNM to nitroform with a rate constant about four times greater than that for its reaction with oxygen to produce HO2.
Aminoglycoside antibiotics. The total synthesis of 5-deoxykanamycin A
Authors: Kavadias Gerry , Dextraze Pierre , Massé Robert , Belleau Bernard
Published: May 2006

Condensation of 1,6-N,O-carbonyl-3-N-ethoxycarbonyl-2,5-dideoxystreptamine (7) with 6-azido-2,3,4-tri-O-benzyl-6-deoxy-α-D-glucopyranosyl chloride by the Koenigs–Knorr reaction produced the α-glycoside 10. The cyclic carbamate of 10 was opened with ethanol in the presence of sodium ethoxide and the resulting 4-O-(6-azido-2,3,4-tri-O-benzyl-6-deoxy-α-D-glucopyranosyl)-N,N′-diethoxycarbonyl-2,5-dideoxystreptamiue (12) was glycosidated with 3-acetamido-2,4,6-tri-O-benzyl-3-deoxy-α-D-glucopyranosyl chloride (21) to give the α,α-diglycoside 22. Hydrogenation of the azido group and removal of the protective groups gave 5-deoxykanamycin A (25), an antibiotic with a potency about half that of kanamycin A.
Reduction of some organic compounds by electrochemically generated titanium(III)
Authors: Christofis Olympia , Habeeb Jacob J. , Steevensz Richard S. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of titanium metal in the presence of an essentially non-aqueous electrolyte phase yields titanium(III) species in solution. It has been shown that this method of generating TiX3 (X = balancing anion) forms the basis of a convenient way of reducing insitu certain organic functional groups (sulfoxide, oxime, haloketone, vinyl dicarboxylic acid, and nitro aromatics). The stoichiometry of the reaction has been established in each case, and corresponds to the oxidation of TiX3 and the formation of the appropriate organic compound. The yields are comparable to those reported in experiments using aqueous titanous chloride.
Infrared studies of carboxylic acids and pyridine in chloroform and methanol
Authors: Dawa B. A. , Gowland Joan A.
Published: May 2006

The reactions of acetic, chloroacetic, and trichloroacetic acids with varying relative concentrations of pyridine in chloroform have been reinvestigated using infrared spectroscopy. The same Systems have also been studied in methanol. Some different assignments of peaks have been made, and the anomalous infrared results previously observed for trichloroacetic acid in chloroform are explained in terms of charge transfer complex formation.
Excited radicals in the gas phase photolysis of butene isomers at different photon energies: energy distribution in reaction products
Authors: Collin Guy J. , Więckowski Andrzej
Published: May 2006

A systematic study of the pressure effects on the quantum yields of some products between 0.1 and 600 Torr (13 and 80 000 N m−2) was carried out in the 7.6 and 8.4 eV photolysis of normal, iso- and cis-2-butenes. The propylene quantum yield (s-C4H9* → C3H6 + CH3) decreased with the increase in the n-butene pressure and a good linearity of S/D (stabilization/decomposition) vs. pressure plot, over a broad pressure region, was observed. It is concluded that hydrogen atoms involved in the s-C4H9* radical formation are produced with a relatively narrow energy distribution. The slope of S/D vs. pressure lines decreased with the increase in photon energy, indicating the trend in the kinetic energy of the H-atoms.In the case of isobutene and cis-2-butene photolysis, the Stern–Volmer plots for allene formation were nonlinear. It is concluded that the formation of two different allene precursors is needed to account for this result. By the use of a simple RRK-type formalism we also conclude that the excess energy of the photon in the primary photoexcited butene molecules is far from being randomized before their fragmentation occurs.[Formula: see text]
Extraction of cadmium salicylate with some nitrogen-containing organic bases
Authors: Singh J. M. , Tandon S. N.
Published: May 2006

Cd(HSal)2 is extracted from aqueous solutions into n-butanol, but not into non-hydroxylic solvents (such as benzene and chloroform) at pH 4.5 to 6.0. Addition of N bases, which have no effect alone, causes extraction into the latter solvents, apparently by displacement of coordinated water, giving Cd(HSal)2•2B. This synergistic effect varies with B (β-picoline > pyridine > quinoline). Formation and distribution constants are given for the experimental conditions.
Complexes of substituted benzothiazoles. 1. Cobalt(II), copper(II), and zinc(II) complexes of 2,2′-o-phenylenebisbenzothiazole; a potential N or S donor ligand
Authors: Rendell John Charles Thomas , Thompson Laurence Kenneth
Published: May 2006

A series of cobalt(II), copper(II), and zinc(II) complexes of the title ligand are reported. 1:1 complexes of cobalt and zinc, M(OBT)X2 (M = Co, Zn; X = Cl, Br, I, NCS), have four-coordinate pseudo-tetrahedral stereochemistries while for copper (X = Cl, Br), distorted square geometries are suggested. Six-coordinate 1:1 derivatives are also obtained for cobalt and copper, M(OBT)(NO3)2 (M = Co, Cu), while the 1:2 derivative Cu(OBT)2(ClO4)2-2H2O may be square planar. OBT appears to coordinate as an N2 donor in all cases. Preliminary X-ray data confirm a distorted square CuN2Cl2 structure for the copper chloride complex. Hydrogen bonded chloroform solvate molecules appear to be present in three cobalt complexes (X = Cl, Br, NCS).
The dependence of ionization and excitation energies for the cis-azo group upon bond angle
Authors: Baird N. Colin
Published: May 2006

Ab initio molecular orbital calculations using STO-3G and 4-31G basis sets have been performed for cis-HNNH and cis-CH3NNCH3 as a function of angle about the nitrogens, and for the cyclic molecules diazirine (1a) and diazetine (1b); in all cases the ground states of the neutral system and of the cation and anion and the first singlet excited state of the neutral molecule were studied. The optimum HNN angles for the cation and neutral excited n − π* singlet state of HNNH are significantly larger than for the anion and neutral ground state. Thus the ionization energy and singlet excitation energies for cis-azo Systems pass through a maximum in the region around a nitrogen angle of about 100°. The implications of these calculations to the excitation and photoelectron spectra of cyclic cis-azo compounds is discussed in some detail, as is the origin of the variation in stability with angle of the n − molecular orbital. Due to the heavy involvement of carbon, the n − MO in diazirine does not follow the angle trends established by the HNNH calculations.