bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and equilibration of conformationally rigid cis and trans tricyclic mono and dithioacetals. An evaluation of stereoelectronic (anomeric) effects in thioacetals
Authors: Deslongchamps Pierre , Guay Daniel
Published: May 2006

The synthesis of cis and trans tricyclic monothioacetals 5–8 and dithioacetals 9 and 10 is reported (Schemes 1 and 2). The cis isomers 5, 7, and 9 are the kinetic products of cyclization, a result which is explained on the basis of stereoelectronic principles. Equilibration studies (Table 1) led to an evaluation of the anomeric effect for sulfur; it was found to be of the same order as that for oxygen.
Configurational and conformational studies on condensation products of biogenic amines with 2,5-anhydro-D-mannose
Authors: Piper Ian M. , MacLean David B. , Faggiani Romolo , Lock Colin J. L. , Szarek Walter A.
Published: May 2006

The products of a Pictet–Spengler condensation of tryptamine and of histamine with 2,5-anhydro-D-mannose have been studied by X-ray crystallography to establish their absolute configuration. 1(S)-(α-D-Arabinofuranosyl)-1,2,3,4-tetrahydro-β-carboline (1), C16H20N20O4, is monoclinic, P21 (No. 4), with cell dimensions a = 13.091(4), b = 5.365(1), c = 11.323(3) Å, β = 115.78(2)°, and Z = 2. 4-(α-D-Arabinofuranosyl)imidazo[4,5-c]-4,5,6,7-tetrahydropyridine (3), C11H17N3O4, is orthorhombic, P212121 (No. 19), with cell dimensions a = 8.118(2), b = 13.715(4), c = 10.963(3) Å, and Z = 4. The structures were determined by direct methods and refined to R1 = 0.0514, R2 = 0.0642 for 3210 reflections in the case of 1, and to R1 = 0.0312, R2 = 0.0335 for 1569 reflections in the case of 3. Bond lengths and angles within both molecules are normal and agree well with those observed in related structures. In 3 the base and sugar adopt a syn arrangement, which is maintained by an internal hydrogen bond between O(2′) and N(3). The sugar adopts a normal 2T3 twist conformation. The sugar has the opposite anti arrangement in the β-carboline 1 and the conformation of the sugar is unusual; it is close to an envelope conformation with O(4′) being the atom out of the plane. This conformation is caused by a strong intermolecular hydrogen bond from O(5′) in a symmetry-related molecule to O(4′). Both compounds are held together in the crystal by extensive hydrogen-bonding networks. The conformations of the compounds in solution have been investigated by 1H nmr spectroscopy, and the results obtained were compared with those obtained by X-ray crystallography for 1 and 3.
Synthesis and study of new mesogen compounds: 4-alkoxy-2-hydroxy-4′-substituted-α,α′-dimethylbenzalazines. Correlation analysis between TN–I transition and electronic parameters in five series of liquid crystals
Authors: Marcos Mercedes , Melendez Enrique , Ros Blanca , Serrano Jose Luis
Published: May 2006

Two new series of compounds with mesomorphic properties were synthesized; the 4-ethoxy and 4-octyloxy-4′-X-2-hydroxy-α,α′-dimethylbenzalazines (X = CN, NO2, F, Cl, Br, CH3, and N(CH3)2). Thermodynamic measurements were made. All the compounds gave mesogenic behaviour. Some of them exhibit polymorphism in the solid state, A study of the existent correlation between the temperatures at which the N–I transition appears in five series of mesogenic compounds and electronic parameters of the polar terminal chain was carried out. Seven terminal groups were studied: —F, —Cl, —Br, —CH3, —OCH3, —NO2, and —CN. None of the electronic parameters used enabled us to obtain a good correlation with all the groups. However, when the methoxy group was omitted, the parameters that measured π electronic delocalization in the aromatic ring showed an excellent correlation with the TN–I. The best correlation was obtained in all cases with Swain and Lupton's [Formula: see text], which defined the resonance effect.
New functionalized water-soluble benzophenones: a laser flash photolysis study
Authors: Lougnot D. J. , Jacques P. , Fouassier J. P. , Casal H. L. , Kim-Thuan Nguyen , Scaiano J. C.
Published: May 2006

Two water-soluble ionic benzophenones containing a quatemized amine and a sulphonate group have been investigated by laser flash photolysis. The decay kinetics and spectra of their triplet states were studied and quenching constants by triethanolamine, isopropanol, and methyl viologen determined. These data are of interest when these benzophenones are used as initiators for photo-polymerizing water-soluble acrylates in homogeneous solution or in reverse micellar assemblies. The high water solubility of these compounds allows the bimolecular deactivations due to triplet–triplet (kTT) and triplet–ground state (kSQ) interactions to be determined more accurately than in the case of benzophenone itself.
Antiferromagnetic super exchange and spectral studies on dimeric 8-quinolinolato complexes of copper(II) imides
Authors: Sharma C. L. , Mishra V.
Published: May 2006

The complexes of the type [Cu(Q)(P)]2 and [Cu(Q)(S)]2 where HQ = 8-hydroxyquinoline and P and S are deprotonated phthalimide and succinimide, respectively, were prepared and characterized on the basis of molecular mass determination, elemental analysis. X-ray diffraction, ir, electronic spectra, conductance, thermal analysis, and magnetic measurements. They were of tetrahedrally distorted square planar structure. The susceptibility data at different temperatures were fitted to the Bleaney–Bowers equation which indicated medium antiferromagnetic super exchange interaction within one dimeric unit. The values of exchange integral and g were found to be −136 cm−1 and 2.18, respectively, for the phthalimide complex and −128 cm−1 and 2.16, respectively, for the succinimide complex.
Densities and apparent molar volumes of aqueous NaCl–KBr mixtures at 298.15 K
Authors: Kumar Anil
Published: May 2006

Experimental differences in densities Δd of aqueous NaCl–KBr mixtures at I = 1, 2, 3, and 4 mol kg−1 and at 298.15 K are reported from pure NaCl to pure KBr solutions. Mean apparent molar volumes [Formula: see text] are calculated and excess volumes of mixing [Formula: see text] are correlated by Friedman equation, Δd and [Formula: see text] are analysed in terms of recently developed the Pitzer formalism without and with mixing terms. Pitzer equations can estimate the densities of such mixtures with uncommon cations and anions within ±0.02% at the high ionic strength of 4 mol kg−1.
Kinetics and mechanism of oxidation of lactic acid by KMnO4 in H2SO4 medium
Authors: Girgis M. M. , El-Shatoury S. A. , Khalil Z. H.
Published: May 2006

The initial oxidation stages of lactic acid by acid permanganate were investigated. The rate of the induction period was slow and then gradually increased. The kinetics of oxidation were second order, first order with respect to both lactic acid and Mn(VII). The reaction was acid catalyzed. Addition of Mn(II) ions largely increased the rate of the initial stages and decreased the rate of the following stages. The oxidation rate was decreased by the addition of F− or [Formula: see text] ions. The Arrhenius equation was valid for the reaction between 16.5 and 34 °C. Activation parameters were evaluated and a mechanism consistent with the results obtained was proposed.
Pd/SiO2–AlPO4 systems. Influence of the preparation variables on their catalytic activity
Authors: Alba A. , Aramendia M. A. , Borau V. , Jimenez C. , Marinas J. M.
Published: May 2006

A study on the liquid phase hydrogenation of cyclohexene over a series of Pd catalysts supported on various SiO2–AlPO4 systems (using a concentration of 2.47 M, with methanol as solvent, the initial hydrogen pressure is 5 bar and reaction temperature 300 K) is reported in this paper. The reaction has been studied as a standard in order to determine the most suitable preparation conditions for these catalystsWe have also studied the influence of other factors such as the kind of support, the nature of the metal precursor, the previous calcination of the precursor, the addition of alkaline hydroxides, and the catalyst reduction with various agents, on the catalytic activity of different Pd-supported systems
Synthèses et analyses structurales de perchlorates anhydres d'In(III) et de Tl(III) M(ClO4)3 et ClO2M(ClO4)4; (M = In, Tl)
Authors: Fourati Mohieddine , Chaabouni Moncef , Ayedi Hassine Ferid , Pascal Jean-Louis , Potier Jacqueline
Published: May 2006

Reactions of chlorine trioxide (Cl2O6) with anhydrous InCl3, TlCl3, and InCl3•4H2O have been investigated. They give two chloryl perchlorato metallates: ClO2In(ClO4)4 and ClO2Tl(ClO4)4, which can be decomposed on heating (80 °C) under dynamic vacuum. They yield respectively In(ClO4)3 and Tl(ClO4)3. Tl(ClO4)3 appears to have weaker thermal stability than In(ClO4)3, which is stable up to 272 °C; the former decomposes starting at 95 °C to give TlO0.5(ClO4)2. In(ClO4)3 and Tl(ClO4)3 have the same space group [Formula: see text]. The best assignment of their ir and Raman vibrational spectra can be made on the basis of a polymeric structure (Asl3 type) with bridging bidentate perchlorato groups strongly bonded to the metal. The ClO2M(ClO4)4 (M = In, Tl) salts are well defined. The cation ClO2+ is unambiguously characterized; it interacts with the anion M(ClO4)4−, which has monodentate and bidentate perchlorate groups.
Synthesis, crystal and molecular structure, and vibrational spectra of the complex (COOH)2•2H2O•18-crown-6
Authors: Deguire Suzanne , Brisse François , Ouellet Jacques , Savoie Rodrigue
Published: May 2006

A stoichiometric complex of formula (COOH)2•2H2O•18-crown-6 has been obtained from oxalic acid and the macrocyclic polyether 18-crown-6. The crystals of the complex have a monoclinic unit cell and belong to the P21/c space group. The components in the adduct are linked through hydrogen bonds in a polymer-like fashion: -crown–H2O–HOOCCOOH–OH2–crown–, where the oxalic acid molecules are present in two distinct disordered orientations. The infrared and Raman spectra of the complex are also reported and interpreted.
Long-range proton coupling constants and molecular orbital calculations as indicators of conformational populations of benzene-1,2- and -1,3-dicarbaldehydes
Authors: Schaefer Ted , Penner Glenn H. , Sebastian Rudy , Takeuchi Craig S.
Published: May 2006

The 1H nmr spectra of the benzene-1,2- and -1,3-dicarbaldehydes in carbon tetrachloride, benzene-d6, and acetone-d6 solutions at 300 K are analyzed. The stereospecific long-range couplings over five formal bonds between the sidechain and ring protons show that the 1,2 isomer exists as an 87:13 mixture of the cis–trans and trans–trans conformers in carbon tetrachloride. These populations are insensitive to solvent. Molecular orbital calculations utilizing extensive geometry optimization procedures imply that the cis–cis form, with proximate C=O bonds, is indeed of negligible significance as assumed in obtaining the populations of the other forms. Further calculations define a pathway of relatively low energy for interconversion of the two abundant forms, in agreement with dynamic nmr studies. For the 1,3 isomer the long-range couplings provide a check of the conformer populations deduced from dipole moment and 13C nmr studies. For example, if the cis–trans form is 70% abundant, as deduced from the dipole moment in benzene solution, then the long-range couplings imply that the population of the cis–cis conformer is insignificant.
Zero-field optical detection of magnetic resonance of chlorophyll b in n-octane
Authors: Hotchandani S. , Clarke R. H. , Leblanc R. M.
Published: May 2006

The zero-field ODMR of triplet state of chlorophyll b in n-octane has been carried out. The ODMR parameters measured at various fluorescence wavelengths suggest that Chl b is probably present in more than two ligated species in which water serves as the ligand.
Hydrolysis and condensation of chlorophosphine and alkyl phosphite ligands on platinum and palladium. 31P and 195Pt nuclear magnetic resonance studies and the crystal and molecular structures of [Pt2Cl4{μ-(EtO)2POP(OEt)2}2] and [Cl2Pt{μ-(P(OEt)2O)2P(O)}PtCl(PEt3)2]
Authors: Berry David Eric , Beveridge Kathryn Anne , Bushnell Gordon William , Dixon Keith Roger , Pidcock Alan
Published: May 2006

Hydrolysis of cis-[PtCl2-{P(OEt)2Cl}2] results in condensation of the phosphite to form [Pt2Cl4{μ-(EtO)2POP(OEt)2}2], which crystallizes in the monoclinic space group P21/n, with a = 13.814(7), b = 11.429(4), c = 10.726(5) Å, β = 106.30(5)°. Reactions of P(OEt)2Cl or (EtO)2POP(OEt)2 with [Pt2Cl4(PEt3)2] also yield very easily hydrolyzed products but in these cases an even more complex condensation occurs to yield [Cl2Pt{(μ-(P(OEt)2O)2P(O)}PtCl(PEt3)2], which crystallizes in the monoclinic space group P21/c, a = 17.547(8), b = 19.775(6), c = 11.268(3) Å, β = 106.42(3)°. Complete X-ray diffraction studies are reported for both crystals, confirming the presence of double (EtO)2POP(OEt)2 bridges in [Pt2Cl4{(μ-(EtO)2POP(OEt)2}2] and a novel triphosphite bridge in [Cl2Pt{μ-(P(OEt)2O)2P(O)}PtCl(PEt3)2]. Detailed analyses and computer simulation of the 31P{1H} and 195Pt{1H} nmr spectra of these complexes are also described, together with studies of the related compounds, [Pt2Me4{μ-(EtO)2POP(OEt)2}2] and [Cl2(Et3P)Pt{μ-(EtO)2POP(OEt)2}PtCl2(PEt3)]. In conjunction with previous studies of [Pt2Cl2(dppm)2] and related complexes, these spectra provide examples of several types of AA′XX′ spin systems and the analysis of these systems is discussed in detail.
Selected-ion flow tube studies of reactions of the radical cation (HC3N)+• in the interstellar chemical synthesis of cyanoacetylene
Authors: Fox A. , Raksit A. B. , Dheandhanoo S. , Bohme D. K.
Published: May 2006

The radical cation (HC3N)+• was produced in a Selected-Ion Flow Tube (SIFT) apparatus from cyanoacetylene by electron impact and reacted at room temperature in helium buffer gas with a selection of molecules including H2, CO, HCN, CH4, H2O, O2, HC3N, C2H2, OCS, C2H4, and C4H2. The observed reactions exhibited a wide range of reactivity and a variety of pathways including charge transfer, hydrogen atom transfer, proton transfer, and association. Association reactions were observed with CO, O2, HCN, and HC3N. With the latter two molecules association was observed to proceed close to the collision limit, which is suggestive of covalent bond formation perhaps involving azine-like N—N bonds. For HC3N an equally rapid association has been observed by Buckley etal. with ICR (Ion Cyclotron Resonance) measurements at low pressures and this is suggestive of radiative association. The hydrogen atom transfer reaction of ionized cyanoacetylene with H2 is slow while similar reactions with CH4 and H2O are fast. The reaction with CO fails to transfer a proton. These results have implications for synthetic schemes for cyanoacetylene as proposed in recent models of the chemistry of interstellar gas clouds. Proton transfer was also observed to be curiously unfavourable with all other molecules having a proton affinity higher than (C3N)•. Also, hydrogen-atom transfer was inefficient with the polar molecules HCN and HC3N. These results suggest that interactions at close separations may lead to preferential alignment of the reacting ion and molecule which is not suited for proton transfer or hydrogen atom transfer.
Electrochemical gasification of lignite in phosphoric acid
Authors: Johnson Keith E. , Verdet Luc
Published: May 2006

A combination of simple voltammetry, cyclic voltammetry, chronopotentiometry, glc, proximate and ultimate analyses, and petrography were applied to the investigation of lignite electrogasification in phosphoric acid. Conversion of ~40% lignite to CO2 occurs, in part by thermal reaction. Electrooxidation of the lignite occurs in part through electrocatalysis due to incorporated Fe(II). Lesser amounts of CO are produced thermally.
Fluorination of uracil with acetylhypofluorite and fluorine in acetic acid: mechanistic investigation
Authors: Diksic Mirko , Farrokhzad Slmin , Colebrook Lawrence D.
Published: May 2006

Fluorination of uracil with acetylhypofluorite and fluorine in acetic acid is described. The influence of the acetate ion on the products of the fluorination reaction was examined. Two stereoisomers (cis (3) and trans (4)) were found in the reaction mixture following fluorination in the absence of the acetate ion, but only one isomer (4) and 5-fluorouracil were found when the acetate ion was present during the fluorination reaction. 2H nuclear magnetic resonance revealed that acetate from the solution containing acetate ion rather than from the residue from acetylhypofluorite binds to position 6 of uracil to form intermediates. The synthesis yields 5-fluorouracil isolated as pure compound in a chemical yield, relative to the fluorine introduced, of about 45%. The influence of inorganic cations on the yield of acetylhypofluorite was also evaluated.
Structural parameters for the chair or twist-boat conformations of 1,3-dioxa-5,6-benzocycloheptene and its 2-methyl and 2,2-dimethyl derivatives
Authors: St-Amour Robert , Olivier Marc J. , St-Jacques Maurice , Brisse François
Published: May 2006

Low temperature X-ray studies of 1,3-dioxa-5,6-benzocycloheptene (1) and its 2-methyl (2) and 2,2-dimethyl derivatives (3) show that 1 and 2 exist in the crystal state exclusively in the chair (C) form while 3 exists exclusively in the twist-boat (TB) form. The final values of the agreement index, Rw, are 0.048, 0.059, and 0.046 for 1, 2, and 3, respectively. Significant structural differences between the g+g+ arrangement of the acetal moiety with the TB form and the g+g− disposition in the C form are revealed. These differences can be interpreted as arising from a less efficient back-donation of an antiperiplanar lone pair on the oxygen atom in the g+g+ relative to the g+g− arrangement. Furthermore, the C—O bond lengths shed some light on the hybridization state of the lone pairs of electrons on oxygen. Finally the results are used to rationalize nmr observations in terms of molecular conformations in solution.
The He(I) and X-ray photoelectron spectra of p-N,N-dimethylaminobenzalmalonitrile
Authors: Katrib A. , El-Issa B.D. , Potts A. W.
Published: May 2006

The assignment of the four outermost ionization energies obtained by uv-photoelectron spectroscopy (UPS) of p-N,N-dimethylaminobenzalmalonitrile is given. The X-ray photoelectron spectroscopy of the N ls and C ls core levels are also discussed. Two "shake-up" lines were observed at the high binding energy side of the N ls spectral line. The energies of these spectral lines were found to correlate very well with the uv–visible spectrum. Also the energy difference of the two "shake-up" lines was found to be similar to the energy difference between the first and second ionization energies obtained by ups techniques. Only one "shake-up" line was observed in the case of C ls photoionization. Theoretical studies by semiempirical methods including HAM/3, MINDO/3, and extended Hückel are also discussed.
Bromation stéréosélective d'alcynes par le tribromure de tétrabutylammonium
Authors: Berthelot Jacques , Fournier Michel
Published: May 2006

The reaction of tetrabutylammonium tribromide (TBABr3) with alkynes (R—C≡C—R′, with R and (or) R′ = H, alkyl, phenyl, carboxyl, carbonyl) in chloroform at 20 °C gives only the corresponding E 1,2-dibromo alkene in high yields. A mechanism involving a cyclic brominated zwitterion is suggested to account for the results, especially the stereospecificity of this E-addition.
Estimation of heats of vaporization for non associating organic liquids from the boiling points at various pressures
Authors: Guthrie J. Peter
Published: May 2006

At any pressure the heat of vaporization can be expressed as a quadratic function of the boiling point at that pressure. A seven parameter equation expressing the simultaneous dependence on boiling point and pressure can be fitted to the data; six pressures from 1 to 760 Torr (1 Torr = 133.3 Pa) were used. ΔHvap = b11 + b12 In (p) + b13p + (b21 + b22 In (p))tbp + (b31 + b32 In (p))tbp2. This relationship served as a guide for developing a relationship between vapour pressure at 25 °C and the calorimetric heat of vaporization, and also a relationship between vapor pressure at 25 °C and the boiling point at some other pressure. Parameters for both these relationships could be derived from the parameters obtained for ΔHvap as a function of temperature and pressure. A third method was developed starting from an equation for vapor pressure and fitting to the heat of vaporization, the heat capacity of vaporization, and at least one t,p point. These methods allow the estimation of the vapor pressure at room temperature from very meager data. The problems of errors in estimated values are discussed.
Sulphur anion chemistry in hydrocarbon flames with H2S, OCS, and SO2 additives
Authors: Goodings John M. , Bohme Diethard K. , Elguindi Kamal , Fox Arnold
Published: May 2006

A premixed, fuel-rich, methane–oxygen flame at atmospheric pressure was doped separately with 0.2 mol% of H2S, OCS, and SO2 to probe the behaviour of fuel sulphur during combustion. These three additives represent compounds occurring early, intermediate, and late in the oxidation sequence of fuel sulphur. They are chemically ionized in the reaction zone of a hydrocarbon flame to give large signals of sulphurous negative ions. Those detected include S−, SH−, SO− (uncertain), SO2− (S2−), SO3−, HSO3−, CH3O−•SO2, SO4− (S2O2−, S3−), and HSO4−. Ion concentration profiles of these ions were measured along the conical flame axis by sampling the flame into a mass spectrometer. The shapes of the profiles are insensitive to the nature of the additive, but their relative magnitudes are indicative of the additive's position in the sulphur oxidation sequence. For each additive, the very large HSO4− signal has analytical implications as an indicator for total fuel sulphur. The sulphurous anion chemistry is discussed for each additive in terms of roughly twenty ion (electron)-molecule reactions of six basic types, whose rate constants were known previously, or were measured at room temperature using the York flowing afterglow apparatus.
Voltammetric studies of the electrochemical behaviour of salicylidene-2-aminopyridine at a hanging-mercury-drop-electrode
Authors: Abdel-Hamid Refat
Published: May 2006

Electrochemical behaviour of salicylidene-2-aminopyridine has been investigated in 0.1 M tetraethylammonium perchlorate–dimethylformamide solutions by cyclic voltammetric and convolution potential sweep voltammetric methods. It was found that the depolarizer exhibits two well-defined diffusion-controlled irreversible one-electron waves. The cyclic voltammetric characteristics and the convolution, deconvolution, and logarithmic convolution analyses reveal that salicylidene-2-aminopyridine in such conditions follows a set of two one-electron transfer reactions each followed by an irreversible chemical reaction. The values of the first-order rate constant of the irreversible chemical reaction and E1/2 were computed.
Substitution régiosélective d'arènesulfonylhydrazones α,β-insaturées via la réaction de Shapiro
Authors: Caille Jean Claude , Farnier Michel , Guilard Roger
Published: May 2006

Arenesulfonylhydrazones of α,β-unsaturated cyclopentanones such as isopropylidene and cyclopentylidene cyclopentanones have been treated with alkyllithium reagents at −78 °C followed by trapping with a variety of electrophiles. The reactivity of these hydrazones depends on the nature of electrophile that controls the regioselectivity of the reaction. The structure of all the products is established by 1H and 13C nmr. The reaction occurs with no inversion of configuration of the hydrazones. The formation of a "six centers" intermediate is discussed. Moreover, such a reactivity is used to prepare monoterpenic aldehydes.
Kinetics and mechanism of dehydrochlorination of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides
Authors: Shawali Ahmad S. , Albar Hassan A.
Published: May 2006

The kinetics of triethylamine (TEA) catalyzed deydrochlorination of a series of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides 1a–m have been studied under pseudo-first-order conditions in 4:1 (v/v) dioxane–water solution at 30 °C. For all compounds studied, the kinetics followed the rate law: kobs = k2 (TEA). The values of the overall second-order rate constants for the studied compounds were correlated by the equation: log k2 = 0.533σ−-0.218. The results are compatible with a mechanism involving a fast reversible deprotonation step leading to the anion of 1, followed by rate-determining step involving the loss of the chloride ion from the anion. The reaction constants of these two steps were estimated to be 0.845 and −0.312, respectively.
The crystal and molecular structure of N-(3,4,5-trimethoxycinnamoyl)-Δ3-piperidine-2-one, an amide alkaloid (piperlongumine), C17H19NO5
Authors: Banerjee Tapati , Chaudhuri Siddhartha
Published: May 2006

The crystals of C17H19NO5 belong to the monoclinic space group P21/n with a = 15.793(3), b = 4.089(4), c = 24.649(5) Å, β = 97.56(3)° V = 157 8(2) Å3, and Z = 4. The structure was solved by MULTAN 78 and refined by full-matrix least-squares to a final R of 0.053 for 1863 observed reflections. X-ray crystallography has revealed that the molecule is the Δ3 isomer and not the Δ5 isomer suggested originally from nmr spectroscopy. The piperidyl nitrogen is sp2 hybridized with its electron lone pair involved in conjugation with the carbonyl groups. The piperidone ring adopts a distorted boat conformation. An interesting feature of the structure is the formation of two C(ethylenic)—H … O(keto) intramolecular hydrogen bonds which stabilize the molecular conformation.
Electrochemical behaviour of the Zn(II)–Zn(Hg) system in aqueous ethylene glycol solutions
Authors: Rodríguez R. M. , Brillas E. , Garrido J. A. , Doménech J.
Published: May 2006

The electrochemical behaviour of the Zn(II)–Zn(Hg) system in aqueous ethylene glycol (EG) solutions containing 5.0 × 10−2 M LiClO4 has been studied by polarography and cyclic voltammetry. The reversible half-wave potentials, the diffusion coefficients and the Walden products for Zn(II) have been polarographically determined. The standard free energies of transfer of 1 mol of Zn(II) ions from water to EG–water mixtures, [Formula: see text], obtained from the reversible half-wave potentials vs. the ferrocene electrode scale, are always negative, indicating a greater stability of Zn(II) in EG–water mixtures than in pure water. The splitting of the [Formula: see text] values into electrostatic and chemical contributions shows that the mixtures are more basic than water. The analysis of the variation of the Walden product with solvent composition indicates an enhancement of the solvent structure in the water-rich region. The diffusion coefficient for Zn in mercury, the transfer coefficients for Zn(II) electroreduction, and the apparent standard rate constants of the Zn(II)–Zn(Hg) system have been determined by cyclic voltammetry. The change in the kinetics with solvent composition is discussed in terms of existing models.
Synthesis, structure, proton-nuclear magnetic resonance, and Fourier transform infrared spectroscopy of several transition and nontransition metal–adenosine-5-triphosphate complexes
Authors: Tajmir-Riahi H. A. , Bertrand M. J. , Theophanides T.
Published: May 2006

Several complexes of adenosine-5-triphosphate disodium salt (Na2H2ATP) with the metal ions, Na+, Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, and cis- and trans-Pt(NH3)2Cl2 and K2PtCl4 at pH = 3.5 and 7.2 have been isolated, identified, and studied. Marked spectral similarities have been observed for the structurally known metal–phosphate bonded compounds, [Cu(H2ATP)(phen)]2•7H2O and [Zn(H2ATP)(bipy)]2•4H2O and all the metal–ATP complexes studied here, except the Pt–ATP complexes. The metal binding is through the α, β, and γ phosphate oxygen atoms when the N1-position of adenine is protonated. Spectral changes have also been observed for the Pt–ATP complexes in which there is a Pt–N7 and –N1 coordination. The sugar pucker in the Na2H2ATP•3H2O crystal dimers is C3′-endo–anti (in one) and C2′-endo–anti (in the other) with a characteristic infrared band at 818 cm−1. In the corresponding Cu2+ and Zn2+ complexes the sugar has C3′-endo–anti conformation with the marker band at about 814 cm−1. The C2′-endo–anti conformation is observed for all the metal–ATP complexes prepared here with a marker band at 825–822 cm−1.
The synthesis and seven-coordinate structure of (CH3)2AsC(CF3=C(CF3)As(CH3)2W(CO)Br2[P(OCH3)3]2
Authors: Mihichuk Lynn , Pizzey Monica , Robertson Beverly , Barton Richard
Published: May 2006

(L–L)W(CO)4 (L–L = (CH3AsC(CF3)=C(CF3)As(CH3)2) is oxidized by Br2 to yield the seven-coordinate complex (L–L)W(CO)3Br2, which reacts with monodentate phosphines or phosphites to form (L–L)W(CO)Br2P2 (P = phosphine or phosphite). Crystals of (L–L)W(CO)Br2[P(OCH3)3]2 are monoclinic, space group P21/c, a = 19.110(5), b = 9.208(3), c = 17.845(6) Å, β = 108.93(2)° at 21 °C with Z = 4. The structure was solved from a Patterson map and refined by least squares to a conventional R value of 0.092 using 2330 independent reflections. The crystal structure indicated the tungsten atom to be seven-coordinate with the geometry most closely approximated by a capped trigonal prismatic environment, the capping group being a bromine atom (W—Br, 2.686(5) Å). The capped face consists of the remaining bromine atom (W—Br, 2.695(5) Å), a phosphorus atom (W—P, 2.465(9) Å), and the two arsenic atoms from the bidentate ligand (W—As, 2.619(3) and 2.526(4) Å). The W—As bond trans to a phosphite is significantly longer (by 0.093 Å) than the W—As bond trans to a bromine. The 1H nmr data indicate that the complex is stereochemically rigid at 25 °C and nonrigid at higher temperatures; however, the data at 25 °C are not consistent with the configuration found in the crystal.
Interdiffusion of acids and bases•HCl and NaOH in aqueous solution
Authors: Leaist Derek G. , Wiens Betty
Published: May 2006

Stokes magnetically stirred diaphragm cells have been used to measure interdiffusion of hydrochloric acid and sodium hydroxide in aqueous solution at 25 °C. Expressions are developed to estimate ternary diffusion coefficients for these mixtures. The analysis reveals sharp discontinuities between the diffusion properties of HCl-rich and NaOH-rich mixtures. Although the diffusion coefficients are sensitive to concentration, accurate analytic approximations for rates of interdiffusion can be obtained by averaging coefficients along the diffusion path. When HCl and NaOH interdiffuse, proton-coupled and hydroxide-coupled diffusion operating simultaneously on opposite sides of the diffusion boundary lead to rapid diffusion of inert Na+ and Cl− species.
Steric activation in prototropic reactions of pyrazine derivatives. I. Polar and conformational effects
Authors: Lee T. W. S. , Stewart Ross
Published: May 2006

The rates of proton loss from methyl groups in a number of pyrazine derivatives have been measured in D2O by monitoring the replacement of protium by deuterium at the acidic sites of the substrates; they include the reaction of four methylpyrazines with NaOD/D2O and nine alkylpyrazinium ions with D2O/DCl. The reactive site, which is a methyl group conjugated to the aza or azonium group of the substrate, is in all cases activated by an adjacent alkyl group, with the greatest effect, a factor of about 30, occurring when a proton on nitrogen is replaced by a methyl group. The phenomenon is analysed in terms of polar effects, ring strain and inter-alkyl interactions (including gear effects), and hybridization changes at nitrogen.
15N Nuclear polarisation in the rearrangement of 2,6-dichloro-N-nitroaniline and 2,6-dibromo-N-nitroaniline
Authors: Abu-Namous Adel M. A. , Ridd John H. , Sandall John P. B.
Published: May 2006

The acid-catalysed rearrangements of 2,6-dichloro-N-nitroaniline and 2,6-dibromo-N-nitroaniline to give the corresponding 4-nitro derivatives have been followed by 1H and 15N nmr spectroscopy in deuteriochloroform at 30 °C. When 15NO2-labelled nitramines are used, the 15N nmr signals for both the substrate and product show enhanced absorption during reaction. When one labelled nitramine and one unlabelled nitramine are rearranged together, isotopic exchange occurs and 15N nmr signals are seen for both substrates and both products. For the initially unlabelled nitramine and its product, these signals are in emission. The change in the enhancement of the signals during reaction shows that the nuclear polarization arises from the rearrangement, not from a preliminary equilibrium.
Acid-catalyzed enolization of acetophenone: catalysis by bisulfate ion in sulfuric acid solutions
Authors: Keeffe J. R. , Kresge A. J. , Toullec J.
Published: May 2006

Rates of acid-catalyzed enolization of acetophenone in dilute aqueous solution, measured under conditions where the solvated proton is the only acidic species present, give a hydrogen ion catalytic coefficient, [Formula: see text], that is 35% smaller than the value obtained by X acidity function extrapolation of measurements made in moderately concentrated sulfuric acid solutions. The difference may be attributed to catalysis by bisulfate ion in the sulfuric acid solutions; this is supported by direct measurement of the bisulfate ion catalytic coefficient in dilute sulfuric acid. This revised value of [Formula: see text] leads to new, but only slightly different, values of the keto–enol equilibrium constant for acetophenone in aqueous solution, pKE = 7.96 ± 0.04, the acidity constant for acetophenone ionizing as a carbon acid, [Formula: see text] and the encounter-controlled rate constant for the reaction of acetophenone enol with molecular bromine, k = (3.2 ± 0.4) × 109 M−1 s−1.
The chlorination of acetone: a complete kinetic analysis
Authors: Guthrie J. Peter , Cossar John
Published: May 2006

Rate constants are reported for all of the major steps followed in the chlorination of acetone, including the chlorination of mono- and 1,1-dichloroacetone, the chlorination of hydroxyacetone, the chlorination and hydroxide-catalyzed rearrangement of 1,1-dihydroxyacetone, and the haloform cleavage of trichloroacetone. pKa values are reported for hydroxyacetone and monochloroacetone. Rate constants for the hydrolyses of chloroacetone and 1,1-dichloroacetone are reported; these reactions are probably not SN2 displacements but proceed by addition of hydroxide and intramolecular displacement.
Gas phase basicity of dihydropyran and dihydro-1,4-dioxin
Authors: Bouchoux G. , Hanna I. , Houriet R. , Rolli E.
Published: May 2006

The gas phase basicity (GB) of dihydropyran 1 and dihydro-1,4-dioxin 2 is measured in equilibrium proton transfer reactions conducted in an ion cyclotron resonance spectrometer. GB(1) is found to be greater than GB(2) by 37 kJ mol−1, this difference parallels the lower reactivity of 2 observed in solution under acidic condition. Conclusion as to the favoured protonation of the C—C double bond, giving rise for both 1 and 2 to oxycarbonium cations, is drawn from comparison with analogous compounds and substantiated by molecular orbital calculations (MNDO) on the protonated structures.
Phosphazène: une étude théorique du spectre d'ionisation
Authors: Gonbeau Danielle , Garcia Jean-Luc , Pfister-Guillouzo Geneviève
Published: May 2006

A study of photoionization cross sections was undertaken in MSXα on the phosphazène HP=NH. For the ionizations involving the phosphorus and nitrogen lone pairs, the results were discussed and compared with those obtained from examination of localizations in the initial state. In parallel the electronic reorganization effects encountered in the ionic states were also analyzed.
Monoozonides of chloro-substituted conjugated dienes: preparation, stability, and some chemical reactions
Authors: Griesbaum Karl , Bandyopadhyay Ashis R. , Meister Martin
Published: May 2006

The chlorodienes (E)-4-chloro-3-methyl-1,3-hexadiene (5a), (E)- and (Z)-4-chloro-2,3-dimethyl-1,3-hexadiene (5b/6b), (E,E)-5-chloro-4-methyl-2,4-heptadiene (5c), (4E)- and (4Z)-5-chloro-3,4-dimethyl-2,4-heptadiene (5d/6d), chloroprene (11a), and 2-chloro-3-methyl-1,3-butadiene (11b) are selectively ozonized at the non-chlorinated double bonds to give the corresponding monoozonides 7, 8, and 12. Further ozonolyses of the monoozonides of 5b and of 11b in methanol as well as epoxidation of the monoozonide of 5b and subsequent reaction of the resulting chloroepoxide with AgBF4 are described.
Enantiospecific synthesis of optically pure (S)-(+)-3-hydroxy-1-phenyl-1-butanone by bakers' yeast reduction
Authors: Chênevert Robert , Thiboutot Sonia
Published: May 2006

Bakers' yeast reduces 1-phenyl-1,3-butanedione with high chemo- and enantio-selectivity to give (S)-(+)-3-hydroxy-1-phenyl-1-butanone. The enantiomeric purity (> 98%) was determined by nmr analysis using a chiral shift reagent and the absolute configuration was determined by correlation with ethyl (S)-(+)-3-hydroxybutyrate.
Utilisation de l'ortho-tolidine pour l'étude des réactions des halogénates et halogénites
Authors: Schmitz Guy , Rooze Henri
Published: May 2006

We have shown previously that ortho-tolidine greatly simplifies the kinetic study of redox reactions of chlorite by reacting with intermediate products and eliminating side reactions. The present study shows the validity of the method in the case of bromate reactions. For the bromate–bromide reaction it gives the classical fourth-order rate law with k = 1.54 M−3 s−1 in perchloric acid solutions at 25 °C and 1 M ionic strength, and an acidity constant of bromic acid of 2.9. This method is then used to study the reaction between bromate and chlorite, a complex reaction in the absence of ortho-tolidine. The rate law is[Formula: see text]with k = 0.83 + 0.76 [H+] in the same conditions. If [H+] = 0.1 M the apparent activation energy is 47.4 kJ/mol.
Structure électronique des dianions B12H122− et B9C2Hn2−
Authors: Goursot Annick , Pénigault Edouard , Chermette Henry , Fripiat Joseph G.
Published: May 2006

MS-Xα molecular orbital calculations have been performed on the dianions B12H122− and B9C2H112−. Their electronic structures are discussed in terms of group charge distributions. For the dicarbollide ion, this study indicates a most probable electrophilic attack on the boron site opposite to the C—C bond, on the pentagonal face.
Structure and conformation of the N-β-propionic acids of cyclohexan[b]indole and cyclooctan[b]indole
Authors: Esteban-Calderon Carmen , Martinez-Ripoll Martín , García-Blanco Severino , Temprano Fernando , Rodriguez José Gonzalo
Published: May 2006

The structures of cyclohexan[b]indole N-β-propionic acid (1) and cyclooctan[b]indole N-β-propionic acid (2) have been determined by X-ray methods. The conformational populations of their N-β-propionic chains have been determined in solution by 1H nmr analyses. Crystals of 1 are triclinic, space group [Formula: see text] with a = 12.3562(4), b = 11.0727(3), c = 10.2050(4) Å, α = 108.519(3), β = 83.941(3), γ = 104.826(3)°, and Z = 4. Crystals of 2 are monoclinic, space group P21/c, with a = 5.636(1), b = 18.937(3), c = 13.976(4) Å, β = 98.84(3)°, and Z = 4. In both structures, the molecules are linked forming dimers through centrosymmetric H bonds. In solution the trans conformation of the chain is the preferred one in both compounds and increases with dilution until a constant value is reached.
Photochemical retro-aldol type reactions of nitrobenzyl derivatives. Mechanistic variations in the elimination of nitrobenzyl carbanions from nitrobenzyl derivatives on photolysis
Authors: Wan Peter , Muralidharan S.
Published: May 2006

The photochemical retro-aldol type reactions of several nitrobenzyl derivatives are reported. The reactions are observed only in aqueous solution with quantum efficiencies being pH dependent for several derivatives, consistent with the existence of several mechanistic pathways for reaction. The primary photochemical event is believed to involve the generation of a nitrobenzyl carbanion, which acts as a photolabile leaving group in these reactions, and the generation of an oxocarbocation (or oxocarbocation-derived) fragment.
Dissolution enthalpy of NaCl in aqueous nonelectrolyte solutions at 298.15 K. Analysis of electrolyte–nonelectrolyte enthalpic pair interaction coefficients in aqueous solution
Authors: Piekarski Henryk
Published: May 2006

Enthalpies of solution of NaCl in aqueous solutions of isopropanol, s-butanol, 2-methoxyethanol, 2-ethoxyethanol, acetone, and N,N-dimethylformamide were measured. The results of enthalpy measurements were analyzed from the point of view of the effect of added nonelectrolyte on water structure, and enthalpic pair interaction coefficients hxy{(Na+ + Cl−)–nonelectrolyte} were calculated and compared with appropriate data for (Na+ + I−)–nonelectrolyte pairs. The group additivity concept appeared to be useful for the analysis of calculated hxy coefficients. The correlations between hxy and the functions characterizing different properties of the solutes under study were examined. It was shown that the correlation with the heat capacity of transfer of the nonelectrolyte molecule from the vapour phase to high dilution in water was the most promising. The interpretation of observed correlations was proposed.
Heat capacities of binary mixtures of n-octane with each of the hexane isomers at 298.15 K
Authors: Benson George C. , D'Arcy Patrick J.
Published: May 2006

Volumetric heat capacities for binary mixtures of n-octane with n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane were measured at 298.15 K in a Picker flow microcalorimeter. The results were combined with previously published excess molar volumes to obtain excess molar isobaric heat capacities. Interpretation of the results in terms of the Flory theory of mixtures is discussed.
Electrometric studies on molecular complexes. Part 1. Biamperometric study of some molecular complexes of iodine
Authors: Singh Ram Adhar
Published: May 2006

A simple method for separate determination of thermodynamic parameters of molecular complexes in solution is reported. It is based on a polyiodide dissociation equilibrium in conjunction with the biamperometry. The equilibrium constants and the enthalpies determined by this method are in good agreement with the recent literature data, lending support for the applicability of the method. The advantages of the present technique over the other have been outlined.
Comparison of oxygen and sulphur adsorption on the (0001) surface of zirconium
Authors: Wong P. C. , Mitchell K. A. R.
Published: May 2006

Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) have been used to compare the adsorption and coadsorption of O2 and H2S on the (0001) surface of zirconium where exposures are in the one to five Langmuir regime. The new observations made are as follows: (i) that sulphur forms a stable (3 × 3) surface structure after heating to 600° C; (ii) that the Zr(0001) surface with high O coverage adsorbs H2S, whereas the surface with high S coverage does not adsorb oxygen in detectable amounts; and (iii) that for surfaces with adsorbed H2S a sudden increase in the 150 eV to 92 eV Auger peak ratio occurs on heating to 530° C.
Mobility of thermal cations in low density alkane gases
Authors: Gee Norman , Floriano M. Antonio , Freeman Gordon R.
Published: May 2006

Mobilities µ of thermal cations were measured in gases of six linear n-alkanes, ethane to n-decane, and in i-butane and neo-pentane, as functions of density n and temperature T. The low density limit was reached where nµ and the temperature coefficient at constant n, (dnµ,/dT)n, were constant. At all temperatures the average momentum transfer cross sections σave equalled (1.2 ± 0.4) times the cross sections expected from simple polarization. At high temperature σave might be approaching a hard sphere limit.
The pKa values of simple aldehydes determined by kinetics of chlorination
Authors: Guthrie J. Peter , Cossar John
Published: May 2006

From the kinetics of chlorination of acetaldehyde and isobutyraldehyde we have been able to determine the pKa values of the free aldehydes (corrected for covalent hydration) as 16.9 ± 0.5 and 15.7 ± 0.5, respectively. These values are in reasonable accord with other work and show that our kinetic method for ketone pKa's can be extended to aldehydes. For isobutyraldehyde the transition from rate-determining halogenation to rate-determining enolization occurs at [OCl−] values around 10−3 M for hydroxide concentrations of 0.1 to 1. For acetaldehyde the transition would only occur at much higher [OCl−].
A general intramolecular Diels–Alder approach to tricyclic sesquiterpenes: stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene
Authors: Antczak Kazimierz , Kingston John F. , Fallis Alex G. , Hanson Alfred W.
Published: May 2006

Stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene are described. The sequence employs a "blocked" cyclopentadiene in which the cyclopropane unit also serves as a latent methyl group. Thus intramolecular [4 + 2] cycloaddition of the substituted methyl spiro[2.4]hepta-4,6-dien-1-yl-2-pentenoate 13c affords 5-benzyloxy-6-isopropyl-8-carbomethoxytetracyclo[5.4.01,7.02,4.02,9]undec-10-ene (14c), which after selective hydrogenolysis generates the tricyclo[4.4.01,6.02,8]decane (sinularene) ring system. Removal of the secondary hydroxyl function by elimination and hydrogenation (Ph3P/CCl4/CH3CN; H2/Pd/C), reduction of the methyl ester (LiAlH4), and introduction of the exocyclic double bond (acetate pyrolysis, 550 °C) completes the synthesis of (±)-sinularene in 12 steps from aldehyde 7. A parallel series of reactions employing the isopropyl triene epimer 13a affords (±)-5-epi-sinularene. X-ray analyses of the triene 13a and the adduct 14a are also reported.
Facial (syn–anti) stereoselectivity in the Diels–Alder reactions of spiro(bicyclo[2.2.2]octane-2,1′-[2,4]cyclopentadiene)
Authors: Burnell D. Jean , Goodbrand H. Bruce , Kaiser Stephanie M. , Valenta Zdenek
Published: May 2006

Spiro(bicyclo[2.2.2]octane-2,1′-[2,4]cyclopentadiene) (3) has been synthesized in ten steps, and its Diels–Alder cycloadditions, both thermal and catalysed, have been studied with a variety of Z-ethylenic dienophiles. No significant differences in facial stereoselectivity were observed. This suggests that, in the exo region, the distance between the addends at the transition state is approximately the same in all the cases studied.
A comparative study on the dynamics of epimeric 1-hydroxymethylquinolizidines: I. Conformational analysis of monomers and spectroscopic data for solid state, liquid state, and dilute solutions
Authors: Kulińska K. , Wiewiórowski M.
Published: May 2006

A systematic comparative study of the conformational dynamics of lupinine and epilupinine, two 1-hydroxymethyl quinolizidine epimers, as a function of phase transition and of their protonation is presented. Lupinine and epilupinine have a trans-quinolizidine configuration and they differ only in the position of the CH2OH group. The axial position of this group allows the formation of an intramolecular hydrogen bond OH … N in lupinine, in contrast to epilupinine in which this group is in the equatorial position. Intrinsic conformational equilibria for both epimers have been defined. Despite the significant difference in the population of the preferred rotamers of lupinine and epilupinine, both epimers adopt very similar crystal structures, but in all other states and forms, e.g., pure liquids, solutions in inert and polar solvents, and protonated salts, they behave in drastically different ways.
Attempted novel preparation of dihydrocoumarin and coumarin; obtention of aryl acrylates and 3-chloropropionates
Authors: Mahajan Jaswant R. , Araújo Hugo C.
Published: May 2006

It has been found that, contrary to the published report, there is no noticeable reaction between phenol and methyl acrylate in the presence of aluminum chloride to produce phenyl acrylate (1) and dihydrocoumarin (2). Although products having the reported spectral data can be obtained by the reaction of phenol with acrylyl chloride, these products are actually phenyl acrylate and phenyl 3-chloropropionate (4), there being detected no dihydrocoumarin. This reaction has now been extended to several substituted phenols and some naphthols. Attempts at cyclization of phenyl acrylate, phenyl 3-chloropropionate, or their mixtures have been unsuccessful.