bluuebunny/crossref_metadata_2025 huggingface dataset:
The acid-catalyzed rearrangement of methyl 3,4-O-benzylidene-β-D-ribopyranoside
Authors: Clode David M.
Published: May 2006

Methyl 3,4-O-(R)-benzylidene-β-D-ribopyranoside (2) rapidly rearranged, under anhydrous acidic conditions, to give methyl 2,3-O-(R)-benzylidene-β-D-ribopyranoside (6). Further rearrangement of 2 and 6 gave the (S)-isomers 4 and 8, an equilibrium mixture of the four pyranoside acetals 2, 4, 6, and 8 resulting. At higher acid concentrations, the rearrangement proceeded, with ring contraction, to give the diastereomeric forms of methyl 2,3-O-benzylidene-β-D-ribofuranoside (11 and 13) as the sole product. Treatment of methyl 3,4-O-(S′)-benzylidene-β-D-ribopyranoside (4) with acid resulted in the immediate formation of the equilibrium mixture of pyranoside acetals. On increasing the acid concentration this mixture again underwent ring contraction to give the diastereomers 11 and 13 as the final product. The rearrangement of 2 and 4 was monitored by following the change in signals in the benzyl proton region of the nmr spectrum.
13C magnetic resonance studies 70. The behavior of bicyclo[2.2.2]octenone under strongly basic conditions. A competition between retro Diels–Alder and Haller-Bauer-cleavages
Authors: Cheng A. K. , Stothers J. B.
Published: May 2006

As a test for possible competitive α- and β-enolization in bicyclic ketones the behavior of bicyclo[2.2.2]octenone in t-BuO−–t-BuOH at 185 °C has been examined. The major reaction (∼90%) involves Claisen condensation followed by retro Diels-Alder elimination of ethylene and Haller–Bauer cleavage. All acidic and phenolic components, accounting for 90% of the product, have been identified and characterized, primarily by their 13Cmr spectra.
Summary of gas phase acidity measurements involving acids AH. Entropy changes in proton transfer reactions involving negative ions. Bond dissociation energies D(A—H) and electron affinities EA(A)
Authors: Cumming J. B. , Kebarle P.
Published: May 2006

The complete ladder of ΔG10 determinations obtained from measurements of some 110 gas phase proton transfer equilibria A1− + A2H = A1H + A2− involving some 60 acids AH and connecting to the standard acid HCl is given. Evaluation of the entropy changes leads to values for the deprotonation energies ΔHD0 and ΔGD0 (at room temperature) corresponding to the gas phase process AH = A− + H+; ΔHD0 = D(A—H) − EA(A) + 313.6 kcal/mol. Comparison of the present data with literature determinations of the bond dissociation energies and electron affinities shows agreement within 2 kcal/mol. Some experimentally determined entropy changes ΔS10 are compared with the theoretically calculated values.
Metal complexes as antioxidants. V. Inhibition of hydrocarbon autoxidation by cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids
Authors: Chenier J. H. B. , Howard J. A. , Tait J. C.
Published: May 2006

Liquid-phase reactions of alkylperoxy radicals with cupric complexes of dialkyldithiophosphoric and dialkyldithiocarbamic acids have been examined. These complexes have been shown to be extremely efficient peroxy radical scavenging antioxidants for hydrocarbon autoxidation. Initial rates of oxygen absorption by typical hydrocarbons were extremely slow implying inhibition rate constants > 106 M−1 s−1. The initial rate of disappearance of the dithiocarbamate was equal to the rate of chain initiation (Ri) whereas the rate of disappearance of the dithiophosphate was twice as fast as Ri. In both cases the rate of complex disappearance slowed down as the complex was consumed. Autoxidation of styrene commenced as soon as the complex disappeared while cumene did not absorb oxygen for a considerable length of time after complex destruction. Cumylperoxy radicals were converted to α-cumyl alcohol, α-methylstyrene, and acetophenone by reaction with these complexes and the copper ions were eventually precipitated as copper sulphate. In the case of the dithiocarbamate three intermediate cupric complexes were detectee by epr spectroscopy.
Resonance Raman labels: spectroscopic studies on cis- and trans-4-benzylidene-2-phenyl-Δ2 -oxazolin-5-one and an isotopically substituted analog
Authors: Kumar K. , Phelps D. J. , Carey P. R.
Published: May 2006

The absorption and preresonance Raman spectra of cis- and trans-4-benzylidene-2-phenyl-Δ2-oxazoIin-5-one are reported. Although steric considerations suggest that the π electron pathway in the cis isomer is considerably distorted compared to the trans isomer, the Raman and absorption spectra of the two isomers are strikingly similar. Preresonance Raman excitation profiles for the cis and trans isomers indicate that the main features in the Raman spectra owe their intensity to coupling to the 360 nm absorption band present in both isomers. It is proposed that both the electronic dipole transition responsible for this absorption and the vibrational modes giving rise to the intense Raman bands are localized in the —C=C—N=C—Ph part of the molecule. Thus the main Raman and absorption bands are insensitive to isomerization in the benzylidene portion. Support for a localized electronic transition, polarized along the —C=C—N=C—Ph long axis, comes from Raman depolarization ratio (ρ) measurements which show that ail intense Raman features in both cis and trans isomers have ρ ∼ 0.33. Further support comes from ir and resonance Raman spectra of trans-4-(4-dimethylamino-3-nitrobenzylidene)-2-phenyloxazolin-5-one substituted either with 13C in the 4 position, or with 15N, in the oxazolinone ring. These spectra indicate that the main Raman feature seen in all 4-benzylidene-2-phenyloxazolinonesat 1561 cm−1 is a symmetric stretching mode associated with the —C=C—N=C— chain and that this feature has some C=N stretching character. The substitution experiments also show that the weak 1654 cm−1 Raman band has a high degree of C=C stretching character and may represent an essentially antisymmetric mode from the C=C—N=C moiety. The preresonance Raman excitation profiles show that the intensity enhancement follows an FB2 type dependence. The utility of the Raman spectrum as a probe for the chromophore responsible for the electronic transition in a highly conjugated system is discussed.
Nitration of 4-tert-butyl-o-xylene in acetic anhydride. Formation and rearomatization of adducts
Authors: Fischer Alfred , Teo Khay Chuan
Published: May 2006

Nitration of 4-tert-butyl-1,2-dimethylbenzene in acetic anhydride gives trans-1-tert-butyl-3,4-dimethyl-4-nitro-1,4-dihydrophenyl acetate (6), trans-1-tert-butyl-3,4-dimethyl-4-nitro-1,4-dihydrophenol, 2-tert-butyl-4,5-dimethylphenyl acetate, 5-tert-butyl-2-methylbenzaldehyde, 4-tert-buty]-1,2-dimethyl-5-nitrobenzene, and 4-tert-butyl-1,2-dimethyl-6-nitrobenzene. 2-tert-Butyl-4,5-dimethylphenyl acetate and 3,4-dimethylphenyl acetate are the major products of solvolysis of 6 in moist acetic acid. Both of these compounds are likely formed via the cation generated by ionization of the nitro group. Under more acidic conditions 5-tert-butyl-2-methylbenzaldehyde and 4-tert-butyl-1,2-dimethyl-6-nitrobenzene, formed via the cation generated by acid-catalysed loss of acetate, become dominant, the balance between these products being controlled by the basicity of the solvent. More basic solvents deprotonate the cation to a triene, a key step in the formation of the aldehyde, at a competitive rate with the nitro group migration.
Vapour pressures of aqueous solutions of (Ag, Tl, Cd)NO3 at 98.5 °C. I. Brunauer–Emmett–Teller isotherms
Authors: Sangster James Malcolm , Abraham Marie-Christine , Abraham Maurice
Published: May 2006

Vapour pressures of aqueous solutions of the mixed melt AgNO3 + TlNO3 + Cd(NO3)2 have been measured at 98.5 °C by the static technique. The Ag/Tl mole ratio was fixed at 1.06, and the mole fractions Cd/(Ag + Tl + Cd) of Cd in the melt were 0, 0.05, 0.075, 0.10, and 0.125. Adapted BET isotherms and their constants were obtained for each of the five melt mixtures. It has been shown, in the present study, from the BET equation itself, and verified experimentally, that certain Systems can give rise to a 'crossover point', that is, a reversal of sign of the deviation from Raoult's law. The BET constants of the systems conform to simple additivity rules. The water concentration range over which the BET equation is valid is unexpectedly wide.
The dielectric relaxation of some diols in p-dioxane solution
Authors: Crossley J.
Published: May 2006

Dielectric constant and loss data at up to nine microwave frequencies have been obtained for 1-butanol, 1,4-butanediol, 1,7-heptanediol, 1,8-octanediol, 1,10-decanediol, and 1,12-do-decanediol at 25 °C, and for 1,6-hexanediol at 15, 25, 40, and 55 °C, in p-dioxane. In each case the dielectric dispersion is adequately described by a Cole-Cole distribution. The relaxation times for the diols are almost independent of the length of the alkyl group. An intramolecular relaxation process appears to be primarily responsible for the dielectric absorption.
Electrolytes in mixed solvents: indium trichloride in water–dimethylsulfoxide mixtures
Authors: Campbell Alan N.
Published: May 2006

This paper is concerned with the investigation of the conductances (some 160 determinations) of potassium chloride and of indium trichloride in water-dimethylsulfoxide mixtures. The behaviour of potassium chloride in these mixtures is practically identical with its behaviour in water, up to 50 wt% DMSO. Thus Walden's rule is followed very closely, implying that the only effect on the speeds of the ions is that of viscosity. The behaviour of indium trichloride is very different. The conductance increases rapidly with dilution, in the dilute region, and it is time dependent. It is practically certain that the ionization of indium trichloride takes place in steps and that, in dilute solution, progressive hydrolysis occurs. By extrapolating the measurements as a straight line, below concentrations of 0.01 N, an approximation to the limiting value of Λ is obtained.
State equation parameters of three homologous series: tetraalkyltin compounds, tetraalkoxysilanes, trialkylamines
Authors: Philippe Robert , Delmas Geneviève , Couchon Michèle
Published: May 2006

Expansion coefficients and thermal pressure coefficients γ have been measured at 25 °C for members of the following series of compounds: (1) SnR4 (R = CH3, C2H5, C3H7, C4H9, C12H25). (2) Si(OR)4 (R = being the same except for C6H13 and C8H17, instead of C12H25). (3)NR3, R from C2H5 to C12H25 except C9H19 and C11H23; two NR3′ where R′ is a branched (br) alkyl radical isopentyl and isooctyl and N(CH3)2(C12H25). (4) n-C7H16, 3-3-diethylpentane (3,3-DEP), dimethylsulfoxide (DMSO), 2,2,4,4,6,8,8-heptamethylnonane (br-C16). The variation of γ between 25 and 80 °C is obtained for the following compounds: br-Q6, N(isopent)3 and N(Dec)3. The comparison of the cohesive energies for the different members of a series or from one series to another is made with P* rather than with γ. [Formula: see text]. For the three series the limiting values, when n increases, of the pressure reduction parameter P* and of the expansion coefficients are very similar. The P* do not have regular values for the NR3, SnR4, and Si(OR)4 series for low values of the molecular weights. One explanation of these irregularities is the different shape of the molecules. The surface to volume ratios of the different molecules are calculated with a spherical model or a cylindrical model. Values of cohesive energies per unit surface P*/s are compared. P*/s for the linear and branched alkanes are on the same curve while the P* were not. However, no similar smoothing is accomplished for the lower members of the other series. The high values of P*/s for the sterically hindered SnEt4, SnPr4, and 3,3-DEP seem to indicate that measurements of y and P* can be a method to evaluate steric hindrance in the different members of a series. Report is made of calorimetric results on the same sterically hindered compounds in solution. Higher P*'s may also come from increased polarity in the lower members of a series.
Cyanoethylations and Michael additions. VIII. The use of preformed enolate ions in Michael additions. Part I
Authors: Dionne Gervais , Engel Ch. R.
Published: May 2006

Some Michael additions involving preformed enolate ions as nucleophiles were studied. High regioselectivity was observed in the additions of the lithium enolate of 2-methylcyclo-hexanone to ethyl acrylate and to methyl β-chloroacrylates, the latter reactions being by far superior to those involving classical Michael additions. The addition to cis- and trans-β-chloroacrylates proceeded with appreciable stereoselectivity. Michael addition of a preformed enolate ion, derived from a ketone, to a cis-β-chloroacrylate constitutes an efficient pathway to 6-substituted α-pyrones, as exemplified by the synthesis of 5,6,7,8-tetrahydrocoumarin from cyclohexanone.
The crystal structure of cis-chlorobis(triethylphosphine)-1,8-naphthyridineplatinum(II) tetrafluoroborate, [PtCl(PEt3)2(naph)]BF4, a complex containing a monodentate 1,8-naphthyridine ligand
Authors: Bushnell Gordon W. , Dixon Keith R. , Khan Masood A.
Published: May 2006

The crystal structure of cis-chlorobis(triethylphosphine)-1,8-naphthyridineplatinum(II) tetrafluoroborate has been determined by single crystal X-ray diffraction and refined to an R-value of 0.063. The cell dimensions are a = 1.4246, b = 1.2676, c = 1.6530 nm, β = 115.66°. The space group is P21/c with 4 molecules per unit cell, and the measured density is 1.665 g cm−3. The structure is essentially a 4-coordinate square planar platinum(II) complex containing monodentate 1,8-naphthyridine. Interatomic distances to platinum are: Pt—Cl, 236.6(4); Pt—P(1), 225.4(4); Pt—P(2), 225.2(4); Pt—N(1), 208.3(11); and Pt—N(2), 304.5(14) pm. The structure is discussed in relation to variable temperature nmr studies of solutions, which indicate fluxional behaviour of the heterocyclic ligand.
Protonated cyclopropanes. X. Studies on the deamination of n-butylamine-1-14C and the decomposition of 3-(n-butyl-1-14C)-1-phenyltriazene
Authors: Lee Choi Chuck , Reichle Randy , Weber Ursula
Published: May 2006

The HNO2 deamination of n-butylamine-1-14C (1-NH2-1-14C) in aqueous HClO4 gave a n-butyl-14C alcohol (1-OH-14C) with about 0.7% scrambling of the label from C-1 to C-2, and a sec-butyl-14C alcohol (2-OH-14C) which showed extensive scrambling between C-1 and C-4, as well as small amounts of rearrangement of the label into C-2 and C-3. Analysis of the data suggested that about 2.5% of the 2-OH-14C product could be derived from equilibrating protonated methylcyclopropane intermediates. The HClO4 catalyzed decomposition of 3-(n-butyl-1-14C)-1-phenyltriazene (1-NNNHPh-1-14C) gave the unrearranged 1-OH-1-14C and a 2-OH-14C which showed only about 17–18% scrambling from C-1 toC-4. It is suggested that the different results observed in the deamination and the triazene decomposition may be due to a more ready initial formation of an ion pair in the triazene decomposition.
The crystal structure of cis-chlorobis(triethylphosphine)phthalazineplatinum(II) tetrafluoroborate, [PtC](PEt3)2(phth)]BF4
Authors: Bushnell Gordon W. , Dixon Keith R.
Published: May 2006

The crystal structure of cis-chlorobis(triethylphosphine)phthalazineplatinum(II) tetrafluoroborate has been determinee by single crystal X-ray diffraction and refined to an R-value of 0.076 for 1935 reflections. The cell dimensions are a = 1315.7(2), b = 2462.7(4), c = 899.6(3) pm, β = 104.99(2)°. The space group is P21/c with 4 molecules per unit cell, ρo = 1.593, ρc = 1.613 g cm−3. The structure is a square planar 4-coordinate platinum(II) complex with an angle of 80.0° between the plane of the phthalazine molecule and that of the coordination. Interatomic distances to platinum are Pt—Cl, 235.4(9); Pt—P(1), 225.2(8); Pt—P(2), 226.9(8); Pt—N(1), 208(3); and Pt—N(2), 297(3) pm, the phthalazine ligand being monodentate. The structure is compared to previous results and discussed in relation to variable temperature nmr studies of solutions, which show that the heterocyclic ligand exchanges its point of attachment to and fro between N(1) and N(2) by a dissociative mechanism at elevated temperatures.
Effect of aromatic substituants on the rates of hydrolysis of ethyl thiolbenzoate and ethyl thionbenzoate in aqueous sulfuric acid
Authors: Edward John T. , Wong Sin Cheong , Welch Graeme
Published: May 2006

The rates of hydrolysis of seven meta- and para-substituted ethyl thiolbenzoates and seven meta- and para-substituted ethyl thionbenzoates in various concentrations of sulfuric acid above 48% have been determined. The Yates–McClelland r and the Hammett ρ parameters indicate that substituted ethyl thiolbenzoates hydrolyze by an AAc1 mechanism but substituted ethyl thionbenzoates by an AAc2 mechanism.
On the construction of the C/D ring systems of chasmanine and napelline by diene addition
Authors: Atwal Karnail S. , Marini-Bettolo Rinaldo , Sanchez Ignacio H. , Tsai Thomas Y. R. , Wiesner Karel
Published: May 2006

The construction of the C/D ring system of the alkaloids chasmanine and napelline by modification and rearrangement of a common intermediate is explored on model compounds.The phenolic acid 9 was oxidized to the spirolactone 10. Addition of benzyl vinyl ether to this material gave the adduct 28 in high yield. This central 'nordenudatine' type intermediate was then modified (in a very few stereospecific steps) to the 'napelline' model compound 47 and to the keto acetal 38. Compound 38 is an intermediate of our photochemical route and we have already described its conversion to a chasmanine model derivative.The new syntheses of chasmanine and napelline foreshadowed by the present model studies are expected to be completely stereo- and regiospecific, almost 10 steps shorter and an order of magnitude more efficient than the total syntheses of these two alkaloids which we have reported in the recent past.Incidentally, with these model studies, the methoxy ketone 20 was prepared. The methoxyl in this compound is epimeric to the corresponding (C16) methoxyl of the aconite alkaloids. Some relevant observations on the nmr spectra and allylic rearrangement (pyro–isopyro rearrangement) of this material are also reported.
Re-examination of the Kirkwood–Westheimer theory of electrostatic effects. III. Dissociation constants of cis-3- and trans-4-substituted cyclohexanecarboxylic acids in water–dimethyl sulfoxide mixtures
Authors: Kirchnerova Jitka , Farrell Patrick G. , Edward John T. , Halle Jean-Claude , Schaal Robert
Published: May 2006

Acid dissociation constants of two cis-3- and of four trans-4-substituted cyclohexanecarboxylic acids in water – dimethyl sulfoxide mixtures of varying composition were determined by a potentiometric method. Results have been analyzed according to the model of Kirkwood and Westheimer, and shown to differ from calculated values because of certain oversimplifications built into the model. Dissociation constant differences between cyclohexanecarboxylic acid and the compounds studied vary only slightly with changing solvent composition.
Towards a complete account of the exchange chemistry of a diastereotopic proton pair. I. Base-catalyzed enolization–exchange of 2-norbornanones; on the rate controlling factors
Authors: Werstiuk Nick Henry , Taillefer Roland , Banerjee Sujit
Published: May 2006

We report the rates of base-catalyzed hydrogen isotope exchange of the exo and endo protons in a series of 2-norbornanones. The exo:enclo rate ratios for 4-methyl-substituted 2-norbornanones 3 and 6 are less than the rate ratios of the 4-demethyl analogs 2 and 5. Therefore, a methyl group is not a useful torsional-effect probe. This is supported by an analysis which established that the small difference in the torsional strain (0.45 kcal) between eclipsed vicinal hydrogens and an eclipsed vicinal methyl and hydrogen would only resuit in a maximum twofold increase in the rate ratio. The decrease in the exo:endo rate ratio is a consequence of the electron-donating effect of a methyl group which affects the exo rate to a greater degree. Introduction of a strain-inducing exo methylene group at C(5) and C(6) in the norbornyl system does not produce a significant change in the exchange rates. The average increase of 7.9 and 2.6 in the exo and endo rates, respectively, in enones 4, 5, and 6 over the ketones 1, 2, and 3 are explicable by an inductive effect. Thus, homoallylic stabilization of the developing carbanion is not important.Through application of a new mechanistic criterion which involves a log–log plot of the exo and endo exchange rate constants, we establish, for the bicyclic ketones, that charge transfer to oxygen is greater in the transition state for endo deprotonation.
Calorimetric study of an electrochemical reduction
Authors: Turner Peter J. , Pritchard Huw O.
Published: May 2006

The aqueous trichloroacetate ion is reduced irreversibly and with unit current efficiency to the dichloroacetate ion. From the total energy release observed when this process is carried out inside a calorimeter, it is possible to deduce the enthalpy change for the reduction reaction.
A new extraction–spectrophotometric method for the determination of phosphate
Authors: Subramanian Kunnath S. , Corsini Alfio
Published: May 2006

A new extraction–spectrophotometric method has been developed for the determination of trace amounts of phosphorus as orthophosphate. The method is based on the chemistry of 12-tungstophosphoric acid, H3PW12O40 (TPA). In the procedure, orthophosphate is converted quantitatively to TPA in aqueous solution at a tungstate–phosphate molar ratio ≥24, in the pH range 1.2 to 1.9 and in the temperature range 60 to 100 °C. The TPA is subsequently extracted into n-amyl alcohol and its absorbance measured at 267 nm. Beer's law is followed up to at least 25 µg/ml P. The method is less prone to solution conditions and species interference (especially As(V) and Si(IV)) than the widely used molybdenum-blue methods and is competitive in terms of sensitivity, precision, and accuracy. The TPA method was applied successfully to the determination of phosphate in a variety of phosphorus-containing specimens including natural waters, ores, and alloys.Based on potentiometric and spectrophotometric studies, a scheme which accounts for the observed heptaproticity of TPA is proposed.
The crystal structure of a dinuclear platinum(II) complex with a bent dihydroxy bridge, di-(μ-hydroxy)tetrakis(triethylphosphine)diplatinum(II).tetrafluoroborate
Authors: Bushnell G. W.
Published: May 2006

The crystal structure of di-(μ-hydroxo)tetrakis(triethylphosphine)diplatinum(II)fluoroborate has been determined and refined to an R value of 0.032. The space group is P21/c and the cell dimensions are a = 1.604(1), b = 1.847(1), c = 1.336(1) nm, β = 101.6 °, with 4 molecules per unit cell. The dimeric cation consists of two square planar Pt(II) centres bridged by a pair of hydroxo ligands. The angle between the mean plane normals is 36.4°. One of the BF4− groups, situated close to the dihydroxo bridge on the more open side, and having lower thermal parameters than the second fluoroborate anion, is hydrogen bonded to the oxygen atoms. The hydrogen atoms were not located. The interatomic distances (pm) are Pt—P = 223.5 (mean), Pt—O = 213.3 (mean), Pt(1)—Pt(2) = 312.1(1), O(1)—O(2) = 272(2), O(1)—F(1) = 288(2), O(2)—F(2) = 282(3). The mean bond angles (deg) are O—Pt—O = 79.4, P—Pt—P = 97.7, P—Pt—O = 91.5, and Pt—O—Pt = 94. One of the triethylphosphine groups is disordered or in thermal motion and was refined by constrained least squares using two superimposed partial structures. The results are discussed in relation to other known hydroxo bridged platinum species relevant to the field of platinum containing, cancer chemotherapeutic drugs.
Apparent molar heat capacities and volumes of aqueous electrolytes at 25 °C: Na2SO4, K2SO4, Na2S2O3, Na2S2O8, K2S2O8, K2CrO4, Na2MoO4, and Na2WO4
Authors: Olofsson Inger V. , Spitzer Jan J. , Hepler Loren G.
Published: May 2006

We have made beat capacity and density measurements leading to apparent molar beat capacities and volumes for dilute aqueous solutions of Na2SO4, K2SO4, Na2S2O3, Na2S2O8, K2S2O8, K2CrO4, Na2MoO4, and Na2WO4. We have used these apparent molar quantifies to extrapolate to infinite dilution to obtain the corresponding standard state apparent and partial molar quantities. These latter values have been used in calculation of conventional ionic beat capacities and volumes.
The synthesis and properties of the hexachloroniobates and hexachlorotantalates of Na, K, Rb, and Cs
Authors: Sadoway Donald R. , Flengas S. N.
Published: May 2006

The compounds NaNbCl6, NaTaCl6, KNbCl6, KTaCl6, RbNbCl6, RbTaCl6, CsNbCl6, and CsTaCl6, were synthesized in a closed system by the reaction of NbCl5 or TaCl5 vapour with solid alkali-metal chloride as follows[Formula: see text]where M is Nb or Ta, and A is Na, K, Rb, or Cs. The X-ray powder diffraction patterns of these compounds were obtained. Temperatures of various phase transformations were determined cryoscopically.
Synthesis and coordinating properties of the anionic tridentate ligand, methyl tris(1-pyrazolyl)gallate, [MeGa(N2C3H3)3]−. X-ray crystal structure of [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5)
Authors: Breakell Kenneth R. , Rettig Steven J. , Singbeil Douglas L. , Storr Alan , Trotter James
Published: May 2006

The anionic tridentate ligand, [MeGa(N2C3H3)3]−, has been characterized and its coordinating properties studied. It acts as a six-electron chelating ligand to divalent transition metal ions giving complexes of the type, [MeGa(N2C3H3)3]2M (M = Mn, Fe, Co, Ni, Cu, Zn), believed to possess an octahedral MN6 core. The ligand also forms numerous carbonyl complexes and its coordinating ability in Mo, W, and Mn carbonyl derivatives is compared with that of similar boron ligands and the η5-C5H5 ligand. From ir measurements and bond length data it appears that the [MeGa(N2C3H3)3]− ligand is superior in creating an electron-rich transition metal centre, and it also affords greater steric protection for the central metal. The expected tridentate chelating nature of the new ligand has been demonstrated through a crystal structure determination of the complex [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5). Crystals of this complex are tetragonal, a = 26.217(3), c = 10.723(2) Å, Z = 16, space group I41/a. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to a final R of 0.030 and Rw of 0.031 for 2582 reflections with I ≥ 3σ(I).
Synthèse et identification spectroscopique d'un hydroxylate-3 d'acyl-2 pyridothiazolium
Authors: Tavernier D. , Jamoulle J. C. , Lapière C. L.
Published: May 2006

The principal product from the cyclization of {[3-(5-nitropyridine-2-yl)-amino]pyridine-2-yl}thioaceticacid is 2-{[3-nitropyridine-2-yl)amino]pyridine-2-yl}thioacetyl-8-[(5-nitropyridine-2-yl)amino]-3-oxidopyrido[2,1-b]thiazolium (4). Its structure was determined primarily by 1H and 13C nmr. [Journal translation]
Organometallic peroxy radicals. 4. Electron spin resonance spectra of the radicals produced by reaction of organophosphorus(IV) and organoarsenic(IV) radicals with 17O-enriched oxygen
Authors: Howard J. A. , Tait J. C.
Published: May 2006

It bas been shown that some tetra-coordinate phosphorus and arsenic radicals combine with oxygen to give peroxy radicals. The magnitude of the oxygen isotropic and anisotropic hyperfine coupling constants indicates that nearly all the unpaired spin is associated with the two oxygen nuclei with ca. 60% on the terminal oxygen. The large isotropic g-factors associated with Group VB peroxy radicals relative to alkylperoxy radicals is attributed to a small change in geometry of the peroxy function.The radicals with ap ∼ 9 G obtained during the reaction of photochemically generated tert-butoxy radicals with trialkylphosphites in the presence of oxygen are secondary species which appear to contain only one oxygen atom.
Further studies of the specificity of carboxypeptidase A towards hippuric acid esters
Authors: Bunting John W. , Chu Samuel S.-T.
Published: May 2006

The kinetics of hydrolysis of a series of 10 new hippurate esters (C6H5CONHCH2CO2CRR1CO2H (I)) by bovine pancreatic carboxypeptidase A have been investigated at pH 7.5, 25 °C, and ionic strength 0.5. Pronounced substrate inhibition was displayed by I: R = H, R1 = C6H5(CH2)2, 3-indolylmethyl, 4-HOC6H4CH2, and 4-FC6H4 whereas pronounced substrate activation was observed for I: R = H, R1 = 4-CH3C6H4, 4-C2H5C6H4, 4-C6H5C6H4, 1-naphthyl, 2-naphthyl, and R = R1 = C2H5. In all cases substrate activation and substrate inhibition were shown to be consistent with ES2 complex formation similar to that previously observed for other hippurate esters. Kinetic parameters were evaluated for each ester and it is noted that ail 13 hippurate esters now known to display substrate inhibition have kcat/Km > 106 M−1 min−1, whereas kcat/km < 106 M−1 min−1 for all 9 hippurate esters known to display substrate activation. The enzymic specificity for the R1 unit of I suggests binding of R1 in a 'bent' hydrophobic pocket having a restricted entrance.
Metabolites of bird's nest fungi. Part 10. Carbon-13 nuclear magnetic resonance studies on the cyathins
Authors: Ayer William A. , Nakashima Thomas T. , Ward Dale E.
Published: May 2006

The carbon-13 magnetic resonance spectra of cyathin A3 and several related compounds have been measured and the chemical shifts have been assigned. The chemical shift data have been used to determine the stereochemistry at C-1 in cyafrin A4 and to determine the position of the bromine in 1-bromoallocyathin A3 methyl acetal.
The effect of diluent gases on ion formation in C2N2 flames
Authors: Chawner Brenda L. , Blades Arthur T.
Published: May 2006

Ion formation from traces of C2N2 in a H2 + He-in-air diffusion flame is enhanced by the presence of traces of Ne, Ar, Kr, Xe, N2, CO, CO2 and CF4. The enhancement is proportional to the concentration of both C2N2 and the diluent gas and the relative efficiencies are identical to those observed when hydrocarbons are the source of ionization. The observations are consistent with the involvement of the diluent in ion formation, parallel to the hydrocarbon system.
Réduction électrolytique de l'aluminium en milieu organique. Caractérisation de l'électrolyte
Authors: Lafortune R. , Bourret J. T. , Capuano G. A.
Published: May 2006

Various alkylbenzene-based electrolytes used in the electrolytic reduction of aluminum were analyzed by gas phase chromatography. Neither oxidation nor reduction products could be detected in the usual electrolysis conditions. Solvents such as toluene, ethylbenzene, or diethylbenzene undergo dismutation reactions in the presence of aluminum bromide. With or without electrolysis, electrolytes based on 1:1 ethylbenzene/toluene and 1:4 diethylbenzene/toluene tend toward nearby equilibrium compositions. This fact explains why electrolytic aluminum coatings of similar quality are obtained.The effect of water content on the quality of aluminum coatings obtained by electrolytic reduction was studied. The study revealed that better coatings are obtained if the organic solvents are used 'as received'. Thus it was possible to avoid the pretreatments of drying or hydrating these solvents. [Journal translation]
Reaction of carbon monoxide with nitrous oxide on scandium and magnesium oxides
Authors: Krupay Bordan W. , Ross Robert A.
Published: May 2006

The kinetics of the catalytic reaction between carbon monoxide and nitrous oxide has been examined on Sc2O3 and MgO in a differential flow reactor at atmospheric pressure. On Sc2O3, the apparent activation energy was 126 ± 4 kJ mol−1 from 633 to 723 K while a value of 63 ± 4 kJ mol−1 was obtained for MgO from 547 to 673 K. On both catalysts, the surface mechanism has been interpreted by a reaction scheme involving each reactant as an adsorbed species with CO and N2O being further involved in subsequent steps during the course of the surface reaction. The metal/oxygen bond polarization appears to influence both the strength and form of CO adsorption where the reactants interact as surface species each bound to two surface sites on Sc2O3 and on one surface site each on MgO.
An esr and CIDEP study of the photoreduction of furil
Authors: Elliot A. John , Wan Jeffrey K. S.
Published: May 2006

The transient free radicals formed when furil was photoreduced have been characterized by esr and CIDEP. Two furil derived radicals were observed: one was the protonated form of the semidione radical (FH•) while the other was an allyl radical formed by radical addition to the furil ring. Initial polarization was observed for FH• which was consistent with the triplet mechanism and these CIDEP results indicate that phenol is a better chemical quencher of the furil triplet than pentachlorophenol which is in turn more efficient than 2-propanol. A method to estimate relative T1 of radicals is also described.
Synthèse de cétones encombrées via réduction de nitriles tertiaires en présence de métaux alcalins
Authors: Mazaleyrat Jean-Paul
Published: May 2006

The reaction of alkali metals with tertiary alkyl nitriles eventually gives, after protonation, an imine. α-tert-Alkylketones are produced by the hydrolysis of these imines. This reaction, involving radical anion intermediates, is a simple method for the synthesis of highly hindered symmetric ketones.
Aminocyclitols. II. Synthesis of thioanalogues of 2,5-dideoxystreptamine
Authors: Kavadias Gerry , Droghini Robert
Published: May 2006

N,N′-Dibenzoyl-2,5-dideoxystreptamine (8b) reacted with thionyl chloride to form the bisoxazoline 9 and the latter compound was treated with thiobenzoic acid to produce the dithiobenzoate 10a. Removal of the protective groups in 10a afforded (l,3/4,6)-4,6-diamino-1,3-cyclohexanedithiol (1) dihydrochloride. Reaction of 8b with triethyl orthoacetate in the presence of boron trifluoride yielded the monooxazoline 12 which, on reaction with thiobenzoic acid followed by deprotection of the resulting 13a, afforded (d,l)-(13/4,6)-4,6-diamino-3-hydroxycyclohexanethiol (2) dihydrochloride. Similarly, 3-N-benzoyl-1-N-ethoxycarbonyl-2,5-dideoxystreptamine (15) and l-N-benzoyl-3-N-ethoxycarbonyl-2,5-dideoxystreptamine (20) were converted via their respective oxazolines 17a and 22a, to the enantiomeric aminothiols 3 and 4. Protected derivatives of 1–4 are also described.
Triplet–triplet absorption of some aryl-substituted 1,3,4-oxadiazoles
Authors: Rullière Claude , Rayez Jean-Claude , Roberge Pierre C.
Published: May 2006

The triplet–triplet absorption spectra of three naphthyl-1,3,4 oxadiazoles have been measured from 400 to 620 nm. The spectra are analyzed in terms of naphthalene perturbed in the α or β position using a theoretical simulation of the perturbation based on Pariser–Parr–Pople approximation. It is concluded that the lowest triplet state of these molecules must involve an important contribution of charge transfer configurations.
Crystal and molecular structures of 2,2,4,4,6,8,8-heptamethyl-6-methylamino-1,3,5-triaza-2,4,6,8(PV)-tetraphosphorin and 2,2,4,4,6,8,8-heptamethyl-6-methylamino-7-benzoyl-1,3,5-triaza-2,4,6,8(PV)-tetraphosphorin
Authors: Calhoun Harry P. , Oakley Richard T. , Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of 2,2,4,4,6,8,8-heptamethyl-6-methylamino-1,3,5-triaza-2,4,6,8(PV)-tetraphosphorin are monoclinic, a = 11.639(4), b = 11.957(7), c = 12.114(4) Å, β = 94.07(2) °, Z = 4, space group P21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.032 and Rw of 0.041 for 2012 reflections with I ≥ 3σ(I). Crystals of 2,2,4,4,6,8,8-heptamethyl-6-methylamino-7-benzoyl-1,3,5-triaza-2,4,6,8(PV)-tetraphosphorin are triclinic, a = 15.513(1), b = 8.422(1), c = 8.933(1) Å, α = 89.24(1), β = 100.18(1), γ = 107.30(1) °, Z = 2, space group [Formula: see text]. The structure was solved by Patterson and Fourier syntheses and was refined to a final R of 0.041 and Rw of 0.044 for 3654 reflections with I ≥ 3σ(I). The eight-membered P4N3C rings in both structures hâve 'tub' conformations. The mean bond lengths (corrected for libration) are: P—N(endo), 1.609(9), P—N(exo), 1.679(2), P—C(endo), 1.717(2), and P—C(exo), 1.815(8) Å for Me7(MeNH)P4N3CH and 1.595(4), 1.655(2), 1.763(4), and 1.804(5) Å respectively for Me7(MeNH)P4N3CC(O)Ph. The near-equivalence of the endocyclic P—N bond lengths in the azaphosphorins is discussed in terms of opposing changes in the in-plane and out-of-plane Π-systems.
Polar substituents in barrelene photochemistry: mechanistic aspects of the photochemistry of 2-cyanobenzobarrelene
Authors: Bender Christopher Owen , Brooks Dee W. , Cheng William , Dolman Douglas , O'Shea Seamus F. , Shugarman Sidney S.
Published: May 2006

The direct photolysis of 2-cyanobenzobarrelene (4) yields 5- and 7-cyanobenzocyclooctatetraene [Formula: see text] and 1-cyanobenzosemibullvalene [Formula: see text], whereas the acetophenone sensitized irradiation of 4 yields only 8 [Formula: see text]. Deuterium labelling studies suggest that 7 derives from an initial 2Π + 2Π cycloaddition between the vinyl and vinylcyano bridges of 4, whereas 8, resulting from direct or sensitized irradiations of 4, derives from di-Π-methane rearrangement involving initial vinyl–vinylcyano bridging. The observed initial bonding preferences of the 2Π + 2Π cycloadditions and di-Π-methane rearrangement of 4 are in accord with predictions based upon CNDO-CI calculations of changes in atom–atom interaction energies between possible bridging sites in singlet and triplet excited states of 4.
Inductive substituent constants from dissociation of methyl-substituted 2-picolinium ions
Authors: Fischer Alfred , King Murray John , Robinson Frank Price
Published: May 2006

The dissociation constants of a series of 28 α-substituted 2-methylpyridinium ions in water at 25 °C have been measured by potentiometric and spectrophotometric methods. Correlation of the −pK values with σI values gives slope ρI = 5.45, intercept −pK0 = −5.81, correlation coefficient r = 0.991, and enables new σI values to be evaluated. Dissociation constants for the 2-pyridinylmethylammonium ion and its N-methyl and N,N-dimethyl derivatives are also reported.
Spectroscopic studies of mercury(II) acetate complexes of some tertiary phosphines
Authors: Alyea Elmer C. , Dias Shelton A.
Published: May 2006

Mercury(II) acetate complexes of the type (R3P)nHg(OAc)2, where n = 1 and 2, and R3P = (p-tolyl)3P, (p-F-C6H4)3P, Ph2MeP, Ph2EtP, and PhEt2P have been prepared in good yields. Only the 1:1 adduct is formed with (o-tolyl)3P. Conductance measurements in nitromethane show that these complexes are non-electrolytes. The 1:1 adducts are monomeric in dichloroethane but the 1:2 adducts are extensively dissociated. Tentative assignments for ν(COO), ν(Hg—O), ν(Hg—P) are made from the infrared and Raman spectral data. The correlation of the coordination chemical shifts, Δδ(31P), with the coupling constants 1J(199Hg–31P) of the complexes is discussed with respect to the bulkiness and the basicity of the phosphine ligands.
The molecular and crystal structure of tetrakis(4-methylpyridine)cobalt(II) hexafluorophosphate
Authors: Morrison Raymond M. , Thompson Robert C. , Trotter James
Published: May 2006

Crystals of tetrakis(4-methylpyridine)cobalt(II) hexafluorophosphate, C24H28CoF12N4P2, are tetragonal, space group I41/acd, a = 18.434(7), c = 18.818(6) Å, Z = 8. The structure was solved by direct and Fourier methods. The positional and anisotropic thermal parameters were refined by full-matrix least-squares methods to R = 0.072 for 346 observed reflexions. The structure consists of discrete [Co(4-mepy)4]2+ and PF6− ions. The structure of the cation is a distorted tetrahedron of 4-methylpyridine ligands around cobalt (crystal symmetry S4) and that of the anion is a distorted octahedron of fluorines around phosphorus (crystal symmetry C2).
Densities and kinematic viscosities of tetra-n-butylammonium iodide–nickel(II) chloride melts
Authors: Islam Nurul , Maroof Abdul , Kochi Ismail
Published: May 2006

Densities and kinematic viscosities of molten mixtures of nickel(II) chloride in tetra-n-butylammonium iodide have been measured as functions of temperature and composition. The data on the kinematic viscosity have been analyzed using both Arrhenius and non-Arrhenius type equations. The heat of activation, the entropy of activation, and the free energy of activation for viscous flow have been computed. At higher concentrations a slight tendency towards non-Arrhenius viscous behaviour is observed. The free energy of activation helps in describing the overall composition dependence of kinematic viscosity.
Alkanes with multiple asymmetric centers: synthesis, identification, and 13C nuclear magnetic resonance spectra
Authors: Lachance Pierre , Brownstein S. , Eastham Arthur M.
Published: May 2006

The identification of aliphatic hydrocarbons containing multiple asymmetric centers can be difficult because of the complexity of the nmr spectra and because in capillary chromatography the diastereomers may be resolved to varying degrees. We suggest that the most effective method for identifying such hydrocarbons is through the pattern of retention times developed by the mixture of diastereomers on a suitable capillary glc column.This paper presents the results of some studies of a series of alkanes having the general form C2H5—(CH—CH3)n—R, where n = 1 to 4, and includes the syntheses and 13C nmr spectra of the compounds.
Branched-chain sugars. Reaction of furanoses with formaldehyde: a stereospecific synthesis of L-dendroketose
Authors: Ho Pak-Tsun
Published: May 2006

A simple conversion of 2,3-O-isopropylidene-D-hamamelose, prepared by reaction of 2,3-O-isopropylidene-D-ribose with formaldehyde, into L-dendroketose is described.
Microbial hydroxylation of steroids. 5. Metabolism of androst-5-ene-3,17-dione and related compounds by Rhizopusarrhizus ATCC 11145
Authors: Holland Herbert L. , Diakow Peter R. P.
Published: May 2006

The products of the incubation of androst-5-ene-3,17-dione (2a), 3β-hydroxyandrost-5-ene-17-one (2b), and androsta-3,5-diene-17-one (3) with Rhizopus arrhizus ATCC 11145 under a variety of conditions have been identified and the mechanisms of their formation discussed. In addition, several C-(4,5)- and C-(5,6)-epoxyandrostanes have been incubated with R. arrhizus, the products identified and possible pathways for their formation presented.
The density and vapour pressure of dimethylsulfoxide at various temperatures and the (hypothetical) critical density
Authors: Campbell Alan N.
Published: May 2006

The density up to 257 °C and the vapour pressure up to 189 °C of dimethylsulfoxide have been determined directly. Dimethylsulfoxide decomposes below the critical temperature, but by indirect methods the (hypothetical) critical density is found to be[Formula: see text]or[Formula: see text]The vapour pressure measurements yield a molar heat of evaporation of 10.84 kcal/mol or 138.7 cal/g
A nuclear magnetic resonance study of pyridoxal phosphate – metal ion interactions. II. Binding of manganese(II)
Authors: Viswanathan Tenkasi S. , Swift Terrence J.
Published: May 2006

The line width and spin–lattice relaxation rates of phosphorus and proton nuclei in PLP have been measured as a function of temperature in the presence of Mn(II) using pulsed nmr methods. The T1M of 31P in PLP-Mn(II) is very close to the T1M values of β- and γ-phosphorus atoms in ATP–Mn(II) at ∼40 °C. The T1 data of 31P and 1H have been interpreted in terms of the dipolar interaction between the electron and nuclear spins. With the assumption that the Mn(II) interacts directly with the phosphate of PLP the rotational correlation time τc at 38 °C was calculated to be 7.6 × 10−10 s from phosphorus T1 data. This τc value was subsequently used to calculate metal–proton distances from proton T1 and T2 data. The results lead to the conclusion that the phosphate-bound metal interacts directly with the aldehyde oxygen in a 1:1 PLP–Mn(II) complex. The linewidth of the 13C resonances of PLP in the presence of Mn(II) supports this conclusion. The structure assigned for PLP–Mn(II) complex is in conformity with the structure for PLP-Co(II) complex.
Photochemical and thermal rearrangements of some 3H-pyrazoles
Authors: Leigh William J. , Arnold Donald R.
Published: May 2006

Low temperature (−70 °C) irradiation of 3,3,4,5-tetramethyl-3H-pyrazole (2a) leads to the formation of the 1,2-diazabicyclo[2.1.0]pent-2-ene (3a), as has been reported previously. Irradiation of 3,3-dimethyl-4,5-diphenyl-3H-pyrazole (2b) under identical conditions did not result in formation of the analogous product but lead instead to formation of the cyclopropene via decomposition of the vinyl diazo compound. The thermal rearrangements of 2a and a series of 5-aryl-3,3-dimethyl-4-phenyl-3H-pyrazoles (2b–d) lead to formation of the 4H-pyrazoles 6a–d and the N-methylpyrazoles 5a–d, resulting from competitive methyl migrations to carbon and nitrogen. The Arrhenius parameters for the rearrangement of 2b were determined. Decomposition of the methiodides derived from the 4H-pyrazoles 6a–d leads to formation of the N-methylpyrazoJes 5a–d; the mechanism of this decomposition was examined by high temperature 1Hmr spectroscopy. The N-methylpyrazoles were synthesized by independent routes and the structures were assigned with the aid of lanthanide shift reagents, 1Hmr solvent shift studies, and 13Cmr spectroscopy. The thermodynamic equilibria of the isomeric N-methylpyrazoles were determined and found to be influenced by a small substituent effect. The photochemical and thermal behaviour of 3H-pyrazoles is discussed and compared to that of 1-pyrazolines.
Thermal decomposition of diazirines in the presence of m-chloroperoxybenzoic acid. A method to determine the partitioning of reaction pathways
Authors: Liu Michael T. H. , Yamamoto Iwao
Published: May 2006

The oxidation of various diazirines by m-chloroperoxybenzoic acid as well as the activation parameters for these reactions have been investigated. The oxidation products and the information derived from kinetic studies indicate that the oxidation does not take place on the diazirine ring as expected but rather on the decomposition products of the diazirines. The oxidation products obtained are shown to be characteristic of the diazirine decomposition by carbenic and diazo pathways and thus the measurement of the oxidation products provides a measure of the partitioning of the two reaction pathways for diazirine decomposition.
A new synthesis of spirovetivanes via the spiro acyloin intermediate
Authors: Ibuka Toshiro , Hayashi Kenji , Minakata Hiroyuki , Ito Yoshikuni , Inubushi Yasuo
Published: May 2006

Ethyl-3-(1-ethoxycarbonyl-2,6-dimethylcyclohex-2-enyl)propionate 5 was stereoselectively synthesized. The diester 5 was spiroannulated by the acyloin condensation to give the bis(tri-methylsiloxy) ether 11. The ether 11 was hydrolyzed to provide the acyloins 6 and 12. The acyloins 6 and 12 were elaborated into (±)-hinesol 1, (±)-agarospirol 2, (±)-β-vetivone 3, and (±)-α-vetispirene 4.