bluuebunny/crossref_metadata_2025 huggingface dataset:
Électrochimie dans l'oxydipropionitrile. Étude des systèmes du mercure en milieu complexant et non complexant
Authors: Persin M. , Gal J. Y.
Published: May 2006

The results obtained show that, in a strongly complexing medium, mercury is oxidized to mercury(II) with the concomitant formation of more highly oxidized complexes like [Formula: see text] and [Formula: see text]. When the reactional medium is less strongly complexing, however, the formation of complexes with Hg(1) can be considered. This complicates the exploitation of titration curves resulting from the progressive transformation of the complexes of mercury(II) into complexes of mercury(I) by contact with metallic mercury. Compared to the behavior observed in numerous organic solvents, the behavior of these systems is not fundamentally different.
Metallophthalocyanine dimers incorporating five-atom covalent bridges
Authors: Leznoff Clifford C. , Marcuccio Sebastian M. , Greenberg Shafrira , Lever A. B. P. , Tomer Kenneth B.
Published: May 2006

Metal-free copper and cobalt(II) binuclear phthalocyanines, in which the two phthalocyanine nuclci are covalently linked through five-atom bridges, have been prepared and characterized. Some new metal-free, copper, cobalt(II), and zinc 2,9,16,23-tetraalkoxyphthalocyanines, some of which are extremely soluble in organic solvents, are described.
Hétérocycles organiques de l'arsenic. Synthèse d'arsinimines hétérocycliques par la "réaction de Staudinger." Mécanisme de la réaction
Authors: Maroni Pierre , Madaule Yves , Seminario Tula , Wolf Jean-Gérard
Published: May 2006

Staudinger's reaction is applied on arsenic hétérocycles. Picryl and tosyl azides lead, by action on tetracoordinated arsatranes, to previously unknown pentacoordinated arsinimines with an "atran" bond (N → As). In a second step, they dimerize to diarsadiazacyclobutanes, bearing hexacoordinated arsenic atoms. Heterocyclic arsanes react only with picryl azide. All imines were obtained as dimers or oligomers, with the single exception of 8A. Ultraviolet studies give evidence for an intermediate complex different from the one demonstrated in the "classical" Staudinger's reaction with phosphorus compounds.
The reactions of sulfur atoms with propadiene and 1,2-butadiene
Authors: Green Martina , Verkoczy Bela , Lown Elizabeth M. , Strausz Otto P.
Published: May 2006

The gas phase reactions of both S(1D) and S(3P) atoms with propadiene afford methylenethiirane in nearly quantitative yields at high pressure. With 1,2-butadiene the three novel unsaturated isomeric thiirane products, resulting from addition to the 2,3 double bond and cis- and trans-addition to the 1,2 double bond, have been characterized. The yields are pressure and exposure-time dependent and, at zero conversion and high pressures, comprise ~94% of the C4H6S adducts, the remainder being two thiol insertion products. The ratio of 2,3-addition to 1,2-addition is ~1.3 forS(1D) atoms and ~2.1 for S(3P) atoms. Rate parameters for the S(3P) + 1,2-butadiene reaction were determined in competition with the S(3P) + 1-C4H8 reaction and found to be A = 6.4 ± 1.1 × 1010 M−1 s−1 and Ea = 1.4 ± 0.2 kcal mol−1. The Ea's associated with 1,2- and 2,3-addition are comparable but the preexponential factors are slightly different.
Stereochemical assignment by X-ray crystallography to the product of trapping by solvent of the intermediate zwitterion on irradiation of a 2,5-cyclohexadienone
Authors: Brisimitzakis Angelo C. , Schuster David I. , Veen James M. van der
Published: May 2006

Ultraviolet irradiation of 4-methyl-4-trichloromethylcyclohexa-2,5-dienone in acidic methanol resulted in the stereospecific generation of a solvent adduct, whose structure has been determined by X-ray crystallography, and whose carbon skeleton can be identified with that of the previously postulated zwitterion intermediate. It is concluded that the photochemical rearrangement of this dienone to the corresponding lumiketone proceeds with inversion of configuration at the migratory carbon.
The anomalous gas phase acidity of ethyl fluoride. An abinitio investigation of the importance of hydrogen bonding between F− and sp2 and sp C—H bonds
Authors: Roy M. , McMahon T. B.
Published: May 2006

Abinitio quantum chemical techniques have been used to investigate the structures and energetics of a number of hydrogen bonded adducts of F− and C—H bonds associated with unsaturated systems as well as their structural isomers. Examination of the possible species of molecular formula C2H4F− reveals that the most stable isomer is a hydrogen bonded adduct of F− and ethylene, while the classical β-fluoroethyl carbanion is found not to be bound with respect to dissociation into F− + C2H4. Similar examination of C2H2F− isomers shows that a hydrogen bonded F−–acetylene adduct is the most stable structure, however, the remaining α and β-fluorovinyl carbanions are found to be bound with respect to F− + C2H2. These results are used to explain the unusual gas phase acidities of ethylfluoride and vinylfluoride. Calculations on C3H4F− isomers show the hydrogen bonded adduct of F− and allene to be more stable than the classical 2-fluoropropenyl anion and on C2H2FO− isomers show the enolate of acetyl fluoride to be more stable than the hydrogen bonded adduct of F− and ketene. These latter results are used to explain the gas phase ion molecule reactivities of C3H4F− (predominantly F− transfer) and C2H2FO− (proton abstraction).
Steroids and related products. LII.11-Aza steroids. Part IV. The synthesis of 11-aza 9α-steroids. II. The synthesis of 11-aza-4,5α-dihydrotestosterone
Authors: Gumulka Maria , Ibrahim Ibrahim Halim , Bończa-Tomaszewski Zbigniew , Engel Ch. R.
Published: May 2006

An efficient synthesis from adrenosterone or 11α-hydroxytestosterone of 17β-hydroxy-11-aza-5α-androstan-3-one, the 11-aza analogue of dihydrotestosterone, is described. For the elaboration of the 11-aza structure, a pathway implying a Curtius-type rearrangement of a 9,11-seco 9-oxo 11-acid was employed.
Pyrrole chemistry. XXVIII. Substitution reactions of 1-(phenylsulfonyl)pyrrole and some derivatives
Authors: Anderson Hugh J. , Loader Charles E. , Xu Ru Xun , Lê Nghia , Gogan Niall J. , McDonald Robert , Edwards Louise G.
Published: May 2006

The preparative value of the 1-(phenylsulfonyl) N-blocking and directing group for the synthesis of 3-acylpyrroles has been further evaluated. Acetylation and benzoylation are strongly regiospecific and give good yields. However, the regiospecificity is not general and other substitution reactions give mixtures of 2- and 3-substitution or even mostly 2-substitution. Friedel and Crafts tert-butylation gives 3-tert-butyl-1-(phenylsulfonyl)pyrrole and provides a useful route to tert-butylpyrrole, but ethylation and isopropylation give mixtures. Acylations of 2- and 3-alkyl-1-(phenylsulfonyl)pyrroles show little evidence of useful regiospecificity.
Free radical mechanisms for the oxidation of 2,3-dihydroxy-2-propenal (triose reductone) by hexacyanoferrate(III)
Authors: Abe Yasuo , Dohmaru Takaaki , Horii Hideo , Taniguchi Setsuo
Published: May 2006

Kinetic studies of the oxidation of 2,3-dihydroxy-2-propenal (triose reductone, RH2) by hexacyanoferrate(III), [Fe(CN)6]3−, were carried out in acidic media ([H+] = 0.02–0.1 M (1 M = 1 mol dm−3)) at various temperatures (10–30° C). The ionic strength of the media (I = 0.04–0.4 M) was adjusted using sodium perchlorate. The second-order rate constants in M−1 s−1 are (0.86 ± 0.06) – (2.83 ± 0.14) for the reactions of hexacyanoferrate(III) with RH2, and [(4.16 ± 0.03) − (12.4 ± 0.2)] × 103 for those with RH− ion. Activation parameters for the oxidation have been reported and compared with those of the oxidation of triose reductone with peroxodisulfate ion. A probable mechanism is proposed for the reaction.
Relaxation and related 1H nmr studies on "asperlin." Configuration and conformation of the epoxypropyl side-chain
Authors: Dais Photis , Perlin Arthur S.
Published: May 2006

Monoselective and biselective spin-lattice relaxation rates, together with nOe experiments, have been used to examine the configuration and conformation of the epoxypropyl side-chain of "asperlin" (1) in benzene solution. The data confirm earlier evidence that the oxirane ring is trans, and indicate that 1 is the 6R, 7S diastereomer. Moreover, it is shown that in the most probable conformation of the side-chain about the C-5, C-6 bond, H-5 and H-6 are anti.
Syntheses of model oligosaccharides of biological significance. 4. Synthesis of a fucosylated N,N′-diacetylchitobioside and related oligosaccharides
Authors: Schwartz David A. , Lee Ho-Huat , Carver Jeremy P. , Krepinsky Jiri J.
Published: May 2006

The synthesis of two trisaccharides and one disaccharide containing L-fucose and 2-acetamido-2-deoxy-D-glucose is reported. Methyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranoside was glycosylated with a 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide. Removal of the phthalimido protecting groups by hydrazinolysis followed by N-acetylation and debenzylation yielded methyl N,N′-diacetylchitobioside 3′,4′,6′-triacetate. The latter was selectively fucosylated at the 6-position with 2,3,4-tri-O-benzyl-α-L-fucopyranosyl bromide to yield, after debenzylation and de-O-acetylation, methyl 2-acetamido-4-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-2-deoxy-6-O-(α-L-fucopyranosyl)-β-D-glucopyranoside. When methyl 3-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranoside was fucosylated, its 6-O-and 4,6-di-O-(α-L-fucopyranosyl) derivatives were obtained by use of 1 and 2 equivalents, respectively, of the protected fucosyl bromide.
Competitive photochlorination and kinetic isotope effects for hydrogen/deuterium abstraction from the methyl group in C2H6, C2D6, CH3CHCl2, CD3CHCl2, CH3CCl3, and CD3CCl3
Authors: Tschuikow-Roux E. , Niedzielski Jan , Faraji F.
Published: May 2006

The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane, 1,1,1-trichloroethane, and some of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigated in the temperature range 7–95 °C using methane as competitor. Rate constants and their temperature coefficients are reported for the following reactions:[Formula: see text]An Arrhenius law temperature dependence was observed in all cases. Mixed primary and α-secondary kinetic isotope effects are k1/k2 = 2.79 ± 0.27, k4/k6 = 4.13 ± 0.32, k7/k8 = 1.46 ± 0.12 at 298 K and decrease to k1/k2 = 2.53 ± 0.22, k4/k6 = 4.06 ± 0.28, k7/k8 = 1.45 ± 0.09 at 370 K, showing a "normal" temperature dependence. The kinetic isotope effect for H/D abstraction from the methyl group decreases with increasing number of chlorine substituents in the adjacent chloromethyl group. The β-secondary isotope effect, k3/k5, is close to unity and shows a slight inverse temperature dependence.
Substituent effects on benzyl radical hyperfine coupling (hfc) constants. Part 3. Comparison of the α-hfc for substituted benzyl radicals with the β-hfc for substituted cumyl radicals
Authors: Arnold Donald R. , Nicholas A. Martin De P. , Snow Miles S.
Published: May 2006

The electron spin resonance (esr) spectra of eighteen para-substituted cumyl radicals were analyzed. The relationship between the β-hyperfine coupling (β-hfc) constants of these cumyl radicals and the corresponding α-hfc constants of benzyl radicals was studied. Although there is a general trend for the α- and β-hfc values to vary in a similar manner, specific deviations from a linear correlation between these parameters were observed. These deviations were rationalized by considering charge effects on spin delcoalization. The correlation coefficient for the linear regression analysis of these α- and β-hfc values was found to significantly improve when β arameters reflecting charge effects on spin delocalization were included in an extended Hammett treatment of the spectral data.
Energy migration in the aromatic vinyl polymers. 5. Poly(2-vinyl naphthalene) and polystyrene
Authors: Semerak Steven N. , Frank Curtis W.
Published: May 2006

Electronic energy migration in pure poly(2-vinyl naphthalene) (P2VN) is analyzed in terms of a theory for three-dimensional transport and trapping in a homogeneous system of randomly distributed chromophores. A simpler theory for 3-D transport on a spatially periodic lattice, which was applied previously to polystyrene (PS) gave self-contradictory results for P2VN because of higher transport rates in P2VN. The fraction of rings in excimer-forming sites (EFS) in pure P2VN, analyzed by the former theory, is found to be 0.072 – moderately larger than the single-chain fraction of 0.026. In contrast, the EFS ring fraction in pure PS was 0.33, much larger than the single-chain fraction of 0.051. This reflects the reduced probability, relative to a phenyl ring pair, of packing a naphthyl ring pair into the necessary sandwich arrangement in the pure polymers. Energy migration in very dilute, miscible blends containing P2VN is analyzed by a one-dimensional transport model, which was applied previously to similar blends containing PS. The nearest-neighbor migration rates obtained from the data for both P2VN and PS are about one hundred times higher than the expected dipole–dipole rates. This suggests that (1) migration is not limited to nearest-neighbor rings, (2) the morphology of the dilute blends does not consist of isolated chains of the aromatic vinyl polymers, or (3) short-range electronic interactions other than dipole–dipole are involved in energy migration.
Reactions of lumiflavin with amine radicals
Authors: Surdhar Parminder S. , Bader Douglas E. , Armstrong David A.
Published: May 2006

The amino radicals (•AH) formed by the 60Co radiolysis of N2O-saturated 0,05 M solutions of ethylene diamine tetraacetate (EDTA) at pH 7 and 11.2 and of glycine at pH 11.2 brought about an efficient two-electron reduction of lumiflavin (Fl). The spectra of the products were identical to those formed by photolysis of the same solutions and by reduction of the lumiflavin with •CO2− radicals. The products were reoxidised to flavin by oxygen. The quantum yield for flavin disappearance was 0.52 ± 0.07 and 0.17 ± 0.01 in the presence of EDTA at pH 7 and 11.2 and 0.065 ± 0.008 and 0.17 ± 0.01 for glycine at the same pHs, respectively.The overall two-electron reduction can be explained by the mechanism:[Formula: see text]The rate constants of reaction [4] were found by pulse radiolysis to be 1.8 ± 0.3 × 109 and 1.5 ± 0.3 × 109 M−1s−1 for the radicals of glycine and EDTA at pH 7 and 3.6 ± 0.3 × 108 M s−1 for glycine radicals at pH 11.2. The spectrum of •FlH formed by glycine radicals at pH 7 is similar to that produced by•CO2−, but there was some perturbation, which is apparently due to interaction with the amine.The radicals formed from the secondary amines piperazine and diethylamine at pH 11.8 also effected reversible two-electron reduction. However, the radicals from glycine anhydride and the primary amine ethylamine yielded significant amounts of non-oxidisable products. The reaction mechanisms are discussed and effects of pH are considered.
Infrared spectra of vitreous lithium and cadmium mixed phosphates
Authors: Garrigou-Lagrange C. , Ouchetto M. , Elouadi B.
Published: May 2006

Infrared reflection spectra of vitreous phosphates (1 − x − χ)Li2O − xCdO − χ P2O5 are analysed in relation to the conformation when it is known. The evolution of the spectra with the different constituents is studied and the oxide forming-character of CdO is discussed.
Low-temperature Raman and Fourier transform infrared spectra of dodecacarbonyldirhenium(0), Re2(CO)10
Authors: Harvey Pierre D. , Butler Ian S.
Published: May 2006

The Raman spectrum of microcrystalline dodecacarbonyldirhenium(0), Re2(CO)10, has been reinvestigated at 67 K using one of the latest fully-computerized spectrometers available. Previously unobserved peaks have been detected mainly in the 13CO-satellite (2150–1900 cm−1), and overtone and combination regions (1300–700 and 4300–3800 cm−1). This is the first time that Raman-active first CO overtones and combinations of a metal carbonyl complex have been reported. They were earlier thought to be too weak to be detected. Assignments are proposed for the majority of these new peaks together with those from a similar low-temperature (~70 K) FT-ir study. In general, the D4d selection rules are obeyed, but the activity of some forbidden bands reveals that the molecule is slightly distorted in the solid state in agreement with its X-ray structure. The similarity of the low-temperature spectra to those obtained at room temperature indicates that no phase change occurs throughout the temperature range investigated.
Abinitio study of rotational isomerism in acrolein
Authors: Maré George R. De
Published: May 2006

Analytic gradient (force) methods at the STO-3G, 3-21G, and 6-31G* basis set levels have been used to optimize the geometry of acrolein completely at each critical point (minima, maximum) in the torsional potential energy curves for rotation about the single C—C bond (dihedral angle θ). The STO-3G and 6-31G* optimizations predict the planar trans conformation (θ = 180°) to be more stable than the cis conformation (θ = 0°) by 1.87 and 6.97 kJ/mol, respectively. The 3-21G optimizations, in disagreement with experiment, place the planar cis structure below the trans by 4.5 J/mol. The predicted relative energy (ΔE) and position for the transition state (TS) for rotation from the trans conformer are ΔE = 22.35, 37.14, and 34.41 kJ/mol and θ = 91.8, 91.6, and 91.0° for the STO-3G, 3-21G, and 6-31G* optimizations, respectively. The computed and experimental geometries, relative energies, dipole moments, and coefficients for the torsional potential expansion are compared.
Adsorption of carbon monoxide on the surfaces of polycrystalline transition metals and alloys: electron energy loss and ultraviolet photoelectron spectral studies
Authors: Rao C. N. R. , Kamath P. Vishnu , Prabhakaran K. , Hegde M. S.
Published: May 2006

Adsorption of CO has been investigated on the surfaces of polycrystalline transition metals as well as alloys by employing electron energy loss spectroscopy (eels) and ultraviolet photoelectron spectroscopy (ups). CO adsorbs on polycrystalline transition metal surfaces with a multiplicity of sites, each being associated with a characteristic CO stretching frequency; the relative intensities vary with temperature as well as coverage. Whilst at low temperatures (80–120 K), low coordination sites are stabilized, the higher coordination sites are stabilized at higher temperatures (270–300 K). Adsorption on surfaces of polycrystalline alloys gives characteristic stretching frequencies due to the constituent metal sites. Alloying, however, causes a shift in the stretching frequencies, indicating the effect of the band structure on the nature of adsorption. The up spectra provide confirmatory evidence for the existence of separate metal sites in the alloys as well as for the high-temperature and low-temperature phases of adsorbed CO.
Photochemistry of alkenes. 9. Medium-sized cycloalkenes
Authors: Kropp Paul J. , Mason J. Derek , Smith Gardiner F. H.
Published: May 2006

The behavior of the three medium-sized cycloalkenes cyclooctene (10), cyclodecene (17), and cyclododecene (21) on direct irradiation in pentane and methanol solution has been studied. The results are summarized in Tables 1–3. Irradiation of medium-sized cycloalkenes is a convenient procedure for the preparation of bicyclic products (cf. 13, 14, 19, 20, and 23) through transannular insertion reactions of carbene intermediates (cf. 11, 18, and 22) thought to arise from rearrangement of the 1[π,R(3s)] state via a 1,2-hydrogen shift. The formation of trans-decalin (20) is in contrast to the reported formation of the cis isomer on base-initiated decomposition of the corresponding tosylhydrazone. None of the three cycloalkenes 10, 17, or 21 underwent competing nucleophilic trapping of the 1[π,R(3s)] state in methanol, in contrast with other alkenes previously studied. However, cyclododecene (21) afforded the methyl ether 25, which apparently resulted from protonation of the 1(π,π*) state, and the epoxide 26, which is thought to arise from electron transfer to oxygen by the 1[π,R(3s)] state followed by protonation of the resulting superoxide ion and oxidation of unreacted cyclododecene (21).
The effects of selected gases upon ethanol: hydrogen bond breaking by O2 and N2
Authors: Mathers T. L. , Schoeffler G. , McGlynn S. P.
Published: May 2006

The temperature dependency of the phosphorescence properties of aromatic hydrocarbons in alcoholic glasses exhibits a number of phenomena that have not been described previously. Chief among these are the effects of added gases (O2, N2, C2H6, Ar), some of which produce major changes in the luminescence characteristics. These are discussed, and rationalized in terms of a model which presumes that O2 and N2 can disrupt the normal hydrogen bonding process between alcohol molecules.
From crystal orbitals to strange electronic states. I. Crystal orbitals by direct recursion (transfer matrix) method (DRM)
Authors: Biczô Géza
Published: May 2006

The history of Bloch's and Tamm's states is sketched. The present stage in the theory of the bounded infinite polymers and crystals and strange electronic states is outlined. To lay the foundations of the SCF LCAO bounded crystal orbital (BCO) method applicable for surface electronic problems, the direct recursion (transfer matrix) method (DRM) is formulated for perfect cyclic polymers and crystals. A simple combination of block-decomposition and matrix transpositions is applied to calculate U−1 directly from the blocks of U, the similarity transformation bringing the recursion matrix T into its normal form. Several forms are given for the auxiliary and fundamental equation of the DRM. The crystal orbitals are derived by the DRM. Full matrix expression is presented for the resolvent (Green) matrix of perfect cyclic polymers, the unperturbed system in the SCF local-density approach of Ladik and Seel. The formulae of the charge-bond order matrix are derived both by the DRM and the indirect (Green matrix) recursion method (IRM).
Selective photoinduced Ca2+ diffusion in rhodopsin–lipid bilayers: an internal transmitter hypothesis
Authors: N'Soukpoé N'Suavi Kossi , Leblanc Roger M.
Published: May 2006

Triton X-100 purified rhodopsin has been incorporated into lipid bilayer membranes prepared by the combined lifting-and-touching method. The illumination of the membranes with white light and monochromatic light of λ = 498 nm resulted in a high selective increase of Ca2+ diffusion through the lipid bilayers compared to Na+ and K+. The stoichiometric ratios of photoinduced ion diffusion were found to be more than 888 Ca2+ Rh*−1 s−1 and 166 Na+ Rh*−1 s−1 at 290 K using the white light, and 1 277 Ca2+ Rh*−1 s−1, 96 K+ Rh*−1 s−1, and 50 Na+ Rh*−1 s−1 at 276 K using the monochromatic light. It was inferred that Ca2+ is an excellent candidate as internal transmitter in the visual photo-transduction.
Réarrangement de thiophénobishomotropones en naphto[1,8-bc]thiophène et benzo[2,3-b]thiophène; études spectroscopique et mécanistique
Authors: Hanquet Bernard , Farnier Michel , Guilard Roger , Lecomte Claude , Dusausoy Yves
Published: May 2006

A non classical rearrangement is observed when thiopheno[c] and [b]bishomotropones react with ethanedithiol, leading to a naphtho[1,8-bc]thiophene and (or) a benzo[b]thiophene. The structure of the products is supported by deuterium labelling, 1H nmr spectra, and X-ray analysis of 5,6-diphenyl naphtho[1,8-bc]thiophene. A mechanism is proposed which implies an electronic transfer between a "soft" nucleophile and a "hard" acid, in the key step.
Towards a complete account of diastereotopic hydrogen isotope exchange of carbon acids. III. Base-catalyzed exchange of sulfoxides. Evidence for exchange by inversion
Authors: Werstiuk Nick Henry , Banerjee Sujit
Published: May 2006

The rate constants for deuteroxide and hydroxide catalyzed H → D and D → H exchange of benzodihydrothiophene oxide (1a) and several of its deuterated analogs 1b, 1c, and 1d at 30.00 ± 0.05 °C are reported along with the rate constants for D → H exchange of deuterated benzyl methyl sulfoxides 2b and 2c. Application of the steady-state assumption to schemes involving equilibrating pyramidal anions yield equations which are used to fit experimentally determined (kf/ks)H → D and (kf/ks)D → H ratios. The analysis supports our view that exchange of the diastereotopic protons (deuterons) occurs by inversion. The inversion component contributes significantly to exchange of the "slow" proton (deuteron) of a diastereotopic pair and this accounts for the observation that (kf/ks)D → H < (kf/ks)H → D. This study establishes an upper limit of 6 kcal for the barrier to inversion of the carbanions derivable from 1 and 2, if pyramidal anions are formed.
Structure and nuclear magnetic resonance spectra of 6-bromo-3,3′,4′,5,7-penta-O-methylcatechin
Authors: Einstein F. W. B. , Kiehlmann E. , Wolowidnyk E. K.
Published: May 2006

The title compound has been synthesized by selective debromination of 6,8-dibromocatechin and indirect methylation of the resulting 6-bromocatechin via its pentaacetate. The structure of C20H23BrO6 has been determined by X-ray crystallography. The compound crystallizes in the space group P1 with a = 9.589(3) Å, b = 11.576(3) Å, c = 11.326(3) Å, α = 118.80(3)°, β = 93.23(3)°, γ = 111.44(3)°, ρc = 1.481 g cm−3, and Z = 2. Intensities were measured for 2584 independent reflections (2θ < 45°) of which 2213 were observed (I > 3.0σ(I)) and used in subsequent refinement (final R values were R = 0.0268 and Rw = 0.0344). Crystallographic and pmr data confirm the position of the bromine atom at C-6, the trans-diaxial arrangement of H-2/H-3 and the quasi-equatorial orientation of the 3,4-dimethoxyphenyl group (ring B). The two heterocyclic ring conformations are consistent with the expected flexibility of the molecule.
Shielding anisotropy in tin compounds: spectroscopic studies of alkyltin cations in strong acid solutions
Authors: Birchall Thomas , Manivannan Veeragathy
Published: May 2006

We have observed that the 119Sn nmr spectra of dialkyltin cationic species in highly acidic solutions are strongly field dependent. Relaxation time measurements at three different magnetic fields have established that the dominant spin-lattice relaxation mechanism for these species at high magnetic field is shielding anisotropy. A comparison of T1−1 and T2−1 values indicates that at room temperature a rapid chemical exchange process is occurring. In the case of the (CH3)2Sn(SO3F)2–HSO3F system variable temperature 119Sn nmr reveals the presence of three tin species which are involved in this exchange process.
Rhenium and manganese carbonyl compounds incorporating tridentate chelating pyrazolyl gallate ligands
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The coordinating properties of a variety of unsymmetrical uninegative tridentate chelating "pyrazolylgallate" ligands have been studied using the tricarbonyl moieties "M(CO)3", where M = Mn or Re, as acceptor species. A series of monomeric, pseudo octahedral complexes has been characterized and a fac mode of coordination established for the tridentate gallate ligands from 1H nmr, ir measurements, and X-ray structure determinations. Nitrosylation of a selection of the rhenium tricarbonyl compounds has yielded a number of cationic rhenium mononitrosyl dicarbonyl species. The reactivity of these cations towards reducing agents has been investigated.
A theoretical study on the structures and stabilities of protonated hydrogen sulphide – hydrogen sulfide clusters
Authors: Yamabe Shinichi , Minato Tsutomu , Sakamoto Makino , Hirao Kimihiko
Published: May 2006

An abinitio MO calculation is made on the H3S+(H2S)n cluster (n = 0–5). For n = 1, full thermodynamic data are reproduced theoretically, and for n = 1, 2, and 3 the effect of d functions on the structure and energies is investigated. On the basis of the present results, the accuracy of two conflicting experimental data is examined.
Facile H–D exchange of the bridgehead methyls of bicyclo[2.2.2]octan-2,5-diones. Evidence for a carbon analogue of the acyloin rearrangement
Authors: Werstiuk Nick Henry , Wade Gwen Irene , Martin Peter John Joseph
Published: May 2006

Hexamethyltwistyl-2,5-dione 4 has been synthesized and its H–D exchange studied in t-BuOK/t-BuOD at 125 °C. We find that the bridgehead methyl at C-3 undergoes exchange 7 × 105 times faster than the bridgehead methyl of bicyclo[2.2.1]heptan-2-one (fenchone). This result, along with a previous study, establishes the first examples of the carbon analogue of the acyloin rearrangement of alicyclic systems.
Molecular recognition. II. The binding of the Lewis b and Y human blood group determinants by the lectin IV of Griffoniasimplicifolia
Authors: Spohr Ulrike , Hindsgaul Ole , Lemieux Raymond U.
Published: May 2006

Using a radioimmunoassay to measure the relative potencies as inhibitors of a wide number of chemically modified structures related to the Lewis b human blood group determinant, it was found that derivatives of the Lewis b (αLFuc(1→2)βDGal(1→3)[αLFuc(1→4)]βDGlcNAc) and the Y (αLFuc(1→2)PDGal(1→4)[αLFuc(1→3)]βDGlcNAc) determinants are complexed by the lectin IV of Griffoniasimplicifolia through the recognition of a topographical feature that is common to both the tetrasaccharides. This surface provides a nonpolar region formed by the two methyl groups of the fucose units and extends along the C-1—O-5—C-5 side of the αLFuc(1→2) unit and terminates at one end by a polar grouping which is formed by OH-3 and OH-4 of the βDGal unit and OH-4 of the αLFuc(1→4) unit. Association constants were determined from changes in ultraviolet absorption that occur as the result of complex formation. For the reaction of the Lewis b-OCH3 tetrasaccharide, the thermodynamic parameters were found to be ΔH = −13 kcal/mol and ΔS = −22 cal/mol/K. The inhibition data for the relevant monodeoxy derivatives indicated that OH-2 and OH-3 of both of the αLFuc units are not directly involved in the binding reaction. The basis for drawing these conclusions was strengthened by finding that the reaction of the simple Lewis b analog, methoxymethyl (1→2)βDGal(1→3)[αLFuc(1→4)]βDGlcNAcOCH3 displayed very similar thermodynamic values; namely, ΔH = −14 kcal/mol and ΔS = −26 cal/mol/K, to those mentioned above for the Leb-OCH3 tetrasaccharide. The OH-4 of the αLFuc(1→2) unit may be bound in an intramolecularly hydrogen bonded form.
The electroreduction of halogenated thiophenes
Authors: Gedye Richard Neville , Sadana Yoginder Nath , Leger Raymond
Published: May 2006

Electroreduction of polyhalothiophenes results in the preferential reduction of the α-halogen atoms. Preparative electrochemical reduction of these compounds at controlled potential can be used to synthesize 2,3,4-trihalo, 3,4-dihalo, and 3-halothiophenes. Experimental conditions were developed under which these reductions could be done selectively, giving good yields of the desired products. Electroreduction of tetrabromothiophene can also lead to the formation of a poly-bromodithienyl mercury compound.
Réduction photochimique des polytungstates. Mise en évidence d'un effet photogalvanique
Authors: Folcher G. , Paris J. , Chauveau F.
Published: May 2006

A photogalvanic cell which functions with an acetronitrile solution of tetrabutylammonium decatungstate [Formula: see text] (0.2 M in gram-atoms of tungsten) has been realized. This cell utilizes an irradiated platinum electrode with a non-illuminated graphite electrode. The conditions giving the best conversion of light to electric power have been determined. An overall mechanism has been proposed. The decatungstate photooxidizes an electron donor like water. The involvement of a two-photon process has been demonstrated. The emf produced is about 650 mV, and the experimental yield is in the neighborhood of 1%.
Kinetics and mechanism of the oxidation of mercury by peroxidase
Authors: Wigfield Donald C. , Tse Season
Published: May 2006

The kinetics of oxidation of zero-valent mercury by the horseradish peroxidase system are reported. The reaction is first order in mercury and first order in peroxidase compound 1, and appear to obey these kinetics to completion of the reaction. The second order rate constant is 8.58 × 105 M−1 min−1 at 23 °C. The data are consistent with a simple two-electron transfer from mercury to the iron–heme system of peroxidase with the enzyme acting as a chemical oxidant that is continually being regenerated by reaction with hydrogen peroxide.
Studies of the dissociation of 2,4,6-trinitrophenol in aqueous mixtures of methanol and ethanol at 25 °C
Authors: De A. L. , Atta A. K.
Published: May 2006

Thermodynamic dissociation constants (sK)m of 2,4,6-trinitrophenol have been determined at 25 °C in aqueous mixtures containing 30, 50, 70, and 90% by weight of methanol and 30, 50, 70, 90, and 95% by weight of ethanol by spectrophotometric method. Solvent effect on the dissociation of the acid: δ(ΔG0) = 2.303RT[p(sK)N − p(wK)N] shows an unusual behaviour, the value decreases and passes through a minimum and ultimately becomes positive as the proportion of organic component in the solvent is progressively increased. The results have been compared with those of other uncharged acids like acetic acid, benzoic acid available from literature. The difference of behaviour (minimum characteristic in δ(ΔG0) curve) has been attributed to very strong dispersion interaction of trinitrophenolate anion with the organic component of the solvent. The overall behaviour of this acid indicates that solvent effect is an involved process being guided by electrostatic and dispersion interactions besides relative solvent basicities.
The acid-catalyzed hydrolysis of phosphinates. IV. Pentacoordinate intermediate formation during hydrolysis of a phosphinothionate
Authors: Cook Robert D. , Metni Marlene
Published: May 2006

The hydrolysis of methyl dimethylphosphinothionate in D2SO4–D2O solution gives as products the phosphinic acid and methyl dimethylphosphinate. The bell-shaped pH–rate profiles for both reactions as well as the values of Bunnett's w and w* (3.31 and −0.21 respectively), Bunnett–Olscn's [Formula: see text] (0.82), and Yates–McClelland's r (6.56) support an A-2 pathway. The results are interpreted in terms of the presence of a common pentacoordinate intermediate along the reaction pathway. The pKa of the above ester as well as that of methyl dimethylphosphinodithioate are reported (−5.53 and −5.38 respectively).
Solvent-induced conformational changes in benzyl fluoride. Long-range C,F; H,H; H,F spin–spin couplings
Authors: Schaefer Ted , Peeling James , Sebastian Rudy
Published: May 2006

The 1H and 19F nmr spectra of benzyl fluoride, although very tightly coupled at 300 MHz, are analyzed for dilute CS2 and acetone solutions. 13C, 19F spin–spin coupling constants for benzyl fluoride in a series of solvents are also measured. Geometry-optimized STO 3G MO computations on benzyl fluoride indicate a small twofold barrier to rotation about the exocyclic C—C bond in the gas phase. All the long-range couplings between 19F and ring protons or carbon-13 nuclei and between methylene and ring protons are consistent with the conclusion that the barrier to internal rotation in benzyl fluoride is small and that the conformation in which the C—F bond lies in a plane perpendicular to the benzene plane is stabilized by 2 kJ/mol in going from CS2 to DMSO or acetone solutions. The solvent dependence of the internal barrier may account for the diversity of conformational conclusions in the literature. Furthermore, it is clear that the internal barrier will depend on the presence of substituents at any site in the ring.
1,n-Radical ions: an abinitio study of racemization and isomerization of the cyclopropane radical cation
Authors: Wayner Danial D. M. , Boyd Russell J. , Arnold Donald R.
Published: May 2006

The surfaces for cis–trans isomerization and racemization of the cyclopropane radical cation (1+) are determined using abinitio calculations. It is found that polarization functions and electron correlation have large effects on the relative energies of 1+. Orbital symmetry arguments predict that conrotatory closure of the 0,0 conformer of 1+ should be preferred. These predictions are supported by the calculations; however, even the conrotatory closure has a significant activation barrier. Conformational changes that accompany single methylene rotation are also discussed. The implication of these results to ion cyclotron resonance and mass spectral experiments is that isomerization of 1+ to the 0,0 conformer can occur at energies far below the barrier required to isomerize 1+ to the propylene radical cation. However, the 0,0 conformer of 1+ and the propylene radical cation should display similar reactivities (e.g. deprotonation). The results also indicate that, contrary to reported esr evidence, 1+ should not exist preferentially in the 90,0 conformation.
Crystal and molecular structure of di-o-anisylketone
Authors: Faerman C. , Nyburg S. C. , Punte G. , Rivero B. E. , Vitale A. A. , Nudelman N. S.
Published: May 2006

The crystal and molecular structure of the title compound, C15H14O3, is described. Crystals are monoclinic, space group P21/n, a = 9.893(5), b = 10.719(5), c = 12.136(3) Å, β = 90.56(3)°. The molecule has a twist conformation and interactions between oxygen atoms of the methoxyl groups are thought to play some part in this.
Complexes of hybrid ligands. Pd2+ and Pt2+ complexes of new fluoro-alcohol thioether ligands; the use of thioether inversions to make structural assignments
Authors: Boeré René T. , Willis Christopher J.
Published: May 2006

The fluorinated alcohol–thioethers RSCH2C(CF3)2OH (R = Me, Ph) have been synthesized by the reaction of RSCH2Li with (CF3)2CO. By ionization of the fluoroalcohol group, these may act as bidentate, uninegative, ligands L−. The presence of the soft thioether function in the hybrid ligand stabilizes the bond to the harder fluoro-alkoxy group, and complexes with soft transition metals are formed. Neutral complexes PdL2 and PtL2 have been synthesized, and, by the use of nmr, the geometry of the complexes is assigned as cis for Pt complexes, while both cis and trans are observed for Pd.The barrier to inversion at coordinated thioether is studied by dynamic nmr, and observation of coalescence temperatures leads to values of ΔG‡ of 73–74 kJ/mol for cis-PdL2, 67–69 kJ/mol for trans-PdL2, and 89 ± 1 kJ/mol for cis-PtL2.
Étude cinétique de l'ouverture thermique de la liaison C—C d'aziridines et d'époxydes dipôles-1,3 potentiels. II. Influence des substituants
Authors: Derdour Aїcha , Texier Fernand
Published: May 2006

A kinetic study concerning the thermal opening of the C—C bond of 2-cyanoaziridines (1), 2-alkoxycarbonylaziridines (2), 2-aroyiaziridines (3), and 1,3-substituted 2,2-dicyanoepoxides (4) has shown that (i) the stereochemistry of the cyclic carbon atoms has little influence on the rate of the electrocyclic opening; (ii) the presence of an aryl substituent in position 1, as opposed to an alkyl substituent, favors this reaction and, in general, the reaction is favored by the presence of substituents which produce energy levels closer to those of the P doublet of the heteroatom and of the σ*C-2−C-3 MO. This reaction is also favored by a dissymmetry of the substitution on the 2 and 3 carbons. The results are discussed in terms of the theory of relaxations. [Journal translation]
An analysis of bond length information for oxygen atoms adsorbed on well-defined metal surfaces
Authors: Mitchell K. A. R. , Schlatter Susan A.
Published: May 2006

New bond valence – bond length relations deduced by Brown and Altermatt for solid state structures have been used for rationalizing O—M interatomic distances, measured by various surface crystallographic techniques, for O atoms chemisorbed on well-defined metal (M) surfaces. The advantages of this approach, over the Pauling–Schomaker–Stevenson approach used previously, are especially apparent for initial rationalizations of new information on the nearest-neighbor and next-nearest–neighbor bond lengths for O adsorbed on long-bridge sites of (110) surfaces of face-centered cubic metals.
Influence de nitrates métalliques sur l'équilibre de dissociation ionique: dans le sulfolane
Authors: Boughriet Abdellatif , Wartel Michel , Fischer Jean-Claude
Published: May 2006

The addition of a metallic nitrate such as Zn(NO3)2, Cu(NO3)2, or UO2(NO3)2 to N2O4 solutions in aprotic media leads to the reclaiming of the NO+ species (which is considered as a catalyst for the nitration of aromatics by N2O4) as follows: [Formula: see text]. Using linear voltammetry, the study of the N2O4 reduction in the presence of metallic nitrates with a platinum electrode has allowed us to derive the equilibrium constant for reaction [1] and that corresponding to the formation of the trinitrato complexes in sulfolane according to: [Formula: see text]. The strong stability of the [Formula: see text] complexes is due to the weak solvating character of the sulfolane. This hypothesis is also confirmed by the stability constants of zinc[II] chloride complexes: [Formula: see text] in sulfolane from a potentiometric study by means of a silver chloride – silver electrode.
Kinetics and mechanisms of oxidations by metal ions. Part VI. Oxidation of α-hydroxy acids by cerium(IV) in aqueous nitric acid
Authors: Datt Narain , Nagori Ratan R. , Mehrotra Raj N.
Published: May 2006

The kinetics of oxidation of glycolic, malic, tartaric, and citric acids by cerium(IV) ammonium nitrate were investigated in 0.006 mol dm−3 nitric acid. The reaction was catalysed by H+ in the range 0.006–0.016 mol dm−3 at constant [Formula: see text] (0.02 mol dm−3). The pseudo first-order rate constant kobs was independent of [CeIII] (0.0004–0.002 mol dm−3). The proposed mechanism is based on the assumption that the formation of the precursor Ce(IV) – α-hydroxy acid complex precedes its rate controlling disproportionation, which is assisted by a proton, possibly due to the formation of the activated state [H+—CeIV – HA]≠ (where CeIV is the reactive cerium(IV) species and HA is the α-hydroxy acid). The free radical R1R2ĊOH produced in the rate controlling step further reacts with a number of Ce(IV) molecules in the fast step to yield the final oxidation product. The activation parameters for the rate controlling step could be evaluated only in the oxidation of tartaric acid.
Ion exchange reactions of n-butylamine intercalates of tin(IV) hydrogen phosphate and hydrogen uranyl phosphate with cobalt(III) complexes
Authors: Pozas-Tormo Rafaela , Moreno-Real Laureano , Martínez-Lara María , Rodríguez-Castellón Enrique
Published: May 2006

The ion exchange reactions of n-butylamine intercalates of tin(IV) hydrogen phosphate and hydrogen uranyl phosphate towards carbonatotetraamminecobalt(III), chloropentaamminecobalt(III), and hexaamminecobalt(III) have been investigated. Independent of the complex cation charges, the amounts of Co(III) complex exchanged by the n-butylamine intercalate of tin(IV) hydrogen phosphate are practically the same. With the n-butylamine intercalate of hydrogen uranyl phosphate, the ionic exchange was completed and the composition was fixed by the exchanged Co(III) complex. The layer charge densities of these phosphates justify the different ionic exchange behaviour observed towards the large complex cations. All the products were characterized by chemical analysis, X-ray diffractometry, infrared spectroscopy, diffuse reflectance spectroscopy, and thermal analysis.
The synthesis and X-ray structural characterization of bis[(2S,3S)-2,3-bis(diphenylphosphino)butane]rhodium(I) chloride and its reactivity towards small gas molecules
Authors: Young Charles G. , Rettig Steven J. , James Brian R.
Published: May 2006

The [Formula: see text] cation, where chiraphos is 2,3-bis(diphenylphosphino)butane, has been synthesized and fully characterized by spectroscopy and single crystal data on the chloride salt (1). Crystals are monoclinic, a = 23.106(3), b = 12.4987(8), c = 21.455(3) Å, β = 128.539(5)°, Z = 4, space group C2. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.046 and Rw = 0.032 for 4509 reflections with I > σ(I). The coordination about Rh is square planar distorted toward tetrahedral within the five-membered chelate rings, similar to that in [Formula: see text], where dpe is 1,2-bis(diphenylphosphino)ethane, but the distortion toward tetrahedral is significantly greater in 1; the methyl substituents further restrict rotational freedom about the P—Ph bonds, which leads to some blocking of the axial ligand sites by the four H atoms of the chelate-ring carbon atoms. In solution, 1 is unreactive towards O2, CO, and H2, but oxidatively adds HX (X = Cl, Br) to give trans-[Formula: see text] species.
Replacement of the carboxylic acid function with fluorine
Authors: Patrick Timothy B. , Johri Kamalesh K. , White David H. , Bertrand William S. , Mokhtar Rodziah , Kilbourn Michael R. , Welch Michael J.
Published: May 2006

Replacement of a carboxyl function by fluorine, fluorodecarboxylation, is a new process that can be accomplished by the reaction of alkanoic acids with xenon difluoride. Primary, tertiary, and benzylic acids perform best in the reaction, which is conducted at room temperature in methylene chloride or chloroform solution. A reaction mechanism is proposed in which the acid is initially converted to a fluoroxenon ester, RCO2XeF. The esters of the primary and secondary acids react by nucleophilic displacement by fluoride, as evidenced by incorporation of 18F− and no reactions common to free radicals or carbocations. The esters of the tertiary and benzylic acids react by converting to free radicals that can be further oxidized to carbocations. Thus incorporation of 18F− and racemization are observed with α-methoxy-α-trifluoromethylphenylacetic acid. Hydroxyl and amino functions inhibit the reaction. Aromatic and vinylic acids do not react.
Limiting activity coefficients in dilute solutions of nonelectrolytes. II. Determination for polar–nonpolar and polar–polar binary mixtures, and the application of some solubility-parameter treatments
Authors: Afrashtehfar Shapour , Cave Genille C. B.
Published: May 2006

Activity coefficients were determined at 293.15 K for the more dilute component in 24 binary solutions of nonelectrolytes, by gas-chromatographic analysis of the equilibrium vapor phase. One component of the binary mixture was either nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, ethanenitrile, propanenitrile, ethyl ethanoate, or butyl ethanoate; and the other component was either heptane, 1-heptene, or 1,6-heptadiene.From the limiting activity coefficients of these components, some factors that affected their magnitude were identified. The values were also used to test the modifications of Prausnitz, Blanks, and Weimer, of Helpinstill and Van Winkle, and of Keller, Karger, and Snyder to the Scatchard–Hildebrand equation modified to accommodate polar components. In addition, the degree of constancy of the ratio of the dipole – induced dipole interaction parameter for a series of solutes in one solvent to that in another was considered.
Synthesis and characterization of durene-capped porphyrins and the crystal structure of a hemin derivative
Authors: David Shantha , Dolphin David , James Brian R. , Paine III John B. , Wijesekera Tilak P. , Einstein Frederick W. B. , Jones Terry
Published: May 2006

Sterically hindered porphyrins having a fully hydrophobic cavity have been prepared. The cavity is capped with a 2,3,5,6-tetramethylbenzene moiety containing at the 1,4-positions methylene —(CH2)n— chains (n = 4, 5, 7) bonded at trans pyrrole rings of a porphyrin that is alkylated with methyl or ethyl groups at the other β-pyrrolic positions. The iron(III) chloride derivative of the 4,4-durene-capped base has been obtained as single crystals, and subjected to X-ray structural analysis. The typical high spin, square pyramidal geometry of five-coordinate hemin chlorides is maintained; the porphyrin core is strongly distorted and there is no interaction between the phenyl group of the strap and the iron.