bluuebunny/crossref_metadata_2025 huggingface dataset:
Étude thermodynamique des trois isomères du dihydroxybenzène
Authors: Sabbah R. , Buluku E. N. L. E.
Published: May 2006

The present work is concerned with a thermodynamic study of the three isomers of dihydroxybenzene. By combustion calorimetry of small amounts of substance, sublimation calorimetry, differential thermal analysis, and heat capacity measurements, it was possible to determine the enthalpies of formation of 1,2-, 1,3-, and 1,4-dihydroxybenzene in the condensed and gaseous phases, their enthalpies of fusion and transition, and the temperature of their triple point and transition. The experimental results are used to discuss the relative stability and determine the conjugation energy of the three compounds. The values are in good agreement with the theoretical values obtained from a quantum chemical calculation. The enthalpies of atomization enabled us to determine an energy value for the intramolecular Cb—OH bond in dihydroxybenzenes and to correlate it with previous results obtained from a study of alkane-diols. The enthalpies of sublimation were discussed. An intramolecular hydrogen bond was displayed in the ortho isomer. Intermolecular hydrogen bonds associated with van der Waals interactions exist in dihydroxybenzenes. Their energy contributions were determined. Key words: thermodynamics, calorimetry, differential thermal analysis, 1,2-benzenediol or 1,2-dihydroxybenzene or catechol; 1,3-benzenediol or 1,3-dihydroxybenzeneorresorcinol; 1,4-benzenediol or 1,4-dihydroxybenzene or hydroquinone or quinol; enthalpies of combustion, of sublimation, of fusion, of transition, energy of conjugation, enthalpies of atomization, of inter- and intramolecular bonds; triple point and transition temperatures.
Dissociation equilibria of picric acid in the binary N, N-dimethylformamide/2-methoxyethanol solvent system
Authors: Marchetti Andrea , Preti Carlo , Tagliazucchi Mara , Tassi Lorenzo , Tosi Giuseppe
Published: May 2006

Three empirical equations are proposed to fit the experimental values of the dissociation constant for picric acid, chosen as guide-solute working in the N, N-dimethylformamide/2-methoxyethanol solvent system. The work was performed operating at 19 temperatures ranging from − 10 to + 80 °C in the pure solvents and in their nine mixtures, identified by the mole fraction (X) of one component. This empirical treatment, which describes the dependence of the dissociation constant on temperature and composition of the solvent mixture, is represented by functions of the type K = K(T), K = K(X), and K = K(T, X). The K = K(T, X) equation in its complete form is composed of 20 terms, some of which can be eliminated because of small statistical weight; the number and type of these terms vary on passing from one solvent system to another and the best-fitting form is suggested. A comparison among various K = K(T, X) equations proposed in the present and in previous works has been made. Key words: dissociation equilibria, binary nonaqueous solvent mixtures, picric acid, N,N-dimethylformamide, 2-methoxyethanol.
New halogenated sesquiterpenes from the red alga Laurencia caespitosa
Authors: Norte Manuel , González Rafael , Padilla Agustín , Fernández José J. , Vázquez Jesús T.
Published: May 2006

Three new brominated sesquiterpenes have been isolated from the red alga Laurencia caespitosa. The structures of these metabolites have been elucidated by spectral analysis and chemical correlations. Their absolute configurations were established by CD methods. Key words; red alga, Rhodomelaceae, halogenated sesquiterpenes, snyderane.
The photochemistry of the rhodizonate dianion in aqueous solution
Authors: Zhao B , Back M. H.
Published: May 2006

The thermal and photochemical reactions of rhodizonate dianion have been studied in aqueous solution in the presence of various oxidizing agents. Both reactions are initiated by electron transfer to an acceptor which is a sufficiently strong oxidizing agent. With hydrogen peroxide and ferricyanide a square root dependence of the rate on the concentration of additive was observed whereas with tetracyanoethylene the rate was first order with respect to additive. This difference in behaviour is explained on the basis of the rate of separation of ions from the initial charge transfer complex. In most cases the main product was croconic acid. NMR analysis of other products indicated some formation of C—H bonds and possibly incorporation of an oxygen atom into the ring. A maximum quantum yield of 0.04 for disappearance of rhodizonate was observed in the presence of tetracyanoethylene. Key words: photochemistry, rhodizonic acid, dianion, electron transfer.
Reactions of benzo[b]thiophene with some aqueous platinum metal species at elevated temperatures
Authors: Clark Peter D. , Fait James F. , Jones Colin G. , Kirk Martin J.
Published: May 2006

The desulfurization of benzo[b]thiophene 1 with aqueous transition metal species in the presence of various hydrocarbons at elevated temperatures is described. Mechanistic studies have shown that treatment of 1 with solutions of RuCl3 and other platinum metal species results in the formation of 2,3-dihydrobenzo[b]thiophene 2 and ethylbenzene 3 as major products. Metal coordinated species are probable intermediates in the formation of 2 and hydrocarbon products. 2 readily coordinates to PdCl2 to form square-planar trans-dichlorobis(2,3-dihydrobenzo[b]thiophene) palladium(II), which decomposes to ethylbenzene at 300 °C. The crystal structure of the complex was determined by a single crystal X-ray diffraction study. The complex crystallized in the monoclinic space group C 2/c with Z = 8 in a cell of dimensions a = 23.057 (3), b = 9.711 (1), c = 15.227 (2) Å and β = 99.74(1)°. The structure was solved by the Fourier method and was refined by full-matrix least-squares calculations to R = 0.042 for 2537 observed data with I > 2.5σ(I). Key words: benzo[b]thiophene, desulfurization, platinum metal species.
Kinetic and electrochemical analysis of Ni(II) reduction at the dropping mercury electrode in the presence of thiourea
Authors: Villamañán Rosa M. , Mata-Pérez Fernando
Published: May 2006

A study of the two polarographic prewaves of the Ni(II)–thiourea system has been made. The results were analysed by determining Koutecky's parameter from the ratio of the limiting current of the prewaves and the main wave. This parameter is considered an experimental rate constant and the influence of different variables on its value was analyzed. An electrochemical study of the prewaves was also made. Two formal mechanisms to explain both prewaves are proposed. Key words: polarographic prewaves, electrochemical kinetics, reaction mechanisms.
Synthèse d'isoxazoles substitués en α de l'oxygène et d'isoxazoles substitués en α de l'azote et de l'oxygène par des chaînes alkyle ou alcényle
Authors: Cherton Jean-Claude , Lanson M. , Ladjama D. , Lefebvre N. , Vossough Z. , Basselier J-J.
Published: May 2006

Two series of isoxazoles substituted by long alkyl or alkenyl chains in the α position with respect to the oxygen atom or in the α position with respect to the two heteroatoms have been synthesized. Starting from 3,5-dimethylisoxazole, the regioselective metalation/alkylation on the α-O methyl group was a very convenient route to a large variety of "α-O substituted isoxazoles". When applied to α-O methylated isoxazoles bearing an α-N alkenyl chain the same method provides an original unequivocal approach to 3,5-dialkenyl isoxazoles. An alternative route to these compounds, despite the formation of di-isoxazoline as by-product and an additional step corresponding to the oxidation of the intermediate isoxazoline, is the 1,3-dipolar cycloaddition, by using terminal dienes as dipolarophiles with alkenyl dipoles. Nevertheless, the cycloaddition between monoalkylated alcynes and alkylated dipoles remains the most straightforward synthesis of 3,5-dialkyl isoxazoles. Key words: isoxazoles, alkenyl side chains, metalation–alkylation, regioselectivity.
The structure of the tetrachlorohydroxotellurate(IV) anion in KTeCl4(OH)•0.5H2O and KTeCl4(OH)
Authors: Milne J. B. , Gabe E. J. , Bensimon C.
Published: May 2006

Three compounds containing the tetrachlorohydroxotellurate(IV) anion, [Formula: see text] K[TeCl4(OH)]•0.5H2O, and K[TeCl4(OH)], have been prepared. The crystal structure of K[TeCl4(OH)]•0.5H2O has been determined. The structure contains isolated square pyramidal TeCl4(OH)− anions with OH axial. Vibrational spectroscopy shows that [Formula: see text] and K[TeCl4(OH)]•0.5H2O both contain isolated anions but that, in K[TeCl4(OH)], the anion is polymerized with chloride bridging. The hydroxo group, like the fluoro group, acts to hinder coordination at the site trans to it on Te(IV). Key words: tellurium(IV) complexes, chlorotellurate(IV), X-ray structure, vibrational spectroscopy.
Poly(vinylbenzo macrocyclic polyethers). Synthesis and cation binding properties of 12-crown-4 derivatives
Authors: Buchanan G. W. , Denike J. K.
Published: May 2006

The synthesis of 4′-vinylbenzo-12-crown-4 ether is reported. Polymerization to relatively low molecular weight polymers can be accomplished with a free radical initiator. A copolymer with styrene can be prepared and the Li+, Na+, and K+ binding properties of these polymers are compared to those of their monomeric analogs using salt distribution equilibria in water – methylene chloride. For all cations the homopolymer is found to extract the salts from the aqueous phase most effectively. The copolymer is slightly less effective than the homopolymer but more effective than either of the monomers by a factor of approximately 7, indicating that cooperative binding is likely. Na+ is the most efficiently extracted cation, followed by K+ and Li+. Key words: crown ether polymers, complexation properties.
Carbohydrate protein interactions. Syntheses of agglutination inhibitors of wheat germ agglutinin by phase transfer catalysis
Authors: Roy René , Tropper François D.
Published: May 2006

Starting from chloride 1, a series of para-substituted aryl 2-acetamido-2-deoxy-β-D-glucopyranosides were prepared using phase transfer catalysis conditions with tetrabutylammonium hydrogen sulfate in 1 M sodium hydroxide and methylene chloride at room temperature. Zemplén de-O-acetylation afforded the unprotected glycosides. Optimization of reaction conditions was evaluated. Several functional group manipulations were effected to widen the number and nature of the para-substituents. Key words: phase transfer catalysis, aryl 2-acetamido-2-deoxy-β-D-glucopyranosides.
Experimental and theoretical conformer distributions of 3-methylbenzaldehyde
Authors: Schaefer Ted , Cox Kerry J. , Sebastian Rudy
Published: May 2006

The long-range coupling constants between the aldehydic and ring protons of 3-methylbenzaldehyde, in CS2/C6D12 and acetone-d6 solutions, imply an equilibrium constant, K(O-cis/O-trans) of 1.07(4) in both solvents at 300 K. The small preference for the O-cis conformer in both solutions suggests that the O-cis conformer is also the more abundant in the vapor, indicating a reassignment of recently reported electronic bands in this state. Geometry-optimized molecular orbital computations, using the AMl, STO-3G, and 6-31G bases, confirm the slightly lower energy of the free O-cis conformer. The 6J(H,CHO) of +0.015(1) Hz for the acetone solution has the correct sign and magnitude implied by a recent simple model for this coupling constant. Other long-range coupling constants are also discussed in terms of their mechanisms. Key words: conformations, 3MB; NMR, 3MB; spin–spin coupling constants, 3MB; MO computations, 3MB.
A versatile synthetic route to the anti-implantation agent, yuehchukene, and its analogues
Authors: Kutney James P. , Lopez Francisco J. , Huang Shyh-Pyng , Kurobe Hiroshi , Flogaus Robert , Piotrowska Krystyna , Rettig Steven J.
Published: May 2006

A detailed study directed toward the development of a versatile synthetic route to the interesting dimeric natural product yuehchukene (1) and its epimer, 6a-epi-yuehchukene (2), has been completed. Due to the anti-implantation activity associated with 1, it was important to provide a synthetic strategy not only to 1, but to a family of yuehchukene analogues that, hopefully, would reveal superior chemical stability and (or) elevated biological activity. The experiments described herein and which utilize the readily available and inexpensive isophorone (6) satisfy these requirements. Key words: yuehchukene synthesis, yuehchukene analogues, anti-implantation activity.
Long-range 1H,19F and 13C,19F coupling constants and molecular orbital computations as indicators of internal motion in C6H5OCF3 and its 4-fluoro derivative
Authors: Schaefer Ted , Penner Glenn H. , Sebastian Rudy , Peeling James , Beaulieu Christian
Published: May 2006

Internal rotational potentials for rotation about the Csp2—O bond in C6H5OCF3 and its 4-fluoro derivative are computed at the STO-3G and 3-12G levels of molecular orbital theory. As for anisole, the perpendicular conformer is calculated as least stable for C6H5OCF3 but the height of the internal barrier is considerably lower than in anisole. The 4-fluoro substituent reduces the twofold component significantly, indicating reduced p …π conjugation, but does not much change the values of the higher terms in the theoretical potentials. The internal potentials are rather flat with minima between about 30° and 45°, these angles measuring the twist away from planarity. The 1H, 13C, and 19F nuclear magnetic resonance spectra in polar and nonpolar solution yield long-range coupling constants, nJ(1H,19F) and nJ(13C,19F). These parameters are qualitatively consistent with relatively low barriers to rotation about the Csp2—O bonds in these molecules and with only a small dependence on solvent polarity. Key words: C6H5OCF3 and 4-F-C6H4OCF3: 1H NMR, 19F NMR, conformations, MO computations.
Comparaison des approches empirique et chimiométrique dans la modélisation des effets de solvant. Cas des propriétés spectrales en RMN, IR et UV–visible
Authors: Auhmani Abdelouahed , Bitar Hassane , Luu Roger Phan Tan , Barrios Laura
Published: May 2006

In this paper, we review a comparison of the empirical and chemiometrical approaches to the modelization of the effects of solvent on a number of NMR, IR and UV–visible spectral properties. The solvents have first been characterized by the π*, α and β scales, which describe respectively the polarity–polarisability, the acidity, and the basicity by hydrogen bond; the 17 most representative, with orthogonal parameters, have been chosen. An attempt has been made to rationalize the observed effects on the observed properties by using simple linear empirical models like the π*, α, and β parameters of Kamlet, Taft, and Abboud; [Formula: see text] of Reichardt; and A and B of Swain. Furthermore, an analysis of the main components has been applied to these effects and to the properties examined; it appears that the quality of the correlations obtained is generally satisfactory and can be compared to the quality that can be observed with the empirical approach. Key words: solvent effect, empirical approach, chemiometrical approach. [Journal translation]
Structural studies of organoboron compounds XLVIII. 1,4-Diphenyl-3,3:6,6-bis(tetramethylene)-2,5,7-trioxa-3,6-diazonia-1,4-diboratabicyclo[2.2.1]heptane
Authors: Kliegel Wolfgang , Riebe Ulf , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of N-hydroxypyrrolidine with either oxybis(diphenylborane) or phenylboronic acid gives 1,4-diphenyl-3,3:6,6-bis(tetramethylene)-2,5,7-trioxa-3,6-diazonia-1,4-diboratabicyclo[2.2.1]heptane in moderate yield. Crystals of the product are orthorhombic, a = 10.984(2), b = 14.619(2), c = 12.311(2) Å, Z = 4, space group Pccn. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.039 and Rw = 0.043 for 908 reflections with I ≥ 3σ(I). This is the first heterocyclic [2.2.1]heptane system containing a six-membered BONBON ring and a B—O—B bridge to be structurally characterized. The molecule has exact C2 symmetry with the twofold axis passing through the bridging oxygen atom. Bond lengths involving the tetrahedrally coordinated boron atom are B—O(B) = 1.423(3), B—O(N) = 1.497(3), B—N = 1.703(3), and B—C(phenyl) = 1.577(4) Å. Key words: 2,5,7-trioxa-3,6-diazonia-1,4-diboratabicyclo[2.2.1]heptane ring system, crystal structure, organoboron compound.
A tensammetric study of the adsorption of cationic polymers and copolymers
Authors: Smith-Palmer Truis , Roberts Cheryl
Published: May 2006

The tensammograms of several sets of cationic polyacrylamide copolymers are discussed and compared. Tensammograms are not affected by molecular weight, but plots of capacitive current at a chosen potential versus charge density give regular curves. Key words: tensammetry, cationic, polyacrylamide, charge density.
Novel, intramolecular hydrogen-transfer and cyclo-addition photochemistry of cyclic 1,3-dienes
Authors: Miesen Franciscus W. A. M. , Baeten Hans C. M. , Langermans Harm A. , Koole Leo H. , Claessens Henk A.
Published: May 2006

With use of one- and two-dimensional NMR spectroscopy and deuterium labelling, the photochemistry of 9-endo-hydroxy-9-exo-vinyl-bicyclo[4.2.1]nonadiene (1) and the 9-exo-(11-dimethylvinyl)- (2) and 9-exo-ethyl- (3) analogues has been studied. Irradiation of 1–3 gave novel 8-membered ring systems 4–6 by a light-induced rearrangement process, in which the hydroxyl proton is transferred on one side of the molecule toward one of the termini of the endocyclic diene. This rearrangement process thus involves a formal hydrogen transfer, during which either H+ or H• may be transferred to a reactive diene intermediate. Replacement of the hydroxyl proton by deuterium in 1–3, and 2H NMR of the corresponding photoproducts, confirmed that the hydrogen translocation occurs intramolecularly. Prolonged irradiation of 4 and 5 results in the formation of pyran products 10 and 11 by an intramolecular photocycloaddition of the triplet excited state of the α,β-unsaturated ketone to 1,3-cis,cis-cyclooctadiene, via a stabilized bisallylic biradical intermediate. Conformational studies of the structurally more rigid system 10, which is derived from 4, revealed that the hydroxyl proton was transferred on the endo side of the molecule. Key words: intramolecular hydrogen transfer, photochemistry of hydroxy-alkyl-bicyclononadienes, intramolecular photocycloaddition, conformational studies.
On vibrational force field calculations
Authors: Murphy W. F.
Published: May 2006

A series of computer routines for performing normal coordinate calculations of harmonic vibrational frequencies is described. These are designed for operation on current-generation computers having direct-access storage. Example results are given for the chain isomer of disulfur difluoride. Key words: vibrational force field calculations, normal coordinate calculations, harmonic force fields.
Relative cross section and time-resolved fluorescence of porphyrin–DNA complexes
Authors: Liu Yixian , Koningstein J. A. , Yevdokimov Y.
Published: May 2006

Relative values have been obtained for the cross section of fluorescence of tetrakis(4-N-methylpyridyl)porphine and the zinc(II) complex with DNA. Time-resolved fluorescence spectra have been used to assign fluorescence of porphyrins which intercalate at or are externally bound to DNA. The experimental data suggest that an equilibrium distribution for intercalated and externally groove-bound to DNA of porphyrin is reached for [Formula: see text] complexes. Radiative lifetimes of the various porphyrin species have been determined and evidence is found suggesting the contribution of non-linear effects to the intensity of laser induced fluorescence of r > 1000 complexes. Key words: cross section, fluorescence, porphyrin–DNA complexes, intercalation, outside bound.
The proton affinities and deprotonation enthalpies of β-D-fructopyranose and α-L-sorbopyranose
Authors: Woods Robert J. , Szarek Walter A. , Smith Jr. Vedene H.
Published: May 2006

The proton affinities (PAs) and deprotonation enthalpies (DPEs) were calculated for the pyranoid forms of two naturally occurring sugars, D-fructose and L-sorbose. In both molecules the PAs of the primary hydroxyl group (HO-1), the anomeric hydroxyl group (HO-2), and the ring-oxygen atom (O-6) were calculated, as were the DPEs of HO-1 and HO-2. The stabilities of the conjugate acids and bases of these sugars are enhanced by the presence of intramolecular hydrogen bonding, a feature that is significant in explaining the differences in sweetness and the rates of mutarotation of the title compounds, as well as the differences in the rates of acid-catalyzed hydrolysis of ketopyranosides. Key words: proton affinity, deprotonation enthalpy, ab initio calculations, AM1, hexuloses.
An NMR study of the structure and reactivity of phosphonium ylides stabilized by a carbonyl function
Authors: Kayser Margaret M. , Hatt Krista L. , Hooper Donald L.
Published: May 2006

The structures of five stabilized phosphonium ylides 1–5 were studied by 1H, 13C, and 31P NMR. Various trapping experiments were followed by investigation of the relative reactivities of these ylides vis-à-vis benzaldehyde. A novel effect of some significance, the influence of acidic contaminants (conjugate acids, H2O, etc.) on the structure and reactivity of these compounds, is discussed. Key words: stabilized phosphoranes, Wittig condensations, acid catalysis.
Hydrolysis of a monocyclic oxyphosphorane containing a five-membered ring
Authors: McGall Glenn H. , McClelland Robert A.
Published: May 2006

A kinetic study is reported for the hydrolysis of 2,2-diphenyl-2-methoxy-1,3,2-dioxaphospholane 1. This phosphorane exists in aqueous solution in a pseudo acid–base equilibrium with an observable phosphonium ion, the ring-opened (2′-hydroxyethoxy)diphenylmethoxyphosphonium ion 5. The equilibrium constant Ka ([1][H+]/[5]) is 9 × 10−9, values determined by kinetic and spectroscopic methods being in good agreement. This phosphonium ion is, however, not involved in the overall hydrolysis reaction, which proceeds via the thermodynamically less stable cyclic five-membered phosphonium ion derived by loss of the exocyclic methoxy group from the phosphorane, the 2,2-diphenyl-1,3,2-dioxaphospholan-2-ylium ion 6. This route for the overall hydrolysis is established by analysis of the products, and by the observation that the rate constant for the disappearance of 5 in acid solutions is 40 000 times greater than that for an analog that differs only in not being able to cyclize, the (2′-methoxyethoxy)diphenylmethoxyphosphonium ion 7. At all pH, the phosphorane 1 and the ring-opened phosphonium ion 5 exist in equilibrium, and the rate-limiting step in the overall hydrolysis is the cleavage of the exocyclic methoxy group to give the cyclic phosphonium ion 6, which is rapidly converted to products by reaction with water. The actual equilibration reaction involving 1 and 5 cannot be observed at any pH, even with stopped-flow spectroscopy. The non-catalyzed ring closure of the phosphonium ion 5 reforming the phosphorane 1 occurs with a rate constant of 200–500 s−1, corresponding to an effective molarity of (2–5) × 107 M for the intramolecular hydroxy group in this reaction. The rate-limiting exocyclic cleavage is assisted by H+, with a very large rate constant 2 × 109 M−1 s−1. Catalysis by general acids is also observed. The Brønsted plot has a slope α of 1.0 for the weaker acids, with a break for acids with pKa < 3. This "Eigen"-type behavior is proposed to arise from a transition state with little phosphonium ion character, in which the proton is almost completely transferred for the weaker acids. Key words: phosphorane, phosphate, phosphonium, hydrolysis.
Nucleic acid related compounds. 67. Synthesis of 5′-amino and 5′-methylthio chain-extended nucleosides from uridine
Authors: Wnuk Stanislaw F. , Dalley N. Kent , Robins Morris J.
Published: May 2006

Treatment of 2′,3′-O-isopropylideneuridine-5′-aldehyde with the stabilized Wittig reagent, (p-toluenesulfonylmethylene)triphenylphosphorane, gave high yields of 1-[5,6-dideoxy-2,3-O-isopropylidene-6-(p-toluenesulfonyl)-β-D-ribo-hex-5(E)-enofuranosyl]uracil (2). This vinylsulfone (2) underwent isomerization readily in base to give the allylic sulfone, 1-[5,6-dideoxy-2,3-O-isopropylidene-6-(p-toluenesulfonyl)-β-D-erythro-hex-4(Z)-enofuranosyl]uracil (3). Treatment of 2 or 3 with aqueous trifluoroacetic acid gave the corresponding deprotected vinyl (5) or allylic (6) sulfones, and 5 was converted to 6 readily in basic solutions. Treatment of 2 with sodium borohydride, sodium thiomethoxide, or ammonia resulted in conjugate addition (at C5′ of the vinyl sulfone) to give the 5′-hydro, 5′-methylthio, or 5′-amino-5′,6′-dideoxy-6′-(p-toluenesulfonyl) nucleosides. The 5′-substituted diastereomers were deprotected, separated, and the configuration of a 5′-amino derivative was established by X-ray crystallography.Key words: allylic sulfones, amino-nucleosides, 5′,6′-dideoxynucleosides, nucleosides, uridine, vinyl sulfones.
Sulfonyl esters 3. The formation of sulfone-sulfonates in the reactions of aryl methanesulfonates with sodium hydride
Authors: Baum James Clayton , Durkin Kathleen Anne , Precedo Laura , O'blenes Stacy Brian , Goehl John Edward , Langler Richard Francis , MacCormack Gerald Kendall , Smith Lana Louise
Published: May 2006

Sodium hydride reductions of aryl methanesulfonates afford dimeric sulfone-sulfonate esters as well as products arising from SO bond rupture. SO bond rupture becomes more competitive as the LUMO energy of the sulfonate ester declines. Exploration of the chemistry of a sulfone-sulfonate ester revealed a complex novel reaction that resulted in the formation of, inter alia, a dichloromethanesulfonate ester and a trichloromethanesulfonate ester. The first successful approaches to the synthesis of the heretofore unknown trichloromethanesulfonates and dichloromethanesulfonates are reported. Key words: sodium hydride reductions, sulfenes, sulfone-sulfonate esters
Kinetics of the photochemical reactions of the croconate dianion in aqueous solution
Authors: Zhao B , Back M. H.
Published: May 2006

The kinetics of the photochemical reactions of the dianion of croconic acid (1,2-dihydroxycyclopentenetrione) have been studied in aqueous solution in the presence of electron acceptors. In neutral solutions the quantum yield for disappearance of croconate dianion was small (< 10−3) but was substantially increased in basic solution and in the presence of electron acceptors. At pH 12 in the presence of 4-nitrobenzylbromide and biacetyl a quantum yield of 1 was obtained. The kinetics of the rate of disappearance of croconate dianion as a function of pH and concentration of acceptor showed that the excited dianion is oxidized by acceptors and reacts with hydroxyl ion. A mechanism is proposed that, by assuming reasonable values for the rate constants involved, is shown to be consistent with the results. Keywords: photolysis, kinetics, croconate dianion, electron transfer.
Open-chain nitrogen compounds. Part XIV. Synthesis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and 1-aryl-3-(hydroxyaryl)methyl-3-methyltriazenes
Authors: Merrin M. P. , Hooper D. L. , LaFrance R. J. , Snooks R. , Vaughan K.
Published: May 2006

The synthesis of a new series of 1-aryl-3-aryloxymethyl-3-methyltriazenes (2) has been achieved by the reaction of the acetoxymethyltriazene (Ar-N=N-NMe-CH2OAc) with the appropriate phenol in dry chloroform solution. Triazenes of type 2 are also formed by reaction of the acetoxymethyltriazene with the sodium phenolate, generated by reaction of the phenol with sodium hydride in dry chloroform, but under these conditions a second product is formed, which has been identified as an isomer of 2. The structure of the second product has been elucidated by spectroscopic analysis to be the 1-aryl-3-(hydroxyaryl)methyl-3-methyltriazene (3). The formation of these two isomeric products is accounted for by the ambident nature of the nucleophilic phenolate ion in the displacement of the acetoxy leaving group. The mass spectra of all the triazenes of type 2 exhibit a fairly intense peak at M – 102, which is suggested to arise from a novel intramolecular rearrangement. Two examples of the triazenes of type 2 have been tested for antitumour activity on the NCI tumour panel and have shown statistically significant differential sensitivity in several cell lines. Preliminary investigation of the stability of these triazenes in physiological-pH buffer suggests that they may have the appropriate chemical stability for pro-drug application in therapy. Keywords: triazene, synthesis, antitumour, phenol, spectroscopy, aryloxymethyltriazene, prodrugs.
An investigation of the rotational isomers of N-acetyl-2,2-dimethyloxazolidine and related compounds by nuclear magnetic resonance spectroscopy and molecular mechanics
Authors: Taylor Wesley G. , Hall Tse Wai , Schreck Carl E.
Published: May 2006

The 15 2,2-dimethyloxazolidines described here were found to exist in solution predominantly as a single rotational isomer, unlike N-acetyloxazolidine (1), N-acetyl-2-methyloxazolidine (2), N-acetyl-2-(n-octyl)oxazolidine (3), and other known 2-substituted N-acyloxazolidines. Using 13C NMR spectroscopy, activation energies for interconversion of the E (minor) and Z (major) rotational isomers of 1–3 were determined from coalescence temperature measurements in pyridine-d5. A sample of N-acetyl-2,2-dimethyloxazolidine (4) was isolated for comparison. The rotational isomer of 4 was found by two-dimensional nuclear Overhauser effect spectroscopy (NOESY) to possess the Z (or trans) stereochemistry. Molecular mechanics (MMX) calculations on the E and Z isomers of 1–4 helped to account for these findings. The conformation of the energy-minimized structures resembled a C-5 envelope. Samples of N-aroyl-2,2-dimethyloxazolidines (5a–5n) were isolated and the rotational isomers were assigned the Z stereochemistry by NOESY and 13C NMR experiments. Most of these 2,2-dimethyloxazolidines were ineffective in a bioassay for mosquito repellent activity. Keywords: N-acyloxazolidines, N-aroyloxazolidines, NMR spectroscopy, rotational isomerism, molecular mechanics.
Characterization of the triplet excited state of the phenylxanthenium carbocation
Authors: Johnston L. J. , Wong D. F.
Published: May 2006

The triplet excited state of the 9-phenylxanthenium cation has been observed directly by both luminescence and transient absorption techniques. The triplet–triplet absorption shows λmax ≤ 300 nm and decays over a period of several microseconds in the absence of easily oxidized donors. The triplet cation reacts with 9-phenylxanthydrol and biphenyl via electron transfer to give the corresponding radical and radical cation and also reacts rapidly with both oxygen and 1,3-cyclohexadiene. Keywords: carbocations, triplets, electron transfer, laser flash photolysis.
Correlation of the effects of alkyl substituents on the basicities of indoles
Authors: Cohen Peter A. , Cohen Louis A.
Published: May 2006

Alkyl groups at C-2 of indole increase basicity at the site of protonation, C-3, while alkyl groups at C-3 decrease basicity. These opposing effects can be incorporated, for both the isomeric mono- and 2,3-dialkylindoles, into a single linear free energy correlation, pKa = −10.05Σσ −3.94, in which [Formula: see text] and Ds is the double bond stabilization parameter at C-3. An analogous correlation for N-methylindoles, pKa = −8.64Σσ −2.80, reveals that the effect of N-alkylation on basicity is predictable but not additive. Keywords: alkylindoles, carbon basicity, free energy correlation, substituent effects, N-alkyl effect.
The use of special coordinate axes in direct and semi-direct implementations of second-order perturbation theory, including the derivation of a horizontal recurrence relation
Authors: Hamilton Tracy P. , Schaefer III Henry F.
Published: May 2006

A horizontal recurrence relation (HRR) is derived which may be used in the generation of two-electron repulsion integrals (ERIs). Also, special Cartesian coordinate axes may be used to reduce the number of intermediate terms. Heretofore, the use of local axis systems entailed rotations every time a shell quadruple of ERIs was computed. Recently, we pointed out the possibility of postponing the transformation using choices of Cartesian reference frames based on nuclear positions. In our pilot implementation of direct and semi-direct Møller–Plesset second-order perturbation theory (MP2) we construct the integrals in local coordinate systems and perform the back-transformation in the middle of the AO to MO integral transformation, rather than rotating the ERIs after the computation of each shell quadruple. The efficacy of this approach depends on whether the gains in ERI computation are greater than the losses incurred in transformation. Preliminary CPU profiles indicate that the increased time spent in rotating axes is quite small. Keywords: horizontal recurrence relation, second-order perturbation theory.
Abinitio relativistic molecular orbital self-consistent field calculations for the thorium–platinum diatomic
Authors: Malli G. L.
Published: May 2006

Abinitio relativistic as well as the corresponding non-relativistic limit (NRL) MO calculations are reported for the ground state (Ω = 0) of the closed-shell diatomic ThPt. It is found that relativistic effects lead to a very pronounced bond shortening of ca 1.68 bohr. The predicted bond length of 2.7398 Å with the relativistic molecular orbital (RMO) wavefunction (WF) for the diatomic ThPt is ca. 0.25 Å shorter than the Th—Pt distance reported in a recently synthesized complex with a thorium–platinum bond as well as the shortest Th—Pt bond distance reported for the Th–Pt alloy. The calculated relativistic total molecular energy and the force constant at the predicted bond distance of 5.1774 bohr are −44 963.5050 hartree and 0.34650 hartree/(Å)2, whereas the corresponding predicted non-relativistic values are 6.824 bohr, −41 690.6970 hartree, and 0.08388 hartree/(Å)2, respectively. The vibrational frequencies predicted by the RMO and the non-relativistic limit MO SCF wavefunctions are 155.4 cm−1 and 76.46 cm−1, respectively. The relativistic effects are very pronounced for ThPt and lead to a very significant bond contraction, an almost fourfold increase in the force constant, and doubling of the vibrational frequency. Keywords: relativistic effects, ThPt, RMO, bond contraction, DF SCF.
Selenium sulfur dihalides, ChnX2 (n = 1, 2, 3; Ch = Se, S; X = Br, Cl). Raman and 77Se NMR spectroscopic characterization
Authors: Milne John B.
Published: May 2006

Solutions of Se2Cl2 in S2Cl2, Se2Br2 in S2Cl2, Se in S2Cl2, and S in Se2Cl2 have been studied by Raman and 77Se NMR spectroscopy. Selenium sulfur dihalides, SeSCl2, SeSBr2, and SeSBrCl, formed in these solutions, have been shown by Raman and 77Se NMR spectroscopy to have chain structures. Solutions of Se2Cl2 in S2Cl2, S in Se2Cl2, and Se in S2Cl2 have been shown to contain, in addition to Se2Cl2, S2Cl2, SeSCl2, Se3Cl2, and S8, trichalcogen dichlorides Se2SCl2 and SeS2Cl2. Selenium-77 signals corresponding to all seven chain isomers of the expected Se-containing dichalcogen dihalides, Se2Br2, Se2Cl2, Se2BrCl, SeSCl2, SeSBr2, BrSeSCl, and ClSeSBr, have been observed in the spectrum of a 1:1 molar mixture of S2Cl2 and Se2Br2. The disulfur dichloride and dibromide, as well as the bromide chloride, are also present. Selenium–bromine and sulphur–chlorine linkages are observed to be preferred over selenium–chlorine and sulphur–bromine bonding in these mixtures. The 77Se chemical shifts correlate well with the electronegativity of the directly bonded neighbour but inversely with that of the next-nearest neighbour. Keywords: selenium halides, sulfur halides, low valent chalcogen halides, 77Se NMR, Raman spectroscopy.
Benzothiarsolium cations: evidence for pπ-bonding between arsenic and sulfur in the first structurally characterized arsenium system
Authors: Burford Neil , Parks Trenton M. , Royan Bruce W. , Richardson John F. , White Peter S.
Published: May 2006

Tetrachloroaluminate salts of the benzothiazarsolium and toluodithiarsolium heteronaphthalenic cations have been prepared from the corresponding chloroarsoles by a routine halide ion abstraction procedure. Characterization data are presented, including the X-ray crystal structure of the thiaza derivative. (Crystal data for C6H5AlAsCl4NS: monoclinic, space group P21/c, a = 6.4259(5) Å, b = 23.654(3) Å, c = 8.5859(7) Å, β = 98.203(6)°, V = 1291.7(2) Å3, Z = 4, R = 0.054.) A planar bicyclic cationic unit is observed, typical of other heteronaphthalenic systems. The crystal structure of 2-chlorobenzo-1,3,2-thiazarsole has been obtained for direct comparison, and also has a close to planar heterobicyclic moiety. (Crystal data for C6H5AsClNS: monoclinic, space group P21/c, a = 8.370(3) Å, b = 10.829(3) Å, c = 8.756(2) Å, β = 95.99(2)°, V = 789.2(3) Å3, Z = 4, R = 0.025.) The planarity and short heterocyclic bond lengths observed in the two compounds imply a significant degree of pπ bonding, which is unique between sulfur and arsenic. In addition, the cation is a rare example of a structurally characterized cationic dicoordinate arsenic, or arsenium, system. Keywords: arsenic, arsolium, arsenium, pπ-bonding, sulfur, heteronaphthalenic.
Physical and structural studies of N-carboxymethyl- and N-(p-methoxyphenyl)-3-hydroxy-2-methyl-4-pyridinone
Authors: Zhang Zaihui , Rettig Steven J. , Orvig Chris
Published: May 2006

3-Hydroxy-1-carboxymethyl-2-methyl-4-pyridinone (Hcmp) and 3-hydroxy-1-(p-methoxyphenyl)-2-methyl-4-pyridine (Hpap) have been prepared and studied by single crystal X-ray diffraction. Crystals of Hemp are monoclinic, a = 6.340 (2), b = 7.705 (1), c = 16.226 (1) Å, β = 94.74 (1), Z = 4, space group P21/n and those for Hap are monoclinic, a = 10.8435 (9), b = 16.680 (2), c = 13.5665 (6) Å, β = 109.450 (4), Z = 8, space group C2/c. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.030 and 0.041 (Rw = 0.039 and 0.058) for 1642 and 1819 reflections with I ≥ 3σ(I), respectively. Bond lengths and bond angles in the two compounds are normal; however, Hcmp forms as a zwitterion in the solid state. The two compounds were also studied by mass spectrometry, UV, infrared, proton NMR spectroscopies, and potentiometric equilibrium measurements. The protonation constants for Hcmp are log K1 = 9.76 (1), log K2 = 3.43 (1), and log K3 = 2.78 (3) and for Hpap are [Formula: see text] and [Formula: see text]. Keywords: 3-hydroxy-4-pyridinone, zwitterion, hydrogen bonding, protonation constant, crystallography, solid state.
Nuclear magnetic resonance studies of the methylammonium hexahalotellurates
Authors: MacIntosh Mark R. , Gruwel Marco L. H. , Robertson Katherine N. , Wasylishen Roderick E.
Published: May 2006

A 2H and 14N NMR study of the solid methylammonium hexahalotellurates, (MA)2TeX6 (MA = CH3ND3+ or CD3NH3+, X = Cl, Br, and I), has been undertaken to characterize the dynamics of the methylammonium (MA) ion as a function of temperature. At room temperature, the MA ion in the hexachlorotellurate (solid II) is confined to C3 jumps about the C—N axis while a small angle libration of the C—N axis is occurring. In the room temperature phase, solid I, of (MA)2TeBr6 and (MA)2TeI6 the MA ions are performing overall reorientations on the ps time scale, averaging the 2H nuclear quadrupolar interactions to zero. Variable temperature 2H NMR spin-lattice relaxation times, T1, indicate an activation energy, EA, for "isotropic" reorientations of the CH3ND3+ ion of 5.2 ± 0.5 and 2.6 ± 0.3 kJ mol−1 for X = Br and I, respectively. Deuterium T1 values for C-deuterated MA ion in the hexaiodotellurate indicate an EA for whole-ion reorientation of 3.1 ± 0.3 kJ mol−1. At any given temperature, the correlation time, τc, derived from the T1 results was found to be the same for the two deuterium-labelled hexaiodotellurates. The similarity of both the EA and the τc values implies correlated motion of the methyl and ammonium groups. The 14N T1 results for solid I of (MA)2TeI6 indicate that C—N axis motions, with an EA = 5.6 ± 0.6 kJ mol−1, are more hindered than N—D or C—D bond dynamics. The 2H NMR spectra for (MA)2TeI6 (solid II) and (MA)2TeBr6 (solids II, III, and IV) are characterized by a Pake doublet line shape. The measured peak-to-peak splittings are less than what is predicted by C3 motion about the molecular symmetry axis. It is possible to model these line shapes by postulating that C3 rotations of the methyl and ammonium groups occur as the C—N axis librates in an effective cone about the position of the static molecular axis. For (CH3ND3)2TeBr6 and (CD3NH3)3TeBr6 the peak-to-peak splittings in the 2H NMR spectra were measured as a function of temperature in solid phases II, III, and IV and were found to be similar. Finally, the 2H NMR line shape relaxation for (MA)2TeBr6 (solid III) displays an orientation dependence indicating that rotations about the C—N axis are discrete rather than diffusive in nature. For solid phase II of (MA)2TeCl6, the line shape is observed to relax isotropically, implying that continuous C3 rotations are taking place. Keywords: 2H and 14N NMR, methylammonium hexahalotellurates, molecular motion.
α-Oxosulfines: reactions with alkenes and alkynes
Authors: Still Ian W. J. , Wilson Donna Kaye T.
Published: May 2006

Thiochroman-4-one 1,1-dioxide has been successfully converted into 3-sulfinylthiochroman-4-one 1,1-dioxide and the reactions of this α-oxosulfine with a series of alkenes have been carefully investigated. The α-oxosulfine was found to react as a Diels–Alder diene with 2-methylpropene, Z- and E-2-butene, 2-ethyl-1-butene, 1-pentene, Z-2-pentene, and cyclopentene and cyclohexene to produce a new group of heterocyclic compounds, the 2,3-dihydro-5H-1,4-oxathiino[3,2-c][1]benzothiopyrans, in yields ranging from 21 to 42%. In all cases, formation of the Diels–Alder adduct was accompanied by a second type of product, identified as the product of electrophilic addition (EA) of a sulfenium species to the alkene, in lesser yields, ranging from 9 to 18%. When the trapping dienophile used was 3,3-dimethyl-1-butene, only the EA adduct was obtained, in 28% yield. Formation of only the EA type of adduct was also observed in reactions of the α-oxosulfine with 2-butyne (21%) and with the thione 2,2,4,4-tetramethylpentane-3-thione (di-tert-butyl thioketone) (16%). Attempts to prepare the α-oxosulfines corresponding to the following ketones are also described: thiochroman-4-one 1-oxide, isothiochromanone and isothiochromanone 2,2-dioxide, tetrahydrothiophen-3-one 1,1-dioxide, 3,3,5,5-tetramethylcyclohexanone, and 2-indanone. Keywords: Diels–Alder, electrophilic addition, sulfenic acid.
Synthesis of bicyclic diones and thiones. Facile methylation of the enolates of bicyclo[2.2.1]heptane-2,5-dione and bicyclo[2.2.2]octane-2,5-dione. An AM1 computational study of bicyclic enolates
Authors: Werstiuk N. H. , Yeroushalmi S. , Guan-Lin Hong
Published: May 2006

A group of bicyclic ketones and thiones have been synthesized for homenolization studies. Bicyclo[2.2.1]heptane-2,5-dione (6) undergoes unusually rapid tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione (1) in good yield. Treatment of 1 with P2S5 in xylene gave 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dithione (2) and 3,3,6,6-tetramethyl 15-oxo-bicyclo[2.2.1]heptane-2-thione (3), which was converted into 4 with Raney nickel. Bicyclo[2,2,2]octane-2,5-dione (7), prepared via a Diels–Alder reaction between 2-trimethylsilyloxy-1,3-cyclohexadiene and and α-acetoxyacrylonitrile followed by a one-step desilylation/hydrolysis, also undergoes facile tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.2]octane-2,5-dione (5) in good yield. AM1 calculations were carried out on the α-enolates of bicyclo[2.2.1]heptan-2-one, 6, 5-methylidenebicyclo[2.2.1]heptan-2-one, and 4-acetylbicyclo[2.2.1]-heptan-2-one in an attempt to gain information on the source of the enhanced acidity of the C-3 hydrogens of 6 and 7. Keywords: bicyclic ketones, thiones, synthesis.
Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals
Authors: Hilborn James W. , Pincock James A.
Published: May 2006

The photolysis of esters 6 and 8 in methanol leads to products resulting from both naphthylmethyl cations and radicals. The product distribution is nearly independent of X for the esters 6 except when X equals methoxy. A mechanism involving initial homolytic cleavage of the carbon–oxygen bond in the excited singlet state of the ester is proposed. Competition between electron transfer in the radical pair to form the ion pair and decarboxylation of the arylacyloxy radical allows calculations of the rates for this decarboxylation process. The ρ value versus σ is close to zero. When X equals methoxy, intramolecular electron transfer occurs with the naphthalene ring serving as the acceptor and the methoxyaromatic as the donor. This exciplex fragments to carbon dioxide and 1-(1-naphthyl)-2-arylethane. Keywords: acyloxy radical, decarboxylation, photolysis of benzylic esters.
Reactions of ferrocene and nickelocene with some stable carbonium ions
Authors: Brownstein Sydney K. , Gabe Eric J. , Hynes Rosemary C.
Published: May 2006

The reaction of ferrocene and tropylium hexafluorophosphate yields ferrocenyltropylium PF6, which crystallizes in the monoclinic space group P21/C (a = 9.7858(10) Å, b = 16.3692(24) Å, c = 10.901(4) Å, β = 113.030(18)°, Z = 4, T = 27 °C, V = 1607.0(7) Å3, Rf = 0.091, Rw = 0.040) for 102 parameters and 929 observed (I > 2.5 σ(I)) out of 2087 total measured reflections. The reaction of nickelocene and triphenylmethyl tetrafluoroborate yields triphenylmethylcyclopentenyl cyclopentadienyl nickel tetrafluoroborate, which crystallizes in the monoclinic space group P21/n (a = 11.0306(19) Å, b = 14.078(4) Å, c = 17.117(4) Å, β = 101.134(18)°, Z = 4, T = 27 °C, V = 2608.0(11) Å3, Rf = 0.091, Rw = 0.035) for 147 parameters and 1334 out of 3361 measured reflections.
Synthesis of cyclopentane analogs of 5-fluorouracil nucleosides
Authors: Hronowski Lucjan J. J. , Szarek Walter A.
Published: May 2006

New carbocyclic analogs (12, 14, and 15) of 5-fluorouracil nucleosides have been prepared by fluorination, using elemental fluorine, of the acetylated analogs (8, 10, and 11, respectively) of 1-(2′,3′-dideoxy-glycero-pentofuranosyl)-and 1-(2′- and 3′-deoxy-β-threo-pentofuranosyl)-uracil nucleosides. The carbocyclic analog (14) of 1-(2′-deoxy-β-threo-pentofuranosyl)-5-fluorouracil was then utilized for the preparation of various new carbocyclic analogs of 1-(3′-substituted-2′,3′-dideoxy-β-erythro-pentofuranosyl)-5-fluorouracil nucleosides by SN2 displacement of the 3′-mesyloxy group in the protected derivative 17. In this way analogs having the chloro (see 23), bromo (see 24), and azido (see 25) groups at the 3′-position were obtained; the analog 29 having a 3′-amino group was obtained by reduction of the azido group. In addition (±)-5-fluoro-1-{3-(hydroxymethyl)-3-cyclopenten-1-yl}-2,4(1H,3H)-pyrimidinedione (26) was obtained as an elimination side-reaction product in the preparation of the 3′-chloro and 3′-bromo analogs. Compounds 8, 9, 12, 14, 15, 25, and 29 were tested against the herpes simplex viruses and were found to be inactive. Compound 26 inhibited the growth of K-562 cells with an ID50 (10−4–10−3), which was about 100-fold greater than that of 5-fluorouracil in this test system. Analogs 12, 25, and 29 were slightly cytotoxic.