bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of thiyl radicals. XIII. Photochemically induced exchange reactions of liquid alkyl disulfides
Authors: Gupta Dinesh , Knight Arthur R.
Published: May 2006

The liquid phase photolysis of some 35 liquid alkyl disulfide mixtures has been studied. The corresponding unsymmetrical disulfide is the only significant product of the reaction and the System attains a photo-equilibrium state at longer exposure times. Product formation is completely eliminated by the addition of nitric oxide.Quantum yields have been redetermined for the methyl disulfide – ethyl disulfide System using four different light sources. Initial rates have been measured for each of the 35 combinations and have been shown to be a function of total molecular weight of the disulfide mixture and to be strongly influenced by steric factors. These effects are most pronounced for mixtures wherein the exchange reaction between thiyl radical and a symmetrical disulfide is important as indicated by quantum yields above unity. Combinations of isodisulfides give rise to anomalously high rates.
Nickel(II)-binding to the NH2-terminal peptide segment of human serum albumin: 13C-and 1H-nuclear magnetic resonance investigation
Authors: Laussac Jean-Pierre , Sarkar Bibudhendra
Published: May 2006

Recent studies have shown that Ni(II) in human blood serum is bound to albumin and the binding site is located at the NH2-terminus of the protein. In this article, the nature of the Ni(II)-binding site of the NH2-terminal tripeptide segment of human albumin: L-aspartyl-L-alanyl-L-histidine-N-methyl amide (AAHNMA) is reported as deduced by 13C- and 1H-nmr spectroscopy. The 13C spectrum shows that the Ni(II) complex is in slow exchange on the nmr time scale, and resonances for Ni(II)–peptide complex and metal-free peptide are observed clearly in the pH range 6.4 to 9.1. The Asp COO− carbon is most affected by Ni(II) binding. The imidazole ring system also shows large variation. Furthermore, the results implicate the involvement of the NH2 group. The introduction of Ni(II) ion into the solution containing peptide causes profound changes in the 1H-nmr spectra in the pH range 6.4 to 9.1. Most significantly, there is a complete disappearance of Ala and His N—H protons which confirm the coordination of these two peptide nitrogens. The measurement of the 13C spin–lattice relaxation times (T1) for AAHNMA and its 1/1 complex provide confirmatory evidence for the existence of a definite complex. The overall results suggest that Ni(II) forms complex with the NH2-terminal peptide of human albumin involving the α-NH2, N(3) imidazole, two deprotonated peptide nitrogens, and Asp COO− group in a pentacoordinated structure.
On the ion exchange sorption of some complex cations and their nature of interaction with chromium ferrocyanide gel
Authors: Saraswat Ishwari P. , Srivastava Suresh K. , Verma Surendra K. , Sharma Ashok K.
Published: May 2006

The sorption of ammine complex cations of Co(III), viz. [Co(NH3)6]3+ and [Co(en)3]3+, on the H+ form of chromium ferrocyanide gel has been studied under static conditions. It is observed that the majority of these complex cations (90%) are sorbed by ion-exchange process. The extent of desorption of these complex ions with some uni- and bivalent cations is in the order K+ > NH4+ > Ba2+ > Sr2+ > Ca2+ > Mg2+.Infrared, Mössbauer, and magnetic susceptibility studies on the air-dried and powdered gel in H+ form and loaded with [Co(NH3)6]3+, [Co(en)3]3+, Fe3+, and La3+ ions show that prussiate compounds are not formed during the gel formation and the sorbed cations are held by the electrostatic attraction forces in the matrix, which is strained by the sorption of the big cations.
Complete analysis of the 1H nmr spectrum of tetrahydrothiophene
Authors: Esteban Angel Luis , Díez Ernesto
Published: May 2006

The 1H nmr spectrum of tetrahydrothiophene has been analyzed. The best set of coupling values (Hz) is: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] (A and B refer to α-and β-protons and c and t denote respectively the same and opposite sides of the ring). The variances observed between the values of this set and those reported by Lozach etal., particularly the interchange of the [Formula: see text] and [Formula: see text] couplings, are discussed and it is concluded that our set is the one that reproduces the most fine details of the spectrum profile. The proposed set has been selected as being the most physically meaningful, from amongst 24 equally valid sets of couplings, on the basis of a better agreement with the [Formula: see text] and [Formula: see text] values calculated from a Karplus relationship and from the INDO-FPT method respectively. In these calculations it was assumed that the molecule was interconverting rapidly (on the nmr time scale) between two puckered conformations with C2 symmetry. A detailed discussion of the dependence of the couplings on the height of the pseudorotational barrier and on the temperature indicate that the minimum values of the potential energy correspond to these conformations.
Direct transformation of carboxylic acids to thiol esters induced by phenyl dichlorophosphate
Authors: Liu Hsing-Jang , Sabesan Subramaniam Iyer
Published: May 2006

The condensation of carboxylic acids and thiols is greatly facilitated by the use of phenyl dichlorophosphate as an activating agent giving thiol esters in good yields.
Synthesis and structure of N,N′-ethylenebis(salicylideneiminato)chlorogallium(III) and its methyl analog
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and physical properties of N,N′-ethylenebis(salicylideneiminato)chlorogallium(III) and N,N′-ethylenebis(salicylideneiminato)methylgallium(III) are described. Crystals of N,N′-ethylenebis(salicylideneiminato)chlorogallium(III) dichloromethane are monoclinic, a = 13.049(1), b = 9.525(1), c = 15.459(2) Å, β = 92.452(5)°, Z = 4, space group P21/a. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.042 and Rw = 0.051 for 1815 reflections with I ≥ 3σ(I). The gallium atom is bonded to one chlorine atom and to the tetradentate N,N′-ethylenebis(salicylideneiminato) ligand to give a coordination geometry which is intermediate between square pyramidal and trigonal bipyramidal. Important bond lengths (corrected for libration) are: Ga—Cl, 2.228(2), Ga—O, 1.868(4) and 1.883(4), Ga—N, 2.019(6) and 2.035(5) Å. The crystal structure consists of discrete (C16H14N2O2)GaCl and CH2Cl2 molecules linked by a[Formula: see text]hydrogen bond [Formula: see text]to form complex-solvate units.
The leaf oil terpene composition of incense cedar and coast redwood
Authors: Rudloff E. von
Published: May 2006

Analysis by an on-line computerized gas chromatographic – mass spectral method of the volatile leaf oils of the North American incense cedar and coast redwood revealed unusual percentage compositions of the major terpenes and presence of unique minor components. The chemosystematic implications are discussed briefly.
Equilibrium decomposition pressures of the compounds Na2ZrCl6 and Na2HfCl6
Authors: Kipouros G. J. , Flengas S. N.
Published: May 2006

The chemical equilibria representing the reactions[Formula: see text]and[Formula: see text]were investigated by direct vapour pressure measurements and thermodynamic data such as free energies and enthalpies of reaction have been calculated.With reference to the separation of Hf from Zr by a recently developed process based on the selective reactivity of ZrCl4 and HfCl4, vapours with alkali chlorides, it is shown that the efficiency of alkali chlorides as separating agents increases in the order of LiCl → NaCl → KCl.
The tryptophan fluorescence lifetime puzzle. A study of decay times in aqueous solution as a function of pH and buffer composition
Authors: Gudgin Eva , Lopez-Delgado Ricardo , Ware William R.
Published: May 2006

Tryptophan fluorescence decay kinetics have been systematically investigated in aqueous solutions as a function of pH as well as in a variety of buffer solutions. Below pH 7.0, the decay appears to be double exponential with a subnanosecond component confirming the previous findings of Rayner and Szabo (3). In the low pH region, where the proton concentration becomes kinetically significant, tryptophan fluorescence is collisionally quenched by [H+] with diffusion controlled rate and no experimental evidence is found regarding the appearance at low pH of a new tryptophan molecular species, namely the cationic form. At pH ≥ 7.0, the decay becomes triple-exponential with the appearance of a long component whose contribution to the total emission intensity increases rapidly with increasing pH at the expense of the other two. Lifetimes and relative intensities of each decay component depend in a complex way on pH and on the buffer chemical composition.
Solvent induced frequency shifts of the C—H stretching bands of n-octane. A Fourier transform infrared study
Authors: Cameron D. G. , Hsi S. C. , Umemura J. , Mantsch H. H.
Published: May 2006

Using a Fourier transform spectrometer the frequencies and bandwidths of the infrared active C—H stretching modes of n-octane were determined in a variety of solvents with refractive indices from 1.63 (carbon disulfide) to 1.28 (n-perfluorooctane), and dielectric constants from 37.5 (acetonitrile) to 1.8 (n-perfluorooctane). The frequency shifts were correlated with the refractive indices and dielectric constants of the solvents, and fitted with the equation of David and Hallam (Spectrochim. Acta, Part A, 23, 593 (1967)). Generally, solution results in shifts to frequencies lower than those observed in the gas phase. However, solution in n-perfluorooctane resulted in a shift to a higher frequency, behavior in accord with the above equation but not previously observed.
Investigation of a Ziegler–Natta catalyst system derived from a mixture of lithium tetraalkylaluminate, aluminum chloride, and titanium tetrachloride and its usefulness in polymerizations involving styrene
Authors: Mishra Anu
Published: May 2006

Vinyl ethers, 1-olefins, and styrene were homo- and copolymerized by the use of catalyst derived from a mixture of lithium tetraalkylaluminate (LiAlR4), aluminum chloride (AlCl3), and titanium tetrachloride (TiCl4), in order to determine the nature of the active components present.It is postulated that the active catalyst in the stereospecific polymerization of vinyl ethers is ether-coordinated TiCl3•LiCl, while in the polymerization of 1-olefins and styrene, it is the alkylated derivatives of TiCl3•LiCl.For homo- and copolymerization of styrene, AlR3 seems to be the preferred alkylating agent. About 3 to 4 equivalents of AlR3 are needed for complete alkylation of TiCl3•LiCl, probably due to heterogeneity of the system.Highly isotactic polystyrene and copolymers of styrene with 1-olefins can be prepared in good yields by the use of this catalyst.
Epithermal neutron activation analysis with a SLOWPOKE nuclear reactor
Authors: Stuart Donald Craig , Ryan Douglas Earl
Published: May 2006

Epithermal neutron activation analysis is examined using a SLOWPOKE nuclear reactor. Data are given for 69 elements using cadmium and boron shielding. Cadmium ratios calculated from literature values of resonance integrals are compared with experimental values. All elements except cadmium are shielded more effectively by boron. Advantage factors for a selection of elements under cadmium, natural boron, and enriched boron shields are given. Boron shields are of particular practical value for rapid instrumental analysis.
Ionic strength effect on extraction of potassium complexed with crown ether 18-crown-6. Preliminary communication
Authors: Kolthoff Izaak Maurits
Published: May 2006

As part of a broad study of the factors which affect extraction of salts of cations, complexed with an uncharged ligand, L, a critical study has been made of the extraction into dichloromethane of K+ complexed with 18-crown ether-6 in the form of picrate (LKPi). In using extraction analysis for the determination of very small concentrations of K+ in the presence of other salts activities of (K+)w and (Pi−)w in the aqueous phase must be written in the expression for Kext(LKPi). The salting out effect on P(L) = [L]0/[L]w can greatly affect the concentration of potassium ions left in the aqueous phase. Selectivity of K+/Na+ in extractions with 18-crown-6 has been determined.The extraction method is very suitable for the determination of traces of potassium in salts of sodium, magnesium, and calcium after calibration with, e.g., potassium chloride in potassium-free salts and also, after proper calibration, in routine analysis of liquids which contain little K+ and a large excess of Na+ (e.g. sea water, blood serum).
Steady state concentration polarization by laser interferometry
Authors: O'Brien R. N. , Kulkarni B. B. , Michalik W. , Santhanam K. S. V.
Published: May 2006

A laser interferometry study was done on the Cu/CuSO4/Cu system at natural pH to investigate the effects of natural convection with plane-parallel horizontal electrodes in the anode over cathode position. A constant concentration profile is established where migration is just equal to diffusion plus convection at cd's less than 0.2 mA cm−2 and electrode separations less than 1 mm. Above these values convective or roll cells reminiscent of Bénard cells always develop.
Field desorption mass spectrometry of sodium carboxylates. Intermolecular exchange of hydrogens and alkyl groups as shown by labelling
Authors: Wood Gordon Walter , Sun Wing Fung
Published: May 2006

Field desorption mass spectra of sodium acetate and sodium propionate, labelled analogs, and mixtures were used to investigate hydrogen and alkyl group exchange accompanying the desorption process. At low anode temperatures, decomposition products are minimized and formation of homologous carboxylates by alkyl transfer is significant. The complexity of these intermolecular reactions precludes a simple mechanistic scheme. Reproducibility of minor ions is much improved by the addition of pentaerythritol to these samples.
Correlation between thermodynamic parameters (GLC) and structure of esters
Authors: Calixto F. Saura , Deyá P. M.
Published: May 2006

The ΔHs and [Formula: see text] values of some one hundred esters belonging to twenty different homologous series are determined experimentally in the polar stationary phase (Carbowax 1540) by gas–liquid chromatography.Correlations between thermodynamic values and the molecular structure of esters are studied. The influence of the number of carbon atoms in the acid and alcohol chains and the position of the carboxylic group and branching chains on the ΔHs and [Formula: see text] values is considered.Faisant appel à la chromatographie en phase gazeuse impliquant du Carbowax 1540 comme phase stationnaire on a déterminé expérimentalement les valeurs de ΔHs et de [Formula: see text] d'une centaine d'esters appartenant à 20 séries homologues différentes.
Rearrangement studies with 14C. XLVI. Isotopic scrambling studies on the acetolysis of trianisylvinyl bromide labeled with 13C and with 14C
Authors: Lee Choi Chuck , Obafemi Craig A. , Quail J. Wilson , Rappoport Zvi
Published: May 2006

Acetolyses of a 15 mM solution of a doubly labeled trianisylvinyl substrate, 1,2-dianisyl-2-p-[14C]methoxyphenyl[2-13C]vinyl bromide (1-Br-2-13C-2-methoxy-14C), were carried out in the presence of different amounts of added NaOAc (30–450 mM) or NaOAc (30 or 300 mM) and Et4NBr (75–1000 mM). Isotopic scramblings of the 13C or 14C label from C-2 to C-1 were observed in both the reaction product and the recovered unconsumed reactant, indicating the occurrence of cycles of ionization, 1,2-anisyl shift, and return. The extent of scrambling was found to decrease with increasing concentrations of NaOAc, and a further decrease in scrambling was noted with the additional presence of Et4NBr. These findings are attributable to a competition between the 1,2-shift process and capture of the cation by the added nucleophiles.Analysis of the experimental data suggests that the nucleophilic species chiefly involved in the product-forming capture reaction is the acetate ion rather than HOAc or the Na+OAc− ion-pair. Comparisons of the scrambling data, expressed as "% rearrangement", with the assumption that 100% rearrangement corresponds to 33.3% and 50.0% scramblings of the 14C ring label and the 13C chain label, respectively, led to the conclusion that complete equilibration of the labels is achieved in that portion of the molecules that have undergone rearrangement only when the acetolyses are carried out in the presence of high concentrations of added salts. Mechanistic implications of these observations are discussed.
Preparation of a series of substituted fluoromethylnaphthalenes
Authors: Dixon Elisabeth A. , Fischer Alfred , Robinson Frank P.
Published: May 2006

A series of 22 3- and 4-substituted 1-fluoromethylnaphthalenes have been synthesized. Details of practical procedures for the preparation of all intermediates are described, and physical properties for all of the substituted naphthalenes synthesized, and spectral parameters for 51 previously unknown compounds, are given.
Pyrrole chemistry. XXIII. The cyanation of substituted pyrroles with chlorosulfonyl isocyanate (CSI). New syntheses of pyrrole-3-carbonitriles
Authors: Loader Charles E. , Anderson Hugh J.
Published: May 2006

Chlorosulfonyl isocyanate (CSI) reacts not only with pyrrole itself but with pyrroles having powerful electron-withdrawing groups in the 2-position. Suitable choice of electron-withdrawing groups allows selective 4-substitution of the pyrrole ring. The N-chlorosulfonyl amides formed are readily converted to the corresponding nitriles. The procedure has been used to provide syntheses of pyrrole-3-carbonitrile and its 1-methyl homologue.
Erysotrine-N-oxide and erythrartine-N-oxide, two novel alkaloids from Erythrina mulungu
Authors: Sarragiotto Maria Helena , Filho Hermogenes Leitão , Marsaioli Anita J.
Published: May 2006

Erysotrine, erythrartine, hypaphorine, and two novel alkaloids, erysotrine-N-oxide and erythrartine-N-oxide, were isolated from the flowers of Erythrina mulungu. The N-oxide structures were determined by spectroscopic analysis (mass, 1H, and 13C nmr) and by partial synthesis.
Nucleophilic substitution of 5,5-dimethyl-2-cyclopentenyl derivatives. Lack of SN2′ reaction
Authors: Kopecky Karl R. , Levine Cyril
Published: May 2006

Treatment of tetramethyl-1,3-cyclobutanedione with two equivalents of allyl oxide anion at 140 °C yields 2,2-dimethyl-4-pentenoic acid which is cyclized via the acid chloride with aluminum chloride to 5,5-dimethyl-2-cyclopentenone, 4. Reduction of 4 with aluminum hydride provides 5,5-dimethyl-2-cyclopentenol 1-OH which is pyrolyzed to 5,5-dimethyl-l,3-cyclopentadiene in dimethylsulfoxide. Reduction of 4 with tri-t-butoxyaluminum hydride at −70 °C gives 2,2-dimethylcyclopentanone.The 2,6-dichlorobenzoate ester of 1-OH failed to yield SN2′ products under a variety of conditions. The rate constants for solvolysis of the p-nitrobenzoate esters of 1-OH, 2-cyclopentenol and Z-2-methyl-4-hexene-3-ol in 80% ethanol at 80 °C are 20.2, 523, and 0.63 × 10−6 s−1, respectively, and the main products of solvolysis are 5-ethoxy-3,3-dimethylcyclopentene, 3-ethoxycyclo-pentene, and E-2-ethoxy-5-methyl-3-hexene, respectively. There is steric hindrance to solvation during ionization of the p-nitrobenzoate of 1-OH.
The synthesis of 2,3,5,6-endo,endo,endo,endo-tetrakis-substituted bicyclo[2.2.1]heptanes
Authors: Butler Douglas N. , Munshaw Timothy J.
Published: May 2006

Oxidation of the readily available diketone 2 affords high yields of the symmetrical dilactone 5, from which the all-endo-tetrakis(hydroxymethyl)norbornane 10 can be made. A related tetrol 22 is also described. These tetrols are dehydrated to polycyclic di-ethers 12, 13, and 23 which constrain their oxygen atoms in rigid proximity within their structures.
Spin trapping of hydroxyl in water: decay kinetics for the•OH and adducts to 5,5-dimethyl-1-pyrroline-N-oxide
Authors: Castelhano Arlindo L. , Perkins M. John , Griller David
Published: May 2006

A spin-trapping technique for distinguishing between free and "bound hydroxyl" radicals has been proposed in the literature. This technique relied upon observations of the steady-state concentrations of the spin-adducts of•OH and [Formula: see text] (from formate) to 5,5-dimethyl-1-pyrroline-N-oxide. In the present work, it is shown that the steady-state approach was only qualitatively correct. An alternative procedure is demonstrated which involves monitoring the growth of the spin-adducts after the start of radical generation. The latter approach is found to be quantitative.
The use of localized and delocalized orbitals in a Rydberg expanded correlation analysis of the cycloaddition of ethylene
Authors: Evleth Earl M. , Kassab Emil
Published: May 2006

Rydberg expanded orbital and state correlation diagrams are shown for the classical cycloaddition of ethylene. The diagrams are first developed at the localized valence MO level and the origins of the S**-bitriplet correlations are shown. When extended to the Rydberg level, the localized state correlation diagram shows that the π3s Rydberg singlet state of ethylene can interact with the ground state of another ethylene to directly yield the same S** surface as found in the valence-level-only diagram. In this manner the Rydberg state eventually derydbergizes.
Structure and magnetism in a hydroxy bridged binuclear copper(II) system with a "tunable" binuclear centre
Authors: Thompson Laurence K.
Published: May 2006

The molecular structure of [Cu2(PAP)(OH)(IO3)3]•4H2O (PAP = 1,4-di(2′-pyridyl)aminophthalazine) has been determined by single crystal X-ray diffraction. [Cu2(PAP)(OH)(IO3)3]•4H2O belongs to the space group P21/c with a = 7.266(1), b = 15.269(1), c = 25.870(1) Å, β = 96.40(I)°, V = 2852.2 Å3, Z = 4. The copper coordination geometry lies between a square pyramid and a trigonal bipyramid and the two copper(II) centres are bridged by three groups: N2 (phthalazine), hydroxide, and bidentate iodate, in a structure which is analogous to that reported for [Cu2(PAP)(OH)Cl3]•1.5H2O. Replacing the chlorine bridge by iodate has the effect of forcing the two metal centres further apart, thus creating a larger Cu—O—Cu bridge angle. This increase in oxygen bridge angle (101° to 114°) is also reflected in the enhanced antiferromagnetic exchange (−2J(Cl) = 201 cm−1, −2J(IO3) = 335 cm−1). Other groups of varying size (e.g. Br, NO3, SO4) can act as bridges between the two copper centres in systems of this sort with the resultant variation in copper–copper separation and oxygen bridge angle.
An MNDO study of sulfenium ions
Authors: Ginsburg Jack Leon , Langler Richard Francis
Published: May 2006

An MNDO study has been carried out on a variety of substituted sulfenium ions and sulfides. Relative stabilities in the gas phase have been calculated for several pairs of regioisomeric sulfenium ions. It is shown that sulfenium ions are stabilized by π-donors and that the substituent electronegativity is not an important factor. The potential implications of this result for the mechanism by which chlorosulfonium cations are converted into sulfenium ions in solution is discussed. Substituent effects on the energetics of sulfenium ion formation from sulfides have been obtained. It is shown that these effects also are related to the substituent's π-donating ability. A frontier-orbital analysis of selected sulfenium ions has been done and is discussed.
The photochemistry of phenanthrene-substituted molecules
Authors: Zimmerman Howard E. , Wu Guo-Sheng
Published: May 2006

The photochemistry of 3-methyl-3-(9-phenanthryl)-1-butene was examined as part of an investigation into the effects of having two π chromophores of widely different energies participating in a di-π-methane rearrangement. We observed both direct and sensitized reactivity with quantum yields [Formula: see text] and [Formula: see text]. The primary reaction product from both direct and sensitized photolyses was 1,1-dimethyl-2-(9-phenanthryl)cyclopropane. However, in practice this product was obtained only from sensitized irradiations where it was almost completely unreactive. The triplet reactivity is unusual in that the typical free rotor decay exhibited by triplets does not lead to inhibition of di-π-methane reactivity in this case. This point is discussed. The intersystem crossing efficiency of the phenanthryl vinyl methane reactant was obtained from the sensitization of biacetyl phosphorescence by the phenanthrene derivative at varying biacetyl concentrations. This was [Formula: see text]. This result and the bracketing relationships signify that essentially all of the direct irradiation rearrangement utilizes T1. In addition, from these experiments, 3kd(tot), was determined as 5.8 × 103 s−1. Similarly,3kr = 250 s−1 which is the slowest di-π-methane rearrangement encountered thus far. The rearrangement of the cyclopropane product to form 2-methyl-4-(9-phenanthryl)-1-butene was also investigated. [Formula: see text] was determined to be 0.091 and [Formula: see text] was determined as 0.00072. Thus the interesting contrast was encountered in which the di-π-methane rearrangement proceeds from the triplet while the rearrangement of the cyclopropane product proceeds most efficiently from the singlet.
Reaction topology of excited state potential energy hypersurfaces
Authors: Mezey Paul G.
Published: May 2006

Topology ("rubber geometry") is an exceptionally suitable mathematical framework for a global quantum chemical description of the fundamental relations between nonrigid molecular systems, chemical reactions, and many photochemical processes. In Reaction Topology the concept of nuclear geometry is replaced by open subsets of an abstract nuclear configuration space nR. The ground and various excited state energy expectation value functionals induce a sequence of topologies in the nuclear configuration space nR, leading to a consistent topological description of molecular structure, excimers, exciplexes, and reaction mechanisms. Utilizing earlier results on topological properties of the abstract nuclear charge space wZ, a theorem is proven on the ordering of excited state potential energy hypersurfaces for sequences of isoelectronic molecules.
The chemistry of thujone. VII. Thujone as a chiral synthon for the preparation of sesquiterpenes. Synthesis of β-elemol
Authors: Kutney James P. , Singh Ashok K.
Published: May 2006

An efficient synthesis of β-elemol (4) from thujone (1) is described. The key intermediate 3 is readily prepared and described in previous studies within the synthesis of (+)-carissone (2).
The preparation of protected arabinonucleosides
Authors: Ogilvie Kelvin K. , McGee Danny P. C. , Boisvert Suzanne M. , Hakimelahi Gholam H. , Proba Zbigniew A.
Published: May 2006

A general procedure is described for the preparation of protected arabinonucleosides. Protection at the 5′-position involves triphenylmethyl groups (DMT and MMT) while the tert-butyldimethylsilyl (TBDMS) group is used to protect the 2′- or 3′-positions. The effects of novel catalysts on the position of silylation have been determined, leading to highly selective reactions at 2′- or 3′-positions.
Crystalline conformation and structure of lichenan and barley β-glucan
Authors: Tvaroska I. , Ogawa K. , Deslandes Y. , Marchessault R. H.
Published: May 2006

An investigation based on X-ray fiber diffraetion and conformational analysis methods has provided a proposed chain conformation and crystalline structure for lichenan, a poly β(1 → 3) cellotriose. The analysis of the fiber diagram of the hydrated form of lichenan led to a trigonal unit cell of dimension a = b = 9.92 Å and c (fiber axis) = 42.03 Å, with cellotriose as the asymmetric unit and six cellotriose residues per unit cell. A unit cell of the dry form is also trigonal with a = b = 9.36 Å and c = 42.03 Å. A right-handed threefold helix made up of three cellotriose residues was derived from a comparison of experimental helical parameters with isoenenergy conformational maps made by plotting dihedral angles ([Formula: see text], ψ) at the β(1 → 3) linkage. A virtual bond approach was also used to arrive at the proposed conformation which is stabilized by intramolecular hydrogen bonds between all carbohydrate units. The refinement of geometrical and packing parameters produced results consistent with an antiparallel arrangement of the two chains corresponding to a space group symmetry of P31. The naturally occurring copolysaccharides known as mixed (1 → 3) and (1 → 4) β-glucans from the cell walls of barley endosperm have been shown to crystallize in the same fashion as lichenan.
A new type of crown ether. III. Triethylene glycolic diester of naphthalene dithioglycolic acid
Authors: Prajer-Janczewski Lidia , Rudolk Krystyna , Lis Tadeusz , Janczewski Marian , Biskup Janina
Published: May 2006

The structure of 2,7-(11,22-diono-12, 15,18.21-tetroxa-9,24-dithia)-hexadecylene-naphthalene was investigated by 1H and 13C nmr and mass spectrometry. An X-ray structural investigation indicated the dissymmetric ansa structure of this compound in the crystalline state.
Reactions of the trisulfur trinitride anion, S3N3−, with halogens and other electrophilic substrates
Authors: Chivers Tristram , Rao M. N. Sudheendra
Published: May 2006

The reactions of the trisulfur trinitride anion, S3N3−, with halogens (Cl2, Br2, l2), AsF5, SOCl2, SO2Cl2, S2Cl2, COCl2, CS2, Me3SiCl, and Ph2PCl have been investigated. In all cases these reactions gave mixtures of known sulfur–nitrogen compounds. Thus the halogens react with S3N3−.to give mainly S4N4, S4N3+X− (X = Br, Cl), (SN)x, and S3N3X3 (X = Cl), while AsF5 oxidizes S3N3− to S4N4•AsF5. The major products of the reaction of S3N3− with SOCl2 or SO2O2 were S4N4, S4N3+Cl−, and (for SOCl2 only) S3N2O2•S3N2Cl was the main product of the reaction of S3N3− with S2Cl2, whereas COCl2 yielded (SN)x in addition to S3N2Cl and S4N4. Carbon disulfide reacts with S3N3− to give S4N2, S4N4, and CNS−. The cyclophosphathiazenes, (Ph2PN)(SN)2, 1,3- and 1,5-(Ph2PN)2(SN)2, in addition to (Ph2PN)x (x = 3, 4), (Ph2PN)3•HCl and (Ph2PN)2NSCl were isolated from the reactions of Ph2PCl with S3N3− in various molar ratios. The latter reaction represents a useful alternative synthesis of the 1,5-isomer of the eight-membered ring (Ph2PN)2(SN)2.
The photochemistry of 9,10-anthracenedione in sulfuric acid solution. The dependence of product yields on reaction conditions
Authors: Broadbent A. Douglas , Stewart John M.
Published: May 2006

Irradiation of a sulfuric acid solution of 9,10-anthracenedione with near-uv light generated 2-hydroxy-9,10-anthracenedione as the major product. In addition, the 1-hydroxy and polyhydroxy derivatives and the reduction products anthrone and bianthronyl were also formed. The yields of these minor produets were markedly influenced by the concentrations of water and oxygen in the sulfuric acid. At low light intensities, oxygen quenched the efficient formation of the hydroxyanthracenediones and also oxidised the initial quinone reduction products. Photoreduction of the anthracenedione and photooxidation of anthrone occurred simultaneously in the solution. The reaction mechanism is more complex than previous studies indicated.
La dissolution de l'anode de cuivre dans les solutions faiblement chlorurées
Authors: Brossard Robert-Louis
Published: May 2006

The dissolution of a copper anode has been studied in aqueous solution at pH 4 and in which the dissolved LiCl was varied between 0.005 M and 0.1 M. In the dissolution zone, the dissolution valence is unity between 0.03 M and 0.1 M and the step controlling the speed of dissolution is almost entirely attributable to the diffusion of CuCl2− ion in solution for the weakest voltage. The order of reaction with respect to the chloride ion (Cl−) is close to unity for voltage close to the reversible voltage (ECu/CuCl) of the reaction Cu + Cl− = CuCl + 1e, suggesting that diffusion of Cl− ions in solution tends also to become a controlling step when the voltage is close to ECu/CuCl.CuCl appears when the voltage reaches ECu/CuCl, that is when the linear sweep voltage curves show two peaks. These two peaks have the diffusion of ions in the solution as their limiting step. The height of these two peaks is explicable by the diffusion of Cl− ions in solution as the slowest step. On the other hand, the ratio between the peak of the second wave and that of the first is 2.14. This behaviour is in agreement with the fact that the valence of dissolution of copper increases from the first peak to the second. [Journal translation]
The electrochemical synthesis of β-diketonato complexes of cadmium(II), and their adducts; the crystal and molecular structure of Cd(acac)2phen
Authors: Bustos Luis , Green James H. , Hencher J. Lawrence , Khan Masood A. , Tuck Dennis G.
Published: May 2006

The cadmium β-diketonate complexes Cd(RCOCHCOR′)2 (R = CH3, R′ = CH3; R = CF3 R′ = CH3, i-C3H7, i-C4H9, t-C4H9, C6H5, 2-naphthyl) can be prepared in good yield by the direct room temperature electrochemical oxidation of the metal into a solution of the parent diketone in acetonitrile. Adducts of the type Cd(RCOCHCOR′)2L (L = 2,2′-bipyridine, 1,10-phenanthroline, N,N,N′,N′-tetramethylethylenediamine) can be prepared insitu, or by subsequent addition of the ligand to the electrolytic solution. X-ray studies show that the molecular structure of both Cd(acac)2phen and Cd(CF3COCHCOC6H5)2phen is based on a CdO4N2 kernel, distorted from octahedral stereochemistry by the bite of the ligands.
Reactions of steroidal 4,5- and 5,6-epoxides with strong bases
Authors: Holland Herbert L.
Published: May 2006

A series of C-3 oxygenated and unsubstituted (4,5)α, (4,5)β, (5,6)α, and (5,6)β epoxy steroids has been prepared, and the reactions of these compounds with strong bases (potassium tert-butoxide, LDA, and LDEA) were investigated. Only LDEA gave rise to product formation; β elimination of the epoxide to give a β-hydroxy olefin was observed in this case. The regioselectivity of product formation is consistent with a mechanism of rearrangement involving removal of a hydrogen located syn to the epoxide oxygen. In some cases, a directing influence from a polar substituent (OH) of the starting material was also apparent. The 13C nmr spectra of the steroidal epoxides used in this study were assigned; these data are diagnostic of the conformation of ring A of (4,5)α and (4,5)β epoxy steroids.
Structure and conformation of the anticodon nucleoside 5-methoxyuridine in the solid state and in solution
Authors: Birnbaum George I. , Blonski Wayne J. P. , Hruska Frank E.
Published: May 2006

The three-dimensional structure of 5-methoxyuridine (mo5U) was determined with much higher precision than in a previous study (Hillen etal. J. Carbohydr. Nucleosides Nucleotides, 5, 23 (1978)). The crystals belong to the monoclinic space group P21 and the cell dimensions are a = 8.916(2), b = 14.372(2), c = 4.714(1) Å, β = 97.44(2)°. Intensity data were measured with a diffractometer and the structure was solved by direct methods. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.031. The conformation about the glycosyl bond is anti (χCN = 23.1°), the pucker of the ribose ring is C(3′)endo, and the conformation of the —CH2OH side chain is gauche+. A comparison of the bond lengths N(3)—C(4) and C(4)—O(4) with those in uridine does not support the conclusion of Hillen etal. about a shift to the enol tautomer in mo5U. However, there are other changes in the geometry of the pyrimidine ring due to substitution at C(5). A conformational analysis, based on 1H and 13C nmr data, shows that the preferred conformation in solution is that observed in the solid state.
On the synthesis of cardioactive steroid glycosides. On cardioactive steroids. XI
Authors: Jin Haolun , Tsai Thomas Y. R. , Wiesner Karbl
Published: May 2006

A stereoselective β-glycosidation of digitoxose and digitoxigenin involving a 1–3 participation of a urethane group is described. The conversion of digitoxin (10) to its furyl derivative 11 and the rcoxidation of 11 to digitoxin and isodigitoxin (12), respectively, in high yield is reported for the first time. This is of fundamental importance for the use of the new glycosidation method in the total synthesis of digitoxin and its analogues.
Conformational analysis of chiral hindered amides
Authors: Rauk Arvi , Tavares Donald F. , Khan Mohsin A. , Borkent Amy J. , Olson John F.
Published: May 2006

The static and dynamic structures of the amide derivatives of racemic and (R)-(+)-2-methoxy-2-phenyl-3,3,3-trifluoropropanoic acid (MPTA) with diisopropyl amine (1), meso-2,6-dimethylpiperidine (2), (R)-(−)- and (S)-(+)-2-methylpiperidine (3 and 4, respectively) were investigated by proton nmr spectroscopy. The piperidine rings adopt a single dominant conformation in which the substituent methyl groups occupy axial positions. One of the isopropyl groups of 1 is oriented in the same way as the corresponding side of the piperidine ring of 2–4 but the other (syn to carbonyl oxygen) is turned so that the methyl groups are toward the carbonyl oxygen and the oxygen lies in the plane bisecting the C—C—C angle. Rotation about the amide C(O)—N bond of 1 is accompanied by concurrent rotation about each of the N—iPr single bonds. The free energies of activation of the hindered rotation about the C(O)—N bond in 1–4, 81 kJ/mol, 77 kJ/mol, 77 kJ/mol, and 79 kJ/mol, respectively, are higher than found in most other hindered amides, suggesting that buttressing due to the steric crowding around the amide functionality is felt throughout the rotational pathway.
Glycosides from Muscaricomosum. 4. Structure of muscaroside A
Authors: Adinolfi M. , Barone G. , Lanzetta R. , Laonigro G. , Mangoni L. , Parrilli M.
Published: May 2006

The less polar component of the glycoside mixture extracted from the bulbs of Muscaricomosum has been completely characterized. This glycoside, 5, possesses an α-L-rhamnopyranosyl(1→2)-β-D-glucopyranosyl(1→2)-α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl chain linked at the C-3 position of eucosterol 1.
Nuclear magnetic resonance studies of microemulsions and related systems: 2-butoxyethanol in water
Authors: Desrosiers O. , Dinter T. Van , Saunders J. K.
Published: May 2006

The 13C chemical shift, T1 and 2H T1 data for 2-butoxyethanol (BE) in D2O as a function of concentration are presented. The nmr parameters are consistent with thermodynamic data for the same system in that it appears that 2-butoxyethanol in water undergoes a pseudo phase transition at about 1.2 M. The chemical shift for each carbon is different in the microphase relative to either aqueous solution or pure BE. The shift differences are due to a combination of factors, conformer population changes, changes in the polarity of the oxygen, and a solvent effect on chemical shift. The more organic the medium, the higher the population of trans relative to gauche conformers. The motion of BE is more restricted in the microphase than in either dilute aqueous solution or in the pure liquid. The number of adsorbed D2O molecules per molecule of BE is less in the microphase than in aqueous solution.
Infrared and Raman spectra of alkali palmityl sulfates
Authors: Kartha V. B. , Leitch L. C. , Mantsch H. H.
Published: May 2006

Lithium, sodium, potassium, cesium, and ammonium palmityl sulfates were prepared by sulfonation of n-hexadecanol, followed by treatment with the corresponding alkali carbonates; selectively deuterated palmityl sulfates were also synthesized to aid the assignment of certain vibrational modes. The infrared and Raman spectra of the polycrystalline solids were interpreted and discussed in terms of acyl chain and head group vibrations. Spectral evidence is presented for the existence of different solid polymorphic forms.
Micellar properties of sodium alkyl sulfoacetates and sodium dialkyl sulfosuccinates in water
Authors: Jobe David J. , Reinsborough Vincent C.
Published: May 2006

Viscosity, conductivity, density, and fluorescence quenching studies were conducted in aqueous micellar solutions at 25.0 °C of sodium alkyl sulfoacetates and sodium dialkyl sulfosuccinates in a comparison of one-tailed and two-tailed surfactant systems. The hexyl, octyl, and decyl members of the former group and the dihexyl and dioctyl members of the latter group were investigated. The results indicated that the sulfoacetates most likely form spherical micelles with aggregation numbers 20 for hexyl, 42 for octyl, and 70 for decyl with three methods for size determination giving concordant results. For the sulfosuccinates, the aggregation numbers from fluorescence quenching were 38 for the dihexyl and 56 for the dioctyl in agreement with the results from the conductance technique which means that spherical micelles are likely formed also. Volume changes on micellization were obtained for the sulfoacetates.
Synthesis of phthalideisoquinolines by direct coupling of phthalide anions with 3,4-dihydroisoquinolinium salts
Authors: Marsden Richard , MacLean David B.
Published: May 2006

The condensation of phthalide anions, derived from phthalide itself and from its 6,7- and 5,6-dimethoxy derivatives, with 6,7-dimethoxy-2-methyl-3,4-dihydroisoquinoline is described. The reaction products obtained in ca. 40% yield are easily separable mixtures of substituted (±)-erythro and (±)-threo-phthalidetetrahydroisoquinolines. The reaction is potentially useful for synthesis of naturally occurring akaloids of this family.
Mechanistic aspects of the methoxide-catalyzed transformation of 4-acyloxy-1,3,4-oxadiazines to N-amino-oxazolidonylhydrazones
Authors: Mackay Donald , McIntyre Deane Douglas
Published: May 2006

When the 1,3,4-oxadiazine 2, one of three known isomers formed by cycloaddition of 2,5-dimethyl-3,4-diphenyl-cyclopentadienone and dimethyl azodicarboxylate, is isomerized by MeO−–MeOH to the hydrazone 4, the MeO of the ester group of 2 is lost and MeO is incorporated into 4 from the solvent. In acid, e.g. trifluoroacetic acid, demethylation of 2 gives 14 in which the ester Me is lost. The hydrazone 4 also gives 14 with acid, but by a different pathway.These results were established using the structurally isomeric oxadiazines 10 and 11 as mechanistic probes; an X-ray analysis of 10 established the individual identities of these.
Studies on the biosynthesis of the sterpurenes
Authors: Ayer William A. , Nakashima Thomas T. , Saeedi-Ghomi M. Hossein
Published: May 2006

The sterpurenes are a unique group of sesquiterpenes produced by the fungus Stereumpurpureum. Biosynthetic studies utilizing [1-13C] and [2-13C] acetate indicate that sterpuric acid (2) and sterpurene-3,12,14-triol (3) are formed from acetate via humulene (5) and the protoilludane cation (6) by one of the paths shown in Scheme 2.
Aminosulfonic acids. Part 1. Crystal structures of N-methylaminomethanesulfonic acid, MeNHCH2SO3H, and disodium N-methyliminobis(methanesulfonate) dihydrate, MeN(CH2SO3Na)2•2H2O
Authors: Cameron T. Stanley , Chute Walter J. , Knop Osvald
Published: May 2006

The crystal structure of N-methylaminomethanesulfonic acid (P212121, a = 5.455(1) Å, b = 7.791(1) Å, c = 11.925(2) Å, Z = 4) consists of +MeNH2CH2SO3− zwitterions hydrogen-bonded to form infinite chains about screw axes parallel to a. In the structure of MeN(CH2SO3Na)2•2H2O (Pbcn, a = 10.469(1) Å, b = 6.039(3) Å, c = 17.549(3) Å, Z = 4), layers of MeN(CH2SO3−)2 anions alternate with layers of Na+ ions parallel to (001). The anions are linked by [Formula: see text] bonds between the water molecules and the O(2) atoms of the sulfonate groups. Because of the twofold orientational disorder of the N—CH3 groups the space group Pbcn is only statistical.The S—C, C—N, and S—O bond lengths in solid aminosulfonic acids and their salts are discussed with a view to detecting the existence of effects due to deprotonation of the amino group and to hydrogen bonding.
The theory of regular solutions applied to molar excess enthalpies and volumes of binary mixtures containing stannic bromide
Authors: Suri S. K. , Maheshwari R. C.
Published: May 2006

The molar excess enthalpies, HmE, at 313.15 K and molar excess volumes, VmE, at 303.15, 308.15, and 313.15 K for the binary mixtures of stannic bromide with benzene, cyclohexane, and tetrachloromethane have been determined. Both HmE and VmE for the three sets of binary mixtures are positive over the entire range of composition. The experimental results have been compared with those predicted by regular solution theory. It is observed that HmE calculated for regular solutions are highly sensitive to the estimation of C12. The calculated VmE are in good agreement with the experimental data if it is assumed that (∂E/∂P)T = 0; and the ratio of the internal pressures to the cohesive energy density are the same for unmixed and the mixed components.
Metal-catalyzed rearrangements of allylic esters
Authors: Oehlschlager C. , Mishra P. , Dhami S.
Published: May 2006

It has been shown that Pd(CH3CN)2Cl2 catalyzes the rearrangement of allylic esters. Carbamates rearrange more rapidly than acetates which in turn rearrange more rapidly than carbonates. Allylic carbamates are more rapidly isomerized by Pd(CH3CN)2Cl2 than by Hg(OCOCF3)2. The rearrangement proceeds well except in cases where the central carbon of the allylic system is fully substituted.In contrast to the reported rearrangement of allylic carbamates by Hg2+ and previous reports of Pd2+-catalyzed rearrangements of allylic esters, this work showed the latter are extremely E specific; thus, E allylic acetates yield equilibrium mixtures free of Z allylic isomers, under conditions in which Z allylic acetates are unreactive. This E specificity is applied to stereospecific 1,3-diene synthesis from bis E,Z-allylic acetates.
Structural studies of organoboron compounds. XVII. Preparation and crystal and molecular structure of 3a-methyl-2,4,9a-triphenyl-1,2,3a,4,9,9a-hexahydro-1,3,9-trioxa-3a-azonia-2-bora-9a-boratacyclopenta[b]naphthalene
Authors: Kliegel W. , Nanninga D. , Rettig Steven J. , Trotter James
Published: May 2006

The title compound was prepared by the reaction of 8-methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene (1) with phenylboronic acid. Crystals of 3a-methyl-2,4,9a-triphenyl-1,2,3a,4,9,9a-hexahydro-1,3,9-trioxa-3a-azonia-2-bora-9a-boratacyclopenta[b]naphthalene are monoclinic, a = 11.8548(4), b = 22.7837(4), c = 8.5457(3) Å, β = 106.952(2)°, Z = 4, space group P21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.047 for 2970 reflections with I ≥ 3σ(I). The molecule was found to be a formal addition product between 1 and PhBO which had undergone a 1,4-shift of a phenyl group from boron to carbon. The backbone of the molecule consists of a folded system of three fused rings. The structure contains the longest known B(sp3)—N(sp3) bond, 1.759(2) Å.
Low-temperature infrared study of ammonium carbamate formation
Authors: Hisatsune C.
Published: May 2006

Two types of infrared spectra observed during the formation of ammonium carbamate [Formula: see text] from the reaction of NH3 and CO2 in the solid state at low temperatures have been re-examined. These spectra had been assigned previously to amorphous and crystalline ammonium carbamate but the present data suggest their origins to be [Formula: see text] and its unstable precursor (NH3)2CO2 in which CO2 is bent. Spectra of amorphous and crystalline ammonium carbamate have been distinguished by comparing the systems NH3/CO2 and NH3/CO2/H2O. Hydrogen ion transfer in the diammoniates occurred at about −80 °C for NH3/CO2 and about −40 °C for ND3/CO2.