bluuebunny/crossref_metadata_2025_split huggingface dataset:
Small Rhodium Aggregates with Unusual Oxidation States. The Synthesis and Structure of [Rh3 ((Ph2PCH2)2PPh)2(CO)I4] [BPh4] · 0.77 Acetone
Authors: Balch Alan L. , Olmstead Marilyn M. 
Published: November 2013

AbstractThe oxidative behavior of rhodium(I) isocyanides and dimers bridged by diisocyanides and diphosphines, which leads to the formation of rhodium—rhodium bonded complexes in the +2, +5\3, +3\2 oxidation states, is reviewed. The results of an X‐ray crystallographic investigation of a new, related compound, [Rh3 ((Ph2PCH2)2‐PPh)2(CO)I4] [BPh4] · 0.77 C3H6O, are described.
Protection of 4‐Fluoroanisole from Aromatic Nucleophilic Photosubstitution by Cyclodextrins [1]
Authors: Liu Jerry H. , Weiss Richard G. 
Published: November 2013

AbstractAromatic nucleophilic photosubstitution reactions of 4‐fluoroanisole with cyanide and water have been investigated in aqueous α‐β‐, and γ‐cyclodextrin solutions. Although photoreactivity of the α‐ or β‐cyclodextrin‐complexed 4‐fluoroanisole toward nucleophilic substitution is suppressed almost completely, none of the cyclodextrins had a measurable influence on the rate of 4‐fluoroanisole fluorescence quenching by I−. In aqueous γ‐cyclodextrin, the efficiency of photohydroxylation was increased slightly but the efficiency of photocyanation was unaffected. From Benesi‐Hildebrand plots, the dissociation constants of the complexes of 4‐fluoroanisole with α‐ and β‐cyclodextrins were obtained. A good correlation between the relative quantum yields and the degree of complexation was found. Explanation for the lack of a marked effect on photosubstitution by γ‐cyclodextrin is presented.
The Effect of the Structural Elements on the Properties of Side Chain Mesomorphic Polymers
Authors: Cser F. , Horváth J. , Nyitrai K. , Hardy GY. 
Published: November 2013

AbstractThe thermal properties of mesomorphic polymers depend on the relative amounts of the different structural elements (hard core, flexible chains, main chain) of the polymer. Literature data are compared with the conclusions obtained from the three‐component thermodynamic model of side chain mesomorphic polymers. The effects of the different soft elements (main chain, spacer and p‐alkyl or alkoxy chain) depend first of all on the length of the spacer and its interaction with the main chain. The thermal properties of the polymer can be well regulated by varying the different structural elements of the homo‐ and co‐polymers. The glass transition temperature (Tg) of the polymer can be reduced by building O and N atoms into the main chain and/or by binding the side chains on 3rd, 4th, etc. atoms of the main chain. The Tg can be further reduced by increasing the length of the spacer. If the spacers are long enough, the layer type structures are favored, with p‐alkoxy chains behaving also as a plasticizer of the main chain. The clearing point can be influenced by copolymerization of monomers with different hard cores. The three‐component thermodynamic model of side‐chain mesomorphic polymers well explains the effect of different structural elements on the structure and properties of these polymers.
Influence of Dye Aggregation on Photosensitized Hole Injection into Anthracene Crystals from Langmuir‐Blodgett Monolayers Containing Cyanine Dyes
Authors: van Der Auweraer M. , Willig F. 
Published: November 2013

AbstractMonolayers containing cyanine dyes can be transferred to anthracene crystals and are able to inject holes into the crystal upon excitation. At low dye coverages only the dye monomer injects holes while at higher coverages energy transfer to aggregates is the most important decay process of an excited dye monomer. These aggregates are also able to inject holes but with a more than ten times smaller efficiency. The occurrence of dye aggregates is confirmed by the absorption spectra of the monolayers. In this system non‐geminate recombination remains an unimportant pathway even at high dye coverages.
The Synthesis, Crystal and Molecular Structure, and Oxidation State of Iron Complex from Pyridoxal Isonicotinoyl Hydrazone and Ferrous Sulphate
Authors: Avramovici‐Grisaru Schely , Sarel Shalom , Cohen Shmuel , Bauminger Rivka E. 
Published: November 2013

AbstractThe reaction of isonicotinoyl hydrazone of pyridoxal (PIH), a biologically active iron‐carrier, with FeSO4‐7H20 at pH ∼ 6 generates the delta, lamda species of the N,N‐trans‐O,O‐cis‐cis coordination isomer of an iron(III) complex with iron‐to‐ligand ratio of 1:2. The dark red‐brown crystals are monoclinic, space group C2/c, with unit‐cell dimensions a = 14.487(2), b = 18.586(2), c = 27.508(4) Å, β = 102.76(3)°, and Z = 8. The coordination around the metal is distorted octahedral and involves the protonated organic ligands, which are chelated through the phenolic oxygen [Fe‐O1 1.941(6), Fe‐O1′ 1.938(6)], an enolic form of the carbonyl oxygen [Fe‐O3 2.017(6), Fe‐O3′ 2.018(6)] and the azomethinic nitrogen [Fe‐N2 2.133(8), Fe‐N2′ 2.133(8)]. Packing is determined by systems of N‐H….O and O‐H….O hydrogen bonds involving the protonated pyridoxal nitrogens, the pyridoxal hydroxymethyl group, and the [SO4]2− group. The Mössbauer spectra at different temperatures (300 K, 88 K and 4.1 K) clearly prove that the iron atom in the complex is in a high‐spin trivalent state.
The Effect of Temperature on Competing Photochemical Hydrogen Abstraction Reactions in the Solid State
Authors: Greenhough Trevor J. , Scheffer John R. , Secco Anthony S. , Trotter James , Walsh Leueen 
Published: November 2013

AbstractIrradiation of 4aα,5,8,8aα‐tetrahydronaphthoquin‐1‐on‐4β‐o1 (1a) and its 6,7‐dimethyl derivative 1b in the solid state leads to two products. The first is formed via intramolecular hydrogen abstraction by carbonyl oxygen followed by radical coupling, and the second is produced through initial hydrogen abstraction by enone carbon and subsequent radical coupling. X‐ray crystallography reveals that both processes are topochemically allowed, and the geometric parameters for the hydrogen transfers and the radical coupling reactions are tabulated. In the case of 1b, the photoproduct ratio was found to be temperature dependent with hydrogen atom abstraction by carbon predominating at lower temperatures. From the slope of the linear plot of the natural logarithm of the photoproduct ratio versus the reciprocal of the temperature, an activation energy difference of approximately 4 kcal/mole is calculated. The results are interpreted as being due to competing reactions from (n,π*)3 and (π*)3 excited states, the latter (hydrogen abstraction by carbon) having a lower activation energy than the former (hydrogen abstraction by oxygen).
Effect of Molecular Symmetry and Intermolecular Halogen‐Halogen Interactions on the Crystal Structures of Halogen‐Substituted Benzoic Acids. X‐ray Crystal Structure of m‐Iodobenzoic Acid
Authors: Patil Anjali A. , Curtin David Y. , Paul Iain C. 
Published: November 2013

AbstractThe crystal structure of m‐iodobenzoic acid is reported. The crystals are monoclinic, P21/c, with a = 6.220(3) Å, b = 4.689(2) Å, c = 26.67(1) Å, β = 101.80(3)°, Z = 4, C7H5IO2. The structure has been determined by direct methods and refined to R 0.026 for 1288 reflections recorded with an automatic single crystal diffractometer. The structure is composed of essentially planar hydrogen‐bonded dimer units with significant intermolecular iodine‐iodine contacts. The configuration of the dimer unit is transoid. Since this is the penultimate member of the family of mono‐halogen‐substituted benzoic acids its structure is compared with those previously reported. In particular, the effects of differences in molecular geometry of the o‐, m‐, and p‐isomers and the strengths of the intermolecular halogen‐halogen interactions are surveyed. The geometry of the carboxyl group of m‐iodobenzoic acid in the solid state and the carbonyl absorption in the Ftir spectrum of the crystalline acid at room temperature suggest the presence of dynamic proton isomerism as has been recently found by other investigators in crystalline benzoic acid and some of its derivatives.
Mechanistic Aspects of Chiral Discrimination by Copper Complexes of N,N‐Dialkyl‐α‐Amino Acids
Authors: Weinstein Shulamith , Leiserowitz Leslie 
Published: November 2013

AbstractA model for the separation of enantiomers of several classes of compounds by copper complexes of N,N‐dialkyl‐α‐amino acids, based on chromatographic results and supported by crystal growth and dissolution studies, is described.
Complex of Tertiary Acetylenic Alcohol and Brucine or Sparteine. X‐Ray Crystal Structural Study and Application to Optical Resolution
Authors: Toda Fumio , Tanaka Koichi , Ueda Hideo , Ōshima Tokio 
Published: November 2013

AbstractSome tertiary acetylenic alcohols were optically resolved efficiently by complexation with brucine or sparteine. In the latter case, mutual optical resolution of sparteine and the tertiary acetylenic alcohol is possible. For an efficient resolution, the tertiary acetylenic alcohol should have at least one aromatic ring such as phenyl, naphthyl, thienyl as a substituent. The crystal structure of the 1:1 brucine complex and of the 1:1 (‐)‐sparteine complex of (‐)‐l‐(o‐bromophenyl)‐1‐phenyl‐2‐propynol (1a) are reported. In both cases, two hydrogen bonds,magnified imageare important to fix the two components at a close position where mutual chiral recognition is efficient.
Stereochemical Discrimination at Organic Crystal Surfaces 2: The Effect of the Molecular Structure and Conformation of Dipeptides Additives on the Morphology of Glyclyglycine Crystals
Authors: Weissbuch I. , Berkovitch‐Yellin Z. , Leiserowitz L. , Lahav M. 
Published: November 2013

AbstractThe centrosymmetric monoclinic crystals of glycyl‐glycine were grown in the presence of three dipeptides (racemic and resolved Gly‐Ala, Ala‐Gly and Gly‐Leu); the presence of each yielded a different morphology. It was found by a combined theoretical and experimental study that the conformation of the guest molecule is determined by the highly stereospecific intermolecular interactions between adsorbed additive and the molecules of particular surface layers of the growing crystals. Theoretical calculations predicted the preferred conformation of the leucine side chain of Gly‐Leu consistent with the change in morphology. Occluded racemic Gly‐Leu segregates along the b axis of the single crystals of Gly‐Gly.
Thermal Rearrangements, XIII [1]. Thermal Isomerization of Exocyclic Allenes
Authors: Hopf Henning , Gottschild Dietmar , Lenk Winfried 
Published: November 2013

AbstractThe thermal isomerization of several exocyclic mono‐ and bis‐allenes in a high‐temperature flow system has been investigated. At 600°C vinylidenecyclobutane (10) rearranges cleanly to the allene dimer 1,2‐bismethylenecyclobutane (12) by an allene‐diene isomerization. The methylallene 16 behaves analogously (600°C), although the primary product 18 does not survive under the reaction conditions: the isolated cross‐conjugated triene 20 is a product of a 1,5‐hydrogen shift followed by an electrocylic ring‐opening reaction. Whereas vinylidenecyclopentane (27) yields aromatic products only (800°C, toluene (36), benzene (38)), the five‐ring 1,3‐bisallene 30 isomerizes to the cyclopentene derivative 43 at 650°C. Vinylidenecyclohexane (46) affords only aromatic products again (760°C, o‐xylene (57), 36, 38) and 1,3‐bisvinylidenecyclohexane (49) isomerizes to the dienynes 60 and 61 by a series of hydrogen shifts at 550°C. On the other hand, the allene‐diene isomerization is observed again, when a C–C bond is doubly activated by an allene and methylene group as in 52 or by two allene moieties as in 53: at 500°C the triene 63 and the exocyclic tetraene 65, respectively, are obtained in good yield.
1,3‐Dipolar Cycloadditions of 1,1‐Difluoroallene, Nitrones, Nitrile‐Oxides and Carbonyl Ylides
Authors: Dolbier William R. , Burkholder Conrad R. 
Published: November 2013

AbstractThe 1,3‐dipolar cycloadditions of C,N‐diphenylnitrone, C‐phenyl‐N‐methylnitrone, triphenylnitrone, mesitylnitrile oxide and tetracyanocarbonyl ylide with 1,1‐difluoroallene (DFA) are reported and discussed with respect to regiochemistry. Each of the dipoles adds exclusively to the C2—C3, non‐fluorine‐substituted π‐bond of DFA. The nitrones all undergo regiospecific reactions while mesitylnitrile oxide does not. The results are discussed with respect to FMO theory and other factors which can give rise to regiochemical variation.
Allene Synthesis by Organo‐Metallic Reactions
Authors: Crabbe Pierre , Schlemper Elmer O. , Fair Kay , Tran P.T. , Searles Scott 
Published: November 2013

AbstractSeveral original allene syntheses are reviewed. Two novel organometallic approaches are discussed in some detail. Recent observations made in the case of the one‐step synthesis of allenes by homologation of alkynes are described. The reaction mechanism which is proposed is supported by X‐ray crystallographic data on a CuBr complex which appears to be a reaction intermediate.
Cyclophilic Reactions of Allene‐1,3‐dicarboxylic Esters. Part 4. Pyrazolone Formation and a Novel Indole Synthesis from the Nucleophilic Addition of 1,2‐Diphenylhydrazine to Dimethyl Allene‐1,3‐dicarboxylate
Authors: Onwuyali E. Ify , Scheinmann Feodor 
Published: November 2013

AbstractExperiments are described for the addition of 1,2‐diphenylhydrazine to dimethyl allene‐1,3‐dicarboxylate and the subsequent conversion of dimethyl 3‐(1,2‐diphenylhydrazino)pent‐2‐enedioate (3) to either the pyrazolone (4) or a mixture of the indole (5) and the pyrazolone (4).
The Effect of the Counter Anion on the Complexation of Alkali Metal Salts to Polyethylene Glycol
Authors: Neumann R. , Dermeik S. , Sasson Y. 
Published: November 2013

AbstractThe complexation of alkali metal salts by polyethylene glycol is strongly dependent on the counter anion of the salt. In general, potassium salts are more easily complexed. In fact, sodium salts at low free energy of formation are barely complexed at all. By conductometric and index of refraction measurements it was shown that anions capable of hydrogen bonding such as OH−, F−, HSO−4 and HCO−3 were ion paired to the complexed potassium cation and existed as relatively “naked” anions. Other anions such as Cl−, Br−, I−, SCN−, NO−3, NO−2 AND HF−2 existed as disassociated anions with significant solvation shells. The use of polyethylene glycol as a phase transfer catalyst considering the results found is discussed.
Anomalous Selectivities in Methyl Transfers to Water: An Explanation Using Free Energy Surfaces which Model the Effects of Non‐Equilibrium Solvation
Authors: Kurz Joseph L. , Kurz Linda C. 
Published: November 2013

AbstractMany experimental observations imply that transition states for methyl‐transfers to water have little or no water—methyl covalent bonding and that the rate‐determining process is predominantly or entirely a fluctuation in solvent structure. Currently accepted descriptions of methyl‐transfer mechanisms cannot easily account for such a transition state structure or for the anomalous selectivities observed in these reactions. This paper derives a model free energy surface, which includes solvent polarization as one of the coordinates, and shows how that surface can account for the observed behavior of these methyl‐transfers. The transition state on that surface has a structure in which the solvent polarization is not in equilibrium with the internal charge distribution.
Limitations of the Reactivity—Selectivity Principle. Application to Free Radical Addition to Alkenes and Nucleophilic Aliphatic Substitution
Authors: Pross Addy 
Published: November 2013

AbstractThe limitations of the reactivity—selectivity principle (RSP) are discussed in terms of the qualitative configuration mixing (CM) model. It is concluded that the RSP is expected to break down for cases in which the reaction transition state takes on character largely absent in reactants or products, though not all breakdowns of the RSP are attributed to this cause. This conclusion is illustrated with two model reactions that do not follow the RSP: (a) radical addition to alkenes, and (b) nucleophilic aliphatic substitution. Analysis leads us to agree with previous statements by Jencks and Arnett that the RSP should be abandoned as a predictive tool.
Application of Aziridine to the Facile Synthesis of (±)‐Supinidine and (±)‐Trachelanthamidine
Authors: Kametani Tetsuji , Higashiyama Kimio , Otomasu Hirotaka , Honda Toshio 
Published: November 2013

AbstractA facile synthesis of the pyrrolizidine alkaloids, (±)‐supinidine (14) and (±)‐trachelanthamidine (8) was achieved by employing aziridine as the reactive species.
Monte Carlo Studies of the Aqueous Hydration of cis‐ and trans‐ N‐ Methyl‐Acetamide: Sensitivity of Results to Convergence and to Choice of Intermolecular Potential Functions
Authors: Mezei M. , Harrison S. W. , Ravishanker G. , Beveridge D. L. 
Published: November 2013

AbstractA series of liquid state Monte Carlo computer simulations on the N‐methyl acetamide in water (NMA molecule) are described, considering both the cis and trans isomeric forms of NMA. Two independent sets of calculations were performed, one set based on the potential functions developed by Clementi and co‐workers (CPF) used in conjunction with the Matsuoka et al. (MCY) water‐water potential, and the other set using the OPLS potential of Jorgensen and coworkers for solute‐water interactions and the TIP4P potential for the water‐water interactions. The relative hydration energies of the cis and trans isomers of NMA and the transfer energies of NMA from free space to water are discussed with respect to the convergence level of the simulations and the sensitivity of results to the choice of the intermolecular potential functions. The structural chemistry of the aqueous hydration for NMA is developed from the simulation result based on Proximity Analysis. The sensitivity of the structural and energetic indices of analysis to choice of potential is described. Preliminary results of the calculation of the hydration contribution to the free energy are also presented.
Linear Chain Ferromagnetic Charge Transfer Compounds
Authors: Miller Joel S. , Epstein Arthur J. , Reiff William M. 
Published: November 2013

AbstractCharge transfer complexes possessing a … DADA … structure with both the donor, D, and acceptor, A, being S = 1/2 radicals may exhibit cooperative magnetic phenomena. The complex [Fe(C5Me5)2]+·[TCNQ]−· exhibits metamagnetic behavior. The similarly structured [TCNE]−· and [C4(CN)6]−· complexes are ferromagnets, whereas the [DDQ]−· salt is a paramagnet. The high temperature magnetic susceptibility obeys the Curie‐Weiss expression with θ = + 30, + 30, and + 3 for the [TCNE]−·, [C4(CN)6]−·, and [TCNQ]−· salts, respectively. The ferromagnetic [TCNE]−· salt exhibits zero field Zeeman split 57Fe Mossbauer spectra with an internal field of 425.6 kOe at 4.23 K. After reviewing the current papers discussing ferromagnetism in molecular (organic) compounds, a qualitative model consistent with the necessary bulk spin alignment required for a ferromagnet is presented.
Photochemical, Electrochemical, and Hydrogen‐Driven Enzymatic Reductions in Reversed Micelles
Authors: Laane Colja , Verhaert Raymond 
Published: November 2013

AbstractA few examples of (multi)enzymatic reactions in reversed micellar media are described and discussed. The key enzymes in these examples are 20β‐hydroxy‐steroid dehydrogenase, enoate reductase, and an NAD+‐independent hydrogenase, catalyzing the reactions of interest, viz., the site‐ and stereo‐specific reduction of 20‐ketosteroids to their corresponding 20β‐hydroxy form, the chiral hydrogenation of α,β‐unsaturated carboxylates, and the production of hydrogen, respectively. These cofactor‐requiring enzymes are coupled to various in situ cofactor‐regenerating systems, powered either by light, electricity, or hydrogen. The performance of all these systems is shown.
Single Crystal Electron Spin Resonance Studies of the Photochemical Reaction Center from Rhodobacter sphaeroides Wild Type Strain 2.4.1
Authors: Budil David E. , Taremi Shahriar S. , Gast Peter , Norris James R. , Frank Harry A. 
Published: November 2013

AbstractSingle crystals were obtained from the photochemical reaction center protein of the photosynthetic bacterium Rhodobacter sphaeroides wild type strain 2.4.1. At low temperatures, the crystals display pronounced anisotropy in their triplet state electron spin resonance (ESR) spectra. An analysis of the angle dependence of the resonance field positions revealed two to four magnetically nonequivalent primary donor molecules per unit cell. This is consistent with the symmetry assignment of P deduced from previous X‐ray diffraction studies (Frank, H.A.; Taremi, S.S.; Knox, J.R. J. Mol. Biol., 1987, 198: 139–141). However, the ESR data could not be fit assuming that the unit cell axes coincide with the crystal morphological axes as was the case previously for Rb. sphaeroides R26 (Gast, P.; Norris, J.R. FEBS Lett., 1984, 177: 277–280). In order to explain the present data, it was necessary to assume a rhombic crystal cross‐section with the unit cell axes lying along the diagonals of the rhombus. The unit cell axes b and c were found to make angles of 60 ± 2° and 30 ± 2°, respectively, with one of the faces of the crystal. The orientation of the triplet state dipolar tensor axes relative to the unit cell axes differs slightly from that in Rb. sphaeroides R26 crystals, suggesting that the Rb. sphaeroides 2.4.1 reaction center is rotated by approximately 7° relative to the orientation found in Rb. sphaeroides R26.
Subpicosecond Spectroscopy of Charge Separation in Rhodobacter capsulatus Reaction Centers
Authors: Kirmaier Christine , Holten Dewey 
Published: November 2013

AbstractThe time‐evolution of the near‐infrared absorption changes accompanying the conversion of the excited primary electron donor, P*, to the radical pair state, P+BPhL−, has been examined in detail in Rhodobacter capsulatus reaction centers. In a series of spectra spanning the time interval from about 600 fs to 15 ps, two isosbestic points occurring at 765 run and 798 nm are maintained throughout. The finding of an isosbestic point at 798 nm in this series of spectra, which encompass the time during which P* decays and BPhL− forms, places severe constraints on the possible reduction of the 800‐nm‐absorbing monomeric BChlL in the initial stage of the charge‐separation process. The near‐infrared P* spectrum, which is revealed clearly only when P is excited directly in its long‐wavelength absorption band, contains bleaching only of the 855‐nm band and a broad featureless transient absorption below 810 nm. This spectrum shows that P does not contribute any significant oscillator strength to the 800‐nm ground state absorption band.