bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of varying solvents and of the addition of sulfur on the rate of thiohydrolysis of aromatic nitriles
Authors: Abbas Khamis A. , Edward John T.
Published: May 2006

Maximal rates of formation of thioamides from m- and p-substituted benzonitriles were obtained by bubbling H2S through solutions of the nitrile in pyridine containing a 0.11 mol fraction of triethylamine or in 95% ethanol containing about 0.22 mol fraction triethylamine; at other mol fractions the rate fell off sharply. The Hammett ρ value of +2.3 in pyridine indicates that HS− is the reactive species. The addition of enough sulfur to saturate the solution leads to about a 3-fold enhancement of rate, probably because of the formation of polysulfide ions in trace amounts.
A formal enantiospecific synthesis of California red scale pheromone
Authors: Hutchinson John H. , Money Thomas
Published: May 2006

Cleavage of α,α-disubstituted β-bromoketone intermediates derived from (+)-camphor forms the basis of an alternative enantiospecific synthesis of (Z)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate (1), one of the sex pheromones of the female California red scale, Aonidiellaaurantii (Maskell).
Analysis of solvent and substituent effects on uv and visible spectra of N-(α-methylarylidene)-p-(N′,N′-dimethylamino)-anilines
Authors: Milart Piotr , Krygowski Tadeusz M.
Published: May 2006

Substituent effect on the long wave band in uv/vis spectra of p-substituted N-(α-methylarylidene)-p-(N′,N′-dimethylamino)-anilines (X = CH3O, CH3, H, Cl, and NO2) measured in eight solvents follows well the Hammett equation. Solvent effect on this band depends well on ET only for Cl- and NO2-substituted species. Both these findings support the conclusion that the long-wave band is in fact intramolecular charge transfer form the basicity center [Formula: see text] towards substituents.
Abinitio SCF and MRD-CI description of the A2A′ – X2A″ transition of the as yet unknown HNCl molecule
Authors: Schürmann Britta L. , Buenker Robert J.
Published: May 2006

Abinitio potential curves of the X2A″ ground state and the first excited A2A′ state (2Π in linear geometry) of HNCl are calculated employing multi-reference single- and double-excitation configuration interaction in order to aid in the search for this system experimentally. A vibrational analysis (frequencies and Franck–Condon factors) of the A2A′ – X2A″ transition is undertaken by neglecting coupling between the various modes. Diagonal and off-diagonal force constants together with the fundamental frequencies have been calculated by including mode coupling for both electronic states, and oscillator strengths and radiative lifetimes are also obtained. Comparison with theoretical and experimental results for other isovalent systems is also made in order to establish trends in this group of HAB systems.
Electrically conducting polymers: a review of the electropolymerization reaction, of the effects of chemical structure on polymer film properties, and of applications towards technology
Authors: Waltman R. J. , Bargon J.
Published: May 2006

The electrochemical oxidation of aromatic heterocyclic compounds thiophene, pyrrole, and indole and benzenoid and nonbenzenoid polycyclic hydrocarbons azulene, fluorene, and pyrene yield electrically conducting polymers with conductivities of 10−5–10 S/cm. The presence of substituents affects the electrical conductivity of these films and also their electroactive properties. Furthermore, substituents determine whether electropolymerization of these compounds can occur or whether soluble products are formed. The relative importance of these pathways is dependent on the stability of the intermediate radical cation. These effects are investigated by INDO molecular orbital calculations.
Thionium analogs of the opiates levorphanol and isolevorphanol: synthesis of the 17-deaza-17-thia isosteres (sulforphanol and isosulforphanol)
Authors: Belleau B. , Gulini U. , Camicioli R. , Gour-Salin B. J. , Sauvé G.
Published: May 2006

The total synthesis of the position-17 sulfur analogs of the perchlorate salts of the morphinans, (±)-levorphanol and (±)-isolevorphanol via4a-(2-aminoethyl)-1,2,3,4,4a,9-hexahydro-6-methoxyphenanthrene, a key intermediate in the synthesis of butorphanol (4), is described. 2D-Correlation and heterocorrelation nuclear magnetic resonance spectroscopy confirmed the configurational relationship of the isosteres.
The preferred conformation of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride. An X-ray crystallographic and 2-dimensional proton nuclear magnetic resonance study
Authors: Withers Stephen G. , Street Ian P. , Rettig Steven J.
Published: May 2006

The preferred conformation of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride has been determined in the solid state by X-ray crystallography and in aqueous solution by 2-dimensional J-resolved proton nuclear magnetic resonance. Crystals of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride are monoclinic, a = 4 10.9150(8), b = 4 4.9079(4), c = 4 6.9902(6) Å, β = 105.158(4)°, Z = 2, space group P21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.028 and Rw = 0.031 for 797 reflections with I ≥ 3σ(I). The sugar ring was present in an essentially undistorted 4C1 chair conformation. Weak, but significant interactions, presumably hydrogen bonding of the type OH … F and CH … F, are observed within the crystal lattice. Coupling constants observed in the proton nmr were consistent only with a 4C1 chair conformation in solution. These observations are briefly discussed in terms of recent findings concerning the interaction of fluorodeoxy sugars with enzymic binding sites.
Kinetics and mechanism of the thermal decomposition of the thiosulphatopentaamminecobalt(III) ion in dilute aqueous acid
Authors: Newton Anthony Martin
Published: May 2006

In acetic acid – sodium acetate buffer of pH 5.6 (25 °C) the Co(NH3)5S2O3+ ion undergoes redox decomposition rather than aquation. First-order kinetic are observed and the reaction products Co2+, NH3, and S4O62− are due to internal reduction of Co(III) by coordinated S2O32−. In dilute perchloric acid of pH < 4 the rate is retarded, first-order plots are not linear, and S4O62− is not a major product of the reaction. It is proposed that, in dilute HClO4, protonation of Co(NH3)5S2O3+ depletes the concentration of the reactive complex and that decomposition of coordinated HS2O3− occurs. Conversion of O-bonded S2O32− to S-bonded S2O32− in the reactive complex is also considered.
A theoretical study on the oxidation mechanism of triose reductone in reference to L-ascorbic acid
Authors: Abe Yasuo , Horii Hideo , Taniguchi Setsuo , Yamabe Shinichi , Minato Tsutomu
Published: May 2006

The oxidation of triose reductone H—CO—C(OH)=C(OH)—H (which has the same functional group as L-ascorbic acid) to dehydroreductone is investigated by abinitio molecular orbital computations. The geometries of the substrate, oxidized product, and of six possible intermediate species are optimized by gradient methods at the STO-3G basis set level. All the species are found to be planar and stable molecules by the vibrational analysis. The most possible oxidation route is shown to consist of four steps. The combination of the enediol and carbonyl groups in the deprotonated molecule 2 gives an effective π conjugation for the electron removal. The oxidation process of L-ascorbic acid is discussed on the basis of the results for triose reductone.
Some physical properties of long chain hydrocarbons
Authors: Chu L. T. , Sindilariu Carmen , Freilich Aaron , Fried Vojtech
Published: May 2006

The densities, refractive indices, and viscosities of liquid n-nonadecane and n-nonadecyl benzene were investigated at temperatures not too far above their respective melting points. Except for the viscosities, no significant differences were observed in the behavior of the two hydrocarbons. The n-nonadecane + n-nonadecyl benzene system exhibits small positive excess volumes and small negative excess viscosities. The excess refractive index is zero in the entire concentration range.
Structural studies of organoboron compounds XXIII: preparation and crystal and molecular structures of 2,2-diphenyl-1,3-dioxa-4a- azonia-2-borata-1,2,3,4-tetrahydronaphthalene and 4,4-diphenyl-3-oxa-1-aza-4a-azonia-4-borata-1,2,3,4-tetrahydronaphthalene
Authors: Kliegel W. , Motzkus H.-W. , Nanninga D. , Rettig Steven J. , Trotter James
Published: May 2006

Details of the synthesis, physical properties, and the crystal molecular structures of 2,2-diphenyl-1,3-dioxa-4a-azonia-2-borata-1,2,3,4-tetrahydronaphthalene, 5, and 4,4-diphenyl-3-oxa-1-aza-4a-azonia-4-borata-1,2,3,4-tetrahydronaphthalene, 9, are reported. Crystals of 5 are monoclinic, a = 9.972(1), b = 11.848(1), c = 13.561(2) Å, β = 106.231(5)°, Z = 4, space group P21/c and those of 9 are orthorhombic, a = 20.676(1), b = 15.4199(9), c = 9.7533(4) Å, Z = 8, space group Pbca. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R values of 0.036 and 0.045 for 1060 and 1700 reflections with I ≥ 3σ(I) respectively. Compound 5 has the expected cyclic B,N-betaine structure, resulting from N-aklylation of 2(1H)-pyridone with formaldehyde followed by reaction with (Ph2B)2O. The aza analog, however, does not have the analogous structure. The alkylation of 2-aminopyridine with formaldehyde in the presence of (Ph2B)2O yields 9, derived from alkylation of the amine rather than the pyridine ring nitrogen atom.
The dilemma of estimating forms of sulfur in low-sulfur low rank coals
Authors: Chakrabartty Sujit K. , Iacchelli Angelo
Published: May 2006

The analytical methods for estimating forms of sulfur in coals are reviewed on the basis of sulfur analyses of Western Canadian low sulfur subbituminous coals. The reasons for the variance in analyses are examined, and a novel method of analysis is recommended for evaluation
Isotope effects in nucleophilic substitution reactions. V. The mechanism of the decomposition of 1-phenylethyldimethylphenylammonium halides in chloroform
Authors: Joly Helen Alma , Westaway Kenneth Charles
Published: May 2006

Secondary α and β hydrogen–deuterium kinetic isotope effects have been used together to show that the SN reaction between 1-phenylethyldimethylphenylammonium ion and bromide or iodide ion in chloroform occurs by way of an SN2 mechanism within a triple ion in spite of the fact that it reacts faster than the primary substrate, benzyldimethylphenylammonium bromide. The very loose transition state and steric effects in the ground state appear to be responsible for the unusually fast SN2 reactions between 1-phenylethyldimethylphenylammonium ion and halide ions in chloroform.
A CIDEP study of the photooxidation of benzoquinone in trifluoroacetic acid
Authors: Craw Marjory T. , Depew M. Catherine , Wan Jeffrey K. S.
Published: May 2006

The combined techniques of electron spin resonance and CIDEP have been used to probe the reactions of 1,4-p-benzoquinone in trifluoroacetic acid. The results led to the establishment of two distinct mechanisms, a thermal and a photochemical pathway, for the formation of the one-electron oxidized species in this solvent. In addition it has also been found that by using time-resolved CIDEP the neutral 1,4-p-benzohydroquinone radical may be readily observed under various conditions.
The influence of the changing of P=O to P=S and P—O—R to P—S—R on the reactivity of phosphinate esters under alkaline hydrolysis conditions
Authors: Cook Robert D. , Farah Selim , Ghawi Labib , Itani Adnan , Rahil Jubrail
Published: May 2006

Alkyl dialkylphosphinates, thionates, thioates, and dithioates have been studied under alkaline hydrolysis conditions in 60% DME – H2O and pure H2O. Substitution of S for O in the phosphoryl group has only a small rate retarding effect, typically less than a factor of 10. The effect of the similar replacement in the leaving group, however, can lead to rate increases greater than a factor of 100. Activation parameters were determined and the ΔS* values range from −19 to −49 eu for the bimolecular reactions. The more negative values are for the esters with higher sulfur content and/or sterically large substituents. The results are discussed in terms of a pathway involving a pentacoordinate intermediate.
Phosphoryl to carbonyl migration of amino groups in mixed anhydrides
Authors: Symes Jill , Modro Tomasz A.
Published: May 2006

Mixed anhydrides derived from carboxylic and amidophosphoric acids, (RO)(R′2N)P(O)OC(O)R″ (1), undergo unimolecular fragmentation yielding carboxyamides, R″C(O)NR′2, and metaphosphate esters, ROPO2. The mechanism of the amino group transfer was studied for substrate 1a (1, R = R′ = Me; R″ = Ph); solvent as well as substituent effects indicate little (if any) charge development in the transition state. The effects of solvents and Lewis acids on the reaction rate and the activation parameters determined for 1a can be explained best in terms of stabilizing interactions with either carboxyamide or metaphosphate being formed in the course of reaction. The transfer of a functional group from one acyl center to another was investigated for other anhydride systems and the relative contributions of the fragmentation vs. disproportionation of substrates are discussed.
Sulphur cation chemistry in a fuel-rich, CH4–O2 flame with OCS additive
Authors: Karellas Nicholas S. , Goodings John M.
Published: May 2006

A fuel-rich, methane–oxygen, premixed flame at atmospheric pressure was doped with 0.2 mol% of OCS. More than 40 different sulphurous cations were observed in the mass range < 100 u by sampling the flame into a flame-ion mass spectrometer. Ion concentration profiles along the flame axis are presented, together with mass spectra at fixed points in the flame. In the reaction zone, primary sulphur ions CHxS+ (x = 1, 3, 5) undergo extensive ion–molecule reactions (association and condensation) with CH4/CH3, C2H2, and OCS to form a considerable variety of secondary sulphurous cations. Just downstream of the reaction zone, the ion chemistry is somewhat different; it appears to be dominated by reactions of primary sulphur ions including HxS+ (x = 0–3) with C2H2 present as an intermediate. A few ions (HxS+, OS+, S2+) persist throughout the burnt gas region in equilibrium with the natural flame ions CHO+ and H3O+. These sulphurous cation signals show the evolution of the sulphur chemistry, both ionic and neutral, through the flame reaction zone into the burnt gas downstream where H2S, not SO2, is the major product in fuel-rich combustion.
Preparation of 2,2-diaryl-1-picrylhydrazyls using potassium permanganate
Authors: Brown K. C. , Weil J. A.
Published: May 2006

Potassium permanganate is used as a reagent for the oxidation of various 2,2-diaryl-1-picrylhydrazines to their corresponding hydrazyls. Thin-layer chromatography indicates complete oxidation of the hydrazine to free radical, unlike the case with PbO2 (the most widely used oxidant for this purpose). Several other advantages over previous oxidants used to produce the hydrazyls are offered.
Excess thermodynamic properties of n-pentane + dichloromethane system at 298.15 K
Authors: Postigo Miguel A. , Zurita José L. , Soria María L. G. De , Katz Miguel
Published: May 2006

Densities, refractive indices, viscosities, enthalpies, vapour–liquid equilibria, and surface tensions were determined for the n-pentane + dichloromethane system at 298.15 K. From the experimental results, excess molar volumes, excess viscosities, excess molar enthalpies, excess molar Gibbs free energies, and excess surface tensions were calculated. From these data, qualitative information could be obtained about the interaction between both chemical species.
Ion/molecule reactions in allene. IV. Kinetic considerations
Authors: Hamon François , Carrier Danielle , Herman Jan A.
Published: May 2006

An analysis of the kinetic rate constants for ion/molecule reactions of allene by use of the Laplace–Carson transform is performed and the results are compared with experimental data.
Enantioselective synthesis of isoquinoline alkaloids
Authors: Czarnocki Zbigniew , Maclean David B. , Szarek Walter A.
Published: May 2006

The utility of the Pictet–Spengler condensation of (R)-(+)-glyceraldehyde with dopamine hydrochloride in the enantioselective synthesis of isoquinoline alkaloids is demonstrated by the preparation of (S)-(−)-carnegine, (R)-(−)-calycotomine, and (S)-(+)-laudanosine.
Benzoyl phenyl 1-methylpyrazoles. Synthesis, characterization, and spectra
Authors: Kano Kunio , Scarpetti David , Warner John C. , Anselme Jean-Pierre , Springer James P. , Arison Byron H.
Published: May 2006

The synthesis and unequivocal characterization of all six isomers of benzoyl phenyl 1-methylpyrazole (2) are described. The isomer of 2 isolated as one of the products of the reaction of 1,1-dimethyl-1-phenacylhydrazinium bromide (1) with base was shown to be the only previously reported isomer, 5-benzoyl-3-phenyl-1-methylpyrazole (2b).
Regioselective reactions of 1,4,5-trihydroxy-9,10-anthraquinone
Authors: Broadbent A. Douglas , Meschwitz Wilfred , Stewart John M.
Published: May 2006

The regioselective alkylation of 1,4,5-trihydroxy-9,10-anthraquinone via reaction of its leuco compound is significant for the synthesis of anthracyclinones. In the presence of pyrrolidine in toluene solution, the leuco compound 3 selectively forms the 4-pyrrolidino enamine 11, which undergoes deamination to give 1,5-dihydroxy-9,10-anthraquinone. If an aldehyde is added, however, the enamine is alkylated, eventually yielding the 3-alky 1-1,4,5-trihydroxy-9,10-anthraquinone. Both of the above reactions of 3 give high yields with 100% regioselectivity. The enamine intermediate 11 has been trapped by oxidation to 4-pyrrolidino-1,5-dihydroxy-9,10-anthraquinone, which, after reduction, undergoes the same reactions as 3 giving either the alkylation or deamination product. The selective formation of 11 is explained in terms of an enhancement of carbonyl group electrophilicity by a relay of hydrogen bonds.
The reactions of trichloromethylium with oxygen- and sulfur-containing compounds
Authors: Stone John Alfred , Moote Nancy Joan
Published: May 2006

The gas phase reactions of CCl3+ with acetone, diethyl ketone, dimethyl ether, diethyl ether, several cyclic ethers, sulfides, and disulfides have been examined using high pressure mass spectrometry. In many of the reactions a stabilized ion–molecule complex is observed which may or may not react further. With disulfides a second reaction channel is electron transfer, the observation of which shows that the 0–0 ionization energies of these compounds are lower than the ionization energy of CCl3 (8.28 eV) and hence lower than the values obtained by photoelectron spectroscopy. Rate constants for the disappearance of CCl3+ in general show an increase in value with increase in reaction exothermicity. The lack of a measurable effect of pressure on rate constants is discussed for some association reactions which have reaction efficiencies well below unity.
Enantiospecific synthesis of estrone
Authors: Hutchinson John H. , Money Thomas
Published: May 2006

Efficient cleavage of the C(1)—C(2) bond in 9,10-dibromocamphor (3) provides a chiral intermediate (5) that can be used in a new enantiospecific synthesis of estrone.
The Michael adduct of L-ascorbic acid to methyl vinyl ketone: its remarkable self-condensation and other reactions
Authors: Arnold Regina , Fodor Gabor , George Clifford , Karle Isabella
Published: May 2006

The structure of the Michael adduct of L-ascorbic acid (1) to methyl vinyl ketone was established as 2-(3-oxobutyl)-3-oxo-L-gulonolactone [Formula: see text] hemiketal (3). In aqueous solution 3 is prone to undergo base- or acid-promoted degradations. 1-(2-Furyl)-1,4-pentanedione was isolated from the acidic product mixture. Under strictly anhydrous acid-catalyzed conditions, if a suitable nucleophile like ethanol is present, the tricyclic ethyl ketal 6b forms. In the absence of a nucleophile, the unexpected self-condensation of 3 occurs leading to cyclo-trimer 7, the structure of which was established by X-ray crystallography. Trimer 7, held together via ketal bridges, is converted quantitatively into the tricyclic methyl ketal 6a in methanolic hydrogen chloride. Mechanisms are proposed for the formation of 6a and b or 7.
γ-Lactam formation by a novel intramolecular rearrangement involving β-cyanoketones. Crystal structure of 1,7-dioxo-10a-methyl-perhydrophenanthrene-4a,8a-carbolactam
Authors: Girard Michel , ApSimon John W. , Huber Carol P.
Published: May 2006

Treatment of cyano-triketone 1 with bases such as ethoxide or methoxide ions affords the tetracyclic lactam 4 in high yield. Its formation can be rationalized by invoking a novel intramolecular rearrangement. Crystals of 4 are orthorhombic, a = 10.351 (3), b = 11.503(2), c = 11.935 (2) Å, Z = 4, space group P212121, R = 0.043 for 2037 observations. The structure analysis establishes the formation of a γ-lactam, with the lactam ring bridging a six-membered ring. The three six-membered rings are in chair conformations with some distortions, and the lactam ring is envelope shaped.
Structure and conformation of 2′,5′-anhydroarabinosylcytosine: X-ray, 1H nmr and 13C nmr analyses
Authors: Birnbaum George I. , Buděšínský Miloš , Berànek Jiří
Published: May 2006

Crystals of 2′,5′-anhydroarabinosylcytosine hemihydrate belong to the monoclinic space group P21. The cell dimensions are a = 9.643(2), b = 10.328(1), c = 10.544(2) Å, β = 94.55(1)°. X-ray intensity data were measured on a diffractometer and the structure was determined by direct methods. Least-squares refinement, which included all nucleoside hydrogen atoms, converged at R = 0.041 for 2298 observed reflections. The asymmetric unit contains two molecules of the nucleoside and one molecule of water. In both nucleoside molecules, the conformation about the glycosyl bond is and, with XCN values of 15.5(3) and 26.3(3)°, respectively. In the bicyclic sugar moiety, the arabinofuranose rings adopt a C(3′)exo/C(2′)endo conformation and are highly puckered (τm = 57°). The solution conformation was studied by 1H and 13C nmr spectroscopy. A difference nOe proton nmr spectrum and 3J(C,H) coupling constants reveal an anti conformation in solution, with torsion angles very similar to those obtained from X-ray analysis. A comparison of observed 3J(H,H) coupling constants with those calculated on the basis of a modified Karplus equation shows significant differences, probably due to the presence of the bicyclic system.
Substitution reactions of some pseudo-halides in trans-[Ru(NH3)P(OEt)3(H2O)]2+
Authors: Neiva Sonia Maria , Santos Lucídio Souza , Araújo Sebastião Barros , Filho José Cardoso Do Nascimento , Franco Douglas Wagner
Published: May 2006

The kinetics and mechanism of the formation of trans-[Ru(NH3)4P(OEt)3X]1+ (X = SCN−, CN−, and[Formula: see text]) have been investigated. The second order specific rate constants k1 for the substitution of the water molecule in trans-[Ru(NH3)4P(OEt)3(H2O)]2+ for CN−, [Formula: see text], and SCN− are (3.1 ± 0.3) × 102, (1.7 ± 0.1) × 102, and (1.4 ± 0.1) × 102 M−1 s−1, respectively, at 25 °C, μ = 1.0 (NaCF3COO). Under the same experimental conditions the aquation of the pseudohalide derivatives, trans-[Ru(NH3)4P(OEt)3X]+ proceeds at specific rates of (1.8 ± 0.1) × 10 and (2.8 ± 0.1) × 10−1 s−1 for X = [Formula: see text] and SCN−, respectively, and the upper limit for the rate of CN− loss from trans-[Ru(NH3)4P(OEt)3CN]+ was estimated as 1.2 × 10−1 s−1. The order of affinities for the monophosphite complex in the series of ligands studied is:[Formula: see text]where imN = imidazol, pyr = pyrazine, and Mepyr+ = methylpyrazinium. From enthalpies of activation it is possible to estimate that net replacement of H2O in trans-[Ru(NH3)4P(OEt)3(H2O)]2+ by azide ions is exothermic by 2.8 ± 2 kcal/mol.
Synthesis and in vitro activity of several new carbapenems
Authors: Ueda Yasutsugu , Vinet Viviane
Published: May 2006

not available
Calculations on the relative energies of complexes of silanes with 2π and 4πNO
Authors: Bell Thomas N. , Perkins Kathryn A. , Perkins Peter G.
Published: May 2006

A theoretical study is presented of the relative enthalpies (calculated through heats of atomisation) of complexes of the silanes SiF4, SiF3Me, and SiF2Me2, with ground state 2πNO, and exciplexes with excited state 4πNO. The calculations favour an increasing relative stability of the complexes and exciplexes with silanes in the order SiF4 < F3SiMe < F2SiMe2 with, in each particular case, a geometry favouring the [Formula: see text] over the [Formula: see text] arrangement.
Acid–base behaviour of the ferrocyanide ion in perchloric acid media potentiometric and spectrophotometric study
Authors: Domingo Pedro L. , Garcia Begoña , Leal Jose M.
Published: May 2006

Ferrocyanide ion behaves as a tetravalent Brønsted base and can react with four protons, forming ferrocyanic acid. By potentiometric and spectrophotometric techniques it is shown that the first two protonation equilibria overlap, as do the third and fourth equilibria. The two techniques yield identical results when processed with the inclusion of non-ideality terms. The method of "separation of equilibria" is proposed to allow separate study of each of the overlapping equilibria. Values of pK1 = −2.54 ± 0.10, pK2 = −1.08 ± 0.03, pK3 = 2.65 ± 0.02, and pK4 = 4.19 ± 0.02 were obtained.
Mixed anhydrides in peptide synthesis. A study of urethane formation with a contribution on minimization of racemization
Authors: Chen Francis M. F. , Lee Young , Steinauer Rene , Benoiton N. Leo
Published: May 2006

A study of the factors contributing to urethane formation during the coupling of N-alkoxycarbonylamino acids with an amino acid ester by the mixed carboxylic–carbonic acid anhydride method has been carried out, using nuclear magnetic resonance spectroscopy and high-performance liquid chromatography for the quantitation of products. Urethane formation is associated primarily with reactions of activated hindered residues such as isoleucine and N-methylamino acids. Of prime importance in dictating the amount of urethane generated is the tertiary amine/solvent combination. N-Methylpiperidine/dichloromethane is the best combination for minimizing urethane formation, N-methylmorpholine/tetrahydrofuran is a good combination, while triethylamine/dichloromethane is a particularly bad one. In dimethylformamide, the differences between these amines are marginal. Aqueous dimethylformamide is a good solvent for mixed anhydride generation and coupling. A small excess of substrate reduces the amount of urethane. Less racemization accompanies the coupling of peptide acids in tetrahydrofuran than in halogen-containing solvents, N-methylpiperidine being the superior base in these solvents, but not in dimethylformamide. Racemization is reduced by one half when menthyl chloroformate instead of isobutyl chloroformate is used in the couplings.
Determination of trace aluminum concentration and homogeneity in biological reference material TORT-1 by instrumental neutron activation analysis and graphite furnace atomic absorption spectroscopy
Authors: Kratochvil Byron , Motkosky Norine , Duke M. John M. , Ng Dennis
Published: May 2006

The biological reference material TORT-1, lobster hepatopancreas, was analyzed for aluminum by instrumental neutron activation analysis (INAA) and graphite furnace atomic absorption spectroscopy (GFAAS). After correction of the INAA results for interferences from 28Al produced by 31P(n,α)28Al and 28Si(n,p)28Al reactions, and use of HNO3 plus HF for sample dissolution for the GFAAS analyses, the methods gave similar results of 43 ± 3 and 42 ± 2 μg/g respectively for 200 to 300-mg test portions. Analysis of six portions from each of six bottles of TORT-1 showed no statistical difference at the 95% confidence level for the between and within bottle variances. Therefore, the material can be considered homogeneous for aluminum if 200- to 300-mg test portions are taken. The variance was greater and the average lower when 30-mg test portions were analyzed for aluminum by GFAAS. The pattern of the results, together with the need for HF in the dissolution procedure, suggests the presence of aluminum-containing microparticulate mineral matter, perhaps silicate material, in the material.
Atomization efficiency of a graphite furnace in atomic absorption spectrometry at high heating rates
Authors: Chakrabarti C. L. , Ferrarotto D. , Cathum S. J. , Rademeyer C. J.
Published: May 2006

The efficiency of an HGA-400 for production and containment of atomic vapour was determined for several elements using relatively high heating rates. Two different atomization efficiencies β1 and β2 were experimentally determined by two variations of a method. Assuming that atomization in the HGA-400 can be described by consecutive, first-order reactions [Formula: see text], the method consisted of making the absorbance signal profile (at least the decay part of it) appear at constant tube wall (at the centre) temperature and determining first-order rate constants for atom formation and atom loss, k1 and k2, respectively. Two atomization efficiencies were calculated: β1 and β2, which gave the fraction of analyte which was present as atomic vapour at the peak of the absorbance signal profile. Experimental atomization efficiencies reported for Al, Cu, Co, Fe, Ag, and Ga average: β1, 0.42 and β2 0.30, with a range from 0.30 to 0.50 for β1, and from 0.18 to 0.43 for β2. Significance of the results and limitations of the two variations of the method in terms of validity of their underlying assumptions have been brought out in a critical assessment of the atomization efficiencies measured by the two variations of the method. In both the variations of the method, the heating rates used were much higher than those used by some other authors, with the result that in agreement with the prediction of the theory, the atomization efficiencies measured in this work were considerably higher than those reported by those authors.
How does the geometry of the tetrahedral XF4−nClnε (X = Al, Si, P) species depend on composition, or abinitiosicertumnescio
Authors: Choi S. C. , Boyd Russell J. , Knop Osvald
Published: May 2006

The molecular parameters of the isoelectronic tetrahedral species NaF43−, MgF42−, AlF4−nCln−, SiF4−nCln PF4−nCln+, SF42+, and ClF43+ have been investigated by abinitio calculations at the 6-31G* level. The bond lengths and the critical radii of X in XF4ε are found to decrease monotonically with the formal oxidation state m of X up to and including X = S but show an upturn at X = Cl. The relative position of the critical point in the X—F bond, rc(X)/(X—F), remains relatively constant for m = 1–3; for m = 4–6 the critical point moves gradually closer to X, but for m = 7 it shifts appreciably away from X. The increase in the electron density at the bond critical point of XF4ε (and probably also of XCl4ε) is represented reasonably closely by a power function amb. The effect of progressive replacement of F in XF4ε (X = Al, Si, P) by Cl on the bond lengths and angles depends on the sign of ε. For ε = −1, X—F and X—Cl decrease and FXF increases; for ε = 0 and 1, X—F and X—Cl increase and FXF decreases. These changes increase in magnitude, in their respective directions, with |ε|. Relationships between the bond lengths and the bond angles are described. The excess total electronic energies [Formula: see text] are negative for all three X; they are largest (and approximately symmetric with respect to n) for Al, smaller (and asymmetric) for P, and very small for Si. The amount of charge transferred from F or Cl to X varies in a complicated manner with m and n, and the rates of transfer of charge with «in an XF4−nClnε molecule are not the same for F and Cl. More than one unit of charge is transferred from a halogen atom to X in ClF43+ and PCl4+.
Reactions of diazoalkanes with isocyanates. Synthesis of imidazolidine-2,4-diones, oxindoles, and oxazolidinones
Authors: Fulton Janet B. , Warkentin John
Published: May 2006

Thermolysis of a 5,5-dialkyl-Δ3-1,3,4-oxadiazolin-2-one in nitrobenzene containing an aryl isocyanate at 150° C affords a 1,3-diaryl-5,5-dialkylimidazolidine-2,4-dione, an N-arylcarbamoyl-3,3-dialkyloxindole, and a 3-aryl-2-arylimino-5,5-dialkyl-1,3-oxazolidin-4-one. Those products arise from attack of a diazoalkane, generated insitu from the oxadiazolinone by thermal cycloreversion, on the isocyanate function. Two imidazolidine diones, three oxazolidinones, and 14 oxindoles were prepared.
ipso Nitration. XXIX. Nitration of substituted 4-methylanisoles and phenols
Authors: Fischer Alfred , Henderson George N. , RayMahasay Sumit
Published: May 2006

Nitration of 2-chloro-4-methylanisole (1a) in acetic anhydride gives (Z)-4-chloro-3-methoxy-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate (2a), 2-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone (3a), and 2-chloro-4-methyl-6-nitroanisole (4a). Similarly 2-bromo-4-methylanisole (1b) gives (Z)-4-bromo-3-methoxy-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate (2b), 2-bromo-4-methyl-4-nitrocyclohexa-2,5-dienone (3b), and 2-bromo-4-methyl-6-nitroanisole (4b), whereas 4-methyl-2-nitroanisole (1c) gives (Z)-3-methoxy-6-methyl-4,6-dinitrocyclohexa-2,4-dienyl acetate (2c), (Z)-3-methoxy-6-methyl-2,6-dinitrocyclohexa-2,4-dienyl acetate (7), and 4-methyl-2,6-dinitroanisole (4c). Nitration of 3-chloro-4-methylanisole (9a) gives 3-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone (10a), 3-chloro-4-methyl-2-nitro anisole (11a), and 5-chloro-4-methyl-2-nitroanisole (12a), and 4-methyl-3-nitroanisole (9c) gives (Z)-3-methoxy-6-methyl-5,6-dinitrocyclohexa-2,4-dienyl acetate (13), 4-methyl-2,3-dinitroanisole (11c), and 4-methyl-2,5-dinitroanisole (12c). Nitration of 2-chloro-4-methylphenol (14) in chloroform gives 3a and 2-chloro-4-methyl-6-nitrophenol (5a), and 3-chloro-4-methylphenol (15) gives dienone 10a, 3-chloro-4-methyl-2-nitrophenol (16), and 5-chloro-4-methyl-2-nitrophenol (17).
Heat capacities and isentropic compressibilities of electrolytes in propylene carbonate at 25 °C
Authors: Perron Gérald , Trudeau Guylaine , Desnoyers Jacques E.
Published: May 2006

The heat capacities per unit volume and sound velocities of many solutions of 1:1 electrolytes in propylene carbonate (PC) were measured at 25 °C. Combining these data with previously published densities, apparent molar heat capacities and isentropic compressibilities were calculated. By extrapolation to infinite dilution, the corresponding standard partial molar quantities were obtained. The heat capacities and compressibilities of water in PC were also calculated. Through ionic additivity, it was possible to calculate these functions for all alkali and tetraalkylammonium halides. The magnitude and trends with ionic size of the heat capacities of electrolytes in PC are similar to those in other aprotic solvents such as acetonitrile (ACN) and dimethylformamide (DMF) and significantly different from those in water. On the other hand, with compressibilities, the magnitudes sssssssare the same in PC and in water for alkali halides but significantly different for tetraalkylammonium halides. The trends with ionic size are similar to those in ACN. These effects can be interpreted through ion–solvent interactions. The separation of these thermodynamic functions into their ionic contributions is also discussed.
Correlations between carbon-13 nuclear magnetic resonance and X-ray crystallography for pyrroles containing electron-withdrawing groups
Authors: Paine III J. B. , Dolphin D. , Trotter J. , Green-hough T. J.
Published: May 2006

not available
The structure and internal rotational barrier of 3-phenyl-1-propyne by molecular orbital calculations and the J method
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

The 1H nuclear magnetic resonance spectral parameters are reported for 3-phenyl-1-propyne dissolved in CCl4, C6D6, and in acetone-d6. The long-range spin–spin coupling constants imply very small and perhaps vanishing barriers to internal rotation about the [Formula: see text] bond in all three solutions, in contrast to benzyl cyanide in which there exist significant solvent perturbations of the internal barrier. STO 3G MO computations, utilizing geometry optimization procedures, imply an internal rotational potential of V/kJ mol−1 = −2.8 sin2 ψ − 0.6 sin2 2ψ; the angle ψ is 90° when the C≡C bond lies in a plane perpendicular to the benzene plane. 6-31G MO energies imply V/kJ mol−1 = −0.3 sin2 ψ − 0.4 sin2 2ψ, the fourfold component being larger than the twofold. A flat minimum occurs near ψ = 50°.
Rotating frame nuclear magnetic resonance experiments on metal complexes
Authors: Buist Richard J. , Eaton Donald R.
Published: May 2006

Measurements of the rate of nuclear magnetic relaxation in the rotating frame (T1ρ) have the potential to provide significant information not readily available by other nmr methods. Some applications to metal complex chemistry are described. The method has been applied to 59Co nmr and used to obtain 59Co–14N spin–spin coupling constants for the tris(ethylenediamine)cobalt(III) and hexanitrocobaltate(III) ions. The larger coupling constant in the latter compound is related to the different hybridization of the nitrogen atom. Proton T1ρ measurements on thiourea and its zinc complex have demonstrated that at room temperature broadening of the 1H resonance is very largely ascribable to scalar relaxation rather than to chemical exchange processes.
Synthesis, structure, and hydrolysis of esters of strained and unstrained N-phosphonylureas
Authors: Kluger Ronald , Thatcher Gregory R. J. , Stallings William C.
Published: May 2006

Compounds 1–5 were prepared to compare reactivity patterns of cyclic and acyclic phosphonylurea esters. The rates and products of reactions of phosphonylurea esters (1–3) with hydroxide in aqueous acetonitrile were analyzed. In these compounds the phosphonate moiety is in a strained five-membered ring, which also contains the ureido group. Structural determination of 1 by X-ray crystallography indicates that the five-membered ring is planar and the internal ring angle at phosphorus is 93.1°. The endocyclic N—C—N angle of the ureido group is 111°. The compounds undergo hydrolysis in alkaline aqueous acetonitrile at 35 °C with a rate about 106 times that of analogues (4, 5) in which the phosphonate group is exocyclic to the ureido ring. Compound 1 undergoes alkaline hydrolysis (k = 9.0 × 103 M−1 s−1) to release the phenoxy group to give 6. The hydrolysis of alkyl esters 2 (k = 2.4 × 104 M−1 s−1)and 3(k = 1.3 × 103 M−1 s−1) leads to cleavage of the endocyclic P—N bond, producing 7 and 8 respectively. The exocyclic alkyl esters (4 and 5) also cleave at the P—N bond with respective rate constants of 6.5 × 10−3 M−1 s−1 and 4.4 × 10−2 M−1 s−1. The data are consistent with a mechanism in which hydroxide adds to 1 to form a pentacoordinate phosphorus intermediate with the phenoxy group in an equatorial position and the ureido ring in apical and equatorial positions (with nitrogen apical). The departure of the urea group is slower than pseudorotation of the intermediate and expulsion of phenoxide. In the isomerized intermediate, phenoxy is apical but the methylene group of the ring, which has low apicophilicity, must also be apical. Reactions of 2 and 3, which have more basic oxygen leaving groups, occur with P—N cleavage because expulsion from the isomerized intermediate in those cases is not sufficiently fast. These results fit reaction patterns at phosphorus that are determined by ring strain and electronegativity of ligands. Contributions from effects due to antiperiplanar interactions between bonding and nonbonding electrons are not detected.
Partial molar volumes of phenalkylamines and their physiologically active derivatives in water
Authors: Shahidi Fereidoon
Published: May 2006

The partial molar volumes at infinite dilution, V0, for a number of phenalkylamines, their physiologically active derivatives, and their hydrochloride salts have been measured and related to their van der Waals volumes. Results indicate a value of 13.8 mL mol−1 for the electrostriction of water molecules by the terminal [Formula: see text] group. Volumes of proton ionization in these compounds vary between 2.90 and 6.26 mL mol−1.
Immobilized replicates of sequence 136–148 of human serum albumin as adsorbents for bilirubin
Authors: Bouvier M. , Brown G. R. , St-Pierre L. E.
Published: May 2006

Strategic peptide sequences, patterned on the sequence 136–148 of the primary structure of human serum albumin, have been immobilized on a cross-linked polyacrylamide support using the solid phase peptide synthesis technique. Certain of the resulting materials proved to be efficient adsorbents for bilirubin from aqueous phosphate buffer solution. Amino acids such as lysine and arginine favour the binding of the ligand, whereas glutamic acid reduces it markedly. From Scatchard plots, first and second equilibrium binding constants, in the range of (0.3–9.6) × 104 M−1, were obtained using a site treatment. These binding constants are comparable to that for the binding of bilirubin by a larger fragment of bovine serum albumin that contains the synthesized sequence.
Phonon spectra of ortho -dinitrotetramethylbenzene crystals
Authors: Sgarabotto Paolo , Braghetti Mario , Cataliotti Rosario Sergio , Paliani Giulio , Sorriso Salvatore , Caia Vincenzo , Santini Sergio
Published: May 2006

We have studied the vibrational spectra and thermal behaviour of ortho-dinitrotetramethylbenzene (o-DNTMB) to learn more about its molecular and lattice dynamics. The molecule undergoes two solid–solid phase transitions, close to the melting point, which could be explained by the relaxation of forces hindering the methyl-group and nitro-group free rotations. We have deduced the nature of the solid state vibrational motions, particularly those of lattice phonons, using group theory.
Syntheses of chiral intermediates of 1-β-methylcarbapenems: (3S,4R)-3-[1(R)-tert-butyldimethylsilyloxyethyl]-4-chloroazetidin-2-one and (3S,4S)-3-[1(R)-tert-butyldimethylsilyloxyethyl]-4-[1(R)-tert-butylthiocarbonylethyl]azetidin-2-one
Authors: Endo Masaki
Published: May 2006

The 4-chloroazetidinone 10, a very reactive chiral intermediate for 1-β-methylcarbapenems (1b), was easily prepared and isolated as a solid crystalline compound from the corresponding sulfide 5. Another chiral intermediate (16d) bearing the 1-β-methyl moiety was prepared by stereoselective aldol type condensation of either azetidinone 4 or 10 with metal enolates 14 (R = S—Bu′, M = ZrCp2Cl, [Formula: see text], and SnBr). The β/α ratios were 9:1, 3:1, 2:1 respectively.
Structure of kerlinic acid from Salviakeerlii. Chemical correlation with melisodoric acid
Authors: Rodríguez-Hahn Lydia , García Adriana , Esquivel Baldomero , Cárdenas Jorge
Published: May 2006

The structure of kerlinic acid, a neo-clerodane diterpenoid isolated from Salviakeerlii (Labiatae), was deduced from spectral data and chemical correlation with melisodoric acid.
Enaminic reactions of 4-tert-butyl-3,3-dimethyl-5-methylene-Δ1-1,2,4-triazoline. Novel heterocycles by sequential [2 + 2] cycloaddition and ylide-forming [3 + 2] cycloreversion
Authors: Schwan Adrian L. , Warkentin John
Published: May 2006

Triazoline 1, which is formally an α azoenamine, reacts with dimethyl acetylenedicarboxylate, acrylonitrile, methacrylonitrile, methyl methacrylate, phenylisocyanate, and sulfene to form products that appear to be derived from a common first step, the formation of a dipolar intermediate (e.g., 5). That intermediate may close to form either a 4-membered ring (6, 8) or ring-open to 7 with subsequent closure to a 5-membered ring (4). Alternatively it may lead to an enamine with extended conjugation (10, 11) by a sequence of proton transfers. The spirotriazolines (e.g., 6) are unstable and decompose by loss of N2 to form spiro aziridines (e.g., 3). Hydrogen cyanide, from acetone cyanohydrin, converts 1 to the cyanoaziridine 13 while methanol adds reversibly under acidic conditions to form 17.
The synthesis and the nuclear magnetic resonance study of β-lactam derivatives of 1,5-benzothiazepines
Authors: Szöllösy Aron , Kotovych George , Tóth Gábor , Lévai Albert
Published: May 2006

The synthesis and stereochemistry of seven β-lactam derivatives of 1,5-benzothiazepines are presented. The configurational and conformational analysis is based on nuclear Overhauser effect experiments, together with analysis of the vicinal proton–proton coupling constants. In the preferred conformation, the seven-membered ring is in a half-chair. Only for one compound, 2-aza-4-bromo-4-methyl-5,7-diphenyl-8-thiatricyclo[7.4.0.02,5]trideca-Δ1,9,10,12-trien-3-one, were two diastereomers isolated (compounds 6a and 6b). Six of the compounds have the 4S*, 5R*, 7R* configuration while compound 6b has the 4R*, 5R*,7R* configuration.
On the spectrophotometric determination of with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol
Authors: Sommer Lumír , Šamlotová Eva
Published: May 2006

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a suitable reagent for the spectrophotometric determination of uranium but results are easily influenced by the reaction conditions as well as various common ions and masking agents. Optimum conditions, which must be carefully maintained, are 30% (v/v) dimethylformamide, 0.1% triton X-100, ≥ 8 × 10−5 M 5-Br-PADAP, 8 × 10−2 M triethanolamine, 7 × 10−3 M sodium fluoride, 10−2 M 5-sulphosalicylic acid, and 579 nm. Sodium sulphate (10−2 M) and CDTA (5.7 × 10−3 M) may serve as additional masking agents. A previous separation of uranium by extraction with 0.1 M tri-n-octylamine in benzene from 4 M HCl and re-extraction of 0.3 M HCl is recommended for analysis of natural water samples.
The thermodynamics of the divalent metal fluorides. I. Heat capacity of lead tetrafluorostannate, PbSnF4, from 10.3 to 352 K
Authors: Callanan Jane E. , Weir Ron D. , Westrum Jr. Edgar F.
Published: May 2006

We have measured the heat capacity of the fast ion conductor PbSnF4 at 10.3 < T < 352 K by adiabatic calorimetry. Our results show anomalous values in the Cp,m in the region 300 < T < 352 K. These are associated with the α–β crystallographic transition reported at 353 K. Because the upper temperature limit of our cryostat is around 354 K, it was impossible to follow the phase transition to completion. A more subtle anomaly in the Cp,m was detected between 130 and 160 K. Standard molar thermodynamic functions are presented at selected temperatures from 5 to 350 K.
Liquid zinc chloride vaporization thermodynamics by modified entrainment
Authors: Gardner Peter J. , Pang Peter
Published: May 2006

The thermodynamics of the vaporization of liquid zinc chloride has been studied in the temperature range 638–978 K by the modified entrainment method. Enthalpy and entropy changes for vaporization have been derived for the monomer and dimer species. These values are unchanged in a melt contaminated with water at a mole ratio of 1%. The proportion of dimer in the saturated vapour is found to decrease with increasing temperature. The vapour pressure equations for monomer and dimer vaporization, ZnCl2(l) = ZnCl2(g) and 2ZnCl2(l) = Zn2Cl4(g) are In [p10/pӨ] = −(15300 ± 60)K/T + (15.39 ± 0.06) and In [p20/pӨ] = −(11000 ± 970)K/T + (6.5 ± 1.3) for the temperature range 640–980 K.
Molar entropies at 80 K of sub-monolayer nitrogen films adsorbed on graphite from heat capacity measurement
Authors: Inaba Akira , Chihara Hideaki
Published: May 2006

The heat capacity of nitrogen adsorbed on an exfoliated graphite (Grafoil GTA) has been measured between 3 and 80 K at surface coverages of [Formula: see text] The molar entropies are determined at 80 K. The effect of energetic heterogeneity of the graphite surface seems to be much less than that expected from the measurements of heats of adsorption. The isosteric heat of adsorption at zero coverage qst(0), for a hypothetical homogeneous graphite surface is estimated to be 9.8 kJ mol−1 at 80 K, which is in good agreement with that obtained from simulations performed at 75 K, 9.9 kJ mol−1.