bluuebunny/crossref_metadata_2025 huggingface dataset:
Substituent effects of phosphorus-containing groups on aromatic reactivity. Determination of substituent constants by 13C nuclear magnetic resonance spectroscopy
Authors: Modro Tomasz A.
Published: May 2006

13C nmr spectra have been obtained for a series of benzene derivatives substituted with phosphorus-containing groups of the type PZ2, P(O)Z2, and P(S)Z2. Inductive and resonance substituent constants were determined from the shielding of meta and para carbon atoms according to the dual-substituent parameter approach. Possible mechanisms of substituent effects of PIII and PV derived functional groups are discussed and in some cases compared with effects of the analogous nitrogen derivatives.
Amino group acidity in aminopyridines and aminopyrimidines
Authors: Harris Madeleine G. , Stewart Ross
Published: May 2006

The acidities of the amino group in 18 heterocyclic compounds, nine pyridines, eight pyrimidines, and one triazine, have been measured. The pKHA values (standard state water) were calculated using the Bunnett–Olsen and Marziano–Cimino–Passerini extrapolative techniques from ultraviolet spectral changes accompanying ionization of the amino group in aqueous DMSO containing base. These compounds, together with seven anilines previously studied, constitute a well-behaved Hammett system (σ dependency) with a ρ value of 5.20, provided compounds containing nitro groups ortho or para to the amino group are excluded. The acid-strengthening effect of aza groups is additive and appears to be primarily due to induction rather than resonance, in contrast to the behaviour of the nitro group.
Limiting equivalent conductances for selected substituted ammonium ions in water
Authors: Lobo Sheila Teresa , Robertson Ross Elmore
Published: May 2006

The temperature dependence of the limiting equivalent conductances of the ions 2-methoxyethylammonium, bis-2-methoxyethylammonium, 3-methoxypropylammonium, piperidinium, quinuclidinium, cyclohexylammonium, and diethylammonium have been determined over the range 5–45 °C. The probable effect of these ions on the adjacent water structure has been explored in terms of an approach used by Kay and co-workers and the behaviour in water has been compared with that of other alkylammonium ions.
Direct electrochemical synthesis of neutral and anionic chloro- and bromo-complexes of titanium, zirconium, and hafnium
Authors: Habeeb Jacob J. , Said Farouq F. , Tuck Dennis G.
Published: May 2006

Electrochemical oxidation of titanium, zirconium, or hafnium(IV) in the presence of a solution of chlorine or bromine (X) in acetonitrile (L) leads to direct synthesis of MX4L2 species in good yield. These compounds are easily transformed into other neutral adducts. On addition of tetraalkylammonium salts to the solution phase, the products are the salts (R4N)MCl5 or (R4N)2MBr6, except that with titanium Et4NTiBr4 was also formed under some conditions. The advantages of this method are discussed, and a possible reaction mechanism proposed.
A new method for the macro- and microdetermination of tri- and tetrathionate
Authors: Idriss K. A. , Issa I. M. , Mahmoud M. R.
Published: May 2006

A rapid and precise method is described for the determination of tri- and tetrathionate. It is based on oxidation of S3O62− or S4O62− with KMnO4 in sulphuric acid medium in the presence of fluoride, required for preventing the formation of insoluble oxides of manganese. The optimum conditions for both the visual and potentiometric end-point detection are 0.1–0.16 M H2SO4 and 0.24–0.38 M NaF. Trithionate is oxidized to sulphate as an end product, whereas the oxidation product of tetrathionate comprises dithionate and sulphate according to[Formula: see text]Examination of the potentiometric titrations and the spectrophotometric scans of samples being titrated showed the presence of intermediate equilibria in solution. The species produced are identified and a theory is given for the net reactions. The method is thoroughly dependable for the determination of amounts of S3O62− or S4O62− corresponding to 0.1–10 mg of sulphur.
The interaction of pulsed CO2-laser radiation with common monomers
Authors: Gandini A.
Published: May 2006

Several monomers were submitted to pulsed TEA-CO2 laser radiation. In the condensed phase neither polymerization nor decomposition was observed. In the vapour phase, polymerization did not take place but extensive decomposition occurred, mainly through molecular elimination reactions. Possible reasons for the lack of polymerization are discussed.
Individual rate constants of methyl radical reactions in the pyrolysis of dimethyl ether
Authors: Held Andrew M. , Manthorne Kim C. , Pacey Philip D. , Reinholdt Howard P.
Published: May 2006

Dimethyl ether was pyrolyzed in a flow system at 10 to 80 Torr and 1005 K. The average concentration of CH3 radicals in the reactor was measured by ultraviolet absorption spectroscopy. Product yields were measured by gas chromatography. The system was simulated using a computer program, taking into account the warm-up of the entering gas and the occurrence of secondary reactions. Rate constants were varied to find values consistent with experimental observations. The limiting, high pressure rate constant for the recombination of CH3 was estimated to be 1010.5 ± 0.5ℓ mol−1 s−1. Estimated rate constants for the reactions[Formula: see text]were 107.12 ± 0.2ℓ mol−1 s−1 and 107.5 ± 0.4ℓ mol−1 s−1, respectively.
Caerulomycins B and C, new 2,2′-dipyridyl derivatives from Streptomyces caeruleus
Authors: McInnes A. G. , Smith D. G. , Wright J. L. C. , Vining L. C.
Published: May 2006

Three new metabolites have been isolated from cultures of Streptomyces caeruleus and are related to caerulomycin, a known antibiotic metabolite of this organism now designated caerulomycin A. The structures of two of the new compounds, caerulomycins B and C, are shown to be 3-hydroxy-4-methoxy- and 3,4-dimethoxy-2,2′-dipyridyl-6-(E)-aldoxime.
Metal complexes as antioxidants. VI. An electron spin resonance study of the transient cupric complexes formed in the reaction of cupric dialkyldithiocarbamates with alkylperoxy radicals and alkyl hydroperoxides
Authors: Howard James Anthony , Tait John Charles
Published: May 2006

The epr spectra of three intermediate copper(II) complexes formed by oxidation of bis[N,N-dialkyl(dithiocarbamato-S,S′)] copper(II) by alkyl hydroperoxides and alkylperoxy radicals are reported. Isotropic and anisotropic spectra of the complexes formed from alkylperoxy radicals enriched with 17O are consistent with the following structures: [Cu(S2CNR2)(OS2CNR2)] (I), [Cu(OS2CNR2)2] (II), and [Cu(OS2CNR2)(O2S2CNR2)] (III). The isotropic 17O hyperfine interaction of I is 19.2 G while the anisotropic spectrum of II indicates that the two oxygen nuclei are equivalent. The anisotropic 17O hyperfine splitting constants are consistent with a structure for these complexes in which the S—O bond(s) is directed out of the plane of the complex and not coordinated to the copper.
Sesquiterpene lactones from Centaurealinifolia Vahl
Authors: González A. G. , Bermejo J. , Amaro J. M. , Massanet G. M. , Galindo A. , Cabrera I.
Published: May 2006

Three new sesquiterpene lactones, linichlorins A, B, and C were isolated from the aerial parts of Centaurealinifolia Vahl and their structures were determined by physical and chemical methods. The sesquiterpene lactones chlorohyssopifolins A, B, C, D, E, aguerin B, and vahlenin were also isolated from the same plant.
Thermodynamics of the salting effect; free energies, enthalpies, entropies, heat capacities, and volumes of the ternary systems electrolyte–alcohol–water at 25 °C
Authors: Perron Gérald , Joly Daniel , Desnoyers Jacques E. , Avédikian Lévon , Morel Jean-Pierre
Published: May 2006

The thermodynamic pair interaction parameters of the ternary systems electrolyte (alkali halides and tetraalkylammonium bromides)–nonelectrolyte (n-alcohols and tert-butylalcohol)–water were measured at 25 °C through enthalpies of solution, of mixing and of dilution, densities and heat capacities per unit volume. Some freezing point and electromotive force data were also combined with previously published data to obtain free energies. From these pair parameters the complete thermodynamics of the salting in and salting out of alcohols can be derived and were used to test various theoretical approaches. Most results are consistent with the cosphere overlap structural model, and the various trends can also be correlated through the scaled-particle theory.
Metabolites of bird's nest fungi. Part 8. Some minor metabolites of Cyathus helenae and some correlations among the cyathins
Authors: Ayer William A. , Browne Lois M. , Mercer John R. , Taylor David R. , Ward Dale E.
Published: May 2006

The isolation and structure determination of neoallocyathin A4 (10a) is described. Structures are proposed for cyathin A4 (11) and cyathin C5 (15). Methods for the transformation of cyathin A3 into cyathin B3, allocyathin B3, and cyathin C3 are reported. The isolation of glochidone (22) and ergosterol from the mycelium of Cyathushelenae is reported.
Phlegmarine, a likely key intermediate in the biosynthesis of the Lycopodium alkaloids
Authors: Nyembo Louis , Goffin André , Hootelé Claude , Braekman Jean-Claude
Published: May 2006

The isolation and structure determination of four novel bases (6, 7, 8, 9), representative of a new type of Lycopodium alkaloids, are reported. The phlegmarine skeleton is proposed to be a key intermediate in the biosynthesis of the Lycopodium alkaloids.
Recherches en série hétérocyclique. XXIX. Sur des voies d'accès à des thiéno, sélénolo, furo et pyrrolopyrroles
Authors: Soth Samreth , Farnierz Michel , Paulmier Claude
Published: May 2006

The reaction of ethyl azidoacetate with the monoaldehydes of furan, thiophene and seleno-phene yields furo-, thieno-, and selenolo[2,3-b]- and [3,2-b]pyrroles. Only pyrrolo[2,3-b]pyrrole could be prepared by this route using ethyl 4-formylpyrrole-2-carboxylate as the substrate. The thieno- and selenolo[3,2-b]pyrroles also could be obtained by the action of ethyl bromoacetate on 3-acetamidothiophene-2-aldehyde, or the corresponding selenolo compound, followed by cyclization of the N-substituted acetamide products.The nmr, uv, and mass spectra are reeorded for the various products described. [Journal translation]
Pyrolysis of bromobenzene by the toluene carrier technique and determination of D(C6H5—Br)
Authors: Kominar R. John , Krech Michael J. , Price Stanley James W.
Published: May 2006

The pyrolysis of C6H5Br bas been studied by the toluene carrier technique over the temperature range 1018 to 1126 K using contact times of 1.18 to 2.85 s and total pressures of 3.8 to 4.4 kPa. Percent decomposition based on analyses of residual C6H5Br ranged from 4 to 89%. When HBr was trapped out and quantitatively determined it accounted for more than 95% of the bromine expected. Within the limits of the experimental method the decomposition was found to be homogeneous and first order.[Formula: see text]The Arrhenius equation for reaction [1] is[Formula: see text]Making an approximate correction of the activation energy to 298 K then gives D(C6H5—Br) = 313 ± 5.4 kJ mol−1.
The internal barriers to rotation about the carbon–carbon bond in 3,5-dichlorobenzyl alcohol and selenol by the J method
Authors: Schaefer Ted , Danchura Werner , Niemczura Walter , Parr William J. E.
Published: May 2006

The J method, depending on a comparison between observed spin–spin coupling constants over six bonds between protons on a side chain and para ring protons and those calculated by a hindered rotor treatment, is applied to the determination of the twofold barrier to internal rotation about the carbon–carbon bonds in 3,5-dichlorobenzyl alcohol and selenol. In the alcohol, the C—O bond prefers the benzene plane by 0.3 ± 0.2 kcal/mol whereas, in the selenol, the C—Se bond prefers a plane perpendicular to the benzene ring by 3.8 ± 0.7 kcal/mol. Comparison with the thiol suggests that a major component of the barrier arises from repulsive interactions, increasing as the size of the XH (X = O, S, Se) group increases.
Theoretical and experimental behaviour of a thermal conductivity detecter for the determination of the ortho/para hydrogen composition of gas mixtures in the temperature-jump region
Authors: Mitchell David N. , Le Roy Donald J.
Published: May 2006

The theoretical characteristics of a thermistor type thermal conductivity detector were determined for gases in the range 1 to 30 Torr, and were tested experimentally for mixtures of ortho- and para-hydrogen in pure hydrogen and in dilute mixtures of hydrogen in helium. It was found that the detector could be treated as being spherically symmetric. For temperature-jumps of up to 100 K, the total heat transfer could be adequately explained by a simplified form of the Kennard temperature-jump theory, only two parameters being required, the radius of the thermistor and its accommodation coefficient. The differential behaviour, the sensitivity to changes in ortho/para composition, required an additional parameter, the apparent gas phase relaxation rate for rotational energy.
Ion association in solutions of HCl in DMSO–water mixtures: ultrasonic absorption studies
Authors: Kruus Peeter , Mcguire M. Jacqueline
Published: May 2006

Ultrasonic absorption measurements are reported for the System HCl–dimethylsulfoxide (DMSO)–water in the frequency range 3.5 to 140 MHz. For ail solutions studied, the excess absorption due to the presence of HCl can be fitted well with a single relaxation equation. For 0.10 mol ℓ−1 solutions of HCl in DMSO–water mixtures, no further relaxations at higher frequencies are likely. Reasonable results are obtained when the ultrasonic results are analyzed assuming the process responsible for the excess absorption to be the dissociation–association equilibrium of HCl, and using equilibrium constants determined from conductivity (C. Cooke etal. Electrochim. Acta, 20, 591 (1975)). The value of |ΔVeff| is 20–25 cm3 mol−1 and Kass is approximately 3 × 109ℓ mol−1 s−1, as compared to a value of 10 × 109ℓ mol−1 s−1 calculated from limiting conductivities assuming diffusion-controlled rate theory.
Some reactions of 2-n-butyl(phenyl)-1,2-dihydropyridines with isocyanates, pyridyl esters, and diethyl chlorophosphate
Authors: Ondrus Theodore A. , Pasutto Frank M. , Knaus Edward E. , Giam C. S.
Published: May 2006

Reaction of the ambident 1-lithio-1,2-dihydropyridines (1) and related dienamines (2) with several electrophiles has been investigtaed. Reaction of 1 with aliphatic isocyanates occurs predominantly or exclusively at nitrogen, whereas similar reactions employing 2 do not proceed and a dimeric product 8 resulting from self condensation of 2 is obtained. In contrast, reaction of 2a with the more electrophilic phenyl isocyanate (3c) gave both N-phenylaminocarbonyl-2-n-butyl-1,2-dihydropyridine (4d) and 2-n-butyl-5-phenylaminocarbonylpyridine (6d) whereas a similar reaction with 1a afforded 4d, 5d, and 6d, as well as the stable N-unsubstituted-1,2-dihydropyridine 7d. Novel 2-n-butyl-5-(2-,3-,4-pyridylcarbonyl)-1,2-dihydropyridines 13a–c are obtained from reaction of 1a with pyridyl esters 12a–c. Reaction of1a with diethyl chlorophosphate and ethyl acetate occurs exclusively at nitrogen to afford high yields of 16a and 16b, respectively. The mechanism for the formation of the 1,5-disubstituted-1,2-dihydropyridines 5 is described.
Analyse des malates de cuivre et d'uranyle par potentiométrie, polarimétrie et spectrophotométrie
Authors: Khalil Ilham , Petit-Ramel Michelle M. , Chapelet-Barbier Claudette
Published: May 2006

The stability and optical constants of the copper malates [CuH2Mal]+, [CuHMal], [CuH2Mal2]2−, [CuMal]−, [Cu2Mal2]2− and [CuH−1,Mal]2− have been fitted by a pit-mapping method, which also gives their confidence limits, from potentiometric, visible spectroscopic and polarimetric measurements.In the case of the uranyle malates, the presence of polynuclear species, detectable in the potentiometric study, have been confirmed by nmr spectrocopy. The constants of [UO2HMal], [UO2Mal]−, [(U02),Mal2]2−, [(UO2)3MaI5]9− and [(UO2)3H−2Mal5]11− have been determined, first by a pit-mapping method, then, by the graphical method of Lefebvre. All the values are given at 25 °C for an ionic strength of 0.5 in NaNO3.
The clathrate hydrate of 2-methylpropanal: dielectric evidence
Authors: Gough S. R.
Published: May 2006

Dielectric relaxation evidence is presented of the encageability of 2-methylpropanal in the structure II clathrate hydrate lattice. The hydrate composition is inferred to be (CH3)2CHCHO 17H2O and, for the 2-methylpropanal/THF mixed hydrate studied in detail, the activation energy for aldehyde reorientation is shown to be 2.0 kcal/mol. The results suggest that the guest–host interactions may be somewhat different for the two guest species.
Molécules modèles des motifs des poly-1,4-glucosides. I. Synthèse et correspondance configurationelle de diastéréoisomères avec les motifs de la cellulose et de l'amylose
Authors: Lafuma Françoise , Quivoron Claude
Published: May 2006

To confirm or to elucidate the most probable types of chelation existing in the chains of cellulose or amylose as well as in the corresponding mono- and disaccharides, we have undertaken studies on model molecules which represent, in part, the cellobiose and maltose entities. These model molecules are some intra- extra cyclic acetals of the type 2-cyclohexytoxytetrahydropyran. These molecules contain primary or secondary hydroxyl groups whose covalent dispositions relative to the acetal function are analogous to those of the groups (OH)2, (OH)3′, (OH)6, and (OH)6′, of amylose and cellulose. Twenty-one model compounds have been pre-pared from 2,3-dihydropyran, 2-hydroxymethyl-2,3-dihydropyran, or their expoxides. Most of the diastereoisomers corresponding to the model compounds containing at least two asymmetric carbon atoms have been separated by gel permeation chromatography using a recycling system to some advantage. The configurational correspondence of the diastereoisomers to the entities α-D- and β-D-glucose of amylose and of cellulose have been studied by proton and carbon-13 nuclear magnetic resonance. These assignments have permitted the recognition, among the 30 diastereoisomers of 6 which have the configuration of amylose and of 5 which have that of cellulose. [Journal translation]
Total synthesis of indole and dihydroindole alkaloids. XVI. Derivatives of vinblastine and vincristine: change of functionality in the vindoline unit
Authors: Kutney James P. , Balsevich John , Honda Toshio , Liao Ping-Huang , Thieelier Herman P. M. , Worth Brian R.
Published: May 2006

Studies describing the preparation of various derivatives of vinblastine and vincristine are presented. Vindoline (3) is transformed into a series of derivatives and the latter via Polonovski-type coupling with catharanthine (2) provide the bisindole alkaloid derivatives of the vinblastine series. Selective Jones' oxidation transforms the vinblastine family into the corresponding vincristine derivatives.
Reactions of hydrogen atoms with hexafluoroacetone
Authors: Grattan D. W. , Kutschke K. O.
Published: May 2006

Attempts were made to study the kinetics of the reaction of atomic H with (CF3)2CO vapour (HFA). Atomic H was generated from H2 by mercury photosensitization in the presence of C2H4 and HFA but the system was complicated by the loss of C2H5 radicals by addition to HFA and the kinetic results were intractable. When atomic H was generated from C3H8, the kinetics again were obscured by some unidentified reaction(s) which became more important at higher [HFA]/[C3H8]. An estimate of the rate constant for the addition of H to HFA obtained at low [HFA]/[C3H8] yielded k9 = 8.5 × 105 l mol−1 s−1. Trifluoroacetaldehyde was identified with some reliability but many of the other heavier products formed in the H2 + HFA reaction could not be identified. Quenching cross-sections were determined for C2H4, C3H8, C4H10, and HFA relative to that for N2O.
Apparent molal volumes and heat capacities of low molecular weight peptides in water at 25 °C
Authors: Jolicoeur Carmel , Boileau Jeannine
Published: May 2006

The apparent molal volumes [Formula: see text] and beat capacities [Formula: see text] of oligopeptides of glycine, alanine, and serine have been determined in water at 25 °C by flow densimetry and flow microcalorimetry. The data are reported for the homologous series: glycine to pentaglycine, L-alanine to tetra-L-alanine and L-serine to tri-L-serine. From the limiting [Formula: see text] and [Formula: see text] values of the glycine oligomers, the contributions of the glycyl residue in an extended polypeptide chain has been evaluated as: [Formula: see text] and [Formula: see text] The data for the other peptides are discussed in terms of contributions from the amino acid side chains, i.e. —CH3 and —CH2OH, and end-group hydration effects. Some necessary conditions for obtaining useful additivity schemes for predicting [Formula: see text] and [Formula: see text] of extended polypeptides and proteins are indicated.
Temperature dependence of rate constants for the reactions of oxygen atoms, O(3P), with HBr and HI
Authors: Singleton D. L. , Cvetanović R. J.
Published: May 2006

Rate constants for the reactions O(3P) + HX → OH + X (X = Br, I) have been determined by a phase shift technique. Oxygen atoms were generated by modulated mercury photosensitized decomposition of nitrous oxide, and were monitored by the chemiluminescence from the reaction with nitric oxide. Over the temperature interval 298–554 K, the rate constants are satisfactorily represented by the Arrhenius expressions kO+HBr = (8.09 ± 0.86) × 109 exp (−3.59 ± 0.08)/RT and kO+HI = (2.82 ± 0.27) × 1010 exp (−1.99 ± 0.07)/RT, where the units are ℓ mol−1 s−1 and kcal mol−1. The indicated uncertainties are one standard deviation. The results of bond energy–bond order calculations, incorporating recently proposed modifications, are discussed.
Bis(ditertiaryphosphine) complexes of rhodium(I). Synthesis, spectroscopy, and activity for catalytic hydrogenation
Authors: James Brian R. , Mahajan Devinder
Published: May 2006

Rhodium(I)–bis(ditertiaryphosphine) complexes of the general formula [Formula: see text]n = 1–4, and (+)-diop (diop = 2,3-O-isopropylidene 2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) have been prepared by treating [Rh(cyclooctene)2Cl]2 with the appropriate ditertiaryphosphine. The n = 1 and n = 4 and diop species are five-coordinate in the solid state and in non-polar solvents, while the n = 2 and 3 species contain ionic chloride. The cationic complexes [Formula: see text] were prepared from the [Formula: see text] species by adding AgX (X = SbF6, PF6, BF4). Reaction of the chloro complexes with borohydride has yielded the hydrides, [Formula: see text] for the n = 2 and 3 diphosphines, and for (+)-diop. 1H and 31P nmr, as well as visible spectral data, are presented: a solvent-dependent deshielding of ortho protons of the phenyl groups is observed in some of the complexes, and the ligand CH2 protons are coupled to the rhodium in the Rh(Ph2PCH2PPh2)2+ cation; the P atom in this bis(diphenylphosphino) ligand shows an usual high field shift on coordination to rhodium.Preliminary kinetic data for catalytic hydrogenation of methylenesuccinic acid show that the cationic and hydrido complexes are more active than the corresponding chloro complexes, and that activity generally increases with increasing chain length of the diphosphine.
Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and pKa values for ionization of the P—H bond in phosphonic acid and phosphonic esters
Authors: Guthrie J. Peter
Published: May 2006

From data in the literature the free energies of formation in aqueous solution of triethyl phosphite and diethyl phosphonate can be calculated as −138.4 ± 1.7 and −165.1 ± 2.0 kcal mol−1, respectively. From these values, by application of free energy relations which we have published, the free energies of formation of the corresponding hydroxy compounds can be calculated and thence the equilibrium constants for tautomerization, which are 107.2, 108.7, and 1010.3 in favor of the tetracoordinate phosphonate tautomer for P(OEt)2OH, P(OEt)(OH)2, and P(OH)3, respectively. Using estimated pKa values for the tricoordinate phosphite species the tautomerization equilibria for the anions could also be calculated, as could the pKa values from the P—H bonds: 13, 26, and 38 for H—PO(OEt)2, H—PO2(OEt)−, and H—PO32−, respectively.
Isomeric cyclic [C6H10]+• ions. The energy barrier to ring opening
Authors: Wolkoff Peder , Holmes John L.
Published: May 2006

Appearance energies and metastable peak shapes for methyl loss from the molecular ions of cyclohexene, methylcyclopentenes, methylenecyclopentane, bicyclo[3.1.0]hexane, and 2-methyl-1,4-pentadiene indicate that they have a common reaction pathway which produces [cyclopentenium]+ as the daughter ion at threshold.From measurements of appearance energies and from relative peak abundances and kinetic energy releases for the metastable losses of CH3• and labelled methyl from the deuterium labelled cyclic [C6H10]+• molecular ions it was concluded that: (a) H/D mixing in [cyclohexene]+• occurs in the intact ring prior to a concerted methyl extrusion; (b) [methylcyclopentenes]+• loses methyl without any H/D mixing at or near to threshold by a straight C—C cleavage, possibly via the 3-isomer. Methyl losses involving H/D mixing are preceded by ring opening which has an activation energy of ca. 1 eV. However, [cyclopentenium]+• is again the daughter ion; (c) methylenecyclopentane and bicyclo[3.1.0]hexane molecular ions isomerize to methylcyclopentenes prior to methyl loss.H/D mixing (prior to methyl loss) in the molecular ion 1,1-2H2-2-methyl-1,4-pentadiene takes place before cyclisation to methylcyclopentene.
Lone pair interactions in dimethoxymethane and anomeric effect
Authors: Tvaroška Igor , Bleha Tomaš
Published: May 2006

Perturbation molecular orbital analysis has been used for a computation of the through-bond and through-space orbital interactions of oxygen lone pairs in dimethoxymethane (DMM). The analysis predicts the symmetrical combination of p-type lone pairs as a highest occupied orbital in an antiperiplanar conformation. The conformational dependence of through-bond orbital interactions has the character of the V2 term in the Fourier expansion of the rotation potential function about the C—O bond. Contrary to the recent theoretical interpretation that the anomeric effect (preference of gauche conformation) is caused by superjacent orbital control, the orbital interactions in DMM are not dominant terms with respect to the anomeric or exoanomeric effect. The dipole–dipole interactions of the C—O bonds stabilizing the gauche conformation should thus be considered as the primary cause of the anomeric effect in DMM. The frontier orbital energies and geometric parameters in DMM are strongly influenced by a variation of orbital interaction with rotation. Results obtained for DMM are used to explain the conformational behaviour of other molecules containing the acetal moiety, such as pyrane heterocycles, sugars, and polyoxymethylene.
Synthesis and absolute configuration of nojigiku alcohol
Authors: Darby Nicholas , Lamb Nancy , Money Thomas
Published: May 2006

The structure, absolute configuration and physical constants of nojigiku alcohol ((+)-6-exo-hydroxycamphene) and derivatives have been established by synthesis from (−)-isobornyl acetate.
Chemical reaction in electric discharge. V. Reaction kinetics in a low frequency modulated discharge
Authors: Smith John N. , Costa Motilal D. , Deckers Jacques M.
Published: May 2006

A current modulation technique has been developed for the determination of kinetic information in glow discharges through flowing gases. A low frequency sinusoidal modulation superimposed on the dc discharge current produces modulations in the electron density and radical concentrations. Measurements of the amplitudes and phase shifts of radical concentrations can be used to elucidate reaction mechanisms and to determine rate constants for some reaction processes.The kinetic response of discharge chemical phenomena to an applied current modulation is discussed for several general types of reaction mechanisms. Rates of O atom production and removal measured in a current modulated O2 glow discharge are compared to rates measured in a dc glow discharge. The excellent agreement of these two sets of results provides an experimental foundation for the current modulation method.
The application of DPASV to the determination of the low temperature solubility of lead sulphate in sulphuric acid solutions
Authors: Valeriote Eugene M. L. , Gallop Lloyd D. , Aragon Pedro J.
Published: May 2006

Measurements of the solubility of lead sulphate in 35% by weight sulphuric acid, pure water, and at two intermediate acid concentrations have been made over the temperature range 25 °C to −50 °C using differential pulse anodic stripping voltammetry.Values of the standard enthalpy of solution, derived from the data and from that of other workers, have been found to be higher than those obtained from emf measurements. The extent of lead sulphate ion pairing is analyzed at 25 °C and discussed. The slowness of equilibration of acid solutions supersaturated with lead sulphate was judged of importance in deciding the relevance of the use of thermodynamically calculated lead ion concentrations with respect to lead acid battery mechanisms.
A new type of Lycopodium alkaloid. The C30N3 alkaloids from Lycopodium lucidulum
Authors: Ayer William A. , Browne Lois M. , Nakahara Yuji , Tori Motoo , Delbaere Louis T. J.
Published: May 2006

The structures of lucidine B, dihydrolycolucine, and lycolucine, representatives of a new type of Lycopodium alkaloid, have been determined, mainly on the basis of an X-ray crystallographic study of a derivative (N,O-di-p-bromobenzoyltetrahydrodeoxyoxolucidine B) of lucidine B. Dehydrogenation of lucidine B gives dihydrolycolucine which in turn has been prepared from lycolucine.
Polarographic reduction of phenolphthalein, cresolphthalein, thymolphthalein, and α-naphtholphthalein in aqueous and nonaqueous ethanolic solutions
Authors: Ghoneim Mohamed M. , Ashy Mohamed A. A.
Published: May 2006

The polarographic reduction of phenolphthalein, cresolphthalein, thymolphthalein, and α-naphtholphthalein has been studied in ethanolic Britton–Robinson buffer series (pH 2–12), non-aqueous ethanolic medium, and water–ethanol mixtures. The compounds are reduced through a single 2e− wave in non-aqueous medium and aqueous buffered solutions of pH < 9 or 1e− steps for pH > 9. The nature of the waves, mechanism of the electrode reaction, and kinetic parameters has been considered.
Hydrogen bonding and vapor pressure isotope effect of ethanethiol
Authors: Szydlowski Jerzy , Wolff Hans
Published: May 2006

The vapor pressure ratios of ethanethiol and ethanethiol-d1 between 223 and 323 K can be represented by the relation[Formula: see text]The PD/PH vs. T curve increases initially and reaches a flat maximum at 293 K; at higher temperatures there is an apparent decrease. This behavior can be explained by the superposition of predominantly the normal effect of the intermolecular vibrations and the SH and SD torsion vibrations, and the inverse effect of the SH and SD stretching vibrations. Contrary to the value of 0.91 reported previously, PD/PH values of 1.002 to 1.008 confirm that for weakly hydrogen-bonded substances and their deuterium-bonded analogues a negligibly normal or a slightly inverse vapor pressure isotope effect should be observed.
Megastachine, a new alkaloid from Lycopodiummegastachyum
Authors: Braekman Jean-Claude , Hootele Claude , Miller Noah , Declercq Jean-Paul , Germain Gabriel , Meerssche Maurice Van
Published: May 2006

The isolation of the novel pentacyclic base megastachine (1), representative of a new type of Lycopodium alkaloid, is reported. Its structure has been determined by X-ray diffraction analysis.
Excess volumes for binary liquid mixtures of butylamine with aromatic and aliphatic hydrocarbons
Authors: Krishnaiah Abburi , Sreenivasulu Maripuri , Naidu Puligundla R.
Published: May 2006

Excess volume data for binary liquid mixtures of butylamine with aromatic and aliphatic hydrocarbons were measured as a function of composition dilatometrically at 303.15 and 313.15 K. The hydrocarbons include: benzene, toluene, three isomeric xylenes, hexane, heptane, and octane. The values of VE were found to be positive over the entire range of composition in all the eight systems at both the temperatures. The positive values were ascribed to the break-up of hydrogen bonds in the aggregates of amine by the hydrocarbons.
An investigation of the photodecomposition of N-bromosuccinimide; the generation and reactivity of succinimidyl radical
Authors: Lu Fu-Lung , Naguib Yousry M. A. , Kitadani Masayuki , Chow Yuan L.
Published: May 2006

The photolysis of acetonitrile solutions of N-bromosuccinimide (NBS) in the presence of ethylene oxide and an excess of olefins or benzene in the −30 ∼ 20 °C range was shown to generate the succinimidyl radical in competition with the bromine atom reactions. The succinimidyl radical preferentially attacked a π bond to give 1-succinimidyl-2-bromoalkanes, rather than abstracting alkyl hydrogens. Allylic bromination also occurred and competed with the 1,2-addition. Formation of 3-bromocyclohexene in the presence of cyclohexene at 10–20 °C could be effectively reduced at lower temperatures or in the presence of a high concentration of ethylene oxide; the 1,2-addition process was favored at low temperature but surprisingly not facilitated significantly in the presence of ethylene oxide. The primary adducts from benzene readily eliminate HBr to give N-phenylsuccinimide. The attack of a bromine atom on a carbon–carbon double bond may become an important step in the 0 ∼ −30 °C range. The ease of the addition reaction suggests that this succinimidyl radical may have a Σ electronic configuration.
The application of resonant ion ejection to quadrupole ion storage mass spectrometry: a study of ion/molecule reactions in the QUISTOR
Authors: Armitage Mary Alison , Fulford John Edward , Hoa Duong-Nhu- , Hughes Richard James , March Raymond Evans
Published: May 2006

Resonant ejection of ion species from the quadrupole ion store (QUISTOR) is shown to reveal the coupling of reactant ions with product ions in ion/molecule reactions studied with the QUISTOR – quadrupole mass filter combination. The technique involves the use of selective ejection of a chosen ionic precursor and the simultaneous observation of the perturbations in the concentration of product ions. The technique is demonstrated in studies of the ion chemistry and reaction kinetics of two known chemical systems.
The mechanism of the solvolysis of p-methoxybenzyl chloride in aqueous acetone containing pyridine or thiourea. Evidence for concurrent substitution by unimolecular and bimolecular processes
Authors: Queen Alan
Published: May 2006

The overall rate of reaction of p-methoxybenzyl chloride with 70% aqueous acetone is increased by the addition of pyridine but the rate of hydrolysis is decreased. Comparison of these data with those for benzhydryl chloride under the same conditions shows that the rate of hydrolysis of p-methoxybenzyl chloride is less than the rate of ionisation. These results are discussed in terms of concurrent operation of the SN1 mechanism and a bimolecular process. Similar results are obtained when thiourea is used instead of pyridine.
Electron spin resonance of Mn2+ impurity ions in MoO3–pumice catalyst
Authors: Khulbe K. C. , Mann R. S. , Tan N. , Manoogian A.
Published: May 2006

The electron spin resonance of Mn2+ impurities in the MoO3–pumice system is studied along with the behavior of the system in the oxidation of methanol to formaldehyde. The intensity of the Mn2+ esr lines and the rate of catalytic conversion were both found to pass through a maximum at the same catalyst concentration. The results can be qualitatively explained in terms of the ion sites at the MoO3–pumice surface.
Acid-catalysed cleavage of 4-halonortricyclenes in deuterated medium; evidence that the norbornyl cation is an unsymmetrical species
Authors: Werstiuk Nick Henry , Dhanoa Daljit , Timmins George
Published: May 2006

We have determined the endo:exo deuterium ratios at C(6) of the exo-acetates obtained by D2SO4-catalysed cleavage of nortricyclene (4a), 4-chloronortricyclene (4b), 4-bromonortricyclene (4d), and 4-iodonortricyclene (4e). That the ratios are 1.09 ± 0.03, 1.30 ± 0.04, 1.40 ± 0.02, and 1.48 ± 0.02 for ring-opening of 4a, 4c, 4d, and 4e, respectively, establishes that the norbornyl cation is an unsymmetrical rapidly-equilibrating species.
Stereoselective synthesis of β-substituted α, β-unsaturated esters by dialkylcuprate coupling to the enol phosphate of β-keto esters
Authors: Sum Fuk-Wah , Weiler Larry
Published: May 2006

not available
The excess acidity method. The basicities, and rates and mechanisms of enolization, of some acetophenones and acetone, in moderately concentrated sulfuric acid
Authors: Cox Robin A. , Smith Clinton R. , Yates Keith
Published: May 2006

The X-function method has been used to evaluate the basicities of six nuclear-substituted acetophenones and acetone, using a combination of new measurements and literature data; the protonation [Formula: see text] of acetone was found to be −5.37. The same method, which involves the excess medium acidity, when used to analyze the enolization rate constants obtained from the measured bromination rates, shows that most of the acetophenones enolize by an A-2 process involving two water molecules in the rate-determining step. Observed linear free energy relationships for the basicities and the enolization rates imply a relatively early transition state for the enolization. Acetone was found to enolize by a similar mechanism in sulfuric acid solutions more dilute than 81% w/w, but at higher acidities bisulfate ion was the preferred base. The mechanistic behaviour of 4-nitroacetophenone was found to be different, not A-2 but either A-1 or A-SE2.
The photoinitiated isomerization and addition reactions of liquid 2-butenes in the presence of hydrogen sulfide
Authors: Garneau François-Xavier , Szczerek Ireneusz
Published: May 2006

The near ultraviolet photolysis (λ > 280 nm) of liquid cis-2-butene in the presence of hydrogen sulfide was shown to result in isomerization and addition reactions. The former was monitored by the formation of trans-2-butene as a function of time and hydrogen sulfide concentration. The latter was observed by the presence of s-butyl mercaptan and di-s-butyl sulfide as products. The total amount of addition products as well as the relative amounts of mercaptan and sulfide were determined as a function of time. Using the foregoing information the extent of the isomerization reaction was shown to be greater than that of the addition reaction during the course of the irradiation at a concentration ratio of H2S/cis-2-butene equal to 0.15.It was also shown that hydrogen sulfide was a more effective sensitizer than s-butyl mercaptan and di-s-butyl sulfide but less effective than di-s-butyl disulfide in the isomerization of liquid cis-2-butene. The extent of isomerization and addition reactions were shown to be greater starting with cis-2-butene than with trans-2-butene in the presence of hydrogen sulfide.
Reactions of Ni(NO)I with pyrazolyl gallate ligands: crystal and molecular structure of [Me2Ga(N2C5H7)(OCH2CH 2NMe2)]Ni(NO)
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Ni(NO)I reacts readily with pyrazolyl gallate ligands Na+L− (where L = MeGa(N2C3H3)3, MeGa(N2C5H7)3, and [Me2Ga(N2C5H7)(OCH2CH2NMe2)]) to yield four-coordinate nickel nitrosyl complexes, LNi(NO). In addition, the compound [Me2Ga(N2-C5H7)(OCH2CH2 NMe2)]Ni(N2C5H7)2Ni(NO) has been isolated from one reaction sequence. 1H nmr data show [Me2Ga(N2C5H7)(OCH2CH2NMe2)]Ni(NO) to be stereochemically non-rigid at room temperature in solution. Crystals of [dimethyl(N,N-dimethylethanol-amino)(3,5-dimethylpyrazolyl)gallato(N(2),N(3),O)] nitrosylnickel(I) are monoclinic, a = 9.119(1), b = 13.900(2), c = 14.284(2) Å, β = 107.96(1)°, Z = 4, space group P21/c. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix leastsquares procedures to R = 0.025 and Rw = 0.032 for 1828 reflections with I ≥ 3σ(I). The coordination about the nickel atom is severely distorted tetrahedral with angles at nickel ranging from 84.4(1) to 133.5(1)°. The nitrosyl group is coordinated in a non-linear fashion with Ni—N—O = 162.3(4)°, Ni—N = 1.632(4) and N—O = 1.147(4) Å. Other important bond lengths (corrected for libration) are: Ni—O, 2.045(2), Ni—N(pyrazolyl), 1.989(3), Ni—N(amino), 2.071(3), Ga—O, 1.922(2), Ga—N, 1.998(3), and Ga—C, two at 1.971(6) Å.
Total synthesis of ryanodol
Authors: Bélanger André , Berney Daniel J. F. , Borschberg H.-Jürg , Brousseau Robert , Doutheau Alain , Durand Robert , Katayama Hajime , Lapalme Richard , Leturc Dominique M. , Liao Chun-Chen , MacLachlan Fred N. , Maffrand Jean-Pierre , Marazza Fabrizio , Martino Robert , Moreau Claude , Saint-Laurent Louiselle , Saintonge Roger , Soucy Pierre , Ruest Luc , Deslongchamps Pierre
Published: May 2006

The total synthesis of (+)-ryanodol (1) is described.
Crystal structure of E-1-(2,4,6-trimethylphenyl)ethanone oxime. The aryl–oxime rotational barrier problem and 13C—15N nmr coupling constant calculations
Authors: Fortier Suzanne , Birnbaum George I. , Buchanan Gerald W. , Dawson Brian A.
Published: May 2006

From an X-ray analysis of the title compound it is found that the dihedral angle between the plane of the aromatic ring and the oxime plane is 70.8 °. This large angle precludes a significant π electron overlap between the oxime function and the benzene ring. The distortions of the internal ring angles attributable to the four substituents are examined in detail, and parameters are derived for the oxime group. The aryl–oxime C—C bond length (1.491 Å) is the longest yet reported for an aromatic oxime. Using the X-ray derived geometry as input for the calculation of 13C—15N coupling constants, one obtains markedly better agreement between calculated and observed couplings than was the case when a force-field calculated molecular geometry was employed. The barrier to rotation about the aryl–oxime bond is estimated to be about 5.8 kcal/mol.
Experimental and theoretical investigation of the unusual substituent effect of the vinyl group
Authors: Reynolds W. F. , Modro T. A. , Mezey P. G. , Skorupowa E. , Maron A.
Published: May 2006

σ+ Substituent constants for the ortho- and para-vinyl group have been determined by the application of the linear free-energy relationship to the nitration of the β-substituted styrene derivatives.Energy changes (relative to benzene system) for the proton and hydride ion transfer to individual positions in the styrene molecule have been calculated. Both approaches indicate that the vinyl group is capable of stabilizing both positively and negatively charged transition states. The interactions of the vinyl group with other substituents in the phenyl ring are also determined. Again, stabilizing effects with respect to both π-donor and π-acceptor substituents have been demonstrated for the vinyl group.
Quantitative determination of tantalum in niobium by neutron activation analysis
Authors: Sadoway Donald R. , Flengas S. N. , Hancock R. G. V.
Published: May 2006

A method was devised for the determination of Ta both in mixtures of NbCl5–TaCl5 and in mixtures of ANbCl6–ATaCl6, where A = Na, K, Rb, or Cs. The method involves neutron activation analysis of Nb2O5–Ta2O5 samples prepared by conversion of the chlorocompounds.
The crystal structure of [Pt(tetraethyldiethylenetriamine)I]I
Authors: Durley Rosemary C. E. , Waltz William L. , Robertson Beverly E.
Published: May 2006

Crystals of [Pt(Et4dien)I]I, where Et4dien = (C2H5)2NC2H4NHC2H4N(C2H5)2, have been prepared. A three dimensional crystal structure analysis has been carried out in a monoclinic unit cell having a = 12.565(8), b = 7.576(6), c = 21.040(15) Å, β = 91.12(2)° and space group P21/c, Z = 4. Full-matrix least-squares using 1982 independent, observed reflections converged at R = 0.067. The platinum atom has square-planar co-ordination. The orientation of the four ethyl groups with respect to the plane of the ligand is similar to that observed in related molecules, in spite of a lack of similarity of the molecular packing. The iodide ion appears to be hydrogen bonded to the ligand.
Complexation of Zn(II) to a native sequence tripeptide of human serum albumin studied by 13C nuclear magnetic resonance
Authors: Lakusta Helen , Deber Charles M. , Sarkar Bibudhendra
Published: May 2006

Serum albumins from several species, which specifically bind and transport several divalent metals in blood, contain an Asp-X-His or Glu-X-His amino acid triad as their NH2-terminal sequence. We have synthesized a tripeptide, Asp-Ala-His-N-methylamide, corresponding to the native sequence of the human serum albumin N-terminus, and examined its interaction with Zn(II) ions in aqueous solution using carbon-13 nmr techniques. Variations in carbon chemical shifts and spin–lattice relaxation times (T1's) as a function of pH and increments of added Zn(II) were used to delineate sites of Zn(II):peptide interactions. Trends in T1 values indicated that local motions of several of the tripeptide carbons were restricted by an induced order accompanying metal binding. Analysis of spectral data suggested that Zn(II) is coordinated to the His imidazole nitrogen atom and the Asp β-carboxylate oxygen atom(s) in each peptide molecule. Similar experiments using a tripeptide analogue, Gly-Gly-His-N-methylamide, demonstrated that in the absence of a side chain carboxylate group, Zn(II) ions will complex the peptide through the His imidazole group and the N-terminal Gly α-amino group. These results support the possibility of a biologically functional role for the Asp-X-His triad as a liganding template for Zn(II)/protein binding.
The crystal and molecular structure of tetrabenzocyclodecan-1,6-dione
Authors: Cameron T. Stanley , Chan Christine , Morris David G. , Shepherd Alistair G.
Published: May 2006

The crystals belong to the orthorhombic space group C222, with a = 9.226, b = 12.092, c = 16.513 Å, Z = 4. A single crystal X-ray diffraction analysis has shown that the title compound, in which all carbon atoms are sp2 hybridized, exists with the ten membered ring in a slightly twisted tub conformation. The 13C nmr spectrum is also reported.
Spin trapping for hydroxyl in water: a kinetic evaluation of two popular traps
Authors: Marriott Paul R. , Perkins M. John , Griller David
Published: May 2006

Two spin traps, 4-(N-methylpyridinium)tert-butyl nitrone (4-MePyBN) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) were examined for their effectiveness at trapping hydroxyl in water. At pH 6 and 22 °C, rate constants for trapping hydroxyl were found to be 0.5 × 109 M−1 s−1 (4-MePyBN) and 2.0 × 109 M−1  s−1 (DMPO). The hydroxyl adduct of DMPO decayed by a first order process with a half-life of 870 s. This was at least three times greater than that of the 4-MePyBN adduct. These and other results suggest that DMPO is the superior trap for this particular application and is well suited for use in biological systems.
Addition of arenesulphenyl chlorides to 2-methylenebicyclo[2.2.1]hept-5-ene: effect of increasing electron demand upon the rate and product determining transition states
Authors: Garratt Dennis G. , Beaulieu Pierre L. , Morisset Veronique M.
Published: May 2006

The rates and products of addition of a series of sixteen arenesulphenyl chlorides to 2-methylenebicyclo[2.2.1]hept-5-ene, 7, and the E, Z isomeric 2-ethylidenebicyclo[2.2.1]hept-5-enes, 8 and 9, have been determined in methylene chloride solution. The major species from attack on 7 is always endo-3-arylthio-1-chloromethyltricyclo[2.2.1.02,6]heptane, the product of exo attack upon the endocyclic double bond with homoallylic participation of the exocyclic π system. No evidence was found for initial electrophilic attack upon the exocyclic double bond.