bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of anhydrous and hydrated dimethylphosphinates of manganese(II). The crystal and molecular structure of poly-bis(μ-dimethylphosphinato)diaquomanganese(II)
Authors: Cicha Walter V. , Haynes John S. , Oliver Katherine W. , Rettig Steven J. , Thompson Robert C. , Trotter James
Published: May 2006

The dimethylphosphinate of manganese(II), Mn[(CH3)2PO2]2, and its dihydrate have been prepared and studied using magnetic susceptibility, differential scanning calorimetry, and electronic and vibrational spectroscopic methods. The dihydrate was obtained in crystalline form and a single crystal X-ray diffraction study revealed a polymeric structure.Crystals of poly-bis(μ-dimethylphosphinato)diaquomanganese(II) are monoclinic, a = 20.722(3), b = 4.8652(2), c = 11.0689(14) Å, β = 102.209(7)°, Z = 4, space group C2/c. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.033 for 983 reflections with I ≥ 3σ(I). The structure consists of infinite centrosymmetric chains of Mn(II) atoms linked by double phosphinate bridges and extending along the crystallographic b axis. The water molecules are involved in both interchain and bifurcated intrachain hydrogen bonding [Formula: see text], 2.899(3) and 3.120(3) Å). The coordination about Mn is slightly distorted octahedral with libration-corrected bond lengths Mn—O(phosphinato) = 2.156(2) and 2.212(2), Mn—OH2 = 2.247(2) Å.Magnetic susceptibility studies on the dihydrate from 300 to 4.2 K reveal a magnetic moment of ~5.9 BM over most of the range and give no evidence for significant magnetic exchange. The anhydrous compound, which is considered on the basis of indirect evidence to retain the double phosphinate bridged structure exhibited by the dihydrate, shows relatively strong antiferromagnetic behaviour. The data have been analyzed according to two theoretical models both of which employ the isotropic Heinsenberg Hamiltonian. The scaling model of Wagner and Friedberg gives J = −2.94 cm−1 and g = 2.02 and the interpolation scheme of Weng gives J = −2.69 cm−1 and g = 2.01. The magnitude of the exchange coupling is considered in relation to that observed in related manganese compounds and possible reasons for the observed damping of the exchange on hydration are discussed.
Magnetic concentration and polymorphism in di-n-octyl-, di-n-decyl-, and di-n-dodecylphosphinates of copper(II)
Authors: Haynes John S. , Oliver Katherine W. , Thompson Robert C.
Published: May 2006

Phosphinates of copper(II) of the type Cu(R2PO2)2 where R is n-octyl, n-decyl, and n-dodecyl have been synthesized and characterized by differential scanning calorimetry, vibrational and electronic spectroscopy, and variable temperature (300 to 4.2 K) magnetic susceptibility studies. Each of these compounds was obtained in distinct α and β structural forms. All materials appear to have the double phosphinate bridged extended chain structure and the magnetic data have been successfully analyzed according to the isotropic Heisenberg model for linear chains. The α forms exhibit antiferromagnetic behaviour with J values of −25, −29, and −29 cm−1 for the octyl, decyl, and dodecyl derivatives respectively. The β forms are ferromagnetic and have corresponding J values of 1.8, 2.1, and 2.3 cm−1 respectively. Magneto-structural correlations in these extended chain coordination polymers are discussed.
The oxidation of organic sulphides by Mortierellaisabellina. 2. Effects of substituents on the stereochemistry of sulphoxide formation
Authors: Holland Herbert L. , Pöpperl Heike , Ninniss Ronald W. , Chenchaiah P. Chinna
Published: May 2006

A series of para-substituted alkyl aryl sulphides has been transformed stereoselectively to the sulphoxide by incubation with the fungus Mortierellaisabellina. The enantiomeric purity of the products was dependent on the nature of substitution in the aromatic ring and at sulphur. Comparisons of the enantiomeric purities obtained from sulphides with para substituents of the same steric size but different electronic properties indicate that the stereoselectivity of S oxidation is susceptible to electron withdrawing or donating factors. This conclusion lends credence to a stepwise oxidation mechanism involving an electron deficient sulphur intermediate.
Microbial hydroxylation of steroids. 10. Rearrangement during epoxidation and hydroxylation, and the stepwise nature of these enzymic reactions
Authors: Holland Herbert L. , Riemland Elly
Published: May 2006

A series of unsaturated steroids has been incubated with fungi which are known to hydroxylate at a site corresponding to the allylic position in the analogous saturated steroids. In some cases, the anticipated hydroxylation occurred without rearrangement of the double bond. In a number of instances, however, products were obtained whose structures implied that allylic rearrangement had occurred during the reaction. The formation of these products is consistent with a stepwise mechanism of enzymatic oxidation. Possible routes for product formation are presented which incorporate this proposal.
Metabolites of Lachnellulafuscosanguinea (Rehm). Part 1. The isolation, structure determination, and synthesis of lachnelluloic acid
Authors: Ayer William A. , Villar J. Daniel Figueroa
Published: May 2006

The metabolites produced in liquid culture by the fungus Lachnellulafuscosanguinea (Rehm) Dennis have been examined and two antifungal agents, lachnelluloic acid and lachnellulone, have been isolated. The structure of lachnelluloic acid has been established as (−)-4-hydroxy-3-octanoyl-6-pentyl-5,6-dihydro-2-pyrone (1) by chemical and spectroscopic methods. The total synthesis of racemic lachnelluloic acid, starting from 6,8-tridecanedione (6) is reported. Lachnelluloic acid (1) shows strong antifungal activity against Ceratocystisulmi, the causative agent of Dutch elm disease.
Structure–sweetness relationships for fructose analogs. Part II. Synthesis and properties of 1,6-dihydroxy-2-hexanone, a simple analog of the ketohexoses, and X-ray structure determination of the corresponding dianhydrides
Authors: Szarek Walter A. , Martin Olivier R. , Rafka Robert J. , Cameron T. Stanley
Published: May 2006

Labile 1,6-dihydroxy-2-hexanone (4) was prepared from the corresponding triol by selective di-O-tritylation, Collins oxidation, and careful detritylation of the resulting keto compound 3 under mild, acidic conditions. As shown by its 1Hmr and 13Cmr spectra, 4 exists as a 3:2 mixture of open-chain and cyclic forms, respectively, at equilibrium in deuterium oxide (25 °C). Upon standing, 4 is slowly converted into a hemiacetalic dimer. Under acidic conditions, dehydrative dimerization takes place to give the corresponding tricyclic dianhydride, one or both of the possible isomers (1:1 mixture) of which being formed according to the presence or absence of water in the medium. The structure (trans) of the thermodynamic isomer 5 was firmly established by an X-ray crystallographic analysis.
13C nuclear magnetic resonance studies. 114. An examination of the [3.3.1.0] → [4.3.0.0] rearrangement via β-enolization and H/D exchange in tricyclic ketones
Authors: Ragauskas Arthur J. , Stothers J. B.
Published: May 2006

The behavior of the exo and endo isomers of 7,7-dimethyltricyclo[3.3.1.02,4]nonan-6-one (5, 6) under strongly basic conditions (t-BuOH/t-BuOH/185 °C) has been examined. In sharp contrast to their [3.2.1.02,4] analogs, the endo isomer is stable while the exo readily rearranges to 8,8-dimethyltricyclo-[4.3.0.02,4]nonan-7-one (16). Experiments were carried out in tert-butyl alcohol-O-d1 to establish the sites of deuterium incorporation in the initial ketones as well as the relative rates and stereoselectivities of the exchange processes. Ketones 5 and 6 were prepared through ring expansion by ketonization of cyclopropoxides generated from the [3.2.1.0] homologs; the stereochemistry of these ketonizations was established by 2H labelling.
Phospholipid – protein molecular interactions. 2. Raman spectroscopic and calorimetric studies of phospholipids – polylysine and phospholipid – histones interactions in model membranes
Authors: Bertoluzza A. , Bonora S. , Fini G. , Morelli M. A.
Published: May 2006

Dimyristoylphosphatidylcholine (DMPC) – polylysine and DMPC–histones systems have been studied by Raman spectroscopy and differential scanning calorimetry. The results of both techniques indicate that the interactions are mainly confined to the lipid–water interface. The protein fraction of histones giving rise to a partial penetration into the bilayer is not the lysine-rich fraction but rather the non-polar component of the proteins. On the basis of the results obtained, the formation of lipoprotein complexes between histones and DMPC appears to be ruled out.
Vibrational spectra and structure of N-methylacetamide in some solid complexes with neutral salts
Authors: Baron M. H. , Fillaux F.
Published: May 2006

Infrared spectra of crystalline complexes of N-methylacetamide (CH3CONHCH3) and of its ND analog with alcaline perchlorates, tetrabutylammonium halogenides, and alcaline halogenides have been investigated in NH stretching (3500–3050 cm−1), CO stretching (amide I, 1750–1500 cm−1), and NH bending (800–400 cm−1) regions. Possible structures for the complexes are proposed and the non-planarity of the amide group is discussed.
One-proton and multiproton hydrogen bonds between ammonium ions and hydrogen fluoride
Authors: Flakus Henryk T. , Boyd Russell J.
Published: May 2006

Extensive abinitio molecular orbital calculations are reported for the hydrogen bonded complexes of the formula [Formula: see text] and, [Formula: see text] where m = 0, 1, 2, and 3. The one-proton ("linear") hydrogen bonded complexes of the ammonium ions and hydrogen fluoride are predicted to be more stable by about 1 or 2 kcal/mol than the two- and three-proton ("bent") complexes. Several systematic trends and a number of differences between the neutral and protonated series of complexes are observed. The basis set dependence of the results, basis set superposition errors and electron correlation effects are discussed.
Molecular orbital studies of carbyne reactions: addition and insertion reaction paths for the reaction
Authors: Gosavi Ratnakar K. , Safarik Imre , Strausz Otto P.
Published: May 2006

Potential energy hypersurfaces have been studied for the [Formula: see text] addition and insertion reactions by abinitio molecular orbital theory. 6-31G basis set was used for complete geometry optimization of CH, C2H4, the cyclopropyl and allyl radicals as well as the reaction intermediates involved, with the RHF open shell SCF method. CI calculations were then performed at the SCF level optimized geometry. Analysis of the potential energy hypersurfaces predicts, in agreement with reported experimental data, a zero activation energy for the addition reaction via a non least motion, asymmetric reaction path, while the insertion reaction features a computed activation energy of 15 kcal mol−1.
Orbital angular momentum eigenfunctions for many-particle systems
Authors: Avery John
Published: May 2006

Methods are presented for constructing eigenfunctions of the total orbital angular momentum operator of a many-particle system without the use of the Clebsch–Gordan coefficients. One of the equations derived in this paper is analogous to Dirac's identity for total spin; and through this equation, a connection is established between eigenfunctions of L2 and irreducible representations of the symmetric group Sn.
The electronic structures of bis(η6-benzene)- and bis(η6-naphthalene)chromium(0)
Authors: Weber Jaques , Kundig E. Peter , Goursot Annick , Penigault Edouard
Published: May 2006

SCF MS Xα molecular orbital calculations are reported for the bis(η6-benzene)- and bis(η6-naphthalene)chromium(0) complexes. The bonding may be essentially discussed in terms of the covalent interactions between the metal 3d and ligand π and π* orbitals. The different charges on chromium atom in the two systems are explained by the different balances between ligand-to-metal (bonding) and metal-to-ligand (back-bonding) electron donations. Some resemblances are found between the electronic structures of the two compounds and it is possible to correlate to a large extent the energy levels of their molecular orbitals. However, a shift towards lower values is predicted for the energy levels of the naphthalene complex, together with a large disruption of all the virtual π* and 3d* levels. This would undoubtedly favor nucleophilic attack followed by metal–ring or carbon–carbon bond cleavage, in agreement with the extreme lability of the coordinated arene rings observed in this complex.
Hartree–Fock instabilities in the trisulphur–trinitride anion
Authors: Bénard M. , Laidlaw W. G. , Paldus J.
Published: May 2006

Crystallographic evidence indicates that the structure of the trisulfur trinitride anion, S3N3−, is planar with equal SN bond lengths. Although the recent literature contains a number of molecular orbital calculations of D3h symmetry there are also calculations which indicate inequivalent nitrogens, suggesting broken symmetry. The results of an investigation of Hartree–Fock instabilities of the abinitio molecular orbital description of this system are reported. The D3h solution is indeed singlet stable but there are relatively close-lying C2v broken-symmetry solutions. In the broken-symmetry solutions the π electron network encompasses only five centres; the sixth centre, essentially free of π charge, may be either a sulphur or a nitrogen, thus yielding two distinct broken-symmetry solutions.
Vacuum–ultraviolet photolysis (185 nm) of liquid 1,3-dioxan
Authors: Schuchmann Heinz-Peter , Sonntag Clemens von
Published: May 2006

1,3-Dioxan photolytic destruction at 185 nm occurs with a quantum yield of about 0.3 in the liquid phase. Of the 22 products determined, the major ones are n-propylformate [Formula: see text], formaldehyde (0.075), 1,3-diox-4-en (0.06), hydrogen (0.05), ethylene (0.04), and 3-methoxypropionaldehyde (0.04). A number of the minor products are of the general type B.[Formula: see text]some of which bear a hydroxyl function at the end of the side chain. N2O interacts with excited 1,3-dioxan, leading to the production of N2.Some experiments have been carried out in the vapour phase, the results of which indicate that considerable fragmentation of hot primary intermediates and products into low-molecular-weight products occurs. The nature of these products cannot be linked directly to the primary photolytic processes inferred from the liquid-phase studies.Certain contrasts in the photolytic behaviour of 1,3-dioxan and 1,4-dioxan are discussed.
Electron states and electron transport in quasi-one-dimensional molecular systems
Authors: Davydov Alexandr S. , Ukrainskii Ivan I.
Published: May 2006

It is shown that the concept of electron pairs may be introduced in conducting quasi-one-dimensional systems with electron delocalization such as (CH)x and the stacks of molecule-donors and acceptors of electrons TMTSF, TTT, TCNQ, etc. The introduction of pairing proves to be useful and electronic structure and electronic processes can be easily visualized. The two causative factors in the appearance of pairs in a many-electron system with repulsion are pointed out. The first one is the electron Fermi-statistics that does not allow a spatial region to be occupied by more than two electrons. The second one is the interaction of electrons with a soft lattice. The first of these factors is important at large and intermediate electron densities ρ ≥ 1, the second one dominates at [Formula: see text]. The kink-type excitation parameters in (CH)x are considered with a non-linear potential obtained in an electron-pair approach for the many-electron wave function of (CH)x.
Characterization of cooperative conformational transitions by Fourier transform infrared spectroscopy: application to phospholipid binary mixtures
Authors: Dluhy R. A. , Moffatt D. , Cameron D. G. , Mendelsohn R. , Mantsch H. H.
Published: May 2006

Temperature-induced cooperative conformational transitions in biopolymers may be examined in aqueous solution by the use of Fourier transform infrared spectroscopy. The transition is described in terms of a two-state model with a fractional population parameter (which describes the degree of transition at various values intermediate between the two limiting cases) that can be generated by a least-squares technique. This procedure allows for calculation of a conformational index without assuming a linear dependence of the infrared parameter on the extent of transition. Calculations based on the Zimm–Bragg theory of cooperative conformational transitions allow thermodynamic quantities to be derived using the conformational index in conjunction with calorimetric measurements.The method is illustrated with data from the gel/liquid-crystalline phase transitions of binary phospholipid vesicles where the use of isotopic substitution allows the conformation of each component of the binary mixture to be independently monitored. The data suggest the coexistence of well-defined structural domains of phospholipid as well as the preferential clustering of one of the lipid components at the interface between the two phases.
The photoabsorption of chlorodifluoroethenes in the vacuum ultraviolet
Authors: Rühl Eckart , Jochims Hans-Werner , Baumgärtel Helmut
Published: May 2006

The gas phase absorption spectra of 2-chloro-1,1-difluoroethene, cis- and trans-1-chloro-1,2-difluoroethene have been measured in the photon energy range from 6.5 to 25 eV. The π → π* transition is assigned to bands centered around 7.17 – 7.20 eV for all three isomers. Four Rydberg series are observed in all the spectra, converging to the π ionization potential: two np-type Rydberg series, one ns, and one nd series are assigned. The convergence limits are: 9.84 eV (2-chloro-1,1-difluoroethene), 9.86 eV (trans-1-chloro-1,2-difluoroethene), and 9.85 eV (trans-1-chloro-1,2-difluoroethene). In the case of 2-chloro-1,1-difluoroethene four additional Rydberg series are found converging to the nCl ionization potential. The convergence limit of these series is 12.15 eV.Above 12 eV broad absorption bands dominate the spectra.
The reaction of 3-methyltricarballylic acid with acetic anhydride: three products of acylative decarboxylation
Authors: Strunz George M. , Brisard Gessie , Giguère Pierre
Published: May 2006

Three products, 2-acetonyl-2-methylsuccinic anhydride (5), 2,7-dioxa-1,5-dimethylbicyclo[3.2. 1]octane-3,6-dione (6), and 3-acetonyl-3,5-dimethyl-2(3H) furanone (7) were identified from the base-catalysed reaction of 3-methyltricarballylic acid with acetic anhydride. These compounds arise as a result of acylative decarboxylation of 3-methyltricarballylic acid.
Chemistry of amido radicals: intramolecular hydrogen abstraction as related to amido radical configurations
Authors: Chow Yuan L. , Mojelsky Thomas W. , Magdzinski Leon J. , Tichý M.
Published: May 2006

Model bromamides were photolysed to investigate the reactivity of intramolecular C-5 hydrogen abstraction (from the nitrogen atom) of the corresponding amidyl radicals and of the cyclization of the resulting C-bromides. The observed results are discussed in terms of stereoelectronic as well as energetic considerations. In the former C-5 hydrogen abstraction, the reactivity difference between semi-rigid trans and cis-oriented reaction centers is only slightly in favor of the latter; the small difference is interpreted as due to the planar ground state Π amidyl radical structure with a low N—CO twisting barrier (4-5 kcal/mol). This interpretation is supported by the efficient C-5 hydrogen abstraction in N-bromo-N-alkyltoluamides, since a rigid planar amidyl radical does not allow the methyl C—H bond to colinearly approach the Π orbital. In marked contrast, there are large reactivity differences in the cyclization of C-bromides derived from these intramolecular H—Br exchanges; these arise from the requirement of colinearity of the approaching and departing bonds. Thus this requires the coplanar orientation of the C—CH3 and C—CO bonds and this is the source of the reactivity differences.
Synthesis and 13C nuclear magnetic resonance assignments of cannithrene 1: a cannabis constituent
Authors: El-Feraly Farouk S. , Cheatham Steve F. , McChesney James D.
Published: May 2006

Two synthetic approaches to cannithrene 1 (1) have been explored. One-pot annelation of 6,8-dimethoxytetralone by first forming a β-keto sulfoxide, then addition of methyl vinyl ketone, gave, unexpectedly, after elimination of the sulfoxide, the naphthol (10). The successful route to cannithrene 1 (1) involved regiospecific demethylation of 6,8-dimethoxytetralone, then its conversion to enone 16. Pyridinium bromide perbromide provided the necessary aromatization to give cannithrene 1 (1) after deprotection by hydrogenolysis. The 13C nmr assignments of 1 were made.
Six-bond 1H,1H and 1H,19F spin coupling constants as indicators of geometry in aniline and p-fluoroaniline
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

The long-range coupling constants between amino protons and the ring proton or fluorine nucleus in the para position of aniline and p-fluoroaniline imply that, in benzene solution, the geometry at the amino group is very similar in the two compounds. The ratio of the two coupling constants is consistent with potential functions for inversion at nitrogen derived from far infrared data, but inconsistent with microwave spectra which indicate that the angle defining the intersection of the amino and benzene planes differs by 9° in these two compounds.
A laser interferometric study of sessile drop shape and contact angle
Authors: O'brien R. N. , Saville Paul
Published: May 2006

Small contact angles, such as water on glass, have been shown to be measurable interferometrically using fringes of equal thickness after the fashion of Newton's rings. The measured angle for the water on glass system was 0.049 ± 0.006 degrees of arc.
Some reactions of 1-methyl-1,2-dihydropyridines with organic azides. Synthesis and reactions of 1,2,5,6-tetrahydropyridylidene-2-cyan(sulfon)amides and piperidylidene-2-cyan(sulfon)amides
Authors: Ondrus Theodore A. , Pednekar Purushottam R. , Knaus Edward E.
Published: May 2006

The regiospecific 1,3-dipolar cycloaddition reaction of 1,2-dihydropyridines 2 with organic azides 3 affords 2,7-diazabicyclo[4.1.0]hept-4-enes 4. Treatment of 4a with neutral aluminum oxide opened the aziridine ring to afford the 1,2,5,6-tetrahydropyridylidene-2-cyanamide 5. Catalytic hydrogenation of 4 and 5 using palladium-on-charcoal and hydrogen yielded the 1-methyl-2-piperidylidenes 6. Oxidation of 1-methyl-1,2,5,6-tetrahydropyridylidene-2-cyanamide (5) with alkaline hydrogen peroxide yielded the oxirane 7 arising from epoxidation of the 3,4-olefenic bond, whereas oxidation of the bicyclic aziridine 4a with m-chloroperbenzoic acid resulted in epoxidation of the 4,5-olefenic bond and opening of the aziridine ring to give the oxirane 3-methyl-3-aza-7-oxabicyclo[4.1.0]heptylidene-4-cyanamide (10). Base-catalyzed abstraction of the C-3 proton of 1-methyl-2-piperidylidenes 6 yielded the 3-lithio analogs which, after bromination, were converted to the target compounds 18 upon condensation with 4-[(2-aminoethyl)thiomethyl]-5-methylimidazole.
Étude d'α-bromo-butyrolactones; application à la préparation du méthyl-3 phényl-4 Δ2 buténolide et du méthyl-2 phényl-1 butène-2 diol-1,4 de configuration Z
Authors: Gharbi-Benarous Josyane , Morales-Rios Martha S. , Dana Gilbert
Published: May 2006

Starting from 2,3-dihydrofuranic compounds, we prepare the corresponding α-bromohydrines and α-bromo-butyrolactones. A solvolytic method of equilibration of these bromolactones in DMF is described. All the stereoisomers are separated and studied. With a Cβ substituant, the elimination promoted by a weak base (LiBr) gives the Δ2 butenolide in good yield, whatever the starting isomer configuration may be. An application is given with the stereoselective synthesis of a trisubstitued ethylenic γ-diol with a Z configuration.
Nuclear magnetic resonance and potentiometric studies of the complexation of methylmercury(II) by dithiols
Authors: Arnold Alan P. , Canty Allan J. , Reid R. Stephen , Rabenstein Dallas L.
Published: May 2006

Complexation of methylmercury, CH3Hg(II), by 2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropanesulfonate (DMPS, Unithiol), dithioerythritol (DTE), and 2,3-dimercaptopropanol (British AntiLewisite, BAL) has been studied by 1H nuclear magnetic resonance spectroscopy and by potentiometric titration. In the nmr study, the equilibrium constants for displacement of mercaptoacetate from its CH3Hg(II) complex by the dithiols were determined over a wide pH range, from mercaptoacetate chemical shift data. Similar competition reactions between the dithiols and mercaptoethanol were used in the potentiometric study. Using previously determined CH3Hg(II) formation constants for the competing ligands, equilibrium constants for the formation of mono- and bis-CH3Hg(II) complexes with the dithiols have been determined. The formation constants for the mono-CH3Hg(II) complexes with the vicinal dithiols BAL and DMPS are significantly higher than expected by consideration of the basicity of the sulfhydryl donors, in comparison with those for DMSA, non-vicinal DTE, and monothiols. We interpret this to indicate chelation of CH3Hg(II) by BAL and DMPS but not by DMSA. The conditional formation constants at physiological pH are discussed with reference to the effectiveness of BAL, DMPS, and DMSA as antidotes for methylmercury poisoning. In particular, the constants obtained indicate that, for dithiol antidotes at concentrations greater than that of methylmercury (II), methylmercury(II) complexes formed at physiological pH are of 1:1 stoichiometry. For BAL, a substantial proportion of the complex will be in the neutral form, in contrast to DMPS and DMSA which form anionic species only.
The influence of ammonium lignosulphonate as an expander on the formation of PbSO4 on lead amalgam electrodes
Authors: Barradas R. G. , Rennie D. A. , Vandernoot T. J.
Published: May 2006

Linear potential sweeps and potentiostatic pulse perturbations have been employed to investigate the influence of the expander ammonium lignosulphonate, on the anodic formation of PbSO4 on lead amalgam electrodes in sulphuric acid solutions at 24 °C. It was found that the expander strongly adsorbs onto the clean amalgam surface thus affecting the formation of the PbSO4 film. The expander increased the charge necessary for passivation, inhibited the cathodic reduction of the film, and produced a more porous film. Evidence is given for the presence of an optimum concentration of expander. Some speculations concerning the mode of action of the expander onto the amalgam surface are presented.
Déplacements homolytiques intramoléculaires. 4. Thermolyse du perpentène-4 oate de tert-butyle dans les acides et leurs derivés: préparation de γ-butyrolactones substituées en 4 par un groupe comportant une fonction ester, acide ou nitrile
Authors: Kharrat A. , Gardrat C. , Maillard B.
Published: May 2006

The thermolysis of tert-butylperpent-4-enoate in various solvents ZH (carboxylic acids, anhydrides, methyl esters, nitriles) led to γ-butyrolactones 4-substituted by the group ZCH2 with good yields. The acidic treatment of the lactones 4 and 6 derived from non-functionalized alkanoic acids and methyl esters gave respectively the isomerized lactones 5 and 7, increasing the synthetic interest of the studied homolytic reaction.
Enthalpies of interaction of nitrogen base solutes with organic solvents
Authors: Stephenson W. Kirk , Fuchs Richard
Published: May 2006

Heats of solution of triethylamine, aniline, pyridine, and model compounds (3-ethylpentane, benzene) in 17 organic solvents (n-heptane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane, α,α,α-trifluorotoluene, triethylamine, butyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, benzene, toluene, mesitylene, t-butyl alcohol, 1-octanol, methanol, 2,2,2-trifluoroethanol) have been combined with solute heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → s)). Differences between solute and model values (ΔΔH(v → s) = ΔH(v → s) (solute) – ΔH(v → s) (model)) were used to evaluate nitrogen base solute–solvent polar interactions. Correlations of ΔΔH(v → s) with Taft–Kamlet solvatochromic parameters (π*, α, β) have been determined.Aniline was found to be a better hydrogen bond donor acid than hydrogen bond acceptor base. Nevertheless, alcohols donate H-bonds to aniline. Triethylamine and pyridine are stronger HBA bases than aniline. The π* (dipolarity–polarizability) parameter of aniline (as a solute) is calculated to be 1.10.
Quantitative studies of the autoxidation of linoleate monomers sequestered in phosphatidylcholine bilayers. Absolute rate constants in bilayers
Authors: Barclay Lawrence Ross Coates , Locke Steven Jeffrey , MacNeil Joseph Mark , Vankessel Joann
Published: May 2006

The kinetics of autoxidation of linoleic acid in dimyristoylphosphatidylcholine (DMPC) bilayers were studied at 30 °C and pH 7 under 760 Torr O2. Reactions were initiated using either the lipid-soluble di-tert-butylhyponitrite (DBHN) or water-soluble azobis(2-amidinopropane)•HCl (ABAP). Rates of chain initiation, Ri, were measured with a lipid-soluble antioxidant, a-tocopherol, or a water-soluble one, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). The slightly higher oxidizability obtained [Formula: see text] compared to methyl linoleate in chlorobenzene [Formula: see text] is attributed to a moderate polar solvent effect on ionized linoleate near the bilayer surface. A low initiator efficiency, e = 0.0895 for DBHN in DMPC, is attributed to the cage effect in the bilayer of high microviscosity. Similar autoxidation experiments on methyl linoleate in DMPC bilayers gave a lower oxidizability [Formula: see text], indicating that the ester is sequestered deeper in the hydrophobic region of DMPC than is ionized linoleate. Some absolute rate constants are determined using the rotating sector technique for linoleic acid in 0.50 M SDS micelles, and egg lecithin and dilinoleoylphosphatidylcholine (DLPC) bilayers. A hundredfold decrease in the termination rate constant, 2kt for DLPC bilayer compared to homogeneous solution is attributed to chain termination in a bilayer region of high polarity. A concomitant reduction (up to tenfold) in the propagation rate constant, kp, is attributed to diffusion of polar peroxyl radicals away from the oxidizable region of the bilayer.
Modification of photochemical reactivity through the use of clathrates: the Norrish type I and type II reactions in Dianin's compound
Authors: Goswami P. C. , Mayo Paul de , Ramnath N. , Bernard G. , Omkaram N. , Scheffer John R. , Wong Y-F.
Published: May 2006

Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) serves as host in a series of well-defined clathrate inclusion complexes with eleven linear, as well as branched chain, phenyl alkyl ketone guest molecules, chosen for their ability to undergo the Norrish type I and type II photochemical reactions in solution. The photochemical reactivity of the guest ketones within the clathrate cavity was determined by irradiation of the inclusion complexes in the solid state. The results were compared to the photoreactivity of the ketones in polar as well as nonpolar liquid media. In general, the inclusion complex medium brings about an enhancement of type I over type II reactivity and causes an increase in type II fragmentation compared to type II cyclization. This change in reactivity is interpreted as resulting from the relatively restricted environment of the clathrate cavity coupled with the greater motion required for the type II process (γ-hydrogen abstraction) compared to the type I reaction (α-cleavage), as well as from the greater steric requirements for type II cyclization (cyclobutanol formation) as compared to type II cleavage (1,4-hydroxybiradical scission).
Permanganate peroxidation of cyclohexene. III. Hydroxide ion and salt effect studies
Authors: Taylor Jay E. , Green Renée
Published: May 2006

Good yields of cis-1,2-cyclohexanediol were formed by the reaction of cyclohexene and aqueous potassium permanganate under turbulent stirring conditions only in the presence of low concentrations of sodium hydroxide. Larger amounts had no further benefit or were deleterious. The lack of sensitivity to low concentrations of hydroxide ion indicated that its benefit is to inhibit acid promoted oxidations. There was no indication of its participation in the mechanism of glycol formation. The addition of the neutral salts, sodium sulfate or sodium nitrate, caused a decrease in glycol yields presumably due to a positive salt effect on a secondary negative ion – negative ion reaction, which formed other oxidation products. Stoichiometric amounts of hydroxide and potassium ions were not isolated as reaction products due to interaction with the hydrated manganese dioxide in a 1:2 ratio. The mechanisms in acidic and basic solutions appear to be quite different. A mechanism for basic solutions is suggested.
An abinitio molecular orbital theory study of the structure and stability of the hydrogen bridged radical cation molecule pairs [CH2CHOH—OH2]+• and [CH2CHOH—OHCH3]+•
Authors: Postma Ron , Ruttink Paul J. A. , Duijneveldt Frans. B. Van , Terlouw Johan K. , Holmes John L.
Published: May 2006

Abinitio molecular orbital theory was used to determine if C2H6O2+• and C3H8O2+• radical cations represented as hydrogen bridged radical cation molecular pairs, viz. [Formula: see text] and [Formula: see text] can be expected to exist as stable species in the gas phase.The use of several basis sets was explored at the SCF level and it was found that the above species have appreciable stabilisation energies with respect to dissociation into CH2=CHOH+• and H2O or CH3OH. Using a 6-31**/4-31G basis set and applying BSSE (Basis Set Superposition Error) corrections, respective stabilisation energies of 88 kJ/mol and 84 kJ/mol were calculated. Preliminary calculations further indicate that conversion barriers towards isomeric structures are high and thus ions of this type may well have been observed by experiment. Several reaction profiles have been calculated at the STO-3G level and at the 4-31G level, which show that the ions can exist in a syn and an anti conformation having comparable energies, their interconversion barrier being small.The structure parameters and stabilisation energies for these two hydrogen bridged ions are similar to those of the well known class of even electron species, usually designated as proton bound dimers.
Excess volumes and excess viscosities of binary liquid mixtures: methylisobutylketone + benzene, toluene, chlorobenzene, bromobenzene, and nitrobenzene
Authors: Jayalakshmi T. , Reddy Kalluru S.
Published: May 2006

Excess volumes for the binary liquid mixtures of methylisobutylketone with benzene, toluene, chlorobenzene, bromobenzene, and nitrobenzene have been measured at 303.15 and 313.15 K. Excess volumes were negative for all the systems over the entire range of composition and at both the temperatures. The behaviour of VE as a function of composition and temperature was studied. Viscosity data have also been determined for the five systems at 303.15 K. The excess viscosity, Δ ln η, has been calculated and its behaviour as a function of composition was investigated. The results of VE and Δ ln η have been discussed in terms of dipole – induced dipole and dipole–dipole interactions between the components. VE and Δ ln η were analysed in the light of Prigogine–Patterson–Flory equation of state theory and Bloomfield and Dewan's viscosity relations.
Investigation of the constituents of RyaniaSpeciosa
Authors: Ruest Luc , Taylor David R. , Deslongchamps Pierre
Published: May 2006

Six new metabolites (2, 5–9) were isolated from the extracts of RyaniaSpeciosa Vahl. These compounds are closely related to ryanodine, the known insecticidal toxic alkaloid from this plant.
The X-ray crystal structure of a Corynanthé-type indole compound, C22H29N2O4+Br−, wherein an unprecedented triaxial conformation is preferred
Authors: Chiaroni Angèle , Riche Claude , Grierson David S. , Husson Henri-Philippe
Published: May 2006

On the basis of 1H and 13C nmr data, a conformation was proposed for the Corynanthé type indole compound 8 in which the substituents at C-3 (indole), C-14 (ethyl), and C-15 (malonyl) were all axial. An X-ray crystal study on the HBr salt of 8 confirmed that this a priori unexpected conformation is also preferred in the solid state.
Proton affinities of the hydrogen, methyl, and trifluoromethyl halides from pulsed electron beam high pressure mass spectrometric equilibria measurements
Authors: McMahon T. B. , Kebarle P.
Published: May 2006

Pulsed electron beam high pressure mass spectrometric techniques have been used to investigate proton transfer equilibria involving hydrogen and trifluoromethyl halides. Methyl cation transfer equilibria have also been used to determine methyl cation affinities of hydrogen halides. Proton affinities obtained are HCl = 137.5, HBr = 142.9, Hl = 150.9, CF3Cl = 139.0, CF3Br = 141.3, and CF3l = 150.4 kcal mol−1. Methyl cation affinities obtained are HF = 15 ± 2, HCl = 19.8, HBr = 21.3, and Hl = 31.1 kcal mol−1. The values of methyl cation affinity of hydrogen halides can in turn be used to calculate proton affinities of the methyl halides of CH3Cl = 160.8; CH3Br = 164.8; and CH3l = 171 kcal mol−1. Linear correlations are found between proton affinities and valence ionization potentials and between proton affinities and methyl cation affinities.
Stereoselective synthesis and X-ray crystallographic analysis of mixed 6,6-dihalo penicillanates
Authors: Belinzoni Diego U. , Mascaretti Oreste A. , Alzari Pedro M. , Punte Graciela , Faerman Carlos , Podjarny Alberto
Published: May 2006

The pivaloyloxy methyl 6,6-dihalo penicillanates 1a, 1b, and 1c have been stereoselectively prepared from the reaction of pivaloyloxy methyl 6-diazo penicillanate 2 with either N-halosuccinimide/halide or the interhalogens Xl (X = Cl, Br). The crystal structures of 3S,5R,6R pivaloyloxy methyl 6-bromo, 6-chloro penicillanate1a; 3S,5R,6R pivaloyloxy methyl 6-iodo, 6-bromo penicillanate 1b, and 3S, 5R, 6R pivaloyloxymethyl 6-iodo, 6-chloro penicillanate 1c have been determined by X-ray single crystal analysis. The stereochemistry of the displacement reaction is discussed.
Excess molar volumes of binary mixtures of 2-hexanone with n-alkane at 298.15 K
Authors: Ortega J. , Paz-Andrade M. I. , Rodriguez-Nunez E. , Jimenez E.
Published: May 2006

The excess molar volumes, [Formula: see text], of 2-hexanone (MBK) with n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and n-tridecane have been obtained at 298.15 K from densities measured with a vibrating tube densimeter. The [Formula: see text] are positive over the entire composition range in all mixtures, with the exception of the MBK + n-hexane system, where an inversion of the sign of [Formula: see text] is observed. In other systems, [Formula: see text] increases with increasing size of the alkyl group in n-alkane.
Solubility of carbon dioxide in water–t-butanol solutions
Authors: Kruus Peeter , Hayes Catherine A.
Published: May 2006

The solubility of carbon dioxide has been determined in tertiary butanol – water mixtures over the temperature range 1–25 °C. The solubility exhibits a sharp, temperature-dependent minimum in water-rich solutions corresponding to a maximum in the activity coefficient of t-butanol, which has also been determined. The activity coefficient of t-butanol has a prominent temperature-dependent maximum (γ > 7.0) at a solution composition of about 0.06 mole fraction alcohol. Application of the scaled particle theory indicates that volume effects are a governing factor in the gas solubility, but are insufficient to explain the total effect. The pH of t-butanol–water and t-butanol–water–CO2 mixtures reveals no major anomalous solvation effect.
Infrared and Raman polarized spectra of ammonium hydrogen bis(trichloroacetate) single crystal
Authors: Videnova-Adrabinska Veneta , Baran Jan , Ratajczak Henryk , Orville-Thomas William J.
Published: May 2006

The polarized infrared and Raman spectra of ammonium hydrogen bis(trichloroacetate) single crystal have been investigated in the 4000–350 cm−1 and 4000–10 cm−1 range, respectively. The infrared spectra have been measured at room and low temperatures. An assignment of the bands in terms of approximate type of motion is given. The asymmetric stretching vibration, vaOHO, of the strong hydrogen bond gives rise to a very broad infrared absorption, with a maximum around 800 ± 50 cm−1, which is polarized strictly along a tetragonal Z(c) direction of this crystal. For this vibration a correlation field (Davydov or factor group) splitting is not observed. The out-of-plane deformation vibration, γOHO, obeys selection rules for the C2 site symmetry group. This result and also an interpretation of the vC=O vibration strongly suggest that a potential energy function of the strong hydrogen bond has a single symmetric minimum.
Complexation of glycylglycine by the methylmercury cation: a vibrational spectroscopy and X-ray diffraction study
Authors: Alex Serge , Savoie Rodrigue , Corbeil Marie-Claude , Beauchamp André L.
Published: May 2006

Two different crystalline complexes have been obtained from aqueous mixtures of glycylglycine (GlyGly) and methylmercury(II), and they were studied by vibrational spectroscopy and X-ray diffraction. In the first compound, a hydrogen atom of the protonated amino group of GlyGly is substituted by the CH3Hg+ cation, giving (CH3Hg)GlyGly: orthorhombic, Pna21, a = 7.920(6) Å, b = 13.473(5) Å, c = 8.059(3) Å, and Z = 4. Further complexation on the carboxylate group yielded the complex [(CH3Hg)2GlyGly]ClO4: monoclinic, P21/c, a = 6.407(4) Å, b = 24.439(6) Å, c = 8.461(2) Å, β = 93.82(4)°, and Z = 4. The sites of complexation and the conformations of these solid complexes are well reflected in their vibrational spectra. Raman spectra indicate that complexation in aqueous solutions is limited to substitution on the —NH3+ group of GlyGly.
Differential heats of dilution of tert-butanol into water-tert-butanol mixtures at 26.90 °C
Authors: Koga Yoshikata
Published: May 2006

The differential heats of dilution of tert-butanol into water-tert-butanol mixtures were measured at 26.90 °C. The results in the range where the mole fraction of tert-butanol, x, is less than 0.05 indicate that the hydrophobic interaction is repulsive and of long range; the interaction appears to extend its tail as far as six molecular distances or longer. Above the threshold concentration [Formula: see text], the differential heats of dilution were close to zero and approximately independent of concentration and temperature.
Open-chain nitrogen compounds. Part IX. 1,2,3-Triazolo[1,5-a]quinazoline and its 5-alkyl and 5-aryl derivatives from alumina-catalysed cyclization of 1-(2′-acylphenyl)-3-cyanomethyltriazene
Authors: Hooper Donald L. , Manning Hartford W. , LaFrance Ronald J. , Vaughan Keith
Published: May 2006

Alumina-catalysed cyclization of a series of 1-(2′-acylphenyl)-3-cyanomethyltriazenes (5) affords good yields of the previously unreported 5-alkyl- and 5-aryl-1,2,3-triazolo[1,5-a]quinazolines (8). The parent heterocycle, 1,2,3-triazolo[1,5-a]quinazoline, has been observed for the first time as the product of cyclization of 1-(2′-formylphenyl)-3-cyanomethyltriazene.
Schmidt reaction of some constrained aromatic acids, and related topics
Authors: Ruediger Edward H. , Gandhi Sham S. , Gibson Martin S. , Fărcaşiu Dan , Uncuţa Cornelia
Published: May 2006

Schmidt reaction of phthalic acid in 90–98% sulfuric acid gives anthranilic acid and anthranilazide (major products) by a process considered to involve 3,1-benzoxazin-2,4(1H)-dione as intermediate. Benzimidazol-2-one is produced in this reaction by a secondary process from anthranilazide; it is also produced by photolysis of anthranilazide. Under Schmidt reaction conditions, 1,2,3-benzotriazin-4(3H)-one gives o-azidobenzamide. Under similar conditions, the lactol of 4-formyl-5-phenanthroic acid gives 1-azapyren-2(1H)-one and phenanthrene-4,5-dicarboximide, while phenanthrene-4,5-dicarboxylic acid gives l-azapyren-2(1H)-one. Diphenic acid yields phenanthridone and 2,2′-diaminobiphenyl in proportions dependent on the sulfuric acid concentration.
Propriétés de solvation des solutions concentrées en acide phosphorique
Authors: Louis C. , Bessière J.
Published: May 2006

Solvation properties of ions inH2O–H3PO4 media (1–14 M) are characterized with their solvation transfer activity coefficients f. These are calculated from normal potential or solubility values, and indicate an increasing solvation for anions and decreasing solvation for cations in concentrated acid solutions. For each species, the range depends on its number of charges, on the existence of oxygen atoms in its structure, and on its basic properties. The consequences of variation of solvation on oxidation–reduction reactions and solubility properties are studied.
Low temperature magnetic and Mössbauer studies on anhydrous iron(II) sulfonates
Authors: Haynes John S. , Sams John R. , Thompson Robert C.
Published: May 2006

Magnetic susceptibilities from 130 to 4.2 K are reported for a series of Fe(RSO3)2 compounds, where R is F, CF3, CH3, and p-CH3C6H4. The β form of Fe(CH3SO3)2 exhibits a maximum in susceptibility at approximately 22.5 K and a sharp drop in susceptibility below the maximum indicating a transition to a magnetically ordered state. None of the other compounds exhibit magnetic ordering although abnormally low magnetic moments down to 2.0 K are observed for α-Fe(CH3SO3)2. Variable-temperature Mössbauer studies on Fe(CF3SO3)2 and β- and α-Fe(CH3SO3)2 are reported and the magnitude of axial field splitting is estimated for these compounds. The first two have trigonally elongated FeO6 chromophores, whereas the third is trigonally compressed. The nature of the distortion in α-Fe(CH3SO3)2 is confirmed by magnetic perturbation Mössbauer studies. Spectra in applied fields of 4.50 and 5.63 T show a doublet–triplet pattern, with the triplet at higher energy, indicating a negative Vzz and an orbital singlet ground state.
A multinuclear nuclear magnetic resonance study of methylammonium nitrate
Authors: Wasylishen Roderick E.
Published: May 2006

Deuterium nmr line shapes in the solid II phase of methylammonium nitrate (MAN) indicate that motion of the cation is restricted to internal rotations of the ND3 group about the C—N axis. In the high temperature plastic phase, solid I, of MAN, 2H, 14N, and 17O nmr results demonstrate that both the cation and anion undergo rapid overall rotations that result in complete averaging of all nuclear quadrupolar interactions. Spin-lattice relaxation results imply that rotations of the cation and anion are anisotropic and that the overall rotations are strongly coupled in both the solid I and liquid phases. At the melting point, overall rotations of the cation are only slightly faster in the liquid phase than in the solid I phase. In the solid I phase, in-plane rotations of the nitrate ion are about twice as rapid as end-over-end rotations of the C3 axis. In the neat liquid, rotations of the NO3− ion are more isotropic, with overall rotations being slightly faster than rotations about the symmetry axis.
E,E- and E,Z-α-phenyl-α′-acetoxyorthoquinodimethane: steric and electronic control of cycloaddition reactions
Authors: Charlton James L. , Alauddin Mian M. , Penner Glenn H.
Published: May 2006

E,E- and E,Z-α-phenyl-α′-acetoxyorthoquinodimethanes have been prepared from the corresponding cis- and trans-1-acetoxy-3-phenyl-1,3-dihydrobenzo[c]thiophene-2,2-dioxides. The regio- and diastereoselectivity of the addition reactions with dimethyl fumarate, dimethyl maleate, maleic anhydride, and methyl crotonate have been determined. Abinitio calculations have been carried out on orthoquinodimethane and its α-phenyl and α-oxy derivatives. A correlation has been made between the steric and electronic properties of the orthoquinodimethanes and the regio- and diastereoselectivity of their Diels–Alder reactions.