bluuebunny/crossref_metadata_2025 huggingface dataset:
The carbon monoxide/nitrous oxide reaction. Kinetics of catalysis on TiO2 (anatase) and ZnO and activity correlations for the first-row transition metal oxides
Authors: Krupay Bordan Walter , Ross Robert Anderson
Published: May 2006

The catalytic reaction between carbon monoxide and nitrous oxide on titanium dioxide (anatase) and zinc oxide has been examined in a continuous flow reactor at atmospheric pressure. The experimental activation energy was 144 ± 4 kJ mol−1 from 723 to 793 K on TiO2 and 121 ± 4 kJ mol−1 from 543 to 653 K on ZnO. Analyses of kinetic results indicated that a transient carbonate-like species may be involved in catalysis on both oxides. Relationships between the experimental activation energies for the CO/N2O reaction on first-row transition metal oxides and (i) activation energies for isotopic oxygen exchange, (ii) heats of carbonate formation, and (iii) the charge/radius ratio of the cation are interpreted in terms of the influence on catalysis of the cohesive properties of the metal/oxygen bonds in the oxide surfaces.
Adsorption of Et4NBr at the mercury/electrolyte interface from water and heavy water solutions
Authors: Kimmerle Frank M. , Menard Hugues
Published: May 2006

Droptime measurements of aqueous and deuterated Et4NBr solutions indicate that the mercury/electrolyte interfacial tension differs by less than 1 mJ m−2 (dyn cm−1). Et4NBr is slightly more adsorbed from heavy water in dilute solutions, but the difference becomes relatively less important in concentrated electrolytes. This behaviour is interpreted in terms of interfacial transfer parameters and attributed to the nature of the solvent–solute interactions.
The conformational preference and barrier to internal rotation of an equatorial 3,5-dichlorophenyl group by the J method. Derivatives of cyclohexane, 1,3-dithiane, 1,3-dioxane, and 1,3-dioxolane
Authors: Schaefer Ted , Niemczura Walter , Danchura Werner
Published: May 2006

We report the preparation and the analysis of the phenyl ring proton magnetic resonance spectra of 3,5-dichlorophenylcyclohexane and of the 2-(3,5-dichlorophenyl) derivatives of 1,3-dioxane, 1,3-dithiane, and 1,3-dioxolane. With the exception of the dioxolanes these compounds exist predominantly as the equatorial isomers. The J method is used to show that the phenyl moiety prefers the conformation in which the α C—H bond lies in the phenyl plane. The predominantly twofold barriers to rotation about the carbon–carbon bond between the two ring systems are 2.0 ± 0.3, 0.4 ± 0.2, 2.2 ± 0.3, 0.85 ± 0.3 kcal/mol for these compounds, in the order given above. The low value for the barrier in the 1,3-dioxane derivative agrees reasonably well with molecular mechanics calculations and with the results of calorimetric and X-ray studies on equatorial 2-phenyl-1,3-dioxane.
Comparison of the intramolecular hydrogen bonds and of the internal barrier to rotation the hydroxyl and sulfhydryl groups in 2-methoxyphenol and 2-methoxythiophenol
Authors: Schaefer Ted , Wildman Timothy A.
Published: May 2006

The long-range spin–spin coupling constants involving the hydroxyl proton in 2-methoxyphenol are consistent with a potential function for rotation of the hydroxyl group derived from far infrared torsion data. The internally hydrogen bonded cis conformer is the only one detected by nmr. In contrast, the long-range couplings of the sulfhydryl group in 2-methoxythiophenol indicate that the trans conformer is favored over the cis conformer by a free energy difference of 0.2 + 0.2 kcal/mol. Furthermore, the barrier to internal rotation of the sulfhydryl group is much smaller than that of the hydroxyl group in these two compounds. It is suggested that the barrier in the thiophenol derivative is 2.7 ± 0.6 kcal/mol, to be compared with a twofold component of 6 kcal/mol in the rotational potential function of the phenol analog.
Application of the Osterberg–Sarkar–Kruck method for obtaining free ion concentrations in solutions of complex equilibria
Authors: Guevremont Roger , Rabenstein Dallas L.
Published: May 2006

A titration system has been developed for collecting pH titration data of sufficient accuracy for use with the method developed by Osterberg, and Sarkar and Kruck, for extracting free metal and free ligand concentrations from pH titration data. Titrant is delivered from a gravimetric buret capable of part per ten thousand precision, and a concentrated metal or ligand solution is added from a second buret to satisfy the theoretical requirement that the total metal or ligand concentration remain constant. The entire system is computer controlled. Application of the titration system and procedures for extracting free ligand and free metal concentrations from pH titration data are demonstrated with a study of the complexation chemistry of zinc with aspartic acid.
Halogen-bridged complexes of platinum(II) and their reactions with dimethylformamide
Authors: Kong Pi-Chang , Rochon F. D.
Published: May 2006

Bridged compounds, [Pt(L)Cl2]2 (L = pyridine, picoline, and lutidine) have been prepared from the reactions between K[Pt(L)Cl3] and perchloric acid. The molecular weight measurements indicate that they are dimers in chloroform solutions. When [Pt(L)Cl2]2 is dissolved in dimethylformamide (DMF), [Pt(L)(DMF)Cl2] is formed and has been isolated. Infrared and nmr studies have shown that DMF is coordinated to platinum through the oxygen atom.
Spin–spin coupling constants between side-chain and ring fluorine nuclei in some benzotrifluoride, benzal fluoride, and benzyl fluoride derivatives: coupling mechanisms
Authors: Schaefer Ted , Niemczura Walter , Wong Chiu-Ming , Marat Kirk
Published: May 2006

A complete analysis of the 1H and 19F nmr spectra of 2,5- and 3,4-difluorobenzotrifluoride, together with multiple resonance experiments, yields the signs and magnitudes of the long-range 19F,19F and 1H,19F spin–spin coupling constants. The coupling mechanisms are discussed. In particular, the coupling over six bonds, [Formula: see text], whose sign is interpretable in terms of a σ–π mechanism, is too large in magnitude when compared to [Formula: see text], and [Formula: see text] in the analogous compounds. These latter three couplings are consistent in sign and magnitude with what is known about hyperfine interaction constants. The magnitudes of [Formula: see text] are reported for 4-fluorobenzotrifluoride, 3-amino-4-fluorobenzotrifluoride, 3-nitro-4-fluorobenzotrifluoride, as are 6JpF,F values for p-fluorobenzal fluoride and p-fluorobenzyl fluoride. In contrast to 6JpH,CH and 6JpF,CH it seems unlikely that, unless its coupling mechanism becomes more precisely understood, 6JpF,CF will be a reliable indicator of conformational preferences.
Etude de l'ion HC2O4− en solution aqueuse par spectrométrie infrarouge et Raman
Authors: Jaber M. , Bertin F. , Forel M. T.
Published: May 2006

The authors have investigated aqueous solution of the hydrogenooxalate ion by infrared and Raman spectroscopy. They show the existence of an equilibrium between a planar monomer structure linked by hydrogen bond to solvent molecules and an associated form. Such an equilibrium can provide a satisfactory explanation for the experimental spectra and their dependence upon temperature and concentration. The assignments for the monomeric form are supported by a normal coordinate analysis and by a calculation of the valence force field.
The kinetics of the reactions of boric acid with 5-substituted salicylate ions
Authors: Queen Alan , Davies Lorne , Con Andrew
Published: May 2006

Salicylate ions form 1:1 complexes with boric acid. The kinetics of these reactions have been studied by the stopped-flow method and stability constants have been calculated from absorption measurements on the solutions at equilibrium. Temperature studies of the rates of reaction of boric acid and unsubstituted salicylate ions at pH 5.29 have been carried out. The data correlate well with the Arrhenius equation.
A Mössbauer study of organotellurium compounds. Part III. Tellurium heterocycles and related compounds
Authors: Dance Nigel S. , Jones Colin H. W.
Published: May 2006

not available
Ultrasonic velocities, compressibilities, and heat capacities of water + tetrahydrofuran mixtures at 298.15 K
Authors: Kiyohara Osamu , D'Arcy Patrick J. , Benson George C.
Published: May 2006

Ultrasonic velocities and volumetric heat capacities at constant pressure were measured at 298.15 K for water + tetrahydrofuran mixtures over the whole concentration range using pulse–echo–overlap equipment and a flow microcalorimeter respectively. Isentropic and isothermal compressibilities and heat capacities at constant pressure and at constant volume were derived from the results in combination with the results of previous studies of thermal expansivities and excess volumes. The significance of the excess compressibilities and excess heat capacities is discussed in terms of molecular interactions.
A gas chromatographic detector based on the quenching of luminescence from a P4/O2 cold flame
Authors: Aue Walter A. , Mielniczuk Zbigniew M.
Published: May 2006

Gas chromatographic effluents were detected by their quenching effect on the luminescence of a steady 'cold flame', as provided by the gas-phase reaction of phosphorus vapor and oxygen. The response of organic compounds correlated with their 'ease of oxidation' in accordance with the literature, suggesting that such compounds act as oxygen atom scavengers in the branched-chain P4/O2 reaction.Most substances showed linear response over one to two orders of magnitude, and minimum detectable amounts ranged from 2 × 10−9g (benzaldehyde) to 2 × 10−4g (dichloromethane). The detector temperature could be varied to (a) alter response ratios, i.e. selectivity, among some types of compounds; and (b) produce easily-obtained Arrhenius plots. However, the response (luminescence quenching) of most compounds was independent of temperature over a considerable range.
The decomposition of cyclobutanone vapor induced by infrared radiation from a pulsed CO2 TEA laser
Authors: Back M. H. , Back R. A.
Published: May 2006

The decomposition of cyclobutanone vapor by infrared radiation from a pulsed CO2 TEA laser at 9.552 μm has been studied at pressures from about 0.1 to 10 Torr. The main decomposition path was [Formula: see text]while the reaction [Formula: see text]was much less important. Very minor amounts of propylene and acetylene were also observed. From the ratio of reaction [2] to reaction [1], information was obtained about the effective temperature of the decomposition and the energy of the decomposing molecules. With the laser beam unfocussed, the decomposition at pressures above about 3 Torr is adequately described as a thermal decomposition, controlled by the initial temperature attained and the rate of cooling of the irradiated gas. At lower pressures, and when the laser beam was focussed, direct excitation and decomposition of individual molecules by multiphoton absorption appears to be involved.
An interesting azirine induced reaction of the cyclopentadienyliron dicarbonyl dimer
Authors: Alper Howard , Sakakibara Tsutomu
Published: May 2006

Reaction of cyclopentadienyliron dicarbonyl dimer with a series of 2-arylazirines in anhydrous benzene (room temperature or 40 °C, 41–96 h) affords cycloaddition products (pyrazines, isoxazoles) and the dimer of cyclopentadienone (1,8-diketo-4,7-methano-3a,4,7,7a-tetrahydroindene). The formation of the latter product is proposed to occur via a complex in which each cyclopentadienyl ring is π-complexed to one iron atom and σ-bound to another.
A versatile synthesis of spirobenzylisoquinoline and phthalideisoquinoline alkaloids. Conversion of a phthalideisoquinoline to spirobenzylisoquinolines
Authors: Nalliah B. C. , MacLean D. B. , Holland H. L. , Rodrigo R.
Published: May 2006

Eight spirobenzylisoquinolines and four phthalideisoquinolines have been synthesized through 1,9-dehydrophthalideisoquinoline intermediates. The latter are reduced and rearranged in one step to spirobenzylisoquinolines of the corydaine–sibiricine type. The phthalideisoquinoline alkaloid hydrastine has been converted by invitro methods to a spirobenzylisoquinoline in two steps.
13C nuclear magnetic resonance studies. 85. 13C spectra of several ring-contracted and -expanded steroids
Authors: Dave Vinod , Stothers J. B.
Published: May 2006

The 13Cmr spectra of several cholestanes including 13 A-homo-B-nor derivatives, 11 A-homo derivatives, and 8 B-nor examples have been examined. In addition the 13C data for a few of the corresponding androstanes and 16 precursors in the cholestane series are reported. Examples in both the 5α- and 5β-cholestane families were included. These results represent the first systematic examination of the 13C spectra of A-homo-B-nor steroids and should be useful for the characterization of other members in each series. These data also permit some tentative conclusions regarding the favored conformation for the seven-membered ring in the A-homo derivatives.
The biosynthesis of the Lythraceae alkaloids. II. The phenylalanine-derived fragments
Authors: Horsewood Peter , Golebiewski W. Marek , Wrobel Jerzy T. , Spenser Ian D. , Cohen Jonathan F. , Comer Fred
Published: May 2006

Label from [1-14C]-, [2-14C]-, [3-14C]-, and [1,3-14C2]phenylalanine is incorporated non-randomly into the Lythraceae alkaloids, decodine and decinine, in Decodonverticillatus. The incorporation pattern, determined by chemical degradation of the alkaloids, demonstrates incorporation of two intact C6—C3 units.
Aliphatic diazo compounds. XIII. The copper-catalyzed decomposition of 5-endo-hetero-atom-substituted 3-diazo-2-norbornanones
Authors: Yates Peter , Hambly Gordon F.
Published: May 2006

The copper-catalyzed decomposition of 5-endo-acetoxy-3-diazo-6,6-dimethyl-2-norbornanone (4) in dilute solution in benzene gives as the major product 2-acetoxy-5,5-dimethyl-tricyclo[2.2.1.02,6]heptan-3-one (12) together with 5-endo-acetoxy-6,6-dimethyl-2-norbornanone (8), 6-endo-acetoxy-5,5-dimethyl-2,3-norbornanedione (9), and 5-endo-acetoxy-3-endo-hydroxy-6,6-dimethyl-2-norbornanone (10). The structure of 12 was established by its independent synthesis from 5-endo-bromo-7,7-dimethyl-2,3-norbornanedione (19) by treatment with lithium followed by acetic anhydride. Copper-catalyzed decomposition of 4 labelled with 18O in the acetoxyl carbonyl shows that the major pathway for the formation of 12 involves bonding of the carbenoid center at C-3 to the carbonyl oxygen of the acetoxyl group and not insertion into the endo C-5–oxygen bond. Similar copper-catalyzed decomposition of 5, the methoxy analogue of 4, gives only 9,9-dimethyl-5-oxatricyclo[4.2.1.03,7]nonan-2-one (31), the product of carbenoid insertion into a C—H bond of the methoxyl methyl group. Copper-catalyzed decomposition of 5-endo-chloro-3-diazo-4,6,6-trimethyl-2-norbornanone (6) and of 7, its bromo analogue, gives as major products the corresponding α-diketones and azines; if insertion into the endo C-5–halogen bond occurs at all it can only represent a minor pathway. Thus although very ready carbenoid insertion into an endo C-5–hydrogen bond occurs in the copper-catalyzed decomposition of 3-diazo-2-norbornanones, such insertion into an endo C-5–hetero atom bond occurs with difficulty, if at all.
Flash photolysis of alkali metal anions in tetrahydrofuran and dimethoxyethane
Authors: Seddon W. A. , Fletcher J. W. , Sopchyshyn F. C. , Selkirk E. B.
Published: May 2006

Flash photolysis of K−, Rb−, and Cs− in tetrahydrofuran (THF) produces the corresponding ion-pairs (K+, es−), (Rb+, es−), and (Cs+, es−), followed by the regeneration of the parent metal anion, M−. In mixed-metal solutions containing Na and M where M is K, Rb, or Cs, photolysis of Na− also forms the (M+, es−) ion-pair and M−, but with the latter then reforming Na− on an extended time scale. Similar results were obtained in dimethoxyethane (DME) at 213 K, but in this case with the initial formation of a loose ion-pair, (M+, es−)loose.Based on a Gaussian–Lorenztian shape function, the 'best-fit' optical bands for the (M+, es−) and M− species were used to simulate the experimental spectra and deduce the corresponding extinction coefficients in both solvents.The overall mechanism is complex but is in good agreement with previous interpretations deduced by pulse radiolysis.
Polymerisation of the 3-halogenomethyl-5-methyl(or 5-phenyl)-3′(5′)-methyl-1,5′(3′)-dipyrazolylmethane. Synthesis of new macrocyclic systems
Authors: Fruchier Alain , Ramdani Abdelkrim , Tarrago Georges
Published: May 2006

The study of the polymerisation of the 3-halogenomethyl-5-methyl(or 5-phenyl)-3′(5′)-methyl-1,5′(3′)-dipyrazolylmethane allowed the isolation of five new macrocyclic compounds with four or six pyrazole rings. Their structures have been determined by mass spectrometry and proton nmr spectroscopy.A scheme is proposed which takes into account the different possible orientations of this reaction.
Interaction of the unusual bonds in cyclopropane with an extra electron in the dense fluid
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

An unexpectedly strong interaction between electrons and closely packed cyclopropane molecules has been discovered through measurement of electron mobilities in the liquid and gas phases. In the low density vapors the mobilities fell in the expected order cyclopropane > propane > propene; at STP they were 9000, 6000, and 2040 cm2/V s, respectively. In the liquids the order was propane > propene > cyclopropane; at 273 K the mobilities were 1.4, 0.12, and 0.017 cm2/V s, respectively. The abnormally low mobility in liquid cyclopropane is attributed to the formation of transient dimeric anions. The reaction is only significant at densities greater than about 0.4 times the critical density.
Thermochemical measurement of the ligand field splitting energies for hexaaquocopper(II) and hexaamminecopper(II)ions
Authors: Badri Muhammad , Jamieson James W. S.
Published: May 2006

The vacuum dehydration of copper(II) sulphate pentahydrate has been shown to pass through the transitory trihydrate state before proceeding to the monohydrate composition. Based on this, the heat of solution data for the high-energy modification hydrates have been reinterpreted and the low-energy crystalline hydrates of various compositions have been prepared and their heats of solution measured. From the heat of solution data the maximum energy difference expressed in kcal/mol heptahydrate appears to be of the right order of magnitude to be regarded as the ligand field splitting energy for the hexaaquocopper(II) ion. Similar measurement for the ammine complexes of copper(II) sulphate has also been done and the maximum energy difference was found to agree well with the value of LFSE obtained by spectroscopic method.
β-Lactams. VI. The synthesis of homocycloanalogues of nocardicin A
Authors: Hakimelahi Gholam Hosein , Just George
Published: May 2006

The synthesis of the title compounds is reported. It is shown that, in contrast to benzylic ketones, benzylic oximes are stable to hydrogenolysis conditions necessary for the removal of benzyl protecting groups of carboxylic acids and phenols.
The mass spectra of trifluoroacetyl-2,5-diketopiperazines. I. cyclo-(-Gly-X), cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile), and cyclo-(-Ala-Ala)
Authors: Slater George P. , Hogge Lawrence R.
Published: May 2006

The trifluoroacetyl derivatives of the 2,5-diketopiperazines cyclo-(-Gly-X), cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile), and cyclo-(-Ala-Ala) were examined by GC–MS. The molecular ion was readily detectable only for TFA-cyclo-(-Gly-Gly) (m/e 306, 9%). For those compounds containing a valyl or leucyl/isoleucyl residue the ion of highest mass in the spectrum was formed by elimination of C3H6 or C4H8, respectively, from the molecular ion. In the TFA-cyclo-(-Gly-X) series this ion corresponded to the molecular ion of TFA-cyclo-(Gly-Gly) (m/e 306), and in the TFA-cyclo-(-Ala-X) series, to the molecular ion of TFA-cyclo-(-Ala-Gly) (m/e 320). The fragmentation patterns proposed for these compounds are based on the further degradation of these parent ions so that each compound within a series has a similar mass spectrum. However, sufficient differences were detectable in the various spectra to permit identification of the individual DKP's.Many of the fragmentation pathways devised to explain the mass spectra were supported by high resolution data and appropriate metastable ions.
Carbon-13 nuclear magnetic resonance spectroscopy of phorbol
Authors: Neeman M. , Simmons O. D.
Published: May 2006

The 13C nmr spectrum of the diterpene phorbol has been recorded and the signals of all carbons assigned.
Conformational preferences of the syn-pyridinecarboxaldehyde oximes
Authors: Danchura Werner , Wasylishen Roderick E. , Delikatny James , Graham Moira R.
Published: May 2006

The results of an 1H and 13C nmr study of the three syn-pyridine aldoximes are reported. Observed 6J(Hα,Hpara) values in the 2- and 3-pyridine aldoximes indicate that the oxime group is twisted approximately 20° out of the pyridine ring plane. Stereospecific 5J(Hα,Hmeta) values measured for acetone solutions of 2-pyridine aldoxime indicate that the ratio of the NCCN trans conformation to the NCCN cis conformation is 0.86 ± 0.14. The results of similar measurements on 3-pyridine aldoxime give 0.60 ± 0.10 for the ratio of the C2CCN trans and C2CCN cis conformations. Abinitio molecular orbital calculations are in good qualitative agreement with experiment. Carbon-13 chemical shifts of the oximes are compared with those previously measured for the parent aldehydes.
Barriers to rotation about the N—CO bond in N-vinyl amides; a new two-site approximation method
Authors: Fraser Robert R. , Roustan Jean-Louis A. , Mahajan Jaswant R.
Published: May 2006

The barriers to rotation about the N—CO bonds in a series of N-vinyl amides have been determined by a study of their proton spectra at variable temperatures. A complete LACN 3 analysis of compound 1 gave the parameters used in a complete line shape (CLS) analysis to obtain ΔG≠. A new approximate method was shown to give a value for ΔG that agreed within 0.1 kcal/mol of that obtained by CLS. The approximate method was employed to determine ΔG≠ for other members of the series. The barrier in the N-vinyl amide 1 was found to be 2.5 kcal/mol higher than that in its saturated analog. Variations within the series of N-vinyl amides amounted to only 1.2 kcal/mol. A steric effect is proposed for the increase in barrier height. The new approximation formula was tested for the general case of unequal singlet coalescence and found to give k's accurate to within 4% for Δν > 10 and to within 10% at lower values of Δν.
Some reactions of 1,2-dihydropyridines with organic azides. Synthesis of diazabicylo[4.1.0]hept-4-enes, 1,2,5,6-tetrahydropyridylidene-2-cyan (sulfon, carbon) amides, and piperidylidene-2-cyan (sulfon, carbon) amides
Authors: Ondrus T. A. , Knaus E. E. , Giam C. S.
Published: May 2006

The regiospecific 1,3-dipolarcycloaddition reaction of 1,2-dihydropyridines 1 with organic azides 2 afford 2,7-diazabicyclo[4.1.0]hept-4-enes 4, whereas solutions of 1 also containing lithium hydroxide give predominately 4 along with the diazo product 6. In contrast, the dimeric product 7 was obtained from the reaction of 1a with hydrazoic acid. Catalytic hydrogenation of 4 gives rise to a tautomeric mixture of 9 and 10; when R2 is methanesulfonyl or p-aminobenzenesulfonyl only 9 was obtained. Treatment of 4 with neutral alumina gives rise to the 1,2,5,6-tetrahydropyridylidenes 8 which are likewise reduced to a mixture of 9 and 10 or 9.
The dual role of the coinitiator in the cationic polymerization of isobutene
Authors: Russell Kenneth E. , Vail Linda G. M. C.
Published: May 2006

The influence of 2,4- and 2,6-dimethylphenol, 2,3,6- and 2,4,6-trimethylphenol, 2,3,4,6- and 2,3,5,6-tetramethylphenol, 2,6-diisopropylphenol, 2-tert-butyl-4-methylphenol and 2,4-di-tert-butylphenol on the stannic chloride initiated polymerization of isobutene has been investigated. At −78.5 °C and with 0.185 M stannic chloride, these phenols act as coinitiators. Rates of polymerizaiton reach maximum values at phenol concentrations which depend greatly on the number and positions of alkyl substituents; molecular weights decrease continuously with phenol concentration. Phenols without 4-substituents are incorporated in polyisobutenes as end groups and those with 4-substituents give rise largely to olefinic end groups. Termination of polymerization occurs mainly by attack at a free 4-position or at the OH group. The initial tert-butyl carbenium ion is more readily terminated by 2,6-di-tert-butylphenol than the polymer carbenium ion.The rate and molecular weight results are interpreted in terms of a simplified reaction scheme in which termination occurs spontaneously or by reaction with uncomplexed phenol. Rate constants for termination by methyl-substituted phenols are of the order of one tenth of the propagation rate constant while those for 2-tert-butyl-4-alkylphenols are about one hundredth of the propagation rate constant.
Ionization of ethylene glycol in isodielectric acetonitrile + ethylene glycol mixtures at 25 °C
Authors: Bose Kumardev , Kundu Kiron K.
Published: May 2006

The autoprotolysis constants (Ksm) of ethylene glycol in isodielectric acetonitrile + ethylene glycol mixtures have been determined at 25 °C from emf measurements on the cell[Formula: see text]From these values, those of δΔG0, the free energy of ionization of ethylene glycol in these mixed solvents relative to that in pure glycol, have been computed. The nature of variation of δΔG0 with solvent composition has been compared with that in two other mixed systems: water + ethylene glycol and methanol + 1,2-propanediol and the intrinsic differences between the solvation characteristics of the various solvents have been pointed out. The standard free energies of transfer of the glycoxide ion, ΔGt0(OEg−), from pure glycol to acetonitrile + glycol mixtures have also been estimated using ΔGt0(H+) values obtained earlier. The glycoxide ion is increasingly desolvated as the acetonitrile content of the solvent increases, as indicated by increasingly positive values of ΔGt0(OEg−). This behaviour has been compared with those of ΔGt0(H+) and ΔGt0(Cl−) determined previously.
Enzymes in organic synthesis 17. Oxidoreductions of alcohols, aldehydes, and ketones using chemically modified horse liver alcohol dehydrogenase
Authors: Jones J. Bryan , Dodds David R.
Published: May 2006

The substrate specificity of acetimidylated (A-HLADH) and hydroxybutyrimidylated horse liver alcohol dehydrogenase (HB-HLADH) has been evaluated for the ethanol–acetaldehyde, trans-2-hexenol–trans-2-hexenal, furfural–furfuryl alcohol, benzaldehyde–benzyl alcohol, cyclobutanol–cyclobutanone, cyclopentanol–cyclopentanone, cyclohexanol–cyclohexanone, and cycloheptanol–cycloheptanone substrate couples. The pH-optima of A- and HB-HLADH are similar to that of native enzyme (∼pH 7) for the reduction mode, but are displaced from the broad ∼8–10.5 range for the native enzyme to ∼11.8 for the modified enzymes in the oxidative mode. However, because of coenzyme instability, the practical pH optimum for oxidations remains 9 for both native and modified HLADH's. The modified enzymes provide limited synthetic advantages for the substrates evaluated.
Isopotential points in the electrosorption of selenite, selenate, selenide, and tellurite at the platinum rotating disc electrode
Authors: Chagas Hélio C.
Published: May 2006

Electrosorption at the platinum rotating disc electrode in sulfuric acid solutions of selenite, selenate, selenide, and tellurite gives rise to isopotential points in the potential range where oxidation of platinum occurs. The data are analyzed with the framework of the model put forward by Untereker and Bruckenstein. Since similar behavior is observed for the selenite, selenate, and selenide systems, it is tentatively inferred that a common electrosorbed species, possibly selenium itself, may be involved in these systems.
Partial molal volumes of organic compounds in carbon tetrachloride. IV. Ketones, alcohols, and ethers
Authors: Edward John T. , Farrell Patrick G. , Shahidi Fereidoon
Published: May 2006

The partial molal volumes [Formula: see text] in carbon tetrachloride at 25 °C of 13 ketones, 18 alcohols, and 17 mono- or poly-functional ethers, all acyclic, have been determined. Results are in reasonable agreement with [Formula: see text] calculated from an equation developed previously, using previous parameters plus the following: increments (in mL mol−1) of 8.72 for carbonyl, 6.1 for hydroxyl, 4.4 for oxygen in a monofunctional ether, and 5.8 for oxygen in a polyfunctional ether; decrements δ (in mL mol−1) of −1.68 for [Formula: see text] for [Formula: see text] for [Formula: see text] for [Formula: see text], and −1.93 for [Formula: see text]. The increments for carbonyl and hydroxyl are smaller than the van der Waals volumes of these groups, and indicate some degree of complexation to carbon tetrachloride. Only a roughly linear relation is found between [Formula: see text] of alcohols in water and [Formula: see text] in carbon tetrachloride, possibly because of the intrusion of additional effects such as structure-promotion in water.
Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 4. Residual autohydrolysis lignin
Authors: Wayman Morris , Chua Miranda G. S.
Published: May 2006

Lignocellulosic residue remaining after autohydrolysis of extractive-free aspen wood meal at 195 °C for periods of time varying from 5 to 120 min followed by extraction with 90% dioxane was subjected to enzymatic hydrolysis to obtain residual lignin. Infrared studies indicated that in the early stages of autohydrolysis residual lignin resembles protolignin, but as autohydrolysis proceeds it changes to resemble more and more the extracted lignin. Residual lignin was found to be higher in carbon but lower in hydrogen and oxygen than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. From alkaline nitrobenzene oxidation, residual lignin is seen to become more condensed with increasing autohydrolysis time. The insolubility of residual lignin is attributed to the existence of strong bonds between this lignin and carbohydrate.
Rare-gas sensitized radiolysis of gaseous isobutene: ionic processes
Authors: Herman Jan A.
Published: May 2006

Irradiation of isobutene at low pressure in the presence of suitable scavengers or mixed with the rare gases Ar, Kr, and Xe shows that 2-methyl-but-2-ene is partially formed in ionic processes. These processes involve polymeric ions of isobutene formed in "head-to-head" reactive encounters with neutral isobutene. The resulting ionic species, which have internal structural tension, can isomerize with a subsequent elimination of ethylene, or decompose to give 2-methyl-but-2-ene. The rare-gas sensitized radiolysis confirms the already established reaction channels for formation of the main products.
Time-resolved CIDEP in the photoreduction of quinones. A study of the spin lattice relaxation time of semiquinone radicals in solution
Authors: DeBoer Jacobus W. M. , Chan Chung Therese Y. C. , Wan Jeffrey K. S.
Published: May 2006

The application of time-resolved CIDEP observations to the measurements of T1 of transient radicals is examined in detail. The importance of proper treatment of the response time is considered theoretically and demonstrated experimentally. By taking into account the variation of response time at high power, a method is described on how to evaluate B1. At low power levels when the response time does not vary significantly, the extrapolation to zero power will provide a good estimate of T1. The method was applied to measure T1 for both the neutral radical and the radical anions of the benzoquinone, tetrachlorobenzoquinone, and duroquinone. It is confirmed that there is no significant difference in T1 between the neutral radical and the radical anions. The values of the estimated T1 are 2.2 μs for semibenzoquinone, 2.7 μs for semitetrachlorobenzoquinone, and 3.2 μs for semiduroquinone, all at 10 °C and in a 50% isopropanol/toluene solvent.
The reaction of ethyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-β-D-glucoside in acetone
Authors: Capon Brian , Labbé Cecilia , Rycroft David S.
Published: May 2006

It is shown by 1H and 13C nmr spectroscopy that ethyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-β-D-glucoside reacts in acetone to yield a Schiff base, not the hemiorthoamide proposed previously.
Quaternization and sodium borohydride reduction of N-(4-pyridylcarbonylamino)-1,2,3,6-tetrahydropyridine. Synthesis of N-amino-1,2,3,6-tetrahydropyridines
Authors: Redda K. , Corleto L. A. , Knaus E. E.
Published: May 2006

Reaction of N-(4-pyridylcarbonylamino)-1,2,3,6-tetrahydropyridine (2a) with methyl chloroformate afforded the quaternary salt 3a whereas reaction with methyl iodide gave a mixture of 3b and 6. Sodium borohydride reduction of 3a using methanol at −65 °C gave the N-methoxycarbonyl-1,2-dihydropyridine 4a whereas reduction using ethanol at 0 °C gave the 1,2,3,6-tetrahydropyridine 4b. Reduction of 3b and 6 gave rise to a mixture of 4c and 7. Catalytic hydrogenation of 4b and 4c afforded the respective piperidyl derivatives 10 and 11. The pharmacological activities of the products are presented.
Entropy changes and structural implications for crystalline phases of pyrazine
Authors: Boyd Robert K. , Comper John , Ferguson George
Published: May 2006

Molar heat capacities of crystalline pyrazine have been measured by adiabatic calorimetry in the range 20–40 °C and interpreted to show that in the crystal structures of phases II and III half the molecules must be disordered. Together with previous X-ray studies, this allows possible structures for phase II and phase III to be deduced. Of the eight molecules in the phase III unit cell, four are disordered over two sites so that the point symmetry is effectively mmm; the remaining four molecules have 2/m symmetry and are not disordered. This structure is consistent with the available spectroscopic evidence. It is likely that the phase II structure is closely related to the phase III structure, for example by the molecules with 2/m symmetry adopting a slightly different orientation.
Ring forming reactions of some amineimides with a note on electrophilic bromination
Authors: Brindle Ian D. , Gibson Martin S.
Published: May 2006

Allylic and propargylic amineimides react with bromine to form 4H-1,3,4-oxadiazinium salts in accord with recent studies of electrophilic brominations. A novel synthesis of 5,6- dihydro-4,4-dimethyl-6-hydroxymethyl-2-phenyl-4H-1,3,4-oxadiazinium bromide by the reaction of N′N′-dimethylbenzohydrazide and epibromohydrin is reported.
Hydrolysis of cyclic unsymmetrical anti imidate salts. New evidence for stereoelectronic control
Authors: Deslongchamps Pierre , Cheriyan Ukken Ouseph , Taillefer Roland J.
Published: May 2006

The synthesis and the hydrolytic behavior of the cyclic imidate salts 7, 8, and 9 is reported. Under acidic conditions, the salt 7 gives the ester ammonium salt 21 and the salt 9 gives a 1:1 mixture of the ester ammonium salt 22 and the amide alcohol 23 as the rotamer 23B only. Under basic conditions, the salt 7 (or 8) gives a 2:8 (or 1:9) mixture of the amide alcohol rotamers 25A and 25B (or 27A and 27B) under kinetically controlled conditions. The salt 9 gives, as the kinetic product, the amide alcohol rotamer 23B only. These results can be rationalized on the basis of the stereoelectronic theory for the cleavage of tetrahedral intermediates and by taking into account that the nitrogen in tetrahedral intermediates must be either protonated under acidic conditions, or hydrogen bonded with the solvent under basic conditions, in order to observe the cleavage of a C—N bond.
Thermal decomposition of ozonides. A complementary method to the Baeyer–Villiger oxidation of hindered ketones
Authors: Lapalme Richard , Borschberg H.-Jürg , Soucy Pierre , Deslongchamps Pierre
Published: May 2006

Treatment of vinyl acetate with ozone yields the mixed anhydride of acetic and formic acids and formaldehyde oxide. The formaldehyde oxide can be trapped by reaction with ketones yielding the corresponding ozonides. Thermal decomposition of these ozonides gave the corresponding lactone and (or) the corresponding olefin carboxylic acid. The ozonides were also prepared by the ozonolysis of the corresponding olefins.
Isotopic exchanges in the treatment of cyclobutane with tritiated or deuterated trifluoromethanesulfonic acid or with tritiated sulfuric acid
Authors: Lee Choi Chuck , Ko Eric C. F.
Published: May 2006

When cyclobutane (1) is shaken at 0 °C with [3H]CF3SO3H (2-t) or with (2H)CF3SO3H (2-d), incorporation of T or D into the hydrocarbon layer readily occurred. All eight H atoms of 1 can be involved in the exchange since polydeuterated species including octadeuterated hydrocarbons were observed by mass spectrometry. In an experiment with 1 and 2-t, quenching of the acid layer with H2O gave a mixture of cyclobutanol, cyclopropylcarbinol, and allylcarbinol in the ratio of 61:37:2, respectively, as estimated by isotopic dilution, while vpc analysis of the hydrocarbon layer showed the presence of 1, methylcyclopropane, and 1-butene in the ratio of 66:30:4. The results are explained by a carbocationic chain mechanism, involving the formation of equilibrating bicyclobutonium ions. Similar but slower incorporation of T into the hydrocarbon layer was observed when 1 was treated with [3H]H2SO4.
Le comportement électrochimique du magnésium en milieux légèrement alcalins
Authors: Brossard Robert-Louis , Piron Dominique-Louis
Published: May 2006

This study of the anodic behavior of magnesium in simulated seawater has shown that the corrosion product formed at the surface of the electrode depends mainly on the nature of ions dissolved in the electrolyte. Analyses of the corrosion product, formed in the presence of a high concentration of chloride ions, are compatible with the formation of a compound having approximately the formula 5Mg(OH)2•MgCl2. However, this complex is gradually transformed over a period of several hours into Mg(OH)2.A model of the oxidation mechanism is presented in which the characteristics of the anodic behavior of magnesium are related to the structure of the oxidation layer. For example, the activation of the surface of the anode, the kinetics of the hydrogen evolution reaction, and the large difference between values of corrected and uncorrected electrode potential can all be explained by this model. It is the resistance of the film to the flow of current which controls the kinetics of anodic dissolution of magnesium.
Acid-catalyzed rearrangement of cyclobutanones. V. Preparation of polycyclic aromatic dihydrofurans and dihydropyrans
Authors: Duperrouzel Paul , Lee-Ruff Edward
Published: May 2006

Cyclobutanones derived from α-phenyl, α,α-diphenyl, and bisphenyleneketene cycloaddition to dihydrofuran and dihydropyran were rearranged under acidic conditions to polycyclic aromatic dihydrofurans and dihydropyrans respectively. A mechanism for these rearrangements is proposed.
Metal complexes as antioxidants. 7. Kinetics of inhibition of styrene autoxidation by zinc di-isopropyldithiophosphate
Authors: Howard J. A. , Tong S-B.
Published: May 2006

Rates of oxygen absorption by styrene (RH) containing 2,2,3,3-tetraphenylbutane and zinc di-isopropyldithiophosphate at 30 °C obey the rate law [Formula: see text] where Ri is the rate of free-radical chain initiation. This order with respect to the styrene concentration implies extensive chain transfer from the poly(peroxystyryl)peroxy radical to a radical derived from the inhibitor. Reaction products confirm the displacement of a di-isopropyldithiophosphoryl radical in the chain termination reaction.Diethyldithiophosphoric acid also inhibits styrene autoxidation by a mechanism which involves extensive chain transfer.
The molecular and crystal structure of trans-dichloro(dimethylformamide) (2,6-lutidine)platinum(II)
Authors: Rochon F. D. , Kong P. C. , Melanson R.
Published: May 2006

The crystal structure of trans-[Pt(DMF)(2,6-lutidine)Cl2] has been determined by X-ray diffraction. The crystals are orthorhombic, space group Pbca, with a = 11.612(13), b = 26.504(33), c = 9.271(9) Å, and Z = 8. The structure was refined by full matrix least-squares analysis to a conventional R factor of 0.051 and a weighted Rw = 0.044. The coordination around the platinum atom is square planar. The 2,6-lutidine ring is perpendicular to the platinum plane. DMF is bonded to platinum through the oxygen atom. It is planar and makes an angle of 71 ° with the platinum plane. The cis–trans configuration of the [Pt(DMF)(L)Cl2] (L = pyridine derivative) complexes in DMF solution is discussed.
3,5-Dimethylpyrazolylphosphine molybdenum(0) and tungsten(0) carbonyl complexes
Authors: Davis Harry B. , Hoyano James K. , Leung Ping Yuen , Peterson Louis K. , Wolstenholme Brian
Published: May 2006

Complexes with the general formula [LnM(CO)m], where [Formula: see text] x = 0–2, n = 1 or 2, M = Mo(0) or W(0), m = 3 or 4, were prepared by thermal or photolytic methods by the reaction of the appropriate 3,5-dimethylpyrazolyl phosphine ligand with M(CO)6, norbornadienemetaltetracarbonyl [C7H8M(CO)4], cycloheptatrienylmetaltricarbonyl [C7H8M(CO)3], [(Me2N(CH2)3NMe2)M(CO)4], [(CH3CN)2M(CO)4], or [(CH3CN)3M(CO)3]. Structural evidence indicates octahedral geometry about the metal atom centre, and several modes of coordination for the ligands in those complexes isolated and characterized. For x = 2, the ligand [Formula: see text] was monodentate, via phosphorus in [Formula: see text] and bidentate in [Formula: see text] where coordination by P and the 2N site of the pyrazolyl ring yielded four-membered [Formula: see text] metallocycles. For x = 1, the [Formula: see text] ligand was bidentate, via the phosphorus atom and one of the 2N sites of one of the pyrazolyl substituents, thus giving the four-membered [Formula: see text] metallocycle in [Formula: see text] and tridentate in [Formula: see text] where three facial CO's, two 2N atoms of the pyrazolyl rings, and a part of the phenyl ring occupy the six coordination sites. For x = 0, the P(Me2pz)3 ligand was tridentate via the 2N atoms of all three pyrazolyl rings, thus giving tricyclic systems [P(Me2pz)3M(CO)3] (VIII, IX).
Thermodynamics of ionization of trans-crotonic and adipic acids in water; the silver – silver adipate electrode
Authors: Dash Upendra Nath , Nayak Uttam Kumar
Published: May 2006

The ionization constant, K, of trans-crotonic acid, and the first and second ionization constants, K1 and K2, of adipic acid have been determined in water at seven different temperatures ranging from 15 to 45 °C with the help of the cells without liquid junction using silver – silver chloride and quinhydrone electrodes. The variations of pK, pK1, and pK2 with temperature have been expressed by the equations[Formula: see text]and[Formula: see text]From the temperature coefficient of the ionization constants, the standard enthalpy, entropy, Gibbs energy, and heat capacity changes of the corresponding dissociation processes have been calculated. Using the values of ionization constants of adipic acid, the standard potential of the Ag(s)/Ag2Ad(s)/Ad2− electrode, and the related standard thermodynamic quantities for the electrode process[Formula: see text]have been calculated in water at those temperatures.
Binding sites between palladium(II) and nucleosides or nucleotides and crystal structure of [Pd(diethylenetriamine)(guanosine)](ClO4)2
Authors: Rochon F. D. , Kong P. C. , Coulombe B. , Melanson R.
Published: May 2006

The interactions between [Pd(dien)Cl]Cl and some nucleosides and nucleotides were studied by nmr. The binding site of guanosine, guanosinemonophosphoric acid, xanthosine, and inosine is N(7). Cytidine is coordinated to palladium through N(3). Adenosinemonophosphate acts as a bidentate, binding two different palladium atoms at N(1) and N(7).The crystal structure of [Pd(dien)(guanosine)](ClO4)2 has been determined by X-ray diffraction. The crystals are orthorhombic, space group P212121, with a = 13.422, b = 14.587, c = 12.432, and Z = 4. The structure was refined by block-diagonal least-squares analysis to a conventional R factor of 0.047 and a weighted Rw = 0.043. The coordination around the palladium atom is square planar. Guanosine is bonded to palladium through N(7). The planar purine ring makes an angle of 63.4° with the palladium coordination plane. The structure is stabilized by hydrogen bonding.
Oxygen exchange in methanol in acid solutions. Transition state activity coefficients
Authors: McClelland Robert A.
Published: May 2006

Rate constants for oxygen exchange of methanol in sulfuric acid and perchloric acid solutions are reported, along with activity coefficients of methanol in sulfuric acid. Transition state activity coefficients (f≠*) for methanol exchange and tert-butanol exchange have been calculated. Values of f≠* for the latter behave very similarly to those for tert-butyl acetate hydrolysis, consistent with a carbonium ion-like transition state. Values for methanol exchange show considerably more salting-out, consistent with an oxonium ion-like transition state. A significant difference with the AAc2 hydrolyses of esters and amides is noted. For the latter the transition state is salted-out relative to its protonated precursor, whereas for methanol exchange, there is little difference between the activity coefficient of the protonated alcohol and the transition state, with the latter actually being somewhat salted-in. It is pointed out that the transition state activity coefficient approach can be rigorously applied even in the absence of protonation data.
Excitation spectrum of the near-ultraviolet bands of CS2
Authors: Vasudev R. , Brand J. C. D.
Published: May 2006

An excitation spectrum of the triplet–singlet band system of CS2 vapor has been measured in the range 365–378 nm using a tunable laser source. Overall intensity is relatively insensitive to pressure in the range (150 m Torr – 340 Torr) tested in these observations. The results indicate that collisions with ground state molecules of CS2 are efficient in promoting intersystem crossing to the ground state, and that the spontaneous emission observed is primarily resonance emission from the state populated by the radiation.
A non-empirical SCF-MO study on the conformational properties and asymmetric deformations of dimethyl sulfoxide
Authors: Mezey Paul G. , Kapur Anil
Published: May 2006

Conformational properties of dimethyl sulfoxide (DMSO) have been studied by abinitio molecular orbital method, using various gaussian basis sets. Polarization d functions are essential in reproducing the correct experimental geometry. Barriers to pyramidal inversion on sulfur and Me—S bond rotation have been calculated. The calculated asymmetric S—Me stretching potential indicates that minor intermolecular interactions may cause considerable geometric distortions in the DMSO molecule. These distortions are likely to contribute to the versatile biochemical effects of DMSO.
Determination of oxalate by gas chromatographic measurement of carbon dioxide evolved from the photochemical decomposition of iron(III) oxalate
Authors: Cooley Jean M. , Kratochvil B.
Published: May 2006

Oxalate over the range of 0.4 M to 1 × 10−5 M can be determined with an accuracy of about 2% by injection of sample solutions into a photolytic cell containing an acidic solution of iron(III). Ultraviolet irradiation decomposes the iron(III) oxalate complex to iron(II) and carbon dioxide. The carbon dioxide then is purged from the cell in a stream of helium, dried, separated from other gases on a column of silica gel, and measured with a thermal conductivity detector. Interference from calcium, magnesium, thorium, aluminum, and several carboxylic acids is slight, while that from malonic. citric, formic, and tartaric acids is moderate. Strong ultraviolet absorbing species affect results by reducing the efficiency of photolysis.