bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitroxide mediated free radical polymerization process – autopolymerization
Authors: Georges Michael K. , Kee R. Andrew , Veregin Richard P. N. , Hamer Gordon K. , Kazmaier Peter M. 
Published: January 2005

AbstractThe autopolymerization of styrene in the presence of TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinyloxy free radical), with and without organic acids, such as benzoic acid and camphorsulfonic acid, was studied. Broad polydispersities are obtained in the absence of acid, whereas narrower polydispersities are obtained in their presence. The significance of these results for the synthesis of narrow polydispersity polystyrene by the TEMPO‐mediated living polymerization process is discussed.
Complexation of spiropyrans with cyclodextrins: Effects of β‐ and γ‐cyclodextrins on the thermal isomerization of 6‐SO‐spiropyran
Authors: Sueishi Yoshimi , Nishimura Tomonori 
Published: January 2005

AbstractThe thermal isomerizations of 1′,3′,3′‐trimethyl‐spiro[2H‐1‐benzopyran‐2,2′‐indoline]‐6‐sulphonic acid (6‐SO‐SP) between its spiro (SP) and merocyanine (MC) forms were followed spectrophotometrically in the presence of cyclodextrins (β‐ and γ‐CDs) at various pressures. From the pressure dependence of the isomerization rate, the activation volumes for the thermal isomerization of 6‐SO‐SP were estimated to be 17·1 cm3 mol−1 for MC → SP and 8·5 cm3 mol−1 for SP → MC. The equilibrium constants (K) for the inclusion complex formation of CDs with 6‐SO‐SP were determined at various pressures. It was found that the stability of the 1:1 inclusion complex between 6‐SO‐SP and CDs decreases in the order β– > γ– > α‐CD. From the pressure dependence of K, the reaction volumes were estimated to be −0·9 cm3 mol−1 for the 6‐SO‐SP–β‐CD system and 4·0 cm3 mol−1 for the 6‐SO‐SP–γ‐CD system. Based on the activation volumes, the structure of the transition state for the thermal isomerization is discussed and an explanation for the effect of CDs on the reaction rate is given. The difference in the reaction volumes for the inclusion complex formation of β‐ and γ‐CDs is explained in terms of the difference in the number of water molecules excluded from the CD cavity.
Electrospray mass spectral studies of aromatic diazonium cations. Part 2. The surprising stability of some substituted 2‐nitrobenzene diazonium cations to collisionally activated fragmentation
Authors: Broxton Trevor J. , Colton Ray , Traeger John C. 
Published: January 2005

AbstractElectrospray mass spectra of a series of substituted 2‐nitrobenzene diazonium cations reveal a surprising stability of the intact ion to the collisionally activated loss of nitrogen, contrary to the behaviour of monosubstituted benzenediazonium ions reported previously. Ions bearing elecron‐releasing groups at the para position, e.g. 4‐CH3, 4‐CH3O, and 4‐C6H5O, all experience loss of this para substituent rather than loss of nitrogen. However, ions bearing electron‐withdrawing para substituents, e.g. 4‐NO2 4‐CN, 4‐CF3 and 4‐Cl, all undergo nuleophilic displacement of the 2‐nitro group by water to give the corresponding phenol derivative, which subsequently loses nitrogen. The exceptional stability of these substituted 2‐nitrobenzene diazonium salts is attributed to a favourable coulombic interaction between the positive charge on the diazonium group and the partial negative charge on one of the oxygen atoms of the nearby nitro group. Once that nitro group has been removed, the resulting substituted 2‐hydroxybenzenediazonium cation loses nitrogen in the normal way.
Quantitative description of acidity of XOH compounds in the gas phase and dimethyl sulphoxide with use of HOMO energies of XO− anions
Authors: Vlasov Vladislav M. , Koppel Ilmar A. , Burk Peeter , Koppel Ivar 
Published: January 2005

AbstractAn approach to the quantitative evaluation of XOH acidity in the gas phase and in dimethyl sulphoxide solution is described. It is based on one‐parameter correlations between the acidities of XOH family members and the electron affinities of the XO radicals or highest occupied molecular orbitals (HOMO) energies of the correspondging XO− anions. The approach is based on Koopmans' theorem and provides familial correlations for the acidities of alcohols, carboxylic acids, phenols and mineral acids with calculated (MNDO, AM1 or PM3) HOMO energies of their anions.
Complexation of tropylium ions with crown ethers and acyclic polyethers examined by fast atom bombardment mass spectrometry
Authors: Lämsä Markku , Kuokkanen Toivo , Jalonen Jorma , Virtanen Olavi 
Published: January 2005

AbstractThe molecular complex formation of six macrocyclic and six acyclic polyethers with tropylium and 4‐methoxyphenyltropylium tetrafluoroborates was observed and characterized in the gas phase by fast atom bombardment mass spectrometry (FABMS), to obtain information on intrinsic molecular interactions in the absence of the complicating effect of solvation. The stoichiometry of the complexes was assessed on the basis of corresponding peaks in FAB mass spectra. In addition to the expected 1 : 1 complexes between polyether and tropylium ion, some 2 : 1 complexes were also formed. The stability order of selected complexes was studied in competition experiments. The complexation equilibrium constant and thermodynamic parameters for the interaction of dibenzo‐18‐crown‐6 with tropylium ion were determined in 1,2‐dichloroethane solution by UV‐visible spectrophotometry. Complexation of polyethers with tropylium salts has not been reported previously.
Kinetic isotope effect probe for the π‐facial stereoselectivity in nucleophilic additions to cyclohexanone: A theoretical study
Authors: Yamataka Hiroshi 
Published: January 2005

AbstractThe origin of the π‐facial selectivity in nucleophilic additions to cyclohexanone was analysed by means of ab initio MO calculations (MP2/6–31G*//HF/6–31G*). The calculations showed that BH3 attacks at the axial side whereas MeLi attacks at the equatorial side. Calculated kinetic and equilibrium deuterium isotope effects and the structures of the transition states (TSs) demonstrated that four factors, stabilization of the axial TS by antiperiplanar allylic bonds, destabilization of the equatorial TS by torsional strain, destabilization of the axial TS by steric hindrance between a nucleophile and the 3,5‐axial hydrogens and destabilization due to the conformational deformation of the ring in both the equatorial and axial TSs, operate in the same direction and can bring about the apparent selectivity changeover. The magnitudes of anti‐D KIEs for the MeLi and the EtLi additions to acetone were consistent with the Anh‐Eisenstein model rather than the Cieplak model.
Multinuclear, variable‐temperature NMR study of hydrogen bonding in two ortho‐Mannich bases
Authors: Sitkowski Jerzy , Stefaniak Lech , Rospenk Maria , Sobczyk Lucjan , Webb Graham A. 
Published: January 2005

Abstract1H and 13C NMR data for 2‐diethylaminomethyl‐3,4,6‐tri‐ and ‐tetrachlorophenols in CH2Cl2 solutions at a variety of temperatures are reported. The results are consistent with intramolecular hydrogen bonding and proton transfer as shown in the structure 3. Concentration dependence of the NMR data for the perchloro compound shows an additional hydrogen bonding process attributed to the solute self‐association. The 1H, 13C and 15N NMR data support the proposed proton transfer structure.
Solvent dependent difference in pK behaviour in N‐methylaniline and N‐phenylhydroxylamine
Authors: Fountain K. R. , Cassely Aaron J. , New Dallas G. , White Robert D. , Xu Yu‐Bo 
Published: January 2005

AbstractThe pK values of the conjugate acids of N‐phenylhydroxylamines change drastically when the pK values are determined in dimethyl sulfoxide (DMSO) rather than methanol. The Hammett ρ values change from −5·69 to −1·20 on going from methanol to DMSO for protonated N‐phenylhydroxylamines, in contrast to a shift of −4·70 to −4·83 for protonated N‐methylanilines in the same two solvents. This large change in susceptibility indicates that the species from which the proton departs is not the same for protonated N‐phenylhydroxylamines in the two solvents. Experimental and computational evidence supports ionization of the H+ from the O atom for the protonated N‐phenylhydroxylamines in DMSO.
Structure–reactivity correlations for aza‐arenes. Proton affinities, pKa values, hydrogen–deuterium exchange rates and radical‐induced 13C shifts
Authors: Spanget‐Larsen Jens 
Published: January 2005

AbstractMolecular reactivity parameters based on the concept of an effective electronic potential and defined as a simple function of the molecular charge distribution were applied in a study of various aspects of the chemical reactivity of azabenzenes and azanaphthalenes. Excellent linear correlations were obtained for proton affinities, pKa values, H–D exchange rate exponents and 13C shifts induced by the paramagnetic shift reagent TEMPO. In the last case, the predictions for quinazoline prompted a reinvestigation of the 13C NMR spectrum of this compound, resulting in a reassignment of the spectrum relative to the assignment assumed by Grant and co‐workers.
Structures and properties of 1,2‐dithiolylium‐4‐methide, 1,2‐dithiolylium‐4‐olate and 1,2‐dithiolylium‐4‐thiolate: An MO study at the HF and post‐HF levels
Authors: Mann Matthias , Fabian Jürgen 
Published: January 2005

AbstractThe molecular and electronic structures of the cyclic 1,2‐dithiolium ylides (2) and their acyclic dithiocarbonyl valence isomers (4) were studied by ab initio methods. All molecular structures were fully optimized at the R(U)HF/6–31G* and R(U)MP2/6–31G* levels of theory. The results of the restricted and unrestricted Hartree–Fock (HF) calculations are less reliable since the RHF wavefunctions of the cyclic compounds proved to be singlet/triplet unstable. A marked ground‐state energy depression occurs on passing from restricted to unrestricted HF methods. The title compounds are of diradicaloid nature and belong to the non‐classical class of structures. The heterocycles are planar and display C2v symmetry, while the cisoid open‐chain dithiocarbonyl isomers are slightly distorted (C2 symmetry). According to the calculated bond lengths and charge distributions, the title compounds are in fact more or less zwitterionic. The thiolate is the most polar compound of this series. According to RMP2 calculations, the thiolate (2, X = S) and olate (2, X = O) should exist in the single ground rather than in the triplet state. However, in these cases the isomeric acyclic compounds are predicted to be almost isoenergetic with the cyclic compounds. Since the cyclic ylides have higher dipole moments than the acyclic dithiocarbonyls, the ylides will gain stability in polar solvents. However, the continuum quantum chemical model used in estimating the solvent effect does not favour the ring compounds sufficiently to exclude valence isomerization between the ring‐closed and ring‐open compounds.
Acid‐catalyzed hydrolysis of phenyldiazoacetic acid. Effect of an α‐diazo group on carboxylic acid acidity
Authors: Kresge A. J. , Mathew L. , Popik V. V. 
Published: January 2005

AbstractRates of acid‐catalysed hydrolysis of phenyldiazoacetic acid were measured in aqueous solution at 25°C across the entire acidity range pC = 1–13. The reaction was found to occur through both the non‐ionized and inonized forms of the substrate, with the ionized form reacting faster by a factor of 650. Appreciable solvent isotope effects in the normal direction (kH/kD > 1) and the occurrence of general acid analysis show that hydrolysis occurs by rate‐determining proton transfer to the diazocarbon atom of the substrate. Analysis of the rate profile for the reaction provides an estimate of the acidity constant of phenyldiazoacetic acid, pKa = 3·70, which is apparently the first determination of the acid strength of an α‐diazocarboxylic acid. Comparison of this result with the pKa of phenylacetic acid shows the diazo group to have a mild (4×) acid‐strengthening effect, whose modest magnitude is attributed to opposing resonance and polar effects.
Protonation of fully aromatic betacarbolines in highly concentrated sulphuric acid media
Authors: Carmona Carmen , Muñoz María A. , Guardado Pilar , Balón Manuel 
Published: January 2005

AbstractThe monocation–dication equilibria of 6‐nitro and 6‐sulphonic acid derivatives of betacarboline (9H‐pyrido[3,4‐b]indole) were investigated mostly by UV‐visible absorption spectroscopy. Dications are formed in very highly concentrated sulphuric acid solutions (>15 M). Ionization constants, pKa values and solvation parameters obtained from the excess acidity method are reported. The unusually high m* parameters are discussed and compared with other related data.
Determination of the empirical polarity parameter ET(30) for binary solvent mixtures
Authors: Mancini P. M. E. , Terenzani A. , Gasparri M. G. , Vottero L. R. 
Published: January 2005

AbstractEmpirical solvent polarity parameters ET(30) were determined by UV–visible spectrophotometry using Dimroth– Reichardt's betaine dye, as a function of composition, for (aprotic + aprotic) and (aprotic + protic) binary solvent mixtures. For (aprotic + aprotic) solvent systems the cosolvent was toluene, and the other solvents used were selected with different structural characteristics and an extensive range of polarity: chloroform, 1,4‐dioxane, ethyl acetate, tetrahydrofuran, acetone, nitromethane and N,N‐dimethylformamide. For (aprotic + protic) solvent systems, the protic cosolvent used was methanol, and the aprotic solvents selected were toluene, chloroform, 1,1,1‐trichloroethane, tetrahydrofuran, acetone, N,N‐dimethylformamide, and dimethyl sulphoxide. Each system was analysed according to its deviations from additivity due to selective solvation of the betaine. A preliminary application of these empirical solvent polarity parameters was related to the solvent effects in a simple example of a nucleophilic aromatic substitution reaction.
Ground‐ and excited‐state prototropic tautomerism in anils of aromatic α‐hydroxy aldehydes studied by electronic absorption, fluorescence and 1H and 13C NMR spectroscopies and semi‐empirical calculations
Authors: Alarcón Sergio H. , Olivieri Alejandro C. , Cravero Raquel M. , Labadie Guillermo , González‐Sierra Manuel 
Published: January 2005

AbstractProton transfer processes in both the ground and excited states in anils of aromatic α‐hydroxyaldehydes (salicylaldehyde, 2‐hydroxynaphthalene‐1‐carbaldehyde and the novel 10‐hydroxyphenanthrene‐9‐carbaldehyde) have been studied by a combination of spectroscopic techniques. Solution 1H and 13C NMR is used to establish the position of the tautomeric equilibria. UV‐visible absorption and fluorescence spectral data help to characterize the existence, in all cases, of excited‐state intramolecular proton transfer (ESIPT) pheonmena. Semi‐empirical calculations involving full geometry optimization and calculation of heats of formation for the ground state (AM1) and vertical excitation energies and oscillator strengths (INDO/S) are in agreement with the experimental observations.
Equilibrium of α‐aminoacetonitrile formation from formaldehyde, hydrogen cyanide and ammonia in aqueous solution: Industrial and prebiotic significance
Authors: Moutou G. , Taillades J. , Bénefice‐Malouet S. , Commeyras A. , Messina G. , Mansani R. 
Published: January 2005

AbstractThe equilibrium constant, K, for the formation of α‐aminoacetonitrile from formaldehyde, ammonia and hydrogen cyanide was evaluated at 25°C. A first estimation of K was obtained from extrathermodynamic relationships of the type log K′ vs ∑σ*. The final value was then obtained from a comparison of the experimental and calculated pH dependences of α‐hydroxy‐ and α‐aminoacetonitrile concentrations. From these results, it appears that, after equilibrium, the ratio between the concentrations of the two precursors glycine and hydroxyethanoic acid, is a linear function of the concentration of free ammonia, i.e. [CH2(OH)CN] [CH2(NH2)CN] = 21 [NH3] at 25°C.
Electronic structure of the 1,3‐diphosphetane
Authors: Schoeller Wolfgang W. , Goette Burkard , Tubbesing Ulrike 
Published: January 2005

AbstractThe equilibrium structures of cis‐ and trans‐1,3‐diphosphetane were evaluated at the RHF/6–31g** level of optimization, with MP2 electron correlation correction. Both structures are puckered, the trans isomer being slightly lower in energy than the cis isomer. The inversion barrier in 1,3‐diphosphetane is lower in energy than in phosphetane.
Ab initio study of the low reactivity of thiophene in Diels–Alder reactions with carbon dienophiles
Authors: Jursic Branko S. , Dzravkovski Zoran , Whittenburg Scott L. 
Published: January 2005

AbstractThe utility of thiophene as a diene for Diels–Alder reactions was studied by ab initio methods. The reactivity was evaluated with three dienophiles, vinyl alcohol, ethylene and acrylonitrile. Qualitatively the reactivity was determined by comparison of the reactant's frontier orbital energies, bond orders and charge transfer in the transition states. Quantitatively the reactivity was determined by estimation of activation energy with RHF/6‐31G*, MP2/6‐31G*, MP3/6‐31G*//MP2/6‐31G*, and MP4/6‐31G//MP2/6‐31G* ab initio calculations. The results of the calculations predicts that the reactivity of thiophene with acrylonitrile is similar to butadiene and ethylene with a preferred formation of the endo isomer.
Successful application of the spin‐delocalization substituent constant σ. to the correlation of the UV spectra of some model compounds with para‐Y‐substituted phenyl groups
Authors: Jiang Xi‐Kui , Ji Guo‐Zhen , Wang Daniel Ze‐Rong , Xie John Rong‐Yuan 
Published: January 2005

AbstractUV spectra of 16 p‐Y‐substituted phenylacetylenes (I‐Ys), nine p‐Y‐substituted acetophenones (2‐Ys) and six p‐Y‐substituted‐p′‐methylsulphonylstilbenes (3‐Ys) were measured and correlated against spin‐delocalization substitutent constants (σ.) with confidence levels above 99·9%. UV spectra of five ethyl 3‐hydroxy‐3‐(p‐Y‐substituted‐phenyl)‐propanates (4‐Ys) and five 1‐(p‐Y‐substituted‐phenyl)‐3‐butyn‐1‐ols (5‐Ys) were also measured. Correlation analysis results are discussed. Some literature UV data were also successfully correlated by the dual‐parameter equation.
Hydride transfer reactions of leuco methylene blue and leuco thionine with some p‐benzoquinones
Authors: Yamamoto Shunzo , Fujiyama Yoshimichi , Shiozaki Miki , Sueishi Yoshimi , Nishimura Norio 
Published: January 2005

AbstractThe kinetics of the oxidation of leuco methylene blue and leuco thionine by some p‐benzoquinones were investigated spectrophotometrically by means of the stopped‐flow technique. Leuco methylene blue and leuco thionine were produced by photoreductions of methylene blue and thionine with triethylamine in ethanol in the drive syringe of the stopped‐flow apparatus and their solutions were used as such in the measurement of the oxidation rates. The kinetic isotope effect on the oxidation rate was observed. The results can be explained by the general mechanism with stepwise electron–proton–‐electron transfers.
Polyfluorene containing diphenylquinoline pendants and their applications in organic light emitting diodes
Authors: Su Huei‐Jen , Wu Fang‐Iy , Shu Ching‐Fong , Tung Yung‐Liang , Chi Yun , Lee Gene‐Hsiang 
Published: January 2005

AbstractWe present a short, efficient synthetic route for the preparation of a novel polyfluorene copolymer (PF‐Q) containing two electron‐deficient, 2,4‐diphenylquinoline groups functionalized at the C‐9 positions of alternate fluorene units that form a three‐dimensional cardostructure. The presence of the rigid bulky pendent groups leads to a polyfluorene possessing a high glass‐transition temperature (207 °C) and very good thermal stability (5% weight loss observed at 460 °C). A photoluminescence study revealed that the Förster energy transfer from the excited quinoline groups to the polyfluorene backbone is very efficient; it also demonstrated that the commonly observed aggregate/excimer formation in polyfluorenes is suppressed very effectively in this polymer, even after it has been annealed at 150 °C for 20 h. A light emitting diode (LED) device prepared with PF‐Q as the emitting layer exhibits a stable blue emission with a maximum brightness of 1121 cd/m2 at 12 V and a maximum external quantum efficiency of 0.80% at 250 cd/m2. We also used PF‐Q, which contains diphenylquinoline units that behave as electron‐transporting side chains, as a host material and doped it with 2.4 wt % of a red‐emitting phosphorescent dye, Os(fppz), to realize a red electroluminescence with CIE color coordinates of (0.66, 0.34). The doped device exhibits a maximum external quantum efficiency of 6.63% (corresponding a luminance efficiency of 8.71 cd/A) at a current density of 47.8 mA/cm2, together with a maximum brightness of 10457 cd/m2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 859–869, 2005
Monte Carlo simulation of the Ising ferromagnetic iron nitride system
Authors: Zhang Qi , Liu Junyou , Wei Guozhu 
Published: January 2005

AbstractUsing Monte Carlo methods, we investigate the magnetic properties of a mixed spin‐3/2 and spin‐1 Ising ferromagnetic system on an expanded FCC lattice in Fe4N. In particular, the expanded FCC lattice was divided into one simple cubic lattice composed of Fe(I) at the corner site and three inhomogeneous simple cubic lattices composed of Fe(II) at the face‐centered one. The effect of the next‐neighbor exchange interaction of Fe(I), the next‐neighbor exchange interaction of Fe(II), and the exchange interaction of Fe(II) due to the nitrogen atoms was studied. The magnetization, internal energy and specific heat curve, and the phase diagrams are given. We found that the transition temperature and magnetic moment increase with the increase of the exchange interaction of next‐nearest atoms Fe(I), Fe(II), and the exchange interaction between Fe(II) via nitrogen atoms. It is because of the exchange interaction due to the nitrogen atoms that Fe4N has a higher saturation magnetization than pure iron. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of linear and nonlinear intersubband refractive‐index changes in an asymmetrical semiparabolic quantum well with applied electric field
Authors: Zhang Li , Shi Jun‐jie 
Published: January 2005

AbstractBy using the displacement harmonic variant method and the compact density matrix approach, the linear and nonlinear intersubband refractive‐index changes (RICs) in a semiparabolic quantum well (QW) with an applied electric field have been investigated in detail. Simple analytical formulae for the linear and nonlinear RICs in the system were also deduced. The effect of the band nonparabolicity has been taken into account. Numerical calculations of typical GaAs semiparabolic QWs were performed. The dependence of the linear and nonlinear RICs on the incident optical intensity, the frequency of the confined potential of the semiparabolic quantum well, and the strength of the applied electric field were discussed under both conditions of considering and ignoring the band nonparabolicity. Results reveal that the RICs in the semiparabolic quantum‐well system sensitively depend on these factors. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic properties of small bimetallic LinCum (n, m ≤ 4) clusters. A comparison with Lin and Cun clusters
Authors: Fuentealba Patricio , Padilla‐Campos Luis 
Published: January 2005

AbstractThe electronic structure and geometry of clusters of the type LinCum, LinCu (n, m ≤ 4), Lin, and Cun (n ≤ 8) were theoretically investigated using density functional methods. The LinCum bimetallic system is important to understand the promotion effects of the alkali atoms on the copper surface. Some clear trends have been found. The inclusion of lithium atoms on a bare copper cluster tends to break the CuCu bond favoring the formation of polar LiCu bonds. In comparison with the bare Lin and Cun clusters the geometrical shape and relative stability follow the same trend. However, the interatomic distances show strong variations. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005