bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel metal chelating chitosan derivative: attachment of iminodiacetate moieties via a hydrophilic spacer group
Authors: Holme Kevin R. , Hall Laurance D.
Published: May 2006

Chitosan has been reductively N-alkylated with a 6-O-substituted galactose derivative bearing an iminodiacetate residue, to give a chitosan derivative having a hydrophilic branch and a metal chelating group. The Cu(II) binding capacity of the derivative was comparable to native chitosan, but showed better ion-exchange ability. The product was water soluble, giving viscous 1% aqueous solutions that showed decreased viscosity upon addition of Cu(II) ions. Key words: chitosan, derivative, chelation, solubilization, viscosity.
Chiral recognition in aqueous solutions at 25 °C. A calorimetric study of the interaction between enantiomeric α-amino acids of different alkyl chain length
Authors: Castronuovo Giuseppina , Elia Vittorio , Magliulo Michela
Published: May 2006

Cross-homo- and cross-heterotactic enthalpic coefficients, [Formula: see text] respectively, were determined at 25 °C, measuring the enthalpies of dilution of ternary aqueous solutions containing two different α-amino acids of the same or different chirality. Differences of about 200–300 J mol−2 kg between cross-homo- and cross-heterotactic coefficients were found, well beyond the experimental uncertainty. The role of the zwitterionic interaction, already proposed to explain the nature of chiral recognition, was strengthened. Key words: α-amino acids, excess enthalpy, chiral recognition.
Excess molar volumes and excess viscosities of n-butylamine + 1,4-dioxane + carbon tetrachloride system at 298.15 K
Authors: Acevedo Inés L. , Pedrosa Graciela C. , Katz Miguel
Published: May 2006

Densities and viscosities were determined for the n-butylamine + 1,4-dioxane + carbon tetrachloride system at 298.15 K. Molar excess volumes and excess viscosities were calculated from the experimental results. Analytical expressions can be used to predict these excess properties from binary data, the empirical correlation of Cibulka being the best for this system. Key words: density; mixture of n-butylamine + 1,4-dioxane + carbon tetrachloride; viscosity, mixture of n-butylamine + 1,4-dioxane + carbon tetrachloride; excess properties of ternary mixture.
On the spin trapping of chlorine atoms. Competition from chloride ions
Authors: Rehorek Detlef , Janzen Edward G. , Kotake Yashige
Published: May 2006

Chlorine atoms generated by photolysis of hexachloroethane add to C-phenyl-N-tert-butyl nitrone (PBN) to form persistent spin adducts that are readily detectable by EPR spectroscopy. The presence of chloride ions reduces spin adduct formation competitively. Chlorine atoms also react with tetraphenylarsenium ions to liberate phenyl radicals by radical replacement. Key words: EPR, spin trapping, C-phenyl-N-tert-butyl nitrone, PBN, photolysis, chlorine atoms, tetraphenylarsenium ion, hexachloroethane.
An unexpected acyloin rearrangement and oxidation of a camphor derivative
Authors: McIntosh John M. , Cassidy Kenneth C.
Published: May 2006

The trimethylsiyl ether 7 derived in two steps from camphor underwent ring expansion via an acylion rearrangement to afford two products (8 and 9) when desilylation was attempted. Compound 9 was stable but 8 was oxidized in air to homocamphoric acid anhydride 11. Key words: camphor, acyloin rearrangement.
Déplacements homolytiques intramoléculaires. 19. Stéréochimie de la décomposition induite de peroxydes insaturés conduisant à la formation d'hétérocycles à trois et quatre chaînons
Authors: Lubeigt X. , Flies F. , Bourgeois M. J. , Montaudon E. , Maillard B.
Published: May 2006

Homolytic decomposition induced by addition of dichloromethyl radicals to β- and γ-unsaturated peroxides having a substituent on the chain linking the unsaturation and the peroxide function was studied. The stereochemistry of the heterocycles produced was determined by I3C NMR and the stereoselectivity of intramolecular homolytic substitution on the peroxidic bond discussed. Key words: unsaturated peroxides, homolytic intramolecular substitutions, radical additions, oxygenated heterocycles.
A theoretical approach to the acid-catalyzed hydration of the carbonyl group: the case of formaldehyde
Authors: Peeters Daniel , Leroy Georges
Published: May 2006

The analysis of the hydration of formaldehyde in the presence of a hydrated proton was performed. Molecular quantum chemistry methods were used to explore the potential energy hypersurface. Calculations were performed at RHF-4-31G level. The structures were obtained through the use of first and second derivatives of the potential energy hypersurface thereby guaranteeing the nature of the extremum. The incidence of one or two water molecules on the reaction is discussed. It has been found that a low energy reaction path exists when the hydration process is catalyzed by a proton and two water molecules. The reaction mechanism rests on successive addition/elimination processes and reveals the respective roles of the oxygen lone pairs and of the C=O double bond upon the mechanism. Key words: ab initio calculations, carbonyl reactivity, acid catalysis, hydration, reaction mechanism.
Photochemical probes of conformational mobility in liquid crystals. The photochemistry of β-phenyl-4-methoxypropiophenone in the nematic and smectic B phases of CCH-n and OS-nm liquid crystals
Authors: Workentin Mark S. , Fahie Brian J. , Leigh William J.
Published: May 2006

The photochemistry of β-phenyl-4-methoxypropiophenone (1) in the isotropic and liquid crystalline (nematic and smectic B) phases of trans, trans-4′-alkyl-(1,1′-bicyclohexyl)-4-carbonitrile (CCH-n) and trans-4-alkylcyclohexyl-trans-4′-alkylcyclohexylcarboxylate (OS-nm) mesogens has been investigated using nanosecond laser flash photolysis techniques. Solubility limits of 1 as a function of temperature in the smectic phases have been rigorously determined by 2H NMR spectroscopy, using α-, methoxy-, and β-phenyl-deuterated analogs of the ketone. Triplet decay of 1 in the smectic (Crystal B) phase of CCH-4 is multiexponential, suggesting that the ketone is solubilized in a distribution of conformations in the highly-ordered liquid crystalline lattice. The average triplet lifetime of 1 at various temperatures throughout the smectic phase is about a factor of three longer than that in homologous nematic and isotropic phases at the same temperature. The differences in the Arrhenius parameters for triplet decay in the smectic and nematic/isotropic phases are very small, however. The present results for 1 in the smectic phase of the CCH-n mesogens correct the interpretation of previously reported data obtained with higher concentration mixtures, and afford an accurate indication of the true effects of smectic B liquid crystalline order on the conformation-dependent triplet state behavior of this molecule. In OS-nm liquid crystals, triplet decay follows clean first order kinetics in all phases, but the variations in Arrhenius dependence with solvent phase are similar to those observed in the CCH-n liquid crystals. Key words: smectic, liquid crystals, 2H NMR, nanosecond laser flash photolysis, intramolecular triplet quenching, photochemistry.
The effect of added salts on carbon monoxide adsorption on platinum and palladium hydrosols: an FTIR study
Authors: Mucalo Michael R. , Cooney Ralph P.
Published: May 2006

Fourier transform infrared spectroscopy has been used to investigate the effect of added cations and anions on CO adsorption on platinum and palladium hydrosols. In general, anion effects on CO adsorption may be classified into three categories. In the first category, poisoning anions (e.g. CN−, SH−) block the surface against CO adsorption so that infrared spectra exhibit either no ν(CO)ads bands or ν(CO)ads bands at lower frequencies (< 2070 cm−1). In the second category, inert anions (e.g. the halides, citrate, EDTA2−) have no apparent effect on ν(CO)ads. The third category is characterised by anions such as PO43−, CO32−, or stearate ion which affect ν(CO)ads via the pH change that the dissolved anions cause in the metal hydrosol dispersion medium. Infrared spectra of platinum and palladium hydrosols in cyanide media were found to exhibit bands due to cyanate, tetracyanoplatinate(II), and tetracyanopalladate(II) arising from cyanide corrosion of the metal hydrosols. Ultraviolet/visible spectra of iodide ion in platinum hydrosols indicated that iodoplatinate(II) species had been produced. The band shape of ν(CO)ads at 2070 cm−1 in platinum hydrosols is found to be sensitive to the state of dispersion of the hydrosol particles. Bands due to CO adsorbed on hydrosol particles in either a completely or partially aggregated state are weaker and broader with a decreased value of ν(CO)ads relative to that of the unaggregated hydrosol. Key words: platinum hydrosols, palladium hydrosols, CO adsorption, infrared spectroscopy, added salts.
Anomalous temperature-dependent Raman scattering in lithium hydrazinium sulfate
Authors: Frech Roger , Brown Scott H.
Published: May 2006

Results of a polarized Raman scattering study of single crystal lithium hydrazinium sulfate, LiN2H5SO4, over a temperature interval from 11 to 300 K are discussed. Unusual temperature dependence of the band center scattering intensity is observed in a few intramolecular hydrazinium modes, intramolecular sulfate ion modes, and lattice modes. The intensity of these modes increases with increasing temperature from 11 K to about 175 K, then abruptly decreases over a small interval between 175 and 200 K. Above 200 K the band center intensity then exhibits normal behavior, slowly decreasing with increasing temperature. Possible explanations for this anomalous behavior are discussed. Key words: lithium hydrazinium sulfate, proton conductor, Raman spectroscopy.
Formation of C6H7+ ions in ion–molecule reactions in vinyl chloride
Authors: Herman Jan A. , Herman Kazimiera , McMahon Terry B.
Published: May 2006

The formation of C6H7+ species in ion/molecule reactions in gaseous vinyl chloride was studied in a high pressure photoionization mass spectrometer and in a Fourier transform ion cyclotron resonance (FT-ICR) spectrometer. Collision-induced dissociation (CID) mass spectra of C4H5Cl+, C4H6Cl+, and C6H7+ species suggest a "butadiene-like" structure for the two former ions, and a non-benzenium structure for the last species. The C6H7+ ions are formed in a two-step mechanism involving C4H5+ as intermediate ions. These processes are in competition with condensation reactions leading to the formation of C6H7–9Cl+ species. Key words: ion–molecule reactions, gaseous vinyl chloride, collision-induced dissociation.
A voltammetric study of the kinetics of the hexacyanomanganate(III) disproportionation in acidic medium
Authors: López-Cueto Guillermo , Ubide Carlos
Published: May 2006

The fast disproportionation of hexacyanomanganate(III) in acidic medium yields Mn(CN)62− and Mn(H2O)62+. The reaction has been studied by amperometry, with a rotating platinum-disk electrode, at a 1.0 V (vs. SCE) constant potential, in the acidity range 0.01–2.0 M and at temperatures between −5 and 15 °C. A reversible one-electron process takes place with a 0.85 V (vs. SCE) half-wave potential that is not dependent on acidity. The reaction kinetics is pseudo-first order in [Mn(CN)63−] and the rate constant depends on acidity according to the equation: kobs = ka + kb[H3O+] + kc[H3O+]2. At 5 °C and ionic strength 2.0, the determined values of ka, kb, and kc were (2.20 ± 0.08) × 10−3 s−1, (4.9 ± 0.2) × 10−3 s−1 M−1 and (1.40 ± 0.10) × 10−3 s−1 M−2, respectively. A mechanism is proposed where the three terms of kobs are assigned to pathways involving hexacyanomanganate(III) in three different states of protonation. From the effect of temperature the activation parameters, ΔH≠ and ΔS≠, for each pathway are also reported.Key words: hexacyanomanganate(IV), disproportionation, kinetics, amperometry, rotating platinum-disk electrode.
The ligand mediated pseudohypersensitivity of the 3H4 → 3P2, 3H4 → 3P1, 3H4 → 3P0, and 3H4 → 1D2 transitions of praseodymium(III) complexes in solution media
Authors: Misra Sudhindra N. , Sommerer Shaun O.
Published: May 2006

The absorption difference, comparative absorption spectrophotometry, and quantitative analysis of 4f–4f spectra of praseodymium(III) complexes with ligands possessing varying structural features and binding capabilities have clearly indicated that the 3H4 → 3P2, 3H4 → 3P1, 3H4 → 3P0, and 3H4 → 1D2 transitions exhibit substantial intensification as well as a wide variation of oscillator strength. Since these transitions do not follow the selection rules they cannot be considered hypersensitive. Ligands such as β-diketones, Schiff bases, amino acids, diols, nucleic bases, nucleosides, nucleotides, alkoxides, and haloacetates with widely differing binding features in terms of coordinating ability, denticity, and normalized bite appear to induce, to varying degrees, high sensitivity in these non-hypersensitive transitions. The present article reports the high sensitivity of the 3H4 → 3P2, 3P1, 3P0, and 1D2, transitions of Pr(III) by considering the solution spectra of 173 species. This unique sensitivity is termed Ligand Mediated Pseudohypersensitivity. Keywords: praseodymium(III), 4f–4f transitions, hypersensitive transitions.
Étude cinétique de la N-chloration de la succinimide en phase aqueuse
Authors: Matte Denise , Solastiouk Bernard , Merlin André , Deglise Xavier
Published: May 2006

A kinetic study of the N-chlorination, in aqueous medium, of succinimide (SH) at low pH (<5) and at high pH (>9) is presented. We have derived the rate constants and activation energies of the processes involved. A stopped-flow spectrophotometric technique was used to study the kinetics. Without chloride ions, our experimental results can be interpreted by two kinetically indistinguishable mechanisms:[Formula: see text]The limiting values of the rate constants for the case in which only one process is involved in the kinetics of chlorination were evaluated: [Formula: see text]; [Formula: see text].In acid medium, in the presence of chloride ions, we observe a nucleophilic attack of the S− ion on molecular chlorine Cl2. This process is added to the two former processes. Keywords: kinetics, N-chlorination, succinimide, aqueous medium, stopped flow.
Atomic orbital-wise characterization of the vibronic attractive interaction in a model of an oxygen-containing organic polymer
Authors: Tachibana Akitomo , Ishikawa Shigeru , Sahara Wataru , Yamabe Tokio
Published: May 2006

The extended local vibronic constant (ELVC) is introduced for the study of the strength of local electron pairing for superconductivity based on vibronic interaction using a model of an oxygen-containing organic polymer. The ELVC consists of the electrostatic part and the two-electron part, which originates in the response of the electron density to the nuclear vibration. It is found that the two-electron part has opposite sign to, and almost the same magnitude as, that of the electrostatic part. The difference between the ELVC and the Fock matrix derivative, which is related to the derivative of the Hückel parameters used as the electron–phonon coupling constant, is discussed. The vibronic interaction in the in-plane orbitals, which is characteristic of the interaction in a two-dimensional conductor, is also discussed. Keywords: vibronic interaction, superconductivity, local electron pairing, extended local vibronic constant, abinitio calculation.
Structure and magnetic properties of monophenylphosphinate bridged chain polymers of manganese(II), [MnL2(HPhPO2)2]x (where L = HPhPO2H, CH3CONH2, H2O, HCONH(CH3), and C5H5N)
Authors: Du Jing-Long , Rettig Steven J. , Thompson Robert C. , Trotter James , Betz Peter , Bino Avi
Published: May 2006

Crystals of Mn(CH3CONH2)2(HPhPO2)2 are monoclinic, a = 5.668(2), b = 7.500(2), c = 23.104(2) Å, β = 95.52(2)°, Z = 2, space group P21/c, and those of Mn(HPhPO2H)2(HPhPO2)2 are monoclinic, a = 23.281(1), b = 5.508(2), c = 20.5489(6) Å, β = 90.424(4)°, Z = 4, space group C2/c. The structures were solved by heavy-atom methods and were refined by full-matrix least-squares procedures to R = 0.028 and 0.035 for 2081 and 2117 reflections with I ≥ 3σ(I), respectively. Both compounds have structures consisting of polymeric chains propagating along the crystallographic b axis; two phosphinate ligands bridge adjacent manganese atoms forming square planar MO4 units, and six coordination about the metal is achieved by axially O-bonded neutral ligands. Indirect evidence supports similar structures for the other complexes studied here. The complexes are antiferromagnetic and the magnetic susceptibilities have been analyzed according to two Heisenberg models for linear chains. The exchange coupling constants range from −0.30 cm−1 for the acetamide complex to −0.06 cm−1 for the pyridine complex. Magnetostructural correlations involving these complexes and the previously studied Mn(HCONH2)2(HPhPO2)2, reveal that the magnitude of the magnetic coupling is enhanced by symmetrically bridging O—P—O units and short Mn–O–P–O–Mn pathways for exchange. Keywords: polymeric manganese monophenylphosphinates, crystal structures, magnetic properties.
Synthesis of torrentin, dihydrosantamarine, and saussurea lactone from santonin
Authors: Blay Gonzalo , Cardona Luz , Garcia Begona , Pedro José R.
Published: May 2006

The synthesis of the eudesmanolide torrentin (1) by sensitized photooxygenation of synthetic dihydrosantamarine (3) is reported. Both dihydrosantamarine and dihydroreynosin (11) were obtained from the 1,2-epoxide 9, which, in turn, was prepared from the diselenide 7. An improved procedure for the synthesis of the elemanolide saussurea lactone (4) is also reported. Keywords: eudesmanolide, elemanolide, santonin, torrentin, saussurea lactone.
Electron ionization mass spectrometry of cobalt(III) β-diketonates and monothio-β-diketonates possessing aryl and fluorinated alkyl substituents
Authors: Reimer Mark L. J. , Westmore John B. , Das Manoranjan
Published: May 2006

Electron ionization positive ion mass spectra of 15 substituted cobalt(III) β-diketonates and monothio-β-diketonates, CoIIIL3, where L = RCXCHCOR′, R = phenyl, 2-thienyl, or 2-naphthyl; X = O or S; and R′ = CHF2, CF3, C2F5, or n-C3F7, show a marked dependence on the ligand. Molecular ions, [CoIIIL3]+•, are observed only for some of the more highly fluorinated complexes (R′ = C2F5 or n-C3F7). The [CoIIIL2]+• ion, possibly generated by ionization of CoIIL2 formed by thermal degradation, or by electron ionization of CoIIIL3, typically decomposes by elimination of a radical, i.e., L• or R′•, to yield ions containing Co(II); subsequent decompositions proceed preferentially by loss of even-electron neutral species, also to yield ions containing Co(II). Cobalt-containing ions in which fluorine has rearranged to the metal decrease in variety and abundance for the ligands with higher fluorine content. When metal-bonded oxygen is replaced by sulfur, fluorine migration to Co(III), rather than to Co(II), is preferred. These trends are consistent with a combination of several different concepts including the ability of the metal to undergo valency change, the principle of Hard and Soft Acids and Bases, and the inductive capabilities of the ligand donor atoms and of the R and R′ groups. Ion decomposition pathways are proposed. Keywords: mass spectrometry, cobalt complexes, β-diketonates, fluorinated chelate complexes.
Straining strained molecules. III. The spectral and mutagenic properties and an alternate synthesis of diaceperylene and dicyclopenta[1,2,3-cd:1′,2′,3′-lm]perylene
Authors: Mitchell Reginald H. , Chaudhary Mahima , Williams Richard Vaughan , Fyles Robert , Gibson Jack , Ashwood-Smith Michael J. , Fry Albert J.
Published: May 2006

The synthesis of diaceperylene (1) from 5,6-dilithioacenaphthene via nickel or cobalt catalysed couplings proceeded in better yield than a multistep synthesis involving formation of 5,5′-diacenaphthene first. Dehydrogenation of 1 to dicyclopenta[1,2,3-cd:1′,2′,3′-lm]perylene (2) proved a better route than coupling of 5,6-disubstituted acenaphthylene derivatives. Ultraviolet, proton, and carbon nuclear magnetic resonance spectra and electrode reduction potential data of 1 and 2 are discussed with respect to molecular mechanics calculations of strain in these and related bridged naphthalenes. Both 1 and 2 were found to be weakly mutagenic in an Ames microsome test, in contrast to cyclopenta[cd]pyrene.
Flame photometric detection of some transition metals. II. Enhancement of selectivity
Authors: Aue Walter A. , Millier Brian , Sun Xun-Yun
Published: May 2006

A flame photometric detector was used in single-channel and in differential dual-channel modes to characterize and control its selectivity for various transition elements against a hydrocarbon background. The experiments included gas-chromatographable compounds of Cr, Mn, Fe, Co, Ni, Ru, Re, and Os. Single-channel dispersive modes brought only modest gains in selectivity vis-a-vis the non-dispersive (no optical filter) mode. In dual-channel differential modes, however, metal–carbon selectivities could be improved by factors of one to two orders of magnitude. The highest still measurable selectivity ratios are now in excess of 107. The differential dual-channel operation of the detector also made it possible to increase the selectivity of one hetero-element vis-a-vis another; and to distinguish between two hetero-elements, by oppositely directed peaks, in a (spectrally suppressed) matrix of carbon compounds. Metal–metal selectivities could be improved by factors of one to three orders of magnitude over the best dispersive single-channel modes.
Synthesis and characterization of derivatized capped porphyrins
Authors: Tang Hang , Wijesekera Tilak P. , Dolphin David
Published: May 2006

The syntheses of porphyrins carrying either a fully hydrophobic cavity with a benzene moiety (32a,b) or a polar cavity with an amidobenzene (32c–d) are described. Terephthaldehyde (1) was converted to benzene-bisalkanoic acids (8, 10) and nitrobenzene-bisalkanoic acids (13 and 16) by using standard methods. The corresponding diacid chlorides 17a–d were used to acylate two equivalents of a β-unsubstituted pyrrole, and the ketonic groups were reduced by diborane. Following the transformation of the nitro function to the acetamide, appropriate modifications of the ethyl ester functions afforded the key bisformylpyrroles 25a–d. The cyanoacrylate-protected formyl pyrrole derivatives were mono-chlorinated at the α-methyl groups and condensed with two equivalents of an α-unsubstitutued pyrrole to give the dipyrromethane dimers. Strong aqueous alkali caused saponification of the two ester groups and deprotection of the formyl functions to produce the dipyrromethane dimer 30, which, after thermal decarboxylation, was cyclized intramolecularly in acidic medium to give the porphyrins 32 (n = 4 or 5, X = H or NHCOCH3).
Approach to the synthesis of candelabrone and synthesis of 3,7-diketo- 12-hydroxyabieta-8,11,13-triene
Authors: Burnell Robert H. , Caron Stéphane
Published: May 2006

An approach to the synthesis of aromatic diterpenes was tested for its generality. Phenylacetonitriles with increasing substitution on the aromatic ring were prepared and alkylated with geranyl bromide and the resulting dienes subjected to cationic cyclization. The less-substituted examples afforded tricyclic products of the required stereochemistry while the more highly substituted compounds cyclized with reduced yields or not at all. One of the intermediates was used to synthesize nimosone (3,7-diketo-12-methoxyabieta-8,11,13-triene), a natural diterpene isolated originally from Chamaecyparisformosensis and recently from Azadirachtaindica.
Molecular recognition XII. The binding of the H human blood group determinants and congeners by a lectin of Galactiatenuiflora
Authors: Cromer Rémy , Spohr Ulrike , Khare Deveshwari P. , LePendu Jacques , Lemieux Raymond U.
Published: May 2006

The H-type 2 human blood group-related trisaccharide (α-L-Fuc-(1c → 2b)-β-D-Gal-(1b → 4a)-β-D-GlcNAc-OMe (52)) is bound by the anti-H lectin of Galactiatenuiflora very differently than by the lectin I of Ulexeuropaeus. The reason why the Galactia lectin binds the H-type 1 related trisaccharide (α-L-Fuc-(1c → 2b)-β-D-Gal-(1b → 3a)-β-D-GlcNAc-OMe (5)) more strongly and methyl α-L-fucopyranoside much more weakly than does the Ulex lectin is that, for the Galactia lectin, the hydroxyl groups at positions 3a, 3b, 4b, and 4c are indispensable to complex formation whereas it is the hydroxyl groups at positions 3b, 2c, 3c, and 4c which provide the key polar intractions in the case of the Ulex lectin. The H-type 2 (52)•Galactia lectin complex appears to have the hydroxyl groups at positions 6b, 2c, and 3c at or near the periphery of the combining site and the three key hydroxyl groups hydrogen bonded to the protein deep within the combining site and sheltered from water. The CH3O-1a, NHAc-2a, and CH2OH-6a groups likely remain in the aqueous phase remote from the surface of the protein.
Syntheses of a potential fluorescence probe, (−)-(R)-7-azatryptophan, via alkylation of the (1R,4R)-camphor imine of tert-butylgycinate
Authors: Sánchez-Obregón Rubén , Fallis Alex G. , Szabo Arthur G.
Published: May 2006

The synthesis of (−)-(R)-7-azatryptophan (2) from commercially available 7-azaindole (4) is described. The key step involved the diastereoselective alkylation of tert-butyl [(1R,4R)-bornylideneamino]acetate (3) with 1-(tert-butyloxycarbonyl-3-(iodomethyl)-7-azaindole (19) derived from 3-formyl-7-azaindole (14). The alkylation, conducted at −100 °C in a THF/HMPA solvent using potassium hexamethyldisilazide as the base, afforded 7 in greater than 98% diastereomeric excess. Hydrolysis and deprotection gave (−)-(R)-7-azatryptophan.
Mathematical analysis of reactive ion transport in dynamic equilibrium: The case of two ionic species
Authors: Iinuma Koichi , Takebe Masahiro
Published: May 2006

An exact solution for the transport of two reacting ion species in a drift tube is developed. The calculation of the temporal variation of ion fluxes is simplified using an approximate formulation in terms of the reaction frequencies, drift velocities, and longitudinal diffusion coefficients. The exact and approximate formulations are compared for the case of (N2+, N4+)/N2 with a view to establishing the approach to equilibrium.
The trans–cis isomerisation of bis(dioxolene)bis(pyridine) ruthenium complexes
Authors: Tse Yu-Hong , Auburn Pamela R. , Lever A. B. P.
Published: May 2006

The isomerisation of trans to cis bis(3,5-di-t-butylbenzosemiquinonato)bis(R-pyridine)ruthenium, Ru(R-Py)2(DTBDiox)2, is induced by warming with an excess of R-pyridine, where R = 3-chloro, 4-methyl, 4-phenyl, or 4-butyl. The rates of these reactions, for the species with R-Py = 3-chloropyridine, were monitored in o-dichlorobenzene by UV–visible spectroscopy against varying 3-chloropyridine and varying trans-[Ru(3-ClPy)2(DTBDiox)2] concentration. The data were found to obey first-order kinetics, −d[Ru(3-ClPy)2(DTBDiox)2/dt = kobsd[Ru(3-ClPy)2(DTBDiox)2], over a considerable range of pyridine concentration. A plot of 1/kobsd vs. [3-chloropyridine] is linear with a positive intercept. A dissociative mechanism is proposed for the isomerisation reaction. The activation parameters were determined for the specific case of R-Py = 3-chloropyridine. Electronic and electrochemical features of these species are briefly discussed.
Short syntheses of rigid acyclic or macrocyclic poly-imine ligands and their use in Ru(II), Fe(III), and alkali metal complexation
Authors: Dash Robert , Potvin Pierre G.
Published: May 2006

Lipophilic derivatives of 2,6-bis(3-pyrazolyl)pyridine and 1,3-bis (3-pyrazolyl)benzene were obtained in acceptable yields by Stork reactions and transformed by N-alkylations into three pentadentates, three bis(bidentates), and one macrocyclic octadentate ligand. The parent bis(pyrazolyl) pyridine constituted a terpyridine analogue and readily formed a Ru(II) complex. By comparison of 1H nuclear magnetic resonance patterns, it was found that the alkylations in the bis(pyrazolyl)pyridine series conferred an anti,anti conformation of the imino nitrogens. The pentadentates were then able to extract alkali metal ions into CHCl3 with only modest strength and selectivity, but the preferred extraction of Li+ by one of these was notable. By variation of the reaction conditions, a tri-iron(III) and a di-iron(III) complex were obtained from a bis(bidentate).
Transient 1,3-dipoles containing sulfur: a novel example of rearrangement from ethyl-1-oxo-1-(2,3-dichloro-4-phenoxyacetic acid)-2-[3-thio-5-(4-chlorophenyl)-1,2- dithiolium] bromide
Authors: Varache-Lembege Martine , Nuhrich Alain , Devaux Guy , Duboudin Françoise
Published: May 2006

During the basic treatment of the compound named in the title the expected ketone was not obtained. The Fast Atom Bombardment (FAB) mass spectrum of the new product formed was reported in this paper: the fragmentation pattern shows an S—S bridge sequence in a dimeric compound. This structure was also investigated by 1H and 13C nuclear magnetic resonance spectroscopy, the results of which were in accordance with the mass spectral data. The formation of this compound was explained by the hypothesis of a thiirane intermediate structure that could spontaneously isomerize to the enethiol form and undergo oxidation to the disulfide.
Reactions of nitriles with binuclear rhodium hydrides. The stepwise reduction of a carbon–nitrogen triple bond at two metal centres
Authors: Fryzuk Michael D. , Piers Warren E. , Rettig Steven J.
Published: May 2006

The reaction of simple nitriles, R′CN (R′ = CH3, Ph, o-tol) with the electron-rich binuclear rhodium hydride derivatives [(R2PCH2CH2PR2)Rh]2(μ-H)2 (R = Pri: [(dippe) Rh]2(μ-H)2; R = OPri: [(dipope)Rh]2(μ-H)2) results in the formation of alkylideneimido derivatives [(R2PCH2CH2PR2)Rh]2(μ-H)(μ-N=CHR′), apparently by insertion of the nitrile moiety into a bridging hydride bond; this was confirmed by the reaction of nitriles with the dideuteride [(dippe)Rh]2(μ-D)2, which resulted in the formation of [(dippe)Rh]2(μ-D)(μ-N=CHR′). Further reduction can take place by addition of H2 to generate the corresponding amide hydride derivatives [(dippe)Rh]2(μ-H)(μ-NHCH2R′); this represents an overall stoichiometric reduction of a nitrile to a coordinated amide at a binuclear centre. These same amido-hydride complexes can be accessed by addition of amine to the starting binuclear rhodium hydride derivatives. The X-ray structure of [(Pri2PCH2CH2PPri2)Rh]2(μ-H)(μ-N=CHCH3) was undertaken to confirm the structure of these particular intermediates. Crystals of this material are monoclinic, a = 19.036(2), b = 15.139(1), c = 13.604(1) Å, β = 104.119(7)°, Z = 4, space group P21/c. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.038 and Rw = 0.041 for 5814 reflections with I ≥ 3σ(I).
Synthesis, multinuclear NMR, and solution conformation of (η5-indenyl)CoIRfL complexes (L = CO, P-donor)
Authors: Jablonski Chet R. , Zhou Zhongxin
Published: May 2006

The preparation, spectroscopic characterization, and conformational analysis of a series of Co(III) indenyl complexes, (C9H7)CoIRfL (Rf = C3F7, C6F13, L = CO, P-donor), 2–8, are described. I3C and 1H NMR parameters are consistent with a slightly distorted -η5-C9H7 coordination. 1H nuclear Overhauser effect difference (nOed) spectra indicate a preferred solution conformation in which the perfluoroalkyl group is trans to the C3a—C7a ring junction.
Viscosities and thermodynamics of viscous flow of binary liquid mixtures of 2-(2-butoxyethoxy)ethanol with aniline and N-alkyl anilines
Authors: Wiseman Paul , Heggie Murray , Palepu Ramamurthy
Published: May 2006

Viscosities and densities of binary mixtures containing 2-(2-butoxyethoxy)ethanol with aniline and N-alkyl-substituted anilines have been determined at five different temperatures over the complete concentration range. Excess volumes, viscosities, and excess molar free energy of activation of flow were calculated and the departure from ideal behavior is explained on the basis of specific interactions between the components in these mixtures. McAllister's approach correlates the viscosity data with a significantly high degree of accuracy for all these systems.
Sedum alkaloids XII. Synthesis of the new piperidine alkaloids homosedinone and dihomosedinone
Authors: Durant Alex , Hootelé Claude
Published: May 2006

The new piperidine alkaloids homosedinone 2 and dihomosedinone 3, isolated from Sedumacre, have been synthesized from (−)-norsedamine 7 by application of the sequence: anodic methoxylation – elimination – nucleophilic addition.
Vibrational spectroscopic study of the interaction of metal ions with diethyl phosphate, a model for biological systems
Authors: Stangret Janusz , Savoie Rodrigue
Published: May 2006

We have studied, using Raman and infrared spectroscopy, the interaction of various monovalent, divalent, and trivalent metal cations with the [Formula: see text] group of diethyl phosphate in aqueous solution, at metal: phosphate ratios ranging from 1:40 to 6:1. The results show that the metal cations interact with the phosphate groups in various ways and to different extents. Spectral characteristics for some specific types of interactions are presented, namely, for direct metal binding by one of the oxygen atoms in the [Formula: see text] group, the formation of water-separated ion pairs, and non-specific electrostatic interactions.
Structural and computational studies of ligands for the glycine binding site on the excitatory amino acid receptor complex: 1. 6,7-Dimethyl and 6,7-dimethoxy 2,3-quinoxalinedione
Authors: Kubicki Maciej , Codding Penelope W.
Published: May 2006

The crystal structures of two quinoxalinedione derivatives, 6,7-dimethyl-1,4-dihydro-2,3-quinoxalinedione dihydrate (1) and 6,7-dimethoxy-1,4-dihydro-2,3-quinoxalinedione hydrate (2), and AM1 molecular orbital computational investigations of electronic properties and hydrogen bond strengths are reported. The space group for 1 is [Formula: see text] with a = 7.0109(1) Å, b = 8.5901(3) Å, c = 10.7890(5) Å, α = 112.704(3)°, β = 96.053(3)°, and γ = 107.589(2)°. For 2, the space group is Pbca with a = 12.2769(6) Å, b = 6.9291(3) Å, and c = 25.8644(7) Å. The geometries of these two compounds are similar; small differences are mostly due to the different electronic characters of the substituents and to intermolecular interactions in the crystals. There are two main factors determining the packing schemes of these compounds, π-stacking between neighboring molecules and hydrogen bonds, including bonds with the water molecules of crystallization. The AM1 semi-empirical calculations show differences between net atomic charges and dipole moments. For both structures, calculations confirm the asymmetry of hydrogen bonds that is observed in the crystal structures.
A study of hydrogen abstraction reactions by halogen atoms with HFCO and HClCO: determination of transition state structures, barrier heights, and vibrational frequencies
Authors: Francisco J. S. , Mina-Camilde N.
Published: May 2006

Theoretical barriers and reaction energetics were determined using ab initio calculations at the PMP4/6-311 + +G** level with UMP2/6-311G** optimized geometries for hydrogen abstraction reactions of HFCO and HClCO by fluorine and chlorine atoms. The largest barriers are predicted for fluorine and chlorine atom abstractions of hydrogen from HFCO. Fluorine and chlorine atom abstractions of hydrogen from HClCO are predicted to be barrierless. The predicted barrier for fluorine atom abstraction of hydrogen from HFCO is calculated to be 1.3 kcal mol−1 and is in good agreement with the experimental value of 1.8 ± 0.4 kcal mol−1.
Solid state intermolecular interactions in cyanofunctionalized diselenadiazolyl dimers
Authors: Davis William M. , Hicks Robin G. , Oakley Richard T. , Zhao Baiyi , Taylor Nicholas J.
Published: May 2006

The preparation and crystal and molecular structure of the monofunctional 1,2,3,5-diselenadiazolyl radical [RCN2Se2] (R = 3,5-dicyanophenyl) are described. Crystals of [(CN)2C6H3CN2Se2] are triclinic, space group [Formula: see text] a = 7.197(2), b = 10.753(3), c = 13.345(5) Å, α = 88.00(3)°, β = 82.05(2)°, γ = 81.00(2)°, MW = 311.1, Z = 4. The structure consists of stacked arrays of radical dimers laced together by networks of short CN---Se contacts, but the steric bulk of the organic ligand leads to a pairwise aggregation of [CN2Se2] columns. These structural features are compared with those observed in related dimers, and the results interpreted in the light of extended Hückel band calculations on a series of model structures. The results provide a qualitative correlation between the size and dimensionality of the intermolecular Se---Se network and the degree of crystal orbital dispersion.
Reduction mechanism of 4-nitrobenzophenone in tetrahydrofuran. Influence of added proton donors
Authors: Gard J. C. , Mugnier Y. , Huang Y. , Lessard J.
Published: May 2006

In tetrahydrofuran, with tetrabutylammonium hexafluorophosphate as supporting electrolyte, 4-nitrobenzophenone is reduced to the radical anion and, at a more negative potential, to the dianion. These two species are stable even on the time scale of electrolysis. In the presence of proton donors of increasing strength, the dianion is protonated to ArNO2H− but the radical anion is protonated to ArNO2H• only with the strongest acids. These species react further and the different mechanisms are discussed.
Molecular modelling of photoactive pigments in the solid state: Investigations of polymorphism
Authors: McKerrow Andrew J. , Buncel Erwin , Kazmaier Peter M.
Published: May 2006

The application of molecular mechanics calculations to the study of solid state organic photoconductors has been investigated. Using X-ray crystallographic information for a series of four N.N′-dialkylperylene pigments, 1–4, lattices of these molecules were modelled using the Dreiding force field. Comparison of the resulting lattices with the experimental data demonstrated that both molecular and physical features of the perylenes could be accurately reproduced in these calculations. When systematic deviations in molecular geometry occurred, these errors could be attributed to the generic nature of the force field. We have extended the computational studies to the problem of polymorphism since this is known to have a profound effect on photoconduction. To model enthalpic polymorphs of N,N′-dimethylperylene, 1, the symmetry relationships and atomic coordinates from the crystal structure of N,N′-di-n-pentylperylene, 4, were utilized. By truncating the pentyl substituents to methyl groups and applying external stresses to the resulting lattice during minimization it was possible to identify two likely polymorphs of 1. The inclusion of Gasteiger's partial equalization of orbital electronegativity (PEOE) charges on the perylenes was not found to be beneficial in locating suitable polymorphs. These computational methods have been successful in modelling perylene pigments in the solid state and have been shown to be useful in investigating polymorphism.
Manifestations of noncovalent interactions in the solid state. 3. X-ray crystal structures of [H4(cyclam)][FeCl5(OH2)](Cl)2 and [H4(cyclam)][CF3COO]4, two network hydrogen bonded solids
Authors: Subramanian S. , Zaworotko Michael J.
Published: May 2006

FeCl2 or FeCl3 react with cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) in an acidic medium (4 M HCl) to afford dark orange-red plates of [H4(cyclam)][FeCl5(OH2)](Cl)2 (1). 1 crystallizes in a polar space group (orthorhombic, Pc21b) with a = 10.7730(6), b = 13.3418(10), c = 14.4564(10) Å, V = 2077.84(24) Å3, and Dcalc = 1.68 g cm−3 for Z = 4. Final values of R = 0.031 and Rw = 0.034 were obtained for 1950 independent observed (I > 3σ(I)) reflections. Cyclam reacts with neat trifluoroacetic acid to afford a colourless salt, [H4(cyclam)][CF3COO]4 (2). 2 crystallizes in a centric space group (monoclinic, P21/c), with a = 8.7442(11), b = 10.5121(11), c = 15.2469(20) Å, β = 102.526(15)°, V = 1368.1(3) Å3, and Dcalc = 1.593 g cm−3 for Z = 2. Final values of R = 0.059 and Rw = 0.067 were obtained for 1336 independent observed (I > 3σ(I)) reflections. Extensive interionic hydrogen bonding between the cyclam cations, which adopt exodentate conformations, and anions results in network polymeric hydrogen bonding (1-D for 1, 2-D for 2). The networking in 1 is intrinsically polar because one chloride anion and the [FeCl5(OH2)]2− complex anion are involved in networking between the H4(cyclam)4+ cations. The implications of the crystal structures are discussed from the perspective of rational design of polar solids.
Stereoisomerism of oxotrichlorobis(triphenylphosphine)rhenium(V), ReOCl3(PPh3)2: a reinvestigation
Authors: Lebuis Anne-Marie , Beauchamp André L.
Published: May 2006

The various preparative procedures described in the literature for ReOCl3(PPh3)2 were repeated. The standard methods were found to yield a yellow triclinic material ([Formula: see text] a = 11.793, b = 14.300, c = 16.422 Å, α = 64.04°, β = 84.31°, γ = 87.32°, R = 0.064). The unit cell contains three discrete monomeric molecules with the trans-bis(phosphine) configuration, one of which has its Cl-Re=O unit disordered over two opposite directions. Recrystallization in CH2Cl2 yielded crystals of the bright green monoclinic polymorph (C2/c, a = 24.347, b = 9.604, c = 15.666 Å, β = 116.77°, R = 0.025) containing the same monomeric molecule, but with a different conformation of the PPh3 ligands and a different packing pattern. These two polymorphs actually correspond to "isomers" 1 and 2 described by Johnson, Lock, and Wilkinson in 1964. Attempts to prepare their third "isomer" yielded powders containing ReOCl3(PPh3)2 (green polymorph) and ReNCl2(PPh3)2. The IR and 31P NMR spectra of these samples are discussed.
Generalization of an empirical model for bond dissociation energies
Authors: Luo Yu-Ran , Pacey Philip D.
Published: May 2006

A relationship between homolytic bond dissociation energies (BDEs) of C—X bonds and the electronegativity of X and the degree of methyl substitution of C has been extended. The range of leaving groups, X, now includes SiH3, GeH3, and PH2 and a variety of C-, N-, and O-centred radicals. Alkyl groups with ethyl and propyl chains attached to the radical centre have been incorporated. Steric effects, including those in bulky silanes, have been treated. The method is believed to be generally applicable where resonance and ring strain are not significant. BDEs for 73 bonds have been calculated; in the 42 cases where experimental data are available, the average deviation is 0.7 kcal/mol.
The vibrational spectra (100–1500 cm−1) of a series of bicyclo[3.2.1]octanes assigned by means of scaled 3-21G ab initio harmonic force fields
Authors: Eggimann Thomas , Ibrahim Nan , Shaw R. Anthony , Wieser Hal
Published: May 2006

The infrared absorption (vapor phase and solution) and Raman (liquid phase) spectra of bicyclo[3.2.1]octane, 8-oxabicyclo[3.2.1]octane, 6-oxabicyclo[3.2.1]octane, 6,8-dioxabicyclo[3.2.1]octane, and the 7,7-dideutero-substituted derivatives of the last two compounds are reported in the region 100–1500 cm−1 for the first time. The vibrational spectra are assigned almost completely with the guidance of ab initio 3-21G geometries and scaled force fields. A total of 14 force-field scale facors are transferred from smaller molecules, predicting the frequencies with an average error of 7.6 cm−1 (1.2%) for 196 assigned transitions. After optimizing the factors in an overlay refinement involving all six molecules, the frequencies are within 5.7 cm−1 (0.75%) of experiment. The ab initio absorption and Raman intensities are calculated with the 3-21G basis set and are demonstrated to be of such accuracy as to be useful for the spectral assignments. These intensities are calculated with uniformly and nonuniformly scaled force fields and compared to the experimental spectra. The intensities derived from the latter force fields are superior, meaning that nonuniform scaling is preferable at this level of theory for both vibrational frequencies and normal mode descriptions.
An X-ray and conformational study of 5,7-dihydro-1,11-dimethyl-6H-dibenzo[a,c]cyclohepten-6-one and its methyl derivatives
Authors: Fraser Robert R. , Bensimon Corinne , Kong Fanzuo , Wu Xinfu
Published: May 2006

The crystal structures for the title compound 1 and its α-methyl derivatives 2–4 have been determined. Molecular mechanics calculations of the conformation of minimum energy for 1, 3, and 4 correspond closely to the symmetric structures observed in the crystal. For 2, rotation at the CO—CH2 bond by 24° produced an asymmetric conformation matching that seen in the solid state. The calculated changes in energy as a function of the torsional angle for 1 and 2 were compared with those for cyclohexanone and the axial conformer of the α-methyl derivative. The energy requirements for conformational change in the seven-membered ring were significantly greater than for the cyclohexane analogue. The calculated energy differences between diastereomeric methyl derivatives 2–4, 6, and 7 were in agreement with epimerization experiments. The distance of closest approach observed between a proton of the axial methyls of 2 and 3 and the distal benzene ring is smaller than expected on the basis of van der Waals' radii.
The mechanism of stereoselectivity in the cycloaddition reactions of α-hydroxy-ortho-quinodimethanes with the fumarate of methyl lactate and mandelate
Authors: Charlton James L. , Maddaford Shawn
Published: May 2006

The Diels–Alder cycloaddition reaction of the fumarate of methyl lactate or methyl mandelate with α-hydroxy-ortho-quinodimethane produces an unexpected exo product with very high asymmetric induction. Experiments and calculations have been carried out that show that the origin of the stereoselectivity in these reactions is related to hydrogen bonding between the α-hydroxy-o-quinodimethane and the lactate or mandelate group in the dienophile.
Formation of isomeric monohalo-n-alkanoic acids in the reactions of γ- and δ-n-alkanolactones with hydrogen halides
Authors: Granata Alessandro , Perlin Arthur S.
Published: May 2006

In 57% hydriodic acid or 48% hydrobromic acid, under reflux, n-alkanoic γ- or δ-lactones of from 5 to 18 carbon atoms undergo facile ring opening to monohalo-n-alkanoic acids. With both reagents the ratio of acid to lactone at equilibrium varies widely, ranging from about 1:3 for γ-valerolactone (C5) to 3:1 or more for γ-octanolactone and the larger members of the series. Extensive scrambling of the halogen atoms accompanies the formation of the haloacids, whereby mixtures of monohalo isomers substituted at all positions from C-4 to the penultimate carbon are found. In an 18 h reaction with HBr, for example, γ-caprolactone was converted into a 1:3 mixture of 4- and 5-bromohexanoic acids, and γ-decanolactone into a 1:1.4:1.4:1.4:2.3:2.3 mixture of 4-, 5-, 6-, 7-, 8-, and 9-bromodecanoic acids. By contrast, the γ-lactones containing 14 or 16 carbon atoms gave only 10:1 mixtures of the 4- and 5-bromoacids, and at the level of 18 carbon atoms rearrangement was no longer evident; i.e., γ-octadecanolactone afforded only 4-bromooctadecanoic acid. Similar isomer distributions were obtained for the iodoacid homologs. Hydrochloric acid (37%) was far less effective in opening the lactone rings, and also in inducing rearrangement of the chlorine atoms introduced. Differences in entropy and in solvation appear to be the main factors contributing to the variations observed among isomeric lactones.