bluuebunny/crossref_metadata_2025 huggingface dataset:
The biosynthesis of protoberberine and related isoquinoline alkaloids
Authors: Holland Herbert L. , Jeffs Peter W. , Capps Thomas M. , MacLean David B.
Published: May 2006

The biosynthesis of berberine and hydrastine (in Hydrastis canadensis), corydaline and protopine (in Corydalis solida), and ochotensimine and protopine (in C. ochotensis), has been investigated by the administration of [3-14C]-3′,4′-dihydroxyphenylalanine ([3-14C]DOPA). In all cases, incorporation of label was predominantly into the isoquinoline portion of the alkaloid. The role of DOPA in the early stages of isoquinoline alkaloid biosynthesis in these plants is discussed in the light of this and other relevant data. In addition, the later stages of corydaline biosynthesis have been studied by the administration of [9-methoxy-14C]palmatine and -tetrahydropalmatine to C. solida, and the origin of the exocyclic carbons of ochotensimine further verified by feeding [methyl-14C,3H]methionine to C. ochotensis.
Pseudozoanthoxanthins from gold coral
Authors: Schwartz Robert E. , Yunker Mark B. , Scheuer Paul J. , Ottersen Tor
Published: May 2006

From a deep water Pacific zoanthid, Gerardia sp., we have isolated two new fluorescent nitrogenous pigments, derivatives of tetrazacyclopentazulene. The first was characterized by uv, 1H and 13C nmr data, and by X-ray diffraction; the second by interconversion.
Stereoselective routes to some unsaturated α- and β-C-glycopyranosides
Authors: Fraser-Reid Bert , Dawe Robert David , Tulshian Deen Bhandu
Published: May 2006

4,6-O-Benzylidene-D-allal, 1a, undergoes the Eschenmoser–Claisen rearrangement giving the unsaturated α-C-hex-2-enopyranoside, 4 (3,7-anhydro-6,7-O-benzylidene-4,5-dideoxy-D-lyxo-oct-4 -N,N-dimethyl amide) in 85% yield. The corresponding β-anomer 13a (methyl 3,7-anhydro-6,7-O-benzylidene-4,5-dideoxy-D-ribo-oct-4- enonate) is prepared by reductive elimination of the β-C-glucopyranoside 11. The latter is obtained as the sole product from 4,6-O-ethylidene-D-glucose in two steps involving Wittig addition of carboxymethylene followed by cyclization of the resulting α,β-unsaturated ester under thermodynamic conditions.
Charge distributions and chemical effects. XIX. Analysis of 'bonded' and 'non-bonded' energy contributions in saturated hydrocarbons
Authors: Fliszár Sándor , Béraldin Marie-Thérèse
Published: May 2006

Total Coulomb interactions between non-bonded atoms behave in general in a 'quasi-additive' fashion, not only in simple linear and branched paraffins, but also in polycyclic hydrocarbons constructed from chair and boat cyclohexane rings. Because of their relative insensitivity to structural features, they cannot be regarded as being the leading terms in the explanation of energetic effects related to structural changes. The prime factors governing molecular stabilities, as well as the explanation of the structural effects which are at their origin, are found in the behavior of the charge dependent energy contributions associated with bonded atoms, i.e., in the chemical bonds themselves.
Determination of solubility products of hydroxylapatite, chlorapatite, and their solid solutions
Authors: Narasaraju T. S. B. , Rao K. K. , Rai U. S.
Published: May 2006

Solubility equilibria of hydroxylapatite, chlorapatite, and a series of their solid solutions were investigated at 37 °C in the pH range 4.25 to 7.40 and their solubility products evaluated. Proof could be obtained for their stoichiometric dissolution.
β-Lactams. V. The synthesis of D,L-4-hydroxymethylnocardicin A (17N), D,L-4-hydroxymethyl-N-phenylacetylnocardicinic acid (8N-f), and their α-epimers 17U and 8U-f
Authors: Hakimelahi Gholam Hosein , Just George
Published: May 2006

The synthesis of title compounds and some aromatic ring substituted analogues is described.
Mass spectrometry of some furanocoumarins
Authors: Tang Sheng-Yuh , Mcgowan John C. , Singh Marsha , Galatsis Paul , Ellis Brian E. , Boyd Robert K. , Brown Stewart A.
Published: May 2006

The mass spectra of two isomeric methoxyfuranocoumarins have been investigated using electron-impact ionisation. Unambiguous distinction between the two isomers is possible through a combination of conventional mass spectra with collision-induced dissociations of the molecular ions and of selected fragment ions. The fragmentation mechanisms of these and related molecular systems were investigated in an attempt to identify the fate of each oxygen atom under electron-impact conditions. To this end, 2-pyrone, benzpyrone (coumarin), benzofuran, and some of its structural isomers were synthesised and studied via metastable spectra, collisionally activated spectra, appearance potentials, and kinetic energy release. Only partial success was achieved in this investigation, but it was possible to write a mechanistic scheme consistent with the present findings and literature data. If valid, this scheme permits identification of two of the four oxygen atoms in the methoxyfuranocoumarins.
The mass spectra of trifluoroacetyl-2,5-diketopiperazines. II. cyclo-(-Val-Val/Leu/Ile), cyclo-(-Leu-Leu/Ile), and cyclo-(-Ile-Ile)
Authors: Slater George P. , Hogge Lawrence R.
Published: May 2006

The trifluoroacetyl derivatives of the 2,5-diketopiperazines cyclo-(-Val-Val/Leu/Ile), cyclo-(-Leu-Leu/Ile), and cyclo-(-Ile-Ile) were examined by GC–MS. The fragmentation of these compounds generally follows the same pathways as previously observed for the TFA-cyclo-(-Gly-X) series (X = Gly, Val, Leu, Ile). However, the spectra can be interpreted on the basis that the molecular ion fragments prior to, or after, one of the alkyl groups is eliminated as olefin. Some ion fragments indicate that both alkyl groups are eliminated but this does not appear to occur directly from the molecular ion. Support for fragmentation of the molecular ion by the suggested route is indicated by a number of isobaric ions although corresponding metastable ions were not observed.The spectra enable the compounds in the series TFA-cyclo-(-Val-X) (X = Val, Leu, Ile) to be readily identified but this is not the case for TFA-cyclo-(-Leu-Leu/Ile) and TFA-cyclo-(-Ile-Ile). However, all of these compounds can be distinguished from TFA-cyclo-(-Gly-X) and TFA-cyclo-(-Ala-X) (X = Gly, Val, Leu, Ile).
Preparation of two metabolites of isometheptene
Authors: Taylor Wesley G. , Coutts Ronald T.
Published: May 2006

trans-(E)-2-Methyl-6-methylamino-2-hepten-1-ol (6) and cis-(Z)-2-methyl-6-methylamino-2-hepten-1-ol (13), two in vivo metabolites from the antispasmodic agent isometheptene (2), ((±)–N,1,5-trimethyl-4-hexenylamine) have been synthesized. In the first synthesis of the trans isomer, the N-trifluoroacetyl derivative of 2 was oxidized with selenium dioxide in ethanol to give trans-2-methyl-6-N-methyltrifluoroacetamido-2-hepten-1-al (4). Aldehyde (4) was converted to 6 by reaction with sodium borohydride in ethanol. In the second synthesis, trans-2-methyl-6-oxo-2-hepten-1-ol ethylene ketal (8) and cis-2-methyl-6-oxo-2-hepten-1-ol ethylene ketal (11) were hydrolyzed without isomerization to hydroxyketones 9 and 12. Both 9 and 12 were reductively aminated to the desired metabolites, 6 and 13.
A 13C nmr study of metal ion binding to pyridoxine
Authors: Hartman J. Stephen , Kelusky Eric C.
Published: May 2006

13C nmr confirms that coordination of metal ions by pyridoxine is through the C-3 and C-4′ oxygens in aqueous solution. Nitrogen appears to become more effective as a donor site in water–dimethylsulfoxide mixtures, while with increasing proportions of DMSO some cations are coordinated by DMSO rather than by pyridoxine. Changes in 13C spin–lattice relaxation times on metal ion coordination are more informative about metal binding sites than changes in 13C chemical shift. Some analogous results are reported for pyridoxamine.
Insertion of an acetylene into the platinum–iodide bond
Authors: Chaudhury N. , Puddephatt R. J.
Published: May 2006

Reaction of [PtIMe(2,2′-bipyridine)], I, with MeO2CC≡CCO2Me gives first a 5 co-ordinate π-complex [PtIMe(MeO2CC≡CCO2Me)(bipy)], II, and then the product of insertion into the PtI bond[PtMe{C(CO2Me)=C(CO2Me)I}(bipy)], III. A study of the kinetics of dissociation of II to I and free alkyne shows that reaction occurs largely by dissociation of iodide followed by loss of alkyne from the resulting cationic alkyne complex. Formation of III may involve nucleophilic attack by I− on the co-ordinated alkyne of this cationic intermediate.
Stereoselectivity in Diels–Alder reactions
Authors: Kakushima Masatoshi
Published: May 2006

Two competing effects, secondary attractive interactions and closed-shell repulsions, provide the main control of endo–exo stereoselectivity of Diels–Alder cycloadditions.
Réarrangement du squelette de la catharanthine. IV. Nor-5 catharanthine et couplage avec la vindoline.
Authors: Andriamialisoa Ratremaniaina Zo , Langlois Nicole , Langlois Yves , Potier Pierre , Bladon Peter
Published: May 2006

5-Norcatharanthine 3 was prepared from catharanthine 5. The coupling of the corresponding Nb-oxide 10 with vindoline 4, under modified Polonovski reaction conditions, led to two dimers without breaking the structural framework.The isolation of 5-nor-16-demethoxycarbonylcatharanthine 20 by cleavage of one of the coupling products (18) of vindoline 4 and the Nb-oxide of 16-demethoxycarbonylcatharanthine 17 corroborates the structure 18 which was assigned to this dimer by our laboratory. [Journal translation]
Cyanoethylation of the salts of cyanoguanidine in aprotic solvents
Authors: Aleksandrowicz Piotr , Bukowska Maria , Maciejewski Mieczysław , Prejzner Jan
Published: May 2006

The reactions of lithium or sodium salts of cyanoguanidine (1) with acrylonitrile in aprotic solvents result in the rapid formation of N,N-bis(2-cyanoethyl)-N′-cyanoguanidine (3) followed by a slower intramolecular cyclization of 3 leading to 4-amino-1-(2-cyanoethyl)-5,6-dihydro-2-pyrimidinylidenecyanamide (4). A tentative assignment of the tautomeric forms to the cyclic derivatives of (β-cyanoethyl) cyanoguanidines and the products of their hydrolysis is described.
Thermal explosions of methyl isocyanide: a re-examination of the data
Authors: Pritchard Huw O.
Published: May 2006

By the use of an improved interpolation method for the rate constants for the thermal isomerisation of methyl isocyanide, it is found that a pattern emerges in the previously unexplained scaling behaviour of the critical explosion parameter (δc). At low Rayleigh number (where δc should be constant) the ratio (δ/Ra)c for a fixed temperature is approximately constant for seven spherical vessels of volumes 0.3 to 5 L. Also, in the limit of very large vessels, or very high temperatures, it appears that the Arrhenius temperature coefficient of (δ/Ra)c tends to the activation energy of the reaction.
Factor analysis as a complement to band resolution techniques. VI. Complex formation between pentachlorophenol-OD and acetone
Authors: Korppi-Tommola J. , Shurvell H. F.
Published: May 2006

Complex formation between pentachlorophenol-OD (PCP-OD) and acetone and acetone-d6 in CCl4 solution has been studied. Digitized infrared spectra in the O—D stretching region ν(OD) of PCP-OD and the C—O stretching region ν(CO) of acetone have been recorded from solutions of various concentrations. The present results are compared with previous work on complex formation between PCP and the same acceptor molecules. In the ν(OD) region, factor analysis (principal component analysis) and a concentration study of the areas of the resolved band components suggest that two (1:1) complexes occur in solution. The equilibrium constant obtained for one of the complexes shows an isotope effect due to deuteration of the proton donor. In the ν(CO) region, only one band due to complexed species was resolved. Equilibrium constants calculated using the results from the ν(OD) and ν(CO) regions are in good agreement with each other.
Infrared laser induced decomposition of pentafluoroacetone
Authors: Drouin M. , Hackett P. A. , Willis C. , Gauthier M.
Published: May 2006

The dissociation of pentafluoroacetone by high power infrared radiation fields is shown to proceed by a free radical mechanism.
13C nuclear magnetic resonance spectra of some halosteroids, 6-ketosteroids, and related compounds
Authors: Holland Herbert L. , Thomas Everton M.
Published: May 2006

The 13Cmr spectra of 21-haloprogesterones have been assigned, and chemical shifts compared with those of simple α-haloketones. In addition, the 13Cmr spectra of some C-5α and C-6β halosteroids are presented, and long range 13C—19F coupling observed between C-19 and the C-6β fluorine in some cases. The spectra of several oxygenated analogues and of a series of 5α-hydroxy-6-ketosteroids are also discussed.
Derivatives of fused 3-hydroxymethyl-pyran-4-ones as a mobile keto–allyl system
Authors: Philipp Adolf , Jirkovsky Ivo
Published: May 2006

Syntheses of 3-hydroxymethyl-4H,5H-pyrano(3,4-c)(1)benzopyran-4-one, 7, and 3-hydroxy-methyl-4H,5H-(1)benzothiopyrano(4,3-b)pyran-4-one, 8, from 2,2-difluoro-4-methyl-5H-(1)benzopyrano- and (1)benzothiopyrano(3,4-e)-1,3,2-dioxaborins, 3 and 4, are reported. Upon treatment with a solution of sodium cyanide, the corresponding mesylates 9 and 10 as well as the chloromethyl derivatives 11 and 12 yielded 3-methyl-4-oxo-4H,5H-pyrano(3,2-c) (1)benzopyran-2-carbonitrile, 13, and 3-methyl-4-oxo-4H,5H-(1)benzothiopyrano(4,3-b)pyran-2-carbonitrile, 14, respectively; these nitriles were converted to carboxylic acids 21 and 22 via methyl esters 19 and 20. Reaction of the mesylate 10 with dimethylamine afforded a normal displacement product 23. A similar reaction of 12 required longer time and led to the vinylogous amide 24.
The synthesis of 5,6-dihydro-3,3-dimethyl-4,1-benzoxazonine-2,7(1H,3H)dione and its conversion into 1,3-dihydro-3,3-dimethylfuro[3,4-b] quinolines
Authors: Demerson Christopher A. , Humber Leslie G.
Published: May 2006

Periodate oxidation of 1,1-dimethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole 1 gave 5,6-dihydro-3,3-dimethyl-4,1-benzoxazonine-2,7(1H,3H) dione 2, a member of the novel 4,1-benzoxazonine ring system. Its conversion into 1,3-dihydro-3,3-dimethylfuro[3,4-b]quinolines is described.
Metabolites of bird's nest fungi. Part 12. Studies on the biosynthesis of the cyathins
Authors: Ayer William A. , Lee Sing Ping , Nakashima Thomas T.
Published: May 2006

The cyathins are a group of diterpenoids of unique structure which are produced by bird's nest fungi of the family Cyathus. Biosynthetic studies utilizing [1-13C], [2-13C], and [1,2-13C2]acetate indicate that 11-O-acetylcyathatriol, produced by the fungus C. earlei, is formed from acetate via the isoprenoid pathway. The labelling experiments are consistent with a route involving cyclization–rearrangement of geranylgeranyl pyrophosphate as shown in Schemes 1 and 3.
Influence des groupes tert-butyle, triméthylsilyle et triméthylgermyle sur la stéréochimie de réactions d'addition en série cyclohexénique. III. Epoxydation de cyclohexènes substitués en position allylique et réduction des époxydes par LiAlH4
Authors: Richer Jean-Claude , Poirier Marc-André , Maroni Yvette , Manuel Georges
Published: May 2006

The epoxidation of allylic alkenes in the 6-tert-bulyl (or 6-trimethylsilyl or 6-trimethylgermyl) 3,3-dimethylcyclohexenes is examined; it has been found that the stereochemistry of these reactions is governed mostly by steric factors. The results obtained by the reduction of cis and trans epoxides by lithium aluminium hydride are also reported, the regiochemistry and the stereochemistry of the reactions of reduction are governed by steric factors as well as by the electronic effects of the trimethylsilyl group.
A kinetic study of the oxidation of N(III) by ClO2− in aqueous acidic media
Authors: Emeish Samir S. , Howlett Keith E.
Published: May 2006

Kinetics of the reaction between nitrous acid and chlorite have been studied spectrophotometrically. The rate equation involves terms [HNO2]1.5 and [ClO2−]0.5, and both an uncatalysed and a chloride ion-catalysed path have been identified. A mechanism involving peroxonitrite and hypochlorous acid as intermediates is shown to be consistent with the observations.
Thermal rearrangement of 5,6,6-triphenylbicyclo[3.1.0]hex-2-ene to 6,7-benzo-1,5-diphenyltricyclo[3.2.1.02,8]octane
Authors: Weigl Stefan , Warkentin John
Published: May 2006

The triphenyl vinylcyclopropane system, 5,6,6-triphenylbicyclo[3.1.0]hex-2-ene, 1, undergoes clean thermal rearrangement, at 210 °C, to 6,7-benzo-1,4-diphenyltricyclo[3.2.1.02,8]octane, 9. This result indicates that 1 behaves like a phenylcyclopropane and not like a vinylcyclopropane in the thermal ring opening. The proposed mechanism involves initial formation of a 1,3-diradical, one site of which is benzyl as well as homoallyl and the other site of which is both benzhydryl and homoallyl. Subsequent steps involve coupling of the radical sites through one of the phenyl groups and a suprafacial 1,5-hydrogen shift concerted with generation of a new cyclopropane ring.The 1Hmr and 13Cmr spectra of 9 are reported and discussed in terms of the shielding properties of cyclopropane and benzene rings.
Excess volumes of toluene mixtures with some alcohols at 303.15 K
Authors: Swamy Goolla Narayana , Dharmaraju Golla , Raman Gurajala Kodanda
Published: May 2006

Excess volumes for binary mixtures of toluene with 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 1-pentanol, 1-hexanol, 1-heptanol, and cyclohexanol have been measured as a function of composition at 303.15 K by a dilatometric method. The excess volume curves for 1-propanol and 1-butanol are sigmoid. For other alcohols VE values are positive over the entire composition range.
Influence de la taille du cycle sur la substitution électrophile des cycloalkyltriméthylsilanes. Synthèse de cycloalkyldiméthylfluorosilanes
Authors: Grignon-Dubois M. , Dunoguès J. , Calas R.
Published: May 2006

Cycloalkyltrimethylsilanes, excepting cyclopropyl-, react with electrophiles by Si—Me bond splitting. Consequently silicon can be functionalized by this route. We also propose a new synthesis of cycloalkyldimethylfluoro (or chloro-)silanes. In the case of five or six member ring derivatives, the observed results are interpreted by a mechanism involving initial abstraction of hydride ion from the silicon substrate.
An analysis of the factors contributing to the regioselectivity observed in the opening of oxiranes
Authors: Kayser Margaret M. , Morand Peter
Published: May 2006

The regioselectivity of epoxide ring opening can be analyzed in terms of hard–soft acid–base (HSAB) theory. The coordination of the hard acid with the oxygen atom of the oxirane ring produces a "pulling effect" which determines the direction of the ring opening. In the absence of a strong "pulling effect" the "pushing effect" of the approaching base is examined and the consequences of relative softness or hardness of the nucleophile on the regioselectivity of the ring opening are discussed.
Hydrogen bond assisted reactions of carboxylic acids with alkyl halides in the gas phase by ion cyclotron resonance spectroscopy
Authors: Clair R. L. , McMahon T. B.
Published: May 2006

The reactions of the strongly hydrogen bonded anions, CH3CO2HF− and (CH3CO2)2H−, with alkyl halides have been studied in the gas phase by ion cyclotron resonance spectroscopy. A novel reaction of nucleophilic attack by (CH3CO2)2H− with alkyl chlorides to produce CH3CO2HCl− and alkyl acetates is reported. Parallels are drawn to synthetically important analogous reactions in glacial acetic acid solutions of alkali metal fluorides.
Part I. Conformational analysis of thiazolidine-2-thione
Authors: Chanon F. , Rajzmann M. , Chanon M. , Metzger J. , Pouzard G.
Published: May 2006

1H nmr (3JHH values) and 13C nmr results (shielding effect of vicinal methyl 13C signals in cis-4,5-dimethylthiazolidine-2-thione) allows an estimation of the puckering in the five-membered monounsaturated heterocycle, thiazolidine-2-thione:[Formula: see text]Application of Lambert's R- value equation provides a value of 41° for the torsional angle between C4 and C5, in contrast to an upper limit value of 25°, deduced from consideration of 13C γ-effects; this disparity is discussed and compared with finite perturbation treatment of 3JHH values.
Synthesis and carbon-13 nuclear magnetic resonance spectra of monoethyl 4-nitro and 4-amino phthalates
Authors: Seshadri Kalkunte S. , Bacha John D.
Published: May 2006

Carbon-13 nmr has been found to be an effective spectroscopic method for measuring the ratio of isomeric monoethyl esters resulting from the esterification of 4-nitrophthalic acid, the alcoholysis of 4-nitrophthalic anhydride, and the catalytic reduction of monoethyl 4-nitrophthalates. Precise values of the 13C chemical shifts for 1-ethyl and 2-ethyl 4-nitrophthalate and the corresponding 4-aminophthalates were determined; the shielding parameters are explained in terms of known structural effects. Details of the esterification, alcoholysis, reduction reactions, and the isolation of 1-ethyl 4-nitrophthalate are described.
Autohydrolysis of aspen milled wood lignin
Authors: Lora Jairo H. , Wayman Morris
Published: May 2006

In order to obtain further understanding of the nature of lignin reactions during autocatalysed hydrolysis (autohydrolysis) of wood, milled wood lignin (MWL) was isolated from aspen (Populus tremuloides) and treated under autohydrolysis conditions. By this means reactions of the lignin itself could be distinguished from those taking place between lignin and the carbohydrate or other components of the wood. The material after the reaction was separated into a dioxane insoluble fraction (DI), a dioxane soluble but ether insoluble fraction (DSEI), and an ether soluble fraction (ES). Studies were carried out on the DI and DSEI fractions; no direct study was made of the small ES fraction.The formation of DI material increased linearly during the first 7.5 min at 170 °C and then levelled off. At the same time DSEI decreased and then levelled off. Gel permeation chromatography of the DSEI fraction suggested that during autohydrolysis there is an initial generation of low molecular weight fragments which recombine to form first a high molecular weight soluble fraction and from this the insoluble product. The DSEI fraction contained increased conjugated and unconjugated keto groups. Carboxylic acids were also detected; they have been attributed to the reincorporation of low molecular weight aromatic acids generated by the hydrolysis of the corresponding esters. The dioxane insoluble (DI) fraction had fewer unconjugated keto groups than the DSEI fraction, indicating that these groups participated in the condensation reactions leading to the formation of insoluble material. These probably involve position 6 of the aromatic ring.
Dianions of glyoxylic acid thioketals: conventent α-keto acid equivalents
Authors: Bates Gordon S. , Ramaswamy S.
Published: May 2006

By varying the solvent, reaction temperature, and bases (i.e., gegenions present), optimum conditions for the alkylation of the dianions of glyoxylic acid derivatives 8 and 9 were established. It was found that the easily prepared, thermally stable, tetrahydrofuran-soluble potassium dianion of bis(ethylthio)acetic acid was readily alkylated by alkyl halides, tosylates, epoxides, and N-tosyl aziridines. The latter alkylation is being used to develop a possible cytochalasin synthesis.The alkylated products may be readily converted into the corresponding α-keto acids or methyl 2,2-bismethoxycarboxylates.
Photoelimination from a γ-substituted α,β-unsaturated ketone
Authors: Charlton James L. , Lypka Gerald N.
Published: May 2006

During a study of unsaturated six membered ring sultones (1), it was found that irradiation of the sultone 7 in methanol gave the esters 8 and 9 as primary photoproducts. These esters, on continued irradiation, led to a completely aromatic compound which has now been identified as 12-hydroxy-11-phenylbenzo(j)fluoranthene 10.
Analysis of 13C nuclear magnetic resonance chemical shifts of acyclic hydrocarbons
Authors: Beierbeck Helmut , Saunders John K.
Published: May 2006

The 13C nmr chemical shifts of aliphatic hydrocarbons were derived from chemical shifts and probabilities of individual chain conformations. Conformer resonances were calculated with parameters developed for conformationally homogeneous cyclic molecules. Conformer populations were derived from bond rotation potentials and steric energy contributions, available from independent sources. This analysis contains non adjustable parameters. It represents a unified treatment of cyclic and acyclic hydrocarbon resonances, which is capable of dealing with molecular asymmetry and thus permits the determination of configuration in aliphatic hydrocarbons.
Axial dissymmetry induced magnetic nonequivalence in the 13C nuclear magnetic resonance spectra of allenes
Authors: Beaulieu Pierre L. , Morisset Veronique M. , Garratt Dennis G.
Published: May 2006

not available
Specific decomposition rate constants in unimolecular reactions
Authors: Pritchard Huw O. , Diker Galina M. , Yau Andrew W.
Published: May 2006

The original treatment of unimolecular reactions given by Polanyi and Wigner in 1928 is recast in quantum terms. It is found that very simple and natural choices for the oscillation which is assumed to cause reaction lead to good predictions of the specific reaction rate constant k(E), and also the overall rate of reaction: nitrous oxide, carbon dioxide, methyl isocyanide, trideuteriomethyl isocyanide, ethyl isocyanide, ethyl chloride, cyclopropane, cyclobutane, and ethane are treated as illustrations.
Stereochemistry of acid-catalyzed cleavage of 7-chloro-1-methylnortricyclene in deuterated medium; evidence for edge protonation of nortricyclenes
Authors: Werstiuk Nick Henry , Cappelli Frank Peter
Published: May 2006

Cleavage of 7-chloro-1-methylnortricyclene (1e) in D2SO4–DOAc yields deuterated syn-7-chloro-1-methyl-exo-2-norbornyl acetate (3a-d) (1.04 excess d per molecule) and deuterated anti-7-chloro-1-methy l-exo-2-norbornyl acetate (3b-d) (1.28 excess d per molecule) as the kinetic products. 1H and 2H nuclear magnetic resonance spectroscopic analysis of the corresponding alcohols complexed with Eu(fod)3 shows that deuterium is located endo at C-6 and in the methyl group of the syn-7-chloroacetate, endo at C-6 and C-2, at C-7, and in the methyl group of the anti-7-chloroacetate. That the deuterium at C-6 of both acetates is 80–90% stereochemically pure endo, in our view, establishes that the bond farthest removed from the electron-withdrawing chlorine is preferentially cleaved via edge deuteronation.
The solvolysis of the p-toluenesulphonate and methanesulphonate of cholesta-1,5-diene-3β-ol
Authors: Georghiou Paris E. , MacDiarmid Margaret A.
Published: May 2006

Insitu preparations of 3β-tosyloxycholesta-1,5-diene and 3β-mesyloxycholesta-1,5-diene were subjected to methanolysis and hydrolysis. The products obtained were those of nucleophilic displacement with inversion at C3, as well as the epimers formed with retention of stereochemistry. No cyclized products could be isolated.
13C nuclear magnetic resonance spectroscopy of methylenedioxy group-containing C19-diterpenoid alkaloids and their derivatives
Authors: Pelletier S. William , Mody Naresh V. , Dailey Jr. Oliver D.
Published: May 2006

The natural abundance carbon-13 nmr spectra of some methylenedioxy group-containing C19-diterpenoid alkaloids and their derivatives (dictyocarpine, 14-acetyldictyocarpine, dictyocarpinine, 14-dehydrodictyocarpine, 14-dehydrodictyocarpinine, 6-dehydrodictyocarpinine, 6,14-didehydrodictyocarpinine, deltaline (eldeline), deltamine (eldelidine), 6-dehydrodeltamine, delcorine, 6-acetyldelcorine, and 6-dehydrodelcorine) have been determined. Self-consistent assignments of nearly all the resonances in these compounds have been made with the aid of single-frequency off-resonance proton decoupling techniques, additivity relationships, and the effects induced by certain structural changes. Particular attention is directed towards features of the spectra which are most useful for structure elucidation and identification of the C19-diterpenoid alkaloids.
Thermodynamics of binary mixtures of 1,2-dichloroethane with aromatic hydrocarbons
Authors: Nigam Ram K. , Singh Prem P. , Singh Krishan C. , Singh Mohan , Mishra Ruchi
Published: May 2006

Molar excess volumes, VE at 298.15 and 308.15 K, molar excess enthalpies HE at 308.15 K, and total vapour pressure at 298.15 and 308.15 K. have been measured for binary mixtures of 1,2-dichloroethane with aromatic hydrocarbons. The VE and HE data for an equimolar mixture at 308.15 K only have been utilized to predict VE, HE, and TSE values (using Sanchez and Lacombe theory) for these mixtures as a function of temperature and composition. The agreement between the predicted and the corresponding experimental values is good so far as VE and HE data are concerned but the same is not true of the TSE values.
Nucleophilic addition to 4-acetyl-1-methylpyridinium iodide studied by 1H nmr
Authors: Tan Liang K. , Cocivera Michael
Published: May 2006

The 1H nuclear magnetic resonance spectra obtained during the addition of amines to 4-acetyl-1-methylpyridinium iodide in aqueous solution provide data for the kinetic parameters associated with: (1) the rapid equilibrium of the addition step to form the carbinolamine intermediate; (2) the rate determining dehydration step to form the syn and anti imines; and (3) the anti to syn isomerization. Depending on the amine used, (1) can result in methyl proton exchange that is either fast or slow relative to the chemical shift between the acetyl-CH3 resonance of 4-acetyl-1-methylpyridinium iodide and the corresponding one due to carbinolamine. The line width data and the equilibrium constant Kn, which is determined by flow uv, provide values for the rate constants (kn and k−n) of the forward and reverse steps of the equilibrium. The logarithm of kn does not correlate with log Kn or pKa of the amines. In addition, the enthalpy change ΔH for the equilibrium step is found not to depend significantly on the nature of the amine. It remains relatively constant at about −11 kcal M−1. The dehydration step is subject to general acid and base catalysis with the effect decreasing in the order hydrazine, hydroxylamine, semicarbazide, and methoxyamine. For hydrazine and hydroxylamine, the syn/anti ratios are pH dependent. For hydrazine and semicarbazide the anti to syn imine conversion depends on pH. The occurrence of anti to syn isomerism indicates that the dehydration of carbinolamine gives the anti imine as the product of kinetic control.
Acylation of aromatic substrates with ketenes. II. Hammett–Brown studies on substituted aromatic compounds
Authors: Fountain K. R. , Heinze Pamela , Maddex Dave , Gerhardt Greg , John Paul
Published: May 2006

Competition reactions using dimethylketene (DMK) – aluminum chloride complexes on a variety of substituted benzene derivatives gave partial rate factors. The logs of these Pfx values when plotted versus σ+ values gave two line segments of ρ = −6.59 for less active substrates, and ρ = −0.92 for more active substrates. Similar results were found for diphenylketene (ρ = −9.47 and −1.07).These results were rationalized by analogy to vinyl cation alkylations. A pair of π complexes (outer then inner) occur between initial approach of the reagent and final, product-determining π-complex formation. In one of these complexes the C=C bond of the ketene complex may be able to back-bond in a manner similar to that found in inorganic complexes of CO and metals.
The synthesis and chlorinolysis of 5-phenyl-2,4,5-trithiapentane-2,2-dioxide
Authors: Ahern Terence Patrick , Langler Richard Francis , McNeil Robert Leonard
Published: May 2006

Application of mercaptide anions to the dechlorination of an α-polychlorosulfonyl substrate has provided the key step in a successful synthesis of the title compound. 5-Phenyl-2,4,5-trithiapentane-2,2-dioxide undergoes chlorinolysis in an aqueous medium to yield products consistent with the view that α-sulfonyl oxodichlorosulfonium chlorides and α-sulfonyl dichlorosulfonium chlorides may undergo unusually facile Pummerer rearrangements.
Photolyse du butyne-1 dans la région de 147 à 174 nm
Authors: Deslauriers Hélène , Deschênes Jovette , Collin Guy J.
Published: May 2006

We have studied the 147, 163, and 174 nm photolysis of 1-butyne. Several products from C1 to C5 were observed under various conditions such as in the presence of additives, or at different pressures between 0.5 and 100 Torr (65 to 13 300 N m−2). The methyl radical is the most important radical intermediate. Acetylene, ethylene, and vinylacetylene are produced in the presence of radical scavengers and are probably the result of the fragmentation of the photoexcited molecule. Propargyl radicals are thought to be produced but appear not to be scavenged by hydrogen iodide. Polymerization was observed even in the presence of radical scavengers. Secondary processes are numerous and make the interpretation of our results difficult; for example, the ethylene quantum yield increased upon addition of 10% oxygen, the simple radical scavenging effect of this additive does not explain such an effect.
Heat capacities of liquid ketones and aldehydes at 298 K
Authors: Fuchs Richard
Published: May 2006

The heat capacities of 25 liquid aliphatic, alicyclic, and aromatic ketones and aldehydes at 298.2 K and atmospheric pressure have been measured calorimetrically with a typical uncertainty of 0.5%. Additive parameters are proposed for estimating Cp(1) of ketones and aldehydes.
Rearrangement studies with 14C. XLIV. Ion-pairs and dissociated ions in the solvolysis of triphenyl[2-14C]vinyl and trianisyl[2-14C]vinyl bromides in 70% acetic acid – 30% water
Authors: Lee Choi Chuck , Ko Eric C. F. , Rappoport Zvi
Published: May 2006

In the solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) in 70% HOAc – 30% H2O, the presence of up to 30 equiv. of added NaOAc or 25 equiv. of added Et4NBr did not significantly change the extent of scrambling of the label from C-2 to C-1 in the reaction product. The mean scrambling value observed for 1-Br-2-14C under a variety of conditions was 14.7 ± 0.7%. On the other hand, in the similar solvolysis of trianisyl[2-14C]vinyl bromide (2-Br-2-14C), the extent of scrambling in the product was found to decrease with increasing amounts of added NaOAc. The observed scramblings varied from a mean of 27.7% to 5.7%, respectively, for reactions without and with 10 M added NaOAc. With 1-Br-2-14C, the possibility is considered that ionization proceeds only to an ion-pair in which the scrambling via 1,2-phenyl shift is not affected by the presence of added OAc−. In the case of 2-Br-2-14C, further dissociation to the free trianisylvinyl cation took place and in the dissociated ion, competition between the scrambling process and capture reactions with all the nucleophiles present resulted in a decrease in the extent of scrambling with the presence of the more nucleophilic OAc−. Using the extents of scrambling as well as product data, various ratios including kSOH/kr, kOAc/kr, [Formula: see text], and kOAc/kHOAc, are evaluated.
Rydberg orbitals and the Woodward–Hoffmann procedure
Authors: Sandorfy C.
Published: May 2006

It is argued that account should be taken of Rydberg states when the course of photochemical reactions is interpreted through correlation diagrams based on the principle of conservation of orbital symmetry. This is expected to be important for molecules whose lowest excited state has Rydberg character and a symmetry different from that of the lowest valence-shell type excited state.
Azapropellanes as phase-transfer catalysts. I. Introduction and synthesis of (±)1-azoniatricyclo[4.4.4.01,6]tetradecane and(±)1-azoniatricyclo[4.4.3.01,6]tridecane salts
Authors: McIntosh John M.
Published: May 2006

The rationale for considering 1-azoniapropellane salts as potential chiral phase-transfer catalysts is presented. The synthesis of two examples of these types of molecules is outlined and their efficacy in phase-transfer catalyzed reactions is established.
An investigation of the Kishner elimination as a route to dideoxy sugars
Authors: Wickremesinghe L. , Slessor Keith N.
Published: May 2006

Methyl 4,6-O-benzylidene-2-O-p-toluenesulphonyl-α-D-ribohexopyranosid-3-ulose has been used as a substrate for an investigation of the Kishner elimination as a route to deoxygenated sugars. The conditions of the reaction of the ketotosylate with hydrazine have a large effect on the outcome of the reaction and the products produced. Conditions have been investigated which provide methyl 4,6-O-benzylidene-α-D-erythrohex-2-enopyranoside (4), methyl 4,6-O-benzylidene-2,3-dideoxy-α-D-erythrohexopyranoside (3), methyl 4,6-O-benzylidene-3-deoxy-α-D-ribohexopyranoside (2), and methyl 4,6-O-benzylidene-2-deoxy-α-D-erythrohexopyranosid-3-ulose (8) in good to moderate yields.
Resolution of conflicting migratory reports in ring expansion of 3-keto steroids to oxygen and nitrogen
Authors: Dave Vinod , Stothers J. B. , Warnhoff E. W.
Published: May 2006

The migration of C-2 and/or C-4 to O or N in the Beckmann, Schmidt, and Baeyer–Villiger reactions of 3-keto steroids has been studied with the aid of 13Cmr spectroscopy. Authentic specimens of the eight possible lactone and lactam products from both 5α- and 5β-cholestan-3-one have been prepared; their physical properties and 13Cmr assignments are given. Seven ring expansion reactions reported to give only one product have been found to give both possible migration products. The much studied reactions of 5α-cholestane-3,6-dioneand its derivatives have been reexamined. The results emphasize again the necessity of using 13C spectra both as an analytical tool and as the best criterion of purity in work with these molecules.
Acyl transfer in o-hydroxybenzenethiol
Authors: McKinnon David M.
Published: May 2006

o-Hydroxybenzenethiol reacts with one equivalent of acetic anhydride to give a mixture of starting materiel, diacylated material, and O- or S- monoacylated products as determined by nmr. The same products are obtained by equilibration of a mixture of o-hydroxybenzenethiol and its diacetate. The mixture does not contain detectable amounts of 2-methylbenzothioxolan-2-ol.
On the chemistry and high field nuclear magnetic resonance spectroscopy of rapamycin
Authors: Findlay John A. , Radics Lajos
Published: May 2006

not available
Osmotic and activity coefficients of sodium sulphate in water from 50 to 150 °C
Authors: Bhatnagar Om. N. , Campbell Alan N.
Published: May 2006

The vapour pressure lowering, ΔP, of sodium sulphate solutions in water was measured in the concentration range 0.4 to 1.8 m and the temperature range 50 to 150 °C by the use of a differential manometer. ΔP values were used to calculate the osmotic coefficient of sodium sulphate solutions. Pitzer's equation for osmotic coefficients was used to evaluate βMX(0), βMX(1), and [Formula: see text] at each temperature. An attempt has been made to explain the changes in these constants in terms of the ion–ion and ion–solvent interactions. Using these constants, the mean activity coefficients, γ±, of sodium sulphate were calculated at different temperatures and concentrations using Pitzer's equation.
Five-coordinated halogenomercurate(II) complexes: crystal structures of bis(L-tryptophanium) trichloromercurate(II) and bis(D,L-homocysteine thiolactonium) tetrabromomercurate(II)
Authors: Book Langford , Carty Arthur J. , Chieh Chung
Published: May 2006

Reactions of L-tryptophan and D,L-homocysteine with mercury(II) halides in acidic ethanol/water solutions result in the formation of bis(L-tryptophanium) trichloromercurate(II) (TPTC) and bis(D,L-homocysteine thiolactonium) tetrabromomercurate(II) (HTTB) respectively. Their crystal structures consist of halide-bridged polymeric chains of quasi HgX3− units. The coordination geometry around Hg(II) in both anions is distorted trigonal bipyramidal. There are no chemical bonds between the amino acid cations and the mercury(II) ions. TPTC is monoclinic, space group P21, with a = 16.688(5), b = 5.626(1), c = 14.022(5) Å, β = 108.17(3)°. The structure was solved and refined from 2433 independent counter measured reflections to an R factor of 0.062. The two independent tryptophan molecules per asymmetric unit form a single cation via a strong hydrogen bond between the carboxylate groups. Thus the compound can be represented by MHgCl3 where M is the cation. One of the three Cl− ions is strongly bonded to one Hg(II) ion and weakly bonded to two other Hg(II) ions. In addition to the three short Hg—Cl distances of 2.403(3), 2.376(4), and 2.614(4) Å, there are two long Hg—Cl bonds of 2.833(4) and 2.888(4) Å to each Hg(II), from the weakly bridged chloride ions. HTTB is orthorhombic, space group Pnma with a = 8.068(3), b = 24.985(7), and c = 8.828(3) Å. The structure was refined to an R value of 0.066 for 819 observed reflections (I ≥ 3σ(I)), however, inclusion of unobserved reflections did not change the parameters. The homocysteine free base used in the reaction was lactonised under the experimental conditions to a thiolactonium ion. There are three relatively short Hg—Br interactions (2.566(3) twice, 2.662(4) Å) within the distorted trigonal bipyramidal stereochemistry of each mercury atom and two longer Hg—Br bonds (2.917(6) and 3.087(5) Å). The polymeric, anion chains arrange in layers on the mirror planes (y = ±1/4) with these layers sandwiched by two layers of cations.
The redetermination of the crystal structure of trisulphur dinitrogen dioxide
Authors: MacLean Greg , Passmore Jack , White Peter S. , Banister Arthur , Durrant James A.
Published: May 2006

The crystal structure of S3N2O2 has been redetermined and the structure refined to a final R of 0.057 and Rw of 0.076 for 550 reflections with I ≥ 2σ(I). S3N2O2 is planar and of C2v symmetry, as previously found by Weiss. The central S—N distances and angle are 1.647(3) Å, NŜN 97.3(2)°, with adjacent N—S distances and angles of 1.535(3) Å, [Formula: see text], and terminal S—O distances and angles of 1.446(4) Å, NŜO 118.0(2)°. The infrared and Raman spectra are reported and some assignments are made.
Mécanisme de la réaction de glycosylation par réversion acide en présence d'anhydride trifluorométhane sulfonique comme agent de condensation
Authors: Pavia André A. , Ung-Chhun Sak N.
Published: May 2006

The acid-catalysed mechanism of the reaction using trifluoromethanesulfonic anhydride to synthesize symmetrical 1,1′-glycosyl-glycosides such as trehalose and galacto, manno, arabino, xylo etc. analogues has been elucidated. The authors were able to prove by 19F nmr study at low temperature that the efficiency of the system is due to the peculiar property of trifluoromethanesulfonic acid generated in situ to form a stable, insoluble hydroxonium trifluoromethanesulfonate CF3SO3− H3O+. The procedure satisfies the two necessary conditions for a glycosylation reaction being workable: (i) the presence in catalytic amounts of free acid which is regenerated during the condensation step; (ii) a very efficient trapping of the water liberated during the protonation step which displaces the equilibrium towards the formation of the glycoside. The α-stereoselectivity of the reaction is discussed in terms of anomerisation of the β-anomers on to the thermodynamically more stable α ones, through a cyclic oxonium intermediate.
Crystal structure of a stemodin intermediate
Authors: Pauptit Richard A. , Trotter James
Published: May 2006

Crystals of the title compound, C22H32O3, are monoclinic, P21/n, a = 11.832(1), b = 11.423(1), c = 14.637(1) Å, β = 98.71(2)°, Z = 4. The structure was solved by direct methods and was refined to R = 0.035 for 2052 reflexions with I ≥ 3σ(I). The X-ray study was carried out in order to determine the structures of two diastereomeric products obtained from a key step in a projected synthesis of the diterpenoids aphidicolin and stemodin. The product examined is the stemodin intermediate.
Halogenocyclopropanation des éthoxy-alcènes diversement alkylés. Effet syn-directeur des groupes éthoxy et alkyles
Authors: Barlet Roger , Goaller Raymond Le , Gey Claude
Published: May 2006

Weakly nucleophilic acceptors such as enol ethers can facilitate cycloaddition reactions with monohalocarbenoids. The high yields and stereoselection towards the more highly hindered adducts are interpreted by complexation of the oxygen atom of the substrate with the metal atom of the carbenoid. [Journal translation]
The photochemical reaction of tris(ethylenediamine)cobalt(III) ion with ferrocyanide
Authors: Langford Cooper H. , Sasseville Roger L. P.
Published: May 2006

The photochemical formation of [Cl(en)2Co—N≡C—Fe(CN)5]2− from Co(en)33+ and Fe(CN)64− is explored. Earlier evidence established that the reaction proceeds via electron transfer. Ligand field Co(III) excited states are clearly indicated to be effective. There is evidence that free Fe(CN)64− can scavenge these excited states or their successors arising in ion pairs with Fe(CN)64−. This suggests that the reactive excited state lifetime is at least comparable to the rate of diffusional encounters. However, racemization does not accompany reaction if (+)589Co(en)33+ is the reactant. Wavelength studies indicate approximate wavelength independence as far as 647.1 nm. These results are in contrast with the behaviour of photosubstitution yields for Co(III) amines.
Constantes d'ionisation de dérivés de la pyrazolidine-3,5-dione dans l'éthanol. Relation avec l'électroactivité
Authors: Gueutin-Pelinard Claire , Nivaud Elisabeth , Boucly Patrick , Guernet Michel
Published: May 2006

Ionisation constants of some pyrazolidine-3,5-dione derivatives were measured in ethanol by potentiometric and spectrophotometric methods. The electroactivity of these compounds is in relation to the enolic and diketonic equilibrium in this medium.
The biosynthesis of cyclopropane fatty acids. I. Feeding experiments with oleic acid-9,10-d2, oleic acid-8,8,11,11-d4, and L-methionine-methyl-d3
Authors: Buist Peter H. , Maclean David B.
Published: May 2006

cis-9-Octadecenoic acid-9,10-d2 and cis-9-octadecenoic acid-8,8,11,11-d4 and L-methionine-methyl-d3 were administered to cultures of Lactobacillus plantarum and converted by the organism to the corresponding cyclopropyl compounds. The first experiment showed that no scrambling or loss of label occurred when a methylene unit was added across the double bond of the labelled substrate. In the second experiment, again, no loss or scrambling of label occurred, a result which ruled out any mechanism for biological cyclopropanation involving allylic activation of the double bond. The third experiment yielded a biosynthetic cyclopropane fatty acid containing deuterium located exclusively at the methylene group of the cyclopropane ring. Up to 17% of a d1-species accompanied the major dideuterated compound. The lone deuterium in the d1-cyclopropane fatty acid occupies both positions of the methylene group to the same extent. It has been shown that the extent to which d1-cyclopropane fatty acid is produced increases with cell growth. The extent of exchange was similar in the cyclopropanation of both the 9,10-and 11,12-isomers of cis-octadecenoic acid.
Photochemical reactions of charge-transfer complexes. IV. The orientation effects of charge-transfer complexes: theory and experiment
Authors: Wong Po Cheong , Arnold Donald R.
Published: May 2006

In paper number III of this series (2) ab initio and PCILO molecular orbital calculations for the four π–π* charge-transfer (ct) complexes formed between maleonitrile (MN) and fumaronitrile (FN), and cis (CS) and trans-1,2-dimethoxyethylene (TR) were reported. This paper reports the ct transition absorption characteristics and association constants of these complexes as a function of temperature. From this data the heats of formation of the complexes are determined and these experimental results are then compared with the theoretical values; good agreement is obtained. The order of complex stability (−ΔHθ (kcal mol)) measured in chloroform solution is: MN−TR(0.55) < FN−TR(0.65) < MN−CS(0.78) < FN−CS(1.25).We reach the conclusion that, for these complexes, orientation effects of the substituents are quite small in magnitude and that the dominant factor influencing complex stability follows the redox potential difference. The structures of the complexes are discussed in view of these results.