bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen fluoride laser induced multiphoton decomposition of 2,2,2-trifluoroethanol
Authors: McAlpine Robert D. , Evans D. K. , Goodale J. W.
Published: May 2006

The HF laser-induced multiphoton decomposition (MPD) of 2,2,2-trifluoroethanol (TFE) was studied for two different "dog-bone" irradiation geometries using TFE pressures from 0.134 to 3.82 kPa. The depletion kinetics of TFE are first order in TFE pressure and the formation kinetics for several of the large number of products display pseudo-first order kinetics with pressure dependent stoichiometric ratios.Three different theoretical models for decomposition probability versus fluence were tested. All were integrated over a complex irradiation geometry and were found to predict equally well the number of decomposed TFE molecules to within a factor of 3 or 4 of the experimental result.
Diffusion with hydrolysis equilibria: transport coefficients of aqueous SO2, NH3, and Na2CO3
Authors: Leaist D. G.
Published: May 2006

Practical equations are derived for estimating diffusion coefficients and Onsager transport coefficients of aqueous solutes subject to hydrolysis. The derivation is based on the Nernst–Hartley method which is extended to include chemical reaction of solute with solvent. The derived equations and existing mobility data are used to estimate transport coefficients of aqueous SO2 (20 °C), NH3 (15 °C), and Na2CO3 (25 °C). In dilute solution where hydrolysis is extensive, rates of diffusion of SO2 and NH3 are increased by about 50% and 25%, respectively, relative to unhydrolyzed solute. Because of the carbonate–bicarbonate equilibrium, diffusion in aqueous Na2CO3 is a ternary process characterized by coupled transport of NaOH. In dilute solution the NaOH flux may exceed the flux of Na2CO3.
Open-chain nitrogen compounds. Part IV. Synthesis of 5-hydroxy-1,2,3-triazoles from 1-aryl-3-(ethoxycarbonylmethyl)triazenes: a new route to α-diazo-N-arylacetamides
Authors: Baines Kim. M. , Vaughan Keith , Hooper Donald L. , Leveck Lorne F.
Published: May 2006

A series of triazenes of type ArN=N—NH—CH2CO2Et, N-arylazoglycinc ethyl esters, have been prepared by coupling the arene diazonium salt, ArN2+•X−, with ethyl glycinate, NH2CH2CO2Et; an electron-withdrawing substituent, e.g. NO2, CN, CO2R, and Cl, in the ortho or para position of the aryl group is essential for efficient coupling. The p-substituted arylazoglycine ethyl esters cyclize when treated with alcoholic potassium hydroxide to afford the potassium salts of the 1-aryl-5-hydroxy-1,2,3-triazoles, which can be obtained free by acidification of the potassium salt solution with acetic acid. Reaction of the potassium salts with acetic anhydride yields the 1-aryl-5-acetoxy-1,2,3-triazoles. The5-hydroxytriazoles, when heated in ethanol, rearrange to α-diazoacetanilides, ArNH•COCHN2. The diazoamides can be obtained in low yield directly from the triazenes by prolonged refluxing in ethanol. o-Substituted aryltriazenes do not cyclize under the same conditions but fragment to the arylamine.
Reaction of methanethiol with species produced in a microwave discharge through water vapor
Authors: Chang C. H. , Goodfriend P. L. , Bentley M. D. , Anderegg R. J.
Published: May 2006

The products of reaction of methanethiol with species produced by passage of water vapor through a microwave discharge were studied. Mass spectrometric analysis demonstrated the presence of SO2. CH3SSCH3, CH3SSSCH3, CH3SSSSCH3, CH3SSCH2SCH3, CH3SCH2SCH3, and S8. These products are consistent with a mechanism involving abstraction of hydrogen from CH3SH by OH and other radicals as the important primary process.
Protecting groups for the pyrrole nitrogen atom. The 2-chloroethyl, 2-phenylsulfonylethyl, and related moieties
Authors: Gonzalez Carlos , Greenhouse Robert , Tallabs Ramon , Muchowski Joseph M.
Published: May 2006

The 2-chloroethyl and 2-phenylsulfonylethyl moieties are versatile protecting groups for the pyrrole nitrogen atom. The 2-chloroethyl group is easily attached under phase transfer conditions using 1,2-dichloroethane. The 2-phenylsulfonylethyl moiety is readily appended under both phase transfer and homogeneous solution conditions using 2-phenylsulfonylcthyl chloride 5. Deprotection of the N-(2-chloroethyl)pyrroles is accomplished by means of efficient three-step, one-pot sequences via the N-vinyl compounds 3 and subsequent degradation of the N-(1-hydroxyethyl) compounds 4 or the acctoxymercuration derivatives 5 obtained therefrom. The 2-phenylsulfonylethyl group is excised by a reverse Michael reaction using sodium hydride or DBN as the base.The utility of the 2-chloroethyl protecting group is exemplified in a synthesis of benzyl cyclopenta[b] |pyrrole-5-carboxylate 13 from 1-(2-chloroethyl)-4-oxotetrahydroindolc 2d.
Ionized ethylidene ketene and its homologue methylene ketene
Authors: Terlouw Johan K. , Holmes John L. , Lossing F. P.
Published: May 2006

The gas phase pyrolyses of crotonic and acrylic-trifluoroacetic anhydrides were shown to yield ethylidene ketene [CH3CH=C=C=O] and methylene ketene [CH2=C=C=O], respectively. The former was identified via the collisional activation mass spectrum of its molecular ion. The ionization energies of the two ketenes, 8.68 and 9.12 ± 0.05 eV respectively, measured using energy selected electrons, lead to 215 and 233 kcal mol−1 for their ionic heats of formation.
The metal nuclear magnetic resonance spectra of some tin(II) and lead(II) complexes with polydentate phosphines
Authors: Dean Philip A. W.
Published: May 2006

The previously reported 1:1 complexes formed in MeNO2, between M(SbF6)2 (M = Sn or Pb) and Ph2P(CH2)2PPh2, PhP[(CH2)2PPh2]2, MeC(CH2PPh2)3, P[(CH2)2PPh2]3, and [Formula: see text] have been studied by metal (119Sn or 207Pb) nmr. The metal chemical shifts span the comparatively narrow range of −586 to −792 ppm and 60 to −269 ppm, relative to the resonance of MMe4, for 119Sn and 207Pb nmr, respectively. The implications of these data regarding the denticity of the ligand in M(P[(CH2)2PPh2]3)2+ are discussed, and a comparison with the metal nmr spectra of related stannous and plumbous complexes is made.
La photolyse du cyclohexène gazeux à 184,9 nm
Authors: Collin Guy J. , Deslauriers Hélène
Published: May 2006

We have studied the 184.9 nm photolysis of gaseous cyclohexene either in the absence or in the presence of radical scavengers such as O2, NO, H2S, or HI at pressures between 1 and 70 Torr. Propane or sulfur hexafluoride has also been used as stabilizing agent. In all cases, ethylene and 1,3-butadiene have rather high quantum yields (Ф ≥ 0.5). The isotopic analysis of the ethylene formed in the photolysis of cyclohexene-3,3,6,6-d4 shows the high importance of the perhydrogenated species. These results, together with others taken from the literature, favor a one-step fragmentation mechanism or a double-step mechanism involving an intermediate which has a lifetime shorter than that of the photoexcited molecule.
Hydroxyacetals, phthalans, and isobenzofurans therefrom
Authors: Keay Brian A. , Plaumann Heinz P. , Rajapaksa Dayananda , Rodrigo Russell
Published: May 2006

A general method for the generation of isobenzofuran intermediates is described. Lithiated aromatic acetals are converted to hydroxyacetals (A) which may be cyclized to isobenzofurans by mild acid treatment through the 1-hydroxyphthalans (B). The isobenzofurans generated insitu are trapped by a variety of dienophiles to provide the expected oxo-bicyclo adducts (C). The mass and 1Hmr spectra of B and C are discussed.
Nuclear analogs of (β-lactam antibiotics. XVIII. A short synthesis of 2-alkylthiocarbapen-2-em-3-carboxylate
Authors: Ueda Yasutsugu , Damas Christopher E. , Belleau Bernard
Published: May 2006

A short synthesis of (±)-2-alkylthiocarbapen-2-em-3-carboxylic acid (2) from sorbic acid via a key intermediate 4 is described.
2,2-Bis(ethylthio)ethanenitrile: preparation and use as a one or two carbon nucleophile
Authors: Bates Gordon S. , Ramaswamy S.
Published: May 2006

2,2-Bis(ethylthio)ethanenitrile 1 was prepared in high yield from 2,2-bis(ethylthio)ethanal 2. Alkylation of the potassium salt of 1 with various alkylating agents and conjugate addition to cyclic α,β-unsaturated ketones provided high yields of the alkylation products of 1. The potential one and two carbon chain extension capability of this new reagent has been demonstrated.
Induction periods in the formation of ethane from the pyrolysis of ethylene
Authors: MacKenzie Allan L. , Pacey Philip D. , Wimalasena Jayantha H.
Published: May 2006

Induction periods have been observed in the formation of C2H6 from C2H4 pyrolysis at 895 K and 23 to 78 Torr. The induction periods were interpreted as evidence of the approach to the steady-state concentration of radicals. The observed inverse pressure dependence of the induction periods was an indication that both chain initiation and termination were bimolecular. Taking the termination rate constant as 1.3 × 1010 L mol−1 s−l and neglecting autocatalysis, for the most likely initiation reaction,[Formula: see text]the rate constant was found to be 2.3 × 10−4 L mol−1 s−l. Assuming further that termination is dominated by recombination and disproportionation of C2H5, the rate constant for[Formula: see text]was found to be 8 × 104 L mol−1 s−1.
Concerning the orientation in free radical additions to olefins
Authors: Poblet Josep M. , Canadell Enric , Sordo Tomás
Published: May 2006

On the basis of MNDO, MINDO/3, and STO-3G calculations, the regioselectivity of radical additions to substituted olefins is rationalized in terms of an electronic effect.
Dielectric relaxation processes of some dialkyl disulfides
Authors: Khwaja H. A. , Walker S.
Published: May 2006

Dielectric relaxation studies have been performed for dimethyl, diethyl, di-isopropyl, di-n-butyl, di-tert-butyl, and di-n-octyl disulfides in a polystyrene matrix. For the last five compounds the absorption appears in two temperature regions. The relaxation data for the higher temperature regions are consistent with intramolecular rotation around the S—S bond with accompanying flexibility in the alkyl chains. The enthalpy barrier to this relaxation process is ~29 kJ mol−1 and is the trans (lower) barrier. This value is typical for all six dialkyl disulfides. The most likely interpretation of the low temperature process is that there is segmental relaxation of the alkyl chains which also involves movement of the main dipoles (S—S and S—C).
Synthèse et thermolyse de vinyl-2 aziridines N-non substituées
Authors: Attia Mohamed El Mekki , Gelas-Mialhe Yvonne , Vessiere Roger
Published: May 2006

N-unsubstituted 2-vinylaziridines are prepared from N-unsubstituted 2-acylaziridines and phosphoranes. Their stereochemistry is established from a study of their nmr spectra. Thermal isomerization of these compounds gives imines by a reaction involving hetcrolytic cleavage of the carbon–carbon bond of the ring and migration of hydrogen initially bound to nitrogen.
Chalcogenide esters as reactive intermediates in selenium and tellurium purifications
Authors: Badesha Santokh S. , Monczka Paul , Smith Steven D.
Published: May 2006

This paper describes a novel application of chalcogenide esters to purify selenium and tellurium to the 99.999% purity level. The chalcogenide esters were prepared from a variety of source materials which include: crude selenium and tellurium and commercial grade selenium dioxide, tellurium dioxide, and selenous acid. Crude selenium and tellurium were first converted to their respective oxides by treatment with concentrated nitric acid. The oxides were condensed with alcohols or diols to obtain the corresponding esters which, on reduction with hydrazine in organic media, provided high purity elemental selenium and tellurium.
The synthesis of cofacial porphyrin dimers
Authors: Hiom John , Paine III John B. , Zapf Udo , Dolphin David
Published: May 2006

A cofacial dimeric porphyrin joined by two hydrocarbon chains has been prepared using a bis-porphyrin already linked by a single hydrocarbon chain. When each porphyrin bears an acetylenic group, copper catalyzed coupling followed by catalytic hydrogenation gives a doubly linked cofacial porphyrin. However, a far superior and more flexible route, involving the use of a dimeric biladiene-ac, gives in one step the same cofacial porphyrin. This latter route has been used to prepare dimeric porphyrins with hydrocarbon linkages of varying lengths.
Nuclear analogs of β-lactam antibiotics. XIX. Syntheses of racemic and enantiomeric p-nitrobenzyl carbapen-2-em-3-carboxylates
Authors: Ueda Yasutsugu , Damas Christopher E. , Vinet Vivianne
Published: May 2006

Racemic and enantiomeric p-nitrobenzyl carbapen-2-em-3-carboxylates 3, 3a, and 3b were prepared starting from inexpensive sorbic acid through the key intermediates, azetidinone esters 4, thus establishing a total synthesis of the p-nitrobenzyl ester of a natural product SQ 27,860. Optical resolution was achieved readily on azetidinone menthyl esters, 12. The absolute configurations were also established.
Low frequency vibrational spectra of lithium formate monohydrate and its aqueous solutions
Authors: Agarwal A. , Khandelwal D. P. , Bist H. D.
Published: May 2006

The far infrared and Raman spectra of polyerystalline lithium formate monohydrate and the Rayleigh wing scattering of its aqueous solutions are reported. Three new bands in solid and bands due to librations of HCOO− and the quasi-tetrahedral structure of water in solutions have been identified.
1,n-Radical ions: the nature of the one-electron two-centre bond in cyclopropane radical cations. An abinitio SCF MO approach
Authors: Wayner Danial D. M. , Boyd Russell J. , Arnold Donald R.
Published: May 2006

The nature of the one-electron two-centre bond in the cyclopropane and 1,2-divinylcyclopropane radical cations is elucidated by use of abinitio self consistent field (SCF) molecular orbital (MO) calculations. The charge and spin distributions in the 90,90 and 90,0 conformations are compared at the STO-3G and 4-31G basis set levels. From energy differences between the radical cations in the 90,90 conformation and the 90,0 (transition state) conformation, the activation barriers for cis–trans isomerization in the 2A1 state of C3H6,+ and of the 1,2-divinylcyclopropane radical cation are estimated. These results are compared to previous calculations and experimental data where possible.
Laser interferometric galvanostatic studies in the Zn/ZnSO4/Zn system with gelled electrolyte short time electrolysis
Authors: O'Brien R. N. , Michalik W.
Published: May 2006

Electrolysis in the system Zn/ZnSO4/Zn with gelled electrolyte was followed for short times to allow use of the first term only of the solution to Fick's Second Law for transient conditions. Sufficiently good agreement was found between theory and experiment to confirm that no convection occurred in the gelled electrolyte. Similarly sufficiently good agreement with liquid electrolyte runs confirmed that no convection occurred in parallel plate, horizontal electrodes when the cathode was over the anode. The conductivity of the gelled electrolyte was about 11% lower than the liquid electrolyte.
Substituent-induced chemical shifts in 3- and 4-substituted styrenes: factor analysis of the styrene data matrix
Authors: Reynolds William F. , Gomes Anabela , Maron Antonina , MacIntyre Douglas W. , Maunder Robert G. , Tanin Ates , Wong Hector E. , Hamer Gordon K. , Peat Ian R.
Published: May 2006

The techniques of factor analysis are used to investigate a data matrix constructed from magnetic resonance parameters for seventy-five 4-substituted styrenes, α-methylstyrenes, and α-tert-butylstyrenes and 3-substituted styrenes and α-methylstyrenes (with fifteen common substituents for each series). Two substituent factors (parameters) are clearly both necessary and sufficient to predict long-range chemical shifts within experimental uncertainty. Target testing indicates that Taft's σ1 and [Formula: see text] constants are appropriate for this purpose. One additional major factor is required for each of ipso and ortho carbons and a minor factor is apparently required for meta carbons.Conclusions do not appear to be sensitive to the weighting of individual variables and the specific variables included in the data matrix. However, the use of an extensive and well-chosen substituent set is essential.
Ozonolysis of vinyl chloride in methanol: a convenient entry to methoxymethylhydroperoxide and its chemistry
Authors: Meister Martin , Zwick Gerhard , Griesbaum Karl
Published: May 2006

Ozonolysis of vinyl chloride (7) in methanol at −78 °C afforded methoxymethylhydroperoxide (10) in high yield along with only trace amounts of methyl formate (14). The former (10) was converted into a mixture of methyl formate (14) as the major and dimethylformal (18) as the minor product by HCl-catalysis in methanol. Reduction of 10 with dimethylsulfide and subsequent treatment with HCl–methanol gave dimethylformal (18). Partial reduction of 10 with a deficient amount of triphenylphosphine gave formaldehyde hemiacetal (19) and methoxymethylhydroxymethylperoxide (20).
Pyrrole chemistry. XXVI. A synthesis of porphobilinogen from pyrrole
Authors: Demopoulos Basil J. , Anderson Hugh J. , Loader Charles E. , Faber Kurt
Published: May 2006

A synthetic strategy has been developed which enables pyrrole to be used as the starting material for the synthesis of 2,3,4-trisubstituted pyrroles of the type used to construct porphyrins. The total synthesis of porphobilinogen has been accomplished as a demonstration of the applicability of the approach.
A model for estimating 59Co nmr chemical shifts and line widths and its application to cobalt dioxygen complexes
Authors: Au-Yeung Steve C. F. , Eaton Donald R.
Published: May 2006

A simple point charge model has been developed for calculating the chemical shifts and line widths obtained from the 59Co nmr spectra of Co(III) complexes. The chemical shift calculations assume the predominance of the paramagnetic term in the Ramsey equation and the relationship of this term to the energies of the d–d electronic transitions. The line width calculations assume the predominance of quadrupolar broadening and use a point charge model to calculate electric field gradients in a manner previously used to interpret Mössbauer spectra. The model is tested by application to some fifty known Co(III) complexes. Most of the 59Co spectra have been remeasured for this purpose. One chemical shift parameter and one line width parameter are required for each different type of ligand. These parameters are related to each other and to the crystal field splitting parameters of the ligands. The calculations can be readily applied to complexes of any symmetry and differentiate between different isomers of the same complex. The calculated chemical shifts cover a range of more than 14 000 ppm and the standard deviation between the calculated and experimental values is 108 ppm. Relative chemical shifts between complexes with similar ligands are calculated with considerably higher accuracy. The agreement between calculated and experimental line widths is only qualitative but the line width calculations provide valuable additional information for making assignments. The model is applied to the assignment of different isomers of cobalt dioxygen compounds and to the identification of products from oxygenation reactions.
Enamines of 2,2-bis(ethylthio)ethanal: a convenient route to γ-keto crotonate derivatives
Authors: Bates Gordon S. , Ramaswamy S.
Published: May 2006

A new α-oxoaldehyde reagent, 2,2-bis(ethylthio)ethanal 1, has been prepared in high yield from ethanedial. Alkylation of the potassium salt of the enamines of 1 with various alkylating agents followed by insitu hydrolysis of the intermediate imine afforded high yields of the alkylation products of 1. This new reagent was used in the synthesis of a chiral potential precursor of the macrocyclic fragment of cytochalasins A, B, and F, as well as in the syntheses of the physiologically active diolides pyrenophorin and norpyrenophorin.
1,3,8-Trimethylxanthine complexes of Cu(II), Zn(II), Cd(II), and Hg(II)
Authors: Colacio-Rodriguez E. , Lopez-Gonzalez J. D. , Salas-Peregrin J. M.
Published: May 2006

New 1,3,8-trimethylxanthine complexes of Cu(II), Zn(II), Cd(II), and Hg(II) were prepared and studied by ir, H-nmr, magnetic measurements, TG, and DSC techniques. In the Cu(II), Zn(II), and Cd(II) complexes, the 1,3,8-trimethylxanthine is present in anionic form and the coordination to metal ion occurs probably through N7 atom. In the mercury complex, coordination to metal ion is realized via the N9 atom of neutral TMH.
The alkaloids of Seneciotriangularis Hook
Authors: Rüeger H. , Benn M. H.
Published: May 2006

Pyrrolizidine alkaloids were isolated from Seneciotriangularis Hook, growing in Alberta, and identified as 7-angelylretronecine, 7-senecioylretronecine, 7-angelyl-9-sarracinylretronecine, and 7-senecioyl-9-sarracinylretronecine, the last three of which appear to be new natural products.
Hydride transfer reactions. Substituent effects in oxidation of N-benzylacridans by π acceptors
Authors: Colter Allan K. , Lai Charles C. , Williamson Terry W. , Berry Raymond E.
Published: May 2006

The kinetics of oxidation of a series of eight N-(substituted benzyl)acridans (3, NBA's) by 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN) and by BQ in 50:50 (v/v) AN-water were measured at 25 °C. Equilibrium constants for pseudobase formation, [Formula: see text], from the corresponding acridinium ions (4) were measured in water at 25 °C. Hammett correlations of the second-order rate constants for reaction of the NBA's without ortho substitutents (3a–e) led to ρ values of −0.29 (BQ, AN), −0.55 (CA), −0.56 (DCBQ), −0.64 (TCNQ), −0.41 (TCNE), and −0.47 (BQ, 50:50 AN–water). The second-order rate constants for 3a–e also give good linear free energy correlations with the [Formula: see text] values of 4a–e. These correlations and the [Formula: see text] values for the ortho-substituted acridinium ions (4f, g, h) are used to calculate rate constants for oxidation of the corresponding ortho-substituted NBA's (3f, g, h). The rate constants calculated in this way are 4.7 to 6.6 times and 6.4 to 12 times larger, respectively, than the observed rate constants for N-(2,4,6-trimethylbenzyl) and N-(2,6-dichlorobenzyl)acridan (3g and h). The variations in ρ values are attributed mainly to differences in the amount of electrostatic stabilization in the transition state resulting from differences in the separation of donor and acceptor and the degree of delocalization of the negative charge. The rate retarding effect of a pair of ortho substituents is attributed to sterie effects in a preferred face-to-face transition state.
Hydrazines et hydrazones hétérocycliques. IV. Synthèses de dérivés de l'hydrazine dans la série des imidazo[4,5-d] pyridazinones-4
Authors: Beljean-Leymarie Martine , Pays Michel , Richer Jean-Claude
Published: May 2006

We report the syntheses of 5-alkyl or 5-aryl-3,5-dihydro[4,5-d]imidazo-4-pyridazinones (or the 1,5-dihydro derivatives) from the corresponding diaminopyridazinones. The methylation of 5-alkyl or 5-aryl-2-mercapto-3,5 (or 1,5)-dihydro [4,5-d]imidazo-4-pyridazinones leads to mixtures of 5-alkyl or 5-aryl-1 methyl-2-methylthio-3,5 (1,5)-dihydro[4,5-d]imidazo-4-pyridazinones and 5-alkyl or 5-aryl-3-methyl-2-methylthio-3,5 (or 1,5)-dihydro[4,5-d]imidazo-4-pyridazinones whose structures have been established by the Overhauser effect. These [4,5-d]imidazo-4-pyridazinones are used for the syntheses of hydrazines and hydrozones. The mass spectra of several key intermediates are presented and discussed. [Journal translation]
Structure of the principal antineoplastic glycosides of Phyllanthusacuminatus Vahl
Authors: Pettit George R. , Cragg Gordon M. , Niven Margaret L. , Nassimbeni Luigi R.
Published: May 2006

A series of degradative and X-ray crystallographic studies has led to unequivocal evidence for the structure (3a) assigned to the unique disaccharide phyllanthose. In turn, the X-ray crystal structure of phyllanthose confirms structures previously assigned to the potentially important antineoplastic plant glycosides phyllanthostatins 1 and 2 (1a, c) and phyllanthoside (1b). The chemical degradation and crystallographic analyses allowed assignment of structure 2a to phyllanthostatin 3.
Détermination cinétique de la nature du conformère réactif dans l'hydrolyse des orthoesters
Authors: Lamaty Gérard , Moreau Claude , Mouloungui Zéphirin
Published: May 2006

The rates of hydrolysis of the following orthoesters, 6 or 7-substituted 1,1-diethoxy 3,4-dihydrobenzo-2-pyrans (R = 6-MeO, H, 7-MeO, 7-NO2 and 6-NO2) were determined at 27 °C in water/dioxan (2:1 by volume). The catalytic rate constants as well as the Hammett ρ constants show that the rate-determining step is the formation of a cyclic carboxonium ion intermediate and constitute a kinetic piece of evidence for the determination of the nature of the reactive conformer in hydrolysis of 2,2-dialkoxy tetrahydropyran orthoesters.
The reactions of O(3P) with the butanols
Authors: Roscoe John M.
Published: May 2006

The reactions of O(3P) with the butanols were studied kinetically as a function of temperature and substrate concentration. The absolute rate constants for the gas phase reactions, in the units M−1 s−1, obey the following relations.[Formula: see text]The results suggest that although the α-CH bond in these alcohols is the most reactive one, reaction of O(3P) with other CH bonds in the alcohols is also appreciable. The kinetic data for these and other alcohols are separated into contributions from the different types of CH bonds and the results are discussed in terms of linear free energy relations.
Nitric oxide and oxygen reactions with 1-butene over manganese(III) oxide
Authors: Ross Robert Anderson , Fairbridge Craig
Published: May 2006

Reactions of 1-butene with nitric oxide from 623 to 723 K and with oxygen from 433 to 573 K have been studied in a differential flow system over manganese(III) oxide. Nitrous oxide was formed in the reaction of the hydrocarbon with nitric oxide along with products of complete combustion. The apparent activation energies were respectively 69 ± 4, 78 ± 4, and 30 ± 4 kJ mol−1 for nitrogen, carbon dioxide, and nitrous oxide reaction rates. The corresponding pre-exponential factors were 1.72 × 10−1 and 1.16 mol0.5 L−0.5 m2 g−1, and 1.99 × 10−2 mol−0.35 L0.35 m2 g−1. In the reaction with oxygen, apparent activation energies of 183 ± 4, 523 to 503 K, and 88 ± 4 kJ mol−1, 503 to 433 K, were determined with pre-exponential factors 1.74 × 1015 and 2.94 × 105 mol0.3 m−2 g−1. During catalysis the oxide underwent a partial phase change from α to γ in both reactions. Additionally, nitrate species were present on the surface after oxidation with nitric oxide. Kinetic expressions have been derived and mechanisms proposed for both reactions which may occur in emission control systems requiring the removal of NOx and unburned hydrocarbons.
Signs and mechanisms of 13C, 19F spin–spin coupling constants in benzotrifluoride and its derivatives
Authors: Schaefer Ted , Marat Kirk , Peeling James , Veregin Richard P.
Published: May 2006

The magnitudes of nJ(C, F) for n = 3, 4, 5 bonds are remeasured for benzotrifluoride. The signs of 2J(C, F) and 3J(C, F) are determined for 4-chloro-3,5-dinitrobenzotrifluoride and that of 5J(C, F) for 2-amino-3,5-dibromobenzotrifluoride. 4J(C, F) is not observable in these compounds. The contact contributions to nJ(C, F) are calculated for benzotrifluoride by INDO MO FPT. The long-range coupling constants are discussed in terms of the mechanisms which transmit nuclear spin state information. It seems that 5J(C, F) is a σ–π coupling, 4J(C, F) is a composite of a and σ–π components of opposite sign, and that 3J(C, F) has a Karplus behaviour modified by a σ–π contribution.
Crystal structure of diethylammonium tetrachloro(p-phenoxyphenyl)tellurate
Authors: Chadha Raj K. , Drake John E. , Khan Masood A.
Published: May 2006

The crystal structure of diethylammonium tetrachloro(p-phenoxyphenyl)tellurate has been determined by the heavy atom method. The crystals are monoclinic, space group C2/c, with unit cell dimensions a = 19.675(5), b = 7.634(3), c = 28.716(6) Å, β = 105.58(2)°, and Z = 8. For 2636 "observed" reflections (I > 3σ(I)), R = 0.030. The primary geometry about tellurium is based on a square pyramid with a secondary interaction on the vacant side of the tellurium coordination octahedron. The ions are apparently linked by weak interionic hydrogen bonding along the crystallographic b axis.
Vinyl ether hydrolysis. XVII. Oxacyclonon-2,8-diene and the question of the unorthodox reaction mechanism for 9-methoxyoxacyclonon-2-ene
Authors: Burt R. A. , Chiang Y. , Kresge A. J. , Szilagyi S.
Published: May 2006

The acid-catalyzed hydrolysis of the nine-membered ring cyclic vinyl ether, oxacyclonon-2,8-diene, occurs with a normal isotope effect, [Formula: see text], which indicates that this reaction proceeds by the conventional vinyl ether hydrolysis mechanism involving rate-determining proton transfer to carbon. The specific rate of this reaction, [Formula: see text], may then be used to show that there is no significant ring-size effect on the rate of hydrolysis of a vinyl ether group in a nine-membered ring. The previously noted unusually great reactivity of the vinyl ether group in 9-methoxyoxacyclonon-2-ene, for which an unorthodox reaction mechanism has been claimed, must therefore be due to some other cause.
Enzymes in organic synthesis. 30. Reaction conditions – control of enantiomeric purities. Horse liver alcohol dehydrogenase-catalyzed reductions of 2-alkylcyclohexanones and their thiopyran analogs
Authors: Jones J. Bryan , Takemura Tetsuo
Published: May 2006

The effects of buffer, pH, reaction time, and [enzyme]/[substrate] ratio on the enantiomeric purities of the alcohol products of horse liver alcohol dehydrogenase-catalyzed reductions of (±)-α-alkylcyclohexanones and -tetrahydrothiopyranones have been studied. For poor substrates of this type, formation of enantiomerically pure products is assured when pH 8 and < 0.5 × 10−4 [E]/[S] ratio conditions are used.
Oxidation ot sultur compounds. I. The photolysis of CH3SH and (CH3S)2 in the presence of NO
Authors: Balla R. Jeffrey , Heicklen Julian
Published: May 2006

Both CH3SH and (CH3S)2, as well as their mixtures, were photolyzed in the presence of NO at 23 ± 1 °C. The photolyses were carried out in a 631 mL quartz vessel with a pinhole bleed to a quadrupole mass spectrometer for continual analysis of products. After the termination of exposure, further product analysis was made by gas chromatography.The identified products of the reaction were CH3SNO, (CH3S)2, H2, and N2. Hydrogen atoms, formed from the photolysis of CH3SH, reacted with both NO and CH3SH:[Formula: see text]with k5/k4 = 626 ± 42 Torr for NO as a chaperone. The CH3S radical adds to NO[Formula: see text]with k−2a/k2b = 83 ± 52 Torr. As the CH3SNO accumulates, CH3S also reacts with CH3SNO[Formula: see text]with [Formula: see text]. At high NO pressures a chain process occurs which is attributed to:[Formula: see text]where ξ is probably 4.0. Termination is most easily represented by[Formula: see text]with k8/k7 = 85.0 ± 7.8 Torr
The importance of the σ*–π* orbital mixing for the nucleophilic displacement on the unsaturated carbon
Authors: Yamabe Shinichi , Minato Tsutomu , Kawabata Yumi
Published: May 2006

The reactivity of carbonyl and aromatic compounds for the nucleophilic displacement is investigated theoretically. LUMO (lowest unoccupied MO) obtained by the mixing of the π* MO with the σ* MO is a uniform criterion of the relative reactivity of substrates. The presence or absence of the tetrahedral intermediate is found to depend on the energy difference between the π* and σ* MO's.
Relative rates of radical–radical processes in the pyrolysis of ethane
Authors: Pacey Philip D. , Wimalasena Jayantha H.
Published: May 2006

Ethane has been pyrolysed in a flow system at 900 to 963 K, at residence times from 0.5 to 50 s and with [C2H6] from 1 × 10−4 to 4 × 10−3 mol L−1. From measurements of yields of minor products at 902 K, it is concluded that the combination reaction, [5a], and disproportionation reaction, [5b], of C2H5 radicals have the rate constant ratio, k5b/k5a = 0.44 ± 0.07. It is suggested that this ratio has a curved Arrhenius plot, which is interpreted in terms of activated complex theory. The cross-combination of CH3 and C2H5 radicals becomes significant at low pressures, reaching 1.5% of the sum of the rates of [5a] and, [5b] when [C2H6] = 10−3 mol L−1 at 902 K. With [C2H6] = 10−4 mol L−1 at 963 K, the yield of CH4 was greater in the presence of an SiO2 surface than in the presence of a PbO surface, consistent with the occurrence of the atom-cracking reaction,[Formula: see text]at 15% of the combined rates of [5a] and [5b]. Rate parameters are also reported for the C—C scission in C2H6, for the abstraction of H from C2H6 by CH3, for the decomposition of C2H5, and for the reaction of C2H5 at PbO surfaces.
Photochemistry of alkyl esters of benzoylformic acid
Authors: Encinas M. V. , Lissi E. A. , Zanocco A. , Stewart L. C. , Scaiano J. C.
Published: May 2006

The photodecomposition of several alkylbenzoylformates has been examined using quantum yield and laser flash photolysis techniques. The Norrish Type II reaction is a major triplet deactivation path in all substrates having γ-hydrogen atoms. Representative triplet lifetimes are 670, 500, and 310 ns, for the methyl, ethyl, and isopropyl esters, respectively, in 1:4 chlorobenzene: n-heptane at 298 K. Product studies suggest that several competing reactions are involved in the decay of the 1,4-biradical; some of these lead to highly absorbing (and presumably quenching) products, that make it essential to extrapolate quantum yields to "zero conversion" conditions.
On the structure of the adduct from the aluminium chloride catalyzed Diels–Alder reaction of 2-methyl-2-cyclohexenone with isoprene
Authors: Das Jagabandhu , Valenta Zdenek , Liu Hsing-Jang , Ngooi Teng Ko
Published: May 2006

An unequivocal correlation of keto ester 3 and the adduct obtained from the aluminium chloride catalyzed Diels–Alder reaction of 2-methyl-2-cyclohexenone with isoprene confirms the structure of the adduct to be 2.
Thermodynamics of solution of gypsum and anhydrite in water over a wide temperature range
Authors: Corti Horacio R. , Fernandez-Prini Roberto
Published: May 2006

The solubility of calcium sulphate in water at different temperatures is important for the description of chemical processes occurring in heat exchangers as well as in geothermal processes. Great discrepancies have been reported between experimental and predicted solubilities at high temperature and the transition temperature for the phase transition process (gypsum → anhydrite) is ill-defined.We have analyzed the available data for the solubility of calcium sulphate in water with no added electrolyte. Ion-pairing has been taken into account to calculate the standard thermodynamic properties of the solution process.It is found that the solubility data for gypsum and anhydrite are thermodynamically very consistent. It is possible to obtain the thermodynamic properties of the phase transition from solution data and, at 298.15 K and 101.325 kPa, they are in very good agreement with reported values from measurements with the pure phases. The transition temperature is calculated to be 315.7 ± 0.4 K.It is also shown that the experimental data agree with values predicted for high temperature by employing well-established methods of calculation of solution thermodynamic properties (e.g., principles of correspondence and of constant charge).
Membrane transport systems. V. Coupled countertransport of alkaline earth cations and protons
Authors: Dulyea Lynn M. , Fyles Thomas M. , Whitfield Dennis M.
Published: May 2006

The extraction and transport of alkaline earth cations from a basic to an acidic solution across an artificial membrane by crown ether carboxylic acids are reported. Monocarboxylate carriers achieve the transport via 2:1 complexes or by ternary complexes in the presence of readily extractible anions, while dicarboxylate carriers transport cations as 1: 1 complexes. Both types of carrier exhibit two regimes of kinetic behaviour depending on the relative concentrations of the carrier and the metal ion: a zero order regime in which the rate depends only on the carrier concentration, and a reversible consecutive first order regime in which the rate depends only on the metal ion concentration. In the former, the rate of adsorption of the carrier on the interface is presumed to be rate limiting while in the latter, the diffusion of metal ion to the interface is rate limiting. Carrier structure exerts a general influence over both the rate and selectivity of transport but this influence varies with the kinetic regime considered.
Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids
Authors: Fyles Thomas M. , Whitfield Dennis M.
Published: May 2006

The complexation of alkali metal and alkaline earth cations by crown ether carboxylic acids has been studied by potentiometric titration and by infrared and nuclear magnetic resonance spectroscopy. Complexation in methanol–water solution is governed by the electrostatic interactions between the cation and the carboxylate, hence discrimination among cations on the basis of ionic radius is poor. The isomers syn and anti (8NH)218-6A2 exhibit differing complexation behaviour towards cations with the anti isomer giving the stronger complexes. Interaction between the carboxylates across the face of the macrocycle of syn (8NH)218-6A2 can be inferred from the potentiometric data. Combined infrared and nuclear magnetic resonance studies of the complexes in chloroform solution show that the cation is held as an asymmetric tight ion pair with the carboxylate. The dimeric salt (4NH18-6)2Ca exhibits both a tight and a symmetric or loose ion pair between the cation and the two carboxylates. The substituents on the macrocycle are pseudoaxially disposed and in some cases gauche ethylenedioxy units can be recognized from the spectra. The complexes are monomeric in solution and in most cases the conformations are unaffected by small amounts of water in the chloroform solution. The structural results correlate with observations from transport experiments.
Structural studies of organoboron compounds. XIX. 1,7-Dimethyl-3,5-diphenyl-2,4,6-trioxa-7-aza-1-azonia-3-bora-5-boratabicyclo[3.3.0]octane
Authors: Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of 1,7-dimethyl-3,5-diphenyl-2,4,6-trioxa-7-aza-1-azonia-3-bora-5-boratabicyclo[3.3.0]octane are triclinic, a = 10.559(2), b = 15.156(3), c = 10.338(2) Å, α = 99.14(1), β = 89.90(1), γ = 96.73(1)°, Z = 4, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.032 and Rw = 0.038 for 2396 reflections with I ≥ 3σ(I). The structure consists of two crystallographically independent, but virtually identical, molecules containing sterically lengthened N—B coordinative bonds (mean 1.740(3) Å). The structurally inequivalent (in the solid state) pairs of N-methyl and B-phenyl groups are observed by variable temperature 1H nmr to be magnetically equivalent in solution, implying a rapid interconversion of "valence tautomers" at temperatures down to −60 °C.
Intramolecular alkylation of cyclopentenones: a general route to conjoint ring systems
Authors: Antczak Kazimierz , Kingston John F. , Alward Sandra J. , Fallis Alex G.
Published: May 2006

The intramolecular alkylation of several bromo- and epoxy-2-methylcyclopentenones, 18–23 and 33, are described. In all cases, except 33, alkylative cyclization occurs at the γ′ position to the conjoint ring systems 25–31. The "blocked" bromide 33 (γ′ geminal dimethyl substituent) cyclizes to the fused ring hydrindenones 35 and/or 34 depending upon conditions. Enolateanion generation from 3-ethyl-2-methyl-2-cyclopentenone (36) with various bases (KH, LDA, Et3N) is described and the anion populations determined by quenching with chlorotrimethylsilane to afford the enol ethers 39–41. The intramolecular alkylations are discussed.
Synthesis and properties of a series of linked porphyrin–quinone molecules designed as models of the reaction centre in photosynthesis
Authors: Ho Te-Fu , McIntosh Alan R. , Weedon Alan C.
Published: May 2006

The synthesis of the covalently linked porphyrin–quinone compounds 4a, 4b, and 4c is described. The structures of the linked compounds and their precursors in the synthetic route are established by ultraviolet/visible absorption spectroscopy, 1H nmr, ir, and mass spectroscopy. Some of the photophysical properties of the compounds prepared are reported with reference to their use as models of the reaction centre in photosynthesis.
Excess heat capacities and excess volumes of tetraalkyltin compounds: . Effect of correlations of molecular orientations and steric hindrance. Part 1
Authors: Riedl Bernard , Delmas Geneviève
Published: May 2006

A Picker flow calorimeter has been used to obtain molar excess capacities [Formula: see text] through the concentration range at 25 °C for the systems [Formula: see text] where R is the alkyl group CnH2n+1, (n = 1, 2, 3, 4, 8, 12). Excess volumes have also been measured for the mixtures. Two contributions to [Formula: see text] and vE were investigated: those associated with disordering the long alkyl chains and with steric hindrance. The steric hindrance contribution has been found to occur for molecules having a highly substituted central atom. The sign of this contribution is negative in hE and positive in [Formula: see text], indicative of an ordering or loss of mobility for the molecules going from pure liquid to solution. The [Formula: see text] results confirm the more sterically hindered character of the ethyl and propyl derivatives already found with hE. The separation of the disorder and steric contribution is possible in systems involving long-chain compounds. It is found that the orientational order contribution diminishes more slowly with temperature than the steric hindrance effect. The trend of vE in the series is reasonably well predicted by the Prigogine–Patterson–Flory theory.
Electrochemical reduction of quinoxalino[2,3-b]quinoxaline: a revised mechanism
Authors: Armand Joseph , Boulares Line , Bellec Christian , Bois Claudette , Philoche-Levisalles Michèle , Pinson Jean
Published: May 2006

The electrochemical reduction of fluoflavine 2 gives compound 9 to which we had previously assigned a hexahydroquinoxalino[2,3-b]quinoxaline structure. A crystallographic study of a diacetylated derivative of 9 shows that 9 is in fact 2-(o-aminoanilinomethyl)benzimidazole. This result permits us to propose a detailed reduction mechanism for 2 and its diacetyl derivative 25.
Hydrolysis of trioxaadamantane ortho esters. I. Dialkoxycarbocation – ortho ester equilibrium and acidity function
Authors: McClelland Robert A. , Lam Patrick W. K.
Published: May 2006

3-Aryl-2,4,10-trioxaadamantane ortho esters (T) undergo a rapid equilibration with a ring-opened dioxan-2-ylium ion (DH+) prior to hydrolysis to product (a 1,3,5-cyclohexanetriol monobenzoate). The cation is stable in concentrated H2SO4 solutions where it has been characterized by nmr spectroscopy. It is observed using uv spectroscopy in dilute acids, and the ratio [DH+]/[T] at equilibrium has been measured as a function of acidity. Reversibility of the ring opening is established by the pattern of plots of cation absorbance versus acid concentration and by the observation that solutions containing cation on neutralization or dilution yield ortho ester, not hydrolysis product. Equilibrium constants for the reaction [Formula: see text] have been measured by obtaining the acidity function HT for this system. The effects of the aromatic substituent and the steepness of the acidity function plot versus acid concentration are interpreted in terms of a strong intramolecular interaction in the cation between the cationic center and the hydroxyl oxygen.
Etude de la dissolution du bromure cuivreux formé sur le cuivre
Authors: Brossard Robert-Louis
Published: May 2006

The dissolution of cuprous bromide, formed by the electrochemical oxidation of copper immersed in aqueous NaBr, has been studied. NaBr concentration was varied between 0.1 and 1.2 M at pH 4. The corrosion product accumulating on the electrode is crystalline γ-CuBr. The presence of this material contributes to the local enrichment of dissolved copper close to the electrode. This enrichment leads to a characteristic electrode voltage in open circuit, which is about −149 mV (ECS) at a stationary electrode immersed in a solution of 0.2 M NaBr. The complete dissolution of CuBr coincides with a rapid fall in voltage which permits the definition of the transition time τ from which the speed of CuBr dissolution has been calculated. For example, the speed of dissolution is 0.074 ± 0.003 mA cm−2 in a current equivalent for a stationary electrode in the presence of a non-stirred solution of 0.2 M NaBr. This is constant until the complete disappearance of the CuBr. On the other hand, use of a rotating disc electrode demonstrates that the dissolution is entirely dominated by the diffusion of ions in the liquid phase. The experimental results are compatible with the simultaneous presence of [Formula: see text] and [Formula: see text] as diffusing species. Finally, the potentiodynamic polarization curves show two oxidation waves. A non-negligible portion of the dissolution current, if not almost all, is associated with the formation of CuBr as the sole corrosion product on the electrode. [Journal translation]
Intermediates from ring-opening reactions. Reactions of 2-chloro-5-nitropyridine and 2-chloro-3-nitropyridine with deuteroxide ion in selected solvents
Authors: Reinheimer John D. , Sourbatis Nicolas , Lavallee Robert L. , Goodwin Douglas , Gould George L.
Published: May 2006

Open chain intermediates from the ring-opening reaction of aqueous sodium deuteroxide (2 mol) with 2-chloro-5-nitropyridine (1 mol) and 2-chloro-3-nitropyridine (1 mol) were isolated. These intermediates were purified, analyzed for elemental composition, and characterized by various spectrophotometric techniques. The intermediate formed from 2-chloro-5-nitropyridine and two equivalents of deuteroxide ion reacts with additional deuteroxide in D2O in various polar solvents to reclose the pyridine ring. The kinetics of the ring closure reaction are reported and are supplemented with observations of salt and solvent effects upon the rate of closure. In addition, a mechanism for the ring closure is presented. The intermediate formed from 2-chloro-3-nitropyridine did not undergo a similar ring closure when reacted with additional deuteroxide, but instead formed various decomposition products. A reason for the failure of this ring closure is suggested.
The electron paramagnetic resonance spectrum of S3N2+
Authors: Fairhurst Shirley A. , Preston Keith F. , Sutcliffe Leslie H.
Published: May 2006

The epr spectrum of a persistent sulfur nitride radical cation, common to the oxidation of many sulphur–nitrogen compounds, has been obtained from materials highly enriched in both 15N and 33S. Analyses of solution and frozen spectra show that the carrier is planar S3N2+ and that its ground state is 2A2 in C2v. symmetry.