bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction of the Hydrated Electron with HS−
Authors: Eager R. L. , Kabachia V. , Waltz W. L. , Woods R. J. , McCallum K. J.
Published: May 2006

Evidence is presented to show that the hydrated electron reacts with monohydrogen sulfide ion with a rate constant of (3.0 ± 0.4) × 107 M−1 s−1 in contrast to an earlier report that this substrate was unreactive. A comparison of the electron reactivity towards hydrogen sulfides and selenides suggests that the reactivity reflects the ability of the substrate to accommodate the electron as opposed to its ability to donate a proton to the electron.
Gas Phase Reactions of Fluorine Atoms
Authors: Pollock Thomas Long , Jones William Ernest
Published: May 2006

The rate of reaction of F atoms with a series of compounds, CH4, CH3F, CH2F2, CHF3, CHClF2, HCl, CBrF3, NH3, and PH3 has been determined relative to the chemiluminescent reaction[Formula: see text]by photometry. The fluorine atoms were produced in a flow system from the fluid mixing of molecular fluorine and nitric oxide diluted with argon.
Crystalline Adduct Formation Between Quaternary Alkyl Ammonium Salts and Simple Aromatic Compounds
Authors: Hardy Joseph W. , Williams Elrick M. , Lipkin Edward , Rosen Jeffrey M. , Roizen Michael F. , Buchin Peter J. , Taylor Edward Godfrey , Taylor Charles Leonard , March Raymond Evans
Published: May 2006

Several crystalline 1:1 adducts of quaternary alkyl ammonium salts with simple aromatic compounds have been prepared. Adduct formation appears to be restricted to certain salt–solvent pairs when the alkyl substituent is n-butyl or i-amyl, the anion is iodide, perchlorate, nitrate, or picrate and the aromatic compound is benzene, fluorobenzene, or toluene. The standard enthalpy and entropy changes of adduct formation at 25 °C have been obtained from vapor pressure measurements. A linear relationship between these thermodynamic parameters is expressed in the form of an isokinetic temperature. An absorption band at 14.4 μ appears to be characteristic of this series.
Comment: Concerning the Cleavage of Tertiary Amines With Acetic Anhydride
Authors: Mariella R. P. , Brown K. H.
Published: May 2006

The failure of methyl-substituted tertiary amines to yield methyl acetate on cleavage by acetic anhydride indicates that the mechanism proposed by Gol'dfarb and Belen'kii cannot be correct. The results of cleavage of cinnamyldimethylamine are offered as support for the mechanism proposed by Mariella and Brown. Catalysis by acetic acid is not considered to be important.
Application de la Trichromie Complémentaire à l'étude des complexes métalliques en solution
Authors: Morin M. , Petit-Ramel M. M. , Scharff J. P. , Pâris M. R.
Published: May 2006

Complementary tri-stimulus spectrophotometry appears as an interesting method for investigation of metal complex equilibria in solution. This has been demonstrated on various examples including bivalent (copper, vanadyl) or trivalent (iron, aluminum, yttrium, lanthanum) metal ions coordinated by several organic ligands.The formation, pH range of existence, and the number of absorbing species in colored solutions of binary or ternary (particularly bimetallic) systems are easily determined by calculation of the complementary tri-stimulus co-ordinates.The advantages (and disadvantages) of the technique are discussed. This qualitative method appears to be very useful for a first approach of coordination phenomena but needs to be completed by quantitative studies using classical methods.
The Anharmonicity Correction for Kinetic Isotope Effect Calculations
Authors: Bron Jan , Hacker Sylvia O.
Published: May 2006

The kinetic isotope effect, in the ring opening of a triatomic system, is corrected for anharmonicity in the vibrational ground state. For this system it is found that the correction is small and not larger than uncertainties caused by other assumptions made in kinetic isotope effect calculations.
The Synthesis of Miserotoxin and Structural Analogs
Authors: Baer Hans H. , Chiu Shuet-Hing Lee , Shields Douglas C.
Published: May 2006

The condensation of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with a variety of nitro alcohols led to nitroalkyl β-D-glucopyranoside tetraacetates. The following nitro alcohols were employed: 3-nitro-1-propanol, 2-nitro-1-propanol, 1-nitro-2-propanol, 2-nitro-1-butanol, 2-nitro-3-pentanol, and 2-methyl-2-nitro-1-propanol. The free 3-nitropropyl and 2-methyl-2-nitropropyl glycosides were obtained from their tetraacetates by deacetylation with sodium methoxide, whereas methanolysis catalyzed by methyl p-toluenesulfonate was employed for deacetylation of the other tetraacetates. Evidence for the presence of epimers in glycosides having a chiral center in the aglycon was obtained. Physical data of synthetic 3-nitropropyl β-D-glucopyranoside agreed with those of miserotoxin, the poisonous principle recently isolated from Astragalus miser varieties.
Photolyse du butène-1 dans l'ultraviolet à vide
Authors: Collin Guy J.
Published: May 2006

The vacuum u.v. photolysis of 1 -butene was studied in the 147–105 nm region. The main products formed from the fragmentation of excited molecules are allene, 1,3-and 1,2-butadienes, ethylene, and acetylene. The addition of a hydrogen atom to the double bond produces mainly secondary butyl radicals (91%) at 147 nm. At 123.6 nm, this proportion becomes 82%. Thus at shorter wavelengths (10 and 11.6–11.8 eV), hydrogen atoms are produced with a kinetic energy higher than the thermal energy.
The Co-Pyrolysis of Acetaldehyde and Propylene
Authors: Simon M. , Back M. H.
Published: May 2006

Analysis of both major and minor products of the thermal reaction of mixtures of propylene and acetaldehyde over the temperature range 750–800 °K and at pressures below atmospheric show that both reactants initiate radical chains and that both addition and abstraction reactions of radicals with propylene are important. The relation to general mechanisms of the inhibiting effect of propylene in pyrolysis reactions is discussed.
Photolyse de l'ammoniac et de l'ammoniac perdeuterié à 185, 147, et 123.6 nm
Authors: Masanet Jeannine , Fournier Janine , Vermeil Catherine
Published: May 2006

A very important isotopic effect for the ratio of molecular and atomic hydrogen yield in the photolysis of ammonia at 147 and 123.6 nm has been found [Formula: see text] while at 185 nm [Formula: see text].The dissociation NH3 + hv → (X3Σ −) + H + H occurs for wavelengths as high as 147 nm which implies that DNH−H ≤ 90 kcal mol−1.The rate constant of the reaction D + ND3 → D2 + ND2 has been evaluated [Formula: see text].
Singlet and Triplet States of Aminonitrenes: An Ab Initio Molecular Orbital Study
Authors: Baird N. C. , Barr R. F.
Published: May 2006

Ab initio STO-3G molecular orbital calculations are reported for the lowest singlet and the lowest triplet state of the aminonitrenes H2NN, CH3(H)NN, F(H)NN, and HCO(H)NN. The optimum geometry calculated for the H2NN triplet is nonplanar (Cs symmetry), with N—N and N—H bond distances of 1.436 and 1.034 Å, and HNN and HNH angles both of 107.5°. The optimum singlet is predicted to be planar (C2v symmetry), with N—N and N—H distances of 1.276 and 1.041 Å respectively, and an HNN angle of 124°. An analysis of the calculated geometries and electron density distributions indicates that the "idealized" representations 3 and 5 are adequate to explain the bonding in the triplet and singlet respectively. The effects of methyl, fluoro, and carbonyl substitution upon the singlet–triplet splitting and upon the charge distribution are discussed. The optimum-geometry triplet is predicted to be slightly more stable than the optimum-geometry singlet in all cases.
Etude cinétique du système Cu(II)–adénine
Authors: Boivin G. , Zador M.
Published: May 2006

The kinetics of formation and dissociation of Cu(II)–adenine complexes have been studied by stopped flow and relaxation methods.Between pH 3.5 and 5 the formation of Cu(II)•aH is too fast to be measured; formation of Cu(II)•(aH)2 has been studied and rate parameters have been determined. At pH < 3 protonated species make an important contribution to measured reaction rates. In basic media two different complexes have been investigated. The exchange reaction with EDTA proceeds by two parallel reaction paths.The mechanism of these reactions is discussed and compared with that proposed for the Cu(II)–adenosine system.La cinétique de la formation et de la dissociation de divers complexes Cu(II)–adénine a été étudiée par les méthodes de la relaxation thermique et du "flux stoppé".
The Infrared and Raman Spectra and Vibrational Assignment of t-Butyl Bromide-h9 and -d9
Authors: Bertie John E. , Sunder Sham
Published: May 2006

The infrared spectra between 4000 and 10 cm−1 of t-butyl bromide-h9 and -d9 in the gas and liquid states, and the Raman spectra between 3500 and 10 cm−1 of the liquids under parallel and perpendicular polarizations, have been recordeds and assigned. The compatibility of the assignments for the light and heavy molecules has been checked by normal coordinate calculations, in which 14 valence force constants have reproduced 40 fundamental frequencies with an average error of 1.5%. The calculated thermodynamic properties of both molecules are presented for temperatures between 50 and 500 °K.
Arylsulfanes—Synthesis and Nuclear Magnetic Resonance Spectra
Authors: Langer H. J. , Hyne J. B.
Published: May 2006

The synthesis of a series of variously substituted arylsulfanes of the general formula RC6H4SxH is described. The proton n.m.r. spectra of the members of the series are reported and discussed in terms of intramolecular electronic effects, conformational factors, and hydrogen bonding.
Mean Lifetime of an Embryo in the Homogeneous Nucleation from Solution of the Tetracyanoplatinates(II) of Barium, Calcium, and Magnesium
Authors: Bempah O. A. , Hileman Jr. O. E.
Published: May 2006

The mean lifetime of an embryo in the homogeneous nucleation from aqueous solution of the tetracyanoplatinates(II) of barium, calcium, and magnesium has been studied using the droplet technique. Supersaturation in the droplets was generated by selective extraction of the solvent into the surrounding silicone oil. Crystallization in the droplets was followed by photomicrography using plane polarized light.The data were analyzed using both the classical model and the mean lifetime model of Carlier and Frisch. The experimental results are consistent with the predicted relationship between the logarithm of the nucleation rate or the logarithm of the mean lifetime of an embryo and the inverse of the square of the logarithm of the supersaturation ratio at high supersaturation ratios. The calculated values of the inter-facial energy, using both models, are in close enough agreement to justify the assumptions made in the analysis.
A Correlation between Critical Volumes and Work Function Data for Electrons in Liquid Hydrocarbons
Authors: Davis H. T. , Schmidt L. D.
Published: May 2006

Electron-molecule hard-core radii determined with the aid of Springett, Jortner, and Cohen's quasi-free electron theory from electron work function data are shown to correlate with the critical volumes of several hydrocarbons. The radii are approximately equal to the van der Waals radii determined from the critical volumes.
Aggregation of p-Nitrophenyl Alkanoates in Aqueous Solution. Limitations on Their Use as Substrates in Enzyme Model Studies
Authors: Guthrie J. Peter
Published: May 2006

p-Nitrophenyl alkanoates are aggregated at extremely low concentrations in aqueous solution. Second-order rate constants for imidazole or hydroxide catalyzed hydrolysis are independent of ester concentration up to a critical concentration of ester, and then decrease with increasing ester concentration. The critical concentrations at 25 °C are: p-nitrophenyl hexanoate, 1 × 10−4 M; octanoate, 9.6 × 10−6 M; decanoate, 1.2 × 10−6 M. For the dodecanoate ester, the critical concentration was estimated as ca. 10−7 M. Addition of 10% methanol causes only a modest increase in the critical concentration. The critical concentration probably represents the solubility limit of the ester. The rate constants for the hydrolysis of the longer chain esters evaluated here are significantly larger than those in the literature, suggesting that the earlier work was done using conditions where the esters were aggregated.
On The "Low" A-Factors of Alkyl Radical Isomerization
Authors: Mintz K. J. , Roy D. J. Le
Published: May 2006

Recent chemical activation studies of isomerizations of alkyl and alkenyl radicals involving 5, 6, and 7 member ring complexes are shown to be consistent with earlier thermal studies and support the conclusion that the A-factors of these reactions are "low", i.e. substantially less than 1011 s−1. A possible explanation, consistent with transition state theory, is given in terms of configurational entropy.
Pulse Radiolysis of Liquid Deuterated Ammonia
Authors: Seddon William Arthur , Fletcher John Wallace , Jevcak John , Sopchyshyn Fred Charles
Published: May 2006

Pulse radiolysis of solutions of alkali metal amides in deuterated ammonia at −15 °C produces an initial absorption with a maximum at 1500 nm due to the solvated electron, eam−. This decays on a microsecond time scale giving a residual long lived absorption with a slightly broader spectrum and a maximum displaced to 1640 nm. We suggest the residual absorption is an equilibrium mixture of eam− and a metal–electron species. The initial decay of eam− is suppressed by scavenging ND2 and/or ND− radicals with dissolved D2 (1 atm) or NaBH4. Evidence is also obtained for the reaction ND− + D2 → eam−. It is estimated that k(eam− + ND2) and k(BH4− + ND2) = 2.5 × 1010 and 7 × 107 M−l s−1, respectively. Measurements of the initial yield in NH3 and ND3 give [Formula: see text]and 3.6 ± 0.4 molecules/100 eV, respectively.
The Rate of Recombination of H Atoms in the Presence of NH3
Authors: Teng L. , Winkler C. A.
Published: May 2006

The rate constant for the homogeneous recombination of H atoms in the presence of NH3, with He as carrier gas, has been determined at 298°K in a fast flow system, over the pressure range 1.50 to 4.55 Torr, using e.s.r. technique. A value of either 4.00 × 1016 or 5.14 × 1016 cm6 mol−2 s−1 was calculated, depending upon the rate constant taken, or estimated, from the literature for the recombination in the presence of helium.
The tert-Butyldimethylsilyl Group as a Protecting Group in Deoxynucleosides
Authors: Ogilvie Kelvin K.
Published: May 2006

tert-Butyldimethylsilyl chloride reacts selectively with hydroxyl groups in nucleosides and preferentially with the 5′-hydroxyl of deoxynucleosides. The tert-butyldimethylsilyl group can be removed under conditions which do not affect other commonly used acid or base labile protecting groups, yet it is stable to phosphorylation conditions. This allows for the synthesis of a variety of protected deoxynucleosides in good yields and introduces a versatile new protecting group to the nucleoside and nucleotide field.
Metabolites of Cyathus helenae. A New Class of Diterpenoids
Authors: Ayer William A. , Taube Hubert
Published: May 2006

Allocyathin B3 and cyathin A3, metabolites of the bird's nest fungus Cyathus helenae Brodie are shown to possess structures [Formula: see text] and [Formula: see text], respectively. In the solid state allocyathin B3 exists in the hydroxyketone form 2a, while cyathin A3 is in the hemiketal form 6a. In each case acetylation gives the diacetyl derivative of the hydroxyketone form whereas treatment with methanolic HCl gives an internal ketal. Allocyathin B3 and cyathin A3 have been correlated by hydrogénation to the common product 13a, and by transformation of each to the aldehyde 12a. These compounds are representatives of a new class of diterpenoids. Their biogenesis from geranylgeranyl pyrophosphate is discussed.
Chain Length Determination of Fatty Acids by Raman Spectroscopy
Authors: Warren Charles H. , Hooper Donald L.
Published: May 2006

For saturated long chain fatty acids, as for hydrocarbons, the odd order "accordion mode" vibrations are Raman active. These "accordion mode" vibrations have been used to provide qualitative and quantitative analysis of mixtures of acids in the range C12–C24.
The Rotational Oscillations of Tetrahydrofuran in Tetrahydrofuran Clathrate Hydrate
Authors: Klug D. D. , Whalley E.
Published: May 2006

The absorptivity of tetrahydrofuran clathrate hydrate in the range 70–7 cm−1 has been measured at several temperatures in the range 17–80 K. There are two broad bands with maxima at 25 and 38 cm−1 which are due to the rotational oscillations of tetrahydrofuran molecules in their cages. The integrated absorptivity yields an effective dipole moment for the oscillation of 1.63 D, which is close to the gas-phase value. The negative second moment of the absorptivity yields the contribution 0.105 ± ~0.007 to the low-frequency refractive index, in good agreement with a less accurate value from dielectric measurements. The orientational disorder of the water molecules causes a distribution of potentials hindering the rotational oscillations of the guest molecules, and a detailed analysis of the shapes of the bands yields directly the distribution of force constants for the oscillations.
Organic Sulfur Mechanisms. 15. The Stereochemistry of α-Hydrogen Exchange in the Simple Cyclic Sulfoxide 1,3 Dihydrobenzo[c]thiophene 2-Oxide
Authors: King James Frederick , Manoir John Richard du
Published: May 2006

In NaOD–D2O at 5.0° the α-hydrogens trans to the oxygen in 1,3-dihydrobenzo[c]thiophene 2-oxide (1) exchange 67 times faster than the cis. The cis hydrogens in turn exchange slightly faster than the faster of the α-hydrogens of the methylene group in benzyl methyl sulfoxide. Treatment of 1 with methyllithium followed by rapid quenching with DCl leads to a predominantly cis-monodeuterated product. It is also shown that the hydrogen removal in the lithiation step involves loss of the cis hydrogen and that the lithiation of 1 is much faster than that of benzyl methyl sulfoxide. Comparison of these results with the Rauk–Wolfe–Csizmadia nonempirical calculations on α-sulfinyl carbanions indicates that current theoretical understanding is as yet incomplete.
Ring C Functionalized Diterpenoids. Part II Cleavage of the Cyclopropane Ring in Methyl ent-Trachyloban-19-oate with Thallic Acetate
Authors: Campbell Helen Margaret , Gunn Patrick Alistair , McAlees Alan James , McCrindle Robert
Published: May 2006

Reaction of methyl ent-trachyloban-19-oate (1a) with thallic acetate gave four major products including the ent-atisane derivatives, 2–4. Since the substrate is readily obtainable from the common sunflower, this reaction provides a valuable route to these and related compounds. The fourth compound, 5, may derive from an ent-atisane intermediate by contraction of ring D.
Theoretical Studies of some Nonbenzenoid Hydrocarbons. II
Authors: DasGupta Archana , DasGupta Nadna K.
Published: May 2006

A semiempirical self-consistent field molecular orbital study has been made on some nonbenzenoid hydrocarbons using a resonance integral value proposed by Lo and Whitehead (2, 4), Chung and Dewar (3), Dewar and Harget (7), and Yamaguchi et al. (6) without using configuration interaction. It has been observed that spectral transitions calculated using the β-value proposed by Lo and Whitehead and Chung and Dewar are in good agreement with experiment and comparable to those calculated by the β-value proposed by Yamaguchi et al. and Dewar et al.
The Crystal and Molecular Structure of Dinitrato(triphenylphosphine)mercury(II)
Authors: Whitlow Simon H.
Published: May 2006

The structure of dinitrato(triphenylphosphine)mercury(II), Hg(N03)2.P(C6H5)3, has been determined from single–crystal X-ray data measured on a computer–controlled diffractometer. The crystals are monoclinic, have a unit cell of dimensions a = 10.39(1), b = 9.56(1), c = 19.44(2) Å, β = 94.3(1)°, which contains 4 molecules, and they belong to the space group, P21/c. The structure has been refined by least–squares methods from 2470 independent observed reflections to a conventional R-factor of 0.061. The Hg atom has a distorted tetrahedral coordination with Hg—O bond lengths of 2.190(8), 2.428(8), and 2.560(9) Å and an Hg—P bond distance of 2.359(3) Å. There are 2 distinct types of NO3 groups bonded to Hg. One is an unshared, unidentate ligand and the other acts as a bridging group joining 2 Hg atoms. Chains of—Hg—NO3—Hg—atoms are formed which follow crystallographic two-fold screw axes in the b-direction.
A Mass Spectrometric Study of the Influence of Electronic and Stereochemical Factors on the Hofmann Elimination Process in Quaternary Ammonium Salts
Authors: Smith Peter James
Published: May 2006

The mass spectra of the thermal decomposition products derived from the geometrical isomers of 2-phenylcyclohexyl- and 2-phenylcyclopentyltrimethylammonium salts together with their 2-d1 analogs have been determined together with the rigid substrate, 3-endo-2-exo-norbornyltrimethylammonium bromide. It is found that the Hofmann elimination reaction is most favored when the departing groups or atoms have the anti coplanar relationship and that the abstracted hydrogen is exclusively the benzylic hydrogen. A series of 1-arylethyltrimethylammonium salts were also examined together with their 1-d1 and 2-d3 analogs. It was found that electron-donating substituents on the phenyl ring favor the Hofmann elimination process while electron withdrawers lead to the pyrolytic reaction of halide substitution at carbon.
Chemistry of Proximal π-Bond Systems. Part II. Synthesis of 2,3-Dimethylenebicyclo[2.2.2]octa-5,7-diene
Authors: Butler D. N. , Snow R. A.
Published: May 2006

The new C10H10 hydrocarbon, 2,3-dimethylenebicyclo[2.2.2]octa-5,7-diene (7), has been synthesized. Diels–Alder additions to 7 afford a useful route to annelated barrelenes.
The Mechanism of Bromination of 2(1H)-Pyrimidinone, its N-Methyl and N,N′-Dimethyl Derivatives in Aqueous Acidic Solution
Authors: Tee Oswald S. , Banerjee Sujit
Published: May 2006

Rates of bromination at the 5-positions of the title compounds have been measured in aqueous sulfuric acid solutions. The reaction involves a rapid irreversible formation of a 5-bromo-4,6-dihydroxy-hexahydro-2-oxopyrimidine which undergoes slow acid-catalyzed conversion to the corresponding 5-bromopyrimidinone. If excess bromine is present the latter product reacts further to produce a 5,5-dibromo-4,6-dihydroxyhexahydropyrimidine.
Asymmetry in the 125Te Mössbauer Spectra of Tellurium Thiourea Complexes: Sign of the Nuclear Quadrupole Moment of the 3/2 State
Authors: Cheyne B. M. , Jones C. H. W.
Published: May 2006

Asymmetry in the Mössbauer spectra of Te(II) thiourea complexes is shown to be due predominantly, if not exclusively, to single crystal orientation effects. The asymmetry in TeTu4Cl2•2H2O is consistent with a negative sign for the nuclear quadrupole moment of the [Formula: see text] excited state in 125Te.
The Photochemical Isomerization of N-Bromo-α,β-unsaturated Lactams; An Intermolecular Allylic Bromination Process Involving a Probable Bromine Radical Chain
Authors: Gravel Denis , Hebert Jacques , Bilodeau Jacques , Cavalieri Ercole , Daris Jean-Paul
Published: May 2006

The photochemical behavior of the N-bromo-α,β-unsaturated lactams 1b and 2b has been investigated with particular regard to their potential intramolecular reactions. In both cases the main product corresponds to an isomerization of bromine to the 5-position. A crossover experiment and free radical initiation by AIBN or benzoyl peroxide indicate that the reaction bears a close mechanistic analogy to the NBS reaction. It was furthermore observed that the allylic bromo derivatives prepared could be smoothly reduced to the corresponding β,γ-unsaturated lactam making available an efficient method of deconjugation of α,β-unsaturated lactams.
The Structure of the Capsular Polysaccharide of Klebsiella K-type 72; Occurrence of 3,4-O-(1-Carboxyethylidene)-L-rhamnose
Authors: Choy Yuen-Min , Dutton Guy G. S.
Published: May 2006

Methylation and partial hydrolysis studies on the capsular polysaccharide of Klebsiella K72 show the structure to consist of a repeating unit[Formula: see text]The anomeric linkages were determined in isolated oligosaccharides by p.m.r. spectroscopy which also showed the presence in the polysaccharide of one pyruvate ketal per four sugar residues.
Phase Transformation Studies in Silver and Thallium Chromates
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

The existence of thermal transformations in silver and thallium chromate has been confirmed by differential thermal analysis, temperature-variable X-ray diffraction, and electrical conductivity measurements. The disputed transition ∼330 °C in Tl2CrO4 has been shown to be due to lattice distortion. The subtle difference in behavior of the pre-annealed and un-sintered samples is brought out by a variety of experimental measurements. The high temperature structure of these chromates is hexagonal. The presence of small amounts of Tl in Ag2CrO4 affects the transition temperature, enthalpy, and the order of the transformation.
Alchemists' Gold, Hg2.86 Asf6; An X-Ray Crystallographic Study of A Novel Disordered Mercury Compound Containing Metallically Bonded Infinite Cations
Authors: Brown I. David , Cutforth Brent D. , Davies Colin G. , Gillespie Ronald J. , Ireland Peter R. , Vekris John E.
Published: May 2006

The compound Hg2.86 AsF6 belongs to the tetragonal space group I41/amd with lattice parameters a = 7.538(4) Å, c = 12.339(5) Å, and Z = 4. The structure was refined using 109 symmetry independent reflections by full matrix least-squares refinement to a final R value of 0.079. The structure may be described as consisting of octahedral AsF6− ions arranged on a lattice which contains linear, non-intersecting channels in two mutually perpendicular directions. Within these channels are infinite chains of mercury atoms, each with a formal charge of +0.35, and with a mercury–mercury distance of 2.64(1) Å.
Unsymmetric Cleavage of C2—C3 in 5β-Steroids
Authors: Paisley Joseph Kenneth , Warneboldt Ronald B. , Weiler Larry
Published: May 2006

A method to achieve the unsymmetric cleavage of C-2 and C-3 in 3-keto-5β-steroids is developed. This involves a cine substitution of 4-bromoketone to produce the 2-acetoxyketone. Possible mechanisms for this transformation are discussed and the route proceeding through the oxyallyl intermediate is considered most plausible. The 2-acetoxyketone is converted into the hydroxyoxime which undergoes a Beckmann fragmentation to yield the 2,3-seco-steroid. These products are useful intermediates for the synthesis of the salamander alkaloids.
Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluene Derivatives. XI. Experimental and Theoretical Barriers to Rotation in α,α,2,4,6-Pentabromo-, α,α-Dibromo-2,4,6-trichloro-, and α,α-Dibromo-2,6-dichlorotoluene
Authors: Peeling James , Ernst Ludger , Schaefer Ted
Published: May 2006

Using rate constants determined from an analysis of the p.m.r. lineshape of the ring protons as a function of temperature, the activation parameters for the hindered rotation about the sp2–sp3 carbon–carbon single bond in α,α,2,4,6-pentabromotoluene dissolved in perchlorobutadiene are determined. Values of ΔG≠ for the analogous hindered rotations in α,α-dibromo-2,6-dichlorotoluene in toluene-d8, and for α,α-dibromo-2,4,6-trichlorotoluene in solutions of toluene-d8 and methylcyclohexane are also given. The results are compared with semiempirical potential energy barrier calculations employing partial geometry optimization. The agreement is satisfactory.
Model Calculations of Kinetic Isotope Effects in Nucleophilic Substitution Reactions
Authors: Bron Jan
Published: May 2006

The results of calculations indicate that a previously proposed model for the transition state in "borderline" substitution reactions can be generalized and, as a result, the observed differences in the carbon-13 and deuterium isotope effects of SN1, SN2, and "borderline" reactions rationalized. Although the conclusions may apply more generally, the standard reaction investigated is the solvolysis of benzyl bromide. The importance of resonance interaction with the phenyl ring, the significance of the product- or reactant-like character of the transition state, and the influence of the magnitude of force constants in determining isotope effects are examined. The temperature dependence of kinetic isotope effects in solvolysis is also investigated.
Chemistry of 2-Substituted Adamantanes. V. Photolysis of 2-Adamantyl Azidoformate
Authors: Greidanus J. W.
Published: May 2006

In an attempt to prepare adamanto[1,2-d]oxazolidin-2-one (2), 2-adamantyl azidoformate was subjected to photolysis in cyclohexane. The main product 8 (yield 41%) is formed by intermolecular insertion of the nitrene in the solvent. The only other pure compound isolated (yield 15%) is a product of intermolecular insertion. The i.r. spectrum of the latter supports the presence of a five-membered cyclic carbamate. The fact that intermolecular insertion is the main reaction is unexpected in view of the results reported by others.
Thermodynamics of Transfer of Organic Molecules from Water to Acid Solutions. The Effects of Nitro Substitution
Authors: Yates Keith , McClelland Robert A.
Published: May 2006

The free energies, enthalpies, and entropies of transfer for a series of neutral aromatic solutes from water to aqueous sulfuric and perchloric acids have been determined by measuring the "medium effect" activity coefficient over a range of temperatures. The more negative free energies of transfer (salting-in) into perchloric acid relative to sulfuric acid are due to more favorable entropy terms, although enthalpies of transfer to perchloric acid solutions are similar to or more positive than those for sulfuric acid solutions. The generally observed salting-in caused by substitution of a nitro group in a neutral solute (the nitro-group effect) results from a more favorable enthalpy of transfer, with a small amount of compensation from the entropy term. A brief discussion of the solute–solvent interactions responsible for these observations is presented.
13C Nuclear Magnetic Resonance Studies of Organometallic Compounds. IV. cis-Dimethylplatinum(II) Derivatives
Authors: Clark Howard Charles , Manzer Leo Ernest , Ward John Edward Henry
Published: May 2006

Data derived from the 13C n.m.r. spectra of seven neutral cis-dimethylplatinum(II) derivatives of the type cis-(CH3)2PtL2 and cis-(CH3)2Pt(L—L) (where L and L—L are neutral donors) are discussed and compared with data derived from the 1H n.m.r. spectra of the complexes. Simultaneous variations in L or L—L reveal that the n.m.r. trans-influence rather than the n.m.r. cis-influence is dominant. The suggestion that the n.m.r. cis- and trans-influences may be additive is discussed. In contrast with data obtained by other workers, it is shown that the 1JCH values of the platinum methyl groups are essentially insensitive to variations in the remaining ligands.
On the Whiteway–Smith–Masson and Flory–Stockmayer Theories of Polymerization
Authors: Masson C. R. , Whiteway S. G.
Published: May 2006

A computer simulation of random polymerization reveals that the Flory–Stockmayer expression describes a model where functional groups are of equal reactivity and all chain and ring configurations are allowed. The Whiteway–Smith–Masson expression describes a model in which rings are formally forbidden by a technique that requires departure from the principle of equal reactivity. The apparent conflict between the two theories thus is resolved, and each appears to have application in describing various real systems.
The High Resolution Photoelectron Spectra of Some Iodoalkanes, Iodocycloalkanes, Iodoalkenes, and Fluoroiodohydrocarbons
Authors: Boschi Roberto Angelo Antonio , Salahub Dennis Russell
Published: May 2006

The high resolution photoelectron spectra for the following iodine-containing molecules have been measured: iodomethane, 1-iodoethane, 1-iodopropane, 1-iodobutane, 1-iodopentane, 1-iodohexane, 2-methyl-1-iodopropane, 3-methyl-1-iodobutane, 2-iodopropane, iodocyclopentane, iodocyclohexane, 2-methyl-2-iodopropane, trifluoroiodomethane, 2,2,2-trifluoro-1-iodoethane, pentafluoroiodoethane, 3,3,3,2,2,1,1-heptafluoro-1-iodopropane, iodobenzene, pentafluoroiodobenzene, vinyl iodide, allyl iodide. The spectra are discussed in terms of extended Hückel (EH) molecular orbital calculations and of the qualitative changes upon variation of the alkyl group.
Photolysis of Ox, HOx, COx, and SOx Compounds
Authors: Welge K. H.
Published: May 2006

This paper gives a review of the homogenous gas phase photolysis of inorganic oxide compounds of aeronomic interest. The review is concerned with results of laboratory investigations at wavelengths from the visible to the Schumann vacuum ultraviolet at about 1050 Å corresponding to the lithium fluoride transmission limit. The discussion is confined largely to the photolytic primary processes which are mostly photodissociation in the systems of interest. As kinetic processes are covered by other papers, secondary reactions of photolysis products are discussed here only in the context of the primary processes. The objective is to provide an overview of, and to critically assess, the state of knowledge as to the observations of dissociation processes and products, measurements of quantum yields, and studies of fragment energy distributions.
The Ozone Distribution in the Atmosphere
Authors: Dütsch H. U.
Published: May 2006

The world wide distribution of total ozone and its changes with season are discussed as well as the variability on different time scales. A climatology of the vertical ozone distribution is presented and an attempt is made to derive some inference on ozone transport by the general circulation and its interaction with photochemical processes. It is found that longer observational series in an improved network are needed for puttting such a derivation on a firmer basis. The observed year-to-year changes of world wide total ozone and of the vertical distribution indicate the importance of the quasi-biennial variation of the circulation in the tropical stratosphere for the poleward ozone flux. The suggested variation of ozone concentration in the upper stratosphere with the sunspot cycle must be further substantiated.
Sampling of Stratospheric Trace Constituents
Authors: H.Ehhalt D.
Published: May 2006

The measurement of stable atmospheric trace constituents is often separated into two steps: (a) the collection of a representative sample and (b) the analysis of the trace constituents in the laboratory. The main advantage of this approach is that the most sensitive detection methods can be used. The main disadvantage is that only a relatively limited number of data points can be taken along one sampling profile.Basically two sampling techniques are used: (a) the collection of whole air samples or (b) the selective collection of one or more trace gases on a suitable trapping device. Whole air samples are taken either in the form of grab samples or by compression of air into pressure tanks or by condensing air in cryogenically cooled vessels. Stratospheric trace gases which have been measured by these methods include: CO2, CH4, CO, H2O, H2, N2O, and the noble gases. Selective sampling is accomplished by passing air through molecular sieve beds, impregnated filters, or liquid nitrogen cooled traps. Trace gases retained and measured this way include CO2, H2O, N2O, HNO3.Whole air samplers have been flown on high-flying aircraft, balloons, and rockets. The maximum altitude to which this technique can be usefully extended is 80 km. Selective trace gas samplers have been operated aboard aircraft and on balloons up to an altitude of about 35 km. Examples of the resulting trace gas profiles will be reported.
Stratospheric Aerosol Determinations
Authors: Hofmann D. J.
Published: May 2006

This review consists of a summary and comparison of the results of ongoing programs to study the stratospheric aerosol by a variety of techniques. In view of the considerable degree of disagreement among various experimental techniques in the past, the importance of comparative studies is emphasized. Many of the results are still in preliminary form, and only relatively new results are presented.Both remote and insitu measurements are discussed; the former consist mainly of lidar observations while the latter comprise impactor sampling and light-scattering particle detectors. Discussion is divided along traditional lines, i.e., by particle size, with "small" particles those of radii ≤0.1 µm and "large" particles those of radii ≥ 0.1 µm, with emphasis on the latter because of the considerably greater body of knowledge available for these particles.
Recent Stratospheric Spectra of NO and NO2
Authors: Ackerman M. , Frimout D. , Muller C. , Nevejans D. , Fontanella J. C. , Girard A. , Gramont L. , Louisnard N.
Published: May 2006

NO and NO2 spectra obtained by means of a grid spectrometer from a balloon gondola and from a Concorde are presented. The corresponding stratospheric abundance of these species is deduced.
Autoprotolysis Constants of Water–N-Methylacetamide Mixtures. A New Application of the Hammett Relationship to Acidity Constants
Authors: Halle Jean-Claude , Harivel Raymond , Gaboriaud Rene
Published: May 2006

The hydrogen electrode can be used to measure proton activities of both acid and basic solutions in water–N-methylacetamide (NMA) mixtures, and hence to calculate autoprotolysis constants for the different mixtures. The intermediate acidities between the acid and basic regions are established by the use of buffer solutions of variously substituted phenols, whose acidities in the different water–NMA mixtures have been established. The diminution of the acidity constants with increasing concentrations of N-methylacetamide cannot be explained by the increased dielectric constants of the solution. Instead, we propose a new adaptation of the Hammett relationship (pKH − pKX = ρσX), which places N-methylacetamide between water and DMSO, and close to alcohols, which have a dielectric constant 5-fold smaller. Because of its precision, this method of analysis allows one to classify into one or more homogeneous families compounds having the same chemical function which would be classified together by the classical treatment of Hammett.
Isomérisation photochimique de l'azobenzène en solution. I
Authors: Ronayette Jacques , Arnaud René , Lebourgeois Philippe , Lemaire Jacques
Published: May 2006

The photochemical isomerization of azobenzene can be sensitized by aromatic compounds (chrysene, phenanthrene, naphthalene) or by carbonyls (benzil, biacetyl). Comparison of the photostationary states and the initial quantum yields of isomerization leads to the deduction of a mechanism for this sensitization. The triplet levels Tβt and Tβc of the trans and cis forms are populated by diffusion-controlled, triplet–triplet energy transfer. These levels are deactivated nonradiatively without giving rise to isomerization. The Tβc level of the cis form undergoes a quantitative internal conversion to another triplet level Tαc, while the Tβt level of the trans form undergoes a nonradiative transition to the ground state. The internal conversion Tβt → Tαt in the trans isomer occurs with low probability (0.04 to 0.06). The levels Tαt and Tαc are the intermediates in the isomerization; they are deactivated to the two isomeric forms of azobenzene with equal probability. [Journal translation]
Redetermination of the Mössbauer 119Sn Chemical Shifts in K, Cs, and Cu Hexafluostannates
Authors: Woodhams Frank W. D. , Howie R. Alan , Knop Osvald
Published: May 2006

The Mössbauer 119Sn chemical shifts in K2SnF6.H2O, Cs2SnF6 and CuSnF6.4H2O have been redetermined. All three values, and the value for SnP2O7, are close, lying within 0.1 mm/s, and they define the lowest points on the 119Sn chemical shift scale known to-date. The small differences in the shifts reflect the degree of hydration of the hexafluostannates.
Trajectory Studies of Atomic Recombination Reactions. VI. Recombination of Oxygen Atoms in Argon
Authors: Wong W. H. , Burns G.
Published: May 2006

The recombination of oxygen in large excess of argon has been studied between 300 and 10 000 °K by trajectory calculations. Reasonable agreement between the computed results and the experimental rate data was obtained by assuming that the interaction between oxygen and argon atoms was 0.3 kcal/mol. The present calculation also showed that the radical-molecule-complex mechanism was the major route to recombination below 1000 °K. At higher temperatures, the energy-transfer mechanism predominated. The vibrational and rotational energy distributions of the nascent product from the energy-transfer mechanism at 10 000 °K were found to be much broader than that from the radical-molecule-complex mechanism at 300 °K. However, the total energy distributions of the nascent product, if expressed in units of kT, were similar in both cases.
The Aldol Condensation of Acetaldehyde: the Equilibrium Constant for the Reaction and the Rate Constant for the Hydroxide Catalyzed RetroAldol Reaction
Authors: Guthrie J. Peter
Published: May 2006

An indirect thermochemical estimate of the equilibrium constant for the aldol condensation of acetaldehyde suggested that this reaction was much less irreversible than has been believed. The rate of the hydroxide catalyzed retroaldol reaction has been measured; k21 = 2.8 × 10−3 M−1 s−1 at 25°, so that the equilibrium constant is 4.0 × 102 M−1. The γ value for acetaldehyde as addend is 0.40. The enthalpy change for the aldol reaction is −9.84 kcal/mol.
A Synthesis of 1-Alkyl-3,5-dimethoxybenzenes
Authors: Bailey Keith
Published: May 2006

The reaction of 3,4,5-trimethoxybenzaldehyde or 3,4,5-trimethoxyphenyl methyl ketone with alkyl magnesium halides gives secondary or tertiary carbinols. These are converted in good yields into 1-alkyl-3,5-dimethoxybenzenes by reaction with dissolving sodium in alcohols.
Sur l'existence des composés P4Sex(x &([a-z]+); 3) et P4Se3−nSn(n = 1,2)
Authors: Monteil Yves , Vincent Henri
Published: May 2006

The phase diagram of P(red) + P4Se3 was studied systematically by differential thermal analysis and X-ray crystallography. P4Se3, which is the sole binary compound in the system, exists as three allotropic forms: P4Se3α transforms at 82 °C into P4Se3β which is transformed at 192 °C into P4Se3γ; the β- and γ- forms were unknown. The heats of the allotropic transformations were evaluated as well as the heat of fusion of P4Se3.In the ternary diagram P–S–Se the isopleth P4Se3–P4S3 is a quasi-binary section. An eutectic is observed at 170 °C with a concentration of 5% in P4Se3. No mixed compound of the type P4Se3−nSn (n an integer = 1 or 2) was found during the study of this isopleth. [Journal translation]
Infrared Studies of Water in Crystalline Hydrates: Location of Hydrogen Atoms and Evidence for a Bifurcated Hydrogen Bond in K2SnCl4•H2O
Authors: Falk Michael , Huang Chung-Hsi , Knop Osvald
Published: May 2006

Infrared spectra of polycrystalline K2SnCl4•H2O at different degrees of deuteration were recorded between 4000 and 300 cm−1 at temperatures between 30 and −160 °C. The spectra are consistent with the crystal structure proposed by Kamenar and Grdenić. The water molecules are all equivalent and asymmetric. They are sufficiently well separated from one another for the dynamic coupling of vibrations to be negligible. Both hydrogens of the water molecule participate in hydrogen bonding; one of the hydrogen bonds is weak and bifurcated. Positional parameters of the hydrogen atoms have been calculated using supplementary information from available n.m.r. studies. Infrared spectral characteristics of water molecules engaged in bifurcated hydrogen bonding are discussed.
Anisotropic Conductivity and Phase Transformation Studies in Potassium Chromate Crystals
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

Electrical conductivity measurements on single crystals of potassium chromate indicate anisotropic behavior in the directions [Formula: see text] to the c0 axis. The cation migration energy, estimated from the conductivity υs. 1/T plots, is slightly higher than the usual value in potassium halides, suggesting the possibility of a different conduction mechanism. The defect formation energy, ∼2.20 eV, is comparable to known values in ionic solids. The phase transformation near 660 °C appears to be a first order transition associated with appreciable hysteresis.
Crystal and Molecular Structure of 4,4-Dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2- boranatacyclopentane
Authors: Rettig Steven J. , Trotter James , Kliegel W.
Published: May 2006

Crystals of 4,4-dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boranatacyclopentane are orthorhombic, a = 17.043(3), b = 6.289(1), c = 13.024(2) Å, Z = 4, space group Pna21. The structure was determined by direct methods, and was refined by full-matrix least-squares procedures to R = 0.071 for 1100 reflections with I ≥ 3σ(I). Bond angles in the five-membered ring, which has a distorted half-chair conformation, range from 101.5(4) for OBO to 107.1(4)° for NOB. Bond lengths are: mean B—C, 1.632(8), B—O, 1.506(7) and 1.556(8), N—O, 1.409(5), C—O, 1.378(9), C—N, 1.467–1.509(7–10), mean C—C(aromatic), 1.395(25) Å. The structure consists of discrete molecules separated by normal van der Waals distances.
Diffusion of Gases in Porous Solids. II. Diffusion of an Isotope Trace through Binary Gaseous Mixtures in a Porous Graphite
Authors: Weller K. R. , Stenhouse N. S. , Watts Harry
Published: May 2006

Diffusion coefficients of krypton-85 and xenon-133 through binary mixtures with He, Ne, Ar, Kr, and Xe permeating a porous graphite were measured. The statistical experimental design employing six 5 × 5 Latin squares permitted determination of the effects of gas type, mixture composition, and gas pressure. Five different cells were used and cell effects also determined. A regression equation which adequately correlated the experimental data was derived. This equation also correlated some literature data with better precision than did other model diffusion equations.
Crystal Structure of Lead meta Vanadate, PbV2O6
Authors: Jordan Byron D. , Calvo Crispin
Published: May 2006

PbV2O6 crystallizes in the orthorhombic space group Pnma with a = 9.771(10), b = 3.684(4), c = 12.713(13) Å, and Z = 4. The structure was determined using 816 reflections measured with an automatic diffractometer and refined by full-matrix least squares to an R value of 0.052. The two unique vanadium ions lie on mirror planes and are each coordinated to five oxygen atoms lying between 1.61 and 2.06 Å. The distorted octahedra are completed by a sixth V–O interaction which is 2.73 Å for V(1) and is 2.57 Å for V(2). The lead ion is coordinated to nine oxygen atoms lying in a spherical shell with inner and outer radii of 2.56 and 2.90 Å. The structure consists of chains of VO6 octahedra paralleling the b axis.
A Theoretical Study of the Conformational Changes in Hydrazine
Authors: Jarvie John O. , Rauk Arvi
Published: May 2006

Abinitio restricted Hartree–Fock–Roothaan l.c.a.o.–m.o.–s.c.f. calculations using a Gaussian lobe basis with bond functions have been performed to determine the characteristics of the potential surface for nuclear motions in hydrazine. It was found that in its equilibrium conformation the molecule has a dihedral angle of 95°. The barrier to pyramidal inversion at one nitrogen is 6.1 kcal/mol and the syn and anti rotational barriers are calculated to be 12.0 and 1.6 kcal/mol, respectively. There is a very slight torsional component in the inversion pathway. During rotation over the anti barrier the bond angles contract from their average equilibrium value of 109.5° to 105.3°. This contraction appears to be an important feature of the rotational potential curve. Features of the surface are used to rationalize experimental results in cyclic and acyclic substituted hydrazines.