bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential energy calculations of the rotational barriers of molecular solids. II. The dynamic structures of adamantane and hexamethylenetetramine in the solid state and the nature of the phase transition in adamantane
Authors: Fyfe C. A. , Harold-Smith D.
Published: May 2006

Nonbonded atom–atom potential functions have been used in conjunction with literature crystal structure data from diffraction measurements to calculate the sublimation energies and also the energy barriers for rotation around the molecular axes for both α and β phases of adamantane and also for hexamethylenetetramine. These results are compared with experimental values and the nature of the dynamic structures deduced.In addition, a detailed consideration of individual intermolecular interactions in the case of adamantane is presented which explains in detail the observed high temperature disordered structure and the nature of the associated order–disorder transition.
The effect of ultrasound on water in the presence of dissolved gases
Authors: Mead Eric L. , Sutherland Ronald G. , Verrall Ronald E.
Published: May 2006

Sonolysis of water at 447 kHz causes a decrease in the pH. The products formed depend to some extent on the nature of the dissolved gases; products observed are hydrogen peroxide, nitrous and nitric acid. The yield of hydrogen peroxide follows the order O2 > air > Ar > N2. In the case of total acid (nitrous and nitric) the yield follows the order air >N2 > Ar > O2. Nitrogen fixation occurs in the presence of Ar and O2 because of the presence of small amounts of N2 either as an impurity in the dissolved gases, or as residual air in the incompletely degassed water.An attempt was made by using the Fricke dosimeter to obtain information on the relative chemical activity of cavitation.
Chemical relaxations in micellar solutions by ultrasonic spectroscopy. II. Sodium heptylsulfate and hexylammonium chloride solutions
Authors: Adair Douglas A. W. , Reinsborough Vincent C. , Trenholm Hayden M. , Valleau John P.
Published: May 2006

Ultrasonic absorptions have been measured by the pulse technique for the dilute and concentrated micellar range for Na heptylsulfate and hexylammonium chloride solutions. The dilute micellar range was also investigated for the Li, K, Rb, and Cs heptylsulfate systems. Single-valued relaxations were found in each system. The relaxation frequencies increased linearly with concentration in the concentrated micellar range but in the dilute range were relatively constant. The relaxation behaviour was interpreted in terms of monomer exchange between micelles.
Constituents of Naucleadiderrichii. Part VII. Synthesis of nauclederine, naucleonine, and naucleonidine; spectroscopic evidence for the structures of 3α-dihydrocadambine and two other constituents
Authors: McLean Stewart , Dmitrienko Gary I. , Szakolcai Akos
Published: May 2006

Evidence is advanced concerning the structures of six N. diderrichii alkaloids, based on synthetic and spectroscopic studies. The synthesis of nauclederine, 2, provides support for the structural assignment made earlier. Synthesis has shown that the structures previously assigned to the alkaloids designated ND-305B and ND-363C are incorrect; this, however, has led to revised structures (19 and 20) for these alkaloids, now named naucleonine and naucleonidine, respectively, and these have been established by synthesis. Based on this study and an examination of data obtained previously, a tentative proposal is made for the structure 21 of another constituent of the plant, designated ND-363B. Spectroscopic studies have allowed a structure 22 to be advanced for the glycosidic alkaloid, which was shown to be identical with the alkaloid 3α-dihydrocadambine obtained by Brown and Fraser. Based on this study and a reexamination of data reported previously, structure 25 is tentatively proposed for another constituent of the plant, designated ND-370.
Isolation and structure of pimaydolide, a cyclodepsipeptide metabolite of Pithomyces maydicus
Authors: Russell D. W. , Jamieson W. D. , Taylor A. , Das B. C.
Published: May 2006

A new metabolite has been isolated from cultures of Pithomyces maydicus. Evidence is presented that suggests its structure is cyclo(L-2-oxy-3-methylbutyryl-D-valyl-D-leucyl-L-2-oxy-4-methylvaleryl-L-2-oxy-3-methylbutyryl-L-N-methylleucyl), 1.
Concerning the influence of inert gas adsorption on the infrared spectrum of OH groups on powdered silica
Authors: Roth J. G. , Dignam M. J.
Published: May 2006

McDonald's study of the absorption band at 3749 cm−1, due to the O—H stretching vibration of hydroxyl groups on outgassed powdered silica, revealed substantial changes in center frequency and band area upon adsorption of Ar. The main features of these changes are accounted for here using an optical model for porous adsorbent–adsorbate systems due to Dignam, Rao, and Roth. The possibility of using the measured change in band intensity on adsorbing an inert gas, as a general indicator of the orientational distribution of the adsorbed species responsible for the band, is noted.
The assignment of 1H and 13C chemical shifts for dihydro-3(2H)-furanone derivatives by means of specific 2H labelling experiments and 13C{1H} decoupling experiments
Authors: Burke Patrick M. , Reynolds William F. , Tam Janet C. L. , Yates Peter
Published: May 2006

The 1H nmr spectrum of dihydro-2,2,5,5-tetramethyl-3(2H)-furanone (1) in 80% sulfuric acid shows a time-dependent decrease in the intensity of the lower-field gem-dimethyl signal relative to the upper-field gem-dimethyl signal. This is interpreted as involving reversible opening of 1 to 2-hydroxy-2,5-dimethyl-4-hexen-3-one, resulting in deuterium exchange at the C-5 methyl groups of 1. The lower-field gem-dimethyl signal of 1 in this medium is therefore assigned to these methyl groups. A similar relationship between the methyl proton signals of 1 in organic solvents has been demonstrated by (i) synthesis of 1-d8 (8), (ii) comparison of the 1H nmr spectra of 1 and its 2,2- and 5,5-dimethyl analogs, and (iii) observation of long range coupling in the spectrum of 1. Assignment of 13C chemical shifts for 1 has been made based on protoncoupled spectra, showing that the signal of the C-5 methyl carbons appears at ca. 4 ppm towards lower field than that of the C-2 methyl carbons. Both the 1H and 13C chemical shift assignments for 1 were confirmed from 13C{1H} spectra using low power single frequency 1H decoupling, demonstrating the utility of this technique for the assignment of chemical shifts.
The interrelation between polarographic half-wave potentials and the energies of electronic excited states
Authors: Loutfy Rafik O. , Loutfy Raouf O.
Published: May 2006

The polarographic half-wave oxidation and reduction potentials, singlet and triplet energies of a series of (i) monocyclic aza-aromatics, (ii) polycyclic aza-aromatics and their N-oxides, (iii) condensed aromatic hydrocarbons, and (iv) substituted benzene derivatives are reported. The interrelation between the spectroscopic and electrochemical data is developed and discussed in regard to theoretical and experimental parameters. A linear free-energy relationship between the triplet energies and the absolute difference between the oxidation and reduction potentials of the first three series was found. These correlations were utilized to estimate the triplet energies of other molecules in the series, to predict the true half-wave oxidation potential of some heteroaromatic N-oxides and to compute the coulomb repulsion integral. No correlation between ET(π, π*) and (E1/2°x − E1/2R) for substituted benzenes was found. The various reasons for this deviation were discussed.
Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds. Part X. Pentafluorophenyl dimethyl derivatives of group V
Authors: Jones Timothy R. B. , Miller Jack M. , Peterson J. Lowell , Meek Devon W.
Published: May 2006

A comprehensive low-resolution study of the mass spectra of the compounds C6F5M(CH3)2, where M = N, P, As, is described, fragmentation pathways being assigned with the aid of normal metastable ions and mass analyzed ion kinetic energy spectra (mikes). A comparison of these spectra has re-affirmed the absence of halogen transfer processes for atoms such as N which are incapable of providing the necessary vacant orbitals apparently prerequisite in the mechanisms. The influence of increased coordination to phosphorus and effects on halogen transfer processes are discussed with respect to the mass spectra of the compounds C6F5PX(CH3)2, X = O, S, Se and the gold adducts C6F5P(CH3)2•AuX, X = Cl, Br, I.
Metabolites of bird's nest fungi. Part 5. The isolation of 1-hydroxy-6-methyl-8-hydroxymethylxanthone, a new xanthone, from Cyathus intermedius. Synthesis via photoenolisation
Authors: Ayer William A. , Taylor David R.
Published: May 2006

The structure of 1-hydroxy-6-methyl-8-hydroxymethylxanthone, a new xanthone isolated from the culture broth of Cyathus intermedius, has been confirmed by synthesis. Regioselective hydroxylation of the 8-methyl of 1-hydroxy-6,8-dimethylxanthone was achieved via the peroxide formed by reaction of oxygen with the photoenol, and also via bromination of the photoenol. Extraction of the mycelia of C. intermedius yielded ergosterol and D-mannitol.
Oligoribonucleotide synthesis. IX. Synthesis of sequences corresponding to the dihydrouridine loop neck region common in several transfer RNA molecules
Authors: England T. E. , Neilson Thomas
Published: May 2006

The syntheses of the oligoribonucleotides GpApGpC, GpCpUpC, and ApGpCpUpC by an improved phosphotriester method are described. These sequences are found in the double-stranded region adjacent to the dihydrouridine loop of several transfer RNAs. Of special significance is the improvement in yields that the activating agent, mesitylenesulfonyl triazolide, provides in coupling reactions involving purine residues.
Determination of D[(C2H5)3Sn—C2H5] by the toluene carrier method and studies of the reaction of C2H5 with toluene
Authors: Daly Mary , Price S. James W.
Published: May 2006

The thermal decomposition of tetraethyltin in a toluene carrier flow System has been studied over the temperature range 725 to 833 K and decompositions of 3.4 to 98.0%. Total pressure in all runs were in the range 0.63 to 0.90 kPa and contact times of 0.59 to 4.2 s were used.The progress of the reaction was followed by carrying out full analysis of all pyrolysis products involving the C2H5 radical, assuming that all four C2H5 groups are released. In selected runs analysis for unreacted alkyl was also performed. The agreement between the two methods indicates that reaction 1 is followed rapidly by reactions 2, 3, and 4,[Formula: see text]or alternate reactions that result in the release of all four C2H5 groups each time reaction 1 occurs. The decomposition is essentially homogeneous and[Formula: see text]or −59 340/4.58T if the activation energy is expressed in cal rather than J. Combination of present values of k5 with data from previous studies
Effets de substituants en résonance magnétique nucléaire du 13C. Etude des dérivés du phényl-2 furanne et du phényl-2 pyrrole
Authors: Dana Gilbert , Convert Odile , Girault Jean-Pierre , Mulliez Etienne
Published: May 2006

The 13C nmr spectra of derivatives of phenylfuran and phenylpyrrole were studied. The α and β carbons of the heterocycle, conjugated to the substituent X in the para position of the benzene ring, show variations in chemical shifts which bear a simple relationship to the donor properties of X. This is interpreted by the change in electron density caused by this conjugation. This conjugation seems more important in the series of 2-phenylpyrroles than in the series of 2-phenyl-furans especially if the behaviour of then α position is considered.[Journal translation]
Enthalpies de mélange du tétrachlorure de carbone avec des hydrocarbures à l'aide d'un microcalorimètre Picker à écoulement continu, équipé de séparateurs
Authors: Grolier Jean-Pierre E. , Inglese Americo
Published: May 2006

Molar enthalpies of mixing for carbon tetrachloride + n-heptane, + n-nonane, + n-decane, and + n-dodecane have been measured at 298.15 K using the Picker dynamic flow microcalorimeter equipped with separators which prevent the direct contact of the reacting liquids with the injection pumps. The apparatus was checked at 298.15 K with two binary mixtures, carbon tetrachloride + benzene and dichloromethane + benzene; and it was shown that its accuracy is not affected by the use of the separators.
The influence of neutral salts on the easily polarizable hydrogen bond of H5O2+ groupings in acid solutions
Authors: Schiöberg Dag , Zundel Georg
Published: May 2006

The influence of neutral salts on the easily polarizable hydrogen bond of H5O2+ groupings in aqueous acid solutions is studied, using ir spectroscopy. The absorbance of the ir continuum, caused by the polarizable hydrogen bond in the H5O2+ groupings, usually decreases with increasing neutral salt concentration. This is explained by the polarization of the hydrogen bonds caused by local fields due to the neutral salt ions. The H+ becomes more or less trapped at one of the H2O of the H5O2+. The prominence of this effect increases with increasing cation field, i.e., from Cs+ to Li+, and is more pronounced with bivalent than with monovalent cations. The opposite effect is observed with tetraethylammonium chloride. The symmetry of H5O2+ groups is less strongly disturbed in the presence of neutral salts with ions with very large radii, i.e., small electrical fields, than in pure acid solutions. Considering the torsional vibration of the water molecules, it is finally shown that the hydrate structure network around the H5O2+ becomes disintegrated due to the presence of neutral salts.It is known from electrochemical investigations that the activity coefficient of the excess proton usually increases strongly due to the addition of neutral salts to acid solutions. The opposite is true with the addition of tetraethylammonium salt. Furthermore, the addition of neutral salt decreases the excess proton conductivity. All these observations are discussed on the basis of the ir spectroscopic results.
Unexpected signs of five-bond and six-bond proton spin–spin coupling constants in some acyclic conjugated systems. Through-space couplings.
Authors: Schaefer Ted , Gesser Hyman D. , Rowbotham J. Brian
Published: May 2006

The signs and magnitudes of spin–spin coupling constants over five and/or six bonds in some N-methyl and N,N-dimethyl hydrazones, in methyl vinyl ether, 4-methoxy-3-butene-2-one, 1-methoxy-1,3-butadiene, 1-butene, and in anisole are discussed in terms of coupling mechanisms. In the hydrazones the five-bond couplings between methyl and olefinic protons are negative, while six-bond couplings between protons in methyl groups are positive, a reversal of the expected sign sequence. INDO-MO-FPT calculations are not in agreement with observation, but the disagreement may be a consequence of faulty structural assumptions. The sizeable six-bond couplings imply a negative σ–π contribution to the five-bond constants. The calculated and observed negative couplings over five bonds in methyl vinyl ether and the other molecules above emphasize their dependence on the proximity of the bonds containing the coupled nuclei and are reliable indicators of bond arrangements in these molecules.
Phase transformation studies on anthranilic acid by thermal analysis, infrared absorption, and X-ray diffraction methods
Authors: Rajeshwar Krishnan , Secco Etalo A.
Published: May 2006

The kinetic, structural, and thermodynamic aspects of the phase transition, orthorhombic I → orthorhombic II, in anthranilic acid (o-C6H4NH2COOH) were investigated by thermal analysis, infrared absorption, and X-ray diffraction methods.
Proton magnetic resonance and Raman spectroscopic studies of methylmercury (II) complexes of inorganic anions
Authors: Rabenstein Dallas L. , Tourangeau M. Coreen , Evans Christopher A.
Published: May 2006

Complexation of methylmercury(II) by sulfate, selenate, carbonate, sulfite, selenite, thiocyanate, selenocyanate, sulfide, and selenide in aqueous solution has been studied by proton magnetic resonance and Raman spectroscopy. Formation constants were determined for the SO42−, SeO42−, CO32−, SO32−, SeO32−, SeO3H−, SCN−, and SeCN− complexes from the pH dependence of the chemical shift and the 199Hg−1H spin–spin coupling constant of the methyl group of CH3Hg(II) in solutions containing both CH3Hg(II) and ligand. The chemical shift and the 199Hg–1H spin–spin coupling constant of the CH3Hg(II) in each of the complexes were also obtained from the same measurements. Proton magnetic resonance parameters were measured for several complexes with sulfide and selenide. The ligand donor atom in each of the complexes was identified using the formation constants, the 199Hg–1H spin–spin coupling constant of the complexed methylmercury and the Raman spectral data. It is of particular interest that, in the selenite complex, the methylmercury is bonded to an oxygen atom whereas sulfur is the donor atom in the sulfite complex.
The dependence on wavelength of 13C isotope effects in photolysis of aqueous solutions of ferrie oxalate
Authors: Betts Robert H. , Buchannon Wayne D.
Published: May 2006

The formation of carbon dioxide by photolysis of aqueous solutions of ferric oxalate is accompanied by carbon isotopic fractionation. 12C appears preferentially in the evolved CO2, but the isotope effect depends markedly on the wavelength of the light used. Fractionation is essentially zero (k12/k13 = 1.001) at 366 nm, and increases with wavelength, reaching 1.050 at 520 nm. It is proposed that this variation of isotopic discrimination arises from the differing properties of the excited levels formed by photochemical activation.
Studies of metal–organic interactions in model systems pertaining to natural waters
Authors: Guy Robert D. , Chakrabarti C. L.
Published: May 2006

The interactions of Cu(II), Pb(II), Cd(II), and Zn(II) with humic and tannic acids were studied to evaluate the possibility of metal speciation using a combination of dialysis/atomic absorption spectroscopy, and the pH characteristics of the metal–organic species. The stability constants of metal–organic complexes were found to decrease in the order Pb(II) > Cu(II) > Cd(II) > Zn(II) and EDTA > humic acid > tannic acid. Scatchard plots for the metal–humic acid systems indicated two types of binding sites with a difference in stability constants of about 10. Ultrafiltration of metal–humic acid solutions indicated that the metal ions were concentrated in the large molecular size fractions (> 3.1 nm). Separation by dialysis was used to investigate the release of metal from model sediment components by the organic acids (the metal–organic complexes were non-dialyzable). For release of copper from bentonite, it was found that the amount of copper released depended on both the concentration of ligand and the stability constant of metal complex, with the ratio of metal release to complexing sites decreasing in the order EDTA > humic acid > tannic acid. Release of metal from the solids decreased in the order: bentonite > MnO2 > humic acid. Release of metal from the hydrous oxides via a redox decomposition of the oxide by natural organics was investigated using pyrogallol, gallic, and tannic acids. At natural water pH levels (6–8), 20 μg/ml solutions of the organic acids released 20 μmol manganese per 100 ml solutions whereas at pH 2, 60 μmol manganese were released. The pH behaviour of the organic acids has been explained in terms of formation of oxalic acid at pH &([a-z]+); 5, which then reduces the hydrous oxide.
[4]Annulene. Comments on its infrared spectrum
Authors: Masamune Satoru , Sugihara Yoshikazu , Morio Kazuhiko , Bertie John E.
Published: May 2006

A photo-precursor (4) of [4]annulene (1) has been irradiated at 4–10 K in argon. The infrared spectrum of the photolysate shows two strong bands at 1240 cm−1 and 570 but, in contradiction to an earlier claim, one at 650 cm−1 is missing. The discrepancy between this and the earlier observation is explained, and comments on the infrared spectrum of 1 are made.
Crystal structures of phenacylkojate (2-(hydroxymethyl)-5-phenacyloxy-4H-pyran-4-one) and its complex with sodium chloride: bis(phenacylkojate)sodium chloride
Authors: Phillips Simon E. V. , Trotter James
Published: May 2006

The structures of the title compounds have been determined by three dimensional X-ray crystal structure analysis.Crystals of anhydrous phenacylkojate are monoclinic, space group P21/c, with unit cell dimensions a = 9.087(4), b = 11.764(3), c = 12.714(4) Å, β = 116.57(2)°, Z = 4. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0.044 for 1225 independent diffractometer observations. The crystal structure is held together by hydrogen bonding between carbonyl and hydroxyl groups and [Formula: see text] interactions.Crystals of the sodium chloride complex are monoclinic, space group C2/c, with unit cell dimensions a = 11.3714(6), b = 15.796(1), c = 14.487(1) Å, β = 97.241(5)°, Z = 4. The structure was solved by heavy atom and Fourier methods and comparison with the previously determined structure of the potassium iodide complex. It was refined to R = 0.040 for 1670 independent diffractometer observations. The structure closely resembles that of the potassium iodide complex (P21/n), but in C2/c, the alkali metal ion being eight co-ordinate in each. Na+—O distances are in the range 2.558–2.674 Å and the [Formula: see text] hydrogen bonded distance is 3.266 Å.
Isotope effects in the gas phase radiolysis of H2S and D2S
Authors: McAlpine Robert D. , Miller O. A. , Boyd A. W.
Published: May 2006

Gas phase radiolysis studies have been carried out on mixtures of H2S and D2S using as irradiation sources, either a Gammacell or a Febetron 705 pulsed electron accelerator. Separation factors (α = (H/D)prod ÷ (H/D)react) were obtained for various values of xD (the mole fraction of D2S), dose rate and temperature, as well as with the addition of SF6. All of the observed α values, for 0.2 ≤ xD ≤ 0.8, fall on the following empirical straight line.[Formula: see text]The addition of neon to a D2S/H2S mixture gives a value of α which decreases as the partial pressure of neon increases. For a 70% D2S/30% H2S mixture, &([a-z]+); = 1.9 ± 0.1 for the pure mixture and 1.28 ± 0.08 when 90 kPa of neon has been added to 10 kPa of the mixture. The &([a-z]+); values described by eq. 1 are interpreted as arising from kinetic isotope effects in the reactions of (translationally) hot H or D atoms with H2S, HDS, or D2S to form H2, HD or D2.Hydrogen yields from the gas phase radiolysis of pure H2S and pure D2S have been determined for dose rates from 4 × 1016 to 2 × 1028 eV g−1 s−1. Using dose rates of up to 2 × 1027 eV g−1 s−1, ΔG = G(H2) − G(D2) = 0.5. For the highest dose rate used (2 × 1028 eV g−1 s−1), ΔG = 1.5. The larger value of ΔG at very high dose rates is thought to arise from the dissociative neutralization processes. A possible mechanism is discussed.
Spectroscopic studies in olefins. VI. The valence angle dependence of interproton nuclear magnetic resonance coupling constants
Authors: Rummens Frans H. A. , Kaslander Lee
Published: May 2006

INDO–MO calculations have been performed for all the proton–proton coupling constants in ethylene, propylene, and cis- and trans-2-butene, both at their equilibrium geometry and at geometries deviating from equilibrium, thus resulting in [Formula: see text] parameters for all coupling constants as a function of all valence angles[Formula: see text]. It is shown that such valence angle effects can be appreciable, particularly for two- and three-bond couplings. The valence angle effects are demonstrated to be independent and additive. The calculated data, in combination with the exact geometrical data and experimental values for the coupling constants allow the separation of (inductive) substitution and rehybridization effects. It is also shown that for three-bond couplings the effects of in-path C—C—H bond angle changes are minor in comparison to the exo-path C=C—C valence angle effects. The new data provide a consistently good model to explain certain empirical trends in two- and three-bond coupling constants as a function of the size of the substituents, assuming a simple steric hindrance induced rehybridization mechanism. On the other hand it is also found that such a mechanism cannot account for similar trends in the H—C=C—CH3 allylic and the CH3—C=C—CH3 homoallylic coupling constants.
The alkaloids of L. magellanicum and the structure of magellanine
Authors: Castillo Mariano , Loyola Luis A. , Morales Glauco , Singh Ishwar , Calvo Crispin , Rolland Herbert L. , MacLean David B.
Published: May 2006

Examination of the alkaloids of Lycopodium magellanicum (Palisot de Beauvois) has revealed the presence of five alkaloids of established structure and a previously unreported alkaloid, magellanine (C17H25NO2). The ring System of magellanine, deduced from an examination of its spectroscopic properties, is identical with that of paniculatine. The structure of magellanine has been confirmed, and its relative stereochemistry established, in an X-ray crystallographic study.
Rearrangement studies with 14C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-14C-phenyltriazene and from trianisylvinyl-2-14C-phenyltriazene
Authors: Lee Choi Chuck , Ko Eric C. F.
Published: May 2006

The triphenylvinyl cation generated from reactions of triphenylvinyl-2-14C-phenyltriazene (1) with a number of acids gave no isotopic scrambling from degenerate 1,2-phenyl shifts. The trianisylvinyl cation generated from reaction of trianisylvinyl-2-14C-phenyltriazene (2) with HOAc showed about 38% scrambling of the label from C-2 to C-1, attributable to degenerate 1,2-anisyl shifts. When 2 was treated with HOAc containing 1.7 equiv. of NaOAc, the extent of scrambling was decreased to about 17%. Mechanistic implications of these results are discussed.
The photochemistry of 2-furaldehyde vapour. I. Photophysical processes: phosphorescence excited in the π* ← n transition
Authors: Gandini A. , Hackett P. A. , Back R. A.
Published: May 2006

A search was made for emission from 2-furaldehyde, following excitation in the first two absorption bands. Only phosphorescence from the 3nπ* state was observed. The pressure dependence of the lifetime and quantum yield of this emission was determined, as well as that of the quantum yield of intersystem crossing. A mechanism involving self-quenching of excited triplet 2-furaldehyde is proposed.
Correlation of optical and electron spin resonance spectra for alkali metal solutions in ethylamine and tetrahydrofuran
Authors: Catterall R. , Slater J. , Seddon W. A. , Fletcher J. W.
Published: May 2006

The band maxima of transient optical absorption spectra observed by pulse radiolysis in ethylamine (EA)/tetrahydrofuran (THF) mixtures containing sodium tetraphenylboron are correlated with electron spin resonance (esr) hyperfine splitting constants obtained in potassium/EA/THF solutions. The data suggest that the optical spectra can be attributed to the same 'monomeric' species as observed by esr in alkali metal solutions.
Mercury photosensitization of 1-hexene and cis-2-octene vapor. Intramolecular hydrogen abstraction of vibrationally excited π,π* triplet state
Authors: Inoue Yoshihisa , Takamuku Setsuo , Sakurai Hiroshi
Published: May 2006

Upon mercury photosensitization, the vibrationally excited triplet of the simple alkenes 1-hexene and cis-2-octene undergoes an olefinic type II reaction consisting of an intramolecular 1,5-hydrogen abstraction via a six-membered transition state and subsequent reaction of the resulting biradical, in sharp contrast to the well established allylic C—C and C—H bond cleavage of alkenes without a γ-hydrogen. The cis–trans photoisomerization of cis-2-octene and other intramolecular hydrogen abstractions of minor importance occurring through unfavorable transition states were also observed. The mercury photosensitization of various cyclic and acyclic alkenes so far reported are comparatively discussed.
Heats of formation of some hydrates
Authors: Phillipson Alan , Finlay Gordon R.
Published: May 2006

Heats of formation of hydrates may be measured by dissolving the hydrate and the corresponding anhydrate in water to attain the same final concentration and measure the difference in heats of solution.Measurements were made at 0 °C in a modified Bunsen ice calorimeter, well insulated, and surrounded with an ice–water mixture.The data obtained are a measure of the enthalpy involved in binding a mole of water into a crystal structure, to shed some light on the nature and mechanism of this binding. Several discrepancies are noted, in particular one involving [Formula: see text]. A method for adjusting calculations from 0 to 25 °C in the absence of heat capacity data is proposed.The following hydrates have been studied: LiCl•H2O, LiBr•2H2O, CaCl2•2 and •6H2O, MnCl2•1 and •2H2O, [Formula: see text], MnSO4•1 and •4H2O, MgSO4•1, •4(?), and •7H2O, and [Formula: see text].Additionally, the heat of hydration of hydrazine to N2H4•H2O has been checked.The formation of a coordinated hydrate, from liquid water, involves a heat effect which in the limit approaches 3 kcal mol−1. The first mole of water added may be most strongly bonded (6–10 kcal), possibly since alternate sites in the coordination sphere may be available to it.Values which differ markedly from these levels deserve a critical examination. Higher values may suggest the presence of OH−, or other structural variations, errors in the published data or mistaken identification of the hydrate.
On the use of the n-propylammonium and n-butylammonium salts of d-10-camphorsulfonic acid for the calibration of spectropolarimeters: the concentration and solvent dependency of the optical rotatory dispersion parameters
Authors: Nakagawa Yasushi , Gillen Michael F. , Williams Ross E.
Published: May 2006

The utility of the title ammonium salts for the calibration of ord spectropolarimeters has been investigated. The solvent and concentration dependency of the measured specific molar rotations at 306 and 270 nm suggest that they may be used for calibration purposes only under well-defined conditions. The results of the Kramers–Kronig transformation of their circular dichroic spectra are presented and compared with the measured ord spectra.
Application of photoelectron spectroscopy to intramolecularly hydrogen-bonded systems. Part II. On the n–π* blue shift of carbonyl-containing molecules
Authors: Brown R. S.
Published: May 2006

The photoelectron spectra of 2-hydroxycyclohexanone and 2-methoxycyclohexanone, show that the ionization assigned to removal of the carbonyl n-electron is 0.6 eV higher in the former, presumably due to the intramolecular hydrogen bond. The ultraviolet spectra of these molecules also exhibit a marked blue shift of the n → π* transition in the former of roughly 0.5 eV. A discussion of the observations includes consideration of the effect of the intramolecular hydrogen bond on the ground and excited or ion state.
13C nuclear magnetic resonance studies. 61. The effect of solute–solvent association on internal rotation in substituted benzaldehydes
Authors: Klinck R. E. , Stothers J. B.
Published: May 2006

Complete lineshape analyses of the 13C nmr signals of the ortho and meta carbons have been carried out for two p-substituted benzaldehydes in methylene chloride-d2 and toluene-d8 solutions over a wide temperature range. The activation parameters have been determined for the formyl group rotation and large negative values are found for ΔS≠ when the latter solvent is used. These results suggest that solute–solvent association has a steric effect on the transition state.
Concerning stereochemical assignments from 13C spectra of systems experiencing γ substituent effects. Deshielding antiperiplanar interactions can mislead the unwary
Authors: Ayer W. A. , Browne L. M. , Fung S. , Stothers J. B.
Published: May 2006

A variety of substituents bonded to quaternary carbons exert marked deshielding effects at antiperiplanar γ carbons. The shifts produced by methyl groups are ca. 2 ppm, while hydroxyl groups cause shifts as large as 6 ppm. These shifts are particularly clearly demonstrated by the C-19 shieldings in 5α-substituted steroids. For 9,10-disubstituted decalins, the effect is such that cis and trans isomers are not easily distinguished from their 13C spectra. These shifts contrast sharply with the corresponding effects found for substituents bonded to less highly substituted carbon skeletons.
L'étude de l'adsorption des halogenures d'ammonium quaternaire à l'interface mercure–solution
Authors: Ménard Hugues , Kimmerle Frank M.
Published: May 2006

not available
H3O+ ions in aqueous acid solutions. The infrared spectra revisited
Authors: Giguère Paul A. , Turrell Sylvia
Published: May 2006

We have re-examined the infrared absorption between 4000 and 800 cm−1 of aqueous solutions of the four hydrogen halides at concentrations up to saturation, and under better experimental conditions than heretofore. The new spectra confirm definitely our previous assignment of the three broad bands around 2900, 1730, and 1200 cm−1 to fundamental vibrations of the H3O+ ion. Other proposed interpretations are shown to be untenable; in particular that of Ackermann, based on alleged similarities in the spectra of strong acids and bases. In hydrofluoric acid, hydrogen-bonded ion pairs are responsible for the shifts of the H3O+ frequencies. There is no evidence in the spectra for higher species, such as H5O2+. We conclude that the H3O+ ion has an appreciably longer lifetime in concentrated aqueous acids than in water. It also forms much stronger hydrogen bonds than H2O because of its ionic charge.
Evaluation of a spin-labeled inhibitor of acetylcholinesterase
Authors: Kavanagh-Caron Catherine , Caron Marcel , Brisson Normand , Dugas Hermann
Published: May 2006

This paper describes the synthesis of 1, a spin-labeled analog of N,N-dimethyl-2-phenyl-aziridinium chloride 2. The compound is formed in situ from 3b and acts as a poor competitive inhibitor of bovine erythrocyte acetylcholinesterase with a Ki value of M.
The ionization constant of heavy water (D2O) in the temperature range 298 to 523 K
Authors: Shoesmith David William , Lee Woon
Published: May 2006

The ionization constant of liquid D2O has been measured over the temperature range 298 to 523 K using an aqueous electrolyte concentration cell. Values for the standard free energy, enthalpy, entropy, and heat capacity of ionization have been calculated. The results are compared to similar results for liquid H2O
Reduction of binary sulfate mixtures containing CuSO4 by H2
Authors: Habashi Fathi , Mikhail Shaheer A.
Published: May 2006

The reduction of a binary sulfate mixture cannot be predicted from the behavior of the individual components. Thus, while CuSO4 is reduced to Cu at 400 °C and NiSO4 is reduced to Ni3S2, the sulfate mixture yields Cu, Ni3S2, and Cu2S. Also while FeSO4 is completely stable in H2 at 400 °C, (Cu,Fe) SO4 yields Cu and Cu5FeS4. The formation of Cu2S in the first case and Cu5FeS4 in the second was unexpected. On the other hand, (Cu,Mn)SO4 is stable in H2 up to 550 °C although pure CuSO4 is completely reduced at 400 °C. CoSO4 also interferes when reduced in presence of CuSO4, while Na2SO4, MgSO4, Al2(SO4)3, ZnSO4, CdSO4 do not interfere within limited temperature range. Of these only Na2SO4 forms a complex sulfate with CuSO4. No Cu2SO4 was identified when CuSO4 was reduced in presence of other sulfates although it is an intermediate product during the reduction of pure CuSO4.
The proton magnetic resonance spectra of phenol in the absence of intermolecular proton exchange
Authors: Schaefer Ted , Rowbotham J. B. , Chum Kalvin
Published: May 2006

The proton magnetic resonance spectra in the absence of intermolecular proton exchange for 0.27, 0.59, and 0.79 M solutions of phenol in CCl4 are analyzed. The long-range coupling over five bonds between the hydroxyl and ring protons is estimated as 0.33 Hz in the monomer and as 0.20 Hz in the trimer of a monomer–trimer model. Support for the decrease in the coupling on trimerization is found in CNDO/2 and INDO MO FPT calculations. The long-range coupling over six bonds is unobservable, consistent with conformations of the trimer in which the phenol molecules remain planar. Water catalyzes the intermolecular proton exchange and, in its absence, the transfer of hydroxyl protons from molecule to molecule within the associated species is inefficient.
Selective, reductive dechlorination of chlorodeoxy sugars. Structural determination of chlorodeoxy and deoxy sugars by 13C nuclear magnetic resonance spectroscopy
Authors: Szarek Walter A. , Zamojski Aleksander , Gibson Alan R. , Vyas Dolatrai M. , Jones J. K. N.
Published: May 2006

The reductive dechlorination of chlorodeoxy sugars by hydrogenation over Raney nickel in the presence of potassium hydroxide or triethylamine has been investigated; a selective dechlorination was observed in most cases with triethylamine. Several new, chlorodeoxy furanoid derivatives have been synthesized by the use of triphenylphosphine–carbon tetrachloride. 13C magnetic resonance spectroscopy has been employed for the assignment of structure to the chlorodeoxy sugars and the corresponding reduced products.
Enthalpies, heat capacities, and volumes of transfer of the tetrabutylammonium ion from water to aqueous mixed solvents from the point of view of the scaled-particle theory
Authors: Desrosiers Nicole , Desnoyers Jacques E.
Published: May 2006

The enthalpies, heat capacities, and volumes of transfer of the tetrabutylammonium ion from water to urea–water, tert-butyl alcohol–water, and sodium chloride–water mixtures have been calculated at 25 °C using the scaled-particle theory. In general, the signs, magnitudes, and overall trends in the cosolvent concentration dependence of the properties are predicted from the cavity contributions only. These calculations are found to be very sensitive to the diameters chosen for the various species.For these calculations it was necessary to measure with a dilatometer the coefficients of thermal expansion of tert-butyl alcohol–water mixtures as a function of concentration and temperature.
The reaction of some heterocyelic thiones with ethyl azidoformate
Authors: Chauhan Mohinder S. , McKinnon David M.
Published: May 2006

A number of heterocyclic thiones react with ethyl azidoformate in boiling carbon tetrachloride to yield the corresponding iminocarboxylic esters. 4-Phenyl-1,2-dithiole-2-thione is an exception and yields both a 1,2,3-dithiazine derivative and a urethane type product. 4-Phenyl-1,2-dithiole-3-one yielded an isothiazolin-3-one product. The mechanisms are discussed briefly.
Association and hydration of alcohols in low-dielectric solvents. I. n-Butanol
Authors: Kirchnerová Jitka , Cave Genille C. B.
Published: May 2006

Formulae and thermodynamic formation constants of the aggregates of n-butanol and their hydrates in six low-dielectric solvents have been deduced by using an iterative mathematical treatment of distribution and isopiestic data. The solvents were cyclohexane, carbon tetrachloride, p-xylene, benzene, chlorobenzene, and o-dichlorobenzene.
Solvolysis of isopropyl bromide in ethanol–water mixtures. Dissection into initial state and transition state contributions
Authors: Drenth Wiendelt , Cocivera Michael
Published: May 2006

Rates were determined for the solvolysis of isopropyl bromide in ethanol–water mixtures (20 to 80% by volume of ethanol) at 50 and 75 °C and the corresponding activation parameters calculated. From the partial vapor pressure of isopropyl bromide over the various solutions at 50 and 75 °C, the variations in its initial state thermodynamic parameters were calculated. Thus, the variation in the activation parameters with solvent composition could be analyzed in terms of initial and transition state contributions. The initial state variation dominates according to a unimolecular as well as to a bimolecular treatment of data.
Ethyl 4-iodo-2,3,4-trideoxy-α-D-threo-hex-2-enopyranoside: synthesis and dehydroiodination
Authors: Yunker Mark Bernard , Fraser-Reid Bert
Published: May 2006

Iodinolysis of ethyl 6-O-benzoyl-4-O-methylsulfonyl-2,3-dideoxy-α-D-erythro-hex-2-enopy-ranoside in the presence of pyridine gives the expected product of inversion, viz. the 4-iodo-2,3,4-trideoxy-α-D-threo congener (8). If, however, the pyridine is omitted, 8 rearranges to give ethyl 6-iodo-4-O-benzoyl-2,3,6-trideoxy-α-D-erythro-hex-2-enopyranoside. Reduction of 8 with lithium aluminum deuteride takes three courses: allylic deuterolysis in the expected SN2′ sense, deuterolysis at C-4 with retention of configuration, and a ring opening reaction giving deuterated hexa-2,4-dien-1,6-diol. Dehydroiodination of 8 with diazabicyclononene gave 1-benzoloxy-6-ethoxy-3(E),5(Z)-hexadiene-2-one in 86% yield.
Kinetics and energetics of the addition of iodonium nitrate to unsaturated systems
Authors: Lown J. William , Joshua Alummoottil V.
Published: May 2006

The stereochemistry of the products of addition of iodonium nitrate to a series of cycloalk-2-en-1-ols indicates that the intermediate iodonium ion is formed cis to the neighbouring hydroxyl in the case of five-, six-, and seven-membered cyclic alkenols and trans to the hydroxyl in the case of cycloct-2-en-1-ol. The rates and Arrhenius parameters for the second-order additions of iodonium nitrate to these and other unsaturated substrates have been determined. An α-hydroxy group enhances the rate of addition over the corresponding alkene when the iodonium ion is formed cis to the hydroxyl and has the opposite effect when it is formed trans to the hydroxyl. This evidence for neighbouring hydroxyl group participation in additions of iodonium nitrate is in contrast to the known chemistry of iodine isocyanate and iodine azide. The effects of structural changes of the substrate on the kinetic and energetic parameters in iodonium nitrate additions are discussed and compared with those of other pseudo-halogens.
Heat capacities of weak electrolytes and ion association reactions: method and application to aqueous MgSO4 and HIO3 at 298 K
Authors: Woolley Earl M. , Hepler Loren G.
Published: May 2006

Analysis of heat capacities for weak electrolytes (or 'almost strong' electrolytes) in terms of the various solute species is shown to require allowance for the thermal effects associated with the shift of the association or dissociation equilibrium when the temperature changes during a calorimetric measurement. This shift of equilibrium state is related to changes in the equilibrium constant and activity coefficient with temperature, as expressed by thermodynamic equations we have derived. These equations have been applied to aqueous MgSO4 and HIO3 to obtain the contributions of the solute species to the apparent molal heat capacities, which are then analyzed to yield heat capacities of MgSO4 (aq, undiss.) and HIO3 (aq, undiss.) and ΔCP0 values for the association reactions of the ions to form these species.
Rearrangements Involving alkoxycarbonyl group migration between nitrogen and oxygen.III. Reactions of modified isoquinoline Reissert compounds with aldehydes
Authors: Rozwadowska M. D.
Published: May 2006

The condensation reaction of modified Reissert compounds with aldehydes was investigated. In the reaction of the N-ethoxycarbonyl Reissert analog 1b, ethoxycarbonyl group migration takes place and carbonates of 1-isoquinolylphenylcarbinols (2b, c) are formed. No alkoxycarbonyl group migration was observed in the case of the dihydro-Reissert derivative 6, but the cyclic urethane 7 and the amide 8 were obtained.
Chemistry of metal hydrides. Part XX. The nature of the insertion rearrangement of acetylenes with platinum(II) hydrides
Authors: Attig T. G. , Clark H. C. , Wong C. S.
Published: May 2006

The reactions of platinum(II) hydrides, trans-PtHXL2, where X = NO3, Cl or CH3OH, and L = PEt3 or tricyclohexylphosphine, with disubstituted acetylenes, R1C≡CR2 have been examined under a variety of conditions. From spectroscopic parameters, the gross geometry at platinum as well as the geometry of the resulting alkenyl groups in the products have been determined. The observation that all alkenyl groups have a cis geometry is consistent with a migratory insertion step involving a four-centred transition state, in which the disposition of the acetylene relative to the Pt—H bond appears to be dependent on the Pt—H bond polarity. Evidence is presented to demonstrate that this polarity depends on several factors including solvent, and ligands on Pt(II). For L = tricyclohexylphosphine, the occurrence of a side reaction which competes with insertion and which leads to a Pt(0) acetylene complex is also demonstrated, and other interesting reactions are described.
An attempted synthesis of an oxacepham derivative using isonitriles as β-lactam forming agents. On the stability of dihydrooxazines and the inadequacy of ammonia as the fourth component in the Ugi reaction
Authors: Just G. , Chung B. Y. , Grözinger K.
Published: May 2006

An attempted synthesis of an oxacepham derivative, using isonitriles as β-lactam forming agents, is described. The reasons for the failure of this approach are discussed.
Vibrational analysis and force field for some secondary iodides
Authors: Crowder G. , Najafi Zahra
Published: May 2006

Normal coordinate calculations were made for 2-iodopropane and the three conformers of 2-iodobutane. A forty-seven parameter modified valence force field was used that fit eighty-four frequencies of those four molecules in the 250–1500 cm−1 region with an average error of 4.8 cm−1, or 0.6%. Infrared spectra were obtained for 2-iodopentane and 3-iodopentane, and zero-order normal coordinate calculations were made for three conformers of 2-iodopentane and for five conformers of 3-iodopentane. The SHH, SHH′, and SCH conformers of 2-iodopentane are present, along with one or two unidentified ones, and 3-iodopentane exists as a mixture of the SHH, SHH′, SCH, and SCH′ conformers. The force constants that were determined for the four conformers of 2-iodopropane and 2-iodobutane were transferred to the two secondary iodo-pentanes with good success. The average difference between observed and calculated wave-numbers for 164 frequencies of seven conformations of these two compounds was 5.8 cm−1.
σ-Aryl complexes of iridium: diphenyliodonium salts as phenylating agents in transition metal chemistry
Authors: Farrell Nicholas , Sutton Derek
Published: May 2006

Diphenyliodonium salts readily react with [IrX(CO)(PR3)2] (X = Cl, Br; PR3 = PPh3 or PMePh2) to yield iridium(III) σ-phenyl complexes of general composition [IrXY(C6H5)(CO)(PR3)2] (Y = Cl, BF4). The possible structures of these compounds, and their occurrence in the decomposition of iridium aryldiazenato complexes, are discussed.
Electronic excited states of small ring compounds. IV. Bicyclo[2.1.0]pentanes by the photocycloaddition of cyclopropenes to olefins
Authors: Arnold D. R. , Morchat R. M.
Published: May 2006

Direct irradiation of the charge-transfer complex between the cyclopropenes 3,3-dimethyl-1,2-diphenylcyclopropene (3) and 1,2,3-triphenylcyclopropene (7), and the electron deficient olefins dimethyl fumarate (5) and maleic anhydride (11) resulted in formation of the cycloadducts 6, 12–15 which are the bicyclo[2.1.0]pentane derivatives. These products were also formed when the reaction was photosensitized by triplet–triplet transfer. The structure of the adducts rests largely upon the interpretation of 13C and 1H nmr spectra. Nuclear Overhauser effect studies were used to assign stereochemistry. The thermal stability of these new bicyclo[2.1.0]-pentane derivatives has been examined, particularly with regard to the ring-flipping process and the rearrangement to the corresponding cyclopentene derivatives.