bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionization of 9-cyanofluorene in Me2SO–water mixtures. The role of solvent reorientation in proton tranfers
Authors: Bernasconi Claude F. , Terrier François
Published: May 2006

Rate constants of the reversible deprotonation of 9-cyanofluorene by primary aliphatic amines were measured in 10%, 50%, and 90% aqueous Me2SO (v/v) by the stopped-flow method. Intrinsic rate constants defined as k0 = k1B/q = k−1BH+/p at ΔpK + log (p/q) = 0 were obtained from Brønsted plots. The values for log k0 are 3.60 ± 0.15 in 10%, 3.81 ± 0.10 in 50%, and 3.61 ± 0.05 in 90% Me2SO. The constancy of k0 with increasing Me2SO content of the solvent contrasts with results obtained by Ritchie (C. D. Ritchie, J. Am. Chem. Soc. 91, 6749 (1969)) who found that k0 for the ionization of 9-carbomethoxyfluorene by carboxylate ions in Me2SO is much higher than for the ionization of the same carbon acid by methoxide ion in methanol. Our findings suggest that it is mainly early desolvation of the oxyanions in the hydroxylic solvent which accounts for Ritchie's results.
Electron transfer and autoxidation kinetics of the bis(imidazole)bis(dimethylglyoximato)iron(II) complex
Authors: Toma Henrique E. , Silva Antonio Carlos C.
Published: May 2006

The properties and reactivity of the bis(imidazole)bis-(dimethylglyoximato)iron(II) complex have been studied based on spectroelectrochemistry, cyclic voltammetry, and stopped-flow kinetics in aqueous solution. The autoxidation reaction was found to be inhibited by the imidazole ligand in excess but susceptible to copper(II) catalysis. In this case a mechanism has been proposed, consisting of a rapid electron transfer followed by the reoxidation of the resulting Cu(I) species by O2.
The crystal structure of N,N′-bismethoxycarbonyl-L-valyl-L-valine, a product of the rearrangement of the symmetrical anhydride of N-methoxycarbonyl-L-valine
Authors: Ahmed Farid R. , Chen Francis M. F. , Benoiton N. Leo
Published: May 2006

A side product accompanying the reaction of N-methoxycarbonyl-L-valine anhydride with an amino acid anion in aqueous dimethylformamide has been characterized by an X-ray analysis as N,N′-bismethoxycarbonyl-L-valyl-L-valine, C14H24N2O7. The crystals are orthorhombic, space group P212121, a = 14.581(2), b = 17.110(2), c = 6.970(1) Å, Z = 4. The structure was determined by the direct method, and refined by block-diagonal least squares to R = 0.046, Rw = 0.053 for 1759 reflections with I ≥ 3σ(i). The carboxy-terminal part of the dimer is in the gauche conformation while the other part is trans. Each molecule at (x, y, z) makes two hydrogen bonds O … H—O and N—H … O to the molecule at (1 − x, y − 1/2, 1/2 − z) and similarly to that at (1 − x, 1/2 + y, 1/2 − z) to form infinite ribbons along y.
Diaulusterols A and B from the skin extracts of the dorid nudibranch Diaululasandiegensis
Authors: Williams David E. , Ayer Stephen W. , Andersen Raymond J.
Published: May 2006

Two new steroids, diaulusterol A (2) and diaulusterol B (3), have been isolated from skin extracts of the dorid nudibranch Diaululasandiegensis. The proposed structures of 2 and 3 are based on spectral arguments.
Effect of geometry on the thermodynamic properties of micellar systems: trialkylamine oxides in water
Authors: Caron Gaston , Gélinas Nadia , Desnoyers Jacques E.
Published: May 2006

The apparent molar volumes, heat capacities, relative enthalpies, and isentropic compressibilities of symmetrical trialkylamine oxides and cyclohexyldimethylamine oxide were measured in water at 25 °C. The data were in most cases analyzed with a mass-action model which was previously developed (J. Phys. Chem. 87, 1397 (1983)) for micellar systems. Trimethylamine oxide shows no sign of micellization while the three next members of this homologous series and cyclohexyldimethylamine oxide form aggregates with relatively low aggregation numbers. The thermodynamic data were compared with those of assymmetrical amine oxides to investigate the effect of geometry on the micellar properties. The thermodynamic properties of the solutes in the pre-micellar region show a very good group additivity which is independent of geometry. On the other hand, with symmetrical isomers, the CMCs are much larger, the aggregation numbers smaller and the thermodynamic functions of micellization larger. These geometrical factors can be taken advantage of for thermal energy storage.
Sulphur-33 nuclear magnetic resonance spectroscopy of sulphones
Authors: Hoyle Jeffrey , Grossert J. Stuart , Hooper Donald L. , Sotheeswaran Subramanian
Published: May 2006

The sulphur-33 nmr spectra of 28 sulphones were measured in deuterochloroform solutions at 27.716172 MHz. The spectra were referenced with respect to an external aqueous ammonium sulphate solution and the chemical shifts lay in the range 0 ± 20 ppm, with many lines having a half-height width of less than 200 Hz. Instrumental parameters that affect the spectra were studied. Some of the sulphur-33 resonances can be correlated well with carbon-13 or oxygen-17 resonances in appropriate analogous compounds, and with the Taft σ* parameter.
Thioether complexes of tungsten hexacarbonyl
Authors: Lucas C. Robert
Published: May 2006

The preparation of a series of organic and organometallic thioethers R3MSR′ (M = C, Si, Ge, or Sn) is reported. From these, several new compounds of type 1 are synthesized, some of which contain para-substituted aryl functions for R′ and R. In hexane solution in the carbonyl stretching region of the ir and in the uv there is evidence for a degree of multiple bonding, at least in the M—S—W—CO portion of these molecules. Multiple bonding extending into aromatic R or R′ is small or non-existent and cannot be assessed precisely because of spontaneous decomposition of the complexes. All the complexes undergo a thermally initiated decomposition, the ease of which depends on the nature of R, R′, and M. The unusual W(I) thiolate cis-[(CO)4W-μ-SR′]2 is the thermal decomposition product.
The carbonyl group as a reluctant transmitter of hyperconjugative or σ–π spin–spin coupling interactions in derivatives of benzaldehyde, acetophenone, and benzophenone
Authors: Schaefer Ted , Peeling James , Penner Glenn H. , Lemire Alberta , Laatikainen Reino
Published: May 2006

Unlike their counterparts in anisole or toluene derivatives, the six-bond spin–spin coupling constants between para ring protons or 19F nuclei and protons or 13C nuclei in the sidechain of derivatives of benzaldehyde, acetophenone, and benzophenone can apparently contain components of opposite sign, at least for the fluorine derivatives. The σ–π components are much smaller in magnitude than in toluene derivatives, leading to very small or unobservable coupling constants. Consequently they are of limited use in conformational analysis. INDO MO FPT computations and their modifications are examined as to the reasons for the small σ–π magnitudes. Although the spin polarizability of the 2pz orbital on oxygen appears to play an important role in the transmission of nuclear spin state information, the computations do not account for a 19F coupling mechanism that appears to be significant for planar conformations. On the other hand, spin–spin coupling constants over five formal bonds to meta protons are sizeable and stereospecific.
Catalysis of ring expansion of 1-methylcyclopropylmethanol to 1-methylcyclobutanol by rhodium(I)
Authors: Burton J. Thomas , Puddephatt Richard J.
Published: May 2006

Stoichiometric reaction between [Rh2(μ-Cl)2(CO)4] and CH2CH2CHCMe2OPNB, OPNB = 4-nitrobenzoate, gave [Rh2(μ-OPNB)2(CO)4] and Me2C=CHCH2CH2Cl. The complex [Rh2(μ-Cl)2(CO)4] in acetone solution catalyzes the ring expansion of CH2CH2CMeCH2OH to give CH2CH2CH2CMeOH, and experiments with labelled derivatives indicate that the rhodium complex acts as a Lewis acid. The reaction is zero order in cyclopropyl derivative but second order in catalyst concentration. The equilibrium constant for the reaction is 21 at 40 °C and a mechanism is proposed.
On why some low-energy decomposition pathways of simple ketone molecular ions do not give rise to metastable peaks. A reappraisal
Authors: Derrick Peter J. , Hammerum Steen
Published: May 2006

The concept of minimum rate constants, k(E)min, for unimolecular decompositions does not, according to the quasi equilibrium theory (QET), provide a rationalisation of the occurrence of the higher energy reaction, loss of methyl, rather than the more favorable process, loss of methane, from metastable butanone and 3-methylbutanone molecular ions.
The Claisen rearrangement of 1,4-bis(m-methoxyphenoxy-)2-butyne
Authors: Kiehlmann E. , Li E. P.-M. , Millar J. G.
Published: May 2006

The Claisen rearrangement of 1,4-bis(m-methoxyphenoxy-)2-butyne (1b) gives four isomeric dimethoxy-6H-benzofuro[3,2-c]-6a,11a-dihydro-11a-methylbenzopyrans (3), three dimethoxy-4b,9b-dihydro-4b,9b-dimethylbenzofuro[3,2-b]benzofurans (4), and, in the presence of acid, three dimethoxy-5a,10b-dihydro-5a,10b-dimethylbenzofuro[2,3-b]benzofurans (5), which have been separated and identified by proton and 13C nmr spectroscopy. Based on the isolation of two chromene intermediates and their conversion to 3 and 4, as well as the isomerization of 3 to 4 and 4 to 5, a "double Claisen" mechanism is proposed. The reaction is not regiospecific but the two [3,3] sigmatropic shifts occur preferentially to the para positions of the methoxy substituents.
Proton magnetic resonance spectra of catechin and bromocatechin derivatives: C6- vs. C8-substitution
Authors: Kiehlmann E. , Tracey A. S.
Published: May 2006

The 1Hmr spectra of 20 catechin derivatives substituted at C-6/C-8 by bromine and/or hydrogen and at oxygen by methyl, acetyl, and/or hydrogen have been analyzed in deuterated acetone, acetonitrile, and chloroform. Because of its dependence on the nature of the solvent and of the oxygen substituent, the difference between H-6 and H-8 chemical shifts has been found to be an unreliable criterion for the distinction between 8-bromo and 6-bromo isomers. In methylated catechins, double irradiation of H-8 and H-6 enhances one (MeO-7) and two (MeO-5 and MeO-7) methoxy signals, respectively, via the nuclear Overhauser effect. This permits unambiguous assignment of chemical shifts to all ring A protons. The H-6 and H-8 resonance frequencies of catechin have been determined by decoupling of the OH-5 and OH-7 protons.
Mobilities of thermal cations in argon and xenon gases: temperature and field dependence
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

In argon at n = (2–6) × 1024 molecules/m3, the density-normalized mobility nμ of argon cations at low electric field strengths E/n is constant from 150 to 300 K; at > 300 K nμ increases. The increase was smaller when the "effective" temperature Teff of the ions was increased by applying higher E/n at 300 K. At 630 K, [Formula: see text] whereas in xenon it was 2.7, and in helium 1.0. The difference in behavior is attributed to the main ions being dimers [Formula: see text] in argon and xenon collision-induced dissociation can occur:[Formula: see text]where * indicates excess kinetic energy acquired by acceleration in the electric field. The dissociation energies of [Formula: see text][Formula: see text] and [Formula: see text] are 2.3, 1.3, and 0.7 eV, respectively. Dissociation of [Formula: see text] is negligible because of its large dissociation energy. Dissociation of [Formula: see text] and reformation of [Formula: see text] is equivalent to the inelastic de-excitation of [Formula: see text]
Structure and reactions of 4-(2,4,6-trimethyl)benzylidene-2-phenyloxazolin-5-one
Authors: Cygler Miroslaw , Huber Carol P. , Godin James R. P. , Phelps David J.
Published: May 2006

The crystal structure of 4-(2,4,6-trimethyl)benzylidene-2-phenyloxazolin-5-one has been determined. Crystals of C19H17NO2, fw 291.35, are monoclinic, P21/c, a = 10.207(2), b = 8.977(2), c = 17.123(4) Å, β = 92.66(1)°. For 2435 observed independent reflections the final R = 0.039 and Rw = 0.042. The molecule has Z configuration about the exocyclic double bond, and the benzylidene ring is twisted 61.3° out of the oxazoline ring plane, thus relieving the overcrowding caused by the two ortho-methyl substituents. The reaction of this compound with benzylamine in acetonitrile occurs almost four times as fast as predicted using model reactions.
Studies of azo and azoxy dyestuffs. Part 18. Kinetics and mechanism of the hydrolysis of 3- and 4-(p′-methoxyphenylazo)pyridines in aqueous sulfuric acid media
Authors: Buncel Erwin , Onyido Ikenna
Published: May 2006

The kinetics of hydrolysis of 4-(p′-methoxyphenylazo)pyridine, 1, and its 3-isomer, 2, have been studied in moderately concentrated sulfuric acid media at 25 °C. In all the acid solutions investigated, 1 reacted faster than 2; rate differences between the two compounds varied from ca. 1000-fold in the dilute region of acidity to ca. 250-fold in the more concentrated acid solutions. The observed first-order rate constants, kψ, for both substrates exhibit a maximum, at ca. 42% H2SO4 and 47% H2SO4 for 1 and 2 respectively. Activation parameters have also been determined. The pKa values for the second protonation equilibria of 1 and 2 have been evaluated and structures of the diprotonated species are discussed. Hydrolysis is shown to occur from the diprotonated substrates and two main mechanisms are operative. The first is an A-2 type mechanism, which involves rate-limiting attack of H2O on the aryl carbon center giving delocalized transition states and intermediates in which the pyridinium and azonium functions are involved in charge delocalization. Subsequent transfer of a proton and detachment of the leaving group are fast processes. In the second A-SE2 type mechanism, nucleophilic attack and transfer of the proton are fast steps preceding the slow general acid catalyzed separation of the leaving group. The difference in reactivity of the two compounds is attributed to differences in extent of charge delocalization in the transition states of the reactions: for 1 both the pyridinium and protonated azonium functions are involved whereas for 2 only the azonium function participates in charge delocalization.
A proton spin-lattice relaxation pathway analysis of conformational preferences of aryl and enol ethers in some cinchona and morphine alkaloids
Authors: Chazin Walter J. , Colebrook Lawrence D.
Published: May 2006

The spin-lattice relaxation rates of protons adjacent to hydroxyl and methoxy groups in aryl and enol ethers are dependent on the orientation of the alkyl group. This property has been employed to identify preferred conformations of these groups in some cinchona and morphine group alkaloids.
Short synthesis of 1,3Z,6Z,9Z-tetraene hydrocarbons. Lepidopteran sex attractants
Authors: Millar Jocelyn G. , Underhill Edward W.
Published: May 2006

A short, convergent synthesis of 1,3Z,6Z,9Z-tetraene hydrocarbons was developed. A key step was the regioselective alkylation of 1,5-dibromo-2-pentyne. The method was used to synthesize tetraenes of chain lengths C18–C20, to be used in field trials as sex attractants and (or) inhibitors of the winter moth, Operophterabrumata L., and the Bruce span worm O. bruceata H. (Lepidoptera: Geometridae).
Reactions of sulfonhydrazides with benzeneseleninic acid, selenium halides, and sulfur halides. A convenient preparation of selenosulfonates and thiosulfonates
Authors: Back Thomas G. , Collins Scott , Krishna M. Vijaya
Published: May 2006

The oxidation of sulfonhydrazides with benzeneseleninic acid provides an efficient and convenient preparation of selenosulfonates. Se-Phenyl p-tolueneselenosulfonate was also produced in good to excellent yield from the reaction of p-toluenesulfonhydrazide with PhSeCl, PhSeBr3, or PhSeCl3. Sulfonhydrazides react with sulfenyl halides or with PhSBr3 to produce thiosulfonates in generally high yield. The treatment of p-toluenesulfonhydrazide with benzenetellurinic acid, PhTeCl3, or PhTeBr3 afforded only diphenyl ditelluride and not the corresponding tellurosulfonate.
Synthesis of erythrina and related alkaloids. 17. Total synthesis of dl-coccuvinine and dl-coccolinine
Authors: Sano Takehiro , Toda Jun , Maehara Nobuteru , Tsuda Yoshisuke
Published: May 2006

Total synthesis of dl-coccuvinine 1a and dl-coccolinine 2a, "abnormal-type" erythrinan alkaloids lacking the C(16) O-function at the aromatic ring, was effectively achieved by using the Diels–Alder reaction of dioxopyrroline. Isoquinolinopyrrolinedione 6a, a key dienophile, was synthesized via the tetrahydroisoquinoline 5a, which was prepared by Bischler–Napieralski cyclization of the amide 4a at the unactivated position. The Diels–Alder adduct 7a of 1,3-bis(trimethylsilyloxy)-butadiene with 6a with converted stereoselectively into these alkaloids in short steps.
Open-chain nitrogen compounds. Part XII. Methanolysis of 3-alkyl-3,4-dihydro-1,2,3-benzotriazin-4-ols: evidence for ring-chain tautomerism with the cytotoxic monoalkyltriazenes
Authors: Lafrance Ronald J. , Manning Hartford W. , Vaughan Keith
Published: May 2006

A series of 4-hydroxy-3,4-dihydro-1,2,3-benzotriazines ("triazinols"), potential pro-drugs for the cytotoxic monoalkyltriazenes, have been investigated for anti-tumor activity and have been found to have marginal activity against the TLX5 tumor. The in vivo anti-tumor activity correlates with previously observed in vitro cytotoxicity of the compounds. The chemical behaviour of the triazinols is consistent with carbinolamine [Formula: see text] triazene ring-chain tautomerism in solution. The triazinols undergo methanolysis to give a series of new 4-methoxytriazines; the rate of methanolysis is primarily dependent on the substituent at C-4 of the triazinol. Those triazinols that undergo methanolysis rapidly are also more active biologically, suggesting that cytotoxicity and anti-tumor activity derive from the insitu generation of the open chain triazene.
Rate constant for chlorine abstraction from CCl4 by the 5-hexenyl radical
Authors: Jewell Deborah Rae , Mathew Lukose , Warkentin John
Published: May 2006

Cyclization of the 5-hexenyl free radical to the cyclopentylmethyl free radical was used to clock chlorine atom abstraction by 5-hexenyl from carbon tetrachloride in solution. The source of 5-hexenyl radicals was 5-hexenyl[1-hydroxy-1-methyl-ethyl]diazene ((CH3)2C(OH)N=N(CH2)4CH=CH2), which decomposes thermally in CCl4 by a radical chain mechanism to afford chloroform, acetone, nitrogen, 6-chloro-1-hexene, cyclopentylchloromethane, 1-hexene, and methylcyclopentane as primary products. 6-Chloro-1-hexene is converted, in part, to a secondary product, 1,1,1,3,7-pentachloroheptane, by radical chain addition of CC14 to the double bond. The rate constant for chlorine atom abstraction, kCl, was calculated from the product composition and the known rate constant for cyclization of the 5-hexenyl radical. For the temperature range 274–353 K, kCl is given by log (kCl/M−1 s−1) = (8.4 ± 0.3) − (6.2 ± 0.4)/θ where θ = 2.3 RT kcal mol−1, which leads to [Formula: see text]. This value is significantly smaller than recently reported estimates for other primary alkyl radicals.
Molecular conformation of 2′-deoxy-3′,5′-di-O-acetyl adenosine. Crystal structure and high resolution proton nuclear magnetic resonance investigations
Authors: Koole Leo H. , Buck Henk M. , Kanters Jan A. , Schouten Arie
Published: May 2006

2′-Deoxy-3′,5′-di-O-acetyl adenosine crystallizes in the orthorhombic space group P212121, and the cell dimensions are a = 7.768(1) Å, b = 12.890(1) Å, c = 15.495(1) Å; Z = 4 molecules per cell. Least-squares refinement converged at R = 0.054 for 1752 observed reflections. The adenine bases are linked via N6—H … N1 and N6—H … N7 hydrogen bonds, in such a way that infinite one-dimensional chains are formed. Comments are made on the fact that this structure is entirely different from the parallel dimer that was found for 3′,5′-di-O-acetyl thymidine. Furthermore, the conformational preferences of the title compound in aqueous solution have been determined with 300- and 500-MHz 1H nmr. It is found that the X-ray structure and the solution conformation are essentially similar, except for the C4′—C5′ conformation, that is γ− in the solid state, and predominantly γ+ in solution.
Minor metabolites of the marine hydroid Garveiaannulata
Authors: Fahy Eoin , Andersen Raymond J.
Published: May 2006

Garvalones A (8) and B (18), garvins A (11) and B (13), garveatin D (20), garveatin A quinone (29), 2-hydroxygarveatins A (21) and B (26), and 2-hydroxygarvin B (16) have been isolated from methanol extracts of the marine hydroid Garveiaannulata. The structures of all nine metabolites were inferred from their spectral data and chemical derivatization reactions. 2-(3-Oxobutyl)garveatin A (10) was synthesized as a model compound for the garvalones and the same methodology was applied to the synthesis of garvalone B (18). Dimeric compounds 30 and 32, formed from 2,2′ coupling of two molecules of garveatin B (2) or one molecule of garveatin B (2) and one molecule of garvin B (13) respectively, were also isolated and shown to be artifacts.
Long chain electrophilic contact poisons from the Dufour's gland of the ant Crematogasterscutellaris (Hymenoptera, Myrmicinae)
Authors: Daloze D. , Braekman J. C. , Vanhecke P. , Boevé J. L. , Pasteels J. M.
Published: May 2006

The Dufour's gland secretion of C. scutellaris contains a series of C23 long chain derivatives characterized by the presence of a cross-conjugated dienone linked to either a primary acetate, an aldehyde, or a carboxylic acid function. These compounds further differ from each other by the degree of unsaturation and (or) the position of an isolated double bond in the carbon atom chain. A combination of spectroscopic data and chemical degradations led to structures 1a–c, 2a–c, and 5a–c for the major components of the secretion. The highly electrophilic character of these compounds accounts for their efficiency as contact poisons.
Preparation of 1-thio and 1-amino substituted 1,3-dihydrobenzo[c]thiophene 2,2-dioxides
Authors: Khan Zafar , Durst Tony
Published: May 2006

The 1-hydroxy substituent in 1-hydroxy-1,3-dihydrobenzo[c]thiophene 2,2-dioxides is readily replaced by alkoxy, alkylthio, and amino groups. These compounds serve as precursors of alkoxy, alkylthio, and amino substituted o-quinodimethanes. Cycloaddition reactions between a series of 1,4-disubstituted o-quinodimethanes bearing a phenyl group and one of the above heteroatoms, and typical dienophiles such as dimethyl fumarate and methyl crotonate were carried out. The phenyl group controlled both the regiochemistry and stereochemistry of these cycloaddition reactions, with the major products being trans-1-phenyl-2-carbomethoxytetrahydronaphthalenes. The amino substituted o-quinodimethanes were trapped only by dimethyl fumarate.
Syntheses of 3-deoxy-3-substituted-D-glucose derivatives. Part I. Improvements in preparation of and nucleophilic additions to 1,6:2,3-dianhydro-4-O-benzyl-β-D-allopyranose
Authors: Grindley T. Bruce , Reimer Gerry J. , Kralovec Jaroslav , Brown Robert G. , Anderson Max
Published: May 2006

The yield of the five-step preparation of 1,6:2,3-dianhydro-4-O-benzyl-β-D-allopyranose from 1,6-anhydro-β-D-glucopyranose has been raised to 33% from 12% by modifying conditions or methods for four of the steps. It has been demonstrated that nucleophilic addition to the former compound provides a general route to 1,6-anhydro-3-deoxy-3-substituted-β-D-glucopyranose derivatives, although reactions with large nucleophiles proceed either slowly or not at all. A number of nucleophiles, including chloride, fluoride, cyanide, alkylsulfide, and dimethylamine, gave this type of product in good yield (73–87%). The conditions used to introduce a chloro group, a catalytic amount of tetraethylammonium chloride in 1,1,2,2-tetrachloroethane at reflux, had not previously been used for carbohydrate epoxides. The methyl substituted product was obtained in highest yield with dimethyl magnesium. By-products from this reaction included the products of a Witting rearrangement and of an elimination. All addition products were present in the 1C4 conformation.
Structure of 5,5-dimethyl-2-phenylimino-Δ3-1,3,4-thiadiazoline from oxidative cyclization of a thiosemicarbazone
Authors: Faggiani R. , Kaminski M. , Lock C. J. L. , Warkentin J.
Published: May 2006

The X-ray crystal structure of 5,5-dimethyl-2-phenylimino-Δ3-1,3,4-thiadiazoline, C10H11N3S, has been determined. The compound is monoclinic, P21/c (No. 14), with a = 13.200(5), b = 6.340(4), and c = 13.823(4) Å, β = 113.50(4)°, and Z = 4. The structure was determined by direct methods and refined to R = 0.061, Rw = 0.067 for 1277 unique reflections. The molecule has the Z configuration. The thiadiazoline ring is planar. C—N and N=N bond lengths are within the normal range. The C—S bond lengths are similar to those we have observed previously in thiazolidines. Angles differ markedly from an expected average 108°. The small C—S—C angle (90.6(2)°) is accompanied by larger C—N=N angles (114.9(3), 117.8(3)°). The phenyl ring is not coplanar with the thiadiazoline ring (dihedral angle 38.6(4)°) because of repulsive interaction of the phenyl o-hydrogen atom with the sulphur atom.
Enthalpy of solution of tris(2,4-pentanedionato)cobalt(III) in aqueous mixed solvents of 1,4-dioxane and 2-methyl-2-propanol
Authors: Yoshimura Yasuki
Published: May 2006

The solubilities Xs of tris(2,4-pentanedionato)cobalt(III) (Co(acac)3) in water – 1,4-dioxane (D) and water – 2-methyl-2-propanol (TBA) mixtures were determined over the temperature range of 15–60 °C and 20–43 °C, respectively. These data were fitted to [Formula: see text] and the enthalpy of solution [Formula: see text] of Co(acac)3 was estimated by differentiating the equation. For the water–D system, a linear correlation was found between the excess enthalpy of solution [Formula: see text] of Co(acac)3 and the excess internal pressure [Formula: see text] of the mixtures. [Formula: see text] of Co(acac)3 in the water–TBA mixtures showed complicated composition dependence due to microheterogeneity in the mixtures. The enthalpy of hydrophobic hydration [Formula: see text] of Co(acac)3 in the water–D mixtures was also estimated from the solubility curves and it was found that [Formula: see text] decreased exponentially with decreasing mole fraction of water.
A simple and direct method of cyclization for the synthesis of 10-membered rings
Authors: Deslongchamps Pierre , Lamothe Serge , Lin Ho-Shen
Published: May 2006

Ten-membered rings containing two unsaturations are produced without the use of high dilution techniques by the intramolecular malonate anion displacement of an allylic chloride.
Selected-ion flow tube studies of reactions of the carbene cation:C4N+ and their implications for interstellar gas cloud chemistry
Authors: Bohme Diethard K. , Wlodek Stanislaw , Raksit Asit B.
Published: May 2006

The carbene cation:C4N+ was generated in a Selected-Ion Flow Tube (SIFT) apparatus from allyl cyanide by electron impact and reacted at room temperature in helium buffer gas at ca. 0.33 mm Hg with the molecules H2, CO, HCN, CH4, CD4, H2O, HC3N, C2H2, CH3CN, CD3CN, H2S, NH3, ND3, and C4H2. The reactions were observed to exhibit a range in reactivity and a variety of reaction products. The observed products are consistent with expectations based on the carbene character of:C4N+. The results have implications for the role of:C4N+ as a reaction intermediate in the chemistry of interstellar gas clouds. Possible synthetic routes initiated by:C4N+ are proposed for the formation of dicyanoacetylene, cyanodiacetylene, and several acyclic as well as cyclic neutral carbenes.
Collisional energy transfer in non-reactive systems
Authors: Forst Wendell , Xu Guo-Ying , Gidiotis Grigorios
Published: May 2006

If the internal energy of target molecules highly dispersed in a heat bath is monitored as a function of time, their one-photon laser excitation and subsequent bulk collisional relaxation yields information only about energy transfer in the bulk system (a macroscopic time-dependent property). This paper discusses three special cases when [Formula: see text], the average energy transferred in a collision (a microscopic property) can be deduced from bulk relaxation data without knowledge of the collisional transition probability: (i) initial excitation is a δ function; (ii) relaxation of bulk average energy follows simple exponential law; or (iii) it is linear in time. The implications of exponential relaxation is that [Formula: see text], which is the first moment of the collisional transition probability, is a linear function of internal energy. These conclusions are illustrated using available laser relaxation data on azulene, benzene, and hexafluorobenzene, and are compared with similar data on toluene and two cycloheptatrienes. Some inconsistencies are noted, the probable origin of which is discussed.
Binding of magnesium and lanthanum ions to heparin in the presence of sodium ions. A relationship between 13C chemical shift displacements and counterion condensation theory
Authors: Dais Photis , Peng Qin-Ji , Perlin Arthur S.
Published: May 2006

Interactions between beef lung heparin and Mg2+ and La3+ counterions, in the presence of sodium ions, have been investigated by 13C-nmr spectroscopy. The chemical shift displacements observed for the carbons of the main disaccharide unit of heparin, when analysed on the basis of counterion condensation theory, indicate that the association between the heparin polyanion and Mg2+ is a delocalized process. This is analogous to the Ca2+/Na+/heparin system, despite the fact that the binding affinity of heparin for Ca2+ is stronger than that for Mg2+. By contrast, the interaction with La3+ is in excess of the theoretical predicted, which suggests that there is at least a partial site-binding of this counterion. In Ca2+/M+/heparin systems in which M+ = Na+ or K+, the selective binding preference of heparin for the univalent cations may be related to the order of their crystallographic ionic radii. A critical assessment is offered of the validity of this nmr spectroscopic approach to the study of counterion binding to heparin.
Vinyl ether hydrolysis. XVIII. The two-stage reaction of 2,3-dimethoxy-1,3-butadiene
Authors: Kresge A. Jerry , Yin Ya
Published: May 2006

The kinetics of acid-catalyzed hydrolysis of 2,3-dimethoxy-1,3-butadiene (1) to 3-methoxy-3-buten-2-one (2) and the subsequent 104 times slower conversion of the latter to biacetyl (3):[Formula: see text]were studied in aqueous solution at 25 °C. Both stages of this process give substantial hydrogen ion isotope effects, [Formula: see text] for Stage I and [Formula: see text] for Stage II, and Stage I shows general acid catalysis in formic and acetic acid buffers; both stages are therefore assigned the conventional mechanism for vinyl ether hydrolysis involving rate-determining proton transfer from catalyzing acid to substrate. The second vinyl ether group of the initial substrate (1) is found to have only a slight (3-fold) accelerative effect on the reactivity of the first group, but the acetyl substituent present in the intermediate 2 decreases its reactivity by a factor of 104; the latter appears to be due largely to the electron-withdrawing inductive effect of acetyl, with little or no influence from a countervailing electron-supplying resonance effect.
Concentration profiles in the electrodeposition of copper ferrocyanide by laser interferometry
Authors: O'Brien R. N. , Santhanam K. S. V.
Published: May 2006

The electrodeposition of cupric ferrocyanide from a solution of potassium ferrocyanide with the convection-free parallel plane horizontal electrodes with the cathode over the anode was followed by multiple beam laser interferometry as well as the conventional electrochemical instrumentation. It is considered that the cupric ion generated immediately reacts with ferrocyanide ion to form a conducting adhering precipitate layer. The initial resistance of this layer is low. Its resistance is constant with thickness until about 5 × 10−8 C mm2 has been passed probably representing ~105 molecular layers when the resistance begins to rise. A magnetic field of 0.47 T caused a slight decrease in the resistance of the cell probably due to slow rotation of the inhomogeneous paramagnetic solution. This coating may be useful as an electrode.
Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene
Authors: Manoharan R. , Dogra Sneh K.
Published: May 2006

The red shift observed in the absorption spectrum of 2,7-diaminofluorene (DAF) in ether and acetonitrile is either due to the proton-donating capacity of the solute or due to its dispersive interactions with the solvent and a blue shift in methanol and water is due to the proton-accepting nature of DAF. DAF acts as a proton donor in S1 state in all solvents. The red shift in the fluorescence spectrum of the monocation of DAF relative to that of DAF is not because of the —NH2 group becoming more basic but because of the large solvent relaxating in aqueous medium. On the other hand, the monocation of DAF in cyclohexane follows the normal blue shift in the fluorescence spectrum. pKa values for the various prototropic reactions in S0 and S1 states are determined and discussed.
Structures of the pyrazolones formed by oxidative coupling of phenols with 4-aminoantipyrine
Authors: Barton Richard J. , Johnson Keith E. , Robertson Beverly E. , Yerhoff F. Wayne , Hu Shengzhi
Published: May 2006

The structures of reaction products between 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and o-cresol, p-cresol, and p-ethylphenol are reported. The reaction of the former compound with phenols is used to estimate the concentration of phenol in potable water supplies. The reaction products are 2,3-dimethyl-4-[4-oxo-2,5-cyclohexadien-1-ylidene)amino]-1-phenyl-3-pyrazolin-5-one (monoclinic, P21/c, red, Z = 4, a = 7.092(1), b = 26.616(2), c = 8.644(2) Å, β = 79.17(3)°, 1432 reflections, R = 0.083, Rw = 0.040), 1,9a-dihydro-1,6,9a-trimethyl-2-phenylpyrazolo[3,4-b][1,4]benzoxazin-3(2H)-one (orthorhombic, Pbca, yellow, Z = 8, a = 18.943(3), b = 12.749(5), c = 13.223(2) Å, 2122 reflections, R = 0.067, Rw = 0.038), and 6-ethyl-1,9a-dihydro-1,9a-dimethyl-2-phenylpyrazolo[3,4-b|[1,4]benzoxazin-3(2H)-one (orthorhombic, Pbca, yellow, a = 18.895(11), b = 12.737(5), c = 14.041(6) Å, Z = 8, 1126 reflections, R = 0.068, Rw = 0.061), respectively. The latter two compounds rearrange to form 1,2,4,10-tetrahydro-1,6-dimethyl-2-phenyl-3H-pyrazolo[3,4-c][1,5]benzoxazepin-3-one (monoclinic, P21/c, white, Z = 8, a = 15.072(4), b = 14.491(4), c = 15.505(3) Å, β = 111.15(1)°, 3416 reflections, R = 0.101, Rw = 0.046) and 6-ethyl-1,2,4,10-tetrahydro-1-methyl-2-phenyl-3H-pyrazolo[3,4-c][1,5]benzoxazepin-3-one (monoclinic, C2/c, white, Z = 8, a = 33.768(3), b = 6.678(1), c = 15.836(2) Å, β = 115.41(1), 2805 reflections, R = 0.076, Rw = 0.043), respectively. The rearrangement is consistent with the observation that the pyrazolone rings of benzoxazinones are strained, as manifested by enlarged perimeters.
Assisted hydrolysis of the nitrile group of 2-aminoadamantane-2-carbonitrile
Authors: Paventi Martino , Chubb Francis L. , Edward John T.
Published: May 2006

Attempts to hydrolyse the nitrile group of 2-aminoadamantane-2-carbonitrile by mineral acid or alkali have been unsuccessful. However, treatment of the aminonitrile with benzaldehyde in alkaline solution gives the benzal derivative of the α-aminoamide, readily hydrolysed to the α-aminoamide. Alternatively, benzoylation of the amino group followed by acid hydrolysis gives successively the α-benzamido acid and the α-amino acid. Possible mechanisms for these facilitated hydrolyses are advanced.
Studies of the synthesis of 5-hydroxy 6-keto steroids and related 6-keto steroids
Authors: Yates Peter , Stiver Shirley
Published: May 2006

Syntheses of 5-hydroxy-5α- and 5β-cholestan-6-one (11 and 13) and their 3β-acetoxy (10 and 21) and 3β-benzyloxy derivatives (12 and 19) are described, as are syntheses of the 7α-deutero derivatives of 10 and 21. Related investigations of the syntheses of the 5-methoxy and 5-methyl analogues of these compounds are also discussed. Treatment of 12 with potassium tert-butoxide has been shown to give 5-hydroxy-5β-cholest-3-en-6-one (14) and its Δ2 isomer 15. Reaction of 6-nitrocholesteryl acetate (50) with lithium dimethylcuprate gives 3α,5-cyclo-5α-cholestan-6-one (E)-oxime (51) as the major product.
Benzophenone-photosensitized autoxidation of linoleate in solution and sodium dodecyl sulfate micelles
Authors: Barclay Lawrence Ross Coates , Baskin Kimberly Ann , Locke Steven Jeffrey , Schaefer Tanya Diane
Published: May 2006

Diffusion studies show that benzophenone (BP), linoleic acid, and methyl linoleate partition completely into the micelles of phosphate buffer/0.10 M SDS. Water-soluble compounds 4-sulphomethylbenzophenone, sodium salt (BP−), azobis(2-amidinopropane•HCl) (ABAP) and 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox) show partial partitioning into the micelles. BP- and BP−-photosensitized oxidation of linoleic acid in 0.50 M SDS exhibited characteristics of free radical chain reactions including: (1) inhibition by phenolic antioxidants, (2) no retardation by singlet oxygen quenchers, and (3) the formation of conjugated hydroperoxides with cis,trans to trans,trans ratios of geometrical isomers typical of autoxidation. Quantitative kinetic studies of the order in substrate, RH, and the rate of chain initiation, Ri, show that the classical rate law, −d[O2]/dt = kp/2kt1/2[RH]Ri1/2 applies to BP-photoinitiated autoxidation of linoleic acid in SDS and the oxidizability (kp/2kt1/2 = 4.42 × 10−2 M−1/2 s−1/2) is the same as that found with a thermal initiator. The rotating sector method gave absolute rate constants for linoleic acid autoxidation in 0.50 M SDS for propagation (kp = 36.2 M−1 s−1) and termination (2kt = 3.52 × 105 M−1 s−1), significantly lower than values in polar organic solvents; attributed to solvation of polar peroxyls in aqueous SDS. Depressed inhibition rate constants (kinh) for α-tocopherol, Trolox, and pentamefhylhydroxychroman (PMHC) in 0.50 M SDS compared to kinh in tert-butyl alcohol are attributed to hydrogen bonding effects on the peroxyl radicals and on the inhibitors.
The X-ray crystal structure of bis(pentafluorophenyl)tellurium difluoride
Authors: Aramini J. , Batchelor R. J. , Jones C. H. W. , Einstein F. W. B. , Sharma R. D.
Published: May 2006

Bis(pentafluorophenyl)tellurium difluoride crystallizes, in the space group Cc, as a molecular solid in which pairs of crystallographically independent molecules are linked by two weak secondary [Formula: see text] interactions. (C12F12Te; a = 11.088(6), b = 20.040(10), c = 13.208(5); β = 109.07(4); U = 2774; Z = 8; fw = 499.7). The structural model was refined by full-matrix least-squares methods to a final residual of R1 = 0.035 for 1621 observed reflections. The stereochemistry of the primary bonding about Te is ψ-trigonal bipyramidal as for other R2TeX2 species and is compared with that of diphenyltellurium difluoride. Differences in the stereochemistry of the primary bonding about tellurium can be attributed to the influence of the more electron-withdrawing C6F5 group, and relates to the different secondary bonding and the crystal packing. 125Te nmr coupling constants, [Formula: see text], are reported for this and two related compounds. Previous 125Te Mössbauer data is discussed in the light of the structure.
A 2-methylthio-3,5-diaryl-1,3,4-thiadiazolium cation; its reactions, and further exploration of the chemistry of 2-alkyl-3,5-diaryl-1,3,4-thiadiazolium cations
Authors: Mastalerz Harold , Mohammad Taj , Gibson Martin S.
Published: May 2006

Activation of a representative 3,5-diaryl-1,3,4-thiadiazole-2-thione by thione S-methylation gives a cation that is readily susceptible to nucleophilic substitution. Reactions with diethyl malonate, ethyl acetoacetate, acetylacetone, cyclopentan-1,3-dione, or 3-ethylrhodanine under basic conditions lead to β,β-disubstituted methine bases and (or) β-substituted methine bases in cases where deacetylation occurs under the reaction conditions. This cation and the 2-alkyl-3,5-diaryl-1,3,4-thiadiazolium cation are convenient sources of a series of neutral and cationic dyes containing the 1,3,4-thiadiazole ring system.
1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations
Authors: Arnold Donald R. , Fahie Brian J. , Lamont Laurie J. , Wierzchowski Jacek , Young Kent M.
Published: May 2006

The photosensitized (electron transfer) reactions of 3-phenyl-2,3-dihydrobenzofuran (8a), 5-methyl-3-phenyl-2,3-dihydrobenzofuran (8b), cis and trans-2-methoxy-1-phenylindane (9, cis and trans), 3,3-diphenyltetrahydrofuran (10), and 2,2-diphenyl-1-methoxycyclopentane (11) have been studied using 1,4-dicyanobenzene as an electron-accepting photosensitizer and acetonitrile–methanol (3:1) as solvent. These reaction conditions cause carbon–carbon bond cleavage of analogous acyclic β,β-diphenylethyl ethers to give products derived from the diphenylmethyl radical and the α-oxycarbocation intermediates. The purpose of this study was to determine if this reaction could be applied to five-membered cyclic derivatives to give 1,5-radical cations.The primary products from 8a and 8b were the dehydrogenated, aromatized 3-phenylbenzofurans 14a and 14b. These products react further; continued irradiation gave the methanol adducts, cis and trans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a and 15b, cis and trans). The only observed reaction of the indanes (9, cis and trans) was cis-trans isomerization. Deuterium was incorporated at the bis-benzylic position of 8 and 9 when the irradiation was carried out in acetonitrilemethanol-O-d. These results are consistent with reversible deprotonation from the radical cations. There was no evidence for carbon–carbon bond cleavage with either 8 or 9. The relative rate, deprotonation faster than carbon–carbon bond cleavage, is explained in terms of the conformation of the bond that cleaves in relation to the singly occupied molecular orbital (SOMO) of the radical cation. Oxidation potential measurements support the conclusion that the SOMO of 8 and 9 is largely associated with the fused phenyl ring and is therefore orthogonal to the benzylic carbon–carbon bond. Irradiation of cis or trans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a, cis or trans), under these conditions, leads to cis–trans isomerization. The mechanism in this case involves the reversible loss of methanol. There is evidence that the addition of methanol to 14 involves the sensitizer radical anion – 14 radical cation pair.In contrast with the fused bicyclic systems, the monocyclic tetrahydrofuran 10 and the methoxycyclopentane 11 both cleave under these conditions; the products are the expected acetals 22 and 29 formed from the intermediate 1,5-radical cations. In 10 and 11 the SOMO, which is largely associated with the diphenylmethyl moiety, can overlap with the adjacent carbon–carbon bond and cleavage occurs as in analogous acyclic systems. Both 10 and 11 are relatively stable to irradiation under conditions that are identical except with acetonitrile as solvent (without methanol). We found no evidence for cyclization of the intermediates (1,5-radical cation or 1,5-diradical) into the terminal phenyl ring.
An unlikely coincidence in coupled 13C nuclear magnetic resonance spectra. 2J(C,H) in 2,6-dichlorotoluene and related molecules
Authors: Schaefer Ted , Peeling James
Published: May 2006

Although as many as 13 peaks are observable in each half of the 13C nuclear magnetic resonance spectrum of C-4 in 2,6-dichlorotoluene at 22.6 MHz, the iterative analysis yields an incorrect value of 2J(C,H). Theoretical spectra for two values of this coupling constant are essentially identical under normal linewidth conditions. At 75.5 MHz, the 13C spectrum displays most of the 48 peaks expected for the X part of an AB2XR3 spectrum, yielding the correct choice for 2J(C,H). The theoretical spectrum at 125 MHz is similar to that at 22.6 MHz but only for the correct 2J(C,H). Correct values of 2J(C-4,H) are given for the 2,6-dichloro derivatives of toluene, ethylbenzene, benzyl alcohol, benzyl bromide, and chloride; these were given incorrectly previously.
The methylenic sequence conformation in a series of isoelectronic molecules
Authors: Deguire Suzanne , Brisse François
Published: May 2006

The crystal structures of 1,4-dibenzoylbutane, 2DBC, and ethyleneglycol dithiobenzoate, 2DBS, have been solved by direct methods in order to follow the evolution of the geometry and the conformation of the Y—CH2—CH2—Y sequence in the isoelectronic series of C6H5—CO—Y—CH2—CH2—Y—CO—C6H5 where Y = CH2, NH, O, and S. 2DBC is monoclinic, a = 7.750(4), b = 21.287(6), c = 8.905(2) Å, β = 100.55(3)°, Z = 4. 2DBS is also monoclinic, with a = 5.702(3), b = 16.171(15), c = 8.001(4) Å, β = 98.79(4)°, and Z = 2. Both compounds belong to the P21/n space group. The weighted least-squares refinements converged to Rw = 0.049 (2DBC) and 0.043 (2DBS). The conformation of the methylenic sequence is all-trans (2DBC) and g+tg− for 2DBS (t = trans, g = gauche). The ir spectra have absorptions at 1467, 1308, and 931 cm−1 (2DBC) and at 1408, 1239, and 727 cm−1 (2DBS), respectively, characteristic of the trans conformation of the Y—CH2—CH2—Y sequence. The 13C CP/MAS solid-state nmr spectra of these and other related compounds have been recorded. It is, in turn, possible to propose that the τ torsion angle between the amide group and the methylenic sequence, has a value of 85° in the aromatic polyamide, Nylon 2T.
Neutron inelastic scattering spectra of methane on graphite at the commensurate–incommensurate phase transition
Authors: Humes R. P. , Smalley M. V. , Rayment T. , Thomas R. K.
Published: May 2006

Neutron scattering spectra associated with rotational tunnelling and low frequency vibrations of CH4 adsorbed on graphite at 4 K and coverages from 0.2 to 1.5 monolayers are reported. Particular consideration is given to the changes which occur across the commensurate–incommensurate phase transition. It is shown that the incommensurate phase has a domain wall structure and is not a floating phase as had previously been proposed from theory.
An investigation of the structures of isomeric ions derived from acetone, diacetone alcohol, and mesityl oxide
Authors: March Raymond Evans , Young Alexander Baldwin
Published: May 2006

An investigation of the structures of isomeric ions formed in ion/molecule reactions occurring in 2-propanone (acetone), 4-hydroxy-4-mefhyl-2-pentanone (diacetone alcohol), and 4-methyl-3-penten-2-one (mesityl oxide) has been performed using a hybrid mass spectrometer of reversed geometry. Ions of m/z 117, which have been observed as products of ion/molecule reactions in acetone and in diacetone alcohol, may have a single structure if an aldol type condensation reaction occurs under acidic conditions in the gas phase; however, high energy collision induced dissociation (CID) results proved the two ions to be isomeric only.Dehydration of the m/z 117 ions produced a species of m/z 99 which, in the case of diacetone alcohol, may have the structure of protonated mesityl oxide. That the m/z 99 ion formed was unique to each system was demonstrated by high energy CID and kinetic energy release (KER) spectrometry. In the acetone system, CID results suggested that m/z 99 was an ion–dipole complex of [Formula: see text]; this hypothesis was tested by clustering [Formula: see text]with (CD3)2CO and comparison of its CID results with those obtained above. In the case of m/z 99 derived from diacetone alcohol or mesityl oxide, the neutral lost via metastable decomposition in the second field-free region was found to be C4H8, presumably 2-methyl propene. While the ion of m/z 99 may also eliminate methane to yield a species of m/z 83, the dominant metastable elimination from this ion is carbon monoxide rather than ethene as shown by collision induced dissociative ionization (CIDI). The ions of m/z 83 observed in the two systems exhibit very similar CID spectra; however, a small variation in the yield of products of m/z 41 and 43 suggests two structures for the ion derived from diacetone alcohol, one of which is identical to that seen in mesityl oxide.