bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron localisation: evolution of optical spectra
Authors: Walker David C.
Published: May 2006

Attention is directed to experiments from several groups which bear on the origin of the electron's absorption band, particularly with regard to the spontaneous progression from metastable to equilibrated states and photoinduced spectral shifts. The absorption band is discussed as being heterogeneously broadened in both solid and liquid phases, the former being space-averaged and the latter time-averaged. This means that the proper extinction coefficients are higher than those currently in use which were evaluated on the presumption that the band was homogeneous. Eλmax is seen as a generally useful measure of the solvating power of solvents.
On the existence of H− in γ-irradiated matrices at 77 K
Authors: Bernas A. , Truong T. B.
Published: May 2006

A band peaking around 1050 nm in the stimulated neutralization luminescence spectrum of γ-irradiated glassy EtOH, pure crystalline and alkaline glassy ices has recently been attributed to H−. Further results on EtOH glass and on EtOH–H2O mixtures are now presented which support our previous interpretation.A shuttle of the electron from the presumed H− to a matrix trapped state and back to H with restoration of the 1050 nm band can be induced in, and only in, alcohol–water mixtures where it has been shown that, contrary to either of the two pure solvents, H atoms can be trapped (Ht). Further, the intensity of the regenerated stimulated band is found to be maximum for the mixture composition which leads to the highest Ht yield.It is noted that the red limit of the H− stimulated band, which corresponds to a photo-detachment energy threshold, is close to the electron affinity value of the isolated H atom. This observation seems to imply that, contrary to expectation, the solvation energy of H− in these matrices is quite low.
Electron reactivity in liquid hydrocarbon mixtures
Authors: Wada Toshinori , Shinsaka Kyoji , Namba Hideki , Hatano Yoshihiko
Published: May 2006

The electron current in neopentane–n-hexane mixtures, produced by a few nanoseconds X-ray pulse in the presence of external electric field, has been observed in the nanosecond–microsecond range. The form of the time dependence of the electron current has been shown to vary with dose per pulse and is analysed accordingly. The electron mobilities μe are thereby determined in the mixtures. The rate constant of electron–ion recombination, kr, is proportional to the mobility over the wide range of μe The rate constant for electron scavenging, ks by CC14 varies with √μe; ks for C2H5Br shows a maximum for a mixture with the mole fraction of n-hexane, xh = 0.48. The results for ks obtained for the mixtures agree with those by Allen and co-workers for various neat hydrocarbons. Further, the mechanism of electron transport in non-polar liquids is discussed. Using experimental results for V0 and Ea for the mixtures (the energy of the electron in its quasifree state and the activation energy of μe, respectively) V0 is expressed by a linear function of Ea: V0 = −0.42 + 2.6Ea at room temperature and μe is correlated with V0 as an empirical formula μe = 125/[1 + 360 exp (15V0)] based on a trapping model.
Scavenging of localized and quasifree electrons in liquid hydrocarbons (Extended Abstract)
Authors: Balakin A. A. , Boriev I. A. , Frankevich E. L. , Lukin L. V. , Yakovlev B. S.
Published: May 2006

not available
Negative ion–molecule reactions in liquid argon following electron capture by N2O
Authors: Bakale George , Sowada Ulrich , Schmidt Werner F.
Published: May 2006

Electrons produced in liquid argon by a short burst of X rays react readily with dissolved N2O with a bimolecular rate constant of 5.8 × 10−10 cm3/s or 3.5 × 1011 M−1 s−1. The addition of H2 or CO to the Ar/N2O solution results in a fast and slower component in the decay of the electron current. We assume that O− ions are formed in the reaction of electrons with N2O and then react with H2 to give[Formula: see text]or with CO to give[Formula: see text]The addition of CH4 does not regenerate electrons since the reaction[Formula: see text]is thought to occur. Reaction 12 is in agreement with the fact that CO2 does not react with electrons in liquid argon.
Some methods for the preparation of α-alkylated vinylphosphonium salts and their use in 2,5-dihydrothiophene synthesis
Authors: McIntosh John M. , Steevensz Richard S.
Published: May 2006

The preparation of a series of vinyltriphenylphosphonium salts, all of which bear a substituent on the carbon attached to phosphorus, is described. Yields are generally poor unless a symmetrical secondary allylic halide can be used. The use of these salts in the preparation of substituted 2,5-dihydrothiophenes has been examined. In general, reaction times are increased and product yields decreased relative to the reactions of the unsubstituted salts previously reported. This result is ascribed to steric inhibition of the intramolecular Wittig reaction.
Nuclear magnetic resonance spin–lattice relaxation and the rotation of adamantane and hexamethylenetetramine in solution
Authors: Wasylishen Roderick E. , Pettitt Brian A.
Published: May 2006

Deuterium nmr spin–lattice relaxation times have been measured for dilute solutions of adamantane-d16 in CH2I2, CHBr3, CCl4, CHCl3, and CH2Cl2. The reorientation correlation times, τ2, calculated from the experimental data are used to calculate τJ, the angular momentum correlation times, assuming both the J-diffusion and Hubbard relations. The derived τJ values suggest that adamantane executes small step diffusion in CH2I2 and CHBr3, and large step diffusion in CCl4, CHCl3, and CH2Cl2. The calculated τJ values do not appear to be related to the mean times between collisions calculated using a hard sphere model. Both variable solvent and variable temperature experiments indicate 1 ps/cP for the viscosity dependence of the adamantane reorientation time, about 1/36th the value predicted using the familiar Stokes–Einstein equation.Carbon-13 and 1H nmr T1 data indicate that reorientation of hexamethylenetetramine in H2O (28 ps/cP), CHCl3 (27 ps/cP), and CHBr3 (18 ps/cP) is severely hindered because of inter-molecular hydrogen bonding.
The effect of substituents on geminal proton–proton coupling constants. III
Authors: Renaud Roger N. , Bovenkamp John W. , Fraser Robert R. , Capoor Raj
Published: May 2006

The effect of substituents at the 3-position in a series of N-methyl 5,6-dihydro-7H,12H-di-benzo[c,f]azocines on the geminal coupling constants of the C-12 methylene protons has been determined. The slope of the Hammett plot of 2J vs. σ has been found to be +0.20. The orientation of the methylene protons with respect to the π orbitals of the benzene ring bearing the substituent is such that no hyperconjugative effect should be present. The value of +0.20 is in contrast to a previously measured slope of −1.9 for compounds having a geometry ideal for hyperconjugative effects and substantiates the predictions of theoretical MO calculations. As a result, the reliability of this conformational dependence of ρ for use in conformational analysis has been strengthened.A comparison of the data for the azocines with those in the literature indicates the difference between the minimum and maximum effects of a phenyl substituent on a geminal coupling constant of an attached methylene group is 5.5 Hz.
Enumeration of structural isomers in alicyclic hydrocarbons and in porphyrins
Authors: Alspach Brian , Aronoff S.
Published: May 2006

The number of structural isomers obtainable from all possible substitutions in an alicyclic hydrocarbon is found by the use of Burnside's Lemma. Four classes of compounds exist according to the number of vertices of the ring, and the number and type of substituents on the carbons. The theory is also applicable to other types of compounds in which paired substituents occur, e.g. in the biologically-synthesisable porphyrins. Where the pairing is not mandatory, Polya's Theorem is utilized for enumeration. Examples are provided for each of the classes of compounds.
Double salts of indium trichloride with the alkali chlorides, with ammonium chloride, and with indium sulfate
Authors: Kartzmark Elinor M.
Published: May 2006

From a determination of the phase diagrams, at 25 °C, the following double salts were shown to exist: 3LiCl•InCl3•8H2O in the system LiCl–InCl3–H2O, 2KCl•InCl3•H2O and 3KCl•InCl3•2H2O in the system KCl–InCl3–H2O, 2RbCI•InCl3•H2O in the system RbCl–InCl3–H2O, 2CsCl•InCl3•H2O in the system CsCl–InCl3–H2O, 2NH4Cl•InCl3•H2O in the system NH4Cl–InCl3–H2O, In2(SO4)3•InCl3•(17 ± 1)H2O in the system In2(SO4)3–InCl3–H2O. No double salt was found in the system NaCl–InCl3–H2O, studied previously (1). All the double salts except the two involving potassium chloride are congruently saturating at 25 °C.
Etude en résonance magnétique nucléaire du 13C des paramètres de substitution de la fonction azide
Authors: Pancrazi A. , Kaboré I. , Delpech B. , Astier A. , Khuong-Huu Q. , Lukacs G.
Published: May 2006

The various effects (α, β, γ and δ) on the 13C nmr of azido steroids have been measured. For cyclohexane azides constrained to equatorial and axial configurations, the α-effects were determined to be 33.6 and 31.2 ppm. Both γ- and δ-effects have magnitudes near those for OH and NH2 groups. On the other hand, the β-effect of the azides is slightly smaller than those of hydroxyls or amines as its magnitude is reduced by a γ-effect of the second nitrogen atom of the azide group. This additional γ-effect is a function of the spatial arrangement of the Cβ—H bond with respect to the azide group. [Journal translation]
Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers
Authors: Schaefer Ted , Parr William J. E.
Published: May 2006

The observed and calculated, negative, long-range spin–spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominant s-cis planar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.
Electron mobilities in fluids through the liquid and critical regions: isomeric butenes
Authors: Dodelet Jean-Pol , Freeman Gordon R.
Published: May 2006

Electron mobilities are similar in all four isomeric butenes near the critical region, ∼ 10 cm2/V s at ∼420 K, and again in the low temperature liquids, ∼10−3 cm2/V s at ∼ 150 K, but not at intermediate temperatures. The Arrhenius temperature coefficient of the mobility decreases with increasing temperature in cis-butene-2 and isobutene, and increases with temperature in butene-1 and trans-butene-2. This difference in behavior is reflected in the temperature dependence of the dispersion parameter σ in the assumed Gaussian distribution of transition energies between localized and extended states. The extreme cases are trans-butene-2, for which dσ/dT = 0, and cis-butene-2, for which dσ/dT ≈ (2kCp)1/2. Mobilities in mixtures of cis- and trans-butene-2 do not display ideal solution behavior; the transition energies E0 go through a maximum. The mobility in liquid cis-butene-2 under its vapor pressure goes through a maximum value of 17 cm2/V s at 426 K, decreases to 14 cm2/V s at Tc = 433 K, then increases with temperature in the constant density supercritical gas. Maxima are not observed in the other butenes. Electron migration in each of the supercritical gases is an activated process with an activation energy of ∼0.3 eV. The present results emphasize the large role played by phase structure in electron migration.
Studies in the usnic acid series. VIII. The biodegradation of (+)-usnic acid by Mortierella isabellina
Authors: Kutney James P. , Baarschers William H. , Chin Oscar , Ebizuka Yutaka , Hurley Laurence , Leman Jeffrey D. , Salisbury Phillip J. , Sanchez Ignacio H. , Yee Trevor , Bandoni Robert J.
Published: May 2006

A study involving the biodegradation of (+)-usnic acid (1) by the microorganism Mortierella isabellina is described. Three metabolic products, 6-acetyl-8,9bα-dimethyl-1,9b,2,3-tetrahydro-1α,7,9-trihydroxy-3-oxodibenzofuran (2, (+)-1α-hydroxy-2-desacetylusnic acid), (+)-2-desacetylusnic acid (3), and (+)-6-acetyl-8,9b α-dimethyl-1,9b-dihydro-2-acetoxy-3,7,9,trihydroxy-1-oxodibenzofuran (4, (+)-2-acetoxyusnic acid) are isolated and characterized. By means of radioactively labelled precursors, some information about the biodegradation sequence is derived.
Definition of bond paths and bond directions in terms of the molecular charge distribution
Authors: Runtz G. R. , Bader R. F. W. , Messer R. R.
Published: May 2006

The virial partitioning of a molecular electronic charge distribution, ρ(r), divides a molecule into a collection of chemically identifiable atomic-like fragments. When two fragments interact strongly the distribution of charge in the region between their nuclei contains a saddle point [Formula: see text] The gradient paths (paths of steepest ascent through ρ(r), as traced by the vectors [Formula: see text]) which terminate at this internuclear saddle point, define the virial partitioning surface which lies between the fragments. The two gradient paths which originate at the internuclear saddle point and terminate at each of the fragment nuclei define a bond path: the path which follows the ridge of maximum charge density between a pair of bonded nuclei. When the internuclear axis does not coincide with a symmetry axis, the internuclear stationary point will, in general, lie off the axis, and the bond path joining the nuclei will deviate or curve from this axis. The magnitude and direction of this 'bond curvature' as determined by the bond path agrees well with chemical expectations.
Photochemical decomposition of EDTA coordinated to cobalt(III): products, thermal reactions, and evidence for outer sphere alcohol oxidation by the excited state
Authors: Langford Cooper H. , Quance Gay Win
Published: May 2006

The photolysis of Co(EDTA)− in the ultraviolet is unlike analogous reactions of Fe(III) complexes. The ratio of products Co(II) to CO2 is 1:1 but we find only [Formula: see text] as much CH2O. For Fe(EDTA)−, yields of photolysis products Fe(II):CO2:CH2O are 2:1:1. This is consistent only with a mechanism where primary photolysis yields Co(II), CO2, and a radical which attacks EDTA in preference to reduction of the slowly reducible metal oxidation state, Co(III). Use of 2-propanol as a scavenger diagnostic of primary radicals is questioned because it is shown that LMCT excited states of Co(III) complexes exhibit the same outer sphere oxidations of alcohols earlier recognized in the photochemistry of a variety of Fe(III) complexes.
Total synthesis of indole and dihydroindole alkaloids. XI.1,2 The synthesis of leurosine and the coupling of 3α,4α-substituted catharanthine derivatives with vindoline
Authors: Kutney James P. , Joshua Alummoottil V. , Liao Ping-Huang , Worth Brian R.
Published: May 2006

A detailed study involving the Polonovski-type coupling of vindoline (2) with several novel catharanthine derivatives is described. Coupling of vindoline (2) with the N-oxide intermediate of 3β,4β-epoxydihydrocatharanthine (1) provides a laboratory synthesis of the bisindole alkaloid leurosine (3, R=CO2CH3) and an unambiguous proof of the stereochemistry of the epoxide function in that alkaloid. The coupling of 2 with the N-oxides of 3α,4α-epoxydihydrocatharanthine (4) and 4α-hydroxydihydrocatharanthinic acid lactone (6) provide the rearranged bisindole products 5, 7, and 8.
Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XIV. The aqueous chemistry of trimethyllead(IV) and its carboxylic acid complexes
Authors: Sayer T. L. , Backs S. , Evans C. A. , Millar E. K. , Rabenstein D. L.
Published: May 2006

The aqueous solution chemistry of the trimethyllead(IV) species and the trimethyllead(IV) complexes of six carboxylic acids of pKa values ranging from 2.75 to 4.95 has been investigated by proton magnetic resonance spectroscopy. Equilibrium constants for the reaction of (CH3)3Pb+ with hydroxide ion to form (CH3)3PbOH and ((CH3)3Pb)2OH+, and the formation constants of the carboxylic acid complexes were determined from the pH dependence of the chemical shift of the methyl protons of trimethyllead. The formation constants of the complexes increase as the pKa of the ligand increases. The lead-207-proton coupling constant was found to be insensitive to complexation.
Synthesis of enantiomers of sulcatol
Authors: Schuler Hermann R. , Slessor Keith N.
Published: May 2006

The synthesis of R-(−)- and S-(+)-6-methylhept-5-en-2-ol (sulcatol) is reported from commercially available carbohydrate precursors. The synthesis of the R-(−) enantiomer utilizes the four hydroxy function of 2-deoxy-D-ribose as a preformed precursor of the chiral secondary alcohol centre. The five hydroxy group of L-fucose provides the basis for a similar synthesis of the S(+) enantiomer. These isomers are to be used to test the aggregation response of Gnathotricus sulcatus, a northwestern American timber pest.
Studies on metal hydroxy compounds. XV. Electrical conductivity measurements on Cd(OH)Cl, Cu(OH)Cl, and PbOHCl
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

The electrical conductivity dependence on temperature measurements for three metal basic chlorides are reported. The conductivity results yield energy values which are interpreted in terms of active solid state processes leading up to, and including, the decomposition step.
Photoisomerization of the boron trihalide complexes of eucarvone
Authors: Childs Ronald F. , Hor Yee-Chee
Published: May 2006

The photoisomerization of the BF3, BCl3 and BBr3 complexes of eucarvone (2,6,6-trimethylcyclohepta-2,4-dienone), 1, have been examined. Irradiation of these zwitterions at low temperature gave, after subsequent recovery of decomplexed materials, 3,7,7-trimethylbicyclo-[4.1.0]hept-2-en-4-one, 2, 2-methyl-5-isopropylphenol, 3, 2-methyl-6-isopropylphenol, 4, dehydrocamphor, 5, and carvone, 6. In the case of 1•BF3 and 1•BCl3 the initial photoproducts were shown to be the complexes of 2, 3, 4, and 5. The complexes of 6 were shown to arise from a secondary photoisomerization of 2•BX3. It was not possible to establish the primary product distribution, obtained from 1•BBr3 as further photoisomerization of 2•BBr3 occurred even at very low degrees of conversion. The mechanisms and synthetic utility of these reactions is discussed.
The crystal structure of bis(ethyldiazoacetate) mercury(II) Hg(CN2CO2C2H5)2
Authors: Smith R. A. , Torres M. , Strausz O. P.
Published: May 2006

Bis(ethyldiazoacetate) mercury(II) is orthorhombic with the following unit cell data at 20 °C: Fdd2, a = 19.810(8), b = 14.387(5), c = 9.015(2) Å, V = 2569.3 Å3, ρ0 = 2.17(2), ρc = 2.21, Z = 8 ([Formula: see text]λ = 0.70930 Å). The structure was solved by heavy atom methods and refined to R = 2.2% for 706 reflections. The molecule has a 2-fold axis of symmetry and all thermal parameters are large in the direction of this axis; diffuse scattering was observed in the rotation photograph taken about this axis. As expected the diazoacetate portion is planar.
Fluorine exchange between four-, five-, and six-coordinate silicon compounds
Authors: Marat Ronald Kirk , Janzen Alexander F.
Published: May 2006

Intermolecular fluorine exchange in the systems SiF4–SiF5−, MeSiF3–MeSiF4−, PhSiF3–PhSiF4−, SiF5−–SiF62−, SiF4–SiF62−, and MeSiF3–SiF62− has been studied by fluorine and proton nmr spectroscopy. Exchange is postulated to involve fluorine-bridged intermediates; alternative pathways of exchange, such as fluoride dissociation or impurity (HF and H2O) catalyzed exchange, have been eliminated. Addition of NH3 to SiF5−–SiF62− slows down exchange whereas addition of Et2NH to MeSiF3 promotes exchange.
wA radiochemical study of the kinetics of ion-exchange on zirconium antimonate
Authors: Mathew John , Tandon Shiv Nath
Published: May 2006

This paper reports the radiochemical study of the kinetics of ion-exchange of Rb+ and Cs+ with H+ on zirconium antimonate. The slow step which determines the rate of exchange of these ions is diffusion through the particle. Values for the diffusion coefficients, energy of activation, and entropy of activation have been calculated. The data obtained have been compared with those reported for other organic and inorganic exchangers.
Catalytic asymmetric hydrogenation using ruthenium(II) complexes with chelating chiral sulfoxide ligands
Authors: James Brian R. , McMillan Roderick S.
Published: May 2006

A chelating sulfoxide ligand, (2R,3R)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulfinyl)butane monohydrate, or 'dios', containing chiral carbons has been synthesized. A corresponding bis(benzyl sulfinyl) compound, 'bdios', and an acetal-cleaved derivative, 'ddios', are also reported. Ruthenium(II) neutral complexes have been made containing such ligands, which can bind via oxygen or sulphur; the complexes are active homogeneous catalysts for hydrogenation of prochiral olefinic acid substrates; optical purities of up to 25% were attained.
Electron scavenging by COS in the radiolysis of supercritical cis- and trans-2- butene
Authors: Nishikawa Masaru , Imai Kazuo , Soma Yuko
Published: May 2006

The electron scavenging reaction with COS was studied in γ-irradiated supercritical butenes in the density range 0.24–0.48 g/cm3 at 170 ± 1°C and in the liquid phase at room temperature. G(CO)fi estimated by means of the 'square root' model at each density studied agreed within experimental accuracy with G(N2)fi obtained previously. In liquid butenes, G(CO)fi, as well as G(N2)fi, agreed with Gfi obtained by electrical measurements. Rate constants estimated from the reactivity parameters for reactions with COS were less than 1/10 of those with N2O at each density studied except at d = 0.48 g/cm3 in trans-2-butene.
Hydrogen/deuterium selectivity in the infrared laser photolysis of chloroethylene
Authors: Gandini A. , Willis C. , Back R. A.
Published: May 2006

The decomposition of chloroethylene to acetylene and hydrogen chloride induced by focused radiation from a CO2 laser has been shown to be H/D isotopically selective at low pressures. As the pressure is reduced below 1 Torr, C—Cl bond scission appears to increase at the expense of molecular fragmentation and gives rise to radical processes which are isotopically non-selective.
The preparation and absolute configuration of trans-2-aminocyclopentanol enantiomers
Authors: Barr Alex A. , Frencel Irena , Robinson J. Barry
Published: May 2006

A method is reported for the resolution of (±)-trans-2-benzylaminocyclopentanol using D-or L-dibenzoyltartaric acid as the resolving agent. Debenzylation of the enantiomeric bases gives the enantiomeric trans-2-aminocyclopentanols. These compounds have been converted to their quaternary ammonium acetate ester derivatives and the absolute configuration assigned by comparison of the ord spectra with the spectra of the appropriate cyclohexane derivatives.
Constituents of Nauclea diderrichii. Part IX. Conversion of sweroside to naucledal and 3-epinaucledal
Authors: Purdy John , McLean Stewart
Published: May 2006

The aglucone of sweroside has been converted to naucledal and its epimer, 3-epinaucledal; the structure and stereochemistry of these products have been established through analysis of their nmr spectra. The course of the rearrangement has been studied and the intermediacy of a ring–opened isomer, seconaucledal, has been demonstrated. The relative amounts of naucledal and 3-epinaucledal produced from seconaucledal depend on the conditions of the cyclization.
The chromous chloride promoted addition of N-haloamides to olefins. V. The addition of N-chloroamides to enol ethers: synthesis of acyloxy and acyl derivatives of α-amino acetals and ketals (aldehydes and ketones) and of 2-amino sugars
Authors: Driguez Hugues , Vermes Jean-Paul , Lessard Jean
Published: May 2006

The chromous chloride promoted addition of N-chlorocarbamates and N-chlorocarboxamides to 1-methoxycyclohexene, ethoxyethylene, dihydropyran, and (1-methoxyethylidene)-cyclohexane gave, in 60 to 85% yields, either α-acyloxy- or α-acylamino ketals and acetals, or the corresponding ketones and aldehydes depending on the work-up conditions. The regio-specificity of the addition was higher with the first two enol ethers (≥97%) than with the latter two (≥85%). N-Chlorourethane was added to 17-methoxymethylenandrost-4-en-3-one (19) and the sole addition product isolated was the 17α-chloro-20-ethoxycarbonylamino derivative 20 in 75% yield. Additions to triacetyl-D-glucal and 3-O-acetyl-4,6-O-benzylidene-D-glucal followed by solvolysis under Koenigs–Knorr conditions led predominantly to 2-amino-gluco-pyranosides in 30 to 65% yields, whereas additions to 3-O-acetyl-4,6-O-benzylidene-D-allal gave 2-amino altropyranosides in 40 to 56% yields.
Hydrogen bonding in organic synthesis. Part 9. The sulphenylation of fluoride-activated β-dicarbonyls
Authors: Clark James H. , Miller Jack M.
Published: May 2006

Various α-arylthio-β-dicarbonyls have been prepared by the room temperature reaction of β-dicarbonyltetraethylammonium fluoride monosolvates with aryl disulphides. The disulphides are formed by the in situ fluoride-assisted air oxidation of aryl thiols.
Rate and equilibrium constant measurements for gas-phase proton-transfer reactions involving H2O, H2S, HCN, and H2CO
Authors: Tanaka Kenichiro , Mackay Gervase I. , Bohme Diethard K.
Published: May 2006

The flowing afterglow technique has been employed in the measurement of rate and equilibrium constants at 296 ± 2 K for unsolvated proton transfer reactions of the type [Formula: see text] and several solvated proton transfer reactions of the type [Formula: see text] where X and Y may be H2O, H2S, HCN, or H2CO. Where possible, direct comparisons are made with similar measurements performed with other techniques. The equilibrium constant measurements provide a measure of the relative proton affinities of H2O, H2S, HCN, and H2CO and absolute values for PA(H2O) = 166.4 ± 2.4 kcal mol−1, PA(H2S) = 170.2 ± 1.8 kcal mol−1, and PA(HCN) = 171.0 ± 1.7 kcal mol−1 when reference is made to PA(H2CO) = 170.9 ± 1.2 kcal mol−1 which can be derived from available thermochemical information. The rate constant measurements reinforce the generalization that unsolvated proton transfer involving simple molecules proceeds with high efficiency and provide information about the influence of solvation on this efficiency.
Some stereochemical aspects of two-bond 13C–1H spin–spin coupling. Sign determination in natural abundance 13C nuclear magnetic resonance spectra
Authors: Cyr Natsuko , Hamer Gordon K. , Perlin Arthur S.
Published: May 2006

The magnitudes and signs of two-bond 13C–1H coupling constants (2J) in the array O—13CA—CB—1H, appear to be determined by the relative orientations of the O—13CA and CB—1H bonds, as shown with a variety of carbohydrate derivatives. The data have been observed from natural abundance lH-coupled 13C nmr spectra, and signs of 2J have been determined by the 'selective population transfer' technique. When CB bears one oxygen atom, the observed 2J values range from −6 to 0 Hz, whereas a range of 0 to +8 Hz is found when CB bears two oxygen atoms. By contrast, for arrays in which CB bears one oxygen atom and CB two, the 2J values vary from −6 to +6 Hz. In general, the results confirm earlier indications that the larger the torsional angle between the O—13CA and CB—1H bonds, the more positive is the value of 2J. These findings are supported by calculations for model compounds, i.e., propane-1,1,2-triol and butane-2,3-diol.
Synthesis and study of the conformational stability of sequential polypeptides containing δ-benzyloxycarbonyl-L-ornithine and benzyl esters of L-aspartic and L-glutamic acids
Authors: Ho-Duc Nga , Daoust Hubert , St-Pierre Serge
Published: May 2006

The synthesis of the sequential polypeptides (N-δ-Z-L-Orn-γ-BzI-L-Glu)n and (N-δ-Z-L-Orn-β-BzI-L-Asp)n by solution methods is described. Both polypeptides are α helical in chloroform as shown by circular dichroism. However, the conformation in this solvent is rather fragile, since small additions of TFA to a dilute solution of the polypeptides in chloroform is sufficient to cause the helix-to-coil transition, as demonstrated by cd and nmr. It is postulated that the low stability of the helical conformation is attributed, in this case, to a cooperative collapse of the ordered conformation.
Time resolved fluorescence of aqueous tryptophan
Authors: Rayner D. M. , Szabo A. G.
Published: May 2006

The fluorescence decay of aqueous tryptophan is shown to be described by a two exponential decay function whose components have life-times of 3.14 ns and 0.51 ns. These components are assigned as the solvent equilibrated 1La and 1Lb, states respectively. The time-resolved emission spectra are presented and can be resolved into two spectra with λmax at 350 nm and 335 nm corresponding to these two states.
Lignin and related compounds. V. The hydrogenolysis of aspen wood lignin using rhodium-on-charcoal as catalyst
Authors: Pepper James M. , Fleming Reginald W.
Published: May 2006

The hydrogenolysis of aspen lignin using rhodium-on-charcoalas catalyst has been studied. The maximum yield of chloroform-soluble lignin degradation products was obtained at a reaction temperature of 195 °C. Analysis of this chloroform-soluble fraction revealed that the monomeric fraction was composed essentially of the four compounds, 1–4, only, and in a total yield representing at least 40% of the original lignin.Solvent extraction was shown to be preferred over thermal distillation as a preparative procedure for the separation of these phenolic derivatives. The significance of the isolation of these lignin degradation products is discussed.
Lignin and related compounds. VI. A study of variables affecting the hydrogenolysis of spruce wood lignin using a rhodium-on-charcoal catalyst
Authors: Pepper James M. , Supathna Punsri
Published: May 2006

The effect of reaction conditions on the hydrogenolysis of spruce wood lignin over a rhodium-on-charcoal catalyst has been studied and monitored by the yields of the three major degradation products, 1, 2, and 5. Variables included: initial pressure of hydrogen, amount of catalyst, and acidity–basicity of the media. Little variation occurred under moderate acidic or basic conditions with yields of 18–20% of lignin recovered as monomers. Under strongly acidic or basic conditions both yields and relative abundances changed appreciably. Initial hydrogen pressures less than 500 psig resulted in slightly decreased yields in some cases. In strongly alkaline media similar results were obtained with or without added hydrogen provided the catalyst were present.
The photochemistry of benzylic sulfonyl compounds: The preparation of sulfones and sulfinic acids
Authors: Langler R. F. , Marini Z. A. , Pincock J. A.
Published: May 2006

The photolysis of benzylic sulfonyl compounds (XSO2CH2Ph) gives products which are explained in terms of the chemistry of the benzyl and sulfonyl (XSO2•) radicals. The synthetic applications of this photocleavage have been examined for two general cases: (i) preparation of sulfones from disulfone precursors, R1SO2CHR2SO2CH2Ph to R1SO2CH2R2 (yields ∼ 90%); (ii) preparation of sulfinic acids and sulfonyl chlorides from mono sulfone precursors, R3SO2CH2Ph to R3SO2H and R3SO2Cl (yields ∼ 55%).
Kinetics of radical reactions in sodium diffusion flames
Authors: Mintz Kenneth J. , Le Roy Donald J.
Published: May 2006

The primary reaction in sodium diffusion flames, Na + RX = NaX + R, has been investigated as a possible source of free radicals for kinetic studies. A number of different alkyl halides were investigated as possible radical sources. Optimum conditions were found to minimize wall reactions and hydrogen abstraction from the halide, the two factors which invalidated previous work using this method. Rate constants were derived from product analyses by the numerical solution of simultaneous non-linear differential equations based on a spherical model involving diffusion. Values were obtained for the two modes of decomposition of n-C3H7, the abstraction of primary and secondary H atoms from C3H8 by CH3, and the addition of CH3 to C2H4. These are in reasonably good agreement with values determined by more conventional methods.
Crystal structure of aquohydronium hexachloroantimonate(V)
Authors: Matheson Hugh M. , Whitla W. Alex
Published: May 2006

Crystals of the compound, H5O2+SbCl6− have been obtained. The structure shows an isolated H5O2+ ion with O—O 2.52(1) Å. Crystal data: orthorhombic (Immm) a = 6.96(1), b = 9.15(1), c = 7.91(1) Å.
Equilibrium constants for a series of simple aldol condensations, and linear free energy relations with other carbonyl addition reactions
Authors: Guthrie J. Peter
Published: May 2006

A set of equilibrium constants for aldol condensations of acetaldehyde, acetone, acetophenone, and acetic acid as nucleophiles and formaldehyde, acetaldehyde, benzaldehyde, acetone, and acetophenone as carbonyl acceptors has been evaluated. The four values determined, directly or indirectly, by experiment have been augmented by values calculated from thermo-chemical data and equilibrium constants for enone hydration, and by estimation of free energies of formation of the reaction products by use of hypothetical disproportionation reactions. When the carbonyl nucleophiles are compared to other nucleophiles which can add to carbonyl compounds, it is found that they can be incorporated in the linear free energy relationship of Sander and Jencks, with γ values of 0.45 for acetaldehyde, 0.16 for acetone, 0.05 for acetophenone, and 3.56 for acetic acid. These results make it possible to predict the equilibrium constants for any of a large number of aldol condensations from the equilibrium constant for the addition of any nucleophile to the carbonyl accepter compound.
Rearrangements of vanadium(III) β diketonate complexes
Authors: Nixon A. J. C. , Eaton D. R.
Published: May 2006

The rearrangement reactions of a number of V(III) β diketonate complexes have been studied by nmr. All reactions proceed by an intramolecular rather than an intermolecular process. The use of a complex with diastereotopic groups on the ligand allowed enantiomerization to be observed. Linkage isomerization was shown to be slow in triacetylmethanato V(III) complexes. Activation parameters are reported for five different complexes in a number of different solvents. Permutational analysis did not unambiguously distinguish between possible twisting and bond rupture mechanisms. The data are consistent either with a rhombic twist (C3(i)) mechanism or with a bond breaking mechanism involving square pyramidal intermediates. The possibility that none of the usual simple intramolecular mechanisms provide a valid description of the rearrangement process is discussed. The rates of rearrangement of these V(III) complexes are consistently somewhat greater than those of analogous Al(III) complexes.
Perepoxide intermediates in the conversion of some β-halohydroperoxides to allylic hydroperoxides by base
Authors: Kopecky Karl R. , Scott Wayne A. , Lockwood Peter A. , Mumford Cedric
Published: May 2006

Migration of the hydroperoxy group occurs during the reaction between base and several β-halohydroperoxides to give allylic hydroperoxides. An 86:14 ratio of 3-hydroperoxy-2-(4-methoxyphenyl)-3-methyl-1-butene-3-hydroperoxy-3-(4-rnethoxyphenyl)-2-methyl-1-butène was formed in 90% yield from 2-bromo-3-hydroperoxy-3-(4-methoxyphenyl)-2-methyibutane. From 1-chloro-, 1-bromo-, and 1-iodo-1-(1-hydroperoxy-1-methylethyl)cyclohexane there were obtained 1-(1-hydroperoxy-1-methylethyl)cyclohexene and 1-hydroperoxy-1-(2-propenyl)cyclohexane in ratios of 93:7, 94:6, and 94:6, respectively, in 98–100% yieid. Isopropylidenecyclohexane was converted with singlet oxygen to these allylic hydroperoxides in a 10:90 ratio. Only the latter allylic hydroperoxide was formed in the reaction between the alkene and triphenyl phosphite ozonide at −70 °C. The p-nitrobenzoate esters of 1-hydroperoxy(1-chloro-, 1-bromo-, and 1-iodo-1-methylethyl)cyciopentane were converted quantitatively to 1-(1-hydroperoxy-1-methylethyl)cyclopentene and 1-hydroperoxy-1-(2-propenyl)-cyclopentane in 77:23, 73:27, and 70:30 ratios, respectively. Oxidation of isopropylidenecyclopentane with triphenyl phosphite ozonide at −70 °C and singlet oxygen produced the allylic hydroperoxides in 62:38 and 58:42 ratios, respectively. The reactions of the β-halohydroperoxides proceed exclusively via perepoxide intermediates. The reactions between the alkenes and singlet oxygen or triphenyl phosphite ozonide do not involve perepoxide inter mediates.
The photolysis of chlorinated p-terphenyls
Authors: Chittim Brock , Safe Stephen , Bunce Nigel J. , Ruzo Luis O. , Olie Karl , Hutzinger Otto
Published: May 2006

A variety of chlorinated p-terphenyls was photolyzed in organic media at 300 nm. Replacement of chlorine by hydrogen (dechlorination) was the major reaction. Substitution products were much more prominent than in the corresponding reactions of polychlorinated biphenyls.Quantum yields of reaction were substantially higher for ortho-chlorinated compounds. Xenon-assisted reactions and benzophenone sensitization indicate a triplet reactive state, although energy transfer from benzophenone is very inefficient. Triethylamine promoted an electron transfer pathway but only for those compounds that were least photolabile.
Nickel(II) and copper(II) complexes of the 'tripod' ligand tris(2-benzimidazylmethyl)amine
Authors: Thompson Laurence K. , Ramaswamy Baratham S. , Dawe Robert D.
Published: May 2006

A series of nickel(II) and copper(II) complexes of the title ligand are reported which appear to exhibit predominantly pseudo-octahedral structures in the solid state. Anion bridged dimeric structures are proposed for both nickel and copper; [Ni2(NTB)2X2]Y2 (X = Y= Cl, Br; X = Cl, Br, NCS; Y = BPh4), [Cu2(NTB)2X2]X2•2H2O (X = Cl, Br). The other octahedral derivatives appear to be monomeric; (Ni(NTB)X2] (X = NO3, NCS), [Ni(NTB)-(H2O)X]Y (X = NCS, Y = BPh4; X = CH3CN, Y = (ClO4)2), [Ni(NTB)(H2O)2]X2•2H2O (X = ClO4, BF4), [Cu(NTB)(NO3)2]•H2O. Five-coordinate derivatives were uncommon and in the case of three copper complexes trigonalbipyramidal structures are suggested in the solid state; [Cu(NTB)CI]BPh4, [Cu(NTB)(H2O)]X2•nH2O (X = BF4, n = 0; X = ClO4, n = 1). In acetone solution ail the copper complexes appear to be five-coordinate. Electron spin resonance data confirm trigonalbipyramidal solution structures and indicate [Formula: see text]with very small values of [Formula: see text] (60 − 80 × 10−4 cm−1).
Synthesis oftrans- and cis-α-damascone
Authors: Liu Hsing-Jang , Hung Hing-Kwok , Mhehe George L. , Weinberg M. L. Duarte
Published: May 2006

Se lective thioketalization of a mixture of keto esters 5 and 6 resulted in the exclusive formation of thioketal 7 and complete recovery of keto ester 6. Lithium aluminum hydride reduction of thioketal 7 followed by Moffatt oxidation of the resulting alcohol 8 gave aldehyde 10 which on treatment with a mixture of cis- and trans-1-propenyl magnesium bromide afforded trans- alcohol 11 and its cis isomer 12. Manganese dioxide oxidation of alcohol 11 followed by desulfurization gave trans α-damascone (3). Similarly, alcohol 12 was converted to cis-α-damascone (4).
Diastereoisomeric 4a,10a-dihydrofusarubins: True metabolites of Fusarium solani
Authors: Kurobane Itsuo , Vining Leo C. , McInnes A. Gavin , Smith Donald G.
Published: May 2006

In alkaline cultures of Ftisarinm solani fusarubin is formed by nonenzymic oxidation of two previously unknown dihydrofusarubins, rel-(3R,4aR,10aR)- and rel-(3R,4aR, 10aS)-5,10-dioxo-3,4,4a,5,10,10a-hexahydro-7-methoxy-3-methyl-3,6,9-trihydroxy-1H-naphtho[2,3-c]pyran.
Anthraniloylanthranilamide (o-amino-N-(o-carbamoylphenyl)benzamide): Preparation and use as a synthetic precursor for quinazolino[1,2,3]benzotriazinones
Authors: Eddy Fitzroy D. , Vaughan Keith , Stevens Malcolm F. G.
Published: May 2006

Several synthetic routes to anthraniloylanthranilamide (6) are described; the problems involved in o-aminobenzoylation reactions are explored. Reduction of N-(o-nitrobenzoyl)anthranilamide by stannous chloride gave a low yield of 6, which was also obtained in low yield by reaction of isatoic anhydride with o-aminobenzamide. The possible use of O-(o-aminobenzoyl)hydroxylamines for o-aminobenzoylation was investigated but proved impractical. Diazotisation of 6 affords 3-(o-carbamoylphenyl)-1,2,3-benzotriazin-4(3H)-one (2), which undergoes base-catalysed cyclisation to the quinazolino[3,2-c]benzotriazine (4). The conversion 2 → 4 probably involves the isomeric quinazolino[1,2-c]benzotriazine (3), which could not be isolated.
A Mössbauer study of organotellurium compounds. Part III. Tellurium heterocycles and related compounds
Authors: Dance Nigel S. , Jones Colin H. W.
Published: May 2006

Mössbauer data are reported for a number of heterocyclic compounds containing tellurium. The influence on the Mössbauer parameters of the constraints imposed by accommodating tellurium in these ring systems are discussed. The influence of the bulky aryl ligand 2-biphenylyl, C12H9—, on the Mössbauer parameters of diaryltellurium dihalides and aryltellurium trihalides has also been investigated.
Kinetics and mechanism of the reaction of dimethyl acetylphosphonate with water. Expulsion of a phosphonate ester from a carbonyl hydrate
Authors: Kluger Ronald , Pire David C. , Chin Jik
Published: May 2006

Dimethyl acetylphosphonate (DAP) is rapidly cleaved in water to acetate and dimethylphosphonic acid. The half time for reaction at pH 7, 25 °C is estimated to be 3 s. The reaction is first order in hydroxide ion concentration and first order in DAP concentration. Rates of reaction were measured over the pH range 3.8 to 6.5 at 25 °C, 6.5 and 7.0 at 5 °C, 4.5 to 6.5 at 35 °C, and 4.5 to 6.0 at 45 °C. The average observed second-order rate constant at 25 °C is 2.4 × 106M−1 s−1. DAP is converted rapidly to a hydrated carbonyl adduct. The mechanism for the formation of the observed products is proposed to be analogous to cleavage reactions of other carbonyl hydrates, proceeding from a monoanion conjugate in this case. The estimated rate constant for the unimolecular cleavage of the carbonyl hydrate anion is 2 × 103 s−1. The rapid hydrolysis of DAP results from energetically favourable formation of a hydrate due to the electronic effect of the phosphonate diester. This effect also promoles ionization of the hydrate. The ionized hydrate readily expels the phosphonate diester to achieve the overall rapid hydrolysis.
Electrochemical reduction of pyridopyrazines
Authors: Armand Joseph , Chekir Khaled , Pinson Jean
Published: May 2006

The electrochemical reduction of several pyrido[2,3-b]pyrazines in hydroorganic or aprotic media leads to 1,4-dihydro derivatives which can be isolated in some cases. Most of these derivatives isomerize into 1,2-, 3,4-, or 5,8-dihydro compounds. A molecule of alcohol is added to these last compounds in alkaline medium. The electrochemical reduction of 1,2- or 3,4-dihydro derivatives gives 1,2,3,4-tetrahydropyridopyrazines. In hydroorganic media, the 7-bromopyrido [2,3-b]pyrazines give a 1,4-dihydro compound which can either isomerize or debromhydrate. In an aprotic medium, the parent heterocycle is obtained. By electrochemical reduction of pyrido[3,4-b]pyrazines, 1,4-dihydro derivatives can be formed which isomerize. The 1,2- or 3,4-dihydro compounds thus obtained can be reduced at the electrode into 1,2,3,4-tetrahydro derivatives.
Apparent molal heat capacities and volumes of amino acids in aqueous polyol solutions
Authors: DiPaola Giuseppa , Belleau Bernard
Published: May 2006

Densities (24 °C) and volumetric specific beats (25 °C) were measured for amino acids (0.05–0.5 m) containing apolar side chains in water, and in aqueous solutions of glycerol, mannitol, sorbitol, NaCl, urea, and Gu•HCl, with a flow densimeter and flow microcalorimeter respectively.The derived apparent molal quantifies and transfer functions of the amino acids in aqueous polyol solutions reveal no specificities which might explain the origin of the unique behavior of polyols in protein systems. However, the study did reveal a regular increase in the structure-making ability of the amino acid as the hydrophobicity of the side chains increased. This structure-making tendency was reduced significantly in dilute solutions of the higher polyols.
The density, electrical conductivity, freezing point, and viscosity of mixtures of trifluoromethanesulfonic acid and water
Authors: Corkum Ronald , Milne John
Published: May 2006

Density, viscosity, specific conductivity, and freezing point measurements over the whole composition range of water–trifluoromethanesulfonic acid mixtures are reported. A maximum in viscosity and minimum in specific conductivity are observed at the composition corresponding to the monohydrate, H3O+SO3CF3−, and a maximum deviation from the ideal density is found at the composition corresponding to H5O2+SO3CF3−. The freezing point curve gives evidence for four hydrates with 1:1, 2:1, 4:1, and 6:1 water/trifluoromethanesulfonic acid mole ratios. An incongruent melting hydrate, probably 2:1 acid to water mole ratio is also indicated.
Vapour pressures of CaCl2–NaCl–H2O and MgCl2–NaCl–H2O at 25 °C. Prediction of the water activity of supersaturated NaCl solutions
Authors: An Doan Thi , Teng Tjoon Tow , Sangster James Malcolm
Published: May 2006

Vapour pressures of concentrated solutions (up to I = 14) of the Systems CaCl2 + NaCl + H2O and MgCl2 + NaCl + H2O have been measured at 25 °C by the static method. By means of reverse application of the Reilly–Wood–Robinson and Zdanovskii–Stokes–Robinson equations to these data, water activities of supersaturated NaCl solutions up to ∼15 m have been deduced, and are represented in polynomial form.
Pulse radiolysis of deuterated aqueous LiCl glasses. Dependence of the yields and rates of reaction of visible and infrared absorbing trapped electrons on LiCl concentration
Authors: Gillis Hugh A. , Teather George G. , Buxton George V.
Published: May 2006

The yields and reactions of trapped electrons which absorb in the visible (evis−) and infrared (eir−) have been studied by pulse radiolysis in deuterated aqueous 6–15 M LiCl glasses at low temperatures. At 76 K G(evis−) increases and G(eir−) decreases as the concentration of LiCl is increased, but [Formula: see text] over the whole concentration range. Because the hydration number of Li+ is 4, G(eir−)/G(evis−) was plotted against [free D2O]/[LiCl•4D2O] and found to give a straight line passing through the origin, for [D2O]/[LiCl] > 4. From this proportionality it is concluded that eir− is an electron trapped in a purely amorphous water environment and evis− is mainly associated with water bound to Li+.The reactions of eir− and evis− with Cu(II) and SeO42− have been investigated. At 138 K the rate of reaction of evis− with SeO42− increases with decreasing [LiCl] whereas its rate of reaction with Cu(Il) is slower and independent of [LiCl]. At 76 K, where the rates of reaction of eir− with the scavengers can also be measured, it is found that in each case evis− and eir− react more slowly in 12 M LiCl glass than in 6 M LiCl glass, the difference being more marked for SeO42−. In the absence of scavenger the electron in the smaller yield decays faster. These observations can be rationalized on the basis that electrons can tunnel in either direction between visible and infrared traps before being scavenged, and it seems they cannot be rationalized in terms of direct tunnelling only.G(Cl2−) is found to be proportional to the electron fraction of Cl−•3D2O in the glass and its extrapolated value for pure Cl−•3D2O is 3.4. It is inferred that Cl2− arises mainly from ionization of the D2O bound to Cl−.