bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of hexacyanomanganate(II) in cyanide medium and kinetics and mechanism of its oxidation by chromate
Authors: López-Cueto Guillermo , Duarte Mlguel
Published: May 2006

The rate of formation of hexacyanomanganate(II) is first-order in Mn(II) and depends on both the cyanide and hydroxide concentrations. The experimental results agree with a reaction mechanism which involves manganese(II) cyano- and hydroxo-complexes. Chromate slowly oxidizes hexacyanomanganate(II). The kinetics of this reaction is first-order on hexacyanomanganate(II), and the experimental rate constant depends on the chromate concentration according to the equation kexp = 3kK[Cr(VI)]/(1 + K[Cr(VI)]). The effect of both the CN− and the OH− ions is slighter. A tentative mechanism is proposed which involves a pre-equilibrium with the formation of a hexacyanomanganate(II)–chromate complex, followed by a monomolecular decomposition. By comparing this reaction mechanism with that of other one-electron chromate reductions, it appears that hexacyanomanganate(II) behaves like octacyanomolybdate(IV) rather than like hexacyanoferrate(II) and other substitution-inert reductants. Both the equilibrium constants for the complex formation and the rate constant for its decomposition are evaluated, and voltammetric evidence of the formation of hexacyanomanganate(III)–chromate complexes is also presented. Keywords: hexacyanomanganate(II), formation rate, oxidation with chromate, kinetics, mechanism.
Vinylogous nucleophilic catalysis. The tertiary amine promoted reaction of ethenesulfonyl chloride with alcohols
Authors: King James Frederick , Loosmore Sheena May , Hillhouse John Henry , Khemani Kishan Chand
Published: May 2006

Ethenesulfonyl chloride (1) reacts with alcohols in the presence of tertiary amines to give a mixture of the alkyl ethenesulfonate (5) and the alkyl betylate (R3′N+CH2CH2SO2OR Cl−). With pyridine and neopentyl alcohol the product composition from the reaction of 1 is identical to that from the pyridinio-sulfonyl chloride (9). These results, when taken with experiments with deuterium labelled reagents, lead to the conclusion that the major (~80%) reaction pathway involves conversion of 1 or 9 to the sulfene 8, which reacts with the alcohol to form 5 or the betylate, and hence vinylogous nucleophilic catalysis is the major process leading to 5. The labelling experiments disclosed a minor pathway, evidently involving interconversion of 1 and 9. Examination of possible mechanisms leads to the suggestion that the sulfene is formed from 1 or 9 by way of the carbanion (14), i.e., that 9 reacts by an E1cB process, and that the minor pathway is simply the result of side reactions of the carbanion (14). Keywords: sulfenes, sulfonyl transfer mechanisms, vinylogous nucleophilic catalysis.
Identification of domoic acid, a neuroexcitatory amino acid, in toxic mussels from eastern Prince Edward Island
Authors: Wright J. L. C. , Boyd R. K. , Freitas A. S. W. de , Falk M. , Foxall R. A. , Jamieson W. D. , Laycock M. V. , McCulloch A. W. , McInnes A. G. , Odense P. , Pathak V. P. , Quilliam M. A. , Ragan M. A. , Sim P. G. , Thibault P. , Walter J. A. , Gilgan M. , Richard D. J. A. , Dewar D.
Published: May 2006

The causative agent of toxicity in cultured mussels from a localized area of eastern Prince Edward Island has been identified as domoic acid, a neuroexcitatory amino acid. The toxin was isolated by a number of different bioassay-directed separation techniques including high-performance liquid chromatography, high-voltage paper electrophoresis, and ion-exchange chromatography, and characterized by a number of spectroscopic techniques including ultraviolet, infrared, mass spectrometry, and nuclear magnetic resonance. The isolation and purification methods are described in detail and some new analytical data for domoic acid are reported. Keywords: shellfish toxin, domoic acid, neurotoxin, bioassay-directed analysis.
Étude de l'annélation à partir de dérivés dibromomés-1,4 et -1,5 en présence de carbanions
Authors: Canonne P. , Plamondon J.
Published: May 2006

Primary–secondary dibromides have been prepared from the corresponding diols and used with carbon acids to prepare 1,2-disubstituted cyclic compounds. With unsymmetrical carbon acid in presence of NaH in DME, a high diastereoselection of the trans isomer is observed. Factors that affect the stereoselectivity are proposed. Keywords: intramolecular SN2, decarboxylation, 2-alkylcycloalkanecarboxylic acids, 1-alkylindan-2-carboxylic acids.
The effect of temperature and salinity on the Setschenow parameters of naphthalene in seawater
Authors: Gold Gerardo , Rodriguez Silvio
Published: May 2006

Solubility measurements of naphthalene in seawater of different salinities have been determined by the Generator Column Method in the 276.6 K to 316.8 K temperature range. The Gibbs free energy, enthalpy, and entropy of solution were evaluated at 298 K by means of the Clarke and Glew equation. The temperature dependence of the Setschenow parameters for naphthalene in seawater has been studied and compared with the values calculated using current models for the salting-out of nonpolar molecules. The Surface Tension Approach gives the best correlation with experimental values. Keywords: Setschenow parameters, solubility of naphthalene in seawater.
Vibrational spectroscopic studies of the phase transition behavior in solid cyclohexene
Authors: Haines Julian , Gilson D. F. R.
Published: May 2006

The vibrational spectra (FT-ir and Raman) of cyclohexene have been examined as functions of temperature. The phase transition behavior is complex and highly dependent upon the thermal treatment of the sample. Spectra of the stable low temperature form (phase II) are quite different from those of the other phases, and suggest that the crystal has either Ci or C2h symmetry with two molecules per primitive unit cell. The asymmetric line shapes of the internal vibrational bands and the presence of broad peaks in the low frequency region of the Raman spectra of the high temperature phase indicate that the molecules undergo anisotropic rotation. The frequency of the ring inversion mode is highly phase dependent. Keywords: cyclohexene, FT-ir, Raman, phase transition.
New trends in differential scanning calorimetry
Authors: Tachoire H. , Torra V.
Published: May 2006

Recent applications of differential scanning calorimetry in the study of solid–solid transformations are presented. The importance of the deconvolution of the thermograms and of the modelling of the calorimetric equipment is stressed.Investigations of the phase transformations of the martensitic type in shape-memory alloys have made clear the influence of thermomechanical treatment of the material and have evaluated the influence of defects on the dynamics of transformation. A combination of calorimetric and acoustical observations has demonstrated irreversibilities, even in the so-called thermoelastic transitions. Keywords: martensitic transformation, differential scanning calorimetry, entropy production, thermomechanical treatments, acoustic emission.
The lone electron pair and crystal packing: observations on pyramidal YEL3ε species, abinitio calculations, and the crystal structures of Me3SOI, Et3SI, (Me3S)2SnCl6, (Me3SO)2SnCl6, and (Et3S)2SnCl6
Authors: Knop Osvald , Linden Anthony , Vincent Beverly R. , Choi S. C. , Cameron T. Stanley , Boyd Russell J.
Published: May 2006

The results of a detailed analysis of typical situations in crystals containing trigonal-pyramidal YEL3ε species are used to argue that, perse, the lone electron pair (E, LP) on the Y atom determines neither the crystal structure nor the orientation of the YEL3ε units in the crystal. Considered as a space-filling entity, the LP has practically no effective volume of its own. Whatever space-filling or orienting properties may be associated with the presence of the LP, they are not autonomous; they arise from the intrinsic stereochemical involvement of the LP in the geometry of and the charge distribution in the free YEL3ε ion or molecule and hence from the consequences of this geometry for crystal packing. Abinitio (6-31G*) calculations show that the electron density in the region of the LP in an ion is only slightly perturbed by the charge on the counter ion at distances observed in crystals. There is considerable similarity in the electron density distribution in the LP region of Y between free anionic (SO32−) and free cationic (Me3S+) species. The problem of the so-called stereochemical inertness of the LP in the 14-electron octahedral YEX62− ions in crystals is examined in detail. It is concluded that the crystallographic Oh symmetry of the ion in cubic crystals is the result of dynamic averaging of possible orientations of the inherently noncubic YX62− octahedron (cf. the abinitio results for SeCl62−). Such averaging also appears to be responsible for the stereochemical "activation" or "inactivation" of the LP in thermally induced crystallographic transitions in the AYX3 halide perovskites and related crystals. To provide a firmer basis for the discussion of the LP, the crystal structures of the five title compounds have been determined. The crystal chemistry of these and related compounds is discussed. Keywords: abinitio calculations, Me3S+ and SeCl62−; group V trihalides; lone electron pair; trialkylsulfonium salts; VSEPR theory.
Synthesis of complexes of the type cis-Pt(amine) (unsaturated ligand)Cl2 and crystal structure cis-Pt(methylaimne) (dimethylhexynediol)Cl2
Authors: Rochon F. D. , Melanson R. , Doyon Monique
Published: May 2006

Complexes of the type cis-Pt(L)(un)Cl2 where L = primary amine or methyl derivative of pyridine and un = cyclopentene, cyclohexene, or dimethylhexynediol, have been synthesized from the reaction of K[Pt(L)Cl3] with the unsaturated ligand in water. The compounds were characterized and studied by 1H NMR and IR spectroscopy. The crystal structure of cis-Pt(CH3NH2)((CH3)2C(OH)—C≡C—C(OH)(CH3)2)Cl2 was determined by X-ray diffraction methods. The crystals are monoclinic, space group P21/c, with a = 6.544(2), b = 14.304(7), c = 15.508(7) Å, β = 109.39(2)°, and Z = 4. The coordinates and the anisotropic thermal factors were refined by full-matrix least-squares analysis to a R factor of 0.048 and wR = 0.047. The coordination around the platinum atom is square planar and the acetylenic ligand is perpendicular to the Pt plane. Keywords: platinum complexes, crystal structure, methylamine, dimethylhexynediol, synthesis.
Determination of the charge density of acrylamide/acrylate copolymers by tensammetry
Authors: Smith-Palmer Truis , Wentzell Byron R.
Published: May 2006

The charge densities of acrylamide/acrylate copolymers can be determined using tensammetry. The tensammograms were run using 20 ppm solutions of polymer in 0.1 M tetraethylammonium chloride. A standard curve of desorption peak height versus mol% anionicity was useful in the range 10–50%. A second standard curve of the potential at which the capacitive current measured 1 μA versus mol% anionicity allowed the determination of charge density in the range 0–15%. Keywords: tensammetry, polyaerylamide, charge density, tetraethylammonium, desortion peaks.
Flash photolysis production of the tetrahedral intermediate of the methanolysis of methyl benzoate. Direct measurement of the rate of breakdown of the conjugate base form
Authors: McClelland Robert A. , Kanagasabapathy V. M. , Steenken Steen
Published: May 2006

Laser flash photolysis in aqueous basic solutions of the ortho acid derivatives 1-(phenyldimethoxymethyl)benzimidazole 2 and 4-bromo-1-(phenyldimethoxymethyl)imidazole 3 results in production of the phenyldimethoxymethyl cation, which has λmax at 260 nm. The cation decays in reactions with water (k = 9.9 × 104 s−1) and hydroxide ion (2.5 × 108 M−1 s−1) to finally yield methyl benzoate, whose formation was monitored at 234 nm. In solutions with pH 10–12, rate constants measured at this wavelength are the same as those obtained at 260 nm, but with pH > 13 and pH < 9, rate constants at 234 nm are smaller. With pH 9–10 and pH 12–13, single exponential kinetics are not observed at 234 nm. This behavior is interpreted in terms of a scheme where at each pH there are two consecutive first-order reactions, cation → phenyldimethoxyhydroxymethane (5) → ester, and the pH dependencies of the rate constants are such that they cross twice over the pH range of this study. The intermediate 5 is the tetrahedral intermediate formed in the methanolysis of methyl benzoate, and the 234-nm buildup at pH > 13 and pH < 9 directly measures its breakdown. At pH > 13 the rate constant is independent of pH with k = 9 × 106 s−1. This represents the rapid expulsion of methoxide from the conjugate base of 5. At pH < 9 the rate constants are proportional to hydroxide ion concentration, with [Formula: see text]. In these solutions the neutral intermediate predominates and the dependence on [OH−] of its rate of conversion to ester is interpreted in terms of breakdown of the anion and protonation of this species by water occurring at comparable rates. Thus, [Formula: see text] represents a situation where there is partial rate-limiting deprotonation of the neutral intermediate by hydroxide. The intermediate of this study bears a close resemblance to the tetrahedral intermediate of the hydrolysis of methyl benzoate. The observation that the anionic forms of such intermediates undergo breakdown at rates similar to those associated with the establishment of proton transfer equilibrium explains why the ester undergoes carbonyl oxygen exchange in base at a rate slower than hydrolysis. Keywords: tetrahedral intermediate, flash photolysis, ester hydrolysis.
Phenylfluorophosphoranes: axial–equatorial fluorine exchange in RC6H4PF3H and intermolecular exchange in the PhPF2(H)OMe–MeOH–base system
Authors: Kruczynski Leonard J. , Lemire Alberta E. , Marat Kirk , Janzen Alexander F.
Published: May 2006

Activation parameters for axial–equatorial fluorine exchange in arylfluorophosphoranes RC6H4PF3H, where R = o-CF3, m-CF3, p-CF3, m-CH3, were studied by the dynamic nmr technique: [Formula: see text] varied between 53 and 56 kJ mol−1.The synthesis of difluoromethoxyphenylphosphorane, PhPF2(H)OMe, from PhPF2 and MeOH is catalyzed by small amounts of Et3N, pyridine, PhPF3H, or HF. Rapid intermolecular ligand exchange occurs in PhPF2(H)OMe after addition of methanol and a base such as triethylamine or pyridine. Under these conditions, exchange of fluorine, hydrogen, and methoxy ligands occurs, as shown by 1H, 19F, and 31P nmr. From a line shape analysis of the 31P{1H} nmr spectrum, the rate of P—F cleavage was found to be first order (1.17 ± 0.2) in Et3N concentration, with [Formula: see text] = 50 kJ mol−1 and ΔS# = −67 J mol−1 deg−1.An equilibrium constant of 1.8 at 25 °C was found for the reaction of PhPF2(H)OMe with PhPF2.Keywords: axial–equatorial fluorine exchange in RC6H4PF3H intermolecular exchange in the PhPF2(H)OMe–MeOH–base system; 31P and 19F nmr study of ligand exchange in phosphoranes.
Pentacarbonylmanganese enolate and dienolate complexes. Preparative and mechanistic considerations
Authors: Masters Andrew P. , Sorensen Ted S.
Published: May 2006

Reactions of pentacarbonyl manganate anion with 4-halocrotonate esters or 2-halocarboxylate esters result in a complex set of inorganic and organic products, usually including the expected dienolate (or enolate) complexes. The reaction variables include the counterion, solvent, and halo group. The mechanism of the reaction has been investigated by conducting a thorough characterization of the reaction products under various conditions and also by carrying out model reactions. One can rationalize most of the non-organometallic products using either a radical or carbanion mechanism, but the latter seems to fit the available data better. Experimental procedures for optimizing the yield of the organometallic dienolate or enolate complexes have been worked out. Keywords: pentacarbonyl manganate, metalate nucleophilicity, enolate complex, nucleophilic substitution, 55Mn NMR spectroscopy.
Effect of substituents on the solvatochromism of stilbazolium merocyanines
Authors: Niedbalska Malgorzata , Gruda Ilona
Published: May 2006

The visible spectra of a series of merocyanines, derivatives of 4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine, have been investigated in a number of solvents and solvent mixtures. The effect of substituents on the solvatochromic behaviour of these compounds is described. All investigated merocyanines exhibited a strong negative solvatochromism. Inverse solvatochromism was observed in solvents of very low polarity for polar dyes, and in polar solvents for dyes containing hydrophobic substituents. This inversion of the solvatochromic behaviour is attributed to aggregation phenomena. Keywords: merocyanines, solvatochromism, betaine, aggregation.
Vilsmeier–Haack reaction with succinamidals. A convenient synthesis of 5-chloropyrrole-2-carboxaldehydes and 5-chloropyrrole-2,4-dicarboxaldehydes
Authors: Guzmán Angel , Romero Moises , Muchowski Joseph M.
Published: May 2006

It is shown that the reaction of N-alkylsuccinamidals (2) with the Vilsmeier–Haack reagent derived from DMF and phosphorus oxychloride can be controlled to preferentially produce either 5-chloropyrrole-2-carboxaldehydes (8) or 5-chloropyrrole-2,4-dicarboxaldehydes (9). The corresponding N-unsubstituted aldehydes are obtained when N-tert-butoxycarbonylsuccinamidal (11) is the substrate in the above reactions. Keywords: Vilsmeier–Haack reaction, succinamidals, 5-chloropyrrole-2-carboxaldehydes, 5-chloropyrrole-2,4-dicarboxaldehydes.
Dialkyl and diaryl boron halides: reductive opening of benzylidene acetals
Authors: Guindon Yvan , Girard Yves , Berthiaume Sylvie , Gorys Vida , Lemieux René , Yoakim Christiane
Published: May 2006

Dimethylboron bromide or diphenylboron bromide can be used in combination with borane to achieve the regiocontrolled conversion of benzylidene acetals to their corresponding hydroxy benzyl ethers with moderate to high yields. Keywords: dimethylboron bromide, diphenylboron bromide, reductive opening, benzylidene, acetals.
Studies in aryltin chemistry. Part 6. Crystal and molecular structures of tetra(p-methylsulphonylphenyl)tin(IV) and tetra(p-methylsulphinylphenyl)tin(IV) monohydrate
Authors: Wharf Ivor , Simard Michel G. , Lamparski Henry
Published: May 2006

Tetrakis(p-methylsulphonylphenyl)tin(IV) and tetrakis(p-methylsulphinylphenyl)tin(IV) n-hydrate have been prepared and their spectra (ir 1350–400 cm−1; nmr, 1H, 13C, 119Sn) and X-ray crystal structures are reported. The first compound is monoclinic, space group C2/c, Z = 4, with a = 21.589(6), b = 6.207(3), c = 22.861(11) Å, β = 93.80(3)° (22 °C); the structure was solved by the direct method and refined by full-matrix least squares calculations to R = 0.043 for 2755 observed reflections. It has 2 molecular symmetry with the methyl group and one oxygen atom completely disordered in both CH3S(O2) groups in the asymmetric unit. The second compound is tetragonal, space group P42/n, Z = 2, with a = b = 15.408(6), c = 6.379(2) Å (−100 °C); the structure was solved by the Patterson method and refined by full-matrix least squares calculations to R = 0.060 for 1209 observed reflections. It has [Formula: see text] molecular symmetry with the whole asymmetric unit disordered. Water molecules occupy positions on parallel 42 axes but molecular packing requirements prevent all sites having 100% occupancy giving n ~ 1 for the hydrate. Keywords: Tetra-aryltins, crystal structures, sulphone, sulphoxide, hydrogen-bonding.
Identification of some L-numbered Lycopodium alkaloids
Authors: Ayer William A. , Browne Lois M. , Elgersma A. Warren , Singer Peter P.
Published: May 2006

The pioneering research on Lycopodium alkaloids carried out by R. H. F. Manske and L. Marion led to the characterization of a large number of alkaloids. Many of these alkaloids were designated by numbers preceded by an L (e.g., L1, which has since been shown to be dihydrolycopodine). While the identity of many of these alkaloids has now been established, several remain unreported. We have examined samples of alkaloids L15, L16, L17, L18, L22, L24, L25, L26, L28, L29, L31, and L35, obtained from Marion's collection, by GC–MS and GC–IR, and report herein the identity of these alkaloids and alkaloid mixtures. Most of the samples proved to be mixtures of known alkaloids. Acetylannofoline (5), a component of alkaloid L17, and 5,15-oxidolycopodane (9), a component of alkaloids L28 and L31, are identified for the first time as natural products. A complete listing of the L-numbered alkaloids is provided. Keywords: Lycopodium alkaloids, alkaloids, acetylannofoline, oxidolycopodane.
Polycarboxylate diaza crown ethers derived from R,R-(+)-tartaric acid: synthesis and complexation of metal ions
Authors: Anantanarayan Ashok , Fyles Thomas M.
Published: May 2006

The synthesis and complexation properties of polycarboxylate diaza crown ethers based on R,R-(+)-tartaric acid are described. Cesium carbonate mediated macrocyclization of a bis-tosylamide precursor with a bis-tosylate precursor provided the protected crown ethers. Photochemical deprotection of the tosylamides and hydrolysis of the carboxamides yielded dicarboxylic and tetracarboxylic acid derivatives of 1,10-diaza-18-crown-6. N-Methylenecarboxylate (N-acetate) derivatives were prepared by N-alkylation with bromoacetic acid. The synthetic and purification procedures developed provide samples of the ligands in a metal-free form. Acidity and stability constants for complexation of alkali metal, alkaline earth, late- and post-transition metal cations were determined by potentiometric titration. The ligands form complexes which show enhancement of stability by charge–charge and chelate interaction with the carboxylates. In comparison with crown ether polycarboxylates these aza crown ethers showed a selectivity for softer metal ions relative to alkali and alkaline earth metal ions. N-Methylenecarboxylate chelate ligands were found to bind almost all types of metal ions, due to a highly co-operative array of charge–charge, chelate and crown ether interactions. Keywords: aza crown ether synthesis, tartaric acid, potentiometric titration, cation complexation, aminocarboxylate complexone.
A study of thermodynamic acidities of enols with the semiempirical computational method AM1
Authors: Werstiuk Nick Henry , Andrew David
Published: May 2006

Using the semiempirical computational method AM1 we have computed the enthalpies of ionization of enols 1–21 and correlated these values with solution and estimated pKa's. From this initial study it appears that, in general, it is possible to predict the pK's of acyclic enols within ± 1 pKa unit. On the basis of this correlation we predict the pKa's of 1-hydroxy-1,3-butadiene (3-butenal enol) (9.7) and 1,1-difluoroacetone enol (9.6) and suggest that the previously estimated pKa of 1,1-dichloroacetone enol (6.2) is low by approximately 3 pK units. We find computationally (this has been established experimentally) that the Z-enol of phenylacetaldehyde is less acidic than the E-enol. Keywords: enols, acidities, computational studies, AM1.
Acidities and homolytic bond dissociation energies of the αC—H bonds in ketones in DMSO
Authors: Bordwell Frederick G. , Harrelson Jr John A.
Published: May 2006

Equilibrium acidities in DMSO are reported for nine cycloalkanones, acetone, acetophenone, and 19 of their α-substituted derivatives. Oxidation potentials in DMSO for the conjugate bases of most of these ketones are also reported. Combination of these EOX(A−) and pKHA values gives estimates of the homolytic bond dissociation energies (BDEs) of the acidic C—H bonds in the ketones. The ΔBDEs, relative to the BDE of CH3-H, or a parent ketone, provide a measure of the radical stabilization energies (RSEs) of the corresponding radicals. The effects of successive α-Me and α-Ph substitutions on RSEs, relative to those of CH3COCH2-H or PhCOCH2-H, are similar to those reported in the gas phase for methane. The RSE for the MeĊHCOPh radical, relative to CH3• is 17 kcal/mol, which is smaller than the sum of the RSEs of the MeCH2• and PhCOCH2• radicals relative to CH3• (7 + 12 = 19), contrary to the prediction of the captodative postulate. When G in PhCOCH2G is PhCO, CH3CO, or CN the ΔBDEs (relative to PhCOCH2-H) are 0, 1, and 3 respectively; for MeCOCH2SO2Ph, PhCOCH2SO2Ph, and PhCOCH2NMe3+ the ΔBDEs are −5, −2, and −4, respectively. The BDEs in C5, C6, C7, C8, C10, and C12 cycloalkanones are within ±2.5 kcal/mol of that of 3-pentanone. Acetophenones bearing meta or para substituents all have BDEs of 93-94 kcal/mol. Ketone radical cations, [RCOR′]+•, appear to be superacids with estimated [Formula: see text] values below −25. Keywords: acidities, bond dissociation energies, ketones.
Photophysical properties of pyridinium salts derived from purine bases
Authors: Skalski Bohdan , Paszyc Stefan , Adamiak Ryszard W. , Steer Ronald P. , Verrall Ronald E.
Published: May 2006

The absorption spectra, fluorescence spectra, fluorescence lifetimes, fluorescence quenching, phosphorescence spectra, phosphorescence lifetimes, and picosecond transient absorption spectra of several purinyl-pyridinium salts have been measured in several solvents at room temperature and in ethanol glasses at 77 K. It is concluded that the previously observed photochemical transformation of N-[9-(2′,3′,5′-tri-O-acetyl-β-D-ribofuranosyl)purin-6-yl]pyridinium chloride 1 into the highly fluorescent tri-O-acetylluminarosine 6 occurs via an excited triplet state. It is also shown that intersystem crossing in purinyl-pyridinium salts is induced by an intermolecular charge-transfer interaction with the counter ions. Keywords: purinyl-pyridinium salts, fluorescence, phosphorescence.
Synthesis, crystal structure, and vibrational spectra of the complex maleic acid•2H2O•18-crown-6
Authors: Audet Pierre , Savoie Rodrigue , Simard Michel
Published: May 2006

A stoichiometric complex of formula maleic acid•2H2O•18-crown-6 has been obtained from maleic acid and the macrocyclic polyether 18-crown-6. Crystals of this complex have been shown by X-ray diffraction crystallography to belong to the Cc space group of the monoclinic system. The acid molecules in the adduct are linked to each other through a water molecule, giving infinite [-acid-H2O-]n chains. They are also linked to the crown ether via water molecules. The infrared and Raman spectra of the complex are presented and compared to those of crystalline maleic acid. Keywords: maleic acid/18-crown-6, structure, X-ray, spectra.
113Cd NMR studies of Hofmann-type clathrates and related compounds: Evidence for two room temperature orientational glasses
Authors: Nishikiori S. , Ratcliffe C. I. , Ripmeester J. A.
Published: May 2006

113Cd magic angle spinning NMR, with and without 1H cross-polarisation and decoupling, has been used to study a number of Hofmann-type clathrates and related compounds. The 113Cd chemical shift shows a great sensitivity to the environment of Cd, even for complexes with closely related structures. The presence of five resonances due to Cd surrounded by CxN(4–x) (where x = 0 to 4) in Cd(CN)2 and Cd(CN)2•C6H12 indicates a static disorder of the CN groups, which makes these materials orientational glasses. Keywords: 113Cd NMR, Hofmann-type clathrates, Cd(CN)2, disorder, orientational glass.
Two 1H-naphtho[2,3-c]pyran-1-one metabolites from the fungus Paecilomyces variotii
Authors: Ayer William A. , Craw Peter A. , Nozawa Koohei
Published: May 2006

The fungus Paecilomyces variotii Bainier, isolated from larvae of Dendroctonus ponderosa Hopk. (mountain pine beetle), is antagonistic to Ophiostoma clavigerum, the fungus believed responsible for tree mortality caused by blue stain fungi. The metabolites produced by P. variotii when grown in liquid culture have been studied and two new 1H-naphtho[2,3-c]pyran-1-ones related to semi-vioxanthin (4) have been isolated. The structures of these two metabolites, semi-viriditoxin (1) and semi-viriditoxic acid (2), have been determined by chemical and spectroscopic methods. Key words: fungal metabolites, blue stain disease, Paecilomyces variotii, semi-viridotoxin, semi-viridotoxic acid.
The VCD spectrum of 2-methylthietane: measured (800–1500 cm−1) and computed with semi-empirical models
Authors: Shaw R. A. , Ibrahim N. , Wieser H.
Published: May 2006

The vibrational circular dichroism (VCD) spectrum (800 to 1500 cm−1) is reported for 2-methylthietane (2MT). Fixed partial charge (FPC), atomic polar tensor (APT), and charge flow (CF) methods are used to compute the VCD spectra for both stable conformers (CH3 in the axial or equatorial orientation) for the complete range of fundamental vibrations, based on 3-21G and 6-31G* harmonic force fields. The experimental and computed absorption and VCD spectra of R-(+)-2MT are compared to the previously reported spectra of R-(−)-2-methyloxetane. The success of the APT and CF models for reproducing the dominant ring stretching IR and VCD features of that compound is rationalized by a comparison of APT and FPC intensity expressions. Further comparison of the APT and FPC calculated electric dipole moment derivatives are interpreted to suggest values for the diagonal CS and CH stretching charge flow terms for 2MT. These investigations then provide a rationale for previously reported successes of the FPC model, and permit identification of specific vibrational modes of 2MT that are amenable to FPC-VCD modeling. The previously established conformational mixture of ~30% axial and 70% equatorial is shown to be in accord with FPC-VCD predictions for the most appropriate (β-CH2 wagging) mode. Key words: vibrational circular dichroism, 2-methylthietane, fixed partial charge, atomic polar tensor, charge flow
An ICR mass spectrometry study of ion/molecule reactions between ethyl chloride and alkylamines
Authors: Xu Guoying , Herman Jan A.
Published: May 2006

Ion/molecule reactions in mixtures of ethyl chloride with C1–C4 alkylamines were studied by ICR mass spectrometry. Ethyl cation transfer to C1–C4 alkylamines proceeds mainly through diethylchloronium ions with rate constants ~3 × 10−10cm3 s−1. In the case of s-butylamine the corresponding rate constant is 0.5 × 10−10 cm3 s−1. Key words: ICR mass spectrometry, ion/molecule reactions, ethylchloride, methylamine, ethylamine, propylamines, butylamines
2-S-Methyl-5,5-dimethylimidazolin-4-one: chemical behaviour and crystal structure of its Δ1 tautomer
Authors: Cristiani Franco , Devillanova Francesco A. , Diaz Angelo , Isaia Francesco , Verani Gaetano , Demartin Francesco , Saba Giuseppe
Published: May 2006

2-S-Methyl-5,5-dimethylimidazolin-4-one can be crystallized as Δ1 or Δ2 tautomers, depending on the solvent polarity. The structure, solved on crystals obtained from benzene, showed it to be the Δ1 tautomer in the anti configuration. Δ1-2-S-Methyl-5,5-dimethylimidazolin-4-one is monoclinic, space group P21/c, with a = 8.347(1), b = 10.121(1), c = 9.996(3) Å, β = 107.20(2)°, R = 0.037 for 1395 independent reflections with I > lσ(I). The quantum mechanical (MNDO, PM3, and AMI) calculations indicate that among the four conformers the anti-Δ1 tautomer has both the lowest dipole moment and the lowest enthalpy of formation. The ultraviolet spectrum of the title compound has been recorded in solvents with different dielectric constants. The infrared spectra of the Δ1 and Δ2 solid samples are discussed relative to the v(NH) and v(CO) absorptions and in comparison with those recorded in carbon tetrachloride and in chloroform solution. Its acid–base behaviour has been studied by determining the pKa in aqueous solutions and the results are compared with those obtained for some related hydantoins. Key words: 2-S-methyl-5,5-dimethylimidazolin-4-one, tautomerism, hydantoin derivatives, crystal structure.
Metal pyrazolate polymers. Part 2. Synthesis, structure, and magnetic properties of [Cu(4-Xpz)2]x polymers (where X = Cl, Br, Me, H; pz = pyrazolate)
Authors: Ehlert Martin K. , Rettig Steven J. , Storr Alan , Thompson Robert C. , Trotter James
Published: May 2006

Novel and reliable methods for the synthesis of the polymers [Cu(4-Xpz)2]x (where X = H, Cl, Br, and Me; pz = pyrazolate) are presented. The X = Cl compound was obtained as green and brown forms. Single crystals of the polymers with X = Me and X = Cl (green form) suitable for X-ray analysis have been obtained. [Cu(4-Mepz)2]x and [Cu(4-Clpz)2]x are isomorphous, crystallizing with four formula units per unit-cell in the orthorhombic space group Ibam, a = 9.7436(6), 9.155(4), b = 12.6106(8), 12.968(6), and c = 7.7482(6), 7.717(5) Å, respectively, for the 4-Me and 4-Cl derivatives. The structures were refined by full-matrix least-squares procedures to R = 0.027 and 0.041 for 430 and 246 reflections with I ≥ 3σ(I), respectively. Magnetic susceptibility studies over the temperature range 2 to 300 K have revealed that all the polymers exhibit very strong antiferromagnetic exchange between copper(II) centres in the extended linear chains. Discontinuities displayed in the susceptibility versus temperature plots suggest the presence of phase transitions at ~133 and ~108 K in the X = Cl (green form) and X = Br materials, respectively. The four compounds, X = H, Br, Me, and Cl (green form) also exhibit thermochromism over the 77 to 176 K region. The magnetic data have been analyzed employing an isotropic Heisenberg model for antiferromagnetic exchange in extended chain polymers. Values of the exchange coupling constant, J, for the room temperature forms of these materials are determined as −81, −105, −96, −104, and −88 cm−1 for 4-X = H, Br, Me, Cl (green form), and Cl (brown form), respectively. The magnitude of the exchange coupling is discussed in relation to structural parameters for the X = H, Me, and Cl (green form) compounds. Key words: copper(II) 4-substituted pyrazolate polymers, crystal structures, magnetic exchange.
Stereoselectivity of C(3) methylation and aldol condensation of camphor and derivatives
Authors: Hutchinson J. H. , Li D. L. F. , Money T. , Palme M. , Agharahimi M. R. , Albizati K. F.
Published: May 2006

The stereoselectivity of methylation and aldol condensation of camphor and derivatives is determined by the presence or absence of a C(7) syn-methyl group and (or) C(5) and C(6) endo-hydrogen atoms. Key words: camphor, C(3) methylation, C(3) aldol.
Ab initio molecular orbital calculations of the infrared spectra of hydrogen bonded complexes of water, ammonia, and hydroxylamine. Part 6. The infrared spectrum of the water–ammonia complex
Authors: Yeo Geoffrey Andrew , Ford Thomas Anthony
Published: May 2006

The molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series of ab initio molecular orbital calculations, at the level of second order Møller–Plesset perturbation theory, using the 6-31G** basis set. The calculated wavenumbers and intensities have been compared with those calculated earlier for the respective monomers, and the wavenumber shifts and intensity changes rationalized in terms of the hydrogen bond interaction responsible for the stability of the complex.The calculated hydrogen bond energy of the complex has been compared with those of the linear water and ammonia dimers, reported in a previous publication, and the relative strengths of interaction of the three aggregates have been rationalized on the basis of the electron donor/acceptor capacities of the respective monomer units. Key words: ab initio, infrared spectrum, water, ammonia.
Synthetic transformations of cyclopropyl annulated dihydroisoquinolines
Authors: Lantos Ivan , Katerinopoulos Haralambos E.
Published: May 2006

Isomeric 3-cyano-3-methyl-2-acetyl-cycloprop[c]isoquinolines, 5 and 6, were prepared by alkylation and cyclopropanation of Reissert compounds and their reactions under basic conditions were examined. Both compounds, under the influence of methoxide, yielded isoquinoline derived products resulting from cleavage of the peripheral C—C bond. The results are postulated to derive from attack of the methoxide on the acyl carbonyl, forming a tetrahedral adduct that undergoes ring opening. Key words: cyclopropanation, ring opening, tetrahedral complex, pyramidalization.
Synthesis and crystal structure of an octahedral nickel(II) complex derived from pentaerythrityl tetraamine.
Authors: McAuley A. , Subramanian S. , Whitcombe T. W.
Published: May 2006

not available
The thermodynamics of the vaporization of liquid indium(I) bromide by modified entrainment
Authors: Gardner Peter J. , Preston Steve R.
Published: May 2006

The transport of gaseous In(I)Br in an argon carrier gas was studied in the temperature range 680 to 935 K by the modified entrainment method. Combination of the entrainment results with a literature equation for the total vapour pressure above the liquid gave the following expressions for the temperature dependence of the vapour pressures of the monomer (In2Br2) and dimer (In2Br2) respectively: [Formula: see text] ln T − 0.001164 ± 0.00021)T, (680 −950 K) and [Formula: see text] (680–810 K); p0 = 105 Pa. The dimer concentration is ca. 14% at 680 K and decreases to ca. 4% at 810 K. Key words: high temperature thermodynamics, indium(I) bromide, vaporization thermodynamics.
Amino acid/zwitterion equilibria II: vibrational and NMR studies of substituted thiazolidine-4-carboxylic acids
Authors: Howard-Lock H. E. , Lock C. J. L. , Martins M. L.
Published: May 2006

Infrared and Raman spectra (4000–100 cm) of solid samples of seven different 2-phenyl-, N-benzoyl-, and 2-ethyl-2 methyl derivatives of L-cysteine and D-penicillamine have been observed and assigned. Proton and 13C nuclear magnetic resonance spectra for the compounds have also been measured. Amino acid/zwitterion equilibria are discussed with reference to pK values and the vibrational spectra. Key words: amino acid/zwitterion equilibria, thiazolidine carboxylic acids.
Structural studies of organoboron compounds XLVII. 6,8-Bis(1-cyno-1-methylethyl)-2,4-diphenyl-1,3,5-trioxa-6,8-diaza-2,4-diboracylcooctane
Authors: Kliegel Wolfgang , Lubkowitz Gottfried , Rettig Steven J. , Trotter James
Published: May 2006

not available
Heat capacity and thermophysical properties of n-heptanoic cid from 5 to 350K
Authors: Labban Abdul Karimeh , Westrum, Jr. Edgar Francis
Published: May 2006

The sub-ambient heat capacity of heptanoic acid is characterized by a first order transition at 219.99 K which shows a Cp,m maximum greater than 400R and ΔtrsSm0 of 1.132R. The acid melts at the triple point 265.98 K and shows a Cp,m maximum greater than 8200R and ΔfusSm0 of 6.891R. At 298.15 K the values of ΔT0KK Sm0, ΔT0 KK Hm0, and Φm(T,0) are 38.89R, 6737R K, and 16.29R. Prior measurements by Adriaanse et al. (1964) with a micro calorimeter between 173 and the melting point did not reveal the transition, nor did the method-of-mixtures ("drop") calorimetry of Garner et al. (1924) between 213 K and the melting point although they claim to have confirmed the presence of both distinct crystalline phases. The somewhat greater measurement range of Schaake et al. (1982)  from 104 to 304 K  by adiabatic calorimetry on a characterized sample did reveal the transition albeit at a temperature 4.8 K higher and with 4% less entropy of transition (double the combined estimated standard deviation).Key words: n-heptanoic acid, heat capacity, transitions, triple point.
Molecular recognition XI. The synthesis of extensively deoxygenated derivatives of the H-type 2 human blood group determinant and their binding by an anti-H-type 2 monoclonal antibody and the lectin 1 of Ulexeuropaeus
Authors: Spohr Ulrike , Paszkiewicz-Hnatiw Eugenia , Morishima Naohiko , Lemieux Raymond U.
Published: May 2006

The relative potencies of a wide variety of deoxygenated derivatives of the methyl glycoside of α-L-Fuc-(1 → 2)-β-D-Gal-(1 → 4)- β-D-GlcNAc (the H-type 2 human blood group related trisaccharide) for the inhibition of the binding of an artificial H-type 2 antigen by the lectin I of Ulexeuropaeus confirmed the previous evidence that the key and productive interaction involves only the three hydroxyl groups of the α-L-fucose unit, the hydroxyl at the 3-position of the β-D-galactose residue, and the nonpolar groups in their immediate environment. Except for the acetamido group and the hydroxymethyl of the β-D-Gal unit, which stay in the aqueous phase, on complex formation the remaining three hydroxyl groups appear to come to reside at or near the periphery of the combining site since their replacement by hydrogen causes relatively small changes (< ± 1 kcal/mol) in the stability of the complex (ΔG0). Relatively much larger but compensating changes occur for the enthalpy and entropy terms, and these may arise primarily from the differences in the water structure about the periphery of the combining site and the oligosaccharide both prior to and after complexation. It is proposed that steric constraints lead to an ordered state of the water molecules hydrogen-bonded to the polar groups within the cleft formed by the key region of the amphiphilic combining site. Their release to form less ordered clusters of more strongly hydrogen-bonded water molecules in bulk solution would contribute importantly to the driving force for complexation. It is demonstrated that the surface used for the binding of H-type 2-OMe by a monoclonal anti-H antibody is virtually identical to that used by the Ulex lectin. Keywords: molecular recognition, H-type 2 blood group determinant and deoxygenated derivatives, lectin I of Ulexeuropaeus, anti-H-type 2 monoclonal antibody, enthalpy–entropy compensation.
New scheme for large-scale eigenvalue problems of the RPA-type matrix equation
Authors: Narita Susumu , Shibuya Tai-ichi
Published: May 2006

A new method is proposed for obtaining a few eigenvalues and eigenvectors of a large-scale RPA-type equation. Some numerical tests are carried out to study the convergence behaviors of this method. It is found that the convergence rate is very fast and quite satisfactory. It depends strongly on the way of estimating the deviation vectors. Our proposed scheme gives a better estimation for the deviation vectors than Davidson's scheme. This scheme is applicable to the eigenvalue problems of nondiagonally dominant matrices as well. Keywords: large-scale eigenvalue problem, RPA-type equation, fast convergence.
The calculation of atomic oscillator strengths: the lithium atom revisited
Authors: Weiss A. W.
Published: May 2006

Extensive configuration interaction calculations have been done for the ground and first excited states of neutral lithium and singly ionized beryllium. While the calculations reproduce the ionization and excitation energies to within 3 cm−1 for Li and 10 cm−1 for Be+, the main purpose of this work is the accurate evaluation of the 2s–2p resonance line oscillator strength. The calculated value of 0.7478 agrees to within less than 1% with the very accurate laser excitation lifetime measurement of 0.7416 ± 0.0012. However, internal consistency checks of the accuracy of these calculations suggest that more precise calculations are unlikely to reduce this discrepancy significantly. Furthermore, when placed together with other independent calculations that should be of comparable, if not better, accuracy, all theoretical predictions strongly indicate an f-value of 0.7475 ± 0.0010, which differs from the experiment by 4 experimental standard deviations. Keywords: configuration interaction, correlation, oscillator strength.
Sulphur–nitrogen anions: 14N and 15N NMR investigations of the deprotonation of cyclic sulphur imides and sulphur–ammonia solutions
Authors: Chivers T. , Schmidt K. J.
Published: May 2006

The following systems have been investigated by 14N and (or)15N NMR spectroscopy: (a) the deprotonation of S7NH by n-BuLi, (b) solutions of S8, S7NH, 1,3- and 1,4-S6(NH)2, and K2SN2 in liquid ammonia, (c) the reaction of sodium azide with sulphur in hexamethylphosphoramide (HMPA), (d) the reactions of S7NH and S4(NH)4 with potassium amide in liquid ammonia in various molar ratios, and (e) the reaction of (NSCl)3 with potassium amide (1:6 molar ratio) in liquid ammonia. These investigations have provided an NMR characterization of the thermally unstable S7N− (δ15N ca. −324 ppm) and S2N2H− ions (δ14N + 7 and −149 ppm, 1J(14N−1H) 36 Hz, 1J(15N−H) 55 Hz, 2J(15N-15N) 2.2 Hz) in liquid ammonia, demonstrated the existence of S7N−, in addition to SSNSS−, as the major nitrogen-containing ingredient of sulphur–ammonia solutions (SAS), and confirmed the formation of the SSNSS−, but not S7N−, from the reaction of sodium azide and sulphur in HMPA. Consistent with previous chemical investigations, the NMR data show that the S7N− and S2N2H− ions are thermally unstable with respect to the formation of SSNSS− and S3N3−, respectively, in solution. Solutions of S4(NH)4/4KNH2 or (NSCl)3/6KNH2 show the same two 14N or 15N NMR resonances at ca. +97 and −108 ppm as a solution of NSN2− in liquid ammonia. Keywords: sulphur–nitrogen anions, nitrogen NMR, liquid ammonia.
A stability and equilibrium study on Cd – salicylidene tris(hydroxymethyl) methylamine – chloride binary and ternary complexes
Authors: Abdel-Hamid Refat , El-Haty Mohamed T.
Published: May 2006

Binary and ternary complexes of Cd(II) with salicylidene tris(hydroxymethyl) methylamine and chloride ion at 298 K were studied polarographically at I = 0.1 mol dm−3 NaClO4 in 30% (v/v) DMF – aqueous medium at pH 10.2. The overall formation constants were found to be, for the binary system, log β1 = 3.55 ± 0.03 and log β2 = 5.40 ± 0.07 and, for the ternary one, log β11 = 7.64 ± 0.06 and log β12 = 9.56 ± 0.06. Keywords: formation constants, binary and ternary complexes of Cd(II).
Study of the dissociation of the products of some proton transfer reactions in acetonitrile solvent
Authors: Galezowski Wlodzimierz , Jarczewski Arnold
Published: May 2006

The conductometric study of the products of the proton transfer reactions of C-acids (nitriles, nitroalkanes, and 2,4,6-trinitrotoluene) with the strong amine bases (1,1,3,3-tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,8-bis(dimethylamino)naphthalene (DMAN), and piperidine) in acetonitrile shows their large degree of dissociation into free ions. The dissociation constant values have been estimated at 25 °C to be larger than 1 × 10−4 M. This weakens the formalism commonly accepted in spectrophotometric kinetic studies of these systems of reactions, based on the assumption that the product is an ion pair. Spectrophotometric equilibrium and kinetic measurements provided evidence that reverse reaction is a second-order process (pseudo-first order because cation concentration is controlled by side reactions). The influence of the common cation (TMGH+) on the equilibria of the proton abstraction from 2-methyl-1-(4-nitrophenyl)-1-nitropropane and 4-nitrophenylcyanomethane with TMG base in acetonitrile at 25 °C was examined and was found to be compatible with the assumption of large dissociation of the reaction product for free ions. "Equilibrium constants" estimated by the Benesi and Hildebrand method (which assumes an ion-pair product) decreased with increasing concentration of added TMGH+ cation, but these "equilibrium constants" multiplied by [TMGH+] are constant. The observed pseudo-first-order rate constants of the proton transfer reaction, measured at large excess of the base over C-acid, grow with the cation concentration due to the increase of the backward reaction rate. The concentration of added common cation shows a negligible influence on the observed rate constants of deuteron transfer reaction. Thus, as a result of side reactions, in which extra amounts of cation are formed, some second-order rate constants [Formula: see text] and also kinetic isotope effects (KIEs) [Formula: see text] that have been measured in acetonitrile can be substantially overestimated. Keywords: ion-pair dissociation, proton transfer reactions, kinetic isotope effects.