bluuebunny/crossref_metadata_2025 huggingface dataset:
Approaches to the total synthesis of triterpenes. VIII. The ABC + D/E approach. Synthesis and X-ray structure determination of 1β,4a β-dimethyl-7-methoxy-1α- (7′,7′-ethyleneketal-6′,6′-dimethyl-3′-ketooctyl)-3,4,4a,9,10,10aα-hexahydro- 2(l-H)phenanthrone
Authors: ApSimon John W. , Sequin Rick P. , Huber Carol P.
Published: May 2006

The title compound was made following a projected synthetic route to pentacyclic triterpenes. The key step in the route is the alkylative trapping of the enolate derived from the enol trimethylsilyl ether 8. The stereochemical consequence of this reaction is confirmed by a single crystal X-ray structure determination on 4, which although of no further utility in the projected synthesis, nevertheless served as a useful template for this determination. In this way, ongoing work in a parallel series of compounds rests on a firm stereochemical footing.
Complexes of substituted benzothiazoles 4. Nickel(II) complexes of the bidentate benzothiazoles 1,2-bis(2-benzothiazolyl)benzene and 1,2-bis(2-benzothiazolyl)ethane
Authors: Thompson Laurence Kenneth , Rendell John Charles Thomas , Wellon George Charles
Published: May 2006

The nickel coordination chemistry of two potentially bidentate bis-benzothiazole ligands is compared. 1,2-Bis(2-benzothiazolyl)-benzene (OBT), which has an o-phenylene bridge, forms square planar derivatives with NiX2 (X = I, ClO4, BF4), octahedral derivatives with NiX2 (X = NCS, NO3), and five-coordinate derivatives with NiX2 (X = CI, Br). 1,2-Bis(2-benzothiazolyl)ethane (BBTE), which has an ethylene bridge, forms tetrahedral derivatives with NiX2 (X = CI, Br, I) and an octahedral complex with Ni(NO3)2. Although both ligands are capable of tetrahedral coordination about a cobalt centre, the apparent preference of tetrahedral coordination with nickel complexes of BBTE seems unusual. The only difference between the two ligands lies in the bridging group between the benzothiazole rings. Structural assignments are supported by ligand field and infrared spectra, magnetic data, and an X-ray structure of the complex [Ni(BBTE)Br2], which has been shown to have a distorted tetrahedral stereochemistry.
1-Pyrazolyl phosphazenes and their complexes with palladium(II) chloride and platinum(II) chloride
Authors: Gallicano Keith D. , Paddock Norman L.
Published: May 2006

The chlorophosphazenes (NPCl2)3–6 and the phenylchlorophosphazenes gem-N3P3Ph4Cl2 and gem-N3P3Ph2Cl4 react with pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole to give (NPpz2)3–6, [NP(Mepz)2]3–5, [NP(Me2pz)2]3,4, N3P3Ph4(Mepz)2, N3P3Ph4(Me2pz)2, and N3P3Ph2(Me2pz)4. Infrared and nmr spectroscopy show the pyrazolyl group to be an electron-withdrawing substituent on the phosphazene ring, resembling a halogen rather than an amino-group. The pyrazolyl group also acts as a donor through its pyridinic nitrogen atom, both intramolecularly and in the formation of the complexes gem-N3P3Ph4(Me2pz)2•PdCl2, gem-N3P3Ph2(Me2pz)4•PdCl2, N3P3(Me2pz)6•2PdCl2, N3P3(Me2pz)6•2PtCl2, and N3P3(Me2pz)6•3PdCl2. No bonding between the metal and a nitrtogen atom in the ring was detected.
Conjugative interactions in 1-methylpyrrol-2-yl derivatives of the cyclic phosphazenes (NPF2)n (n = 3–6): the crystal and molecular structure of 1-methylpyrrol-2-ylheptafluorocyclotetraphosphazene
Authors: Sharma Rajendra D. , Rettig Steven J. , Paddock Norman L. , Trotter James
Published: May 2006

1-Methylpyrroles, in which the 2-position is occupied by a pentafluorocyclotriphosphazenyl (1a), heptafluorocyclotetraphosphazenyl (1b), nonafluorocyclopentaphosphazenyl (1c), or undecafluorocyclohexaphosphazenyl group (1d), have been prepared from 2-lithio-1-methylpyrrole and the corresponding fluorophosphazene. Crystals of 1b are monoclinic, a = 17.300(2), b = 5.0281(3), c = 16.902(2) Å, β = 108.904(4)°, Z = 4, space group P2/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.038 and Rw = 0.047 for 1167 observed reflections. The N4P4 ring is nearly planar. The P—N bond lengths (corrected for libration) range from 1.524(5) to 1.562(5) Å with a mean value of 1.541(17) Å, and the mean ring angles are 122.9(20)° at phosphorus and 146.4(23)° at nitrogen. The geometry of the 1-methylpyrryl group shows no unexpected features, but the P—C bond (1.756(5) Å) is significantly shorter than in typical P-phenyl derivatives, and the P—F bond at the same atom is comparatively long (1.561(4) Å). Conjugative electron release from the pyrryl group, involving pπ–dπ bonding, is indicated both by these geometrical features and by the appearance of intramolecular charge transfer bands in the electronic spectra of 1(a–d).
Bimolecular production of proton bound dimers in the gas phase. A low pressure ion cyclotron resonance technique for examination of solvent exchange equilibria and determination of single molecule solvation energetics
Authors: Larson J. W. , Clair R. L. , McMahon T. B.
Published: May 2006

A scheme is presented whereby sequences of fast bimolecular gas phase ion molecule reactions in mixtures containing (CHF2)2O may be used to generate proton bound dimer species at low pressures in an ion cyclotron resonance spectrometer. Using competitive solvent switching reactions it is demonstrated that solvent exchange equilibria may be readily established and from the thermochemical data derived from such equilibria accurate relative single molecule solvation energetics obtained.
The isolation and structure of phyllanthostatins 2 and 3
Authors: Pettit George R. , Cragg Gordon M. , Gust Devens , Brown Peter
Published: May 2006

A new antineoplastic glycoside, phyllanthostatin 2, and a related glycoside, phyllanthostatin 3, have been isolated from the Central American tree, Phyllanthusacuminatus and their structures assigned as 1c and 2 respectively.
La polymérisation anionique en masse de l'α-méthyl styrène. I. Etude de la stabilité des centres actifs
Authors: Ades Dominique , Fontanille Michel , Leonard Jacques
Published: May 2006

The anionic bulk polymerization of α-methylstyrene (αMS) has been carried out using tert-butyllithium (t-BuLi) as initiator with or without N,N,N′,N′-tetramethylethylenediamine (TMEDA). In absence of TMEDA, the "living ends" are rapidly deactivated at 62 °C whereas they are relatively more stable at 25 °C. The "living ends" are much more stable in presence of TMEDA; however, their stability is a function of the order in which t-BuLi and TMEDA are added to αMS. The stability of "living ends" is also a function of the ratio r = [TMEDA]/[t-BuLi] and best results are obtained with a one to one ratio. At high temperature, the formation of species with absorption bands at 390 and 424 nm and the broadening of the molecular weight distribution are observed. These results are explained in terms of a transfer reaction to the monomer or to the deactivated polymer.
High yield "one-pot" synthesis of 2-hydroxy-3-methylcyclopent-2-en-1-one and related compounds
Authors: Strunz George M. , Lal G. Sankar
Published: May 2006

A convenient "one-pot" modification of a conventional synthetic route affords 2-hydroxy-3-methylcyclopent-2-en-1-one and related compounds in high overall yields.
On the origin of regioselectivity in the photorearrangement of 4,4-diphenyl-2,5-cyclohexadiene systems. Synthesis and photochemistry of 4,4-diphenyl-γ-thiopyran and -γ-thiopyran-1,1-dioxide
Authors: Gravel Denis , Leboeuf Christian
Published: May 2006

The synthesis from diphenylmethane of 4,4-diphenyl-γ-thiopyran and 4,4-diphenyl-γ-thiopyran-1,1-dioxide is described. Upon direct photolysis at 254 nm the γ-thiopyran derivative undergoes rearrangement to a mixture of 5,6-diphenyl-2-thiabicyclo-[3.1.0]hexene and 2,4-diphenyl-α-thiopyran. The corresponding 1,1-dioxide derivative on the other hand undergoes, upon direct photolysis at 254 nm or sensitized (acetone) photolysis at 350 nm, rearrangement to 6,6-diphenyl-2-thiabicyclo[3.1.0]hexene-2,2-dioxide accompanied by a solvent addition product: 3-methoxy-4,4-diphenyl-2,3-dihydro-γ-thiopyran-1,1-dioxide. The results, along with those observed for 4,4-diphenyl-γ-pyran studied in this series, and other literature results are rationalized in terms of Zimmerman's reacting chromophore simulation using the Möbius–Hückel concept to evaluate competing excited state energies of the isoconjugate chromophores.
Optical and Raman spectra of single crystals of perylene-TCNQ charge transfer complexes
Authors: Bandrauk A. D. , Truong K. D. , Carlone C.
Published: May 2006

Optical transmission and reflection measurements are reported for the quasi one dimensional solids perylene-TCNQ (P1T1) and (perylene)3-TCNQ (P3T1) in the region from 300 to 1200 nm. Raman spectra of single crystals of both compounds were obtained from 20 to 3000 cm−1. With 457.9 nm excitation, combinations and overtones of perylene are observed for the first time. A complete Raman spectrum of perylene and its deuterated homologue including librations is thus obtained via selective resonance enhancement of that molecule.
Excited states of acrolein: abinitio model studies on α,β-unsaturated carbonyl compounds
Authors: Valenta Katherine , Grein Friedrich
Published: May 2006

As an explanation of the stereochemistry of photoaddition between α,β-unsaturated carbonyl compounds and olefins, Wiesner suggested that the excited state of the α,β-unsaturated carbonyl compound is pyramidal at the β-carbon. It is shown by abinitio SCF and CI studies that for acrolein in the 1nπ*, 3nπ*, and 3ππ* excited states the β-carbon remains planar. In addition, vertical excitation energies for the 1nπ* and 1ππ*, and adiabatic excitation energies for the 1nπ* and 3nπ* states of trans-acrolein have been calculated.
Sterically hindered aromatic compounds. XI. Spectral and product studies of the decomposition of N-nitrosoacetanilides
Authors: Barclay L. Ross C. , Dust Julian M.
Published: May 2006

Decomposition of N-nitroso-2,4,6-tri-tert-butylacetanilide (1) in benzene forms products 2,4,6-tri-tert-butylphenyl acetate (3), 3-(3,5-di-tert-butylphenyl)-2-acetoxy-2-methylpropane (4), and hydrocarbons 3-(3,5-di-tert-butylphenyl)- and 1-(3,5-di-tert-butylphenyl)-2-methylpropene (5 and 6) explained by a reactive aryl cation (2), the rearranged products (4, 5, 6) originating from a 1,5-hydride shift from an orthotert-butyl group in 2. In contrast, decomposition of 1 in triethylamine forms products 1,3,5-tri-tert-butylbenzene (10), 2,4,6-tri-tert-butylacetanilide (15), and 2-(3,5-di-tert-butylphenyl)-2-methylpropanal oxime (13), expected of a free radical pathway. Electron spin resonance evidence is given for intermediates formed by rearrangement of the 2,4,6-tri-tert-butylphenyl radical and spin trapped by the nitroso group of 1. CIDNP and esr studies on the dediazoniation of N-nitrosoacetanilide and aniline in the presence of tertiary amines support the proposed electron transfer mechanism. The results are briefly discussed in terms of the role of steric effects and electron transfer in the dediazoniation of nitrosoacetanilides and diazonium salts.
Enolates de β-cétoesters: conformations et stabilités des formes dissociées
Authors: Cambillau C. , Guibe F.
Published: May 2006

The problem of the conformation of β-ketoester enolates has been investigated through 1H nmr studies and through conductimetrie studies. We have compared the dissociative properties of the K+ enolates of acyclic β-ketoesters which can a priori adopt any possible ZE, ZZ, EE, or EZ conformations and of hemicyclic β-ketoesters (2-carbethoxycyclopentanone, 2-acetyl γ-butyrolactone) in which geometrical constraints excluded some of them. The results lead to the conclusion that the EE conformation is more stable than either the ZZ or EZ ones. Confirmation of this point, which implies that the acyclic dissociated enolates exist in the EE conformation, is afforded by 1H nmr spectroscopy. Those experimental results have been complemented with abinitio STO-3G calculations performed on the methyl formylacetate anion and on the formylacetone anion (the diketonic analog). The method of conductimétrie titration by cryptand (2,2,2) used for the determination of the dissociation coefficient of K+ enolates in DMSO is discussed in some detail.
Regiospecific addition of benzeneselenenyl halide to 1,1-dis ubstituted olefins
Authors: Ho Pak-Tsun , Kolt Ralph J.
Published: May 2006

The reaction of benzeneselenenyl halide with a variety of 1,1-disubstituted olefins under controlled conditions yields regiospecifically the anti-Markovnikov adducts which have been converted into the synthetically useful vinyl halides and allylhalides.
Lanthanide complexes of potentially heptadentate Schiff base ligands
Authors: Alyea Elmer C. , Malek Abdul , Vougioukas Angelos E.
Published: May 2006

The potentially heptadentate trianionic Schiff base ligands derived from tris(2-aminoethyl)amine and 3 mol of (substituted) salicylaldehyde react with lanthanide metal nitrates to form neutral 1:1 compounds of formula Ln(X-Saltren). Physicochemical measurements are described for the following complexes: Ln = La, Pr, Nd, Eu, Gd, Dy, Ho, Yb, X = 3,5-Cl2; Ln = La, X = 5-Cl and 5-NO2; and the analogous complexes, M = Sc, Y, Co, X = 3,5-Cl2. Discussion of the spectroscopic data focuses on far infrared ν(Ln—O) and ν(Ln—N) bands, 1H nmr pseudocontact shifts and hypersensitive f–f transitions.
Electrophilic cyclization of polyene allylsilanes. Synthesis of albicanyl acetate
Authors: Armstrong Rosemary J. , Harris Francis L. , Weiler Larry
Published: May 2006

The allylsilanes 5 [Formula: see text] were prepared by a nickel(II) catalyzed coupling of trimethylsilylmethylmagnesium chloride with the enol phosphate of the corresponding β-keto esters. Stannic chloride and mercuric trifluoroacetate effected a cyclization of 5. The product from 5b was converted into the marine natural product, albicanyl acetate (1)[Formula: see text]
The microwave spectrum, harmonic force field, structure, and dipole moment of propiolyl chloride
Authors: Davis R. Wellington , Gerry M. C. L.
Published: May 2006

The microwave spectra of four isotopic species of propiolyl chloride, HCCCOCl, have been measured for their ground and υ9 = 1 excited vibrational states. Values for the rotational constants, quartic centrifugal distortion constants, chlorine nuclear quadrupole coupling constants, and the molecular dipole moment have been obtained. The centrifugal distortion constants have been combined with vibrational wavenumbers from the literature to calculate an approximate harmonic force field. Effective and ground state average structures of the most abundant isotopic species, H12C12C12C16O35Cl, are presented.
Coordination compounds of indium. Part 39. Some neutral adducts of In2Br4 and In2I4
Authors: Taylor Michael J. , Tuck Dennis G. , Victoriano Luis
Published: May 2006

The neutral indium(II) compounds In2X4(Et3P)2, In2X4(TMED)2, and In2X4(TMED)2C6H6 (X = Br, I; TMED = N,N,N′,N′-tetramethylethylenediamine) have been prepared by the reaction of InX2 and donor in benzene or toluene. With several other neutral donors, and in all systems involving InCl2, decomposition to In0 is the predominant process. Analysis of the vibrational spectra demonstrates that these structures involve X2In-InX2 kernels. Slight revisions are proposed to previous discussions of the infrared spectra of In2X62− anions.
Neutral complexes of the indium dihalides
Authors: Sinclair Ian , Worrall Ian J.
Published: May 2006

The neutral complexes In2X4•2L (X = Cl, Br, I; L = 1,4-dioxan, tetrahydropyran, tetrahydrofuran, tetrahydrothiophene), In2X4•2L (X = Br, I; L = dimethylsulphide), In2X4•4L (X = Cl, Br, I; L = piperidine, piperazine, morpholine), and In2X4•4L (X = Br, I; L = pyridine, dimethylsulphoxide) have been prepared. Solid state Raman spectra indicate that the compounds contain indium–indium bonds.
The electronic structure of cyclopentadienylindium
Authors: Lin C. S. , Tuck Dennis G.
Published: May 2006

CNDO calculations have been carried out for the molecule InC5H5 of C5υ symmetry. Overlap populations were calculated and compared with those for related species. The bonding between In and the organic moiety can be described as essentially a covalent interaction involving mainly indium 5s and 5p orbitals with ring pπ orbitals. A lone pair on indium is a dominant feature of the structure, and is largely responsible for a (calculated) dipole moment of 4.75 D. The calculated orbital energies are compared with experimental photoelectron spectra.
An electron spin resonance study of organomercury radical complexes with ortho-quinones and vitamin C
Authors: Weir Douglas , Hutchinson Douglas A. , Russell Judy , Wan Jeffrey K. S.
Published: May 2006

Photochemical and thermal reactions of ortho-quinones and organomercury lead to the formation of a series of quinine–HgR• radical complexes. Hyperfine splittings due to 199Hg isotope were resolved for the 3,5-di-t-butylbenzoquinone complexes. Photochemical reactions of vitamin C in ethanol with a number of mercuric salts produce a paramagnetic intermediate which is assigned to the ion-pair involving the ascorbate radical anion and the mercuric ion. In di-n-butyl mercury, photolysis of vitamin C leads to the formation of a radical complex similar to those of quinine–HgR• but with a much smaller hyperfine coupling constant for 199Hg. A simple theoretical model using some MO calculations on the π system of these organometal–quinone radical complexes, which include the metal atom, was developed to account for the systematic experimental observations.
Synthesis and properties of some spin labeled long chain aliphatic acids
Authors: Gala D. , Schultz R. , Kreilick R.
Published: May 2006

We have synthesized and characterized a series of spin labeled aliphatic acids with variable chain lengths between the nitroxide radicals and the carboxylic group. These molecules should be of general utility in labeling a variety of substrates which can react with the free carboxylic acid group. Variable temperature esr studies have been conducted with some of these molecules to characterize molecular motion as a function of solvent viscosity.
The basicity of phosphines
Authors: Allman Tim , Goel Ram G.
Published: May 2006

The basicities of the triarylphosphines P(4-XC6H4)3 (X = Cl, F, H, CH3, CH3O, (CH3)2N), P(3-CH3C6H4)3, and P(2-CH3C6H7)3 as well as the trialkylphosphines P(t-Bu)3 and PCy3 have been measured by the nitromethane titration method. The range of basicity available by aryl substitution is very large, being pKa = 8.65 for X = (CH3)2N to 1.03 for X = Cl. The most basic phosphine is P(t-Bu)3 whose pKa = 11.40. The measured basicities correlate well with σp, [Formula: see text], and ν as well as with the lone pair ionisation potentials of the triarylphosphines. Generally the 1H, 31P, and 13C nmr spectral parameters of the free and protonated phosphines do not correlate well with pKa.
Molecular orbital structures of sulfones
Authors: Boyd Russell J. , Szabo Jeffrey P.
Published: May 2006

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.
Effect of hydrogen bonding on the π-electronic absorption spectra of some bicyclic secondary amines
Authors: Ganguly Tapan , Banerjee Sukhendu B.
Published: May 2006

Spectral shift and change in the intensity of electronic absorption bands of bicyclic molecules, 1,2,3,4-tetrahydroquinoline (THQ) and 1,2,3,4-tetrahydroisoquinoline (THIQ), on hydrogen bond formation in binary and ternary solutions were investigated. Roles of factors contributing to the spectral changes such as change in configuration of the molecules and σ–π interaction are discussed in this paper.
Charge distributions and chemical effects. XXVII. Molecular energies of carbonyl compounds and ethers, a calculation involving the charges of the bond-forming atoms
Authors: Fliszár S. , Béraldin M. T.
Published: May 2006

Energy calculations are presented for carbonyl compounds and ethers by applying the equation εij = εij0 + aijΔqi + ajiΔqj which describes individual bond contributions in terms of electronic charge increments Δq at the bond-forming atoms i and j, relative to atomic charges in selected reference bonds with energies εij0. At a molecular level, the sum ΣiΣjaijΔqi accounts for virtually the entire energy variations due to charge redistributions accompanying isodesmic structural changes. Coulomb-type interactions between nonbonded atoms play only a minor role in that respect. Using charges derived from 13C and 17O nmr shift-charge correlations, calculated and experimental energies agree within 0.16 kcal/mol (average deviation).
The crystal and molecular structure of N,N′-ethylenebis(benzoylacetoniminato)-nickel(II)
Authors: Malatesta Vincenzo , Mugnoli Angelo
Published: May 2006

not available
Abinitio SCF MO calculations on the reactions of OH radical with pyridine and pyridinium ion
Authors: Anthony M. C. , Waltz W. L. , Mezey P. G.
Published: May 2006

Relative energies of various products formed in the reaction of pyridine and pyridinium ion with the hydroxyl radical are calculated using non-empirical SCF MO techniques. The favourable electron delocalization in the meta-products, rather than the electrophilic character of the OH radical is the determining factor of relative stabilities. Calculated energy barriers along approximate reaction paths correlate with the available experimental information.
Marine natural products: highly functionalized steroids (12β-hydroxy-24-norcholesta-1,4,22-trien-3-one and 12β-acetoxy-24-norcholesta-1,4,22-trien-3-one) from the sea raspberry, Gersemiarubiformis
Authors: Kingston John F. , Fallis Alex G.
Published: May 2006

Two new C26 steroid Δ1.4-dien-3-ones 5 and 6 with 12β oxygen functions have been isolated from the soft coral Gersemiarubiformis and their structures elucidated from their spectral data and chemical transformations.
Synthesis of cedranoid sesquiterpenes. II. Functionalization at carbon 12
Authors: Yates Peter , Stevens Kenneth E.
Published: May 2006

Dimethyl 6,6-dimethyl-7-oxotricyclo[3.2.1.02,8]octane-1,8-dicarboxylate (6) undergoes homoconjugate addition with lithium diphenylcuprate to give dimethyl 3-hydroxy-4,4-dimethyl-exo-8-phenyl-cis-bicyclo[3.3.0]oct-2-ene-1,2-dicarboxylate (12a), which on monodecarboxymethylation, ozonolysis, and esterification with diazomethane gives dimethyl 6,6-dimethyl-7-oxo-cis-bicyclo-[3.3.0]octane-1,exo-2-dicarboxylate (15). Reaction of 6 with diethylaluminum cyanide gives dimethyl exo-8-cyano-3-hydroxy-4,4-dimethyl-cis-bicyclo[3.3.0]oct-2-ene-1,2-dicarboxylate (16), which on hydrolysis and esterification with diazomethane also gives 15. Sensitized photolysis of dimethyl 5-oxo-6,6-dimethylbicyclo[2.2.2]octa-2,7-diene-2,3-dicarboxylate (19) gives dimethyl 4,4-dimethyl-3-oxotricyclo[3.2.1.02.8]oct-6-ene-1,8-dicarboxylate (20), which on reduction with lithium in ammonia gives dimethyl 6,6-dimethyl-7-oxobicyclo[3.3.0]oct-3-ene-1,exo-2-dicarboxylate (31); conversion of 31 to its 2-ene isomer 32 followed by catalytic hydrogénation gives 15 and its endo-2 epimer 33.
Ene-type adducts from the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with β-alkyl s-cis enones
Authors: Hunter Norman Robert , Krawchuk Bert Paul , Shiloff Janice Deborah
Published: May 2006

The adducts from the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with a number of α,β-unsaturated ketones have been isolated and characterized. The reaction generally proceeds with migration of the double bond to the β,γ-position and is highly chemoselective towards reaction with enones which have, or can assume, an s-cis conformation.
Concerning the conformational distribution in isopropylcyclopropane
Authors: Schaefer Ted , Sebastian Rudy , Wasylishen Roderick E.
Published: May 2006

A partial analysis of the 400 MHz 1H nmr spectrum of isopropylcyclopropane yields 8.6 ± 0.2 Hz for the vicinal proton–proton coupling constant between a cyclopropyl proton and the methine proton of the isopropyl group. The fractional population of the s-trans conformer is estimated as 0.65 ± 0.l0 at 300 K, in reasonable agreement with molecular mechanics and INDO MO computations of the energies of the gauche and trans forms.The conformational preference of this molecule is similar to that in n-butane and in vinylcyclopropane but contrasts with that in biisopropyl and bicyclopropyl.
Synthesis and vibrational study of a 1:1 stoichiometric complex of hydronium tetrafluoroborate and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)
Authors: Chênevert Robert , Rodrigue André , Pigeon-Gosselin Marie , Savoie Rodrigue
Published: May 2006

The macrocyclic ether 1,4,7,10,13,16-hexaoxaoctadecane (18-crown-6) has the remarkable property of being able to transfer the hydronium (H3O+) ion from an aqueous solution to an organic medium. This property has been used to synthetize a 1:1 stoichiometric complex of this ether with hydronium tetrafluoroborate. This complex is very stable (mp 145 °C) and dissolves readily, without decomposition, in solvents such as CHCl3. The presence of the H3O+ and BF4− ions in the complex has been confirmed by chemical analysis, and by 1H nmr, Raman, and ir spectroscopy. The vibrational spectra indicate that a conformational change of the crown ether takes place in the complex over the temperature range −50 °C to −100 °C. The symmetry of the crown ether, which appears to be relatively high at room temperature, is considerably reduced below the transition temperature.
Clathrate and other solid phases in the tetrahydrofuran–water system: thermal conductivity and heat capacity under pressure
Authors: Ross Russell G. , Andersson Per
Published: May 2006

Solid phases in the tetrahydrofuran–water (THF–H2O) system were investigated in the temperature range 100–260 K and at pressures up to 1.5 GPa. Thermal conductivity, λ, and heat capacity per unit volume, ρcp, were measured, using the transient hot-wire method. We made measurements on solid phases having nominal compositions THF•17H2O, THF•7•1H2O, and THF•4•6H2O, which we refer to as phases α, β, and γ, respectively. Phase α is known to be a structure II clathrate hydrate, and λ for this phase was found to be similar to other crystalline solids which are glass-like in relation to their thermal properties. Low-energy excitations are known to be relevant to the properties of glass-like solids, and, in the case of phase α, were probably rotational vibrations of the THF guest molecules. Phase β was similar, and we inferred that it was probably a structure I clathrate hydrate. Phase γ behaved nearly like a normal crystal phase at low temperatures, but λ became almost independent of temperature near melting. At 1.1 GPa and 130 K, we found evidence that phase α transformed, on pressurization, to a metastable modification which may be a new high-density form of clathrate hydrate. The astrophysical implications of our results were mentioned briefly.
A kinetic and surface study of the oxidation of ethane by nitrous oxide and by oxygen over manganese(III) oxide
Authors: Fairbridge Craig , Ross Robert Anderson
Published: May 2006

The kinetics of the nitrous oxide/ethane and oxygen/ethane reactions on manganese(III) oxide have been studied from 573 to 673 K and from 523 to 593 K, respectively. The apparent activation energy for carbon dioxide formation was 130 ± 4 kJ mol−1 in both reactions while that for nitrogen formation in the nitrous oxide/ethane reaction changed from 106 ± 4 kJ mol−1, 573–613 K, to 133 ± 4 kJ mol−, 623–673 K. The kinetic results for both reactions fit the same rate equation:[Formula: see text]where px represents either [Formula: see text]. The rate-controlling step has been associated with the interaction of adsorbed species on the catalyst surface while both ethane and the oxidising gas appear to be directly involved in further steps in the mechanism. Samples were analysed routinely by scanning electron microscopy, X-ray powder diffraction, and infrared spectroscopy. Electron spectroscopy results from samples treated in various ways with hydrocarbon/oxidant mixtures gave O(1s) values from 528.7 to 529.7 eV which are indicative of binding energies usually associated with chemisorbed oxygen. No N(1s) spectrum was obtained from catalysts exposed to hydrocarbon/nitrous oxide mixtures, in agreement with the absence of bands in the infrared which are usually associated with nitrates or nitrogen/oxygen complexes. A binding energy value of 406.5 eV was measured in the comparable N(1s) spectrum of a catalyst used at 623 K for the oxidation of ethane by nitric oxide — a result which confirms conclusions from previous surface studies on the same system using infrared spectroscopy.
The pressure dependence of the rate of isomerization of cyclopropane at 897 K
Authors: Furue Hlroshi , Pacey Philip D.
Published: May 2006

The isomerization of cyclopropane has been studied in a flow reactor at 897 K and from 4 to 406 Torr. The pressure dependence of the rate constants from this work and from the literature have been compared with predictions obtained from two models based on the theory of Yau and Pritchard and from three RRKM models. The collisional deactivation efficiency was found to generally decline with increasing temperature. The average energy removed per collision was calculated by the method of Tardy and Rabinovitch and was found to have values from 15 to 23 kJ mol−1 at 897 K. Combining the results of this work with data from the literature from 690 to 1038 K, the limiting high pressure rate constants follow the relation log k∞ = 15.50 ± 0.14 – (276.0 ± 2.1 kJ mol−1)/2.3RT.
Stéréochimie de diéthylphosphono carbéthoxy-4 pyrrolidines. Étude par rmn du proton à haut champ (250 MHz) et du carbone (13C)
Authors: Rabiller C. , Dehnel A. , Lavielle G.
Published: May 2006

A series of 2-diethylphosphono 4-carbethoxy pyrrolidines has been studied by 250 MHz 1H nmr and 13C nmr. A study of the chemical shifts allows us to establish the structures and the analysis of the 3JHH, 3JPH and 3JPC coupling constants leads to designation of preferred conformations for these rings. Good agreement is noted between the angular dependence of these coupling constants and the dihedral angles.

[Journal Translation]
The crystal structure of bis(μ-trichloroacetato-O,O′)-bis[dimethyltin(IV)] and its relationship to other (μ-acetato derivatives
Authors: Birchall Thomas , Johnson James P.
Published: May 2006

The X-ray crystal structre of bis(μ-trichloroacetato-O,O′)-bis[dimethyltin(IV)] has been determined: R′ = 0.0518. The crystals were monoclinic, space group P2/c, a = 10.223(3) Å, b = 7.539(2) Å, c = 12.711(4) Å, β = 97.76(2) and Z = 2. The molecular structure consists of a planar (CH3)2Sn—Sn(CH3)2 unit with the tin atoms bridged asymmetrically by two trichloroacetato groups to give each tin atom five coordination.
The structures of phyllanthostatin 1 and phyllanthoside from the Central American tree Phyllanthusacuminatus Vahl
Authors: Pettit George R. , Cragg Gordon M. , Gust Devens , Brown Peter , Schmidt Jean M.
Published: May 2006

A new antineoplastic glycoside, phyllanthostatin 1, and the related glycoside, phyllanthoside, have been isolated from the Central American tree, Phyllanthusacuminatus Vahl. The structures of phyllanthostatin (1a) and phyllanthoside (1b) were completely assigned by analyses of spectral data, principally by high resolution (400 MHz) nmr. In addition to exhibiting activity against the National Cancer Institute's P388 lymphocytic leukemia, phyllanthoside was found to possess a curative level of activity against the murine B16 melanoma.
One-electron photooxidation of carbazole in the presence of carbon tetrachloride. Part I. Carbon tetrachloride and ethanol used as reaction media
Authors: Zelent Bogumil , Durocher Gilles
Published: May 2006

The photochemical reaction products of carbazole with carbon tetrachloride in ethanol have been isolated and identified along with photoproducts in the irradiated solution of carbazole in pure CCl4 using water and ethanol added after the irradiation. This allowed us to discuss the complex mechanism of secondary photochemical changes in the carbazole–CCl4 system. We propose that the electron transfer from carbazole to CCl4 molecule in the excited CT complex, [Formula: see text] is the primary photochemical reaction followed by an heterolytic dissociation of a C—Cl bond which gives rise to the primary photoproducts in the solvent cage [C+•Cl−ĊCl3]. Secondary photochemical reactions initiate transformation of the radical cation of carbazole in the solvent cage giving rise to the following intermediate species:[Formula: see text]The probability of formation and further transformations of these Transient products: α, β, and γi, depends strongly on the nature of the reaction media. Thermodynamically stable products are formed depending on the reaction media; (carboethoxy)carbazoles, (carbo-N-carbazyl)carbazoles, and carbazole – carboxylic acids can serve as a proof for the formation of the above listed intermediates. All the results reported on the secondary photochemical reactions strongly support the electron-transfer primary mechanism used to explain the fluorescence quenching of carbazole by CCl4.These results also explain the changes observed in the fluorescence spectrum of carbazole when the ethanol solution of carbazole in the presence of CCl4 is irradiated.
Étude comparée de trois antibiotiques ionophores: X.537 A (lasalocide), A.23187 (calcimycine) et X.14547 A. Complexation des cations IA et IIA, transport de Ca++
Authors: Bolte Jean , Demuynck Colette , Jeminet Georges , Juillard Jean , Tissier Claude
Published: May 2006

Using a potentiometric method, both the stoechiometry and the stability of complexes formed in methanol between the three natural ionophores and cations IA and IIA have been obtained. With alkali metal ions, neutral complexes of stoechiometry 1:1 for X.537 A and A.23187, 2:1 for X.14547 A are formed. Complexes of higher stability are obtained with alkaline-earth cations, corresponding to two types of association; 1:1 charged and 2:1 neutral. A.23187 and X.14547 A show similar behaviour as far as the sequence of formation of these two complexes is concerned, but the stability constants are higher for the first one. For X.537 A, the existence of a 2:1 complex is not detectable by our method, except for magnesium.Calcium transport by these ionophores through a cell such as: aqueous phase/chloroformic phase/aqueous phase has also been studied. An attempt is made to relate ionic fluxes to the preceding equilibrium constants.
Aryl radicals from hexazadienes and tetrazenes
Authors: Mackay Donald , McIntyre Deane Douglas
Published: May 2006

Aryl radicals are produced from both ends of the hexazadienes 1 and 2 and from the tetrazene 3, either thermally or photolytically. They attack aromatic compounds in the nucleus, the yield of biaryl being in the range 40–70%, though it can be made nearly quantitative by using m-dinitrobenzene as an additive. The aryl radicals also oxidize 2-propanol to acetone, the reduction products being the halogenobenzene and 1,2-diacetylhydrazine.Photolysis of 1 goes mainly by way of the tetrazene 3, and this may also be a significant pathway in the thermal reaction. Azodiacetyl is an intermediate in the thermal reaction of 1 with 2-propanol and may be generally so in all its reactions.Radical induced decomposition is believed to be important in the reactions of 1, 2, and 3, and it is probably responsible for the formation of 1-acetyl-1-arylhydrazines, routinely produced in yields of up to 25%.
1H and 13C nuclear magnetic resonance study of the complexation of uranyl ion with malic acid
Authors: Nunes M. Teresa , Gil Victor M. S. , Xavier António V.
Published: May 2006

A full pH range 1H and 13C nmr study was performed of the complexation of UO22+ with malic acid, for variable concentrations and molar ratios. Spectral evidence for the existence of at least five complexes was found, and their stoichiometry and dependence on pH were investigated. Information on the conformation of the bound ligand molecules was also obtained.
The design and synthesis of nonpeptide compounds as mimics of a conformation of methionine-enkephaline
Authors: Belanger Patrice C. , Dufresne Claude , Scheigetz John , Young Robert N. , Springer James P. , Dmitrienko Gary I.
Published: May 2006

A model for the active conformation of methionine-enkephalin containing a β-turn was derived from computer modeling. Using a trans-perhydronaphthalene as a structural template and a mimic of the β-turn, target compounds were designed and synthesized. Thus, a key intermediate, trans-3-oxo-5β-formamidomethyl-8a-phenylmethylperhydronaphthalene, was prepared by two different routes from cyclohexanone.The addition of a methionine-like side-chain to this key intermediate was best achieved by a reaction with the anion of methyl 2-trimethylsilyl-4-methylthiobutanoate. This led to the preparation of an exo-tetrasubstituted double bond in high yield. Subsequent addition of tyrosine through coupling with the 5β-aminomethyl group provided the desired perhydronaphthalene mimics of met-enkaphalin.
Electron and cation transport in fluid dimethyl ether: effects of density and temperature
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

The effect of molecular electric dipole moment D on charge transport in fluids was examined by measurement of electron and ion mobilities in dimethyl ether (D = 1.3 D) and comparing them with the behavior in hydrocarbons. The fluid density was varied continuously from that of the normal vapor to that of the normal liquid, passing through the critical region. The density normalized mobility nμe of electrons in dimethyl ether vapor at low densities is 30-fold smaller than that in propane, although for the cations nμ+ in the ether is only 1.4-fold smaller than that in the alkane. The permanent dipole moment of the ether dominates the scattering of low energy electrons but not that of cations. The electron momentum transfer cross section is roughly 33% larger than that predicted by the Altshuler point dipole model, and has a minimum at ~0.12 eV. The energy gained from the electric field is removed mainly through inelastic collisions, even in the thermal energy range.Molecular clustering decreases both electron and ion mobilities, but the effect on the former is much larger due to the greater change in reduced mass. The extent of electron quasilocalization in the dense vapor of dimethyl ether is four times greater than that in nonpolar hydrocarbons. Electrons form relatively stable localized states in the liquid at n/ne > 2.0. Ion mobility undergoes a transition from "density control" to "viscosity control" with increasing density in the low density liquid. Viscosity control is operative at n/ne > 2.4.
Arene carbonyl rhodium(I) complexes
Authors: Valderrama Mauricio , Oro Luis A.
Published: May 2006

The arene carbonyl rhodium complexes, [Rh(C6Me6)(CO)2]PF6 and [Rh(C6Me6)(CO)PPh3]PF6, have been prepared by treating the dimeric complexes, [RhCl(CO)2]2 and [RhCl(CO)PPh3]2, with AgPF6 in the presence of hexamethylbenzene. The reaction of [Rh(C6Me6)(CO)2]PF6 with tetrafluorobenzobarrelene affords [Rh(C6Me6)(TFB)]PF6. On the other hand, the reaction of [Rh(arene)(CO)2]PF6 with a stoichiometric amount of triphenylphosphine gives [Rh(arene)(CO)PPh3]PF6 (arene = C6Me6 or C6H3Me3), whereas with excess of this ligand [Rh(CO)(PPh3)3]PF6 is formed. The related [Rh(C6Me6)(CO)P(p-MeC6H4)3]PF6 derivative has also been prepared.The reactivity of both hexamethylbenzene carbonyl rhodium complexes has been examined. The addition of bipyridine to solutions of [Rh(C6Me6)(CO)L]PF6 (L = CO or PPh3) causes the immediate displacement of the coordinated hexamethylbenzene. Their reactions with the nucleophiles, acetylacetonate, tropolonate, or pyrazolate in the presence of triethylamine afford neutral derivatives of the type [RhA(CO)L]x (L = CO or PPh3; A = acac or trop, x = 1; A = pz, x = 2).
Interaction en milieu eau–dioxane des ions Cu2+, Ni2+ et Ag+ avec les acides furannecarboxylique-2 et tetrahydrofurannecarboxylique-2
Authors: Michaud Emmanuelle , Pivert Gilles , Duc Gérard , Petit-Ramel Michelle , Thomas-David Germaine
Published: May 2006

The protonation constants of furan-2 carboxylic (HFC) and tetrahydrofuran-2 carboxylic (THFC) acids and the stability constants of their copper, nickel and silver 1:1 complexes have been measured in water containing 50% dioxane (I = 0.1 (NaNO3); t = 25 °C). Treatment of the potentiometric data has been completed by uv–visible spectrophotometric measurements. The results are discussed and a chelate structure is displayed for the Cu – tetrahydrofuran-2 carboxylic acid system.
The crystal structure of 1-azoniatricyclo[4.4.4.01,6]tetradecane and 1-azoniatricyclo[4.4.3.01,6]tridecane bromides
Authors: McIntosh John M. , Khan Masood A. , Delbaere Louis T. J.
Published: May 2006

The crystal structures of 1-azoniatricyclo[4.4.4.01,6]tetradecane bromide (1) and 1-azoniatricyclo[4.4.3.01,6]tridecane bromide (2) are reported. Compound 1, C13H24NBr, crystallizes in space group P63/mmc with a = 8.383(2) Å, c = 10.092 Å, γ = 120°, Z = 2. Compound 2, C12H22NBr, crystallizes in space group P63/mmc with a = 8.283(2) Å, c = 10.046(2) Å, γ = 120°, Z = 2. The crystal structures of 1 and 2 are statistically disordered with both enantiomers occurring in the unit cell. Compound 2 is further disordered with the one five-membered ring and the two six-membered rings of the cation being averaged over the same site in the unit cell.The structures confirm the previously reported conclusions based on the 400 MHz nmr spectra of 1.
Nematic phase nuclear magnetic resonance measurement of the 19F chemical shift anisotropy in fluoranil
Authors: Gilson D. F. R. , Brownstein S.
Published: May 2006

The 19F nmr spectra of fluoranil (2,3,5,6-tetrafluoro-p-quinone) partially oriented in a phenyl-cyclohexyl type of nematic solvent have been studied as a function of temperature and the anisotropy of the fluorine chemical shift determined. The results, [Formula: see text] and (σxx−σvv) = −41 ppm are in good agreement with the values obtained for the solid phase.
Total synthesis of zizaane sesquiterpenes: (−)-khusimone, (+)-zizanoic acid, and (−)-epizizanoic acid
Authors: Liu Hsing-Jang , Chan Wing Hong
Published: May 2006

Three sesquiterpenes of the zizaane family, khusimone (1), epizizanoic acid (3), and zizanoic acid (2) have been synthesized in optically active form from the ammonium salt of (−)-l-10-camphorsulfonic acid in sixteen, nineteen, and twenty steps respectively.
Formation and reactivity of 1,3-benzodioxol-2-yl, 1,3-benzodioxan-2-yl, and related radicals. A search for an aromatic analog of the radical acetoxy rearrangement (Surzur–Tanner reaction)
Authors: Shahidi Fereidoon , Tidwell Thomas T.
Published: May 2006

Reaction of the 1,3-dioxole, 9, the 1,3-dioxan, 18, and the 1,3-dioxepin, 29, with tert-butoxy radicals gave evidence in each case for formation of the corresponding 1,1-dioxyethyl radicals. No conclusive evidence for formation of any of these radicals by cyclization of acetoxyaryl radicals could be obtained. Several of the 1,1-dioxyethyl radicals reacted by rearrangement.
Alkylation of enolate anions with dimethyl 3-bromo-2-ethoxypropenylphosphonate. A convergent cyclopentenone annulation method
Authors: Piers Edward , Abeysekera Brian
Published: May 2006

A new, convergent synthesis of 2-cyclopenten-1 -ones is reported. Treatment of dimethyl 2-oxopropylphosphonate (21) with excess triethyl orthoformate in the presence of ferric chloride hexahydrate provides the enol ether 22, which upon allylic bromination with N-bromosuccinimide yields the allylic bromide 19. Alkylation of the ketones 24–28 with 19, followed by mild acid hydrolysis of the resultant products 29–33, affords the diketo phosphonates 34–38. When the latter substances are treated with sodium hydride in dimethoxyethane, the corresponding 2-cyclopenten-1 -ones 40–44 are formed in good yields.
Syntheses of condensed imidazoles by lead tetraacetate oxidation of amidines
Authors: Chaudhury S. , Debroy A. , Mahajan M. P.
Published: May 2006

2-Phenylbenzimidazoles, 2-benzylbenzimidazoles, 2-phenyl-1H-naphtho[1,2-d]imidazole, and 2-benzyl-1H-naphtho[1,2-d]-imidazole have been synthesized in excellent yields (77–98%) by lead tetraacetate oxidation of suitable N-arylbenzamidines, N-arylphenylacetamidines, N-α-naphthylbenzamidine, and N-α-naphthylphenylacetamidine respectively. The mechanism of nitrene insertion and intramolecular competitive nitrene insertion leading to these heterocycles has also been discussed.
Étude structurale d'aldimines derivées des furanne-, thiophène- et N-méthylpyrrolecarboxaldéhydes-2.I. N-hétéroarylidèneanilines
Authors: Audoye Paul , Coumes René-Charles , Gaset Antoine , Gorrichon Jean-Pierre
Published: May 2006

We have studied a series of five N-heteroarylideneanilines, either nitrated or not on the heterocyclic ring, in which the hetero atom can be O, S or N—CH3. The uv and 13C nmr results obtained suggest that these molecules are, as in the case of benzylideneaniline, not entirely planar. In addition, 1H nmr shows that only a single rotamer exists out of the four possibilities (or, at the limit, a rapid equilibrium between two rotamers).

[Journal Translation]
Molecular motion and methyl group rotation barriers from 13C nmr relaxation times. Podacarpic acid derivatives
Authors: Beierbeck Helmut , Easton John W. , Saunders John K. , Bell Russell A.
Published: May 2006

The 13C nmr relaxation time data for a number of compounds related to podocarpic acid are presented. The T1 values of these molecules were satisfactorily reproduced by application of Woessner's equations for an asymmetric top assuming that the preferred principal axis of the rotational diffusion tensor was either the preferred principal inertial axis or an axis containing the centre of mass and the heterosubstituent at C-4. The values for hindrance to rotation for the various methyl groups are given and their variations discussed.
Solvent effects on the tautomeric equilibrium of 2,4-pentanedione
Authors: Spencer J. N. , Holmboe Eric S. , Kirshenbaum Mindy R. , Firth Daniel W. , Pinto Patricia B.
Published: May 2006

The influence of solvent on the equilibrium position of the tautomeric forms of 2,4-pentanedione was studied by calorimetric and nmr spectroscopic techniques. For solvents such as CCl4 and cyclohexane the intramolecular bond of the enol form persists and bulk solvent effects account for the equilibrium enol–keto content. In solvents such as DMSO, disruption of the intramolecular bond occurs and the percentage of enol falls due to unfavorable entropy changes. The enol intramolecular bond is disrupted by the solvents water and methanol. Enol hydrogen bond formation through self-association and with the solvent accounts for the entropy changes upon enolization in these solvents. The thermodynamic parameters for enolization in neat 2,4-pentanedione are rationalized by the disruption of the enol intramolecular hydrogen bond through consequent polymerization of the enol tautomer.