bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol
Authors: Terrier François , Lelièvre Jacques , Chatrousse Alain-Pierre , Schaal Robert , Farrell Patrick G.
Published: May 2006

Rates of deprotonation of 2,2′,4,4′-tetranitrodiphenylmethane (1) by a variety of bases B− and of protonation of the resulting carbanion (2) by the conjugated acids BH in methanol have been measured at 20 °C. The Brønsted αBH coefficients for protonation of 2 by phenol and carboxylic acid buffers are equal to 0.58 and 0.43, respectively, as compared with αBH values of 0.59 and 0.52 respectively, for the same reactions in 50% H2O – 50% DMSO. On the other hand, a comparison of the intrinsic rate constants [Formula: see text] (in the Marcus sense) in the two solvents reveals that the effect of going from 50% H2O – 50% DMSO to methanol is to lower [Formula: see text] for the phenol reactions by a factor of 2 but to increase [Formula: see text]for carboxylic acid reactions by a factor of 5. It is shown that the solvent effects on αBH and [Formula: see text] can all be understood in the context of the Principle of Imperfect Synchronisation (PIS) recently proposed by Bernasconi. In addition, a fast equilibrium protonation of the carbanion 2 is found to precede its conversion to 1 at low pH, i.e., pH < 5. The resulting protonated species is suggested to be the nitronic acid 2,H arising from fast protonation of a para NO2 group of 2. The [Formula: see text] value associated with the ionization of 2,H is ∼4.25.
Photochemistry of halogenated benzene derivatives. Part VIII. Photoformation of 2-methyl-4,5,6,7-tetrachlorobenzoxazole from pentachlorophenol in water–acetonitrile
Authors: Choudhry Ghulam Ghaus , Graham Norma Jean , Webster G. R. Barrie
Published: May 2006

Photolysis of a solution of pentachlorophenol (1) in H2O–CH3CN (2:3 v/v) was conducted on a synthetic scale using wavelengths ≥290 nm. After changing the pH of the photolyzate of 1 to ≥12, the photoproduct 2-methyl-4,5,6,7-tetrachloro-benzoxazole (2) was extracted with n-hexane. The product 2 was crystallized from methanolic solution. Ultraviolet, IR, FT-1H-NMR, proton-decoupled normal FT-13C-NMR, and proton-decoupled DEPT (distortionless enhancement by polarization transfer) sequence FT-13C-NMR spectroscopy were used to identify photoproduct 2 as 2-methyl-4,5,6,7-tetrachlorobenzoxazole. A mechanism for the photoformation of benzoxazole 2 from 1 is proposed. 3,4,5,6-Tetrachlorocyclohexa-3,5-diene-1,2-ketocarbene formed from 2-hydroxy-3,4,5,6-tetrachlorophenyl radical is suggested as key intermediate involved in the generation of oxazole 2 from phenol 1. The chemical yield of 2 on the basis of 1 was ca. 1%. A mechanism is proposed to explain the mass spectral fragmentation of 2 via the losses of Ċl,:C=O, Cl—Ċ=O, CH3—Ċ=O, CH3CN, and C3H3ClNO species from the parent molecular ion.
Thermodynamic properties and structure of the water–ethanol silicone oil interface
Authors: Sohounhloue Dominique , Tenebre Louis , Privat Mireille , Douillard Jean-Marc , Bennes René , Tronel-Peyroz Emmanuel
Published: May 2006

The interface between the water (1) – ethanol (2) system and silicone oil was studied over the whole composition range of the aqueous mixtures by means of adsorption and ellipticity measurements. The adsorbed layer was treated as a phase and, after derelativization of the relative surface excess, the adsorption isotherm (in term of molar fractions) as well as the activity coefficients of water and ethanol were calculated. From the above results and by analysing the ellipticity coefficient, we calculated the contribution to this latter due to the anisotropy of the adsorbed layer; the resulting "polynomial of anisotropy" was analyzed as a consequence of water and ethanol reorientations as the surface composition is changed.
Ion–ion–solvent interactions in aqueous ionic cosolvent systems. II. Single-ion transfer free energies and entropies using tetraphenylarsonium tetraphenylborate reference electrolyte assumption in aqueous sodium nitrate solvent system
Authors: Rudra Sibaprasad , Talukdar Himansu , Kundu Kiron K.
Published: May 2006

Single-ion tranfer free energies [Formula: see text] and entropies [Formula: see text] of some electrolytes from water to 1, 2, and 4m aqueous NaNO3 solvents have been determined at 25 °C using the widely used tetraphenylarsonium tetraphenylborate (Ph4AsBPh4) reference electrolyte assumption, after due modification for this solvent system. The required [Formula: see text] and [Formula: see text] values of Ph4AsPi, KBPh4, KPi, AgPi, PbPi2, Ag2CrO4, and AgCl where Pi = picrate, were determined by measuring solubilities at 15–35 °C of the solutes except AgCl, the values of which were determined from emf measurements. Analysis of [Formula: see text] and [Formula: see text] values of the ions as well as their respective true interaction effects, [Formula: see text] and [Formula: see text] as obtained after correcting for their cavity effects [Formula: see text] and [Formula: see text] estimated by the scaled particle theory (SPT) and Born-type electrostatic effects, [Formula: see text] and [Formula: see text] computed by simple Born equation, reveals that the behaviour of the ions in this ionic cosolvent system is chiefly guided by one or several effects of ion–ion–solvent, Born and cavity forming interactions. Moreover, a rational explanation has been offered to explain the observed mirror-image entropie behaviour of simple cations and anions in light of Kundu etal.'s four-steps transfer process.
The preparation of SeI3SbF6 and TeI3SbF6; the X-ray crystal structures of SBr3AsF6, SeI3AsF6, SeI3SbF6, and TeI3SbF6; some considerations of the energetics of the formation of SBr3AsF6 and SeI3AsF6
Authors: Johnson James P. , Murchie Michael , Passmore Jack , Tajik Mahmoud , White Peter S. , Wong Chi-Ming
Published: May 2006

The crystal structures of the compounds SBr3AsF6 (1), SeI3AsF6 (2), SeI3SbF6 (3), and TeI3SbF6 (4) are reported and the quantitative preparation of the hitherto unknown 3 and 4 from SbF5 and the respective elements in SO2 are given. Crystal data are as follows: 1, monoclinic, space group P21/c, with a = 8.015(1) Å, b = 9.342(1) Å, c = 12.126(2), β = 97.81(1)°, and Z = 4; 2, monoclinic, space group P21/c, with a = 8.380(2) Å, b = 10.237(1) Å, c = 12.524(1) Å, β = 99.36(1)°, and Z = 4; 3, monoclinic, space group P21/c, with a = 8.548(2) Å, b = 10.297(6) Å, c = 12.877(8) Å, β = 98.70(3)°, and Z = 4; 4, monoclinic, space group P21/c, with a = 8.463(1) Å, b = 10.676(2) Å, c = 13.121(4) Å, β = 100.05(1), and Z = 4. Compounds 1, 2, 3, and 4 are isostructural and were refined to a final R values of 0.040, 0.051, 0.047, and 0.037, respectively. The structures of these salts consist of essentially discrete MX3+ cations and M′F6− anions (M = S, Se, Te; X = Br, I; M′ = As, Sb) with some cation–anion interactions. TheSeI3+ bond distances and angles were essentially identical in both AsF6− and SbF6− salts (average Se—I distance and I—Se—I angle for AsF6− salt; 2.508(2) Å, 102.4(1)° and for SbF6− salt; 2.512(1) Å, 102.3(1)°). Similarly the average Te—I bond distance and I—Te—I angle for TeI3SbF6 were 2.666(1) Å and 99.8(1)° which are essentially identical to those in the previously reported TeI3AsF6. The average S—Br distance and Br—S—Br angle were 2.142(6) Å and 103.4(2)° in SBr3AsF6. Estimates of the S—I bond distance and I—S—I bond angle in the as yet unknown SI3M′F6 are made from the extrapolation of MX3+ data. The bond distances observed in the simple MX3+ cations (M = S, Se, Te; X = Cl, Br, I) with anions of very low basicity are within 0.02 Å of the corresponding distances calculated by the Schomaker–Stevenson equation. The observed and estimated bond distances in SBr3+, SI3+, and SeI3+ are significantly longer than the corresponding S—Br, S—I, and Se—I distances in S7I+, S7Br+, and Se6I22+. This observation is used to support the thesis that the long intra-cationic halogen–chalcogen contacts in polychalcogen–halogen cations are weakly bonding, and responsible for the cluster-like nature of these cations. The heats of formation of 1 and 2 from their respective elements and AsF5 were estimated.
Platinum complexes with sterically demanding ligands: trans-bis(2,7-diazatetracyclo[6.3.0.04,9.05,11]undecane-N, N′)platinum(II) dichloride tetrahydrate
Authors: Brown B. E. , Faggiani R. , Hughes D. , Lock C. J. L.
Published: May 2006

The complex [Pt(C9H14N2)2]Cl2•4H2O was isolated from a reaction mixture containing K2[PtCl4] and a norbornane-based diamine, C9H14N2. This product was analyzed with use of elemental analysis, nuclear magnetic resonance spectroscopy, and X-ray crystallography. [Pt(C9H14N2)2]Cl2•4H2O crystallized in the triclinic system, space group [Formula: see text], a = 9.437(1) Å, b = 9.975(1) Å, c = 6.888(1) Å, a = 109.54(1)°, β = 109.71(1)°, 7 = 93.63(1)°, Z = 1. The X-ray data were collected with use of a Syntex P21 diffractometer and MoKα radiation and the structure solved by the heavy atom method. Based on 1983 reflections, the structure was refined to R = 0.0310 and Rw = 0.0408. The platinum resides on an inversion center and is coordinated to the nitrogen atoms of the secondary amines. The chelating N—Pt—N angle is 79° but otherwise the bond lengths and angles agree well with values for similar structures.
Methylation of polymethylbenzenesulfonic acids by hexamethylbenzene and pentamethylbenzenesulfonic acid in concentrated sulfuric acid
Authors: Cerfontain Hans , Koeberg-Telder Ankie
Published: May 2006

The methylation of a series of polymethylbenzenes (PoMB's) or their sulfonic acids by added hexamethylbenzene (HMB) and pentamethylbenzene-1-sulfonic acid (PeMB-1-S) as reagents in 95.5 and 98.4% H2SO4 as solvent has been studied under homogeneous conditions. HMB effects methylation of 2,4,6-trimethylbenzene-1-sulfonic acid (2,4,6-TrMB-1-S), 2,3,4,6-tetramethylbenzene-1-sulfonic acid (2,3,4,6-TeMB-1-S), and 2,3,5,6-TeMB-1-S, but not of the sulfonic acids of 1,3-dimethylbenzene (1,3-DMB), 1,2,3-TrMB, 1,2,4-TrMB, and 1,2,3,4-TeMB. PeMB-1-S is less reactive as methylating reagent than HMB. The observed substrate reactivity towards methylation by HMB was observed to decrease in the order [Formula: see text], and towards methylation by PeMB-1-S to decrease in the order [Formula: see text]. On the basis of a comparison of these orders of substrate reactivities with those predicted for the series of the PoMB-1-sulfonates and the corresponding PoMB's, it is concluded that the substrate species undergoing methylation are the PoMB's and not the corresponding sulfonates.
Chelation vs. non-chelation control in addition reactions of ethylmetallic reagents to acrolein dimer
Authors: Singh Shankar M. , Oehlschlager Allan C.
Published: May 2006

Reactions of 3,4-dihydro-2H-pyran-2-carboxaldehyde (acrolein dimer) with ethylmetallics based on lithium, titanium, and copper were examined for stereoselectivity. High selectivity (92:8) was found for non-chelation controlled addition yielding the erythro product when ethyllithium was employed in the presence of BF3•OEt2. High selectivity (89:11) for products of chelation controlled addition (threo) was observed for ethylcopper reagents in the presence of magnesium salts. Titanium reagents yielded mixtures rich in products of either chelation or non-chelation controlled addition depending on the titanium substituents. In no cases were stereoselectivities obtained with titanium reagents better than those obtained by use of the aforementioned lithium and copper reagents.
Spectroscopic properties of SO4 in different molecular and crystalline environments. II. Identification and infrared spectra of Cu3O2SO4 and its hydroxylated derivative
Authors: Secco Etalo A.
Published: May 2006

The infrared spectra of Cu3O2SO4, identified for the first time and obtained from three different preparations are reported. The proposed structure of Cu3O2SO4 contains the copper oxysulfate anion [(CuO)2SO4]2− of Cs symmetry with each CuO attached by the Cu to two oxygens of the SO4 group. Of the 21 infrared-active modes predicted for this anion 17 modes are discernible. Its hydroxylated derivative Cu3(OH)4SO4 shows clearly resolved and evenly split peaks of the v3 mode of SO4 in strong contrast to the strong overlap of this mode in its crystalline analog; the frequencies of the remaining SO4 modes stay effectively unchanged.
Excess molar volumes and excess viscosities of 2-propanol + methylacetate + dichloromethane system at 298.15 K
Authors: Acevedo Inès L. , Postigo Miguel A. , Katz Miguel
Published: May 2006

Densities and viscosities were determined for the 2-propanol + methylacetate + dichloromethane system at 298.15 K. From the experimental results, molar excess volumes and excess viscosities were calculated. Different expressions exist in the literature to predict these excess properties from the binary mixtures. The empirical correlation of Tsao–Smith and Toop is the best for this system.
Thermal intramolecular reactions of Δ1-1,2,4-triazolines with extended exocyclic unsaturation
Authors: Schwan Adrian L. , Warkentin John
Published: May 2006

Fumaratotriazoline (1) and amidotriazoline (3) undergo thermal first-order transformations in solution at 65 °C. The former affords the isomeric pyrrole 5 and its hydrolysis product 6. A mechanism involving opening of the initial five-membered ring to form 8, followed by closure to a new five-membered ring (9), is proposed. Amidotriazoline (3) loses N2 on heating to form 19. The experimental results are best accommodated in terms of a novel mechanism involving an electrocyclic ring closure, a [3 + 2] cycloreversion to form an ylide, a sigmatropic rearrangement of the ylide, and, finally, an electrocyclic ring-opening reaction.
Molybdenum-95 nuclear magnetic resonance studies on disubstituted molybdenum(0) carbonyls
Authors: Alyea Elmer C. , Somogyvari Arpad
Published: May 2006

Molybdenum-95 nmr spectral data are reported for 40 cis- and trans-Mo(CO)4LL′ compounds and the chemical shifts discussed in relation to a simplified Ramsey expression for the paramagnetic shielding term. The identification of mixtures of products of the type Mo(CO)6−nLn is shown to be easily accomplished by 95Mo nmr spectroscopy. The 95Mo chemical shifts provide a sensitive probe of structural and electronic effects, as illustrated for several cyclic nitrogen ligands as well as a range of phosphine ligands in the Mo(CO)4LL′ complexes.
Heat of transport and heat capacity of transport of some aqueous electrolytes
Authors: Sanyal S. K. , Mukherjee Ashis K.
Published: May 2006

The thermal diffusion of aqueous solutions of NaCl, KCl, MgCl2, BaCl2, MgSO4, and CuSO4 (0.05 m) contained in the pores of a sintered glass diaphragm has been studied. A cell is designed and fabricated for this purpose, and the resulting heat of transport values are compared with those available from the literature and obtained by using independent techniques.
Kinetically cooperative models: boundary movement in optical resolution, phase transitions, and biological morphogenesis
Authors: Harrison Lionel G. , Green Beverley R.
Published: May 2006

Computer simulations are described for simple models of kinetically cooperative competition between two or more a priori equally matched antagonists. These might be optically enantiomeric molecules, crystal defects in two phases, differentiation states of biological cells, etc. The models give a perspective on the relationship between the reaction–diffusion theory of pattern formation, homeogenetic induction between biological cells, and the currently popular "cellular automaton" computer programmes. The models express self-activation without inhibition. Therefore, they do not have all that is needed for indefinitely long stabilization of pattern by reaction–diffusion, as first established in the Turing activator–inhibitor model and used later in most reaction–diffusion models. But by the same token, boundaries between disparate regions do not reach stable positions, but must move until they finally reach the edges of the system and disappear. Therefore, these models are convenient for studying aspects of boundary movement in the régime of small-number statistics. To see this without artefacts from array geometry, we use hexagonal arrays in place of the more popular square ones.We conclude that the behaviour of these models in one respect contrasts with and in another resembles the expected deterministic behaviour in large-number statistics. Regions totally surrounded by an antagonist often grow, while deterministically they must shrink. On the other hand, boundaries tend to straighten, as they would deterministically. In a system of overall rectangular habit, with or without periodic edge conditions making it a cylinder or a torus, boundaries tend to align with the shorter dimension, making a pattern of "square stripes".
Photocycloaddition of cytosine to 5-methoxyuracil in dinucleotide model compound
Authors: Skalski Bohdan , Wenska Grazyna , Paszyc Stefan , Stefaniak Zdzislaw
Published: May 2006

The intramolecular photocycloaddition of cytosine (Cyt) to 5-methoxyuracil (mo5U) in Cyt-(CH2)3-mo5Ura, a dinucleotide model compound, occurs upon irradiation with near ultraviolet light (λ > 300 nm) with the formation of an unstable cyclobutane dimer. The dimer undergoes spontaneous dark deamination with a rate constant k = 9.0 × 10−5 s−1 and t1/2 = 128 min, to give a related uracil derivative.
Nucleofugality effects in the pyridine promoted formation of esters from 2-substituted ethanesulfonyl chlorides
Authors: King James Frederick , Hillhouse John Henry , Lauriston Toyanne Marie , Khemani Kishan Chand
Published: May 2006

The products of reaction of a series of 10 2-substituted ethanesulfonyl chlorides, X—CH2CH2SO2Cl (1), with neopentyl alcohol and pyridine-d5 in nitromethane-d3 showed three reaction pathways depending on the nucleofugality of the substituent, X. These routes lead, respectively, to (i) the corresponding neopentyl ester (4), via the sulfene (3) (low substituent nucleofugality); (ii) a mixture of ester 4 and neopentyl ethenesulfonate (5), by the same route except for a partial loss of the 2-substituent during trapping of the sulfene (3) (intermediate nucleofugality); and (iii) a mixture of the ethenesulfonate (5) and the pyridino-betylate (4g) esters, arising from initial elimination of HX to form ethenesulfonyl chloride (2) followed by its further reaction (high substituent nucleofugality). A set of nucleofugality values closely related to, and partly complementing, those derived by Stirling and co-workers can be estimated from the product ratios in those reactions proceeding (at least in part) by route (ii) above. Old reports of anomalous products from 1,2-ethanedisulfonyl chloride (1i) and 2-chloroethanesulfonyl chloride (1j) are simply accounted for on the basis of the initial conversion to ethenesulfonyl chloride (2).
Mechanisms of long-range 13C, 13C spin–spin coupling in thioanisole and its derivatives. Conformational applications
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

The 13C nuclear magnetic resonance chemical shifts and the long-range 13C,13C spin–spin coupling constants are reported for 23 thioanisole derivatives enriched in 13C at the methyl position. For para and meta substituted thioanisole derivatives, nJ(C,C) (n being the formal number of bonds intervening between the coupled nuclei) can be related to functions of the angle by which the thiomethyl group twists out of the aromatic plane. For n = 3,4,5, the ensuing relationships yield estimates of the twofold barriers to rotation about the C(1)—S bond. The barrier is lower in ethyl phenyl sulfide than in thioanisole derivatives. Complications arise for ortho substituted thioanisole derivatives but estimates of the torsional motion about the C(1)—S bond can be obtained from the observed nJ(C,C). Among the complications is the expected fact that 3J(C,C), which is shown to be larger in the cis than the trans orientation of the intervening bonds ("anti-Karplus" behaviour), is perturbed by the substituent attached to the coupled nucleus. It is confirmed that in 2-hydroxythioanisole the thiomethyl group is oriented effectively perpendicular to the benzene plane, attributable to a stereospecific hydrogen bond between the hydroxyl group and the 3p lone-pair on the sulfur atom. In acetone-d6 solution, an equilibrium exists between this conformation and one in which an intermolecular hydrogen bond exists with solvent molecules. In the latter, the thiomethyl group prefers a coplanar orientation. In 2-aminothioanisole, the thiomethyl group twists out of the plane by about 60° so as to optimize the N—H … 3p interaction. This twist angle is changed very little in acetone-d6 solution because the second N—H bond can hydrogen bond to the solvent molecules without disrupting the intramolecular N—H … 3p interaction. It is also shown that the chemical shift of the 13C nucleus in the methyl group is a good conformational indicator in meta and para substituted thioanisoles. Therefore it can be used as such for molecules in which nJ(C,C) is difficult to find, in 1,4-dithiomethylbenzene, for example.
Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of SN2 reactions
Authors: Westaway Kenneth Charles , Lai Zhu-Gen
Published: May 2006

Spectroscopic and conductivity studies of sodium thiophenoxide solutions in four different solvents and the secondary α-deuterium kinetic isotope effects found in the presence of 15-crown-5 ether demonstrate that the secondary α-deuterium kinetic isotope effect and transition state structure for the SN2 reaction between sodium thiophenoxide and n-butyl chloride are significantly different, depending on whether the ionic reactant is a solvent-separated ion-pair complex or a free ion. In all three solvents in which the form of the ionic reactant changes, a smaller isotope effect and tighter transition state are found for the reaction with the ion-pair complex.
Platinum and palladium complexes of [R2PCH2P(Y)R′2] and [R2PCHP(Y)R′2]− ligands, Y = O,S, or Se: 13C, 31P, 77Se, and 195Pt nuclear magnetic resonance studies and the crystal and molecular structures of trans-[PtCl(PEt3){But2PCH2P(O)Me2}][ClO4] and trans-PtCl(PEt3){Ph2PCH2P(S)But2}|[ClO4]
Authors: Berry David Eric , Browning Jane , Dixon Keith Roger , Hilts Robert Wayne
Published: May 2006

Reactions of the bisphosphine monochalcogenides, [Ph2PCH2P(Y)R2], Y = O, S, or Se, R = Ph, Pri, or But, with the chloro-bridged dimers [M2Cl4(PR′3)2], M = Pd or Pt, R′ = Et or Bun, in the presence of either NaClO4 or NaBF4 yield perchlorate and fluoroborate salts of the complex cations cis- and trans-[PtCl(PR′3){Ph2PCH2P(Y)R2}]+. In many cases both cis and trans isomers (defined by the relative orientation of the two M—P bonds) are obtained and the precise isomer distribution is a sensitive function of the substituents. Corresponding neutral complexes, cis- and trans-[PtCl(PR′3){Ph2PCHP(Y)R2}], can be synthesized either by deprotonation of the cations using NaH or by use of the salts Li[Ph2PCHP(Y)R2] in the initial bridge cleavage reactions. These and related complexes are characterized by complete 13C, 31P, 77Se, and 195Pt NMR studies and by two crystal structure determinations. The complexes I, trans-[PtCl(PEt3){But2PCH2P(O)Me2}][ClO4], and II, trans-[PtCl(PEt3){Ph2PCH2P(S)But2}][ClO4], crystallize in the monoclinic space group P21/c, respective cell dimensions: a = 15.579(2), b = 13.590(3), c = 13.578(1) Å;β= 105.96(1)°; and a = 14.002(4), b = 16.366(5), c = 15.524(5) Å; β = 106.01 (3)°. Complete X-ray diffraction studies show that both complexes contain closely square planar platinum centres with the R2PCH2P(Y)R′2 ligands coordinated via phosphorus and the Y atom so as to form five-membered chelate rings. The molecular dimensions suggest that the bond to sulphur is stronger than that to oxygen and exerts a larger trans influence.
7-Diethylamino-3-((4′-iodoacetylamino)phenyl)-4-methylcoumarin, a fluorescent probe of the hydrophobic cleft in the tropomyosin coiled coil
Authors: Burtnick Leslie D. , Racic Anita
Published: May 2006

A sulfhydryl-specific fluorescent reagent, 7-diethylamino-3-((4′-iodoacetylamino)phenyl)-4-methylcoumarin (DCIA) was used to label cysteine residues on tropomyosin (TM) from rabbit cardiac and rabbit skeletal muscles. The emission maximum at 486 nm, the high degree of fluorescence polarization, and the limited accessibility of the bound probe to quenching by iodide suggest that the probe is bound in the hydrophobic cleft between polypeptide chains of the TM coiled coil, as well as being bound covalently at a cysteine residue. The labelled TMs retain their abilities to bind F-actin and are able to interact with deoxyribonuclease I. They, however, show a reduced tendency to aggregate into filaments in low ionic strength solutions.
Cation mobility in gaseous, critical, and liquid deuterated methanes
Authors: Floriano M. Antonio , Gee Norman , Freeman Gordon R.
Published: May 2006

Cation mobilities µ have been measured in the deuterated methanes CHxD4−x (x = 0–4) at field strengths E/n < 4 × 10−21 V m2/molecule, 92 ≤ T/K ≤ 598 and 0.025 ≤ n/1026 molecules m−3 ≤ 171. The mobility in the equilibrium fluids was the same at a given number density n for all five methanes. In the liquid the mobility decreased as the critical region was approached. Changes in nµ in the nonsaturated gases reflected changes in clustering, which was favored at lower T or higher n. The Arrhenius temperature coefficients of ion mobilities at constant gas density near the vapor/liquid coexistence curve nearly equalled those of electron mobilities at similar experimental conditions. The ion mobility in the saturated gas was determined mainly by density and in the liquid by the viscosity.
Étude expérimentale et modélisation théorique de la décomposition du radical éthyle
Authors: Simon Yves , Foucaut Jean François , Scacchi Gérard
Published: May 2006

A bibliographical study of the thermal decomposition of the ethyl radical shows that the kinetic parameters for the upper and lower limits of the pressure are rather scattered. This observation explains why we have carried out a new study of this elementary process in the pyrolysis of ethane, around 800 K, in a closed vessel and at pressures of the hydrocarbon varying from 1 to 300 Torr. The experimental results have been treated according to three theoretical approaches: the RRKM theory and two methods proposed by Troe. In each case, an excellent fit of the theoretical curves with the experimental data is obtained, as well as Arrhenius expressions for the reaction rate constants at high and low pressures. A detailed critical analysis of our results as well as those found in the literature shows that as yet there is no good agreement between recent studies on this subject. However, it is possible to present two Arrhenius expressions for the reaction rate constants at high and low pressures; these expressions represent a good compromise for the results obtained by various authors:[Formula: see text][Journal translation]
Interpretation of n-donor specific solvent effect on electronic spectra of copper acetate and chloride complexes by intermolecular perturbation theory
Authors: Szpakowska Mariola , Nagy Ottó B.
Published: May 2006

A simple second order intermolecular perturbation theory is proposed in the Fukui approximation to account for the electronic spectral behavior of electron acceptor solutes dissolved in pure n-donor solvents. This double perturbation theory considers explicitly both the solvating and complexing effects of the solvent. Using the electronic spectral data of mono- and binuclear copper acetate and chloride complexes obtained in pure pyridine derivatives it is shown that the predicted shifts brought about by increasing n-donor ability of solvent are fully corroborated by experiment. The sensitivity of mononuclear copper complexes to steric effects is also confirmed and it is shown that binuclear ones are not sensitive to this effect. New ionization potential values have also been determined using a simple interpolation–standardization procedure.
The synthesis and unimolecular decomposition of four novel Δ1-1,2,4-triazolines
Authors: Schwan Adrian L. , Warkentin John
Published: May 2006

Treatment of 4-tert-butyl-3,3-dimethyl-5-methylene-Δ1-1,2,4-triazoline (3) with benzonitrile oxide (9), diphenylnitrile imine (10), phenyl azide, and p-nitrophenyl azide led, in each case, to 1,3-dipolar cycloaddition. The products, Δ1-1,2,4-tri-azolines that are spiro-fused to another 5-membered ring, could be isolated in pure form in three of the four cases. All four are thermally unstable and decompose by loss of N2 from the Δ1-1,2,4-triazoline moiety to form an azomethine ylide. Subsequent reactions of those ylides are described.
Catalytic polarographic waves of cobalt(II) in the presence of sodium sulfide (SH− form) in borax – ammonium chloride
Authors: Marin Dolores , Teijeiro Carmen
Published: May 2006

The presence of SH− ions in a medium containing ammonia (borax–NH4Cl) and cobalt(II) gives rise to a catalytic cobalt(II) prewave and a catalytic hydrogen wave, both of which manifest more positive potentials than the cobalt(II) reduction wave. The effects of time, sulfide and cobalt concentrations, mercury column height, and gelatine and neutral salts addition are discussed. In addition, the characteristics of the current–time and electrocapillary curves are shown. The results obtained suggest a mechanism whereby a cobalt(II) prewave is produced by a cobalt(II) complex with SH− in the 1:2 relationship. Hydrogen catalytic evolution is attributed to the reduction of a protonated complex.
Orientation specific Diels–Alder addition of isoprene to an activated 4,4-dimethylcyclohexenone. An improved route to himachalenes
Authors: Liu Hsing-Jang , Browne Eric N. C. , Chew Sew Yeu
Published: May 2006

Diels–Alder addition of isoprene to enone-ester 3 proceeds exclusively to the para-addition product 6. The specificity of this route constitutes a significant improvement in the previously reported total synthesis of himachalenes via 6. The mechanistic significance of the observed specificity of addition is discussed.
The solvent deuterium isotope effect on the hydroxide-ion-catalyzed conversion of acetaldehyde to its enolate ion
Authors: Keeffe J. R. , Kresge A. J.
Published: May 2006

Rates of proton transfer from acetaldehyde to the hydroxide ion were measured by iodine scavenging in H2O and in D2O solution at 25 °C; the results give the solvent isotope effect [Formula: see text]. This value is somewhat more consistent with an estimate, made using fractionation factor theory, for hydron transfer directly from the substrate to the hydroxide ion than with another estimate, made similarly, for hydron transfer through an intervening water molecule.
Halogen and pseudohalogen substitution of some adamantanoid chalcogenate clusters [(μ-EPh)6(MEPh)4]2− using methylmercury and triphenyltin derivatives. A multinuclear nuclear magnetic resonance study
Authors: Dean Philip A. W. , Vittal Jagadese J.
Published: May 2006

Multinuclear nmr (1H, 77Se, 111/113Cd, 119Sn, 199Hg, as appropriate) has been used to study Y−−EPh− exchange in Me2CO or MeCN between RnM′Y (RnM′ = Ph3Sn or MeHg; Y = Cl, Br, I, NCO, or NCS) and the adamantane-like anions [(μ-EPh)6(MEPh)4]2− (E = S, M = Zn, Cd, or Co; E = Se, M = Zn or Cd), as their tetraalkylammonium salts. Quantitative terminal substitution of the clusters occurs in most cases, giving [(μ-EPh)6(MEPh)4 − x(MY)x]2−(x = 1–4). However, reaction is incomplete for M = Cd, E = S or Se, RnM′Y = Ph3SnNCO or Ph3SnNCS and for M = Zn or Co, E = S, RnM′Y = MeHgI. Differences in the extents of reaction for Ph3SnY and MeHgY are consistent with the position of equilibrium in MeHgY:Ph3SnEPh mixtures.Group interchange provides a convenient alternative synthesis of the known halogen-substituted clusters [(μ-EPh)6(MY)4]2−(M = Zn or Cd, Y = Cl, Br, or I; M = Co, Y = Cl), and the first syntheses of [(μ-SPh)6(CoY)4]2− (Y = Br or I) and various pseudohalogen-substituted adamantanoid anions. The nuclei used for full direct nmr characterization of the new clusters in solution were: 77Se and 113Cd for [(μ-SePh)6(CdSePh)4 − x(CdY)x]2− (x = 1–4; Y = NCO or NCS); 77Se for [(μ-SePh)6(ZnSePh)4 − x(ZnY)x]2− (x = 1–4, Y = NCO or NCS); 113Cd for [(μ-SPh)6(CdSPh)4 − x(CdY)x]2−(x = 1–4; Y = NCO or NCS); 1H for [(μ-SPh)6(CoY)4]2− (Y = Br, I, NCO, or NCS). The first solution 1H nmr spectrum of [(μ-SPh)6(CoCl)4]2− is also reported.
Palladium phthalocyanine and its polymorphic forms
Authors: Kempa Arnold , Dobrowolski Jan
Published: May 2006

Pd(II) phthalocyanine (PdPc) was obtained by reaction of PdCl2 with phthalimide and urea in the presence of ammonium molybdate in boiling nitrobenzene, resulting in a good yield equal to 68%. This method has not been used previously. The following polymorphic forms were obtained: metastable α- and γ-PdPc, not previous described in the literature, and stable β-PdPc. The IR spectra and X-ray powder diffraction spectra of these phases were measured and interpreted. The results were compared with the literature data on polymorphic forms of other phthalocyanines. At this time we do not know if any of the PdPc polymorphs are isomorphous with the various forms of nickel, copper, and platinum phthalocyanine.
Excess properties of mixtures of some n-alkoxyethanols with organic solvents. V. Excess enthalpies of 2-butoxyethanol with normal alkanes at 298.15 K
Authors: Cobos Jose Carlos , Garcia Isaias , Casanova Carlos
Published: May 2006

The excess molar enthalpy HE has been determined as a function of mole fraction x at 298.15 K and atmospheric pressure for five (2-butoxyethanol + n-alkane) mixtures. The n-alkanes were n-heptane, n-octane, n-decane, n-dodecane, and n-tetradecane. The mixtures show positive and unsymmetrical HE, skewed towards low mole fractions of 2-butoxyethanol, and whose value increases with the chain length n of the alkane.
Phenceptin: a biomimetic model of the phenytoin receptor
Authors: Wolfe Saul , Bowers Raymond John , Shin Hee-Sook , Sohn Chang-Kook , Weaver Donald Fredric , Yang Kiyull
Published: May 2006

5,5-Diphenylhydanytoin (phenytoin) is the most widely used anticonvulsant drug, but has many side effects. Although its chemical mode of action is unknown, phenytoin is believed to function primarily by interference with the transport of sodium ions across the neuronal membrane. Structure–activity and lipophilicity–activity studies suggest that the drug interacts with its receptor through hydrogen bonding to the N3—C4 amide bond, and an aromatic–aromatic interaction with the C5 substituent. Since sodium channels are cysteine-rich peptides, whose function depends upon the cysteine[Formula: see text]cystine redox process, it has been hypothesized that the action of the phenytoin receptor may be mimicked by a properly designed cyclodepsipeptide containing a cystinyl moiety, a cavity lined with five oxygen atoms oriented in the trigonal-bipyramidal manner appropriate for selective transport of sodium ions, and a site for the binding of phenytoin. A computer programme and strategy were developed to permit the three-dimensional structures of potential target molecules to be viewed, prior to synthesis. Use of this programme led to the discovery of Boc-L-cystinyl-glycyl-L-prolyl-glycyl-L-prolyl-L-cystine-OCHPh2. This compound, termed phenceptin, was synthesized from a linear precursor containing tert-butoxycarbonyl protection at the N-terminus, benzhydryl ester protection at the C-terminus, and trityl protection at sulfur. Detritylation and cyclization to phenceptin were accomplished with iodine in methanol–pyridine. Using an n-octanol membrane to study the kinetics of ion transport, phenceptin was found to transport sodium ions selectively, but only in its oxidized, cyclic form. This transport was inhibited significantly by one mol-equiv. of phenytoin, and not at all by biologically inactive analogs of the drug. The nature of the binding of phenytoin to phenceptin was examined by nuclear magnetic resonance, in n-C8D17-OH solvent, and found to involve hydrogen bonding of the drug to a glycine residue whose oxygen atom is involved in complexation to sodium ions.
Some aspects of the alkylation of epoxides of 1,6-anhydropyranoses
Authors: Magdzinski Leon , Fraser-Reid Bert
Published: May 2006

The formation of C-alkyl derivatives from 1,6:2,3-dianhydro-manno-pyranose precursors has been examined. Regioselectivity at C2 is excellent when the C4 substituent is benzyloxy. However, with CH3, reaction at C2 and C3 occurs, although the ratio of products can be altered substantially depending on the nature of the nucleophile and the reaction conditions.
Structure-activity studies of β-carbolines. 4. Crystal and molecular structures of t-butyl β-carboline-3-carboxylate and 2-(methoxycarbonyl)canthine-6-one
Authors: Codding Penelope W. , Szkaradzinska Maria B. , Roszak Aleksander W. , Aha Lorraine J. , Hagen Timothy J. , Cook James M.
Published: May 2006

The crystal and molecular structures of two ligands for the benzodiazepine (BZ) receptor, t-butyl β-carboline-3-carboxylate, I (C16H16N2O2), and 2-(methoxycarbonyl)canthin-6-one, II (C16H10N2O3), are reported. The t-butyl β-carboline compound has high affinity for the receptor and is an antagonist; in contrast, the canthin-6-one has a 10-fold lower affinity for the receptor and no determinable in vivo activity. The space group for I is P21/c with a = 11.756(1), b = 11.2324(8), c = 11.964(1) Å, and β = 105.99(1)°. For II, the space group is also P21/c with a = 9.317(1), b = 7.964(1), c = 17.180(3) Å, and β = 104.173(7)°. The orientation of the alkyl-carboxylate side chain is different in the two molecules and may be related to the difference in affinity and in vivo activity of the ligands. In addition, the packing arrangements in the two structures are dominated by π-stacking interactions; and, in the case of the t-butyl compound, by hydrogen bonding.
The photochemical nucleophile–olefin combination, aromatic substitution reaction (Part 2): methanol – cyclic olefins, 1,4-dicyanobenzene
Authors: Arnold Donald R. , Snow Miles S.
Published: May 2006

Direct irradiation of acetonitrile–methanol (3:1) solutions of 1,4-dicyanobenzene and the cyclic olefins, cyclohexene, 1-methylcyclohexene, norbornene, and 2-methylnorbornene, leads to formation of regio- and stereoisomers of the 1:1:1 (alcohol:olefin:aromatic) adducts. This reaction can be photosensitized by electron transfer; addition of electron donors, biphenyl or phenanthrene, to the irradiation mixture generally increases the efficiency and yield of adduct formation. The efficiency of the reaction and the ratio of isomeric adducts are also affected by the addition of salts, particularly magnesium perchlorate. All of the possible regio- and stereoisomers from cyclohexene and 1-methylcyclohexene have been identified, two from cyclohexene and four from 1-methylcyclohexene. Three of the four possible isomers from norbornene were characterized; the endo,endo isomer was not detected. There are eight possible isomers from 2-methylnorbornene; six were detected and five have been isolated and identified. The two sterically hindered isomers, those having both the 4-cyanophenyl and the methoxy groups in the endo position, and exo-3-(4-cyanophenyl)-endo-2-methoxy-exo-2-methylnorbornane, were not characterized. The structures of the products were established largely on the basis of the 1H and 13C nuclear magnetic resonance spectra. The mechanism of the reaction is discussed, with emphasis on those factors that may affect the product ratio. The most striking observation is that the reaction is regioselective when magnesium perchlorate is added to the irradiation mixture.
The chemistry of thujone. XII. The synthesis of pyrethroid analogues via chiral cyclopropanation
Authors: Becalski Adam , Cullen William R. , Fryzuk Michael D. , Herb Georg , James Brian R. , Kutney James P. , Piotrowska Krystyna , Tapiolas Dianne
Published: May 2006

An extensive study involving achiral and chiral cyclopropanation of various isoprenoid units derived from the monoterpene thujone is presented. Carbenoid intermediates generated from ethyl and L-menthyl diazoacetates and various achiral and chiral copper catalysts are employed to achieve the desired cyclopropanation reaction. It is shown that high levels of enantiomeric excess can be achieved, particularly when L-menthyl diazoacetate and a chiral catalyst are employed. The resultant products are then converted to pyrethroid-like analogues.
The conversion of 7-acetoxyroyleanone to 14-methoxytaxodione
Authors: Faucher Anne-Marie , Burnell Robert H.
Published: May 2006

7-Acetoxyroyleanone (1a) has been converted in five steps to the methoxy-p-quinone 9. Since the latter was the penultimate intermediate in Eugster's partial synthesis of 14-methoxytaxodione (2), the transformation reported represents a formal synthesis of the latter. Keywords: 7-acetoxyroyleanone, 14-methoxytaxodione, synthesis.
Synthesis, characterization, and exchange of complexes of (R)-N,N-dimethylaminoethylferrocene with SO2 and BF3
Authors: Brownstein Sydney , Han Nam Fong , Gabe Eric , Lee Florence
Published: May 2006

Sulfur dioxide and (R)-N,N-dimethylaminoethylferrocene (I) react with an enthalpy of formation of 21.5 ± 1 kcal mol−1 to give a complex with sulfur bonded to nitrogen. The SO2 exchanges between adduct molecules by a dissociation mechanism. BF3 reacts with the above amine to give an adduct and its partly hydrolyzed product, [(η5-C5H5)Fe(η5-C5H4—CH(CH3)N(CH3)2•BF(OH)2] (II). II crystallizes in the orthorhombic space group P212121 with a = 9.882(3), b = 10.625(5), and c = 13.988(13) Å and z = 4. Rf = 0.102 and Rw = 0.104. Keywords: N,N-dimethylaminoethylferrocene complexes, X-ray structure, NMR exchange.
Organic reactions in liquid crystalline solvents. 8. Deuterium NMR studies of the solubilization of some aromatic ketones in the liquid crystalline phases of 4′-butylbicyclohexyl-4-carbonitrile
Authors: Fahie Brian J. , Mitchell D. Scott , Leigh William J.
Published: May 2006

The nature of the solubilization of β-phenyl-4-mefhoxypropiophenone (1) in the nematic and crystal-B liquid crystalline phases of trans,trans-4′-butyl-(1, 1′-bicyclohexyl)-4-carbonitrile (CCH-4) has been investigated by deuterium nmr spectroscopy. This has been carried out using deuterium quadrupolar splitting (ΔvQ) and T1 measurements on 1–15 mol% solutions of two selectively deuterated derivatives of the ketone in CCH-4 over the 25–110 °C temperature range. The nmr studies have been supplemented with differential scanning calorimetry (DSC) and thermal microscopic investigations of variously proportioned mixtures of the parent ketone with CCH-4, over a similar temperature range. For comparison, 2H nmr measurements have also been carried out for solutions of 4-methoxyacetophenone-α,α,α,d3 benzene-d6 and β-(4-cyclohexylphenyl)-4-methoxypro-piophenone-α,α-d2 in the same liquid crystal as a function of temperature. Our results indicate that the limit of solubility of 1 in the smectic phase of CCH-4 is less than 0.5 mol%. At temperatures above 35 °C, excess ketone is solubilized in a ketone-rich nematic phase that coexists with the bulk smectic phase, and the composition of the ketone-rich phase varies continuously with temperature throughout this range. At around 35 °C, the ketone-rich phase transforms into a metastable, non-birefringent phase which is characterized by isotropic nmr behaviour. Prolonged storage at room temperature causes crystallization of this phase, forming a stable binary mixture of ca. 9:1 CCH-4/1 that undergoes a K–Sm transition at 27–28 °C, a Sm–N transition at 43.5–44 °C, and a broad N–I transition at 58–63 °C. This stable modification can also be prepared by rapid cooling of a 10 mol% 1/CCH-4 mixure from the nematic phase. The 2H nmr studies of 4-methoxyacetophenone-α,α,α-d3 and benzene-d6 in CCH-4 indicate that these solutes have somewhat higher solubility in the crystal-B phase of this mesogen. The data necessitate a re-interpretation of our previously reported studies of the excited triplet state behaviour of 1 in the liquid crystalline phases of this material, and may be broadly applicable to numerous other studies of photochemical reactivity in this mesogen that have been reported. Keywords: liquid crystal, smectic, 2H nmr, photochemistry, aromatic ketone, bicyclohexyl-4-carbonitrile,4′-butyl.
Isotherme d'adsorption du phénanthrène et de ses dérivés hydrogénés sur du nickel de Raney
Authors: Bossányi François , Hassani Chakib Ameziane , Ménard Hugues , Lessard Jean
Published: May 2006

The adsorption isotherms of phenanthrene and its hydrogenated derivatives, of naphthalene, and of tetralin on Raney nickel have been determined by chromatographic studies. The adsorption of these molecules on Raney nickel depends on the number of π electrons and on the position and orientation of hydrogen atoms that can interfere with the interaction of the π electrons with the catalyst. Keywords: adsorption, phenanthrene, chromatographic studies.
Conformational analysis of configurationally isomeric dicyclohexano-12-crown-4 ethers and their lithium complexes in solution as studied via 13C NMR spectroscopy
Authors: Buchanan G. W. , Kirby R. A. , Bourque. K.
Published: May 2006

From 13C NMR coalescence temperature measurements, the cis-syn-cis isomer of the title crown ether is shown to undergo a single degenerate ring inversion process with a barrier of 45.9 ± 0.3 kJ/mol. For the corresponding cis-anti-cis isomer, a second ring inversion process has been detected, giving rise to two conformations whose free energies differ by ca. 1.5 kJ/mol. The influence of lithium ion complexation on these barriers as well as on the 13C spin-lattice relaxation times has been investigated. Keywords: crown ethers, dynamic stereochemistry.
Coordinatively unsaturated binuclear clusters of rhodium. The reactivity of [{Pri2P(CH2)nPPri2}Rh]2(μ-H)2 (n = 2, 3, and 4) with dihydrogen, and their use in the catalytic hydrogenation of olefins
Authors: Fryzuk Michael D. , Piers Warren E. , Einstein Frederick W. B. , Jones Terry
Published: May 2006

The coordinatively unsaturated binuclear rhodium hydrides [{Pri2P(CH2)nPPri2}Rh]2(μ-H)2 (n = 2: 1b; n = 3: 1c; n = 4: 1d) react rapidly with dihydrogen to yield the fluxional binuclear tetrahydrides [{Pri2P(CH2)nPPri2}RhH]((μ-H)3[Rh{Pri2P(CH2)nPPri2}] 2b–d(n = 2–4). The dihydride 1b was structurally characterized by single crystal X-ray diffraction. While the tetrahydrides 2b and 2c were found to be stable only in solution in the presence of excess dihydrogen, 2d was stable in the solid state. Three separate exchange processes were characterized for 2b–d via 1H and 31P{1H} NMR spectroscopy: intermolecular exchange with free dihydrogen, and two intramolecular processes exchanging the four hydride ligands. The geometry about the rhodium centres in the limiting structures involved in these processes is affected by the chelate ring size of the ancillary diphosphine ligand. A "rocking" process observed at low temperatures for each of these tetrahydrides has a ΔG≠ of <7.0(5) kcal/mol, 8.6(5) kcal/mol, and 11.5(5) kcal/mol for 2b, 2c, and 2d, respectively. The dihydrides 1b and 1c were found to catalyze the hydrogenation of 1-hexene. Turnover numbers of 850–950 h−1 and 700 h−1 were observed for 1b and 1c, respectively, along with isomerization side reactions. Catalyst concentration studies on the hydrogenation of styrene using 1c as the catalyst precursor revealed a decrease in turnover frequency with increasing total metal concentration, suggesting that the active catalyst is a mononuclear species. Chemical evidence suggests that a pathway involving binuclear intermediates is also available, but that in the 1c system at least, a pathway utilizing mononuclear species as intermediates predominates. Keywords: binuclear rhodium hydrides, homogeneous catalysis.