bluuebunny/crossref_metadata_2025 huggingface dataset:
The reaction between 2,2-diphenyl-1-picrylhydrazyl and bromine
Authors: Currie Patricia F. , Quail J. Wilson , Weil John A.
Published: May 2006

The reaction between 2,2-diphenyl-1-picrylhydrazyl and bromine in solution bas been studied at several temperatures. Despite the literature, reporting simple phenyl bromination products, a substantial yield of nitration products is observed. These have been identified by use of thin-layer chromatography, mass spectrometry, nuclear magnetic resonance, and elemental analysis. Among various products, 2-(p-nitrophenyl)-2-phenyl-1-picrylhydrazine is a major one at room temperature and above. It is thought that this compound is formed by reaction of DPPH with NO2, displaced from ortho nitro groups in the picryl rings by bromine. Yields were found to vary, depending on experimental conditions, with the temperature and the rate of bromine addition as primary controlling factors.
The preparation of polymeric siloxyphosphine rhodium(I) complexes
Authors: Brzezińska Zofia C. , Cullen William R.
Published: May 2006

Hydrolysis in dioxane/water (4:1 by volume) of performed rhodium(I) complexes of the phosphines Cl3Si(CH2)nP(C6H5)2 (n = 2, 8) either alone or in the presence of excess ligand or Cl3SiCH3 affords insoluble polymeric globules. Typical products have idealized formulae {[O3/2Si(CH2)2P(C6H5)2]3RhCl•(O3/2SiCH3)200}x, {[O3/2Si(CH2)8P(C6H5)2]4Rh2Cl2}x, and {[O3/2Si(CH2)2P(C6H5)2]2Rh(CO)Cl}x and seem to contain only rhodium(I). Apart from the last example the polymers in toluene suspension react with H2 and CO at 60 °C. In the case of CO the uptake ranges from 0.27–1.30 mol of CO per atom of rhodium. The main products appear to be Rh(CO)Cl derivatives.
Synthesis of maytansinoids: synthesis of an intermediate from D-glucose for the construction of maytansine
Authors: Ho Pak-Tsun
Published: May 2006

D-Glucose was converted to the lactone 1, an intermediate containing the appropriate functionalities and correct stereochemistry for the construction of maytansine.
The migratory aptitudes of some aryl groops in triarylvinyl cations
Authors: Lee Choi Chuck , Ko Eric C. F. , Rappoport Zvi
Published: May 2006

Errors reported in the literature on the migratory aptitudes of some aryl groups in triarylvinyl cations have been corrected. From the corrected as well as some new data, the relative migratory aptitudes for Ph: Tol: An in triarylvinyl cations in acetic acid media are calculated to be 1:4–5:162, based on kr(Tol)/kr(Ph) derived from migrations in the tritolylvinyl and 2-phenyl-1,2-ditolylvinyl cations and kr(An)/kr(Ph) derived from migrations in the 2-anisyl-1,2-diphenylvinyl and triphenylvinyl cations.
Solvent effect on the rate of N(III)/Cl(V) reaction
Authors: Emeish Samir S.
Published: May 2006

Kinetics of the reaction between N(III) and Cl(V) have been studied in water and water–dioxan solutions. The rate equation of the reaction in each solvent could be written as[Formula: see text]and the rate rises as the dielectric constant of the medium is lowered. This observation is in accord with suggested mechanistic details involving the intermediate H2NClO5.
The dynamic structure of acenaphthalene in the solid state: pulse nuclear magnetic resonance measurements
Authors: Sanford W. E. , Kupferschmidt G. J. , Fyfe C. A. , Boyd R. K. , Ripmeester J. A.
Published: May 2006

Pulse nmr has been used to determine the temperature dependence of T1 at 9.2, 18, and 60 MHz and also T1ρ at 9.2 MHz and T1D at 18 MHz, for the proton resonance of solid acenaphthalene. The data indicate a discontinuity at ~130 K, coincident with the main thermal anomaly in the specific heat curve, and suggest the occurrence of two distinct molecular motions with activation energies 14.2 kJ mol−1 and 18.9 kJ mol−1. Calculations using non-bonded atom–atom potential functions explain qualitatively the results of the nmr study and it is suggested that the two motional processes may be due to two sets of crystallographically different acenaphthalene molecules.
Etude paramétrique de l'enrichissement en carbone-13 dans la décomposition polyphotonique de CF3Cl
Authors: Gauthier M. , Willis C. , Hackett P. A.
Published: May 2006

The yield and 13C content of the product C2F6 were measured following the multiphoton infrared decomposition of CF3Cl. These factors were studied as a function of the activation frequency ω, of the pressure of CF3Cl, of the temperature T, and of the incident energy E0. As in the case of CF3Br and CF3I the yield increases according to P2E02. [Journal translation]
The reaction of some nuclear substituted acyclic conjugated styryl ketones and related Mannich bases with ethanethiol
Authors: Dimmock J. R. , Smith L. M. , Smith P. J.
Published: May 2006

The second order rate constants for the reaction of ethanethiol with a number of conjugated nuclear-substituted styryl ketones and related Mannich bases in 50% aqueous acetonitrile was undertaken. Variation of the alkyl group adjacent to the carbonyl function was accompanied by altered avidity to ethanethiol which was explained as being due in part to the varying inductive effects of the alkyl groups which would, in turn, affect the stability of the reaction intermediates. The greatest disparity in reactivity between groups of compounds was between the ketones and analogous Mannich bases which was in accord with the marked difference in bioactivities between these two groups of compounds.
Standard electrode potentials of the chloranil electrode in formamide at different temperatures
Authors: Dash Upendra Nath , Nayak Surendra Kumar
Published: May 2006

From the emf measurements of the buffered cell[Formula: see text]the standard potentials of the chloranil electrode have been determined in formamide at 15, 25, 35, and 45 °C. The standard molal potential of the chloranil electrode has been expressed through the equation[Formula: see text]The standard thermodynamic quantifies, ΔG0, ΔH0, ΔS0, and ΔCP0 for the electrode reaction have been calculated from the standard molal potential, Em0 of the electrode at these temperatures.
Stereocontrolled catalytic hydrogenations of 3-oxocholestanes and some related compounds to the corresponding axial 3-alcohols
Authors: Ishige Masayoshi , Shiota Michio
Published: May 2006

Catalytic hydrogenations of 5α-cholestan-3-ones and related compounds with Urushibara nickel A catalyst in cyclohexane gave a distinct preponderance of unstable axial 3α-ols. Product ratios of axial alcohols decreased with increasing solvent polarity. For 3-oxo-5α-steroids, the cobalt catalyst was less selective for the axial alcohol formation. On the other hand, conversion of 5β-cholestan-3-one into the corresponding axial 3β-ol was most successfully attained by hydrogenation catalyzed by Urushibara cobalt A catalyst in methanol. For such a 5β-ketone, alcoholic media with higher polarities were more favorable for giving the product rich in axial alcohol. The stereochemistry of the products obtained from hydrogenations conducted in nonpolar solvents may be understood in terms of the steric congestion around the ketone carbonyl group. However, when alcohols were used as solvents, the product ratios obtained did not correlate well with the congestion ratios of substrates.
A study of the donor properties of the phenoxachalcogenines II: 7,7,8,8-tetracyanoquinodimethane as the acceptor
Authors: Rainville David P. , Zingaro Ralph A. , Ferraris John P.
Published: May 2006

The phenoxachalcogenines have been studied as donors towards 7,7,8,8-tetracyanoquinodimethane. For the 1:1 complexes studied, the equilibrium constants, K, vary over the range 4–6; the enthalpy, ΔH0, is about −2.0 kcal/mol; the free energy, ΔG0, is −1.4 to −1.0 kcal/mol, and the entropy change, ΔS0, is −7.3 to −3.5 eu. The entropy change is greatest in the case of the dibenzo-1,4-dioxane – 7,7,8,8-tetracyanoquinodimethane charge-transfer complex. This is attributed to the planarity of the dibenzo-1,4-dioxane molecule. The extinction coefficient, εc, for the series studied varies from 115 to 230, and no regularity in the trend has been noted.The lack of any significant changes (with change in the chalcogen atom) in the thermodynamic values for the phenoxachalcogenine – 7,7,8,8-tetracyanoquinodimethane charge-transfer complexes is interpreted in terms of a similar π to π type interaction involving a delocalized π orbital of the phenoxachalcogenine rather than a localized n orbital of the hetero atom.The room temperature four-probe dc conductivities of single crystals of PSe–TCNQ and PS–TCNQ were found to be 4 × 10−8 and 3 × 10−7 ohm−1 cm−1, respectively.
Water attack at an sp2 hybridized-carbon: the hydroxyl σ-complex of 4,6-dinitrobenzofuroxan in water–DMSO–tetramethylammonium chloride mixtures
Authors: Terrier François , Sorkhabi Habib Achassi , Millot François , Halle Jean-Claude , Schaal Robert
Published: May 2006

The kinetics of formation and decomposition of the hydroxyl-σ adduct 2 derived from 4,6-dinitrobenzofuroxan 1 have been studied in various water – dimethylsulphoxide (DMSO) – tetramethylammonium chloride (I = 0.5 M) mixtures. At pH < 7, the formation of 2 occurs exclusively from water attack at the 7-carbon of 1. This process is strongly favored by DMSO: the first-order rate constant k1H2O changes from 1.9 × 10−2 s−1 in water to 1.33 s−1 in 90% DMSO. Taking into account the decrease in the water content of the solutions, and assuming that only one water molecule participates in the reaction, this increase in k1H2O reflects a 103-fold increase in the ability of a water molecule to act as a nucleophile. This interesting result compares well with previous data reported by Murto for the solvolysis of 2,4-dinitrofluorobenzene in the same solvent mixtures.
The activity coefficients of some polar solutes in benzene
Authors: Anantaraman A. V. , Goldman Saul
Published: May 2006

Cryoscopy was used to determine the low concentration (< 1 molal) stoichiometric molal activity coefficients of: chlorobenzene, m-dichlorobenzene, o-dichlorobenzene, and nitromethane in benzene. The data were corrected to a fixed temperature (10 °C) by using pre-existing heat of mixing data. The activity coefficients all showed negative deviations from Henry's law ideality, and some of the factors that contribute to this non-ideality were discussed.
Carbon-13 chemical shift assignments of chromones and isoflavones
Authors: Jha Hem Chandra , Zilliken Fritz , Breitmaier Eberhard
Published: May 2006

Carbon-13 chemical shifts of 8 chromones and 35 isoflavones variously substituted by hydroxy-, acetoxy-, and methoxy-groups are assigned. The applicability of chemical shift increments reflecting inductive and resonance effects is discussed. Some general relations between substitution patterns and carbon shielding useful for the identification of naturally occurring isoflavones are outlined. Typical C—H couplings of chromone and phenyl carbons are analyzed for a 4′,6,7-trisubstituted derivative.
The conformations of tartaric acids in aqueous solution studied by 1H and 13C nuclear magnetic resonance
Authors: Ascenso José , Gil Victor M. S.
Published: May 2006

Vicinal H—H and C—H coupling constants are reported for (+)-tartaric acid and meso-tartaric acid at various pH values and used in a discussion of the conformation of these molecules. This is found not to change much with pH. For the meso form, in particular, the most favoured conformer is determined not so much by the possibility of internai [Formula: see text] hydrogen bonding but, at least in part, by stabilization of polar conformations in a sol vent (H2O) of high dielectric constant.
Déshydratation des diols-1,2 α,β-éthyléniques IV: rôle de la stéréomutation des carbocations allyliques α-hydroxylés sur l'orientation des réactions observées
Authors: Dana Gilbert , Gharbi-Benarous Josyane , Thuan Sa Le Thi
Published: May 2006

The allylic carbocations[Formula: see text]formed during the dehydration of diols of type A[Formula: see text]are found to react by five different processes: three nucleophilic attacks (by solvent at the β or δ positions, or by the intramolecular hydroxyl group at δ), a degradation reaction between Cα, and Cβ and the classical pinacol rearrangement.Nucleophilic attack at the carbon δ is a very efficient reaction and sometimes (for monosubstituted substrates in β, γ or δ) gives quasi-exclusive products: a ketone for the reaction with H2O in δ or a 2,5-dihydrofuran product for the intramolecular reaction.In the case of γ and δ disubstituted carbocations, the selectivity is less and we show that it is possible to analyze the different steric effects commanding the stereomutation equilibrium of the allylic carbocation and so determining the orientation in the dehydration.
The distribution of trialkylphosphates between dodecane and water
Authors: Sagert Norman H. , Lee Woon
Published: May 2006

The distribution of the four lower trialkylphosphates, triethyl, trimethyl, tripropyl, and tributylphosphates, between dodecane and water has been measured as a function of temperature between 293.15 K and 313.15 K, and as a function of trialkylphosphate concentration at concentrations below 0.1 mol/dm3. From these results, the thermodynamic functions associated with the transfer of each of these trialkylphosphates from water to dodecane were calculated. With the exception of trimethylphosphate, free energies of transfer changed by −3.5 kJ/mol for each methylene group added to the solute. The enthalpies of transfer for all the trialkylphosphates were in the range of 26 to 30 kJ/mol, so that most of the differences in the free energies of transfer arise from entropic differences.Dimerization constants for the trialkylphosphates in dodecane were consistent with those available in the literature.
Mercury(II) and cadmium(II) halide complexes of tertiary phosphine sulfides and selenides
Authors: Grim Samuel O. , Walton Edward D. , Satek Larry C.
Published: May 2006

Phosphorus-31 nmr data are reported for tri-n-butylphosphine selenide complexes of mercury(II) and cadmium halides and for some miscellaneous complexes of tertiary phosphine sulfides and selenides with the same metal halides. The ligands in the complexes are labile in solution at room temperature but the exchange can be "frozen out" in certain cases at reduced temperature. Selenium-77–phosphorus-31 coupling constants are less in the complexes than in the free ligands and 1JPSe decreases in each observable case with decreasing temperature. Two bond mercury-199–phosphorus-31 coupling is observed in some of the cooled solutions of the complexes.
Etude en rmn 13C de bicyclo[4,n,0]alcanones-3 trans α-substitués. Influence de la nature et de l'orientation du substituant sur le déplacement chimique du 13C du carbonyle
Authors: Metzger Pierre , Casadevall Eliette , Casadevall André , Pouet Marie-José
Published: May 2006

The 13C nmr spectra of α, αα, and αα′ substituted trans-fused bicyclo [4,n,0]alkan-3 ones, are described. Substituent effects are discussed in terms of their electron withdrawing character, axial or equatorial configuration, and cyclohexane deformation. 13C=O chemical shifts are shown to be based on the polarization of π bond and on C=O/X non-bonded interactions. As in ir and uv spectroscopy, 13C nmr is a convenient method for detecting an a substituent configuration in fixed ring ketones.
N,N-Dimethylpicramide–methoxide ion interactions: 1:1 and 2:1 σ-complex formation
Authors: Buncel Erwin , Hamaguchi Masashi , Norris Albert R.
Published: May 2006

The interactions of N,N-dimethylpicramide (DMP) with methoxide ion in dimethylsulfoxide–methanol media have been investigated spectrophotometrically at 25.0 °C. Both the 1:1 and 2:1 σ-complexes of DMP and methoxide ion have been observed under the various reaction conditions employed. However, dimethylsulfoxide has been found to preferentially stabilize the 1:1 σ-complex relative to the 2:1 σ-complex. As a consequence, at low base concentrations in dimethylsulfoxide–methanol solutions rich in dimethylsulfoxide (i.e. 95/5, v/v, DMSO/MeOH), the 1:1 σ-complex can be formed in the absence of any 2:1 σ-complex. This observation has been used to obtain, for the first time, values of the absorption maxima and molar absorptivities at the absorption maxima of both the 1:1 and 2:1 σ-complexes.
The role of the molecular environment for the primary photoprocesses of phenol in solution
Authors: Zechner J. , Köhler G. , Grabner G. , Getoff N.
Published: May 2006

Quantum yields of fluorescence as well as of solvated electron and H atom formation have been measured for phenol in several pure solvents and mixtures of varying polarity. The influence of excitation energy has been studied by excitation of phenol in the first and second excited singlet states. The solvent dependences of fluorescence and photoejection parameters are strongly correlated. The results are interpreted in terms of specific solute–solvent interactions, in particular H-bonded structures.
Hydrolytic behavior of two β-lactams and their corresponding imidate salts. New evidence for stereoelectronic control
Authors: Deslongchamps Pierre , Caron Maurice
Published: May 2006

The basic hydrolysis and the concurrent carbonyl–oxygen exchange of 18O-labelled N-phenyl-4-phenyl-2-azetidinone (5*) and N-2,6-dimethylphenyl-2-azetidinone (6*) have been studied. β-Lactam 5* was easily hydrolysed and showed no carbonyl–oxygen exchange with 0.1 N sodium hydroxide (dioxane–water, 9:1). Under the same conditions, β-lactam 6* gave no exchange and was found resistant to basic hydrolysis. Hydrolysis and exchange was observed when 6* was refluxed with 0.1 N and 1 N sodium hydroxide in water.The hydrolysis of the corresponding imidate salts 7 and 8 was also investigated. Under basic conditions, salt 7 gave an 8:2 mixture of ester amine 9 and β-lactam 5, while under acidic conditions the hydrochloride salt of ester amine 9 was the only product. Under basic conditions, the imidate salt 8 produced only the β-lactam 6, and under acidic conditions, a 3:7 mixture of the hydrochloride salt of 10 and β-lactam 6. Under stronger acidic conditions (≥3 N HCl), 8 gave only the starting β-lactam 6.The results of these hydrolysis reactions are easily explained on the basis of the stereoelectronic theory for the cleavage of tetrahedral intermediates, and by taking into account that the nitrogen of tetrahedral intermediates must be either protonated under acidic conditions, or hydrogen bonded with the solvent under basic conditions in order to observe the cleavage of the C—N bond.
Enthalpies of interaction of polar and nonpolar solutes with a perfluoro solvent
Authors: Fuchs Richard , Peacock L. Alan , Das Kamalendu
Published: May 2006

Enthalpies of solution of 51 polar and nonpolar organic solutes have been determined in the solvent perfluoro-1,3-dimethylcyclo-hexane. The values have been combined with solute enthalpies of vaporization to give the enthalpies of transfer from vapor to solvent. These solvation enthalpies are for most solutes substantially less exothermic than those measured in other solvents. Polar interactions appear to be stronger than with hydrocarbon solvents; but this may result, in part, from incomplete dissociation of strongly associated solutes in the perfluoro solvent.
The gas phase acidities of fluorinated acetones. An ion cyclotron resonance investigation of the role of fluorine substituents in the stabilization of planar carbanions
Authors: Faird R. , McMahon T. B.
Published: May 2006

The gas phase acidities of a series of fluorinated acetones and acetylfluoride have been determined. The results obtained are interpreted in terms of a model for fluorine substituents in planar carbanions in which fluorine exerts an overall stabilizing influence on enolate ions, but also has a component in the interaction which is destabilizing via a repulsive interaction between fluorine lone pair electrons and the carbanion centre. Comparisons with solution phase acidities are made and the validity of the model for fluorine substituents discussed.
Electrophilic additions to strained alkenes. II. The reaction of benzeneselenenyl chloride with tricyclo[4.2.2.02,5]deca-3,7-diene derivatives
Authors: Garratt Dennis G. , Ryan M. Dominic , Kabo Ann
Published: May 2006

The reactions of benzeneselenenyl chloride with three derivatives of tricyclo[4.2.2.02,5]deca-3,7-diene have been investigated in four solvent systems: methylene chloride, acetic acid, acetic acid/LiClO4, and methanol. Under conditions of kinetic control only products of exo–anti attack upon the cyclobutene moiety are isolable when the solvent system is methylene chloride or acetic acid. This observation also holds in acetic acid/LiClO4 except in the case of dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate where the major product is that of cross-bonding with solvent incorporation. In methanol products of solvent incorporation, transannular cross-bonding and lactonization (where possible) are observed. A general mechanistic scheme is proposed to account for these observations in accord with earlier results for the analogous arenesulphenylations.
Sulfonation of strychnine and some related compounds by sulfur dioxide – manganese dioxide (the Leuchs reaction)
Authors: Edward John T. , Farrell Patrick G. , Samad Syed A. , Wojtowski Richard , Wong Sin Cheong
Published: May 2006

On the basis of pK measurements, 13C nmr, and chemical arguments, the zwitterionic structures 3 and 4 have been assigned to the two minor products obtained by sulfonating strychnine or brucine in water with a mixture of sulfur dioxide and manganese dioxide. The same reagent sulfonates the quaternary salts of strychnine and brucine to give betaines, but fails to sulfonate many other strychnine derivatives as well as a number of other alkaloids examined.
A nitrogen-15 nuclear magnetic resonance study of N-aryl phosphoramidates and phosphorimidates
Authors: Buchanan G. W. , Morin F. G. , Fraser R. R.
Published: May 2006

15N nuclear magnetic resonance chemical shifts and one-bond 15N—31P couplings are reported for a series of five N-arylphosphoramidates and four N-arylphosphorimidates. Results are interpreted in terms of an extensively delocalized N lone pair in the phosphoramidates, with pπ–pπ donation into the aromatic ring being dominant over pπ–dπ donation from nitrogen to phosphorus.
A nuclear Overhauser effect difference study of the solution conformation of (6R)-prostaglandin I1
Authors: Kotovych George , Aarts Gerdy H. M.
Published: May 2006

Proton magnetic resonance studies at 400 MHz allowed the complete assignment of the spectra for (6R)-prostaglandin I1 in phosphate buffer and in CDCl3 solutions. The spectral analysis was based on the nuclear Overhauser effect difference measurements, which also provide accurate chemical shifts and coupling constants. Conformational differences in the two solvents for the ring portion of the molecule are indicated.
Polymérisation du norbornène par des amorceurs au ruthénium. Etude cinétique de la réaction
Authors: Tanielian Charles , Kiennemann Alain , Ösparpucu Temel
Published: May 2006

The kinetic parameters for the polymerisation reaction of norbornene with RuCl3•3H2O, and RuCl2(PΦ3)3 using homogeneous catalysis have been determined (first-order with respect to two initiators, zero-order with respect to the monomer with RuCl3•3H2O, and variable order with RuCl2(PΦ3)3: Ea 6.2 kcal/mol for RuCl2(PΦ3)3 and 22.8 for RuCl3•3H2O) and leads us to propose different reaction mechanisms for the polymerisation starting from the two initiators, at least for the initiation step. With RuCl2(PΦ3)3 the slow step of the reaction is the metathesis whereas with RuCl3•3H2O the slow step is a ligand exchange at the initiator involving solvent (alcohol) by a dissociative or associative mechanism. This slow step is confirmed by a study of varying alcohol concentration and initiator aging. [Journal translation]
The photolysis of tetrahydrofuran and of some of its methyl derivatives at 185 nm
Authors: Klzilkilic Nuray , Schuchmann Heinz-Peter , Sonntag Clemens von
Published: May 2006

The uv photolysis of tetrahydrofuran, 1, 2-methyltetrahydrofuran, 2, cis-2,5-dimethyltetrahydrofuran, 3, trans-2,5-dimethyltetrahydrofuran, 4, and 2,2,5,5-tetramethyltetrahydrofuran, 5, has been investigated by product analysis in the liquid phase, and quantum yields have been determined. The photolysis of tetrahydrofuran itself was also studied in the gas phase at pressures ranging from 1 to 120 atm (pressurizing gas N2); and very little difference was found between the photolytic behaviour of the vapour at 120 atm and that of the liquid. The major products are in ail cases the cyclopropanes and the corresponding carbonyl compounds, as well as the olefinic alcohols and the carbonyl compounds that are isomeric with the starting material. These products are considered to be formed by the two major primary processes [i] and [ii].[Formula: see text]The cyclopropanes formed in reaction [i] retain some excess energy (apparently more than is needed to realize the trimethylene form), and in the photolysis of tetrahydrofuran vapour the hot cyclopropane rearranges to a considerable extent into propene. The propene to cyclopropane yield ratio falls strongly with increasing pressure, to a value of 0.065 at 120 atm. A similar value is observed in the liquid phase photolysis.The five-membered oxyl alkyl diradical from reaction [ii] is the likely intermediate in the cis-trans photoisomerization that is observable with the 2,5-dimethyltetrahydrofurans [Formula: see text]. The photolysis of these compounds also demonstrates that steric factors have a strong bearing on the course of the reaction, e.g. the quantum yield of methylcyclopropane from the cis compound is 0.22, vs. 0.08 from the trans compound.Molecular hydrogen is produced if the tetrahydrofurans carry hydrogen in α-position. Its production is enhanced if the α-position is shared with a methyl group (1 gives a hydrogen quantum yield of 0.07, 2 of 0.17, 3 of 0.27, 4 of 0.29, and 5 of zero).
Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects
Authors: Cabelkova-Taguchi Lubomira M. , Warkentin John
Published: May 2006

A series of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina. The triazolinones decompose in solution to N2, CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148–200 °C. Average activation parameters are ΔH≠ = 35 kcal mol−1 and ΔS≠ = 8 cal K−1 mol−1. Substituent effects are correlated through σ-constants but the thermolyses are relatively insensitive to substituents, with ρ = −0.17 at 172.5 °C. Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation. Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.
Solvent effects on the visible absorption spectrum of crystal violet
Authors: Korppi-Tommola J. , Yip R. W.
Published: May 2006

Addition of polar solvents to non-polar solutions of crystal violet results in dramatic changes in the visible absorption spectra. The observed changes are explained in terms of crystal violet existing as an ion-pair in non-polar solutions and as a solvated ion in polar solutions.The spectrum of crystal violet in toluene and in acetone solution remains virtually unchanged over a wide temperature range. However in methanol, as was reported for ethanol (1), the short wavelength component of the absorption in the visible region disappears as the temperature is lowered. The spectral behaviour in alcoholic solutions suggests a decreasing solvent–solute interaction around the dye cation due to increased self-association of the solvent molecules as the temperature is decreased. Our observations have a direct application in interpreting some of the results of the photodynamics of crystal violet in solution.
Selective transformations of secologanin: dihydroxylation
Authors: Purdy John Richard , Hamilton Raymond G. , Akhter Lalarukh , McLean Stewart
Published: May 2006

Sweroside tetraacetate (2b) has been converted in high yield by osmylation to the epimeric glycols 3 and 4 (R = H) which have been separated. This reaction proceeds with high chemoselectivity for reaction at the vinyl side chain but with low stereoselectivity, leading to a small excess of the 3-R isomer. Secologanin derivatives appear to show a much lower chemoselectivity in this reaction, but the stereoselectivity is considerably higher, and opposite to that in the sweroside example. Conditions have been found for oxidizing the dimethylacetal 5b of secologanin tetraacetate in useful yields to the epimeric glycols 6 and 7 (R = H); in this reaction a large excess of the 3-S isomer is formed. The reasons for these differences in selectivity appear to be related to differences between the two series in conformational preference.
Adsorption of N-methylacetamide and L-arginine onto apatitic phosphates
Authors: Garcia-Ramos J. V. , Carmona P.
Published: May 2006

The adsorption of N-methylacetamide and of L-arginine on apatitic phosphates has been studied by infrared spectroscopy. During the initial adsorption, the bands of adsorbed N-methylacetamide indicate the presence of the trans form attached to surface cations via the carbonyl group. The position of the amide I band is found to give a linear correlation with q/r for apatitic cations (where q is the charge and r the radius of a cation). At higher amounts of adsorbed amide, hydrogen bonding arises either from the self-association of amide molecules or from the binding of these to the surface phosphate anions. L-Arginine can be adsorbed through the groups containing NH bonds or through the carboxyl group. Infrared spectra of calcinated samples as well as the Ca/P ratio determinations point out that a substitution of L-arginine positive ions for surface cations takes place upon adsorption of this amino acid on apatitic calcium phosphate.
9-Oxobenzomorphans. IV. 9-Oxo-5-[3″-(1″-hydroxypropyl)]- and 9-oxo-5-[3″-(1″-sulfidrylpropyl)]-6,7-benzomorphans as cyclic hemiketals and hemithioketals
Authors: Kavadias Gerry , Velkof Stephan
Published: May 2006

The syntheses of 9-oxobenzomorphans 10 and 12 are described. Both products exist in the cyclic forms 11 and 13 respectively. Hydrobromide and oxalate salts of the 9-oxobenzomorphan 1 when crystallized from methanol form stable methylhemiketals 4 and 5. Bromination of 5 yielded benzomorphan 8 which on treatment with sodium hydroxide produced, via 10, the cyclic hemiketal 11. Reaction of 8 with sodium hydrogen sulfide afforded, via 12, the cyclic hemithioketals 13.
A novel synthesis of 2,4,6-trithiaheptane and its conversion into 2,6-bis(methylthio)thiane. Spectral properties of some thiaalkanes
Authors: Grossert J. Stuart , Hooper Donald L. , Neaves William M.
Published: May 2006

2,4,6-Trithiaheptane (1a) has been prepared by lithium tetrahydridoaluminate reduction of the methiodide of 1,3,5-trithiane (2). Treatment of 1a with strong bases permitted formation of 3-alkylated derivatives (3) which could in turn be converted into diastereomeric mixtures of 3,5-dialkyl derivatives (4). A two-step alkylation of 1a with 1-bromo-3-chloropropane led to the formation of 2,6-bis(methylthio)thiane (5). Proton and 13C nmr spectral studies on these compounds, including the measurement of long-range carbon–proton coupling constants, are described; their mass spectra showed elimination of methanethiol as a characteristic major fragmentation pathway.
Synthesis of fluoro derivatives of 2-amino-2-deoxy-D-galactose and -D-glucose
Authors: Hough Leslie , Penglis Anna A. E. , Richardson Anthony C.
Published: May 2006

Selective fluoride displacement of the 6-mesyloxy group of methyl 2-benzamido-3-O-benzyl-2-deoxy-4,6-di-O-mesyl-α-D-glucopyranoside 4 gave the 6-fluoride 5. Subsequent removal of the blocking substituents afforded 2-amino-2,6-dideoxy-6-fluoro-D-glucose, isolated as its hydrochloride 11 and its N-acetyl derivative 12. Nucleophilic displacement of the remaining 4-mesyloxy group of the intermediary 6-fluoro-4-mesylate 5, by benzoate anion afforded derivatives of 2-amino-2,6-deoxy-6-fluoro-D-galactose (18). An interplay of similar substitutions on 4 gave, after deprotection, methyl 2-acetamido-4,6-difluoro-2,4,6-trideoxy-α-D-galactopyranoside (22), methyl 2-acetamido-3-O-acetyl-4,6-difluoro-2,4,6-trideoxy-α-D-glucopyranoside (27), and methyl 2-benzamido-3-O-benzyl-6-fluoro-2,4,6-trideoxy-β-L-threo-hex-4-enopyranoside(28).Methyl 2-acetamido-2,4-dideoxy-4-fluoro-α-D-glucopyranoside diacetate (31) was synthesized from the 4-O-mesyl-6-O-trityl-galactopyranoside 29.
Electrochemical reduction of nitroethylenic ketones in hydroorganic medium. Preparation of 4,5-dihydroxy-2-isoxazolines
Authors: Bellec Christian , Maitte Pierre , Armand Joseph , Viel Claude
Published: May 2006

The electrochemical reduction of compounds of the type[Formula: see text]has been investigated in hydroorganic medium between pH 0 and 7. For 3 (R1 = R2 = R3 = C6H5), the 3,4,5-triphenylisoxazole is obtained at pH 1. 3 in neutral medium, 1 (R1 = CH3, R2 = R3 = C6H5) and 2 (R1 = C2H5, R2 = R3 = C6H5) lead to 4,5-dihydroxy-2-isoxazoline (only one of such compounds is described in the literature). The structure of these compounds has been determined by the usual spectroscopic methods (ir, nmr, mass spectrometry) and by radiocrystallography. A mechanism which accounts for the whole set of our results is proposed: it involves an intermediate α,β-nitrosoethylenic compound which cyclizes into a 4,5-dihydroxy-2-isoxazoline or gives an 1,3-diketone oxime upon reduction; this last compound cyclizes into an isoxazole.
Vacuum-ultraviolet (147.0 nm and 123.6 nm) photolysis of 1,1-dimethylcyclopropane
Authors: Binkewicz Joseph B. , Kaplan Michael , Doepker Richard D.
Published: May 2006

The gas-phase photolysis of 1,1-dimethylcyclopropane has been investigated using xenon (147.0 nm) and krypton (123.6 nm) resonance radiation. Major products observed in order of decreasing importance were isobutene, ethylene, hydrogen, 1,3-butadiene 2-methyl-1,3-butadiene, propylene, allene, methylacetylene, and acetylene. Radical scavengers, NO and O2, and radical interceptors, H2S/D2S and HI, were used to determine the relative importance of radical and molecular processes. CH3, C2H3, C3H5, and C4H7 radical species were identified and quantified. Ten primary reaction channels were postulated, of which the elimination of methylene was the most predominant, accounting for 34% of the photo-decomposition at 147.0 nm and 39% at 123.6 nm. Although ionization was established at 123.6 nm (η = 0.10) the nature of a charge transfer or other ion-molecule reaction channel leading to the formation of 2-methyl-1-butene and 2-methyl-2-butene could not be determined.
Mass spectral studies of symmetrical and unsymmetrical dialkyl disulfides
Authors: Gupta Dinesh , Knight Arthur R. , Smith Peter J.
Published: May 2006

The mass spectra for thirteen symmetrical and thirty-five unsymmetrical dialkyl disulfides have been determined at 70 eV. Carbon–sulfur bond cleavage to give hydrocarbon ions was observed as well as the formation of RS+ ions. Factors affecting these two processes are discussed. The most favoured decomposition pathway for the molecular ions of most of the dialkyl disulfides (RSSR′) studied was intramolecular hydrogen transfer to give RSSH and R′SSH. The effect of varying the structure of the alkyl groups on this process has been investigated.
Synthèse totale des acides (+) et (–) nonactique à partir de carbohydrates
Authors: Ireland Robert E. , Vevert Jean-Paul
Published: May 2006

The synthesis of (−) and (+) nonactic acids (2a) and (2b) has been achieved starting from D-mannose (7) and D-gluono-γ-lactone (22) respectively. The key step in the synthesis is the [3,3]-sigmatropic rearrangement of the silylated ketene-acetals IV leading to control of the C-2 configuration of nonactic acid. The ketene-acetals were prepared from aliphatic esters of furanoid-glycals II, which were prepared in ten steps from the carbohydrate precursor. The chiral sites of the glycals arise from the corresponding centres in the starting monosaccharide. This type of ketene-acetal Claisen rearrangement leads to products containing the aldol portion required. At the same time knowledge of the absolute configuration of the chiral carbon atom of nonactic acid allows for the determination of the chair or boat form of the transition state of the [3,3]-sigmatropic rearrangement. [Journal translation]
Stereochemical studies. IX. Acid-catalyzed rearrangement of δ- to γ-lactones
Authors: Edward John T. , Cooke Ellen , Paradellis Themistocles C.
Published: May 2006

Depending on their constitution and stereochemistry, δ-lactones are converted by hot formic acid into pendant or spiro γ-lactones.
Kinetics and mechanism of unimolecular decomposition of 3-methyl-1-p-tolyltriazene
Authors: Vaughan Keith , Liu Michael T. H.
Published: May 2006

Kinetic parameters (Ea and ΔS≠) for the thermolysis of 3-methyl-1-p-tolyltriazene (1) in tetrachloroethylene have been determined. The near-zero value for ΔS≠ suggests a transition state with minimal stretching of the N—N bonds in tautomers 1a or 1b. The activation energy (Ea = 29.2 kcal/mol) and ΔS≠ for the decomposition of 1 are very similar to those of the azoarylalkanes (Ar—N=N—R), suggesting a similar mechanism of degradation. The major products of the thermolysis of 1 are p-toluidine, N-methyl-p-toluidine, and p-chlorotoluene, which are rationalized in terms of homolytic breakdown of both tautomers.
β-Lactams. VIII. The synthesis of iso-oxapenams from N-substituted-4-hydroxymethylazetidinones
Authors: Hakimelahi Gholam Hosein , Just George
Published: May 2006

The synthesis of 3,3-disubstituted iso-oxapenams is described.
Etude rmn (1H et 13C) des interactions entre les nucléosides et les bleus de platine obtenus à partir du méthyle-1 nicotinamide
Authors: Laurent Jean-Pierre , Lepage Paule
Published: May 2006

The interactions between two "platinum blues", obtained from 1-methylnicotinamide, and various nucleoside (guanosine, cytidine, uridine, and adenosine) have been studied by 1H and 13C nmr spectroscopy. The results obtained show that the interaction sites are identical to those usually observed for normal Pt(II) complexes, e.g. cis-Pt(NH3)2Cl2. [Journal translation]
Hydrolyse des dérivés de cyclopropylidène-3 propyle. Structure et stéréochimie des alcools précurseurs et des produits résultant de l'hydrolyse
Authors: Faure Robert , Leandri Gilbert , Meou Alain
Published: May 2006

The 13C nmr spectra of 14 β-cyclopropylidenic alcohols 1 have been determined:[Formula: see text]All the chemical shifts were assigned and the substituent effects are discussed as a function of molecular conformation. The stereochemistry of two diastereoisomers of alcohols 1e (R1 = R3 = H; R2 = R4 = CH3) and 1k (R3 = H; R1 = R2 = R4 = CH3) was established from ir spectroscopy and 1H nmr results.The 13C nmr spectra of products arising from hydrolysis of 3-cyclopropylidene propanol 1a and 4-cyclopropylidene 2-butanol 1b tosylates have been also recorded. The analysis of these data enables us to establish unambiguously the structure and the stereochemistry of the hydrolysis products.
The transfer of alkanoic acids from dodecane to water
Authors: Sagert Norman H. , Quinn Michael J. , Dixon Robert S.
Published: May 2006

A rotating diffusion cell was used to study the transfer of five alkanoic acids from dodecane to water under conditions of known interfacial area and hydrodynamics. The acids studied were acetic, butanoic, hexanoic, 2-methylbutanoic and 2,2-dimethyl-propanoic acids. Small interfacial resistances to mass transfer were noted, the mass transfer coefficients for interfacial transfer being in the range 2.6 to 4.7 μm/s at 25 °C. This small range means that the effects of the length and structure of the alkane chain on the resistance to mass transfer are minimal. A study of the temperature dependence of the resistance to mass transfer at the interface showed that the resistance is largely entropic rather than enthalpic.
13C chemical shift data for 1,7-dioxaspiro[5.5]undecanes and related compounds
Authors: Pothier Normand , Rowan Daryl D. , Deslongchamps Pierre , Saunders John K.
Published: May 2006

The carbon-13 chemical shift data for a series of 1,7-dioxa-, 1-oxa-7-thia-, and 1,7-dithiaspiro[5,5]undecanes and related compounds are presented. Analysis of this data led to structural and stereochemical assignments. The results show that the unsubstituted spiro bicyclic compounds exist in the conformation shown as conformation a. It is shown that the 13C chemical shift parameters developed for cyclohexane derivatives can be applied to the sulfur but not to the oxygen heterocycles.
Reactions of phthalans with dienophiles. III. Formation of homoquinones by reaction of 1,1-diethoxyphthalans with quinones
Authors: Contreras Luis , MacLean David B. , Faggiani Romolo , Lock Colin J. L.
Published: May 2006

Treatment of 1,1-diethoxyphthalan with 1,4-benzoquinone gave the homoquinone, ethyl 2-[(1′R*,6′S*,7′S*)-2′,5′-dioxo-3′-norcaren-7′-yl]benzoate, 3, instead of an anthracene derivative expected of a normal cycloaddition reaction. The structure of the homoquinone was deduced from an examination of its spectroscopic properties (ir, 1H nmr, and 13C nmr) and verified by an X-ray crystallographic study. The homoquinone, 3, is triclinic, P1, with a = 10.601(2), b = 10.434(3), c = 6.491(3) Å, α = 105.53(3), β = 95.21(2), γ = 100.66(2)° and has two formula units per unit cell. The crystal structure was determined by direct methods and refined to R1 = 0.059, R2 = 0.048, based on 2378 independent reflections. The data set was obtained using a Syntex P21 diffractometer and MoKα radiation. Bond angles and distances within the molecule are normal. Homoquinones were also isolated as major products of reaction of 1,1-diethoxyphthalan and 5,6-dimethoxy-1,1-diethoxyphthalan with 1,4-benzoquinone and 1,4-naphthoquinone. A mechanism for the formation of homoquinones is offered that involves the same type of transient intermediates proposed for the reactions of 1,1-diethoxyphthalans with activated acetylenes and ethylenes.
Boron trihalide adducts of 1,1-bis(piperidinyl)ethylene. 13C and 11B nmr studies of a model system for β-carbon donation in enamine adducts
Authors: Hartman J. Stephen , Kelusky Eric C.
Published: May 2006

1,1-Bis(piperidinyl)ethylene coordinates to the boron trihalides through the CH2 carbon, but the covalent adducts D.BX3 undergo rearrangement to give predominantly the ionic adducts D2BX2+.BX4−. Striking variations in 11B and 13C nmr peak widths support our proposed structures. The disappearance of peaks due to excessive broadening can be misleading in the interpretation of such systems.
Ab initio CI calculation of the band structure in the A2B1–X2A1 electronic transition of BH2
Authors: Perić Miljenko , Peyerimhoff Sigrid D. , Buenker Robert J.
Published: May 2006

Ab initio MRD-CI calculations have been carried out to nearly full-CI accuracy for several large AO basis sets (including f functions) for the potential curves of the BH2 molecule in its X2A1 and A2B1 electronic states. A two-dimensional vibrational treatment of the bending modes in this system has been performed employing a variational method which takes account of both Renner–Teller coupling and large-amplitude motion. The resulting structural data agree to within 0.002 Å and 2° of measured bond distance and angles and the computed bending frequencies are found to be in error by less than 30 cm−1; in addition predictions of the as yet unobserved stretching frequencies are also reported for both electronic states. In the best theoretical treatment the v2′′ = 0 → v2′ = 1 transition energy to the linear upper state is calculated to be 4145 cm−1, in excellent agreement with the corresponding value of 4190 cm−1 obtained by extrapolation of the three higher-energy band frequencies actually observed by Herzberg and Johns provided a renumbering of these levels (namely as v2′ = 9, 11, and 13) is undertaken relative to the originally preferred experimental interpretation. It is also pointed out that some of the earlier reported discrepancies between calculation and experiment regarding transition energies in this band system are actually due to a misinterpretation of the definition of the experimental fitting parameter T00 in previous theoretical work.
Effect of short-chained sodium alkylsulfate micelles on the kinetics of metal complex formation
Authors: Fletcher Paul D. I. , Reinsborough Vincent C.
Published: May 2006

The kinetics of the reaction between Niaq2+ and the bidentate ligand pyridine-2-azo-p-dimethylaniline (PADA) have been investigated in micellar solutions of sodium decyl-, octyl-, and hexylsulfates using the stopped-flow technique. The rate of enhancement decreased with decreasing alkyl-chain length and from the Berezin or Robinson model could be quantitatively related to the independently measured binding constants of Ni2+ ion and PADA to the micelle surface. The dramatic effect of micelles upon the reaction rates in different directions of the Ni2+/PADA and the Ni2+/murexide reactions served as sensitive indicators of the cmc even at the very limit of micelle formation which relatively concentrated sodium hexylsulfate solutions represent.
Synthesis and properties of silicon, germanium, and tin derivatives of cyclopentadienyltricarbonylrhenium
Authors: Dong D. F. , Hoyano J. K. , Graham W. A. G.
Published: May 2006

The preparation and properties of a series of rhenium compounds of the general formula (η-C5H5)Re(CO)2XY in which X or Y or both is a silyl, germyl, or stannyl ligand are reported. The silyl hydrides cis-(η-C5H5)Re(CO)2(SiR3)H (R = Ph, CH2Ph) and cis-(η-C5H5)Re(CO)2(SiPh2H)H were obtained by ultraviolet irradiation of (η-C5H5)Re(CO)3 and the appropriate silane. The hydrides trans-(η-C5H5)Re(CO)2XH(X = SiPh3, GeCl3, GeBr3, SnCl3) were obtained by protonation of the corresponding anions. These new anions [(η-C5H5)Re(CO)2X]− also reacted with other electrophiles to yield compounds of the type trans-(η-C5H5) Re(CO)2XY (Y = Me, halogen, SnR3). The reaction of (η-C5H5)Re(CO)3 with Cl3GeH or Ph3SnH yielded only the compounds trans-(η-C5H5)Re(CO)2(GeCl3)2 and trans-(η-C5H5)Re(CO)2(SnPh3)2 respectively. Infrared and 1H nmr spectra are reported for all compounds, and v(Re–H) values for the hydrides have been obtained from Raman spectra.
The extraction of alkali metal picrates by polyurethane foam using crown ether
Authors: Khan Anjum S. , Baldwin W. G. , Chow A.
Published: May 2006

The distribution of alkali metal picrates between water and polyurethane foam was studied in the presence of dicyclohexyl 18-crown-6 (DCHC-6). The extraction constants and dissociation constants for the ion pair (MCrA) in polyurethane foam were determined. The extraction constant sequence of the alkali metal ions with DCHC-6 is K+ > Rb+ > Cs+ > Na+ and mainly depends on the stability of the alkali metal – crown ether complex.
Comportement anodique des alliages Nb–Co en milieu alcalin
Authors: Umetsu Y. , Baillon J. P. , Piron D. L. , Bélanger G.
Published: May 2006

Niobium–cobalt alloys are stable to corrosion in an open circuit in the presence of oxygen in 25% KOH solution as long as the weight percentage of cobalt exceeds 50%. Below this value, samples submitted to these conditions disintegrate after 30 days. When these alloys are submitted to anodic polarization an active dissolution is noted followed by passivation and in the presence of cobalt production of oxygen occurs. Electronic Auger Spectroscopic (EAS) analysis of pure niobium and its alloys with 30% and 90% cobalt indicates that the oxide film grows in an irregular manner according to the nature of the surface. Thus, for an identical anodic polarization (0.845 V vs. ENH for 6 hours) the oxide film changes from 4.13 × 10−2 μm for pure Nb to 0.10 μm for the 30% Co–Nb alloy and becomes as thin as 8 × 10−4 μm for the 90% Co–Nb alloy. The concentration profile as shown by EAS indicates a preferential dissolution of Nb over Co in the oxide film. [Journal translation]