bluuebunny/crossref_metadata_2025 huggingface dataset:
Two independent isotope effects and their magnetic field dependences in the photoreduction of menadione in deuterium labeled SDS micellar solutions. A spin trapping study
Authors: Okazaki Masaharu , Toriyama Kazumi , Nunome Keichi , Muto Hachizo , Shiga Takeshi
Published: May 2006

Spin adduct yields in the photoreduction of menadione (2-methylnaphthoquinone) in isotope labeled micellar solutions were measured as functions of the external magnetic field. As surfactants, ordinary SDS, perdeuteriated SDS, and a mixture of the two were employed. In a mixed micellar solution, a normal isotope effect on the spin adduct yield was observed. On the other hand, in the pure micellar solutions with each of the former two surfactants, a reversed isotope effect was observed. These two apparent isotope effects depend on the external magnetic field and were separated into two independent isotope effects: one is the primary isotope effect on the hydrogen abstraction step and the other is the secondary magnetic isotope effect on the intersystem crossing step of the intermediate radical pair.
High-resolution solid-state NMR investigation of the nature of the interaction between organic substrates and the zeolite ZSM-5 lattice
Authors: Fyfe C. A. , Strobl H. , Gies H. , Kokotailo G. T.
Published: May 2006

The compounds p-xylene, p-chlorotoluene, and p-dichlorobenzene induce essentially identical changes in the 29Si MAS NMR spectrum of zeolite ZSM-5, indicating that the major contribution to the induced phase change of the lattice structure in these cases is the size and shape of the sorbed organic molecules. Based on these results, p-dichlorobenzene may be used as a model system in future diffraction studies of the sorbate/lattice structure greatly facilitating these investigations.
Phase transitions in adamantane derivatives: 2-chloroadamantane
Authors: Paroli Ralph M. , Kawai Nancy T. , Butler Ian S. , Gilson Denis F. R.
Published: May 2006

The phase transition behaviour of 2-chloroadamantane, 2-C10H15Cl, has been investigated by differential scanning calorimetry (DSC), and FT-IR and Raman spectroscopy. Two transitions were detected by both DSC and vibrational spectroscopy at 231 and 178 K, on cooling, and at 242 and 227 K, on heating. The measured enthalpies were 8.3 kJ mol−1 for the first transition (phase I → phase II), and 0.47 kJ mol−1 for the second (phase II → phase III). The entropies were 35 and 2.3 J K−1 mol−1, respectively. These are similar to those observed for other 2-substituted adamantanes, but significantly different from those for 1-substituted derivatives. The large hystereses observed for the two transitions are independent of the DSC scanning rate and are characteristic of first-order phase transitions. The dramatic differences observed in the vibrational spectra of phases I and II provide clear evidence of an order–disorder transition at about 235 K.
LEED crystallographic studies for the chemisorption of oxygen on the (100) surface of copper
Authors: Zeng H. C. , McFarlane R. A. , Sodhi R. N. S. , Mitchell K. A. R.
Published: May 2006

Intensity analyses with low-energy electron diffraction (LEED) are reported for surface structures obtained by adsorbing submonolayer amounts of oxygen on the (100) surface of copper. It is found for chemisorption on the four-coordinate hollow sites that the correspondence between experimental and calculated intensity-versus-energy curves, for 10 diffracted beams, is slightly better for coplanar adsorption than for adsorption about 0.75 Å above the surface (the latter model is essentially as proposed previously by both SEXAFS and photoelectron diffraction). Nevertheless, in neither of these contrasting situations is the agreement sufficient to conclude that the structural analysis is complete. Evidence is presented that nearly coplanar chemisorption, in combination with a missing row model, can accommodate a number of structural features for this system, including the existence of the (2√2 × √2)45°−O phase, beam splittings resulting from antiphase domain boundaries, and the structural analogy noted in other studies between the (2√2 × √2)45°−O phase and the stepped nature of the (410) copper surface which can form by faceting in oxygen. Considerations of O–Cu surface bond lengths, guided by those in bulk Cu2O, suggest that additional lateral relaxations are likely in the topmost copper layer. This study provides no support for the O chemisorption occurring in tetrahedral-type sites.
Synthesis and characterization of (η5-C5Me5)W(NO)I2, a monomeric, formally 16-electron complex
Authors: Dryden Neil H. , Legzdins Peter , Einstein Frederick W. B. , Jones Richard H.
Published: May 2006

The compound (η5-C5Me5)W(NO)I2 has been prepared by treating (η5-C5Me5)W(NO)(CO)2 with I2. A single crystal X-ray crystallographic analysis establishes that the formally 16-electron complex possesses a monomeric, three-legged piano stool molecular structure in the solid state. Solution molecular weight measurements also indicate no significant degree of association of the compound.
Alkylation of tert-butyl lithiohydrazones of aldehydes and ketones
Authors: Wang Shao-Fang , Warkentin John
Published: May 2006

Treatment of the tert-butylhydrazones of formaldehyde, acetaldehyde, and acetone with butyllithium afforded the corresponding tert-butyl lithiohydrazones, which were alkylated with alkyl, allyl, and benzyl halides. Fourteen new tert-butylazo compounds were prepared in yields ranging from 38 to 86%.
Protium–deuterium exchange of styrenes in dilute acid at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

A modified high temperature – dilute acid method is used to synthesize phenylethene-2,2-d2 ("styrene-2,2-d2") (1b), 2-phenylpropene-1,1,3,3,3-d5 ("α-trideuteriomethylstyrene-2,2-d5") (2b), and E-1-phenylpropene-2-d ("trans-β-methylstyrene-2-d") (3b) from phenylethene ("styrene") (1a), 2-phenylpropene ("α-methylstyrene") (2a), and E-1-phenylpropene ("trans-β-methylstyrene") (3a), respectively. The deuteriated substitution product E-1,3-diphenyl-1-butene-2,4,4,4-d4 (4b) is also obtained from 1a. Labelled substitution products 1,3,3-tri-trideuteriomethyl-1-phenylindane-2,2-d11 (5b), 4-trideuteriomethyl-2,4-diphenyl-1-pentene-1,1,3,3,5,5,5-d10 (6b), and E-4-trideuteriomethyl-2,4-diphenyl-2-pentene-1,1,1,3,5,5,5-d10 (7b) are obtained from 2-phenylpropene.
Conversion of some azaheterocyclic-acetic esters and -acetonitriles into fused heterocycles
Authors: McKinnon David M. , Spevack Perry , Tipples Graham
Published: May 2006

Various heterocyclic acetic esters and nitriles of the pyridine, thiazole, and imidazole series react with 3-methylthio-4-phenyl-1,2-dithiolium perchlorate to form fused pyridinethiones or dithiolylidene esters. These esters or nitriles also react with trichloromethanesulfenyl chloride to form fused isothiazoles.
Formation constants of trivalent lanthanide metal ions and hydrazone β-diketones in 75% dioxane – water solvent
Authors: El-Shetary Basheir A. , Stefan Shaker L. , Abdel-Moez Mohamed S. , Mashaly Mahmoud M.
Published: May 2006

A new series of hydrazone β-diketone organic ligands were prepared: 3-(2-acetylphenylhydrazone)pentane-2,4-dione (2-APHA), 2-(2-acetylphenylhydrazone)-1-phenyl-1,3-butane dione (2-APHB), 2-(2-acetylphenylhydrazone)-1,3-diphenyl-1,3-propane dione (2-APHDB), 3-(2-acetylphenylhydrazone) 1,1,1-trifluoropentane-2,4-dione (2-APHTA) and 2-(2-acetyl-phenylhydrazone)-5,5-dimethyl-1,3-cyclohexane dione (2-APHDm). The step formation constants of their 1:1 and 1:2 rare-earth complexes were determined at 30 °C by pH titration in 75% (v/v) dioxane–water solvent. The ionization constant of ligands were also measured. A curious odd–even stability differential was apparent in the (2-APHDm) ligand with the heavier rare earths Gd–Lu. The differential was apparent in both log K1 and log β values and may be sufficient to cause reversal of the usual ion-exchange elution sequence.
Preparations, X-ray crystal structures, and spectral studies of seleninyl bis(trifluoromethanesulfonate) and seleninyl bis(acetate)
Authors: Kapoor Ramesh , Wadhawan Poonam , Kapoor Pratibha , Sawyer Jeffery F.
Published: May 2006

The compounds seleninyl bis(trifluoromethanesulphonate) (1) and seleninyl bis(acetate) (2) have been prepared and characterized by elemental analysis, ir and Raman spectroscopy, and X-ray crystallography. Crystals of 1 are monoclinic, space group P21/n with a = 12.735(1) Å, b = 5.163(4) Å, c = 16.133(2) Å, β = 96.426(8)°, U = 1054 Å3, Dx = 2.48 g cm−3 for Z = 4, R = 0.038 for 1745 observed reflections with I > 2.5σ(I). Those of 2 are orthorhombic, space group Pcab with a = 6,845(3) Å, b = 8.992(2) Å, c = 23.560(9) Å, U = 1450 Å3Dx = 1.95 g cm−3 for Z = 8, R = 0.074 for 1073 observed reflections with I > 3.0σ(I). The primary geometry of the Se atom in SeO(O3SCF3)2 is AX3E with a Se=O distance of 1.571(3) Å and Se—O bond lengths to the CF3SO3 ligands of 1.902(3) and 1.922(3) Å. Completing the overall coordination geometry of the Se atom are 2 intramolecular and 4 intermolecular Se … O contacts which are less than van der Waals limits. The overall coordination geometry is somewhat irregular since the two triflate anions are significantly differently arranged with respect to the SeO3E tetrahedron. The crystal packing consists of layers of interacting molecules. In 2 there is some disorder. However, the major arrangement of the molecule has Se=O and Se—O(1), Se—O(3) distances to the acetate ligands of lengths 1.575(9), 1.847(7), and 1.831(8) Å respectively. The overall geometry of the Se atom in this compound is completed by two intramolecular secondary Se … O contacts involving the second O atoms of both acetates and two intermolecular contacts involving the seleninyl oxygen atom and atom O(2) of an acetate group in two different symmetry related molecules. Overall, the crystal packing consists of essentially centrosymmetric dimeric units linked together through Se=O—Se bridges. A 1:2 adduct of 1 with pyridine has also been prepared and characterised.
The first 1H and 14N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones
Authors: Haire D. Larry , Oehler Uwe M. , Goldman H. Duane , Dudley Robert L. , Janzen Edward G.
Published: May 2006

We report the first 1H and 14N electron nuclear double resonance (ENDOR) spectra of oxygen-centered radical adducts (i.e., derived from the addition of tert-butoxyl radicals) of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as well as the related cyclic nitrones: 4-phenyl-5,5-dimethyl-1-pyrroline-N-oxide (4-Ph-DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO). Features of the electron paramagnetic resonance (EPR) and ENDOR spectra of these cyclic (pyrrolidine) aminoxyl (nitroxide) species along with some deuterated analogues in liquid toluene solutions are highlighted. For instance, we found several long-range γ-H hyperfine splittings (HFS's) detectable by ENDOR that provide unique spectral signatures for these radical adducts. Conformational assignments of the pyrrolidine aminoxyl structures based upon the EPR and ENDOR findings are also discussed. Signs of the various hyperfine splittings (i.e., aN, [Formula: see text]) investigated by cross-relaxation intensity sequence patterns (CRISP) in the ENDOR spectra are also presented.
Methylmercury(II) complexes with tryptophan and its N-acetyl derivative
Authors: Corbeil Marie-Claude , Beauchamp André L.
Published: May 2006

CH3HgOH reacts with tryptophan in aqueous ethanol to form a 2:1 neutral complex in which CH3Hg groups are bound to the terminal amino group and to the deprotonated indole nitrogen. When this complex is dissolved in water, 1H and 13C nuclear magnetic resonance show that the indole CH3Hg group hydrolyzes, leading to an amino-bound 1:1 species. Under the same conditions, N-acetyltryptophan forms a neutral 1:1 compound where the metal is bound to a carboxylate oxygen, and a neutral 2:1 complex in which an extra CH3Hg group is fixed to the deprotonated indole ring. It is shown by 1H and 13C nuclear magnetic resonance that the 1:1 species is stable in DMSO-d6, but that the 2:1 compound is readily hydrolyzed to the 1:1 compound by traces of water. The solid-state infrared and Raman spectra are discussed. In the crystal structure of the 2:1 tryptophan complex, the ligand adopts a conformation favoring a short intramolecular π interaction between Hg and the indole ring. No such π interaction is found in the crystal structure of the 1:1 carboxylate-bonded complex with acetyltryptophan.
Arylation of cyclic ethers by gaseous phenylium ions. Formation and behavior of phenoxenium ions in the gas phase
Authors: Fornarini Simonetta , Speranza Maurizio
Published: May 2006

Free, unsolvated phenylium ions formed by the spontaneous decay of 1,4-ditritiobenzene have been allowed to react with gaseous cyclic ethers (oxirane, propene oxide, and oxetane) and acetaldehyde in the pressure range 30–250 Torr and in the presence of a thermal radical scavenger (O2, 4 Torr). The effects of a gaseous base (NMe3, 20 Torr) and of an energy moderator (He, 630–720 Torr) were also investigated. Phenylium ion confirms its considerable site selectivity, demonstrated by the distinct preference for the n-type center of the substrate, although appreciable insertion into the carbocyclic structure of propene oxide and oxetane is observed as well. The stability features of the ionic intermediates from addition of phenylium ion to selected substrates have been evaluated as well as their fragmentation and isomerization mechanisms. The behavior of gaseous phenylium ion toward cyclic ethers, in particular its ability to formally abstract an oxygen atom from the ether to give the phenoxenium ion, a reaction first observed in the present study, is discussed and compared with previous mechanistic investigations carried out in the gas phase and in solution.
Studies on the kinetics of racemization of 2,4-disubstituted-5(4H)-oxazolones
Authors: Slebioda Marek , St-Amand Marc A. , Chen Francis M. F. , Benoiton N. Leo
Published: May 2006

The kinetics of racemization of 2,4-disubstituted-5(4H)-oxazolones obtained from N-acetyl, N-benzoyl, and N-benzyloxycarbonylglycyl-L-leucine, -valine, and -phenylalanine have been studied in several solvents alone and in the presence of tertiary amines. The influence of the nature of the substituents on the rate of the reaction has been evaluated, and the values of the activation parameters ΔH≠ and ΔS≠ for the base-catalyzed reactions have been determined. The racemization process is governed by electronic effects of the C(2)-substituents and steric effects of the C(4)-substituents of the oxazolones. The thermodynamic data suggest that the 2-substituted-4-benzyl-5(4H)-oxazolones racemize more readily than the 4-alkyl analogues (alkyl ≠ benzyl) because of the unique conformation assumed by the benzyl substituent. The rate of the base-catalyzed reaction depends on the extent of hindrance about the nitrogen atom of the tertiary amine as well as on its basicity. The data suggest that the relative rates of racemization of oxazolones are not a true reflection of the relative tendencies to racemize of the pertinent residues during couplings of the parent acids.
The effect of substitution on the conformation in para-substituted ethylene glycol dibenzoate molecules
Authors: Deguire Suzanne , Brisse François
Published: May 2006

The series of ethylene glycol di-para-X-benzoates, where X = Me, OMe, CN, and NO2, has been studied by infrared spectroscopy and solid state CP/MAS 13C nuclear magnetic resonance. The crystal structures were established for X = Me and OMe. Bond distances, bond angles, and torsion angles were compared to those of related molecules (X = H, Ph, Cl). It was found that the conformation of the CO—O—CH2—CH2—O—CO sequence is either trans-trans-trans or trans-gauche-trans. (trans = t, gauche = g). The CH2—CH2 bond distance ranging from 1.471(2) to 1.499(3) Å is always very short. The O—CH2—CH2 bond angle is around 105° for the ttt conformation and 107° for the tgt conformation. It was confirmed that the infrared frequencies for the CH2 bending, CH2 wagging, C–C stretching, and CH2 rocking modes are observed at 1470–1485, 1335–1340, 975–980, 845–855 cm−1 and at 1460, 1370–1375, 1040, 895–900 cm−1 for the ttt and tgt conformations respectively. The substitution effect on the nmr chemical shifts, both in solution and the solid state, can be rationalized in terms of induction and resonance contributions. On the basis of the ir and nmr spectra, it is proposed that for both the p-NO2 and p-CN substituted molecules, for which no crystal structure has been established, the conformation of the methylenic sequence is trans-trans-trans.
Interlayer ammine complexes of metal uranyl phosphates
Authors: Pozas-Tormo Rafaela , Gamez Sebastián Bruque , Martinez-Lara María , Moreno-Real Laureano
Published: May 2006

The solids derived from HUP by substituting metallic ions for protons, take up Lewis base molecules (like NH3 and C4H9NH2) in the interlamellar space. The diffractograms of these inclusion compounds indicate that the host crystallinity was preserved.The infrared spectroscopy of the Ni, Co, Cu, Zn, and Cd intercalates revealed that part of the sorbate was protonated in the interlaminar space while the other part displaced the water in their coordination spheres. However, in the Mn derivative, no coordinated or free Lewis base could be detected: it was all in the protonated form.
Fragmentation of alkoxide ions following collisional activation. An energy-resolved study
Authors: Mercer Roger S. , Harrison Alex G.
Published: May 2006

The collisionally activated dissociation reactions of the C2 to C5 alkoxide ions have been studied for collisons occurring at 8 keV kinetic energy and also over the range 5 to 100 eV kinetic energy. The alkoxide ions fragment by 1,2-elimination of H2 and/or an alkane. Thus, primary alkoxide ions fragment by elimination of H2 only, secondary alkoxide ions show elimination of H2 and alkane molecules, while tertiary alkoxide ions show elimination of alkanes only. In alkane elimination, loss of CH4 is much more facilie than loss of larger alkanes. For secondary alkoxide ions, where more than one elimination reaction occurs, the energy dependence of fragmentation has been explored over the collision energy range 5 to 100 eV. The results are interpreted in terms of a step-wise mechanism involving formation of an anion-carbonyl compound ion-dipole complex, followed by proton abstraction by the H− or alkyl anion leading to the final products. The relative importance of the reaction channels is determined by the relative stabilities of these ion-dipole complexes.
The correspondence between Hückel theory and ab initio atomic charges in allyl ions
Authors: Slee Tom S. , MacDougall Preston J.
Published: May 2006

Atomic charges for the allyl cation and anion are reported, as defined by the quantum theory of atoms in molecules. An interesting feature of these charges is that they differ considerably from expectations based on simple π orbital models. The reasons for the difference are investigated and it is shown that the charges are both compatible with and understandable in terms of simple orbital models.
Solvent effect on the solution, ionization, and structure of aminosulfonic acids
Authors: Benoit Robert L. , Boulet Danielle , Fréchette Monique
Published: May 2006

We have determined thermodynamic parameters for the solution and ionization in dimethylsulfoxide and water of four aminosulfonic acids: NH2(CH2)nSO3H with n = 0,1, and 2, and NH2C6H4SO3H. Potentiometric and calorimetric methods were used. The solubilities of the four acids in Me2SO are either nearly equal to or lower than in water, but the enthalpies of solution are 15–40 kJ mol−1 more exothermic in Me2SO. The three aliphatic acids are much weaker (2.1 ≤ ΔpKa ≤ 5.5) in Me2SO than in water and their heats of ionization are some 30 kJ mol−1 more endothermic in Me2SO. The discussion of our results is based on comparisons with corresponding data for related substituted amines and ammonium ions, and sulfonic acids and sulfonate ions. We conclude that the four aminosulfonic acids are mostly present as zwitterions in Me2SO just as in water.
Experimental and theoretical investigation of C-nitroso rotation in 2-nitrosoimidazoles
Authors: Bolton Judy L. , Peterson Michael R. , Mcclelland Robert A.
Published: May 2006

1-Methyl-2-nitrosoimidazole exhibits broadened 1H nuclear magnetic resonance signals at room temperature. The concentration independency of this spectrum as well as the linearity of the 700-nm absorbance with concentration rules out equilibrating nitroso monomer – nitroso dimer. It is suggested that there are equilibrating s-cis and s-trans nitroso monomer rotational isomers. At −59 °C two sets of signals in a 3:1 ratio are observed. Analysis of CH3 chemical shifts in terms of the magnetic anisotropy of the nitroso group suggests that the s-trans is the major isomer. The broadening observed at higher temperatures leads to a barrier for rotation (from the trans isomer) of 12.4 kcal mol−1. Ab initio calculations with 2-nitrosoimidazole using the 3-21G basis set show that the fully planar s-cis and s-trans forms are minima, with the s-trans more stable by 2.5 kcal mol−1, and a barrier to rotation (from the s-trans) of 13.0 kcal mol−1. These results are in good agreement with those from solution phase. Various factors suggest that the π conjugative interaction between the nitroso group and imidazole ring is relatively unimportant.
Sulfonyl esters 1: The reduction of tribromophenyl sulfonates with mercaptide anions
Authors: Durkin Kathleen Anne , Langler Richard Francis , Morrison Nancy Ann
Published: May 2006

2,4,6-Tribromophenyl sulfonates have been shown to undergo unusually efficient reduction by mercaptide anions in hexamethylphosphoramide. The reduction products include the sulfinate anion derived from the sulfonate ester and the disulfide derived from the mercaptide anions.
Correlation of 31P nuclear magnetic resonance chemical shifts in aryl phosphinates with Hammett substituent constants: Inductive versus resonance interactions and relevance to pπ–dπ bonding
Authors: Dunn E. J. , Purdon J. G. , Bannard R. A. B. , Albright K. , Buncel E.
Published: May 2006

Substituent-induced chemical shifts and coupling constants in the 31P, 13C, and 1H nuclear magnetic resonance spectra of meta- and para-substituted phenyl dimethylphosphinates (1), methylphenylphosphinates (2), and diphenylphosphinates (3) have been determined in CDCl3 solvent. For all three series, a correlation of δ 31P with Hammett–Taft σ0 (or σ) constants is preferred over σ− on the basis of the correlation coefficient and standard deviations of the slope and intercept values. Electron-withdrawing substituents induce downfield shifts in δ 31P, in contrast to the inverse trends observed for structurally related series of oxyphosphorus acids and their derivatives. It is proposed that electron-withdrawing substituents act to deplete the electron density on the aryl oxygen, thereby weakening a pπ–dπ bonding interaction between the aryl oxygen and phosphorus. The resultants loss of d-orbital density on phosphorus causes a downfield shift in δ 31P in each of the phosphinate series. Phenyl substituents attached directly to phosphorus in series 2 and 3 increase the phosphoryl pπ–dπ back-bonding interactions, either through inductive or resonance effects, which leads to shielding of the phosphorus atom, overriding the anticipated downfield shift through inductive electron withdrawal of the phenyl substituents in series 2 and 3, relative to the methyls in series 1. Trends in Hammett ρ values for the plots of δ 31P and δ 13C versus σ0 and differences in the shielding of 13C and 1H nuclei of the methyl attached to phosphorus in series 1 and 2 suggest that the phenyl groups may interact in π bonding with the phosphorus atom through a resonance interaction.
Diels–Alder reactions of 2-carbomethoxy-2-cyclohexen-1-one
Authors: Liu Hsing-Jang , Ngooi Teng Ko , Browne Eric N. C.
Published: May 2006

Under stannic chloride catalysis, 2-carbomethoxy-2-cyclohexen-1-one (5) was found to undergo Diels–Alder reaction with a variety of dienes to give directly the cis-1-octalone system possessing a functionalized substituent at the angular position. With unsymmetrically substituted dienes, the adducts were those predicted on the basis of the normal rules (ortho and para) governing the orientation of Diels–Alder addition. In cases where differing secondary orbital overlap would affect the stereochemistry of the adducts, the major isomer in each case was that produced by secondary overlap of the diene with the ester carbonyl rather than the ketone carbonyl, presumably due in part to a steric effect. The degree of stereoselectivity was further shown to be dependent upon both the reaction temperature and the diene used and was generally enhanced when the reaction was carried out at lower temperatures or when a bulkier diene was involved.
Investigation of stereoelectronic bond–antibond orbital interactions in 3-halogenated-1-benzoxepins
Authors: Dionne P. , St-Jacques M.
Published: May 2006

The conformational properties of the 3-halogenated-1-benzoxepins (compounds 6–9) have been studied by 1H and 13C dynamic nuclear magnetic resonance. The results show that for the heavier halogen derivatives (Cl, Br, and I), only two chair forms (Ca and Ce) are observed while for the F substituent, three forms (Ca, Ce, and TB) are detected. This is in contrast with the 3-halogenated-1,5-benzodioxepins (2–5), which were shown to exist as a mixture of three forms for the heavier halogens (Cl, Br, and I) and, show only two forms (Ca and TB) for the F substituent. The results for these two systems characterize the conformational effects produced by one and two O—C—C—X vicinal interactions between polar bonds, which shed light on the nature of the intramolecular stereoelectronic σ–σ* orbital interactions operative in both families of molecules. Keywords: 3-halogenated-1-benzoxepins, conformational properties, nuclear magnetic resonance, stereoelectronic orbital interactions
Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels–Alder reactions with dimethyl acetylenedicarboxylate
Authors: Yates Peter , Gomes Anabela , Burnell D. Jean , Cong Dong Dao , Sawyer Jeffery F.
Published: May 2006

6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that the endo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed. Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.
The direct electrochemical synthesis of phenylselenolato complexes of some main group and late transition elements
Authors: Kumar Rajesh , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of anodes of selected Main Group or late transition metals (M) in non-aqueous solutions of diphenyl diselenide gives the corresponding M(SePh)n compounds in high yields (M = Zn, Cd, n = 2; M = Cu, Ag, Tl, n = 1; M = Sn, n = 4). The addition of either 1,10-phenanthroline or triphenylphosphine to the electrochemical cell yields adducts in the case of cadmium and copper. The 77Se nmr spectra have been recorded. Keywords: electrochemistry, synthesis, phenylselenates, 77Se nmr spectra.
Electron affinities and Marcus reorganization energies. A correlation between gas phase electron affinities and solution phase redox potentials
Authors: Tanner Dennis D. , Deonarian Natasha , Kharrat Abdelmajid
Published: May 2006

Redox potentials determined by cyclic voltammetry were used in conjunction with published electron affinities to determine the solvation energies for series of three classes of compounds: substituted benzoquinones, substituted nitrobenzenes, and polynuclear aromatic hydrocarbons. Excellent linear correlations were obtained between the measured electron affinities and the E0 of the substrates. The calculated electron affinities, EA (E0), were computed using the average solvation energies for the three classes of compounds, and were found to be in excellent agreement with the measured values. The nitrobenzenes and quinones had one solvation energy, while the aromatic hydrocarbons were correlated with a significantly different value. The solvation energy of a variety of compounds could also be related to their Marcus reorganization energiesλ(0), by a linear plot with a high correlation coefficient. From simple electrochemical measurements of similar compounds, either electron affinities or Marcus λ(0) values can be estimated. Keywords: electron affinities, Marcus reorganization energies, cyclic voltammetry.
Microbial hydroxylation of steroids. Part 12. Hydroxylation of testosterone and related steroids by Gnomoniafructicola ATCC 11430
Authors: Holland Herbert L. , Brown Frances M. , Chenchaiah P. Chinna , Chernishenko Michael J. , Khan Shaheer H. , Rao J. Appa
Published: May 2006

The fungus Gnomoniafructicola ATCC 11430 hydroxylates testosterone at C-2β in 40–60% yield. The enzyme involved has been shown to be an inducible CO sensitive, cyanide insensitive oxygenase, with a requirement for theΔ4-3-ketosteroid substrate functionality. The use of 2α- and 2β-deuterium labelled substrates has shown that hydrogen loss from C-2 during 2β hydroxylation is isotope dependent and non-stereospecific. This is interpreted in terms of a Δ2,4-dienolic enzyme-bound intermediate form of the substrate. Keywords: Gnomoniafructicola, hydroxylation, steroids, testosterone.
Dielectric polarization and molecular interaction. Part II. Acetylacetone, benzoylacetone, and dibenzoylmethane – triethyl amine – cyclohexane systems
Authors: Saad Gamal R. , Naoum Magdi M. , Rizk Hanna A.
Published: May 2006

A modified form of Few and Smith equation applicable to dilute solutions of acetylacetone, benzoylacetone, and dibenzoylmethane in constant-ratio mixtures of triethylamine in cyclohexane is confirmed. The changes in dielectric polarization of diketones with amine concentration in the mixed solvents are used to deduce the equilibrium constants of the association process, and the dipole moments of the complexes formed. Further, an inference is made of the relative polarities of the keto and enol tautomers of these diketones, and of the ketoanilides previously investigated (1). Keywords: dielectric polarization, molecular interaction, β-diketones, triethylamine.
Protected porous polymers
Authors: Wu Cai-Ying , Aue Walter A.
Published: May 2006

This study was designed to answer the question whether the chromatographic performance of porous polymers — serving here as a model system for pressure-sensitive separation media of relatively large mass transfer resistance — could be improved (a) by imposing on them a chromatographically favorable, extrinsic macrostructure and (b) by protecting that macrostructure against physical deformation. Packed-column gas chromatography was used as the test system.Protected porous polymers (PPP's) were synthesized from pure divinylbenzene (DVB) inside conventional diatomaceous supports, using various amounts and types of porogens. The non-extractable polymer loads ranged from 10 to 40% and conformed to (i.e. formed layers on) the diatomaceous macrostructures. The best plate numbers were in excess of 4000/m on a 100/120 mesh Chromosorb W base. The mass transfer resistance of these materials was very low and permitted high flow rates. The PPP's could be used up to 280 °C and did not appear to suffer deformation; in fact, the polymer appeared to shield the diatom supports from abrasion. The data indicate that the porous polymer deposits had relatively high specific surface areas, and produced a relatively large value for the free energy of sorption per methylene group, as compared with conventional porous polymer beads. Otherwise, protected and unprotected types of porous polymers had similar chromatographic characteristics. Keywords: porous polymer, poly(divinylbenzene), gas chromatography, protected polymer, diatoms.
Rate and equilibrium studies of the deprotonation of benzylic ketones bearing pyridinium cations
Authors: Bunting John W. , Stefanidis Dimitrios
Published: May 2006

Rates and equilibria for the deprotonation of four benzylic ketones containing pyridinium substituents (1, 2, 5, and 6) have been investigated in basic aqueous solution (ionic strength 0.1) over the range 15–45 °C, and thermodynamic and activation parameters have been evaluated. Similar data are also reported for the deprotonation of nitroethane. The kinetic preference for hydroxide ion addition to the carbonyl group in competition with the thermodynamically preferred enolate ion formation, which was previously reported for the 1-methyl-4-phenylacetylpyridinium cation (1) and its 3-phenylacetyl isomer (2), is also found for the 1-(1-methyl-2-oxo-2-phenylethyl)pyridinium cation (6). Rates of equilibration of the 1-(2-oxo-2-phenylethyl)-pyridinium cation (5) with its enolate ion conjugate base are too rapid to allow investigation by stopped-flow spectrophotometry. For the hydroxide ion catalyzed deprotonation of each of 1, 2, 6, and nitroethane, [Formula: see text] is more negative than ΔS0. This difference, which represents the entropy of activation for protonation of the conjugate base of each of these carbon acids by water, is approximately constant at [Formula: see text] = −4.9 ± 0.5 cal deg−1 mol−1. Keywords: carbon acids, kinetic studies, deprotonation, activation parameters, pKa values.
Pressure-dependent study of ultrasonic velocity of benzene + nitrobenzene system at 293.15, 303.15, and 313.15 K
Authors: Pandey J. D. , Rai R. D. , Shukla R. K.
Published: May 2006

Various statistical and empirical theories of ultrasonic velocity have been applied to a binary liquid mixture (benzene + nitrobenzene) at elevated pressures and their validity have been tested. A pressure-dependent study of ultrasonic velocities has been made at three different temperatures (293.15, 303.15, and 313.15 K). The agreement between the theory and experiment is found to be satisfactory. Keywords: ultrasonic velocity, benzene + nitrobenzene, pressure dependent, theoretical evaluation, binary mixtures at elevated pressures.
Phosphorus-31 solid-state nuclear magnetic resonance study of monophosphazenes
Authors: Power William P. , Wasylishen Roderick E. , Curtis Ronald D.
Published: May 2006

Simultaneous observation of anisotropic chemical shielding and dipolar coupling in polycrystalline monophosphazenes has been used to obtain information on the 31P–14N spin pair. Phosphorus-31 chemical shielding tensor components have been determined; the most shielded component was found to lie along the P=N bond. The 31P–14N dipolar coupling constants have provided P=N bond lengths from powder samples, equivalent for all compounds within experimental error; the value obtained for N–(triphenylphosphoranylidene)-aniline is in excellent agreement with that obtained in a recent X-ray diffraction study. Features of crystallographic significance have been determined from the solid-state nuclear magnetic resonance spectra for two of the compounds without resorting to diffraction techniques. Information on the magnitude and orientation of the 14N electric field gradient tensor has been inferred from 31P MAS spectra and abinitio calculations. Keywords: monophosphazenes, dipolar nmr, 31P chemical shielding anisotropies, solid-state nmr.
Block synthesis of two pentasaccharide determinants of the Brucella M antigen using thioglycoside methodologies
Authors: Peters Thomas , Bundle David R.
Published: May 2006

Two frame shifted pentasaccharides containing 4,6-dideoxy-4-formamido-D-mannose (4-deoxy-4-formamido-D-rhamnose) have been synthesized by application of a strategy utilizing S-ethyl disaccharide glycoside building blocks 16 and 25. The target molecules contain a single α1,3 linkage as either the first or last inter-residue linkage in an otherwise α1,2-linked homo-pentameric structure:[Formula: see text]and[Formula: see text]These structures represent possible biological repeating units of the Brucella M antigen and their synthesis is designed to facilitate the identification of the structural element that is polymerized to provide the intact polysaccharide antigen. The α1,2-linked tetrasaccharide component of each pentasaccharide was constructed by methyl triflate promoted activation of the α1,2-linked S-ethyl disaccharide glycoside 16. Glycosylation of methyl 4-azido-2-O-benzyl-4,6-dideoxy-α-D-mannopyranoside 3 by 16, followed by a second block extension, gave the pentasaccharide 22 with an α1,3 linkage at the reducing terminus. In analogous fashion the α1,3-linked S-ethyl derivative 25 was used in conjunction with methyl triflate to glycosylate the α1,2-linked trisaccharide 26, and provided the pentasaccharide 27 that possesses a 1,3 linkage at its non-reducing end. The synthesis of an α1,3-linked disaccharide and a trisaccharide are also reported. Keywords: Brucella M antigen, synthesis of frame shifted pentasaccharides, thioglycoside building units, 4,6-dideoxy-4-formamido-D-mannose, biological repeating unit.
The use of perchlorato(tetraphenylporphinato)manganese(III) as a reagent for the spectrophotometric determination of anions in nonaqueous solvents
Authors: Hinman A. Scott , McGarty Karen , Tang Clement , Pavelich. Brad J.
Published: May 2006

Perchlorato(tetraphenylporphinato)manganese(III) (TPPMnClO4) is shown to be a useful reagent for the determination of a variety of anions in nonaqueous media. The analysis is based on the displacement of coordinated perchlorate by more strongly coordinating anions as monitored spectrophotometrically. The procedure is demonstrated for the determination of tetra-alkylammonium salts of nitrate, nitrite, chloride, bromide, iodide, acetate, trifluoroacetate, cyanate, and thiocyanate in acetonitrile. Relative precisions and accuracies of the order of five parts per thousand are indicated. Keywords: perchlorato(tetraphenylporphinato)manganese(III), specrophotometric determination of anions, anions in nonaqueous media.
Gas phase acidities of aliphatic carboxylic acids, based on measurements of proton transfer equilibria
Authors: Caldwell Gary , Renneboog Richard , Kebarle Paul
Published: May 2006

Measurements of the gas phase proton transfer equilibrium [1]: AH + B− = A− + BH with a pulsed electron high pressure mass spectrometer (PHPMS) lead to [Formula: see text] and [Formula: see text] data. These relative acidities are converted to the absolute acidities [2]: AH = A− + H+bycalibration of the relative [Formula: see text] and [Formula: see text] scale to the known values for [Formula: see text] and [Formula: see text] of a reference compound(HCl). Earlier determinations that included 16 aliphatic AH are extended in the present work and provide data for 47 aliphatic carboxylic acids. These include halogen, OH, CH3O, C2H5O, PhO, and NH2 substituted acetic acids, and halogen substituted, unsaturated, and cyclic RCO2H of higher carbon number. The effects of the various substituents on the gas phase acidity are briefly examined. Keywords: acidities in gas phase, proton transfer equilibria, ion-molecule equilibria, mass spectrometry.
Excess molar volumes, speeds of sound, and isentropic compressibilities of binary mixtures of furfural with some aliphatic alcohols
Authors: Naorem Homendra , Kishore Nand , Suri S. K.
Published: May 2006

Excess molar volumes and isentropic compressibilities for the binary mixtures of furfural with methanol, ethanol, 1 -propanol, 2-propanol, 1-butanol, and 2-butanol have been computed from the experimentally measured densities and sound speeds at 308.15 K over the entire composition range. All the systems studied exhibit contraction on mixing. The results have been discussed in terms of the specific interactions between the component molecules of the binary mixtures. Keywords: excess molar volumes, isentropic compressibilities, furfural, aliphatic alcohols, unlike reactions.
Sulfonation reactions of (β-carbolines
Authors: Guzmàn M. C. Carmona , Almeida M. Balôn , Toledo J. Hidalgo , Perez M. A. Munoz , Poveda M. Lopez
Published: May 2006

The homogeneous sulfonations of (β-carboline derivatives norharmane 2, harmane 3, harmine 4, harmol 5, -N,N′-dimethyl-harmane 6, and harmaline 7 have been studied in 80–90% w/w sulfuric acid solutions at 25 °C. Ultraviolet–visible and 13C nuclear magnetic resonance spectra and chemical analysis of the reaction mixtures show that for all the substrates studied only C-6 sulfonated products are obtained. The sulfonation reactions of the benzene unsubstituted substrates 2, 3, and 6 and the partially aromatic substrate 7 proceed by direct electrophilic attack of the H3SO4+ cation on the benzene ring of the (β-carboline skeleton. Sulfonation of 4 and 5 at the lower sulfuric acid concentrations is effected by the H3SO4+ entity. With increasing sulfuric acid concentration there is a gradual changeover of the sulfonating entity from H3SO4+ to H2S2O7. The different mechanisms of sulfonation are discussed. Keywords: β-carbolines, sulfonation, kinetics.
Solubility of nonpolar gases in 2-methylcyclohexanone between 273.15 and 303.15 K at 101.32 kPa partial pressure of gas
Authors: Gallardo Maria Asuncion , Lopez Maria del Carmen , Urieta Jose Santiago , Losa Celso Gutierrez
Published: May 2006

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H2, D2, N2, CH4, C2H4, C2H6, CF4, SF6, and CO2) in 2-methylcyclohexanone at 273.15–303.15 K and a partial pressure of gas of 101.32 kPa are reported. Thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the solution process at 298.15 K and 101.32 kPa partial pressure of gas are evaluated. Use is made of the Scaled Particle Theory applied to gas solubility for determining Lennard-Jones (6, 12) pair-potential parameters and temperature dependence of the effective hard-sphere diameter of the solvent. The values that this theory predicts for the solution thermodynamic functions are also calculated. Keywords: 2-methylcyclohexanone, gas solubility, thermodynamic functions of solution, Henry coefficient, scaled particle theory.
Antiferromagnetic exchange in manganese(II) monophenylphosphinate and the effects of cadmium doping
Authors: Du Jlng-Long , Thompson Robert C.
Published: May 2006

Mn[H(C6H5)PO2]2, its cadmium analogue, and mixed metal materials of composition Mn1−xCdx[H(C6H5)PO2]2 (x = 0.005, 0.01, 0.09, 0.27, and 0.47) have been synthesized and characterized by X-ray powder diffraction, infrared spectroscopy, differential scanning calorimetry and low-temperature (4.2 to 80 K) magnetic susceptibility studies. The materials are shown to be isomorphous and are considered to have polymeric structures in which chains of metal atoms are linked by bridging phosphinate groups. The pure manganese compound is antiferromagnetic (maximum in xm at ~35 K) and the magnetic data for the compound have been analyzed according to two theoretical models for linear chains of antiferromagnetically coupled manganese(II) (d5, spin-free) ions. The Wagner and Friedberg model gives J = −3.00 cm−1 and the Weng model gives J = −2.78 cm−1. The effects of replacing Mn2+ by Cd2+ ions in the polymer is to increase the magnetic susceptibility (per mol of Mn) at all temperatures. Analysis of the data as a function of Cd doping indicates the incorporation of a paramagnetic component to the susceptibility which increases with increasing Cd content. In addition, the absolute value of the exchange coupling constant appears to decrease as the Cd content increases. These effects are considered in terms of a random defect model in which the replacement of Mn ions in the polymer by Cd ions results in the formation of Cd ion separated finite magnetic chain fragments. Keywords: manganese(II) monophenylphosphinate, magnetic properties, coordination polymer, cadmium doped antiferromagnet.
Preparation of and addition of carbanions to 6-methyl-6-nitrocyclohexa-2,4-dienones
Authors: Fischer Alfred , Henderson George N. , Sankararaman S.
Published: May 2006

Nitration of 2-methylphenols with nitric acid and trifluoroacetic anhydride in ether at −78 °C gives 6-methyl-6-nitrocyclo-hexa-2,4-dienones that can be isolated. Carbanions add to 5,6-dimethyl-6-nitrocyclohexa-2,4-dienone to give the 5-substituted 2,3-dimethyl-2-nitrocyclohex-3-enone anion, which, with additional carbanion, gives the 5-substituted 2,3-dimethylphenoxide anion by elimination of nitrous acid. Keywords: nitration, dienone, addition, carbanion, nucleophilic.
Synthesis and reaction of ortho-fluoronitroaryl nitroxides. Novel versatile synthons and reagents for spin-labelling studies
Authors: Hankovszky H. Olga , Hideg Kálmán , Lovas M. Judit , Jerkovich Gyula , Rockenbauer Antal , Györ Miklós , Sohár Pál
Published: May 2006

2-Flurophenyl- and 2,5-bis(fluorophenyl)pyrrolidin-1-oxyls (2 and 6) were synthesized from the corresponding nitrones 1,4, and 5 with the Grignard reagent prepared from 1-bromo-4-fluorobenzene. The reaction of 2,2,5,5-tetramethyl-3-formyl-3-pyrrolin-1-oxyl (8) with (4-FC6H4)2Cd gave 2,2,5,5-tetramethyl-3-(α-hydroxy-4-fluorobenzyl)-3-pyrrolin-1-oxyl (9), which was oxidized with MnO2 to 2,2,5,5-tetramethyl-3-(4-fluorobenzoyl)-3-pyrrolin-1-oxyl (10). The aryl nitroxides 2, 6, and 10 were nitrated with concentrated H2SO4/HNO3 to ortho-fluoronitrophenyl compounds 3, 7, and 11. The fluoro nitro derivatives served as versatile synthons in the nucleophilic replacement of fluorine with OH, NH2, α-amino acid ester, or thiol. The hydroxy nitroaryl compounds 16, 26, and 30 were nitrated further to give dinitrophenol derivatives 17, 27, and 31. Keywords: fluorophenyl nitroxides, nitroaryl nitroxides, NMR spectra of nitroxides.
Thermodynamic analysis of phase diagrams of binary solid solutions of ascending and minimum types: Na2SO4–Ag2SO4, Ag2SO4–K2SO4, Na2SO4–K2SO4
Authors: Dawson Patrick C. , Secco E. A. , Oxner William M.
Published: May 2006

The thermodynamic analysis of the condensed phase diagrams of binary system solid solutions of the ascending type, viz. Na2SO4–Ag2SO4 and of the minimum type, ameltrope, viz. Ag2SO4–K2SO4, Na2SO4–K2SO4 is presented. The analysis identifies the basis for ameltrope behavior and provides for the evaluation of α, the fraction of dissociation, and ΔHDiss, the enthalpy of dissociation, of the dissociating component. Keywords: alkali sulfates solid solutions, thermodynamic analysis ameltropes, molten alkali sulfates dissociation, solid–solid phase diagrams, ionic melts.
Solution inclusion complexes of cyclodextrins with sodium perfluorooctanoate
Authors: Palepu Ramamurthy , Reinsborough Vincent C.
Published: May 2006

Pre-micellar and micellar sodium perfluorooctanoate solutions (SPFO) were examined conductometrically with added α-cyclodextrin(α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD). The order of stability of the 1:1 inclusion complex was (β-CD > γ-CD > α-CD determined largely by the goodness of fit of the fluorocarbon chain in the CD cavity. Sodium ion electrode studies revealed that some Na+ ion is associated with the (β-CD/SPFO complex. As shown by fluorine-19 nmr, (β-CD girds the SPFO molecule snugly amidship with the terminal CF3 group still in solution. On the other hand, SPFO manages only a weak penetration of the fluorocarbon chain into the smaller α-CD cavity. Keywords: perflurooctanoate, cyclodextrin complexes, fluorocarbon surfactant, 19F nmr.