bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyaniline intercalated into zeolites, zirconium phosphate and zirconium arsenate
Authors: Chang Te‐Chuan , Ho Shih‐Yeng , Chao Kuei‐Jung 
Published: January 2005

AbstractAniline (or aniline hydrochloride) was intercalated into zeolite, zirconium phosphate and zirconium arsenate (proton form and sodium form) and subsequently oxidized to polyaniline (PAN) by ammonium peroxodisulphate. The structure of PAN in the host was studied by electron paramagnetic resonance spectroscopy. PAN in the host gave a free‐radical EPR signal at 2·0035‐2·0037 for the hydrogen or 2·0047‐2·0049 for the sodium form of the host, similarly to the ermeraldine salt (PAN–2S) or emeraldine base (PAN–2A) form of PAN. Saturation occurs in PAN–HZ and PAN–HS. In contrast, the intrachannel PAN in HY was unsaturated under the same conditions. Conduction in PAN–HZ and PAN–HS was predominately carried out by variable‐range hopping and tunnelling respectively, and PAN–HY showed insulating properties.
The kinetics and mechanism(S) of nucleophilic attack by catecholate anion on epibromohydrin‐d2
Authors: Cawley John J. , Onat Ediz 
Published: January 2005

AbstractThe reaction which forms hydroxymethylbenzodioxane from epibromohydrin and catecholate anion was examined by ultraviolet spectroscopy for the kinetics and by proton nuclear magnetic resonance spectroscopy to follow the fate of CD2 from reactant to product. Over the practical temperature range it was found that both CH2 positions in the epihalohydrin are attacked by catecholate anion to give product. Therefore, the difference in energy for the two pathways was small. The individual rate constants were obtained from the total rate constants. Further, the individual ΔH‡ and ΔS‡ values were calculated. It was found that the pathway of higher ΔH‡ had the less negative ΔS‡, which explains the subtlety of two mechanisms being operative over the available temperature range. Interestingly, it proved impossible to prepare epibromohydrin with two deuteriums at only one position in what appeared to be a relatively straightforward synthesis.
Micellar catalysis of organic reactions. Part 35. Kinetic determination of the critical micelle concentration of cationic micelles in the presence of additives
Authors: Broxton Trevor J. , Christie John R. , Dole Anthony J. 
Published: January 2005

AbstractThe critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method. This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations. Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic. Conventional methods cannot be applied with confidence to such systems. The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated. It was wound that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC. The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC. The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.
Intramolecular exchange coupling of arylnitrenes by OXYGEN
Authors: Minato Masaki , Lahti Paul M. 
Published: January 2005

AbstractA series of m,n′‐diazidodiphenyl ethers (m ≤ n, m = 3,4; n = 3,4) was photolyzed at 77 K in frozen, glassy 2‐methyltetrahydrofuran matrices to generate the corresponding diphenyl ether m,n′‐dinitrenes for study by electron spin resonance (ESR) spectroscopy. 3,4′‐Diazidodiphenyl ether gave an ESR spectrum dominated by a mononitrene peak with ∣D/hc∣ = 0·972 cm−1, and also showed a weak dinitrene quintet spectrum with ∣D/hc∣ = 0·162 cm−1 having ESR spectral intensity vs temperature dependence (Curie law) consistent with either a high‐spin ground state or a very small singlet–quintet gap. Di(3‐azidophenyl) ether gave a strong mononitrene peak with ∣D/hc∣ = 0·996 cm−1 and a quintet dinitrene ESR spectrum (∣D/hc∣ = 0·162 cm−1) which exhibited non‐linear Curie law intensity behavior consistent with the quintet being a thermally populated excited state 40 cal mol−1 above a singlet ground state. Di(4‐azidophenyl) ether gave a strong mononitrene peak with ∣D/hc∣ = 0·961 cm−1, but no observable spectrum related to a high‐spin open‐shell dinitrene. The results are consistent with oxygen being a weak exchange coupling linker in pi‐conjugated open‐shell molecules. The observed ground‐state spin multiplicities are in accord with qualitative superexchange and connectivity models, despite any perturbations due to resonance effects between the oxygen linker and p‐nitrene sites.
Kinetics and mechanism of the interaction of amines with aryl β‐haloethyl sulphones
Authors: Matvienko Viktor N. , Perepichka Igor F. , Popov Anatoly F. , Piskunova Zhanna P. 
Published: January 2005

AbstractThe influence of a number of factors, i.e. amine basicity, substrate structure, temperature and deuterium isotope effect, on the rate of phenyl β‐bromoethyl sulphone and aryl β‐chloroethyl sulphone 1,2‐elimination by reaction with amines in acetonitrile was investigated. On the basis of a comparative analysis of the ρ0, β, kH/kD, ΔH‡ and ΔS values obtained with those for the reaction of β‐halopropiophenone 1,2‐elimination, the conclusion was drawn that the E2 mechanism with an anion‐like transition state occurs for the given substrates under the conditions studied.
Unproductive sigma and pi complexes in the reaction of 2‐chloroquinoxaline with piperidine in dimethyl sulphoxide
Authors: Nasielski J. , Rypens C. 
Published: January 2005

AbstractThe rate of the reaction of 2‐chloroquinoxaline with piperidine in dimethyl sulphoxide was measured over a wide range of amine concentrations and at several temperatures. It was found that the order with respect to the nucleophile is close to 1 between 300 and 320 K, but is definitely less at lower and higher temperature. It is suggested that below 300 K an unreactive charge‐transfer complex is formed between the reactants which dissociates at higher temperatures, whereas at temperatures higher than 320 K an unproductive σ complex is formed, the concentration of which increases with increase in temperature.
Molecular mechanics (MM3) study of the structures and energetics of corannulene (C20H10), cyclopentacorannulene (C22H12) and the hemi‐spherical C30H10
Authors: Liu Ruifeng , Zhou Xuefeng , Allinger Norman L. 
Published: January 2005

AbstractMolecular mechanics (MM3) calculations were carried out on the title compounds. Comparison between the MM3 results and those of semi‐empirical and ab initio calculations and experiment indicates that the MM3 results are at least as good as results of much more expensive calculations. The MM3 calculations predict that unlike corannulene and cyclopentacorannulene, the transition state of the bowl‐to‐bowl inversion of the related C30H10 is non‐planar, and the activation barrier is too high for this motion to occur.
Gas phase thermolysis of N‐(tert‐butylthio)allylamine and N‐(tert‐butylthio)diethylamine
Authors: Martin Gonzalo , Ascanio Julian , Rodriguez Jesus 
Published: January 2005

AbstractThe title sulphenamides were pyrolysed in a stirred‐flow reactor at temperatures of 310–410°C, pressures of 8–15 Torr and residence times of 0·4–2 s using toluene as the carrier gas. N‐(tert‐Butylthio)allylamine formed 73 ± 4% isobutene, 23 ± 3% propene and N‐allylthiohydroxylamine. The first‐order rate coefficients for the formation of isobutene and propene, respectively, followed the Arrhenius equations kC4(s−1) = 1012·52 ± 0·36 exp(−163 ± 5 kJ mol−1 RT) and kC3(s−1) = 1010·99 ± 0·29 exp(−151 ± 4 kJ mol−1 RT) N‐(tert‐Butylthio)diethylamine gave 97 ± 1% isobutene, 1·9 ± 0·4% isobutane and N,N‐diethylthiohydroxylamine. The first‐order rate coefficients for isobutene elimination followed the Arrhenius equation k(s−1) = 1013·45 ± 0·24 exp(−164 ± 3 kJ mol−1 RT). The formation of the products is interpreted in terms of an elimination reaction with a unimolecular, four‐centered, cyclic transition state. The reactivity of these sulphenamides was found to be much higher than that of previously studied alkyl or aryl tert‐butyl sulphides and disulphides.
AB initio calculations of Diels–Alder transition structures for hetero‐dienophile additions to cyclopentadiene
Authors: Jursic Branko S. , Zdravkovski Zoran 
Published: January 2005

AbstractTransition states for the hetero‐Diels–Alder addition of formaldehyde, formaldimine, diazene and nitrosyl hydride to cyclopentadiene were located with ab initio molecular orbital calculations. Asynchronous transition structures were located for the asymmetric hetero‐dienophiles, whereas the symmetrical hetero‐dienophile, cis‐diazene, produced a synchronous transition structure. The relative reactivities are in good agreement with the LUMO energies of the hetero‐dienophiles, and the transition states with the exo oxygen or nitrogen lone pairs have lower energies than the corresponding endo lone electron pair transition states. Endo/exo energy differences are much higher than in the addition of ethylene derivatives to cyclopentadiene.
Similarity in physical organic chemistry: Substituent effects on the intrinsic basicity of 4‐substituted pyrazoles
Authors: Notario R. , Herreros M. , Hammadi A. El , Homan H. , Abboud J.‐L. M. , Forfar I. , Claramunt R. M. , Elguero J. 
Published: January 2005

AbstractThe gas‐phase basicities of eight pyrazoles substituted only at position 4 (R4 = H, NO2, F, Cl, CO2C2H5, CH3, NH2, 1‐adamantyl) were measured by Fourier transform ion cyclotron resonance. The experimental values were treated in two ways, first by comparing these values with the AM1‐calculated proton affinities. Since the correlation was reasonably good [PA(calc.) = −11·3 + 1·063PA(exp.), n = 8, r = 0·984], a set of 17 further 4‐substituted pyrazoles and their cations were calculated using the AM1 approximation and their gas‐phase basicities were estimated. Second, both the experimental and the AM1‐calculated values were considered within the framework of the Taft–Topsom analysis of substituent effects. Comparison of the analyses for pyrazoles and pyridines led to the unexpected result that, in spite of differences in ring size and number of heteroatoms, both systems behave remarkably alike.
Stabilities of some 2‐(para‐substituted‐phenyl)‐4,4,5,5‐tetramethyl‐1,3‐dioxolanes relative to their conjugate dioxolenium ions, radicals and carbanions as determined by thermodynamics for hydride and electron transfer in solution
Authors: Arnett Edward M. , Flowers Robert A. , Meekhof Alison E. , Pourjavadi Ali , Walek Stuart A. 
Published: January 2005

AbstractA calorimetric method is described for the determination of the hydride affinities, ΔH(R+) of seven dioxolenium ions from the title compounds and also tropylium, trityl and 9‐phenyl xanthylium cations by hydride transfer to the carbocations from BH3CN−. Cyclic voltammetric methods yield free energies for reduction of the cations to the conjugate radicals and to the carbanions. The ΔH(R+) values correlate well with the first reduction potentials of the cations.
Hydrogen bonding. 38. Effect of solute structure and mobile phase composition on reversed‐phase high‐performance liquid chromatographic capacity factors
Authors: Abraham Michael H. , Rosés Martía 
Published: January 2005

AbstractReversed‐phase HPLC capacity factors, as log k′, have been correlated through the LFER equation:

where k′ is the capacity factor for a series of solutes in a given stationary phase–mobile phase system, and the explanatory variables are the solute descriptors: R2 an excess molar refraction, π the dipolarity/polarizability, Σα the overall hydrogen‐bond acidity, Σβ the overall hydrogen‐bond basicity and Vx the McGowan volume. This equation was applied to various C18 stationary phases with methanol–water, acetonitrile–water and tetrahydrofuran–water buffered mobile phases. The solute and mobile phase factors that influence log k′ values are set out, and a comparison is made between log k′ values and water–octanol partition coefficients.
Superbases in the gas phase. Part II. Further extension of the basicity scale using acyclic and cyclic guanidines
Authors: Raczyńska E. D. , Maria P.‐C. , Gal J.‐F. , Decouzon M. 
Published: January 2005

AbstractThe superbase gas‐phase scale has been further extended up to proton affinities of ca 1080 kJ mol−1 by use of cyclic and acyclic guanidines and vinamidines. Structural features such as Y‐conjugation, vinylogy and intramolecular ionic hydrogen bonding leading to their superbasic behaviour are analysed. Solvation effects by water and acetonitrile on basicity are discussed. From a correlation pKa(acetonitrile) vs gas‐phase basicity, proton affinity values in the range 1070–1410 kJ mol−1 are predicted for Schwesinger phosphazene compounds.
Substituent effects for the BF3‐mediated reactions of allyltributyltin and allyltriethyllead with benzaldehyde
Authors: Yamataka Hiroshi , Nishikawa Kazuyoshi , Takatsuka Tsutomu , Hanafusa Terukiyo 
Published: January 2005

AbstractSubstituent effects were measured for the reactions of substituted benzaldehydes with allytributylin (1) and allyltriethyllead (2) reagents in the presence of BF3.OEt2 in CH2Cl2. The Hammett p values were small and positive at 25 °C and negative at −78 °C for both 1 and 2. These could be interpreted in terms of the contribution of electrophilic complexation between the aldehyde function and BF3 as a rate‐limiting step. A large negative p value was observed for the complex‐formation equilibria between substituted benzaldehydes and BF3.
Pressure and solvent effects on the kinetics of a Menshutkin reaction in aliphatic alcohols
Authors: Viana César A. N. , Calado António R. T. , Pinheiro Lídia M. V. 
Published: January 2005

AbstractThe kinetics of the Menshutkin reaction between triethylamine and iodoethane was studied at 313 K in seven primary and secondary alkanols. An accurate conductimetric method was employed to obtain second‐order rate constants at pressures of 0·1–200 MPa. Volumes and isothermal compressions of activation were calculated by different model‐based equations which are compared. Activation volumes at 0·1 MPa are in the range −26 to −33 cm3 mol−1. Procedures for dissecting intra‐ and intermolecular contributions to the volume of activation are discussed. A clear dependence of model parameters on the solvent volumetric properties was found.
Infrared study of the proton acceptor ability of metyrapone
Authors: Migchels P. , Zeegers‐Huyskens Th. 
Published: January 2005

AbstractThe hydrogen bond complexes between metyrapone [methyl‐1,2‐di(3‐pyridyl)propan‐1‐one] and hydroxylic proton donors (phenols, water) were investigated by infrared spectroscopy. The thermodynamic and spectroscopic data determined in carbon tetrachloride suggest that the nitrogen atom of the pyridine ring A [bonded to the C(CH3)2 group] is the main hydrogen bond interaction site. The data are compared with di‐2‐pyridylglyoxal complexes where the hydrogen bonds are formed on the oxygen atom of the carbonyl function. In the solid adduct of metyrapone with HCl, protonation takes place on the two nitrogen atoms of the pyridine rings. The data from this work are compared with those from chemical oxidation, which leads predominantly to the formation of mono‐N‐oxide A and di‐N‐oxide.
Kinetics of the reaction of amines with 1,1,1‐trichloro‐4‐methoxy‐3‐penten‐2‐one
Authors: Gesser José Carlos , Zucco César , Nome Faruk 
Published: January 2005

AbstractThe kinetics of the reaction of 1,1,1‐trichloro‐4‐methoxy‐3‐penten‐2‐one with various aliphatic and aromatic amines was studied at 25°C in water, dimethyl sulphoxide, methanol, ethanol, chloroform, toluene and hexane. The formation of the corresponding 1,1,1‐trichloro‐4‐amino‐3‐penten‐2‐one is explained in terms of an addition–elimination mechanism.
Efficient and/or selective methylation by diazomethane of alcohols, halo alcohols, glycols, amino alcohols and mercapto alcohols with the use of a proton‐exchanged X‐type zeolite as an acid–base bifunctional catalyst
Authors: Takeuchi Hiroshi , Kishioka Hiroaki , Kitajima Kunio 
Published: January 2005

AbstractReactions of diazomethane with butanol, allyl alcohol and β‐ and γ‐halo alcohols led to efficient methylation (giving the corresponding methyl ethers) with the use of a proton‐exchanged X‐type zeolite compared with H2SO4. The reactions with propylene and isobutylene glycols using the zeolite provided regioselective methylation of the primary OH rather than the secondary or tertiary OH, whereas regioselectivity was not observed in the reactions using H2SO4. The reactions with 2‐aminoethanol and 2‐mercaptoethanol showed high chemoselective S‐methylation and N‐monomethylation, respectively, in the presence of the zeolite instead of H2SO4. The mechanism for the reactions is proposed to involve acid–base bifunctional catalysis of the zeolite in which the acidic site reacts with diazomethane to form its conjugate acid, and the nucleophilicity of OH and SH groups is enhanced by the interaction of the basic site with the proton of the groups.
Kinetic studies on the pyramidal inversion of optically active selenonium imides
Authors: Kamigata Nobumasa , Taka Hideo , Matsuhisa Ayumi , Shimizu Toshio 
Published: January 2005

AbstractKinetic studies were carried out on the thermal epimerization by pyramidal inversion of optically active (S)‐(−)Se‐ and (R)‐(+)Se‐4‐[(‐)‐menthyloxycarbonyl]phenyl(2′,4′,6′‐triisopropylphenyl)selenonium‐N‐toluene‐4″‐sulphonimides (1). The first‐order rate constants for the pyramidal inversion of (S)‐(−)Se‐1 and (R)‐(+)Se‐1 were determined and the activation enthalpies and entropies were calculated. A fairly large difference was found in the activation parameters between optically active (S)‐(−)Se‐1 and (R)‐(+)Se‐1, i.e. a large negative activation entropy was obtained in the case of (R)‐(+)Se‐1.
Mechanistic aspects of ‘ligated’ anionic living polymerization (LAP): The case of (meth)acrylic ester monomers
Authors: Wang Jin‐Shan , Jérôme Robert , Teyssieacute; Philippe 
Published: January 2005

AbstractThe recently developed ‘ligated’ technique has proved to be very successful in promoting living anionic polymerization of (meth) acrylic ester monomers. The efficient ligands discovered to date include μ, σ and μ–σ dual types. The roles of these ligands in the control of livingness and stereoregularity of anionic polymerization of (meth) acrylates are discussed in detail. There is convincing evidences that both ligation thermodynamics (electron density redistribution and steric hindrance in the formed active complex) and kinetics (how fast and in which way ligation occurs) are very critical in promoting the livingness. Moreover, steric hindrance appears to be a determining factor maintaining the process ‘living’ under more demanding conditions.
Synthetic and mechanistic aspects of anionic polymerization of (METH)acrylates initiated by metal‐free salts of CH‐acidic compounds
Authors: Reetz Manfred T. , Hütte Stephan , Goddard Richard 
Published: January 2005

AbstractThe tetrabutylammonium salts of CH‐acidic compounds (malonic acid diesters and diamides, nitropropane, phenylacetic and phenylpropionic acid esters and 9‐ethyltfuorene) serve as inexpensive initiators for the anionic polymerization of acrylates and methacrylates at room temperature. Molecular weights of 1500–25,000 can be reached, the molecular weight distributions being fairly narrow (D = 1·1–1·4 in optimized cases). Side‐reactions as monitored by GC analyses include backbiting and Hofmann elimination, which means that the process is not a true living polymerization. The x‐ray structural analyses of the tetrabutylammonium salts of phenylacetic and 2‐phenylpropionic and 2‐phenylbutyric acid esters show that anions and cations interact with one another via hydrogen bonding. Therefore, the initiators cannot be considered to be naked anions, a conclusin which very likely also applies to the growing polymer chain end during polymerization.
Living cationic polymerization of isobutyl vinyl ether by the CF3CO2H–SnCl4–nBu4NCl system: In situ direct analysis of the growing species by 1H, 13C and 19F NMR spectroscopy
Authors: Katayama Hiroshi , Kamigaito Masami , Sawamoto Mitsuo , Higashimura Toshinobu 
Published: January 2005

AbstractDirect 1H, 13C and 19F NMR spectroscopic analysis was carried out on the carbocationic intermediate generated in the interaction of tin(IV) chloride (SnCl4) with the adduct [4, CH3CH(OiBu)OCOCF3] of isobutyl vinyl ether (IBVE) and trifluoroacetic acid (CF3CO2H), either in the presence or in the absence of tetrabutylammonium chloride. The reactions were to mimic the living cationic polymerization of IBVE by the 4–SnCl4 initiating system (with added nBu4NCl) that was also found in this study. In CD2Cl2 solvent at −78°C, the 1H and 13C NMR analysis revealed the formation of a carbocationic intermediate [CH3C+H(OiBu)] that is in a rapid exchange equilibrium with the covalent counterpart 4. For the first time, the cation formation was further supported by 19F NMR analysis on the counteranionic part (CF3COO−) in 4, where, with SnCl4, the CF3 group gave a broadened signal that appeared clearly downfield relative to that in the covalent form. These and other results, which are in close correlation with the corresponding polymerizations, demonstrated the following: (i) the SnCl4‐assisted generation of carbocationic species from the covalent ester 4; (ii) a rapid exchange between the cation and its covalent precursor 4; (iii) the relatively high cationic concentration in the salt‐free system, where no living polymerization occurs; and (iv) the effective suppression of the cationic species in the presence of the salt, which proved to be the prime key factor for living polymerization.
Nature and concentration of active species in cationic polymerization of vinyl ethers: A kinetic investigation
Authors: Cramail Henri , Deffieux Alain 
Published: January 2005

AbstractThe Kinetics of the polymerization of isopropyl vinyl ether, isobutyl vinyl ether (IBVE) and chloroethyl vinyl ether initiated by HI in CH2Cl2, in the presence and in the absence of tetrabutylammonium iodide as common anion salt, were investigated. The polymerizations proceed directly through the carbon–iodide termini without any necessary electrophilic activator. As previously observed with cyclohexyl vinyl ether, it was found that the addition of small amounts of salt, (0·5–10% with respect to initial [HI], depending on the monomer) drastically reduces the polymerization rate and leads to living‐type polymerizations. Higher amounts of salt have no influence on the polymerization rate which remains constant over a broad range of [NBu4I]/[HI] ratios. This general behaviour, observed for the all vinyl ethers, suggests a common ion salt effect and therefore an ionic polymerization mechanism involving ion pairs and free ions. In the absence of salt, both ion pairs and free ions of higher reactivity participate in the propagation, whereas only ion pairs contribute to the propagation in the presence of a common ion salt. According to this scheme, the living character of the polymerization is assumed to result from a propagation reaction governed by undissociated ionic species. The validity and the implications of this reaction scheme, in terms of active centre concentrations, are also discussed.