bluuebunny/crossref_metadata_2025 huggingface dataset:
A phosphorus-31 nuclear magnetic resonance spectroscopic study of complexes of zinc with some phosphine oxides, sulfides, and selenides
Authors: Dean Philip A. W. , Carson Geetha K.
Published: May 2006

Zn(SbF6)2 in liquid SO2 has been shown to act as an acceptor towards a variety of phosphine oxides, sulfides, and selenides, forming complexes which have been characterized in solution using 31P nmr. Slow-exchange 31P nmr spectra are reported for the complexes ZnLn2+ (n = 6, L2 = Ph2P(O)CH2P(O)Ph2 or L3 = (Ph2P(O)(CH2)2)2P(O)Ph; n = 4, L2 = Ph2P(E)CH2P(E)Ph2 (E = O, S, or Se) or bidentate (Ph2P(E)CH2)3CMe (E = S or Se), or L = (C6H11)3PE (E = O, S, or Se) or R3PE (E = S or Se, R = Ph or o-C6H4Me); n = 3, L3 = (Ph2P(E)(CH2)2)2P(E)Ph (E = S or Se) or L = R3PE (E = S or Se, R = C6H11, Ph, or o-C6H4Me); n = 2, L = R3PE (E = S or Se, R = o-C6H4Me or, perhaps, C6H11); n = 1 (possibly), L = (o-C6H4Me)3PS), and partial spectra for [Zn(SeP(C6H11)3)x(SP(C6H11)3)n−x]2+ (n = 3 or 4). No evidence was found for the mixed oxide-chalcogenide species [Zn(EP(C6H11)3)x(OP(C6H11)3)4−x]2+. In most cases the 31P nmr spectra are very similar to those reported earlier for the corresponding cadmium complexes. However, in most instances where comparison could be made it was found that the rate of intermolecular ligand exchange was less for the zinc complexes than for their cadmium counterparts. (Complexes with (Ph2P(O)(CH2)2)2P(O)Ph and Ph2P(O)(CH2)2P(O)Ph2 arc exceptional in being more labile for zinc than cadmium.)
Régiosélectivité d'additions de nucléophiles sur des dialkoxycarbonyle quinoxalinotropones
Authors: Turck Alain , Boutte Roland , Quéguiner Guy
Published: May 2006

We have studied the regioselectivity of Michael type additions on tropones attached to quinoxalines, i.e. dialkoxycarbonyl quinoxalinotropones. We used carbon nucleophiles (ethyl malonate and malononitrile), oxygen nucleophiles (sodium methoxide), sulphur nucleophiles (methyl and benzyl mercaptans), and nitrogen nucleophiles (methyl and phenylhydrazine, aniline). We have shown that, in general, these reactions lead to 1,4-monoadditions or to bridged products arising from a bis-1,4-addition process. We have determined the structures of the complexes obtained by comparison to the work of Fohlisch etal. in the homoaromatic series. For the case of substituted hydrazines, we present some evidence on the rearrangement mechanisms proposed by these authors. [Journal translation]
Molecular conformation of di-o-anisylcarbinol: an X-ray diffraction study
Authors: Faerman C. , Negri H. , Punte G. , Vitale A. A. , Nudelman N. S.
Published: May 2006

Di-o-anisylcarbinol crystallizes in the triclinic system, space group [Formula: see text] with a = 7.50 (4), b = 10.89 (4), c = 7.98 (3) Å, α = 101.9 (1), β = 94.1 (1), γ = 94.6 (1)°, Z = 2, V = 633.11 Å3, Dc = 1.28 mg m−3, Dm = 1.26 (1) mg m−3, CuKα radiation, λ = 1.54178 Å, μ(CuKα) = 0.633 mm−1, F(000) = 260. The structure has been determined by direct methods using single crystal X-ray data and refined by least-squares to the final R factors R = 5.89% and Rw = 5.35%. The molecule has a twist-skewed conformation with the phenyl rings on nearly orthogonal planes. The crystal structure shows a hydrogen-bonded dimer and a peculiar arrangement of the methoxy and phenyl groups.
Dielectric evidence for the formation of a clathrate hydrate by sulfuryl chloride
Authors: Gough S. R. , Ripmeester J. A. , Davidson D. W.
Published: May 2006

A hydrate formed by SO2Cl2 at −20 °C is shown by its low temperature dielectric absorption to be a structure II clathrate hydrate. The activation energy for reorientation of encaged SO2Cl2 molecules is 1.1 kcal mol−1 between 19 and 41 K.
Hydrolysis rates of some acetylimidazole derivatives
Authors: Gour-Salin B. J.
Published: May 2006

N-Acetylbenzimidazole (4), N-acetyl-N′-methylbenzimidazolium acetate (5), and N-acetyl-N′-methyltetrahydrobenzimidazolium acetate (6) were synthesized and their hydrolysis rates were studied.
Condensed-phase reactions of O3 with NH3 and NH2OH
Authors: Huston Theresa , Hisatsune I. C. , Heicklen Julian
Published: May 2006

The reactions of O3 with NH3 and NH2OH were studied in the condensed phase. A yellow ozonide was formed immediately upon the addition of O3 to the NH2OH solid maintained at −190 °C, but the yellow–orange ozonide seen in the NH3 case was not formed until the system was warmed to −170 °C. These ozonides could be reconverted to reactants by photolysis with near ultraviolet light or by heating to −90 °C (NH3+O3−) or −115 °C (NH2OH+O3−).Upon warming the NH3–O3 system to −130 °C, NH4NO3•3NH3 appeared. It started to deamminate at about −105 °C to give NH4NO3. In the NH3–O3 system a second species, tentatively identified as NH2O+HO2−, was also formed at −170 °C. It began to decompose with the evolution of O2 at about −10 °C.In the NH2OH–O3 system, HNO3 was also seen immediately upon addition of O3 to NH2OH. It appeared as NH2OH•HNO3, a hydrogen-bonded complex with NH2OH. At about −100 °C, NH2OH started to anneal and the NH2OH•HNO3 bands grew rapidly and converted to NH3OH+NO3−.There was no evidence of NH2OH as an intermediate in the NH3–O3 system, but since NH2OH reacted so readily with O3, this possibility could not be ruled out. These ozonolysis reactions may be represented as[Formula: see text]and[Formula: see text]
Solvolytic studies with 2-methyl[1-13C]-1-propyl tosylate
Authors: Lee Choi Chuck , Zohdi Hussein F.
Published: May 2006

Solvolysis of 2-methyl[1-13C]-1-propyl tosylate was carried out in HOAc or CF3COOH without or with the presence of 2.0 equivalents of NaOAc or CF3COONa, respectively. Isobutyl, sec-butyl and tert-butyl products were obtained. With the use of 13C as label, isotopic scramblings were analyzed by 13C nmr, avoiding the necessity of chemical degradations associated with the use of 14C. There was no isotopic scrambling in the isobutyl product and scrambling of the 13C-label was observed only between C-2 and C-3 in the sec-butyl product, indicating 1,2-hydride shifts in the sec-butyl cation. In contrast to the involvement of equilibrating protonated methylcyclopropane intermediates observed in the trifluoroacetolysis of [1-14C]-1-butyl tosylate, the present results indicated that protonated methylcyclopropane intermediates did not play a significant role in the acetolysis or trifluoroacetolysis of isobutyl tosylate.
Réduction électrochimique de cétones aromatiques encombrées en milieu aprotique et en présence de chlorure de manganèse
Authors: Fournier Françoise , Berthelot Jacques , Pascal Yves-Louis
Published: May 2006

The electrochemical reduction of hindered aromatic ketones which are difficult to reduce can be achieved in an aprotic medium (DMF) on a mercury pool cathode, in presence of Mn(II) chloride, at the reduction potential of the Mn(II)/Mn(0) system, but less negative than that of the ketone itself. There is selective hydrodimerization into an α-glycol, with total lack of polymerization. With dissymmetric ketones, the dl diastereoisomers of the diols are produced preferentially. The effect of manganese is due either to the reduction of a Mn(I) or Mn(0) – ketone complex or to the reduction of the ketone by a film of colloidal manganese on the electrode surface.
Thiirene formation in the reactions of sulfur atoms with alkynes
Authors: Verkoczy Bela , Sherwood Alden G. , Safarik Imre , Strausz Otto P.
Published: May 2006

The gas phase reactions of S(1D2) and S(3PJ) atoms with alkynes have been studied by photolyzing COS in the presence of CH≡CH, CF3C≡CH, and CF3C≡CCF3. In the reactions with CH≡CH, CS2, benzene, and thiophene were formed; with CF3C≡CH, eight products were found with disubstituted thiophenes and trisubstituted benzenes as the major products. In the case of CF3C≡CCF3, only perfluorotetramethylthiophene was detected at low conversion but at long photolysis several new products were observed. Many of the reaction products characterized here have not been reported before.The formation and distribution of the reaction products could be rationalized by an overall mechanism in which the formation of the highly reactive primary adducts, thiirene and thioformylmethylene, is followed by bimolecular reactions yielding the principal end products. The formation of minor products could be explained by secondary photoisomerizations, secondary photolysis, and by secondary decompositions and the secondary reactions of sulfur atoms with primary products.
Application en série benzofurannique d'un nouveau procédé de nitration par l'acide nitrique en présence de chlorure stannique
Authors: Einhorn Jacques , Demerseman Pierre , Royer René
Published: May 2006

A new nitration technique, using nitric acid in the presence of stannic chloride in dichloromethane, has been extended to a series of benzofurans. The ease of performing the reaction as well as the diversity of products that can be obtained under various experimental conditions make it a worthwhile technique. [Journal translation]
Vibrations of the scissile C—O bond in an acyl-chymotrypsin observed by resonance Raman spectroscopy
Authors: Carey P. R. , Phelps D. J.
Published: May 2006

5-Methylthienylacryloyl chymotrypsin has been prepared with 13C at the carbonyl and, separately, at the α carbon atoms of the acyl moiety. The isotopically labelled species confirm the assignments of several of the bands in the resonance Raman (RR) spectrum of the acyl-enzyme and show that the feature occurring near 1260 cm−1 involves the motion of the carbonyl carbon atom. It is likely that the 1260 cm−1 band is associated with the stretching vibration of the C—O bond in the =C—C(=O)—O— chymotrypsin moiety, i.e. the vibration of the bond being cleaved in the active site. A moderately intense 1260 cm−1 feature occurs only in the RR spectrum of the native acyl-enzyme and possible reasons are given for its appearance. The labelled species also confirm that the bands appearing near 1715 cm−1 in the RR spectrum of the acyl-enzyme are associated with the stretching mode of the acyl carbonyl, νC=O. This frequency is that expected for an unperturbed α, β-unsaturated ester. Additionally, RR data are presented for 5-methylthienylacrylic acid in its —COOH and —COO− forms labelled with 13C at the C=O and α carbon positions.
Abinitio molecular orbital studies on thiirene and its isomeric structures
Authors: Gosavi Ratnakar K. , Strausz Otto P.
Published: May 2006

Abinitio molecular orbital calculations have been carried out on the lowest closed shell singlet states of six isomeric forms of C2H2S at the SCF and CI levels using STO-3G and 6-31G* basis sets. Molecular geometries of the isomers and the activated complexes for their isomerization reactions were optimized by the energy gradient method at the SCF level and the CI calculations were performed at these geometries. In addition, the lowest singlet and triplet states of the •SCHĊH diradical were also studied and their geometries optimized by the Restricted Hartree Fock method.The computed stabilities follow the order [Formula: see text]The pseudo antiaromatic character of the 4n-π electron thiirene is manifested by its drastically reduced C—S bond energy, ~15 kcal mol−1 as compared to the value of > 40 kcal mol−1 estimated for its 2n-π electron analog, thiirane. This explains why thiirenes can be stabilized in inert matrices at 8 K but decompose readily at higher temperatures. In agreement with experimental results the lowest energy path for the unimolecular decomposition of thiirene leads to thioketene via the lowest singlet (or triplet) state of thioformylmethylene.The ir frequencies calculated for thiirene from abinitio mo theory using 6-31G + polarization functions on the sulfur show reasonably good agreement with the experimental frequencies, confirming the earlier assignments of the ir spectrum of thiirene.
Hydrogen isotope exchange between fluoroform (CF3H) and water. 4. Catalysis by NaOH and anionic resin above 100 °C as an alternative to DMSO addition for rate enhancement
Authors: Symons E. Allan , Bonnett J. Douglas , Martins M. de Lurdes
Published: May 2006

Measurement of rate constants for NaOH-catalyzed CF3D/H2O isotopic exchange has been extended from 80 to 140 °C. Corresponding CF3H solubility data were obtained for water and 1.0 mol/L NaOH solution up to 120 °C. Above 120 °C, the NaOH solution provides sufficient catalytic activity to be considered as a simple alternative to the use of aqueous DMSO systems containing NaOH for a CF3H redeuteration process.Tests done with both Ionac A-935 and regular types of anion exchange resin in the hydroxide ion form indicate that these resins, although initially quite effective for deuterium exchange catalysis, lose their reactivity when employed above 100 °C. The thermal instability of this type of supported −OH catalyst makes it unsuitable for use (as a substitute for NaOH) at elevated temperatures in packed towers in a commercial process.
Effet de groupe partant dans l'hydrolyse d'orthoesters cycliques: changement de conformère réactif dans l'hydrolyse des diéthoxy-2,2 tétrahydropyrannes
Authors: Lamaty Gérard , Lorente Philippe , Moreau Claude
Published: May 2006

The rates of hydrolysis of 6-substituted 2,2-diethoxy 3,4-dihydro benzo-1-pyrans (X = MeO, Me, H and Cl) were determined at two temperatures in water/dioxane 2:1 by volume. The observed change of sign of the Hammett ρ constants [Formula: see text] is characteristic of a phenolate leaving group, i.e. of the rate-determining cleavage of the endocyclic C—O bond in the systems here studied; these results clearly indicate a change in the nature of the reactive conformer in hydrolysis of 2,2-diethoxy tetrahydropyrans.
Reaction of γ-carboxyglutamic acid with aldehydes
Authors: Capasso Renato , Randazzo Giacomino , Pecci Laura
Published: May 2006

The DL-γ-carboxyglutamic acid (Gla) reacts quantitatively with formaldehyde to give 4,4-dicarboxyproline and with other aldehydes to give the racemic diastereoisomers of the 5-substituted 4,4-dicarboxyprolines. The pH-dependent reaction rate and the stereochemical behaviour suggest an intramolecular Mannich mechanism.After heating at 100 °C for 30 min, the 4,4-dicarboxyproline and the 5-substituted 4,4-dicarboxyprolines lose a carboxyl group from C4 to give the racemic diastereoisomers of the cyclic analogs of glutamic acid.
State-resolved quantum yields of the reactions of metastable Ca(3P, 1D) with NO2 and N2O
Authors: Wang Hui , Menzinger Michael
Published: May 2006

Absolute chemiluminescence and quenching (beam attenuation) cross sections were measured for the title reactions in a beam/gas experiment. In the Ca* + NO2 system, both quantities are about twice as large as in the N2O reaction. The chemiluminescence quantum yields, corrected for infrared emission from the A1Σ+ and A′ 1Π states, are of similar magnitude YCL(Ca* + N2O) = 7.2 ± 1.1% and YCL(Ca* + N2O) = 8.0 ± 0.9%. The quenching cross sections are στ(Ca* + N2O) = 153 ± 32 Å2 and στ(Ca* + N2O) = 73.2 ± 5.7 Å2, consistent with a long-range harpooning process in the former and an electron transfer at closer range for the latter system. The partial resolution of CL spectra was aided by lifetime-separated spectroscopy. The principal emitter in both systems is the long-lived CaO(A′ 1Π), next to minor yields of CaO in the short-lived A1Σ+, B1Π, and "orange and green arc band" states. The results are discussed in light of adiabatic correlations. The arc states are argued to arise in nearly coplanar collisions from the rearrangement of an excited intermediate. An information theoretical analysis reveals considerable dynamical bias in the form of non-linear surprisal plots.
Pictet–Spengler reaction of biogenic amines with carbohydrates. Synthesis of novel C-nucleosides
Authors: Piper Ian M. , MacLean David B. , Kvarnstrôm Ingemar , Szarek Walter A.
Published: May 2006

Several novel C-nucleosides have been prepared by Pictet–Spengler condensations between biogenic amines and carbohydrates. Dopamine hydrochloride reacted with D-glucose to give 6,7-dihydroxy-1(R)- and -1(S)-(D-gluco-pentitol-1′-yl)-1,2,3,4-tetrahydroisoquinoline hydrochlorides, and with 2,5-anhydro-D-mannose to give 1(R)- and 1(S)-(α-D-arabinofuranosyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline hydrochlorides. Tryptamine hydrochloride and histamine did not react with D-glucose, but with 2,5-anhydro-D-mannose gave 1(R)- and 1(S)-(α-D-arabinofuranosyl)-1,2,3,4-tetrahydro-β-carboline and 4-(α-D-arabinofuranosyl)-imidazo[4,5-c]-4,5,6,7-tetrahydropyridine, respectively. The structures of the compounds have been established by nmr experiments and by mass spectrometry.
The thermal and photochemical decompositions of succinic anhydride and 2,3-dimethyl succinic anhydride in the gas phase
Authors: Yamamoto S. , Back R. A.
Published: May 2006

The absorption spectrum of succinic anhydride shows a broad maximum near 220 nm, attributed to the lowest π*–n− transition. Photolysis in this region (220–270 nm) gives CO2, CO, and C2H4, but not in the equimolar quantities expected from a simple molecular dissociation. Production of CO also shows a time dependence, increasing with time, and a free-radical mechanism is tentatively suggested to account for this. The thermal decomposition of succinic anhydride at 625–775 K yields the same products, but is more complex, with larger deviations from the simple stoichiometry, and product formation non-linear with time and pressure. At short times, production of CO, the most abundant product, is described by first-order Arrhenius parameters of log A (s−1) = 11.6 and E = 53 kcal/mol, apparently independent of surface.The photolysis of the cis and trans isomers of 2,3-dimethylsuccinic anhydride at 250 and 230 nm is simpler than that of succinic anhydride, giving equimolar CO and CO2, but with butene-2 still falling short of a stoichiometric yield by from 10 to 40%. Both cis- and trans-butene-2 were produced, with the latter always in excess and with no retention of the configuration of the original anhydride. The thermal decomposition of 2,3-dimethylsuccinic anhydride is more complex than the photolysis, with much less butene-2 produced (again with no retention of cis–trans configuration) and methane an important product. Activation energies for CO formation were about 48 and 45 kcal/mol and log A (s−1) was 10.4 and 9.5 for the cis and trans isomers, respectively.
Cellulose organic solvents: V. Conformational aspects of N,N-dimethyl ethanolamine N-oxide in its crystalline and diluted states
Authors: Maia E. R. , Péguy A. , Pérez S.
Published: May 2006

N,N-Dimethyl ethanolamine N-oxide (DMEAO) belongs to the class of tertiary amine oxide molecules that are good solvents for cellulose, although not being cyclic. Crystallographic investigation shows that anhydrous DMEAO is monoclinic, space group Cc, a = 25.725(9), b = 7.023(4), c = 9.483(5) Å, β = 101.16(10)°, Z = 12. The crystal structure has been solved by direct methods and refined to a final R value of 0.063 for 575 observed reflexions. Three independent molecules are found within the asymmetric unit; one of these displays a pseudo-cyclic form dictated by the occurrence of a strong intramolecular hydrogen bond. Conformational investigation of DMEAO in solution, using ir and nmr spectroscopy shows that this pseudo-cyclic form is more likely to occur in diluted states. These findings are related to the ability of this tertiary amine oxide to act as a good solvent, up to a water content of one water molecule per DMEAO molecule.
Complexes des ions Hg2+ avec Le monomère et le dimère de la thymine: 5-methyl-2,4 (1H, 3H) pyrimidinedione
Authors: Petit-Ramel M. M. , Thomas-David G. , Perichet G. , Pouyet P.
Published: May 2006

The association constants for Hg2+-complexes involving monomeric (TM) and dimeric (TD) forms of thymine are determined by pH-titration measurements made over a wide pH range 2 < pH < 11. In both systems, the experimental data have been analyzed by a pit-mapping method and the concentration distribution of the various complex species is plotted versus a pH gradient.Because of the tendency of Hg2+ to form two bonds in a linear configuration, non-chelate complexes [Hg(TM)+] (log β101 = 10.65) and [Hg(TM)2] (log β102 = 20.70) are formed with the monomer thymine.Photodimers, obtained after irradiation of monomer thymine at 260 nm in frozen water (−10 °C), are the (meso)-cis, syn forms and can be complexed by the Hg2+ ions in [Hg(TD)] (log β101 = 13.55), [HgH−1 (TD)]− (log β1−11 = 6.73), and [HgH−2 (TD)]2− (log β1−21 = 1.69) species. [Hg(TD)] complex shows an absorption spectrum shifting towards 280 nm, whereas the free dimer ligand absorbs lower than 240 nm only. An irradiation at 280 nm provides the formation of the [Hg (TM)2] complex and consequently the breaking of the cyclobutane cycle in the dimer molecule.
Salting-out of triethylphosphate by inorganic electrolytes
Authors: Sagert Norman H. , Lau Danny W. P.
Published: May 2006

The salting-out of triethylphosphate (TEP) from water was measured at 25 °C for twelve inorganic electrolytes. If salting out is taken as an additive property of ions, then the effectiveness for salting TEP out of water is [Formula: see text] for anions and [Formula: see text] for cations. The results were fitted to three theories. The distribution theory of Conway, Desnoyers, and Smith predicts the order of magnitude of the experimental results, but does not discriminate well between salts of the same valence type. The electrostriction theory of McDevit and Long discriminates well between ions but gives results three or five times larger than those observed. Scaled particle theory predicts the results reasonably well, but the predictions depend critically on the choice of ionic and molecular parameters. Thus, none of these theories is entirely satisfactory.
Substituent effects in the hydrogenation of Δ1,9-octalins
Authors: Schmidt Cirill , Breining Tibor
Published: May 2006

The presence of the 4α-methyl group in olefin 4 or in conjugated ketone 10 prevents catalytic hydrogenation from the α side, leading exclusively to cis-fused decalins.
Transference numbers and solvation studies in n-butanol
Authors: Banait J. S. , Sidhu K. S. , Walia J. S.
Published: May 2006

Transference numbers of tetrabutylammonium bromide have been measured in n-butanol at 25 °C in the concentration range 5.79 − 12.86 × 10−2 mol dm−3. The variation of transference number with concentration is negligible. The limiting transference number of tetrabutylammonium ion has been determined by the Longsworth method. Combining the limiting transference number and limiting equivalent conductance of this salt, limiting ionic conductances of tetrabutylammonium and bromide ions have been found to be 8.05 and 8.02 ohm−1 cm2 mol−1, respectively. From these values limiting ionic conductances of other univalent ions, effective ionic radii and solvation numbers have been computed. The solvation numbers of anions have been found to be more than those of cations which shows the protic nature of this solvent.
Studies in the usnic acid series. IX. The biodegradation of (+)-usnic acid by Mucorglobosus
Authors: Kutney James P. , Leman Jeffrey D. , Salisbury Phillip J. , Yee Trevor , Sánchez Ignacio H.
Published: May 2006

The microbial degradation of the lichen antibiotic (+)-usnic acid (1) by means of the fungal isolate Mucorglobosus has been studied. It is shown that this organism provides the metabolite (+)-2-desacetylusnic acid (2) as a major component via a novel deacylation reaction.
Olefin hydrogenation catalysed by chrysotile asbestos fibres and supported titanocene
Authors: Cozak Daniel , Deblois Christian
Published: May 2006

The double bond hydrogenation at NTP catalysed by both natural short fibre chrysotile asbestos and (η5-C5H5)2TiCl treated fibres is reported for some linear and cyclic olefins.
Surface photochemistry: generation of benzyl radical pairs on dry silica gel
Authors: Frederick Bradley , Johnston Linda J. , Mayo Paul De , Wong S. King
Published: May 2006

Singlet and triplet benzyl radical pairs have been generated on silica gel by photolysis of a benzyl phenylacetate, a dibenzyl ketone, and a dibenzyl sulfone. The extent of geminate radical recombination has been measured and requires that translational motion of radicals occur on the silica gel surface. This motion was affected by the radical pair multiplicity and the photolysis temperature, but was relatively insensitive to the state of hydration of the silica gel and the presence of coadsorbates. The presence of certain rearranged starting materials, which are not formed in solution, amongst the products from photolysis of both dibenzyl ketone and dibenzyl sulfone on silica gel indicates the restrictions on radical movement on the surface on the shorter timescale of the benzyl–phenylacetyl and benzyl – benzyl sulfonyl radical pairs.
Photoinduced electron transfer C—C bond cleavage reactions; oxidations and isomerizations
Authors: Reichel L. W. , Griffin G. W. , Muller A. J. , Das P. K. , Ege Seyhan N.
Published: May 2006

We have shown that radical cations generated by photoinduced electron transfer (ET) in 1,2-diarylethanes, aryl pinacols, and their derivatives undergo fragmentation reactions. In the presence of oxygen oxidative products are obtained. Time-resolved laser flash photolysis and other ancillary techniques have permitted us to define the mechanisms of certain oxidative processes observed.
A new glucosinolate synthesis
Authors: Keller Thomas H. , Yelland Lois J. , Benn M. H.
Published: May 2006

The tert-butyldimethylsilyl nitronate derived from 1-nitropropane was condensed with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosylthiol to yield two geometrically isomeric thiohydroximates; the Z-isomeric form was then converted by conventional procedures into potassium ethylglucosinolate ("glucolepidiin").
Quantitative IR-ATR spectrometry of asbestos fibers on membrane filters
Authors: Kimmerle F. M. , Noël Luc , Khorami Jaleh
Published: May 2006

We have developed a new IR-ATR spectroscopic technique for the identification and quantification of fibers collected on PVC filters. This nondestructive method has a detection limit of about 10 μg, involves no sample preparation, and is relatively insensitive to nonserpentine dusts normally associated with the asbestos mining and milling industries.An analysis of the ATR phenomena for a fiber matt indicates that the logarithmic ratio of the reflectivity varies with the surface concentration C as:[Formula: see text]where Cs is the concentration for a monolayer of fiber, r the mean fiber diameter. Thus, the absorption should reach a plateau when a sufficient thickness is obtained, and this nonlinear region should be attained at lower wavelength, and at lower concentrations for long fibers having a high aspect ratio. We further predict that the relative absorption A(λ1)/A(λ2) where λ1 < λ2, should decrease with fiber dimension.The ATR signal at 303 cm−1, corresponding to a lattice vibration, varies linearly with fiber concentration up to 100 μg/cm2, whereas the intensity of this band relative to the OH stretching band at 3690 cm−1 is a monotonic function, representing the fiber morphology. Dust levels and fiber morphology established from the IR-ATR spectroscopy are consistent with measurements by light and electron microscopy.
The cathodic reduction of PbO in the passive layer on lead in aqueous sulphuric acid
Authors: Barradas R. G. , Nadezhdin D. S.
Published: May 2006

The cathodic reduction of the lead monoxide layer formed on lead in 30% aqueous H2SO4 under anodic oxidation at 0.6 V (vs. Hg/HgSO4 reference electrode) was investigated by linear sweep voltammetry, potential step and admittance measurements. The experimental data were analyzed respectively in terms of thin-layer electrochemistry, electrocrystallisation, and changes of resistance of the PbO layer under reduction. The results seem to be best interpreted from the theory of three-dimensional electrocrystallisation as PbO is reduced to Pb. At sub-zero temperatures the PbO peak observed on our voltammograms and potentiostatic current time transients reveals the splitting of the curves into two peaks, which may be a result of reduction of the same material but of different phases, namely, orthorhombic and tetragonal PbO.
Solvent and temperature dependence of absorption and phosphorescence of trans-diisothiocyanate (bis)ethylenediaminechromium(III) ion
Authors: Langford Cooper H. , Schear Thomas M.
Published: May 2006

An unusual case of absorption and fluorescence bands shifting in the same direction as solvent varies is reported. Solvent shifts in the quartet absorption maximum and doublet or phosphorescence emission maximum of trans-Cren2(NCS)2+ ion are related to the Gutmann solvent donor number. The correlation is discussed in terms of solvent effects on the vibrations identified as responsible for the vibronic transitions and are in agreement with Hollebone's notion of "vibronic" intersystem crossing. The activation parameters for decay of phosphorescence in eight solvents correlate by a Barclay–Butler plot and are consistent with the possibility of a single common dominant mechanism for the T-dependent decay path. They do not, however, depend on solvent donor numbers as quantum yields for substitution do. Therefore, they offered no new support for the notion that the pathway is by chemical reaction. The activation parameters also fail to correlate with solvent fluidity.
Calcul des intensités des transitions laser dans 12C16O2 et ses molécules isotopiques
Authors: Millie Philippe
Published: May 2006

The laser emission-line intensities of 12C16O2 and several isotopes were theoretically calculated. The vibrational wave functions were obtained to a direct diagonalization by utilizing a previously known potential function. These values are compared to the experimental ones. The effect of electrical anharmonicity is discussed. The validity of the contact transformation method is briefly analyzed.
Gas chromatography – mass spectrometry of osulose derivatives: O-trimethylsilyl, O-acetyl, O-isopropylidene, methyl glycosides, and 1,1-dimethyl acetals
Authors: Ruiz Pedro Antonio García , Travesedo Inmaculada Cartagena , Martinez Antonio Soler
Published: May 2006

Structure determination of the O-trimethylsilyl, O-acetyl, and O-isopropylidene derivatives of some hexosuloses, pentosuloses, and one tetrosulose, as well as their methyl glycosides and 1,1-dimethyl acetals has been achieved by gas chromatography – mass spectrometry.By study based on the qualitative and quantitative differences in the 36 derivatives obtained, and their analogues prepared from tetradeuterio methanol and/or hexadeuterio acetone, and comparison with results reported in the literature, criteria for the unambiguous determination of the structural grouping are proposed. The relative abundance of each compound when the osulose forms more than one isomeric derivative in the same reaction, as well as chromatographic data for the isolated products, are reported.
An abinitio molecular orbital study of isomers on the C2NH5+• and C2NH5 surfaces
Authors: Lien Min H. , Hopkinson Alan C.
Published: May 2006

The structures and relative energies of seven possible C2NH5+•isomers have been calculated using abinitio molecular orbital theory. Structure optimisations have been performed with a 4-31G basis set, using both the restricted (RHF) and unrestricted (UHF) Hartree–Fock methods. The optimum geometries were then used for single point calculations using the 6-31G* basis set. The relative energies are 1 < 7 < 5 < 3 ≈ 2 ≈ 6 < 4. This order is the same, with the exception of 6, as for isomers on the C2H4O+•surface and the relative energies are very similar to those on the C2H4O+• surface. The structures of the radical cations C2NH5+• are compared with those of the neutral molecules C2NH5.
Thermodynamic properties of binary mixtures containing ketones. VIII. Heat capacities and volumes of some n-alkanone + n-alkane mixtures at 298.15 K
Authors: Grolier Jean-Pierre E. , Benson George C.
Published: May 2006

Excess molar volumes, [Formula: see text], and excess molar heat capacities at constant pressure, [Formula: see text], have been obtained for some n-alkanone + n-alkane mixtures at 298.15 K from density and volumetric heat capacity measurements using liquid-flow techniques. The [Formula: see text] data are much more accurate than those estimated from the temperature dependence of other thermodynamic properties (excess free energies and/or excess enthalpies). The rather unusual composition dependence of the excess heat capacities — two minima, or W-shape curves — is most likely due to cooperative induced conformational molecular "arrangements" in these mixtures.
Chemistry of shikimic acid derivatives. Synthesis of specifically labelled shikimic acid at C-3 or C-4
Authors: Zamir Lolita O. , Luthe Corinne
Published: May 2006

Specifically labeled shikimic acids with tritium or deuterium at positions C-3 or C-4 were synthesized. Commercially available L-shikimic acid was converted to its 3- and 4-ketones, after suitable protection of the hydroxy¡ groups at C-4,C-5 and C-3,C-5. Reduction of the 3-keto- or 4-keto-shikimic acid derivatives with sodium borodeuteride and deprotection gave mostly 3-D-epi-shikimic acid or 4-D-shikimic acid. An internally assisted inversion of the 3-D-epi-shikimic acid derivative and deprotection gave 3-D-shikimic acid.
33S and 17O nuclear magnetic resonance study of liquid sulfur dioxide
Authors: Wasylishen Roderick E. , Macdonald J. Bruce , Friedrich Jan O.
Published: May 2006

The sulfur-33 chemical shift and 33S and 17O nmr relaxation data are reported for liquid sulfur dioxide. The 33S nucleus in SO2 is highly deshielded, 375 ± 2 ppm to high frequency of the sulfate anion. The rotational correlation time of SO2 at 294 K, 0.3 ps, is only about twice that calculated using an inertial model. The temperature dependence of the 33S and 17O nmr relaxation data can be described by an average activation energy of 6.3 ± 0.6 kJ mol−1. The effective rotational correlation time derived from 33S nmr line widths is used to calculate the 17O quadrupolar coupling constant, e2qQ/h = 6.6 ± 0.7 MHz, in SO2.
Kinetic and thermodynamic control of pseudobase formation from C-3 substituted 1-methylquinolinium cations
Authors: Bunting John W. , Fitzgerald Norman P.
Published: May 2006

The kinetic and thermodynamic control of pseudobase formation from 3-W-1-methylquinolinium cations has been studied for a variety of substituents (W). Spectral data indicate that, in both aqueous and methanolic solution, the C-2 pseudobases predominate at equilibrium for W = H and Br, while the C-4 pseudobases are the thermodynamically preferred species for W = CONH2, CO2CH3, CN, and NO2. Stopped-flow studies indicate that in all cases the C-2 pseudobases are the kineticallycontrolled products upon basification of the aqueous solutions of these cations. Equilibrium constants (pKR+) have been measured for pseudobase formation at both C-2 and C-4 for each W in all cases where they are experimentally accessible. Substituent effects upon [Formula: see text] correlate with σm for W, while [Formula: see text] depends upon σp−. These substituent effects allow the prediction of [Formula: see text] and [Formula: see text] for the 1-methylquinolinium cation. Rates of C-2 to C-4 pseudobase equilibration have been measured in all cases where the latter species is thermodynamically more stable. These kinetic data allow the evaluation of rate constants for C-4 pseudobase equilibration with each cation. In all cases except W = CN, C-2 pseudobase formation is complete within the mixing time of the stopped-flow instrument.
Aromatic sulphonates and the hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran
Authors: O'Leary Stella
Published: May 2006

The rate of hydrolyis of 2-(p-nitrophenoxy)tetrahydropyran was measured in a variety of buffers in water at 30 °C. At low ionic strength (μ = 0.05), 3,6-disulphonaphthoxyacetic acid catalysed the reaction. The second-order rate constant was 20 times faster than predicted from pKa. At high ionic strength (μ = 0.5), plots of kobs vs. total buffer concentration for both 3,6-disulphonaphthoxyacetic acid and 6,8-disulphonaphthyoxyacetic acid go through a maximum. Polyacrylic acid catalysed the reaction. The results are discussed in terms of aggregation and salt effects.
An FT-ir study of cis study of trans-dichlorodiammineplatinum(II) bound to inosine-5′-monophosphate
Authors: Tajmir-Riahi H. A. , Theophanides T.
Published: May 2006

Inosine-5′-monophosphate disodium salt (5′-IMPNa2) reacts with cis-dichlorodiammineplatinum(II) (cis-DDP) and its trans-isomer (trans-DDP) to give complexes of the type cis- and trans-Pt(NH3)2(IMPNa2)nCl2•xH2O, n = 1 or 2 and Pt(IMPNa2)nCl2•xH2O, where n = 1, 2, or 3 and x = 0–6. In the 1:2 platinum complexes the nucleotide binds only to the N7-atom of the purine ring system, while in the 1:1 metal complexes there is indication for Pt–carbonyl interaction (bridging or chelation) in addition to the N7-bonding at neutral pH values with cis-DDP.Solution FT-ir studies (H2O and D2O) showed that the 1:1 species formed with cis-DDP at neutral pH's behaved differently from those with trans-DDP. The carbonyl stretching vibration of the free base at 1685 cm−1 (H2O) and 1670 cm−1 (D2O) exhibited marked spectral changes in intensity, shifting, and shape upon complexation, whereas the reaction with the trans-isomer produced only slight perturbations in the above region.
A change in rate-determining step in the hydrolysis of cyclic ketals
Authors: McClelland Robert A. , Seaman N. Esther
Published: May 2006

A kinetic study is reported of the hydrolysis of 2-methoxy-2-phenyltetrahydrofuran and 2-ethoxy-2-phenyltetrahydrofuran. At pH > 6 the rate-determining step involves H+-catalyzed formation of the oxocarbocation, this reaction occurring with cleavage of the exocyclic alkoxy group to produce a cyclic cation. Between pH 5 and pH 6 a change-over occurs and at pH < 5, the rate-determining step in product formation is breakdown of the cyclic hemiketal intermediate, 2-hydroxy-2-phenyltetrahydrofuran. The changeover occurs because the H+-catalyzed breakdown of this intermediate is a slower process than the H+-catalyzed oxocarbocation-forming step. Hydroxide ion catalysis makes the hemiketal decomposition faster at higher pH. Analogous cyclic ortho esters (2-alkoxy-1,3-dioxolanes) show this same change in rate-determining step between high pH and low pH, while acyclic acetals, ketals, and ortho esters generally have the oxocarbocation-forming stage rate determining at all acidities. It is concluded that the structural features inherent in the cyclic systems are responsible for the difference. In particular, the oxocarbocation-forming stage involves exocyclic bond cleavage, giving it an entropic advantage over the hemiketal or hemiorthoester breakdown which is endocyclic.
Hydrolysis mechanisms for acylhydrazines in aqueous sulfuric acid, determined using the excess acidity method
Authors: Cox Robin A. , Yates Keith
Published: May 2006

The excess acidity method has been applied to hydrolysis rate data for some acyl- and benzoylhydrazines, obtained as a function of medium composition in aqueous sulfuric acid mixtures. Two hydrolysis mechanisms are indicated, both involving a second proton transfer to monoprotonated substrate. In the first mechanism this transfer is to oxygen, which is the rate-determining step in dilute acid, followed by attack of a water molecule in an A-2 hydrolysis, which is rate determining in more concentrated acid. Bisulfate ion becomes the nucleophile at high acidity. The second mechanism, found at higher acid concentrations, involves rate-determining nitrogen protonation, probably concerted with C—N bond rupture, to give an acylium ion, for those substrates capable of forming one.
Etude du système acridine orange – poly(C) et de son interaction avec les complexes du palladium(II)
Authors: Ménard Robert , Zador Miklos
Published: May 2006

The complex formed between acridine orange (AO) and polycytidylic acid (poly(C)) was studied by spectrophotometry and spectrofluorometry. The complex was characterized by its stoichiometry, structure, and the thermodynamic parameters of its formation. The results are in agreement with an external aggregation of the protonated dye along the negatively charged poly(C) chain and indicate that approximately two AO molecules are bound per nucleotide unit of poly(C). The kinetics of the reaction between this complex and a Pd(II) complex was studied by the stopped-flow method. The addition of (dien)Pd(II) to the AO–poly(C) complex leads to the dissociation of the latter, due to fixation of the Pd(II) complex to the N3 site of the cytosine base of poly(C). The rate constant for the AO liberation, extrapolated at zero AO concentration, corresponds to the rate constant of Pd(II) fixation on poly(C). This indicates that AO can be used as an indicator for this reaction and allows kinetic studies at very low concentrations (≤ 5 × 10−6 M).
An improved synthesis of m-diazirinophenol
Authors: Leblanc Pierre , Gerber Gerhard E.
Published: May 2006

The published synthesis of phenolic diazirine was shown to result in products which were chlorinated during the hypochlorite oxidation while the desired unchlorinated product was lost during the usual work-up. A superior synthesis is described: inclusion of pyridine during the oxidation step prevents the chlorination; the desired volatile diazirine was isolated in good yield using silica gel and reverse phase high pressure liquid chromatography.
Structure–activity studies of β-carbolines. 2. Crystal and molecular structures of N-ethyl-3-carbamoyl-β-carboline
Authors: Muir Alastair K. S. , Codding Penelope W.
Published: May 2006

The crystal and molecular structures of N-ethyl-3-carbamoyl-β-carboline, C14H13N3O, a synthetic ligand of the benzodiazepine receptor are reported. The space group is C2/c with a = 16.220(4), b = 7.728(4), c = 19.623(6) Å, β = 104.16(1)°, Z = 8. The carboxyamide side chain assumes an extended conformation and is almost coplanar with the β-carboline skeleton. The observed molecular conformation is compared to the current model for the receptor binding site. Hydrogen bonding and aromatic ring stacking determine the molecular packing arrangement.
The influence of hydrogen bonding on the character of N—H and C=O stretching modes in 2-thiopyrrole-1,2-dicarboximide
Authors: Ram Shanker
Published: May 2006

The infrared spectra (200–4000 cm−1) of 2-thiopyrrole-1,2-dicarboximide (TPH) in solid and solution forms have been measured as a function of temperature, and a direct correlation has been obtained between the two phases and the type and extent of hydrogen bonding. It is suggested that TPH exists as cyclic dimer in the solid state (below 310 K) and in dilute solutions by the formation of two equivalent hydrogen bonds. At the transition temperature, ~310 K, the cyclic dimer undergoes to the open-cyclic dimer and persists in this structure till 410 K. In addition, the thermodynamical functions ΔH0, and ΔS0 have been estimated using the spectral data in solution.
Observation of a radical intermediate in the one electron oxidation of 5-methyl-1-thia-5-azacyclooctane by •Br2−
Authors: Musker Warren Kenneth , Surdhar Parminder S. , Ahmad Rizwan , Armstrong David A.
Published: May 2006

The one electron oxidant •Br2− reacts with 5-methyl-1-thia-5-azacyclooctane (4) in aqueous solution at high pH with an overall rate constant of ~2 × 108 M s−1. The radical intermediate produced has a broad maximum at 500 nm with ε = 2400 M−1 cm−1 and at pH 10 decays with a first order rate constant of 2.3 ± 0.3 × 104 s−1, first half-life of 30 ± 5 μs. Its characteristics do not correspond to those of the [Formula: see text] species reported by Asmus and co-workers. The species appears to be the same as the cation radical reported earlier in the one electron oxidation of 4 in acetonitrile. This species is considered to have an [Formula: see text] type structure, which provides transannular stabilization.
Electrochemical evaluation of electron acceptor materials
Authors: Loutfy R. O. , Hsiao C. K. , Ong B. S. , Keoshkerian B.
Published: May 2006

The electrochemical half-wave reduction potential (E1/2) of 33 electron acceptor molecules in dry methylene chloride has been measured by cyclic voltammetry (CV) at a mercury electrode. The differences in E1/2 values for the reversible reduction to the corresponding anion radicals reflect the electronic influence of the substituent at different ring positions.The measurements of the half-wave reduction potentials provided a convenient method for determining the conducting energy levels of the electron relay molecules in condensed media. Repetitive potential cycle measurements provided information on the chemical stability and cyclability of the intermediate anion radicals formed during electron transport processes.
Preparation and evaluation of a perhydroazulene intermediate for lactarane sesquiterpene synthesis
Authors: Christensen Joel R. , Reusch William
Published: May 2006

A facile preparation of 6,9,9-trimethylbicyclo[5.3.0]deca-1,6-dien-3-one (6) from 2,5,5-trimethylcyclohexane-1,3-dione is described. Enolate reactions of 6 do not yield norcaradiene products, but proceed in the conventional manner (e.g., α-methylation and O-silylation). Nucleophilic addition reactions at the carbonyl function, and epoxidation of the γ,δ double bond are also observed. Under a variety of conditions, singlet oxygen reacts with the diene moiety in 6 to give both endoperoxide (13) and ene reaction (14) products in roughly equal amounts. The endoperoxide rearranges to cyclic hemiketal (15) on treatment with base.
Stereospecific trans-elimination of 2-alkoxy- and 2-cycloalkoxytropones to alkenes and cycloalkenes
Authors: Takeshita Hitoshi , Mametsuka Hiroaki
Published: May 2006

The title compounds undergo thermal fragmentation to tropolones and alkenes and cycloalkenes. Product distribution and kinetic analyses of specifically labelled deuterio compounds establish the process to be a concerted [s8π + a2σ + s2σ] electrocyclic reaction.
Electrogenerated luminescence in the Kolbe reactions of pyruvic and phenylglyoxylic acids
Authors: Fuente J. De La , Lissi E. A. , Rozas R.
Published: May 2006

The Kolbe reaction of pyruvic and phenylglyoxylic acids in acetonitrile takes place with high yields of biacetyl and benzil, respectively. Electroluminescence is produced during the electrolysis. This luminescence can be attributed to phosphorescence following the generation of excited triplets of the α-diketones in the acyl radical recombination. The efficiencies of the triplet production, relative to ground state formation, were evaluated to be of the order of 8 × 10−3 and 10−1 for the recombination leading to benzil and biacetyl, respectively.
Thermodynamics of protonation of weak bases in H2SO4-H2O media, determined using the excess acidity method
Authors: Cox Robin A. , Yates Keith
Published: May 2006

The excess acidity method has been used to investigate the thermodynamics of the protonation process for those weak bases for which the ionization ratios (or optical densities) at several temperatures have been measured in aqueous sulfuric acid. Standard enthalpies and entropies, at 25 °C in the aqueous reference state, are given for thirteen primary, one secondary, and two tertiary nitroanilines, three cyanocompounds, thirteen triphenylmethanols, three other carbocation precursors, two ketones, nine pyridines, and nine azine N-oxides. Guidelines for estimating pKBH+ at any temperature for other weak bases are discussed.
A five-coordinate dicarbonyl rhodium(I) complex containing monohapto-2-diphenylphosphinothiophene: [RhCl(CO)2(DPT)2]
Authors: Sanger Alan R.
Published: May 2006

Facile reversible addition of CO to trans-[RhCl(CO)(Ph2PC4H3S)2] gives the five-coordinate complex [RhCl(CO)2(Ph2PC4H3S)2], which represents the first complex of the type [RhCl(CO)2(PR3)2] to be identified, and which is trigonal bipyramidal with axial carbonyls and equatorial phosphine ligands.