bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deuterium conformational equilibrium isotope effects in 1,3,5‐cycloheptatriene‐7‐d
Authors: Freedberg Darón I. , Kopelevich Max , Anet Frank A. L. 
Published: January 2005

AbstractWe report a reinvestigation of the conformational equilibrium of 1,3,5‐cycloheptatriene‐7‐d (CHT‐7‐d) by solution 1H NMR at 500 MHz over a wide range of temperatures, and ab initio calculations up to the MP4 level. Lineshape analysis provided a barrier to ring inversion of approximately 6 kcal mol−1. Equilibrium constants were measured in CBrF3 and CClF2H by: integration when the ring‐inversion rate is low; lineshape analysis when the ­ring‐inversion rate is on the order of the chemical shift difference; and temperature‐dependent chemical shift differences between CHT and CHT‐7‐d when the ring‐inversion rate is fast. The three independent measure‐ments confirm an equilibrium biased toward an equatorial deuterium, with ΔG° = 52 ± 8 cal mol−1 (at −173 °C), ΔH° = 55 ± 8 cal mol−1 and ΔS° = 0.03 ± 0.05 cal mol−1 K−1 in CBrF3. Supporting ab initio calculations yield: ΔH° = 34 cal mol−1, ΔS° = 0.014 cal mol−1 K−1 (MP2/6‐31G*); ΔH° = 57 cal mol−1 and ΔS° = 0.03 cal mol−1 K−1 (RHF/6‐31G*); and a barrier to ring inversion in CHT of 4.26 kcal mol−1 (RHF/6‐31G*), 9.76 kcal mol−1 (MP2/6‐31G*), and 7.34 kcal mol−1 (MP4/6‐31G* single point). The differences in calculated barrier heights due to exclusion or inclusion of Møller–Plesset energies indicate that the ground state is stabilized relative to the transition state at ­the MP2 and MP4 levels. This implies that homoconjugation is important in CHT, a neutral molecule. Our experimental values differ from those originally deduced by Jensen and Smith (J. Am. Chem. Soc. 1964; 86: 956): ΔG° = 72 cal mol−1, ΔH° = 142 ± 30 cal mol−1 and ΔS° = 0.7 ± 0.3 cal mol−1 K−1. Copyright © 2001 John Wiley & Sons, Ltd.
Stability of 2‐naphthalenediazonium ion and its complexation with crown ethers and acyclic polyethers in solution
Authors: Kuokkanen Toivo , Palokangas Jarmo , Talvensaari Merja 
Published: January 2005

AbstractThe effects of solvent, temperature and pH (in aqueous solution) on the rate of decomposition of 2‐naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The host–guest complexation and the kinetics of thermal dediazoniation of this model naphthalenediazonium ion, in the presence of four crown ethers and three acyclic polyethers, were studied in 1,2‐dichloroethane (DCE) at 40 °C by UV spectrometry. Fast atom bombardment mass spectrometry (FAB‐MS) was used for the gas phase complexation and characterization.The values of the activation enthalpy ΔH# for the thermal dediazoniation of the uncomplexed salt were observed to be high, and the corresponding values of activation entropy ΔS# were clearly positive. All hosts, except short 12‐crown‐4, formed 1:1 complexes under FAB conditions. The complexation equilibrium constant K and the values of the stabilizing ability of the complexation (k2/k1) in DCE were calculated using a kinetic method. In accordance with earlier studies of arene‐ and 1‐naphthalene diazonium ions, the thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex—the largest for 21‐crown‐7 and its derivatives, formed with crown ethers containing at least six oxygen atoms—than for the non‐specific adduct formation formed with 15‐crown‐5. The values of the thermodynamic and kinetic macrocyclic effect were discussed. The results are consistent with a heterolytic SN1‐like mechanism involving the decomposition of the uncomplexed and complexed naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product‐determining reactions with nucleophiles to give the products. Copyright © 2001 John Wiley & Sons, Ltd.
Protonation of alkylpyridines: polarizability and steric effects in the base and in the cation
Authors: Roithová Jana , Exner Otto 
Published: January 2005

AbstractThe energies of alkyl‐substituted pyridines in the 2‐, 3‐, 4‐ and 2,6‐positions, of their protonated forms and of reference derivatives of benzene were calculated at the RHF/6–31G(d,p) and B3LYP/6–31G(d,p) levels. The results were processed by isodesmic reactions, expressing the substituent effect separately for the base molecules, their protonated forms and for the gas‐phase basicity. The substituent effect is greatest in the protonated forms, and in the uncharged bases it is approximately three times smaller. In both cases, it is stabilizing: basicity is given by the difference. No actual steric effect was revealed, merely a stabilizing effect in the 2‐position, which can be explained in terms of polarization. This effect is almost equal in the protonated and unprotonated forms, so that it is not operative in the basicity. In water solution, all effects are attenuated and steric inhibition of solvation appears, particularly with 2,6‐di‐tert‐butylpyridine and 2,6‐diisopropylpyridine. Copyright © 2001 John Wiley & Sons, Ltd.
Product selectivities and third‐order rate laws for solvolyses of ethyl phenylphosphonochloridate in aqueous alcohols
Authors: Bentley T. William , Ebdon David N. 
Published: January 2005

AbstractRate constants and product selectivities (S) for solvolyses of ethyl phenylphosphonochloridate [PhP(O)OEtCl] in aqueous ethanol and methanol at 0 °C are reported; S = ([ester product]/[acid product]) ×­([water]/[alcohol solvent]). The results show trends very similar to those previously reported for solvolyses of diphenyl phosphorochloridate [(PhO)2P(O)Cl] and p,p′‐dichlorodiphenyl phosphorochloridate, much more hydrophobic substrates. Implications of these results are as follows: (i) as S increases about threefold from 99.8 to 90% alcohol–water and only about the same amount from 90 to 40% alcohol–water, the main cause of variations in S does not appear to be medium effects of the solvents; (ii) contrary to the general trend to increase, values of S may decrease slightly (ca 15%) in highly aqueous alcohol–water mixtures, even when (as in this case) there is no evidence for mechanistic changes; (iii) the deviations from expected third‐order rate product correlations previously reported for solvolyses of diphenyl phosphorochloridate and the p,p′‐dichloro derivative do not appear to be due solely to their high hydrophobicity. Copyright © 2001 John Wiley & Sons, Ltd.
Syntheses and UV–visible spectroscopic properties of new ‘fluorophilic’ fluorine‐ and perfluoroalkyl‐substituted solvatochromic pyridinium N‐phenolate betaine dyes
Authors: Reichardt Christian , Eschner Michael , Schäfer Gerhard 
Published: January 2005

AbstractSyntheses and negative solvatochromism of three new ‘fluorophilic’ fluorine‐ and perfluoroalkyl‐substituted pyridinium N‐phenolate betaine dyes 3–5 are described in order to obtain new zwitterionic dyes which should be less basic and better soluble in perfluorinated solvents than the solvatochromic standard betaine dyes 1 and 2, used to establish an empirical scale of solvent polarity, called the E
T (30) or $E_{T}^{N}$ scale. The new betaine dyes 3–5 were designed to allow an extension of the existing E
T (30) scale to new solvents. Copyright © 2001 John Wiley & Sons, Ltd.
Angular group induced bond alternation (AGIBA). Part VI — Competition between the AGIBA and through resonance effects
Authors: Pindelska Edyta , Krygowski Tadeusz M. , Anulewicz‐Ostrowska Romana , Cyrański Michal K. , Nowacki Jacek 
Published: January 2005

AbstractAnalysis of the molecular geometry of three experimental model compounds, 2,3‐dimethyl‐p‐anisaldehyde, 2,5‐dimethyl‐p‐anisaldoxime and 2,3‐dimethyl‐p‐anisaldoxime, and eight compounds (p‐nitrosoaniline, p‐nitroanisole and two conformers each of p‐nitrosoanisole, p‐anisaldehyde and p‐anisaldimide) whose molecular geometry was obtained by optimization at the B3LYP/6–311G** level of theory, where both the AGIBA and through resonance effects were present, led to the conclusion that the competition between these effects does not reduce any of them significantly. Copyright © 2001 John Wiley & Sons, Ltd.
Revisit of the leaving group (LG)/halogen exchange in 1,2‐dimesityl‐2‐phenylvinyl–LG systems: a caveat about ‘mistaken identity’ by X‐ray diffraction
Authors: Salim Hatim , Chen Xin , Rappoport Zvi 
Published: January 2005

AbstractThe unusual report that Z‐1,2‐dimesityl‐2‐phenylethenol (Z
‐4‐OH) affords with POBr3 the crystallographically identified E‐1,2‐dimesityl‐2‐phenylvinyl bromide (E
‐4‐Br) was reinvestigated together with related reactions. Reaction of Z
‐4‐OH with tosyl chloride gave Z
‐4‐OTs, Z
‐4‐Cl with SOCl2 and Z
‐4‐Br with Me3SiCl/LiBr, PBr3 or PPh3/Br2. Reaction of Z
‐4‐OTs with Br− or I− in MeCN gave Z
‐4‐Br or Z
‐4‐I respectively. The reaction of Z
‐4‐OH with POBr3 was repeated under several conditions and gave Z
‐4‐Br, which was identified by X‐ray diffraction. The discrepancy with the previous experiment was ascribed to the formation of a minute percentage of E
‐4‐Br within the bulk of Z
‐4‐Br and to analysis of a crystal of E
‐4‐Br by X‐ray diffraction. The generalization that MesC(Ph) = C*‐Mes (* = · or +) species capture reagents (e.g. Br−, I− for 2 when * = +) from the face carrying the β‐mesityl ring is corroborated and extended. It is suggested that the reactions of Z
‐4‐OH with SOCl2, PBr3 or POBr3 proceed via initial formation of chlorosulfite or phosphorus‐containing ester leaving groups that solvolyze to 2 or its ion pair, which react with halide ions formed from the anionic leaving group to give Z
‐4‐X (X = Cl, Br). From the X‐ray data of MesC(Ph) = C(X)Mes, (X = Br, OAc, E and Z isomers; X = OTs, Cl, I, Z isomer; X = H, E isomer) the effect of X on bond lengths, angles and dihedral angles, as well as on the difference between the E/Z isomers (X = OAc, Br), is determined and discussed. Although steric crowding is important, its effect is significant mainly on the ArCC dihedral angles. 1H δ values for the nine systems show free rotation of all rings around the ArCC bonds on the NMR time scale. Higher field o‐Mes‐Me, m‐Mes‐H signals and lower field Ph‐H signals for the Z‐ than for the E‐isomers for X = OAc, Br were observed. Copyright © 2001 John Wiley & Sons, Ltd.
Evaluation of the steric substituent effect by ΩS: reinvestigation of the reaction dependency of the steric substituent constant
Authors: Hirota Minoru , Sakakibara Kazuhisa , Yuzuri Tomoaki , Kuroda Shin‐ichi 
Published: January 2005

AbstractUsing the OMEGAS program, two sets [ΩS(0.5,0.5) and ΩS(0.9,0.5)] of steric substituents were calculated by assuming different sizes of effective radii for the reaction center atom. The former set reproduces the steric substituent effect on the nucleophilic reactions of carboxylic acid derivatives better; the latter set is far better for the reactions of amines and alcohol derivatives. Our results clearly show that the effective size of the reaction center atom is another important factor in characterizing the steric effect in addition to the bulkiness of the substituent. This can be rationalized by the fact that such a general steric constant cannot be used to evaluate all sorts of steric effects using a single set of substituent constants. Copyright © 2001 John Wiley & Sons, Ltd.
Tautomerism of neutral and monoprotonated histamine—a comparison of semi‐empirical and ab initio quantum mechanical predictions for ‘essential’ and ‘scorpio’ conformations
Authors: Raczyńska Ewa D. , Darowska Małgorzata , Rudka Tomasz , Makowski Mariusz 
Published: January 2005

AbstractRelative energies were calculated at different semi‐empirical (CNDO, INDO, MINDO/3, MNDO, AM1, and PM3) and ab initio levels (RHF/STO‐3G//STO‐3G, RHF/STO‐4G//STO‐4G, RHF/3‐21G//3‐21G, RHF/6‐31G//6‐31G, RHF/6‐31G*//6‐31G, RHF/6‐31G*//6‐31G*, RHF/6‐31 ++ G**//6‐31G*, RHF/6‐311 ++ G**/6‐31G*, RHF/6‐31G**//6‐31G**, RHF/31 ++ G**//6‐31 ++ G**, MP2/6‐31G*//6‐31G* and MP2/6‐31G**//6‐31G**) for so‐called ‘essential’ (trans) and ‘scorpio’ (gauche) conformations of the neutral and monoprotonated histamine tautomers. For the monocationic forms, the polarizable continuous model was applied to geometries optimized at the RHF/6‐31G* level. The comparison shows that, generally, both types of calculation (semi‐empirical and ab initio) predict the same tautomeric preference for the conformations of histamine and its monoprotonated cation when not interacting with the environment, i.e. for conditions corresponding to the gas phase. For the monocation, the ring N‐aza protonated form (ImH+) is favoured in the gas phase for both conformations (trans and gauche); this is contrary to water solution, where the chain N‐amino (AmH+‐T1) predominates. This difference results mainly from the high polarizability of the imidazole ring in the gas phase which is strongly reduced in solution. Some ‘discrepancies’ are only observed for neutral histamine, for which the relative energy is close to zero. Good agreement of results predicted by various methods can result from the fact that in histamine the proton is transferred between atoms of the same element (nitrogen). Copyright © 2001 John Wiley & Sons, Ltd.
Reactions of carbonyl compounds in basic solutions. Part 36: The base‐catalysed reactions of 1,2‐dicarbonyl compounds
Authors: Bowden Keith , Fabian Walter M. F. 
Published: January 2005

Abstract1,2‐Dicarbonyl compounds can undergo base‐catalysed reactions in three ways: rearrangement of the benzil–benzilic acid type, fission of the carbon–carbonyl carbon bond and fission of the carbonyl carbon–carbonyl carbon bond. The requirements for the observation of the variant reaction types are discussed both for open‐chain and for ring systems in terms of electronic and stereochemical factors. Copyright © 2001 John Wiley & Sons, Ltd.
Concerning the extent of nucleophilic participation in solvolyses of glucopyranosyl derivatives
Authors: Kevill Dennis N. , D'Souza Malcolm J. 
Published: January 2005

AbstractThe specific rates of solvolysis of 2‐deoxy‐α‐ and ‐β‐D‐glucopyranosyl‐4′‐bromoisoquinolinium ions (1 and 2) give excellent correlations in a Grunwald–Winstein equation approach for solvents with NT values more positive than −1.4; the sensitivity to changes in NT value is considerably reduced in less nucleophilic solvents. Copyright © 2001 John Wiley & Sons, Ltd.
Structural study of ethyl 3‐arylcarbamoyl‐2,3‐diazabicyclo[2.2.1]hept‐5‐ene‐2‐carboxylates: conformation and transmission of substituent effects across the diazabicycloheptene ring
Authors: Perjéssy A. , Meyer P. , Rudorf W.‐D. , Loos D. , Kolehmainen E. , Laihia K. , Nissinen M. , Koivisto J. , Kauppinen R. 
Published: January 2005

AbstractNine new ethyl 3‐arylcarbamoyl‐2,3‐diazabicyclo[2.2.1]hept‐5‐ene‐2‐carboxylates were prepared by a [4 + 2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X‐ray data were obtained. The electronic structure and the conformations were calculated by the semi‐empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those for a previously reported series of analogous ethyl 2‐arylcarbamoyl‐4,5‐dimethyl‐1,2,3,6‐tetrahydropyridazine‐1‐carboxylates. Copyright © 2001 John Wiley & Sons, Ltd.
An enthalpic scale of hydrogen‐bond basicity, part 1: halogenoalkanes
Authors: Ouvrard Carole , Berthelot Michel , Laurence Christian 
Published: January 2005

AbstractHydrogen bond enthalpies ΔH° for the interaction of 4‐fluorophenol with 18 fluoro‐, chloro‐, bromo‐, and iodo‐alkanes in CCl4 solution have been determined through the temperature variation of hydrogen‐bond equilibrium constants. A statistical analysis of the ΔH°–ΔS° correlation shows that this extrathermodynamic relationship is valid for the family of halogenoalkanes. The enthalpic data are also used to test the correlation of ΔH° versus Δν(OH), the IR frequency shifts of the OH band of 4‐fluorophenol caused by the hydrogen bonding (the Badger–Bauer relationship). This relationship is family dependent, and, for fluoroalkanes and iodoalkanes, does not pass through the origin. These findings allow a safer use of the Badger–Bauer relationship to predict hydrogen‐bond enthalpies accurately. Copyright © 2001 John Wiley & Sons, Ltd.
Large structural effects in neutral and protonated species: a computational study
Authors: Abboud José‐Luis M. , Alkorta Ibon , Dávalos Juan Z. 
Published: January 2005

AbstractThe B3LYP/6‐31G(d) methodology was applied to the study of the diketone pentacyclo[5.4.0.02,6.03,10.05,9]undecane‐8,11‐dione (1), the hydrocarbon pentacyclo[5.4.0.02,6.03,10.05,9]undecane (2) and the ketone pentacyclo[5.4.0.02,6.03,10.05,9]undecane‐8‐one (3). Also examined were the oxygen‐protonated species 1H+ and 3H+. The diketone pentacyclo[5.4.0.02,6.03,10.05,9]undecane‐4,8‐dione (4) and the ketone pentacyclo[5.4.0.02,6.03,10.05,9]undecane‐4‐one (5) and their protonated forms were used for comparison purposes. This information was used to construct several isodesmic reactions, allowing the quantitative estimate of the influence of the carbonyl groups on the stability of the various species in the gas phase. These results were in excellent agreement with the experimental thermochemical and structural data available. Analyses by means of the natural bond orbital theory and simple electrostatic models were also performed. Copyright © 2001 John Wiley & Sons, Ltd.
Miscibility and properties of polyurethane/benzyl starch semi‐interpenetrating polymer networks
Authors: Cao Xiaodong , Zhang Lina 
Published: January 2005

AbstractWe successfully prepared a series of transparent materials with semi‐interpenetrating polymer networks (semi‐IPNs) from castor‐oil‐based polyurethane (PU) and benzyl starch (BS). The miscibility, morphology, and properties of the semi‐IPN films were investigated with attenuated total reflection/Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, wide‐angle X‐ray diffraction, electron spin resonance (ESR), ultraviolet–visible spectroscopy, and tensile testing. The results revealed that the semi‐IPN films had good or certain miscibility with BS concentrations of 5–70 wt % because of the strong intermolecular interactions between PU and BS. With an increase in the concentration of BS, the tensile strength and Young's modulus of the semi‐IPN materials increased. The ESR data confirmed that the segment volume of PU in the semi‐IPNs increased with the addition of BS; that is, the chain stiffness increased as a result of strong interactions between PU and BS macromolecules. It was concluded that starch derivatives containing benzyl groups in the side chains more easily penetrated the PU networks to form semi‐IPNs than those containing aliphatic groups, and this led to improved properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 603–615, 2005
Relaxations during the postcure of unsaturated polyester networks by ultrasonic wave propagation, dynamic mechanical analysis, and dielectric analysis
Authors: Lionetto Francesca , Maffezzoli Alfonso 
Published: January 2005

AbstractUltrasonic wave propagation, dynamic mechanical analysis, and dielectric analysis were used to monitor relaxation phenomena during the nonisothermal postcure of unsaturated polyester networks. The measurements covered 6 decades of frequency. As a result, the residual reactive groups, immobilized in the glassy state by vitrification during an isothermal cure step, gained molecular mobility, which promoted the formation of additional crosslinks. After the postcure, the reaction was complete, and the maximum achievable glass‐transition temperature was reached. Moreover, the frequency and temperature dependence of the two relaxations, one related to the glass‐transition temperature of the partially cured sample and the other to the glass transition of the fully cured sample, was evaluated. The Williams–Landel–Ferry equation was used to model the frequency dependence of the main α‐relaxation data obtained with the different techniques. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 596–602, 2005
Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering
Authors: Matsuoka Norikazu 
Published: January 2005

AbstractThe application of laboratory criteria for frost weathering to field problems needs caution, because a number of discrepancies lie between the laboratory and field conditions. This paper reviews thresholds for microgelivation of soft, intact rocks and macrogelivation of hard, jointed rocks, aiming at proposing better criteria in accordance with field conditions. The temperature at which ice segregation induces microgelivation varies significantly with lithology, ranging from about −1 °C in high porosity rocks to below −4 °C in low porosity rocks. Microgelivation can occur in initially unsaturated rocks when slow (seasonal) freezing drives prolonged water migration from surrounding rock or an external moisture source, while the occurrence requires a high degree of saturation (>80%) or a nearby moisture source when a rock undergoes rapid (diurnal) freezing. Rocks with a high internal surface area and low tensile strength favour microgelivation. These criteria are invalid for macrogelivation that tends to take place just below 0 °C in water‐filled joints. In addition, because the depth reached by cracking varies with the type of freeze‐thaw action, the analysis of thermal regimes should be based on data at the depth of actual cracking. Future targets for macrogelivation studies include the formation of new cracks in hard, intact rocks, as indicated by in situ shattering of clasts or bedrock typically observed in optimal moisture environments. Copyright © 2001 John Wiley & Sons, Ltd.
Stability of the tranquilizer drug propionylpromazine hydrochloride in formulated products
Authors: Primus Thomas M , Kimball Bruce A , Hurley Jerome , Johnston John J , Blom Sherm , Savarie Peter J 
Published: January 2005

AbstractAn analytical method to evaluate propionylpromazine hydrochloride (PPZHCl) in tranquilizer formulations was developed using high‐performance liquid chromatography (HPLC). During analysis of aged quality‐control samples, a previously unreported chromatographic response was observed at a shorter retention time than PPZHCl. Further investigation of formulations stored in trap tap devices at temperatures ranging from 5 to 40 °C during field trials at four different locations confirmed the degradation of the active ingredient. Further investigation using HPLC/tandem mass spectrometry revealed two to five degradates, with the major degradates being oxidation products of the active ingredient, PPZHCl. As PPZHCl formulations must be stable when stored at 5 to 40 °C for 6 to 12 months, reformulation with the anti‐oxidant ascorbic acid was utilized to achieve the required PPZHCl stability. Copyright © 2005 Society of Chemical Industry