bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas phase observation of the first overtone of the H—F stretching fundamental in hydrogen bonded complexes
Authors: Bevan J. W. , Martineau B. , Sandorfy C.
Published: May 2006

First overtones of H—F and D—F stretching vibrations in hydrogen bonded complexes with dimethylether, diethylether, and acetone have been measured in the gas phase. The assignment of the observed bands is discussed together with previously made observations on the fundamentals. Anharmonicity constants of the order of −200 and −100 cm−1 are determined for the most probable assignments from the available data for the H—F and D—F stretching vibrations (ν1) while their values in the "free" H—F and D—F molecules are −90 and −46 cm−1 respectively. The spectra are compatible with a coupling constant between the ν1 and the bridge stretching vibration (ν3) of the order of +70 cm−1.
Rearrangement studies with 14C. XLIII. The acetolysis of trianisyl[2-14C]vinyl bromide
Authors: Lee Choi Chuck , Weber Ursula , Obafemi Craig A.
Published: May 2006

Acetolyses of trianisyl[2-14C]vinyl bromide (1-Br-2-14C) were carried out in the presence of various amounts of added NaOAc or NaOAc and LiBr. Scramblings of the isotopic label from C-2 to C-1 arising from 1,2-anisyl shifts in the trianisylvinyl cation were observed in both the reaction product and the recovered, unconsumed reactant. The results indicate that the relative contribution of the 1,2-shift process is decreased with an increase in the amount of NaOAc or LiBr, in support of a mechanism involving formation of the dissociated trianisylvinyl cation which will competitively undergo 1,2-anisyl shift to give scrambling, be captured by Br− ion and return to scrambled starting material, and be captured by OAc− ion to give scrambled product. The results are also compared with previous data from solvolyses of triphenyl[2-14C]vinyl bromide and the differences are discussed.
The 13C chemical shifts of various methylgermanium derivatives
Authors: Drake John E. , Glavinčevski Boris M. , Humphries Robyn E. , Majid Abdul
Published: May 2006

This paper reports 13C chemical shifts for 20 methylgermanium compounds. These shifts are correlated against (i) the electronegativity of halogen in the Me3GeX compounds, (ii) the calculated charge on the carbon atom, (iii) the 1H shifts of the methyl protons, and (iv) the 13C shifts for the analogous carbon, silicon, and tin compounds.
Photoisomerization of protonated cyclohex-2-enones
Authors: Childs Ronald F. , Hine Kenneth E. , Hung Frederick A.
Published: May 2006

Protonated 4,4-dimethylcyclohex-2-enone, 1H, has been shown to isomerize on irradiation in FSO3H at −85 °C to give protonated 6,6-dimethylbicyclo[3.1.0]hexan-2-one, 5H, and protonated 3-isopropylcyclopent-2-enone, 4H. The protonated bicyclic ketone 5H was found to be both thermally and photochemically labile, in both instances rearranging to 4H. The first order rate constant for the thermal isomerization of 5H to 4H at −60 °C was 1.73 × 10−4 s−1. As 5H was shown to be photolabile in the presence of 1H, it was not possible to establish whether 4H was a primary photoproduct of 1H. No photoisomerizations of protonated cyclohex-2-enone and protonated 4-methylcyclohex-2-enone could be detected. The photoisomerization of protonated Δ1,9-10-methyl-2-octalone has been re-examined at low temperature in an attempt to detect tricyclic products.
Effets des substituants dans les spectres de rmn de benzhydrols substitués en présence de Eu (dcm)3
Authors: Capillon Joël , Lacombe Liliane
Published: May 2006

Para mono- or disubstituted chiral benzhydrols have been studied by nmr in the presence of Eu(dcm)3. The influence of association constants and structural parameters has been assessed separately. The observed nonequivalence cannot be related to a difference between the association constants but is primarily due to a difference between the geometries of the lanthanide–substrate complexes, correlated with the electronic nature of the substituents. A rule for the determination of the absolute configuration of such compounds has been established.
Electron spin resonance study of radical adducts of unsaturated dicarboxylic and tricarboxylic acids
Authors: Adeleke Babatunde B. , Faniran Joshua A.
Published: May 2006

An esr study of the addition reactions of •OH, CO2−•, SCO3−•, and •PO32− radicals to the anions of aconitic, itaconic, and chelidonic acids is reported. There was an electron transfer reaction between CO2−• and chelidonic acid anion. The phosphite radical reacted with chelidonic acid to produce two types of radicals resulting from addition to C=C and the oxygen of the carbonyl group in the acid. The radical adducts of the anions of aconitic and itaconic acids exhibited extensive linebroadenings due to hindered internal rotations. The barrier to internal rotations is shown to be the repulsive forces between the negative charges on the various substituents.
Isolation of ergovaline, ergoptine, and ergonine, new alkaloids of the peptide type, from ergot sclerotia
Authors: Brunner Rudolf , Stütz Peter Leopold , Tscherter Hans , Stadler Paul Albert
Published: May 2006

The isolation of three new ergot alkaloids of the peptide type from sclerotia of Clavicepspurpurea and from mother liquors of rye ergot alkaloid extraction processes is described. The constitution of the new alkaloids ergovaline, ergoptine, and ergonine has been established by comparison with compounds previously obtained by total synthesis.
Reactions of triethylenetetramine with protons and bivalent zinc, cadmium, and lead in aqueous solution and aqueous dioxane (50% v/v)
Authors: McBryde W. A. E. , Powell H. K. J.
Published: May 2006

The reactions of triethylenetetramine with protons and with bivalent Zn, Cd, and Pb have been studied in aqueous solution and in 50% (v/v) aqueous 1,4-dioxane, 25 °C, I = 0.10 M KNO3. log K (potentiometric) and ΔH (calorimetric) data are interpreted in terms of electrostatic effects and solvation effects operative in the two solvents.Protonation constants are higher by 0.2–0.6 log units in aqueous solution. Stepwise enthalpies of protonation −ΔHn (n = 2,3,4) are significantly higher, and the corresponding entropies lower, in aqueous solution. The complexes [ML]2+ are of similar stability in the two solvents but −ΔH is ca. 10–20% lower in aqueous dioxane.
9-Oxobenzomorphans. I. General syntheses of dihydrobenz[e]indolines as key intermediates
Authors: Kavadias Gerry , Velkof Stephan , Belleau Bernard
Published: May 2006

Various 5,9b-dihydrobenz[e]indolines were synthesized by three general methods: (a) by alkylation with the appropriate alkyl halide of 1,2,4,5-tetrahydro-1H-benz[e]indoles, themselves obtained by alkylation with bromochloroethane of enamines derived from 7-alkoxy-2- tetralones; (b) from 1-alkylaminoethyl-2,2-ethylenedioxy-1,2,3,4-tetrahydronaphthalenes by acid hydrolysis, and (c) by reduction of 2-oxo-2,3,5,9b-tetrahydro-1 H-benz[e]indoles which in turn were obtained from ethyl 2-oxo-1,2,3,4-tetrahydro-1-naphthalene acetates by reaction with methylamine followed by dehydration. These substances are key intermediates in the synthesis of 9-oxobenzomorphans.
9-Oxobenzomorphans. II. A versatile process for the synthesis of 9-oxo-6,7-benzomorphans
Authors: Kavadias Gerry , Velkof Stephan , Belleau Bernard
Published: May 2006

The synthesis of 5-allyl-2′-methoxy-2-methyl-9-oxo-, 2′-methoxy-2,5-dimethyl-9-oxo-, 5-allyl-2-cyclopropylmethyl-2′-methoxy-9-oxo-, and 5-(3-ethylenedioxy)butyl-2′-methoxy-3-methyl-9-oxo-6,7-benzomorphans (5a–d) by an improved process is described. It involves bromination of the 5,9b-dihydrobenz[e]indolines to the bromoiminium bromides, followed by hydrolysis with ammonium bicarbonate which converted them to 4-bromo-5,9b-dihydro-benz[e]indolines (in a fast step). These underwent hydration (in a slow step) followed by rearrangement to 5a–d. The course of these reactions was different when sodium, potassium, and ammonium hydroxides were substituted for ammonium bicarbonate.
Solvent-induced changes in 2J(H, F) for fluoroform via van der Waals interactions. Non-contact contributions to spin–spin coupling constants involving a proton?
Authors: Schaefer Ted , Hutton Harold M. , Salman Salman R.
Published: May 2006

The spin–spin coupling between the proton and the fluorine nuclei, 2J, in fluoroform varies by 1% in a range of solvents. It is argued that 2J decreases algebraically as the van der Waals solute–solvent interactions increase in magnitude. Such a decrease is also observed for coupling constants which likely contain a substantial positive orbital contribution. If the van der Waals interactions perturb the spin–orbital term in J, then 2J in fluoroform may well contain orbital contributions, as recently calculated for 2J in methyl fluoride. In that event, the large discrepancies between observed 2J(H,F) values and those calculated by semiempirical theories of the contact term may be partially attributed to the neglect of orbital terms.
Derivatives of diphenylmethane. Preferred conformations and barriers to internal rotation by the J method
Authors: Schaefer Ted , Niemczura Walter , Danchura Werner , Wildman Timothy A.
Published: May 2006

The long-range spin–spin coupling constants over six bonds, 6JpH,CH, in 3,5-dibromodiphenylmethane and 4,4′-difluorodiphenylmethane, respectively, imply that the ground state conformations of these molecules have C2v symmetry (gable conformations). In terms of a hindered rotor model which assumes a twofold barrier to internal rotation about the exocyclic carbon–carbon bond, the barrier in the dibromo derivatives is 1.1 ± 0.3 kcal/mol. A satisfactory fit to the temperature dependence of 6JpF,CH is found for a gable conformation. If the conformational properties of these molecules and of diphenylmethane are determined mainly by steric interactions between ortho C—H bonds on neighbouring phenyl groups, it seems likely that the results above are a first approximation to the conformational behaviour of diphenylmethane. Some molecular orbital calculations are in semiquantitative agreement with the conclusions based on coupling constants.
Fluoride ion promoted synthesis of alkyl phenyl ethers
Authors: Miller Jack M. , So K. H. , Clark James H.
Published: May 2006

Tetraethylammonium fluoride in dimethylformamide promotes the alkylation of phenols with alkyl iodides and benzyl chloride to provide good yields of alkyl phenyl ethers. A number of phenols have been investigated including examples of sterically hindered phenols, phenols containing anion stabilising groups, and intramolecularly hydrogen bonded phenols, the majority of which react smoothly and efficiently in the fluoride system.
Acidity function 'failure.' I. 2-Thiohydantoins
Authors: Edward John T. , Wong Sin Cheong
Published: May 2006

The protonation of 2-thiohydantoin and of eight derivatives variously substituted at the 1-, 3-, and 5-positions with alkyl groups or a single phenyl followed h0 (Cox–Yates m* ∼ 1.1); however, the protonation of 3,5-diphenyl-2-thiohydantoin followed hT (m* = 1.50), and of 5,5-diphenyl-2-thiohydantoin an acidity function intermediate between h0 and hT (m* = 1.24). Results were analyzed also in terms of the Cox–Yates X function to obtain [Formula: see text] values, which were compared with those obtained by alternative analyses of the data.
Primary mechanisms in the radiolysis of amines: pulse and γ-radiolysis of neutral and acidic ethylamine, n-propylamine and ethylenediamine
Authors: Delaire J. A. , Bazouin J. R.
Published: May 2006

The transient spectra in pure ethylamine (EA), n-propylamine (nPA), and ethylenediamine (EDA) show, besides the visible and infrared band associated with the solvated electron, e−s, a small ultraviolet band attributed to oxidizing radicals. Upper limits for the recombination rate constants k of e−s with the acidic cation are 1.5 × 1012 L mol−1 and 3.5 × 1012 L mol−1s−1 in EA and nPA respectively, and k = 2 × 1010 L mol−1 s−1 in EDA. The yield of e−s at 3 ns (G(e−s)3ns = 1.5, 1.2, and 3.1 molecules/100 eV in EA, nPA, and EDA respectively) has been deduced by biphenyl scavenging. The yield of molecular hydrogen after γ-radiolysis G0(H2) = 5.7 and 3.6 in pure nPA and EDA respectively. The effect of solutes, such as biphenyl, alkyl-ammonium chloride, and allyl alcohol, on G(H2) is interpreted in terms of scavenging of e−s and/or H atoms. From the pulse-radiolysis determination of G(e−s), we deduce [Formula: see text] in nPA.Finally, the decay of solvated electrons seems to occur only via recombination with the cation in EA and nPA, but in EDA there is a competition between this reaction and reaction with oxidizing radicals.
Crystal structures of medium ring compounds. Part III. The crystal and molecular structure of trans-anti-trans-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane
Authors: Terzis Aris , Grindley T. Bruce
Published: May 2006

The crystal structure of trans-anti-trans-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane (3) has been determined by X-ray diffraction. The crystals are monoclinic, a = 11.919(3), b = 17.330(7), c = 7.019(2) Å, β = 98.91(1)°, P21/c, with Z = 4. The structure was solved by application of the tangent formula and refined by large block least squares to a final R value of 0.060 (Rw = 0.058).The ten-membered ring is present in the crystal in a twist-chair-boat-chair conformation — one which has been calculated to be relatively unstable for cyclodecane. Possible reasons why 3 adopts this conformation are discussed.
Sterically hindered aromatic compounds. IX. Electron spin resonance and product studies of the dediazoniation reaction
Authors: Barclay L. Ross C. , Briggs Alexander G. , Briggs William E. , Dust Julian M. , Gray Jean A.
Published: May 2006

An esr study of the dediazoniation of 2,4,6-tri-tert-butylaniline with butyl nitrite in methylene chloride indicated the formation of the 2,4,6-tri-tert-butylphenyl radical which was spin trapped by the butyl nitrite. The persistent 2,4,6-tri-tert-butylphenoxy radical was also formed. Product studies from reactions catalyzed by pivalic acid indicate a novel rearrangement of an ortho-tert-butyl group under dediazoniation conditions forming such products as: 3-(3,5-di-tert-butylphenyl)-2-methylpropene (4), 1-(3,5-di-tert-butylphenyl)-2-methylpropene (5), 3-(3,5-di-tert-butylphenyl)-2-methyl-2-propanol (6), 3-(3,5-di-tert-butylphenyl)-2-butoxy-2-methylpropane (7), 3-(3,5-di-tert-butylphenyl)-2-methyl-2-trimethylacetoxypropane (8), 2,4,6-tri-tert-butylphenyl trimethylacetate (9), and 2,4,6-tri-tert-butyl-1,4-quinol (10). The major products (4–7) are accounted for by a free radical pathway by rearrangement of the 2,4,6-tri-tert-butyl-phenyl radical. The minor products (esters 8 and 9) probably form by competing ionic reactions. N-Nitroso-2,4,6-tri-tert-butylacetanilide decomposes (at least in part) by a radical pathway leading to the rearranged radical (CH3)2ĊCH2—Ar which was spin trapped by the nitroso group of the substrate. Spin trapping experiments during the dediazoniation of 2,5-di-tert-butylaniline similarly gave evidence for the formation of aryl radicals.
The consequences of steric effects in the cleavage step of the sulfohaloform reaction
Authors: Kay Denis George , Langler Richard Francis , Trenholm June Ellen
Published: May 2006

The pathway for the aqueous chlorinolysis of a series of β-sulfonyl-sulfides is elucidated and the SN2 cleavage step examined. Steric effects in the cleavage of the α-polychloro-oxochloro-sulfonium chloride intermediates are held to be responsible for the suppression of the established nucleophilic competition between water molecules and chloride ions with the result that all cleavage products arise from nucleophilic attack by chloride ions. This report details the second known example of successful SN2 displacement on a carbon atom α to a sulfonyl group.
The electrochemical synthesis of some heteronuclear metal carbonyls
Authors: Habeeb Jacob J. , Tuck Dennis G. , Zhandire Samuel
Published: May 2006

The electrochemical oxidation of zinc, cadmium, or indium in the presence of Co2(CO)8 or Mn2(CO)10 in an organic solvent gives rise to the appropriate heteronuclear metal carbonyl M[M′(CO)n]m (M = Zn, Cd, In; M′ = Co, Mn; n = 4, 5; m = 2, 3). The advantages of this method are discussed, as is the mechanism of the processes which lead to the reaction products.
The synthesis of oligoribonucleotides. III. The use of silyl protecting groups in nucleoside and nucleotide chemistry. VIII
Authors: Ogilvie Kelvin K. , Schifman Aria L. , Penney Christopher L.
Published: May 2006

The synthesis of all isomeric mono- and disilyl derivatives of cytidine, guanosine, and their N-benzoyl analogues using the tert-butyldimethylsilyl protecting group is described. These compounds and those containing a 5′-monomethoxytrityl group have been condensed via the phosphodichloridite procedure to produce nucleotides rapidly and in good yields. The synthesis of 2′–5′-linked nucleotides is described. A cautionary note is introduced in regard to the preparation of 5′-monomethoxytritylguanosine and a novel methanolysis of certain N-benzoylcytidines is mentioned.
The hydrolysis of coumarin diethyl acetal and the lactonization of coumarinic acid ethyl ester. The partitioning of tetrahedral intermediates generated from independent sources
Authors: McClelland R. A. , Somani R. , Kresge A. J.
Published: May 2006

The hydrolysis of coumarin diethyl acetal to coumarin proceeds via two detectable intermediates. A short-lived transient is observed in strongly acidic solutions (pH < 2.5); this is the oxocarbonium ion intermediate of the hydrolysis. That this cation can be detected suggests unusual stability, a fact which can be explained in terms of its pyrilium ion nature. A long-lived intermediate is also observed; kinetic and spectral evidence suggest that this is coumarinic acid ethyl ester. The lactonization of this ester shows a change in rate-determining step as the pH is varied. A corresponding change in products is found in the acetal hydrolysis, the coumarinic acid ester being the major product at high pH, with coumarin the major product at low pH. Both observations can be explained in terms of different modes of partitioning of cationic and neutral tetrahedral intermediates. Analysis in quantitative terms shows that the same tetrahedral intermediate is generated in the two different cases.
The crystal and molecular structures of bromotricarbonyl(phenylbis(3,5-dimethylpyrazolyl)phosphine)rhenium(I) and tricarbonyl(phenylbis(3,5-dimethylpyrazolyl)phosphine)tungsten(0)
Authors: Cobbledick R. E. , Dowdell L. R. J. , Einstein F. W. B. , Hoyano J. K. , Peterson L. K.
Published: May 2006

Crystals of [Re(CO)3(P(Me2pz)2C6H5)Br] (where Me2pz is 3,5-dimethylpyrazolyl) are monoclinic, space group P21/c, with a = 8.964(4), b = 14.441(10), c = 18.156(8) Å, β = 111.32(4)°, and Z = 4. Crystals of W(CO)3(P(Me2pz)2(C6H5)) are monoclinic, space group P21/c, with a = 12.479(7), b = 10.207(4), c = 16.118(7) Å, β = 98.77(2)°, and Z = 4. In both structures there is irregular octahedral geometry about the metal atom with the carbonyl groups in a fac arrangement. The phenylbis(3,5-dimethylpyrazolyl)phosphine ligand, [P(Me2pz)2(C6H5)], is coordinated to the tungsten atom through the two 2N nitrogen atoms of the pyrazolyl rings and to two carbon atoms of the phenyl ring so that the ligand is essentially tridentate. In the rhenium complex this ligand is bidentate with coordination via the 2N nitrogen atoms with a bromine atom occupying the sixth site.
Heats of vaporization and gaseous heats of formation of some five- and six-membered ring alkenes
Authors: Fuchs Richard , Peacock L. Alan
Published: May 2006

The heats of vaporization of 1-methylcyclopentene, 3-methylcyclopentene, ethylidenecyclopentane, 1-ethylcyclopentene, methylenecyclohexane, allylcyclopentane, vinylcyclohexane, ethylidenecyclohexane, allylcyclohexane, 3,3-diethylpentane, 2,2,4,4-tetramethylpentane, and trans-2,2,5,5-tetramethyl-3-hexene have been measured by the gas chromatography – calorimetry method. These values have been combined with previously reported liquid heats of formation to give gaseous values of ΔHf. The results indicate that the internal double bond is favored by about 0.5 kcal over the exo in both 5- and 6-membered rings, but the endo–exo differences are much smaller than previously believed. Several of the liquid heat capacities that were measured were not well predicted by group additivity schemes.
Identification des configurations relatives d'alcools secondaires α-cyclopropylidéniques et α-vinylcyclopropaniques. Attribution de structure aux éthyl-6 diméthyl-2,4 oxa-3 bicyclo [3.1.01,5]hexanes
Authors: Vincens Maurice , Dumont Claude , Vidal Michel
Published: May 2006

During a stereochemical study of α-cyclic secondary alcohols, the relative configurations of the E, R*, and S* isomers of 1-(2-ethyl-3-ethylidene(1R*,2R*)cyclopropyl)ethanol was determined. Treatment in a basic medium of these secondary diastereomeric alcohols leads to the R* and S* isomers of 1-(2-ethyl-3-vinyl(1R*,2S*,3S*)cyclopropyl)ethanol. Cyclic oxymercuration of these cyclopropanoic derivatives yields the di-endo, di-exo, and exo–endo derivatives of 6-ethyl-2,4-dimethyl-3-oxabicyclo[3.1.0.1,5]hexane. The determination of the structure as bicyclic ethers, based on ir and 1H and 13C nmr studies, permits the assignment of the relative configurations of the vinylcyclopropanoic and cyclopropylidene alcohols. [Journal translation]
Vibrational theory of polyatomic molecules: energy levels of CH4/CD4 and CH3Cl/CD3Cl
Authors: Bron Jan , Wallace R.
Published: May 2006

A relatively simple model, previously used to describe polyatomic vibrations of nonlinear triatomic molecules, has been employed to evaluate the fundamentals, first overtones and combination bands of CX4 and CX3Cl (X = H, D). Relatively good agreement is obtained between calculated and observed frequencies. Interesting splittings of certain overtone and combination bands result from these calculations.
The electron-donating properties of some phenylfurans. Charge transfer studies
Authors: Abu-Eittah Rafie , Hamed Maher M.
Published: May 2006

The formation of the molecular complexes of some phenylfurans with TCNE has been investigated by spectroscopic methods. The formation constants were determined by graphical and iterative procedures and some thermodynamic parameters were calculated. The formed molecular complexes were π ones. Diphenylfuran proved to be a much stronger electron donor than phenylfuran and the latter stronger than furan. Results at hand suggest that the donors investigated assume an all-planar conformation.
A room-temperature study of the kinetics of protonation of formaldehyde
Authors: Tanner Scott D. , Mackay Gervase I. , Bohme Diethard K.
Published: May 2006

Rate constants measured with the flowing afterglow technique at 297 ± 2 K are reported for the protonation of CH2O by H3+, N2H+, CH5+, HCO+, C2H5+, H3O+, H3S+, and HCNH+ and for the subsequent deprotonation by NH3. The rate constants are compared with predictions of various theories for ion–molecule collisions. The protonation was observed to proceed in the absence of competing channels and further decomposition and is discussed in terms of the energetics of the two sites of protonation and the energetics and mechanism of H2 elimination. The rate measurements provide evidence for the room-temperature conversion of the adduct C2H3+•H2 to the more stable isomer derived from the direct protonation of C2H4.
Electronic spectroscopy of aromatic Schiff's bases. III. Luminescence in some p-substituted benzylideneaniline molecules
Authors: Belletête Michel , Durocher Gilles
Published: May 2006

Fluorescence and phosphorescence spectra of a few p-substituted benzylideneaniline (BA) molecules have been obtained in the EPA solvent. Results show that the [Formula: see text] ratio increases regularly with an increase in the static dipole moment of the molecules except for the most polar molecule where the fluorescence is much more intense.Moreover, it has been shown that the interaction of the BA molecules with aprotic polar solvents is solvatochromic in origin, meaning that no specific solute–solvent interactions had been detected. It has been shown that the BA molecules behave like the D—Ar—A molecular type as far as the photophysical aspect is concerned.
Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 3. Infrared and ultraviolet studies of extracted autohydrolysis lignin
Authors: Chua Miranda G. S. , Wayman Morris
Published: May 2006

Infrared and ultraviolet studies of the lignins extracted from extractive-free aspen wood meal after autohydrolysis at 195 °C for periods varying from 5 min to 2 h indicated that these lignins were functionally modified and different from aspen milled wood lignin. The extracted lignins changed from a guaiacyl–syringyl type lignin to a syringyl-deficient type lignin with increasing autohydrolysis time. Extracted lignins were also observed to contain unconjugated β-ketone groups and conjugated carboxylic acid groups. It is proposed that the unconjugated β-ketone groups resulted from the depolymerization reactions of the lignin macromolecule under acidic conditions which formed monomeric, dimeric, and oligomeric/polymeric lignin fragments with Hibbert's ketone side chains. The conjugated carboxylic acid group observed to be present was attributed to p-hydroxybenzoic acid. p-Hydroxybenzoic acid has been postulated as contributing to the extractability of aspen lignin by acting as a blocking agent in the repolymerization of lignin fragments to form insoluble lignin.
Preparation of copper(1) carbonyl hexafluoroarsenate, CuCO+AsF6−, and copper(1) trifluorophosphine hexafluoroarsenate, CuPF3+AsF6−
Authors: Desjardins C. David , Edwards D. Brian , Passmore Jack
Published: May 2006

PF3 and CO react with CuAsF6 in SO2 solution to form 1:1 addition compounds, the vibrational spectra of which are consistent with the formulations [CuPF3]+[AsF6]− and [CuCO]+[AsF6]−. The latter has a v[CO] stretch at 2180 ± 5 cm−1, the highest yet observed for a monocarbonyl.
Absolute rate constants for hydrocarbon autoxidation. 27. On the question of a reversible rate controlling propagation reaction
Authors: Howard J. A. , Tong Shiu Bor
Published: May 2006

Autoxidations of cumene, 3-methylpentane, cyclopentane, and cyclohexane have been performed to high conversion in the presence of (CH3)3COOD from 0.1 to 1 atm of oxygen and it has been found that very low yields of C6H5C(CH3)2D, C6H13D, c-C5H9D, and c-C6H11D are produced. Furthermore, autoxidation of C6H5C(CH3)2D in the presence of (CH3)3COOH does not give detectable concentrations of C6H5C(CH3)2H and relative reactivities of cumene and 3-methylpentane to the tert-butylperoxy radical in solution do not depend on the pressure of oxygen above the liquid from 1 to 100 atm. These results have been interpreted in term of a slow reaction of the alkyl radical with alkyl hydroperoxide outside the solvent cage in competition with a fast reaction of the alkyl radical with oxygen. A rate constant for the former reaction has been estimated from the relative yields of 5-hexene and methylcyclopentane produced by decomposition of 5-hexenylformyl peroxide in an inert solvent containing tert-butyl hydroperoxide.The relative reactivity of the tertiary hydrogens in cumene and 3-methylpentane to the tert-butylperoxy radical in the gas phase is about 0.8 times the value in solution. This relative reactivity difference between the two phases is probably due to the involvement of tert-butoxy radicals in rate controlling propagation reactions in the gas phase rather than to significant reversal of the H-atom transfer reaction between the peroxy radical and the substrate inside the solvent cage.
Rate–acidity profiles for exchange of the 4-methyl protons in amino, imino, and keto pyrimidines
Authors: Stewart Ross , Gumbley Stewart J. , Srinivasan R.
Published: May 2006

The rate of exchange of deuterium for protium in the 4-methyl groups of 2-imino-1,4-dimethyl-1,2-dihydropyrimidine (1), 1,4-dimethyl-2-pyrimidone (2), and 4-methyl-2-amino-pyrimidine (3) has been determined in aqueous solution over an acidity range of some 21 pH(H0) units. The various exchange routes involve attack by base (water, hydroxide ion, buffer anion) on substrate (neutral, singly protonated, doubly protonated) and the identities of the principal components across the acidity spectrum have been established for all three compounds. The Brønsted slope, kinetic isotope effect, and activation parameters for 1 have also been determined. Protonating 1 activates it toward exchange by a factor of 103; addition of a second proton has a further effect of >105. The activating effects of the imino group, the carbonyl group, and the protonated imino group in these compounds are in the ratio 10−1:1:102.
Effect of solvent (benzene, ethanol, cyclohexane) on the partial molal volumes of organic compounds
Authors: Edward John T. , Farrell Patrick G. , Shahidi Fereidoon
Published: May 2006

The partial molal volumes of n-alkanes and n-alkanols dissolved in benzene, ethanol, or cyclohexane are given with satisfactory accuracy by the equation previously developed for solutions in carbon tetrachloride, if certain parameters (the covolume, the volume increment for the hydroxyl group, and the volume decrement for some gauche interactions) are changed. Additionally, it is necessary to postulate a greater coiling of the alkyl chains when dissolved in cyclohexane.
Generation of aminyl and aminium radicals by photolysis of N-nitrodialkylamines in solution
Authors: Chow Yuan L. , Richard Hervé , Snyder Rodney Williams , Lockhart Robert W.
Published: May 2006

Photolysis of nitramines in a neutral solvent generated nitrogen dioxide and aminyl radicals which abstracted a hydrogen but did not add to a π-bond. In dilute acidic solution, the aminyl radicals generated from the photolysis were protonated to the corresponding aminium radicals that preferentially added to π-bonds rather than abstracted a hydrogen. However, complex mixtures of addition products were obtained when nitramines were photolysed in the presence of cyclohexene under nitrogen. The plethora of the products is believed to arise from the complex behavior of nitrogen dioxide in solution; for example, (i) nitrogen dioxide may react as O- or N-radical, (ii) nitrogen dioxide exists in equilibrium with nitrogen tetraoxide, and (iii) both oxides can react as oxidizing or radical trapping agents. Under oxygen, the oxidative addition of nitramines to cyclohexene gave 1-dialkylamino-2-nitratocyclohexenes which could be treated with lithium aluminium hydride to give good yields of the corresponding amino alcohols. The quantum yields of nitramine disappearance indicated that the photolysis followed short chain processes either in neutral or acidic conditions. The decrease in quantum yield at >2 N H2SO4 is believed to be due to a reduced reactivity of aminium radicals in a highly acidic environment. The probable mechanisms of these photolytic radical chain processes are discussed.
Etude par résonance magnétique nucléaire de composés organiques contenant des chalcogènes. II. L'éther de diphényle et ses analogues soufré, sélénié et telluré
Authors: Llabrès Gabriel , Baiwir Marcel , Christiaens Léon , Piette Jean-Louis
Published: May 2006

The 1Hmr study of the title compounds has revealed a screw conformation, with defined interconversion processes, in good agreement with crystal structure determinations and theoretical calculations. The mesomeric effect of the heteroatom is smaller than in the anisole series, due to steric inhibitions.The 13Cmr enhances, to some extent, these conclusions. In the case of Te compounds, a heavy atom effect adds to the classical mesomeric and inductive effects to account for the experimental observations.
Magnetic field effect on the fluorescence from γ-irradiated solutions of perfluorocarbons
Authors: Dixon Robert Smith , Lopata Vincent John
Published: May 2006

The effect of an applied magnetic field on the fluorescence from γ-irradiated solutions of perfluorobiphenyl and perfluoronaphthalene has been measured in various solvents. In all the solvents used (cyclohexane, squalane, isooctane) the fluorescence intensity increases with increasing field and tends towards a plateau at high fields (>0.1 T). At low fields, the fluorescence enhancement is smaller for the perfluorocarbons than for the parent hydrocarbons, due to the larger electron–nuclear hyperfine coupling and broader spread of the hyperfine levels in the radical ions of the perfluorocarbons. At high fields the fluorescence enhancement is also smaller for the perfluorocarbons than for the parent hydrocarbons, indicating a larger relative proportion of prompt (field-independent) fluorescence for the perfluorocarbons than for the parent hydrocarbons.
Kinetic studies on the catalytic reduction of nitrotoluene by hydrazine
Authors: Goswami N. , Rahman M. L.
Published: May 2006

Kinetics of reduction of p-nitrotoluene by hydrazine in presence of Raney nickel catalyst have been studied spectrophotometrically. It has been found that the reaction is first order with respect to both hydrazine and nitrotoluene. The influence of solvent, salt, and the amount of catalyst on the reaction rate has been investigated. The rate constant was found to depend on the dielectric constant, the ionic strength, and on the catalyst concentration. The activation energy was estimated to be 103.92 kJ mol−1 in 73.58% ethanol in water. This value decreases considerably when the polarity of the solvent increases and when other salts are added. In pure water the value is 32.25 kJ mol−1.
Synthesis and structure of 3,5-dimethylpyrazolyl iron and cobalt dinitrosyl dimers
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and characterization of two 3,5-dimethylpyrazolyl metal dinitrosyl dimers [(N2C5H7)M(NO)2]2 (where M = Fe or Co) are described and their X-ray crystal structures detailed. Both complexes crystallize in the monoclinic space group C2/c, a = 23.848(2), 23.722(4), b = 10.7775(7), 10.6888(6), c = 14.764(1), 14.712(2) Å, β = 117.366(6), 117.094(7)°, Z = 8 (for the iron and cobalt complexes respectively). The structure of the iron complex was solved by Patterson and Fourier syntheses. The cobalt complex is isomorphous with the iron analog. Both structures were refined by full-matrix least-squares procedures to R = 0.028 and 0.035 for 4251 and 3376 reflections with I ≥ 3σ(I) respectively. Both complexes adopt a boat conformation for the central M—(N—N)2—M ring and display significantly non-linear M—N—O groups. The coordination geometry about the metal atoms is distorted tetrahedral. Important molecular dimensions (distances corrected for libration) are: mean Fe—N(pyrazolyl), 2.009(5), mean Fe—NO, 1.696(2) Å, Fe—N—O, 158.5(3)–168.2(2)°, mean Co—N(pyrazolyl), 1.992(7), Co—NO, 1.646(3)–1.680(3) Å, and Co—N—O, 161.6(3)–173.5(3)°. The iron complex is paramagnetic with formally "17-electron" iron atoms. Both structures are compared with similar four-coordinate metal dinitrosyl compounds.
Theoretical study of isotropic hyperfine coupling constants in small radicals by MINDO/3 method
Authors: Pandey Prabhat K. K. , Chandra P.
Published: May 2006

Isotropic hyperfine coupling constants for 1H, 13C, 14N, 17O, and 19F nuclei in a large number of small radicals as obtained by the SCF-MO-LCAO-UHF-MINDO/3 scheme are presented. It is seen that whereas calculated 1H, 13C, and 14N hyperfine couplings agree fairly well with experiment, the agreement is not so satisfactory for 17O and 19F couplings.
Carbon-13 nuclear magnetic resonance spectra of oxazoles
Authors: Hiemstra Henk , Houwing Hendrik A. , Possel Okko , van Leusen Albert M.
Published: May 2006

The 13C nmr spectra of oxazole and eight mono- and disubstituted derivatives have been analyzed with regard to the chemical shifts and the various carbon–proton coupling constants of the ring carbons. The data of the parent oxazole are compared with thiazole and 1-methylimidazole.
Proton and carbon-13 nuclear magnetic resonance studies of the conformational properties of seven-membered heterocycles. 2,4-Benzodithiepin and its derivatives
Authors: Sauriol-Lord F. , St-Jacques M.
Published: May 2006

The conformational properties of 1,3-dithia-5,6-benzocycloheptene (7) (2,4-benzodithiepin), three 2,2-dialkyl derivatives, and two monosubstituted derivatives (2-CH3 and 2-OCH3) have been investigated by 1H and 13C dnmr methods. It is reported that the most stable conformation of the seven-membered ring is a chair on which, in the case of the monosubstituted compounds, the 2-CH3 group adopts an equatorial position while the 2-OCH3 group takes the axial position. Only for the 2,2-pentamethylene derivative (10) was a minor amount (13%) of TB form detected. These results are markedly different from those found previously for the oxygen analogs and the conformational effect of the cyclic heteroatoms will be discussed in terms of the anomeric and steric effects.
Metal derivatives of azoles. Part V. Platinum(II) and palladium(II) pyrazolates as a new type of neutral bidentate ligands
Authors: Bandini Anna Laura , Banditelli Guido , Minghetti Giovanni , Bonati Flavio
Published: May 2006

The complexes (L—L)M(pz)2 {(L—L) = (Ph2PCH2)2, M = Pt, Pd; (L—L) = 2,2′-dipyridine, M = Pt} and (L—L)M(pz′)2 {(L—L = (Ph2PCH2)2, M = Pt; (L—L) = 2,2′-dipyridine, M = Pt, Pd} where pzH = pyrazole and pz′H = 3,5-dimethylpyrazole, behave as ligands towards suitable acceptors affording 1:1 or 1:2 adducts.The 1:1 adducts are obtained by reaction with group IIB metal halides, cobalt(II) chloride, copper(II), or zinc(II) sulphate and are likely to be binuclear complexes, (ligand)MX2, with two pyrazolato anions bridging the different metals.The nature of the 1:2 adducts [(ligand)2M′][BF4]2 (M′ = Zn, Ni, Co) as well as of the adduct (dipy)Pt(pz)2•2Rh(CO)2Cl, are discussed.
Contribution to the solution chemistry and polarographic behaviour of anthrapurpurin complexan
Authors: Capitan F. , Guiraum A. , Vilchez J. L. , Arenas J. F.
Published: May 2006

The reduction of the 1,2,7-trihydroxyanthraquinone-3-methylamino-N,N-diacetic acid at dropping mercury electrode has been investigated. The reduction involves two electrons as well as either one or two hydrogen ions depending on the pH. Two alternative reaction mechanisms are proposed. Five acid-dissociation constants have been determined by potentiometric and spectrophotometric methods. A sequence for the dissociation of the protons is proposed. Thermal gravimetric and differential analysis of the anhydrous and dihydrated reagent are reported.
Organic sulfur mechanisms. 21. The reaction of arylsulfenes with sulfur dioxide
Authors: King James Frederick , Aslam Mohammad
Published: May 2006

Phenylsulfene and diphenylsulfene (2), obtained by reaction of 2,6-lutidine with appropriate precursors, react with sulfur dioxide to give, respectively, benzaldehyde and benzophenone, in confirmation of the suggestion of Staudinger and Pfenninger that the benzophenone formed in the reaction of diphenyldiazomethane (1) with sulfur dioxide arises from reaction of the latter with the sulfene (2). The reaction of sulfenes with sulfur dioxide would appear to have only limited scope, all known examples occurring with a sulfene having at least one aryl group attached to the sulfene carbon atom; even with these sulfenes the reaction is apparently readily precluded in the presence of most other sulfene traps. 18O-Labelling experiments in the reaction of diphenylsulfene (2) with sulfur dioxide indicate that the oxygen atoms in about two-thirds of the benzophenone molecules come from the sulfur dioxide, whereas 2 itself supplies the oxygen atoms for the remaining third. Previously suggested mechanisms predict that the benzophenone oxygens come only from the sulfur dioxide. General processes that could lead to the observed labelling pattern are discussed and specific examples presented. The available evidence, including reported labelling studies on the related reaction of sulfur dioxide with sulfur trioxide, provides a basis for excluding certain possible mechanisms and for preferring some over others, but is not sufficient to establish a single mechanism for the reaction of arylsulfenes with sulfur dioxide.
Claisen rearrangement of allyloxyanthraquinones
Authors: Wong C. M. , Singh R. , Singh K. , Lam H. Y. P.
Published: May 2006

Allyloxyanthraquinones showed unusual behaviour during the Claisen rearrangement. Thus, 1-allyloxyanthraquinone 9 rearranged very readily in the presence of benzylamine while 2-allyloxyanthraquinone 13 refused to do rearrangement even under very drastic conditions. On the other hand, 1,2-diallyloxyanthraquinone rearranged with the loss of the 2-allyloxy group as the result of a retro-ene reaction which has not been previously observed while 1,4-di(2′-chloro-2′-propenyloxy)anthraquinone 18 rearranged to give, as a major product, the unsymmetrically substituted anthraquinone 19 which is useful in the synthesis of anthracycline aglycones.
Pyridazino[3,4,5-de]phthalazines. I. Synthesis of the heterocyclic system and key intermediates
Authors: Francis John E. , Doebel Karl J. , Schutte Paula M. , Savarese Edgar C. , Hopkins Stephen E. , Bachmann Ernst F.
Published: May 2006

1H-Pyridazino[3,4,5-de]phthalazine (4) and 3-hydrazino-1(or 9) H-pyridazino[3,4,5-de]-phthalazine (6) represent intramolecular hydrazones of the drugs hydralazine and dihydralazine, respectively. These novel heterocycles were synthesized by several different routes starting from 2,6-dimethylbenzoic acid, 3-methylphthalic anhydride, or hemimellitic acid. Tetrabromination of 2,6-dimethylbenzoic acid with bromine and carbon tetrachloride under free radical conditions followed by treatment with dilute aqueous hydrazine hydrate produced pure 4 in yields up to 58%. Treatment of 3-methylphthalic anhydride with 2 mol of N-bromosuccinimide under radical conditions followed by reaction of the dibromo compound with hydrazine hydrate in methyl Cellosolve produced 3-oxo-3H-2,9(or 1,2)-dihydropyridazino[3,4,5-de]phthalazine in 60% yield. This intermediate was converted to the 3-thiono compound or 3-chloro-1(or 9)H-pyridazino[3,4,5-de]phthalazine from which the hydrazine 6 was generated by hydrazine hydrate treatment. This hydrazine was further characterized by conversion with acid chlorides to novel tetracyclic condensed triazoles or by nitrous acid to a tetracyclic condensed tetrazole. The unsubstituted heterocycle 4 was uninteresting in pharmacological screens but the hydrazine 6 resembled hydralazine by lowering blood pressure in several animal test models and in limited clinical trials.
A synthetic approach to quassin. Synthesis of a ring A seco derivative
Authors: Stojanac Nada , Stojanac Žarko , White Peter S. , Valenta Zdenek
Published: May 2006

Synthesis of compound 16, a ring A seco derivative of quassin (1), is described. The overall strategy consists of manipulations within a rigid system established by a Diels–Alder reaction, followed by unfolding of the molecule. The sequence includes a cyclization of a 1,5-bromoketone with Zn and a selective oxidation of one carbonyl group in a tricyclic diketo diester with peracetic acid.
Trifluoromethylsulfonyl aryl derivatives: competitive nucleophilic attack at an aromatic carbon and at the sulfur atom of an aromatic SO2CF3 group
Authors: Terrier François , Morel Jean , Pouet Marie-José , Simonnin Marie-Paule
Published: May 2006

The reaction of methoxide ion with 2-nitro-4-trifluoromethylsulfonylanisole, 4-nitro-2-triftuoromethylsulfonylanisole and 2,4- bis(trifluoromethylsulfonyl)anisole in DMSO has been studied by 1H and 19F nmr. Evidence for the transient formation of gem-dimethoxy σ-adducts arising from nucleophilic attack at the aromatic C1 carbon is given. Concurrent methoxide ion attack occurs at the sulfur atom of the SO2CF3 group to give the aryl methyl sulfonates ArSO3CH3, which are slowly converted into aryl sulfonates ArSO3−. The 1H chemical shifts of the anisoles are consistent with a greater electron-withdrawing effect of the SO2CF3 group compared to the nitro group. In contrast, a 4-nitro group appears to be more efficient than a 4-SO2CF3 group in delocalizing the negative charge of the σ-adducts.
Vinyl ether hydrolysis. XIII. The failure of I-strain to produce a change in rate-determining step
Authors: Chiang Y. , Chwang W. K. , Kresge A. J. , Szilagyi S.
Published: May 2006

Rates of hydrolysis of 1-ethoxy-3,3,5,5-tetramethylcyclopentene and 1-methoxy-2,3,3,5,5-pentamethylcyclopentene measured in mineral acid and formic and acetic acid buffer solutions show general acid catalysis and give large kinetic isotope effects in the normal direction (kH/kD > 1). This indicates that these reactions proceed by the conventional mechanism for vinyl ether hydrolysis in which proton transfer from the catalyzing acid to the substrate is rate-determining, and that the I-strain in these substrates is insufficiently great to shift the reaction mechanism to rapidly reversible substrate protonation followed by rate-determining hydration of the ensuing cationic intermediate.
The reaction of cis-Ru(CO)4(SiCl3)2 with bidentate ligands
Authors: Pomeroy R. K. , Wijesekera K. S.
Published: May 2006

The substitution of the equatorial carbonyl groups in cis-Ru(CO)4(SiCl3)2 by a variety of bidentate ligands (L—L) to give compounds of the type Ru(L—L)(CO)2(SiCl3)2 is described. With Ph2E(CH2)2EPh2 (E = P, As) it was also possible to isolate the bridging derivatives, (Cl3Si)2(OC)3Ru(L—L)Ru(CO)3(SiCl3)2. The 31P nmr spectra (of the phosphorus compounds) are discussed.
Evidence for anion coordination in hexafluorophosphate and hexafluoroarsenate complexes of nickel(II)
Authors: Morrison Raymond M. , Thompson Robert C. , Trotter James
Published: May 2006

Yellow crystals of tetrakis(4-methylpyridine)nickel(II)hexafluorophosphate, C24H28F12N4NiP2, are monoclinic, a = 19.709(5), b = 9.866(2), c = 16.515(9) Å, β = 101.54(4)°, Z = 4, space group C2/c. The structure was solved by Patterson methods and refined by full-matrix least-squares methods to R = 0.071 for 1002 observed reflections. The structure consists of a square-planar array of 4-methylpyridine ligands about nickel with hexafluorophosphate groups above and below the plane. The Ni—N distances are 1.916(9) and 1.919(10) Å with the pitch of the rings 102.06° and 97.32°. The shortest Ni—F distances are 3.031(8) Å. The structure shows that the anions are not fully coordinated to nickel but are nonetheless held in axial positions by weak, essentially ionic, interactions.Tetrakis(pyridine)nickel(II)hexafluoroarsenate has been found to undergo a reversible structure change over the temperature range 180 to 200 K. Electronic and vibrational spectra and magnetic susceptibility studies suggest that the compound has a structure similar to that of Ni(4-mepy)4(PF6)2 with the anions only weakly interacting with cations in the high temperature form and fully coordinated in the low temperature form.
The mechanism of hydrogenation of activated olefins, including prochiral ones, using trans-chlorohydridobis(diop)ruthenium(II)
Authors: James Brian R. , Wang Daniel K. W.
Published: May 2006

Solutions of the title complex trans-HRuCl(diop)2, where diop is an optically active chelating ditertiary, hydrogenate under mild conditions activated olefinic substrates, including prochiral ones in high optical yields. Kinetic and spectroscopic studies on hydrogenation of acrylamide and β-phenylacrylic acid indicate an 'unsaturate' mechanism involving rapid coordination of the substrate to give an alkyl intermediate, that subsequently reacts with H2 in a rate-determining step to yield the saturated product and the starting monohydride complex. A diop ligand dissociates to provide necessary coordination sites at the metal. The α-phenylacrylic acid coordinates more strongly than acrylamide, but hydrogenates more slowly.