bluuebunny/crossref_metadata_2025 huggingface dataset:
Isomérisation des époxydes
Authors: Jankowski Krzysztof , Daigle Jean-Yves
Published: May 2006

Isomerization of five and six-membered ring epoxides was realized through the action of potassium cyanate in ethanol-water medium. The n.m.r. spectra of trans and cis epoxides were studied.
The Master Equation for the Dissociation of a Dilute Diatomic Gas. IV. The Bottleneck Phenomenon
Authors: Kamaratos E. , Pritchard H. O.
Published: May 2006

Once the initial transients have died out, the rate constant for the dissociation or recombination of a dilute diatomic gas bears the same kind of relationship to individual translation–vibration transition probabilities as does the conductance of a generalized resistance network to the individual resistance components. Thus, it is not possible to single out any one transition which "controls" the rate of dissociation or recombination.
Photochemistry of Metal Olefin Complexes. Isomerization and Stereospecific Cyclodimerization of Silver Cycloalkene Complexes
Authors: Leh F. , Wong S. K. , Wan J. K. S.
Published: May 2006

Photolysis of AgClO4 – 1-methylene cyclohexane complex in pure polycrystalline state or in methanol solution leads to isomerization of the complex to AgClO4 – 1-methylcyclohexene. The isomerized complex undergoes further photochemical cyclodimerization giving the stereospecific exo-trans-exo dimer of the 1-methylcyclohexene and colloidal silver. Similar photoisomerization and a less stereospecific photodimerization were observed in the photolysis of the polycyclic AgClO4 – β-pinene complex.
Novel Chemical Shift Changes of Carbohydrates Induced by Lanthanide Shift Reagents: Some Experimental Optimizations
Authors: Armitage Ian , Hall L. D.
Published: May 2006

The 1H n.m.r. spectra of 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (4), of 1,2:5,6-di-O-isopropylidene-α-D-allofuranose (5), and of their 3-O-acetyl derivatives 6 and 7, respectively have been separately measured in the presence of varying concentrations of the tris {dipivaloylmethane} derivatives of europium (1), thulium (2), and praseodymium (3). For these derivatives, both europium (1) and thulium (2) induce shifts to low field whereas praseodymium (3) produces high field shifts; for any individual proton the magnitude of the induced shift is shown to be linearly proportional to the amount of added reagent and is best followed by addition of volume aliquots of a dilute solution of the lanthanide. It is shown that simplistic rationales concerning the relationship between the magnitudes of induced shifts and the geometry of the substrate system can be entirely misleading; the D-gluco -derivative 4 is particularly noteworthy in this regard. Since the magnitudes of the induced shifts are temperature dependent it is important to report the temperature at which experiments are performed. For 1 the induced shifts are ca. 2.2 times larger for carbon tetrachloride solutions than for deuterochloroform solutions when operating under otherwise identical conditions.
An Attempted Synthesis of 4,5-Bis(dimethylamino)-1,2,3-thiadiazole
Authors: Oliver James E. , Stores Jerry B.
Published: May 2006

Oxidation of 2-hydrazono-N,N,N′,N′ tetramethylthiooxamide (8) by various reagents did not provide the expected thiadiazole 4, but rather gave azines 11 and 12. It is postulated that the hydrazone derived from 8 lost nitrogen to give carbene 14 which in turn produced 11 and 12.
Ion Pairing and the Reaction of Alkali Metal Ferrocyanides and Persulfates
Authors: Chlebek R. W. , Lister M.W.
Published: May 2006

Osmometric measurements have been made on the alkali metal persulfates, and these are interpreted in terms of formation of ion pairs, MS2O8−, by means of the method of Masterton and Berka (5). Equilibrium constants, and the derived thermodynamic quantities are deduced for the reactions [Formula: see text]. These results are applied to the interpretation of the kinetics of the reactions[Formula: see text]With M = K+, Rb+, and Cs+, the reacting species are MFe(CN)63− + MS2O8−, with very similar rate constants; with M = Li+, Na+ the species are MFe(CN)63− + S2O82−; and for lithium the reaction of Fe(CN)64− + S2O82− is also important. Rate constants and activation parameters are deduced.
Crystal Structure of α-Zn3(VO4)2
Authors: Gopal R. , Calvo C.
Published: May 2006

α-Zn3(VO4)2, the low temperature form of this compound, crystallizes in the orthorhombic space group Cmca with a = 6.088(3), b = 11.489(3), and c = 8.280(3) Å and Z = 4. A total of 726 unique reflections were recorded from integrated precession photographs or with a manually set scintillation counter and used in a full matrix least squares refinement to a final R value of 0.089. The Zn ions lie in two types of octahedral sites while the V ions lie in sites showing tetrahedral coordination to oxygen atoms. The mean V—O bond length is 1.71 Å but one of the V—O bond lengths, involving an oxygen atom bonded to three Zn2+, is 1.78(1) Å long. The average Zn—O bond lengths are 2.13 and 2.10 Å for the Zn ion with site symmetry 2/m and m site symmetry, respectively. α-Zn3(VO4)2 is isostructural with Mg3(VO4)2 and thus has a structure based upon a closest packing of oxygen atoms much like that found in spinel.
Studies on Horseradish Peroxidase. VII. A Kinetic Study of the Oxidation of Iodide by Horseradish Peroxidase Compound II
Authors: Roman R. , Dunford H. B. , Evett M.
Published: May 2006

The kinetics of the oxidation of iodide ion by horseradish peroxidase compound II have been studied as a function of pH at 25° and ionic strength of 0.11. The logarithm of the second-order rate constant decreases linearly from 2.3 × 105 to 0.1 M−1 s−1 with increasing pH over the pH range 2.7 to 9.0. The pH dependence of the reaction is explained in terms of an acid dissociation outside the pH range of the study.
Ion Pair Formation in Solutions of Alkali Halides in Dimethyl Sulfoxide: Ultrasonic Absorption Studies
Authors: Dickson D. R. , Kruus P.
Published: May 2006

The ultrasonic absorption of dimethyl sulfoxide solutions of several alkali halides has been studied in the frequency range 1.5 to 52 MHz. An excess absorption, relaxing between 3 and 8 MHz, was observed. The relaxation was assigned to the final step in the stepwise formation of a contact ion pair, with the relaxation frequency controlled by the rate of movement of a solvent molecule rather than an ion. Data on the system water – dimethyl sulfoxide are also presented and the effect of water on the relaxation discussed.
Nuclear Magnetic Resonance Spectra, Conformations, Spin Coupling Mechanisms, and INDO Molecular Orbital Calculations for the Monofluorobenzaldehydes and some Derivatives
Authors: Wasylishen R. , Schaefer T.
Published: May 2006

Precise analyses of the proton and some fluorine magnetic resonance spectra in acetone solution are reported for the three monofluorobenzaldehydes as well as for 2-chloro-6-fluorobenzaldehyde and for 4-fluoro-2-nitrobenzaldehyde. The conformational dependence of the coupling parameters allows the measurement of energy differences between the O-cis and O-trans conformations. The energy differences are in better agreement with the INDO predictions than they are with energies derived from i.r. data. Di-pole moments are computed reliably and their measurement is suggested as a good guide to conformational preferences for molecules of this kind. The spin–spin coupling constants between the aldehyde proton and the ring protons and fluorine nuclei are computed for benzaldehyde and the three monofluorobenzaldehydes by the INDO and CNDO molecular orbital approximations. In many instances the agreement between calculated and observed couplings is quantitative.
K-Absorption Spectroscopic Investigations on Mixed Valency
Authors: Nigam H. L. , Srivastava U. C.
Published: May 2006

Evidence for the existence of mixed valency Cu(I)–Cu(II) in some copper complexes has been adduced from X-ray absorption spectroscopic study. Two distinct edges K1 and K2 have been observed for the uni and divalent states of copper.
The Effect of S-Substituent Variation on the Pyrolysis of Xanthates of Primary Alcohols
Authors: Gilman R. E. , Bogdanowicz M. J.
Published: May 2006

A study of the pyrolysis of a series of S-substituted xanthates of cyclohexanemethanol was undertaken to determine the effect of variations in the nature of the S-substituent on the course of the pyrolysis of xanthates. Xanthates with the following S-substituents were prepared by standard reactions and pyrolyzed at 240°: n-hexyl, 2-phenylethyl, benzyl, phenacyl, and diphenylmethyl. Evidence is presented that supports the view that a competitive homolytic pathway becomes more significant as the stability of the free radical derived from the S-substituent increases. At the two extremes, the S-hexyl xanthate yields 90% methylenecyclohexane and no cyclohexanemethanol whereas the S-diphenylmethyl xanthate yields only 25% alkenes (methylenecyclohexane and 1-methylcyclohexene) along with 65% cyclohexanemethanol.
The Dissolution of Magnesium Oxide in Dilute Sulfuric Acid
Authors: Macdonald Digby D. , Owen D.
Published: May 2006

The kinetics of dissolution of sintered magnesium oxide pellets in dilute sulfuric acid at 4.00 and 25.00 °C have been investigated using the rotating disc technique. The rate of depletion of hydrogen ions in the bulk solution is found to be controlled by both transport through the diffusion layer and chemical reaction with the oxide surface. The chemical reaction occurring at the oxide surface has an activation energy of 13 kcal mol−1. The diffusion coefficients for hydrogen ion in dilute sulfuric acid at the two temperatures of interest have been calculated. These coefficients yield an activation energy of 3.6 kcal mol−1 for the diffusion of hydrogen ions to the oxide surface.
Preparation and Transformations of Three p-Menthane-3-methanesulfonyloxy-4,8-diols
Authors: Lange G. L. , Bosch M.
Published: May 2006

Three diastereomeric p-menthane-3-methanesulfonyloxy-4,8-diols were synthesized from (+)-pulegone. Treatment of each methanesulfonate with aqueous base resulted in a stereospecific reaction involving antiperiplanar groups to give one product: either an α-ketol by a pinacol-type rearrangement or an epoxide by an intramolecular SN2-type reaction. Although the possibility existed for 1,3- as well as 1,2-diol monomethanesulfonate transformations, only products from the latter type of reaction were isolated.
Effect of Solvent Upon the Vicinal Proton Coupling Constants of Complex Substituted Ethanes. III. 1,2-Dihaloalkanes
Authors: Dawson D. A. , Reynolds W. F.
Published: May 2006

The n.m.r. spectra of eight 1,2-dihaloalkanes have been determined in solvents of differing polarity. The relative rotamer stabilities for each compound have been deduced from the variation of the difference and sum of vicinal coupling constants with solvent. Variations in geminal and long range coupling constants with solvent are also attributed to conformational changes.
A Paramagnetic Resonance Study of Unhindered Biphenyl Anion Radicals (III)
Authors: Adam F. C. , Kepford C. R.
Published: May 2006

The radical anions of biphenyl and some of its bridged derivatives have been studied by e.s.r. It is found that the proton hyperfine coupling constants change monotonically through the series of radical anions derived from biphenyl, 9,10-dihydrophenanthrene, fluorene, dibenzothiophene, and dibenzofuran. Deuterations have been carried out for the latter two compounds and the hyperfine coupling constants are assigned to specific positions in these anions. The data are displayed in the form of a correlation diagram from which assignments for other bridged biphenyl anions can be made.
Free Energy Barrier to Rotation of the Amino Group in 2-Aminoacetophenone
Authors: Wasylishen R. , Schaefer T.
Published: May 2006

The free energy of activation for hindered rotation of the amino group about the N-aryl bond in 2-aminoacetophenone is found to be 10.6 ± 0.5 kcal/mol in toluene solution at 233 ± 10 °K. Separate amino p.m.r. peaks are observed at low temperatures and these are strongly broadened by incompletely relaxed spin–spin coupling to the quadrupolar 14N nucleus, making a more accurate determination of activation parameters impractical. Some INDO molecular orbital calculations are performed in an attempt to rationalize the barrier magnitude.
Kinetic Study of the Acetate-catalyzed Aldol Reaction Between Chloral and Alkyl Methyl Ketones
Authors: Menon B. C. , Kiehlmann Eberhard
Published: May 2006

A kinetic study of the acetate-catalyzed crossed aldol reaction of chloral with butanone, 2-heptanone, and 4-methyl-2-pentanone, respectively, in glacial acetic acid at 60° has been carried out. A comparison of the condensation rates with those for the acetate-catalyzed deuterium exchange of the ketones in glacial acetic acid at 60° indicates that the carbon—carbon bond formation in the aldol reaction is the rate-determining step. The relative rate constants for the crossed aldol reaction and the deuterium exchange of the corresponding ketones are best interpreted in terms of steric rather than polar effects.
Nuclear Magnetic Resonance Studies of Multi-site Chemical Exchange. III. Hindered Rotation in Dimethylacetamide, Dimethyl Trifluoro-acetamide, and Dimethyl Benzamide
Authors: Reeves L. W. , Shaddick R. C. , Shaw K. N.
Published: May 2006

The experimental application of a multi-site exchange theory developed recently has been made to three restricted rotation barriers in amido-type systems. Inclusion of 8 spin-sites in the analyses of the line shapes for spectra of N,N-dimethyl trifluoroacetamide and dimethyl acetamide leads to improved values for the activation parameters. Variation of chemical shifts with temperature is included in the iterative fitting procedure. The determination of the relative signs of long range couplings and the inclusion and measurement of unresolved couplings has been accomplished. The barrier for hindered rotation in N,N-dimethyl benzamide has been re-investigated including the effect of relatively large chemical shift changes with temperature. The internal consistency of the measurements from all aspects indicates that systematic errors common in the determination of energy barriers by steady-state nuclear magnetic resonance (n.m.r.) have been largely eliminated and hence the activation parameters obtained form a reliable addition to a compilation of experimental data pertaining to the bonding in a related series of simple C-substituted amides.
An ab initio Molecular Orbital Study of Bonding in Fluorocarbonium Ions
Authors: Baird N. C. , Datta R. K.
Published: May 2006

Ab initio molecular orbital calculations are reported for the series of carbonium ions (CH3)+, (FCH2)+, and (F2CH)+ and for their neutral molecule counterparts CH4, CH3F, and CH2F2. The energies and wavefunctions for the carbonium ions have been calculated both with and without including the carbon 2pπ orbital in the minimal basis set in order to unravel the inductive destabilization and resonance stabilization due to fluorine substitution. The increase in bonding energy with multiple fluorine substitution is less than linear, due primarily to nonadditivity in the dative carbon–fluorine π bonding. The "saturation" effect noted previously for the hydride abstraction reaction enthalpies is shown to be due primarily to stability effects in the neutral molecules themselves rather than to energetic effects of the carbonium ions.
Proton Magnetic Resonance Studies of Some 1-X-2,4-Dinitrobenzenes
Authors: Stephens Michael D. , Reinheimer John D. , Kappelman Allan H.
Published: May 2006

Shaefer's additivity rules for coupling constants have been applied to trisubstituted benzenes. If a resonance interaction between substituents is possible, the observed coupling constants are larger than those predicted. For other substituents, the additivity rules are followed.
The Crystal and Molecular Structure of (PPh3)2PtO2•2CHCl3
Authors: Cheng P. T. , Cook C. D. , Nyburg S. C. , Wan K. Y.
Published: May 2006

The X-ray crystal structure analysis of the chloroform adduct of the bis(triphenylphosphine) platinum di-oxygen complex (PPh3)2PtO2•2CHCl3 is reported. The crystals belong to the monoclinic System a = 15.492(7), b = 13.520(5), c = 19.187(6) Å; β = 98.97(6)°. Space group C2/c. Z = 4 molecules per cell.A total of 2740 independent X-ray reflections were measured and refinement gave a final conventional R of 6.6%.The molecule has a two-fold axis of symmetry through the Pt atom with O—O normal to the axis. The O—O distance of 1.505(16) Å is in accord with that found with other transition elements when oxygen is taken up irreversibly to form di-oxygen complexes.
35Cl Nuclear Quadrupole Resonance of Some Phosphorus–Chlorine Compounds
Authors: Bishop J. K. B. , Cullen W. R. , Gerry M. C. L.
Published: May 2006

Chlorine nuclear quadrupole resonance spectra have been observed for several compounds containing phosphorus–chlorine bonds. The compounds included some complexes of phosphorus trichloride with transition metals as well as some alkyl derivatives of thiophosphoryl chloride and phosphorus trichloride.
Identification of ν(N=N) in Metal Arylazo Complexes: The Infrared and Raman Spectra of some Arylazo Complexes of Rhodium(III)
Authors: Rayner-Canham G. W. , Sutton D.
Published: May 2006

The Raman and infrared spectra have been obtained for a series of rhodium-arylazo complexes RhCl2(PPh3)2(p-XC6H4N2) where X = H, F, Br, CF3, NO2, OCH3, NEt2. The N=N stretching frequency ν(N=N) has been unambiguously identified from its strong appearance in the Raman spectrum and from isotopic substitution studies using 15N. Trends in the value of ν(N=N) with the p-substituent X are discussed, in terms of the apparent degree of metal–ligand π-interaction.
Reductions with Sulfurated Borohydrides. VII. Reactions with Epoxides
Authors: Lalancette J. M. , Frêche A.
Published: May 2006

The reaction of NaBH2S3 with epoxides gives symmetrical bis-(2-hydroxyethyl) disulfides. The stereochemistry of the reaction is similar to the attack of H2S on the epoxides in basic solution. Substituted epoxides are opened from the less hindered side. The reaction proceeds with good yield and is general. An improved method of preparation of the 1,2-mercaptols is presented.
Flash Thermolysis: Quinones
Authors: Champlain P. De , Mayo P. De
Published: May 2006

The flash thermolysis of a number of quinones is reported. p-Benzoquinone gives cyclopentadienone, isolated as the dimer. 2,5-Diphenylbenzoquinone gives 1- and 2-phenylnaphthalene together with benzo-[1,2-b:4,5-b′]bisbenzofuran. Yields are very poor. Anthraquinone and phenanthraquinone give fluorenone, and the latter quinone gives small amounts of biphenylene.
Proton Magnetic Resonance Spectra, Conformational Preferences, and Approximate Molecular Orbital Calculations for the syn and anti 2-Furanaldoximes
Authors: Wasylishen R. , Schaefer T.
Published: May 2006

Evidence is adduced, mainly from proton chemical shift and long-range coupling constant data, that the anti isomer of 2-furanaldoxime exists almost exclusively in the s-cis form in solution, independently of the type of intermolecular association that occurs. Intramolecular hydrogen bonding apparently is absent in this isomer. Similarly, the syn isomer exists in roughly equal mixtures of s-cis and s-trans forms in solvents of widely different polarities. A variety of nuclear spin–spin coupling constants are calculated via the INDO and CNDO molecular orbital approximations, as are the dipole moments and conformational energies, for 2-furanaldehyde and its oximes. On the whole the experimental trends are well reproduced by the computations.
Use of N-Carboxyanhydrides in the Synthesis of Dipeptides. The Improvement of Isolated Yields by the Facile Removal of Buffer Components
Authors: Gait R. J. , Langlois J. R. , Williams R. E.
Published: May 2006

A modification of the N-carboxyanhydride synthesis of dipeptides is described. An improvement in the yield during dipeptide preparation is made possible by use of only organic acids and bases during the reaction to facilitate their removal before product isolation.
Dipole Moments and Conformation of Sultones, Thiosultones, and Sultines
Authors: Exner O. , Harpp David N. , Gleason John G.
Published: May 2006

Dipole moments of five- and six-membered sultones and thiosultones have been used to establish the values of bond moments used in conformational studies of open-chain analogues. Hence, the gauche conformation of acyclic sulfonic esters has been confirmed and the same conformation deduced from published data for thiolsulfonate esters. The dipole moment of a five-membered sultine has been interpreted similarly, while in the case of the six-membered derivative, the axial sulfinyl conformation has been determined in agreement with n.m.r. data.
Theory of Ionic Conduction in Solids
Authors: Young L.
Published: May 2006

When a constant field in the 10 V cm−1 range is applied to annealed anodic oxide films the ion current builds up in accelerating fashion. It is shown that a model in which the ions move through channels in the oxide and in which the moving ions clear the initially blocked channels reproduces the general form of the ion current vs. time behavior. Dignam's theory of this process is discussed. A recent claim that considerations of mean free path render inapplicable to these films models in which the concentration of ions changes with field due to homogeneous generation of Frenkel defects is shown to be unjustified.A further observed phenomenon in which the latent ionic conductivity of the films decays at zero field is also discussed in terms of the competing models.
Second Cross Virial Coefficients of Carbon Tetrachloride – Gas Mixtures Determined from Solubility Measurements at High Pressures
Authors: Gupta S. K. , King Jr. A. D.
Published: May 2006

The solubility of carbon tetrachloride in compressed helium, hydrogen, nitrogen, argon, methane, carbon dioxide, and ethylene has been measured over pressure ranges of 1–60 atm at temperatures ranging from −10 to 75 °C. Second cross virial coefficients representing carbon tetrachloride – gas interactions are evaluated from the data. It is shown that when allowance is made for the effects of quantum deviations and quadrupolar interaction on the critical temperatures and volumes of helium, hydrogen, and carbon dioxide, respectively, ordinary combining rules produce pseudocritical parameters which reduce all of the measured cross virial coefficients to a single function of reduced temperature. When reduced on a Boyle point basis, it is found that the data are best represented by virial coefficients corresponding to a 7-28 Mie type potential or a Kihara core potential having a core radius somewhat smaller than the carbon–chlorine bond length in carbon tetrachloride.
Tricarbonylchromium π-Complexes of αβγδ-Tetraphenylporphin and its Metal Chelates
Authors: Gogan Niall J. , Siddiqui Zahir U.
Published: May 2006

Tricarbonylchromium π-complexes of αβγδ-tetraphenylporphin and its Cr(II), Mn(III), Ni(II), Cu(II), and Zn(II) chelates have been prepared. The complexes vary in stability with the Zn compound being the most stable. The complexes have been studied by their visible and i.r. spectra and their n.m.r. spectra where applicable. A study of the CO stretching vibrations in the i.r. shows no appreciable interaction between the two metals and arguments are made to show that this lack of interaction is due to absence of π interactions between the porphin and phenyl ring systems.
Optical Activities of Two Steroids Containing a Chiral Cyclopentene Ring
Authors: Edward J. T. , Lawson N. E. , L'Anglais Daphne
Published: May 2006

The direction of the optical rotation of the steroid 3 can be reconciled with Brewster's rules, if account is taken of "bond fixation", but the direction of the optical rotation of 2 cannot be.
Synthesis and Stereochemistry of Diastereoisomeric 1,3-Dimethylpiperidin-4-ols and Related Compounds
Authors: Casy A. F. , Jeffery W. K.
Published: May 2006

The synthesis of cis and trans 1,3-dimethylpiperidin-4-ols and derived acetate, benzilate, and diphenylacetate esters is described. Configurations and preferred conformations of these derivatives are assigned on the basis of 4-methine and 4-hydroxyl p.m.r. characteristics. Conformational studies of esters of 1-methyl-piperidin-3-ol and isomeric 3-tropanols are also described. Epimeric conjugate acids are well defined in 3-acetoxy-1-methylpiperidine hydrochloride as solute in CDCl3.
Cancentrine. II. The Structure of Cancentrine
Authors: Rodrigo R. , Manske R. H. F. , MacLean D. B. , Baczynskyj L. , Saunders J. K.
Published: May 2006

The structure of cancentrine (F22), an alkaloid of Dicentracanadensis (Goldie) Walp., is reported. Some reactions of the base are described and an analysis of the p.m.r. and mass spectra of cancentrine and several derivatives is made.
Photolysis of Ammine and Alkylamine Chromium(III) Complexes in Water and Dimethylsulfoxide: Mechanistic Evidence from Luminescence and Medium Effects
Authors: Langford Cooper H. , Tipping Leigh
Published: May 2006

Photosolvolysis of [Formula: see text] Cr(NH3)5Cl2+, Cr(CH3NH2)5Cl2+, and Cr(CH3CH2NH2)5Cl2+ in water and DMSO is described. Phosphorescence of [Formula: see text] is completely quenched in base but loss of NH3 is not. This implies that photosolvolysis arises in the quartet excited state and not the phosphorescent doublet. The increase in ammine quantum yield in DMSO as compared to water can be understood in terms of a tetragonal distortion model for the quartet which also accommodates phosphorescence activation energy data. Unfavorable solvation of Cl− of Cr(RNH2)5Cl2+ (R = H, CH3, CH3CH2) after tetragonal distortion can also explain the reversal of solvent effect in these systems wherein quantum yields are lower in DMSO than in water for both release of RNH2 and Cl−.
Aromatic Halogenation with Titanium (IV) Chloride in Presence of Peroxytrifluoroacetic Acid
Authors: Chip G. K. , Grossert J. S.
Published: May 2006

Titanium(IV) chloride in the presence of an oxidizing reagent such as peroxytrifluoroacetic acid is shown to chlorinate a variety of aromatic substrates. The substitution orientation patterns suggest that the reaction is an electrophilic substitution process, which possibly involves the intermediacy of hypochlorous acid. Chlorination fails to occur with ring systems bearing strongly deactivating substituents, but it proceeds very cleanly and in high yield with activated rings, e.g. phenol. The reaction conditions are mild and are adaptable for bromination or iodination as well as chlorination.
The Effect of Aromatic Tertiary Amines on the Copper(II) Catalyzed Decarboxylation of 3-Oxo-Glutaric Acid
Authors: Leong K. N. , Lister M. W.
Published: May 2006

The kinetics of the copper(II) catalyzed decarboxylation of 3-oxo-glutaric acid have been investigated in unbuffered solutions at 25 °C and 0.60 M ionic strength, both in the presence of aromatic tertiary amines, and with hydrated copper ions alone. The amines used were 2,2′-bipyridyl and 1,10-phenanthroline. Equilibrium constants for the formation of the various copper complexes were determined with a copper ion selective electrode, particularly for the species CuAB, where A is the 3-oxo-glutarate ion, and B is an aromatic amine. The kinetic behavior was then interpreted as arising from the simultaneous decarboxylation of all the species present containing a 3-oxo-glutarate ligand. The resulting rate constants indicated that some kinetic effect was transmitted through the copper from the base to the 3-oxo-glutarate, but the effect was relatively small, and the bulk of the catalytic effect caused by the base arose from changes in equilibrium concentrations.
The Constituents of Naucleadiderrichii. Part II. Isolation and Classification of Constituents; Simple β-Carboline and Pyridine Alkaloids
Authors: McLean Stewart , Murray D. G.
Published: May 2006

The bark of Naucleadiderrichii (Rubiaceae) has afforded a considerable number of constituents, mainly alkaloids. For convenience these have been placed in four categories: (1) simple β-carbolines, (2) simple pyridines, (3) indole-pyridines, and (4) miscellaneous substances. Isolation procedures and the elucidation of the structures of constituents in categories (1) and (2) are described in this paper. Spectroscopic evidence supported by synthesis has been used to assign structures 1, 2, 3, and 4 to the four simple β-carbolines and structures 5, 6, 7, and 8 to the four simple pyridines isolated.
Spectroscopie de masse des gem-diesters cycliques. Fragment anhydride
Authors: Jankowski Krzysztof , Couturier Jean , Daigle Jean-Yves
Published: May 2006

Mass spectra of four gem-diesters on three-, four-, five-, and six-member rings are analyzed. The fragmentation patterns of the investigated compounds supported by metastable ions are illustrated by Schemes 1–5 and Tables. A new fragment anhydride is proposed.
Kinetics of Sulfonation of Phenylmethanesulfonic Acid
Authors: Nienhuis Mrs. Z. R. H. , Spillane W. J. , Cerfontain H.
Published: May 2006

The kinetics of the sulfonation of phenylmethanesulfonic acid in 96.32–99.96% H2SO4 has been studied and partial rate factors for the —CH2SO3H substituent are reported.
Equilibrium Dissociation Pressures of NbBr5 over NbBr4
Authors: Westland A. D. , Lal D.
Published: May 2006

Equilibrium pressures of the dissociation of niobium tetrabromide into pentabromide and tribromide:[Formula: see text]where x lies in the range 2.67 to 3.03 have been measured over the temperature range 275–365 °C. The dissociation pressures were determined by measuring the dew points of NbBr5 vapor in a closed system containing NbBr4 and NbBrx The equilibrium decomposition pressure of NbBr4 at a given temperature was found to be much lower than that of NbCl4, thereby indicating that NbBr4 is significantly more stable than NbCl4.
Formation Constants of Copper(II) and Zinc(II) with N-salicylideneanthranilic Acid in 50–50 Water–dioxane
Authors: Mehta R. K. , Gupta R K
Published: May 2006

Protonation constants of N-salicylideneanthranilic acid and formation constants of its Cu(II) and Zn(II)complexes have been studied potentiometrically in 50% dioxane (vol/vol) solutions (μ = 0.1 sodium perchlorate) at 30 ± 0.2 °C. The color changes observed during titrations have been related to the formation of different complex species in solution. The formation constants are in fair agreement with the Irving and Williams rule.
Photolysis of 2,5- and 2,4-Dimethylpyrrole Vapors at Room Temperature
Authors: Wu E. Chung , Heicklen Julian
Published: May 2006

Both 2,5- and 2,4-dimethylpyrrole vapors at pressures from 0.05 to 0.70 Torr were irradiated at 2139 and 2288 Å at room temperature. The products were H2, CH4, C2H6, and polymer. No ring cleavage products were found. Φ{H2} and Φ{CH4} were remarkably insensitive to which pyrrole was used, its pressure,Ia, or the wavelength of the incident radiation. They were ~0.10–0.15 and ~0.01–0.02, respectively. Φ{C2H6} was comparable to Φ{CH4} and was also invariant to which substrate was used or the incident wavelength. However Φ{C2H6} did increase at low pressure or as Ia was reduced.The effect of scavengers showed that the products were produced mainly from free radical precursors. The main primary steps are:[Formula: see text]where DMP* is an electronically excited state of the dimethylpyrrole and Fa and Fb are radical fragments. Experiments with quenching gases showed that DMP* could be quenched, but that this reaction was less important than the first-order steps below 1 Torr.
Reactions of Thiyl Radicals. VIII. Photolysis of Methyl Ethyl Sulfide Vapor
Authors: Tycholiz D. R. , Knight A. R.
Published: May 2006

Methyl ethyl sulfide has been photolyzed in the vapor phase with wavelengths between 2000 and 2350 Å and the effects of pressure, temperature, and exposure time investigated. The vapor phase absorption spectrum of the sulfide has been determined and the variation in the nature and rates of formation of products in the presence of CO2, CF4, propylene, and 2-pentene measured. Quantum yields of products from the decomposition of the pure substrate were determined at 2288 Å.The products of the reaction are, in order of decreasing importance, C2H6, CH3SSC2H5, C2H5SSC2H5, CH4, CH3SCH3, C2H5SC2H5, C3H8, C2H4, CH3SSCH3, C4H10, C2H5SH, and CH3SH. A carbon/sulfur mass balance is obtained at all substrate pressures at 25 °C, and at the single substrate pressure examined at 120 °C. In the presence of propylene four additional products, n-C5H12, CH3S(CH2)2CH3, (CH3CH2CH2)2S, and CH2=CH—CH2SC2H5, were found.Only a small fraction of photochemically excited methyl ethyl sulfide molecules undergoes chemical decomposition. The two primary processes[Formula: see text]and subsequent reactions of the radicals so formed account for the observed products. R3a/R3b has a value of 1.32 at 25 °C.
Mechanisms of SNi Reactions. The Kinetics of the Decomposition of Aralkyl Carbonates
Authors: Prokipcak J. M. , Breckles T. H.
Published: May 2006

Anisylic phenyl carbonates decomposed at elevated temperatures to give CO2 and the corresponding anisylic phenyl esters. The decomposition follows first order kinetics very similar to those found for alkyl chloroformates. The decompositions involve the heterolysis of the aralkyl oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. The dependence of the decomposition rates on the nature of the solvent and structural changes of the starting carbonates is discussed.
Aqueous Reactions of Sparingly Soluble Tellurites I. Silver Tellurite
Authors: Mehra M. C. , Kahn S. M.
Published: May 2006

The aqueous interactions of the sparingly soluble silver tellurite show that in a controlled ionic medium and at a constant temperature, an aqueous complex,[Formula: see text] is formed in presence of free tellurite ions. The solubility product of silver tellurite and the stability constant of the complex species have been evaluated from the experimental data.
The Preparation, Physical Properties, and Structure of Oxotetrachloroaquorhenium(VI), ReOCl4(OH2)
Authors: Frais P. W. , Lock C. J. L.
Published: May 2006

Oxotetrachloroaquorhenium(VI), ReOCl4•H2O, has been prepared and characterized for the first time by analysis, infrared spectroscopy and single crystal X-ray diffraction. The crystals were orthorhombic, a = 10.834(8), b = 11.089(8), c = 5.517(4) Å, Pn21a, Z = 4. Intensity data were recorded by integrating film methods and measured with a Joyce–Loebl microdensitometer, and 624 observable of the 704 measured independent reflections were given non-zero weight in the final cycle of full matrix least-squares refinement where R1 = 0.0572 and R2 = 0.0687. The molecular structure is based on a very distorted octahedron with a strongly bonded oxo-group (Re—O, 1.63(2) Å) trans (177(2)°) to a weakly bonded aquo-group (Re—O, 2.27 (2) Å). The Re—Cl distances do not differ significantly (2.29(1) Å av). The chlorine atoms are bent away from the oxo-group (angles vary from (94–102°(1)).
The Structure of Nupharolutine, an Alkaloid of Nupharluteum
Authors: Wrobel J. T. , Iwanow A. , Braekman-Danheux C. , Martin T. I. , MacLean D. B.
Published: May 2006

A new alkaloid, nupharolutine, (C15H23NO2) has been isolated from the basic extract of the rhizomes of Nupharluteum. By spectroscopic and chemical methods it is shown to be a hydroxy derivative of deoxynupharidine. The mass spectra of the new base and several isomers are reported.
Nature de la luminescence de la colchicine
Authors: Roigt H. , Leblanc R. M.
Published: May 2006

Measurements of the emission decrease and polarization, as well as solvent and heavy-atom effect observations, have led us to determine the excited states multiplicity of absorption and emission in colchicine.
Vapor–Liquid Equilibria of Cyclohexane–cis-Decalin Mixtures at 25 °C
Authors: Boublík Tomás , Benson G. C.
Published: May 2006

Vapor–liquid equilibria of cyclohexane–cis-decalin mixtures were determined at 25 °C in a circulation still. Excess Gibbs free energies derived from the experimental results are in reasonable agreement with values calculated from the theory of Flory.
A Novel Class of Isomeric Phosphate Esters
Authors: Hall L. D. , Malcolm R. B.
Published: May 2006

Reaction of phenyl phosphorodichloridate with pentane-2,4-diol affords a mixture of isomeric cyclic phosphates. These have been separated and characterized. Analysis of the 1H and 31P n.m.r. spectra of these derivatives has confirmed the stereospecificity of several sets of 31P–1H coupling constants.
On the Extent of Transannular Rearrangement in the Formolysis of 1,5-Cyclooctadiene Monoepoxide
Authors: McIntosh John M.
Published: May 2006

Formolysis of 1,5-cyclooctadiene monoepoxide (1) has been shown to give only ca. 25% of products of transannular reactions. The difference between this result and those from the solvolyses of cyclooctene oxide and 4-cyclooctenyl brosylate is attributed to conformational and ring-strain effects.
An Intermediate in the Conversion of an Acetylene to a Vinyl Derivative: The Crystal and Molecular Structure of trans-Chloromethylbis(trimethylarsine)-platinum(II) Hexafluorobut-2-yne
Authors: Davies Brian W. , Puddephatt Richard J. , Payne Nicholas C.
Published: May 2006

The crystal and molecular structure of trans-chloromethylbis(trimethylarsine)platinum(II) hexafluorobut-2-yne has been determined from three dimensional X-ray diffraction data recorded by diffractometric methods. The structure has been refined by full-matrix least-squares methods on F using 1156 reflections to an agreement factor R = 0.077. The crystals are monoclinic, space group [Formula: see text] with a = 6.803(8), b = 14.93(2), c = 20.20(2) Å, β = 104.9(1)°, and Z = 4. The coordination of the platinum atom is trigonal bipyramidal, with the acetylene considered a monodentate ligand, and the two trimethylarsine ligands occupying the equatorial plane. The chlorine atom and the methyl ligand occupy the apical positions, with Pt—Cl and Pt—C distances of 2.47(1) Å and 2.10(4) Å, respectively. The long Pt—Cl bond length indicates the strong trans-influence of the methyl ligand. The observed C—C bond length of 1.32(4) Å in the acetylene ligand is lengthened from the value of 1.22(9) Å measured in the free ligand. The geometry of the coordinated ligand is discussed in terms of the bonding scheme proposed by Greaves etal.
Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in the Methyl Derivatives of the Fluoropyridines
Authors: Rowbotham J. B. , Schaefer T.
Published: May 2006

Seven methyl derivatives of the 3- and 4-fluoropyridines are synthesized and their p.m.r. spectra are analyzed. The nuclear spin–spin coupling constants are compared with previous results for the four methyl derivatives of 2-fluoropyridine. A model in which the nitrogen atom polarizes primarily the σ electron system of the ring, leaving the π electron contribution to the coupling mechanism relatively unaffected, qualitatively accounts for the large majority of the coupling constants. For example, the coupling over six bonds between methyl protons and a fluorine nucleus, [Formula: see text] is the same whether the fluorine atom or the methyl group is placed ortho to the nitrogen atom and is little different from its value in p-fluorotoluene. The model is consistent with significant σ electron contributions to long-range couplings over four and five bonds from methyl protons to fluorine nuclei or ring protons. Evidence is adduced for resonance structures in which fluorine conjugates with nitrogen or with ring carbon atoms. An earlier suggestion, that hyperconjugation of the methyl group with nitrogen is necessary to the interpretation of the observed couplings, is dropped. Instead, a substantial polarization of the σ electron core near C-2 and -6 is invoked but apparently does not extend appreciably beyond these atoms in the ring.
A Nuclear Magnetic Resonance Study of the Symmetry of the Proton Spins in Ethylene Sulfite in a Nematic Solvent
Authors: Raza M. A. , Reeves L. W.
Published: May 2006

The proton magnetic resonance spectrum of ethylene sulfite dissolved in the nematic phase N(p-methoxybenzylidene)-p-n-butylaniline has been recorded and analyzed. The dipole–dipole coupling constants derived show that the four protons are arranged in an effective plane with C2v symmetry. The spectrum is deceptively similar to that expected for D2h symmetry but errors between the experimental and the optimized computed spectrum are unacceptably large with this assumption. The two vicinal protons cis to the extra ring oxygen are closer together than the two trans vicinal protons. A comparison is made with the molecule ethylene carbonate studied previously in the same nematic solvent.
Fluorine and Proton Nuclear Magnetic Resonance Spectra of N-Dialkylaminosulfur Trifluorides
Authors: Ibbott D. G. , Janzen A. F.
Published: May 2006

The fluorine and proton n.m.r. spectra of N-dimethylaminosulfur trifluoride and N-diethylaminosulfur trifluoride have been recorded under anhydrous conditions at −68 and +22°. Chemical shifts and coupling constants of axial and equatorial fluorines are reported.
Rhodium(I) Complexes of 1,2,5-Triphenylphosphole Oxide
Authors: Holah D. G. , Hughes A. N. , Hui B. C.
Published: May 2006

Rhodium trichloride hydrate and rhodium carbonyl chloride react with 1,2,5-triphenylphosphole oxide (TPPO) to produce a rhodium(I) complex [RhCl(TPPO)]2, where the metal is bonded to the ligand through the π system. This complex reacts with FeCl3 to produce RhCl(TPPO).FeCl3 where the iron is bonded through the oxygen of the P=O group. Reactions of [RhCl(TPPO)]2 with other species including nitrogen, phosphorus, and sulfur bases and carbon monoxide are described.
The Thermolytic Generation of Benzofuran from o-Hydroxyacetophenone
Authors: Mamer O. A.
Published: May 2006

The flash thermolysis of o-hydroxyacetophenone in a low pressure inert carrier occurs with an apparent rearrangement and subsequent elimination of water to yield benzofuran. A competing minor thermolytic pathway involves the elimination of the elements of acetaldehyde to yield cyclopentadienylidenecarbonyl. There appears to be little similarity between the mechanisms of the thermal and electron impact fragmentations.
Possible Intermediates in the Biosynthesis of Porphyrins
Authors: Osgerby J. M. , Pluscec J. , Kim Y. C. , Boyer F. , Stojanac N. , Mah H. D. , MacDonald S. F.
Published: May 2006

Details of our synthesis of 5-aminomethyl-4,3′-dicarboxymethyl-3,4′-di-(2-carboxyethyl)-dipyrrylmethane (1b), as a stable potassium salt are now reported. This synthetic product had been shown to be an intermediate in the biosynthesis of uroporphinogen 1. The analogous tripyrrane, 15, should be available from the lactam of 2-(2-methoxycarbonylethyl)-3-methoxycarbonylmethyl-4,6-di-(2-ethoxycarbonylethyl)-5-ethoxy-carbonylmethyl-7-carboxymethyl-8-aminomethyl-tripyrrane (22) which has also been synthesized.5-Formyl-4,3′-di-ethoxycarbonylmethyl-3,4′-di-(2-ethoxycarbonylethyl)-5′-benzyloxycarbonyldipyrryl-methane (24), was obtained through the condensation of the bromomethyl pyrrole 2b with the hydrazone, 23, from a 2-formyl-5-free pyrrole and Girard's "T" reagent. This depends on the supression of the deactivating effect of the aldehyde group in a hydrazone from which the aldehyde is easily regenerated.
Hydrazine Derivatives. I. Transcarbamylation Reaction
Authors: Lenoir Jacques A. , Colebrook Lawrence D. , Williams Donald F.
Published: May 2006

Improvements in the synthesis of urazoles via a proposed transcarbamylation reaction are reported. Some experimental evidence for a transcarbamylation mechanism as indicated by the formation of identified intermediate products is shown. 13C n.m.r. studies on 1-phenyl-4-anilinourazole have settled the controversy on the structure of Pinner's compounds by establishing that they are 1,2,4-triazoles rather than.sym-tetrazines.
Steroids and Steroidases. XVI. An Evaluation of Synthetic Routes to Variously C-17-Substituted Δ5-3-Ketosteroids
Authors: Jones J. Bryan , Gordon Keith D.
Published: May 2006

Several routes to variously C-17-substituted Δ5-3-ketosteroids have been surveyed. The most convenient method was found to be oxidation of Δ5-3β-alcohol precursors with the Collins reagent, dipyridine chromium trioxide in méthylène chloride. The purities of the desired acid- and base-labile compounds obtained were ≥ 99% in each case.
Infrared Band Progressions in the CH2 Scissoring Region and the Ring Puckering Vibration of Trimethylene Oxide and some Deuterated Analogs
Authors: Wieser H. , Danyluk M.
Published: May 2006

Band progressions have been observed in the CH2 scissoring region of the i.r. spectra of trimethylene oxide (C3H6O) and three of its deuterated analogs (α-d2, β-d2, and α,α′-d4). With the aid of the pure ring puckering transitions (published previously) and a simple theoretical model of puckering–vibrational interactions the absorptions have been assigned to combination tones of CH2 scissoring vibrations with the ring puckering mode and its overtones. The scissoring fundamentals of the α- and β-methylene groups have been identified and assigned. Of all the vibrations for which combination progressions are observed, only the β-CH2 scissoring mode of the normal compound exhibits significant differences between the ring puckering transitions in the ground state and the vibrational excited state.
Photolyse dans l'ultraviolet à vide du Cis- et du trans-butène-2
Authors: Collin Guy J. , Perrin Patrick M.
Published: May 2006

In the far u.v. photolysis of cis- and trans-2-butene in the gas phase with the xenon and krypton resonance lines (8.4 and 10.0 eV), we show the main decomposition reactions of the excited 2-butene molecules. Main products from these reactions are 1,3-butadiene (0.4), acetylene (0.3), propadiene + propyne (0.2), and ethylene (0.1) at 8.4 eV. The pressure effect on the decomposition reaction of the chemically activated s-butyl radical was also examined. From these studies, it appears that some of the hydrogen atoms are not "thermal", but carry kinetic energy, although this amount is probably not very large. Decomposition reactions of excited 2-butene molecules (8.4 eV) give one hydrogen atom plus a free radical.
Electrical Conduction Properties of Liquid Vanadates. II. The Sodium Vanadates
Authors: Kerby R. C. , Wilson J. R.
Published: May 2006

The liquid sodium vanadates exhibited n-type semiconduction properties at sodium oxide concentrations less than 10 mol% and ionic conduction properties at concentrations greater than 25 mol%. The transition from semiconduction to ionic conduction occurred gradually as the sodium oxide concentration increased. The activation energy of conduction decreased with increasing sodium oxide concentration and increasing temperature. Negative oxygen partial pressure coefficients of conduction were found for sodium oxide concentrations less than 25 mol%. The oxygen partial pressure coefficient decreased with increasing temperature and sodium oxide concentration. The electrical conduction mechanism was considered to change from delocalized electron or polaron movement between V4+ and V5+ centers for the semiconducting liquid sodium vanadates to the probable movement of sodium and oxygen ions as the charge-carrying species forthe ionic liquid sodium vanadates.
Electric Moments and Conformations of ortho-, meta-, and para-Fluorobenzaldehyde
Authors: Bock E. , Tomchuk E.
Published: May 2006

The dipole moments of ortho-, meta-, and para-fluorobenzaldehyde were determined in dilute benzene solutions at 25 °C. The experimental data are in complete agreement with the conclusions reached by Wasylishen and Schaefer (1), viz. the O-trans conformer is the more stable conformer for ortho- and meta-fluorobenzaldehyde.