bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalytic transfer hydrogenation of benzylic and styryl compounds with palladium/carbon and 2-propanol. Selective removal of O-benzyl groups from carbohydrate derivatives
Authors: Rao Vanga S. , Perlin Arthur S.
Published: May 2006

2-Propanol is shown to be an effective hydrogen donor, in the presence of palladium/carbon, for catalytic transfer hydrogenation reactions of benzylic and styryl compounds, e.g., for the quantitative conversion of cinnamyl alcohol into 3-phenylpropanol. In the reduction of derivatives of cinnamic acid, decarboxylation also occurs. During the latter reaction, the phenyl group appears to function as an anchoring group for the palladium atom, because derivatives of phenylpropanoic acid are decarboxylated more readily than are those of phenylacetic acid. In hydrogenolysis reactions, aryl alcohols undergo disporportionation whereas benzyl ethers, represented by O-benzyl and related derivatives of carbohydrates, are smoothly cleaved. Although 2-propanol is less reactive as a hydrogen donor than formic acid, it exhibits greater selectivity, as illustrated by relative rates of hydrogenolysis of O-benzyl and O-benzylidene substituents. The use of alumina-supported palladium is more effective than palladium/carbon for promoting stepwise removal of O-benzyl substituents, as shown by the preparation of methyl 2-O-benzyl- and -3-O-benzyl-α-D-glucopyranoside from the 2,3-di-O-benzyl derivative. A possible relationship between the orientation of O-benzyl groups and the chemical shift differences between the diastereotopic benzylic protons is described.
Identification of 26-minute Zr-84
Authors: Shibata Seiichi , Karol Paul J.
Published: May 2006

An unknown γ-ray of energy 112.5 keV was found in zirconium fractions chemically extracted from isotopically enriched molybdenum targets bombarded with 500 and 800 MeV protons. All evidence suggests that the γ-ray is identifiable with the decay of 84Zr to 84Y. A half-life of 25.7 ± 0.5 min was obtained for 84Zr, which is considerably longer than previously reported half-lives. The absolute abundance of the 112.5 keV γ-ray was also determined. Relative production cross sections for 84Zr were calculated using these results and were consistent with the values interpolated from isotopic distribution curves for spallation reactions.
Archaeological ceramic differentiation using trace element patterns
Authors: Snow Bryan E. , D'auria John M. , Shutler Jr. Richard , Payne John G.
Published: May 2006

Ceramic sherds of "primitive" manufacture from an archaeological site on Fuga Moro Island, Philippines, were analyzed for trace element contents using energy dispersive X-ray fluorescence (EDXRF) to ascertain the probability of obtaining differentiation between stylistic classes (wares) and technological types within the ware. Following analysis and differentiation of these samples, using standard archaeologic and petrographic techniques, the initial focus of the study was to isolate surface factors which could distort or otherwise affect the final elemental characterizations. Once these factors were identified and eliminated, a simple procedure was then developed employing trivariate analysis of specific observed elements that unambiguously segregated the studied sherds, both according to ware and technological type within each ware. The key elements for ware differentiation were Zn, Br, and Sr while type differentiation was achieved using Ca, Ti, Mn, and Rb.
Infrared absorption and resonance Raman scattering of photochromic triphenylformazans
Authors: Lewis J. W. , Sandorfy C.
Published: May 2006

The infrared and resonance Raman spectra of the two long-lived forms of triphenylformazan and several of its derivatives have been examined. The spectra of unsymmetrically 15N-labelled derivatives suggest that two tautomers exist for each of the two forms. This observation is confirmed by the spectra of 1-(p-halophenyl)-3,5-diphenylformazans. The spectra of the non-chelate forms of these latter compounds demonstrate that the position of the tautomeric equilibrium is influenced by the electron-attracting ability of the para-halo-substituent. A comparison of the resonance Raman spectra of the two forms leads to the conclusion that excited state proton transfer is the initial photoevent in the photochromism of the triphenylformazans.
Rotational relaxation of the A1π(ν′ = 13, J′ = 13+) state of 13C16O by various gases
Authors: Vikis A.C.
Published: May 2006

Rotational relaxation of the A1π (ν′ = 13, J′ = 13+) state of 13C16O was studied in the presence of H2, D2, He, Ne, Ar, Xe, N2, CO, 13C16O, and 12C18O. The rotational relaxation cross sections Σσ13 → J′, in cm2 × 1016 and in the above order, were: 19 ± 1, 27 ± 1, 23 ± 1, 32 ± 1, 55 ± 2, 14 ± 1, 43 ± 3, 69 ± 5, 23 ± 1, and 100 ± 15. The rotational relaxation probabilities per gas-kinetic collision correlate with the square root of the reduced mass, except for Xe and the CO isotopic molecules. The latter molecules have several electronic states accessible at this energy. Their rotational relaxation cross sections depend on the magnitude of their respective electronic quenching cross sections, in a manner indicating preemption by fast electronic–electronic energy transfer.
Subpicosecond laser spectroscopy: strong field effects on molecular photophysics and dynamics
Authors: Quitevis E. , Kroger P. M. , Kalpouzos C. , Kenney-Wallace G. A.
Published: May 2006

The possible role of strong field effects is discussed in the context of picosecond relaxation and reaction in polyatomic systems. The picosecond pulse diagnostics from an argon-ion synchronously pumped dye laser are then outlined in terms of cavity detuning and laser pumping parameters. A profile of auto-correlation data on ensemble-averaged pulses and streak camera data on single pulses is presented, from which the domain of stable, single pulse operation can be deduced. Finally data are presented on the photoionization and energy relaxation of pyrene in alcohols and micelles, and for the reorientational dynamics of liquid chlorobenzene, which illustrate different consequences of strong field phenomena in dense media.
On the chemistry of metastable species
Authors: Hilinski E. F. , Milton S. V. , Ramana C. , Rentzepis P. M.
Published: May 2006

The mechanisms of a variety of chemical, physical, and biological processes are now understood more clearly as a result of picosecond spectroscopic studies. The identification of metastable species and transient states and the measurement of their formation and decay kinetics are made possible by means of picosecond emission and absorption spectroscopy. The data from these studies provide detailed mechanistic information about a reaction as it evolves. In this paper, we describe a laser system used for picosecond spectroscopy along with several chemical applications of picosecond absorption and emission spectroscopy performed in our laboratories. These include studies on the photochemical generation of trimethylenemethane biradicals from azo compounds, excited-state relaxation dynamics of p-dimethylaminobenzonitrile, and photodissociation of haloaromatic compounds.
Tritium isotope fractionation between hydrogen sulphide and methanol
Authors: Wawer Andrzej , Szydlowski Jerzy
Published: May 2006

Tritium isotope fractionation in the exchange reaction between methanol and hydrogen sulphide has been studied in the gaseous phase over the temperature range 283–373 K. It was found that the heavier isotope accumulates in methanol and that the tritium–protium isotope effect characterizing the exchange reaction studied reaches large values: from 2.70 at 373 K to 3.72 at 283 K. The temperature dependence can be described by the simple relation: In α = −0.1221 + 431.5/T. Using observed vibrational frequencies, theoretical fractionation factors could be calculated and good agreement with the experimentally determined values was observed. The results presently obtained were also compared with those obtained for the CH3SH–H2S system.
The structure and conformation of cis-2-phenylcyclobutanecarboxylic acid and cis-3-(p-fluorophenyl)cyclobutanecarboxylic acid
Authors: Reisner George M. , Korp James D. , Bernal Ivan , Fuchs Richard
Published: May 2006

The structure of cis-2-phenylcyclobutanecarboxylic acid (1) and cis-3-(p-fluorophenyl)cyclobutanecarboxylic acid (2) have been determined by X-ray diffraction methods. Crystals of 1 are monoclinic, space group C2/c with a = 15.420(8), b = 11.687(6), c = 11.226(5) Å, β = 112.45(4)°, and eight molecules in the unit cell. Crystals of 2 are monoclinic, space group P21/n, a = 8.038(5), b = 5.405(4), c = 22.69(1) Å, and β = 97.30(4)°, with four molecules in the unit cell. In both compounds the cyclobutane ring is puckered, with dihedral angles of 27° and 31°. The bond joining the substituted ring atoms in 1 is significantly longer (1.581(2) Å) than the other three (average 1.535(2) Å), due to crowding of substituents. In 2 both the carboxyl and phenyl substituents are close to the bisecting geometry, whereas in 1 both substituents deviate from this conformation, the carboxyl more than the phenyl.
A systematic study on volumetric interactions of cyclohexanone with various aliphatic hydrocarbons
Authors: Chawla B. , Parkash Ram , Suri S. K.
Published: May 2006

Excess volumes of mixing, VE, for binary mixtures of eyelohexanone with n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, n-tetradecane, and n-hexadecane at 25 °C were determined from the precise and accurate experimental density data. The sign and magnitude of VE were discussed in terms of the strength of the unlike interactions present in the binary mixtures.Excess volumes of mixing of equimolar concentration [Formula: see text] were also obtained. Attempts were made to interpret [Formula: see text] in terms of the size and polarity of the constituent molecule. The two effects could not be separated, but a good linear relation between [Formula: see text] and the solubility parameter was found.
The cycloaddition of norbornadiene to (triphenylphosphoranediyl)aminocyclotrithiatriazene; the crystal and molecular structure of Ph3PN—S3N3•C7H8
Authors: Liblong Stephen W. , Oakley Richard T. , Cordes A. Wallace , Noble Mark C.
Published: May 2006

The reaction of norbornadiene with (triphenylphosphoranediyl)aminocyclotrithiatriazene produces the cycloadduct Ph3PN—S3N3•C7H8. The crystal and molecular structure of this compound has been determined by X-ray crystallography. Crystals of Ph3PN—S3N3•C7H8 are monoclinic, space group P21/c, a = 9.757(1), b = 15.114(1), c = 16.535(2) Å, β = 100.73(1)°, V = 2395.7(9) Å3, and Z = 4. The structure was solved by direct methods and refined by Fourier and full-matrix least-squares procedures to give a final R of 0.040 and Rw of 0.058 for 2620 observed reflections. The structure reveals that the S3N3 ring adds to norbornadiene in an exo fashion via two sulphur atoms. The S3N3 ring adopts a chair conformation with the three ligands occupying axial positions on the same side of the ring. The relative rates of this and other cycloadditions involving SN substrates and olefins are discussed in terms of the energies of the interacting frontier orbitals. The results suggest that HOMO(olefin)–LUMO(SN substrate) interactions control the kinetics of these reactions.
Substituent-induced chemical shifts in 3- and 4-substituted styrenes: definition of substituent constants and determination of mechanisms of transmission of substituent effects by iterative multiple linear regression
Authors: Reynolds William F. , Gomes Anablla , Maron Antonina , MacIntyre Douglas W. , Tanin Ates , Hamer Gordon K. , Peat Ian R.
Published: May 2006

Iterative multiple linear regression analysis of substituent-induced chemical shifts in 3- and 4-substituted styrene derivatives is used to redefine σF and [Formula: see text] substituent constants (with respective standard errors of ca. 0.01 and 0.005). Correlations with the data for various model systems indicate that these substituent constants are applicable to data sets involving both chemical shift and acidity measurements in aprotic media. The approach we have used involving a homogeneous data set with a large number of variables is particularly suited for providing well-defined dual substituent parameter constants for the more common neutral substituents.Correlations for individual nuclei are entirely consistent with a previously proposed model of substituent effects involving field, resonance, and polarization effects. From these results and the results for other model systems, it is concluded that σF and [Formula: see text] are respectively pure field and resonance substituent constants. It is pointed out that a combination of detailed statistical testing and chemical modelling is essential for a thorough understanding of aromatic substituent effects.Parameters for predicting non-electronic contributions to ortho and meta chemical shifts are derived, thus allowing the patterns of electronic substituent effects for these carbons to be determined. However, only an approximate ipso factor can be deduced.
Dérivés allyliques de la colonne IV-A, de type R3ECH2CH=CH—CH3 et R3ECH(CH3)CH=CH2. Approche des effets électroniques par résonance magnétique nucléaire 13C et 1H
Authors: Matarasso-Tchiroukhine E. , Cadiot P.
Published: May 2006

A comparative 1H and 13C nmr study of allylic derivatives of the IV-A group elements, of the type R3ECH2CH=CH—CH31E, Z and R3ECH(CH3)CH=CH2, 2, was performed (R = —C6H5, —CH3, E = C, Si, Ge, Sn, Pb). The present paper dealing with the allylic moiety concerns both the chemical shifts, δ1H and δ13C, and the homonuclear J(H—H) and heteronuclear couplings 1J(13C—H), nJ(13C—E), n = 1 to 4, nJ(E—C—H), n = 2 and 5. The spectra are consistent with a σ-allylic structure. In order to obtain an inductive order for the groups G(E) = —E(C6H5)3 a coherent group electronegativity scale was established. The intrinsic group electronegativities, without appreciable change, obey the following sequence:[Formula: see text]Both the changes along the series, in spectroscopic parameters, δ1H, δ13C, and the unusually large heteronuclear couplings, 2J(E—C—H), 5J(E—C—H), 4J(E—13C) (E = Sn, Pb), are interpreted in terms of an electronic mesomeric donating effect for the substituent σ, R3ECH2— and R3ECH(CH3)—, by σ–π hyperconjugation. Factors intrinsic to the main-group element control the chemical shifts δ1Hα and δ13Cα. The s-character of the bond Cα—Hα appears to control the 1J(13Cα—Hα) couplings; no correlation with a σ → π hyperconjugation could be established.
Reactions of elemental sulfur with tetrakis(triphenylphosphine)platinum(0). Formation of a complex containing very nucleophilic bridging sulfido ligands
Authors: Gukathasan Ravi R. , Morris Robert H. , Walker Alan
Published: May 2006

The reactions of Pt(PPh3)4 with elemental sulfur in ratios S/Pt = 3, 4, 5, and 6 give a mixture of compounds identified as [PtS(PPh3)2]2 and PtS4(PPh3)2; PtS2(PPh3)2 is not detected. The dimeric complex also forms on reaction of PtS4(PPh3)2 with 3 mol of Pt(C2H4)(PPh3)2. It is alkylated at one bridging sulfido ligand by CH2Cl2 and CHCl3 to give cations [Pt2(μ-S)-(μ-SR)(PPh3)4]+, R = CH2Cl and CHCl2, respectively, which are characterized as their hexafluorophosphate salts. The cations give extreme AA′BB′X 31Pmr spectra since their cis-phosphorus atoms (A,B) have very similar chemical shifts but different coupling constants to 195Pt(X); spectral features are broadened by thiolate inversion processes. Reactions of bridging sulfido ligands with other electrophiles are discussed.
Structural studies of organoboron compounds. XVIII. Crystal and molecular structures of 2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan and 4-cyclohexyl-6-methyl-2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan
Authors: Kliegel W. , Nanninga D. , Rettig Steven J. , Trotter James
Published: May 2006

The crystal structures of 2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan, 6a, and 4-cyclohexyl-6-methyl-2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan, 6b, reported here represent the first crystallographic examples of coordination complexes of the anionic ligand derived from 2-hydroxypyridine N-oxide. Crystals of 6a are monoclinic, a = 11.5210(13), b = 10.2860(8), c = 12.7354(15) Å, β = 101.878(5)°, Z = 4, space group P21/c; and those of 6b are monoclinic, a = 8.5047(8), b = 15.6603(14), c = 16.0501(18) Å, β = 104.776(5)°, Z = 4, space group P21/n. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.039 and 0.042 for 1440 and 1750 reflections with I ≥ 3σ(I), respectively. Both molecules feature tetrahedrally coordinated boron atoms incorporated into five-membered OBOCN chelate rings which have B-envelope conformations. The observed molecular geometries indicate that the ligand may be classed as a hybrid of the 2-hydroxypyridine N-oxide and 1-hydroxy-2-pyridinone tautomers of the parent alcohol. Important bond lengths (corrected for libration) are: O—B = 1.557(3)−1.580(3), mean C—B = 1.600(4), C—O = 1.316(3), and N—O = 1.389(3) Å.
Studies on double malonates. I. Sodium lanthanide malonates, Na5Ln(C3H2O4)4•7•5H2O (Ln = Gd–Ho or Y)
Authors: Nabar Mahadeo A. , Jukar Bharat N.
Published: May 2006

A new series of double malonates of some of the lanthanides and yttrium with sodium having the formula Na5Ln(C3H2O4)4•7•5 H2O was synthesised. The compounds were characterised using X-ray powder diffractometry and infrared absorption spectroscopy.
Propriétés physiques et basicité de l'oxydipropionitrile
Authors: Bollinger Jean-Claude , Yvernault Germaine , Yvernault Théophile , Houriet Raymond
Published: May 2006

Physical constants (density, refractive index, viscosity, dielectric constant, dipole moment, solubility parameter) and some basicity parameters (donor number, proton chemical shift variation for CHCl3, gas phase basicity) have been determined for 3,3′-oxydipropionitrile (ODPN) at 25 °C. These results are compared with those for other usual solvents; they permit an explanation of its properties as a solvent for acid–base titrations, and the appearance of homohydrogen bonding in this medium.
Stability and solubility relationships between some solids in the system PbO–CO2–H2O
Authors: Taylor Peter , Lopata Vincent J.
Published: May 2006

We have determined equilibrium conditions for each reaction in the solid interconversion sequence [Formula: see text], in aqueous carbonate solutions near 25 °C. Our data yield the following Gibbs energies of formation from the elements, ΔfG°(298.15 K): plumbonacrite, −5310 ± 31 kJ mol−1; hydrocerussite, −1705 ± 11 kJ mol−1; cerussite, −628.0 ± 3.9 kJ mol−1. Corresponding estimated values of ΔfG°(373 K) are −5120 ± 50, −1643 ± 18, and −612 ± 9 kJ mol−1, respectively. We have demonstrated the existence of a narrow stability field for plumbonacrite, and convenient small-scale preparations of hydrocerussite and plumbonacrite are described. Gibbs energy data for the solids have been combined with selected data for aqueous lead species in a detailed computation of solubility behaviour for this system at 25 °C.
Calculation of phase diagrams and thermodynamic properties of 14 additive and reciprocal ternary systems containing Li2CO3, Na2CO3, K2CO3, Li2SO4, Na2SO4, K2SO4, LiOH, NaOH, and KOH
Authors: Pelton A. D. , Bale C. W. , Lin P. L.
Published: May 2006

Phase diagrams and thermodynamic properties of five additive molten salt ternary systems and nine reciprocal molten salt ternary systems containing the ions Li+, Na+, [Formula: see text], OH− are calculated from the thermodynamic properties of their binary subsystems which were obtained previously by a critical assessment of the thermodynamic data and the phase diagrams in these binary systems. Thermodynamic properties of ternary liquid phases are estimated from the binary properties by means of the Conformal Ionic Solution Theory. The ternary phase diagrams are then calculated from these thermodynamic properties by means of computer programs designed for the purpose. It is found that a ternary phase diagram can generally be calculated in this way with a maximum error about twice that of the maximum error in the binary phase diagrams upon which the calculations are based. If, in addition, some reliable ternary phase diagram measurements are available, these can be used to obtain small ternary correction terms. In this way, ternary phase diagram measurements can be smoothed and the isotherms drawn in a thermodynamically correct way. The thermodynamic approach permits experimental data to be critically assessed in the light of thermodynamic principles and accepted solution models. A critical assessment of error limits on all the calculated ternary diagrams is made, and suggestions as to which composition regions merit further experimental study are given.
Synthesis and crystal structure of tri(μ-carbonyl)bis[methyltris(1-pyrazolyl)gallato]dirhodium – benzene (1:1)
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis, physical properties, and crystal structure of the dirhodium species [MeGa(N2C3H3)3]2Rh2(μ-CO)3 containing three carbonyl bridges are reported. Crystals of tri(μ-carbonyl)bis[methyltris(1-pyrazolyl)gallato]dirhodium – benzene (1:1) are monoclinic, a = 11.660(4), b = 15.2917(7), c = 11.750(4) Å, β = 119.09(1)°, Z = 2, space group P21. The structure was solved by conventional heavy-atom techniques and was refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.033 for 2604 reflections with I ≥ 3σ(I). The molecule contains a Rh—Rh single bond of 2.5818(8) Å bridged by three CO ligands, the overall molecular symmetry being close to D3h. Other important mean structural parameters are: Rh—C = 2.007(10), Rh—N = 2.181(14) Å, Rh—C—Rh = 80.1(5)°, and Rh—C—O = 140.0(7)°.
Synthesis of tri- and tetrasaccharide haptens related to the Asialo forms of the gangliosides GM2 and GM1
Authors: Sabesan Subramaniam , Lemieux Raymond U.
Published: May 2006

Synthesis of βDGalNAc(1→4)βDGal(1→4)βDGlc—O(CH2)8COOCH3 (21) and βDGal(1→3)βDGalNAc(1→4)βDGal(1→4)βDGlc—O(CH2)8COOCH3 (33) are presented starting from βDGal(1→4)βDGlc—O(CH2)8COOCH3 (1) and D-galactose. Improvements in the preparations of D-galactal triacetate (7) and tri-O-acetyl-2-azido-2-deoxy-α-D-galactopyranosyl bromide (11) are reported. The syntheses proceeded by way of the tri-O-acetyl-2-deoxy-2-phthalimido-β-D-galacto-pyranosyl and 4,6-di-O-acetyl-3-O-(tetra-O-acetyl-β-D-galactopyranosyl)-2-deoxy-2-phthalimido-β-D-galactopyranosyl bromides (18 and 30), which, in turn, were prepared from the corresponding allyl glycosides (15 and 23). The 13C chemical shifts for the tri- and tetrasaccharide portions of 21 and 33 are assigned from the chemical shifts that were observed for the carbon atoms in the disaccharides which make up these structures. The trisaccharide (21) only very weakly inhibited the agglutination of human A red cells by the lectin of Dolichosbiflorus. The tetrasaccharide (33) was inactive.
Gas phase negative ion chemistry of alkylchloroformates. A convenient method for bimolecular generation of chloride ion adducts and determination of chloride affinities from ion cyclotron resonance thermal equilibrium measurements
Authors: Larson J. W. , McMahon T. B.
Published: May 2006

A new method for production of chloride ion adducts, MCl−, via a sequence of bimolecular ion molecule reactions involving chloroformate esters is described. These reactions have been used in trapped-ion ion cyclotron resonance thermal equilibrium studies to determine the relative chloride ion affinities of twenty compounds with Cl− binding energies in the range 10–25 kcal mol−1. The present results are found to be in good agreement with chloride affinities obtained by other methods. The resulting chloride affinity scale establishes a convenient framework for the systematic investigation of effects of molecular structure and chemical properties on the binding energy of Cl− to both Lewis and Brønsted acids.
Kinetics and mechanism of disproportionation and ferricyanide oxidation of the 10-methylacridinium cation in aqueous base
Authors: Bunting John W. , Kauffman Glenn M.
Published: May 2006

The kinetics of disproportionation and ferricyanide ion oxidation of the 10-methylacridinium cation have been measured spectrophotometrically over the pH range 9–14 in.20% CH3CN – 80% H2O (v/v) and ionic strength 1.0 at 25 °C. Disproportionation is kinetically second-order in total acridine species. The pH–rate profile is consistent with the rate-determining reaction of one acridinium cation with the pseudobase alkoxide anion derived from a second acridinium cation. Ferricyanide ion oxidation is kinetically first-order in each of ferricyanide ion and total acridine species. The pH–rate profile requires three distinct pathways for the ferricyanide ion oxidation of the 10-methylacridinium cation. For pH < 9.7, rate-determining attack of ferricyanide ion on the neutral pseudobase predominates, while for pH > 12.8 the predominant oxidation pathway involves reaction of ferricyanide ion with the pseudobase alkoxide ion. Between pH 9.7 and 12.8, the major oxidation pathway involves initial disproportionation of the acridinium cation followed by ferricyanide ion oxidation of the 9,10-dihydro-10-methylacridine product. This latter route accounts for a maximum of 69% of the total ferricyanide ion oxidation at pH 11.1.
Preparation and characterization of some ruthenium(II) porphyrins containing tertiary phosphine axial ligands, including the crystal structure of (octaethylporphinato)bis(triphenylphosphine)ruthenium(II)
Authors: Ariel Sara , Dolphin David , Domazetis George , James Brian R. , Leung Tak W. , Rettig Steven J. , Trotter James , Williams Gregory M.
Published: May 2006

The ruthenium(II) porphyrin complex Ru(OEP)(PPh3)2 (OEP = the dianion of octaethylporphyrin) has been prepared from Ru(OEP)(CO)EtOH, and the X-ray crystal structure determined; as expected, the six-coordinate ruthenium is situated in the porphyrin plane and has two axial phosphine ligands. Synthesized also from the carbonyl(ethanol) precursors were the corresponding tris(p-methoxyphenyl)phosphine complex, and the Ru(TPP)L2 (TPP = the dianion of tetraphenylporphyrin, L = PPh3, P(p-CH3OC6H4)3, P″Bu3) and Ru(TPP)(CO)PPh3 complexes. Optical and 1H nmr data are presented for the complexes in solution. In some cases dissociation of a phosphine ligand to generate five-coordinate species occurs and this has been studied quantitatively in toluene at 20 °C for the Ru(OEP)L2 and Ru(TPP)L2 systems.
Protonation de l'adénine, de la purine et de l'adénosine en milieu acide fort
Authors: Benoit Robert L. , Fréchette Monique
Published: May 2006

In view of a previously proposed enthalpy value for the second protonation of adenine, a calorimetric and nmr spectroscopic study has been made of the protonation of biologically important bases B: adenine, purine, adenosine and, incidentally, that of imidazole and 3-amino pyridine. Heats of solution of the solid bases, and their carbon-13 and proton chemical shifts were determined as a function of HClO4 and H2SO4 concentration. Our results demonstrate that, contrary to previous usage, a strong medium effect precludes the use of the calorimetric results to calculate the thermodynamic functions for the protonation reactions. On the other hand, the carbon-13 nmr data are successfully interpreted on the basis of the Cox and Yates excess acidity method. The values obtained for [Formula: see text] and [Formula: see text] are, respectively: adenine −0.43, −4.23, purine −1.66, < −6, adenosine −1.4 with hydrolytic cleavage of the glycosidic bond. The protonation sites are confirmed as being essentially on the imidazole ring for the second protonation and on the pyrimidine ring (N-3) for the third one.
The crystal and molecular structure of endo-7-hydroxy-2,4-dioxa-3-oxobicyclo[3.3.1]nonane
Authors: Wong-Ng Winnie , Nyburg Stanley C.
Published: May 2006

The crystal and molecular structure of the title compound are described. Crystals are orthorhombic, space group Pna21, a = 10.977(3), b = 6.489(2), c = 9.811(2) Å, Z = four molecules per cell. Atom C(4), to which the hydroxyl group is attached, appears to have been moved outwards (away from hydroxyl). This resembles similar movements in chair–chair bicyclo[3.3.1]nonanes where intramolecular repulsion is thought to be responsible. In the present molecule, however, the more likely cause is the presence of an intermolecular hydrogen bond.
Rhenium carbonyl derivatives incorporating the bidentate chelating pyrazolyl gallate ligands, [Me2Ga(N2C3HR2)2]− and [Me2Ga(N2C3HR2)(OH)]− (where R = H or Me)
Authors: Louie Brenda M. , Storr Alan
Published: May 2006

The reaction of the symmetrical bidentate chelating pyrazolyl gallate ligands [Me2Ga(N2C3HR2)2]− (where R = H or Me) with the rhenium dimer molecule [Re(CO)4Cl]2 are described. In addition, the novel unsymmetrical bidentate chelating pyrazolyl gallate ligands [Me2Ga(N2C3HR2)(OH)]− are introduced and their reactivities towards the [Re(CO)4Cl]2 molecule detailed. Substitution reactions of the tetracarbonyl rhenium species produced by the above reactions are described, and possible conformations for the various complexes are suggested on the basis of 1H nmr and ir results.
Simple lower and upper bounds for isomerization energies
Authors: Mezey Paul G.
Published: May 2006

Lower and upper bounds for the energies of various isomers can be obtained by a simple inspection of the nuclear charges. The bounds are quantum-mechanically rigorous, and are strictly applicable only to specific nuclear geometries and require only back-of-the-envelope type calculations.
The far-infrared spectra and the ring inversion vibrations of a series of methylenecyclohexanes
Authors: Wieser Hal , Smithson Tracy L. , Ibrahim Nan , Krueger Peter J.
Published: May 2006

The far-infrared spectra in the region of 50 to 400 cm−1 are reported for the vapours of methylenecyclohexane and the related compounds 4-methylenetetrahydro-4H-pyran, 4-methylenetetrahydro-4H-thiopyran and 3-methylenetetrahydro-4H-pyran. The absorptions are assigned to the three out-of-plane deformations of the six-membered rings. The observed series of Q branches are ascribed to combination sequences involving the three modes. The lowest wavenumber sequence in each compound is believed to arise from a vibration which if completely executed would take the chair conformation to its equivalent via an inversion through the planar form. With the use of a one-dimensional Hamiltonian incorporating a quadratic-quartic double minimum potential function, barriers to planarity for the rings are estimated. The similarities between these compounds and the corresponding ketones are discussed.
The conversions of isothiazolium salts into thiophenecarboxylic ester derivatives
Authors: McKinnon David M. , Duncan K. Ann , Millar Lesley M.
Published: May 2006

Several 3-aminothiophene-2-carboxylic ester derivatives are made by reaction of potassium 3-ethoxy-3-oxopropanoate with isothiazolium salts or by reaction with 2-ethoxy-2-oxoethylidenedimethylsulfurane. In the latter case deaminated products are also isolated. These products are consistent with initial nucleophilic attack on the sulfur atom of the isothiazolium salt. In one case a pyrrole derivative is formed by a novel rearrangement of an intermediate aziridine derivative. Some further derivatives of 3-benzylaminobenzo[b]thiophene are described.
Heteroanthracyclines. 2. 4-Demethoxythioxanthodaunomycinone (7,8,9,10-tetrahydrobenzo(b)-6,7,9,11-tetrahydroxy-9-acetylthioxanthen-12-one)
Authors: Wong Chiu-Ming , Mi Ai-Qiao , Ren Jiali , Haque Wasimul , Lam Hing-Yat , Marat Kirk
Published: May 2006

The title compound, a new heteroanthracyclinone was synthesized in five steps starting with 5,8-dimethoxy-2-acetyltetralin (15). Reaction of 2,2′-dithiosalicylic acid (16) with the tetralin 15 in concentrated sulfuric acid gave the tetracyclic thioxanthones 17 and 18. Conversion of 18 to 24 by demethylation and realkylation followed by oxidation and acid hydrolysis gave the title compound 27.
The sulfohaloform reaction revisited and revised
Authors: Baum James Clayton , Hardstaff William Rayne , Langler Richard Francis , Makkinje Anthony
Published: May 2006

A study of the aqueous chlorinolyses of a series of benzylic dithioacetals along with related α-chlorobenzylic sulfides is reported. These results require a modification of our previously proposed sulfohaloform reaction, so that thionium ion intermediates which have at least one alkyl group on sp2 carbon follow a different pathway.
Carbon atom insertion bicycloannulation: total syntheses of ishwarane and ishwarone
Authors: Cory Robert M. , Burton Lester P. J. , Chan Dominic M. T. , McLaren Fred R. , Rastall Mary H. , Renneboog Richard M.
Published: May 2006

Insertion of a carbon atom into a methyl cyclohexene, leading in a single synthetic step to a bicyclo[3.2.1.02.7]octane by carbene addition to the double bond and carbene insertion into a methyl C—H bond, has been accomplished by treating the cyclohexene with carbon tetrabromide and methyllithium at low temperatures. This new bicycloannulation method has been employed in a total synthesis of ishwarane (1), the naturally occurring parent hydrocarbon of the ishwarane class of tetracyclic sesquiterpenes. Although this reaction was not successful with various possible precursors of ishwarone (2), this natural product was prepared in low yield by a two-step version of the carbon atom insertion bicycloannulation (CAIB) procedure involving addition of bromoform-derived dibromocarbene to the octalone (5) followed by treatment of the resulting dibromocyclopropane (56) with methyllithium. The same two-step sequence was also successful in the first synthesis of norishwarane (20), the hydrocarbon comprising the bare ring system of the ishwarane sesquiterpenoids. The Diels–Alder synthesis used in the preparation of the octalin precursor (18) of norishwarane could not be used for the terpenes themselves because of the lack of dienophilic reactivity of the required cyclohexenone (7). A regioselective Diels–Alder equivalent sequence was therefore developed, consisting of conjugate addition of lithium di(3-methyl-3-butenyl)cuprate (42) to 2,3,4-trimethylcyclohex-2-en-1-one (7), epoxidation, base-catalyzed cyclization of the resulting epoxide (47) to a mixture of primary and tertiary alcohols (50 and 49, respectively), and dehydration of 49 to give 5. In the case of ishwarane, the octalin precursor (62) was synthesized by conjugate addition of lithium dimethylcuprate to octalone 59, addition of methyl magnesium bromide to the resulting decalone (60) to give octalol 61, and dehydration.
The dependence of the rates of reduction of cobalt(III)-μ-peroxo complexes on isomeric structure
Authors: Au-Yeung Steve C. F. , Eaton Donald R.
Published: May 2006

The reaction of μ-peroxybis(ethylenediamine)bis(diethylenetriamine)cobalt(III) with ferrous ions has been studied by stopped flow spectrophotometry and by 59Co nmr. Two separate initial reduction steps with second order rate constants of 1.07 and 3.04 M−1 s−1, respectively, can be discerned in the stopped flow experiments. These two rate constants are assigned to inner sphere reduction of the aef,cd,b and edf,ac,b isomers of the peroxy cobalt complex, respectively. The different isomers can be distinguished by 59Co nmr. If there is insufficient Fe2+ present to completely reduce the complex to Co(II) and water, the change in the relative intensities of the 59Co resonances after partial reduction shows that one isomer has reacted faster than the other. The 59Co resonances can be assigned to the different isomers on the basis of a point charge model for the chemical shifts and line widths. Based on this model it is concluded that the isomer with the central NH of the diethylenetriamine trans to the peroxy ligand reacts faster. This result is compared to literature reports on the relative rates of substitution of isomers of Co(III) complexes with ethylenediamine and diethylenetriamine ligands.
Les liaisons phosphore-azote via l'étude cristalline et moléculaire d'un iminodiazaphospholane
Authors: Marre Marie-Rose , Sanchez Michel , Wolf Robert , Jaud Joël , Galy Jean
Published: May 2006

Iminodiazophospholane 1 was obtained as monoclinic crystals, space group P21/c with a = 10.243(9), b = 17.236(5), c = 11.992(9) Å, and Z = 4. The structure was determined by single-crystal X-ray diffraction and was refined up to R = 0.056[Formula: see text]for 1342 reflections. The geometry of the molecule is that of a distorted tetrahedron with [Formula: see text] angles varying from 91.8° (ring angle) to 121.7° for [Formula: see text]. The diazophospholane ring has an envelope conformation where one of the 2 carbon atoms is at the tip. The three tricoordinated nitrogen atoms have a planar structure; the lone pairs on the two ring nitrogens have parallel orientation and both are orthogonal to the lone pair of the exocyclic nitrogen atom (N7). The P—N bond lengths are relatively short, falling between 1.620 Å and 1.669 Å, while the P2=N6 bond of 1.539 Å is among the smallest values ever reported. The multiplicities of the P—N bonds were assigned on the basis of an empirical method: 0.10 for the two cyclic P—N, 0.25 for the exocyclic P—N, and 0.60 for [Formula: see text] [Journal translation]
Thermostable sites of palladium phthalocyanine in Shpol'skii matrices of mixed solvents
Authors: Chen Wen-Hsiung , Rieckhoff Klaus E. , Voigt Eva-Maria
Published: May 2006

A study was made of the effects of three different mixed solvent Shpol'skii matrices at 4.2 K on site formation and on vibronic progressions of palladium phthalocyanine. It is found that only a limited number of thermostable sites are formed and these sites are common to all three matrices, but vary in their statistical weights. However, in all solvents the statistical weights of the first few most important sites are similar, with the predominant site at least eight or nine times stronger than the next. As well, the vibrational features of both the ground state and the first excited states of a few of the most populated sites examined are practically the same for the different mixed solvents. The absence of any significant differences in site splitting implies the absence of any dipolar interaction effects on these splittings.The above findings provide a better insight into the interaction between phthalocyanine, intermediate solvent, and basic solvent (n-octane) in the three-component solutions and give a clear guideline for choosing convenient solvents and for using Shpol'skii matrices as a simple effective mechanism for producing quasi-line vibronic spectra of phthalocyanines and other related large molecules insoluble in the alkanes.
A vectorial model of photon–molecule interactions and the development of an Octupole Rule of vibrational excitation
Authors: Hollebone B. R.
Published: May 2006

An alternative approach to the assignment of molecular vibrations is suggested in which both the molecule and the photon are taken as coincident quantum mechanical entities at the instant of impulse. This model permits the description of the excitation in a simple vectorial form. Using subduction techniques, complete and orthonormal basis vectors for both particles can be defined and the probabilities of excitation are directly related to the overlap of these basis vectors at the instant of space and time coincidence. The model obeys fully the requirements of the 3n – 6 degrees of freedom rule and is found to express the motions of atoms in terms of their overlap with available multipole fields of the photon. To first order the photon–molecule interaction is taken as the Coulomb potential between the electric fields of the photon and those of the shielded atomic nuclei. The relatively low valence electron density is ignored but becomes important in second order. With this assumption, molecular translational motion correlates to, and exhausts, the dipolar photon field, rotation corresponds to three of the five components of the photon quadrupole and ungerade internal modes are first permitted by overlap with the photon octupole. Some of the consequences of this Octupole Rule are discussed with particular reference to octahedral molecules from which molecules of lower symmetry can be algebraically subduced.
Stability constants and spectral studies of complexes of 2-hydroxy-5-methylazobenzene-2′-carboxylic acid with some divalent metal ions
Authors: Mahalingam C. , Sthapak J. K. , Sharma D. D. , Tiwari R. L. , Sthapak Smita
Published: May 2006

The stability constants of metal complexes of 2-hydroxy-5-methylazobenzene-2′-carboxylic acid have been determined spectrophotometrically. These follow the Irving–Williams sequence: log KOH(H) = 10.67, log K1(Co) = 9.02, log K1(Ni) = 9.68, log K1(Cu) = 13.37, log K1(Zn) = 7.58, and [Formula: see text]The chelates of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and [Formula: see text] with the dye have been prepared and characterized on the basis of their ir and reflectance spectra.
Etude vibrationnelle des associations ioniques dans les solvants aprotiques. 7. Solvatation de (LiNCS)p par les solvants peu polaires
Authors: Chabanel Martial , Wang Zhenglie
Published: May 2006

Solutions of LiSCN in donor solvent – benzene mixtures have been investigated by solubility measurements and by infrared spectrometry. The state of aggregation of LiSCN has been obtained from the ir spectra in the ν(CN) region 2100–2000 cm−1. The selected solvents (tetrahydrofuran, pyridine, acetone, diethylcarbonate, butylacetate, ethylmethylketone) are more or less associating towards LiSCN. The addition of benzene causes an increase of the associating ability of the solvents. By changing the donor solvent and the amount of benzene it has been possible to obtain the ion pair LiNCS, the dimer (LiNCS)2, and higher aggregates in various proportions. The solvation number of lithium has been measured in solvent vibration regions. Each step of aggregation is accompanied by lithium desolvation. The coordination of lithium in all the species which are formed remains equal to 4, or slightly lower in some cases.
Electron transfer from anthracenes. Comparison of photoionization, charge-transfer excitation and electrochemical oxidation
Authors: Masnovi J. M. , Seddon E. A. , Kochi J. K.
Published: May 2006

Quantitative measures of electron detachment from anthracene and various meso-substituted derivatives (D) are examined in the gas phase and in solution. The photoelectron spectra show well-resolved bands for E1 corresponding to the first ionization [Formula: see text] from a π-molecular orbital (HOMO) with maximum electron density at the 9,10-positions. The same series of anthracenes form 1:1 electron donor–acceptor complexes with tetracyanoethylene [D,TCNE], which exhibit distinctive colors associated with charge transfer transitions hvCT to the ion pair[Formula: see text]. These measures of the gas phase energetics of electron transfer from the anthracenes are compared with their standard oxidation potentials [Formula: see text] determined from the reversible cyclic voltammograms in methylene chloride and trifluoroacetic acid solutions. Although there are direct, linear free energy relationships between E1and hvCT as well as E1and [Formula: see text], the best correlation is observed between [Formula: see text] and hvCT. The validity of the latter is discussed in terms of offsetting effects arising from differences in solvation energy and steric effects attendant upon 9,10-substitution in anthracenes.
Amino derivatives of anhydrotetracycline
Authors: Menachery Mary D. , Cava Michael P.
Published: May 2006

Nitrosation of anhydrotetracycline (5) affords 9-nitrosoanhydrotetracycline (6), which is converted by sodium dithionite into 9-aminoanhydrotetracycline (7). Alkaline coupling of anhydrotetracycline with diazotized sulfanilic acid gives an azo dye which is reduced by sodium dithionite to give 7-aminoanhydrotetracycline (9). Reductive methylation of amines 7 and 9 with formaldehyde and sodium cyanoborohydride yields 9-dimethylaminoanhydrotetracycline (8) and 7-dimethylaminoanhydrotetracycline (10), respectively.
Adriamycin analogues. Synthesis of the α and β anomers of 7-O-(3-amino-3,5-dideoxy-D-ribofuranosyl)adriamycinone and some related compounds
Authors: Kumar Narendra , Israel Mervyn
Published: May 2006

2-O-Acetyl-3,5-dideoxy-3-trifluoracetamido-D-ribofuranosyl bromide, prepared by an improved 10-step synthesis from 1,2-isopropylidene-D-xylofuranose, was coupled under Koenigs–Knorr glycosidation conditions with a side-chain protected aglycone derivative of the antitumor antibiotic adriamycin. Complete removal of the blocking groups from the anomeric coupling products afforded glycoside ring-contracted analogs of adriamycin. Selective removal of blocking groups resulted in analogs of N-trifluoroacetyladriamycin-14-valerate (AD 32), an non-DNA binding analog of adriamycin with clinical activity and reduced toxicity. Anomeric assignment of coupling products was derived from nmr spectral data consistent with Karplus equation considerations. In vitro growth-inhibition and DNA binding assays were performed with a number of the target compounds. Of interest is the observation that, although binding to calf thymus DNA to a lesser extent than adriamycin, the isosteric 7-O-(3-amino-3,5-dideoxy-β-D-ribofuranosyl)adriamycinone produced a greater inhibition of growth of CCRF–CEM human-derived lymphoblastic leukemic cells in culture.
A nuclear magnetic resonance study of the formation and conformational equilibria of symmetrical and mixed disulfides of captopril
Authors: Rabenstein Dallas L. , Theriault Yvon
Published: May 2006

The oxidation of captopril (CpSH, 1-(D-3-mercapto-2-methylpropanoyl)-1-proline) by glutathione disulfide (GSSG) via thiol/disulfide exchange to form, in the first step, CpSSG and GSH and, in the second step, CpSSCp and GSH, has been studied in aqueous solution by 1H nmr. Due to slow rotation around the amide bond(s) of CpSH and CpSSCp and of the captopril part of CpSSG, separate resonances are observed for the cis and trans conformations across these bonds. Conformational equilibrium constants were estimated as a function of pH for CpSH, CpSSCp, and CpSSG from the intensities of resonances for the cis and trans isomers. These equilibrium constants were used in the determination of equilibrium constants for the two steps in the oxidation of CpSH by GSSG. The results suggest that CpSH has a greater tendency to reduce disulfide bonds by thiol/disulfide exchange at physiological pH, and thus form mixed disulfides, than do the thiol groups in amino acids. Also, the conformational equilibrium constants indicate that, at physiological pH, approximately two thirds of the captopril, either free or in a disulfide form, has the trans conformation.
Molecular orbital calculations for dialuminum and disilicon hydrides and related systems
Authors: Baird N. Colin
Published: May 2006

Abinitio MO calculations for Si2H2 are reviewed and discussed in qualitative terms. New calculations are reported, by MNDO for Si2H2 and Si2H4, and using both MNDO and abinitio methods (including electron correlation at the MP2 level) for various possible structures for Al2H2 (3). As with the analogous silicon dihydride, a dibridged structure 3a is found to be superior to classical structures 3b, 3c, and 3d. MNDO calculations for derivatives of Al2H2 are reported. Finally, some implications of the calculations for the surface structures of partially-hydrogenated elemental aluminum and silicon are discussed.
Photogeneration of hydrogen peroxide in aqueous TiO2 dispersions
Authors: Harbour John R. , Tromp John , Hair Michael L.
Published: May 2006

Evidence is presented which demonstrates that titanium dioxide does in fact photogenerate H2O2 in the presence of the donor sodium formate. However, this H2O2 has only a transient existence in aqueous dispersions. This was confirmed by experiments in which H2O2 was injected into the dispersion. The reasons for the lability of H2O2 are discussed and possible mechanisms presented. Electron paramagnetic resonance experiments using spin traps reveal that photolysis of TiO2 dispersion generates •OH radicals in the donor-free case while •CO2 radicals are observed in the presence of formate. These results are also consistent with H2O2 generation.