bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection in the 1H NMR spectrum of 37Cl/35Cl isotope effects on the 19F NMR chemical shifts of 1-chloro-2,4-difluorobenzene. An isotope effect over five bonds
Authors: Schaefer Ted , Bernard Guy M. , Hruska Frank E.
Published: May 2006

In an ABX high-resolution NMR spectrum the detection of combination peaks in the X region yields only the chemical shift of X, JAX + JBX and the positive quantities [Formula: see text]. However, the presence of an additional isotopic perturbation on νA − νB, the difference between the resonance frequencies of A and B, yields two X spectra; therefore four quantities, C. Hence all quantities in the surd become available from the composite X spectrum. A generalization to ABMRX spin systems, applicable to the 1H and 19F NMR spectra of the two isotopic molecules of 1-chloro-2,4-difluorobenzene, is possible. It turns out that, from the H-5(X) spectrum alone, the following spectral quantities are extractable; the two values of νA − νB where A and B are the 19F nuclei; JAB; JAX and JBX with their relative signs; JMX and JRX where M and R are H-3 and H-6. No 37Cl/35Cl isotope effect is detectable on the 1H shielding nor on any coupling constants. F-2 undergoes an isotope shift of −1.64(3) ppb. The isotope shift, over five formal bonds, of F-4 is −0.54(3) ppb (larger shielding in the presence of 37Cl). This magnitude is three times larger than that over four formal bonds in another molecule, 2,6-dichloro-4-fluorophenol. Key words: 1H NMR, of 1-chloro-2,4-difluorobenzene, isotope effects in NMR, reflection of 37Cl/35Cl isotope effects on 19F shielding in the 1H NMR spectrum of 1-chloro-2,4-difluorobenzene; isotope effects in NMR, over three and five bonds by 37Cl/35Cl on 19F shielding in 1-chloro-2,4-difluorobenzene; 19F NMR, 37Cl/35Cl isotope effects over three and five bonds in 1-chloro-2,4-difluorobenzene.
1996 Noranda Award Lecture Thermal properties of solids: Étude in three-part anharmony
Authors: White Mary Anne
Published: May 2006

The harmonic oscillator is a useful starting point for understanding many intermolecular interactions, and it successfully predicts many properties. However, anharmonic terms in the interaction potential are responsible for several observed phenomena. This review summarizes our recent experimental investigations of three thermal properties of molecular solids that result from anharmonic intermolecular interactions, viz. thermal expansion, Grüneisen parameters, and thermal conductivity. Key words: anharmonicity, thermal expansion, Grüneisen parameter, thermal conductivity.
Micelle-induced change of mechanism in the reaction of muonium with acetone
Authors: Stadlbauer John M. , Venkateswaran Krishnan , Gillis Hugh A. , Porter Gerald B. , Walker David C.
Published: May 2006

Muonium atoms add to the O atom of the carbonyl group of acetone to give the muonated free radical (CH3)2Ċ-O-Mu when the reaction takes place in water or hydrocarbons, but not when the acetone is localized in micelles. Micelles have no effect on the formation of muonated cyclohexadienyl radicals when muonium reacts with benzene under similar conditions. The addition reaction with acetone appears to have been subsumed by a faster alternative reaction in the micellar environment. Evidence is presented for this interpretation rather than for an inhibition of the radical or for a shift in the muon level-crossing resonance spectrum with hydrogen (muonium) bonding, though major shifts are seen for the spectrum of this radical in pure solvents of widely different dielectric constant. It is suggested that muonium's "abstraction" reaction takes over in micelles because significant micelle-induced enhancement effects were previously observed in that type of reaction. The data are consistent with a rate constant for the abstraction reaction of muonium with acetone in micelles of >6 × 108 M−1 s−1. Key words: muonium, kinetic isotope effects, micelle enhancement, H/Mu-addition, H/Mu abstraction.
Synthesis, spectroscopic and structural studies of O-methyl and O-isopropyl monothiocarbonate (monoxanthate) derivatives of dimethyl-and diphenyltellurium(IV). Crystal structures of Me2Te[SCO2(i-Pr)]2, Ph2Te[SCO2(i-Pr)]2, Me2TeCl[SCO2Me], and Me2TeBr[SCO2(i-Pr)]
Authors: Drake John E. , Drake Robert J. , Khasrou Layla N. , Mislankar Anil G. , Ratnani Raju , Yang Jincai
Published: May 2006

Monothiocarbonate derivatives of diorganotellurium(IV), R2Te[SCO2R′]2, and R2TeX[SCO2R′], where R = Me, Ph; R′ = Me, i-Pr; X = Cl, Br, and I, have been prepared and characterized by vibrational and 1H, 13C, and 125Te NMR spectroscopy. Me2Te[SCO2(i-Pr)]2 (2): P21/n (No. 14) with cell parameters a = 6.942(6) Å, b = 25.599(3) Å, c = 9.404(6) Å, β = 94.48(6)°, V = 1666(1) Å3, Z = 4, R = 0.0648, Rw = 0.0624; Ph2Te[SCO2(i-Pr)]2 (4): P21/n (No. 14) with a = 12.360(4) Å, b = 12.277(3) Å, c = 15.066(3) Å, β = 102.82(2)°, V = 2229.1(9) Å3, Z = 4, R = 0.0368, Rw = 0.0312; Me2TeCl[SCO2Me] (5); P21/c (No. 14) with a = 5.193(2) Å, b = 18.118(4) Å, c = 9.613(5) Å, β = 91.31(6)°, V = 904.2(6) Å3, Z = 4, R = 0.0396, Rw = 0.0361; and Me2TeBr[SCO2(i-Pr)] (8): P21/n (No. 14) with a = 11.701(2) Å, b = 6.250(2) Å, c = 16.152(2) Å, β = 98.43(1)°, V = 1168.4(4) Å3, Z = 4, R = 0.0369, Rw = 0.0325. In all molecules, the immediate environment about tellurium is that of the saw-horse structure in which the lone pair is assumed to be stereochemically active and occupying an equatorial position in a distorted trigonal bipyramid. In 2 and 5, the terminal oxygen atoms are oriented toward tellurium, whereas in 4, one O(i-Pr) group is oriented toward tellurium, as it is in 8. In the latter cases, the terminal oxygen atoms act as weak bridges to form a pseudo dimeric species in 4 and a pseudo polymer in 8. Supramolecular interactions in 2 and 5 lead to a sulfur-bridged dimer in the former and a chlorine-bridged polymer in the latter. Key words: structure, tellurium, dimethyl, diphenyl, monothiocarbonates.
Oxidative fluorination in the Ph2SO–XeF2–Cl− system and fluorine exchange in the Ph2S(O)F2–Ph2S(O)F+ system
Authors: Ou Xiaobo , Janzen Alexander F.
Published: May 2006

Oxidative fluorination of diphenyl sulfoxide with xenon difluoride occurs under mild conditions in the presence of chloride ion to give Ph2S(O)F2 in quantitative yield. Chloride ion appears to react with xenon difluoride to generate fluoride ion, and a mechanism of oxidative fluorination is proposed that involves anionic Ph2S(O)F− and radical Ph2S(O)F• intermediates. Addition of cationic Ph2S(O)F+ to Ph2S(O)F2 initiates rapid fluorine exchange, presumably via a symmetrical fluorine-bridged intermediate, and this exchange process was monitored by 13C and 19F NMR spectroscopy. In the presence of chloride ion, Ph2S(O)Cl2 is formed and can be identified by 13C NMR and by its hydrolysis to Ph2SO2. Mechanisms are proposed for these reactions, and ab initio molecular orbital calculations (GAUSSIAN92) were carried out of the postulated intermediates. Key words: preparation of Ph2S(O)F2, Ph2S(O)F+, and Ph2S(O)Cl2; oxidative fluorination in the Ph2SO–XeF2–Cl− system; fluorine exchange in the Ph2S(O)F2–Ph2S(O)F+ system.
Synthesis and characterization of mono-and bi-nuclear palladium(II) and platinum(II) complexes containing acetamidine ligands
Authors: Singhal Anshu , Jain Vimal K.
Published: May 2006

The reactions of [M2Cl2(μ-Cl)2(PR3)2] with acetamidines in 1:2 stoichiometry afforded mononuclear complexes, [MCl2{ArNHC(Me)NAr}(PR3)] (I) (M = Pd or Pt; R3 = Et3, Bu3, Me2Ph, MePh2; Ar = Ph or 4-MeC6H4(tol)). Treatment of [M2Cl4(PR3)2] with Li[ArNC(Me)NAr] under anerobic conditions gave acetamidino-bridged binuclear complexes, [M2Cl2(μ-ArNC(Me)NAr)2(PR3)2] (II). The reaction of [Pd2(μ-Cl)2(η3-allyl)2] with Ag[ArNC(Me)NAr] gave acetamidino-bridged allyl complexes [Pd2(μ-ArNC(Me)NAr)2(η3-allyl)2] (III). All the complexes were characterized by elemental analyses and NMR (1H,31P,195Pt) spectroscopy. The mononuclear complexes (I) exist in two isomeric forms differing in the coordination of monodentate acetamidine ligand. The31P and195Pt NMR data on binuclear complexes (II) indicate that there is no significant Pt–Pt interaction. The allyl complexes (III) (allyl = C3H5) exhibit formation of all three possible isomers, whereas methallyl (allyl = C4H7) derivatives exist only in one configuration. Key words: palladium, platinum, acetamidine, NMR (1H,31P,195Pt), mononuclear complexes, binuclear complexes.
Bis- and tris(amidine)fluoroboron cations and mixed tetrahaloborate anions: NMR studies of mixed boron trihalide adduct redistribution reactions involving amidines as strong nitrogen bases
Authors: Hartman J. Stephen , Yuan Zheng , Fox Arnold , Nguyen Anh
Published: May 2006

Amidines as strong Lewis bases react with amidine–mixed boron trihalide adduct systems D•BFnCl3−n (n = 0–3) in the presence of excess boron trihalide to give complex mixtures of products including the mixed tetrahaloborate anions BFnCl4−n− and the fluoroboron cations D2BF2+ and D3BF2+, which coexist with the neutral adducts D•BFnCl3−n. Excess amidine rapidly displaces chloride ion from the chlorofluoroborate anions and neutral mixed boron trihalide adducts to give high yields of the fluoroboron cations. The D3BF2+ cations of the amidines 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) and 1,5-diazabicyclo[4,3,0]non-5-ene (DBN) are inert and have been isolated as their hexafluorophosphate salts. (DBN)2BF2+ is inert and has been isolated as its hexafluorophosphate salt, but (DBU)2BF2+ is highly reactive. Key words: amidines, fluoroboron cations, mixed boron trihalide adducts, redistribution reactions, fluorine-19 NMR, boron-11 NMR, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), 1,5-diazabicyclo[4,3,0]non-5-ene (DBN)
Photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction, Part 12. Factors controlling the regiochemistry of the reaction with alcohol as the nucleophile
Authors: Arnold Donald R. , Chan Mary S. W. , McManus Kimberly A.
Published: May 2006

The photo-NOCAS reaction that combines methanol, serving as the nucleophile, and the radical cation of 4-methyl-1,3-pentadiene (14+•), substituting on the 1,4-dicyanobenzene radical anion (1−•), yields (E)-1-(4-cyanophenyl)-4-methoxy-4-methyl-2-pentene (15) as the major product. This regioisomer arises from bonding of methanol to C-4, the more heavily alkyl-substituted carbon of the diene, giving the less alkyl-substituted allylic radical. All previous examples of the photo-NOCAS reaction have yielded major adduct(s) having regiochemistry consistent with the anti-Markovnikov rule; the more heavily substituted (more stable?) β-alkoxyalkyl radical was the predominant intermediate. Empirically derived heats of formation and high-level ab initio molecular orbital calculations (MP2/6-31G*//HF/6-31G*) provide convincing evidence that of the two alternative allylic radicals, generated upon addition of methanol to 14+•, that which has the more alkyl substituted allylic radical moiety is, in fact, not the more stable. Of course, the total structure of the intermediate must be considered; the stabilizing effect of alkyl substitution on the carbon next to the oxygen of the ether moiety cannot be ignored. Ab initio molecular orbital calculations (MP2/6-31G*//HF/6-31G*) are reported for the radical cations of 2-methylpropene (2+•), 2-methyl-2-butene (6+•), 2-methyl-1,3-butadiene (9+•), 4-methyl-1,3-pentadiene (14+•), and 2,4-dimethyl-1,3-pentadiene (18+•) Calculations were also carried out on possible intermediates (bridged radical cations, distonic radical cations, and β-alkoxyalkyl radicals) involved upon reaction of these radical cations with methanol. Results of these calculations provide a basis for explaining/predicting the regiochemistry of the photo-NOCAS reaction involving methanol as the nucleophile: the major adduct(s) result(s) from attachment of methanol to that end of the alkene or diene which gives rise to the more stable intermediate radical. The more stable radical is not necessarily the more heavily alkyl substituted. Key words: photoinduced electron transfer, radicals, radical cations, ab initio molecular orbital calculations.
Polycarbon ligands: synthesis and characterization of the phosphinodiynes Ph2PC≡C-C≡CR (R = But, Ph, SiMe3), the μ-η1,η2α,β-butadiynyl complexes Ru2(CO)6-(μ-PPh2)(μ-η1,η2α,β-C≡C-C≡CR), and the molecular structure of a cobalt carbonyl derivative Ru2(CO)6(μ-PPh2)(μ-η1,η2α,β:-μ-η2,η2γ,δ-C≡C-C≡CBut)Co2(CO)6
Authors: Blenkiron Peter , Carty Arthur J. , Corrigan John F. , Pilette Didier , Taylor Nicholas J.
Published: May 2006

The phosphino-diynes (PPh2C≡C-C≡CR) (R = But, Ph, SiMe3) are obtained in excellent yield from the corresponding diyne anions RC≡C-C≡C− by quenching with PPh2Cl. Monosubstitution on Ru3(CO)12 yields the trinuclear clusters Ru3(CO)11,(PPh2C≡C-C≡CR), which upon thermolysis afford the butadiynyl complexes Ru2(CO)6(μ-η1,η2α,β-C≡C-C≡CR)(μ-PPh2) (R = But, 7a; R = Ph, 7b;R = SiMe3, 7c) as the major products. The full characterization of the series of compounds (7a–c) Ru2(CO)6(μ-η1,η2α,β-C≡C-C≡CR)(μ-PPh2) is reported including an X-ray diffraction study of 7a. Crystals of 7a are monoclinic, a = 9.849(2), b = 9.886(2), c = 28.368(9) Å, β = 95.18(2)°, space group P21/n, and Z = 4; refinement converged to R = 0.0243 (Rw = 0.0253). The structure shows that the tetracarbon chain is bonded to the first metal atom by a simple M—C σ bond and to the second via a dative π interaction leaving an outer alkyne unit uncoordinated. In the reaction between 7a and cobalt carbonyl, a Co2(CO)6 moiety becomes attached to the -Cγ≡C8- bond in a tetrahedral arrangement to give the tetranuclear mixed-metal species Ru2(CO)6(μ-PPh2)(μ-η1,η2α,β;μ-η1,η2γ,δ-C≡C-C≡But)Co2(CO)68, as confirmed by X-ray crystallography: triclinic, a = 9.9969(9), b = 11.3018(9), c = 17.268(1) Å, α = 90.653(6)°, β = 100.911(6)°, γ = 110.465(5)°, space group [Formula: see text] and Z = 2; refinement converged to R = 0.0222 (Rw = 0.0264). Key words: diruthenium complexes, butadiynyl, synthesis, structure.
Mo2(OCH2tBu)6(Cp)Na(DME). Preparation, structure, and solution behavior
Authors: Budzichowski Theodore A. , Chisholm Malcolm H. , Streib William E.
Published: May 2006

From the reaction between Mo2(OCH2tBu)6 and NaCp (Cp = C5H5) in THF the title complex was obtained as a crystalline product in the presence of DME (DME = dimethoxyethane). Crystal data for Mo2(OCH2tBu)6(Cp)Na(DME) at −167 °C: a = 11.885(2) Å, b = 19.240(1) Å, c = 11.562(2) Å, α = 102.73(1)°, β = 106.95(1)°, γ = 98.55(1)°, Z = 2 and space group of [Formula: see text]. In the solid state there is an unbridged Mo≡Mo bond of distance 2.276(1) Å. One Mo atom is bonded to four alkoxides, two of which are also bonded to Na+ while the other is η5-bonded to the Cp ligand, with Mo—C distances ranging from 2.34 to 2.66 Å, and to two OR groups, one of which is bound to the Na+ ion. In addition to the coordination to three OR groups the Na+ ion binds one DME molecule via both of its ether oxygen atoms. The Mo—O distances fall in the range 1.91–2.01 Å with the longer distances being associated with those groups that are also bonded to the Na+ ion. In polar solvents the title complex dissociates to give Mo2(OCH2tBu)6 and Na+ Cp−. Key words: molybdenum, alkoxide, cyclopentadienyl, metal–metal triple bonds.
Nitrobenzoxadiazole-labelled polyisoprenoid alcohols
Authors: Balcom Bruce J. , Petersen Nils O.
Published: May 2006

We have prepared, isolated, and characterized a series of nitrobenzoxadiazole labelled polyisoprenoid alcohols. The coupling reaction employed was a dicyclohexylcarbodiimide mediated condensation between a carboxylic acid derivative of nitrobenzoxadiazole and the polyisoprenoid alcohols citronellol, solanesol, and dolichol. Upon exposure to visible light, a self-sensitized singlet oxygen "ene" reaction oxidized double bonds in the isoprene moiety. The rate of oxidation is greatly reduced in solvents where singlet oxygen is short-lived. Key words: nitrobenzoxadiazole, isoprenoid, dolichol, citronellol, solanesol, fluorescence labelling, singlet oxygen, ene reaction.
The oxidation of secondary alcohols by potassium tetraoxoferrate(VI)
Authors: Norcross Bruce E. , Lewis William C. , Gai Huifa , Noureldin Nazih A. , Lee Donald G.
Published: May 2006

The kinetics of the oxidation of 2-propanol, 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 1-phenyl-2,2,2-trifluoroethanol, 1-(4-methylphenyl)-2,2,2-trifluoroethanol, 1-(3-bromophenyl)-2,2,2-trifluoroethanol, and 1-(3-nitrophenyl)-2,2,2-trifluoroethanol by potassium tetraoxoferrate(VI) have been studied under basic conditions. The products are ketones, formed in almost quantitative yields, iron(III) hydroxide, and dioxygen. The reactions are characterized by substantial enthalpies of activation (40–60 kJ/mol), very unfavorable entropies of activation, large primary deuterium isotope effects, and a positive Hammett ρ value. Both acid and base catalysis are observed. Acid catalysis is attributed to formation of a more reactive oxidant, HFeO4−, at low pH. Base catalysis is attributed partly to the conversion of the reductants to alkoxide ions at high pH, and partly to the reaction of hydroxide ion with tetraoxoferrate(VI) to give a five-coordinated species, HOFeO43−, that reacts rapidly with nucleophiles. A reaction mechanism involving formation of an intermediate ferrate ester is proposed. Keywords: oxidation, alcohols, potassium tetraoxoferrate(VI), ferrate esters, base catalysis, acid catalysis.
Electrochemical studies on sulphonephthaleins. Part 3. Kinetics of electrochemical reduction of xylenol orange and square-wave adsorptive cathodic stripping voltammetry of its lanthanum complex
Authors: Abdel-Hamid Refat , El-Sagher Hussein M. , Rabia Mostafa K.
Published: May 2006

The electrochemical reduction behaviour of xylenol orange, XO, in aqueous medium was studied over a pH range of 2.3–9.6 at a hanging mercury drop electrode, HMDE, on the basis of cyclic voltammetric, and double-potential step chronoamperometric and chronocoulometric data. The experimental results indicate that in acid medium (pH 2.28) the reduction of XO proceeds via an ECEC, first-order mechanism giving a single two-electron diffusion-controlled cyclic voltammetric wave. It was concluded that the rate-determining step is the protonation of the protonated anion intermediate to the final product, with rate constant k2 of 0.26 s−1. At pH 7.25 the reduction follows an ECE kinetics along two cyclic voltammetric waves in which the first wave was attributed to an EC, first-order process and the second wave to an irreversible electron transfer step, E. On addition of lanthanum(III) to xylenol orange, it forms 1:1 and 1.2 La(III)–XO chelates, which are adsorbed and reduced on the HMDE at more negative potentials than the peak potential of free XO. The adsorptive cathodic stripping voltammetry, ACSV, of these chelates was studied using the square-wave, SW, method. It was found that the SW-ACSV of La(III)–XO can be applied to the determination of lanthanum at the nanomole level. Optimum conditions and the analytical method of determination were presented and discussed. Keywords: electrochemical, reduction mechanism, xylenol orange, lanthanum complex, double potential step chronoamperometry and chronocoulometry, stripping voltammetric determination.
Three-dimensional electron delocalization: a theoretical study based on the pentacyclo[3.3.1.13,7.01,3.05,7]decane system
Authors: Chan Mary S.W. , Arnold Donald R.
Published: May 2006

The concept of electron delocalization, and the possibility of aromaticity in three dimensions has been introduced, but remains relatively unexplored. This work examines the structure and energy of a series of ions generated from pentacyclo[3.3.1.13,7.01,3.05,7]decane (1). The ions considered are the dication (12+), the radical cation (1+•), the radical anion (1−•), and the dianion (12−). The dication belongs to a small group of organic compounds that shows three-dimensional electron delocalization and it has been classified as "three-dimensionally homoaromatic." The relative stability of these ions is estimated by the enthalpy change of isodesmic and disproportionation reactions using energies obtained from HF, MP2, and DFT methods. The structural changes and the reorganization of the frontier orbitals when electrons are successively added to or removed from the neutral molecule (1) are also explored. The results confirm the three-dimensional electron delocalization in 12+ and indicate that it is stable relative to a localized structure with similar features; however, it is highly unstable compared to the radical cation (1+•). The dianion (12−), on the other hand, did not show any evidence for electron delocalization and it is unstable relative to the radical anion (1−•). Keywords: three-dimensional aromaticity, electron derealization, resonance, radical cations, radical anions.
The importance of conformational effects on the carbon–carbon bond cleavage of β-phenethyl ether radical cations
Authors: Perrott A.L. , Lijser H.J.P. De , Arnold D.R.
Published: May 2006

The photosensitized (electron transfer) bond cleavage of some β-phenylethyl ether radical cations has been investigated. In previous studies the feasibility of the bond cleavage was thought to depend on the bond dissociation energy (BDE). However, this simple hypothesis led to several incorrect predictions and therefore additional criteria, conformational effects, were added to the hypothesis. This study has now been extended and additional examples of the importance of the conformation on the carbon–carbon bond cleavage of radical cations are provided. The four β-phenylethyl ethers studied are 2-methoxy-3-phenylbutane (9, both diastereomers), and cis- and trans-2-methyl-3-phenyltetrahydropyran (10c, 10t). Generally, bond cleavage will occur if the (calculated) BDE in the radical cation is less than 55 kJ/mol, and if there is significant overlap between the singly occupied molecular orbital (SOMO) and the vulnerable (C—C or C—H) bond. In the case of a β-phenylethyl ether radical cation, the alkoxy group must also be oriented so that an oxygen lone pair of electrons can overlap with the C—C sigma antibonding (σ*) orbital. The calculated BDE values of the vulnerable C—C bond in the radical cations of the four ethers studied here are well below the threshold value, 55 kJ/mol, and C—C cleavage will therefore be governed by conformational effects. Molecular mechanics (MM3) calculations were used to identify the most stable conformers of the neutral molecules. Based on the calculated angles and overlap between orbitals it was predicted that the global-minimum conformers of the ethers 9 and 10c would not give C—C bond cleavage products or deprotonation to any significant extent. The global minimum of ether 10t is well oriented for C—C cleavage but not for deprotonation. Irradiation of an electron-accepting photosensitizer, 1,4-dicyanobenzene (2), in the presence of the ethers showed that the ethers 9 did not cleave efficiently; no deprotonation or isomerization was observed. This is in good agreement with the predictions based on the MM3 calculations. Both ethers 10c and 10t gave reasonable yields of the C—C cleavage products; in fact, ether 10c cleaved more efficiently than 10t. This can be explained by the fact that a conformer of 10c, only 4.35 kJ/mol higher in energy than the global minimum, is perfectly aligned for cleavage. Ether 10t did not show any evidence for deprotonation whereas 10c did. This is also in good agreement with the calculations. Keywords: photoinduced electron transfer, radical cations, bond cleavage, conformation, molecular mechanics calculations.
Reexamination of the Kirkwood–Westheimer theory of electrostatic effects. V. Effect of charged substituents on the rates of alkaline hydrolysis of substituted strychnines
Authors: Abbas Khamis A. , Hurst Phillip , Edward John T.
Published: May 2006

The rates of hydrolysis in aqueous sodium hydroxide of the alkaloid strychnine and seven of its derivatives have been determined at 50 and 75 °C. The kinetic data indicate that all the compounds, except strychninesulfoni acid-I, hydrolyze by competing second- and third-order mechanisms, involving one and two hydroxide ions, respectively; strychninesulfonic acid-I hydrolyzes by the second-order mechanism only. The quantitative effect of positively charged groups in enhancing, and negatively charged groups in depressing, the rates of hydrolysis is in rough agreement with calculations using Kirkwood–Westheimer theory. Keywords: Kirkwood–Westheimer theory; strychnine derivatives, hydrolysis of; lactams, hydrolysis of; electrostatic effects on rates of alkaline hydrolysis; alkaloids, reactions of.
Arene–manganese and arene–rhenium compounds of formula (arene)M(CO)2(SiCl3)
Authors: Hansen Valerie M. , Male Jonathan L. , Pomeroy Roland K.
Published: May 2006

Derivatives of formula (arene)M(CO)2(SiCl3) (M = Mn, Re) have been prepared in moderate to good yield by the reaction of M(CO)5(SiCl3) and the appropriate arene (with heptane in those cases where the arene was a solid) in an evacuated sealed tube at 230–260 °C for 12–24 h, depending on the arene and the metal. Carefully purified reagents were necessary to obtain satisfactory yields. The (η6-1,4-C6H4tBu2)M(CO)2(SiCl3) complexes in solution exhibit free rotation of the arene ring about the metal atom to −120 °C as ascertained by 1H NMR spectroscopy. The manganese compound did show the onset of decoalescence of two of the signals due to the arene ligand in the 13C{1H} NMR spectrum in CD2Cl2, solution below −90 °C. This, however, is interpreted in terms of restricted rotation of the tert-butyl substituent rather than restricted rotation of the arene ring. Keywords: arene, manganese, rhenium, restricted rotation.
Solvent structure effects on electrical conductivities of small-ion salts compared to large-ion salts in C1–C4 alcohols and water
Authors: Zhao Yixing , Freeman Gordon R.
Published: May 2006

The electrical conductances of the small-ion salts LiI and LiNO3 in water and C1–C4 alcohols were measured at different temperatures. At the concentrations used, ion association was negligible except when εT < 4200 K, where ε is the relative permittivity of the solvent at temperature T. Consistent with Walden's rule, the values of ηΛ0 in each solvent are nearly constant as the temperature is increased; the value for LiI in each solvent is slightly higher than that for LiNO3. Ion association occurs in tert-butanol and is more extensive for LiNO3 than that for LiI; the planar NO3− ions fit less well than the spherical I− ions into the packing of the rigid, spherical tert-butanol molecules. The effective radius of solvated ions in CN primary alcohols increases approximately as the length of the randomly folded chain, (N + 1)1/2. For secondary alcohols this factor is somewhat too small for small-ions and too large for large tetraphenyl ions. The values of EΛ0 are close to the values of Eη in the corresponding alcohols. Keywords: electrical conductivity, large ions, small-ions, alcohols, solvent effects.
The design, production, purification, and testing of a chimeric antigen protein to be used as an immunosterilant in domestic animals
Authors: Manns J.G. , Barker C. , Attah-Poku S.K.
Published: May 2006

A method is described for the design of a protein that incorporates a carrier molecule fused to a novel tandem repeat configuration of a 10 amino acid peptide, Gonadotrophin Releasing Hormone (GnRH), which normally would not be immunogenic because it is a self-antigen. This molecule can be produced with adequate yield in E. coli bacteria and purified to homogeneity using standard chromatographic procedures. When low doses of the molecule are injected with an appropriate adjuvant, rats and pigs respond by producing high antibody titres to GnRH. The immunization results in a dramatic reduction of pituitary gonadotrophin secretion and, as a consequence, reduces steroid secretion and causes gonadal atrophy. Keywords: GnRH, fusion protein, immunosterilant, vaccine
The electronic absorption spectra of some N-sulfinylanilines. A molecular orbital treatment
Authors: Abu-Eittah R. , Moustafa H. , Al-Omar A.M.
Published: May 2006

The electronic absorption spectra of N-sulfinylaniline and some of its derivatives were investigated using different solvents. The spectral behavior of the molecules indicated their planarity and that the NSO group is a strong electron acceptor. All the observed bands correspond to delocalized π → π* transitions; n → π* transition were not observed as discrete bands. Ab initio molecular orbital calculations were performed using four different basis sets. The results showed that the NSO group is nonlinear, the molecules studied are planar, and the syn conformer is more stable than the anti conformer. Keywords: N-sulfinylanilines, spectra and theoretical treatment.
A 51V NMR investigation of the interactions of aqueous vanadate with hydroxylamine
Authors: Angus-Dunne Sarah J. , Paul Pradip C. , Tracey Alan S.
Published: May 2006

The aqueous reactions of hydroxylamine and N-methylhydroxylamine with vanadate have been studied. Ligand, vanadium, and proton stoichiometries of the products have been obtained as have their formation constants. At lower ligand concentrations the predominant complex contains a single hydroxamido ligand and this has been assigned a five-coordinate, tetrahedral-like structure where the hydroxamido group is coordinated in a side-on fashion. Four bishydroxamido products were observed. These four complexes consisted of two distinct groups of two isomeric complexes each and have been assigned six-coordinate (tetrahedral-like) and seven-coordinate (trigonal bipyramidal-like) geometries. For the N-methylhydroxamido ligand, 10 bisligand products in 2 groups of 5 isomers each were observed. The additional products over the hydroxylamine situation arise from the relative orientations of the ligand methyl groups. For both ligands, the monoligand products carried a single negative charge and did not have a pKa, within the range of about 6–10. The bisligand products did not carry a charge under neutral conditions. The tetrahedral bisligand products could be protonated under acidic conditions (pKa ~ 6.6) but could not be deprotonated. In contrast, the trigonal bipyramidal products were not protonated under acidic conditions but could give up a proton under basic conditions (pKa ~ 7.4) to form anionic complexes. The relative orientations of the ligands and also the number of methyl groups and their relative orientations in the complex have a significant influence on the 51V chemical shifts. One additional complex was observed to form and was assigned to an ester-like product formed by reaction at the hydroxyl group. Keywords: vanadate, complexes, hydroxylamine, methylhydroxylamine, peroxovanadate.
Rate constants for the reaction of the hydrogen atom with aliphatic ketones in water
Authors: Mezyk Stephen P. , Lossack Annett , Bartels David M.
Published: May 2006

Arrhenius parameters for the reaction of hydrogen atoms with 3-methyl-2-butanone, 3-pentanone, cyclopentanone, 4-methyl-2-pentanone, and 2-butanone in aqueous solution have been directly calculated from electron paramagnetic resonance free induction decay (FID) attenuation measurements. For these compounds, absolute scavenging rate constants at 25.0 °C of (8.84 ± 0.26) × 107, (4.20 ± 0.15) × 107, (4.91 ± 0.28) × 107, (3.25 ± 0.27) × 107, and (2.20 ± 0.32) × 107 dm3 mol−1 s−1, with corresponding activation energies of 17.43 ± 0.29, 20.69 ± 0.31, 18.73 ± 0.36, 22.24 ± 0.80, and 22.30 ± 1.04 kJ mol−1 were determined, respectively. Competition kinetic measurements based on total H2 yields have established that for all of these ketones the dominant hydrogen atom reaction path is by •H atom abstraction. The new activation energy for 2-butanone is much lower than the previously reported value of 40.1 ± 0.7 kJ mol−1 with this difference attributed to interfering reactions from the added bromide previously used as a hydroxyl radical scavenger. Keywords: Arrhenius, kinetics, hydrogen atom, aqueous, ketones.
Orientational order of 1,3-dichloro-2-ethenylbenzene in liquid-crystal solvents
Authors: Rendell J.C.T. , Zimmerman D.S. , Est A.J. van der , Burnell E.E.
Published: May 2006

The order parameter matrices of a molecule that has no symmetry, 1,3-dichloro-2-ethenylbenzene, dissolved in two different nematic liquid-crystal solvents are analyzed in terms of various models for the intermolecular mean-field potential. In a mixture of liquid crystals for which the interaction between the molecular quadrupole moment tensor and the average electric field gradient of the nematic solvent has been minimized, the orientational order is best described by models for the short-range anisotropic potential. The most successful potentials are written in terms of anisotropic interactions between the solute surface and the liquid-crystal mean field. This represents a strong test of such models because they simultaneously fit the five independent orientational parameters obtained from the same solute, thus removing the problems associated with comparing results among different solutes in either the same or a different sample tube. Keywords: liquid crystals, intermolecular forces, order parameters, anisotropic.
Thermodynamics of micellization and solubilization in systems of water – sodium n-alkylcarboxylates – alkoxyethanols at 25 °C
Authors: Huang H. , Verrall R.E.
Published: May 2006

The apparent molar volumes and adiabatic compressibilities, [Formula: see text] of carboxylate surfactants, CnNa (n = 8, 10, 12), in aqueous solutions in the absence and presence of medium-chain-length alkoxyethanols, C4EOX (EO = ethylene oxide group, X = 0–4), and of alkoxyethanols, [Formula: see text] in aqueous solutions in the absence and presence of surfactant, were determined at 25 °C from density and sound velocity measurements as a function of both the surfactant and alcohol concentrations. The partial molar volumetric properties of CnNa and the transfer functions of C4EOX from water to aqueous surfactant solutions were calculated from the apparent molar properties. Values of the thermodynamic parameters of micellization for CnNa, i.e., the critical micelle concentration, the partial molar property of the monomer at infinite dilution, [Formula: see text] and in the micellar state, [Formula: see text] were obtained from simulations of the experimental data, [Formula: see text] using a mass-action model. As expected, these properties are strongly dependent on the surfactant chain length. The distribution coefficient of C4EOX between the micelle and aqueous phases, KD, and the change in the molar property of alcohols due to micellization, [Formula: see text] extracted from fitting the transfer function data of C4EOX using a chemical equilibrium model, show that the solubilization of alkoxyethanols in carboxylate micelles is enhanced by increasing the surfactant chain length and the number of EO groups in the alcohol. The deeper penetration of C4EOX into the micelles of longer chain surfactants is associated with increasingly stronger interactions between surfactant head groups and EO segments of the alcohol on (or near) the micelle surface. Aggregation numbers of CnNa–C4EOX mixed micelles show that addition of a small amount of C4EOX has little effect on the structure of the micelles formed from C8Na and C10Na, but leads to significant change in C12Na micelles. Keywords: sodium carboxylate salts, alkoxyethanols, partial molar volume and compressibility, transfer functions, distribution coefficient, mean aggregation number.
Electrochemical and Raman spectroscopic studies of pyrazine adsorption at the Au(210) electrode surface
Authors: Lannelli Anna , Lipkowski Jacek , Brolo Alexandre G. , Irish Donald E.
Published: May 2006

Chronocoulometry and Raman spectroscopy have been applied to study pyrazine adsorption at the Au(210) electrode surface. The adsorption isotherms, Gibbs energies of adsorption, and the electrosorption valency for pyrazine adsorption at the Au(210) electrode surface have been determined. Surface-enhanced Raman Scattering (SERS) spectra of pyrazine adsorbed on an "unroughened" Au(210) electrode surface have been obtained for the first time. The thermodynamic data and the SERS spectra indicate that pyrazine adsorbs on the Au(210) electrode via the nitrogen lone pair (N-bonded configuration) over the whole range of electrode potentials investigated. Consequently, the pyrazine molecule assumes only the vertical orientation at this surface of gold. The adsorption of pyrazine at the Au(210) and Au(111) surfaces is compared and the influence of the surface crystallography on the adsorption of this molecule at gold electrodes is discussed. Keywords: adsorption at Au(210), pyrazine, SERS, chronocoulometry.
Products from photochemical reactions and electrochemical oxidation of methylenecyclopropane
Authors: Lijser H.J.P. de , Cameron T. Stanley , Arnold Donald R.
Published: May 2006

The reactivity of methylenecyclopropane (MCP, 1) and its radical cation (1+•) have been studied in the presence and absence of a nucleophile (methanol). Photochemical reactions of 1 in the presence of an electron-acceptor (1,4-dicyanobenzene, 6) and a codonor (biphenyl, 7) in acetonitrile (with and without methanol present) or chloroform lead to cycloadditions (ortho, meta, and para; products 12–17) rather than products from photoinduced electron transfer (PET). Based on the measured (cyclic voltammetry, CV) oxidation potential, using the Weller equation, electron transfer (ET) was predicted to occur. It was shown that the measured oxidation potential of 1 represents the adiabatic ionization potential. For PET processes the value for the vertical ionization potential must be used. Electrochemical (EC) generation of 1+• without a nucleophile present results in the formation of one major product: tert-butyl acetamide (25). A series of rearrangements leading to the tert-butyl cation is proposed. Addition of a nucleophile (methanol) to the mixture leads to the formation of 3-methoxy-2-(methoxymethyl)-1-propene (26). This product may arise from trapping of the initially formed ring-opened (trimethylenemethane) radical cation (1a+•), which undergoes a second oxidation and nucleophilic addition (ECE). Keywords: methylenecyclopropane, radical cation, photochemistry, electrochemistry, photocycloaddition.
SCATTERING OF NONCOMMUTATIVE STRINGS
Authors: KAR SUPRIYA , MAJUMDAR SUMIT
Published: May 2006

We obtain S-matrix, for the scattering of two string states, on a noncommutative D3-brane in a path integral formalism. The framework provides a natural setting at Planck energy. It is argued that the effective theory is governed by two different length scales, respectively along the longitudinal and transverse directions. This in turn allows one to view an emerging semiclassical D-string in the theory. Interestingly, the S-matrix generalizes the case of a point-particle Planckian scattering studied in literatures. Our analysis may shed light on the issue of "imaginary string," originally raised by 't Hooft in a point-particle scattering at Planck energy.
A PIECEWISE SMOOTH RANGELAND GRAZING MODEL SHOWS THAT SETTING RECOVERY PERIOD OF PLANT IS BENEFICIAL TO PREVENT OVERGRAZING
Authors: HUI JING , CHEN LAN-SUN
Published: May 2006

Recently, people pay more attention to overgrazing due to its extensive damaging effects on ecological systems. How to solve the remarkable problem is essentially an important topic. In this paper, setting the recovery period of plant population, we simulate the dynamics of rangeland grazing pattern with a mathematical model. Using the corresponding difference system determined by the model, we obtain the critical value of recovery period which is a ratio of the birth rate of grazer population during the grazing period to the sum of it and the death rate of grazer population during the recovery period. If the recovery period is above the critical value, the grazer population will become extinct; if the recovery period is below the critical value, we obtain the explicit expression of the positive periodic solution which is globally stable, i.e. two kinds of population are all persistent. Further, we find the maximum of grazer population's density when the density of grass population is not below a threshold. Our research demonstrates that properly timed grazing plays a key role in protecting grassland environment, or say, the recovery period of plant population is below the critical value; managed grazing is arguably the only natural process by which grassland can be improved on a sustainable basis. Controlled grazing can regenerate grassland, preserve healthy soil and improve livestock production simultaneously. Our results are valuable for rangeland grazing management in practice.
Eastern Literacy, Greek Alphabet, and Homer
Authors: Teodorsson Sven-Tage
Published: May 2006

The still ongoing discussion about the question as to when the Homeric poems were recorded in writing is paradoxical, considering that Milman Parry did not present a clear idea of this issue, while Albert Lord declared his unequivocal opinion that Homer himself dictated them. The notion of a long period of oral transmission until they were finally recorded in the Pisistratean recension can be seen as a continuation of the old 'analyst' theory. It is now time to abandon this theory, seeing that the evidence in favour of recording in the eighth century has become increasingly stronger in recent decades. Three contemporary factors in that century together form decisive evidence indicating that the recording happened at that time, (1) the intense influence of Eastern culture, not least the influence of literacy, (2) the newly invented Greek alphabet, and (3) the appearance of the genius of Homer.
An Example of the Value of Strong Climatological Signals in Tropical Cyclone Track Forecasting: Hurricane Ivan (2004)
Authors: Barrett Bradford S. , Leslie Lance M. , Fiedler Brian H.
Published: May 2006

Since 1970, tropical cyclone (TC) track forecasts have improved steadily in the Atlantic basin. This improvement has been linked primarily to advances in numerical weather prediction (NWP) models. Concurrently, with few exceptions, the development and operational use of statistical track prediction schemes have experienced a relative decline. Statistical schemes provided the most accurate TC track forecasts until approximately the late 1980s. In this note, it is shown that increased reliance on the global NWP models does not always guarantee the best forecast. Here, Hurricane Ivan is used from the 2004 Atlantic TC season as a classical example, and reminder, of how strong climatological signals still can add substantial value to TC track forecasts, in the form of improved accuracy and increased timeliness at minimal computational cost.

In an 8-day period in early September 2004, Hurricane Ivan was repeatedly, and incorrectly, forecast by 12 operational NWP models to move with a significant northward (poleward) component. It was found that the mean 24-h trajectory forecasts of a consensus of five commonly used NWP track prediction aids had a statistically significant right-of-track bias. Furthermore, the official track forecasts, which relied heavily on erroneous numerical guidance over this period, were also found to have significant poleward trajectory errors. At the same time, a climatology-based prediction technique, drawn entirely from the historical record of motion characteristics of TCs in geographical locations similar to Ivan, correctly and consistently indicated a more westward motion component, had a small directional spread, and was supported by a large number of archived cases. This climatological signal was in conflict with the deterministic NWP model output, and it is suggested that the large errors in the official track forecast for TC Ivan could have been reduced considerably by taking into greater account such a strong climatological signal. The potential impact of such an error reduction is a saving of lives and billions of dollars in both actual damage and unnecessary evacuations costs, for just this one hurricane. We also suggest that this simple strategy of examining the strength of the climatological signal be considered for all TCs to identify cases where the NWP and official forecasts differ significantly from strong, persistent climatological signals.
The Power Not to Be (What We Are): The Politics and Ethics of Self-creation in Foucault
Authors: Hofmeyr Benda
Published: May 2006

To some extent, Foucault’s later works on ethics provides an opportunity to go beyond some of the controversies generated by his work of the 1970s. It was thought, for example, that Foucault had overstated the extent to which individuals could be ‘subjected’ to the influence of power, leaving them little room to resist. This paper will consider the ‘politics’ of self-creation. We shall attempt to establish to what extent Foucault’s later notion of self-formation does in fact succeed in countering an over determination by power. In the end, though, it would appear as if Foucault’s turn to ethics amounts to a substitution of ethics, understood as an individualized task, for the political task of collective social transformation. What is at stake is whether or not Foucault’s insistence on individual acts of resistance amounts to more than an empty claim that ethics still somehow has political implications whilst having in fact effectively given up on politics. It will be argued that the subject of the later Foucault’s ethics, the individual, can only be understood as political subjectivity, i.e. that the political potential of individual action is not only ‘added on’ as an adjunct, but that individual action is intrinsically invested with political purport.
Adherence to the screening program for HBV infection in pregnant women delivering in Greece
Authors: Papaevangelou Vassiliki , Hadjichristodoulou Christos , Cassimos Dimitrios , Theodoridou Maria
Published: May 2006

Background

Hepatitis B infection (HBV) is a major Public Health Problem.

Perinatal transmission can be prevented with the identification of HBsAg(+) women and administration of immunoprophylaxis to their newborns. A national prevention programme for HBV with universal screening of pregnant women and vaccination of infants is in effect since 1998 in Greece.

Methods

To evaluate adherence to the national guidelines, all women delivering in Greece between 17–30/03/03 were included in the study. Trained health professionals completed a questionnaire on demographic data, prenatal or perinatal screening for HBsAg and the implementation of appropriate immunoprophylaxis.

Results

During the study period 3,760 women delivered. Prenatal screening for HBsAg was documented in 91.3%. Greek women were more likely to have had prenatal testing. HBsAg prevalence was 2.89% (95%CI 2.3–3.4%). Higher prevalence of HBV-infection was noted in immigrant women, especially those born in Albania (9.8%). Other risk factors associated with maternal HBsAg (+) included young maternal age and absence of prenatal testing. No prenatal or perinatal HBsAg testing was performed in 3.2% women. Delivering in public hospital and illiteracy were identifiable risk factors for never being tested. All newborns of identified HBsAg (+) mothers received appropriate immunoprophylaxis.

Conclusion

The prevalence of HBsAg in Greek pregnant women is low and comparable to other European countries. However, immigrant women composing almost 20% of our childbearing population, have significant higher prevalence rates. There are still women who never get tested. Universal vaccination against HBV at birth and reinforcement of perinatal testing of all women not prenatally tested should be discussed with Public Health Authorities.