bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Routes to Substituted Cyclopentadienes
Authors: Findlay D. M. , Roy Marie Lessard , McLean Stewart
Published: May 2006

An investigation has been made with the aim of finding a route to cyclopentadienes, particularly those with a single substituent at the 5-position, in which the final step is a thermal process of low enough activation energy that the cyclopentadiene produced does not undergo rearrangement by hydrogen migration under the reaction conditions. In the routes studied the final intermediates have been suitably substituted norbornenes which can lead to the required cyclopentadiene and an aromatic fragment by a retro-Diels–Alder reaction. In one series the intermediate was a phenyl azide adduct of norbornadiene which fragmented to cyclopentadiene and phenyltriazole, but the temperature required for this was clearly too high to allow substituted cyclopentadienes to be isolated before they had rearranged. In the course of this work, in addition to the exo-adduct of phenyl azide, the endo-adduct and a number of bisadducts were obtained and studied. In another series, adducts of tetraphenylcyclopentadienone and dimethyldiphenylcyclopentadienone with norbornadiene and 7-phenylnorbornadiene were prepared and studied. Decarbonylation of the adducts was effected both thermally and photochemically; in the latter case the reaction could be carried out at low temperature and the dihydrobenzene (a dihydrobenzonorbornadiene) produced was isolable. With or without isolation, the dihydrobenzene underwent a subsequent retro-Diels–Alder reaction to provide the cyclopentadiene and a substituted benzene. Kinetic studies showed that the activation energy for this process was almost but not quite low enough to satisfy the conditions stipulated, and in no case was a 5-substituted cyclopentadiene isolated before it had rearranged.
The Chlorination of Pyrroles. Part III
Authors: Durham D. G. , Hughes C. G. , Rees A. H.
Published: May 2006

The chlorination and subsequent demethylation of 2-(2′-methoxybenzoyl) and 2-(2′,6′-dimethoxybenzoyl)-pyrroles are described, giving deoxypyoluteorin and pyoluteorin as main products. A number of minor products of under- and overchlorination have been characterized. Alternative syntheses of some of these antibiotics are detailed. Two routes to 2,3-dichloropyrrole are given and the Friedel–Crafts reaction of this compound utilized in synthesizing deoxypyoluteorin and pyoluteorin. A number of analogs have been made and their microbiological activities compared. The monodeoxy series is generally more active.
The Effect of Bridge Size on the Sigmatropic Rearrangement of 2,3-Dibenzoyl-2,3-diazabicyclo[2.2.n]alk-5-enes
Authors: Chung Miss C. Y-J. , Mackay Donald , Sauer T. D.
Published: May 2006

The thermal isomerization of the title compounds 3a–d to the bicyclic oxadiazines 4a–d becomes increasingly difficult with bridge size n and could not be detected in the case of 3d. The reversibility of the isomerization has been demonstrated for [Formula: see text].Cyclooctadiene behaves both as a diene and as a dienophile in its reaction with azodibenzoyl.
The Preparation, Properties, and some Complexes of Anhydrous Manganese(III) Nitrate
Authors: Johnson D. W. , Sutton D.
Published: May 2006

Manganese(III) nitrate and its dinitrogen pentoxide "adduct" have been prepared by the reaction of N2O5 with MnF3. Infrared spectra and magnetic susceptibility measurements show these compounds to contain high-spin manganese(III) coordinated by nitrate groups and the "adduct" to be the nitronium salt, [NO2]+[Mn(NO3)4]−. The syntheses of complexes of Mn(NO3)3 with some organic ligands, e.g., 2,2′-bipyridyl, o-phenanthroline, acetonitrile, and triphenyl phosphine oxide are described.
Remarks on the Concept of Minimum State Density in the Activated Complex Theory
Authors: Wong W. H.
Published: May 2006

The concept of minimum state density in the activated complex theory and its relation to the transmission coefficient were discussed by formulating the average reaction cross-section.
The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Esters. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation
Authors: Deslongchamps Pierre , Atlani Paul , Fréhel Daniel , Malaval Alain
Published: May 2006

The hydrolysis or the transesterification of esters proceeds via a hemi-orthoester tetrahedral intermediate. There are nine different gauche conformers possible for such a tetrahedral intermediate and it is proposed that each of them should decompose in a highly selective manner. It is further proposed that the lone pair orbitals of the oxygen atoms control this selective decomposition.
Étude par spectromètrie i.r. des effets de solvant sur les fréquences fondamentale et harmoniques de l'acide iodhydrique
Authors: Van-Thanh Nguyen- , Rossi Inga
Published: May 2006

The wavenumbers of the fundamental, first and second overtones have been measured for HI in liquid CCl4. The solvent shifts calculated, assuming a Lennard–Jones–Devonshire cell model of the solution, are in good agreement with the experimental data.
Cycloaddition and Related Reactions of Some Unsaturated Phosphines with Dimethyl Acetylenedicarboxylate
Authors: Davies Maureen , Hughes A. N. , Jafry S. W. S.
Published: May 2006

Diphenylvinylphosphine reacts with dimethyl acetylenedicarboxylate to give either an equilibrium mixture of two cyclic ylidic 1:1 adducts or a strained bicyclic ylidic 1:2 adduct depending upon the reaction conditions. The adducts have been characterized by trapping them as their hydrolysis or deuterolysis products or by their Wittig reactions. trans-1,2-Bis(diphenylphosphino)ethylene reacts with the ester to give a 1:1 zwitterionic adduct which exhibits some ylidic properties and hydrolyzes by a very unexpected mechanism. The cis isomer of this phosphine reacts with the ester to give the expected 1,4-diphosphorin which has been fully characterized.
Pyrochlores. VIII. Studies of some 2–5 Pyrochlores and Related Compounds and Minerals
Authors: Brisse François , Stewart David J. , Seidl V. , Knop Osvald
Published: May 2006

The cubic pyrochlores Cd2Nb2O7, Cd2Ta2O7, Sn2Nb2O7, Sn2Ta2O7. Cd2Sb7O7, Ca2Sb2O7, Mn2Sb2O7, Pb2Sb2O7, and related compounds were prepared and investigated by a number of methods. On heating above 700°. Ca2Sb2O7(pyrochlore) transformed to Ca2Sb2O7(weberite), while Pb2Sb2O7(pyrochlore) changed to a rhombohedrally distorted Pb2Sb2O7 pyrochlore. Refinement of the crystal structures of Cd2Nb2O7 and Cd2Ta2O7 from powder diffractometer intensities yielded 0.434(2) and 0.434(3) respectively as the best estimates of x(O2). Specimens of natural bindheimite and stibiconite were also examined. Stibiconite from San Luis Potosi (Mexico) was shown, on the evidence of its Mössbauer 121Sb spectrum, to contain Sb(V) and Sb(III) in the approximate ratio of 0.2.BaCd2Cl6•5H2O and BaCd2Cl6•2H2O both give powder diffraction patterns of the pyrochlore type. The chlorine could be partially replaced by Br to give mixed crystals BaCd2Cl6−zBrz•5H2O almost up to z = 2.The crystal chemistry of 2–5 oxide pyrochlores and the relationship of the weberite to the pyrochlore phases are discussed.
On the Rate Constant for n-Pentyl Radical Isomerization
Authors: Watkins K. W.
Published: May 2006

A new interpretation of the mechanism used by Endrenyi and LeRoy for the calculation of the rate constant for n-pentyl isomerization is proposed. The addition of one step to the scheme makes possible a recalculation of the Arrhenius parameters. Significantly different values are found which eliminate the previously reported low A-factor.
Synthesis and Structural Investigation of cis-8-Oxabicyclo[4.3.0]nonan-3-ols
Authors: Kimoto Koichi , Leong Ta-Yan , Imagawa Takeshi , Kawanisi Mituyosi
Published: May 2006

A variety of methods of synthesis of hitherto unknown isomeric cis-8-oxabicyclo[4.3.0]nonan-3-ols were studied, and the best method for obtaining cis-8-oxabicyclo[4.3.0]nonan-3β-ol (2) was hydroboration of cis-8-oxabicyclo[4.3.0]non-3-ene (1). cis-8-Oxabicyclo[4.3.0]nonan-3α-ol (3) could be obtained highly stereoselectively by the hydrogenation of cis-8-oxabicyclo[4.3.0]nonan-3-one (4) over platinum oxide in an acidic medium. The configurations of 2 and 3 were deduced mainly from the chemical and spectral similarity with the known cis-bicyclo[4.3.0]nonan-3-ols. The preferred conformations of the two isomeric alcohols were discussed in terms of i.r. as well as n.m.r. spectroscopy using paramagnetic shift reagents. There is almost no difference in the coordination abilities of europium ions with the alcoholic and ethereal oxygen atoms in these compounds.
Identification and Thermal Stability of Copper(I) Sulfate
Authors: Van Kim Vo , Habashi Fathi
Published: May 2006

Anhydrous CU2SO4 was prepared and its X-ray diffraction pattern was established. Differential thermal analysis, thermogravimetric analysis, and X-ray diffraction methods were used to study the effect of heating in different atmospheres. The formation of CU2SO4 as an intermediate in chemical processes has been discussed.
The Investigation of Cation–Anion Interactions by 39K Nuclear Magnetic Resonance
Authors: Bloor E. G. , Kidd R. G.
Published: May 2006

The 39K chemical shifts in a number of aqueous electrolyte solutions have been determined. These arise from the overlapping of the outer electron orbitals of the anion and cation during random ionic collisions. The magnitudes of the chemical shifts are shown to be directly proportional to the effectiveness of this overlap interaction.
Coordination Compounds of Indium. Part XIX. Ligand Exchange Studies with Indium(III) Complexes of Trifluoromethyl-β-diketonates
Authors: Tanner Mrs. G. M. , Tuck D. G. , Wells E. J.
Published: May 2006

The ligand exchange reaction between InL3 con plexes (L = CF3•CO•CH•CO•R− anion; R = methyl, i-butyl, phenyl, 2-naphthyl, and 2-thienyl) and excess free ligand (HL) has been studied in the solvents diisopropyl ketone, acetonitrile, benzene, and dimethylsulfoxide. Studies of the lifetimes of the reactants as obtained from their 19F n.m.r. line-widths show that the exchange is first order in InL3 concentration, but zero order in free ligand concentration. The coalescence temperature for the collapse of the n.m.r. 19F chemical shift between free and complexed ligand (~50 Hz) yields ΔG≠ for the exchange. The results are in agreement with the known stereochemical properties of indium(III) complexes. The rate-controlling process in the exchange is identified as the. rotation of one monodentate ligand about a partial double bond prior to intramolecular proton transfer to a second monodentate ligand.
Deuterium Isotope Effects in the Oxidation of 2,3-Dimethyl-2-butene via the Bromohydroperoxide, by Singlet Oxygen and by Triphenyl Phosphite Ozonide
Authors: Kopecky Karl R. , Sande Johan H. van de
Published: May 2006

The partially deuterated alkenes (CH3)2C = C(CD3)2 (1b) and CH3CD3C = CCH3CD3 (1c) were prepared and converted to the corresponding allylic hydroperoxides by the routes shown in the title. Two bromohydroperoxides were formed from 1b in a 1.6:1 ratio with the major isomer having the OOH group on the carbon bearing the CH3's. On treatment with base at 0° this mixture formed two allylic hydroperoxides in a 2.2:1 ratio with the major isomer having the OOH group on the carbon bearing the CD3's, showing migration of the OOH group. This isomer predominated in a 1.4:1 ratio when 1b was oxidized with singlet oxygen at 15 or −52° and in a 1.6:1 ratio when 1b was oxidized with triphenyl phosphite ozonide at −70°. Under the same conditions C—H bond breaking also predominated in the oxidation of 1c, by 2.1:1 via the bromohydroperoxide, by 1.4:1 with singlet oxygen, and by 1.3:1 with triphenyl phosphite ozonide. Migration of the OOH group in the reaction of the bromohydroperoxide of 1b does not occur by way of a 1,2-dioxetane. A perepoxide may be the intermediate. Neither perepoxides nor 1,2-dioxetanes are involved in the singlet oxygen oxidation of 1b and c. At −70° the triphenyl phosphite ozonide oxidations do not proceed by way of these intermediates, either, or by way of singlet oxygen. The intermolecular deuterium isotope effect in the singlet oxygen oxidation of both cis- and trans-2,3-diphenyl-2-butene was found to be 1.1.
The Reaction of Dimeric Tri-O-acetyl-2-deoxy-2-nitroso-α-D-hexopyranosyl Chlorides with Alcohols
Authors: Lemieux R. U. , Ito Y. , James K. , Nagabhushan T. L.
Published: May 2006

The kinetics of the reactions of dimeric tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride (1) with simple aliphatic alcohols (4 mol equiv) in dimethylformamide to form alkyl tri-O-acetyl-2-oximino-α-D-arabino-hexopyranosides (5) were investigated by n.m.r. and optical rotation. It is concluded that the conversion of 1 to 5 proceeds basically by way of three successively formed intermediates, namely, the monomeric form (2) of 1, the tri-O-acetyl-2-oximino-α-D-arabino-hexopyranosyl chloride (3), and the tri-O-acetyl-1,5-anhydro-2-deoxy-2-nitroso-D-arabino-hex-1-enitol (4). Direct evidence was obtained only for the intermediacy of 3 and the transient existence at low concentration of an uncharacterized intermediate which may be the β-anomer of 5. The intermediate 4 could form directly from 2 and thereby provide a mechanism for the formation of 5 which by-passes 3. However, the kinetic investigations showed this route to be of very minor, if any, importance. In all cases, the rate of the disappearance of 1 was virtually the same and within experimental error the same as for the isomerization of 1 to 3 in the absence of the alcohol for which the rate-controlling stage is dissociation of 1 to 2. Methanol reacts with 4 only about 5 times faster than does t-butanol.The utility of the reaction for the preparation of oximinoglycosidic structures related to disaccharides is illustrated by glycosidations of 1,2;3,4-di-O-isopropylidene-α-D-galactopyranose, 1,2;5,6-di-O-isopropylidene-α-D-glucofuranose both by 1 and by the dimeric tri-O-acetyl-2-deoxy-2-nitroso-α-D-galactopyranosyl chloride (6) and of 2,3;5,6-di-O-isopropylidene-α-D-mannofuranose by 1. The reaction of 6 with 1,2,3,4-di-O-isopropylidene-α-D-galactopyranose provided an 8.7% yield of the β-oximinoglycoside along with an 80% yield of the α-anomer.
Halogenoammine Complexes of Osmium(III)
Authors: Allen A. D. , Stevens J. R.
Published: May 2006

The complexes [Os(NH3)5X]X2, cis-[Os(NH3)4X2]X, and trans-[Os(NH3)4X2]X (X = Cl, Br, I) have been prepared and their infrared spectra measured between 4000–150 cm−1 Assignments have been made for the observed absorption bands. The electronic spectra of the complexes were measured and compared with those of the analogous ruthenium(III) species.
Phosphonic Acid Analogs of Carbohydrate Metabolites. IV. Synthesis of DL-Glyceraldehyde-3-phosphonic Acid
Authors: Baer Erich , Robinson Ranga
Published: May 2006

A chemical synthesis of DL-glyceraldehyde-3-phosphonic acid, the phosphonic acid analog of DL-glyceraldehyde-3-phosphoric acid, is reported. It was obtained from dimer DL-glyceraldehyde by two procedures differing solely in their protective groups via the following intermediates. Procedure 1: 2,5-diiodomethyl-3,6-dimethoxy-1,4-dioxane → 2,5-bis(methylphosphonic acid diethyl ester)-3,6-dimethoxy-1,4-dioxane → 2,5-bis(methylphosphonic acid)-3,6-dimethoxy-1,4-dioxane → DL-glyceraldehyde-3-phosphonic acid. Procedure 2: 2,5-bis(p-toluenesulfonyloxymethyl)-3,6-dibenzoxy-l,4-dioxane → 2,5-diiodomethyl-3,6-dibenzoxy-l,4-dioxane → 2,5-bis(methylphosphonic acid diethyl ester)-3,6-dibenzoxy-l,4-dioxane → 2,5-bis(methylphosphonicacid)-3,6-dibenzoxy-1,4-dioxane → DL-glyceraldehyde-3-phosphonic acid.
Theoretical Evidence for a Stable form of Cyclic Ozone, and its Chemical Consequences
Authors: Wright James S.
Published: May 2006

The total energy of the symmetrical, bent O3 molecule is studied as a function of internuclear angle and internuclear distance. The method used is an ab initio molecular orbital calculation with a minimum basis set of Slater-type orbitals, plus limited configuration interaction. Best single configuration energies show the existence of two stable minima: a cyclic (60°) structure and a bent (115°) structure. The cyclic structure is preferred by 48 kcal/mol, contrary to experiment (116° 48′) Configuration interaction results with two low lying orbitals show the cyclic form still preferred by 6 kcal/mol. A transition state for the bent-cyclic pathway lies 26 kcal/mol (or less) above the bent form. Based on these results, a possible low energy path via the cyclic form is proposed for the thermal decomposition of ozone. It is also proposed that cyclic ozone may have been observed in the pulse radiolysis of oxygen.
Volumes and Heat Capacities of Transfer of Tetraalkylammonium Bromides from Water to Aqueous Urea Solutions at 25 °C
Authors: Philip P. R. , Desnoyers J. E. , Hade A.
Published: May 2006

The apparent molal volumes and heat capacities of tetraalkylammonium bromides were measured in urea–water mixtures at 25 °C. The volumes and heat capacities of transfer from water to urea-water mixtures indicate that structural hydration effects are smaller in urea–water mixtures than in water. Also a comparison with the corresponding transfer functions from H2O to D2O suggests that urea–water mixtures are less structured than pure water.
1-Propanethiol as a Radical Scavenger in the γ-Radiolysis of Liquid Cyclohexane
Authors: Esser Joseph , Stone John A.
Published: May 2006

1-Propanethiol is an excellent H atom and alkyl radical scavenger in the γ-radiolysis of liquid cyclohexane. The total radical yield (5.2) is measured by twice the yield of propyldisulfide which appears to be invariant with propanethiol concentration. 1-Propanethiol-d is about as efficient an H atom scavenger as ethylene. C3H7S• radicals add reversibly to cyclohexene.
Preparation of 6′-Substituted Maltoses
Authors: Melton Laurence David , Slessor Keith Norman
Published: May 2006

A relatively simple procedure for the preparation of 6′-substituted maltoses has been developed through the action of Aspergillus oryzae amylase on mono-substituted cyclohexaamyloses. 6′-Azido-, -chloro-, -bromo-, -iodo-, and -tosyl-maltose have been prepared in this way. 6′-Deoxy- and 6′-amino-6′-deoxy-maltose were easily prepared from the 6′-iodo- and 6′-azido-maltoses respectively.
Photolysis of Acylsilanes in Cyclohexane and Other Solvents
Authors: Brook A. G. , Duff J. M.
Published: May 2006

Whereas photolysis of acylsilanes in carbon tetrachloride has been shown to generate silyl radicals which yield chlorosilanes exclusively, and photolyses in alcohols yield siloxycarbenes which yield "mixed acetal" insertion products, it is shown that photolysis of acylsilanes in non-polar, non-halogenated solvents such as cyclohexane give complex mixtures of products which result primarily from the attack of silyl radicals on the carbonyl oxygen of an acylsilane, followed by conventional disproportionation or recombination reactions. Under some circumstances silyl radicals add to carbon–carbon double bonds. The structures of the products formed and the mechanism of their formation are described.
The Elimination Reactions of Some Alkyl Cyanides in the Gas Phase
Authors: Dastoor P. N. , Emovon E. U.
Published: May 2006

The kinetics of the thermal decomposition of ethyl, isopropyl, and t-butyl cyanides into HCN and the corresponding defines have been studied in a seasoned silica vessel in a flow system in the absence and presence of toluene as inhibitor. The reactions are homogeneous and the unimolecular rate constants are expressible by the following Arrhenius equations:[Formula: see text]
Kinetics and Temperature Dependence of the Hydration of NO+ in the Gas Phase
Authors: French Margaret A. , Hills L. P. , Kebarle P.
Published: May 2006

The kinetics of the atmospherically important hydration sequence: NO+(H2O)n−1 + H2O = NO+(H2O)n and the transfer reaction NO+(H2O)n + H2O = HNO2 + H+(H2O)n were examined in nitrogen containing small quantities of NO and H2O with a pulsed high pressure ion source mass spectrometer. The room temperature mechanism and rate constants were found to be in agreement with earlier work in other laboratories. The temperature dependence of the reaction was examined for the range 27–157 °C. The transfer reaction does not occur at higher temperatures so that the NO+ hydration equilibria for n = 1 and 2 could be measured leading to ΔH1,0 = 18.5 and ΔH2,1 = 16.1 kcal/mol. The third order forward clustering rate constants were found to have negative temperature coefficients.
Five Co-ordinate Complexes of Platinum(II) and Palladium(II)
Authors: Dixon K. R. , Rattray A. D.
Published: May 2006

Reactions of 1,10-phenanthroline with halogen bridged dinuclear species, [M2X2(PPh2O)2(PPh2OH)2] and [M2X2(PR3)4][BF4]2, give the new five co-ordinate complexes, [MX(PPh2O)(PPh2OH)(Phen)] and [MX(PR3)2(Phen)][BF4], where M = Pd or Pt, X = Cl or Br, Ph = phenyl, and R = ethyl (or phenyl when M = Pd). Decomposition of the [MX(PR3)2(Phen)][BF4] complexes in hot solvents gives the four co-ordinate species, [MX(PR3)(Phen)][BF4]. The complexes are characterized by elemental analyses, molecular weight, and conductance measurements and infrared and nuclear magnetic resonance spectroscopy. The spectroscopic data show that [PtCl(PEt3)2(Phen)][BF4] has a trigonal bipyramidal structure with the phenanthroline and one triethylphosphine in the equatorial plane and a chlorine and a triethylphosphine in the axial positions.
Pulse Radiolysis of Aqueous Papain
Authors: Clement J. R. , Armstrong D. A. , Klassen N. V. , Gillis H. A.
Published: May 2006

not available
"Sideways" Bonded Dinitrogen in Matrix Isolated Cobalt Dinitrogen, CoN2
Authors: Ozin G. A. , Voet A. Vander
Published: May 2006

Infrared spectra are reported for matrix isolated cobalt dinitrogen isotopic species, Co14N2, Co14N15N and Co15N2, formed in the cocondensation reaction of atomic cobalt with dilute nitrogen–argon matrices at 10°K. The data provide the first unambiguous spectroscopic evidence for a dinitrogen molecule bonded in a "sideways" fashion to a transition metal atom.
The Preparation and Properties of Complexes of Antimony and Bismuth Trifluorides with Strong Fluoride Acceptors
Authors: Birchall T. , Dean P. A. W. , Valle B. Della , Gillespie R. J.
Published: May 2006

The reactions of antimony and bismuth trifluorides with the pentafluorides of antimony and arsenic in liquid sulfur dioxide yield the adducts SbF3•SbF5 (type A), SbF3•AsF5, BiF3•3SbF5, and BiF3•AsF5; no adducts of the trifluorides with BF3 were isolated. Antimony metal reacts with excess of antimony pentafluoride and arsenic pentafluoride in liquid sulfur dioxide giving a second form of SbF3•SbF5 (type B) and the same form of SbF3•AsF5 as produced from SbF3, respectively. BiF3•3SbF5 can be formulated as Bi(SbF6)3, but its Raman spectrum indicates the presence of extensive cation–anion fluorine-bridging. Their Raman spectra suggest that BiF3•AsF5, SbF3•AsF5, and SbF3•SbF5 (type B) have similar structures, possibly containing polymeric fluorine-bridged cations, but that SbF3•SbF5 (type A) has a different structure probably like that of AsF3•SbF5. The 121Sb Mössbauer spectra of the SbF3 adducts support the assignment of similar structures to SbF3•AsF5 and SbF3•SbF5 (type B), and the suggestion that SbF3•AsF5 and both forms of SbF3•SbF5 contain antimony (III) fluoro-cations. 19F n.m.r. shows that SbF3 has appreciable solubility in SO2 solutions of SbF5 and indicates the possible formation of "fluxional" SbF2–SbnF5n+1 molecules in SbF3–SbF5 solutions.
Vibrational Spectroscopic Studies of Aqueous Alkali Metal Bicarbonate and Carbonate Solutions
Authors: Oliver Barry G. , Davis Anthony R.
Published: May 2006

The laser Raman and infrared spectra of Li, Na, K, Rb, Cs bicarbonates and carbonates in H2O and D2O have been determined at 25 °C. The relative integrated intensities of the Raman bands have been measured for each salt from 0.01 M up to saturation. Changes observed in the carbonate spectrum with concentration have been interpreted in terms of solvation and ion-pairing of the carbonate ion. Based on the vibrational spectrum, there was no evidence for ionic interactions in the bicarbonate solutions. The hydrogen–deuterium exchange on the bicarbonate ion in H2O–D2O mixtures has been followed using Raman spectroscopy and the concentration quotients for the pertinent reactions have been calculated.
Post-infectional Inhibitors from Plants. IV.The Structure of Capsidiol, an Antifungal Sesquiterpene from Sweet Peppers
Authors: Gordon M. , Stoessl A. , Stothers J. B.
Published: May 2006

Chemical and spectroscopic studies of the title compound have led to 1 as a representation of its structure.
The Wittig Reaction of Indole-2-methyltriphenylphosphonium Iodide with 4-Piperidone Derivatives and Aromatic Aldehydes
Authors: Eenkhoorn Johan A. , Osmund de Silva S. , Snieckus Victor
Published: May 2006

2-(4-Piperidylidene)methylindole (8a–e, 21) and 2-(2-aryl)vinyl indole (25a–e, 27, 32) derivatives have been obtained from the Wittig reaction of indole-2-methyltriphenylphosphonium iodides (6, 20, 26) with 4-piperidones (7a–e) and aromatic aldehydes (24a–e), respectively. Yields have been optimized by studying a variety of base-solvent combinations. The reaction failed in the case of 6 with 3-ethyl-4-piperidones (10); instead of compound 11, 2-methylindole (12) was produced. The utility of phosphonium salts 9a–c and phosphonate ester 33a has been tested: compounds 9a and 33a showed some advantage in the preparation of Wittig adducts 8e and 25c respectively but the steric problems associated with hindered ketones (10) were not overcome even with the reactive phosphonium salts 9b and c. A mechanism is advanced for the formation of 2-methylindole analogous to that proposed for the base-promoted decomposition of benzylphosphonium salts (Scheme 2). Aromatic aldehydes yield mainly trans-Wittig adducts (25) with the exception of pyridine-2-aldehyde which produces exclusively cis-25c in nonpolar solvent due to preferred formation of the hydrogen-bonded betaine 29. Interconversion of [Formula: see text] and their photochemical reaction to pyridocarbazole 28 are reported (Scheme 5). The chemistry of some 2-(4-piperidylidene)methylindoles has been briefly studied (Scheme 3).
Charge Distributions and Chemical Effects. III. A Comparison with PCILO and CNDO/2 Calculations
Authors: Fliszár S. , Sygusch J.
Published: May 2006

The PCILO charge distributions of a number of alkanes are in excellent agreement with charge distributions derived on the assumption that the inductive effects can be described in a Taft-like manner. This agreement with "quantitative chemical intuition" stresses the strong chemical character of the PCILO method. The CNDO/2 results are only in qualitative agreement with "chemical expectancy" and suffer apparently from the same difficulties as PCILO used with zero C—C and C—H polarities.
Reactivity of Substituted Benzenethiols Towards Chlorotris(triphenylphosphine)iridium(I) and Chlorotris(triphenylarsine)iridium(I)
Authors: Herdé Joseph L. , Senoff Caesar V.
Published: May 2006

A series of substituted benzenethiols, HSC6H4Y (Y = 4-Br, 4-F, 4-H, 4-CH3, or 4-CH3O) have been shown to react with IrCl(Ph3M′)3 (M′ = P or As) in benzene to form dimeric iridium(III) complexes of the type, [IrHCl(SC6H4Y)(Ph3M′)2]2, 1. The thiol, 4-nitrobenzenethiol, reacts with IrCl(Ph3M′)3(M′ = P or As) to form complexes of the type [IrCl2(SC6H4NO2)(Ph3M′)2]2, 2. Complexes 1 undergo reductive elimination with carbon monoxide to form trans-[Ir(CO)2(Ph3M′)2]Cl whereas complexes 2 do not react with carbon monoxide. Spectroscopic properties (i.r. and n.m.r.) of these complexes are discussed in relation to their structure in the solid state and in solution.
The Photo-addition of Naphthalene and Acrylonitrile. An X-ray and Nuclear Magnetic Resonance Study of the Cycloadducts
Authors: Bowman R. M. , Calvo C. , McCullough J. J. , Miller R. C. , Singh I.
Published: May 2006

The photoaddition of naphthalene and acrylonitrile has been reinvestigated. It was found that the cyclobutane adduct described previously is endo-7-cyano-2,3-benzobicyclo[4.2.0]-octa-2,4-diene (7), and not the exo-8-cyano compound. The structure was determined from an X-ray diffraction study on the p-bromophenylurethane of the carbinol derived from the cyano-compound. The structural details are described. The crystallographic data are a = 13.85(1), b = 7.976(2), c = 12.752(4) Å, α = 90.80(3), β = 87.02(6), γ = 90.99(5)° space group [Formula: see text], Z = 2 units of C20H18O2NBr. The least-squares residual R was 0.085 for 651 X-ray reflections measured on a Syntex P1 diffractometer using graphite-monochromatized Mo radiation. The methine proton resonances in the 220 MHz n.m.r. spectrum of 7 were resolved using pyridine solvent, and the coupling constants are consistent with the structure and geometry, as derived from the X-ray work. A small fraction (7%) of 8-cyano-2,3-benzo-bicyclo[4.2.0.]octa-2,4-diene was also formed. This is tentatively assigned as the endo isomer, and on base treatment it isomerizes to a new compound, identified as the exo isomer. In contrast, the major cycloadduct 7 is recovered unchanged from base treatment. The folded geometry of the four-membered ring in these adducts apparently determines the stabilities of the epimers, and the proton–proton vicinal coupling constants.
The Influence of Coordinating Solvents on the Thermal Decomposition of Methyl Titanium Trichloride
Authors: McCowan James D.
Published: May 2006

The mechanism of decomposition of CH3TiCl3 in coordinating solvents is shown not to involve free radicals in some cases. An analysis of published work on the decomposition of titanium alkyls suggests mechanisms of decomposition similar to those postulated for alkyls of other transition metals.
Studies of Rhenium β-diketone Complexes. IV. The Synthesis, Properties, and Crystal Structure of Bis(μ-chlorotricarbonyl(1-phenyl-1-hydroxobut-1-ene-3-one)rhenium(I)), a Compound Containing a Monodentate Neutral β-Ketoenol
Authors: Fredette M. C. , Lock C. J. L.
Published: May 2006

The title compound, [Re(CO)3Cl(C6H5•COH•CH•CO•CH3)]2, is one of a series of compounds obtained by the reaction of chloropentacarbonylrhenium(I) with β-diketones and has been characterized by n.m.r. and infrared spectroscopy and single crystal X-ray diffraction. The crystals are monoclinic with lattice parameters a = 14.77(2), b = 17.98(2), c = 13.48(2) Å, β = 124.34(9)°; C2/c, Z = 4. A total of 1293 independent reflections were measured on a single crystal X-ray diffractometer and the structure was refined by full matrix least squares analysis to a weighted R2 value of 0.0444. The dimeric halves of the molecules are held together by two chlorine atoms symmetrically bridging the rhenium atoms (Re—Cl = 2.511(5) Å The structure is thus very like that of [Re(CO)4Cl]2, except that two neutral β-ketoenol molecules replace two carbon monoxide molecules (one on each rhenium) and are bonded through the ketone group (Re—O = 2.16(1) Å). The arrangement of the keto and enol groups is such that hydrogen bonding can occur between them.
Synthesis and Nuclear Magnetic Resonance Spectroscopy of some Substituted Aryldiazoalkanephosphonates
Authors: Gurudata N. , Benezra C. , Cohen H.
Published: May 2006

Six aryl diazoalkanephosphonates have been prepared and their proton and 13C n.m.r. spectra analyzed. The results suggest that the carbon bearing phosphorus (and the diazo-group) is essentially sp2 hybridized and that the dominant canonical form depends on the substitution of the aryl ring. Evidence is given for double bond character in the C—P bond.
Palladium(II), Platinum(II), and Copper(I) N-Bonded Complexes with Thiazolidine-2-thione as Ligand
Authors: Filippo D. De , Devillanova F. , Trogu E. F. , Verani G. , Preti C. , Viglino P.
Published: May 2006

The preparation and characterization of the (MttznX2) complexes (where M = Pd; or Pt; ttz = thiazolidine-2-thione; n = 2, 3 or 4; X = Cl, Br, I) are reported. By i.r., p.m.r., and u.v.–visible spectra and by magnetic susceptibility and conductivity measurements it appears that in all complexes the ligand is N-bonded to the metal and that many equilibria are present in polar solvents. In particular, for (Mttz4I2)-derivatives there is an equilibrium between a square-planar and a penta-coordinate species. Furthermore, water is competing with the ligands and counterions in the coordination sphere. Our ligand is placed near water in the spectrochemical series. With copper(I) we have obtained complexes of the type (Cuttz3X) (where X = Cl, Br, I, NO3, ClO4, and [Formula: see text]), and in each case the anion is coordinated to the metal. The ttz molecule in these complexes behaves as a hard-base.
Regiospecificity and Stereoselectivity in the Photodimerization of 2,3-Dihydro-2,6-dimethyl-4-pyrone
Authors: Yates Peter , MacGregor Donald J.
Published: May 2006

Ultraviolet irradiation of 2,3-dihydro-2,6-dimethyl-4-pyrone in aqueous solution leads to the regiospecific and stereoselective formation of three cis–anti–cis photodimers of the cyclobutane type, i.e0., octahydro-2,7-8a,8b-tetramethylcyclobuta[1,2-b:4,3-b′]dipyran-4,5-diones, whose structures have been established by chemical and spectroscopic methods, including studies of nuclear Overhauser effects in the proton magnetic spectrum of one of them. The dimers undergo photointerconversion, and it is proposed that this process involves photoreversion to monomer and that the reversibility of the dimerization reaction may be a factor in determining the regiochemistry and stereochemistry of the photodimers. A bisdehydro product prepared from the dimers of the dihydropyrone has been shown to undergo photocleavage to 2,6-dimethyl-4-pyrone, and it is proposed that reversibility may also be a factor affecting the course of the photodimerization of this pyrone.
Acyl Alkyl Diimides. III. Influence of Structure on Decomposition
Authors: Lynch Thomas R. , MacLachlan Frederick N. , Suschitzky John L.
Published: May 2006

Eleven compounds of general structure RCON=NC(CN)R2′, where R = C6H5, CH3, C6H5CH2, and R2′ = (CH3)2, (CH2)4, (CH2)5, (CH2)6, have been found to decompose in a first-order manner in dilute toluene solution in the temperature range 60–100°. The N-acetyl compounds decompose ca. four times faster than the corresponding N-benzoyl cases. Variation in R2′ causes changes in rate parallel to those observed by Overberger for the analogous bis-α-cyanoalkyl diimides but of smaller magnitude. The products are those expected from homolytic cleavage, and intermediate N-acylketenimines have been trapped by added water in two cases.
Partial Oxidation of Vicinal Hydroxyl Groups of Methyl 4,6-O-Benzylidene-α-and β-D-Glucopyranosides with Dimethyl Sulfoxide and Phosphorus Pentoxide
Authors: Kondo Yôtaro , Takao Fujikazu
Published: May 2006

Oxidation of methyl 4,6-O-benzylidene-α-D-glucopyranoside with dimethyl sulfoxide – phosphorus pentoxide gives the corresponding 3-ketone (3), the 2,3-O-oxidomethylenebenzylidene acetal (5), and the 2,3-O-oxidodimethylene acetal (6). By a similar treatment of methyl 4,6-O-benzylidene-β-D-glucopyranoside only starting material was recovered.
Studies on Hydrogen–Oxygen Systems in the Electrical Discharge. VI. Detection by Laser Raman Spectroscopy of O2 and O3 Trapped at 80 °K
Authors: Arnau José L. , Giguère Paul A.
Published: May 2006

Further study by Raman spectroscopy of the condensed products from electrically dissociated water vapor and other related systems has revealed the presence, not only of ozone in appreciable amounts, but also of molecular oxygen in still greater amounts trapped at 80 °K. The concentration of ozone relative to the hydrogen oxides varied somewhat with experimental conditions, and also locally due to some segregation effect in the glassy condensate. The concentration of trapped oxygen showed still wider fluctuations depending particularly on surface effects in the discharge–flow system. On warming up under vacuum the intensity of the O2 and O3 bands began to decrease even before the crystallization temperature was reached (about 150 °K), thereby confirming that the gas evolution at that stage is mainly a desorption process. Therefore, the often quoted ratio of total evolved O2 to residual H2O2 could not be a reliable index of the formation of hydrogen polyoxides, H2O3 and H2O4, in these systems. A mechanism is proposed for the formation in situ of the trapped gases and in particular, for a source of oxygen atoms in dissociated water vapor.The fundamental vibrations of the ozone molecule, ν1 = 1106, ν2 = 703, and ν3 = 1036 cm−1, were confirmed by polarization and isotope shift measurements.
Isotopic Studies of the Metal–Ligand Bond. Part IV. Variable Temperature and Isotopic Studies of the Metal–Ligand Vibrations in Substituted Pyridine Metal Dihalides. Complexes of Cobalt(II), Nickel(II), and Copper(II)
Authors: Lever A. B. P. , Ramaswamy Baratham S.
Published: May 2006

The far infrared spectra (500–200 cm−1) of a series of picoline and ethylpyridine derivatives of cobalt(II), nickel(II), and copper(II) are reported. Metal–ligand assignments are based on isotopic substitution experiments with 65Cu and 62Ni. Low temperature data are also reported and it is noted that the energies of metal–ligand modes are much more sensitive to temperature than the energies of purely ligand vibrations. This observation is discussed and it is suggested, with some caution, that the low temperature behavior may be used as a guide to band assignment.
A Determination of σ+ Values for the Pyridine Aza Group
Authors: Broxton Trevor James , Butt Graeme Lyle , Deady Leslie William , Toh Swee Hin , Topsom Ronald David , Fischer Alfred , Morgan Michael Woodford
Published: May 2006

From the solvolysis of the pyridyldimethylcarbinyl chlorides in acetone–water and in methanol, σ+ values of 0.73, 0.57, 1.13 and 0.72, 0.45, 1.14, respectively, are derived for the 2-, 3-, and 4-aza groups.
The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Amides. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation
Authors: Deslongchamps Pierre , Lebreux Claude , Taillefer Roland
Published: May 2006

The basic hydrolysis of N-disubstituted imidate salts proceeds via a hemi-orthoamide tetrahedral intermediate which can in principle give amide–alcohol or ester–amine products. Experimental evidence has been obtained which shows that the specific conformation of the tetrahedral intermediate determines products formation and it is further suggested that the orientation of the lone pair orbitals of the heteroatoms governs this remarkable selective decomposition.
The Synthesis of a 5,6-Dihydropyridazine
Authors: Mayo P. De , Usselman M. C.
Published: May 2006

The synthesis of 3,6-dimethyl-6-n-butyl-5,6-dihydropyridazine, the first 5,6-dihydropyridazine, is described. On heating it undergoes a [1,5] sigmatropic hydrogen rearrangement to give the corresponding 1,6-dihydropyridazine.
Chemisorption of Ammonia on Silica
Authors: Blomfield G. A. , Little L. H.
Published: May 2006

The interaction of ammonia with silicas prepared by a variety of methods was studied to resolve conflicting reports of the mode of ammonia adsorption and to determine the role of chlorine impurities (present in the silica) in the adsorption process. Results for the adsorption of water on silica assisted in making band assignments and competition between ammonia and water for silica adsorption sites was observed. It was concluded that dehydroxylated silicas contain sites which dissociate ammonia to form Si—NH2 groups having infrared bands at 3540, 3450, and 1550 cm−1 (the surface amine groups are not displaced by added water). The presence of chlorine in the silica is not a prerequisite for chemisorption of ammonia.
The Triplet State of Ketones in Solution: The Role of the Charge Transfer State in the Quenching of Triplet Acetone by Aromatic Molecules
Authors: Loutfy R. O. , Yip R. W.
Published: May 2006

The rate constants for quenching of triplet acetone by a series of halobenzenes have been determined by flash emission technique. Quenching was found to be approximately a hundred times faster than that for triplet benzophenone. For both triplet ketones, quenching did not decrease with the increase in triplet energy difference between ketone and quencher (as expected for normal endothermic triplet energy transfer) and did not correlate with the i.p. of all of the quenchers studied. All of the qualitative features of the quenching results can be simply interpreted in terms of enhanced coupling of the locally excited triplet ketone and quencher states as a result of interaction with the charge transfer state.
Bufadienolides. 17. Synthesis of 14α- and 14β-Artebufogenin
Authors: Kamano Yoshiaki , Pettit George R.
Published: May 2006

Treatment of resibufogenin (1a) or its acetate (1b) with perchloric acid or hydrochloric acid gave 14α-and 14β-artebufogenin (5a and 6a, or 5b and 6b), in addition to 15α-hydroxy-bufalin (4a or b). Reaction of epoxide 1b with chloranil or boron trifluoride etherate easily afforded 14α- and 14β-artebufogenin acetate (5b and 6b) in good yields. Analogous reaction of the isomeric 3β-hydroxy-14α,15α-epoxide 3a with perchloric acid, hydrochloric acid, or sulfuric acid again led to 14α- and 14β-artebufogenin (5a and 6a) and the 14β,15α-dihydroxy-derivative 4a, Similar reaction with periodic acid gave 6a and 4a.
A Wide Line Nuclear Magnetic Resonance Study of Molecular Motion in n-Alkyl Ammonium Chlorides
Authors: Tsau J. , Gilson D. F. R.
Published: May 2006

Wide line n.m.r. studies of n-alkyl ammonium chlorides, C3–C10, show two transitions. The first transition is due to reorientation about the chain axis, the second to a transition to a mesomorphic phase. This phase is probably similar to that observed for the alkali metal salts of fatty acids.
13C Nuclear Magnetic Resonance Studies on Molecular Association. I. Self-association of Dipolar Molecules
Authors: Saitô Hazime , Tanaka Yuji , Nagata Sachiko , Nukada Kenkichi
Published: May 2006

Self-association of dipolar substances is studied by 13C magnetic resonance. The dilution shifts in carbon tetrachloride are analyzed in terms of the monomer–dimer equilibrium. Downfield 13C shifts of the nitrile and carbonyl groups are observed for the formation of the dimer of acetone, acetonitrile, and ethyl acetate. Upfield 13C shifts, on the other hand, are observed in the methyl and methylene groups of acetone, methylethyl ketone, ethyl acetate, acetonitrile, propionitrile, nitromethane, nitroethane, N,N-di-methylformamide, and N,N-dimethylacetamide. The equilibrium constants are 0.1–0.5 in units of mole fraction. The downfield 13C shifts of the nitrile and carbonyl groups are interpreted in terms of electric (reaction) field effects imposed by another molecule through dimer formation. The alternation of polarity by polarization of the X–Y group explains the upfield 13C shifts of methyl and methylene groups as shown in the following scheme: Hs+—C−—X+—Y−, where X—Y stands for C=O, C≡N, and NO2 groups which have been classified as –I− groups by Pople and Gordon.
CNDO–MO Study of the Ozonide Ion and Related Species
Authors: Sichel John M.
Published: May 2006

The unpaired electron in the ozonide ion (O3−) is expected to occupy an antibonding molecular orbital; yet published experimental results indicate a shorter bond length and larger force constants than in neutral ozone. Molecular orbital calculations in the CNDO approximation are reported for this ion and related species (O3, SO2, SO2−, OF2+, OF2), using both the CNDO/2 and CNDO/BW parametrizations. Both methods predict that the bond lengths in O3− are 0.04 Å longer than in O3, in agreement with qualitative molecular orbital theory, and that the bond angle is 1° less than in O3. The CNDO/BW method predicts that the electron affinity of O3 is higher than that of the O atom, in agreement with experiment, since a stabilizing exchange effect outweighs the antibonding nature of the orbital occupied by the extra electron.
Thermodynamic and Transport Properties of Sodium Benzoate and Hydroxy Benzoates in Water at 25 °C
Authors: Desnoyers Jacques E. , Pagé Robert , Perron Gérald , Fortier Jean-Luc , Leduc Paul-André , Platford Robert F.
Published: May 2006

The densities, heat capacities, heats of dilution, osmotic coefficients, viscosities, and conductivities of sodium benzoate and the ortho, meta, and para isomers of sodium hydroxybenzoate have been measured in water at 25 °C. The densities and heat capacities of phenol solutions and the osmotic coefficients of aqueous potassium benzoate have also been determined. The addition of an —OH or a —COONa group on a benzene ring has little effect on the properties related to the effective size of the solute (apparent molal volume, Bη viscosity coefficient, and ionic conductivity) but decreases significantly the apparent molal heat capacity. The addition of an —OH group in the meta or para position of sodium benzoate has a similar effect. The large negative contribution to the heat capacity probably reflects the solute–solvent hydrogen bonding. The ortho isomer, which can form an internal hydrogen bond, has a significantly different behavior from that of the other isomers.The excess properties show no evidence of association at low concentrations although some specific interaction is apparent for the ortho isomer at high concentration. There seems to be some cation–anion structural attraction with the meta and para isomers which again may be related to the hydrogen-bonding ability of these solutes. Sodium and potassium benzoates show signs of association above 1 m.
Examination of Possible Non-Arrhenius Behavior in the reactions
Authors: Clark Thomas C. , Dove John E.
Published: May 2006

We present a simplified form of the bond-energy–bond-order method of calculating rate coefficients which can be applied to reactions involving multi-atom reactants. Rate coefficients for the reactions[Formula: see text]are calculated for 300 < T < 1800°K. The Arrhenius plots of the calculated coefficients are curved, but in the temperature range 400–850°K where most kinetic measurements have been made the curvature is not large enough to be readily detected. However deviations from a linear Arrhenius plot should be observable if rate measurements are extended to higher temperatures by, e.g., shock tube experiments. The calculated rate coefficients at 300–1800°K are fitted by the expressions[Formula: see text]in liter mole second units. These expressions contain powers of T which in each case are greater than predicted by the classical limit of transition state theory. For all three reactions there is now some experimental evidence that the predicted curvature does occur. Some consequences of this behavior are examined.
Total Synthesis of Eremophilane-type Sesquiterpenoids: (±)-Eremophilenolide, (±)-Tetrahydroligularenolide, and (±)-Aristolochene
Authors: Piers Edward , Geraghty Michael Bert
Published: May 2006

The total synthesis of the racemic forms of the eremophilane-type sesquiterpenoids eremophilenolide (2), tetrahydroligularenolide (3), and aristolochene (4) is described. The octalone 7 was converted via an efficient, regioselective route into the keto ester 12, which served as a common synthetic intermediate for the preparation of the three sesquiterpenoids. Successive subjection of 12 to alkylation, hydrolysis, and decarboxylation afforded the keto acid 14. Hydrogenation of the latter provided both the cis-fused keto acid 20, which was readily converted into (±)-eremophilenolide (2), and the trans-fused keto acid 15, which was similarly transformed into (±)-tetrahydroligularenolide (3). Conversion of 12 into the dithioketal 23, followed by desulfurization and treatment of the resultant olefinic ester 25 with excess methyllithium, provided the olefinic alcohol 27. Dehydration of the latter yielded (±)-aristolochene (4).