bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent effects on the rates and equilibria of the proton transfer reaction of 4-nitrophenylphenylcyanomethane to tetramethylguanidine
Authors: Hojatti Mahmood , Leffek Kenneth T.
Published: May 2006

The equilibrium constants and second-order rate constants, both at 25 °C, have been determined for the proton transfer reaction from 4-nitrophenylphenylcyanomethane to tetramethylguanidine in a number of different solvents. While the equilibrium constants show a good correlation with the dielectric constant function D − 1/2D + 1, the rate constants are randomly scattered with respect to this parameter and also the solvent parameter ET. The rate constants do show a general trend in relation to the solvent parameters AN and DN. These results are interpreted as support for the hypothesis that the transition state of the proton transfer occurs early along the reaction path.
Experimentally determined proton affinities of 4-methyl-3-penten-2-one, 2-propyl ethanoate, and 4-hydroxy-4-methyl-2-pentanone in the gas phase
Authors: Kamar Afaf , Young Alexander Baldwin , March Raymond Evans
Published: May 2006

Proton affinities have been determined for 4-methyl-3-penten-2-one, 2-propyl ethanoate, and 4-hydroxy-4-methyl-2-pentanone in the gas phase at 333 K. A quadrupole ion store (QUISTOR) was employed to study mass spectrometrically the equilibrium between a species of known proton affinity and one of the above compounds; equilibrium between protonated species was monitored over an ion storage duration of 100 ms. The values of the proton affinities were found to be 870.5 ± 0.8 kJ mol−1 for 4-methyl-3-penten-2-one (mesityl oxide); 842.7 ± 0.6 kJ mol−1 for 2-propyl ethanoate; and 831.6 ± 0.8 kJ mol−1 for 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol).
Kinetic benzylidenation. Part II. Rearrangement of the kinetic products from benzylidenation of aldose diethyl dithioacetals
Authors: Grindley T. Bruce , Kusuma Srihari
Published: May 2006

Terminal five-membered O-benzylidene derivatives of aldose diethyl dithioacetals can be rearranged at room temperature in N,N-dimethylformamide, often in high yields. Derivatives with the arabino configuration for their three terminal secondary hydroxyl groups, i.e. D-glucose, D-mannose, and D-arabinose derivatives, rearranged to structures containing terminal six-membered O-benzylidene rings. 4,5-O-Benzylidene-D-ribose diethyl dithioacetal rearranged chiefly to the 2,4 isomer, which was obtained by crystallization. Chromatography yielded some of the 3,5 isomer. 5,6-O-Benzylidene-D-galactose diethyl dithioacetal rearranged to a mixture of the two 4,5-O-benzylidene diastereomers, contrary to predictions based on the Hann–Hudson rules. A revised set of rules for acetal stability in N,N-dimethylformamide has been formulated. D-arabinose and D-ribose diethyl dithioacetal were shown to react with α, α-dimethoxytoluene under rearrangement conditions to give the products noted above in good yields.
Bullerone, a novel sesquiterpenoid from Cyathusbulleri Brodie
Authors: Ayer William A. , McCaskill Robert H.
Published: May 2006

The structure of bullerone (3), a minor metabolite of the bird's nest fungus Cyathusbulleri Brodie, has been determined by a combination of chemical and spectroscopic methods. The possible biogenesis of bullerone, a new skeletal class of sesquiterpenoid, is discussed.
The conversion of podocarpic acid to hexahydrophenalene derivatives: an approach to the synthesis of edulone A
Authors: Burnell Robert H. , Dufour Jean-Marc
Published: May 2006

To test the feasibility of a biogenetically inspired synthesis of edulone A 1, podocarpic acid 3a has been transformed into a substituted hexahydrophenalene 16b. The critical steps involve introduction of a double bond into the A ring, cleavage by ozone, and, after suitable manipulation, an epoxy-arene cyclization. A second product from this cyclization is an octahydrophenaleno[1,9-bc]furan 17.
Medium effects on activation parameters on alkaline hydrolysis of 2-carbomethoxypropionate ion in aqueous mixtures of ethylene glycol
Authors: Biswas Prasanta Kumar , Bag Bikas Chandra , Das Mihir Nath
Published: May 2006

The standard free energies of transfer [Formula: see text] of the 2-carbomethoxypropionate ion (R−) have been determined from the solubilities of the silver salt (AgR) in water and six aqueous mixtures of ethylene glycol (1–60%) at 25 °C, using the literature values of [Formula: see text] of Ag+. Utilizing these values of the R− ion as well as the literature values of [Formula: see text] of the OH− ion, combined with the experimental values of ΔG≠ for the alkaline hydrolysis of R− ion, the corresponding transfer parameters of the transition states [Formula: see text] for the hydrolysis reaction in aquo-glycolic media at 25 °C have been calculated. Attempts have been made to correlate the rates and activation parameters with the transfer quantities and solvent properties.
The synthesis of D-asperlin
Authors: Valverde Serafin , Herradon Bernardo , Rabanal Rosa M. , Martin-Lomas Manuel
Published: May 2006

The synthesis of the D-enantiomer of asperlin has been carried out. The stereochemistry of the epoxide ring has been assigned as 6R,7S for this D-enantiomer.
Solution and solid state studies of some ternary complexes of Cu(II) involving heteroaromatic N-bases and o-hydroxy aromatic carbonyls
Authors: Kulkarni Neelima D. , Bhattacharya P. K.
Published: May 2006

Stability constants of some ternary complexes of o-hydroxy aldehydes (HL) with Cu(II) as central metal ion and bis(2-pyridyl)amine (dpa) and 5-nitro-1,10-phenanthroline (5-N-phen) as primary ligands (A) have been determined potentiometrically in 50% aqueous dioxane medium using a computer technique. The values of [Formula: see text] have been compared within the series as well as with the corresponding bipyridyl complexes. The stability order has been explained on the basis of the electron repulsion concept. The complexes have been isolated in the solid state and characterized by elemental analysis, conductance and magnetic measurements, and ir and electronic spectral studies. Shifts in ligand field absorption wave numbers of the mixed ligand complex from the average value of the ligand field absorption wave numbers of [MA2]2+ and [ML2] have been correlated with the potentiometrically determined Δ log K values.
Étude comparative de l'adsorption d'acide déoxyribonucléique sur le chrysotile et le chrysotile phosphorylé (chrysophosphate)
Authors: Touray Jean-Claude , Baillif Patrick , Jaurand Marie-Claude , Bignon Jean , Magne Laure
Published: May 2006

Deoxyribonucleic acid (DNA) adsorption on one sample of Canadian chrysotile and two samples of chrysophosphate has been studied using chemical analysis and a surface method of analysis (photoelectron spectroscopy, XPS). Chrysophosphate was obtained using a phosphorylation process applied to chrysotile fibres; one chrysophosphate sample was opened in a Pallmann device. XPS analysis of the samples before DNA adsorption has shown that some surface phosphorus was dissolved following suspension of the fibres in distilled water. After DNA treatment, the amount of DNA adsorbed at the surface of the chrysophosphate sample was lower than that adsorbed at the chrysotile surface (12.6 ± 1.7 μg/mg and 74.0 ± 4.0 μg/mg respectively). In addition, the opened sample adsorbed an intermediary DNA amount (28.3 ± 5.6 μg/mg), suggesting that the phosphorylation process has not reached all the bulk fibres. The results indicate that DNA adsorption is a sensitive method for investigation of the surface state of the fibre. Moreover, it seems that the phosphorylation process masks or blocks the reactive surface sites for DNA adsorption.
Electrical breakdown phenomenon and electronic conduction during the anodic growth of Nb2O5
Authors: Nigam R. K. , Singh K. C. , Maken Sanjeev
Published: May 2006

Electrical breakdown voltage studies on Nb2O5 films in aqueous solutions of weak organic acid as a function of concentration, temperature, and applied field are carried out under galvanostatic conditions. Electronic conduction measurement through the Nb2O5 film as a function of temperature and applied field are also determined so as to examine the validity of Ikonopisov theory of electrical breakdown quantitatively.
Étude des complexes fluorés et chlorés du plomb dans les mélanges eau–HF
Authors: Beaudoin Réjean , Ménard Hugues
Published: May 2006

The polarographic study of lead fluoride and of lead chloride complexes has been done in water – hydrogen fluoride solutions. The successive formation of PbF2 and of PbF+ is in agreement with the reduction of the fluoride ion activity, R0(F), measured with the augmentation of the HF content of the solution. The formation of two crystalline structures of PbF2 is in accord with the existence of two complexes in solution. The formation of PbFCl shows the existence of mixed fluoride–chloride complexes in water–HF solutions.
Lanostane to cucurbitane transformations
Authors: Edwards O. E. , Kolt R. J.
Published: May 2006

Transformation of 3,7,9,11-tetraoxygenated lanostane derivatives into 3,7,11-trioxygenated cucurbit-1(10)-enes and cucurbit-5(10)-enes has been achieved. Attempts to convert the latter in good yield into cucurbit-5-enes are documented. The steric and electronic factors influencing the course of dehydration, under Westphalen conditions, of 9α-hydroxylanostane derivatives are discussed. Unusual autooxidation and dehydrogenation promoted by rhodium trichloride and iron pentacarbonyl are described.
The preparation and reactions of mixed anhydrides of N-alkoxycarbonylamino acids
Authors: Chen Francis M. F. , Benoiton N. Leo
Published: May 2006

Pure mixed anhydrides R1OCO-Xxx-O-COOR2 (Xxx=NHCHRCO) have been obtained by reaction of N-alkoxycarbonyl-amino acids R1OCO-Xxx-OH with alkyl chloroformate R2OCOCl (R2 = methyl, ethyl, isobutyl, menthyl) in the presence of N-methylmorpholine or N-methylpiperidine (NMP) in dichloromethane at −5 °C, followed by washing the mixtures with aqueous solutions and removal of the solvent. R1OCO-Xxx-O-COOR2 (R2 = ethyl, tert-butyl) have been obtained by reaction of R1OCO-Xxx-O−•+HNMP with the corresponding dialkyl dicarbonates followed by the same work-up. Mixed anhydride generation is much slower when triethylamine is used as base. The initial reaction in the decomposition of mixed anhydrides is cyclization to the 2-alkoxy-5(4H)-oxazolone (R1O-oxazolone) followed by release of alcohol R2OH. Symmetrical anhydride (R1OCO-Xxx)2O and ester R1OCO-Xxx-OR2 are also formed. The ease of cyclization depends on R2, and is in the order methylsulfonylethyl (Ms) [Formula: see text] methyl/ethyl/isobutyl [Formula: see text] menthyl. R1OCO-Xxx-O-COOMs preparations contained a substantial amount of R1O-oxazolone. Attempts to use this reaction as a preparative procedure for obtaining R1O-oxazolones failed because they are too sensitive to hydrolysis and react too quickly with the product, forming the symmetrical anhydride. The effect of various parameters on the amount of urethane generated by aminolysis at the carbonate moiety of R1OCO-Xxx-O-COOR2 was examined without the uncertainty that any urethane arose from aminolysis of unconsumed chloroformate.
Solvolytic rearrangement studies with (E)- and (Z)-2-anisyl-1,2-ditolyl[2-13C]vinyl bromides
Authors: Lee Choi Chuck , Wanigasekera Dave
Published: May 2006

Reaction of (E,Z)-or (E)-2-anisyl-1,2-ditolyl[2-13C]vinyl bromides ((E,Z)- or (E)-6-Br-2-13C) with HOAc–AgOAc gave a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl acetates ((E,Z)-6-OAc-1,2-13C), with about 37.4% scrambling of the label from C-2 to C-1 arising from degenerate 1,2-anisyl shifts in the 2-anisyl-1,2-ditolyl[2-13C]vinyl cation (6-2-13C). No detectable amount of 1-anisyl-2,2-ditolylvinyl acetate was formed, indicating no nondegenerate 1,2-tolyl shift in cation 6 to give the more stable 1 -anisyl-2,2-ditolylvinyl cation (10) in the reaction with HOAc–AgOAc. Reaction of (E)-6-Br-2-13C with 2,2,2-trifluoroethanol (TFE) in the presence of 2,6-lutidine gave as major product 1-anisyl-2,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ether (10-OTFE-1,2-13C) and a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ethers ((E,Z)-6-OTFE-1,2-13C) as minor products, the ratio of 10-OTFE to (E,Z)-6-OTFE being about 80:20. Scrambling on the 13C label in the major product, 10-OTFE-1,2-13C, was 48.8 ± 0.9% and scrambling in the minor products, (E,Z)-6-OTFE-1,2-13C, was 47.2 ± 1.4%. The present work with cation 6 completes the series of nine possible triarylvinyl cations, with various combinations of phenyl (Ph), p-tolyl (Tol), and (or) p-anisyl (An) as the three aryl groups, that can give rise to degenerate 1,2-aryl shifts across the double bond, and the present results are discussed in conjunction with data from previous work on the other eight triarylvinyl cationic systems.
Analytical chemists and dinosaurs
Authors: Brooks R. R.
Published: May 2006

The role of the analytical chemist in the development of the extraterrestrial impact theory for mass extinctions at the terminal Cretaceous Period is reviewed. High iridium concentrations in Cretaceous/Tertiary boundary clays have been linked to a terrestrial impact from an iridium-rich asteroid or large meteorite some 65 million years ago. Other evidence in favour of the occurrence of such an impact has been provided by the detection of shocked quartz grains originating from impact and of amorphous carbon particles similar to soot, derived presumably from wordwide wildfires at the terminal Cretaceous. Further evidence provided by the analytical chemist involves the determination of isotopic ratios such as 144Nd/143Nd, 187Os/186Os, and 87Sr/86Sr. Countervailing arguments put forward by the gradualist school (mainly palaeontological) as opposed to the catastrophists (mainly chemists and geochemists) are also presented and discussed.
Nafion-coated mercury-coated glassy carbon electrodes for metals analysis and speciation
Authors: Guy Robert D. , Namaratne Sarath
Published: May 2006

The properties of mercury-coated glassy carbon electrodes coated with a thin membrane of Nation 117 were studied to evaluate the potential analytical applications in metal ion analysis. The Nation membrane was found to contain two types of binding sites — a strong site that bound metal ions in a nonelectroactive form and cation exchange sites that were useful for preconcentrations prior to differential pulse voltammetry. The exchange constants for the weak sites ranged from 0.413 for copper to 12.5 for methyl viologen. The differential pulse currents were increased by a factor of 75 to 100 and a linear calibration curve was observed from about 25 n M to 1000 n M for copper, lead, cadmium, and zinc. The ion exchange reaction is very sensitive to ionic strength and significant enrichments occur only in solutions of ionic strength below 0.10. The Nafion-coated glassy carbon electrode in a flow cell can be used to determine the free copper ion concentration in samples by a combination of ion exchange and differential pulse voltammetry. The flow-through system required about 15 mL of sample solution and an analysis time of about 10 min. The ion exchange measurement gave a linear calibration from 40 n M to 10 μ M for free copper.
Crystal and molecular structure of 9-(2,4,6-trinitroanilino)-carbazole, C18H11N5O6
Authors: Wang Hong , Barton Richard J. , Robertson Beverly E. , Weil John A. , Brown Keith C.
Published: May 2006

The crystal structure of 9-(2,4,6-trinitroanilino)-carbazole, C18H11N5O6, has been determined by X-ray diffraction. Crystals are monoclinic, space group P21/c, a = 14.686(11), b = 24.601(12), c = 10.047(5) Å, β = 107.76(5)° at 292 K, with Z = 8. The two nitrogen atoms in the central fragment have a staggered conformation with an N—N distance of 1.381(4) Å, which is considerably shorter than N—N distances in related N-picrylhydrazine molecules. The picryl moiety has a geometry similar to that of related N-picrylhydrazine molecules. The title compound contains an [Formula: see text] intramolecular bond to one of the ortho nitro groups on the picryl ring. The carbazole plane of one molecule and the picryl plane of a neighboring molecule overlap to form an infinite linear chain of the form … DhA:DhA … where D represents the carbazole donor, h the linear chain linkage within the molecule, and A represents the picryl acceptor of one molecule. The two interplanar distances between D of one molecule and A of an adjacent molecule are 3.28(13) and 3.34(13) Å, indicating a strong π-molecular interaction.
Major saponins from the starfish Asteriasforbesi. Complete structures by nuclear magnetic resonance methods
Authors: Findlay John A. , Jaseja Mahesh , Burnell D. Jean , Brisson Jean-Robert
Published: May 2006

The structures of the two major saponins isolated from the starfish Asteriasforbesi have been deduced totally by nuclear magnetic resonance methods applied to the undegraded molecules. The structure of forbeside A, 6α-O-{β-D-galactopyranosyl-(1 → 3)-β-D-fucopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 4)-[β-D-quinovopyranosyl-(1 → 2)]-β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl}-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl sodium sulfate, was deduced principally from 1H 2D-COSY, J-resolved, nuclear Overhauser enhancement and selected decoupling experiments. The structure of forbeside B, 6α-O-{β-D-quinovopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 4)-[β-D-quinovopyranosyl-(1 → 2)]-β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl}-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl sodium sulfate, was deduced principally from 2D-COSY, HCORR, RECSY, and NOESY experiments.
The structures of some sulphur-stabilized carbanions and stereoelectronic requirements for the formation of α-sulphonyl carbanions
Authors: Grossert J. Stuart , Hoyle Jeffrey , Cameron T. Stanley , Roe Stephen P. , Vincent Beverly R.
Published: May 2006

Relatively few structure determinations of α-sulphonyl stabilized carbanions have been reported. The salient features of these are summarized and discussed in the light of the X-ray crystal structures of the potassium salt from bis(methylsulfonyl)-3-(2,6-dimethoxypyridyl)sulfonylmethane (5), the carbon acid bis(methylsulphonyl-4-(1,3-dimethoxyphenyl)sulphonylmethane (6), the triethylammonium salt of 2-methylsulphonyl-2-phenylthio-1-(3-pyridyl)-1-ethanone (7), the carbon acid 2-methyl-sulphonyl-2-phenylthio-1-phenylethanone (8), and its triethylammonium salt (9). Results of these structure determinations show that the α-sulphonyl carbanion has a significantly shorter −C—SO2 bond distance than the free sulphone, but that the S—O bond distances are essentially unchanged. The coordination about the carbanionic carbon atoms is planar; these atoms can be described as interacting with the sulphur atoms in an ylid-like manner, with a barrier to rotation about the −C—SO2 bond. The sulphonyl oxygen atoms do interact to a significant degree with the counterion, but there is no close contact between the counterion and the carbanionic carbon atom. A comparison of the structures of 6 and 5, or of 8 and 9, permits an assessment to be made concerning the stereoelectronics of deprotonation reactions on carbon atoms adjacent to sulphones.
Enthalpies and heat capacities of solution for tert-butyl chloride and bromide in alcohols. Application of SPT, SRMR, and MS
Authors: Gonçalves R. M. C. , Simões A. M. N.
Published: May 2006

Enthalpies and heat capacities of solution at infinite dilution for tert-butyl chloride and bromide in several alcohols are reported at 30, 35, and 40 °C.The Scaled Particle Theory (SPT), the Sinanoglu, Reiss, and Moura Ramos (SRMR) and the Model Solute (MS) methods were applied to the enthalpies of solvation. Significant differences in the results calculated from these theories were analysed and data discussed in terms of solute–solvent–solvent interactions.
13C magnetic resonance studies. 131. An examination of β-enolization in an unsaturated [3.2.1] system: 3,3-dimethylbicyclo[3.2.1]oct-6-en-2-one
Authors: Antoniadis Greg A. , Clements Michael T. M. , Peiris Sriyawathie , Stothers J. B.
Published: May 2006

Under homoenolization conditions (t-BuO−/t-BuOH/185 °C), 3,3-dimethylbicyclo[3.2.1]oct-6-en-2-one (5) is converted into six products through three reaction pathways. The major product, 3,3-dimethylbicyclo[3.3.0]octan-2-one, arises by unidirectional β-enolate rearrangement of 5 to the isomeric unsaturated [3.3.0] ketones, which (a) undergo efficient reduction to 2, by single electron transfer, and (b) suffer Haller–Bauer cleavage to two isomeric 2,2-dimethyl-3-cyclopentenylpropanoic acids. In competition with these processes is the reversible conjugate addition of t-BuO− to 5 to furnish the 6-tert-butoxy derivative, which undergoes β-enolate rearrangement to two isomeric ketones. The structures of these products were established primarily from their 1H and 13C magnetic resonance spectra.
A 13C and 15N nuclear magnetic resonance study of the protonation of a retinal Schiff base by acids of different pKas and in solvents of different polarities
Authors: Cossette Daniel , Vocelle Daniel
Published: May 2006

13C and 15N nuclear magnetic resonance spectra of mixtures of all-trans-retinylidene tert-butylamine (RtBA) and substituted acetic acids in equimolar concentrations in both CDCl3 and CD3OD were studied in relation to two questions: the nature of the state of protonation of a retinal Schiff base in the presence of carboxylic and mineral acids in solvents of different polarities, and secondly, to determine the nature of the interactions (if any) between the polar groups located on the acids and the polyenic chain of the retinal derivative. Using carboxylic acids of different pKas and three mineral acids, we present results that indicate that, in solvents of low polarity, weak acids can only partially protonate RtBA while, in a more polar milieu, the protonation percentages are higher. With polar groups such asNO2, Cl, Br, I, and CN, no specific interaction could be found between the polyenic chain of the imine and these groups. Variations in the intensity of certain peaks of RtBA were noted and these could possibly be related to the presence of the polar groups on the acids. Comparisons of our results with those obtained on rhodopsin and bacteriorhodopsin indicate that the milieu surrounding the chromophore must be polar if protonation is complete, while in a less polar environment partial protonation can be expected.
Benzodiazepine stereochemistry: crystal structures of the diazepam antagonist Ro 15-1788 and the anomalous benzodiazepine Ro 5-4864
Authors: Hempel Andrew , Camerman Norman , Camerman Arthur
Published: May 2006

The crystal and molecular structures of the benzodiazepine antagonist Ro 15-1788, and of Ro 5-4864, a diazepam derivative with low affinity for central benzodiazepine receptors, have been determined. Stereochemical comparisons with diazepam have resulted in the conclusion that the steric bulk of the 4′-chlorine atom alone is responsible for the lowered activity of Ro 5-4864, and have suggested possible structural reasons for the antagonist/weak agonist activities of Ro 15-1788.
Bond angle variations in XCY fragments and their relationship to the anomeric effect
Authors: Pinto B. Mario , Schlegel H. Bernhard , Wolfe Saul
Published: May 2006

The crystal structures of 2-substituted heterocyclohexanes containing exocyclic X and endocyclic Y exhibit systematic variations in their XCY bond angles. When X is in the more stable axial orientation, corresponding to the anomeric effect, the XCY angle is larger than tetrahedral; when X is in the equatorial orientation the XCY angle is smaller than tetrahedral. These geometrical effects are predicted by the perturbational molecular orbital analysis employed previously to account for the existence of the anomeric effect and its variation with changes in X and Y. Abinitio molecular orbital calculations, with full geometry opimization, of selected conformations of XCH2YH molecules also reproduce this geometrical effect.
Kinetic and equilibrium study of the ring opening of 2-aryl-1-methyl-1-pyrrolinium ions in aqueous solution
Authors: McClelland Robert A. , Seaman N. Esther
Published: May 2006

Ultraviolet spectral and kinetic measurements are reported for the transformations in aqueous solution undergone by the cyclic iminium ion, the 2-aryl-1-methyl-1-pyrrolinium ion I+. In solutions with pH < 9.5 this ion equilibrates with a ring-opened hydrated form, the protonated 4-methylaminobutyrophenone SH+. The concentration of the latter at equilibrium is small, but it can be observed using nuclear magnetic resonance spectroscopy. A kinetic analysis provides a measure of the [Formula: see text] equilibrium constant. Values range from 0.06 for 4-methoxyphenyl to 0.17 for 3-chlorophenyl. In acid solutions (pH < 5) the equilibration is slow (half-life ≈ 20 min for phenyl) and pH independent. Above pH 5 this process becomes first order in hydroxide ion. In strongly basic solutions a neutral species is formed in equilibrium with these two cations, with pK(app) for the transformation cations [Formula: see text] neutral + H+ ranging from 11.8 to 11.3. Spectral arguments imply that the base species is the ring-opened 4-methylaminobutyrophenone S, with less than ten percent of the pseudobase of I+ present.
Destabilized carbocations. Nuclear magnetic resonance detection and reactivities of aryl α-thioformamidyl cations
Authors: Ablenas F. J. , George B. E. , Maleki M. , Jain R. , Hopkinson A. C. , Lee-Ruff E.
Published: May 2006

A series of α-aryl and diarylthioformamidyl cations were observed by low-temperature nuclear magnetic resonance spectroscopy. These ions undergo efficient cyclization and deprotonation to give benzothiophenes.
Direct observation of dienols produced by photochemical enolisation of α,β-unsaturated ketones: rates and activation parameters for dienol reketonisation via a 1,5-hydrogen shift
Authors: Duhaime Randy M. , Weedon Alan C.
Published: May 2006

The production of stable solutions of Z-dienols by ultraviolet light irradiation of α,β-unsaturated ketones at low temperatures (ca. −76 °C) in d4-methanol is reported. The rates of reketonisation of the dienols via a 1,5-sigmatropic hydrogen shift were determined at various temperatures between −43 °C and + 2 °C by monitoring the proton nmr spectra of the dienols. From the data the activation parameters for the reaction were calculated. For the dienol Z-2-hydroxy-4-methyl-2,4-pentadiene, 2, derived from photoenolisation of 4-methyl-3-penten-2-one, 1, the activation energy from the Arrhenius plot is 62 ± 4 kJ/mol, and the activation entropy and enthalpy from the Eyring plot are −87 ± 15 J/mol K and 60 ± 4 kJ/mol, respectively. For the dienol Z-4-tert-butyl-2-hydroxy-2,4-pentadiene, 4, obtained from photoenolisation of 4,5,5-trimethyl-3-hexen-2-one, 3, the activation energy, entropy, and enthalpy were found to be 47 ± 5 kJ/mol, −135 ± 19 J/mol K, and 45 ± 5 kJ/mol, respectively.
A heuristic formalism for dynamics of spins larger than 1/2 in nuclear magnetic resonance
Authors: Eu Byung Chan
Published: May 2006

A simple heuristic method of constructing tensor operator bases for spins larger than 1/2 is presented which yields the same matrix representations as reported in the literature. By using the basis sets, we discuss the evolution of density matrices which can be put in Sylvester's form for an exponential operator. Use of quaternions is discussed for constructing tensor operator bases for half integer spins.
Kinetics of the thermolysis of para-substituted benzylcobalamins and derivatives
Authors: Nome Faruk , Rezende Marcos Caroli , Sabóia Claudia Maria , Silva Arlindo Clemente Da
Published: May 2006

The thermolysis of five para-substituted benzylcobalamins was studied at different temperatures. In the presence of KCN the observed rates increase with the cyanide concentration until a constant value is attained at high [CN−]. In both series the homolytic cleavage of the Co—C bond is slightly dependent on the para-substituent of the benzyl moiety, with ρ values of −0.1 and −0.2 when 5,6-dimethylbenzimidazole (Bzm) and cyanide are the axial ligands respectively. The Co—C bond is weakened by electron-donating axial ligands and the homolytic cleavage rates increase in the order H2O < Bzm < CN.
Radical reactions of N-haloamides with olefins. XIII. Quantum yields for the photochemical addition of N-halo-N-hydroamides and N-chlorosuccinimide to 3,3-dimethyl-1-butene
Authors: Tuaillon Jacques , Couture Yvon , Lessard Jean
Published: May 2006

The quantum yield of the photochemically initiated radical chain addition of ZCONHX to 3,3-dimethyl-1-butene increases with Z in the order CH3 < ClCH2 < C2H5O < CCl3 < CF3 and is governed by the transfer step. The quantum yields are similar for N-chloroacetamide and N-chlorosuccinimide but the yield of addition is lower with the latter due to photodecomposition of the 1,2-adduct.
The stereoselective alkylation and conformational analysis of 14-membered lactones
Authors: Ferreira J. Tercio B. , Neeland Edward G. , Ounsworth James P. , Weiler Larry
Published: May 2006

The 14-membered lactone, 13-tetradecanolide, can be alkylated to give mainly the 2R*, 13S*-dimethyltridecanolide. A second alkylation gives the 2,2-dimethyl lactone. The conformation of the starting material and alkylation products exist in the regular [3434] conformation. This model is used to rationalize the stereochemical outcome of the reaction and suggest the conformation of the intermediate enolate.
Application of an advanced technique of data analysis by analytical potentiometry and comparison of results by SUPERQUAD. Studies of nickel(II) – glycine, copper(II) – glycylglycyl-L-tyrosine-N-methyl amide, and zinc(II) – 3,6-diazaoctane-1,8-diamine systems
Authors: Decock Patrick , Sarkar Bibudhendra
Published: May 2006

An advanced methodology for the data analysis by analytical potentiometry (Decock and Sarkar. Can. J. Chem. 65, 0000 (1987)) has been utilized to analyze three different metal–ligand systems. The results are compared with those obtained by SUPERQUAD adapted for microcomputer. An excellent agreement has been attained with the stability constant data of Ni(II)–glycine complexes of an earlier multi-laboratory study. The technique has been utilized to investigate the effect of ligand concentration in the equilibria of Cu(II) complexes of glycylglycyl-L-tyrosine-N-methyl amide. The third system studied by this technique was Zn(II) complexes of 3,6-diazaoctane-1,8-diamine, a ligand of potential therapeutic efficacy against metal toxicity.
Studies of the synthesis of 8a-hydroxy-4a-methyloctahydronaphthalen-1(2H)-ones and their 2α-deutero derivatives
Authors: Stiver Shirley , Clark Peter D. , Yates Peter
Published: May 2006

Two syntheses of the bicyclic α-ketols, 8a-hydroxy-4a-methyl-trans- and -cis-octahydronaphthalen-1(2H)-ones (1 and 2), have been effected. One involves epoxidation of 4a-methyl-1,2,3,4,4a,5,6,7-octahydronaphthalene (4), followed by hydrolysis and oxidation; direct "hydroxy ketonization" of 4 was found not to be practicable. The second involves treatment of 3,4,5,6,7,8-hexahydronaphthalen-1(2H)-one (14) with lithium dimethylcuprate, trimethylsilylation of the resulting enolate, oxidation of the enol ether, and hydrolysis. Syntheses of the 2α-deutero derivatives of 1 and 2 are also described.
Structural studies of organoboron compounds. XXVII. (3-Hydroxy-2-methyl-4-pyridinonato)diphenylboron and (3-hydroxy-1,2-dimethyl-4-pyridinonato)diphenylboron
Authors: Nelson William O. , Orvig Chris , Rettig Steven J. , Trotter James
Published: May 2006

Details of the preparation and crystal structures of the title compounds are given. Crystals of (3-hydroxy-2-methyl-4-pyridinonato)diphenylboron, 1, are orthorhombic, a = 13.4010(6), b = 15.005(1), c = 14.833(1) Å, Z = 8, space group Pbca, and those of (3-hydroxy-1,2-dimethyl-4-pyridinonato)diphenylboron, 2, are monoclinic, a = 8.2617(5), b = 12.374(1), c = 16.104(1) Å, β = 92.741(5)°, Z = 4, space group P21/n. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.047 and 0.071 for 1654 and 1831 reflections with I ≥ 3σ(I), respectively. Both molecules contain five-membered C2O2B chelate rings, that in 2 being nearly planar. Structural data indicate weaker overall binding of the ligand oxygen atoms to boron in 1 than in 2. Bond lengths (corrected for libration) are O—B = 1.497(5) and 1.650(5), C—B = 1.600(5) and 1.599(5) Å for 1; O—B = 1.542(5) and 1.569(5), C—B = 1.607(6) and 1.609(6) Å for 2.
Trace analysis for aluminum by furnace atomic absorption spectroscopy and differential pulse polarography
Authors: Johnson Keith E. , Brichta A. Karen , Holter Kathy-Lynn
Published: May 2006

The determination of total aluminum in water by furnace atomic absorption spectrometry is best performed with a prior sample treatment with 1% HNO3 + 2% H2O2 or Acid Alizarin Violet N: detection limits of a few μgL−1 are reliably obtained. Ionic aluminum may be measured at levels down to 25 μgL−1 by differential pulse polarography of the aluminum complex with Acid Alizarin Violet N; excesses of Fe3+, Cl−, and EDTA interfere.
The He(I) photoelectron spectra of 2-butynal and related oxyalkynes
Authors: Klapstein Dieter , O'Brien Robert T.
Published: May 2006

The He(I), λ = 58.4 nm, photoelectron spectra of 2-butynal and the related compounds 2-butynol, 2-butynoic acid, 2-butynoyl fluoride, and 2-butynoyl chloride were obtained. The lower ionization energy bands may be assigned to photoionization from specific orbitals by comparison within the series, with related species and with the use of semi-empirical MO calculations. The energy variation of the more localized orbitals with substituent variation may be rationalized in terms of the inductive and resonance effects of the substituents.
Synthesis of rigid, chiral 1,5-diamino-3-oxapentanes and incorporation into chiral macrocyclic polyether ligands
Authors: Lehn Jean-Marie , Potvin Pierre G.
Published: May 2006

The syntheses of 2,5-anhydro-1,6-di-C-amino-1,6-dideoxy-3,4-di-O-methyl-D-mannitol 11 and its N,N′-dimethyl analogue 15 are described, as are couplings to bis-tartaro-18-crown-6 1 to give a macrobicyclic cryptand 16, and macrocycles 17 and 18 bearing four lateral groups, which are potential precursors of a cylindrical stacked macrocyclic system such as 6.
Photochemistry of cyclic α-hydroxy ketones. I. The nature and genesis of the photoproducts from steroidal 5-hydroxy 6-keto steroids and related compounds
Authors: Stiver Shirley , Yates Peter
Published: May 2006

Photolyses of 5-hydroxy-5α- and 5β-cholestan-6-one and their 3β-acetoxy- and 3β-benzyloxy derivatives in benzene or ethanol proceed stereospecifically with retention of configuration at C-5 to give the corresponding lactones, 6-oxa-B-homocholestan-7-ones. Photolyses of 3β-acetoxy-7α-deutero-5-hydroxy-5α- and 5β-cholestan-6-ones also proceed stereospecifically to give the corresponding 5-deutero lactones. 3β-Acetoxy-5-deuteroxy-5α- and 5β-cholestan-6-one give on irradiation 1:3 and 7:1 mixtures, respectively, of the corresponding 7aα- and 7aβ-deutero lactones. Irradiation of 3β-acetoxy-5-methoxy-5α-cholestan-6-one in ethanol leads to the stereoselective formation of ethyl 3β-acetoxy-5-methoxy-5,6-seco-5α-cholestan-6-oate, while that of 3β-acetoxy-5α-cholestan-6-one gives mainly photoreduction products. These observations are interpreted in terms of α-cleavage of the C-5—C-6 bond of the ketols to give alkyl acyl diradicals that undergo hydrogen transfer to give hydroxy ketenes, which then form the lactones. It is proposed that retention of configuration at C-5 results from two major factors—the nonplanar geometry of the hydroxyalkyl radical center, and fast hydrogen transfer in the diradical, the latter resulting from restricted rotation about the C-9—C-10 bond. The specific transfer of the 7α-deuterium atom in the 7α-deutero ketols is attributed to these factors and to the preferred direction of opening to the diradical on α-cleavage. The O-deuterium labelling results are interpreted in terms of product development control in the conversion of the hydroxy ketenes to the lactones and are in accord with restricted rotation about the C-9—C-10 bond. The photolysis of 3β-acetoxy-5-amino-5α-cholestan-6-one proceeds stereoselectively to give the 5β-lactam analogue of the 5β-lactone formed from the analogous 5α-ketol.
Thermodynamic investigation of molecular complexation in binary acetone + bromoform mixture
Authors: Dahiya Hari P. , Singh Prem P. , Dagar Shashi
Published: May 2006

Molar excess volumes, VE, and molar excess enthalpies, HE, have been measured for acetone (A) + bromoform (B) mixtures at 298.15 and 308.15 K. Results of these measurements suggest the formation of a 1:1 acetone–bromoform molecular complex. The equilibrium constant, K, the enthalpy of formation, ΔH, of the AB complex as also the molar volume change, ΔV, accompanying the complexation reaction [Formula: see text] have been evaluated from the measured HE and VE data. The K value so obtained has further been substantiated by the K value determined for the AB molecular entity from nmr studies on this mixture. Partial molar enthalpy of B (at infinite dilution) in A and vice versa have also been evaluated from the measured HE data at 298.15 K and used to calculate a consistent molar enthalpy of AB complex formation.
Total synthesis of natural quadrone
Authors: Liu Hsing-Jang , Llinas-Brunet Montse
Published: May 2006

Starting from the ammonium salt of (–)-10-camphorsulfonic acid (4), an efficient synthesis of quadrone (1) in natural form has been accomplished.
Excess enthalpies of dibutyl ether + n-alkane mixtures at 298.15 K
Authors: Benson George C. , Luo Beichen , Lu Benjamin C.-Y.
Published: May 2006

Calorimetric measurements of excess enthalpies are reported over the entire composition range for dibutyl ether + n-heptane, + n-deeane, + n-dodecane, and + n-hexadecane at 298.15 K. The results are compared with data from the literature, and a correlation of the excess enthalpies of dibutyl ether + n-alkane mixtures in terms of the Flory theory is described.
Rydberg states in adamantanethione, thiofenchone, and thiocamphor
Authors: Falk K. J. , Steer R. P.
Published: May 2006

The absorption spectra of adamantanethione (I), thiofenchone (II), and thiocamphor (III) have been measured in the quartz ultraviolet region in both the vapor phase and in perfluoroalkane solutions. Rydberg as well as π → π* transitions are identified in the gas phase spectra, and are discussed in terms of the known photochemistry of these compounds.
Standard enthalpies of formation of tris(β-diketonate)manganese(III) complexes: the mean (Mn—O) bond-dissociation enthalpies
Authors: Da Silva Manuel A. V. Ribeiro , Ferrāo M. Luisa C. C. H.
Published: May 2006

The standard molar enthalpies of formation of the crystalline complexes of manganese(III) with 1-phenyl-1,3-butanedione (HBZAC) and 2,2,6,6-tetramethyl-3,5-heptanedione (HDPM) were determined, at 298.15 K, by solution–reaction calorimetry:[Formula: see text]The mean molar bond-dissociation enthalpies, [Formula: see text], were derived as 163 ± 10 kJ mol−1 and 170 ± 10 kJ mol−1, respectively.
Neutron scattering studies of potassium-ammonia layers in graphite
Authors: Zabel H. , Neumann D. A.
Published: May 2006

Neutron scattering investigations of the structural and dynamical properties of ammonia molecules in the stage 1 compound KC24(NH3)4.3 are discussed. The K–NH3 intercalate layers represent the two-dimensional analogue of the well-known metal–ammonia solutions. At room temperature the intercalate liquid structure factor can be described by a model in which the K ions are surrounded on the average by four NH3 molecules, and the remaining molecules are essentially free. Quasi-elastic neutron scattering revealed two independent rotational motions of the NH3 molecule, one associated with the rotation about the C3 symmetry axis and the other one about the K ions. Above 200 K translational diffusion also becomes noticeable. The phonon dispersion of the [00q] longitudinal modes show clear signs of a phonon–libron coupling which causes the acoustic branch to split.
Temperature variation of nuclear magnetic resonance line shape in solid CHD3
Authors: Okada Kenkichi , Ozaki Yoshiaki , Maki Kazuo
Published: May 2006

The nuclear magnetic resonance line shape in solid CHD3 is calculated under the assumption of consecutive interspin modifications conversion. A variable concentration of nuclear spin species can be used to fit the temperature variation of the nuclear magnetic resonance absorption lines as observed at low temperatures with the help of a simple Gaussian line width.
CO/N2/Ar orientational glass: magnetic resonance
Authors: Walton J. H. , Wu Meng-Chou , Conradi Mark S.
Published: May 2006

The nmr lineshapes and linewidths of KCN/KBr, N2/Ar, and CO/N2/Ar are compared at corresponding states and are found to agree closely. This indicates a similar kind of orientational freezing, despite major differences in the anisotropic molecular interactions. The line narrowing and T2 data are explicable by two different theories. The one involves an orientation probability function, while the other invokes a broad homogeneous distribution of correlation times. Spin–lattice relaxation measurements indicate that T1 and dielectric loss are controlled at low temperatures by nearly π flips of CO molecules.
Heat of re-forming a coal liquefaction product from distillate fractions
Authors: Hansen Lee D. , Randzio Stanislaw L. , Lewis Laura , Lewis Edwin A. , Eatough Delbert J.
Published: May 2006

Results of calorimetric measurements of the heat of mixing of distillates from distillation of an H-coal liquefaction product are reported. The measurements were made at 373 K with mixing ratios such that the resultant mixture was the same as before distillation. The heat of mixing, which was endothermic in all cases, was found not to be a result of hydrogen bond formation. Intermolecular interactions of aromatic compounds are the probable source of the heats of mixing observed.
Molecular to atomic transformation in solid iodine under high pressure
Authors: Luty Tadeusz , Raich John C.
Published: May 2006

Structural transformations in solid iodine under high pressure are analyzed from the point of view of symmetries of possible charge density distortions coupled to phonons. The transition from the high pressure atomic phase to the low pressure molecular phase is interpreted in terms of phonon softening and formation of molecular bonds and is seen as a condensation of a charge density distortion wave coupled to a phonon mode.
Polymorphs of rubidium nitrate and their crystallographic relationships
Authors: Shamsuzzoha M. , Lucas B. W.
Published: May 2006

The crystal structure relationships between the four thermal polymorphs (IV – 437 K – III – 492 K – II – 564 K – I) of RbNO3 are discussed. Trigonal IV, a = 10.55(2), c = 7.47(2) Å at 298 K, Z = 9, and space group P31 (or its enantiomorph P32) has Rb atoms arranged on a pseudocubic sublattice defined by [Formula: see text] and related segments. The ordered NO3 groups are enclosed within respective pseudocubes and form close to ideal 8-fold anion–cation coordination with the surrounding Rb atoms. At IV → III, each of the appropriate (1/3) <10.1> and (1/3) <11.1> segments of IV (forming the Rb atom sublattice) transform to a cell edge of an ideal s.c. lattice of Rb atoms, a = 4.39(1) Å, Z = 1, and space group Pm3m. The orientationally disordered NO3 groups in III form another close to ideal 8-fold anion–cation coordination with the Rb atoms. At III → II, the s.c. lattice of III changes to form a larger b.c.c. lattice, a = 8.84(3) Å, Z = 8, in II. A parallel-axes unit cell relationship, i.e. <100>III//<100>II and 2(a)III = (a)II, exists between III and II. The NO3 group in II is postulated to form a close to ideal 8-fold anion–cation coordination with the surrounding Rb atoms. At II → I, II transforms to a f.c.c. lattice, a = 7.32 Å, Z = 4, and space group Fm3m. The NO3 group in I forms a close to ideal 6-fold anion–cation coordination with the surrounding Rb atoms. It is suggested that [Formula: see text] and related segments in II, which form a trigonal Rb atom sublattice, a = 7.65(3) Å and α = 109.47°, after II → I, transform to orthogonal cell edges of the cubic lattice of I.
Microcalorimetry and thermochemistry of alloys
Authors: Bros Jean Pierre
Published: May 2006

High temperature microcalorimetry is a very fruitful technique for increasing our knowledge of the thermochemistry of multicomponent alloys. As a good example, calorimetric results obtained for the Al + Bi + Ga system have been selected. Using a Calvet microcalorimeter and the indirect drop method, enthalpies of formation were measured over the entire concentration range between 725 and 1170 K and several points of the phase diagram were deduced from these calorimetric results. By means of a computer program, the Al + Bi + Ga equilibrium phase diagram was calculated and thus a thermodynamic description can be predicted. Making use of some simplifying hypotheses, the results indicate a satisfactory agreement between the experimental and the calculated liquid miscibility gap.
Phase transitions in the organic semiconductor dipropylamine tetracyanoquinodimethane: DPA TCNQ2
Authors: Bandrauk André D. , Truong Kim D. , Aubin Marcel
Published: May 2006

Dipropylamine tetracyanoquinodimethane, DPA TCNQ2, is by stoichiometry a 1:2 organic salt giving rise to a [Formula: see text] filled band quasi one dimensional electronic system. Conductivity measurements indicate the presence of at least three phase transitions. A dominant transition at 215 K shows simultaneous large discontinuities in both electric and magnetic properties. Infrared measurements suggest a structural change at 215 K related to conduction electron–molecular vibration interactions in view of the appearance of Ag TCNQ modes in the infrared spectrum. Deuteration of the donor [Formula: see text]bond lowers the main transition temperature by 5 K but maintains the same physical properties as in the nondeuterated compound.
Structural, spectroscopic, and electron paramagnetic resonance studies on two solid phases of bis-dipropylammonium tetrachlorocuprate(II) (DPACC)
Authors: Bond Marcus R. , Johnson Timothy J. , Willett Roger D.
Published: May 2006

Bis-dipropylammonium tetrachlorocuprate(II) exists in two known crystalline phases. Below 330 K (β phase) the crystal is orthorhombic Pbca with cell constants (at 293(1) K) a = 13.029(2) Å, b = 15.252(3) Å, c = 20.997(2) Å, V = 4175.5(9) Å3 The crystal undergoes a phase transition at 330 K to the α phase, which is monoclinic P21/n with cell constants (at 342(1) K) a = 13.277(4) Å, b = 10.280(3) Å, c = 16.362(13) Å, β = 104.31(5)°, V = 2164(2) Å3. The β phase consists of discrete, distorted tetrahedral CuCl42− anions, which are surrounded by dipropylammonium cations. Hydrogen bonding between the anions and cations results in a two-dimensional network of linked anions coplanar with the c-glide plane of the unit cell. The terminal carbon of one of the dipropylammonium chains assumes the higher energy gauche conformation while all other carbon and nitrogen atoms are found in the anti conformation. The local geometry of the α phase is very similar to that of the β phase. Powder electron paramagnetic resonance measurements in both phases confirm the persistence of the β phase anion geometry in the α phase. The disorder and increased thermal motion of the alkyl groups of the cation account for observed differences between the crystal structures of the two phases. This phase transition is similar to those found in long chain monoalkylammonium metal halide layer compounds that involve "melting" of the alkyl chain. Near infrared – visible spectra at 77 and 295 K show two distinct peaks at 12 700 and 9800 cm−1 in the first case and a very broad band maximizing at 11 200 cm−1 in the latter case. The highest-energy d-d transition correlates well with those of other CuCl42− anions of varying tetragonal distortion from tetrahedral geometry. The present data are used in conjunction with earlier data to develop the correlation between the highest-energy d-d transition and the distortion from tetrahedral symmetry.