bluuebunny/crossref_metadata_2025 huggingface dataset:
Water-soluble lysine-containing polypeptides. VI. A study of annealed complexes between calf thymus DNA and the following copolymers: poly-(L-lysyl-X), where X = Gly, L-Ala, L-Val, L-Leu, and L-Phe
Authors: Kielland Sandra L. , Slotin Lewis A. , Williams Ross E.
Published: May 2006

Turbidity measurements, circular dichroism spectra, electron micrographs, and thermal–optical measurements have been made on complexes between sonicated DNA and several polypeptides with the following structure: poly-(L-lysine-L-X) where X = Gly, Ala, Val, Leu, Phe. The results are influenced by any method of polypeptide synthesis which results in chain branching of the polypeptide. When polypeptides prepared by the same synthetic route are incorporated into the complexes the results also depend on the polypeptide used. Five possible explanations are offered as sources of the latter observations.
A facile synthesis of methyl 3,6-dideoxy-α-L-xylo-hexopyranoside (colitose)
Authors: Bundle David R. , Josephson Staffan
Published: May 2006

Methyl 3,6-dideoxy-α-L-xylo-hexopyranoside (7) bas been synthesised in four steps from methyl α-L-fucopyranoside. The intermediate methyl 3,4-O-benzylidene-α-L-fucopyranoside was separated into the S (1a) and R (1b) diastereoisomers and the absolute configuration established by proton and carbon-13 nmr spectroscopy. Under the conditions of the Hanessian–Hullar reaction methyl 4-O-benzoyl-3-bromo-3,6-dideoxy-α-L-gulopyranoside was the major product. Each diastereoisomer 1a or 1b gave identical products and product ratios; the stereochemistry and relative proportions of these products were determined by proton and carbon-13 nmr. The synthesis of ascarylose from methyl α-L-rhamnopyranoside by an analogous route is also reported. The bromo deoxy intermediates were reduced to the dideoxy sugars by catalytic hydrogenation with palladium.
La formation des liaisons éthériques lors de la production du polytéréphthalate d'éthylène glycol
Authors: Hornof Vladimir , Zeman Leoš
Published: May 2006

Ether-type linkages are formed as by-products during the preparation of polyethylene terephthalate from dimethyl terephthalate and ethylene glycol. Incorporated in the polymer, these linkages affect its physical and mechanical properties such as tensile strength, melting point, and resistance to oxidation. An improved chemical method of analysis has been developed allowing an accurate determination of ether bonds in polyester fibres. The method is based on the selective oxidation of ethylene glycol with periodic acid and takes advantage of hydrolysis with water under pressure to decompose the polymer. The method has been employed to study the effect of the concentration of polycondensation catalyst on the formation of ethers.
Synthesis of the 3,3′-dinitro and 3,3′-diamino derivatives of α,α-trehalose and its D-gluco, D-manno and D-manno, D-manno isomers
Authors: Baer Hans H. , Bell Anna J.
Published: May 2006

The tetraaldehyde 2 obtained from α,α-trehalose (1) by periodate oxidation was cyclized with nitromethane in the presence of sodium methoxide to give a mixture of 3,3′-dideoxy-3,3′-dinitro disaccharides in good yield. Acetalation of the product with benzaldehyde followed by chromatographic separation of the bisacetals afforded crystalline 4,6;4′,6′-di-O-benzylidene derivatives (3, 4, and 5) of 3-deoxy-3-nitro-α-D-glucopyranosyl 3-deoxy-3-nitro-α-D-glucopyranoside (6, 3,3′-dideoxy-3,3′-dinitro-α,α-trehalose), 3-deoxy-3-nitro-α-D-glucopyranosyl 3-deoxy-3-nitro-α-D-mannopyranoside (7), and 3-deoxy-3-nitro-α-D-mannopyranosyl 3-deoxy-3-nitro-α-D-mannopyranoside (8), respectively. Acid debenzylidenation then gave crystalline 6–8, and these were hydrogenated catalytically to produce the corresponding diamino disaccharide dihydrochlorides 9–11.
The crystal structures of S7NSN(CH3)2 and (C6H11)2NSN(C6H11)2
Authors: Bruce Robert B. , Gillespie Ronald J. , Slim David R.
Published: May 2006

The compound S7NSN(CH3)2 has been prepared by the reaction of S7NH with S[N(CH3)2]2. Crystals are orthorhombic with a = 12.412(4), b = 23.894(6), c = 8.132(2) Å, Z = 8, space group Pbca. The structure was refined to a final agreement index R1 of 0.051 for 1721 observed reflections. The structure of S[N(C6H11)2] was also determined for comparison. The crystals are monoclinic with a = 13.74(2), b = 6.196(8), c = 13.74(2) Å, (β = 91.26(8)°, Z = 2, space group I2. The structure was refined to a final agreement index, R1 of 0.052 for 1024 observed reflections.
Stéréochimie de β-diols et de leurs dérivés cycliques. XIII. Etude structurale en résonance magnétique nucléaire du proton de dioxanne-1,3-4-spirocyclohexanes: tert-butyl-6-c méthyl-2-r (série II) et diméthyl-2-r, 5-t ou 5-c (série III) dioxanne-1,3-4-t ou -c-spirotriméthyl-3′,3′,5′-cyclohexanes-trans ou -cis
Authors: Cazaux Louis , Gorrichon Jean-Pierre , Koudsi Yahia , Maroni Pierre
Published: May 2006

The nmr spectra at 60, 100, and 250 MHz in CCl4 of two series of four and eight diastereoisomers of the title 1,3-dioxanespiro-4-cyclohexanes have been analysed. In particular, use of the empirical calculation of chemical shifts allows for the unambiguous determination of structure without the need for chemical methods. With two exceptions, these compounds exist in the double chair conformation. In these molecules the γ intercyclic effect of the methyl groups in position 5 have been calculated. [Journal translation]
Stéréochimie de β-diols et de leurs dérivés cycliques. XIV. Analyse structurale de dioxanne-1,3-4-spirocyclohexanes par résonance magnétique nucléaire du 13C
Authors: Cazaux Louis , Gorrichon Jean-Pierre , Maroni Pierre
Published: May 2006

Following the methods of Grant and Saunders the empirical calculation of the 13C chemical shift in five series of 1,3-dioxanespiro-4-cyclohexanes, including one with eight diastereoisomers, is reported. The increments used in these calculations have been derived from the literature or determined from model compounds and their use leads to unambiguous structural assignments. [Journal translation]
13C and 1H nuclear magnetic resonance spectroscopy of C-19 and 6β-methyl substituted steroids: long-range shift effects in conformational analysis
Authors: Scott Katherine Násfay , Mareci Thomas Harold
Published: May 2006

13C and 1H nmr spectra were obtained and assigned for nine C-19 substituted cholest-5-enes, three 6β-substituted 19-norcholest-5(10)-enes, and several related steroids. 13C chemical shift effects have previously not been studied in either C-19 substituted steroids or in cholest-5(10)-enes. In the present study, substituent effects on the 13C chemical shifts of the α, β, γ, and δ carbons were evaluated in detail. Although the substituent in C-19 substituted and 6β-methyl substituted steroids is less rigidly oriented with respect to the rest of the molecule than in ring-substituted steroids, similar shift effects were observed. In cholest-5-enes the observed 13C and 1H shift effects and the temperature dependence of the 13C shifts indicate that the preferred orientation of the C-19 substituent is anti to C-1. The relative stabilities of the rotamers can be attributed to the orientation of the C-19 substituent with respect to the double bond. This interpretation is supported by the fact that the preferred orientation of the iodine in 6β-iodomethyl-19-norcholest-5(10)-en-3β-ol has the same spacial relationship with respect to the double bond, i.e., gauche to C-5 and C-7.
Fast reaction kinetics of the binding of bromide to iron(III) studied on a high pressure laser temperature jump apparatus
Authors: Hasinoff Brian B.
Published: May 2006

The kinetics of the binding of Br− to Fe(III) were studied as a function of [H+] and [Br−] on a high pressure laser temperature jump apparatus up to 2.76 kbar. At constant [H+] the pseudo first order rate constant for formation of FeBr2+ showed little dependence on pressure or on [Br−] over the range 0.02 to 1.9 M. The results were interpreted by a mechanism in which Fe3+ and FeOH2+ react with Br− to form ion pairs prior to formation of their inner sphere complexes. The kinetic activation volume for the conversion of the Fe3+, Br− ion pair to FeBr2+ appears to be quite negative, consistent with an associative interchange (Ia) mechanism.
The crystal and molecular structure of 6,7-bis(methoxycarbonyloxy)-1,2,3,4-tetrahydroisoquinoline-[1,2-c]-oxazol-2-one-[3,4-b]-1-chloro-3-methoxycarbonyloxy-6,7-methylenedioxyindane
Authors: Wong-Ng Winnie , Nyburg S. C.
Published: May 2006

A synthetic intermediate expected to be a spirobenzylisoquinoline bromo-derivative proved, on X-ray crystal structure analysis, to be the title compound, a chloro-derivative with the isoquinoline nitrogen ring-closed. Crystals belong to the monoclinic system, space group P21/c, a = 13.68(2), b = 10.81(2), c = 22.12(4) Å, β = 129.2(4)°, Z = 4 molecules per cell. Intensity data were collected by diffractometer and the structure refined to a conventional R of 0.051.
Chemical reactions in glow discharges. IV. Production and removal of oxygen atoms in the dc glow discharge
Authors: Costa Motilal D. , Zuliani Preston A. , Deckers Jacques M.
Published: May 2006

An experimental technique for the measurement of the rate of formation and removal of atomic oxygen in an active glow discharge is described. The concentration of atomic oxygen was monitored with a mass spectrometer by sampling the gases flowing through the discharge. The rate of removal of oxygen atoms was found to be first order in atomic oxygen and 10 to 100 times faster than the corresponding recombination rate in the afterglow region. The measured rates of atom production are in agreement with those calculated by assuming electron impact dissociation of ground state molecular oxygen. The atoms are removed by a wall recombination process.The ability of trace amounts of certain gases to enhance significantly the extent of dissociation in an electric discharge in oxygen has been studied. Only those added gases which contain a hydrogen or nitrogen atom are effective in enhancing the yield of atomic oxygen. For each hydrogen atom introduced into the oxygen stream about 300 extra oxygen atoms could be produced. This 'catalytic' effect is shown to be due to a marked decrease in the rate of recombination of O-atoms at the walls of the discharge tube. Whatever small change that occurs in the rate of O-atom production can be easily accounted for by a change in the energy distribution of the electrons in the discharge due to the effect of the additives.
Stereoselective interaction of a tridentate Schiff base complex of nickel(II) and amino acids
Authors: Erno B. , Jordan R. B.
Published: May 2006

It has been observed that a tridentate Schiff base complex of nickel(II), triaquotribenzo-[b,f,j][1.5.9]-triazacyclodecinenickel(II), commonly called (TRI)Ni(OH2)32+, shows substantial stereoselectivity on complexing with several amino acids. This provides a convenient way to resolve (TRI)Ni(OH2)32+ using histidine as a resolving agent, and either ion exchange or perchlorate salt crystallization techniques.The resolved (TRI)Ni(OH2)32+ may then be used to resolve other amino acids or as a sensitive test of the stereochemistry of an amino acid. The test can be done on milligram quantities because of the insolubility of the complex perchlorate salt and because of the relatively large molecular rotation (2 × 105 deg at 283 nm) of (TRI)Ni(OH2)32+. The amino acid is easily released by treatment of the complex with dilute acid (Ph ≈ 2). The procedure has been tested with histidine, tyrosine, methionine, and phenylglycine.
Synthesis related to the octodiose in apramycin. Part III
Authors: Jarrell Harold C. , Szarek Walter A.
Published: May 2006

A synthesis of methyl 2,3-di-O-benzyl-7,8-dideoxy-4-O-methylthiomethyl-D-glycero- and L-glycero-α-D-gluco-oct-7-enopyranoside (11 and 12) has been achieved by the reaction of methyl 2,3-di-O-benzyl-4-O-methylthiomethyl-α-D-gluco-hexodialdo-l,5-pyranoside (9) with vinylmagnesium bromide; the stereochemistry at C-6 was established by degradation of 12 to the enantiomer of a known heptose derivative. Olefin 12 was converted, in six steps, into a mixture of dialdose derivatives 18 and 19 from which methyl glycosides 21 and 20, respectively, were prepared and shown to have the desired trans-decalin structure. The stereochemistry at C-7 in glycosides 20 and 21 was established by nmr spectroscopy.An intramolecular reaction involving the methylthiomethyl function has been observed and shown to give rise to O-methylene derivatives.
Enzymes in organic synthesis. 14. Stereoselective horse liver alcohol dehydrogenase catalyzed oxidations of diols containing a prochiral centre and of related hemiacetals
Authors: Jones J. Bryan , Lok Kar P.
Published: May 2006

The asymmetric synthetic potential of horse liver alcohol dehydrogenase catalyzed oxidations of variously 3-substituted pentane-1,5-diols has been further delineated. The oxidations proceed with enantiotopic selectivity to give the corresponding (3S)-3-substituted valerolactones of up to 78% ee. The reactions occur via initial oxidation of the pro-S hydroxyethyl group, with the initially-formed hydroxyaldehydes undergoing further in situ enzyme-catalyzed oxidation in their hemiacetal forms to give the (3S)-lactones directly. The hemiacetal oxidation step is also stereoselective, with oxidation of the (4S)-enantiomer being much preferred. The size of the substituent at C-3 in the diols (C-4 in the hemiacetals) affects both the enantiotopic and enantiomeric specificity of the enzyme. Both types of stereospecificity are highest when the substituents are smallest, such as methyl or ethyl, and diminish progressively for diol or hemiacetal substrates bearing large aliphatic or aromatic substituents. All reactions were carried out on a preparative (up to 2 g) scale.
Isotope effects in nucleophilic substitution reactions. II. Secondary α-deuterium kinetic isotope effects: a criterion of mechanism?
Authors: Westaway Kenneth Charles , Ali Syed Fasahat
Published: May 2006

A very large secondary α-deuterium kinetic isotope effect of 1.179 ± 0.007 (1.086 ± 0.003 per α-deuterium) has been observed for the SN2 reaction of thiophenoxide ion with benzyldimethylphenylammonium ion in DMF at 0°C. This large isotope effect which is far outside the range reported for SN2 reactions, is attributed to the fact that the extraordinarily large steric crowding around the Cα—H bonds in the substrate is reduced in the SN2 transition state. The structure of the transition state is shown to be consistent with this hypothesis.
Anisotropic motion in 1-substituted adamantanes from 13Cmr relaxation time data
Authors: Beierbeck Helmut , Martino Robert , Saunders John K.
Published: May 2006

The carbon-13 relaxation time data and the calculated diffusion constants for several 1-substituted adamantane derivatives in various solvents are presented. The ratio of the diffusion constants for rotation about the principal axis relative to that about the two mutually perpendicular axes is found to vary significantly with substituent and to a lesser extent with solvent. The order for this ratio is CO2H > OH > NH2 ≈ Br, which is interpreted in terms of the degree of association, either solute–solute or solute–solvent, and also the ease of rotation about the carbon–substituent bond.
Complexation of cadmium(II) with water- and soil-derived fulvic acids: effect of pH and fulvic acid concentration
Authors: Saar Robert A. , Weber James H.
Published: May 2006

We studied the conditional stability constants of cadmium(II) bound to fulvic acid derived from water and soil, and found that (1) stability constants increased with increasing pH, and (2) stability constants decreased as we increased the fulvic acid concentration toward 70 mg/L. The second effect does not occur for the copper(II)–fulvate system. Conformational changes that occur when a fulvic acid solution becomes more concentrated apparently weaken sites that are otherwise more accessible to weak-binding cadmium. From pH 4 to 8, the overall conditional stability constant increases from 1.4 to 12 × 103 for water-derived fulvic acid and from 1.7 to 43 × 103 for soil-derived fulvic acid. Increases in fulvic acid concentration from 20 mg/L to 70 mg/L halve the conditional stability constant at a given pH.
The photoelectron spectra of the methylbromamines and unsubstituted bromamines
Authors: Colbourne D. , Frost D. C. , McDowell C. A. , Westwood N. P. C.
Published: May 2006

HeI photoelectron spectra are reported for pure gas-phase samples of the unstable methylbromamines, CH3NHBr, CH3NBr2, and (CH3)2NBr. Results are also presented for the unsubstituted bromamines NH2Br and NHBr2 obtained as products from a gas-phase mixing of NH3 and Br2. The spectra are compared with those of the corresponding chloramines.
Total synthesis of 14β-hydroxy-4,9(11)- androstadiene-3,17-dione
Authors: Daniewski Andrzej Robert , White Peter S. , Valenta Zdenek
Published: May 2006

The title compound 8, a potential intermediate in the total synthesis of cardiac-active principles and other polyfunctional steroids, is prepared in nine steps using methyl vinyl ketone and 2-methylcyclohexane-1,3-dione as starting materials and acetylene and 2-methylcyclopentane-1,3-dione as additional sources of carbon atoms. In a crucial aldol condensation leading to the closure of steroid ring C, an efficient asymmetric induction by one chiral center leads to the establishment of three new chiral centers.
Analytical potentiometric and spectroscopic study of the equilibria in the aqueous nickel(II)–triethylenetetramine and nickel(II)–D-penicillamine systems
Authors: Laurie Stuart H. , Prime Diana H. , Sarkar Bibudhendra
Published: May 2006

The complexation of nickel(II) with triethylenetetramine and D-penicillamine has been examined in 0.15 M NaCl solution at 25 °C by a combined potentiometric–spectroscopic approach. Trien (A) forms the following complexes with Ni(II): MA, MA2, MH2A2, M2A3, M2HA3, and M2H2A3 with overall log stability constants: 14.34, 20.64, 37.28, 40.05, 49.20, and 55.02, respectively. Their concentrations as a function of pH are presented and their likely structures discussed. In contrast, D-penicillamine forms the species MA and MA2 only. The latter species, which is the only species from pH 5.8 to 10.0, is shown to be square-planar via coordination of the N, S atoms of the ligand molecules. The overall log stability constants of MA and MA2 are 11.22 and 22.71, respectively. The significance of these results in relation to the effectiveness of these ligands in preventing nickel toxicity in rats is discussed.
In-plane and out-of-plane conformational preferences of the sulfhydryl group in some halothiophenol derivatives
Authors: Schaefer Ted , Parr William J. E.
Published: May 2006

Long-range spin–spin coupling constants between sulfhydryl protons and ring protons in some halothiophenol derivatives in CCl4 solutions are reported. In contrast to the corresponding phenol derivatives, substantial amounts of out-of-plane conformers are present at 305 K for all but 2,6-dichlorothiophenol. The cis and trans conformers differ by only about 0.2 kcal/mol in free energy for 2,4-dibromothiophenol and 2,4-dichlorothiophenol, in good agreement with a recent analysis of the dipole moment observed for the latter compound. The barrier to internal rotation of the sulfhydryl group is considerably smaller than for a hydroxyl group and rough estimates are given for the barrier in a few compounds. For example, the barrier in 2,3,5,6-tetrafluorothiophenol is lower than in 2,6-dichlorothiophenol. STO-3G MO calculations overestimate the internal barrier to rotation of the sulfhydryl group, but yield charge densities for this group which indicate that a major cause of the relative weakness of its intramolecular hydrogen bonds resides in its lack of polarity.
13C nuclear magnetic resonance spectra of some C19-diterpenoid alkaloids and their derivatives
Authors: Pelletier S. William , Mody Naresh V. , Sawhney Rajinder S.
Published: May 2006

The natural abundance carbon-13 nuclear magnetic resonance spectra of some C19-diterpenoid alkaloids and their alkamines (lappaconitine, lappaconine, lapaconidine, ranaconine, 14-dehydrobrowniine, aconine, pseudoaconine, deoxyaconine, and hypaconine) have been determined at 15.03 MHz. With the aid of proton decoupling techniques, additivity relationships, and comparison with spectra of related alkaloids, self-consistent and unambiguous assignments of nearly all carbon resonances for these alkaloids have been made. Some important chemical shift trends have been observed, which are useful for identifying the basic C19-diterpenoid alkaloid skeleton and the hydroxy and methoxy group substitution patterns in these alkaloids. On the basis of 13C nmr spectra of lappaconitine and lappaconine, the anthranoyl ester moiety is assigned to the C-4 position in lappaconitine. The 13C nmr spectra of lapaconidine, aconine, and pseudoaconine taken in pyridine and chloroform have been compared to determine the conformational changes of the ring A hydroxy groups in these alkaloids.
Photolysis of diarylcadmium compounds in benzene
Authors: Osman A. M. , Khodair Ahmed I. , Abdel-Wahab A. A. , El-Khawaga A. M.
Published: May 2006

Photochemical decomposition of selected diarylcadmium compounds in dilute benzene solutions was investigated. This reaction was found to involve initial cleavage of the aryl–cadmium bonds followed by coupling of the aryl radicals to give symmetrical biaryls in good yields. Arylation products were obtained in only 5–25% yields, in contrast with the photolysis of iodoaromatic compounds in benzene which gives arylation products in high yields. Diarylcadmium compounds derived from polynuclear aromatic compounds, e.g. di(p-biphenyl)cadmium and di(α-naphthyl)cadmium gave, under the same conditions, predominantly hydrogen transfer products. In carbon tetrachloride, photolysis of diarylcadmium compounds gave chloroarenes in high yields.
Kinetics and mechanism of oxidation of tris-(1,10-phenanthroline)iron(II) by chlorine and bromine and of the reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions
Authors: Ige Jide , Ojo J. Folorunso , Olubuyide Olusegun
Published: May 2006

The rates of the oxidation of tris-(1,10-phenanthroline)iron(II) by chlorine and bromine, and of the reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions have been measured at ionic strength I = 1.0 mol dm−3 (LiClO4). All the reactions obey second-order rate law:[Formula: see text]The activation parameters for the reactions are: Fe(Phen)32+/Br2: ΔH≠ = (64.2 ± 3.2) kJ mol−1, ΔS≠ = −(24.9 ± 1.5) J mol−1 K−1. Fe(Phen)33+/I−:ΔH≠ = (39.8 ± 2.1) kJ mol−1, ΔS≠ = −(19.7 ± 0.8) J mol−1 K−1.The reactions of tris-(1,10-phenanthroline)iron(II) with chlorine and bromine are unaffected by chloride, bromide, and acid. The proposed mechanism for these reactions involves a series of one-electron changes, with the species X2− (X = Cl, Br) as reaction intermediates, since good linear free energy correlations for the primary step, resulting in the formation of X2−, are obtained. The reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions is catalysed by bromide and chloride ions, whereas the reduction of aquoiron(III) by iodide ions is known to be inhibited by bromide and chloride ions. A mechanistic interpretation of this observation is suggested.
A nuclear magnetic resonance study of pyridinium and p-anisidinium carboxylate salts
Authors: Gowland Joan A. , McClelland Robert A.
Published: May 2006

not available
Stereochemistry of six coordinate organotin(IV) compounds with bidentate ligands
Authors: Tse J. S. , Sham T. K. , Bancroft G. M.
Published: May 2006

Extended ligand–ligand repulsion calculations have been applied to a number of six coordinate organotin complexes of the type RR′Sn(bidentate)2 (R, R′ = Me, Ph, Cl). Qualitatively, the calculations readily predict the decrease in the R—Sn—R′ angle with decrease in bite size of the bidentate ligand. The steric calculations are generally successful in predicting both the cis–trans preference of the R groups and the bond angles about the Sn atom. For the Me2Sn complexes, electronic effects (as expressed by Bent's rule) sometimes have to be used in conjunction with the steric calculations to rationalize the observed stereochemistry.
X-ray crystallographic study of Ni(II) bis(morpholine-N-carbodithioate) and epr studies of Cu(II) bis(morpholine-N-carbodithioate) and Cu(II) bis(pyrrolidine-N-carbodithioate)
Authors: Herring F. G. , Park J. M. , Rettig S. J. , Trotter J.
Published: May 2006

Crystals of Ni(II) bis(morpholine-N-carbodithioate) are monoclinic, a = 4.291(1), b = 20.584(2), c = 8.365(1) Å, β = 97.39(2)°, Z = 2, space group P21/n. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.036 and Rw = 0.044 for 1800 reflections with I ≥ 3σ(I). The crystal structure consists of discrete molecules having approximate C2h and exact (crystallographic) Ci symmetry. The nickel atom is coordinated to four sulphur atoms in a planar arrangement with Ni—S = 2.2122(7) and 2.2134(6) Å and S—Ni—S = 79.16(2) and 100.84(2)°.The electron paramagnetic resonance spectra of 63Cu(II) bis(morpholine-N-carbodithioate) and 63Cu(II) bis(pyrrolidine-N-carbodithioate) doped in the respective Ni(II) analogues have been recorded at room temperature. The spin Hamiltonian parameters obtained from an analysis of the spectra of the polycrystalline samples have been used to investigate the bonding in these complexes. The results are compared to previous studies in carbodithioates.
Stereochemical aspects of the Pummerer reaction. Regioselectivity as a criterion for the differentiation of ylide and E2 pathways in the product-determining step of the reactions of benzyl methyl halo- and oxysulfonium cations
Authors: Wolfe Saul , Kazmaier Peter Michael
Published: May 2006

The conversion of [Formula: see text] (X = Cl, OCH3, OCOCH3, OCOCHCl2, OCOCF3) to a regioisomeric mixture of p-Y-C6H4CHXSCH3 and p-Y-C6H4CH2SCH2X has been studied as a function of X, Y, and deuteration in the benzyl and methyl positions. The conclusion is reached that, when X is acyloxy, the transformation of the sulfonium cation to an α-thiocarbonium ion and thence to the products proceeds via an E2 pathway. Trifluoroacetic anhydride is a much more reactive reagent than acetic anhydride for Pummerer reactions of benzyl methyl sulfoxides. However, with other sulfoxides, this reagent is not as effective as acetic anhydride. Acetyl trifluoroacetate is not effective as a Pummerer reagent.
Absolute rate constants for hydrocarbon autoxidation. 26. Rate constants for reaction of the tert-butylperoxy radical with 1-bromo-2-methylbutane and 1-bromo-3-methylbutane and some related substituted butanes
Authors: Howard J. A. , Chenier J. H. B.
Published: May 2006

Rate constants and Arrhenius parameters for reaction of the tert-butylperoxy radical with 1-bromo-2-methylbutane and 1-bromo-3-methylbutane in solution from 30–80 °C have been estimated. The magnitude of these kinetic parameters are consistent with activation of the tertiary hydrogen vicinal to the bromine substituent and the involvement of a "bridged" transition state in the hydrogen atom transfer reaction.Chloro, trimethylsilyl, and trimethylstannyl substituents also activate a vicinal tertiary hydrogen and activation increases in the order trimethylsilyl ∼ trimethylstannyl < chloro < bromo.
Cobalt(II), nickel(II), and copper(II) complexes of di- and tetrapeptides containing tyrosine and glycine residues
Authors: El-Ezaby Mohamed S. , Al-Hassan Jassim M. , Eweiss Namek F. , Al-Massaad Farida
Published: May 2006

not available
Some thermodynamic aspects of dissolution of solid solutions of hydroxylapatites of phosphorus and arsenic
Authors: Narasaraju T. S. B. , Rai U. S.
Published: May 2006

The solubility equilibria of synthetic samples of hydroxylapatite, its arsenic isomorph, and a series of their solid solutions, spread over the entire compositional range, were investigated at 37 °C in the pH range 5.0 to 7.6 in buffered systems through microanalytical determinations of calcium, phosphorus, and arsenic in their saturated solutions. From the ionic products of the samples so determined their stoichiometric dissolution was established and their free energies of solution evaluated.
Reactions of 4-phenyl-3H-1,2,4-triazole-3,5 (4H)-dione with alcohols and amines
Authors: Dao Lê H. , Mackay Donald
Published: May 2006

Two equivalents of the title compound (1) react with one equivalent of primary alcohols to give good yields of nitrogen and 1-alkoxycarbonyl-2-N-phenylcarbamoyl-4-phenyl-1,2,4-triazolidine-3,5-di ones (3). With secondary alcohols or benzyl alcohol the major products are the ketone or benzaldehyde, while 3 are minor products. The latter can, however, be made the major products if pyridine is used to catalyze the reaction. Compound 3a dissociates on heating or in pyridine solution into the 1-methoxycarbonyltriazolidinedione 4.If alcohols are absent 1 is converted by pyridine or other tertiary amines into nitrogen and the bicyclic compound 9; if diethyl azodicarboxylate is present in the reaction compound 13 can be trapped.Primary and secondary amines react very rapidly with 1 to give nitrogen and complex products. It is likely that these are 1,2-dicarbamoyl-4-phenyltriazolidine diones, analogous to 3, and that they are very prone to dissociate in solution.
Mechanistic and theoretical studies of the photochemistry of 5,6-dihydro-2-cyanobenzobarrelene
Authors: Bender Christopher Owen , O'Shea Seamus F.
Published: May 2006

The direct (Φ6 = 0.04) or acetone sensitized (Φ6 = 0.51) photolysis of 2-cyano-1,4-dihydro-1,4-ethanonaphthalene (5) yields 1-cyanobenzotricyclo[3.3.0.02,8]octa-3-ene (6). Deuterium labelling studies suggest that 6 derives from a Zimmerman di-π-methane rearrangement and not from the McCullough 1-cyanocyclohexene rearrangement. The observed rearrangement and regioselectivity are in accord with predictions based upon CNDO-CI calculations of changes in atom–atom interaction energies on excitation to the S1 and T1 excited states of 5.
A synthetic route to 4-C-methyl-xylo-furanose
Authors: Tam Tim Fat , Fraser-Reid Bert
Published: May 2006

3-O-benzyl-1,2-isopropylidene-α-D-xylo-pentodialdofuranose could not be α-methylated by direct or indirect methods. The aldol product from reaction of the dialdofuranose with formaldehyde could not be trapped, but underwent a Cannizzaro reaction to give the C-4-bis-hydroxymethyl product. The latter can be regioselectively sulfonated at the pro-(S) hydroxymethyl group. Reduction with lithium aluminum hydride then affords 3-O-benzyl-1,2-isopropylidene-4-C-methyl-α-D-xylo-furanose as the major isomer, the configuration of which is proved by transformation into an oxetane.
Nuclear magnetic resonance studies of the solvation of phosphorus(V)selenides, 1,2-bis(diphenylphosphino)ethane, and tris(dimethylamino)phosphine telluride by sulfur dioxide
Authors: Dean Philip A. W.
Published: May 2006

not available
Stannic tetrachloride catalysed glycosylation of 8-ethoxycarbonyloctanol by ceHobiose, lactose, and maltose octaacetates; synthesis of α- and β-glycosidic linkages: 1,2-Orthoacetate intermediates in silver trifluoromethanesulphonate promoted Koenigs–Knorr synthesis of disaccharide glycosides
Authors: Banoub Joseph , Bundle David R.
Published: May 2006

not available
Studies on the mass spectrometry of some acyclic nuclear substituted styryl ketoximes and ketones with special reference to the ortho effect
Authors: Nyathi C. B. , Dimmock J. R. , Smith L. M.
Published: May 2006

The mass spectra of several ring substituted acyclic styryl ketoximes and analogous ketones have been determined at 70 eV and also at low ionization voltages. The major fragmentation pathways for the oximes are loss of the ortho substituent from the parent ion as well as loss of the hydroxyl and hydroxylamine radicals. Other fragmentation pathways include γ- and δ-cleavages as well as the McLafferty rearrangement. While there was a total absence of α-cleavage from the parent ions, the facility of loss of the ortho substituents from the oxime molecular ions was compared with the same process occurring in the corresponding acyclic ketones, as well as the related cyclic derivatives, namely the substituted 2-benzylidinecyclohexanones and oximes. Stabilization of the resultant cyclized ion as well as steric factors are considered as factors favouring the cyclization process.
The crystal and molecular structure of syn-2,11-dithia[3,3]metacyclophane
Authors: Anker Willem , Bushnell Gordon W. , Mitchell Reginald H.
Published: May 2006

The crystal structure of syn-2,11-dithia[3,3]metacyclophane, C16H16S2, has been determined by single crystal X-ray diffraction and refined to an R-value of 0.049. The crystal is monoclinic with cell dimensions a = 1898.2(5), b = 795.7(3), c = 924.1(4) pm, β = 100.03°(4). The space group is P21/n with 4 molecules per cell, Dm = 1.34 g cm−3, Dc = 1.317 g cm−3. Of several possible syn conformations, the molecule is found in that with the largest S—S distance of 697.4 pm. The benzenoid rings form a dihedral angle of 20.6°. The distance between the pair of aromatic H atoms which are ortho to two methylene groups is 273.0 pm, with 305.2 pm between the carbon atoms to which they are attached. Small angular distortions are observed at these carbon atoms. Mean bond lengths are: C—S 181.0(12), C—C (aromatic) 138.5(8), C—C (bridge) 151.0(11) pm. Mean bond angles are: C—S—C 104°(1), S—C—C 115.4°(9). The C—C—C angles are in the range 117.9–122.7°. The molecule possesses an approximate (non-crystallographic) 2-fold axis of symmetry passing through the midpoints of C(8)—C(18) and C(4)—C(14). The aromatic rings are planar, with the methylene carbons 5–11 pm out of plane on the sulphur side. The S(1) is 171.8(2) pm from plane 1 and 136.8(2) pm from plane 2, while for S(2) the corresponding values are 136.0(2) and 175.3(2) respectively.1Hmr data have been re-examined and compared with those obtained for other cyclophanes, together with 13Cmr data and are consistent with the fact that in solution 2,11-dithia[3,3]metacyclophane, 1, exists as the syn-conformer with no appreciable participation of the anti-conformer. All related dithia[3,3]metacyclophanes which have internal aryl hydrogens (i.e., no internal substituents) likewise appear to be syn from 1Hmr data.
The crystal and molecular structure of a compound containing a novel ring system:(E)-6-(bromomethylene)-5,6-dihydro-4,4-dimethyl-2-phenyl-4H-1,3,4-oxadiazinium bromide
Authors: Thompson Doris Margaret , Brindle Ian David , Richardson Mary Frances
Published: May 2006

The crystal structure of (E)-6-(bromomethylene)-5,6-dihydro-4,4-dimethyl-2-phenyl-4H-1,3,4-oxadiazinium bromide has been determined by single crystal X-ray diffraction methods. The crystals are monoclinic, space group P21/c, with a = 12.002(5), b = 6.414(4), c = 17.881(7) Å, β = 101.42(7)°, and Z = 4 formula units of C12H14N2OBr2. The structure was refined by full-matrix least-squares analysis to a conventional R-factor of 0.0491 for 1019 observed reflections. The oxadiazinium ring is in the half-chair form, with the methylene group out of the plane defined by the other five atoms. The C—O bond distances in the ring are somewhat shorter than the distance observed for a carbon–oxygen single bond, suggesting that some delocalization of electron density occurs over part of the ring.
Solvent effects on the photocycloaddition and photoenolisation reactions of isophorone
Authors: Shiloff Janice Deborah , Hunter Norman Robert
Published: May 2006

The influence of solvent on two photochemical reactions of isophorone has been investigated. The photocycloaddition of isopropenyl acetate to isophorone (3,5,5-trimethylcyclohex-2-en-1-one) (1) is best achieved using methanol as solvent. Photodeconjugation of isophorone (1) to the exocyclic methylene isomer 2 proceeds most efficiently in ethyl acetate.
Total synthesis of androstanes
Authors: Kakushima Masatoshi , Das Jagabandhu , Reid Gary R. , White Peter S. , Valenta Zdenek
Published: May 2006

A total synthesis of androstane derivatives is described. The desired configuration at C8 and at C13 is achieved in a ring C forming SnCl4-catalyzed Diels–Alder reaction. The preparation of methyl Z-2-methyl-4-oxo-2-pentenoate and the cyclization of a keto ester to a steroid 15,17-dione are also reported.
Photochemistry of selenoketones
Authors: Fung Norman Y. M. , Mayo Paul de , Ruge Bernd , Weedon Alan C. , Wong S. King
Published: May 2006

The photochemistry of di-tert-butylselenoketone 1 and selenofenchone 2 has been examined. Their photochemical properties resemble those of thioketones rather than ketones in that hydrogen abstraction occurs from an upper excited state and not from the lowest (n → π*) excited state. Di-tert-butylselenoketone, 1, on irradiation into the S2 band forms the diselenide 3. The quantum yield for this process was found to be 0.0055 and was increased in the presence of a good hydrogen atom donor. No reaction was observed following excitation into the S1 state unless a good hydrogen atom donor was present, and even then the photoreaction was very inefficient. Quenching experiments with biacetyl demonstrated the lifetime of the abstracting state to be in the order of 10−11 s. The formation of the diselenide 3 has been rationalized in terms of hydrogen abstraction from solvent by photoexcited 1 and trapping of the radicals produced by ground state 1, leading to the radical 6. The mechanism is supported by esr evidence for the existence of 6. Selenofenchone, 2, also, did not react following excitation into the S1 state, but underwent intramolecular cyclization in a similar manner to bicyclic thioketones following excitation into the S2 state.
Unequal primary kinetic isotope effects in the base-catalysed H–D exchange of diastereotopic protons
Authors: Fraser Robert R. , Champagne Philippe J.
Published: May 2006

Primary kinetic isotope effects have been measured for the base-catalyzed exchange reaction of 4′,1″-dimethyl-1,2,3,4-dibenzcyclohepta-1,3-diene-6-one, 1. It was found that the isotope effects kH/kT and kD/kT for the faster exchanging protons (13.6 and 3.8 respectively) are significantly larger than the corresponding values for the slower exchanging protons (4.6 and 1.6 respectively). These differences could result from truly unequal isotope effects due to transition state differences or intrusion of a second pathway for exchange of the less reactive proton in the dedeuteration reaction. The data appear to support the latter interpretation. The secondary deuterium isotope effect was found to be 1.18.
The reaction of with iron carbonyls. Unusual complexes formed by ligand cleavage reactions
Authors: Cullen William R. , Williams Mangayarkarasy
Published: May 2006

The phosphines [Formula: see text] and arsine [Formula: see text] (L; R = C6H5 or C6H11; n = 2, 3, 4) react with iron carbonyls to afford a range of products. Simple substitution yields (L)Fe(CO)4 and L2Fe(CO)3. Loss of chlorine from the ligands, symbolized (L–Cl), gives coupled complexes of formula [(L–Cl)Fe(CO)4]2 and loss of chlorine and fluorine gives the η3-allyl bridged derivatives (L–Cl–F)Fe2(CO)6. Only substitution products are obtained from the cyclobutenes.
SN2 iodide displacement on unsymmetrical cyclic dioxenium salts. A stereoelectronically controlled reaction
Authors: Beaulieu Normand , Deslongchamps Pierre
Published: May 2006

Iodide ion reacts with the cyclic dioxenium salts 1–6 to yield mixtures of iodoester and lactone plus alkyl iodide (Table 1). The formation of iodoester competing with the formation of lactone appears to be an unexpected result. It can, however, be explained by a stereoelectronic effect, similar to the anomeric effect in acetals, which is also responsible for the greater stability of the Z over the E form in dioxenium salts and in esters.
The effect of the variation of potential on progressive three-dimensional nucleation and growth
Authors: Smith Arthur , Fletcher Stephen
Published: May 2006

not available
An INDO-MO study of the spectral properties and transannular interaction in [6]-helicene
Authors: Deb B. M. , Kavu Geetharani
Published: May 2006

The INDO-MO calculations on [6]-helicene reported here enable one to classify the four HOMO's as predominantly π, in contrast to other occupied MO's. A linear adjustment of these four HOMO's correlates well with the experimental photoelectron and optical spectra. Viewed through Mulliken's overlap population between overlapping rings, the transannular interaction in [6]-helicene appears to be unfavourable and therefore minimised. The use of a skeleton representation of the molecule is considered and found inadvisable.
Pyrrole chemistry. XXI. Synthetic approaches to cyanopyrroles
Authors: Barnett Graham H. , Anderson Hugh J. , Loader Charles E.
Published: May 2006

The Vilsmeier–Haack reaction with pyrrole and 1-methylpyrrole has been modified to provide a direct synthesis of the corresponding 2-nitriles. Chlorosulfonyl isocyanate may be used to prepare the same compounds, but less satisfactorily. The latter reagent does enable the synthesis of pyrrole-2,4-dicarbonitrile in one step. This dinitrile may be reduced to pyrrole-2,4-dicarboxaldehyde.
Absolute rate constants for hydrocarbon autoxidation. 28. A low temperature kinetic electron spin resonance study of the self-reactions of isopropylperoxy and related secondary alkylperoxy radicals in solution
Authors: Furimsky Edward , Howard James A. , Selwyn Jennifer
Published: May 2006

Isopropylperoxy radicals at low temperatures exist in equilibrium with di-isopropyl tetroxide. The thermodynamic parameters for this equilibrium are very similar to the values of ΔH0 and ΔS0 for the tert-butylperoxy radical – di-tert-butyl tetroxide equilibrium. Differences in second-order rate constants for mutual destruction of secondary and tertiary alkylperoxy radical appear to result from differences in rate constants for unimolecular decomposition of secondary and tertiary alkyl tetroxides.Isopropylperoxy radicals have the same termination rate constant in the gas phase and in solution.
Reactions of some substituted phenols with chromyl and vanadyl chlorides
Authors: Harrod John F. , Pathak Asha
Published: May 2006

The oxidation of 2,4,6-tritertbutylphenol and several other alkyl and halophenols by CrO2Cl2 and VOCl3 was studied. The products of CrO2Cl2 oxidation are mostly quinones and diphenoquinones, whilst those of VOCL3 oxidation also include major amounts of dealkylated phenols and C—C coupled dimers. The product distributions are interpreted in terms of a mechanism involving phenoxyl radicals, ligand transfer from metal to radical, and either phenoxonium ions or metallate esters where there is sufficient electron withdrawal from the organic group for it to exhibit carbenium ion properties. The differences in behaviour between CrO2Cl2, VOCl3, and CuCl2 are attributed to different balances between the oxidation potential and Lewis acidity of the metal complexes. It is concluded that CrO2Cl2 is not a good model for proposed ferryl intermediate in heme oxidase systems since it induces 1 → 3 rather than 1 → 2 halogen shifts and an NIH shift that is best explained by carbenium ion-like intermediates.
Synthesis of a protein modifying agent. A water-soluble stable free radical
Authors: Sisodia Sangram , Martz R. Dean , Bosworth N. , Lammert Gary , Reinheimer J. D.
Published: May 2006

Two synthetic routes to prepare a water-soluble stable free radical were investigated. The first product, sodium-2,4-dinitro-5-(4′-amino-2′,2′,6′,6′-tetramethylpiperidine-1-oxyl)benzene sulfonate, was water soluble but the sulfonate group was not readily replaceable with nucleophiles. The second synthetic route yielded N(4′-(2′,2′,6′,6′-tetramethylpiperidine-1-oxyl))-3,5-dinitro-4-sodium sulfonate benzamide, which was water soluble and its sulfonate group was readily replaced by nucleophiles.
The Fe1−xS–PbS–ZnS phase System
Authors: Dutrizac J. E.
Published: May 2006

High temperature phase relationships have been determined for the binary systems FeS–PbS, Fe0.92S–PbS, Fe0.92S–ZnS, and PbS–ZnS, and for the ternary System Fe0.92S–PbS–ZnS. All the Systems were of the eutectic-type with eutectic points being noted at 53 mol% FeS–47 mol% PbS and 850 °C, 53 mol% Fe0.92S–47 mol% PbS and 852 °C, 90 mol% Fe0.92S–10 mol% ZnS and 1178 °C, 87 mol% PbS–13 mol% ZnS and 1050 °C, and at 46 mol% Fe0.92S–41 mol% PbS – 13 mol% ZnS and 850 °C, respectively. Solid solubilities were less than 1 mol% except for an appreciable solubility of Fe1−xS in ZnS.
Polymeric siloxyphosphine rhodium(I) complexes as hydrogenation catalysts
Authors: Brzezińska Zofia C. , Cullen William R. , Strukul Giorgio
Published: May 2006

Polymers of idealized formulae [O3/2Si(CH2)nP(C6H5)2]3RhCl•(O3/2SiCH3)m, B(n,m), [O3/2Si(CH2)2P(C6H5)2]4Rh2Cl2•(O3/2SiCH3)m, C(2,m), and [O3/2Si(CH2)2P(C6H5)2]3RhCl•(O3/2Si (CH2)2P(C6H5)2)0.7, D are hydrogenation catalysts for olefins in benzene suspension at 25 °C and 1 atm H2. With respect to styrene, the activity order is B > D ~ C. All the catalysts lose activity on recycling but the copolymers retain their activity over a greater number of cycles with D being the best catalyst in this regard. Possible reasons for this behaviour are discussed.
The bromination and chlorination of 2,3-dialkylindoles. Isolation of 3-bromo- and 3-chloro-2,3-dialkylindolenines and acid catalyzed conversion to 3-methoxyindolenines
Authors: Dmitrienko Gary I. , Gross Edward A. , Vice Susan F.
Published: May 2006

The bromination of 2,3-dimethylindole in acetic acid followed by hydrolysis has been shown to yield the known dimer 16 of 3-hydroxy-2,3-dimethylindolenine 15 and not 3-hydroxymethyl-2-methylindole 12 as reported previously by others. Bromination of 2,3-dimethylindole in the presence of triethylamine has yielded 3-bromo-2,3-dimethylindolenine 17 as a crystalline solid which is stable at room temperature in a nitrogen atmosphere in the presence of triethylamine but decomposes vigorously in the absence of base. Under mildly acidic conditions 17 reacts rapidly with methanol to yield 3-methoxy-2,3-dimethylindolenine 3 in good yield. With tert-butyl hypochlorite in the presence of triethylamine, 2,3-dimethylindole gives 3-chloro-2,3-dimethylindolenine 2 which has chemical properties similar to 17 reacting readily with methanol to give 3. Similarly tetrahydrocarbazole was converted to the analogous chloroindolenine 5 and bromoindolenine 18 both of which readily underwent methanolysis to give 6 in good yield. A mechanism for the acid catalyzed methanolysis of 3-chloro- and 3-bromoindolenines is proposed.
Synthesis, X-ray structure determination, and formation of 3,4,5-trichloroguaiacol occurring in kraft pulp spent bleach liquors
Authors: Lindström K. , Österberg F.
Published: May 2006

3,4,5-Trichloroguaiacol, which is formed during bleaching of chemical pulp and shown to bioaccumulate in fish, has been synthesized. The structure of the compound has been determined by means of X-ray analysis. The values of the 13C nmr chemical shifts and melting point differ from those previously reported. A reaction mechanism is suggested for the formation of 3,4,5- and 4,5,6-trichloroguaiacol.
Field ionisation/field desorption mass spectrometry of polynuclear metal carbonyls
Authors: Tuck Dennis G. , Wood Gordon W. , Zhandhire Samuel
Published: May 2006

Field ionisation/field desorption mass spectra are reported for Mn2(CO)10, Cd[Co(CO)4]2 and some adducts, In[Co(CO)4]3, bipy•Zn[Co(CO)4]2, and bipy•M[Mn(CO)5]2 (M = Zn, Cd). The spectra are extremely simple, and the small number of easily identified species includes the molecular ion in some cases. The relative abundance of the fragments is discussed in terms of known stabilising factors in such compounds. No spectra could be obtained from Co2(CO)8 or Fe2(CO)9, which may be the result of their carbonyl-bridged structures.