bluuebunny/crossref_metadata_2025 huggingface dataset:
On catalyzed additions of trans-piperylene to 2-cyclohexenones. A short route to potential precursors of eremophilane sesquiterpenoids
Authors: Das Jagabandhu , Kakushima Masatoshi , Valenta Zdenek , Jankowski Krzysztof , Luce Rhéal
Published: May 2006

A chemical correlation is described by which the two adducts resulting from a catalyzed addition of trans-piperylene to 2-methyl-2-cyclohexenone, 7 and 8, are proven to be stereoisomers. Various reaction conditions for the addition of trans-piperylene to 2-cyclohexenone are also summarized.
Structure determination of the hexosulose dimers
Authors: Ruiz Pedro Antonio García , Travesedo Inmaculada Cartagena , Martínez Antonio Soler
Published: May 2006

The structure determination of the dimers of three hexosuloses has been achieved by mass spectrometry of their acetates and trimethylsilyl derivatives. The analysis of the mass spectra and the chemical evidence for the claim that the dimers are 1,2′:2,1′-di-hexosulofuranose dianhydrides have been reported.
Effects of solvents on a model of rhodopsin consisting of a conjugated imine and substituted acetic acids
Authors: Bissonnette Martine , Thanh Hoa Le , Vocelle Daniel
Published: May 2006

A model system of rhodopsin consisting of a dienylidene Schiff base and different halogeno acids has been studied in two solvents, chloroform and methanol, by uv and 400-MHz nmr spectroscopies. The uv results indicate that in chloroform, a nonpolar solvent, monohalogenoacetic acids can protonate the Schiff base only partially, while nmr data show that the aldimine hydrogen is slightly affected by acids and that the acidic proton is moving rapidly between the donor and the acceptor. In methanol, data indicate a leveling effect. In relation with rhodopsin, our results imply that, depending on the environment surrounding the chromophore, the state of protonation of the Schiff base could be strongly affected. Finally, our model shows experimental evidence that Nakanishi's external point charge could be operating in visual pigments.
Thermolysis of gem-dimethyl-2-cyclohexenones. Evidence for [1,5] sigmatropic methyl shifts
Authors: Lange G. L. , Nye M. J. , Pereira V. A. , Stratton V. , Yurkevich T.
Published: May 2006

The vapour phase thermolyses at 400 °C of three gem-dimethylated 2-cyclohexenones 1, 2, and 3 were studied to determine the effect of blocking the direct conversion of these substrates to aromatic systems. In all three reactions it is proposed the major pathway taken was enolization followed by elimination of methane to yield a substituted phenol. This elimination reaction proceeded more readily with 2 than with either 1 or 3, and HMO calculations which are consistent with this order of reactivity are presented. A general mechanistic scheme is proposed to account for the products formed and it is necessary to include a [1,5] sigmatropic methyl shift to explain the formation of at least one product in each thermolysis.
Condensation inhabituelle d'un pyrrole et d'un benzaldéhyde encombré
Authors: Lecas-Nawrocka Alexandra , Levisalles Jacques , Mariacher Claire , Rose Eric
Published: May 2006

The condensation between 2,6-dinitrobenzaldehyde and a pyrrole does not afford a dipyrrylmethane but products which result from a duplication of the starting pyrrole or from oxydo-reduction reactions of the pyrryl-arylcarbinol 9 which arise from the condensation between one molecule of pyrrole and one molecule of aldehyde. The nitro groups of the benzaldehyde play a crucial role in these reactions.
Solvent effect on the dissociation of p-nitroanilinium ion in glycerol–water media at 25 °C
Authors: De Amrita Lal , De Tapas Kumar
Published: May 2006

Thermodynamic dissociation constants (sK) of p-nitroanilinium ion (BH+) have been determined at 25 °C in aqueous mixtures of 10, 30, 50, 70, and 90 wt.% of glycerol (GL) by spectrophotometric measurements. Standard free energies, [Formula: see text], of p-nitroaniline (B) from water to mixed solvents have been evaluated from the measurement of solubilities at 25 °C. p(sK) values decrease with increase in mol% of GL and pass through a minimum and then increase very slowly. The solvent effect on the dissociation, δ(ΔG0) = 2.303RT [p(sK)N – p(wK)N] has been discussed in terms of the standard free energies of transfer [Formula: see text] from water to aqueous mixtures of GL of the uncharged base (B), the hydrochloride of the base (BHCl), hydrochloric acid (HCl), and also in terms of the individual species involved in the dissociation process. The solvent effect in trihydric alcohol – water (GL + H2O) system has been compared with those in dihydric alcohol – water (ethylene glycol + water) and monohydric alcohol – water (ethanol + water) systems available from literature. The much less solvent effect in GL + H2O has been primarily attributed to the contrasting nature of interaction of H+ and of partially charged H atoms of—NH3+ group in BH+ compared to those in other two solvent systems.
Etude structurale et thermodynamique des interactions entre des dérivés chlorés et bromés du méthane et des amides tertiaires
Authors: Dumas J. M. , Geron C. , Kribii A. R. , Lakraimi M.
Published: May 2006

A study by dielectric polarization, microcalorimetry, and infrared spectrometry has allowed us to demonstrate the role played by the halogen in interactions between a series of chlorinated and brominated derivatives of methane (considered as types of halogenated anesthetics) and two tertiary amides taken as models for an element of the membranes of the nervous cells. The inert organic solvent used was cyclohexane. The interactions are of the hydrogen bonding and (or) halogen bonding types.
The total synthesis of (±)-petasitolone
Authors: Liu Hsing-Jang , Ngooi Teng Ko
Published: May 2006

The total synthesis of petasitolone (1), a sesquiterpenoid of the eremophilane family, has been accomplished. The key step of this efficient synthesis is the Lewis acid catalyzed Diels–Alder addition of 2-carbomethoxy-2-cyclohexenone (3) to diene 9. The cycloaddition, which gives adduct 16 in good yield, facilitates the rapid construction of the parent ring system of the target molecule and allows an excellent control of the required stereochemistry.
Copper(II) acetates: from dimer to monomer
Authors: Sharrock Patrick , Melník Milan
Published: May 2006

The epr spectra at various frequencies of copper(II) acetate anhydrous, monohydrate, monoacetic acid, and water – acetic acid adduct are presented and analysed. The presence of copper hyperfine splittings in the solid state epr spectra of this series of compounds is discussed. The frozen solution spectrum of copper(II) acetate in acetic acid solution containing ~2% water shows an exceptional resolution of [Formula: see text] hyperfine of 24 G. This is attributed to a key intermediate which explains the monomer–dimer dissociation mechanism. The influence of distortions on the structures of these compounds is presented.
Particles in polymers: surface chemistry of their nucleation, growth, configuration, and interactions with the matrix
Authors: Kovacs G. J. , Vincett P. S.
Published: May 2006

The surface chemistry and thermodynamics of the nucleation, growth, configuration, and host–guest interactions of small particles within softenable substrates is investigated. It is found that novel subsurface particle monolayers form rather generally when inorganic materials are appropriately deposited onto softened (or subsequently softened) organic polymer substrates; partially embedded structures are generally formed by organic particulate materials, although these can also be embedded by exposure to a solvent vapour. For both rigid preformed particles spread onto the polymer surface, and for flexible growing clusters (as occur in vacuum deposition), the tendency for complete immersion is thermodynamically determined by the same simple inequality among the surface and interfacial tensions. Modelling of the polymer molecule configurations in the vicinity of subsurface particles predicts a novel entropic force of sufficient magnitude to explain why the particles form a monolayer a few tens of nm below the surface, rather than dispersing throughout the polymer, and why this structure is remarkably stable on extended heating. With the convenient fabrication technique of vacuum deposition, subsurface formation is further limited kinetically, by growth mode and sinking rate considerations, to generally low melting point inorganics and to certain ranges of deposition conditions; once subsurface particles are formed, their subsequent growth during the deposition process generally occurs at constant (nearly close-packed) surface coverage by a combination of material-capture and coalescence. After these nearly monodisperse particles grow beyond ~0.4 μm, they begin to bridge into a continuous subsurface structure. These vacuum-deposition phenomena are quantitatively explained by kinetic models of the formation and growth mechanisms.
Synthesis of heterocyclic 1,4-dihydropyridylacetic acid derivatives of 6-aminopenicillanic acid and D-α-aminobenzylpenicillin with antibacterial activity
Authors: Dubey Sushil K. , Knaus Edward E.
Published: May 2006

Condensation of 4-substituted 3-(4,4-dimethyloxazolin-2-yl)-1,4-dihydropyridylacetic acids 3 with the C-2 p-bromophenacyl esters of 6-aminopenicillanic acid salt 4 and D-α-aminobenzylpenicillin 8 afforded the respective 1,4-dihydropyridylacetic acid analogs 6 and 10 which exhibited moderate antibacterial activity toward Gram-positive strains. The 6-APA derivatives 6 exhibited dual 1H nmr resonances for H2′, H2, H5, and one of the C3-Me groups, suggesting the presence of two rotamers which differ in configuration at the carbonyl-to-nitrogen bond. The D-aminobenzylpenicillin derivatives 9 may exist in more than one conformation, one of which may be an intramolecular hydrogen bonded species such as 11.
The preparation of S7BrMF6 (M = As, Sb), and the preparation and crystal structure of (S7Br)4S4(AsF6)6 containing the bromo-cycloheptasulphur (1+) cation
Authors: Passmore Jack , Sutherland George , Whidden Tom K. , White Peter S. , Wong Chi-Ming
Published: May 2006

S7BrMF6 (M = As, Sb) were prepared essentially quantitatively by a variety of similar routes to those that led to S7IMF6; and in addition, by the reaction of bromine and S7IAsF6. (S7Br)4S4(AsF6)6 was prepared essentially quantitatively directly from sulphur, bromine, and arsenic pentafluoride in the appropriate ratios. Crystals of (S7Br)4S4(AsF6)6 are isostructural with (S7I)4S4(AsF6)6 space group P4/n, a = 19.19(3), c = 8.01(1) Å. The structure was refined from a low temperature set of data to a final R = 0.12. The salt contains a discrete planar S42+ and bromo-cycloheptasulphur (1+) cations, the latter having a similar geometry, sulphur–sulphur bond distances and an intra-cationic halogen–sulphur contact to that observed in S7I+.
The conformational changes accompanying the triplet–singlet electronic excitation of acetaldehyde, CH3CHO
Authors: Moule D. C. , Ng K. H. K.
Published: May 2006

The first electronic absorption system of acetaldehyde was recorded in the vapour phase at room temperature. The many-banded spectrum proved to be very complex and it was only at the extreme red edge of the absorption that the pattern became simple enough to analyze. The major experimental requirement was a high pressure × path length (500 Torr × 168 m). Spectra were interpreted in terms of the torsional mode ν′15 and ν″15 attached to the ν′14 out-of-plane bending mode. Both modes were highly Franck–Condon active and the [Formula: see text] band at 27240.4 cm−1 was not directly observed. The barrier to rotation of the methyl group was 618.5 cm−1. More surprising was the observation that the methyl group undergoes a rotation from a [Formula: see text] eclipsed configuration to a staggered configuration. The intensity of the ν′14 quantum addition and its position in the spectrum suggest that the aldehydic hydrogen is nonplanar in the ã state.
Deep levels in semiconductors
Authors: Lombos B. A.
Published: May 2006

The role of deep-lying trapping centers in semi-insulating GaAs, polysilicon and polycrystalline tin oxide transparent electrode has been systematically investigated. It was demonstrated that some of the peculiar transport properties of these semiconductors can be elucidated by deep level compensation. A multilevel model is presented to determine the position of the Fermi level as a function of impurity concentrations. These include, quantitatively, the deep-lying levels which have been introduced by doping in the case of GaAs and by grain boundaries in the case of polycrystalline films. In the latter cases the dangling bonds, associated to lattice defects, are characterized by energy levels which are localized in the energy gap. These dangling bonds can act as electron traps when empty and hole traps when occupied. These are the deep levels.In each of the investigated three cases, this concept permitted the elucidation of some of the transport properties of these semiconductors.
Époxydes α-éthyléniques et phénate de sodium: accès à des éthers phénoliques et phénols ortho-allyliques
Authors: David Michèle , Sauleau Jean , Sauleau Armelle
Published: May 2006

The ring cleavage reactions of α-ethylenic epoxides by sodium phenoxide afforded a mixture of products. Problems of competitive attack by this nucleophile, at the less substituted carbon (compounds A) or at the β-ethylenic carbon atom (compounds B and C), were encountered and could be resolved by judicious choice of reaction conditions (solvents, stereochemistry of the oxiranes). The regioselectivity of the attack was dependent on the transition states, implying weak steric hindrance and a conjugation oxirane – double bond.
Nitro-olefin bicycloannulation: one-step synthesis of tricyclo[3.2.1.02,7]octan-6-ones from cyclohexenones and of tricyclo[2.2.1.02,6]heptan-3-ones from cyclopentenones
Authors: Cory Robert M. , Anderson Paul C. , Bailey Murray D. , McLaren Fred R. , Renneboog Richard M. , Yamamoto Brian R.
Published: May 2006

Nitro-olefins bicycloannulate the α′-enolates of α-cyclohexenones and α-cyclopentenones by initial addition at −78 °C, followed by further reaction insitu in the presence of hexamethylphosphoramide in refluxing tetrahydrofuran to give tricyclo[3.2.1.02,7]octan-6-ones and tricyclo[2.2.1.02,6]heptan-3-ones in a single synthetic step. The reactions with 1-nitropropene and with a nitro-olefin having a more complex β-substituent are stereoselective, forming predominantly the tricyclic diastereomer in which the group derived from the β-substituent of the nitro-olefin is syn to the carbonyl bridge. Based on the isolation of intermediates and side products, the mechanism of the bicycloannulation is shown to proceed via sequential kinetically controlled conjugate addition of the enolate to the nitro-olefin at low temperatures, thermodynamically controlled intramolecular Michael addition at higher temperatures to give a bicyclo[2.2.2]octanone intermediate, and hexamethylphosphoramide-assisted expulsion of the nitro group as nitrite ion with formation of the cyclopropane ring. For the first time this type of bicycloannulation has been applied to cyclopentenones, and a one-step synthesis of tricyclenone has been carried out to demonstrate the synthetic utility of this new reaction.
Crystal structure and infrared spectra of an inclusion compound of cyclotriveratrylene and water
Authors: Birnbaum George I. , Klug Dennis D. , Ripmeester John A. , Tse John S.
Published: May 2006

A crystal grown by slow evaporation from a solution of cyclotriveratrylene (CTV) in toluene was found to be an inclusion compound with water as the only encaged guest. Its stoichiometry is C27H30O6•xH2O (x = 0.16) and it belongs to the monoclinic space group C2/c, with a = 24.216(21), b = 9.636(2), c = 23.117(4) Å, β = 118.08(5)°, Z = 8. X-ray intensity data were measured with a diffractometer and the structure was solved by direct methods. Least-squares refinement, which included all hydrogen atoms of the host molecule, converged at R = 0.046 for 3986 observed reflections. The geometry of the host molecule is compared to that of analogous structures and to cyclononatriene. Significant differences are ascribed to the effects of homoaromaticity and steric strain. Both the X-ray analysis and an FTIR study of the OH stretching show that the water molecules are weakly bound to the methoxy oxygen atoms of CTV. The molecular packing of CTV clathrates is discussed on the basis of crystallographic and spectroscopic evidence.
Stress metabolites of Solanummelongena: biosynthetic studies and isolation of auberganol and α- and β-eudesmol
Authors: Stoessl Albert , Stothers J.B.
Published: May 2006

Attempts to clarify the biosynthetic origin of the eggplant stress metabolite aubergenone (1) by incorporation of label from sodium [2-2H3,1-13C]acetate were frustrated by low yields and enrichment levels. However, the presence of deuterium in the biosynthetically significant 5-position was demonstrated by 2Hmr for the closely related auberganol (5) and α-and β-eudesmol (10 and 11), suggesting that these compounds, and hence also 1, are normal eudesmanes and not the products of a possible double rearrangement. Deuterium was also incorporated into the expected positions of 9-oxonerolidol (12), 9-oxynerolidol (13), and lubimin (4). Incorporation of label from [1,2-13C2]acetate could be determined satisfactorily only for 13 and its allylic isomer 14, corresponding with expectations. This is the first report of 5 as a natural product and of 10, 11, and the 10-epimer of 4 as eggplant stress metabolites.
The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO2 and dithiothreitol
Authors: Surdhar Parminder S. , Armstrong David A. , Massey Vincent
Published: May 2006

The one- and two-electron reductions of 2-thioriboflavin with[Formula: see text] and cyclic disulphide anion of dithiothreitol [Formula: see text] have been studied by the steady state γ and pulse radiolysis techniques. The [Formula: see text] radical reacted with 2-thioriboflavin to give the neutral semiquinone (•FlH) and the radical anion (•Fl−) at pH 5 and 10 respectively. The pK of the •FlH radical was determined to be 7.4. In the case of the anion, the 2-thioriboflavin spectrum is similar in shape to that of FAD radical anion, but red shifted by 40–50 nm. Red shifts are also seen in the neutral •FlH form for the 370-nm peak and 580-nm shoulder. However, in addition, there is strong enhancement of the absorbance at 500 nm. The spectrum of 2-thioriboflavin semiquinone produced in the presence of 2–5 mM dithiothreitol was perturbed, as was observed previously for unsubstituted flavin semiquinones in the presence of sulphydryls. The rate constants for the initial one-electron reduction step viz: [Formula: see text] were 4.0 ± 0.5 × 109 M−1 s−1 and 1.3 ± 0.2 × 109 M−1 s−1 at pH 7 and 10 respectively. The corresponding rate for the reaction of [Formula: see text] with 2-thioriboflavin at pH 7 was determined to be 2.4 ± 0.2 × 109 M−1 s−l. The continuous production of [Formula: see text] radicals by γ radiolysis reduced 2-thioriboflavin to the dihydro form, and the flavin was regenerated on the addition of air. The[Formula: see text] radical also effected a two-electron reduction. However, in this case, if the process was taken beyond the equivalence point, the dihydroflavin spectrum was bleached and the oxidized flavin could not be recovered.
The synthesis and structure of some 4-aryloxymethyl-2,2,6,6-tetramethyl-4-piperidinol and 4-aryloxymethyl-4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy derivatives
Authors: Cygler M. , Grabowski M. J. , Strzyžewski W. , Turała L. , Skowroński R.
Published: May 2006

The synthesis of 5,5,7,7-tetramethyl-1-oxa-6-azaspiro[2.5]octane and modified synthesis of 5,5,7,7-tetramethyl-1-oxa-6-azaspiro[2.5]oct-6-yloxy are described. Reaction of these spiro-oxiranes with phenols gave corresponding 4-aryloxymethyl 4-piperidinols and their 1-piperidinyloxy derivatives. The same products have also been obtained by reaction with ethanol. The crystal structures of two derivatives: 4-phenoxymethyl-2,2,6,6-tetramethyl-4-piperidinol (3a, 2880 reflections, R = 0.054) and 4-phenoxymethyl-4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (6a, 4395 reflections, R = 0.084) have been determined. Piperidine rings are in a chair conformation in both compounds with the phenoxymethyl substituent in an equatorial position. The [Formula: see text] group is not planar, with the N—O bond inclined by 18.4° to the CNC plane. Although the space groups are different for these two compounds the molecules are packed in the crystal lattice in a topologically equivalent way.
Alkoxyphosphonium ions. 5. Kinetics of the Michaelis–Arbuzov intermediate
Authors: Lewis Edward S. , McCortney Bridget A.
Published: May 2006

Rates of formation and destruction of the alkoxyphosphonium ion, the intermediate in the Michaelis–Arbuzov reactions of some methyl esters of trivalent phosphorus acids with methyl iodide, are followed by a conductivity method in the solvent propylene carbonate. Specific conductances of the unstable intermediates are well estimated through stable model salts. Rate constants for both the alkylation of the reagent and the dealkylation of the intermediate are obtained. The conductivity time curves are simulated by adjusting rate constants for two sequential second order reactions, assuming no ion pairing at the concentrations used. In these measurements of the intermediate only, there is no rate-determining step; for the overall reaction the first step is in most cases rate-determining.
The relative rate constants of oxygen, O(3P), atoms with different gaseous unsaturated compounds at room temperature
Authors: Deslauriers H. , Collin G. J.
Published: May 2006

A simple method is proposed in order to measure the relative rate constants of the interactions between oxygen O(3P) atoms and unsaturated hydrocarbon. A 147 nm photolysis of air is used to produce the O(3P) atoms. In the presence of 1,2-butadiene, these oxygen atoms have a very clean reaction that gives rise to propylene formation. By including a suitable additive, and by looking at the formation of propene versus the [additive]/[1,2-butadiene] ratio, the absolute values of the various O(3P) + unsaturated hydrocarbon interactions can be evaluated. These rate constants increase with the number of substituents attached to the double bond. Moreover, a correlation between the total rate constants and ionization potentials is also observed.
Azictes. Part VI. Thermolysis of ethyl azidoformate in dimethyl terephthalate; formation of a diazabicyclooctadiene heterocycle
Authors: Ayyangar N. R. , Bambal R. B. , Srinivasan K. V. , Row T. N. Guru , Puranik V. G. , Tavale S. S. , Kulkarni P. S.
Published: May 2006

Thermal decomposition of ethyl azidoformate in excess of dimethyl terephthalate (DMT) (1) in acetic anhydride as solvent results in the formation of N,N-dicarbethoxy-4,8-dicarbomethoxy-2,6-diazabicyclo[3.3.0]octa-3,7-diene (3) in addition to N-carbethoxy-2,5-dicarbomethoxy-1H-azepine (2) and ethyl N-(2,5-dicarbomethoxyphenyl)carbamate (4). The structure of the diazabicyclooctadiene (3) was established on the basis of spectral, elemental, and X-ray crystallographic analyses.
Stereochemistry of 3-carboxylated 2,5-dihydrothiophene formation
Authors: McIntosh John M. , Hayes Ivy E. E.
Published: May 2006

The preparation of 2-carboxylated-1,3-dienes from carbomethoxy vinylphosphonates and 2-mercaptocarbonyl compounds has been shown to give stereoisomeric mixtures. This may be due to the formation of stereoisomers of the intermediate 2,5-dihydrothiophenes and (or) to the occurrence of both modes of disrotatory sulfur dioxide elimination.
Structural and vibrational studies of 1,1,3,3-tetracyanopropane and 2,2,4,4,6-pentacyanocyclohexenamine
Authors: Bell R. A. , Brown B. E. , Duarte M. , Howard-Lock H. E. , Lock C. J. L.
Published: May 2006

1,1,3,3-Tetracyanopropane, 1, was prepared in low yields by a literature method with 2,2,4,4,6-pentacyanocyclohexenamine, 2, as a major by-product. The products were examined by X-ray crystallography. 1 has an orthorhombic space group, Pbcn (No. 60) with cell dimensions, a = 7.158(2), b = 10.510(3), c = 9.733(2) Å and has four formula units in the unit cell. 2 has a monoclinic cell, P21/c (No. 14) with cell dimensions a = 14.368(3), b = 6.626(1), c = 12.300(2) Å, β = 115.60(1)° and has 4 formula units in the unit cell. Data were collected with use of MoKα radiation and a Nicolet P3 diffractometer. The crystal structures were determined by standard methods and refined to Rw = 0.037 (1) and Rw = 0.040 (2) on the basis of 782 and 2108 unique reflections. Bond lengths and angles in the two compounds are normal. 2 has what has been considered to be the less likely tautomeric structure. Both compounds were examined by 1H, 13C nmr, vibrational spectroscopy, and mass spectroscopy. For 2 there was no evidence of the alternative tautomeric structure. New methods were developed for the preparation of both compounds and the mechanism of the original reaction rationalized.
The reaction of 2,1-benzisothiazoline-3-thiones with acetylenic reagents
Authors: Mckinnon David M. , Secco Anthony S. , Duncan K. Ann
Published: May 2006

N-Methyl-2,1-benzisothiazoline-3-thione reacts with acetylene esters to form o-iminobenzoquinone methides which either form diazocines 2 by head-to-tail dimerisation, or react further with the acetylenic ester forming diadducts. With phenylacetylene a 1,2-difhiolo[2,3-b]2,1-benzisofhiazole structure is obtained by rearrangement of an initial adduct. Related thiones and acetylenes react similarly but in poorer yields. The crystal and molecular structures of the diazocine were determined by single crystal X-ray diffractometry techniques. The compound crystallizes in space group [Formula: see text] with unit cell dimensions a = 7.9465(10), b = 13.6421(14), c = 13.9183(18) Å, α = 82.38(1), β = 83.67(1), γ = 85.77(1) deg, and Z = 2. The structure was solved by direct methods and refined to an R value of 0.056 for 3037 observed reflections. The structure consists of molecules of 2a which have an approximate C2 axis passing through the center of the eight-membered ring. Deviations from true symmetry result from internal ring strain, lone pair–lone pair repulsions, and packing effects.
A new procedure for the insitu generation of methylene ketenes
Authors: Masters Andrew P. , Sorensen Ted S. , Tran Phu Manh
Published: May 2006

The reaction of pentacarbonylmanganate anion 3 and 2-bromopropenoyl chlorides 2 leads to 2,4-alkylidenecyclobutane-1,3-diones 5. The latter are formed from dimerization of the corresponding methylene ketenes 1 so that the reaction of 2 and 3 constitutes a new synthetic procedure for the insitu generation of these very reactive intermediates. Acid chlorides 2 are readily available from α,β-unsaturated acids via bromination–dehydrobromination – thionyl chloride sequences.
A proton nuclear magnetic resonance relaxation study of the glycine, alanine, and lactate complexes of gadolinium(III) in aqueous solution
Authors: Reid R. Stephen , Podányi Benjamin
Published: May 2006

The 1H nuclear magnetic resonance spin-lattice and spin–spin relaxation rate enhancements induced by the gadolinium(III) ion were measured in solutions of glycine, alanine, and sodium lactate containing different amounts of Gd(III). The proton relaxation rates in the Gd(III) complexes were calculated from these data, and were used to calculate metal–hydrogen atom distances. Comparison of these data with corresponding distances calculated from literature X-ray crystallographic data for model compounds shows that in the two amino acid complexes the Gd(III) ion is coordinated in a four-membered ring through the two oxygen atoms of the carboxylate group. By contrast, in the lactate complex coordination is via a five-membered ring involving one oxygen atom of the carboxylate group and the α-hydroxyl oxygen.
Structure and conformation of 3′-azido-3′-deoxythymidine (AZT), an inhibitor of the HIV (AIDS) virus
Authors: Birnbaum George I. , Giziewicz Jerzy , Gabe Eric J. , Lin Tai-Shun , Prusoff William H.
Published: May 2006

3′-Azido-3′-deoxythymidine (AZT), an inhibitor of HIV (human immunodeficiency virus) replication, was recently found to improve the condition of patients suffering from AIDS (acquired immunodeficiency syndrome) or ARC (AIDS-related complex). An X-ray analysis of AZT was undertaken in order to determine the three-dimensional structure of this thymidine analogue. The crystals belong to the monoclinic space group P21 and the cell dimensions are a = 5.6282(4), b = 12.0130(7), c = 17.5072(10) Å, β = 95.946(5)°. The structure was determined by direct methods and refined to R = 0.028 for 2029 observed reflections. Two crystallographically independent molecules were found in the asymmetric unit. One of them, molecule A, adopts a conformation which is fairly common in nucleosides, viz. a C2′ endo/C3′ exo pucker of the furanose ring and a glycosidic torsion angle χCN = 53.4°. However, the conformation of molecule B is highly unusual. The sugar ring pucker is C3′ exo/C4′ endo and χCN = 2.3°. This high-energy conformation may represent the biologically active form of AZT. Its determination may therefore assist in the design of other inhibitors of HIV.
Characterization of a γ-radiation-induced decomposition product of thymidine. Crystal and molecular structure of the (−)cis(5R,6S) thymidine glycol
Authors: Hruska Frank E. , Sebastian Rudy , Grand André , Voituriez Lucienne , Cadet Jean
Published: May 2006

X-ray crystallography was used to determine the structure of (−)cis(5R,6S)-5,6-dihydroxy-5,6-dihydrothymidine, a γ-radiation induced product of thymidine. The crystals belong to the orthorhombic space group P212121 and have cell dimensions a = 8.420(1) Å, b = 10.422(1) Å, and 13.552(1) Å. The half-chair pucker of the 5,6-saturated pyrimidine ring is similar to that observed for the isolated base with the cis configuration, and is described by the Cremer–Pople parameters Q = 0.48 Å, θ = 62°, and [Formula: see text]. The conformation about the N-glycosyl bond is anti; the χ angle (−111.6(5)°) lies at one extreme of the range previously seen for nucleosides (−180 to −115°). The pucker 2T1 of the sugar (P = 151.2°; τm = 36.5°) contrasts with the O4′-endo type of pucker seen in 5,6-dihydrothymidine (0T4) and (5S)-5-hydroxy-5,6-dihydrothymidine (0T1). The conformation about the C4′—C5′ bond is gauche+. The solid state structure is similar to that determined in aqueous solution by 1H nmr.
α-Aminophosphonates. III. Cycloaddition anionique-1,3 des esters α,β-insaturés: Préparation et transformations des Δ1-pyrrolines
Authors: Dehnel André , Kanabus-Kaminska Jolanta M. , Lavielle Gilbert
Published: May 2006

The anions of the 2-azaallylphosphonates 1 react with the α,β-unsaturated esters 2 to yield the intermediates 4′. These intermediates form the 2-diethoxyphosphonyl-4-ethoxycarbonylpyrrolidines 4 following a protonation while an elimination of the anion of the diethylphosphonate leads to the 4-ethoxycarbonyl-Δ1-pyrrolines 5. The proportions of these two products vary with the experimental conditions and the bulkiness of the substrates. The formation of the cyclic products has been studied for numerous substrates and in the presence of a number of bases. The reaction is regioselective and stereospecific and on the basis of the formation of the kinetically more strained diastereoisomer it is possible to conclude that the cycloaddition is a concerted one. The thermodynamically less strained diastereoisomers 6 and 7 are obtained from the compounds 4 and 5 respectively when they are subjected to the action of a base in a protic media. The other epimers of 4, the compounds 8 and 9, have been obtained by the addition of diethylphosphite to the pyrrolines 5 and 7. The pyrrolines 5 have been reduced to the 3-ethoxycarbonylpyrrolidines 12. The isomerization of the pyrrolines 5 with a phenyl substituent in position 5 leads to the formation of the 3-ethoxycarbonyl-2-phenyl-Δ1-pyrrolines 10. The latter spontaneously oxidize with atmospheric oxygen to yield the 3-ethoxycarbonyl-3-hydroxy-2-phenyl-Δ1-pyrrolines 11. [Journal translation]
The transformation of levopimaric acid into warburganal
Authors: Ayer William A. , Talamas Francisco X.
Published: May 2006

The chiral resin acid levopimaric acid (1), isolated from pine oleoresin, is used as a starting material for the synthesis of (−)-warburganal (2). The synthesis proceeds via the endoperoxide of methyl levopimarate, which after ozonolysis, protection of the resulting aldehyde function, reduction, and treatment with sodium methoxide provides the tetranorditerpenoid 12a. The hemiacetal 12a is then transformed to a mixture of hemithioacetals. At this point the carbomethoxyl group at C-4 is reduced to a methyl group, and then a C-11, C-12 double bond is introduced. Ozonolysis followed by elimination of formic acid provides a mixture of olefins (27) that is hydroxylated at C-9. Removal of the protecting group then gives (−)-warburganal (2). The sequence requires 15 steps and the overall yield from levopimaric acid to warburganal is 2.7%.
Anodic behaviour of limonene in low aqueous acetonitrile solutions of Cl−
Authors: Caram J. A. , Martins M. E. , Gros E. G. , Marschoff C. M.
Published: May 2006

The anodic behaviour of limonene on Pt electrodes was studied in LiCl solutions in acetonitrile with low water content. It was found that cis-6-acetamido-p-menth-1,8-diene is formed with acceptable yields. This compound is of interest as a potential intermediate for obtaining oxidation derivatives of limonene. Other products, among them the new compound 8-acetamido-2,4,8-trimethyl-4-chloromethyl-3-aza-bicyclo[3.3.1]non-2-ene, were identified. Reaction routes are proposed.
Acceleration of the mercury-induced aquation of bromopentammine Co(III) by naturally occurring glycosaminoglycans.
Authors: Templeton Douglas M.
Published: May 2006

not available
Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance
Authors: Chihara Yukiko N. , Nakamura Nobuo , Chihara Hideaki
Published: May 2006

The proton and fluorine second moments and the spin-lattice relaxation times T1 (at 25.75 MHz) were measured in the solid complex trimethylamine–trifluoroborane from 53 to 300 K. There is a cross-relaxation effect between 1H and 19F below 120 K. Their T1 minima near 140 K led to activation energies of 10.6 and 11.1 kJ mol−1 for the reorientation of the methyl and the trifluoride groups, respectively. An additional minimum observed in the T1 of protons at about 240 K was attributed to the reorientation of the trimethylamine group about the N—B bond with an activation energy of 25.0 kJ mol−1. A comparison of these potential parameters with those in other trimethylamine complexes led to a notion that the activation energies for the reorientation of the (CH3)3N group in the trimethylamine–trifluoroborane complex are mainly governed by the intramolecular steric effect.
Light-induced reversible ionization of tetramethylphenylenediamine in an inorganic polymer of n-butyl orthotitanate
Authors: Ueda Hisashi , Kaise Masahiro
Published: May 2006

n-Butyl orthotitanate, BT, polymerized in tetrahydrofuran, if irradiated by visible light, gives a new electron spin resonance absorption that is not found before irradiation. In the present work, three different polymers of BT were synthesized by adding tetramethyl phenylenediamine (TMPD), dimethyl phenylenediamine (DMPD), or phenylenediamine (PD), to the solution of BT. The polymers thus prepared were tested to see if they give a new esr signal when irradiated by visible light. The polymer to which 1 mol% of TMPD was added gave TMPD•+ when irradiated by visible light, but the TMPD•+ signal decayed after the irradiation was discontinued. This change, therefore, is reversible. The resonant position of every hyperfine splitting line of the TMPD•+ found in this polymer coincided with that of TMPD•+ in solution, but the relative intensity ratios and the line width of each line depended on the nuclear spin quantum number of the coupling nuclei. This can be interpreted by the restricted rotational motion of TMPD•+ in the polymer matrix. The contribution of the non-diagonal term to the spin relaxation time would explain this phenomenon. In the case of the polymer to which DMPD was added, a small amount of DMPD•+ seemed to be formed, but no radical was detected in the case of the polymer to which PD was added.
EPR study of the long-range effect of a β-carbon chiral center on the magnetic equivalence of β-methylene protons
Authors: Smith Peter , Donovan William Harley
Published: May 2006

Using aqueous TiCl3-based continuous-flow, radical-generating methods at 25 °C we have carried out a comprehensive EPR study of hydroxyl- and aminyl-radical addition to eight alkene substrates that yielded radicals of general formula XCH2—ĊY—C*HR1R2, where C* is a chiral center, to investigate the magnetic inequivalence of β-CH2 protons arising from a nonadjacent β-C chiral center. We attribute the observed nonequivalence to the long-range influence of the chiral center in these radicals, and note that our results are consistent with the reasonable expectation that the presence of bulky groups in the radicals is likely to favor particular conformations, leading to more easily observed inequivalence of the β-CH2 proton splittings.
Synthesis of cedranoid sesquiterpenes. V. The biotols
Authors: Yates Peter , Grewal Rupinder S. , Hayes Peter C. , Sawyer Jeffery F.
Published: May 2006

Reduction of dimethyl 3-hydroxy-4,4,8-trimethyl-6-oxo-cis-bicyclo[3.3.0]octa-2,7-diene-1,2-dicarboxylate (8) with lithium and ammonia gives dimethyl 3-hydroxy-4,4,exo-8-trimethyl-6-oxo-cis-bicyclo[3.3.0]oct-2-ene-1,2-dicarboxylate (9), which on acetylation, reduction with sodium borohydride, and methanolysis gives dimethyl 3,exo-6-dihydroxy-4,4,exo-8-trimethyl-cis-bicyclo[3.3.0]oct-2-ene-1,2-dicarboxylate (12). This on 2-decarbomethoxylation followed by treatment with lithium acetylide in the presence of cerium trichloride gives methyl 3-ethynyl-3,exo-6-dihydroxy-4,4,exo-8-trimethyl-cis-bicyclo[3.3.0]octane-1-carboxylate (21), which on hydration, diacetylation, and treatment with tri-n-butyltin hydride and azoisobutyronitrile is converted to methyl exo-6-acetoxy-3-acetyl-4,4,exo-8-trimethyl-cis-bicyclo[3.3.0]octane-1-carboxylate (31). Methanolysis of 31. tert-butyldimethylsilylation, and reaction with potassium tert-butoxide in tert-butyl alcohol gives exo-4-tert-butyldimethylsilyloxy-exo-2,6,6-trimethyl[5.3.11,5]undecane-8,10-dione (35). This on treatment with lithium aluminum hydride followed by oxidation and hydrogenation provides the corresponding 10-deoxo compound, 39. Reaction of this with methyllithium, dehydration, and desilylation with hydrogen fluoride in acetonitrile gives a mixture of (±)-α-biotol (1) and (±)-β-biotol (2); desilylation with hydrogen chloride in methanol gives solely (±)-1.
Solution and solid phase chemical synthesis of arabinonucleotides
Authors: Damha Masad José , Usman Nassim , Ogilvie Kelvin Kenneth
Published: May 2006

A fast and convenient procedure for the chemical synthesis of arabinonucleotides, which eliminates the multistep protection of the arabinonucleoside building blocks, is described. The results of these studies were successfully applied to the automated chemical synthesis of the hexanucleotide 5′-aUpaApaUpaApaUpaA-3′. Both solution and solid phase phosphite triester procedures are described. Keywords: arabinonucleotides, arabinophosphoramidites, automated chemical synthesis, protected arabinonucleosides.
The effect of the nature of the amine leaving group on the nature of the E2 transition state for the reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol
Authors: Smith Peter James , Amin Md.
Published: May 2006

To investigate the effect of the leaving group on the elimination reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol at 60 °C, the reaction of seven different quaternary ammonium salts and their β-deuterated analogues with trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, N,N-dimethylbenzylamine, tripropylamine, and N,N-diethylbenzylamine as leaving groups has been studied. In all cases the elimination, which was shown to proceed via the concerted E2 process, was accompanied by competing substitution reactions. Although a significant dependence of the rate of the elimination process on the nature of the leaving group was noted, there was not any linear correlation with the basicity of the amine leaving group. The primary hydrogen–deuterium kinetic isotope effect for the elimination process, (kH/kD)E, was found to increase initially with an increase of reaction rate, [Formula: see text] for substrates containing the leaving groups trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, and N,N-dimethylbenzylamine; i.e., (kH/kD)E = 5.03, 5.26, 5.40, 5.83, and 5.85, respectively. A further increase in rate, using substrates with tripropylamine and N,N-diethylbenzylamine as leaving groups resulted in a decrease of the magnitude of the hydrogen–deuterium isotope effect; i. e., (kH/kD)E = 5.42 and 4.67, respectively. It is concluded that steric effects mainly determine leaving group ability. As well, it is concluded that the leaving group ability of the amine determines the structure of the E2 transition state. For the reaction of the poorer leaving groups, trimethylamine, N-methylpiperidine, and N-methyldiethylamine, the proton is morethan one-half transferred at the transition state while for reaction involving the two best leaving groups, tripropylamine and N,N-diethylbenzylamine, the Cβ—H bond is lessthan one-half broken at the transition state. The conclusions are considered in the light of the More O'Ferrall – Jencks potential energy surface diagram. Keywords: elimination mechanism, transition state, isotope effects, leaving group, quaternary salts.
Gas-phase measurements of the kinetics of BF2+-induced polymerization of olefinic monomers
Authors: Forte Leonard , Lien Min H. , Hopkinson Alan C. , Bohme Diethard K.
Published: May 2006

The initial steps in the BF2+-induced polymerization of the monomers of ethylene, propylene, cis-2-butene, isobutene, and styrene have been observed in the gas phase at room temperature using the Selected-Ion Flow Tube (SIFT) technique. Rate constants and product distributions have been determined for the initiation of the polymerization in each case. All five initiation reactions were found to be rapid (k ≥ 5.0 × 10−10 cm3 molecule−1 s−1). The primary product ions that propagate polymerization have been identified and sequential addition reactions have been followed in all five systems. For ethylene the energetics of the initial steps have been followed using abinitio molecular orbital theory. Reactions of BF2+ with the vapours of water and benzene have also been characterized. Keywords: ion-induced polymerization, alkenes, kinetics, gas phase ion chemistry.
Synthesis and crystal structure of an octahedral nickel(II) complex derived from pentaerythrityl tetraamine
Authors: McAuley A. , Subramanian S. , Whitcombe T. W.
Published: May 2006

The Ni(II) complex, Ni(Htam)24+ (tam = pentaerythrityl tetraamine), has been prepared under controlled conditions. In this ion, three of the four amino groups of each ligand are coordinated to yield an octahedral structure which shows tetragonal and trigonal distortion. The fourth amino group is protonated in each case and binds strongly to the counter ion SO42−. The crystal structure (triclinic, [Formula: see text], a = 8.913(3), b = 9.775(2), c = 7.505(3), α = 102.61(4)°, β = 106.28(4)°, γ = 96.40(3)°) has been refined, converging to final values of R = 0.0347 and Rw = 0.0386. The three dimensional nature of the hydrogen bonding in the crystal structure has been described. Differences in Ni—N bond lengths are observed. A transient nickel(III) species is generated chemically or electrochemically. The esr spectrum is consistent with a low spin d7 centre and is axial in nature. Keywords: nickel, pentaerythrityl tetraamine, hydrogen bonding, oxidation.
The disproportionation of diselenium dichloride, Se2Cl2, and diselenium dibromide, Se2Br2
Authors: Lamoureux Marc , Milne John
Published: May 2006

Diselenium dichloride and dibromide have been shown by Raman and 77Se-nmr spectroscopy to be equilibrium mixtures of Se2X2 and small amounts of SeX2 and SenX2. Equilibrium constants have been estimated for the disproportionation reactions,[Formula: see text]The origin of "spurious" peaks in the reported vibrational spectra of Se2Br2 and Se2Cl2, which have been variously assigned to overtone and combination bands and impurities has been clarified. Mixtures of Se2Br2 and Se2Cl2 are shown to contain Se2BrCl in equilibrium according to[Formula: see text]Keywords: 77Se nmr, Raman spectroscopy, selenium halides, diselenium dichloride, diselenium dibromide.
New pentafluorothio(SF5) alkylsulfonic acids
Authors: Willenbring Robert J. , Mohtasham Javid , Winter R. , Gard Gary L.
Published: May 2006

New pentafluorothioalkylsulfonic acids, F5SCXHCY2SO3H (X, Y = H, F), and the corresponding salts have been prepared from pentafluorothioalkyl bromides or olefins with sodium sulfite or sodium bisulfite. The compounds are characterized by ir, nmr (1H, 19F, 13C), and mass spectra. Keywords: new pentafluorothioalkylsulfonic acids.
Thermolysis of 2-acyloxy-Δ3-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement
Authors: Majchrzak Michael W. , Warkentin John
Published: May 2006

not available
Liquid chromatographic retention behaviour and separation of chlorophenols on a β-cyclodextrin bonded-phase column. Part III. Diaromatic chlorophenols
Authors: Paleologou Michael , Li Song , Purdy William C.
Published: May 2006

The liquid chromatographic retention behaviour of 16 diaromatic phenols and chlorophenols (PCB metabolic analogues) on a β-cyclodextrin bonded-phase column was investigated with respect to mobile-phase composition, pH, temperature, and ionic strength. The mechanistic aspects of retention of these compounds on the β-cyclodextrin column were studied and compared to other reversed-phase columns. Comparison is also made to the liquid chromatographic retention behaviour and separation of monoaromatic chlorophenols on the same column. The size, shape, and spatial geometry of each substrate appears to affect retention and selectivity. Most of the evidence suggests that inclusion complex formation, which involves hydrophobic interactions with the interior of the cavity and/or van der Waals interactions of the chlorine substituents with the backbone of the cavity, provides the physical basis for the resolution of these positional isomers. Under certain chromatographic conditions, however, it appears that, for certain congeners, all or part of the molecule is excluded from the cyclodextrin cavity; in such cases a normal-phase or mixed chromatographic mechanism is postulated based on the interaction of the substrates with the secondary hydroxyls on the periphery of the cyclodextrin moieties. The gradient–elution separation of 14 out of 16 of this type of compound on a single chromatogram is also reported and discussed. Keywords: biphenylols, chlorobiphenylols, biphenyldiols, liquid chromatographic retention behaviour, gradient-elution separation, β-cyclodextrin bonded-phase column.
The structure of the antigenic lipopolysaccharide O-chain produced by Escherichiahermannii ATCC 33650 and 33652
Authors: Beynon Linda M. , Bundle David R. , Perry Malcolm B.
Published: May 2006

High resolution two-dimensional 1H and 13C nuclear magnetic resonance at 500 MHz was used in combination with molecular modelling to solve the structures of the antigenic O-polysaccharides produced by Escherichiahermannii strains ATCC 33650 and 33652. Classical structural methods such as methylation analysis, selective and partial hydrolysis, and periodate oxidations confirmed that the O-polysaccharides had a branched tetrasaccharide repeating unit with the structure:[Formula: see text]Keywords: Escherichiahermannii, lipopolysaccharide, magnetic resonance, polysaccharide.