bluuebunny/crossref_metadata_2025 huggingface dataset:
Janovsky reactions between cyclopentadienyliron complexes of substituted benzenes and carbanions derived from ketones
Authors: Sutherland Ronald G. , Chowdhury Ratan L. , Piórko Adam , Lee Choi Chuck
Published: May 2006

Janovsky reactions were carried out between various η6-substituted benzene-η5-cyclopentadienyliron cations containing at least one electron-withdrawing substituent in the complexed arene and the enolate-carbanion derived from acetone, butanone, or 3-pentanone. Highly colored adducts were obtained from reactions of the cyclopentadienyliron (CpFe) complexes of nitrobenzene, cyanobenzene, p-tolylsulfonylbenzene, benzoylbenzene, o-, p-, or m-nitrotoluene, and o-, p-, or m-dichlorobenzene with acetone in aqueous KOH, the products being derived from exo-addition of the acetonyl anion regioselectively at a position ortho to an electron-withdrawing substituent. For example, reaction of the η6-nitrobenzene-η5-cyclopentadienyliron cation (1a) with acetone in aqueous KOH gave (R,S)-(1-5-η5-1-nitro-6-exo-(2-oxo-1-propyl)-cyclohexadienyl)(η5-cyclopentadienyl)iron (2a), isolated as a purple solid. Similarly, reaction of the nitrobenzene complex 1a with 3-pentanone in aqueous KOH gave two diastereomeric adducts, (R,R-S,S)- and (R,S-S, R)-(1-5-η5 1-niro-6-exo-(3-oxo-2-pentyl)-cyclohexadienyl)(η5-cyclopentadienyl)iron (11a, b). Reactions of the CpFe complexes of chlorobenzene and o- or p-dichlorobenzene with butanone in aqueous KOH were also investigated. In each case, three Janovsky adducts, two being diastereomers, were obtained from addition of the two carbanions derived from loss of either α-proton of butanone. Potential synthetic applications via these Janovsky adducts are pointed out since their treatment with ammonium ceric nitrate could lead to demetallation–oxidation; for example, (2,5-dichlorophenyl)propanone, a new compound, was obtained from the adduct formed between the p-dichlorobenzene complex and the acetonyl anion.
Pyridoxal and pyridoxal 5′-phosphate catalyzed β-deuteration of α-aminobutyric acid and homoserine. I. Metal-free systems
Authors: Tatsumoto Kuniyasu , Reddy Rabindra P. , Martell Arthur E.
Published: May 2006

As the initial step in the investigation of metal ion- and vitamin B6-catalyzed, β, γ-elimination in α-amino acids, the pyridoxal-and pyridoxal 5′-phosphate-catalyzed β-deuteration of α-aminobutyric acid and homoserine in D2O in metal-free systems has been studied by nuclear magnetic resonance. The reaction kinetics of α-H, β-H, and 4′-CH exchange rates were measured by following the rates of deuteration of these positions. The kinetic data obtained for these reactions lead to a proposed mechanism for β-deuteration. The relative rates of the deuteration reactions observed, and the order in which deuteration products were obtained are: α-H exchange > transamination (4′-CH exchange) > β-H exchange. The observed rates of β-proton exchange exhibit specific base catalysis and are dependent on the activation of the α-hydrogen of the amino acid moiety in the aldimine, and on the activation of the β-hydrogens of the amino acids in the ketimine.
Photoredox chemistry of nitrobenzyl alcohols in aqueous solution. Acid and base catalysis of reaction
Authors: Wan Peter , Yates Keith
Published: May 2006

The photochemistry of several m- and p-nitrobenzyl alcohols (1–5) has been studied in aqueous solution. These compounds react via an intramolecular photoredox pathway to give reduced and oxidized moieties of the substituent groups. The reaction is an example of a new type of photoreaction of nitro-substituted aromatic derivatives that is not observed in organic solvents, the presence of water being essential. This effect is exemplified by measuring the quantum efficiency as a function of mol% water in aqueous acetonitrile, methanol, and formamide: the reaction efficiency decreases rapidly as water is depleted in the mixture. Catalytic effects due to the hydronium and hydroxide ions were studied: the para derivatives exhibited hydroxide ion catalysis; the meta derivatives exhibited hydronium ion catalysis. Quantum yields, solvent isotope effects, and α-deuterium isotope effects are reported for the parent derivatives.
Autoxidation of phosphatidylcholines initiated with dicumylhyponitrite in solution and in bilayers
Authors: Barclay Lawrence Ross Coates , Kong David , VanKessel Joann
Published: May 2006

Dicumylhyponitrite (DCHN) was used as a thermal initiator of autoxidation of unsaturated phosphatidylcholines in o-dichlorobenzene and in mixed bilayers of dilinoleoylphosphatidylcholine (DLPC) with dimyristoylphosphatidylcholine (DMPC). Quantitative studies were made of the products, α,α-dimethylbenzyl alcohol (DMBA), acetophenone (AP), and dicumylperoxide (DCP) from DCHN. The ratio DMBA/Δ2DCHN (37 ± 6%) indicates the effectiveness of cumyloxy in hydrogen abstraction from the phospholipid in solution. The overall efficiency (e) of DCHN determined by the inhibitor method with α-tocopherol (α-T) was 84 ± 5%, close to the overall ratio (DMBA + AP)/Δ2DCHN (90 ± 6%), and indicates either significant initiation through the methylperoxy radical in o-dichlorobenzene solution or that α-tocopherol traps cumyloxy radical before β-scission occurs. The thermal decomposition rate constant of DCHN is greatly reduced in a medium of high viscosity; in DLPC to one-quarter, in Nujol to one-sixth that in isooctane and this is interpreted in terms of a one-bond scission of DCHN. In DLPC + DMPC mixed bilayers the effectiveness of the cumyloxy radical to initiate reaction varied from 30 to 19% depending on the amount of DLPC and in this medium there is little or no initiation by methylperoxy according to product analysis and α-T inhibition studies. In mixed bilayers, the rate of oxidation was directly related to the [DLPC] indicating that the classical rate law applies. The oxidizability of DLPC in mixed bilayers (0.046 M−1/2 s−1/2) is comparable to that of neat DLPC.
The visible absorption spectrum of 1,2-cyclobutanedione in the gas phase
Authors: Back R. A. , Parsons J. M.
Published: May 2006

The visible absorption spectrum of 1,2-cyclobutanedione has been measured in the gas phase at wavelengths between 4000 and 5100 Å. The absorption is attributed to the allowed π* ← n+, 1B1 ← 1A1 transition corresponding to the first excited singlet state. The spectrum shows a complex well-resolved vibrational structure which has been analysed, with some 125 bands measured and assigned. The bands at the longer wavelengths show sharp rotational fine structure, not yet analysed. The strongest band in the spectrum at 4933 Å has been assigned as the 0–0 band, while a band almost as strong at 4820 Å is attributed to excitation of one quantum of [Formula: see text], the a2 out-of-plane carbonyl bending vibration, and it is suggested that this band owes its intensity to vibronic coupling. A number of symmetric vibrations are also excited in the spectrum, but with no long progressions. Sequence bands running to the blue with an interval of about 72 cm−1 are prominent throughout the spectrum, and are assigned to v13, the a2 ring-twisting vibration. Other hot bands were also observed involving v13 which permitted estimation of energy levels for this vibration both in the ground state and the excited state. The infrared spectrum was also measured and analysed in the gas phase between 600 and 4000 cm−1, and 14 bands were assigned to fundamental vibrations; some of these assignments, at the lower frequencies, are uncertain.
An electron spin resonance study of the reactions of hydrogen atoms with halocarbons
Authors: Jones William E. , Ma Joseph L.
Published: May 2006

The absolute rate constants for the reaction of H atoms with methyl- and vinyl-halides have been determined using esr spectroscopy and a conventional gas flow system. The rate constants determined at 298 ± 2 K at a pressure of 0.55 Torr are methane, (1.7 ± 0.3) × 10−17; ethane, (2.3 ± 0.5) × 10−17; methylfluoride, (4 ± 3) × 10−15; methylchloride, (8 ± 2) × 10−16; methylbromide, (2.1 ± 0.6) × 10−14; vinylfluoride, (1.47 ± 0.02) × 10−13; vinylchloride, (1.66 ± 0.08) × 10−13; and vinylbromide (4.07 ± 0.73) × 10−13 in units of cm3 molecule−1 s−1.
The photochemical event in rhodopsins
Authors: Sandorfy C. , Vocelle D.
Published: May 2006

The photochemical step in the functioning of visual and bacterial rhodopsins entails cis–trans or trans–cis isomerization and changes in the state of protonation of the retinylidene Schiff base chromophore. In this review our present knowledge on these two events is discussed as well as the role of interactions between the chromophore and the surrounding protein, opsin. The relation between protonation and hydrogen bonding at the Schiff base nitrogen, the problems of stabilization of the proton bridge and charge separation are also discussed. A new proposal is made which implies Schiff base to counter-ion proton translocation with concomitant isomerization and reprotonation of the chromophore.
An infrared study of the interaction between ethyl N-(diphenylmethylene)glycinate with proton donors: comparison with N-benzylidenemethylamine
Authors: Ruysen Marleen , Zeegers-Huyskens Thérèse
Published: May 2006

The interaction between ethyl N-(diphenylmethylene)glycinate (DPG) and hydroxy proton donors or pyrrole has been investigated by ir spectrometry. The equilibrium constants, enthalpies, and entropies of complex formation have been determined in carbon tetrachloride solution and compared with the data obtained for the complexes involving N-benzylidene-methylamine and the same proton donors. The ir spectra studied mainly in the νOH, νC=N, νC=O, and νC—O regions suggest that hydrogen bond formation occurs at the N atom of the imino group and at the O atom of the carbonyl group. The results are discussed in terms of the basicity at the two acceptor sites and of the accessibility of the lone pair of electrons. The ir spectra of the solid adduct of DPG with HCl show that protonation takes place on the N atom. The protonated structure is possibly stabilized by an intramolecular hydrogen bond.
Configurational assignment of epimeric secondary six-membered allylic alcohols by 13C nuclear magnetic resonance spectroscopy. A new approach
Authors: Kaufman Teodoro S. , Mischne Mirta P. , Gonzalez-Sierra Manuel , Ruveda Edmundo A.
Published: May 2006

On the basis of the effects of the hydroxyl group on the 13C nuclear magnetic resonance chemical shifts of the olefinic carbons, a new parameter was defined and a new rule was proposed for the assignment of the stereochemistry of secondary six-membered cyclic allylic alcohols.
Electrostatic interactions as a factor in the determination of the HOMO in the liquid state
Authors: Marcos Enrique Sánchez , Maraver Joaquín , Ruíz-López Manuel F. , Bertrán Juan
Published: May 2006

An ellipsoidal cavity model has been used to study the energy changes in occupied molecular orbitals induced by solute–solvent electrostatic interactions. Some benzene derivatives have been selected as solutes. Calculations have been carried out at the CNDO and abinitio STO-4G levels. Important variations in the molecular orbital sequence, involving a change in the HOMO nature, have been observed. A perturbation analysis is employed to understand the orbital evolution from gas phase to solution.
A quantum approach to the mechanism of electrochemical reductions
Authors: Novoa Juan J.
Published: May 2006

Using the Hartree–Fock method and, in some cases, the second order Moller–Plesset perturbational method, with 4-31G, 4-31 + G, and 4-31 + G* basis sets, a first approach to the study of the mechanism of electrochemical reduction from formaldehyde to ethanol is presented. The total energy and optimized geometry of each of the molecules involved are also given. A proton–electron–proton–electron type mechanism is proposed.
Freeze-drying Fourier transform infrared attenuated total reflection spectroscopy of surface adsorbed layers. Water-assisted proton transfer in cytidine-5′-phosphoric acid
Authors: Badilescu Simona , Sandorfy Camille
Published: May 2006

The zwitterionic structure of cytidine-5′-phosphoric acid (5′-CMP) in the acid form has been studied by means of freeze-drying ATR spectroscopy. Surface deuteration and protonation studies of the hydrated sample were accomplished and some band assignments are made. The dependence of the proton transfer process in the zwitterionic CMP(H) on relative humidity is evidenced. The ability of the water molecules adsorbed on the thallium bromide iodide crystal to act as proton donors and the enhancement of the degree of dissociation of the adsorbed water are demonstrated.
Sulfoconjugation of dopamine. A critical examination of the reaction between dopamine and concentrated sulfuric acid
Authors: Jain Tikam , Kaiser Carl , Ackerman Dennis M. , Ladd David L. , Fong Kei-Lai , Roberts Gerald D. , Staiger David B. , Davis Louisa Lam , Webb R. Lee , Jackman Lloyd M.
Published: May 2006

Dopamine, a physiologically important biogenic amine, is readily sulfoconjugated in vivo to give the 3- and 4-O-sulfates of pharmacologic importance. A major synthetic source of these esters has involved reaction of dopamine with sulfuric acid; however, the homogeneity of the products of this apparently straightforward reaction has been questioned. For this reason, in the present study this reaction was studied in considerable detail and our results establish that the concern about the authenticity and purity of dopamine-O-sulfates used for pharmacological studies is justified. In addition to the esters, difficultly separable dopamine-2, -5, and -6-sulfonic acids, plus several unidentified products, were obtained. A detailed account of the isolation and physicochemical characteristics of the identified products is presented. The dopamine-O-sulfates, whose structures have recently been established unequivocally by single crystal X-ray diffractometric analysis in this laboratory, were further characterized by means of mass (electron impact, field desorption, and fast atom bombardment) and 1H and 13C nuclear magnetic resonance spectroscopy. In addition, redox potentials for the isolated reaction products, as well as high performance liquid chromatography, thin-layer chromatography, and color reactions of the dopamine-O-sulfates, are reported. Thermolysis of the 3- and 4-O-sulfates yielded similar mixtures of products.
Metabolites of the honey mushroom, Armillariamellea
Authors: Ayer William A. , Macaulay John B.
Published: May 2006

The fungus Armillariamellea (Vahl ex. Fr.) Kummer is responsible for severe losses in timber and fruit production. The metabolites isolated when certain strains of this fungus are grown in liquid culture have been identified as diterpenoid acids possessing the abietane (1) and pimarane (2) skeletons. These compounds, known collectively as resin acids, have not been reported previously from a fungal source. In addition to the resin acids dehydroabietic acid (3), pimaric acid (4), isopimaric acid (5), and sandaracopimaric acid (6), three additional acids, levopimaric acid endo-peroxide (7), 7-oxodehydroabietic acid (9), and 7-oxo-15-hydroxydehydroabietic acid (10) were obtained. On one occasion three orange pigments, austocystin F (11), averufin (12), and averufanin (13), all previously known fungal metabolites, were isolated.
Synthesis of 11-and 12-membered rings by a direct cyclization method
Authors: Brillon Denis , Deslongchamps Pierre
Published: May 2006

The malonate anion intramolecular displacement of propargylic or allylic chlorides, and of primary bromide, in eleven- and twelve-carbon chains containing either two, one, or no unsaturation centers leads to the corresponding 11- and 12-membered ring compounds in good yield under conditions of medium dilution.
Synthesis of 13- and 14-membered rings by a direct cyclization method
Authors: Brillon Denis , Deslongchamps Pierre
Published: May 2006

The malonate anion intramolecular displacement of propargylic or allylic chlorides, and primary bromide, in thirteen- and fourteen-carbon chains containing either two, one, or no unsaturation sites, yields the corresponding 13- and 14-membered ring compounds under conditions of medium dilution.
13C Nuclear magnetic resonance spectroscopy in the elucidation of structures of diterpenoid alkaloids
Authors: Joshi Balawant S. , Wunderlich John K. , Pelletier S. William
Published: May 2006

13C Nuclear magnetic resonance spectroscopy is an exceptionally useful tool for the structure determination of diterpenoid alkaloids. A detailed study of the 1H and 13C nmr spectra of aconitine and 3-deoxyaconitine has permitted definite assignments to all the carbon atoms of the molecule. Chemical shift revisions have been suggested for certain carbon atoms of the C19-diterpenoid alkaloids. Chemical examination of Aconitumcolumbianum Nutt. ssp. columbianum, A. forrestii Stapf, Delphiniumtatsienense Franch., and D. vestitum Wall, resulted in the isolation of several new C19-diterpenoid alkaloids. The structure derivation of those alkaloids was based mainly on 13C nmr spectroscopic evidence.
Directed ortho metalation reactions. Convergent synthesis of "angular" anthracyclinones ochromycinone and X-14881 C
Authors: Katsuura K. , Snieckus V.
Published: May 2006

Convergent syntheses of the benz[a]anthraquinone natural products X-14881 C (2c) and ochromycinone (2d) have been achieved using aromatic directed metalation strategies. Key steps involve (a) the condensations of dilithiated cis-tetralol (13a) with the aldehydo o-anisamide 14 and of methoxymethyl protected aldehyde 17b with lithiated o-anisamide (18) to give, after acid-catalyzed cyclization, the phthalide 16, and (b) the regiospeciflc hydroxyselenylation of anthraquinone 22 to provide the hydroxyselenide 23.
Spiro steroids via the Barbier–Grignard reaction of steroidal ketones with allyl bromide and magnesium
Authors: Paryzek Zdzislaw , Blaszczyk Krzysztof
Published: May 2006

Barbier–Grignard reaction of 3- and 17-steroidal ketones gave excellent yields of the allyl steroids 1 + 2 and 15. These were transformed into a mixture of 1,3- and 1,4-diols by hydroboration–oxidation. The diols 3,5, and 18 were used for the preparation of spirolactones and spiroethers. Thus, the Barbier–Grignard allylation–hydroboration–cyclization sequence proved to be an effective method for the spiroannelation of steroidal ketones. It was also shown that an earlier assignment of the stereochemistry of the diols 3 and 5 was erroneous.
Kinetics of the reaction of p-dinitrobenzene with basic hydrogen peroxide
Authors: Heller Raymond A. , Weiler Richard
Published: May 2006

Kinetic studies of the reaction of p-dinitrobenzene with H2O2 and NaOH in 10%, 30%, and 50% aqueous dioxane have been carried out at 30.0 °C. The reaction involves the formation of a reasonably stable intermediate which absorbs strongly in the visible region, with the rate of formation being about 18 times faster than the rate of conversion to final product which is p-nitrophenol. Proton and 13C nmr spectra of the kinetic solution provide strong evidence that the intermediate is p-nitrophenyl hydroperoxide, apparently the first time that a true aryl peroxide species has been identified.
Ultrasonic and thermodynamic studies of tetracyclines in solutions
Authors: Pandey J. D. , Mishra K. , Shukla A. , Rai R. D.
Published: May 2006

The ultrasonic velocity, U, density, and viscosity of aqueous and non-aqueous (water + dioxan) solutions of tetracycline hydrochloride and chlorotetracycline have been measured at two different temperatures. Partial molal volumes, [Formula: see text] partial molal compressibility, [Formula: see text], Vand's interaction coefficients, Q and C, and thermodynamic activation parameters ΔG*, ΔS*, and ΔH* of these solutions have been computed from the ultrasonic velocity, density, and viscosity data. The results are interpreted in terms of solute–solvent interaction.
Ultrasonic speeds and isentropic compressibilities of binary mixtures of n-octane with each of the hexane isomers at 298.15 K
Authors: Benson George C. , Halpin Carl J.
Published: May 2006

Measurements of ultrasonic speed were carried out for n-octane + each of the five hexanes at 298.15 K. The results were combined with excess molar volumes reported previously to obtain excess isentropic compressibilities and isentropic pressure derivatives of the excess molar volumes. These are in good agreement with estimates from the Flory theory of mixtures.
4,6-Dinitro-benzofuroxan and -benzofurazan adducts of 1,8-bis(dimethylamino)naphthalene. A conformational study by low temperature nuclear magnetic resonance
Authors: Simonnin Marie-Paule , Halle Jean-Claude , Pouet Marie-José , Terrier François , Davoust Daniel
Published: May 2006

Low temperature 1H nuclear magnetic resonance spectra of the zwitterionic and anionic carbon-bonded adducts resulting from the addition of 4,6-dinitrobenzofuroxan (DNBF) or 4,6-dinitrobenzofurazan (DNBZ) to 1,8-bis(dimethylamino)naphthalene, the proton sponge PS, have been recorded at 500 MHz inDMF-d7. They reveal the presence of two conformers due to restricted rotation around the [Formula: see text] bond between C-4 of PS and the sp3 carbon C-7′ of the negatively charged DNBF− or DNBZ− moiety. The geometry of these conformers was deduced from nuclear Overhauser enhancement difference spectra. The results show that in all systems there is a large preference for the less strained s-trans type of conformation, whose population lies between 80 and 90%. An interesting feature is the dependence of the chemical shift of the peri H5 proton on the conformation. In accordance with previously reported peri effects, a significant deshielding of H5 is observed in the major conformers, where this proton is spatially close to H7′. In contrast, H5 moves upfield in the minor conformers, in which it lies in the vicinity of the DNBF− or DNBZ− moiety.
The rapid synthesis of deoxyfluoro sugars using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF)
Authors: Doboszewski Bogdan , Hay George W. , Szarek Walter A.
Published: May 2006

Deoxyfluoro sugars were synthesized rapidly by the reaction of trifluoromethanesulfonyl derivatives of partially protected sugars with tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) under mild conditions. The displacements occurred with inversion of configuration; fluorine has been introduced stereospecifically at each of the secondary alcoholic sites of aldohexopyranosides and in one example of a furanoid system. In some instances unsaturated compounds that contained no fluorine were produced.
The dynamics of the reaction of F atoms with trans-diimide
Authors: Back R. A. , Neudorfl P. S. , Sloan J. J. , Wassell P. T.
Published: May 2006

Emission from the HF product of the reaction F + N2H2 has been measured in an arrested-relaxation infrared chemiluminescence experiment. The vibrational distribution is inverted, peaking in HF(ν′ = 2). This energy partitioning indicates that the reaction occurs without the formation of a long-lived intermediate species. The detailed shape of the primary energy distribution could not be determined due to severe difficulties in the production of N2H2.
Side chain hydroxylation of aromatic compounds by fungi.: 1. Products and stereochemistry
Authors: Holland Herbert L. , Bergen Eleanor J. , Chenchaiah P. Chinna , Khan Shaheer H. , Munoz Benito , Ninniss Ronald W. , Richards Denise
Published: May 2006

The fungus Mortierellaisabellina can convert ethylbenzene and a number of para-substituted derivatives to the corresponding optically active 1-phenylethanols with enantiomeric excesses between 5 and 40% and chemical yields up to 45%. 2-Ethylnaphthalene, 2-ethylthiophene, and n-propylbenzene were similarly converted, as were the bicyclic compounds indane and tetralin. In most cases, the R absolute configuration of product predominated. The fungi Cunninghamellaechinulata var. elegans and Helminthosporium species are also capable of performing some of these transformations. M. isabellina and C. elegans also produce 2-phenylethanols as products in some cases. The highest enantiomeric excesses during benzylic hydroxylation were obtained with Helminthosporium and are attributable, at least in part, to further stereoselective oxidation of the alcohol. Cross induction experiments with M. isabellina indicate that the same enzyme may be responsible for the benzylic hydroxylation of ethylbenzene, 2-ethylthiophene, and 2-ethylnaphthalene.
Relations entre les tungstophosphates apparentés à l'anion PW12O403−. Synthèse et propriétés d'un nouveau polyoxotungstophosphate lacunaire K10P2W20O70•24H2O
Authors: Contant Roland
Published: May 2006

The relationship between all the polyoxotungstophosphates related to PW12O403− and P2W21O716− anions was established. A new compound K10P2W20O70 was synthesized and characterized by infrared and Raman spectroscopy. These properties, and especially the 31P and 183W nuclear magnetic resonance spectra, allowed us to propose the structure. It is a lacunary species that reacts with Co(II) to give two 1–1 complexes, probably coordination isomers. In the presence of Co(II) the A-type → B-type PW9 isomerization occurs in several steps, which are specified. The tungstophosphate β isomers are less stable than the corresponding tungstosilicates or germanates, and β-PW12 was only identified as a reduced species PW12O404−.
Synthesis of yomogin, 1-deoxyivangustin, and 1-deoxy-8-epiivangustin
Authors: Marco Juan Alberto , Arno Manuel , Carda Miguel
Published: May 2006

The chemical transformation of (−)-artemisin 1 into the natural sesquiterpene lactones yomogin 2, 1-deoxyivangustin 3, and 1-deoxy-8-epiivangustin 4 is described.
Spectroscopic evidence for surface hydronium (H3O+) ions on hydrated single crystals
Authors: Bădilescu Simona , Sandorfy Camille
Published: May 2006

Evidence has been obtained by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) for the existence of hydronium ions on the surfaces of hydrated single crystals. The band near 1740 cm−1 due to the ν4 (e) bending vibration of the hydronium ion has been identified on silicon, germanium, thallium bromide iodide (KRS-5), and zinc selenide single crystals. The protonating capability of these hydronium ions was demonstrated with pyridine derivatives.
The preparation and characterization of polysulfanotungsten complexes of the type (η5-C5H5)W(CO)3SxR, where x = 2, 3 and (η5-C5H5)W(CO)3SS(O)R, where R = CH2C6H5, p-C6H4CH3
Authors: Shaver Alan , Hartgerink Judy
Published: May 2006

The polysulfano complexes (η5-C5H5)W(CO)3Q, where Q = SSR, SSSR, SS(O)R, and R = CH2C6H5 and p-C6H4CH3 have been prepared via treatment of (η5-C5H5)W(CO)3SH with RSphth, RSSphth, and RS(O)phth, respectively, at −20 °C, where phth = N-phthalimido. The complexes where Q = SSR and SSSR lost sulfur spontaneously in solution to give the thiolato complexes (η5-C5H5)W(CO)3SR and the disulfano complexes, respectively. The presence of PPh3 accelerated this reaction for Q = SSR. Treatment of (η5-C5H5)W(CO)3SSR with m-chloroperbenzoic acid gave a mixture of complexes for which Q = SR, SO2R, SS(O)R, and higher oxidized sulfur ligands. As(C6H5)4[W(CO)5SH] reacted with p-CH3C6H4Sphth to give an unstable first product, tentatively identified as As(C6H5)4[W(CO)5SS-p-C6H4CH3], the isolated product being As(C6H5)4[W(CO)5S-p-C6H4CH3].
Preparation, properties, and characterization of methanesulfonato complexes of arsenic(III), antimony (III), and bismuth(III)
Authors: Kapoor Ramesh , Wadhawan Poonam , Kapoor Pratibha
Published: May 2006

Arsenic(III), antimony (III), and bismuth(III) oxides, sodium arsenite and bismuthate react with methanesulfonic anhydride, (CH3)2S2O5, to yield M(SO3CH3)3 (M = As(III), Sb(III), and Bi(III)), Na[AsO(SO3CH3)2], and Na[Bi(SO3CH3)4], respectively, in quantitative yield. Reaction of arsenic(III) oxide with pure methanesulfonic acid yields oxo(methanesulfonato)arsenic(III), AsO(SO3CH3), which behaves as a non-electrolyte in 100% methanesulfonic acid. The compounds have been characterized by elemental analysis, conductance, infrared, 1H nmr and thermal measurements. Their properties have been studied by ligand substitution and complex formation reactions. The M(SO3CH3)3 (M = As(III), Sb(III), and Bi(III)) compounds are capable of functioning both as Lewis acids and bases. These compounds exhibit basic behaviour in 100% methanesulfonic acid. The synthesis of complex mathanesulfonates Cs[M(SO3CH3)4] (M = As(III), Sb(III), and Bi(III)) is also described.
A theoretical study of the structures and stabilities of C2H3S+ ions
Authors: Rodriquez Christopher F. , Hopkinson Alan C.
Published: May 2006

Abinitio molecular orbital calculations at the 6-31G* level have been used to locate eight minima and five saddle points on the C2H3S+ hypersurface. The thioacetyl ion, H3CCS+ (1), is the global minimum and the 1-thiovinyl cation (4), 106 kJ mol−1 higher, is the next lowest. Interconversion of 1 and 4 has the highest barrier calculated for this surface (250 kJ mol−1 above 4) but all transition structures to intramolecular rearrangement are lower than the energies of the dissociation products. These results are consistent with the experimental observation that there is only one dissociation channel for ions C2H3S+, regardless of the structure of organosulphur compound from which C2H3S+ was produced. Comparisons are made with the C2H3O+ hypersurface.
Relationship between gas-phase proton affinities of conjugate bases B's and free energies of hydration of conjugate acid ions BH+'s for B = alkyl-substituted H2O and NH3
Authors: Hiraoka Kenzo
Published: May 2006

An approximate linear relationship between the proton affinities of conjugate bases (B's) and the free energies of hydration of conjugate acid ions (BH+'s) is found for B = alkyl-substituted H2O and NH3. With increase in proton affinities, the free energies of hydration increase linearly with a slope of about 1 for analogous compounds. The charge derealization in the protonated bases and the structure-making effect induced by the hydrophobic groups in the alkyl-substituted H3O+ and NH4+ are crucial factors in the determination of the free energies of hydration.
Diels–Alder reactions of 4,4-dimethyl-2-cyclohexenones. A direct route to the 4,4-dimethyl-1-decalones
Authors: Liu Hsing-Jang , Browne Eric N. C.
Published: May 2006

Diels–Alder additions to enones 1 and 2, synthetic equivalents of the synthon 3, were studied using a variety of hydrocarbon dienes. The two enones have been shown to be effective and synthetically useful dienophiles. Spectroscopic (especially 1H and 13C magnetic resonance) and chemical techniques were used to define unambiguously the full structures of the adducts. The structures of the various reaction products were used to draw qualitative conclusions about the nature of the transition states involved and the various electronic and steric effects that play a role in the mechanistic course of the Diels–Alder reaction.
Étude conformationnelle de cétopipérazines: (I) 3R-méthyl-6-carbéthoxy-2 oxopipérazine, (II) 3R-[p-hydroxybenzyl]-6-carbéthoxy-2 oxopipérazine: I, II en solution et structure cristalline de II
Authors: Michel André , Evrard Guy , Norberg B.
Published: May 2006

The synthesis of the title compounds has been described recently. It was anticipated that the product would be a diastereomeric mixture. Surprisingly, only one isomer was obtained. The present work is an attempt to find the conformationnal properties accounting for those observations. X-ray structure determination of 3R-[p-hydroxybenzyl]-6-carbethoxy-2-oxopiperazine shows that the molecule adopts a folded conformation and that the absolute configuration at C6 is [R]. Investigation in solution using 1H nuclear magnetic resonance shows the existence of three conformers and discusses the relative populations. Those findings are also relevant in terms of the activity of such compounds at the opiate receptor level.
Adsorption de l'azote sur l'amiante chrysotile phosphaté et lixivié
Authors: Khorami Jaleh , Noel Luc , Ménard Hugues
Published: May 2006

Adsorption and desorption isotherms of nitrogen, obtained by the volumetric (B.E.T.) method, have been used to determine the specific surface and the porosity of a series of chrysotile asbestos fibers, before and after chemical treatments. It was shown that the phosphorus compounds that are formed by the reaction of POCl3 and chrysotile asbestos seal the surface of the fibrils and block the pores between the fibrils. These chemical modifications result in an important diminution of the specific surface and of the porosity of the fibers. Washing the fibers with 0.1 M HCl results in an increase of the specific surface and of the porosity. Solvation of the impurities and leaching of the brucitic surface of the fibers are responsible for this increase. [Journal translation]
Interactions du Cu(II), du Hg(II) et du Pt(II) avec les formes monomères et dimères de la thymine, de la thymidine et de l'acide orotique
Authors: M'Boungou Raoul , Petit-Ramel Michelle , Thomas-David Germaine , Perichet Gérard , Pouyet Bernard
Published: May 2006

The protonation constants of monomeric (TM) and dimeric (TD) forms of thymine and monomeric (OM) and dimeric (OD) forms of orotic acid and thymidine (TY) have been calculated at 25 and 37 °C and at ionic strength μ = 0.1 (NaNO3). Under the same conditions the stability constants of their Cu(II), Hg(II), and Pt(II) complexes have been determined by protometric methods. The results have been discussed and a comparison has been established in terms of binding sites: nitrogen N3 for monomeric and dimeric forms of thymine and thymidine; carboxylate anion at C6 and adjacent ring nitrogen N1 for monomeric and dimeric forms of orotic acid.
The synthesis of 3-carboxymethyleneazetidinones
Authors: Hinz Werner , Just George
Published: May 2006

A series of novel azetidinones bearing the methoxycarbonylmethylene, thioethoxycarbonylmethylene, and alkylaminocarbonylmethylene side chain in their three position have been synthesized from the reaction of the potassium salt of 4,4′-bis(thioethoxy)-3-butenoic acid with a number of Schiff bases.
Caractérisation et spectres de vibration du sulpiride
Authors: Maury Luc , Delarbre Jean-Louis , Rambaud Joëlle , Pauvert Bernard
Published: May 2006

The authors have characterized two forms for sulpiride by infrared spectroscopy and Raman scattering (lattice vibrations). An assignment of the fundamental vibrations of the amide and sulfonamide groups involved in the inter or intramolecular hydrogen bonds has been proposed. Comparison of the sulpiride chlorhydrate spectra with those of sulpiride indicates that the chlorhydrate itself will be in the chelated form.
Acid-catalyzed rearrangement of cyclobutanols. A novel rearrangement
Authors: Lee-Ruff E. , Ablenas Fred J.
Published: May 2006

The acid-catalysed dehydration–rearrangement reaction of α-thienyl cyclobutanols 3 and 4 resulted in the formation of tetrahydronaphtho[2,3-b]thiophenes 5a and 6a. The rearrangement to the linearly fused PAH system instead of the expected angularly fused system reflects α-scission of the cyclobutyl ring. A mechanism based on deuterium labelling studies is proposed to account for the product formation.
Metallacyclohexasulfanes: the crystal and molecular structures of (η5-C5H5)2MS5, M = Zr and Hf
Authors: Shaver Alan , McCall James M. , Day Victor W. , Vollmer Sarah
Published: May 2006

The crystal and molecular structures of (η5-C5H5)2ZrS5, 2, and (η5-C5H5)HfS5, 3, have been determined by single crystal diffractometry methods. Both compounds crystallized with four molecules in a monoclinic unit cell of dimensions: a = 8.984(3) Å, b = 13.336(4) Å, c = 11.421(2), β = 93.10(2)° for 2, and a = 9.012(2) Å, b = 13.291(2) Å, c = 11.381(2) Å, β = 93.25(1)° for 3; the space group is P21/n for both. These crystals of 2 and 3 are thus isomorphous with those of (C5H5)2TiS5, 1, studied by Epstein etal. (3a). The structures of all three complexes are very similar consisting of a cyclohexane-like six-membered MS5 ring with two C5H5 rings attached to the metals in an axial and equatorial position. The coordination spheres of 2 and 3 are less crowded than that of 1. The consequences of this are discussed with respect to the barriers to ring inversion in these complexes.
The syntheses of mono- and disubstituted phthalocyanines using a dithioimide
Authors: Leznoff Clifford C. , Greenberg Shafrira , Khouw Ben , Lever A. B. P.
Published: May 2006

Hydrolysis of 5-neopentoxy-1,3-diiminoisoindoline gave 5-neopentoxy-1H-isoindole-1,3(2H)-dione (4-neopentoxyphthalimide), which, on treatment with Lawesson's reagent, yielded the thiophthalimides, 5-neopentoxy-1H-isoindole-1,3(2H)-dithione, 2,3-dihydro-6-neopentoxy-3-thioxo-1H-isoindol-1-one, and 2,3-dihydro-5-neopentoxy-3-thioxo-1H-isoindol-1-one. Attempted S-alkylations of the thiophthalimides resulted in the formation of β-isoindigos and N-alkylation products. In a new phthalocyanine synthesis crossed condensations of 1,3-diiminoisoindoline with 5-neopentoxy-1H-isoindole-1,3(2H)-dithione yielded mixtures of phthalocyanines from which 2-neopentoxyphthalocyanine and 2,16-dineopentoxyphthalocyanine could be purified in part from other phthalocyanines.
A carbon-13 nuclear magnetic resonance study of the basicities of aliphatic alcohols
Authors: Lee Donald G. , Demchuk Kenneth J.
Published: May 2006

Carbon-13 nmr chemical shifts have been used to determine the basicity constants for nine alcohols. The method involves comparing the chemical shifts for carbon atoms adjacent to the site of protonation with those for carbon atoms in a more remote position. The differences in the chemical shifts (Δ values) at different acidities are then used to calculate basicity constants for the alcohols. The pKBH+ values, determined by use of the "X function" are as follows: ethanol −2.12, 1-propanol −2.12, 3-chloro-1-propanol −2.24, 2-chloroethanol −2.45, 2-bromoethanol −2.41, 2-nitroethanol −2.09, 2-methoxyethanol −1.93, 2-phenoxyethanol −1.87, and 2-propanol −2.06. The typical slope parameter, m*, is 0.17. Two linear free energy correlations are obtained: when the alcohols are considered to be a series of monosubstituted ethanols, the Hammett plot has a slope of 0.65; when they are considered to be a series of mono- and disubstituted methanols, the slope is 1.7. Alcohols bearing oxygen-containing substituents are more basic than predicted by about 0.5 pK units, presumably because their conjugate acids can be stabilized by intramolecular hydrogen bonding.
1H and 13C nuclear magnetic resonance assignment of fluorescent olefinic sterol derivatives for use as membrane probes
Authors: Drew Jacinta , Brisson Jean-Robert , Morand Peter , Szabo Arthur G.
Published: May 2006

A number of fluorescent steroids with unsaturated sidechains have been analyzed by high resolution 1H and 13C nmr spectroscopy. The geometry of the olefinic systems was assigned on the basis of 1H–1H shift-correlated spectra (COSY) and selected nOe difference experiments. For one of these compounds, a 13C–1H shift-correlated spectrum, a COSY spectrum, a 1H J-resolved spectrum as well as nOe experiments on the angular methyl groups permitted complete ring proton assignment and coupling constant analysis. The high degree of similarity of the ring carbon 13C chemical shifts of these steroids and cholesterol would indicate that the former have the potential for use as fluorescent probes of cholesterol domains in membranes.
Studies in iridoid chemistry and spruce budworm (Choristoneurafumiferana) antifeedants
Authors: Chan T. H. , Zhang Y. J. , Sauriol F. , Thomas A. W. , Strunz G. M.
Published: May 2006

Several compounds derived from aucubin and catalposide were prepared and tested for spruce budworm antifeeding activities. Definite biological activity was observed for compound 11.
Hydration of acylimidazoles: tetrahedral intermediates in acylimidazole hydrolysis and nucleophilic attack by imidazole on esters. The question of concerted mechanisms for acyl transfers
Authors: Guthrie J. Peter , Pike David C.
Published: May 2006

Heats of hydrolysis have been measured for three acylimidazole acetals. From these results free energies of formation in aqueous solution have been calculated for the acetals and the corresponding tetrahedral intermediates. Having free energies of formation for the tetrahedral intermediates allows a detailed analysis of the energetics of both the unobservable nucleophilic reaction of imidazole with ethyl acetate and also the observable reaction of imidazole with p-nitrophenyl acetate. pKa values of 1-(3-aminopropyl)-imidazole and 1-(2-aminoethyl)-imidazole have been determined to allow calculation of the σ* value for the imidazolyl substituent. The dependence of imidazole pKa values on the electron-withdrawing properties of the 1-substituent was also determined. There is a linear free energy relation between the free energy change for replacement of OH in a carbonyl hydrate by imidazolyl and the sum of the σ* values for the other substituents. The implications of these results for the question of concerted versus stepwise mechanisms for the reactions of imidazole with aryl acetates have been examined. An equilibrium constant has been calculated for the addition of imidazole to p-nitrophenyl acetate. A simple extension of Marcus theory allows the free energy surface for a three-dimensional reaction coordinate diagram to be calculated using the energy levels of the tetrahedral intermediate determined in this work, the energy level of the acylium ion derived from literature data, and intrinsic barriers for the edge reactions. It is shown that the reaction of imidazole with p-nitrophenyl acetate probably follows a concerted path. General conclusions from this theory of concerted reactions are discussed.
A theoretical insight into the insertion reaction of singlet methylene to the hydrogen molecule
Authors: Ortega M. , Lluch J. M. , Oliva A. , Bertran J.
Published: May 2006

The least-motion and non-least-motion energy profiles for the insertion reaction of singlet methylene into the hydrogen molecule have been calculated using the 6-31G* basis set and introducing the correlation energy with the Møller–Plesset perturbation theory and with the MC-SCF technique. From the results obtained the effect of geometry optimization including electron correlation on the shape of the energy surface is discussed. The building up of a bidimensional biconfigurational energy surface has permitted one to interpret the opening of the methylene angle during the least-motion process as a direct consequence of the change in the electronic configuration. The TC-SCF/6-31G* second order transition structure for this forbidden process has been directly located using gradient minimization methods.
Crystal and molecular structure of 8-acetamido-2,4,4,8-tetramethyl-3-azaniumbicyclo[3.3.1]non-2-ene perchlorate
Authors: Viturro H. R. , Rivero B. E. , Piro O. E. , Caram J. A. , Martins M. E. , Marschoff C. M.
Published: May 2006

X-ray single crystal analysis sheds further light on the structure of this new iminium salt. ATABNEP crystallizes in the monoclinic system, space group P21 and shows a very short value for the C—N distance in the iminium group, thus suggesting that the contribution of the carbonium ion form in this particular case is much lower than usual, a fact that can be considered a rationale for the reluctance of ATABNEP to undergo hydrolysis.
Electron transfer reactions. Reaction of nitrones with potassium
Authors: Ashok Konda , Scaria Pallikkaparambil M. , Kamat Prashant V. , George Manapurathu V.
Published: May 2006

Treatment of nitrones (1a–d, 26a,b, 34, 49) with potassium in tetrahydrofuran (THF) gives rise to radical anion (2a–d, 27a,b, 35, 50) and dianion intermediates (3a–d, 28a,b, 36) through electron transfer reactions. These intermediates undergo further transformations to give a variety of products. Thus, the aldehydonitrones (1a–d) give the corresponding aldehydes (10a–c), carboxylic acids (25a–c), and azobenzenes (19a,d), whereas the ketonitrones (26a,b) give deoxygenation products (31a,b). The nitrone 34 gave a mixture of products consisting of benzoic acid (25a), dibenzyl (48), the dimeric product 38, and tetraphenylpyrazine (46), whereas 49 did not give any isolable product. Cyclic voltammetric studies have been employed to measure the reduction potentials for both one-electron and two-electron transfer processes, leading to the radical anions and dianions respectively. These intermediates have been characterized through their electronic spectra and they were quenched by oxygen. Pulse radiolysis of the nitrones 1a–d, 26a,b, 34, and 49 also gave the corresponding radical anions 2a–d, 27a,b, 35, and 50, characterized by their spectra.
An electrochemical and spectroelectrochemical study of substituted alkylidenecyclopropabenzenes: 1-(diphenylmethylene)cyclopropabenzene in the first anodic and cathodic voltammetric waves in acetonitrile
Authors: Ashley Kevin , Sarfarazi Fereshteh , Buckland Simon J. , Foley John K. , Mei Qui , Halton Brian , Stang Peter J. , Pons Stanley
Published: May 2006

Electrochemical and modulated specular reflectance spectroelectrochemical (MSRS) investigations were performed on 1-(diphenylmethylene)cyclopropabenzene in nominally dry acetonitrile solution. The results indicate the formation of a stable anion radical (λmax = 587 nm) and a quasi stable cation radical (λmax = 473 nm). The first order homogeneous rate constant for the decay of the cation radical was computed.
A nuclear magnetic resonance relaxation study of liquid hydrogen cyanide
Authors: Wasylishen Roderick E.
Published: May 2006

The rates of 2H, 13C, and 14N spin-lattice relaxation for liquid deuterium cyanide have been studied as a function of temperature. The quadrupolar nuclei relax exclusively by the quadrupolar relaxation mechanism while the rate of 13C and 15N relaxation is completely dominated by the spin-rotation mechanism. The apparent activation energy that describes the temperature dependence of spin-lattice relaxation for all nuclei studied is approximately 1.6 kcal mol−1. The temperature dependence of the rate of 13C relaxation in liquid HCN was also investigated. Although the determination of very accurate rotational and angular momentum correlation times is hampered by intermolecular effects on the nuclear quadrupolar coupling constants and the appropriately averaged C—H bond separation, the derived correlation times for DCN and HCN are in reasonable agreement (± 15%).
The constitution and properties of a pyochelin–zinc complex
Authors: Cuppels Diane A. , Stipanovic Robert D. , Stoessl Albert , Stothers J. B.
Published: May 2006

The siderophore pyochelin, identified for the first time as a metabolite of Pseudomonasfluorescens, was isolated in highly pure form as a dimeric complex with two zinc atoms. The 1H and 13C magnetic resonance data for the two pyochelin moieties of the complex differ significantly from each other and from those of free pyochelin. The complex also exhibits unusual solubility and stability properties. Since it is easily isolable and can be readily converted into highly pure, free pyochelin, it offers an excellent entry to further biological studies on this important metabolite.
Diels–Alder reactions of methyl-N-acyl-α,β-dehydroalaninates with cyclopentadiene
Authors: Bueno M. P. , Cativiela C. , Finol C. , Mayoral J. A. , Jaime C.
Published: May 2006

A study has been made of the Diels–Alder reaction of methyl-N-acetyl (and benzoyl)-α,β-dehydroalaninates with cyclopentadiene. In the reaction of methyl-N-acetyl-α,β-dehydroalaninate total conversion is obtained under several conditions, while the N-benzoyl derivative shows a lower reactivity. The stereoselectivity of the reaction is determined by 1H nuclear magnetic resonance spectroscopy. Perturbation MO calculations, using wave functions generated by the MNDO method, are used to rationalize the relative reactivity of the dienophiles and the stereoselectivity observed.