bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal and Molecular Structure of [2,3-Bis(dimethylarsino)-1,1,1,4,4,4,-hexafluorobut-2-ene-As, As]tricarbonyldiiodotungsten(II)
Authors: Mercer Anthony , Trotter James
Published: May 2006

Crystals of the title compound, Me2AsC(CF3):C(CF3)AsMe2WI2(CO)3, are monoclinic, a = 15.37(2), b = 9.529(1), c = 15.967(3) Å, β = 112.03(2)°, Z = 4, space group P21/c. The structure was determined by Patterson and Fourier syntheses and refined by full-matrix least-squares procedures to a final R of 0.069 for 1823 observed (of a total of 2778) reflexions. The tungsten atom is seven-coordinate with a distorted capped octahedral environment, the capping group being a carbonyl (W—C, 1.94(3) Å). The capped face consists of the two remaining carbonyl groups (W—C, 1.97(4) and 2.00(4) Å) and one of the arsenic atoms from the bidentate ligand (W—As, 2.556(3) Å). The uncapped face contains the two iodine atoms (W—I, 2.848(2) and 2.856(2) Å) and the remaining arsenic atom (W—As, 2.618(3) Å), this bond length (trans to CO), being significantly longer (by 0.062 Å) than the other (trans to I) W—As distance.
An Investigation of Substituent Effects on Coupling Constants to Vinyl Protons in Styrene Derivatives
Authors: Reynolds William F. , Peat Ian R. , Hamer Gordon K.
Published: May 2006

Experimental long-range phenyl proton–vinyl proton coupling constants in 4-substituted styrenes are substituent independent. This is also predicted by INDO–finite perturbation theory calculations of these coupling constants. Comparison with calculated and experimental long-range coupling constants for 4-substituted benzaldehydes suggests that the previously reported substituent dependence for the latter coupling constants arises from substituent-induced changes in molecular geometry.Geminal vinyl coupling constants in 4-substituted styrenes, α-methylstyrenes, and α-t-butylstyrenes are substituent dependent with substituent effects increasing as phenyl and vinyl groups are twisted out of planarity. These trends are reproduced by INDO–FPT calculations. It is concluded that the substituent effects are primarily transmitted through space.Both experimental and calculated vinyl 13C–1H coupling constants show strong stereospecific substituent effects. From the pattern of results (particularly the greater field dependence for JC(β)H(9) than JC β)H(8)) it is concluded that these coupling constants.also reflect through-space substituent effects. This is supported by calculations on model compounds with no intervening phenyl group.
Epithermal Electron Ranges and Thermal Electron Mobilities in Liquid Aromatic Hydrocarbons
Authors: Shinsaka Kyoji , Freeman Gordon R.
Published: May 2006

Radiolysis free ion yields were measured as functions of electric field strength and temperature in benzene, toluene, 1,2-, 1,3-, and 1,4-dimethylbenzene, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, naphthalene, and anthracene. Secondary electron ranges bGP were estimated from the yields. The density-normalized ranges bGPd were almost constant, 34−38 × 10−8 g/cm2, from benzene up to the tetramethylbenzenes, then increased to 47 × 10−8 in pentamethyl- and 52 × 10−8 in hexamethylbenzene. In naphthalene and anthracene the normalized ranges were 32 and ∼20 × 10−8 g/cm2, respectively. Electron mobilities in the liquids at 293 K, and their activation energies, expressed in (cm2/V s, kcal/mol) were: benzene (0.114, 7.4); toluene (0.063, 3.4); 1,2-dimethylbenzene (0.018, 4.4); 1,3-dimethylbenzene (0.057, 4.5); 1,4-dimethylbenzene (0.062, —); 1,2,3-trimethylbenzene (0.022, 4.8); 1,2,4-trimethylbenzene (0.035, 4.3); 1,3,5-trimethyl-benzene (0.17, 3.2); 1,2,3,4-tetramethylbenzene (∼0.02, 5). The mobilities reflect migration retarding influences of the aromatic ring and molecular asymmetry, and a slight ring-shielding effect of methyl groups that tends to enhance the mobility.
A Proton Magnetic Resonance Study of 1,4-Dibromobenzene-13C Partially Oriented in Nematic Phases
Authors: Burnell E. E. , Sweeney M. A. J.
Published: May 2006

Proton magnetic resonance spectra of 1,4-dibromobenzene (13C and 12C) partially oriented in nematic phases have been measured and analyzed, and the geometry of the molecule has been determined. The angle [Formula: see text] is found to be 120.02 ± 0.01° and the angle [Formula: see text]with the assumption that all CC bond distances are of equal length the angle [Formula: see text] The JCH are determined using three spectra of samples with differing degrees of orientation.
A Carbon-13 Nuclear Magnetic Resonance Investigation of Some Substituted Methyl Phenyl Sulfides, Sulfoxides, and Sulfones
Authors: Buchanan Gerald W. , Reyes-Zamora Cesar , Clarke Douglas E.
Published: May 2006

Carbon-13 chemical shifts for 33 methyl phenyl sulfides, sulfoxides, and sulfones are reported. Observed trends are discussed in terms of the steric and electronic influences of the substituent groups. Additivity correlations for para-disubstituted materials are noted. In general, the shieldings of methyl carbons bonded to sulfur are rather insensitive to the nature of the aromatic substituents. By contrast to the proton shieldings, the CH3SO and CH3SO2 carbons exhibit nearly identical chemical shifts.
Thermolysis of 3,3,5,5,5-Tetramethyl-4-methylene-1-pyrazoline and the Thermal Isomerization of Some Alkylidenecyclopropanes
Authors: Crawford Robert J. , Tokunaga Hirokazu
Published: May 2006

The thermolysis of 3,3,5,5-tetramethyl-4-methylene-1-pyrazoline (1) proceeds at 1/63 the rate of 4-methylene-1-pyrazoline. The activation parameters, log (k/s−1) = (15.53 ± 0.3) − (40.7 ± 0.4)/θ where θ = 2.303 RT in kcal mol−1, suggest that 1 is undergoing thermolysis by a mechanism different from that for 4-methylene-1-pyrazoline. The 2,2,3,3-tetramethylmethylenecyclopropane (5) produced rapidly isomerizes under the reaction conditions to 2,2-dimethylisopropylidenecyclopropane (4). The four opposed methyl groups of 5 have created sufficient ground state destabilization as to cause its isomerization to be 147 times faster than the conversion of 2,2-dimethylmethylenecyclopropane to isopropylidenecyclopropane.The products are considered in terms of two possible intermediates, one wherein an allylic diazenyl diradical is considered and the second wherein a Chesick type of intermediate is invoked. For the latter it is demonstrated that substituents on the orthogonal radical center can affect the rotational propensities of methylene vs. isopropylidene of the allylic system.
Cyclizations of Azidoformates to Tetrahydro-1,3-oxazin-2-ones and Oxazolidin-2-ones
Authors: Alewood Paul Francis , Benn Michael , Reinfried Rolf
Published: May 2006

Thermolysis of azidoformates in polychloromethane solvents was found to be superior to photolysis as a method for preparing perhydro-1,3-oxazin-2-ones and oxazolidin-2-ones. For some substrates preparatively useful yields of the oxazinones could be obtained but more usually oxazolidone formation competed effectively and often was predominant.
Carbon-13 Fourier Transform Nuclear Magnetic Resonance. IX. Complete Assignments of Some Prodigiosins. Bioincorporation of Label
Authors: Cushley Robert J. , Sykes Richard J. , Shaw C.-K. , Wasserman Harry H.
Published: May 2006

A comprehensive study has been made of the carbon-13 chemical shifts of substituted pyrroles. The data, together with perdeuteration, single resonance, and off-resonance techniques, formed the basis for the complete interpretation of the carbon-13 spectra of the prodigiosins. Based on these assignments the biosynthetic origin of the prodigiosin carbons was elucidated, with further biosynthetic studies to be reported.Carbon-13 chemical shifts are shown to be an effective means of determining sites of protonation.
The Structure of The Dimethylthallium Ion Oriented in a Lyotropic Nematic Phase
Authors: Lee Yunko , Reeves Leonard W.
Published: May 2006

The proton magnetic resonance spectra of dimethylthallium ion has been studied in both anionic and cationic detergent nematic phases. The spectra were analyzed to derive the values of inter- and intramethyl proton–proton dipolar coupling and the intermethyl scalar coupling constants. The degree of orientation of the dimethylthallium cation is much higher in the anionic nematic phase than in the cationic phase. It is proposed that electrostatic interactions play a significant role in the orientation of complex ions in ionic detergent nematic phases.
13C Nuclear Magnetic Resonance Studies of Organometallic Compounds. IX. Phenylaminocarbene Derivatives
Authors: Clark Howard C. , Ward John E. H. , Asufuku Katsutoshi Y
Published: May 2006

The 13C nuclear magnetic resonance parameters for a series of transition metal carbene complexes of the type trans-[(CH3)Pt(As(CH3)3)2(p-XC6H4NH(CH3)C)]+PF6− are presented. Comparisons of the σ+ substituent constants for —X with the carbene carbon shieldings reveal that both σ and π interactions are occurring between the aromatic rings and the carbene carbons. A quantitative inverse relationship between these carbene carbon shieldings and those of analogous phenylthiocarbene complexes is discussed. The phenyl rings are shown to adopt cis orientations with respect to the carbene methyl groups.
Nuclear Magnetic Resonance Evidence for High Barrier of Conformational Inversion in Hexahydro-3,3,7,7-tetramethyl-1,2-oxazepine-5-one
Authors: Wasylishen Roderick E. , Rice Kenner C. , Weiss Ulrich
Published: May 2006

Variable temperature proton n.m.r. spectra indicate an activation energy of 19.0 ± 0.5 kcal/mol for conformational equilibration in hexahydro-3,3,7,7-tetramethyl-1,2-oxazepine-5-one. It is suggested that the rate process involves slow conformational interconversion of the seven-membered ring and not slow inversion at the nitrogen atom. The synthesis of several related 1,2-oxazepines is described.
A Photochemical Route to N-Acyl Imines
Authors: Court William A. , Edwards Oliver E. , Grieco Ciro , Rank Werner , Sano Takehiro
Published: May 2006

Irradiation of two steroidal α-azido ketones gave N-acyl imines by formal acyl migration onto nitrogen. Spectroscopic characteristics (u.v., i.r., 1H n.m.r., and 13C n.m.r.) and chemistry of these is described. Similarly an α-azido γ-lactone gave a 5,6-dihydro-1,3-oxazin-2-one which added methanol readily to give a 4-methoxytetrahydro-1,3-oxazine-2-one. Possible mechanisms are considered for the observed rearrangements.
Silyl-, Germyl-, and Stannyl-Pentacarbonylmetalates Of Chromium, Molybdenum, and Tungsten
Authors: Isaacs E. E. , Graham W. A. G.
Published: May 2006

The new anions [R3M′M(CO)5]− (R3M′ = Ph3Si, MePh2Si, Ph3Ge, Ph3Sn, Me3Sn, and Ph3Pb; M = Cr, Mo, W) have been prepared as tetraethylammonium salts by reaction of R3M′Li with [Et4N(ClM(CO)5]. The redistribution reaction between [Ph3SnW(CO)5]− and [Cl3SnW(CO)5]− affords [PhCl2SnW(CO)5]− or [Ph2ClSnW(CO)5]−. Anhydrous HCl reacts with [Ph3SiW(CO)5]− and [Ph3GeW(CO)5]− to form [ClW(CO)5]− but with [Ph3SnW(CO)5]−to form [Cl3SnW(CO)5]−. An insertion reaction of SnBr2 with [BrW(CO)5]− forms the new anion [Br3SnW(CO)5]− while SnCl2 and GeCl2 (from HGeCl3) react with [ClM(CO)5]− to produce the known species [Cl3M'M(CO)5]− (M′ = Ge, Sn; M = Cr, Mo, W). Infrared spectra in the carbonyl stretching region are reported for all anions.
Deacylation of Fluorine-substituted trans-Cinnamoyl-α-chymotrypsins
Authors: Gerig J. T. , McLeod R. S.
Published: May 2006

Deacylation of unsubstituted and of o-F-, m-F, p-F, α-F, pentafluoro-, p-methyl-, and p-trifluoromethyl-substituted trans-cinnamoyl- α-chymotrypsins has been studied from pH 4 to 8. The deacylation rate constants were found to depend upon the ionization state of a group on the enzyme with an apparent pK in the range 6.3–7.3. The hydrolysis rates of the correspondingly substituted p-nitrophenylcinnamate esters were determined at pH 10.6. Correlation of the data for these model reactions with the corresponding rates of enzyme deacylation suggests that the p-methyl-substituted acylenzyme is about an order of magnitude more reactive than expected while p-trifluoromethyl substitution results in deacylation at a rate 10 times slower than expected. The remaining substituents exert about the anticipated rate effect on deacylation.
13C Nuclear Magnetic Resonance Studies. 47. 13C Spectra of some exo-Methylenecycloalkanes and -norbornanes
Authors: Grover S. H. , Stothers J. B.
Published: May 2006

The shielding effects of the exo-methylene group on neighboring carbons in several cycloalkanes, methylcyclohexanes, and in the norbornane ring system have been characterized by 13C n. m. r. examination of 28 compounds. The results are compared with those for the carbonyl group and the utility of these data for structural elucidations is discussed. The more distinctive trends exhibited by the methyl carbons in these systems are compared with those for cyclohexanes, cyclohexanones, norbornanes, and norcamphors.
Kinetic Studies of Copper(II)-exchange from L-Histidine to Human Serum Albumin and Diglycyl-L-histidine, a Peptide Mimicking the Copper(II)-transport Site of Albumin
Authors: Lau Show-Jy , Sarkar Bibudhendra
Published: May 2006

The Cu(II)-exchange reactions of L-histidine with human serum albumin and diglycyl-L-histidine were studied at pH 7.53 in 0.1 MN-ethylmorpholine–HCl buffer. The exchange rates from L-histidine to albumin and peptide were determined as 0.67 and 0.42 s−1 respectively. Those from albumin and peptide to L-histidine were obtained as 0.04 and 0.07 s−1 respectively. This result is in accord with the earlier observations of the equilibrium study that the peptide has about half the Cu(II)-binding affinity as compared to albumin. The difference in the Cu(II)-exchange rates of albumin and peptide may reflect the influence of either the COOH-terminal free carboxyl group of the peptide or the side-chain residues of the Cu(II)-binding site in the native protein or both. An exchange mechanism is proposed in which the ternary complexes are shown to play the important role in the rate-determining step in the Cu(II)-exchange between a macromolecule and a small substance.
Spectrophotometric Studies on Sb(III) in Hydrochloric Acid Solutions
Authors: Milne John
Published: May 2006

Ultraviolet spectroscopy confirms the findings of solubility studies that Sb(III) in 3–12 M hydrochloric acid solutions is present as an equilibrium mixture of SbCl4− and SbCl63− ions. In the presence of H2SO4 a further equilibrium with the SbCl3(HSO4)− ion is found. The spectrum of the SbCl63− ion in solution is unlike the diffuse reflectance spectrum of this anion in Co(NH3)6SbCl6 but is similar to that in K3SbCl6. The Raman spectrum of 2 M SbCl3 in 2.8 M hydrochloric acid is shown to be due to the SbCl4− ion and the spectrum is assigned under C2υ symmetry. The Raman spectrum of the SbCl63− ion in solution is discussed.
An Extension of the Hückel 4N + 2 Rule to Polycyclic Non-alternant Conjugated Hydrocarbons
Authors: Kruszewski Jerzy , Krygowski Tadeusz Marek
Published: May 2006

A general rule of aromatic stability of non-alternant polycyclic conjugated hydrocarbons has been detailed and using aromatic stability indices, corroborated. The π-electron system is said to be relatively more stable if the difference between number of 4N + 3-type rings minus number of 4N + 1-type rings is 0 or divisible by 4. If not, the system is assumed to be relatively unstable. The presence of benzene rings does not affect the rule. A further extension for intramolecular H-bonded systems is also suggested. The rule suggested permits prediction of substituent effects on stability as well as the ionic form being most stable if the rule is not fulfilled.
Steric Crowding and the Reactivity of Substituted tert-Butyl Perbenzoates
Authors: Icli Siddick , Kandil Kandil A. , Thankachan C. , Tidwell Thomas T.
Published: May 2006

The relative rates of decomposition of peroxyesters in cumene at 100° and their activation parameters ΔH≠ (kcal/mol) and ΔS≠ (cal deg−1 mol−1) were tert-butyl perbenzoate (1) 1.0, 34.0, 9.3; tert-butyl pertoluate (7) 1.3, 32.2, 4.8; tert-butyl permesitoate (8) 11, 31.9, 8.4; and tert-butyl 2,4,6-tri-tert-butylperbenzoate (9) 29, 32.9, 13.0. Each peroxyester yielded the corresponding acid as one of the products. The reactions are all interpreted as proceeding through a rate-determining scission of the O—O bond to yield a benzoyloxy radical, which then undergoes competitive decarboxylation and hydrogen abstraction from the solvent. The small rate acceleration due to a para substituent is interpreted as due to a polar factor and the larger rate enhancing effect of the ortho substituents is interpreted as due to destabilization of the ground state due to twisting of the carboxyl group out of conjugation with the ring.
β-Carbon Shielding Effects in Carbon-13 Nuclear Magnetic Resonance Spectroscopy
Authors: Beierbeck H. , Saunders J. K.
Published: May 2006

Carbon-13 chemical shifts in saturated hydrocarbons of staggered conformation may be derived from the corresponding resonances in ethane, propane, isobutane, and neopentane in the following way: every H—C—C(α)—C(β) gauche interaction between an α-hydrogen and a 3-carbon deshields a carbon nucleus by ca. 4.7 p.p.m. Every exocyclic carbon–carbon gauche configuration H—C(α)—C—C(α)—C(β)—H has a deshielding effect of ca. 1.7 p.p.m., as the result of nonbonded hydrogen–hydrogen γ-interactions. Every nonbonded interaction between an α-hydrogen and a hydrogen on a γ-carbon makes a shielding contribution of ca.−4.5 p.p.m.
Isotope Effect Studies on Elimination Reactions. X. The Nature of The Transition State for the ECO2 Reaction of Para- substituted Benzyl Nitrates with Base in 90% by Volume Ethanol–Water
Authors: Smith Peter James , Pollock Carol Audrey , Bourns Arthur Newcombe
Published: May 2006

Kinetic isotope effects have been determined for the Eco2 reaction of para-substituted benzyl nitrates with ethoxide in 90 vol.% ethanol–water at 20°. The nitrogen isotope effect, (k14/k15−1)100 decreased with increasing electron-withdrawing ability of the para-substituent; i.e. 2.26, 1.95, 1.60, and 0.84 for p-CH3, p-H, p-CF3, and p-NO2, respectively. Furthermore, the primary hydrogen–deuterium isotope effects increased also for electron-withdrawing substituents; i.e. kH/kD = 5.78, 6.06, 6.40, 6.67, and 7.05 for p-CH3, p-H, p-Br, p-CF3, and p-NO2, respectively. The results are discussed in terms of a recent theoretical treatment dealing with the effect of substituents on the nature of the transition state for a concerted E2 process. The conclusion is reached that any structural change which causes one bond (carbon–hydrogen) to be weakened more at the transition state will have a corresponding effect on the other bond (oxygen–nitrogen).
The Electronic Structure and Localized Molecular Orbitals in S4N4 by the CNDO/BW Theory
Authors: Gopinathan M. S. , Whitehead M. A.
Published: May 2006

The energies calculated for tetranitrogen tetrasulfide, S4N4, by the CNDO/BW theory favor a structure with coplanar nitrogen atoms and not a structure with coplanar sulfur atoms. Both structures have been proposed from experimental studies. Localized molecular orbitals are calculated for S4N4 and used to choose the appropriate Lewis structure for the molecule. The hybridization at the nitrogen and sulfur atoms is discussed. There is electron delocalization in the molecule, the S—N bond is a bent bond involving pure p-orbitals on the sulfur and nitrogen atoms and there is a pure p-bent bond between the sulfur atoms on the same side of the coplanar nitrogen atoms. There is no N—N bond in S4N4.
Tetrafluoro- and Octafluoro[4.2]paracyclophanes
Authors: Filler Robert , Choe Eui W.
Published: May 2006

Synthetic sequences for the preparation of 6,7,9,10,14,15,17,18-octafluoro[4.2]paracyclophane (1) and 6,7,9,10-tetrafluoro[4.2]paracyclophane (2) are outlined. The u.v. absorption of compound 1 is hypsochromically shifted more than 20 nm from the long wavelength band (286–291 nm) characteristic of the [2.2]paracyclophanes.
Reaction of 2,5-Dimethylfuran with Ethyl Propiolate: The Chemistry of Ethyl 1,4-Dimethyl-7-oxabicyclo[2.2.1]hepta-2,5-diene-2-carboxylate
Authors: McCulloch Archibald Wilson , McInnes Alister Gavin
Published: May 2006

Thermal reaction of 2,5-dimethylfuran (1) and ethyl propiolate (2) affords the Diels–Alder adduct (3) and seven additional products, all of which are derived from 3. The major products, depending on the conditions, are the endo-exo 2:1 diadducts (4 and 5) and two nortricyclenes (8 and 10). The last two products arise by homo Diels–Alder type dimerization of 3 (to give 10) and subsequent Diels–Alder retrogression (to give 8). The minor reaction products include a third nortricyclene (9), isomeric with 8.
The Question of σ Participation in the Bonding of Fluorosubstituted Arenes to Chromium Tricarbonyl. A 19F Nuclear Magnetic Resonance Investigation
Authors: Fletcher John L. , McGlinchey Michael J.
Published: May 2006

I9F n.m.r. chemical shifts of free fluoroarenes have been correlated with the Swain–Lupton field and resonance parameters. Comparison of these data with the corresponding Cr(CO)3 complexes shows little change in the transmission of mesomeric effects by para-substituents. Meta-substituents which interact primarily by a field effect have very little influence on the fluorine chemical shift in the complexes suggesting that the σ framework of the ring interacts with the chromium.
Five-coordinate Bromobis(dialkyldithiocarbamate) Complexes of Arsenic, Antimony, and Bismuth
Authors: Manoussakis George E. , Tsipis Constantinos A. , Hadjikostas Christos C.
Published: May 2006

Fifteen bromobis(dialkyldithiocarbamate) complexes of arsenic, antimony, and bismuth have been prepared by reacting the corresponding tris(dialkyldithiocarbamates) with bromine. The structure of these compounds is studied by i.r., n.m.r., and electronic spectra. From the interpretation of the spectroscopic data it is deduced that each dithiocarbamate group acts as a bidentate ligand. The spectral data are discussed and compared to those of the corresponding tris(dialkyldithiocarbamate) complexes.
Electrical Conductivity and Phase Transformation Studies on Pure and Doped (Mg2+, Zn2+, Cu2+, and Mn2+) Crystals of K2SO4
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

Electrical conductivity measurements have been made on single crystals of undoped potassium sulfate and on single crystals of K2SO4 doped with divalent ions, viz. Mg2+, Zn2+, Cu2+, and Mn2+. The presence of the divalent ion increases the cation migration energy. The lower defect formation energy is attributed to the lower symmetry of K2SO4 relative to the high symmetry cubic systems previously studied.The presence of the dopants and dopant concentration, i.e. Cu2+, show varying effects on the magnitude and nature of the conductivity discontinuity at the orthorhombic–hexagonal phase transition temperature. The phenomenon of "pretransition", 350 to 425 °C, is observed in both pure and doped crystals. Preannealing the crystal contributes to interesting behavior on all the crystals studied. The σ–T behavior of K2SO4 crystal doped with radioactive 65Zn, however, exhibits a simpler linear dependence and the absence of "pretransition" anomaly.
Nitration of 3,4-Dimethylacetophenone and 3,4-Dimethylbenzophenone. Formation and Rearomatization of Adducts
Authors: Fischer Alfred , Greig Colin Campbell , Röderer Rolf
Published: May 2006

Nitration of 3,4-dimethylacetophenone in acetic anhydride gives a mixture of cis-and trans-2-acetyl-4,5-dimethyl-4-nitro-1,4-dihydrophenyl acetate as the main product, together with 3,4-dimethyl-2-, 3,4-dimethyl-5-, and 3,4-dimethyl-6-nitroacetophenone. Analogous products are obtained from 3,4-dimethylbenzophenone. Rearomatization of the adducts under mildly acidic conditions occurs via 1,4-elimination of nitrous acid to form 2-acetyl- and 2-benzoyl-4,5-dimethylphenyl acetate, respectively. In strongly acidic conditions elimination of acetic acid accompanied by 1,2- and 1,3-shifts of the nitro group occurs to form the 2- and 5-nitro derivatives of the parent ketones. The rearomatization to the nitro derivatives involves the intermediate formation of an ipso-cyclohexadienyl cation which may be trapped by anisole or mesitylene to form biphenyl derivatives.
The Stereochemistry of Some Organic Derivatives of Group Vb Elements. Part X. The Crystal and Molecular Structure of Triphenylarsenic Difluoride
Authors: Augustine Ann , Ferguson George , March Frank C.
Published: May 2006

The crystal structure of triphenylarsenic difluoride has been determined from three-dimensional X-ray diffractometer data. Crystals of Ph3AsF2 are orthorhombic, space group Pbcn, with four molecules of C18H15AsF2 in a unit cell of dimensions a = 6.270, b = 16.593, c = 14.519 Å; molecular symmetry C2 is required. The structure was solved by the heavy atom method and refined by full-matrix least-squares calculations to a final residual R of 0.054 for 979 intensities regarded as "observed" (I > 3σ(I)). The crystals contain well separated discrete molecules. The arsenic atom has near regular trigonal bipyramidal geometry with apical fluorine atoms (As—F 1.834(7) Å) and equatorial phenyl rings (mean As—C 1.925(5) Å). Idealized D3 symmetry is not achieved because of unequal rotations of the phenyl rings about the As—C bonds.
Polar Substituents in Pericyclic Reactions: Mechanistic Course of the 2π + 2π Photocycloaddition of Dimethyl 1,4-Dihydro-1,4-ethenonaphthalene-2,3-dicarboxylate
Authors: Bender Christopher Owen , Brooks Dee Winton
Published: May 2006

Deuterium labeling studies are consistent with the initial photochemical 2π + 2π closure of singlet excited dimethyl 1,4-dihydro-1,4-ethenonaphthalene-2,3-dicarboxylate (4) proceeding via bridging between the vinyl and vinyl diester moieties and not via the vinyl–benzo bridging mode favored by Grovenstein and by the Epiotis polar pericyclic theory. The possible involvement of the charge-transfer excited state of 4 in the reaction is discussed.
Complexes of Dimethylaminophosphazenes with Metal Ions
Authors: Calhoun H. P. , Paddock N. L. , Wingfield J. N.
Published: May 2006

The preparation of complexes DDPN.2MCl2 (M = Mn, Fe, Co, Zn ), DDPN.M(NO3)2, (M = Mn, Co, Ni, Cu, Zn), (DDPN = N6P6(NMe2)12) ), and N9P9(NMe2)18.2CoCl2 is described. All the complexes of the hexamer are of the high spin type and contain the cations DDPNMX+ (X = Cl, NO3 ). Their infrared and electronic spectra show that their molecular structures are essentially the same as those established crystallographically for the chlorocations (M = Co, Cu ), in which, as a consequence of steric interactions, the metal has a distorted trigonal-bipyramidal environment. The complex with Cu(NO3)2 is exceptional in that the DDPNCu2+ ion is formed in ionizing solvents, with a change in the stereochemistry of the metal. Coordination localizes π-electrons in nitrogen, weakens the ring bonds, and strengthens the exocyclic P—N bonds, as expected theoretically. Approximate values of ligand field parameters of the Co(NO3)2 and Ni(NO3)2 complexes are similar to those of complexes formed by simple amines; the phosphazenes act as σ-donors, their acceptor levels not being used significantly.
L'effet de la longueur de la chaîne et du pH sur la conformation de polyampholytes alternés du type (L-lysyl-L-aspartyl)n
Authors: Daoust Hubert , St-Pierre Serge
Published: May 2006

The synthesis of alternating (L-lysyl-L-aspartyl)n co-oligopeptides (n = 4–10 ) was realized by the solid phase method, to study the effect of chain length and pH on the conformation of polyampholytes in aqueous solution. The c.d. spectra do not show as important a dependance on pH and chain length as those observed with the nonampholytic homooligoelectrolytes. Our results suggest that the peptides are globular in shape when the pH of the solution is close to the isoelectric point but are extended in strong acid and base solutions.
Reversible Inhibition of Carboxypeptidase A. III. Inhibition of Specific Esterase Activity by Substituted Benzoate and Related Anions
Authors: Bunting John W. , Myers Chester D.
Published: May 2006

The reversible inhibition of the hydrolysis of O-hippuryl-L-3-phenyllactic acid by bovine carboxypeptidase A, has been studied for a series of para-substituted benzoate ions (p-XC6H4-CO2−) at pH 7.5, 25°, ionic strength 0.2. For X = H, F, CN, NH2, CH3 competitive inhibition occurs, whereas non-competitive inhibition occurs for X = CF3, NO2, Cl, Br, (CH3)2N, CH3O, (CH3)2CH, (CH3)3C. For X = C2H5 mixed inhibition is observed and this can be separated into individual competitive and noncompetitive components. Uncompetitive inhibition occurs with X = I. The distinction between competitive and noncompetitive inhibition appears to depend on the size of X rather than on its chemical properties. The p-tolylacetate and 3-(p-tolyl)propanoate ions display partially competitive inhibition consistent with the formation of E.I2 species. The inhibition by the 3-(p-iodophenyl)propanoate ion is complex and depends on the binding of at least two inhibitor ions per enzyme molecule.
Phosphorescence Lifetime of S02 in the ã3B1 State at Low Pressure
Authors: Briggs J. Philip , Caton Robert B. , Smith Michael J.
Published: May 2006

The emission decay rate (inverse lifetime) of the optically-excited ã3B1 electronic state of SO2 vapor at approximately 25 °C has been measured in a 35 cm diameter spherical container over the pressure range 1 < P < 500 m Torr in pure SO2 and in mixtures of SO2 with He, Ar, or Xe. The Stern–Volmer rate constant for quenching by [Formula: see text]was determined to be (4.46 ± 0.11) × 108 1 mol−1 s−1, and the extrapolated, zero-pressure decay rate was calculated to be (3.75 ± 0.58) × 102 s−1. The latter quantity implies a considerably greater proportionate contribution by radiative, as opposed to nonradiative, relaxation of this state than has been reported previously.
Palladium(II) Catalyzed Exchange Reactions. XI. Vinyl Propionate Exchange with Acetic Acid Catalyzed by Palladium(II) Acetate
Authors: Pandey Raj N. , Henry Patrick M.
Published: May 2006

The kinetics of the palladium(II) acetate catalyzed exchange of vinyl propionate with acetic acid solvent to give vinyl acetate has been studied in the sodium acetate concentration range from 0 to 1 M. The exchange rate first sharply increases as [NaOAc] increases, reaches a maximum at about 0.2 M and then gradually decreases as the sodium acetate concentration is in-creased to 1.0 M. Using previous results on the equilibrium between palladium(II) acetate and sodium acetate in acetic acid it can be shown that the rate expression for exchange is: rate = (ko + kt[Pd3(OAc)6] + kd[Na2Pd2(OAc)6]) [CH2=CHO2CC2H5] where ko = 2 × 10−4 s−1, kt = 0.045 M−1 s−1, and kd = 0.089 M−1 s−1. A monomeric palladium(II) species, Na2Pd(OAc)4, formed at high [NaOAc] is unreactive. Since the rate expression does not contain a term in [NaOAc], the sodium acetate serves only to convert one palladium(II) species to another. The lack of a [NaOAc] term in the rate expression for the Na2Pd2(OAc)6 catalyzed reaction is believed to result from cancellation of an inhibitory term for π-complex formation by a catalytic term in [NaOAc] in the rate determining conversion of π -complex to σ-complex (acetoxypalladation). Stereochemical studies indicate that acetoxypalladation is nonstereospecific. This result is expected since in the chloride free system acetate is both a ligand and a reactant. Thus it can attack from both inside and outside the coordination sphere of Pd(II).
3,4-Dihydro-2H-1,5-benzodioxepins. A Novel Class of β-Adrenergic Stimulants
Authors: Rooney C. S. , Stuart R. S. , Wasson B. K. , Williams H. W. R.
Published: May 2006

A series of 3-substituted-aminomethy1-3-hydroxy-3,4-dihydro-2H-1,5-benzodioxepins is described. Members of the series constitute a unique class of β-adrenergic stimulants and possess interesting bronchial dilator activity.
Models for the Role of Magnesium in Enzymic Catalysis. The Effect of Magnesium Ion on the General Base Catalyzed Enolization of Methyl Acetonylphosphonate
Authors: Kluger Ronald , Wayda Andrea
Published: May 2006

Magnesium ion promotes the general base catalyzed iodination of methyl acetonylphosphonate (MAP), 1. Although the concentration of complex is very low, definite rate constant increases are observed. The rate determining step under the experimental conditions is enolization of the substrate. Acceleration is observed for both charged and uncharged bases. The acceleration for charged bases is about twice that for uncharged bases. Thus, electrostatic effects are probably important but not exclusive. It is proposed that efficient catalysis by magnesium ion in related enzymic reactions is a consequence of the ability of magnesium ion to form a stabilizing complex with an enolate-like transition state and to reduce repulsive electrostatic interactions of the substrate and a catalytic base.
Semi-empirical Calculations on the Free Energy and Enthalpy of Hydration for the Trivalent Lanthanides and Actinides
Authors: Goldman Saul , Morss Lester R.
Published: May 2006

An electrostatic hydration model, that had previously been developed for ions of the noble–gas structure, was applied to the trivalent lanthanide and trivalent actinide ions. For the trivalent lanthanides it was found that a single primary hydration number resulted in a satisfactory fit of the model to the experimental free energy and enthalpy data. Subsequently, the model was applied to the trivalent actinide ions with a view to predicting values for the free energy and enthalpy of hydration for this series. A primary hydration number for the actinide series was determined by fitting the model to existing experimental enthalpy data for Pu3+. The predictions for this series were found to compare favorably with the few experimental and estimated values that exist.
Free Ion Yields and Electron Ranges in X Irradiated Simple Liquids: Unusual Behavior in Carbon Dioxide and Carbon Disulfide
Authors: Sambrook Terance E. M. , Freeman Gordon R.
Published: May 2006

The radiolysis free ion yields Gfi0 and electron penetration ranges bGP in the liquids carbon dioxide and carbon disulfide are much larger than would be predicted by extrapolation from earlier studies of unsaturated hydrocarbons. In the isoelectronic, nonpolar compounds carbon dioxide and propadiene at 212 ± 4 K Gfi0 = 0.19 and 0.022, respectively, with bGP = 116 and 37 Å. In carbon disulfide Gfi0 = 0.44 ± 0.02, independent of temperature over the range 169 to 354 K; the electron penetration range appears to increase with decreasing temperature in this liquid. In the unsymmetrical, polar compound carbonyl sulfide, Gfi0 = 0.089 and bGP = 37 Å at 214 K; the behavior is similar to that in ethers.
Analyse en résonance magnétique nucléaire du 1H et du 13C de dérivés azuléniques extraits de l'Eriocephalaepunctulactus
Authors: Llinas J.-R. , Roard D. , Derbesy M. , Vincent E.-J.
Published: May 2006

Two azulene compounds were isolated from the extract of Eriocephalaepunctulactus; their structures were determined unambiguously by n.m.r. as those of 1,4-dimethylazulene and 1,4-dimethyl-7-ethylazulene. These structures were confirmed by 13C n.m.r. The effects of substitution in the azulene ring on the 13C n.m.r. spectra were demonstrated using these compounds as well as guaiazulene (l,4-dimethyl-7-isopropylazulene). [Journal translation]
Relation between van der Waals and Partial Molal Volumes of Organic Molecules in Water
Authors: Edward John T. , Farrell Patrick G.
Published: May 2006

The partial molal volumes [Formula: see text] of nonpolar organic molecules (i.e. those having more than three aliphatic carbon atoms per polar hydroxyl, ether, amine, amide, or urea group) in water at 25 °C are given by their van der Waals volumes υw plus the additional empty volume provided by an enclosing shell 0.53 Å thick. An equation relates [Formula: see text] to υw More polar compounds (i.e. those having fewer than two or three aliphatic carbon atoms per polar group) have [Formula: see text] smaller than calculated by the equation; the shrinkage in [Formula: see text] from that computed is linearly related to the fraction of the total surface area of the molecule occupied by the polar group.
Photoreaction of Nitroso Compounds in Solution. Part XXXI. Mechanisms of Intramolecular Acid Catalyzed Cleavage Reactions and a Hydride Initiated Rearrangement of C-Nitroso Alkanes
Authors: Pillay K. Somosekharen , Chen Shi C. , Mojelsky Thomas , Chow Yuan L.
Published: May 2006

Two novel rearrangements of nitroso alkanes, one intramolecular acid catalyzed cleavage reaction and the other ring enlargement during hydride reduction, are described. Aminium radical initiated addition to norbornene under nitrogen gave cis-exo- and trans-2-nitroso-3-ammonium norbornanes in a good yield. Whereas the trans isomer underwent the usual nitroso group reactions, i.e., tautomerization, dimerization, and HNO addition, the cis-exo isomer and its hydroxy analog cleaved extremely readily to give 1,3-bisformylcyclopentane derivatives. The stereoelectronic driving force in this cleavage is interpreted as the intramolecular proton transfer and the electron reorganization via a cyclic transition state. Metal hydride reduction of the trans isomer was accompanied by ejection of the neighboring amino group and an expansion of the ring to form an azabicyclic compound. A sequence involving an intramolecular displacement to form aziridine followed by the reductive cleavage is proposed.
The Radical Ion S3N2+. Preparation, Electron Spin Resonance Spectrum, and Crystal Structure of Thiodithiazyl Hexafluoroarsenate S3N2+AsF6−
Authors: Gillespie R. J. , Ireland P. R. , Vekris J. E.
Published: May 2006

The compound S3N2+AsF6− has been prepared by the reaction of S4N4 with AsF5. The crystal structure has been determined from three-dimensional X-ray counter data. Crystals are monoclinic, space group P21/c with a = 8.499(4), b = 8.298(4), c = 11.069(8), β = 94.59(5), V = 778.1 Å3, Z = 4, and Dc = 2.67 g cm−3. The structure was solved by Patterson methods and refined to a conventional R factor of 0.028 for 798 independent reflections with I ≥ 3σ(I). The structure consists of discrete AsF6− ions and planar cyclic S3N2+ ions. Solutions of S3N2+AsF6− in methylene chloride gave a five-line electron spin resonance spectrum with an intensity ratio of 1:2:3:2:1 showing that the unpaired electron in S3N2+ is coupled to two equivalent nitrogen atoms in full accord with the results of the crystal structure determination.
On the Mechanism of Oxetan Formation in the Photocycloaddition of p-Benzoquinone to Alkenes
Authors: Bunce Nigel J. , Hadley Mary
Published: May 2006

Photochemical oxetan formation from p-benzoquinone and simple alkenes takes place from the lowest 3n,π* state of the quinone. It is suggested that an exciplex is formed between the alkene and the excited quinone, but that a biradical is nevertheless the immediate precursor of the oxetan.
Kinetics and Mechanism of the Oxidation of Thiocyanate by Tris(1,10-phenanthroline)iron(III) and its Derivatives
Authors: Ng Flora T. T. , Henry Patrick M.
Published: May 2006

Oxidation of thiocyanate by tris(1,10-phenanthroline)Fe(III) to give cyanide and sulfate ions was studied at 25 °C in both H2SO4 and HClO4 media. The rate of oxidation showed a first order dependence on the Fe(III) complex and a second order dependence on potassium thiocyanate at ≥ 4.0 × 10−4 M potassium thiocyanate. The value of kobs decreased with increasing [H+]. This acid inhibition is consistent with the protonation of SCN− to give an inactive HSCN species. A mechanism consistent with the data involved an initial equilibrium formation of [Fephen3SCN]2+ which subsequently undergoes an outer-sphere electron transfer with SCN− to eventually give Fe(II)phen3, CN−, and SO42−. Similar kinetic behavior was found with the substituted tris(1,10-phenanthroline)Fe(III) complexes. The value of the third order rate constant was found to increase with the increase in the reduction potential of the complexes. This result indicates a direct dependence of the standard free energy of the reaction and the free energy of activation.
The Structure of Acetaldehyde Enolate Anion
Authors: Wolfe Saul , Schlegel H. Bernhard , Csizmadia Imre G. , Bernardi Fernando
Published: May 2006

Non-empirical SCF–MO computations have been performed on [CH2CHO]−, the simplest enolate anion. Following a preliminary search of the conformational hypersurface using an STO-3G basis set to determine the C—C and C—O bond lengths as a function of rotation about the C—C bond, the rotation–inversion surface has been generated with an STO-4G basis set. The energy minimum of this surface is the all-planar anion whose C—C and C—O bond lengths are entirely compatible with the usual description [Formula: see text] The planar structure results from extensive conjugative stabilization amounting to over 30 kcal/mol (based on the C—C rotational barrier). When the CH2 plane is perpendicular to the CHO plane, the conjugative interaction is symmetry forbidden and the electron-withdrawing inductive effect of the formyl substituent leads to a pyramidal carbanion. Experimental implications of these results are discussed.
Kinetic Study of the Reaction between Substituted Triphenylmethyl Perchlorates with Pyridines in Nitromethane and 1,2-Dichloroethane Solvents
Authors: Kim Chang B. , Leffek Kenneth T.
Published: May 2006

Second-order rate constants at 25 °C have been measured for the reaction of triphenylmethyl carbonium ion with pyridine and substituted pyridines in nitromethane and 1,2-dichloroethane solvent. The activation parameters are in the range 1 to 3 kcal mol−1 for the enthalpies of activation and −20 to −45 cal mol−1 deg−1 for the entropies of activation. The results are compared to the analogous measurements for Menschutkin reactions and it is concluded that the enthalpy of activation of a Menschutkin reaction results mainly from the bond breaking process and solvation changes associated with it, since the carbon-nitrogen bond making process seems to be entropy controlled.Rate measurements have also been made for 2-methylpyridine reacting with a series of para-substituted triphenylmethyl carbonium ion substrates in 1,2-dichloroethane solvent. A plot of log k2vs ∑σ+ is non-linear and the curvature is interpreted as a saturation effect.
Sur la structure cristalline des dimethyl-1,1 germa-1 (et sila-1) cycloundécanediols-6,7
Authors: Brisse François , Battat Aviva , Richer Jean-Claude , Mazerolles Pierre , Faucher Alfreda
Published: May 2006

1,1-Dimethyl-1-germa (and-1-sila) -6,7-cycloundecanediol (C12H26O2Ge and C12H26O2Si) are isostructural as established by their X-ray powder patterns. The dimensions of the triclinic cells are as follows: for the silicon derivative, a = 10.53, b = 12.45, and c = 12.43 Å, α = 81.5°, β = 67.0°, and γ = 76.3°; for the germanium derivative, a = 10.56, b = 12.50, and c = 12.58 Å, α = 82.1°, β = 67.8°, and γ = 76.1°. If the space group is [Formula: see text] there will be two independent molecules in each asymmetric unit.
Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids
Authors: Krygowski T. M. , Fawcett W. R.
Published: May 2006

Separation of the substituent effect ρσ into entropie ρSσS and enthalpic ρHσH contributions is presented within the framework of the general Hammett equation. Analysis of the experimental data for aromatic acids shows that, in general, entropie effects are the major contribution to the total substituent effect, the entropic reaction constant being approximately equal to the normal Hammett ρ A comparison of the present results with those based on a separation of inductive and resonance effects shows that the entropie and inductive effects are directly related. On the other hand, strongly resonance interacting substituents were found to be enthalpy controlled. The substituent effect on enthalpy and entropy changes is discussed from a molecular point of view and related to inductive and resonance effects. A list of 16 enthalpic (σH) and entropie (σS) substituent constants are presented.
Direct Specific Heat Measurements on Solutions of Volatile Solutes by Flow Microcalorimetry: Partial Molal Heat Capacity of Benzene in Water at 25 °C
Authors: Jolicoeur Carmel , Picker Patrick , Perron Gérald
Published: May 2006

The direct specific heat measurement on aqueous benzene solutions by flow microcalorimetry have been repeated to elucidate discrepancies among earlier results. Through extensive variations of experimental conditions, the origin of difficulties encountered previously has been investigated and a simple procedure has been devised to circumvent problems inherent to this particular type of measurements.
A Systematic abinitio LCAO–MO–SCF Study of the Ionization Potentials, Electron, Proton, Hydrogen, and Hydride Affinities of SHn Molecules and Ions
Authors: Kari Roy E. , Csizmadia Imre G.A
Published: May 2006

Equilibrium geometries and energies are obtained for SHn (n = 0, 1, 2, 3) neutral and charged species by the Roothaan LCAO–MO–SCF method. A large gaussian basis set including d and p polarization functions was employed. The calculated ionization potentials, electron, proton, hydrogen, and hydride affinities are discussed as well as compared with similar previously calculated properties for OHn (n = 0, 1, 2, 3) species.
The Distribution of Oxidation States of Iodine Isotopes in the Fission by Protons of Natural Uranium
Authors: Dikšić M. , Yaffe L.
Published: May 2006

Oxidation states of iodine, produced in the fission of uranium by protons of energies 30 and 80 MeV in solid matrices of UO2(NO3)2.6H2O and UO2SO4.3H2O, have been studied. No proton energy dependence was found. The percentage distribution of I7+ as (IO4)− is independent of the matrix. However I5+ (as IO3−) is enriched at the expense of the reduced state (I2° + I−) due to oxidation by the (NO3)− formed by the radiation decomposition of UO2(NO3)2.6H2O. Formation of the nuclide by isomeric decay does not perturb the distribution. The result of β−decay is to increase the I7+ component. Iodine isotopes formed independently in fission have the same distribution of oxidation states, but not unique enough to serve as a measure of this mode of formation.
Muscle cell survival mediated by the transcriptional coactivators p300 and PCAF displays different requirements for acetyltransferase activity
Authors: Kuninger David , Wright Alistair , Rotwein Peter
Published: May 2006

Normal skeletal muscle development requires the proper orchestration of genetic programs by myogenic regulatory factors (MRFs). The actions of the MRF protein MyoD are enhanced by the transcriptional coactivators p300 and the p300/CBP-associated factor (PCAF). We previously described C2 skeletal myoblasts lacking expression of insulin-like growth factor-II (IGF-II) that underwent progressive apoptotic death when incubated in differentiation-promoting medium. Viability of these cells was sustained by addition of IGF analogs or unrelated peptide growth factors. We now show that p300 or PCAF maintains myoblast viability as effectively as added growth factors through mechanisms requiring the acetyltransferase activity of PCAF but not of p300. The actions of p300 to promote cell survival were not secondary to increased expression of known MyoD targets, as evidenced by results of gene microarray experiments, but rather appeared to be mediated by induction of other genes, including fibroblast growth factor-1 (FGF-1). Conditioned culture medium from cells expressing p300 increased myoblast viability, and this was blocked by pharmacological inhibition of FGF receptors. Our results define a role for p300 in promoting cell survival, which is independent of its acetyltransferase activity and acts at least in part through FGF-1.
Freedom of Contract: What Does it Mean in the Context of Arab Laws?
Authors:   Saleh
Published: May 2006

No Abstract