bluuebunny/crossref_metadata_2025 huggingface dataset:
Some reactions of ferrocenyl phosphines with M3(CO)12 (M = Fe, Ru). The structures of Ru3(CO)11(PFcPh2) and Ru3(CO)10{(PPh2-η-C5H4)2Fe}
Authors: Chacon Stephanie T. , Cullen William R. , Bruce Michael I. , Shawkataly Omar Bin , Einstein Frederick W. B. , Jones Richard H. , Willis Anthony C.
Published: May 2006

Substitution reactions of M3(CO)12 (M = Fe, Ru) and Ru4((μ-H)4(CO)12 involving a range of ferrocenyl phosphines are described. Compounds isolated and characterized include Fe3(CO)11PFcPh2, Fe3(CO)10(PBuFcPh)2, Fe(CO)4L (L = PFc2Ph, PFc3), Ru3(CO)11L (L = PFc3, PFc2Ph, PFcPh2), Ru3(CO)10L2 (L = PFc2Ph, PFcPh2), and Ru(CO)4PFc3. Ru4((μ-H)4(CO)10 (L—L) and Ru3(CO)10(L—L) result from reactions with L—L = (Ph2PC5H4)2Fe. The structure of two derivatives are described. Crystals of Ru3(CO)11(PFcPh2) are triclinic, space group P-1, a = 8.576(1), b = 11.150(2), c = 9.160(3) Å, α = 76.65(1), β = 80.75(1), γ = 72.02(1)°, Z = 2, final RW = 0.027 from 3144 observed reflections. Ru3(CO)10(Ph2PC5H4)2Fc, monoclinic crystals, space group C 2/c, a = 17.005(2), b = 18.411(1), c = 14.961(1) Å, β = 117.112(8)°, Z = 4, final RW = 0.023 from 2395 observed reflections. Keywords: ferrocenylphosphines, ruthenium carbonyl derivatives, structures, synthesis, iron carbonyl derivatives.
1H–1H internuclear distance measurements in carbohydrates: proton transient nuclear Overhauser enhancement and spin-lattice relaxation in (13C)- and (2H)-substituted compounds
Authors: Kline Paul C. , Serianni Anthony S. , Huang Shaw-Guang , Hayes Michael , Barker Robert
Published: May 2006

Proton transient nuclear Overhauser enhancement (TnOe) and spin-lattice relaxation times (T1) have been used to evaluate the conformations of several monosaccharides and disaccharides containing (13C) and (2H) substitution. Absolute 1H–1H internuclear distances were determined by TnOe and DESERT (deuterium substitution effects on relaxation times) experiments on conformationally rigid methyl β-D-galactopyranoside and α- and β-D-xyloses, respectively. The DESERT method was extended to examine O-glycoside conformation in two blood-group disaccharides that were prepared enzymically with (13C) and (or) (2H) substitution. Preferred disaccharide conformations deduced from these distance measurements are compared to those determined from 13C–13C and 13C–1H spin coupling constants, theoretical calculations, and crystallographic studies. Keywords: TnOe, DESERT, carbohydrate conformation.
Synthesis of chromanes using pyruvic acid dimethylhydrazone dianion
Authors: Tapia I. , Alcázar V. , Morán J. R.
Published: May 2006

Chromanes were prepared in medium yield from methyl salicylate and the dianions of pyruvic or α-oxobutyric acid dimethylhydrazones. Keywords: chromane, pyruvic acid, dimethylhydrazone, dianion.
New precursors for organometallic chemical vapor deposition of rhodium
Authors: Kumar R. , Puddephatt R. J.
Published: May 2006

The η-cyclopentadienyl (Cp) and η-allyl (C3H5) complexes [RhCp(CO)2], [RhCp(cod)] where cod = 1,5-cyclooctadiene, [Rh(η-C3H5)(CO)2], and [Rh(η-C3H5)3] have been shown to be useful precursors for the chemical vapour deposition (CVD) of rhodium films. The rhodium films contain carbon impurities but these can be greatly reduced if CVD is carried out in the presence of hydrogen. The films adhere well to a silicon substrate. The pyrolysis of [RhCp(CO)2] gives CO and [Rh2Cp2(CO)2(μ-CO)] and [Rh3Cp3(μ-CO)3] at intermediate stages. Pyrolysis of [Rh(η-C3H5)3] or [Rh(η-C3H5)(CO)2] gives 1,5-hexadiene as the only organic product, but similar pyrolysis in the presence of hydrogen gives much propene as well as 1,5-hexadiene. Key words: rhodium, deposition, allyl, cyclopentadienyl.
Activity coefficients of NaCl in NaCl–NaOAc–H2O at 25, 35, and 45 °C
Authors: Manohar S. , Ananthaswamy J.
Published: May 2006

The activity coefficients of NaCl were estimated by measuring the EMFs of the cell[Formula: see text]at four ionic strengths, i.e., 0.5, 1.0, 2.0, and 3.0 mol/kg and at temperatures 25, 35, and 45 °C. The results were analyzed in terms of Harned's rule, the Pitzer and Rush–Johnson–Scatchard treatments. Osmotic coefficients and excess free energies of mixing were calculated at all ionic strengths and temperatures studied. Key words: activity coefficients, sodium chloride, sodium acetate, Pitzer formalism, Scatchard equation.
Solvent structure effects on solvated electron reactions in mixed solvents: positive ions in 1-propanol/water and 2-propanol/water
Authors: Peiris Sedigallage A. , Freeman Gordon R.
Published: May 2006

In models of the kinetics of chemical reactions in solution the solvent is commonly assumed to be a uniform continuum. An example is the Smoluchowski–Debye–Stokes–Einstein equation for the rate constant k2 of a bimolecular reaction between charged or polar species:[Formula: see text]where κ is the probability that a reactant encounter pair will react, R is the gas constant, T is the temperature, f is a factor that reflects the effect of electrostatic interaction between the reactants on their probability of attaining the closeness of approach rr at which reaction occurs, η is the solvent viscosity, and rd is the effective radius of the reactant entities for mutual diffusion. The equation is useful in evaluating effects of bulk fluid properties on reaction rates. Residual effects are attributed to more specific solvent behaviour.Rate constants k2, activation energies E2, and pre-exponential factors A2 of reactions of solvated electrons [Formula: see text] with [Formula: see text] [Formula: see text] and [Formula: see text] ions vary with the composition of 1-propanol/water and 2-propanol/water mixed solvents. Plots of k2η/fT against solvent composition are nonlinear and change with the solvent pair and with reactant pair. Measured molar conductivities [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] indicate that the values of rd for the mutual diffusion of the cations and anions have a minimum near 90 mol% water, and that the values in pure propanol-1 or −2 (150–190 pm) are larger than those in pure water solvent (26 pm for [Formula: see text] 70 pm for the metal ions). The liquid structure influences both the rate of diffusion and the probability of reaction of a reactant encounter pair. Key words: alcohol/water mixed solvents, positive ions, reaction kinetics, solvated electron, solvent effects.
The direct electrochemical synthesis of the novel copper(I) complex Cu2[OC6Cl4(OH)]2[(C6H5)2PCH2P(C6H5)2]2
Authors: Annan Theodore A. , Kickham James E. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of copper in an acetonitrile solution of an aromatic diol (R(OH)2 = catechol, tetrachloro-1,2-dihydroxybenzene, 2,2'-dihydroxybiphenyl) gives soluble copper(I) products which are reduced to copper at a platinum cathode. In the presence of R(OH)2 + L (L = 2,2'-bipyridine, triphenylphosphine, bis(diphenylphosphino)methane (= dppm)), the products are adducts of copper(I) species in which the anionic ligand is [R(O)OH]−. The crystal structure of Cu2[OC6Cl4(OH)]2(dppm)2 is triclinic, with a = 22.418(5) Ǻ b = 1.784(4) Ǻ, c = 13.492(4) Ǻ, α = 61.63(2)°, β = 86.66(2)°, γ = 80.61(2), V = 3093(2) Ǻ3, Z = 2, and space group [Formula: see text] The molecule consists of a Cu—P—C—P—Cu—P—C—P ring, with copper ligated by [R(O)OH]− groups external to this. Intramolecular O—H—O hydrogen-bonding contributes to the stabilization of this novel complex. Key words: Copper, electrochemical synthesis, hydrogen bonding, aromatic diols, crystal structure.
Reactions of silanes with bis(cyclopentadienyl)dialkylzirconium complexes
Authors: Mu Ying , Aitken Clare , Cote Bruno , Harrod John F. , Samuel Edmond
Published: May 2006

A systematic comparison between the dimethylzirconocene (DMZ) and dimethyltitanocene (DMT) catalyzed dehydrocoupling of organosilanes is reported. The polymerization rates of primary silanes are about ten times faster for DMZ than for DMT, but the characteristics of the polymers produced are essentially identical. Variations of molecular weight and molecular weight distribution with varying monomer and reaction time, and the relative amounts of linear and cyclic polymer are also essentially the same for the two catalysts.Oligomerizations of phenylmethylsilane, diphenylsilane, and 1,2-diphenyldisilane are described. The compound Cp2Zr(SiPhMeH)(μ-H)2(SiPhMe2)ZrCp2 (1b) is isolated from the reaction of phenylmethylsilane with DMZ and its structure confirmed by crystallography and 1H-NMR spectroscopy. The compound Cp2Zr(Me)(μ-H)2(SiPh2H)ZrCp2 (1d) is isolated from the reaction of diphenylsilane with DMZ and its structure assigned by NMR spectroscopy. A number of other hydride bridged species are observed by 1H-NMR in the reactions of DMZ with phenylmethyl-, diphenyl-, and n-butylmethylsilanes and their structures are tentatively assigned. The implications of these observations on the mechanism of transformation of DMZ into active catalyst and our current views of the polymerisation mechanism are also discussed. Key words: silanes, dehydrocoupling, titanocene, zirconocene, polysilanes.
Polar trifluoromethylation reactions: the formation of bis(trifluoromethyl)iodine(III) compounds and trifluoromethyl iodine(III) cations and anions
Authors: Tyrra Wieland , Naumann Dieter
Published: May 2006

IX3 (X = Cl, OCOCF3, ONO2) reacts with Cd(CF3)2 complexes or Bi(CF3)3 to yield the corresponding CF3IX2 derivatives. 19F nuclear magnetic resonance spectroscopic evidence is found for [I(CF3)2]+ and I(CF3)2X (X = Cl, OCOCF3) in the reactions of CF3IX2 with Cd(CF3)2 complexes. During the reaction of CF3IF2 and Hg(CF3)2 the new species I(CF3)2F and cis-[I(CF3)2F2]− are identified by nuclear magnetic resonance spectroscopy. The reactions proceed under polar conditions and can be accelerated by the addition of a Lewis acid such as BF3, B(OCOCF3)3, or Sb(V) compounds. Difluoromethyl compounds are formed as by-products. Key words: polar trifluoromethylations, trifluoromethyl iodine(III) compounds, difluoromethyl group formation.
Sense of sequential 1,5-sigmatropic rearrangements of dimethyl-3,3-dialkyl-3H-pyrazole-4,5-dicarboxylates. Crystal and molecular structures of two dimethyl-4,5-dialkyl-1H-pyrazole-1,3-dicarboxylates
Authors: Frampton Christopher S. , Majchrzak Michael W. , Warkentin John
Published: May 2006

3,3-Dialkyl-3H-pyrazole-4,5-dicarboxylic acid dimethyl esters (4), obtained by cycloaddition of R1R2C=N+=N− (R1 = R2 = CH3; R1 = CH3, R2 = CH2CH3) to CH3O2CC≡CCO2CH3, rearrange thermally by 1,5-sigmatropic alkyl shifts to both N and C. The latter rearrangement is followed by two successive 1,5-sigmatropic shifts of a methoxycarbonyl group. Final products of the threefold rearrangement were shown to be 4,5-dialkyl-1H-pyrazole-1,3-dicarboxylic acid dimethyl esters (6), rather than the isomeric 3,4-dialkyl-1H-pyrazole-1,5-dicarboxylic acid dimethyl esters (7), by means of single crystal X-ray diffraction. Those products therefore result from alkyl migration to C-4 of 4, followed by sequential migration of the methoxycarbonyl group, initially at C-4, to C-3 and then to N-2 of 4. In the initial alkyl migration step, ethyl migrates in preference to methyl, and in subsequent migration steps the methoxycarbonyl group migrates faster than the ethyl or methyl group. Crystals of 4-ethyl-5-methyl-1H-pyrazole-1,3-dicarboxylic acid dimethyl ester (6b) are monoclinic, of space group P21/n, with a = 7.907(1) Å, b = 11.087(2) Å, c = 13.199(3) Å, V = 1124.9(4) Å 3, Dc = 1.34 g cm−3, Dm = 1.33 g cm−3 for Z = 4, and R1 = 0.0772 (R2 = 0.0626) for 1474 reflections (R1 = 0.0428, R2 = 0.0422 for 903 reflections with I > 3σ(I)). The structure of 6a is similar. Key words: 3,3-dialkyl-3H-pyrazoles, 1,5-sigmatropic rearrangements of; 4,5-dialkyl-1H-pyrazoles, crystal and molecular structures; 1,5-sigmatropic rearrangements of pyrazoles, sense of.
Reaction products of ammonium pertechnetate(VII) with triphenylphosphine and crystal structures of mer-Tc(PPh3)2Cl3(DMF) •2PPh3 and NH2(CH3)2+DMAH+ [TcCl6]2−•PPh3O
Authors: Rochon Fernande D. , Melanson Robert , Kong Pi-Chang
Published: May 2006

The reaction of NH4TcO4 with PPh3 in DMF solution in the presence of HCl produces mer-Tciii(PPh3)2Cl3(DMF)•2PPh3 (1). When the reaction is done in acidic DMA, the yellow product isolated was identified as NH2(CH3)2+DMAH+ [TcCl6]2−•PPh3O (2). The dimethylammonium cation was produced from the reaction of the solvent (DMA) with aqueous HCl. The reaction of NH4TcO4 with PPh3 in acidic acetone solution produces yellow (PPh3H)2[TcCl6] (≈15% yield) and some orange crystals (≈65% yield) identified by X-ray diffraction as [Ph3P-C(CH3)2-CH2-CO-CH3]+ [Tc(PPh3)Cl5]−. The cation was produced from the reaction of acetone used as solvent with HCl and PPh3. The crystals of 1 are monoclinic with P21/m space group, a = 11.393(4), b = 24.993(11), c = 12.398(4) Å, β = 106.98(3)°, Z = 2. The structure was refined to R = 0.072 and wR = 0.058. The Tc—O bond distance is 2.115(12) Å while the Tc—P bond lengths are 2.496(5) and 2.499(5) Å and the Tc—Cl are 2.399(5) and 2.342(3) Å. The C atoms of the DMF ligand are disordered. The crystals of 2 are triclinic, [Formula: see text] space group with a = 8.627(5), b = 13.308(7), c = 14.401(9) Å, α = 97.62(5), β = 91.31(5), γ = 106.42(5)°, and Z = 2. The structure was refined to R = 0.060 and wR = 0.076. The proton on DMAH+ is hydrogen bonded to the oxygen of PPh3O with a distance [Formula: see text] Key words: technetium, DMF, triphenylphosphine, dimethylacetamide.
The photoaddition of 1,3-diketonatoboron difluorides with benzene derivatives
Authors: Chow Yuan L. , Ouyang Xinxin
Published: May 2006

The boron difluoride complexes of 2-acetylcyclohexanone, 2-acetylcyclopentanone, and acetylacetone (abbreviated as ACHBF2, ACPBF2, and AABF2) were irradiated in the presence of benzene to give the 1:1 adducts as the primary photoadducts; for certain BF2 complexes, toluene, chlorobenzene, benzonitrile, and methyl benzoate were also used as substrates. The 1,5-diketone photoadducts were assumed to form by a [2+2] photocycloaddition followed by cyclobutane opening and hydrolysis to give 1,2 adducts. They undergo a variety of secondary thermal reactions, probably acid catalyzed, to give enol ethers, enol acetates, acetophenones, and ketonylacetophenones. The efficiency of these secondary reactions determines the final products. Photoaddition with a monosubstituted benzene preferentially occurs at the 3,4 bond without regioselectivity. Under oxygen, ACHBF2 photolytically reacts with benzene to give a secondary oxidation product of a 10-membered cyclic alkylphe-none, which is proven by X-ray crystallographic analysis to have the benzene ring and carbonyl group in orthogonal orientation. It is shown that the singlet excited state ACHBF2 initiates the photoaddition, probably through the formation of the benzene exciplex, which could be detected by its emission. While the Stern–Volmer rates are small, the quantum yield of photoaddition products is as high as 0.12–0.19 under limiting conditions. Key words: [2+2] photocycloaddition, non-planar alkanophenone, macrocyclic alkanophenone, boron difluoride complexes, photoaddition to benzenes.
Thermodynamic investigation of the ternary K–Pb–Sn and Rb–Pb–Sn alloys
Authors: Tumidajski Peter J.
Published: May 2006

Activity coefficients for alkali metals in the K–Pb–Sn and Rb–Pb–Sn alloys were measured at 606 °C (879 K) for compositions generally less than about 10 at.% alkali metal. An alkali metal concentration cell with a potassium or rubidium substituted β-Al2O3 solid electrolyte was used to perform the experiments. A coulometric titration technique was used to electrochemically generate the alkali metal in the Pb–Sn alloys. The results indicated that, for both potassium and rubidium alloys, as solvent composition is varied from pure tin to pure lead the liquid becomes more associated, suggesting the formation of complex species. Key words: thermodynamics, alkali metals, liquid alloys.
2-Phenyladamantane as a model for axial phenylcyclohexane. 1H NMR and molecular orbital studies of motion about the Csp2—Csp3 bond
Authors: Schaefer Ted , Beaulieu Christian , Sebastian Rudy
Published: May 2006

The 1H NMR spectra of the aromatic groups of 2-phenylcyclohexane and 2-phenyladamantane, in CS2/C6D12 solution at 300 K, are analyzed to yield the long-range coupling constants between the α and ring protons. The coupling over six bonds is related to the internal rotational potential about the Csp2—Csp3 bond in these molecules. It is confirmed that the equatorial isomer of phenylcyclohexane has the parallel conformer, that in which the aromatic plane lies in the symmetry plane bisecting the cyclohexane moiety, as the most stable. The apparent twofold barrier to rotation about the exocyclic carbon–carbon bond follows as 7.1 kJ/mol from the six-bond coupling constant. For 2-phenyladamantane, the six-bond coupling constant strongly implies that the perpendicular conformer, perhaps slightly skewed, is that of lowest energy and that the apparent twofold barrier to rotation about the Csp2—Csp3 bond is about 7.5 kJ/mol. Insofar as 2-phenyladamantane mimics axial phenylcyclohexane, these results confirm recent conclusions about the conformation of the latter and provide evidence for its internal mobility. Geometry-optimized AMI and STO-3G MO computations are reported for the internal motion in both isomers of phenylcyclohexane. The former agree best with experiment for the equatorial isomer, but both imply a significant fourfold, of opposite sign to the twofold, component of the internal rotational potential. For the axial isomer, the two sets of computations find a skewed perpendicular conformer as most stable, in rough agreement with force-field results. However, the barrier to rotation about the Csp2—Csp3 bond is computed as small and AMI has the parallel conformer as more stable than the perpendicular. Key words: 2-phenyladamantane, 1H NMR and internal rotation; phenylcyclohexane, 1H NMR and internal rotation; MO computations, 2-phenyladamantane and phenylcyclohexane.
Redox reactions with ferrocene/ferricenium species of radicals derived by H atom abstraction from alcohols and diols
Authors: Logan S. R.
Published: May 2006

The effect of various alcohols and diols in diminishing the extent of the photo-oxidation of 4-ferrocenylbutanoate ion in the presence of N2O has been investigated. Where the hydroxyl radical generated in the photo-initiated electron transfer reacts with an alcohol by H atom abstraction at the α-position, the resulting radical is capable of reducing the ferricenium zwitterion to the ferrocenyl anion. Abstraction at other positions produces radicals that are essentially inert in this system and rate constants are derived for the reaction of OH with some such compounds. Non-vicinal diols behave similarly to the corresponding alcohols. With vicinal diols, a dehydration process, which occurs the more slowly the more highly substituted the diol, converts the radical -CR(OH)Ċ(OH)- into -ĊRCO-, which is an oxidizing species. The behaviour of pinacol was found to be anomalous. Key words: radical reactions, redox behaviour, alcohols.
Recovery of silica from aqueous silicate solutions via trialkyl or tetraalkylammonium silicomolybdate
Authors: Freitas A. S. W. De , McCulloch A. W. , McInnes A. G.
Published: May 2006

Reaction of aqueous silicate with ammonium molybdate at pH 1.5 affords the β form of silicomolybdic acid. The latter can be precipitated by the addition of a variety of quaternary ammonium salts. The precipitated silicomolybdate can then be decomposed to silica in a two-step combustion process (at 350 and 1000 °C). Recoveries of Si are nearly complete, but the starting silicate solution must be made strongly basic prior to the reaction with molybdate. The overall process can be utilized for the recovery of silicon isotopes and as a method of silica purification. Key words: silica, silicate, silicomolybdate, silicon-29.
Synthetic studies towards bruceantin. Part 2. The synthesis of a pentacyclic intermediate
Authors: Darvesh Sultan , Grant Andrew S. , MaGee David I. , Valenta Zdenek
Published: May 2006

In a synthetic approach to the quassinoid bruceantin (2), the key intermediate 8 obtained via alkylation of a dianion has been transformed into the pentacyclic intermediate 33 via an ABDC ring forming strategy. The key steps involved in this route are as follows: a unique acid catalyzed cyclization, 19 → 20; an intramolecular Michael reaction, 24 → 28; and an allyl sulfoxide [2,3]-sigmatropic rearrangement to introduce the axial C12 alcohol, 31 → 33. Key words: bruceantin, quassinoids, cyclization, sulfoxides, sigmatropic rearrangement.
Kinetics of the detritiation of [10,10-3H] mianserin and related compounds in highly basic media.
Authors: Jones John R. , Wickenden David A. , Funke Carel W. , Kaspersen. Fransm M.
Published: May 2006

not available
Substitution reactions of benzethonium chloride with ion associates of bromocresol green – quinine and bromophenol blue – quinine in dichloromethane
Authors: Gainza Alberto Hernandez , Konyeaso Roy Ikemefula
Published: May 2006

An excess concentration of base quinine (Q) reacts with a sulphonphthalein diacidic dye XH2, (bromocresol green, BCGH2, or bromophenol blue, BPBH2) in dichloromethane solution to form an ion associate (X2−(QH+)2) of stoichiometry 1:2 (dye:amine). Benzethonium chloride (ClB) reacts with the 1:2 ion associate to form an ion associate (QH+,X2−,B+) and quinine hydrochloride ClQH+. This substitution reaction is a chemical equilibrium with formation constants of 1.50 ± 0.67, 1.61 ± 0.54, 1.07 ± 0.29, 1.04 ± 0.20, and 0.84 ± 0.26 for BCG and 1.86 ± 0.59, 1.47 ± 0.23, 1.40 ± 0.65, 1.13 ± 0.37, and 1.11 ± 0.27 for BPB at 283.16, 288.16, 293.16, 298.16, and 303.16 K respectively. The thermodynamic parameters determined by van't Hoff's equation are ΔH0 = −21.766 ± 7.482 kJ mol−1, ΔS0 = −73 ± 51 J mol−1 K−1, and ΔG0 = −1.134 ± 0.972 kJ mol−1for BCG and ΔH0 = −18.678 ± 7.482 kJ mol−1, ΔS0 = −61 ± 26 J mol−1 K−1, ΔG0 = −0.916 ± 0.401 kJ mol−1 for BPB (ΔG0 at 293.16 K; and ΔH0 and ΔS0 determined in the range 283–303 K). Key words: bromocresol green – quinine–benzethonium, ion associate mixture, bromophenol blue – quinine–benzethonium, equilibrium constants, thermodynamic parameters.
The synthesis of 3H-naphthol[1,8-bc]thiophene derivatives
Authors: Clark Peter D. , Irvine Nicholas M. , Sarkar Pratibha
Published: May 2006

Methods for the synthesis of keto derivatives of the little studied naphtho[1,8-bc]thiophene system have been developed. Using the readily available benzothiophene derivative 6,7-dihydrobenzo[b]thiophen-4(5H)-one 4, a 3-keto-naphtho[1,8-bc]thiophene 14 was synthesized by a tin(IV) chloride catalyzed cyclization of the acid chloride derivative of the saturated acid 13b. The bicyclic ketone 4 was also used to prepare the keto-sulfoxide 7, which was cyclized to the 4-keto-naphtho[1,8-bc]thiophene system 9 in a Pummerer-type rearrangement. Key words: synthesis, organosulfur, naphtho[1,8-bc]thiophenones.
Selenium-77 and phosphorus-31 nuclear spin relaxation in tri-(tert-butyl) phosphine selenide
Authors: Penner Glenn H.
Published: May 2006

Selenium-77 and phosphorus-31 spin-lattice relaxation times are reported for tri-tert-butylphosphine selenide in chloroform-d, at 303 K and at several different magnetic field strengths. At moderate fields the 31P–1H dipole–dipole, spin-rotation, and chemical shift anisotropy mechanisms contribute significantly towards the 31P T1. At high fields chemical shift anisotropy dominates. The selenium-77 nuclear spin relaxes almost exclusively by spin rotation at low to moderate fields and the chemical shift anisotropy contribution only becomes significant at very high fields. This is due to an unusually small 77Se CSA. The contribution due to 31P–77Se dipole–dipole interactions is small but significant. Key words: 77Se NMR, NMR relaxation, phosphine selenide.
Azo pigments and their intermediates. A reinvestigation of the tetrazotization of 1,4-diaminoanthraquinone
Authors: Law Kock-Yee , Tarnawskyj Ihor W. , Kaplan Samuel
Published: May 2006

The azotization of 1,4-diaminoanthraquinone (1) by n-amyl nitrite in glacial acetic was reinvestigated. The structure of a red-brown precipitate, which was previously identified as anthraquinone-1,4-tetrazonium dichloride (3) by Schaarschmidt, was found to be incorrect. In this work, we have identified the red-brown solid as 4-aminoanthraquinone-1-diazonium chloride (2), a diazotized product of 1. The yield of 2 was 80%. The tetrazonium dichloride 3 was actually formed in minute quantity and is soluble in acetic acid. The tetrazonium product of 1 can be isolated as tetrafluoroborate salt 4 in 3.4% yield by adding fluoboric acid into the acetic acid solution. The structure 4 was confirmed by IR and cross-polarization magic angle spinning13C NMR spectroscopy. Further investigations showed that 1 can be quantitatively tetrazotized by nitrosylsulfuric acid in 78% sulfuric acid. The tetrazonium product was isolated as 4 in 74% yield. Key words: 1,4-diaminoanthraquinone, diazotization, tetrazotization, azo pigments.
Improvements in the quantitation of NMR spectra by the use of statistical methods
Authors: Bain Alex D. , Fahie Brian J. , Kozluk Tomasz , Leigh William J.
Published: May 2006

In many applications of NMR spectroscopy to chemistry, quantitation play s a key role. This paper argues that peak heights not only can be used for quantitative work in NMR but that for careful work they should be used. Integrals are accurate, but because they depend on many subjective factors, their precision is suspect. Peak heights are very reproducible on modern spectrometers and so, given this precision, the accuracy can be obtained as well by using calibration methods. An example of the application of these methods is given in the case of a 13C labelling experiment that elucidates a photochemical transformation. Key words: NMR, labelling, quantitation, peak heights, integrals.
Structural studies of organoboron compounds. XLIX. 4,6-Bis(1-phenyl-2-nitroethyl)-2-(4-methoxyphenyl)-1,3-dioxa-4,6-diaza-2-boracyclohexane
Authors: Kliegel Wolfgang , Lubkowitz Gottfried , Rettig Steven J. , Trotter James
Published: May 2006

The preparation of N,N′-bis(1-phenyl-2-nitroethyl)-N,N′-dihydroxymethanediamine and its subsequent reaction with 4-methoxyphenylboronicacid to yield 4,6-bis(1-phenyl-2-nitroethyl)-2-(4-methoxyphenyl)-1,3-dioxa-4,6-diaza-2-boracyclohexane are described. Crystals of the latter compound are monoclinic, a = 8.4790(8), b = 16.2100(9), c = 9.4367(6) Å, β = 109.342(5)°, Z = 2, space groupP21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.032 and Rw = 0.039 for 1749 reflections with I ≥ 3σ(I). The molecule has a six-membered BONCNO cycloboronate structure. Bond lengths involving the trigonal planar boron atom are (N)O—B = 1.362(4) and 1.364(5), (aryl)C—B = 1.548(4) Å. Key words: organoboron compound, crystal structure, cycloboronate, methanediamine.
Study of the properties of pyridine-2-azo-p-phenyltetramethylguanidine as a metal ion complexing agent
Authors: Leffek Kenneth T. , Jarczewski Arnold
Published: May 2006

Pyridine-2-azo-p-phenyltetramethylguanidine (PAPT) was synthesized and the properties of this compound examined. The dissociation constants of the conjugate acids in H2O are [Formula: see text] and [Formula: see text] at 25 °C at I = 0.1, and in acetonitrile are [Formula: see text] and [Formula: see text]. The properties of metal–ligand chelates in acetonitrile have been examined and the stability constants for Ni2+, Co2+, and Zn2+ complexes measured. The rates of reaction of PAPT with Ni2+, Co2+, and Zn2+ in acetonitrile have been determined and the activation parameters measured for the complex formation of LNi2+. The stability constants for both complexing centres of PAPT have been calculated. The 13C NMR spectra for PAPT and LNi2+ are quoted. The expected enhancement of the metal ion complexing ability of PAPT due to the strongly electron-releasing nature of the tetramethylguanidinyl group was not found. Key words: metal ion complexes, pyridine-2-azo-p-phenyltetramethylguanidine, stability constants, pKa.
Reaction of carbonyl ylides with chloroform
Authors: Békhazi Michel , Lawrynowicz Witold , Warkentin John
Published: May 2006

Carbonyl ylides 2, generated by thermolysis of alkoxyoxadiazolines 1 in chloroform, react with chloroform to form ketals (3) of 1,1,1-trichloropropanone. The isotope effect at 80 °C, determined by analysis of products from thermolysis of 1 in mixed solvent (CHCl3/CDCl3, both in large excess) was estimated to be kH/kD = 5. A mechanism involving concerted C—Cl and C—H bond formation between the ylide C atoms and the Cl and H atoms of chloroform is proposed. The ketals of 1,1,1-trichloropropanone are the first to be reported. Key words: carbonyl ylide, reaction with chloroform; chloroform, reaction with carbonyl ylides; ketals, of 1,1,1-trichloropropanone; 1,1,1-trichloropropanone, ketals of.
Hydroxyproline adsorption on a mercury electrode in neutral solution
Authors: Gómez M. M.
Published: May 2006

The adsorption of hydroxyproline (HPRO) on mercury in aqueous solutions of 10−2 M KClO4 has been determined from electrocapillary and capacity measurements. Comparison of the results obtained for HPRO with those reported for proline (PRO) shows that the presence of a hydroxyl group in the molecule has a small effect on the adsorption process. The respective values for adsorption parameters are −7 and −5 μC cm−2 for the charges of maximum adsorption, −13.0 and −10.4 kj mol−1 for the standard Gibbs energies of adsorption at zero charge, and −1.28 and +0.6 for the α parameter in the Frumkin isotherms. According to the analysis carried out for the normal component of the dipole moment of HPRO, −0.8 D, the more probable orientation of this aminoacid adsorbed on mercury is with the pyrrolidine ring parallel to the electrode surface resting the OH group away from the surface. Key words: adsorption, double layer, aminoacids, hydroxyproline.
The dual pathway in photocycloaddition of 1,3-diketonatoboron difluorides: excimer reactions
Authors: Chow Yuan L. , Cheng Xianen
Published: May 2006

The lowest singlet excited state of dibenzoylmethanatoboron difluoride DBMBF2, a model compound of the BF2 complexes of 1,3-diketones, reacted with various simple olefins to give regiospecific and stereospecific photocycloadducts of 1,5-diketones similar to those from the de Mayo type reaction. DBMBF2 in acetonitrile exhibited two discrete fluorescences at 398 and 416 nm for the monomer and at 522 nm for the excimer; they were both quenched, but in different proportions, by a simple olefin. An "oxygen test" showed that the excimer of DBMBF2 is formed irreversibly in acetonitrile. The quantum yields of the photocycloaddition were shown to be proportional not only to olefin concentrations but also to DBMBF2 concentrations. Kinetic analysis has established that the total quantum yield is the sum of those arising from the interactions of the singlet excited DBMBF2 and its excimer, respectively, with an olefin, i.e., the sum of the quantum yields of exciplex and triplex pathways. The contributions from the two pathways are determined by the type of olefins and the range of DBMBF2 concentrations. For endocyclic olefins, the triplex pathway is more important and the corresponding photocycloaddition becomes very efficient as soon as the excimer starts to form in [DBMBF2] > 0.001 M. For the monosubstituted olefins, on the contrary, the exciplex pathway is always more important than the triplex pathway; they react primarily from the singlet excited state of DBMBF2. Key words: singlet state photocycloaddition, irreversible excimer formation, excimer cycloaddition, triplex and exciplex reactions.
Molecular orbital studies of the singlet and triplet states of formylmethylene conformers
Authors: Gosavi Ratnakar K. , Torres Manuel , Strausz Otto P.
Published: May 2006

The energies and geometries of the low-lying electronic states of formylmethylene have been calculated at the SCF and CI levels using 6-31G** basis set. In agreement with previous reports and accumulated experimental observations, the ground state is the carbenoid triplet with a planar geometry. Also, in agreement with all previous single configuration SCF and CI calculations, the lowest excited singlet state is computed to be the nonplanar closed shell carbenoid structure. In contrast, accumulated experimental evidence along with previously reported MC–SCF results require this state to be planar. The present calculation predicts the existence of a (σ–σ) 1,3-diradical 1A′ state, which appears to be identical to the MC–SCF lowest singlet state, but this state lies some 11 kcal/mol above the closed shell carbenoid 1A state. Apparently, single configuration SCF methods are inadequate for the correct description of the electronic manifold of formylmethylene. Key words: formylmethylene, singlet and triplet states, ab initio MO calculations, conformers, molecular structure.
Fourier-transform infrared and circular dichroism studies on temperature dependence of the secondary structure of troponin C from bullfrog skeletal muscle
Authors: Yamamoto Tatsuyuki , Tasumi Mitsuo , Tanokura Masaru
Published: May 2006

The infrared spectra and circular dichroism of bullfrog (Rana catesbeiana) skeletal muscle troponin C with and without Ca2+ have been measured in aqueous solution at temperatures between 24 and 80 °C at pH 7.0. Infrared spectral changes with increasing temperature, particularly in the amide I region, have been extensively examined by using the techniques of thermal difference spectrum and deconvolution. Ca2+-free troponin C seems to be denatured at about 70 °C, but its denaturation proceeds gradually without an abrupt structural change. Ca2+ binding causes a considerable change in the secondary structure of the whole protein. Consequently, Ca2+-bound troponin C has a higher α-helix content and is thermally more stable than the Ca2+-free protein. Both the deconvolved amide I bands and circular dichroism data indicate that there are similarities between the secondary structure (and probably the tertiary structure as well) of the Ca2+-bound protein at 80 °C and that of the Ca2+-free protein at room temperature. Key words: bullfrog skeletal muscle troponin C, Fourier transform infrared and circular dichroism studies.
Pressure effect on hydrogen isotope exchange kinetics in chymotrypsinogen investigated by FT-IR spectroscopy
Authors: Wong P. T. T.
Published: May 2006

Hydrogen/deuterium (H/D) exchange rate constants in chymotrypsinogen have been determined at several pressures up to 28.9 kbar by FTIR spectroscopy. The secondary structure of the protein molecules was monitored simultaneously at the corresponding pressures by the intensity redistribution of the infrared amide I band at these pressures. As in other proteins, the labile protons on the amide groups in chymotrypsinogen can, to a good approximation, be separated into two classes, each with distinct first order H/D exchange rates constants in the time period from 10 min to ~24 h. The fast exchange rate constant increases while the slow exchange rate constant decreases with increasing pressure. The increase in the fast exchange rate constant at high pressure is largely associated with the pressure-induced unfolding of the protein molecules. At extremely high pressure (12.8 kbar), in addition to the unfolding of protein molecules, pressure induced a distortion and weakening of the hydrogen bonds of the fold protein segments also contribute to an increase in the overall H/D exchange rate. The present results confirm that when chymotrypsinogen is dissolved in D2O, a considerable amount of D2O molecules is bound to the protein molecules on the surface as well as in the interior cavities of the molecules. The H/D exchange takes place between these bound D2O and the protons in the protein molecules. The mechanism of the H/D exchange and the interior dynamics in proteins are discussed on the basis of the present results. Key words: hydrogen/deuterium exchange, exchange kinetics, rate constant, pressure effects, infrared spectroscopy, protein, conformation structure, bound water.
Dihydroxyacids from the chlorination of ketones: an unexpected process
Authors: Guthrie J. Peter , Cossar John , Lu Jinqiao
Published: May 2006

Chlorination of propiophenone in aqueous alkali at room temperature, with low concentrations of hypochlorite, leads to 2-phenylglyceric acid as the major product. This acid is formed by further oxidation of 1-phenyl-1,2-propanedione, which is an intermediate in the oxidation of propiophenone. Formation of this acid is reasonable in the light of other halogenation chemistry. Analogous reactions are observed for butyrophenone, which yields 2,3-dihydroxy-2-phenylbutanoic acid, and for cycloheptanone, which yields 1,2-dihydroxycyclohexanecarboxylic acid. Key words: 2-phenylglyceric acid, propiophenone, chlorination, hydrolysis, rearrangement, cycloheptanone, 1,2-dihydroxycyclohexanecarboxylic acid.
An ion exchange atomic absorption method for the determination of ionized calcium at millimolar levels
Authors: Hewavitharana Amitha K. , Mutucumarana Vasantha , Kratochvil Byron
Published: May 2006

A quantitative ion exchange/atomic absorption method is described for measuring the fraction of free calcium in solution at millimolar levels. Sample solutions are equilibrated with a micro-column of strong-acid type cation-exchange resin under electrolyte concentrations (0.75 mol/L NaNO3) high enough to provide conditions where the calcium sorbed on the resin is proportional to the free calcium in solution. After a water wash, the sorbed calcium is eluted from the resin with nitric acid directly into an atomic absorption spectophotometer. Free calcium levels were estimated using calibration curves obtained over the range 0–5 mM calcium with a precision of ± 0.05 mM. The effect of magnesium, at concentrations twice that of calcium, on measured calcium levels is negligible. The method is pH insensitive over the range 5–7. Selectivity for free calcium in the presence of complexing ligands such as citrate and phosphate is high. The method shows promise for the determination of ionized calcium in biological systems. Key words: ion exchange, atomic absorption, free calcium determination, ion speciation.
Effect of methyl substitution on the intramolecular triplet deactivation of p-methoxy-β-phenylpropiophenone
Authors: Boch R. , Bohne C. , Netto-Ferreira J. C. , Scaiano J. C.
Published: May 2006

The photochemistry of several methyl-substituted p-methoxy-β-phenylpropiophenones (1–5) has been examined by nanosecond laser flash photolysis using 337-nm laser excitation. The ketone triplets decay by intramolecular β-aryl quenching of the carbonyl in a well-known process that is believed to involve charge transfer. Surprisingly, methyl substitution at the β-methylene group, which is not a participant in the deactiviation mechanism, causes a dramatic decrease in the triplet lifetime; the effect is attributed to different conformational preferences in ketones 1–3 and is rationalized on the basis of MMX calculations. Methyl substitution in the β-aryl ring affects the ease of oxidation of this ring and as a result induces changes in the kinetics for intramolecular charge transfer. This conclusion is further supported by electrochemical studies of ketones 1, 4, and 5. Key words: laser flash photolysis, triplet ketones, intramolecular quenching, charge transfer.
The 119Sn Mössbauer and solid-state NMR and the crystal and molecular structure of tin(II) bisfluorosulfate, Sn(OSO2F)2
Authors: Adams David C. , Birchall Thomas , Faggiani Romolo , Gillespie Ronald J. , Vekris John E.
Published: May 2006

The reaction of tin(II) fluoride with fluorosulfuric acid has been shown to produce tin(II) bisfluorosulfate. Crystals of Sn(OSO2F)2 are monoclinic, space group P21/c with a = 5.195(1), b = 9.709(1), c = 13.861(1) Å, β = 110.12(1)°, Z = 4, R = 0.029, and Rw = 0.030 for 1461 unique reflections. The structure consists of a three-dimensional framework of fluorosulfate groups linked by O—Sn—O bridges with the two crystallographically independent fluorosulfates acting as tridentate bridging ligands between tin atoms. There are four short bonds (Sn—O = 2.338(3), 2.350(3), 2.398(4), and 2.427(3) Å) and two longer ones (Sn—O = 2.695(3) and 2.702(3) Å) around tin. The four short bonds have a disphenoidal, AX4E, primary geometry with the lone pair occupying an equatorial site. If the two longer interactions are also considered the geometry is distorted octahedral, AX4Y2E. Two more non-bonding contacts of 3.420(4) and 3.319(4) Å complete an approximately dodecahedral arrangement of oxygen atoms around the tin. The fluorosulfate groups deviate significantly from C3υ symmetry and have the mean dimensions, S(1)—O = 1.419(4), S(1)—F = 1.541(4), S(2)—O = 1.435(3), S(2)—F = 1.539(3) Å, O—S(1)—O = 114.3(2)°, F—S(1)—O = 104.1(3)°, O—S(2)—O = 114.2(2)°, and F—S(2)—O = 104.1(2)°, respectively. The solid-state 119Sn nmr spectrum shows only one single resonance with a shift of −1534 ppm which is substantially different from that of a solution in HSO3F. The 119Sn Mössbauer spectrum shows an unresolved quadrupole splitting as a result of a distorted environment around tin, produced by the stereochemically active non-bonding electron pair. Key words: tin(II) bisfluorosulfate, 119Sn Mössbauer, solid-state nmr, X-ray crystallography
Preparation of nitrogen heterocycles from aromatic amines using tris(isopropylthio)cyclopropenyl cation as a three-carbon building block
Authors: Kojima Hideo , Matsumura Noboru , Inoue Hiroo
Published: May 2006

Quinolines (2 and 3) and naphthazepines (8 and 9) are prepared in high yields by the reaction of tris(isopropylthio)-cyclopropenylium perchlorate (1) with anilines and 1-naphthylamines, respectively, under nitrogen in N,N-dimethylformamide at 80–85 °C. The reactions are proven to proceed through the intermediary formation of iminium salts (5, 10, and 11) derived from 1 and amines. The reaction of 1 with pyrrole and indole in dimethyl sulfoxide, containing sodium hydride, at 25 °C gives 5,6,7-tris(isopropylthio)-1H-pyrrolizine (12) and 1,2,3-tris(isopropylthio)-9H-fluorazene (14), respectively, in high yields by intramolecular cyclization of a vinylcarbene intermediate. The possible pathway for the formation of these nitrogen heterocycles is proposed. Keywords: cyclopropenyl cation, aromatic amines, nitrogen heterocycles, three-carbon building block.
Étude thermodynamique de l'acridone et de la thioxanthone
Authors: Sabbah Raphaël , Watik Lahcen El
Published: May 2006

In the present work we studied acridone and thioxanthone by combustion calorimetry of small amounts of substance, by sublimation calorimetry, by differential thermal analysis, and by heat capacity measurements. The thermodynamic quantities derived are as follows: For acridone: [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] For thioxanthone: [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] ΔfusHm = (35.50 ± 0.28) kJ mol−1, Ttp = (487.88 ± 0.02) K. The experimental results permitted us to determine for each molecule its resonance energy and to compare it with the theoretical value. This comparison fits well for acridone, which is planar. The difference observed in the case of thioxanthone shows that this molecule is not planar, in accord with literature structural results. From the experimental enthalpy of atomization of acridone, we determined an enthalpy value for the Cb—N bond. Using the enthalpy contributions previously determined in our laboratory, we found a value for the enthalpy of atomization of thioxanthone in accord with the experimental result. Keywords: thermodynamics; calorimetry; differential thermal analysis; acridone; thioxanthone; enthalpies of combustion, of sublimation, of fusion; resonance energy; enthalpies of atomization, of intramolecular bonds; triple point temperature.
A comparative study of the liquid-phase reduction of acrylamide and methacrylamide with cyclohexene and with molecular hydrogen over sepiolite-supported catalysts
Authors: Aramendia M. A. , Borau V. , Jimenez C. , Marinas J. M. , Sempere M. E. , Urbano F. J.
Published: May 2006

This paper deals with the optimization of the variables involved in the synthesis of Pd/sepiolite catalysts used in the individual and competitive reduction of acrylamide and methacrylamide with molecular hydrogen and by hydrogen transfer with cyclohexene as donor. From the reaction profiles of the acrylamide/methacrylamide pair were determined the relative reactivities and relative coefficients of adsorption corresponding to the competitive liquid-phase reductions with molecular hydrogen obtained for different catalysts, solvents, and temperatures. A similar study on the competitive hydrogen transfer reduction of both amides was rendered unfeasible by the fact that acrylamide was strongly adsorbed on the same types of sites as cyclohexene. This completely hindered cyclohexene adsorption and, as a result, inhibited the reaction altogether. Keywords: reduction, acrylamide, methacrylamide, Pd/sepiolite, hydrogen transfer
Structure and bonding in square-planar chalcogen rings
Authors: Saethre Leif J. , Gropen Odd
Published: May 2006

The molecular structures of square-planar X42+, X4+, and X4 (X = S, Se, Te) have been calculated using the effective core potential model. For X42+ the agreement between experimental and calculated values is excellent provided that d orbitals are included in the basis set. For the hypothetical molecules X4+ and X4 the bond lengths are found to increase dramatically as one and, subsequently, two electrons are added to the systems. Extensive population analysis shows that this increase is almost exclusively due to loss of bonding in the π system, whereas the bonding in the σ system remains relatively unaltered. These results make it possible to predict covalent single bond radii for S, Se, and Te for which the influence of π repulsion is removed. From the calculated variation of bond lengths with atomic charge, bond lengths are predicted for a series of planar disulphide rings. Keywords: structure, bonding, chalcogen, theoretical, ECP.
Improvement of the long-range behavior of Gaussian basis sets using asymptotic constraints
Authors: Koga Toshikatsu , Thakkar Ajit J.
Published: May 2006

It is suggested that atomic orbitals with improved long-range behavior can be obtained by using energy-optimized Gaussian basis sets to which Gaussians have been added to satisfy a subset of some recently derived constraints that must be satisfied by the exact Hartree–Fock orbitals. This procedure is demonstrated by illustrative calculations for helium. This method is found to be superior to the adhoc method of adding diffuse Gaussians in an even-tempered fashion. Keywords: Gaussian basis sets, long-range behavior, asymptotic constraints.