bluuebunny/crossref_metadata_2025 huggingface dataset:
The photolysis and thermal decomposition of pyruvic acid in the gas phase
Authors: Yamamoto S. , Back R. A.
Published: May 2006

The photolysis of pyruvic acid vapour has been studied at wavelengths of 366, 345, and 320 nm, at a temperature of 340 K and pressures from about 1 to 10 Torr. Products observed were CO2 and CH3CHO, with the former always in excess, and a quantum yield of CO2 of 0.9 ± 0.1 at 366 nm. Light emission was also observed, and from the effect of added O2 it was concluded that emission occurred from both singlet and triplet states. It is suggested that the primary process in the photolysis is an internal hydrogen-atom transfer followed by dissociation into CO2 and CH3—C—OH, with the latter then rearranging to give CH3CHO and other products.The absorption spectrum is reported; the first system begins at about 380 nm, rising to a maximum at about 350 nm, with εmax = 10 M−1 cm−1, and is attributed to the first excited π* ← n+ singlet state. Weak absorption below 300 nm is probably due to the π* ← n− state and much stronger absorption below 220 nm to the π* ← π state.The thermal decomposition was studied briefly at temperatures from 455 to 584 K and pressures from about 0.8 to 7 Torr. Products were the same as in the photolysis, and Arrhenius parameters of log A (s−1) = 7.19 and E = 27.7 kcal/mol were obtained, based on the formation of CO2, which was apparently a simple, homogeneous unimolecular process.
The kinetics, isotope effects, and mechanism of the reaction of 2,2-di(4-nitrophenyl)-1,1,1-trifluoroethane with alkoxide bases in alcohol solvents
Authors: Jarczewski Arnold , Schroeder Grzegorz , Galezowski Wlodzimierz , Leffek Kenneth T. , Maciejewska Urszula
Published: May 2006

The reaction between 2,2-di(4-nitrophenyl)-1,1,1-trifluoroethane and the alkoxide bases ŌCH3, ŌC2H5, ŌnC4H9, ŌCH(CH3)2, and ŌC(CH3)3 in their corresponding alcohol solvents is a multistep reaction with several intermediates: 2,2-di(4-nitrophenyl)-1,1-difluoro-1-alkoxyethane (A), 2,2-di(4-nitrophenyl)-1-fluoro-1-alkoxyethene (B), 2,2-di(4-nitrophenyl)-1,1-dialkoxyethene (C), 2,2-di(4-nitrophenyl)-1,1-difluoroethene (D), and 4,4′-dinitrobenzophene (E). Rate constants and activation parameters have been measured for the appearance of the two stable products B and C. The kinetic deuterium isotope effects for the appearance of B fell in the range of kH/kD = 1 to 2 at 25 °C for the primary and secondary alkoxides, whereas kH/kD = 5.4 at 30 °C for the appearance of D with tert-butoxide. Exchange experiments showed that H/D exchange took place between the substrate and solvent to the extent of 100% with methoxide, 50% with ethoxide and isopropoxide, and 0% with tert-butoxide. It is concluded the HF elimination from the substrate follows an (ElcB)R mechanism with methoxide/methanol, changing to (ElcB)I or E2 with tert-butoxide/tert-butanol.
Structure and fragmentation of C5H11O+ ions formed by chemical ionization
Authors: Headley John V. , Harrison Alex. G.
Published: May 2006

The proton transfer chemical ionization mass spectra of eleven C5H10O isomers have been obtained using H3+, N2H+, HCO+, and D3+ as reagent ions. The chemical ionization mass spectra in combination with isotopic labelling and metastable ion studies have made it possible to elucidate the major fragmentation reaction channels of the C5H11O+ ions formed and their dependence on precursor structure. From collision induced dissociation studies nine stable distinct C5H11O+ ion structures have been identified; protonated 3-methylbutanone and protonated 2,2-dimethylpropanal readily interconvert by a pinacolic – retro-pinacolic rearrangement.
Lactams of sparteine
Authors: Golebiewskl W. Marek , Spenser Ian D.
Published: May 2006

(2,2-2H2)Sparteine, (6-2H)sparteine, (10,10-2H2)sparteine, (15,15-2H2)sparteine, (17α-2H)sparteine, (17β-2H)sparteine, (17,17-2H2)sparteine, (17α-2H)lupanine, and (17β-2H)lupanine were prepared and employed to assign the 1H nmr spectrum of sparteine. Contrary to a published report, photochemical oxidation of sparteine does not lead to 15-oxosparteine but to 17-oxosparteine.
1,n-Radical ions. Photosensitized (electron transfer) and electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane
Authors: Wayner Danial D. M. , Arnold Donald R.
Published: May 2006

The photosensitized (electron transfer) and the electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane (1) have been studied. The products obtained from the photosensitized (electron transfer) study are 1,1,3,3-tetraphenylpropene (2), 1,3,3-triphenylindene (3), tetraphenylallene (4), and 3-methoxy-1,1,3,3-tetraphenylpropene (8). The product ratios are dramatically dependent upon the reaction conditions, particularly sensitizer (aromatic nitriles, tetracyanoethylene, chloranil, and 2,3-dichloro-5,6-dicyanobenzoquinone were used), and solvent. The variations in product ratios are attributed to variations in the redox behaviour of the sensitizer radical anion and upon the basicity and nucleophilicity of the medium. The products in the electrochemical study are 3, 4, and 8. Common intermediates have been identified and a mechanism for the formation of products is proposed.
An electrochemical investigation on mononuclear and dinuclear copper(I) aminocarbonyl complexes
Authors: zanello Piero , leoni Piero
Published: May 2006

The electrochemical behaviour of some copper(I) aminocarbonyl derivatives, namely, [Cu(dien)(CO)]+ (dien = diethylenetriamine), [Cu(Medpt)(CO)]+ (Medpt = N,N-bis(3-aminopropyl)methylamine), [Cu2(tmen)2(μ-PhCO2)(μ-CO)]+ (tmen = N,N,N′,N′-tetramethylethylenediamine), has been studied in dimethyl sulfoxide solution at platinum electrodes by cyclic and dc voltammetry, and controlled potential coulometry. In all studied complexes each copper(I) centre undergoes one-electron charge transfers in both anodic and cathodic processes. The electrogenerated copper(II) complexes, fully characterized, can be reversibly reduced to the starting copper(I) carbonyl derivatives in the presence of carbon monoxide. The electron-transfer sequences in which these copper(I) complexes may be involved have been elucidated.
Complex formation between cuprous iodide and phenyl phosphine: a nuclear magnetic resonance and X-ray crystallographic study
Authors: Batchelor Raymond J. , Birchall Thomas , Faggiani Romolo
Published: May 2006

The X-ray crystal structure of di-μ-iodobis[bis(phenylphosphine)copper(I)] has been determined: R1 = 0.0460. The crystals were monoclinic, space group Cc, a = 10.625(2) Å, b = 25.115(8) Å, c = 11.361(2) Å, β = 105.929(15)°, fw = 821.28, and Z = 4. The molecular structure consists of two CuI(C6H5PH2)2 units bridged via the iodines so that each copper achieves tetrahedral coordination. Nuclear magnetic resonance data provides evidence that the phenylphosphines remain coordinated in solution but undergo rapid exchange at room temperature.
The mechanism of enzymic hydroxyl group removal from C-21 of tetrahydrodeoxycorticosterone
Authors: Holland Herbert L. , Riemland Elly
Published: May 2006

The C-21 hydroxyl group of C-17- and C-21-deuterium labelled tetrahydrodeoxycorticosterone is removed by the anaerobic intestinal bacterium Eubacteriumlentum ATCC 25559 with retention of deuterium label at C-17α and loss of one of the two deuterium atoms originally present at C-21. Dehydroxylation at C-21 proceeds with an apparent primary kinetic isotope effect, KH/KD, at C-21 of 2.6. These data suggest a route for C-21 dehydroxylation involving a C-20(21)-enediol intermediate.
Preparation, crystal and molecular structures of Ph2CNSNSO and a comparison of the —SNSO and —SNSS chromophores
Authors: Chivers Tristram , Oakley Richard T. , Pieters Roger , Richardson John F.
Published: May 2006

The sulphenyl chloride, Ph2CNSCl, prepared insitu from Ph2CNSiMe3 and sulphur dichloride, has been employed in the synthesis of Ph2CNSNSO and Ph2CNSNSNSNCPh2 by reaction with Me3SiNSO and Me3SiNSNSiMe3, respectively. An X-ray structural determination of Ph2CNSNSO shows it to consist of a planar cis-trans chain. The crystals are triclinic and belong to the space group[Formula: see text], a = 9.9078(8), b = 10.0967(9), c = 15.1682(14) Å, α = 78.646(7), β = 71.065(7), γ = 63.449(7)°, V = 1281.5(5) Å3, Z = 4. The final R and Rw values were 0.033 and 0.027, respectively. The π* → π* excitation energies for the RSNSO and RSNSS chromophores are compared for different R groups and discussed in the light of MNDO calculations on the model compounds HSNSX (X = S, O). The thermal decomposition of both Ph2CNSNSO and Ph2CNSNSNSNCPh2 produced S4N4 and Ph2CO or (Ph2CN)2S, respectively.
Electrostatic effects on ionization equilibria: MNDO study of proton and hydrogen transfer reactions of 5-fluoropentanoic acid
Authors: Friedl Zdenek
Published: May 2006

Relative proton transfer enthalpies δΔH0 and homolytic bond strengths δΔH0 (A—H) of sp and ap conformers of 5-fluoropentanoic acid, as well as some related aliphatic and 4-X-bicyclo[2.2.2]octane-1-carboxylic halogenoacids, have been calculated by the MNDO method. The results, together with literature data concerning the gas phase acidities, were compared with the prediction of the electrostatic theory. It is shown that the substituent effects on acidities of carboxylic acids are largely due to substituent interactions in the anions and only to a smaller extent to interactions in the neutral acids. A small contribution (about one-eighth to one-fourth as large in magnitude but of opposite sign) is possibly also made by substituent effects on homolytic bond strengths DH0 (A—H).
The conformations of prostacyclin and related prostaglandins
Authors: Beierbeck Helmut , Kotovych George , Sugiura Makiko
Published: May 2006

The conformations of prostacyclin, PGI2, and three of its analogues, 6R- and 6S-PGI1 and carbacyclin, were studied by high field 1H nmr spectroscopy. The cis-bicyclo- and cis-oxabicyclo[3.3.0]octane ring conformations were completely assigned. The minima for the pseudorotational conformations are observed at 7E/12E for PGI2, [Formula: see text] for 6R-PGI1, and 6E/11E for 6S-PGI1, and carbacyclin. The data indicate that each molecule adopts a narrow pseudolibrational range, if not a single conformation. The α- and ω-side chain conformations were characterized, but not unambiguously. Vicinal coupling constants and nuclear Overhauser enhancements proved to be the most useful spectroscopic parameters in this study.
Crystal structure determination of the conformation of two bicyclo[3.3.1]nonan-ones
Authors: Richardson John F. , Sorensen Ted S.
Published: May 2006

The molecular structures of exo-7-methylbicyclo[3.3.1]nonan-3-one, 3, and the endo-7-methyl isomer, 4, have been determined using X-ray-diffraction techniques. Compound 3 crystallizes in the space group [Formula: see text] with a = 15.115(1), c = 7.677(2) Å, and Z = 8 while 4 crystallizes in the space group P21 with a = 6.446(1), b = 7.831(1), c = 8.414(2) Å, β = 94.42(2)°, and Z = 2. The structures were solved by direct methods and refined to final agreement factors of R = 0.041 and R = 0.034 for 3 and 4 respectively. Compound 3 exists in a chair–chair conformation and there is no significant flattening of the chair rings. However, in 4, the non-ketone ring is forced into a boat conformation. These results are significant in interpreting what conformations may be present in the related sp2-hybridized carbocations.
Thermodynamic behaviour of adenosine in water–DMSO mixtures in the presence of K+ and Ca2+ ions at 25, 30, 35, and 40 °C
Authors: Puri Anil K.
Published: May 2006

Partial molar volume [Formula: see text] partial molar compressibility [Formula: see text] Jones–Dole viscosity B coefficient, and solute activation parameters of adenosine in water–DMSO mixtures in the presence of Ca2+ and K+ ions have been calculated from ultrasonic, volumetric, and viscometric studies at 25, 30, 35, and 40 °C(± 0.01° C). The results are discussed in terms of the Jones–Dole viscosity B coefficients and the transition state parameters for viscous flow.
Solid state and solution conformations of 1 -(β-D-2′,3′-secoribofuranosyl)-5,6-dichlorobenzimidazole, an acyclonucleoside analogue
Authors: Birnbaum George I. , Stolarski Ryszard , Kazimierczuk Zygmunt , Shugar David
Published: May 2006

The title compound crystallizes in the monoclinic space group P21, with two independent molecules in the asymmetric unit (Z = 4). The unit cell dimensions are a = 11.861(2), b = 7.897(1), c = 14.527(3) Å, β = 91.28(1)°. X-ray intensity data were measured on a diffractometer, and the crystal structure was determined by direct methods. Least-squares refinement converged at R = 0.036 for 2980 reflections. The glycosidic torsion angle [C(2)—N(1)—C(1′)—O(1′)] is 53.9° in molecule A and 129.8° in molecule B. In both molecules, the orientation of C(1′)—O(1′) to C(2′)—O(2′) is trans. The conformations about C(3′)—C(4′) and C(4′)—C(5′) are different in each of the two molecules. These features are compared with those of acyclonucleoside analogues with antiviral activity. The conformation in aqueous medium was examined with the aid of high-resolution 1H nmr spectroscopy, and the results are compared with those obtained from the X-ray analysis.
Raman spectral studies of solutions of alkali metal perchlorates in dimethyl sulfoxide and water
Authors: Sastry M. I. S. , Singh Surjit
Published: May 2006

Raman spectra of solutions of alkali metal perchlorates in dimethyl sulfoxide (DMSO) in the Cl—O, C—S, and S=O stretching regions, as well as of perchlorates in aqueous solutions in the Cl—O stretching region are reported. The results are discussed in terms of half-bandwidths, relative intensities, and depolarization ratios. For H2O the half-bandwidth of the Cl—O stretching band at ~935 cm−1 is almost double the value in DMSO solutions. Solutions of perchlorates in DMSO show two symmetric bands in the Cl—O stretching region, whereas in aqueous solutions only one band is observed. The half-bandwidths in perchlorate solutions in DMSO for the C—S stretching band increase with increase in concentration of perchlorate compared to that of liquid DMSO. The band contours in the S=O stretching region in DMSO solutions also show significant changes. These observations are explained on the basis of formation of ion pairs of metal perchlorates in solutions of DMSO and ion hydrates in the case of aqueous solutions.
Determination of stretching force constants of weakly bound dimers from centrifugal distortion constants
Authors: Millen D. J.
Published: May 2006

Expressions are derived from which stretching force constants for the weak bond in weakly bound dimers may be evaluated directly from observed rotational constants and centrifugal stretching distortion constants.
Supersonic beam investigations of indole and indole–halomethane complexes: intermolecular interactions
Authors: Hager James , Wallace Stephen C.
Published: May 2006

We report the findings of a supersonic beam investigation of the 1:1 gas phase complexes of indole with various halomethanes. The unique environment of the supersonic jet provides a method by which the pairwise intermolecular interactions of these complexes can be studied without the complications of condensed media effects. The behavior of argon and methane van der Waals molecules is described first in order to provide examples of simple dispersive interactions. These are then contrasted with complexing species such as CF4 and CCl4 where repulsive interactions offset the stabilization due to dispersive and dipole – induced dipole forces. Finally, we show that the interaction between the probe molecule and CHCl3 and CH2Cl2 is apparently hydrogen bonding with the indole π electronic system. The implications of these intermolecular interactions on the area of general anesthesia are discussed in terms of a picture in which both the hydrophobic and polar portions of cell membrane may be reversibly affected.
Vibrational analysis of (E,E)-2,4-hexadienal, (E,E,E)-2,4,6-octatrienal, and (E,E,E)-3-methyl-2,4,6-octatrienal
Authors: Aly M. M. Abo , Baron M. H. , Favrot J. , Belloc J. , Revault M.
Published: May 2006

Attempted vibrational assignments of (E,E)-2,4-hexadienal, (E,E,E)-2,4,6-octatrienal, and (E,E,E)-3-methyl-2,4,6-octatrienal are given between 3100 and 50 cm−1. We particularly discuss spectroscopic effects of the aldehydic group presence, enlargement of the polyenal chain length, and methyl lateral substitution.
One-electron photooxidation of N-ethylcarbazole in the presence of carbon tetrachloride. Products and mechanism of the photochemical reaction
Authors: Zelent Bogumil , Durocher Gilles
Published: May 2006

The mechanism of the photodecomposition of N-ethylcarbazole (NEC) in the presence of carbon tetrachloride has been discussed on the basis of the photoproducts identified. The photodissociation of the N-ethyl bond and the electron transfer in the transiently formed ex-CT complex, [Formula: see text], have been proposed as the primary photochemical processes involved irr the singlet excited NEC molecule. The latter, treated as the main process, leads to the radical cation of NEC, chloride ion, and trichloromethyl radical in the solvent cage, [NEC+•Cl−ĊCl3]. The other reactions in the system studied are analysed following the decomposition of NEC+• in the presence of Cl− and ĊCl3, which can occur by the N-ethyl group and (or) by the aromatic ring. The formation of intermediate products such as[Formula: see text]in the solvent cage gives rise to secondary photochemical reactions in the system studied. The polarity and chemical activity of the reaction media used strongly influence the nature of the secondary photochemical transformations both in and outside the solvent cage. The formation mechanism of the photochemical reaction products in CCl4 when ammonia was used, after and during irradiation, has been explained mainly by the transformations of the radical αr and cation αk as well as by the carbazyl radical β, which is also formed in the reaction medium. On the other hand, reaction of the cation [Formula: see text] explains the formation of the photoproducts in the irradiated solution of NEC with CCl4 in ethanol. These photochemical results have been compared to the photochemical reactions involved in the carbazole–CCl4 system.
Effect of salt on the tyrosine and protonated Schiff base deprotonation kinetics in bacteriorhodopsin
Authors: Dupuis Paul , El-Sayed M. A.
Published: May 2006

It is observed that the number of protons pumped per M412 formed in the bacteriorhodopsin photocycle almost doubles at high salt concentrations. In this paper, we studied the rates of deprotonation of tyrosine and of the two components of the protonated Schiff base at high salt concentrations, and at different pHs and temperatures. It is found that at pH = 7, increasing the salt concentration decreases the rates of deprotonation of the protonated Schiff base and tyrosine. This strongly suggests that the observed gain in the quantum yield of proton release per M412 formed when the salt concentration is increased is not a result of an increase in these rates. However, at high pH, e.g. 9.6, increasing the salt concentration increases the rate of deprotonation of the Schiff base by about 50%. Under all conditions, the slow component of the Schiff base is found to lose its proton prior to tyrosine.
A theoretical study of the electronic structure and spectra of metalloporphine cations
Authors: Edwards W. Daniel , Zerner Michael C.
Published: May 2006

A theoretical study is made of the electronic spectra of Mg(II), Zn(II), and Co(III) porphine and their π cations using the INDO/S-CI spectroscopic model. The calculated electronic spectra for the neutral compounds compare well with experiment. The two low-lying π cations, one of 2A1u and one of 2A2u symmetry are both examined for each of these systems. The 2A1u cations are calculated to lie lower in energy than the 2A2u cations by only 4 kcal/mol, consistent with the findings that both ions are found depending on substituents and solvent.The visible region of the spectrum of the 2A1u species is predicted to consist of three separate bands decreasing in intensity with increasing energy, while that of the 2A2u species is calculated to consist of three allowed transitions of near equal intensity, in agreement with experimental findings. In general the Soret region of the 2A1u ions is dominated by one transition, while at least three strong bands are calculated in the Soret region for the 2A2u ions, again in reasonable accord with experiment. Charges, ionization energies, and spin densities are reported and discussed for all compounds.
The adiabatic approximation in the ground-state manifold
Authors: Craig D. P. , Thirunamachandran T.
Published: May 2006

The adiabatic approximation to vibronic interactions, and its relation to the crude adiabatic and other methods, need careful scrutiny when applied to processes where both participating states belong to the same electronic manifold. The processes include vibrational transitions by both electronic and magnetic mechanisms, and the property of vibrational circular dichroism in chiral systems. When moments and properties are calculated, general questions of dependence on the chosen origin of coordinates have to be resolved. These problems are examined.
Tautomeric equilibrium of cyclic β-ketoester enamines
Authors: Labelle Marc , Gravel Denis
Published: May 2006

The conjugated–unconjugated tautomerism of β-ketoester enamines has been investigated. Enamines with different amine ring size, ketone ring size, and ester alkyl group have been prepared. Equilibrium ratios of the conjugated and unconjugated forms have been determined. A three-point rationalization is presented: (1) the relative instability of the conjugated form is due to a large steric interaction; (2) the ring size combination largely determines the equilibrium ratio because of energy differences between the resonance hybrid structures of the conjugated forms; (3) the ester alkyl group slightly affects the equilibrium ratio, through a difference in rotational freedom in the conjugated form. The degree of instability of double bonds exocyclic to 5-, and 6-, and 7-membered rings is discussed.
Carbon-13 nuclear magnetic resonance study of potassium and thallium ion binding to the Gramicidin A transmembrane channel
Authors: Urry D. W. , Trapane T. L. , Venkatachalam C. M. , Prasad K. U.
Published: May 2006

By means of carbon-13 nuclear magnetic resonance, carbonyl carbon ion-induced chemical shifts of the Gramicidin A channel are determined at 70 °C and analyzed as a function of potassium ion concentration and as a function of thallium ion concentration. In both cases two binding processes are observed. The estimated binding constants for potassium ion binding are 28/M and 2.4/M for the tight (single ion occupancy) and weak (double ion occupancy) sites, respectively, and for thallium ion binding are of the order of 103/M for the tight site and approximately 70/M for the weak site. These studies, which utilize a 90% enriched carbonyl carbon within the binding site of the channel to monitor ion interaction, argue for the presence of two ions in the channel for conditions under which planar bilayer transport studies are commonly carried out.
Raman investigations of collective vibrational motions in van der Waals liquids
Authors: Bratos S. , Tarjus G.
Published: May 2006

Recent investigations of collective vibrational motions in pure van der Waals liquids and in their isotopic mixtures are reviewed. Experimental data are enumerated first. The theory is presented later, separately, for non-composite and composite bands of both isotropic and anisotropic Raman spectra. It is shown that isotropic Raman processes are partially coherent and contain information about collective vibrational motions in liquids. In turn, anisotropic Raman processes are incoherent in the zero-order description and their study is less important in the present context.
Vibrational intensities in molecules with strained bonds: cyclopropane
Authors: Gussoni M. , Castiglioni C. , Zerbi G.
Published: May 2006

Static and dynamic electronic charges in cyclopropane are derived from infrared intensities using parametric methods already successfully tested on many other organic molecules. Rigorous and somewhat simpler methods are adopted and the results compared. It is shown that, because of the presence of strained CC bonds in the molecule, the electrical behaviour of the C—H groups approaches that of C—H bonds in =CH2 groups. Comparison of data from cyclopropane and ethylene oxide is made.
The kinetics of the reactions of atomic hydrogen with halo-ethylenes
Authors: Ahmed Mahmooda G. , Jones William E.
Published: May 2006

The absolute rate constants for the addition of H atoms to C2H3F, 1,1-C2H2F2, C2HF3, C2H3Cl, 1,1 -C2H2Cl2, C2HCl3, and C2H3Br have been determined at 298 ± 2 K over the pressure range 0.70–1.35 Torr. For each of the compounds, the rate constants are found to undergo a modest increase with pressure. At 1.00 Torr the values determined for the rate constants are: C2H3F, (8.86 ± 1.12) × 10−14; 1,1-C2H2F2, (8.16 ± 0.66) × 10−14; C2HF3, (6.21 ± 0.53) × 10−14; C2H3Cl, (27.0 ± 0.5) × 10−14; 1,1-C2H2Cl2, (59.6 ± 3.4) × 10−14; C2HCl3, (10.4 ± 0.8) × 10−14; C2H3Br, (27.8 ± 2.5) × 10−14; in units of cm3 molecule−1 s−1.
Application of 13C nuclear magnetic resonance to the conformational analysis of vicinally di- and trisubstituted cyclohexanes: halohydrins, methoxyhalohydrins, and their acetates
Authors: Buchanan G. W. , Bovenkamp J. W. , Rodrigue A. , Bannard R. A. B. , Moir R. Y.
Published: May 2006

Low temperature 13C nuclear magnetic resonance spectroscopy has been employed to obtain the chemical shifts and to examine the conformational equilibria of the four chlorohydrins and bromohydrins of 3-methoxycyclohexene. The corresponding acetates and the unsubstituted halohydrins have also been examined. The observed chemical shifts were compared with those calculated from additivity considerations. Limitations of this approach are discussed. Relative peak area measurements have been used to obtain conformational free energies in favourable cases.
A vanadium-51 nuclear magnetic resonance investigation of vanadate oxyanions in a lyotropic liquid crystalline bilayer system
Authors: Tracey Alan S. , Radley Keith
Published: May 2006

The vanadate ion VO4H2− and two of its polymeric forms contained in mixed lyotropic mesophase prepared from potassium dodecanoate/n-alkyltrimethylammonium bromide in water have been investigated by 51V nuclear magnetic resonance spectroscopy. The results indicate that the tetrahedral ion interacts with the micellar surface through the hydrating water associated with this ion. The ion undergoes strong interactions with the carboxylate head group of the dodecanoate as well as with the headgroup of the alkyltrimethylammonium detergent, which of course is of opposite charge. The other two species investigated have previously been assigned by various workers to V2O74− and its cyclic dimer V4O124−. The results obtained here are not consistent with those assignments but rather with more symmetrical compounds such as the tetrahedral uncharged molecule V4O10 and a higher analogue of this, respectively. The nmr spectra from these latter species show that they undergo, at best, extremely weak interactions with the cationic surface but strong interactions with an anionic one. The behaviour of the quadrupole splittings observed is consistent with specific interactions to the carboxylate moiety. The observation of an induced chemical shift separation between vanadium resonances from the same highly symmetric species confirms that binding of this compound is very strong.
Photocyclization of 2-vinylbiphenyls: stereochemistry of the triplet state cyclization
Authors: Lapouyade René , Manigand Claude , Nourmamode Aziz
Published: May 2006

The photochemistry of five- to eight-membered ring containing 2-cycloalkenyl biphenyls was examined under direct and sensitized irradiation. From the singlet excited state only trans 9,10-cycloalkyl-9,10-dihydrophenanthrenes were obtained. From the triplet state the trans isomer was exclusively formed from 2-cyclopentenyl and 2-cyclohexenyl biphenyls while the cis isomer also appeared with 2-cycloheptenyl and 2-cyclooctenyl biphenyls. We propose that the cis isomers resulted from the cyclization of the perpendicular triplet of cycloheptenyl biphenyl and from the perpendicular and trans triplet of cyclooctenyl biphenyl. Whereas the photocyclization of 2-vinylbiphenyls was regarded as a singlet-state reaction, the quantum yields of reaction of 2-cycloalkenyl biphenyls, from both singlet and triplet states, were high (ΦS = 0.20–0.26; ΦT = 0.15–0.46).
Stéréochimie de la réduction des α-iminocétones. Étude de l'effet des substituants par une approche quantitative des facteurs gouvernant la stéréosélectivité
Authors: Alcaide Benito , Mardomingo Carmen L. , Pérez-Ossorio Rafael , Plumet Joaquin , Phan-Tan-Luu Roger , Sargent Michelle
Published: May 2006

Using the isomeric ratio of RR,SS to RS,SR of a series of 2-aminoethanols obtained by the LiAlH4 reduction of 24 α-iminoketones we propose a mathematical model with 7 coefficients for the effect of substituent on the stereochemical course of the reaction. The values of these coefficients obtained by multilinear regression analysis are in agreement with the previously proposed mechanism for reduction but allow for some additional conclusions. The use of modern methods for the construction of experimental matrices allows us to choose 10 from a total of 24 experiments and shows that information of the same quality can be obtained from this subset.
Studies of infrared multiphoton dissociation rates of protonated aliphatic alcohol dimers
Authors: Young Alexander Baldwin , March Raymond Evans , Hughes Richard James
Published: May 2006

The rates of photodissociation induced by absorption of infrared radiation of protonated dimers of 2-propanol and its deuterated analogues are reported. Protonated alcohol dimer ions created in a quadrupole ion store (QUISTOR) were irradiated in isolation and as a function of parent gas pressure and added collision gas (N2). The relative weights and nature of ionic photoproducts were determined by mass spectrometry. The effect upon photolysis of collisions both prior to and during irradiation were examined. Photodissociation rates were defined by σD, which is the measured photodissociation rate constant normalized to the laser intensity. Nascent dimer ions which can possess up to 130 kJ mol−1 internal energy dissociated readily with σD of 15.8 × 10−2 cm2 extrapolated to collision-free conditions. Photodissociation products from nascent dimer ions were produced via two major reaction channels. As the number of collisions suffered by the nascent dimer ion prior to irradiation was increased, the value of σD diminished and a single reaction channel became more prevalent. After some 270 collisions the ions appear to be collisionally relaxed prior to photolysis. The value of σD of 13.1 × 10−21 cm2 extrapolated to collision-free conditions was obtained. The products from photodissociation of relaxed ions were obtained from a single reaction channel. An increase in σD values obtained with added nitrogen collision gas indicated a blockage or "bottleneck" in multiphoton absorption which is attributed to rotational population depletion. Three deuterated analogues of 2-propanol showed similar behaviour to that of 2-propanol with the exception that deuteron-bound dimers formed from 2-propanol (OD) and perdeutero-2-propanol failed to show rotational population depletion. The apparent lack of a "bottleneck" in multiphoton absorption by deuteron bound dimers is attributed to the diminished spacings between rotational levels of these species compared with the rotational level spacings for proton-bound dimers. Proton-bound ethanol dimers were selected for the examination of temperature effects upon photodissociation rates. While values for σD, extrapolated to collision-free conditions, of 15.6 × 10−21 cm2 at 321 K (in agreement with the 2-propanol results obtained solely at this temperature) and 8.55 × 10−21 cm2 at 293 K were obtained, the precise interpretation of such a marked temperature effect is not immediately obvious.
(S)-2,2,5,5-Tetramethylthiazolidine-4-carboxylic acid: a compound which exists in the amino acid rather than the zwitterion form
Authors: Howard-Lock Helen Elaine , Lock Colin James Lyne , Smalley Philip Stuart
Published: May 2006

The X-ray crystal structure of (S)-2,2,5,5-tetramethylthiazolidine-4-carboxylic acid, 1, has been determined. Crystals are monoclinic, P21, with cell dimensions a = 11.351(4) b = 8.303(2), c = 11.969(3) Å, β = 116.69(2)°, and Z = 4. The structure was solved by standard methods and refined to R1 = 0.0774, R2 = 0.0670 for 2388 independent reflections. Compound 1 exists in the amino-acid form as shown by two distinctly different C—O bond lengths, 1.209 and 1.309 Å, typical of the COOH group, and by the positions of the hydrogen atoms. The amino-acid form of 1 found in the solid also exists in solution as shown by infrared and Raman spectra. The mass spectra, and 1H and 13C nmr spectra are reported, as well as detailed infrared and Raman spectra for the title compound and several deuterated species.
An increased internal rotational barrier in thiophenol caused by meta substituents
Authors: Schaefer Ted , Baleja James D. , Penner Glenn H.
Published: May 2006

The twofold internal barriers to rotation about the C—S bond in 3,5-diX-thiophenols were determined in solution from long-range spin–spin coupling constants. They are 3.4, 4.85, 5.3, 6.45, and 7.25 ± 10% kJ/mol for X = H, CH3, OCH3, F, and Cl, respectively. In 3,5-dichloro-4-hydroxythiophenol, V2 is −0.8 kJ/mol as compared to −1.9 kJ/mol in 4-methoxythiophenol. The para substituent here dominates. The observed barriers are in rough agreement with arguments based on perturbation molecular orbital theory and with MO calculations of changes in the barrier caused by substituents. The computed values appear as nearly pure twofold barriers with very small fourfold components.
Le radical méthylènecyclopropyle: étude théorique. Chloration par t-BuOCl et réduction par (nBu)3SnH de dérivés cyclopropéniques
Authors: Arnaud R. , Choubani S. , Subra R. , Vidal M. , Vincens M. , Barone V.
Published: May 2006

The allylic chlorination of ethyl 2,3-dialkyl 2-cyclopropenecarboxylate or primary and tertiary alcohols is highly regio- and stereoselective. The halogenated methylenecyclopropane derivative only is observed. In that compound, the halogen substituent and the functional group are in a trans position with respect to the ring. The halogenated allylic compounds of methylenecyclopropane and of cyclopropene undergo reduction by (nBu)3SnH with the same stereochemistry. Products arising from ring opening are also observed. The exocyclic migration of the double bond can be related to the formation of a transient allylic radical. A theoretical study performed within the MNDO (UHF and RHF) framework leads to a planar allylic radical, whatever the substituent. The radical abstraction reaction which takes place during the reduction process is easier for a cyclic carbon atom than for an exocyclic one. In the former case, the faster reaction is obtained for a chlorinated carbon atom.
Enthalpies of interaction of hydroxylic solutes with organic solvents
Authors: Stephenson W. Kirk , Fuchs Richard
Published: May 2006

Heats of solution of m-cresol, 1-butanol, 1-pentanol, t-amyl alcohol, and model compounds (toluene, ethyl ether, n-butyl methyl ether, t-butyl methyl ether) in 17 organic solvents (n-heptane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane, α,α,α-trifluorotoluene, triethylamine, butyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, benzene, toluene, mesitylene, t-butyl alcohol, 1-octanol, methanol, 2,2,2-trifluoroethanol) have been combined with solute heats of vaporization to give solvation enthalpies (ΔH(v → S)). Dependencies of solute vs. model solvation enthalpy differences on solvent dipolarity–polarizability and hydrogen-bond-accepting basicity were determined via correlations with Taft–Kamlet solvatochromic parameters (π*, β, ξ).m-Cresol is a substantially stronger H-bond donor than 1-butanol, 1-pentanol, and t-amyl alcohol, and H-bonds to acceptor solvents including alcohols. Cresol acts as an H-bond acceptor with the strong H-bond donor solvent trifluoroethanol.
The preparation and structure of methanedithiolatobis(dimethylphenylphosphine)platinum(II), (PMe2Ph)2Pt(S2CH2)
Authors: Shaver Alan , Lai Rabin D. , Bird Peter H. , Wickramasinghe Wasantha
Published: May 2006

Attempts to prepare the complexes cis-L2Pt(SH)2, where L = PPh3, PMePh2, and PMePh by treatment of the appropriate dichloro complexes with NaSH in the presence of CH2Cl2 have resulted in the isolation of the complexes L2Pt(S2CH2). The X-ray structure determination of the compound for which L = PMe2Ph confirms the presence of the CH2S22−ligand.
Spectroscopic, magnetic, biological, and structural characterization of tetrakis(μ-3-chloropropanoato)bis(triphenylphosphine oxide)dicopper(II)
Authors: Sharrock Patrick , Melnik Milan , Belanger-Gariepy Francine , Beauchamp André L.
Published: May 2006

Tetrakis(μ-3-chloropropanoato)bis(triphenylphosphine oxide)dicopper(II) is formed by the reaction of the phosphine oxide on the parent copper carboxylate. It belongs to the triclinic space group [Formula: see text], with a = 8.603(6), b = 12.605(4), c = 12.624(5) Å, α = 76.94(3), β = 71.74(4), and γ = 74.42(4)°. The complex has the copper acetate dimer structure, in which two Cu atoms separated by 2.649(1) Å are bridged by four bidentate carboxylate groups (mean Cu—O = 1.969 Å). The Cu—O apical bond to triphenylphosphine oxide is relatively short (2.097(2) Å). The epr spectra of the solid are interpreted in terms of a dimeric species with a paramagnetic triplet state. The same signals are found in the spectra of frozen ethanol solutions, indicating that the dimer structure is retained. Magnetic susceptibility was determined in the range 81–293 K and the energy separation −2J = 328(4) cm−1 was found between the two spin states. The phosphine oxide adduct is toxic to Escherichiacoli with ID50 values near 100 μg/mL.
Kinetics and mechanism of the oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide
Authors: Kothari Seema , Banerji Kalyan Kumar
Published: May 2006

The oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide (BAB) in acid solution results in the formation of the corresponding benzaldehydes. The reaction is first order with respect to BAB, the alcohol, and hydrogen ions. The reaction exhibits a primary kinetic isotope effect (kH/kD = 5.26). The value of the solvent isotope effect, k(H2O)/k(D2O), equals 0.43 at 298 K. Addition of benzenesulfonamide has no effect on the rate. Increase in amount of acetic acid in the solvent increases the rate. The reaction rate has been determined at five different temperatures and the activation parameters have been calculated. (PhSO2NH2Br)+ has been postulated as the reactive oxidizing species. The rates of oxidation of substituted benzyl alcohols correlate very well with Brown's σ+ constants. The value of the reaction constant is −2.84 at 298 K. A hydride transfer from the alcohol to the oxidant, in the rate-determining step, has been proposed.
Formal total synthesis of erythromycin A. Part III. Synthesis of Woodward's carbamate key intermediate from a 1,7-dioxaspiro[5.5]undecane derivative of erythronolide A
Authors: Bernet Bruno , Bishop Paul M. , Caron Maurice , Kawamata Takeshi , Roy Bernard L. , Ruest Luc , Sauvé Gilles , Soucy Pierre , Deslongchamps Pierre
Published: May 2006

The spirocompound 1 which was obtained by total synthesis (Part I) and by degradation from erythromycin (Part II) was converted into carbamate product 15, a key intermediate in the Woodward's total synthesis of erythromycin A.
Tricyclic system containing large rings. The synthesis of fully-conjugated [12](1,3)[12](4,6)cyclophanpolyenepolyynes and related compounds
Authors: Ojima Juro , Kakumi Hiroshi , Kitatani Kazuto , Wada Kazuyo , Ejiri Emiko , Nakada Tetsuya
Published: May 2006

For the purpose of preparing the ring-expanded analogue of anthracene, 1,2,4,5-tetrakis[(1E,3Z)-4-methylhexa-1,3-dien-5-ynyl]benzene, 8, and 1,2,4,5-tetrakis[(Z)-2(2-ethnylphenyl)ethenyl]benzene, 16, were oxidatively coupled; however, both of them afforded m-bridged derivatives, i.e., 1,3:4,6-bis[(1E,3Z,9Z,11E)-4,9-dimethyldodeca-1,3,9,11-tetraene-5,7-diyne-1,12-diyl]benzene, 3, and 1,3:4,6-bis[(1E,11E)-3,4:9,10-dibenzdodeca-1,11-diene-5,7-diyne-1,12-diyl]benzene, 5. To ascertain the structures of 3 and 5, the related model compounds were also prepared.
Binuclear phthalocyanines covalently linked through two- and four-atom bridges
Authors: Marcuccio Sebastian M. , Svirskaya Polina I. , Greenberg Shafrira , Lever A. B. P. , Leznoff Clifford C. , Tomer Kenneth B.
Published: May 2006

Binuclear phthalocyanines in which the two phthalocyanine nuclei are covalently linked through four-atom bridges, derived from catechol, have been prepared and characterized. Metal-free 2,9,16,23-tetra-(3,3-dimethylbutyl)phthalocyanine and 2,9,16,23-tetra-(2-trimethylsilylethyl)phthalocyanine were prepared as examples of non-oxygenated mononuclear phthalocyanines soluble in organic solvents. Catalytic hydrogénation of 1,2-bis-(3,4-dicyanophenyl)ethyne and 1,4-bis-(3,4-dicyanophenyl)buta-1,3-diyne gave 1,2-bis-(3,4-dicyanophenyl)ethane and 1,4-bis-(3,4-dicyanophenyl)butane respectively. From these precursors, metal-free phthalocyanine dimers containing ethylene and tetramethylene bridges, joining the phthalocyanine nuclei, were prepared. Two of the two-atom bridge phthalocyanine dimers represent the first characterized phthalocyanine dimers not containing alkoxy or oxygenated groups.
Kinetic mechanism of copper(II) transfer between the native sequence peptide representing the copper(II)-transport site of human serum albumin and L-histidine
Authors: Tabata Masaaki , Sarkar Bibudhendra
Published: May 2006

The kinetics for Cu(II)-transfer reaction of the native sequence tripeptide, L-aspartyl-L-alanyl-L-histidine-N-methyl amide (AAHNMA), representing the Cu(II)-transport site of human serum albumin (HSA), and L-histidine (L-His) was studied in the forward and reverse reactions in a pH range 6.5–10.0 at I = 0.2 and 25°. For the Cu(II)-transfer from Cu(II)-L-His2 to native sequence peptide, the rate-determining step is a bond formation between Cu(II) and peptide nitrogen to form CuH−1AB from CuAB by deprotonation of peptide nitrogen atom, where A and B denote the anionic forms of AAHNMA and L-His, respectively. For the Cu(II)-transfer reaction from Cu(II)–peptide to L-His, the rate-determining step is a bond breaking between Cu(II) and peptide nitrogen to form CuAB fromCuH−1AB by protonation to a peptide nitrogen. The effect of carboxyl group of aspartyl residue in the native sequence peptide on the kinetic and equilibrium constants are discussed.
Fletcher–Powell minimization of analytical potentiometric data by microcomputer: application to the Cu(II) complexes of biological polyamines
Authors: Templeton Douglas M. , Sarkar Bibudhendra
Published: May 2006

The Fletcher–Powell minimization algorithm has been successfully implemented for the extraction of metal complex stability constants from analytical potentiometric data. The procedure has been adapted to run on a microcomputer with acceptable execution times, and several strategies are employed to speed convergence and avoid false minima. This allows economical minimization for a large number of models of speciation, and improves the reliability of the proposed best fit by encouraging the checking of more models than previously possible. The Ni(II)–glycine system has been analyzed and excellent agreement with the stability constants of an earlier multi-laboratory study has been attained. The system proves useful in the evaluation of both analytical and computational methods. The procedure has also been used for speciation analysis of the Cu(II) complexes of the growth regulating polyamines, spermine, and spermidine. Both systems form fully deprotonated complexes at physiological pH, which are relevant to their biological activity.
Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives
Authors: Arnold B. , Donald L. , Jurgens A. , Pincock J. A.
Published: May 2006

The photochemical cleavage of the 1-naphthylmethyl derivatives, 1–7, has been examined in methanol solvent under both direct and sensitized conditions. The competitition between homolytic and heterolytic cleavage as a function of multiplicity and leaving group has been studied in detail. Only substrates 1, 2, 3, and 7 react on sensitization with xanthone but evidence is presented that the resulting reactivity of 1, 2, and 3 may not be triplet energy transfer but rather exciplex formation. A semi-quantitative scale for photofugacities of the leaving groups from the excited singlet states has been established.
Synthesis and conformational assignment of cis- and trans-2-amino-1-arylcyclohexanols
Authors: Delgado Antonio , Granados Ricardo , Mauleon David , Soucheiron Inmaculada , Feliz Miguel
Published: May 2006

The synthesis of cis- and trans-2-amino-1-arylcyclohexanols 1–8, conformationally restricted analogues of the α-adrenergic drugs norephedrine 9, methoxamine 10, and isopropylmethoxamine 11, is described. trans-Aminoalcohols were obtained through reaction of epoxides 12 or 13 with isopropylamine (to afford 4 and 8) or with sodium azide followed by lithium aluminum hydride reduction (to afford 2 and 6), whereas cis-aminoalcohols 1 and 5 were obtained by condensation of 2-aminocyclohexanone hydrobromide 26 with the appropriate organometallic reagent. Treatment of 1 and 5 with acetone followed by sodium borohydride reduction gave isopropylaminoalcohols 3 and 7. Configurational and conformational assignments of aminoalcohols 1–8 have been carried out on the basis of their 1H nmr and 13C nmr data and by comparison with reference diols 18 and 30. The major or exclusive chair conformation observed for all the compounds has an equatorial aryl group.
Ozonides de phosphite source d'oxygène singulet: rendement, mécanisme
Authors: CaMinade Anne Marie , Khatib Fayez El , Koenig Max , Aubry Jean Marie
Published: May 2006

The ozonides of several phosphites in solution in dichloromethane have been reacted with some scavengers of singlet oxygen (1O2) like rubrene (2), tetraphenylcyclopentadienone (4), and 9,10-diphenylanthracene (6). These ozonides react on the scavengers (−47 °C < t <30 °C) upon their decomposition. The Foote curves obtained by varying the respective concentrations of ozonides and of scavengers lead to parameters similar to those obtained upon the photooxidation of the scavengers by 1O2. Results confirm that these ozonides can lead to the formation of 1O2. The absolute yield of 1O2 is 100% (ρ = 1). These results also confirm the high efficiency of the rubrene toward 1O2 (γ = 1) and the lower efficiency of the tetraphenylcyclopentadienone (γ = 0.46). However, the low value (γ = 0.3) for the efficiency of the 9,10-diphenylanthracene (4) is unexpected.
An analysis of a second-order chemical reaction involving a single intermediate between reactants and products
Authors: Blandamer Michael Jesse , Scott John Marshall William , Summers Danny
Published: May 2006

The differential equations which describe the kinetics of the general reaction[Formula: see text]are cast in a nondimensional form and analysed. The problem reduces to two first-order nonlinear ordinary differential equations containing three nondimensional constants together with two initial conditions. Composition–time curves are deduced for the general case. For the case when [Formula: see text], where [A]0 is the initial concentration of A, simple analytical solutions are obtained. Numerical integrations of the full equations are reported and the analytical solutions are found to represent accurate solutions to the nonlinear problem for sufficiently small values of k2.