bluuebunny/crossref_metadata_2025 huggingface dataset:
Equilibrium and kinetic studies of reactions of 2‐methyl‐2‐propanesulfenic acid
Authors: Okuyama Tadashi , Miyake Katsuji , Fueno Takayuki , Yoshimura Toshiaki , Soga Shinichi , Tsukurimichi Eiichi
Published: January 2005

2‐Methyl‐2‐propanesulfenic acid readily undergoes self‐condensation to give S‐t‐butyl 2‐methyl‐2‐propane‐thiosufinate. Rates of the reaction were measured in aqueous acetonitrile solution by use of NMR and UV spectroscopy. The reaction is second order in the substrate. The half‐life in a neutral aqueous solution is about 150 hours at 35°C when the initial substrate concentration is 0.003 M. The rate is proportional to acid concentration in the range 0.004–0.2 M. In alkaline solution, the main reaction is self‐condensation but some side reactions also seem to occur. The disappearance of the substrate does not follow satisfactory second‐order kinetics, but the second‐order rate constants obtained by the time‐lag method show a maximum around pH 10–11. The pKa (10.47) of the sulfenic acid was obtained at 14°C from a sig‐moid curve of the initial absorbances (240 nm) determined by extrapolation of the time‐dependent curve.
An observable model for the SN2 transition state [1a]. Hypervalent trigonal bipyramidal carbon (10‐C‐5) [1b]
Authors: Forbus T. R. , Martin J. C.
Published: January 2005

Dicationic 10‐C‐5 species 14, formally two‐electron oxidation products of 1,8‐bis(arylthio)‐9‐(2,6‐dimethoxyaryl)‐10‐phenylanthracenes, are prepared and characterized by NMR spectroscopy. Evidence is presented for a bis‐sulfonium structure containing a hypervalent trigonal bipyramidal (TBP) carbon atom. Dicationic species 14, prepared by the reaction of the appropriate diol with strong acid in liquid sulfur dioxide or sulfurylchlorofluoride, are stable for indefinite periods at room temperature in these solutions. Structural features common to these compounds which stabilize the TBP geometry sufficiently to allow their direct observation are as follows: (a) electronegative apical ligands (sulfonium sulfur atoms), (b) five‐membered rings linking each apical position to an equatorial position, (c) geometric constraints built into the tridentate ligand in a pattern designed to stabilize TBP, relative to tetrahedral carbon, (d) three relatively electropositive (sigma‐donor) equatorial ligands, which decrease the effective electronegativity of the central carbon atom of the threecenter bond, (e) a strain‐free, bidentate π‐acceptor equatorial ligand with its π‐axis parallel with the electron‐rich three‐center four‐electron bond axis, and (f) possible residual aromaticity (bis‐ipso‐aromaticity) in the equatorial six‐membered ring incorporating the hypervalent carbon atom.

A low‐temperature19F NMR study of 14b sets an upper limit for ΔG≠−100°C of ca. 4 kcal/mol for a hypothetical process which would interconvert unsymmetrical species 30 and 30′ if such a tautomeric mixture were to represent the structure of 14. Evidence against such a tautomeric equilibrium is adduced from the upfield shift of 0.65 ppm observed for the proton meta to the two methoxyl substituents of dication 14a relative to the comparable proton in 21a, the model dication lacking one of the two arylthio substituents of 14a. This is most easily explained by postulating a nucleophilic interaction of the second thioaryl group in 14 at the hypervalent, 10‐C‐5 carbon.
New cascade molecules centered about phosphorus
Authors: Engel Robert , Rengan Kasthuri , Chan Ching‐See
Published: January 2005

Cascade molecules in which the branch points are phosphonium ion sites have been synthesized bearing phosphorus in a variety of oxidation states at the core. In addition to the previously reported phosphonium ion core species, these new cascade molecules include those bearing phosphine, phosphine oxide, and phosphorane cores.
The origin of the sulfone in photooxidations involving sulfurane intermediates
Authors: Clennan Edward L. , Yang Kang
Published: January 2005

The photooxidations of γ‐hydroxysulfides which give abnormally high yields of sulfones have been investigated. This unusual result is attributed to the potent trapping ability of a hydrogen bonded sulfoxide intermediate. This suggestion is supported by measuring the ability of a γ‐hydroxysulfoxide to trap the persulfoxide formed in the photooxidation of diethyl sulfide and by careful analysis of the reaction composition as a function of time.
Facile synthesis of urea derivatives under mild conditions
Authors: Mizuno Takumi , Matsumoto Manabu , Nishiguchi Ikuzo , Hirashima Tsuneaki
Published: January 2005

Urea derivatives were readily synthesized in good yields under quite mild conditions, i.e., at ambient pressure and room temperature by sulfur‐assisted carbonylation of primary amines with carbon monoxide followed by oxidation of the resulting ammonium thiocarbamates with molecular oxygen.
NMR studies of 1,1‐diphenylboroxazolidone derivatives of α‐aminoacids
Authors: Farfán Norberto , Silva David , Santillan Rosa
Published: January 2005

A series of twelve 1,1‐diphenylboroxazolidones (1b–12b) prepared from α‐aminoacids and diphenylborinic acid were studied using one‐ and, in some cases, two‐dimensional (HETCOR) NMR techniques. Interpretation of these spectra led to definitive assignment of all carbon, hydrogen, and boron resonances.
Reaction of dichlorocarbene with 1‐(2,4,6‐tri‐t‐butylphenyl)‐1‐phosphaallenes
Authors: Yoshifuji Masaaki , Shibata Manabu , Toyota Kozo , Miyahara Ikuko , Hirotsu Ken
Published: January 2005

1‐(2,4,6‐Tri‐t‐butylphenyl)‐1‐phosphaallene reacted with dichlorocarbene to give 2‐dichloromethylene‐1‐(2,4,6‐tri‐t‐butylphenyl)‐1‐phosphirane. The structure was confirmed by X‐ray crystal structure analysis. A similar isomerization product was obtained in the reaction of dichlorocarbene with 3‐phenyl‐1‐(2,4,6‐tri‐t‐butylphenyl)‐1‐phosphaallene.
Reactions of heteroaryllithium compounds with phosphorus trichloride, phosphorus oxychloride, and thionyl chloride. Formation of heterocyclic biaryls
Authors: Uchida Yuzuru , Echikawa Naoji , Oae Shigeru
Published: January 2005

The reactions of four equivalents of heterocyclic aryllithium compounds with phosphorus trichloride or phosphorus oxychloride gave symmetrical heterocyclic biaryls in good yields. A similar coupling was found in the reactions of three equivalents of the lithium compounds with thionyl chloride.
Synthesis and spectral analysis of 6‐substituted‐1,2,4,8,10,11‐hexachloro‐12H‐dibenzo[d,g][1,3,2]dioxaphosphocin 6‐oxides
Authors: Reddy B. Sankara , Reddy C. Devendranath , Reddy P. Mallikarjuna
Published: January 2005

Synthesis of several 6‐substituted‐1,2,4,8,10,11‐hexachloro‐12H‐dibenzo[d,g][1,3,2]dioxaphosphocin 6‐oxides and their IR, 1H, 13C, and 31P NMR and mass spectral analyses are described. Observation of geminal coupling [2J(H,H) = 16.0 Hz] between bridged methylene protons (12‐CH2) suggested their non‐equivalence and is consistent with a boat‐chair form which may be in conformational equilibrium with either a boat‐boat or a distorted and extended boatlike conformation.
5‐Amino‐3H‐1,2,4‐dithiazole‐3‐thione as a synthon: New synthesis of 2‐thioureidobenzheteroazoles
Authors: Krishnaswamy N. R. , Sundaresan C. N. , Nambisan P. N. K. , Sandya K.
Published: January 2005

New and efficient one pot syntheses of 2‐thioureidobenzimidazole (V), 2‐thioureidobenzoxazole (VI), and 2‐thioureidobenzothiazole (VII) have been developed. The target compounds were obtained in good yields by condensing the title synthon commonly known as isoperthiocyanic acid (I) with 1,2‐diaminobenzene (II), 2‐aminophenol (III), and 2‐aminothiophenol (IV), respectively, in various organic solvent and in the solid state.
N‐alkyl‐C‐polyfluoroalkyl‐C‐chlorosulfinimides RFC(Cl)SNR
Authors: Ahlemann Jens‐Thomas , Roesky Herbert W. , Markovsky Leonid N. , Timoshenko Vadim M. , Shermolovich Yuri G.
Published: January 2005

The N‐alkyl‐C‐polyfluoroalkyl‐C‐chlorosulfinimides RFC(Cl)SNR have been investigated. Some aspects of their thermal stability and their [3 + 2] and [3 + 1] cycloaddition reactions have been examined.
Heterocyclic synthesis with nitriles: Synthesis of some new thiocyanato‐substituted heterocycles from alkylidene malononitrile
Authors: Abdelrazek Fathy M.
Published: January 2005

α‐(Thiocyanatomethyl)benzylidenemalononitrile undergoes bromination with N‐bromo succinimide to afford α‐(bromothiocyanatomethyl)benzylidenemalononitrile. This bromo derivative undergoes reactions with sodium hydrogen sulfide, thioglycollic acid, hydroxylamine hydrochloride, phenylhydrazine, and hydrazine hydrate to afford thiophene, 4H‐thiopyran, 4H‐oxazine, pyridazine, and bis(thiazol‐2‐ylidene)azine derivatives, respectively. Mechanistic explanations as well as structure elucidations are discussed.
A useful synthesis of α,β‐bis(methylseleno)alkanes and α,δ‐bis(methylseleno)alk‐2‐enes by the reactions of alkenes and 1,3‐dienes with B(SeMe)3‐Lewis acid
Authors: Yoshimatsu Mitsuhiro , Asahi Takashi , Shimizu Hiroshi , Kataoka Tadashi
Published: January 2005

Reactions of tris(methylsenleno)borane‐SnCl4 with alkenes 1a–g gave α,β‐bis(methylseleno)alkanes 2a–g, stereospecifically, and reactions with 1,3‐dienes 1i–k afforded α,β‐bis(methylseleno)alk‐2‐enes 2i–k, regioselectively.
A novel strategy for the synthesis of 4,5‐dihydroisoxazoles via conjugate additions to α‐nitroalkenes
Authors: Yuan Chengye , Li Chaozhong
Published: January 2005

Michael condensation of α‐nitroalkenes with various nucleophiles, followed by the addition of trimethylchlorosilane, led to novel syntheses of 4,5‐dihydroisoxazoles via cycloadditions of silyl nitronates.
Electron and X‐ray diffraction studies of chemically deposited thin films of cadmium selenide following reaction with mercury(II) chloride solution
Authors: Estrada C. A. , Meyers E. A. , Zingaro R. A. , Dufner D. C. , Nair P. K. , Nair M. T. S.
Published: January 2005

The reaction between thin films of CdSe and aqueous HgCl2 was studied using electron diffraction (ED) powder X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). It was found that α‐Hg3Se2Cl2 is formed in the CdSe film following its reaction with 0.01 M HgCl2 for a period of 5 minutes. Upon completion of the reaction of CdSe powder with 0.01 M HgCl2, Hg2Cl2 is present in addition to α‐Hg3Se2Cl2 in a molar ratio of 1:3.1. The effect of air annealing on CdSe powder was also studied. Heating in air to 450°C for 1 hour resulted in an XRD pattern corresponding to the hexagonal form of CdSe.
Stereospecific synthesis of P‐epimeric (Rp1, Rp2)‐bis‐[O‐l‐menthylphenylphosphonothionyl] diselenide. A new variant of the stereoselective Staudinger reaction
Authors: Łopusiński Andrzej , Łuczak Leszek , Michalski Jan
Published: January 2005

An efficient procedure is described that leads to pure (SP)‐O‐l‐menthylphenylthiophosphinate. The absolute configuration of this diastereomer was assigned by chemical correlation and confirmed by X‐ray crystallography. The reaction of the isomer with phenyl azide, leading to amidate, is a new variant of the stereoselective Staudinger reaction. Addition of elemental selenium to the (SP)‐thiophosphinate led to diastereomeric O‐l‐menthylphenylselenophosphonothioic acid, which was finally oxidized to the diastereomeric (RP1,RP2)‐bis‐[O‐l‐menthylphenylphosphonothionyl] diselenide. The diselenide structure was unambiguously confirmed by 31P NMR spectroscopy.
Synthesis of pentacoordinated germanium compounds containing a phosphonyl group
Authors: Chen Ruyu , Liu Lunzu , Zhang Zhongbiao
Published: January 2005

The title compounds were prepared by the reaction of germanium sesquioxides with diethyl N,N‐bis(2‐hydroxyethyl)aminomethylphosphonate in good yields (72–94%). The X‐ray analyses showed that the geometry about the germanium atom was a distorted trigonal bipyramid. © John Wiley & Sons, Inc.
Super‐resolution bright‐field optical microscopy based on nanometer topographic contrast
Authors: Huang Shu‐Wei , Mong Hong‐Yao , Lee Chau‐Hwang
Published: January 2005

By using an expectation‐maximization maximum likelihood estimation algorithm to improve the lateral resolution of a recently developed non‐interferometric wide‐field optical profilometer, we obtain super‐resolution bright‐field optical images of nanometer features on a flat surface. The optical profilometer employs a 365‐nm light source and an ordinary objective lens of a 0.95 numerical aperture. For objects of 100 nm thickness, lateral features about λ/7 can be resolved in the restored images without fluorescence labeling. Current image acquisition rate is 0.1 frame/sec, which is limited by the brightness of the light source. With a brighter light source, the imaging speed can be fast enough for real‐time observation of dynamic activities in the nanometer scale. Microsc. Res. Tech. 65:180–185, 2004. © 2005 Wiley‐Liss, Inc.
Single molecule studies of RNA secondary structure: AFM of TYMV viral RNA
Authors: Giro Andrea , Bergia Anna , Zuccheri Giampaolo , Bink Hugo H.J. , Pleij Cornelis W.A. , Samorì Bruno
Published: January 2005

Nowadays, the development of experimental procedures for the determination of the secondary structure of RNA molecules is taking advantage of the novel single‐molecule probing and imaging techniques. We report a method for the mapping of the secondary structure of RNA molecules spread on a flat surface by means of the atomic force microscope. Globular domains comprising groups of RNA secondary and tertiary structure elements separated by unstructured domains can be discerned in the micrographs and their position along the molecule contour can be measured directly on unstained specimens. We have analyzed the morphology of a population of single molecules of 3′ fragments of the Turnip Yellow Mosaic Virus RNA shorter than 1 kb in different temperature and electrolytic conditions. We found a satisfying agreement of the shape of the imaged structures with previously available evidence. The method we have developed can be used to map also different types of RNA molecules and has the advantage of showing the distribution of the single molecule conformations within the population. Microsc. Res. Tech. 65:235–245, 2004. © 2005 Wiley‐Liss, Inc.
Exploring molecular motors and switches at the single‐molecule level
Authors: Capitanio M. , Vanzi F. , Broggio C. , Cicchi R. , Normanno D. , Romano G. , Sacconi L. , Pavone F.S.
Published: January 2005

Single‐molecule techniques have propelled an impressive number of biophysical studies during the last decade. From relatively simple video‐microscopy techniques, to sophisticated manipulation and detection apparata, single‐molecule techniques are capable of tracking the movements and the reaction trajectories of single enzymatic units. By observing microspheres attached to biomolecules it is possible to follow the motion of molecular motors, or to detect conformational “switching” induced by regulatory proteins. Micromanipulation tools like optical tweezers have been widely applied to understand the mechanisms of linear molecular motors, and have allowed the measurement of the elementary steps and the forces produced by several motor proteins, including myosin, kinesin, and dynein. New experimental assays based on magnetic or optical “wrenches,” which are able to apply and detect torques on rotary motors and biopolymers, are opening new possibilities in this field. Here, established and emerging magneto‐optical manipulation and video‐tracking techniques are reviewed, in the perspective of single molecular motors and regulatory proteins studies. Microsc. Res. Tech. 65:194–204, 2004. © 2005 Wiley‐Liss, Inc.
Diffusion of microspheres in sealed and open microarrays
Authors: Rieger B. , Dietrich H.R.C. , Doel L.R. Van Den , Vliet L.J. Van
Published: January 2005

In several experiments, we study the diffusion of microspheres with different radii in microarrays filled with a variety of aqueous solutions of ethylene glycol. We study diffusion in open and closed (sealed) microarrays. In sealed nanoliter wells, the tracers show pure diffusion, whereas in open reactors, a radial outward‐directed evaporation‐induced liquid flow is superimposed onto the diffusion. In general, one of the following quantities can be calculated if the others are known: the temperature, the viscosity of the medium, the radius of the microbeads, or the diffusion constant. The estimated diffusion constants in closed microarrays are in good agreement with theoretical predictions based on the Brownian motion. We monitor the motion of the microbeads under a microscope and extract their paths in time from the digital recordings. Ambiguous paths due to the crossing of two trajectories can be detected. We show that low microsphere concentrations or high viscosities do not hamper a robust estimation of the diffusion parameters. Microsc. Res. Tech. 65:218–225, 2004. © 2005 Wiley‐Liss, Inc.
Recent work on entropically‐driven ring‐opening polymerizations: some potential applications
Authors: Hodge Philip , Colquhoun Howard M.
Published: January 2005

The entropically‐driven ring‐opening polymerization of macrocyclic monomers (>ca. 14 ring atoms per repeat unit) and/or macrocyclic oligomers is a relatively new method of polymer synthesis that exploits the well‐known phenomenon of ring‐chain equilibria. It attracts interest because of its novel features. For example, these ring‐opening polymerizations emit no volatiles and little or no heat. This review considers the principles of entropically‐driven ring‐opening polymerizations, gives selected examples and discusses potential applications. The latter include micromolding, high throughput syntheses and the synthesis of supramolecular polymers. Copyright © 2005 John Wiley & Sons, Ltd.
Nanostructuring polymers with cyclodextrins
Authors: Rusa Cristian C. , Wei Min , Bullions Todd A. , Shuai Xintao , Uyar Tamer , Tonelli Alan E.
Published: January 2005

Bulk solid polymer samples formed by the coalescence of guest polymer chains from their inclusion compounds (ICs) formed with host cyclodextrins (CDs) can result in significant reorganization of their phase structures, morphologies, and even chain conformations from those more commonly produced from randomly‐coiled, entangled polymer solutions and melts. When the cyclic host CDs are threaded by polymer chains to form crystalline polymer‐CD‐ICs, the guest polymers become highly extended due to the narrow host CD diameters (∼5, 7, and 9 Å for α‐, β‐, and γ‐CDs) and are segregated from neighboring guest polymer chains by the CD‐IC channel walls. As a consequence, when polymer‐CD‐IC crystals are treated with CD solvents that do not dissolve the guest polymers or are treated with amylase enzymes, the resulting coalesced bulk polymer samples often display properties distinct from those of normally produced bulk samples of the same polymers. In this article the CD‐IC processing of polymers to generate novel polymer microstructures and morphologies are described, to control the phase separation of immiscible blocks in block copolymers, and to form well‐mixed intimate blends of two or more polymers that are normally incompatible. The thermal and temporal stabilities of polymer samples coalesced from their ICs formed with CDs will also be mentioned, and it is suggested that the range of polymer properties can be greatly expanded by their CD‐IC processing. Copyright © 2005 John Wiley & Sons, Ltd.
Composition, preparation procedure and physical properties of linear homogeneous polyurethanes for membranes
Authors: Laporta Marcello , Pegoraro Mario , Bianchi Fiorenzo , Consolati Giovanni , Zanderighi Luciano
Published: January 2005

Linear polyurethanes (PUs) were prepared in solution in two steps. In the first step, toluene‐diisocyanate (TDI) 80:20 (T) was reacted with a short‐chain poly(oxypropylene) diol (V) to obtain prepolymers characterized by various ratios of R = [T]°/[V]°. In the second step, the prepolymers were reacted with the extender 1,4‐cyclohexanedimethanol (E) with various extension ratios RE = (R − 1)[V]°/[E]°. The PU properties were analyzed by various techniques. In particular, the molecular weights determined by gel permeation chromatography (GPC), the thermal properties such as glass transition temperature Tg and specific heat variation ΔCp measured by differential scanning calorimetry (DSC), the chemical composition of the PUs and the various types of hydrogen bonds present in the polymers evidenced by Fourier‐transform infrared (FTIR) spectroscopy, the monophasic structure evidenced by small‐angle X‐ray scattering (SAXS), and the existence of only one Tg confirmed that these PUs were linear, amorphous and monophasic. Positron annihilation lifetime spectroscopy (PALS) analysis showed that the mean volume of the nanoholes increased with increasing temperature, but was not dependent on the composition, as expected for a monophasic system. A stoichiometric semi‐empirical model was proposed that relates the PU blocks' micro‐composition to the R and RE macro‐parameters, chosen for the synthesis. The polymer assumes various expressions of the general formula X[(TV)k(TE)n]mX for different values of the R and RE ratios. The micro‐parameters k and m have a direct connection with the experimental mean molecular weights of the prepolymer and the polymer, respectively: n depends only on R. The model could foresee the density of hydrogen bonds and distinguished the bonds connected to either V or E, which could be shown by FTIR analysis. This paper shows that, when using stereo‐irregular diols and blends of 2,4‐ and 2,6‐TDI, non‐stereoregular PUs are obtained. If low‐molecular‐weight diols are used and R < 3.3, it is quite improbable that the PU blocks separate into macrophases and therefore monophasic amorphous PUs are obtained. Monophasic PUs can be useful for applications such as in the field of membrane gas and vapour separation. Copyright © 2005 Society of Chemical Industry
Dynamic rheological properties of Yam starch/hectorite composite gels
Authors: Wilhelm Helena‐M , Sierakowski Maria‐R , Reicher Fany , Wypych Fernando , Souza Gabriel P
Published: January 2005

The rheological properties of composite gels of starch extracted from Yam roots (Discorea sp) and hectorite (a mineral clay belonging to the smectite group) were studied in aqueous solutions as a function of hectorite concentration. The elastic (G′) and viscous (G″) moduli of the composite gels were dependent on the clay content, and for all samples G′ was greater than G″. Composite gels with clay contents of <30% presented higher G′, G″ and viscosities |η*| when compared with pure starch gel, while those with a content of 50 % showed lower values. The addition of hectorite significantly inhibited the creeping properties in relation to pure starch at 25 °C but, after heating/cooling cycles between 25 and 85 °C, this effect was not observed and the composite gel showed similar behavior to that of pure starch. Copyright © 2005 Society of Chemical Industry
Ethenediylidene‐2,2′ ‐bis(1,3‐dithiole) and butatriene‐1,4‐diylidene‐2,2′‐bis(1,3‐dithiole)
Authors: Awaji Hiroshi , Sugimoto Toyonari , Yoshida Zen‐Ichi
Published: January 2005

This paper describes the synthesis and electrochemical behavior of dicationic salts of ethenediylidene‐2,2′ ‐bis(1,3‐dithiole) (3) and butatriene‐1,4‐diylidene‐2,2′ ‐bis(1,3‐dithiole) (4). These are expected as donor components for developing organic conducting and superconducting materials, on the grounds of high electron donating ability and of rigid skeletal structure with two and four cumulenic carbons inserted between two 1,3‐dithioles. These salts were obtained in good overall yields by several steps starting from (2‐morpholino‐4,5‐dimethyl or ‐diphenyl)‐1,3‐dithiolylium salt. From the 1H and 13C NMR, and electronic spectra it is suggested that the π conjugation between two 1,3‐dithiolylium ions through an acetylenic bond is less effective than that through an olefinic bond of the corresponding salts of ethanediylidene‐2,2′ ‐bis(1,3‐dithiole) (1) and 2‐butene‐1,4‐diylidene‐2,2′‐bis(1,3‐dithiole) (2). The cyclic voltammetric study shows that the corresponding radical cations, and in particular 3 and 4, are less stable even at −40°C, thus providing reasons for our current lack of success in isolation of 3 and 4. From comparison of the first redox potentials of neutral species, it is deduced that the donating ability increases in the order of TTF < 1 ⋍ 2 ≲ 3 ≪ 4.
Intramolecular orientation at the micellar interface: Control of norrish type I and type II reactivity of benzoinalkylethers via conformational effects
Authors: Devanathan S. , Ramamurthy V.
Published: January 2005

The photolysis of benzoinalkylethers 1‐5 solubilized in detergents show a significant deviation from the course of reaction in isotropic organic solvents. Remarkable difference in photobehaviour is noticed between the short chain (1‐3) and the long chain (4 and 5) benzoinalkylethers in the micellar media. However, the influence of the micellar media on the photobehaviour of alkyldeoxybenzoins 6 and 7 was small. The importance of ‘cage effect’ in controlling the product distribution was evident from its dependence on the micellar size and on the occupancy number. More importantly, a comparative analysis of the photobehaviour of the ketone 1‐7 reveals that the micellar interface can be used to control the conformations of organic molecules.
Oxygen induced reduction: Reaction of benzeneselenol with aromatic aldehydes in the presence of oxygen
Authors: Masawaki Teruyuki , Ogawa Akiya , Kambe Nobuaki , Murai Shinji , Sonoda Noboru
Published: January 2005

Reduction of aromatic aldehydes by benzeneselenol is found to be promoted by molecular oxygen to give corresponding alcohols in good yields. No reduction took place without oxygen.

A free radical process involving SH2 reaction at the selenium atom is proposed where the phenylseleno radical attacks the selenium atom of selenohemiacetal, the adduct of benzeneselenol to aldehyde, to give the ketyl radical which then abstracts hydrogen from benzeneselenol. The intermediacy of selenohemiacetal is supported by a quantitative reduction of α‐methoxybenzyl phenyl selenide, which is used as a model compound of the intermediate.
ESR studies of photochemical reaction of 2‐methyl‐3‐acetylquinoxaline N,N′‐dioxide(MAQO)
Authors: Wang Hanqing , Feng Liangbo
Published: January 2005

The photochemical reaction of MAQO with various aromatic amines were studied by ESR. The results show that nitroxide radicals are stable productrs of the photooxidation of both diphenylamines and phenylamines. The photolyzed phenothiazine does not yield nitroxide as the final product, instead it gives the neutral radical as the stable final product.
2,3:5,6‐bis(ethylenedithio)‐ and bis(trimethylenedithio)‐N,N′‐ dicyanoquinonediimines as new electron acceptors
Authors: Otsubo T. , Nobuhara Y. , Kanefuji K. , Aso Y. , Ogura F.
Published: January 2005

In order to examine the substituent effect of ethylenedithio and trimethylenedithio groups on electron acceptors, the two title compounds were prepared in one step from the corresponding quinones. These species behave as weak π‐electron acceptors owing to the electronic and sterical effects of the fused groups. Only the bis(ethylenedithio) derivative formed a charge‐transfer complex with tetrathiotetracene, which showed a moderate electric conductivity of 2·0 × 10−2 S cm−1. In addition, both species oxidized copper, sodium, and potassium iodides to give the corresponding deeply colored metal salts, most of which were semiconductive. The naphtho analogs were similarly studied, but hardly served as electron acceptors.
Extrusions of dibromocarbene under neutral conditions
Authors: Warner Philip M. , Lu Shih‐Lai , Gurumurthy R.
Published: January 2005

The thermal and photochemical decompositions of 5 have been studied. Both reactions lead to CBr2 transfer in good to high yields. With the 2‐pentenes as substrates, CBr2 transfer is stereospecific in the classical singlet carbene manner.magnified image
Free radical chain reactions of ate complexes. Electron transfer processes 42
Authors: Russell Glen A. , Hu Shuisheng , Herron S. , Baik Woonphil , Ngoviwatchai P. , Jiang W. , Nebgen M. , Wu Y.‐W.
Published: January 2005

Iodide ion promotes the free radical reaction of isopropylmercury idide with bromotrichloromethane to yield isopropyl bromide with rate enhancement in the order of 104. The reaction involves electron transfer from i‐PrHgI2− to the trichloromethyl radical in a long kinetic chain process. Iodide ion also promotes the free radical chain conjugate addition of tert‐butylmercury chloride to α,β‐unsaturated ketones, esters, phosphonate esters and sulfones. Competitive reactivity studies indicate that lithium di‐tert‐butylcuprates or tri‐tert‐butylzincates react with 2‐cycloalkenones by a mechanism involving attack by tert‐butyl radicals. No evidence for radical attack is observed for the corresponding n‐butyl ate complexes of copper or zinc.
Complex formation between 1,3,5‐trinitrobenzene and 1,8‐diazabicyclo‐[5,4,0]‐undec‐7‐ene
Authors: Collina Gianni , Forlani Luciano
Published: January 2005

The title reaction is an instance of a simple nucleophilic attack of neutral nitrogen on aromatic sp2 carbon. The kinetic data (obtained in dimethyl sulphoxide) are compared to the results reported by the literature for the same reaction of aliphatic amines. Some possible interactions (substrate/nucleophile, substrate/salt) preceding the attack of the nucleophile are discussed.
Studies on organophosphorus compounds. XXXVI.. Substituent effects of alkylphosphonates and ‐phosphinates in alkaline hydrolysis
Authors: Yuan Chengye , Li Shusen , Liao Xiugao
Published: January 2005

Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
Stern–Volmer quenching kinetics in photoreaction systems with strong internal filtering: Type II photoreaction of 2‐benzoylcyclohexanone
Authors: Hasegawa Tadashi , Nishimura Michiko , Yoshioka Michikazu
Published: January 2005

The Stern–Volmer quenching equation for a photochemical reaction in the presence of internal filtering was obtained by applying the steady‐state approximation to the system. The equation was used for the kinetic analysis of the Type II photoreaction of 2‐benzoylcyclohexanone yielding 1‐phenylhept‐6‐ene‐1,3‐dione, the enol form of which acts as an effective internal filter. The kqτ value for quenching of the photoreaction by 2,5‐dimethylhexa‐2,4‐diene was determined to be 9·1 ± 0·5 l mol−1.
Anomalous salt effects on a micellar‐mediated reaction of bromide ion
Authors: Bunton Clifford A. , Cowell Charles P. , Nome Faruk , Romsted Laurence S.
Published: January 2005

Reaction of bromide ion with α‐picryl‐p‐bromoacetophenone (1) is speeded by aqueous cationic micelles of cetyltrimethylammonium bromide (CTABr; C16H33NMe3Br) and dodecyltrimethylammonium bromide (DoTABr; C12H25NMe3Br) and rate constants reach limiting values when 1 is fully bound to micelles of CTABr. Limiting values are not reached in DoTABr, but the data can be fitted to a simple model for the distribution of reactants between water and micelles. Estimated second‐order rate constants at the micellar surface are similar to values in water, but this model cannot explain the observed rate enhancements on addition of NaBr to CTABr. Inert anions such as nitrate, mesylate, n‐butanesulfonate, phenylmethanesulfonate and camphor‐10‐sulfonate inhibit reaction in CTABr by competing with Br− at the micellar surface. Other n‐alkanesulfonate ions (RSO, R = n‐C5H11, n‐C6H13, n‐C7H15, n‐C8H17) and arenesulfonate ions (benzene‐, toluene‐, naphthalene‐1‐ and naphthalene‐2‐sulfonate) behave anomalously. These ions expel Br− from the micelle, as shown electrochemically, but there are maxima in plots of rate constant against mole fraction of Br−. These rate extrema are apparently due to perturbation of the micellar surface structure that overcomes the inhibition due to competition with Br−. These results show that the simple pseudo‐phase, ion‐exchange model can be applied only in dilute electrolyte and in the absence of hydrophobic anions.
Reaction of aryliminodimagnesium with diphenyl diketones: Heat evolution accompanying single electron transfer and chelate formation, and product distribution
Authors: Ōkubo Masao , Fukuyama Yoshinori , Sato Miyuki , Matsuo Koji , Kitahara Tetsuhiro , Nakashima Michio
Published: January 2005

Reaction of diphenyl diketones (benzils) with aryliminodimagnesium [ArN(MgBr)2, IDMg], a magnesium reagent having condensation ability, was investigated. By comparison of the relative amounts of heat evolved in the reactions of IDMg (mildly electron donating) and ArMgBr (strongly electron donating) with some carbonyl and nitro compounds, results were obtained supporting the reported correlation of the relative yields of normal and abnormal (radical) products with single electron transfer (SET) efficiency estimated by the oxidation and reduction potentials of reactants. A sole exceptional result, i.e. the great heat evolution caused by the combination of benzil and IDMg, was attributed to the generation of tightly chelated radicals via SET. The involvement of stepwise SET was confirmed by ESR. On the basis of these results, substituent effects of benzil and mono‐condensation products on their reduction potentials and on the relative yields of normal (mono‐ and di‐condensation) and abnormal (dimerization) products were examined. All the results were consistently explained in terms of the relative efficiency of chelation (or σ‐complexation) and SET in two main processes. The role of the initial stages involved in the processes governing the final product distribution is discussed.
Correlations of rate and selectivity of a Diels–Alder reaction with Sp parameters
Authors: Cativiela Carlos , Mayoral Jose A. , Avenoza Alberto , Peregrina Jesus M. , Roy Miguel A.
Published: January 2005

The rate and endo/exo selectivity of the Diels–Alder reaction between cyclopentadiene and methyl (E)‐α‐cyanocinnamate at 25°C, in several acetone–water and 1,4‐dioxane–water mixtures, were measured. The linear correlations of log k and log(endo/exo) vs solvophobicity are reported. Correlations for selectivity are considerably improved when the results obtained in acetone–water and 1,4‐dioxane–water are taken as separate series.
N‐Carbeniopyridinium salts: Charge‐transfer complexes with the C5 (COOMe)5 anion; CC bond formation with the TCNQ radical anion
Authors: Maas Gerhard , Weber Hans Martin , Exner Reiner , Salbeck Josef
Published: January 2005

N‐[2,3‐Bis(dimethylamino)cyclopropenylio]‐ and N‐(tetramethylamidinio)pyridinium salts (trifluoromethanesulphonates and tetrafluoroborates) form 1:1 and 1:2 charge‐transfer complexes with the pentakis(methoxycarbonyl)cyclopentadienide anion. The x‐ray crystal structures of 1‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium pentakis(methoxycarbonyl)cyclopentadienide tetrafluoroborate hydrate and of 1‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium bis[pentakis(methoxycarbonyl)cyclopentadienide] were determined. In constrast, the tetra‐cyano‐p‐quinodimethane (TCNQ) radical anion reacts with the first‐mentioned salts by CC bond formation to give novel dicationic salts. Thereby, the radical anion attacks the pyridinium γ‐position of the N‐(tetramethylamidinio)‐pyridinium dication, but the three‐membered ring of the N‐[2,3‐bis(dimethylamino)cyclopropenylio] pyridinium system.
Solvent polarity scales. 1. Determination of ET and π* values for phosphonium and ammonium melts
Authors: Harrod W. Brian , Pienta Norbert J.
Published: January 2005

The solvent polarity of a series of organic salts in their molten state has been determined using the solvatochromic dyes: pyridinium N‐phenolate betaine, the basis of the ET scale, and N,N‐diethyl‐4‐nitroniline, one of the primary standards for the π* scale. Each of these dyes was dissolved in the following liquids: lithium acetate–sodium acetate–potassium acetate eutectic; ethylammonium chloride; dimethylammonium cloride; diethylammonium nitrate; ammonium trifluoracetate; tetraethylammonium acetate; tetrabutylphosphonium chloride; octyltributylphosphonium chloride; dodecyltributylphosphonium chloride; tetrabutylammonium bromide; tetrabutylphosphonium bromide; octyltributylphosphonium bromide; dodecyltributylphosphonium bromide; octyltributylphosphonium iodide; dodecyltributylphosphonium iodide; tetrahexylammonium benzoate; methyltrioctylphosphonium dimethylphosphate; and methyltrioctylammonium chloride. The ultraviolet and visible spectra were measured for each of these. In addition, data were collected as a function of temperature and in the presence of neutral and ionic additives. In general, these molten salts represent solvent polarities equivalent to moderately polar aprotic solvents such as acetone and acetonitrile. The salts with cations capable of being hydrogen bond donors gave considerably higher values, equivalent to or higher than water, the solvent with the highest value on the ET scale. These and the eutectic mixture are thought to involve specific dye–solvent interactions which cause these anomalously high values.
NMR spectroscopic study of configurations and conformations of 5‐pyridylmethylenehydantoins
Authors: Tan Sau‐Fun , Ang Kok‐Peng , How Gee‐Fung
Published: January 2005

Nine 5‐pyridylmethylenehydantoins were prepared. Each of the 1‐methyl‐substitute compounds was obtained in two stereoisomeric forms. Only one form of each of the 3‐methyl‐substituted and N‐unsubstituted compounds was obtained directly from synthesis but could be partially converted into the other stereoisomer photochemically. The Z/E configurations and the conformational relationship between the pyridine and hydantoin rings were studied by 1H and 13C NMR spectroscopy, including variable‐temperature 1H NMR. The existence of NH…︁N or CH…︁N interactions and the possibility of tautomerism are suggested for some of the compounds. The Z‐isomers of compounds with 2‐ or 3‐pyridyl rings prefer an s‐cis conformation whereas the E‐isomers prefer an s‐trans conformation.
Interpretation of1H NMR spectra of 2‐benzopyrylium salts with the use of the CNDO/2 method
Authors: Shcherbakova Irina V. , Yudilevich Iosif A. , Kuznetsov Evgenii V.
Published: January 2005

The1H NMR spectra of eleven substituted 2‐benzopyrylium salts are interpreted with the aid of the CNDO/2 method for standard geometry. Some effects of the substituents are considered for the charge distribution in the 2‐benzopyrylium cation.
Taft's substituent constants, σ* and σI, and Huheey's group electronegativity
Authors: Datta Dipankar
Published: January 2005

For 34 groups, Taft's substituent constants σ* and σI are found to correlate well (r = 0.962 and 0.948) with Huheey's group electronegativity (χH) when Taft's steric parameter Es for a group is mixed with σ* and σI:
equation image

From these equations, it follows that for a particular chemical group G, σ*(G) ≈︁ 8σI(G). Since the σ* scale is essentially based on the σI scale, the small inherent steric component in σI is amplified in the case of the σ* by a factor of ca 8. An analysis shows that χH represents the electronegativity of a group when the group is considered to be a mere collection of non‐bonded, charged and suitably hybridized atoms. Thus σ* and σI are found to represent the electronegativity of a group in the spirit of the χH. It is concluded that a chemical group can be viewed as a collection of non‐interacting atoms. Although there is evidence that a molecule can sometimes be treated similarly, for a group such a situation is novel.
Aromaticity as a multi‐dimensional phenomenon
Authors: Jug Karl , Köster Andreas M.
Published: January 2005

The classification of aromaticity criteria is studied. New aromaticity criteria are developed and discussed. A statistical analysis of such criteria is presented and compared with a similar analysis of the recent literature. It is shown that aromaticity is at least a two‐dimensional phenomenon. The classification of the compounds depends on the type of criteria included in the analysis.
Substituent effects in the photohydration of styrenes and phenylacetylenes. An attempt to establish a σhν scale for excited‐state reactions
Authors: Mcewen John , Yates Keith
Published: January 2005

The acid‐catalysed rate constants (kH+) for the photohydration of 18 meta‐ and para‐substituted styrenes and phenylacetylenes were determined in H2SO4 solutions by means of fluorescence quenching measurements and the standard Stern–Volmer approach. Singlet lifetimes of the substrates were determined in the reference solution (water at pH 7) by single photon counting. The log k values obtained did not correlate well with any previously reported σ scales, and were used to try to establish a σhν scale (for H‐, p‐F, m‐F, p‐Me, m‐Me, p‐Et, m‐Et, p‐OMe and m‐OMe substituents) for possible use in other photochemical reactions. Correlation of all available literature data versus the new σhv scale gave reasonable correlations (r = 0.957–0.966). The problems associated with establishing linear free energy relationships for photoreactions are discussed.
Product‐determining factors in the grignard reactions of benzophenones. The role of the structure of alkyl groups in grignard reagents
Authors: Maruyama Kazuhiro , Matano Yoshihiro , Katagiri Toshimasa
Published: January 2005

The mechanism of the Grignard reactions of substituted benzophenones with two kinds of alkyl Grignard reagent, n‐C3H7MgBr, and i‐C3H7MgBr, was investigated. In these reactions, both addition and reduction products were also generated. Based on the results of product analysis and stopped‐flow, ESR and association measurements, it was confirmed that the product distribution was governed by several factors: the oxidizing ability of benzophenones, the association ability of Grignard reagents and the structure of alkyl groups of Grignard reagents. In particular, the strength of CMg and β‐CH bonds of Grignard reagents could strongly affect the product distribution.
Ambident electrophilicity of alkyl aryl phosphates
Authors: Wagener Carl C. P. , Modro Agnes M. , Modro Tom A.
Published: January 2005

Hydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N‐methyl‐8‐hydroxyquinolinium or 4‐hydroxy‐(N,N,N‐trimethylanilinium) ion, proceeds with the cleavage of the POAr and MeO bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water‐triffuoracetic acid mixtures only the POAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the MeO bond fission by thiosulphate ion (ca 60‐fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500‐fold acceleration).
Multiplicities of π‐ylide ground states: Computational evidence for a breakdown of aromaticity arguments
Authors: Langler Richard Francis , Ginsburg Jack Leon , Snooks Rodney , Boyd Russell J.
Published: January 2005

AM1 and 3–21G computations, on the lowest singlet state of selected π‐ylides, support the earlier conclusion that π‐ylides are highly polar with highly reactive side‐chains. The computations also indicate that the corresponding triplet states are lower in energy and have substantially reduced polarity. Contrary to the expectations derived from Hückel calculations, AM1 and 3–21G calculations suggest that the best π‐ylide structures have non‐aromatic rings. The heats of isomerization contradict earlier conclusions reached using topological resonance energies. π‐Ylides are expected to afford different product structures depending on the electronic state of the π‐ylide involved in a given cycloaddition reaction.
Kinetic probe to study the structural behaviour of mixed aqueous—organic solvents. Effects of inorganic and organic salts on the kinetics and mechanism of intramolecular general base‐catalysed methanolysis of ionized phenyl salicylate
Authors: Niyaz Khan M. , Audu A. A.
Published: January 2005

The effects of inorganic and organic salts on the rates of methanolysis of ionized phenyl salicylate, PS−, were studied at 30°C in H2O–MeOH solvents. The observed pseudo‐first‐order rate constants, kobs, for methanolysis of PS− represent a non‐linear incrrease with increase in methanol contents in mixed H2O–MeOH solvents. The observed data are explained in terms of the proposal that methanol molecules exist in monomeric, dimeric and in general polymeric forms in H2O–MeOH solvents. The rate constants, kobs, at alkanol [ROH (R = Me, HOCH2CH2)] contents of ca ≤ 55% (v/v), fit the relationship kobs = k [ROH]T/(1 + kA [ROH]), (1 + KA [ROH]), where k and KA represent the nucleophilic second‐order rate constant for the reaction of ROH with PS− and the association constant for the dimerization of ROH, respectively, and [ROH]T is the total concentration of ROH. The rate constants, k, appear to be independent of total concentrations of inorganic salts [MX]T (M = Li, Na, K and X = OH, Cl), but the values of KA increase with increase in [MX]T and this increase varies in the order Li+ > Na++ > K+. The values of both k and KA show a decrease with increase in the total concentrations of organic salts, [R4MX]T (R = Et, Prn, Bun and X = Br, I). The effects of [MX]T and [R4MX]T on kobs versus content of ROH (%, v/v) profiles reveal the following inferences: (i) in the water‐rich region of H2O‐ROH solvents [at ca < 55% (v/v) ROH] the solvation shells of M+ and X− contain preferentially only water molecules whereas in the methanol‐rich region [at ca > 55% (v/v) ROH] of solvents some cosolvent methanol molecules also enter into these solvation shells; (ii) the solvation shells of tetraalkylammonium ions, R4N+, contain some methanol molecules even in the water‐rich region of the solvents; (iii) Li+ cause a methanol structure‐making effect whereas Na+ and K+ ions show a methanol structurebreaking effect; and (iv) organic cations such as Et4N+, Prn4N+ and Bun4N+ reveal a methanol structure‐breaking effect through an interaction mechanism different from that operating for Na+ and K+. Both k and KA show significant normal deuterium isotope effects in the reactions of MeOH and PS− which indicates the probable occurrence of proton transfer in the rate‐determining step.
Ionization constants of 5‐furylmethylenehydantoins and 5‐thienylmethylenehydantoins in 80% (w/w) dimethyl sulphoxide–water at 25°C
Authors: Tan Sau‐Fun , Yeoh Phee‐Teik
Published: January 2005

The ionization constants of sixteen 5‐furylmethylenehydantoins and 5‐thienylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide–water solvent at 25°C. The effects of the 2‐/3‐furyl and 2‐/‐3‐thienyl rings and the effects of configuration and conformation on acidity are discussed. The very low acidity of (Z)‐5‐(2‐furyl)methylene‐3‐methylhydantoin suggests the possibility of some weak intramolecular interaction between the proton at N‐1 and the 2‐furyl oxygen in the s‐cis conformation.