bluuebunny/crossref_metadata_2025 huggingface dataset:
An investigation into the origins of polar substituent effects upon 19F chemical shifts, using 4-substituted β,β-difluorostyrenes
Authors: Reynolds William F. , Gibb Victoria G. , Plavac Nick
Published: May 2006

19F, 13C, and 1H chemical shifts have been determined for β,β-difluorostyrene and eight 4-substituted derivatives. The β-fluorine chemical shift difference, ΔδF, is used to evaluate the constant in the Buckingham equation. A = 3.0 × 10−11 esu for C—F bonds which is in excellent agreement with the value derived by Adcock and Khor. This allows accurate estimates of direct field effect contributions to 19F chemical shifts in aryl fluorides. Substituent parameter correlations demonstrate that the primary polar effect on 19F chemical shifts is field-induced π polarization. Abinitio molecular orbital calculations confirm that the substituent-induced 19F chemical shifts reflect changes in fluorine π electron density.
Axial dissymmetry induced magnetic nonequivalence in the 13C nuclear magnetic resonance spectra of allenes
Authors: Beaulieu Pierre L. , Morisset Veronique M. , Garratt Dennis G.
Published: May 2006

The observation of the magnetic nonequivalence of isopropyl methyl carbon resonances as a result of axial dissymmetry in 27 appropriately substituted allenes is reported. The magnitude of the nonequivalence Δ is more dependent upon the adjacent substituent group than upon the substituents which are bonded to the remote sp2 carbon of the allene. A mechanism based upon the transmission of substituent effects from the remote substituents to the collinear π orbitals is proposed.
Etude par resonance magnétique multinucléaire d'intermédiaires réactionnels électrophiles. Partie 8. Action des acides de Lewis chlorés COCl2, POCl3, (CH3)2N=CHCl+Cl− et Cl2 sur l'hexaméthylphosphotriamide (HMPT)
Authors: Poignant S. , Gauvreau J. R. , Martin G. J.
Published: May 2006

The structural study of the electrophilic intermediates obtained from carboxamides and chlorinated Lewis acids is extended to the phosphoric amides. The action of COCl2 and POCl3 on hexamethylphosphotriamide (HMPT) can lead to a chlorophosphonium salt (3a) the structure of which is proved by nmr spectroscopy (1H, 13C, 31P, 15N). The mechanism of formation is comparable to that of the chloroiminium chloride (Vilsmeier reagent) from the corresponding amides. The action of chlorine on HMPT does not lead to a stable salt of the same kind but essentially to the substitution product (2). A new biphosphorylated compound (6) has been identified when an excess of chlorine is reacted with HMPT.
Thermodynamics of ionization of 2,4- and 2,5-dinitrophenol in dimethylsulfoxide
Authors: Siow Kok-Siong , Ang Kok-Peng
Published: May 2006

Ionization constants of 2,4- and 2,5-dinitrophenol in dimethylsulfoxide were measured by the conductance method at five temperatures ranging from 20 to 40 °C. The ionization constants of 2,4-dinitrophenol are much larger than those of 2,5-dinitrophenol, and in both cases they increase with temperature. The thermodynamic functions of ionization are discussed in terms of Hepler's theory for substituent and solvent effects. The ionization of phenols in dimethylsulfoxide is controlled by the enthalpy factor, both internal and environmental, which is in contrast to the entropy-controlled process in water.
Application de la spectrométrie infrarouge et Raman à l'étude des complexes en solution aqueuse: Fe3+–H2C2O4
Authors: Jaber Mohsen , Bertin François , Thomas-David Germaine
Published: May 2006

A study by Raman spectrometry of the System Fe3+–H2C2O4 in aqueous solution shows very clearly the successive formation of the three complexes: Fe(C2O4)+, Fe(C2O4)2−, Fe(C2O4)33−. Each species is characterised by a specific Raman spectrum.The evolution of Raman band intensities with the range of exciting line, and the comparison between ir and Raman spectra of Fe(III) and Al(III) complexes, show for Fe(III) species a pre-resonance Raman effect.
Vapor phase Beckmann rearrangement of the cyclohexanone oxime catalyzed by AlPO4–γAl2O3 Systems
Authors: Costa A. , Deyá P. M. , Sinisterra J. V. , Marinas J. M.
Published: May 2006

Beckmann rearrangement of cyclohexanone oxime has been carried out in vapor phase by means of a pulse reactor unit directly coupled to a gas chromatograph. The catalysts chosen gave good yields of ε-caprolactam. Apparent rate constants and activation energies were calculated in terms of the kinetic model of Bassett and Habgood. Selectivity studies, using pulse experiments interpreted by OPE curves, led to the conclusion that ε-caprolactam and 5-cyanopent-1-ene were competitive products. A reaction pathway is proposed which is in agreement with both the observed rates and selectivities.
A tunable pulsed Raman spectrometer capable of probing picosecond processes
Authors: Nicollin D. , Bertels P. , Koningstein J. A.
Published: May 2006

A pulsed tunable laser Raman spectrometer is described. The relevant characteristics are: tunability in the range of 355–755 nm, peak power of > 100 kW, pulse duration 3.2 ns, spectral line width < 0.1 cm−1. Raman pulses can be studied in real time with a resolution > 10 ns while Raman spectra can be recorded with an experimental slit width > 0.5 cm−1. The overall performance of the instrument may be compared to that of a conventional cw laser Raman spectrometer having typical power levels of 100 mW. Spectroscopic measurements are discussed which demonstrate the capability of the apparatus to probe Raman processes which occur at the pico and microsecond time scale.
The crystal structure of the neuroleptic agent (±)-deoxybutaclamol and its significance for the topography of the central dopamine receptor
Authors: Fortier S. , Przybylska M. , Humber L. G.
Published: May 2006

(±)-Deoxybutaclamol, C25H31N, crystallizes in space group P21/a with cell dimensions: a = 16.626(3), b = 10.646(2), c = 11.278(3) Å, β = 90.47(4)°. The structure was solved by direct methods using the QTAN program. The coordinates were refined by block-diagonal least-squares calculations to R = 0.052 for 3147 observed reflections.The structure of (±)-deoxybutaclamol was found to be very similar to that of equipotent (±)-butaclamol and is in agreement with that assigned on the basis of chemical, spectral, crystallographic, and pharmacological studies. This confirmation validates the coordinates of a lipophilic accessory binding site in a proposed model of the central dopamine receptor.
Some studies on the solvolysis of 1-chloro-1-alkyl cycloalkanes
Authors: Ranganayakulu K. , Devi M. Vasumathi , Rao R. Balaji , Rajeswari K.
Published: May 2006

The effect of the bulk of the sidechain on the rate of solvolysis of 1-alkyl cyclopentyl, cyclohexyl, and cycloheptyl chlorides has been studied. With the exception of the t-butyl systems, the ratio of solvolysis rates for the three ring systems falls in a given series. The slower rate of solvolysis in the six-membered ring system may be due to an extra activation energy contribution caused by the conversion of a neutral chair form to the twist boat or half chair conformation, prior to the actual solvolysis. In the case of five- and seven-membered ring systems the formation of an intermediate carbonium ion is sterically favoured (I-strain or eclipsing interaction) consistent with earlier findings. The faster rate of solvolysis of 1-t-butylcycloalkyl chlorides is likely due to a rearrangement reaction where alkyl participation enhances the rate of solvolysis.
Extraction of Zn(II) and Cd(II) with anthranilic acid in the presence of nitrogen-containing organic bases
Authors: Jain Bina , Singh J. M. , Goyal R. N. , Tandon S. N.
Published: May 2006

Zinc and cadmium anthranilates do not extract into non-polar solvents alone in the pH range 4.5–6.5. But their extraction is synergistically enhanced in presence of N bases, apparently by displacement of coordinated water. The synergistic effect varies with the bases in the order β-picoline > pyridine > quinoline. The values of extraction constants suggest that cadmium forms more stable complexes than zinc.
Théorie de l'absorption ultrasonore des solutions micellaires d'amphiphiles. Application à l'effet de la force ionique sur la dynamique d'échange d'amphiphiles entre micelles et solution environnante
Authors: Zana R. , Yiv S.
Published: May 2006

An expression for the amplitude of the ultrasonic relaxation arising from the exchange of amphiphiles between micelles and surrounding solution has been derived on the basis of the same assumptions as used by Aniansson and Wall to obtain the expression of the relaxation time for this process. The derived expression somewhat extends the range of investigation of micellar systems which can be performed by means of the ultrasonic relaxation method. It has been used for the quantitative interpretation of ultrasonic absorption measurements concerning the effect of ionic strength on the dynamics of the exchange process in micellar solutions of potassium decanoate.
(−)-4-Hydroxy-N-formylmorphinan-6-one, a versatile intermediate for the synthesis of 3-deoxyopioids
Authors: Rozwadowska Maria D. , Hsu Fu-Lian , Jacobson Arthur E. , Rice Kenner C. , Brossi Arnold
Published: May 2006

(−)-4-Hydroxy-N-formylmorphinan-6-one (4) was prepared in 70% overall yield from ketone 1, via carbamate 2, and N-formylation of ketone 3. Bromination of 4 afforded either the 6-ketomorphinan 7 or the ketone 8, depending on the reaction conditions applied. Both bromo ketones 7 and 8 could be converted by standard reactions into 4,5-epoxy-N-methylmorphinan-6-one (1). The ketomorphinan 4 emerges from these investigations as a versatile intermediate, well suited for the synthesis of 4-hydroxymorphinans and 3-deoxyopioids.
A note on the application of graph theory to the thermodynamic properties of isomeric alkanes
Authors: Edward John T.
Published: May 2006

It has been claimed that trends in the thermodynamic properties of alkane isomers follow an ordering based on p2 and p3, the number of paths of length two or three, respectively (M. Randic and C. L. Wilkins. J. Phys. Chem. 83, 1525 (1979)). A possible explanation of the approximate ordering of the partial molal volumes [Formula: see text] of isomers in carbon tetrachloride at 25 °C comes from the ordering, based on p2 and p3, of (a) the number N of methyl groups, and (b) the mole fraction Zg of gauche arrangements in the different isomers. However, N and Zg have opposite effects on [Formula: see text], and specific cases of isomeric heptanes and nonanes are noted in which a reversal in trends in [Formula: see text] may be expected.
The metabolism of 2-hydroxymethyl-3-methylquinoxaline-di-N-oxide in the chicken, rat, and dog
Authors: Figdor S. K. , Hobbs D. C.
Published: May 2006

2-Hydroxymethyl-3-methylquinoxaline-di-N-oxide (GS-7443) is rapidly metabolized in the chicken, rat, and dog to 3-carboxy-2-methylquinoxaline-1-oxide and a conjugate of 3-carboxy-2-methylquinoxaline-di-N-oxide. No appreciable amounts of other metabolites nor unchanged GS-7443 could be detected in the excreta from these animals. There were minor quantitative differences in the relative amounts of the two metabolites; moreover, the conjugating group employed by the chicken is different from that of the dog but the material being conjugated is the same. Although measurable tissue levels of drug-related material were noted in several organs of the chicken 6 day s after drug administration, all chicken tissues examined were cleared of radioactivity within 21 days.
γ-Radiosensitized isomerization of gaseous butenes and methylbutenes
Authors: Collin Guy J. , Herman Jan A.
Published: May 2006

We have studied the isomerization of butenes and methylbutenes by noble gas-sensitized radiolysis. The isomerization of isobutene to but-2-ene is more efficient in the presence of xenon than in the presence of krypton or argon. The isomerization of but-1-ene into isobutene has a low radiolytic yield and occurs only in the presence of small quantities of dimethylamine. These observations are in agreement with the isomerization of the excited parent ion.In the methylbutene systems, whatever the sensitizing agent, isomerization occurs with a high radiolytic yield. Thus, a chain mechanism is needed to explain the results. The addition of dimethylamine has a reverse effect relative to that observed in but-1-ene. It is concluded that the mechanism invoked for the butene systems is not adequate for explaining the isomerization observed in the methylbutene systems.
The reaction between 2,2-di(4-nitrophenyl)1,1,1-trifluoroethane and tert-butoxide ion in tert-butyl alcohol solvent
Authors: Jarczewski Arnold , Leffek Kenneth T.
Published: May 2006

The reaction between 2,2-di(4-nitrophenyl) 1,1,1-trifluoroethane and excess sodium tert-butoxide in tert-butyl alcohol takes place rapidly to yield first the olefin, by elimination of HF. This is followed by a slower addition of tert-butoxide to the olefin, which upon reaction with the solvent gives the tert-butyl ether as the final product. The blue anions involved in each of these reactions are observed.Rate constants, the primary deuterium kinetic isotope effects, and the activation parameters have been measured for the appearance of the initial blue colour and also for the formation of the olefin. It is concluded that the reaction proceeds by a reversible ElcB mechanism.
Cyclopentadienyl platinum(IV) complexes: 1H, 13C nuclear magnetic resonance and optically active shift reagent study
Authors: Hamer Gordon , Shaver Alan
Published: May 2006

The 1H and 13C nmr parameters for the recently reported complexes (η5-C5H5)PtR1R2R3 where R1, R2, and R3 are combinations of CH3, C2H5, and C(O)CH3 groups are reported and compared to those for known octahedral di- and trimethylplatinium (IV) complexes. The C5H5 group has a relatively weak nmr trans-influence. A chiral shift reagent study on complex 5 (R1 = C(O)CH3, R2 = CH3, and R3 = C2H5) resolved the peaks due to the enantiomers, consistent with its structure and establishing its stereochemical stability. The four groups attached to the platinum atom in 5 differed greatly in their sensitivity to the shift reagent. The methyl groups in complex 4 (R1 = C(O)CH3, and R2 = R3 = CH3) become diastereotopic in the presence of chiral shift reagent. The J(Pt—H) values for 5 were not affected by the shift reagent.
Thermolysis and photolysis of 3,3:4,4-dibutano-1,2-dioxetane
Authors: Kopecky Karl R. , Lopez Sastre Juan A.
Published: May 2006

Thermolysis of 5 × 10−3 M 3,3:4,4-dibutano-1,2-dioxetane 2, Ea = 25.3 ± 0.3 kcal/mol, ΔS≠ = 0 ± 2 eu, in degassed decane solution at 42 °C produced a 300:1 ratio of cyclopentanone 3:4-pentenal, 4. From the quantum yield of photolysis of 3 to 4, determined to be 0.27 using 313 nm light, it is calculated that 2.5% excited 3 is formed on thermolysis of 2. Photolysis of (>380 nm) 5 × 10−4 M2 produces a 54:1 ratio of 3:4 corresponding to a 13.5% yield of excited 3. Excited state yields determined by measuring luminescence of benzene solutions of 2 containing DPA and DBA were 1 × 10−4% singlet and 8.7% triplet. The reason for the 300% discrepancy between the two methods for determining excited state yields is not known.
SO2 diffusion through acetonitrile-saturated perfluorosulfonic acid membranes
Authors: Kimmerle Frank M. , Breault Raymond
Published: May 2006

The diffusion coefficient of SO2 and acetonitrile in Nafion perfluorinated ion exchange membranes have been determined from chromatographic measurements of SO2 concentration and the isotopic ratios in acetonitrile solutions. The diffusion coefficients vary with residual water content and attain values about one fifth those reported for water-saturated membranes falling in the range 1–2 × 10−7 cm2 s−1. Values obtained for Teflon reinforced material indicates diffusion takes place over an effective surface more than twice the optically open area.
Oxidation products of arachidonic acid. III. The synthesis of methyl 8R,9R,11R-, 8S,9R,11R-, and 8S,9S,11R-triacetoxyeicosa-5Z,12E,14Z-trienoate
Authors: Just George , Luthe Corinne
Published: May 2006

A stereospecific synthesis of the title compounds, starting from readily available glucose derivatives, is described, and methods for differentiating them and the already reported 8S,9S,11R-eicosatrienoate are discussed.
Etude des complexes chlorés de cadmium dans des mélanges HF/H2O
Authors: Ménard Hugues , Leblond-Routhier Francine
Published: May 2006

The formation constants of CdCl2, CdCl+, and Cd2+ have been determined by polarography from 2.5 to 27.6 molar in HF/H2O.
The partitioning of tetrahedral intermediates of the hydrolysis of benzimidatonium ions in acid solutions
Authors: McClelland Robert A. , Potter Janet P.
Published: May 2006

The products (a benzoate ester or an N,N-dimethylbenzamide) have been accurately determined for the hydrolysis of the O-ethyl-N,N-dimethylbenzimidatonium ion (1) and its 4-nitro derivative (2) in dilute and moderately concentrated H2SO4 solutions. In dilute acid the ratio of amide:ester is very small (0.0005–0.001). It is proposed that the ester product arises from the zwitterionic form of the tetrahedral intermediate of the hydrolysis. The small amount of amide is due to an SN2 hydrolysis reaction and to the non-catalyzed breakdown of the neutral form of the tetrahedral intermediate, the relative contributions of the two being unknown. Although ester remains the major product throughout, at some intermediate acid concentration (20% H2SO4 for 1 and 35% H2SO4 for 2) a sharp increase in the amide:ester ratio is observed, followed by a levelling-off. This change is shown to be associated with tetrahedral intermediate partitioning, and not the SN2 reaction. It is argued that the strong acid product ratio represents the breakdown of the tetrahedral intermediate via cationic transition States. Two kinetically equivalent reactions are involved, the breakdown of the N-protonated tetrahedral intermediate producing a protonated ester and amine and the H+-catalyzed breakdown of the neutral tetrahedral intermediate producing a protonated amide and alcohol. Analogous pathways are also observed for the decomposition in acid of the amide acetals ArC(OMe)2NMe2, and the two systems are compared. A similar effect of the aromatic substituent on the partitioning ratio is noted, but the tetrahedral intermediate exhibits a greater tendency for amine expulsion. A kinetic analysis produces the estimate of 1011 s−1 for the rate constant for the breakdown of the zwitterionic form of the tetrahedral intermediate. This very large rate explains why its decomposition remains important even in concentrated acids, where the amount of tetrahedral intermediate which actually exists as zwitterion must be extremely low.
The crystal structure of 1-O-acetyl-17-p-bromobenzoylsideritol, a diterpenoid of the ent-atisane class
Authors: Ayer William A. , Forsythe Jo-Ann H. , Delbaere Louis T. J. , Delbaere Caroline U.
Published: May 2006

The crystal structure of 1-O-acetyl-17-p-bromobenzoylsideritol (ent-1α-acetoxy-16β-hydroxy-17-p-bromobenzoyloxyatis-13-ene) is presented. This crystal structure establishes unequivocally the structure of sideritol (1).
Conformational preferences about both exocyclic carbon–carbon bonds in some phenyl derivatives of ethane, propene, and 4-picoline
Authors: Schaefer Ted , Kruczynski Leonard J. , Krawchuk Bert , Sebastian Rudy , Charlton James L. , McKinnon David M.
Published: May 2006

The 1H nmr spectra in solution of 1-R-(3,5-dibromophenyl) ethanes (R = CH3, C2H5, n-C3H7 to n-C6H13, OH, F, Br), of 1-amino-2-(3,5-dichlorophenyl) ethane, of 3,5-dichloroallylbenzene, and of 4-(3,5-dibromobenzyl) pyridine are analyzed at 305 K. For the ethane derivatives, the populations of anti and gauche conformers are derived from the vicinal proton–proton coupling constants. The conformation about the C1—Cα bond in both gauche and anti forms is discussed in terms of long-range couplings to the ring protons and some approximate barriers about this bond are suggested for both conformers. Greater rigidity exists in the gauche than in the anti conformations. In some cases the measurements are compared with extensive molecular orbital calculations, for example, for phenethylamine. The low-energy conformations and the barriers about the C1—Cα bond are deduced for the allyl and pyridyl compounds.
Pyrrole chemistry. XXII. A "one-pot" synthesis of some 4-acylpyrrole-2-carboxaldehydes from pyrrole
Authors: Anderson Hugh J. , Loader Charles E. , Poster Aidan
Published: May 2006

The Vilsmeier–Haack intermediates formed from pyrrole and from 1-methylpyrrole may be acylated under normal Friedel–Crafts conditions. Hydrolytic work-up then gives 4-acylpyrrole-2-carboxaldehydes in good yield. The methoxide/methanol treatment of the 4-trichloroacetylated intermediate leads to methyl 2-formylpyrrole-4-carboxylate. These are all "one-pot" syntheses from pyrrole. The formyl group has been removed from several of the products thus affording some 3-acylpyrroles in two operations.
Use of a bacteriophage to depolymerize a polysaccharide to an oligosaccharide; comparison of the 1H and 13C nuclear magnetic resonance spectra of the polymer and its hexasaccharide repeating unit
Authors: Dutton Guy G. S. , Savage Angela V. , Vignon Michel
Published: May 2006

A β-D-galactosidase associated with bacteriophage [Formula: see text] has been used to depolymerize the capsular polysaccharide of Klebsiella serotype K18 into the hexasaccharide corresponding to one repeating unit of the polymer. The nmr spectra of the polymer and of the oligosaccharide are comparable, leading to the conclusion that the conformations in solution of the repeating unit of the two substances are similar.
The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane
Authors: Booth Harold , Everett Jeremy Ramsey
Published: May 2006

The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane has been assessed by (a) direct integration of signals due to equatorial and axial methyl carbons in the 13C nmr spectrum at 172 K and (b) by measurement of the 13C chemical shifts of C-1 and C-4 in the spectrum at 300 K. It is concluded that a 13C isotope effect on the position of the degenerate equilibrium in cis-1,4-dimethylcyclohexane is either nonexistent, or is too small to be detected by methods of analyses employed. The 13C nmr data incidental to the study (chemical shifts, coupling constants, spin–lattice relaxation times, nuclear Overhauser enhancements, and 1-bond isotope shifts) are recorded for the title compound and its trans-isomer.
The action of hypochlorite on m-cresol. Part 2. Muconic acid derivatives
Authors: Strunz George M. , Kakushima Masatoshi , Gibson Alan D. , McCulloch Archibald W. , White Peter S.
Published: May 2006

Two new crystalline products were isolated from the chlorination of m-cresol in cold alkaline solution. These products have been identified as E,Z-2-chloro-5-methyl muconic acid and 5Z-carboxymethylene-3-chloro-4-methyl-2(5H) furanone.
Total synthesis of (−)-phytuberin
Authors: Findlay John A. , Desai Dixit N. , Lonergan Greg C. , White Peter S.
Published: May 2006

An efficient, total synthesis of the phytoalexin (−)-phytuberin 10 is described starting from (−)-carvone 1.
Nitrogen- and sulfur-containing models for metallo-enzymes. Part I. Synthesis and physical studies of 2(2-pyridyl)-1,3-dithioalkyl-2-propanols, 2(2-pyridyl)- and 2(2-imidazolyl)-1,3-dimercapto-2-propanols
Authors: Curtis N. J. , Brown R. S.
Published: May 2006

Several compounds of the title class have been synthesized as small-molecule analogues for the metal-binding sites in such biochemical systems as ADH. The ligands containing pyridine and two thioethers do not bind divalent metals (Co2+, Zn2+, Cu2+, Ni2+), strongly suggesting that thioethers are poorly chelated. However, the analogues containing free SH groups bind divalent metals very strongly, producing complexes with limited solubility at pH values in excess of 6. Titration of the latter ligands in the presence of 1 equiv. Zn2+ indicates the consumption of 3 equiv. OH− by pH 6, one for the [Formula: see text] ionization, and one for each S—H bound to Zn2+. On the basis of these data the resulting complexes are considered to neutral bis-thiolates. The relationship of these data to the state of ionization of the Zn2+-cysteine SH's in ADH is discussed.
The interaction of a soil fulvic acid with precipitating hydrous ferric oxide at pH = 6
Authors: Langford Cooper H. , Wong Shui Mui , Underdown Alan W.
Published: May 2006

A kinetic method of analysis which distinguishes Fe(II) from Fe(III) and Fe(III) forms of various labilities from each other is based on spectrophotometric monitoring of the reaction of Fe(II) with ferrozine. Reduction of Fe(III) with hydroxylamine hydrochloride allows the single colourimetric reagent to detect all forms of Fe. The method is applied to study of the effects of a well characterized soluble soil organic acid sample, a fulvic acid, on the speciation of Fe(III) under conditions (pH = 6) where Fe(III) forms a colloidal hydrous oxide in the absence of fulvic acid. The effect of fulvic acid is to greatly increase the lability of Fe(III) compared to that in a hydrous oxide colloid. However, ultrafiltration and light scattering experiments indicate that the Fe(III) – fulvic acid species is larger than the hydrous ferric oxide colloid particles. Kinetic studies in the absence of hydroxylamine hydrochloride show that fulvic acid can act as a reducing agent for iron in the presence of an Fe(II) complexing agent like ferrozine but neither kinetic studies with an Fe(III) reagent nor Mössbauer spectra suggest significant initial presence of Fe(II) in the aged Fe(III) – fulvic acid samples.
Stability of the 1,4-bis(2′-haloethyl)-1,4-diazabicyclo[2.2.1]heptane dication
Authors: Pettit George R. , Gieschen Donald P. , Pettit William E. , Rawson Thomas E.
Published: May 2006

Certain derivatives of the 1,4-bis(2′-haloethyl)-1,4-diazabicyclo[2.2.1]heptane dication system ranging from dibromide 2b to ethanesulfonate 2g were found to be quite stable under essentially neutral conditions. A very convenient synthesis of 1,4-bis(2′-chloroethyl)-1,4-diazabicyclo [2.2.1]heptane dichloride (2d) was developed in order to compare the relative stability of this system with that of dibromide 2b. While dichloride 2d was found to be less stable than dibromide 2b, it did prove very useful for rapid preparation of other anion derivatives such as dinitrate 2e, dihydrogen dimaleate 2h, diperiodate 2i, tetrachloroplatinate 2j, and tetrachloroaurate 2k. At temperatures near 150 °C, or upon ignition (in the open) or gentle shock, diperiodate2i detonated violently. The ethanesulfonate 2g was obtained from diperchlorate 2a employing an ion-exchange procedure. Stabilization of dication 2 provides an unusual heterocyclic system with exceptional anticancer properties.
One-stage glycosylation using protected glycose: the synthesis of O-β-D-glucopyranosyl-(1 → 3)-O-[β-D-glucopyranosyl-(1 → 6)]-D-glucopyranose
Authors: Koto Shinkiti , Inada Shigeru , Yoshida Toyosaku , Toyama Miyako , Zen Shonosuke
Published: May 2006

The one-stage β-glucosylation of benzyl 3-O-acetyl-2,4-di-O-benzyl-α-D-glucopyranoside (1) with 2,3,4,6-tetra-O-benzyl-α-D-glucopyranose (2) using a mixture of p-nitrobenzenesulfonyl chloride, silver trifluoromethanesulfonate, and triethylamine, followed by deacetylation, gave benzyl O-(2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl)-(1 → 6)-2,4-di-O-benzyl-α-D-glucopyranoside (3). The disaccharide derivative 3 was then subjected to the β-glucosylation, followed by catalytic hydrogénation, to afford O-β-D-glucopyranosyl-(1 → 3)-O-[β-D-glucopyranosyl-(1 → 6)]-D-glucopyranose (4). The key intermediate 1 was prepared from D-glucose by way of a Fischer reaction, triphenylmethylation, a controlled benzylation, and detriphenylmethylation.
Evidence for the generation of free hydroxyl radicals from certain quinone antitumor antibiotics upon reductive activation in solution
Authors: Lown J. William , Chen Hsiao-Hsiung
Published: May 2006

The nature of the reactive oxygen species generated from certain quinone antitumor antibiotics upon reductive activation in aqueous solution was investigated. A kinetic criterion was employed involving the relative rate of trapping of hydroxyl and formate radicals by the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in conjunction with epr spectroscopy. By comparison with a system involving the photolysis of hydrogen peroxide as a standard free hydroxyl system it was concluded that at pH 7 and at 37 °C reductive activation of adriamycin, daunorubicin, mitomycin B, mitomycin C, and streptonigrin gives rise to free hydroxyl radicals in direct contrast with, for example, the photolysis of quinones in solution.
Synthesis and structural studies of iron(II) and iron(III) sulfonates
Authors: Haynes John S. , Sams John R. , Thompson Robert C.
Published: May 2006

The iron(II) sulfonates Fe(CF3SO3)2 and Fe(p-CH3C6H4SO3)2 have been prepared and on the basis of vibrational and electronic spectra and magnetic and MÖssbauer data have been assigned a layer lattice structure involving hexacoordinated iron(II) and terdentate bridging anions. The FeO6 chromophore in these compounds is distorted by a trigonal elongation along the C3 axis. Fe(CH3SO3)2 has been obtained in two isomeric forms, one having a trigonal elongation of the FeO6 chromophore, the other a trigonal compression. No structural isomerism has been found for the other iron(II) sulfonates; however, evidence for such isomerism in methanesulfonates of cobalt(II) and zinc(II) is presented. While Fe(CF3SO3)2 and Fe(p-CH3C6H4SO3)2 appear to be magnetically dilute the presence of antiferromagnetic coupling in both forms of Fe(CH3SO3)2 is indicated. The iron(III) sulfonates, Fe(CF3SO3)3, Fe(p-CH3C6H4SO3)3, and Fe(CH3SO3)3, have been prepared and all three are magnetically concentrated exhibiting magnetic moments which are significantly less than 5.92 BM and which decrease with decreasing temperature.
Substituent effects on the spectral behavior and synthesis of mercury 1,5-diarylthiocarbazonates
Authors: Chu Nori Y. C. , Goldstein Steven A. , Keehn Philip M.
Published: May 2006

Symmetric and unsymmetric substituted 1,5-diarylthiocarbazones, and their mono- and bismercury complexes, were synthesized for spectral analysis. The first singlet–singlet transition of the mercury complexes was determined and the spectral shift produced by trifluoromethyl substitution was compared with that caused by different substituents in similar complexes. The large magnitude of the hypsochromic shift produced by the trifluoromethyl substituent can be explained by concerted steric and inductive effects, while the smaller bathochromic shift induced by the methoxy substituent is a result of opposing steric and electronic effects. In the trifluoromethyl substitution, a hypsochromic shift caused by steric influences was found to be 500 cm−1 in the photochromic unactivated state, and 250 cm−1 in the photochromic activated state. A similar shift caused by inductive influences was found to be 750 cm−1 in the photochromic unactivated state, and 600 cm−1 in the photochromic activated state. The smaller spectral shift observed in the photochromic activated state is consistent with the elucidated structure of the unsymmetric 1,5-diarylthiocarbazone, 6d, which was shown that the trifluoromethyl substitution was on the phenylazo portion of the molecule by chemical and spectral studies.
Influence of stereochemistry, screening, and deuteration of long and short intramolecular easily polarizable hydrogen bonds on their infrared continua
Authors: Brzezinski Bogumil , Zundel Georg
Published: May 2006

HClO4 salts of N,N′-tetramethylalkanes (compounds 1–6) and of N,N′-tetraalkyl-o-xylildiamines (compounds 7–11) and HAuCl4 salts of N,N′-tetramethyl-o-xylildiamine-di-N-oxide (compound 12) and of o-xylildipiperidyl-di-N-oxides (compounds 13–14) were studied by nmr and ir spectroscopy. It is shown that in the compounds 3, 4, 5, and 7–11, long intramolecular [Formula: see text] hydrogen bonds with large proton polarizability and in compounds 12–14, short intramolecular [Formula: see text] hydrogen bonds with large proton polarizability are formed. The study of the compounds 1–6 shows that the most favorable conditions for the formation of the intramolecular easily polarizable hydrogen bonds occur with compound 4, i.e., if these hydrogen bonds are present in the 7-membered rings. In the case of compounds 7–14 it is shown that the continua usually observed with easily polarizable hydrogen bonds vanish when these bonds become screened from their solvent environments. Then, instead of continua only bands of the fundamental transitions are observed, with the long [Formula: see text] bonds in the region 2800–1800 cm−1 and with the short [Formula: see text] bonds in the region 1200–850 cm−1. This result demonstrates that for the occurrence of the ir continua, the interaction of the easily polarizable hydrogen bonds with their solvent environments is absolutely necessary. Furthermore, it is shown with the long as well as the short hydrogen bonds that the intensity of the continua decreases strongly with deuteration, demonstrating that in both cases the deuteron polarizabilities are much smaller than the proton polarizabilities of the hydrogen or deuterium bonds, respectively. From this observation it is concluded that the proton potentials of these structurally symmetrical hydrogen bonds are considerably deformed by their molecular surroundings.
Some comments on Linnett Double Quartet theory
Authors: Jensen William B.
Published: May 2006

The recent critical evaluation of Linnett Double Quartet theory by Langler, Trenholm, and Wasson is critically examined and found to be based on misrepresentations of the theory's basic postulates and its use in predicting chemical reactivity. Various ways in which Linnett's original work can be profitably extended are suggested and briefly discussed.
The preparation of amino sugars and branched-chain sugars by palladium-catalyzed, allylic substitution of alkyl hex-2-enopyranosides
Authors: Baer Hans H. , Hanna Zaher S.
Published: May 2006

Ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (1) in the presence of triphenylphosphine and a catalytic amount of tetrakis(triphenylphosphine)palladium(0) reacted with a variety of amines or with reactive methylene compounds to give high yields of products aminated or C-alkylated, respectively, in an allylic position. Some analogous experiments were performed using the β-D-erythro anomer (2) and the α-D-threo epimer (3) of 1. The constitutions and configurations of the new products were established by means of mass spectra, 13C- and 1H-nmr spectra, and optical rotation data. The reactions of 1 were found to be highly regio- and stereoselective, giving almost exclusively 4-substituted 2-enopyranosides with retention of configuration, except in the case of dibenzylamine which produced a mixture of the corresponding enoside and its 2-substituted, 3,4-unsaturated isomer having the α-D-threo configuration. The reactions of 2 appeared slightly less selective although they, too, furnished mainly 4-substituted 2-enopyranosides with retention of configuration. Regioselectivity was low or lacking in two C-alkylations performed with 3, which gave mixtures of 4-substituted 2-enosides and 2-substituted 3-enosides. Some aspects of conformation and optical rotation in enopyranosides are discussed.
Separation of short fibers from bulk chrysotile asbestos fiber materials: analysis and physico-chemical characterization.
Authors: Jolicoeur Carmel , Roberge Pierre , Fortier Jean-Luc
Published: May 2006

The aqueous sedimentation behavior of commercial chrysotile asbestos fibers has been investigated and a simple method for separating short fibers (90% < 2 μm) could be devised based on selective sedimentation. Chemical, X-ray structural, and differential thermal analyses show that the short fibers have chrysotile composition and structure, with lower brucite (Mg(OH)2) and iron contents than the bulk fibers. The length distribution of these short fibers exhibits a maximum at 0.3 μm and a width-at-half-height of ∼0.5 μm. Surface adsorption studies yield specific areas of 20 and 28 m2/g for N2 and H2O respectively. Because of their finely divided state and narrow length distribution, such fibers should be well suited for a variety of physico-chemical, chemical, and biological investigations on chrysotile fibers.
Mechanism of 2-quinizarinsulphonic acid reduction on a mercury electrode
Authors: Capitan F. , Guiraum A. , Vilchez J. L.
Published: May 2006

The reduction of the 1,4-dihydroxyanthraquinone-2-sulphonic acid (quinizarinsulphonic acid) at a dropping mercury electrode has been investigated. The reduction takes place in two monoelectronic steps and show E1/2 values vs. sce (E1/2)1 = −0.380 V and (E1/2)2 = −1.045 V at pH 4.60. The first wave is diffusion controlled, while the second wave is kinetically controlled. The reagent captures one electron and one proton to form the semiquinonic system. The semiquinone is dimerized. The dimer captures one electron and one proton, per molecule, to form the hydroquinone. The reaction orders, together with Tafel's slopes, have been calculated.
Polarisation cathodique en milieu alcalin des alliages Nb–Co
Authors: Umetsu Y. , Piron D. L. , Bélanger G.
Published: May 2006

NbCo alloys were prepared and their composition characterized by optical microscopy. These alloys were evaluated for their electrochemical activity towards the hydrogen evolution reaction (HER) at 25 °C in a 25% KOH solution. The alloys between 20 and 70wt% Co showed an increased activity compared to their parent metals. However the activity is below the one observed for pure Ni. As for the NbNi alloys, the NbCo undergo some surface degradation under prolonged (6 h) cathodic polarization at 400–700 mA cm−2. This disintegration of the surfaces is observed for alloys below 50% in Co. Above this proportion, the alloys remain stable towards the RDH. This degradation is associated with the presence of the δ phase in the alloy: this phase is the solid solution of Nb in the alloy.
γ- and δ-epoxy sulfones. Formation of different ring-sized products upon reaction with CH3MgI or LiN[CH(CH3)2]2
Authors: Decesare John M. , Corbel Bernard , Durst Tony , Blount John F.
Published: May 2006

γ-Epoxy sulfones in which the epoxide function is terminal yield cyclopropylmethanol derivatives on reaction with methyllithium or lithium diisopropylamide. In contrast, treatment of these epoxides with two equivalents of CH3MgI gives only cis-3-phenylsulfonylcyclobutanols. The cis-relationship between the OH and sulfonyl groups was proven in one instance by an X-ray structure determination. Internal γ-epoxy sulfones yield cyclopropylmethanols with all bases studied. All δ-epoxy sulfones studied furnished cis-3-phenylsulfonylcyclopentanols upon reaction with the Grignard reagent. These same epoxides gave either cyclopentanols or noncyclic products upon reaction with LDA; no cyclobutane ring containing products were obtained contrary to the expectations based on Stork's results with the corresponding epoxy nitriles (ref. 2). The mechanism of the Grignard-mediated reaction involves epoxide opening by iodide ion, α-sulfonyl Grignard formation, and, finally, cyclization. When LDA or CH3Li is used the products are formed by an intramolecular SN2 opening of the epoxide by an α-lithio sulfone.
Solvent extraction of anionic surfactants. The stearic acid–metal triethylenetetramine chelate ion-pair
Authors: Jeffries David , Fresco James
Published: May 2006

The solvent extraction behaviour of nickel(II) and copper(II) chelates of triethylenetetramine with stearic acid in a cyclohexane–isobutanol mixed solvent has been investigated. The results indicate that carboxylic acid selectivity by charged chelate extraction is based on partition constant differences rather than ion-pair formation constants. A computational technique for determination of partition and dimerization constants of high molecular weight carboxylic acids has been tested.
Enzymes in organic syntheses. 19. Evaluation of the stereoselectivities of horse liver alcohol dehydrogenase; catalyzed oxidoreductions of hydroxy- and ketothiolanes, -thianes, and -thiepanes
Authors: Jones J. Bryan , Schwartz Harold M.
Published: May 2006

The specificity of horse liver alcohol dehydrogenase (HLADH) with respect to unsubstituted five-, six-, and seven-membered ring 3- and 4-thiaketone and -thiaalcohol substrates has been examined. The enzyme is found to have a broad tolerance of the structural variations within this series. HLADH also exhibits encouraging (up to 46%) enantiotopic and enantiomeric specificity in preparative-scale reduction and oxidation reactions of the heterocyclic ketones and alcohols respectively.
Quantum yield of solution photolysis of bicyclo[3.1.0]hexan-3-one and derivatives
Authors: Kopecky Karl R. , Gomez Rodrigo Rico
Published: May 2006

The quantum yields for photolysis of 0.25 M solutions of bicyclo[3.1.0]hexan-3-one, 1,5-dimethylbicyclo[3.1.0]hexan-3-one, and tricyclo[4.3.1.0]decan-8-one in pentane or cyclohexane with 313 nm light are 0.44, 0.52, and 0.32, respectively.
Membrane transport systems. I. Synthesis and characterization of carriers for a proton driven alkali metal cation pump
Authors: Frederick Laurel A. , Fyles Thomas M. , Gurprasad Narine P. , Whitfield Dennis M.
Published: May 2006

The synthesis of a series of macrocyclic polyethers (crown ethers) of interest as carriers for the countertransport of metal ions and protons across artificial membranes is described. Thallium mediated cyclization of oligoethyleneglycol diiodides with (+)–N,N,-N′,N′-tetramethyltartaramide gave 15-crown-5 and 18-crown-6 diamides which were converted, via the diacids and anhydrides, to crown ether monoamides bearing long chain alkyl groups (octyl, tetradecyl, and octadecyl). The alkali metal salts and complexes of these carriers are soluble in nonpolar solvents and alkali metal ions are extracted from aqueous solutions into chloroform solutions of the carriers. Acidity constants and stability constants for complex formation in methanol/water (90:10 v/v) solutions have been determined using a combination of ion selective electrode and pH-metric techniques. Deprotonation of the ligand carboxylic acid group results not only in more stable complexes but also more selective complexation. Implications for membrane transport are discussed.
Ion–molecule equilibria measurements by high pressure mass spectrometry. Some recent advances in concepts and technique
Authors: Sunner Jan , Magnera Tom F. , Kebarle Paul
Published: May 2006

Two efforts to improve ion–molecule equilibrium measurement methodology and instrumentation are described. The first part deals with dissociation of ions AB+ in the mass analysis system of the mass spectrometer. To measure the equilibrium constant of the association equilibrium A+ + B = AB+ one needs to sample both A+ and AB+. The AB+ ions escaping from the high pressure ion source have a thermal energy distribution. A fraction fex has internal energy which is higher than the dissociation energy for AB+ → A+ + B. This fraction can dissociate before detection. A theoretical analysis for the system K+(H2O)n is made which is based on calculated vibrational frequencies and geometries of K+(H2O)n. From these fn,ex can be evaluated. RRKM calculations also provide rates for the dissociation of the AB+ex. It is found that severe dissociation during mass analysis can occur if the experimental conditions are not selected carefully. Results for H+(H2O)2 and (C6H6+)2 are also presented. Measurements of the association equilibria must be done at low pressures of B in the presence of high pressure of an inert bath gas.By connecting the repeller to a gated radio frequency source, pulses of RF can be applied in the high pressure ion source. These increase the internal energy of the ions. If the reaction system was at equilibrium a displacement of the equilibrium is produced by the RF pulse. The system relaxes to the original state after the RF has been shut off. Kinetic measurements of the relaxation times provide rate constants form which an equilibrium constant not affected by ion mass discrimination can be determined. Fast reaction kinetics also can be studied with this technique.
Effect of organic compounds on electrolyte chemical potential in aqueous solutions at various temperatures
Authors: Mohilner David M. , Kakiuchi Takashi , Taraszewska Joanna
Published: May 2006

Data are reported on the concentration of Na2SO4 required to hold its chemical potential equal to its value in a 0.10045 m solution in pure water for aqueous solutions containing 2-butanol and 1-propanol at six different temperatures. The data were obtained from emf measurements on a galvanic cell without liquid junction containing a sodium reversible glass electrode and a 2-phase lead amalgam – lead sulfate electrode. The results of the measurements are interpreted in terms of the water structure making properties of the organic compound.
Electrophilic cyclization of an olefinic β-keto ester
Authors: Alderdice Margot , Weiler Larry
Published: May 2006

Benzeneselenenyl chloride and aluminum chloride or benzenesulphenyl chloride and silica gel initiate an electrophilic cyclization of methyl 7-methyl-3-oxo-7-octenoate to cyclohexyl derivatives. These products of the cyclization reaction have been converted into intermediates of potential use in the synthesis of unusual carotenoids.
The synthesis of uridine diphosphate N-acetylhexosamines and uridine 5′-(2-acetamido-2-deoxy-α-D-mannopyranosyluronic acid diphosphate)
Authors: Yamazaki Tatsumi , Warren Christopher D. , Herscovics Annette , Jeanloz Roger W.
Published: May 2006

2-Methyl-(2-acetamido-3,4,6-tri-O-acetyl-l,2-dideoxy-β-D-mannopyrano)-[2,1-d]-2-oxazoline was efficiently converted into 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl phosphate, by treatment with dibenzyl phosphate, followed by catalytic hydrogenolysis of the benzyl groups. Similarly, 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl phosphate and -galactopyranosyl phosphate were synthesized from the respective peracetyl oxazolines. In each case, the procedures for preparing the oxazoline, and conversion into the glycosyl phosphate, were modified to give high yields of pure products. 2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl phosphate was coupled with 2′,3′-di-O-acetyluridine 5′-monophosphate by a modification of the mixed anhydride procedure, to give 2',3'-di-O-acetyluridine 5′-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl diphosphate), which was readily purified by preparative tic and O-deacetylated to give "uridine diphosphate N-acetylmannosamine" in high yield. Similarly, uridine 5′-(2-acetamido-2-deoxy-α-D-glucopyranosyl- and -galactopyranosyl diphosphates) were synthesized by rapid, efficient procedures, not involving ion-exchange chromatography. Uridine 5′-(2-acetamido-2-deoxy-α-D-mannopyranosyl diphosphate) was converted into uridine 5′-(2-acetamido-2-deoxy-α-D-mannopyranosyluronic acid diphosphate), required for biosynthetic studies, without the preparation of a special platinum catalyst. All the synthetic uridine diphosphate sugars were characterized by optical rotation, 1H nmr spectrum, and elemental analysis.
Lactonisation par ouverture, en milieu acide, de cyclopropanes γ-carboxyliques
Authors: Chiche Laurent , Christol Henri , Coste Jacques , Plénat Françoise
Published: May 2006

The opening of cyclopropanes, bearing a carboxyl group, in formic acid leads to complex mixtures containing less than 30% lactones formed by an intramolecular nucleophilic process during the reaction. We show that the relative stereochemistry of the carboxyl group and the cyclopropyl group does not determine the proportion of lactone formed. On the other hand, when the opening is performed by a Lewis acid (BF3−etherate), lactonisation is the major route (84%) and although the mechanism of intramolecular cyclisation is not yet clear, this reaction provides a good route to lactones. [Journal translation]