bluuebunny/crossref_metadata_2025 huggingface dataset:
Some regularities in the behavior of salting constants for polar molecules in aqueous electrolyte solutions
Authors: Treiner Claude
Published: May 2006

The salting effect of polar molecules in aqueous electrolyte solutions has been examined in the case of 22 solute molecules. It is observed that the salting constants of polar and nonpolar molecules of the same size in a given salt solution are close to each other and are generally greater than a critical diameter of the solute molecules. Using the available data from the literature, the salting constants ks of neutral polar molecules by univalent cation electrolytes has been classified in three groups: (1) Organic molecules and inorganic salts: for a given electrolyte ks is a monotonous function of the solute size and the nonelectrolyte dipole moment plays no role. (2) Organic molecules and organic salts: again a smooth variation of ks with size is observed whatever the polar mono-functional molecule. (3) Inorganic molecules and inorganic salts: a correlation is exhibited between ks and the solute dipole moment. These observations may be interpreted by assuming that both ends of a dipole are to be available to solute + solvent interactions for a dipole effect to be observed.Furthermore it is shown that in case 1, the scaled-particle theory with incorporation of a preferential solvation phenomenon may be useful for predicting salting out effects of polar molecules in inorganic salt solutions. In case 2 an approach based on microscopic surface tension and molecular surface area is also considered.
Nuclear magnetic resonance studies of proton exchange in imidate esters and amides in strong acid
Authors: Perrin Charles L. , Johnston Eric R.
Published: May 2006

Saturation-transfer or lineshape measurements of kinetics of proton exchange show that HZ of ethyl acetimidate in 46% H2SO4 or ethyl N-methylformimidate in 40% H2SO4 exchanges faster than HE, and HE of protonated 2-iminotetrahydrofuran exchanges faster than HZ, as expected on the basis of the stabilities of the stereoisomeric imidate esters. In contrast, amide exchange is too fast to measure in aqueous H2SO4, but can be measured in 100% H2SO4, where HE and HZ exchange at equal rates. Also, there is intramolecular exchange occurring at this same rate. These results are interpreted as evidence for exchange in amides via the N-protonated intermediate, whose lifetime in H2SO4 is sufficiently long to permit the protons on nitrogen to become equivalent. By comparing OH exchange with NH exchange, it is concluded that N-protonation is the rate-limiting step. Even though this is a thermodynamically favorable proton transfer in H2SO4, its rate constant is significantly lower than the diffusion-controlled limit. The contrasts between imidate esters and amides and between dilute solutions and H2SO4 are discussed.
Nucleic acid related compounds. 34. Non-aqueous diazotization with tert-butyl nitrite. Introduction of fluorine, chlorine, and bromine at C-2 of purine nucleosides
Authors: Robins Morris J. , Uznański Bogdan
Published: May 2006

Treatment of 2,6-diamino-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purine (1c) with tert-butyl nitrite (TBN) in 60% anhydrous hydrogen fluoride/pyridine at −20 °C gave 2-fluoroadenosine triacetate (2) in 48% yield. Analogous treatment of the acetylated 2-amino-6-fluoropurine nucleoside (1a) gave the 2,6-difluoro compound (3a) in 63% yield. Anhydrous ammonia in 1,2-dimethoxy-ethane converted 3a → 2 without ammonolysis of the acetate groups. The overall conversion of 1a → 3a → 2 without isolation of 3a proceeded in 80% yield. Similar diazotization of the 2-amino-6-chloro nucleoside (1b) in HF/pyridine gave the 2-fluoro-6-chloro analogue (3b) in 89% yield. Treatment of 1b with TBN and pyridine hydrochloride in dichloromethane (77%) or TBN and antimony trichloride in 1,2-dichloroethane (84%) gave the 2,6-dichloropurine nucleoside (4b). The latter conditions converted 1a to the 2-chloro-6-fluoro product (4a) in 77% yield. Conversions of 1a and 1b to the 2-bromo-6-fluoro (5a, 67%) and 2-bromo-6-chloro (5b, 78%) analogues were effected using TBN and antimony tribromide in dibromomethane.
The synthesis of the cyathins. Part 1. Synthesis of a tricyclic intermediate
Authors: Ayer William A. , Ward Dale E. , Browne Lois M. , Delbaere Louis T. J. , Hoyano Yumiko
Published: May 2006

The tricyclic diketoalcohol 5(3-phenylthio-6,9,10-trimethyl-12-hydroxytricyclo[7.4.0.02,6]trideca-2,10-diene-4,8-dione), a potential intermediate in the synthesis of the cyathins, has been prepared starting from 2,5-dimethyl-p-benzoquinone. The structure and stereochemistry of 5 was proven by an X-ray crystallographic study of the corresponding p-bromobenzoate (6). Attempts to isomerize the cis BC ring junction in 5 to give the corresponding trans compound were unsuccessful. Removal of the thiophenyl group from 5 gave compound 18a which on base-catalyzed isomerization provided an equilibrium mixture of the cis and trans compounds.
The oxidation of phenol and chlorophenols by alkaline permanganate
Authors: Lee Donald G. , Sebastián Carlos F.
Published: May 2006

A kinetic study has been made of the oxidation of phenol and seven chlorophenols by alkaline permanganate. The initial reaction, which results in the formation of manganate(VI) ion, is first order with respect to permanganate ion, independent of the concentration of hydroxide ion, and of variable order with respect to phenol. At low phenol concentrations the order is unity, but at high concentrations it becomes zero. These observations can be accounted for quantitatively by the following mechanism:[Formula: see text]
Preparation and reactions of 4b-acetoxy-4b,9b-dihydroindeno[2,1-a]indene-5,10-dione
Authors: Wawzonek Stanley
Published: May 2006

4b-Acetoxy-4b,9b-dihydroindeno[2,1-a]indene-5,10-dione prepared by treating 4b,9b-dihydroindeno[2,1-a]indene-5,10-dione with lead tetraacetate was hydrolyzed to the alcohol, 4b-hydroxy-4b,9b-dihydroindeno[2,1-a]indene-5,10-dione with hydrochloric acid and converted to 4b-methoxy-4b,9b-dihydroindeno[2,1-a]indene-5,10-dione with sodium hydroxide in methanol. The alcohol was stable to base and could not be converted to dibenzo[a,c]cyclooctadiene-5,6,11-trione. Attempts to form the epoxydiketone from the acetate with sodium hydroxide and hydrogen peroxide gave benzil dicarboxylic acid, 11-keto[1,2-c]isocoumarin and 4b-methoxy-4b,9b-dihydroindeno[2,1-a]indene-5,10-dione.
The 1,3-dimethoxytrimethylene bridge as two latent carboxyl groups: synthesis of cis-isoaposantenic and cis-apocamphoric acids
Authors: Camps Pelayo , Jaime Carlos
Published: May 2006

The syntheses of cis-cyclopentane-1,3-dicarboxylic acid, cis-cyclohexane-1,3-dicarboxylic acid, cis-isoaposantenic acid, and cis-apocamphoric acid are described. The key step of each synthesis is the bromine oxidation of an appropriate bicyclic compound in which a 1,3-dimethoxytrimethylene bridge is converted into two cis-carboxyl groups.
Action des hydroxyurées sur les maléate et fumarate de méthyle. Obtention des carbométhoxy-5 oxa-6 dihydrouraciles; transposition en carbométhoxyméthylène-5 hydantoïnes
Authors: Bennouna Chakib , Petrus Françoise , Verducci Jean , Hauw Christian , Gaultier Jacques
Published: May 2006

We describe in this paper the Michael-type addition of hydroxyureas with methyl maleate and fumarate. The cyclization of the ureidoxyester intermediates obtained leads to the isolation of 5-carbomethoxy 6-oxadihydrouracils; their structure is proved by X-ray analysis. These relatively unstable compounds undergo transposition under basic conditions and give 5-carbomethoxyhydantoins.
Phosphine–borane derivatives. 10. Vibrational spectra of the dimethylphosphine adducts of boron trihalides
Authors: Drake John E. , Hencher J. Lawrence , Khasrou Layla N.
Published: May 2006

The infrared (200–4000 cm−1) and Raman (0–3100 cm−1) spectra of (CH3)2PHBX3, (CH3)2PDBX3, and (CD3)2PHBX3, where X = Cl, Br, I, have been recorded in solid state and in solutions at room temperature. The fundamentals have been assigned on the basis of Cs molecular symmetry. A modified Urey–Bradley force field model has been used in calculating the frequencies and potential energy distributions as well as the force constants. The (P—B) force constant was found to be consistent with the structural change upon adduct formation.
Diels–Alder adducts of 2-acetoxyfuran as a route to 2,3-functionalized 4-hydroxycyclohexanones. Application of X-ray diffraction to the problem of regio- and stereochemistry
Authors: Gravel D. , Deziel R. , Brisse F. , Hechler L.
Published: May 2006

The Diels–Alder adducts of 2-acetoxyfuran and maleic anhydride and 2-acetoxyfuran and chloromethylmaleic anhydride have been obtained and their dihydro derivatives manipulated in high yield to various 2,3-functionalized 4-hydroxycyclohexanones. In all cases the hemiketal acetate bridge of the oxabicyclo[2.2.1] derivatives was cleaved smoothly using sodium methoxide in methanol at 0 °C; however, in the case of the chloromethyl compounds the reaction proceeds further to give an almost quantitative yield of the corresponding fused cyclopropane derivatives. These sequences, starting from the readily accessible but seldom used 2-acetoxyfuran, are therefore extremely advantageous to gain rapid and efficient access to a number of 2,3-functionalized 4-hydroxycyclohexanones. In the case of the adduct involving chloromethylmaleic anhydride, stereochemistry and regiochemistry were established by X-ray diffraction on the dihydro derivative.
Information from stereospecific spin–spin couplings about the relative absorptivities of the hydroxyl stretching bands in 2-iodophenol solutions
Authors: Schaefer Ted , Sebastian Rudy , Wildman Timothy A.
Published: May 2006

The stereospecific spin–spin coupling constants between the hydroxyl proton and the ring protons for 2-iodophenol in various solvents yield some free energy differences between the cis and trans conformations of this molecule at 305 K. Comparison with areas of the hydroxyl stretching bands in the same or similar solvents shows that the ratio of the absorptivity coefficients for the two conformers is sensitive to solvent. It is suggested that this ratio is temperature dependent and therefore apparent enthalpy differences must be considered tentative for at least some solutions. Molecular orbital calculations are consistent with the arguments concerning the absorptivity coefficients.
The σ–π transmitted coupling over five and six bonds in pyridine–borane complexes. MO calculations on structure and spin–spin couplings
Authors: Schaefer Ted , Sebastian Rudy , Salman Salman R.
Published: May 2006

The spin–spin coupling over six bonds between borane and ring protons in the borane complexes of pyridine and 2,6-lutidine has the same magnitude as in toluene. This σ–π transmitted coupling suggests that the hyperfine parameters QCCH and QNBH have the same magnitude. Comparison of INDO MO FPT calculations of 6J for these compounds and the methyl borazines with experiment indicates the relative degree of electron delocalization in these systems. An STO-3G structure is calculated for pyridine–borane. Almost free rotation about the B—N bond is predicted (sixfold barrier). The calculated [Formula: see text]depends exponentially on the B—N bond length. Solvent effects on the proton chemical shift are in qualitative agreement with the reaction field model.
Merostabilization in radical ions, triplets, and biradicals. 6. The excited state behaviour of para-substituted tetraphenylethylenes
Authors: Leigh William J. , Arnold Donald R.
Published: May 2006

The half-wave oxidation and reduction potentials, measured by cyclic voltammetry, of tetraphenylethylene and a series of para-substituted (cyano, methyl, and methoxy) derivatives are found to correlate with σ+ and σ− values respectively. The deviations from these correlations that are observed for one of the derivatives (unsymmetrically substituted) are attributed to merostabilization.The nature of the first excited singlet state of these compounds is investigated by spectroscopic and photochemical means. Quantum yields for the direct cis–trans photoisomerization demonstrate that this provides the dominant pathway for decay of the singlet state. The π,π* triplet energies are estimated from a qualitative investigation of the relative efficiencies of triplet-sensitized cis–trans isomerization as a function of sensitizer triplet energy.
Crystal and molecular structure of cis,anti,cis-N,N′-dibenzoyl-3,12-diazatricyclo[6.4.0.02,7]dodecan-6,12-dione and cis,anti,cis-N,N′-dibenzoyl-3,9-diazatricyclo[6.4.0.02,7]dodecan-6,9-dione. Photodimers of N-benzoylcyclohex-2-ene-4-one
Authors: Cameron T. Stanley , Cordes Ruth E. , Pinto B. Mario , Szarek Walter A.
Published: May 2006

The products of photodimerization of N-benzoylazacyclohex-2-ene-4-one (1) have been investigated by X-ray crystallography. Irradiation of a benzene solution of compound 1 leads to a mixture of head-to-head and head-to-tail, cis,anti,cis adducts, namely, cis,anti,cis-N,N′-dibenzoyl-3,12-diazatricyclo[6.4.0.02,7]dodecan-6,12-dione and cis,anti,cis-N,N′-dibenzoyl-3,9-diazatricyclo[6.4.0.02,7]dodecan-6,9-dione, compounds 2 and 3 respectively.
The action of hypochlorite on m-cresol. Part 2. Muconic acid derivatives
Authors: Strunz George M. , Kakushima Masatoshi , Gibson Alan D. , McCulloch Archibald W. , White Peter S.
Published: May 2006

not available
Nucleic acid related compounds. 35. Synthesis of 5-bromo- and 5-deuterio-3-deazauridine
Authors: Robins Morris J. , Kaneko Chisato , Kaneko Masakatsu
Published: May 2006

Bromination of 3-deazauracil (4-hydroxy-2-pyridinone) (1) gave the 3,5-dibromo compound (2). Selective debromination of 2 gave 5-bromo-4-hydroxy-2-pyridinone (3). Trimethylsilylation of 3 and condensation of the product (4) in situ with tetra-O-acetyl-β-D-ribofuranose (5) using tin(IV) chloride as catalyst gave 1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-5-bromo-4-hydroxy-2-pyridinone (7). Deprotection of 7 gave 5-bromo-3-deazauridine (6). Catalytic hydrogenolysis of 7 gave 3-deazauridine triacetate (8a) and deuteriolysis gave the 5-deuterio product (8b). Deprotection of 8b gave the isotope-labeled anticancer agent, 5-deuterio-3-deazauridine (9). Biochemical and clinical implications are discussed.
Homoenolization and H/D exchange in tricyclic ketones. Rearrangement via a γ-enolate
Authors: Cheng A. K. , Ghosh A. K. , Sheepy I. (Tse) , Stothers J. B.
Published: May 2006

Under homoenolization conditions (t-BuO−, t-BuOH, 185 °C), 7,7-dimethyltricyclo[3.2.1.02,4]octan-6-one (5) readily rearranges to 4,4-dimethyltricyclo[3.3.0.02,8]octan-3-one (6) which subsequently suffers reduction of the three-membered ring, presumably by electron transfer from the tert-butoxide anion for which some evidence has been obtained. The conversion of 5 to 6 constitutes one of very few examples of rearrangement via a γ-enolate. From reactions in tert-butyl alcohol-O-d1, deuterium incorporation at the several sites in 5 and 6 undergoing H/D exchange was directly monitored by 2Hmr spectroscopy; these results shed light on the stereochemistry of homoenolate formation and cleavage.
Theory for electronic Raman activity of chlorophyll dimers
Authors: Haley L. V. , Koningstein J. A.
Published: May 2006

We present a modification of a supermolecule model of a general chlorophyll dimer, and calculate the excited state electronic Raman selection rules between the various singlet states. The model utilizes the electronic part of the total wavefunction within the strong intermolecular coupling scheme. Under this condition and the neglect of underlying orbitals, the electronic wave function of the dimer is reduced to a four orbital function with each monomer contributing one HOMO and one LUMO. Using a Hückel type molecular orbital calculation, the one electron orbital energies and coefficients of the ground and excited state wavefunctions of the dimer are obtained and are shown to depend explicitly on the ground and excited state intermolecular interaction terms. The resulting Raman activity calculation between the various excited state configurations yields two types of tensor elements: (1) contains only coordinates of the individual monomer α1 (molecule 1) and α2 (molecule 2) and are called spatially localized elements and (2) labelled spatially delocalized and contains coordinates of both monomer molecules simultaneously (α3 and α4).
Changing regioselectivity patterns in metal hydride reductions of unsymmetrically substituted cyclic anhydrides
Authors: Kayser Margaret M. , Salvador Judith , Morand Peter
Published: May 2006

A study of L- and K-selectride reductions of unsymmetrical cyclic anhydrides attached to six-membered rings and to bridged six-membered systems sheds a new light on the effect of the conformation of the substrate molecule on the regioselectivity of metal hydride reductions. Thus, in addition to intrinsic reactivity of the carbonyl group, the antiperiplanar effect, and steric congestion, the conformation of the parent molecule should be considered in predicting regioselectivity of nucleophilic additions to cyclic anhydrides.
Muonium atoms in liquid and solid neopentane
Authors: Ng B. W. , Stadlbauer J. M. , Jean Y. C. , Walker D. C.
Published: May 2006

Relatively long-lived muonium atoms have been observed in neopentane (dimethylpropane). The yields of all muon states are found to be essentially the same in liquid and solid neopentane and the same as those in water. These results have bearings on three matters of current interest in muonium chemistry: the origin of the "background" spin relaxation; the formation mechanism; and the change in yields at the liquid–solid phase transition. These data were obtained by the μSR technique (muon spin rotation) at the TRIUMF accelerator.
Quantum capture and redox storage
Authors: Calvin Melvin
Published: May 2006

Over many years multiple investigations of the mechanism of the primary quantum conversion steps in natural photosynthesis have exposed the participation of some kind of manganese complex in the oxidation of water to molecular oxygen and the participation of a number of iron hemes in the electron transport chain between the two photosystems. It is almost certain that the participation of an iron–sulfur protein on the reduction side of the photosynthetic electron transfer scheme plays a role in the formation of reduced pyridine nucleotide through ferredoxin and in the evolution of hydrogen in plants deprived of CO2 but having the hydrogenase present. The physical arrangement of the components is important as well, and the participation of at least one phase boundary (and probably two) in the same transport chain is likely. We have used this information to try to construct a synthetic chloroplast that would accomplish quantum conversion into stored energy in the form of intermediate oxidant and intermediate reductant. These could then be converted, respectively, into a useful oxidation product, or molecular oxygen, on the one hand, and molecular hydrogen, or a more useful reduction product, on the other.
The formation of ozone and peroxyacetyl nitrate (PAN) in the urban atmospheres of Alberta
Authors: Peake E. , Sandhu H. S.
Published: May 2006

Atmospheric temperature inversions frequently trap pollutants in the urban atmospheres of Alberta leading to photochemical air pollution. Peroxyacetyl nitrate (PAN) was monitored, for the first time in Alberta, from November 1980 to August 1981 at the University of Calgary using electron capture gas chromatography. Measurements were made at one-half-hour intervals from July, 1981 to February, 1982 at a downtown location. Maximum PAN concentrations were recorded at the University and downtown sites on August 14 at 1400 h, 1981 and the values were 2.4 and 6.6 ppb, respectively. In each case the maximum PAN peak coincided with the afternoon peak in ozone concentrations, 79 ppb at the University and 59 ppb at the downtown site. Surprisingly, a high value of 2.3 ppb PAN was recorded at the University during January of 1981 giving rise to questions regarding the influence of low temperatures and solar radiation on the photochemical formation of PAN. Calculations employing a simple photochemical model for PAN and ozone formation have been carried out and comparisons made between the observed and the computed values.
Reaction of 6,7-dimethoxy-3-isochromanone with hydrazine: a reinvestigation
Authors: Bird Paul , Sainsbury Malcolm , Scopes David I. C.
Published: May 2006

We find that the product from the interaction of 6,7-dimethoxy-3-isochromanone and hydrazine, followed by treatment of the intermediate hydrazide with mineral acid, is not 6,7-dimethoxy-1,3-dihydro-3-(2H)isoquinolone as stated in the literature, but rather bis-2,2-(6,7-dimethoxy-1,4-dihydro-3(2H)isoquinolonyl). An explanation of the formation of this product is provided.
Solvent structure effects on electron thermalization ranges in water–alcohol mixed solvents; preferred EAmax values for e−s in alcohols
Authors: Leu Ah-Dong , Jha Kamal N. , Freeman Gordon R.
Published: May 2006

Addition of 2 mol% of an alcohol to water or of 1 mol% of water to an alcohol increases the value of Gfi εmax (e−s) above that in the pure solvent. The effect is attributed mainly to an increasing free ion yield Gfi. The increase of Gfi correlates with a "stiffening" of the solvent molecular rotational motions and a corresponding lower rate of energy loss by the epithermal electrons to dipole rotations. Thus the increase of Gfi is mainly attributed to a larger electron thermalization range bGP. The value of Gfi εmax passes through a maximum at 2 mol% of an alcohol in water; the maximum increases in the order methanol< ethanol< 1-propanol as additive. The solvent "stiffening" effect of these solutes increases in the same order.Some of the published values of EAmax and W1/2 for solvated electrons in alcohols appear to be too low. A set of preferred values is reported herein.
Enchaînements hétéroatomiques et leurs produits de cyclisation. VI. Nouvelle synthèse de céphèmes: acétyl-3 méthyl-7 phtalimido-7 oxo-8 thia-5 aza-1 bicyclo[4.2.0]octènes-2 diastéréomères
Authors: Rozé Jean-Claude , Pradere Jean-Paul , Duguay Guy , Guevel André , Quiniou Hervé , Poignant Serge
Published: May 2006

The total synthesis of two diastereomeric cephems is described with three original steps in excellent yields: construction of the 1,3-thiazine ring via a (4+2) cycloaddition reaction, regioselective hydrogenation of the carbon–nitrogen double bond, and lactamization using BOP.
Initial state and transition state solvation effects in the oxidation of iodide and catechol by hexachloroiridate(IV) in binary aqueous solvent mixtures
Authors: Blandamer Michael J. , Burgess John , Hamshere Stephen J. , White Colin , Haines Robert I. , McAuley Alexander
Published: May 2006

Rate constants are reported for hexachloroiridate(IV) oxidation of iodide in methanol–, ethanol–, t-butyl alcohol–, ethylene glycol–, glycerol–, acetone–, acetonitrile–, and dimethyl sulphoxide – water solvent mixtures, and for the hexachloroiridate(IV) oxidation of catechol in methanol–water mixtures. With the aid of ancillary solubility data and measurements, solvent effects on reactivity have been analysed into initial state and transition state components. In the latter, there are probably both electron transfer and diffusion contributions since it is not possible to identify uniquely the separate kinetic steps associated with the activation process. In these redox systems, however, transition state solvation changes dominate. This conclusion is compared with initial state – transition state effects in the reaction of catechol with hexahydroxoantimonic acid, in the bromate oxidation of bromide, the peroxodisulphate oxidation of iodide, and with patterns established earlier for substitution at inorganic centres. In view of some disagreements and uncertainties in the literature concerning the number of molecules of water of crystallisation in potassium hexachloroiridate(III) and hexachloroiridate(IV), this matter, of considerable importance to hexachloroiridate transfer parameter estimation, is briefly reviewed.
Synthesis and conformational studies of phosphate esters of 1,2-O-isopropylidene-α-D-ribo- and xylo- pentofuranoses
Authors: Neeser Jean-Richard , Tronchet Jean M. J. , Charollais Etienne J.
Published: May 2006

The synthesis and properties, particularly 1H, 31P, and 13C nmr, of new phosphate esters of 1,2-O-isopropylidene-α-D-ribo-and xylo-furanoses are described. For the cyclic phosphates the configuration at the asymmetric phosphorus atom is determined and for all derivatives the preferred conformation of the furanose and dioxaphosphorinane rings and the conformation around the phosphoester bonds are presented. The dependency of 3JPOCC coupling constants on factors other than dihedral angles is reported and discussed.
An investigation of the biphasic kinetics observed during the hydroxide ion-catalyzed hydrolysis of alkyl dithioesters
Authors: Storer A. C.
Published: May 2006

Kinetic evidence is presented for the establishment of an equilibrium, in dilute aqueous alkaline solutions, between alkyl dithioesters and a species I. The species I is formed cither by the extraction of a proton from, or by the addition of an hydroxide ion to, the dithioester. In the former case I would be an anion (probably an enethiolate) formed by the removal of a proton from the α-carbon atom, and in the latter case I would be a stabilized tetrahedral intermediate formed by the addition of an hydroxide ion to the thiocarbonyl carbon atom. It has not been possible, using kinetic evidence alone, to distinguish conclusively between these two possibilities. However, using the available evidence, arguments are presented in favor of I being an enethiolate anion.
Crystal structures of two methylmercury complexes with 1-methylimidazoline-2-thione
Authors: Norris Albert R. , Taylor Spencer E. , Buncel Erwin , Bélanger-Gariépy Francine , Beauchamp André L.
Published: May 2006

[CH3Hg(C4H6N2S)]NO3 belongs to space group [Formula: see text], a = 7.146(2), b = 7.783(3), c = 10.184(5) Å, α = 72.95(3), β = 71.09(3), γ = 81.83(2)°, and Z = 2. The structure was refined to R = 0.039 (1850 nonzero reflections). The crystal contains complex cations in which the CH3Hg+ ion is bonded to the exocyclic sulfur atom by a Hg—S bond of 2.382(2) Å. The nitrate ions form secondary bonds to mercury and hydrogen bonds to the acidic proton attached to N(3). [CH3Hg(C4H5N2S)] is monoclinic, space group Cc, a = 7.734(1), b = 17.125(3), c = 6.061(3) Å, β = 99.66(3)°, and Z = 4. Refinement converged to R = 0.039 (678 nonzero reflections). The crystal consists of individual monomeric molecules in which the CH3Hg+ ion forms a Hg—S bond of 2.338(7) Å. The molecular packing is considered as unusual, since Hg forms no intermolecular secondary bonds in the equatorial plane, even though N(3) has an available lone pair. This lone pair on N(3) is completely free, owing to the absence of H-bond donors in the structure. The applicability of HSAB theory to the present results (S- versus N-binding) is considered.
Sulphurous negative ions in a fuel-rich, CH4–O2 flame with OCS additive
Authors: Goodings John M. , Elguindi Kamal , Bohme Diethard K.
Published: May 2006

Sulphurous negative ions S • SH • SO • SO2/S2• SO3• HSO3• SO4• and HSO4 were observed when 0.2% of carbonyl sulphide (OCS) was added to a conical, laminar, premixed. fuel-rich (equivalence ratio [Formula: see text]) CH4–O2 flame burning at atmospheric pressure. Profiles were obtained of ion concentration vs. distance along the flame axis by sampling the flame through a pinhole into a quadrupole mass spectrometer. Some of the ion signals observed in the flame reaction zone are very large, particularly that for HSO4. None of the sulphurous ions detected contain carbon. Of those listed above, only S−,•SH, • SO • and SO2 persist downstream through the burnt gas. The sulphurous ions are formed by chemical ionization processes of neutral sulphurous intermediates reacting with the naturally-occurring ions present in any hydrocarbon flame. The ion chemistry is discussed, as is the underlying neutral chemistry of sulphur relevant to the flame environment. The ion profiles show the rapidity with which OCS is oxidized through SH and SO to SO2 even within the reaction zone of this fuel-rich flame. No evidence was obtained for the presence of sulphuric or sulphurous acids, and the presence of S2: was not confirmed.
Kinetics and isotope effects ort the proton transfer reaction of 4-nitrophenylphenylcyanomethane with tetramethylguanidine in acetonitrile and benzonitrile solvents
Authors: Jarczewski Arnold , Pruszynski Przemyslaw , Leffek Kenneth T.
Published: May 2006

The kinetic deuterium isotope effect for the proton transfer reaction between 4-nitrophenylphenylcyanomethane and tetramethylguanidine, kH/kD, at 25 °C, is 10.7 in acetonitrile solvent and 12.5 in benzonitrile. The enthalpy of activation difference, [Formula: see text], in both solvents is large, 2.2 kcal mol−1, and 2.4 kcal mol−1; respectively, indicating a significant contribution from proton tunnelling to the reaction. The equilibrium constants, K, measured spectrophotometrically are large, 6000 dm3 mol−1 in acetonitrile and 2000 dm3 mol−1 in benzonitrile and in good agreement with the values calculated from the kinetic measurements.
Quantitative determination of hafnium in mixtures of zirconium–hafnium hexachloro alkali compounds by neutron activation analysis and X-ray fluorescence
Authors: Pickles C. A. , Kipouros G. J. , Flengas S. N. , Hancock R. G. V.
Published: May 2006

A procedure for the determination of Hf in both mixtures of HfCl4–ZrCl4 and A2HfCl6–A2ZrCl6, where A = Li, Na, K, Rb, or Cs, is described. The method involves conversion of the chlorocompounds into HfO2–ZrO2 mixtures and subsequent analysis by either X-ray fluorescence or neutron activation analysis. The two analytical techniques are compared with regard to accuracy and simplicity.
Complexes of platinum group metals with the ambidentate ligands Ph2P(CF2)nSPh (n = 1, 2)
Authors: Sanger Alan R.
Published: May 2006

The potentially bidentate ligands Ph2P(CH2)nSPh (n = 1, 2) form complexes of rhodium(I), iridium(I), palladium(II), or platinum(II) in which ligands are coordinated to a metal centre either by the phosphine function alone, or by the phosphine and thioether functions, or both. Successive displacement of chloro-ligands from [MCl2(Ph2PCH2CH2SPh)2] (M = Pd, Pt) gives the cationic complexes (MCl(Ph2PCH2CH2SPh)2]+ and [M(Ph2PCH2CH2SPh)2]2+. In the latter each ligand is chelating, but in the former, one ligand is monodentate and the other bidentate. Homopolynuclear complexes may also be synthesized in which metal centres are bridged by Ph2P(CH2)nSPh. The complex [RhCl(Ph2PCH2SPh)(C8H12)] contains cyclooctadiene as a monodentate ligand.
The crystal structure and single crystal polarized spectra of trans-bis(trichloroacetato)bis(N,N-dimethylethylenediamine)cobalt(II)
Authors: Evans David B. , Richardson Mary Frances , McCarthy Paul J. , Lever A. B. P. , Pickens S. R. , Walker I. M.
Published: May 2006

CO[(CH3)2NCH2CH2NH2]2[CCl3CO2]2 belongs to the monoclinic crystal system, space group P21/c with a = 7.216(1) Å, b = 12.117(3) Å, c = 13.616(4) Å, β = 103.27(2)°, V = 1158.7 Å3, Z = 2. The structure was solved by the heavy atom method and was refined to R = 0.048, Rw = 0.056 for 1761 reflections with I ≥ 3σ(I). The complexes lie on crystallographic centers of symmetry. Deviations from regular octahedral coordination are due to steric crowding and chelate ring constraints. The Co—NMe2 bond is longer than the Co—NH2 bond (2.258(3) vs. 2.100(3) Å). The Co—O distance is 2.138(3) Å. The chelate rings each contain a disordered carbon atom such that these rings are 54% gauche and 46% envelope. There are intramolecular and intermolecular H-bonds between the Me2en and trichloracetate ligands. The polarized single crystal spectra are interpreted in terms of D2h symmetry for the complex.
Acid-catalyzed cleavage of 4-halonortricyclanes. Evidence that the 2-norbornyl cation is an unsymmetrical species
Authors: Werstiuk Nick Henry , Dhanoa Daljit , Timmins George
Published: May 2006

Nortrieyclanes 4a, 4c, 4d, and 4e were prepared and ring opened in D2SO4/CD3COOD. We found that the ratios of endo/exo deuterium at C(6) were 1.09 ± 0.02, 1.30 ± 0.03, 1.40 ± 0.04. and 1.45 ± 0.05 for cleavage of 4a, 4c, 4d, and 4e, respectively. The amount of 6,2-hydride shift decreased from 14.3 ± 1.0% in the case of nortricyclane (4a) to 6.0 ± 1.1%, 6.4 ± 0.5%, and 8.1 ± 0.7% for 4c, 4d, and 4e, respectively. Although four distinct mechanisms involving either nonclassical or rapidly-equilibrating cations arc possible, cleavage most probably occurs to generate 6,2-unsymmetrically-bridged norbornyl cations.
Synthesis of coleon B tetramethyl ether
Authors: Burnell Robert H. , Jean Michel , Savard Sylvain
Published: May 2006

Using a simple model available from podocarpic acid, a method to synthesize the Ring A and B chromophore of coleon B (6b) was elaborated. When applied to the correctly substituted starting ketone 8, this reaction sequence afforded the first synthesis of coleon B, as the tetra-O-methyl ether 15a.
Two channel competitive photodecomposition reaction of gaseous bromoethane at 193.1 nm
Authors: Jung Kyung-Hoon , Lee Chong Mok , Yoo Hee Soo
Published: May 2006

The vacuum ultraviolet photolysis of gas phase bromoethane at 193.1 nm (6.42 eV) was studied over the pressure range of 1.1–303.2 Torr at room temperature using a carbon atom lamp. The pressure effect with and without inert gas, i.e., He or N2, was investigated. A scavenger effect of the reaction was also observed by adding NO as a radical scavenger. The principal reaction products were C2H6, C2H4, 1,1-C2H4Br2, and n-C4H10. The quantum yields of C2H4 and C2H6 were found to increase slightly with the reactant pressure. When the pressure of He or N2 was varied at a constant pressure of C2H5Br, however, the quantum yields of C2H4 and C2H6 were found to be pressure independent. Addition of NO completely suppressed the formation of C2H6, C2H4Br2, and C4H10, and partially reduced that of C2H4. These results were interpreted in terms of two channel competition between the molecular elimination and the formation of radicals. Two different decomposition modes were 82% radical reaction and 18% molecular elimination.
Synthesis of spin-labeled analogues of drug molecules with potential action on neuroreceptors
Authors: Dugas H. , Spino C. , Ouellette M.
Published: May 2006

The syntheses of novel spin-labeled analogues of butaclamol, a spin-labeled phenylaziridinium and two amino derivatives of butaclamol, are presented. Preliminary results of in vitro activity of these compounds on dopaminergie, serotoninergic, and adrenergic receptors correlate with the importance of the previously proposed lipophilic accessory binding site in CNS dopamine receptor.
The retroaldol reaction of chalcone
Authors: Guthrie J. Peter , Cossar John , Cullimore Patricia A. , Kamkar Nayyer Monshizadeh , Taylor Kathleen F.
Published: May 2006

All four rate constants required to describe the hydration and aldolization/dealdolization reactions of chalcone (1,3-diphenyl-2-propen-1-one) have been determined in aqueous sodium hydroxide solutions. Kinetics were studied starting with chalcone, with its hydrate, 1,3-diphenyl-3-hydroxy-1-propanone, and with benzaldehyde in the presence of excess acetophenone. The rate constants for hydroxide catalyzed reactions, defined in terms of eq. [1] are: k12 = 10.5 ± 0.5 × 10−4 M−1 s−1; k21 = 0.026 ± 0.002 M−1 s−1; k23 = 0.194 ± 0.017 M−1 s−1; and k32 = 0.84 ± 0.12 M−2 s−1 (all at ionic strength 0.1). The corresponding equilibrium constants for aldol adduct formation and dehydration are 4.3 M−1 and 25.
Deuterium isotope effects on the partial molal volumes of cyclohexane, acetone, and acetonitrile in carbon tetrachloride
Authors: Brown G. Ronald , Edward Julian K. , Edward John T.
Published: May 2006

At 25 °C both molar volumes V and partial molal volumes [Formula: see text] in carbon tetrachloride of cyclohexane-d12 and of acetone-d6 are smaller than V and [Formula: see text] of the corresponding protio compounds. However, both V and [Formula: see text] of acetonitrile-d3 are larger than V and [Formula: see text] of acetonitrile-h3, and in solvent cyclohexane [Formula: see text] of acetone-d6 and of acetone-h6 are approximately equal. Apparently deuteration has not only a steric effect, but (in polar compounds) a counter-balancing effect, which may be polar.
Étude polarographique du niobium dans les mélanges eau – fluorure d'hydrogène
Authors: Ménard H. , Beaudoin R.
Published: May 2006

Solubilization in hydrogen fluoride is required for the analysis of some minerals. A method of analysis directly applicable to water – hydrogen fluoride mixtures was worked out.However, in 50% hydrofluoric acid niobium is soluble as [Formula: see text] complex, which can be reduced with a polarographic electrode at a potential of −0.880 V vs. E.C.S. For concentrations lower than 45% in HF, the niobium complex is hydrated and exists as a non-reducible ion [Formula: see text].
New multidentate ligands. XXI. Synthesis, proton, and metal ion binding affinities of N,N′,N″-tris[2-(N-hydroxycarbamoyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH)
Authors: Yoshida Isao , Murase Ichiro , Motekaitis Ramunas J. , Martell Arthur E.
Published: May 2006

Synthesis of a new tris-bidentate multidentate ligand, N,N′,N″-tris[2-(N-hydroxycarbamoyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH), designed for the binding of trivalent metal ions such as Fe(III), Ga(III), and Al(III), is described. Its cation binding affinities for hydrogen ion and for Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ga(III), and Al(III) ions are described, and the equilibrium data are compared with those of analogous ligands. The binding constants of trivalent metal ions with the ligand do not show a chelate effect relative to the binding to individual bidentate hydroxamic acids.
Picosecond excited state absorption studies of isothiocyanato complexes of Cr(III) in solution
Authors: Sage R. Le , Sala K. L. , Yip R. W. , Langford C. H.
Published: May 2006

The spectra and risetimes for the doublet excited state absorption (ESA) of t-[Cr(NH3)2(NCS)4]− (Reineckate ion), [Cr(NCS)6]3−, and t-[Cr(en)2(NCS)2]+ have been measured at picosecond times in several solvents. The ESA spectra observed after approximately one half the risetimes showed no measurable change with time. The result is consistent with vibrational relaxation times which are comparable to or faster than the risetimes. The ESA risetimes for Reineckate ion and t-[Cr(en)2(NCS)2]+ were found to be fastest in hydroxylic solvents and slowest in non-hydroxylic solvents. No such solvent trend was found for [Cr(NCS)6]3−. Possible photophysical models to account for the observed solvent-dependent risetimes are discussed. Kinetic simulations based on a quasi four-level model which explicitly includes the pump pulse function are reported.
III. Order–disorder transitions and electrical conductivity studies in Na2SO4 – Ag2SO4 system
Authors: Kumari M. Sunitha , Secco Etalo A.
Published: May 2006

The physico-chemical aspects of the order–disorder phase transitions occurring in the Na2SO4–Ag2SO4 system were investigated by thermal analyses, X-ray diffraction, and electrical conductivity techniques. Electrical conductivity data on pure and doped compositions reveal high conductivity values in the high temperature phase.The lower conductivity of Ag2SO4 with Na+ presence relative to pure Ag2SO4 is attributed to lattice contraction effecting lower mobility of ions.
Theoretical study on the gas-phase solvation of acetone and dimethylsulfoxide toward the proton
Authors: Yamabe Shinichi , Minato Tsutomu , Hirao Kimihiko
Published: May 2006

An abinitio MO calculation is made for the H+(acetone)n and H+(DMSO)n gas-phase clusters. In the "shells" of n = 2, the cationic nature for the attack of the third solvent molecule is dispersed to the methyl hydrogens and the S atom (in DMSO) as well as to the proton. This leads to the small difference of stability for several geometries of n = 3. A noticeable disagreement between experimental and calculated energies for n = 1 → 2 in H+(DMSO)n is discussed.
L'électrodissolution du cuivre dans les solutions bromurées
Authors: Brossard Robert-Louis
Published: May 2006

The dissolution of a copper anode has been studied in aqueous solutions, at pH 4, for a range of concentrations varying from 0.1 M to 1.2 M in NaBr. Where the accumulation of the corrosion product on the copper was nonexistent or negligible, two phenomena account for the dissolution current: a surface phenomenon and a phenomenon of diffusion of the ions into the solution. The current associated with each of these slow steps has been determined from the linear relationship i−1 vs. ω−1/2.The main characteristics of the copper anode behavior are expressed as partial derivatives: [Formula: see text], [Formula: see text], [Formula: see text], while the reaction order for the bromide ions is equal to 2. Furthermore, the linearity of the relationship E vs. log10i arises as a direct consequence of a surface phenomenon limited by an electron transfer. A dissolution model that describes the main characteristics of the copper dissolution is presented. According to this model, the term id is entirely ascribable to the diffusion of a copper bromide complex, CuBr2−, from the surface of the electrode into the solution. The apparent activation energy calculation is 7 kcal/mol according to the model, while the experimental value is 6.5 kcal/mol.Finally, the observed oxidation wave when the electrode potential becomes sufficiently anodic compared to the reversible potential of the reaction Cu + Br− = CuBr + e, is associated with the passivation of the copper by γ-CuBr. [Journal translation]
The structure of cubane mono and 1,4-dicarboxylic acids in lyotropic liquid crystalline solution
Authors: Tracey Alan S.
Published: May 2006

Proton nmr studies of cubane mono and 1,4-dicarboxylic acids in lyotropic liquid crystalline solution show that these molecules are distorted from the cubane structure. The protons of cubane dicarboxylate which are vicinal to their respective carboxylate group are displaced towards those groups along the C3 axis resulting in an elongation relative to a cube. In cubane monocarboxylate there is also a displacement of vicinal protons toward the carboxyl group, but this is accompanied by a displacement of the protons one carbon further removed, away from the carboxyl groups. The shape of this latter compound is comparable to that of a section of a cone with the narrow end of the cone defining the proton positions adjacent to the carboxyl group while the wide end of the cone defines the positions of the adjacent set of protons. The remaining proton of course sits on the C3 axis which determines the centre of symmetry of the cone.
Spin–spin coupling between hydroxyl and aldehydic protons in some salicylaldehyde derivatives. Correlation with the hydroxyl proton chemical shift
Authors: Schaefer Ted , Sebastian Rudy , Laatikainen Reino , Salman Salman R.
Published: May 2006

1H nmr spectral parameters are reported for salicylaldehyde and 15 of its derivatives in dilute CCl4 solutions. In those compounds in which sufficiently large substituents are placed ortho to either of the functional groups or in which substituents enhance the charge density in the carbonyl group, a positive spin–spin coupling is observed between the two sidechain protons. This coupling, formally over five bonds, correlates with the chemical shift of the hydroxyl proton. The coupling mechanism is discussed from various viewpoints. STO 3G MO calculations give an optimized planar structure for salicylaldehyde. Nonplanar structures are less stable than the planar form. The energy of the hydrogen bond in salicylaldehyde lies near 30 kJ/mol and increases to 36 kJ/mol in the 4,6-dimethoxy derivative. Other small long-range spin–spin coupling constants in these compounds are also discussed.
MNDO calculations for some allotropes, hydrides, and oxides of phosphorus
Authors: Baird N. Colin
Published: May 2006

Molecular orbital calculations by the MNDO method are reported for some allotropes, hydrides, and oxides of phosphorus. The aim of the study is to test further the ability of MNDO to reproduce the energetics of PP, PH, and PO bonds, and to apply MNDO to interesting problems in the chemistry of such systems. Different isomers of P4, P6, and P8 are considered, as well as ions of P3, P5, and P7. The method is found to overestimate strain energy in three-membered rings, and to underestimate the strength of three-electron PP bonds. The strength of PO π bonds apparently also is overestimated. Possible isomers of P2O2 and P2O3 are discussed.
Pseudobase formation from 9-substituted 10-methylacridinium cations in aqueous solution
Authors: Bunting John W. , Chew Vivian S. F. , Abhyankar Sudhir B. , Goda Yukiko
Published: May 2006

Rates of cation–pseudobase equilibration have been measured for a series of C-9 substituted (CH3, CH3CH2, C6H5CH2, (CH3)2CH, C6H5, 4-(CH3)2NC6H4) 10-methylacridinium cations in aqueous solution at 25 °C over the pH range of approximately 9–13. Separation of the rate constants for formation (kOH) and decomposition (k2) of each of these pseudobases allowed the calculation of the [Formula: see text] value for each cation. The presence of a C-9 isopropyl substituent enhances the stability of the pseudobase relative to the cation, whereas all other C-9 substituted cations have [Formula: see text] values greater than the 10-methylacridinium cation. There is no simple quantitative relationship between [Formula: see text] and the size of the C-9 substituent. Rate constants (kOH) for hydroxide ion attack on these C-9 substituted cations are in the order: H > primary alkyl > secondary alkyl > aryl, while rate constants (k2) for pseudobase decomposition are less predictable but generally follow the order: H > primary alkyl > aryl > secondary alkyl. These phenomena are shown to be consistent with a competition between destabilization of the cation by peri interactions between the C-9 substituent and H(1) and H(8) and reduced pseudobase solvation for large C-9 substituents. Resonance interactions of 9-aryl substituents with the acridine moiety of these cations are shown to be quite small. 9-Aryl-10-methylacridinium cations are approximately 30-fold more reactive towards hydroxide ion attack than are their triphenylmethyl carbocation analogues.
A 19F, 119Sn nuclear magnetic resonance and 119Sn Mössbauer study of the SnF2–MF–H2O system
Authors: Birchall Thomas , Dénès Georges
Published: May 2006

19F and 119Sn nmr spectroscopy has been used to study the SnF2–MF–H2O (M = Li+, Na+, K+, Rb+, Cs+, and [NH4]+) system. The nmr data have been supplemented by frozen solution 119Sn Mössbauer measurements. The evidence suggests that the dominant species in the SnF2–H2O system is a hydrated stannous fluoride, probably SnF2•H2O having Mössbauer parameters of δ = 3.46 mm s−1 and Δ = 1.70 mm s−1. When F− is added to these solutions rapid F− exchange occurs with the hydrated SnF2 and the dominant species becomes [SnF3]−. The 119Sn nmr chemical shift of [SnF3]− is ~ −700 ppm from (CH3)4Sn. The 119Sn Mössbauer parameters for frozen solutions of [SnF3]− are δ = ~ 3.1 mm s−1 Δ = 1.9 mm s−1. These spectroscopic data are cation dependent. We could find no strong evidence for high concentrations of [Sn2F5]− in any of these solutions.
Mechanisms in the chlorinolysis of sulfinyl chlorides
Authors: Ahern Terence Patrick , Haley Michael Francis , Langler Richard Francis , Trenholm June Ellen
Published: May 2006

The successful synthesis and chlorinolysis of α-mercaptodimefhyl sulfone have provided additional support for our contention that Pummerer rearrangements may occur during the chlorinolyses of α-sulfonyl sulfinyl chlorides. Further exploration of chlorinolyses of α-sulfonyl systems has uncovered the first observations of CS bond cleavage during the chlorinolyses of (i) a sulfinyl chloride and (ii) a sulfinate ester.