bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and structural features of complexes [(P∩P)2Rh][hfacac] containing hexafluoroacetyl- acetonate as a noncoordinating anion
Authors: Fornika Roland , Six Christian , Görls Helmar , Kessler Magnus , Krüger Carl , Leitner Walter
Published: April 2011

The synthesis and characterization of complexes [(P∩P)2Rh][hfacac] (P∩P = chelating bidentate phosphine ligand R2P(CH2)nPR2 (2a-g), hfacac = hexafluoroacetylacetonate anion) (4) is reported. The molecular structures of 4a (R = Ph, n = 1) and 4f (R = Cy, n = 2) in the solid state were determined by single-crystal X-ray diffraction. The complexes crystallize in the monoclinic space groups C2/c (No. 15) and P21/n (No. 14), respectively. No coordinative interaction between the rhodium center of the cation [(P∩P)2Rh]+ (4a+, 4f+) and the hfacac anion is evident in either cases. In the crystal structure of 4a, hydrogen bonds between the oxygen atoms of the hfacac anion and methylene protons of the CH2 bridges of the phosphine ligand lead to highly symmetric chains of regularly alternating cations and anions. The coordination geometry around the rhodium center in 4a+ is ideally square-planar, whereas 4f+ is significantly distorted towards a tetrahedron with an angle between the two P2Rh moieties of 18.6°. The cation 4b+ (R = Cy, n = 1) was investigated in form of the tetrafluoroborate salt for comparison. The compound [{Cy2P(CH2)PCy2}2Rh][BF4] crystallizes as a THF solvate (4b′) in the triclinic space group P[Formula: see text] (No. 2) containing ideally square-planar [(P∩P)2Rh]+ cations. Key words: rhodium, chelating ligands, coordination modes, 1,3-diketonates, phosphorus ligands.
BINAPS - An axially chiral P,S-heterodonor ligand for asymmetric catalysis based on binaphthalene backbone
Authors: Gladiali Serafino , Medici Serenella , Pirri Giovanna , Pulacchini Sonia , Fabbri Davide
Published: April 2011

The chelating P,S-heterodonor ligand 2-diphenylphosphanyl-1,1'-binaphthalene-2'-thiol (11) (BINAPS), which features a chiral axis as the unique stereogenic element, has been prepared in both racemic and enantiopure form through a multistep reaction sequence using 2,2'-dihydroxy-1,1'-binaphthalene (BINOL) as the starting material. The reaction sequence is completely stereoconservative and (S)-11 is obtained with no loss of enantiopurity from pure (S)-BINOL. (R)-11 can be alternatively obtained by resolution of racemic 11 using the chiral (S)-benzylaminato Pd(II)-complex 19 as the resolving agent. The S-methyl or the S-i-propyl derivatives 14 have been used as chiral ligands in the Rh(I)-catalyzed asymmetric hydroformylation of styrene and in the hydrogen transfer reduction of acetophenone with modest success (up to 20% ee). In the presence of suitable Pd-complexes the same ligands provide higher ees in the hydrosilylation of styrene (50% ee) and in the allylic alkylation of 1,3-diphenylprop-2-enyl acetate (60% ee).Key words: heterodonor ligands, binaphthalene derivatives, enantioselective catalysis, transition metal catalysts, allylic alkylation.
Oxidation of copper(II) hydroxyporphyrin (oxophlorin); oxidative ring opening and formation of an ester-linked, dinuclear copper complex
Authors: Phillips Shane , Noll Bruce C , Olmstead Marilyn M , Balch Alan L
Published: April 2011

Addition of copper(II) acetate to octaethyl(meso-hydroxy)porphyrin (H2OEPOH) in THF under a dinitrogen atmosphere produces CuII(OEPOH), which has been isolated as red crystals and shown to have a meso-hydroxyporphyrin structure by UV-vis and EPR spectroscopy. CuII(OEPOH) undergoes oxidation by dioxygen to form a novel dinuclear copper complex {CuII(OEPOC(O)OEB)CuII}. This dinuclear complex is composed of a copper(II) meso-substituted porphyrin portion (with a planar CuN4 unit), which is attached through an ester linkage to a helical copper(II) tetrapyrrole that has been ring-opened through oxidative cleavage of a second molecule of CuII(OEPOH). The oxidative ring-opening reaction resembles that of natural heme catabolism but is arrested at a stage where the oxidized meso-carbon is still appended to the helical open tetrapyrrole. A mechanism is suggested for this process.Key words: copper porphyrin, crystal structure, porphyrin oxidation, linear tetrapyrrole, hydroxy-porphyrin, oxophlorin.
DISQUAC predictions on thermodynamic properties of ternary and higher multicomponent mixtures. II. Results for HE of ternary mixtures containing nonpolar components, or one polar compound, two polar compounds, or one alcohol and hydrocarbons, or CCl4
Authors: Gonzalez Juan Antonio , Carmona Javier , Riesco Nicolas , de la Fuente Isaias Garcia , Cobos Jose Carlos
Published: April 2011

The ability of the DISQUAC model for predicting excess enthalpies (HE) of ternary systems on the basis of binary parameters only, i.e., neglecting ternary interactions is analyzed. At this end, DISQUAC results for a set of 95 ternary systems are examined. The solutions studied are formed by only hydrocarbons (or CCl4); or by one polar compound (not alcohols) and two hydrocarbons (or CCl4); or by two polar compounds (not alcohols) and one hydrocarbon (or CCl4); or by one alcohol and two hydrocarbons (or CCl4). Most of the HEs analyzed are endothermic, and valid at 298.15 K and atmospheric pressure. The mean deviation between experimental values and DISQUAC results is 5.5% for the ternary systems and 6.5% for the constituent binaries (181 mixtures). The interaction parameters used are valid for the description of thermodynamic properties of binary systems: vaporliquid equilibria (VLE), liquidliquid (LLE), and solidliquid equilibria (SLE), HE and excess heat capacities at constant pressure (CEP), as well as HE and VLE of ternary solutions. Predictions are, in most of the cases, independent of the mixture compounds, or the number of groups present in the system. Larger deviations underline typical shortcomings of the group contributions methods (e.g., Patterson's effect; branching). Note that results for the ternaries and for the constituent binaries are of the same order. This is not the case for the Dortmund version of UNIFAC. The mean deviations obtained using this model are 10.5% and 14% for the ternary and binary mixtures, respectively. Results from other models (original UNIFAC, Flory's theory, NittaChao, UNIQUAC association model) for a number of systems are also compared to those obtained using DISQUAC.Key words: predictions, HE, ternary systems, binary parameters, geometrical methods, Flory, group contributions.
2001 E.W.R. Steacie Award LectureThe imido ligand in main group element chemistry
Authors: Chivers Tristram
Published: April 2011

The imido group (NR) is a versatile ligand in main group chemistry. The high reactivity of multiply bonded (terminal) imido derivatives of p-block elements is used, for example, in the aza-Wittig reaction, allylic aminations, and in peptide synthesis. As a bridging ligand, the imido group provides a cornerstone for a wide variety of binary cluster structures. This review is primarily concerned with the synthesis, structures, reactions, and ligand behaviour of imido derivatives of the heavy chalcogens (selenium and tellurium) as exemplified by the tellurium diimide dimer t-BuNTe(µ-N-t-Bu)2TeN-t-Bu and the homoleptic trisimido-tellurite dianion [Te(N-t-Bu)3]2. The synthesis and cluster structures of alkali metal and alkaline earth metal derivatives of heteroleptic imido-oxo anions of sulfur, e.g., [OxS(NR)3  x]2 (x = 1, 2) and [O2S(µ-NPh)SO2]2, are also discussed.Key words: main group chemistry, imido ligand, chalcogens.
One-pot multicomponent synthesis of β-acetamidoketones catalysed by pTSA1
Authors: Das Biswanath , Reddy Kongara Ravinder , Srinivas Yallamalla , Kumar Rathod Aravind
Published: April 2011

A catalytic amount of pTSA has been found to be effective to carry out a one-pot three-component coupling of aromatic aldehydes, enolizable ketones or ketoesters, and acetonitrile in the presence of acetyl chloride to afford β-acetamidoketones in high yields. Short reaction times and inexpensive catalyst are main advantages of this protocol.Key words: β-acetamidoketone, pTSA, multicomponent reaction, diastereoselectivity.
Fluorescence quenching of gramicidin D in model membranes by halothane
Authors: Carnini Anna , Nguyen Trinh T , Cramb David T
Published: April 2011

Inhaled anesthetics were introduced in surgery over a century ago. To this day, the molecular mechanism of anesthetic action remains largely unknown. However, ion-channels of neuronal membranes are believed to be the most- likely molecular targets of inhaled anesthetics. In the study presented here, we investigated the interaction of a simplified ion-channel system, gramicidin, with halothane, a small haloalkane inhaled anesthetic in various environments. Fluorescence-quenching experiments of gramicidin D in dioleoylphosphatidylcholine (DOPC) large unilamellar vesicles (LUVS) have shown that halothane can directly interact with the ion channel (KSV = 66 M–1). Halothane quenched the fluorescence from tryptophan residues located at the lipid bilayer – aqueous interfaces as well as those tryptophans located deeper in the bilayer. Quenching data from gramicidin D in sodium dodecyl sulfide (SDS) micelles revealed that the tryptophan residues located at the micelle–solvent interface were preferentially quenched by halothane (KSV = 22 M–1). In 1-octanol, fluorescence quenching was observed, but with a lower KSV value (KSV = 6 M–1) than in DOPC LUVS and SDS micelles. Taken together, these results indicate that halothane interactions with gramicidin, mediated by a lipid bilayer, are the strongest, and that the mechanism of anesthetic action may also be lipid-mediated.
Studies on chitan (β-(1 → 4)-linked 2-acetamido-2-deoxy-D-glucan) fibers of the diatom Thalassiosira fluviatilis, Hustedt. III. The structure of chitan from x-ray diffraction and electron microscope observations
Authors: Dweltz N. E. , Colvin J. Ross , McInnes A. G.
Published: April 2011

The form and crystal structure of the fibers attached to the diatom Thalassiosira fluviatilis were studied by the electron microscope and x-ray diffraction.These fibers, which were shown previously to be pure, highly crystalline β-(1 → 4) linked poly-N-acetyl-D-glucosamine (chitan), are strap-like in cross section, 1000–2000 Å in width at their widest point close to the base, from which they taper uniformly to a very small tip at their outer extremity. Three connected filaments or microfibrils form the fiber at its widest point.The unit cell of chitan is monoclinic with the space group P21. The parameters of the unit cell are a = 4.80, b = 10.32, c = 9.83 Å, and β = 112°. The density of the chitan fibers is 1.495 g/cm3. There is only one polymeric chain per unit cell with a two-fold screw axis and therefore the chains are parallel to each other. A three-dimensional structure is proposed for chitan which is reasonable from stereochemical considerations and which is in good agreement with all observed x-ray diffraction data.
Etude de configuration en série bicyclo[2•2•1] hepténique
Authors: Brown G. M. , Dubreuil P.
Published: April 2011

not available
On the chemistry of iodonyl radicals. The oxidation of iodobenzene by t-butyl hypochlorite
Authors: Tanner Dennis D. , Gidley Geoffrey C.
Published: April 2011

The reaction of iodobenzene with t-butyl hypochlorite proceeds by a free radical chain mechanism, forming as the sole product iodobenzene t-butoxy chloride (IBBC). The photoinduced or thermally induced reactions of IBBC with hydrocarbon substrates yield chlorinated hydrocarbons by a radical chain halogenation sequence involving t-butoxyiodonyl benzene as the principal chain-carrying species. The photolysis or thermolysis of IBBC in the absence of molecular oxygen yields products resulting from a variety of free radical chain reactions, while thermolysis in the presence of oxygen yields only iodobenzene and t-butyl hypochlorite.
Non-equivalence of gem-dimethyl protons in some bi- and tricyclic compounds. Stereochemical assignments in the khusenic, isokhusenic, and chamigrene series
Authors: Neville George A. , Nigam Ishwar C.
Published: April 2011

The non-equivalence of gem-dimethyl protons in two novel series of tricyclic sesquiterpenes, khusenic (1) and isokhusenic (2), is discussed in terms of anisotropy effects and compared with that found in the analogous monoterpenic compounds, fenchone (8), pinocamphone (9), camphene (10a), methylenenorbornane (10b), camphenilone (11), and dimethylnorcampholide (12). The stereochemistry of the gem-dimethyl groups has been assigned in the above compounds. The chemical shift data and the stereochemistry of the above compounds has been used to make stereochemical assignments in the novel chamigrene series 13, 15, 17, and 19.
Spin trapping in photochemistry of coordination compounds
Authors: Rehorek Detlef , Hennig Horst
Published: April 2011

The application of spin-trapping technique to detect short-lived paramagnetic species formed during photochemical reactions of coordination compounds is reviewed. Interference of radical recombinations by scavenging action of spin traps has been pointed out to be important at high spin-trap concentrations only. Due to only a limited extent of side reactions, nitrosodurene and phenyl N-tert-butyl nitrone were found to be excellent spin traps for the study of photoreactions of metal complexes in nonpolar solutions, whereas 5,5-dimethyl pyrroline-1-oxide is recommended for aqueous solutions. Using these spin traps, both organic and inorganic radicals, e.g. H, Cl, N3, CN, OH, O2−, as well as solvated electrons and metal-centered free radicals have been detected during the photolysis of coordination compounds. The detection of singlet oxygen by reaction with 2,2,6,6-tetramethyl piperidine is briefly discussed.
Synthesis, characterization, and crystal and molecular structures of the coordination compounds, [Me2Ga•O(C5H3N)CH2NMe2] and [Me2Ga•O(C9H6N)]2
Authors: Onyiriuka Emmanuel C. , Rettig Steven J. , Storr Alan , Trotter James
Published: April 2011

Crystals of (2-dimethylaminomethyl-3-pyridolato)dimethylgallium are monoclinic, a = 13.443(3), b = 6.7563(3), c = 13.046(2) Å, β = 100.38(1)°, Z = 4, space group I2/m, and those of bis[(8-quinolinolato)dimethylgallium] are monoclinic, a = 9.7340(4), b = 12.7135(5), c = 9.6843(4) Å, β = 117.014(3)°, Z = 2, space group P21/c. Both structures were solved by conventional heavy atom methods and were refined by full-matrix least-squares procedures to R = 0.044 and 0.032 for 1485 and 1567 reflections with I ≥ 3σ(I), respectively. The structure of [Me2Ga•O(C5H3N)CH2NMe2] consists of discrete monomeric molecules which contain tetrahedrally coordinated gallium atoms. The bidentate anionic 2-dimethylaminomethyl-3-pyridolate ligand coordinates Ga via the oxygen and amino nitrogen atoms (Ga—O = 1.892(3), Ga—N = 2.127(4), Ga—C = 1.950(5) and 1.939(6) Å). The structure of [Me2Ga•O(C9H6N)]2 consists of centrosymmetric dimers which contain a nearly planar system of seven fused rings. The Ga atoms are five-coordinate, having distorted trigonal bipyramidal coordination geometry. The dimerization occurs via the formation of a central, planar, four-membered (Ga—O)2 ring in which each asymmetrically bridging oxygen atom occupies an equatorial coordination site on one gallium atom and an axial site on the other. Important geometrical parameters for [Me2Ga•O(C9H6N)]2 are Ga—O(eq) = 1.937(3), Ga—O(ax) = 2.297(3), Ga—N(ax) = 2.211(3), Ga—C(eq) = 1.948(6) and 1.945(5) Å, O(ax)—Ga—N(ax) = 149.7(1)°.
An asymmetrical disulfide-containing photoreactive heterobifunctional reagent designed to introduce radioactive labeling into biological receptors
Authors: Dupuis Gilles
Published: April 2011

The synthesis of succinimido 1-amino-(4-azidosalicyloyl)-3,4-dithio-5-carboxylate, a heterobifunctional photoaffinity labeling reagent, is described. The cross-linker possesses an asymmetrical disulfide bond, and a general method for generating a spacer arm bearing an asymmetrical or symmetrical disulfide bond is detailed. The heterobifunctional reagent has been obtained in a minimum of steps and intermediates have been characterized. It is further shown that the reagent can be trace-labeled with [125I]-iodine and it has been used to modify phytohemagglutinin, a model protein. Upon irradiation, polymeric phytohemagglutinin derivatives are produced, as evidenced by electrophoretic analysis.
The effect of the water–cation interaction on the polarisability and second hyperpolarisability of hydrated Li+. A comparative study
Authors: Waite J. , Papadopoulos M. G.
Published: April 2011

The CHF-PT-EB-CNDO method has been used to compute the polarisability and second hyperpolarisability of the hydrated lithium cation with one and two hydration shells. The effect of the Li+… (H2O)n interaction on these properties is discussed and the main findings are confirmed in hydrated Na+, Be2+, and Al3+.
Article
Authors: Shinozuka Kazuo , Kohda Junya , Sawai Hiroaki
Published: April 2011

The bleomycin (BLM) model iron complexes bearing either a hydrophobic or hydrophilic steric factor around the sixth coordination sphere exhibited considerable substrate specificity and stereoselectivity in the oxidation of cis- and trans-olefins in a methanol solution in the presence of H2O2. The catalytic efficiency of the complexes was somehow correlated with the nature of the steric factor rather than with their oxygen-activating ability. In a benzene-phosphate buffer (micelle-forming condition), on the other hand, only the complex having micelle-forming ability exhibited the epoxidation of the substrates.Key words: bleomycin model compound, steric factor, substrate specificity, asymmetric oxidation, oxidation in micelle.
Skeletal vibrational circular dichroism of a series of bicyclic dilactones: the fingerprint region?
Authors: Rauk A , McCann J L , Wieser H , Bour P , El'natanov Yu.I. , Kostyanovsky R G
Published: April 2011

The vibrational circular dichroism (VCD) spectra of 2,5-dioxabicyclo[2.2.1]heptane-3,6-dione 1 (R = H) and the 1,4-dialkyl derivatives, 1 (R = Me) and 1 (R = t-Bu), were calculated by the ab initio magnetic field perturbation (MFP) procedure with a B3LYP/6-31G* force field, and the VCD spectra of the dimethyl and di-t-butyl derivatives were measured in the region 800-1500 cm-1. While the absolute configurations of 1 (R = Me) and 1 (R = t-Bu) could be assigned unambiguously by comparison of the experimental and predicted spectra, there is little obvious correspondence between the spectra of the series of compounds. The VCD spectra are analysed on the basis of operation of a coupled oscillator mechanism involving motions of the polar bonds. In the case of the parent dihydro system, bridgehead C-H bond motions appear to dominate contributions to the VCD of vibrational transitions into which they are mixed.Key words: vibrational circular dichroism (VCD), 2,5-dioxabicyclo[2.2.1]heptane-3,6-dione, dilactones, optical activity.
Syntheses and Fe(II)/Fe(III) equilibria of the new multidentate ligands pyridine-2-phosphonic- 6-carboxylic acid and 2,6-pyridinediphosphonic acid for the use of their iron chelates as catalysts for the oxidation of H2S to S8 by air
Authors: Chen Dian , Martell Arthur E , Motekaitis Ramunas J , McManus Derek
Published: April 2011

The syntheses of two terdentate chelating agents, pyridine-2-phosphonic-6-carboxylic acid (2PP6C) and 2,6-pyridinediphosphonic acid (2,6PDPA), are described. The stepwise stability constants for the ferric complexes at 25.0°C and μ = 0.100 M (KNO3) are log KML = 15.97 and log KML2 = 9.50 for 2PP6C, and log KML = 20.87 and log KML2 = 7.81 for 2,6PDPA. Under the same conditions the stepwise formation constants for the ferrous chelates are log KML = 8.70 and log KML2 = 5.10 for 2PP6C, and log KML = 10.12 and log KML2 = 5.33 for 2,6PDPA. The stabilities of the Fe(III) and Fe(II) chelates are high enough to prevent precipitation of Fe(OH)3 and FeS, respectively, from solutions having pH as high as 10.0. The rates of oxidative degradation of these ligands are very slow when the iron chelates are used as redox catalysts for the oxidation of H2S to S8 by air. The rates of oxidative degradation are immeasurably slow when the iron chelates are used with sodium thiosulfate as a radical scavenger.Key words: 2,6-pyridinediphosphonic acid, pyridine-2-phosphonic-6-carboxylic acid, hydrogen sulfide oxidation, oxidative degradation, nitrilotriacetic acid.
Preparation, properties, and reductive alkylation of arylhydrazides
Authors: Verardo Giancarlo , Toniutti Nicoletta , Giumanini Angelo G
Published: April 2011

1-Acyl-2-arylhydrazines (1), readily obtained in high yield from the condensation of arylhydrazines and the appropriate liquid carboxylic acid (2), underwent reductive alkylation with the same or different liquid carboxylic acids (2) and NaBH4 to give 1-acyl-2-alkyl-2-arylhydrazines (3) in good to moderate yields. The carboxylic acid has both the role of supplying the entering alkyl group and of acting as solvent. Most likely, it also modifies the BH4- anion to an active reducing agent under those conditions. The 1H NMR criteria for identifying the location of acylation of hydrazines and E and Z isomers are given. The MS spectra of the prepared hydrazides were analyzed in order to identify relevant structural features leading to specific fragmentations.Key words: 1-acyl-2-arylhydrazine, 1-acyl-2-alkyl-2-arylhydrazine, reductive alkylation, sodium tetrahydroborate, carboxylic acid.
Aqueous nonelectrolyte solutions. Part XV. The deuterium sulfide - deuterium oxide system and the deuterium sulfide D-hydrate
Authors: Clarke Colin W , Glew David N
Published: April 2011

The univariant (l1l2g) saturation vapor pressure of liquid deuterium oxide (phase l1) with liquid deuterium sulfide (phase l2) in equilibrium with a gas phase (g) has been measured in a stirred titanium reaction vessel at 19 temperatures from 33.003 to 18.905°C and at total pressures from 2.4500 to 1.7428 MPa. The univariant (hl1g) saturation vapor pressure of deuterium sulfide D-hydrate (phase h) in equilibrium with liquid deuterium oxide and a gas phase has been measured at 58 temperatures from 30.666 to 2.798°C and at pressures from 2.2959 to 0.11629 MPa. The maximum temperature for deuterium sulfide D-hydrate with a gas phase, the invariant quadruple point Q(hl1l2g), has been determined from the cut of the (hl1g) and the (l1l2g) curves at temperature 30.770°C with standard error 0.0043°C and at pressure 2.3263 MPa with standard error 0.00018 MPa. The univariant (s1l1g) equilibrium of D-ice (phase s1) with liquid deuterium oxide and a gas phase containing deuterium sulfide has been measured at 11 temperatures from 3.8061 to 3.4540°C and at pressures between 0.00242 and 0.10542 MPa. The lowest temperature for stability of deuterium sulfide D-hydrate with liquid deuterium oxide, the invariant quadruple point Q(hs1l1g), has been determined directly at 3.3917°C with standard error 0.0009°C and at pressure 0.12364 MPa with standard error 0.000011 MPa. This quadruple point Q(hs1l1g) has also been defined by the cut of the (hl1g) and the (s1l1g) curves at temperature 3.3912°C with standard error 0.0006°C and at pressure 0.12363 MPa with standard error 0.000002 MPa. The deuterium sulfide - deuterium oxide gas mixture, represented by a Redlich-Kwong equation of state, has been used to evaluate the fugacities and compositions of the gaseous and liquid deuterium oxide phases for all equilibria. Raoult's law using fugacities has been used to evaluate the saturation mole fraction of deuterium oxide in liquid deuterium sulfide and the Henry's law constant for deuterium oxide solubility in liquid deuterium sulfide between 33.003 and 18.905°C. Data for the (l1l2g) and (s1l1g) equilibria have been accurately represented by simple two-parameter equations. Data for the (hl1g) equilibrium have required a model with seven significant parameters for proper representation betweem 30.666 and 2.798°C.Key words: deuterium sulfide - deuterium oxide system, clathrate D-hydrate of deuterium sulfide, deuterium sulfide D-hydrate stability, freezing of deuterium oxide - deuterium sulfide, phase equilibria of deuterium sulfide - deuterium oxide.
Article
Authors: Tremblay Luc , Lacelle Serge , Fry Charles G
Published: April 2011

A study of the intensity fluctuations in one-dimensional NMR microimaging profiles of imbibed porous Pyrex glass filters is presented. An approach to characterize some aspects of the macroscopic randomness from the NMR microimaging profiles of this porous medium is developed. Statistical properties, such as the arithmetic and geometric means, of the distributions of peak separations between the intensity fluctuations are shown to reveal information about the pore size and the pore-to-pore distances in porous media. The intensity-intensity correlation functions of the one-dimensional NMR profiles display an interplay, as a function of length scale, among the dimensions of the porous network and its embedding space, and their respective dimensions in the projections. Corroboration of these NMR results are achieved with similar analysis of SEM two-dimensional images and their corresponding one-dimensional projections obtained with the same porous Pyrex glass. The approach developed to characterize the macroscopic randomness in these porous glass filters should prove generic for the study of other random materials.Key words: NMR imaging, scanning electron microscopy, porous media, disorder, statistical characterization.
Orientation in stretched polymer-dispersed liquid crystals
Authors: Brazeau Julien , Chénard Yanick , Zhao Yue
Published: April 2011

The orientation behavior of liquid crystal molecules in stretched films of polymer-dispersed liquid crystals (PDLC) was investigated by means of infrared dichroism. The liquid crystal used is 4prime-octyl-4-biphenyl-carbonitrile (8CN); the polymer matrices are semicrystalline poly(epsilon-caprolactone) (PCL) and an amorphous miscible blend of PCL with poly(vinyl chloride) (PVC). 8CN was found to have a limit of solubility below 5 wt.% in PCL. We show that an uniaxial stretching can effectively induce a macroscopic orientation of 8CN, and that this orientation can be preserved in the films after removal of the extensional force at room temperature, where 8CN is in its liquid crystalline phase. The molecular orientation is obtained even by stretching PDLC films with 8CN in the liquid state. These results suggest that an elongated polymer cavity in stretched PDLC imposes LC director fields with respect to the long axes of the droplets, which are aligned parallel to the strain direction. The experiments also reveal that the orientation of 8CN is higher in stretched PDLC with a semicrystalline matrix (PCL) than with an amorphous matrix (the PCL-PVC blend), and that the sizes of the LC droplets also have a slight effect on the induced orientation. This work represents a first step in the exploration of new electrooptical effects of PDLC through the presence of a uniform orientation of the liquid crystal molecules and modifications of the polymer cavity at the electrical field-off state.Key words: polymer-dispersed liquid crystals, molecular orientation, infrared dichroism, electrooptical materials.
Solubility of fluoranthene in organic nonelectrolyte solvents. Comparison of observed versus predicted values based upon Mobile Order theory
Authors: Hernández Carmen E , Acree, Jr. William E
Published: April 2011

Experimental solubilities are reported at 25.0°C for fluoranthene dissolved in 36 different organic nonelectrolyte solvents containing ester, ether, hydroxy, chloro, methyl, and tert-butyl functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 28 solvents for which predictions could be made, computations show that Mobile Order theory does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 53%. In comparison, the average absolute deviation is 1574% when ideal solution behavior is assumed.Key words: fluoranthene solubilities, organic nonelectrolyte solvents, solubility predictions.
Synthesis of a new class of difunctional tetraphenylene crown ethers
Authors: Gibson Harry W , Nagvekar Devdatt S , Delaviz Yadollah , Bryant William S
Published: April 2011

Three new substituted tetraphenylene crown ethers have been made. Bis(5-carbomethoxy-1,3-phenylene)-bis(p-phenylene)-(3x + 6)-crown-x, where x = 12, 16, and 20 (11b-11d) were synthesized via [1 + 1] cyclization of methyl 3,5-bis[omega-chloro(oligoethyleneoxy)]benzoates (13b-3d) with methyl 3,5-bis[omega-(p-hydroxyphenoxy)(oligoethyleneoxy)]benzoates (16b-6d) using K2CO3 as base and tetrabutylammonium iodide as a phase transfer agent in dimethylformamide (DMF). The corresponding 30-membered (x = 8) macrocycle 11a could not be made by this approach; only the elimination product, 3,5-bis(vinyloxy)benzoic acid (19), was isolated. 16a-16d were made via alkylation of p-benzyloxyphenol (14) with 13a-13d, respectively, followed by hydrogenolysis with Pd/C as catalyst. No complexation of these macrocycles with dibenzylammonium ions was detected by NMR spectroscopy, but weak complexation of 11d with a paraquat derivative was observed.Key words: crown ethers, cyclization, macrocycles.
Crystal structures of highly stabilized ylides: methyl(3-methoxy,2-methoxycarbonylbenzoyl) triphenyl- phosphoranylideneacetate and methyl(2-methoxycarb-6-nitrobenzoyl)triphenyl phos phoranyl ideneacetate and the salt methyl(triphenylphosphoranylidene)acetate tetrafluoroborate
Authors: Rochon Fernande D , Melanson Robert , Kayser Margaret M
Published: April 2011

At lower temperatures stabilized ylides react with unsymmetrically substituted phthalic anhydrides to give two acyclic adducts. When the reactions are allowed to proceed at higher temperature enol lactones are formed. Identification of the acyclic intermediates was necessary to understand the mechanism of these Wittig reactions. The transient species trapped in the reaction with trimethyloxonium tetrafluoroborate were unambiguously identified by crystallographic methods. The crystal structures of the tetrafluoroborate salt of methyl(triphenylphosphoranyl idene)- acetate (8), methyl(3-methoxy,2-methoxycarbonylbenzoyl)triphenylphosphoranylideneacetate (6β), and methyl(2-methoxycarbonyl,6-nitrobenzoyl)triphenylphosphoranylideneacetate (7α) were studied by X-ray diffraction. The ionic salt (8) is monoclinic, P21c,a= 12.640(5), b = 13.945(9), c = 14.825(6) Å, β = 125.32(3)°, Z = 4, and R = 0.065 (F >5.4 σ(F)). Crystal 6 β is monoclinic, P21c,a = 16.391(16), b = 9.029(6), c = 19.835(19) Å, β = 116.60(6)°, Z = 4, and R = 0.070 (F > 4.6 σ(F)), while crystal 7α is also monoclinic, P21c,a = 9.513(5), b = 9.361(3), c = 30.908(13) Å, β = 98.42(3)°, Z = 4, and R = 0.057 (F >5 σ(F)). In the BF 4- salt (12), the four P-C distances are equal (1.791(5)-1.801(7) Å) with identical tetrahedral angles. For the two triphenylphosphoranylideneacetate compounds, the fourth P-C(1) bond is shorter (1.762(6)-1.734(5) Å) than the three P-C(Ph) bonds (avg. 1.809(5) Å). The angles C(1)-P-C(Ph) are also larger (avg. 112.9(2)° for 6β and 111.9(2)° for 7α) than the C(Ph)-P-C(Ph) angles (avg. 105.8(2)° for 6 β and 106.9(2)° for 7α). These values suggest a multiple nature for the P-C(1) bond. In the nitro derivative, the nitro and the ester groups are disordered equally in positions 2 and 6. Key words: Wittig reactions, cyclic anhydrides, stabilized ylide, phosphoranylidenes, crystal structures.
Reactivity of aminyl radicals in radical nucleophilic substitution reactions with diphenylphosphide anion
Authors: Foray Gabriela S , Peñéñory Alicia B , Rossi Roberto A
Published: April 2011

The photostimulated reactions of N-cyclopropyl-N-ethyl p-toluensulfonamide (4) with diphenylphosphide ions (2) in liquid ammonia gave 1,3-bis(diphenylphosphinyl)-1-(N-ethyl)propylamine, isolated as the oxide 5, and 1,3-bis(diphenylphosphinyl)-1-propanol, isolated as the oxide 6, all of them corresponding to the aperture of the cyclopropylaminyl radical intermediate. The reaction of 4 with 2 in excess and longer reaction times gave only 5 (73% yield). The photostimulated reactions of N-(n-butyl)-N-cyclobutyl p-toluensulfonamide (13) with 2 in liquid ammonia gave, after oxidation, N-(n-butyl)-N-cyclobutyl diphenylphosphonamide (14) in 94% yield. All these reactions occur by the radical nucleophilic substitution in which aminyl radicals are intermediates. The order of the magnitude of the rate constant for the coupling reaction of a dialkylaminyl radical with 2 could be intermediate between those of the rearrangements of the cyclopropyl and cyclobutylaminyl radicals.Key words: aminyl radicals, SRN1 reactions, radical clocks, photochemistry.
Partial leaching as an aid to slurry nebulization for the analysis of soils by ICP-MS with flow injection and mixed-gas plasmas
Authors: Persaud Anthony Treveidi , Beauchemin Diane , Jamieson Heather Edith , McLean Robert JC
Published: April 2011

Acid leaching (with 1 mol dm-3 HNO3) was combined with slurry nebulization in inductively coupled plasma mass spectrometry, with mixed-gas plasmas and flow injection, in an attempt to facilitate the quantitative analysis of heterogeneous materials such as soils. Matrices analyzed ranged from marine sediment to metal-contaminated soil, and were chosen for their variety in elemental composition and matrix structure. Slurries were prepared by first grinding the material to less than 3 μm in high-purity water and then diluting to 0.1% (w/v) with 1 mol dm-3 HNO3, which served as both a dispersing and a leaching agent. The resulting slurries were injected (0.25 cm3) into a deionized distilled water carrier. Under these conditions, the sensitivity was about 85% of that achieved by continuous nebulization. Multivariate optimization of the nitrogen percentage, forward torch power, and aerosol carrier gas flow rate was conducted to find conditions maintaining sensitivity constant between different slurries. Since no set of conditions was optimal for all elements, a compromise set was selected, which resulted in accurate results for La and Pb in a series of reference materials, by calibrating with aqueous standards. On the other hand, the results for V and Cr were almost systematically low, indicating that the compromise plasma conditions did not allow complete atomization/ionization of these elements.Key words: inductively coupled plasma mass spectrometry, slurry nebulization, flow injection, mixed-gas plasma.
Addition of the nitroxyl radical TEMPO to 1-naphthylketene: formation of an unusual adduct
Authors: Carter Jennifer , Fenwick Michael H , Huang Wen-wei , Popik Vladimir V , Tidwell Thomas T
Published: April 2011

1-Naphthylketene (2), generated by thermal Wolff-rearrangement, is trapped in situ by 2,2,6,6-tetramethylpiridinyloxy radical (TEMPO, TO·) to form the adduct 1-naphthCH(OT)CO2T (4), whose structure is confirmed by an X-ray determination. The 1H NMR spectrum of 4 displays three CH3 groups with very high field chemical shifts (δ 0.10-0.47), and this is attributed to the location of these groups in the shielding region above the π system of the naphthyl ring. At -40°C, doubling of most of the 1H NMR signals occurs, and this is attributed to a freezing out of two conformations differing by rotation around the naphthylCH bond.Key words: ketene, TEMPO, restricted rotation, 1H NMR, conformational analysis, free radicals.
13C, 15N, and 18O equilibrium isotope effects and fractionation factors1
Authors: Rishavy Mark A , Cleland W W
Published: April 2011

A listing of 13C, 15N, and 18O equilibrium isotope effects and fractionation factors for atoms in specific positions is provided. Empirical factors that can be used to adjust these fractionation factors for more complex structures are presented and discussed. While much work needs to be done to determine equilibrium isotope effects for these heavy atoms, the values tabulated here should be useful to anyone working with isotope effects involving these atoms.Key words: equilibrium isotope effects, fractionation factors, 13C, 15N, 18O.
Reactions of aminoboron compounds with palladium and platinum complexes
Authors: Vogels Christopher M , Wellwood Heather L , Biradha Kumar , Zaworotko Michael J , Westcott Stephen A
Published: April 2011

Reactions of 3-NH2C6H4B(OH)2 (1, APBA) with [MCl4]2- (M = Pd, Pt) give the boronic acid-containing complexes, MCl2(APBA)2 (M = Pd, 2; M = Pt, 3). Addition of 1 to [PdCl2(COE)]2 (COE = η2-C8H14) ultimately led to PdCl2(APBA)2 (2). The pinacol derivative PdCl2(APBpin)2 (5, pin = O2C2Me4) was characterized by an X-ray diffraction study. Crystals of 5 were monoclinic, a = 13.836(5), b = 14.937(5), c = 11.287(5) Å, β = 99.042(9)°, Z = 2, with space group P21/c. Monoalkene complexes PtCl2(COE)(APBA) (8) and PtCl2(COE)(APBpin) (9) were generated from the addition of APBA and APBpin, respectively, to [PtCl2(COE)]2. Reactions of 2-NMe2CH2C6H4B(OH)2 (10) with palladium complex [PdCl2(COE)]2 proceed via selective BC bond cleavage to give the cyclopalladated dimer [PdCl(2-NMe2CH2C6H4)]2 as the major amine-containing product. Likewise, reactions with borinic esters H2NCH2CH2OBR2 (R = Bu, 14; R = Ph, 15) give products derived from cleavage of the BO bond. The unique palladium complex PdCl2[3-NC5H4B(OH)2]2 (19) was prepared by addition of (3-NC5H4BEt2)4 (18) to [PdCl2(COE)]2 in wet methylene chloride, where adventitious water was used to convert the organoborane product into the corresponding boronic acid moiety.Key words: aminoboronic acids, platinum, palladium, cyclomηllation.
Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes
Authors: Leigh William J , Boukherroub Rabah , Bradaric Christine J , Cserti Christine C , Schmeisser Jennifer M
Published: April 2011

Direct photolysis of 1-phenylsilacyclobutane and 1-phenyl-, 1-(2-phenylethynyl)-, and 1-(4'-biphenylyl)-1-methylsilacyclobutane in hexane solution leads to the formation of ethylene and the corresponding 1-arylsilenes, which have been trapped by photolysis in the presence of methanol. Quantum yields for photolysis of the three methyl-substituted compounds have been determined to be 0.04, 0.26, and 0.29, respectively, using the photolysis of 1,1-diphenylsilacyclobutane Φsilene = 0.21) as the actinometer. The corresponding silenes have been detected by laser flash photolysis; they have lifetimes of several microseconds, exhibit UV absorption maxima ranging from 315 to 330 nm, and react with methanol with rate constants on the order of (2-5) × 109 M-1 s-1 in hexane. Absolute rate constants for reaction of 1-phenylsilene and 1-methyl-1-phenylsilene with water, methanol, tert-butanol, and acetic acid in acetonitrile solution have been determined, and are compared to those of 1,1-diphenylsilene under the same conditions. With the phenylethynyl- and biphenyl-substituted methylsilacyclobutanes, the triplet states can also be detected by laser flash photolysis, and are shown to not be involved in silene formation on the basis of triplet sensitization and (or) quenching experiments. Fluorescence emission spectra and singlet lifetimes have been determined for the three 1-aryl-1-methylsilacyclobutanes, 1,1-diphenylsilacyclobutane, and a series of acyclic arylmethylsilane model compounds. These data, along with the reaction quantum yields, allow estimates to be made of the rate constants for the excited singlet state reaction responsible for silene formation. 1-Methyl-1-phenylsilacyclobutane undergoes reaction from its lowest excited singlet state with a rate constant 10-80 times lower than those of the other three derivatives. The results are consistent with a stepwise mechanism for silene formation, involving a 1,4-biradicaloid intermediate that partitions between product and starting material.Key words: silene, silacyclobutane, photochemistry, biradical.
Apparent molar volume of some ω-amino acids in aqueous electrolyte systems
Authors: Kumar D
Published: April 2011

Apparent molar volumes (Vϕ) of some ω-amino acids have been determined in aqueous guanidine hydrochloride (6 m GuHCl) and sodium sulphate (2 m Na2SO4) solutions at 288.15 and 298.15 K using a vibrating tube digital densimeter. The transfer volumes of amino acids from water to aqueous electrolyte systems have been reported. The transfer properties are interpreted in terms of strong interactions, based on a cosphere overlap model of guanidine hydrochloride/sodium sulphate molecules with the charged centers of the zwitterions (amino acid molecules), as compared to ion - nonpolar group interactions.Key words: amino acids, denaturation, guanidine hydrochloride, sodium sulphate, apparent molar volume, zwitterions, limiting apparent molar volume.
1998 J.C. Polanyi Award Lecture Fullerene ions in the gas phase: chemistry as a function of charge state
Authors: Böhme Diethard K
Published: April 2011

Results of recent measurements in the Ion Chemistry Laboratory at York University using the Selected-Ion Flow Tube (SIFT) technique are surveyed for reactions of singly, doubly, and triply charged buckminsterfullerene C60n+ cations proceeding at room temperature in helium buffer gas at 0.35 Torr (1 Torr = 133.3 Pa). Measured rate coefficients and observed product channels for reactions with a variety of inorganic and organic molecules depend strongly on the charge state of the reactant ion. The measured rate coefficients span more than four orders of magnitude. Primary product channels observed include attachment, dissociative attachment, dissociative attachment with charge separation, single-electron transfer, dissociative single-electron transfer, and two-electron transfer. A qualitative description of the potential-energy profiles associated with these reaction channels is provided. The observed higher order chemistry of derivatized C60n+ cations and of atomic exohedral adduct ions is also described. This chemistry includes cation-transfer reactions, surface derivatization, and "ball-and-chain" polymerization. Finally, results are presented that provide insight into the influence of surface strain on the reactivities of fullerene ions.Key words: fullerenes, ions, electron transfer, charge separation, surface derivatization.
Controlled molecular design of ether- and ester-bridged norbornenes and their ring-opening metathesis polymerizations
Authors: Abd-El-Aziz Alaa S , Edel Andrea L , May Leslie J , Epp Karen M , Hutton Harold M
Published: April 2011

A series of functionalized polynorbornenes containing pendent ether- or ester-bridged poly(aromatic ether) chains were prepared. The ether-bridged norbornene complex was synthesized via cyclopentadienyliron-mediated nucleophilic aromatic substitution reactions. This methodology, combined with that of dicyclohexylcarbodiimide-mediated coupling, allowed for the formation of novel oligomeric aryl ether and ester substituted norbornene complexes. Photolytic demetallation gave the monomers in good yields. Structural identification of the exo and endo isomers of both the metallated and demetallated norbornene derivatives was accomplished using HH and CH COSY NMR techniques. Ring-opening metathesis polymerization (ROMP) of these monomers using RuCl3(hydrate) and (Cy3P)2Cl2Ru=CHPh allowed for the preparation of the functionalized polynorbornenes. Thermal analysis of the resulting polymeric materials demonstrated greater thermal stability as the number of aryl ether groups increased.Key words: aromatic ethers, cyclopentadienyliron, polynorbornene, ROMP, ruthenium catalysts.
Addition of cyclopentadiene derivatives on aromatic aldehydes or nitrosobenzene initiated by electrochemical reduction
Authors: Williot F , Bernard M , Lucas D , Mugnier Y , Lessard J
Published: April 2011

The electrochemical reduction of nitrosobenzene (PhNO) in the presence of cyclopentadiene derivatives containing the indenyl group represented as In'H2 (10a, 10b, and 12b) gives the imine derivatives PhN=In'. The process requires only a catalytic amount of electricity. When the electrolysis of aromatic aldehydes (ArCHO), 2,6-dichlorobenzaldehyde (1a), benzaldehyde (1b) and terephthalaldehyde (2), is performed in the presence of the In'H2 derivatives, compounds ArCH=In' are obtained in low yields. These compounds have been characterized by mass spectrometry and microanalysis. The overall process involves two consecutive chain reactions with regeneration of the anion In'H-.Key words: electrochemical reduction, nitrosobenzene, aromatic aldehydes, base catalysis, chain reaction.
Mn(OAc)3-promoted hydroxylation of α-carbomethoxy-γ-lactones by molecular oxygen
Authors: Lamarque Laurent , Méou Alain , Brun Pierre
Published: April 2011

The Mn(OAc)3-mediated hydroxylation of a series of α-carbomethoxy-γ-lactones by molecular oxygen is described. The reaction is regio- and stereoselective and gives α-carbomethoxy-α-hydroxy-γ-lactones. Key words: manganese acetate, γ-lactones, hydroxylation, molecular oxygen.
Ethylene-polymerization by surface supported Cr(IV) species: possible reaction mechanisms revisited by theoretical calculations
Authors: Schmid Rochus , Ziegler Tom
Published: April 2011

Possible reaction mechanisms of olefin polymerization catalyzed by surface supported Cr(IV) species have been investigated by first principles density functional theory (DFT). Pathways starting from neutral alkylidene or bisalkyl complexes were found to suffer from high ethylene insertion barriers, whereas a cationic system formed by protonation of the alkylidene show a low barrier for chain propagation.Key words: density functional theory, alkylidene, olefin polymerization, Cr(IV) species.
The one- and two-photon photochemistry of benzylsilacyclobutanes, acyclic benzylsilanes, and 1,1,2-triphenylsilacyclobutane
Authors: Leigh William J , Owens Thomas R
Published: April 2011

The photochemistry of several α-silylbenzyl compounds has been investigated in hexane and in methanol solution. Direct photolysis of 1-benzyl-1-methylsilacyclobutane (1) in methanolic hexane solution produces 1-propyl-1-methyl-2,3-benzosilacyclobutene (6) in quantitative yield, by a sequential two-photon process involving the photoactive isotoluene derivative 1-methylene-6-(1-methylsilacyclobutyl)-2,4-cyclohexadiene (13a), which has been identified on the basis of its 1H NMR and UV absorption spectra. In contrast, direct irradiation of 1-benzyl-1-phenylsilacyclobutane (2) under similar conditions results in the formation of a complex mixture of products consistent with the competing formation of 1-benzyl-1-phenylsilene and benzyl- and 1-phenylsilacyclobutyl radicals. The silene is a transient which has been detected directly by laser flash photolysis of 2 (λmax = 315 nm, τ ~ 4.5 µs). Free radical formation is shown to be due to secondary photolysis of a second primary product, 1-methylene-6-(1-phenylsilacyclobutyl)-2,4-cyclohexadiene (13b), which has also been detected and identified by static UV absorption (λmax = 335 nm) and 1H NMR spectroscopy. In a reaction with some analogy to the acid-catalyzed desilylation of allylsilanes, both 13a and 13b can be intercepted in neutral or acidic methanol solution to yield toluene and 1-methyl- or 1-phenyl-1-methoxysilacyclobutane, respectively. Direct photolysis of benzyldimethylphenylsilane (4) also leads to the formation of the corresponding isotoluene derivative, while benzyltrimethylsilane (3) exhibits negligible photoreactivity. The endocyclic benzylsilane 1,1,2-triphenylsilacyclobutane (5) is shown to undergo competing [2 + 2]-cycloreversion and [1,3]-silyl migration to yield a bicyclic isotoluene analogue, which reacts rapidly with methanol to yield the acyclic methoxysilane reported previously to be the main product of photolysis of this silacyclobutane in methanol solution. Relative quantum yields for isotoluene formation from photolysis of 1-4 and absolute rate constants for methanolysis of several of these compounds under neutral and acidic conditions have also been determined.Key words: photochemistry, organosilicon, benzylsilane, silacyclobutane, silene, kinetics, isotoluene.