bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemistry of dibenzylketone in Nafion membranes
Authors: Wintgens V. , Scaiano J. C.
Published: May 2006

Photolysis of dibenzyl ketone in vacuum-dried Nafion membranes leads to the detection of fluorescence from the protonated ketone and formation of modest yields of benzyl cations characterized using laser photolysis techniques. Exchange of the acid sites in Nafion by cationic surfactants leads to decreased environmental polarity and a change in mechanism towards the benzyl radical chemistry which is common in organic solvents. The decay of benzyl radicals in Nafion membranes shows magnetic field dependence which indicates that geminate processes play an important role.
The conformational properties of some phenyl esters. Molecular orbital and nuclear magnetic resonance studies
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

Extensive, geometry-optimized, STO-3G MO computations on phenyl formate imply a strongly nonplanar Z conformer (C=O bond cis to the phenyl group) at ambient temperatures. The internal barrier to rotation about the C(1)—O bond in this conformer is computed as V/kJ mol−1 = (−5.17 ± 0.27) sin2 θ − (2.42 ± 0.27) sin2 2θ, θ being zero for the planar conformer; the twofold is nearly twice as large as the fourfold component. The expectation value of θ is 58° at 300 K. The spin–spin coupling constants over six bonds between 13C and I9F nuclei in 4-fluorophenyl formate, acetate, propionate, and isobutyrate, as well as in the 2,6-dichloro-4-fluorophenyl acetate, are adduced as evidence for nonplanar conformers of these molecules. The magnitudes of these six-bond coupling constants are consistent with internal barriers to rotation about the C(1)—O bonds, which are similar in magnitude to those given by the computations on the Z conformer of phenyl formate. The energies of the planar and nonplanar E conformers, as well as the interconversion energies for [Formula: see text] isomerization, are computed. Small amounts of the nonplanar E conformer are predicted at ambient temperatures. The 13C chemical shifts and the one-bond 13C, 19F coupling constants are consistent, respectively, with only minor variations in the conformational behavior of the ester moieties caused by the fluorine substituent and by changes in the structures of these moieties themselves.
Étude radiocristallographique comparée de quelques Δ-2 imidazolines substituées
Authors: Brouant Pierre , Barbe Jacques , Marsura Alain , Soula Catherine , Luu-Duc Cuong
Published: May 2006

The solid state structures of three compounds belonging to the Δ-2 imidazoline series have been compared. X-ray data and molecular parameters are given. It is noteworthy to point out that substituents are trans to one another in these structures. Moreover, the spatial orientation of the carbonyl group attached to C(4) depends on the nature of the substituent attached to nitrogen N(3). In addition, results are in close agreement with those of nuclear magnetic resonance spectroscopy.
Kinetics of hydrolysis of aromatic mono- and disulfonyl chlorides
Authors: Sanecki Przemyslaw , Rokaszewski Edward
Published: May 2006

A continuous polarographic method of recording instantaneous concentrations of —SO2Cl groups in an aqueous acetic acid system containing CH3CO2Na has been elaborated. Ten model monosulfonyl chlorides underwent hydrolysis according to pseudo-first order kinetics (20% H2O, 80% v.v. CH3CO2H, 0.5 mol × dm−3 CH3CO2Na). Plots of hydrolysis for seven disulfonyl dichlorides with different number of —CH3 groups have been determined. Pseudo-first order rate constants for two consecutive reactions of hydrolysis (k1 and k2) have been computed and the influence of —SO2Cl and [Formula: see text] groups on the reactivity of the second group —SO2Cl has been discussed. The mechanism of nucleophilic substitution has also been discussed.
Étude vibrationnelle du méthyl-4 triazole-1,2,4 et de son chlorhydrate
Authors: Zaydoun S. , Idrissi M. Saidi , Garrigou-Lagrange C.
Published: May 2006

Vibrational spectra of 4-methyl-1,2,4-triazole, its hydrochloride salt, and some of their deuterated homologs have been studied from 4000 to 200 cm−1. An attribution of most of the fundamental modes is proposed, and the effect of protonation on fundamental frequency values is explained.
Orientation behaviour of chlorobenzene in nematic solvents
Authors: Yim C. T. , Gilson D. F. R.
Published: May 2006

The orientational order parameters of monochlorobenzene have been determined, as functions of temperature and concentration, in two nematic solvents, EBBA and ZLI-1132. There are significant differences in the orientation of the solute molecule in the two solvents as reflected in the values of corresponding potential energy parameters as well as in the concentration dependence of the order parameters. These differences are caused mainly by a stronger interaction between the aromatic ring and the solvent ZLI-1132, since the change in the potential function terms for chlorobenzene parallel those for unsubstituted benzene. Attempts to correlate the orientation potential with molecular polarizability and molecular shape lead to the conclusion that neither of these properties plays a dominant role in determining the potential.
Conformational analysis of 3-substituted-2,3,4,5-tetrahydro-1-benzoxepin by 1H and 13C nuclear magnetic resonance
Authors: Lachapelle A. , St-Jacques M.
Published: May 2006

2,3,4,5-Tetrahedro-1-benzoxepin (8) and its 3-substituted derivatives (9–13) have been studied by 1H and 13C dynamic nuclear magnetic resonance in a few solvent systems. The results show that, while 8 and its methyl derivative 9 exist solely in chair forms (C for 8 and Ce:Ca (96:4) for 9), the twist-boat (TB) conformation contributes significantly to the conformational equilibria of the derivatives 3-methoxy 10 (Ca:Ce:TB, 70:20:10), 3,3-dimethyl 11 (C:TB, 90:10), 3,3-methylmethoxy 12(Ca:Ce:TB, 89:4:7), and 3,3-dimethoxy 13 (C:TB, 92:8). The analysis of several factors (steric, electrostatic, and electronic) on the conformational behaviour of these molecules shows why the TB form is a viable conformational alternative to destabilized chair forms in this benzoxepin system.
The synthesis and characterisation of hetero-bimetallic sulfonate bridged coordination polymers of the type MIISnIV(SO3X)6 with X = F or CF3
Authors: Mallela S. P. , Lee K. , Gehrs P. F. , Christensen J. I. , Sams J. R. , Aubke F.
Published: May 2006

The synthesis of a series of hetero-bimetallic fluorosulfate bridged coordination polymers of the type M(II)Sn(SO3F)6, with M(II) = Mn, Fe, Co, Ni, or Cu, by interaction of the metal bisfluorosulfate with the strong fluorosulfate acceptor Sn(SO3F)4 in fluorosulfuric acid is described. Subsequent solvolysis of either stoichiometric 1:1 mixtures of M(SO3F)2 and Sn(SO3F)4or the bimetallic polymer M(II)Sn(IV)(SO3F)6 in an excess of trifluoromethyl sulfuric acid affords the corresponding SO3CF3-bridged polymers of the composition M(II)Sn(SO3CF3)6 with M(II) = Mn, Fe, Co, Ni, or Cu. The new compounds are characterized by infrared and 119Sn Mössbauer spectroscopy.
The reactions of the chromate, dichromate, and permanganate ions with 100% sulfuric acid and dilute oleum
Authors: Gillespie R. J. , Kapoor R.
Published: May 2006

Solutions of potassium chromate and potassium dichromate in 100% sulfuric acid and dilute oleum have been investigated by cryoscopic and conductimetric methods. It is shown that they both react to give the compound CrO2(HSO4)2. The absorption spectra of solutions of potassium chromate and dichromate in 100% sulfuric acid are very similar to the spectra of species of the type CrO2X2. Potassium permanganate dissolves in 100% sulfuric acid to give green solutions which are shown to contain MnO3•SO4H. The formation of this compound has been further confirmed by conductimetric measurements in dilute oleum. The absorption spectra of these green solutions are also consistent with the formation of a species of the type MnO3X.
Electrocatalytic reduction of molecular oxygen by mononuclear and binuclear cobalt phthalocyanines
Authors: Hempstead Michael R. , Lever A. B. P. , Leznoff Clifford C.
Published: May 2006

Investigations of the electrocatalytic activity of mononuclear and binuclear cobalt phthalocyanines for the reduction of molecular oxygen established that the latter compounds are more effective catalysts than the corresponding mononuclear species. A correlation between the half-band widths for the Q band of these species and their catalytic efficiency, expressed as a kinetically-limited current, suggests that the increase in activity may be attributed to electronic coupling between the phthalocyanine rings.
15N nuclear magnetic resonance spectra of nucleoside compounds. Reflection of modifications at N1 and N6 of adenosine derivatives
Authors: Uzawa Jun , Anzai Kentaro
Published: May 2006

15N nuclear magnetic resonance spectra of adenosine derivatives were taken at the natural abundance level, and the reflection of structural modifications on the spectra was considered on the basis of the electronic behaviour of the molecules.
Condensation reactions of 1,1-dimorpholinoethene and of 1,1-dipiperidinoethene with carbon acids
Authors: Gandhi Sham S. , Gibson Martin S.
Published: May 2006

1,1-Dimorpholinoethene and 1,1-dipiperidinoethene condense with such compounds as malononitrile, ethyl cyanoacetate, cyanoacetamide, and diethyl malonate to give the corresponding β,β-disubstituted enamine, a molecule of morpholine or piperidine being eliminated in the process. Similar reactions with acetylacetone and ethyl acetoacetate proceed with loss of the acetyl group to give the β-substituted enamine. 1,1-Dipiperidinoethene and nitromethane give the β-nitroenamine. Secondary processes of either hydrolysis or further Michael addition and elimination are noted in condensations of 1,1-dimorpholinoethene or 1,1-dipiperidinoethene with cyanoacetamide under more basic conditions.1,1-Dipiperidinoethene is arylated at the 2-position by 2,4-dinitrochlorobenzene.
Surface tension and density of the molten LaCl3–NaCl binary system
Authors: Liu G. , Toguri J. M. , Stubina N. M.
Published: May 2006

The surface tension and density of the LaCl3–NaCl system were determined as a function of temperature by the maximum bubble pressure technique. The surface tension and density were found to vary linearly with temperature (1123 < T < 1248 K). At constant temperature, the surface tensions of LaCl3–NaCl melts showed a small negative deviation from Guggenheim's Equation.
Use of Pd/sepiolite systems as hydrogenation catalysts. II. Hydrogenolysis of N-blocked amino acids and dipeptides by hydrogen transfer
Authors: Aramendia A. , Borau V. , Jimenez C. , Marinas J. M. , Sempere M. E.
Published: May 2006

We have carried out the deprotecting of various N-protected amino acids and dipeptides by subjecting them to hydrogen transfer with several palladium catalysts supported on different solids. The hydrogen donor itself has been used "insitu" to reduce the corresponding Pd salt on the support. We have also analyzed the effect of various factors on the deprotecting rate for Z-glycine. Such factors include the procedure used in synthesizing the catalysts ("insitu" or by conventional reduction), the type of support, hydrogen donor, promoting effect of alkaline hydroxides, type of reactor (closed or open), and magnetic or ultrasonic agitation. We have found that the ease of adsorption of the protected amino groups (Z—NH—) is fundamental in accounting for the order of deprotecting rates found. We have compared the activity of new catalysts in the deprotecting process with that of a commercial one containing 10% Pd over carbon, supplied by Fluka (ref. 75990).
Analytical potentiometric data analyses of metal–ligand equilibria by microcomputer. A general procedure for minimizing potential sources of errors and a fast linear-scaled least-squares algorithm
Authors: Decock Patrick , Sarkar Bibudhendra
Published: May 2006

Analytical potentiometry is a powerful technique to investigate multiple species in solution and their formation constants. However, there have been some difficulties in this method resulting primarily from the theoretical approach. In this paper we critically examined them and improvements have been implemented successfully. Suitable experimental designs are adapted and preliminary computation of potentiometric data are performed to minimize potential sources of errors. Criteria are proposed to choose the best set of titration curves. A correction is introduced to partially minimize the errors originating from the volume variation. A linear-scaled minimization algorithm has been implemented to extract the value of the complex stability constants from the experimental free ion concentrations. This has two advantages over the earlier non-linear minimization process. The execution time is faster and it facilitates the selection of the best fit of species. A series of 14 programs are introduced to run on a low memory microcomputer.
Heat capacities and volumes of some non-electrolytes in N,N-dimethylformamide at 298.15 K
Authors: Piekarski Henryk
Published: May 2006

Heat capacities and densities of dilute solutions of formamide, acetone, tetrahydrofuran, ethylene glycol, 2-methoxyethanol, and 2-ethoxyethanol in N,N-dimethylformamide were determined at 298.15 K. Apparent molal heat capacities and volumes for these solutes in DMF were calculated and compared with the analogous data for other substances in DMF solution as well as with the data concerning solutions in methanol and water. Heat capacities of cavity formation (ΔCcav) in DMF were calculated on the basis of the Scaled Particle Theory. ΔCcav appeared to be linearly correlated with the standard partial molal volume of corresponding solutes in DMF. Similar dependences were also found for aqueous and methanolic solutions of the non-electrolytes.
Selenium-77 nuclear magnetic resonance studies of selenols, diselenides, and selenenyl sulfides
Authors: Tan Khoon-Sin , Arnold Alan P. , Rabenstein Dallas L.
Published: May 2006

77Se and 1H nuclear magnetic resonance spectra have been measured for selenols (RSeH), diselenides (RSeSeR), and selenenyl sulfides (RSeSR′), including selenenyl sulfides formed by reaction of glutathione and penicillamine with selenocystine and related diselenides. Exchange processes strongly affect the 77Se and 1H nuclear magnetic resonance spectra of all three classes of compounds. Sharp, exchange-averaged resonances are observed in the 1H nuclear magnetic resonance spectra of selenols; however, selenol proton exchange causes the 77Se resonances to be extremely broad over the pH range where the selenol group is titrated. Selenol/diselenide exchange [Formula: see text] also results in exchange-averaged 1H resonances for solutions containing RSeH and RSeSeR; however, the 77Se resonances were too broad to detect. Exchange reactions have similar effects on nuclear magnetic resonance spectra of solutions containing selenols and selenenyl sulfides. The results indicate selenol/diselenide exchange is much faster than thiol/disulfide exchange. The 77Se chemical shift depends on the chemical state of the selenium, e.g., titration of the selenol group of selenocysteamine causes the 77Se resonance to be shielded by 164 ppm, oxidation of the selenol to form the diselenide selenocystamine causes a deshielding of 333 ppm, and oxidation to form the selenenyl sulfide [Formula: see text] results in a deshielding of 404 ppm. 77Se chemical shifts were found to be in the range −240 to −270 ppm (relative to (CH3)2Se) for selenolates, approximately −80 ppm for selenols, 230–360 ppm for diselenides, and 250–340 ppm for selenenyl sulfides. The 77Se chemical shift is also affected by titration of neighboring carboxylic acid and ammonium groups, and their pkA values can be calculated from 77Se chemical shift data.
Studies on density, viscosity, dielectric constant, and refractive index of binary mixtures of esters in benzene and carbon tetrachloride
Authors: Oswal Shantilal
Published: May 2006

Densities, viscosities, dielectric constants, and refractive indices have been determined for six binary mixtures of propyl acetate, butyl acetate, and ethyl butyrate in benzene and carbon tetrachloride at different mole fractions and temperatures. The excess volumes VE, apparent excess values of viscosity δη, excess Gibbs energy of activation of flow ΔG*E, excess molar polarizations [Formula: see text], excess molar refraction [Formula: see text], and excess dielectric constants εE have been calculated from the experimental data. The results for these binary mixtures are compared with those of ethyl acetate with benzene, carbon tetrachloride, and cyclohexane and of propyl acetate, butyl acetate, and ethyl butyrate with cyclohexane. The results for VE, ΔG*E, [Formula: see text], and εE indicate specific molecular interaction between unlike molecules in ester + benzene and ester + carbon tetrachloride. The specific molecular interaction for mixtures of esters with benzene may be due to n–π complex formation between the free electrons of carboxylic group and aromatic ring while with carbon tetrachloride it may be due to dipole – induced dipole interactions. The molar refractions for all six mixtures vary linearly with mole fraction of components. Comparison between experimental excess volume VE and excess viscosity Δ ln η and that calculated from Flory theory for ethyl acetate + benzene and ethyl acetate + carbon tetrachloride has also been made.
Étude cinétique et thermodynamique de l'interaction d'un complexe de Pd(II) avec l'inosine et l'acide polyinosinique
Authors: Ménard Robert , Zador Miklos
Published: May 2006

Reactions of the (dien)Pd(II) complex with inosine and polyinosinic acid were studied by spectroscopic and stopped-flow methods. In both cases, the metal initially binds at the N7 site of the hypoxanthine base. The results of kinetic studies indicate the existence of a two-path mechanism: a direct nucleophilic substitution and a solvent path with formation of an aquo intermediate. The reactions are faster for poly(I), due to the high density of negative charges for this polymer. The initial reaction at N7 is followed by a slow redistribution of the metal towards the thermodynamically more stable N1 site. Binding of (dien)Pd(II) to poly(I) leads to formation of a stable, multistranded helicoidal structure of the polymer. This structure was characterized by absorption and circular dichroism measurements and by the melting curve of the polymer. It was also observed that in presence of the Pd(II) complex, poly(I) can be hydrolyzed at relatively mild conditions at high pH.
Cinétique et mécanisme des réactions bromate–chlorite et bromate – dioxyde de chlore
Authors: Schmitz Guy , Rooze Henri
Published: May 2006

In an acidic solution, containing initially chlorous acid and bromate in excess, two consecutive reactions are observed, the oxidation of chlorous acid to chlorine dioxide followed by the oxidation of chlorine dioxide: BrO3− + 4ClO2 + 2H2O = 4ClO3− + 3H+ + HOBr. The kinetics of this reaction has been studied and a mechanism proposed. It agrees with the one accepted for the related reaction between bromate and Ce(III). Extended by reactions of chlorous acid, the mechanism reproduces the experimental curves of chlorine dioxide evolution in chlorous acid – bromate solutions. The values of the equilibrium and kinetic constantes are discussed.
Surface condensation products: their influence on the activity of carbon in cyclohexene conversion
Authors: Selim M. M. , El-Nabarawy Th. A. , Youssef N. A.
Published: May 2006

The catalytic conversion of cyclohexene was studied on steam-activated carbon using microcatalytic technique. Three sets of experiments were carried out to investigate the conversion of cyclohexene, depending on reaction temperature. The first set was conducted at a constant temperature while the other two sets were performed either by increasing the temperature from 300 to 400 °C or by decreasing it from 400 to 300 °C. In all cases, the activity of carbon in cyclohexene conversion was influenced by the nature of condensation products formed on the surface during conversion.
Anodic oxidation of UO2. V. Electrochemical and X-ray photoelectron spectroscopic studies of film-growth and dissolution in phosphate-containing solutions
Authors: Shoesmith D. W. , Sunder S. , Bailey M. G. , Wallace G. J.
Published: May 2006

The anodic oxidation of UO2 has been studied in aqueous phosphate solutions over the pH range 4 to 11, using a combination of electrochemical and X-ray photoelectron spectroscopic techniques. The early stages of oxidation, leading to the formation of a film of composition UO2.33, are unaffected by the presence of phosphate in the solutions. Phosphate concentrations [Formula: see text]prevent the formation of higher-oxide films that are present in phosphate-free solutions at higher oxidation potentials. Dissolution under steady-state conditions proceeds via a surface film of uranyl phosphate. For potentials [Formula: see text] (vs. SCE), the rate of dissolution to yield[Formula: see text] is controlled by charge-transfer kinetics. For potentials[Formula: see text], the rate-determining step is the chemical dissolution of the uranyl phosphate layer.
Oxidation of 3-alkylidene-β-lactams. A preparation of 3-alkenyl-3-hydroxy-β-lactams
Authors: Ogilvie William W. , Durst Tony
Published: May 2006

Hydroxylation of the enolates of several 3-alkylideneazetidin-2-ones with MoOPH leads to the formation of 3-hydroxy-3-alkenylazetidin-2-ones in fair to good yields. The products were formed with trans stereochemistry in the alkenyl moiety and a presumed trans relationship between the hydroxyl substituent and a 4-substituent. Hydrogenation leads to 3-alkyl-3-hydroxy-azetidin-2-ones. The prerequisite 3-alkylideneazetidin-2-ones were formed from 3-trimethylsilylazetidin-2-ones and aldehydes via a Peterson olefin synthesis.
Vibrational analysis of the low resolution absorption spectra of BrClCS and Br2CS
Authors: Simard B. , Steer R. P. , Judge R. H. , Moule D. C.
Published: May 2006

The [Formula: see text] absorption spectra of BrClCS and Br2CS have been photographed under low resolution at room temperature. The electronic origins of BrClCS and Br2CS have been placed at 17116 and 16859 cm−1, respectively. Vibronic analyses show that the molecules are non-planar in their ā states. By fitting quadratic–Gaussian and quadratic–quartic double-minimum potentials to the observed vibrational levels of the out-of-plane manifolds, the equilibrium out-of-plane angles and the barrier heights to molecular inversion have been estimated to be 25 ± 1 deg and 541 ± 10 cm−1 for BrClCS, and 17.5 ± 1 deg and 524 ± 10 cm−1 for Br2CS. In the case of BrClCS, all six ā state vibrational frequencies have been obtained. In the case of Br2CS, only modes 1 (C—S stretch), 2 (symmetric C—Br stretch), 3 (in-plane Br—C—Br scissor), and 4 (out-of-plane bend) are active in the spectrum. Comparisons with other tetraatomic thiocarbonyls support the given assignments.
Structural studies of organoboron compounds. XXVIII. 5,5-Trimethylene-2,2-diphenyl-1,3-dioxa-5-azonia-2-boratacyclohexane and 5,5-dimethyl-2,2-diphenyl-1,3-dioxa-5-azonia-2-boratacyclohexane monohydrate
Authors: Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

The preparation of the title compounds demonstrates the bis-N-alkylation of secondary amines by formaldehyde, these labile ammonium inner salts being captured as diphenylboron chelates. Crystals of 5,5-trimethylene-2,2-diphenyl-1,3-dioxa-5-azonia-2-boratacyclohexane are orthorhombic, a = 8.8461(3), b = 10.7290(4), c = 15.8773(5) Å, Z = 4, space group P212121, and those of 5,5-dimethyl-2,2-diphenyl-1,3-dioxa-5-azonia-2-boratacyclohexane monohydrate are monoclinic, a = 6.2432(3), b = 17.1469(8), c = 14.3701(5) Å, β = 90.647(3)°, Z = 4, space group P21/n. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.030 and 0.047 for 1400 and 2258 reflections with I ≥ 3σ(I), respectively. Both compounds have a B,N-betaine structure, the six-membered chelate rings adopting chair conformations. Libration-corrected bond lengths, O—B = 1.508(3)−1.522(3) and C—B = 1.612(4)−1.637(4) Å, indicate relatively strong binding of the diphenylboron moiety to the oxygen atoms of the O,O-chelating ligands.
Cyclopentadienyl–metal bond cleavage and stereospecific bromination. The structure of (η-C5H5)2Ti(OOCPh)2 and its reactions with bromine
Authors: Lucas C. Robert , Gabe Eric J. , Lee Florence L.
Published: May 2006

The 13C and 1H nmr spectra as well as the X-ray structure determination for (η-C5H5)2Ti(OOCPh)2 are described. The compound crystallizes in space group P21212I with a = 7.5135, b = 12.5166, c = 21.1416 Å, Z = 4, dcalcd = 1.40 g cm−3 (MoKα1, λ = 0.70932 Å). The structure was solved with MULTAN using data collected at 115 K and refined to the final R = 0.059 for 1500 significant reflections. The molecule has two different carboxylate ligands, one of which has a Ti—O—C angle of 135.4(6)° and longer Ti—O (1.976(5) Å) and O—C (1.300(10) Å) bonds while the other has a Ti—O—C angle of 157.0(7)° with shorter Ti—O (1.913(6) Å) and O—C (1.267(10) Å) bonds. With bromine, ring cleavage occurs giving C5H5Br3 or C5H5Br5 in which bromination has occurred stereospecifically. The same reaction occurs with chlorine but not with iodine or iodine monochloride. Related reactions have been observed with (η-C5H5)2MCl2 (M = Ti, Zr, and V). A non-radical mechanism is proposed in which the LUMO and HOMO of Br2 interact simultaneously with one cyclopentadienyl ring and with the metal. This interaction is a consequence of the structure of (η-C5H5)2M(OOCPh)2.
Intramolecular Diels–Alder reactions of cyclopentadiene systems: Model studies for the total synthesis of the capnellenes
Authors: Hellou Jocelyne , Bérubé Gervais , Newlands Michael J. , Fallis Alex G. , Gabe Eric J.
Published: May 2006

Model studies for a general intramolecular Diels–Alder approach to the tricyclo[6.3.0.02,6]undecene skeleton common to the capnellene marine sesquiterpenes are described. Suitably functionalized cyclopentadiene systems 14 and 21 were synthesized and their cycloaddition reactivity examined. Triene 14 cyclized to the tricyclic adducts 15 and 16. In contrast, the anticipated product 22 from intramolecular cycloaddition of triene 21 was not formed in isolatable yield. Instead the minor adduct (10% yield) possessed an exocyclic double bond and was assigned structure 30 based on its relative stability, as determined by MM2 type calculations, and nuclear magnetic resonance data. X-ray analysis established that the major adduct (40% yield) was a tetracyclic[6.3.1.01,6,01,10]dodecene system corresponding to 32, and which arose from competitive isomerization of the initial diene and cyclization via an exo transition state.
Photochemistry of cyclic α-hydroxy ketones. II. The nature of the photoproducts from 8a-hydroxy-4a-methyl-trans- and -cis-octahydronaphthalen-1(2H)-one and an interpretation of the contrast between the photochemistry of these and of analogous steroidal α-hydroxy ketones
Authors: Yates Peter , Stiver Shirley
Published: May 2006

Photolysis of either 8a-hydroxy-4a-methyl-trans- or -cis-octahydro-naphthalen-1(2H)-one (3 or 4) in benzene gives a 96:4 mixture of the lactones, 5a-methyl-trans- and -cis-octahydro-1-benzoxepin-2(3H)-ones (7 and 8). Photolysis of 3 or 4 in ethanol gives identical mixtures of the lactones 7 and 8 and ethyl (2S*,1R*)- and (2R*,1R*)-2-hydroxy-1-methylcyclo-hexanebutyrates (11 and 12). Photolysis of the 2α-deutero derivatives of 3 or 4 in benzene gives mixtures of the 9a-, 3α-, and 3β-deutero derivatives of lactone 7. The striking difference between these results and those for photolyses of analogous 5α- and 5β-hydroxy 6-keto steroids, which are stereospecific, is interpreted in terms of the greater flexibility in the cases of 3 and 4 of the acyl side chain in the acyl alkyl diradicals formed by α-cleavage. A further difference—the sole formation of lactones on photolysis of the steroidal α-ketols in ethanol—is interpreted in terms of an analogous increased flexibility in the cases of 3 and 4 of the ketene side chain in the hydroxy ketene intermediates formed from the acyl alkyl diradicals.
Solvation of urea and methyl-substituted ureas by water and DMF
Authors: Spencer J. N. , Hovick James W.
Published: May 2006

The hydrogen bond enthalpies of urea and methyl-substituted ureas with water and DMF have been determined by the pure-base calorimetric method. Transfer enthalpies between water and DMF have been calculated for dilute solutions of the ureas according to a previously developed model. The first solvation sphere of urea in water consists of five water molecules. Solvation spheres are given for other methyl-substituted ureas in water and DMF.
Nitrosodisulphonates and hydroxylamine-N,N-disulphonates. V. A potassium salt of hydroxylamine-N,N-disulphonic acid with a displacive superlattice structure
Authors: Rutherford John S. , Robertson Beverly E. , Guttormson Richard J. , Russell David B.
Published: May 2006

The structure of the potassium salt of hydroxylamine-N,N-disulphonate, with the formula K5HN2S4O14•H2O, has been determined by X-ray diffraction. The crystals are triclinic, a = 14.011(6), b = 16.118(9), c = 11.867(6) Å, α = 103.28(6), β = 106.76(3), γ = 86.38(3)°, [Formula: see text] with Z = 6. The integrated intensities of 8694 independent reflections were measured on a four-circle diffractometer, 5236 of which were used in the refinement to give a final least-squares weighted residual of 0.107 and a conventional R factor of 0.081.The structure forms a six-fold derivative lattice, which arises by small displacements (ca. 0.2 Å) of the atom positions from an average structure which is triclinic with Z = 1. This results in three very short H bonds, average length 2.46 Å, which link the three independent anion-dimers, being symmetry-free in this structure. Other bond lengths and angles in the anions are very similar to those in the Rb salt. The K+ ions show 8, 9, and 10 coordination, in a number of different polyhedral types. The three independent water molecules are each coordinated to three totally distinct K+ ions, and are linked to the anions by weak H bonds. The structural complexity may be explained in terms of a Lewis acid–base "mismatch" of the cations and anions present.
A study of iron–tungsten oxides and iron–chromium–tungsten oxides
Authors: Birchall Thomas , Hallett Christopher , Vaillancourt Ann , Ruebenbauer Krzysztof
Published: May 2006

A 57Fe Moessbauer study of the Fe2O3–WO3 and Fe2O3–Cr2O3–WO3 systems has been carried out. Single phase materials could be prepared having the composition Fe2−xWO6−3x/2 (x = 0.28), the stoichiometric Fe2WO6 always contained detectable amounts of α-Fe2O3. The iron tungstates are found to be unstable to prolonged heating at 1000 °C. The Cr2−yFeyWO6 (0 < y ≤ 2) system was shown to be of the trirutile type when y ≤ 1.7 but multiphasic when y ≥ 1.7, these latter phases have structures based upon the iron and chromium tungstate phases, respectively. The Moessbauer parameters for the Cr2−xFeyWO6 compositions do not appear to behave in the same fashion as the related Fe2−xCrxTeO6 system.
Molar excess volumes, isentropic compressions, and isobaric heat capacities of methanol – isomeric butanol systems at 298.15 K
Authors: Okano Tsukasa , Ogawa Hideo , Murakami Sachio
Published: May 2006

Molar excess volumes, molar excess isentropic compressions, and molar excess isobaric heat capacities for binary liquid mixtures of methanol with 2-methylpropanol, 2-butanol, and 2-methyl-2-propanol have been determined at 298.15 K. The concentration dependence and magnitude of these thermodynamic functions are quite different from those of the methanol – 1-butanol system, which had been previously determined. Molar excess volumes for two of the present systems are positive over the whole concentration range, except for the 2-methyl-2-propanol system. For the latter system they are negative in the butanol-rich range. Molar excess isentropic compressions of these systems show slightly different concentration dependence from that of the excess volumes, but the order in magnitude resembles that of the excess volumes. Molar excess isobaric heat capacities for all systems are negative and show simple concentration dependence. The minimum values of excess heat capacities are correlated with the magnitude of molar isobaric heat capacities of the pure isomeric butanols. The behavior of these excess functions is discussed with reference to the differences in numbers and strength of hydrogen bonding between the pure liquid and the solution.
Volumes and heat capacities of transfer of ammonium salts from water to aqueous octyldimethylamine oxide at 25 °C
Authors: Hétu Daniel , Desnoyers Jacques E.
Published: May 2006

The effect of an additive on a water–surfactant system can be studied through thermodynamic functions of transfer of the additive from water to aqueous solutions of the surfactant. These thermodynamic functions often go through extrema in the region of the critical micellar concentration (cmc) of the surfactant. As it can be shown with a simple chemical equilibrium model, the general shape of the transfer functions is primarily related to the pair-wise hydrophobic interactions between the additive and the surfactant monomers, to a shift in the monomer–micelle equilibrium and to the distribution of the additive between the aqueous phase and the micelles. Medium and electrostatic effects are also possible, especially with ionic systems. To separate these effects and identify the salts which distribute themselves in the micelles, the volumes and heat capacities of transfer of hydrophobic ammonium salts from water to aqueous solutions of dimethyloctylamine oxide have been investigated. The short chain salts have only a small effect on monomer–micelle equilibrium by salting out the monomers, whereas the more hydrophobic ones participate also to the micellization process, shifting more strongly the surfactant monomer–micelle equilibrium.
Ionic conductivity of pure and doped sodium chloride crystals
Authors: Hooton Irene E. , Jacobs P. W. M.
Published: May 2006

New measurements are reported for the ionic conductivity of well-annealed crystals of pure NaCl, NaCl doped with Sr2+ ions, and NaCl doped with S2− ions. Analysis of these data leads to the conclusions (i) that the Schottky defect model is entirely adequate for NaCl (in contrast to KCl); and (ii) that the activation energy for the migration of anion vacancies is 0.74 eV. This last result is in agreement with values derived from the analysis of conductivity and diffusion data for pure NaCl and NaCl doped with Sr2+, and with theoretically-calculated values, but at variance with results from recent measurements on quenched sulphide-doped crystals.
Thermal effects in polyelectrolyte ion exchange reactions: the Jahn–Teller effect
Authors: Sun Kang , Boyd George E.
Published: May 2006

Microcalorimetric determinations were made of the thermal effects accompanying the exchange of the divalent cations of Mn, Fe, Co, Ni, Cu, and Zn in dilute aqueous perchlorate solutions with Mg2+ ion initially bound in a crosslinked polyelectrolyte gel. The calorimetric measurements, together with microchemical equilibrium distribution determinations with the same cations, were employed to estimate the standard state Gibbs energy, enthalpy, and entropy changes associated with their ion exchange reactions.All the transition elements were selectively absorbed relative to Mg2+ with the sequence being: Mn < Fe < Co < Ni > Cu > Zn, showing divalent Ni(II) cation to possess the greatest affinity for the polyelectrolyte phase. The sequence of standard state reaction enthalpy change, ΔH0, revealed that Ni2+ also was the most exothermic of all 3d transition element cations. However, the ΔH0 values became more negative in the order: Mn < Fe < Co < Ni > Cu < Zn, showing that Cu2+ ion behaved anomalously in being less negative than expected. This behavior (and that in the ΔS0 values also) suggested that a destabilization of the octahedrally coordinated Cu2+ in aqueous solutions must occur, possibly because of Jahn–Teller effects on its d9 electronic configuration when the cation is placed in an environment of cubic symmetry. Because of a thermodynamic compensation of the magnitudes of ΔH0 and ΔS0, the position of Cu2+ in the ΔG0 value sequence was regular.
Convolutive voltammetry with microelectrodes
Authors: Harman A. R. , Baranski A. S.
Published: May 2006

Hemispherical microelectrodes prepared by electroplating of mercury on platinum microelectrodes were used in studies of fast charge transfer processes under convolutive voltammetry conditions. The algorithm used in the convolutive transformation was modified to account for spherical symmetry of diffusion. The sweep rate was varied from 0.1 to 220 V/s. Low sweep rate experiments were used to test the symmetry of the mass transport. It was found that the mass transport to (and inside) the electrodes can be described with good accuracy by the spherical symmetry diffusion. It was shown that the spherical convolution can be used to determine from cyclic voltammetric data the diffusion coefficient of a depolarizer and the number of electrons transfered to (or from) the depolarizer molecule in the electrode process.At high sweep rates the technique was found useful in studies of fast electrode reactions. The technique was tested in the determination of kinetic parameters for Cd2+ reduction in aqueous solutions and p-dicyanobenzene reduction in DMF solutions. In both cases good agreement with values reported in literature was found. Properties of Hg/Pt microelectrodes were also studied using the ac impedance techniques. The ac impedance measurements were carried out at various frequencies (0.1 Hz to 100 kHz) in solutions containing 0.1 to 10−5 M of the supporting electrolyte.
Structural studies of organoboron compounds. XXIX. 6,6-Diethyl-2,2-diphenyl-1,3-dioxa-6-azonia-2-boratacyclooctane monohydrate
Authors: Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

Details of the preparation and structure of the title compound are given. Crystals of 6,6-diethyl-2,2-diphenvl-1,3-dioxa-6-azonia-2-boratacyclooctane monohydrate are orthorhombic, a = 7.0322(2), b = 16.3505(7), c = 16.8164(4) Å, Z = 4, space group P212121. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.045 and Rw = 0.050 for 2013 reflections with I ≥ 3σ(I). The monocyclic eight-membered B, N-betaine is the first to be structurally characterized. The eight-membered chelate ring has a conformation intermediate between the S4 and boat-boat forms which is probably stabilized by transannular [Formula: see text] interactions. The average libration-corrected O—B and B—C bond lengths of 1.500 and 1.639 Å are, respectively, the shortest and longest yet observed for an O,O-chelate of diphenylboron.
Reactions of 1,2-dehydropyrrolidin-5-one with 1,3-dienes. Synthesis of dl-gephyrotoxin 223AB
Authors: Edwards Oliver E. , Greaves Austin M. , Sy Wing-Wah
Published: May 2006

Evidence is presented that the regiospecific and often stereospecific pseudo-Diels–Alder reactions of 1,3-dienes with N-acyl immonium salts, derived from 5-ethoxy-2-pyrrolidinone, are stepwise reactions. 6,7-Dehydroindolizidinones, unsaturated lactam esters, and new indene and furan derivatives are described. A synthesis of dl-gephyrotoxin 223AB (indolizidine 223AB) from trans-1,3-heptadiene was achieved.
A Raman and infrared spectroscopic study of triethylenediamine (DABCO) and its protonated forms
Authors: Guzonas David A. , Irish Donald E.
Published: May 2006

The Raman and infrared spectra of DABCO have been measured as a function of the pH, and the vibrational bands of the two protonated forms of DABCO have been tabulated and assigned. The frequencies of several of the Raman bands were found to exhibit substantial shifts upon protonation, and the appearance of the Raman spectrum in the region between 900 and 1100 cm−1 in particular shows differences which can be used to differentiate between the three forms of DABCO. The values of the two pKa's were determined from the intensity versus pH plots for the three species.
Nucleic acid related compounds. 53. Synthesis and biological evaluation of 2′-deoxy-β-threo-pentofuranosyl nucleosides. "Reversion to starting alcohol" in Barton-type reductions of thionocarbonates
Authors: Robins Morris J. , Madej Danuta , Hansske Fritz , Wilson John S. , Gosselin Gilles , Bergogne Marie-Christine , Imbach Jean-Louis , Balzarini Jan , Clercq Erik De
Published: May 2006

Treatment of selectively 3′,5′-protected β-D-xylofuranosyl nucleosides (4) with phenyl chlorothionocarbonate and DMAP followed by hydrogenolysis of the resulting (2′-O-phenoxythiocarbonyl) phenyl thionocarbonate esters (6) with tributylstannane/AIBN, and deprotection, gave 2′-deoxy-β-D-threo-pentofuranosyl nucleosides (7). Formation of a by-product bis(nucleosid-2′-yl)thionocarbonate dimer (8) was detected in the uracil nucleoside reaction sequence. Its subsequent reduction provides one explanation for "reversion to starting alcohol" in Barton-type deoxygenation reactions. Only the guanine 2′-deoxynucleoside analogue (7b) had (weak) antiviral activity (against herpes simplex virus type 1).
The proton affinity of triethylsilanol obtained by proton transfer equilibrium measurements using a high pressure mass spectrometer
Authors: Li Xiaoping , Stone John A.
Published: May 2006

The proton affinity (PA) of triethylsilanol has been determined by equilibrium proton transfer measurements using a high pressure mass spectrometer. The reference bases were naphthalene and m-xylene which have the required low affinities for trialkylsilylium. van't Hoff plots were used to obtain PA((C2H5)3SiOH) = 197.9 ± 0.4 kcal mol−1•This value is used to recommend that. PA((CH3)3SiOH) ≈ 192 kcal mol−1•(C2H5)3Si+ has been produced by the protonation of (C2H5)4Si and the enthalpy change for the reaction [Formula: see text] has been determined to be 32 ± 1 kcal mol−1 which gives [Formula: see text]((C2H5)3Si+) = 135 kcal mol−1•A value of ~ 141 kcal mol−1 is recommended for [Formula: see text].
Comparison of STO-3G and 3-21G ab initio harmonic force fields for ethane, propane, dimethyl ether, and cyclobutane: effects of geometry and scaling on calculated frequencies, eigenvectors, and infrared absorption intensities
Authors: Shaw R. Anthony , Ursenbach Charles , Rauk Arvi , Wieser Hal
Published: May 2006

Ab initio harmonic force fields were calculated for ethane, propane, dimethyl ether, and cyclobutane at the STO-3G and 3-21G levels. The calculated frequencies, displacement eigenvectors, and calculated infrared absorption intensities were compared as they derive from force constants that were (i) unsealed; (ii) scaled to fit observed vibrational frequencies reported in the literature; (iii) evaluated at the optimized geometries; and (iv) evaluated at structures for which the bond lengths were corrected from the optimized geometries according to published procedures. A total of nine combinations of ab initio force field/reference geometry/G-matrix geometry were investigated for each of the four molecules. The ability of scaling factors as the only variables to predict vibrational parameters from STO-3G and 3-21G force fields was explored. Conditions were examined for which the scaling factors are satisfactorily transferable among different molecules.
Cyclobutene photochemistry. Involvement of carbene intermediates in the photochemistry of alkylcyclobutenes
Authors: Clark K. Brady , Leigh William J.
Published: May 2006

The photochemistry of 1,3,3,4- and 1,3,4,4-tetramethylcyclobutene has been investigated in pentane solution with monochromatic far ultraviolet (185, 193, and 214 nm) light sources, as well as in methanol solution with 214-nm excitation. Photolysis of each of the two isomeric cyclobutene derivatives results in competitive electrocyclic ring opening (yielding mixtures of stereoisomeric dienes in each case), fragmentation to yield propyne and methyl-2-butene, and isomerization to the other cyclobutene isomer. Quantum yields for product formation with 185-nm excitation have been measured in each case by cyclooctene actinometry. The occurrence of the interconversion process is offered as evidence for the intermediacy of cyclopropyl carbenes in the photochemistry of simple cyclobutenes in solution. On the basis of the known chemistry of carbenes of this type, their intermediacy in cyclobutene photochemistry may account at least partially for the formation of the formal (2π + 2π) cycloreversion products from photolysis of simple cyclobutene derivatives.
Carcinogenic alkylation of nucleic acid bases. Solid state and solution studies of O2-isopropyl-2′-deoxythymidine
Authors: Birnbaum George I. , Sadana Krishan L. , Razi M. Tahir , Lee Terry , Sebastian Rudy , Buchko Garry W. , Hruska Frank E.
Published: May 2006

O2-Isopropyl-2′-deoxythymidine (i2dT) crystallizes in the tetragonal space group P43212, and the cell dimensions are a = b = 8.7667(2), c = 37.1943(12) Å. X-ray intensity data were measured with a diffractometer, and the structure was solved by direct methods. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.036 for 1780 observed reflections. In analogy with other O-alkylated bases, the exocyclic O2—C8 bond is syn-periplanar to the C2—N3 bond in the pyrimidine ring. Angular distortions in the base can be correlated with those observed in O4-alkylated pyrimidines and O6-alkylated guanines. The conformation of the glycosyl bond is anti with χCN = 27.1°. The furanose ring adopts a C2′ endo pucker and the conformation about C4′—C5′ is gauche+. 1H nmr data show that these conformations are also preferred in solution.
Cerium(IV)-induced nitration of cinnamic acids. Novel remote electrophilic substitution
Authors: Peterson John R. , Do Hoang D. , Dunham Andrew J.
Published: May 2006

The treatment of (E)-3,4-dimethoxycinnamic acid with ceric ammonium nitrate in trifluoroacetic acid afforded (E)-1,2-dimethoxy-4-nitro-5-(2-nitroethenyl)benzene in 79% yield. The unusual ipso substitution of the carboxylic acid moiety by a nitro functional center illustrated a new reaction manifold of cerium(IV). Six cinnamic acids were examined to ascertain the generality of the transformation. The bidentate nitrato structure of the metal salt is believed to account for the nitrating ability of this system.
Azapropellanes 5. Synthesis of chiral (non-racemic) 2-methyl azapropellanes
Authors: McIntosh John M. , Acquaah Samuel O.
Published: May 2006

The preparation of S-(−)-6-methyl-2-piperidinone from S-alanine and R-(−)-5-methyl-2-pyrrolidinone from S-glutamic acid and their conversion into S-2-methyl-1-azoniatricyclo[4.4.4.01,6]tetradecane (2a) and R-2-methyl-1-azoniatricyclo-[4.4.3.01,6]tridecane (2b) with enantiomeric excesses of 95 and 92% respectively are described. The use of these compounds as phase-transfer catalysts did not lead to significant asymmetric induction.
First observation and analysis of the ion-pair state of Br2 by optical–optical double resonance
Authors: Ishiwata Takashi , Nakamura Osamu , Obi Kinichi , Tanaka Ikuzo
Published: May 2006

The technique of optical–optical double resonance has been applied to a study of the [Formula: see text] ion-pair state of Br2. Two pulsed dye lasers excite the molecules from the ground state to the [Formula: see text] ion-pair state stepwise through the [Formula: see text] state in the pump-probe scheme: [Formula: see text]. The [Formula: see text] emission identified at around 215 nm is used to detect the double resonance signals when the probe laser frequency (ν2) is scanned by fixing the pump laser frequency (v1) to appropriate [Formula: see text] transitions. The emission spectra are resolved to establish the absolute vibrational numbering of the ion-pair state in terms of the Franck–Condon calculations. The Dunham coefficients of the [Formula: see text] state obtained in a global least-squares fit analysis of 377 transitions [Formula: see text] are Y00 = 57929.724(24), Y10 = 212.227(23), Y20 = −1.5683(56), Y30 = 1.606(40) × 10−2, Y01 = 0.0465652(89), Y11 = −4.500(36) × 10−4, Y21 = 1.133(41) × 10−5, and Y02 = −9.37(94) × 10−9 for 79Br2 isotope species (all in cm−1 with 3σ in parentheses).