bluuebunny/crossref_metadata_2025 huggingface dataset:
Ligand properties of phosphinito platinum complexes: 31P and 195Pt nuclear magnetic resonance studies and the crystal and molecular structure of [Cl(Et3P)Pt(μ-PPh2O)2Pt(PEt3)2][BF4]
Authors: Berry David Eric , Beveridge Kathryn Anne , Browning Jane , Bushnell Gordon William , Dixon Keith Roger
Published: May 2006

Reaction of sodium hydride in tetrahydrofuran with the hydrogen-bonded phosphinito complex, [PtCl(PEt3){(PPh2O)2H}], gives a solution of the salt, [PtCl(PEt3){(PPh2O)2Na}], which is a precusor to synthesis of other bimetallic derivatives, [PtCl(PEt3){(μ-PPh2O)2Q}]n+: n = 0, Q = Rh(COD) or Ir(COD); n = 1, Q = Pd(PEt3)2 or Pt(PEt3)2. Detailed 31P and 195Pt nmr studies are reported for these and related examples including a titanium complex (n = 0, Q = Ti(acac)Cl2) synthesised by direct reaction of [PtCl(PEt3){(PPh2O)2H}] with [TiCl2(acac)2]. The diplatinurn complex, [Cl(PEt3)Pt(μ-PPh2O)2Pt(PEt3)2][BF4] crystallizes in the monoclinic space group P21/n, with a = 13.018(2), b = 34.205(9), c = 11.279(2) Å, β = 91.71(2)°. A complete X-ray diffraction study shows that the two platinum centres are significantly non-planar and are linked by the phosphinito ligands to form a six-membered ring in a boat conformation with phosphorus and oxygen atoms forming the prows of the boat.
The oxidation of hydrogen peroxide by tris(polypyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel(III) in aqueous media
Authors: Macartney Donal H.
Published: May 2006

The stoichiometry and kinetics of the oxidation of hydrogen peroxide by tris(2,2′-bipyridine) and tris(4,4′-dimethyl-2,2′-bipyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel (III) were studied in acidic and neutral aqueous media at 25 °C and I = 0.50 M (LiCF3SO3). The reaction 2M(bpy)33+ + H2O2 → 2M(bpy)32+ + O2 + 2H+ is observed with quantitative yields of dioxygen gas. The observed rate constants displayed an inverse acid dependence over the pH range 6.0–8.5; kobsd = k1 + k2K1/[H+], attributed to the oxidations of H2O2(k1) and HO2− (k2). An application of the Marcus theory relationship to the cross-reaction data gave a self-exchange rate constant of 10−2–10−1 M−1 s−1 for the HO2−/HO2 couple. The electron exchange rate constant is evaluated in terms of the inner-sphere and solvent reorganizational barriers and is compared to values reported for other small molecule couples. Rate and activation parameters for the reduction of the nickel(III) complexes by the hydroxide ion have been determined and are compared with the corresponding values for other metal tris(poly pyridine) complexes.
Mechanisms of 1H,1H; 1H,13C; and 13C,13C spin–spin coupling constants in benzyl cyanide and some derivatives. Experimental and theoretical estimates of internal rotational potentials
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

The mechanisms of long-range spin–spin coupling constants involving the methylene protons and the 13C nucleus of the cyano group are discussed for benzyl cyanide. Analysis of the 1H nmr spectrum of benzyl cyanide-8-13C in benzene-d6 solution yields nJ(H,CH2) and nJ(H,13CN) for n = 4–6. Similar data are reported for the 2,6-dichloro and 2,6-difluoro derivatives, together with some sign determinations. nJ(13C,13CN), n = 1–5, are given for the three compounds. It is shown that all these parameters are consistent with a small barrier to internal rotation about the [Formula: see text] bond in benzyl cyanide in solution. Computations at various levels of molecular orbital theory agree that this barrier is small. The nJ(13C, 13CN) imply a stabilization in polar solvents of the conformation in which the cyano group of benzyl cyanide lies in a plane perpendicular to the benzene plane. The molecular orbital calculations indicate a predominantly twofold nature of the internal barrier, although a significant fourfold component is also present. The coupling constants cannot discern the presence of the fourfold component for benzyl cyanide nor for its 2,6-difluoro derivative. 1J(13C,13CN) is solvent dependent. A table of the computed sidechain geometries is appended.
Influence of alkene structure on the formation constants of alkene–ICl molecular complexes
Authors: Schmid George H. , Gordon James W.
Published: May 2006

The experimentally determined rate law for the addition of ICl to 22 alkenes in CCl4 at 25 °C under conditions of (alkene)0 [Formula: see text] (ICl)0 is −d(ICl)/dt = kexp(alkene)0(ICl)3/{1 + C2(alkene)0}3. The constant C2 is shown to be equal to Kapp which is a measure of the formation constant or constants of the molecular complexes in this system. Under the experimental conditions used, C2 is a good approximation of the formation constant of the 1:1 alkene–ICl molecular complex. Thus the values of C2 obtained allow an estimate of the effect of alkene structure on the formation constant of the first molecular complex involved in this addition reaction. The contribution of the effect of substituents on C2 is estimated to be approximately 24% of the overall change in rate due to change in the alkene structure.
Nucleophilic attack on the carbon–carbon double bond. I. Reaction of primary and secondary amines with 2,2-di(4-nitrophenyl)-1,1-difluoroethene
Authors: Leffek Kenneth T. , Maciejewska Urszula
Published: May 2006

The reaction of primary and secondary amines with 2,2-di(4-nitrophenyl)-1,1-difluoroethene (1) in acetonitrile solvent gives first 2,2-di(4-nitrophenyl)-1-fluoro-1-aminoethene (2) and then 2,2-di(4-nitrophenyl)-1,1-difluoro-1-aminoethane (3). With excess amine, pseudo-first-order rate constants for the production of 2 were measured, which showed a second-order reaction, together with a catalysed third-order reaction. In addition to the reagent amines, the reaction is also catalysed by tertiary amines and bases such as oxalate and acetate, but not by chloride and perchlorate, nor by ammonium ions. The enthalpy of activation for the reaction of piperidine with 1 in acetonitrile is 3.7 kcalmol−1, but for the catalysed reaction an apparent value of −2.2 kcal mol−1 was obtained. It is concluded that the reaction proceeds via a pre-equilibrium to a zwitterion, followed by another equilibrium giving a carbanion that yields the product (2) by a rate-determining cleavage of the carbon–fluorine bond.
Molybdenum(VI) and phenol reactions in concentrated aqueous sulphuric acid
Authors: Marković Dragan A. , Veselinović Dragan S. , Obradović Mirjana V.
Published: May 2006

Depending on molybdenum, phenol, and acid concentrations, and time and the method of solution preparation, molybdenum and phenol can react in several ways. In 96% sulphuric acid Mo(VI) can be reduced to Mo(V) by adding solid phenol to the solution. In other cases molybdenum and phenol form stable or unstable complexes which can be in equilibrium with each other. For excess phenol the recorded spectra show two bands at around 600 and 423 nm; the first one, decreasing with time, is ascribed to the formation of an unstable complex of phenol and Mo(VI). At approximately equal concentrations of molybdenum and phenol the band at 423 nm does not appear, but two time-dependent absorption maxima are formed at 600 and 470 nm with a well defined isosbestic point at 505 nm. The complex is unstable because of the sulphonation of phenol. In 80% sulphuric acid molybdenum and phenol form a stable 1:1 complex which absorbs at 480 nm; its pKs value is 1.44 ± 0.03 at room temperature.
Stereochemistry of the 1,2-migration of the carboxyl group that occurs during the biosynthesis of tropic acid from phenylalanine
Authors: Leete Edward
Published: May 2006

(2S,3R)- and (2S,3S)-[1-14C,3-3H] phenylalanine were fed in separate experiments to Daturainnoxia plants. The distribution of isotopes in the resultant labeled hyoscyamine and scopolamine indicates that the biosynthesis of the acid moiety of these ester alkaloids, namely (S)-tropic acid, involves the migration of the carboxyl group of phenylalanine to its prochiral C-3 position with retention of configuration.
The ion-pair mechanism and bimolecular displacement at saturated carbon. VI. Racemization and radio-bromide exchange for substituted 1-phenylbromoethanes; solvent effects
Authors: Stein Allan R.
Published: May 2006

Racemization and radio-bromide exchange kinetics for 1-phenylbromoethanes in acetonitrile and in nitromethane using tetrabutylammonium bromide are reported. The results, together with those previously reported for acetone solutions, provide direct empirical support for the ion-pair mechanism for nucleophilic substitution at saturated carbon. Changing the substituents on the phenyl from the 4-nitro through to the 3,4-dimethyl substrate and the solvent from acetone to the more polar acetonitrile and nitromethane shifts the transition state for bromide substitution from an early to a late stage of the equilibria series substrate [Formula: see text] intimate ion pair [Formula: see text] various solvated ion pairs [Formula: see text] free or dissociated ions. For all the substrates in acetone and, for the species giving the less stable carbocations, in acetonitrile and nitromethane, both racemizations and exchanges are bimolecular. In the latter solvents, the substrates giving the more stable carbocations show mixed kinetics.
Ternary charge transfer complexes. IV. Complexes with Fe, Nb, Ta, Mo, W, or U in the anion
Authors: Brownstein Sydney , Gabe Eric , Irish Bridget , Lee Florence , Louie Brenda , Piotrowski Andrej
Published: May 2006

NOMX6•aromatic charge transfer complexes are formed from NOX and NbX5 or TaX5, where X may be F or Cl and the aromatic portion is a methyl-substituted benzene. NOMoF6, NOUF6, NOUF7, and NOWCl7•aromatic complexes have been identified but only oxyfluoro species have been isolated when M is Mo, W, or U. NOTaCl6•hexamethylbenzene crystallizes in the trigonal space group P32, with a = 9.822(3), c = 17.469(7) Å. NOFeCl4•hexamethylbenzene [Formula: see text] crystallizes in the orthorhombic space group Ccmb, with a = 14.8009(20), b = 15.7683(10), c = 17.3913(14) Å. High conductivity in these complexes appears to depend upon a long N—O bond.
Detection of the isotopes of lithium using the Faraday effect
Authors: Jing Shi-Lian , Stephens Roger
Published: May 2006

Lithium is atomised in an air–acetylene flame within a longitudinal magnetic field. Birefringent and dichroic signals are separately measured using a pulsed hollow cathode source. The arrangement is found to give isotopic selectivity and is useable down to concentrations of about 10 μg/mL. The signal ratio of birefringence: dichroism is found to be approximately independent of sample concentration at the high and low extremes of the calibration curve. However, severe distortions occur at intermediate concentrations. In addition, a reversal of signal magnitudes is observed between 6Li and 7Li. This effect is attributed primarily to a distortion of the source profile as a result of self-absorption.
Pulse cyclic voltammetry. I. Static solutions
Authors: Eccles Gordon N. , Purdy William C.
Published: May 2006

By using pulse cyclic voltammetry rather than cyclic voltammetry at a relatively high scan rate, an increase in sensitivity and a lowering of the detection limit by more than a factor of two are demonstrated for the ferricyanide–ferrocyanide couple at a carbon electrode. The test for reversibility based on peak shape or symmetry comparison is enhanced significantly with pulse cyclic voltammetry. Another reversibility test, by observing peak variations as a function of scan rate, was applied to pulse cyclic voltammetry and was found to be as diagnostically informative as the cyclic voltammetry test. These tests are illustrated by a study of the hydroquinone–quinone couple.
N,N-Dialkoxycarbonylamino acid formation from a mixed anhydride through intramolecular urethane acylation
Authors: Chen Francis M. F. , Benoiton N. Leo
Published: May 2006

Methoxycarbonylation at the urethane nitrogen of N-benzyloxycarbonyl- and N-methoxycarbonylvaline has been identified as a side reaction accompanying the aminolysis of the mixed anhydride formed from the acid and methyl chloroformate when the anhydride is coupled in aqueous dimethylformamide and the nucleophile is an amino acid anion. The side reaction occurs to a lesser but still significant extent when the activated residue is leucyl.
The direct electrochemical synthesis of thiolato complexes of copper, silver, and gold; the molecular structure of [Cu(SC6H4CH3-o)(1,10-phenanthroline)]2•CH3CN
Authors: Chadha Raj K. , Kumar Rajesh , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of anodic copper or silver (= M) into non-aqueous solutions of RSH (R = alkyl, axyl) gives MISR as insoluble materials in high yield. In the presence of 1,10-phenanthroline (= L), the products are MISR•phen for M = Cu, but not Ag. Gold resists oxidation under such conditions, and AuISR (R = n-C4H9, C6H5) was obtained in only poor yield. The crystal structure of the solvated dimeric adduct [Cu(SC6H4CH3-o)•phen]2•CH3CN is triclinic, with a = 10.682(3) Å, b = 11.729(4) Å, c = 15.608(5) Å, α = 76.87(2)°, β = 76.35(2)°, γ = 68.07(2)°, V = 1742(1) Å3, Z = 2 and space group [Formula: see text]. The structure is based on a folded Cu2S2 ring with an unusually short Cu—Cu distance of 2.613(3) Å Each copper atom has CuS2N2 pseudo-tetrahedral stereochemistry, with Cu—S = 2.337 Å(av) and Cu—N = 2.10 Å(av).
The reduction of specific disulfides with titanium(III) chloride
Authors: Akers Hugh A. , Vang Meng C. , Updike Tracie D.
Published: May 2006

The reaction between titanium(III) chloride and disulfides was investigated. Aryl and alkyl disulfides did not react while heterocyclic aromatic disulfides with a nitrogen α to the sulfur were reduced to the corresponding thiols. Products were identified and characterized by nuclear magnetic resonance and infrared spectra, and melting point comparisons with authentic compounds. The reductions occurred only in the presence of citrate and were found to require 2 moles of titanium(III) per mole of disulfide.
Photoacoustic infrared spectra (250–10 000 cm−1) of partially deuterated kaolinite #9
Authors: Mlchaelian K. H. , Bukka K. , Permann D. N. S.
Published: May 2006

Partial deuteration of kaolinite #9 was accomplished by grinding lumps to a size of 9 μm and refluxing a D2O suspension for periods ranging from 8 to 146 h. Photoacoustic infrared spectra were obtained and compared with previously published infrared and Raman spectra of undeuterated kaolinite and with infrared spectra of deuterated kaolinite. Data from this investigation indicate an extent of deuteration of about 20%; with the exception of the OD stretching bands near 2700 cm−1, most of the bands observed are attributable to undeuterated kaolinite. The infrared band at 2718 cm−1, which was previously assigned to uncoupled inner surface OD stretching, is the analogue of the 3684 cm−1 band observed in Raman and photoacoustic infrared spectra of undeuterated kaolinite. The results support assignment of the 3684 cm−1 band to uncoupled inner surface hydroxyl stretching vibrations.
Structural studies of oligosilanes produced by catalytic dehydrogenative coupling of primary organosilanes
Authors: Aitken C. , Harrod J. F. , Gill U. S.
Published: May 2006

The structures of some poly(organosilylenes), [Formula: see text] (R = Ph, p-tolyl, n-hexyl, and benzyl), produced by catalytic dehydrogenative coupling of primary silanes have been studied by infrared, nuclear magnetic resonance, and mass spectroscopies. These results, combined with data on molecular weights and molecular weight distributions from vapour pressure osmometry and gel permeation chromatography, lead to the conclusion that the polymers are linear and have SiH2R end groups. The polymers all have degrees of polymerization of ca. 10 and very narrow molecular weight dipersions. Some possible features of the mechanism that gives rise to this behaviour are discussed.
Étude de l'action des organomagnésiens sur les dérivés carboxyliques de la pyridine
Authors: Canonne P. , Belley M.
Published: May 2006

Reactions of Grignard reagents with pyridinecarboxylic esters 1, 2, pyridine-2-carboxylic acid (3), and 2,3-pyridinedicarboxylic acid anhydride (5) show regioselectivity at the carbonyl in position 2. This is exemplified by an efficient synthesis of 7,7-dialkylated-7H-furo[3,4-b]-substituted pyridin-5-ones.
Anhydropenicillin: a key intermediate for the stereocontrolled introduction of the 6-R-hydroxyethyl side chain of the penem and carbapenem antibiotics
Authors: Martel Alain , Daris Jean-Paul , Bachand Carol , Menard Marcel
Published: May 2006

Aldol condensation of the magnesium enolate derived from anhydro-6,6-dibromopenicillin with acetaldehyde allows for the stereospecific introduction of a 1-R-hydroxyethyl substituent at C-6. Protection of the hydroxy group followed by reductive dehalogenation provides anhydro-6(α)-[(1-R)-(tert;-butyldimethylsilyloxy)-ethyl]-penicillin, an intermediate in the synthesis of thienamycin. A high yield conversion of this anhydro derivative to (4-R)-acetoxy-(3-S)-[(1-R)-(tert-butyldimethylsilyloxy-ethyl]-azetidin-2-one (5) is also reported.
Reactivity and photophysical behavior of chromone triplet. A laser flash photolysis study
Authors: Rajadurai S. , Das P. K.
Published: May 2006

The chromone triplet ([Formula: see text] in acetonitrile) is produced in quantitative yields upon 308- or 337.1-nm laser pulse excitation and is characterized by submicrosecond lifetimes in solutions at room temperature. The short-lived nature of the triplet is attributable to intrinsically fast T1 [Formula: see text] S0 intersystem crossing, nearly diffusion-limited self-quenching, and facile interactions with solvents in the form of charge and hydrogen-atom transfer. The unusually high self-quenching rate constants, (0.9–4.0) × 109 M−1 s−1, are related in a major part to the presence of the ene double bond at which the photocycloaddition of the triplet may occur; this is supported by large bimolecular rate constants [Formula: see text] observed for chromone triplet quenching by various alkene derivatives. Although, based on low-temperature photophysical behaviors, the lowest triplet state of chromone in polar solvents is expected to be of reduced n,π* character, the reactivity of the triplet toward hydrogen donors is very pronounced in acetonitrile (for example, [Formula: see text] for tri-n-butylstannane and 2-propanol, respectively). Carbon tetrachloride and benzene prove to be facile quenchers of chromone triplet; the quenching interactions probably involve charge transfer, the carbonyl triplet acting as a donor and an acceptor, respectively. The electrophilic role of chromone triplet in the quenching by benzene derivatives is supported by a good correlation between [Formula: see text] and quencher oxidation potential.
Seven coordination. 1. Synthesis, structure, and fluxionality of(CH3)2AsC(CF3)=C(CF3)As(CH3)2W(CO)2I2P(OCH3)3
Authors: Mihichuk Lynn M. , Giesinger Carolyn L. , Robertson Beverly E. , Barton Richard J.
Published: May 2006

(L—L)W(CO)4 (L—L = (CH3)2AsC(CF3)=C(CF3)As(CH3)2) is oxidized by I2 to yield the seven-coordinate complex (L—L)W(CO)3I2 which reacts with monodentate phosphines or phosphites to form (L—L)W(CO)2I2P (P = phosphine or phosphite). Crystals of (L—L)W(CO)2I2P(OCH3)3 are monoclinic, space group P21/c, a = 15.711(3), b = 13.134(2), c = 13.800(3) Å, β = 111.81(2)° with Z = 4. The structure was solved from a Patterson map and anisotropically refined by least squares to a conventional R value of 0.039 using 3737 independent reflections. The crystal structure showed the tungsten atom to be seven-coordinate with a geometry most closely approximated by a capped octahedral environment, the capping group being a carbonyl moiety ([W—C] = 1.95 (1) Å). The capped face consists of the carbon atom ([W—C] = 1.98(1) Å) of the remaining carbonyl, an arsenic atom ([W—As] = 2.556(1) Å), and the phosphorus atom ([W—P] = 2.466(3) Å). The W—As bond trans to a phosphite group is longer (by 0.050(2) Å) than the W—As bond trans to an iodine atom. 1H nmr data indicate the complex to be fluxional at 298 K and rigid at lower temperatures, the data at lower temperatures being consistent with the configuration found in the crystal. The nmr data at lower temperatures suggest two exchange processes are occurring; one which averages two sets of As—CH3 groups and another process which averages all four As—CH3 groups.
The influence of charge on nuclear magnetic resonance isotope effects
Authors: Wasylishen Roderick E. , Burford Neil
Published: May 2006

Deuterium isotope effects on the 31P shielding constants and spin–spin coupling constants in the isoelectronic series, PH2−, PH3, PH4+, are examined. Also, deuterium isotope effects on the nuclear magnetic resonance parameters of SnH3− are examined and compared with our earlier results on SnH4 and SnH3+. The experimental results are analyzed using the models of Jameson and Osten. In each isoelectronic series it is found that the isotope effects on the heavy atom chemical shifts are largest for the negatively charged ions and essentially zero for the positively charged ions, as predicted by recent molecular orbital calculations. The primary isotope effects on J(A,H) are positive for all species containing lone-pair electrons, otherwise Δp1J(A,H) is negative. The primary and secondary isotope effects on J(Sn,H) in the SnH3− ion are the largest reported to date.
Synthèses des alkyl-1 cyclanols fonctionnalisés aux positions α, β et γ de la chaîne hydrocarbonée
Authors: Canonne P. , Belley M. , Fytas G. , Plamondon J.
Published: May 2006

We have developed a general and versatile synthesis of N,N-dialkylaminoalkyl-, 1-chloroalkyl-, 1-phenoxyalkyl-, 1-thiophenoxyalkyl-, 1-diethyoxyalkyl-, and 1-(1,3-dithiolane)alkylcyclanols in good yields by the reaction of α,ω-bis(bromomagnesio)alkanes with the corresponding functionalized carboxylic acid esters.
The microwave spectrum and structure of bromine thiocyanate, BrSCN.
Authors: Jemson H. M. , Lewis-Bevan W. , Gerry M. C. L.
Published: May 2006

not available
Régiosélectivité de la réaction des radicaux hydroxyle et hydroxy-2 propyle-2 avec l'hypoxanthine
Authors: Zylber Jean , Zylber Nicole , Lefort Daniel , Ferradini Christiane , Hickel Bernard
Published: May 2006

The reactivity of [Formula: see text] and (CH3)2ĊOH radicals with hypoxanthine was studied under comparable γ-irradiation conditions. A difference in regioselectivity of attack by the electrophilic [Formula: see text] radical and the nucleophilic (CH3)2ĊOH radical is observed, the latter leading in 70% yield to a C-8 substituted product. The rate constants of the addition of the radical to hypoxanthine were determined by pulse radiolysis to be k = 1.4 × 108 M−1 s−1 in acid medium, and in neutral medium k = 7 × 105 M−1 s−1. The much more reactive [Formula: see text] radical leads essentially to degradation products arising, interalia, from attack on C-2 (resulting in the formation of xanthine, which disappears rapidly), while attack at C-8, approximately three times less rapid, leads to the6,8-diketo purine, which does not undergo further reactions and thus accumulates in the medium. [Journal translation]
On the free energy of nematic wetting layers
Authors: Sullivan Donald E. , Lipowsky Reinhard
Published: May 2006

The contributions to the free energy of a nematic wetting layer as a function of its thickness l are analyzed. The longest-range contribution is due to distortion of the nematic director across the film, resulting from different preferred molecular orientations at the two interfaces bounding the film. Van der Waals forces as well as the decaying tails of the interfacial order-parameter profiles yield contributions to the free energy of successively shorter range. These effects lead to crossovers between different scaling régimes for variation of the mean wetting-layer thickness with temperature. Experimental implications of the results are described.
The 9.3547 GHz complex permittivity of water in the temperature interval 0–10 °C
Authors: Kalleveen T. H. T. Van , Buckmaster H. A.
Published: May 2006

This paper reports the results of a high precision study of the 9.3547 GHz complex permittivity of water in the temperature interval from 0–10°C. Measurements were made in ≈0.5 °C steps in the interval 0–5°C and ≈1.0 °C steps in the interval 5–10 °C. The precision for the permittivity and for the dielectric loss was typically ≈0.03% and ≈0.04%, respectively, whereas the accuracy is better than 0.15%. The values of the permittivity ε′(T), the dielectric loss ε″(T), the attenuation per unit length α(T), and the phase shift per unit length β(T) have been fitted to the empirical polynomial expressions[Formula: see text]
Approximations for the inner branch of potential curves of diatomic molecules
Authors: Varshni Y. P.
Published: May 2006

Three potential energy functions are examined with respect to their ability to reproduce the inner branch of the potential curve for 43 molecular states. Two of the states turn out to be unusual. In the remaining 41 cases, it is found that a potential proposed by the author gives the least error in 28 cases and is close to the least error in another six. The potential curves of NaAr(X) and XeCl(X) are very different from those of the other 41 states considered in this paper. The Born–Mayer potential appears to provide a reasonable representation of the inner branch of the potential curve for XeCl(X).
Enthalpies of mixing of ternary alkane mixtures with branched chain components
Authors: Shen Wei-Guo , Williamson Arthur G.
Published: May 2006

Measurements at 25 °C are reported for the enthalpies of mixing of 2-methyl pentane with n-dodecane and with each of three pseudo n-dodecanes prepared from equimolar mixtures of n-undecane + n-tridecane, n-decane + n-tetradecane, and n-octane + n-hexadecane respectively. Measurements for mixtures of the equimolar decane + tetradecane mixture with each of the other three branched hexane isomers are also reported. The results are compared with the work of Benson and co-workers for binary mixtures of n-dodecane with the same hexanes. The deviations of 1–2% from the principle of congruence are similar to those reported previously for the ternary n-alkane mixtures.
X-Ray structure determination of 1,2-anhydro-3,4:5,6-di-O-isopropylidene-1-C-nitro-D-mannitol
Authors: Szarek Walter A. , Hay George W. , Sood Ramesh K. , Trouton Konia , Fortier Suzanne
Published: May 2006

The structure of the major product of the reaction of 1,2-dideoxy-3,4:5,6-di-O-isopropylidene-1-C-nitro-D-arabino-hex-1-enitol with 30% hydrogen peroxide and aqueous sodium hydrogencarbonate has been confirmed by X-ray crystallography to be that of 1,2-anhydro-3,4:5,6-di-O-isopropylidene-1-C-nitro-D-mannitol (2). The crystal structure of 2, C12H19NO7, is orthorhombic, P212121, with cell dimensions a = 10.269(3), b = 15.115(7), c = 9.295(8) Å, and Z = 4. The calculated density is Dx = 1.336 gcm−3. The structure was solved by direct methods and refined to a residual R = 0.052. The molecule has a 2G− conformation having bond lengths and angles in agreement with those observed in related structures, except for the C(1)—C(2), C(2)—C(3), and O(2N)—N bond distances which were found to be unusually small.
Conductance behavior of some electrolytes in tetramethylurea
Authors: Hanna E. M. , Tossonian A. a.
Published: May 2006

Conductance investigations have been done at 25 °C on tetramethylurea solutions containing NaI, KI, RbI, CsI, NH4I, LiBr, NaBr, NH4Br, or LiCl in the concentration range 2.0 × 10−4–3.6 × 10−3 M. The conductance data have been analyzed using the full equations of Pitts, Fuoss, and Lee–Wheaton for the conductivity of free ions. The best-fit values of Λ0 are consistent with strong cation solvation and weak anion solvation by tetramethylurea. The KA values indicate that these salts are associated electrolytes in this solvent.
Heats of mixing of binary mixtures of pyridine base with n-alkane
Authors: Kasprzycka-Guttman Teresa , Vera Juan H.
Published: May 2006

Heats of mixing of 2,4-lutidine and 2,4,6-collidine with n-alkanes were measured at 293.15 K using an isothermal dilution calorimeter. Experimental results were fitted with a Redlich–Kister polynomial. Experimental data and coefficients for the Redlich–Kister polynomials are reported.
The photochemistry of 8-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene
Authors: Bender Christopher Owen , Dolman Douglas , Murphy Gaetanne Kathryn
Published: May 2006

The direct irradiation of 6-cyanobenzocyclooctatetraene (7) led to 5- and 8-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (9 and 8), isolated in 21 and 63% yields, respectively. On triplet sensitized irradiation 8 gave 1- and 6-cyanobenzosemi-bullvalenes (4 and 12; Φ = 0.006 and 0.088, respectively) and naphthalene (Φ = 0.012). The direct irradiation of 8 yielded 12 (Φ = 0.050), naphthalene (Φ = 0.015), 7 (Φ = 0.007), 7-cyanobenzocyclooctatetraene (13; Φ = 0.007), and 5-cyano-7,8-benzotetracyclo[3.3.0.02,4.03,6]oct-7-ene (14; Φ = 0.004). Deuterium labelling studies suggest that 12 derives from Zimmerman di-π-methane rearrangement of 8, and that photoproduct cyclooctatetraene 7 is not formed by simple electrocyclic opening of the cyclobutene ring of 8.
A novel method of complete activation by carbonyldiimidazole: application to ester synthesis
Authors: Morton Robert C. , Mangroo Dev , Gerber Gerhard E.
Published: May 2006

The activation of carboxylic groups by carbonyldiimidazole (CDI) results in the presence of excess CDI; it is shown that this reacts rapidly with the target hydroxyl groups under acylation conditions, thus preventing the desired acylation even when an excess of reagent is present and resulting in poor yields. The methods described result in rapid, complete, and convenient removal of the excess CDI. This procedure thus permits the use of sufficient excess of CDI to effect complete activation of the acid to the imidazolide. The imidazolides prepared in this manner, when used in limiting amounts, can be quantitatively converted to esters or amides; when used in slight excess, these imidazolides result in the quantitative acylation of target groups.
Enantiospecific synthesis of longiborneol and longifolene
Authors: Kuo David L. , Money Thomas
Published: May 2006

A trimethylsilyl enol ether (34) derived from camphor (1) undergoes intramolecular Mukaiyama reaction to provide a tricyclic ketone (36) that can serve as a key intermediate in a new enantiospecific synthesis of longiborneol (11) and longifolene (12).
Gas phase flash pyrolysis of 3-azido-1,2,4-triazole: generation and ultraviolet photoelectron spectrum of N-cyanomethanimine
Authors: B'Shary I. , Guimon C. , Grimaud M. , Pfister-Guillouzo G. , Liotard D.
Published: May 2006

A dimer of HCN, N-cyanomethanimine 6, was prepared by flash pyrolysis (gas phase, 10−2 mbar) from 3-azido-1,2,4-triazole 1a and detected by ultraviolet photoelectron spectroscopy (HeI). Its ionization potentials were measured and the ionic states sequence proposed, with the aid of ab initio – CI (configuration interaction) calculations. The study of the MNDO potential hypersurface enabled us to propose a mechanism of the thermal reorganization of the precursor 1a. It is shown that the reaction path passes through the formation of the protomer 1b before thermal decomposition and the generation of the nitrene 2b.
Electronic structure of zinc phthalocyanine
Authors: Khatib N. El , Boudjema B. , Maitrot M. , Chermette H. , Porte L.
Published: May 2006

The electronic structure of zinc phthalocyanine is investigated through MSXα computations and XPS experiments. Reasonable argeement is found between the qualitative structure of the molecular orbital diagram and the XPS spectrum. The visible spectrum is also discussed and the calculation is compared to previous semi-empirical computations. On the other hand, it is shown that a similar calculation on the zinc tetraazaporphyrin — selected as a model molecule — cannot be used to interpret the electronic properties of the phthalocyanine.
Solvation properties in iso-acidic media involving phosphoric acid
Authors: Louis C. , Bebba A. , Bessière J.
Published: May 2006

Concentrated solutions of mineral acids (phosphoric, hydrochloric, perchloric, sulfuric) are characterized, for an equal value of their water activity, by an equal R0(H) acidity level (iso-acidic solutions). By mixing them, we prepare what we call iso-acidic mixtures which keep the same acidity level as the constitutive solutions whatever the proportions; their redox and solvating properties depend both on the nature and on the ratio of the constitutive solutions. Reactivity variations for ionic species: Cl−, Br−,I−, diethyldithiophosphate (LET−), Si(W3Ol0)44−, Si(W3O10)45−, Cu2+, Cu+, Pb2+, Sn2+, Cd2+, Zn2+, Ag+, Fe3+, Fe2+, UO22+, U4+ in the iso-acidic mixtures are characterized by their ƒ solvation-transfer activity coefficients. Relations between ƒ coefficient values and complexation properties are established and it is shown that phosphoric acid has comparatively weak solvating properties toward most species. The possibility for anticipating reaction changes with the iso-acidic mixture composition by using the ƒ coefficients is demonstrated in the case of cadmium ionic flotation with diethyldithiophosphate and silver extraction with dithizone in carbon tetrachloride.
A 13C nuclear magnetic resonance study of selectivity in the binding of univalent counterions by heparin
Authors: Dais Photis , Holme Kevin R. , Perlin Arthur S.
Published: May 2006

The binding selectivities of univalent counterions for heparin in the systems Ca2+/M+/HEP, where M+ = Li+, Na+, K+, Cs+, TMA+, have been studied by 13C nuclear magnetic resonance spectroscopy. Chemical shift displacements of the various 13C nuclei of heparin in these systems clearly indicate that the binding selectivity of the polymer for univalent counterions increases with an increase in the radius of the hydrated cation form, namely Li+ > Na+ > K+ > Cs+ > TMA+. An explanation for this binding preference is offered on the basis of electrostatic and entropic terms, whereby the latter is reflected in changes in the hydration volumes of the univalent cations. Differences in the magnitude of these hydration volumes, in relation to the free energies of hydration, may account for a binding selectivity that favours the more highly hydrated ions.
Stereochemical studies on the formation of α,β-epoxysulfones using α-chloro-β-hydroxysulfones of known configuration
Authors: Grossert J. Stuart , Sotheeswaran Subramanian , Dharmaratne H. Ranjith W. , Cameron T. Stanley
Published: May 2006

Substitution reactions adjacent to sulfonyl groups are known to proceed with difficulty, and there is evidence to suggest that these may not necessarily proceed by an SN2 pathway. The mechanism of these reactions could be studied in principle by using the conversion of α-chloro-β-hydroxysulfones of known configuration into α,β-epoxysulfones of known configuration. This paper describes results in which this has been attempted. However, the stereochemical aspects of the epoxide formation could not be assigned unequivocally because of the intervention of a very facile "retro-aldol" process when the chlorohydrins are subjected to treatment with bases, although the experimental results do suggest that the reaction does proceed in a regular SN2-like manner, with inversion at carbon. The X-ray crystal structures of two highly substituted α,β-epoxysulfones are presented, thus putting the structures, including stereochemistry, of a range of these compounds on firm ground.
Strong cooperative protonation of a small tris-urea cryptand
Authors: Potvin Pierre G. , Wong Man Hung
Published: May 2006

A small bicyclic cryptand 3 bearing urea groups along the 7-atom bridges was synthesized in 22% yield by a novel tripod-tripod coupling procedure. Protonation and complexation studies are reported and compared with results with polyoxa-[2]-cryptands and [3]-cryptand 6. These show that 3 is a moderate base, a weak metal ion binder, but a two-proton binder exhibiting strong positive cooperativity (pKa2 > pKa1) and fast proton exchange kinetics. As demonstrated by molecular mechanics calculations, an inward rotation of the carbonyl groups to form hydrogen bonds to cryptated protons was invoked to explain the cooperativity.
Obtention de nouveaux squelettes diterpéniques lors de l'isomérisation d'époxydes diterpéniques sur alumine active
Authors: Taran Martine , Delmond Bernard
Published: May 2006

not available
Molecular recognition. VIII. The binding of the β-D-galactopyranosyl residue of the Lewis b human blood group determinant by the lectin IV of Griffonia simplicifolia and by a monoclonal anti-Lewis b antibody. Evidence for intramolecular hydrogen bonding
Authors: Lemieux Raymond U. , Cromer Rémy , Spohr Ulrike
Published: May 2006

The 3b-deoxy, 4b-deoxy, 6b-deoxy, 6b-deoxy-6b-fluoro, 6b-chloro-6b-deoxy, and the 5b-des-hydroxymethyl derivatives of the Lewis b (αLFucd(1 → 2)βDGalb(1 → 3)[αLFucc(1 → 4)]βDGlcNAca-OMe) human blood group determinant were synthesized in order to examine the involvement of the βDGal b unit in the binding of the Leb-OMe tetrasaccharide both by the lectin IV of Griffonia simplicifolia and a hybridoma monoclonal anti-Leb antibody. The replacement of the CH2OH-5b group by hydrogen resulted in very weak binding by both the proteins, but the 6b-deoxy derivative was bound nearly as strongly as the parent compound in the case of the lectin but nine times more strongly in the case of the antibody. The 6b-fluoride was slightly more strongly bound than the 6b-deoxy derivative by both the proteins. On the other hand, the 6b-chloride was bound three times more strongly by the lectin but three times more weakly by the antibody than the 6b-deoxy derivative. The thermodynamic parameters for the binding of the 6b-deoxy derivative by the lectin as compared to those for Leb-OMe confirmed that OH-6b interacts within the combining site of the complex. The results appear to require that for both proteins the CH2OH-5b group becomes involved in nonpolar interactions within the combining site. It seems probable that OH-6b is accepted intramolecularly hydrogen bonded to O-5b in the case of the lectin but to OH-4b in the case of the antibody. The involvement of OH-3b, OH-4b, and OH-4c as the key polar grouping for the binding of Leb-OMe by the lectin and of OH-3b and OH-2d in the case of the antibody was reported previously.
Gold(I) dimers. The synthesis and reactions of [tert-BuC≡CAu(dmpm—P)], and the crystal and molecular structures of [Au2(µ-dmpm)2]X2•2H2O, X = Cl, I
Authors: Payne N. C. , Puddephatt R. J. , Ravindranath R. , Treurnicht I.
Published: May 2006

Acetylide complexes of formula [tert-BuC≡CAu(R2PCH2PR2)], R = CH3 (6a) and C6H5 (6b), have been prepared, and characterized by spectroscopic methods. These complexes undergo a fluxional process involving a three-coordinate Au(I) centre. Complex 6a dimerizes by a first-order process in chlorinated solvents, with substitution of the acetylide ligand by chloride ion, to form [Au2(µ-dmpm)2]Cl2•2H2O (7a). The crystal and molecular structures of 7a and the iodide salt 7b have been determined by single crystal X-ray diffraction methods. Both crystallize in the triclinic space group [Formula: see text] with Z = 1; unit cell dimensions are a = 7.962(1), b = 9.987(1), c = 7.895(1) Å, α = 90.11, β = 109.13(1), and γ = 112.84(1)° for 7a; a = 8.243(1), b = 9.057(1), c = 8.167(1) Å, α = 90.23, β = 110.33(1), and γ = 89.92(1)° for 7b. The analyses refined to final agreement factors on F of R = 0.035 based on 3225 unique reflections with I > 3σ (I) for 7a, and R = 0.030 based on 2971 unique reflections with I > 3σ(I) for 7b. The structures are closely related, with the cations containing an eight-membered centrosymmetric ring formed by the Au(I) centres and the bridging dmpm ligands. The Au … Au′ distances are 3.014(1) and 3.019(1) Å in 7a and 7b, respectively. In the solid state, the halide ions bridge the two Au centres, and, together with the water molecules, form a network of hydrogen bonds running at an angle of 104° to the eight-membered Au2P4C2 rings.
Pentacoordination and ionic character: crystal structure of Ph4SbBr
Authors: Knop Osvald , Vincent Beverly R. , Cameron T. Stanley
Published: May 2006

Ph4SbBr (P21/n, a = 12.282(2) Å, b = 10.656(1) Å, c = 16.156(1) Å, β = 104.92(7)°, Z = 4) crystallizes with the same space group as Ph4SbCl, but the two compounds are not isostructural. The structure of Ph4SbBr consists of layers of Ph4SbBr molecules with the Br atoms almost exactly in the [Formula: see text] planes. The coordination figure of the Sb atom is a trigonal bipyramid (TBP) with Br in an axial position. The Sb—Br distance, 2.950(1) Å is the longest reported for Sb(V) to date. The Sb(V)—Hal bond lengths and the Ph4SbBr and Ph4SbCl structures are compared in detail. Analysis of a large sample of Ph4EX (E = P, As) structures and of all the available R4EX (E = Sb, Bi; R = Ph, Me) structures shows that the former are always ionic, R4E+X−, whereas in the latter the observed coordination figures represent R4EX trigonal bipyramids with various degrees of axial distortion. The inverse variation of the axial bond lengths (the trans effect) in the TBP Sb compounds can be quantified as Sb—Cax ~ 2.4(Sb—X)−1/9 to a very high degree of correlation. This and other geometric relationships show that there exists a limiting E—X bond length (~3.3 Å for E = Sb and ~3.5 Å for E = Bi when X is oxygen) at which the TBP coordination becomes unstable and changes over to a tetrahedral R4E. This change is accompanied by a rearrangement of the structure to an ionic R4E+X− solid (of high symmetry where permitted by the size and shape of the anion) with [Formula: see text] separations no smaller than ~4 Å when E = Sb or Bi and X = O. The distribution of the CEC angles in the Ph4EX (E = P, As) sample is analyzed; the mean (uncorrected) P—C and As—C bond lengths in Ph4E+ are found to be 1.789(11) and 1.902(12) Å, respectively. Keywords: crystal structure, organoantimony compounds, Ph4SbBr, pentacoordination, tetraphenylantimony bromide.
An NMR study of dinucleoside monophosphates with an O4-ethylated thymine. d(e4TpT) and d(Tpe4T)
Authors: Buchko Garry W. , Hruska Frank E. , Sadana Krishan L.
Published: May 2006

Syntheses are described for d(e4pT) (1) and d(Tpe4) (2), the O4-ethylated analogues of d(TpT) (3), and mass spectrometric (FAB), 1H nuclear magnetic resonance (300 MHz), and circular dichroic data are provided for the three molecules. The [M –H]− ions as well as the aggregates [2M – H]− and, in the case of 1, [3M – H]−, are easily detected by FAB mass spectrometry operating in the negative ion mode. In contrast with the modified nucleoside, e4dT, the two methylene protons of the O4-ethyl groups of 1 and 2 are nonequivalent in the NMR spectra, and their chemical shift difference decreases with increasing temperature. This chemical shift difference can be related to intramolecular base stacking. The vicinal coupling constants of the sugar rings reveal an unusual shift at low temperature towards the 3′-endo conformation of the e4p unit of 1, but this shift is not noted for the pe4 unit of 2. O4-Alkylation of either unit of 3 effects a large reduction in the amplitude of the negative CD peak at 252 nm. The CD spectra of 1 and 2 are qualitatively similar to those of d(CpT) and d(TpC), respectively, and suggest that in some respects an O4-alkylated thymine base is "cytosine-like". The amplitudes of the positive CD peaks of 1 and 3 are reduced by 40% as the temperature is increased from 10 to 65 °C, indicating the presence of some base stacking at low temperatures. However, the CD spectrum of 2 shows a much smaller reduction (<10%). Keywords: O-alkylation, oligonucleotides, stereochemistry, NMR, mass spectrometry.
13C magnetic resonance studies. 138. An examination of the [3.2.2.0] → [4.2.1.0] rearrangement via β-enolization and H/D exchange in tricyclic ketones
Authors: Peiris Sriyawathie , Stothers J. B. , Thomas Shirley E.
Published: May 2006

The behavior of the endo and exo isomers of 7,7-dimethyltricyclo[3.2.2.02,4]nonan-6-one (9, 17) under strongly basic conditions (t-BuO−/t-BuOH/185 °C) has been examined. In both cases rearrangement to the corresponding 8,8-dimethyl-tricyclo[4.2.1.02,4]nonan-7-one (11, 18) was found, with the exo isomer reacting approximately 8 times faster. Experiments in tert-butyl alcohol-O-d1 were carried out to determine the specific sites, the relative rates, and the stereochemistry of deuterium incorporation in the initial ketones. Although H/D exchange occurs most readily at the cyclopropyl methylene carbon in the endo isomer, none of the rearrangement product expected to arise via γ-enolate formation was observed. The results for these ketones are compared with our earlier observations in the related [2.2.2], [3.2.1.0], and [3.3.1.0] systems. Keywords: homoenolization, tricyclic ketones, H/D exchange.
The degradation of Indulin ATR by Streptomyces: chemical characterization of the water soluble acid precipitable products
Authors: Vidal P. F. , Bouchard J. , Chornet E. , Overend R. P. , Giroux H. , Lamy F.
Published: May 2006

Two strains of Streptomyces, S. badius and S. virdosporus, when incubated with kraft lignin (Indulin ATR) produce water soluble acid precipitable compounds. We show by a combination of elemental analysis, amino acid analysis, and FTIR that these are complexes of lignin fragments strongly associated with proteins. The latter, which can be separated by solvent extraction, are added by the microorganisms themselves. The lignin fraction, which represents approximately 60% of the complex weight, consists of lower molecular weight, lower methoxyl content Indulin fragments. KeyWords: lignin, Indulin, lignin–protein complexes, Fourier transform infrared spectrophotometry, high performance size exclusion chromatography, Streptomyces.
Carbohydrate metal ion complexes. Interaction of D-glucono-1,5-lactone with Zn(II), Cd(II), and Hg(II) ions in the solid and aqueous solution, studied by 13C-NMR, FT-IR, and X-ray powder diffraction measurements
Authors: Tajmir-Riahi H. A.
Published: May 2006

D-Glucono-1,5-lactone interaction with zinc group metal ions has been studied in aqueous solution and solid salts of the type Zn(D-gluconate)2.2H2O, Cd(D-gluconate)2 and Hg(D-gluconate)2 have been isolated. These metal sugar salts were characterized by elemental analysis, 13C-NMR, FT-IR spectroscopy, and X-ray powder diffraction measurements.X-ray powder diffraction diagrams and other spectroscopic evidence showed that Zn(D-gluconate)2.2H2O is isomorphous with the structurally identified Mn(D-gluconate)2.2H2O, suggesting a similar metal–sugar binding mode, through a carboxylate oxygen atom (O-1) and an OH group of the two sugars anions as well as to two H2O molecules, resulting in a six-coordinate Zn(II) ion. The Cd(II)- and Hg-D-gluconate salts are not similar and show dissimilarities to the Zn(II) compound. The Cd(II) ion binds to two D-gluconate anions possibly through the carboxylate O-1 and sugar O(2)—H, and O(3)—H groups of each anion, giving a six-coordinate Cd(II) ion. The Hg(II) ion is possibly four-coordinate, binding to two sugar anions via a carboxylate O-1 and O(2)—H groups of each D-gluconate anion. The zinc group metal-D-gluconate salts are aggregated through bridging sugar OCO− groups with sugar anion possibly having bent-chain conformation. Keywords: carbohydrate, metal ions, 13C-NMR, FT-IR, X-ray powder diffraction.