bluuebunny/crossref_metadata_2025 huggingface dataset:
Alkoxylation of 2,3-dialkylindoles utilizing iodosobenzene diacetate
Authors: Awangz Dennis V. C. , Vincent André
Published: May 2006

Iodosobenzene diacetate has been employed in the development of a simple procedure for the production of 3-alkoxyindolenines from 2,3-disubstituted indoles, by treatment of the indoles with the reagent in alcoholic solvent.Primary and secondary alkoxy functions have been incorporated at the β-site of 2,3-dimethylindole but the reaction with tert-butanol leads to other complex products. Good yields of 9-n-alkoxy-9H-reserpines have been realised but no reaction is observed in secondary alcohols.
Ultraviolet photoelectron spectra of 2-norbornanone, 2,5-norbornanedione, their alkyl derivatives and thio-analogues. An investigation of transannular interactions by photoelectron spectroscopy
Authors: Frost David C. , Westwood Nicholas P. C. , Werstiuk Nick H.
Published: May 2006

HeI photoelectron spectra are reported for a series of methyl-substituted monoketones and diketones based on 2-norbornanone. The effect of methyl substitution, and the inductive effect of a second carbonyl group has been studied. The diketones show a small separation between the two ketone moieties due to a through-bond interaction. Replacement with a thiocarbonyl group permits a comparison of the relative C=S and C=O interactions. The relative merits of the semi-empirical HAM/3 and CNDO/2 methods for such molecules are assessed.
Kinetics of the magnetite–maghemite–hematite transformation, with special reference to hydrothermal systems
Authors: Swaddle Thomas Wilson , Oltmann Phillip
Published: May 2006

Maghemite, prepared in the usual way (but with exclusion of silica, e.g., from glassware) by precipitation of non-stoichiometric magnetite Fe3−xO4−x in aqueous MOH (M = Na, K) followed by air oxidation, picks up moisture from the air to reach the limiting composition MδH1−δFe5O8, where δ ~ 0.02–0.03 for fresh material, but changes under hydrothermal conditions because of ion exchange. Despite the role of absorbed moisture in stabilizing maghemite, formation of the latter from Fe3−x O4−x is markedly retarded, and its decomposition to α-Fe2O3 greatly accelerated, under hydrothermal conditions relative to the rates of the corresponding reactions of the dry solids. The rate of hydrothermal decomposition of maghemite is strongly retarded by silica. Over the range 160–187 °C at least, silica-free maghemite decomposes in water according to the empirical equation −ln (1 − α) = (kt)n, where α is the fractional extent of decomposition, and n ~ 2.5 for neutral water (with k = 1.3 × 10−5 s−1 at 160 °C and 3.1 × 10−5 s−1 at 175 °C) but approaches unity, without major effects on the overall time-scale of reaction, at high [MOH]. The mechanistic significance of these and previous results are considered; the hydrothermal conversion of maghemite to hematite evidently proceeds by a dissolution–reprecipitation sequence.
Conversion of stereoisomeric 2-amino-1-carbamoylcyclohexane-5,5-dicarboxylates into 6-amino-3-azabicyclo[3.3.1]nona-2,4-dione-1-carboxylates
Authors: Škarić Vinko , Sedjak Mirjana , Turjak-Zebić Vera , Škarić Djurdjica
Published: May 2006

The separation of cis- and trans-2-amino-r-1-carbamoylcyclohexane-5,5-dicarboxylates 2 and 3 as 2-N-benzyloxycarbonyl (15, 16) and 2-N-benzoyl- (17, 18) derivatives is described. A dipeptide containing suitably protected L-phenylalanine and cis-2-amino-1-carbamoylcyclohexane (2) was also prepared. Moreover, cis- (17) and trans- (18) benzamido isomers were converted into ethyl t-6- (23) and c-6- (24) benzamido-r-1-carboxylate-3-azabicyclo[3.3.1]nona-2,4-dione, respectively. Similarly, ethyl c-6- phthalimido-r-1-carboxylate-3-azabicyclo[3.3.1]nona-2,4-dione (25) was obtained from diethyl t-2-phthalimido-r-1-carbamoylcyclohexane-5,5-dicarboxylate (22).
An investigation of anthraquinone-catalysed alkaline pulping via component modeling and electron spin resonance experiments
Authors: Hocking M. B. , Bolker H. I. , Fleming B. I.
Published: May 2006

The radical anion of anthraquinone (AQ•−) has been generated by the reduction of anthraquinone (AQ) with sugars in aqueous alkaline solution. This appears to be the first time that the radical has been observed (esr spectrometry) in an entirely aqueous medium. Alkaline methanol solutions of AQ, when irradiated with light, yielded colourless solutions also exhibiting strong esr signals characteristic of. AQ•−.The ability of various carbohydrate and lignin preparations to reduce AQ, or to oxidize the reduced forms of AQ, was also investigated, both by direct observation and by electrode potential measurements. In very concentrated alkali, AQ was reduced by glucose to a green solid thought to be a quinhydrone.
Processus primaire de la photolyse et de la photo-oxydation de l'o-phényl-phénol
Authors: Coulangeon Louise-Marie , Perbet Gilles , Boule Pierre , Lemaire Jacques
Published: May 2006

The dual fluorescence observed in aqueous solution of o-phenyl-phenol is attributed to a deprotonation equilibrium in the excited singlet state. The effect of oxygen on the primary photochemical process of formation of phenoxy radicals can be explained in a parallel study of the variations of fluorescence and photo-oxidation quantum yields of this phenolic compound at different pH. It is shown that photoionisation occurs only from the excited singlet state of the phenolate form. Oxygen inhibits recombination of the solvated electron and phenoxy radical. Increase of quantum yield for the disappearance of irradiated o-phenyl-phenol in degased solution also is observed in the presence of electron scavengers like Cd2+ or NO3− ions. Even when the phenoxy radicals are not able to react with oxygen, quantum yield for the disappearance of the phenolic compounds is higher in an aerated than in a degassed solution; the oxygen effect on the primary photochemical step may explain this difference.
Ion molecule reactions in ethane. Thermochemistry and structures of the intermediate complexes: C4H11+ and C4H10+ formed in the reactions of C2H5+ and C2H4+ with C2H6
Authors: Hiraoka K. , Kebarle P.
Published: May 2006

The reactions of C2H5+ and C2H4+ with ethane were studied in a pulsed electron beam high ion source pressure mass spectrometer. Ethane at variable pressures in the 10–100 m Torr range in ~5 Torr hydrogen was used in experiments covering the temperature range −145 to 400 °C. Reaction [7]: C2H5+ + C2H6 = sec-C4H9+ + H2 was found to have a rate constant whose magnitude decreased with temperature: k7 = 10−5.12 T−2 (molecule−1 cm3 s−1). The reaction proceeds via a C4H11+ (b) intermediate, which at low temperature can be stabilized and becomes the major product. The rate constant for thermal decomposition of C4H11(b) by reaction [6t]: C4H11+ (b) = sec-C4H9+ + H2 could be measured. The activation energy was found to be E6t = 9.6 kcal/mol. From consideration of the above data and the known ΔH7, it was concluded that C4H11+ (b) has the structure[Formula: see text]Before dissociation to sec-C4H9+ + H2, this ion rearranges to[Formula: see text]The barrier for this rearrangement is ~9.6 kcal/mol.C2H4+ reacts with C2H6 to give C4H10+ (d) at low temperatures. At high temperatures C4H10+ (d) becomes an intermediate in the dissociation to sec-C3H7+ + H2. The formation of C4H10+ at low temperature has a rate constant whose magnitude decreases with temperature. The temperature dependence of the equilibrium constant K10 for the reaction [10]: C2H4+ + C2H6 = C4H10+ (d) could be determined. This led to ΔH10 = −15.3 kcal/mol. The rate constant for the high temperature reaction [11]: C2H4+ + C2H6 = sec-C3H7+ + H2 was k11 = 8.4 × 10−10 exp (−3.9/RT kcal/mol) (molecule−1 cm3 s−1). A potential energy diagram for the reaction system is proposed. C4H10+ (d) is probably a complex between C2H4+ and C2H6 held largely by ion induced dipole process. Reaction [11] probably proceeds via C4H10+ (d) → n-C4H10+ → sec-C3H7+ + H2. The barrier between C7H10+ (d) and n-C4H10+ is ~20 kcal/mol.
Physico-chemical studies on areno tropilidenes and tropones. II. The polarographic reduction and electrode kinetics of some furotropone derivatives
Authors: Etaiw Safaa H. , El-Borai Mohamed , Ismail Mohamed I.
Published: May 2006

The polarographic reduction of nine furotropone derivatives has been studied in Thiel buffers and in DMF. The reduction of compounds having two methyl or two phenyl groups proceeds via two electron waves along the whole pH range studied. The reduction of furotropone and derivatives having one substituent or three methyl groups proceeds via one reversible electron wave in acid media while in neutral and alkaline media two waves each corresponding to 1 F are observed. Above pH 12, the limiting current decreases and one wave appears, corresponding to 1 F. The values of n were determined coulometrically using the Ilkovic equation. All waves are diffusion controlled while the electrode process along these waves is irreversible. The rate constant, the free energy of activation, and the electron affinities of these compounds were computed.
The kinetics and mechanism of acid catalysed hydrolysis of lactams
Authors: Wan Peter , Modro Tomasz A. , Yates Keith
Published: May 2006

The acid-catalysed hydrolysis of lactams of ring size 4–7, and of N-ethylacetamide, has been studied at various temperatures in 0–70% aqueous sulfuric acids. The kinetics have been analysed by means of the r-hydration parameter treatment and the transition-state activity coefficient (TSAC) approach. Except for the β-lactam, all substrates show a strong positive rate dependence on water activity, indicating a tetrahedral intermediate type of mechanism [Formula: see text], similar to that found for simple (acyclic) amide hydrolyses; only the β-lactam shows a negative rate – water activity dependence, which is interpreted in terms of a unimolecular [Formula: see text] mechanism, involving rate-determining acylium ion formation. Similarly, all substrates except the β-lactam show a pronounced destabilization of the transition-state as acidity is increased, typical of oxonium ion species. The behaviour of the β-lactam resembles that of methyl mesitoate hydrolysis. Basicity constants for lactams of ring size 4–9 show a definite dependence on ring size, with the δ-lactam being unusually basic. Both rate and pK dependence on ring size are discussed in terms of ring strain and steric effects. The activation parameters, particularly ΔS≠, are fully consistent with the conclusions drawn concerning transition-state hydration.
Marine organic chemistry. IV. Isolation of (20R)-5α-pregn-9(11)-ene-3β,6α,20-triol from the saponins of the starfish, Asteriasforbesi and Asteriasvulgaris, and its synthesis
Authors: Arsimon John W. , Badripersaud Satyanand , Buccini John A. , Eenkhoorn Joop , Gilgan Michael W.
Published: May 2006

A minor constituent of the saponin hydrolysate of the starfishes Asteriasforbesi and Asteriasvulgaris is shown to be (20R)-5α-pregn-9(11)-ene-3β,6α,20-triol by synthesis from 11-oxoprogesterone. The occurrence of the reduced progesterone side chain could have implications concerning the origins of progesterone-type compounds in saponin hydrolysates from starfish.
Assignment of anomeric configuration and identification of carbohydrate residues by 13C nmr. 1. Galacto- and glucopyranosides and furanosides
Authors: Beier Ross C. , Mundy Bradford P. , Strobel Gary A.
Published: May 2006

A 13C nmr analysis method is described for the identification of carbohydrate residues in galactosides and glucosides. This method reveals the capability of 13C nmr to distinguish the difference in structural configuration of these carbohydrate residues. Not only can the anomeric configuration be assigned, the furanyl and pyranyl nature of the ring is concomitantly determined. This method is consistent for all reported 13C nmr spectra of nonaromatic galactosides and glucosides.
Towards a general scheme for estimating the heats of formation of organic ions in the gas phase. Part I. Odd-electron cations
Authors: Holmes John L. , Fingas Mervin , Lossing F. P.
Published: May 2006

It is shown that gas-phase heats of formation of homologous odd-electron organic cations can be well represented by an equation of the form ΔHf[ion]+• = A − Bn + C/n, where A, B, and C are constants and n is the total number of atoms in the molecule. Values for A, B, and C have been determined for the linear homologous series: alkanes, olefins, alkynes, alkanols, aliphatic ethers, aliphatic aldehydes, aliphatic ketones, alkanoic acids, alkyl chlorides, bromides, and iodides. For each of these series, correction terms for chain branching, double-bond position, and asymmetry effects are also given. These equations can be applied to molecules containing 40 or more atoms. The data base for this work is also presented.
The photochemical addition of N-haloamides to olefins: the influence of various factors on the competition between 1,2-addition and hydrogen abstraction
Authors: Lessard Jean , Mondon Martine , Touchard Daniel
Published: May 2006

In the photodecomposition of N-haloamides (ZCONRX) in the presence of olefins, the 1,2-addition chain competes with the hydrogen abstraction chain(s) leading to the parent amide (the quantum yields for these processes are greater than unity). The following factors were shown to have an influence on this competition as measured by the yield of 1,2-addition and the yield of parent amide in methylene chloride solutions: (i) the N-halogen (higher yields of addition with X = Cl than with X = Br); (ii) the electronegativity of Z (increase of the yield of addition as the electronegativity of Z increases); (iii) the temperature (higher yields of addition at lower temperatures, and at −70 °C, better yields of addition (>90%, R = H) for X = Br than for X = Cl); and (iv) the size of R (dramatic decrease of the yield of 1,2-addition in going from R = H to R = CH3). Surprisingly, the presence of a scavenger for HX had no influence on the yield of 1,2-addition. Both the size and electronegativity of Z had an effect on the stereochemistry of 1,2-addition to cyclohexene. High yields of addition to a variety of olefins were obtained with N-chloroamides such as ClCH2CONHCl, C2H5OCONHCl, CF3CONHCl. Their addition to enol ethers at −70 °C led to the synthesis of α-amido acetals or ketals (aldehydes or ketones) and to an α-amido glycoside in good yields.
Nucleosides. 118. Total syntheses of pentopyranine B and D. Cytosine nucleosides elaborated by Streptomyces griseochromogenes
Authors: Watanabe Kyoichi A. , Matsuda Akira , Itoh Tsuneo
Published: May 2006

Pentopyranine B and D, pentopyranosylcytosine nucleosides elaborated by Streptomyces griseochromogenes, have been synthesized from the common intermediate, methyl 4-O-benzoyl-3-deoxy-3-iodo-β-D-xylopyranoside (1). The synthetic products, l-(2,3-dideoxy-β-D-glyceropentopyranosyl)cytosine (18) and l-(3-deoxy-β-D-erythropentopyranosyl)cytosine (7) were identical with the natural products, pentopyranine B and D, respectively.
Apparent stability constants of proton and metal ion complexes of glycine, iminodiacetic acid, nitrilotriacetic acid, and triethylenetetramine in aqueous methanol
Authors: Field Terrence B. , McBryde W. A. E.
Published: May 2006

Conditional formation constants were determined at 25 °C and with a background electrolyte of 0.1 mol dm−3 NaNO3 for the proton, nickel(II), copper(II), and zinc(II) complexes of glycine, iminodiacetic acid, and nitrilotriacetic acid in 0, 20, 50, 80, and 95 volume percent methanol mixed with water. Similar measurements were made for triethylenetetramine in all but 95% methanol, and the formation constants so determined were used to determine KMNTA by a competitive method.The variation of all constants with solvent composition was examined from the point of view that complex formation is accompanied by solvent displacement. Accordingly it should be possible to correlate the observations by means of an over-all formation constant, valid for any solvent concentration. It was concluded that for two solvents as similar as water and methanol, both of which appear to be involved in solvation or desolvation in the reaction, the correlations sought could not very precisely fix the amounts of solvents displaced or taken up. The goodness of fit to the attempted correlations suggests that they would be useful for interpolations to solvent compositions other than those studied.
Abinitio molecular orbital calculations for SF4, SOF2, and SO2F2
Authors: Baird N. Colin , Taylor Kathleen F.
Published: May 2006

Abinitio molecular orbital calculations are reported for SF4 (both C2v and C4v symmetries), SOF2, and SO2F2. Geometry searches were conducted using the STO-3G* basis set; the energies were recalculated at the predicted equilibrium structures also using STO-3G and 44-31G, and the latter basis set with the addition of five real d Gaussian orbitals on the sulfur atom. The predicted geometries agree well with experiment, although S=O bonds are consistently predicted too long by ∼0.03 Å, and the variation in S—F bond lengths among different environments is underestimated. The energy stabilization associated with the addition of d orbitals is generally consistent with our previous calculations, i.e. it is a constant amount per bond in hypervalent sulfur compounds in extended basis calculations. Replacement of F by OH is predicted to be more exothermic in SO2F2 than in SOF2, and the relevance of this prediction to estimated heats of formation for SOF2 and SO(OH)2 is discussed.
Synthesis of inorganic multilayers on chromatographic supports
Authors: Wickramanayake Palitha P. , Chatt Amares , Aue Walter A.
Published: May 2006

Multilayers of various metal oxides have been produced on typical chromatographic supports such as diatomaceous earth and silica gel. The layer thickness was characterized for phases based on iron and chromium. These data, as well as chromatographic evidence obtained on chromium oxide, suggest that the layers are homogeneous. Similar, but less well characterized layers of aluminum and titanium oxides have been obtained.
Thermodynamics of acid dissociation of aqueous bisulfite ion: ΔH0, ΔCP0, and ΔV0 at 298.15 K
Authors: Allred Gregory C. , Larson John W. , Hepler Loren G.
Published: May 2006

Calorimetric measurements of the enthalpy of protonation of sulfite ion and the enthalpy of proton transfer from bisulfite ion to carbonate ion have led to two independent values for the standard enthalpy of the acid dissociation reaction represented by HSO3−(aq) = H+(aq) + SO32− (aq). Further calorimetric and density measurements have led to apparent and partial molar heat capacities and volumes for sulfite and bisulfite ions. Results of all of these measurements are summarized by ΔH0 = −3.59 ± 0.10 kJ mol−1, ΔCP0 = −262 ± 7 J K−1 mol−1, and ΔV0 = −28.7 ± 1.0cm3 mol−1 for the acid dissociation of HSO3− (aq) at 298.15 K. These results are used for thermodynamic calculations of the temperature and pressure dependence of the equilibrium constant for acid dissociation of HSO3− (aq).
1,7-Dithia and 1-oxa-7-thiaspiro[5.5]undecanes. Excellent systems for the study of stereoelectronic effects (anomeric and exo-anomeric effects) in the monothio and the dithioacetal functions
Authors: Deslongchamps Pierre , Rowan Daryl D. , Pothier Normand , Saunders John K.
Published: May 2006

1,7-Dithiaspiro[5.5]undecane (2), 1-oxa-7-thiaspiro[5.5]undecane (4), and the tricyclic systems 3, 5, and 6 have been prepared by the acid cyclization of the appropriate ketone dithiol or hydroxy ketone thiol precursors.The configuration and the conformation of the products obtained was determined by 13C nmr analysis and equilibration studies. The experimental results can be rationalized by taking into account the anomeric and the exo-anomeric effects and the usual steric interactions.
Determination of absolute transfer free energies of hydroxyl ion from water to aqueous 2-methoxy ethanol
Authors: Bhattacharya Abhijit , Das Asim K. , Kundu Kiron K.
Published: May 2006

Absolute standard free energies of transfer ΔGt0 of OH− from water to aqueous mixtures of 2-methoxy ethanol (ME) have been evaluated at 298.15 K by combining the apparent transfer free energies of the lyate ion that were obtained from the standard emf's of the double cell:[Formula: see text]and that from the autoionization constants of these mixed solvents determined by use of the cell comprising H2– and Ag–AgCl electrodes. The required ΔGt0 values of K+ and H+ were determined earlier using the well-known tetraphenyl arsonium tetraphenyl boride (TATB) reference electrolyte method. These values and their non-Born type contributions in particular, are found to be increasingly positive in water-rich compositions, indicating that the relative stabilization of OH− and the acidity of the mixed solvents decrease with increasing cosolvent composition. These, when compared with those in aqueous mixtures of ethylene glycol and 1,2-dimethoxy ethane, are found to lie intermediate between the latter solvent systems conforming to what is expected from the structural and electronic features of the cosolvents.
Préparation, réduction chimique et électrochimique d'α-nitrostyrylcétones — synthèse d'hétérocycles azotés
Authors: Marçot Bernard , Rabaron Alain , Viel Claude , Bellec Christian , Deswarte Stéphane , Maitte Pierre
Published: May 2006

Nitration of styryl ketones with nitrogen peroxide leads to the corresponding α-nitroethylenic ketones in good yield. However, the presence of methoxy groups involves a nitration on the aromatic nucleus.LiAlH4 reduction of α-nitrostyrylketones yields the corresponding racemic erythro- and threo-aminoalcohols; after acylation and cyclisation a dihydro-quinoline or a 2-oxazoline is obtained.Electrochemical reduction of these nitrostyryl-ketones selectively provides the α-ketoximes, which are themselves reduced electrolytically to α-aminoketones. These latter compounds dimerise in neutral medium to dihydro-2,5-pyrazines which aromatise to the corresponding pyrazines. In acid medium an α-ketol is obtained.A mechanism for the reduction is proposed implicating an enaminol intermediate.
Metal derivatives of azoles. Part VII. Gold(I) derivatives of pyrazoles
Authors: Banditelli Guido , Bandini Anna Laura , Minghetti Giovanni , Bonati Flavio
Published: May 2006

Ligand displacement by a pyrazole on Me2SAuCl afforded LnAUAuCl (n = 1 or 2, and L = 3,5-Me2pzH, 3(5)-Me-5(3)-PhpzH; n = 1, and L = pyrazole or 3,5-Me2-4-(p-tolylazo)pyrazole), while Ph3PAuCl, silver fluoborate, and ligand gave both [(Ph3P)Au(3,5-Me2pzH)]BF4 and [(Ph3PAu)2(μ-3,5-Me2pz-N,N′)]BF4. With iodine the last compound underwent reaction on the bridging μ-azolato ligand yielding [(Ph3PAu)2(μ-3,5-Me2-4-Ipz-N,N′)]BF4. The possible structures are discussed on the basis of spectral data (ir; 1H, 13C, and 3lP nmr).
Influence des groupes tert-butyle, triméthylsilyle et triméthylgermyle sur la stéréochimie de réactions d'addition en série cyclohexénique. IV. Réduction, par des hydrures complexes, de cyclohexanones β ou γ substituées
Authors: Richer Jean-Claude , Poirier Marc-André , Maroni Yvette , Manuel Georges
Published: May 2006

The synthesis of 5,5-dimethyl-2-tert-butyl-(1a), -2-triméthylsilyl-(1b), and -2-trimethylgermyl-(1c) cyclohexanones is described as well as those of 2,2-dimethyl-5-tert-butyl-(2a), -5-trimethylsilyl-(2b), and -5-trimethylgermyl-(2c) cyclohexanones. The stereochemistry of the reduction of these ketones by different hydrides is examined. This latter reaction competes with the cleavage reaction of the C—M bond in the case of β-substituted ketones (M = Si, Ge).
Crystallographic studies and physico-chemical properties of π-electron compounds. Part I. Crystal and molecular structure of 6-N,N-diacetylaminochrysene (DAAC)
Authors: Więckowski Tadeusz , Krygowski Tadeusz M.
Published: May 2006

The molecules of 6-N,N-diacetylaminochrysene, C22HI7NO2, crystallize in orthorhombic space group Pbca with a = 15.120(1) Å,b = 7.8706(9) Å, and c = 28.504(2) Å, Z = 8, V = 3392.3(6) Å3, Dx = 1.28 g cm−1. The structure was essentially solved by direct phase determination with assistance of Fourier and difference Fourier maps and finally was refined to R = 0.050 for 2320 reflections. The DAA-group is almost perpendicular to the plane of chrysene moiety. The simple harmonic oscillator model for calculating the stabilization energy of π-electron systems by means of negative value of energy deformation necessary to transform the real molecule (or its fragments) to its Kekulé structure is presented. It shows high delocalization of π-electrons in both independent π-electron systems of DAAC molecule: the DAA-group and the chrysene moiety.
The electrophoretic mobility of large colloidal particles
Authors: O'Brien Richard Wyndham , Hunter Robert John
Published: May 2006

Analytical approximation formulae linking ζ potential and electrophoretic mobility have been derived for a variety of limiting conditions. In this paper we present a simplified derivation of an equation first established by Dukhin and his collaborators for a large spherical particle with a thin double layer. Although potentially a very useful expression it has been little used to date, partly because of the complicated nature of Dukhin's derivation and partly because of the lack of a reliable method of testing its validity. The expression compares very favourably with the computer calculations of O'Brien and White, provided κa is sufficiently large.
Perturbation theory, the mean spherical approximation, and the electrical double layer
Authors: Henderson Douglas , Blum Lesser
Published: May 2006

Simple arguments, based on perturbation theory, are used to derive expressions for the energy of a bulk ionic fluid and the potential difference in an electric double layer. These expressions are identical to those obtained from the much more elaborate mean spherical approximation.
The application of the generalized mean spherical approximation to the theory of the diffuse double layer
Authors: Henderson Douglas , Blum Lesser
Published: May 2006

A system of charged hard spheres near a uniformly charged hard wall is considered. An approximation is established by postulating a closure for the Ornstein–Zernike (OZ) equations for this system. In this paper these OZ equations are solved for a closure in which the direct correlation functions are equal to the wall-ion potentials plus a sum of exponential functions. As a specific application of this solution we use one exponential and adjust two parameters to satisfy an approximate contact value theorem and give the same diffuse layer potential as is obtained using the hypernetted chain (HNC) approximation. Once this fit is made, the density, charge, and potential profiles can be easily calculated. The agreement with the corresponding HNC results is good. Comparison with the simpler Poisson–Boltzmann theory of Gouy and Chapman (GC) shows the GC theory to be better than one would expect. However, appreciable differences between the present results and the GC results for the diffuse layer potential are found.
The total synthesis of the cybrodins
Authors: Ayer William A. , McCaskill Robert H.
Published: May 2006

The total syntheses of cybrodol (1), isocybrodol (2), cybrodal (3), cybrodic acid (4), and trisnorcybrodolide (5), starting from 2-bromomesitylene (6) are described. The route involves oxidation of the 5-methyl group of 6 by means of chromyl acetate, addition of the β-hydroxyethyl chain by aryllithiation and reaction with ethylene oxide, and addition of the fifth carbon substituent by aryllithiation and treatment with ethyl chloroformate to give the key intermediate, methyl 3-(2-hydroxyethyl)-6-methoxymethyl-2,4-dimethylbenzoate (18d). The latter was transformed into trisnorcybrodolide (5), and further elaborated via the corresponding aldehyde 21 into the remaining cybrodins.
Gas phase heats of formation of alkyl immonium ions
Authors: Lossing F. P. , Lam Yai-Tai , Maccoll Allan
Published: May 2006

Using an energy-resolved electron beam, the gas-phase heats of formation of [CH2NH2]+, [CH3CHNH2]+, [CH3NHCH2]+, [(CH3)2CNH2]+, [(CH3)2NCH2]+, [CH3CHNHCH3]+, [CH3CH2NHCH2]+, and [CH3CH2CHNH2]+ ions have been measured from their appearance energies in ionic dissociations. All of these ions can have a quaternary immonium structure as one of the canonical forms and are consequently more stable than other isomers. Introduction of the —NH2 group into a CH3+ ion brings about a decrease of over 4 eV in the heterolytic bond dissociation energy D(R+—H−), with slightly larger decreases for —NHR and —NR2 groups.
Kinetics of the oxidation of ethane by nitric oxide over manganese(III) oxide
Authors: Ross R. A. , Fairbridge C.
Published: May 2006

The catalytic reaction between ethane and nitric oxide over manganese(III) oxide has been investigated in a continuous flow system from 673 to 573 K at atmospheric pressure. The products of catalysis were nitrogen, carbon dioxide, nitrous oxide, and water. The rate of nitrous oxide formation was constant over this temperature region, while the apparent activation energies for nitrogen and carbon dioxide formation increased from 32 ± 4 and 22 ± 4 kJ mol−1, respectively, at 573 to 613 K, to 78 ± 4 and 63 ± 4 kJ mol−1 between 613 and 673 K. The kinetic results were best described by the rate equation:[Formula: see text]The surface mechanism appears to be complex and has been interpreted by a scheme involving interaction of the reactants in an absorbed layer. Both nitric oxide and ethane are believed to be involved further in subsequent steps. Infrared evidence indicates the possibility of a surface nitrate intermediate consistent with the mechanistic proposal. Scanning electron microscopy and X-ray powder diffraction techniques were used to assess the catalyst structure.
Dynamic aspects of the behavior of aromatic ketone triplets in anionic micelles. A laser flash photolysis study
Authors: Scaiano J. C. , Selwyn J. C.
Published: May 2006

The behavior of several aromatic ketone triplets has been examined in sodium dodecyl sulfate micelles using laser flash photolysis techniques. The molecules examined, acetophenone, propiophenone, isobutyrophenone, p-methoxyacetophenone, benzophenone, and xanthone are mainly resident in the micellar phase. Phenyl alkyl ketones show considerable self-quenching, a process that is rather sensitive to steric factors. All the molecules examined seem to reside near the Stern layer. Typical rate constants for triplet state entry into the micelle are around 1.8 × 1010 M−1 s−1.
Complexes of dodecamethylcyclohexaphosphazene with palladium(II) chloride and platinum(II) chloride. Crystal and molecular structure of cis-dichloro[η2-dodecamethylcyclohexaphosphazene (N,N′)] palladium(II) sesquihydrate
Authors: Paddock Norman L. , Ranganathan T. N. , Rettig Steven J. , Sharma Rajendra D. , Trotter James
Published: May 2006

Dodecamethylcyclohexaphosphazene N6P6Me12, 1, forms 1:1 complexes with palladium(II) chloride, 2, and platinum(II) chloride, 3. Their 31P, 1H, and 13C nmr spectra show them to be rigid molecules in solution, with an approximate plane of symmetry. Crystals of 2 are orthorhombic, a = 17.4030(3), b = 15.4897(5), c = 10.7417(2) Å, Z = 4, space group P21212. The structure was determined from diffractometer X-ray data and refined by full-matrix least-squares methods to R = 0.031 for 3545 reflections with I ≥ 3σ(I). The metal atom has square planar coordination, and forms 6- and 10-membered chelate rings with the phosphazene ligand. The mean P—N bond length is 1.609 Å; the variation of bond lengths within the ring is consistent with model calculations of changes in bond order arising from the localization of bonding electrons.
Theoretical study of regioselectivity in nucleophilic addition to unsymmetrical cyclic anhydrides. Intrinsic reactivity and influence of the cation
Authors: Kayser Margaret M. , Eisenstein Odile
Published: May 2006

Ab initio molecular orbital calculations have been carried out for the series of succinic, maleic, and phthalic anhydrides unsymmetrically substituted with CH3, CH3O, Cl, F, and CN. The size of the LUMO coefficient on the carbon atom of the carbonyl group provides a reliable guide to the relative reactivities of the two carbonyl functions. The predictions based on the intrinsic reactivities are in good agreement with the regioselectivities observed in metal hydride reductions of succinic anhydrides. In the series of maleic and phthalic anhydrides the above considerations are applicable only to methyl derivatives. The compounds substituted with lone pairs-bearing groups (OCH3, Cl, F) form stable chelates with the cations present in the reaction media. Since the chelated carbonyl group is strongly activated toward the nucleophilic addition, the "bridging" effect is the dominant factor controlling orientation of hydride addition. The optimum position for the nucleophilic attack in cyclic anhydrides was calculated. The results confirm the generality of the nonperpendicular, restricted path of nucleophilic attack on the carbonyl group in succinic anhydride.
The total synthesis of (±)-Nα-methyl-Nβ-acetylphlegmarine
Authors: Leniewski Andrzej , Szychowski Jerzy , MacLean David B.
Published: May 2006

(±)-Nα-Methyl-Nβ-acetylphlegmarine has been synthesized in a manner that defines the relative configuration at four of the five chiral centres of the molecule. Five isomers of the title compound have also been prepared and characterized.
The effect of methanol on the stability of clathrate hydrates
Authors: Davidson D. W. , Gough S. R. , Ripmeester J. A. , Nakayama Haruo
Published: May 2006

From the effect of added methanol on the decomposition temperatures of the clathrate hydrates of ethylene oxide and tetrahydrofuran, it was recently reported that methanol can be readily enclathrated in hydrates of both structure I and II. Dielectric and nmr studies of these two hydrates prepared in the presence of methanol do not support this conclusion. It is shown thermodynamically that the original measurements may be interpreted without the need for incorporation of methanol in the hydrates formed.
Resolution of Raman spectra of aqueous sulfuric acid mixtures using principal factor analysis
Authors: Cox Robin A. , Haldna Ülo L. , Idler K. Loralee , Yates Keith
Published: May 2006

Principal factor analysis has been applied to Raman spectra of 26 sulfuric acid/water mixtures covering the 0–100% H2SO4 concentration range. The analysis greatly facilitates the identification of peaks due to different species. The results show that SO42− ions and "free" HSO4− ions do not co-exist with undissociated H2SO4 molecules in solution and that two water molecules rather than one are required for the first ionization of H2SO4. A species with the composition H2SO4•2H2O, assigned a hydrated ion pair structure, reaches maximum concentration at the same medium composition at which SO42−, free HSO4−, and H2SO4 are at concentration minima, about 75% w/w. The only species apparent in the more concentrated solutions are the ion pair and undissociated H2SO4, which could be taken to mean that H2SO4 is a weaker acid than H3O+, but a stronger one than H3O+•H2O (or H5O2+, if this entity has a real existence). Separate peaks due to the postulated H3O+•H2SO4 (or H5SO5+) were not observed.
Gas phase basicities of fluorocarbonyl compounds. An ion cyclotron resonance investigation of the effects of fluorine and trifluoromethyl substituents on hydroxy carbonium ion stabilities
Authors: Doiron C. E. , McMahon T. B.
Published: May 2006

Gas phase proton affinities for a number of fluoro- and trifluoromethyl-substituted carbonyl compounds have been obtained using a combination of proton transfer equilibria and bracketing experiments. Absolute and relative substituent effects for F and CF3 on carbonyl basicities are determined and discussed in terms of inductive, resonance, polarization, and hydrogen bonding interactions. The data are used to interpolate basicities for HCOF and CF3CHO and are compared to theoretical ab initio calculations.
An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K1
Authors: Depew M. Catherine , Adeleke Babatunde B. , Wan Jeffrey K. S.
Published: May 2006

The photooxidation of vitamin C by pyruvic acid and its derivatives, duroquinone, and vitamin K1, is systematically studied by the combined esr and time-resolved CIDEP technique. Because of the unique property of the triplet pyruvic acid which is different from that of the duroquinone triplet, the choice of these model systems allowed the CIDEP observations of the initial polarization of the ascorbate radical anion and its counter primary radical in either the enhanced absorptive or the emissive mode. The results demonstrate the efficient photooxidation of vitamin C by the triplet vitamin K1 and that the latter triplet possesses similar properties as the triplet quinones. In the photooxidation system involving vitamin C and pyruvic acid, the adjustment of the pH of the aqueous solution afforded an opportunity to observe the photochemical reaction between two anions, the pyruvate anion and the ascorbate anion. Arguments were made in favor of an electron transfer mechanism for the oxidation of vitamin C by triplet vitamin K1 but against the electron transfer mechanism for the oxidation of vitamin C by triplet pyruvate anion. T1 values of the primary radicals estimated from their CIDEP transient responses at low microwave power are reported and it was suggested that the hydrogen-bonding capacity of the ascorbate radical anion in water does not contribute significantly to the relative difference of T1's between itself and the counter pyruvic ketyl radical.
Conditions for excited-state Raman and absorption processes during optical pumping
Authors: Halperin B. , Koningstein J. A.
Published: May 2006

A theoretical analysis is presented for conditions of optical pumping of an electronic excited state and the subsequent induction of Raman scattering thereof, using the radiation of a tunable laser with a specific λ for pumping and Raman probing.The analysis shows that the number of excited states created by the optical pump can be estimated as a function of the photon flux from the (non-linear) behaviour of the transmission of the sample at the selected laser wavelength. It is shown that such transmission studies are a prerequisite before attempts are made to record any excited level Raman spectrum.
The dependence of acid dissociation constants in water on temperature as expressed by the Gurney equation
Authors: Blandamer Michael J. , Burgess John , Duce Philip P. , Robertson Ross E. , Scott John W. M.
Published: May 2006

The dependence on temperature of the acid dissociation constants in water for a range of carboxylic acids has been fitted to the Gurney equation using a modified Gauss–Newton method. The equation fits the data reasonably well and identifies the dependence on temperature of the electrical and non-electrical contributions to ln K.
Hydrogen–deuterium exchange of heteroaromatics in neutral D2O at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

not available
Synthesis of phthalideisoquinolines from 3-halophthamdes and 3,4-dihydroisoquinolinium salts
Authors: Slemon Clarke E. , Hellwig Louise C. , Ruder Jean-Pierre , Hoskins Eric W. , MacLean David B.
Published: May 2006

Phthalideisoquinoline alkaloids have been synthesized by coupling appropriately substituted 3-halophthalides and 2-methyl-3,4-dihydroisoquinolinium salts in the presence of Zn(Cu) couple or metallic Zn. Both erythro and threo isomers are formed in the reaction. The nmr spectra of the (±)-erythro- and (±)-threo-isocordrastines have been reinvestigated. The results, which differ from those previously reported, lead to a different conclusion regarding the conformation of the molecules.
Ultrasonic dispersion studies in 3-methylcyclohexanone
Authors: Reddy Budideti Ananda , Rao Nagineni Prabhakara
Published: May 2006

Using a variable path interferometer, ultrasonic velocity dispersion in 3-methylcyclohexanone was studied in the temperature range 323.15 K to 363.15 K and in the frequency range 0.5 MHz to 5.0 MHz. The relaxation parameters were evaluated from the experimental data. These values were utilised to evaluate the energy parameters; the differences in the enthalpy (ΔH0), the free energy (ΔG0), and the entropy (ΔS0) are 2.79 kcal/mol, 0.88 kcal/mol, and 5.9 cal/mol K, respectively. The enthalpy (ΔHr) for the backward reaction was 7.63 kcal/mol.
A thermal [1,3] sigmatropic rearrangement: thermolysis of 2,2-bis(ethylthio)-3,3-dimethyl-4-pentenal
Authors: Bates Gordon S. , Ramaswamy S.
Published: May 2006

2,2-Bis(ethylthio)-3,3-dimethyl-4-pentenal was found to quantitatively isomerize to 2,2-bis(ethylthio)-5-methyl-4-hexenal over a wide temperature range (130–170 °C). This rearrangement can formally be regarded as a [1,3] sigmatropic shift. The reaction, which could be conveniently monitored by 1Hmr spectroscopy, was found to obey first order kinetics. The substantial positive entropy of activation (+ 61.5 J deg−1 mol−1) for the reaction and the negligible solvent effect (decane vs. DMF) are both consistent with a proposed diradical pathway.
Electron paramagnetic resonance characterization and conformation of daunorubicin semiquinone intermediate implicated in anthracycline metabolism, cardiotoxicity, and anticancer action
Authors: Lown J. William , Chen Hsiao-Hsiung
Published: May 2006

The antitumor antibiotic daunorubicin, upon reduction in aqueous solution, gives a transient resolved epr spectrum of linewidth 17.0 G and g value of 2.0024. This is ascribed to the semiquinone previously tentatively assigned in the unresolved epr spectrum obtained by microsomal activation of the antibiotic. By reference to the epr spectrum of quinizarin semiquinone in aqueous solution the individual proton hyperfine splitting constants in both spectra were tentatively assigned by computer simulation. LCAO–MO calculations of one-electron wave function spin densities in both species gave good agreement between calculated and observed hfs for values of the parameters βCO/βCC = 1.8, δα = 1.4, allowing definite assignment of the aromatic protons. By considering the angular dependence of the ring A benzylic proton hfs it was possible to discriminate between two alternative half-chair conformations of daunorubicin semiquinone. The preferred conformation of the intermediate is tentatively assigned as that which places both 7 and 9 oxygen functions equatorial and the C-9 acetyl group axial.
A theoretical study of the CSH4 and CPH5 hypersurfaces. Geometries, tautomerization, and dissociation of sulfonium and phosphonium ylides
Authors: Mitchell David John , Wolfe Saul , Schlegel H. Bernhard
Published: May 2006

Calculations have been performed at four basis set levels (STO-3G, STO-3G*, 4-31G, 4-31G*) on the model ylides methylenesulfurane (CH2SH2) and methylenephosphorane (CH2PH3), their stable tautomers (CH3SH and CH3PH2), their dissociation products (SH2, PH3 and CH2), and the protonated species CH3SH2+ and CH3PH3+. At each basis set level all geometries have been optimized fully, using the FORCE method. The conformational behaviour of the ylides as a function of C—X bond-stretching, C—X torsion, and CH2 (or SH2) bending has been examined in some detail. The experimental properties (i.e., geometries, relative stabilities, proton affinities, rotation–inversion behaviour) of sulfonium and phosphonium ylides are reproduced well by the model calculations with the 4-31G* basis set, which contains d-type functions on both carbon and sulfur (or phosphorus). All other basis sets are deficient in different ways and for different reasons, which are discussed in detail. The principal result of this work is the conclusion that d-type functions are essential for a proper description of the hypervalent species CH2SH2 and CH2PH3, but not for the normal-valent species SH2, PH3, CH3SH, and CH3PH2. The conclusion concerning hypervalent species reverses our earlier views. The role of the d-type functions is to concentrate charge into the C—X region of the ylides, and thus to stabilize the system. Evidence for this effect has been obtained from quantitative perturbational molecular orbital (PMO) analyses of interactions associated with the carbon lone pair, as well as comparisons of electron density plots with and without the d AO's. A second conclusion is that the imposition of various geometrical constraints such as assumed C—X, C—H, or X—H bond lengths, and HCH or XHn bond angles, as was necessary for computational reasons in all previous work on such systems, has major and previously unrecognized consequences. For example, the assumption that the CH2 moiety is planar in CH2SH2 leads to very similar geometries with and without d AO's, although only in the latter case does such a geometry at carbon correspond to the true energy minimum; in the absence of d AO's the C—S bond length is maintained by a symmetry-enforced barrier to dissociation. These and other consequences of geometrical constraints at carbon, sulfur, or phosphorus are analyzed in detail.
Formation and characterization of transitory platinum–ammonia complex ions using pulse radiolysis
Authors: Khan Hasan M. , Waltz William L. , Woods Robert J. , Lilie Jochen
Published: May 2006

The reactions of tetraammineplatinum(II) complex ion with the hydrated electron and hydrogen atom have been investigated in aqueous media using the technique of pulse radiolysis coupled with absorption and conductivity detection. Analysis has also been carried on pulse-irradiated solutions for the formation of free ammonia and for changes in concentration of Pt(II). The hydrated electron and hydrogen atom react with the complex at near diffusion-controlled rates, with the respective rate constant being 1.9 ± 0.1 × 1010 M−1 s−1 and 2.8 ± 0.3 × 1010 M−1 s−1. The nascent products of these reactions are shown to be different transitory species. For the electron reaction, the initial product is Pt(NH3)4+ in which the metal center is formally Pt(I). In acidic media, there is a subsequent and rapid release of two ammonia ligands, with only the second step being measurable (k = 4.2 ± 1.7 × 104 s−1). In the reaction of H atom, the results support the occurrence of an addition process, giving rise to a hydrido type product. This species undergoes a first-order reaction (k = 2.2 ± 0.6 × 104 s−1); however the process is not associated with a change in conductivity, and thus it is not one involving loss of ammonia. Subsequent to this process, the loss of one ammonia ligand is observed, with k = 2.0 ± 0.6 × 103 s−1. The natures of these transients and the long term behavior of these systems are discussed.
Application of the Hammett equation in the esterification of substituted benzoic acids, catalyzed by AlPO4 in the gas phase
Authors: Sinisterra J. V. , Marinas J. M. , Llobera A.
Published: May 2006

The Hammett equation has for the first time been applied to the esterification in the gas phase of m-MeO, p-MeO, m-Me, p-Me, H, m-NO2, m-Cl, and m-Br benzoic acids, catalyzed by AlPO4 of the F type. It is shown that the Hammett equation could be applied to the adsorption equilibrium constant, KA, and to the apparent kinetic constant, [Formula: see text] The KA and [Formula: see text] values used in this paper have been taken from a study by the same authors. The m-NO2 benzoic acid is in disagreement with the general behavior of the other acids in the application of the Hammett equation to the adsorption process. The p-MeO benzoic acid is in disagreement with the behavior of the acids in the application of the equation to the surface reaction. In these cases, the ρ values were negative. It can be deduced that a positive charge is generated in the adsorption process and in the surface reaction. The AAc2 mechanism is discussed according to the values of ρ, and a more detailed mechanism is proposed. The separation of the enthalpic and entropic contributions to the substituent effect is carried out. [Formula: see text] and[Formula: see text] are nearly 50% in the adsorption process. In the surface reaction, the entropie contribution is greater (72.5%) than the enthalpic (27.5%).