bluuebunny/crossref_metadata_2025 huggingface dataset:
'Breaking' and formation of hydrogen bonds by proton donor anesthetics
Authors: Massuda Rachel , Sandorfy C.
Published: May 2006

It has been shown previously that halofluorocarbons having anesthetic potency hinder the formation of hydrogen bonds (HB) of the [Formula: see text] types and it has been suggested that this is linked to a competitive mechanism involving another type of association. Since some of the most potent and widely used fluorocarbon anesthetics contain a mobile hydrogen atom the question arises if in such molecules the competitive mechanism involves the formation of HB's with the anesthetic as the proton donor instead of, or in addition to, association due to the electron acceptor properties of the higher halogens as seems to be the case for those fluorocarbon anesthetics which contain no hydrogen. Chloroform, halothane, methoxyflurane, enflurane, and 4,5-dichloro-2,2-difluoro-l,3-dioxolane have been studied from this point of view with the result that both mechanisms appear to operate.
Metal-ion oxidations in solution. Part XX. The mechanism of the reaction of thallium (III) with 2-mercaptosuccinic acid in perchlorate media
Authors: Amjad Zahid , Chambers John G. , McAuley Alexander
Published: May 2006

The oxidation of 2-mercaptosuccinic (thiomalic) acid (HRSH) by thallium(III) proceeds via an inner sphere mechanism. Spectrophotometric and kinetic evidence are provided for the formation of a sulphur-bonded thallium(III) intermediate. The data are consistent with the reaction scheme[Formula: see text]in which the complex decomposes via a one-electron intramolecular transfer k2 = 3.8 × 10−4 s−1 at 25 °C, with K2 = 1650 M−1. The enthalpy of activation ΔH2≠ for the redox reaction (11.8 ± 1.2 kcal/mol) is considerably smaller than for other systems of this type and reflects the greater ease of reaction. Comparison is made of possible one- and two-electron transfer pathways.
The deprotonation and rearrangement of N-methyl methylphosphazenium quaternary salts: a novel synthetic route to cyclic azaphosphorins
Authors: Oakley Richard T. , Paddock Norman L.
Published: May 2006

The N-methyl methylphosphazenium salts (NPMe2)3,4•MeI and N3P3Ph4Me2•MeI can be deprotonated by a variety of bases to yield the novel azaphosphorins Me2n−1(NHMe)PnNn−1CH (n = 3,4) and Me(NHMe)Ph4P3N2CH, formed by a rearrangement in which the methylated nitrogen atom is displaced from the PN ring by the initially produced exocyclic methylene group. The 1H nmr spectra of the azaphosphorins indicate a rapid proton exchange between the endocyclic carbon and the exocyclic nitrogen, which can be slowed by the addition of an auxiliary base. When KO-t-Bu reacts with the quaternary salts, nucleophilic attack competes with proton removal, and the linear oxides (NHMe)(PMe2N)nPMe2O (n = 2−4) have been isolated from these reactions. The azaphosphorins Me2n−1(NHMe)PnNn−1CH (n = 3, 4) are hydrolysed in aqueous ethanol to give the cyclic oxides Me2n−1(O)PnNn−1CH2, and react with methyl iodide by a proton transfer reaction to give the hydroiodides Me2n−1(NHMe)PnNn−1CH•HI. Their reaction with benzoyl chloride leads to the derivatives Me7(NHMe)P4N3CCOPh and Me7(NMeCOPh)P3N2CCOPh, the initial substitution on carbon indicating that it is the primary basic centre. Model calculations of π-electron energies suggest that both the azaphosphorin rearrangement and the proton exchange reactions depend on the relative orbital electronegativity of the ring and exocyclic atoms, the less electronegative atom being more stable in the endocyclic position.
Un exemple d'isomérisation radicalaire en chaînes: la photoinduction de l'isomérisation cis–trans de la pentène-3 one-2
Authors: Rioual Armel , Deflandre André , Lemaire Jacques
Published: May 2006

Mechanisms of the photosensitized cis–trans photoisomerization of 3-penten-2-one which do not imply only classical triplet–triplet energy transfer are proposed; they are based upon measurements of the variations of initial quantum yields of isomerization with the initial donor and acceptor concentrations, the wavelength of excitation, and the nature of the donor and of the solvent. Carbonyl donors (acetophenone, benzophenone, acetone) induce a radical isomerization by a chain process in reducing solvents; the example of acetophenone is specially interesting. In solvents in which the donor is not photoreduced (as benzene or CCl4) classical triplet–triplet energy transfers occur. Sensitization with aromatic donors (benzene, mesitylene) proceeds through triplet–triplet energy transfer at low concentrations of the acceptor. At higher concentrations of acceptor, an exciplex is formed between the ketone and the aromatic in its singlet excited state; this exciplex is deactivated by dissociation and by causing the isomerization of the α,β-unsaturated ketone.
Effect of an external electric field on the yield of trapped electrons in a γ-irradiated hydrocarbon glass
Authors: Kato Noriyuki , Kimura Toyoaki , Fueki Kenji
Published: May 2006

Trapped electron yields were measured by means of optical absorption spectroscopy for a hydrocarbon glass γ-irradiated at 77 K in the presence of an external electric field. It was observed that the yield of trapped electrons increased in the presence of an external electric field as compared with that in the absence of an external electric field. The experimental results were analyzed theoretically and interpreted as due to overall effects involving changes in geminate recombination times which were caused by an external electric field.
The synthesis of methyl 2-O-benzoyl-3,4-O-(S)- and methyl 2-O-benzoyl-3,4-O-(R)-benzylidene-β-L-ribopyranoside
Authors: Clode David M.
Published: May 2006

Benzylidenation of methyl β-L-arabinopyranoside, by the method of Oldham and Honeyman, followed by benzoylation, gave methyl 2-O-benzoyl-3,4-O-(S)-benzylidene-β-L-arabinopyranoside (1). Selective acid hydrolysis of a 1:1 mixture of the diastereomeric forms of methyl 2-O-benzoyl-3,4-O-benzylidene-β-L-arabinopyranoside gave the (R)-isomer (3). Debenzoylation of 1 and 3 gave methyl 3,4-O-(S)-and methyl 3,4-O-(R)-benzylidene-β-L-arabinopyranoside (2 and 4) respectively. Oxidation of 2, followed by reduction and benzoylation, gave methyl 2-O-benzoyl-3,4-O-(S)-benzylidene-β-L-ribopyranoside (7). A similar reaction sequence with 4 gave methyl 2-O-benzoyl-3,4-O-(R)-benzylidene-β-L-ribopyranoside (8).
The use of polymer supports in organic synthesis. XII. The total stereoselective synthesis of cis insect sex attractants on solid phases
Authors: Fyles Thomas M. , Leznoff Clifford C. , Weatherston John
Published: May 2006

A 2% crosslinked divinylbenzene-styrene copolymer, incorporating trityl chloride groups (2) was used in the synthesis of insect sex attractants of Lepidoptera by a two-step alkyne coupling route. Polymer 2 reacted with the symmetrical diols, 1,8-octanediol and1,10-decanediol, to give the monoblocked polymer-bound diols 5 and 6 respectively. Mesylation of 5 and 6 gave the polymer-bound monomesylates 7 and 8 which on coupling with lithioacetylide gave the polymer-bound terminal alkynes 9 and 10 respectively. Acid cleavage of 9 and 10 provide 9-decyn-1-ol and 11-dodecyn-1-ol respectively. A second coupling step was performed by lithiation of 9 and 10 with n-butyllithium or tert-butyllithium followed by treatment with n-butyl bromide or ethyl bromide to give polymer-bound internal alkynes, which on acid hydrolysis gave 9-tetradecyn-1-ol (22), 11-hexadecyn-1-ol (23), and 11-tetradecyn-1-ol (24). If 10 had been lithiated with n-butyllithium and coupled with ethyl bromide, some translithiation occurred to liberate n-butyl bromide which entered into the coupling reaction eventually giving a mixture of 23 and 24. This problem was resolved by the use of tert-butyllithium in the lithiation step. Attempts were made to reduce polymer-bound internal alkynes stereoselectively to cis-alkenes with 9-borabicyclononane, diisobutylaluminum hydride, and catechol borane but all these reagents proved inadequate due to incomplete reduction, overreduction, hydrogenolysis of the alkyne from the polymer, and non-selectivity. Polymer-bound internal alkynes were quantitatively reduced exclusively to cis insect sex attractants using disiamylborane without concurrent overreduction or hydrogenolysis.
Differential thermal analysis and infrared studies on the effect of impurities on aragonite–calcite transformation
Authors: Rao Chebrolu RamaMohan , Mehrotra Pratap Narain
Published: May 2006

The transformation of aragonite to calcite (A–C) is an irreversible reconstructive transformation involving a change from 6 to 9 in the primary coordination. Cationic impurities like Na+, Mg2+, Zn2+, Y3+, La3+, Nd3+, Gd3+, Dy3+ have been doped in pure aragonite and their effect on the kinetics and energetics of its transformation to calcite is studied. By employing a DTA technique, the enthalpy and energy of activation for the transformation have been calculated. The ir spectra of aragonite and calcite in pure form and with various impurities have been studied and the effect of impurities on absorption bands discussed.
Limits to barriers to internal rotation in benzal fluoride, chloride, and bromide solution by the J method
Authors: Schaefer Ted , Danchura Werner , Niemczura Walter
Published: May 2006

On the basis of the long-range couplings over six bonds between the protons on the side chain and the ring protons in benzal fluoride, chloride, and bromide and some of their derivatives, a hindered rotor model (J method) yields limits to the barriers to internal rotation. These are 0.0 to 1.8, 0.7 to 2.4, and 1.7 to 3.8 kcal/mol for the fluoride, chloride, and bromide, respectively. Refinement of the model suggests barriers of 1.1 ± 0.2, 2.2 ± 0.3, and 3.5 ± 0.6 kcal/mol, respectively. The barrier values in the chloride and bromide are considerably less sensitive to the model parameters than is the barrier in the fluoride. It would be of interest to have gas phase values for these barriers. It is also shown that a σ–π mechanism holds for the six-bond proton–proton coupling constant in benzal fluoride but that the analogous coupling between 19F on the side chain and the para ring proton carries a non σ–π contribution of +0.3 Hz.
Photoreactions of iminophosphoranes
Authors: Yim A. S. , Akhtar M. H. , Unrau A. M. , Oehlschlager A. C.
Published: May 2006

The irradiation of N-aryltriphenyliminophosphoranes in inert solvents leads to efficient production of triphenylphosphine and the diaryl azo compounds derived from the N-aryl ylide substituent. The irradiation of N-alkyltriphenyliminophosphoranes leads to rearrangements of the N-alkyl substituent analogous to those observed during the irradiation of the corresponding azides. Triphenyliminophosphoranes which possess N-substituents capable of strong delocalization of the nitrogen lone pair (e.g. benzene sulfonyl, benzoyl) are photostable. Since all attempts to trap nitrene intermediates suspected to be formed during the photoreactions of the photolabile iminophosphoranes were unsuccessful, the reactions are considered to proceed via excited ylide intermediates.
Evidence for five-coordination in titanium(IV) complexes. A nuclear magnetic resonance investigation
Authors: Somogyvari Arpad , Serpone Nick
Published: May 2006

Diketonato complexes of titanium(IV), (X3Ti(dik))2 (X = Cl, Br; dik = anions of dipivaloylmethane and benzoylacetone), of apparent five-coordinate stoichiometry have been prepared and investigated in nitrobenzene solutions using the variable temperature nuclear magnetic resonance technique. The nmr spectra reveal the existence of two equilibrium species; a five-coordinate X3Ti(dik) and a six-coordinate X2Ti(dik)2 complex. The data are interpreted in terms of a symmetric dissociation of the six-coordinate titanium(IV) dimer, (X3Ti(dik))2, into two five-coordinate monomers which then undergo a disproportionation reaction to the four-coordinate titanium tetrahalide and the six-coordinate X2Ti(dik)2 species.
Synthesis of cyclohexapyrrolizidines: C-methylation of vinylogous amides
Authors: Kelly Ronald B. , Alward Sandra J.
Published: May 2006

A synthesis of the cyclohexapyrrolizidines 32 and 33 is described; the structure of the latter was determined by X-ray crystallography. It is anticipated that this synthesis will serve as a model for the construction of a similar pyrrolizidine system during a projected synthesis of thelepogine 2.A convenient method for the C-methylation of cyclic vinylogous amides is also described. This procedure, which is similar to published procedures, affords high yields of methylated product and is regiospecific.
Solidaline. A modified protoberberine alkaloid from Corydalissolida
Authors: Manske Richard H. F. , Rodrigo Russell , Holland Herbert L. , Hughes Donald W. , MacLean David B. , Saunders John K.
Published: May 2006

Re-investigation of the alkaloids of Corydalissolida yielded two further bases, ochotensine and solidaline. Spectral analysis has shown the latter to be representative of a new class of protoberberine-related isoquinoline alkaloids.
The α-alkoxycarbonylation of saturated carbonyl compounds. The synthesis of 17α-hydroxymethyl 20-keto steroids
Authors: Mukherjee D. , Engel CH. R.
Published: May 2006

It is shown that enolate ions, in particular lithium enolates obtained from enol acetates of saturated ketones by reaction with methyllithium, may not only be alkylated and carboxylated, but also alkoxycarbonylated (in position a to the original saturated keto group). By this method, saturated 20-keto steroids were transformed into 17α-methoxycarbonyl 20-ketones. Thus, from pregnenolone, 17-methoxycarbonylpregnenolone was prepared and was then converted to 17-hydroxymethylprogesterone and to some of its esters. This method for preparing 17-hydroxymethylated hormone analogues of the progesterone-corticoid group is simpler and more efficient than the pathway implying a free-radical functionalization of a 17α-methyl group.
Diffusion coefficients and viscosities in glycol and glycerol solutions
Authors: Evanoff John E. , Harris Walter E.
Published: May 2006

Diffusion coefficients have been measured polarographically in media with a wide range of viscosities. The range covers five orders of magnitude up to the limits of high viscosity possible by normal polarographic means. The diffusion coefficients obtained are nearly inversely proportional to the viscosity. The diffusion coefficients are in the range of interest to chromatography theory.
Studies on nucleation phenomena occurring in aqueous solutions supersaturated with calcium sulfate
Authors: Keller D. M. , Massey Ronald E. , Hileman Jr. O. E.
Published: May 2006

The results of a set of experiments designed to delineate the nucleation rate, supersaturation, temperature surface for the system CaSO4•2H2O/H2O are reported. The data were obtained using the droplet technique coupled with in situ generation of SO42− under the conditions that dS/dt was large during the early part of the induction period and it was zero during the actual nucleation events. The observed shape of the surface is compared with that suggested by the classical theory of nucleation and differences are commented on. The critical parameters important in classical nucleation theory are reported.
Synthesis and structure of 4-methylpyridine complexes of cobalt(II) and nickel(II) hexafluorophosphate and hexafluoroarsenate
Authors: Morrison Raymond M. , Thompson Robert C.
Published: May 2006

The complexes M(4mepy)4A2 and M(H2O)2(4mepy)8A2 (where M is Ni or Co and A is PF6 or AsF6) have been prepared and their electronic spectra and magnetic properties studied. A preliminary report is made of single crystal X-ray diffraction studies on Ni(H2O)2(4mepy)8(PF6)2, Co(H2O)2(4mepy)8(PF6)2, and Co(4mepy)4(PF6)2. All of the complexes have structures involving complex cations and non-coordinated anions, consistent with extremely weak ligating abilities for both PF6− and AsF6−. Cations identified and characterized are the squashed tetrahedral [Co(4mepy)4]2+ ion, the square planar [Ni(4mepy)4]2+ ion, and the tetragonal [Co(4mepy)4((4mepy)2H2O)2]2+and [Ni(4mepy)4((4mepy)2H2O)2]2+ ions. The ligand field strength of 4-methylpyridine is found to be indistinguishable from that of pyridine in these complexes. Infrared spectra are reported and infrared criteria for establishing the presence of non-coordinated anions in PF6− and AsF6− complexes are suggested.
Novel aspects of the optical spectra of dichlorotetrakis(thiourea)iron(II)
Authors: McCarthy Paul James , Walker Ian Munro
Published: May 2006

The low-temperature optical spectra of dichlorotetrakis(thiourea)iron(II) contain strong bands at 16.24 and 24.66 kK. The former gives an intense green color to freshly prepared crystals of this material. Upon long standing at room temperature or when briefly heated to about 150 °C the crystals become colorless and both bands disappear. The bands are assigned to allowed metal-to-ligand electron-transfer processes in an FeCl2(thiourea)2(disulfide) impurity, which is postulated to be present in minute amounts. Most freshly prepared crystals also show ligand field bands ca. 8 kK which are identical at room temperature and 10 K. Disorder in the crystals is presumed to set up an unsymmetrical ligand field which provides the intensity-gaining mechanism for these forbidden transitions. Well-aged crystals, or fresh crystals that have been heated for 15 min at 150 °C, are more ordered and show typical vibronic spectra with the bands decreasing greatly in intensity as the temperature is lowered. The ground state of the complex is shown to be 5B2g.
Kinetics of Z–E isomerization of spiroindolinopyrans
Authors: Gruda Ilona , Leblanc Roger M. , Sochanski Jerzy
Published: May 2006

The kinetics of the Z–E isomerization of a series of 3′-nonsymmetrically substituted spiroindolinopyrans bas been studied by nmr in different solvents.The rate-determining step in nonpolar solvents was found to be the cleavage of the C—O bond whereas in polar solvents it was the C(2)—C(3) bond rotation.A strong steric hindrance of substituents at carbon 3 was observed. It was found that the rate of the isomerization is more sensitive to the bulkiness of the substituent at C(3′) than at the N(1′). Protic solvents enhance the reaction more than nonprotic polar solvents.
Ipso nitration. XVIII. Nitrationof 2-chloro-1,3,5-trimethylbenzene: nitration ipso to chlorine
Authors: Fischer Alfred , Seyan Sachdev Singh
Published: May 2006

Nitration of 2-chloro-1,3,5-trimethylbenzene in acetic anhydride gives the cis and trans isomers of 4-chloro-1,3,5-trimethyl-4-nitrocyclohexa-2,5-dienyl acetate (1, 21%), the cis and trans isomers of 3-chloro-2,4,6-trimethyl-4-nitrocyclohexa-2,5-dienyl acetate (2, 6%), and 2-chloro-1,3,5-trimethyl-4-nitrobenzene (73%). Diene 1 reacts with acidified aqueous acetone to form the corresponding dienol, acidified methanol to form the methyl ether, and hydrogen chloride to form the corresponding chloride. In acetic acid a mixture of 4-chloro-3,5-dimethyl-benzyl derivatives and 3-chloro-2,4,6-trimethylphenyl acetate are formed. In trifluoroacetic acid – trifluoroacetic anhydride and also in boron trifluoride etherate, 2-chloro-1,3,5-trimethyl-4-nitrobenzene is the predominant product. Diene 2 on reaction with acetic acid, acidified methanol, trifluoroacetic acid – trifluoroacetic anhydride, and boron trifluoride etherate gives 3-chloro-2,4,6-trimethylphenyl acetate. Some 2-chloro-4-nitromesitylene is obtained in trifluoromethanesulfonic acid. Diene 2 also gives the acetate on standing at ambient temperature or at −20 °C, and on pyrolysis. Diene 1 gives 4-chloro-3,5-dimethylphenylnitromethane on standing at ambient temperature or at −20 °C but a mixture of 2-chloro-1,3,5-trimethyl-4-nitrobenzene, chloromesitylene, and 3-chloro-2,4,6-trimethylphenyl acetate on pyrolysis.
The crystal and molecular structure of anti-1,2,4,5-tetraphenyl-3,6-dicarbomethoxytricyclo[3.1.0.02,4]hexane
Authors: Bennett M. J. , Purdham J. T.
Published: May 2006

1,2,4,5-Tetraphenyl-3,6-dicarbornethoxytricyclo[3.1.0.02,4]hexane crystallizes in the monoclinic space group P21/c with a = 10.044(4), b = 9.500(2), c = 14.172(4) Å, β = 104.38(2)°, and Z = 2. Using 1032 unique reflections with I > 3σ(I), the structural data were refined by full matrix least-squares techniques to R = 0.038. The molecule was found to be in the anti-configuration. All bond lengths within the highly strained central tricyclic framework were equal within experimental error and average 1.531 Å.
Arene–chromium complexes: Photochemical substitution of phosphine and phosphite ligands by olefin
Authors: Donnini G. Paul , Shaver Alan
Published: May 2006

Complexes of the type (η6-C6H5XCH2CH=CH2)Cr(CO)2L, where X = O, CH2 and L = P(C6H5)3, P(OC6H5)3, P(OC2H5)3, and P(CH3)2(C6H5) are photochemically labile. Ultraviolet irradiation leads to rapid displacement of L and coordination of the pendent olefin. [1,3,5-(CH3)3C6H3]Cr(CO)2P(C6H5)3 undergoes the same reaction in the presence of cis-cyclooctene. These observations are related to the general inability to substitute a second carbonyl ligand in (arene)Cr(CO)2Y by photochemical methods. Two new complexes (η6-C6H5XCH2CH=CH2)Cr(CO)2CS are reported but these decompose under ultraviolet irradiation.
Aminoglycoside antibiotics: The formation and characterization of dihydrooxazine derivatives in the paromomycin series
Authors: Hanessian Stephen , Massé Robert , Ekborg Goran
Published: May 2006

Treatment of penta-N-benzyloxycarbonylparomomycin with benzaldehyde and excess zinc chloride gives a dibenzylidene derivative in high yield. This consists of the 4′,6′-O-benzylidene 4′′′,6′′′-N,O-benzylidene (dihydrooxazine) derivative of penta-N-benzyloxycarbonylparomomycin. Chemical evidence is presented to support this structure and model studies are reported for the formation of dihydrooxazine and oxazolidine derivatives of benzyloxycarbonylamino sugars containing suitably situated hydroxyl groups. The easily obtained dihydrooxazine derivative of paromomycin constitutes an interesting, preferentially blocked derivative, that is useful for the chemical modification of the parent antibiotic.
Intermediates in the γ-radiolysis of diraient sulfur compounds in dilute glass matrices
Authors: Adam Frank Cuthbert , Smith Glenn Edward , Elliot Allen John
Published: May 2006

The optical spectra of the charged ions obtained from γ-irradiation of dilute alkyl mercaptans, sulfides, and disulfides in a variety of dilute rigid glasses are measured at 77 K. The photochemical stability of these ions is determined. A new photochromic species has been found. It is derived from a mercaptan dimer cation and is analogous to the photochromic anion produced from alkyl disulfides. The results of γ-radiation are compared to the uv photolysis of similar matrices, and it is found that the thiyl (RS•) and perthiyl radicals (RS2•) are not generally in evidence in γ-irradiated matrices although they may be obtained by appropriate annealing or photobleaching of the irradiated matrix. The ions which have been characterized optically are RSH+, RSH−, RSSR+ or their dimers, and RSS(H)R. The relative stabilities of these species in the low temperature glasses are determined.
Identification of C-24 alkyl epimers of marine sterols by 13C nuclear magnetic resonance spectroscopy
Authors: Sright J. L. C. , McInnes A. G. , Shimizu S. , Smith D. G. , Walter J. A. , Idler D. , Khalil W.
Published: May 2006

13C nuclear magnetic resonance spectra of diastereomeric C-24 alkyl sterols have been assigned. Differences in the chemical shifts of side-chain carbons permitted the determination of the absolute configuration at C-24 in several sterols since these chemical shifts are insensitive to structural changes remote from the asymmetric centre. An unknown sterol from Tetraselmissuecica has been identified as (24R)-24-methylcholest-5-en-3β-ol and the configuration assigned from 1H nmr data to the sterol from Phaeodoctylumtricornutum has been confirmed. The utility and potential of this method in characterising new sterols and their biological precursors is discussed.
Polarized fluorescence study of retinals at room temperature
Authors: Hotchandani Surat , Paquin Paul , Leblanc Roger M.
Published: May 2006

The solid films of all-trans, 9-cis, and 13-cis retinals have been found to be fluorescent at room temperature. Their polarization study with the aim of understanding the nature of their fluorescent state has also been carried out at room temperature. The high positive polarization of fluorescence with respect to the excitation carried out in the main 1Bu ← 1Ag absorption transition of retinals suggests that their fluorescent state possesses a large amount of 1Bu character. A vibronic coupling mechanism that suggests the 1Ag− (a weakly allowed π,π*) state or 1n,π* state being the lowest singlet state in retinals has also been considered.
Trimethylene sulfite conformations: Effects of sterically demanding substituants at C-4,6 on ring geometry as assessed by 1H and 13C nuclear magnetic resonance
Authors: Buchanan Gerald W. , Cousineau Catherine M. E. , Mundell Thomas C.
Published: May 2006

1H and 13C nmr data for eight phenyl, diphenyl- and di-tert-butyl-2-oxo-1,3,2-dioxathianes, substituted at C-4 and/or C-6 are presented. Vicinal couplings obtained from 1H spectra by iterative computer analysis indicate chair geometries for all materials except trans-4,6-disubstituted compounds. 13C chemical shifts are corroborative.
The effect of diluent gases on ion formation in hydrocarbon flames
Authors: Chawner Brenda L. , Blades Arthur T.
Published: May 2006

It has been demonstrated that the addition of N2, CO, Ne, Ar, Kr, Xe, CO2, and CF4 to a H2-air diffusion flame containing He and traces of CH4 enhances the level of ion formation. This enhancement is proportional to the concentration of both CH4 and the diluent gas, consistent with the proposition that the diluent gas participates in the ion formation process.
Preparation of some cyclopentadienyl platinum (IV) complexes
Authors: Shaver Alan
Published: May 2006

Two routes to the synthesis of (η5-C5H5)PtR1R2R3, where R1, R2, and R3 are not all CH3, were explored. The complexes [PtR1R2R3X]4, where R1 = R2 = CH3, R3 = C(O)CH3, C2H5; R1 = R2 = C2H5, R3 = CH3, C(O)CH3; R1 = CH3, R2 = C2H5, R3 = C(O)CH3; X = Cl or I, were prepared and treated with TlCp to give (η5-C5H5)PtR1R2R3. The latter are the first polyfunctionalized cyclopentadienyl platinum(IV) complexes. Conformational isomerism about the platinum to acetyl–carbon bond was detected by infrared spectroscopy. The cleavage of a Pt—CH3 or Pt—C(O)CH3 bond in CpPt(CH3)2R using the reagents HCl, HgCl2, or I2 was not successful; the appropriate [Pt(CH3),RX]4 being isolated instead. The chiral nature of (η5-C5H5)Pt(CH3)(C2H5)[C(O)CH3] is noted.
Cancentrine. V. The 13C magnetic resonance spectra of cancentrine and some derivatives; the structure of 10-oxocancentrine
Authors: Holland Herbert L. , Hughes Donald W. , MacLean David B. , Rodrigo Russell G. A.
Published: May 2006

The 13C magnetic resonance spectrum of cancentrine is reported. Assignments of chemical shifts have been made by comparison of the cancentrine spectrum with the published spectra of codeine, codeinone, and cularine and with the spectra reported here for the first time of 9,10-dihydrocancentrine methine-O-methyl ether and 10-oxocodeinone. The spectral data so obtained have been used to interpret the 13C spectrum of 10-oxocancentrine, a new alkaloid of the cancentrine family, and to verify the structure deduced for it from 1H nmr, ir, uv, and mass spectral data.
The formation of propane, propylene, and acetone from 2-propanol over vanadium pentoxide and modified vanadium pentoxide catalysts
Authors: Fikis David V. , Murphy William J. , Ross Robert A.
Published: May 2006

The catalytic decomposition of 2-propanol has been studied in a flow System from 200 to 280 °C on vanadium pentoxide and modified vanadium pentoxide catalysts. Results were obtained with separate melts of the oxide containing 9.09 mol% of each of the alkali metal sulfates and with individual preparations of the pentoxide containing 1.01, 2.00, and 4.98 mol% potassium sulfate, respectively. In addition to expected dehydration and dehydrogenation reactions, propane was formed over the entire temperature range and became a dominant product at higher temperatures.Kinetic experiments showed that the dehydration and dehydrogenation reactions were zero order with respect to ail components while the propane-forming reaction gave a rate order of 0.3 with respect to 2-propanol concentration. Elimination-type mechanisms have been proposed to explain the results and some evidence of a relationship between catalyst activities and surface acidity is presented. The observed kinetic compensation effect bas been shown to compare well with previous work on 2-propanol decomposition on metal oxides.
Mechanism of SNi reactions. The effect of the base strength of the anionic fragments
Authors: Verrinder D. J. , Hourigan M. J. , Prokipcak J. M.
Published: May 2006

The kinetics and stereochemical aspects of the thermal decomposition of aralkyl carbonates, thiocarbonates, and carbamates were examined. The rates for the decompositions as well as the rates of loss of optical activity followed first-order kinetics. The decompositions appear to involve the heterolysis of the aralkyl–oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. However, it was found that this ion pair could return to covalency without completely decomposing to products leading to the racemization of the starting materials. This type of racemization occurred more readily in the case of the carbamates than in the thiocarbonates and carbonates. The dependence of the decomposition rates and the loss of optical activity on the nature of the hetero atom of the anionic fragment of the starting material is discussed.
Detection of intermediates and isolation of hydroquinone monoacetate in the Dakin oxidation of p-hydroxyacetophenone
Authors: Hocking Martin B. , Ko Ming , Smyth Trevor A.
Published: May 2006

Oxidation of o-, m-, and p-hydroxyacetophenone with peracetic acid or tert-butyl hydroperoxide, oxidants relatively readily monitored by nmr, failed to generate isolable intermediates though an intermediate was detected for the p-ketone. Attempted oxidation of a number of related ketones under Dakin conditions failed either to react, or to generate a detectable intermediate. However, with delicate adjustment of pH and careful timing of the isolation procedure, hydroquinone monoacetate has for the first time been successfully isolated from an alkaline aqueous hydrogen peroxide oxidation (Dakin oxidation) of p-hydroxyacetophenone.
Water-soluble lysine-containing polypeptides. V. Circular dichroisrm, electron microscopic, and thermal denaturation studies of the interaction of poly(L-lysyl-L-alanine) and poly(L-lysyl-D-alanine) with calf thymus DNA
Authors: Kielland Sandra L. , Slotin Lewis A. , Williams Ross E.
Published: May 2006

Turbidity measurements, circular dichroism spectra, electron micrographs and thermal denaturation profiles of complexes between sonicated DNA and either poly(L-lysyl-L-alanine) or poly(L-lysyl-D-alanine) show significant differences which might be related to the primary or secondary structure of the polypeptides.
The line-shape analysis of nuclear magnetic resonance peaks broadened by the presence of a 'hidden' exchange partner
Authors: Okazawa Nancy , Sorensen Ted S.
Published: May 2006

In nmr spectroscopy involving organic substrates, one often has a situation in which there is a dominant species in rapid equilibrium with one or more minor components. In general, one knows, a priori, neither the population of these minor components nor the rate constants involved in the equilibrium process. In fact, from the physical appearance of these spectra, one cannot normally even deduce that such an equilibrium exists. For example, in cases involving 13C nmr spectroscopy, this minor component may not be observable under slow exchange nmr conditions because of signal-to-noise ratio problems and hence is referred to as a 'hidden' exchange partner. In this paper, we have analyzed the extent of nmr line broadening to be expected from a two-component system of this type, varying the populations, chemical shift separations, and intrinsic line widths. Thus, the presence of a 'hidden' partner can sometimes be detected by a characteristic, but often very subtle, peak broadening–resharpening sequence involving first of all the 'averaged' peak and finally the peak of the dominant component, these peaks being virtually identical in area and very similar in chemical shift so that one is not easily alerted. Assuming there is some experimental line broadening, equations developed in this paper, together with chemical shift estimates for this 'hidden' partner, allow one to quickly estimate both the amount of the minor partner and the rate constant involved. Three 'real life' situations are subsequently analyzed.
Nitration and bromination of l,1-diphenyl-2-(2-thienyl)ethylene
Authors: Bottino Francesco A. , Pappalardo Giuseppe C. , Scarlata Giuseppe , Sciotto Domenico , Torre Michele
Published: May 2006

The behaviour of 1,1-diphenyl-2-(2-thienyl)ethylene towards electrophilic agents (Br2, HNO3) has been investigated and the structure of reaction products assigned by uv, 1H nmr spectra, and dipole moment measurements.
Memory impairment in flowing suspensions. II. Experimental results
Authors: Ennis G. J. , Okagawa A. , Mason S. G.
Published: May 2006

Experiments on the reversibility of particle orientation distributions in suspensions of nearly monodisperse rigid rods and hardened red blood cells (HRBC) subjected to cyclic shearing are described.The orientation distributions of initially aligned rods measured by direct observation exhibited a gradual loss in memory as flow was reversed back and forth which was attributed mainly to non-reversible particle interactions. When an electric field was applied continuously during cyclic shear flow, the rate of memory loss was increased. However, if an electrical shock was applied momentarily between each reversal of flow, the suspension maintained some memory. These results are generally in agreement with the theory presented in the preceding paper.With suspensions of HRBC, the particles were initially randomly oriented and the light transmittance across the planes of shear was used to measure changes in orientation distribution. Since HRBC are small enough to exhibit appreciable rotary Brownian motion, memory loss was inevitable and increased with the duration of each shear cycle and the cell concentration.Memory loss was also observed for rods and HRBC in non-Newtonian media and was attributed to drift in the rotational orbit constants of the particles.
Selective reduction of a carboxyl group with diborane. Synthesis of specifically carbon-14 labelled D,L-2-Amino-4-(2-aminoethoxy)butanoic acid
Authors: Liu Yu-Ying , Thom Edna , Liebman Arnold A.
Published: May 2006

Specific labelling of the title compound was achieved through intermediate 3a, methyl 2-(2-phthalimidoethoxy)acetate, derived from methyl bromoacetate-2-14C. Conversion to the corresponding acid (4) was followed with selective diborane reduction which provided 2-(2-phthalimidoethoxy)ethanol-2-14C (5). Treatment with thionyl chloride yielded the chloride 6 which is identical with the intermediate used in the nonlabelled synthesis and reaction with sodium ethyl phthalimidomalonate provided the title compound after hydrolytic work-up.
Syntheses of azapolycyclic compounds by aminium radical routes: trapping of the radical intermediates
Authors: Perry Richard A. , Lockhart Robert W. , Kitadani Masayuki , Chow Yuan L.
Published: May 2006

Photolysis of three alkenyl nitrosamines in the presence of oxygen or bromotrichloromethane resulted in the interception of the intermediate C-radicals by these radical trapping agents and the reaction pathways were cleanly diverted leading to the formation of the nitrate esters or halides with pyrrolidine rings as the primary products. The exo-nitrates in the oxidative photolyses decomposed by secondary ionic pathways; these reactions were hydrolysis, nitrous acid elimination and a cleavage reaction (promoted by a β-amino group), among others. The efficiency of the cleavage reaction is controlled by a stereoelectronic factor that requires the participating bonds and the lone-pair nitrogen orbital be oriented in an antiperiplanar conformation. When such a conformation exists in a rigid or semiflexible framework, cleavage occurs extensively. However, in freely rotating acyclic systems, cleavage does not occur even when the required conformation can be attained. Only halides resistant to intramolecular nucleophilic displacement to form the aziridinium intermediates were isolated in the bromotrichloromethane trapping experiments. Other exo-halides underwent solvolysis via aziridinium ion intermediates.
Cobalt(II), nickel(II), and copper(II) complexes of di- and tetrapeptides containing tyrosine and glycine residues
Authors: Ezaby Mohamed S. El- , Al-Hassan Jassim M. , Eweiss Namek F. , Al-Massaad Farida
Published: May 2006

The solution equilibria of di- and tetrapeptides containing tyrosine and glycine residues have been investigated in absence and presence of cobalt(II), nickel(II), and copper(II) ions. The equilibrium constants have been determined by pH titration at 30 °C and μ = 0.1 M(NaNO3) in 80% by weight DMSO – water mixed solvent. Protons are ionized from terminal (protonated amino and carboxyl) groups as well as from peptidic nitrogens. Complexes of 1:1 composition of metal ion – tetrapeptides were formed in quite a wide range of pH; also 1:1 complexes of the metal ions – dipeptides were formed in solution under the same conditions. Other higher complexes cannot be proved to form in the pH range studied. The complexes of these metal ions with glycine and O-Bzl-L-tyrosine were also studied under the same experimental conditions as control experiments and their equilibrium constants were calculated.
Complexes of the methyl tris(3,5-dimethylpyrazol-1-yl) gallate ligand, MeGa(N2C5H7)3−, and its hydroxy derivative, MeGa(N2C5H7)2(OH)−. Crystal and molecular structure of [MeGa(N2C5H7)2(OH)]Mo(CO)2(η3-C4H7)
Authors: Breakell Kenneth R. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and coordinating properties of the tridentate tris-chelating ligand, methyl tris(3,5-dimethylpyrazol-1-yl)gallate, MeGa(N2C5H7)3−, are described. Carbonyl and nitrosyl carbonyl compounds of manganese, molybdenum, and tungsten incorporating this ligand are detailed. The ready conversion of the above ligand to the less sterically demanding tris-chelating 'hydroxy' ligand [MeGa(N2C5H7)2(OH)]− occurs in attempted syntheses of the 'η3-allyl' complexes, [MeGa(N2C5H7)3]M(CO)2'η3-allyl', (where M = Mo or W, 'η3-allyl' = η3-C3H5, η3-C4H7). The tridentate chelating nature of this 'hydroxy' ligand is conclusively demonstrated in the crystal structure determination of the complex, [MeGa(N2C5H7)2(OH)]-Mo(CO)2(η3-C4H7). Crystals of this complex are monoclinic, a = 14.020(4), b = 10.110(1), c = 15.493(7) Å, β = 111.58(3)°, Z = 4, space group P21/n. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to a final R of 0.40 and Rw of 0.043 for 3374 reflections with I ≥ 3.5σ(I).
Nucleic acid related compounds. 29. Thionyl chloride reactions with adenine nucleosides. Course of nucleophilic displacements and a preferential route to the 2′-chloro-arabino isomer
Authors: Robins Morris J. , Sporns Peter , Muhs Wolfgang H.
Published: May 2006

A multistage sequence gave 5′-O-pivalyl-3′-O-methyladenosine (2e) which was treated with thionyl chloride in hot pyridine to give the corresponding 2'-chloro-arabino product 3a. Hydrogenolysis using tri-n-butyltin hydride and deblocking gave 2′-deoxy-3′-O-methyl-adenosine (3b). Analogous treatment of a mixture of 3′(2′),5′-di-O-acetyladenosines (5a,b) with SOCl2-pyridine gave the 3′-O-acetyl-2′-chloro-arabino (6a) and 2′-O-acetyl-3′-chloro-xylo (7a) derivatives in a ratio of ∼3:2, respectively. Hydrogenolysis and deprotection gave 2′-deoxyadenosine (6c) and 3′-deoxyadenosine (7c) (∼3:2) in ∼45% overall yield from adenosine (based on recovered starting materials). This represents the first example of preferential external nucleophilic displacement at C-2′ (vs. C-3′) in an equilibrating purine ribonucleoside system. Treatment of 9-β-D-xylofuranosyladenine (9) with SOCl2–HMPA gave the 5′-chloro-5′-deoxy product 10a rather than the previously suggested 2′-chloro-2′-deoxy derivative.
The reactions of arenesulphonyl azides with tetrahydropyrido[1,2-a]indoles and the X-ray crystallographic structure determination of a resultant novel zwitterion, 1,2,3,4-tetrahydro-10-methyl-4a-p-tolylsulphonylaminopyrido[1,2-a] indole
Authors: Cameron T. Stanley , Cordes Ruth E. , Terzis Aris , Bailey A. Sydney , Scott Peter W.
Published: May 2006

The reactions of arenesulphonyl azides with tetrahydropyrido[1,2-a]indoles have been examined. Compounds formed by elimination and by ring enlargement are obtained, including a compound with a novel zwitterion structure. The structure of this compound has been determined by X-ray crystallography.
Anomalie de formation d'une goutte de mercure à une électrode polarographique
Authors: Ménard Hugues , Dubois Jacques
Published: May 2006

Using a polyethylene capillary as polarographic electrode we could notice the formation of a mercury drop with an abnormal cylindric neck. This can be justified mathematically but chemically we must use NaOH so as to have the formation of mercuric oxide.
The crystal and molelcular structure of benzil bisthiosemicarbazonatocopper(II) and the antitumour mechanism of related compounds
Authors: Bushnell Gordon W. , Tsang Annie Y. M.
Published: May 2006

The crystal structure of benzil bisthiosemicarbazonatocopper(II) has been solved and refined to an R-value of 0.082. The dark red triclinic crystal has cell dimensions a = 960.8(4), b = 1090.7(6), c = 895.8(4) pm, α = 106.23°(4), β = 92.36°(7), γ = 99.50°(7), and belongs to space group [Formula: see text] with two molecules per cell. The measured and calculated densities are 1.571 and 1.568 g cm−3, respectively, using C16H14CuN6S2 (mol. wt. 417.99). The copper coordination is significantly non-planar. The five non-hydrogen atoms of each original thiosemicarbazide molecule lie close to planes set at a dihedral angle of 8.9°. The fold is away from the origin and the neighbouring molecule. Bond lengths to copper are: Cu—S(1) = 223.7(3), Cu—S(2) = 223.4(3), Cu—N(13) = 197.1(6), Cu—N(23) = 197.0(7) pm. The bond angles at the Cu atom are S(1)—Cu—S(2) = 108.62°(9), N(13)—Cu—N(23) = 81.1°(3), N(13)—Cu—S(1) = 85.1°(2), and N(23)—Cu—S(2) = 85.0°(2). The first and second phenyl rings are at 100.3° and 93.0° to the mean Cu coordination plane, which is at a perpendicular distance of 330 pm from a similar plane in the inverse molecule. Intermolecular double hydrogen bonding occurs at each side of the complex between the uncoordinated nitrogen atoms, thus linking the molecules into parallel ribbons.
Polymorphism of crystalline tert-butyl chloride-d0 and tert-butyl chloride-d9: a Raman spectroscopic study
Authors: Sunder S.
Published: May 2006

Raman spectra of the three solid phases of tert-butyl chloride-d0 and -d9 have been recorded for the regions of the intramolecular vibrations. The spectra of solid I are typical of those seen for plastic crystals and those of solid II of solids with partial orientational order. The transition from solid I to solid II results in the ordering of the three-fold molecular symmetry axes but the axes perpendicular to the molecular symmetry axes remain randomly oriented. The transition from solid II to III results in a more-or-less ordered structure. The spectra of phase III at 90 K suggest an ordered solid with the molecules on sites of symmetry Cs or C1.
Sur quelques sulfites de cations monovalents; étude structurale de LiCsSO3•2H2O
Authors: Archer Christian , Durand Jean , Cot Louis , Galigne Jean Louis
Published: May 2006

A crystallographic study of some monovalent cation sulfites allows us to propose a larger number of salt anions with C3v symmetry (e.g., PO3F2−) than with Td symmetry (SO42− or BeF42−). In PO3F2− the F atom and the lone pair of SIV in SO32− are not bonded to neighbouring atoms.LiCsSO3•2H2O crystallises in the monoclinic system, a = 11.927(7), b = 5.670(3), c = 4.828(2) Å, β = 109.26(4)°, V = 308.2(9) Å3, ρo = 2.758(9)g/cm3, Z = 2, ρx = 2.771(6)g/cm3 (20°C; MoKα, d = 0.7107 Å).The structure is characterised by chains of SO3 and LiO4 groups parallel to the b axis. These chains are connected by a system of hydrogen bonds. The SO32− anion is pyramidal with the sulphur lone pair on the ternary axis. The average dimensions of the sulfite ion are S—O = 1.526 Å and O—S—O = 105.4°. The final R value is 0.046. [Journal translation]
Kinetics and mechanism of decarboxylation of some pyridinecarboxylic acids in aqueous solution. III. 3-Hydroxy- and 3-aminopyridine-2-carboxylic acids
Authors: Dunn Gerald E. , Thimm Harald F. , Mohanty Rajani K.
Published: May 2006

Pseudo-first-order rate constants for the decarboxylation of 3-hydroxy- and 3-amino- picolinic acids in aqueous solution at 150 °C were determined and plotted as a function of acidity. Each rate profile has a maximum at an acidity well above the isoelectric point and this is attributed to decarboxylation of an intermediate protonated at the 2-position, analogous to the intermediates involved in the decarboxylation of salicylic and anthranilic acids. There is also a shoulder on each rate profile at a lower acidity corresponding to the isoelectric point where the Hammick ylide mechanism has a rate maximum in most picolinic acid decarboxylations. It is concluded that 3-hydroxy- and 3-aminopicolinic acids decarboxylate by the ylide mechanism at low acidity and by the protonation mechanism at higher acidities. In agreement with this interpretation, the 13C kinetic isotope effect in 3-hydroxypicolinic acid decarboxylation is 2.0% on the ylide part of the curve, 1.3% where decarboxylation of the protonated intermediate is rate determining, and drops to 0.4% in the intermediate region. Comparison of the rate constants for ylide decarboxylation with those for other 3-substituted picolinic acids shows that 3-hydroxy and 3-amino substituents facilitate decarboxylation, probably by their inductive and field effects on the developing negative charge at the 2-position of the transition state.
Formation of aminals from amines via Pummerer rearrangement
Authors: Rakhit Suman , Georges Michael , Bagli Jehan F.
Published: May 2006

Reaction of 2-amino-3-nitropyridine with acid chlorides in the presence of dimethyl sulfoxide and a tertiary base, such as pyridine, unexpectedly yielded the aminal N,N′-bis(3-nitro-2-pyridinylimino)methylene 5. A similar aminal 6 formed when 2-amino-5-nitropyridine was treated under the same conditions. However, simple aminopyridines such as 2-aminopyridine or 2-amino-6-methylpyridine gave only the 2-N-methylenethiomethyl derivatives. It was proved that the aminals are formed by the attack of a suitable base on the N-methylenethiomethyl intermediates with expulsion of methyl mercaptan. The formation of these unusual aminals may be explained to be taking place via a Pummerer type rearrangement.
Mass spectra of bis(trimethylsilyl)- and bis(trimethylgermyl)carbodiimide
Authors: Drake John E. , Glavinčevski Boris M. , Henderson H. Ernest , Wong Clara
Published: May 2006

The mass spectral fragmentation patterns of bis(trimethylsilyl)- and bis(trimethylgermyl)carbodiimides are compared. Metastable confirmed transitions involve elimination of neutral fragments apparently containing Si=N and/or Si=C bonds. The fragmentation pathways are similar for the germyl analogue but no proof of a fragment containing a Ge=C bond was observed.
Chromium exchange between chromium(II) and benzylchromium(III) ions
Authors: Parris M. , Ashbrook A. W.
Published: May 2006

The rate of first-order hydrogen-ion independent chromium isotope exchange between benzylchromium(III) and chromium(II) ions is 1.2 × 10−2 M−1 s−1 at 0°C in a 70% methanol-water solvent, ΔS≠ = −28.5 eu, ΔH≠ = 10.3 kcal M−1. For the corresponding exchange between benzylchromium(III) and p-chlorobenzylchromium(III) ions, these figures are 1.2 × 10−3M−1 s−1, −32.2 eu, and 10.9 kcal M−1.