bluuebunny/crossref_metadata_2025 huggingface dataset:
A kinetic study of the H2O2-accelerated formation of o-nitrophenol from o-dinitrobenzene
Authors: Heller Raymond A. , Fewster Marilyn , Lambert Tayler
Published: May 2006

At 30 °C in 50% v/v dioxane in water, the reaction of o-dinitrobenzene with hydroxide ion to form o-nitrophenolate anion is very slow but it proceeds much more rapidly when H2O2 is also present. Although the phenolate product absorbs strongly in the visible region, standard kinetic analysis of the spectral data fails for both the peroxide-free and the peroxide-accelerated reactions. A more thorough examination of the spectral evidence reveals that, for the peroxide-accelerated reaction, a reasonably stable intermediate is first formed so that the overall reaction is in fact a two-step sequence. We have used a computer modelling technique to determine rate constants for the two steps and we find that both rate constants are dependent on [H2O2]. Several possible structures for the intermediate are discussed, with the radical anion being preferred.
High resolution HeI and HeII photoelectron spectra of the thallium halides: valence bands and Tl 5d ligand field splittings
Authors: Bancroft G. M. , Bristow D. J.
Published: May 2006

We report high resolution photoelectron spectra of both the valence bands and Tl 5d levels of the thallium halides (TlX; X = Cl, Br, I) in the gas phase. A transition state Xα-SW calculation on TlCl agrees with previous valence band assignments, although our calculated orbital characters are quite different from those reported previously. The calculated spin–orbit splitting of the 22II state in TlI is in good agreement with the observed value of 0.83 eV. Line width variations are rationalized considering the increase in covalency from TlCl to TlI, and variations in the slope of the excited state potential curve.Ligand field splitting of the Tl 5d level has been resolved in all three compounds. The observed values of the non-cubic part of the crystal field (C20) are: −0.0210 eV (TlCl), −0.0233 eV (TlBr), and −0.0258 eV (TlI). The above trend is due to the increasing covalency from TlCl to TlI, with a concomitant increase in the Tl 6p orbital population. Calculated C20 values are in good agreement with those observed. The configuration interaction structure in the Tl 5d region is explained qualitatively using Xα-SW calculations of two-hole valence band energies in TlCl.
Concerning the mechanism of in toluene and its derivatives
Authors: Schaefer Ted , Laatikainen Reino
Published: May 2006

On the basis of the observed five-bond spin–spin coupling constants between the α protons and the meta ring protons in the 2,6-difluoro derivatives of toluene, ethylbenzene, and cumene, it is argued that [Formula: see text] in toluene can be written as A[Formula: see text]. A and B are of the same sign and of very similar magnitude. In consequence, [Formula: see text] cannot be used to measure the conformational preference of the methyl group. However, [Formula: see text] and [Formula: see text] in α-substituted toluene derivatives will be useful in conformational studies. [Formula: see text] in toluene derivatives varies between 0.30 and 0.46 Hz and some patterns in its ring substituent dependence can be gleaned from some fifty precise values.
O-Methylation of a sulfone with methyl fluoride – antimony pentafluoride – sulfur dioxide. Preparation and properties of tetrahydro-1-methoxythiophenium 1-oxide hexafluoroantimonate
Authors: Abdel-Malik Magdy Malak , Woodworth Dean Philip Arthur , King James Frederick
Published: May 2006

Reaction of sulfolane (tetrahydrothiophene 1,1-dioxide) (1) with methyl fluoride – antimony pentafluoride in liquid sulfur dioxide gives crystalline tetrahydro-1-methoxythiophenium 1-oxide hexafluoroantimonate (2), thereby providing the first characterized example of an alkoxysulfoxonium salt. This salt (2) is also formed, but more slowly, by reaction of methyl fluoride with the crystalline 1:1 complex of sulfolane and antimony pentafluoride. Reaction of 2 with nucleophiles leads to transfer of the methyl group, a facile process even with such weak nucleophiles as nitrobenzene and phenyl N,N-dimethylsulfamate. Spectroscopic evidence has been obtained for O-methylation of other sulfones, either by reaction with MeF•SbF5•SO2, or via the sulfone•SbF5 complex and methyl fluoride, or by transmethylation with 2.
On the structure and energies of protonated cations of H2CS, HFCS, and F2CS
Authors: Grein Friedrich
Published: May 2006

Using 4-31G basis sets, the geometries of H2CS, HFCS, and F2CS as well as their protonated cations were optimized. In each case, three protonation sites, S, C, and H (for H2CS) or F (for HFCS and F2CS) were considered. The H or F protonation leads to molecular complexes of the form HX … YCS+. For H2CS and F2CS, the S-protonation site is favored, whereas for HFCS the linear complex HF … HCS+ is the most stable protonated form. Predicted proton affinities are 177.4 for H2CS (180.9 experimental), 172.0 for HFCS, and 149.1 kcal/mol for F2CS.
An investigation of the effects of the medium and the type of fluoride on the hydrogen bond assisted alkylation of phenols
Authors: Alauddin M. M. , Miller Jack M. , Clark James H.
Published: May 2006

Several sources of the fluoride anion have been compared as electron donors in the hydrogen bond assisted alkylation of phenols.
O—O stretching frequencies of cyclic peroxides. Stabilization of peroxides by alkoxy substituents
Authors: Kopecky Karl R. , Gomez Rodrigo Rico
Published: May 2006

The O—O stretching frequencies of some alkyl substituted 1,2-dioxacyclohexanes are near 730 cm−1 and those of some alkyl substituted 1,2-dioxetanes are in the range 670 ± 20 cm−1. Alkoxy substituents cause the frequency to increase; that for tetramethoxy-1,2-dioxetane is 752 cm−1. Alkoxy substituents appear to stabilize peroxides.
15-Oxa-D-homosteroids
Authors: Ferland J. M. , Lefebvre Y.
Published: May 2006

Novel 15-oxa-D-homosteroids related to pregnane and estrane derivatives have been prepared.
Additivity methods for estimating heat capacities of vaporization for organic compounds
Authors: Guthrie J. Peter , Taylor Kathleen F.
Published: May 2006

Additivity methods permitting the estimation of heat capacities of vaporization for organic liquids have been developed, using atom, bond, and group additivity parameters. Previously it had been common to use an average value for all organic liquids, which can lead to considerable errors. For the atom level scheme, 193 compounds could be fitted using 20 parameters, with a standard deviation of 1.50 cal/deg/mol, and only 29 deviations greater than 2 cal/deg/mol. For the bond level scheme, 197 compounds could be fitted using 23 parameters, with a standard deviation of 1.47 cal/deg/mol, and only 37 deviations greater than 2 cal/deg/mol. For the group level scheme, 177 compounds could be fitted using 39 parameters, with a standard deviation of 1.05 cal/deg/mol, and only 13 deviations greater than 2 cal/deg/mol. The significant terms in the correlation matrix are given for each set of parameters.
Across-space double bond interactions: the crystal and molecular structures of two chlorinated endo-endo-dienes and comparisons with a third homolog
Authors: Dong Dao Cong , Wong-Ng Winnie , Nyburg Stanley C. , Siew Pik Yuen , Edward J. T.
Published: May 2006

The crystal structures of two endo-endo-dienes, 5,6,7,8,9,9-hexachloro-1,4,4a,5,8,8a-hexahydro-endo-endo-1,4-ethano (and propano)-5,8-dimethanonaphthalene, 1b and 1c have been determined. These, together with the methano-homolog 1a (of known structure), are shown to exhibit decreasing across-space double-bond/double-bond repulsion which correlates with the observed decrease in the ease of cyclization in solution.
Chemical behavior of an α-azidosulfide, and the related sulfoxide and sulfone, in the tetrahydrothiophene series
Authors: Still Ian W. J. , Brown William L. , Colville Robin J. , Kutney Gerald W.
Published: May 2006

The thermal, photochemical, base-catalyzed, and Lewis acid-catalyzed reactivity of 2-azidotetrahydrothiophene (1a) and the related α-azidosulfoxide and sulfone have been found to lead to a number of interesting rearrangement products. The 13C nmr data for these compounds are also reported and discussed and the results of attempted deoxygenation of the α-azidosulfoxide 1b with a variety of reagents are compared.
Electron impact mass spectrometry in a series of methyl-2-pyrimidones
Authors: Picquenard Eric , Riand Jacques , Brun Jean-Pierre
Published: May 2006

The fragmentation under electron impact of various methyl-2-pyrimidones is investigated. The fragmentation is markedly influenced by the methyl substituent in the 4- or 5-position and the main fragmentation pathways of the molecular ion involve the loss of carbon monoxide or methyl radical. The latter fragmentation process shows that the methyl groups are more labile in the 4- and(or) 6-position than in the 5-position. This is corroborated by the study of trideuteriomethylated analogues. One can thus distinguish by mass spectrometry the different isomers of position, 4-methyl and 5-methyl or 4,5-dimethyl and 4,6-dimethyl-2-pyrimidones.
The electrochemical reduction of N-fluorourethans in acetonitrile. The generation of carbethoxynitrene
Authors: Lessard Jean , Bérubé Denis
Published: May 2006

The electrochemical reduction of N-fluoro-N-methylurethan (1a) and N-fluorourethan (2a) in acetonitrile generates the amide anion and a fluoride ion. Both the fluoride and the amide anion can react with the starting N-fluoroamide either as bases or as nucleophiles. Many products are formed and the coulometric results are low (0.5 to 0.7 F/mol). In the case of NFU (2a), abstraction of the proton on nitrogen both by the urethan anion and the fluoride anion generates the conjugate base [Formula: see text] (7) which immediately undergoes α-elimination of the fluoride ion to give carbethoxynitrene (11). This nitrene was generated also by treating NFU (2a) with a base such as triethylamine or lithium hydride. The α-elimination of F− from [Formula: see text] is much easier than the α-elimination of Cl− from [Formula: see text].
Structural studies of organoboron compounds. XVI. Preparation and crystal and molecular structures of 4,4-dimethyl-2,5,5-triphenyl-1,3-dioxa-4-azonia-2-bora-5-boratacyclopentane and 4,4,5,5-tetramethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclopentane
Authors: Kliegel W. , Motzkus H.-W. , Rettig Steven J. , Trotter James
Published: May 2006

Details of the synthesis, physical properties, and molecular structures of 4,4-dimethyl-2,5,5-triphenyl-1,3-dioxa-4-azonia-2-bora-5-boratacyclopentane, 4, and 4,4,5,5-tetramethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclopentane, 5, are reported. Crystals of 4 are triclinic, a = 9.841(2), b = 14.722(3), c = 6.6701(12) Å, α = 86.79(1), β = 102.95(1), γ = 93.89(1)°, Z = 2, space group [Formula: see text]; and those of 5 are monoclinic, a = 14.9164(12), b = 6.4732(3), c = 18.2248(15) Å, β = 117.263(3)°, Z = 4, space group Cc. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.032 and 0.035 for 1456 and 1649 observed reflections, respectively. Molecules of 4 contain non-planar BOBON rings with an unusually long N(sp3)—B(sp3) distance of 1.728(3) Å and in 5 there is a long N(sp3)—C(sp3) bond of 1.591(3) Å. These structural features are ascribed to steric hindrance.
The vibrational spectra, crystal and molecular structure of bis(acetonitrile)dichloroplatinum(II)
Authors: Rochon F. D. , Melanson R. , Howard-Lock H. E. , Lock C. J. L. , Turner G.
Published: May 2006

The crystal structure of Pt(CH3CN)2Cl2 has been determined twice independently. The compound is the cis isomer. It crystallizes in the monoclinic P21/c space group, a = 6.660(3) [6.668(4)], b = 12.500(7) [12.519(8)], c = 10.277(6) [10.308(5)] Å, β = 105.42(4) [105.41(4)]°, V = 824.7(8) [829.6(9)] Å3. The structure was refined by full-matrix least-squares analysis to a conventional R factor of 0.054 [0.058] and Rw = 0.053 [0.057] for 1578 [1226] observed reflections. The coordination is square planar with bond lengths (Pt—N = 1.98(1), 1.98(1) [1.95(2), 1.99(2)] Å and Pt—Cl = 2.264(4), 2.263(3) [2.270(6), 2.277(5)] Å) slightly shorter than normal. The N—C bonds are 1.10(2), 1.11(2) [1. 11(3), 1.16(2)] Å. The C—CH3 bonds are shorter than normal single bonds (1.48(2), 1.45(2) [1.49(3), 1.45(3)] Å and the N—C—C framework is almost linear. Infrared (4000–100 cm−1) and Raman (4000–60 cm−1) spectra of the crystalline solid have been measured and assigned; the vibrational spectra confirm the cis structure. A rough molecular force constant analysis based on a cw-planar C2v. skeleton (ignoring H atoms) was carried out and aided in the vibrational assignments. The v(Pt—Cl) bands occur at 362 and 333 cm−1; the v(Pt—N) bands occur at 463 and 408 cm−1, and show strong coupling with the PtNC deformations.
Comparative extraction studies of potassium phenoxide, p-nitrophenoxide, and picrate into methylene chloride by macrocyclic crown ether and cryptand complexing agents
Authors: Buncel E. , Shin H. S. , Bannard R. A. B. , Purdon J. G.
Published: May 2006

The results of a comparative extraction study of potassium phenoxide, p-nitrophenoxide, and picrate, from aqueous medium into methylene chloride in the presence of crown ether and cryptand complexing agents, are reported. The efficiency of extraction varies extremely widely with the nature of the anion and the ligand. An analysis of the results in terms of constituent equilibrium constants, and the factors which influence these, is presented. The significance of the results to other areas including phase transfer catalysis is pointed out.
Reactions between Ni(II) and NaBH3CN in the presence of bidentate phosphines
Authors: Holah David G. , Hughes Alan N. , Khan Nazrul I.
Published: May 2006

Reactions between Ni(II) and NaBH3CN in the presence of Ph2P(CH2)nPPh2 (n = 1, Dppm; n = 2, Diphos) have been studied. With Dppm, the main products are Ni(I)–CN–Dppm complexes and the nature of the actual product formed depends critically upon the reaction conditions. With Diphos, the products mainly involve coordinated BH3CN− in Ni(II)–Diphos complexes. Evidence from 31P nmr and ir spectra are used to support proposed structural assignments.
Hydrolysis of trioxaadamantane ortho esters. II. Kinetic analysis and the nature of the rate-determining step
Authors: McClelland Robert A. , Lam Patrick W. K.
Published: May 2006

A detailed kinetic study of the hydrolysis of a series of 3-aryl-2,4,10-trioxaadamantanes is reported. These ortho esters equilibrate with the ring-opened dialkoxycarbocation, in a very rapid process which could be studied using temperature-jump spectroscopy for aryl = 2,4-dimethylphenyl. Relaxation rate constants are of the order of 104 s−1; these could be analyzed to provide the rate constants for both the ring opening and the ring closing. Product formation from this equilibrating mixture is much slower. In acid solutions (0.01 M H+ −50% H2SO4), first-order rate constants for product formation initially increase with increasing acidity, but a maximum is reached at 20–35% H2SO4 and the rate then falls. This behavior is explained by a counterbalancing of two factors. Increasing acidity increases the amount of the dialkoxycarbocation in the initial equilibrium, but, outside the pH region, it decreases the rate of hydrolysis of this cation through a medium effect. Rate constants over a range of pH have been measured for two trioxaadamantanes and for the cation DEt+ derived by treatment of the ortho ester with triethyloxonium tetraafluoroborate. The latter models the cation formed in the ortho ester hydrolysis but it cannot ring close. Rate–pH profiles obtained in these systems are more complex than expected on the basis of rate-determining cation hydration. An interpretation is proposed with a change in rate-determining step between high pH and low pH. Cation hydration is rate determining at high pH but at low pH hemiorthoester decomposition becomes rate determining. Under these conditions the hemiorthoester equilibrates with both the dialkoxycarbocation and with the trioxaadamantane. The change in rate-determining step occurs because acid-catalyzed reversion of the hemiorthoester to dialkoxycarbocation is a faster process than acid-catalyzed hemiorthoester decomposition. This makes the latter rate-determining in acid solutions. Additional pathways available to the decomposition, however, make it the faster process at higher pH. A kinetic analysis furnishes all of the rate and equilibrium constants for the system, and provides support for the mechanistic interpretation. A comparison of these numbers with those obtained for the three stages in the hydrolysis of a simple monocyclic ortho ester underlines the novelty of the trioxaadamantane system.
The application of double-quantum and spin echo nuclear magnetic resonance spectroscopy to the assignment of 1H chemical shifts of RNA oligomers
Authors: Hughes Donald W. , Neilson Thomas , Coddington Jan M. , Bell Russell A.
Published: May 2006

Specific assignment of the non-exchangeable base and ribose anomeric protons is difficult for oligoribonucleotides with a high pyrimidine content. Problems arise from the narrow range of pyrimidine H-6 chemical shifts and the overlap of pyrimidine H-5 resonances with the ribose anomeric proton signals. To solve these problems two multiple pulse methods were used which depend on the scalar coupling between H-6 and H-5. The first method was double-quantum nmr which established the connectivity between specific pyrimidine H-6 and H-5 resonances. A refocussing pulse was added to the end of the double-quantum pulse sequence to improve the identification of several H-6 and H-5 connectivities in a single experiment. The second procedure involved homonuclear decoupled spin echo nmr to remove H-5 signals selectively from the ribose anomeric proton region. These techniques are illustrated by the assignment of the spectra of the oligoribonucleotides UpUpC, UpUpU, GpCpUpC, and UpApGpCpUpU.
Quadrupolar interactions in amines as determined by 1H nuclear magnetic resonance: mono- and dimethylamines
Authors: Halliday James D. , Bindner Patrick E. , Padamshi Shahsultan
Published: May 2006

Nitrogen-14 quadrupole interactions have been observed in the nonexchanging amino proton 1H nmr spectra of rigorously purified liquid mono- and dimethylamines over the temperature range −82 °C to +81 °C. The proton lineshapes have been analyzed to yield 14N spin-lifetimes (τ) as a function of temperature. Activation energies and correlation times for molecular reorientation in the liquids have been calculated from these data and the results compared with those from 14N nmr measurements.
Theoretical study on dinitrogen complexes. Relation between facility of protonation and difference of electronic structures of d6 and d8 complexes
Authors: Hori Kenzi , Yamabe Tokio
Published: May 2006

Electronic structures of different d configurations have been studied in relation to the facility of protonation to dinitrogen ligand in Cr(0) and Co(I) complexes. The d6 Cr complex has much better MO's for protonation than the d8 Co complex. This difference largely affects the protonation energies and the reduction of nitrogen molecule in these complexes.
Marcus theory and the existence or non-existence of transition states in gas phase deprotonation of carbon acids
Authors: Wolfe Saul
Published: May 2006

At the 3-21G (3-21G*) computational level, the intrinsic barriers associated with proton transfer between XCH2− and CH3X have been found to be essentially constant (ca. 10 kcal/mol) for X = H, F, SH, Cl. According to the Marcus rate-equilibrium treatment of proton transfer reactions, this result means that transition states should not exist for gas phase reactions [Formula: see text], when the energy change exceeds 20 kcal/mol. This prediction has been confirmed for two cases (X = H, F) in which the energy change is less than 20 kcal/mol, and two cases (X = SH, Cl) in which the energy change is greater than 20 kcal/mol.
Quenching of the singlet and triplet state of benzene in condensed phase
Authors: Khwaja H. A. , Semeluk G. P. , Unger I.
Published: May 2006

Quenching of the fluorescence of benzene by halocarbons in methanol, ethanol, acetonitrile, and cyclohexane has been investigated. It proceeds via a reversible exciplex intermediate formed between excited singlet benzene and ground state halocarbon. Quenching is controlled by the polarity of the medium. Excited singlet benzene interacts with acetonitrile solvent and a longer wavelength emission due to this complex is observed.The effect of CCl4, CH3CN, CHCl3, and CH3CCl3 on the triplet and singlet excited states of benzene in a methylcyclohexane–isopentane mixture at 77 K has been examined. Carbon tetrachloride and acetonitrile are far more effective quenchers than either CHCl3 or CH3CCl3. In the case of the latter pair enhanced intersystem crossover competes with complex formation.
Condensation of thiophenols with aryl halides using metallic copper as a reactant. Intermediation of cuprous thiophenolates
Authors: Yamamoto Takakazu , Sekine Yasuhiro
Published: May 2006

The reaction of thiophenol (PhSH) with metallic copper affords CuSPh and H2 through Cu-catalyzed dehydrogenative coupling of PhSH to PhSSPh and ensuing addition of PhSSPh to Cu. Condensation between thiophenols (ArSH) and aryl iodides or bromides (Ar′X) in the presence of Cu affords diaryl sulfides (ArSAr′) in good or moderate yields (ArSH + Ar′X + Cu → ArSAr′ + CuX + 1/2H2). Use of alkyl iodides (RI), instead of Ar′X, affords alkyl aryl sulfides (ArSR) in good yields. These condensations are considered to proceed mainly through (1) copper-catalyzed dehydrogenative coupling of ArSH to ArSSAr with evolution of H2, (2) addition of ArSSAr to Cu giving CuSAr, and (3) coupling of CuSAr with Ar′X giving ArSAr′ and CuX; temperature dependence of products, time course of the reaction, the reaction of PhSSPh with Cu, and the reaction of Ar′X with CuSPh support this view. Use of copper oxides (Cu2O and CuO), instead of Cu, also affords diaryl sulfides in good or moderate yields.
Discussion on 13C nuclear magnetic resonance spectra of structurally rigid cyclonucleosides. Violation of Karplus relationship between 3JC,H and dihedral angles
Authors: Uzawa Jun , Anzai Kentaro
Published: May 2006

Using structurally rigid cyclonucleoside derivatives of adenosine, the effect of the oxygen functional groups on the vicinal coupling constants between carbon and hydrogen in, 13C nmr was investigated.
Etude par activation collisionnelle des ions [C4H7O]+ provenant des ions penténols et méthylcetones [C5H10O]•+ métastables
Authors: Bouchoux G. , Hoppilliard Y. , Flammang R. , Maquestiau A. , Meyrant P.
Published: May 2006

The [C4H7O]+ ions arising from 2-pentanone (1), 3-methylbutanone (2), 2-methylbut-3-en-2-ol (3), pent-3-en-2-ol (4), and 3-methylbut-3-en-2-ol (5) by methyl loss were studied by collisional activation. A triple sector (E/B/E) mass spectrometer was used to distinguish between fragment ion structures produced in the source and in the first field free region. The collision induced dissociations confirm or demonstrate that: (i) in the source, the methyl originally on the position 1 in compounds 1–5 is lost to give, respectively, [n-C3H7CO]+ (a), [i-C3H7CO] + (b), [CH3COHCHCH2] + (c), [CH3CHCHCHOH]+ (d), and [CH2C(CH3)CHOH]+ (e), while the methyl loss from the side chain gives, competitively, ion c for the five precursors; (ii) in the first field free region molecular ions 1,3,4, and 5 produce an identical mixture of structures a, b, and c; the molecular ion 2 leads essentially to acylium ion b. The mechanisms and the thermochemistry of the isomerization path of 1–5 are discussed.
A new route to the cis–anti–cis triquinane ring system. The synthesis of 4,4-dimethyltricyclo[6.3.0.02,6]undecan-3-one via β-enolate rearrangement
Authors: Patel Hemant A. , Stothers J. B.
Published: May 2006

A synthesis of cis, anti, cis-4,4-dimethyltricyclo[6.3.0.026]undecan-3-one is described in which the key step is β-enolate rearrangement of 9,9-dimethyltricyclo[5.3.1.01.5]undecan-10-one proceeding with retention of configuration. The required [5.3.1.01.5] ketone was prepared in six steps from tricyclo[5.2.1.01.5]dec-8-ene. This sequence constitutes a new route to the tricyclo[6.3.0.02.6]undecane ring system characteristic of the hirsutane sesquiterpenes. The 13C data for several tricyclic derivatives are reported.
4-Iodophenylcholine: a potential myocardial imaging agent
Authors: Hunter Duncan H. , Ponce Yolanda Zea , Brown G. William , Chamberlain Michael J. , Driedger Albert A. , Morrissey Gary
Published: May 2006

The compound O-(4-iodophenyl)choline iodide has been synthesized using iodine-125, iodine-127, and iodine-131 by diazonium salt and melt exchange procedures. Radiochemical yields of approximately 2% and 56%, respectively, were obtained. The biodistribution of this compound in mice was analyzed in order to determine its potential as a myocardial imaging agent. Selective myocardial concentration was observed at 5 min post-injection, with a heart-to-blood ratio of 18:1.
Une synthèse hautement stéréosélective de diènes conjugués (E)
Authors: Bloch R. , Abecassis J. , Hassan D.
Published: May 2006

A general method for the preparation of (E) terminal conjugated dienes was developed by the flash thermolysis of 2-substituted 2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels–Alder reaction. This process allows the obtention of conjugated dienes, bearing or not a functionality (alcohols, esters), with an excellent stereoisomeric purity (in general higher than 98%). An application to the synthesis of (E)-9,11-dodecadien-1-yl acetate, the major component of the sex pheromone of Diparopsiscastanea, shows the generality and the efficacy of this method.
Nuclear magnetic resonance study of conformation and dynamics in solution of p-(o-propyloxybenzamido)benzoate diethyl(2-hydroxyethyl)methylammonium bromide: a smooth muscle relaxant agent
Authors: Valensin Gianni , Pogliani Lionello , Ghelardoni Mario , Pestellini Vittorio , Sega Alessandro
Published: May 2006

The relative conformation of the aromatic rings and the amide bridge as well as important details of the two side chains of the title compound in a DMSO-d6 solution have been established by use of non-selective and selective proton spin-lattice relaxation times coupled with nOe experiments. The complete analysis of 13C spin-lattice relaxation times has shown the main features of the dynamic behavior of the title compound.
Mécanisme des réactions du chlorite et du dioxyde de chlore. 2. Cinétique des réactions du chlorite en présence d'ortho-tolidine
Authors: Schmitz Guy , Rooze Henri
Published: May 2006

With added ortho-tolidine (NH2RNH2) in order to eliminate complicating side reactions of the intermediate products of the disproportionation of chlorite, the stoichiometry is HClO2 + 2NH2RNH2 → Cl− + H+ + 2NHRNH + 2H2O. No chlorate is formed. The rate law, in the absence of chloride ions, is[Formula: see text]k = 269 M−1 s−1 at 25 °C and 1 M ionic strength. Without added iron, the observed rate is only due to the small amount of iron always present as an impurity in the reactants. Thus the reaction [Formula: see text] is not an elementary reaction.
Experiments with a cyclic closed-loop gas chromatograph
Authors: Back Roberta , Back R. A.
Published: May 2006

A cyclic closed-loop gas chromatrograph, comprising a column, a thermal conductivity detector, and a peristaltic circulating pump, together with valves for sample pick-up and carrier gas admission, is described. Injected samples could be recycled many times, providing very long effective column lengths, and separations were markedly better than on a single-pass column of equivalent length. Separation of two components, and peak broadening with single components, were measured over many successive cycles for a variety of samples, carrier gases, and conditions. The use of the cyclic chromatograph for testing columns and for studying basic processes in gas chromatography is demonstrated and discussed.
Synthesis of some 3-arylisochromene, 3-arylisoquinoline, 6H-5-oxachrysene, and benzo[c]phenanthridine analogs of some naturally occurring alkaloids
Authors: Carty Antoine , Elliott I. Wesley , Lenior Grefonda M.
Published: May 2006

A 2-benzopyrylium perchlorate 6 was prepared from the keto ester 5. Reduction of 6 followed by dilute HCl affords 6H-5-oxachrysene 10. Reaction of 6 with ammonia solution gives the isoquinoline acid 13. By a short series of steps 13 is cyclized to the dihydrobenzo[c]phenanthridine 16.
Evidence for molecular complexes in the mechanism of additions of iodine mono-chloride to alkenes
Authors: Sçhmid George H. , Gordon James W.
Published: May 2006

Immediately upon mixing ICls and 2,3-dimethyl-2-butene in CCl4 at 25 °C a new absorption band due to an alkene–ICl molecular complex appears at 295 ± 5 nm and decreases rapidly with time. The rate law under conditions of (alkene)0 [Formula: see text] (ICl)0 for the electrophilic addition of ICl to 2,3-dimethyl-2-butene, E- and Z-2-butene, and E- and Z-1-phenylpropene is −d(ICl)/dt = kexpt(alkene)(ICl)3/{1 + kAD(alkene)}3 where KAD is the equilibrium constant for the formation of a 1:1 alkene–ICl molecular complex. The addition of ICl to the Z and E isomers of 2-butene and 1-phenylpropene occurs by anti-stereospecific addition. The negative enthalpy of activation for the addition of ICl to 2,3-dimethyl-2-butene is evidence that one or more complexes are involved on the reaction coordinate prior to the rate-determining step. On the basis of analysis of the enthalpy changes during the reaction, it is proposed that both a 1:1 and a 1:2 alkene–ICl molecular complex is involved in the mechanism prior to the rate-determining step.
A conformational study of the adducts of 2′-deoxythymidine and 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl by 1H and 13C nuclear magnetic resonance
Authors: Hruska Frank E. , Berger Maurice , Cadet Jean , Remin Mieczyslaw
Published: May 2006

γ-Irradiation of oxygen-free, aqueous solutions of 2′-deoxythymidine in the presence of the organic nitroxide free radical, 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl (TAN), leads to a complex mixture of products in which the TAN moiety is linked to the C5 or C6 position of a 5,6-saturated thymine ring. Extensive 1H and 13C nmr data are provided for the eight TAN–dT adducts which are produced in the largest amounts. The results show that the conformational properties of the sugar moiety are dependent on the point of attachment of the TAN group and the configuration of the saturated thymine ring.
Studies of medium effects on the DPASV determination of Cu in natural waters using conventional and flow-through electrodes
Authors: Alzand Ibrahim K. , Langford Cooper H.
Published: May 2006

A survey of DPASV signals for Cu in a variety of media and under varying conditions has been undertaken. It is possible to identify the circumstances associated with two distinct problems in Cu determination which have not been clearly distinguished in earlier literature. The role of Cl− in influencing the Hg wave form (which in turn affects the relative apparent peak heights and widths of the two Cu signals arising from Cu(Hg) amalgam and undissolved Cu(solid)) is distinguished from the role of Cl− as a complexing agent in solution at higher Cl− concentration. Effects of dissolved organic matter in natural waters are shown to resemble Cl− effects. Data are also presented on two related matters: (1) some factors in a natural water sample that confuse the use of DPASV as a tool for Cu species identification, and (2) the effects of high Cl− concentration on Cd, Pb, and Cu signals.Following the study of medium effects and interferences influencing DPASV signals, a fresh water sample has been examined at the conventional hanging Hg drop electrode, thin Hg films on graphite and Hg thin films on a novel reticulated vitreous carbon flow-through electrode. Hg thin film electrodes deposited insitu are confirmed to be very sensitive for analysis of river water samples. The flow-through electrode has excellent sensitivity. Promising storage characteristics of the flow-through electrode are evaluated with a view to suggesting an ASV system using a simple electronic unit for field sampling.
Some isotopic scrambling studies with singly or doubly labeled triphenylvinyl bromide
Authors: Lee Choi Chuck , Fiakpui Charles Y.
Published: May 2006

The solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) in 70% HOAc – 30% H2O or in 2,2,2-trifluoroethanol (TFE) carried out in the presence of an excess of p-CH3C6H4SNa gave the triphenylvinyl p-tolyl thioether (1-STol) with a greatly decreased extent of scrambling of the 14C-label from C-2 to C-1 when compared with analogous reactions without the presence of the p-toluenethiolate anion. For example, the 1-STol product from the reaction of 1-Br-2-14C in 70% HOAc – p-CH3C6H4SNa showed only 0.5–0.9% scrambling, while previous studies on the reaction of 1-Br-2-14C in 70% HOAc – NaOAc gave 14.7 ± 0.7% scrambling. Previous work on the solvolysis of 1,2-diphenyl-2-[2H5]phenyl[2-13C]vinyl bromide (1-Br-2-13C-2-Ph-d5 in 70% HOAc, as well as the present results from the solvolysis of 1-Br-2-13C-2-Ph-d5 in TFE – 2,6-lutidine, gave products derived from all 4 possible isotopomeric triphenylvinyi cations 3, 4, 5, and 6 arising from successive 1,2-phenyl shifts. On the other hand, solvolysis of 1-Br-2-13C-2-Ph-d5 in 70% HOAc or TFE containing an excess of p-CH3C6H4SNa gave 1-STol in which the isotopically rearranged product was derived only from ion 5 arising from a 1,2-shift of the unlabeled phenyl group with no detectable amount of production derived from a 1,2-shift of the perdeuterophenyl group. These results are interpreted by the rapid trapping of the triphenylvinyi cation by the highly nucleophilic p-toluenethiolate anion.
Crystal structure of di-μ-hydroxobis[fac-trichloroaquotin(IV)] tetrahydrate, [Cl3(H2O)Sn—OH—]2•4H2O, with observations on distances and MOM angles in di-μ-oxygen bridges
Authors: Cameron T. Stanley , Knop Osvald , Vincent Beverly R.
Published: May 2006

The present redetermination of the crystal structure of the title compound agrees well with a previous determination by Barnes etal., which it supplements by providing details of the hydrogen-bonding scheme. Scrutiny of the [Formula: see text] distances in homonuclear di-μ-oxygen M2O2 bridges in well over a hundred compounds shows that the lower limit for this distance is ~2.3 Å, and that the corresponding distance in the title compound, 2.44(1) Å, is closer to this limit than the [Formula: see text] distances in the majority of the compounds surveyed. Appreciably shorter nonbonded [Formula: see text] distances are found only in oxyanions, in particular those acting as bidentate ligands of metal atoms and thus forming heteronuclear di-μ-oxo bridges; an [Formula: see text] distance as short as ~2.0 Å has been reported and may constitute the limit of such nonbonded [Formula: see text] distances in general.
Ambident nucleophiles. III. N-bonded vs. C-bonded adduct formation on reaction of imidazolide anions with 1,3,5-trinitrobenzene
Authors: Simonnin M. P. , Halle J. C. , Terrier F. , Pouet M. J.
Published: May 2006

Imidazolide anions of imidazole, 2- and 4-methylimidazoles, 4,5-dimethyl and 4,5-diphenylimidazoles react with 1,3,5-trinitrobenzene (TNB) in dimethylsulfoxide (DMSO) to yield, initially, N-bonded σ-adducts under kinetic control. These undergo a subsequent conversion to C-adducts, which are the thermodynamically stable products. The formation of N,C-diadducts from the reversible attack of a second TNB molecule on the imidazolide moiety of the C-adducts is also observed. Provided that the corresponding position of the parent imidazolide anion is free, the formation of C-adducts occurs preferentially at the C-4 or C-5 carbon atom. However, C-2 substitution is observed in 4,5-disubstituted derivatives. Structures and preferred conformations of some adducts and diadducts are deduced from nOe experiments. The mechanisms of the various reactions are discussed. Evidence is presented that adduct formation results in a low-field shift of methyl groups located in a position adjacent to the substitution site, while all the other protons move upfield. This unusual deshielding presumably reflects a proximity effect between a methyl group and the hydrogen atom attached to the sp3 carbon of the adducts.
Extended basis abinitio calculations on conformers of propanal
Authors: Gupta V. P.
Published: May 2006

Extended basis abinitio calculations on four conformations of propanal at the 4-31G and 6-31G** levels followed by many-body perturbative interaction calculations MP2 and MP3 have been conducted. Optimized geometries, heights of rotational barriers, dipole moments, ionisation potentials, and diagonal harmonic force constants have been reported. The s-cis conformer (dihedral angle CCCO = 0°) is found to be more stable than the gauche conformer (dihedral angle CCCO = 129.84°) by 5.07 kJ mol−1. Torisonal potential barriers s-cis/gauche, gauche/s-cis, and gauche/gauche have values 8.81, 3.74, and 1.84 kJ mol−1, respectively. It appears that meaningful values of rotational barriers can be obtained only after a careful optimization of the geometries of the conformations involved.
Cation transport in isomeric pentanes: effects of temperature, density, and molecular shape
Authors: György Istvan , Gee Norman , Freeman Gordon R.
Published: May 2006

The cation mobility (μ+ is measured in n-pentane, iso-pentane, neo-pentane, and mixtures of n- and neo-pentane over conditions from the normal liquid, through the critical fluid, to the low density gas. Most of the liquid data correlate with the reduced temperature T/Tc. The T/Tc reflects free volume and viscosity changes. Comparison is made to neutral molecule diffusion. The transition from viscosity control of mobility in the liquid to density control in the dilute gas occurs over the reduced viscosity region 3 > η/ηc > 0.6, which corresponds to the reduced density region 1.9 > n/nc > 0.5. In the saturated gas nμ+ is similar in all pentanes, but iso- ≥ n- > neo-pentane. At constant density dμ+/dT ≥ 0 for gases. The average momentum transfer cross sections in the n-/neo-pentane mixtures are similar to those in neo-pentane at low T but similar to those in n-pentane at high T. The present findings are combined with previous electron mobility data in addressing the effect of hydrocarbon molecular (external) shape on the electric breakdown strength of gases.
Bicyclization of aza-compounds by positive halide ions. I. Cyclic amines
Authors: Elofson R. M. , Gadallah F. F. , Laidler J. K.
Published: May 2006

Cyclic amines are oxidized to the bicyclic compounds by electrochemical oxidation. The presence of halide ions is found necessary for the reaction to proceed and to produce any bicyclic products. It is postulated that a positive halide species, X(+), is produced electrochemically and stabilized under the specific reaction conditions. The X(+) ion forms a complex with the parent cyclic amine which decomposes to the bicyclic product and HX. An analogy between the Hofer–Moest reaction to produce C(+) and this reaction to produce X(+) is postulated
Propagation of error in fulvic acid titration data: a comparison of three analytical methods
Authors: Fish William , Morel François M. M.
Published: May 2006

Many methods have been employed for measuring the interactions of trace metals and humic materials but little consideration has been given to the magnitude of error in the resulting titration data. Most common metal-titration methods can be placed into one of three categories based on the chemical species that is most directly measured: free ionic metal, total labile metal, or ligand-bound metal. The propagation of random instrument error into a titration data set is not uniform throughout a titration and the pattern of propagation is shown to be characteristic of the category of method used. Standard deviations are determined for measurements by ion-selective electrodes, fluorescence quenching, and fixed potential amperometry (each representative of a category of methods). Error propagation in resulting titration data is quantified. No single titration method yields uniformly precise data in all concentration ranges and a combination of complementary methods yields the best characterization of metal binding to a humic material.
Synthesis and crystal structure of 17-deaza-17-methyl thionium isomorphinan (isosulforphanol) perchlorate, an isostere of the opiate isolevorphanol
Authors: Belleau Bernard , Gulini Ugo , Gour-Salin Barbara , Ahmed F. R.
Published: May 2006

No morphinan analog carrying a heteroatom other than nitrogen at position 17 has yet been synthesized. The synthesis of the position 17 sulfur analog of the perchlorate salt of (±)-isolevorphanol is described. The strategy adopted is based on the classical Grewe synthesis of morphinans and, under narrowly defined conditions, the title compound isosulforphanol (3a) and an intermediate by-product 13 resulting from an unusual non-bridged head ring closure of 11a were obtained. The X-ray structures of both 3a and 13 were determined. Crystals of 13 (C17H22OS) are monoclinic, space group P21/a, a = 17.080(2), b = 9.372(1), c = 9.327(1) Å, β = 108.67(1), V = 1414.4 Å3, Z = 4. Final R = 0.034 for 2545 reflections. The crystals of 3a(C17H23OS+•ClO4−)are orthorhombic, space group Pna21,a = 10.934(1), b = 9.219(1), c = 17.131(2) Å, V = 1726.8 Å3, Z = 4. Final R = 0.053 for 1018 reflections. The C17H23OS+ molecule has been identified by this X-ray analysis as S-methyl isosulforphanol (Fig. 2). The structure of 13 is shown in Fig. 1. The stereochemical outcome of the Grewe-like synthesis is thus established as proceeding in a reversed manner when sulfur replaces the nitrogen in the final cyclization step. Preliminary pharmacological studies showed that 3a is a potent agonist in the central nervous system but a potent antagonist on the guinea-pig ileum.
Intermolecular perturbation approach to specific solvent effects
Authors: Nagy Ottó B.
Published: May 2006

One possible specific solvent effect, namely, the π-donor ability is considered in the light of simple intermolecular second order perturbation theory. By using the Polányi–Evans–Bell principle this theory predicts that increasing -π-donor ability of solvent should decrease the reaction rate. This prediction is fully borne out by experimental data observed for the solvent effect on 4 + 2 cycloaddition of tétracyanoethylène to anthracene.
Vibrational spectra and rotational isomerism of ethanethiol and ethanethiol-D1
Authors: Wolff Hans , Szydlowski Jerzy
Published: May 2006

The infrared spectra of gaseous, liquid, and solid C2H5SD, and the Raman spectrum of the liquid compound are analyzed and the corresponding spectra of C2H5SH were reinvestigated under improved conditions. In the deuterated compound the CH2 rocking vibration does not interact with the SD bending vibration and therefore does not split into vibrations of the conformers. The measurements suggest for gaseous and liquid C2H5SH and C2H5SD the simultaneous presence of the trans and gauche conformers, appearing at room temperature in the ratio of the order of 1:3. In analogy to solid C2H5SH, the exclusive presence of the gauche conformers can be inferred for solid C2H5SD. The spectra reported in the literature for the C2H5SH molecules embedded in matrices at low temperatures permit a similar interpretation. The doublet structure observed for the vibrational bands, not only of pure solid C2H5SH and C2H5SD but also of their solid mixtures, may be due to non-equivalent sites of the unit cell.
Charge distributions and chemical effects. XXXVI. Charge analysis involving configuration interaction: application to alkanes
Authors: Mijoule C. , Leclercq J.-M. , Odiot S. , Fliszár S.
Published: May 2006

An analysis of atomic charges is presented for simple alkanes. Basically, Mulliken's scheme is followed, except for the partitioning of CH overlap populations. This achieves a relative ordering of atomic charges which is independent of the basis sets used in abinitio calculations. The absolute magnitude of atomic charges, however, is basis set dependent. Extensive geometry and scale factor optimizations yield the following results (in 10−3 e units) for the carbon net charge in ethane: 69.4 (STO-3G), 55.1 (STO-3G + CI), 42.8 (4-31G), and 37.8 (4-31G + CI). It appears that charge analyses converge toward the empirical result, 35.1 × 10−3 e, provided they are carried out after configuration interaction involving reasonably large optimized basis sets.
The γ-alkylation of cyclic β-ketoesters via their enamine derivatives
Authors: Gravel Denis , Labelle Marc
Published: May 2006

The γ-alkylation – functionalization of cyclic β-ketoesters via their enamine derivatives is discussed with particular emphasis on their preparation from β-ketoesters and their reaction with various electrophiles such as electrophilic olefins, halogenoïds, and allylic and benzylic halides. Although the amine ring size does not appear to affect reactivity to a great extent, the reaction is very sensitive to β-ketoester ring size, with six-membered rings giving the best results. In the latter case the alkylation–functionalization is general and specific to the γ-position and therefore provides an important complement to the dianion and related methodologies.
Abinitio studies on structures and proton affinities of fluorométhanols
Authors: Grein F.
Published: May 2006

Using gradient optimization techniques with 4-31G basis sets, the geometries of methanol, the three fluoromethanols, and their protonated species were optimized. Protonation on oxygen and fluorine was considered. The calculated proton affinities (PA) in kcal/mol are 181.0/178.1 for CH2FOH, 162.3/162.6 for CHF2OH, and 148.0/142.5 for CF3OH, the first number for O- and the second for F-protonation.
Chemistry of amidyl radicals: intramolecular reactivities of alkenyl amidyl radicals
Authors: Chow Yuan L. , Perry Richard A.
Published: May 2006

Amidyl radicals possessing Δ4,5, Δ5,6, and Δ6,7 double bonds were generated from the photodecomposition of nitrosamides and chloramides and the products were identified. Dichotomies of amidyl radical reactivities were discovered and compared with published kinetic rate constants. In complete reversal to intermolecular reactivities, intramolecularly the alkenyl amidyl radicals preferentially add to the double bonds rather than abstract a C-5 hydrogen even if it is allylic. In intramolecular competition, amidyl radicals add to an acyl side chain double bond more efficiently than to an alkyl one; this is just the opposite to intramolecular H-abstraction of amidyl radicals. Taken together with the published results, it is established that, in intramolecular attacks of double bonds, amidyl radicals selectively undergo the propia-addition to generate an exo-cyclic radical rather than the longa-addition to an endo-cyclic radical: this rule should replace the old one that amidyl radicals preferentially cyclize to form five-membered rings if choices are available.
Hydride transfer reactions. A kinetic study of oxidation of 10-methyl-9-phenylacridan by some π acceptors and a one-electron oxidant
Authors: Colter Allan K. , Parsons A. Gregg , Foohey Karen
Published: May 2006

The kinetics of oxidation of 10-methyl-9-phenylacridan (1(H)) and 9-deuterio-10-methyl-9-phenylacridan (1(D)) to 10-methyl-9-phenylacridinium ion (3) by eight oxidants have been investigated. The oxidants included the π-acceptors 1,4-benzoquinone (BQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), p-bromanil (BA), p-chloranil (CA), tetracyanoethylene (TCNE), 2,3-dicyano-1,4-benzoquinone (DCBQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile (AN), BQ in 50:50 (v/v) AN-water, and the one-electron oxidant tris(2,2′-bipyridyl)cobalt(III), [Formula: see text] in AN. The seven π acceptors cover a 109-fold range of reactivity from BQ to DDQ and the deuterium kinetic isotope effect varies from 11.9 (BQ in AN) to 5.8 (DDQ). For π acceptors (BQ, TCNQ, CA, TCNE, and DCBQ) previously investigated with 10-methylacridan (NMA), 1(H) is less reactive than NMA by factors ranging from 9.1 (BQ) to 1.7 × 102 (TCNE). The isotope effects and relative reactivities for the π acceptor oxidations are most simply explained by a one-step hydride transfer mechanism.