bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective Formation of Formic Acid, Oxalic Acid, and Carbon Monoxide by Electrochemical Reduction of Carbon Dioxide
Authors: Ikeda Shoichiro , Takagi Takehiko , Ito Kaname
Published: July 2006

Selective formation of formic acid, oxalic acid, and carbon monoxide by electrochemical reduction of carbon dioxide (CO2) is demonstrated using several metallic electrodes in aqueous and nonaqueous electrolytes. The electrode metals catalyze the electrochemical reduction of CO2 and are classified to three groups according to their main products from CO2. In and Pb electrodes as well as Hg electrodes are useful for the selective formation of formic acid by electrochemical reduction of CO2 in aqueous electrolytes. In the case of nonaqueous electrolytes, Pb, Hg, and Tl are useful for oxalic acid, and In, Zn, Au, and Sn electrodes are useful for carbon monoxide. Also, reaction mechanisms of CO2 electrochemical reduction are discussed.
Stereochemical Properties of Copper(II) Complexes of (RS)-3-Aminohexahydroazepine: Crystal and Molecular Structures of [(R)-3-Aminohexahydroazepine][(S)-3-aminohexahydroazepine]copper(II) Diperchlorate, [Cu(R-ahaz)(S-ahaz)](ClO4)2 and Related Complexes
Authors: Saburi Masahiko , Miyamura Kazuo , Morita Masatoshi , Yoshikawa Sadao , Tsuboyama Sei , Sakurai Tosio , Yamazaki Hiroshi , Tsuboyama Kaoru
Published: July 2006

Orange-red copper(II) complexes of (RS)-3-aminohexahydroazepine (=RS-ahaz), Cu(RS-ahaz)2X2·nH2O (X−=ClO4−, BF4−, NO3−, Br−, I−) were prepared, and the molecular structures of complex 1 (X−=ClO4−; n=0) and complex 2 (X−=Br−; n=2) were determined by the single-crystal X-ray diffraction method. The complex 1 has centrosymmetry, and the complex cation in 1 involves a pair of R- and S-ahaz (R- and S-ahaz refer to (R)-and (S)-3-aminohexahydroazepine) and takes a strict four-coordination geometry, so that 1 is formulated as [Cu(R-ahaz)(S-ahaz)](ClO4)2. The complex cation in 2 resembles closely that of 1, and 2 can be represented as [Cu(R-ahaz)(S-ahaz)]Br2·2H2O. The other orange-red complexes of RS-ahaz (X−=BF4−, NO3−, I−) were concluded to take similar strict four-coordinated structures. Blue-violet hetero-anion complexes Cu(RS-ahaz)2X(ClO4) were obtained from complex 1 and LiX (X−=Cl−, Br−). The crystal structure determination of Cu(RS-ahaz)2Br(ClO4) (=complex 3) revealed that 3 involves a pair of enantiomeric five-coordinated cations, [CuBr(R-ahaz)2]+ and [CuBr(S-ahaz)2]+, in the single crystal, whereby the ligand exchange which proceeds during the transformation from 1 to 3 is indicated.
Approximate Formulas for Hosoya’s Topological Index
Authors: Gutman Ivan , Markovic Zoran
Published: July 2006

Approximate formulas for Hosoya’s topological index (Z) are reported for the first time. These formulas reproduce In Z with an error of some 1–2% and require the knowledge of only a few easily obtainable invariants of the molecular graph.
Activation Parameters of Bromoacetate–Thiosulfate Reaction in Ethylene Glycol–Water Mixtures
Authors: Biswas Prasanta Kumar , Maula Anwarul , Das Mihir Nath
Published: July 2006

The activation parameters for the reaction between bromoacetate (\barR) and S2O32− ions in water and aqueous mixtures of ethylene glycol (5–50% by weight) have been evaluated from the rate constants, corresponding to zero ionic strength, at 15, 25, and 35 °C. The standard free energies of transfer (ΔGtr°) of the reacting ions and hence of the transition state (ΔGtr#) from water to the mixed media at 25 °C have been determined from the measured solubilities of AgR, TlCl, and Tl2S2O3 in the different media, using the reported values of ΔGtr° of Ag+ and Cl− ions. Attempts have been made to interpret the kinetic results in the light of solvent properties and free energies of transfer. Although both the reacting ions are destabilized, on adding glycol to the medium, the larger destabilization of the transition state, arising from decreased dielectric constant as well as solvating capacity of the medium, outweighs the combined effects on the reactants leading to reduced reaction rates.
Electrochemical Preparation of Tetrakis(isocyanide)dipalladium(I) Dichloride
Authors: Yamamoto Yasuhiro , Takahashi Katsuo , Yamazaki Hiroshi
Published: July 2006

The electrochemical behavior of PdCl2(RNC)2 (1) has been investigated in acetonitrile at Pt and Hg electrodes. The cyclic voltammogram of 1 showed a reduction wave at ca. −1.2 V, corresponding to a two-electron transfer. Coulometric reduction of 1 at the Pt electrode gave a binuclear complex, Pd2Cl2(RNC)4 (2). A similar reaction at the Hg electrode gave 2 in a relatively low yield. A Pt electrode was superior to a Hg one in the electrochemical synthesis of 2. The polarogram of 1 at a Hg electrode suggested a CE mechanism of the electrode reaction.
Evaluation of the Hydrogen Shuttling Ability of Coal Liquefaction Solvents
Authors: Chiba Koji , Tagaya Hideyuki , Suzuki Tohru , Suzuki Takashi
Published: July 2006

The hydrogen-shuttling ability of coal liquefaction solvents were evaluated using benzophenone and dibenzyl ether as hydrogen acceptors. Hydrogen-transfer reactions from tetralin to acceptors were accelerated by shuttiers and the ranking of the shuttling ability was determined to be as follows: anthracene>fluorene>pyrene≅triphenylmethane>phenanthrene>1-methylnaphthalene
A Light-Scattering Study of Temperature Effect on Micelle Formation of N-Alkanoyl-N-methylglucamines in Aqueous Solution
Authors: Okawauchi Makoto , Hagio Mayumi , Ikawa Yoshitomi , Sugihara Gohsuke , Murata Yoshio , Tanaka Mitsuru
Published: July 2006

The physicochemical properties of N-alkanoyl-N-methylglucamine in aqueous solution have been studied by applying a Debye plot and small-system thermodynamics to an analysis of static light scattering data in the temperature range from 25 to 55 °C. A small minimum was found in a plot of the critical micelle concentration vs. temperature, instead of the monotonously decreasing tendency, as in the case of poly(oxyethylene) alkyl ether. The temperature dependence of the aggregation number of the micelle and the spread of the aggregation number distribution of micelle are both very small. The standard enthalpy change associated with micelle formation varies from positive to negative as the temperature is raised. The micellization of N-alkanoyl-N-methylglucamine surfactants is discussed separately in terms of the respective contributions from the hydrophilic and hydrophobic groups.
Time-Resolved Unimolecular Fragmentations of C3H7O+ Ions
Authors: Arakawa Ryuichi , Yoshikawa Yozaburo
Published: July 2006

The unimolecular dissociations of the C3H7O+ ions produced by the dissociative ionization of t-butyl and s-butyl alcohols have been studied by means of trapped ion mass spectrometry(TIMS). The metastable peak intensities for two competing formations of C3H5+ and CH3O+ have been measured for the ion lifetimes of 0–50 μs. Also, the shifts of the electron-ionization-efficiency(EIE) curves for these ions have been observed between the ion-storage times of 2 and 800 μs. These data have then been fitted by means of QET model calculations. The dissociation paths of C3H7O+ can be interpreted without any assumption of a ratedetermining isomerization process.
Polarized Raman and Infrared Spectra of 2-Amino- and 2-Amino-d2-pyrimidines
Authors: Maehara Masayoshi , Nakama Sekiichiro , Nibu Yoshinori , Shimada Hiroko , Shimada Ryoichi
Published: July 2006

An assignment of the normal vibrations of 2-aminopyrimidine was made through the vibrational analyses of the polarized Raman and infrared spectra and also through the normal coordinate calculation. The assignment was confirmed by the same study made on 2-amino-d2-pyrimidine.
Photochemical C–P Bond Cleavage of Nitrobenzylphosphonate Ions
Authors: Okamoto Yoshiki , Iwamoto Narimasa , Toki Susumu , Takamuku Setsuo
Published: July 2006

Upon UV-irradiation, the C–P bond of p-nitrobenzylphosphonate ions cleaved with a quantum yield of about 0.7 in an aqueous alcohol solution to give 1,2-bis(4-nitrophenyl)ethane, p-nitrotoluene, orthophosphate, and alkyl dihydrogenphosphate. Whereas in an aqueous solution 1,2-bis(4-nitrophenyl)ethane was produced as a main product, in an alcohol solution only p-nitrotoluene was produced. This photolysis may proceed via intramolecular electron transfer from PO32− group to nitro aromatic moiety to form an excited state, which undergoes C–P bond cleavage to give p-nitrobenzyl anion and monomeric metaphosphate anion as intermediates. The C–P bond cleavage of p-nitrobenzylphosphonate ion occurred more readily than those of o- and m-nitrobenzylphosphonate ions.
Effect of an Ionic Surfactant on the Kinetic Properties of an Aqueous Nonelectrolyte Solution Studied by Ultrasonic Methods
Authors: Nishikawa Sadakatsu
Published: July 2006

In order to investigate the effect of ionic surfactant on the dynamic properties of nonelectrolyte aqueous solutions, the ultrasonic absorption, velocity and the conductivity have been measured for aqueous solutions of triethylene glycol monobutyl ether (TGBE) in the presence of sodium dodecyl sulfate (SDS) at 25 °C. In aqueous solution of TGBE, a clear single relaxational ultrasonic absorption is observed in the MHz frequency range. When SDS is added the relaxation process is observed in the more dilute solutions, the relaxation frequency shifts to lower frequency and the amplitude of the excess absorption increases in the TGBE concentration range of less than 1.0 mol dm−3. Further, for TGBE concentration greater than 1.0 mol dm−3, the relaxation frequency is found to be almost independent of SDS concentration and the amplitude of the excess absorption decreases with increasing SDS concentration. The observed relaxation is well accounted for by a kinetic scheme involving the interaction between the nonelectrolyte and water. From the concentration dependence of TGBE, the rate and thermodynamic parameters have been determined as a function of SDS concentration. The obtained data have been interpreted in terms of the structural changes of the solvent water by SDS molecules. As the results, it has been proposed that the hydrophobic parts of SDS have a considerable effect on water structure.
A Novel Method for Determining the Chelation Ability of the Cysteine-Containing Peptides with 3,4-Toluenedithiol. Application to [2Fe–2S]-Ferredoxin Model Systems
Authors: Ueyama Norikazu , Ueno Satoru , Nakamura Akira
Published: July 2006

The chelating ability of a bidentate ligand, Cys–X–Y–Cys (X, Y=amino acid residue), in 2Fe–2S peptide model complexes was examined by a ligand-exchange method using 3,4-toluenedithiol (tdt-H2) or o-xylene-α,α′-dithiol. The addition of tdt-H2 to an N,N-dimethylformamide solution of [Fe2S2(Z–cys–Ala–Ala–cys–OMe)2]2− results in the cleavage pf Fe–S* (S*=inorganic sulfur) bond and in the formation of hydrogen sulfide and mononuclear Fe(III) peptide thiolate complex, [Fe(Z–cys–Ala–Ala–cys–OMe)(tdt)]1−. In the case of [Fe2S2(Z–Ala–cys–OMe)4]2−, [Fe2S2(tdt)2]2− was obtained by the substitution of Z–Ala–Cys–OMe with the chelating reagent. On the other hand, o-xylene-α,α′-dithiol expels both Z–Cys–Ala–Ala–Cys–OMe and Z–Ala–Cys–OMe ligands from these complexes.
Preparation and Metal-Adsorption Properties of the Polymer-Coated Silica Gel Having Iminodiacetate Functional Group
Authors: Suzuki Toshishige M , Itabashi Osamu , Goto Tomio , Yokoyama Toshiro , Kimura Tetsuo
Published: July 2006

A new adsorbent containing an iminodiacetate group has been prepared by the surface modification of a polymer-coated silica gel. The obtained beads (SG–IDA) are porous and have a high specific surface area (≈350 m2 g−1). The adsorption properties of SG-IDA, including the adsorption capacities, equilibrium distribution coefficients (Kd) and adsorption rates, have been examined for divalent metal ions. The selectivity order of SG–IDA is Cu(II)>Pb(II)>Ni(II)>Zn(II)>>Ca(II)>Mg(II). The SG–IDA shows appreciably high Kd values and rapid kinetics toward the adsorption of heavy metal ions. The concentration of 10 ppb level of metal ions [Cu(II), Zn(II), and Cd(II)] has been demonstrated using the SG-IDA column.
Magnetic Properties of Dimeric Copper(II) Trichloroacetate Adducts with 3-Substituted Pyridines
Authors: Muto Yoneichiro , Nakashima Michio , Tokii Tadashi , Kato Michinobu , Suzuki Ikuo
Published: July 2006

Dimeric copper(II) trichloroacetate adducts with 3-substituted pyridines, [Cu(Cl3CCOO)2(3-Xpy)]2 where X=Cl, Br, H, CN, and CH3, have been prepared. Magnetic susceptibility and ESR data show that both the singlet–triplet separation (−2J) and the zero field splitting (D) decrease in the order: 3-Clpy adduct (193 and 0.397 cm−1)≈3-Brpy adduct (191 and 0.399 cm−1)>py adduct (188 and 0.385 cm−1)>3-CNpy adduct (138 and 0.216 cm−1)>3-CH3py adduct (83 and 0.182 cm−1). Electronic spectra indicate that the adducts with X=Cl, Br, and H have a distorted square-pyramidal copper(II) geometry and that those X=CN and CH3 have a distorted trigonalbipyramidal geometry. Form these results, it is concluded that the strength of antiferromagnetic interaction in [Cu(Cl3CCOO)2(3-Xpy)]2 complexes decreases as the distortion of copper(II) geometry increases from squarepyramid toward trigonal-bipyramid.
Control of the Impregnation Profile of Co in an Al2O3 Sphere
Authors: Otsuka Masashi , Fujiyama Takeshi , Tsukamoto Yoshikazu , Tsuiki Hideyasu , Ueno Akifumi
Published: July 2006

A radial distribution of cobalt metal particles in an alumina sphere was controlled by impregnation of the spheres with a solution composed of cobalt nitrate dissolved in ethylene glycol, ethyl silicate, and a small amount of nitric acid. The radial position of cobalt narrow band in the sphere was varied with the impregnation time and the cobalt loading was controlled by the concentration of cobalt nitrate in the impregnation solution. It was also found that porous SiO2 film resulted from the gelling of ethyl silicate covered whole external surface of the sphere.
Liquid Crystalline Compounds Bearing Pyridine Ring: Azoxy Compounds with Alkyl Substituents
Authors: Kamogawa Hiroyoshi , Kasai Tsuneharu , Andoh Toshio , Nakamura Tomoyuki
Published: July 2006

Azoxy compounds bearing a 2,5-disubstituted pyridine ring as a principal constituent and at least one alkyl group at a molecular end were synthesized and their mesomorphic (nematic) ranges were examined. As for azoxy compounds containing an alkyl and an alkoxy group at both ends, respectively, mesomorphic ranges appeared with lower alkyl groups than those for azo compounds, their precursors. The ranges were also lower than those with both alkoxy ends. As regards an azoxy compound containing alkyl groups at both ends, no mesomorphic phenomenon appeared within the scope of this study.
Synthesis of Opically Active 3-Morpholinecarboxylic Acid and Tetrahydro-2H-1,4-thiazine-3-carboxylic Acid
Authors: Kogami Yuji , Okawa Kenji
Published: July 2006

A convenient synthesis of optically active 3-morpholinecarboxylic acid and its thio analogue, tetrahydro-2H-1,4-thiazine-3-carboxylic acid, has been developed. These intermediates were obtained by reaction of benzyl (S)-N-benzyloxycarbonyl-2-aziridinecarboxylate and its enantiomer with 2-chloroethanol or 2-chloroethanethiol, respectively.
In Situ Trapping of NO: Application of S-Nitroso Derivatives for Metal Nitrosyls Synthesis
Authors: Pandey Daya Shankar , Saini S K , Agarwala Umesh Chandra
Published: July 2006

Several known nitrosyl complexes of Ru, Rh, and Co have been synthesized using S-nitroso organic compound (S-nitrosocysteine). Physicochemical methods such as IR, magnetic measurements, conductance measurements, and elemental analysis were used for characterization of the reaction products.
Photochemical Behavior of Aluminum–Ethyl Complex with Tetraaza Macrocyclic Ligand, Al(C22H22N4(C2H5)
Authors: Oshio Hiroki , Tero-Kubota Shozo , Ito Tasuku
Published: July 2006

Homolytic photocleavage of an aluminum carbon bond in ethyl(1,8-dehydro-5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinato)aluminum was confirmed by using EPR technique. The photochemistry of this aluminum carbon bond was also studied by NMR and emission spectroscopic experiments.
Polymers as Reagents and Catalysts. XI. Stereospecific Iodofluorination of Alkenes in the Presence of Polymer Supported Hydrogen Fluoride
Authors: Gregorcic Ana , Zupan Marko
Published: July 2006

N-Iodosuccinimide reacted with phenyl substituted alkenes in the presence of insoluble polymer supported hydrogen fluoride, which was prepared by reaction of hydrogen fluoride with crosslinked poly(styrene-co-4-vinylpyridine) containing 40–45 mol% of 4-vinylpyridine, thus forming vicinal iodofluorides in high yields. Reactions proceeded with Markovnikov type regioselectivity, and in the case of (Z)- and (E)-stilbene, (Z)- and (E)-1-phenylpropene and indene anti stereospecificity was also observed. Iodofluorinations of phenyl substituted acetylenes occurred regio and stereospecifically, forming (Z)-1-fluoro-2-iodo-1-phenylalkenes, with lower yields than those observed in the case of alkenes.
The Liquid-Junction Potential at the Contact of Two Immiscible Electrolyte Solutions in the Absence of Supporting Electrolytes Reference Electrodes Reversible to Alkylammonium Ions and Tetraphenylborate Ion in Nitrobenzene
Authors: Kakiuchi Takashi , Senda Mitsugi
Published: July 2006

The liquid-junction potentials between two immiscible electrolyte solutions have been studied for the interface: R1+TPB−(nitrobenzene)/R1+X−(water) and R1+TPB− (nitrobenzene)/Li+TPB−(water), where R1+ is a tetraalkylammonium ion, TPB− is tetraphenylborate ion, and X− is a halide ion. These interfaces may be seen as a simplest form of either a liquid ion-exchange membrane ion-selective electrode sensing the activity of the ion in the aqueous phase or a reference electrode of a liquid membrane type reversible to the ion in the nonaqueous phase. The effects of the cationic species(R1+), the anionic species(X−) and the concentration of the electrolytes on the electrical potential difference developed at the interface have been studied. These properties of the interfaces were compared with a simplified theoretical treatment of the liquid-junction potential between the two immiscible solutions. The theory can predict the basic features of the system by knowing the standard ion-transfer potentials and the diffusion coefficients of the relevant ions as well as its concentration. In the concentration range where a significant deviation from the Nernstian response of the liquid-junction potential occurred, the diffusion potential has been demonstrated to contribute significantly to the liquid-junction potential.
Electrical Conductivities of Tetrakis(alkylthio)tetrathiafulvalene (TTCn–TTF) and Tetrakis(alkyltelluro)tetrathiafulvalene (TTeCn–TTF)
Authors: Imaeda Kenichi , Enoki Toshiaki , Shi Zurong , Wu Peiji , Okada Naoko , Yamochi Hideki , Saito Gunzi , Inokuchi Hiroo
Published: July 2006

Electrical conductivities have been measured for TTCn–TTF and TTeCn–TTF. In the case of TTCn–TTF, the compounds with short alkyl chains (n=1–3) show the high resistivities above 1010 Ω cm, while the resistivities of the compounds with long alkyl chains (n≥4) decrease to 105–107 Ω cm. The relatively low resistivities of the compounds with long alkyl chains are attributed to the considerable reduction in intermolecular distance between adjacent TTF skeletons caused by intermolecular interactions through alkyl chain groups taking into account the results of their crystal structures, thermal properties and densities. As for TTeCn–TTF compounds, the carbon number dependence of resistivity is almost similar to that of TTCn–TTF in the range of large n (n≥8). Exceptionally, TTeC1–TTF exhibits noticeably low resistivity of 6.9×104 Ω cm. X-Ray diffraction study confirms that the high conductivity of TTeC1–TTF is caused by the formation of zigzag Te chains due to the presence of strong intermolecular Te–Te atomic contacts.
Photo-Excitable Membranes. Photoinduced Potential Changes across Poly(vinyl chloride)/Spirobenzopyran Membranes Doped with Valinomycin and Nonactin
Authors: Anzai Jun-ichi , Hasebe Yasushi , Ueno Akihiko , Osa Tetsuo
Published: July 2006

Poly(vinyl chloride)/spirobenzopyran membranes doped with valinomycin or nonactin were prepared to study the photoresponse of the membrane potential in the presence of K+ or NH4+ ion. Ultraviolet (UV) light irradiation induced more than 100 mV of potential change across the membrane doped with valinomycin in the presence of 10−8–10−6 M KCl, whereas the potential change was extremely suppressed in the presence of higher KCl concentration (>10−3 M). The photoresponse of the membrane potential depended upon the direction from which the membrane was irradiated. The nonactin-doped membranes showed a similar tendency in photoresponse in the presence of NH4Cl to that observed for the valinomycin-doped membrane in the presence of KCl. The results were explained in terms of surface potential changes at the irradiated surface of the membrane, associated with the photochemical reaction of spirobenzopyran and the specific adsorption of cations to the surface of the membrane.
Fluorescence Reactions of “Crowned” Benzothiazolylphenols with Alkali and Alkaline Earth Metal Ions and Their Analytical Applications
Authors: Nakashima Kenichiro , Nagaoka Yukari , Nakatsuji Shin’ichi , Kaneda Takahiro , Tanigawa Isamu , Hirose Keiji , Misumi Soichi , Akiyama Shuzo
Published: July 2006

The fluorescence behavior by a complexation of “crowned” benzothiazolylphenols (CBTP and CBBTP) with alkali and alkaline earth metal ions in the presence of triethylamine was examined in various organic solvents. The fluorescence spectra of these CBTP– and CBBTP–metal ion complexes were measured in order to compare mutually both their excitation and emission maxima together with the relative fluorescence intensities (RFI). Both the Li–CBTP and Li–CBBTP complexes showed considerably higher RFI than the other metal complexes. The stability of the fluorescence intensity and various conditions for the determination of Li+ or Ca2+ were fully examined. On the basis of these experiments, fluorometric methods were developed for a sensitive determination of trace amounts of Li or Ca by using the crown compounds (CBTP and/or CBBTP). Moreover, a thin-layer chromatographic method for the separation of Li from other metal ions was examined in order to selectively determine Li by using CBBTP.
Estimation of Salt and Temperature Effects on Ion Product of Water in Aqueous Solution
Authors: Maeda Masunobu , Hisada Osamu , Kinjo Yoshiaki , Ito Kaname
Published: July 2006

The ion product of water at 298.15 K was evaluated according to the Pitzer ionic interaction theory in LiCl, NaCl, KCl, KNO3, LiClO4, and NaClO4 media of different concentrations (0.1–5 mol kg−1) and in artificial seawaters at different salinities (20–44%). The Pitzer approach was also applied to the estimation of the ion products of water in NaCl media at temperatures (288–373 K) different from 298.15 K. The theoretically evaluated values showed reasonable agreement with experimental ones.
Mössbauer Study of Iron Oxide Surface Layers Formed on Fine Iron Particles
Authors: Maeda Yonezo , Aramaki Masaaki , Takashima Yoshimasa , Oogai Michiharu , Goto Takeshi
Published: July 2006

Mössbauer studies of iron oxides formed on the surface of fine iron particles (acicular type about 15 nm in diameter and 100 nm long) and of an oxidation process in air have been done in the temperature range from 4.2 to 298 K. The Mössbauer spectra indicate that the main component of the oxide layers 2.1–5.6 nm thick, except for a few oxide layers from the iron surface, is composed of fine particles of γ-Fe2O3, and that fine iron oxide particles are produced freshly during the oxidation process at 110 °C in air with the growth of iron oxide particles. It is concluded that an oxide layer 2.1 nm thick is formed on the iron surface if a fresh iron surface is exposed to air at room temperature.
Synthesis of Hexahydroindenones through a Diels–Alder Cycloaddition and Nazarov Cyclization Sequence of Triene Alcohols
Authors: Wada Eiji , Fujiwara Isamu , Kanemasa Shuji , Tsuge Otohiko
Published: July 2006

The Diels–Alder cycloaddition of 4-methylene-1,5-hexadien-3-ols with olefinic dienophiles such as dimethyl maleate, fumarate, and N-methylmaleimide produces 1-(1-cyclohexenyl)-2-propen-1-ols. These diene alcohols are oxidized with activated manganese(IV) oxide to give dienones, which are then treated with acid catalysts to undergo ready electrocyclization leading to hexahydroindenones with functional groups. Stereoselectivity at the electrocyclization step is found to depend upon the stereostructures of cyclohexene skeleton of the dienones as well as the reaction conditions.
Photochromic Behavior of Pyridoxal–α-Amino Acid–Zn(II) Complexes in Methanol
Authors: Ohga Kazuya , Kurauchi Yoshiaki
Published: July 2006

Zn(II) complexes of pyridoxal–α-amino acid Schiff bases showed photochromic behavior in methanol. Spectral studies revealed that intramolecular nucleophilic attack of 5′-hydroxyl group on imine linkage forms cyclic α-amino ether intermediates which thermally return to the original complexes. The photochromism was characteristic of complexes having a 1:1 ligand–metal ratio. Analogous photochromism was also observed with the Cd(II) complex of N-pyridoxylidenevaline having a fully occupied d-orbital like the Zn(II) complexes, whereas no photochromism was observed with other transition metal complexes such as Ni(II), Cu(II), Mn(II), and Co(II) complexes.
Michael Addition and Alkylation of 2-Azaallyl Anions Derived from N-(1-Cyanoalkyl)imines, and Stereoselective Cyclization of Imine Esters or Ketones Leading to 1-Pyrrolines
Authors: Tsuge Otohiko , Ueno Kazunori , Kanemasa Shuji , Yorozu Kiyotaka
Published: July 2006

The 2-azaallyl anions derived from N-(1-cyanoalkyl)imines and DBU undergo Michael addition or alkylation to produce N-(1-alkylated 1-cyanoalkyl)imines. The Michael addition of some aryl-substituted imines are highly diastereoselective. The alkylated Michael adducts are converted into lactams through a hydrolysis and recyclization sequence. Base-induced cyclization furnishes 1-pyrrolines through a cyclization and HCN elimination sequence. In the latter reaction, 4,5-cis-1-pyrrolines are selectively produced when the adducts are treated with LDA in the presence of lithium iodide.
Metallic Base-Induced Cycloadditions of N-(1-Cyanoalkyl)imines via N-Metalated Azomethine Ylides: Enhanced Reactivity and High Regio- and Stereoselectivity
Authors: Tsuge Otohiko , Kanemasa Shuji , Yorozu Kiyotaka , Ueno Kazunori
Published: July 2006

Lithiation of N-(1-cyanoalkyl)imines with LDA generates new N-lithiated azomethine ylide 1,3-dipoles which show enhanced reactivity toward dipolarophiles. They undergo exclusively regio- and stereoselective 3+2 cycloaddition reaction with α,β-unsaturated esters to give 1-pyrrolines after the elimination of LiCN. Metallic bases other than LDA can be also effective. Such high regio- and stereoselectivity is explained by the involvement of N-metalated azomethine ylides.
An Efficient Regeneration of Singlet Oxygen from 2,5-Diphenylfuran Endoperoxide Produced by a Dye-Sensitized Oxygenation
Authors: Usui Yoshiharu , Koike Hiroshi , Kurimura Yoshimi
Published: July 2006

The maximum quantum yield of 4.5 was evaluated from the kinetic analysis for the Methylene Blue-sensitized oxygenation of 2,5-diphenylfuran, and the contribution of a chain process to produce the furan endoperoxide was suggested. After the photoreaction, the thermolysis of the endoperoxide occurred to regenerate 2,5-diphenylfuran and singlet oxygen and to produce cis-1,2-dibenzoylethylene simultaneously. The activation energy of singlet oxygen recovery was estimated to be 18.5 kcal mol−1. The reversible conversion of singlet oxygen took place efficiently with thiazine and xanthene dyes. A concerted dissociation of singlet oxygen from the endoperoxide was supposed from the negative value of activation enthropy (−9.8 e.u.) for the reaction.
Hydrogenation of Aromatic Nitro Compounds with A Pt/SiO2–AlPO4 Catalyst
Authors: Aramendía Lopidana M Angeles , Borau Bolos Victoriano , Jiménez Sanchi̊dri̊an Cesar , Marinas Rubio J María , Rodero Luque Francisco
Published: July 2006

In this work we have carried out the reduction of aromatic nitro compounds bearing different substituents with gaseous hydrogen, over a Pt catalyst (3% by weight) supported on a SiO2–AlPO4 system. The catalyst was obtained by impregnation, the impregnating metal salt being reduced with α-phellandrene. The kinetic data found allow us to describe the reduction of nitrobenzene as a Langmuir–Hinslwood kinetic. The sequence of reaction rates for the different nitro compounds assayed conforms to the Hammett–Taft equation, which allows relating the electron density of the aromatic ring to the reduction rate of the nitro group. Finally, we propose mechanism for the process, characterized by the absence of intermediates with net charges.
Irreversible Nature of the Stacked β-Pleated Sheets of a Model Polypeptide
Authors: Maeda Hiroshi
Published: July 2006

A mode of association of β-sheets, most probably the stacking of the pleated sheets, has been studied by circular dichroism and light scattering on the 5×10−2 mol dm−3 NaCl solutions of poly(S-carboxymethyl-l-cysteine). It was found that the association is highly irreversible with respect to concentration change at constant pH. Relevance of the study of synthetic polypeptides is discussed in relation to the association mode found in proteins.
Asymmetric Synthesis Using Chiral Piperazine. I. Asymmetric Synthesis of 2-Substituted Alcohol and Carboxylic Acid by Diastereoselective Alkylation of Chiral Diamides Derived from Piperazines
Authors: Soai Kenso , Hayashi Hiroshi , Shinozaki Akihiro , Umebayashi Hideaki , Yamada Yasuyuki
Published: July 2006

The diastereoselective alkylation of chiral diamides derived from chiral piperazines afforded optically active alcohols and acids in moderate enantiomeric excesses (up to 68% e.e.).
An Anion Radical Salt of a Quinone Fused with 1,3-Dithiole Units. Crystal and Molecular Structure of a Tetraethylammonium Salt of 2,6-Dithioxobenzo[1,2-d:4,5-d′]bis[1,3]dithiole-4,8-dione
Authors: Suzuki Takanori , Kabuto Chizuko , Yamashita Yoshiro , Miyashi Tsutomu
Published: July 2006

Crystal structure of the title salt was determined by the X-ray analysis. Segregated columnar stacks of anion radicals are formed along the c axis, in which quinone molecules are not spaced equally but forming dyads with short contacts between sulfur atoms.
Stereoselective Synthesis of Conjugated Dienones via the Palladium-Catalyzed Cross-Coupling Reaction of 1-Alkenylboronates with 3-Halo-2-alken-1-ones
Authors: Satoh Naoyuki , Ishiyama Tatsuo , Miyaura Norio , Suzuki Akira
Published: July 2006

The synthesis of conjugated dienones by means of palladium-catalyzed cross-coupling reaction between (E)-1-alkenyl-1,3,2-benzodioxaboroles or diisopropyl (Z)-1-hexenylboronate with 3-halo-2-alken-1-ones is described.
Synthesis and Chromotropic Behavior of Nickel(II) Complexes with 1,4-Diazacycloheptane-N,N′-dicarboxylates in Solution
Authors: Fukuda Yutaka , Yamagata Keiko , Kaden Thomas A
Published: July 2006

A new series of nickel(II) complexes containing 1,4-diazacycloheptane-N,N′-dicarboxylates (dachdx, where x=a means the acetate derivative, x=m, e, and p are the α-methyl, α-ethyl, and α-propyl substituents of the carboxyl side chain, respectively) were prepared as solids, Ni(dachdx)Ln (L=H2O or pyridine, n=0, 1, or 2). These complexes can be classified according to their geometry into three types: (1) Octahedral [Ni(dachda)(H2O)2], (2) square planar [Ni(dachdx)](x=m, p, or e) and (3) penta-coordinate [Ni(dachdm)(py)]. In the solid state the strength of the bonds between the metal ion and the carboxylate groups increases in the order: Octahedral<penta-coordinate<square planar. In solution, some of these compounds show chromotropic behavior, e.g. solvatochromism, thermochromism, and inert salt or active salt effects. The stability constants of the Ni2+ complexes were determined by pH-titrations and spectrophotometry. The following equilibria were found:

[Ni(aq)]2++dachdx2−\ightleftharpoons[Ni(dachdx)];

[Ni(dachdx)]+X−\ightleftharpoons[Ni(dachdx)X]−;

where X−=NCS−, Cl−, or Br−. It is shown that the substituent of the carboxylate side chain plays an important steric role, thus determining the value of the stability constant of [Ni(dachdx)].
The Synthesis of Lycoxanthol and Its C-15 Epimer
Authors: Matsumoto Takashi , Imai Sachihiko , Yoshinari Takashi
Published: July 2006

In order to elucidate the absolute configuration of C-15 in natural lycoxanthol, (15R)-11,16-dihydroxy-12-methoxymethoxy-8,11,13-abietatrien-7-one and its (15S)-epimer were transformed into (15R)-12,16-epoxy-6,11,14-trihydroxy-5,8,11,13-abietatetraen-7-one (1a) and its (15S)-epimer, respectively. The synthetic 1a was identical with natural lycoxanthol. Thus, the stereochemistry of C-15 in the natural compound was conclusively assigned as R-configuration.
Practical Method for the Synthesis and Optical Resolution of Axially Dissymmetric 6,6′-Dimethylbiphenyl-2,2′-dicarboxylic Acid
Authors: Kanoh Shigeyoshi , Muramoto Hiroki , Kobayashi Natsumi , Motoi Masatoshi , Suda Hiroshi
Published: July 2006

Racemic 6,6′-dimethylbiphenyl-2,2′-dicarboxylic acid (1) could be conveniently synthesized and efficiently resolved by the recrystallization of the brucine salts in satisfactory yields. Each enantiomer, thus obtained, was confirmed to be optically pure from a high-performance liquid chromatographic (HPLC) analysis on an optically active column.
Synthesis of (−)-8a-epi-Swainsonine, (1S,2R,8R,8aS)-Octahydro-1,2,8-indolizinetriol
Authors: Tadano Kin-ichi , Hotta Yukinori , Morita Masahiro , Suami Tetsuo , Winchester Bryan , Bello Isabello Centi di
Published: July 2006

(−)-8a-epi-Swainsonine (4), one of the stereocongeners of physiologically interesting indolizidine alkaloid (−)-swainsonine (1), has been synthesized starting from known methyl 3-azido-4,6-O-benzylidene-3-deoxy-α-d-altropyranoside. The α-d-mannosidase inhibitory activity of 4 was compared with natural 1.
400 MHz Two-Dimensional NMR Studies of Cyclodextrin Derivatives for 1H and 13C Chemical Shift Determination
Authors: Tabushi Iwao , Nabeshima Tatsuya , Yamamura Kazuo , Fujita Haruo
Published: July 2006

Two-dimensional (2D) NMR spectroscopies, proton (400 MHZ)– proton (400 MHz) and carbon (100 MHz)– proton (400 MHz) chemical shift correlation spectroscopy, were developed as a reliable technique for the strict assignment of crowded and complicated NMR absorptions of substituted cyclodextrin derivatives, pentakis[2,6-O-(t-butyldimethylsilyl)]-A,B-bis-[2-O-(t-butyldimethylsilyl)-6-deoxy-6-(methylthio)]-β-cyclodextrin (2) and A,B-bis[6-deoxy-6-(methylthio)]-β-cyclodextrin (1).
The Study of Planarized and Planar Cyclohexane Rings on the Basis of Molecular Mechanics
Authors: Dodziuk Helena
Published: July 2006

Recent rapid development of synthetic and theoretical methods has yielded molecules with unusual stereochemistry on carbon atom. One of the most interesting examples of such earlier unsought of arrangements is provided by planar cyclohexane rings. Few molecules of this kind have been synthesized and two others have been postulated on the basis of molecular mechanics calculations. In the present article a critical review of existing experimental and theoretical results is supplemented with a molecular mechanics study of a series of cyclohexanes fused with up to six 3-, 4-, and 5-membered rings causing the flattening of C6 ring. The existing experimental data and the results of the calculations seem to indicate that the flattening is more pronounced when smaller and/or larger number of rings are fused. The applicability and limitations of molecular mechanics with the MM2 parameterization to the study of the flattening of cyclohexane ring have been critically analyzed. The synthetic efforts in this field seem to indicate that some results calculated for hypothetical molecules will be checked in the near future. Similarly to hypothetical [6]asterane and hexaprismane, the planarity of [6.3]coronane has been postulated.
An Ab Initio Molecular Orbital Study of Lithiopyridines
Authors: Kikuchi Osamu , Togo Hideo , Furukawa Naomichi
Published: July 2006

Ab initio molecular orbital calculations were performed for 2-, 3-, and 4-lithiopyridine monomers, and the molecular and electronic structures of lithiopyridines and their reactivity with electrophiles were examined.
(3E)-Laureatin and (3E)-Isolaureatin, Halogenated C-15 Non-Terpenoid Compounds from the Red Alga Laurencia nipponica Yamada
Authors: Suzuki Minoru , Kurosawa Etsuro
Published: July 2006

(3E)-Laureatin and (3E)-isolaureatin have been isolated as major metabolites from the red alga Laurencia nipponica Yamada, and their structures were confirmed on the basis of spectral and chemical evidence.
Majusculone, a Novel Norchamigrane-Type Metabolite from the Red Alga Laurencia majuscula Harvey
Authors: Suzuki Minoru , Kurosawa Etsuro , Kurata Kazuya
Published: July 2006

The structure of majusculone, a novel norchamigrane-type terpene isolated from the red alga Laurencia majuscula Harvey, was deduced from the spectral data.
The Simple Synthesis of Cordiachrome B, a Terpenoid Benzoquinone from Cordia Millenii
Authors: Watabe Takashi , Hosoda Yasushi , Okada Keiji , Oda Masaji
Published: July 2006

Cordiachrome B, a tricyclic terpenoid p-benzoquinone isolated from Cordia millenii, was synthesized in three steps from 1,2-dihydro-3,6-dimethoxybenzocyclobutene employing a Diels–Alder reaction in a key step.
Neutralization Dialysis for Deionization
Authors: Igawa Manabu , Echizenya Kiyoyuki , Hayashita Takashi , Seno Manabu
Published: July 2006

In neutralization dialysis, cations are exchanged with protons across a cation-exchange membrane, while anions are exchanged with hydroxide ions across an anion-exchange membrane, and the effective deionization and the neutralization occur simultaneously on the base of Donnan equilibrium. The ion-exchange membranes are much more permeable to the electrolytes than the nonelectrolytes and their mutual separation is possible by this method.
Preparations and Structures of 3-Chloro-ONN-4′-methylazoxybenzene and 4-Methoxy-ONN-4′-methylazoxybenzene
Authors: Yamamoto Jiro , Tsuboi Takashi , Sumi Yasunori , Oda Noriyasu , Fukuyama Keiichi
Published: July 2006

A treatment of 3-chloro-NNO-4′-methylazoxybenzene (1β) with CrO3 in acetic acid gave 3-chloro-ONN-4′-methylazoxybenzene (1α) in good yield, whereas 4-methoxy-ONN-4′-methylazoxybenzene (2α) isomerized partially to 4-methoxy-NNO-4′-methylazoxybenzene (2β) under the same conditions. The structures of 1α and 2α have been determined by X-ray analysis.
Excited-State Reactions of Coumarins in Aqueous Solutions. IV. The Fluorescence Quenching of 7-Ethoxycoumarins by Inorganic Ions in Micellar Solutions of Sodium Dodecyl Sulfate
Authors: Moriya Tetsuo
Published: July 2006

The effect of added salts (NaCl, NaBr, CsCl) on the fluorescence behavior of 7-ethoxycoumarin (7EC) and 7-ethoxy-4-methylcoumarin (7E4MC) has been studied in aqueous micellar solutions of sodium dodecyl sulfate (SDS). Data on the fluorescence quenching as a function of the salt concentration are analyzed in terms of a proposed two-reactive-state (aqueous and micellar phases) model. The results are in good accord with the model and permit the evaluation of the quenching-rate constants attributable to Br− and Cs+ respectively in the two phases. Quenching mechanisms influencing the fluorescence yield are discussed on the basis of the electrostatic force among micelles and quenchers, the electron-transfer reaction from anion to fluorescer, and the hydration degree of the quencher ions.
A Simple Model for the Kinetics of Beta Meander Formation of Homopolypeptide Chains
Authors: Maeda Hiroshi
Published: July 2006

A simple kinetic theory is presented concerning the irreversible formation of intramolecularly folded β-structure of homopolypeptide chains through a bend formation. To reduce the number of parameters, the number of strands is limited to be less than five and the growth rate of the third and fourth strands is assumed to be so fast that the final strand length is attained immediately after the bend formation. Numerical calculations were carried out on relevant ranges of rate costants for relatively short chains. It was shown that experimentally found diverse kinetic patterns were all explicable based on the present model.
Potentiometric Study of Equilibria in H+–MoO42−–RAsO3H−(R=OH, C6H5, CH3) Systems
Authors: Yagasaki Atsushi , Takahama Hironobu , Sasaki Yukiyoshi
Published: July 2006

The equilibria pH++qMoO42−+rRAsO3H−\ightleftharpoons(H+)p(MoO42−)q(RAsO3H−)r have been studied in 1 M Na(Cl) (1 M=1 mol dm−3) at 25 °C by potentiometry. Heteropoly species which have q⁄r ratios higher than 5 have been found in the R=CH3 and R=C6H5 systems besides the well known species of q⁄r=3. The species, denoted by (p,q,r) according to the equation above, (10, 7, 1), (11, 7, 1), and (11, 6, 1) are proposed as those high ratio species. The formation constant of each species has been determined. The result showed an apparent correlation with pKa’s of arsenic acid and its organic derivatives. Solution structures of the heteropoly species are also discussed.
The Vapor Saturation Method for Preparing Aqueous Solutions of Solid Aromatic Hydrocarbons
Authors: Akiyoshi Mayumi , Deguchi Toshio , Sanemasa Isao
Published: July 2006

A new method to prepare aqueous solutions saturated with solid aromatic hydrocarbons by making use of solute vapor is presented. Air is bubbled through an organic solvent in which an excess quantity of a solid hydrocarbon to be studied has been added, and the resulting vapor is introduced into water and circulated in a closed system. An aqueous solution saturated with a solid solute can thus be prepared in a short time without any need to remove solute microcrystals. Of benzene, cyclohexane, and 1-octanol used as organic solvents, 1-octanol is most promising for this purpose. Solubilities in water at 25.0 °C of nine aromatic hydrocarbons have been measured: Naphthalene, biphenyl, anthracene, phenanthrene, fluoranthene, (o-, m-, p-)terphenyl, and triphenylene. This method can be used for these solutes except phenanthrene.
Preparation and Reaction of Optically Active Organotransition Metal Complexes. II. Preparation and Photoracemization of Optically Active (1-Cyanoethyl)cobaloxime Complexes Coordinated with Various Axial Ligands
Authors: Baba Shoe , Ohgo Yoshiaki , Takeuchi Seiji
Published: July 2006

Optically active (1-cyanoethyl)cobaloxime complexes coordinated with various pyridines, phosphines and amines etc. as axial ligands were prepared and their photoracemization rates were measured in a solution state. It was found that the steric factor, rather than the electronic, of the axial ligand controlled, predominantly, the rate of Co–C bond homolysis in these alkylcobaloximes.
The Effect of Intramolecular Hydrogen Bonding on the Rotational Barriers about the C–N Bonds of o-Hydroxyarenecarboxamides
Authors: Suezawa Hiroko , Tsuchiya Kin-ya , Tahara Eiji , Hirota Minoru
Published: July 2006

Rotational barriers about the C–N bonds of several o-hydroxyarenecarboxamides were determined in four solvents (namely, chloroform, pyridine, methanol, and dimethyl sulfoxide) by DNMR spectroscopy and compared with those of arenecarboxamides void of ortho-hydroxyl group. The height of the rotational barrier is correlated with the strength of the intramolecular O–H···O=C hydrogen bond. The unusual solvent effect on the rotational barriers of these hydroxy–amides are ascribed to the cleavage of the intramolecularly hydrogen bonded chelate ring which occurs in both hydrogen-donating and -accepting solvents.
NAD(P)+–NAD(P)H Models. 64. The Quantitative Elucidation of the Mechanistic Aspects in the Silica Gel-Catalyzed Reduction of α,β-Unsaturated Carbonyl Compounds by a Model of NAD(P)H
Authors: Yasui Shinro , Fujii Masayuki , Ohno Atsuyoshi
Published: July 2006

Eight α,β-unsaturated carbonyl compounds, 1-(2′- or 4′-substituted phenyl)-3-phenyl-2-propen-1-ones (2′- or 4′-substituted chalcones), were subjected to the reduction by an NAD(P)H model in the presence of silica gel in benzene. All of these afforded quantitatively the corresponding saturated carbonyl compounds, whereas no 1,2-reduction took place. For 2′-methoxy, 4′-methyl, 4′-bromo, and 4′-nitro derivatives as well as the unsubstituted carbonyl compound, the apparent reactivity of the substrate increases with the increase in electronwithdrawing ability of the substituent, whereas the degree of the adsorption onto the surface of silica gel decreases. It is also apparent that the 4′-hydroxy derivative exerts lower reactivity than the 2′-hydroxy derivative in spite of much more efficient adsorption of the former. In order to uniformly interpret the apparent results, the data obtained were quantitatively analyzed in terms of kinetics as well as equilibrium constants for the adsorption of the substrates onto the surface of silica gel. It has been revealed that the silanol group on the surface of silica gel acts as a general-acid catalyst in the reduction.
Chemical Studies on Products Obtained from Verdohemochrome IXα Dimethyl Ester by Treatment with Ammonia under Air
Authors: Saito Setsuo , Tamura Norihiro
Published: July 2006

Verdohemochrome IXα dimethyl ester [bis(pyridine)iron(II) 5-oxaprotoporphyrin IX dimethyl ester] gave 5-azaprotohemin IX dimethyl ester (2) and six tripyrrin derivatives upon treatment with ammonia under air, followed by methylation. The reaction of 2 with coned HCl in acetic acid in the presence of ferrous sulfate, followed by methylation gave demetallated product, 5-azaprotoporphyrin IX dimethyl ester (8), accompanied by products obtained by the hydration and reduction of both or one of the vinyl groups of 8. 8,12-Bis[2-(methoxycarbonyl)ethyl]-3,7,13-trimethyl-1-oxo-2-vinyltripyrrin-14-carbaldehyde, obtained as a major tripyrrin product by an oxidative degradation of 1, gave a pyrromethene derivative, 3,7-bis[2-(methoxycarbonyl)ethyl]-2,8-dimethyl-l-methoxy-5-pyrromethene-9-carbaldehyde by the reaction with Tl(OAc)3 under air. The structures of all products obtained in the present study were determined by spectral measurements.
Utilization of Sulfide, Sulfoxide, and Sulfone Groups as Regiochemical Control Elements in the Diels–Alder Reaction of Naphthoquinones
Authors: Iwao Masatomo , Kuraishi Tsukasa
Published: July 2006

The Diels–Alder reactions of 2-phenylthio-, 2-phenylsulfinyl-, and 2-phenylsulfonyl-1,4-naphthoquinones, which were unsymmetrically substituted by methoxyl group on the benzenoid ring, with some vinylketene acetals were studied. The regioselectivity of the reactions was cleanly controlled by each of these sulfur substituents. In addition, the reactivity of the naphthoquinones were greatly enhanced by introduction of the sulfone or sulfoxide group. As a result of this study, several anthraquinones including natural products, such as pachybasin and phomarin 6-methyl ether, and 11-deoxyanthracyclinones were efficiently synthesized.
The Mechanism of the Reaction of (Arylthio)trimethylgermanes with Benzyl Bromides Giving Aryl Benzyl Sulfides. A Kinetic Study
Authors: Kozuka Seizi , Tamura Shoji , Ishibashi Satoshi , Ohya Sadamu , Tagaki Waichiro
Published: July 2006

A kinetic study has been conducted on the reaction of (arylthio)trimethylgermanes with benzyl bromides. The reaction was found to be second order and the rate was largely accelerated in polar solvents. Both ρ values due to substituents on arylthio and benzyl groups revealed nucleophilic attack of the sulfur atom on benzylic carbon atom as the reaction mechanism. Rates of the reactions of trimethyl(p-tolylthio)stannane with substituted benzyl chlorides were also examined to compare the substituent effects. Steric crowd around the sulfur atom has been found as an important factor to control the reaction mechanism.