bluuebunny/crossref_metadata_2025 huggingface dataset:
The outer-sphere oxidation of ascorbic acid by the thioureapentacyanoferrate(III) ion
Authors: Macartney Donal H. , McAuley Alexander
Published: May 2006

The oxidation of ascorbic acid by thioureapentacyanoferrate(III) has been investigated over the pH range 0.8–7.2 at an ionic strength of 1.0 M (NaClO4). The variations in the rates of oxidation with hydrogen ion concentration are consistent with a reaction scheme involving three pH-related species; ascorbic acid (H2A) (k1 = 0.111 M−1 s−1, ΔH1≠ = 5.1 kcal mol−1, ΔS≠ = −46 cal deg−1 mol−1), the ascorbic anion, (HA−) (k2 = 66 M−1s−1, ΔH2≠ = 5.4 kcal mol−1, ΔS2≠ = −32 cal deg−1 mol−1) and the ascorbic dianion, (A2−) (k3 = 8.78 × 107 M−1 s−1, ΔH3≠ = 3.1 kcal mol−1, ΔS3≠ = −12 cal deg−1 mol−1). The low reduction potential of Fe(CN)5TU2− (E0 = 0.35 V) permits the measurement of the rate of oxidation of the ascorbate dianion, not previously investigated with metal complexes. The second acid dissociation constant of ascorbic acid [Formula: see text] has been measured in 1.0 M NaClO4 over the temperature range studied. A relationship between the rate of oxidation and the reduction potentials of the ascorbic acid species is shown.
Synthesis, characterization, and X-ray structural analysis of the Cu(I) derivative, [Me2Ga(OCH2CH2NMe2)N2C5H7]Cu• PPh3
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The Cu(I) complex [Me2Ga(OCH2CH2NMe2)N2C5H7]Cu•PPh3 has been synthesized and its fluxional behavior in solution probed. Attempts have been made to isolate the analogous Cu(I) carbonyl complex. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl)(N,N-dimethylethanolamino)gallato (N(2),O,N(3))](triphenylphosphine)copper(I) are monoclinic, a = 18.871(2), b = 9.464(1), c = 18.374(2) Ā, β = 109.62(1)°, Z = 4, space group P21/c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.028 and Rw = 0.035 for 2729 reflections with I ≥ 3σ(I). The copper atom is bonded to the phosphine and to the tridentate Me2Ga(OCH2CH2NMe2)N2C5H7− ligand resulting in a distorted tetrahedral coordination geometry. The Cu—P distance of 2.156(1) Å is unusually short. Other important bond distances (corrected for libration) are: Cu—O, 2.163(2), Cu—N(pyrazolyl), 2.025(3), Cu—N(amino), 2.144(3), Ga—O, 1.896(3), Ga—N, 2.005(3), and Ga—C, 1.972(5) and 1.987(5) Å.
Total synthesis of α- and β-himachalene by an intermolecular Diels–Alder approach
Authors: Liu Hsing-Jang , Browne Eric N. C.
Published: May 2006

A total synthesis of α-himachalene (2) and β-himachalene (3) has been achieved in eleven steps and in an effective overall yield of 21% from 4,4-dimethyl-2-cyclohexenone (4). The synthesis involves keto ester 7 as a key intermediate which is conveniently prepared by the Diels–Alder addition of dienone ester 6 to isoprene.
Solubility of water in vinyl chloride
Authors: Clarke E. Colin , Glew David N. , Maisonneuve Denis J.
Published: May 2006

The solubility of water in liquid vinyl chloride has been measured over the temperature range −17° to 60 °C by a classical water absorption method. Solubility equations for water in vinyl chloride have been derived and the standard thermodynamic function changes for water transfer have been evaluated.
Total synthesis of (+)-thromboxane B2 from D-glucose. A detailed account
Authors: Hanessian Stephen , Lavallee Pierre
Published: May 2006

The total synthesis of thromboxane B2 from D-glucose is described, based on the recognition of hidden carbohydrate-type symmetry in the molecule. Methyl 2-deoxy-α-D-ribo-hexopyranoside was prepared from D-glucose and manipulated in such a way as to introduce C-branching at C-4 in a stereocontrolled manner. This crucial intermediate was then transformed into the target compound by adaptations of established methodology in the field.
The reaction of some propargyl alcohols with benzeneselenenyl chloride
Authors: Garratt Dennis G. , Beaulieu Pierre L. , Morisset Veronique M.
Published: May 2006

The reaction of benzeneselenenyl chloride with twenty-two propargyl alcohols in methylene chloride solution is reported. Products of both Markownikoff and anti-Markownikoff regiochemistry are formed in an anti stereospecific manner. The regioselectivity or specificity is found to be very dependent upon the nature of the substituents geminal to the alcoholic moiety. In general the presence of bulky substituents geminal to the alcoholic moiety tend to favour formation of the anti-Markownikoff adduct under conditions of kinetic control. The Markownikoff adducts are found to be favoured thermodynamically.
Rydberg and valence-shell transitions in the quartz ultraviolet spectra of aliphatic thiones
Authors: Bruno A. E. , Clouthier D. J. , Mezey P. G. , Steer R. P.
Published: May 2006

The electronic absorption spectra of 3,3-dimethylbutane-2-thione and 3-methylbutane-2-thione in the gas phase have been measured and the observed transitions assigned with the aid of abinitio and semi-empirical calculations. In the quartz ultraviolet region four transitions are observed. A strong, broad, structureless band is assigned to the π → π* transition and three weaker, narrower bands are assigned to Rydberg n → 4s, n → 4py and n → 4pz transitions on sulfur.
Photochemical reactions of charge-transfer complexes. III. Molecular orbital studies of the charge-transfer complexes between 1,2-dimethoxyethylenes and 1,2-dicyanoethylenes
Authors: Wong Po Cheong , Boyd Russell J.
Published: May 2006

Ab initio and PCILO molecular orbital (MO) calculations for the four π–π* charge-transfer complexes formed between maleonitrile (MN) and fumaronitrile (FN), and cis (CS) and trans-1,2-dimethoxyethyIene (TR) are reported. The donor and the acceptor molecules are stacked in parallel planes. Trans and cis-l,2-dihydroxyethylene are used as the model compounds for TR and CS in the determination of the optimum geometries of the complexes. Both types of MO calculations indicate that the eclipsed geometry (with the two central double bonds parallel and the centres of the double bonds centred over one another) is relatively unstable. With limited geometry searching, we find that the slipped geometry (with the two central double bonds parallel but separated at a projected distance of 2.2 Å and the oxygen atoms above the cyanocarbon atoms) is the preferred structure. According to the ab initio calculations the relative order of the calculated heats of formation (ΔHθ's) for these complexes is: MN−CS > FN−CS > FN−TR > MN−TR.
Allylic derivatives of nickel and palladium
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis of novel allylic derivatives of Ni and Pd incorporating the bispyrazolylgallate ligand Me2Ga(N2C5H7)2− is described. Pyrazolyl-bridged homobinuclear and trinuclear nickel allyl systems are also presented. Crystal structures of [Me2Ga(N2C5H7)2]Ni(η3-C3H5) and [(η3-C3H5)Ni(N2C5H7)2]2Ni are described. Crystals of the former are triclinic, a = 8.265(1), b = 10.487(1), c = 11.755(2) Å, α = 72.60(1), β = 87.28(1), γ = 67.58(1)°, Z = 2, space group [Formula: see text] and crystals of the latter are monoclinic, a = 7.9172(3), b = 10.6929(1), c = 16.9118(6) Å, β = 102.887(2)°, Z = 2, space group P21/c. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to R = 0.026 and 0.025 for 3329 and 2914 reflections with I ≥ 3σ(I) respectively. In both structures the M—(N—N)2—M rings are in the boat conformation and the allyl groups display twofold orientational disorder. In [Me2Ga(N2C5H7)2]Ni(η3-C3H5) the nickel coordination may be regarded as square-planar with the allyl ligand occupying two coordination sites and the coordination about the gallium is distorted tetrahedral. Important bond lengths (corrected for libration) are: Ni—N, 1.926(2) and 1.929(2), Ni—C, 1.971(5)–2.025(3), Ga—N, 1.994(2) and 1.996(2), Ga—C, 1.966(3) and 1.988(3) Å. The trinuclear complex [(η3-C3H5)Ni(N2C5H7)2]2Ni is centrosymmetric with the central Ni(1) atom bonded to four pyrazolyl nitrogen atoms in square-planar fashion. The outer Ni(2) atom is bonded to two pyrazolyl nitrogens and to an allyl group and also has square-planar coordination geometry. Important bond distances in this complex are: Ni(1)—N, 1.897(1) and 1.901(1), Ni(2)—N, 1.908(2) and 1.912(2), Ni(2)—C, 1.97(l)–2.022(3) Å.
Dielectric relaxation of lithium and sodium perchlorates in 1,2-dimethoxyethane and propylene carbonate
Authors: Cachet Hubert , Fekir Mohamed , Lestrade Jean-Claude
Published: May 2006

The complex permittivity of LiClO4 and NaClO4 solutions in 1,2-dimethoxyethane (DME) has been measured in the frequency range 0.140–123.2 GHz. The data have been analysed according to a model for the reorientation of ion pairs given in a previous paper. The dielectric data are supplemented by conductivity measurements in a broad concentration range (10−4–1 mol/L) which evidence the large extent of salt association. The main result is that the solvation of Li+ and Na+ by DME cannot be described as simply as in the case of other solvents, such as tetrahydrofuran or ethyl acetate, as far as the dielectric properties are concerned: while the assumption of rigidly bound solvating molecules was acceptable for the latter solvents, some freedom in the reorientation of these molecules has to be taken into account for the case of DME. LiClO4 solutions in propylene carbonate (PC) + benzene and PC + DME mixtures have also been studied. The data, for the latter, can be qualitatively interpreted under the assumption that PC molecules take the place of DME molecules in the solvation sheath, even at low PC concentration.
The tetrahedral intermediate of a lactonization reaction
Authors: McClelland Robert A. , Alibhai Masuma
Published: May 2006

The hydrolysis of the ortho ester 1,1-diethoxy-1,3-dihydroisobenzofuran (1) is described. This hydrolysis proceeds with initial expulsion of an exocyclic ethoxy group, producing upon hydration of the oxocarbonium ion 1-hydroxy-1-ethoxy-1,3-dihydroisobenzofuran (7), the tetrahedral intermediate of the lactonization of ethyl (2-hydroxymethyl)benzoate (6) to phthalide (8). Based on the kinetic behavior of the ortho ester hydrolysis, the pH variation in the ratio of 6:8 initially formed from the ortho ester, and the kinetic behavior of the lactonization reaction, rate constants for the breakdown of the tetrahedral intermediate 7 have been determined, along with the equilibrium constant for its formation from the hydroxy ester 6. The breakdown occurs in an extremely rapid hydroxide-ion-catalyzed reaction, with the rate being at the diffusion limit. Hydronium ion catalysis is also observed; this breakdown is also rapid although considerably less so than the hydroxide ion reaction. The changeover from H+ to OH− catalysis occurs at pH 3.5. The rate of breakdown is a minimum at this point, and corresponds to a half-life for the tetrahedral intermediate of about 0.1 s. It is concluded that this allows sufficient time for conformational changes in the tetrahedral intermediate prior to breakdown; this factor must be taken into account in stereoelectronic considerations.
Rational orbitals for two-electron S states
Authors: Birss F. W. , Hertog W. den
Published: May 2006

The concept of rational orbitals is introduced, based upon finding that pair of orbitals which yield the single configuration function which maximally overlaps with a configuration interaction wave function. They are simply obtained from the natural orbitals by an elementary orthogonal transformation and are more appropriate than natural orbitals to analysis of functions for open-shell states. The CI wave functions of a number of lS states of helium are analyzed and the nature of the rational orbitals investigated.
Hydrocarbon ions in fuel-rich, CH4–C2H2–O2 flames as a probe for the initiation of soot: an experimental approach
Authors: Tanner Scott D. , Goodings John M. , Bohme Diethard K.
Published: May 2006

The natural hydrocarbon ions CnHx± (n ≥ 2, x ≥ 0) present in premixed, fuel-rich, nearly sooting, CH4–C2H2–O2 flames at atmospheric pressure were studied as a probe of the early chemical stages of soot formation. Ion concentration profiles were measured mass-spectrometrically along the flame axis through the reaction zone into the burnt gas downstream. Total ionization profiles were examined for their dependence on both temperature and equivalence ratio, [Formula: see text] Families of individual CnHx− negative ion profiles exhibit concentration peaks in three distinct regions; predominantly oxygenated ions occur upstream, giving way to moderately unsaturated hydrocarbon ions near the end of the reaction zone, leading to highly unsaturated carbonaceous ions further downstream. The concentrations of the downstream ions alternate with the parity of n, the even-n species being larger. Series of CnHx+ positive ion profiles, for a given n, show profile peak positions which move steadily downstream with decreasing x, indicative of progressive dehydrogenation. The positive ion chemistry of these series is essentially independent of n. As [Formula: see text] is increased at constant temperature towards the sooting point, the concentrations of CnHx± ions increase while those of the oxygenated ions decrease; the positive ions show a relative enhancement of species having high values of n.
Relative methylmercury cation affinities in the gas phase determined by high pressure mass spectrometry
Authors: Stone John A. , Splinter Dena E.
Published: May 2006

A pulsed electron beam, high pressure mass spectrometer has been used to determine equilibrium constants for the exchange of CH3Hg+ between bases; [Formula: see text] A series of aromatic, hydrocarbon bases has been studied at 417 K and several nitrogen bases have been studied at 580 K. There is a good linear correlation between differences in CH3Hg+ affinity (ΔG0) and H+ affinity for bases in each series. The single sulfur base examined ((C3H7)2S) shows anomalously high relative affinity for CH3Hg+ compared with H+ while two oxygen bases (CH3COOCH3 and C6H5NO2) show lesser relative affinity. These results are in qualitative agreement with the hard–soft acid base theory. ΔH0 and ΔS0 values have been obtained from Arrhenius plots. For a pair of aromatic bases (toluene–ethylbenzene) ΔH0 is of the same magnitude as that for H+ and ΔS0 may be calculated using partition functions for translation and external rotation. For toluene/methylacetate the difference in binding energy is much greater for H+ than for CH3Hg+ and a similar calculation of ΔS0 gives a result not consistent with the experimental value.
Observation of two oxa-azabicyclo[2.2.0]hexenone intermediates along the reaction pathway of the photochemical isomerization of 1,3-oxazin-6-ones
Authors: Mayo Paul De , Weedon Alan C. , Zabel Ralph W.
Published: May 2006

Irradiation of 4-methyl-2-phenyl-1,3-oxazin-6-one, 1, yields a photochemical equilibrium between 1 and 2-methyl-4-phenyl-1,3-oxazin-6-one, 2. The isomerization proceeds through two intermediates, the oxa-azabicyclo[2.2.0]hexenones 3 and 4, both of which can be observed spectroscopically (ir, uv, 1H nmr) at low temperature.
A reinvestigation of the rate of reaction of N-decylimidazole with p-nitrophenyl decanoate
Authors: Guthrie J. Peter , O'leary Stella
Published: May 2006

Reinvestigation of the reaction of p-nitrophenyl decanoate with N-decylimidazole shows that the rate enhancement attributable to 1:1 complex formation between reactants is small (12-fold), consistent with what we have found in related systems, and much less than values reported by other workers. Kinetics were carried out at very low concentrations to avoid problems of aggregation, and at pH 8.0 to minimize the contribution from solvolysis. Numerous difficulties were encountered with reactive degradation products from Tris buffers. At pH 8.0 the apparent second order rate constant was 2.25 ± 0.64 M−1 s−1.
Purification and characterization of the indicator calmagite
Authors: Kratochvil Byron , Nolan James , Cantwell Frederick F. , Fulton Robert B.
Published: May 2006

A scheme for the purification of the azo dye calmagite is described which involves solvent extraction, column partition chromatography, and adsorption chromatography on a nonpolar adsorbent. The final product, analyzed by thin-layer chromatography and by acid–base and ion-pair titrations, is of >99% purity. Molar absorptivities and acid ionization constants are reported for the conjugate species.
The direct electrochemical synthesis of triphenylphosphine adducts of Group IB monohalides
Authors: Khan Masood , Oldham Colin , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of copper, silver, or gold into acetonitrile solutions of benzyl chloride or hydrogen halide plus triphenylphosphine leads to the formation of the adducts MXLn (M = Cu, Ag, Au; X = Cl, Br, I; L = Ph3P; n = 1, 1.5, 2; not all combinations). The value of n depends markedly on the mole ratio Ph3P:dissolved metal. The reaction pathway is discussed in the light of measurements of current efficiency. The results of X-ray structural studies of AuCl•L and AuClL2 are briefly reported.
Fluorosulfates of palladium. Part 3. The tetrakis(fluorosulfato)palladate(II) ion
Authors: Lee Keith C. , Aubke Friedhelm
Published: May 2006

The reduction of ternary fluorosulfato complexes of palladium(IV) like cesium hexakis(fluorosulfato)palladate(IV) by bromine in liquid sulfur dioxide at room temperature or at slightly elevated temperatures results in the formation of cesium tetrakis(fluorosulfato)palladate(II), according to:[Formula: see text]In contrast to all previously reported palladium(II) fluorosulfato derivatives, Pd2+ is found in a square planar environment resulting in diamagnetism.
Successive electron transfers to dibiphenylene-ethene molecule — effect of solvent and electrolyte
Authors: Wagner Elżbieta , Parol Teresa , Kalinowski Marek K.
Published: May 2006

The polarographic and voltammetric behaviour of dibiphenylene-ethene (DBPE) has been studied in benzonitrile, acetonitrile, propylene carbonate, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, N,N-diethylformamide, pyridine, and ethylenediamine. The two successive reversible electron transfers have been observed in all these solvents. The separation between the formal potentials of DBPE/DBPE−• and DBPE−•/DBPE2− systems was found to vary with the properties of solvents and with the kind of supporting elecrtrolyte cations (tetraethylammonium and sodium perchlorates were used as electrolytes). The variation of redox potentials both with the solvent and the cation is discussed in terms of the donor–acceptor concept for solvent–solute interaction. Numerical analysis using both the values of the donor numbers and the acceptor numbers leads to successful description of experimental results. It has further been observed that DBPE2– dianion is protonized in ethylenediamine solutions.
β-Lactams. IX. The synthesis of 7-β-phenylacetamido-3′-hydroxybenzo-[3,4]-O-2-isocephem, a weak antibacterial β-lactam antibiotic
Authors: Just George , Tsantrizos Youla S. , Ugolini Antonio
Published: May 2006

The synthesis of the title compound is described.
Some chemical and analytical aspects of polysaccharide modifications. I. Nitroxide spin-labelling studies of alginic acid, cellulose, and xanthan gum
Authors: Yalpani Mansur , Hall Laurance D.
Published: May 2006

Nitroxide spin labels have been employed as model reagents for evaluating several aspects of the synthesis of covalently modified polysaccharide derivatives using alginic acid 1, xanthan gum 19, and cellulose 23 as exemplars. Modifications were accomplished both nonspecifically, by the alkylation of hydroxyl groups, and specifically, either by direct transformation of the carboxylate function of 1 and 19 or after introduction of appropriate prominent functions, such as aldehydes or amines. Thus, the acetamido ether 3 was obtained from 1 and chloroacetamide 2. The carboxylate functions of 1 and 19 were condensed with amines to yield the corresponding amides 8, 10, 20, 21, and 22 either by direct reaction, by carbodiimide-mediated coupling, or by transesterification. The amine derivatives 12,13, 25, and 18 were obtained either from dialdehyde derivatives via periodate oxidation or from s-triazine intermediates, using sodium cyanoborohydride. Similarly, the keto spin label 15 reacted with hydrazide intermediates 14 and 29 in the presence of sodium cyanoborohydride to afford the hydrazide derivatives 16 and 30. The cellulose urethane derivative 27 was obtained via the cyclic carbonate precursor. The products were characterized by esr and other spectroscopic techniques.
Palladium compounds of pyrimidine and pyridine derivatives – proposed structure assignment changes
Authors: Kong Pi-Chang , Rochon F. D.
Published: May 2006

The complexes [PdL2X2] where L = cytosine, 1-methylcytosine, cytidine, 2-amino-4-methylpyrimidine, 2-hydroxy-4-methylpyrimidine, 4-methylpyrimidine, 2-hydroxypyrimidine, 2,4-diethoxy-5-methylpyrimidine, 2-hydroxypyridine, and methyl-4-picolinate, and X = Cl and Br, were prepared from the reaction of K2PdCl4 and L in aqueous solution. When L = cytosine, the cis-isomer was obtained, trans-Compounds were obtained with all other ligands. The trans-isomer of cytosine was prepared from the cis-isomer. The configuration of the reported compounds of cytidine and methyl-4-picolinate has been reassigned.
Détermination d'un champ de force de valence pour le chloro-3 triazole-l,2,4[4H] et ses dérivés deutériés (a)
Authors: Saidi-Idrissi Malika , Garrigou-Lagrange Chantal , Pouchan Claude
Published: May 2006

The vibrational frequencies of chloro-3 triazole-1,2,4[4H] and its deuterated derivatives have been used to calculate a valence force field. Previous assignments are discussed.
Crystal structures of optically active naphthidine (4,4′-diamino-1,1′-binaphthyl) and 1,1′-binaphthyl
Authors: Pauptit Richard A. , Trotter James
Published: May 2006

Crystals of optically active naphthidine and of binaphthyl are tetragonal, P41212 (or P43212), a = 7.945(1), 7.164(2), c = 24.264(5), 27.70(1) Å, respectively, Z = 4. The structures were solved by direct methods and refined by full-matrix least-squares techniques to respective R = 0.068 and 0.030 for 548 and 562 reflexions. The dihedral angles between the planes of the naphthalene residues are 87 and 102°, respectively. Bond lengths and angles are normal.
Nucleophilic and acid-catalyzed cleavage of the cyclopropane rings of β,γ-unsaturated α-spirocyclopropyl ketones
Authors: Yates Peter , Helferty Patrick Hugh , Mahler Paul
Published: May 2006

Treatment of isophorone (8) with sodium amide and 1,2-dibromomethane gives 6,6-dimethyl-8-methylenespiro[2.5]octan-4-one (9) and 6,6,8-trimethylspiro[2.5]oct-7-en-4-one (10); similar treatment of 3-methylcyclohex-2-en-1-one (5) gives analogous spiro compounds 6 and 7 together with 8-methylenedispiro[2.1.2.3]decan-4-one (11) and 8-methyldispiro[2.1.2.3]dec-8-en-4-one (12). The spiro ketones 6, 7, 9, and 10 undergo homoconjugate nucleophilic addition on being heated in morpholine with cleavage of the cyclopropane rings to give 2-[2-(4-morpholinyl)ethyl]cyclohex-2-en-1-ones. The rates of reaction are much greater for the exo methylene compounds 6 and 9 than for their endo isomers 7 and 10, but the rate of reaction of 10 is only slightly greater than that of the corresponding saturated compound, 6,6,8-trimethylspiro[2.5]octan-4-one (15). A corresponding rate differential between 9 and 10 is observed in their reactions with isophorone (8) and sodium hydride to give 2,2′-(ethanediyl)bis[3,5,5-trimethylcyclohex-2-en-1-one] (18). The acceleration in the cases of 6 and 9 relative to that of 15 is attributed to spiroactivation by both the carbonyl and exocyclic ethylenic groups; the much smaller effect of the endocyclic ethylenic groups in the cases of 7 and 10 is ascribed to torsional strain in the transition states for ring opening. The spiro ketones 6, 7, 9, and 10 also undergo acid-catalyzed cyclopropane ring cleavage in ethanol, giving 2-(2-ethoxyethyl)cyclohex-2-en-1-ones. Again the exo methylene compounds 6 and 9 react much more rapidly than their endo isomers 7 and 10; this is considered to be due to factors analogous to those operative in the nucleophilic addition reactions and/or the more rapid protonation of the exo methylene compounds.
A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines
Authors: Ikuta S. , Kebarle P.
Published: May 2006

The proton affinities of phenyl phosphine and cyclohexylphosphine were measured by determining the equilibrium constants of proton transfer equilibria with a pulsed electron beam high ion source pressure mass spectrometer. These proton affinities combined with values for methyl and phenyl phosphines and the analogous amines provide an interesting comparison of the methyl and phenyl substituent effects on the basicities of phosphine and ammonia. Methyl substitution increases the basicity of both ammonia and phosphine; however, the increase is significantly larger for the phosphine. Phenyl substitution increases the basicity of ammonia and phosphine and the increase for phosphine is very much larger. Calculations at the STO-3G, 4-31G, STO-3G*, and 4-31G* (* with d orbitals) for PH3, MePH2, PhPH2, the protonated species, and the nitrogen analogues predict proton transfer reaction energies in good agreement with the experimental results. A shortening of the C—P bond is predicted for protonation of MePH2 and particularly PhPH2, while a lengthening of the C—N bond is predicted for the corresponding nitrogen compounds. The much stronger increase in proton affinity of the phosphines caused by phenyl substitution is due to the stabilization of the phenyl phosphonium ion by π donation from the phenyl group to the empty orbitals of phosphorus in the [Formula: see text] group; in contrast, in the amines, it is the free base aniline which is stabilized by conjugation of the nitrogen lone pair with the aromatic ring. This stabilization of the free base is less important in phenyl phosphine. The participating empty orbitals of phosphorus in the conjugation of phenyl with [Formula: see text] in phenyl phosphonium are mostly π* with some -πd participation. The stabilization of the aniline free base contributes considerably more than the conjugation in the phosphonium ion, to the phenyl substituent difference for the amines and phosphines. The factors involved in the bigger substituent effect of methyl in the phosphines are somewhat similar to those for phenyl: stabilization of the methyl amine by conjugation of the nitrogen lone pair with empty orbitals of CH3 and stabilization of the [Formula: see text] by hyperconjugation. An alternate description can be given in terms of hybridization changes.
Nuclear magnetic resonance characterization of the ring conformations of monosubstituted derivatives of 1,3-dioxa-5,6-benzocycloheptene
Authors: St-Amour R. , St-Jacques M.
Published: May 2006

The conformational properties of 2-alkyl (Me, Et, i-Pr, and t-Bu) and 2-phenyl derivatives of 1,3-dioxa-5,6-benzocycloheptene (1) were studied by 13C dnmr. Analysis of slow exchange spectra at 100.6 MHz indicates that all derivatives except tert-butyl exist in an equilibrium of chair (major) and twist-boat (minor) conformations. Substituent effects on the position of the equilibrium are rationalized in terms of steric effects.
Solubilization of some related para-substituted benzenes in Type II DM mesophases
Authors: Paoli-Monteiro V. R. , Suzuki M. , Vanin J. A. , Reeves L. W.
Published: May 2006

A series of chemically related para-disubstituted aromatic solutes have been dissolved in two type II DM systems. The Saupe matrix elements of order have been determined for the solutes and the degrees of order of some segments in the amphiphiles have been derived from deuterium quadrupole splittings. The comparison of deuterium quadrupole splittings in uncontaminated mesophases with those containing the solutes leads to the conclusion that four solutes are located in the bilayer disk of the component micelles of one meosphase. A consideration of the structure and alignment of the disc micelles leads to absolute sign attribution for degrees of order of detergent segments and matrix elements for solute axes. A consideration of the orientations of the solute axes with respect to the mesophase director suggests the type of molecular interactions and motions which apply to solutes.
Structure et réactivité. V. Étude par résonance magnétique nucléaire des produits d'halogénation des tert-butyl-3 methoxycarbonyl-4 cyclohexènes
Authors: Bouteiller-Prati Jeanine , Bouteiller Jean-Claude , Aycard Jean-Pierre
Published: May 2006

The product of the bromination (chlorination) reaction on cis and trans 3-tert-butyl 4-carbomethoxy cyclohexene is studied by nmr. The results show that the reaction of the cis isomer gives 90% of the trans 4-bromo (chloro) cis 3-hydroxy trans 2-tert-butyl cyclohexane 1-carboxylic acid lactone and the reaction of the trans isomer gives trans 1,2-dibromo (dichloro) cis 3-tert-butyl trans 4-carbomethoxy cyclohexane which adopts a twist conformation. For the dibromo compound this kinetic product gives the corresponding thermodynamically more stable isomer, trans 1,2-dibromo trans 3-tert-butyl cis 4-carbomethoxy cyclohexane, by a diotropic rearrangement. The formation of the kinetic product is explained by the reaction of the less stable diaxial conformer of the cyclohexene derivative.
The composition of the carbohydrates in the middle lamella and secondary wall of tracheids from black spruce wood
Authors: Whiting P. , Goring D. A. I.
Published: May 2006

Carbohydrate analyses were performed on fractions of tissue from the middle lamella and secondary wall of black spruce tracheids. The concentrations of glucose and mannose were found to be smaller in the middle lamella than in the secondary wall while the concentrations of galactose, arabinose, and xylose were slightly larger in the middle lamella than in the secondary wall. The results obtained are compared with data available in the literature for other softwood species.
Calculation of vertical ionization potentials of hydrogen peroxide by perturbation corrections to Koopmans' theorem
Authors: Minato Tsutomu , Chong Delano P.
Published: May 2006

Vertical ionization potentials (VIP's) of hydrogen peroxide are calculated by perturbation corrections to Koopmans' theorem and its conformation is investigated on the basis of the calculated VIP's. The calculated VIP's compare well with the observed values. The analysis based on the VIP's gives a reasonable conformation, although the energy-optimizing procedure cannot reproduce the skew conformation. The lone pair – lone pair interactions are also discussed.
A practical synthesis of an anthracyclinone synthon
Authors: Wong Chiu-Ming , Lam Hing-Yat , Haque Wasimul , Mi Ai-Qiao , Yang Gui-Shu
Published: May 2006

The important intermediate 2-acetyl-5,8-dimethoxytetralin (8) in the syntheses of anthracycline antitumor drugs is easily prepared in high yield on a large scale. Conversion of 2,4-pentanedione to 3-(2,5-dimethoxybenzyl)-hex-5-en-2-one (9) was carried out in a three-step, one-pot process by C-alkylating it with 2,5-dimethoxybenzyl bromide, then allyl bromide followed by a retro-Claisen condensation. Conversion of 9 to the tetralin (8) was done first by ozonolysis to the aldehyde (10) followed by cyclization and reduction of the latter by trimethylsilane in trifluoracetic acid – acetone.
Some new amide complexes of thorium tetrachloride and N-thiocyanate
Authors: Bagnall Kenneth W. , Li Xing-Fu , Pao Po-Jung , Al-Daher Abdul-Ghany Mohammad
Published: May 2006

The amide complexes [ThCl4L3], where L = CH3CON(CH3)2 (dma), C2H5CON(CH3)2 (dmpa), C2H5CON(C2H5)2 (depa), or (CH3)3CCON(CH3)2 (dmpva), [Th(NCS)4L4], where L = dmpa, depa, dmiba ((CH3)2CHCON(CH3)2), or dmpva, and [Th(NCS)4 (dmpva)3] have been prepared and their ir spectra reported. The observations are discussed in terms of the steric crowding about the thorium atom using a cone-packing model.
Triplet-state benzophenone-sensitized photoreduction of bis(acetylacetonato)copper(II): the generation and stability of copper(I) complexes
Authors: Chow Yuan L. , Buono-Core Gonzalo E.
Published: May 2006

Triplet-state benzophenone rapidly sensitized the photoreduction of Cu(acac)2 in alcohols to give polymeric Cu(acac) as black precipitates. The binary complexes of Cu(acac) of polypyridines, polysulfide, olefins, acetylenes, and carbon monoxide could be generated in solution under an inert atmosphere when a ligand was present insitu during photoreduction or added after an appropriate photoreduction was completed. Except Cu(acac)—(PPh3)2, the Cu(acac) complexes of various ligands are sensitive to air oxidation, but show a wide range of reactivity towards disproportionation and photolysis. In the presence of terminal acetylenes, amorphous copper(I) acetylides were isolated in good yields.
Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)
Authors: Chow Yuan L. , Buono-Core Gonzalo E. , Marciniak Bronislaw , Beddard Carol
Published: May 2006

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.
Photovoltaic properties of CdS/phthalocyanine heterojunction cells
Authors: Hor A.M. , Loutfy R. O.
Published: May 2006

Photovoltaic heterojunction solar cells formed between n-type cadmium sulfide, CdS, and various p-type phthaloeyanines (Pc) such as H2Pc, ZnPc, MgPc, CuPc, MnPc, PbPc, and VOPc were investigated. The cells were prepared by electrodepositing thin CdS films onto conducting indium-tin oxide (ITO) followed by sequential vacuum deposition of the phthaloeyanines and gold layers. Among the seven phthaloeyanines studied, ZnPc and MgPc exhibited the highest photovoltaic activity. Some optimization work was done for both the ZnPc and MgPc heterojunction devices. The optimum thickness of CdS and phthaloeyanines was found to be 500 and 850 Å, respectively. Under an illumination of 50 mW cm−2, the photovoltaic characteristics of the ITO/CdS/ZnPc/Au cell were: Voc = 0.54 volts, Jsc = 285 μA cm−2, and η = 0.10%, while the ITO/CdS/MgPc/Au cell delivered Voc = 0.46 volts, Jsc = 231 μA cm−2, and η = 0.066%.
The intermediate formation of ketocarbenes and the conformational control in the Wolff rearrangement of α-diazoketones
Authors: Torres Manuel , Ribo Juan , Clement Allan , Strausz Otto P.
Published: May 2006

The conformational control of the Wolff rearrangement (WR) has been studied by means of a comparative study of the low temperature photolysis of argon-matrix isolated α-diazo ketones, 1, and of vinylene thioxocarbonates, 2. Under these conditions the s-E, s-Z conformational equilibrium of 1 will be hindered whereas 2 has a fixed s-Z conformation. The results indicate that the conformational control observed in the WR of α-diazo ketones is not per se a proof for a concerted mechanism and that a mechanism involving a ketocarbene intermediate is the most reasonable.
Some alkali metal alkyl amides as alkyne isomerization reagents: selective isomerization of one triple bond of a diynol
Authors: Abrams Suzanne R. , Nucciarone Donato D. , Steck Warren F.
Published: May 2006

The lithium and sodium salts of 1,2-diaminoethane, 1,3-diaminopropane, n-butylamine, and the lithium salt of isobutylamine were studied as potential reagents for isomerization of triple bonds in alkyn-1-ols. The sodium salts of the diamines afforded high yields of the ω-alkyn-1-ol. Somewhat surprisingly, the sodium salt of n-butylamine also effects isomerization to the terminal position. The lithium salt of 1,3-diaminopropane gave the highest conversion of 2- to 3-alkyn-1-ol. A novel, selective rearrangement of one triple bond of a diynol, a 2, ω- to 3, ω-diyn-1-ol isomerization, was incorporated into a synthesis of the insect sex pheromone 3,13-octadecadienol acetate.
A homoallyl radical rearrangement. Kinetics of the isomerization of the 2,2-dimethyl-3-buten-1-yl radical to the 1,1-dimethyl-3-buten-1-yl radical
Authors: Chatgilialoglu Chryssostomos , Ingold Keith U. , Tse-Sheepy Irene , Warkentin John
Published: May 2006

Rate constants for the overall rearrangement of the 2,2-dimethyl-3-buten-1-yl radical to the 1,1 -dimethyl-3-buten-1-yl radical, kC=C, have been measured from −145 °C to −101 °C by kinetic epr spectroscopy and at 40 °C by spin trapping with 1-methyl-4-nitroso-3,5-diphenylpyrazole. The temperature dependence can be represented by[Formula: see text]where θ = 2.3RT kcal mol−1. This rearrangement, which must proceed via a 2,2-dimethylcyclopropylcarbinyl radical as an intermediate, is one of the fastest rearrangements involving a primary alkyl radical. At 25 °C, kC=C = 4.3 × 107 s−1, which makes this rearrangement about 10 000 times faster than the rearrangement of the simplest homoallyl radical, 3-buten-1-yl. This rate enhancement is attributed to steric acceleration of ring closure by the gem dimethyl groups (Thorpe–Ingold effect).
Motional behavior of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose in solution. A 13C spin-lattice relaxation study
Authors: Dais Photis , Perlin Arthur S.
Published: May 2006

13C nuclear magnetic resonance spin-lattice relaxation times (T1) have been used to probe the motional behavior of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose (1) in dimethyl sulfoxide solution. This system offers structural features well suited to the study of a variety of internal motions, i.e., ring oscillation, ring puckering interconversion, and methyl internal rotation, all of which are superimposed on an isotropic overall reorientation. Among various models examined to evaluate internal rotations, a two-sites jump model was found satisfactory for interpreting the oscillation and puckering motions of the flexible 5,6-O-isopropylidene ring, whereas a diffusional model described hindered rotation of the geminal methyl groups of the rigid 2,3-O-isopropylidene ring from 15° to 80 °C. The activation energy associated with the temperature dependence of the rate of overall molecular tumbling was found to agree with the hydrodynamical prediction of 4.57 kcal/mol associated with the temperature dependence of the ratio (η/T). In addition, an explicit treatment of the relaxation data vs. solution viscosities, as a function of temperature, indicated that 1 reorients under the "slip" boundary conditions.
An experimental study of the influence of hydration on the reactivity of the hydroxide anion in the gas phase at room temperature
Authors: Raksit Asit B. , Bohme Diethard K.
Published: May 2006

Flowing afterglow measurements of rate constants and ionic products are reported which explore the influence of step-wise hydration on the reactivity of the hydroxide anion in the gas phase at 296 ± 2 K. Rate constants have been measured for the reactions of OH−•(H2O)n and/or OD−•(D2O)n with CO2, SO2, CH3OH, C2H5OH, C2H2, CH3COCH3, CH3NO2, and HCN, in most instances for values of n from 0 to 3. The reactions with CO2 and SO2 involve ligand addition or exchange and the results of their study corroborate earlier measurements. The remaining reactions proceed by proton transfer. For these reactions the results establish trends in reactivity as a function of step-wise hydration when relative acidity is preserved and when a reversal occurs in the relative acidity upon hydration. The fast hydrated acid–base reactions were observed to establish interesting hydrated product ions many of which underwent secondary reactions involving the exchange of H2O or D2O for the reagent molecule.
An iterative technique for calculating surface tensions of -on-electrolyte solutions
Authors: Goldsack Douglas E. , White Brian R.
Published: May 2006

The surface tension of mixtures of organic non-electrolytes of high polarity difference has been shown to be calculable to within a 1% average error using a Newton–Raphson iterative technique to solve the implicit Butler equations for the surface concentrations combined with a better approximation to the surface density of the pure components through an anisotropic surface model. Application of these same techniques to aqueous systems was attempted with some success. However, significant deviations between observed and calculated surface tensions for some binary aqueous systems still remain. It is suggested that these deviations could be accounted for by the inclusion of non-ideal behaviour in the surface and bulk phases.
Electronic spectral study of amino-acid complexes of Nd(III)
Authors: Kothari Ashok , Misra Sudhindra N.
Published: May 2006

Neodymium(III) complexes with histidine and diols (ethancdiol, prop-1,2-diol. but-2,3-diol, 2-butene-1,4-cliol, pent-1,5-diol, and hex-1,6-diol) of the type MAB, MA2B, and MAB2 have been synthesized and characterised. The values of Slater–Condon (Fk), Lande (ζ4f) spin orbital interactions, oscillator strength (P). and Judd–Ofelt (Tλ) intensity parameters have been calculated. Using these parameters, energies and intensities often levels in all the complexes in the region 360–920 nm have been computed. The agreement between the computed and experimental values is good. Using F2 values, the nephelauxetic ratio β, and bonding parameter b1/2 have been calculated, these infer the incidence of some covalent character in these complexes.
Kinetics and thermodynamics of dissociation of nickel(II)–isoquinoline complexes in tetrahydrofuran. Effect of trace water on ligand substitution kinetics
Authors: Chattopadhyay P. K. , Kratochvil B.
Published: May 2006

Rate constants and associated activation parameters for the dissociation of (solv)5Ni(isoquin)2+(solv = solvent, isoquin = isoquinoline) were determined in tetrahydrofuran (THF) over the range 15 to 35 °C by stopped-flow spectrophotometry. Comparison of the enthalpy of activation [Formula: see text] for the dissociation of (solv)5Ni(isoquin)2+ in THF with previous results in other solvents reveals that the linear relation between [Formula: see text] for the dissociation of this ion in the various solvents and the Gutmann donicity can be extended to THF. From this relation the donor number of THF is found to be 18.8 ± 0.5, in agreement with the value 19.3 reported from other methods. Dissociation of (solv)5Ni(isoquin)2+ in THF is controlled by an Id-type mechanism, as was previously observed in other protic and aprotic solvents. The rate of dissociation in THF is strongly affected by the free-water concentration in the medium.
Quenching of the fluorescence of substituted benzenes by halomethanes
Authors: Khwaja H. A. , Semeluk G. P. , Unger I.
Published: May 2006

Rate constants, kq, for the quenching of the singlet state of benzene, toluene, p-xylene, fluorobenzene, trifluoromethyl benzene, p-bis(trifluoromethyl)benzene, and aniline by CCl4, CH3CCl3, CHCl3, and CFCl3, in the gas phase have been determined. In each instance the quenching is via a charge-transfer complex with the aromatic acting as donor. There is a linear dependence between ln kq and IP (ionization potential) of the aromatics which supports Klein's model for exciplex formation. The most effective quencher is CCl4 while the least effective is CFCl3. The most effective donor was aniline while the least effective one was p-bis(trifluoromethyl)benzene. In general, fluorinated aromatics are less effective donors than the corresponding protonated molecules.
Structural analysis of 3-C-phosphonates, -phosphinates, and -phosphine oxides of branched-chain sugars
Authors: Neeser Jean-Richard , Tronchet Jean M. J. , Charollais Etienne J.
Published: May 2006

A complete nmr study (1H, 13C, 31P) of twelve 3-C-phosphonates, -phosphinates, and -phosphine oxide derivatives of 3-C-branched-chain pento- and hexo-furanoses is reported. For all compounds the configuration at C3 is determined and, for oxaphospholanes 9 to 12, the configuration at the asymmetric phosphorus atom. The 3T2 conformation of the furanose ring of acyclic derivatives 1 to 8 and the conformationally rigid cis-fused oxaphospholane-furanose bicyclic systems of 9 to 12 have been used to study the 3JPCCH vs. θP.H and 3JPCCC vs. θP.C relationships which are specific to this series of compounds. The use of the ν P=O ir stretching frequency, δ 31P chemical shift, and 1JP.C coupling constant values in structural analysis of C-phosphorus-bearing sugars is also reported and discussed.
Thermodynamics of ternary mixtures of non-electrolytes: excess volumes
Authors: Singh Prem P. , Sharma Vinod K.
Published: May 2006

Molar excess volumes, [Formula: see text], of some (i + j + k) ternary mixtures of non-electrolytes have been determined dilatometrically at 298.15 and 308.15 K and the same have been analysed in terms of (a) Lacombe and Sanchez theory and (b) an approach based on the mathematical discipline of graph theory utilizing information on the (i + j), (j + k), and (k + i) binary mixtures alone. It has been observed that the [Formula: see text] data predicted by the graph theoretical approach employing the graph theoretical binary interaction coefficients αij, αjk, and αki compare better with the corresponding experimental values than the [Formula: see text] values predicted by Lacombe and Sanchez theory utilizing Lacombe and Sanchez's binary interaction coefficients χij, χjk, and χki of the (i + j), (j + k), and (k + i) mixtures. The [Formula: see text] data have also been utilized to extract, via the Mayer–McMillan approach, self and cross volume interaction coefficients Vjj, Vkk, Vjk. Vjjk, and Vjkk and the Vjk values have been utilized to study molecular interactions between the jth and the kth components in the presence of the ith component of these (I + j + k) mixtures.
Réduction électrochimique de γ-nitrocétones. Conditions expérimentales d'accès à des dérivés de la pyrroline et de la pyrrolidine
Authors: Cariou Michel , Hazard Roland , Jubault Michel , Tallec André
Published: May 2006

Optimal conditions for electrosynthesis, at a mercury cathode in hydroalcoholic media, of three classes of nitrogen heterocyclic compounds are set up from an exhaustive study of the electrochemical behaviour of γ-nitroketones 1 and their reduction products.Pyrroline-N-oxides 3 are obtained by cyclization of the hydroxylamine when the nitro compounds are reduced at sufficiently low cathodic potentials. Quantitative yields are achieved in the case of tertiary nitro compounds. In other cases (primary and secondary nitro compounds), simultaneous formation of ketone-oximes 6 occurs.According to the nature of the α-substituent of the carbonyl, the other heterocyclic derivatives can be prepared as follows. In the case of a methyl substituent, pyrrolines 4 can be obtained by reduction of nitro compounds 1 or of N-oxyde pyrrolines 3. Pyrrolidines 5 are prepared by reduction of 1, or 3 and 4 in the case of tertiary compounds. In the case of a phenyl substituent, pyrrolines 4 can only be obtained by reduction of compounds 3 arising from a tertiary nitro compound. Pyrrolines 5 are prepared by direct reduction of 1 (primary and secondary nitro compounds) or of 3 and 4 (tertiary nitro compounds).