bluuebunny/crossref_metadata_2025 huggingface dataset:
Thomsenolite, NaCaAlF6•H2O: hydrogen bonding and comparison with pachnolite
Authors: Adhikesavalu D. , Cameron T. Stanley , Knop Osvald
Published: May 2006

The crystal structure of thomsenolite, NaCaAlF6•H2O, has been redetermined to establish the hydrogen-bonding scheme in this mineral. Both hydrogen atoms participate in branched [Formula: see text] bonds. The hydrogen bonds link the AlF6, octahedra to form infinite chains ||b, which in turn are cross-linked to form infinite double sheets {[AlF6] + Ca}—(H2O)—{[AlF6] + Ca}||(001). The Na atoms are located exclusively in layers ||(001) which separate the double sheets. A detailed comparison of thomsenolite with its dimorph, pachnolite, shows that the structure of pachnolite is obtained in essence by interchanging the positions of one half of the Na atoms and one half of the water molecules in thomsenolite. The two-dimensional, layerlike hydrogen-bonding network in thomsenolite is thereby changed to one of a three-dimensional character in pachnolite. Other features of the two structures, including the Al—F and [Formula: see text] distances, are compared and discussed in some detail.
Total synthesis of the stemodane-type diterpenoids (±)-stemodin and (±)-maritimol. Formal total synthesis of (±)-stemodinone and (±)-2-desoxystemodinone
Authors: Piers Edward , Abeysekera Brian F. , Herbert David J. , Suckling Ian D.
Published: May 2006

Total syntheses of the stemodane-type diterpenoids (±)-stemodin (2) and (±)-maritimol (4), as well as formal total syntheses of (±)-stemodinone (3) and (±)-2-desoxystemodinone (5), are described. The known ketol 12 was converted into the tricyclic enone 7. Photoaddition of aliène to 7 gave (96%) a mixture of the photoadducts 20–23 (40:51:6:3, respectively). Ozonolysis of 20, followed by treatment of the resultant dione 24 with MeONa–MeOH (room temperature, 2.5 h), provided the keto ester 26 (94%). Subjection of 21 to an identical sequence of reactions gave (86%) the same product 26. On the other hand, when the dione 25 was treated with MeONa–MeOH under much milder conditions (0 °C, 5 min), the isomeric keto esters 27 (39%) and 28 (33%) were produced. Both 27 and 28, upon reaction with MeONa–MeOH at room temperature, were converted efficiently into 26. Reduction (NaBH4 or Lisec-Bu3BH) of 26 provided separable mixtures of the ester alcohol 32 and the lactone 33, which could be transformed readily into the dimesylates 35 and 39, respectively. Reaction of 35 and 39 with NaCN in warm hexamethylphosphoramide afforded the dinitriles 37 and 40, both of which, upon treatment with t-BuOK in refluxing t-BuOH, produced the sameenaminonitrile 41. Acid hydrolysis of 41 provided the dione 42. Preparatively, compound 26 could be transformed conveniently into the dione 42 (52% overall yield) without separation of mixtures of isomeric synthetic intermediates. Treatment (CH2Cl2, −95 °C) of 42 with Mc3Sil–Et3N, followed by oxidation of the resultant products 46 and 47 with Pd(OAc)2 in acetonitrile, gave the bis enones 48 (67%) and 49 (19%). Compound 48 was converted into the dione 52 which, upon reaction with (i-PrO)3 TiMe in ether, provided an 86:14 mixture of the keto alcohols 53 and 54 (63% from 48). Reduction (NaBH4) of 53 afforded (±)-maritimol (4). On the other hand, conversion of the 86:14 mixture of 53 and 54 into the p-toluenesulfonylhydrazones 55 and subsequent reaction of 55 with NaH in refluxing toluene gave the alkene alcohols 56 (58%) and 57 (12%). Hydroboration–oxidation (9-BBN, refluxing tetrahydrofuran; NaOH, H2O2) of 56 afforded (88%) (±)-stemodin (2).
Oxidation of hydrocarbons. 15. A study of the oxidation of alkenes by methyltributylammonium permanganate
Authors: Perez-Benito Joaquin F. , Lee Donald G.
Published: May 2006

A study of the reduction of methyltributylammonium permanganate by a large number of alkenes in methylene chloride has dispelled a current uncertainty concerning the nature of the inorganic product obtained. It is colloidal manganese dioxide and not a manganate(V) cyclic diester as previously supposed. This product is stabilized in methylene chloride solutions by adsorption of the alkene, which decreases its polarity at the solvent interphase. The solubility of the colloid is therefore a function of both the concentration and the identity of the alkene. In certain (atypical) cases, where acidic compounds are present, the product is further reduced to manganese(III).
Charge distributions and chemical effects. XXXIX. Atomization energies and insitu atomic orbitals in ethylenic hydrocarbons
Authors: Fliszár Sándor , Re Giuseppe Del , Comeau Michel
Published: May 2006

A simple expression already used with success for computing atomization energies of alkanes and other molecules has been applied to alkenes. This has required evaluation of a term F which had been taken equal to zero in previous applications of the same equation. In order to explain the physical meaning of this novelty, we have been led to introduce a "principle" stating that the electrostatic potential created by σ electrons associated to any given atom of a molecule is well reproduced by a single charge centered at the nucleus and that the special behavior of alkenes is associated with residual π AO-centroid displacements with respect to the carbon nuclei. Direct computation of insitu valence AO's from optimized 4-31G* molecular orbitals yields a pd hybridization of the π AO's of the carbon atoms which does account for most of the expected F value. This indicated that use of simple equations derived from general theory and the application of simple principles or rules to the analysis of sophisticated molecular computations can yield a simple and quantitatively satisfactory picture of molecular reality.
Zn(II), Cd(II), and Hg(II) complexes of 6-amino-3-methyl-5-nitrosouracil
Authors: Salas-Peregrin J. M. , Moreno-Carretero M. N. , Colacio-Rodriguez E.
Published: May 2006

The preparation and spectral properties of the complexes of 6-amino-3-methyl-5-nitroso-uracil (HAMNU) with Zn(II), Cd(II), and Hg(II) ions are reported. The results suggest that the exocyclic oxygen and nitrogen atoms have a much greater tendency to bind to these ions than the ring nitrogen atoms. In Zn(II) and Cd(II) complexes, the ligand is N,O-coordinated through the 5-nitroso and 6-oxide groups of (AMNU) in nitrosophenolic anionic form. In the Hg(II) complexes, the ligand seems to be bound in neutral form. Tetrahedral structures are proposed in all cases.
Design and reactivity of organic functional groups—utility of imidazolylsulfonates in the synthesis of monobactams and 3-amino nocardicinic acid
Authors: Hanessian Stephen , Couture Claude , Wyss Heinz
Published: May 2006

The imidazolylsulfonate group has been found to be a versatile leaving group in the intramolecular cyclization of p-methoxyphenyl amides and related derivatives of N-substituted L-serine to give the corresponding β-lactams.
The geometry of 4-(1-ethoxyethylidene)-5-oxazolones and thiazolones: 1H and 13C studies and the crystal structure of 4-[(Z)-1-ethoxyethylidene]-2-phenyl-5-oxazolone
Authors: Bell R. A. , Faggiani R. , Lock C. J. L. , McLeod R. A.
Published: May 2006

A series of E and Z isomers of substituted 4-(1-ethoxyethylidene)-5-oxazolones and thiazolones have been prepared and their 1H and 13C spectra recorded. The vinylic methyl 1H chemical shifts showed minimal differences between E and Z isomers whereas the vinylic OCH21H signals differed by 0.15–0.43 ppm, with the Z isomer being consistently the more deshielded. Both vinylic methyl and OCH2 groups showed different 13C resonances for each isomer, with the Z isomers being the more deshielded. The Z geometry was conclusively defined for one isomer of 4-(1-ethoxyethylidene)-2-phenyl-5-oxazolone, 5, by X-ray crystallography and this was sufficient to assign the geometry of the remaining pairs of E and Z isomers. Oxazolone 5 has the space group P21/n and cell dimensions a = 9.219(3), b = 19.899(5), c = 7.459(1) Å, β = 118.01(2)°, and has four formula units in the unit cell. Intensities were measured with use of MoKα radiation and a Nicolet P3 diffractometer. The crystal structure was determined by standard methods and refined to R1 = 0.0709, R2 = 0.0696 based on 1419 independent reflections. The molecule is essentially planar and most bond lengths and angles are normal. Exceptions are the very short C(olefin)—O(ether) bond (1.339(4) Å) and the large ether C—O—C angle (122.1(3)°) caused by extreme delocalization in the O(ether)CCCO(carbonyl) system. The planarity causes a number of strong intramolecular repulsive interactions, causing an exceptionally small external olefin angle, O(ether)CC(methyl), of 108.1(4)°. The ethoxyl side chain of 5 adopts a conformation in the solid state which places the methylene of the OCH2 group adjacent to the oxazole ring nitrogen. This conformation is proposed to persist in solution phases and is consistent with the observed 13C chemical shifts and known γ and δ substituent effects.
Thermodynamics of solvent mixtures. I. Density and viscosity of binary mixtures of N-methylpyrrolidinone – tetrahydrofuran and propylene carbonate – acetonitrile
Authors: Anantaraman A. V.
Published: May 2006

Excess volumes and viscosities of binary liquid mixtures of N-methylpyrrolidinone – tetrahydrofuran and propylene carbonate – acetonitrile are measured and examined in the light of empirical theories such as absolute rate, free volume, and regular solution theories. It is shown that non-ideality arises due to (a) shape factors, (b) molecular interaction, and that the two properties, excess volume and viscosity, illustrate these two aspects of non-ideality.
Regioselectivity control in metal hydride reductions of substituted maleic anhydrides
Authors: Kayser Margaret M. , Breau Livain , Eliev Sonia , Morand Peter , Ip H. S.
Published: May 2006

A systematic study of reductions of unsymmetrically substituted maleic anhydrides by a variety of metal hydride reagents indicates that the high regioselectivity observed in these reactions is controlled chiefly by electronic factors.
Characterization and elimination of cationic interferences on platinum
Authors: Mostafa M. A. , Kabil M. A.
Published: May 2006

Interfering effects of different cations on the atomic absorption signal of platinum can be completely eliminated by adding n-butylamine. The releasing action of n-butylamine comes through the formation of a volatile, platinum–amine complex, so the platinum species reaching the flame will normally be independent of the original composition of the solution. The inhibition release titration method has been used in studying the interfering effects to achieve a determinate characterization of compound formation.
Kinetics of acid and nucleophile catalysis of the diazotization of 1-naphthylamine
Authors: Casado Julio , Castro Albino , Iglesias Emilia , Peña M. Elena , Tato José Vázquez
Published: May 2006

The diazotization of 1-naphthylamine has been studied at acidities ranging from 10−2 to 1.5 M. At low acidities nitrosation takes place via the unprotonated form of the amine, and the rate-controlling step is either the interaction with the nitrosating agent or, if high concentrations of a nucleophile are present, the loss of a proton from the protonated nitrosamine (the nucleophiles studied were Cl−, Br−, SCN−, and thiourea). At high acidities the protonated and free amines also react, the former of these reactions involving proton transfer to the solvent. In each case the proposed mechanism was supported by studying the reaction in D2O, which also allowed the isotopic effect of the solvent on the formation equilibria of the various nitrosating agents to be obtained.
Thermal rearrangement of functionalized 1,2-divinylcyclopropane systems. A convenient synthesis of substituted 4-cyclohepten-1-ones
Authors: Piers Edward , Burmeister Max S. , Reissig Hans-Ulrich
Published: May 2006

Reaction of the acyl chlorides 14–21 with lithium (phenylthio)(cis-2-vinylcyclopropyl)cuprate (2) provided the ketones 22–29. Compounds 22–25, upon treatment with i-Pr2NLi-Me3SiCl, were converted cleanly into the enol silyl ethers 30–33, which gave the 1,4-cycloheptadienes 34–37 upon thermolysis (100–110 °C). Acid hydrolysis of the latter materials produced the corresponding 4-cyclohepten-1-ones 38–41. However, subjection of the cis-2-vinylcyclopropyl ketones 26–29 to i-Pr2NLi-t-BuMe2SiCl afforded, in each case, a mixture of isomeric enol ethers (26 → 42 + 44 (1:1); 27 → 43 + 45 (1:9); 28 → 56 + 58 (1:1); 29 → 57 + 59 (4:1)). Thermolysis (150–175 °C) of these mixtures, followed by acid hydrolysis of the resultant products, gave the 4-cyclohepten-1-ones 54, 55, 64, and 65, admixed with the corresponding 3-methylenecyclopentenes 52, 53, 62, and 63. On the other hand, treatment of the trans-2-vinylcyclopropyl ketones 70–74 with i-Pr2NLi–t-BuMe2SiCl provided exclusively or predominantly the enol ethers 75–79. Thermolysis (230 °C) of the latter materials and subsequent acid hydrolysis of the resultant products 80, 50, 51, 60, and 61 afforded the 4-cyclopenten-1-ones 38, 54, 55, 64, and 65.
The aminolysis of phosphinates; the kinetics and mechanism of the aminolysis of phosphinate esters in acetonitrile
Authors: Cook Robert D. , Daouk Wafa A. , Hajj Asaad N. , Kabbani Ahmad , Kurku Anwar , Samaha Muna , Shayban Fuad , Tanielian Ohannes V.
Published: May 2006

The aminolysis of aryl diphenylphosphinates, p-nitrophenyl diphenylphosphinothionate, -phosphinothioate, and -phosphinodithioate by n-butylamine, by the secondary amines piperidine, pyrrolidine, morpholine, and dipropylamine, as well as by a series of diamines, has been studied in acetonitrile. The general reactivity order is diamines > butylamine > sec-amines. Butylaminolysis follows a two-term rate law, one first order in amine and the other second order in amine. The second order in amine term predominates. sec-Amines and diamines follow a rate law which is first order in amine only. Leaving group effects, solvent effects, and activation parameters support a pathway which involves rate-determining collapse of a zwitterionic pentacoordinate intermediate. In the case of butylamine this collapse is general base catalyzed and for the diamines the reaction is intramolecularly general base catalyzed.
The Raman spectrum of kaolinite #9 at 21°C
Authors: Michaelian K. H.
Published: May 2006

The Raman spectrum of kaolinite #9, a layer silicate of composition Al2Si2O5(OH)4 from Mesa Alta, New Mexico, USA, is reported and compared to previously published Raman and infrared spectra, as well as calculated lattice vibration frequencies, of other kaolinite samples. In the OH stretching region, a Raman band is observed at 3684 cm−1, a frequency which is generally unknown in infrared spectra of kaolinite. The two most likely origins of this band are (a) uncoupled inner-surface hydroxyl stretching, and (b) transverse/longitudinal splitting involving the 3695 cm−1 band, which occurs in both Raman and infrared spectra of kaolinite. The existing data do not conclusively show which of these explanations is correct. In the lattice vibration region, most of the observed Raman bands of kaolinite #9 have been tentatively assigned by comparison with published frequency calculations and existing assignments of infrared spectra of various kaolinites. The descriptions of many of the vibrational modes are approximate, partly because extensive mixing of vibrations makes a simple description of them impossible.
Coadsorption of triphenylphosphine – triphenylphosphine oxide, triphenylphosphine – dodecyldiphenylphosphine oxide, and dodecyldiphenylphosphine oxide – tri(n)octylphosphine oxide from methanolic solutions on a polarized mercury electrode
Authors: Pappa-Louisi Adriani , Nikitas Panaghiotis
Published: May 2006

The coadsorption of triphenylphosphine – triphenylphosphine oxide, triphenylphosphine – dodecyldiphenylphosphine oxide, and dodecyldiphenylphosphine oxide – tri(n)octylphosphine oxide on a polarized mercury electrode from methanolic solutions of LiCl is investigated by means of electrocapillary measurements. Results show that reorientation or other molecular modifications do not take place during the coadsorption process. The adsorbed molecules maintain their orientation with the phenyl and alkyl groups in contact with the electrode surface. Thus, the adsorption maxima of the substances in the mixed adsorption are located at the same polarization region as in the single adsorption, although their separation distance increases as the bulk concentration of adsorbates rises due to changes in the electrical characteristics of the interface. This shift is not observed when the two substances are adsorbed at the same, or nearly the same, potentials (charges). In all cases the adsorption of a substance leads to a decrease in the adsorption of the coadsorbate to an extent depending on the electric field. The influence of the field on the adsorption isotherms cannot be determined by means of the surface pressure method but by determining the type of adsorption isotherm. It was found that all the systems studied follow an isotherm based on the strictly regular solutions theory. The interaction parameters are independent of the field, while the standard free energy of adsorption of an adsorbate, within experimental error, is independent of the presence of the coadsorbate. This is due to the insignificant change in the bulk adsorbate solvent interactions caused by the presence of the coadsorbed substance in the solution
Apparent molar heat capacities and volumes of alkylbenzenesulfonate salts in water: substituent group additivity
Authors: Sway K. , Hovey Jamey K. , Tremaine Peter R.
Published: May 2006

Densities and specific heats were measured for the aqueous sodium salts of benzenesulfonate, p-toluenesulfonate, 2,4- and 2,5-dimethylbenzenesulfonate, mesitylenesulfonate, and p-ethylbenzenesulfonate. The limiting partial molar volumes, [Formula: see text] and heat capacities, [Formula: see text], lead to revised values in the group contributions for aromatic —CH2— and —CH3 groups in the additivity scheme proposed by Perron and Desnoyers. The heat capacities of substituted alkylbenzenes can deviate from group additivity by as much as 70 and 40 J K−1 mol,−1, respectively, when polar groups are located on the α and β positions of the alkyl chain.
Isomerization of alkyl branched alkynoic acids
Authors: Abrams Suzanne R.
Published: May 2006

Acetylenic acids are isomerized by alkali metal amides of 1,3-diaminopropane to 3,5-dienoic acids. An acid with a methyl branch at C-3 separating the carboxyl from the triple bond is rearranged to a mixture of the terminal alkynoic acid and two isomeric 3,5-dienoic acids. The corresponding 4-methyl compound affords the terminal alkynoic acid, one 3,5-dienoic acid, and two cyclized products, cis- and trans-3-methyl-5-(octylidene)-1-cyclopentanecarboxylic acids. Propargylic acids branched at C-5 and C-6 are rearranged to the appropriately substituted 3,5-dienoic acids in moderate yield.
Transformation of β-diketones to β-chloro-α,β-unsaturated ketones induced by lithium hydride and phenyl dichlorophosphate
Authors: Liu Hsing-Jang , Lamoureux Guy V. , Llinas-Brunet Montse
Published: May 2006

The conversion of β-diketones to the corresponding β-chloro-α,β-unsaturated ketones is facilitated by using lithium hydride as a base and phenyl dichlorophosphate as an activating agent.
Synthèse de dérivés N-5 substitués des 5H-pyrido[4,3-b]benzo[f]indoles, isomères des 6H-pyrido[4,3-b]carbazoles (ellipticines)
Authors: Nguyen Chi Hung , Bisagni Émile , Lhoste Jean-Marc
Published: May 2006

2-Lithio dérivatives of 1-alkyl-4-chloropyrrolo[3,2-c]pyridines react with acetophenones, giving the corresponding tertiary alcohols. After déhydration into 1,1-diarylethylenes and subsequent reduction to 1,1 -diarylethanes, the synthesis of 1-chloro-5-alkyl-5H-pyrido[4,3-b]benzo[f]indoles was achieved either by direct cyclization with dichloromethylmethylether plus stannic chloride or by formylation and cyclodehydration with polyphosphoric acid. Finally, the substitution of the chlorine atom with dialkylaminoalkylamines leads to 1-amino substituted 5-alkyl-5H-pyrido[4,3-b]benzo[f]indoles, isomers of 1-dialkylaminoalkylamino 6-substituted ellipticines.
Isolation of 5-methoxy-2,2-dimethyl-1-2H-benzopyran-6-propanoic acid methyl ester and characterization by two-dimensional nuclear magnetic resonance spectroscopy
Authors: Jacobs Helen , Ramdayal Frank , Reynolds William F. , Poplawski Janusz , McLean Stewart
Published: May 2006

The structure of the title compound (1), isolated from Hortiaregia, was established by nuclear magnetic resonance spectroscopy. The investigation demonstrates the value of indirect shift correlation experiments. The compound was further characterized by chemical and spectroscopic methods.
Cyanothiolacetate as a masked β-hydroxyproprionitrile carbanion in Michael reactions
Authors: Liu Hsing-Jang , Wynn Hla
Published: May 2006

A facile method for the introduction of a highly functionalized isopropyl unit, in the form of β-hydroxyproprionitrile or acrylonitrile, to the β carbon of an α,β-unsaturated ketone has been developed using S-tert-butyl cyanothiolacetate as a β-hydroxyproprionitrile equivalent in Michael reactions.
Thiol esters in organic synthesis. XIV. The total synthesis of racemic α-costal
Authors: Liu Hsing-Jang , Wynn Hla
Published: May 2006

The first total synthesis of α-costal (1) in racemic form has been achieved in an unequivocal manner whereby the structure previously assigned to the natural aldehyde is confirmed. A salient feature of the synthesis is the use of S-tert-butyl cyanothiolacetate to facilitate the introduction of the labile acrolein unit.
Heats of transport of some aqueous nonelectrolytes
Authors: Murkherjee A. K. , Sanyal S. K.
Published: May 2006

The thermal diffusion of aqueous solutions of glucose, sucrose, ethylacetate, and 1,4-dioxan (0.1 m) contained in the pores of a sintered glass disc (or porosity G4), which is subjected to a temperature gradient, has been studied. The resulting heat of transport data have been interpreted, in terms of local changes in entropy in the solvent brought forth by the presence of the solutes, and correlated to the hydrophobic hydration effects.
Alkylation of camphor imines of glycinates. Diastereoselectivity as a function of electronic factors in the alkylating agent
Authors: McIntosh John M. , Mishra Pratibha
Published: May 2006

Alkylation of the (R)-camphor imine of tert-butyl glycinate with a variety of alkylating agents gave diastereoselectivities ranging from 0–100%. Simple alkyl halides larger than methyl give de's (diastereomeric excesses) of ca. 50% whereas those derived from allylic type systems afford de's of 75–100%. The results are best explained by invoking a transition state interaction between the π system of the alkylating agent and the imine which, for steric reasons, requires alkylation to occur from the pro-R face.
Electrostatic and nonelectrostatic, conventional and unitary thermodynamic quantities of reaction. I. Metal–ligand reactions in aqueous solvent
Authors: Aruga Roberto
Published: May 2006

A calculation method of the electrostatic and nonelectrostatic parts of thermodynamic quantities of reaction, previously proposed and applied to complex-formation reactions of aminic and carboxylic ligands, is applied, in the present work, to association reactions of several other ligands. In particular, to check its reliability, this method is applied to ΔG0, ΔH0, and ΔS0 data of literature for the formation of metal–anion pairs and for associations of metals with ligands containing pyridine nitrogen, ethereal oxygen, or thioethereal sulfur. Experimental data referring only to aqueous solutions are considered. The results obtained by this method are in agreement, in most cases, with those expected for the reactions examined. Therefore, it seems reliable and useful for a more significant interpretation of conventional thermodynamic parameters.
Ring cleavage of camphor derivatives: formation of chiral synthons for natural product synthesis
Authors: Hutchinson J. H. , Money T. , Piper S. E.
Published: May 2006

Base-promoted ring cleavage of 9,10- and 8,10-dibromocamphor provides chiral intermediates for natural product synthesis.
The chemistry of the blue stain fungi. Part 1. Some metabolites of Ceratocystis species associated with mountain pine beetle infected lodgepole pine
Authors: Ayer William A. , Browne Lois M. , Feng Meow-Chen , Orszanska Helena , Saeedi-Ghomi Hussein
Published: May 2006

Metabolites formed in still culture by Ceratocystisclavigera, C. ips, and C. huntii, three of the four Ceratocystis species associated with the blue stain disease of pine, have been identified. In addition to the ubiquitous fungal metabolites ergosterol, ergosterol peroxide, and fatty acids we have isolated succinic acid, β-phenethyl alcohol (1), tryptophol (2), prolylleucyl anhydride (3), tyrosol (4), 3-phenylpropane-1,2-diol (5), 6,8-dihydroxy-3-methylisocoumarin (8), 6,8-dihydroxy-3-hydroxymethylisocoumarin (9), p-hydroxybenzaldehyde (10), phenylacetic acid (11), p-hydroxyphenylacetic acid (12), phenyllactic acid (13), p-hydroxyphenyllactic acid (14), and 2,3-dihydroxybenzoic acid (15). The complex formed by chelation of iron with 2,3-dihydroxybenzoic acid may be responsible, at least in part, for the blue staining of the sapwood of diseased pine.
The chemistry of the blue stain fungi. Part 2. Some essential metal levels of diseased and healthy lodgepole pine
Authors: Ayer William A. , Kratochvil Byron , Allen Eric , Browne Lois M. , Dufresne Claude , Figueroa Daniel , Szenthe Anna
Published: May 2006

The concentrations of 13 trace elements were determined in the needles and wood of a closely grouped stand of lodgepole pine infected with blue stain disease. Over 100 samples each of needles and wood from both healthy and diseased trees were analyzed to assess possible correlation between metal levels and degree of infection. Statistical analysis showed no difference in the concentrations of essential trace elements in the wood at the 95% confidence level. Differences were observed at this confidence level in the needles, however, for calcium, iron, zinc, and chromium, calcium being lower and the other three elements higher in the diseased trees. Levels of aluminum, iron, manganese, and calcium in the needles increase 20–30% per year in both diseased and healthy trees.
Kinetics of the interactions between dyes and micelles
Authors: Reinsborough Vincent C. , Holzwarth Josef F.
Published: May 2006

The rates of association of three azo dyes, methyl red (MR), methyl orange (MO), and pyridine-2-azo-p-dimethylaniline (PADA), with sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles in water were measured at 25 °C over a wide pH range by the continuous flow method of integrating observation (CFMIO). The association was considered in 3 steps: bulk solution encounter, pH jump, and electrostatic and hydrophobic interactions. Either the first or third step is rate limiting depending on the charge of the dye. The rate constant of association of neutral PADA, MR, and MO with SDS micelles is approximately 2 × 106 dm3mol−1s−1 while charging the dyes positively increases k to 109 dm3mol−1 s−1. Increasing the hydrophobicity of dye or micelle increases k for the interaction with the neutral dye species. Changes in k with pH for the dye–CTAB association were less pronounced.
The thermolysis and photolysis of malonic acid in the gas phase
Authors: Cao J.-R. , Back R. A.
Published: May 2006

The thermolysis of malonic acid has been studied briefly in the gas phase at temperatures from 92 to 151 °C at pressures around 0.1 Torr. Major products were CO2 and acetic acid, while smaller amounts (< 5% of the CO2) of CO, acetone, C2H6, and CH4 were formed. Arrhenius parameters of E = 30.9 kcal/mol and log A (s−1) = 13.27 were obtained, based on first-order rate constants for the formation of CO2. It is suggested that the major products are formed by an internal hydrogen-atom transfer through a 4-centre transition state. The gas-phase photolysis was examined briefly using light of 228.8 nm, and gave products very similar to those of the thermolysis.
Oxidation of the mercurous ion by peroxidase
Authors: Wigfield Donald C. , Tse Season
Published: May 2006

The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.
A tellurium-125 Mössbauer study of bis(trifluoromethyl)- and bis(pentafluorophenyl)- tellurides and their dihalides
Authors: Jones C. H. W. , Sharma R. D. , Naumann D.
Published: May 2006

The 125Te Mössbauer spectra for (CF3)2Te and (C6F5)2Te have been recorded and exhibit significantly larger quadrupole splittings (14.02 and 13.40 mm s−1 respectively) than those of Me2Te (10.5 mm s−1) and Ph2Te (11.0 mm s−1). The dihalides (CF3)2TeX2 and (C66F5)2TeX2 (X = F, Cl,Br) have consistently smaller quadrupole splittings than the dihalides Me2Tex2 and Ph2TeX2. These observations are consistent with the greater electronegativity of the CF3 and C6F5 ligands. The 125Te nmr chemical shifts of (C6F5)Te and its dihalides show a consistent trend to more positive values (increased deshielding) as the electronegativity of the ligands attached to tellurium increases ((C6F5)Te, 297.6 ppm; (C6F5)2TeF2, 1060 ppm). However, for (CF3)2Te and its dihalides a more complex pattern is observed which may be explained by changes in the mean electronic excitation term in the Ramsey paramagnetic shielding term.
Properties of atoms and bonds in carbocations
Authors: Bader R. F. W.
Published: May 2006

The quantum theory of atoms in molecules defines structures for and determines the properties of the atoms and bonds in the series of carbocations [(CH3)nCH3−n]+ with n = 0–3, and their parent hydrocarbons. In this theory, an atom in a molecule and its properties are defined by quantum mechanics. The quantum condition defining the atom is given in terms of a property derived from the charge density, as are the other concepts of the molecular structure hypothesis. In terms of the amount of electronic charge density accumulated between the carbon nuclei and its spatial distribution, a C—C bond of the carbocations exhibits an order greater than one. There is a transfer of charge from the hydrogens of methyl to the central carbon that destroys the axial symmetry of these C—C bonds and concentrates the charge in a plane perpendicular to the plane of substitution, in a manner consistent with the hyperconjugative mechanism of electron transfer. The positive charge of a carbocation is thus delocalized over all the atoms in the molecule, and the extent of this delocalization increases with increased methyl substitution. The electron population of each atom in a carbocation increases with this increase in the delocalization of positive charge and its energy is correspondingly decreased (the atom becomes more stable). These effects are most pronounced for the carbon atom bearing the methyl groups and they account for the observed increase in the relative stabilities of the carbocations with increasing methyl substitution. The electron populations and energies of the atoms in saturated hydrocarbons are also determined. The group additivity scheme for the energy in the homologous series of normal alkanes is predicted and explained in terms of the properties of the quantum atoms. It is the possibility of such transferability of the quantum atoms and their properties between systems that identifies them with the atoms of chemistry.
Gas-phase reactions of the hydroperoxide and peroxyformate anions
Authors: Bowie John H. , Depuy Charles H. , Sullivan Sally A. , Bierbaum Veronica M.
Published: May 2006

The flowing afterglow technique has been used to study the reactions of HO2−and HC3− in the gas phase. The hydroperoxide ion reacts slowly with CO to form HO−, and oxidizes CO2, OCS, CS2, NO, SO2, CH3NCO, and CH3NCS in fast reactions to form CO3−, CO2S−, COS2−, NO2−, SO3−, CH3NCO2−, and CH3NCOS−, respectively. Reactions of HO2− with certain amides and esters provide synthetic routes for a number of interesting peracyl anions. One of these, the peroxyformate ion, HCO3−, reacts with CO and NO in slow oxidation reactions to form the formate ion HCO2−. It also forms HCO2− upon reaction with acetone and pivalaldehyde, perhaps by Baeyer–Villiger oxidation.
Oxidation of hydrocarbons. 17. Solvent and substituent effects on the oxidation of styrene derivatives by quaternary ammonium permanganates
Authors: Lee Donald G. , Brown Keith C. , Karaman Hasan
Published: May 2006

When alkenes are oxidized by quaternary ammonium or phosphonium permanganates in polar organic solvents, such as acetone, the structures of the cations have little or no effect on the rates of reaction. In less polar solvents, such as methylene chloride or toluene, the rates of reaction are, however, dependent on the identity of the quaternary ammonium or phosphonium ions. It thus appears as if the reacting species may exist as solvent-separated ion pairs in polar solvents and as intimate ion pairs in nonpolar solvents. The rates of reaction are also very sensitive to substituent effects, a nonlinear (concave upward) Hammett plot being obtained for the oxidation of substituted β-bromo and β-methoxystyrenes. The mechanism is best visualized as proceeding by way of a continuum of transition states that can vary from electron rich to electron poor depending on the capacity of the substrate structures to accommodate either negative or positive charges.
Photochemical transformations. 42. Photoreactions of certain bridged bicyclic and tricyclic chlorides and bromides containing aromatic chromophores
Authors: Cristol Stanley J. , Braun Dieter , Schloemer George C. , Plas Bart J. Vanden
Published: May 2006

Irradiations of a number of bicyclic and tricyclic bromides and chlorides containing aromatic rings have been carried out. With the allylic chlorides 2-Cl and 3-Cl, triplet-sensitized photoreactions in acetone (or in acetonitrile with acetophenone sensitizer) lead to allylic scrambling and allyl-to-cyclopropyl isomerization to 5-Cl, while the corresponding bromides, under similar conditions, give allylic scrambling, photo-Wagner–Meerwein rearrangement, and photosolvolysis, but no allyl-to-cyclopropyl isomerization. The differences in reaction types are ascribed to the requirement for intramolecular electron transfer for the "ionic" reactions, which may be exothermic in the triplet states of the bromides, but not in those of the chlorides. In direct irradiations in acetic acid with 254-nm light, the singlet state of the chloride 2-Cl is photoactive in the "ionic" sense, giving a mixture of acetates, benzofluorenes, and 1-methylfluoranthene. The latter hydrocarbon is the major product in the direct irradiation of 5-Cl in acetic acid, along with a mixture of acetates. The photochemical results are contrasted with ground-state solvolyses of these compounds.
Pseudoxandrine, pseudoxandrinine, oxandrine et oxandrinine, premières α ou α′ céto-bisbenzyltétrahydroisoquinoléines à pont biphénylique
Authors: Cortes Diego , Hocquemiller Reynald , Cavé André , Saez Jairo , Cavé Adrien
Published: May 2006

The alkaloids pseudoxandrine, pseudoxandrinine, oxandrine, and oxandrinine have been isolated from a Colombian Annonaceous, Pseudoxandra aff. lucida. These bases belong to the small group of bisbenzyisoquinolines with a C(11)—C(11′) biphenyl bond, and are the first α or α′ mono-keto-bisbenzyltetrahydroisoquinolines. These structures were elucidated by ms, 1H nmr (including double resonance and nOe experiments), and 13C nmr.
Electrochemical nucleation in the electroreduction of silver(I) from molten calcium nitrate tetrahydrate
Authors: Jain Surender K. , Johnson Keith E.
Published: May 2006

The electroreduction of silver(I) on a platinum electrode from its solution in molten calcium nitrate tetrahydrate has been studied using voltammetric, chronopotentiometric, and chronoamperomeric techniques. The early stages of metal deposition appear to be controlled by a nucleation step as indicated by potential overshoots in chronopotentiometric and maxima in chronoamperometric transients. From the rising portion of the current–time transients, the number-density of the surface nuclei has been estimated. Diffusion coefficients calculated from the data obtained from different techniques are in good agreement.
Further syntheses with nitroxide α,β-unsaturated aldehydes and allylic bromides
Authors: Hideg Kálmán , Csekö József , Hankovszky H. Olga , Sohár Pál
Published: May 2006

The enhanced reactivity of nitroxide allylic bromides is used for preparation of spin-labelled analogues of biologically active compounds (morphine, Nalorphine, barbituric acid, choline and acetyl choline). Nitroxide α,β-unsaturated aldehydes are reacted with phosphoranes to give nitroxide polyenes. The nitroxides are reduced to diamagnetic N-hydroxy hydrochloride salts, which can be converted in the presence of base to N-acetoxy derivatives.
n-π Electron donor–acceptor complexes. III. Aliphatic amines with dicyanobenzenes. Electric and steric effects of the N-substituents on complex formation
Authors: Anunziata Jorge D. , Galaverna Norma S. , Singh Joaquín O. , Silber Juana J.
Published: May 2006

The interaction of several aliphatic amines as n-donors with 1,2-, 1,3-, and 1,4-dicyanobenzenes as π acceptors in n-hexane has been studied. The spectroscopic behaviour of the mixtures leads us to propose that Electron Donor – Acceptor (EDA) complexes are formed. Correlations of the experimental data with the amine structure were performed for the amine–1,4-dicyanobenzene complexes. By means of free energy related substituents and regression analysis, the electronic and steric effects of three N-substituents were quantitatively separated. Thus, with K representing the stability constants of the complexes, the values of log K are correlated with Taft's polar substituent constants, σ*, and Hancock's corrected steric substituent constants, [Formula: see text] The results allowed the proposal of a probable structure of the complex, at least with respect to the donor orientation.
A pulse radiolysis study of solvated electrons in tert-butanol/water solutions
Authors: Cygler Joanna , Klassen Norman V. , Ross Carl K.
Published: May 2006

Many solutes, added to water in amounts of a few mol%, cause an increase in the yield of solvated electrons (es−) measured by pulse radiolysis. A pulse radiolysis study of tert-butanol (tBuOH) in D2O has been carried out to investigate this phenomenon. Detailed measurements of the yield, measured as Gεmax(es−), and the deeay of solvated electrons were made at 6, 25, and 46 °C over the range 0–5mol% tBuOH. The maximum Gεmax(es−) occurs at about 1 mol% tBuOH, but the exact concentration depends on the temperature of the sample and the time after the pulse at which the measurement is made. Three factors are examined as contributing to the increased Gεmax(es−) in the presence of tBuOH and certain other solutes. They are (i) the change in viscosity produced by the added solute, (ii) the scavenging of OH radicals by the solute, thereby reducing the reaction of OH with es− and (iii) the possibility that the addition of the solute leads to an increase in the thermalization distance of the secondary electrons. It is concluded that effects (i) and (ii) are sufficient to explain the existing experimental data.
The structure and resonance Raman spectra – structure correlations for methyloxycarbonyl-L-phenylalanyl-L-alanine ethyl dithioester
Authors: Varughese K. A. , Angus R. H. , Carey P. R. , Lee H. , Storer A. C.
Published: May 2006

The structure of methyloxycarbonyl-L-phenylalanyl-L-alanine ethyl dithioester has been determined by X-ray crystallographic analysis. The N—C—C—S(thiol) and C—N—C—C(S) torsional angles are 141(1)° and −69(2)°, respectively. Consequently, the N and thiono (C=S) sulfur atoms are in close contact and the [Formula: see text](thiono) distance is 3.078(5) Å. The structure is a perturbed A conformer, which we designate A′, by analogy to a previously characterised A conformer (Huber etal., Biochemistry, 21 3109 (1982)). The [Formula: see text] angles for the Phe residue are −87(2) and 151(2)°, respectively. A Raman spectroscopic study of a single crystal of the LL form and a resonance Raman (RR) spectroscopic study of powdered methyloxycarbonyl-L-phenylalanyl-DL-alanine ethyl dithioester establish the RR signature of the dithio moiety for the compound in the A′ form. The RR spectrum of the dithioester in CCl4 defines the RR signature for the C5 form in solution, while the RR spectrum from a solution in H2O/CH3CN provides information on the signatures of the A and B conformers. As for the case of N-benzoyl-DL-alanine dithioester, the A and C5 signatures of the title compound closely resemble those for glycine-based dithioesters but the key marker bands for the B conformer are shifted by ≈30 cm−1 to lower frequency compared to those for a glycine dithioester.
Kinetic and equilibrium studies of the σ-adduct forming reactions of 1,3,5-trinitrobenzene and picryl chloride with some carbon bases
Authors: Crampton Michael R. , Kee Terence P. , Wilcock Jennifer R.
Published: May 2006

Reaction of 1,3,5-trinitrobenzene (TNB) with the malononitrile anion in methanol yields a carbon-bonded σ-adduct, (3). Ionisation of the remaining exocyclic hydrogen is favourable and yields the dianion (4). The initial reaction of 1-chloro-2,4,6-trinitrobenzene similarly occurs at an unsubstituted ring position, but is followed by slower nucleophilic attack at the 1-position yielding the substituted product. A major difference in the reaction of the ethyl malononitrile anion with TNB is that the adduct formed (11) has no readily dissociable proton. Hence, here, conversion to the carbon-bonded adduct is less favourable. Kinetic and equilibrium data are reported for these reactions and are compared with data for adduct formation involving methoxide ions.
Enthalpies of solution of urea in water–alkanol mixtures and the enthalpic pair interaction coefficients of urea and several nonelectrolytes in water
Authors: Piekarski Henryk , Somsen Gus
Published: May 2006

Enthalpies of solution of urea in binary mixtures of isopropanol, s-butanol, and ethoxyethanol with water have been measured at high water content. Those in the binaries isopropanol + water and ethoxyethanol + water show endothermic maxima at 8 and 4 mol% alkanol, respectively. Enthalpic pair interaction coefficients are calculated for the interactions between urea and the alkanols and discussed in connection with these coefficients for interactions between urea and other nonelectrolytes and between N,N-dimethylformamide and several nonelectrolytes. The enthalpic pair interaction coefficients correlate linearly with the heat capacity change on hydration of the nonelectrolytes and with the enthalpy of hydrophobic hydration of the alkanols.
ipso Nitration. XXVIII. Nitration of 4-substituted toluenes: 1,2 adducts
Authors: Fischer Alfred , Fyles Deborah L. , Henderson George N. , Mahasay Sumit Ray
Published: May 2006

Nitration of 4-acetamido-, 4-chloro-, and 4-methoxy-toluene in acetic anhydride gives in each case a cis 1,2 nitronium acetate adduct in addition to the nitro substitution product(s). Nitration of 4-fluorotoluene gives a pair of diastereomeric 1,4 nitronium acetate adducts and the cis 1,2 adduct.
Study on the enolization of alkylation of cis and trans 2-tert-5-X-1,3-dioxanes (X = CO2CH3, CHO, COPh, NO2, and CN). Evidence for stereoelectronic control
Authors: Ndibwami Alexis , Deslongchamps Pierre
Published: May 2006

Alkylation of 2-tert-butyl-5-X-1,3-dioxanes (X = CO2CH3, COPh, and NO2) was studied. Products resulting from an equatorial approach of the alkylating agent are preferentially formed when X = CO2CH3 and NO2. Also, the cis isomers that have an equatorial hydrogen at C-5 were found to deprotonate at a faster rate than the trans isomers when X = CO2CH3, COPh, CHO, and CN. These results are compared with those obtained with methyl 2-tert-butyl cyclohexane carboxylate and are interpreted by taking into account stereoelectronic principles.
Zn(II)–D-(−)penicillamine complexes in aqueous solution. Zn-67 nuclear magnetic resonance study
Authors: Delville Alfred , Detellier Christian
Published: May 2006

D–(−)-Penicillamine interactions with Zn(II) have been studied in aqueous solutions as a function of pH, penicillamine concentration, and temperature, using Zn-67 nuclear magnetic resonance. Longitudinal and transverse relaxation rate measurements show the presence in solution of complexes in fast exchange with the aquated Zn(II) cation, and belonging to the extreme narrowing regime. Using equilibrium constant values from the literature, the relaxation behaviour was modelled. Characteristic Zn-67 line width values for the two complexes Zn(Pen) (v = (6200 ± 500) Hz) and [Zn(Pen H)]+ (v = (6000 ± 1000) Hz) were found. Equality of the two values is in agreement with zinc chelation by the sulfhydryl and the amino groups.
Interaction of the methylmercury cation with glycine and alanine: a vibrational and X-ray diffraction study
Authors: Corbeil Marie-Claude , Beauchamp André L. , Alex Serge , Savoie Rodrigue
Published: May 2006

The complexes (CH3Hg)Gly, (CH3Hg)(L-Ala), and (CH3Hg)(DL-Ala) were prepared by reacting CH3HgOH with glycine (HGly) and alanine (HAla). Crystals of (CH3Hg)(DL-Ala) are monoclinic, space group P21/c, a = 9.460(2), b = 8.794(2), c = 8.723(2) Å, β = 97.49(2)°, Z = 4. The structure was refined on 935 MoKα reflections to R = 0.042. The complex results from displacement of an alanine NH3+ proton by the CH3Hg+ ion, which is linearly bonded to the —NH2 group. An intramolecular Hg … O contact of 2.63 Å is also formed with a carboxylate oxygen. The Raman and infrared spectra of solid (CH3Hg)Gly and (CH3Hg)(L-Ala) are compared with those of the ligands. Raman spectra of aqueous solutions at different pH indicate that the NH2-bonded structure is retained in solution, although no complexation via the carboxylate occurs.
A comparative ion chemistry study of acetone, diacetone alcohol, and mesityl oxide
Authors: Kamar Afaf , Young Alexander Baldwin , March Raymond Evans
Published: May 2006

The evolution of ion species by unimolecular and bimolecular reactions, both concurrent and sequential, has been investigated for each of 2-propanone, d6-2-propanone, 4-hydroxy-4-methyl-2-pentanone, and 4-methyl-3-penten-2-one. Infrared multiphoton dissociation (IRMPD) has been used in order to differentiate between gaseous ionic isomers. It is concluded that the isomeric species, protonated 2-propanone dimer and protonated 4-hydroxy-4-methyl-2-pentanone, both of m/z 117, are of different structures. The ion species C6H11O+ of m/z 99, and its perdeuterated analogue, which is observed in all three systems, may exist in two forms, one of which is unique to 2-propanone while an alternative form appears to be common to 4-hydroxy-4-methyl-2-pentanone and 4-methyl-3-penten-2-one. The ion species of m/z 83 (C5H7O+) which is observed only in the latter two systems only could not be differentiated and may have a common structure. In the protonated dimers of 2-propanone and 4-hydroxy-4-methyl-2-pentanone, evidence obtained by IRMPD indicates that the activation energy for dedimerization (134 kJ mol−1) is less than that for the dehydration process.