bluuebunny/crossref_metadata_2025 huggingface dataset:
Dihydro-9,14(4H)tripyrazolo(1,5-a:1′,5′-d:1″,5″-g)triazonine-1,4,7. Synthèse et étude par résonance magnétique nucléaire
Authors: Fruchier Alain , Lupo Brigitte , Tarrago Georges
Published: May 2006

We have accomplished an unequivocal synthesis of 2,7,12-trimethyl-9,14-dihydro-1,5-a;1′,5′-d;1″,5″-g-(4H)tripyrazolo-1,4,7-triazonine. An nmr study of this new molecule in different solvents shows, for the first time, the existence of a crown [Formula: see text] saddle conformationl equilibrium in a triazacyclononatriène derivative.
A new synthesis of 3-amino-3-deoxy-α-D-mannopyranosyl 3-amino-3-deoxy-α-D-mannopyranoside, a potential antituberculous agent
Authors: Baer Hans H. , Radatus Bruno , Defaye Jacques
Published: May 2006

A practical, four-step synthesis of the title compound starting from 2-O-benzyl-4,6-O-benzylidene-α-D-altropyranosyl 2-O-benzyl-4,6-O-benzylidene-α-D-altropyranoside is described. Trifluoromethylsulfonylation followed by azide displacement furnished the corresponding α-D-manno,α-D-manno 3,3′-diazido-3,3′-dideoxy derivative, and subsequent hydrolytic deacetalation, followed by catalytic transfer hydrogenolysis to simultaneously reduce the azido groups and cleave the benzyl ether groups, gave the title disaccharide in 30% overall yield. As preceding work had provided the blocked starting disaccharide in a sequence of four facile operations departing from commercial α,α-trehalose (overall yield, 53%), the title compound can now be prepared conveniently on a multigram scale.
Propriétés volumiques du nitrate d'éthylammonium fondu à 298 K et de ses mélanges avec l'eau
Authors: Hadded M. , Biquard M. , Letellier P. , Schaal R.
Published: May 2006

Partial molar volumes of water and ethylammonium nitrate EAN are determined accurately in all water–EAN mixtures, between pure water and pure fused salt at 298 K. It has been found that the partial molar volume of water decreases linearly with molar fraction of salt, x, in concentrated solution of EAN (C > 2 mol L−1, x > 0.04). The main thermodynamic relations are established to describe the volumetric behaviour of salt, water, and solution. It has been shown that the intrinsic volume of salt can be identified roughly with the molar volume of the pure fused salt and the value of apparent molar volume of water with the actual volume of water in solution.
Kinetics and mechanisms of oxidations by metal ions. Part IV. Oxidation of phenylphosphinic acid by aquavanadium(V) ions
Authors: Mehrotra Raj Narain
Published: May 2006

The kinetics of the oxidation of phenylphosphinic acid by quinquevalent vanadium ion have been investigated in aqueous perchlorate media under pseudo-first order conditions (phenylphosphinic acid in excess). The reaction has a first order dependence in [V(V)] and [phenylphosphinic acid] and the observed pseudo-first order rate constant kobs is given by kobs = a + b[H+].The acid-independent path is considered to be due to the reaction between VO2+ (aq.) and C6H5P:(OH)2, the active form of phenylphosphinic acid, while the reaction between V(OH)32+ (aq.) and C6H5P(O)(OH)H, the inactive form of phenylphosphinic acid, is considered to explain the acid-dependent path. Phenylphosphinic acid in aqueous acidic solution is known to exist as an equilibrium mixture of the active and inactive forms. The composite activation and thermodynamic parameters associated with the constants a and b are reported.
Iridium(I) complexes containing bidentate pyrazolylgallate ligands. X-ray crystal structures of [Me2Gapz2]Ir(COD), [Ir(μ-pz)(CO)2]2, and [Ir(μ-3,5-Me2pz)(CO)2]2
Authors: Nussbaum Sophia , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and characterization of a number of Ir(I) complexes incorporating bidentate, chelating, pyrazolylgallate ligands are described. Non-rigidity for some of the complexes in solution has been demonstrated by variable temperature 1H nmr studies. Crystal structures of three complexes, [Me2Gapz2]Ir(COD), [Ir(μ-pz)(CO)2]2, and [Ir(μ-3,5-Me2pz)(CO)2]2 are reported and confirm the expected boat conformations for the six-membered M—(N—N)2—Ir rings (where M = Ir or Ga) in the compounds. One of the complexes studied has exhibited measurable activity as a catalyst in the hydrogenation reaction of cyclohexene.
Thermal rearrangement of functionalized 6-exo-(1-alkenyl)bicyclo[3.1.0]hex-2-enes. A total synthesis of (±)-sinularene
Authors: Piers Edward , Jung Grace L.
Published: May 2006

A total synthesis of the racemic form of the marine sesquiterpenoid (−)-sinularene (1) is described. The key step of the synthesis involved the stereoselective thermal rearrangement of the highly functionalized bicyclo[3.1.0]hexene 12 to provide, in 86% yield, the substituted bicyclo[3.2.1]octadiene 13. Conversion of the latter substance into (±)-sinularene (1) was accomplished via an efficient 4-step sequence.
1H and 13C nuclear magnetic resonance studies on the Diels–Alder adducts of isoquinolin-3(2H)-ones
Authors: Tóth Gâbor , Almásy Attila , Hazai László , Schnitta Antal , Devák Gyula
Published: May 2006

The stereochemistry of the adducts of isoquinolin-3(2H)-ones and maleimides was studied and 1H and 13C spectral parameters of the endo and exo stereoisomers were determined. The predominant rotamers generated by rotation about the C(7)—C(7a) and (C1)—C(1′) bonds were identified.
Thermodynamic properties of the dilute solutions of silver chloride and aluminum trichloride in alkali chlorides by electromotive force measurements
Authors: Tumidajski P. J. , Flengas S. N.
Published: May 2006

Thermodynamic data for dilute solutions of AgCl and AlCl3 in molten alkali chlorides were derived from the emf's of formation and of galvanic cells, respectively, given as, Ag/AgCl–ACl/C,Cl2 and Ag/AgCl–ACl//AlCl3–ACl/Al. ACl represents NaCl, KCl, CsCl, or the equimolar mixtures of NaCl–CsCl and KCl–CsCl. It was found that the thermodynamic properties of the ternary melts could be predicted from the results of the binary melts using the relationship (17, 20, 21), [Formula: see text] where Z represents any partial molar property. The ternary solution is denoted by the subscript 1, 2, 3 while the two binaries are denoted by 1, 2 and 1, 3; t is a concentration variable given as t = X3/(X2 + X3). These expressions are valid when the binary and the ternary solutions have the same content of either AgCl or AlCl3, respectively.
Chemical deoxygenation of the epoxide moiety in deoxynivalenol (vomitoxin)
Authors: King Russell R. , Greenhalgh Roy
Published: May 2006

Reaction of triacetoxydeoxynivalenol (3) with hydrobromic acid–acetic acid at reflux temperatures yielded 3α,7α, 13,15-tetraacetoxy-2-bromo apotrichothec-9-en-8-one (5) and 3α,7α,15-triacetoxy-13-bromo-12-hydroxytrichothec-9-en-8-one (4). Dehalohydrination of the 13,12-bromohydrin derivative with Zn–acetic acid followed by deacetylation with sodium ethoxide gave 3α,7α,15-trihydroxytrichothec-9,12-dien-8-one (2). This compound proved identical to the transformation product isolated from incubation of deoxynivalenol (vomitoxin) in vitro with rumen microorganisms.
The sorption of uranyl species on a hematite sol
Authors: Ho C. H. , Doern D. C.
Published: May 2006

The sorption of uranyl species on a hematite sol of narrow size distribution has been studied as a function of uranium concentration and solution pH. The adsorption increases with increasing uranium content in the solution. Raising the pH from 5 to about 6.2 markedly enhances the uptake of uranium. The enhanced uptake coincides with a proportional increase of [Formula: see text]. The sudden increase in adsorption around this pH region does not appear to be due to changes in surface charge of the hematite particles. It may be due to specific interactions between [Formula: see text] and the hematite particles. Results of desorption experiments show that different binding sites may exist on the hematite surface.
Novel coincidence effects in a bimetallic phase transfer catalyzed reaction. Biphasic reduction reactions catalyzed by rhodium carbonylmetallate clusters
Authors: Joó Ferenc , Alper Howard
Published: May 2006

Bimetallic and cluster rhodium carbonyl complexes catalyze the biphasic reduction of nitro compounds under mild conditions (using CO/5 M NaOH, C6H6 or PhCH3). Rate studies indicate the sensitivity of the reaction to the nature of the organic substrate, base concentration, and the temperature. A previously observed bimetallic (Co2(CO)8 and (1,5-HDRhCl)2) and phase transfer catalyzed [R4N+X−] reduction of nitro compounds was found to be a consequence of the inhibition and reactivation of the true catalyst by the quaternary ammonium salt and cobalt carbonyl, respectively.
Germathione–silathione spectres photoélectroniques et structures électroniques par la méthode MS Xα
Authors: Garcia Jean-Luc , Gonbeau Danielle , Pfister-Guillouzo Geneviève , Roch Michel , Weber Jacques
Published: May 2006

A study was undertaken in MS Xα on new short-life species: dimethylgermathione and dimethylsilathione. The spectroscopic detection of dimethylgermathione was confirmed by calculations performed on this compound and the corresponding dimer and trimer: ionization potentials and photoionization cross sections. The analysis of results obtained for the dimethylgermathione, the dimethylsilathione and the parent compound, thioformaldehyde, has shown certain characteristics of their electronic structure: strong polarity of the bond, low-energy Rydberg states.
Relativistic Hartree–Fock–Roothaan wavefunctions for atoms
Authors: Kagawa Takashi , Malli Gulzari
Published: May 2006

Relativistic Hartree–Fock–Roothaan (RHFR) wavefunctions have been calculated for a large number of atoms up to radon (Z = 86) under the point nucleus approximation using STO's as basis functions. The calculated total as well as orbital energies are in very good agreement with the corresponding results obtained by the numerical integration method.
Bonding in H3AB compounds
Authors: Schmidt Michael W. , Gordon Mark S.
Published: May 2006

The nature of binding in the 14 valence electron H3AB molecules is examined, where A and B are taken from the second and third rows. The AB bonding is inferred from the computed structures, d orbital populations, and localized orbitals. Near Hartree–Fock results are reported for the strongest bonding compounds, which are those with third row atoms A, and second row atoms B. Phosphine oxide, and to a lesser extent phosphine sulfide, are found to be effectively doubly bound. Amine oxide and sulfide are found to be ionic complexes. The thiazyl bond is confirmed as triple in nature. The exotic compound F3IC is proposed as a synthetic target.
Rôle de la liaison hydrogène intra et intermoléculaire dans l'étude des propriétés spectroscopiques et photophysiques. Cas types: dérivés du carbazole
Authors: Harvey Pierre D. , Durocher Gilles
Published: May 2006

The absorption and fluorescence spectra along with the fluorescence quantum yields and lifetimes of the 1-cyano and 1-carboethoxy derivatives of carbazole in polar and non-polar fluids and in rigid solutions at 77 K have been investigated. The existence of the cyclic dimer has been confirmed for 1-cyanocarbazole in 3-methylpentane. The enthalpy and entropy of complexation are evaluated to be −39 kJ mol−1 and −78 J mol−1 K−1 respectively. No tautomeric species has been observed following excitation of the dimer. On the other hand, the intramolecular hydrogen bonding system always predominates in the gas phase and in non-polar solvents in the ground electronic state. This intramolecular hydrogen bonding has been shown to be broken in ethanol, where intermolecular hydrogen bonding to the solvent takes place. 1-Cyano carbazole follows the same behaviour in ethanol. All the 1-substituted derivatives of carbazole show exciplex fluorescence in ethanol and the formation of these exciplexes has been explained by the strong charge transfer character involved in the excited 1Lb states of these molecules.
Spherical box model and reduction of Coulomb interactions in the crystal field theory of 3dn ions
Authors: Julg André , Julg Odette
Published: May 2006

With an accuracy of 0.1 eV, all the electron transitions in any 3d transition element and in the corresponding ions, isolated or inside a crystal, can be obtained with the Hartree–Fock model by using hydrogen d orbitals with suitable effective charges ζ. When the ion is embedded in a crystal, the value of ζ is generally weaker than that in the isolated state. For a given ion, the value of the reduction factor depends on the nature of the crystal. This phenomenon is explained by the boundaries imposed on the ion by the presence of the first neighboring ions (box effect). The application to some crystals (oxides and carbonates) corroborates this interpretation. An empirical relationship between the size of the ion and that of the cavity in which it is confined is proposed.
Pressure broadening effects in the far-infrared vibration–rotation spectra of several alkylamines and alkylethers
Authors: Gerson D. J. , Fateley W. G.
Published: May 2006

The far-infrared vibration–rotation spectra of the infrared-active internal rotation mode of dimethylether, dimethylamine, methylamine, and ethylamine have been recorded at several vapor pressures. The effect of pressure broadening on the 1 ← 0 torsional transition has been experimentally determined. It was found that the Van Vleck – Weisskopf model gave the best fit to these experimental results. It was also found that pressure broadening of the 1 ← 0 transition did not overlap the next transition in the series at sample vapor pressures less than 50 Torr.
Synthetic study on N-hydroxyaspartic acid
Authors: Kolasa T.
Published: May 2006

The synthesis of N-acyl derivatives of N-hydroxyaspartic acid was achieved by use of N-benzyloxyaspartic acid esters as starting material. The preparation of N-benzyloxyaspartic acid is described.
The photoreactions of 2-isopropoxy-1,4-naphthoquinone in the presence of cobalt acetylacetonate and other organometallics: an esr and CIDEP study
Authors: Depew M. Catherine , Adeleke B. B. , Rutter Allison , Wan J. K. S.
Published: May 2006

2-Isopropoxy-1,4-naphthoquinone has been used as a photoredox reagent in non-silver imaging process. The present study showed that the photoreactions of this quinone are very sensitive to solvent due to the competing intramolecular hydrogen abstraction from the isopropoxy group. The presence of cobalt acetylacetonate often modifies the reactions which leads to a very high quantum efficiency of producing the radical intermediates. The ether oxygen in the 2-substituent provides a further coordinating site for organometallic compounds and the quinone behaves as a 1,2-quinone when interacting with metals.
Mechanism of the oxidation of triphenyl derivatives of P, As, and Sb by peroxodiphosphate
Authors: Srinivasan C. , Pitchumani K.
Published: May 2006

Rate coefficients have been determined for the oxidation of Ph3M (M = P, As, Sb) by potassium peroxodiphosphate. The reaction is found to follow second-order kinetics, first order in each in the oxidant and Ph3M. [H+] has a pronounced accelerating effect on the reaction rate. An interesting dependence of the active species on the nature of the substrate has been observed. The reaction rate is influenced by changing the ionic strength of the medium. Acrylonitrile has no effect on the rate of oxidation. On the basis of the kinetic evidence, a general mechanism involving a biomolecular nucleophilic displacement of the substrate on the peroxo ion has been proposed. The relative rate order is found to be Ph3P > Ph3Sb > Ph3As and an explanation has been offered for the transposition of Ph3Sb and Ph3As.
Radical ions in photochemistry. 16. The photosensitized (electron transfer) carbon–carbon bond-cleavage reaction of radical cations
Authors: Okamoto Akio , Arnold Donald R.
Published: May 2006

The photosensitized (electron transfer) carbon–carbon bond cleavage of 1,1,2,2-tetraphenylethane (1b), 2-(4-methoxy-phenyl)-1,1-diphenyl-2-niethylpropane (1c), 1,1,2-triphenyl-2-methylpropane (1d), and 2-(4-trifluoromethylphenyl)-1,1-diphenyl-2-methylpropane (1e) has been studied with 1,4-dicyanobenzene (2) serving as the electron-accepting sensitizer. The oxidation potential of 1b–e have been measured by cyclic voltammetry. Estimation of the free-energy associated with the electron transfer between these donors (1b–e) and the first excited singlet state of 2, using the Weller equation, indicates the process is favorable in every case. There is, in every case, a one-to-one correspondence of products derived from reaction of the carbocation fragment and from the carbanion derived from the initially formed radical fragment. The efficiency of the reaction of 1b, which gives a good yield of diphenylmethane (3) and methyl diphenylmethyl ether, has been studied as a function of temperature. The observed activation energy (7.2 kcal mol−1) is equated to the bond dissociation energy of the central bond of the radical cation (1b+•). The ratio of products from the unsymmetric compounds is dependent upon the redox potentials of the fragment radicals and carbocations.
On the electrical double layer between mercury and aqueous solutions of sodium citrate
Authors: Gonzalez S. , Alvarez S. V. , Arévalo A.
Published: May 2006

The adsorption of citrate ions at the Hg/aqueous CitNa3 interface was studied, using both differential capacity and electrocapillary measurements. The results contrast with those obtained previously by Barradas etal. The hump of the Cd–E curve increases as the concentration of the solution increases to 0.5 M, to diminish beyond 1 M. The plots of [Formula: see text] vs. q−1 are linear and parallel to one another for the different values of q, which is in agreement with the results obtained by other authors for different anions. A Frumkin isotherm is also associated for the adsorption process and, finally, the parameters are obtained for the interface, using a type of isotherm proposed by Grahame.
The conformational analysis of piriprost, an inhibitor of leukotriene synthesis, based on high-field nuclear magnetic resonance studies
Authors: Kotovych George , Beierbeck Helmut , Salmon David
Published: May 2006

The analysis of proton nuclear Overhauser effect data for piriprost, (6,9-deepoxy)-6,9-(phenylimino)-Δ6,8 prostaglandin I1, indicates that the cyclopentene ring has the 11E conformation. A long-range nOe effect indicates that the α-chain is folded near the pyrrole and the phenyl rings.
Reversible ring opening in the hydrolysis of spiro ortho esters
Authors: McClelland Robert A. , Moreau Claude
Published: May 2006

Hydrolysis kinetics are reported for four spiro ortho esters: 3,4-dihydro-6-methoxy-1H-2-benzopyran-1-spiro-2′-1′,3′-dioxolane (13), its 1′,3′-dioxane analog (14), and the 6-unsubstituted versions of each (11 and 12). For comparison, also included are the diethoxy analogs: 1,1-diethoxy-3,4-dihydro-6-methoxy-1H-2-benzopyran (10) and the 6-unsubstituted compound (9). Product analysis implicates an initial opening of the dioxolane or dioxane ring in the spiro ortho esters, as expected on the basis of stereoelectronic considerations. The intermediate dialkoxycarbocations can be observed in HCl solutions. A detailed analysis has been carried out for the 6-methoxy systems to provide the rate constants k1, the second-order rate constant for H+-catalyzed formation of the cation from the ortho ester, k2, the first-order rate constant for water addition to the cation, and k−1, the first-order rate constant for ring closing of the cation to reform the ortho ester. The two spiro ortho esters are shown in this analysis to undergo reversible ring opening in their hydrolysis, in that values of k−1, are greater than k2. The differences, however, are not large, k−1/k2 being 1.2 (dioxolane, 13) and 3.8 (dioxane, 14). Comparison with the diethoxy ortho ester also reveals that the ring opening process (k1, rate constants) is inherently more difficult with the dioxolane, although not with the dioxane. An argument involving lone pair orientation is advanced to explain this.
Ni(H2O)2(3-CH3C5H4N)6(PF6)2: a revision of the crystal data
Authors: Morrison Raymond M. , Thompson Robert C. , Evans Stephen V. , Trotter James
Published: May 2006

The crystal structure of the title compound is revised and described in the orthorhombic space group F2dd, rather than in monoclinic Cc. Chemical conclusions are unchanged.
Formal total synthesis of erythromycin A. Part I. Total synthesis of a 1,7-dioxaspiro[5.5]undecane derivative of erythronolide A
Authors: Bernet Bruno , Bishop Paul M. , Caron Maurice , Kawamata Takeshi , Roy Bernard L. , Ruest Luc , Sauvé Gilles , Soucy Pierre , Deslongchamps Pierre
Published: May 2006

The total synthesis of compound 1, a 1,7-dioxaspiro[5.5]undecane derivative of the seco acid methyl ester of erythronolide A, is reported.
Formal total synthesis of erythromycin A. Part II. Preparation of a 1,7-dioxaspiro[5.5]undecane derivative of erythronolide A seco acid methyl ester from erythromycin A
Authors: Bernet Bruno , Bishop Paul M. , Caron Maurice , Kawamata Takeshi , Roy Bernard L. , Ruest Luc , Sauvé Gilles , Soucy Pierre , Deslongchamps Pierre
Published: May 2006

Degradation of erythromycin A gives spirocompound 18A. Compound 18A is then converted into the spirolactone 22 via 21. Compound 21 is then reconverted into spiro product 18A.
Quadrupolar relaxation effects in methyl-substituted ammonium ions as determined by 1H nuclear magnetic resonance
Authors: Halliday James D. , Bindner Patrick E. , Padamshi Shahsultan
Published: May 2006

Nitrogen-14 quadrupole interactions broaden the 1H nuclear magnetic resonances of the ammonium protons spin-coupled to 14N in the methyl-substituted ammonium chlorides (methylammonium, dimethylammonium, and trimethylammonium). These proton lineshapes have been determined over the temperature range −8.3 to +93.6 °C in 6 mol L−1 aqueous HCl solution. The 14N spin-lifetimes, τ, have been calculated from the Arrhenius form equation In τ vs. 1/T (K), and yield activation energies of 10.63 ± 0.92, 10.60 ± 0.52, and 11.12 ± 0.39 kJ mol−1 for the mono-, di-, and tri-methyl species, respectively. The 14N nmr linewidths have been extracted from these data and a comparison is made with 14N nmr spectra obtained by Ogg and Ray.
Electron transfer reactions of nickel complexes of 1,4,7-triazacyclodecane
Authors: Fairbank M. G. , McAuley A. , Norman P. R. , Olubuyide O.
Published: May 2006

The preparation of [Ni(1,4,7-triazacyciodecane)2]3+, (Ni(10-aneN3)23+) is described. The existing procedure has been modified leading to good yields of the ligand trihydrochloride. The nickel(II) analogue (reported previously) is oxidised in a facile manner, either by Co3+aq in acidic aqueous media or by NO+ in CH3CN. Since the octahedral NiN6, chromophore is retained upon electron transfer, outer sphere reactions both of the Ni(II) and Ni(III) species have been studied. Rates of oxidation by various nickel(III) macrocycles have been measured and details are provided. Electrochemical oxidation of the Ni(II) complex is consistent with E0(Ni(10-aneN3)23+/2+) = 0.997 V (vs. NHE). The data have been used in a Marcus correlation, leading to the self-exchange rate k11 for the couple (Ni(10-aneN3)23+/2+) = (2 ± 1) × 104 M−1 s−1. This value is compared with other data derived using octahedral Ni(II)/Ni(III) centres. The oxidation of the Ni(II) complex by Co(III)aq has been studied in both protonated and deuterated media. There is no evidence for any proton transfer (from the N—H) being coupled to the electron transfer step. The observed rate constant for the reaction of Co3+ with Ni(II)(10-aneN3)22+ (550 M−1 s−1) may be compared with the calculated outer sphere rate (270 M−1 s−1). An estimate of k11 (CoOH2+/+) ~ 3 M−1 s−1 for the CoOH2+/+ exchange is discussed.
Stereochemical dependence of the mechanism of deoxygenation, with lithium triethylborohydride, in 4,6-O-benzylidenehexopyranoside p-toluenesulfonates
Authors: Baer Hans H. , Mekarska-Falicki Miroslawa
Published: May 2006

Lithium triethylborohydride was shown to react with methyl 4,6-O-benzylidene-α-D-hexopyranoside 2- and 3-tosylates, and 2,3-ditosylates, in the manno, allo, and altro configurational series both by O—S fission (O-desulfonylation) and by C—O fission (C-desulfonyloxylation), to produce carbinol and deoxy functions, respectively. The results were compared with those previously obtained with the corresponding gluco and galacto isomers, and the degree of facility of the cleavage reactions was seen to depend on the position of the sulfonic ester groups and the overall configuration of the molecules. The mechanism of reductive desulfonyloxylation also depended on configuration and was demonstrated to involve intermediary epoxide formation or displacement by internal hydride shift as the principal paths; competing elimination and direct nucleophilic displacement were found to occur in the allo series, whereas reduction accompanied by ring contraction has thus far been encountered only in the conformationally less constrained, cis-fused acetal system of the galacto series. Like the borohydride reagent, lithium aluminum hydride was found to react (though much more slowly) with the altro 2,3-ditosylate by the epoxide-mediated mechanism, although the latter hydride is known to desulfonyloxylate the α-D-gluco-isomer by a different, intramolecular reduction mechanism.
Effects of neutral and anionic substituents on the carbonyl stretching bands of ring-substituted acetophenones
Authors: Binev Ivan G. , Kolev Tsonko M. , Juchnovski Ivan N.
Published: May 2006

Satisfactory single-parameter (σ+) and dual-parameter (according to Yukawa–Tsuno and Taft) correlations have been found between frequencies of the title bands (νCO) and substituent constants. It has been found that use of dimethyl sulphoxide instead of carbon tetrachloride as solvent does not lower the relative accuracy of the studied correlations. The integrated intensities of the νCO bands do not correlate with any type of substituent constants. The constants σ+, σ0, σI, [Formula: see text], and [Formula: see text] of the anionic substituents NC—HC−, O−, CH3CON−, and CO2−, recently determined on the basis of cyano infrared frequencies and intensities, have proved satisfactorily reliable with respect to the νCO of acetophenones. The σ+ constants of m-CH2CO2− (−0.22 ± 0.08) and m-C6H5CON− (−0.66 ± 0.13) have been estimated on the basis of νCO data and νCO/σ+ correlations (solvent DMSO).
Preparation, structure, and conformation in solution of diacetyl derivatives of 6,7-dimethyl-1,4-dihydroquinoxaline and of dihydropyridotriazines
Authors: Armand Joseph , Boulares Line , Simonnin Marie-Paule , Bellec Christian , Convert Odile , Ple Nelly , Queguiner Guy
Published: May 2006

A conformational study of 1,4-diacetyl-1,4-dihydro-6,7-dimethylquinoxaline is carried out by low temperature nmr in CD2Cl2. Important acetyl rotation induced shifts have been observed for the peri and ortho protons. These results, together with low temperature nOe experiments, permit the determination of the structures and conformations of four diacetyl derivatives of dihydropyrido[3,4-e] as-triazines and of one diacetyl derivative of a dihydropyrido[4,3-e] as-triazine.
La liaison phosphore–azote. Étude quantochimique de modèles neutres et ioniques H3PNH, , , H2PNH− et
Authors: Gonbeau Danielle , Pfister-Guillouzo Geneviève , Mazières Marie-Rose , Sanchez Michel
Published: May 2006

Abinitio molecular orbital calculations have been performed on the phosphazene bond using a split valence basis set on neutral and ionic compounds. The nature of the P—N multiple bond in H3PNH shows similarities with that of the P—C bond in phosphorus ylides. Electronic characteristics of cations (H2PNH3)+, (H3PNH2)+ and anions (HPNH2)−, (H2PNH)− related to H3PNH and its tautomer H2PNH2 were investigated. The results obtained were used to explain experimental observations for this type of compounds.
Étude comparative dans la série des dibenzamido-alcanes, composés modèles des poly(oligométhylènes téréphtalamides)
Authors: Brisson Josée , Brisse François
Published: May 2006

The dibenzamido alcanes, nDBN, for n = 2–10, have been synthesized and characterized by X-ray diffraction and infrared and Raman spectroscopy. From X-ray diffraction it was observed than the dihedral angle ε between the aromatic ring and the amido group averaged 28.3° and did not vary significantly with n. The torsion angle τ between the amide group and the aliphatic chain was found to be near 180° for n = 4, 6, 8, and 10. However, for n = 2, 3, 5, and 7, τ averaged 98°. In this last case the plane of the aliphatic chain is nearly perpendicular to the plane of the amide group. The study of ir and Raman spectra in relation to conformation revealed that the position of the amide V band depends on the value of the τ angle and could be used to infer if the latter is close to 180° or not.
Preparation of chiral 1-phenylethanols and bromides
Authors: Stein Allan R. , Dawe Robert D. , Sweet James R.
Published: May 2006

A fast, convenient procedure for preparing and resolving moderate to large quantities of chiral secondary alcohols is described. The general procedure involves a one-pot conversion of the ketone (various acetophenones) to the half-ester of a diacid (succinic, phthalic… ) and resolution with (+)- and (−)-1-phenylethylamines. Overall yields of the enantiomeric alcohols, the variously substituted 1-phenylethanols, are generally 65–85% with optical purities of approximately 90%. Properties and optical rotations of a number of chiral 1-phenylethanols and of the bromides made from them are tabulated. A discussion of optical purity determinations using nmr methods is included and absolute configurations are reported.
Pressions de vapeur des mélanges eau – nitrate d'éthylammonium à 298,15 K. Propriétés thermodynamiques des milieux eau – sel fondu
Authors: Biquard M. , Letellier P. , Fromon M.
Published: May 2006

The activity and activity coefficient of water in water and ethylammonium nitrate (EAN) mixtures were determined by vapor pressure measurements between pure water and pure fused salt at 298.15 K. For a wide range of mole fractions of salt, (0.3 < X ≤ 1) the behaviour of water can be described very accurately by a "one parameter" empirical equation which involves activity coefficient, γE, mole fraction of EAN, and limiting Gibbs energy of the dilution of water in pure fused salt, [Formula: see text]:[Formula: see text]Interpretation of experimental results was also attempted by use of the B.E.T. equation. It appears that the energy, ΔEd = E − EL, in those solutions is very low. Partial molar volumes of water and salt are also discussed in relation to empirical and B.E.T. equations. It can be shown that the two equations lead to similar results.
The influence of pH in the tautomerism of 9,10-anthracenediols and 1,3-diketones
Authors: Anderson John C. , Broadbent A. Douglas
Published: May 2006

Equations have been derived to describe how the ratio of the total concentration of all keto forms to that of all enolic forms (K′) varies with changing pH, for a tautomeric system in which the enol and ketone are polyprotic acids. The influence of pH on the tautomerism of 2-amino-9,10-anthracenediol, 2,9,10-anthracenetriol, 2,4-pentanedione, and 1-(3-pyridyl)-1,3-butanedione was examined. The equilibrium constants for all the acid–base equilibria involved were calculated from the dependence of K′ on pH.
The photochemistry of 6- and 7-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene
Authors: Bender Christopher Owen , Bengtson Donald Laverne , Dolman Douglas , O'Shea Seamus Francis
Published: May 2006

The direct irradiation of 7-cyanobenzocyclooctatetraene (5) led to 6- and 7-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (7 and 8; Φ7 = Φ8 < 0.0001). On direct irradiation, 7 gave 1-cyanobenzosemibullvalene (6; Φ = 0.19), 5 (Φ = 0.022), and 2-cyanonaphthalene (Φ = 0.04), whereas 8 gave 7-cyanobenzosemibullvalene (16; Φ = 0.03), 5 (Φ = 0.22), naphthalene (Φ = 0.12), and 4-cyano-7,8-benzotetracyclo[3.3.0.02,4.03,6]oct-7-ene (17, Φ = 0.03). Upon sensitized irradiation, 7 gave 6 (Φ = 0.68) and 2-cyanonaphthalene (Φ = 0.007), while 8 gave 16 (Φ = 0.01) and naphthalene (Φ = 0.52). Deuterium labelling studies suggest that 6 and 16 derive from Zimmerman di-π-methane rearrangements.
Synthesis and characterization of molybdenum–tin complexes derived from the molybdenum tricarbonyl anion, [MeGapz3]Mo(CO)3−, and organotin chlorides. X-ray crystal structure of [MeGapz3]Mo(CO)3SnPh3 (where pz = pyrazolyl, N2C3H3)
Authors: Onyiriuka Emmanuel C. , Rettig Steven J. , Storr Alan
Published: May 2006

The reaction of the molybdenum tricarbonyl anion, [MeGapz3]Mo(CO)3−, with the organotin chlorides, Ph3SnCl, Me3SnCl, and Me2SnCl2, has yielded a series of complexes in which direct Mo—Sn single bonds are featured. The [MeGapz3]Mo(CO)3SnMe2Cl complex shows an interesting solution behavior in which a transition from a 3:4, or piano stool structure, to a 3:3:1, or capped octahedral arrangement, is thought to occur. The 3:3:1 structure has been demonstrated in the solid state for the [MeGapz3]Mo(CO)3SnPh3 compound by means of a crystal structure determination. Crystals of [methyltris(1-pyrazolyl)gallato-N,N,N](triphenylstannyl)tricarbonylmolybdenum are monoclinic, a = 11.4439(8), b = 19.5116(8), c = 15.2686(12) Å β = 111.370(3)°, Z = 4, space group P21/c. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.025 and Rw = 0.031 for 5259 reflections with I ≥ 3σ(I). Important bond lengths include: Mo—Sn = 2.8579(3), Mo—N = 2.239(2)–2.244(2), Mo—C = 1.967(3)–2.000(3), Sn—C = 2.151(3)–2.166(3), Ga—N = 1.920(3)–1.931(3), and Ga—C = 1.943(4) Å.
Synthesis and characterization of LMo(CO)3M(PPh3)x (where L = tridentate pyrazolyl-gallate or -borate ligand; M = Rh, x = 2; M = Cu, x = 1). X-ray crystal structures of [MeGapz3]Mo(CO)3Rh(PPh3)2 and [MeGapz3]Mo(CO)3Cu(PPh3) (where pz = pyrazolyl, N2C3H3)
Authors: Banta Gregory A. , Louie Brenda M. , Onyiriuka Emmanuel , Rettig Steven J. , Storr Alan
Published: May 2006

The reactions of the LMo(CO)3− ions (L = MeGapz3, HBpz3, Me2Gapz(OCH2CH2NMe2)) with [Cu(PPh3)Cl]4 and Rh(PPh3)3Cl have yielded complexes with Mo—Cu and Mo—Rh bonds. The X-ray crystal structures of two such complexes have been determined. Crystals of [MeGapz3]Mo(CO)3Cu(PPh3) are monoclinic, a = 17.071(2), b = 16.738(1), c = 23.641(3) Å, β = 104.899(6)°, Z = 8, space group P21/n, and those of [MeGapz3]Mo(CO)3Rh(PPh3)2, are triclinic, a = 12.519(3), b = 17.182(4), c = 12.071(2) Å, α = 105.02(1), β = 109.87(1), γ = 97.10(2)°, Z = 2, space group [Formula: see text]. Both structures were solved by conventional heavy atom methods and were refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.035 for 6296 reflections with I ≥ 2σ(I) and R = 0.036 and Rw = 0.037 for 5642 reflections with I ≥ 3σ(I), respectively. The former complex provides a rare example of a 3:3:1, or capped octahedral structure, with a short (mean) Mo—Cu distance of 2.513(9) Å. The latter compound displays one terminal and two bridging CO ligands and a Mo—Rh distance of 2.6066(5) Å.
The influence of ionic strength on the adsorption of azide ions on mercury electrodes
Authors: Motheo Artur J. , Gonzalez Ernesto R. , Avaca Luis A.
Published: May 2006

The adsorption of azide ions on mercury electrodes has been studied from constant ionic strength solutions of composition χ M NaN3 + (μ–χ) M NaF with μ = 0.25 and 0.5. Double layer parameters were obtained by taking into account the change in activity coefficients with solution composition. The results were analyzed together with those reported previously for μ = 0.95, recalculated to take into account the change in activity coefficients. The influence of the ionic strength on the amount adsorbed, the properties of the inner layer, and the parameters of an adsorption isotherm for azide anions are discussed in terms of the electrostatic model of the double layer.
Complexes of hybrid ligands. Some Pd2+ and Pt2+ complexes of fluoro-alkoxy thioether ligands; the measurement of the trans-effect of phosphines on thioether inversion
Authors: Boeré René T. , Willis Christopher J.
Published: May 2006

The hybrid ligands R—S—CH2—C(CF3)2—O− (R = CH3 or C6H5) have been used in conjunction with the other donors to prepare complexes of Pt2+ and Pd2+. Five-membered chelate rings are formed by coordination through the hard alkoxy and the soft thioether donor sites. Products are of two types: neutral MCl{RSCH2C(CF3)2O}(PR3) or cationic [M{RSCH2C(CF3)2O}(PR3)2]+, and their geometry is assigned. Variable temperature nmr measurements are used to follow the inversion of the thioether function in the hybrid chelate ring, and values of ΔG‡ are calculated. From a comparison of the barrier to inversion in various complexes, the dynamic trans effect of various ligands is assessed including, for the first time using this criterion, the trialkylphosphines.
Application des conditions de réaction par transfert de phase à la synthèse d'amino-éthers dérivés du trans phénoxy-2 cyclohexanol
Authors: Depreux P. , Marcincal-Lefebvre A.
Published: May 2006

Amino-ethers of trans-2-phenoxycyclohexanol were prepared by methods involving anhydrous conditions (sodium alkoxides in xylene) or phase transfer catalysis conditions (liquid–liquid or solid–liquid two-phase systems). Various factors were optimized. In the liquid–liquid two-phase system, when no catalyst was added, reaction proceeds with comparable or even better yields than with some PTC catalysts, a quaternary salt being formed insitu. It was shown that the deprotonation of ROH takes place at the interface, since there was no OH− extraction in organic medium and the yield depends on the stirring speed. In the presence of Aliquat, the yield does not change with the organic concentration of the catalyst. Statistical correlations obtained between the variations in yield and several other parameters were good.
Electrostatic and nonelectrostatic, conventional and unitary thermodynamic quantities of reaction. II. Proton–ligand and metal–ligand reactions in mixed solvents
Authors: Aruga Roberto
Published: May 2006

A calculation method of the electrostatic and the nonelectrostatic parts of thermodynamic quantities of reaction, previously proposed and applied to association reactions in aqueous medium, is applied, in the present work, to reactions in mixed solvents. The aim of the present treatment is to clarify the importance of the various factors (dependent and independent of the dielectric constant) through which the solvent affects complex stability. The method is applied to ΔG0, ΔH0, and ΔS0 data of literature for proton–ligand and metal–ligand reactions in several water–methanol, water–ethanol, and water–dioxane mixtures. The conclusions of the present study seem to confirm a leading role of solvation equilibria in determining different stabilities of complex in different solvents, while a minor role is assigned to the dielectric properties of the solvent.
Complexes of 18-crown-6 macrocyclic ethers obtained from ethereal solvents. Complexes of potassium and sodium salts with host:guest ratios of 1:2 and 1:3
Authors: Rodrigue André , Bovenkamp John W. , Lacroix Benoit V. , Bannard Robert A. B. , Buchanan Gerald W.
Published: May 2006

This paper describes the synthesis, in ethereal solvents, of the complexes of 18-crown-6, the cis–syn–cis and the cis–anti–cis isomers of dicyclohexano-18-crown-6, and dibenzo-18-crown-6 with the potassium and sodium salts of phenoxide and thiocyanate (as well as some potassium oximate salts). In general, the macrocycles break down the aggregates of the potassium salts so that the complexes of the contact ion pairs are isolated. The complex of the cis–anti–cis isomer of dicyclohexano-18-crown-6, however, which has a low stability constant, complexes the dimer of potassium phenoxide to give a complex with a 1:2 host:guest ratio. This appears to be the first example of a 1:2 host:guest ratio of a potassium salt with an 18-crown-6 macrocycle. There is a greater tendency for the complexes of sodium salts to have host:guest ratios less than 1:1. Thus, 18-crown-6 gives complexes with sodium phenoxide and sodium thiocyanate which have 1:3 and 1:2 host:guest ratios, respectively. Host:guest ratios of 1:2 are also obtained for the two above-mentioned isomers of dicyclohexano-18-crown-6 and for dibenzo-18-crown-6 with sodium phenoxide. Sodium thiocyanate gives complexes with either 1:1 or 1:2 host:guest ratios depending on the macrocycle. With dibenzo-18-crown-6, sodium thiocyanate gives a 1:1 complex in which one molecule of the solvent used is incorporated into the complex. The infrared and ultraviolet spectra of the complexes are discussed.
Sur une nouvelle méthode de synthèse de δ-lactones cyclopenténiques
Authors: Caille Jean Claude , Farnier Michel , Guilard Roger , Aubry André , Lecomte Claude
Published: May 2006

Synthesis of two cyclopentenic δ-lactones, 1,3,4,4a,5,6-hexahydrocyclopenta[c]pyran-1-one and its analogue possessing a cyclopentenyl group bonded to the carbon atom 4a is described, starting from the cyclopentanone or cyclopentylidene cyclopentanone. The remarkable reactivity of the tosylhydrazones allows transformation of these compounds into substituted cyclopentenes, which lead to δ-lactones by cyclization. The conditions of cyclization depend on the nature of the cyclopentanone. The structure of the two δ-lactones is established by 1H and 13C nmr data, mass spectrometry, and, in one case, by X-ray analysis.
Isotope effects and activation parameters for the proton transfer reaction from 1-(4-nitrophenyl)-1-nitroethane to free anions and ion pairs of cesium n-propoxide in n-propanol solvent
Authors: Jarczewski Arnold , Schroeder Grzegorz , Pruszynski Przemyslaw , Leffek Kenneth T.
Published: May 2006

Rate constants for the proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to cesium n-propoxide in n-propanol have been measured under pseudo-first-order conditions with an excess of base for four temperatures between 5 and 35 °C. Using literature values of the fraction of cesium n-propoxide ion pairs that are dissociated into free ions, separate second-order rate constants for the proton and deuteron transfer to the ion pair and to the free ion have been calculated. The cesium n-propoxide ion pair is about 2.8 times more reactive than the free n-propoxide ion. The primary kinetic isotope effects for the two reactions are the same (kH/kD = 6.1–6.3 at 25 °C) within experimental error. The enthalpy of activation is smaller for the ion-pair reaction and the entropy of activation more negative than for the free-ion reaction. For proton transfer, ΔH±ion pair = 8.3 ± 0.2 kcal mol−1, ΔH±ion = 9.6 ± 1.0 kcal mol−1, ΔS±ion pair = −12.3 ± 0.6 cal mol−1 deg−1, ΔS±ion = −10.1 ± 3.4 cal mol−1 deg−1. The greater reactivity of the ion pair relative to the free ion is interpreted in terms of the weaker solvation shell of the ion pair in the initial state.
Organic reactions in liquid crystalline solvents. 4. Nanosecond laser flash photolysis studies of intramolecular motions of rod-like solutes in liquid crystals
Authors: Leigh William J.
Published: May 2006

The rates of triplet decay of a series of β-aryl-(4-alkoxypropiophenone)s in the smectic, nematic, and isotropic phases of 4′-butyl- and 4′-ethylbicyclohexyl-4-carbonitrile (BCCN and ECCN, respectively) have been measured over the 30–95 °C temperature range by nanosecond laser flash photolysis. The rates of triplet decay for these probe molecules in fluid solution are governed by the rates of Cα—Cβ bond rotation, which allows intramolecular quenching of the carbonyl triplet state by the β-aryl ring. The ketones are substituted with alkyl groups of varying length, shape, and flexibility in the para positions of the β-phenyl (H, n-hexyl, cyclohexyl) and benzoyl (meth-, n-pent-, and n-octoxy) rings. With the exception of β-phenyl-(4-methoxypropiophenone), for each ketone the Arrhenius parameters for triplet decay in the smectic phase of BCCN are similar to those in the nematic phase of the same solvent, and in all cases, the Arrhenius plots exhibit perfect continuity at the S—N transition temperature. A solvation model is tentatively advanced to explain these results. In the nematic phase of BCCN, the Arrhenius activation energy and entropy are significantly more positive than those in isotropic ECCN for all the ketones studied, but variations in the energetics of triplet decay in the nematic phase as a function of solute structure are parallelled in the isotropic solvent. Thus, the inhibiting effect of the nematic solvent on the bond rotations leading to intramolecular triplet quenching in these probes is attributed to the predominant influence of microviscosity (viscous drag) effects; the presence of solvent orientational order appears to have little or no effect on the intramolecular mobility of these ketones. The results and conclusions of earlier studies of unimolecular reactions in nematic solvents are discussed in light of these results.
Structure électronique et réactivité des pyridyl-isothiocyanates. Étude quantique et photoélectronique
Authors: Guimon C. , Pfister-Guillouzo G. , Ilavsky D. , Marchalin M. , Martvon A.
Published: May 2006

On the basis of molecular orbital calculations made in association with ultraviolet photoélectron spectroscopy (ups), it is demonstrated that the regioselectivity of the cycloadditions of pyridyl-2-isothiocyanate with 1,3-dipoles is directed by frontier orbitals. The different cycloadditions (4 + 2, 2 + 3, 2 + 2) vary with the overlap of these orbitals and this shows the importance of secondary interactions, namely the localization of the orbitals on the atoms adjacent to the bonds that are formed during the addition.
Synthesis and structural characterization of an unusual silylzirconium hydride complex
Authors: Aitken Clare , Harrod John F. , Samuel Edmond
Published: May 2006

Dimethylzirconocene and dihydridozirconocene both catalyze the dehydrogenative coupling of primary and secondary organosilanes. Primary silanes give linear polysilanes and secondary silanes give tetraorganodisilanes. The reaction of dimethylzirconocene with a small excess of phenylsilane gives the unusual unsymmetrically substituted zirconocenesilylhydride dimer: Cp2Zr(SiMePhH)(μ-H)2(PhH2Si)ZrCp2. The structure of this product is deduced from a combination of nmr and crystallographic results. Although the nmr data suggest that dihydridozirconocene reacts with phenylsilane to give the corresponding symmetrical dimer (Me replaced by H) in solution, attempts to isolate this compound have not been successful.
The crystal structure and vibrational spectrum of (C8H20N2)[InBr5(H2O)]•H2O, a salt of the 1,1,4,4-tetramethylpiperazonium dication containing the aquopentabromoindate complex anion
Authors: Clark George R. , Rickard Clifton E. F. , Taylor Michael J.
Published: May 2006

The preparation, crystal structure, and vibrational spectra of the title compound are reported. The compound crystallizes in the triclinic space group [Formula: see text] with a = 7.386(2), b = 8.637(1), c = 16.546(2) Å, α = 97.40(1)°, β = 95.51(2)°, γ = 112.91(2)°, V = 951.6 Å3, ρobs = 2.43 g cm−3, Z = 2, ρcalcd = 2.424 g cm−3 (MoKα, λ = 0.71069 Å). The structure was solved by direct methods and electron density maps, and refined by full-matrix least squares to the final R = 0.038 for 3343 observed reflections. The structure consists of N,N,N′,N′-tetramethylpiperazonium cations containing a six-membered C4N2 heterocycle, InBr5(OH2)2− anions, and additional H2O solvent molecules. Infrared and Raman spectral bands of the InBr5(OH2)2− complex are assigned on the basis of C4v skeletal symmetry, and the H2O molecule of crystallization is also detected spectroscopically.