bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and mechanism of the aminolysis of benzoic anhydrides
Authors: Choon Lee Byung , Hyun Yoon Ji , Gyu Lee Cheal , Lee Ikchoon
Published: January 2005

Nucleophilic substitution reactions of benzoic anhydrides, in which one of the rings is substituted, with anilines were investigated in methanol. The product‐formation step coincides with the rate–limiting step so that the two rate constants, kXZ and kXZ, for the competitive reaction pathways can be dissected. The two cross‐interaction constants, ρXY and ρXY, especially an unusually large magnitude of the latter, indicate that the reaction proceeds by a frontside SN2 attack on either one of the caronyl carbon with a strong interaction between the nucleophile (X) and the leaving group (Z). The mechanism is also supposed by the trends in the activation parameters.
Anomalous polar substituent effect on 15N NMR chemical shifts of Aniline derivatives. Acylanilides and related compounds
Authors: Yuzuri Tomoaki , Wada Hajime , Suezawa Hiroko , Hirota Minoru
Published: January 2005

The 15N chemical shifts of various m‐ and p‐substituted anilides and related derivatives, ZNHC6H4Y [Z = C6H5CO, CH3CO, CF3CO, CH3SO2, (C6H5O)2PO and H], were correlated with σ− constants. With all series of anilides investigated, the plotted points for the m‐ and p‐substituted derivatives tend to be separated from each other and to lie on two different regression lines. Reinvestigation from this point of view revealed that similar separations occur generally with substituted aniline derivatives. The anomalous polar substituent effect was ascribed to the very large contribution of a resonance effect. In addition, the local π‐polarization effect causes a negative slope for the m‐substituted series in the case of carboxylic anilides.
Water‐Catalysed hydrolysis of p‐nitrobenzyl cellulose xanthate
Authors: Humeres Eduardo , Sequinel Luiz Fernando , Nunes Mauricéa , Oliveira Célia M. S. , Barrie Patrick J.
Published: January 2005

The spontaneous hydrolysis of p‐nitrobenzyl cellulose xanthate (CelXNB) with a degree of substitution (DS) in the range 2–9 was studied in 10% aqueous ethanol at pH 10, and was followed spectrophotometrically by the appearance of p‐nitro‐α‐toluenethiol, in a continuous‐flow system where the reactor was shaken. CelXNB was characterized by solid‐state 13C NMR spectra. The reaction occurs through two parallel processes due to two xanthate ester groups with different reactivities. The fast hydrolysis was ascribed to the reaction of the C‐2 + C‐3 isomers, whereas the slow hydrolysis was due to the C‐6 isomer. The percentage of the latter is much higher than C‐2 + C‐3. The solvent isotope effect of the fast hydrolysis (k′/)k′ 11 was 2·22 ± 0·16 and the proton inventory indicated that there is only one proton transfer involved in the transition state, where a second water (or a neighbouring OH group) acts as a general base. The entropy of activation of the fast hydrolysis was only 3·3 ± 0·8 e.u., suggesting that the water molecules involved are highly oriented with respect to the coordinates required to reach the transition state. It is proposed that they form part of the three‐dimensional hydrogen‐bonded ice‐like structure that involves the cellulose matrix.
Stereochemistry and kinetics of methoxide ion substitution in (Z)‐ and (E)‐O‐methylbenzohydroximoyl cyanides
Authors: Johnson James Elver , Todd Susan L. , Gardner Jana L. , Gardner Toni M. , Buck Patricia , Ghafouripour Abdolkarim , Zimmerman Wayne
Published: January 2005

The stereochemistry and kinetics of the methoxide ion substitution reactions (Z)‐ and (E)‐methylbenzohydroximoyl cyanidc [PhC(CN)NOCH3] were investigated. The reaction of the (Z)‐hydroximoyl cyanide with sodium methoxide in DMSO–methanol (9:1) solution at 44·8°C gives a mixture of methyl (Z)‐O‐methylbenzohydroximate [PhC(OCH3)NOCH3] and the O‐methyloxime of α‐ketophenylacetamide PhC(CONH2)NOCH3. The (E)‐hydroximoyl cyanide undergoes methoxide ion‐catalyzed isomerization to the E‐isomer faster than it undergoes nucleophilic substitution. These observations were interpreted in terms of an addition–elimination mechanism in which the rate‐limiting step is elimination of the nucleofuge (AN + DN#).
Polyaniline intercalated into zeolites, zirconium phosphate and zirconium arsenate
Authors: Chang Te‐Chuan , Ho Shih‐Yeng , Chao Kuei‐Jung
Published: January 2005

Aniline (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

The 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

The 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

A 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

The 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

The 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

Molecular 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

The 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

Transition 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

The 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

A 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

Reversed‐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

The 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

Substituent 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

The 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

The 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

The 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

Reactions 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

Kinetic 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

The 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

The 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

Direct 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

The 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.
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

The 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

The 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

Electrospray 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

An 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

The 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

The 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

1H 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

The 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

Molecular 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

The 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

Rates 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

The 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

Empirical 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

Proton 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

The 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

The 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

The 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

UV 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

The 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

We 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