bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen exchange and isomerization in ortho substituted benzamides. On the question of free rotation in an N-protonated amide
Authors: McClelland Robert A. , Reynolds William F.
Published: May 2006

Rate constants have been obtained for the acid-catalyzed N–H exchange of N-methyl, 2,N-dimethyl, and 2,4,6,N-tetramethylbenzamide and the acid-catalyzed isomerization of the three corresponding N,N-dimethylbenzamides. The ratio [Formula: see text] increases significantly with increased number of ortho methyl substituents. This is explained in terms of a suggestion of Perrin, that C—N bond rotation is not completely free in the N-protonated amide, since it must compete with a diffusion limited deprotonation reaction. The isomerization reaction, which requires such a rotation, is therefore slowed by ortho methyl substituents which hinder rotation, relative to the exchange reaction, which does not require rotation.
Synthesis, reactions, and nuclear magnetic resonance spectroscopy of 4-methyl-6H-pyrazolo(3,4-b)azepin-7-ones
Authors: Sharma Suresh Chandra , Lynch Brian Maurice
Published: May 2006

Reactions of various 5-aminopyrazoles with ethyl levulinate in acetic acid have been shown to furnish moderate to good yields of the correspondingly substituted 4-methyl-6H-pyrazolo-(3,4-b)azepin-7-ones, accompanied by the acetamidopyrazoles. The courses of methylation and of bromination reactions of some of the pyrazoloazepinones have been explored and defined, and conversion of one pyrazoloazepinone into 7-chloropyrazoloazepine and thence by nucleophilic displacements into 7-(substituted amino)pyrazoloazepines has been effected. Structural assignments, tautomeric preferences, and through-space interactions between substituents were established through nuclear magnetic resonance spectroscopy (1H and 13C). Some members of the pyrazoloazepinone series exhibit significant anti-inflammatory and analgesic effects in mice.
Anionic pyrazolyl-bridged nickel nitrosyl complexes. Synthesis, structure, and reactivity
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

A series of anionic pyrazolyl-bridged nickel nitrosyl complexes, M+[(ON)Ni(μ-L2)(μ-X)Ni(NO)]− (where L = pyrazolyl, N2C3H3, or 3,5-dimethylpyrazolyl, N2C5H7; X = Cl, Br, I, or N2C5H7; and M = Na, (CH3)4N, or (C2H5)4N) is described. Crystallographic analyses have been carried out on two of these complexes. Crystals of [(C2H5)4N]+[(ON)Ni(μ-I)(μ- N2C5H7)2Ni(NO)]− are orthorhombic, a = 19.910(1), b = 14.0330(7), c = 9.3195(9) Å, Z = 4, space group Pn21a and crystals of [(C4H8O)2Na][(ON)Ni(μ-N2C5 H7)3Ni(NO)] are orthorhombic, a = 19.897(2), b = 19.529(3), c = 15.894(2) Å, Z = 8, space group Pbca. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to R = 0.027 and 0.057 for 2572 and 2168 reflections with I ≥ 3σ(I) respectively. The structure of [(C2H5)4N]+[(ON)Ni(μ-I)(μ-N2C5H7)2Ni(NO)]− consists of discrete cations and binuclear anions which have approximate C2v symmetry. The nickel atoms have distorted tetrahedral coordination geometry. Important mean molecular dimensions (distances corrected for libration) are: Ni—I—Ni, 73.67(2)°, Ni—I, 2.765(3), Ni—NO, 1.649(5), Ni—N(pyrazolyl), 1.980(14) Å, and Ni—N—O, 172.5(18)°. The structure of [(C4H8O)2Na][(ON)Ni(μ-N2C5 H7)3Ni(NO)] consists of discrete ion-pair units in which the two NiNO moieties are bridged by three N2C5H7 ligands, two of which are coordinated to the sodium ion via a novel η2(N,N) π-interaction (mean Na—N = 2.61(3) Å). The sodium is also coordinated to two tetrahydrofuran oxygen atoms to give a distorted tetrahedral coordination geometry about the sodium (Na—O = 2.301(6) and 2.266(5) Å). Except for disordered tetrahydrofuran carbon atoms, the molecular unit has approximate C2v symmetry. The nickel atoms have distorted tetrahedral coordination geometry, the mean distances being Ni—NO, 1.591(6), Ni—N(pyrazolyl), 1.985(2) for the unique pyrazolyl group and 2.016(5) Å for the pyrazolyl nitrogen atoms coordinated to Na. The mean Ni—N—O angle is 176.9(11)°.
Thermodynamic properties of binary mixtures containing thiaalkanes. II. Thermal pressure coefficients of pure compounds at 298.15 K
Authors: Philippe R. , Ferhat-Hamida Z. , Merlin J. C.
Published: May 2006

An apparatus for the measurement of thermal pressure coefficients of pure compounds is described. The thermal pressure coefficient β of n-thiaalkanes R2S (R = CH3, C2H5, n-C3H7, n-C4H9, n-C7H15) and of dithiaalkanes R2S2 (R = CH3, C2H5, iso-C3H7) were measured at 298.15 K and at zero pressure. These experimental results in conjunction with data from literature for other compounds are compared using the reduced parameter of pressure P* proposed by Flory. The P* do not have regular values for the lower members of thiaalkanes series. One explanation of these irregularities is the different size of the molecules.
Isotopically-enriched carbohydrates: The preparation of [2H]-enriched aldoses by catalytic hydrogenolysis of cyanohydrins with 2H2
Authors: Serianni Anthony Stephen , Barker Robert
Published: May 2006

A procedure is described for the preparation of aldoses and aldose phosphates enriched with 2H by hydrogenolysis of aldononitriles and aldononitrile phosphates over palladium using 2H2. Aldoses, aldose phosphates, and derivatives prepared with 13C and (or) 2H enrichment and characterized by 1H and 13C nmr were: DL-[1-14C, 2H]glyceraldehyde, D-[1-13C, 2H]erythrose, D-[1-13C, 2H]threose, D-[2-13C, 2H]ribose, D-[2-13C, 2H]arabinose, methyl α-D-[2-13C, 2H]ribofuranoside, methyl β-D-[2-13C, 2H]ribofuranoside, DL-[3-2H]erythrose, DL-[3-2H]threose, DL-[1-13C, 2H]glyceraldehyde 3-phosphate, and D-[1-13C, 2H]ribose 5-phosphate. 13C isotope shifts, 1H and 13C chemical shifts, and homo- and heteronuclear coupling constants are reported.
The formation and structure of a 1,5-disubstituted S4N4 ring, (Ph3P=N)2S4N4, from the reaction of triphenylphosphine with tetrasulphur tetranitride
Authors: Bojes Josef , Chivers Tristram , MacLean Greg , Oakley Richard T. , Cordes A. Wallace
Published: May 2006

Two novel products, (Ph3P=N)2S4N4 and (Ph3P=N)3S+S4N5−, have been isolated from the reaction of triphenylphosphine with S4N4; an X-ray structural determination of (Ph3P=N)2S4N4 shows it to consist of a 1,5-disubstituted S4N4 ring with the exocyclic substituents in an axial, equatorial configuration.
Electrostatic effects of substrate charge on base-catalyzed proton exchange in purines. Implications for the involvement of zwitterions
Authors: Taylor Spencer E.
Published: May 2006

Rates of detritiation from the C-8 position of various ionized purine molecules have been shown to reflect electrostatic interactions occurring within the transition state of the exchange reaction. The purines are capable of existing as protonated, anionic, neutral, and zwitterionic species in aqueous solution, each of which have been shown previously to undergo specific hydroxide ion-catalyzed detritiation. The effects of substrate charge are quantified as the protonactivatingfactor, aniondeactivatingfactor, and zwitterionactivatingfactor. Localized charge and not net charge is shown to govern the reactivities of the various species, especially the zwitterions.Estimation of rate constants for the zwitterionic species (hitherto only postulated to account for the observed rate behaviour) has enabled the calculation of the corresponding zwitterionic equilibrium constants (Kzw). Kzw values calculated in this manner agree with those estimated from suitable literature pKa data.
A 31P nuclear magnetic resonance spectroscopic study of complexes of cadmium(II) with some phosphine oxides, sulfides, and selenides
Authors: Dean Philip A. W. , Hughes Mary K.
Published: May 2006

Complexation between Cd(SbF6)2 and the ligands Ph3PE (E = S or Se), Ph2P(E)(CH2)nP(E)Ph2 (n = 1 or 2, E = O, S or Se; n = 3, E = Se), [Ph2P(E)CH2]3CMe (E = S or Se) and Ph2P(E)(CH2)2PPh(E)(CH2)2P(E)Ph2 (E = O, S, or Se) in liquid SO2 has been studied, mainly by low-temperature 31P nmr spectroscopy. With the sulfides and selenides the maximum donor atom/Cd ratio observed is four, as shown by the limiting low temperature spectra of (Ph3PE)4Cd2+ (E = S or Se), [CH2(PPh2(Se))2]2Cd2+, and [Ph2P(E)CH2CMe(CH2PPh2(E))2]2Cd2+ (E = S or Se). The last two complexes both contain a potentially tridentate ligand behaving in a bidentate manner and their spectra are unexpectedly complicated due, perhaps, to conformational effects. Slow exchange spectra of [Ph2P(E)(CH2)2PPh(E)(CH2)2PPh2(E)]Cd2+ (E = S or Se) show that in each complex the ligand behaves in a tridentate manner. For the preceding complexes, two-bond 111/113Cd–31P coupling is observed at the donor sites, and for the selenides a reduction in |1J(31P—77Se)| on complexation further identifies the bound —PSe groups.The maximum coordination number appears to be six in the complexes of the phosphine oxides. Both 2:1 and 3:1 L:Cd complexes exist for both of the bidentate ligands Ph2P(O)(CH2)nP(O)Ph2 (n = 1 or 2) whereas in the system Ph2P(O) (CH2)2P(O)Ph(CH2)2P(O)Ph2–Cd2+ the species identified is the presumably six-coordinate 2:1 complex. For comparison, the six-coordinate complex [{CH2(PPh2(O))2}3Hg]2+ has been identified in solution also.Competition studies between the dioxides, disulfides, and diselenides of the diphosphines show that the disulfides and diselenides cannot compete with the dioxides for cadmium, but that the diselenides can compete with the disulfides to a limited extent.
The solid phase synthesis of tertiary hydroxyesters from symmetrical diacid chlorides using organomanganese reagents
Authors: Leznoff Clifford C. , Yedidia Varda
Published: May 2006

A 1% crosslinked divinylbenzene–styrene copolymer, incorporating benzyl alcohol groups, was used to monoblock the symmetrical diacid chlorides, ClOC(CH2)nCOCl (where n = 4 and 8). Further reaction of the polymer-bound monoester monoacid chloride with phenylmanganese iodide or butylmanganese iodide gave their respective polymer-bound tertiary hydroxyesters. Subsequent base cleavage and esterification yielded methyl 6-hydroxy-6, 6-diphenylhexanoate, methyl 10-hydroxy-10,10-diphenyldecanoate, methyl 6-butyl-6-hydroxydecanoate, and methyl 10-butyl-10-hydroxytetradecanoate and some recovered dimethyl alkanoates. The reactions of some polymer-bound monoester monoacid chlorides with phenylcadmium chloride were also studied.
The structure of Schiff reagent aldehyde adducts and the mechanism of the Schiff reaction as determined by nuclear magnetic resonance spectroscopy
Authors: Robins J. H. , Abrams G. D. , Pincock J. A.
Published: May 2006

An nmr study of compounds isolated from the Schiff aldehyde reaction between pararosaniline hydrochloride, sulfur dioxide, and acetaldehyde has demonstrated that these adducts are α-anilinoalkylsulfonic acids. The evidence is incompatible with the other structures most often accepted in the literature, N-phenyl alkylsulfonamides. In combination with nmr spectra obtained from solutions of the Schiff reagent and the Schiff reaction and with literature spectrophotometric data, this result leads to a reasonable proposal for the mechanism of the colour development. The effects of the concentrations of the dye, acetaldehyde, and in particular, sulfur dioxide are explained and suggest that the dominant coloured species is a 2:1 acetaldehyde–dye adduct. The nmr results also reveal a kinetic/thermodynamic competition for acetaldehyde between the aniline of the dye and the aldehyde carbonyl leading to bisulfite addition. The relation of the Schiff test with acetaldehyde and the Feulgen test for aldehydes in biological samples is also discussed.
A 13Cmr study of 2′-deoxynucleotides in the syn and anti conformation
Authors: Niemczura Walter P. , Hruska Frank E.
Published: May 2006

The geminal and vicinal 13C—31P coupling constants for the 3′- and 5′-monophosphates and 3′,5′-diphosphates of thymidine and its isomer 6-methyl-2′-deoxyuridine have been obtained for aqueous solutions at varions pH values. Since the thymine base is anti and the 6-methyluracil base is syn, the data provide information about the influence of the orientation about the N-glycosyl linkage on the conformation about the [Formula: see text] and [Formula: see text] bonds. The 3J(C4′—P5′) couplings reveal a preference for the [Formula: see text] conformer of the 5′-nucleotidyl units, in agreement with previous measurements of 1H—31P coupling constants. The 3J(C4′—P3′) and 3J(C2′—P3′) couplings are consistent with a preference for the [Formula: see text] conformer for both the syn and anti3′-nucleotidyl units. The response of these couplings to secondary ionization of the phosphate is different for the thymine and 6-methyluracil derivatives and suggests a phosphate–phosphate interaction for the syn, but not the anti, 3′,5′-diphosphates. A correlation between the sugar-pucker and the [Formula: see text] orientation is revealed. The 2J(C5′—P5′) and 2J(C3′—P3′) are relatively insensitive to the ionization state of the phosphate as well as to other structural features of the deoxyribose phosphate backbone.
Thermochemistry of the lower bromides of tantalum
Authors: Westland Alan D.
Published: May 2006

The standard enthalpy of formation of tantalum(IV) bromide has been determined by solution calorimetry: ΔHf0(TaBr4(c) 298 K) = −125.6 ± 0.5 kcal mol−1. Experimental estimates of the enthalpies of formation of tantalum(III) bromide and tantalum(II,III) bromide were also obtained. Estimates of the entropies and heat capacities of the compounds are also given.
Regioselectivity in cycloaddition reactions on solid phases
Authors: Yedidia Varda , Leznoff Clifford C.
Published: May 2006

A 1% crosslinked divinylbenzene-styrene copolymer, incorporating benzyl acrylate groups, reacted in normal Diels–Alder reactions with E-1-phenyl-1,3-butadiene or methyl E-2,4-pentadienoate to give their respective polymer-bound benzyl cyclohexenecarboxylates. Polymer-bound benzyl propiolate and polymer-bound benzyl phenylpropiolate reacted with benzonitrile oxide in a typical 1,3-dipolar addition reaction to give their respective polymer-bound isoxazoles. Cleavage of the polymer-bound Diels–Alder adducts and the polymer-bound 1,3-dipolar addition adduct derived from polymer-bound benzyl propiolate gave mixtures of ortho and meta regiomers similar to those produced in analogous reactions in solution. Cleavage of the polymer-bound 1,3-dipolar addition adduct, derived from polymer-bound benzyl phenylpropiolate, followed by esterification, gave a solitary adduct, 4-carbomethoxy-3,5-diphenylisoxazole, but an analogous solution 1,3-dipolar addition yielded a 1:1 ratio of the two possible regiomers.
Molecular rearrangements. Part XVI. Thermolysis and photolysis of N-benzyldiphenylamine and N-phenylacetyldiphenylamine
Authors: Badr M. Z. A. , Aly M. M. , Fahmy A. M.
Published: May 2006

Heating N-phenylacetyldiphenylamine in a sealed tube at 360 °C gave rise to carbon monoxide, bibenzyl, toluene, stilbene, diphenylmethane, aniline, carbazole, N-benzylcarbazole, acridine, 9-phenylacridine, 4-aminotriphenylmethane, diphenylamine, p-benzyldiphenylamine, and o-aminodiphenylmethane. A similar result was also obtained on heating N-benzyldiphenylamine, with the exception of carbon monoxide. Such results in addition to those obtained from photolysis of N-phenylacetyldiphenylamine are interpreted in terms of a free-radical mechanism.
Viscosities of glycine and DL–alanine in water acetonitrile mixtures between 25 and 40 °C
Authors: Dey Nibaran C. , Saikia Birendra K. , Haque Inamul
Published: May 2006

The relative viscosities and densities of glycine in 5%, 10%, 15%, and 20% w/w acetonitrile–water mixtures at 25, 30, 35, and 40 °C and of DL-alanine in water, 5%, 15%, and 20% w/w acetonitrile water mixtures at 30 and 40 °C have been determined. The viscosity B coefficients have been found to increase with increase in concentration of acetonitrile and also with the increase of temperature in both cases.The limiting apparent molar volumes and limiting value of effective flow volumes have also been calculated.
Formation of furofurans from tetraacetylethylene. Molecular and crystal structure of a spiro[furan-2(5H),2′(3′H)-furo[2,3-b]furan]
Authors: Adembri Giorgio , Donati Donato , Cini Renzo , Nesi Rodolfo , Scotton Mirella
Published: May 2006

Dimerization of tetraacetylethylene (TAE) 1 has led to a spiro[furan-2(5H),2′(3′H)-furo[2,3-b]furan], whose structure was established by X-ray analysis. The trend of TAE to furan ring closure was confirmed by the reaction with ethyl vinyl ether, where the first product of the reaction, the pyran adduct 8, smoothly rearranged to a furo[2,3-b]furan derivative 9.
Kinetics and mechanism of the oxidation of tris(4,7-dihydroxy-1,10-phenanthroline)-iron(II) by molecular oxygen
Authors: Ng Flora T. T. , Henry Patrick M.
Published: May 2006

The reaction of (OHP)3Fe(II) (OHP = 4,7-dihydroxy-1,10-phenanthroline) with oxygen in aqueous 0.1 N NaOH solution takes place according to the stoichiometry:[Formula: see text]This stoichiometry holds whether (OHP)3Fe(II) or O2 is in excess. The rate law over a wide range of (OHP)3Fe(II) and O2 concentrations at 0.1 N NaOH has the form:[Formula: see text]A notable feature of this oxidation is that free HO2− is not produced as an intermediate. A plausible mechanism involving bound superoxide or peroxide as intermediates is proposed. Due to the redox nature of the OHP ligand and the low potenial of the (OHP)3Fe(II) complex, a 4 electron transfer from one (OHP)3Fe(II) to one O2 to give a Fe(IV) species with an oxidized ligand is a distinct possibility. The rate–pH profile is consistent with the protonation of (OHP)3Fe(II) (pKa ≈ 9.4) to give a more reactive species.
Tetranortriterpenoids and related compounds. Part 25. Two 3,4-secotirucallane derivatives and 2′-hydroxyrohitukin from the bark of Guareacedrata (Meliaceae)
Authors: Akinniyi John A. , Connolly Joseph D. , Rycroft David S. , Sondengam B. Lucas , Ifeadike N. Patience
Published: May 2006

Three new compounds, 3,4-secotirucalla-4(28),7,24-trien-3,21-dioic acid 1, the corresponding 3-monomethyl ester 12, and 2′-hydroxyrohitukin 13, have been isolated from the bark of Guareacedrata (Meliaceae). The structures of 1 and 12 were confirmed by correlation with methyl 3-oxotirucalla-8,24-dien-21-oate (methyl isoelemonate) 6. The 1H and 13C nmr data are reported.
Determination of D[C6F5CH2—Br] by the toluene carrier method
Authors: Kominar R. John , Krech Michael J. , Price Stanley James W.
Published: May 2006

The pyrolysis of C6F5CH2Br has been studied by the toluene carrier technique over the temperature range 727–800 °C. Rate constants are based on analysis for residual parent compound by gas chromatography using an internal standard technique. In selected runs a material balance of 100 ± 2% was obtained for bromine based on C6F5CH2Br plus HBr. Within the limits of the experimental technique the process appears to be first order and homogeneous. In addition to HBr the other major products of the thermal decomposition are C6F5CH3, (C6F5CH2)2, C6F5CH2CH2C6H5, and (C6H5CH2)2. The Arrhenius equation obtained is[Formula: see text]The log A value is very close to the value of 14.6 recommended by Benson and O'Neal for the decomposition of C6H5CH2Br. The activation energy, 225 ± 6 kJ mol−1, should be a reasonable estimate of D[C6F5CH2—Br].
The sonolysis of uracil
Authors: Yu Tain-Jen , Sutherland Ronald G. , Verrall Ronald E.
Published: May 2006

The sonolysis of uracil (1) has been studied at 630 kHz in the presence of air, oxygen, nitrogen, and argon. The degradation products were identified by gc–ms analysis. Under aerated conditions the following products were found: uracil glycols (7), isobarbituric acid (8), N-formyl-N′-glyoxylurea (6), 5-hydroxyhydantoin (9), dialuric acid (10), alloxan monohydrate (12), parabanic acid (13), and oxaluric acid (14). In deaerated solutions 6, 13, and 14 were not observed but either 6-hydroxy-5,6-dihydrouracil(17) or its isomer (18) were detected in addition to 7, 8, 9, 10, and 12. The observed products have been used to develop a possible mechanism for the sonolytic degradation and the results are similar to those obtained in radiolysis.The sonolytic degradation of 5-bromouracil (19) is also reported; the products observed were 5-bromobarbituric acid (20), 12, 13, 14, and 9 and these can be rationalized by a similar mechanistic scheme.
Reactions of singlet oxygen. Part V. Dye sensitized photooxidation of m-hydroxydiphenylamine
Authors: Ram Nathu , Sidhu K. S.
Published: May 2006

Methylene blue sensitized photooxidation of m-hydroxydiphenylamine gives N-(3-hydroxyphenyl)-p-benzoquinoneimine as the primary product in acetonitrile–water medium. The experimental results are in good agreement with the theoretical plots calculated on the basis of the reaction undergoing through the participation of [Formula: see text] as well as the excited dye interacting with the substrate. β-Value and rate constant of reactivity of m-hydroxydiphenylamine with singlet oxygen have been calculated. The effects of β-carotene, 1,4-diazabicyclo[2,2,2]octane, triethylamine, allyl thiourea, 2,5-diphenylfuran, and dielectric of different solvents show the participation of singlet oxygen at low substrate concentration and interaction of the excited dye with the substrate at its high concentrations. The data on oxygen concentration effect fit into the derived rate expressions. No complexation between methylene blue and m-hydroxydiphenylamine is observed.
Linear peptide alkaloids from the sponge Clionacelata (Grant). Celenamides C and D
Authors: Stonard Richard J. , Andersen Raymond J.
Published: May 2006

Celenamides C (7) and D (8), two novel alkaloids closely related to peptide alkaloids found in higher plants, have been isolated as their penta (12) and nonacetyl (13) derivatives, respectively, from acetylated extracts of the sponge Clionacelata (Grant). The structure elucidation of 7 and 8 is described.
51V FT-nmr investigations of metavanadate ions in aqueous solutions
Authors: Habayeb Mahmoud Adam , Hileman Jr O. E.
Published: May 2006

51V-nmr chemical shifts, line widths, and area ratios obtained for various vanadium(V) species in aqueous solutions as a function of counter ion, pH, and analytical vanadium concentration changes are reported. From these data the eight vanadium(V) species shown to be present in significant amounts are identified. In the pH range 8.5 to 7.0, 51V-nmr resonances were observed at 574 ppm and 582 ppm. The 574 ppm resonance is assigned to both V3O93− and V4O124− while the 582 ppm resonance has been assigned to the V6O174− species. The suggestion that tetra alkyl ammonium cations stabilize V4O124− species in solution is confirmed.
Quand la résonance paramagnétique électronique de l'uranium(IV) est-elle observable?
Authors: Soulié Edgar , Folcher Gérard , Kanellakopulos Basil
Published: May 2006

For non-Kramers ions, the electronic ground state may be nondegenerate. Then, if the first electronic excited level lies more than 0.3 cm−1 above the ground state, no electron paramagnetic resonance can occur between them in the X band. This is the case whenever a temperature-independent paramagnetism is observed in the magnetic susceptibility of the powder. An example of this situation, conflicting with published epr spectra, is provided by U(cupferron)4.
The synthesis of 8-aza-3-deazaguanosine [6-amino-1-(β-D-ribofuranosyl)-υ-triazolo[4,5-c]pyridin-4-one] via a novel 1,3-dipolar cycloaddition reaction
Authors: Earl Robert A. , Townsend Leroy B.
Published: May 2006

8-Aza-3-deazaguanosine (2) bas been prepared via a route which used a 1,3-dipolar cycloaddition reaction to provide a key intermediate. The reaction of 2′,3′,5′-tri-O-benzoyl-β-D-ribofuranosyl azide (13) with methyl 4-hydroxy-2-butynoate (11) provided a good yield of crystalline methyl 5-hydroxymethyl-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-υ-triazole-4-carboxylate (14). A series of functional group transformations were then used to convert 14 into methyl 5-cyanomethyl-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-υ-triazolo-4-carboxylate (19). Treatment of 19 with liquid ammonia effected not only a smooth removal of the blocking groups, but also an aminolysis of the ester function which was then followed by a ring annulation to provide 8-aza-3-deazaguanosine (2). The structures of these nucleosides were established on the basis of proton nmr spectral data and nuclear Overhauser enhancement data. The nucleosides obtained in this study were also converted through a chemical degradation sequence into nucleosides which had been obtained during an earlier work from our laboratory. The present study also provides unequivocal proof of the structures of some triazole nucleosides obtained in the earlier study.
Heats of vaporization of esters by the gas chromatography–calorimetry method
Authors: Fuchs Richard , Peacock L. Alan
Published: May 2006

A recently developed gc–calorimetry procedure involving a combination of gas chromatography and heat of solution measurements has been used to measure heats of vaporization of 17 esters, including methyl 2,2-dimethylpropanoate, butyl acetate, glyceryl triacetate, diethyl phthalate, methyl 9-octadecenoate, and 12 methyl esters of C3- to C15-fatty acids. Comparison with measurements of ΔHv reported in the literature indicates that the gc–calorimetry method often has smaller uncertainties in measurements (0.25 to 1.00 kJ mol−1) and more consistent methylene increments for the series of fatty acid methyl esters. Two of the experimental ΔHv measurements which differ appreciably from recent literature values have been verified by vaporization calorimetry.
Crystal structure of camphor-1,4-homoenol p-bromobenzoate
Authors: Pauptit Richard A. , Trotter James
Published: May 2006

Crystals of the title compound, C17H19BrO2, are orthorhombic, P212121, a = 6.875(1), b = 8.522(2), c = 26.658(6) Å, Z = 4. The structure was determined by Patterson and Fourier methods, and refined to R = 0.045 for 697 reflections with I ≥ 3σ(I); the absolute configuration was established. The four-membered ring is tightly folded, and bond angles in the vicinity of this ring indicate considerable strain.
Action de l'hydroxyurée sur les esters α-acétyléniques
Authors: Lassalvy Christiane , Petrus Clément , Petrus Françoise
Published: May 2006

Hydroxyurea, in its oxanion form NH2—CO—NHO− reacts in basic medium by a 1,4-addition to α-acetylenic esters leading to the E and Z ethylenic β-ureidoxy ester isomers. The E isomer can be isolated and identified from reaction with ethyl tetrolate and ethyl propiolate. The Z isomer undergoes cyclisation in situ to give the 2-carboxamido-5-methyl-3-isoxazolone. With phenyl propiolate, the 3-hydroxy-5-phenyl isoxazole is directly obtained without isolation of the intermediate N-carboxamido derivative. In the case of ethyl propiolate two cyclic compounds are obtained: 3-hydroxyisoxazole and 2-N-carboxamido-5-ethoxy-3-isoxazolidinone. The formation of the former is due to the in situ cyclisation of the Z isomer. The isolation of the latter compound can be explained by solvent addition to the E β-ureidoxyacrylate intermediate in a Michaël addition followed by cyclisation.
Synthesis of colchifoline from deacetylcolchiceine
Authors: Iorio Maria A. , Molinari Marisa , Brossi Arnold
Published: May 2006

Treatment of a mixture of deacetylcolchicine and deacetylisocolchicine, obtained by diazomethane methylation of deacetylcolchiceine, with trifluoroacetylglycolyl chloride in pyridine, afforded directly colchifoline and isocolchifoline. The two ether isomers could be separated by chromatography and the material eluted first proved to be identical with colchifoline isolated from commercial samples of colchicine.
Conversion of hydroxyl groups into bromo groups in carbohydrates with inversion of configuration
Authors: Classon Björn , Garegg Per J. , Samuelsson Bertil
Published: May 2006

A novel reagent system is described for the efficient, one-step transformation of hydroxyl groups in carbohydrates to bromodeoxy groups. The reaction proceeds with inversion of configuration. The reagent system consists of triphenylphosphine, tribromoimidazole, and imidazole in toluene at elevated temperature. The carbohydrate need not be soluble in toluene. The examples given include substitution of isolated primary and secondary hydroxyl groups in otherwise protected carbohydrates as well as disubstitution involving one primary and one secondary position in hexopyranosides. High yields are obtained in the replacement of hydroxyl by bromine in the 2-position of 3,4,6-protected methyl α-D-gluco- and -mannopyranosides.
The twist angle approach to the stereoselectivity in reduction of ketones
Authors: Giddings Michael R. , Hudec John
Published: May 2006

Semiempirical MO calculations show that the π* orbital of the carbonyl carbon of asymmetric ketones deviates from orthogonality. These small deviations, measured by twist angles, are used to predict the configurations of the diastereoisomeric alcohols formed on reduction of the ketones with complex metal hydrides. The method is particularly suitable for predicting the changes in stereoselectivity when the carbonyl compound is substituted. This is illustrated by a number of examples of reduction of substituted rigid polycyclic ketones. It is proposed that a nucleophile approaches a carbonyl group preferentially from the side of obtuse angle with respect to the O—C bond. The twists incorporate the electronic nature of the substitent and help to understand the steric effect. The application of the twist angle approach to other reactions is briefly mentioned.
Static and dynamic phenomena in the quenching of phenanthrene triplets by conjugated dienes in anionic micelles
Authors: Selwyn J. C. , Scaiano J. C.
Published: May 2006

The photochemistry of phenanthrene in sodium dodecyl sulfate micelles in the presence of conjugated dienes having from five to eight carbon atoms has been examined using laser flash photolysis techniques. The effect of the addition of the diene quenchers on the intensity of the T–T absorptions immediately after singlet decay reflects largely the distribution of the quenchers and can be used to determine micellar properties, e.g. the aggregation number. The effect of quenchers on the lifetime of triplet phenanthrene is largely controlled by the rate constants for quencher entry and exit from the micelles. Typical rates of entry are in the 1–2 × 109 M−1 s−1 range, while the exit rates are strongly dependent on the number of carbon atoms and are different for open and cyclic molecules; for example the exit rate constants are 1.3 × 105 and 3.5 × 105 s−1 for 1,3-octadiene and 1,3-cyclooctadiene, respectively.
Application of the Hancock steric constants to interpretation of heat of solution of benzamide in aliphatic alcohols
Authors: Taniewska-Osińska Stefania , Kamińska-Bartel Leokadia , Piekarski Henryk , Krygowski Tadeusz M.
Published: May 2006

The enthalpies of solution of benzamide in several aliphatic alcohols and of benzoic acid in n-hexanol have been measured. A linear correlation has been found between standard enthalpies of solution of benzamide and benzoic acid and Hancock steric constants.
Echange isotopique hydrogène–deutérium subi par les groupements méthyles de la triméthyl-4,5,6 pyrimidone-2
Authors: Picquenard Eric , Dizabo Pierre
Published: May 2006

The rate of deuterium exchange of 4 and 6 methyl protons in 4,5,6-trimethyl-2-pyrimidone has been followed in D2O over a range of acidity from pD 0.4 to 7.7 by means of proton magnetic resonance spectroscopy. The maximum of exchange rate represents equimolar proportions of the pyrimidone and its conjugate acid. The maximum is due to the neutral molecule acting as a base and removing a proton from one of the methyl groups of its conjugate acid. The exchange study of methyl protons in 1,4,5,6-tetramethyl-2-pyrimidone corroborates this mechanism.
On cardioactive steroids. IV. A new synthesis of cardenolides
Authors: Marini-Bettolo Rinaldo , Flecker Petr , Tsai Thomas Y. R. , Wiesner Karel
Published: May 2006

A new and efficient synthesis of Digitalis cardenolides via methoxyfuryl intermediates is described.
The role of the molecular environment for the primary photoprocesses of phenol in solution
Authors: Zechner J. , Köhler G. , Grabner G. , Getoff N.
Published: May 2006

not available
Ionization energies of metal chelates. Acetylacetonates, trifluoroacetylacetonates, and hexafluoroacetylacetonates of trivalent metals of the first transition series
Authors: Westmore John B. , Reimer Mark L. J. , Reichert Charles
Published: May 2006

For several β-diketonate complexes of metals of the first transition series the electron impact ionization efficiency curves obtained using unfiltered electron beams were fitted to empirical post-threshold ionization laws. In the energy region extending to 2–3 V above threshold, fits of high quality were obtained for a second power ionization law (i.e. ion current was proportional to the square of the electron energy in excess of the threshold energy) for complexes of Al(III), Sc(III), Mn(III), Fe(III), and Co(III) (d0, d0, d4, d5, and d6, respectively). In the cases of Ti(III), V(III), and Cr(III) complexes (d1, d2, and d3, respectively) the experimental points lay above the "best fit" curves in the immediate post-threshold region. Electron energies were initially calibrated by fitting experimental data points for xenon to its published ionization functions. In later experiments, Al(tfa)3 or Al(hfa)3 was used for calibration purposes. When the electron impact results were compared with published photoelectron spectra of the complexes (where available) it became apparent that, in the threshold region, the strongest ionization processes involved electron removal from ligand dominated π orbitals. In the cases of Ti(III), V(III), and Cr(III) complexes, weaker ionization processes involving electron removal from orbitals of predominantly metal 3d character (correlating with t2g in octahedral symmetry) could also be detected at lower electron energies.
Flame-ion probe of the reaction zone in a CH4–O2–Ar flame with added HCN, NH3 and NO
Authors: Goodings John M. , De Brou Gary B. , Bohme Diethard K.
Published: May 2006

The addition of 0.3% of the fuel-nitrogen (fuel-N) compounds HCN, NH3, or NO to a premixed, fuel-rich, CH4–O2–Ar flame burning at atmospheric pressure demonstrated the rapid interconversion of nitrogenous intermediates in the reaction zone. The nitrogenous species (HCN/CN, HNCO/NCO, NH3, NH2, NH, NO, NO2) were observed as ions (CN−, H2CN+, NCO−, H2NCO+, NH4+, NH3+, NH2+, NO+, NO2−, and hydrate ions) formed in chemical ionization processes discussed previously (1). The ions were sampled directly into a flame-ion mass spectrometer which had sufficient spatial resolution for the measurement of ion concentration profiles through the reaction zone. The study bears on Fenimore's suggestion for the formation of "prompt NO" in fuel-rich hydrocarbon flames. These additive results were compared with previous results involving nitrogenous species present in a similar CH4–O2 flame doped with 10% N2. The increased sensitivity of the additive approach confirmed many of the mass assignments and mechanisms involved in the N2 study. Reasonably good evidence was obtained for the elusive intermediate HNCO (and possibly isomeric HCNO as well) in protonated form, and also formamide, NH2CHO, which had not been detected previously. Similarities in profile peak positions and magnitudes observed for many ions, irrespective of the nature of the fuel-N additive, indicated that the nitrogenous species were linked by a network of fast bimolecular reactions, many of which appeared to be balanced in the reaction zone.
The contribution to the capacity of an electrode from a species adsorbed with partial charge transfer
Authors: Parsons Roger
Published: May 2006

The effect of partial charge transfer on the observed capacity of an electrode adsorbing a species from solution is discussed in a general way for the condition of constant fraction of charge transferred. It is confirmed that the width of the peaks is primarily determined by the interaction between adsorbed species. A simple model in which the degree of charge transfer changes rapidly with electrode potential is suggested. This may account for some of the sharp peaks observed experimentally.
Determination of single ion activities by relying on the electrical double layer model: NaF aqueous solutions
Authors: Daghetti Anna , Trasatti Sergio
Published: May 2006

Single ion activity coefficients for aqueous solutions of NaF in the range m = 0.1 up to m = 0.9 mol kg−1 have been derived by measuring the potential difference of the cell Hg (σ = const)/NaF(m)/F−-selective electrode. The approach rests on the assumption that the electric potential drop across the Hg/solution interface is independent of the electrolyte concentration once the diffuse layer effects are accounted for by the Gouy–Chapman theory, provided specific adsorption of ions is absent. The derived γ− values have been compared with the "real" activity coefficients as determined by Rabinovich and Titov and with the predictions of the hydration theory of Bates and Robinson. It is shown that the latter do not agree with the present experimental observations. Possible reasons for this apparent discrepancy are discussed.
Patchwise interfacial dipole layers on solids. Application to the silver iodide – aqueous solution interface
Authors: Keizer Arie de , Lyklema Johannes
Published: May 2006

The hydration of solid particles in aqueous solution is treated as a patchwise phenomenon, in which the orientation of water dipoles varies in a patchwise fashion along the surface. The idea is applied to the AgI system where besides the neutral surface Ag+ patches and I− patches are distinguished. A first-order elaboration is offered, including an analysis of the relation between overall macroscopic quantities and local properties. The model offers an interpretation of two characteristics of double layers on silver iodide: the asymmetry of its p.z.c. and the conspicuous capacitance rise on the positive side and may serve as a starting point for a better description of the typical differences between the double layers on AgI and Hg.
London – van der Waals forces and torques exerted on an ellipsoidal particle by a nearby semi-infinite slab
Authors: Brenner Howard , Gajdos Lawrence J.
Published: May 2006

A Hamaker-type integration of the pairwise en vacuo intermolecular forces is performed for a homogeneous triaxial ellipsoidal particle in proximity to a homogeneous semi-infinite slab bounded by a plane wall. The orientation of the ellipsoid relative to the plane is taken to be arbitrary, as too is its distance from the plane. The integrated potential energy function of the ellipsoid with respect to the slab is found to possess nonadditive positional and orientational contributions. This macroscopic potential is employed to compute the force and torque on the ellipsoid as functions of both its position and orientation relative to the plane.The novel integration scheme pertains to centrally-symmetric pairwise intermolecular potentials of arbitrary functional form. Specific results are derived for classical inverse-power intermolecular potentials possessing both attractive (r−n) and repulsive (−r−m) additive components (with n > m). In stable equilibrium the ellipsoid aligns itself with the shortest of its three principal axes perpendicular to the bounding wall, and at a separation distance comparable to the length scale of the intermolecular potential itself.
Kinetics of electrode processes in the presence of a discrete layer of a specifically adsorbed organic substance
Authors: Krylov V. S. , Fishtik I. F.
Published: May 2006

The problem of an adequate statistical mechanical approach to the transition from the description of the elementary act of an electrochemical process occurring in the presence of electrochemically inactive specifically adsorbed species to the description of the resulting heterogeneous process for which the rate is measured in experiments is discussed. The analysis of the electrode kinetics is given for the particular case where the irreversible electron transfer reaction at the metal/solution takes place in the presence of a fixed discrete layer of specifically adsorbed dipole molecules. The theoretical results are compared with the available experimental data on the influence of adsorbed organic substances on the electrochemical reaction rate.
Microscopic modelling of adsorption and the generalised surface layer hypothesis
Authors: Sangaranarayanan M. V. , Rangarajan S. K.
Published: May 2006

Two- and three-state models for the adsorption of organic compounds at the electrode/electrolyte interface are proposed. Different size requirements, if any, for the neutral molecule and the adsorbing solvent are also considered. It is shown how the empirical, generalised surface layer (GSL) relationship (between the potential difference and the electrode charge) formulated by Damaskin et al. can be understood at the molecular level.
Oxidation of hydrocarbons. X. Concerning the formation of ketols and diones during the oxidation of alkenes by permanganate ion
Authors: Lee Donald G. , Srinivasan N. S.
Published: May 2006

The oxidation of E-5-decene by potassium permanganate in slightly acidic aqueous acetone solutions has been studied. An analysis of the reaction mixture at various time intervals indicates that the ketol, 5-hydroxy-6-decanone, is the initially formed product under these conditions. The other major product, 5,6-decanedione, is formed sequentially from oxidation of the ketol rather than directly from the alkene.
Effect of bis(acetylacetonato) copper(II) catalyst on the reaction of benzoylphenyldiazomethane with primary amines. A novel example of insertion of benzoylphenylcarbene into N—H bonds of amines
Authors: Singh S. B. , Mehrotra K. N.
Published: May 2006

Bis(acetylacetonato) copper(II) catalysed thermal decomposition of benzoylphenyldiazomethane (1) leads to the insertion of benzoylphenylcarbene into the N—H bond of amines; the insertion products undergo facile air oxidation giving rise to ketoimines. The uncatalysed thermal decomposition of benzoylphenyldiazomethane yields the corresponding diphenylacetamide derivatives of amines.
Ozonolysis of substituted 1,2-dichloroethylenes in methanol: products and reaction course
Authors: Huh Tae-Seong , Neumeister Joachim , Griesbaum Karl
Published: May 2006

Ozonolysis of trans-2,3-dichloro-2-butene (5a), of trans-3,4-dichloro-3-hexene (5b), and of 1,2-dichlorocyclohexene in methanol and in solutions of sodium methoxide in methanol have been examined. They afforded in high yields the corresponding ester fragments methyl acetate (6a), methyl propionate (6b), and dimethyl adipate (8), respectively. By trapping with phenylacetylene and formation of 1,1-dichloro-2,2-dimethoxy-2-phenylethane, the presence of methyl hypochlorite in the ozonolysis products was established. A reaction course has been proposed which is in accord with these results.
Hydrogen–deuterium exchange and rearrangement of polycyclic aromatic hydrocarbons in dilute acid medium at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

The high temperature – dilute acid (HTDA) method has been applied to the preparation of perdeuterated polycyclic aromatic hydrocarbons. Naphthalene (1), 1-methylnaphthalene (2), 2-methylnaphthalene (3), anthracene (4), phenanthrene (5), chrysene (6), pyrene (7), benz[a]anthracene (8), benzo[a]pyrene (9), 1,1′-binaphthyl (10), 1,2′-binaphthyl (11), and 2,2′-binaphthyl (12) have been perdeuterated in high yield in dilute DCl–D2O solutions at elevated temperatures (240–280 °C). 2, 3, 10, 11, and 12 also rearrange.
Mononuclear and binuclear copper(II) complexes of some polyfunctional pyridyl phthalazines
Authors: Bullock Graham , Hartstock Frederick W. , Thompson Laurence K.
Published: May 2006

Mononuclear and binuclear copper(II) complexes of the potentially tetradentate binucleating ligands 1,4-di(3′-methyl-2′-pyridyl)aminophthalazine (PAP3Me) and 1,4-di(5′-methyl-2′-pyridyl)aminophthalazine (PAP5Me) are reported. In the case of the ligand 1,4-di(4′,6′-dimethyl-2′-pyridyl)aminophthalazine (PAP46DiMe) only binuclear derivatives were obtained. The mononuclear complexes, involving protonated ligand, result from the sensitivity of these ligands to mildly acidic conditions in aqueous solutions of certain copper salts. Binuclear, neutral ligand, complexes are also formed when the pH increases. Hydroxy bridged binuclear structures exist in all the binuclear complexes described with the exception of one acetate bridged derivative. Sub normal magnetic moments are observed for all the binuclear complexes (< 1.74 BM) indicating spin coupled systems with very low values (< 0.88 BM) for binuclear complexes of PAP46DiMe, indicating the possibility of strong antiferromagnetic exchange between the metal centres.
Setchenow coefficients for naphthols by distribution method
Authors: Almeida M. Balón , Alvarez A. Maestre , Miguel E. Munoz De , Hoyo E. Soria Del
Published: May 2006

Salting constant measurements have been made on 1-naphthol, 2-naphthol, and 1-NO-2-naphthol using a distribution method at 298 K. In general, the order of the salting effect is similar to that for other acidic nonelectrolytes. However, a net salting-in is observed in the pair 1-NO-2-naphthol – NaF, and such an effect is interpreted by postulating hydrogen bonding. A comparison of results with those found for benzene, naphthalene, phenol, etc …, reveals that salt effects for organic nonelectrolytes depend upon the solute size for a given salt.Experimental ks are compared with those calculated using various salting theories. The agreement is not quantitative.
Conductimetric studies on aqueous solutions of electrolytes. I. Conductivities of copper sulphate
Authors: Acevedo Victor Hugo , Morán Juana Albarracín De , Sales Leopoldo Armando
Published: May 2006

The specific conductivities and pH values of copper sulphate solutions in water were measured in the temperature range from 10 °C to 50 °C. The data, previously corrected by hydrolysis, were analyzed by means of the Lee Wheaton theory.This fit, for the evaluation of Λ0, R, and KA parameters, is quite satisfactory up to a maximum concentration of 25 × 10−4 moldm−3 and the agreement between experimental data and the literature value for 25 °C is acceptable.
Additivity methods for estimating heats of vaporization of organic compounds
Authors: Guthrie J. Peter , Taylor Kathleen F.
Published: May 2006

Additivity methods for heats of vaporization of organic liquids have been developed using both bond and group additivity parameters. For the bond level parameters, 429 compounds could be fitted using 36 parameters, with a weighted standard deviation of 0.32 kcal/mol, and only 23 deviations of more than 1 kcal/mol. For the group level parameters, 388 compounds could be fitted using 57 parameters, with a weighted standard deviation of 0.19 kcal/mol, and only 7 deviations of more than 1 kcal/mol. The problem of correlation among parameters is discussed and the significant terms in the correlation matrix are given. The new parameters are compared to previous parameterization schemes.
Yields of products in the spontaneous fission of 252Cf by direct γ-ray spectroscopy
Authors: Toppare L. , Erten H. N. , Aras N. K.
Published: May 2006

Yields of products both in the light and heavy sides in the spontaneous fission of 252Cf were measured by direct γ-ray spectroscopy technique. By suitably choosing collection, cooling, and counting times, it was possible to observe products with half-lives between 1 min and 1 h. A definite fine structure, as observed in the case of thermal neutron fission of 235U and 239Pu, was not observed. A graphical method was utilized to obtain the number of neutrons as a function of fragment mass using cumulative chain yields.