bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyrochlores. IX. Partially Oxidized Sn2Nb2O7 and Sn2Ta2O7: A Mössbauer Study of Sn(II,IV) Compounds
Authors: Stewart David J. , Knop Osvald , Meads Roy E. , Parker William G.
Published: May 2006

Partially oxidized tin(II) niobate and tantalate pyrochlores are homogeneous cubic phases. They have been shown by Mössbauer 119Sn spectroscopy to contain both Sn(II) and Sn(IV). Each valency state is segregated on its own, crystallographically distinct sublattice as a consequence of the size disparity of Sn2+ and Sn4+ atoms. The strong temperature dependence of the Mössbauer Sn2+:Sn4+ area ratios between room temperature and 4.2 °K indicates that the recoil-free fractions of the Sn2+ and Sn4+ atoms in these structures are noticeably different. The values of the recoil-free fractions at 0 °K, which were estimated from simple Einstein and Debye models, were used to obtain Sn2+:Sn4+ population ratios from the Mössbauer area ratios extrapolated to 0 °K. The area ratios were shown to differ from the population ratios by 15–20% at 0 °K and by as much as 70% at room temperature. The formulae of the two nonstoichiometric pyrochlores based on the population ratios are Sn2−2u2+(Snu4+B2−u5+)O7−(5/2)u (B = Nb, Ta; u = 0.18–0.20). These formulae are consistent with chemical and other evidence. Mössbauer parameters and the limitations of using a Mössbauer area ratio to determine the Sn2+:Sn4+ population ratio in Sn(II,IV) compounds are discussed.
Low Temperature Infrared Study of Hydrogen Bonding in Dissolved Pyrrole and Indole
Authors: Bernard-Houplain Marie-Claude , Sandorfy C.
Published: May 2006

Self-association by hydrogen bonding in the case ot pyrrole was studied by i.r. spectroscopic methods. The fundamental first and second overtones of the NH stretching vibration were measured at different concentrations and at temperatures ranging from 22 to −190 °C. The existence of at least two associated species in solution has been ascertained. 2,5-Dimethylpyrrole and indole were also studied and gave similar results.
On the Bond Order between Atoms in Approximate SCF-MO Theory
Authors: Boyd R. J.
Published: May 2006

The bond order between two atoms is discussed within the framework of all-valence-electron SCF-MO theories based on the Zero-Differential Overlap Approximation, and a definition of the bond order is proposed which is analogous to the procedure used to extract charge distributions from approximate SCF-MO calculations. Bond orders are calculated for a variety of small molecules and relationships similar to those found in π-electron theory between bond lengths and bond orders are observed. CNDO wave functions are used in this work, although the definition may also be used for calculations based on the INDO and NDDO approximations.
The Infrared Spectrum of Ethylene Oxide Clathrate Hydrate at 100°K between 4000 and 360 cm−1
Authors: Bertie John E. , Othen David. A.
Published: May 2006

The infrared spectra of characterized samples of ethylene oxide hydrate made from 100% H2O, 99.7% D2O, and several dilute isotopic solutions, are presented between 4000 and 360 cm−1. The similarity between the absorption by the water molecules in the hydrate and in ice I is discussed. The frequency and halfwidth of the OH and OD stretching modes of isolated HDO molecules in the hydrate are related to those in the disordered ice phases; the frequencies correlate rather well with the weighted-mean hydrogen bond lengths in these phases.The ethylene oxide vibrations show sharp, single-line absorption. The only exceptions are the ring-breathing mode which appears as a doublet, separated by 2 cm−1, with much weaker absorption about 13 cm−1 away on either side, and the ring deformation modes which interact with the vR(H2O) modes. The possible causes of this behavior are discussed, but no firm conclusions can be drawn. The sharpness of the absorption by enclathrated ethylene oxide, compared to that by liquid ethylene oxide, is briefly discussed in the light of modern theories of bandshapes in liquids.
On the Mechanism of Ring Inversion in Cycloheptene and Its Derivatives
Authors: St-Jacques Maurice , Vaziri Cambyse
Published: May 2006

Free energy barriers to ring inversion of 3,3-dimethyl-, 4,4-dimethyl-, and 5,5-dimethylcycloheptene were found to be much smaller than those of corresponding benzocycloheptene derivatives but show the same trend. This observation strongly suggests that the chair conformation of both types of molecules inter-converts through the same mechanism. On the other hand, the ΔG≠ value for 4,4,6,6-tetramethyl-cycloheptene is about 3 kcal/mol out of line from that expected from a consideration of the behavior of the corresponding benzocycloheptene derivative. An explanation is offered.
Studies of the Carbonyl Group in Some Five-membered Ring Compounds by Photoelectron Spectroscopy
Authors: Bain A. D. , Frost D. C.
Published: May 2006

A study has been made of the ionization potentials (IP) of the carbonyl lone pair orbitals in a series of five-membered carbonyl ring compounds. CNDO/2 and INDO calculations have been performed on these molecules, and correlation of IP shifts with changes in molecular bonding is obtained.
The Reaction of CH3+ with D2
Authors: Harrison Alex. G. , Keyes Bernard G.
Published: May 2006

The exchange reaction between CH3+ and D2 leading to CH2D+ and CHD2+ is shown to proceed through a collision complex in which the hydrogens and deuteriums become equivalent. The rate coefficient for reaction of CH3+ with D2 is 6.1 ± 0.1 × 10−10 cm3 molecule−1 s−1.
Constituents of Solidago Species. Part V. Non-acidic Diterpenoids from Solidago gigantea var. serotina
Authors: Henderson M. S. , McCrindle R. , McMaster D.
Published: May 2006

Eight new furan-containing diterpenoids from Solidago gigantea Ait. var. serotina (Kuntze) Cronqu., are formulated as 1c–g, 2, 3a, and 4a on the basis of chemical and spectroscopic evidence and by correlation with solidagoic acid A of previously defined constitution and stereochemistry. The structure (5a) of a ninth related compound is tentatively assigned. The allylic oxidation of some of these new diterpenoids and related compounds with the chromium trioxide – pyridine complex is reported. In the course of this investigation of formal total synthesis of compound Y from Leonotis leonurus was achieved.
Reactions of Thiyl Radicals. XI. Further Investigations of Thiol–Disulfide Photolyses in the Liquid Phase
Authors: Carlson Donna D. , Knight Arthur R.
Published: May 2006

The photolysis of C2H5SH liquid at 2537 Å has been shown to give H2 and C2H5SSC2H5 at equal rates with a quantum yield of 0.25. The photolysis of ethanethiol – methyl disulfide liquid mixtures leads, via a chain reaction involving propagation by attack of thiyl radicals on the disulfide S—S bond, to the formation with high quantum efficiency of CH3SH, C2H5SSC2H5 and, as an intermediate that is consumed after long exposures, CH3SSC2H5. The net result of the sequence of exchange processes is the essentially irreversible conversion of the methyl disulfide into methanethiol. The same overall reaction occurs thermally at room temperature, but the rate is appreciably less than that of the photochemical process. The quantum yields of formation of the unsymmetrical disulfides arising from the photochemically initiated exchange reaction in equimolar mixtures of CH3SSCH3 + n-C3H7SSC3H7 and C2H5SSC2H5 + n-C3H7SSC3H7 have been shown to be 6.9 and 4.4, compared to 355 for CH3-SSCH3 + C2H5SSC2H5 mixtures. In all three types of system examined in this investigation all thiyl radicals can be accounted for stoichiometrically on the basis of exchange and combination reactions alone, indicating negligible disproportionation of these species in condensed phase.
Chemistry of Metal Hydrides. XIV. Insertion Reactions of an Iridium(III) Hydride
Authors: Clark H. C. , Mittal R. K.
Published: May 2006

The iridium(III) hydride, IrHCl2 {P(C2H5)3}3, gave 1:1 insertion products with perfluoropropene and 3,3,3-trifluoropropyne containing two and three phosphines per iridium respectively. With tetrafluoroethylene, or 1,1-difluoroethylene a simple fluorine – hydridic hydrogen exchange reaction appears to occur. An unusual tricyanovinylic derivative is obtained as a major product of the reaction with tetracyanoethylene, while dimethylacetylene dicarboxylate gave an interesting product containing two acetylene molecules per molecule of hydride. This is formulated as the π-acetylenic complex of the vinylic insertion product. The importance of ligand dissociation in these insertion processes is discussed.
The Infrared Spectrum of the Hydrogen-Bonded Molecule Dimethyl Ether … Hydrogen Chloride in the Gas Phase
Authors: Bertie John E. , Falk M. Victor
Published: May 2006

A detailed study of the infrared spectra of (CH3)2O … HCl and its isotopic modifications is presented. The hydrogen-bond stretching mode occurs at 119 ± 4 cm−1 in (CH3)2O … HCl, (CD3)2O … HCl, and (CH3)2O … DCl. The O … H—Cl deformation modes yield a band centered at 470 cm−1, which is broad and complex. It is interpreted in terms of sum and difference transitions involving the HCl rocking modes, which are deduced to be at about 50 cm−1. The O … D—Cl deformation band is centered at 360 cm−1. A band at 790 cm−1 in (CH3)2O … HCl and 600 cm−1 in (CH3)2O … DCl is assigned to the overtone of the deformation modes. The shapes of the bands due to the ethereal modes in the molecule can not indicate the molecular geometry and do not agree with the shapes calculated from reasonable moments of inertia. The temperature dependence of the band due to the HCl stretching mode indicates that the fundamental transition is at 2480 cm−1, not at 2574 cm−1 as previously postulated. The DCl stretching band in (CH3)2O … DCl has a different shape to that in (CD3)2O … DCl. The differences are attributed to combination transitions involving the ethereal modes. It is suggested that the DCl and HCl stretching modes interact with the DCl or HCl rocking modes, thus causing shoulders 50 cm−1 away from the DCl stretching fundamental, and contributing to the general diffuseness of the HCl stretching band. The relative intensities of the bands due to (CH3)2O … HCl are presented.
Allene Oxide Intermediates: Vinylidene Carbene Addition to Carbonyl Compounds
Authors: Kuo Yu-Neng , Nye Martin J.
Published: May 2006

Solutions of fluorenylidene carbene (10) have been generated by treatment of 9-(aminomethylene)-fluorene (9) with n-butyl nitrite. This vinylidene carbene forms a 1:1 adduct with azobenzene, and with acetone pivaldehyde and tolualdehyde it forms 1:2 adducts containing the 5-fluorenylidene-1,3-dioxolane ring system. Evidence for the intermediacy of an allene oxide (3) is presented.
Vinyl Azides as Diazoenamines
Authors: Thakore A. N. , Buchshriber J. , Oehlschlager A. C.
Published: May 2006

Reaction of vinyl azides with nitrosyl tetrafluoroborate yields 1,2,5-oxadiazoles and 1,2,4-oxadiazoles depending on the structure of the azide. Reaction of 1,2-dialkyl vinyl azides with nitryl tetrafluoroborate gives 2-oxo-1,2,5-oxadiazoles in high yields whereas 1-aryl-2-alkyl vinyl azides gave moderate yields of 3-aryl-1,2,5-oxadiazoles and 5-aryl-1,2,4-oxadiazoles. Acyl chlorides condense with vinyl azides in the presence of aluminum chloride to yield oxazoles. Dimethyl acetylenedicarboxylate condenses with vinyl azides by cycloaddition of the azido function with the alkyne and by cycloaddition of the vinyl group with the alkyne. The latter process occurs only under the influence of AlCl3. The observed reactions are viewed as involving the participation of vinyl azides as N-diazoenamines.
Oxidation of Some Transition-Metal Cyanide Compounds by Hydroxyl Radical
Authors: Waltz W. L. , Akhtar S. S. , Eager R. L.
Published: May 2006

The oxidation of some transition-metal cyanide compounds by hydroxyl radical in aqueous media has been investigated by pulse radiolysis. For compounds of the type, M(CN)64− where M is Fe, Ru, and Os, and for Mo(CN)84−, the mechanism of their reaction with hydroxyl radical involves single electron transfer with the formation of the intensely colored metal complexes of the same stoichiometry as the starting materials. The u.v.–visible absorption spectra for these products for the iron, ruthenium, and osmium systems are reported along with the associated second order rate constants for their formation. The reaction of Mo(CN)84− with hydroxyl radical has been studied by a competition technique using sodium bicarbonate. The values of the second order rate constants are near those expected of diffusion-controlled reactions and they range between ca. 5 × 109 to 1 × 1010 M−1 s−1.
Total Synthesis of (±)-Trachylobane, a Pentacyclic Diterpenoid with a Tricyclooctane System
Authors: Kelly R. B. , Eber J. , Hung H. K.
Published: May 2006

A total synthesis of (±)-trachylobane, a pentacyclic diterpenoid possessing a tricyclo[3.2.1.02,7]octane system, is described. Completion of the synthesis of trachylobane confirms the validity of the structure assigned to this diterpenoid and provides corroboration of structures assigned to diterpenoids from which it has been obtained as a conversion product.
Binary Mixed Dinitrogen–Carbonyl Complexes of Nickel(0), Ni(N2)m(CO)4−m (where m = 1–3)
Authors: Kündig E. P. , Moskovits M. , Ozin G. A.
Published: May 2006

Nickel atoms have been cocondensed in various 12C16O/14N2, 12C16O/14N2/Ar, and 12C18O/14N2/15/N2/Ar matrices and the infrared and Raman spectra of the products recorded at 4.2–10 °K. In addition to the infrared absorptions associated with the known compounds Ni(N2)4 and Ni(CO)4, other NN and CO stretching modes are observed which can be ascribed to the mixed carbonyl–dinitrogen species Ni(N2)m (CO)4−m where m = 1–3. Confirmation of the molecular constitutions and vibrational assignments of the isolated species was obtained from (a) variable concentration experiments in which either N2 or CO was arranged to be in excess, (b) diffusion controlled warm-up experiments in the range 10–35 °K, and (c) isotope substitution experiments using 14N2/15N2/12C18O/Ar matrices in which the total nitrogen to carbon monoxide ratio was varied. Cotton–Kraihanzel kCO and kNN force constants are computed for the mixed compounds Ni(CO)3(N2), Ni(CO)2(N2)2, and Ni(CO)(N2)3 and trends within the series are discussed in terms of the σ-donor and π-acceptor bonding properties of the N2 and CO ligands. An analysis is presented in which the changes in the CO and N2 bond stretching force constants in passing from Ni(CO)m to Ni(CO)m(N2)4−m and from Ni(N2)4−m to Ni(CO)m(N2)4−m are related to the change in σ and π orbital populations. The results of that analysis indicate that CO is both a better σ donor and a better π acceptor than N2. Integrated absorbances of the bands associated with the species Ni(CO)m(N2)4−m are measured and are used to compute ratios of the transition dipole moments (μco′)m and [Formula: see text] for CO and N2 respectively. The observed trends for (μco′)m and [Formula: see text] as functions of m are found to be in keeping with the changes in the respective CO and N2 π orbital populations.
The Crystal and Molecular Structure of Penta-P-tolylantimony, (p-CH3C6H4)5Sb
Authors: Brabant C. , Hubert J. , Beauchamp A. L.
Published: May 2006

Penta-p-tolylantimony crystals are monoclinic, space group P21/c, with a = 14.545(5), b = 4(6), c = 19.754(8) Å, β = 122.88(4)°, and Z = 4. The structure was solved by the standard heavy-atom method and anisotropic refinement on 1677 independent observed reflections led to a conventional R factor of 0.051. Unlike pentaphenylantimony, which is known to exist as square pyramidal molecules in the crystal, the corresponding penta-p-tolyl derivative exhibits the more common trigonal bipyramid structure. The Sb—C equatorial bond length average, 2.16 Å, is significantly shorter than the axial average, 2.26 Å. Two of the C—Sb—C bond angles in the equatorial plane (113, 130°) differ considerably from 120°, but the other angles around antimony are normal. Packing forces appear to play a determining role in the structures observed for penta-aryl derivatives of antimony in the solid state.
Structure of the Capsular Polysaccharide of Klebsiella K-type 56
Authors: Choy Yuen-Min , Dutton Guy G. S.
Published: May 2006

Methylation, periodate oxidation, and partial hydrolysis studies on the capsular polysaccharide of Klebsiella K-type 56 show the structure to be a repeating unit consisting of[Formula: see text]The nature of the anomeric linkages was determined by p.m.r. spectroscopy of isolated oligosaccharides. The position of the L-rhamnose side chain was defined by characterization of the di- and tetrasaccharides obtained by partial hydrolysis of the fully methylated polysaccharide.This structure represents the first capsular polysaccharide lacking uronic acid to be studied in the genus Klebsiella.
Thermal Isomerization of α,β-Epoxyketones
Authors: Khazanie Prabhaker G. , Lee-Ruff Edward
Published: May 2006

Pyrolysis of α,β-epoxyketones at 260° resulted in the formation of β-diketones derived from a 1,2 shift of a β hydrogen or alkyl substituent to the α carbon. Hydrogen migrates in preference to methyl in the case of 2-ethylidenecyclopentanone and 2-ethylidenecyclohexanone oxides. Thermal conversion of 2-cyclopentylidenecyclopentanone oxide to the spiro β-diketone 4 was quantitative.
Infrared Absorption Band Shape Studies: Fundamental OH Stretching Vibration of Benzyl Alcohol Conformers in Dilute Carbon Tetrachloride Solution
Authors: Krueger P. J. , Hawkins B. F.
Published: May 2006

The fundamental OH stretching doublet in the i.r. spectra of a series of a monomeric p-X-benzyl alcohols (X = OCH3, CH3, H, Cl, NO2) observed in dilute CCl4 solution over the temperature range −5 to+40 °C is resolved into two components corresponding to different molecular conformers, using digital computing techniques and a Cauchy–Gauss sum band model. The temperature and substituent dependence of frequencies, band shape indices, and band widths are discussed in terms of intramolecular (electronic displacements and [Formula: see text] hydrogen bonds) and intermolecular ([Formula: see text] and π–σ electron donor–acceptor) interactions. The OH band shapes, which range from 60–98% Cauchy character, reflect variations in the intermolecular interactions which impede molecular re-orientation, and can be correlated with the electronic nature of X and the molecular conformation. The formation of an intramolecular [Formula: see text] hydrogen bond results in significantly slower rotational relaxation of the alcohol molecule. The enthalpy differences between the two conformers are found to be 1.52 ± 0.13, 1.57 ± 0.15, 1.53 ± 0.08, 1.06 ± 0.13, and 1.15 ± 0.11 kcal/mol for the compounds in the order stated above.
Selective Benzoylation of Methyl 6-Deoxy-α- and β-D-glucopyranosides
Authors: Kondo Yôtaro , Miyahara Kiyoshi , Kashimura Naoki
Published: May 2006

Selective dimolar benzoylation of methyl 6-deoxy-α- and β-D-glucopyranosides yielded the 2,3-di-O-benzoate of the respective glucopyranoside as the major product in 61 and 29% yields. The orders of the reactivity of the secondary hydroxyl groups in α- and β-anomers were different, i.e., the order was 2-OH > 3-OH > 4-OH for the former and 3-OH > 2-OH > 4-OH for the latter.
On An Extension of the Use of pH-Titrations for Determination of Free Metal and Free Ligand Concentrations During Metal Complex Formation
Authors: McBryde W. A. E.
Published: May 2006

A method introduced by R. Osterberg for the measurement of free ligand concentration during the formation of metal complexes has recently been extended by Sarkar and Kruck to include measurement of free metal concentration. The method is based on suitable manipulation of the data from sets of pH titrations. This paper gives a new theoretical treatment of the method and its extension, and shows how the functions developed are related to other parameters of complex formation. A special advantage of Osterberg's method as extended is its capability of being applied when protonated or deprotonated complexes form.
A Modified Triester Method for the Synthesis of Deoxyribopolynucleotides
Authors: Itakura K. , Bahl C. P. , Katagiri N. , Michniewicz J. J. , Wightman R. H. , Narang S. A.
Published: May 2006

A modified triester method has been developed for the synthesis of oligonucleotides starting from mononucleosides as more economical starting materials. A pentadecanucleotide has been successfully prepared.
Determination of the Heat of Formation of Octafluorotoluene and Calculation of D[C6F5—F] – D[C6F5—CF3]
Authors: Krech Michael J. , Price Stanley James W. , Yared Wayne F.
Published: May 2006

The heat of formation of octafluorotoluene has been determined using the direct combustion method previously developed for hexafluorobenzene. As in the hexafluorobenzene case the combustion of octafluorotoluene in oxygen yields CO2, CF4, and F2. With a ten-fold excess of oxygen the CO2 to CF4 ratio is 3.85 ± 0.06. A full material balance was obtained. The value of ΔHf2980(C6F5CF3,g) = −303.2 ± 1.8 kcal mol−1 may be combined with the enthalpies of formation of C6F6, CF3, and F to give D[C6F5—F] – D[C6F5—CF3] = 55.7 ± 4.0 kcal mol−1.
Kinetics of the Gas Phase Reactions of (+)-trans-2,3-Divinyloxirane
Authors: Crawford Robert J. , Vukov Vesna , Tokunaga Hirokazu
Published: May 2006

'The racemization of (+)-2,3-divinyloxirane is facile at 150°, log (k1/s−1) = (11.3 ± 0.5) − (30.1 ± 0.4)/θ where θ = 2.303 RT in kcal mol−1. A slower but competitive rearrangement yields racemic 2-vinyl-2,3-dihydrofuran. The mechanisms of these reactions are discussed in terms of electrocyclic processes.
Lanthanide Induced Enhancement of Enantiomeric Shifts in Chiral Solvents and its Use in the Determination of Optical Purity
Authors: Jennison C. P. R. , Mackay Donald
Published: May 2006

The chemical shift difference (Δv) between corresponding groups in enantiomers in the presence of both a chiral solvent ((−)-2,2,2-trifluorophenylethanol or (+)-1-phenylethylamine) and an achiral lanthanide shift reagent (Eu(dpm)3 or Eu(fod)3) is much greater than in the chiral solvent alone. In general, for simple molecules having one coordination site the Δv was smaller than that obtained with the chiral shift reagent Eu(HFC)3. Comparable values of Δv, however, were obtained with the 1,3,4-oxadiazine derivatives 4a and b, and 5, suggesting that the "chiral solvate shift system" is best suited to differentiating more complex enantiomers having several coordination sites.The shift system was used to determine the optical purity of two partially resolved substances. One of these was the (+)-oxadiazine 4a, produced in the asymmetric isomerization of the bridged pyridazine 3a by (+)-camphor-10-sulfonic acid, and optically enriched by only one fractional crystallization. The enantiomeric enrichment in the isomerization was 4.21 ± 0.08%.
Organic Sulfur Mechanisms. 14. Kinetic Resolution in the Reaction of a Sulfene with an Amine
Authors: King James Frederick , Sim Soo-Khoon , Li Shiu-Kang Laurence
Published: May 2006

The reaction of camphor-10-sulfonyl chloride (1) with menthylamine (2) is shown by deuterium exchange experiments to proceed principally via the sulfene and the kinetic resolution first observed by Read and Storey (1) demonstrated to arise in the sulfene trapping step. This work constitutes the first authenticated kinetic resolution by a sulfene and also provides new kinetic evidence complementary to earlier work for the existence of a sulfene in the reaction of an alkanesulfonyl chloride with an amine. Evidence is also presented that a small but clearly detectable amount of "unexchanged" product in the deuterium exchange reactions arises via a direct displacement of the amine on the sulfonyl chloride; no kinetic resolution in this latter process was detectable.
Carbonium Ion Rearrangement with Retention at the Migration Terminus
Authors: Clark Ferrers R. S. , Warkentin John
Published: May 2006

The isomeric 7-t-butylbicyclo[2.2.1]hept-2-en-7-ols afford isomeric dienes (7-methyl-7-(2′-propenyl)-bicyclo[2.2.1]hept-2-enes) by Wagner–Meerwein rearrangement on treatment with thionyl bromide or acid. Methyl migration in the nonclassical 7-t-butylbicyclo[2.2.1]hept-2-en-7-yl cation intermediate occurs with a substantial syn preference, in sharp contrast to the anti preference exhibited in capture of similar cations by external nucleophiles. The result is interpreted in terms of a steric factor.
Electron Spin Resonance Study of the Cation Radicals of 1,5-Dihydronaphthyridine and Di-N-methyl-1,5-Naphthyridine
Authors: Sullivan Paul D. , Paudler William W.
Published: May 2006

The e.s.r. spectra of the cation radicals 1,5-di-N-methylnaphthyridine (1) and 1,5-dihydronaphthyridine (2) in trifluoroacetic acid have been reported and analyzed. The splitting constants of 2 are unequivocally assigned by comparison of the spectra of several partially deuterated derivatives. The methyl proton splitting constant of 1 is thought to be low in comparison with other similar radicals and possible reasons for this anomaly are discussed.
The Addition of Hypobromous Acid to Δ4-Steroids
Authors: Morand Peter , Polakova-Paquet Alenka
Published: May 2006

The addition of hypobromous acid to 4-cholesten-3β-yl acetate (1) has been found to result in the formation of a significant amount of 4β-bromo-5α-cholestane-3β,5-diol 3-acetate (3) as well as of 5-bromo-5α-choIestane-3β,4β-diol 4-acetate (2a). Evidence is presented in support of the structure proposed for the former and confirmation of the structure of the latter, about which there is disagreement, is adduced. The conversion of 2a to 4-cholestene-3β,19-diol 3-acetate (9) by treatment with lead tetraacetate and subsequent opening of the 4β,19-oxide ring is described.
Detection of Reversible Reactions in Solution Using Group Enthalpies of Transfer. Formation of Benzaldehyde Hemiacetals in Methanol
Authors: Fuchs Richard , Young Thomas M. , Rodewald Randolph F.
Published: May 2006

The enthalpies of transfer from methanol to dimethylformamide for a wide variety of aromatic compounds are additive properties of the groups present within the molecules. Values of ΔΔHs fail to be additive for benzaldehydes by an amount of energy which increases with increasing electron withdrawing power of the substituent. Nuclear magnetic resonance studies indicate that this results from hemiacetal formation in methanol, which varies from nil for p-dimethylamino-, p-hydroxy-, and p-methoxybenzaldehyde to 71% for the p-nitro compound. The non-additivity of group ΔΔHs values can indicate that specific interactions are occurring with a solvent, even though no stable product can be isolated.
Oxidative Addition of 3,5-Dinitrobenzoyl Chloride to trans-Chlorocarbonylbis(dimethylphenylphosphine)iridium(I)
Authors: Norris Albert Richard , Kessel Johannes Antonius Van
Published: May 2006

Trans-[IrClCO{(CH3)2C6H5P}2] undergoes oxidative addition with 3,5-dinitrobenzoyl chloride in benzene, ether, and benzene–ether mixtures to yield two isomeric Ir(III) complexes containing the 3,5-dinitrobenzoyl group σ-bonded to the metal via the acyl carbon atom. The structures and properties of these two complexes are described.
The Charge Transfer Spectra of d8 Transition Metal Halide Complexes and the 1849 Å Photolysis of Aqueous PtCl42−
Authors: Batiste John L. H. , Rumfeldt Robert
Published: May 2006

The ultraviolet spectra of the d8 complexes PtX42−, AuX4−, and Pd2X62− (X = Cl− or Br−) are reported. The assignments are based on a standard ordering of molecular orbital energy levels and on the trends in the band frequencies as related to the different metals and ligands. In addition to the low intensity d–d bands, two distinct high intensity regions are identified, an initial set of charge transfer ligand to metal bands followed by a sequence of essentially d → p bands. The 1849 Å irradiation of aqueous PtCl42− results in a redox reaction via photoelectron formation with [Formula: see text].The primary photolytic act is interpreted as initial excitation of the d → p transition 1A1g → 1Eu(3) (egπ* → a2uπ*).
Direct Formation of the Carbonyl Anion of Diisopropyl Formamide
Authors: Fraser Robert R. , Hubert Patrick R.
Published: May 2006

The reaction of diisopropyl formamide with lithium diisopropylamide produces, by abstraction of the formyl proton, the carbonyl anion, LiCON[CH(CH3)2]2. Reactions of this anion with benzaldehyde, benzophenone, ethyl benzoate, acetone, and propionaldehyde occur in yields ranging from 30–92%. Thus, this anion provides a useful method for the synthesis of α-hydroxy and α-keto acids, particularly in cases where cyanohydrin formation is difficult.
Effects of Solvent on the 1,2-Hydrogen Shift to a Divalent Carbon
Authors: Liu Michael T. H. , Chien David H. T.
Published: May 2006

The thermal decomposition of 3-chloro and 3-bromo-3-ethyldiazirine in various solvents has been investigated. A comparison was made between the decomposition in gas phase and in solution. The nature of the solvent does not affect the rate of diazirine decomposition, but does alter the subsequent reactions of the carbene. The results show that the cis olefin is predominant in a non-polar solvent but less so in polar solvent. These results were successfully explained by considering the electrostatic interaction of the CH3δ+ and Clδ− groups.
Infrared Spectra of Metal Bisfluorosulfates
Authors: Alleyne Carl Stanley , Mailer Kathleen O'sullivan , Thompson Robert Clayton
Published: May 2006

The infrared spectra, over the frequency range 250 to 1400 cm−1, of fourteen metal bisfluorosulfates are tabulated and discussed. The fluorosulfates of Fe(II), Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Mg(II), and Ca(II) give simple spectra which are assigned to the fundamental modes of vibration of fluorosulfate groups of C3v symmetry. The spectra of the Mn(II), Cu(II), Ba(II), Pb(II), and Sn(II) compounds are assigned to fluorosulfate groups of reduced symmetry. The spectrum of Sr(II) fluorosulfate suggests the presence of at least two non-equivalent fluorosulfate environments in this compound. The general features of the infrared spectra of compounds containing tridentate coordinated fluorosulfate groups are summarized.
Hydrated Electrons Produced by the Flash Photolysis of Co+, Ni+, Zn+, and Cd+ Ions
Authors: Basco Norman , Vidyarthi Sunil K. , Walker David C.
Published: May 2006

Hydrated electrons are produced with a quantum yield of about unity when the low valence state ions Co+, Ni+, Zn+, and Cd+ are photolyzed by light within their absorption bands centered at ∼300 nm. The observations seem to offer direct evidence that these absorption bands may be assigned as charge-transfer bands, and specifically as charge-transfer-to-solvent (c.t.t.s.). The ions are probably present as simple aquo complexes, since they were formed initially in very dilute aqueous solution from the divalent sulfate salts; but they may be solvated ion–electron pairs. Cu+ ions do not show a similar strong charge-transfer band at any wavelengths >230 nm and the second maximum in the case of Co+ at 360 nm is not of the c.t.t.s. type.The experiments used a double flash photolysis method whereby the first flash photolyzed SO42− with light at λ < 220 nm to produce hydrated electrons which then reacted with Co2+, Ni2+, Zn2+, or Cd2+ ions present at 10−5 to 10−6 M. The short-lived monovalent ions so formed were photolyzed 10–300 µs later by the second flash of restricted wavelengths.
The Conformation of β-Pseudouridine about the Glycosidic Bond as Studied by 1H Homonuclear Overhauser Measurements and Molecular Orbital Calculations
Authors: Nanda R. K. , Tewari R. , Govil G. , Smith Ian C. P.
Published: May 2006

The conformation of β-pseudouridine about the glycosidic bond has been studied by both the internal nuclear Overhauser effect and CNDO molecular orbital calculations. Both syn and anti conformations are found to exist in rapid equilibrium, with roughly equal populations of each. The proportion of syn to anti conformations does not change significantly with pD over the range 7.1 to 11.6. The CNDO calculations suggest that the syn conformation is stabilized by formation of a hydrogen bond, C4=O … O—H5′, but the n.m.r. data indicate that if such a bond exists its probability is the same at pD 7.1 and 11.6. Major contributions to n.O.e. may occur through conformations other than those which are most stable.
Isothermal and Photostimulated Emissions of Indole and Tryptophan in Two Polar Matrices at 77 °K
Authors: Muller D. , Ewald M. , Durocher G.
Published: May 2006

The isothermal delayed fluorescence along with the visible photostimulated fluorescence and phosphorescence emissions have been recorded and studied for the following systems: a 10−3 M solution of indole in an ether glassy matrix, a 10−3 M solution of indole in an ethylene glycol–water glassy matrix (EG–W) (70–30 by volume), a 10−3M solution of tryptophan in an EG–W glassy matrix (70–30 by volume). All these experiments have been performed at the temperature of liquid nitrogen. It has also become possible to record the action spectra of the photostimulated emissions which give us information about the entities playing an active part in the recombination processes. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model based on the assumption that upon neutralization an intermediate state is formed from which the molecule decides what its spin multiplicity will be. It was found that in an EG–W glass at 77 °K about 80% of the recombination events lack the energy necessary to reach the first excited singlet state of the amines studied. In an ether glass this percentage decreases to about 28%. This result is qualitatively in accord with the fact that the photostimulated electrons are more stabilized in an EG–W glass by an amount of energy equal to 1.5 eV.
Chemical Relaxations in Aqueous Micellar Solutions by Ultrasonic Spectroscopy. I. Alkali Metal Hexyl and Octyl Sulfates
Authors: Adair Douglas A. W. , Reinsborough Vincent C. , Plavac Nick , Valleau John P.
Published: May 2006

Ultrasonic absorption studies have been performed in dilute micellar solutions of Li, Na, and K octylsulfates, Na methylhexylsulfate, and Na hexylsulfate at 40° by the pulse technique in the range 13–143 MHz. Chemical relaxations associated with micelle formation were found in each system. The single-valued relaxation frequencies were concentration independent in solutions as concentrated as twice the critical micelle concentration. The relaxation data can be accounted for in terms of monomer–micelle association–dissociation.
Microwave Spectrum of Methoxyacetonitrile
Authors: Kewley Roger
Published: May 2006

The pure rotational spectrum of methoxyacetonitrile, CH3OCH2CN, has been investigated in the 8–40 GHz region. Spectra of the gauche and trans conformers, with respect to rotation about the O—CH2 bond, have been assigned. The rotational constants for the ground vibrational state are (in MHz) gauche: A = 11893.36(0.05), B = 3423.26(0.02), and C = 2871.53(0.02); trans: A = 29610(90), B = 2470.96(0.02), and C = 2348.07(0.02). The centrifugal distortion parameters DJ and DJK have also been determined for each conformer. The dipole moment components for the gauche conformer have been measured as (in D): µa = 2.40(0.03), µb = 1.37(0.10), µc = 1.11(0.11), and µ = 2.98(0.07). On the basis of relative intensity measurements at 25 °C the abundance of the trans form has been estimated as 4.8 ± 2.4% with the energy difference Etrans − Egauche having the value 5.7 ± 1.7 kJ mol−1 (1.35 ± 0.4 kcal mol−1). From vibrational satellite intensities the frequency for the first excited state of skeletal torsion about the O—CH2 bond has been found as (in cm−1) gauche: 93(25) and trans: 74(32). From the observed values of the rotational constants the dihedral angle in the gauche conformer is found to be near to 69° from the cis position.
Mercury(II) Complexation of Cysteine, Methyl Cysteineate, and S-Methylcysteine in Acidic Media
Authors: Neville George A. , Drakenberg Torbjörn
Published: May 2006

Bis(cysteineato)mercury(II) hydrochloride hemihydrate, [Formula: see text] was obtained by reaction of ethanolic solutions of L-cysteine hydrochloride with either HgCl2 in 95% EtOH, Hg(OAc)2 in MeOH, Hg(NO3)2 in HOAc, or by reaction of L-cysteine (free base) with HgCl2. Reaction of L-cysteine (free base) with Hg(OAc)2 gave a mercury(II) cysteineate with composition (C3H6O2NS)5Hg2. Bis(S-methyl-L-cysteineate)mercury (II), (C4H8O2NS)2Hg, was obtained by reaction of S-methyl-L-cysteine with Hg(OAc)2. 1H- and 13C-n.m.r. spectral data are reported and compared for acidic solutions of cysteine, methyl cysteineate, S-methylcysteine, and their mercury(II) complexes. The proton spectra for S-methyl-L-cysteine and L-cysteine hydrochloride have been analyzed as ABC systems and relative rotamer populations have been determined. In acidic solution, mercury bonding is localized to sulfur and the complexes appear to have an extended molecular configuration resulting from a trans orientation of the COOH group and the Hg site.
Metabolites of an Unidentified Fungus: a New 5,6-Dihydro-2-pyrone Related to Pestalotin
Authors: Strunz George M. , Heissner Christopher J. , Kakushima Masatoshi , Stillwell Merlyn A.
Published: May 2006

Spectroscopic and chemical studies, including correlation with pestalotin (LL-P880α), show that a new metabolite isolated from cultures of an unidentified fungus is 5-hydroxy-3-methoxy-6-oxo-2-decenoic acid δ-lactone.
Friedel–Crafts Condensations with Maleic Anhydrides. III. The Synthesis of Polyhydroxylated Naphthoquinones
Authors: Huot Richard , Brassard Paul
Published: May 2006

The condensation of hydroquinone ethers with an excess of dihalomaleic anhydrides has been found to give particularly good yields of dihalonaphthazarins. The etherification of the latter and the nucleophilic substitution of 2,3-dichloronaphthoquinones have been examined. Finally the structures of the products obtained from the Fries rearrangement of polyacetoxynaphthalenes have been definitively established.
Quaternary Nitrogen Heterocycles. VII. Reactions of some Tricyclic Heteroaromatic Cations in Basic Solutions
Authors: Bunting John W. , Meathrel William G.
Published: May 2006

Pseudobase formation and methoxide ion addition have been investigated spectroscopically for some N-methylacridinium, -phenanthridinium, and -benzoquinolinium cations. Susceptibility to nucleophilic attack decreases in the order 10-methylacridinium (pKROH = 9.86) > 5-methylphenanthridinium (pKROH = 11.94) > 1-methyl-5,6-benzoquinolinium ≈ 1-methyl-7,8-benzoquinolinium (pKROH &([a-z]+); 14). A qualitative correlation of pKROH with loss of resonance energy upon pseudobase formation is shown to exist. For the 9,10-dimethylacridinium cation, the C-9 pseudobase (or methoxide adduct) is the kinetically preferred product in basic solutions but this is subsequently converted to the thermodynamically more stable anhydrobase. With the corresponding 9-ethyl- and 9-benzyl-10-methylacridinium cations, the pseudobase, rather than the anhydrobase, seems to predominate at equilibrium.
The Complete Stereostructure of Capsidiol. X-Ray Analysis and 13C Nuclear Magnetic Resonance of Eremophilane Derivatives Having trans-Vicinal Methyl Groups
Authors: Birnbaum George I. , Stoessl A. , Grover S. H. , Stothers J. B.
Published: May 2006

To define the stereochemistry of capsidiol (1), an antifungal sesquiterpene isolated from sweet peppers, a detailed 13C n.m.r. investigation was carried out. From the results for 1 and a series of its derivatives (2–6) compared with those for several well-defined model compounds (7–21) it has been established that the vicinal methyl groups are trans, in contrast to all other previously described eremophilanes. This was confirmed by an X-ray structure analysis of 1 which also established the stereochemistry of the isopropenyl group as well as the detailed conformations of the two rings.The 13C spectra for the series 1–21 have been completely analyzed and these results are discussed in terms of the observed substituent effects. Further evidence of deshielding syn-axial δ effects is presented.
The Rate of Ionization of Some Aromatic Hydrocarbons in Ethanolic Dimethyl Sulfoxide
Authors: Albagli A. , Jones J. R. , Stewart Ross
Published: May 2006

The rates of detritiation of triphenlymethane, 9-phenylxanthene, fluorene, 9-ethylfluorene, 9-phenylfiuorene, and 2,3-benzofluorene have been measured in ethanolic dimethyl sulfoxide (DMSO) containing sodium ethoxide. When the logarithm of the ionization rate is plotted against the logarithm of the ionization rate of DMSO a straight line of near-to-unit slope is obtained in each case. There are significant differences, however, between relative ionization rates and equilibrium acidities.
Shock Tube Studies of the Reactions of Hydrogen Atoms. I. The Reaction H + NH3 → H2 + NH2
Authors: Dove John E. , Nip Wing S.
Published: May 2006

The partial equilibrium state following the branched-chain explosion of shock-heated rich H2/O2/diluent mixtures contains a high concentration of H atoms. The conditions under which this state can be used as a source of H atoms for the study of elementary reactions have been investigated. A small amount of NH3 was added to H2/O2/inert gas mixtures in order to measure the rate of the reaction H + NH3 → H2 + NH2. The pseudo-first order decay of NH3 in an approximately ten-fold excess of H atoms was followed by a time-of-flight mass spectrometer which sampled from the reflected shock region in a shock tube. The rate coefficient for this reaction, determined over the temperature range 1500–2150 °K, is 1013.44±0.10 exp −(17 400 ± 1 300 cal mol−1)/RT cm3 mol−1 s−1.It is pointed out that, under certain stated conditions, the method can also be extended to study the rates of elementary reactions involving O atoms and OH radicals. From our experiments, upper limits on the rate coefficients of the reactions OH + NH3 → H2O + NH2 and O + NH3 → OH + NH2 over the temperature range 1620–1920 °K are 8 × 109T0.08 exp (−1100/RT) and 1 × 1013 exp (−6600/RT), respectively.
The Wittig Synthesis and Photocyclodehydrogenation of 3-(2-Aryl)Vinylindole Derivatives
Authors: Silva S. Osmund de , Snieckus Victor
Published: May 2006

Wittig condensation of indole-1-(p-toluenesulfonyl)-3-methyltriphenylphosphonium iodide (8) with aromatic and heterocyclic aldehydes gives good yields of the 3-(2-aryl)-vinylindole derivatives 9a–g (Scheme 1). Compounds 11a and 11b are obtained similarly starting with the known indole-1-methyl-3-methyltriphenylphosphonium salt 10 and pyridine-3- and -4-aldehydes. An alternate Perkin-type condensation route provides the trisubstituted 3-vinylindoles 15a and 15b (Scheme 2) which cannot be synthesized by the Wittig route.Compounds 9a and 9b; 9e and 11b; 13, 15a, and 15b; as well as the previously known 12a-c undergo photocyclodehydrogenation to give benzo- and pyridocarbazole derivatives 16a and 16b; 18a and 19a, 18b and 19b; 17a, 17b, and 17c; and 16c–e, respectively in fair to good yields (Scheme 3). Compounds 9d, 9f, and 11a fail to photocyclize. The reasons for these failures are briefly explored and discussed.
The Crystal Structure of cis-Chlorobis(triethylphosphine)-1,10-phenanthrolineplatinum(II) fluoroborate, (PtCl(PEt3)2(phen))BF4, a Complex Containing Monodentate 1,10-Phenanthroline
Authors: Bushnell Gordon W. , Dixon Keith R. , Khan Masood A.
Published: May 2006

The crystal structure of cis-chlorobis(triethylphosphine)-1,10-phenanthrolineplatinum(II) fluoroborate has been determined and refined to an R-value of 0.051. The space group is P21/c and the cell dimensions are a = 0.9215(2), b = 1.1991(3), c = 2.6832(6) nm, β = 99.38(3)°, with 4 molecules per unit cell. The interatomic distances to Pt are: Pt—N(1), 213.7(19); Pt—N(2), 284.3(20); Pt—P(1), 223.9(7); Pt—P(2), 224.1(6); Pt—Cl, 236.1(6) pm.The coordination number and geometry is discussed in terms of 5-coordinate tetragonal pyramidal and 4-coordinate square planar models, the latter being regarded as the more acceptable.Monodentate o-phenanthroline is thus observed for the first time in the solid state. The structure of the complex in solution is discussed with the aid of conductance and nuclear magnetic resonance results which suggest the possibility of a novel fluxional system.
C-Acetylation of Ketones
Authors: Huckin Stuart Nicholas , Weiler Larry
Published: May 2006

The action of 2 equiv. of methyllithium on the monoanion of simple β-keto esters gives the β-diketone in good yield. This represents a facile and new method to achieve the C-acylation of a ketone.
Studies of β-Diketone Complexes of Rhenium. VI. The Crystal and Molecular Structure of cis-Dichloropentane-2,4-dionato-trans-bis(triphenylphosphine)rhenium(III)
Authors: Brown I. D. , Lock C. J. L. , Wan Che'ng
Published: May 2006

A compound, obtained in large yields from the reaction of acetylacetone and oxodichloroethoxobis(triphenylphosphine)rhenium(V) in benzene, has been shown by single crystal X-ray diffraction to be cis-dichloropentane-2,4-dionato-trans-bis(triphenylphosphine)rhenium(III). The crystals are monoclinic with a = 13.06(1), b = 18.30(1), c = 16.55(1) Å, and β = 112.7(2)°. The space group is P21/c and there are four molecules per unit cell. A total of 3841 independent reflections, of which 2686 were observed, were examined by film methods, the intensities being measured with a microdensitometer. The structure was refined by full matrix least-squares analysis to an R2 value of 0.068. The ligands are arranged around the rhenium atom in the manner described by the compound name to give a rough octahedron of nearest neighbours and the Re—Cl (2.369 Å av.), Re—O (2.02 Å av.), and Re—P (2.474 Å av.) distances are as expected.
Apparent Molal Volumes and Heat Capacities of Urea and Methyl-Substituted Ureas in H2O and D2O at 25 °C
Authors: Philip Patrick R. , Perron Gérald , Desnoyers Jacques E.
Published: May 2006

The apparent molal volumes and heat capacities of urea, 1,1- and 1,3-dimethylurea, and tetramethylurea were measured in H2O and D2O at 25 °C. From these data, urea–water interactions seem to cause an overall structure-breaking effect and the substituted ureas, an overall structure-making effect. The effect of the hydrogen-bonding interactions to the volume and heat capacity seems to be small compared with the intrinsic and hydrophobic contributions of a methylene group, as reflected by the isotope effect. Furthermore, transfer values seem to show a significant specificity to the degree and position of methyl substitution.
Preparation and Characterization of Nitrogen Bonded Nitrile and Amide Complexes of Pentaamminecobalt(III)-Linkage Isomers of Cyanopyridines
Authors: Balahura Robert J.
Published: May 2006

The preparation, characterization, and properties of pentaamminecobalt(III) complexes with 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene; 3-and 4-cyano-benzaldehyde; 4-acetylbenzonitrile; and 2-, 3-, and 4-cyanopyridine are described. The ligands are all bonded to cobalt via the nitrile nitrogen and undergo facile hydrolysis to the corresponding carboxamides according to the equation:[Formula: see text]Production of a carboxamido complex provides a chemical proof for bonding via the nitrile nitrogen. For the ambidentate cyanopyridines this has been used to assign nitrile bonding. For the 4-cyanopyridine ligand the linkage isomer bonded through the pyridine nitrogen has also been prepared and characterized.