bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic studies in solution. Part IV. Solvent effect on the solvolysis of tert-butyl chloride. A new treatment of the experimental data
Authors: Ramos Joaquim Jose Moura , Reisse Jacques , Abraham M. H.
Published: May 2006

A new treatment of the solvent effect on the solvolysis of tert-butyl chloride is proposed. This treatment is based on activation free energy measurements and on transfer free energy measurements of the reactant (R) on the one hand and of a model (M) of the activated complex (AC) on the other hand. Solute–solvent interaction free energies for the reactant, the activated complex and the model compound are estimated. This estimation involves the calculation of the free energy of cavity formation of these various solutes (R, AC, and M) in all the solvents. These cavity terms, which are a function of the cohesive properties of the solvent and of the surface of the cavity do not reflect the electronic structure of the solute whereas the interaction free energy term does. The method we propose can be described as a new 'experimental' approach for the study of the charge separation in an activated complex.
cis- and trans-Platinum compounds of substituted pyrimidines and their products from thiourea in Kurnakov's reaction
Authors: Kong Pi-Chang , Rochon F. D.
Published: May 2006

cis- and trans-[Pt(pm)2X2] (where pm = 2-aminopyrimidine, 4-phenylpyrimidine, 4-methyl-pyrimidine and X = Cl, Br) were prepared and characterized. The cis compounds were isolated from the reaction of K2PtCl4 and pm in water, while trans-[Pt(pm)2X2] was obtained by isomerization of cis-[Pt(pm)2X2] in dimethylsulfoxide. The cis- and trans-isomers react with thiourea (tu) to give different products (Kurnakov's test).[Formula: see text]The complexes trans-[Pt(pm)2(tu)2]X2 were isolated and characterized.
Correlation of the photoelectron and electronic spectra of thiochromones and thiochromanones with their electrochemical data
Authors: Loutfy Rafik O. , Still Ian W. J. , Thompson Michael , Leong Toong S.
Published: May 2006

The gas phase ionization potentials, electrochemical redox potentials and spectroscopic properties of a series of thiochroman-4-one and thiochromone derivatives have been studied. A dramatic shift in the energies of the lowest vacant and highest occupied molecular orbitals of the parent thiochromanone as a function of the addition of a double bond and/or oxidation of the sulphur atom was observed. This shift in energy of the molecular orbitals was reflected in their spectroscopic characteristics. The lowest singlet (and triplet) state of compounds 1–3 in solution is π,π* in nature, while that of compounds 4–6 is n,π*. These results are best explained in terms of substituent effects on the energetics of the acetophenone moiety. The change in the nature of the lowest excited state from π,π* (1–3) to n,π* (4–6) should result in quite different types of photochemistry for the two series.A linear free-energy relationship between the singlet and triplet energies and the absolute difference between the oxidation and reduction potentials of the two series was found. These correlations have been utilized to estimate the half-wave oxidation potentials of compounds 3–6. A correlation was found to exist between the gas phase ionization potential and the solution electrochemical oxidation potential.
Artificial carbohydrate antigens: synthesis of rhamnose disaccharides common to ShigellaflexneriO-antigen determinants
Authors: Bundle David R. , Josephson Staffan
Published: May 2006

Three disaccharides containing α-linked rhamnopyranoside units have been synthesised in a form suitable for covalent linkage to protein. The artificial antigens obtained in this manner represent structural elements similar to portions of the repeating unit of the ShigellaflexneriO-antigen. The glycosylation reactions leading to the disaccharides utilised silver trifluoromethanesulphonate and N,N-tetramethylurea, or sym-collidine, conditions which generated the three 1,2-trans-linked glycosides in high yield and stereospecificity. The blocking groups used in these syntheses are consistent with further chain extension to tri- and tetrasaccharides.2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl chloride and the 1,2-oxazoline derivative obtained from it were not effective in glycosylating the C-2 position of partially blocked rhamnopyranoside but 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-D-glucosyl bromide gave the desired 1,2-trans-2-amino-2-deoxyglucoside in good yield. Selective conversion of the phthalimido group to an acetamido function in the presence of an ester function was achieved, thereby extending the utility of the phthalimido protecting group to sequential oligosaccharide synthesis, in which 2-acetamido-2-deoxy-β-D-glucosides are internal units. Proton nmr evidence in support of the exo-anomeric effect is presented.
Excess properties of cumene + p-dioxane system at 30 °C
Authors: Sólimo Horacio N. , Alonso Silvia Del V. , Katz Miguel
Published: May 2006

Densities, viscosities, enthalpies, and magnetic susceptibilities at 30 °C were determined for the system cumene + p-dioxane. From the experimental results, the excess viscosity, excess enthalpy, excess volume, and excess molar magnetic susceptibility were calculated. The excess functions show deviations from the additivity law. An attempt has been made to explain the observed deviations on the basis of intermolecular interactions.
Determination of ΔH0f298(C6F10,g) and ΔH0f298(C6F12,g) from studies of the combustion of decafluorocyclohexene and dodecafluorocyclohexane in oxygen and calculation of the resonance energy of hexafluorobenzene
Authors: Price Stanley James W. , Sapiano Henry J.
Published: May 2006

The heats of formation of decafluorocyclohexene and dodecafluorocyclohexane have been determined by the direct combustion method previously developed and used for hexafluorobenzene and related compounds. The combustion of decafluorocyclohexene and dodecafluorocyclohexane formed the reaction products CO2, CF4, and F2. In both cases a portion of the compound remained unburned. The unburned material was collected and quantitatively determined gravimetrically. A material balance was obtained for carbon and fluorine on the basis of CO2, CF4, and F2 and the amount of unburned compound. With a ten-fold excess of oxygen, the average CO2-to-CF4 molar ratios for C6F10 and C6F12 are 2.03 ± 0.01 and 1.35 ± 0.01, respectively. The values obtained for the heats of formation are ΔH0f298(C6F10,g) = −1906.6 ± 7.2 kJ mol−1 and ΔH0f298(C6F12,g) = −2368.9 ± 7.6 kJ mol−1. ΔH0f298 for the reaction C6F10(g) + F2(g) → C6F12(g) was calculated to be −462.3 ± 14.8 kJ mol−1 and the 'resonance energy' of C6F6 is estimated at −36.4 kJ mol−1.
Raman spectra of single-crystal and liquid s-trioxane
Authors: Nakahara M. , Wong P. T. T. , Whalley E.
Published: May 2006

The polarized Raman spectrum of s-trioxane has been measured in single-crystal phase I, the melt, and the chloroform-d solution and the measurements used to improve the assignments, particularly in the C—H stretching region.
The catalytic reaction between carbon monoxide and nitrous oxide over chromium(III) oxide
Authors: Krupay Bordan W. , Ross Robert A.
Published: May 2006

The catalytic reaction between carbon monoxide and nitrous oxide over chromium(III) oxide has been investigated in a continuous flow system at atmospheric pressure from 525 to 583 K. Two kinetic regions with apparent activation energies of 172 ± 4 kJ mol−1 (525 to 559 K) and 239 ± 4 kJ mol−1 (565 to 583 K) were observed. The rate-controlling step in both regions was associated with the formation of an intermediate carbonate-like species during the consecutive decompositions of two nitrous oxide molecules. In the region of higher apparent activation energy, the presence of polymeric surface chromate groups may influence the reactivity of any carbonate-like intermediate and the subsequent desorption of carbon dioxide thereby leaving a vacant site for nitrous oxide decomposition.
Mercury(II) cyanide complexes of bulky phosphines. Preparation, characterization, and spectral studies
Authors: Goel Ram G. , Henry William P. , Ogini William O.
Published: May 2006

Mercury(II) cyanide forms 1:2 complexes with triphenylphosphine and tri-p-tolylphosphine. Both 1:1 and 1:2 complexes are formed with tricyclohexylphosphine but only the 1:1 complex is obtained with tri-tert-butylphosphine, and no complex is formed with tri-o-tolylphosphine. The complexes have been characterized by elemental analyses and by infrared and Raman spectral measurements. Their behaviour in solution has been investigated by conductance, molecular weight, and 31P nmr measurements. The infrared and Raman data for the 1:2 complexes are in accord with a pseudotetrahedral structure of C2v skeletal symmetry. At least one of the 1:1 complexes is indicated to have a dimeric structure involving terminal and bridging CN ligands. The C≡N, Hg—CN, and Hg—P stretching frequencies and the 31P—199Hg spin–spin coupling for the complexes are discussed.
Determination of rates of hydrogen atom reactions with alkenes at 298 K by a double modulation technique
Authors: Oka K. , Cvetanović R. J.
Published: May 2006

Hydrogen atoms and HgH radicals are the two precursors of the HNO(1A′′) chemiluminescence in the mercury photosensitized reaction of gaseous mixtures of H2, NO, and Hg and are responsible, respectively, for its slow and fast decaying component. The total intensity of the chemiluminescence is decreased when an olefin is added to the gaseous mixture and, with an excess of the olefin added, 85% of the luminescence is eliminated. This fraction corresponds to the slow component of the chemiluminescence, due to the reaction H + NO + M → HNO* + M, while the residual 15% is due to the reaction HgH + NO → HNO* + Hg. The magnitudes of the decrease of chemiluminescence intensity and of the increase of the rate of decay of its slow component at a given concentration of an added olefin provide information on the rate of H atom reaction with the olefin.Relative values of the rate constants of H atom reactions with ethylene, propene, 1-butene, cis-2-butene, trans-2-butene, isobutene, and 1,3-butadiene have been determined in the present work from the observed dependence of the luminescence intensity on olefin concentration. At the same time, the absolute values of these rate constants have been determined from the relation between the decay rate of the slower component of the chemiluminescence and olefin concentration. The relative and the absolute values of the rate constants are compared with each other, to check their mutual consistency, and with the available relative and absolute values in the literature.
Salt desorption from surfaces of non-aqueous solvents
Authors: Aveyard Robert , Thompson Yvonne
Published: May 2006

Following previous studies of the desorption of salts from the surface of water, the desorption of several salts from various non-aqueous solvents has been investigated. Three protic and 3 dipolar-aprotic liquids were used. The surface properties of the solvents in the absence of electrolytes are discussed and it is observed that the molar excess surface entropies of the aprotic solvents are more positive than those of the protic solvents. Salt desorption, determined from measurements of surface tension, is discussed in terms of purely electrostatic models, and also ion solvation. The extent of salt desorption in systems where strong ion solvation exists is related to the thickness of the primary solvation sheath around the ions. In the present context water does not behave as an anomalous solvent but in a way similar to the other protic solvents.
Etude des mobilités ioniques dans les mélanges eau–hexaméthylphosphotriamide (HMPT) à 25 °C. II. Application de la théorie de Zwanzig au comportement des ions monovalents
Authors: Gal Jean-Yves , Laville Christine , Persin Françoise , Persin Michel , Bollinger Jean-Claude , Yvernault Théophile
Published: May 2006

The electrical conductibilities of 19 1-1 MX electrolytes (M = alkaline, quaternary ammonium; X = perchlorate, halide, nitrate) in water–hexamethylphosphotriamide mixtures at 25 °C has been measured. The individual conductibilities of 17 monovalent ions in these mixtures were calculated using the hypothesis of ion equimobility in Bu4NBPh4. Following a critical review of the traditionally used methods, it has been shown that, from these results, Zwanzig's theory alone allows the objective assessment of ion–solvent interactions. However, this theory at its present state of development cannot be used to elucidate all the problems (because Zwanzig considers the displacement of the free ion) but it does distinguish the nature of the interactions between an ion and the solvent, depending on the mobility of that ion.
Bound complex and triple collision mechanisms for diatom dissociation and recombination
Authors: Snider Neil
Published: May 2006

A method was devised for estimating relative contributions to atom recombination from the bound complex and triple collision mechanisms. The method is based on three assumptions: a collinear model is valid, recrossings of a suitably chosen transition state surface equally affect both contributions to the recombination rate, and the two contributions correspond to crossings of parts of the transition state surface which differ only in total energy. Ratios of the rate constants for recombination by the two mechanisms were calculated for a classical model of Br and I atom recombination in rare gases. The ratios had already been obtained for the model from three-dimensional trajectory calculations. The results disagreed by as much as a factor of ten for helium as the third body, but they were within 50% or better for xenon. It was argued that the discrepancies are largely due to a breakdown of the second of the foregoing assumptions. The formula for the rate constant for recombination by both mechanisms together was extended to three dimensions at the expense of introducing an adjustable parameter. The extended formula was found to give results in agreement with the trajectory calculation to within 30% or better.
Crystal structure of dichlorobis(1-methylcytosine)cadmium(II)
Authors: Gagnon Carole , Beauchamp André L. , Tranqui Duc
Published: May 2006

Crystals of CdCl2(1-methylcytosine)2 belong to space group Cc, with a = 10.571(7), b = 24.35(2), c = 7.097(3) Å, β = 57.33(4)°, and Z = 4. The structure was refined over 1988 independent reflections to an R factor of 0.026. The structure consists of monomeric molecules in which cadmium has a (4 + 2)-coordination. Four strong bonds, two Cd—Cl (2.497, 2.485 Å) and two Cd—N(3) (2.281, 2.296 Å), define an approximate tetrahedron around the metal. Two carbonyl oxygens take part in weak Cd—O bonding interactions (2.677, 2.780 Å). The amino groups form only very weak intramolecular hydrogen bonds with chlorine and the difference >30° between angles Cd—N(3)—C(4) and Cd—N(3)—C(2) is ascribed to Cd—O bonding. Similar effects for other metal complexes are discussed in terms of steric hindrance of the amino group and bonding of the carbonyl group.
Reactions at the nitrogen atoms in azafluorene systems
Authors: Kloc Krystian , Młochowski Jacek , Szulc Zdzisław
Published: May 2006

Isomeric azafluorenones have been oxidized to N-oxides with H2O2 in acetic acid or in the presence of Na2WO4.In the same manner monoazafluorenes have been converted into azafluorene N-oxides, but oxidation of diazafluorenes led first to diazafluorenones which then formed diazafluorenone N-oxides. Azafluorenones and azafluorenes are readily N-methylated with CH3I to give methiodides. The relations between the rate constants of N-methylation and structural factors have been discussed.
Substituent effects in electron transfer reactions. II. The chromium(II) reduction of 2-acetylbutane-1,3-dionatobis(ethylenediamine)cobalt(III) and 3-acetylpentane-2,4-dionatobis(ethylenediamine)cobalt(III)
Authors: Balahura Robert J. , Lewis Nita A.
Published: May 2006

The chromium(II) reduction of the complexes en2Co(3-acetyl-ptdn)2+ (1) and en2Co(2-acetyl-btdn)2+ (2) has been studied. Both complexes obey the rate law [Formula: see text]At 25 °C, I = 1.0 M (LiClO4), k = (4.5 ± 0.2) × 10−4 M−1 s−1, ΔH≠ = 13.0 ± 0.7 kcal mol−1, ΔS≠ = −30 ± 2 eu for complex 1 and k = (5.6 ± 0.4) × 10−3 M−1 s−1, ΔH≠ = 11 ± 1 kcal mol−1, ΔS≠ = −30 ± 4 eu for complex 2. Product studies indicate attack at the uncoordinated acetyl functions in both complexes. The results are compared to those obtained for reduction of en2Co(3-formyl-ptdn)2+ and en2Co(ptdn)2+ by chromium(II).
Ab initio SCF and CI calculations for ground and low-lying valence and Rydberg excited states of HOCl and HClO in linear and bent nuclear conformations
Authors: Bruna Pablo J. , Hirsch Gerhard , Peyerimhoff Sigrid D. , Buenker Robert J.
Published: May 2006

Potential curves are reported for the ground and various valence and Rydberg excited states of HOCl and HClO using abinitio SCF and CI methods. The states of HOCl are found to be generally favored over their counterparts in HClO, but the calculations indicate that small barriers nevertheless exist for angular interconversion between at least some pairs of such states; they also show that dissociation processes involving ClO bond breaking are universally favored for both HOCl and HClO. Additional calculations for the ions have also been carried out, from which the heat of formation of HOCl+ is calculated to be 237 kcal/mol and it is pointed out that a previous estimate for the corresponding HOCl quantity has subsequently been substantiated by experiment; the relative energies of the first four states of HOCl+ are found to be in good agreement with experiment as well.
β-Lactams. VII. The synthesis of 3-vinyl and 3-isopropenyl 4-substituted azetidinones
Authors: Zamboni Robert , Just George
Published: May 2006

The reaction of crotonyl and dimethylacryloyl chloride with various Schiff bases is described. The resulting β-lactams derived from aliphatic amines all have a cis stereochemistry.
The self-association of naturally occurring purine nucleoside 5′-monophosphates in aqueous solution
Authors: Neurohr Klaus J. , Mantsch Henry H.
Published: May 2006

The parameters characterizing the base-stacking self-association of adenosine, inosine, and guanosine 5′-monophosphate have been obtained from 1H nmr dilution studies. The thermodynamic parameters for the formation of adenosine 5′-monophosphate stacks are ΔH0 = −14.5 kJ mol−1 and ΔS0 = −42.3 J K−1 mol−1, with an apparent equilibrium constant of Kc = 1.92 M−1 at 30 °C. The corresponding equilibrium constants for the self-association of inosine and guanosine 5′-monophosphate are 1.36 M−1 and 1.29 M−1, respectively. The negative enthalpy and entropy changes cannot be explained by the concept of classical hydrophobic interactions; however, they strongly support the conclusion that dipole induced dipole forces play a major role for base-stacking in aqueous solution. The sequence of the equilibrium constants for the purine nucleoside 5′-monophosphates can be well explained by the concept of mutual polarization. The stacking geometries for adenosine and inosine 5′-monophosphate are presented as obtained from fitting the experimental shift data to refined isoshielding contours. It is concluded that the stacking pattern is not restricted to a unique geometry.
1,2-Orthoacetate intermediates in silver trifluoromethanesulphonate promoted Koenigs–Knorr synthesis of disaccharide glycosides
Authors: Banoub Joseph , Bundle David R.
Published: May 2006

The three disaccharides lactose, cellobiose, and maltose in the form of their acetylated glycosyl bromides have been reacted with 8-ethoxycarbonyloctanol to provide the 1,2-trans-glycosides. Conventional Koenigs–Knorr and Helferich conditions provided these glycosides in poor yield but silver trifluoromethanesulphonate, N,N-tetramethylurea gave the disaccharide glycosides in 50–60% yield. Use of 2,4,6-trimethylpyridine as proton acceptor provided the corresponding 1,2-orthoacetates in 60–70% yield. These 1,2-orthoesters were rearranged by stannic tetrachloride to the 1,2-trans-glycosides. The isolation of acetylated 8-ethoxycarbonyloctanol from Lewis acid catalysed isomerisation of 1,2-orthoesters and from Koenigs–Knorr reactions in which N,N-tetramethylurea was the proton acceptor is discussed in terms of a reaction mechanism proceeding from glycosyl halide to glycosidic products via a 1,2-orthoester intermediate. This proposal is supported by 1H nmr evidence for the presence of 1,2-orthoacetate in Koenigs–Knorr reaction mixtures, and by 1,2-orthoacetate isomerisation to glycoside by the conjugate acid of N,N-tetramethylurea.
Stabilities of complexes (N2)nH+, and (O2)nH+ for n = 1 to 7 based on gas phase ion-equilibria measurements
Authors: Hiraoka K. , Saluja P. P. S. , Kebarle P.
Published: May 2006

The equilibria Bn−1H+ + B = BnH+ for B = N2, CO, and O2 were measured with a pulsed electron beam high ion source pressure mass spectrometer. Equilibria up to n = 7 could be observed. van't Hoff plots of the equilibrium constants lead to ΔGn−1,n0, ΔHn−1,n0, and ΔSn−1,n0. While the proton affinities increase in the order O2 < N2 < CO, the stabilities of the B2H+ towards dissociation to BH+ + B increase in the reverse order, i.e. CO < N2 < O2. The stabilities towards dissociation of B for BnH+ where n > 2 are much lower for all three compounds; however for N2 and CO the stability decreases only very slowly from n = 3 to n = 6, then there is a large fall off for n = 7. The (O2)nH+ clusters show large decrease of stabilities as n increases. The BnH+ (for n > 3) of CO are more stable than those of N2 or O2. The above experimental results can be partially explained with the help of results from molecular orbital STO-3G calculations for B, BH+, and B2H+ and general considerations. BH+ and B2H+ for CO and N2 are found to be linear while those for O2 are bent. The most stable O2H+ is a triplet, while (O2)2H+ is a quintuplet.
Double layer structure at the mercury/dimethylformamide interface
Authors: Fawcett W. Ronald , Ikeda Brian M. , Sellan James B.
Published: May 2006

The differential capacity of the mercury/solution interface has been measured for various tetraalkylammonium and alkali metal perchlorates in dimethylformamide (DMF) at 25 °C, and for tetraethylammonium perchlorate (TEAP) in DMF at −15 °C, 0 °C, and 40 °C. On the basis of established analyses, it is shown that ionic specific adsorption at mercury from TEAP solutions in DMF is negligible. The properties of the inner layer are analyzed in detail on the basis of a statistical mechanical model in which the solvent molecules represented as hard polarizable spheres can occupy three orientations: with their dipole vectors towards the surface, away from the surface, and parallel to the surface. It is shown that this model provides a reasonable description of the electrostatic properties of the inner layer at the Hg/DMF interface.
The nature of the NADP complex with manganese(II) ions as studied by proton and phosphorus magnetic resonance
Authors: Green M. Kirk , Kotowycz George
Published: May 2006

Proton and phosphorus magnetic resonance techniques have been applied to study the conformation of the complex formed between Mn(II) ions and nicotinamide adenine dinucleotide phosphate (NADP) in aqueous solutions at a pH of 7.5 and 20 °C. The dipolar correlation time (τc) for the Mn(II)–NADP complex at 20 °C was calculated to be 1.7 × 10−10 s, based on the measurement of proton longitudinal relaxation time ratios and a literature value of τc for nicotinamide adenine dinucleotide (NAD). The τc, as well as the 1H and 31P relaxation data together with the measured stability constant for this complex, were used to calculate the distances from the 1H and 31P nuclei to the Mn(II) ion. These distances are 3.8 Å to A8, 5.0 Å to A2, 4.5 Å to A1′, 5.3 Å to N2, 5.4 Å to N6, 5.5 Å to N5, 5.8 Å to N1′, and 6.3 Å to N4. The distances to the linkage 31P nuclei are 3.7 Å, and 3.3 Å to the adenosine ribose 2′-phosphate. Based on these distances, a model is proposed for the Mn(II)–NADP complex. In this complex, the Mn(II) ion is bonded to the oxygens of all three phosphates, and the adenine and nicotinamide bases are 7–8 Å apart and parallel. Hence the Mn(II) ion is located between and to one side of the two bases but is distinctly closer to the adenine base. The adenine base is in the anti conformation, whereas the nicotinamide moiety can be either syn or anti. Hence there is little or no close stacking of the two bases in the complex. The addition of Mg(II) ions to a solution of free NADP caused no observable shift of the aromatic proton peaks, indicating no differences in shielding effects. Hence the rings are probably similarly oriented in both free NADP and the metal–NADP complex. Effects on the transverse relaxation rates due to the paramagnetic metal ion (T2p−1) were also measured from the 31P linewidths as a function of temperature. The lifetime of the metal ion in the complex is 4.0 ± 0.5 × 10−6 s and ΔH≠ for the exchange process is 13.7 ± 0.5 kcal/mol.
Subtilisin Carlsberg, a chiral catalyst: an organic co-solvent
Authors: Beck John F. , McMullan John F.
Published: May 2006

The kinetics of subtilisin Carlsberg catalyzed hydrolyses of typical substrates in the presence of isopropanol indicate that this secondary alcohol could serve as a suitable organic co-solvent in synthetic applications of this enzyme.
Ketone or diazoalkane formation from Δ3-1,3,4-oxadiazolin-2-ones. Details of two competing thermolysis mechanisms
Authors: Paine Anthony James , Warkentin John
Published: May 2006

The title compounds thermolyse at 50–100 °C in a variety of solvents via two (and only two) competing unimolecular pathways, one producing a diazoalkane and carbon dioxide, the other a ketone, carbon monoxide, and dinitrogen. Diazoalkane formation is favoured by polar solvents and electron-donating substituents, with a Hammett ρ of −1.93 for seven p-substituted 5-methyl-5-phenyloxadiazolinones. Moderate solvent polarity effects, secondary kinetic isotope effects (2.1 ± 0.3% per D for 2b-d6), the Hammett ρ, and Frontier Molecular Orbital Theory, all support concerted diazoalkane formation through a transition state with nonsynchronous bond rupture.Neither decomposition mode shows any correlation with Taft steric parameters, Es, and ketone formation does not correlate with inductive parameters. The enthalpy change during the exothermic three piece fragmentation was calculated to be only −30 ± 2 kcal mol−1, precluding chemiluminescence. A vigorous search for intermediates by esr, ms, CIDNP, trapping, and racemization experiments leads to the conclusion that ketone formation must also be concerted.A new oxidation procedure using lead tetraacetate in the presence of five equivalents of trifluoroacetic acid was useful in the synthesis of oxadiazolinones from ketone semicarbazones which would not cyclize under normal LTA oxidation conditions.
Structure et réactivité. IV. Diastéréosélectivité de la réduction de cétones par le borohydrure de sodium. De l'influence de l'effet de champs de substituants polaires éloignés
Authors: Aycard Jean-Pierre , Lafrance Ronald , Boyer Bernard
Published: May 2006

The cyano group effect on diastereoselectivity is studied through the reduction of cis and trans 3-R 4-cyano cyclohexanones with NaBH4; the diastereoselectivity (zero for R = H) is 74 and 62% respectively (R = CH3) and 74 and 50% (R = (CH3)3C), the more stable isomer being always the major one. These stereoselectivities are rationalized from the experimental values of free enthalpy between conformers and from the diastereoselectivities of the 3-t-butyl (and 4-t-butyl) cyclohexanones, cis 3,5-dimethyl and 3,3,5-trimethyl cyclohexanones, without taking account of a cyano group specific effect. The decrease in diastereoselectivity for R = (CH3)3C (trans isomer) is associated with deformation induced by steric strain between the substituents.
Kinetics of solvent extraction of metal ions with HEDHP. III. The kinetics and mechanism of solvent extraction of Cr(III) from acidic aqueous solutions with bis-(2-ethyl hexyl) phosphoric acid in benzene
Authors: Islam Muhammad Fakhrul , Biswas Ranjit Kumar
Published: May 2006

The rate of solvent extraction of chromium(III) from aqueous sulphuric acid solutions (containing 0.05 mol dm−3 sulphate ion and 0.25 mol dm−3 acetate buffer, ionic strength, I = 0.40 mol dm−3) with bis-(2-ethyl hexyl) phosphoric acid (HDEHP or H2A2) in benzene has been measured under various conditions. The rate of backward extraction measurement of Cr(III) from organic phase to aqueous phase is not possible due to the inert property of Cr(III)–DEHP chelate. The forward rate is found to be first-order w.r.t. Cr(III) concentration in the aqueous phase and HDEHP concentration in the organic phase. The order w.r.t. H+ concentration varies from −1 to 1 over the pH range 1.5 to 5.25. The rate is found to decrease with increasing sulphate and nitrate ions concentrations in the aqueous phase. At (30 ± 1) °C, the rate expression, in the presence of sulphate, acetate, and nitrate ions, is found to be represented by:[Formula: see text]In the absence of the anions, the formation of CrHA22+ intermediate complex (Cr(OH)2+ + H2A2(0) → CrHA22+ + H2O) is the rate determining step at all acidities. The effects of the anions on the rate are discussed.
Comment: 7α-Acetoxydihydronomilin and mexicanolide: limonoids from Xylocarpus granatum (Koenig)
Authors: Ng Ang S. , Fallis Alex G.
Published: May 2006

A recent report by the present authors (Can. J. Chem. 56, 1020 (1978)) of the isolation of 7α-acetoxydihydronomilin from the seeds of Uncariagambia (Roxb.) contains a taxonomic error. The seeds were in fact from Xylocarpusgranatum (Koenig).
Infrared multiphoton chemistry of fluoroform-d
Authors: Gauthier M. , Pilon R. , Hackett P. A. , Willis C.
Published: May 2006

The infrared multiphoton chemistry of CF3D has been investigated in the ν2 and ν5 bands. The primary dissociation step forms DF and CF2. The major sink for the biradical is dimerization to form C2F4; this process preserves the 13C/12C isotopic selectivity which is reasonably high (α ≈ 20). The isotopic selectivity for 2H/1H is impaired by some scrambling reaction involving excited substrate. The possible nature of this scrambling reaction is discussed. In comparison with other CF3X systems (X = I, Br, Cl), CF3D is difficult to decompose, having low dissociation probability, and appears to decompose only after collisional activation.
A 1H and 13C nuclear magnetic resonance study of silicon and germanium chalcogenide derivatives
Authors: Drake John E. , Glavinćevski Boris M. , Humphries Robyn , Majid Abdul
Published: May 2006

This paper reports the 1H and 13C nmr parameters of the disilyl- and digermyl-chalcogenide species (MenH3−nM)2E, where M = Si, Ge; E = O, S, Se, Te and n = 0 to 3. The general pattern of changing shifts is markedly influenced by methyl substitution.
Metabolites of bird's nest fungi. Part 11. Diterpenoid metabolites of Cyathusearlei Lloyd
Authors: Ayer William A. , Lee Sing Ping
Published: May 2006

The bird's nest fungus Cyathusearlei Lloyd produces new diterpenoid metabolites of the cyathin type. Cyathatriol is shown to have structure 1 and has been correlated with cyathin A3. 11,15-O,O-Diacetylcyathatriol (2), 15-O-acetylcyathatriol (3), and 11-O-acetylcyathatriol (4) have also been isolated. The first cyathins containing only two oxygens, cyathin B2 (19) and allocyathin B2 (12), are also described.
Studies in membrane processes. IX. The bilayer structure in mixed dodecanoate/decyltrimethylammonium micelles of a novel type II mesophase
Authors: Lee Yunko , Reeves Leonard W. , Tracey Alan S.
Published: May 2006

Nematic lyotropic liquid crystalline materials, which spontaneously align in a magnetic field (Type II) have been prepared from a mixed detergent system consisting of potassium dodecanoate and decyltrimethylammonium bromide. This system has an advantage that the charge on the interface of the finite disc micelles can be readily varied. Sodium and bromide ion interactions with the interface have been investigated by nuclear magnetic resonance of the ions. Deuterium magnetic resonance spectra of deuteriated water and specifically deuteriated detergent chains have been obtained. The results show that there is a water structure built around the carboxylate headgroups which ceases to be stable when about 30% of potassium dodecanoate is replaced by decyltrimethylammonium bromide. Bromine magnetic resonance studies show that the bromide ion interacts only weakly with carboxylate but indicates, as would be expected, much stronger interaction with the trimethylammonium groups. The sodium ion in contrast was found to bind strongly with carboxylate and weakly with trimethylammonium. The sodium spectra indicate that the association of sodium with carboxylate is complex, involving two specific binding sites. Deuterium spectra from deuteriated hydrocarbon chains are interpreted in terms of the motional freedom of the individual chains. The results re-emphasize that the motional properties of a particular hydrocarbon chain of an amphiphile in the micellar bilayer is determined to a large extent by its headgroup and that the behaviour of one chemical species cannot be inferred from that of another.
Carbon catalyzed organic reactions: carbon promoted solvolysis of a phosphate ester derived from 1,1′-bi-2-naphthol
Authors: Hoyano Yumiko Y. , Pincock Richard E.
Published: May 2006

Active carbons which catalyze the racemization of 1,1′-binaphthyl are not effective in racemizing the 2,2′-dihydroxyl and the 8,8′-dicarbomethoxyl derivatives of binaphthyl. The 2,2′-binaphthyl methyl phosphate ester derived from optically active 1,1′-bi-2-naphthol undergoes slow thermal racemization at 190 °C (t1/2 100 min, ▵H≠ 26.1 kcal/mol, ▵S≠ −21 cal/mol deg) in triglyme and this racemization rate is also unaffected by active carbon. However, in the hydroxylic solvent 2-(2-ethoxyethoxy)ethanol at 130 °C the rate of solvolysis of the phosphate ester is increased ca. tenfold by carbon blacks or decolorizing carbon at 1 mg/mL concentration. Control experiments show that the acceleration is not due to soluble impurities released by the carbons; heterogeneous catalysis, probably by acidic and/or nucleophilic functional groups on the carbon surfaces, is involved.
Long-range phosphorus hyperfine coupling in a persistent nitroxide radical
Authors: Livant P. , Dudley R. L.
Published: May 2006

An unusually large long-range hyperfine coupling to γ-phosphorus has been observed in nitroxide 2. The magnitude of the coupling is ascribed to the rigidity of the ring system and the consequent importance of conformations like 7. The radical forms upon lengthy exposure of 1 to air. It may also be prepared by standard methods, and is stable over a period of months at 0 °C. Transient and as yet unidentified radicals are observed during the oxidation of 1 to 2 with aryl peracids.
Carbon-13 nuclear magnetic resonance spectra of E-silyl-alkenes
Authors: Tsipis Constantinos A. , Tsoleridis Constantinos A.
Published: May 2006

Carbon-13 nmr chemical shifts of a number of E-silyl-alkenes containing the silyl substituent at an sp2 carbon atom are presented. Assignments of the chemical shifts have been made by noting systematic variations in the spectra with changes in substituents and by comparison of the chemical shifts to those of the corresponding unsubstituted alkenes. The substituent effects observed were explained on the basis of the π-acceptor ability of the silyl substituents and the structure of the molecules. Comparing the 13C nmr spectra of the E-silyl-alkenes and those of the corresponding unsubstituted alkenes, differential chemical shifts have been obtained which can be used as empirical substituent parameters for the prediction of the 13C nmr spectra of other E-silyl-alkenes not yet studied. It was also demonstrated that 13C nmr spectroscopy can be used without resorting to special techniques (gated decoupling and the addition of paramagnetics) as an alternative method to the 1H nmr for the quantitative analysis of mixtures of regio-isomer E-silyl-alkenes.
Interaction of ruthenium(II) octaethylporphyrin with carbon monoxide on a fused-quartz surface
Authors: Corsini Alfio , Mehdi Husain , Chan Allen
Published: May 2006

When carbon monoxide gas is interacted with a methanolic reagent solution of hydrazine and K[Ru(III)OEP(CN)2] (OEP = octaethylporphyrin), a carbonylated complex of Ru(II)OEP is formed and excess carbon monoxide is strongly adsorbed on the walls of the fused-quartz reaction cell. The adsorbed carbon monoxide is very difficult to remove and unless appropriate measures are taken, it remains on the cell walls to interact with the reagent solution in subsequent experiments, thus leading to the possibility of erroneous interpretation. The amount of adsorbed carbon monoxide, while less than a complete monolayer, is significant.
The phase diagrams of the chlorides of the metals of Groups IIa and IIb with indium trichloride and water at 24 °C
Authors: Kartzmark Elinor M.
Published: May 2006

The double salt formation between indium chloride and the chlorides of Groups IIa and IIb has been investigated, and a comparison is made with the double salts of the Group I chlorides and indium trichloride. Three double salts of formula 2BeCl2•InCl3•(4–5)H2O, MgCl2•InCl3•(6–8)H2O, and CaCl2•InCl3•7H2O were found. The phase diagrams of the chlorides of Groups IIa and IIb with indium trichloride and water prove that the double salts MgCl2•2InCl3•10H2O, 2MgCl2•InCl3•12H2O, CaCl2•2InCl3•12H2O, 3CaCl2•4InCl3•30H2O, SrCl2•2InCl3•8H2O, SrCl2•InCl3•8H2O, ZnCl2•2InCl3•8H2O, and 2ZnCl2•InCl3•5H2O reported by Ensslin etal. (1) and recorded in Solubility of inorganic and metal organic compounds by Linke and Seidell (2) do not exist.
Acid catalysed hydrolysis of orthoesters: mechanism of hydrolysis of 2,4,10-trioxaadamantanes substituted in position 3
Authors: Bouab Otmane , Lamaty Gérard , Moreau Claude , Pomares Odile , Deslongchamps Pierre , Ruest Luc
Published: May 2006

The rates of hydrolysis of orthoesters, 2,4,10-trioxaadamantanes, substituted in position 3 (R = H, CH3, C2H5, C6H5) have been determined at 25 and 40 °C in dioxane/water (60:40 by volume). Substitution of hydrogen by the groups CH3, C2H5, and C6H5 shows clearly a decrease in rate: 0.018 (CH3), 0.014 (C2H5), and 0.003 (C6H5). This decrease, in accord with substituent effects, plus the strongly negative entropies of activation observed, suggests that the rate-determining step is the addition of water to the carboxonium ion intermediate.
Conformations of bridged diphenyls. XV. Crystal structure of (4′-carbomethoxy-2′-nitrophenoxy)benzene and the effect of intramolecular interactions in nitro substituents
Authors: Gopal Ramanathan , Chandler W. David , Robertson Beverly E.
Published: May 2006

The structure of (4′-carbomethoxy-2′-nitrophenoxy)benzene, C14H11NO5, has been determined by X-ray diffraction. The crystals are monoclinic, a = 8.880(7), b = 9.792(4), c = 14.820(5), β = 90.07(5), P21/c with Z = 4. The integrated intensities of 2966 independent reflections were measured on a four-circle diffractometer, 2072 of which were used in the refinement to give a final least-squares weighted residual of 0.062 and a conventional R factor of 0.086. The absence of ortho substituents on one ring of the molecule allows it to adopt the twist-nitro-distal conformation. The lengths of the bonds from the unsubstituted ring and the substituted ring to the bridging oxygen atom are 1.409(3) and 1.353(3) Å respectively. The torsional angles about those bonds are 54.6° and 16.5°. The angle subtended at the bridging oxygen atom is 120.0(3)°.The unusual thermal ellipsoids associated with one of the nitro oxygen atoms of this structure and with a nitro oxygen atom of three related structures occur when the nitro substituent is nearly coplanar with the phenyl ring on which it is substituted and also has a neighbouring substituent or bridging group. The unusual thermal ellipsoids then result from repulsive exchange forces.
Abinitio MO predictions for the geometries and energies of the Σ and II states of some conjugated free radicals
Authors: Baird N. Colin , Taylor Kathleen F.
Published: May 2006

Abinitio MO calculations are reported for the lowest Σ and Π doublet states of the radicals 1–10. Configuration interaction is included, using the restricted open-shell MO's as a base. The important geometric variables are optimized in calculations using the STO-3G basis set; in some cases energies and geometries are redetermined using the 4-31G basis. In most cases the energy separation between the Σ and Π doublet states is calculated to be small; the results are very dependent upon the basis set whenever the radical is localized upon a nitrogen atom. For radicals XYZ with different terminal groups, a valid prediction of the structure is obtained only if the basis set properly distinguishes between the π energies of X=Y and Y=Z bonds. Small basis sets appear to underestimate the π energy of carbonyl bonds, and thus are overbiased in favour of X=C—O••structures. Unsymmetrical structures are predicted for the Σ states of some radicals, even when the terminal groups are identical.
Infrared spectra of the ammonium ion in crystals. Part VIII. Spectroscopic criteria of highly-bent hydrogen bonds
Authors: Knop Osvald , Westerhaus Wolfgang J. , Falk Michael
Published: May 2006

Available evidence suggests that (1) the stretching frequencies of highly-bent hydrogen bonds decrease with increasing temperature, regardless of whether the bonds are static or dynamic in character, to a single acceptor or to several competing acceptors; and (2) departures from symmetric trifurcation (or bifurcation) toward asymmetric situations lower the stretching frequency. In further support of these criteria isotopic probe ion spectra between 10 K and room temperature have been obtained for taurine and for trigonal (NH4)2MF6 (M = Si, Ge, Sn, Ti). Evidence of a low-temperature transition at 100(10) K in trigonal (NH4)2SnF6 is presented, and existence of the previously reported transition at 38.6 K in trigonal (NH4)2SiF6 is confirmed. Symmetry changes associated with these transitions are discussed.
The preparation and oxidation of disulfides as a route to sulfone-sulfides
Authors: Ahern Terence Patrick , Fong Harvey Owen , Langler Richard Francis , Mason Peter Michael
Published: May 2006

Mercaptide/alkoxide competition in substitution and addition reactions is discussed as it applies to the preparation of disulfides. Oxidation of an asymmetric disulfide with H2O2 is shown to exhibit high regioselectivity which may be rationalized in the same terms employed for other sulfide oxidations, viz. substituent electron withdrawing ability (Xp) and steric effects.
On the nature of the radical pairs involved in the Grignard reaction
Authors: Schaart Barend Johannes , Blomberg Cornelis , Akkerman Otto Sjouke , Bickelhaupt Friedrich
Published: May 2006

During the simultaneous reaction of alkyl bromides and of p-halosubstituted benzyl bromides with magnesium in THF/C6D6 (1:4), CIDNP net effects (emission) are observed in the 1H nmr spectrum. The effects are opposite to those occurring during the reaction of preformed ethylmagnesium bromide and the benzyl bromides. These results constitute firm evidence that only alkyl radical pairs [Formula: see text] are responsible for the CIDNP effects, and that the radicals R• are generated in the Grignard reaction proper, rather than in unrelated side reactions such as Wurtz coupling or metal halogen exchange.
Synthesis and characterization of octahedral and trigonal bipyramidal transition metal complexes incorporating chelating gallate ligands: crystal and molecular structure of [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Ni[(N2C5H7)2GaMe2]
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The preparation and physical properties of octahedral and trigonal bipyramidal complexes incorporating the tris-chelating ligands [Me2Ga(N2C5H7)(OCH2CH2NR′2)]− (R′ = H or Me) are described. Crystals of [dimethylbis(3,5-dimethyl-1-pyrazolyl)gallato (N(2),N′(2))][dimethyl (3,5 - dimethyl-1-pyrazolyl) (N,N-dimethylethanolamino(gallato (N(2), O, N(3))]nickel(II) are triclinic, a = 20.8562(11), b = 9.1536(4), c = 8.2798(4) Å, α = 100.204(3), β = 85.513(4), γ = 101.989(3)°, Z = 2, space group [Formula: see text]. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.048 and Rw = 0.078 for 5508 reflections with I ≥ 3σ(I). The coordination about the Ni atom is distorted trigonal bipyramidal with the two nitrogen atoms from the Me2Ga(N2C5H7)2 ligand occupying equatorial positions. The tridentate Me2Ga(N2C5H7)(OCH2CH2NMe2) ligand is meridionally coordinated with the oxygen in the equatorial and the two nitrogens in the axial positions. Important bond lengths (corrected for libration) are: Ni—N(eq), 2.005(3) and 2.006(3), Ni—O, 1.993(3), Ni—N(pz—ax), 2.072(3), Ni—N(amino), 2.229(3), Ga—O, 1.913(3), Ga—N, 1.971(3)–1.989(3), and Ga—C, 1.961(10)–1.986(6) Å.
Activity corrections for ionic equilibria in aqueous solutions
Authors: Sun Mian S. , Harriss Donald K. , Magnuson Vincent R.
Published: May 2006

Activity corrections for ionic equilibria in aqueous solutions at 25 °C and ionic strengths up to 0.5 have been investigated. An empirical formula for activity corrections was generated by statistically fitting stability constant data for approximately 540 complexes, for which both thermodynamic and concentration stability constants were known, to a modified Debye – Hückel relationship. The general formula is[Formula: see text]χ > 0, where Δ log K is the difference in the logarithms of the stability constants at infinite dilution and finite I (I ≤ 0.5), and χ is an even integer dependent only on the stoichiometry and charge of the ions involved. Activity correction formulae for ionic equilibria involving classes of ligands (amino acid, inorganic, amine, and organic acid) also were developed. The general formula predicts stability constant corrections within 0.1 log unit for 87 % of the data used at ionic strength 0.1 and 64 % of the data at ionic strength 0.5. In addition, single ion activity coefficients as a function of ionic strength, 0 < I ≤ 0.5, are presented.
An infrared study of water in perfluorosulfonate (Nafion) membranes
Authors: Falk Michael
Published: May 2006

We have studied the infrared spectra of H2O, D2O, and HDO in hydrated Nafion membranes in the sodium form. The spectrum of isotopically isolated HDO exhibits two distinct absorption bands in the OH stretching region and similarly in the OD stretching region. These bands have been taken to correspond to two distinct environments of the OH groups in Nafion, identified as [Formula: see text] and[Formula: see text]. It appears that a substantial proportion of water molecules have an OH group (or occasionally both OH groups) exposed to the fluorocarbon environment. This implies that the hydrated ion clusters are either much smaller than previously estimated or, more likely, are non-spherical in shape with frequent local intrusions of the fluorocarbon phase. Water in Nafion is much less strongly hydrogen-bonded than water in aqueous salt solutions at the same temperature and may be expected to have distinct physical properties.