bluuebunny/crossref_metadata_2025_split huggingface dataset:
Free radical chain reactions of ate complexes. Electron transfer processes 42
Authors: Russell Glen A. , Hu Shuisheng , Herron S. , Baik Woonphil , Ngoviwatchai P. , Jiang W. , Nebgen M. , Wu Y.‐W. 
Published: January 2005

AbstractIodide ion promotes the free radical reaction of isopropylmercury idide with bromotrichloromethane to yield isopropyl bromide with rate enhancement in the order of 104. The reaction involves electron transfer from i‐PrHgI2− to the trichloromethyl radical in a long kinetic chain process. Iodide ion also promotes the free radical chain conjugate addition of tert‐butylmercury chloride to α,β‐unsaturated ketones, esters, phosphonate esters and sulfones. Competitive reactivity studies indicate that lithium di‐tert‐butylcuprates or tri‐tert‐butylzincates react with 2‐cycloalkenones by a mechanism involving attack by tert‐butyl radicals. No evidence for radical attack is observed for the corresponding n‐butyl ate complexes of copper or zinc.
Complex formation between 1,3,5‐trinitrobenzene and 1,8‐diazabicyclo‐[5,4,0]‐undec‐7‐ene
Authors: Collina Gianni , Forlani Luciano 
Published: January 2005

AbstractThe title reaction is an instance of a simple nucleophilic attack of neutral nitrogen on aromatic sp2 carbon. The kinetic data (obtained in dimethyl sulphoxide) are compared to the results reported by the literature for the same reaction of aliphatic amines. Some possible interactions (substrate/nucleophile, substrate/salt) preceding the attack of the nucleophile are discussed.
Studies on organophosphorus compounds. XXXVI.. Substituent effects of alkylphosphonates and ‐phosphinates in alkaline hydrolysis
Authors: Yuan Chengye , Li Shusen , Liao Xiugao 
Published: January 2005

AbstractAlkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
Stern–Volmer quenching kinetics in photoreaction systems with strong internal filtering: Type II photoreaction of 2‐benzoylcyclohexanone
Authors: Hasegawa Tadashi , Nishimura Michiko , Yoshioka Michikazu 
Published: January 2005

AbstractThe Stern–Volmer quenching equation for a photochemical reaction in the presence of internal filtering was obtained by applying the steady‐state approximation to the system. The equation was used for the kinetic analysis of the Type II photoreaction of 2‐benzoylcyclohexanone yielding 1‐phenylhept‐6‐ene‐1,3‐dione, the enol form of which acts as an effective internal filter. The kqτ value for quenching of the photoreaction by 2,5‐dimethylhexa‐2,4‐diene was determined to be 9·1 ± 0·5 l mol−1.
Anomalous salt effects on a micellar‐mediated reaction of bromide ion
Authors: Bunton Clifford A. , Cowell Charles P. , Nome Faruk , Romsted Laurence S. 
Published: January 2005

AbstractReaction of bromide ion with α‐picryl‐p‐bromoacetophenone (1) is speeded by aqueous cationic micelles of cetyltrimethylammonium bromide (CTABr; C16H33NMe3Br) and dodecyltrimethylammonium bromide (DoTABr; C12H25NMe3Br) and rate constants reach limiting values when 1 is fully bound to micelles of CTABr. Limiting values are not reached in DoTABr, but the data can be fitted to a simple model for the distribution of reactants between water and micelles. Estimated second‐order rate constants at the micellar surface are similar to values in water, but this model cannot explain the observed rate enhancements on addition of NaBr to CTABr. Inert anions such as nitrate, mesylate, n‐butanesulfonate, phenylmethanesulfonate and camphor‐10‐sulfonate inhibit reaction in CTABr by competing with Br− at the micellar surface. Other n‐alkanesulfonate ions (RSO, R = n‐C5H11, n‐C6H13, n‐C7H15, n‐C8H17) and arenesulfonate ions (benzene‐, toluene‐, naphthalene‐1‐ and naphthalene‐2‐sulfonate) behave anomalously. These ions expel Br− from the micelle, as shown electrochemically, but there are maxima in plots of rate constant against mole fraction of Br−. These rate extrema are apparently due to perturbation of the micellar surface structure that overcomes the inhibition due to competition with Br−. These results show that the simple pseudo‐phase, ion‐exchange model can be applied only in dilute electrolyte and in the absence of hydrophobic anions.
Reaction of aryliminodimagnesium with diphenyl diketones: Heat evolution accompanying single electron transfer and chelate formation, and product distribution
Authors: Ōkubo Masao , Fukuyama Yoshinori , Sato Miyuki , Matsuo Koji , Kitahara Tetsuhiro , Nakashima Michio 
Published: January 2005

AbstractReaction of diphenyl diketones (benzils) with aryliminodimagnesium [ArN(MgBr)2, IDMg], a magnesium reagent having condensation ability, was investigated. By comparison of the relative amounts of heat evolved in the reactions of IDMg (mildly electron donating) and ArMgBr (strongly electron donating) with some carbonyl and nitro compounds, results were obtained supporting the reported correlation of the relative yields of normal and abnormal (radical) products with single electron transfer (SET) efficiency estimated by the oxidation and reduction potentials of reactants. A sole exceptional result, i.e. the great heat evolution caused by the combination of benzil and IDMg, was attributed to the generation of tightly chelated radicals via SET. The involvement of stepwise SET was confirmed by ESR. On the basis of these results, substituent effects of benzil and mono‐condensation products on their reduction potentials and on the relative yields of normal (mono‐ and di‐condensation) and abnormal (dimerization) products were examined. All the results were consistently explained in terms of the relative efficiency of chelation (or σ‐complexation) and SET in two main processes. The role of the initial stages involved in the processes governing the final product distribution is discussed.
Correlations of rate and selectivity of a Diels–Alder reaction with Sp parameters
Authors: Cativiela Carlos , Mayoral Jose A. , Avenoza Alberto , Peregrina Jesus M. , Roy Miguel A. 
Published: January 2005

AbstractThe rate and endo/exo selectivity of the Diels–Alder reaction between cyclopentadiene and methyl (E)‐α‐cyanocinnamate at 25°C, in several acetone–water and 1,4‐dioxane–water mixtures, were measured. The linear correlations of log k and log(endo/exo) vs solvophobicity are reported. Correlations for selectivity are considerably improved when the results obtained in acetone–water and 1,4‐dioxane–water are taken as separate series.
N‐Carbeniopyridinium salts: Charge‐transfer complexes with the C5 (COOMe)5 anion; CC bond formation with the TCNQ radical anion
Authors: Maas Gerhard , Weber Hans Martin , Exner Reiner , Salbeck Josef 
Published: January 2005

AbstractN‐[2,3‐Bis(dimethylamino)cyclopropenylio]‐ and N‐(tetramethylamidinio)pyridinium salts (trifluoromethanesulphonates and tetrafluoroborates) form 1:1 and 1:2 charge‐transfer complexes with the pentakis(methoxycarbonyl)cyclopentadienide anion. The x‐ray crystal structures of 1‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium pentakis(methoxycarbonyl)cyclopentadienide tetrafluoroborate hydrate and of 1‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium bis[pentakis(methoxycarbonyl)cyclopentadienide] were determined. In constrast, the tetra‐cyano‐p‐quinodimethane (TCNQ) radical anion reacts with the first‐mentioned salts by CC bond formation to give novel dicationic salts. Thereby, the radical anion attacks the pyridinium γ‐position of the N‐(tetramethylamidinio)‐pyridinium dication, but the three‐membered ring of the N‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium system.
Solvent polarity scales. 1. Determination of ET and π* values for phosphonium and ammonium melts
Authors: Harrod W. Brian , Pienta Norbert J. 
Published: January 2005

AbstractThe solvent polarity of a series of organic salts in their molten state has been determined using the solvatochromic dyes: pyridinium N‐phenolate betaine, the basis of the ET scale, and N,N‐diethyl‐4‐nitroniline, one of the primary standards for the π* scale. Each of these dyes was dissolved in the following liquids: lithium acetate–sodium acetate–potassium acetate eutectic; ethylammonium chloride; dimethylammonium cloride; diethylammonium nitrate; ammonium trifluoracetate; tetraethylammonium acetate; tetrabutylphosphonium chloride; octyltributylphosphonium chloride; dodecyltributylphosphonium chloride; tetrabutylammonium bromide; tetrabutylphosphonium bromide; octyltributylphosphonium bromide; dodecyltributylphosphonium bromide; octyltributylphosphonium iodide; dodecyltributylphosphonium iodide; tetrahexylammonium benzoate; methyltrioctylphosphonium dimethylphosphate; and methyltrioctylammonium chloride. The ultraviolet and visible spectra were measured for each of these. In addition, data were collected as a function of temperature and in the presence of neutral and ionic additives. In general, these molten salts represent solvent polarities equivalent to moderately polar aprotic solvents such as acetone and acetonitrile. The salts with cations capable of being hydrogen bond donors gave considerably higher values, equivalent to or higher than water, the solvent with the highest value on the ET scale. These and the eutectic mixture are thought to involve specific dye–solvent interactions which cause these anomalously high values.
NMR spectroscopic study of configurations and conformations of 5‐pyridylmethylenehydantoins
Authors: Tan Sau‐Fun , Ang Kok‐Peng , How Gee‐Fung 
Published: January 2005

AbstractNine 5‐pyridylmethylenehydantoins were prepared. Each of the 1‐methyl‐substitute compounds was obtained in two stereoisomeric forms. Only one form of each of the 3‐methyl‐substituted and N‐unsubstituted compounds was obtained directly from synthesis but could be partially converted into the other stereoisomer photochemically. The Z/E configurations and the conformational relationship between the pyridine and hydantoin rings were studied by 1H and 13C NMR spectroscopy, including variable‐temperature 1H NMR. The existence of NH…︁N or CH…︁N interactions and the possibility of tautomerism are suggested for some of the compounds. The Z‐isomers of compounds with 2‐ or 3‐pyridyl rings prefer an s‐cis conformation whereas the E‐isomers prefer an s‐trans conformation.
Interpretation of1H NMR spectra of 2‐benzopyrylium salts with the use of the CNDO/2 method
Authors: Shcherbakova Irina V. , Yudilevich Iosif A. , Kuznetsov Evgenii V. 
Published: January 2005

AbstractThe1H NMR spectra of eleven substituted 2‐benzopyrylium salts are interpreted with the aid of the CNDO/2 method for standard geometry. Some effects of the substituents are considered for the charge distribution in the 2‐benzopyrylium cation.
Taft's substituent constants, σ* and σI, and Huheey's group electronegativity
Authors: Datta Dipankar 
Published: January 2005

AbstractFor 34 groups, Taft's substituent constants σ* and σI are found to correlate well (r = 0.962 and 0.948) with Huheey's group electronegativity (χH) when Taft's steric parameter Es for a group is mixed with σ* and σI:
equation image
From these equations, it follows that for a particular chemical group G, σ*(G) ≈︁ 8σI(G). Since the σ* scale is essentially based on the σI scale, the small inherent steric component in σI is amplified in the case of the σ* by a factor of ca 8. An analysis shows that χH represents the electronegativity of a group when the group is considered to be a mere collection of non‐bonded, charged and suitably hybridized atoms. Thus σ* and σI are found to represent the electronegativity of a group in the spirit of the χH. It is concluded that a chemical group can be viewed as a collection of non‐interacting atoms. Although there is evidence that a molecule can sometimes be treated similarly, for a group such a situation is novel.
Aromaticity as a multi‐dimensional phenomenon
Authors: Jug Karl , Köster Andreas M. 
Published: January 2005

AbstractThe classification of aromaticity criteria is studied. New aromaticity criteria are developed and discussed. A statistical analysis of such criteria is presented and compared with a similar analysis of the recent literature. It is shown that aromaticity is at least a two‐dimensional phenomenon. The classification of the compounds depends on the type of criteria included in the analysis.
Substituent effects in the photohydration of styrenes and phenylacetylenes. An attempt to establish a σhν scale for excited‐state reactions
Authors: Mcewen John , Yates Keith 
Published: January 2005

AbstractThe acid‐catalysed rate constants (kH+) for the photohydration of 18 meta‐ and para‐substituted styrenes and phenylacetylenes were determined in H2SO4 solutions by means of fluorescence quenching measurements and the standard Stern–Volmer approach. Singlet lifetimes of the substrates were determined in the reference solution (water at pH 7) by single photon counting. The log k values obtained did not correlate well with any previously reported σ scales, and were used to try to establish a σhν scale (for H‐, p‐F, m‐F, p‐Me, m‐Me, p‐Et, m‐Et, p‐OMe and m‐OMe substituents) for possible use in other photochemical reactions. Correlation of all available literature data versus the new σhv scale gave reasonable correlations (r = 0.957–0.966). The problems associated with establishing linear free energy relationships for photoreactions are discussed.
Product‐determining factors in the grignard reactions of benzophenones. The role of the structure of alkyl groups in grignard reagents
Authors: Maruyama Kazuhiro , Matano Yoshihiro , Katagiri Toshimasa 
Published: January 2005

AbstractThe mechanism of the Grignard reactions of substituted benzophenones with two kinds of alkyl Grignard reagent, n‐C3H7MgBr, and i‐C3H7MgBr, was investigated. In these reactions, both addition and reduction products were also generated. Based on the results of product analysis and stopped‐flow, ESR and association measurements, it was confirmed that the product distribution was governed by several factors: the oxidizing ability of benzophenones, the association ability of Grignard reagents and the structure of alkyl groups of Grignard reagents. In particular, the strength of CMg and β‐CH bonds of Grignard reagents could strongly affect the product distribution.
Ambident electrophilicity of alkyl aryl phosphates
Authors: Wagener Carl C. P. , Modro Agnes M. , Modro Tom A. 
Published: January 2005

AbstractHydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N‐methyl‐8‐hydroxyquinolinium or 4‐hydroxy‐(N,N,N‐trimethylanilinium) ion, proceeds with the cleavage of the POAr and MeO bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water‐triffuoracetic acid mixtures only the POAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the MeO bond fission by thiosulphate ion (ca 60‐fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500‐fold acceleration).
Multiplicities of π‐ylide ground states: Computational evidence for a breakdown of aromaticity arguments
Authors: Langler Richard Francis , Ginsburg Jack Leon , Snooks Rodney , Boyd Russell J. 
Published: January 2005

AbstractAM1 and 3–21G computations, on the lowest singlet state of selected π‐ylides, support the earlier conclusion that π‐ylides are highly polar with highly reactive side‐chains. The computations also indicate that the corresponding triplet states are lower in energy and have substantially reduced polarity. Contrary to the expectations derived from Hückel calculations, AM1 and 3–21G calculations suggest that the best π‐ylide structures have non‐aromatic rings. The heats of isomerization contradict earlier conclusions reached using topological resonance energies. π‐Ylides are expected to afford different product structures depending on the electronic state of the π‐ylide involved in a given cycloaddition reaction.
Kinetic probe to study the structural behaviour of mixed aqueous—organic solvents. Effects of inorganic and organic salts on the kinetics and mechanism of intramolecular general base‐catalysed methanolysis of ionized phenyl salicylate
Authors: Niyaz Khan M. , Audu A. A. 
Published: January 2005

AbstractThe effects of inorganic and organic salts on the rates of methanolysis of ionized phenyl salicylate, PS−, were studied at 30°C in H2O–MeOH solvents. The observed pseudo‐first‐order rate constants, kobs, for methanolysis of PS− represent a non‐linear incrrease with increase in methanol contents in mixed H2O–MeOH solvents. The observed data are explained in terms of the proposal that methanol molecules exist in monomeric, dimeric and in general polymeric forms in H2O–MeOH solvents. The rate constants, kobs, at alkanol [ROH (R = Me, HOCH2CH2)] contents of ca ≤ 55% (v/v), fit the relationship kobs = k [ROH]T/(1 + kA [ROH]), (1 + KA [ROH]), where k and KA represent the nucleophilic second‐order rate constant for the reaction of ROH with PS− and the association constant for the dimerization of ROH, respectively, and [ROH]T is the total concentration of ROH. The rate constants, k, appear to be independent of total concentrations of inorganic salts [MX]T (M = Li, Na, K and X = OH, Cl), but the values of KA increase with increase in [MX]T and this increase varies in the order Li+ > Na++ > K+. The values of both k and KA show a decrease with increase in the total concentrations of organic salts, [R4MX]T (R = Et, Prn, Bun and X = Br, I). The effects of [MX]T and [R4MX]T on kobs versus content of ROH (%, v/v) profiles reveal the following inferences: (i) in the water‐rich region of H2O‐ROH solvents [at ca < 55% (v/v) ROH] the solvation shells of M+ and X− contain preferentially only water molecules whereas in the methanol‐rich region [at ca > 55% (v/v) ROH] of solvents some cosolvent methanol molecules also enter into these solvation shells; (ii) the solvation shells of tetraalkylammonium ions, R4N+, contain some methanol molecules even in the water‐rich region of the solvents; (iii) Li+ cause a methanol structure‐making effect whereas Na+ and K+ ions show a methanol structurebreaking effect; and (iv) organic cations such as Et4N+, Prn4N+ and Bun4N+ reveal a methanol structure‐breaking effect through an interaction mechanism different from that operating for Na+ and K+. Both k and KA show significant normal deuterium isotope effects in the reactions of MeOH and PS− which indicates the probable occurrence of proton transfer in the rate‐determining step.
Ionization constants of 5‐furylmethylenehydantoins and 5‐thienylmethylenehydantoins in 80% (w/w) dimethyl sulphoxide–water at 25°C
Authors: Tan Sau‐Fun , Yeoh Phee‐Teik 
Published: January 2005

AbstractThe ionization constants of sixteen 5‐furylmethylenehydantoins and 5‐thienylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide–water solvent at 25°C. The effects of the 2‐/3‐furyl and 2‐/‐3‐thienyl rings and the effects of configuration and conformation on acidity are discussed. The very low acidity of (Z)‐5‐(2‐furyl)methylene‐3‐methylhydantoin suggests the possibility of some weak intramolecular interaction between the proton at N‐1 and the 2‐furyl oxygen in the s‐cis conformation.
Effect of counterion binding and alkyl chain length on the phase transition behaviour of DI‐n‐alkyl phosphate vesicles
Authors: Wagenaar Anno , Streefland Lisette , Hoekstra Dick , Engberts Jan B. F. N. 
Published: January 2005

AbstractThis paper describes a fluorescence depolarization and 31P NMR spectroscopic study of the phase transition behaviour of a series of identical and mixed‐chain di‐n‐alkyl phosphate vesicles in the presence of different counterions (Na+,K+,Me4N+,Ca2+). Using trans, trans, trans‐1, 6‐diphenyl‐1, 3, 5‐hexatriene (DPH) as a fluorescent probe, the fluorescence polarization (P) was measured for the identical‐chain vesicles (Na+, K+, Me4N+) as a function of temperature. The temperature for the main phase transition (Tm) only responded to variation of the counterion in the case of the longer‐chain di‐n‐alkyl phosphates, with Tm decreasing in the sequence Na+ > K+ > Me4N+. This result is rationalized in terms of a decreasing counterion binding, which affects chain ordening in the core of the bilayer. Peak intensities and line widths of the 31P NMR resonances for the bilayer vesicles suggest a more complex phase behaviour, but the overall results are reconcilable with the picture emerging from the fluorescence depolarization experiments. Fluorescence depolarization measurements were also carried out with vesicles formed from the sodium di‐n‐alkyl phosphates and in the presence of various concentrations of Ca2+ (0‐6 mM) at temperatures above Tm. For both the identical‐chain and mixed‐chain di‐n‐alkyl phosphate vesicles, a steep increase in P was found between ca 1.0 and 1.4 mM Ca2+, indicative of a strong Ca2+‐induced ordening of the alkyl chains.
Self‐organizing systems based on amphiphilic cyclodextrin diesters
Authors: Zhang Ping , Parrot‐lopez Hélène , Tchoreloff Pierre , Baszkin Adam , Ling Chang‐chun , de Rango Colette , Coleman Anthony W. 
Published: January 2005

AbstractThe formation of micelles, vesicles and monomolecular layers by amphiphilic cyclodextrins possessing hydrophobic ester groups on the secondary hydroxyl face is described. The physico‐chemical properties of these self‐organizing systems were studied by dynamic light scattering, variable‐temperature 1H NMR, the use of lanthanide shift reagents, deposition of Langmuir layers, variable‐temperature solubility measurements and aqueous and non‐aqueous surface tension activity measurements. The results are interpreted in terms of the cylindrical geometry of the compounds which, coupled with the presence of a large planar polar head group, lead to the formation of self‐organized systems both in polar organic solvents and also at the air–water interface.
Structure and conformation of pyridino‐ and diesterpyridino‐18‐crown‐6 complexes with primary ammonium salts in solution and crystalline states
Authors: Izatt Reed M. , Zhu Cheng Y. , Dalley N. Kent , Curtis Janet C. , Kou Xiaolan , Bradshaw Jerald S. 
Published: January 2005

AbstractStructures in CD3ODCDCl3 mixtures of pyridino‐18‐crown‐6 and diesterpyridino‐18‐crown‐6 complexes with primary ammonium cations containing an α‐phenyl group were found to be significantly different. The π–π overlap between the α‐phenyl group of the ammonium cation and the pyridine ring of the ligand occurs in the pyridino‐18‐crown‐6 complexes but not in the diesterpyridino‐18‐crown‐6 complexes. The solution structure of a diesterpyridino‐18‐crown‐6 complex with an α‐phenyl‐containing primary ammonium cation was also found to differ markedly from the corresponding crystal structure in that π–π overlap occurs in the crystal structure, but not in the solution structure.