bluuebunny/crossref_metadata_2025 huggingface dataset:
Diastereomers of the insect repellent 3-acetyl-2-(2′,6′-dimethyl-5′-heptenyl)oxazolidine. Isolation by high pressure liquid chromatography and characterization by 13C nuclear magnetic resonance spectroscopy
Authors: Taylor Wesley G. , Nakashima Tom T.
Published: May 2006

Preparative-scale high pressure liquid chromatography on 3-acetyl-2-(2′,6′-dimethyl-5′-heptenyl)oxazolidine (1), a complex acetamide derivative of citronellal, resulted in isolation of the diastereomeric forms of this insect repellent. The two diastereomers were designated as 1a and 1b on the basis of their order of elution from silica gel and from a variety of capillary gas chromatography columns. Interpretation of the 13C nuclear magnetic resonance spectra of 1a and 1b was accomplished by comparison with model compounds and by off-resonance proton-decoupling experiments. Absolute stereochemical assignments were not made. Because of the amide group, the diastereomers existed in solution at ambient temperature as cis and trans rotational isomers, which caused nonequivalence of most of the carbon atoms, including the olefinic carbons at C-5′ and C-6′. trans Isomer (5) was concluded to be the major contributor to the rotational equilibrium. The spectrum of 3-acetyl-2-(4′-methyl-3′-pentenyl)oxazolidine (7) was also recorded for comparison.
A kinetic study of the influence of alcohols on the nitrosation of morpholine in acid media. Equilibrium constants for the formation of alkyl nitrites
Authors: Casado Julio , Lorenzo Francisco Manuel , Mosquera Manuel , Prieto Maria Flor Rodriguez
Published: May 2006

The effect of the aliphatic alcohols methanol, ethanol, propanol, isopropanol, 2-butanol, isobutanol, and tert-butanol on the rate of nitrosation of morpholine at pH 3 and 25 °C has been studied. The inhibition observed is attributed to the formation of alkyl nitrites, which are poor nitrosating agents in acid media. The equilibrium constants for the formation of alkyl nitrites from nitrous acid and alcohols have been calculated both spectrophotometrically and from kinetic data for the inhibitory effect, and there is agreement between the two sets of results. The molar absorptivities at 265 nm of the alkyl nitrites have also been determined. When the concentration of alkyl nitrite is very low, a slight catalytic effect considered to be an effect of the medium has been observed.
Rate of lactamization of benzylstrychnine in acid solution
Authors: Edward John T. , Wong Sin Cheong , McClelland Robert A.
Published: May 2006

The rate of lactamization of benzylstrychnine in aqueous solution at 25 °C increases with acid concentration up to 5–10% sulfuric acid, and thereafter decreases. The maximum can be explained by taking account of the extent of protonation of the aromatic amino group with increasing acid concentration. This amino group is unusually weakly basic [Formula: see text], perhaps because it is locked in an extremely rigid cage structure which opposes the rehybridization of N which must take place when it is protonated.
Novel gas phase ions. II. [CH2=CHOH/CH3OH]+• and [CH2=CHOH/H2O]+•
Authors: Terlouw Johan K. , Heerma Wigger , Burgers Peter C. , Holmes John L.
Published: May 2006

The title ions are generated by the loss of C2H4 from ionised 4-methoxybutan-1-ol and butan-1,4-diol, respectively, and are best described as complexes between [CH2=CHOH]+• and CH3OH (dissociation energy 21 kcal mol−1) and between ionised vinyl alcohol and H2O (dissociation energy ≥ 13 kcal mol−1). [Formula: see text] of the ions [CH2=CHOH/H2O]+• and [CH2=CHOH/CH3OH]+• were measured as ≤ 110 and 112 kcal mol−1, respectively.
Synthesis and electron paramagnetic resonance studies of chiral spin-labeled crown ethers
Authors: Dugas H. , Keroack P. , Ptak M.
Published: May 2006

The synthesis of syn and anti chiral dinitroxide [18]-crown-6 ethers and of a tetranitroxide crown ether is described. The existence of a spin–spin interaction for the syn isomer makes this spin-labeled crown ether probe particularly useful to follow by epr the effects of K+ ion binding, pH, solvent, and temperature. These observations are discussed in terms of a global dynamical fluctuation of the substituted crown ether.
"Through-space" spin–spin coupling between thallium and hydrogen in o-alkylphenylthallium compounds
Authors: Cheesman Bruce Victor , White Raymond Frederick Martin
Published: May 2006

In this study a comparison was made of the [Formula: see text] sidechain coupling constants for mono- and di-arylthallium derivatives in which a series of alkyl groups (CH3, C2H5, i-C3H7, t-C4H9) are o- and p- to the thallium atom. The results provide evidence of "through-space" coupling between thallium and hydrogen in some of the o-alkylphenylthallium compounds, with the "through-space" contribution to [Formula: see text] in the o-tert-butylphenylthallium derivatives being considerable.
Alternaric acid. Proof of biosynthesis via condensation of two polyketide chains. Complete assignment of the 1H and 13C magnetic resonance spectra by 2D techniques
Authors: Stoessl Albert , Stothers J. B.
Published: May 2006

Incorporation studies utilizing [1,2-13C2]acetate have established that the fungal phytotoxin alternaric acid is biosynthesized by an uncommon condensation of two polyketide chains rather than from a single chain undergoing an a priori possible, albeit improbable, rearrangement. Unequivocal assignments for the 13Cmr spectra followed from the results of three 2D experiments, namely, homonuclear (1H) and heteronuclear (1H, 13C) correlation spectra and double quantum coherence (13C). Attempts to distinguish between the two possible loci of the chain junction were unsuccessful, suggesting that the synthesis may proceed on a single enzyme complex, without intervention of discrete intermediates.
Metal salt catalyzed carbenoids. XVIII. The electron impact mass spectral behavior of diazocarbonyl compounds. I.
Authors: Wulfman D. S. , Roberts James , Henderson Dennis K. , Romine J. C. , McDaniel Jr. R. S. , Carver L. , Beistel D. W.
Published: May 2006

Electron impact (EI) mass spectral studies of methyl diazoacetate, ethyl diazoacetate (1), methyl diazoacetoacetate (2), and dimethyl diazomalonate (3) indicate that loss of N2 is exceedingly difficult from the parent ion and was observed only with 3. Diazoacetylacetone exhibits an appreciable (M − 28)+. ExactMass and metastable transitions indicate fragmentation occurs in part via 1,2,3-oxadiazolium ion-radicals (6) or α-lactones (7) to furnish N2O and hyponitrite esters. (M − 28)+ from 1 results from loss of ethylene.
Structural studies on the dichlorocarbene adducts with (−)-R-carvone. I. The crystal structures of [1R, 4R, 6R, 9R]-7,7-dichloro-1-methyl-4-[2′,2′-dichloro-1′-methyl- cyclopropyl]-bicyclo[4.1.0]-heptan-2-one and [1R, 4R, 6R, 9S]-7,7-dichloro-1-methyl-4-[2′,2′-dichloro-1′-methylcyclopropyl]-bicyclo[4.1.0]-heptan-2-one
Authors: Zukerman-Schpector J. , Castellano E. E. , Oliva G. , Brocksom Timothy John , Canevarolo Elisabete Terezinha
Published: May 2006

The crystal structures of the title compounds have been determined from diffractometric X-ray data and refined by full-matrix least-squares to final R factors of 0.047 and 0.060 from 830 and 620 independent reflections above background, respectively. The space group and the number of molecules per unit cell are the same in both cases: P212121 and Z = 4. Cell dimensions are: a = 7.982(2), b = 9.538(3), c = 18.785(3) Å for the S form and a = 10.339(3), b = 11.510(3), and c = 11.886(6) Å for the R form. The molecules, produced simultaneously in the same chemical reaction, have essentially identical configuration except for the location of the chlorine atoms at C-11 (in the S case) and at C-10 (in the R case). This difference gives rise to a completely different molecular packing of the structures. In each compound the two cyclopropane rings present a cis relationship to one another, with an identical dihedral angle of 77.0°.
Synthesis and spreading behaviour of some reactive derivatives of long-chain alcohols and carboxylic acids
Authors: Holden David A.
Published: May 2006

Procedures are described for the synthesis of several azides, diimides, and azodiformates from long-chain alcohols and fatty acids. These reactive compounds have potential applications as thermal and photochemical curing agents, and as surface-modifying agents for the preparation of filled plastics and chromatographic packings. The surface activity of the compounds was characterized by investigations of their spreading behaviour in monolayers on water. Unlike the single-chain azides and azo compounds, which give well-defined monolayers at all temperatures, monolayers of diacyl diimides and dialkyl azodiformates with two long-chain substituents are unstable with respect to collapse to the bulk solid. The photoreaction of monolayers of octadecanoyl azide to give a mixture of products derived from an intermediate isocyanate was demonstrated by ir and mass spectrometry.
The crystal and molecular structure of the bis(N,N,N′,N′-tetramethylethanediamine) adduct of I(Br)InInBr2, In2Br3I•2C6H16N2, an indium–indium bonded molecule
Authors: Khan Masood A. , Peppe Clovis , Tuck Dennis G.
Published: May 2006

The crystal structure of the title compound has been determined by the heavy atom method. The crystals are orthorhombic, space group Pbca, with unit cell dimensions a = 22.795(3) Å, b = 17.518(2) Å, c = 12.396(3) Å, Z = 8; R = 0.0409 for 1527 unique "observed" reflections. The structure is disordered, with each halogen site (X) occupied by 75% Br, 25% I. The molecule consists of two X2(tmen)In units (tmen = N,N,N′,N′-tetramethylethanediamine) with distorted trigonal bipyramidal geometry, joined by an In—In bond 2.775(2) Å in length.
A 31P and 199Hg nuclear magnetic resonance and vibrational spectroscopic study of phosphine complexes of Hg(ClO4)2
Authors: Allman Tim , Goel Ram G.
Published: May 2006

Cationic complexes of the type [Hg(phosphine)n](ClO4)2 (n = 2, 3, 4) (phosphine = P(t-Bu)3, PCy3, P(4-Me2NC6H4)3, P(4-MeOC6H4)3, P(4-MeC6H4)3, P(3-MeC6H4)3, P(2-MeC6H4)3, P(4-FC6H4)3, P(4-ClC6H4)3) have been prepared and studied by vibrational spectroscopy in the perchlorate and low frequency regions, as well as by 31P and 199Hg nmr. The skeletal Hg—P frequencies have been assigned in both solution and the solid state. It was found that 1J(Hg—P) decreases with increasing phosphine basicity and that it is also dependent upon sample concentration and temperature.
Hydrogen bonding in the crystal structures of the adducts between 1-phenyl-3,5-dimethylpyrazole with oxalic and perchloric acids
Authors: Zukerman-Schpector J. , Castellano E. E. , Oliva G. , Massabni A. C. , Pinto A. Derbli
Published: May 2006

The crystal structures of the title compounds have been determined from diffractometric X-ray data and refined by full-matrix least-squares to final R factors of 0.057 and 0.071 for the oxalic and perchloric adducts respectively.The space groups and cell dimensions are: (oxalic) C2/c, a = 16.516(3), b = 11.685(2), c = 12.587(3) Å, β = 107.11(2)° with Z = 4; (perchloric) Pbca, a = 16.204(3), b = 15.329(6), c = 10.296(3) Å with Z = 8.In both structures the complex is stabilized by a strong hydrogen bond between the N(2) of the 1-phenyl-3,5-dimethylpyrazole (PDMP) group and an oxygen of the acid. In the oxalic adduct the PDMP group is neutral and the N(2) atom acts as a proton acceptor, while in the perchloric complex the PDMP group is positively charged with the N(2) atom acting as a proton donor.
Open-chain nitrogen compounds. Part VI. The formation of bis(1-aryl-3- methyltriazen-3-ylmethyl) methylamines in the reaction of diazonium ions with mixtures of formaldehyde and methylamine
Authors: Manning Hartford W. , Hemens Chantal M. , LaFrance Ronald J. , Tang York , Vaughan Keith
Published: May 2006

The synthesis of a series of N,N-bis(1-aryl-3-methyltriazen-3-ylmethyl) methylamines from coupling diazonium salts with mixtures of methylamine and formaldehyde is described. These novel bis-triazenes, or heptazanonadienes, have significant anti-tumour activity against the TLX5 lymphoma in mouse. The mechanism of formation of these triazenes is discussed with reference to the implication to the presumed equilibria taking place in the methylamine/formaldehyde solution. The formation of the bis-triazene is usually accompanied by the formation of a 3-hydroxymethyitriazene, and it has been shown that the hydroxymethyltriazene can be transformed into the bis-triazene. The proportions of the two products are strongly influenced by the relative amounts of methylamine and formaldehyde. Coupling the p-bromobenzenediazonium salt to a 1:1 methylamine/formaldehyde mixture affords mainly the bis-triazene, whereas a 1:50 mixture gives almost totally the hydroxymethyl triazene. These results suggest that the two triazenes arise from diazonium coupling to different species in the amine/formaldehyde mixture; this hypothesis is supported by the formation of identical product mixtures from coupling the diazonium ion with (a) a 1:1 MeNH2/CH2O mixture, and (b) the cyclic trimer of the carbinolamine MeNHCH2OH, and by the identification of a minor product from the reaction of p-chlorobenzenediazonium fluoroborate with MeNH2/CH2O as bis(1-p-chlorophenyl-3-methyltriazen-3-yl) methane.
N-acylglycine dithioesters form enethiolates near pH 9
Authors: Lee H. , Carey P. R. , Storer A. C.
Published: May 2006

It is demonstrated that N-acylglycine ethyl dithioesters have fairly acidic α-CH protons, and that ionization leads to the formation of enethiolatc anions. For example, the pKa's of N-benzoyl- and N-(β-phenylpropionyl)glycine ethyl dithioesters are 9.04 and 9.62, respectively. N-acylglycine papain dithioesters are formed during the papain catalyzed hydrolysis of the corresponding methyl thionoesters. However, for the papain dithioesters, no evidence was found for the formation of enethiolate anions.
Dissolution enthalpy of NaI in water–alcohol mixtures at 288.15 and 308.15 K. Enthalpy of interaction in electrolyte–alcohol–water systems
Authors: Piekarski Henryk , Piekarska Alina , Taniewska-Osińska Stefania
Published: May 2006

The enthalpy of NaI solution was determined in water mixtures with methanol, ethanol, propanol, and isopropanol in the entire range of mixed-solvent concentration at 288.15 and 308.15 K, and in water mixtures with s-butanol and tert-butanol in the range of 0–5 mol% alcohol at 308.15 K. The dependence of [Formula: see text] on solvent composition was studied. The enthalpic pair interaction coefficients hEN for NaI–alcohol in water and NaI–water in alcohols were determined, and the effect of temperature on hEN values in the systems under study was analyzed.
The proton activating factor and its application to acid and base catalysis of aldehyde hydration
Authors: Stewart Ross
Published: May 2006

The data of McClelland and Coe for the general acid and general base catalyzed hydration of a series of substituted benzaldehydes has been analyzed in terms of the proton activating factor, paf, and concepts related thereto. Although the latter were derived for use with prototropic systems, the present work shows that they have application to nucleophilic addition as well. Three conclusions emerge from the analysis. 1. Alternative means of calculating paf from buffer catalytic data that were previously derived on theoretical grounds can be used in practice to give essentially the same results. 2. The mechanism of the general acid catalyzed pathway for aldehyde hydration is that favoured by McClelland and Coe and by Jencks, to wit the class (e) mechanism, rather than the class (n) mechanism. 3. Electron-withdrawing groups in the benzaldehyde ring cause the disparity between the contributions of alternative, kinetically equivalent, pathways for the uncatalyzed reaction to become greater.
Structures cristallines des (±) oxy-2β bis(bromo-3α phényl-5β tétrahydrofuranne), (±) oxy-2β bis(bromo-3α méthyl-4α phényl-5β tétrahydrofuranne) et (±) oxy-2β bis(bromo-3α (triméthyl-2′,4′,6′ phényl)-5β tétrahydrofuranne)
Authors: Dana Gilbert , Touboul Estera , Morales-Rios Martha , Philoche-Levisalles Michèle , Bois Claudette
Published: May 2006

The three ethers A, B, and C formed during the hydrolysis of dibrominated tetrahydrofuran derivatives 1 are racemic. In all three cases, the reaction selectivity corresponds to an association between enantiomers of the same absolute configuration. In the three molecules studied, the tetrahydrofuran ring assumes a conformation characterized by polar groups in the 2-position (anomeric effect) and in the 3-position being diaxial and by the bulky aromatic group being equatorial. [Journal translation]
Orientation et dynamique moléculaire de sondes paramagnétiques en phase lamellaire dibutylephosphate de sodium/eau
Authors: Chachaty C.
Published: May 2006

Aqueous solutions of sodium dibutylphosphate (NaDBP) give rise to lamellar liquid crystalline phase between 280 and 340 K for NaDBP concentrations ranging from 3 to 4 mol L−1. The orientation and dynamic behaviour of several paramagnetic probes such as the vanadyl ion, tempoamine, tempone and tempobutanamide dissolved in this phase have been investigated by esr.The vanadyl ion binds to the phosphate group, forming a complex, the z magnetic axis of which is on the average perpendicular to the lamellar plane. The molecular mobility at the H2O/DBP− interface is given by the reorientation correlation time of the z axis, which is derived from the total width of the spectrum, using the empirical relation [Formula: see text]. The parameters a = 2.95 × 10−11 s and b = −1.42 are obtained from the viscosity dependence of the esr line widths and of the anisotropic hyperfine couplings.The tempone and tempoamine are localized in the polar domains of the mesophase, reorienting rapidly about the N—O direction which is, on the average, parallel to the director of the lamellar plane. The anisotropic motion of these radicals is assigned to hydrogen bonding which occurs, according to the cases, with water molecules or phosphate groups. Some correlations are established between the esr of spin probes and 2H and 31P nmr experiments on substrate molecules.
Electron paramagnetic resonance characterization and conformation of daunorubicin semiquinone intermediate implicated in anthracycline metabolism, cardiotoxicity, and anticancer action
Authors: Mukherjee Tulsi , Dodd Nicholas J. F.
Published: May 2006

not available
Comparison of conformational information obtained by nuclear magnetic resonance and X-ray spectroscopies for 3-substituted thiazolidine-2-thiones
Authors: Nuzzo Olivier , Pierrot Marcel , Baldy André , Chanon Michel , Chanon Françoise
Published: May 2006

X-ray crystallographic determinations of 3-phenyl- and 3-cyclohexyl-thiazolidine-2-thiones are reported as a method for finding the origin of the discrepancy between 13C and R-(Lambert) methods of determining the puckering in the ring. It is found that in the solid state, the puckering angles are 23.2° and 7.5° for the 3-phenyl and 3-cyclohexyl derivatives, respectively. The comparison of intramolecular and intermolecular distances for both compounds strongly suggests that these values are a fair representation of what is going on in solution. Therefore it is deduced that the puckering angle in these systems is probably better obtained by the 13C nmr shift approach than by the R-Lambert method (in agreement with the most recent Lambert results). Both thiazolidine-2-thiones display a common property – S(1)C(2)S(2)N(3) lie in the same plane. N substitution is, however, different; all of the atoms of either the N-phenyl or of the N-cyclohexyl substituent are not in the S(1)C(2)S(2)N(3) plane. Only the C(6) atom of the N-cyclohexyl group is in the plane and the C(6) atom of the N-phenyl moiety is 0.12 Å out of this plane.
Oxidation of 1-butene by nitrous oxide over manganese(III) and related transition metal oxides
Authors: Ross Robert A. , Fairbridge Craig
Published: May 2006

The oxidation of 1-butene by nitrous oxide over manganese(III) oxide was studied in a continuous flow system from 573 to 673 K. Kinetic parameters were derived from the exponential relationship:[Formula: see text] over reactant partial pressure ranges, [Formula: see text] and [Formula: see text]. The reaction mechanism proposed involves a complex sequence of steps which include surface radical reactions. On the basis of a comparison of specific reaction rates, the catalytic activity series for the reaction over a number of transition metal oxides was: CuO > Fe2O3 > NiO > Mn2O3 > Cr2O3 > TiO2 > Sc2O3 > SnO > ZnO > V2O5 > AlO3.
1,5-Acyclic stereoselection. The stereocontrolled synthesis of optically active vitamin E fourteen-carbon side chain alcohol
Authors: Bérubé Gervais , Deslongchamps Pierre
Published: May 2006

The Diels–Alder product 3 was first transformed into the symmetrical nine-membered cyclic carbonate 8. Reaction of 8 with l-(−)-α-methylbenzylamine (12) yielded a mixture of optically active diastereoisomeric urethanes 9a (9, R = H, R′ = C6H5CHCH3NHCO—) and 9b (9, R = C6H5CHCH3NHCO—, R′ = H) which were separated and respectively converted into 11a and 11b. Compounds 11a and 11b were then transformed respectively into the optically active side chain alcohol 2 (R = H) of vitamine E (1).
Substituent effects on rates of formation of methoxy-substituted carbonyl ylides from 2-aryl-2-methoxy- and 5-aryl-2-methoxy-Δ3-1,3,4-oxadiazolines
Authors: Békhazi Michel , Smith Peter J. , Warkentin John
Published: May 2006

2-Aryl-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines (4) and 5-aryl-2-methoxy-2,5-dimethyl-Δ3-1,3,4-oxadiazolines (5) were synthesized. Compounds 4 decompose in solution with first order kinetics. Rate constants are correlated with Hammett substituent constants (σ−) with ρ(49.2 °C) = 0.74 and 0.89 for CCl4, and CD3OD, respectively. The final products from 4 indicate that thermolysis involves the cleavage of both C—N bonds, to form N2 and, initially, a carbonyl ylide. Compounds 5, which were obtained as mixtures of cis/trans isomers containing several impurities, and which therefore gave poorer kinetic data, decomposed in CDCl3 solution with [Formula: see text] Carbonyl ylide intermediates, similar to those from the closelyrelated compounds 4, were assumed on the basis of analogy and on the basis of partial identification of products. The effects of para substituents in the aryl groups of 4 and 5 show that the transition states have greater electron density at C-2 of 4 and at C-5 of 5 than do the starting materials. In spite of the increase in electron density at C-2 of 4, the transition state must be less polar, overall, than the ground state because rate constants for thermolysis of 4 in methanol are smaller than those for CCl4, solvent. A plausible explanation for the substituent effects and the solvent effects is that the loss of N2 is concerted, with a transition state resembling more closely a spin paired 1,3-diradical than a 1,3-dipole. Alternative stepwise mechanisms, in which C2—N3 bond scission of 4 and C5—N4 bond scission of 5 are the rate-determining steps, leading to 1,5-diradical intermediates, can not be excluded on the basis of the evidence.
Thermochemical parameters for organic radicals and radical ions. Part 4. The relationship between bond dissociation enthalpy and radical stability in benzenoid systems
Authors: Nicholas A. Martin de P. , Arnold Donald R.
Published: May 2006

It is shown that isodesmic reactions used to assess interaction energies between substituents (X and Y) in benzenoid compounds have not been corrected for X/H and Y/H interactions. Excellent linear Mulliken charge – interaction energy relationships are established for meta- and para-substituted toluenes. These studies illustrate the relative importance of σ- and π-effects on a quantitative basis. The ρ-values obtained show an equal importance of -π-effects in meta- and para-substituted toluenes. The signs of the ρ(π)-values confirm the presence of resonance type -π-interactions. The role of ring hydrogens in σ-type interactions cannot be assessed from this study. At present, BDH values in benzenoid systems cannot be corrected such that they can be used to define radical stability. 13C chemical shifts are found not to correlate with isodesmic interaction energies. The application of 13C chemical shifts is limited by the inability to independently relate these shifts to σ- and -π-effects.
Preparation and crystal and molecular structure of (η3-nonamethylcyclotetraphosphazanium-P,P,P)tricarbonylmolybdenum(0) iodide – acetonitrile (1:1), [(η3-Me(MeNPMe)4)Mo(CO)3]I•MeCN
Authors: Gallicano Keith D. , Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

The synthesis and physical properties of [(η3-Me(MeNPMe)4)Mo(CO)3]l are reported. Crystals of (η3-nonamethylcyclotetraphosphazanium-P,P,P)tricarbonylmolybdenum(0) iodide – acetonitrile (1:1) are orthorhombic, a = 13.1938(4), b = 13.7847(5), c = 29.281(2) Å, Z = 8, space group Pcab. The structure was solved by Patterson and Fourier techniques and was refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.034 for 2388 reflections with I ≥ 3σ(I). The structure consists of discrete cations, anions, and solvent molecules. The complex cation has approximate mirror symmetry in the solid state, the Mo atom being coordinated to three phosphazane P atoms and three carbonyl ligands in a distorted octahedral arrangement. Important bond lengths (corrected for libration) are: Mo—P = 2.483(2), 2.439(2), and 2.474(2), mean Mo—C = 1.984(3), mean P—N = 1.710(11) for coordinated P and 1.669(5) Å for quaternized P. The stronger bonding of the cationic ligand to the metal relative to that of the neutral species (CH3NPCH3)4Mo(CO)3, and the strengthening of the ring bonds in both molecules relative to (CH3NPCH3)4, are discussed in terms of d-orbital contraction.
An efficient synthesis of pterosin C and other pterosins
Authors: Ng Kam-Mui Eva , McMorris Trevor C.
Published: May 2006

A versatile synthetic route to pterosins, sesquiterpenoid indanones present in bracken, Pteridiumaquilinum, has been developed. The route is exemplified by the synthesis of (2S,3S)-pterosin C by Friedel–Crafts bisacylation of the methyl ether of 2-(2,6-dimethylphenyl)ethanol with methylmalonyl chloride. Demethylation of the resulting 1,3-indandione and reduction with zinc and acetic acid in the presence of acetic anhydride and sodium acetate afforded a mixture of racemic cis and trans isomers of pterosin C diacetate, which was hydrolysed to the corresponding pterosins. Separation and resolution via the S-(+)-α-phenylbutyric esters gave (2S,3S)-pterosin C and (2R,3R)-pterosin C. Other pterosins were prepared as racemates from the 1,3-indandione.
The formation and hydrolytic cleavage of substituted benzalacetones
Authors: Guthrie J. Peter , Cossar John , Taylor Kathleen F.
Published: May 2006

The base catalyzed aldol condensation of acetone and benzaldehyde, as well as two substituted benzaldehydes, has been reinvestigated in both the formation and cleavage directions. Microscopic rate and equilibrium constants have been deduced from the experimental data in a fashion consistent with the rigorously correct integrated rate law. The values so obtained are as follows: (substituent, rate constants, equilibrium constants);[Formula: see text][Formula: see text][Formula: see text][Formula: see text]K12 = 0.042, K32 = 12. M−1, Koverall = 286; [Formula: see text][Formula: see text][Formula: see text][Formula: see text]K12 = 0.012, K32 = 1.6 M−1, Koverall = 131; [Formula: see text][Formula: see text][Formula: see text][Formula: see text]; K12 = 0.14, K32 = 235 M−1, Koverall = 1730.
Structure-reactivity correlation in inclusion complexes: deoxycholic acid di-tert-butyl thioketone
Authors: Padmanabhan K. , Venkatesan K. , Ramamurthy V.
Published: May 2006

Ultraviolet irradiation of crystalline molecular inclusion complexes of deoxycholic acid with di-tert-butyl thioketone results in no reaction. The structure of the above complex has been determined via X-ray diffraction. The absence of expected photoreactions, namely, photoreduction and photooxidation, is rationalized on the basis of the X-ray structure analysis of the complex.
Photochemistry of methyl(hydrido)diplatinum(II) complexes, including examples of C—H and C—C bond formation by intramolecular reductive elimination
Authors: Azam Kazi A. , Hill Ross H. , Puddephatt Richard J.
Published: May 2006

Photolyses of the complex cations [Pt2H(μ-H)Me(μ-dppm)2]+, [Pt2(μ-H)Me2(μ-dppm)2]+, and [Pt2Me3(μ-dppm)2]+ lead to reductive elimination of H2, CH4, and C2H6, respectively. However, photolysis of [Pt2Me2(μ-dppm)2]+ in pyridine gives [PtMe2(dppm)] and [PtMe(C5H5N)(dppm)]+. The reductive eliminations of CH4 and C2H6 are shown to be primarily intramolecular reactions by isotopic labelling. Quantum yields are reported and the mechanisms of reaction discussed.
The effect of heavy-atom solvents on the photooxidation of anthracene
Authors: Toshima Naoki , Sugano Toshihiko , Hirai Hidefumi
Published: May 2006

Photoirradiation of anthracene in benzene in the presence of oxygen gave predominantly a photodimer of anthracene, and very little oxidation product. Similar irradiation of anthracene in bromobenzene, however, produced 9,10-anthraquinone in high yield. The yield of anthraquinone increased in the presence of a heavy-atom solvent such as bromobenzene, p-dibromobenzene, 1,3,5-tribromobenzene, 1-bromopropane, and dibromomethane in proportion to the sum of squares of the spin–orbit coupling parameter ζ of the solvent molecule. This relationship indicates an external heavy-atom effect on the photooxidation of anthracene. The mechanistic investigations suggest the involvement of singlet oxygen, anthracene peroxide, and a radical intermediate in the formation of anthraquinone.
Electron behavior in mixed solvents: optical spectra and reactivities in water/alkane diols
Authors: Idriss-Ali K. M. , Freeman Gordon R.
Published: May 2006

Investigation of the effect of solvent structure on the optical absorption spectrum and reactivity of solvated electrons has been extended to diol/water mixed solvents, using 1,2-ethanediol (12ED) and 1,4-butanediol (14BD). The large effects that had been found in mono-ol/water mixed solvents did not occur in diol/water. Although addition of 3 mol% of a diol to water increased the optical absorption energies of e−s by 0.06 eV, similar to the shift caused by addition of 3 mol% of a mono-ol, the variation of the spectrum over the rest of the composition range was nearly ideal in diol/water, in contrast to the very non-ideal variation in mono-ol/water. Reaction rate constants kS at 298 K in the diol/water mixed solvents vary approximately as the inverse viscosity,η−1.0, in the diffusion-controlled limit. However, when reactions are two or three orders of magnitude slower than diffusion controlled, kS at 298 K is independent of η. Toluene reacts with e−s at a 10−3-fold smaller rate than does nitrobenzene; the difference is nearly completely due to a ~50 J/mol K lower entropy of activation of the former reaction.
Nuclear analogs of β-lactam antibiotics. XX. Synthesis and X-ray structure determination of exocyclic penems: sulfur analogs of clavulanic acid
Authors: Douglas James L. , Martel Alain , Caron Gilles , Ménard Marcel , Silveira Linda , Clardy Jon
Published: May 2006

Penems 5 were converted to exocyclic analogs 6 and 10. These served as substrates for conversion to the sulfone 11 and oxopenam 12. None of the products showed any activity as antibiotics or as β-lactamase inhibitors. A single cyrstal X-ray diffraction analysis of compound 6a verified the exocyclic penem structure.
Photoisomerization of N,N′-disubstituted indigos. A search for energy storage
Authors: Pouliquen Joseph , Wintgens Véronique , Toscano Vicente , Jaafar Brahim Ben , Tripathi Sadhana , Kossanyi Jean , Valat Pierre
Published: May 2006

The photochemical behaviour of N,N′-disubstituted indigo dyes has been investigated. The trans to cis and cis to trans photoisomerization quantum yields are found to be of the order of 0.25 or less (down to 0.03). These dyes, which fluoresce only weakly in solution and at room temperature, show a drastic increase in their fluorescence when inserted into a polymer matrix or at 77 K in butyronitrile glass. This has been interpreted in terms of the inhibition of formation of a twisted excited intermediate as well as of the rotation of the substituent on the nitrogen atom. An important electron transfer occurs from the singlet excited state when the indigo dyes are placed in the presence of electron-donating molecules. When irradiating with visible light, the photostationary state is always in favour of the trans isomers. This, and kinetic as well as thermodynamic considerations, excludes these compounds as candidates for solar energy storage.
Intramolecular fluorescence energy transfer in nitrobenzoxadiazole derivatives of polyene antibiotics
Authors: Petersen Nils O.
Published: May 2006

Spectroscopic properties of the polyene antibiotic Nystatin and its nitrobenzoxadiazole derivative have been characterized by lifetime and quantum yield measurements. The data suggest that Nystatin and other polyene antibiotics exhibit spectral features common to other linear polyenes such as diphenylhexatriene and parinaric acid, and support the conclusion that the strong absorption (εmax ~70 000 M−1 cm−1; λ = 306 nm) is due to a symmetry-allowed transition to a higher excited state while the red-shifted emission occurs from a lower lying excited state through a weak, symmetry-forbidden transition.Nitrobenzoxadiazole derivatives also exhibit efficient intramolecular fluorescence energy transfer from the polyene chromophore to the nitrobenzoxadiazole chromophore (λcm = 535 nm). The lifetime and quantum yield measurements suggest that the predominant mechanism of energy transfer is via a Dexter type transfer in a fraction of molecules with appropriate conformations.
Réactivité du nucléophile azoture vis à vis de cations hétérocycliques aromatiques. VI. Cas des triaryl-2,4,6 oxaziniums-1,3
Authors: Cherton Jean-Claude , Desbene Paul-Louis , Bazinet Marc , Lanson Marc , Convert Odile , Basselier Jean-Jacques
Published: May 2006

Nucleophilic attack of sodium azide on 2,4,6-triaryl-1,3-oxazinium species gives high yields of β-tetrazolo-trans-benzalacetophenones from the corresponding 2-azido-1,3-oxazines. The rearrangement of the azido oxazines likely proceeds via tautomerism of the intermediate iminoazides. If the formation of the 2-azido-1,3-oxazines is under kinetic control, these results are a rare example of high regioselectivity in nucleophilic attack at the C2 carbon of 1,3-oxazinium species.The reaction behaviour of the 1,3-oxazinium/N3− system is discussed, together with results obtained from the 2,4,6-triphenylpyrilium/N3−.
Kinetics and equilibrium in the ammonolysis of substituted phthalimides
Authors: McClelland Robert A. , Seaman N. Esther , Duff James M. , Branston R. E.
Published: May 2006

Kinetic studies are reported for the base hydrolysis to phthalamic acid anions (H) and ammonolysis to phthalamides (A) for seven phthalimides (P): 1, unsubstituted; 2, 4-NO2; 3, 4-Cl; 4, 4-t Bu; 5, 3-NO2; 6, 3-Me; 7, 3-Me3Si. The hydrolysis kinetics require two mechanisms, one which is first order in neutral imide and first order in hydroxide ion, and a second, which is important only in quite concentrated NaOH, which is first order in neutral phthalimide and second order in hydroxide ion. Ammonolysis kinetics for 1–5 revealed the rate law: Rate = kN [Unionized phthalimide] [NH3][OH−]. A mechanism is proposed with rate-determining breakdown of the anionic form of the tetrahedral intermediate derived by addition of NH3 to the phthalimide. The ammonolysis is reversible. The phthalamide hydrolyzes to the phthalamic acid via cyclization to an intermediate phthalimide, which is detected in concentrated base where its formation from phthalamide is more rapid than its subsequent hydrolysis. Rate constants for the cyclization follow the rate law: Rate = kcyc [Phthalamide][OH−]. This reaction is the microscopic reverse of the ammonolysis, and the ratio kN/kcyc provides the equilibrium constant Keq for the reaction P + NH3 = A. Values for 1–5 lie in the range 2 × 102 – 4 × 103. With 3-methylphthalimide, kinetics in aqueous ammonia do not obey a first-order relationship, but they could be analyzed by a scheme whereby the phthalimide is converted reversibly to the phthalamide and simultaneously undergoes an irreversible hydrolysis. The value of Keq in the system is 1.8. With 3-trimethylsilylphthalimide the value of Keq is further reduced to 0.01. The ammonolysis reaction does occur more quickly than hydrolysis but the equilibrium is so unfavorable that even in concentrated ammonia only a small amount of the phthalamide is ever formed.
Thermodynamic miscibility of polystyrene–poly(2,6-dimethyl-1,4-phenylene oxide) blends
Authors: DiPaola-Baranyi Giuseppa , Richer Jocelyn , Prest Jr. William M.
Published: May 2006

Inverse gas chromatography was used to investigate the miscibility behaviour of molten polystyrene–poly(2,6-dimethyl-1,4-phenylene oxide) blends as a function of composition (0, 25, 50, 75, 85, and 100 wt.% PS). Specific retention volumes were measured for various solutes in pure and mixed stationary phases of these polymers at 240 °C. Infinite dilution weight fraction activity coefficients and Flory–Huggins polymer–solute (χ) and polymer–polymer (χ23′) interaction parameters were derived from these data.Negative polymer–polymer interaction parameters were obtained for blends containing more than 60 wt.% PS, suggesting strong intermolecular interactions in the molten state. This is in accord with the well-known compatibility of PS–PPO blends. However, positive χ23′ values were observed for blends containing less than 60 wt.% PS. This suggests weak intermolecular interactions, and perhaps some microheterogeneity in PS–PPO blends with a low PS content. In view of the single, composition dependent Tg measured for each of these blends the microheterogeneity or microphase separation must be on a finer scale than that measured by the glass transition.
Kinetics and mechanism of oxidation of N,N′-dimethyl-9,9′-biacridanyl by some π acceptors and a one-electron oxidant
Authors: Colter Allan K. , Lai Charles C. , Parsons A. Gregg , Ramsey N. Bruce , Saito Gunzi
Published: May 2006

Oxidation of N,N′-dimethyl-9,9′-biacridanyl (DD) has been investigated as a model for single electron transfer (SET)-initiated oxidation of NADH coenzyme models such as N-methylacridan (DH). Oxidants investigated cover a 1010-fold range of reactivity in acetonitrile and include the π acceptors 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCIBQ), p-chloranil (CA), 2,3-dicyanobenzoquinone (DCBQ), 2,3-dicyano-1,4-naphthoquinone (DCNQ), 2,3-dicyano-5-nitro-1,4-naphthoquinone (DCNNQ), 9-dicyanomethylene-2,4,7-trinitrofluorene (DCMTNF), 9-dicyanomethylene-2,4,5,7-tetranitrofluorene (DCMTENF), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE), and the one-electron oxidant tris(2,2′-bipyridyl)cobalt(III), [Formula: see text] The oxidation product is, in every case, N-methylacridinium ion (D+). A mechanism involving a rate-determining electron transfer with simultaneous fragmentation to D+ and N-methyl-9-acridanyl radical (D•) is proposed. This mechanism is supported by the observed dependence of the rate on oxidant reduction potential, by spin-trapping experiments, by kinetic isotope effects in oxidation of 9,9′-dideuterio-DD, and by substituent effects in oxidation of 2,2′- and 3,3′-dimethoxy-DD. The rate of oxidation of DD relative to that of DH is 3.4 × 102 with [Formula: see text] and with the π acceptors varies from ea. 0.3 (BQ) to 8.1 × 104 (DCMTENF). The results rule out a SET-initiated mechanism for oxidation of DH by all of the oxidants studied except TCNQ and DCMTENF.
Towards a complete account of the mechanism of hydrogen isotope exchange of diastereotopic protons of carbon acids. II. Acid- and base-catalyzed enolization of bicyclo[2.2.1]heptan-2-ones. Evidence for exchange by inversion
Authors: Werstiuk Nick Henry , Banerjee Sujit
Published: May 2006

A study of acid- and base-catalyzed hydrogen isotope exchange of bicyclo[2.2.1]heptan-2-one (1a) and its 3-deuteriated analogs has been carried out. We find that the kexo/kendo ratio (658 ± 66) for deuteroxide-catalyzed H → D exchange of 1a at C-3 is 7.2 ± 1.5 times greater than the kexo/kendo ratio (91 ± 9) for hydroxide-catalyzed D → H exchange of 1b. For acid-catalyzed exchange in CH3COOD(H)–D(H)Cl the rate ratios are 156 ± 20 and 29 ± 2 for H → D and D → H exchange, respectively. Equations which relate the observed selectivity kexo/kendo (kfast/kslow) to the intrinsic selectivity and the primary, secondary, and solvent KIEs are developed. The differences between the rate ratios for H → D and D → H exchange are interpreted on the basis of a significant contribution of an inversion pathway to exchange of the slow proton (deuteron). The significance of our study – it relates to the mechanism of hydrogen isotope exchange of diastereotopic protons (deuterons, tritons) of any carbon acid – is discussed.
Utilization of thiocarbonyl transfer reagents. Preparation of thioamides, mercapto esters, and thiapyran derivatives
Authors: Harpp David N. , MacDonald J. Gavin , Larsen Charles
Published: May 2006

The reaction of 1,1′-thiocarbonyldiimidazole and 1,1′-thiocarbonylbis(1,2,4-triazole) with several aldonitrones has been found to afford thioamides in good yield. Several 1,1′-thiocarbonylbisazoles, which have been shown to undergo Diels–Alder additions with dienes to give cyclic and bicyclic adducts, can be further converted to mercapto esters, thiapyrans, and thiapyranones in good yield.
Kinetics and isotope effects of the β-elimination reactions of some 2,2-di(4-nitrophenyl)chloroethanes promoted by tetramethylguanidine in aprotic solvents
Authors: Jarczewski Arnold , Waligorska Malgorzata , Leffek Kenneth T.
Published: May 2006

Rate constants for the β-elimination of HCl from 2,2-di(4-nitrophenyl)-1,1-dichloroethane (I) and 2,2-di(4-nitrophenyl)-1,1,1-trichloroéthane (II) promoted by tetramethylguanidine in the aprotic solvents acetonitrile, tetrahydrofuran, and n-hexane have been measured. The activation parameters are characterized by small enthalpies of activation (4.1 to 7.3 kcal mol−1) and large negative entropies of activation (−35 to −50 cal mol−1 deg−1). The primary deuterium isotope effects at 20° C range from kH/kD = 4.8 to 10.3. The results are interpreted to indicate an (EcB)1 mechanism for both substrates I and II in acetonitrile solvent and an E2H or mixed (ElcB)1–E2H mechanism in the less polar solvents, tetrahydrofuran and n-hexane.
Minor anthraquinonoid metabolites of Cercosporaarachidicola
Authors: Stoessl Albert , Stothers J. B.
Published: May 2006

Minor metabolites of the fungus Cercosporaarachidicola have been identified as the known pigments versicolorin B (3), averantin (4), and nidurufin (2b) and the new, but closely related compounds 4′-deoxydothistromin (1b), 3′,4′-dehydro-4′-deoxydothistromin (5a), and 4′,5-bisdeoxydothistromin (1d). The 1H and 13Cmr spectra of 1d, 2b, and the tetracetates 1c and 5b are presented in detail. Biosynthetic and chemotaxonomic aspects are discussed.
Tetracyclic triterpenes. VIII. The skeletal rearrangement of 3β-acetoxy-9α,11α-epoxy-5α-lanostan-7-one: 13- and 10-methyl group migration
Authors: Paryzek Zdzisław , Wydra Roman
Published: May 2006

The boron trifluoride etherate catalyzed rearrangement of 3β-acetoxy-9α, 11α-epoxy-5α-lanostan-7-one (1) in acetic anhydride resulted in formation of 19(10 → 9β)abeo compounds 2 and 4 along with 18(13 → 12β)abeo compound 5, as the major product. These structures are supported by spectral data and chemical transformations. The possible mechanism of the rearrangement is discussed.
Intrazeolite photochemistry. II. Evidence for site inhomogeneity from studies of aromatic ketone phosphorescence
Authors: Casal H. L. , Scaiano J. C.
Published: May 2006

The luminescent properties of several aromatic ketones included in the hydrophobic zeolite Silicalite have been examined. Acetophenone, benzophenone, and β-phenylpropiophenone show readily detectable phosphorescence; by contrast, valerophenone does not luminesce, but undergoes the Norrish Type II reaction. Thus, irradiated samples of valerophenone in Silicalite show phosphorescence due to the accumulation of acetophenone. In the case of β-phenylpropiophenone the triplet lifetime is ca. 100 000 times longer than the solution value, suggesting severe conformational restrictions. Co-inclusion of acetophenone with various substrates and oxygen quenching studies indicate that Silicalite has at least two distinct classes of inclusion sites. In one of them energy transfer processes are rapid and efficient, suggesting a cooperative effect in the inclusion of ketones in these regions of the Silicalite framework.
Polymérisation du chloroformiate de vinyle et de ses dérivés
Authors: Boivin Sylviane , Hemery Patrick , Boileau Sylvie
Published: May 2006

The free-radical polymerization of vinyl chloroformate has been studied in methylene chloride at 35 °C using dicyclohexyl peroxydicarbonate as initiator. Kinetic measurements performed by dilatometry under high vacuum have shown that the reaction order in monomer is equal to one whereas that in catalyst is equal to 0.5.New polymers have been prepared either by free-radical polymerization of monomers derived from vinyl chloroformate or by chemical modification of poly(vinyl chloroformate) with amines, alcohols, thiols, carboxylic acids, KCN … using phase transfer catalysis. The structure of these polymers as well as their thermal behaviour have been studied.
Vibronic analysis of the spectrum of Br2CS
Authors: Simard B. , Steer R. P.
Published: May 2006

[Formula: see text] fluorescence excitation and emission spectra of Br2CS have been recorded. A vibronic analysis shows that the molecule is non-planar in the [Formula: see text] state with an equilibrium out-of-plane angle of 13° and a barrier to inversion of l64 cm−1. Upper state vibrational frequencies of modes 1, 2, 3, 4, and 6 have been obtained. Comparisons with other tetraatomic thiocarbonyls support the assignments. A ground state C—Br dissociation energy of 52.3 kcal mol−1 has been obtained from the onset of diffuseness in the [Formula: see text] spectra. A search for phosphorescence proved unsuccessful.
A theoretical investigation of energetics and structures of CH5+(CH4)n clusters for n = 1–4
Authors: Fois Ettore , Gamba Aldo , Simonetta Massimo
Published: May 2006

The structures of CH5+(CH4)n (n = 1–4) are determined by semiempirical and abinitio MO calculations. The results of the present calculations are in fair agreement with the values of −ΔH obtained in mass spectrometric experiments. It appears that a three-center–two-electron bond has the most efficient attractive power for the incoming methane molecules.
Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen
Authors: Re Giuseppe Del , Fliszár Sándor , Comeau Michel , Mijoule Claude
Published: May 2006

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.