bluuebunny/crossref_metadata_2025 huggingface dataset:
Excess molar volumes of binary mixtures with 2-pentanone and 1-chloroalkanes at 298.15 and 308.15 K
Authors: Pico José M. , Menaut Consolaciôn P. , Jiménez Eulogio , Legido José L. , Fernàndez Josefa , Andrade M. Inmaculada Paz
Published: May 2006

Excess molar volumes υEat 298.15 and 308.15 K and normal atmospheric pressure for the binary mixtures 2-pentanone + 1-chloroalkane (from 1-chlorobutane to 1-chlorooctane) were obtained from measurements of the density with an Anton Paar densimeter. The υEvalues for all mixtures were positive, and increase as the 1-chloroalkane length increases. Excess molar volumes depend slightly on the temperature. The same characteristics were found previously for the excess molar enthalpies of the same mixtures. Experimental υEvalues are compared with theoretical results using the Prigogine–Flory–Patterson model. Keywords: thermodynamics, liquid mixtures, excess volumes, ketones, chloroalkanes.
A study of the vacuum pyrolysis of 1,2,3-benzotriazines. The Hel ultraviolet photoelectron spectra of benzazete and o-benzyne
Authors: Werstiuk Nick Henry , Roy Chandra Deo , Ma Jiangong
Published: May 2006

A CW CO2 laser is used as a directed heat source to carry out the vacuum pyrolysis of 1,2,3-benzo-triazine (1a) and 4-methyl-1,2,3-benzotriazine (1b). We report the first HeI photoelectron (pe) spectrum of benzazete (2a), which correlates with ionization energies calculated with HAM/3 using an equilibrium geometry obtained at the ab initio HF/6-31G** level of the theory. The pe spectrum of o-benzyne (3) obtained in this study correlates with the spectrum published by Zhang and Chen, but not with the spectra reported in two earlier publications. Keywords: 1,2,3-benzotriazines, vacuum pyrolysis, HeI ultraviolet photoelectron spectra, benzazete, benzyne.
Electrochemical investigations on some potential antibacterials, I
Authors: Jain Rajeev , Damodharan M.
Published: May 2006

Electrochemical behaviour of the medicinally important 4-(4′-sulphonamoyl)hydrazono-1-phenyl-3-methyl-2-pyrazolin-5-ones has been studied at d.m.e. and glassy carbon electrodes. At d.m.e., all six compounds exhibited a single, well-defined, four-electron wave in the pH range 2.5–12.0. Polarographic four-electron wave was found to be diffusion-controlled and irreversible. Similarly, cyclic voltammetry of these compounds at glassy carbon electrode exhibited a single peak. Peak potential shows shifts towards negative potential with pH, with linear segments up to pH 8.2 and are practically pH independent at higher pH values. An anodic peak at far-off positive potential was observed in the reverse scan, indicating the irreversible nature of the electrode process. Controlled potential electrolysis and coulometric studies gave the value of n as 4.0 ± 0.1 in the pH range 2.5 to 10.0. Out of the two major end products formed, one was identified as sulphanilamide and the other as 1-phenyl-3-methyl-4-amino-2-pyrazolin-5-one on the basis of IR and NMR studies. On the basis of DCP, LSV, CV, CPE, coulometry and spectral analysis, a mechanism has been postulated for the reduction of these compounds at d.m.e. and glassy carbon electrodes. Keywords: polarography, cyclic voltammetry, antibacterials, pyrazolin-5-ones.
Single-crystal absorption spectroscopy of binuclear complexes of iron(III) and manganese(III) with the μ-oxo-bis(μ-acetato)dimetal core
Authors: Pelletier Yanick , Reber Christian
Published: May 2006

Single-crystal absorption spectroscopy at variable temperature is used to determine exchange couplings between transition metal centers in both the electronic ground and excited states in two new homobimetallic complexes with the formula [LM(μ-O)(μ-CH3CO2)2ML′](ClO4)2, where M is iron(III) or manganese(III). L and L' denote 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane, respectively. Values for the ground state exchange coupling constant J are −295 cm−1and +10 cm−1for the iron and manganese compounds, respectively, using Hex = −JS1•S2. Exchange interactions in excited states are qualitatively analyzed, indicating that a spin-forbidden transition of the Fe–Fe binuclear unit occurs with significant intensity by the single-ion mechanism, and not as expected by the Tanabe pair intensity mechanism for spin-forbidden transitions, the dominant mechanism for isoelectronic complexes of manganese(II). Keywords: absorption spectra, exchange interaction, magnetic properties, bimetallic complexes of iron(III), bimetallic complexes of manganese(III)
Subpicosecond vibrational relaxation of the S1 states of azulene and guaiazulene in solution
Authors: Tittelbach-Helmrich Dietrich , Wagner Brian D. , Steer Ronald P.
Published: May 2006

The S1 population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (guaiazulene) in solution have been determined as a function of their initial vibrational energy content, [Formula: see text] using a pump–probe experiment with subpicosecond time resolution. The S1 lifetime of azulene does not depend on [Formula: see text] for energies up to 1760 cm−1, whereas the lifetime of the shorter-lived S1 state of guaiazulene is independent of [Formula: see text] only for energies up to ~1000 cm−1. At higher energies, the lifetime decreases with increasing [Formula: see text] and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S1 state is responsible for the effects observed in guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds. Keywords: pump–probe spectroscopy, azulene, femtosecond processes.
Multisubstituted phthalonitriles, naphthalenedicarbonitriles, and phenanthrenetetracarbonitriles as precursors for phthalocyanine syntheses
Authors: Leznoff Clifford C. , Terekhov Dmitri S. , McArthur Colin R. , Vigh Steven , Li Jing
Published: May 2006

Electrophilic aromatic nitration under mild conditions of 4-hydroxyphthalonitrile gave 4-hydroxy-3-nitrophthalonitrile and 4-hydroxy-5-nitrophthalonitrile, while bromination yielded 3-bromo-4-hydroxyphthalonitrile, 4-bromo-5-hydroxyphthalonitrile, and 3,5-dibromo-4-hydroxyphthalonitrile. Iodination gave 4-hydroxy-5-iodophthalonitrile and 4-hydroxy-3,5-diidophthalonitrile. Coupling of 4-iodophthalonitrile, 3-iodophthalonitrile, and 5-iodo-2,3-dicyanonaphthalene with trans-1,2-bis(tri-n-butylstannyl)ethene gave trans-1,2-bis(3,4-dicyanophenyl)ethene, trans-1,2-bis(2,3-dicyanophenyl)ethene, and trans-1,2-bis(6,7-dicyanonaphthyl)ethene. Photocyclization of a dilute solution of cis- or trans-1,2-bis(3,4-dicyanophenyl)ethene in dioxane gave a 1:1 mixture of 2,3,6,7- and 2,3,5,6-tetracyanophenanthrenes separable by chromatography. Keywords: phthalonitriles, naphthalenedicarbonitriles, phenanthrenetetracarbonitriles, electrophilic substitution.
Family-independent relationships between computed molecular surface quantities and solute hydrogen bond acidity/basicity and solute-induced methanol O–H infrared frequency shifts
Authors: Hagelin Helena , Murray Jane S. , Politzer Peter , Brinck Tore , Berthelot Michel
Published: May 2006

Family-independent relationships between computed molecular surface properties and solute hydrogen bond acidity/basicity and solute-induced methanol O–H infrared frequency shifts are presented. The molecular surface quantities, computed at the ab initio HF/6-31G* level, are primarily related to the electrostatic potential of the molecule, but also include the average local ionization energy on its surface. Keywords: hydrogen bond acidity/basicity, O–H frequency shifts, molecular electrostatic potential.
Structure–activity relationship study of synthetic hydrazines as ecdysone agonists in the control of spruce budworm (Choristoneurafumiferana)
Authors: Mohammed-Ali Anmar K. , Chan Tak-Hang , Thomas Anthony W. , Strunz George M. , Jewett Brent
Published: May 2006

A quantitative structure–activity relationship study was performed for a number of aroylhydrazine compounds with respect to their biological activity against spruce budworm. It was found that the biological activity can be modulated by substituents on the aromatic rings. Substituents with high π value and small L value lead to increase in biological activity. Molecular mechanics calculations were used to explain how the active compounds may mimic the strong-binding Y region of ecdysone. Keywords: spruce budworm, ecdysone, agonist, hydrazines, quantitative structure–activity relationship.
Preparation and properties of rhodium(I) and iridium(I) diolefin complexes of heterodifunctional phosphorus–imine chelating ligands and a related iminophosphine. 103Rh NMR parameters of the rhodium complexes obtained via indirect two-dimensional 31P, 103Rh{1H} NMR spectroscopy
Authors: Law David J. , Bigam Glen , Cavell Ronald G.
Published: May 2006

Treatment of [M(cod)Cl]2 (M = Rh, Ir) with iminophosphoranophosphine ligands of the type Ph2PQP(Ph2)=NSiMe3 (Q = CH2, CH2CH2, 1,2-C6H4) afforded the new metallacycles [Formula: see text] through elimination of Me3SiCl, ultimately "anchoring" the ligand to the metal through a metal–nitrogen σ bond. The phosphine functionality completes the chelate. Cationic complexes of the type [M(cod)L2]+PF6− (M = Rh or Ir; L2 = Ph2PQPPh2NR where Q = CH2, CH(CH3), 1,2-C6H4, and R = p-C6F4CN, C6H2F(NO2)2, and C6H3(NO2)2 or L = Ph2PN=C(H)Ph) were readily prepared by treating [M(cod)Cl]2 with L2 and KPF6. The detection and chemical shift determination of the insensitive 103Rh nucleus was easily accomplished via 31P detected indirect two-dimensional 31P, 103Rh{1H} NMR spectroscopy. The 103Rh, 1H, and 31P NMR data are discussed. Keywords: rhodium, iridium, phosphoranimine, iminophosphine, Rh NMR.
Electrochemistry of polyoxometalates immobilized in ion exchange polymer films
Authors: Kasem Kasem K. , Schultz Franklin A.
Published: May 2006

The polyoxometalate ions PMo12O403−, PW12O403−, and SiW12O404−are incorporated in polymeric ruthenium(II)(vinyl)bipyridine (poly-Ru(vbpy)32+) films from aqueous and dioxane–water electrolytes. Despite their large mass the ions exist as freely diffusing species that compensate for up to 30% of the charge in poly-Ru(vbpy)32+. An investigation of the effect of environmental conditions on electrochemical behavior reveals that the first two one-electron reduction waves of SiW12O404−coalesce into a single two-electron reaction and those of PW12O403−shift significantly in potential upon a change from pure aqueous to 50(v/v)% dioxane/water solvent. The observation is attributed to destabilization of the one-electron reaction products as the solvent is enriched is dioxane. Incorporation of polyoxometalates in protonated poly(vinyl)pyridine and poly-Ru(vbpy)32+films from dioxane–water solvent results in differences in electrochemical behavior. Polyoxometalate anions incorporated in poly-Ru(vbpy)32+films catalyze the electrochemical reduction of hydrogen ion. Keywords: polyoxometalate, electrochemistry, poly-Ru(vbpy)32+, electrocatalysis, immobilization.
Ruthenium carbonyl complexes of the bridging tetradentate ligands Ph4P2N4S2and Ph4P2N4S2Me+
Authors: Chivers Tristram , Hilts Robert W. , Parvez Masood , Ristic-Petrovic Dusan
Published: May 2006

The reaction of Ru(CO)4(C2H4) or Ru(CO)5with 1,5-Ph4P2N4S2in CH2Cl2-hexane at 23 °C produces the dimer [Ru(CO)2(Ph4P2N4S2)]2(4) in 54% and 11% yields, respectively. The treatment of 4 with methyl triflate (1:1 molar ratio) in dichloromethane yields the mono(N-methylated) derivative [Ru2(CO)4(Ph4P2N4S2)(Ph4P2N4S2Me)][CF3SO3] (5) or, in a 1:2 molar ratio, the dimethylated derivative [Ru(CO)2(Ph4P2N4S2Me)]2[CF3SO3]2, which exists as a ca. equal mixture of two symmetrical isomers on the basis of1H and31P NMR, and IR spectra. The reaction of 4 with two equivalents of Me3NO in the presence of acetonitrile generates [Ru(CO)(CH3CN)(Ph4P2N4S2)]2, which is also formed as a mixture of isomers in a ratio of ca. 2:1 on the basis of1H and31P NMR, and IR spectra. The X-ray structure of 4•CH2Cl2shows that the P2N4S2ring is bonded to one ruthenium through two (geminal) nitrogen atoms and the remote sulfur atom while the second sulfur atom acts as a bridge to the other ruthenium. The crystals of 4•CH2Cl2are triclinic, space group [Formula: see text] with a = 12.901(1) Å, b = 13.072(1) Å, c = 10.123(1) Å, α = 100.88(1)°, β = 98.90(1)°,γ = 67.50(1)°, V = 1542.4(3) Å3, and Z = 2. The final R and Rw, values were 0.040 and 0.027, respectively. The X-ray structure of 5 reveals that N-methylation does not significantly perturb the bonding between the heterocyclic ligand and ruthenium. The crystals of 5 are triclinic, space group [Formula: see text] with a = 12.912(6) Å, b = 13.435(7) Å, c = 9.948(3) Å, α = 105.04(3)°, β = 102.85(3)°, γ = 70.74(4)°, V = 1555(1) Å3, and Z = 2. The final R and Rwvalues were 0.063 and 0.071, respectively. Keywords: ruthenium, tetradentate ligand, P2N4S2ring.
Bidentate and terdentate (P-N-S) complexes of a new thioether azine phosphine Z,E-PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4) with molybdenum, tungsten, or platinum
Authors: Perera Sarath D. , Shamsuddin Mustaffa , Shaw Bernard L.
Published: May 2006

Treatment of Z-PPh2CH2C(But)=NNH2 with 4-methylphenylthiomethyl methyl ketone gave the thioether azine phosphine Z,E-PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4) 1, which with H2O2 gave the corresponding phosphine oxide 2. Treatment of 1 with [Mo(CO)3(η6-cht)] or [W(CO)3(NCEt)3] gave the yellow tricarbonyl complexes fac-[M(CO)3{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}] 3a (Mo) or 3b (W), respectively. Treatment of 1 with [Mo(CO)4(nbd)] gave the pale yellow tetracarbonylmolbdenum(0) complex [Mo(CO)4{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}] 4, in which the ligand 1 is bidentate through P and N. Oxidation of either 3a or 4 with 1 equivalent of bromine gave the orange neutral seven-coordinate dicarbonylmolybdenum(II) complex [MoBr2(CO)2{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}] 5, whereas the tungsten complex 3b with 1 equivalent of bromine gave the seven-coordinate tricarbonyltungsten(II) cation [WBr(CO)3{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}]+ isolated as the PF6 salt 6. Treatment of 1 with [PtCl2(NCMe)2]gave the yellow dichloroplatinum(II) complex [PtCl2{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}] 7, in which 1 is bidentate through P and N. When 7 was treated with NH4PF6 in methanol it gave the terdentate salt [PtCl{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}]PF68a. Deprotonation of 7 with NEt3-NaOH gave the orange neutral chloroplatinum(II) complex [PtCl{PPh2-CH2C(But)N-NC(Me)=CHS(C6H4Me-4)}] 9, containing a terdentate ene-hydrazone phosphine ligand. This neutral complex 9 was reprotonated using HBF4 to give the BF4 salt 8b. Treatment of the phosphine 1 with [PtMe2(cod)] gave the white dimethylplatinum(II) complex [PtMe2{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}] 10, containing the bidentate azine ligand. Treatment of 10 with MeI gave the white platinum(IV) iodide salt fac-[PtMe3{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}]I 11a in which the azine is terdentate. When 11a was treated with NH4PF6 in MeOH the PF6 salt 11b was obtained. Treatment of 10 with picric acid gave the yellow methylplatinum(II) picrate salt [PtMe{PPh2CH2C(But)=N-N=C(Me)CH2S(C6H4Me-4)}][OC6H2(NO2)3-2,4,6] 12 and methane. Infrared, 31P–[1H], 1H, and some 13C–[1H] NMRdata are given. Keywords: azine phosphine, thioether, metal-carbonyls, platinum.
Synthesis, characterization, and properties of [Cp*M(NO)(η2-CH2Ph)-(NCMe)]BF4salts (M = Mo, W) and related complexes: the stabilizing influence of benzyl ligands
Authors: Dryden N.H. , Legzdins P. , Sayers S.F. , Trotter J. , Yee V.C.
Published: May 2006

Treatment of orange solutions of Cp*M(NO)(η2-CH2Ph)Cl (M = Mo or W) with an equimolar amount of solid AgBF4in MeCN affords the salts [Cp*M(NO)(η2-CH2Ph)(NCMe)]BF4as analytically pure crystals in good yields. Both orange complexes have been subjected to single-crystal X-ray crystallographic analyses in order to establish their molecular geometries and their intramolecular metrical parameters. Both salts consist of discrete organometallic cations and tetrahedral BF4−anions, the intramolecular dimensions of the two cationic complexes being essentially the same and resembling those found for related Cp*M(NO)-containing compounds. The isolated [Cp*M(NO)(η2-CH2Ph)(NCMe)]+cations are quite electrophilic, being able to abstract Cl−from a NaCl IR cell to revert to their chloro precursors. However, treatment of the [Cp*W(NO)(η2-CH2Ph)(NCMe)]BF4salt with various unsaturated substrates (e.g., diphenylacetylene, 2,3-dimethyl-1,3-butadiene, carbon monoxide, and acetone) in CDCl3results in no detectable chemical reaction. Lewis bases weaker than Cl−evidently cannot displace the acetonitrile ligand from the coordination sphere of the metal or induce the benzyl ligand to diminish its hapticity. Such a diminution does occur for the CH2Ph ligand when the MeCN group in the cationic complexes is replaced by a carboxylate anion to produce neutral Cp′M(NO)(η1-CH2Ph)(η2-O2CR) complexes. The latter complexes are obtainable by treatment of Cp*M(NO)(η2-CH2Ph)Cl with AgO2CR (R = CH(Et)(Ph)) in CH2Cl2and have been fully characterized by conventional spectroscopic methods. Keywords: organomolybdenum, organotungsten, benzyl, cations.
ansa-Metallocene imide niobium compounds
Authors: Chernega Alexander N. , Green Malcolm L.H. , Suárez Alehandra G.
Published: May 2006

The ansa-metallocene imide compounds of niobium {Nb[Me2C(η5-C5H4)(σ-C5H4)](η5-C5H5)(NBut)} and {Nb[Me2C(σ-C5H4)(η3-C9H6)](η5-C5H5)(NBut)} have been prepared and their crystal structures have been determined. Keywords: ansa, metallocene, niobium, cyclopentadienyl.
Synthesis, structure, and nonrigidity of Os4(CO)15, Os4(CO)13(PMe3)[P(OMe)3], and Os4(CO)14(CNBut)
Authors: Einstein Frederick W.B. , Johnston Victor J. , Ma Andrew K. , Pomeroy Roland K.
Published: May 2006

The binary carbonyl Os4(CO)15, 1, has been prepared by the addition of Os(CO)5 to Os3(CO)10(cyclooctene)2 at −15 °C. The related clusters Os4(CO)13(PMe3)[P(OMe)3], 2, and Os4(CO)14(CNBu′), 3, have been synthesized from Os4(CO)13(PMe3) and Os4(CO)15(CNBu′), respectively. The crystal structures of 1, 2, and 3 reveal similar planar metal skeletons with short (2.774 (1) − 2.793 (2) Å) and long (2.978 (2) − 3.019 (2) Å) peripheral Os—Os bonds; the hinge Os—Os bond in 1–3 ranges in length from 2.936 (2) to 2.948 (1) Å. The variable temperature 13C nuclear magnetic resonance spectra of 1 and 3 show that both are highly nonrigid in solution even at −120 °C. The mechanism of nonrigidity is believed to be an all-equatorial, merry-go-round carbonyl exchange. The variable temperature 13C nmr spectra of 2 indicate it is rigid on the nmr time scale in solution at −45 °C. Carbonyl exchange is, however, observed in the spectrum at −6 °C. From the mode of collapse of the signals it is believed that the lowest energy exchange processes in 3 involve axial-equatorial, merry-go-round CO exchanges in the two planes that each contain a short Os—Os bond. Crystallographic data for compound 1: space group C2/c; a = 12.802 (3) Å, b = 10.217 (3) Å, c = 16.380 (5) Å, β = 91.39 (2)°; R = 0.044, 1204 observed reflections. For compound 2: space group P21/c; a = 11.106 (7) Å, b = 16.931 (5) Å, c = 16.481 (5) Å, β = 97.71 (5)°; R = 0.051, 2117 observed reflections. For compound 3: space group P21/n; a = 11.747 (3) Å, b = 18.009 (5) Å, c = 12.448 (2) Å, β = 92.65 (2)°; R = 0.054, 2131 observed reflections. Keywords: osmium, carbonyl, cluster, nonrigidity.
Methine bases in the benzothiazole, benzoselenazole, and quinoline series, and geometry and conformational preferences of their acyl derivatives
Authors: Gupta Ajay K. , Ben-Mahmud Ali , Kamphuis Lisa J. , Mueller Jennifer L. , Rigby Suzie S. , Gibson Martin S. , Richardson Mary Frances , Humeniuk Linda , Walker Stanley
Published: May 2006

Dimeric structures 2a–c are confirmed for the "methine bases" obtained from 2-methylbenzo-thiazolium and -selenazolium salts and aqueous sodium hydroxide, whereas monomeric structures 3 are confirmed for methine bases similarly derived from 2-methylquinolinium salts. The latter monomers dimerize slowly on standing. Monomeric methine bases 6–9, too hindered to dimerize, are described. 2-Acetonylidene-2,3-dihydro-3-methylbenzothiazole 10a and related compounds are assigned (Z) configurations on the basis of NOE difference spectra. Molecular mechanics calculations predict a slightly higher steric energy for the observed s-cis conformer of 10a than for the s-trans, indicating a stabilizing [Formula: see text] interaction in the s conformer that need only be a few kJ mol−1 in magnitude. For the quinolines 13a and b, the (E) configuration/s-cis conformation is favoured. The dielectric absorption method provides a rotational energy barrier of approximately 60 kJ mol−1 for acetyl group relaxation in 10a. Oxygen–sulfur exchange is observed in the conversion of 10a to 12a by thioacetic acid. Keywords: conformation, configuration, heterocyclic compounds, [Formula: see text] interaction.
A study of the negative ion FABMS of tris(perfluorophenyl)phosphine and related compounds: matrix effects
Authors: Saraswathi Mandapati , Miller Jack M. , Jones Tim R.B.
Published: May 2006

The mass spectra of tris(perfluorophenyl)phosphine obtained under negative ion Fast Atom Bombardment conditions showed formation of an unusual ion at m/z 397 attributed to ((C6F5)2PO2)−. The matrix effects involved in this reaction are discussed. Negative ion FAB spectra of tris(perfluorophenyl)arsine and tris(perfluorophenyl)stibine are also reported. Keywords: pentafluorophenylphosphine, -arsine, -stibine; negative ion FABMS; matrix effects.
1-Deoxy-D-xylulose
Authors: Kennedy Isaac A. , Hemscheidt Thomas , Britten James F. , Spenser Ian D.
Published: May 2006

1-Deoxy-D-xylulose (= 1-deoxy-D-theropentulose) is a precursor of thiamin (Vitamin B1) and of pyridoxine (Vitamin B6) in bacteria. The synthesis of a [2,3-13C2] bond-labeled sample of the compound, to be used for investigations of the biosynthesis of the two vitamins, is described. In aqueous solution 1-deoxy-D-xylulose exists mainly as the open chain ketone. In methanol solution the compound exists as a mixture of the open chain ketone and the two corresponding epimeric furanoses. In acid solution the compound yields a dimeric anhydride, di-β-1-deoxy-D-xylulofuranose 2,3′:3,2′-dianhydride, whose structure was established by X-ray crystallography. Keywords: [2,3-13C2]-1-deoxy-D-xylulose, di-β-1-deoxy-D-xylulofuranose 2,3′:3,2′-dianhydride, 5-O-benzyl-3,4-O-isopropylidene-1-deoxy-D-xylulose, 4-O-benzyl-2,3-O-isoproylidene-D-threose.
Electrochemical and spectroscopic behavior of trifluoromethylacetophenone in aqueous and micellar medium
Authors: Liotier Elodie , Mousset Guy , Mousty Christine
Published: May 2006

The electrochemical behavior of 4-trifluoromethylacetophenone (TFMA) has been studied in aqueous (2 ≤ pH ≤ 10), micellar, and ethanolic solutions using polarographic techniques. A slow hydration process of the carbonyl group has been observed by means of polarography and UV–visible spectrophotometry. Besides the well-known pH dependence of the electroreduction of aromatic ketones, C—F bond cleavages concomitant to the ketone reduction occur under electrolysis conditions in alkaline medium (pH = 10) at a very negative potential (−1.7 V), leading to the formation of 4-methylacetophenone, which is reduced at this potential with formation of the carbinol and of symmetrical and dissymmetrical pinacols. Finally, the reduction of TFMA has been performed in the presence of chiral surfactants in order to test their ability to induce an asymmetric induction. Keywords: 4-trifluoromethylacetophenone, 4-methylacetophenone, electroreduction, micellar medium, chiral surfactants, hydration, C—F bond fission.
Organic nitrates, thionitrates, peroxynitrites, and nitric oxide: a molecular orbital study of the (X = O, S) rearrangement, a reaction of potential biological significance
Authors: Cameron Dale R. , Borrajo Alison M.P. , Thatcher Gregory R.J. , Bennett Brian M.
Published: May 2006

The rearrangement of organic thionitrate to sulfenyl nitrite potentially mediates the release of nitric oxide from organic nitrates, such as nitroglycerin, in the presence of thiol. The biological activity of these nitrovasodilators is proposed to result from release of nitric oxide in vivo. The thionitrate rearrangement bears analogy to the rearrangement of peroxynitrous acid to nitric acid, which has been proposed to mediate the biological toxicity of nitric oxide and superoxide. In this paper, the two concerted rearrangement processes and competing homolytic reactions are explored using molecular orbital calculations at levels up to MP4SDQ/6-31G*//MP2/6-31G*. Examination of structure and energy for all conformers and isomers of RSONO2 (R = H, Me), models for organic thionitrates and their isomers, demonstrates that structures corresponding to thionitrates and sulfenyl nitrates are of similar energy. Free energies of reaction for homolysis of these compounds are low (ΔG0 < 19 kcal/mol), whereas the barrier for concerted rearrangement is large (ΔG≠(aq.) = 56 kcal/mol). The larger barrier for concerted rearrangement of peroxynitrous acid to nitric acid (ΔG≠(aq.) = 60 kcal/mol) again compares unfavourably with homolysis (ΔG0 < 11 kcal/mol for homolysis to NO2 or •NO). The transition state structures, confirmed by normal mode and intrinsic reaction coordinate analysis, indicate that considerable structural reorganization is required for concerted rearrangement of the ground state species. These results suggest that concerted rearrangement is not likely to be a viable step in either biological process. However, rearrangement via homolysis and radical recombination may provide an energetically accessible pathway for peroxynitrous acid rearrangement to nitric acid and rearrangement of thionitrate to sulfenyl nitrite. In this case, NO2 will be a primary product of both reactions. Keywords: thionitrate, nitric oxide, peroxynitrite, nitrovasodilator, nitrate.
Photo-initiated and thermal curing of epoxides by the use of photo-base generators bearing acyloxyimino groups
Authors: Ito Ken-ichi , Shigeru Yoshitaka , Kawata Yu-uichi , Ito Katsuhiko , Tsunooka Masahiro
Published: May 2006

The formation of amines by the photolysis of O-acyloximes derived from acetophenone oxime, benzophenone oxime, fluorenone oxime, and 2-acetonaphthone oxime and the curing of epoxides by the resulting amines were investigated. The quantum yields of their photolysis at 366 nm in polystyrene films depend on their structures, and those for bifunctional ones bearing phenyl or naphthyl moieties were found to be very high, at 0.88 and 0.76, respectively. The yields of the resulting amines in polymer matrices were higher than those in solution. The yields for O-acyloximes bearing a naphthyl moiety were ca. 90% and higher than for those bearing a phenyl moiety. Although the resulting amines were efficient photo-cross-linkers for poly(glycidyl methacrylate), they were not effective for curing of epoxy resins (oligomers). On the other hand, polymer amines with a glass transition temperature lower than room temperature, which were obtained by the photolysis of copolymers bearing acyloxyimino groups, were found to be effective photo-cross-linkers for the epoxy resins. Keywords: photo-base generator, acyloxyimino group, photo-initiated and thermal curing, poly(glycidyl methacrylate), epoxy resin.
Chain exchange kinetics of diblock copolymer micelles studied by nonradiative energy transfer. 1. Experimental design and theory
Authors: Liu Guojun
Published: May 2006

A fluorescence experiment involving mixing donor-labeled micelles with acceptor-labeled unimers has been designed and a kinetic scheme for describing such an experiment has been proposed. An approximate analytical solution was found for the decrease in the donor fluorescence intensity at time t after sample mixing relative to that at time zero, I(t)/I(0). Treating the data of this decrease in donor fluorescence intensity as a function of time using the derived equation allows the simultaneous determination of the rate constant kn for unimer incorporation into micelles and the quenching efficiency φ of donor fluorescence by an acceptor in a micelle. Keywords: polymer micelles, dynamics, chain exchange, energy transfer.
Solvent effect on the photophysics of bisphenol-A-based polycarbonate and diphenylcarbonate
Authors: Hoyle Charles E. , Rufus Isaac B. , Shah Himanshu
Published: May 2006

Polycarbonate and diphenylcarbonate exhibit an anomalous fluorescence emission with peak maximum around 350 nm in polar solvents that may be attributed to the association of diarylcarbonate moieties in a polar solvent cage. The red-shifted emission is attributed to intermolecular interactions in polar solvents and intramolecular interactions in polycarbonate. The photophysical behavior of polycarbonate and diphenylcarbonate is different from that of 1,3-diphenylpropane where a red-shifted emission is due to excimers formed by phenyl groups separated by three carbon atoms and is independent of the polarity of the solvent. Keywords: diphenylcarbonate, polycarbonate, aggregates, photophysics.
1H nuclear magnetic resonance and molecular orbital studies of 2-formylstyrene. Three significant nonplanar conformers at 300 K
Authors: Schaefer Ted , Kroeker Scott , McKinnon David M.
Published: May 2006

The 1H nuclear magnetic resonance spectra of 2-formylstyrene, from dilute solutions in CS2–C6DI2 and acetone-d6, are analyzed to yield precise chemical shifts and spin–spin coupling constants. The long-range coupling constants imply a conformational distribution in which the O-trans conformer is 55% abundant in both polar and nonpolar environments. They also imply that the vinyl group, on average, is twisted out of the aromatic plane to a much larger extent than in styrene. The 6-31G* basis set gives an ab initio potential for the torsion of the vinyl moiety with a relatively deep minimum at 38° out-of-plane, for the O-cis conformer. For the O-trans conformer, two minima are found, one at 45° and another at 129.6°. Essentially the same potential is obtained with the 6-31G** basis. The latter corresponds to a close approach of the hydrogen atom of the formyl group and π orbitals or the β-carbon atom of the olefinic side chain. This local minimum is interesting in terms of a hypothesis used to explain the photochemistry of the molecule. The long-range coupling constants are consistent with the conformational properties calculated for the free molecule; they also indicate no significant difference between the conformational behaviour of the molecule in the two solvents. A proximate coupling constant of −0.16 Hz exists between the formyl and methine (α) protons. The latter is strongly deshielded in the presence of the formyl group, so that it becomes even less shielded than some of the aromatic protons. Keywords: 1H NMR, 2-formylstyrene (o-vinylbenzaldehyde); long-range spin–spin coupling constants, 2-formylstyrene; conformations, three nonplanar of 2-formylstyrene; molecular orbital calculations, conformations of 2-formylstyrene.
Électrons en excès dans les milieux polaires homogènes et hétérogènes
Authors: Bernas Annette , Ferradini Christiane , Jay-Gerin Jean-Paul
Published: May 2006

A review of our present knowledge concerning the solvation of excess electrons e−exc → e−solv produced by photoionization or radiolysis in polar media has been attempted. Various properties of the solvated electron (proposed solvation mechanisms, structure, physicochemical characteristics) are considered. In spite of some similarities, e−solv does not seem to be a good prototype for solvated halide anions. The behavior of e−exc in heterogeneous model systems, such as micellar solutions and molecular clusters, is described and correlated with that observed in homogeneous media. Key words: excess electrons, homogeneous and heterogeneous polar media, photoionization, radiolysis, solvation, charge transfer to solvent, properties of the solvated electron, micellar solutions, molecular clusters, comparison with the solvation of anions.
Electrochemically induced chain reactions: the addition of fluorene and indene to aromatic aldehydes initiated by electrochemical reduction
Authors: Gard J. C. , Hanquet B. , Roullier L. , Mugnier Y. , Lessard J.
Published: May 2006

The electrochemical reduction at −30 °C of 2,6-dichlorobenzaldehyde (1a), benzaldehyde (1b), and terephthalaldehyde (2) in tetrahydrofuran with tetrabutylammonium perchlorate as supporting electrolyte, under an argon atmosphere and in the presence of fluorene or indene, gives carbinols resulting from the addition of fluorene or indene and requires only a catalytic amount of electricity. The chain reaction is initiated by proton abstraction from fluorene or indene by a base electrogenerated by reduction of the aldehyde and the propagation involves the addition of the carbanion to the aldehyde followed by regeneration of the nucleophile by proton transfer from the proton donor to the alkoxide anion (base-catalyzed addition). The voltammetric behavior of the aldehydes in the absence and in the presence of fluorene or indene is also presented. Key words: electrochemical reduction, aromatic aldehydes, addition of fluorene (indene), base catalysis, chain reaction.
SCF-MO computational analysis of the geometric conformation and charge distribution in picric acid and alkali picrate salts
Authors: Zimpel Zbigniew , Nelson Barbara R. , Weil John A.
Published: May 2006

SCF-MO computations were employed in a study of picric acid, the –1 picrate ion, and Li, Na, and K picrates. Atomic coordinates from crystallographic structural analyses were used as initial parameters in the computation of the minimum-energy conformations of each free molecule at the 6-31G level. The Mulliken charge numbers for each atom in the optimized model molecules were calculated at the 6-31G** level. The induction and resonance effects of the OX group (X = H, Li, Na, K) on the trinitrophenyl ring are discussed. It is demonstrated that molecular (electron) isodensity surfaces (MIDCOs) describe charge-density results nicely compatible with the point Mulliken charge numbers. Key words: picrates, SCF-MO, charge distribution.
Radiation-induced dissolution of chromium oxide in aqueous solutions
Authors: Rodenas Luis García , Chocrón Mauricio , Morando Pedro J. , Blesa Miguel A.
Published: May 2006

Gamma irradiation of suspensions of a commercial sample of α-Cr2O3 in the presence of KBrO3 in the concentration range 0.1 ≤ [BrO3−] ≤ 0.4 mol dm−3, at pH 4 and 25 °C brings about oxidative dissolution. Release of Cr(VI) to the solution proceeds at a constant rate that increases with bromate concentration, even in conditions of quantitative eaq− scavenging. A mechanism of reactions is proposed in which OH and BrO2 radicals oxidize surface Cr(III) to Cr(IV), and ionic release is achieved by oxidation of surface Cr(IV) by bromate. The corresponding set of equations was solved by a rigid method for the integration of ordinary differential equations, using these two heterogeneous rate constants as adjustable parameters. The calculated profiles are in close agreement with the experimental data. Key words: chromium oxides, radiation-induced dissolution, oxidation dissolution.
Wavelength dependence and solvent effects on the ligand field photochemistry: the ring closure process in the excited [Fe(CN)5(tn)]3− complex
Authors: Lima Jailson Farias De , Iha Neyde Yukie Murakami
Published: May 2006

The solvent composition and wavelength effects on the quantum yield of the photoinduced ring closure process of the [Fe(CN)5(tn)]3− complex (tn = 1,3-diaminopropane) were investigated. The reactivity was shown to be controlled by the macroscopic properties of water–glycerol mixtures. A sharp decrease in quantum yields with increasing medium viscosity was observed for all the irradiation wavelengths employed (313, 334, 365, 404, and 434 nm). The observed quantum yields ranged from 0.24 (λirr = 313 nm, 66.48 wt.% of acetonitrile) to 0.010 (λirr = 404 or 434 nm, 61.85 wt.% of glycerol). The overall efficiency is a complex function of the dynamics of radical recombination and dissociation pathways. The proposed cage model for the deactivation dynamics of the excited states illustrates that the decrease in medium viscosity favors a diffusional escape of the cyanide from the solvent cage. Key words: photochemistry, pentacyanoferrate(II) complexes, solvent effect, wavelength effect.
Asymmetric synthesis of taxol arid taxotère side chains by enolate hydroxylation
Authors: Hanessian Stephen , Sancéau Jean-Yves
Published: May 2006

We report an asymmetric synthesis of the taxol and taxotère side chains by hydroxylation of enolates derived from N-substitued methyl 3-amino-3-phenyl propionate with the oxodiperoxymolybdenum (pyridine) (hexamethyl phosphoric triamide) complex (MoOPH). Key words: taxol and taxotère side chains, hydroxylation.
Dissociation constants of host–guest complexes of alkyl-bearing compounds with β-cyclodextrin and "hydroxypropyl-β-cyclodextrin"
Authors: Tee Oswald S. , Gadosy Timothy A. , Giorgi Javier B.
Published: May 2006

Dissociation constants (Kd) of host–guest complexes formed from β-cyclodextrin or "hydroxypropyl-β-cyclodextrin" (β-CD and Hp-β-CD) and several types of aliphatic guests (alcohols, alkanesulfonate ions, alkylamines, and α-amino acids), with up to eight carbons in a chain, are reported. These constants were determined by inhibition kinetics and by a spectrofluorometric displacement method based on competition with 1-anilino-8-naphthalenesulfonate ion as a fluorescent probe. The value of Kdfor a particular amine is close to that for the corresponding alcohol. For linear alkyl derivatives, there are strong correlations between pKd(= −log Kd) and the chain length of the guest, with slopes around 0.5, complementing trends that were noted earlier. Furthermore, the strengths of binding of various aliphatic derivatives to β-CD and to Hp-β-CD are close, with Kdvalues for the two CDs usually being within a factor of 2 of each other. Overall, for the binding of over 50 alkyl-bearing derivatives, there is a good correlation of pKdfor Hp-β-CD with that for β-CD, with unit slope. These observations imply that the binding of simple aliphatic guests to Hp-β-CD is not greatly influenced by the modification of the hydroxyl groups on the primary side of the β-CD cavity but this may not be true for longer aliphatic derivatives (>C8) or for aromatics that penetrate farther into the CD cavity. Key words: cyclodextrins, host–guest complexes, dissociation constants.
The 1,2,3,5-ditelluradiazolyl [HCN2Te2] species. Theoretical characterizations of the cation, radical, and radical dimers
Authors: Davis William M. , Goddard John D.
Published: May 2006

Dithia- and diselena-diazolyl radicals (HCN2E2 E = S, Se) and dimers are important building blocks in the design of low-dimensional molecular conductors. Research on the tellurium-based analogues is much rarer. This work reports the molecular and electronic structures of the cation, radical, and radical dimers of 1,2,3,5-ditelluradiazolyl using ab initio theory including electron correlation by Møller–Plesset perturbation theory up to partial fourth order (MP4SDQ). A face-to-face C2v dimer is predicted to be bound with respect to two radicals by approximately 18 kcal/mol. A C2h, dimer also has been studied and is ca. 2 kcal/mol less stable than the C2v conformer. Relaxing symmetry constraints on the dimers led to more energetically stable structures at the Hartree–Fock level but the C2v structure remains the most stable at a level of theory including electron correlation effects. The results for the Te compounds along with our earlier research on the S and Se analogues provide predictions for the geometries, vibrational frequencies, and ionization potentials for the Te species to assist in future experiments. Key words: tellurium, ab initio, ditelluradiazolyl, dimers, binding.
Solvent isotope effects as a probe of general catalysis and solvation in phosphoryl transfer
Authors: Bryan Clinton D. , Schowen K. Barbara , Schowen Richard L.
Published: May 2006

Phosphoryl transfer to methanol from tris(p-nitrophenyl) phosphate (PNNN), methyl bis(p-nitrophenyl) phosphate (PMNN), and dimethyl p-nitrophenyl phosphate (PMMN) exhibits general base catalysis by acetate ion but no detectable catalysis by acetic acid. For PNNN, acetate catalysis produces normal solvent isotope effects kROH/kRODof 1.68 ± 0.01 at high ionic strength (0.475) and 1.77 ± 0.04 at low ionic strength (0.048). A linear proton inventory indicates most simply that the isotope effect arises from a one-proton catalytic bridge in the transition state, although this model cannot strongly be distinguished from a generalized solvation effect. Reactions of methoxide ions produce slight inverse isotope effects kROD/kROHof 1.1–1.2, far smaller than the inverseeffect of about 2.5 expected for complete and uncompensated desolvation of the reactant-state methoxide ion. The transition state is thus stabilized by substantial interaction with the solvent. The proton inventory for the least reactive substrate PMMN (relative rate constant 1) is suggestive of transition-state stabilization by a combination of one-proton catalytic bridge(s) and distributed sites, while the proton inventory for the most reactive substrate PNNN (relative rate constant 1388) suggests only generalized transition-state solvation (many distributed sites); the proton inventory for PMNN, a substrate of intermediate reactivity (relative rate constant 60), suggests an intermediate situation. The data are consistent with a model in which transition states with exterior concentrations of charge favor stabilization of the charge by isotope-fractionating one-proton bridges, while transition states with distributed charge favor stabilization of the charge by many distributed sites. Key words: phosphoryl transfer, proton inventories, solvent isotope effects.
On the stability of endoliedral rare gas fullerenes
Authors: Clougherty Dennis P.
Published: May 2006

The stability of He@C60 and Ne@C60 is discussed in the context of a spherical model where the carbon atoms are smeared out into a uniform shell. The electronic properties of the 60 π-electrons together with those of the central atom are treated in the Thomas–Fermi approximation. Simple electrostatic reasoning elucidates the nature of the radial stability of the complex. A method to include nonspherical corrections is outlined. Possible bonding topologies of the central atom and the C60 cage are discussed, as well as the relevance of these topologies to incipient central atom distortions. Key words: fullerenes, Thomas–Fermi, dopeyball, He@C60, Ne@C60.
The topology of the valence shell and the electric field gradient at the nitrogen nucleus in aziridines
Authors: Rosillo Félix , Aray Yosslen , Rodríguez Jesús , Murgich Juan
Published: May 2006

The ab initio molecular charge density ρ(r) of substituted aziridines was calculated at the MP2 level for R = -H, -CH3, -CF3, -Cl, -NO2, -CN, -OH, -NO, and -F. The use of the topology of the Laplacian of ρ(r) allowed the analysis of the electric field gradient (EFG) at the nitrogen nucleus directly in terms of its valence shell charge concentration. The EFG changed sign and the orientation of its y- and z-axes with respect to aziridine when R = -Cl, -NO2, -CN, -OH, -NO, and -F. The changes in the EFG in these aziridines upon substitution were correlated with those calculated in the valence charge concentrations along the direction of the N—R bond. The sign of the qzz component and the orientation of the principal axes of the EFG tensor were found to be determined by the relative value of the contributions from the charge concentrations at the points in the valence shell along the N—C and N—R bond directions. Key words: molecular charge distribution, aziridines, Laplacian of the charge density, electric field gradient.
Zirconium complexes of a cyclopentadienyl-amido ligand with a pendant amine donor via amine and alkane elimination
Authors: Mu Ying , Piers Warren E. , MacQuarrie Donald C. , Zaworotko Michael J.
Published: May 2006

Zirconium complexes of the multidentate ligand CpHNMeSiN(H)R (SiNR = -SiMe2N-t-butyl; NMe = -CH2CH2NMe2, 1) were prepared and characterized via amine and alkane elimination procedures. Reaction of 1 with Zr(NMe2)4 gave a mixture of bis-amido complexes 2 in which the ligand was 1,2 and 1,3 substituted. This mixture was converted to the analogous dichlorides 3 using Me2NH•HCl and 1,3-3 was purified at this stage; alternatively, 1,3-3 was obtained in one pot from 1 and Zr(NMe2)4 in ≈70% yield. Conversion of 1,3-3 to dimethyl compound (CpNMeSiNR)Zr(CH3)2, 1,3-4, was accomplished via reaction of the dichloride with methyllithium; methide abstraction with the Lewis acids B(C6F5)3 and [Ph3C]+[B(C6F5)4]− generated the cationic alkyls [(CpNMeSiNR)Zr(CH3)]+[R′B(C6F5)3]− (R′ = CH3, 6a; C6F6, 6b), which were characterized by NMR spectroscopy. Zirconium complexes containing 1 ligated as its 1,2 isomer were obtained from alkane elimination reactions between 1 and in situ prepared RnZrCl4−n (R = CH3, n = 3; R = CH2SiMe3, n = 2). 1,2-3 and the methyl chloride complex 1,2-(CpNMeSiNR)Zr(CH3)Cl, 5, were obtained in 18 and 30% yield, respectively. Complex 5 was characterized by X-ray crystallography (monoclinic, space group P21/a, a = 9.6951(10) Å, b = 14.3794(16) Å, c = 14.364(3) Å, V = 1990.3(5) Å3, Z = 4, R = 0.046, Rw = 0.041.) Key words: amine elimination, Cp-amido, zirconium complexes.
Oxidation pathways of hydroxydopamines and their chloride and bromide salts: an electrochemical study in acidic solutions
Authors: Kokkinidis Georgios , Papoutsis Achilleas , Coutouli-Argyropoulou Evdoxia
Published: May 2006

The anodic oxidation of 6-hydroxydopamine and 5-hydroxydopamine and their chloride and bromide salts was studied in aqueous acidic solutions. The electrodes used were Pt and Pt/M (UPD) (M = Bi, Tl, Pb) modified surfaces. The electrochemical studies revealed that the first two-electron oxidation leads to formation of reactive quinoid intermediates. Reactions of these quinoid intermediates with nucleophiles yield substituted quinones that are not stable in solution. The reactions are initiated by the oxidation of the third hydroxyl group at more positive potentials. Cyclic voltammetry and rotating ring-disc electrode voltammetry were used to elucidate the reaction mechanisms. These techniques provide powerful tools to generate and detect transient intermediates and products and give valuable information regarding the pathways and mechanisms of the redox reactions. Key words: 6-hydroxydopamine, 5-hydroxydopamine, voltammetry, electrolysis, oxidation mechanism, nucleophilic attack.