bluuebunny/crossref_metadata_2025 huggingface dataset:
Dicarboximide‐based clathrate design. Host synthesis, inclusion formation and x‐ray crystal structures of a free host and of inclusion compounds with 2‐ and 3‐ methylcyclohexanone, 3‐methylcyclopentanone, butyronitrile, propan‐1‐ol and (−)‐fenchone guests
Authors: Weber Edwin , Reutel Christiane , Foces‐Foces Concepción , Llamas‐Saiz Antonio L.
Published: January 2005

Crystalline host compounds consisting of a roof‐shaped dicarboxinide framework and pendant diarylethanol analogous subunits were synthesized and shown to form inclusion complexes with small organic molecules such as alcohols, amines, ketones or polar and apolar organic solvents. Clathrate efficiency and selectivity depend on the particular host structure. The crystal and molecular structures of a free host compound (2a) and inclusion compounds [2a·3‐methylcyclohexanone (1 : 1), 1a·3‐methylcyclopentanone (1 : 1), 1a·2‐methylcyclohexanone (1 : 1), 1b·butyronitrile (1 : 1), 1b·propan‐1‐ol (2 : 1) and 1b·(–)‐fenchone (1 : 1)] were determined by x‐ray diffraction analysis. In all the structures, the hydroxyl group is involved in intramolecular hydrogen bonds and the host and guest molecules are held by lattice forces only. The channels and cavities left in the host matrix are large enough to allow disorder or high thermal displacement parameters of the guest molecules. The local packing coefficients for all guests are 0·42 on average.
Kinetics and mechanism of reaction of acridine orange with bromateion at low pH
Authors: Sawunyama P. , Jonnalagadda S. B.
Published: January 2005

The reaction between acridine orange hydrochloride [3,6‐bis(dimethylamino)acridine hydrochloride] and potassium bromate in dilute sulphuric acid was studied by monitoring the absorbance change at 492 nm. The reaction exhibited complex kinetic behaviour. In excess bromate the reaction had an induction period with slow depletion of acridine orange (AC) followed by a fast depletion step. The initial reaction step was found to be first order with respect to both AC and bromate and second order with respect to H+. The stoichiometric ratio of AC to bromate was 3 : 2. At the end of the induction period, the redox potential of the reaction mixture has shown a distinct rise, while the Br− concentration dropped sharply. The dual role of bromide ion both as an inhibitor and autocatalyst is discussed. A 16‐step reaction mechanism is proposed and the simulated curves agreed well with the kinetic curves.
Unusually large kinetic deuterium isotope effects on oxidation reactions. 1. The mechanism of hydroxide‐catalysed permanganate oxidation of PhCD(CF3)OH and PhCD(CH3)OH in Water
Authors: Thibblin Alf
Published: January 2005

The oxidation of 1‐phenyl‐2,2,2‐trifluoroethanol (ROH) with potassium permanganate in 0.2 M aqueous sodium hydroxide solution at 25 °C provides 2,2,2‐trifluoroacetophenone as the sole product. The reaction rate constant, which was measured under pseudo‐first order conditions by following the decrease in substrate concentration as a function of time, was found to be substantially smaller than previously reported. The primary kinetic deuterium isotope effect was measured as k/k = 14·7 ± 1·0. A hydrogen‐transfer mechanism involving significant tunnelling is proposed. The oxidation of 1‐phenylethanol under similar reaction conditions yields acetophenone as the initial product. The kinetic deuterium isotope effect was found to be k/k = 5·2 ± 0·8.
Introduction to living polymeriz. Living and/or controlled polymerization
Authors: Matyjaszewski Krzysztof
Published: January 2005

The effects of various imperfections such as slow initiation, termination, transfer and slow exchange on kinetics, molecular weights and polydispersities in chain growth polymerizations are simulated. The simukations demonstrate that well defined polymers polymers can be prepared in systems with chain‐breaking reactions. Thus, under carefully selected conditions, non‐living polyumerizations may provide controlled polymers. On the other hand, polymers with unpredictable molecular weights and broad and even polymodal molecular weight distributions can be formed in living systems without irreversible transfer and termination. In some living systems molecular weights may stay constant or even decrease with conversion. Therefore, a clear distrinction should be made between living and polymerizations.
Living carbocationic copolymerizations. I. Synthesis and characterization of isobutylene/p‐methylstyrene copolymers
Authors: Országh I. , Nagy A. , Kennedy J. P.
Published: January 2005

The isobutylene (IB)–p‐methylstyrene (pMeSt) monomer pair readily produces by living copolymerization nearly random copolymers with up to M̄n ≈ 50,000 g mol−1 and M̄w/M̄n ≈ 1·4. The livingness of the copolymerization process and the compositional homogeneity of the copolymers have been demonstrated by the following four diagnostic plots: (A) M̄n (number‐average molecular weight) and corresponding N (number of moles of copolymer formed) vs Wp (weight of copolymer formed) for the diagnosis of chaintransfer; (B) −ln (1 – C) (C = conversion of monomers) vs time for the diagnosis of termination; (C) copolymer composition vs molecular weight; and (D) cumulative copolymer composition vs conversion for the diagnosis of true homogeneous copolymers. The theory for the use of the −ln(1 – C) vs time plot for the quantitation of irreversible termination in copolymerization has been developed. The exact conditions (i.e. nature of reagents, reagent concentrations, temperature, etc.) which lead to desirable products in terms of conversion, molecular weight, molecular weight distribution (MWD) and copolymer composition, were developed systematically by analyzing the results of a large number of experiments. The following combination of chemicals was found to lead to living copolymerization, and uniform high molecular weight, narrow MWD copolymers: IB–pMeSt 97 : 3 mol/mol with 5‐tert‐butyl‐1,3‐dicumyl methyl ether (5‐tBu‐1,3‐DiCumOMe) initiator, TiCl4 coinitiator, ethyl chloride (EtCl) solvent, triethylamine (TEA) electron pair donor (ED) and 2,6‐di‐tert‐butylpyridine (DtBP) proton trap at −52, −65 and −85°C.
Polymerization of acrylates and methacrylates to make homopolmers and block copolymers initiated by N‐alkoxyphthalimides and succinimides
Authors: Druliner J. D.
Published: January 2005

Various N‐alkoxyphthalimides were prepared and tested as initiators for polymerization of a variety of monomers. Acrylates and methacrylates polymerized at 40–50°C. Vinyl acetate and styrene were moderately reactive at 60–65°C. Rates of reaction were sensitive to the choice of solvent. THF generally gave the highest conversions, with much reduced reactivities in solvents of higher polarity, such as acetonitrile, acetone, DMSO or DMF. In aliphatic hydrocarbon solvents or di‐n‐butyl ether no polymers were obtained. Bulk polymerizations proceeded well, depending on the monomer. Rates of polymerization were sensitive to the structure of the group attached to nitrogen. OR groups, where R contained α‐electron‐withdrawing esters, benzylic or allylic groups, were more reactive than when R was an aliphatic group. A–B block copolymers were readily prepared, starting with PMA, PBA or PMMA. However, because the rates of initiation were slow, relative to rates of propagation, N‐alkoxyphthalimide initiators survived mostly intact. Consequently, final A–B block copolymers were invariably contaminated with indeterminate amounts of homopolymer from polymerization of the second monomer.
Ab initio molecular orbital study of the O + C6H5O reaction
Authors: Lin M. C. , Mebel A. M.
Published: January 2005

An ab initio molecular orbital study of the potential energy surface of the C6H5O + O reaction was performed at the (PUMP3/6‐31G*//UHF/6‐31G*) level of theory. Various reaction channels were considered. The most favorable mechanism, la and Ib, start from the attachment of the oxygen atom to the carbon atom of the C6 ring in the ortho‐ or para position with respect to CO, taking place without activation energy. Then, either hydrogen elimination by mechanism Ia or 1,2‐H shift from the C(H)(O) group takes place; the latter process leads to the formation of the very stable C6H4(O)(OH) radical, which can also eliminate H by mechanism Ib. Thus, the main products of the C6H5O (2B1) + O(3P) reaction are o/p‐benzoquinones and the hydrogen atom. At low temperatures, however, the system may be trapped in the potential well of the C6H4(O)(OH) intermediate. At high temperatures, the reaction may proceed by the formation and decomposition of o/p‐benzoquinones. Because of their higher activation energies, the reaction mechanisms giving rise to other products–the attachment of the oxygen atom to the bridging position to form an epoxy intermediate, followed by insertion of O into the CC bond and dissociation to give C5H5 and CO2 (channel IIc), in addition to the attachment of oxygen to the terminal O atom of C6H5O followed by elimination of O2 (channel III) – cannot compete with channel Ia or Ib. RRKM calculation was carried out for the total and individual rate constants for channels Ia and Ib. The three‐parameter expression for the total rate constant, fitted by the least‐squares method for the temperature range of 300–3000 K, is given as ktot = 5·52×10−17 T1·38 e+148/T cm3 mol−1 s−1.
Kinetics and mechanism of oxidation of (arylthio)acetic acids by pyridinium hydrobromide perbromide
Authors: Karunakaran K. , Elango K. P.
Published: January 2005

Oxidation of several monosubstituted (phenylthio)acetic acids (PTAA) by pyridinium hydrobromide perbromide (PHPB) was studied in aqueous acetic acid. The reaction is first order with respect to PHPB. Michaelis–Menten type kinetics are observed with respect to (arylthio)acetic acid. The effect of solvent composition indicates that the transition state is more polar than the reactants. The formation constants of the intermediate substrate–PHPB complexes and the rates of their decomposition were determined at different temperatures. The rates of oxidation of para and meta‐substituted (phenylthio)acetic acids were correlated with Hammett's substituent constants. The ρ value is −1·60 at 35°C. The rates of oxidation of ortho substituted compounds are correlated with Charton's triparametric equation. A mechanism involving the decomposition of the intermediate complex in the slow rate‐determining step affording a sulphonium ion which hydrolyses in a subsequent fast step to the sulphoxide is proposed.
Competitive product inhibition in a clay‐catalysed Diels–Alder reaction
Authors: Collet Christine , Laszlo Pierre
Published: January 2005

The normal electron‐demand Diels–Alder cycloaddition between cyclopentadiene and methyl vinyl ketone is inhibited by the cycloadduct, when catalyzed by kaolinite‐supported zinc chloride. This inhibition stems from occupation of the catalytic sites by both the cycloadduct and methyl vinyl ketone. Catalysis occurs in this case exclusively by a decrease in the enthalpy of activation.
Theoretical studies of the identity allyl transfer reactions
Authors: Lee Ikchoon , Kim Chang Kon , Lee Bon‐Su
Published: January 2005

Ab initio studies on the SN2 identity exchange reactions RCH2X + X− → X− + RCH2X for R = CH2CH with X− = H, NH2, OH, F, PH2, SH and Cl, and for R = CH3 and CHC with X− = Cl were carried out at the HF and MP2 levels using the 6–31 ++ G** basis sets. The activation barriers, ΔE≠, and major structural changes, Δd≠ (C–X), in the activation process are closely related to the electronegativity of the R and X groups. The effect of electronegativity is twofold: a stronger electronegativity of R and/or X leads to a lesser electronic as well as structural reorganization required in the activation and to a greater correlation energy in the transition state. The former effect lowers the energy barriers at both the HF and MP2 levels whereas the latter lowers only the correlated (MP2) activation energies. Results with R = CH2CH, as a model for R = C6H5, indicate that ‘benzylic effect’ arises mainly from the relatively stronger electron acceptor ability of the phenyl group.
Atomic force microscopy and Solid‐State rearrangement of benzopinacol
Authors: Kaupp Gerd , Haak Michael , Toda Fumio
Published: January 2005

The solid–solid chemical reaction of benzopinacol (1) with p‐toluenesulphonic acid monohydrate (2) to give a quantitatively proton‐catalysed pinacol rearrangement with formation of triphenylacetophenone (3) in the absence of a solvent was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and known crystal structure data. The reaction rate is dramatically enhanced if the water of reaction is continuously removed. AFM reveals that no reaction occurs on (001) of 1 whereas (100) exhibits distance dependent craters and volcano‐like mounds over areas extending to 1·5 mm from the contact edge of the crystals with 1 undergoing phase rebuilding while reacting. A mechanism resembling the formation of membrane potentials is seen for the first time in crystals. Thus it appears that catalytic protons migrate without their counterions from one molecular compartment to the next by proton consumption at its inside and proton liberation at its outside, which is the inside of the next compartment. The uppermost molecular layer determines reactivity or non‐reactivity. On (001) of 1 the hydroxyl groups occur with their hydrogens up. Hence no AFM features are found and crystals of 2 do not become adhered to 1. However, on (100) the hydroxyl hydrogens point down (free electron pair up). Protonation is possible, chemical reaction is indicated by the formation of the AFM features and crystals of 2 adhere firmly to the surface of 1 after reaction.
Mechanism of electrophilic aromatic substitutions: Comments on a recent criticism concerning the use of the mesitylene/durene reactivity ratio as a probe to distinguish between ionic and et pathways
Authors: Baciocchi Enrico , Galli Carlo
Published: January 2005

As a rebuttal to recent criticisms aimed at the mechanistic significance of the determination of the mesitylene/durene relative reactivity, it is argued that this ratio does provide reliable information about the structure of the transition state of many SEAr reactions, supporting the operation of the ‘conventional’ ionic mechanism, as opposed to the ET mechanism. Not even in the case of competitive experiments does it appear that the criticisms are justified.
ortho‐Substituent effects in N‐arylacetamides. NMR and molecular mechanics investigation
Authors: Kolehmainen Erkki , Laihia Katri , Kauppinen Reijo , Rasała Danuta , Puchała Agnigeszka
Published: January 2005

1H, 13C, 15N and 17O NMR spectra of N‐phenylacetamide (acetanilide) and 21 ortho‐substituted acetanilides were measured and assigned. The observed NMR parameters are related to the Hammett substituent parameters and conformational characteristics of the acetamido moiety estimated by molecular mechanics calculations. Significant relationships were found for the 13C NMR chemical shifts of C‐5 (para to substituent) and the direct spin–spin coupling constant, 1J(C, H), of C‐3 (ortho to substituent) with Hammett substituent parameters. For 15N NMR chemical shifts of the amido nitrogen, no general correlation with the Hammett substituent parameters was found. The interactions between functionalities contiguous to the carbonyl group and the amino nitrogen in acetanilides are effectively hampered owing to the increased twist angle between the planes containing the phenyl ring and the H–N–C fragment in derivatives bearing bulky ortho substituents. Especially in ortho‐halogen‐substituted derivatives the 15N NMR chemical shift of the amino nitrogen is very clearly related to the twist angle between the phenyl ring and H–N–C fragment. For 17O NMR chemical shifts of the acetamido carbonyl, the observed variations can be related to the steric inhibition of resonance between the benzene ring and the acetamido group.
Radiolytic studies of the reductive cyclization of 2‐nitroarylamides: Cyclization via hydroxylamine intermediates
Authors: Sykes Bridget M. , Atwell Graham J. , Denny William A. , O'Connor Charmian J.
Published: January 2005

The reductive cyclization of several 2‐nitroarylamides was studied by radiolytic reduction, examining the effects of substituents on the nitrophenyl ring and on the leaving aniline and variations in the nature of the link between the nitrophenyl ring and the leaving aniline. The stoichiometry of the reduction and the identification of N‐hydroxylactam and aniline products suggest that the major initial products of such a reduction of the nitroamides are the corresponding hydroxylamines. Under anaerobic conditions, cyclization via the hydroxylamines was considerably faster (up to 160‐fold) than via the corresponding amines under comparable conditions, but was similarly influenced by changes in geometry. Unlike cyclization via the amines, rates of cyclization via the hydroxylamines were sensitive to substitution on the leaving aniline, being accelerated by electron‐withdrawing groups. The rate‐determining step in the cyclization of the hydroxylamines is proposed to be breakdown of the tetrahedral intermediate.
Mono‐, bis‐ and tetra‐acridine ligands: Synthesis, X‐ray structural determination and dynamic fluorescence microscopic studies on the modification of the higher order structure of DNA
Authors: Atwell Graham J. , Denny William A. , Clark George R. , O'Connor Charmian J. , Matsuzawa Yukiko , Yoshikawa Kenichi
Published: January 2005

A series of mono‐, bis‐ and tetra‐acridine ligands were prepared and their effects on the higher order structure of DNA were studied by dynamic fluorescence microscopy. The single‐crystal structure of the bis‐acridine derivative N‐[2‐(dimethylamino) ethyl]‐4‐[2‐(9‐acridinylamino)benzamido]‐2‐(9‐acridinylamino)benzamide trihydrochloride (4) was determined, and shows that the molecule is sufficiently flexible to fold into an intramolecular stacking interaction in the crystal, supporting earlier hydrodynamic evidence that this compound can bis‐intercalate into DNA forming a single base pair (bp) sandwich complex. The corresponding tetra‐acridine analogue 1,11‐bis[4‐[2‐(9‐acridinylamino)benzamido]‐2‐(9‐acridinylamino)phenyl]‐1,11‐dioxo‐6‐methyl‐2,6,10‐triazaundecane pentahydrochloride (6) was synthesized, and dynamic fluorescence microscopy was used to study the effects of 4 and 6 on the higher order structure of large T4 DNA molecules (166 kbp), by measuring the average long‐axis legth (persistence length, l) of the complexes. The mono‐intercalating ligand acridine orange (5) increase l, whereas the bisintercalating diacridine 4 has no apparent effect and the putative multi‐intercalating tetracridine derivative 6 decreases l by compacting the higher order DNA structure. These results demonstrate the usefulness of the technique for directly observing ligand–DNA complexes, and show that ligands with suitably positioned multiple binding sites can influence the higher order structure of DNA (and thus possibly gene expression).
Aminolysis and hydrolysis of sulphamate esters: Substantial NS bonding in the transition state leading to Nsulfonylamines
Authors: Spillane William J. , Hogan Geraldine , McGrath Paul
Published: January 2005

The aminolysis and hydrolysis of several sulphamate esters, RNHSO2ONp (R = PhCH2, Ph, 4‐MeC6H44, 3‐MeC6H4, 4‐FC6H4, 4‐ClC6H4, 3‐ClC6H4, H; Np = 4‐NO2C6H4) were been studied in 50% (v/v) aqueous acetonitrile at various temperatures. Reaction of the esters with an amine (R1NH2) gives −ONp and both sulphamide, (RNHSO2NHR1) and sulphamate (RNHSO2O−R1NH3+) products. First‐order rates were determined by the appearance of −ONp and sometimes also by the disapperance of ester. The reaction was found to be independent of amine type and concentration and at the high pHs that obtain the substrate esters are fully ionized. A Hammett ρacyl of −;1·8 was obtained for the decomposition of the sulphamate anions and this is consistent with substantial NS bonding in the transition state leading to N‐sulphonylamine, RNSO2. This intermediate then partitions very rapidly, reacting with R1NH2 and H2O respectively. ΔH‡, ΔS‡ and a deuterium solvent isotope effect were determined and were also interpreted in favour of the proposed mechanism. The dimethyl sulphamate ester (Me2NSO2ONp) does not react under the conditions used.
Molecular complexes between octaethyltetrathiaporphyrin dication and electron donors: A spectroscopic and electrochemical study
Authors: Mahammed Atif , Rabinovitz Mordecai , Willner Itamar , Vogel Emanuel , Pohl Michael
Published: January 2005

Octaethyltetrathiaporphyrin dication, OTP2+, is electrochemically reduced by two successive electron‐transfer processes to OPT0. OPT2+ forms intermolecular complexes with a series of π‐donors. The association constants of the resulting complexes are controlled by the oxidation potentials of the π‐donors and solvent properties. OTP2+ was incorporated into a Nafion membrane cast on a Pt electrode. Formation of OTP2+–π‐donor complexes in the polymer membrane was followed by electrochemical and spectroscopic means. The association constants of the OTP2+–π‐donor complexes in the Nafion membrane exhibit lower values than a homogeneous phase owing to the high ionic strength in the polyelectrolyte.
Molecular aggregates between octaethyltetrathiaporphyrin dication (OTP2+) and octaethylporphyrin (H2OEP) and its metal complexes
Authors: Mahammed Atif , Rabinovitz Mordecai , Hoffman Roy E. , Willner Itamar , Vogel Emanuel , Pohl Michael
Published: January 2005

The octaethyltetrathiaporphyrin dication, OTP2+, forms 1:1 intermolecular donor–acceptor complexes with NiII‐, VIVO‐ and FeIII‐octaethylporphyrins. The association constants of the complexes are governed by the oxidation potential of the metallo‐octaethylporphyrins and by secondary electrostatic interactions. Octaethylporphyrin, H2OEP, forms intermolecular complexes with OTP2+. Kinetic analyses of the formation of the various complexes revealed the formation of a primary complex exhibiting the stoichiometry (OTP2+)2(H2OEP). This intermolecular complex transforms into a thermodynamically stabilized intermolecular assembly with a stoichiometry corresponding to (OTP2+)4H2OEP. The activation barrier associated with the conversion of the primary complex to the thermodynamically stabilized assembly is Ea = 16·5 kcal mol−1 (1 kcal = 4·184 kJ). The association constant of the complex (OTP2+)2(H2OEP) is K1 = 1·3 × 1010 M−2 and the equilibrium constant between the two coexisting intermolecular complexes (OTP2+)4(H2OEP) and (OTP2+)2(H2OEP) is K2 = 7·4.
AM1 study of single‐atom peri‐bridged naphthalenes
Authors: Yavari Issa , Nori‐Shargh Davood
Published: January 2005

peri‐Bridged naphthalenes in which the C‐1 and C‐8 atoms of the naphthalene ring are bonded to a single atom in a bridging group Z (Z = CH2, CHBr, CO, NH, O, S, SO and SO2) were studied by the AM1 semi‐empirical SCF MO method. Although in peri‐naphthalenes bridged by carbon or sulfur the naphthalene structure is planar, the corresponding nitrogen‐ or oxygen‐bridged molecules are distorted about 15 and 23°, respectively. There are significant variations (from 92 to 106°) of the C‐1–C‐9–C‐8 angle that is calculated in the cycle formed by the bridge. The calculated strain‐energy barrier for pyramidal atom inversion in amine 4 and sulfoxide 7 are 32·5 and 174 kJ mol−1, respectively.
Yield of ions produced in the luminescence quenching of tris (2,2′‐bipyridine)ruthenium(II) by dichlorophenolate ions
Authors: Senz A. , Gsponer H. E.
Published: January 2005

The electron‐transfer quenching of Ru(bpy) (tris(2,2′‐bipyridine)ruthenium(II) excited state by 2,4‐dichlorophenol (2,4‐DCP), 2,5‐dichlorophenol (2,5‐DCP) and 2,6‐dichlorophenol (2,6‐DCP), in their anionic forms, was studied in de‐aerated solutions of neat methanol and 25, 50 and 75% v/v aqueous methanol at 30°C. The quenching rate constants (kq) were determined and their values range from 1 × 107 to 8 × 109 M−1 s−1. In all the mixtures methanol : water the kq values for 2,5‐DCP were lower than for 2,4‐DCP and 2,6‐DCP. This result was discussed in terms of the effect of chloro atom on the quencher oxidation reaction. The photoredox product Ru(bpy) was observed by laser flash photolysis and its quantum yield (ΦRu(+)) calculated by using a comparative method with the formation of zinctetraphenylporphyrin triplet state. The yields of cage escape (Yce) for the different methanol/water mixtures were calculated from the obtained values of ΦRu(+)). Yce increases from 0·1–0·2 in 25% v/v aqueous methanol to 0·5–0·6 in neat methanol. This change of Yce with the solvent composition was discussed in terms of combined effects of viscosity and solvent cage on the rate constant of cage escape (k−d) and the rate constant for back electron‐transfer to the ground state from geminate pair (kbc), respectively. The constants k−d were calculated with the Eigen equation. The constants kbc were estimated from Yce and k‐d by applying a simplified reaction scheme. The kbc kbc values range from 3·2 × 109 to 1·3 × 1010 s−1.
Chiral polymethine dyes: A remarkable but forgotten conjugated π system
Authors: Reichardt Christian
Published: January 2005

Chiral polymethine dyes constitute a particular class of conjugated π systems. Artificial chiral polymethine dyes were first synthesized by König and Langbein in 1928 in order to clarify the electronic structure of cyanine dyes; some natural dyes such as musca‐aurin I (from the toadstool fly agaric) and betanin (from the vegetable red beets) are known to be chiral pentamethinium cyanine dyes, the chirality of which stems fromL‐α‐amino acids as end‐groups. The reasons why chiral polymethine dyes are not only of historical interest but once again the subject of research are explained.
Compensation effects in the complexation reactions of α‐ and β‐cyclodextrin
Authors: Gelb Robert I. , Alper Joseph S.
Published: January 2005

Analysis of temperature dependent equilibrium constant data for the complexation of α‐cyclodextrin with approximately 70 different substrates demonstrates the existence of a general compensation effect. Enthalpies (kJ mol−1) and entropies (J K−1 mol−1) of complexation are related by ΔH = −5·70(±0·05) + [421·1(±1·2)]ΔS. A few substrates deviate from the general effect, possibly owing to reorganization of internal hydrogen bonding interactions. Complexation reactions involving β‐cyclodextrin are found to divide into two groups. Eleven small molecule or ion substrates undergo isoentropic complexations with ΔS = −5·7±2 J K−1 mol−1. Fourteen larger substrate species exhibit a compensation effect with ΔH = −23·5(±0·2) + [634(±26)]ΔS. The compensation behavior of the two cyclodextrins is discussed in terms of bonding mechanisms and cavity size.
Dielectric properties of a ferroelectric superlattice with two alternating layers
Authors: Jiang Wei , Cheong Lo Veng
Published: January 2005

The phase transition temperature, polarization and susceptibility of a ferroelectric superlattice with two alternating layers have been studied using the transverse Ising model based on the effective‐field theory with the differential technique. The effects of the transverse field and the ferroelectric or antiferroelectric interfacial coupling strength between two ferroelectric materials on the physical properties of superlattices are discussed in detail. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theory of strongly correlated electron systems. I. Intersite Coulomb interaction and the approximation of renormalized fermions in total energy calculations
Authors: Sandalov I. , Lundin U. , Eriksson O.
Published: January 2005

The diagrammatic strong‐coupling perturbation theory (SCPT) for correlated electron systems is developed for intersite Coulomb interaction and for a nonorthogonal basis set. The construction is based on iterations of exact closed equations for many‐electron Green functions (GFs) for Hubbard operators in terms of functional derivatives with respect to external sources. The graphs, which do not contain the contributions from the fluctuations of the local population numbers of the ion states, play a special role: a one‐to‐one correspondence is found between the subset of such graphs for the many‐electron GFs and the complete set of Feynman graphs of weak‐coupling perturbation theory (WCPT) for single‐electron GFs. This fact is used for formulation of the approximation of renormalized Fermions (ARF) in which the many‐electron quasi‐particles behave analogously to normal Fermions. Then, by analyzing: (a) Sham's equation, which connects the self‐energy and the exchange–correlation potential in density functional theory (DFT); and (b) the Galitskii and Migdal expressions for the total energy, written within WCPT and within ARF SCPT, a way we suggest a method to improve the description of the systems with correlated electrons within the local density approximation (LDA) to DFT. The formulation, in terms of renormalized Fermions LDA (RF LDA), is obtained by introducing the spectral weights of the many‐electron GFs into the definitions of the charge density, the overlap matrices, effective mixing and hopping matrix elements, into existing electronic structure codes, whereas the weights themselves have to be found from an additional set of equations. Compared with LDA+U and self‐interaction correction (SIC) methods, RF LDA has the advantage of taking into account the transfer of spectral weights, and, when formulated in terms of GFs, also allows for consideration of excitations and nonzero temperature. Going beyond the ARF SCPT, as well as RF LDA, and taking into account the fluctuations of ion population numbers would require writing completely new codes for ab initio calculations. The application of RF LDA for ab initio band structure calculations for rare earth metals is presented in part II of this study (this issue). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Theory of strongly correlated electron systems. II. Including correlation effects into electronic structure calculations
Authors: Lundin U. , Sandalov I. , Eriksson O.
Published: January 2005

We have previously shown that a division of the f‐shell into two subsystems gives a better understanding of the cohesive properties as well the general behavior of lanthanide systems. In this article, we present numerical computations, using the suggested method. We show that the picture is consistent with most experimental data, e.g., the equilibrium volume and electronic structure in general. Compared with standard energy band calculations and calculations based on the self‐interaction correction and LDA + U, the f‐(non‐f)‐mixing interaction is decreased by spectral weights of the many‐body states of the f‐ion. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Correlating the positional reactivity of a masked electrophilic center to the topology of the electron density
Authors: Price Harry L.
Published: January 2005

Masking of electrophilic centers in biological molecules via structural modifications serves to control chemical reactivity and in some cases may affect the regioselectivity of a reaction. In the work presented the regioselective reactivity of the electrophilic cyclopropylpyrrololindole (CPI) center in the DNA alkylator CC‐1065, a highly toxic antibiotic that has served as a structural template for the development of a series of novel anticancer drugs containing the CPI reactive center has been examined. The CPI reactive center is an interesting example of chemical masking as it relates to acid‐dependent electrophilicity, and regioselective addition of a nucleophile to an electrophilic center. In an effort to better understand the reactivity of the CPI center, calculations using the B3LYP density functional theory (DFT) method, the 6‐31G(d)basis set, and the atoms in molecules (AIM) theory were performed on unprotonated and protonated forms of the CPI reactive center. The results of these calculations demonstrate that activation of the CPI group via protonation induces significant changes in the electron density (ρ), the Laplacian of the density (∇2ρ), and the bond ellipticity (ε), and that these changes are linked to the observed reactivity of the CPI reaction center. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Potential energy surfaces in Coulomb explosion of polyatomic molecules: Benzene and cyclohexane trications and acetylene dication
Authors: Mebel A. M. , Zyubina T. S. , Dyakov Y. A. , Bandrauk A. D. , Lin S. H.
Published: January 2005

We report density functional and ab initio calculations of potential energy surfaces (PES) for benzene and cyclohexane trications relevant to the Coulomb explosion mechanisms of C6H6 and C6H12. Numerous isomerization and dissociation mechanisms on these PES have been considered, and the products most favorable thermodynamically and kinetically have been predicted. We also demonstrate applications of RRKM theory to the calculation of product branching ratios in decomposition of multiply charged cations. Significant common features of PES related to Coulomb explosion experiments on hydrocarbon molecules have been described. Calculations along minimal energy reaction paths for some representative isomerization and dissociation channels have been carried out in the presence of strong external electric field for C6H and C2H and the influence of the field on molecular orientation and PES have been analyzed. The results show that proton mobility in nonaromatic hydrocarbon cations is high due to nearly zero barriers for the H+ migrations. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Irreducible charge density matrices for analysis of many‐electron wave functions
Authors: Luzanov A. V. , Prezhdo O. V.
Published: January 2005

A novel procedure for deriving multicenter bond indices on the basis of irreducible spinless charge density matrices that are naturally introduced as in the Ursell–Mayer theory is presented. Unlike earlier schemes using central moments of the charge operator, the procedure presented here leads to a proper definition of multicenter bond indices for an arbitrary number of atoms. Formal relationships and numerical techniques for the typical configuration interaction (CI) approaches, up to full CI, are given and illustrated with simple molecular systems. Comparison of the molecular orbital and full CI results indicates strong electron correlation effects, especially for the 3‐center and 4‐center bond indices. Excited state multicenter bond indices are described within the CI singles approach. The problem of proper definition of atomic valence and bond indices for electronic states with nonzero spin is raised. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Convergence enhancement in the iterative solution of the second‐order contracted Schrödinger equation
Authors: Alcoba D. R. , Casquero F. J. , Tel L. M. , Pérez‐Romero E. , Valdemoro C.
Published: January 2005

The iterative solution of the contracted Schrödinger equation is coupled with a second‐order reduced density matrix purification procedure, which corrects its N‐ and S‐representability defects, and with a regulating convergence device. An analysis of the effects of these new implementations is reported. The method is applied to the calculation of the potential energy curves of the BeH2 and Li2 molecules. The results compare very closely with those of the full configurations interaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Moments of the electron momentum density: Requirements for ab initio and density functional theory calculations
Authors: Hart James R. , Thakkar Ajit J.
Published: January 2005

Moments of the electron momentum density are calculated for 68 closed‐shell molecules in their ground states and equilibrium geometries. The computations are made with the Hartree–Fock (HF), Møller–Plesset (MP) perturbation theory, coupled cluster, and six density functional theory (DFT) methods, using a number of basis sets of contracted Gaussian‐type functions. Guidelines for the choice of basis sets for these properties are given. Electron correlation effects are found to be less than 8% and can often be accounted for by the second‐order MP method. DFT methods are found to give relatively poor results, often worse than the HF method. The coupled cluster results should provide a benchmark for future experiments and methodological developments. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Löslichkeitsprodukte anorganischer Salze im flüssigen Ammoniak und ihr Vergleich mit den Verhältnissen in anderen Lösungsmitteln unter besonderer Berücksichtigung ihrer Dielektrizitätskonstanten. Nach Versuchen von Kurt Krieghoff (Leitfähigkeitsmessungen) und Bernhard von Freytag‐Loringhofen (Messungen von Konzentrationsketten)
Authors: Fredenhagen Karl
Published: January 2005

Durch die Untersuchungen amerikanischer Forscher war schon bekannt, daß viele anorganische Salze in [NH3] ganz andere Löslichkeiten zeigen als in [H2O]. Teils durch Messungen der Leitfähigkeiten der gesättigten Lösungen, teils durch Konzentrationskettenmessungen wurden die Löslichkeiten der folgenden Salze in [NH3] quantitative bestimmt: AgNO3, AgJ, AgBr, AgCl, AgF, NH4NO3, NH4J, NH4Br, NH4Cl, NH4F, KNO3, KJ, KBr, KCl, KF, KOH, LiF. Hierbei wurde im einzelnen folgendes festgestellt: Die Nitrate zeigen in [H2O] und in [NH3] im allgemeinen angenähert gleiche Sättigungsionenkonzentrationen. Bei den Jodiden sind die Sättigungskonzentrationen in [NH3] erheblich größer als in [H2O], und zwar beim AgJ um das 108‐fache. Beim AgF liegen die Verhältnisse dagegen umgekehrt. Hier ist die Sättigungskonzentration in [H2O] um rund 1015mal größer als in [NH3], in dem die Fluoride — näher untersucht wurden noch KF, NH4F und LiF — überhaupt keine nachweisbare Löslichkeit zeigen. Die Löslichkeitsverhältnisse der Chloride und Bromide liegen zwischen diesen beiden Extremen, und zwar zeigen die Bromide in [NH3] allgemein eine größere Sättigungsionenkonzentration als die Chloride.
Schillerschichten als Reaktionsprodukte der langsamen Eisenchlorid‐Hydrolyse
Authors: Zocher Hans , Heller Wilfried
Published: January 2005

1. Die langsame Hydrolyse liefert nach einer gewissen Zeit, die mit abnehmender Konzentration bis zu Jahren zunimmt, in Lösungen von rund 1/10 bis über 8% Eisenchloridgehalt anisotrope Sedimente von in gleicher Richtung abnehmendem Solcharakter. Zwischen 1/3 und 1% haben diese die Eigenschaften eines Taktosols vom Typus der ZOCHER'schen Eisenoxydsolschillerschichten.
Über die Dissoziation der Kohlensäure und über ihre Einwirkung auf metallisches Nickel unter Druck
Authors: Müller Ernst , Luber Anton
Published: January 2005

In der vorliegenden Arbeit wurde zunächst die Einwirkung von wäßriger Kohlensäure auf metallisches Nickel bei verschiedenen Drucken und Temperaturen eingehend untersucht; dabei zeigte sich, daß die Geschwindigkeit der Auflösung des Metalles van den beiden genannten Faktoren derart abhängig ist, daß für jede Temperatur und jeden Druck schließlich jeweils eine ganz bestimmte Konzentration an gelöstem Nickel erreicht wird.
Über die Struktur des Strontiumchlorid‐Hexahydrats
Authors: Hermann Z.
Published: January 2005

Mit Hilfe der Drehkristallaufnahmen um [001] [010] und [100] wurden die Identitätsperioden des Strontiumchlorid‐Hexahydrats bestimmt. Als Kantenlängen der orthohexagonalen Elementarzelle wurden

gefunden. Die Raumgruppe des Strontiumchlorid‐Hexahydrats ist C. In der orthohexagonalen Grundzelle sind 2 Moleküle enthalten.
Über die Konstitution der Platintetramminsalze
Authors: Hantzch A. , Rosenblatt F.
Published: January 2005

Die Platintetramminsalze, z. B. Pt(NH3)4Cl2, können nicht, wie A. WERNER annahm, plan konfiguriert sein, weil das nahe verwandte Äthyelnderivat, PtN(CH2 · CH2NH2)3Cl2, nicht zwei durch die Äthylenbrücke verbundene Stickstoffatome in trans‐Stellung besitzen kann. Auch die symmetrisch tetraedrische Konfiguration ist unmöglich, weil damit die Isomerie von Salzen wie die der eis‐ und trans‐chloride, Pt(NH3)2py2Cl2, unvereinbar ist. Die unsymmetrischtetraedrische oder bisphenoidische Konfiguration könnte zwar die Existenz dieser Isomeren erklären, aber nicht folgenden einfachen Reaktionsverlauf: magnified image. Denn hierbei bleibt der Unterschied zwischen den eis‐ und trans‐Formen in allen Reaktionsstufen erhalten, während die Konfiguration vom planen Bau ü das unsymmetrische Tetraeder zum symmetrischen Oktaeder wechseln müßte. Mit dem einfachen Reaktionsverlauf ist ein solcher doppelter radikaler Wechsel der Konfiguration ebenso unvereinbar, wie mit den neueren theoretischen Vorstellungen, welche die Anordnung der Liganden in Beziehung zum Elektronenbau des Zentralatoms setzen und deshalb eine möglichst gleichartige Konfiguration fü alle Komplexverbindungen desselben Zentralatoms fordern.
Eine bequeme und zuverlässige Methode zur gravimetrischen Bestimmung des Aluminiums als Oxyd
Authors: Fricke R. , Meyring K.
Published: January 2005

1. A1 läßt sich bequem und genau bestimmen durch Fällung mit CO2aus alkalischer Lösung.
Über die Bildung von Jodaten aus Jodiden durch molekularen Sauerstoff
Authors: Henglein F. A. , Teichmann L.
Published: January 2005

Es wird die Reaktion 2KJ + 32 ⇄ 2KJO3 im Sinne der Reaktionsgleichung von links nach rechts untersucht und gefunden, daß die Reaktion durch Alkalihydroxyde, sowohl im geschmolzenen als auch im wäßrigen Zustande, beschleunigt wird. Unter günstigen Bedingungen bilden sich auch Perjodate. Auf die Bedeutung der Reaktion in der Biologie wird hingewiesen.
Die spezifische Wärme einiger Metalle und Metallegierungen bei tiefen Temperaturen
Authors: Eucken A. , Werth H.
Published: January 2005

1. Die Temperaturkurven der spezifischen Wärme werden experimentell (mit Hilfe der Methode der elektrischen Heizung im Vakuum) ermittelt beim Cu (zwischen 83 und 215° abs.), beim Ni, Konstantan (etwa 60%, Cu, 40%, Ni), α‐Eisen sowie einigen Mn‐Fe‐ Legierungen (zwischen etwa 15 und 200° abs.).
Zur physikalischen Chemie des Schwefelsäureanhydrids
Authors: Grau R. , Roth W. A.
Published: January 2005

1. Es werden mit reinem, ganz wasserfreiem SO3 Dampfdruckmessungen gemacht, die oberhalb 25° C mit den Resultaten früherer Forscher ziemlich gut übereinstimmen. Unterhalb 25° C sind unsere Werte höher als die von SMITS‐SCHOESNAKER gefundenen.
Verdünnungswärme der Schwefelsäure
Authors: Grau R. , Roth W. A.
Published: January 2005

Es wurden von H2SO4 die Verdünnungswämen in dem Bereich OH2O bis 10000H2O pro Mol H2SO2 bei 18° neu bestimmt und mit den vorliegenden Werten von BRÖNSTED und NAUDÉ verglichen. Während mit BRÖNSTED eine sehr gute Übereinstimmung erzielt wird, ist diejenige mit NAUDÉ nicht so gut. Die Temperaturkoeffizienten der Verdünnungswämen zwischen + 8° und + 8° wer den bestimmt.
Die Hydrate des Calciumcarbonats
Authors: Krauss F. , Schriever W.
Published: January 2005

1. Das Hexahydrat des Calciumcarbonats wird zum ersten Male rein hergestellt.
Über Quecksilber‐ und Wismutverbindungen des 8‐Oxychinolins
Authors: Dede L. , Hessler W.
Published: January 2005

Das 8‐Oxychinolin hat infolge seines koordinativ ungesättigten Stickstoffs und eines besonders in 5,7‐Stellung hervortretenden Restfeldes starke Tendenz zur Komplexbildung. Bei den meisten bereits früher von anderen Autoren untersuchten Salzen entstehen durch die koordinative Absättigung des Stickstoffs innerkomplexe Phenolate. Bei den von uns untersuchten Quecksilber‐ und Wismutverbindungen kommt in der Hauptsache das Restfeld in 5,7‐Stellung zur Wirkung.
Über das dielektrische Verhalten von Oxydhydraten
Authors: Havestadt L. , Fricke R.
Published: January 2005

1. Von einer größeren Zahl auf sehr verschiedene Weise hergestellter Oxydhydrate des Th, Si, Sn, Cr, Ga, A1 und Be wurden die DEK‐Werte in Abhängigkeit von der Zeit (Alterungszustand) gemessen. Hierbei ergaben sich fur die meisten Oxydhydrate Werte, die erheblich über der DEK des Wassers lagen. Mit fortschreitender Alterung änderten sich diese Werte auf sehr charakteristischen Kurven.
Über die Zersetzung der Selenbromwasserstoffsäure und ihrer Salze
Authors: Meyer Julius , Wurm V.
Published: January 2005

Reine Selenbromwasserstoffsäure H2SeBr6 löst sich in Wasser klar und ohne Zersetzung auf. Die von GUTBIER und ENGEROFF beobachtete Bildung von kolloidalem Selen ist auf die leichte Zersetzlichkeit der Selenbromwasserstoffsäure in Diselendibromid zurück‐ zuführen. Die Salze der Selenbromwasserstoffsäure sind ebenfalls ohne Abscheidung von Selen in Wasser löslich, spalten aber an der Luft, vor allem bei höheren Temperaturen, ebenfalls Brom ab, und können dann Lösungen von kolloidalem Selen liefern.
Über Anlagerungsverbindungen des Phosphorwasserstoffs
Authors: Höltje Robert
Published: January 2005

PH3 zeigt in seinem Verhalten gegen die Tetrahalogenide der 4. Gruppe des periodischen Systems große Ähnlichkeit mit H2S. Wie dieser wirkt er in verflüssigtem Zustand auf einige Salze lösend; mit anderen bildet er Anlagerungsverbindungen, die denen des H2S sehr ähneln. (Zusammenstellung in Tabelle 1, S. 253.) Jedoch ist PH3 in den bisher aufgefundenen Verbindungen trotz seines kleineren Dipolmoments fester gebunden als H2S in den entsprechenden Thiohydraten. Diese Erscheinung wird mit der größeren Deformierbarkeit des PH3 erklärt. Die Versuche sollen fortgesetzt werden.
Die Schmelztemperaturen des Sauerstoff‐2‐fluorids und Stickstoff‐3‐fluorids
Authors: Ruff Otto , Clusius Klaus
Published: January 2005

Die Schmelztemperatur von etwa 98,5O%igem OF2 wurde zu 49,30° abs. oder −223,8° C gefunden.

Ein ziemlich reines Präparat von NF3 erstarrte bis −2100°C noch nicht; von einem etwas weniger reinen schmolz die Hauptmenge bei 56,5O° abs. = −216,60°C. Das Schmelzen war aber erst bei 64,30° abs. = −208,8°C beendet. Die Schmelztemperatur des NF3 liegt somit etwas oberhalb 56,5° abs. = −216,6°C.
Über ein neues Chlorfluorid‐CIF3
Authors: Ruff Otto , Krug Herbert
Published: January 2005

Neben den1 Chlor‐1‐fluorid besteht auch ein Chlor‐3‐fluorid, welches durch Erhitzen von CI2 oder CIF mit überschüssigem F2 dar‐ gestellt wird. Die umkehrbare Reaktion CIF + F2 ⇆ CIF3 führt zu einem Gleichgewicht, in dem bei 250° Zahl der CIF‐Moleküle ein Mehrfaches der CIF3‐Moleküle ist. Die Zusammensetzung des neuen Fluorids is durch Analysen und Dichtebestimmungen sichergestellt. Seine physikalischen und chemischen Eigenschaften werden mit ‐ geteilt.

Besonders bemerkenswert ist die Lebhaftigkeit und die Mannigfaltigkeit der Reaktionen des CIF3.
Über die Oxydationsgeschwindigkeit von Jodwasserstoff mittels Arsensäure in Gegenwart von Säuren und Salzen
Authors: Bobtelsky M. , Rosowskaja‐Rossienskaja R.
Published: January 2005

Die Oxydation von HJ mittels Arsensäure verläuft bei 30° mit meßbarer Geschwindigkeit nur in Gegenwart von größeren Mengen freier Säure. Die Wirkung der Säure ist keine katalytische, sondern eine Neutralsäurewirkung.

In Gegenwart größerer Mengen Säure beschleunigt die weitere Zugabe einer Säure den Prozeß stärker als irgendein anderes Salz mit demselben Anion.
Untersuchungen im System Na2O‐SiO2‐ZrO2
Authors: D'Ans J. , Löffler J.
Published: January 2005

1. In dem bearbeiteten Teil des ternären Systems Na2O–Si02–ZrO2 werden ganz oder teilweise neu beschrieben die Verbindungen:
magnified image
Als primare Ausscheidung kommt außerdem noch das Zirkonoxyd und das Zirkonsiliket vor, die nicht naher uniersucht wurden.
Über ein wahres Maß der Aggressivität natürlicher Wässer
Authors: Orlow J. E.
Published: January 2005

1. Es wurde festgestellt, daß die Zersetzung des Calciumcarbonats in wäßrigen Lösungen in breiten Konzentrationsintervallen bei Zimmertemperatur nur in Gegenwart von Katalysatoren vor sich geht. Als Katalysatoren wurden Marmorpulver und metallisches Eisen ausprobiert.
Die Löslichkeit der Halogenide des Zirkoniums und Hafniums
Authors: v. Hevesy G. , Wagner O. H.
Published: January 2005

Die Löslichkeit des Zirkonylbromids und Hafnylbromids wurde in 1 bis 13 n‐HBr‐Lösung bestimmt. In sehr konzentrierten HBr‐Lösungen ist bei 25° die Hafnylverbindung beträchtlich (bis zu 4,5mal) weniger löslich als die Zirkonylverbindung.
Über die Neutralsalzwirkung der Ferri‐Jodionenreaktion. I. Die Neutralsalzwirkung in verdünnten Lösungen
Authors: v. Kiss A. , Bossányi Irene
Published: January 2005

Es wurde in verdünnten Lösungen der Mechanismus der Ferri‐ und Jodionenreaktion untersucht und gefunden, daß monomolekular für die Ferriionen und bimolekular für die Jodionen vor sich geht. Die hydrolysierten Ferriionen reagieren nicht mit meßbarer Geschwindigkeit.