bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of strong acids with a conjugated imine
Authors: Bissonnette Martine , Thanh Hoa Le , Vocelle Daniel
Published: May 2006

The state of protonation of a Schiff base, trans-trans-heptadienylidene tert-butylamine (HBA) was evaluated by uv and 1H nmr spectroscopies. Using three strong acids, HCl, HBr, HI and by taking spectra at low temperatures, it was found that in a non-polar solvent like chloroform (or CDCl3), no proton exchange occurred between the iminium ion and the halide anion. In contrast, CD3OH induced a leveling effect and some proton transfer occurred between the iminium ion and the solvent for the HBr and HI salts. No proton exchange was present for the HBA:HCl salt. The interaction of trichloroacetic acid with HBA was also studied: full proton exchange occurred between the iminium ion and CD3OH. In CDCl3, proton transfer was also present between the iminium ion and the carboxylate anion. These facts are discussed in relation with the controversy surrounding the true state of protonation of rhodopsin.
Molecular recognition. III. The binding of the H-type 2 human blood group determinant by the lectin I of Ulexeuropaeus
Authors: Hindsgaul Ole , Khare Deveshwari P. , Bach Mimi , Lemieux Raymond U.
Published: May 2006

Using a radioimmunoassay to measure the relative potencies of a wide range of chemically modified structures related to the H-type 2 human blood group determinant, evidence was accumulated that the binding of αLFuc(1→2)βDGal(1→4)-βDGlcNAc-OMe by the lectin I of Ulexeuropaeus involves a wedge-shaped amphiphilic surface which extends on one side of the molecule from the methoxy aglycon to OH-3 of the βDGal unit. A cluster which involves OH-3, OH-4, and OH-2 of the αLFuc unit along with OH-3 of the βDGal unit provides the polar interactions with the lectin. However, only OH-3 and OH-4 of the αLFuc are indispensable to complex formation and are regarded as providing the key polar interaction. The binding reaction involves both a decrease in enthalpy of 29 kcal/mol and a decrease of 68 cal/mol/K in entropy. It is submitted that the main source of the decrease in enthalpy is the establishment of nonpolar interactions that extend from the aglycon over the nonpolar portion of the β-side of the βDGlcNAc unit and on to include a major portion of the α-side of the αLFuc unit. The binding of the βDGlcNAc unit includes OH-6 intramolecularly hydrogen bonded to O-5 in order to extend the nonpolar interactions to the α-side of this unit and perhaps beyond. The decreases in enthalpy (6.0 kcal/mol) and entropy (2.7 cal/mol/K) which occur on the binding of methyl α-L-fucopyranoside are much smaller than for the H-type 2 trisaccharide and are compatible with the much smaller surface that interacts to form the complex. The inhibition data obtained using a range of structures related to methyl α-L-fucopyranoside are in general accord with expectations based on the results obtained with the more complex structures.
Biosynthesis of the lupine alkaloids. I. Lupinine
Authors: Golebiewski W. Marek , Spenser Ian D.
Published: May 2006

The mode of incorporation into lupinine of cadaverine, intramolecularly doubly labelled with,15N and with,13C at the C-atom adjacent to 15N, i.e., 13C, 15N-"bond-labelled", was determined by,13C nmr spectroscopy; lupinine is generated from two cadaverine-derived C5-units by a route which excludes a "dimeric" intermediate with C2v symmetry. The mode of incorporation of 2H from L-(2-2H)lysine, from (R)- and (S)-(1-2H)cadaverine, and from (2-2H)-Δ1-piperideine into lupinine was determined by 2H nmr spectroscopy. The results corroborate the conclusions from the 13C,15N experiment and they establish the stereochemistry of six of the steps in the biosynthetic conversion of L-lysine into lupinine.
Reactions of steroidal 5,6-epoxides and cyclohexene oxide with aluminum alkoxides
Authors: Holland Herbert L. , Khan Saeed R.
Published: May 2006

The isomeric 5,6α- and 5,6β-epoxycholestanes, in addition to an analogous series of compounds substituted at C-3 with hydroxy (α or β stereochemistry) or ethylene ketal groups, have been treated with aluminum isopropoxide or tert-butoxide. The latter series of reactions did not give identifiable material, but aluminum isopropoxide gave products derived from epoxide opening and rearrangement in all cases. With epoxides unsubstituted at C-3, aluminum isopropoxide functioned as a Lewis acid in promoting epoxide rearrangements. In the presence of a C-3 alcohol function, additional products were obtained arising from fragmentation of the C-4,C-5 bond, or from β-elimination of the epoxide involving the loss of a C-7 hydrogen. Meerwein–Pondorff reduction of product carbonyl groups was also observed. C-3 ketal substituted epoxides were rearranged cleanly to 6-hydroxy-Δ4-3-ketones. Cyclohexene oxide reacted with aluminum isopropoxide (but not with tert-butoxide) to give two products arising from epoxide addition reactions. Structures for these products are proposed based on their 13C nmr spectra, and a possible route for their formation is presented. None of the epoxides examined in this study reacted with magnesium methoxide.
Asymmetric synthesis towards (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate, a component of the California red scale pheromone
Authors: Whittaker Mark , McArthur Colin R. , Leznoff Clifford C.
Published: May 2006

The key chiral synthons, (R)-3-isopropenyl-6-heptenoic acid and (R)-3-isopropenyl-6-heptenal, needed for the synthesis of (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate, a component of the sex pheromone of the California red scale, Aonidiellaaurantii, have been prepared by asymmetric synthesis. The chiral acid was synthesized in 86% ee by an asymmetric 1,4-addition of isopropenylmagnesium bromide to the l-ephedrine amide derived from (E)-2,6-heptadienoic acid, followed by base hydrolysis. Acid hydrolysis gave the chiral 3-(3-buten-1-yl)-4,4-dimethylbutyrolactone. The chiral aldehyde was prepared in greater than 99% ee by an asymmetric 1,4-addition of isopropenylmagnesium bromide to the imine derived from (S)-(+)-tert-butyl 2-amino-3,3-dimethylbutyrate and (E)-2,6-heptadienal. The 1,4-addition reactions of n-butyllithium or isopropenyllithium to (4S,5S)-(+)-2-[1-(E-1,5-hexadienyl)]-4-methoxymethyl-5-phenyl-2-oxazoline gave the addition products, and sequential mild hydrolysis and reduction of these adducts yielded chiral 3-n-butyl-6-hepten-1-ol for the former adduct but a mixture of products was obtained from the latter adduct.
Influence cinétique et chimique d'alcènes sur la pyrolyse d'alcanes: mise au point et nouveaux résultats
Authors: Billaud Francis , Baronnet François , Niclause Michel
Published: May 2006

On the basis of previously reported, as well as new, experimental results, a review is presented of the kinetic and chemical influences of alkenes on the pyrolysis of alkanes. The results confirm that the addition of free H• atoms to the double bonds of alkenes is not sufficient to explain their inhibiting influence on the pyrolysis of alkanes. On the contrary, our results show that the processes of addition can account for the chemical effects of added alkenes on the pyrolysis of alkanes, namely, the modifications brought to the nature and the ratio of the products formed during the reaction. The results presented here confirm that the addition of alkyl free radicals to the double bond of alkenes does not lead to important chemical effects. The previously reported experimental results (pyrolysis of ethane in the presence of ethylene or propene, the pyrolysis of 2,2-dimethylbutane in the presence of propene, isobutene, or two isopentenes), completed by our new results (pyrolysis of ethane in the presence of isobutene, pyrolysis of isobutane in the presence of ethylene, of propene, of trans-2-butene, or of 2-methyl-2-butene), can lead to very simple general rules, on the basis of which it is possible to explain the results and to predict the modifications (relating to the nature of the products and to their ratios) that will result from the addition of an alkene during the pyrolysis of an alkane at a temperature of 500 °C (773 K). Aside from their fundamental aspects, these observations and their mechanistic consequences could be useful for the preparation of models for these thermal reactions, especially for the simplification of complex models. These observations also explain certain facts observed in industry and can help in solving some of the problems associated with the thermal cracking of heavy oils.
Moments analysis of restricted ternary diffusion: sodium sulfite + sodium hydroxide + water
Authors: Leaist Derek G.
Published: May 2006

Ternary diffusion coefficients can be determined from restricted-diffusion experiments by evaluating zeroth and first time moments of the difference in a concentration-dependent property measured at two levels along the diffusion column. The method is used to determine ternary diffusion coefficients for aqueous sodium sulfite + sodium hydroxide solutions from conductance measurements. It is shown that these data can be analyzed to obtain the ternary diffusivity of sulfur dioxide in strongly alkaline solutions where sulfite is the major transporting species for the sulfur dioxide component. At high pH values, coupled flow of hydroxide ions leads to a significant increase in the diffusivity of the sulfur dioxide component relative to its diffusivity in pure water. Binary diffusion coefficients for aqueous sodium sulfite solutions are also reported.
Étude physico-chimique, spectres de vibration et structure du sulfaméthoxazole
Authors: Maury Luc , Rambaud Joëlle , Pauvert Bernard , Lasserre Yves , Berge G. , Audran Michel
Published: May 2006

Two polymorphic and one solvate forms of sulfamethaxozole have been identified and characterized using various thermal and spectral methods. The crystal structure of form II has been solved and compared with that of form I recently published: the lengths of the intermolecular H bonds mainly differentiate the two polymorphic forms. An assignment of the fundamental vibrations of the amine, amide, and sulfone groups involved in the H intermolecular bonds has been proposed from the analysis of the Raman and infrared spectra.
Réaction de quelques pyrazolines substituées par deux groupes électroattracteurs géminés avec Ce(NH4)2(NO3)6: nouvelle synthèse de pyrones-2 électrophiles
Authors: Abdallah Hassan , Grée René , Carrié Robert
Published: May 2006

Reaction of type 3 ketal pyrazolines with Ce(NH4)2(NO3)6 is studied. This leads generally to olefins 4, which are good starting materials for the synthesis of electrophilic pyrones 5. In two cases, another pathway leading to cyclobutanes is observed.
Regioselective fluoroalkoxylation and polyfluoroalkoxylation of aromatic and heteroaromatic polyhalides
Authors: Gupton John T. , Hertel George , DeCrescenzo Gary , Colon Cesar , Baran Donna , Dukesherer Dan , Novick Steve , Liotta Dennis , Idoux John P.
Published: May 2006

A series of activated polyhalobenzenes and polyhaloheteroaromatic compounds have been reacted with a variety of fluoroalkoxide anions. In most cases, regioselective monosubstitution or polysubstitution was observed. The nature of these monosubstitution and polysubstitution reactions is described.
Assignment of the deoxyribofuranoside protons in DNA oligomers by the application of relayed coherence transfer two-dimensional nuclear magnetic resonance spectroscopy
Authors: Hughes Donald W. , Bell Russell A. , Neilson Thomas , Bain Alex D.
Published: May 2006

Assignment of the deoxyribofuranose protons in short DNA oligomers by techniques such as homonuclear shift-correlated (COSY) 2-D nmr becomes difficult when there are overlapping diagonal signals. To solve this problem we have applied the method of relayed coherence transfer 2-D nmr to generate cross-peaks between protons such as 1′ and 3′, 3′ and 5′ and 5″ which are not coupled but belong to the same spin system. Plotting cross-sections through the diagonal peaks of the 3′ protons produced completely resolved spectra of the deoxyribofuranoside protons for each nucleotide. Chemical shifts were assigned by comparing each cross-section with the one-dimensional spectrum. A new phase-cycling procedure for the transmitter and receiver was determined and allowed data acquisition with suppression of p-type peaks. This technique is illustrated by the spectra of deoxycytidine and the deoxytriribonucleotide, dCpTpGp.
Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms
Authors: Comeau M. , Béraldin M.-T. , Vauthier E. C. , Fliszár S.
Published: May 2006

Correlations between nuclear magnetic resonance shifts and atomic charges of nitrogen in selected alkylamines, nitroalkanes, isonitriles, and azines consistently follow the general trends observed for carbon and oxygen nuclei. In azines, any increase in total electronic population on nitrogen, resulting from a gain in π charge prevailing over a concurrent loss of σ electrons, is accompanied by an upfield resonance shift—as found for aromatic and ethylenic carbon and carbonyl oxygen atoms. On the other hand, any gain in total charge dictated by that of σ populations translates into a downfield 15N shift, which is the trend exhibited by alkylamines, nitroalkanes, and isonitriles—a situation encountered earlier with sp3-hybridized carbon, carbonyl carbon, and dialkyl ether oxygen atoms.
The dependence of the photochemically induced reduction of lumiflavin on pH, light intensity, and concentration of sulphydryl compounds
Authors: Surdhar Parminder S. , Armstrong David A.
Published: May 2006

The spectral changes which occur on photolysis of flavin solutions containing β-mercaptoethanol (RSH) and lipoamide (L(SH)2) are in accord with the formation of dihydroflavin, except at pH values below 3 for RSH. Here an oxygen-stable product is formed, which has λmax 360 nm and is probably a C-4a substituted dihydroflavin. The fraction of flavin present when FlH2 reaches a photostationary statef(FlH2)ps is dependent on pH and on the absorbed light intensity Ia. At certain pH values the actual photostationary concentration of FlH2 is linear in the concentration of RSH, but for the lipoamide system shows a more complex dependence on concentration. The initial quantum yields are independent of absorbed light intensity in the pH range 7 to 10 for RSH, and increase strongly with pH in the region 7 to 9 for both sulphydryl compounds. In the pH range 5–6 they are linear in sulphydryl concentration. For RSH the results can be explained by a mechanism in which flavin triplet abstracts a hydrogen atom from RSH to form RS• and •FlH radicals. These radicals undergo back reaction to RSH and Fl or form RSSR and FlH2 by one of two mechanisms: (a) formation of RSSR−, which electron transfers to Fl or •FIH or (b) reaction of RS• with •FlH--RSH complexes. The results with L(SH)2 can be explained similarly.
Étude statistique des effets de solvant. III. Calcul et interprétation de paramètres empiriques de polarité à partir de propriétés physicochimiques des solvants purs
Authors: Chastrette M. , Carretto J.
Published: May 2006

Using multivariational statistical methods, the calculation and interpretation of empirical parameters of the polarity of solvents has been reexamined. The size of the sample used (57 aprotic solvents and 24 protic solvents) assures that it is representative. For each solvent, the data tabulated include some physical constants (dielectric constants, dipole moments, refractive indices, molar refractions, boiling points, Hildebrand's δ parameters) or theoretical values (energy levels of frontier orbitals). The methods used are factorial analysis and multiple regression. The results obtained show that, for the aprotic solvents, the parameter ET is a measure of the polarity, of the polarizability, and of the cohesion of the solvent to the extent of 43, 39, and 18% respectively. For the parameter π*, these proportions are respectively 53, 18, and 29%. For the protic solvents, the parameter ET is explained by the same variables except for 5 solvents more acidic than water; this anomaly is explained by the basicity of the oxygen of the betaine used to define ET.
Flow calorimetry of viscous liquids. Volumes and heat capacities of mixtures of N,N-dimethylformamide with N-alkylacetamides
Authors: Zegers H. C. , Boegschoten R. , Mels W. , Somsen G.
Published: May 2006

A sampling device is described which enables the Picker flow heat capacity calorimeter to handle viscous liquids. The necessary constant liquid flow through the calorimetric cell is achieved by an overpressure on the entering liquids, and can be maintained by pressure control. In addition, the device permits automatic measurement of a number of samples. The approach is applied to densities and heat capacities of binary mixtures of dimethylformamide and the viscous liquids N-ethylacetamide, N-n-propylacetamide, and N-n-butylacetamide. The results appear to be accurate enough to establish excess molar heat capacities as well as apparent molar heat capacities.
Free-radical redox reactions of uranium ions in sulphuric acid solutions
Authors: Elliot A. John , Padamshi Shahsultan , Pika Jana
Published: May 2006

The radiolytic reduction of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while ĊOOH, CO2−, and α-hydroxy-alkyl radicals reduced uranyl ions, the β-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(IV) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(IV) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygen-uranium(IV) reactions.
Crystal structure of tris(o-phenylenethiourea)selenium(II) bromide pentahydrate, C21H18N6S3Br2Se•5H2O
Authors: Chidambaram Sp. , Aravamudan G. , Rout G. C. , Seshasayee M.
Published: May 2006

The synthesis and crystal structure of the title complex are reported. Crystals are triclinic, space group [Formula: see text] with a = 10.359(2), b = 10.742(2), and c = 13.604(2) A, α = 87.25(1), β = 88.89(1), γ = 83.63(2)°, and Z = 2. The structure was solved by the heavy atom method and refined by least squares to final R and Rw of 0.055 and 0.06 for 1707 unique reflections. The structure is comprised of planar [Se2(o-phenylenethiourea)6]4+ ions and bromide counterions with the water molecules providing extensive lattice stabilization through hydrogen bonding. The dinuclear complex arises by the fusion of two SeS4 trapezoids with each Se bonded strongly to two terminal sulfur atoms Se—S(1) = 2.306(4), Se—S(3) = 2.286(5) Å and weakly to two other bridging sulfur atoms Se—S(2) = 2.840(5) and Se—S(2)′ = 2.852(5) Å.
Determination of solubility products of phosphate and vanadate apatites of lead and their solid solutions in 0.165 M sodium chloride solution
Authors: Rao P. V. R. , Gupta S. K. , Narasaraju T. S. B.
Published: May 2006

The solubility products of phosphate and vanadate apatites of lead and seven of their solid solutions, spread over the entire compositional range, were determined in 0.165 M sodium chloride solution at 37 °C. These solubility products decreased with an increase in vanadium content. A theoretical interpretation was advanced based on changes in lattice and hydration energies resulting from isomorphous ionic substitutions. The aim of the studies was the understanding of the toxic effects of lead and vanadium on the human skeletal system.
Motional behavior of "asperlin" in solution. A 13C spin-lattice relaxation study
Authors: Dais Photis , Fainos George
Published: May 2006

l3C nuclear magnetic resonance spin-lattice relaxation times (T1) have been used to probe the motional behavior of 5-acetoxy-5,6-dihydro-6-(1,2-epoxypropyl)-2-pyrone ("asperlin") in dimethyl sulfoxide solution. This molecule offers structural features suited to a study of internal motions, i.e., epoxypropyl and methyl internal motions superimposed on an anisotropic overall reorientation. The rigidity of the pyrone ring and its semiplanar conformation result in an overall ellipsoidal shape, and hence the rotational dynamics of asperlin are adequately approximated by the diffusion of a prolate ellipsoid with the major axis passing through the C(2)—H(2) bond. The description of the internal motion of the epoxypropyl ring is strongly model dependent. Furthermore, the relaxation data for the oxirane ring carbons do not uniquely define a dynamic model. Due to similarities in the activation energies of the overall and internal motions, based on temperature-dependent measurements, it has not been feasible to interpret the relaxation data by a single type of motion. Internal rotation of the epoxymethyl substituent is rationalized by applying the stochastic diffusion model of multiple internal rotations
The condensation of trimethylsilylium with water and the proton affinity of trimethylsilanol
Authors: Stone John A. , Wojtyniak Anastasia C. M. , Wytenburg Willum
Published: May 2006

The proton affinity (PA) of trimethylsilanol has been determined by high pressure mass spectrometry from the enthalpy change for the reaction [Formula: see text]. ΔH0 = −30.1 ± 1.9 kcal mol−1 giving PA (Me3SiOH) = 183.7 kcal mol−1. This latter value is 10 kcal mol−1 less than that of the carbon analogue, tert-butanol.
The anesthetic potency of n-alcohols. A model spectroscopic study in inverted micelles
Authors: Ménassa Pierre , Lussier Thérèse , Sandorfy Camille
Published: May 2006

A relation has been found between the anesthetic potency of n-alcohols (n = 1, 3, 6, 7, 9, 11, 14, and 16) and their association constants with polar groups in inverted micelles. From this point of view, cholesterol and 7-dehydrocholesterol behave like short-chain n-alcohols while cholestanol behaves like a long-chain n-alcohol.
A photoconductivity study in γ-irradiated polyethylene at 77 K
Authors: Kimura Toyoaki , Ueda Yutaka , Hirai Yohichi
Published: May 2006

A photoconductivity study was made on γ-irradiated low and high density polyethylene using 3-methylpentane, methylene chloride, and hexafluorobenzene as dopants. Electron spin resonance (esr) and optical absorption measurements were made together with photoconductivity. A study was also made for poly(4-methylpentene-1). The process of photocurrent generation is not ascribed totally to photodetrapping of trapped electrons in polyethylene; the process by photodetrapping of trapped electrons dominantly contributes to photocurrent generation in the ir region and may partly contribute in the visible region but not in the uv region. Another process for photocurrent generation other than photodetrapping of trapped electrons exists in the uv and perhaps partly in the visible region. We have tentatively ascribed this process to photodetachent of electrons from carbanions whch are formed by the reaction between radicals and electrons.
Nuclear magnetic resonance spectra of oriented bicyclic systems containing heteroatom(s): the spectrum of 2-thiocoumarin
Authors: Arumugam S. , Khetrapal C. L.
Published: May 2006

From the proton nmr studies of 2-thiocoumarin and coumarin, it is concluded that the relative interproton distances in the two oxygen heteroatom bicyclic systems are similar. The values for the phenyl ring protons do not deviate significantly from the regular hexagonal geometry, unlike bicyclic systems with nitrogens as the heteroatoms, such as diazanaphthalenes. Larger values of the indirect spin–spin couplings within the protons of the ring containing the oxygen heteroatom, compared to the values between the ortho protons in the phenyl rings in coumarin and 2-thiocoumarin, correspond to the olefinic nature of these protons. This is in contrast to results for the nitrogen heterocycles where both the rings are aromatic.
Structure and conformation of 5-methoxymethyl-1-(2′-deoxy-β-D-lyxofuranosyl)uracil
Authors: Quail J. Wilson , Ekiel Irena , El-Kabbani Ossama A. L. , Tourigny Guy , Delbaere Louis T. J. , Stuart Allan L. , Gupta Sagar V.
Published: May 2006

The structure of the nucleoside 5-methoxymethyl-1-(2′-deoxy-β-D-lyxofuranosyl)uracil (MMdLU) was deduced by X-ray crystallographic analysis. MMdLU crystallized in space group P21 with a = 8.719(4), b = 13.188(3), c = 5.701(3) Å, β = 109.56(2)° and Z = 2; R = 0.040 for 1208 unique reflections with net I > 2σ(I). The furanose ring adopts the rare C(4′)—exo envelope conformation (4E). The glycosyl linkage is anti (χ = 243.5°) and the C(5′) side chain has the t conformation. The conformation was also determined in solution by nmr analysis. The sugar ring exists in the N-conformation (97 ± 5%), the populations of the three rotamers about the exocyclic C(4′)—C(5′) bond were estimated to be g+:t:g− = 23%:59%:18% and the glycosidic conformation is predominantly anti.
High-field 2Hmr spectrometry of deuteriated 1,3,3-trimethylbicyclo[2.2.1]heptan-2-ones. Determination of geminal deuterium isotope effects on deuterium chemical shift
Authors: Werstiuk Nick Henry , Timmins George , Sayer Brian
Published: May 2006

By a high-field 2Hmr study of deuteriated 1,3,3-trimethylbicyclo[2.2.1]heptan-2-ones (fenchones), we have established that the geminal deuterium isotope effects on the exo-6-, endo-6-, and methyl deuterons are 1.46 ± 0.06 Hz (0.019 ppm), 1.61 ± 0.06 Hz (0.021 ppm), and 1.46 ± 0.06 Hz (0.019 ppm), respectively. From this study it is clear that high-field 2Hmr has the potential of providing directly all the information on the degree of deuterium substitution at carbon previously obtained indirectly by 13Cmr, while retaining the ability to identify chemically nonequivalent deuterons.
H–D exchange of 1-methylcycloalkenes in dilute acid at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

Specifically deuteriated cycloalkenes 1-trideuteriomethylcyclopentene-2,5,5-d6 (1b), 1-trideuteriomethylcyclohexene-2,6,6-d6(2b), 1-trideuteriomethylcycloheptene-2,7,7-d6 (3b), and 1-trideuteriomethylcyclooctene-2,8,8-d6 (4b) have been prepared from the corresponding protiated substrates 1a, 2a, 3a, and 4a using a modified HTDA exchange method. The perlabelled analogues of 1a and 2a, 5 and 6, have been synthesized by the same method.
Synthèse et caractérisation du α-hydroxy, ω-(4-N,N-diméthylaminophényl) polystyrène
Authors: Beinert Gérard , Winnik Mitchell A.
Published: May 2006

To prepare polymers carrying a donor chromophore at one end and an acceptor chromophore at the other, anionic initiators carrying the 4-N,N-dimethylaminophenyl group were synthesized by two different methods. These polymers were needed for the purpose of studying intramolecular cyclization via observation of exciplex formation. It was established that metal cleavage of appropriately substituted ethers was the most advantageous way to synthesize these functionalized initiators. These compounds proved very reactive toward styrene, yielding quantitatively polymers bearing 4-(N,N-dimethylaminophenyl) groups at one end of the chain. At the other end of the chain, induced deactivation of the "living" sites by means of oxirane created a hydroxy function that could be used in a later step to attach various other groups. Attachment of pyrene to this end would lead to a system in which intramolecular exciplex formation could occur.
Structural studies of organoboron compounds. XXIV. 5-Methyl-5-nitro-2-phenyl-1,3-dioxa-2-boracyclohexane
Authors: Kliegel W. , Preu L. , Rettig Steven J. , Trotter James
Published: May 2006

The title compound was prepared according to the literature in order to determine whether it has a bicyclic cage structure resulting from intramolecular O → B coordination or a monocyclic boronate structure incorporating a trigonal planar boron atom. Crystals of 5-methyl-5-nitro-2-phenyl-1,3-dioxa-2-boracyclohexane are orthorhombic, a = 17.2358(4), b = 6.5007(2), c = 9.9225(3) Å, Z = 4, space group Pnam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.064 and Rw = 0.070 for 798 reflections with I ≥ 3σ(I). The molecule actually has C1symmetry but, in the solid state, is located at a site of crystallographic Cs symmetry. In order to maintain the apparent mirror symmetry the nitro oxygen atoms are disordered over two mirror-related rotational positions around the C(2)—N bond. The molecule was found to have a monocyclic boronate structure, in agreement with earlier predictions. The six-membered heterocyclic ring has a "semi-planar" conformation. Bond distances and angles are normal.
Iodo-bridged complexes of platinum(II) and synthesis of cis mixed-amine platinum(II) compounds
Authors: Rochon F. D. , Kong P. C.
Published: May 2006

Iodo-bridged platinum(II) dimers, [Pt(L)I2]2 with ligands (L) containing nitrogen as the donor atom, have been synthesized from the reactions of cis-[Pt(L)2I2] with perchloric acid. The dimers can be cleaved in aqueous media by a second nitrogen ligand to produce isometrically pure cis-[Pt(L)(L′)I2].These compounds can finally be converted to the chloro or carboxylato compounds by precipitating the iodo ligands with a silver salt and adding KCl or a carboxylate salt. Several compounds of the types cis-[Pt(L)(L′)Cl2] and cis-[Pt(L)(L′)(dicarboxylate)] were thus prepared. A few dimers of the type [(L)(L′)Pt(tetra-carboxylate)Pt(L)(L′)] were also synthesized.
Synthesis of some ring-substituted ruthenocenes and their use in the preparation of Ru/ZSM-5 catalysts
Authors: Lemay G. , Kaliaguine S. , Adnot A. , Nahar S. , Cozak D. , Monnier J.
Published: May 2006

A method is proposed for the preparation of Ru/ZSM-5 catalysts using substituted and non-substituted ruthenocenes. To this end, the following complexes have been synthesized and characterized: dimethyl-1,1′; diphenyl-1,1′; dibenzoyl-1,1′, and monobenzoyl ruthenocene. Results of ESC A intensity ratio and ir of adsorbed pyridine show differences in the surface segregation of Ru as well as in the cationic exchange of Ru with Brønsted acid sites of the zeolite, when the catalyst is prepared using ring-substituted ruthenocene instead of ruthenocene itself. The binding energies of Ru 3d5/2 measured by ESCA are discussed.
A C-13 nuclear magnetic resonance study of the pyrimidine synthesis by the reactions of 1,3-dicarbonyl compounds with amidines and ureas
Authors: Katritzky Alan R. , Yousaf Taher I.
Published: May 2006

The detailed mechanistic pathways are elucidated for the reactions of acetylacetone, methyl acetoacetate, and dimethyl malonate with a variety of amidines and ureas. In many cases the identification of a single intermediate allows the definition of the reaction path and identification of two slow steps. Intermediates characterized include ring-closed dihydroxytetrahydropyrimidines, dihydrohydroxypyrimidinones, open-chain enamides, and carbonyl addition compounds.
Thermolysis of N-alkylated ethylenediamines: an ultraviolet photoelectron spectroscopy study
Authors: Werstiuk N. H.
Published: May 2006

Thermolyses of N,N,N′,N′-tetramethylethylenediamine (1a), N,N,N′,N′-tetraethylethylenediamine (1b) and sym-N,N′-dimethylethylenediamine (1c) at 760–825 °C have been studied by ultraviolet photoelectron spectroscopy. Although the corresponding N-alkylated aminomethylene radicals were not observed, this study establishes that thermolysis of 1a is an efficient route to N-methylenimine (3a); methane, ethane, and ethene are the other major products. Diamine 1b yields, besides ethane, ethene, and propane, heretofore unreported N-ethylmethylenimine (3b). Diamine 1c yields imine 3a and methylenimine (3c), as well as hydrogen, methane, ethane, and ethene. Molecular orbital eigenvalues of the imines are calculated using HAM/3, MNDO, HF/STO-3G, HF/3-21G, and HF/6-31G* methods.
A high temperature, pressure study of the comparative rates of enolization and oxidation of acetone in aqueous solution
Authors: Thomas John W. , Taylor Jay E.
Published: May 2006

The rate of enolization and acetone has been determined as 6.6 × 10−4 s−1 at 193.5 °C under nitrogen at 136 atm total pressure via isotopic exchange. The rate of oxidation was determined to be 8.8 × 10−6 s−1 at 193.5 °C in 123 atm partial pressure of oxygen (136 atm total pressure). In a previous study it was shown that the rates of oxidation of several ketones correlated with the extents of enolization at room temperature. This prompted the suggestion that the enol is an intermediate in the oxidation. Since the rate of enolization exceeded the rate of oxidation by a factor of 75, this suggestion is further supported. A dependence of the rate of oxidation of acetone on oxygen concentration was also demonstrated.
X-ray and 1H nmr analyses of 5-(m-benzyloxybenzyl)-1-[(1,3-dihydroxy-2-propoxy)methyl]uracil, an acyclonucleoside inhibitor of uridine phosphorylase
Authors: Birnbaum George I. , Brisson Jean-Robert , Chu Shi Hsi , Chen Zhi Hao , Rowe Elizabeth C.
Published: May 2006

The title compound crystallizes in the triclinic space group [Formula: see text] and the cell dimensions are a = 16.890(3), b = 9.586(2), c = 6.316(1) Å, α = 91.09(1), β = 93.50(1), γ = 93.04(1)°. X-ray intensity data were measured on a diffractometer, and the crystal structure was determined by direct methods. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.056 for 3454 observed reflections. Adjacent six-membered rings are approximately perpendicular to one another. The glycosidic torsion angle [C(6)—N(1)—C(1′)—O(4′)] is 96.2(2)°. In the acyclic moiety, both C—OH bonds are gauche with respect to C(4′)—O(4′). The gauche conformation is also dominant in solution, as determined by high-resolution 1H nmr spectroscopy. Results of nuclear Overhauser experiments lead to conclusions about the flexibility of the molecule.
Acylation of aromatic substrates with ketene. II. Hammett–Brown studies on substituted aromatic compounds
Authors: Fountain K. R. , Heinze Pamela , Maddox Dave , Gerhardt Greg , John Paul
Published: May 2006

not available
Acylation of aromatic substrates with ketenes. An example of vinyl oxocation reactivity
Authors: Fountain K. R. , Heinze Pamela , Sherwood Mark , Maddox Dave , Gerhardt Greg
Published: May 2006

not available
Synthesis of cedranoid sesquiterpenes. III. Functionalization at carbon 4
Authors: Yates Peter , Burnell D. Jean , Freer Vernon J. , Sawyer Jeffery F.
Published: May 2006

Dimethyl 6,6-dimethyl-5,7-dioxobicyclo[2.2.2]oct-2-ene-2,3-dicarboxylate (8) on irradiation in acetophenone gives dimethyl 6,6-dimethyl-4,7-dioxotricyclo[3.2.1.02,8]octane-1,8-dicarboxylate (13), which on treatment with lithium dimethylcuprate followed by monodecarbomethoxylation gives methyl 4,4-endo-8-trimethyl-3,6-dioxo-cis-bicyclo[3.3.0]octane-1-carboxylate (17). Similar irradiation of dimethyl 4,6,6-trimethyl-5,7-dioxobicyclo[2.2.2]oct-2-ene-2,3-dicarboxylate (24) and its 7,7-ethylenedioxy derivative (25) followed by treatment with DBU and concentrated H2SO4, respectively, gives dimethyl 3-hydroxy-4,4,8-trimethyl-6-oxo-cis-bicyclo[3.3.0]-octa-2,7-diene-1,2-dicarboxylate (30). This, on acetylation, reduction with NaBH4/CeCl3, methanolysis, monodecarbomethoxylation, and hydrogenation, gives methyl endo-6-hydxoxy 4,4-endo-8-trimethyl-3-oxo-cis-bicyclo[3.3.0]octane-1-carboxylate (38), while on reduction with Li/NH3 followed by monodecarbomethoxylation it gives a methyl 6-hydroxy-4,4-exo-8-trimethyl-3-oxo-cis-bicyclo[3.3.0]octane-1-carboxylate (33).
A Raman spectroscopic study of the complexation of the methylmercury(II) cation by amino acids
Authors: Alex Serge , Savoie Rodrigue
Published: May 2006

A systematic Raman spectroscopic investigation of the complexation of CH3Hg+ by the standard amino acids is reported. It is shown that the vibrational bands due to the ligand—Hg and Hg—CH3 stretching modes and to the symmetric —CH3 bending mode of the —HgCH3 unit are well suited to characterize the extent of complexation and the sites of attachment of the cation. Coordination, which occurs mostly on sulfur and nitrogen atoms by substitution of a proton on the thiol group of cysteine or on amino groups in general, is best identified by the frequency of the ligand—Hg stretching vibration in the 250–550 cm−1 region of the spectrum.
Concerning lone-pair stereospecificity of intramolecular OH hydrogen bonds to oxygen and sulfur in solution
Authors: Schaefer Ted , McKinnon David M. , Sebastian Rudy , Peeling James , Penner Glenn H. , Veregin Richard P.
Published: May 2006

The 1H nuclear magnetic resonance spectra for CCl4 solutions are analyzed for 2-(thioethyl)phenol, 2,3-dimethoxyphenol, and 8-hydroxythiochroman. The chemical shifts of the hydroxyl protons in these compounds, in 2,3-dihydroxyanisole, and 2-hydroxybenzyl methyl ether are discussed in terms of stereospecific intramolecular OH hydrogen bonds to lone-pair electrons on oxygen and sulfur. The O—H … O hydrogen bonds can be adequately discussed in terms of equivalent lone pairs on oxygen. There is very little difference between the hydrogen bond energies for 2,3-dihydroxyanisole and 2,3-dimethoxyphenol. In the latter the central hydrogen bonded methoxy group lies nearly perpendicular to the ring plane. The O—H … S hydrogen bonds are best described in terms of nonequivalent, 3s and 3p, lone pairs on sulfur. It is estimated that an O—H … H 3s hydrogen bond is at least 8 kJ/mol weaker than an O—H … 3p hydrogen bond. The former is predominant in the thiochroman derivative and the latter in the thioethylphenol, in which the thioethyl group prefers a plane perpendicular to the benzene ring. The long-range benzylic coupling constants in the thiochroman derivative indicate inversion of the saturated ring between distorted half-chair conformations. The boat conformation can be ruled out.
Heat capacities and volumes in aqueous polymer and polymer–surfactant solutions
Authors: Perron Gérald , Francoeur Josée , Desnoyers Jacques E. , Kwak Jan C. T.
Published: May 2006

The apparent molar volumes and heat capacities of aqueous mixtures of neutral polymers and ionic surfactants were measured at 25 °C. The polymers chosen were poly(vinylpyrrolidone) (PVP) and poly(ethyleneoxide) (PEO) and the surfactants were the C8, C10, and C12 homologs of sodium alkylsulfates and the C10, C12, and C16 homologs of alkyltrimethylammonium bromides. The polymer–surfactant interactions depend on the nature of both components and on the chain length of the surfactant. The thermodynamic properties of the cationic surfactants are essentially the same in the absence and presence of polymer indicating little surfactant–polymer interaction. On the other hand, the thermodynamic properties of anionic surfactants are shifted, upon the addition of polymers, in the direction of enhanced hydrophobic association. The effect increases with the surfactant chain length and with the polymer concentration. The effect is larger with PVP than with PEO.
The rates and products of addition of 4-chlorobenzenesulfenyl chloride to a series of trisubstituted alkenes
Authors: Schmid George H. , Garratt Dennis G. , Dean Coleen L.
Published: May 2006

The rates and products of addition of 4-chlorobenzenesulfenyl chloride to E- and Z-3-methyl-2-pentene, E- and Z-3,4-dimethyl-2-pentene, E- and Z-3,4,4-trimethyl-2-pentene, and 2,4,4-trimethyl-2-pentene were studied to determine if the mechanism involved a tertiary β arylthio carbocation. It was found that the rates of addition are not as fast as one would predict based on the polar effects of the substituents on the rate of addition to mono- and disubstituted alkenes. The products are formed by anti-stereospecific addition as in the case of addition to 1,2-disubstituted alkenes. As a result it is concluded that the reaction occurs by means of the usual mechanism involving a bridged thiiranium ion.
Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides
Authors: Foster B. , Gaillard B. , Mathur N. , Pincock A. L. , Pincock J. A. , Sehmbey C.
Published: May 2006

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.
Preparation and thermal rearrangement of 2-(tert-butyldimethylsiloxy)-5-methyl-6-exo-[(Z)-3-methyl-1-butenyl]- 4 - exo - vinylbicyclo[3.1.0]hex-2-ene. A total synthesis of (±)-sinularene
Authors: Piers Edward , Jung Grace L.
Published: May 2006

A total synthesis of the marine sesquiterpenoid (±)-sinularene (1) is described. The alcohol 19 was converted via an 8-step sequence into the bicyclic enone 28. Conjugate addition of lithium divinylcuprate to the latter substance afforded mainly the ketone 30, which was transformed into the enol silyl ether 6. Thermolysis (220 °C, 4.5 h) of 6 provided cleanly the bicyclic triene 7, which, in two steps, was converted into the tricyclic olefinic ketone 34. Hydrogenation of 34 and subsequent Wittig olefination of the resultant ketone 4 with methylenetriphenylphosphorane provided (±)-sinularene (1).
39K and 13C nuclear magnetic resonance studies of the potassium cation – dibenzo-30-crown-10 complex in solution
Authors: Detellier Christian , Robillard Marc
Published: May 2006

The structure and microdynamics in solution of the dibenzo-30-crown-10–potassium thiocyanate complex have been studied by 39K and 13C nuclear magnetic resonance. In the four solvents studied (nitromethane, acetonitrile, acetone, and pyridine), the large crown ether wraps around the potassium cation and expels the conjugate anion and the solvent molecules from the cation coordination sphere. Measurements of 39K quadrupolar and 13C dipole–dipole relaxation times in acetone-d6 gave the effective correlation time of the complex and the 39K quadrupolar coupling constant (1.4 ± 0.3 MHz). The comparison between 23Na and 39K quadrupolar coupling constants for the complexes Na+–dibenzo-24-crown-8 and K+–dibenzo-30-crown-10 showed that the electric field gradients at the metal nucleus sites are quasi identical [Formula: see text] in the two complexes.
Enolization of the benzocyclohexadienone formed during the bromination of 1-naphthol in aqueous solution
Authors: Tee Oswald S. , Iyengar N. Rani
Published: May 2006

Benzo-4-bromo-2,5-cyclohexadienone (5) has been observed in the aqueous bromination of 1-naphthol and the kinetics of its enolization to 4-bromo-1-naphthol have been studied in the pH range 0–7. This process is catalyzed by the proton, hydroxide ion, water, buffer acids, and by buffer bases. For catalysis by general bases the Brønsted β = 0.59 whereas catalysis by general acids has a value of α ~ 0. These findings are very similar to those obtained previously for the 4-bromo-2,5-cyclohexadienone 2b, formed during the aqueous bromination of 2,6-dimethylphenol. The mechanistic implications of the results are discussed. The enolization of the related dienone 8, formed from bromine and 1-naphthol-2-carboxylic acid, was also studied. At acidic pHs the dienone 8 is much more reactive than 5, with the 2-COOH behaving as an internal catalyst having an "effective molarity" of about 110 M. The enolization of 8 is also catalyzed by buffer bases.
Principal property values for six non-natural amino acids and their application to a structure–activity relationship for oxytocin peptide analogues
Authors: Wold Svante , Eriksson Lennart , Hellberg Sven , Jonsson Jörgen , Sjöström Michael , Skagerberg Bert , Wikström Conny
Published: May 2006

Previously derived principal property scales for the 20 coded amino acids have been extended to six noncoded amino acids, namely ornithine, norvaline, norleucine, O-methylated threonine, α-amino butyric acid, and citrulline. This has been done first, for the 20 coded amino acids, by developing PLS models for the relations between the previously derived scales (z1, z2, and z3) and newly measured thin-layer chromatography data, proton nuclear magnetic resonance data, plus literature data describing amino acid "bulk" (van der Waals volume and molecular mass). Thereafter, z values for the noncoded amino acids were calculated by inserting the same measured data for these compounds into the PLS models. As a validation, the calculated z values were then used to describe the structural variation of a set of 60 oxytocin peptide analogues for which literature data on biological measurements existed. The models explain 71–81% of the variance of the biological data and are highly significant according to cross-validation. Prediction errors of about twice the estimated biological measurement error are obtained for the 11 peptide analogues containing noncoded amino acids.
A novel reaction of α-haloepoxides with trialkylstannates
Authors: Corey L. D. , Singh S. M. , Oehlschlager A. C.
Published: May 2006

The reaction of α-haloepoxides with zinc powder or reagents containing the trialkylstannate anion yields allylic alcohols by anti elimination of the carbon halogen and adjacent carbon epoxy oxygen bonds. Appreciable Z → E isomerization occurs in both types of reactions but the experimental results indicate that the conversion of erythro α-bromoepoxides to E allylic alcohols by zinc or trialkylstannates shows sufficient stereospecificity to be synthetically useful.
Solvent effects on the photoisomerization of bilirubin
Authors: Sailofsky B. M. , Brown G. R.
Published: May 2006

Studies of the photolysis of bilirubin IX-α by absorbance difference (AD) spectroscopy show that in solvents which do not interfere with the intramolecular hydrogen bonding, e.g., CHCl3, EZ/ZE isomers and lumirubins are formed, with the former being predominant. The addition of ethanol to CHCl3, either before or during photolysis, greatly changes the AD spectra, possibly because of a reaction of photoproducts with the ethanol or solvatochromism of the EZ/ZE isomers. Solvents which interfere with the intramolecular hydrogen bonding of bilirubin, e.g., DMSO, increase the importance of the photoreaction that forms lumirubins. The kinetics of product formation indicate that the lumirubins result from a photoreaction of EZ/ZE isomers. The addition of aqueous buffer to DMSO lowers the extent of photoisomerization and leads to AD spectra that resemble those obtained for the photolysis in CHCl3. The addition of human serum albumin (HSA), using stopped flow techniques, to aqueous buffer solution of bilirubin immediately after photolysis gives evidence that the HSA traps the EZ/ZE isomers and prevents their reversion. However, in the presence of HSA the predominant pathway for photoreaction of bilirubin to EZ/ZE isomers is by reaction of the bound bilirubin. The AD spectra are similar to those obtained for solvents that interfere with hydrogen bonding.
Proton spin-lattice relaxation time studies and atom–atom non-bonded potential calculations on ferrocenecarbaldehyde (η5-C5H5)Fe(η5-C5H4CHO)
Authors: Pazur Richard J. , Gilson D. F. R. , Harvey Pierre D. , Butler Ian S.
Published: May 2006

The barriers to molecular rotations in the low temperature crystal phase of ferrocenecarbaldehyde, (η5-C5H5)Fe(η5-C5H4CHO), have been measured using proton spin-lattice relaxation methods and assigned to different motions, based on the results of non-bonded atom–atom potential calculations. The principal relaxation is interpreted in terms of a Cole–Davidson distribution of correlation times, and assigned to rotation of the unsubstituted ring, with an activation energy of 15.3 kJ mol−1. Other relaxation processes, observed via T1D measurements, include rotation of the aldehyde group and oscillations of the whole molecule, with barriers of 42.4 and 25.6 kJmol−1, respectively.