bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of homogeneous and heterogeneous Lewis acids to catalyse the photoisomerizations of phenols
Authors: Chadda Satish K. , Childs Ronald F.
Published: May 2006

The reaction of methyl substituted phenols with CH2Cl2 solutions of Al2Br6, leads to the formation of two types of complexes. In both of these the aluminum is bound to the oxygen atom of the phenol but they differ in that the OH proton can either remain on oxygen, oxonium complex, or migrate to one, usually the para, ring carbon, keto complex. The equilibrium position between the two types of complex depends on the position of the methyl groups. Irradiation of a complex of the keto type leads initially to the formation of a complexed bicyclo[3.1.0]hexenone and subsequently to the formation of an isomeric complexed phenol. Only in the case of the tetramethylphenols is the yield of the bicyclic ketone high enough to warrant the use of this photoisomerization as a preparative procedure, although the technique can be used to isomerize a range of phenols to their 4-substituted isomers. The photoisomerizations are not restricted to the use of a homogeneous Lewis acid such as Al2Br6 but heterogeneous aluminosilicates can also be used. The adsorption of 2,3,5,6-tetramethylphenol,1h, on an aluminosilicate was monitored quantitatively and it was shown that a monolayer was formed in which the phenol was at least partially present in the keto form. Irradiation of 1h in the presence of stirred slurries of the aluminosilicate led to the formation of 2,3,4,6-tetramethylphenol. No bicyclic ketones were present in the contacting solution but traces were detected on the catalyst when the irradiations were carried out on adsorbed material in the absence of a solvent. In the case of heterogeneous acids, the selectivity in the adsorption of the starting phenol and the photoproducts is important in determining the composition of the final mixture
The electrochemical oxidation of 2,5-dihydroxybenzoic acid on a mercury electrode in aqueous solutions
Authors: Sazou D. , Papadopoulos N.
Published: May 2006

The electrochemical behaviour of 2,5-dihydroxybenzoic acid (2,5-DHBA) has been studied in the pH range 5.5–12.7 at a hanging mercury drop electrode (HMDE). Voltammograms show the existence of one reversible wave of 2,5-DHBA governed by diffusion conditions. In the oxidation process a two-electron transfer takes place, as shown by the controlled potential electrolysis. From the calculation of the voltammetric parameters (peak width Ep − Ep/2, peak current function [Formula: see text]and from the other experimental data, a mechanism for the overall reaction in two different pH ranges, 5.5–9.5 and 9.5–12, is proposed.
Étude des Hernandiacées. XII. Dimères aporphine–benzylisoquinoléine originaux isolés de Hernandiapeltata
Authors: Chalandre M. C. , Bruneton J. , Cabalion P. , Guinaudeau H.
Published: May 2006

The bark of Hernandiapeltata Meissner (Hernandiaceae) has yielded four new dimeric alkaloids, namely (+)-6-northalicarpine 6, (+)-thalicarpine 2′-N-oxide 10, (+)-hebridamine 11, and (+)-vilaportine 12. Hebridamine is the first example of a benzylisoquinoline-phenanthrene dimer and (+)-vilaportine is a dimer with an oxoaporphinium zwitterionic moiety. The 6a,7-dehydrothalmelatine 9, previously known as a synthetic compound, has been isolated from a natural source for the first time. The possibility of a biogenetic relationship between (+)-vanuatine and (+)-thalicarpine 7 is considered.
Ion/molecule reactions in allene. III. Reactions of the parent ion with neutral alkanes
Authors: Nagase Kenzo , Herman Jan A.
Published: May 2006

Ion/molecule reactions between the ion C3H4+• ion, from allene and neutral alkanes were investigated by mass spectrometry. There are four H•/CH3•/H−/H2− transfer reactions and relative rate constants were calculated. The overall rates increased in the order CH4 < C2H6 < C3H8 < i-C4H10 < n-C4H10. There is also a stabilization process by alkanes of CeH8+• ion species, but its importance is lower than the above transfer processes.
Reactions of 1-hydroxy-1,3-dihydrobenzo[c]thiophen-2,2-dioxides. Preparation of benz-fused δ-sultines
Authors: Durst Tony , Charlton James L. , Mount David B.
Published: May 2006

4,5-Benzo-3,6-dihydro-1,2-oxathiin-2-oxides (benz-fused δ-sultines) 1, were prepared by reaction of 1-hydroxy-1,3-dihydrobenzo[c]thiophen-2,2-dioxides 6 with NaBH4. Derivatives of 1 bearing alkyl substituents at position 6 are accessible from 1 upon reaction of 6 with 2RLi. 3-Aryl substituted derivatives were prepared by converting 2-benzylbenzylalcohols into their O, C dianion followed by quenching with SO2 and acidification. Benz-fused δ-sultines such as 15–17 were also prepared via the dianion route.
Partial molal volumes of amines in benzene. Specific interactions
Authors: Barbosa Ester F. G. , Lampreia Isabel M. S.
Published: May 2006

Apparent molal volumes, [Formula: see text], of secondary and tertiary amines and linear hydrocarbons were determined in benzene at 25 °C, using a vibrating tube densimeter. These quantities have been extrapolated to infinite dilution to obtain partial molal volumes. The contribution to partial molal volume of the amine groups, calculated using a simple additive scheme, [Formula: see text], were interpreted in terms of conformational effects present in these molecules. A first attempt to find a measure of the contribution to the partial molal volume of the specific interaction amine–benzene in tertiary and secondary amines was made. The results agree well in the two different approaches used.
A bonded polyoxyethylene phase for gas and liquid chromatography
Authors: Wickramanayake Palitha P. , Aue Walter A.
Published: May 2006

Bonded phases were produced by reacting 2,4,7,9-tetramethyl-5-decyne-4,7-bis(polyethyleneoxide 30 mol) ether (Surf[Formula: see text]nol® 485) with silicic supports of high and low surface area. There is circumstantial evidence (a) that the nonextractable layer is held by multiple hydrogen bonding and (b) that the synthesis of these packings involves a reaction at the crosslinking site of the surfactant. The bonded phases, with layer thicknesses between 10 and 30 Å, were tested with three chromatographic techniques. In gas–solid chromatography, the phase proved well deactivated and yielded a reduced plate height of 2.5 (using a silica gel support). In gel permeation chromatography, polyethyleneglycols eluted within the mobile-phase volume. In liquid–solid (normal-phase adsorption) chromatography, the elution pattern differed significantly from that of unmodified silica gel. In each case, high-efficiency separations were obtained. The chromatographic experiments thus demonstrated the potential usefulness of the new phase for both gas and liquid chromatography. However, it was not tested in direct comparison with conventional phases nor was its utility established by subjecting it to routine analytical use.
Intrazeolite photochemistry. IV. Studies of carbonyl photochemistry on the hydrophobic zeolite Silicalite using time-resolved diffuse reflectance techniques
Authors: Wilkinson F. , Willsher C. J. , Casal H. L. , Johnston Linda J. , Scaiano J. C.
Published: May 2006

Transient absorption and luminescence from aromatic ketone triplets (xanthone, acetophenone, butyrophenone, valerophenone, p-methoxyacetophenone, β-phenyl-p-methoxypropiophenone and benzil) supported on the hydrophobic zeolite Silicalite have been obtained by time-resolved diffuse reflectance laser flash photolysis. These experiments were aimed at establishing the usefulness of this technique for studies of zeolite supported photoreactions. While the transient spectral properties can be used to examine the properties of the supporting media, the decays of the signals frequently follow complex kinetic behaviour. The decays for such heterogeneous systems cannot be easily fit to clean first or second order kinetics and are thought to be a mixture of several first order decays arising from triplets in different inclusion and adsorption sites. Evidence is presented for close-packing of the aromatic substrates and for triplet lifetime enhancement. Although the triplet spectrum of included benzil shows evidence for considerable axial freedom, the results for β-phenylpropiophenones indicate that other types of motion are restricted for included ketones. It is also found that the rate of the Norrish Type II reactions of valerophenone and butyrophenone supported on Silicalite are decreased with respect to the rates in solution.
Synthesis of (±)-karahana ether and a (±)-labdadienoic acid by the electrophilic cyclization of epoxy allylsilanes
Authors: Armstrong Rosemary J. , Weiler Larry
Published: May 2006

The epoxy allysilanes 7 and 16 were synthesized by stereoselective routes from β-keto esters and cyclized with Lewis acids in good yield. The monocyclic product from 7 was converted into (±)-karahana ether (10), and the bicyclic product from 20 was used in a synthesis of the 3-hydroxylabdadienoic acid 24b.[Formula: see text]
Excess thermodynamic properties of tetraalkyltin compounds with Trans-decalin and highly branched alkanes. Effect of steric hindrance
Authors: Phuong-Nguyen Hong , Delmas Geneviève
Published: May 2006

Molar excess thermodynamic quantities hE, [Formula: see text], and vE have been measured at 25 °C over the whole composition range for mixtures of four globular Sn(CnH2n+1)4 (SnR4) (n = 1–4) with t-decalin, and 2,2,4,4,6,8,8-heptamethylnonane (br-C16) as well as hE for the same SnR4 compounds with 2,2,4-trimethylpentane (br-C8). The excess viscosities are measured at −20, 25, and 40 °C for the t-decalin + SnR4 systems. By introducing gE in the solution activation energy, the free energy of mixing can be related to and calculated from the excess viscosities. The steric hindrance contribution, corresponding to an increase of order or diminution of mobility in solution, known to occur either with compounds having highly substituted atoms or with flat-shaped molecules, was investigated. The free volume contribution to the different thermodynamic properties is calculated from the Prigogine–Patterson–Flory theory. The difference between the experimental and calculated excess data is associated with the steric hindrance contribution. Values of hE, [Formula: see text], vE, and sE confirm the existence of a large steric hindrance contribution (hE < −200 J mol−1 and TsE < −400 J mol−1 for two systems). Another contribution, found to occur for the two smaller globular SnR4, may originate in the liberation of movement induced in solution by the second component.
A fast atom bombardment mass spectrometry study of H-bonded complexes of imidazole with various electron donors
Authors: Brown Stephen J. , Miller Jack M. , Theberge Roger , Clark James H.
Published: May 2006

Fast Atom Bombardment mass spectrometry is shown to be a useful tool in the investigation of strongly hydrogen bonded complexes of imidazole with various electron donors.
Dipole interactions in models of the dense part of the electrical double layer
Authors: Nikitas Panaghiotis
Published: May 2006

Since Monte-Carlo studies on freely oriented dipoles suggest that at zero external field the dipoles are oriented preferentially in-plane in ordered configurations, an attempt is made here to incorporate dipole in-plane interactions in the multi-state model of the inner layer. It is found that the predictions of the model become unsatisfactory as ordered structures are taken into consideration. Polarization catastrophe and concentration dependent adsorption maxima are the main problems. Analysis of the polarization behaviour of the inner layer at the adsorption maximum of an adsorbate suggests that in aqueous interfaces and possibly in other real interfaces the dipole in-plane interactions should be quite weak. This is attributed to rotational barriers leading to an almost random distribution of the dipoles in the monolayer.
Synthèses, réactivité et études structurales en série thiophéno[b]homotroponique
Authors: Hanquet Bernard , Guilard Roger
Published: May 2006

Thiopheno[b]mono and bishomotropones are readily synthesized from thiopheno[b]tropones and dimethyloxosulfonium methylide. The position, the nature of the seven-membered ring substituents, and the reaction medium are the most important parameters of the cyclopropanation reaction. The structure of the monohomotropones is established by comparison with deuteriated analogues. The cis or trans configuration of the bishomotropones is determined by nmr data analysis of the corresponding alcohols. Clemmensen reduction leads to cycloocta or cyclonona[b]thiophenones. The structure of the latter is proved by 2D nmr.
A study of chromium-exchanged zeolites as potential catalysts for thermolysis of water
Authors: Miedzinska K. M. , Hollebone B. R.
Published: May 2006

Evidence was found that the Cr(III)/Cr(II) redox cycle previously described to occur upon dehydration and rehydration of exchanged zeolite 13X, does not occur reversibly. Data suggest dimerization of the metal ion at high levels of exchange. The bridging provideu by the oxygen atoms of the lattice probably stabilize these dimers and lead to initial but irreversible reduction at very low temperatures. Evidence also indicates irreversible formation of new lattices at very high dehydration temperatures.
Complexes of hybrid ligands. Comparative studies on two cationic Pt2+ complexes of a fluorinated alkoxy-thioether ligand: solid-state structures and evidence for coupled ring-thioether inversion in solution
Authors: Boeré René T. , Payne Nicholas C. , Willis Christopher J.
Published: May 2006

Complete structural determinations are reported for two cationic platinum(II) complexes of the chelating, hybrid, alkoxythioether ligand CH3SCH2O(CF3)2O− with phosphine coligands and BF4− counterions. Complex 1, [Pt(PPh3)2{CH3SCH2C(CF3)2O}]BF4, C42H37BCl2F10OP2PtS (CH2Cl2 solvate) is monoclinic, space groupP21/c, with a = 12.2534(9), b = 18.584(2), c = 19.612(3) Å, β = 97.36(1)°, V = 4466(1) Å3, Z = 4. Complex 2, [Pt(PPh2Me)2{CH3SCH2C(CF3)2O}]BF4, C31H31BF10OP2PtS, is orthorhombic, space group Pna21, with a = 23.093(4), b = 11.362(3), c = 12.880(2) Å, V = 3379(2) Å3, Z = 4. The structures show the five-membered chelate ring to have similar conformations in the two complexes, the CH3S and axial CF3 groups being in an anti conformation.The structural results are discussed in relation to previous nmr studies on these and related complexes. It is concluded that an anisotropic shielding effect on the CH3S and CF3 resonances is present in both complexes, but that it is significantly greater in 1, where PPh3 is the coligand, and anomalies in the 19F nmr spectra are explained on this basis. A careful consideration of the nmr data, in light of the crystal structures, demonstrates the persistence of preferred chelate ring conformations in solution. Thioether inversion induces ring inversion in these complexes.
Convenient synthesis, X-ray crystal structure, and Raman spectrum of the heptasulphide dianion, S72−, in [PPN]2S7•2EtOH
Authors: Chivers Tristram , Edelmann Frank , Richardson John F. , Schmidt Kenneth J.
Published: May 2006

The S72− ion is readily prepared in high yield by the reaction of [PPN]SH with cyclo-S8 in ethanol. The crystal and molecular structures of [PPN]2S7•2EtOH have been determined by X-ray crystallography. The crystals are monoclinic and belong to the space group P21, a = 13.199(2), b = 19.414(2), c = 14.046(2) Å, β = 94.027(6)°, V = 3590.3(7) Å3, Z = 2. The final R and Rw values were 0.064 and 0.060, respectively. The S72− ion is an unbranched chain of sulphur atoms in the cis,trans,cis-configuration with torsion angles of 89.99(18), 71.84(16), 76.54(16), and 94.19(18)°. The S—S distances (in Å) become progressively smaller in the sequence d(S—S central) [2.072(3) and 2.070(3)] > d(S—S internal) [2.050(2) and 2.037(3)] > d(S—S) terminal [2.044(3) and 2.026(4)]. The Raman spectrum of the S72− ion in [PPN]2S7•2EtOH exhibits characteristic S—S stretching vibrations at 503, 453, 419, and 395 cm−1.
Synthesis of 6-alkynylated uridines
Authors: Tanaka Hiromichi , Haraguchi Kazuhiro , Koizumi Yachiyo , Fukui Mariko , Miyasaka Tadashi
Published: May 2006

6-Alkynylated uridines, a hitherto unknown class of compounds, were synthesized by a coupling reaction of terminal alkynes with 6-iodo-2′,3′-O-isopropylidene-5′-O-methoxymethyluridine in the presence of bis(triphenylphosphine)palladium(II) chloride and copper(I) iodide. 6-Ethynyl-2′-deoxyuridine was also prepared by using 6-iodo-3′,5′-O-(tetraisopropyldisiloxan-1,3-diyl)-2′-deoxyuridine as a starting material.
Kinetic solvent effects on acid-catalyzed hydrolysis of sucrose in aqueous mixtures of some protic, aprotic, and dipolar aprotic solvents
Authors: Mandal Urmila , Das Kaushik , Kundu Kiron Kumar
Published: May 2006

Rate constants of acid-catalyzed hydrolysis of sucrose (S) to D-glucose and L-fructose have been determined at 25 °C by optical rotation measurements in aqueous mixtures of protophobic protic glycerol (GL), protophilic protic urea (UH), aprotic dioxane (D), and dipolar aprotic dimethyl sulphoxide (DMSO). Transfer free energies of the substrate sucrose, [Formula: see text] have also been determined in the solvents from solubility measurements. These values as well as those of H+, as obtained earlier by use of the widely used tetraphenylarsonium tetraphenylboron (TATB) reference electrolyte assumption, yielded transfer free energies of the transition state. The observed log (ks/kw) – composition profiles reveal that the rates increase monotonically in GL–water mixtures, that decrease more or less monotonically in UH– and DMSO–water mixtures, and decrease up to 10 mol% D in D–water mixtures, beyond which the values tend to increase. Examination of [Formula: see text]–composition profiles for the different species in each case indicates that the initial and transition state solvation get more or less compensated and the observed rates are dictated by the increased solvation of H+ in aqueous UH, DMSO, and D co-solvent systems. But in GL–water mixtures the decreased solvation of the transition state compared with the initial state is overcome by the decreased solvation of H+, thus resulting in the gradual enhancement of the rates of the reaction. The observed linearity of the correlative plots of −δ(ΔG≠) [= RT ln (ks/kw)] vs. [Formula: see text] with distinctly different slopes in the two cases also substantiates the relative importance of H+ solvation in dictating the rates of the reaction in these widely different aqueous co-solvents.
The 2-mercapto-1-methylimidazolyl moiety as a bridging ligand in complexes of gallium, rhenium, and molybdenum
Authors: Cooper D. A. , Rettig S. J. , Storr A. , Trotter J.
Published: May 2006

The synthesis and characterization of complexes containing the 2-mercapto-1-methylimidazolyl ligand are described. [Formula: see text] occurs as a dimer, crystals of which are monoclinic, C2/c, a = 14.140(2), b = 7.4098(4), c = 18.024(2) Å, β = 106.38(1)°, Z = 4 dimers; the structure was determined by conventional heavy atom methods and refined by full-matrix least-squares techniques to a final R value of 0.039 for 1767 reflections. The crystal contains centrosymmetric dimeric molecules, with a central 8-membered ring, formed by mercaptoimidazolyl ligand bridging between dimethylgallium groups; galliumm has tetrahedral geometry, with no tendency to five-coordination, Ga—S = 2.3697(8), Ga—N = 2.019(2) Å. Reaction of [Formula: see text] L−, with [Re(CO)4Cl]2 results in the formation of LRe(CO)3, whose physical properties indicate a fac arrangement of the organogallate ligand. Attempts to synthesize corresponding LMo(η3-C4H7)(CO)2 and LMo(η3-C3H5)(CO)2 complexes yielded the dimeric species [Formula: see text] and [Formula: see text] Crystals of the [Formula: see text] complex are monoclinic, I2/a, a = 15.057(2), b = 9.4853(9), c = 18.240(2) Å, β = 108.67(1)°, Z = 4 dimers, R = 0.028 for 2363 reflexions. The structure contains dimeric molecules with C2 symmetry, and five fused rings, a central group of three 4-membered rings being formed by bonding of the S atoms of the ligands to both Mo atoms (in contrast to the gallium complex). The molecule has a U-shape, with Mo atoms having pseudo-octahedral environments, Mo—S = 2.6868(7), 2.5576(7), Mo—N = 2.253(2), Mo—CO = 1.950(2), Mo—C(allyl) = 2.259(3), 2.326(3) Å. Considerable strain in the chelate rings is indicated by angles as low as S—Mo—N = 63.9(1)°.
The demicellization temperature of potassium n-octanoate in deuterium oxide as estimated from 1H and 13C nuclear magnetic resonance spectra
Authors: Desando M. A. , Reeves L. W.
Published: May 2006

Measurements of the proton nmr peak positions and carbon-13 nmr chemical shifts as a function of concentration and of temperature estimate the demicellization temperature to be in the range ca. 115–227 °C for potassium n-octanoate in deuterium oxide at concentrations around the critical micelle concentration.
Viscosities of dilute aqueous suspensions of montmorillonite and kaolinite clays
Authors: Kasperski Kim L. , Hepler Charles T. , Hepler Loren G.
Published: May 2006

We have measured viscosities and densities of dilute aqueous suspensions of Na-kaolinite (25 °C), of Na-montmorillonite (25–55 °C), and of mixtures of Na-kaolinite/Na-montmorillonite (25 °C). Results of the measurements at 25 °C have been analyzed in terms of the Einstein equation with conclusions that are consistent with previous knowledge that colloidal particles of these clays are non-spherical and that montmorillonite is a swelling clay. Viscosities of mixed clay systems are nearly consistent with a simple additivity model; the small non-additivities are in accord with previous evidence that relatively small montmorillonite particles are adsorbed on the surface of relatively large kaolinite particles. The effect of temperature on the viscosities of suspensions of montmorillonite is consistent with the idea that aggregation of clay particles diminishes with increasing temperature.
High-performance liquid chromatography of some bis(ethylenediamine)cobalt(III) complexes
Authors: Abou-El-Wafa Moustafa H. M. , Mansour Hesham , Noubi G. A.
Published: May 2006

Chromatographic separation of the complexes cis- and trans-Co(en)2(S2O3)2−, cis- and trans-Co(en)2(SO3)2−, cis- and trans-Co(en)2Cl2+,cis-Co(en)2(N3)2+, cis-Co(en)2(SO3)(N3)0, Co(en)2(S2O3)(N3)0, and Co(en)2(S2O3)(OH2)+ (en = ethylenediamine) was carried out by high-performance liquid chromatography. Good separations were achieved on a μ-Bondapak C18 reversed-phase octadecyldimethylsilane (ODS) column using tributylmethylammonium cations and octylsulphonate anions. The efficiency and speed of the separations were superior to those obtained on a Partisil SCX ion exchange column.
Ring inversion in solid fluorocyclohexane
Authors: Wasylishen Roderick E.
Published: May 2006

Inversion of the cyclohexane ring system in the solid state has been directly observed in a 19F nmr study of solid fluorocyclohexane. The barrier to ring inversion in the orientationally disordered solid phase, ΔG≠e→a = 44.1 ± 0.9 kJ mol−1 at 263 K is found to be only slightly larger than the value previously reported for a CFCl3 solution of fluorocyclohexane. The population of the equatorial conformation is slightly favored over the axial conformation with K = Pe/Pa = 1.56 at 281 K; similar values have been obtained in CFCl3 and in the gas phase.
High-field proton and carbon-13 nuclear magnetic resonance studies of the conformational dynamic properties of seven-membered rings. 1,5-Benzodithiepin and 3-substituted derivatives
Authors: Ménard D. , St-Jacques M.
Published: May 2006

The conformational and dynamic properties of 1,5-benzodithiepin (1), its 3,3-dimethyl (2), 3-methyl (3), and 3-methoxy (4) derivatives have been investigated by high-field 1H and 13C dynamic nuclear magnetic resonance methods. Analyses of the spectra at low temperatures indicate that, in CS2, both 1 and 2 exist as a mixture of C and TB forms (97:3 for 1; 63:37 for 2). In contrast, both 3 and 4 exist as a mixture of three equilibrating conformations Ce, Ca, and TB in ratios of 55:25:20 and 88:8:4 respectively. Comparison with analogues derived from 1,5-benzodioxepins (1a–4a) indicates that the replacement of O by S decreases the amount of the TB form for all four compounds studied. The observation that Ce is the most abundant form for 4 while it is not observed for 4a can be explained by a repulsive S/O gauche interaction in 4 compared to an attractive O/O interaction in 4a.
The mechanisms of long-range 13C,19F and 19F,19F coupling constants in derivatives of biphenyl and fluorene. Differential isotope shifts
Authors: Schaefer Ted , Peeling James , Penner Glenn H.
Published: May 2006

13C,19F and 19F,19F nuclear spin–spin coupling constants over n formal bonds, n = 1–9, are reported for 4-fluorobiphenyl, 4,4′-difluorobiphenyl, 4,4′-difluoro-2,2′,6,6′-tetramethylbiphenyl, 2,7-difluorofluorene, 2-fluoro-9-fluorenone, and 2,7-difluoro-9-fluorenone in acetone solutions. The signs of many of the coupling constants are deduced from second-order spectral phenomena caused by differential 13C isotope effects on the I9F nmr chemical shifts. Theoretical potentials, based on geometry-optimized STO 3G MO computations for 4-fluorobiphenyl and 4,4′-difluorobiphenyl, yield expectation values for the torsion angles about the exocyclic C—C linkage that are very close to those deduced from electron diffraction patterns. These potentials and INDO MO FPT computations of the long-range coupling constants allow a discussion of the coupling mechanisms. In Hz, 9J(F,F) = 1.3(1) cos2 θ, where θ is zero for a planar biphenyl, while 8J(C,F) = 0.8(1) cos2 θ and 7J(C,F) = −0.43(5) cos2 θ. 6J(C,F) is a composite of σ–π and π electron coupling components and is written in Hz as 0.57(1) + 0.29(1) sin2 θ. The corresponding coupling constants in the fluorene and 9-fluorenone derivatives are enhanced in magnitude relative to a hypothetical planar biphenyl derivative. It is tentatively suggested that 5J(C,F) consists of three coupling components, one negative and proportional to cos2 θ, the other two positive and independent of θ. 4J(C,F) is suggested to consist of a σ component of −1.0 Hz and a π component proportional to the atom–atom polarizability for the parent hydrocarbon.
1H and 13C nuclear magnetic resonance and ultraviolet studies of the protonation of cytosine, uracil, thymine, and related compounds
Authors: Benoit Robert L. , Frechette Monique
Published: May 2006

The protonation of the three nucleic acid bases, cytosine, uracil, and thymine, and of related 4-amino-2,6-dimethylpyrimidine and 2-hydroxypyridine has been studied by 1H and 13C nuclear magnetic resonance and ultraviolet spectroscopies mostly in 0.18–18 M aqueous sulfuric acid. The experimental data have been interpreted on the basis of the excess acidity method. The pKn values as well as the assigned protonation sites are discussed and contrasted with other data.
Trijugins A and B, tetranortriterpenoids with a novel rearranged carbon skeleton from Heyneatrijuga (Meliaceae)
Authors: Purushothaman Kozhiparambil K. , Venkatanarasimhan Mathuram , Sarada Ayyappath , Connolly Joseph D. , Rycroft David S.
Published: May 2006

Two new tetranortriterpenoids, trijugins A (1) and B (3), isolated from the leaves of Heyneatrijuga (Meliaceae), have been shown to be derivatives of methyl angolensate but with a novel carbon skeleton having a contracted ring C. The structures were assigned on the basis of detailed 1H and 13C nuclear magnetic resonance spectroscopic examination including 2D long-range δC/δH correlation and homonuclear 1H nuclear Overhauser effect difference experiments.
Total synthesis of a proposed structure of isohimachalone
Authors: Liu Hsing-Jang , Browne Eric N. C.
Published: May 2006

A proposed structure 5 of the naturally occurring sesquiterpene ketone isohimachalone has been synthesized by a route using the unique Diels–Alder chemistry developed in our laboratory. The product has been shown to be non-identical with the natural material by comparison of spectral data, a result which has been implied by the work of an independent group using direct methods. Spectroscopic differences between our synthetic material and the natural and closely related products are discussed.
Assignment of the 1H and 13C spectra of aspidocarpine and assignment of the structure and stereochemistry of the von Braun reaction product of aspidocarpine by 2D nmr spectroscopy
Authors: McLean Stewart , Reynolds William F. , Zhu Xingpei
Published: May 2006

The 13C and 1H spectra of aspidocarpine and the spectra, structure, and stereochemistry of the product of its von Braun reaction with cyanogen bromide have been totally assigned by a combination of homonuclear (COSY-45) and direct and indirect heteronuclear shift-correlated 2D nmr spectra.
Haloselenate(IV) formation and selenous acid dissociation equilibria in hydrochloric and hydrofluoric acids
Authors: Milne John
Published: May 2006

Raman spectroscopy has shown that the initial stages of haloselenate(IV) formation equilibria are the same in HF and HC1 solutions.[Formula: see text]The constants K4 and K5, evaluated by quantitative Raman measurements, for HCl solutions are 0.015 (± 0.001) L2 mol−2 and 0.9 (± 0.1) × 10−5 L2 mol−2, respectively. These constants yield the minimum average deviation in normalized molar scattering intensity for the species formed in three regions of the spectra, 690 and 890 cm−1 (SeO stretching) and 100–450 cm−1 (deformation and SeCl stretching). Before the onset of haloselenate(IV) formation, changes in the SeO stretching band intensities with HX concentration occur due to repression of ionic dissociation of selenious acid[Formula: see text]Quantitative Raman measurements yield K1 = 9.8 (± 0.3) × 10−3 mol L−1. Reasons for the high value of this constant, compared to reported values, are discussed.
Isomérisation des radicaux insaturés. IV. Les radicaux méthyl-1-, méthyl-2- et diméthyl-1,2-propène-1 yles produits dans la photolyse des tri- et tétraméthyléthylènes à 147 nm
Authors: Collin Guy J. , Deslauriers Hélène , De Maré George R.
Published: May 2006

Direct photolysis at 147 nm of tri- and tetramethylethylenes has been used to produce highly excited vinylic 1-methyl- and 2-methyl-1-propene-1-yl radicals (C4H7), as well as the 1,2-dimethyl-1-propen-1-yl radical (C5H9). In both cases, the primary fragmentation of the photoexcited molecules involved the split of an α(C—C) bond with high yields. The excess esnergy is sufficiently important that the majority of the vinylic radicals are very hot, and are able to isomerize towards an allylic structure before the occurrence of fragmentation. At a pressure of a few Torr, most of the vinylic C4H7 radicals (ca. 70%) isomerize to an allylic structure, and its lifetime is estimated to be less than one nanosecond under the present conditions. Although the mechanism is less simple, the excited vinylic C5H9 radical exhibits similar behaviour.
An improved route to pregna-5,20-dien-3β-ol (muricin aglycone): Carbon and proton nuclear magnetic resonance assignments for the aglycone and a number of related pregnene derivatives
Authors: Dawe R. D. , Wright J. L. C.
Published: May 2006

Carbon and proton assignments for muricin aglycone (5) and a number of related pregnenes, carried out with the aid of two-dimensional homo- and heteronuclear chemical shift correlation experiments, have resulted in previously reported carbon assignments for the aglycone being revised. An improved route to muricin aglycone is also reported.
A nuclear magnetic resonance study of aqueous solutions of several nitrate salts
Authors: Nicholas A. Martin de P. , Wasylishen Roderick E.
Published: May 2006

Rotational correlation times for the end-over-end rotation of the C3 symmetry axis of the nitrate anion in the temperature range 3–80 °C are studied by nuclear magnetic resonance spectroscopy for a variety of nitrate salts in aqueous solution. The counterion is found to retard the rotation of the anion in the following order: Sc3+ > La3+ > Pb2+ > Ca2+, Sr2+ > Al3+, K+, Na+, (CH3)4N+ > Zn2+, Mg2+, Li+, NH4+, H3O+. This relative order is discussed in terms of the association of the nitrate ion with the cation. Oxygen-17 nmr spin-lattice relaxation times in combination with 14N nmr T1values are used to derive rotational diffusion constants for the in-plane rotations of the nitrate anion. In all cases the in-plane rotations are found to be slower than the corresponding end-over-end motion.
Surface photochemistry: Semiconductor mediated reactions of some 1,2-diarylcyclopropanes
Authors: Carson Philip A. , Mayo Paul de
Published: May 2006

1,2-Diphenylcyclopropane (1) was found to be oxidized on illuminated ZnO in the presence of air while 1-(p-methoxyphenyl)-2-phenylcyclopropane (2) and 1,2-bis(p-methoxyphenyl)cyclopropane (3) were found to be similarly oxidized on illuminated CdS. Compounds 2 and 3 were found, also, to undergo a rapid photochemical cis-trans isomerization on CdS whereas 1 did not undergo such isomerization. An electron transfer mechanism involving formation of the radical cations of the substrates is proposed.
The significance of the variability in analytical results for lead, copper, nickel, and zinc in street dust
Authors: Fergusson Jack E.
Published: May 2006

Street dust has frequently been used as a material for the monitoring of trace element pollution, and in particular for the metal lead. The value of the analytical data, as a measure of pollution, depends on understanding the spatial, temporal, and bulk characteristics of the dust. The influence of each of these factors on the variability of trace element analytical results has been investigated in order to determine whether or not the variations reflect differing pollution levels. The concentrations of the four metals Pb, Cu, Ni, and Zn have been measured in street dust collected from a variety of situations. Coefficients of variation > 20% (particularly for lead) for a series of samples have been taken as a guide to real differences in lead levels between samples in the series. An important factor in the variability of heavy metal levels in dust is the distribution of particle size within a sample. Concentrations of the trace metals fall and then rise as the particle size decreases from 1000 μm down to silt sized particles.
Alkylammonium lead halides. Part 1. Isolated PbI64− ions in (CH3NH3)4PbI6•2H2O
Authors: Vincent Beverly R. , Robertson Katherine N. , Cameron T. Stanley , Knop Osvald
Published: May 2006

The yellow (CH3NH3)4PbI6•2H2O(P21/n, a = 10.421(3) Å, b = 11.334(2) Å, c = 10.668(2) Å, β = 91.73(2)°, Z = 2) contains isolated PbI64− octahedra, CH3NH3+ cations of two types and H2O molecules. The cations and the water molecules are hydrogen-bonded to form [Formula: see text] units arranged in centrosymmtric [Formula: see text] pairs; the centres of these composite units and the Pb atoms form a distorted NaCl-type lattice. The Pb—I bond lengths in the PbI64− anions are compared with those in [Pb(II)I6]ε complexes containing shared I atoms and the effect of the sharing on the bond lengths is discussed. A scheme is proposed for the extensive three-dimensional hydrogen bonding in the structure.
Étude du comportement d'un alliage Cu–Ni 70:30 dans une solution de NaCl à 3% par la détermination de sa résistance de polarisation
Authors: Massiani Yvan , Petetin Sylvie , Ngoc Guy Ngo , Crousier Jean-Pierre
Published: May 2006

A galvanostatic method can be used to measure the evolution of the polarization resistance of a 70:30 copper–nickel alloy with time, in spite of the presence of a layer of corrosion products formed on the surface of the sample after a few days of immersion. At the beginning, the polarization resistance of the alloy is similar to that of copper; after many days, it evolves toward that of pure nickel.
Cyclopentadienyl complexes with transition metal – main group metal bonds. VII. 207Pb and 95Mo nuclear magnetic resonance studies on molybdenum and tungsten complexes [(η5-C5H5)(CO)3M]nPbR4−n (n = 1, R = Me, Et, Ph; n = 2, R = Ph)
Authors: Kubicki Marek M. , Gall Jean-Yves Le , Kergoat René , Gomes De Lima Luiz C.
Published: May 2006

Nuclear magnetic resonance measurements of metallic nuclei (δ 207Pb, δ 95Mo, and 1J(W–Pb)) have been carried out on dimetallic Cp(CO)3MPbR3 (M = Mo, W; R = Me, Et, Ph) and trimetallic [Cp(CO)3M]2PbPh2 (M = Mo, W) complexes. 207Pb chemical shifts increase in the sequence PbEt3 < PbMe3 < PbPh3 and are observed at higher fields in the tungsten compounds than in the molybdenum ones. It is suggested that both paramagnetic and diamagnetic contributions determine the overall shielding of lead, and that the higher field resonances of 207Pb in the case of W–Pb compounds are due to an efficacious operation of the Z/r dependent diamagnetic term (higher atomic number Z of tungsten and roughly the same Mo–Pb and W–Pb distances resulting from the 4f level induced lanthanide contraction). 95Mo chemical shifts (−1838 to −2007 ppm) lie in the region typical of the molybdenum – main group metal bonded complexes but at lower fields than in the corresponding Mo–Sn compounds. It is concluded from this observation that the Z/r dependent diamagnetic contribution does not operate efficaciously for 95Mo shieldings, which are hence primarily dominated by the paramagnetic term. The nature of metal–metal interactions is discussed.
Synthesis and structural characterization of glycinatodimethylgallium, (C2H4NO2)Ga(CH3)2
Authors: Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the preparation and crystal structure of the title compound are given. Crystals of glycinatodimethylgallium are monoclinic, a = 12.502(1), b = 12.023(1), c = 10.732(1) Å, β = 110.05(1)°, Z = 8, space group P21/c. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.039 for 1172 reflections with I ≥ 3σ(I). The structure consists of monomeric (C2H4NO2)GaMe2 molecules which are linked together by an extensive network of [Formula: see text] hydrogen bonds. The Ga atoms have tetrahedral coordination geometry with bond lengths averaged over the two crystallographically independent molecules: Ga—O = 1.958(18), Ga—N = 2.031(5), and Ga—C = 1.937(7) Å.
The synthesis and structure of
Authors: Butler Ian R. , Cullen William R. , Rettig Steven J.
Published: May 2006

The novel ferroceneophane [Formula: see text] 1c, is the product of the reaction of silicon tetrachloride with the dilithio derivative of N,N-dimethyl-α-ferrocenylethylamine. Crystals of 1c are monoclinic, space group C2/c, a = 15.275(2), b = 9.0869(4), c = 22.363(2) Å, β = 95.814(5)°, Z = 8, R = 0.037 for 2274 reflections. The tilt angle between the cyclopentadieneyl rings is 19.0(2)° and the bridge-head angle at silicon is 100.7(1)°. Other angles at silicon indicate some repulsive interaction with the CHMeNMe2 group. Silica rapidly reacts with 1c to give materials which have essentially the same Mössbauer spectra as the starting material. 1c reacts with methanol to give Fe(C5H3(CHMeNMe2)Si(OMe)3-1,2)(C5H5) and other products.
Keto ethers. IV. Products formed on reaction of dihydro-2,2,5,5-tetramethyl-3(2H)-furanone with strong acids
Authors: Yates Peter , Burke Patrick Michael
Published: May 2006

Reaction of tetrahydro-2,2,5,5-tetramethyl-3(2H)-furanone (1) with 96 or ca. 100% sulfuric acid or hot polyphosphoric acid followed by aqueous quenching gave the following products: 2-hydroxy-2,5-dimethyl-4-hexen-3-one (3), 2,4,4-trimethyl-2-cyclopenten-1-one (7), 3,5,5-trimethyl-2-cyclopenten-1-one (8), tetrahydro-3,4,5,5-tetramethylfuran-2,3-diol (11), 2,5-dihydro-3,5,5-trimethyl-2-methylenefuran (17) and its dimer 20, 2,5-dihydro-2,3,5,5-tetramethyl-2-furanol (18), 4-hydroxy-2,4-dimethyl-2-pentenoic acid γ-lactone (22), 2,3,5-trimethyl-2-cyclopenten-1-one (23), and tetramethylfuran (25). In 96% sulfuric acid the products arise by ring opening, ring opening followed by reclosure to carbocyclic products, methyl migration from C-2 to C-3 to give rearranged furan derivatives, and oxidation. In ca. 100% sulfuric acid or hot polyphosphoric acid further methyl migrations can occur to give 23 and 25.
Photooxygenation of nitrobenzyl derivatives. Mechanisms of photogeneration and hydrolysis of α-hydroperoxy nitrobenzyl ethers
Authors: Wan Peter , Muralidharan S. , McAuley Iain , Babbage Christopher A.
Published: May 2006

The photooxygenation of nitrobenzyl derivatives 1–10 has been studied in aqueous solution as a function of pH. For m-nitrobenzyl ethers 2–4 and 9, stable α-hydroperoxy ethers (11–13) are the primary photochemical products. Acid hydrolysis of 11–13 gives m-nitrobenzaldehyde and hydrogen peroxide. Quantum yields for photooxygenation are reported for a number of derivatives as a function of pH. Acid and base catalyses of photooxygenation are observed for several compounds. A mechanism involving photogenerated nitrobenzyl carbanion intermediates is proposed.
Synthesis of carbocycles from ω-substituted α,β-unsaturated esters via radical-induced cyclizations
Authors: Hanessian Stephen , Dhanoa Daljit S. , Beaulieu Pierre L.
Published: May 2006

The intramolecular radical cyclization of ω-bromo α,β-unsaturated esters for the synthesis of carbocyclic compounds is described. The effect of carbon chain substituents, the bulk of the ester group, and the olefin geometry were examined. The highest level of stereoselectivity (trans/cis: 9/1) was achieved with the Z ester via an exo cyclization. The sequential radical cyclization of a dihalodienoate to give a cis-fused bicyclic structure is also described.
Réactivité des α-halobutyrolactones à halogènes tertiaires vis-à-vis des nucléophiles faiblement basiques
Authors: Gharbi-Benarous Josyane , Essayegh Mounir M. , Dana Gilbert
Published: May 2006

2-Methyl-4-phenylbutenolide (5) is prepared in a quantitative manner by an elimination of HBr from the corresponding bromolactones 3. This reaction, induced by halide ions at 100 °C in polar aprotic solvents (DMF, DMSO), is accompanied by a bimolecular nucleophilic substitution. In these reactions, the solvent seems able to play an active role. A polar solvent induces the necessary activation of the substrate (by a prior strong polarization of the C—Br bond). In the absence of halide ions, a solvolytic reaction takes place. As soon as the elimination reaction produces enough halide ions, the bimolecular reaction takes over. The activation of the chlorolactones 4 is much more difficult than that of the bromolactones 3; however, each elimination is of the E2ip type with some E2C type. [Journal translation]
The hex-5-enose degradation: cleavage of glycosiduronic acid linkages in modified methylated Sterculia gums
Authors: Aspinall Gerald Oliver , Khondo Lev , Williams Bruce Alan
Published: May 2006

Reduction of uronic acid residues in permethylated polysaccharides from Sterculiaurens and S. caudata gums, followed by transformation of the resulting hexose into 6-deoxy-6-iodohexose residues, affords modified polysaccharides that undergo depolymerization on treatment with zinc dust. The main products after reduction with sodium borohydride are hexenitolterminated oligosaccharides. Their structures have been assigned as members of a series of O-[α-L-rhamnopyranosyl]-(1 → 3)-1,2-dideoxyhex-1-enitol derivatives, with and without attendant β-D-galactopyranosyl substituents, on the basis of nuclear magnetic resonance and mass spectral data and compositional analysis of trideuteriomethylated derivatives. The structures of the polysaccharides have been reassessed in the light of these and other experiments, and may now be formulated as containing a backbone of alternating 4-linked α-D-galacturonic acid and 2-linked α-L-rhamnopyranose residues bearing a minimum of three types of side chains attached at specific sites. Characterization of some of the degradation products provides evidence that limited degradation had occurred during methylation of the glycuronans.
Topsentins, new toxic bis-indole alkaloids from the marine sponge Topsentiagenitrix
Authors: Bartik Kristin , Braekman Jean-Claude , Daloze Désiré , Stoller Catherine , Huysecom Joëlle , Vandevyver Gysèle , Ottinger Robert
Published: May 2006

Three new bis-indole alkaloids, topsentin-A (1), -B1 (2), and -B2 (3) have been isolated from the Mediterranean sponge Topsentiagenitrix and their structure determined by spectroscopic methods. These compounds are weakly toxic for fish and for dissociated cells of the freshwater sponge Ephydatiafluviatilis and thus might be partially responsible for the chemical defense of the sponge.
Bicyclization of aza-compounds by positive halide ions. II. Lactams and some related cyclizations
Authors: Elofson Richard M. , Gadallah Fahmi F. , Laidler James K.
Published: May 2006

Anodic oxidation of lactams in the presence of halide ions produced excellent yields of bicyclic compounds with reactants having rings in the range of eight to ten atoms (C7 to C9). Smaller rings did not react to form bicyclic products and larger rings gave reduced yields. Attempts were made to cyclize non-cyclic amides and to bicyclize cycloheptyl and cyclooctyl acetamide with limited success.
Ion–ion–solvent interactions in aqueous ionic cosolvent systems. III. Thermodynamics of hydrogen bromide and hydrogen iodide from water to aqueous solutions of sodium nitrate from emf measurements at different temperatures and the structuredness of the solvents
Authors: Rudra Sibaprasad , Talukdar Himansu , Kundu Kiron K.
Published: May 2006

Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of hydrogen bromide and iodide from water to the aqueous 1, 2, and 4 m of sodium nitrate have been determined by measuring the emf's of the cell: Pt, H2(g, 1 atm)/KOH(m1), KX(m2), solvent/AgX–Ag where X = Br or I at five equidistant temperatures ranging from 15–35°C. [Formula: see text] values of HBr, HI as well as that of HCl obtained from earlier paper and particularly of the individual ions [Formula: see text](i), obtained by use of modified TATB assumption reported earlier and also [Formula: see text](i) obtained after correcting for "cavity" effect and Born-type electrostatic effect estimated tentatively by the scaled particle theory (SPT) and simple Bom equation, respectively, reveal the relative order of stabilisation of Cl−, Br−, and I− ions. Analysis of [Formula: see text]–composition profile (X = Cl, Br, and I) exhibits a characteristic "maxima" around 1.5 m NaNO3 with the relative order HI > HBr > HCl in the region of maxima. Moreover, dissection of [Formula: see text] values into the individual ion contributions by use of the modified TATB assumption reported earlier, results in the characteristic "maxima" around 1.5 m NaNO3 in [Formula: see text] or [Formula: see text]–composition profiles for H+ and "minima" for Cl−, Br−, and I−. The results are discussed in terms of ion–ion–solvent interactions as well as the structural changes of the solvents.
Reactions between Co(II) and bis(diphenylphosphino)methane in the presence of NaBH4 or NaBH3CN
Authors: Elliot David J. , Holah David G. , Hughes Alan N. , Maciaszek Stanislaw , Magnuson Vincent R. , Parker Kenneth O.
Published: May 2006

Reactions between Co(II) and bis(diphenylphosphino)methane (dppm) in the presence of NaBH4 or NaBH3CN are described. The main products are the Co(I) complex, CoCl(dppm)3, and Co(III) complexes of the type [CoHX(dppm)2]Y (where X = Cl, Y = Cl or BPh4; X = Y = Br; X = Y = I; X = BH3CN, Y = BH3CN, ClO4, or BPh4). The former has been shown by X-ray crystallography to contain a Co atom tetrahedrally coordinated by a Cl and three P atoms from three monodentate dppm ligands. Possible mechanisms for the formation of Co(III) are discussed.