bluuebunny/crossref_metadata_2025 huggingface dataset:
Some chemical and analytical aspects of polysaccharide modifications. IV. Electron spin resonance studies of nitroxide-labelled chitin and chitosan derivatives
Authors: Yalpani Manssur , Hall Laurance D.
Published: May 2006

Nitroxide spin labels have been attached to chitin, chitosan, and their derivatives in order to investigate the solution and gel characteristics of these polymers. Thus, chitin was nonselectively acylated using the chloroacetamide label 3 to afford. the corresponding nitroxide derivative 4. Selective and nonselective labelling of chitosan was accomplished either via reductive alkylation using the keto label 5 and sodium cyanoborohydride or via a chitosan sulfate intermediate using labels 3 or 5. Two branched water soluble chitosan derivatives, carrying C-6 oxidized, terminal galactose side chains were selectively labelled by reductive animation using the amine label 13 to yield derivatives 14 and 15. Motional correlation values of the covalently-linked nitroxide moieties were shown to reflect the nature of the linkage between spin label and polymer, as well as structural differences between the branch residues of derivatives 14 and 15. The spin-probe – spin-label method was employed to demonstrate structural heterogeneities for the chitosan derivatives 7 and 15.
Effects of added cations on rate enhancements for the nickel(II)–PADA reaction in micellar solutions
Authors: Hicks Joanne R. , Reinsborough Vincent C.
Published: May 2006

Rate enhancements of the Ni2+–PADA bidentate formation reaction have been obtained at 25.0 °C in anionic micellar solutions with added electrolyte. Sodium dodecylsulfate, sodium octanesulfonate, and sodium octylsulfate were the surfactants employed and Na+, Ca2+, and Mg2+ were the added cations. Kinetic analyses revealed that the chief effect in leading to a decreased rate enhancement with salt present was a lowering of the surface potential manifested by an increase in the reaction volume. The binding of the Ni2+ ion to the micelles showed little change beyond an initial drop with the lowest Na+ addition with sodium dodecylsulfate. The binding of the hydrophobic reagent PADA decreased more gradually but not sufficiently to account for the reduction in rate enhancements. In the presence of Ca2+ or Mg2+ ions, the rate enhancements and the kinetic parameters did not show unusual behaviour except that Mg2+ ion appeared to be slightly more effective in excluding Ni2+ ion from the micellar surface region. The sphere-to-rod micellar transformation that occurs at 0.4 mol dm−3 Na+ does not have a pronounced effect on the micellar surface region.
Glycosides from Muscaricomosum. 4. Structure of muscaroside A
Authors: Adinolfi M. , Barone G. , Lanzetta R. , Laonigro G. , Mangoni L. , Parrilli M.
Published: May 2006

not available
The structure of merosinigrin confirmed
Authors: Richardson John F. , Benn M. H.
Published: May 2006

An X-ray crystallographic study of merosinigrin confirmed the structure as 1,2-S,O-(1R,2S-1-cyano-2-methyl-1,2-ethanediyl)-1-thio-β-D-glucopyranose. The compound crystallizes in the space group P1 with a = 6.699(1), b = 9.347(1), c = 5.328(2) Å, α = 103.56(2), β = 109.14(3), γ = 86.71(1)°, and Z = 1. The structure was refined by full-matrix least-squares techniques to a final agreement value of R = 0.031. Merosinigrin provides what appears to be the first example of the anomeric effect in a thiane (1,4-oxathiane) system with cyano as the polar substituent.
A spin-lattice relaxation study of the molecular reorientation of 2-methylindole as a function of viscosity and complex formation
Authors: Friesen Kenneth J. , Blackburn Barry J.
Published: May 2006

The viscosity (η) dependence of the 13C spin-lattice relaxation time (T1) of C-3 of 2-methylindole was investigated by changing the temperature (T) and by changing the solvent system. The observed η/T dependence of the effective reorientation correlation time (calculated from T1) is compared with those derived from theory based on hydrodynamic rotation with "stick" and with "slip" boundary conditions. This data implies that the reorientation of 2-methylindole obeys a near-slip condition in 1,2-dichloroethane. The 13C T1 of C-3 of 2-methylindole was also determined as a function of the fraction complexed with 1,3,5-trinitrobenzene (TNB) at 35 °C in 1,2-dichloroethane. The observed T1 in this case, depends on the rates of reorientation of the molecule in the free and the bound states, the rate of association of the molecules, the rate of dissociation of the complex, as well as increases in viscosity brought about by increases in the concentration of TNB. Analysis of the data, by application of the Anderson–Fryer formulation, gives a rate of reorientation in the bound state of 55 ns−1 at 35 °C and 0.69 cP as compared to a value of 150 ns−1 in the free state under the same conditions.
Radical ions in photochemistry. 15. The photosubstitution reaction between dicyanobenzenes and alkyl olefins
Authors: Borg Robert M. , Arnold Donald R. , Cameron T. Stanley
Published: May 2006

The photosubstitution (electron transfer) reaction between 1,4-dicyanobenzene (1) and 2,3-dimethyl-2-butene (2), which gives 1-(4-cyanophenyl)-2,3-dimethyl-2-butene (3) and 3-(4-cyanophenyl)-2,3-dimethyl-1-butene (4), has been extended to other dicyanobenzene–olefin mixtures. Substitution of a cyano group occurs when both 1 or 1,2-dicyanobenzene (5) are irradiated in acetonitrile solution, in the presence of 2 or cyclohexene (16). Under comparable conditions, 1,3-dicyanobenzene (6) failed to react. Little or no substitution was observed in any case when the olefin was methylpropene (19). The results for 1 and 5 are in agreement with empirical free energy calculations (Weller equation) for the electron transfer process which, however, fail to explain the general lack of reactivity of 1,3-dicyanobenzene. Phenanthrene (11) has been shown to photosensitize the photosubstitution reaction between dicyanobenzenes and 2. Under these conditions the olefin reacts with 6 predominantly at the 4-position, resulting in overall substitution of a hydrogen atom. This reaction occurs regiospecifically, resulting in the formation of only one of the two possible isomeric side chains. The mechanistic details of these reactions have been substantiated by means of deuterium labelling studies. The aromatic nitriles also undergo photosubstitution by 2, in acetonitrile–methanol solution, resulting in methanol-incorporated products. Whereas reaction with 1 or 5 results in substitution of a cyano group, 6 was observed to give isomeric dicyanocyclohexenes, resulting from initial reaction at the 4-position, followed by reduction. A detailed mechanism for this secondary photoreduction has been substantiated by deuterium labelling studies. The anomalous behaviour of 1,3-dicyanobenzene has been attributed to a difference in the reactivity of the radical anion.
Complexation par transfert de charge de la chlorpromazine en présence d'iode; action thyroïdienne sécondaire de cette molécule
Authors: Absil Anne-Catherine , Buxeraud Jacques , Raby Claude
Published: May 2006

Molecular interaction between iodine and chlorpromazine is investigated by electron spectroscopy. Iodine forms a charge transfer complex with chlorpromazine, with 1:1 stoichiometry and of the n–σ type. The values of the formation constant (Kc at20 °C = 3166 ± 19 L mol−1) and thermodynamic parameters (ΔH0 = −11.22 ± 0.11 kcal mol−1, ΔS0 = −22.29 ± 0.38 cal mol−1 K−1) show a strong donor–acceptor interaction, comparable to that obtained with tertiary amines. The formation constant is compared to those obtained with antithyroid molecules. Chlorpromazine appears to have no effect on the intrathyroid cycle of iodine.
Internal rotation in [p-(dialkylamino)benzylidene]malononitriles
Authors: Safarzadeh-Amiri A.
Published: May 2006

The dynamic structures of [p-(dialkylamino)benzylidene]malononitriles have been investigated by 1H nmr, and the kinetic and thermodynamic parameters for the partial rotation of the malononitrile moiety were obtained and those of the dialkylamino group were estimated. The rate of rotation of the above rotors were found to be of the order of ~104 s−1 and ~107 s−1, respectively.
Photochemical and mass spectrometric transformation of gibberellenic acid to 9-epiallogibberic acid
Authors: Al-Ekabi Hussain K. , Derwish Ghazi A. W.
Published: May 2006

Gibberellenic acid (2) reacted thermally in a modified immersion photochemical reactor, to give an intermediate triene (3). This triene then isomerized photochemically, via suprafacial [1,3]-hydrogen migration, to 9-epiallogibberic acid (5). On the other hand, comparison of the positive mass spectra of gibberellenic acid (2), allogibberic acid (4), and 9-epiallogibberic acid (5) showed that gibberellenic acid underwent electron impact fragmentation to the triene 3 cation. This cation then rearranged through suprafacial [1,3]-hydrogen migration to the 9-epiallogibberic acid (5) cation.
Facile access to (S)-1,2,4-butanetriol and its derivatives
Authors: Hanessian Stephen , Ugolini Antonio , Dubé Daniel , Glamyan Ani
Published: May 2006

The synthesis of (S)-1,2,4-butanetriol from the readily available (S)-malic acid in one step using borane – dimethyl sulfide is described.
The mass spectra of pyrimidines. II. 2(1H)-Pyrimidinethiones and some N(1)-substituted derivatives
Authors: Rye Robin T. B. , Tee Oswald S. , Kazdan Eva M.
Published: May 2006

The EI induced fragmentation of 2(1H)-pyrimidinethione (1), some N(1)-substituted derivatives, and 2(1H)-pyrimidineselenone (4) have been studied. Principal fragmentation pathways have been identified using 2H-labelling, metastable defocussing, and exact mass measurements.The fragmentations of 1 and 4 generally parallel those reported for 2(1H)-pyrimidinone. In contrast to the oxo-compound, however, direct expulsion of the exocyclic hetero atom is significant in the fragmentation of 1, and dominates the spectrum of 4.Based on metastable peak abundances and kinetic energy release measurements, it is postulated that the [M – H]+ entity generated from N-ethyl-2-pyrimidinethione has a thiazolinium structure.
Stereocontrolled total synthesis of the triquinane marine sesquiterpene Δ9(12)-capnellene
Authors: Paquette Leo A. , Stevens Kenneth E.
Published: May 2006

A total synthesis of Δ9(12)-capnellene, a cis-anti-cis-tricyclo[6.3.0.02,6]undecane sesquiterpene of marine origin, is described. Starting with bicyclic enone 5, which was prepared by a Nazarov cyclization, the remaining portion of the molecule is elaborated by means of a new and relatively efficient cyclopentenone annulation scheme. The relative stereochemistries of the chiral centers are properly incorporated by taking advantage of prevailing steric factors.
Stereospecific cyclization of β-hydroxy aryl amides to β-lactams
Authors: Bose Ajay K. , Manhas M. S. , Sahu D. P. , Hegde V. R.
Published: May 2006

N-Aryl-β-lactams can be prepared conveniently by an intramolecular reaction of β-hydroxyarylamides under the influence of diethyl azodicarboxylate (DEAD) and triphenylphosphine (TPP). Optically active 3-amino-2-azetidinone derivatives can be prepared by this method starting with a suitably protected α-amino-β-hydroxy carboxylic acid amide. This cyclization involves the retention of configuration at C2 and complete inversion at C3 of the starting acid. In some cases diamides of azodicarboxylic acid have been used by replacing TPP with the more reactive tributyl phosphine. Other phosphorus reagents such as phosphite esters and hexamethyl phosphorus triamide could also be used.
A synthesis of hirsutene: a simple route via β-enolization
Authors: Dawson Brian A. , Ghosh Ashim K. , Jurlina Jeffrey L. , Ragauskas Arthur J. , Stothers J. B.
Published: May 2006

A simple sequence from dicyclopentadiene to the cis,anti,cis-tricyclopentanoid carbon skeleton of the hirsutanes is described. A key step employs a β-enolate rearrangement to generate the ring system having the desired stereochemistry. The route to the requisite ketone for this rearrangement utilizes efficient ring expansion via homoketonization.
Enzymes in organic synthesis. 32. Stereospecific horse liver alcohol dehydrogenase-catalyzed oxidations of exo- and endo-oxabicyclic meso diols
Authors: Jones J. Bryan , Francis Christopher J.
Published: May 2006

Preparative-scale horse liver alcohol dehydrogenase-catalyzed oxidation of mesoexo- and endo-7-oxabicyclo[2.2.1]heptane diols provides a direct one-step route to enantiomerically pure chiral γ-lactones of the oxabicyclic series.
Permanganate peroxidation of cyclohexene. II. Temperature, solvent, and concentration effects
Authors: Taylor Jay. E.
Published: May 2006

An investigation of the peroxidation of cyclohexene to form cis 1,2-cyclohexanediol has been continued using an improved turbulent stirring apparatus. Varying conditions of temperature, methanol concentration, dilution, and permanganate/cyclohexene ratios have been evaluated by the method of comparative product yields. The temperature effect was quite modest since only at the extremes of −20 and 40 °C were decreases in yields noted. Added methanol in low concentrations, > 10%, gave slightly increased yields, but decreased yields were observed when methanol was added in 75% concentration. Under the new stirring conditions, 83–86% yields were obtained with ~0.05 M added potassium permanganate, but only 70–74% yields were obtained at higher concentrations. This effect appeared to relate to the increased viscosity of the mixture which results from the formation of gelatinous manganese oxides. Ratios of cyclohexene to permanganate ion greater than 2:1 gave no significant yield increases, based on permanganate utilization. All of the above data have been interpreted with the assumption of an intermediate alkene – permanganate ion addition complex. Preparative scale syntheses of cis-1,2-cyclohexanediol have produced 83–87% yields with either 0.2 or 0.5 molar quantities of cyclohexene.
Complexation du cuivre(II) par les phénylsérines thréo et érythro: étude thermodynamique
Authors: Sharrock Patrick
Published: May 2006

Conductimetric and potentiometric measurements in aqueous solution as a function of temperature show that cupric ions promote the deprotonation of the hydroxy side chain of threo and erythro β-phenylserines. The threo ligand yields at 298 K the formation constants: Cu(L), K1 = 7.99; Cu(L)2, K2 = 6.71; Cu(L2H−1), K3 = −9.51; Cu(L2H−2), K4 = −10.83. The erythro isomer yields the corresponding constants: K1 = 7.70, K2 = 6.70, K3 = −9.82, and K4 = −11.20. Thermodynamic parameters for the first two complexation steps are −ΔH = 21.3 and 44.7 kJ mol−1; ΔS = 82 and 132 J K−1 mol−1, respectively, for the threo form and −ΔH = 20.7 and 44.1, ΔS = 79 and 129 for the erythro form. Deprotonation of the complexes corresponds to an additional enthalpy of −21 kJ mol−1. These results and the structures of the complexes are discussed.
Secondary α-deuterium kinetic isotope effects for the E2 reaction of the 2-phenylethyl halides with tert-butoxide ion in tert-butyl alcohol
Authors: Smith Peter James , Rangappa Kanchugarakoppal S. , Westaway Kenneth Charles
Published: May 2006

Secondary α-deuterium kinetic isotope effects have been determined for the elimination reactions of 2-phenylethyl halides with tert-butoxide in tert-butyl alcohol at 40 °C in the presence and absence of the crown ether 18C6. The second-order rate constant k2 and the normal (kH/kD)α effect remained constant when the tert-butoxide concentration was varied for reaction of the iodo and bromo compounds. However, both the magnitude of k2 and the secondary α-deuterium isotope effect were significantly dependent on [t-BuO−] when chlorine and fluorine are the leaving groups. It is noteworthy that (kH/kD)α is inverse for the reaction of both the chloro and fluoro compounds at "low" base concentrations and normal at "high" base concentrations. These results are discussed in terms of both syn- and anti-elimination pathways promoted by various associated and dissociated base species. It is suggested that the (kH/kD)α effect may be useful as a criterion for determining the stereochemistry of E2 elimination reactions.
Influence of molecular structure on the dynamic thermoelasticity of polyphasic polymer systems
Authors: Marchessault Robert H. , Bluhm Terry L. , Gharapetian Hrire M. , Sundararajan Pudupadi R.
Published: May 2006

The relationship between the dynamic thermoelastic behavior and molecular morphology of polyphasic polymer systems was studied. A sensitive tensometer equipped with a 50 W/I2 V heating lamp provided uniform and controlled heat pulses to one side of the film. For various extension ratios, the stress change (Δσ) as a function of the sample temperature, was recorded, both for increasing and decreasing extension ratios.The amount of increase in stress Δσ with temperature was different for Kraton GX-6500 samples cast from either toluene, cyclohexane, or heptane. The variation of Act with temperature was dependent on the extension ratio and was always greater for increasing extension. The slope of Δσ with temperature decreased at 100–150% elongation in all Kraton GX-6500 samples during increasing extension. However, this slope increased at higher elongations. Small angle X-ray scattering studies on Kraton GX-6500 showed the presence of lamellar, rod shape, and spherical structures in samples cast from toluene, cyclohexane, and heptane solvents, respectively. The extreme dependence of elastomeric behavior on polyphasic morphology caused Kraton samples to show a strong decline in thermoelastic response with cycling.X-ray studies on the films of Spandex, cast from dimethyl formamide, at different extension ratios showed the onset of crystallization at about 150% elongation. The thermoelastic studies performed on Spandex films also showed an increase in slope of Δσ vs. T at 150–170% elongations, which was attributed to the influence of increased crystalline orientation on thermoelastic response. X-ray studies on unstretched and stretched Hytrel films showed the presence of crystallinity. The magnitude of Δσ and variation with temperature for Hytrel films was greater than that of either Spandex, Kraton GX-6500, or cross-linked natural rubber.By comparison with the latter, only Hytrel was superior in the magnitude of Δσ variations with temperature. This was attributed to intrinsic crystallinity and the orientation which developed on stretching. At extension ratios λ = 2, Δσ for Hytrel was an order of magnitude greater than for cross-linked natural rubber.
Etude de l'anharmonicité électrique dans 12C16O2
Authors: Millié Philippe
Published: May 2006

The dipole moment derivatives up to the fourth order are determined for the 12C16O2 molecule by fitting the experimental values of several transition intensities. The convergence is fast, but the third order is significant in order to obtain an acceptable accuracy (~20%).
Thermodynamic control in the reactions of gas phase anions. An abinitio and ion cyclotron resonance study of the reactions of anions with diborane
Authors: Elsenstein O. , Kayser M. , Roy M. , McMahon T. B.
Published: May 2006

The gas phase ion molecule reactions of a number of anions, X−, with diborane, B2H6 have been investigated using ion cyclotron resonance spectroscopy. Two distinct reaction channels are observed in addition to simple proton transfer. The first of these is production of BH4− and BH2X while the second is formation of BH3X− and BH3. In order to determine the importance of thermodynamic factors in the course of reaction abinitio calculations have been carried out on the species involved to obtain the relative stabilities of the two possible pairs of products. The 4-31 +G basis set incorporating additional flat s and p functions has been used since this basis set has been demonstrated to give the most accurate description of anions to date. The results obtained indicate that the thermochemical factors are instrumental in determining the reaction pathway.
On the infrared spectrum and dipole moment of dichloroketene
Authors: Gerry M. C. L. , Lewis-Bevan W. , Westwood N. P. C.
Published: May 2006

The failure to observe a microwave spectrum of dichloroketene prepared in a low temperature flow system is contrasted with the successful observation of its Fourier Transform infrared spectrum under the same conditions. It is concluded that the lack of a microwave spectrum is a result of a near-zero dipole moment for dichloroketene.
High temperature potential/pH diagrams for the chlorine–water system
Authors: Kolodziej Barbara , Habashi Fathi
Published: May 2006

Thermodynamic evidence supports the view that the reaction [Formula: see text] takes place above 127 °C at pH = 0. An increase in HCl concentration and/or oxygen partial pressure allow the reaction to proceed at lower temperature.
Formation de l'état triplet du benzaldéhyde dans sa réaction en phase gazeuse avec l'azote activé
Authors: Dessaux Odile , Dupret Christian , Goudmand Pierre
Published: May 2006

The reaction of active nitrogen with benzaldehyde gives a chemiluminescent reaction mainly attributed to the T1(nπ*) → S0 transition of benzaldehyde. Two steps of the mechanism are proposed.
Isolation and structure of bryostatins 5–7
Authors: Pettit George R. , Kamano Yoshiaki , Herald Cherry L. , Tozawa Machiko
Published: May 2006

American (Gulf of Mexico), Mexican (Gulf of California), and Japanese (Gulf of Sagami) specimens of the marine bryozoan Bugulaneritina were found to contain in addition to bryostatin 4 (3a) the new bryostatins 5–7 (3b–d) as major antineoplastic components effective against the murine P388 lymphocytic leukemia. A total of 50 kg of wet B. neritina from the Northeastern Gulf of Mexico led to bryostatins 5–7 in 14.1, 61.9, and 31.2 mg yields respectively. The structural assignments for each of these potentially important substances were derived from detailed interpretation of the 400 MHz 1H nmr and solution phase secondary ion mass spectral measurements, combined with the results of selective acid-catalyzed hydrolyses.
Enantioselective ester hydrolyses using Rhizopusnigricans: stereoselective synthesis and absolute stereochemistry of (−)-cis- and (−)-trans-1-hydroxy-4-methyl-1,2,3,4-tetrahydronaphthalene
Authors: Kasai Masaji , Ziffer Herman , Silverton J. V.
Published: May 2006

Enantioselective hydrolysis of racemic acetates of cis- and trans-1-hydroxy-4-methyl-1,2,3,4-tetrahydronaphthalene using Rhizopusnigricans yields chiral alcohols. The absolutestereochemistry of these compounds, and that of a key intermediate in their stereoselective synthesis, r-1-hydroxy-2,t-bromo-4,c-methyl-1,2,3,4-tetrahydronaphthalene, were determined by chemical transformations to 1-oxo-4-methyl-1,2,3,4-tetrahydronaphthalene of known absolute stereochemistry. The relativestereochemistry of the acetate of the key intermediate was established by X-ray crystallography.
Photochemical reactions in organized assemblies. 40. Amylose and carboxymethylamylose inclusion complexes with photoreactive molecules
Authors: Suddaby Brian R. , Dominey Raymond N. , Hui Y. , Whitten David G.
Published: May 2006

This paper focuses on a study of unimolecular and bimolecular photoreactions occurring with reactants which can be incorporated into the linear polysugars amylose and carboxymethylamylose. Hydrophobic and surfactant trans (E) stilbene derivatives form complexes in which the stilbene chromophore shows enhanced fluorescence and reduced trans → cis isomerization efficiencies. The reactivity of the excited surfactant–stilbene singlet towards the quencher iodide ion has been compared in water/dimethylsulfoxide in the presence and absence of amylose under conditions where complex formation is nearly complete. Some relatively hydrophobic viologen dications have also been found to form complexes with the water soluble carboxymethylamylose. Although the dications complex relatively weakly, the partially reduced monocations complex more strongly. This results in selective retardation of back electron transfer rates when the viologens are used as electron transfer quencher-oxidants for certain luminescent ruthenium polypyridine complexes.
Étude vibrationnelle des acides deltiques C3O3H2 et C3O3D2
Authors: Lautié Alain , Lautié Marie-France , Novak Alexandre
Published: May 2006

The infrared and Raman spectra of crystalline deltic acid and its deuterated derivative have been investigated in the 4000–20[Formula: see text]cm−1 range. An assignment of all the intramolecular fundamentals has been proposed assuming a C2v molecular symmetry. The crystal symmetry is likely to be described by the [Formula: see text] or P2/m space group with Z = 2. Deltic acid molecules probably form infinite chains linked with two very strong, asymmetric, and different OH … O hydrogen bonds, with O … O distances estimated at 2.49 and 2.56 Å.
Réflexions multiples et prédissociations moléculaires
Authors: Lefebvre R.
Published: May 2006

The semi-classical theory of molecular predissociation puts emphasis on the multiple reflections of waves and the resulting interferences. This approach is used to examine a case with two channels including a competition between a shape resonance and a Fesbach resonance. In the limit of low predissociation rates there is additivity of the two effects.
Cluster expansion of the wavefunction. Potential energy curves of the ground, excited, and ionized states of Li2
Authors: Nakatsuji H. , Ushio J. , Yonezawa T.
Published: May 2006

The SAC (symmetry-adapted-cluster) and SAC-CI theories based on the cluster expansion of the wavefunction have been applied to the calculations of the potential energy curves of the ground, excited, and ionized states of the Li2 molecule. The potential energy curves and the spectroscopic properties calculated agree well with the available experimental data and the previous theoretical results of Olson and Konowalow. For the [Formula: see text] state, our calculation is the first and predicts a bound state whose minimum is at Re = 6.8 bohr and 2.5 eV above the ground state. This state dissociates into 2P and 2S states of the Li atoms and has a hump which is higher than and outside of the hump of the B1IIu state. The long-range behavior of the states which dissociate into 2P and 2S states of the Li atom is well predicted by the resonance interaction theory.
Pseudopotentials for second row atoms. Abinitio molecular calculations on PH3, H2S, and HCl
Authors: Gáspár Rezső , Gáspár Jr. Rezső
Published: May 2006

Gaussian nonlocal pseudopotentials are introduced for the simplification of the description of second row elements. Pseudopotential parameters for P, S, and Cl are presented. The pseudopotential method is applied to HCl, H2S, and PH3. Substantial reduction in the dimension of the orbital basis set is achieved. Results on total valence energies, binding energies, ionization potentials, force constants, equilibrium bond angles, bond lengths, and dipole moments are presented and compared to experiment as well as to the results of calculations with other methods.
Investigations of the assignment of the 2190 cm−1 infrared band in polyfumaronitrile
Authors: Gallaher Kenneth L. , Lukco Dorothy , Grasselli Jeanette G.
Published: May 2006

Polyfumaronitrile exhibits a band at 2190 cm−1 which has at various times been associated with a β-aminonitrile, an iminonitrile, or with C=N in an α-pyrrolenine ring. This band is of particular interest because it sometimes appears in degraded polyacrylonitrile and nitrile-containing resins. The previous conflicting assignments were made on the basis of ir, uv, 1H nmr, and chemical results. This paper reports new infrared, esr, and solid-state carbon nmr results which indicate that the 2190 cm−1 band is most likely due to a β-aminonitrile functionality. The close spectral similarity with 3-amino crotonitrile is particularly noted. A mechanism is proposed which would explain the presence of such a nitrile in polyfumaronitrile.
Group theory of constrained reaction mechanisms
Authors: Mezey Paul G.
Published: May 2006

It is shown that the family of all possible reaction mechanisms on a given potential energy hypersurface, which reaction mechanisms are constrained by a localstabilitycriterion, has an algebraic structure. The fundamental relations among all such "λ-constrained" reaction mechanisms are described in terms of a group, the one dimensional homotopygroup π1(Y). In contrast with the energy-dependentgroup π1(F) of fundamentalreactionmechanisms, proposed earlier for the lowenergydomainsF of potential energy hypersurfaces, the new group π1(Y) is fully determined by the distributionofcatchmentregions, representingchemicalspecies on the potential energy hypersurface.
The molecular conformations of 8,11-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin and 4,4-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin
Authors: Lachapelle A. , St-Jacques M.
Published: May 2006

The conformational properties of 8,11-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin (5) and of 4,4-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin (6) have been investigated using 1H and 13C dnmr as well as ir spectroscopy. Analysis of low temperature nmr spectra (down to −148 °C) and of S=O stretching vibrations in room temperature ir spectra indicates that the most stable conformations detected for solutions in CHF2Cl/CD2Cl2 (80:20) are TB (83%) and C-a (17%) for 5 and only the TB 7 for 6. Substituent effects of methyl groups at the peri and the benzylic positions on the conformational properties of the seven-membered sulfites are discussed.
5J(CH3,SH) as a negative proximate or as a positive σ−π coupling in 2-methylthiophenol derivatives
Authors: Schaefer Ted , Peeling James , Sebastian Rudy , Baleja James D.
Published: May 2006

Analyses of the 1H nmr spectra of 6-chloro-2-methylthiophenol and of 4-tert-butyl-2-methylthiophenol in CCl4 solution, together with double irradiation experiments, show that 5J(CH5,SH) in the former compound is −0.66 Hz and is +0.47 Hz in the latter. In the chloro compound, the sulfhydryl group spends relatively little time in out-of-plane conformations at 300 K. The negative coupling is a consequence of a through-space or proximate coupling mechanism. In the other compound, the sulfhydryl group samples many out-of-plane conformations but relatively few in which the S—H bond lies near the methyl group. Therefore 5J(CH3,SH) is now dominated by a σ−π electron mechanism and is positive. Probably by coincidence, 4J(H,SH) in this compound is equal in magnitude but opposite in sign to 5J(CH3,SH).
The conformational behaviour of 2-fluoro and of 2,6-difluoroacetophenone implied by proximate spin–spin coupling constants and MO calculations
Authors: Schaefer Ted , Penner Glenn H. , Wildman Timothy A. , Peeling James
Published: May 2006

The temperature dependence of [Formula: see text], the nuclear spin–spin coupling constant over five formal bonds between the methyl protons and the 19F nucleus in 2-fluoroacetophenone and 2,6-difluoroacetophenone, is modelled on the assumption that 5J is a proximate coupling and that the STO 3G MO potential functions describe the population distributions of the rotamers defined by rotation about the exocyclic sp2–sp2 carbon–carbon bond. It is assumed that 5J has a cos4 θ dependence between 0 and 90°, where θ is the angle by which the acetyl group twists out of the plane of the benzene plane. The potential function is obtained from extensive geometry optimization procedures for a range of θ values. At 305 K, nonplanar conformations are substantially populated in 2-fluoroacetophenone, according to this model, which is also consistent with the idea that the 2,6-difluoro derivative has a markedly nonplanar ground state. The model reproduces the large 5J in the monofluoro relative to the difluoro compound, as well as the much larger temperature dependence in the former.
Novel sterols from the finger sponge Haliclonaoculata
Authors: Findlay John A. , Patil Ashok D.
Published: May 2006

From the finger sponge, Haliclonaoculata (Linnaeus), six new polar sterols have been isolated and their structures determined by chemical and spectroscopic means. These are 3β-hydroxy-cholesta-5,25-dien-24-one (2), 3β-hydroxy-24-methylene-5-cholesten-7-one (6), 24-methylene-5-cholesten-3β,7β-diol (9), 24-methylcholesta-5,22-dien-3β,7β-diol (11), 24-methylene-5-cholesten-3β,7α-diol (12), and 5β,6-epoxy-24-methylene-cholestan-3β-ol (16). Also shown to be present are the known monohydroxysterols (22E,24S)-24-methylcholesta-5,22-dien-3β-ol (1), (22Z)-24-norcholesta-5,22-dien-3β-ol, 24-methylene-5-cholesten-3β-ol, 24-isoethylidene-5-cholesten-3β-ol, (22E)-24-norcholesta-5,22-dien-3β-ol and (23E)-cholesta-5,23-dien-3β,25-diol. The structure 14 is tentatively proposed for a novel C24 sterol and 8 is suggested for the structure of a compound accompanying 6.
Hydrodynamic studies on micellar solutions of styrene–butadiene block copolymers in selective solvents
Authors: Oranli Levent , Bahadur Pratap , Riess Gérard
Published: May 2006

Hydrodynamic radius of micelles of several block copolymers in different selective solvents (for both types of blocks) was determined from photon correlation spectroscopy. The boundaries of micellar solutions in heptane (good solvent for polybutadiene block) and dimethylformamide (good solvent for polystyrene block) were established for polymers in terms of their molecular mass and block composition. The photon correlation spectroscopy data in combination with intrinsic viscosities of block copolymers in selective solvents were used to determine micellar molecular mass and aggregation number. The influence of temperature on the micelle size was examined. The block copolymer micelles could solubilize a certain amount of insoluble homopolymer within their insoluble core. 1H nmr spectra were examined to study the influence of temperature on micellar systems.
Benzylic substitution in ring A of daunomycinone. Conversion of daunomycinone into thiodaunomycinone and related deoxy analogs
Authors: Sallam Mohammed A. E. , Whistler Roy L. , Cassady John M.
Published: May 2006

Catalytic hydrogenolysis of daunomycinone (4) over palladium–carbon or palladium – barium sulfate afforded a mixture of 7-deoxydaunomycinone (5) and 7,11-dideoxydaunomycinone (6). 7-Deoxy-7-thioacetyldaunomycinone (8) and its 7-epimer (9) were prepared from 5 via the intermediate 7-deoxy-7-bromo derivative 7 in 33% yield. Compound 8 was prepared from 4 in a one-step reaction by treatment with thioacetic acid (THAA) and trifluoroacetic acid (TFAA), in 13% yield. Refluxing 4 in a mixture of THAA and glacial acetic acid (GAA) increased the yield of 8 and 9 to 83%. Epimerization of 9 with TFAA afforded 8. Hydrolysis of 8 gave a mixture of thiodaunomycinone (10), 5, and bisanhydrodaunomycinone (11). Compound 10 converts partially into its dimeric form (12) on standing.
Protonation of hypoxanthine, guanine, xanthine, and caffeine
Authors: Benoit Robert L. , Fréchette Monique
Published: May 2006

The protonation equilibria of three hydroxypurines, hypoxanthine, guanine, and xanthine, and of related caffeine have been studied by 1H and 13C nmr and uv spectroscopies in aqueous sulfuric or perchloric acids. The results have been interpreted on the basis of the excess acidity method. The [Formula: see text] values and the protonation sites are discussed and comparisons are made with results of recent theoretical calculations.
Qinghaosu: 1H and 13C nuclear magnetic resonance spectral assignments and luminescence
Authors: Zhongshan Wang , Nakashima Thomas T. , Kopecky Karl R. , Molina José
Published: May 2006

The complete assignment of the 1H and 13C nmr signals for Qinghaosu 1 has been made. Treatment of 1 with methoxide ion at 80 °C results in bright luminescence when carried out in the presence of fluorescers. Several products are formed when methanol is present, but in toluene only one product is formed when methanol-free methoxide is used. Its structure is tentatively assigned as 1-(1-methoxycarbonylethyl)-2,6-dimethyl-2-hydroxybicyclo[3.3.1]nonan-9-one.
Excess volumes and excess enthalpies of acetic and its methyl-substituted acids + acetonitrile
Authors: Lark B. S. , Banipal T. S.
Published: May 2006

Excess volumes of the systems acetonitrile (ACN) + acetic acid (AA), + propionic acid (PA) and + isobutyric acid (IBA) at 298.15 and 308.15 K and + trimethylacetic acid (TMA) at 313.15 K have been measured using dilatometric method. The observed values are found to be negative for the first three systems while the last system has sigmoid concentration dependence. Excess enthalpies for the first three systems at 308.15 K and for the last system at 313.15 K have also been determined and found to be positive. The results have been explained in terms of depolymerization of the acids, dipole–dipole interactions between heteromolecules and the steric hindrance caused by the increasing methylation.
Formation constants for selected organo—metal (Al3+, Fe3+)—phosphate complexes
Authors: Arp Paul A. , Meyer W. Lense
Published: May 2006

The possible formation of organo–metal–phosphate complexes (O–M–P) in aqueous solutions is examined by potentiometric titration analysis. The complex-forming solutions contain Al3+-ions or Fe3+-ions, organic acids (salicylic, phthalic, oxalic, and citric acids) and phosphate ions. The titrations are done within the precipitation-free pH-region from 2 to 4.5 (approximately) at 25 °C under nitrogen at an ionic strength of 0.2 M KCl. The calibration of the electrode pair (glass-electrode, calomel-reference electrode) and the determination of the formation constants are facilitated by analyzing the pertinent curves with the ACBA-(Arena etal.) and MINIQUAD-(Gans etal.) computer programs. The results suggest (i) that O–M–P complexes are readily formed, and that the power of selected organic acids to form ternary mixed-ligand complexes with Al3+-ions and phosphate ions decreases in the order salycilate > citrate > oxalate > phthalate. Also, Fe3+-ions are found to be more strongly bound by salicylate and phosphate ions than Al3+-ions. The effect of O–M–P formation on the chemical speciation of Al in buffered aqueous solutions containing mineral nutrients for the growth of biological organisms is demonstrated for a special case study.
The ion-pair mechanism and bimolecular displacement at saturated carbon. V. Racemization and bromide – radio-bromide exchange for substituted 1-phenylbromoethanes in acetone
Authors: Stein Allan R. , Moffatt Elizabeth A.
Published: May 2006

Results of kinetic studies of the racemizations and radio-bromide exchanges with 1 -arylbromoethanes in acetone with added LiBr are reported. The results are direct empirical evidence supporting the ion-pair mechanism for bimolecular nucleophilic displacement at saturated carbon. For the unsubstituted and less electron rich substrates, behaviour expected for a classical Sn2 mechanism is found, but for 1-(4-methylphenyl)bromoethane, the racemization rate is greater than twice the exchange rate, indicating internal return with racemization from a solvated ion pair. For 1-(3,4-dimethylphenyl)bromoethane, the carbocation is sufficiently stabilized that the reaction shows intermediate behaviour; the racemization rate is significantly less than twice the exchange rate, for example. Through the series from the electron withdrawer to electron donor substituted substrate, the activation parameter ΔH≠ progressively decreases and ΔS≠ becomes rapidly more negative.
Substituent effects in carbocations CX+, CHX+•, and CH2X+, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes
Authors: Hopkinson A. C. , Lien M. H.
Published: May 2006

Abinitio molecular orbital calculations with a 6-31G* basis set have been used to optimise structures for CX+, CHX+•, CHX (both singlets and triplets), H2CX+ and H3CX (X = H, CH3, NH2, OH, F, CN, and NC). Single point calculations were then performed on the 6-31G* optimised structures using a configuration interaction method involving all single and double excitations from the valence shell. Stabilisation energies for the carbocations are compared with those already reported for H2CX+. For the carbenes the single-triplet energy gap is examined as a function of substituent and the stabilisation energies of the singlet carbenes are compared with those of the isoelectronic carbocations H2CX+. Proton affinities are reported for the singlet carbenes and are compared with the proton affinities of similarly substituted ethylenes, H2C=CHX.
The reaction of 3-methyltricarballylic acid with acetic anhydride. Addendum: On Fittig's product from acylative decarboxylation of camphoronic acid
Authors: Strunz George M. , Giguère Pierre
Published: May 2006

Two products, 2,7-dioxa-1,4,4,5-tetramethylbicyclo[3.2.1]octane-3,6-dione (5), and 2-acetonyl-2,3,3-trimethylsuccinic anhydride (4) were identified from the base-catalysed reaction of camphoronic acid, 2 (R′, R″ = CH3), with acetic anhydride. The former (5) is believed to be identical with the product described by Fittig and assigned an isomeric formulation.
Two-dimensional nuclear magnetic resonance at 500 MHz: the structural elucidation of a Salmonella serogroup N polysaccharide antigen
Authors: Bundle David R. , Gerken Manfred , Perry Malcolm B.
Published: May 2006

High resolution 1H and 13C nmr spectroscopy at 500 MHz and 125 MHz was used for the structural analysis of the O-antigen of Salmonellalandau, which belongs to the Kauffmann–White serogroup N. This bacterial lipopolysaccharide was extracted from whole cells and hydrolyzed by mild acid to give lipid-free O-polysaccharide. Conventional one-dimensional 1H and 13C nmr data showed the polysaccharide to contain four monosaccharides in each repeating unit and, in addition, to carry an average of one O-acetyl group for every two repeating units. Two-dimensional nmr experiments aided the unambiguous assignment of the 1H and 13C resonances and thereby permitted the structural analysis of this polysaccharide by nmr techniques alone. The structure of the de-O-acetylated repeating unit was established as [Formula: see text][Formula: see text] through the use of methods which included homonuclear shift correlated (COSY and NOESY) experiments. The interpretation of this data was supported and simplified by consideration of firmly established 13C chemical shift assignments obtained from a heteronuclear 1H/13C shift correlated experiment. A three-dimensional model of the O-antigen obtained by semi-empirical calculations is shown to be consistent with interatomic distance constraints imposed by data from 2-D NOESY and one-dimensional nOe difference spectroscopy.
Synthesis of N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED) and derivatives
Authors: Martell Arthur E. , Motekaitis Ramunas J. , Clarke Eric T. , Harrison J. J.
Published: May 2006

Two synthetic approaches for the synthesis of N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED) and derivatives are reported. The first involves conversion of N,N′-di(2-hydroxybenzyl)ethylenediamine to the diamide HBEDDA via reaction with formaldehyde and HCN followed by hydrolysis. Analysis of the species distribution curves of the Cu(II) chelates of N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED) and its diamide, HBEDDA, and of the nature of the coordination in each complex species formed, suggest the selection of the reaction conditions most favorable for the Cu(II)-catalyzed hydrolysis of HBEDDA to HBED. The rate of conversion was found to be low, and the reasons for these findings are described. Iron(III) catalysis of the conversion of HBEDDA to HBED was found to be rapid and complete with a pseudo-first-order rate constant of 3.1 × 10−3 s−1 at 25.0 °C. The results provide the final step of a new method for the synthesis of HBED. The second synthetic approach involves reaction of N,N′-ethylenediamine-diacetic acid (EDDA) with substituted phenols and formaldehyde. These approaches appear to be general for the synthesis of HBED and derivatives.
A new truxillate and some flavonoid esters from the leaf gum of Traversiabaccharoides Hook. f.
Authors: Kulanthaivel Palaniappan , Benn M. H.
Published: May 2006

Investigation of the leaf washings of Traversiabaccharoides Hook. f. (Asteraceae: Senecionae) revealed the presence, besides typical cuticular lipids, of labd-13-ene-5,18-diol, 13-epi-ent.-manoyl oxide, n-butyl caffeate and its mono-O-isobutyrate derivatives, an α-truxillate photodimer of n-butyl caffeate (di-n-butyl traversate), (2S)-5,3′,4′-trihydroxy-7-methoxyflavanone, and various derivatives of quercetin including the 3-, 3′-, and 4′-mono-O-isobutyrates.
Ion-molecule reactions with carbon chain molecules: reactions with diacetylene and the diacetylene cation
Authors: Dheandhanoo Seksan , Forte Leonard , Fox Arnold , Bohme Diethard K.
Published: May 2006

Reactions of hydrocarbon and carbon/nitrogen ions with diacetylene and of the diacetylene radical cation with various molecules have been examined with a view to molecular growth by ion–molecule reaction. Measurements were performed with a Selected-Ion Flow Tube (SIFT) apparatus at 296 ± 2 K of the rate constants and product distributions for the reactions of C+, CH3+, C2H2+, C3H+, CN+, C2N+, and C2N2+ with C4H2 and of C4H2+ with H2, CO, C2H2, C2N2, and C4H2. Condensation and association reactions which build up the carbon content of the ion were observed to compete with charge transfer. For the reactions of CN+ and C2N2+ with C4H2 this growth involved the addition of cyanide to the carbon chain. The kinetics of protonation of diacetylene were also investigated. It was possible to bracket the proton affinity of diacetylene between the known proton affinities of HCN and CH3OH with a value for PA(C4H2) = 177 ± 5 kcal mol−1, which results in a heat of formation for C4H3+ of 305 ± 5 kcal mol−1. Numerous secondary association reactions were observed to form adduct ions in helium buffer gas at total pressures of a few tenths of a Torr with rates near the collision rate. This was the case for C6H4+ (C4H2+•C2H2), C7H5+ (C3H3+•C4H2), C8H4+ (C4H2+•C4H2), C8H5+ (C4H3+•C4H2), C9H3+ (C5H+•C4H2), C9H4+ (C5H2+•C4H2), C9H5 (C5H3+•C4H2), C10H4+ (C6H2+•C4H2), C10H5+ (C6H3+•C4H2), C11H7+ (C3H3+•(C4H2)2), C12H6+ (C4H2+•(C4H2)2), C9H3N+ (HC5N+•C4H2), and C10H4N+ (C2N+•(C4H2)2) where the reactants are indicated in parentheses. The observed high rates of association imply the formation of chemical bonds in the adduct ions but the structures of these ions were not resolved experimentally. In most instances there seems little basis for preferring acyclic over cyclic adduct ions.
AbInitio SCF MO calculations on the reaction of hydroxyl radical with cytosine
Authors: Eatock Beverley G. , Waltz William L. , Mezey Paul G.
Published: May 2006

Abinitio calculations have been carried out on the relative stabilities of various possible products of the reaction between cytosine and the OH radical. These products are of importance in modelling radiation damage to living tissues. The preferred theoretical gas-phase addition site is the C6 ring atom according to these calculations. The analysis of a series of possible contributions to solvent effects strongly suggests the predominance of intermolecular H bonds in stabilizing the experimentally observed C5 adduct.