bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adsorption Behavior of Vanadium on Macroreticular Chelating Resins Containing Amidoxime Groups
Authors: Egawa Hiroaki , Nonaka Takamasa , Matsumoto Setsuo , Nakayama Morio 
Published: November 2013

AbstractThe macroreticular chelating resins containing amidoxime groups (RNH) showed high affinity for V(V), and were a high capacity of 2.30 mmol/g‐R at pH 5. In particular, it was found that RNH, which were prepared by using 10–16 mol% of DVB in the presence of toluene (80–100 vol%), exhibited the highest adsorption ability for V(V) in a dilute solution. When RNH exhibited the sufficient adsorption ability for V(V), the average pore radius, specific surface area, and pore volume were found to be 140–160 Å, 40–91 m2/g, and 0.26–0.36 ml/g, respectively. Vanadium adsorbed on RNH could be eluted by the treatment with 1 M sodium hydroxide solution.
Cation Transport Through Liquid Membranes Mediated by Photoreactive Crown Ethers. Effects of Alkali Metal Cations on Their Photoreactivities and Transporting Properties
Authors: Anzai Jun‐Ichi , Suzuki Yasuhiro , Ueno Akihiko , Osa Tetsuo 
Published: November 2013

AbstractPhotoreactivities and cation transporting properties of monomeric, dimeric, and polymeric crown ethers which contain cinnamoyl residues were investigated. Photochemical cycloaddition reaction of the cinnamoyl moieties was accelerated by NaCl or KCl for the dimeric and polymeric derivatives but not for the monomeric one. The dimeric and polymeric crown ethers after irradiation in the presence of KCl showed a significant enhancement in the transport rates for Rb+ cation.
On the Stereochemistry of Organocopper Mediated Conversion of Propargylic Esters to Allenes
Authors: Haces Alberto , van Kruchten Eugène M.G.A. , Okamura William H. 
Published: November 2013

AbstractUsing a vitamin D‐related steroidal CD fragment as a stereochemical probe, the effect of various factors on the stereochemical course of the organocopper induced conversion of propargylic esters to allenes has been studied. In all cases, an anti mode of attack by the organocopper species was found to be preferred. The effectiveness of Gilman‐type reagents (R2CuLi) versus that of the Lipshutz‐type higher‐order mixed cuprate systems (R2CuCNLi2) in promoting the reaction was also studied.
Nitrous Deamination of β‐Allenic Amines
Authors: Dulcere Jean‐Pierre , Santelli Maurice 
Published: November 2013

AbstractDeamination of seven allenic amines 1Ad to 1Dd and 14, 15, 16 was performed in protic and aprotic media. Homoallenic participation has been shown to be the major process in deamination of acyclic amines 1Cd and 1Dd. In the latter case, intramolecular retentive substitution was observed.
Optical Rotations of Open‐Chain Allenes Revisited
Authors: Elsevier Cornelis J. , Vermeer Peter , Runge Wolfgang 
Published: November 2013

AbstractA semiempirical theory for the calculation of optical rotations of allenes in the transparent region is presented. The significance of the suggested model is demonstrated by comparison between calculated and observed rotations of 75 open‐chain allenes with various chemically relevant (carbon and hetero‐) substituents. The physical interpretation of the model reveals that the substituent effect on the optical rotation is exerted via the substituent's polarity (field effect through space) and its polarizability.
Carbonium Ion and Hydridocobalt Intermediates in the Acidic Phase Transfer Catalyzed Reactions of Olefins and Dienes with Cobalt Carbonyl
Authors: Galamb Vilmos , Shim Sang Chul , Sibtain Fazle , Alper Howard 
Published: November 2013

AbstractThe intermediates mentioned in the title are probably involved in the hydrogenation of olefins and dienes; bidentate phosphine and arsine cobalt complexes are useful reagents for these reactions.
Phase Transfer Catalyzed Hypochlorite Oxidations Yielding Carbodiimides and Certain Heterocycles (Applications of Phase Transfer Catalysis, Part 27 [1])
Authors: Broda Witold , Dehmlow Eckehard V. 
Published: November 2013

AbstractThe known hypochlorite oxidation of thioureas to the corresponding carbodiimides becomes faster and more convenient by the use of PTC. Aromatic thioamides are transformed into 3,5‐substituted 1,2,4‐thiadiazoles by the same technique, and substituted 2,5‐diamino‐1,3,4‐thiadiazoles as well as 2‐phenylamino‐benzimidazoles and ‐benzoxazoles can be prepared similarly.
Onium Salt Catalyzed Preparation of Isocyanurates (Applications of Phase Transfer Catalysis, Part 28 [1])
Authors: Broda Witold , Dehmlow Eckehard V. , Schulz Hans‐Joachim 
Published: November 2013

AbstractTrimerizations of isocyanates give isocyanurates (N.N.N‐trisubstituted 1,3,5‐triazinetriones) in an exothermic, high yield PTC process. Catalysis by various inorganic salts combined with onium salts or crown ethers is effective, Aliquat 336 being the best catalyst.
Halogenation by Phase Transfer Catalysis
Authors: Preston Reeves W. , Creswell Mark W. , Glass Dale S. , Scheide Gary M. 
Published: November 2013

AbstractSeveral ketones have been halogenated with carbon tetrachloride employing basic phase transfer catalytic conditions. Acetophenone and phenylace‐tone yield halogenated epoxides while several other aromatic compounds underwent α‐oxidation.
Phase Transfer Oxidations with Hypochlorite: Scope and Mechanism
Authors: Lee George A. , Freedman H.H. 
Published: November 2013

AbstractThe use of phase transfer catalysis (PTC), with catalytic amounts of lipophilic quaternary ammonium salts for the transfer of hypochlorite ion from aqueous to organic media, has been found to be an extremely effective and convenient method for the oxidation of many alcohols and amines. An interesting and unexpected specific solvent effect has also been discovered with the use of ethyl acetate which greatly expands the synthetic utility of this method. Both the synthetic scope and mechanistic aspects of these reactions are reported.
Metal Carbonyls in Phase Transfer Catalysis
Authors: Abbayes Herve Des 
Published: November 2013

AbstractThis review is limited to phase transfer systems (solid—liquid and liquid—liquid) involving metal carbonyls. The principles of phase transfer catalysis, related to metal carbonyl properties which play a key role in these two‐phase systems, are first briefly recalled. Then, in the light of these principles, applications to inorganic chemistry (ligand exchange, preparation of metal carbonyl anions), organometallic chemistry (synthesis of π allyl complexes, clusters, orthometalated compounds, acylmetal carbonyls, complexed ylids), and finally to organic chemistry are comprehensively reviewed. In this last part, both stoichiometric and catalytic systems (with respect to the metal carbonyl) are reviewed essentially in the fields of functional reduction and carbonylation.
Phase Transfer Catalysis and Selectivity in Organic Synthesis
Authors: D'Incan E. , Viout P. , Gallo R. 
Published: November 2013

AbstractBesides practical advantages and high versatility, phase transfer catalysis (PTC) gives important improvements in selectivity of organic reactions. This paper presents a discussion of selectivity changes induced under phase transfer conditions. Three main aspects are considered: chemoselectivity, regioselectivity and stereoselectivity.
Methyl Transfer Reaction IX. Linear Free Energy Relations and the Reactivity—Selectivity Principle
Authors: Lewis Edward S. , Douglas Thomas A. , Mclaughlin Mark L. 
Published: November 2013

AbstractMethyl transfers between nucleophiles are representative and uncomplicated examples of group transfer reactions. Data are shown for rates and equilibria sufficient to allow a nearly rigorous application of the Marcus equation. Selectivities with a series of nucleophiles do not vary significantly with reactivity over a wide range of reactivities, except for diffusion controlled reactions. The Marcus equation, for which the necessary data are now available to calculate the rate, fits very well in cases to which it has been applied. It is shown that the (quadratic) Marcus equation is expected to be compatible with experimental linear free energy relations for most reactions; generally only very fast reactions will reveal the curvature, thus the Hammond postulate, the reactivity—selectivity principle, the variable transition state and the Marcus equation are not incompatible with linear free energy relations.
Nitrogen‐15 Kinetic Isotope Effects in the Menschutkin‐Type Reaction of Benzyl Benzenesulfonates with N,N‐Dimethylanilines
Authors: Ando Takashi , Yamataka Hiroshi , Wada Eitaro 
Published: November 2013

AbstractNitrogen‐15 kinetic isotope effects were measured for the Menschutkin‐type reaction of Z‐substituted benzyl X‐substituted benzenesulfonates with Y‐substituted N,N‐dimethylanilines (Eq. 1) in acetone at 35°C. The values of 14k/15k for six combinations of X, Y, and Z fell in the range of 1.002–1.004. These small and almost constant nitrogen isotope effects are in contrast to the large and extensively varying carbon‐14 and small but distinctly changing α‐tritium isotope effects observed for this reaction series. The results are discussed in connection with the reactivity–selectivity relationships.
Identity SN2 Reactions. The Relationship Between Transition State Geometry, Selectivity and the Mechanism of Solvent Action
Authors: Shaik Sason S. 
Published: November 2013

AbstractReactivity trends in the identity SN2 reaction (X−+ CH3X → XCH3+ X−) are discussed using the state correlation diagram model. The model projects that the activation process can be defined as adistortion effortto transfer asingle electronfrom the nucleophile to the leaving group across the alkyl group (CH3). Three domains of reactivity are discussed (a) the geometry of the transition state (looseness and tightness), (b) the intrinsic selectivity of substrates, and (c) the mechanism of solvent action. A link is drawn between these three domains, and a physical insight is provided.
Extensions of the Melander–Westheimer Postulate: Isotope Effects in Reactions with Equilibrium Values Far from Unity
Authors: Agmon Noam 
Published: November 2013

AbstractThe symmetric dependence of experimental primary kinetic isotope effects on the free energy change, obtained for reaction series with zero equilibrium isotope effects, can be inverted to obtain the free energy profile along the reaction coordinate. Trends in the kinetic isotope effects for the general case of non‐vanishing equilibrium effects can be understood by an extension of the same theory. Comparison is made with experiments for reactions of halogen atoms with hydrogen/deuterium molecules.
Electrophilic Additions to Highly Reactive Enol Ethers. The Particular Role of Resonance in Determining the Kinetic Selectivity Evidenced by Extensive Comparison of Olefin Bromination and Hydration
Authors: Ruasse Marie‐FrançOise 
Published: November 2013

AbstractThe kinetic selectivity of aliphatic enol ethers, EtOCR = CHR' (R and R′ = H or Me), towards electrophiles, I2, Br2 and H3O+, is expressed by the kinetic effect of a methyl substituent in the α position with respect to the ethoxy group, kα‐Me/kH. As expected from the reactivity–selectivity principle, RSP, these selectivities are small, 16, 18 and 330, respectively, as compared to those observed for less reactive olefins. However, a more general comparison of the selectivities of various XCH = CH2 olefins (X = Br, Me, Ph, OAc, OEt) reveals anomalies in their behavior with respect to the RSP: (i) enol ether iodination and bromination exhibit the same selectivity although their rates differ by 4 powers of ten, (ii) enol acetate and enol ether show similar selectivities in bromination but the rate of acetate is 3 × 105 times smaller than that of ether and (iii) in hydration the selectivities of these two olefins are similar to that of styrene although rates range over 7 powers of ten from styrene to enol ether. In contrast with what was previously observed for homogeneous series of R‐substituted styrenes (Ph(R)C = CH2), there is no reactivity–selectivity relationship for electrophilic additions to XCH = CH2 olefins. There is a parallelism, however, between the selectivities and the transition‐state position estimated by the Brønsted exponents for hydration and by the Winstein–Grunwald coefficients for solvent effects on halogenations. These results are discussed in terms of different resonance effects on transition states and on reactivities which could arise from differences in the relative contributions of thermodynamic and intrinsic kinetic (Hammond effects) factors on the selectivities.
On the Ring‐Opening of Some 3‐Lithiobithienyls and 3′‐Lithio‐α‐terthienyls
Authors: Gronowitz Salo , Svensson Arne 
Published: November 2013

Abstract3‐Halobithienyls have been prepared through the Pd(PPh3)4‐catalyzed coupling of thiopheneboronic acids with 2,4‐dihalothiophenes. The ring‐opening of the corresponding 3‐lithiobithienyls obtained upon halogen‐metal exchange with phenyllithium has been investigated. Compound 12, 3′‐iodo‐2,2′,2″‐terthienyl, was prepared in one step through the Pd(PPh3)4‐catalyzed coupling of two equivalents of 2‐thiopheneboronic acid with 2,3,5‐triiodothiophene. Treatment of 12 with phenyllithium and methyl iodide gave a mixture of compounds 10 and 11 occurring in Berkheya and Cullumia species.
Regiocontrolled Synthesis of 4‐Halo‐5,6‐Dihydro‐4H‐1,2‐Oxazines; A Novel Route for α‐Fluorovinyl Ketones
Authors: Shatzmiller Shimon , Lidor Ramy , Shalom Eytan 
Published: November 2013

AbstractRegiocontrolled deprotonation (e.g. lithiation) of 3‐methyl‐4‐H‐5,6‐dihydro‐1,2‐oxazine 1 is achieved at −65°C. The lithiated compound reacts cleanly with the halogens Cl2, Br2 and I2 at low temperatures (−65°C) to give the corresponding 4‐halo derivatives. Reaction of the 4‐iodo compound 2a with KF in diethyleneglycol gives the elimination product 4 whereas the bromo compound 2b reacts under substitution to the 4‐fluoro derivatives 5. The fluorooxazine derivatives 8a‐c were converted to the αfluoroenones 11 a‐c via the oxoiminium salts 10a‐c. The U.V. and 1HNMR of the novel series of halides 2a‐c and 5 were studied.
Stereoselectivity in the Wittig‐Horner‐Emmons Synthesis of Vinylphosphonates by the Reaction of Acylphosphonates with Acyclic or Heterocyclic Phosphonoacetates
Authors: Breuer Eli , Moshe Ruth 
Published: November 2013

AbstractA new synthetic approach to vinylphosphonates is presented. The reaction of diethyl benzoylphosphonate (1) with diethyl methoxycarbonyl‐methyl‐phosphonate (2) gives diethyl 2‐methoxycarbonyl‐l‐styrylphosphonate (3) as a mixture of geometrical isomers (Z‐3) and (E‐3) in the ratio of 83:17. In contrast, reaction of 1 with the heterocyclic phosphonate reagent, 2‐methoxycarbonyl‐methyl‐2‐oxo‐4,5‐dimethyl [1,3,2] dioxaphospholane (4) leads to a mixture of the isomers (Z‐3) and (E‐3) in the ratio of 20:80.
A New Indole Synthesis Promoted by Metal Triflates
Authors: Kozikowski Alan P. , Cheng Xue‐Min , Li Chun‐Sing , Scripko James G. 
Published: November 2013

AbstractA new synthesis of 4‐ and 7‐carbon‐substituted indoles is described. The overall sequence involves the addition of a nitrile oxide to 1 carboethoxy‐2‐(or 3‐) allylpyrrole, hydrogenation of the intermediate isoxazoline to β‐hydroxy ketone and cyclization of the ketol using magnesium or zinc triflate to the substituted indole. This new indole‐forming strategy can also accommodate the introduction of oxygen functionality into the indole 6‐position. Possible mechanistic aspects of the reaction are detailed.
Synthetic Studies on Mitomycins: The Synthesis of Mitosene
Authors: Ohnuma Takeshi , Sekine Yasuo , Ban Yoshio 
Published: November 2013

AbstractThe crisscross annulation, developed towards synthesis of diverse nitrogen‐containing heterocycles via a one‐pot reaction, is remarkably effective in the construction of pyrrolo[1,2‐α] indole derivatives (7 and 22) as the possible intermediates for syntheses of mitomycins. These were converted to mitosene derivatives (34 and 40) through the various repeated oxidation processes.
Pteridines, LXXVI [1]. Synthesis and Properties of New Condensed Pyrazolo‐, Thieno‐ and Pyrrolo‐Pteridines
Authors: Baur Ralph H. , Pfleiderer Wolfgang 
Published: November 2013

AbstractThe lumazines 1,3 dimethyl‐7‐methylthio‐6‐propionyl‐ (1) and 6‐chloro‐1,3‐dimethyl‐7‐propionyllumazine (7) provide an easy entry into the pyrazolo [4,5‐g] and ‐[5,4‐g] lumazine system by reaction with hydrazine and methylhydrazine to give 3–6. Thieno [2,3‐g] ‐ (22) and ‐ [3,2‐g] lumazines (21) can be synthesized from 6‐ (19) and 7‐carbomethoxymethylthio‐1,3‐dimethyllumazine (16) by homolytic acylation at the adjacent ring ‐ C ‐ atoms, followed by base‐catalyzed cyclization. A pyrrolo [3,2‐g] lumazine (28) is achieved in an analogous manner from 7‐(N‐carboethoxymethyl‐N‐methyl)amino‐1,3‐dimethyllumazine (25) by radical propionylation and subsequent ring closure. The newly synthesized compounds have been characterized by UV‐ and NMR spectra as well as pKa determinations.
The Structural Elucidation of Oligomeric Blue Dyes Derived from 9‐Alkylcarbazoles
Authors: Katritzky Alan R. , Saczewski Franciszek , Marson Charles M. 
Published: November 2013

AbstractCarbazoles react with a variety of one‐carbon fragments at the 3‐ or 3,6‐positions to give di‐ and trimeric products with CH2: links. These precursors react by losing hydride ion to give blue oligomeric dyes. Carbazoles substituted in the 9‐position by CH2SPh, CH2SOPh, and CH2SO2Ph rearrange to give carbazole oligomers linked at the 3,6‐positions. Products are characterised spectrally, and their mechanism of formation is discussed.
Supercomputers for Quantum Chemistry, Statistical Mechanics and Fluid Dynamics of Biological Systems
Authors: Clementi E. , Chin S. , Logan D. 
Published: November 2013

AbstractAn experimental parallel computer system which is expected to achieve supercomputing performance is described. This system allows the execution of single large jobs on multiple processors. The system hardwares and softwares will be briefly described. The validity of this approach to performing large scale simulations of biological systems is verified by analyzing the performance results of a variety of application programs. Among the applications to be discussed are programs in quantum chemistry, statistical mechanics and fluid dynamics. Specific examples of large biological systems which have been studied shall also be discussed.
A Comparison of the Binding of the Ligand Trimethoprim to Bacterial and Vertebrate Dihydrofolate Reductases
Authors: Roberts Victoria A. , Dauber‐Osguthorpe Pnina , Osguthorpe David J. , Levin Eugene , Hagler Arnold T. 
Published: November 2013

AbstractIn this paper, we report on studies of ligand binding to the enzyme dihydrofolate reductase (DHFR). Energy minimizations of four complexes of DHFR with the inhibitor trimethoprim, an antibiotic, and the cofactor NADPH have been carried out in order to investigate the energetics responsible for the 100,000‐fold increase in binding affinity of trimethoprim to E. coli DHFR compared with chicken liver DHFR. Several factors suggested to be responsible for the enhanced binding in bacterial DHFR's were investigated in terms of intermolecular and intramolecular energetics. The strain energies of trimethoprim in the four complexes were calculated and found to be about 6 kcal mol−1 in all complexes of the two species. In the binary complex of chicken liver DHFR, where the largest variation was observed, 2 kcal mol−1 higher than in the other complexes, it was found that this increase was compensated for by the slightly more favorable intermolecular interaction of the trimethoxyphenyl moiety with the protein.Comparison of the minimized binary and ternary complexes of E. coli allowed us to investigate the cooperativity in the binding of trimethoprim and NADPH in the bacterial enzyme in terms of the underlying intermolecular forces. This cooperativity was found to be due to a direct trimethoprim ‐ NADPH interaction in the E. coli enzyme rather than enhanced protein‐inhibitor interactions induced upon binding of the cofactor. These interactions are not as favorable in the vertebrate enzyme, consistent with the significantly diminished cooperativity observed in this enzyme.
Homogeneous Catalytic Cleavage of Saturated Carbon‐Nitrogen Bonds
Authors: Shvo Y. , Abed M. , Blum Y. , Laine R.M. 
Published: November 2013

AbstractAn evaluation of the catalytic reactivity of [CPD (CO)2RuH]2 (1) and (CPD)(CO)3Ru (2) (where CPD = tetraphenylcyclopentadienone) with amines suggests that these complexes catalyze C‐N bond cleavage by activating C‐H bonds alpha to the nitrogen atom of tertiary, secondary and primary amines at ca. 140° C. When two different amines are used, transalkylation takes place. With secondary and primary amines, ammonia and tertiary amines are formed. A series of amine complexes (CPD)(CO)2Ru.NR3 (R = alkyl/H) was isolated from stoichiometric reactions of 1 or 2 with primary and secondary amines. It was found that tertiary amines do not generate complexes of the above type but rather unexpectedly give secondary amine complexes by cleavage of an alkyl group. The only isolatable tertiary amine complex is the moderately stable (CPD)(CO)2RuNMe3. All amine complexes were characterized by spectral and elemental analyses. Catalytic aspects of C‐N bond cleavage were studied. Complexes (1) and (2) were found to react with primary, secondary and tertiary amines to generate imminium or eneamine species which subsequently undergo hydrolysis with water. This is in contrast to the Ru carbene mechanism previously proposed for cluster catalyzed C‐N bond activation and cleavage. The two reactions are compared with respect to D for H exchange (with D2O), water requirement and production of trace products during catalysis. A primary alcohol was found to substitute alkyl groups of a tertiary amine under the catalytic action of 1. A catalytic reaction cycle is proposed.
Donors for Organic Metals: Molecular Aspects
Authors: Sandman Daniel J. , Ceasar Gerald P. 
Published: November 2013

AbstractPhysicochemical issues are discussed which are relevant to chemists interested in the synthesis of unknown compounds to serve as precursors to organic metals. Molecular topics are emphasized, physical and structural concepts which motivate synthetic activity in chalogen chemistry are presented, and new results in selenium and tellurium systems are summarized. Two model representations for donor molecular structures based on polyenes and polyacenes are presented and known examples are discussed. Quantitative correlations between gas phase vertical ionization potential and solution electrochemical redox potential are examined using donors of interest for organic metals as data. Limitations of such correlations and consequences of these shortcomings are given. Finally, possible future directions for several of these topics are posed.
Electron Donation in Photosystem II
Authors: Thompson Lynmarie K. , Miller Anne‐Frances , De Paula Julio C. , Brudvig Gary W. 
Published: November 2013

AbstractThe pathways of electron donation in Photosystem II (PS II) as studied by electron paramagnetic resonance (EPR) and time‐resolved optical spectroscopy are discussed. The EPR studies have defined two competing pathways of electron donation in PS II, from cytochrome b559 and from the Mn site of the oxygen‐evolving center. The kinetics of re‐reduction of the primary electron donor of PS II (P680). as measured by optical spectroscopy, are re‐evaluated in light of the EPR results. We propose that the 35‐μs kinetic component is due to the reduction of chlorophyll, an alternate electron donor on the cytochrome b559 pathway, rather than to the reduction of P680. The chlorophyll/cytochrome b559 pathway has been proposed to be part of a cyclic electron transfer pathway around PS II; we suggest that photooxidation of chlorophyll is the first step leading to photoinhibition and that cytochrome b559 serves to protect PS II from photoinhibition by rapidly re‐reducing the oxidized chlorophyll (Thompson, L.K.; Brudvig, G.W. Biochemistry, 1988, 27: 6653). These results and proposals are summarized in an overall scheme of electron transfer pathways and rates in PS II.