bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron paramagnetic resonance spectra of the tert-butylperoxy and tert-butoxy adducts to phenyl tert-butyl nitrone and 2-methyl-2-nitrosopropane. Oxygen-17 hyperfine coupling constants
Authors: Howard James Anthony , Tait John Charles
Published: May 2006

tert-Butylperoxy radicals enriched with oxygen-17 react with phenyl tert-butyl nitrone to give α-tert-butylperoxybenzyl tert-butyl nitroxide with aN = 13.42 G, aH = 0.95 G, aoβ = 2.9 G, g = 2.0064. The O-hfsc decreases with an increase in temperature while the H-hfsc increases with an increase in temperature. This radical is not stable above about 273 K and is replaced by α-tert-butoxybenzyl tert-butyl nitroxide, aN = 13.62 G, aH = 1.72 G, aoβ = 5.05 G, g = 2.0064.Alkylperoxy radicals are also trapped by 2-methyl-2-nitrosopropane to give alkylperoxy tert-butyl nitroxide aN = 28.7 G, aoROO = 4.6 G, g = 2.0056 while the epr parameters for alkoxy tert-butyl nitroxide are aN = 27.25 G, aoRO = 1.03 G, g = 2.0057.
Pyrrole chemistry. XVIII. The thio-Claisen rearrangement
Authors: Teo Kang-Er , Barnett Graham H. , Anderson Hugh J. , Loader Charles E.
Published: May 2006

The thio-Claisen rearrangement has been carried out on 2-allylthiopyrrole, l-methyl-2-allylthiopyrrole, and 2,5-diallylthiopyrrole. The products were trapped by acetylation of the β-allyl-α-thiols. Raney nickel desulfurization of these products gave the corresponding β-propylpyrroles but attempts to functionalize the β-allyl group failed. l-Methyl-3-propylpyrrole and 3,4-dipropylpyrrole were also synthesized by other routes for comparison.
Crystal and molecular structure of bis(perchlorato)(γ-C-meso-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II)
Authors: Ochiai Ei-Ichiro , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of bis(perchlorato) (γ-C-meso-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) are monoclinic, a = 14.061(1), b = 8.908(1), c = 19.710(1) Å, β = 90.912(5)°, Z = 4, space group P21/c. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to a final R of 0.054 and Rw of 0.069 for 2945 reflections with I ≥ 3σ(I). The copper(II) ion has tetragonally distorted octahedral coordination geometry. The four nitrogen atoms of the macrocyclic ligand occupy the equatorial sites and two perchlorate oxygen atoms are in the axial positions. Bond lengths (corrected for libration) are: Cu—N, 2.024(4)–2.051(4), Cu—O, 2.657(5) and 2.697(5), Cl—O, 1.420(4)–1.473(6), N—C, 1.463(6)–1.508(6), and C—C, 1.498(8)–1.542(8) Å.
Deactivation of HF(ν = 1,2) by fluoroethylenes
Authors: Arnold S. J. , Kimbell G. H.
Published: May 2006

A discharge flow tube technique has been used to measure the deactivation of HF(ν = 1,2). Effective vibrational deactivation rate constants for HF(ν = 1,2) relaxed by C2H4, C2H3F, 1,1-C2H2F2, cis-1,2-C2H2F2, trans-1,2-C2H2F, C2HF3, and C2F4 have been determined. For HF(ν = 1) the values of the rate constants range from 4.9 × 104 s−1 Torr−1 for C2H4 to 3.5 × 103 s−1 Torr−1 for C2F4 and for HF(ν = 2) from 1.3 × 105 s−1 Torr−1 to 8.8 × 103 s−1 Torr−1. The cross sections for the deactivation of HF(ν = 1) and HF(ν = 2) by C2H4 and the fluoroethylenes are observed to scale linearly with the number of hydrogen atoms.
Hydrolysis of Co(II) at elevated temperatures
Authors: Giasson Gaétan , Tewari Param H.
Published: May 2006

Hydrolysis of Co(II) has been studied up to 200 °C using a concentration cell with liquid junction of the type Pt(H2)|H+(a1)||H+(a2)|(H2)Pt. The effect of varying the initial solution pH and cobalt concentration has been studied at different ionic strengths. The hydrothermal hydrolysis for cobalt solutions between pH 3.9 and 9.6 is consistent with the equilibrium Co2+ + H2O → CoOH+ + H+. Higher hydrolytic species are not important. Hydrolysis increases with temperature and produces a buffering action at 200 °C. Thermodynamic quantifies for the hydrolysed species are reported.
Studies of silyl and germyl Group VI species. Part II. Bis(methylgermyl) and bis(dimethylgermyl) chalcogenides and related species
Authors: Drake John E. , Glavinčevski Boris M. , Henderson H. Ernest , Hemmings Raymond T.
Published: May 2006

Comparative reactions of some halogenogermanes with lithium(I), lead(II), and organosilicon Group VI species have been investigated, leading to the efficient syntheses of the chalcogermanes of the formula (MenH3−nGe)2E, where E = O, S, Se, Te; n = 0 → 3. The spectroscopic properties of the new bis(methylgermyl) and bis(dimethylgermyl) chalcogenides are discussed. Germanethiols and germaneselenols, viz. MenH3−nGeEH (E = S, Se; n = 0, 3) are isolated as intermediates in the reaction of digermoxanes with H2E and from equilibrium mixtures of (MenH3−nGe)2E with excess H2E. Evidence is presented for the condensation of the chalcogermanes to species of the type MenH3−nGe(EGeH3−nMen)2 (n = 1, 2) and for the elimination of metallic selenium or tellurium giving digermanes of the type (MenH3−nGe)2 (n = 1, 2).
Oligoribonucleotide synthesis. XI. Improved preparation of 2′-O-tetrahydropyranyl derivatives of guanosine and adenosine necessary for insertion in phosphotriester synthesis
Authors: Gregoire Rene J. , Neilson Thomas
Published: May 2006

Treatment of N2-benzoyl-2′,3′,5′-O-triacetylguanosine and 2′,3′,5′-O-triacetyladenosine with buffered hydrazine gave equilibrium mixtures of N2-benzoyl-2′(3′),5′-diacetylguanosine and 2′(3′),5′-diacetyladenosine, greatly enriched in the desired 3′-acetates. Fractional crystallization effected recovery of pure 3′,5′-diacetates in 60% yields. From these were prepared the 2′-O-tetrahydropyranyl derivatives required for guanosine and adenosine insertion in phosphotriester oligonucleotide synthesis.
Photoelectron spectra of substituted benzamides
Authors: McAlduff E. J. , Lynch B. M. , Houk K. N.
Published: May 2006

The photoelectron spectra of the following substituted benzamides have been determined: p-CH3O, p-CH3, p-Cl, H, p-F, p-CN, p-NO2, m-CH3O, m-CH3, m-Cl, and m-NO2. The first six ionization potentials have been assigned with reference to the phenyl and amide moieties. As an aid to the assignment CNDO/S calculations have been performed on the methoxy, methyl, and nitro benzamides. Linear relationships have been shown to exist between the first phenyl IP of disubstituted and monosubstituted benzenes. The slopes of these relationships have been shown to be related to the electron releasing ability of the substituent.By comparison of the pes data with nmr chemical shifts, the first phenyl IP has been shown to be related to the electron density at the position of substitution of the amide group. Likewise, the amide IP centered on the nitrogen has been shown to be related to the electron density on nitrogen.
Ribo-2′-deoxyribo hybrid dinucleoside monophosphates. Proton magnetic resonance studies of 3′,5′- and 2′,5′-uridylyl-2′-deoxythymidine
Authors: Peeling James , Hruska Frank E. , Loewen Peter C.
Published: May 2006

This 1Hmr study initiates our examination of the conformations of dinucleoside monophosphates possessing ribo 2′- or 3′-nucleotidyl units linked to 5′-nucleotidyl units possessing the 2′-deoxyribo sugar. The syntheses of uridylyl-3′,5′-2′-deoxythymidine (3′,5′-UpdT) and its 2′,5′-isomer, 2′,5′-UpdT, were carried out with standard techniques. The 1Hmr data were obtained at frequencies up to 270 MHz and used to derive the dominant conformation of the dimers in aqueous solution. Comparison with data for the component mononucleotides reveals that dimerization does not lead to drastic changes in the molecular conformation. Literature data for dimers possessing only the ribo sugar (3′,5′-UpU) and the 2′-deoxyribo sugar (3′,5′-d(TpT)) are also presented. The results indicate that, at least for our dipyrimidine dimers, the molecular conformation of a particular fragment is not critically dependent on the nature (ribo or 2′-deoxyribo) of the other nucleotide unit.
An interferometric study of a convectionless steady state of concentration polarization
Authors: O'Brien Robert N. , Kolny Henryk
Published: May 2006

The use of interferometry to make visible concentration gradients at working electrodes has progressed to video tape recording of interferograms. Rapid accurate analysis should be able to gain sufficient data from experimental runs where migration effects are just balanced by diffusion effects to help evolve a better mathematical formula with which to predict concentration changes at working convectionless electrodes. Data are presented showing a quasi-steady state polarization in a low current density electrolysis run with Fe2+ the electroactive species.
Intermediates in the cycloanhydrotetramerization of furan with aliphatic and alicyclic ketones
Authors: Brown William Hamilton , Hutchinson Bruce James
Published: May 2006

The acid-catalysed reaction of furan with acetone has been investigated for the presence of intermediates by vapour phase chromatography of the reaction mixture. It has been shown that 2-furyl-2-propene is a component of the furan–acetone reaction mixture. Other possible intermediates have been prepared and their reactions investigated. It is our conclusion that the alcohol, 2-furyl-2-propanol, is the initial intermediate in the condensation reaction. We have also reexamined some reactions between furan and cyclohexanone reported by other investigators.
1,2-Dihydroquinolines: preparation and isolation as intermediates in the synthesis of quinolines
Authors: Dauphinee G. A. , Forrest T. P.
Published: May 2006

2,6-Dimethyl-1,2-dihydroquinoline has been isolated as an intermediate in the Doebner-Miller synthesis of 2,6-dimethylquinoline. Dihydroquinolines may be efficiently prepared by the acid catalysed elimination of water from a 4-hydroxy-1,2,3,4-tetrahydroquinoline. The analogous 4-phenylamino derivatives also undergo facile elimination of the benzylic amino group under similar conditions.
A synthesis of 3-acetamido-3-deoxy-D-glycero-D-gulo-heptose and 3-acetamido-3-deoxy-D-glycero-D-ido-heptose from 2-acetamido-2-deoxy-D-glucose
Authors: Benzing Laure , Perry Malcolm B.
Published: May 2006

The reluctance of 2-acetamido-2-deoxy-D-glucose to undergo base catalyzed addition with nitromethane was overcome by using the acetamidoglycose in the form of a substituted acyclic aldehydo derivative. 2-Acetamido-2-deoxy-D-glucose diethyl dithioacetal was isopropylidenated to yield 2-acetamido-2-deoxy-3,4:5,6-di-O-isopropylidene-D-glucose diethyl dithioacetal which on demercaptalation afforded 2-acetamido-2-deoxy-3,4:5,6-di-O-isopropylidene-aldehydo-D-glucose. The aldehydo derivative readily underwent base catalyzed addition of nitromethane to give the expected epimers 3-acetamido 1,3-dideoxy-4,5:6,7-di O-isopropylidene-1-nitro-D-glycero-D-gulo-heptitol and 3-acetamido-1,3-dideoxy-4,5:6,7-di-O-isopropylidene-1-nitro-D-glycero-D-ido-heptitol which, after deisopropylidenation by mild acid treatment, were converted under modified Nef reaction conditions to give 3-acetamido-3-deoxy-D-glycero-D-gulo-heptose and 3-acetamido-3-deoxy-D-glycero-D-ido-heptose, respectively.
The mechanism of the microbial hydroxylation of steroids. Part 4. The C-6 β hydroxylation of androst-4-ene-3,17-dione and related compounds by Rhizopusarrhizus ATCC 11145
Authors: Holland Herbert L. , Diakow Peter R. P.
Published: May 2006

The steroid analogue 4,4a,5,6,7,8-hexahydro-2(3H)-naphthalenone was hydroxylated at C-8α, C-8β, and C-4a by Rhizopusarrhizus. Similar products were obtained by peracid oxidation of the corresponding enol ethers: hydroxylation of estr-4-ene-3,17-dione by the same fungus occurred at the analogous C-6 and C-10 positions. These results are consistent with a mechanism of microbial hydroxylation involving the enol form of the Δ4-3-ketone. Data from the incubations with R. arrhizus of androst-4-ene-3,17-dione specifically labelled with deuterium at C-4, C-6α, or C-6β and from those of other deuterium labelled substrates have been interpreted in terms of a mechanism of C-β hydroxylation involving a rate-determining step before enolization of the ketone, followed by rapid enolization and oxidation of the enol to give the 6β-hydroxy-Δ4-3-ketone. The kinetic isotope effect, kH/kD, for the hydroxylation of androst-4-ene-3,17-dione at C-6β has been found to be 1.2 ± 0.1.
The Darzens glycidic ester condensation of indan-1-ones. A reinvestigation of the reaction
Authors: Kavadias Gerry , Velkof Stephan
Published: May 2006

The Darzens glycidic ester condensation of indan-1-one (1a) with ethyl chloroacetate was reinvestigated. Contrary to previous reports, the reaction proceeded normally yielding the glycidic ester 2a in high yield. Similarly, 5-cyclohexylindan-1-one (1b) produced the glycidic ester 2b. The glycidic esters 2a,b were converted to the corresponding aldehydes 4a,b by hydrolysis and decarboxylation. Oxidation of 4b yielded (±)-5-cyclohexylindan-1-carboxylic acid (3), a potent anti-inflammatory agent.
Effect of hydrocarbon solutes on electron mobilities in liquid xenon
Authors: Kimura Toyoaki , Freeman Gordon R.
Published: May 2006

Ethylene, propylene, cis-butene-2, trans-butene-2, ethane, propane, and n-butane were added to xenon at 168 and 192 K. At concentrations up to 4 mol%, electrons were scattered by one hydrocarbon molecule at a time and a gas phase model was used to estimate the scattering cross sections. The values for thermal electrons were, in Å2: ethane, 2.7; propane, 4.6; n-butane, 7.2; ethylene, 4.7; propylene, 5.4; cis-butene-2, 7.4; trans-butene-2, 9.4. The scattering cross sections of the hydrocarbons dissolved in liquid xenon were about half of those in the gas phase, where comparisons could be made.The mobility of electrons in pure xenon decreases with increasing electric field strength, due to heating of the electrons by the field. Addition of a small amount of hydrocarbon increases the mobility at high fields, eightfold by 4% of ethylene, propylene, or cis-butene-2 at 23.4 kV/cm and 192 K. The scattering cross sections of the hydrocarbons are two orders of magnitude larger than the effective cross section of liquid xenon, and the collisions with the hydrocarbons tend to prevent the electrons from becoming heated.Electrons begin to form localized states in solutions containing 10 mol% hydrocarbon, or 20 mol% in the case of ethane. The mobility decreases approximately exponentially with concentration above these thresholds. The values of μ0 for these exponential regions reflect the different scattering coefficients of the hydrocarbons: μ = μ0 exp (−Eμ/RT). The values of Eμ increase with molecular size in a series, and are greater for olefins than for alkanes. For the C2 and C3 hydrocarbons Eμ increases linearly with the mol fraction of hydrocarbon. cis-Butene-2 shows anomalous behaviour, as found earlier for electrons in the pure compound.
Microwave spectrum of methylthioacetonitrile
Authors: Kewley R.
Published: May 2006

The microwave rotational spectrum of methylthioacetonitrile has been studied in the frequency range 18–37 GHz. The spectrum found is that of the gauche conformer. The non-observation of the spectrum of the trans conformer indicates that its abundance is less than about 5%. The rotational and centrifugal distortion constants for the ground vibrational state of the gauche conformer are: A = 7715.123 MHz, B = 2641.756 MHz, C = 2174.538 MHz, DK = 0.6824 MHz, DJK = −2.52 kHz, and DJ = 1.96 kHz. The observed rotational constants are compatible with a dihedral angle of 66 ± 5° and a CSC angle of 104 ± 2°. The dipole moment of the gauche conformer has been determined as 3.02 D. Vibrational satellites due to S—CH2 torsion have been observed and a torsional frequency of 101 cm−1 has been estimated from relative intensity measurements.
Structure and properties of a trans–anti photodimer of 5-methylorotate
Authors: Huber Carol P. , Birnbaum George I. , Post Michael L. , Kulikowska Ewa , Gajewska Lucyna , Shugar David
Published: May 2006

5-Methylorotate is relatively radiation resistant in aqueous fluid medium, but readily photodimerizes in an ice matrix. Rapid formation of such a matrix made possible the preparative isolation of the photodimer in good yield. The potassium salt of the photodimer crystallizes as the hexahydrate, C12H10N4O8K2•6H2O. The crystals are triclinic with space group [Formula: see text]a = 8.139(3), b = 9.759(3), c = 7.398(3) Å, a = 100.28(7), β = 74.22(5), γ = 108.67(7)°, and V = 533.0 Å3, Z = 1. The structure was solved by Patterson and direct methods; refinement by block-diagonal least-squares converged at R = 0.041 for all 1671 observed reflections. The pyrimidine rings of the centrosymmetric photodimer are arranged in trans–anti configuration across the planar cyclobutane ring. The potassium ion is seven-coordinated. In aqueous medium the photodimer exhibits a pKa of 12.8 due to dissociation of the ring N(3) hydrogen. Irradiation in aqueous medium at 254 nm leads to quantitative regeneration of the monomer with a quantum yield of 0.8. Thermal regeneration of the monomer also occurs in neutral and acid aqueous media, but at a slower rate than for the trans–syn orotate photodimer. In contrast to the orotate photodimer, which undergoes alkali-catalyzed opening of the 3,4 bonds of the pyrimidine rings, the 5-methylorotate photodimer under these conditions dissociates to the parent monomer.
Resonance Raman in platinum phthalocyanine
Authors: Huang Tzer-Hsiang , Rieckhoff Klaus E. , Voigt Eva-Maria
Published: May 2006

The resonance Raman spectra and excitation profiles of platinum phthalocyanine (PtPc) in α-chloronaphthalene (α-ClN) and in mixtures of α-ClN and n-octane were obtained at 295 K with excitation from 660 to 570 nm covering the total lower energy absorption region of PtPc. Eighteen fundamentals and overtone-combinations were observed. Our data show that the third absorption maximum of PtPc in the visible region is actually the (0–1), but not the (0–2) as previously interpreted, transition. The (0–1) bands in the excitation profiles of most resonance-enhanced-vibrations were found to be more intense and frequency shifted compared with their counterparts in absorption. Based on the depolarization ratios, we deduced the symmetry of PtPc in α-ClN in the excited singlets to be D2h, C2v, or D2; no differences were found in the mixed solvents. The small Stokes loss observed in the absorption spectra, as well as the absence of the (0–2) maxima in the excitation profiles, indicate that the equilibrium position of the first excited singlet is only slightly different from that of the ground state.
Some reactions of N-substituted-1,2-dihydropyridines with cyanogen azide. Synthesis of 1,2,3,4-tetrahydropyridylidene-4-cyanamides
Authors: Ondrus Theodore A. , Knaus Edward E. , Giam C. S.
Published: May 2006

The reaction of cyanogen azide (2) with several N-substituted-1,2-dihydropyridines (1) has been investigated. Reaction of 1,2-dihydropyridines (1a–d) possessing a N-methoxycarbonyl or N-methanesulfonyl substituent with 2 afford a 1:1 mixture of stereoisomers E- and Z-1,2,3,4-tetrahydropyridylidene-4-cyanamides (3 and 4). In contrast, reaction of N-acetyl-2-butyl-1,2-dihydropyridine (1e) with 2 gave rise to the unexpected 2,7-diazabicyclo[4.1.0]hept-4-ene (7) and 2-diazo-1,2,3,6-tetrahydropyridylidene-3-cyanamide (9) together with a 1:1 isomeric mixture of 3e and 4e. Mechanisms for the formation of 3, 4, 7, and 9 are discussed.
Determination of stability constants by pH titrations: a critical examination of data handling
Authors: Field Terrence B. , McBryde W. A. E.
Published: May 2006

Data from simulated titrations (pH, titer, and pM) were generated from literature values of equilibrium constants, and then submitted to various published methods of calculation to regenerate the indicated equilibrium constants. These calculations were done with error-free input data, and the same with imposed random errors. In other experiments data from real titrations were subjected to the same analysis, and additional checks were made on the output of the calculations with an ion-selective electrode as a probe for pM. One method of data analysis was prone to cause errors in the finally recovered constants, and causes for this are suggested.
Constituents of commercial methoxychlor-III. The mechanism of tetraanisylethylene formation. unsym-Tetraarylethylenes (Ar2C=CAr2′): synthesis from DT class pesticides, and conversion to phenanthrenes and dibenzo[g,p]chrysenes
Authors: Mitchell Reginald H. , Mazuch Ludvik , Shell Barry , West Paul R.
Published: May 2006

Reaction of DT type pesticides with anisoie and A1Cl3 in CS2 yielded unsym-tetraarylethylenes (Ar2C=Ar2′), which on photocyclisation yielded phenanthrenes. Further oxidative closure to dibenzo[g,p]chrysenes occurs under conditions that faveur cation radical intermediates. Chromatography of commercial methoxychlor (DMDT) yielded tetraanisylethylene together with minor amounts of the corresponding photo products, 3,6-dimethoxy-9,10-dianisylphenanthrene and 3,6,11,14-tetramethoxydibenzo[g,p]chrysene, as well as other chloroanisylethylenes.
The proton magnetic resonance determination of the hindered rotation in α,α,α′,α′,3,4,6-heptachloro-o-xylene
Authors: Hutton Harold M. , Hiebert Walter E. , Mark Victor
Published: May 2006

A high resolution proton magnetic resonance investigation of the hindered rotation of the dichloromethyl groups as a function of temperature in α,α,α′,α′,3,4,6-heptachloro-o-xylene (HCOX) has been conducted using dynamic nuclear magnetic resonance line shape analysis, supplemented with a homonuclear double resonance saturation transfer technique. The rate process in HCOX involves a coupled rotation of the two substituted methyl groups and the nonmutual exchange of the three pairs of protons between two equally populated conformers. The Arrhenius and transition state parameters were determined from the rate constants obtained over a temperature range of −5 °C to 93 °C for a 5 mol% solution of HCOX in methylcyclohexane: ΔG≠ = 17.22 ± 0.07 kcal mol−1 at 298 K, ΔH≠ = 14.6 ± 0.3 kcal mol−1, ΔS≠ = −8.8 ± 0.8 cal mol−1 deg−1, and Ea = 15.3 ± 0.3 kcal mol−1. The results obtained for HCOX are compared with those for other chloro-substituted xylenes and toluenes.
The chemistry of N,N′-dimethylformamidine. II. Hydrolysis. Kinetically controlled formation of cis-N-methylformamide
Authors: Halliday James D. , Symons E. Allan
Published: May 2006

The hydrolysis of N,N′-dimethylformamidine (DMFA) has been investigated in acid and alkaline aqueous media by 1H nmr; only a narrow basic pH range could be extensively studied kinetically. The pseudo-first-order kobs rose steadily from pH 11.5 to 13.0 (reaction approximately first order in OH−), then became independent of pH above 13.5 (9.3 × 10−4 s−1 at 10 °C). In contrast to many amidines, DMFA is quite stable in acid solution (estimated value of the pseudo-first-order hydrolysis rate constant is 1.4 × 10−1 s−1 at 10 °C, pH 0.05, from measurements at 100 and 140 °C). This stability is ascribed to the difficulty of eliminating the fairly strong base methylamine from the tetrahedral intermediate in acid solution.N-Methylformamide (NMF), one of the products, is formed initially as the cis isomer. A somewhat slower conversion then occurs to the thermodynamically more stable trans isomer. This unusual result is explained in terms of Deslongchamps and co-workers' theory of stereoelectronic control for the orbital-assisted breakdown of tetrahedral intermediates.
Mechanism of L-ascorbic acid oxidation on a mercury electrode. II. Basic medium
Authors: Ruiz Juan José , Aldaz Antonio , Dominguez Manuel
Published: May 2006

A polarographic study of the oxidation mechanism of L-ascorbic acid is carried out in a basic medium and two oxidation waves are observed.An analysis of these waves shows that the limiting current is governed by diffusion and that in each reaction a two electron transfer takes place. On the rising portion of the waves, the oxidation process consists of two consecutive one electron transfers. In the first wave, the second transfer is the rate determining step, whilst in the second wave, a chemical stage subsequent to the second electron transfer is the rate determining step. The reaction orders, together with the Tafel slopes, are calculated.The oxidation mechanism of this acid in basic media is different from that in acid media.
The crystal and molecular structure of trans-chloro(3-hydroxypropyl-N,N-dimethylaininocarbene)-bis(dimethylphenylphosphine)platinum(II) hexafluorophosphate
Authors: Stepaniak Robert F. , Payne Nicholas C.
Published: May 2006

The crystal and molecular structure of trans-chloro(3-hydroxypropyl-N,N-dimethylaminocarbene)bis(dimethylphenylphosphine)platinum(II) hexafluorophosphate has been determined from three-dimensional X-ray data collected on an automated four circle diffractometer using CuKα radiation. The compound crystallizes in the orthorhombic space group Pna21, with Z = 4, and cell dimensions a = 14.403(2), b = 12.631(2), and c = 16.151(2) Å. Full matrix least-squares refinement on F gave a final conventional R factor of 0.047 for 3442 observations with I > 3σ(I). The cation coordination geometry is square planar, with the carbene ligand lying approximately perpendicular to the plane. The Pt—Cl bond length is 2.356(4) Å and the Pt—C(carbene) distance is 1.978(12) Å. The C(carbene)—N bond length is 1.293(16) Å. These dimensions are discussed in terms of the trans influences of the carbene and chloride ligands and the bonding in the carbene species.
Synthesis of the spirosesquiterpene (−)-acorenone and related cyclopentanoid monoterpenes
Authors: Lange Gordon L. , Neidert Eli E. , Orrom Will J. , Wallace David J.
Published: May 2006

The first total synthesis of the spirosesquiterpene (−)-acorenone (1) is described. The critical step involves a spiroannelation of the enamine of aldehyde 11 with 1-methoxy-3-buten-2-one (16) in the presence of acetic acid to give ketone 17. Reaction of 17 with methylmagnesium iodide followed by treatment of the resultant alcohol 18 with p-toluenesulfonic acid in refluxing benzene leads directly to 1 in good overall yield. As the starting material for the preparation of the cyclopentanoid aldehyde 11 was (+)-limonene the final product is optically active and thus the absolute configuration of naturally occurring (−)-acorenone (1) is established. The preparation of a number of other optically active cyclopentanoid monoterpenes (4 and 13) is also described.
Approaches to the synthesis of triterpenoids. III. Some cis-decalins corresponding to rings D and E of some pentacyclic triterpenes
Authors: ApSimon John W. , Badripersaud Satyanand , Nguyen Tung T. T. , Pike Richard
Published: May 2006

The synthesis of 10-methoxycarbonyl-1,7,7-trimethyl-cis-2-decaIone (6c) is described as well as that of the corresponding trans isomer. The stereochemistry of catalytic hydrogenation of the carbon–carbon double bond of Δ1,9-2-octalones is shown to be controlled by the angular substituent at position 10.The cis-decalin system is considered as a synthon for the DE ring system of certain pentacyclic triterpenes.
Crystal and molecular structure of diphenylboron N-methylacethydroxamate (4,5-dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclopent-4-ene)
Authors: Rettig Steven J. , Trotter James , Kliegel W. , Nanninga D.
Published: May 2006

Crystals of diphenylboron N-methylacethydroxamate are orthorhombic, a = 12.5478(8), b = 7.8735(3), c = 13.6809(5) Å, Z = 4, space group Pnam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.037 and Rw = 0.054 for 1265 reflections with I ≥ 3σ(I). The molecule features a five-membered BO2CN ring which lies in the crystallographic mirror plane. The carbon and nitrogen atoms of the heterocyclic ring are positionally disordered. Mean bond lengths (corrected for libration) are: O—B, 1.550(2), B—C, 1.609(2), O—C/N, 1.340(3), C—N, 1.300(2), C/N—CH, 1.470(2), and C—C(phenyl), 1.394(8) Å.
Crystal structures of medium ring compounds. Part II. The crystal and molecular structure of cis-anti-cis-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane
Authors: Terzis Aris , Faught J. Brian , Grindley T. Bruce
Published: May 2006

The crystal structure of cis-anti-cis-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane (2) has been determined by X-ray diffraction. The crystals are monoclinic, a = 11.120(1), b = 8.127(1), c = 7.990(1) Å, β = 110.01(1)°, P21/c, with Z = 2. The structure was solved by the application of symbolic addition procedures and refined to a final R value of 0.031 (Rw 0.040) for 989 reflections with I > 2.0σ(I).This structural determination confirms a previous tentative assignment of the relative configuration of 2. In the crystal, the two cis-substituted cyclohexane rings adopt chair conformations in which the equatorial oxygens on different rings are linked through methylene groups to axial oxygens on the other rings. The central 10-membered tetraoxecane ring adopts the boat–chair–boat conformation, the most stable conformation for cyclodecane.
Synthesis of covalently-linked dimeric porphyrins
Authors: Paine III John B. , Dolphin David
Published: May 2006

Dimeric porphyrins covalently linked directly at their periphery (β,β′-biporphyrins) or via a hydrocarbon chain (CH2)n, where n = 1–8, have been synthesized from the corresponding β,β′-linked bispyrroles.
On the existence of cis and trans conformational isomers in 2-methylphenol and 4-chloro-2-methylphenol
Authors: Schaefer Ted , Chum Kalvin
Published: May 2006

The analysis of the proton magnetic resonance spectra of 2-methylphenol and of 4-chloro-2-methylphenol in benzene-d6 and CCl4 solutions yields spin–spin coupling constants over five bonds between the hydroxyl proton and the meta ring protons. These coupling constants are related to the intramolecular equilibrium between conformers in which the hydroxyl group is oriented cis or trans to the methyl group. The free energy difference between the conformers is 0.4 ± 0.1 kcal/mol, with the trans form being the more stable. The concentration dependence of the hydroxyl proton chemical shift of the chloro compound in CCl4 suggests that dimerization is relatively unimportant and yields rough values for the extent of self-association. It is argued that the derived free energy values refer to the intramolecular equilibrium for the monomers.
Caerulomycin D, a novel glycosidic derivative of 3,4-dihydroxy-2,2′-dipyridyl 6-aldoxime from Streptomyces caeruleus
Authors: McInnes A. Gavin , Smith Donald G. , Walter John A. , Wright Jeffrey L. C. , Vining Leo C. , Arsenault Guy P.
Published: May 2006

Analysis by 1H and 13C nmr spectrometry showed that caerulomycin D, a new metabolite isolated from S. caeruleus, possessed a novel ring system and had the structure (2S,3R,4R,4aS,10aS)-3,4,4a,10a-tetrahydro-4-hydroxy-3,4a-diniethoxy-2-methyl-9-(2-pyridyl)-2H-pyrano[3′,2′:5,6]-p-dioxino[2,3-c]pyridine-7-carboxaldenyde (E)-oxime.
The photochemical reactivity of some benzoylthiophenes. IV. The effect of an adjacent methyl group on the excited state reactivity of 3-benzoylthiophene
Authors: Arnold D. R. , Hadjiantoniou C. P.
Published: May 2006

The electronic absorption and phosphorescence emission spectra and the photochemical reactivity of several methyl-3-benzoylthiophenes (2- and 4-methyl-3-benzoylthiophene (1, 2), 2,5-dimethyl-3-benzoylthiophene (3), and 3-(2-methylbenzoyl)thiophene (4)) have been studied. Partial state diagrams have been constructed. The lowest energy absorption in hexane solution in every case is the carbonyl n → π* transition. The two lowest triplet states of these ketones are close in energy and, in fact, the nature of the emitting triplet (n,π* or π,π*) depends upon the position of methyl substitution and upon the solvent. The photochemical reactions studied include intramolecular hydrogen abstraction (revealed by deuterium exchange in the adjacent methyl group upon irradiation in perdeuteriomethanol solution), photocycloaddition of dimethyl acetylenedicarboxylate to the thiophene ring, and photocycloaddition of isobutylene to the carbonyl group. Generalizations, potentially useful for predicting photochemical reactivity of these and other aromatic ketones are summarized.
Dehydrogenation of Δ3-carene over chromia and chromia–alumina catalysts
Authors: Krishnasamy V.
Published: May 2006

3-Carene is dehydrogenated over oxidized and reduced chromia and chromia–alumina catalysts at 340 to 500 °C, without and with pyridine. Dehydrogenation is found to be more effective over reduced than oxidized catalysts; in either state, however, chromia–alumina is more active than chromia. Pyridine brings down the dehydrogenation ability of chromia and chromia–alumina in both reduced and oxidized states, more markedly in the reduced state. The ratio of p-cymene to m-cymene at 360 to 425 °C is higher over chromia than over chromia–alumina. Increase of temperature from 360 °C to higher values decreases the ratio of cymenes over chromia but does not affect the ratio over chromia–alumina. Pyridine has no effect on the ratio of cymenes over chromia; over chromia–alumina, neither, pyridine nor the pretreatment of the catalyst with oxygen or hydrogen has any effect on the ratio.
The photochemistry of acrylonitrile vapour at 213.9 nm
Authors: Gandini A. , Hackett P. A.
Published: May 2006

The photolysis of acrylonitrile vapour in the π* ← n transition was carried out at 213.9 nm. Evidence is presented for two molecular elimination channels, one to yield acetylene and hydrogen cyanide (Ф = 0.50), the other to yield cyanoacetylene and hydrogen (Ф = 0.31). Experiments on acrylonitrile-1-d gave evidence that molecular elimination proceeds by α–β elimination following rapid intramolecular scrambling of deuterium by H/D migration in the excited state.
Synthesis of a 4,5-unsaturated-3-keto sugar (methyl 2-O-benzoyl-4-deoxy-6-O-triphenylmethyl-α-D-glcero-hex-4-enopyranosid-3-ulose)
Authors: Yunker Mark Bernard , Fraser-Reid Bert
Published: May 2006

An approach to the synthesis of the hex-4-enopyranosid-3-ulose 5 has been investigated. The readily available 3-keto derivative 8 is easily debenzylidinated but the resulting diol is benzoylated preferentially at carbon 4 rather than at the primary position. However, tritylation occurs at the primary position and the product is sulfonylated to give the 4-O-methylsulfonyl derivative (11b). lodinolysis of this α-ketosulfonate did not follow an SN2 course giving the desired axial iodide 14b. Instead a course of reductive elimination was observed involving the presumed intermediacy of an enolic hypoiodite. β elimination of methanesulfonic acid from 11b was in fact possible by using diazabicyclononene in benzene-tetrahydrofuran solution. The process undoubtedly involves epimerisation, and the product consists of a mixture of the desired 5 (R = CPh3) and its 2-epimer 22. These enones are prone to base-catalysed decomposition so that although the three steps from the starting ketone 8 to the sulfonate 11b can each be carried out in excellent yield, the final elimination proceeds in 39% yield after isolation.
Hétérobicycles oxygénés. Synthèse d'alkyl-3,6,8-trioxabicyclo[3.2.1]octanes et d'alkyl-3,7,9 et -4,7,9-trioxabicyclo[4.2.1]nonanes
Authors: Calinaud Pierre , Gelas Jacques
Published: May 2006

The cyclization in a basic medium of 2 (or 4)-chloroalkyl-4 (or 2) -hydroxyalkyl-1,3-dioxolanes leads to bicyclic acetals, the 3,6,8-trioxabicyclo[3.2.1]octanes, which are useful intermediates for synthesis, yielding notably functionalized 1,4-dioxanes. The nmr spectra of these heterobicyclics were studied. The geminal proton coupling constants permit oneto distinguish between five- and six-membered rings and the determination of couplings over several bonds (4J and 5J) yields information concerning the conformation of the model bicyclics.Two isomeric series of alkylated bicyclic acetals (3,7,9- and 4,7,9-trioxabicyclo[4.2.1]nonanes) are accessible by the following routes: (a) the intramolecular addition of a 4-hydroxy-alkyl group to the ethylenic double bond on the carbon atom a to C-2 in the 1,3-dioxolanes; (b) the dechlorohydration of 2-chloromethyl-4-hydroxyalkyl-1,3-dioxolanes; (c) the dehydration of dioxolane-diols. The main interest in these heterobicyclics is to prepare a seven-membered ring and to be able to prepare functionalized 1,4-dioxepanes. [Journal translation]
Some reactions of 10-methyl-10H-pyrido[3,2-b][1,4]benzothiazine-n-butyllithium adduct with electrophiles
Authors: Pasutto Frank M. , Knaus Edward E.
Published: May 2006

Reaction of 10-methyl-10H-pyrido[3,2-b][1,4]benzothiazine (4) with n-butyllithium affords a mixture of the C-4 proton abstraction product 5a and 2-n-butyl-4a-lithio-10-methyl-2,4a-dihydropyridyl[3,2-b][1,4]benzothiazine 6a which results from nucleophilic addition at the C-2 position. Treatment of 5a and 6a with deuterium oxide gave the deuterated products 5c and 6c in a ratio of 1:4.4 whereas reaction with diethyl chlorophosphate afforded a mixture of the 4-substituted product 5d, 4a-ethyl derivative 6e, oxidation product 7 as well as the N-substituted-1,2-dihydropyridyl derivative 13. The stability of the 4a-lithio-2,4a-dihydropyridyl adduct 6a is attributed to the ability of sulfur to stabilize an adjacent carbanion. The mechanism for the formation of 6e is described.
Derivatives of porphobilinogen and isoporphobilinogen
Authors: Ufer Guenter , Tjoa Sioe S. , MacDonald S. Ferguson
Published: May 2006

One of the more convenient syntheses of porphobilinogen has been adapted to that of isoporphobilinogen and extended to the lactams of both. Aminomethylation of appropriate 2-free pyrroles by the Tscherniac-Einhorn method gives derivatives of porphobilinogen and isoporphobilinogen. A method for aminomethylating reactive pyrroles is illustrated by the conversion of 2,4-dimethylpyrrole into its 5-N-acetylthiocarboxamide, then into its 5-acetylaminomethyl derivative, using acetyl isothiocyanate then Raney nickel, both at ≤20 °C.
Concerning the extension of the J method for internal barriers to six-bond couplings to 19F in the 4-fluorophenyl fragment
Authors: Schaefer Ted , Danchura Werner , Niemczura Walter , Peeling James
Published: May 2006

The long-range coupling constants over six bonds from the side-chain protons to the fluorine nucleus on the ring are extracted from the proton magnetic resonance spectra of p-fluorobenzyl cyanide, chloride, and bromide; of p-fluorobenzal chloride; and of p-fluoroisopropylbenzene. On the assumption that these couplings are transmitted via a σ–π mechanism, a hindered rotor treatment yields the barriers to internal rotation about the carbon–carbon bond which attaches the substituent to the benzene ring. These barriers, when compared to those derived from the analogous proton–proton coupling constants, apparently are accurate enough for the determination of ground state conformations and for a rough assessment of the energetics of conformational interconversions.
13C and 2H spin–lattice relaxation in neopentane-d12
Authors: Pettitt Brian A. , Wasylishen Roderick E. , Donc Ronald Y. , Pitner T. Phil
Published: May 2006

The results of a variable temperature study of the 2H and 13C spin–lattice relaxation times in neopentane-d12 are reported. along with those for the 13C's in neopentane at a single temperature. Orientational and angular momentum correlation times derived from these T1's exhibit the following: (i) τ2 is continuous through the melting point with an activation energy of 0.98 kcal/mol, (ii) τJ is more or less constant at 0.33 ± 0.03 ps within 40 K of either side of the melting point, and (iii) they do not conform to the theoretical relationships of extended diffusion, Fokker–Planck, or Langevin theories. The spin–rotation coupling constants are calculated to be −0.69 kHz for neopentane and −0.52 kHz for neopentane-d12
Appearance potentials of ion fragments of iron pentacarbonyl
Authors: Conard B. R. , Sridhar R.
Published: May 2006

The previously reported fragments and a new fragment, FeC2+, have been observed in the mass spectrum of iron pentacarbonyl. The electron impact appearance potentials for the minor fragments of Fe(CO)5 are (in eV): FeC3O2+, 18.2; FeC2O+, 20.2; FeC2+, 29.9; FeO+, 22.5; and Fe(CO)32+, 24.0. Electron energy calibration was carried out using existing data for the major fragments of Fe(CO)5.
β-Lactams. III. The synthesis of 7-β-phenyiacetamido-3′-carboxybenzo[3,4]-O-2-isocephem
Authors: Just George , Zamboni Robert
Published: May 2006

The synthesis of the β-lactam 34 from 3-methoxy-2-nitrobenzaldehyde is described.
A new regiospecific synthesis of α,β-unsaturated ketones via acetylene derivatives
Authors: Hooz John , Mortimer Richard D.
Published: May 2006

The reaction of trialkylalkynylborate salts with benzeneselenenyl chloride, followed by selective oxidation, provides a new synthetic pathway from acetylenes to acyclic trans-α,β-unsaturated ketones. The method is especially useful for preparing unsymmetric acyclic enones which are difficultly accessible using current procedures.
The heat capacities and volumes of some low molecular weight amides, ketones, esters, and ethers in water over the whole solubility range
Authors: Roux Geneviève , Perron Gérald , Desnoyers Jacques E.
Published: May 2006

The densities and heat capacities per unit volume of aqueous solutions of propionamide, methylacetate, ethylacetate, methylethylketone and diethylketone, and bis(2-ethoxyethyl)ether were measured over the whole solubility range with a flow densimeter and a flow microcalorimeter. Most systems were studied at 10, 25, and 40 °C. Properties of the pure liquids were also measured whenever possible. The derived apparent molal volumes [Formula: see text] all decrease with concentration in the water-rich region, except with ethyl acetate which increases at high temperature. In general the more hydrophobic the solute the more negative the initial slope. All apparent molal heat capacities [Formula: see text] decrease as a function of concentration and the decrease is more important for more hydrophobic solutes. The apparent molal expansibilities [Formula: see text] are obtained from [Formula: see text]. They are positive for all solutes but, at low concentrations, they are smaller than the corresponding molar value of the pure liquid. Various factors affecting hydrophobic interactions are examined.
Memory impairment in flowing suspensions. I. Some theoretical considerations
Authors: Okagawa A. , Ennis G. J. , Mason S. G.
Published: May 2006

When a suspension of nearly monodisperse rigid axisymmetric particles in a Newtonian liquid is sheared, the orientation distributions of the particle undergo damped oscillations of frequency twice that of the rotating particles. If the flow is stopped and then reversed, the oscillations regrow under certain restricted conditions until the initial state is fully restored: the system has perfect memory. Removing some of the restrictions causes imperfect recovery of the initial orientation distribution, so that when the flow is reversed cyclically back and forth, the orientation distribution eventually becomes time-independent: the system has lost all of its memory. A number of sources of memory impairment are considered theoretically, several of which are amenable to experimental verification and are illustrated by numerical calculation.
Fluorinated alkoxides. Part XIII. The reduction of β-imino-alkoxy complexes to give stable, polydentate, amino-alcohols; their coordination to Co2+, Ni2+, and Cu2+
Authors: Martin John W. L. , Willis C. J.
Published: May 2006

The amino-alcohols HOC(CF3)2CH2CH(CH3)NH(CH2)3NHCH(CH3)CH2C(CF3)2OH and HOC(CF3)2CH2CH(CH3)NH(CH2)3NH(CH2)3NHCH(CH3)CH2C(CF3)2OH have been prepared by reduction of the corresponding imino-alcohols coordinated to, e.g., Cu2+, by use of LiAlH4. The products are capable of acting as polydentate, dinegative, ligands (following ionization of the fluorinated alcohol groups) and the second compound gives stable, neutral, complexes of Co2+, Ni2+, and Cu2+ in which the metal atom is five-coordinate.
Simultaneous determination of relative and absolute rate constants in racemization studies; applications to kinetic isotope effects
Authors: Tencer Michal , Stein Allan R.
Published: May 2006

The method reported allows the simultaneous determination of relative and absolute rate constants for two substances in a single kinetic run. The approach is of special interest for kinetic isotope effect determinations where rate ratios are often near one and failure to exactly duplicate reaction conditions can lead to uncertainties in the values calculated from independently measured rate constants. For racemization studies, using two optically active materials with opposite signs of rotation, knowing their initial rotational contribution and having the faster racemizing one in higher concentration, the rates can be calculated if the times required to reach zero net rotation and the extremum value are measured. Other systems to which the method can be extended are suggested.
The oxygen exchange from O2/C18O2 with surfaces of vanadium pentoxide and alkali metal-promoted vanadium pentoxide catalysts
Authors: Fikis David Victor , Heckley Keith Walter , Murphy William John , Ross Robert Anderson
Published: May 2006

The oxygen exchange reaction between O2/C18O2 and the surfaces of vanadium pentoxide and promoted vanadium pentoxide catalysts has been studied in a circulation system using a quartz differential reactor. Isotopic compositions were analysed with an in-line mass spectrometer. Alkali metal sulphates, Li to Cs, were added to the pentoxide as individual promoters at a concentration level of 9 mol % and the effect of variation of promoter concentration was examined with melts containing potassium sulphate at additional levels of 1, 2, and 5 mol%. The structures of the solids were studied by X-ray diffraction and by ATR and transmission infrared spectroscopy. The latter results have been used to explain the two activity series for the exchange rates: (i)V2O5 < Na < Li < K < Rb < Cs (melts) and (ii) V2O5 < 1 mol% < 2 mol% < 5 mol% < 9 mol% (K), in terms of additive effects on the relative abundance and strength of identified vanadium/oxygen linkages in the surfaces of the catalysts.
13C nuclear magnetic resonance spectra of some C-19-hydroxy, C-5,6 epoxy, C-24 ethyl, and C-19-norsteroids
Authors: Holland Herbert L. , Diakow Peter R. P. , Taylor Gregg J.
Published: May 2006

The carbon magnetic resonance spectra of a series of C-19 hydroxy, C-5β,6β epoxy, C-5α,6α epoxy, and C-24 ethyl steroids have been assigned. Shift parameters for the C-19 hydroxyl function are listed. The data presented has led to a reassignment of the published spectra of several C5α,6 α epoxy steroids. In addition, 13Cmr spectral data for several bicyclic enones and a Δ5(10)-3-estrone are presented.
Structure and bonding in cyclic phosphoramidates as determined by carbon-13 magnetic resonance
Authors: Buchanan Gerald W. , Morin Frederick G.
Published: May 2006

13C chemical shifts and 13C–31P couplings are reported for 11 cyclic phosphoramidates of ring sizes from four to nine. Vicinal couplings are compared with those of carbocyclic analogs and provide insight regarding the degree of nitrogen lone pair derealization into the N—P bond. For six-membered and larger rings, there appears to be nearly complete lone pair delocalization, i.e., a trigonal planar nitrogen atom. In azetidine derivatives the nitrogen lone pair remains localized, giving rise to a highly puckered ring conformation. Pyrrolidine derivatives are viewed as having a nitrogen with a partially delocalized electron pair.