bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic absorption studies in aqueous solutions of modified β-cyclodextrins
Authors: Jobe David J. , Verrall Ronald E. , Reinsborough Vincent C.
Published: May 2006

Ultrasonic absorption studies over the frequency range 0.6–210 MHz were conducted in aqueous solutions of the following modified β-cyclodextrins (β-CD): 2,6-O-dimethyl-β-CD (DMβCD), 2,3,6-O-trimethyl-β-CD(TMβCD), and hydroxypropyl-β-CD (HPβCD). Anomalous ultrasonic absorption found in the three systems was attributed to three relaxations in the DMβCD and HPβCD systems and two in the TMβCD system. These relaxations were assigned to hydrogen bond "wig-wagging", to CD cavity water exchange, and to bond rotation within the CD units. The 1:1 DMβCD/decyltrimethylammonium bromide system was also investigated ultrasonically in solution. Keywords: ultrasonic absorption, modified β-cyclodextrins, surfactant inclusion, relaxation frequency.
Stereocontrolled construction of A.B.C.[6.6.6] tricycle via transannular Diels–Alder reaction of 14-membered triene macrocycle
Authors: Cantin Michel , Xu Yao-Chang , Deslongchamps Pierre
Published: May 2006

The synthesis of the four acyclic trienes 11a, b and 20a, b is reported. The tandem macrocyclization and stereoselective transannular Diels–Alder reaction of acyclic trienes 11b (trans-trans-cis) and 20b (trans-trans-trans) were observed in the presence of Cs2CO3 at 85 °C to give tricycles 30 (TST) and 32 (CAT) respectively. However, treatment of acyclic trienes 11a (cis-trans-cis) and 20a (cis-trans-trans) under the same conditions yielded the 14-membered macrocycles 21 and 23, which were stereoselectively transformed at 250 °C into tricycles 22 (CST) and 24 (CAT) respectively in excellent yield. Keywords: stereocontrolled synthesis, macrocycle, tricyclic compound, transannular Diels–Alder reaction.
Spinel ferrites as catalysts: A study on catalytic effect of coprecipitated ferrites on hydrogen peroxide decomposition
Authors: Lahiri Preeti , Sengupta Susanta K.
Published: May 2006

Some ferrospinels act as catalysts for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst. This study is to find the most effective catalyst of stoichiometry MIIFe2IIIO4. A set of ferrites of different composition MIIFe2II04 (MII = Mn, Co, Ni, Cu, Zn, Cd) was synthesized by co-precipitation and characterized by chemical analysis, X-ray diffractometry, and B.E.T. technique. A comparative assessment of the catalytic power of these ferrites from investigations of their influence on the kinetics of H2O2 decomposition in a neutral medium was made. An analysis of the data on specific rate, and the Eyrings activation parameters for the reaction sharply reveal the following: (a) The catalytic power follows the order MnFe2O4 > CoFe2O4 > CuFe2O4 > NiFe2O4 > CdFe2O4 > ZnFe2O4, MnFe2O4 is much more highly effective than the others (50–100 fold). (b) A compensation effect has been noted from the observed linearity with slightly less than unity slope between TΔ≠S0 and Δ≠H0 over the entire series. Key words: Ferrospinels, catalysis, hydrogen peroxide decomposition kinetics.
Photodegradation of the lignin model α-guaiacoxyacetoveratrone, unusual effects of solvent, oxygen, and singlet state participation
Authors: Schmidt John A. , Berinstain Alain B. , Rege Francis de , Heitner Cyril , Johnston Linda J. , Scaiano J. C.
Published: May 2006

α-Guaiacoxyacetoveratrone, a lignin model compound, has been studied using a combination of laser flash photolysis and steady state quantum yields. Triplet lifetimes range from 175 to 600 ns while the quantum yields of photodegradation vary from 0.06 to 0.6, depending on the solvent. Singlet processes (Φ ~ 0.1), previously unobserved for aromatic ketones, are implicated in the mechanism, and account for most or all of the degradation in aprotic solvents. Key words: photodegradation, α-guaiacoxyacetoveratrone.
Studies on the thermal coking of bitumen. I. The use of pyrene-d10 as a probe for evaluating the extent of hydrogen shuttling reaction
Authors: Kirk M. J. , Sorensen T. S.
Published: May 2006

The organic reactions that take place during the thermal coking of bitumen are extremely complex and deep-seated, but obviously hydrogen atoms originally attached to carbons that form coke will have moved to a new carbon site (net addition of hydrogen, resulting in upgraded bitumen). Accompanying this process, one expects some general hydrogen shuttling between non-coking molecules. This paper describes an approach to determing the extent of this latter process by the addition of a small amount of perdeuterated pyrene to the bitumen prior to the coking operation. The in situ pyrene functions as in indicator, allowing one to establish the extent and other mechanistic details of the "hydrogen donor" reactions that take place during coking. There is no indication that the pyrene substantially modifies the normal course of the reaction, hence the analogy to an indicator. Key words: bitumen coking, pyrene, hydrogen exchange, donor solvent, free radicals.
Cyclodextrin-based enzyme models. Part 1. Synthesis of a tosylate and an epoxide derived from heptakis(6-O-tert-butyldimethylsilyl)-β-cyclodextrin and their characterization using 2D NMR techniques. An improved route to cyclodextrins functionalized on the secondary face
Authors: Pregel Marko J. , Buncel Erwin
Published: May 2006

An improved route for the synthesis of cyclodextrin (CD)-based enzyme models having catalytic groups on the secondary face is presented. An epoxide derived from heptakis(6-O-tert-butyldimethylsilyl)-β-CD was prepared via intermediates that can be purified by conventional flash chromatography on a preparative scale. Reaction of β-cyclodextrin with; tert-butyldimethylsilyl chloride in pyridine gave heptakis(6-O-tert-butyldimethylsilyl)-β-CD (1). Treatment of 1 with N-tosylimidazole and NaOMe in chloroform gave mono(2-O-tosyl) heptakis(6-O-tert-butyldimethylsilyl)-β-CD (2) in 22% yield. The latter was converted smoothly to mono(2A, 3A-anhydro) heptakis(6-O-tert-butyldimethylsilyl)-β-CD (3), in which one glucose subunit has been converted to a manno-epoxide, by treatment with KOEt in refluxing ethanol (87% yield). Compounds 1, 2, and 3 were characterized by a variety of one- and two-dimensional NMR techniques. These results open the door to attachment of catalytic groups to the cyclodextrin in a well-defined manner. Nucleophilic attack on the epoxide, followed by removal of the silyl groups, can be used to prepare a wide variety of enzyme model systems. Key words: functionalized cyclodextrins, silylation, 2D NMR, enzyme models.
Towards supported catalyst models: the synthesis, characterization, redox chemistry, and structures of the complexes Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), C6H(2,3,5,6-Me)4)
Authors: Toth Robert T. , Stephan Douglas W.
Published: May 2006

Reaction of substituted phenoxides with TiCl4 affords the species Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), 1; Ar′ = C6H(2,3,5,6-Me)4, 2). The compound Ti(OC6H4(2-t-Bu))4, 1, crystallizes in the tetragonal space group [Formula: see text], with a = 15.203(4) Å, c = 8.026(3) Å, Z = 2, and V = 1855(2) Å3. The compound Ti(OC6H(2,3,5,6-Me)4)4, 2, crystallizes in the orthorhombic space group Pbcn, with a = 16.539(7) Å, b = 16.136(6) Å, c = 27.716(12) Å, Z = 8, and V = 7397(9) Å3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. In the case of 1 strict crystallographic [Formula: see text] symmetry is imposed. The complex 2 exhibits reversible cyclic voltammetric behaviour consistent with a one electron reduction to the Ti(III) analogue. Chemical reduction of 2 employing sodium amalgam affords the quantitative formation of (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Na(THF)2, 3. The reaction of 3 with [(COD)Rh(μ-Cl)]2 does not afford the Ti(III)/Rh(I) early–late heterobimetallic (ELHB) complex (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Rh(COD). The nature of all products is not known; however, redox chemistry, in which electron transfer from Ti(III) to Rh(I) occurs is evidenced by the generation of 2 and Rh(0). In addition, ligand transfer reactions giving uncharacterized Rh-alkoxides are suggested by the spectral data. The implications and ramifications for the synthesis of alkoxide bridged ELHB models of bimetallic heterogeneous catalyst systems are discussed. Key words: titanium phenoxides, redox chemistry, structures.
Synthesis, electrochemical and spectroscopic investigations of 2,2′:4,4″-terpyridine and 2,2′:4,4″:6,2″-quaterpyridine ligands for metal complex photoelectrochemistry
Authors: Persaud L. , Barbiero G.
Published: May 2006

The synthesis of 2,2′:4,4″:6,2′″-quaterpyridine and 2,2′:4,4″-terpyridine was accomplished by a reverse aldol condensation reaction of the appropriate aldehyde with alkyl and pyridyl acetyls. A selective quaternization method in toluene is described. In this method the 1,1′ nitrogens survive alkylation and are free to coordinate with metals to form metal complexes. The electrochemical behaviour of the neutral ligands as well as the monoquaternized cations was established by linear sweep cyclic voltammetry. Spectroelectrochemical techniques were used to establish the electronic spectral behaviour and stability of the radicals obtained upon reduction. Key words: 2,2′:4,4″-terpyridine, quaterpyridine, selective quaternization.
Nucleic acid related compounds. 63. Synthesis of 5′-deoxy-5′-methyleneadenosine and related Wittig-extended nucleosides
Authors: Wnuk Stanislaw F. , Robins Morris J.
Published: May 2006

Treatment of the purified 5′-aldehyde (2a) (derived from 6-N-benzoyl-2′,3′-O-isopropylideneadenosine (1a)) with methylenetriphenylphosphorane and successive deprotection with ammonia and acid gave 9-(5,6-dideoxy-β-D-ribo-hex-5-enofuranosyl)adenine (5′-deoxy-5′-methyleneadenosine) (4). Oxidation of 1a or 2′,3′-O-isopropylideneadenosine (1b) and treatment of the crude 5′-aldehydes (2a or 2b) with (p-toluenesulfonylmethylene)triphenylphosphorane gave high yields of the 5′-deoxy-5′-tosylmethylene derivatives (5a or 5b). Removal of the tosyl group from 5b to give 3b was effected with tributylstannyllithium, but sulfone cleavage by the usual reductive methods failed. Reduction and deprotection of 5a or 5b gave 9-[5,6-dideoxy-6-(p-toluenesulfonyl)-β-D-ribo-hexofuranosyl]adenine (6b). Isomerization of the vinyl tosyl (5b) to a 4′,5′-unsaturated allylic tosyl derivative (7) occurred under cleavage conditions and in solutions of aqueous or organic bases. Key words: adenosine, 5′-deoxyadenosine, 5′-methylene-5′-deoxyadenosine, nucleosides.
Lewis acidic titanium species: the synthesis, structure, bonding and molecular modelling considerations of the complexes Ti(NR2)3Cl (R = Me, Et)
Authors: Dick David G. , Rousseau Roger , Stephan Douglas W.
Published: May 2006

Reaction of simple amides with TiCl4 affords mixed amido-chloride species Ti(NR2)4−nCln. The trisamide-chloride species Ti(NR2)3Cl can be prepared directly employing three equivalents of amide or by reaction Ti(NR2)4 with TiCl4. The compound Ti(NMe2)3Cl, 1, crystallizes in the trigonal space group [Formula: see text] with a = 11.525(5), c = 14.939(3) Å, Z = 6, and V = 1718(1) Å3. The compound Ti(NEt2)3Cl, 2, crystallizes in the monoclinic space group P21/c, with a = 8.385(2) Å, b = 15.958(2) Å, c = 14.230(4) Å, β = 107.79(1)°, Z = 4, and V = 1813(1) Å3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. The structural data are consistent with Ti—N multiple bonding. Preliminary results of EHMO calculations are consistent with dπ—pπ Ti—N bonding. Attempts to replace the halides with phosphides (LiPR2, R = Me, Et, Ph) led not to the Ti(IV) phosphido species, but rather to redox chemistry yielding Ti(III) amides and P2R4. The barrier to rotation about the Ti—N bonds has been considered. Variable temperature 1H NMR studies reveal that the barrier is small. Extended Hückel total energy minimization calculations have been performed. In addition, MMX calculations of the barrier to Ti—N rotation are reported. The results of these calculations imply that the rotational barrier is dominated by steric effects. Key words: titanium amides, structures, Ti—N bonding
Reactions of δ-valerolactone with lithio trithio-orthoformates
Authors: Yates Peter , Seif-El-Nasr Azza , Stanton Jennifer , Krepinsky Jiri J.
Published: May 2006

δ-Valerolactone (3), on treatment with tris(methylthio)methyllithium (7) followed by weakly acidic aqueous work-up, gave a tautomeric mixture of 1, 1-bis(methylthio)-6-hydroxy-2-hexanone (8a) and tetrahydro-2-bis(methylthio)methyl-2-pyranol (8b). Under analogous conditions 3 reacted with tris(phenylthio)methyllithium (10) to form tetrahydro-3-(phenylthiocarbonyl)-2-pyranone (11). With 2-(methylthio)-1,3-dithian-2-yllithium (16) it gave a tautomeric mixture of 2-(5-hydroxy-1-oxopentyl)-2-(methylthio)-1,3-dithiane (17a) and 2-(tetrahydro-2-hydroxy-2-pyranyl)-2-(methylthio)-1,3-dithiane (17b). Treatment of 17 with methanol in the presence of acidic ion-exchange resin gave a mixture of 2-(5,6-dihydro-3-(methylthio)-2(4H)-pyranyl)-1,3-dithiane (20), 2-(tetrahydro-2-methoxy-2-pyranyl)-1,3-dithiane (21), and 2-(tetrahydro-2-methoxy-4-(methylthio)-2-pyranyl)-1,3-dithiane (22). Similar treatment of 20 gave a mixture of 20, 21, and 22. Compound 21 was synthesized independently by similar treatment of 2-(tetrahydro-2-hydroxy-2-pyranyl)-1,3-dithiane (23). The origins of the anomalous products are discussed briefly. It is concluded that because of these anomalies the preparation of tetrahydro-2-hydroxypyran-2-carboxylic acid acetals and related glycosides via trithio-orthoformate derivatives can encounter difficulties, although dithioacetals may serve this purpose. Key words: 1,3-dithianes, α-hydroxy acids,δ-lactones, trithio-orthoformates.
Theoretical and experimental approaches to the barrier to rotation about the Csp2—Csp3 bond in benzyl silane. Hyperconjugative stabilization of the perpendicular conformation
Authors: Schaefer Ted , Sebastian Rudy , Penner Glenn H.
Published: May 2006

The 1H nuclear magnetic resonance spectra of benzyl silane and benzyl trichlorosilane, obtained in CS2 and benzene-d6 solutions, are analyzed. The long-range coupling constants between the methylene and para ring protons are used to derive apparent twofold barriers about the Csp2—Csp3 bonds of 7.4 ± 1.6 and 8.1 ± 1.1 kJ/mol for the silane and the trichlorosilane, respectively. These are higher than that for ethylbenzene and are attributed mainly to the stabilization of the perpendicular conformer, that with the C—Si bond in a plane perpendicular to the phenyl plane, by σ–π conjugation (hyperconjugation) of the C—Si bond and the π electron system. Molecular orbital computations confirm the predominantly twofold nature of the internal barrier in benzyl silane and also for benzyl germane and stannane. The calculated barriers for the silane derivatives are rather higher than the experimental values. The computed barriers have magnitudes that appear to change with X in much the same order as do the hyperconjugative interactions deduced in other ways for CH2X(CH3)3 groups (X = Sn, Ge, Si, C). The angles CCX in benzyl-X (X = CH3, SiH3, SiCl3, GeH3, SnH3) are all computed to decrease smoothly as sin2ψ, where ψ is the angle by which the C—X bond twists out of the phenyl plane. Key words: conformations, benzyl silane and trichlorosilane; NMR, benzyl silane and trichlorosilane; MO calculations, benzyl silane and trichlorosilane.
Synthèse, structure et études spectroscopiques RMN 1H et 13C de dérivés perhydrocyclododéca[b]furaniques
Authors: Albrand Michel , Dolmazon René , Pollet Patrick
Published: May 2006

A synthetic route to perhydrocyclododeca[b]furan-3-ols, perhydrocyclododeca[b]furan-3-ones, and perhydrocyclododeca[b]furan derivatives is described. Their configurations were determined. For the perhydrocyclododeca[b]furan-3-one and perhydrocyclododeca[b]furan pairs, the cis isomer was much less stable than the trans isomer. This agrees well with results from a conformational analysis, carried out by molecular mechanics. The 1H and l3C NMR spectra are reported. Key words: perhydrocyclododeca[b]furans, conformations, force field calculations, 1H and 13C NMR.
Radical reductions of Cu(II)-penicillamine complexes: Evidence for a Cu(II)-disulphide anion intermediate
Authors: Mezyk Stephen P. , Armstrong David A.
Published: May 2006

In basic solution Cu(II) ions form planar complexes of stoichiometry Cu(II)•L2 with penicillamine molecules, where both the nitrogen and sulphur atoms of the thiol [(NH2)CH(CO2−)C(CH3)2S−] are involved in the coordination. The rates of reduction of this complex by the formate radical and the thiyl radical of penicillamine have been measured by pulse radiolysisThe rate constant for reaction [14] has been found to be 1.2 ± 0.2 × 108M−1 s−1[Formula: see text]For the thiyl radical, which is not inherently reducing, reduction must involve the [Formula: see text] anion complex.
Tautomerism in ketomethyl quinolines. Part 3. 4-Ketomethylquinolines
Authors: Greenhill John V. , Loghmani-Khouzani Hossein , Maitland Derek J.
Published: May 2006

A series of 4-ketomethylquinolines has been prepared and their tautomerism investigated. The compounds were prepared from 4-methylquinoline deprotonated with lithium diisopropylamide or potassium ethoxide and treated with esters. Attempted deprotonation with tert-butyllithium or phenyllithium led to 2-substituted-4-methylquinolines. The simple alkyl or aryl 4-keto methylquinolines exist essentially as the keto forms, but the quinoline-4-pyruvates are exclusively or substantially in the enol forms. Key words: ketomethyl quinolines, pyruvates, tautomerism, enols.
The rapid synthesis of organic compounds in microwave ovens. II
Authors: Gedye Richard N. , Rank Werner , Westaway Kenneth C.
Published: May 2006

Using microwaves to carry out organic reactions does not significantly alter the product composition. The small changes in product composition that are observed when microwaves are used arise because the microwave reactions occur at higher temperatures than reflux reactions. The results demonstrate that ions in the reaction mixture alter the heating rate of the microwave reactions. Although scaling-up the reaction leads to a slightly lower rate of reaction (lower percentage yield), one still retains large rate enhancements. Key words: microwave, synthesis, product composition, scale-up, ionic strength effects.
Gas-phase heteroaromatic substitution. 11. Electron transfer mechanism in the gas-phase acylation of simple five-membered heteroarenes
Authors: Filippi Antonello , Occhiucci Giorgio , Sparapani Cinzia , Speranza Maurizio
Published: May 2006

The results of a study of the gas-phase reactions of unsaturated carbocations, such as the CH3CO+ ion from γ-radiolysis of CH3F/CO mixtures, and the C6H4TCO+ ion from the β-decay of 1,4-ditritiobenzene in the presence of CO, with pyrrole, N-methylpyrrole, furan, and thiophene, are reported. In all systems investigated, acylated heteroarenes represent the predominant reaction products, accompanied by the methylated derivatives in the CH3F/CO radiolytic mixtures, and by the phenylated ones in the 1,4-ditritiobenzene/CO decay samples. All substrates investigated are found to undergo predominant α substitution by both acetyl (88.6–98.4% (pyrrole); 90.8–98.7% (N-methylpyrrole); 97.2–98.9% (furan); 94.9–98.6% (thiophene)) and benzoyl cations (92.6–96.5% (pyrrole)) under all conditions. The predominant formation of the α-acylated pyrroles from both reactants (>88%), whose relative yields appear unaffected within the temperature interval from 303 to 383 K, indicates, in agreement with ancillary FT-ICR mass spectrometric evidence, that gas-phase acylation reactions toward simple five-membered heteroarenes proceed via a two-step substitution mechanism, involving a quasi-resonant single-electron transfer (SET) step followed by recombination of the ensuing radical – radical ion pair. By virtue of this entropy-favored mechanism, gaseous electrophiles with relatively high SCF STO-3G calculated LUMO energies such as CH3CO+ and C6H4TCO+ are effectively oriented toward the "soft" Cα sites of the selected heteroarenes, at variance with Klopman's Charge and Frontier Orbital Control predictions. The behavior of gaseous acylating reactants toward simple heteroarenes is discussed and compared with that of other gaseous electrophiles, whose reactivity appears instead in qualitative agreement with Klopman's model. Key words: gas-phase ion chemistry, electrophilic heteroaromatic substitution, nuclear decay and radiolysis, acylium ions, electron transfer.
Bipolar charge carrier transport in amorphous molecular solid solution of arylamine and diphenoquinone derivatives
Authors: Yamaguchi Yasuhiro , Fujiyama Takahiro , Yokoyama Masaaki
Published: May 2006

Amorphous molecular composites of N,N,N′,N′-tetra(m-tolyl)-1,3-diaminobenzene as an electron donor and 3,5-dimethyl-3′,5′-di-tert-butyl-4,4′-diphenoquinone as an electron acceptor have been found to be capable of transporting both hole and electron. Based on drift mobility measurements, it is demonstrated that the donor and acceptor components function independently as hole- and electron-hopping sites, respectively, with no electronic interaction between them. Key words: bipolar charge transport, arylamine, diphenoquinone, molecular solid solution.
On the reaction of A-nor-5α-cholestan-2-one with benzeneseleninic anhydride
Authors: Morzycki Jacek W. , Obidzińska Jolanta
Published: May 2006

A-Nor-5α-cholestan-2-one (1) was oxidized with BSA under various conditions. The stoichiometric reaction afforded diketones (3 and 4) and α-phenylseleno-ketone (2) while catalytic oxidation with the BSA/PhIO2/p-TsOH system resulted in lactones (7a and 7b) and anhydrides (5 and 6). The mechanism of these reactions is discussed. Key words: benzeneseleninic anhydride, A-nor-5α-cholestan-2-one, catalytic oxidation.
Reactivity patterns of N-methylbenzhydroxamates. I. Studies of methyl transfer between N-methylbenzhydroxamates and arenesulfonates
Authors: Fountain Kenneth R. , Fountain Daniel P. , Michaels Bernice , Myers D. Brenton , Salmon Jon K. , Galen Dean A. Van , Yu Pat
Published: May 2006

The rates of methyl transfer between benzohydroxamates and sulfonates show large βnuc values (ca. 0.8) indicating much charge transfer to the C atom, similar to the results of N,N-dialkylaminofluorene anions. A small α effect shows that even in methyl substrates, with certain leaving groups, the effect is displayed. Investigation of the β1g shows that from the leaving group side of the reaction it is a normal SN2 reaction. Correlation of the reactivity with computed gas phase ionization potentials shows that desolvation of anions is probably not important. These results suggest an α-effect model that explains the larger size of the effect at carbonyl groups in terms of greater solvation of the charge transferred to the O atom. Key words: α effect, Brønsted plot, ionization potentials, cyclic voltammetry, β1g, βnuc, AMl, [Formula: see text]
Phosphoric amides. Part 11. Intramolecular reactivity of phosphorotriamidates
Authors: Bauermeister Slegelinde , Modro Agnes M. , Modro Tom A. , Zwierzak Andrzej
Published: May 2006

Five N-(2-chloroethyl)phosphorotriamidates, (RNH)2P(O)NHCH2CH2Cl, have been synthesized, and their behavior under strongly basic conditions was studied. For N-alkyl derivatives (R = Me, PhCH2), base-promoted intramolecular displacement of chloride yielded the N-phosphorylated aziridine, (RNH)2P(O)NC2H4, as the exclusive cyclization product. For N-aryl derivatives (R = Ar), both the aziridine and the 1,3,2-diazaphospholidine, [Formula: see text], products could be obtained in comparable yields. The N-aromatic cyclic products are mutually interconvertible: 1,3,2-diazaphospholidines rearrange to the corresponding aziridines upon treatment with base, while bromide ions catalyze the reverse isomerization. Key words: phosphoramidates acidity, N-phosphorylated aziridines – 1,3,2-diazaphospholidines isomerization, 1,3 vs. 1,5 cyclization.
Densities and viscosities of binary and ternary liquid mixtures at 25 °C
Authors: Aminabhavi Tejraj M. , Joshi Shrikant S. , Balundgi Ramachandra H. , Shukla Shyam S.
Published: May 2006

Densities and viscosities of ten binary and four ternary mixtures containing bromoform, bromobenzene, chlorobenzene, toluene, mesitylene, and dimethylformamide at 25 °C have been measured over the whole range of mixture compositions. Excess molar volumes, apparent values of excess molar viscosities, and Gibbs energy of activation of flow have been calculated for these mixtures. The calculated results have been fitted to a linear regression equation to estimate the parameters and the standard deviation between the calculated and the experimental data. Key words: ternary systems, excess quantities, bromoform, density, viscosity.
Vibrational and electronic spectra of new liposoluble metalloporphyrins in a nonpolar noncoordinating solvent
Authors: Ringuet Michel , Girard Denis , Chapados Camille
Published: May 2006

A new liposoluble porphyrin, 2,7,12,17-tetrahexyl-3,8,13,18-tetramethylporphin(THTMP), and its complexes with divalent (Mg, Co, Ni, Cu, Zn, Cd, Hg) and trivalent (Mn, Fe) metals have been synthesized. The electronic, infrared, and far-infrared spectra of these compounds were obtained in the same nonpolar, noncoordinating solvent, CCl4. After comparison with the experimental data and the results of normal coordinate analyses from the literature, the assignment of the vibrational bands of THTMP and its complexes is made. Some correlations between the shifts of the metal sensitive bands in the diffferent regions and the structural characteristics of the porphyrin complexes are reported. Some emphasis is made on the magnesium complex in relation to chlorophyll. Key words: Metalloporphyrin, porphyrin, infrared spectroscopy, far-infrared spectroscopy, electronic spectroscopy, nitrogen-metal bond, covalent radius, reduced mass.
Analysis of reactive ion transport in weakly ionized gas mixtures
Authors: Iinuma Koichi
Published: May 2006

A new formulation for the analysis of low density multiple-ion swarms drifting, diffusing, and inter-reacting in a neutral gas is proposed on a transport theory basis. A set of coupled three-dimensional transport equations for an arbitrary number of ion species, which governs the number densities of the ion swarms as functions of time and position coordinates, is exactly solved using a Fourier transform in a matrix representation. A picture of dynamic equilibrium state for hypothetical four ion swarms in a neutral gas is numerically obtained. Also, experimental data of transport coefficients and reaction rates for (Li+, Li+•N2, Li+•2N2)flN2 system are examined in a complete reversible cyclic reaction scheme and compared with a Green's function method. The initial and boundary conditions, the analysis in gas mixtures, and the inelastic process associated with the present formulation are briefly discussed. Key words: ion swarm, cluster ion, transport equation, ion–molecule reaction.
Stereoselective syntheses of isomers of 3,7-dimethylnonadecane, a sex pheromone of the alfalfa blotch leafminer (Agromyza frontella (Rondani))
Authors: Miller David , Bilodeau François , Burnell Robert H.
Published: May 2006

Two related stereoselective syntheses of 3,7-dimethylnonadecane, a sex pheromone of the alfalfa leafminer, are described to show that pulegone can serve as a useful starting material for the preparation of chiral aliphatic isoprenoid compounds. The schemes are designed to place the stereogenic center of pulegone at C.3 in one synthesis and at C.7 in the other so that the optical properties of the products can be compared with one another and with the values calculated using Brewster's rules. Key words: chiral hydrocarbons, stereoselective synthesis, pheromone, Agromyza frontella.
Structure and magnetic properties of [Cp2M(μ-PEt2)]2 (M = Ti, Zr)
Authors: Dick David G. , Stephan Douglas W.
Published: May 2006

The complex [Cp2Ti(μ-PEt2)]2 (1) crystallizes in the monoclinic space group P21/n with a = 16.591(3) Å, b = 8.662(2) Å, c = 37.407(2) Å, β = 102.40(1)°, Z = 8, and V = 5250(2) Å3. The Ti2P2 core of the dimeric complex is planar and the angles at Ti and P are close to 90°. The Ti … Ti separations were found to be 3.732(1) and 3.706(1) Å in the two independent molecules in the unit cell. Bulk magnetic susceptibility measurements on solid 1 show that the species is diamagnetic over the range 5–340 K. The coupling constant for the antiferromagnetic interaction between the Ti centers of 1 is found to be at least −300 cm−1. Extended Hückel Molecular Orbital calculations suggest that mixing of the frontier 1a1 orbitals of the Cp2Ti fragments with the p orbitals of the phosphide fragments affords a mechanism for super-exchange through the ligands. In THF solution, variable temperature 1H, and 31P{1H} NMR and EPR spectra for 1 are consistent with the generation of the paramagnetic monomeric species Cp2TiPEt2, 3. As well, the data suggest thermal populations of the paramagnetic triplet state of the dimer may occur to a small extent at 340 K. In contrast, the analogous Zr dimer 2 shows no evidence of dissociation or of thermal population of the triplet state at temperatures to 340 K. Key words: titanium phosphides, structures, magnetic properties.
Synthesis and nuclear magnetic resonance spectroscopy of indane structures: indanes mono- and disubstituted in the pentagonal ring
Authors: Alesso Elba N. , Tombari Dora G. , Ibañez Adriana F. , Iglesias Graciela Y. Moltrasio , Aguirre José M.
Published: May 2006

Indanes monosubstituted and 1,2- and 1,3-disubstituted in the pentagonal ring were synthesized, and configurations were assigned to the 1,2-disubstituted compounds by means of nuclear magnetic resonance spectroscopy. Key words: mono- and disubstituted indanes, conformation, configuration, 1H and 13C NMR, synthesis.
Excess molar volumes of (a cycloalkane + an alkanol) at 298.15 K
Authors: Letcher T. M. , Mercer-Chalmers J.
Published: May 2006

In this work we report the excess molar volumes, [Formula: see text] for the miscible mixtures {xc-C5H10 + (1 − x)CH3OH} and {xc-CkH2k + (1 − x)ClH2l+1OH} where k = 5, 6, 7, 8, or 10 and l = 2 or 3. The [Formula: see text] results are discussed in terms of the size of the cycloalkane ring and the type of alcohol. Key words: Excess volumes, cycloalkane + alkanol.
Inhibition of papain by peptide nitriles: conversion of the nitrile group into other functionalities via the papain:nitrile thioimidate ester adduct
Authors: Gour-Salin Barbara J. , Lachance Paule , Storer Andrew C.
Published: May 2006

Peptide nitriles are reversible inhibitors of papain that form thioimidates with the cysteine thiol in the enzyme's active site. These thioimidates undergo reactions with thiols and amines to form acids and amidines, respectively. These reactions were also found to be stereospecific. Only a thioimidate derived from an L-amino acid nitrile will react with exogenous nucleophiles. These reactions were followed by 13C and 15N NMR techniques. Key words: papain, nitrile, l3C NMR, 15N NMR, thioimidate.
π-Facial stereoselectivity in the Diels–Alder reactions of benzene oxides
Authors: Gillard James R. , Newlands Michael J. , Bridson John N. , Burnell D. Jean
Published: May 2006

The Diels–Alder reactions of N-phenylmaleimide and dimethyl acetylenedicarboxylate with benzene oxide (1,3,5-cyclohexatriene 1,2-oxide, 3) and its more substituted derivatives 1,2-dimethyl-1,3,5-cyclohexatriene 1,2-oxide (7) and 10-oxatricyclo[4.3.1.0]deca-2,4-diene (11) in a kinetic manner gave exclusively products of addition anti to the plane-nonsymmetrical oxygen. The structures of the adducts were determined unequivocally by nuclear Overhauser enhancements in their 1H nuclear magnetic resonance spectra and by X-ray crystallographic methods. The π-facial stereoselectivity was rationalized in terms of unfavorable orbital interactions, steric hindrance between the dienophile and the syn face of benzene oxide, and σ-donation by the oxygen. Key words: cycloaddition, Diels–Alder, syn-anti, π-facial stereoselectivity, benzene oxide.
Complexes binaires du nickel(II) et du zinc(II) avec la 1-canavanine et la 1-arginine, études potentiométriques et spectroscopiques
Authors: Albourine Abdallah , Petit-Ramel Michelle , Thomas-David Germaine , Vallon Jean Jacques
Published: May 2006

The stability constants of binary complexes of 1-canavanine (Can) and 1-arginine (Arg) with Ni2+ and Zn2+ have been calculated at 25 °C and at ionic strength μ = 0.1 (NaNO3). This technique is completed with spectrophotometry and circular dichroïsm measurements in the ultraviolet and visible ranges. Thus we determined the molar absorbances and the molar circular dichroïsm of ligands and complexes with Ni2+ and Zn2+. Concerning the nickel(II), these measurements display three complexes, NiL, NiL2, and NiL3. 1-Canavanine, which generally has a tridentate ligand behaviour, becomes a bidentate ligand in the Ni(Can)3 complex. With regard to zinc(II), this study only displays the ZnL and ZnL2 species. Key words: 1-arginine, 1-canavanine, circular dichroïsm, nickel binary coordination, zinc binary coordination.
A novel type of active site at the surface of crystalline SiO2 (a-quartz) and its possible impact on pathogenicity
Authors: Costa Dominique , Fubini Bice , Giamello Elio , Volante Marco
Published: May 2006

A new type of surface site, different from those previously described, which gives rise to a paramagnetic oxygen species upon adsorption of O2 at low temperature, has been found at the surface of crystalline quartz. This site is abundant on freshly cleaved surfaces or on chemically etched ones but absent on crystal growth faces or on samples annealed at high temperature. The abundance of this site is not related to the other surface radicals characteristic of the quartz surface originated by mechanical grinding in air. The EPR spectral features of the signal suggest an ozonide type radical O3−. The adsorption of oxygen onto quartz dusts variously treated in order to modulate their fibrogenic potential in vivo indicates that a relationship may exist between the presence of this site and quartz pathogenicity. Key words: quartz, oxygen radical species, ozonide, silicosis, EPR.
Stereochemistry and kinetics of amines addition to acetylenic esters
Authors: Sharaf Saber M. , El-Sadany Samir K. , Hamed Ezzat A. , Youssef Abdel-Hamid A.
Published: May 2006

The reactions of a series of methyl para-substituted phenylpropiolates 1a–e with piperidine, morpholine, and diethylamine in methanol and dimethylformamide (DMF) have been studied and their rates measured. The products were methyl β-(N,N-dialkylamino)-p-substituted cinnamates 2–4a–e. 1H NMR spectra were used to determine the configuration of the products. The ρ values in methanol ranged between 0.34 and 1.24 whereas in DMF they were between 0.85 and 1.88. The values of ΔS≠ favor a bimolecular rate-limiting step mechanism. Key words: nucleophilic addition to acetylenic esters.
Cadmium chloride mediated regiocontrol of dienolates and ketene thioacetals: γ condensation with aldehydes
Authors: Lei Bo , Fallis Alex G.
Published: May 2006

The use of cadmium chloride to control the regioselectivity of vinylogous anions upon condensation with aldehydes is described. Addition occurred preferentially at the γ position with substituted crotonates and 2-ethylidene-1,3-dithiane (6). Experiments demonstrated that this selectivity arose as a consequence of isomerization of the initially formed kinetic α product to the thermodynamic γ product (e.g., 2 to 4). The optimum results were achieved with 2 equivalents of cadmium chloride and quenching at 0 °C. Key words: vinylogous anions, cadmium, condensation, dithiane.
Diels–Alder reactions of activated 2H-thiopyrans
Authors: Ward Dale E. , Gai Yuanzhu , Zoghaib Wajdi M.
Published: May 2006

The Diels–Alder reactivity of various 2H-thiopyrans bearing electron-donating substituents has been investigated. The approximate order of reactivity among the 2H-thiopyrans studied was 4,6-disubstituted [Formula: see text] 5-substituted > 4-substituted, 3,5-disubstituted [Formula: see text] 3-substituted. Good yields of predominantly endo adducts are obtained with reactive dienophiles. With less reactive dienophiles, reactions are much slower and yields are attenuated due to the competing thermal decomposition of the dienes under the reaction conditions. The adducts obtained are equivalent (via desulfurization) to those from unreactive cis-substituted dienes. Key words: Diels–Alder, 2H-thiopyran.
Hétéropolyanions de type Dawson. 2. Synthèses de polyoxotungstoarsénates lacunaires dérivant de l'octadécatungstodiarsénate. Étude structurale par RMN du tungstène-183 des octadéca(molybdotungstovanado)diarsénates apparentés
Authors: Contant Roland , Thouvenot René
Published: May 2006

The di-, tri-, and hexavacant lacunary tungstoarsenates α-[HAs2W16O59]11−, α-[As2W15O56]12−, and α-[H2As2W12O48]12− were prepared by controlled alkaline degradation of the Dawson-type anion α-[As2W18O62]6−. The relationships between all these anions and the two α-[As2W17O61]10− isomers were established. The mixed saturated derivatives α-[As2VxW18−xO62](6+x)− (x = 1,2,3) and α-[As2MoxW18−xO62]6− (x = 1, 3) were obtained by refilling the lacunas with vanadium and molybdenum respectively. The new mixed anion α2-[As2Mo2W15O61]10− was used concurrently with α-[HAs2WI6O59]11− to obtain α-[As2Mo2W16O62]6−; in both cases minor parts of α-[As2MoxW18−xO62]6− (x = 1 and 3) were obtained simultaneously. All species have been characterized by polarography and by IR spectrometry. Proposed structures, based on the similarity of the redox properties and syntheses processes to those of the corresponding Dawson-type lacunary and mixed tungstophosphates, were given for all these species. The structures of the "saturated" tungstovanado- and molybdotungstoarsenates were confirmed by 183W solution NMR. In addition the 183W solution NMR spectra of all these latter species are discussed in relation to those of the analogous phosphoric derivatives. Finally, the main differences with the corresponding tungstophosphoric anions lie in (i) the existence of [HAs2W16O59]11−, whose protonation satisfies Lipscomb's rule, (ii) the lack of a stable oligomer like [P8W48O184]40−, and (iii) the lower stability of the octadeca(molybdotungsto)diarsenates. Key words: heteropolyanions, tungstoarsenate, molybdotungstoarsenate, tungstovanadoarsenate, l83W NMR.
Electronic absorption and fluorescence spectra of 2-phenyl-substituted benzothiazoles: study of excited-state proton transfer reactions
Authors: Dey Joykrishna , Dogra Sneh K.
Published: May 2006

The absorption and fluorescence spectral properties of 2-(3′-hydroxyphenyl)-, 2-(4′-hydroxyphenyl)-, and 2-(3′,4′-dihydroxyphenyl)-, and 2-(4′-hydroxy-3′-methoxyphenyl), 2-(3′-hydroxy-4′-methoxyphenyl)-, and 2-(3′-methoxyphenyl)benzothiazoles have been studied in a number of solvents of varying polarity. The ionization constants (pKa) for various prototropic reactions of these molecules in both S0 and S1 states are determined. The effect of substitution on the spectral properties and on the pKa values are discussed. The molecules have been found to undergo biprotonic phototautomerism in dilute acid solutions. On the basis of the fluorimetric titration behaviour of the molecules (except 2-(3′-methoxyphenyl)benzothiazole), the existence of monocation–zwitterion equilibrium in the S1 state is proposed. PPP-SCF-MO-CI method has been used to calculate charge densities on the heteroatoms. Key words: spectra, proton transfer.
Infrared and Raman microscopy of fowl feather barb
Authors: Tsuboi Masamichi , Kaneuchi Fumiko , Ikeda Teruki , Akahane Kiso
Published: May 2006

A fowl feather barb 10 μm in thickness was subjected to a polarized infrared spectroscopic measurement by the use of a microscopic device. Nearly 50% of its peptide groups were found to give the 1633 and 1684 cm−1 bands characteristic of the antiparallel-chain pleated sheet structure, and the remaining 50% gave the 1659 cm−1 band assignable to unordered polypeptide chains. The orientation of the pleated sheet was determined to be on average θ = 52° and χ = 39°, where θ and χ are the angles for the transformation of the XYZ coordinate system fixed on the pleated sheet and the abc coordinate system fixed on the sample barb. The Raman spectra of the barb were also examined with another microscopic device and a 488.0-nm laser beam. A sharp aa component of the Raman scattering tensor was observed at 1667 cm−1. Based on this fact, a revised set of parameters for the vibrational couplings among the peptide groups in the pleated sheet has been proposed. Some discussions have been made on the amide I Raman tensor of the antiparallel-chain pleated sheet. Key words: fowl feather barb, Raman microscope, infrared microscope, antiparallel-chain pleated sheet, Raman scattering tensor.
The polymorphism of alkali metal formates. Part 4. A Raman study of the phase transition in KHCOO
Authors: Heyns A. M. , Range K.-J. , Müller K.
Published: May 2006

KHCOO II is orthorhombic at ambient conditions and it is shown that traces of moisture affect the polymorphism of these very hygroscopic crystals. Dry KHCOO II transforms into phase I at 417 K (144 °C), and this phase can be supercooled to room temperature, remaining metastable for several days before transforming back to the orthorhombic phase II. The Raman spectra of phases I and II, as well as of supercooled phase I, are reported in the present study. The absence of some prominent translational modes in the Raman spectra of KHCOO II, compared to NaHCOO II, can be explained on the basis of a group-theoretical treatment. From the temperature dependence of the linewidths of various Raman-active librational and internal modes, activation energies are obtained for intramolecular motions of the formate ions. Fermi resonance occurs between the overtone of the bending mode 2ν5 and the C—H stretching mode ν1 in KHCOO II and the coupling constant W increases with temperature. The Raman and X-ray data show that KHCOO I is structurally different from NaCHOO I, but it is not possible to assign a definite structure to this phase on the basis of a Raman spectrum alone. Key words: Potassium formate, phase transition, Raman spectra.
Étude potentiométrique de la stabilité de complexes tensioactif–β-cyclodextrine
Authors: Jezequel D. , Mayaffre A. , Letellier P.
Published: May 2006

The complexation constants K of β-cyclodextrine with 13 ammonium surfactants were determined by a potentiometric method using electrodes selective to amphiphilic ions. Especially for C12, C14, and C16 tails, a model that provides for the formation of a second complex (β-CD)2M+, with a K1/K2 ratio of about 600, provides a good fit with the experimental curves. Results show a poor influence of the polar group, for example in the case of the dodecyl chain. On the other hand, the pK1 values and the hydrophobic tail length are linked by a linear relation up to n = 12 carbon atoms; beyond, pK1 tends to be proportionally smaller and pK2 more important. Key words: surfactant, β-cyclodextrin, selective electrodes, complexation constants, potentiometric study.
Étude théorique (AM1) de l'affinité protonique des polyéthers cycliques (éthers couronnes) et non cycliques (glymes)
Authors: Esseffar M'hamed , Mouhtadi Mohamed El , Abboud José-Luis M. , Elguero José , Liotard Daniel
Published: May 2006

Semi-empirical calculations at the AM1 level have been used to study the proton affinity (PA) of polyether compounds (dioxane, glymes, and crown ethers). The calculated values, although systematically lower than the experimental ones, are linearly correlated with eight experimental PA's (r = 0.993). Taking into account the considerable conformational changes that take place upon protonation, the result is highly satisfactory and provides an estimate of proton affinity for 9-ether-crown-3 (206.5 kcal mol−1) and glyme-5 (231.1 kcal mol−1). Moreover, this work provides a rationale for the fact that, for the same number of oxygen atoms, glymes are more basic than crown ethers. For the crown ethers, the proton affinity depends on angular strain in the base and on intramolecular hydrogen bonds in the cation. Key words: protonation, reactivity, glymes, crown ethers, coordination.
Alkylation of α-tert-butoxycarbonylamino ketone enolate anions. A useful synthesis of α-alkyl-α-amino ketones, 2-acylpyrrolidines, and 2-acylpiperidines
Authors: Guzman Angel , Quintero Clara , Muchowski Joseph M.
Published: May 2006

A versatile synthesis of α-alkyl-α-amino ketones 5 and cyclic α-amino ketones 7 based on the selective mono-α-alkylation and C(α), N-cycloalkylation of α-tert-butoxycarbonylamino ketones 2 and subsequent acidic hydrolysis is described. Key words: α-tert-butoxycarbonylamino ketones, α-alkyl-α-amino ketones, 2-acylpyrrolidines, and 2-acylpiperidines.
Kinetics of breakdown of aryl hemiacetals of α-bromoacetophenone. Effect of phenol leaving groups on the lifetimes of tetrahedral intermediates
Authors: McClelland Robert A. , Kanagasabapathy V. M. , Mathivanan N.
Published: May 2006

The kinetics of breakdown of seven aryl hemiacetals of α-bromoacetophenone (TOH) have been examined, with aryl substituents 4-MeO, 4-Me, 3-Me, H, 3-MeO, 4-Cl, 3-Cl. The hemiacetals were generated as intermediates in the aqueous bromination of α-aryloxystyrenes, where the breakdown of the hemiacetal is the rate-limiting stage in the overall reaction. Base catalysis of the breakdown shows large Brønsted β values (0.8–1.0) and similarly large βlg values (−0.8 to −1.0). These are argued to arise because of a preassociation mechanism in which the hydrogen-bonded intermediate [Formula: see text] loses aryloxide faster than diffusional separation of the acid–base pair. This mechanism is enforced by lifetimes of the deprotonated hemiacetals TO− in the 1010–1012 s−1 range. Such lifetimes were estimated in two independent ways, by extrapolation of data previously obtained for alkyl hemiacetals of α-bromoacetophenone, and through a calculation based upon the experimental catalytic coefficients, and estimates of the acidity constants for TOH and the equilibrium constants for formation of hydrogen-bonded complexes. The pH-independent breakdown has βlg = −1.03, and the point lies near the Brønsted line for the carboxylate catalysts. This, therefore, also occurs by a preassociation mechanism with water as the catalyst forming the intermediate [Formula: see text], which loses aryloxide faster than diffusional separation. Catalysis by hydroxide ion occurs with rate constants of 8 × 109 M−1 s−1 independent of aryl substituent. This represents rate-limiting diffusional encounter of the hemiacetal and hydroxide ion, the hydrogen-bonded intermediate [Formula: see text] rapidly proceeding on to products. Acid catalysis of the hemiacetal breakdown occurs by a class "n" mechanism in which the acid assists departure of the substitued phenol. Alkyl hemiacetals of α-bromoacetophenone break down by a class "e" mechanism where the leaving group is fully protonated before bond cleavage. The class "e" mechanism can be excluded for the aryl derivatives, since rate constants much greater then diffusion are required to explain the observed catalytic coefficients. The different mechanism is followed in order to avoid the fully protonated hemiacetal, which, being of an O-protonated anisole structure, is of very high energy. Key words: hemiacetal kinetics, preassociation, intermediate lifetime.
Synthetic studies towards bruceantin. Part 1. Establishment of the carbon network
Authors: Darvesh Sultan , Grant Andrew S , MaGee David I , Valenta Zdenek
Published: May 2006

In a synthetic approach to the biologically active quassinoid bruceantin 1, intermediate 47 was prepared, which contains all required C-atoms, rings A and B, and four of the 10 chiral centers of bruceantin. The possibilities for a convergent strategy were explored, in which a 5-carbon unit would be joined to a 15-carbon unit by three bonds. After the study of various alkylations and Michael additions needed for the key step, it was found that 3-iodo-1-trimethylsilyl-5-hexenyne44adds to the dianion of methyl ketone nitriles 3 and 13 cheme-, diastereo-, and enantioselectively.Key words: bruceantin, quassinoids, alkylation, Michael addition.