bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and evaluation of novel β-lactam inhibitors of human leukocyte elastase
Authors: Koteva K P , Cantin André M , Neugebauer W A , Escher E
Published: April 2011

A series of β-lactam derivatives were synthesized and tested to determine the structure-activity relationship for inhibition of human leukocyte elastase (HLE), a serine protease involved in several degenerative lung and tissue diseases. The most potent IC50values were obtained with neutral hydrophobic 7α-methoxy cephalosporanic acid derivatives. Tryptophanyl-9-fluorenylmethyl ester and N-benzhydryl piperazine derivatives of 7α-methoxy cephalosporanic acid represent two novel HLE inhibitors, with length of action persisting beyond 24 h.Key words: β-lactams, neutrophil elastase, protease inhibitors, peptides.
Détermination de la stabilité du complexonate peu soluble à partir des données pH-métriques
Authors: Povar Igor
Published: April 2011

A new method has been developed for the determination of the solubility product of complexonate of known composition; because of the initial composition of the heterogeneous mixture (lot a), it uses only the equilibrium values of the pH. For the determination of the stability constant in solution, these data have been completed with information on the solubility of the precipitate. We have shown that, on the basis of lot a and in the absence of reactions of formation of complexes in solution, it is possible to evaluate the equilibrium constants, since they are residuals of the compositions of the precipitate. We conclude on the possibility of applying this method to the test and standardization of ion-selective electrodes. The qualities and defect of the method are discussed. Otherwise, the values for the equilibrium constants and the equilibrium as well as the residual concentrations that we have calculated for a series of real systems from known experimental data are in good accord with those reported in tables under the same conditions.Key words: potentiometric method, heterogeneous system, slightly soluble complexonate, complexone, equilibrium concentration, solubility product, stability constant, hydrolysis reaction.[Journal Translation]
Intra- and inter-ion-pair protonic-hydridic bonding in polyhydridobis(phosphine)rhenates
Authors: Abdur-Rashid Kamaluddin , Lough Alan J , Morris Robert H
Published: April 2011

The hexahydridobis(phosphine)rhenate anions, [ReH6(PR3)2]- (PR3 = PCy3, P-i-Pr3, PPh3, PMe3) were generated by potassium hydride deprotonation of the neutral heptahydride conjugate acids (ReH7(PR3)2), isolated as their [K(18-crown-6)]+ and [K(1,10-diaza-18-crown-6)]+ salts, and characterized by NMR and IR spectroscopy and elemental analyses. Structures from single crystal X-ray diffraction were obtained for the [K(1,10-diaza-18-crown-6)]+salts and these indicate the presence of short protonichydridic bonds involving the hydrides of the anions and the proton donor NH moieties of the cations. The structure of [K(1,10-diaza-18-crown-6)][ReH6(P-i-Pr3)2] adopts a one-dimensional zigzag chain with alternating cations and anions connected and held together by inter-ion N-H···Hx-Re interactions (x = 1 or 2). Short distances between the NH protons of the cations and hydrides of the anion ranging from 1.6 to 1.9 Å are estimated for this complex. A different kind of chain structure is observed for [K(1,10-diaza-18-crown-6)][ReH6(PMe3)2] in which the combined effects of inter-ion protonichydridic bonding (N-H···Hx-Re) and inter-ion electrostatic interactions (ReH-x···K+···H-xRe), result in one-dimensional networks of alternating cations and anions, with the metals and hydrides occupying the interior and the organic moieties of the phosphine ligands and crown ether lining the exterior of cylindrical supramolecular assemblies. A combination of intra- and inter-ion protonic-hydridic and intra-ion-pair electrostatic interactions in [K(1,10-diaza-18-crown-6)][ReH6(PPh3)2] result in the formation of discrete two-dimensional {[K(1,10-diaza-18-crown-6)][ReH6(PPh3)2]}4 tetramers. The PCy3 salt is disordered but appears to consist of isolated 1:1 ion pairs containing strong intra-ion-pair NH···HRe bonding. The solid-state IR spectra of the [K(1,10-diaza-18-crown-6)]+ salts show low-frequency shifts for the NH bands relative to [K(1,10-diaza-18-crown-6)][BPh4], and perturbed Re-H bands relative to those in the [K(18-crown-6)]+ salts. The magnitude of ΔνNH is related to the basicity of the anion as indicated by the pKαTHF of the conjugate acid form (ReH7(PR3)2), which increases as PPh3 < < PMe3 < P-i-Pr3 < PCy3. Solution 1H NMR, NOE, and T1 relaxation measurements of [K(1,10-diaza-18-crown-6)][ReH6(PPh3)2] indicate that these interactions also persist in toluene solutions of this compound.Key words: rhenium, hydride, phosphine, hydrogen bonding, self-assembly.
Equilibrium geometry, vibrational frequencies, and heat of formation of HOBr, HBrO2, and HBrO3 isomers
Authors: Santos Cristina Maria P , Faria Roberto B , Machuca-Herrera Juan O , Machado Sérgio de P
Published: April 2011

The equilibrium geometries, vibrational frequencies, heat capacity, and heat of formation for compounds of general formula HBrOx were calculated by DFT (BP and pBP methods) with DN* and DN** numerical basis sets. The comparison of our HOBr calculated results with the HOBr experimental values points out that the BP and pBP methods are as good as other ab initio and DFT methods related in the literature employing extended basis sets. The calculated HBrOx total energy and heat of formation values, at 0 and 298.15 K, present the following order: HOBr < HBrO; HOOBr < HOBrO < HBrO2; HOOOBr < HOBrO2 < HOOBrO < HBrO3. The HBrOx heat of formation was calculated using isodesmic and homodesmic reactions and the results show that, in general, the use of these reactions gives similar results.Key words: HOBr, HBrO2, HBrO3, DFT, numerical basis.
Reduction of hexaammineruthenium(III) ions by a series of tris(polypyridyl)chromium(II) ions  Revisiting the Cr(NN)33+/2+ self-exchange rate
Authors: Zahir K Omar
Published: April 2011

The kinetics of the outer-sphere oxidation of Cr(NN)32+ ions (NN = 2,2'-bipyridine, 1,10-phenanthroline, and their substituted analogs) by hexaammineruthenium(III) was studied using laser flash photolysis. The Cr(NN)32+ ions were generated via the reductive quenching of the *Cr(NN)33+ excited states by oxalate ions or by H2edta2. The second-order rate constants were found to vary with the driving force of the reaction. The rate constants increase from (7.1 ± 0.5) × 106 M1 s1 for Cr(5-Clphen)32+ to (2.6 ± 0.2) × 108 M1 s1 for Cr(4,7-Me2phen)32+. The self-exchange rate constant for the couple (Cr(NN)33+/2+) was calculated by applying Marcus cross relation to present and other known reactions of Cr(NN)3n+ ions, where n = 3 or 2 with various reactants and is estimated to be (6 ± 4) × 107 M1 s1.Key words: tris(polypyridyl)chromium(II)/(III) self-exchange rate, hexaammineruthenium(III), oxidation of Cr(NN)32+.
Kinetic study of the proton transfer reaction between 1-nitro-1-(4-nitrophenyl)alkanes and TBD and MTBD bases in acetonitrile solvent
Authors: Grzeskowiak Iwona , Galezowski Wtodzimierz , Jarczewski Arnold
Published: April 2011

The rates of proton transfer reactions between C-acids of the series of nitroalkanes with increasing bulk of R = H, Me, Et, i-Pr substituent as: 4-nitrophenylnitromethane (0), 1-(4-nitrophenyl)-1-nitroethane (1), 1-(4-nitrophenyl)-1-nitropropane (2), 2-methyl-1-(4-nitrophenyl)-1-nitropropane (3) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) have been measured in acetonitrile at pseudo-first-order conditions. The product of the proton transfer reaction with MTBD in acetonitrile is dissociated into free ions while that of the TBD reaction is composed of a comparable amount of ions and ion pairs. The second-order rate constants (k2H) for these bases of almost equal strength in acetonitrile (pKa= 24.70, 24.97 for MTBD and TBD) and C-acids 1, 2, and 3 are: 317, 86, 7.6 dm3mol1s1; and 15 200, 5300, 1100 dm3mol1s1, respectively. The appropriate primary deuterium kinetic isotope effects (kH/kD) are 12.5, 10.8, 6.9; and 9.9, 11.2, 12.6. The influence of steric hindrance brought by reacting C-acids and bases is discussed. The different structure of the transition states and the products as mono- and double-hydrogen bonded complexes for these series of C-acids and MTBD and TBD bases is manifested by a distinct reaction mechanism which we attempt to explain.Key words: proton transfer, kinetic study, C-acids, organic bases, acetonitrile, kinetic isotope effects.
Alkaline oxidative degradation of diphenylmethane structures  Activation energy and computational analysis of the reaction mechanism
Authors: Jurasek Lubo , Kritofová Lívia , Sun Yujun , Argyropoulos Dimitris S
Published: April 2011

A diphenylmethane model compound (2,2'-methylenebis[6-methoxy-4-methylphenol]) and residual kraft lignin were treated with alkaline hydrogen peroxide. Kinetic data for the disappearance of the model and the diphenylmethane structures in the residual lignin was collected. The activation energies for the degradation were found to be similar (54 ± 11 kJ mol1 for the model and 58 ± 5 kJ mol1 for the residual lignin). A comparison of the activation energies with the data of a previous study on a biphenyl model compound (3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol) showed a substantially higher activation energy for the degradation of the latter. Pathways for the degradation of 2,2'-methylenebis[6-methoxy-4-methylphenol] were proposed and the intermediates subjected to computational analysis using a semiempirical method (PM3). The results suggest that initially a common pathway exists, resulting in 2-[2-hydroxy-3-methoxy-5-methyl-phenylmethyl]-4-methyl-2,4-hexadienedioic acid. Then the pathway branches into three, resulting in three major degradation products. The main driving force of the reactions is the formation of radical sites after reaction with hydroxyl radicals and subsequent radical coupling with perhydroxyl radicals to form peroxides. All the reactions on the pathways are exothermic except for the transformations of peroxides into dioxetanes. The dioxetanes cleave exothermically resulting in ring cleavage and fragmentation. The computed data permitted for the rationalization as to why the diphenylmethane structures appear to be more labile than biphenyl structures under alkaline oxidative conditions.Key words: activation energy, alkaline oxidative degradation, computational chemistry, lignin, reaction mechanism.
1H NMR studies of proton transfer equilibria in hydrogen bonds  the role of the entropy
Authors: Langner Roland , Zundel Georg
Published: April 2011

The influence of the entropy on the proton transfer equilibria AH···B [Formula: see text]A···H+B in the dimethylphosphinic acid (DMP)-N-base and in the methanesulfonic acid (MSA)-N-oxide hydrogen bonds is studied by 1H NMR spectroscopy as a function of the ΔpKa, i.e., the pKa of the base minus the pKa of the acid. It is shown that with increasing ΔpKa the proton transfers to the N-oxide acceptor. In the DMP + N-base family of systems, first the double-minimum proton potentials (ΔH = 0) occurs and only with further increasing ΔpKa do the POH···N [Formula: see text] PO···H+N equilibria become symmetrical (ΔG = 0). ΔG and ΔH are connected by the GibbsHelmholtz equation, ΔG = ΔH TΔS. Hence, the reason of this effect is the large negative interaction entropy term (ΔSI) arising from the large order around the polar structure, which shifts the equilibria strongly to the left-hand side. With the MSA-N-oxide hydrogen bonds a single-minimum proton potential was found. The minimum shifts with increasing ΔpKa from the donor to the acceptor of the O···H+···N hydrogen bonds. It is shown that with increasing ΔpKa the proton potential becomes on average symmetrical, whereas the proton is still largely on the left-hand side. This result is also explained by the large negative interaction entropy due to the order of the environment if the proton is at the acceptor B.Key words: entropy, hydrogen bonds, infrared, spectroscopy, proton transfer.
Enantioselective synthesis of peperomins A, C, D, and analogs  Examination of diastereoselective cuprate conjugate additions to N-enoyl-4-diphenylmethyl-2-oxazolidinones
Authors: Sibi Mukund P , Johnson Michael D , Punniyamurthy T
Published: April 2011

A concise and general route to secolignans has been developed. The first total synthesis of secolignans peperomin A (1a), peperomin C (1b), and peperomin D (1c) was accomplished in ~28% overall yield over five synthetic steps. Peperomin analogs (1d) and (1e), possessing two differentially substituted aryl groups, were synthesized by a highly selective conjugate addition. The overall yield for the analogs 1d and 1e were 27 and 26%, respectively.Key words: peperomins, secoliganans, conjugate additions, 4-diphenylmethyl-oxazolidin-2-one.
A highly efficient strategy for the synthesis of 3-substituted salicylic acids by either directed ortho-lithiation or halogenmetal exchange of substituted MOM protected phenols followed by carboxylation.
Authors: Lau Stephen YW , Keay Brian A
Published: April 2011

A highly efficient synthesis of various 3-substituted salicylic acids is described starting from inexpensive starting materials and requiring no special apparatus.Key words: salicylic acids, ortho-metalation, halogenmetal exchange, methoxymethyl group.
Fourfold homologous anionic ortho-Fries rearrangement on a partially bridged resorc[4]arene
Authors: Middel Oskar , Verboom Willem , Reinhoudt David N
Published: April 2011

Fourfold homologous anionic ortho-Fries rearrangement in the twofold bridged tetra-O-carbamate 3 gave the tetrakis(carboxamidomethyl)resorc[4]arene 4 in 68% yield. Compound 3 was prepared by selective carbamoylation of methylresorc[4]arene 1, followed by the bridging of the remaining OH groups in tetra-O-carbamate 2.Key words: resorc[4]arenes, selective functionalizations, homologous anionic ortho-Fries rearrangement.
The nature of the transition state in diarylmethyl cation  nucleophile combination reactions as probed by secondary α-deuterium isotope effects
Authors: Pham Thuy Van , McClelland Robert A
Published: April 2011

Transition-state structures for the carbocationnucleophile combination reactions of (4-substituted-4'- methoxydiphenyl)methyl cations with water, chloride, and bromide ions in acetonitrilewater mixtures have been investigated by measuring the secondary α-deuterium kinetic and equilibrium isotope effects. Rate constants in the combination direction were measured with laser flash photolysis. Equilibrium constants were measured for the water reaction by a comparison method in moderately concentrated sulfuric acid solutions, for the bromide reaction via the observation of reversible combination, and for the chloride reaction from the ratio of the combination rate constant and the rate constant for the ionization of the diarylmethyl chloride product. The fraction of bond making in the transition state has been calculated as the ratio log (kinetic isotope effect):log (equilibrium isotope effect). For the water reaction, there is 5065% bond making in the transition state; this is also true for cations that are many orders of magnitude less reactive. The same conclusions, 5065% bond formation in the transition state independent of reactivity, have previously been made in correlations of log kw vs. log KR. Thus, two quite different measures of transition structure provide the same result. The kH:kD values for the halide combinations in 100% acetonitrile are within experimental error of unity. This is consistent with suggestions that these reactions are occurring with diffusional encounter as the rate-limiting step. Addition of water has a dramatic retarding effect on the halide reactions, with rate constants decreasing steadily with increased water content. Small inverse kinetic isotope effects are observed (in 20% acetonitrile:80% water) indicating that carbonhalogen bond formation is rate-limiting. Comparison of the kinetic and equilibrium isotope effects shows ~25 and ~40% bond formation in the transition states for the reactions with bromide and chloride, respectively.Key words: carbocation, isotope effect, transition state, halide.
Diastereoselective formation of 18-membered ring BINOL-hydrogen phosphonate dimers - Quasi-covalent hydrogen bonds?
Authors: Dabbagh Hossein A , Noroozi-Pesyan Nader , Najafi-Chermahini Ali R , Patrick Brian O , James Brian R
Published: April 2011

Diastereoselective syntheses of the unusual dimers, 4-heptyl-2-(2′-hydroxy-binaphthyl)hydrogen phosphonate (5) and the cyclohexyl analogue (7), are achieved by hydrolysis of 4-(3,5-dioxa-4-phosphacyclohepta[2,1-α;3,4-α′]-dinaphthalene-4-yloxy)heptane (4) and the cyclohexane analogue (6), respectively. Two out of eight possible pairs of monomers units are involved in the stereoselective formation of the dimer 5a of configuration BINOLR-PS:BINOLR-PS; this is determined by X-ray crystallographic data, which reveal a centrosymmetric, 18-membered ring structure with Ci symmetry, consisting of two monomers strongly hydrogen-bonded between the oxygen of P=O units and hydroxyl hydrogen atoms. Mass spectrometric, melting point, and thermal decomposition point data, as well as NMR data, support the presence of strong, quasi-covalent hydrogen bonds. Computational analysis suggests that the diastereoselectivity is controlled by molecularly constrained geometry of the monomer. Compound 7, although not characterized crystallographically, appears to be analogous to 5.Key words: 18-membered ring, phosphonate dimer, diastereoselectivity, hydrogen-bonds, computational analysis.
SOME COMPLEXES PRESENT IN AQUEOUS FERRIC CHLORIDE SOLUTIONS
Authors: Manning P. G.
Published: April 2011

not available
Thermal decomposition studies of ω-iodoacyl peroxides
Authors: Woolford R. G. , Gedye R. N.
Published: April 2011

The synthesis and thermal decomposition reactions in various solvents of 5-iodovaleryl, 6-iodohexanoyl, and 11-iodoundecanoyl peroxides are reported. In general, monomeric and dimeric ω,ω′-diiodides as well as varying amounts of alkyl iodides and, from the C5 peroxide, δ-valerolactone were found in all solvent systems. The corresponding ω-iodoacids were important as products only in methanol, where the methyl esters were found as well. Specific products such as cyclohexyl iodide, ω,ω′-chloroiodoalkanes, etc. from reaction with individual solvents were also obtained. The product formations are interpreted in terms of reactions of the appropriate ω-iodoacyl and ω-iodoalkyl radicals.
Models for the assignment of the chemical shifts for protons on the epoxide ring of 2,3-anhydroglycopyranosides
Authors: Sweet F. , Brown R. K.
Published: April 2011

The signal assignments for the protons of the epoxide ring in several 3,4-epoxy-2-alkoxytetrahydropyrans have been made by spin decoupling. Because of the close resemblance of these tetrahydropyrans to 2,3-anhydroglycopyranosides, these results have been used to make chemical shift assignments for the H-2 and H-3 protons of the latter compounds. For the compounds examined, the H-2 proton signal occurs at higher field compared to the position of the H-3 proton signal.
Mass spectra of alkylquinolines
Authors: Draper P. M. , MacLean D. B.
Published: April 2011

A study has been made of the fragmentation upon electron impact of monomethylquinolines, di-methylquinolines, monoethylquinolines, and monopropylquinolines. Deuterium labelled analogues of some of the alkylquinolines have been prepared and their fragmentation studied to gain insight into the mechanism of fragmentation. The fragmentation of the alkylquinolines is closely analogous to that of alkylbenzenes. Rearrangement of the molecular ion appears to precede the fragmentation process in many of the compounds studied. The fragmentation of 2- and 8-ethyl- and n-propylquinolines are influenced by the proximity of their alkyl side chains to the nitrogen atom.
Fermentation of long-chain compounds by Torulopsis apicola. IV. Products from esters and hydrocarbons with 14 and 15 carbon atoms and from methyl palmitoleate
Authors: Tulloch A. P. , Spencer J. F. T.
Published: April 2011

Esters and hydrocarbons, containing 14 and 15 carbon atoms, are converted to the hydroxy fatty acid portions of glycosides by Torulopsis apicola in yields of 10–20%. When C-15 compounds are fermented, almost half of the hydroxy acids which are produced are 16-hydroxy C-17 acids. The carbon chain of the substrate is first lengthened by two carbon atoms and then hydroxylated. Direct hydroxylation also occurs, to a lesser extent, giving both 14-hydroxy- and 15-hydroxypentadecanoic acids. Similar results are obtained when C-14 compounds are used. Lengthening of the chain followed by hydroxylation gives rise to hydroxy C-16 acids and direct hydroxylation produces 13-hydroxy- and 14-hydroxytetradecanoic acids. Primary and secondary C-14 and C-15 alcohols were also isolated from the products of hydrocarbon fermentation (2.5–5 % yield). Methyl palmitoleate is converted to hydroxy fatty acids in yields of 40–70%, the major component of which is 16-hydroxy-cis-9-hexadecenoic acid.
Synthesis of benzylidene-flavanones
Authors: Széll T. , Zarandy M.
Published: April 2011

Various procedures for the preparation of benzylidene-flavanones have been examined and von Kostanecki's method was found to give best results. A number of new 6-nitroflavanones are reported.
Sur la réduction par les hydrures complexes d'éthers énoliques dérivés de formyl-2 cyclanones. III. Ethers dérivés de la formyl-2 diméthyl-6,6 cyclohexanone
Authors: Richer Jean-Claude , Hachey Jean-Marie
Published: April 2011

The reduction of the O- and S-butylether derived from the 2-hydroxymethylene-6,6-dimethylcyclohexanone yields, in addition to the expected unsaturated aldehyde, 2-methylene-6,6-dimethylcyclohexanol.
Binuclear copper(I) complexes with bridging bis(diphenylphosphino)acetylene groups
Authors: Carty A. J. , Efraty A.
Published: April 2011

The preparations of some novel copper(I) complexes of the ligand bis(diphenylphosphino)acetylene are described.
Studies in ferrocene derivatives. V. Synthesis and nuclear magnetic resonance spectra of some ferrocenyl ethylenes
Authors: Horspool W. M. , Sutherland R. G.
Published: April 2011

Ferrocenylethylenes are readily synthesized from acylferrocenes and the appropriate triphenylphosphorane in dimethylsulfoxide. Details of the nuclear magnetic resonance spectra of 12 ethylenes have been recorded.
Refinement of the crystal structure of zirconyl chloride octahydrate
Authors: Mak Thomas C. W.
Published: April 2011

The crystal structure of zirconyl chloride octahydrate, ZrOCl2•8H2O, has been refined by the least-squares method with new three-dimensional data. Existence of the [Zr4(OH)8(H2O)16]8+ tetranuclear complex has been confirmed. However, the coordination polyhedron about each zirconium atom differs considerably from the D4d antiprismatic geometry reported previously. It is, in fact, more closely related to the D2d dodecahedron, and has twofold axial symmetry within the limits of experimental error. Mean bond lengths in the [Zr4(OH)8(H2O)16]8+ complex, which approximates closely to D2d point-group symmetry, are: Zr—OH (bridging) = 2.142 ± 0.019 Å and Zr—OH2 (terminal) = 2.272 ± 0.032 Å.
Angular distributions of recoil products from some reactions induced in 65Cu and 197Au by protons of energy 30–85 MeV
Authors: Dewanjee M. K. , Saha G. B. , Yaffe L.
Published: April 2011

Angular distributions of products formed in the reactions 65Cu(p,pn)64Cu, 197Au(p,pn)I96Au, and 197Au(p,p3n)194Au in the range of proton energy 30–85 MeV were studied. The angular distribution results of 64Cu and 196Au show forward peaking at low energy and sidewise peaking at higher energies. Approximate symmetry about 90° was observed for the angular distribution of 194Au in the center-of-mass system. The experimental results have been compared with (a) Monte Carlo evaporation calculations, (b) cascade–evaporation calculations at 85 MeV for 64Cu, and (c) inelastic scattering plus evaporation calculations.Good agreement was obtained with statistical theory calculations at low energy and inelastic scattering model calculations at higher energies. The comparisons indicate that the reactions proceed by the compound nucleus mechanism at lower energies and the direct interaction mechanism predominates at higher energies.
Cleavage of the carbon–phosphorus bond in chloromethyl–phosphorus compounds by phosphorus pentachloride
Authors: Frank Arlen W.
Published: April 2011

A novel carbon–phosphorus bond cleavage is described. Chloromethylphosphonic dichloride (2) and bis(chloromethyl)phosphinic chloride (1) both react smoothly and quantitatively with phosphorus pentachloride at 95–100°, giving carbon tetrachloride and a P(III) fragment containing one less carbon–phosphorus bond: phosphorus trichloride from 2 and trichloromethylphosphonous dichloride from 1. Under the same conditions, tris(chloromethyl)phosphine oxide (3) forms a complex (4) which subsequently breaks down to trichlorobis(trichloromethyl)phosphorane (5), diphenyl chloromethylphosphonate (7) suffers chlorination without cleavage, and tetrakis(chloromethyl)phosphonium chloride (6) is neither chlorinated nor cleaved. A concerted mechanism is proposed which accounts for ail of these results.
Polyatomic cations of the Group VIB elements. II. Compounds of the Se42+ cation
Authors: Barr J. , Crump D. B. , Gillespie R. J. , Kapoor R. , Ummat P. K.
Published: April 2011

The preparation and characterization of the compounds Se4(HS2O7)2, Se4S4O13, Se4(SO3F)2, and Se4(Sb2F11)2 are described. All four compounds are shown to contain the Se42+ cation.
Functionally substituted oligomeric stannoxanes
Authors: Wagner D. , Gertner D. , Zilkha A.
Published: April 2011

The successive insertion of Bu2SnO units of into Sn—Cl, Sn—OOCR, Sn—OAR, and [Formula: see text] bonds was found to lead to functionally substituted oligomeric stannoxanes.
Reaction of thionyl bromide with tropolone and phenol
Authors: Saraf S. D.
Published: April 2011

Tropolone and phenol react with thionyl bromide forming 3,7-dibromotropolone and 2,4-dibromophenol respectively.
Estimation expérimentale et théorique de l'effet de l'encombrement stérique du groupement tert-butyle sur le déplacement chimique des protons aromatiques de nitro-1 naphtalènes substitués
Authors: Odiot S. , Richer J. C. , Tonnard F.
Published: April 2011

not available
Heterocyclic system containing bridgehead nitrogen atom. Part III. 3-Substituted-, 2,3-disubstituted-5,6-dihydro-4H-imidazo[2,1-b]thiazoles and 3-substituted-, 2,3-disubstituted-4,5,6,7-tetrahydrothiazolo[3,2-a]pyrimidines
Authors: Chadha Vijay K. , Pujari H. K.
Published: April 2011

The syntheses of 3-substituted-, 2,3-disubstituted-5,6-dihydro-4H-imidazo[2,1-b]thiazoles and 3-substituted-, 2,3-disubstituted-4,5,6,7-tetrahydrothiazolo[3,2-a]pyrimidines have been achieved by reacting ketones with 2-mercaptoimidazoline and 2-mercapto-3,4,5,6-tetrahydropyrimidine respectively in the presence of iodine. The condensation has also been affected by replacing iodine with bromine.
Nuclear magnetic resonance studies of cyanide ion–2,4,6-trinitroanisole σ-complexes
Authors: Norris A. R.
Published: April 2011

Nuclear magnetic resonance studies at −30 °C reveal that the cyanide ion reacts with 2,4,6-trini-troanisole to form σ-complexes by attachment of the cyanide ion at both the C-1 and C-3 positions on the ring. In contrast to the methoxide ion adducts of 2,4,6-trinitroanisole, the cyanide ion adduct resulting from attack of the cyanide at the C-3 position is the more stable species.
Fluorinated alkoxides. Part X. Template syntheses leading to fluorinated β-imino-alkoxy complexes of four- and five-coordinate nickel(I1) and copper(I1)
Authors: Martin John W. L. , Willis Christopher J.
Published: April 2011

Hexafluorodiacetonealcohol, HFDA, HOC(CF3)2CH2COCH3, is sufficiently acidic to coordinate to metal ions in an ionized form as a chelating, uninegative ligand. Complexes of Ni2 + and Cu2+ may be isolated, most conveniently by using a tridentate nitrogen-containing macrocycle as co-ligand so that five-coordinate unipositive compounds are produced. In the presence of metal ions, HFDA readily undergoes template condensation reactions with diamino-ethane or -propane to give conplexes of ionized β-imino alcohols, e.g. -OC(CF3)2- CH2C(CH3) : N(CH2)2N : C(CH3)CH2C(CF3)20- ; these conplexes are neutral and square planar but become five-coordinate by solvation in, e.g., pyridine. The use of triamines H2N- (CH2),NH(CH2).NH2 (where n = 2 or 3) in template syntheses with HFDA gives complexes in which the metal ion is five-coordinate; these do not undergo solvation.
Spin trapping in heterogeneous electron transfer processes
Authors: Walter Thomas H , Bancroft Eric E , McIntire Gregory L , Davis Edward R , Gierasch Lila M , Blount Henry N
Published: April 2011

An overview of applications of spin trapping to electrochemical investigations is presented. Cited studies include characteriza­tions of primary electrode reaction products (e.g., electrooxidations of hal.ide and pseudohalide species, electroreduction of N-methylpyridinium ion) as well as the identification of transient intermediates arising from homogeneous reactions which are electroinitiated. The validity of spatially resolved spin trapping as a probe in the investigation of interfacial processes is demonstrated with examples drawn both from the previously reported co valent attachment of nitrone derived spin traps to silaceous surfaces and from recent studies of spin trapping in micelle and vesicle systems. Amphiphilic nitrone spin traps have been shown to coassemble with both micelles and vesicles such that the nitrone functionality resides in the interfacial region of the ordered system. The ability of these interfacially localized nitrones to trap transient radicals generated both in the hydrophobic domain of the micelle or vesicle and in the aqueous exterior domain is demonstrated.
Synthesis and structural study of aminals derived from 8-aminoquinoline and 1-aminonaphtalene
Authors: Galvez Enrique , Iriepa Isabel , Lorente Antonio , Mohedano Jose Miguel , Florencio Feliciana , Garcia-Blanco Severino
Published: April 2011

Reaction of 8-aminoquinoline with pyridine-2-carboxaldehyde (2), pyridine-3-carboxaldehyde (3), pyridine-4-carboxaldehyde (4), and benzaldehyde (5) yields the corresponding aminals or Schiff's bases according to reaction conditions; analogous results are obtained from the reaction of 1-amino-naphtalene with pyridine-2-carboxaldehyde (6). On the other hand, reaction of 8-aminoquinoline with thiophene-2-carboxaldehyde or pyrrole-2-carboxaldehyde yields neither the aminal nor the Schiff's base. Crystals of 4 (C24H19N5) belong to the triclinic space group [Formula: see text]. Cell dimensions are a = 11.547(3), b = 11.759(2), c = 15.687(5) Å, α = 98.50(2)°, β = 101.61(2)°, γ = 107.28(2)°, V = 1942.6(9) Å3. Final R = 0.077 and Rw = 0.064; 3160 reflections were observed. The ir, 1H nmr of 2–6, the mass spectra of 4 and 5 and the X-ray analysis of 4 are described and discussed. Preparative features, ir, 1H nmr, analyses and crystal structure indicate that the formation of 2–6 are governed mainly by the nucleophilicity at the aldehyde carbon atom and the existence of the hydrogen bonds in the aminal.
Mechanism of electroreduction of 9-anthraldehyde
Authors: Lasia Andrzej , Rami Abdelhaq
Published: April 2011

The electroreduction of 9-anthraldehyde (ANCHO) and 10-methyl-9-anthraldehyde (MeANCHO) has been studied in aprotic solvents. The anion free radicals of both compounds undergo subsequent dimerization reaction with [Formula: see text] being more reactive than [Formula: see text]. The rate constant of the dimerization reaction depends on the solvent and for [Formula: see text] in HMPA is equal to 2 × 104M−1 s−1. Using spectroscopic measurements it has been shown that the dimerization takes place at position 10.
Metabolites produced by the scleroderris canker fungus, Gremmeniellaabietina. Part 2. The structure of scleroderolide
Authors: Ayer William A. , Hoyano Yumiko , Pedras M. Soledade , Clardy Jon , Arnold Edward
Published: April 2011

Scleroderolide, a yellow pigment produced by the Scleroderris canker fungus Gremmeniellaabietina (Lagerb.) Morelet, is shown to possess structure 1. The structure was determined by an X-ray crystallographic study of the racemic monoacetate 1a. The crystal of 1a belongs to the triclinic system space group, P1, the R-factor converged to 0.047 for the 1957 observed reflections. Scleroderolide occurs mainly as the levorotatory enantiomer (S configuration at C-2′) although on one occasion it was obtained in partially racemic form. The absolute stereochemistry of the levorotatory form was determined by transformation of (−)-sclerodione (5) of known absolute configuration into (−)-scleroderolide. The absolute configuration of (−)-sclerodione was established by correlation with (−)-sclerodin (3). The diacetyl derivative of scleroderolide (1b) shows interesting temperature dependent nuclear magnetic resonance spectral properties due to restricted rotation of the C-4 O-acetyl group. Oxidation of the red pigment sclerodione (5) with m-chloroperbenzoic acid provides both sclerodin (3) and scleroderolide (1). Scleroderolide (1) is the first natural product to be reported that contains a phenylglyoxylate lactone functionality.
Metabolites produced by the Scleroderris canker fungus, Gremmeniellaabietina. Part 3. Some further metabolites
Authors: Ayer William A. , Pedras M. Soledade
Published: April 2011

This article describes the metabolites of a strain of Gremmeniellaabietina (Lagerb.) Morelet indigenous to Alberta. This strain does not produce the phenalenone derived metabolites isolated from the other strains of G. abietina examined to date. Only fatty acids and esters, glycerides, and sterol esters were produced. This raises a question regarding the identity of this particular strain. A greenish-yellow metabolite named Scleroderris green, isolated from a New Brunswick strain of G. abietina, is shown to have structure 12. Scleroderris green (12) is structurally related to Scleroderris blue (4) and is produced when the latter compound is reduced with sodium bisulfite. Air oxidation of Scleroderris green (12) gives rise to Scleroderris blue (4). The structure of compound 12 was established by a study of the 13C nmr spectra of the three pentamethyl derivatives (8, 9, and 10) produced when 12 is treated with ethereal diazomethane. It is suggested that the greenish discoloration of the wood of Scleroderris infected pine may be due to the presence of compound 12.
On the interaction of copper with tris(hydroxymethyl)aminomethane
Authors: Colombo M. F. , Austrilino L. , Nascimento O. R. , Castellano E. E. , Tabak M.
Published: April 2011

The interaction of copper with tris(hydroxymethyl)aminomethane (TRIS) has been studied by optical and esr spectroscopic techniques. In solution, three different copper complexes are obtained as a function of pH. At pH 10 the room temperature esr parameters are g0 = 2.135, A0 = 82 G and nitrogen superhyperfine structure AN = 9.5 G, characteristic of two nitrogen ligands; at pH 6.5, g0 = 2.147, A0 = 65 G and at pH 5.0, g0 = 2.180, A0 = 44 G. The high pH complex was crystallized and its molecular structure determined by X-ray methods. Space group and cell dimensions are C2/c, a = 12.955(2) Å, b = 10.793(1) Å, c = 10.091(2) Å, β = 116.62(1)°, V = 1261.4(6) Å3, Z = 4, Dc = 1.694 g cm−3, R = 0.034 for938 reflections with I > 3σ(I). The Cu2+ ion is located on the two-fold axis and coordinated to the oxygen and nitrogen atoms of two TRIS moieties; these ligand atoms form the rectangular base of a pyramid structure in which oxygen from a water molecule acts as the fifth ligand.
Bis((S)-5,5-dimethylthiazolidine-4-carboxylic acid) protium chloride hydrate [(C6H11NO2S)2H]Cl•H2O, a salt containing a hemi-protonated zwitterion
Authors: Howard-Lock H. E. , Lock C. J. L. , Martins M. L. , Faggiani R. , Duarte M.
Published: April 2011

The X-ray crystal structure of bis((S)-5,5-dimethylthiazolidine-4-carboxylic acid) protium chloride hydrate, I, has been determined. Crystals are orthorhombic, P212121, with cell dimensions a = 6.463(2), b = 11.832(3), c = 23.966(6) Å, and Z = 4. The structure was solved by standard methods and refined to R = 0.073, Rw = 0.064 for 2969 independent reflections. Compound I is composed of two zwitterion molecules bridged through a proton which causes a very short hydrogen bond, O … O′ = 2.450 Å. The proton is located roughly halfway between the two carboxylate oxygen atoms, but is not on a special crystallographic position. Characteristic features of the infrared and Raman spectra, mass spectra, and 1H and 13C nmr spectra are discussed.
Acetyl transfer reactions on AlPO4–Al2O3
Authors: Costa Antonio , Riego Juan Martin
Published: April 2011

An efficient acetylation of alcohols and aliphatic amines promoted by the AlPO4–Al2O3/ethyl acetate system is described. The solid catalyst acts, at least in part, as the acetyl carrier.
Synthetic studies on cyathins. Synthesis of the ring system
Authors: Ward Dale E.
Published: April 2011

The tricyclic intermediate 4 has been converted into 2, a compound that possesses the ring system and stereochemistry of the cyathins. The transformation was accomplished by the preparation of 11, which underwent efficient base catalysed epimerization to give 12. Functional group manipulation and selective oxidation provided keto-aldehyde 16. Upon treatment with acid, 16 undergoes stereoselective aldol cyclization, transacylation, and hemiacetal formation to give 18. Methylation under basic conditions provides 4.
Chemoselective reaction of a sulfonate ester with methoxide ions in preference to benzyl mercaptide anions
Authors: Langler Richard Francis , Morrison Nancy Ann
Published: April 2011

Trifluoroethyl benzyl sulfide was prepared (in 2-propanol) and subsequently chlorinated as a further test of substituent electronegativity based regiochemical predictions. The initial attempt to prepare that sulfide by reaction of 2,2,2-trifluoroethyl methanesulfonate and benzyl mercaptide anions (in methanol) furnished benzyl methyl sulfide. Mechanistic possibilities are discussed in detail and some synthetic consequences of this novel reaction are presented.
A conformational analysis of adriamycin based upon its 1H nuclear magnetic resonance spectrum in various solvents
Authors: Allman Tim , Lenkinski R. E.
Published: April 2011

The solution conformation of adriamycin was studied by 1H nuclear magnetic resonance spectroscopy. The hydrochloride was found to be rigid on the nmr time scale in each of CDCl3, DMF-d7, and DMSO-d6. The sugar and D rings were found to have the same conformations as were found previously by X-ray crystallography. Similar results were found for the free base in DMF-d7 and CDCl3 solutions although the free base was found to be conformationally mobile in acetone-d6 and CD3OD solutions.
Acceleration of the mercury-induced aquation of bromopentammine Co(III) by naturally occurring glycosaminoglycans
Authors: Templeton Douglas M.
Published: April 2011

The glycosaminoglycans are naturally occurring anionic polysaccharides whose polyelectrolyte properties and counterion interactions may underlie a number of biological activities. We have investigated the ability of the sulfated glycosaminoglycans to accelerate the reaction of Br(NH3)5Co2+ with Hg2+. Chondroitin sulfates A, B, and C, heparin, and heparan sulfates all accelerate this reaction to nearly the same extent, but do so at different optimal concentrations, above which inhibition is observed. This phenomenon of rate acceleration, sometimes called "polyelectrolyte catalysis", has previously been explained by a two-phase model, in which the reactant counterions are thought to equilibrate rapidly between the polymer domain and the bulk phase. Rate effects would then be due to higher local concentrations in the neighbourhood of the polymer. Our results show that this is an oversimplified view for the glycosaminoglycans. Rather, they demonstrate similar rate accelerations independent of net structural charge density. It is argued that counterion condensation, as described by Manning, reduces the surface potential of all glycosaminoglycans to nearly constant values. Different optimal concentrations of the glycosaminoglycans may arise in part from the unreactivity of a subpopulation of bound ions.
Contribution à l'étude des réactions d'alkylation et de polyalkylation de l'adamantane et de ses homologues
Authors: Molle G. , Dubois J. E. , Bauer P.
Published: April 2011

A method for preparing alkyl derivatives of cage-structure compounds is proposed. It relies on the use of Grignard reactions with a high boiling point solvent. The reactions take place at atmospheric pressure. Methylation of adamantane, diamantane, and homoadamantane occurs with quantitative yield. With other primary alkyl groups, yields are better than 60%. Competition between alkylation and secondary reactions is discussed on the basis of a free radical mechanism.
The microwave spectrum and structure of bromine thiocyanate, BrSCN
Authors: Jemson H. M. , Lewis-Bevan W. , Gerry M. C. L.
Published: April 2011

The microwave spectra of 79BrSCN and 81BrSCN have been measured and analysed to give rotational, centrifugal distortion, and Br quadrupole coupling constants. The molecule has been shown unambiguously to be BrSCN rather than BrNCS. A harmonic force field has been determined from combined vibrational and distortion data. With structural parameters for the SCN chain transferred from S(CN)2, both effective and ground state average values for the BrS length and BrSC angle have been estimated. The Br quadrupole tensor has been diagonalized, and the BrS bond is shown not to be bent.
A quantitative examination of the photoisomerization of some protonated phenols
Authors: Childs Ronald F. , George Baha E.
Published: April 2011

The photoisomerization of a series of protonated, methyl substituted phenols to protonated bicyclo[3.1.0]hexenones has been examined. These reactions, which were carried out in CF3SO3H as a strong acid solvent at ambient temperatures, provide a convenient route to a variety of bicyclo[3.1.0]hexenones. The quantum yields for these photoisomerizations vary from 0.018 for protonated 3,5-dimethylphenol to 0.65 for protonated 2,6-dimethylphenol. This variation in efficiency can be understood in terms of a competition between ring opening, to regenerate the starting phenol, or cyclopropyl migration, to give product, of an initially formed intermediate.
On the role of partition and surface reactions in the adsorption of binary liquid mixtures on silica gel
Authors: Singh Prem P. , Sharma Krishan K.
Published: April 2011

The adsorption behaviour of benzene (A), toluene (A), p-xylene (A), and o-xylene (A) in their binary mixtures with o-chlorotoluene (B) on silica gel has been studied at 308.15 K. The data have been analysed in terms of a model that assumes that partition and surface reactions play an important role in the adsorption process, and have revealed that while both partition and surface reactions dictate the adsorption (U-shaped isotherms) of o-chlorotoluene (OCTE) (B) from benzene (A) or toluene (A) + OCTE (B) mixtures, the adsorption of A and B entities of p-xylene (A) or o-xylene (A) + OCTE (B) mixtures (S-shaped isotherms) onto the silica gel surface is governed primarily by the distribution process and secondarily by the surface reaction.
Conformational changes in serine on methylmercury complexation
Authors: Corbeil Marie-Claude , Beauchamp André L.
Published: April 2011

The CH3Hg+ cation forms a zwitterionic complex CH3Hg[HOCH2CH(NH2)CO2—N,O,O] with serine in aqueous solution. X-ray diffraction (P212121, a = 5.821, b = 8.052, c = 14.307 Å, R = 0.021) shows that mercury is linearly bonded to the NH2 end of the amino acid, whereas one carboxylate oxygen and the side-chain hydroxyl group establish secondary Hg—O bonds. Coordination leads to characteristic changes in the infrared and Raman spectra of serine. From the 1H and 13C nmr spectra, N-coordination is found to be retained in aqueous solution, whereas the ligand conformation observed in the solid accounts for 76% of the conformer distribution.
Enzymes in organic synthesis. 44. Stereoselective pig liver esterase-catalyzed hydrolyses of 3-substituted glutarate diesters of compactin-synthon interest
Authors: Lam Lister K.-P. , Jones J. Bryan
Published: April 2011

Pig liver esterase-catalyzed hydrolyses of dimethyl 3-hydroxy-, 3-methoxyethoxymethoxy-, and 3-benzyloxyglutarates occur with enantiotopic stereoselectivity to give the corresponding acid-ester products of 16–40% enantiomeric excess (ee). The results also provide another example of reversal of PLE-stereoselectivity.
Reaction of Me3SnCu•Me2S with terminal alkynes. Preparation of 2-trimethylstannyl-1-alkenes
Authors: Piers Edward , Chong J. Michael
Published: April 2011

Reaction of ω-substituted terminal alkynes 5 with (trimethylstannyl)copper(I) dimethyl sulfide (1) under suitable reaction conditions provides good to excellent yields of the corresponding 2-trimethylstannyl-1-alkenes 6.
An ICR mass spectrometry study of ion/molecule reactions in mixtures of methylamine with ethylamine, propylamine, or butylamine
Authors: Xu Guoying , Herman Jan A. , Wójcik Leszek
Published: April 2011

Ion/molecule reactions of protonated alkylamine ion species, RNH3+, were studied in mixtures of methylamine with ethylamine, propylamine, or butylamine by ICR mass spectrometry at 10−5 Torr. The occurrence of methyl group transfer from methylamine to higher protonated alkylamine ion species was observed. The rate constants of some bimolecular reactions occurring in these systems were estimated by numerical simulation. Keywords: ion/molecule reactions, methylamine, ethylamine, propylamine, butylamine, ICR mass spectrometry.
Facile 5-endo ring closures to the azo group. A free radical synthesis of indazoles
Authors: Kunka Cheryl P. A. , Warkentin John
Published: April 2011

Five 1-alkyl-3-methylindazoles were prepared by treatment of 1-(2-bromophenyl)-1-methoxy-1-(2-alkylazo)ethanes with tri-n-butyl stannane and AIBN at 80 °C in benzene. Yields in the radical cyclization step ranged from 39 to 92%. 1-Phenyl-3-methylindazole was prepared by an analogous route but in very poor yield (<5%). Rate constants for the 5-endo radical closures [Formula: see text], estimated by the radical clock method, were 5.2 × 109 s−1 and 9.2 × 108 s−1 for two of the alkyl systems. Rate constants for analogous 5-endo cyclizations of aryl radicals onto C—C double bonds are much smaller than those for cyclizations to the azo functional group. Keywords: cyclization, radical; azo group, radical closure to; indazoles, radical synthesis of.
Photooxidation of 9,10-diethoxyanthracene: mechanistic dichotomies between homogeneous solution and reverse micelle photoprocesses
Authors: DeVoe R. J. , Sahyun M. R. V. , Schmidt E. , Sharma D. K.
Published: April 2011

We have compared the photooxidation of the title compound, DEA, by diphenyliodonium salts in homogeneous acetonitrile (AN) and in heptane/AOT/water reverse micelle solutions. The reaction is efficient, which we attribute to rapid (ca. 10 ps) deethylation of the DEA radical cation, initially formed by photoinduced electron transfer. In AN, the electron transfer occurs from singlet excited DEA, but in reverse micelles it is gated by intersystem crossing to triplet DEA. Under these conditions, DEA fluorescence quenching by the iodonium cation may still be observed; we infer operation of the external heavy atom effect as the primary mechanism. Keywords: anthracene, electron transfer, reverse micelle, photochemistry, picosecond.