bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of reactant purity on the radiolysis of gaseous ethane and propane
Authors: Gawłowski Janusz , Niedzielski Jan , Herman Jan A.
Published: May 2006

The yields of products formed in the recombination of free radicals in the radiolysis of gaseous ethane and propane have been determined. The yields of butane from ethane radiolysis, and of 2, 3-dimethylbutane from propane radiolysis were found to be much lower than those reported in the literature.The yields of these products increased markedly in the presence of the traces of water, either desorbed from the walls or introduced with insufficiently dried reagents. The details of experimental procedures warranting the total elimination of water are given.
The preparation and characterisation of Sb3Cl11F4
Authors: Ballard Jack G. , Birchall Thomas , Slim David R.
Published: May 2006

The title compound has been prepared by the reaction of SbF5 and SbCl5 in liquid SO2. Raman and Mössbauer spectra have been recorded and its crystal structure determined by three-dimensional X-ray counter measurements. Crystals are monoclinic with a = 12.359(6) Å, b = 16.480(10) Å, c = 9.387(3) Å, β = 103.96(5)°. The structure has been refined in the space group P21/n to a final agreement index R2 of 0.113 for 2415 independent reflections. The structure consists of a cis fluorine-bridged trimer with one of the chlorine atoms 25% substituted by fluorine.
Conformational and configurational analysis of hydrocarbon chains based on time-averaged carbon-13 chemical shifts
Authors: Beierbeck Helmut , Saunders John K.
Published: May 2006

The conformations of saturated hydrocarbon chains are analysed by a least-squares fit of calculated to observed time-averaged carbon-13 chemical shifts. The calculated resonances are the sums of products of conformer resonances and conformer probabilities. The conformer shieldings are derived with predictive parameters developed earlier for conformationally well defined systems. The conformer probabilities are taken to be products of rotamer probabilities. The rotamer probabilities are variables in the analysis.
Triazolopyridine nucleosides. II. Glycosylations of 3-oxo-s-triazolo[4,3-a]pyridines with accompanying conversions into 2-oxo-s-triazolo[1,5-a]pyridine nucleosides
Authors: Lynch Brian Maurice , Sharma Suresh Chandra
Published: May 2006

3-Oxo-s-triazolo[4,3-a]pyridine and various C-methyl derivatives (general structure 1) have been converted into the 2-β-D-ribofuranosyl species 2 and thence 4 via Friedel–Crafts catalyzed reaction with tetra-O-acetyl-β-D-ribofuranose, followed by deblocking. During the course of these reactions, rearrangements into the isomeric 3-β-D-ribofuranosyl-2-oxo-s-triazolo[1,5-a]-pyridines occur through ring-opening of the pyridine rings yielding species 3 and 5. The proportion of rearrangement products is dependent upon the position and number of the C-methyl substituents.Structural assignments for these compounds are based upon comparisons of spectroscopic properties (1H nmr, 13C nmr, uv) with model compounds from each isomeric series; structural assignments for these models are based on unequivocal mass-spectral fragmentation patterns. Unlike related triazolopyridine nucleosides with the ribose moiety attached to a pyridine nitrogen (Lynch and Sharma (1976)), there are no unusual aspects in the conformations of the nueleosides of types 4 and 5.
The structure and energetics of low-lying states of RCO and RNN free radicals
Authors: Baird N. Colin , Kathpal Harish B.
Published: May 2006

The important geometrical variables in the structures of the lowest 2A′ and 2A′′ states of the free radicals HCO, CH3CO, NH2CO, HNN, and CH3NN have been determined by ab initio MO calculations using the STO-3G basis set. The energy differences between the states, and the energies of the radicals relative to their decomposition products and relative to their hydrogen atom addition products, are reported using both STO-3G and 4-31G basis sets in the restricted open-shell calculations. The trends in these results and their relation to available experimental data are discussed.
Total synthesis of spirobenzylisoquinoline alkaloids. Part IV
Authors: McLean Stewart , Dime David
Published: May 2006

The stereoselective synthesis of the racemic forms of the spirobenzylisoquinoline alkaloids corydaine and yenhusomidine is reported.
Density of states and the steepest descent method: a non-iterative procedure
Authors: Yau Andrew W. , Pritchard Huw O.
Published: May 2006

A non-iterative approximation to the method of steepest descent is given for the evaluation of state density in a molecular system. Test calculations on 'large' and 'small' model molecules consisting of harmonic oscillators and rigid rotors show excellent agreement with the 'exact' first-order steepest-descent solutions, but are almost an order of magnitude faster in computing times.
Effect of aza-substitution on the geometry and electrocyclization of pentadienyl anions: an apparent exception to the Woodward-Hoffmann rules?
Authors: Hunter D. H. , Sim S. K. , Steiner R. P.
Published: May 2006

Two geometrical isomers of 1,3,5-triphenyl-1,3-pentadiene 1 have been prepared and characterized; trans,cis-1 and trans,trans-1.These have been used to prepare and characterize the 1,3,5-triphenylpentadienyl anion by quenching the lithium salt in THF and by following hydrogen–deuterium exchange in methanol-O-d with potassium methoxide. Attempts to induce electrocyclization (130 °C in THF or 200 °C in KOtBu–HOtBu) have proven unsuccessful. A comparison of the behaviour of this anion with the 2-aza and 2,4-diaza analogues has helped in elucidating the mechanisms for their electrocyclization and the apparent exception to the Woodward-Hoffmann rules.
Raman study of the structural properties of KNO3(II)
Authors: Brooker M. H.
Published: May 2006

Raman spectra of oriented single crystals of KNO3(II) have been recorded at 298 and 77 K. At both temperatures the data are in excellent agreement with the factor group analysis based on the generally accepted Pmcn space group. Additional spectral features observed near room temperature suggest the presence of a significant number of disordered nitrate groups on alternate lattice sites, although the majority of nitrate groups occupy the ordered sites. As the temperature is lowered, the disordered groups freeze out until near the temperature of reported electrical anomalies (213 K) only the ordered sites are occupied. Improved resolution has resulted in detection of a number of new spectral features while improved depolarization data have resulted in reassignment of several peaks.
Studies on thermodynamics of solution by gas chromatography: solubility measurements of hydrocarbons in cycloalkanols
Authors: Kuchhal Rakesh K. , Mallik Kanai L. , Gupta Pyare L.
Published: May 2006

Activity coefficients at infinite dilution have been determined by gas–liquid chromatography for nine hydrocarbons solutes in cyclopentanol, cyclohexanol, cycloheptanol, benzyl alcohol, and n-heptanol at 25 °C. Experimental results for cyclopentane and cyclohexane in cycloalkanols compare favourably with the values obtained by extrapolation to infinite dilution of activity coefficient data calculated from Benson et al.'s static (vapour–liquid equilibrium) measurements. Some characteristics of the solute–solvent interaction in the systems are discussed in light of statistical approaches (thermal and athermal contributions).
Excess enthalpies and volumes of water + tetrahydrofuran mixtures at 298.15 K
Authors: Kiyohara Osamu , Benson George C.
Published: May 2006

Excess enthalpies and volumes of water + tetrahydrofuran mixtures were measured at 298.15 K, using an LKB flow microcalorimeter and a successive dilution dilatometer. The effect of flow rate on the enthalpy results was investigated. Partial molar excess enthalpies and volumes were derived from the results, and their significance is discussed with reference to the molecular interactions in the mixture.
The photodissociation of ammonia in the absorption system. Part II. Translational excitation of the hydrogen atoms produced, and the mechanism of the predissociation
Authors: Back R. A. , Koda S.
Published: May 2006

The photolyses of NH3 and ND3 have been studied at 2139, 2062, and 1850 Å in the presence of propane and ethylene. Upper limits (none was actually observed) were established for the quantum yields of molecular dissociation of D2 from ND3 of 0.003 and 0.004 at 2139 and 2062 Å, while at 1850 Å a definite yield of 0.009 was obtained. Similar results were observed with NH3. From the dependence of hydrogen yields on the ratio of ethylene to propane, it was concluded that H and D atoms were produced in the photolysis with excess translational energy. Values of the integrated reaction probability (IRP) of hot H atoms with propane were estimated to be 0.078, 0.070, and 0.045 at 2139, 2062, and 1850 Å respectively, while corresponding values for hot D atoms from ND3 were 0.083, 0.062, and 0.029. Implications of the decrease in IRP with increasing photon energy are discussed, and it is concluded that at the shorter wavelengths a second dissociation channel leading to NH2(2A1) becomes important. A mechanism for the predissociation of the Ã-state of ammonia is presented which accounts for this behaviour and for the deuterium isotope effects observed previously. It is suggested that the dissociation does not follow the state correlation rules for dissociation in the plane of the molecule, at least when the ν2 out-of-plane bending vibration in the Ã-state is excited to levels of υ2 = 2 or higher.
Solvent effect correlations and the mechanism of solvolysis of alkyl chlorosulfates
Authors: Buncel Erwin , Millington J. Peter , Wiltshire James F.
Published: May 2006

The rate of hydrolysis of the series of alkyl chlorosulfates ROSO2Cl (R = ethyl, n-propyl, isobutyl, neopentyl) has been measured as a function of solvent composition in dioxane–water media. The solvent effect is examined from the viewpoint of dielectric constant, solvation number, and solvent ionizing power. The results point to a continuous variation of solvolytic mechanisms (from SN2, through borderline, to SN1) along the series. The correlations are also considered with respect to the 'entropy criterion' for multiple bond scission previously advanced for solvolysis of the alkyl chlorosulfates. Solute–solvent interactions are identified as a possible alternative origin of the abnormally large ΔS≠ values observed in chlorosulfate solvolysis.
Transition metal complexes of deprotonated 2-mercaptobenzoxazole. Study of the thiol–thioketo form equilibrium
Authors: Preti Carlo , Tosi Giuseppe
Published: May 2006

Complexes of 2-mercaptobenzoxazole (mbo) with Zn(II), Cd(II), Hg(II), Cu(I), Ag(I), Au(I), Ni(II), Pd(II), Pt(II), Co(II), Rh(III), and Ir(III) were prepared and characterized. Their structures have been assigned on the basis of chemical analysis, ir and far ir spectroscopy, electronic spectra, and magnetic susceptibility measurements. The ligand always bonds through both the sulphur and the nitrogen heteroatoms. The ligand field parameters have been evaluated and are in keeping with the proposed structures confirming the presence of MS2N2 and MS3N3 chromophores.
Photochemistry of 1,4-diphenyl-1,4-epoxy-1,4-dihydronaphthalene 2-carboxylate and 2,3-dicarboxylate esters
Authors: Matheson R. A. F. , McCulloch A. W. , McInnes A. G. , Smith D. G.
Published: May 2006

Direct irradiation (2537 Å) of methyl 1,4-diphenyl-1,4-epoxy-1,4-dihydronaphthalene-2-carboxylate (13b) affords methyl 2,4-diphenyl-3-benzoxepine-1-carboxylate (17b) and methyl 1-benzoyl-3-phenylindene-2-carboxylate (19b), while acetone-sensitized irradiation yields chiefly 19b. The latter can be converted to methyl 3-phenylindene-2-carboxylate (21b).Direct irradiation of dimethyl 1,4-diphenyl-1,4-epoxy-1,4-dihydronaphthalene-2,3-dicarboxylate (13a) affords a mixture of dimethyl 2,4-diphenyl-3-benzoxepine-1,5-dicarboxylate (17a), dimethyl 1-benzoyl-3-phenylindene-1,2-dicarboxylate (19a), and dimethyl 1-benzoyl-2-phenylindene-1,3-dicarboxylate (18). The latter two products cleave readily to give dimethyl 3-phenylindene-1,2-dicarboxylate (21a) and dimethyl 2-phenylindene-1,3-dicarboxylate (20) respectively. Sensitized irradiation yields mainly 19a. The formation of 19a and 19b as major products of photorearrangement of 13a and 13b is consistent with a di-π-methane pathway producing methyl 4,6-diphenyl-5-oxatetracyclo[5.4.0.0.2,403,6]undeca-1(7),8,10-triene 2-carboxylate and 2,3-dicarboxylate (25a,b), intermediates similar to those previously observed by other workers for benzonorbornadienes and 7-azabenzonorbornadienes. Compound 18 is derived by photo-induced rearrangement of the benzoxepine 17a.The AlCl3-catalyzed rearrangement of 13a yields a mixture of dimethyl 2,4-diphenyl-1(2H)-naphthalenone-2,3-dicarboxylate (15) and methyl 1,3-diphenyl-4-hydroxynaphthalene-2-carboxylate (16), while that of 13b affords only 16.
Résonance quadripolaire nucléaire du brome dans des composés organomagnésiens
Authors: Kress Jacky , Guibé Lucien
Published: May 2006

Bromine nuclear quadrupole resonance signals corresponding to both isotopes 79Br and 81Br have been observed, at 77 °K, in some crystallized organomagnesium bromides of formula RMgBr•nR′2O, and in MgBr2•nEt2O. The low value of the resonance frequencies, of about 33 MHz-to be compared to 220 MHz for a typical [Formula: see text] bond, bond, shows the ionic character of the Mg—Br bond. The fact that the resonance frequencies are found within a restricted frequency range, between 30 and 42 MHz, shows that the Mg—Br bond is only slightly affected by the nature of the radicals R and R′ through the series studied; However the variation of the bromine resonance frequency in this series may be interpreted in terms of the nature of R and R′.
Coordination compounds of indium. Part XXXIII. X-Ray photoelectron spectroscopy of neutral and anionic indium halide species
Authors: Freeland Brian H. , Habeeb Jacob J. , Tuck Dennis G.
Published: May 2006

The X-ray photoelectron spectra (metal and halogen energy levels) have been recorded for binary halides of indium in the +I, +II, and +III states, and for anionic halide complexes of indium(I) and (III). The results are internally consistent in terms of the relation between metal and ligand levels, but lattice effects prevent any detailed interpretation of indium levels in terms of oxidation state, ligand electronegativity, and/or coordination number.
An improved synthesis of ishwarane: conversion of bicyclo[2.2.2]octenes to tricyclo[3.2.1.02,7]octanes via reductive homoallylic cyclization
Authors: Kelly Ronald B. , Alward Sandra J.
Published: May 2006

Conversion of the alcohol 4 into the mesylate 5 and reduction of the latter with LiAlH4 under mild conditions afforded ishwarane 1 in 65% yield, thereby providing a further demonstration of the synthetic utility of such reductive, homoallylic cyclizations and a substantially improved synthesis of ishwarane.
Ion recombination processes in rigid solutions
Authors: Miller John R.
Published: May 2006

It is known that the free ion yield is small in irradiated aromatic hydrocarbon liquids. This study uses pulse radiolysis to observe anions of aromatic solutes in matrices at 77 K. In aliphatic matrices, trapped electrons tunnel to aromatic solutes and the anion yield is observed to grow with time. If the concentration of aromatic solute is large (0.1 M) or if the matrix is aromatic, ion recombination via tunneling dominates the anion kinetics, and long lived triplet states are observed to grow in. These results and the effects of other charge scavengers indicate that just a few percent of added aromatic material can dramatically increase the probability of charge recombination in aliphatic media, and that this effect involves decreased charge separation distances. The same effect apparently also occurs in alkane liquids at room temperature.
High-speed schlieren studies of electrical breakdown in liquid hydrocarbons
Authors: Wong P. , Forster E. O.
Published: May 2006

High-speed schlieren studies have been carried out on the electrical breakdown of liquid hydrocarbons using a pulsed ruby laser. The development and propagation of charge carrier trajectories were recorded photographically on prebreakdown, breakdown, and postbreakdown events occurring in very pure, oxygen-free samples of hexane, benzene, toluene, and isooctane using a parallel plate electrode geometry. The initiation of breakdown was characterized by the growth of narrow streamers the creation of which was attributed to field injected electrons at local asperities of the cathode surface. Once the streamers reached the anode, large currents were found to flow through the gap leading to formation of a plasma column. Subsequent emissions occurring at the anode were attributed to field reversal. Details of the schlieren pictures have been interpreted in terms of classical electromagnetic theory.
Electron spin resonance studies of preferential solvation in solutions of potassium in amines and ethers
Authors: Catterall R. , Slater J. , Symons M. C. R.
Published: May 2006

Electron spin resonance spectra of solutions of potassium in tetrahydrofuran–ethylamine, tetrahydrofuran–diglyme, ethylamine–diglyme, and ethylamine–ethylenediamine mixtures are reported and compared with spectra obtained from the four pure solvents. Strong evidence for preferential solvation was observed in all mixtures, with the strength of solvation increasing in the order tetrahydrofuran < ethylamine < diglyme < ethylenediamine. Electron spin resonance spectra of mixtures containing ethylenediamine were used to investigate the nature of the single line spectrum obtained from solutions in ethylenediamine alone. It is concluded that this signal is an 'ammonia-like' time averaged spectrum arising from solvated electrons and ion-pairs.
Field-assisted photo-stimulated charge transfer across photoconductor–dielectric liquid interfaces
Authors: Yang C. C. , Noolandi J.
Published: May 2006

Field-assisted photo-stimulated charge transfer across a photoconductor–dielectric liquid interface has been studied by a high sensitivity signal averaging transient measurement technique. The effects of both the temperature and electric field (below 2 × 105 V/cm) have been investigated. Experimental results were analyzed using an interface model developed earlier to describe the charge transfer kinetics. We have found evidence of direct and indirect transfer of charge across the interface and we have identified the controlling parameters for the desorption rate of charge carriers from the interface into the fluid.
Electron reactivity as a function of phase
Authors: Henglein A.
Published: May 2006

Reactions of free electrons in the gas phase, of quasi-free electrons and solvated electrons in dielectric liquids, of hydrated electrons in water, and of electrons originating from an electrode in contact with a solution are among the great variety of electronic processes in chemistry. It is the purpose of this paper to describe a few phase effects. Reactions of electrons in dielectric liquids will be discussed with respect to the corresponding processes in the gas phase. Furthermore, certain aspects in the transfer of an electron from a hydrocarbon phase into the aqueous phase will be dealt with. The processes will be described in terms of electronic redox level distributions of the acceptor redox systems.
Comparison of solvated electron reaction rates in water and ammonia
Authors: Schindewolf U. , Wünschel P.
Published: May 2006

New and literature data of solvated electron reactions in ammonia with some inorganic ions and organic neutral molecules are compared with corresponding data in water. In ammonia only a few reactions with aromatic molecules are diffusion controlled and therefore faster than in water (k ≈ 1 × 1011 and 1 × 1010 M−1 s−1,respectively). After correcting for the electrostatic contribution to the rate constant of the other reactions it is concluded that in general the reactivity of the solvated electron in ammonia is appreciably lower, than in water. For the slow reactions of ammoniated electrons with acetonitrile and dimethylsulfoxide we find activation energies of 7 to 9 kcal/mol and activation volumes of −40 to −60 ml/mol. In these reactions it is suggested that the rate determining step is associated with the collapse of the large electron cavity in liquid ammonia.
Metallic condensation of Wannier-Mott impurity states in lithium-hexamethylphosphoramide glasses
Authors: Edwards Peter P. , Catterall Ron
Published: May 2006

A metal to non-metal (MNM) transition observed in frozen solutions of lithium in hexamethylphosphoramide (HMPA) was tentatively interpreted as a Mott transition in which localized Wannier-type impurity states were the source of electrons in the metallic state. In this paper this assertion is examined in greater detail by calculating critical densities (nc) on the basis of a scaled (variational) form of Mott's original criterion for the onset of localization in a dielectrically screened Coulomb potential, and also on the basis of the Hubbard tight-binding model. Mott's model for the transition is based upon the screening properties of a freely propagating gas of metallic electrons. In the Hubbard regime, however, the phenomenon is viewed from the tight-binding limit; the transition from localized to delocalized states occurs when the bandwidth (Δ) of a regular lattice of isolated centres exceeds the value of the intra-atomic Coulombic repulsion integral (U) associated with electron correlation.Both electron-gas (Mott) and tight-binding (Hubbard) approaches give calculated critical densities (5.6 × 1018, 3.2 × 1018 cm−3, respectively) in good agreement with the experimental value (∼3 × 1018 cm−3). These results therefore support the earlier suggestion that the MNM transition in frozen lithium-HMPA solutions is a Mott-transition associated with electron-interaction effects.
Linear free energy relationships. VIII. Ionization potentials of aliphatic compounds
Authors: Gibson Harry W.
Published: May 2006

Ionization potentials (IP) of HX, CH3X, C2H5X, and i-C3H7X, where X is a substituent with non-bonded electrons, are directly proportional to ionization potentials of 4-substituted quinuclidines. This is taken as evidence that in general the energy required to remove an electron from a substituent X, as is the case in HX, CH3X, C2H5X, and i-C3H7X, is directly proportional to the energy required to remove an electron from a site remote from the substituent, as in the quinuclidines in which an electron is lost from the ring nitrogen. Furthermore, the IP's of the HX-i-C3H7X series are directly proportional to inductive substituent constants, σI, providing a valuable correlation between gas and solution phase behavior.
Molecular orbitals from group orbitals. IV. Quantitative perturbational molecular orbital analysis of the methyl rotational barriers in (CH3)2X molecules. Effect of the fragmentation mode upon the results of the analysis
Authors: Whangbo Myung-Hwan , Wolfe Saul
Published: May 2006

A quantitative perturbational molecular orbital (PMO) analysis has been performed on ab initio SCF-MO wavefunctions associated with the rotation of the methyl groups in a series of (CH3)2X molecules (X = CH2, O, S, C=O, C=CH2). Two fragmentation modes have been investigated: Method a, in which the system is dissected into X and (CH3)2; and Method b, in which the system is dissected into CH3X and CH3. Both fragmentation modes reproduce the principal property of these molecules, viz., that the more crowded SS conformation is preferred. However, whether this conformational preference is controlled by two-electron stabilizing effects or four-electron destabilizing effects is found to depend upon both the mode of fragmentation and the nature of the substituent X. The quantitative results are supplemented by a detailed qualitative description of the nature of the group orbitals associated with the two fragmentation modes and the various types of orbital interactions. It is shown that orbital energy differences control the qualitative discussion of Method a, and overlap effects control that of Method b. Although the final result, i.e., the preference for the SS conformation, and the behaviour of individual orbital interactions are anticipated correctly by the qualitative arguments, these are unable to assess the relative contributions of the stabilizing and destabilizing interactions.
Polarographic studies of the interaction of boric acid with 1-hydroxy- and 1,2-dihydroxy-9,10-anthraquinones and -anthrahydroquinones
Authors: Broadbent Arthur D. , Hewson W. Donald , McDonald Heather A. , Melanson Ronald J.
Published: May 2006

The interaction of 1-hydroxy-9,10-anthrahydroquinones (1-HOAHQ) with boric acid in aqueous borate buffer solutions at pH 9.5 causes a decrease in the anodic limiting current of the 1-HOAHQ and the simultaneous appearance of a new diffusion-controlled anodic wave at more positive potentials. This is attributed to the formation of a cyclic borate ester of the 1-HOAHQ involving the peri-hydroxyl groups. Ester formation is much slower but still complete when the boric acid – borate to 1-HOAHQ molar ratio exceeds 10–15. These esters are most stable at pH 7.5–9.5 and completely unstable above pH 12. 1,2-Dihydroxy-9,10-anthraquinones (1,2-diHOAQ) react with boric acid to give cyclic esters involving the 1- and 2-hydroxyl groups, but of lower stability than those from 1-HOAHQ. On reduction of a 1,2-diHOAQ in the presence of boric acid at pH 9.5, cyclic borate esters involving the peri-hydroxyl groups are rapidly produced in preference to those involving the ortho-hydroxyl groups.
Effect of the hexadecapole moment on the translational vibrational absorption by carbon-dioxide-type crystals
Authors: Whalley E.
Published: May 2006

The effect of a hexadecapole moment on the absorption by the translational vibrations of carbon-dioxide-type crystals has been calculated. If the qudrupole and hexadecapole moments have the same sign the absorption is relatively insensitive to the hexadecapole moment and the hexadecapole moment may reduce the integrated absorptivity to a minimum of about 0.85 of the value for the quadrupole moment alone. If the moments have opposite signs, the absorptivity can be increased significantly by a hexadecapole moment of the expected magnitude.
Vapour phase catalytic transformations of terpene hydrocarbons in the C10H16 series. IV. Effect of nitrogen, hydrogen, and pyridine on the dehydrogenation of Δ3-carene over chromia and chromia-alumina catalysts
Authors: Krishnasamy V. , Yeddanapalli L. M.
Published: May 2006

The influences of nitrogen, hydrogen, and pyridine on the conversion of 3-carene into various products over chromia catalyst at 450 °C and over chromia–alumina at 400 °C have been investigated. Nitrogen acts as a diluent over these catalysts; hydrogen at low partial pressures enhances the formation of cymenes over chromia, but suppresses its formation over chromia–alumina. Increase of the partial pressure of hydrogen increases the proportion of men thanes over chromia–alumina, but decreases it over chromia catalyst. Pyridine suppresses the over-all conversion of 3-carene and the formation of cymenes over chromia and chromia–alumina; however, it increases the formation of menthadienes over chromia–alumina. These observations are explained in terms of the acidity of chromia and chromia–alumina, the diluting effects of nitrogen, hydrogen, and pyridine, and their ability to adsorb and desorb over the catalyst surfaces.
Transition state activity coefficients in the acid-catalyzed hydrolysis of amides
Authors: Modro Tomasz A. , Yates Keith , Beaufays Françoise
Published: May 2006

The transition-state activity coefficient [Formula: see text] approach has been applied to the acid-catalyzed hydrolysis of benzamide and its N-alkyl derivatives. For all systems (with the exception of the N-tert-butyl derivative which reacts via carbon–nitrogen bond cleavage) a uniform type of medium dependence of [Formula: see text] is observed. The reaction shows a pronounced destabilization of S≠ over the whole region of acidity studied, practically identical to that found for the AAc-2 type of ester hydrolysis. This is interpreted in terms of an AoT2 mechanism of amide hydrolysis, that is the rate-determining formation of the oxonium-type tetrahedral intermediate from the O-protonated form of substrate conjugate acid.
Structural effects on reactivity in the oxymercuration reaction
Authors: Ambidge I. C. , Dwight Stephen K. , Rynard Carolyn M. , Tidwell Thomas T.
Published: May 2006

The kinetics of the reaction of mercuric acetate with alkenes in methanol can be measured directly by observing the ultraviolet absorbance of the solution at 265 nm. For more reactive alkenes stopped flow techniques are required, but for less reactive substrates conventional spectrophotometers are adequate. The measured rates are in satisfactory agreement with values obtained by other methods. The rates of several cyclopropylalkenes were measured in this way, and relative reactivities of some of the same substrates were obtained by the competition method. Rates obtained by both methods are in qualitative agreement, and show very high reactivity for the cyclopropylalkenes. These rates are analyzed by comparison with model reactions involving open ions (acid-catalyzed hydration) and bridged ions (sulfenyl halide addition). The comparisons suggest that the oxymercuration of alkenes not substituted with strongly resonance electron-donating substituents, for example ethylene, proceeds through bridged rate-determining transition states that put very little positive charge on carbon, but that when strongly resonance electron-donating substituents such as cyclopropyls are present, the rate-determining transition state resembles an open carbonium ion.
Syntheses in the group of Nuphar alkaloids. III. Total synthesis of (±)-nupharamine and (±)-3-epinupharamine
Authors: Szychowski Jerzy , Wróbel Jerzy T. , Leniewski Andrzej
Published: May 2006

The alkaloids (±)-nupharamine and (±)-3-epinupharamine were synthesized using 3-acetylfuran as the starting material. The conditions for stereoselective reduction of pyridine derivatives are described.
Substituent effects on the 13C chemical shifts of monosubstituted twistanes
Authors: Beierbeck Helmut , Saunders John K.
Published: May 2006

The 13C chemical shift data for some hydroxy, chloro, bromo, and oxo twistane derivatives are presented and compared to the shifts observed in corresponding adamantanes. The substituent effect at the α and β carbons is more pronounced in twistanes than in adamantanes. The substituent shift induced at an antiperiplanar γ carbon is shown to depend on the presence or absence of 1,3-diaxial hydrogen–hydrogen interactions between the substituted and γ carbons. If such an interaction is present the effect is of shielding whereas if it is absent, the effect is of deshielding. The deshielding effect appears to occur via a through bond interaction.
The comparative chemistry of ammine and methylamine complexes of rhodium(III) and cobalt(III)
Authors: Swaddle Thomas Wilson
Published: May 2006

For the aquation of (CH3NH2)5RhCl2+, the first order rate coefficients are represented by ΔHaq* = 101.9 kJ mol−1 and ΔSaq* = −50.2 JK−1 mol−1 in 0.1 M HClO4, while for base hydrolysis the rate is first order in [(CH3NH2)5RhCl2+] and [OH−] at ionic strength 0.10 M and the rate coefficients (in M−1 s−1) are represented by ΔHOH*> = 108.6 kJ mol−1 and ΔSOH* = 74.1 J K−1 mol−1. Acid dissociation constants are reported for (RNH2)5MOH23+ (R = H or CH3; M = Rh or Co), and these, combined with spectral data, show CH3NH2 to be a poorer electron donor than NH3 in complexes of this type, contrary to expectations. The comparative kinetics of reactions of (RNH2)5MCl2+ support the assignment of an Ia mechanism to aquation when M = Rh or Cr, Id to aquation when M = Co, and Dcb for base hydrolysis in all these cases.
Long-range proton–19F spin–spin coupling interactions in phenyltrifluorosilane
Authors: Parr William J. E. , Schaefer T. , Marat K.
Published: May 2006

Analysis of the proton magnetic resonance spectrum of phenyltrifluorosilane yields the spin–spin coupling constants between the fluorine nuclei and the protons. These are compared with the analogous long-range coupling constants in benzotrifluoride, toluene, and phenylsilane and are rationalized in terms of coupling mechanisms. The coupling over six bonds is assessed as a base point for the estimation of hindered rotation about the carbon–silicon bond.
Sterically hindered aromatic compounds. VII. Deoxygenation of 2,5-di-tert-butyl- and 2,4,6-tri-tert-butylnitrosobenzene
Authors: Barclay L. Ross C. , Khazanie Prabhaker G. , Adams Kenneth A. H. , Reid Elaine
Published: May 2006

Deoxygenation of 2,5-di-tert-butylnitrosobenzene (1) by triethylphosphite gave a complex mixture containing 2,5-di-tert-butylaniline, 2,5,2′,5′-tetra-tert-butylazobenzene, N-(2,5-di-tert-butylphenyl)-α-tert-butyl-α-2-(5-tert-butylpyridyl)nitrone, and diethyl N-(2,5-di-tert-butylphenyl)phosphoramidate. In contrast deoxygenation of 2,4,6-tri-tert-butylnitrosobenzene (2) yielded mainly 3,3-dimethyl-5,7-di-tert-butyl-2,3-dihydroindole (80%), together with small amounts of 2,4,6-tri-tert-butylaniline and a product of side chain rearrangement, 2-(2-methyl-3-propenyl)-4,6-di-tert-butylaniline. Reaction pathways involving nitrenoid intermediates account for the various products. The different types of products from 1 and 2 are explained in terms of differential steric and conformational effects.
The crystal structure of bis(diethylamino)dithiaboretane, a compound with a four-membered alternating boron–sulfur ring
Authors: Bushnell G. W. , Rivett G. A.
Published: May 2006

The crystal structure of bis(diethylamino)dithiaboretane, C8H20B2N2S2, is determined by single crystal X-ray diffraction and refined to R = 0.120, Rw = 0.091 for 373 independent reflections. The tetragonal cell dimensions are a = 10.396(3), c = 25.589(7). The space group is [Formula: see text] (No. 92) or its enantiomorph (No. 96); Dm = 1.08(8), Dc = 1.10 g cm−3; n = 8. The asymmetric unit is one half of a pair of molecules. Both molecules have approximate symmetry 222 with one of these symmetry elements being a crystallographic axis. The latter passes through all the B and N atoms of molecule 1, and is perpendicular to the B,S ring of molecule 2. The four-membered B,S rings are planar. The nitrogen coordination is trigonal, planar, and set at<10° to the ring planes within each molecule. The mean bond lengths are: B—S = 1.84(4), B—N = 1.38(5) Å, and the mean bond angles: S—B—S = 105(3)°, B—S—B = 76(2)°. The results suggest single B—S and double exocyclic BN bonds.
Structures of toxic constituents in kraft mill caustic extraction effluents from 13C and 1H nuclear magnetic resonance
Authors: Thakore A. N. , Oehlschlager A. C.
Published: May 2006

Arguments based on 13C and 1H nmr spectroscopy are presented to elucidate the structures of 3,4,5- and 4,5,6-trichloroguaiacol, 12- and 14-monochlorodehydroabietic acid, and 12,14-dichlorodehydroabietic acid. These compounds were recently isolated and tentatively identified as major components toxic to fish in kraft mill caustic extraction effluents.
Metal-ion oxidations in solution. Part XVIII. Characterization, rates, and mechanism of formation of the intermediates in the oxidation of thiols by chromium(VI)
Authors: McAuley Alexander , Olatunji M. Adegboyega
Published: May 2006

The stopped-flow technique has been used to study the reactions of [HCrO4−] and penicillamine, glutathione and β-mercaptoethylamine (RSH) in perchlorate media, [H+] = 0.02−0.100 M, I = 1.00 M over the temperature range 10–30 °C. The transient orange species formed as intermediates are 1:1 chromate esters,[Formula: see text]with λmax ∼ 420–430 nm and K1 ∼ 700 (DL-penicillamine) to 1440 M−1 (glutathione) at T = 25 °C. Thermodynamic parameters for complex formation have been derived from initial absorbance data and the evidence for sulphur bonding is discussed. Kinetics of the reactions conform to the rate law[Formula: see text]Activation enthalpies lie in the range 6–10 kcal/mol but ΔS≠ values vary considerably possibly reflecting solvation effects. The rate constants kfH+ are several orders of magnitude lower than those found for this parameter in other reactions of this type. The complex formation mechanisms are discussed and the possibility of some associative character in the present reactions is considered.
Microwave spectrum of trans-1-methoxy-1,3-butadiene
Authors: Kewley R. , Dass S. C.
Published: May 2006

The microwave spectra of two conformers of 1-methoxy-1,3-butadiene have been studied in the 18 to 40 GHz region. One conformer is the s-trans conformer of trans-1-methoxy-1,3-butadiene. The other is most likely the corresponding s-cis conformer. The rotational constants for the ground vibrational state are (in MHz) s-trans: A = 24 524(16); B = 1336.51(1); C = 1277.76(1); s-cis: A = 12 642.73(23); B = 1607.61(1); and C = 1439.64(1). The centrifugal distortion parameters DJK and DJ have also been determined for each conformer.For the s-trans conformer two series of torsional satellites have been found which are assigned as O—CH torsion with frequency 60(20) cm−1 and =C—C= torsion, frequency 80(30) cm−1. For the s-cis conformer one series of satellites has been observed, which has been assigned to =C—C= torsion, of frequency 103(30) cm−1.
Mixed valence properties of a pyrazine bridged ruthenium–iron complex
Authors: Toma Henrique E. , Santos Paulo S.
Published: May 2006

A study is presented on the chemistry of the binuclear complex [(CN)5FepzRu(NH3)5]n (n = 0 for the II–III complex and n = −1 for the II–II complex, pz = pyrazine) in solid state and in aqueous solution. Evidence for a mixed valence transition for the II–III complex was observed in the near infrared region. Based on infrared and resonance Raman spectra, a trapped-valence or class II formulation was proposed for the complex. Cyclic voltammetry indicated the occurrence of two reversible waves at 0.48 V and 0.72 V vs. NHE, which were assigned to the oxidation of the ruthenium(II) and iron(II) centers, respectively.
The reaction of iodine with lithium tri-tert-butoxyaluminohydride. A reaction with variable stoichiometry unsuitable for analytical standardization
Authors: Wigfield Donald C. , Gowland Frederick W.
Published: May 2006

Solutions of lithium tri-tert-butoxyaluminohydride (LTBA) have been standardized by reduction of cyclohexanone, followed by gas–liquid chromatography (glc) and/or spectral analysis of the extent of reaction. These results are compared with the standard titrimetric analysis of LTBA by iodine, to determine whether the standardizing equation is[Formula: see text]Or[Formula: see text]It is clear that in fact both of these reactions occur, with [5] predominating at low hydride to iodine ratios, and [3] becoming increasingly significant when the hydride and iodine concentrations become comparable. The usual titrimetric method of standardizing LTBA is therefore essentially unusable.
The reaction of 2-aminopyridine 1-oxides with thiophosgene. 2H-[1,2,4]Oxadiazolo[2,3-a]pyridin-2-thiones
Authors: Rousseau Danielle , Taurins Alfred
Published: May 2006

2-Aminopyridine 1-oxides react with thiophosgene in ethanol solution in the presence of sodium bicarbonate to produce 2H-[1,2,4]oxadiazolo[2,3-af]pyridin-2-thiones. The products are stable at room temperature, however, they explode on being heated at the temperature range 121 to 137 °C.
Preparation of N,N,N′,N′-tetramethylphosphorodiamidate intermediates for reductive deoxygenation of alcohols using N,N-dimethylphosphoramidic dichloride
Authors: Liu Hsing-Jang , Lee Sing Ping , Chan Wing Hong
Published: May 2006

Treatment of alcohols with n-butyllithium and N,N-dimethylphosphoramidic dichloride followed by addition of dimethylamine gave rise to N,N,N′,N′-tetramethylphosphorodiamidates, intermediates involved in a process for reductive deoxygenation of alcohols. This procedure should prove especially useful for alcohols in which the hydroxyl group is sterically hindered.
Thermodynamics of transfer of p-nitroaniline from water to alcohol + water mixtures at 25 °C and the structure of water in these media
Authors: Bose Kumardev , Kundu Kiron K.
Published: May 2006

Free energies (ΔGt0) and entropies (ΔSt0) of transfer at 25 °C of the nonelectrolyte p-nitroaniline from water to various alcohol + water mixtures have been determined from solubility measurements at seven temperatures from 10–40 °C. Increasing specific solute–solvent interactions have been proposed to interpret the nature of the ΔGt0-composition profiles and the enhanced structure of water in the water-rich mixed solvents has been correlated with maxima in the ΔSt0-composition profiles. The effectiveness of p-nitroaniline as a useful probe for studying solvent structure has been pointed out.
The yellow pigments of Beauveria species. Structures of tenellin and bassianin
Authors: Wat Chi-Kit , Mcinnes A. Gavin , Smith Donald G. , Wright Jeffrey L. C. , Vining Leo C.
Published: May 2006

Tenellin and bassianin are deduced from chemical and spectroscopic evidence to be the 3-[(E,E)-4,6-dimethylocta-2,4-dienoyl] and 3-[(E,E,E)-6,8-dimethyldeca-2,4,6-trienoyl] derivatives of 1,4-dihydroxy-5-(p-hydroxyphenyl)-2(1H)-pyridone. Spin–spin coupling information in the 1H and 13C nuclear magnetic resonance spectra after biosynthetic enrichment of tenellin with 13C and 15N isotopes was a valuable aid in elucidating the structure.
A study of the Osterberg–Sarkar–Kruck method for evaluating free metal and free ligand concentrations in solutions of complex equilibria
Authors: Guevremont Roger , Rabenstein Dallas L.
Published: May 2006

The method developed by Osterberg, Sarkar, and Kruck for obtaining the concentrations of free ions in solutions of complex equilibria from pH titration data has been studied to establish the conditions under which the method gives accurate values for free ligand and free metal concentrations in systems containing a variety of complexes, including protonated, hydroxy, mixed ligand, and polynuclear complexes. Simulated titration data have been used so that the true values of free ligand and free metal concentrations would be known. Calculation procedures are described for each step in the data evaluation, including procedures for extracting information about the stoichiometry of the complexes from the unique information provided by this method. The effect of various systematic and random errors is also considered.
Water-soluble lysine-containing polypeptides. IV. The synthesis, characterization,and circular dichroism spectra of sequential polypeptides formed from dipeptides of lysine and amino acids of increasing side chain size
Authors: Slotin Lewis A. , Lauren Denis R. , Williams Ross E.
Published: May 2006

Several polypeptides have been synthesized which contain the alternating sequence lysyl-X, where X = gly, L-ala, D-ala, L-val, L-leu, and L-phe. The polypeptides have been characterized by gel filtration (molecular weight) and by circular dichroism spectroscopy (secondary structure).
Sur la réduction par NaBH4 de quelques nitriles α, β-insaturés
Authors: Pépin Yvon , Nazémi Hassan , Payette Daniel
Published: May 2006

A study of several different reductions of α, β-unsaturated nitriles by NaBH4 shows that these proceed by way of a 1:4 addition to form saturated nitriles. At long reaction times, hydrolysis products or those of substitution of the saturated nitrile are observed. The relative rates of reduction follow the order: 2-phenyl-2-butenenitrile 1 > 2,3-diphenyl-2-propenenitrile 2 > 3-phenyl-2-propenenitrile 3 > 2-butenenitriIe 4. [Journal translation]
Acid-catalyzed reactions of cyclobutanones. III. Formation of substituted 2-tetralones from α-phenylcyclobutanones
Authors: Abegg Victor P. , Hopkinson Alan C. , Lee-Ruff Edward
Published: May 2006

A series of cyclobutanones 1–5 were found to rearrange to β-tetralones 6–10, respectively, in the presence of phosphorous pentoxide in benzene at room temperature. The structures of the β-tetralones were inferred by conversion of a number of these known naphthalene derivatives. Possible mechanistic pathways are discussed.
Experimental and theoretical studies of proton removal from propene
Authors: Mackay Gervase I. , Lien Min H. , Hopkinson Alan C. , Bohme Diethard K.
Published: May 2006

The kinetics and energetics of proton removal from propene, which contains several sites of different acidities, were investigated both theoretically and experimentally. Rate and equilibrium constants were measured for the proton-transfer reaction [Formula: see text]at 296 ± 2 K using the flowing afterglow technique. The rate constants were determined to be kforward = (1.1 ± 0.3) × 10−9 cm3 molecule−1 s−1 and kreverse = (5.4 ± 1.9) × 10−10 cm3 molecule−1 s−1. The ratio of rate constants, kf/kr = 2.1 ± 0.7, was found to be in agreement with the equilibrium constant, K = 2.2 ± 0.8, determined from equilibrium concentrations. Abinitio molecular orbital calculations predicted the removal of a methyl proton from propene to yield the allyl anion to be energetically favoured. This prediction was supported by measurements of deuteron removal from CD3CHCH2. The measured value of K corresponds to a standard free energy change, ΔG0298, of −0.44 ± 0.14 kcal mol−1 which provided values for the standard enthalpy change ΔH0298 = +0.5 ± 0.4 kcal mol−1, the proton affinity, PA298(C3H5−) = 391 ± 1 kcal mol−1, the heat of formation, ΔH0f,298(C3H5−) = 29.0 ± 0.8 kcal mol−1, and the electron affinity EA(CH2CHCH2) = 12.4 ± 1.9 kcal mol−1. The experimentally established value for the proton affinity of the allyl anion was in reasonable accord with the value of 422.3 kcal mol−1 determined by calculation. The electron affinity of the allyl radical derived in this study is supported by previous calculations and several limiting values obtained experimentally.
Raman and nuclear quadrupole resonance studies of the phase transition in pentachlorophenol
Authors: Shurvell H. F. , Korppi-Tommola J. , Brown R. J. C.
Published: May 2006

Raman and nqr spectra of pentachlorophenol (PCP) have been recorded at temperatures above and below the transition at 62 + 2 °C. The complete loss of structure in the Raman external mode region and the disappearance of the 35Cl nuclear quadrupole resonances above the transition temperature indicate a disordered structure for the high temperature phase. Super-cooling is observed in nqr and Raman spectra when the sample is cooled through the transition temperature. No evidence for any new crystal phase is observed on cooling the sample to liquid nitrogen temperature. Eleven of the 12 external modes predicted from the reported crystal structure of PCP have been observed in the Raman spectrum at 77 K.
Reactions of K2PtCl4 with pyridine derivatives in dimethylformamide and synthesis of potassium trichloro(pyridine)platinum(II)
Authors: Kong Pi-Chang , Rochon F. D.
Published: May 2006

The reactions of K2PtCl4 with pyridine derivatives L (L = py = pyridine, pic = picoline, and lut = lutidine) were studied in dimethylformamide (DMF).[Formula: see text]The complexes (1) were isolated and the yield decreased with the order, 2,4-lut = 2-pic > 2,6-lut > 4-pic = py, which can be correlated to the steric hindrance of the ortho methyl groups. The compounds (2) can be converted to the compounds (3), the free ligand acting as catalyst and (3) is the final product of the above reactions. The compounds (3) can also be obtained from a DMF solution of [Pt(L)4]Cl2 (L = py) at room temperature. A comparison of the above reactions in water and in DMF was also made.
Photochemical extrusion of sulfur dioxide from sultines
Authors: Durst Tony , Huang John C. , Sharma Narendra K. , Smith David J. H.
Published: May 2006

γ-Sultines having an aryl substituent α to the oxygen atom have been shown to undergo photochemically induced loss of SO2, via radical intermediates. In the case of the monocyclic derivatives, arylcyclopropanes are formed in excellent yield. 3-Phenylbenz-2,1-thiole-2-oxides yield fluorene derivatives as the major photolysis product.