bluuebunny/crossref_metadata_2025 huggingface dataset:
The intramolecular Cannizzaro reaction of phthalaldehyde
Authors: McDonald Robert S. , Sibley Christine E.
Published: May 2006

Phthalaldehyde undergoes an intramolecular Cannizzaro reaction in aqueous base to produce the o-hydroxymethylbenzoate ion. The kinetics of the reaction have been measured over a range of sodium hydroxide concentration at 40 °C. The reaction is considerably slower than that of the analogous reaction of phenylglyoxal since it proceeds exclusively via the cyclic hydrate dianion which must undergo a very unfavorable ring opening before internal hydride transfer can occur.
Charge distributions and chemical effects. XXV. On the homogeneity of total molecular energies and the relationships between electronic, orbital, and total energies
Authors: Fliszár Sándor , Foucrault Marielle , Béraldin Marie-Thèrése , Bridet Jacques
Published: May 2006

With the definition of a "screening factor" σk transforming the nuclear charge Zk of an atom k into an "effective" nuclear charge Zk* = Zkσk, the total energy E = E(Zk*, Z*,...) of a molecule at equilibrium can be expressed as a homogeneous function of degree γ/α in Zk*, Zl*,..., i.e. E = −∑kZk*γ/α, where α is the average of the αk's(αk = ∂ ln Zkσk/∂ ln Zk) and γ = (Vne + 2Vnn)/E is a function of the nuclear-electronic, nuclear-nuclear, and total energies. Molecular energies calculated in this manner agree within 0.045% (average deviation) with their SCF counterparts. The sums of the orbital energies are correctly predicted from the equation [Formula: see text] A separation of the individual nuclear–electronic and nuclear–nuclear contributions to the total potential energy V(k, mol) of each nucleus k indicates that the Kkmol factors of the energy formula E = ∑kKkmolV(k, mol) are constant for each type of atom, thus stressing the basic homogeneity of the total energy rather than of the electronic energy only. The γ function, which is the inverse of the molecular average of the Kkmol's, can be estimated in a simple way from atomic data.
Stereospecifïc total synthesis of (±)-cassipurine, an alkaloid from rhizophoraceae
Authors: Wróbel Jerzy Tadeusz , Gliński Jan Adam
Published: May 2006

Two isomeric 1α,2α-epoxy- and 1β,2β-epoxypyrrolizidines have been obtained from 1,2-dehydropyrrolizidine. The structure of both isomers has been determined enabling a study of the stereochemistry of their reactions with a number of sulfur-containing nucleophilic reagents. The BzS− anion has been shown to stereospecifically attack the C2 carbon atom of both compounds. In the three-stage process 1β,2β-epoxypyrrolizidine was transformed into 1α,2α-epithiopyrrolizidine, which reacts stereospecifically with benzylthiol to yield 1α-(2β-thiobenzylpyrrolizidine)-thiol. This, in turn, oxidizes in air to give a mixture of three diastereomeric 1α,1′α-dithio-2β,2′β-dithiobenzyldipyrrolizidines. These diastereomers were chromatographically separated into the racemic mixture and the meso diastereomer. Treatment of the racemic mixture with Na/liquid NH3 induced debenzylation without cleavage of the disulfide bond. The resulting enantiomeric α,1′α-dithio-2β,2′β-dimercaptodipyrrolizidines were oxidized in air to give racemic cassipurine.
Consideration on rotational isomerism in connection with its influence on some electrical properties of an interface
Authors: Dutkiewicz Edward , Lamperski Stanisław
Published: May 2006

The rotational isomerism contribution to some electric properties of an interface region has been considered. The mean electric dipole [Formula: see text] the mean equilibrium constant [Formula: see text] expressing the ratio of gauche and trans conformers, surface charge density σ, electric permittivity ε, differential capacity C were calculated as a function of electric field for 1,2-dichloroethane, 1-chloro-2-bromoethane, and 1,2-dibromoethane.The results obtained suggest that in the case of adsorbed molecules exhibiting rotational isomerism, their structure and behaviour in the electrical double layer field have to be taken into account.
Cyclic neutron activation analysis of biological and metallurgical samples
Authors: Chatt A. , Desilva K. N. , Holzbecher J. , Stuart D. C. , Tout R. E. , Ryan D. E.
Published: May 2006

A rapid pneumatic transfer cyclic system for use with the SLOWPOKE reactor has been designed which allows detection of nuclides with half-lives as short as 0.8 s. Reliable reproducibility is achieved with a 1 s transfer period from reactor to detector. Both accuracy and relative standard deviation are significantly improved with some matrices as the number of cycles is increased but the gains in detection limits increase with the square root of the number of cycles. Cyclic instrumental neutron activation analysis has been successfully applied to the determination of Ag, F, Hf, Pb, Rb, Sc, and Se in a variety of biological and metallurgical matrices. The detection limits ranged from 0.01 to 2.2 ppm for all elements studied except Pb.
Ionization of nitromethane in the flame ionization detector
Authors: McAllister T. , Nicholson A. J. C. , Scott J. D.
Published: May 2006

The mass spectra observed on sampling the unburnt gases of a flame ionization detector to which nitromethane has been added are due mostly to proton transfer reactions of NH4+ and H3O+. These are formed in the reaction zone from the primary ion HCO+, and pass through the unburnt gases to the sampling orifice. The ions which are detected may be attributed to pyrolysis (CH4NO+ and NO+) or hydrogenation products (CH2NH2+ and CH3NH2+) of nitromethane. The small amount of NO+ observed in the unburnt gases is attributed either to a primary ionization mechanism which produces NO+ from excited nitrogen atoms or molecules in the reaction zone, or to a reaction of H3O+ with HNO2, a pyrolysis product of nitromethane. Observations of CH2NH2+ in the flame and in double resonance experiments performed in an ion cyclotron resonance mass spectrometer give limits on the proton affinity of methanimine (CH2NH) of 847.6–862.3 kJ mol−1.
Importance of lignosulfonates in petroleum recovery operations
Authors: Neale Graham , Hornof Vladimir , Chiwetelu Christopher
Published: May 2006

This paper reviews the potential importance of aqueous lignosulfonate solutions in the recovery of petroleum from existing partially depleted oil fields. The surfactant qualities of lignosulfonates are described and their ability to interact synergistically with petroleum sulfonate surfactants (which are currently popular in the industry) to produce ultra-low interfacial tensions with crude oil is discussed. The phase behaviour characteristics and oil recovery efficacies of these mixed surfactant systems are also examined.
Protonated cyclopropanes in α-aminoketone deamination
Authors: Edwards Oliver E. , Dixon John , Elder John W. , Kolt Ralph J. , Lesage Maurice
Published: May 2006

Deamination of 2-amino-4,4-dideuterio-6,6-dimethylcyclohexanone, 2-exo-amino- and 2-endo-amino-norbornane-3-one, 2-diazo-norbornan-3-one, 2-exo-amino-5,6-exo-dideuterionorbornan-3-one and the corresponding 5,6-endo-dideuterio isomer has been studied. The nature of the products, the deuterium location in them, and the high retention of steric identity in the carbocations are interpreted in terms of σ-bond participation leading to corner- and edge-protonated cyclopropanes as reaction intermediates. Results with other destabilized carbocations are correlated.
Effect of reaction exothermicity on the proton transfer chemical ionization mass spectra of isomeric C5 and C6 alkanols
Authors: Herman Jan A. , Harrison Alex. G.
Published: May 2006

The chemical ionization mass spectra of eight C5 alkanols and fourteen C6 alkanols have been obtained using H3+, N2H+, CO2H+, N2OH+, and HCO+ as reactant ions. This choice of reactant ions allows the exothermicity of the protonation reaction to be varied from ∼90 kcal mol−1 (H3+) to ∼50 kcal mol−1 (HCO+). The major fragmentation reaction in all cases was H2O elimination from the protonated alcohol forming the appropriate C5H11+ or C6H13+ alkyl ion. The extent of further fragmentation of the alkyl ions decreased with decreasing exothermicity of the protonation reaction and was greatest for alkyl ions derived from primary alcohols, less for alkyl ions derived from secondary alcohols, and very small for alkyl ions derived from tertiary alcohols. The results indicate that there is negligible rearrangement to more stable alkyl ions prior to attaining the critical configuration which determines the energy partitioning between R+ and H2O in the fragmentation of ROH2+. Other less important reaction modes in the CI spectra involved formation of (M – H)+ ions and formation of oxycarbonium ions by alkane elimination from protonated alcohols.
The stereochemistry and regiochemistry of the Diels–Alder reactions of 6-acetoxy-2,6-dimethyl-2,4-cyclohexadienone
Authors: Auksi Hillar , Yates Peter
Published: May 2006

6-Acetoxy-2,6-dimethyl-2,4-cyclohexadienone (1) and maleic anhydride in boiling benzene give a single adduct, exo-5-acetoxy-l,5-dimethyl-6-oxobicyclo[2.2.2]oct-7-ene-endo-2,3-dicarboxylic acid anhydride (2). With propiolic acid 1 gives exo-5-hydroxy-l,5-dimethyl-6-oxobicyclo[2.2.2]octa-2,7-diene-2-carboxylic acid (15). The high stereoselectivity and regioselectivity of these reactions is interpretable in terms of orbital overlap, closed-shell repulsion, steric, and van der Waals – London effects.
Substituent effects in fluoromethylnaphthalenes by 19F nuclear magnetic resonance
Authors: Dixon Elisabeth A. , Fischer Alfred , Robinson Frank P.
Published: May 2006

19F substituent chemical shifts (SCS) are reported for a series of twenty-one 3- and 4-substituted 1-fluoromethylnaphthalenes. The fluoromethylnaphthalenes exhibit an inverse SCS dependence: electron-withdrawing substituents produce upfield shifts. The results correlate well with SCS values previously reported for substituted benzyl fluorides. Hammett correlations are poor with conjugatively electron-withdrawing substituents exhibiting weaker than expected effects in the 3-position and stronger than expected effects in the 4-position. Dual substituent parameter analysis confirms the enhanced substituent–aromatic ring resonance interaction when the substituent is in the 4-position (ρR/ρI = 2). There is no evidence for enhanced resonance interaction between fluoromethyl side-chain and aromatic ring. The 19F chemical shift of 1-fluoromethylnaphthalene is markedly temperature dependent.
Application of carbon-13 nuclear magnetic resonance to the configurational analysis of stereoisomeric Nα-methyl-Nβ-acetylphlegmarines
Authors: Leniewski Andrzej , MacLean David B. , Saunders John K.
Published: May 2006

The carbon-13 chemical shifts of isomeric phlegmarines and analogues are presented. The chemical shifts at C-7 and C-9 confirm the assignment of the stereochemistry at C-5. The stereochemistry at C-2' of the isomeric phlegmarines was assigned by comparing the observed shifts with those predicted from conformer populations and conformer shifts for the various conformers obtained by rotation about the (C-5, C-11) and (C-11, C-2') bonds. In particular it is possible to assign the relative configuration 1b to the naturally occurring Nα-methyl-Nβ-acetylphlegmarine.
Chemical reactivity of lumazine derivatives. Acid–base and redox reactions of a number of lumazines, deazalumazines, and isoalloxazines. An unusual effect of methyl substitution
Authors: Stewart Ross , Srinivasan R. , Gumbley Stewart J.
Published: May 2006

Three lumazines, seven deazalumazines, and two isoalloxazines have been studied and the following chemical properties measured; equilibrium acidity (pKa), equilibrium basicity [Formula: see text] polarographic reduction potential [Formula: see text] and, where applicable, the rates of the general acid and general base catalyzed dissociation of the protons in the C-5 and C-7 methyl groups [Formula: see text] The latter quantities were determined by means of isotope exchange or iodination. Structural variations in the substrate produce compatible results in pKa and [Formula: see text] and, to lesser extents, in [Formula: see text] and in the catalytic rate data. Anomalies in the rate constants appear when a methyl group is present at C-6; it facilitates ionization of the C-5 and C-7 methyl groups, reversing the quite large effect of more distant methyl. Buttressing effects appear to be absent. The effects of methyl substitution are attributed, in part, to (a) resonance stabilization by 5- and 7-methyl groups in the reactant molecules (neutral substrate and conjugate acid), and (b) relief of steric strain in going from essentially aromatic reactants to nonplanar intermediates. The significance of the 6-methyl group in the lumazine–flavin conversion is noted.
Studies of silyl and germyl group VI species. Part VI. Synthesis and vibrational spectra of methylthiosilanes
Authors: Drake John E. , Glavinčevski Boris M. , Khasrou Layla N.
Published: May 2006

Methylthiosilanes of the type (CH3)nH3−nSiSCH3, n = 0–3, and (CH3)HSi(SCH3)2 have been prepared. Their ir and Raman spectra were recorded and assigned. The assignments were supported by normal coordinate analyses based on a modified valence force field.
Isotope effects in the diphenylpicrylhydrazyl-inhibited thermal polymerization of 2,6-dideuteriostyrene
Authors: Kopecky Karl R. , Hall Michael C.
Published: May 2006

There is an inverse isotope effect in the reaction between 2,2-diphenyl-1-picrylhydrazyl DPPH and 2,6-dideuteriostyrene of 0.75 ± 0.07 at 75 °C in degassed neat styrene. This result is consistent with the proposal that the reaction involves hydrogen transfer to DPPH from a Diels–Alder dimer of styrene. The rate constant for dimerization of styrene to this dimer is calculated to be 1.8 × 10−10 L mol−1 s−1 at 75 °C.
Studies in general acid and general base catalysis. Rate–acidity profiles for prototropic processes
Authors: Stewart Ross , Srinivasan R.
Published: May 2006

not available
Kinetic β-deuterium isotope effects for solvolysis of 1-methyl cyclopentyl chloride in an ethanol+ water mixture
Authors: Robertson Ross Elmore , Wong Edward , William Scott John Marshall , Blandamer Michael Jesse , Khan Rehmat , Johnson Clive
Published: May 2006

Kinetic data are reported for the solvolysis of 1-methyl cyclopentyl chloride in a 50% by volume ethanol+ water mixture. These data are combined with kinetic data for solvolysis of three deuterated analogues; 1-methyl-d3 cyclopentyl chloride, 1-methyl-2,2,5,5-d4 cyclopentyl chloride, and 1-methyl-d3-2,2,5,5-d4 cyclopentyl chloride, being the d3d4, and d7, derivatives respectively. The kinetic data are used to calculate the kinetic deuterium isotope effect, kH/kD. For these systems, the d7-isotope effect is close to the product of the d3 and d4 effects.
A constrained Roothaan–Hartree–Fock method
Authors: Zeiss G. D. , Whitehead M. A.
Published: May 2006

Nonperturbational and perturbation–iteration procedures for determining constrained Roothaan–Hartree–Fock wave-functions are described and compared. The perturbation–iteration procedure most rapidly converges, the secant-parameterization method requires less computation and is less sensitive to numerical errors.
Solvation of aminopyridines by water and methanol
Authors: Spencer J. N. , Barton S. W. , Smith K. A. , Wolbach W. S. , Powell J. F. , Kirshenbaum M. R. , Firth D. W.
Published: May 2006

The hydrogen-bonded interactions by water and methanol in the first solvation shell of 2-aminopyrimidine, 2-, 3-, and 4-aminopyridine were determined by calorimetric analysis. The aminopyridines are enthalpically more stable in methanol than in water. This is due to methanol interactions at the amino nitrogen which do not seem to occur in water. The transfer enthalpies from water to methanol are determined primarily by the making and breaking of hydrogen bonds in the two solvents.
Charge distributions and chemical effects. XXXI. Molecular energies of ethylenic compounds
Authors: Béraldin M.-T. , Fliszâr S.
Published: May 2006

The energy formula describing bond contributions in terms of the charges carried by the bond-forming atoms is applied to ethylenic compounds. It is shown in what manner σ and π electrons can be treated within the framework of the bond energy theory giving the atomization energy of the vibrationless molecule at 0 K. Proper consideration of zero-point and thermal vibrational energies leads to standard enthalpies of formation. These calculations, which are carried out on the basis of, 13C nuclear magnetic resonance spectra, agree with their experimental counterparts, within experimental uncertainties (~0.3 kcal mol−1 average deviation).
Five-membered ring spiro-annulation via thermal rearrangement of enol silyl ethers of 2-(cyclopropylmethylene)cycloalkanones. A formal total synthesis of some spirovetivane-type sesquiterpenoids
Authors: Piers Edward , Lau Cheuk Kun , Nagakura Isao
Published: May 2006

Treatment of the 2-(iodomethylene)cycloalkanones 10 and 11 with lithium (phenylthio)(cyclopropyl)cuprate provided good yields of the corresponding β-cyclopropyl enones 12 and 13, respectively. Thermolysis of the latter substances produced relatively poor yields of the desired spiro-annulation products 14 and 15. However, conversion of 12 and 13 into the corresponding enol silyl ethers 24 and 25, followed by thermal rearrangement of the latter materials and acid hydrolysis of the resulting products, provided synthetically useful yields of the spiro enones 14 and 15. Cuprous iodide-catalyzed addition of methyl magnesium iodide to 2-cyclohexen-1-one, followed by trapping of the resultant enolate anion with cyclopropanecarboxaldehyde, provided the ketols 38, which could be converted readily into the mixture of enol silyl ethers 34 and 35. Thermal rearrangement of the latter substances gave, after acid hydrolysis of the crude thermolysate, the spiro enones 42 and 43 in a ratio of ~2.5:1 (57% yield). Treatment of 42 with methyllithium in ether gave the tertiary alcohols 44 and 45 (ratio ~4:1). Hydroboration (disiamylborane, tetrahydrofuran; H2O2, NaOH) of 44, followed by oxidation of the resultant diol 46 with pyridinium chlorochromate, provided the ketol 47. A similar sequence of reactions converted the olefinic alcohol 45 into the ketol 49. Dehydration (p-toluenesulfonic acid in benzene) of 47 gave the spiro enones 28 and 48, in a ratio of ~9:1. Compound 28, also prepared previously from the ketol 49, had been converted earlier into the spirovetivane-type sesquiterpenoids (±)-α-vetispirene (29), (±)-β-vetivone (30), (±)-hinesol (31), (±)-hinesol acetate (32), and (±)-agarospirol (33).
On the structure, chemistry, and 13C nuclear magnetic resonance of ravidomycin
Authors: Findlay John A. , Liu Jia-Sen , Radics Lajos
Published: May 2006

Full spectral details in support of the earlier proposed structure 1a for the antitumor antibiotic ravidomycin are presented together with an account of chemical degradation products. A complete corroboration of structure is provided by cross correlation of 1H and 13C nmr for ravidomycin and its diacetate 1b.
Carbon-13 chemical shifts as a probe for conformational and electronic effects in alkyl vinyl ethers
Authors: Webb John G. K. , Yung David K.
Published: May 2006

The principle of additivity of substituent chemical shifts (SCS) is applied to the carbon-13 chemical shifts of β carbons (δβ) in a number of 1,1-disubstituted ethylenes and propenes, which includes some α-substituted alkyl vinyl ethers. An additivity relationship is observed for 34 compounds that indicates an independent polarization mechanism across the double bond for each geminal substituent. Positive deviations from additivity are observed for compounds bearing bulky substituents. The magnitude of deviations is taken as an indication of the severity of steric interactions among substituents.Reductions in efficiency of transmission of substituent effects in ring substituted α-phenyl alkyl vinyl ethers, relative to para-substituted styrenes, are interpreted as the result of a variable dihedral angle between the ring and vinyl group. An explanation of the relationship between conformation and transmission of substituent effects is presented as an alternative to existing views. An angular dependence of π-polarization and resonance effects is consistent with the chemical shift data.
Synthetic approaches to haplophytine. 1. Synthesis of 1-methoxy- and 1-hydroxy-6-phenyl-6-(2-pivaloylamidophenyl)non-8-ene-4,5-dione and 1-methyl-3-phenyl-3-(2-pivaloylamidophenyl)-2-pyrrolidinone
Authors: Yates Peter , Schwartz David Aaron
Published: May 2006

An analysis of the structures of the alkaloid haplophytine and its dihydrobromide which is formed with rearrangement, shows that they are both derived from a 7-(2-amino-3-hydroxyphenyl)-7-aryl-9-(methylamino)-5,6-dioxononanoic acid moiety (3). Approaches to the synthesis of compounds related to 3 are described. The dianion 13 of phenyl(2-pivaloylamidophenyl)methane, that of methyl 2-phenyl-2-(2-pivaloylamidophenyl)acetate, and the trianion 37 of 2-phenyl-2-(2-pivaloylamidophenyl)acetic acid undergo C-alkylation and C-acylation with nucleophiles. Acylation of 13 with methyl 2,2,5-trimethoxypentanoate followed by hydrolysis gives 6-methoxy-1-phenyl-1-(2-pivaloylamidophenyl)-2,3-hexanedione. This with allyl bromide and sodium carbonate gives the O-allyl derivative, which on thermolysis is converted to its C-allyl isomer, 1-methoxy-6-phenyl-6-(2-pivaloylamidophenyl)non-8-ene-4,5-dione. The corresponding 1-hydroxy compound was prepared analogously via acylation of 13 with methyl tetrahydro-2-methoxyfuran-2-carboxylate. C-allylation of the trianion 37 gives 2-phenyl-2-(2-pivaloylamidophenyl)pent-4-enoic acid, whose methyl ester on ozonolysis followed by treatment with methylamine hydrochloride and sodium cyanoborohydride gives 1-methyl-3-phenyl-3-(2-pivaloylamidophenyl)-2-pyrrolidinone, a potential advanced intermediate for the synthesis of compounds related to 3.
Crystal and molecular structure of hexadecamethylcyclooctasiloxane, [(CH3)2SiO]8
Authors: Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of hexadecamethylcyclooctasiloxane are tetragonal, a = 13.9442(5), c = 8.5573(4) Å, Z = 2, space group P4/nnc. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.034 and Rw = 0.042 for 730 reflections with I ≥ 3σ(I). The molecular structure closely resembles that of [(CH3)2PN]8. Its comparatively rigid conformation, in which the silicon atoms form a crown, is dependent on the efficient use of van der Waals interactions between two sets of four methyl groups. Important molecular dimensions (bond lengths corrected for libration) are: Si—O = 1.629(1) and 1.635(1), Si—C = 1.862(2) and 1.848(3) Å, O—Si—O = 108.99(6), Si—O—Si = 157.8(1) and 148.8(2)°.
Electron trapping in alcohol clusters in γ-irradiated alcohol-2,2,4-trimethylpentane- 2,2-dimethylbutane glasses at 77 K
Authors: Kimura Toyoaki , Yasuda Kazuhiro , Fukuda Shigeki , Fueki Kenji
Published: May 2006

An optical absorption study has been made on electrons [Formula: see text] trapped in alcohol clusters in γ-irradiated 1-propanol (PrOH) – 2,2,4-trimethylpentane (TMP) – 2,2-dimethylbutane (DMB), 1-butanol (BuOH) – TMP – DMB, and 1-pentanol (PnOH) –– TMP – DMB mixture glasses at 77 K. Hitherto electron transfer from the hydrocarbon region into alcohol clusters has been known to be a major process for [Formula: see text] formation in γ-irradiated alcohol–hydrocarbon glasses. However, in the present systems of PrOH–TMP–DMB, BuOH–TMP–DMB, and PnOH–TMP–DMB, this type of electron transfer was not observed and the [Formula: see text] formation was found to result only from the direct radiolysis of alcohols. In the alcohol concentration range lower than 0.2 electron fraction the yields of [Formula: see text] are less than those expected from the direct radiolysis of alcohols. The average number of alcohol molecules in a cluster in these systems is estimated to be four in the lower alcohol concentration range studied. The position of the absorption maxima for [Formula: see text] in these systems is constant within experimental uncertainties independent of alchohol concentration, which is consistent with the results of a semicontinuum model calculation.
Transfer thermodynamics of p-nitroaniline in aqueous solutions of some ionic and non-ionic cosolvents and the structuredness of the solvents
Authors: Datta Jayati , Kundu Kiron K.
Published: May 2006

Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of p-nitroaniline (pNA) from water to aqueous mixtures of some ionic and non-ionic cosolvents like KBr, urea (U), propylene glycol (PG), glycerol (GL), dioxane (D), and 1,2-dimethoxyethane (DME) have been determined from solubility measurements at different temperatures. The observed [Formula: see text]–composition profile in KBr solution appears to result from the well known salting-out effect of the salt and those in aqueous poly-ols and ethers are the result of the combined effects of dispersion and "acid–base" type interactions but that in aqueous urea solutions is governed by the "salting-out" type interaction by the predominant zwitterionic form of urea. The observed [Formula: see text]–composition profiles as well as those obtained after correcting for the "cavity-effect", as estimated tentatively by the scaled particle theory (SPT), were examined in the light of Kundu et al.'s semi-quantitative theory proposed earlier. The latter profiles suggest that unlike isopropyl alcohol (IPA), the poly-ols and ethers as well as KBr and urea induce structure breaking of three dimensional (3D) water structure right from the initial compositions. Moreover, the observed "roller-coaster" type behaviour of the profile in aqueous urea is indicative of the effect of urea–water aggregation around 4–10 m urea. Also, the observed graded reduction of structure-promoting effect of IPA in PG and GL cosolvent systems confirms that structuring and destructuring ability of a cosolvent depends on the ratio of hydrophobicity to hydrophilicity of the cosolvent.
The mechanisms of the physicochemical reactions in diorite used in the construction of ancient royal Egyptian statues
Authors: McFarlane Joanna , Wilson-Yang Kristine M. , Joseph Sidney , Frey Carla , Burns George
Published: May 2006

During the heights of ancient Egyptian civilization, statues of deities and pharaohs were often constructed of hard and colourful igneous rocks, such as granite and diorite. Most of these statues remain in an excellent state of preservation. However, others have unexpectedly fragmented, in some cases only a few years after having been excavated in near-perfect condition. In the present work it is shown that two interrelated physicochemical processes contribute to this degradation: (1) the infiltration of saline H2O and (2) subsequent alteration of the constituent minerals. Conclusions were reached on the basis of neutron activation and atomic absorption analyses of rock samples from two sites in Upper Egypt and leached soluble salts therefrom. These samples were identified as quartz diorites on the basis of petrographic and X-ray spectroscopic examination. The chemical significance of the geological nature of the stone is discussed. Possible precautions to be observed in the field are presented.
The irradiation of alkyl siloxanes in the adsorbed state. Part 3. The irradiation chemistry of hexamethyldisiloxane adsorbed onto silica
Authors: Maeng K-S. , Brown G. R. , Trudel G. J. , St-Pierre L. E.
Published: May 2006

Enhanced production of hydrogen, methane, and ethane from the γ-irradiation of hexamethyldisiloxane (MM) adsorbed onto silica compared to that from liquid MM results from energy transfer from the solid to the adsorbed layer. Chemical reactions with the surface are shown by deuterated products from the irradiation of MM on a deuterated silica and from extensive chemical cross-linking to the surface. These reactions predominate in the first monolayer of coverage.
Mass spectra of some substituted methylcyclosiloxanes
Authors: Pelletier E. , Harrod J. F.
Published: May 2006

The mass spectra of the substituted methylcyclosiloxanes [Formula: see text] where X = H (n = 4, 5 and 6), X = C6H5 (n = 3 and 4), X = Br (n = 3 and 4), X = Co(CO)4 (n = 4 and 5) have been measured. The compounds X = H fragment by the same kinds of substituent loss and ring contraction mechanisms as previously reported for the compounds X = CH3 but also by the loss of methylhydrogensilanone. The compounds X = Ph fragment by loss of benzene from an intramolecularly bridging benzenonium ion, formed from [M − CH3]+• and by losses of the phenylmethylsilanone fragments. The compounds X = Br only undergo substituent loss without ring fragmentation. The compounds X = Co(CO)4 show stepwise loss of all CO groups from [M]+•, [M − Co(CO)4]+, and [M]++.
The decay of 56-s, 148Ce to levels of odd–odd 148Pr
Authors: Aras N. K. , Chung C. , Faller S. , Stone C. A. , Walters W. B. , Gill R. L. , Shmid M. , Chrien R. E.
Published: May 2006

The decay of 148Ce to levels of 148Pr has been studied using mass-separated sources. A half-life of 56 ± 1 s has been measured for the decay of 148Ce. A level scheme containing 40 γ rays and 15 excited levels is proposed for 148Pr. Strongly β-fed 1+ levels have been identified at 390 and 520 keV that are similar in position to 1+ levels observed in isotonic 146La and isotopic 146Pr.
Mass spectrometric determination of Rb fission yields from 3He and 4He induced fission of 238U and 232Th
Authors: Reeder P. L.
Published: May 2006

Cumulative and independent fission yields of Rb isotopes have been measured for 3He and 4He induced fission of 232Th and 238U at bombarding energies slightly above the Coulomb barriers. The on-line mass spectrometric technique provided yields for masses 89–97. Mean masses and widths of the Rb independent yield distributions were obtained and were compared to other fissioning systems with excitation energies up to 160 MeV.
Factors affecting product formation in the photolysis of α-spirocyclopropyl ketones
Authors: Yates Peter , Helferty Patrick Hugh
Published: May 2006

Photolysis of spiro[2.5]oct-7-en-4-ones results in exclusive β-cleavage in methanol to give 2-ethenylcyclohex-2-en-1-ones and in hydrocarbon solvents to give (E)- and (Z)-2-ethylidenecyclohex-3-en-1-ones. The solvent effect is ascribed to the role of methanol in stabilizing trienol intermediates and engendering their intermolecular ketonization. Photolysis of 8-methylenespiro[2.5]octan-4-ones in methanol gives 2-ethenylcyclohex-2-en-1-ones and bicyclo[4.3.0]non-1(6)-en-2-ones; irradiation in methanol-O-d indicates that the former type of product is formed mainly via a trienol intermediate. Photolysis of 8-methylenespiro[2.5]octan-4-ones in benzene gives 2-ethenylcyclohex-2-en-1-ones together with (E)- and (Z)-2-ethylidene-3-methylenecyclohexan-1-ones; the latter undergo photoconversion to the former during the irradiation. 6,6-Dimethylspiro[2.4]-heptan-4-one on photolysis in methanol undergoes ct-cleavage to give 4-methoxy-7,7-dimethyl-5-oxaspiro[2.5]octane as the major product, whereas under the same conditions 6,6-dimethylspiro[2.5]octan-4-one is reduced to the corresponding alcohol and 6,6,8-trimethylspiro[2.5]octan-4-one undergoes β-cleavage to give 2-ethyl-3,5,5-trimethylcyclohexan-1-one as the major primary product; this trichotomy is interpreted in terms of ring-size and steric factors.
The effect of silanes on the mercury-photosensitized decomposition of nitric oxide
Authors: Bell T. N. , Soto-Garrido G. , Sherwood A. G.
Published: May 2006

The decomposition of NO, photosensitized by Hg63P atoms, leads to N2 and N2O. The decomposition rate is enhanced by the silanes Me2SiF2 and MeSiF3. A mechanism is proposed involving the formation of complexes of the silanes with electronically-excited NO.
Deviations from the O3–NO–NO2 photostationary state in tropospheric chemistry
Authors: Calvert Jack G. , Stockwell William R.
Published: May 2006

A theoretical study of the magnitude and origin of deviations in the photostationary state relation, [Formula: see text] has been carried out by computer simulation. Various homogeneous tropospheric mixtures were chosen with initial pollutant concentrations varied from those of highly polluted to very clean atmospheres. Even for the homogeneous conditions assumed here, strong negative deviations were observed ([O3]t[NO]t/[NO2]t < (k1/k3)t for many of the conditions chosen. Failure of [I] in many cases resulted largely from the non-zero value of d[O3]/dt. Many other factors, including significant rates of O3 reaction with NO2, alkene, HO2, HO, and ozone photolysis, contribute significantly to the deviations seen in several cases considered.
The determination of the stoichiometry and stability constant of weak complexes in solution: a restatement of the "straight-line" method
Authors: Beltrán-Porter Aurelio , Ramírez José A.
Published: May 2006

Usually, to establish the degree of condensation of a complex species in solution, primarily when it is a weak complex, is more cumbersome than to determine the stoichiometric ratio itself. The present work describes a modification of the Asmus method in order to render it suitable for the determination of the actual stoichiometric coefficients and the stability constant of weak complexes whatever the degree of condensation may be.
The reaction of trimethylamine in liquid hydrogen sulphide: an electrical conductivity study
Authors: Halliday James D. , Bindner Patrick E.
Published: May 2006

The electrical conductivity of trimethylamine solutions (2.26 × 10−4 to 2.89 × 10−1 mol L−1) in liquid hydrogen sulphide over the temperature range −72.5 °C to +25.0 °C has been measured. The data indicate that the trimethylamine behaves as a Brønsted base in liquid hydrogen sulphide [1] and is protonated to form trimethylammonium hydrogensulphide. The latter[Formula: see text]behaves as a normal weak electrolyte in a solvent of low to medium dielectric constant [Formula: see text]. The conductance data as a function of temperature also show that trimethylamine exists both as a hydrogen bonded complex with H2S and as an unassociated molecule in liquid H2S.
Neutral and anionic derivatives of toluene-3,4-dithiolatocadmium(II); the crystal structure of di(tetraphenylarsonium) bis(toluene-3,4-dithiolato)cadmate(II)
Authors: Bustos Luis , Khan Masood A. , Tuck Dennis G.
Published: May 2006

Cadmium(II) chloride reacts with toluene-3,4-dithiol (H2TDT) to give Cd (TDT), which is apparently a homopolymer in the solid state. Adducts with neutral monodentate and bidentate donors have been prepared. The structure of the salt (Ph4As)2 [Cd(TDT)2] was determined by X-ray crystallography. Crystals of this compound are monoclinic (P21/c), with a = 23.032 (4) Å, b = 12.396(4) Å, c = 22.529(5) Å, β = 111.106(2)°. The structure was refined by least-squares methods to a final R-valueof 0.0469 for 2523 "observed" reflections. The anion is a distorted tetrahedral, mononuclear species with Cd—S bond distances ranging from 2.488(5) Å to 2.531(4) Å. This anion is also a Lewis acid, forming complexes of the type [Cd(TDT)2L]2− with neutral bidentate ligands.
Generalized rate law for vibrational relaxation of a pure diatomic gas
Authors: Teitelbaum Heshel
Published: May 2006

The master equation for the vibrational relaxation of a pure gas of diatomic molecules AB is reduced to a simple analytical rate law. Anharmonicity is accounted to first order, and both T–V and near-resonant V–V energy transfer processes are included with the limitation that Δν = ± 1. L and au–Teller type transition probabilities are used to scale the rate constants. The rate law consists of a pair of simultaneous first order non-linear differential equations — one for the mean vibrational energy, [Formula: see text], and one for the mean squared vibrational energy [Formula: see text]; or equivalently a non-linear second order differential equation for [Formula: see text], with respect to time, t, plus an algebraic equation for [Formula: see text] These lead to[Formula: see text]where χe is the anharmonicity factor, N the molecular concentration, νe,. the spectroscopic vibrational frequency; ν′ = νe (1 − χe); ν″ = νe. (1 − 3χe); [Formula: see text]; 1/τ = Nk1.0(1 − e−hν″/KT); k1.0 the rate constant for the process AB(ν = 1) + AB(ν) → AB(ν = 0) + AB(ν); and [Formula: see text] the rate constant for the process 2AB(ν = 1) → AB(ν = 0) + AB(ν = 2). It is shown that the Bethe–Teller law, [Formula: see text], is valid only in the limit of zero anharmonicity or slow V–V processes, or when the initial population is Boltzmann, such as in shock tube experiments. Furthermore, a population distribution which is initially Boltzmann will remain so; whereas a non-Boltzmann distribution rapidly becomes a Boltzmann distribution on a time scale determined by the sum of T–V and V–V rate constants. The present study allows one to gauge the importance of two common assumptions: the validity of the Bethe–Teller law and the existence of a Boltzmann distribution or vibrational temperature during the relaxation.
Conformation of purine mononucleotides by H{H} and P{H} nuclear Overhauser effects
Authors: Santos H. , Xavier A. V. , Geraldes C.F.G.C.
Published: May 2006

The proton–proton and phosphorus–proton nuclear Overhauser effect (nOe) of guanosine 5′-monophosphate (5′-GMP) was measured in aqueous solution at different pH values and in the presence of excess LaIII at acid pH. These data and nOe data from the literature for other mononucleotides were used together with vicinal proton–proton coupling constants to investigate the conformations of mononucleotides in aqueous solution, especially their rotational state about the glycosidic bond. Comparison of observed and calculated enhancements using various conformational models for the glycosidic bond gave predominantly anti conformations for 5′-AMP and 5′-GMP and a mixture of syn and anti conformations for 2′-AMP, 2′-GMP, 3′-AMP, and 3′-GMP. Protonation of 5′-GMP at N-7 of the guanine base alters the amplitude of its torsion angle within the anti range. The agreement between the glycosidic nucleotide conformations defined by nOe and by the lanthanide probe method is good but not perfect. As complexation of 5′-GMP with LaIII through the phosphate group has only a small effect on the conformation of its exocyclic group, a comparison of the two methods is justified.
Investigation of the possible pathways for magnetic exchange interactions in homobinuclear chelates of naphthazarin
Authors: Tsipis Constantinos A. , Sigalas Michael P. , Papageorgiou Vasilios P. , Bakola-Christianopoulou Maria N.
Published: May 2006

Homobinuclear complexes of the binucleating naphthazarinato ligand of the general formula [Formula: see text] where M = Cu, Ni, and Zn, C10H4O4 = naphthazarinato ligand, and C10H8N2 = 2,2′-bipyridyl, have been prepared and studied. In these complexes the naphthazarinato ligand, acting as a bridging unit between the two metal centers, supports the propagation of magnetic exchange interactions through its extensive π-electron system. The spectroscopic and magnetic data of the compounds showed that each metal ion is surrounded by two oxygen and two nitrogen donor atoms in a nearly tetrahedral configuration (C2v point group) with the naphthazarinato ligand adopting a centrosymmetrical structure of C2h symmetry. The room-temperature magnetic data of the copper(II) and nickel(II) homobinuclear chelates (1.32 and 1.73 BM per metal ion at 8000 G, respectively), as well as the slight decrease of the magnetic moments as the magnetic field strength decreases are indicative of the operation of antiferromagnetism in these chelates. Quantum mechanical calculations of the Hückel LCAO-MO type improved by ω-technique have been used to provide a qualitative guide to the possible pathways for the superexchange processes observed in the tetrahedral copper(II) and nickel(II) chelates, as well as to explain qualitatively why there is no antiferromagnetic interactions propagated by the bridging naphthazarinato ligand in analogous homobinuclear chelates with other coordination geometries such as square planar, square-pyramidal, trigonal bipyramidal, and octahedral.
3-Methylpyridine complexes of cobalt(II) and nickel(II) hexafluorophosphate and hexafluoroarsenate. Crystal and molecular structure of Ni(H2O)2(3-CH3C5H4N)6(PF6)2
Authors: Morrison Raymond M. , Thompson Robert C. , Trotter James
Published: May 2006

Reaction of aqueous solutions containing CO2+ or Ni2+ and PF6−, or AsF6− with excess 3-methylpyridine yields crystals of compounds of composition M(H2O)2(3mpy)6(EF6)2. Blue crystals of diaquohexakis(3-methylpyridine)nickel(II) hexafluorophosphate, C36H46F12NiN6O2P2, are monoclinic, a = 10.497(1), b = 20.074(3), c = 21.836(5) Å, β = 103.93(2)°, Z = 4, space group Cc. The structure was determined with MoKα CAD4 diffractometer data by direct methods, and refined by full-matrix least-squares procedures to R = 0.048 for 2723 reflections with I ≥ 3σ(I). The structure consists of {Ni(3mpy)4[(OH2)(3mpy)]2}2+ cations and PF6− anions. The cation contains a NiN4O2 chromophore with water molecules occupying trans positions of a distorted octahedron about nickel. One additional 3-methylpyridine molecule is H-bonded to each of the water molecules with [Formula: see text] distances of 2.717(11) and 2.719(11) Å. Weak interaction of each water molecule via its second hydrogen atom with a PF6− ion is indicated by the positioning of the anions. The [Formula: see text] distances are 2.958(11) and 2.959(11) Å. Two other complexes of this type, where M is Ni and E is As and where M is Co and E is P, are reported here and on the basis of spectroscopic and magnetic studies are assigned structures similar to the Ni/P complex.Decomposition of the aquo complexes under mild conditions yields compounds of composition M(3mpy)4(EF6)2. Ni(3mpy)4(PF6)2 is assigned a square planar structure with weakly interacting PF6−, anions in axial positions. Both Co(3mpy)4(EF6)2 complexes, where E is P or As, have tetrahedral [Co(3mpy)4]2+ cations and non-coordinated anions.
The determination of technetium-99 in urine
Authors: Kramer Gary H.
Published: May 2006

A method has been developed for the routine radiochemical analysis of technetium-99 in human urine. The excreted technetium is coprecipitated from a 200 mL urine sample with CuS. Valence state adjustments are performed with K2S2O8. The precipitate is dissolved in ammoniacal peroxide and, after the Cu(II) is removed by ion exchange, the Tc-99 is extracted with 2-butanone (MEK). Subsequent evaporation of the organic solvent gives an essentially weightless source that if counted with a gas proportional counter will give a better limit of detection than liquid scintillation methods. The recovery of Tc-99 using this procedure is 80% (σ = 4%) and the limit of detection is 20 mBq (0.6 pCi) at the 95% confidence level for a routine sample – counting time 20 minutes, counting efficiency 24%, ambient background 1.3 counts per minute (cpm).
Lewis acid complexes of 1,2-diketones and their derivatives. The synthesis of seven-membered rings
Authors: Blackburn Christopher , Childs Ronald F. , Kennedy Roger A.
Published: May 2006

The structures and charge distributions of Lewis and complexes of butane-2,3-dione, 1, cyclohexane-1,2-dione, 2, and 2-methoxycyclohex-2-en-1-one, 5, have been investigated by 1H nmr spectroscopy. A 1:1 complex was formed between 1 and SnCl4 which appeared to have a bridged structure. In the case of 2 and 5 both oxygens were again involved in complex formation with TiCl4 or SnCl4. In each case the large downfield shift of the vinyl proton resonance, H3, indicated extensive charge delocalization within the complexes and that these systems can be regarded as complexed α,β-unsaturated enones. The reactions of Lewis acid complexes of 2, 5, and the silyl ethers 2-(trimethylsiloxy)cyclohex-2-en-1-one, and 3-(trimethylsiloxy)-but-3-en-2-one, 11, with butadiene have been investigated. The acyclic enol ether 11 reacted with butadiene in the presence of either TiCl4 or SnCl4 to give products corresponding to both 4C + 3C and 4C + 2C cycloaddition reactions; in all other cases 4C + 2C products only could be isolated.
Spectre de vibration de quelques N-méthyl-halogénotriazoles-1,2,4
Authors: Idrissi M. Saidi , Senechal M. , Sauvaitre H. , Garrigou-Lagrange C.
Published: May 2006

Vibrational spectra of some N-methyl chloro and N-methyl bromotriazoles-1,2,4 are reported. An assignment of the normal modes is proposed. This study was done in order to find new elements to solve the problem of tautomerism in C-substituted triazoles-1,2,4.
The isotropic hyperfine interaction in ternary complexes of copper(II) with 8-hydroxyquinoline and various salicylic acids
Authors: Anjaneyulu Y. , Rao N. V. S. , Swamy R. Y. , Rao R. P. , Pisipati V. G. K. M.
Published: May 2006

Electron spin resonance and optical absorption studies are carried out on bis(8-hydroxyquinolinato)copper(II) and seven ternary copper(II) complexes with 8-hydroxyquinoline and salicylic acid or substituted salicylic acids. Electron spin resonance spectra of all these complexes give well-resolved lines. An unusual splitting of the parallel lines in frozen solution spectra and four line fluid (DMF) solution spectra at room temperature are observed. It is explained on the basis of either partial dissociation of 8-hydroxyquinoline ligand or the solvation effect of DMF which solvates some copper chelate molecules even at room temperature. This is more prominent on the parallel lines in frozen solution spectra of all the ternary complexes. The molecular orbital coefficients are estimated assuming an axial symmetry and these indicate that the in-plane π bonding is weak compared to σ-bond in the ternary complexes. The value of χ, which is proportional to hyperfine constants, indicates that it is quite independent of either ligand substitutions or substitutions in the ligand, but purely depends upon the immediate environment which constitutes the coordination around the paramagnetic ion.
Bis(diethylammonium) hexachlorostannate(IV), (Et2NH2)2SnCl6, and tris-(di-n-propylammonium) hexachlorostannate(IV) chloride, (n-Pr2NH2)3(SnCl6)Cl: crystal structure and hydrogen bonding
Authors: Cameron T. Stanley , James Margaret Ann , Knop Osvald , Falk Michael
Published: May 2006

The crystal structure of (Et2NH2)2SnCl6 (P21/n, Z = 2, a = 9.078(1) Å, b = 10.644(2) Å, c = 9.801(2) Å, β = 93.02(1)°) consists of a monoclinically distorted antifluorite arrangement of Et2NH2+ and SnCl62− ions. The SnCl6 octahedra are linked by hydrogen bonds to form infinite chains separated from one another by the Et groups. The temperature variation of the spectral features in the NH and ND stretching regions points to the existence of a transition in the vicinity of 320 K. The structure of (n-Pr2NH2)3(SnCl6)Cl (P21/c, Z = 4, a = 10.265(4) Å, b = 30.428(4) Å, c = 10.380(2) Å, β = 92.75(3)°) consists of n-Pr2NH2+ cations of three types, SnCl62−, and Cl−. All the ions are interconnected by hydrogen bonds, those to Cl− being of a strength comparable to the strength of the short, linear [Formula: see text] bond in Et3NHCl. Spectroscopic evidence indicates the probable existence of a transition at ~170 K.
A serendipitous, high yield conversion of norbornenone to tricyclo[3.2.1.02,7]octan-4-one
Authors: Ragauskas Arthur J. , Stothers J. B.
Published: May 2006

Simmons-Smith cyclopropanation of the trimethylsilyl enol ether of norbornenone has been found to generate the 2-trimethylsilyl ether of homoquadricyclene, homoketonization of which affords the symmetrical tricyclo[3.2.1.02,7]octan-4-one regiospecifically with high stereoselectivity favoring inversion of configuration.