bluuebunny/crossref_metadata_2025 huggingface dataset:
Chelating agents in high temperature aqueous chemistry. 1. The kinetics of the thermal decomposition of aqueous nitrilotriacetate (NTA), iminodiacetate (IDA), and N-methyliminodiacetate (MIDA)
Authors: Booy Meindert , Swaddle Thomas Wilson
Published: May 2006

Aqueous H3NTA, H2MIDA, H2IDA, and their anions decompose under hydrothermal conditions (400–580 K) according to first order kinetics by successive decarboxylations, oxidation by O2 being unimportant except at the highest temperatures. In the presence of added H+, the species H4NTA+ and, to a lesser extent, H3MIDA+ (but not H3IDA+), provide significant decomposition pathways through elimination of a —CH2COO— group (deacetylation). For HnNTA(3−n)−, first order rate coefficients kn for decomposition are k0 = 4.5 × 10−7, k1 ∼ 1 × 10−6, k2 ∼ 7 × 10−5, k3 = 2.1 × 10−4, and k4 = 1.0 × 10−2 s1, at 503 K and ionic strength 2.0 m, the spread in rates being due to differences in ΔS* rather than ΔH*. H2MIDA and H2IDA are comparable in reactivity to H3NTA, while their anions are much less reactive than the NTA species of the same charge. The good thermal stability of aqueous NTA commends it as a reagent for boiler servicing and for decontamination of water-cooled nuclear reactors. A potentiometric method for the estimation of mono-, di-, and tribasic aminoacids in aqueous mixtures of these is described.
Hall effect at the metal–nonmetal transition in metal–ammonia solutions
Authors: Even U. , Swenumson R. D. , Thompson J. C.
Published: May 2006

The conductivity and Hall coefficient have been measured for solutions of Li, Na, K, and Cs in liquid NH3 using a double ac method over a concentration range of 1–10 mol% metal (mpm). The conductivities vary from 10−1 to near 104 Ω−1 cm−1 and the Hall coefficients from 10−6 to 10−9 m3C−1 over the 1–10 mpm range. Hall mobilities vary from 10−2 to 100 cm2V−1 s−1 over the same range. The mobility for Na–NH3 solutions shows a maximum at 4 mpm while the others are monotonie. The mobility peak in Na–NH3 solutions appears to be related to the presence of substantial composition fluctuations in that system.
Anchoring of the amide acidity function in dilute aqueous acid: a corrected HA scale
Authors: Edward John T. , Wong Sin Cheong
Published: May 2006

Amide indicators ionizing over the range 0–30% sulfuric acid indicate that values of the HA scale established by Yates etal. (Can. J. Chem. 42, 1957 (1964)) should be corrected by +0.33 unit.
Solubilities of the silver halides in propylene carbonate mixtures with bis(trifluoroethyl)sulfite
Authors: Salomon Mark
Published: May 2006

The complex solubilities of AgCl, AgBr, and AgI have been measured in several mixed solvents containing propylene carbonate and bis(trifluoroethyl)sulfite. The results indicate that a large inductive effect destabilizes the solvation of silver ions whereas the halide ions appear to be stabilized by coordination with the sulfinyl sulfur. Several physio-chemical properties of pure bis(trifluoroethyl)sulfite are reported.
Photoreactions of 1- and 2-naphthonitriles with tetramethylethylene in various solvents
Authors: McCullough John J. , Miller Roderick C. , Wu Wei-Sai
Published: May 2006

The photoreactions of 1- and 2-naphthonitriles with tetramethylethylene have been studied in the solvents hexane, benzene, dimethoxyethane, methanol, and acetonitrile. In hexane, benzene, or dimethoxyethane, the exclusive products are the cyclobutanes 1-cyano-7,7,8,8-tetramethyl-2,3-benzobicyclo[4.2.0]octa-2,4-diene (from 1-naphthonitrile and tetramethylethylene), and 6-cyano-7,7,8,8-tetramethyl-2,3-benzobicyclo[4.2.0]octa-2,4-diene (from 2-naphthonitrile). In methanol, products of photoreduction are formed. From 2-naphthonitrile and tetramethylethylene in methanol are obtained 1-(2′-methoxy-1′,1′,2′,2′-tetramethyl)-3-cyano-1,4-dihydronaphthalene, 1-(2′-methoxy-1′,1′,2′,2′-tetramethyl)-2-cyano-2,4-dihydronaphthalene, and l,2-dihydro-2-naphthonitrile. Deuterium incorporation is observed with CH3OD as solvent, and the stereochemistry of solvent incorporation is discussed. Reaction in 2,2,2-trifluoroethanol proceeds similarly. In methanol, 1-naphthonitrile and tetramethylethylene give products of reductive dimerization, whose exact structures were not determined. In acetonitrile, both naphthonitriles give complex mixtures of products on reaction with tetramethylethylene. It is proposed that the cyclobutane formation in non-polar solvents involves exciplex intermediates, while in polar media electron transfer occurs and results in photoreduction.On a étudié les photoréactions des naphtonitriles-1 et -2 avec le tétraméthyléthyléne dans l'hexane, le benzène, le diméthoxyéthane, le méthanol et 1'acétonitrile comme solvants. Dans l'hexane, le benzène ou le diméthoxyéthane, les produits exclusifs sont les cyclobutanes, cyano-1 tétraméthyl-7,7,8,8 benzo-2,3 bicyclo[4.2.0] octadiène-2,4 (à partir du naphtonitrile-1 et du tétraméthyléthyléne) et le cyano-6 tétraméthyl-7,7,8,8 benzo-2,3 bicyclo[4.2.0] octadiène-2,4 (a partir du naphtonitrile-2). Dans le méthanol il y a formation de produits de photoréduction. A partir du naphtonitrile-2 et du tétraméthyléthyléne dans le méthanol on obtient le (méthoxy-2′ tétraméthyl-1′,1′,2′,2′)-1 cyano-3 dihydro-1,4 naphtalène, le (méthoxy-2′ tétraméthyl-1′,1′,-2′,2′)-l cyano-2 dihydro-2,4 naphtalène et le dihydro-1,2 naphtonitrile-2. On observe une incorporation de deutérium lorsque le CH3OD est utilisé comme solvant et on discute de la stéréochimie de l'incorporation du solvant. La réaction dans le trifluoro-2,2,2 éthanol se produit d'une manière similaire. Dans le méthanol, le naphtonitrile-1 et le tétraméthyléthyléne donnent des produits de dimérisation réductive dont on n'a pas déterminé les structures exactes. Dans 1'acétonitrile, les deux naphtonitriles conduisent á des mélanges complexes de produits de réaction avec le tétraméthyléthyléne. On propose que la formation de cyclobutane dans des solvants non-polaires implique des intermédiaires exciplexes alors que dans des milieux polaires, il se produit des transferts d'électrons et il en résulte une photoréduction. [Traduit par le journal]
Tricyclic aromatic hydrocarbons. III. Isomerically pure meta-bis-annelated benzenes: a simple synthesis
Authors: Isabelle M. Elaine , Lake Darryl H. , Wightman Robert H.
Published: May 2006

A short, general synthetic sequence has been developed, involving cycloaddition and a new decarboxylation/aromatization step, to prepare isomerically pure meta-bis-annelated benzenes. Some new bis annelated benzoic acids were isolated as by-products. Examples of a new decar–boxylation of (annelated) benzoic acids catalyzed by Pd/C are reported.
Metal-ion oxidations in solution. Part XXI. Kinetics and mechanism of the reaction of ascorbic acid, hydroquinone, and catechol with 12-tungstocobaltoate(III)
Authors: Amjad Zahid , Brodovitch Jean-Claude , McAuley Alexander
Published: May 2006

The mechanisms of oxidation of the three di-hydroxy substrates in the title reactions have been investigated in acid media [HClO4] = 0.04–1.00 M, at an ionic strength of 1.0 M [LiClO4] over the temperature range 5–35 °C using the stopped-flow method. In contrast to the reactions of hydroquinone (k2(25 °C) = 1.43 × 104 M−1 s−1, ΔH≠ = 3.6 ± 0.4 kcal mol−1, ΔS≠ = −34 ± 8 cal deg−1 mol−1) and catechol (k2(25 °C) = 9.5 × 102 M−1 s−1, ΔH≠ = 5.9 ± 0.9 kcal mol−1, ΔS≠ = 27 ± 8 cal deg−1 mol−1) where no hydrogen ion dependence is observed over the range studied, the rate variations of oxidation of ascorbic acid (H2A) are consistent with two reactions involving H2A (k5 = 77.4 M−1 s−1, ΔH≠ = 4.5 ± 0.6 kcal mol−1, ΔS≠ = −35 ± 5 cal deg−1 mol−1) and HA− (k6 = 2.41 × 105M−1 s−1, ΔH≠ = 2.0 ± 1 kcal mol−1, ΔS≠ = −17 ± 6 cal deg−1 mol−1). The dissociation constant of ascorbic acid has been re-determined over the temperature range studied. Solvation effects are considered important in these outer-sphere systems, which may be discussed in terms of the Marcus relationship. Comparisons with related reactions are discussed.
Influence de la coordination du thallium sur la cinétique de décomposition du composé d'oxythallation: C6H5—CH(OCH3)—CH2Tl(OAc)2
Authors: Nadon Louise , Zador Miklos
Published: May 2006

The effect of coordination of thallium was studied on the rate of decomposition in methanol–water of the product of oxythallation, C6H5—CH(OCH3)—CH2TlX2(R′TlX2). At low Cl− ion concentrations, the rate of the oxidative decomposition decreased because of the formation of R′TlCl+ and R′TlClOH, both of which are less reactive than R′Tl2+. At high Cl− ion concentration, R′TlCl2 or R′TlCl3− are formed and a decomposition to the starting materials, namely styrene and Tl(III), was observed; this is analogous to the behaviour of organomercurials.The mechanism of the reactions is discussed in terms of the electrophilic character of thallium effected by the coordination by ligand. [Journal translation]
Proton and fluorine magnetic resonance studies of some benzoyl fluoride derivatives. Sensitivity of the fluorine shifts to intramolecular van der Waals interactions and steric effects
Authors: Schaefer Ted , Marat Kirk , Chum Kalvin , Janzen Alexander F.
Published: May 2006

The syntheses and the analyses of the high resolution proton and fluorine magnetic resonance spectra of the 3-fluoro-4-methyl-, 2-fluoro-5-chloro-, 2-fluoro-6-chloro-, 2,6-difluoro-, and of the pentafluorobenzoyl fluorides are reported. The spin–spin coupling constants over five bonds between the sidechain fluorine-19 and the ring protons are sensitive to intrinsic substituent perturbations. Their use in the deduction of conformational preferences is much more problematical than is the use of the corresponding proton–proton couplings in benzaldehyde derivatives. The 2-fluoro-6-chloro compound is nonplanar, as indicated by a finite magnitude of the long-range proton–fluorine coupling over six bonds. The nonplanarity is also indicated by a comparison of the through-space fluorine–fluorine coupling to those in the other compounds. The chemical shift of the sidechain fluorine moves to low field by over 35 ppm as the size of the two ortho substituents increases. The individual shifts are discussed in terms of intramolecular van der Waals interactions and of out-of-plane twisting of the COF group.
A simple synthesis of aucantene
Authors: Liu Hsing-Jang , Browne Eric N. C.
Published: May 2006

Aucantene (1) bas been synthesized from propynal in three stages involving the conjugate addition of lithium di-(E)-propenylcuprate to α,β-unsaturated aldehyde 2 as a key step.
Synthetic routes to nucleoside analogs of N-substituted 1,3-thiazolidines
Authors: Iwakawa Masaharu , Pinto B. Mario , Szarek Walter A.
Published: May 2006

Nucleoside analogs, namely 6-benzamido-9-(3-benzoyl-4(R))-methoxycarbonyl-2,2-dimethyl-thiazolidin-5(S)-yl)-9H-purine (7) and 6-chloro-9-[(3-benzoyl-2,2-dimethylthiazolidin-4(R)-yl)methyl]-9H-purine (8), were obtained from 3-benzoyl-5(S)-benzoyloxy-4(R)-methoxycarbonyl-2,2-dimethylthiazolidine (23) and 3-benzoyl-4(R)-hydroxymethyl-2,2-dimethylthiazolidine (24), respectively, the former, by treatment with 6-benzamidochloromercuripurine and titanium tetrachloride in 1,2-dichloroethane and the latter, by treatment with 6-chloropurine, triphenylphosphine, and diethyl azodicarboxylate in tetrahydrofuran. Compound 23 was obtained from 3-benzoyl-4(R)-methoxycarbonyl-2,2-dimethylthiazolidine (13) by treatment with benzoyl peroxide in refluxing benzene whereas compound 24 was obtained from 13 by borohydride reduction. The stereochemistry of the isomeric sulfoxides 18a and 18b, obtained from 13 by treatment with m-chloroperbenzoic acid, was assigned by means of 1Hmr spectroscopy. Reaction of the sulfoxides 18a and 18b under the Pummerer-reaction conditions afforded the rearranged product, 4-benzoyl-3(R)-methoxycarbonyl-5-methyl-3,4-dihydro-2H-1,4-thiazine (20). The chiral shift reagent, tris-[3-(trifluoromethylhydroxymethylene)-d-camphorato]europium(III), was used to confirm the enantiomeric purity of the key intermediates and the product nucleosides. The carbon-13 nmr spectra of the key compounds are reported.
Chemical behavior of charge-transfer complexes. VII. Solvolysis of alkyl arenesulfonate donors in the presence of aromatic acceptors
Authors: Colter Allan K. , Turkos Robert E. C.
Published: May 2006

Rates of solvolysis of several ethyl and 2-propyl arenesulfonates having π donor leaving groups were measured in the absence of accepter and in the presence of the π acceptors 1,3,5-trinitrobenzene (TNB) and 2,4,7-trinitrofluorenone (TNF). With four of the nine combinations investigated, added accepter produced small but measurable rate enhancements. Ester–TNF 1:1 association constants were measured spectrophotometrically at 20, 30, and 40 °C in acetic acid for 2-propyl 4-methoxy-1-naphthalenesulfonate (3b), 4,8-dimethoxy-1-naphthalenesulfonate (4), 3,7-dimethyl-1-naphthalenesulfonate (5), and 1-pyrenesulfonate (6). From the equilibrium and kinetic data, the reactivity of the 1:1 ester–TNF complex relative to that of the uncomplexed ester (kc/ku) in acetolysis at 85.73 °C was estimated to be lessthan 4.2 and 1.4 for 3b and 4, respectively, 4.4 ± 2.0 for 5, and 2.8 ± 0.4 for 6. The value of kc/ku for 6 determined from analysis of the kinetic data alone is 2.7 ± 0.8.
Paramagnetic effects in flavin spectroscopy. A 13C nuclear magnetic resonance study
Authors: Macmurchie Donald David , Cushley Robert John
Published: May 2006

Experiments are described whose results indicate that semiquinones produced by intramolecular photoreduction of FMN in basic solution are responsible for specific line broadening observed in the 13C nmr spectrum. Tests with oxidizing agents as well as singlet and triplet quenchers are shown to support this theory rather than the proposition that the paramagnetic species effective in relaxation enhancement is a flavin triplet state. A mechanism for the production of semiquinones and their interaction with the FMN population is discussed.
The viscosity of concentrated electrolyte solutions. II. Temperature dependence
Authors: Goldsack Douglas E. , Franchetto Raymond C.
Published: May 2006

The temperature dependence of the viscosity of concentrated aqueous electrolyte solutions has been explained in terms of the temperature dependence of the E and V parameters of an equation previously developed for the viscosity of such solutions. Analysis of the V parameters for the alkali halide and ammonium halide salts leads to absolute ionic hydration numbers. The temperature dependence of these hydration numbers reveals two types of ionic behaviour: structure making ions and structure breaking ions. The Gourary–Adrian scale of ionic radii is found to be more consistent with these data and the temperature dependence than the Pauling ionic radii scale.Analysis of the E parameters leads to the ionic free energy of activation parameters for viscous flow of the ions. The Furth model for hole formation in a liquid is found to correlate these ionic free energy values with the absolute ionic volume parameters obtained from the analysis of the V parameter for all salts. Again the ions are found to break into structure making and structure breaking groups in terms of the surface tension values for the water about the hydrated ions.
Rupture du lien C—S lors de la réduction de sulfones par LiAlH4
Authors: Dufort Normand , Jodoin Dernard
Published: May 2006

Different α,β-unsaturated and saturated sulfones are reduced by LiAlH4. A cleavage of the C—S bond occurs according to the kind of sulfones.
Photolyse de l'isoprène gazeux entre son seuil d'absorption (ca. 255 nm) et 147.0 nm
Authors: Demers Rosaire , Collin Guy J. , Gagnon-Deslauriers H.
Published: May 2006

We studied the photolysis of isoprene at wavelengths between the absorption threshold (ca. 255 nm) and 147.0 nm. The pressure effect was studied between 30 and 2660 N m−2. At the lower energy, light products are formed and their yields decrease with an increase in the pressure. From Stern–Volmer plots, we have concluded that the photoexcited molecule is collision stabilized at high pressure. Less pressure dependence was observed at 174 and at 163.3 nm. At these energies, and at 147 nm, all of the photoexcited molecules decompose. At 147 nm, no pressure effect was observed, and the main product is vinylacetylene (Ф = 0.66). The formation of this product was explained on the basis of the CH3—C4H5 split followed by the fragmentation of the excited C4H5* radicals. At 174 nm, this last radical is collisionally stabilized. Finally we have measured the ratio k(CH3 + H2S)/k(CH3 + isoprene) = k1/k12 and k1/k12 = 41 + 3
Etude par résonance magnétique nucléaire de composés organiques contenant des chalcogènes. I. L'anisole et ses analogues soufré, sélénié et tellure
Authors: Llabres Gabriel , Baiwir Marcel , Christiaens Léon , Denoel José , Laitem Léopold , Piette Jean-Louis
Published: May 2006

Results are reported of a study by 1H and 13C nuclear magnetic resonance of anisole, thioanisole, selenoanisole and telluroanisole as well as of several of their para-substituted derivatives. If these compounds are considered as substituted methyl groups, they display a behaviour analogous to that of the methyl halides. It is possible to demonstrate that a linear relation exists between the proton and the carbon chemical shifts in the anisole series as well as in the methyl halides. Although these results most frequently are interpreted in terms of electronic effects, a 'heavy atom effect' must be invoked for the tellurium compounds. The experimental results do not contradict the hypothesis that the compounds studied have a planar configuration [Journal translation]
Stereochemical analysis of aromatic oximes. 13C–15N nuclear spin coupling and 13C shieldings as conformational probes
Authors: Buchanan Gerald W. , Dawson Brian A.
Published: May 2006

13C nmr chemical shifts and 13C–15N spin couplings over one, two, and three bonds are reported for six aromatic oximes including two benz annelated compounds. Preferred geometries have been calculated via the GEMO program. Fermi contact contributions to carbon–nitrogen coupling have been evaluated and, in general, agreement between experimental and theoretical values is poor. Vicinal 13C–15N couplings are shown to depend on both dihedral angle and oxime valence angle. Oxime carbon chemical shifts do not provide a measure of deviation from planarity between the oxime group and the aromatic ring.The sign of 1JCN in E-benzaldoxime has been determined to be negative.
Effects of potassium ion on the electron-transfer reaction between Fe(CN)64− and TCNQ or chloranil
Authors: Matsuda Sadayuki , Yamagishi Akihiko
Published: May 2006

The effects of potassium ion on the electron-transfer reactions between Fe(CN)64− and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or chloranil (QCl4) were studied with temperature-jump equipment; [Formula: see text]. The solvent was a 1:1 (v/v) mixture of acetonitrile–water. In both Systems, the forward rate constants (kr) were unaffected by the addition of KCl; kf(Fe(CN)64−/TCNQ) = (2.9 ± 0.2) × 106 M−1 s−1, and kr(Fe(CN)64−/QCl4) = (5.2 ± 0.4) × 104 M−1 s−1 On the other hand, the backward rate constants (kb) increased with the increase of the KCl concentration. The results are interpreted in terms of ion-pairing equilibria of Fe(CN)64− and Fe(CN)63−.
Proton magnetic resonance spectra of 3-fluorotoluene and 2-chloro-5-fluorotoluene. The sign and coupling mechanism of
Authors: Schaefer Ted , Danchura Werner , Niemczura Walter
Published: May 2006

A full analysis of the proton magnetic resonance spectra of 3-fluorotoluene and of 2-chloro-5-fluorotoluene, as 10 mol% solutions in CS2, demonstrates that the long-range spin–spin coupling constant over five bonds between methyl protons and fluorine-19 is negative. The coupling mechanism consists of a large positive σ electron component and a negative π electron component. The negative sign of the π electron contribution arises from a spin density in the 2pz orbital at carbon-3, which is opposite in sign to that of the spin densities at C-2 and C-4. Combined with positive hyperfine interaction constants, QCCH and QCF, the consequence is a negative π electron component.
Proton magnetic resonance studies on short duplexes. I. Helix formation by the duplex set GpApGpC:GpCpUpC
Authors: Hughes Donald W. , Bell Russell A. , England Thomas E. , Neilson Thomas
Published: May 2006

Proton magnetic resonance bas been used to investigate the double stranded RNA helix GAGC:GCUC, whose sequence corresponds to the duplex neck region of several tRNAs, a possible aminoacyl-tRNA synthetase recognition site. The nonexchangeable base and ribose anomeric resonances of the separate tetranucleotides were characterized by linear and predominantly upfield chemical shift changes as the temperature was decreased from 65 to 15 °C. When these strands were mixed nonlinear, sigmoidal shift changes consistent with base pairing were observed. The melting temperature of the duplex was determined to be 42 ± 1 °C which was in excellent agreement with the value obtained from optical methods. This is the first 1Hmr study of a non-self-complementary duplex prepared from synthetic tetraribonucleotides.
Proton magnetic resonance studies on short duplexes. II. The self-complementary oligoribonucleotide CpApUpG
Authors: Romaniuk Paul J. , Neilson Thomas , Hughes Donald W. , Bell Russell A.
Published: May 2006

Proton nuclear magnetic resonance was used to examine double helix formation in the self-complementary oligoribonucleotide CAUG in neutral D2O containing 1.0 M NaCl. Using the procedure of incremental assignment all the nonexchangeable base and ribose anomeric protons could be assigned and were observed over the temperature range of 70 to 4 °C. The chemical shift changes that occurred over this temperature range were sigmoidal in nature which is indicative of base-pairing. From the plot of chemical shift vs. temperature a Tm of 24 ± 1 °C was determined. This is the first nmr study of a duplex formed from tetranucleotides which contains two internal A•U base pairs.
Hydrolysis of esters of oxy acids: pKa values for strong acids; Brønsted relationship for attack of water at methyl; free energies of hydrolysis of esters of oxy acids; and a linear relationship between free energy of hydrolysis and pKa holding over a range of 20 pK units
Authors: Guthrie J. Peter
Published: May 2006

By combining various kinds of evidence from the literature it is possible to derive an internally consistent set of pKa values for the strong mineral acids and the arenesulfonic acids; the values are referred to dilute aqueous solution as standard state and are expected to be correct within 0.5 log unit. Using these pKa values and literature data for hydrolysis of methyl esters of acids of the type Y—XO3Men, where Y is O, OH, OMe, alkyl, or aryl and X is Cl, S, or P, a Brønsted plot can be constructed with slope equal to 1.02 ± 0.04. From the free energies of hydrolysis for dimethyl sulfate and the methyl phosphates it is possible to calculate rate constants for the microscopic reverse reaction. These define a Brønsted line of slope 0.27 ± 0.3, from which rate constants for the formation of the esters of perchloric and various sulfonic acids may be estimated. This permits calculation of free energies of hydrolysis for these esters.Thermochemical data in the literature permit calculation of the free energies of hydrolysis of dimethyl sulfate, trimethyl arsenite, and tetraethyl orthosilicate. In the case of dimethyl sulfate the calculation (using the previously reported eq. [1]) leads to a pKa value in close agreement with theoretical expectation, confirming that eq. [1] is valid for acids of pKa ≥ −3. For tetraethyl orthosilicate the thermochemical data are less precise but are in satisfactory agreement with the predictions of eq. [1]. The free energies of hydrolysis derived from the Brønsted correlations are also in good agreement with expectation based on eq. [1].For acids where resonance phenomena are important either in the acid itself (boric acid) or in the anion (nitric acid, nitrous acid, carboxylic acids) the experimental free energies of formation fall far from the line defined by eq. [1]. It is concluded that eq. [1] is limited to species where there is no n delocalization involving the reacting oxygen, but where this condition is satisfied, the equation holds over the entire accessible range of oxy acid pKa values, i.e., from −6.4 to 16.
Determination of oxalate by continuons analysis using photochemical oxidation by iron(III) and a CO2 electrode detector
Authors: Cooley Jean Margaret , Kratochvil Byron
Published: May 2006

Oxalate concentrations were measured by photochemical oxidation with iron(III) to carbon dioxide. Technicon AutoAnalyzer components were used to automate the sampling and mixing steps, and the carbon dioxide produced in the radiation step was measured with a CO2 electrode. Variables in the System were evaluated and the optimum conditions identified. A theoretical study was made of the effect on ionic species concentrations of variations in iron(III), acid, and counter ion concentrations. A linear calibration curve could be obtained for oxalate concentrations in the range of 2 × 10−4 to 0.02 M; by modifying conditions linearity could be achieved at both higher and lower concentration ranges. Several other acids are partially oxidized under optimum conditions for oxalate. Tartrate, citrate, and malonate introduce errors of 2% or less at concentrations equivalent to oxalate; malate and pyruvate cause errors on the order of 10%. Several small carboxylic acids were found to interfere with the CO2 electrode.
Rearrangement studies with 14C. XLII. The solvolysis of triphenylvinyl-2-14C bromide in aqueous acetic acid and in 2,2,2-trifluoroethanol
Authors: Lee Choi Chuck , Ko Eric C. F.
Published: May 2006

Solvolytic studies with triphenylvinyl-2-14C bromide (l-Br-2-14C) in HOAc–H2O and in 2,2,2-trifluoroethanol (TFE) containing 2,6-lutidine were carried out under a variety of conditions. Scramblings of the label from C-2 to C-l in the reaction product and in the unconsumed reactant were determined. For solvolyses in HOAc–H2O, scrambling was observed in the product, but not in the recovered reactant. The extent of scrambling was higher when the proportion of H2O in the solvent was lower. With a given solvent composition, the amount of scrambling did not change with reaction time, the average extents of scrambling being 9.6,12.7, 15.3, 16.7, and 18.4%, respectively, for solvolysis in 50, 60, 70, 80, and 90% HOAc. With 70% HOAc, the presence of about 3 equiv. of NaOAc or NaBr did not influence the extent of scrambling. For the reactions in TFE, there was scrambling in both the reaction product and the recovered reactant, indicating the occurrence of a return process, The presence of added Et4NBr did not affect the extent of scrambling, suggesting that the 1,2-phenyl shift occurred in the ion-pair stage and the return is, therefore, an ion-pair return. The amount of scrambling in the product and in the recovered reactant increased with increasing reaction time, but for a given reaction time, the extents of scrambling in the product and in the recovered reactant were the same. The mean values for the scrambling of the label from C-2 to C-l in the product and the recovered reactant, after a reaction time of 1, 2, 4, and 20 days at 150 °C, were 20.1, 30.0,40.0, and 44.1%, respectively. Mechanistic explanations for both reactions in HOAc-H2O and in TFE are discussed.
Production of Ni(I) complexes from reactions between Ni(II) and NaBH4 in the presence of triphenylphosphine and some bidentate phosphines
Authors: Holah David G. , Hughes Alan N. , Hui Benjamin C. , Kan Chi-Tat
Published: May 2006

The reactions between a variety of Ni(II) compounds and NaBH4 have been studied in the presence of triphenylphosphine (P) and the bidentate phosphines 1,2-bis(diphenylphosphino)-ethane (diphos), bis(diphenylphosphino)methane (dppm), and cis-1,2-bis(diphenylphosphino)-ethylene (vpp). In ethanol, NiCl2•6H2O, P, and NaBH4 give [Ni(BH4)P3]2 while NiX2P2 X = Cl, Br, I) and NaBH4 produce Ni(BH4)P1.5. Further reactions of the former complex leading to [Ni2P6](PF6)2 and [NiP4](PF6) have been studied. Reactions of Ni(ClO4)2•6H2O, P, and NaBH4 produce Ni(ClO4)P3 and [NiP4](ClO4). The bidentate phosphines, Ni(ClO4)2•-6H2O and NaBH4 in ethanol all lead to quite different products. For example, with diphos, Ni(II) is stabilized and [HNi(diphos)2](ClO4) is formed, but with the other two bidentate phosphines, reduction occurs. With dppm, [Ni2(dppm)4](ClO4)2 is produced, while vpp produces [Ni(vpp)2](ClO4). Physical properties, possible structures, and suggested mechanisms of reduction are discussed.
Kinetics and mechanism of substitution reactions of (N,N-dimethylformamide)pentaammine–cobalt(III) and –rhodium(III) ions in DMF as solvent
Authors: Lo S. T. Danny , Sisley Margaret J. , Swaddle Thomas W.
Published: May 2006

The exchange of N,N-dimethylformamide (DMF) between M(NH3)5DMF3+ and solvent in acidic DMF solutions proceeds with pseudo-first-order kinetics governed by the parameters kex(55 °C) = 8 × 10−5 and 1.1 × 10−4 s−1, ΔHex* = 113 and 99 kJ mol−1, ΔSex* = +22 and −20 J K−1 mol−1, and ΔVex* = +3.2 and −1.4 cm3 mol−1 for M = Co and Rh respectively. For M = Co (but not Rh), the exchange rate was much faster in the absence of acid, and reduction of Co(III) to Co(II) was significant at low acidities. Solubility problems precluded the measurement of meaningful rate data for the reactions of M(NH3)5DMF3+ with nucleophiles X− in acidic DMF solution except for the case M = Co with X = Br−, for which a limiting first-order rate coefficient 2.5 times kex was obtained for the formation of Co(NH3)5Br2+ at high [Br−] at 55 °C. Despite this last result, the mechanism of simple substitution reactions is evidently dissociative interchange (Id) for pentaamminecobalt(III) complexes in general, but associative interchange (Ia) for pentaamminerhodium(III) analogues.
The heat of mixing of hydrogen cyanide and hydrogen fluoride in the liquid phase
Authors: Collister John L. , Pritchard Huw O.
Published: May 2006

An approximate measurement is reported for the heat of mixing of hydrogen cyanide and hydrogen fluoride in the liquid phase.
Rotamers arising from restricted motions and electromc interactions of acetoxymethyl groups in carbohydrates
Authors: Perez S. , St-Pierre J. , Marchessault R. H.
Published: May 2006

The two dimensional conformational spaces available for acetoxymethyl groups in carbohydrates are reported. The studies were performed on two molecules differing in their C-4 configurations, i.e. gluco and galacto. The acetoxymethyl group was assigned a mean geometry derived from the computation of 19 equivalent groups as found in pertinent acetylated carbohydrates. The internal energy calculations were performed by including the partitioned contributions arising from the non-bonded energies, electrostatic interactions, and torsion energy. An instability rating of 3 kcal/mol was assigned to conformations involving peri interactions, i.e., trans–gauche and gauche–gauche forms in gluco and galacto carbohydrates, respectively. The results which are best described in term of topology show that several conformations corresponding to the trans and gauche states of the C—O single bond are preferred. However, significant shifts from perfect staggering are observed. The predicted regions of low energy are found to be in good agreement with experimental data from crystal structures of acetylated carbohydrates.
Crystal and molecular structure of two C-phenyl pentitol derivatives
Authors: Rohrer Douglas C. , Fischer Jean-Claude , Horton Derek , Weckerle Wolfgang
Published: May 2006

Grignard addition of phenylmagnesium bromide to 3,5-O-benzylidene-1-deoxy-D-erythro-2-pentulose (1) affords C-phenyl branched-chain pentitols having exclusively either the D-arabino (2) or D-ribo (5) stereochemistry according to the mode of substitution of 1. In order to determine the chirality of these products conclusively, the crystal and molecular structure of the unsubstituted pentitol 6 (from 2) has been determined. Crystals of 1-deoxy-2-C-phenyl-D-arabinitol (6; C11H16O4) are orthorhombic, space group P212121, with cell dimensions a = 8.9420(6), b = 18.910(1), c = 6.4263(6) Å, and Z = 4. The structure was solved by multi-solution direct methods and refined to a final discrepancy index of 5.6%. The molecule has an extended, planar zigzag conformation with the phenyl ring nearly perpendicular to this plane. Compound 6 forms one intramolecular (between 2-OH and O-4) and three intermolecular hydrogen bonds. Palladium-catalyzed hydrogenolysis of the 2-phenylcarbamate of 2 results in deoxygenation of the benzylic center with complete-inversion of configuration, as established by crystal-structure determination of the product 7. Crystals of 2(S)-4-O-acetyl-3,5-O-benzylidene-1,2-dideoxy-2-C-phenyl-D-erytro-pentitol (7; C20H22O4) are monoclinic, space group C2, with cell dimensions a = 19.102(1), b = 6.1925(5), c = 16.098(1) Å, β = 108.325(9)°, and Z = 4. The structure was solved by multi-solution direct methods and refined to a final discrepancy index of 5.9%. The molecule has an almost ideal planar, zigzag backbone conformation which incorporates the 1,3-dioxane ring. Comparison of the conformation observed in the crystal with that calculated from proton–proton coupling constants shows good agreement
A conformational study of methyl β-cellobioside-d8 by 13C nuclear magnetic resonance spectroscopy: dihedral angle dependence of 3JC–H in 13C—O—C—1H arrays
Authors: Hamer Gordon K. , Balza Felipe , Cyr Natsuko , Perlin Arthur S.
Published: May 2006

Methyl β-cellobioside (2) has been deuterated at positions C-2, -3, -3′, -4, -6, and -6′ by 1H–2H exchange with deuterium oxide in the presence of Raney nickel catalyst. The resulting simplification in the 13C nmr spectrum of this isotopically-labelled compound has facilitated the measurement of interresidue 13C–1H coupling, as a means of determining the orientation of the glycosidic linkage in 2. Three-bond coupling across the linkage between 13C-4′ and H-1 is found to be 4.3 Hz and that between 13C-4′ and H-1, 4.2 Hz. By reference to other 13C–1H coupling data, which exhibit a Karplus type of relationship between the magnitude of 3JC—H and dihedral angle in 13C—O—C—1H arrays of bonded atoms, it appears that torsion angles [Formula: see text] and ψ of the disaccharide in aqueous solution are in the region of 25–30°, i.e., close to the angles of crystalline 2. Corresponding data for the hepta-O-acetyl derivative indicate that ψ is smaller by ∼10° and [Formula: see text] is unchanged. An analysis of the 1H-coupled 13C spectrum of cyclohexaamylose-2,3,6,6′-d4 is presented in relation to these findings. Computer simulations of the observed spectra have been used to determine coupling constants and to assess the importance of second-order effects on the measurement of JC—H.
Allergenic α-methylene-γ-butyrolactones. A one-carbon degradation of isoalantolactone via Pummerer rearrangement of sulfoxides
Authors: Corbet Jean-Pierre , Benezra Claude
Published: May 2006

Isoalantolactone and α-methylene-γ-butyrolactone were separately treated with NaSPh, transformed into sulfoxides, and rearranged under Pummerer conditions (Ac2O + (CF3CO)2O). The Pummerer products were hydrolyzed, oxidized, and decarboxylated resulting in the formation of 13-norisoalantolactone (with migration of the exo-C(4) double bond into position C(4)—C(5)) on the one hand and of γ-butyrolactone on the other. The isomeric norisoalantolactone 17 is a starting material for the synthesis of 14C-labelled alantolactone, 18.
Dihydropyridines in synthesis and biosynthesis. II. Stable tricarbonylchromium(0) complexes
Authors: Kutney James P. , Badger Rodney A. , Cullen William R. , Greenhouse Robert , Noda Masaki , Ridaura-Sanz Vicente E. , So Ying Hung , Zanarotti Antonio , Worth Brian R.
Published: May 2006

Controlled reduction of N-methyl-3-ethylpyridinium iodide afforded the corresponding 1,2-dihydropyridine which was stabilised by complexation to give 1,2- and 1,6-dihydro-3-ethyl-N-methylpyridinetricarbonylchromium(0). These stable, isomeric complexes were interrelated by thermal equilibration. Analogous sequences with more complex, alkaloid derivatives enabled formation, and stabilisation by complexation, of 1,2- and 1,6-dihydropyridines in the presence of other functions such as the indole unit and ester groups.
13C nuclear magnetic resonance studies. 81. Conformational inversion barriers of some cis-decalins determined by 13C nuclear magnetic resonance
Authors: Browne Lois M. , Klinck R. E. , Stothers J. B.
Published: May 2006

The 13Cmr spectra of 5β,10β-dimethyldecalin, 10β-decal-5β-ol, and 10β-methyldecal-5β-ol have been examined as a function of temperature to determine the barriers to conformational inversion. Lineshape fitting was employed to extract rate data from which the thermodynamic parameters governing the inversion processes were extracted. Comparison of these results with those obtained by molecular mechanics calculations indicates that the barrier for chair-twist to twist-twist interconversion dominates the conformational inversion profile.
Decomposition of vinyl chloride induced by multiphoton absorption of infrared radiation. I. Decomposition yields
Authors: Gandini A. , Willis C. , Back R. A. , Parsons J. M.
Published: May 2006

The infrared induced decomposition of vinyl chloride has been studied as a function of pressure and as a function of exciting wavelength with a pulsed CO2 laser. The main reaction gives C2H2 and HCl[Formula: see text]but smaller amounts of C2H4 are observed. At pressures below 0.5 Torr, the yield of C2H4 shows apparent enhancement relative to C2H2. In an earlier publication it had been speculated that this was due to dissociation from higher vibrational levels attained in the multiphoton absorption process. Present data indicate this is not the case and suggest rather strongly that the enhanced C2H4 yield is derived from infrared induced decomposition of C2H3Cl on cell windows and walls.The effective quantum yield of C2H2 increases approximately linearly with pressure in the range 0–2.5 Torr and C2H3Cl, H2, and O2 produce similar behaviour. This is interpreted in terms of collisional enhancement of photon absorption associated with depletion of specific rotational states by the laser radiation.
The preparation and crystal structure of pentaiodinium hexafluoroantimonate(V) containing I153+
Authors: Passmore Jack , Taylor Peter , Whidden Tom , White Peter S.
Published: May 2006

Crystalline pentaiodinium hexafluoroantimonate was prepared by the reaction of I2 and SbF5 in AsF3. The crystals were triclinic, a = 8.295(4) Å, b = 15.61(1) Å, c = 8.390(4) Å, α = 81.49(4)°, β = 110.02(4)°, γ = 85.06(4)°, Z = 3, space group [Formula: see text]. The structure was solved by multiple-solution direct methods and Fourier syntheses and refined by full-matrix and blocked-matrix least-squares procedures to a final R of 0.062 and Rw of 0.090 for 2229 reflections with I ≥ 3σ(I). The two crystallographically independent planar, bent I5+ chains (one centrosymmetric, the other essentially centrosymmetric), each have two collinear central bonds of 2.899(2) Å (× 2); 2.896(2), and 2.920(2) Å, bond angles 180° and 178.7(6)°, respectively, and two shorter terminal bonds of 2.680(3) Å (× 2); 2.666(3) and 2.698(2) Å, with bond angles between central and terminal bonds of 94.53(6)° (× 2); 93.86(7) and 93.17(7)°, respectively. Three I5+ units are joined by a weak (3.416(3) Å) interaction to form what may be regarded as an I153+ unit. The SbF6− anions are approximately octahedral.
π-Complex equilibria between ethylene and PdCl42− in aqueous solution
Authors: Pandey Raj N. , Henry Patrick M.
Published: May 2006

The interaction of aqueous PdCl42− with ethylene to form π-complexes has been reinvestigated using a reactor with high efficiency gas-liquid mixing. This reactor permitted study of the equilibria at low [H+] and [Cl−], the conditions under which the oxidation of ethylene to acetaldehyde proceeds rapidly.[Formula: see text]Previously the π-complex formation had been determined at high [H+] and [Cl−] to retard the oxidation reaction which interfered with study of the non-oxidative equilibria.Two equilibria reactions were reported where K1 and K2 have appreciable values.[Formula: see text]The present measurements give K1 values close to those previously reported: K1 = 19.6 at μ = 2 M (adjusted with NaClO4); 11.0 at μ = 3 M (adjusted with NaClO4); and 14.7 at μ = 3 M (adjusted with LiClO4). However, the K2 values are much less than those reported earlier. Thus the maximum possible value of K2 at μ = 3 M (LiClO4) consistent with the present data is less than 0.01 while the previously reported value was 0.22. Possible reasons for the differences between the two studies are discussed.The values of the aquation constant Kh needed for treating the gas uptake data were determined spectrally[Formula: see text]and found to be 0.012 at μ = 2 M and 0.0060 at μ = 3 M (NaClO4). Spectra taken at high [Pd(II)] indicate dimeric species are not formed under these conditions.
Interaction entre les réactifs lanthanidiques et les bases de Lewis: Application à l'analyse conformationnelle d'alcools cyclohexaniques
Authors: Bouquant James , Maujean Alain , Chuche Josselin
Published: May 2006

A method for the determination of the intrinsic parameters K and Δ for lanthanide–substrate complexes has been extended to conformationally mobile molecules. These parameters, determined for a series of secondary cyclohexane alcohols (cyclohexanol and 2-methylcyclohexanol) and for tertiary alcohols (1-methylcyclohexanol and 1-ethylcyclohexanol) complexed with Eu(DPM)3 and Yb(DPM)3 lead to the determination of the conformational equilibrium constants between) the free species on one part and the complexed species on the other.The results obtained for the free species are in good agreement with those obtained by other physicochemical methods. For the complexed species an appreciable shift of conformational equilibrium is noted for low values of the association constants.For the first time, the tert-butyl group of Yb(DPM)3 has been used as a conformational probe. [Journal translation]
Etude chimique et spectroscopique du système B(SCH3)3–B(NCS)3
Authors: Atchekzai Habib-Raman , Mongeot Henri , Dazord Jacques , Tuchagues Jean-Pierre
Published: May 2006

Reaction of trimethylthioborate, B(SMe)3, with triisothiocyanatoborane, B(NCS)3, at room temperature gives mixtures containing B(SMe)3, the mixed compounds B(NCS)(SMe)2 and B(NCS)2(SMe) in low concentration, and association compounds. The previous compounds cannot be isolated due to equilibria being set up. Mass spectrometry, infrared and nmr data are reported. Structures involving S–B donor–acceptor bonds between the monomers are proposed for the association compounds {B(NCS)2(SMe)}2, {B(NCS)2(SMe)}2{B(NCS)3}, and {B(NCS)2(SMe)}2{B(NCS)3}2. Reaction of these compounds with trimethylamine yields Me3NB(NCS)3 and Me3NB(NCS)2(SMe). The same reaction with dimethylsulphide is incomplete and yields only Me2SB(NCS)3. Acidity strength decreases in the order B(NCS)3 > B(NCS)2(SMe) > B(NCS)(SMe)2 > B(SMe)3. This trend explains why dimerization of B(NCS)2(SMe) occurs whereas B(NCS)(SMe)2 is unassociated.
Pyrones. IV. Phacidin, a fungal growth inhibitor from Potebniamycesbalsamicola Smerlis var. boycei Funk
Authors: Poulton Gerald Arthur , Cyr Terry Donald , McMullan Eleanor E.
Published: May 2006

Phacidin, an antifungal antibiotic, isolated from the canker fungus Potebniamycesbalsamicola Smerlis var. boycei Funk is shown to be 2-methoxy-6-nonanoyl-4H-pyran-4-one-3-carboxaldehyde. Carbon-13 nmr spectra of phacidin and several related γ-pyrones are discussed.
Effect of temperature on the fluorescence quenching by N-bromosuccinamide of tryptophan residues in proteins
Authors: Peterman Branko F. , Laidler Keith J.
Published: May 2006

The quenching of tryptophan fluorescence by N-bromosuccinamide was studied by the fluorescence stopped-flow technique over a temperature range of 5 to 35 °C in order to compare the reactivities of tryptophan residues in various molecules. The highest rates and lowest activation energies were found with the simple molecule N-acetyltryptophanamide. The hormone glucagon, which contains a single tryptophan residue, showed a somewhat lower rate and higher activation energy. α-Chymotrypsin, which has three groups of tryptophan residues in different environments, gave three rate constants which were lower than those with the other compounds, and the activation energies were correspondingly higher. There was a linear relationship between enthalpy of activation and the Gibbs energy of activation, the proportionality factor being 6.7. This indicates a ΔH≠ − ΔS≠ compensation, with an isokinetic temperature of 350 K. The compensation is discussed in the light of the steric effects.
Vibrations de réseau de quelques dérivés dihalogénés du benzène
Authors: Serrier J. , Brehat F. , Wyncke B. , Hadni A.
Published: May 2006

Low frequency lattice modes of p-C6H4X2 (X = Cl, Br, I), m-C6H4I2, and o-C6H4I2 were observed by infrared absorption. Raman scattering spectra were recorded in the case of m-C6H4I2.When atomic positions were known in the unit cell (p-C6H4X2), the lattice mode frequencies were computed by the GF matrix method.The agreement between calculated and experimental values is reasonable although we did not consider the multipole–multipole long range interactions.
Fluorosulfates of palladium. Part 2. The hexakis(fluorosulfato)palladate (IV)ion and palladium(II) hexakis(fluorosulfato)metallates(IV)
Authors: Lee Keith C. , Aubke Friedhelm
Published: May 2006

The synthesis of a number of compounds containing the hexakis(fluorosulfato)palladate(IV) anion and the cations Cs+, Ba2+,NO+, and ClO2+ is reported. All compounds are diamagnetic. Also reported is the synthesis of Pd[M(SO3F)6], where M = Pt(IV) and Sn(IV). Here, palladium(II) is found in a regular octahedral environment. Both compounds are paramagnetic, consistent with a 3A2g ground state. Curie–Weiss law behavior is found and ligand field parameters for the Pd(II) derivatives are reported. Vibrational spectra are reported for all new fluorosulfato complexes.
The photoelectron spectra of dimethylgermane, difluoro- and dichlorodimethyl germane
Authors: Drake John E. , Glavinćevski Boris M. , Gorzelska Krystyna
Published: May 2006

He(I) and He(II) pe spectra of the series Me2GeX2 (X = H, F, Cl) are reported. Assignments are based on comparisons with the spectra of related Me3GeX and MeGeX3 series as well as semi-empirical CNDO/2 calculations.
Thermochemistry of tantalum(V) bromide
Authors: Westland Alan D.
Published: May 2006

The enthalpy of formation of crystalline TaBr5 is found by solution calorimetry to be −142.9 ± 0.4 kcal mol−1. Estimates of entropies and heat capacities lead to thermochemical quantities for the liquid and gaseous compound as well.
Organometallic peroxy radicals. Part 5. Trialkylsilylperoxy and trialkylstannylperoxy radicals
Authors: Howard James Anthony , Tait John Charles , Tong Shiu Bor
Published: May 2006

A variety of organosilylperoxy and organostannylperoxy radicals, R3MO2•(R = Me, Et, n-Bu, t-Bu, and Ph and M = Si and Sn) have been prepared and studied by electron spin resonance spectroscopy. Trialkylsilylperoxy radicals exist in equilibrium with a tetroxide at temperatures below 233 K with ΔH0 = −11 ± 2 kcal mol−1 and ΔS0 < −30 cal deg−1 mol−1. Above 233 K these radicals decay either with first-order, one half-order, or zero-order kinetics depending on the radical and its concentration. Trialkylstannylperoxy radicals do not exist in reversible equilibrium with a dimer below ambient temperature and they undergo self-reaction with second-order kinetics. Tri-n-butylstannylperoxy radicals react with 2,6-di-tert-butyl-4-methylphenol and cobalt(II) acetylacetonate and Arrhenius parameters for these two reactions are reported. The structure of R3SiO2•resembles the structure of alkylperoxy radicals whereas the two oxygen nuclei of R3SnO2. are magnetically equivalent and the peroxy group becomes a bidentate ligand. This structural difference has a significant effect on radical reactivity.