bluuebunny/crossref_metadata_2025 huggingface dataset:
The resonance Raman spectra and excitation profiles of some 4-sulfamylazobenzenes
Authors: Kumar Kamal , Carey P. R.
Published: May 2006

The resonance Raman spectra of three pharmacologically important sulfonamides, 4-sulfamyl-4′-dimethylaminoazobenzene (1), 4-sulfamyl-4′-hydroxyazobenzene (2), and 4-sulfamyl-4′-aminoazobenzene (3), are compared with those of analogues lacking the sulfonamide group. The —SO2NH2 moiety does not directly contribute intense or moderately intense bands to the resonance Raman spectra of 1, 2, and 3. However, —SO2NH2 ionization is reflected by frequency changes in a band near 1140 cm−1 and intensity changes in the 1420 cm−1 region. The normal Raman spectrum of 2 confirms that the intensity changes reflect —SO2NH2 ionization rather than unrelated changes in vibronic coupling. The effect of —OH ionization on the resonance Raman spectrum of 2 emphasizes that caution must be exercised when relating spectral perturbations to changes in contributions from valence bond type structures. Resonance Raman excitation profiles for the 1138, 1387, and 1416 cm−1 bands of 2 show that these bands gain intensity by coupling with the electronic transitions in the 240 to 450 nm region and that, more than 1000 cm−1 to the red of λmax, the wavelength dependence can be closely reproduced by the FB type terms of Albrecht and Hutley. The excitation profile for each band shows evidence for structure in the 470 nm region, although lack of sufficient excitation wavelengths prevents accurate estimation of the spacing. Under conditions of rigorous resonance the intense Raman lines all occur in the 1400 cm−1 region, i.e. they are 'bunched' in the region known to contain the —N=N— stretching vibration.
Theoretical study of the vibrational structure of the 1(n,π*) transition in diimide: potential curves and Franck–Condon analysis
Authors: Perić M. , Buenker R. J. , Peyerimhoff S. D.
Published: May 2006

Ab initio CI potential curves are reported for the ground and 1(n,π*) excited states of diimide for each of the six possible internal coordinates. These results are then used to obtain vibrational wavefunctions and frequencies for both states, which in turn are combined with electronic transition moment data to allow a Franck–Condon analysis of the band structure of the (dipole-forbidden) n–π* absorption system. This procedure allows one to reproduce the main features of the observed spectra of N2H2 and N2D2 and indicates that the majority of the vibrational transitions seen are vibronically induced via the antisymmetric NH stretching mode v5. The calculations are in essential agreement with the earlier experimental interpretation of the vibrational structure of this transition in terms of progressions in the symmetric bending (v2) and NN stretching (v3) frequencies, except that they indicate that the previous v2′ numbering should be altered by three units. According to this interpretation the isotope shift for the vibronic origin is 672 cm−1 compared with the corresponding calculated value of 666 cm−1. It is argued that several other weaker transitions seen experimentally arise via a different inducement mechanism, namely the torsion (v4) mode, and as such are only observed in energy regions where v5-induced transitions cannot occur.
The trifluoroacetic acid solvent system. Part V. Cryoscopic measurements
Authors: Harriss Michael G. , Milne John B.
Published: May 2006

not available
Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes
Authors: Kurzawa Jan , Leffek Kenneth T.
Published: May 2006

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.
Effect of temperature and phase on the photoionization energy threshold of TMPD in hydrocarbon solvents
Authors: Bullot J. , Gauthier M.
Published: May 2006

The temperature dependence of the TMPD photoionization energy threshold, I, in a set of eight hydrocarbon solvents has been systematically studied, from room temperature down to 77 K. For this purpose ion-pair formation is detected either by measuring the photocurrents in the liquid phase or by measuring the recombination luminescence intensity in the solid phase. It is found that I(liquid) increases linearly when the temperature is decreased down to the liquid–solid transition temperature. At this temperature I undergoes an abrupt increase of 0.2–0.6 eV depending on the hydrocarbon and the nature of the phase transition. Any subsequent solid–solid phase change is accompanied by a new shift towards higher energy. In the low temperature phase of all the studied crystals, I(solid) has a constant value down to 77 K. Glass-forming liquids have a very different behavior: I varies linearly in the liquid and the straight line extrapolates to the I(glass) value at 77 K. The applicability of the two methods is discussed. From the present data it is concluded that the conduction state energy, V0, is constant in the low-temperature phase of crystals. By calculating the polarization energy due to the TMPD+ cation and from data on the temperature dependence of V0 in the liquid phase, we have estimated V0 in crystalline n-hexane (0.64 eV) and 2,2,4-trimethylpentane (0.44 eV) and in the plastic phase of cyclohexane (0.47 eV) and 2,2-dimethylbutane (0.01 eV). Finally a correlation of I with the medium density is described.
Time resolved magnetic modulation of ion recombination in organic solutions: spin motion in radical ion pairs
Authors: Klein Jean , Voltz René
Published: May 2006

The evolution of the singlet character of correlated ion radical pairs, prepared by high energy impact (3 particles) in organic liquid and solid solutions, is monitored by nanosecond time resolved solute recombination fluorescence. Results obtained show that the relative variations [IB(t) − I0(t)]/I0(t) of the luminescence intensity in presence IB(t) and in absence I0(t) of magnetic fields (B < 5 kG) decrease exponentially with time, according to a field and solute concentration dependent rate, in liquid but not in solid solutions; in the case of 2b PPD as solute, a damped oscillating component could be observed. The results are interpreted in terms of hyperfine interaction induced coherent singlet–triplet mixing and of field and solute concentration dependent spin–lattice relaxation.
Electron mobilities in alkanes through the liquid and critical regions
Authors: Dodelet Jean-Pol , Freeman Gordon R.
Published: May 2006

Three properties of electrons in liquids are governed by scattering at low energies and show similar dependence upon liquid density and molecular shape. They are the mobility, the dependence of the mobility upon electric field strength, and the penetration range of low energy (<10 eV) electrons. The scattering cross sections of hydrocarbons in the liquid phase (near or below the normal boiling point) are smaller when the molecules are more sphere-like. The degree of sphericity of the molecules in the present series decreases in the order 2,2-dimethylpropane (DMPr) > 2,2-dimethylbutane (DMB) > cyclopentane (cP) > n-pentane (nP).Electron mobilities in DMPr and DMB measured as functions of the liquid density pass through maxima similar to those observed earlier in argon and xenon. The magnitudes of the maxima decrease in the order Xe > Ar > DMPr > DMB. The maxima occur at densities approximately double the critical density dc. There is a small maximum for electrons in cP, but none for those in nP.The mobilities in the supercritical gases are similar for the four compounds. The Arrhenius temperature coefficients are all 7–10 kcal/mol (0.3–0.4 eV/electron) for temperatures and densities near the critical values. This implies that electrons form localized states in the gases. The extent of localization in supercritical DMPr appears to be greater than that in the normal liquid. The localization is not the critical phenomenon predicted by Lekner.The mobility in liquid DMPr decreases at high electric field strengths. The magnitude of the field dependence changes with the liquid density and passes through a maximum similar to that of the mobility itself. The field dependence in liquid DMB is smaller than that in DMPr, but it also passes through a maximum at a density about double dc.Equations are given that describe the mobility in nP at all temperatures from the triple point through to the supercritical gas. The electrons reside mainly in localized states over the entire temperature range, but transport occurs mainly in extended states to which the electrons are thermally excited.The penetration range parameter bGP of secondary electrons in these liquids is normalized for comparison by multiplying by the liquid density d. The values of bGPd plotted against d form curves similar in shape to the μ against d curves, but the relative variations in bGPd are much smaller.
Characterization of the triplet state of aromatic esters and nitriles. Evaluation of the steric effect on the triplet of methyl mesitoate
Authors: Arnold D. R. , Bolton J. R. , Palmer G. E. , Prabhu K. V.
Published: May 2006

The phosphorescence emission and electron spin resonance spectra of methyl mesitoate (1) and mesitonitrile (2) have been studied in order to assess the steric effect (inhibition of resonance) in the former. The triplet energy of 1 (80.5 kcal mol−1) is considerably higher than that of 2 (74.2 kcal mol−1) while the zero-field splitting parameters are very similar (1, D/hc = 0.127 cm−1, E/hc = 0.013 cm−1; 2, D/hc = 0.127 cm−1, E/hc = 0.006 cm−1). The triplet energy and zero-field splitting parameters of o-, m-, and p-methyl toluate and o-, m-, and p-tolunitrile are also reported.
The crystal structure of tert- butyl ethyldiazoacetate mercury(II)
Authors: Smith R. A. , Torres M. , Strausz O. P.
Published: May 2006

tert-Butyl ethyldiazoacetate mercury(II) is monoclinic with the following unit cell data at 20 °C: P21/n, a = 8.089(3), b = 18.720(10), c = 7.893(3) Å, β = 93.20(3)°, V = 1193.3 Å3, ρo = 2.09(1), ρc = 2.06, Z = 4. The structure was solved by heavy atom methods and refined to R = 6.6% for 1003 reflections. The diazoacetate portion is planar; the CN2 portion is linear.
Total synthesis of indole and dihydroindole alkaloids. X.1,2 The preparation of novel oxygenated catharanthine derivatives
Authors: Kutney James P. , Bokelman Gordon H. , Ichikawa Masahiro , Jahngen Edwin , Joshua Alummoottil V. , Liao Ping-Huang , Worth Brian R.
Published: May 2006

Detailed investigations involving the electrophilic attack of various reagents on the 3,4-double bond of catharanthine derivatives (e.g. 3, R = O) furnished a series of novel derivatives of potential use in the syntheses of naturally occurring bisindole alkaloids. These studies include such reagents as peracid, osmium tetroxide, and positive iodine.
Solvated electrons and the effect of coordination on the optical spectra of alkali metal cation – electron pairs in ethers
Authors: Seddon William Arthur , Fletcher John Wallace , Sopchyshyn Fred Charles , Catterall Ron
Published: May 2006

Pulse radiolysis of tetrahydrofuran (THF), dimethoxyethane (DME), diglyme (DG), and triglyme (TG), results in the formation of solvated electrons, es−, with optical band maxima λmax ≥ 1840 nm. In the presence of alkali metal salts transient optical bands are observed with λmax at ∼900 and ≥1600 nm. The latter bands are assigned to the formation of 'monomeric' species of stoichiometry M considered to be 'tight' and 'loose' ion-pairs, respectively. The proportion of 'loose' ion-pairs increases with decreasing temperature and increasing coordination of the solvent in the order [Formula: see text] These results demonstrate a good correlation with established electron spin resonance data in alkali metal solutions and substantiate the coexistence of at least two 'monomeric' species in DME and the glymes.
13C and 33,34S isotope effects on the vapor pressure of liquid carbon disulfide
Authors: Jancsó Gábor , Hook W. Alexander Van
Published: May 2006

Prompted by the experimental investigation of Betts and Buchannon a thorough analysis of CS2 vapor pressure isotope effects has been made in the context of the theory of isotope effects in condensed phases and the available spectroscopic information. The agreement between the calculated and experimental results is satisfactory. The calculated results may be empirically described by the equations[Formula: see text]and[Formula: see text]The analysis indicates that the principal contribution to the 13C isotope effect is due to the shift on condensation of the asymmetric stretching frequency Δν3, and quantitatively corroborates the theoretical conclusion reached earlier by Akopyan, Girin, and Bakshiev and others of the magnitude of the dielectric correction for this band. The 34S effects are principally determined by the hindered rotation and translation in the liquid and the shift in the symmetric stretching motion Δν1
An electron impact study of the two isomeric tricarbonylchromium complexes of N-benzylideneaniline
Authors: Neuse Eberhard W.
Published: May 2006

Under electron impact, the two isomers resulting from tricarbonylchromium complexation of N-benzylideneaniline decarbonylate completely before the chromium-ring bond is broken and the azomethine ligand undergoes further fragmentation. The loss of two CO molecules is favored over the competitive process involving elimination of a single CO molecule, especially at high ionizing voltage. In both cases the highly stable benzylideneanilinechromium cations decompose primarily through fission of the metal-ring bond, although additional fragmentation pathways of minor importance are also observed. The decay patterns of the benzylideneaniline ligand cation are identical in the spectra of both complexes and very nearly coincide with that shown by benzylideneaniline itself under the same conditions of electron impact.
Semi-emprical non-adiabatic potential energy curves for hydrogen, deutirium, and their molecule-ions
Authors: Kuriyan Mary , Pritchard Huw O.
Published: May 2006

Effective non-adiabatic potential curves were constructed for the ground states of the deuterium molecule and of the hydrogen and deuterium molecule-ions by scaling our empirical non-adiabatic coupling correction for hydrogen according to the approximate rules given by Bunker. These effective potentials were refined by the techniques we have described previously, and were then used to generate the rotation–vibration energy-level spectra for H2+ and D2+; tables of these energy levels, which we consider to be the best available at the present time, are presented.
Intrinsic acidities of carbon acids: the nitroalkanes. Solvation effects in water and DMSO
Authors: Cumming J. B. , Magnera T. F. , Kebarle P.
Published: May 2006

The ion equilibria R1H + R2− = R1− + R2H involving nitroalkanes and compounds with known gas phase acidity were measured at 500 K with a pulsed high pressure mass spectrometer. The resulting ΔG0°= −RT ln K combined with calculated ΔS0 values lead to the corresponding ΔH changes. The enthalpy changes are used for the evaluation of the difference between the bond dissociation energy and the electron affinity D(R—H) – EA(R). The values obtained are: CH3NO2 44.0, CH3CH2NO2 43.7, (CH3)2CHNO2 43.0 kcal/mol. D(R—H) – EA(R) is a measure of the gas phase acidity. The nearly equal gas phase acidities of the nitroalkanes above are due to a decrease of D(R—H) and to a decrease of EA(R) with methyl substitution. In aqueous solution the acidities are known to increase substantially for the above nitroalkane order. Decrease of EA with methyl substitution indicates that there will be more charge localization on the O atoms in R− with methyl substitution. This leads to better H bonding and solvation of R− in protic solvents. This explains the higher acidity of the methyl substituted nitroalkanes in aqueous solution. The acidities in DMSO are closer to those in the gas phase since DMSO is not so sensitive to the charge distribution in R−.
Ultrasonic velocities for deuterium oxide – water mixtures at 298.15 K
Authors: Kiyohara Osamu , Halpin Carl J. , Benson George C.
Published: May 2006

Ultrasonic velocities in deuterium oxide – water mixtures were measured at 298.15 K and 1 atm pressure using the pulse-echo-overlap method in a successive dilution mixing cell. On a mole fraction basis, the velocities show negative deviations from linearity. Excess adiabatic compressibilities derived from the results are almost zero or slightly negative.
The synthesis, thermochromism, and cycloadditive properties of an O-methylenethioquinone system
Authors: Mayo P. de , Ng H. Y.
Published: May 2006

The irradiation of 4,5-benzo-1,2-dithiole-3-thione (1) in the presence of cyclopentene and of tetramethylethylene gives 1:1 adducts. In solution these adducts are in equilibrium with eight-membered-ring dimers. The thermodynamic parameters for this equilibrium have been determined. The available evidence suggests a head-to-head configuration. These same monomeric adducts give Diels–Alder addition products with normal dienophiles, but also react similarly with simple thiones (adamantanethione, norbornanethione, cyclohexanethione) to give thioorthoesters. The structures of the latter substances have been demonstrated both spectroscopically and, chemically, by hydrolysis to a thiosalicylic acid derivative. The thioorthoesters have been shown to undergo stereoisomerization on acid catalysis. Of the two mechanisms considered for this process (reversal to thiones and ion-pair formation) the former has been excluded.
The electro-deposition of silver on stationary and rotating glassy carbon discs
Authors: Barradas Remigio Germano , Fletcher Stephen , Szabo Sandor
Published: May 2006

The deposition of silver onto glassy carbon is described. The solution consisted of 10−2 M AgClO4 in 1.0 M HClO4. Experiments reveal the difficulties in trying to separate nucleation and growth phenomena from mass transport effects. A simple semi-quantitative model is proposed to explain the experimental data. It is also shown that the deposition reaction is not completely reversible under certain experimental conditions.
On the application of RRKM theory to the unimolecular isomerization of monofluorocyclopropane: a reaction with multiple fall-off characteristics?
Authors: Flowers Michael C.
Published: May 2006

Monofluorocyclopropane isomerizes at 475 °C to form cis- and trans-1-fluoropropene, 2-fluoropropene, and 3-fluoropropene. The relative amounts of these products formed are pressure dependent. It is shown that, using the previously determined Arrhenius parameters for the formation of each product, RRKM theory does account satisfactorily for the pressure dependence of the product yields for all the reaction products.
Synthesis of 3-carboxylated 2,5-dihydrothiophenes
Authors: McIntosh John M. , Sieler Robert A.
Published: May 2006

Vinylphosphonates 11, readily prepared from diethyl carbomethoxymethyl phosphonate (10) react with α-mercaptocarbonyl compounds to afford substituted 3-carbomethoxy-2,5-dihydrothiophenes in excellent yields. The scope of this synthesis is indicated and the use of the products in the synthesis of substituted 2-carboxy-1,3-butadienes is illustrated.
A simpler method to evaluate the isotopic shifts in fondamental stretching frequencies of polyatomic molecules
Authors: Bron Jan , Wallace R.
Published: May 2006

As an alternative to the more exact, but much more complex theory, a simpler method to estimate the isotope shifts in fundamental (stretching) frequencies of molecules is proposed. By means of examples, it is shown that good agreement between calculated and observed frequencies can be obtained.
Mesure de la constante de vitesse de réaction des atomes d'hydrogène sur l'éthane et le propane en réacteurs tubulaire et parfaitement agité ouverts
Authors: Lede Jacques , Villermaux Jacques
Published: May 2006

The rate constant for the reaction of hydrogen atoms, generated by electrical discharge, with ethane and propane has been studied in tubular and perfectly stirred open reactors. Measurements are made with a new and very sensitive method of analysis of the hydrogen atom concentration. The results obtained near room temperature are in good agreement with those of other authors operating at much higher temperatures. The following estimates may be made:[Formula: see text]
Substituent effect on the carbon-13 nuclear magnetic resonance spectra of 2-substituted tropones. Troponoid-I
Authors: Bagli J. F. , St-Jacques M.
Published: May 2006

The 13Cmr spectra of a series of 2-substituted tropones were analysed using a combination of methods including specific deuteration, multiplicities in coupled 13Cmr spectra and proton off-resonance decoupling techniques. The published 13C assignment for tropolone acetate was proven wrong and was corrected. Substituent parameters were defined and shown to exhibit two linear relationships with the corresponding substituent parameters for analogous monosubstituted benzenes. The significance of the results is discussed.
Effect of hydrocarbon solutes on electron ranges and free ion yields in liquid xenon
Authors: Kimura Toyoaki , Freeman Gordon R.
Published: May 2006

The energy transfer efficiency ratio, ETE=(σhΔEh/σxΔEx), for hydrocarbons dissolved in liquid xenon has the following values: ethane, 96; propane, 180; n-butane, 485; ethylene, 193; propylene, 255; cis-butene-2, 425; trans-butene-2, 665. The large increase on going from propane to butane is attributed to the energy absorption capability of the C2H5 groups through rotation about the central bond in butane. The presence of a double bond in the molecule enhances ETE, presumably through the participation of transient negative ion states in the energy transfer process. The cis–trans effect in butene-2 is still not understood.
An electron spin resonance and CIDEP study of the photoreduction of tert-butyl-p-benzoquinones
Authors: Foster Terry , Elliot A. John , Adeleke Babatunde B. , Wan Jeffrey K. S.
Published: May 2006

The photoreduction of 2-tert-butyl-p-benzoquinone and 2,5- and 2,6-di-tert-butyl-p-benzoquinone were studied by esr spectroscopy. In the photolysis of 2,6-di-tert-butyl-p-benzoquinone, only one semiquinone radical was observed and its decay kinetics were monitored by esr. The reduction of the triplet 2-tert-butyl-p-benzoqinone leads to the formation of isomeric semiquinone radicals 1 and 2 in the primary photochemical processes, and this is then followed by a chemical equilibrium between the two isomeric radicals. The relative rates of formation of the two radicals cannot be monitored by conventional esr methods but the CIDEP results show that the formation of radical 2 is about five to seven times faster than that of radical 1. A secondary reaction of the phenoxy radical with a product benzohydrofuran 4 leads to the observation of a polarized radical 3 which derives all its polarization from the primary phenoxy radical.
Variational energies for highly excited states of the helium atom
Authors: Ma Wai-Tak , Kuriyan Mary , Pritchard Huw O.
Published: May 2006

The efficient correlated variational wave functions used previously to study the higher 1 sns states of helium have been extended to other states of the helium atom, 1 snp (n ≤ 23), 2pnp1P (n ≤ 25), and 2pnp3P (n ≤ 25); similar uncorrelated wave functions were used for 1snd (n ≤ 21), 2pnp1D (n ≤ 10), and 2pnp3D (n ≤ 10). Attempts to use the same techniques for the 2pnp1,3S states appear to converge variationally to the energies of the 2s21S and 2s3s3S states respectively. Comparison is made with experimental results where appropriate, and agreement is excellent except in the case of the 1snd states above n = 13.A search was made for excited states of H− in each of these configurations, but no new states were found.
Galvanostatic transients and crystallization overvoltage
Authors: Fletcher Stephen , Smith Arthur
Published: May 2006

The theory of galvanostatic transients is extended to include the formation of a three-dimensional crystalline layer. The mechanism of formation of this layer is assumed to be one of nucleation and subsequent growth of randomly distributed nuclei on the electrode surface. The resulting crystallization overvoltage is shown to be a complex function of the applied current density, as well as being related to the potential-dependence of the rate constants for lattice growth and the potential-dependence of the nucleation rate constant. The complete E–t response is calculated numerically and also certain limiting cases are described which have exact analytical solutions. A method of testing the model experimentally is briefly discussed.
Proton magnetic resonance studies of 2′-deoxynucleosides and nucleotides in the syn conformation
Authors: George Arthur L. , Hruska Frank E. , Ogilvie Kelvin K. , Holy Antonin
Published: May 2006

Proton magnetic resonance data for 6-methyl-2′-deoxyuridine and its 3′- and 5′-monophosphate derivatives are obtained in aqueous solution and compared with data for corresponding thymine derivatives. The data show that the derivatives of the 6-methyluracil base occupy the syn conformation. The presence of the syn base leads to a flattening of the sugar ring and destabilization of the g+ conformer about the C(4′)—C(5′) bond. This destabilization is particularly large at the 5′-nucleotide level and is discussed in terms of a repulsive interaction involving the 2-keto oxygen of the base and the negatively charged 5′-group.
Synthesis, characterization, and X-ray structural studies of octahedral transition metal complexes incorporating the novel anionic tridentate ligand, dimethyl(ethanolamino)(1-pyrazolyl)- gallate, [Me2Ga(OCH2CH2NH2)(N2C3H3)]−
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis and physical properties of octahedral transition metal complexes of the tridentate tris chelating ligand [Me2Ga(OCH2CH2NH2)(N2C3H3)]− are given. Crystals of sym-fac-bis[dimethyl(ethanolamino)(1-pyrazolyl)gallato(N(2),O,N]nickel(II) are monoclinic, a = 11.7908(6), b = 7.3158(6), c = 12.5797(8), β = 97.035(7)°, Z = 2, space group P21/n and crystals of the mer isomer are monoclinic, a = 18.6617(7), b = 8.7941(4), c = 13.5670(8), β = 91,766(4)°, Z = 4, space group P21/c. The structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to final R values of 0.048 and 0.052 for 1881 and 2573 reflections with I ≥ 3σ(I) for the fac and mer isomers respectively. The nickel atoms in both structures were found to have distorted octahedral coordination geometry. Bond lengths (corrected for libration) are: Ni—O, 2.090(3); Ni—N, 2.085(3) and 2.112(3); Ga—O, 1.908(3); Ga—N, 2.010(3); and Ga—C, 1.979(5) and 1.981(6) Å for the fac isomer, and Ni—O, 2.045(4) and 2.049(4); Ni—N, 2.091 (4)-2.156(5); Ga—O, 1.898(4) and 1.899(4); Ga—N, two at 1.991 (5); and Ga—C, 1.948(8)-1.971 (7) Å for the mer isomer.
Equilibrium decomposition pressures of the compounds K2ZrCl6 and K2HfCl6
Authors: Kipouros G. J. , Flengas S. N.
Published: May 2006

The chemical equilibria representing the reactions[Formula: see text]and[Formula: see text]were investigated by direct vapour pressure measurements. The thermodynamic data for these reactions, such as free energies and enthalpies of reaction, have been calculated. With reference to the separation of Hf from Zr by a recently developed process based on the selective reactivity of ZrCI4 and HfCl4 vapours with alkali chlorides, it is shown that KCl is a better separating agent than LiCl.
The near-ultraviolet absorption spectrum of diimide: a re-examination
Authors: Back R. A. , Willis C. , Ramsay D. A.
Published: May 2006

The absorption spectra of N2H2 and N2D2 in the region 3000–4300 Å have been re-examined with somewhat higher resolution than was used in earlier work. The vibrational assignments of the principal progressions are unchanged except for the revision of the vibrational numbering suggested by the calculations of Perić, Buenker, and Peyerimhoff in 1977. The transition is electronically forbidden (1Bg–1Ag) but is made vibronically allowed by excitation of one quantum of the antisymmetric stretching vibration ν4′(bu). Weaker progressions are induced by the torsional vibration ν4′(au) and the antisymmetric H—N—N bending vibration ν6′(bu). Agreement between experiment and theory is generally satisfactory though some significant discrepancies in Franck–Condon factors have been noted.
Deactivation of singlet oxygen and triplet pentacene by transition metal complexes
Authors: Furue Hiroshi , Russell Kenneth E.
Published: May 2006

Rate constants, kQ, have been determined for the deactivation of singlet oxygen in carbon tetrachloride by a range of transition metal complexes. The singlet oxygen was produced by flash photolysis of air-saturated carbon tetrachloride solutions with methylene blue as sensitizer, and the decay followed by observing the concentration of the accepter 1,3-diphenyliso-benzofuran at 435 nm. The high rate constants of certain diamagnetic nickel complexes are accounted for by a spin-allowed transfer of electronic energy from singlet oxygen to the complex. Rate constants have also been determined for the deactivation of triplet pentacene by a number of these metal complexes. The triplet pentacene was produced by flash photolysis of dilute solutions of pentacene in benzene and the decay monitored at 492 nm. The rate constants for quenching of triplet pentacene are generally lower than those for quenching of singlet oxygen but there is a good correlation between the two sets of results. Both processes appear to proceed by way of electronic energy transfer without the intervention of complex formation between donor and accepter.
The volume of activation for benzyl chloride hydrolysis and its pressure dependence
Authors: Lohmüller R. , Macdonald D. D. , Mackinnon M. , Hyne J. B.
Published: May 2006

Various equations which have been proposed to provide the 'best' functional form for the dependence of rate upon pressure for reactions in solution have been tested for the extraction of ΔV≠ and dΔV≠/dp for the hydrolysis of benzyl chloride at 30 °C and at pressures over the range 1 to 6895 bar. One hundred individual rate constants were determined for this reaction at pressure increments of 345 bar and provide a sufficiently large body of data to permit application of statistical methods for testing the various rate–pressure functions with little risk of bias.
Electron spin resonance studies of the surface chemistry of molybdenum–alumina catalysts
Authors: Khulbe K. C. , Mann R. S. , Ternan M.
Published: May 2006

When alumina was doped with molybdenum oxide, the concentration of the electron accepting sites increased linearly up to 18 wt% MoO3, and then decreased. The colour of the Mo–alumina changed from whitish yellow to grayish black when degassed at 320 °C for 2 h. This depended on the concentration of Mo. A strong signal for Mo5+ was observed. Oxygen species were formed when the degassed sample was treated with oxygen or air. A reversible behaviour of oxygen on these species was observed. A possible mechanism has been discussed for the formation of O2− species and the reversible behaviour of oxygen. The concentration of electron accepting centers has been correlated with the activity for the hydrodenitrogenation of heavy oils over MoO3–alumina catalysts.
Activation energy for methoxy group relaxation
Authors: Mazid M. A. , Shukla J. P. , Walker S.
Published: May 2006

Dielectric absorption studies hove been made on seven compounds which hove methoxy groups attached to an aromatic ring and on some related rigid molecules. The solutes hove been dispersed in a polystyrene matrix. In some cases, the absorptions due to the group and the molecular process have been separated completely, and this has permitted the estimation of more accurate Eyring enthalpies of activation for methoxy group relaxation. These values hove been compared with those in the literature and, on the whole, it would seem likely that the energy barrier to group relaxation is small and of the order of 10 kJ mol−1 for cases where there is no mutual conjugation or steric effects.
The thermal desorption of surface species from sulfur dioxide adsorption on natural chrysotile asbestos and calorimetric sorption heats at 298, 323, 373, and 423 K
Authors: Murphy William John , Ross Robert Anderson
Published: May 2006

Calorimetric heats of adsorption have been determined for sulfur dioxide adsorbed at 298, 323, 373, and 423 K on both Californian and Quebec chrysotiles. Adsorption isotherms have been measured and some differential molar entropies calculated. Thermal desorption of surface species resulting from the adsorption of sulfur dioxide on Californian chrysotile at 298 K have been studied from 25 to 450 °C. Sulfurous and carbonic acids, in addition to sulfites and other trace species, have been shown to result from the adsorbent–adsorbate interactions. A mechanism for sulfur dioxide adsorption on chrysotile has been prepared which accounts for the observed high heats of adsorption measured at low surface coverages.
Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy
Authors: Geneste Patrick , Durand Robert , Kamenka Jean-Marc , Beierbeck Helmut , Martino Robert , Saunders John K.
Published: May 2006

The carbon-13 chemical shifts for a number of relatively rigid ketoximes are presented. It is shown that the chemical shift difference, Δδ (syn—anti), for the carbons α to the oxime carbon depends on the dihedral angle between the C=N and Cα—H bonds. This stereochemical dependence is then used to determine the preferred conformation of substituted cyclohexanone oximes.
Kinetics and mechanism for the formation of oxygenated products from the photolysis of hexafluoroacetone–methane system
Authors: Wu E-Chung , Clark Robert Richmond , Tang Yi-Noo
Published: May 2006

In addition to CF3H and C2F6, four oxygenated products were identified in the photolysis of hexafluoroacetone–methane system: CH3COCF3, (CF3)3COH, (CF3)2(CH3)COH, and (CF3)2(CH3)COCF3. The mechanism for the formation of these compounds is discussed, and the activation energies of several of the reactions involved are evaluated from detailed temperature and composition studies.
pKa values of protonated α,β-unsaturated cyclic carboxylic acids. Effect of ring size on acidities
Authors: Bhat S. N. , Rao Rama , Ranganayakulu K.
Published: May 2006

The pKa values of protonated α,β-unsaturated acids, namely tiglic, cyclopentene carboxylic, cyclohexene carboxylic, and cycloheptene carboxylic acids have been determined spectrophotometrically and the values are −4.08, −4.05, −3.88, and −3.84, respectively. The conjugate acid of tiglic acid is a stronger acid than that of crotonic acid (pKa − 3.94) and the difference in acid strength is explained on the basis of steric inhibition of resonance by the α-methyl group. All the protonated cyclic acids are shown to be somewhat weaker than the corresponding acyclic ones. Several factors have been considered to explain the acid strength of these cyclic α,β-unsaturated acids. It has been shown that the ease of placing the double bond exo to the ring system is responsible for the changes in acidity of the above cyclic systems.
Catalyst modification by metal deposition: the deposition of silver on platinum at underpotential and overpotential
Authors: Barradas Remigio Germano , Fletcher Stephen , Szabo Sandor
Published: May 2006

It is demonstrated that platinum catalysts can be modified by electrochemical means. The deposition of silver is described at both underpotential and overpotential. Although the deposition reactions can be quantified, the electrode kinetics cannot be investigated because of the simultaneous formation and reduction of platinum oxides.
Study of the electrolytic reduction of Cr(VI) in aqueous solutions of chromic acid by the rotating disc electrode method
Authors: Chagas Hélio C.
Published: May 2006

The Cr6+/Cr3+ reduction in aqueous solution is studied in the presence of sulfate and chloride ions by the rotating disc electrode method. In the low chromic acid concentration region, the results exhibit some differences in relation to those obtained using more concentrated solutions. However, it is demonstrated that in the presence of sulfate and chloride ions there is a chemical reaction preceding the electrochemical process, confirming a previous suggestion. Results for Cr6+/Cr3+ reduction process in perchloric acid medium at various temperatures are presented and a reduction mechanism is suggested.
Molécules modèles des motifs des poly-1,4-glucosides. II. Etude, par spectroscopie infrarouge, des conformations chélatées des diastéréoisomères modèles et discussion dans le cadre des chélations glucosidiques
Authors: Lafuma Françoise , Quivoron Claude
Published: May 2006

We have made a systematic study of the infrared spectra, in the chelation region 3700–3300 cm−1, of each of 30 separate diastereoisomers in dilute solution in carbon tetrachloride. Those diastereoisomers which have configurations corresponding to those of cellulose or amylose were examined more carefully. Depending on the structure of the model molecule and its diastereoisomeric configuration, it was possible to observe absorption bands corresponding to chelation in rings of 5, 6, 7 or 8 members. Most frequently the geometry of the chelated conformations varies from one diastereoisomer to another of a single molecule. The diastereoisomers of hydroxylated acetals have permitted the recognition of the result of a competition between two hydroxyl groups for the same proton accepting site. Discussion of these experimental results in terms of glucosidic chelations have led to the hypothesis that the chelations are[Formula: see text] in cellobiose, in methyl β-cellobioside and in cellulose, respectively. We have confirmed the chelation [Formula: see text] in the case of maltose, methyl β-maltoside and amylose and it seems reasonable to suggest that a chelation [Formula: see text], can exist in these α-1,4-glucosides.[Journal translation]
Scavenging of electrons prior to solvation in liquid alcohols
Authors: Okazaki Kiyoshi , Freeman Gordon R.
Published: May 2006

A solvent effect similar to that reported earlier (J. Am. Chem. Soc. 98, 6825 (1976)) has been found for the rates of reaction of solvated electrons with benzene and toluene in a series of alcohols. The value of the rate constant for benzene at 299 K increases abruptly from 1.0 (106 M−l s−1) in methanol to 6.8 in ethanol, then increases only slightly to 7.0 in 1-propanol and 8.4 in 1-butanol. A further large increase occurs on going to a secondary alcohol solvent: 42 (106 M−1 s−1) in 2-propanol and 69 in 2-butanol. The activation energies are ∼ 30 kJ/mol in all cases, so the rate constants reflect different entropies of activation. The entropies are affected by the solvation energies of the species.The reactions of benzene and toluene with electrons prior to solvation show relatively little solvent effect, due to their higher energy state. In 2-butanol at 163 K, reactions of quasifree, localized (absorbing in the infrared), and equilibrium solvated electrons have been distinguished. Reactions of eqf− obey the relation (Aio/Ai)qf ≈ 1 + [P/(1 − P)]fqfNs, where Ai/Aio is the fraction of electrons that have not been scavenged up to time i, and Ni is the mol fraction of scavenger. See text for remaining symbols. Reactions of eloc− obey the relation (Ai/Aio)loc ≈ exp(−nflocNs). The total probability that electrons reach the equilibrium solvated state is Ai/Aio ≈ exp (−nflocNs)/{1 + [P/(l − P)]fqfNs}. Both diffusion and tunneling may contribute to scavenging of eloc−. The contribution of these processes, compared to the amount of scavenging eqf− increases with increasing scavenger concentration and decreasing temperature.The parameters fqfP/(l − P) and nfloc each vary approximately as T−4, which is equivalent to an Arrhenius temperature coefficient of about −8 kJ/mol. The negative temperature coefficients could imply either that the scavenging step has a negative temperature coefficient, or that the lowering of the electron energy state has a positive temperature coefficient.
Ion mobilities in gaseous ammonia
Authors: Sennhauser Eric S. , Armstrong David A.
Published: May 2006

Gaseous ammonia at pressures in the range 200 to 1200 Torr was subjected to continuous irradiation by 40 kVp X-rays and the mobilities of the positive and negative ions (μ+ and μ−, respectively) were determined by a pulsed-drift method. The averages of μ+ and μ− agreed well with results obtained by another method. The magnitude of μ+ varied from 3.2 ± 0.2 cm2 V−1 s−1 at 200 Torr to 0.53 ± 0.04 cm2 V−1 s−1 at 1200 Torr. While μ− converged to the same value at 1200 Torr, it was slightly higher, 3.3 ± 0.2 cm2 V−1 s−1, at 200 Torr. The pressure dependence and actual magnitudes of u+ were found to be in good agreement with theoretical predictions based on ion–molecule collision rate theory for NH4+•xNH3 clustered ions of known x.
Complex fluoroanions in solution. IX. BF3–anion complexes and their disproportionation
Authors: Brownstein S. , Latremouille G.
Published: May 2006

Complex fluoroanions have been prepared with boron trifluoride and perchlorate, nitrate, nitrite, acetate, formate, azide, cyanide, cyanate, thiocyanate, and thiophenolate ions. The complexes formed from the anions of the strong acids, except the hydrogen halides, do not disproportionate to BF2(anion)2−. Complexes of anions of weaker acids may disproportionate and, or, complex a second molecule of BF3. Regularities in fluorine–boron coupling constants are tabulated.
Enrichment of nitrogen-15 by the direct laser photolysis of ammonia-d3 in the transition
Authors: Hackett P. A. , Back R. A. , Koda S.
Published: May 2006

Ammonia-d3 of differing 14N/15N ratios has been photolysed in the [Formula: see text] transition using a narrow-band-width, frequency-doubled, pulsed dye laser. At specific excitation wavelengths, chosen by absorption spectroscopy, the product nitrogen is enriched in 15N, a maximum enrichment factor of 4.8 being attained. The initial isotopic selectivity of excitation is largely retained in the nitrogen product, even though the primary photodissociation forms free radicals and N2 is formed only after a sequence of secondary reactions. Quantum yields of nitrogen and hydrogen formation have been measured at very low conversions as a function of the time of irradiation. The initial yield of nitrogen appears to be zero and that of hydrogen 0.25.
The standard enthalpy of ionization of water at 298 K from calorimetric measurements on iodine pentoxide
Authors: Cerutti Paul J. , Ko Hon Chung , McCurdy Keith G. , Hepler Loren G.
Published: May 2006

We have made calorimetric measurements of the enthalpies of reaction of I2O5(c) with water and with a small excess of OH−(aq) and have combined the results to obtain ΔH0 = 13.340 kcal mol−1 for the standard enthalpy of ionization of water. It is suggested that this approach can be applied usefully to investigation of the enthalpy of ionization of D2O for which there are still unresolved differences between reported values.
Dissolution of iron during the initial corrosion of carbon steel in aqueous H2S solutions
Authors: Tewari Param H. , Campbell Allan B.
Published: May 2006

The dissolution of iron from carbon steel in aqueous H2S solutions has been studied as a function of time and temperature at 0.1 MPa H2S pressure using the rotating disc technique. The iron sulfide film formed on the disc surface has been identified by X-ray diffraction analysis. The solubility and dissolution rate of synthesized mackinawite, FeS(1−x), have also been determined to help establish the mechanism of release of iron from carbon steel corroding in aqueous H2S solutions.The rate data have been analysed by an equation for a joint chemical and transport controlled process. At 22 °C and 0.1 MPa H2S, the maximum rate of release of Fe2+, obtained by extrapolating the data to infinite rotation speed, is 7.4 ± 0.5 μmol/m2s. This is similar to the dissolution rate determined for synthesized mackinawite powders, but is 20 times faster than the rate of dissolution for troilite and more than 1000 times faster than the dissolution rates for pyrrhotite and pyrite. Thus, troilite and iron sulfide phases that form subsequently are not major contributors to Fe2+ release during the corrosion of carbon steel.At 22 °C the diffusion coefficient for the FeSH+ ion is (1.4 ± 0.2) × 10−9 m2/s and the activation energy of the diffusion process is 25 ± 7 kJ/mol. The chemical reaction occurring at the surface has an activation energy of 77 ± 14 kJ/mol.It is concluded that the release of iron from corroding carbon steel is governed by the dissolution rate of mackinawite, the initial corrosion product. This dissolution is controlled by the chemical reaction between mackinawite and H+ and by the transport of the complexed FeSH+ from the interface to the bulk solution.
Yields of excited states from thermolysis of some 1,2-dioxetanes
Authors: Kopecky Karl R. , Filby John E.
Published: May 2006

The singlet 1Φ and triplet 3Φ excited state product yields produced on thermolysis in toluene of trimethyl- (1), tetramethyl- (2), cis-3, 4-butano-3,4-dimethyl- (3), and 3,4:3,4-dibutano-1,2-dioxetane (4) were determined to be as follows (dioxetane, °C, 1Φ, 3Φ): 1, 40, 1.1 × 10−3, 0.15; 2, 45, 4.4 × 10−4, 0.31; 3, 26, 8.5 × 10−4, 0.23; 4, 24, 4.8 × 10−6, 0.011. The reason for the low yield of excited states obtained from 4 is not known. Thermochemical calculation indicate that as much energy is available from thermolysis of 4 as is available from 2.Dioxetane-energized dimerization of acenaphthylene, accompanied by an intense yellow luminescence, produced mainly the trans dimer in 1–3% yield. Dioxetane-energized cyclization of 1-(2,4-dimethylphenyl)-1,2-propanedione produced 2-hydroxy-2,5-dimethylindan-1-one in 0.5–6% yields.
Infrared spectra of the ammonium ion in crystals. Part VI. Hydrogen bonding in simple and complex ammonium halides
Authors: Knop Osvald , Oxton Ian A. , Falk Michael
Published: May 2006

The ν1 and ν4bc infrared absorptions of the NH3D+ probe ion dispersed at low concentration in polycrystalline ammonium halides were used to investigate possible correlations between the frequencies of these absorptions and various structural and other parameters of the ammonium compounds. The most important among these parameters are the H … X distance, the acceptor strength of the halogen atom X for hydrogen bonding, and the coordination number C.N. and activation energy Ea for reorientation of the ammonium ion. It is found that the ν1 and ν4bc frequencies are affected by the acceptor strength and by the degree of 'compression' of the ammonium ion in the crystal, the volume effect. These two factors affect ν4bc in the same direction but ν1 in opposite directions. As a consequence, in a ν4bc vs. ν1 plot the halides are separated according to X, C.N., and certain other parameters. The effective radius of the ammonium ion in cubic (NH4)2MX6 is shown to increase with the strength of hydrogen bonding.The Ea vs ν1 plot contains two branches. The low-frequency branch is dominated principally by the strength of the hydrogen bonding and corresponds to C.N. 4 and 8 and to normal hydrogen bonds. The high-frequency branch is dominated principally by the volume effect and corresponds to C.N. 12 and to hydrogen bonds of highly dynamic character (fluxional hydrogen bonds). Ammonium ions with C.N. 6 may correspond to either branch, depending on the formal charge on X. Existence of the so-called symmetrically trifurcated hydrogen bond that has been proposed for the ammonium ion in certain coordinations is not supported by the present evidence.The problem of the fundamental vibrational frequencies of the 'free' ammonium ion is discussed and values are proposed for the 'limiting' ν1. and ν4bc frequencies in ammonium halides. Criteria of hydrogen bonding in ammonium halides are reviewed and comment is offered on symmetry aspects of crystallographic transformations in cubic hexahalometallates(IV), A2MX6.