bluuebunny/crossref_metadata_2025 huggingface dataset:
Product yields and mechanism of penicillamine radiolysis at pH 5
Authors: Goyal Greesh Chand , Armstrong David Anthony
Published: May 2006

The major products from the radiolysis of penicillamine in N2O-saturated solutions at pH 5 are penicillamine disulfide, penicillamine trisulfide, and valine with yields of 2.0, 1.2, and 1.5 molecules per 100 eV in 10−2 M solutions and 1.8, 0.94, and 0.60 molecules per 100 eV in 10−3 M solutions respectively. These yields remain essentially the same when the major attacking radical is changed from •OH to••CH2OH, •Br2−or •(CNS)2−, and it is concluded that all four species produce predominantly penS• radicals on attacking penicillamine. The formation of trisulfide and an equivalent amount of valine is attributed to secondary reactions of penS• radicals and discussed in the light of recent pulse radiolysis experiments and other work.In deaerated solutions hydrogen and H2S were observed in significant yields and the valine yield increased. These observations can be accounted for quantitatively by the reactions:[Formula: see text]The yields of minor (G < 0.5 molecules per 100 eV) products like NH3 and CH2=C(CH3)CH(NH3+)COO− indicated that fragmentation of pen• and other secondary radicals from penSH was more important than for cys••and other radicals from cysSH.
Perfluoroalkyl- and fluoroalkyl- complexes of rhodium(III)
Authors: Clark Howard C. , Reimer Kenneth J.
Published: May 2006

A series of perfluoroalkyl (Rf—) and fluoroalkyl (RfCH2—) complexes of rhodium(III) have been prepared by oxidative addition reactions of RfI and RfCH2I (Rf = CF3, C2F5 and C3F7) with trans-RhClCO(PMe2Ph)2. The reaction of CF3I with trans-RhClCO(PMePH2)2 gave RhClI(CF3)CO(PMePh2)2 but no reaction was observed with CF3CH2I. The trans stereochemistry of addition has been assigned to all complexes by nuclear magnetic resonance measurements and the comparison of the far-infrared spectra to those of some bromo compounds: RhBrI(CF3)CO(PMe2Ph)2 and RhBrI(C3F7CH2)CO(PMe2Ph)2. Both 1H and 19F nmr data are presented and discussed.
Stereoselective epimerization of pilocarpine in aqueous solution as determined by 13C nuclear magnetic resonance spectroscopy
Authors: Neville George A. , Hasan Fariza B. , Smith Ian C. P.
Published: May 2006

Cleavage and recyclization of the lactone ring of pilocarpine (1) and of isopilocarpine (2) in D2O with varying pD have been studied by 13C nmr spectroscopy. Alkaline treatment (pD 10–13) results in rapid epimerization of pilocarpine to form isopilocarpine (28 ± 3% at 30 °C) and hydrolysis of the parent compound(s) to form the open chain pilocarpinate (isopilocarpinate). By contrast, isopilocarpine does not epimerize to pilocarpine under similar treatment. A mechanism is discussed for the epimerization of pilocarpine and the nonepimerization of the isopilocarpine is rationalized. pKa values of 5.7 and 8.5, respectively, have been determined for pilocarpinic acid and for the dissociation of the protonated quaternary nitrogen of the imidazole ring of pilocarpine. A basis for assay of degradation products in aqueous pilocarpine solutions utilizing differences in 13C chemical shift for C-8 is discussed.
A potentiometric study of the effects of molecular complexing on acid–base equilibria
Authors: Colter A. K. , Buben D.
Published: May 2006

The effect of molecular complexing on several acid–base equilibria involving organic π donor acids has been studied by a potentiometric method. The method leads to complexation constants for the acceptor with the donor acid and its conjugate base. In several cases the two association constants can be determined with sufficient precision to obtain an estimate of the acidity constant for the 1:1 acceptor–donor acid complex. In all situations where charge-transfer and electrostatic interactions are expected to have opposing effects on the acidity, electrostatic effects dominate. The range of the validity and usefulness of the potentiometric method in studies of molecular complexation equilibria is discussed, together with the results obtained in this work.
Theoretical study of the ν3 and ν4 Raman bands of methane in rare gas matrices
Authors: Kobashi Koji , Kataoka Yosuke , Yamamoto Tsunenobu
Published: May 2006

Theoretical study has been carried out on the Raman spectra of the ν3 and ν4 vibration bands of methane in Ar, Kr, and Xe matrices at low temperatures. The present study is a continuation of a theoretical work by Nishiyama and Yamamoto on the infrared spectra of the same Systems. We consider the symmetry of the System under the group [Formula: see text] introducing the inversion functions to generalize Wigner's rotational functions. As a result, dual assignments are given to each vibration–rotation state. The allowed transitions of the Raman scattering are compared with those of the infrared absorption, and it is found that a kind of 'rule of mutual exclusion' holds. The relative intensities and spacings of the Raman spectra are calculated and successfully compared with experiment.
Pyrochlores. X. Madelung energies of pyrochlores and defect fluorites
Authors: Barker William W. , White Peter S. , Knop Osvald
Published: May 2006

Electrostatic (Madelung) lattice energies have been calculated for a wide range of compounds A2B2X6Y with the pyrochlore-type structure. The cases of disorder and partial disorder on the non-metal sites have been examined, as well as the inverse case, where Y is a positive ion. The results of the calculations are compared with those for defect fluorite structure and an attempt is made to relate them to the conditions under which the pyrochlore phase is found. The effect of the site potential in restricting the existence boundaries of the pyrochlore phase is examined, as the potential must have the correct sign relative to the charge occupying the site. Alternative pyrochlore arrangements in which the 8(b) or 32(e) equipoints are occupied have also been explored.
Photochemistry of trans-[Cr(en)2Br2]+ and trans-[Cr(en)2Cl2]+
Authors: Rosebush W. J. , Kirk A. D.
Published: May 2006

trans-[Cr(en)2Br2]+ has been found to photoaquate mainly with bromide loss [Formula: see text] but accompanied by a small, also wavelength dependent, proton uptake [Formula: see text] The main photoproduct of trans-[Cr(en)2Br2]+ and trans-[Cr(en)2Cl2]+ has been shown to be predominantly cis in configuration (95 ± 5% for the dibromo and 99.2% for the dichloro system). The results are discussed in the context of current models of chromium(III) photochemistry. The observed wavelength dependence requires participation of more than one excited state in reaction. The high degree of stereochemical change requires entry of solvent in a manner concerted with halide loss.
The thermal isomerisation of methyl isocyanide in the temperature range 120–320 °C
Authors: Collister John Lewis , Pritchard Huw Owen
Published: May 2006

The thermal isomerisation of methyl isocyanide has been measured in the rigorous absence of self-heating over a temperature range from 120–320 °C and at pressures from 2–100 torr. Expressions are given for the rate constant as functions of both temperature and pressure in these ranges of the two variables. The infinite-pressure rate constant is accurately represented by an Arrhenius line with no curvature having E∞ = 38.2 ± 0.2 kcal mol−1 and log10A∞ (s−1) = 13.35 ± 0.11, although at all other pressures, E is a function of temperature.
Equilibrium protonation of the 1,3,5-trinitrobenzene–phenoxide σ-complex
Authors: Buncel Erwin , Eggimann Walter
Published: May 2006

The protonation behavior of the trinitrobenzene–phenoxide σ-complex has been determined in aqueous sulfuric acid, aqueous hydrochloric acid, and ethanolic hydrogen chloride. The conjugate acid of the σ-complex, a nitronic acid, exhibits acidic properties similar to those of picric acid and the cyanocarbon acids. The acidity (pKa) of the nitronic acid has been evaluated with the aid of various acidity function techniques and using the Bunnett–Olsen method. The nitronic acid is ca. 1 pK unit stronger than picric acid. However, both the nitronic acid and picric acid are considerably weaker acids in ethanolic than in aqueous media (ΔpK ca. 4 units). The results provide a preliminary H− acidity function scale for aqueous and ethanolic hydrogen chloride.
Redox potentials of metal phthalocyanines in non-aqueous media
Authors: Lever A. B. P. , Wilshire J. P.
Published: May 2006

A study of the redox potentials of a range of metal phthalocyanines in non-aqueous media compared with analogous data for some porphyrin complexes provides evidence for extensive back donation in metallophthalocyanines. The potentials for some couples are exceedingly sensitive to axial ligation. It is suggested that this sensitivity may be used to 'tune' a redox couple for a specific purpose such as designing a reversible oxygen breathing system.
A theoretical study on the stereochemistry and protonation of −:CH2—NO2
Authors: Mezey P. G. , Kresge A. J. , Csizmadia I. G.
Published: May 2006

The molecular conformation of −:CH2NO2 is found to be planar with an extremely shallow potential curve to pyramidal inversion. This suggests that suitable substituents could conceivably perturb the System into a pyramidal configuration corresponding to double minimum on the potential surface and that a chiral carbanion might therefore exist. Rotating the NO2 group out of planarity by 90° raises the barrier to inversion at carbon by an appreciable amount.A Mulliken population analysis gives a charge distribution in which a substantial portion of the negative charge has shifted from carbon to oxygen; this is consistent with the well-known tendency of nitronate ions to undergo simultaneous competitive protonation on carbon and oxygen.
Syntheses and properties of phosphino- and phosphinatopyrazoles
Authors: Fischer Sven , Hoyano James , Peterson Louis K.
Published: May 2006

The new P—N bonded phosphino- and phosphinatopyrazoles [Formula: see text][Formula: see text] and (C2H5)2P(pz) and the arsenic derivative (pz)3As have been prepared and characterized (pz = pyrazolyl, Me2pz = 3,5-dimethylpyrazolyl).The reactivity of the P—N bond in phosphinopyrazoles towards electrophiles and nucleophiles is discussed. HCl, H2O, CH3OH, and BCl3 cleave the P—N bond, presumably via attack at the 2-N site. BF3 forms 1:1 adducts bonded to phosphorus which are reasonably stable in the solid state. CH3I forms a phosphonium salt with diphenyl(pyrazolyl)phosphine while other members of the series do not react. All members are inert toward CS2. Nucleophiles like sodium methoxide or phenyllithium displace the pyrazolyl moiety by attack at the phosphorus. Comparisons are made with the P—N bond in dialkylaminophosphines.
Pulse radiolytic formation of solvated electrons in hydrazine
Authors: Seddon William Arthur , Fletcher John Wallace , Sopchyshyn Fred Charles
Published: May 2006

The spectrum and yield of solvated electrons in anhydrous hydrazine have been investigated by pulse radiolysis. At room temperature the optical absorption band has a maximum at 1.22 eV (1015 nm) with a molar extinction coefficient of 2.2 ± 0.1 × 104 M−1 cm−1 and a temperature coefficient of 1.5 × 10−3 eV deg−1 from 7–45 °C. The oscillator strength is estimated to be 0.6. The optical transition energy is in reasonable agreement with an empirical correlation of solvent properties proposed by Freeman provided that only the polarisability of the nitrogen lone-pair electrons contribute to Emax. Comparisons are made with liquid amides which also have lone-pair polarisable groups and with water and liquid ammonia which have physical properties very similar to hydrazine. Electron yields increase from [Formula: see text] in pure hydrazine to 2.65 + 0.15 in basic solutions containing ≥0.1 M sodium hydrazide.
Synthesis of pencolide and corroboration of its revised stereochemistry
Authors: Strunz George M. , Ren Wu-Yun
Published: May 2006

A synthesis of the fungal metabolite pencolide from citraconic anhydride and threonine is described. Evidence is presented which corroborates the Z configuration recently assigned to the metabolite.
Complexes of niobium(III) with bidentate ligands
Authors: Allen A. D. , Naito S.
Published: May 2006

A novel method is reported for the convenient preparation of new niobium(III) chloro complexes containing the ligands SMe2, CH3C(CH2AsMe2)3, o-C6H4(AsMe2)2, and ((C6H5)2P—CH2—)2. Details of the preparation and characterization of the compounds are given. In each case the compounds are diamagnetic, and a dimeric metal–metal bonded structure is proposed.
Solvation effects on the conductivity of concentrated electrolyte solutions
Authors: Goldsack Douglas E. , Franchetto Raymond , Franchetto Arlene (Anttila)
Published: May 2006

The Falkenhagen–Leist–Kelbg equation for the conductivity of electrolyte solutions has been extended to include the effect of solvation on the concentration of the salt. Two equations have been derived, both of which have only two freely adjustable parameters at any temperature: Λ0 the molar conductance of the salt at infinite dilution and H0, a solvation number parameter for the salt. In one of these equations H0 is assumed to be independent of concentration. In the other, H0 is assumed to be dependent on concentration and an explicit concentration dependent formula is derived for H0. Conductance data for the alkali halide salts in the 0.5 to 10 m concentration range and 0 to 60 °C temperature range were found to be adequately reproduced by both these equations, but with the variable hydration parameter equation yielding better fits to the data. The H0 parameters from the fixed hydration parameter equation are found to be similar to those obtained from the analysis of activity coefficient and other data whereas the variable hydration parameter equation yields H0 parameters which are much larger.
On the photoelectron and ultraviolet spectra of molecules containing a divalent sulfur atom and a carbonyl group separated by a methylene group
Authors: Olivato P. R. , Viertler H. , Wladislaw B. , Cole K. C. , Sandorfy C.
Published: May 2006

Photoelectron spectra show that in CH3SCH2COCH3 the sulfur and carbonyl lone pair orbitals [Formula: see text] are both stabilized with respect to the compounds containing S or CO only. This is in keeping with the observed values of the basicity constants. The ultraviolet absorption spectra contain the expected [Formula: see text] and [Formula: see text] bands and give evidence for a significant amount of mixing between the excited orbitals.
Disubstituted derivatives of (L—L)Fe2(CO)6 (L—L = fluorocarbon bridged ligand)
Authors: Chia Lian Sai , Cullen William R. , Sams John R. , Scott James C.
Published: May 2006

The complexes (L—L)Fe2(CO)6 react with a range of bidentate ligands to give the complexes (L—L)′(L—L)Fe2(CO)4 ((L—L) = fluorocarbon-bridged ligand such as f4fars, f4AsP etc. (L—L)′ = fluorocarbon- and hydrocarbon-bridged ligands such as f4AsP diars etc.). Spectroscopic studies, in particular magnetically perturbed Mössbauer measurements, indicate that (L—L)′ in most complexes is chelated to one iron atom, FeA. This leaves one CO group on FeAcis to the FeA—FeB bond and three on FeB. A smaller class of derivatives appear to have (L—L)′ bridging the two iron atoms cis to the FeA—FeB bond. The sign of Vzz is positive at both iron sites in the bridged derivatives. It is negative at FeA and positive at FeB in the other complexes.
A Mössbauer study of organotellurium compounds. Part I
Authors: Jones Colin H. W. , Schultz Robert , McWhinnie William R. , Dance Nigel S.
Published: May 2006

Mössbauer data for a wide range of organotellurium compounds are reported, including compounds of the type: R2Te, Ar2Te, Ar2Te2, R2TeX2, Ar2TeX2, and ArTeX3; where R = alkyl, Ar = aryl, and X = Cl, Br, or I. The isomer shifts and quadrupole splittings are interpreted in terms of the relative populations of the tellurium 5s and 5p orbitals. The quadrupole splittings are rationalized in terms of a simple additive model, formulated within the framework of the Townes and Dailey theory.
A characteristic vector analysis of solvent effects for thermodynamic data
Authors: Fawcett W. Ronald , Krygowski T. Marek
Published: May 2006

Characteristic vector analysis has been performed on six sets of thermodynamic data relating to the solvation of electrolytes, polar molecules, and single ions in pure solvents. The analysis shows that variation in a given thermodynamic property with nature of the solvent can be accounted for with two characteristic vectors and that these vectors are linearly related to empirical measures of solvent basicity and acidity. The results confirm that an empirical relation proposed earlier by the present authors can be used to describe solvation effects with the limitation that the basicity of strongly structured protic solvents is difficult to describe quantitatively.
Vibrational spectra of crystalline malononitrile
Authors: Savoie R. , Brousseau R. , Nolin C.
Published: May 2006

The infrared and Raman spectra of the four solid phases of malononitrile have been recorded. The crystal structures of these solids are now relatively well established from the present results and from previous X-ray and nuclear quadrupole resonance data. Phase I belongs to the P21/n space group of the monoclinic system, with four molecules per unit cell. In phase II, the molecules occupy two sets of general positions in a crystal of P21 symmetry. The molecular site symmetry is Cs in phase III which is highly symmetric. The structure of the low-temperature metastable phase IV appears to be very similar to that of phase I.
Heat capacities of aqueous electrolytes: eight 1:1 electrolytes and ΔCp0 for ionization of water at 298 K
Authors: Singh Prem Paul , Woolley Earl M. , McCurdy Keith G. , Hepler Loren G.
Published: May 2006

We have made measurements with a flow calorimeter leading to apparent molal heat capacities of aqueous solutions of NaCl, HCl, KBr, KCl, KOH, NaBr, HBr, and NaOH at 298 K. Results have been used to derive apparent molal heat capacities of these electrolytes at infinite dilution and thence ΔCp0 = −215.2 ± 4 J K−1mol−1 for ionization of H2O(liq) at 298 K.
Structural and energetics effects in the chemical ionization of halogen-substituted benzenes and toluenes
Authors: Leung Hei-Wun , Harrison Alex G.
Published: May 2006

The H2, D2, CH4, and CD4 chemical ionization (CI) mass spectra of XC6H5, C6H5CH2X, and XC6H4CH3 (X = Cl, Br, and I) have been determined. For the benzyl halides the dominant ion observed in all CI spectra is the m/q 91 (benzyl) ion formed by loss of HX(DX) from the protonated (deuteronated) molecule. The CI spectra of the isomeric halotoluenes differ substantially from the spectra of the benzyl halides indicating that isomerization to a common (tropylium-like) structure does not occur in CI. In the H2 CI of XC6H4Y (Y = H or CH3) the major fragment ions observed are YC6H5•H+, [Formula: see text], and YC6H4+, with the relative yields depending strongly on the halogen substituent. Neither the YC6H5•H+ ion, resulting from HX loss from the H3+•XC6H4Y complex, nor the YC6H4+ ion, resulting from HX loss from XC6H4Y•H+, are observed when X = I. On the other hand [Formula: see text], resulting from elimination of X• from XC6H4Y•H+, is observed only for X = Br and I. In the CH4 CI of XC6H4Y, in addition to XC6H4Y•H+ ions, CH3C6H4Y•H+ ions (HX loss from the CH5+•XC6H4Y complex) are observed for X = F and Cl, while [Formula: see text] ions (loss of X• from XC6H4Y•H+) are observed only when X = I. In addition, displacement of I• by C2H5+, and by C3H5+, is observed in the CH4 CI of the iodo-substituted compounds. The dependency of the products observed and their relative yields on the identity of the halogen substituent is discussed in relation to the reaction energetics.
Photolyse du chloro-2 propane gazeux à λ = 147 et 123.6–116.5 nm
Authors: Gagnon Pierre , Herman Jan A.
Published: May 2006

In the photolysis at λ = 147 nm and 123.5–116.5 nm of gaseous 2-chloropropane the preponderant decomposition process (∼70%) gives propene and HCl (or H + Cl). Allene, propyne, and a fraction of the ethylene and acetylene are formed in the secondary decomposition of excited propene. The use of scavengers allowed the identification of the following free radicals: [Formula: see text] CH3•, C2H5•, iso-C3H7•, C3H4Cl• and C4H9•.
A wide-line nuclear magnetic resonance study of molecular motions in piperidinium salts
Authors: Bernard Marie-Claude , Orvig Christopher , Gilson D. F. R.
Published: May 2006

Wide line nmr and differential scanning calorimetric studies confirm the existence of crystal phase transitions in piperidinium iodide. The highest temperature phase involves isotropic rotation of the piperidinium ion. No crystal structure transitions occur in the chloride, bromide, or hexafluorophosphate salts although these compounds undergo second moment transitions indicating probable rotation of the piperidinium ion about the N—C3 axis.
Thermodynamic parameters for the basic ionization of some cyclic amines in water
Authors: Lobo Sheila Teresa , Murty Tanikella S. S. R. , Robertson Ross Elmore
Published: May 2006

The thermodynamic parameters defining the basic dissociation in water of diethylamine, cyclohexylamine, piperidine, and quinuclidine have been determined by a dilution method based on conductance measurements. The values of ΔSa0 and ΔCpa0 for the acid ionization of the corresponding ammonium ions at 25 °C are ΔSa0 −8.08, −1.24, −8.51, −13.65 cal deg−1 mol−1 and ΔCpa0 13.9, −2.7, 18.0, 4.2 cal deg−1 mol−1. The relation between these derived values and solvation changes are discussed, the apparent anomalous values of ΔCpa0 for cyclohexylamine and quinuclidine being noted, but not rationalized.
The conductances and viscosities of aqueous solutions of indium tribromide, indium nitrate, and aluminum bromide at 25 °C
Authors: Campbell Alan N.
Published: May 2006

The specific and equivalent conductances of aqueous solutions of indium tribromide, aluminum tribromide, and indium nitrate at 25 °C have been determined at concentrations ranging from 4.771 to 0.00577 N. The results for indium tribromide are in good agreement with those of Heydweiller (for 18 °C), the only previous figures, and which are limited to the relatively concentrated range. Below a concentration of 0.005 N, results for indium tribromide are valueless, because the conductance increases with time, owing to progressive hydrolysis. It is therefore not possible to determine the limiting conductance of indium tribromide experimentally. Although the aluminum trichloride results are independent of time, there is probably also a certain amount of hydrolysis at extreme dilution.The transport number of In3+ in InBr3 was determined at different concentrations, using the Hittorf method. The limiting value of the transport number, obtained by extrapolation to zero concentration, was 0.454. This leads to values of 62.1 mhos for [Formula: see text] and 140.5 mhos for Λ0 for [Formula: see text] These values are very different from those previously obtained (1), which were founded on an assumption which now appears to be untenable.The viscosities of aqueous solutions have also been determined and the results for the dilute region fitted to the Jones and Dole rule.
Cinétique de l'interaction des complexes Cu(II)–oxine, Cu(II)–biuret et Cu(II)–acide salicylique avec l'EDTA
Authors: Mallaret-Gout Elisabeth , Zador Miklos
Published: May 2006

The kinetics of the interaction of the complexes Cu(II)–biuret, Cu(II)–oxine, and Cu(II)–salicyclic acid with EDTA has been studied. The mechanism of the reaction involves a slow transfer of a proton followed by the rapid reaction of the protonated complex with EDTA. The rate constant contains contributions from the various forms of EDTA in solution as well as those from H2O and H3O+. However, the relative importance of the various terms varies from one system to another. [Journal translation]
Orthokinetic collisions of hard spheres in simple shear flow
Authors: Arp P. A. , Mason S. G.
Published: May 2006

From the rigorous hydrodynamic interaction theory of a pair of neutral hard spheres of radius b in a viscous fluid undergoing simple shear flow, the two-body collision theory has been developed which corrects the classical Smoluchowski theory based on rectilinear approach by applying the modern rigorous (and experimentally verified) curvilinear theory of approach. The difficulties in defining a collision are eliminated by defining a curvilinear collision sphere of radius ρm around a reference sphere. In this way correction factors for the area of the collision cross-section, the collision frequency, the average doublet life time, and the steady-state doublet concentrations of separating (or transient) doublets have been calculated as a function of ρm. The results show that the two theories are compatible for a ρm/b close to 2.38.
The X-ray photoelectron spectrum of hydrogen peroxide
Authors: Banna M. S. , Frost D. C. , McDowell C. A. , Wallbank B.
Published: May 2006

The oxygen 1s photoelectron spectrum of hydrogen peroxide in the gas phase has been investigated using AlKα radiation. The binding energy has been found to be 1.8(1) eV lower than the oxygen 1s level in carbon monoxide, as expected from simple electrostatic considerations.
Pulsed nuclear magnetic resonance study of deuteron lineshapes in clathrate hydrates
Authors: Ripmeester John A.
Published: May 2006

D nmr lineshape information was obtained from the echo response following a pair of phase shifted pulses using a method first proposed by Clark. In this manner the D quadrupole coupling constant and asymmetry parameter for D2O in p-dioxane•17D2O were found to be 217 kHz and 0.10 at 63 K. The D nmr lineshape for ethylene oxide-d4•7H2O shows that at 17 K the guest molecules are held rigidly in their cages. At higher temperatures the doublet lineshape collapses to a broad structureless line characteristic of molecules for which the reorientational modes vary from cage to cage.
Aliphatic diazo compounds. X. The reaction of α-diazoacetophenone with methanolic sodium methoxide
Authors: Yates Peter , Mayfield R. J.
Published: May 2006

The reaction of α-diazoacetophenone (1) with methanolic sodium methoxide in dilute solution gives 3-benzoyl-5-hydroxy-4-phenylpyrazole (4), 3-benzoyl-4-hydroxy-5-phenyl-pyrazole (5), 3-benzoyl-5-methoxy-4-phenylpyrazole (9), 3-benzoyl-4-phenylpyrazole (6), 5-benzoyltetrazole (7), 3,6-dibenzoyldihydro-s-tetrazine (10), cis- and trans- β-benzoyl- α-phenyl-acrylic acid, acetophenone, methyl benzoate, and benzoic acid. The pyrazoles 4, 5, and 9 are considered to arise via reaction of 1 to give α-methoxyacetophenone followed by further reaction of the anion of the latter with 1. Evidence in accord with this view was obtained by a study of the products formed when 1 was treated with methanolic sodium methoxide in the presence of 2-methoxy-4′-methylacetophenone. Acetophenone is considered to arise by reduction of 1 via phenylglyoxal 2-monohydrazone (37); condensation of 1 with the enolate ion derived from acetophenone then can give the pyrazole 6, while condensation of 1 with 37 could give the tetrazole 7.
The intra- and intermolecular copper (I) catalyzed couplings of vinyl Grignards. A facile synthesis of pleiadiene and a synthesis of a conjugated 14-membered ring system
Authors: Mitchell Reginald H. , Ghose Bhupendra N. , Williams Mary E.
Published: May 2006

Pleiadiene, 27, can be efficiently prepared in 45% yield by copper catalyzed intramolecular coupling of the bis-Grignard reagent of 1,8-trans-(β-bromovinyl)naphthalene, 5. Also obtained in 6% yield is the unsaturated 14-membered ring compound 28. Whereas the bis(β-bromovinyl) compound 5 is readily available from 1,8-divinylnaphthalene, α-bromovinyl compounds are obtained from divinylbenzenes. On coupling the Grignard reagent from 1,4-bis(β-bromovinyl)-benzene, only linear dimeric products were obtained.
The stereochemistry of addition of cyclopropanes to tetrachloro(diethylene)platinum(II)
Authors: Dominelli N. , Oehlschlager A. C.
Published: May 2006

The synthesis of trans-1-n-hexyl-cis-2,3-dideuterio cyclopropane and cis-1-n-hexyl-cis-2,3-dideuterio cyclopropane are reported. These specifically deuterated cyclopropanes were reacted with tetrachloro(diethylene)diplatinum to yield the product (dichloro(2-n-hexylpropane-1,3-diyl)platinum) of addition of Pt11 across the cyclopropyl C2C3 bond. It was shown by nmr spectroscopic analysis of the deuterated cyclopropanes and the bispyridine derivatives of the adducts that the Pt11–cyclopropane reaction was stereospecific and involved retention of configuration at both reacting carbons. This outcome is interpreted in terms of a concerted cycloaddition mechanism.
The sulfohaloform reaction. The stepwise conversion of dialkyl sulfides into alkanesulfonyl chlorides
Authors: Grossert J. Stuart , Langler Richard F.
Published: May 2006

A thorough examination of the aqueous oxidative chlorination of 1,3,5-trithiane is described. The results are utilized to explore and delineate the scope of a general, stepwise, oxidative cleavage reaction of dialkyl sulfides in which they are successively halogenated and oxidized to α-polychlorosulfoxides; subsequently, these cleave to form sulfinyl chlorides, which hydrolyze and become further oxidized to yield alkanesulfonyl chlorides. The overall stepwise process is named the 'Sulfohaloform reaction' and the structural requirements of the substrates at each step are explored in detail. A practical, general synthesis of sulfonyl chlorides is presented.
C-Nucleosides and related compounds. XII. The synthesis of the carbocyclic analogues of D, L-6-azapseudouridine, 2-thio-6-azapseu douridine, and pyrazofurin A. On the cyclization of semicarbazones of α-keto esters
Authors: Just George , Kim Sunggak
Published: May 2006

The preparation of the title compounds is described. The cyclization of the syn- and anti-isomers of semicarbazones, thiosemicarbazones, and carbomethoxymethyl hydrazones to azauracils, thioazauracils, and pyrazoles is described. The photochemical isomerization of the hydrazones has been carried out. Whereas both syn- and anti-isomers of the thiosemicarbazones and carbomethoxymethyl hydrazones cyclize, only the syn-isomer of the semicarbazones can be converted to the corresponding azauracil.
Nuclear analogs of β-lactam antibiotics. I. Synthesis of O-2-isocephams
Authors: Doyle Terrence William , Belleau Bernard , Luh Bing-Yu , Ferrari Carrado F. , Cunningham Michael Patrick
Published: May 2006

The preparation by total synthesis of a saturated cephalosporin analog 7-β-phenoxyacet-amido-3-ethoxy-O-2-isocepham-4-α-carboxylic acid 30, is described. Compound 30 was prepared via cycloaddition of azidoacetyl chloride to the cinnamylidene Schiff base of ethyl 2-amino-3, 3-diethoxypropionate 13b to give the cis-3-azido-4-styryl β-lactam 15b. Ozonolysis of 15b followed by sodium borohydride reduction gave the alcohol 18b. Boron trifluoride treatment of 18b gave ethyl 7-β-azido-3- β-ethoxy-O-2-isocephem-4-carboxylate 27. Reduction of the azido group followed by coupling with phenoxyacetic acid and saponification of the ester gave 30. The mechanism of the cycloaddition reaction and the stereochemical assignments are also discussed.
A stereospecifie, total synthesis of thromboxane B2
Authors: Hanessian Stephen , Lavallee Pierre
Published: May 2006

A stereospecific, total synthesis of crystalline thromboxane B2 from D-glucose is described.
Carbon-13, proton spin–spin coupling constants in some 4-substituted isothiazoles and related heterocyclics
Authors: Wasylishen Roderick E. , Hutton Harold M.
Published: May 2006

Carbon-13, proton nuclear spin–spin coupling constants have been measured for a number of 4-substituted isothiazoles. The observed values are compared with those measured in other heterocyclic systems and those calculated in the parent and related heterocyclics using finite perturbation theory and semi-empirical molecular orbital theory at the CNDO/2 and INDO levels of approximation.
Information theory and bulk rotational or vibrational relaxation processes
Authors: Yau Andrew W. , Pritchard Huw O.
Published: May 2006

The possible occurrence in bulk relaxation of pure-exponential, near-exponential, and non-exponential decay of the total energy is examined in terms of the normal-mode and information-theoretic approaches. Experimental tests are suggested for the identification of pure-exponential decay caused by adherence to the 'sum rule', and of near-exponential decay. In the case of near-exponential decay (as opposed to pure-exponential decay), it is not possible to derive reliable state-to-state rate constants by invoking approximate adherence to the sum rule.
Recombination of iodine atoms by flash photolysis over a wide temperature range. VIII. I2 in O2
Authors: Antrim R. E. , Burns George , Ip J. K. K.
Published: May 2006

Flash photolysis of I2 in a large excess of O2 was studied between 300 and 1173 K. Between 573 and 1173 K the rate of atomic recombination [Formula: see text]was measured without interference of side reactions. Its rate constant was found to be [Formula: see text]. Between 573 and 873 K there is an induction period lasting several hundred microseconds during which only a small net change in the iodine molecule concentration takes place. This induction period is consistent with the reaction [Formula: see text] Beow 573 K, the overall recombination rate constant has a temperature dependent negative temperature coefficient and is enhanced when the flash includes radiation in the neighborhood of 200 nm. Evidently this occurs because the flash photolysis of O2 creates new efficient third bodies, such as O3 and O2 (1Δg), which accelerate the recombination reaction either directly or via an IO intermediate. The mechanism for the formation of IO during the flash photolysis of I2 in an excess of O2 was studied. It was shown that the reactions O(3P) or [Formula: see text], where O3* refers to an electronically or vibrationally excited state of O3, account for the formation of IO under our experimental conditions. IO may also possibly be formed via the reaction [Formula: see text]. On the other hand, reactions between excited or ground state I atoms and O2 suggested by earlier workers do not occur. Thus, all experimental complications observed are traceable to the presence of O2 photolysis products and to the reaction of I(2P1/2) with O2(3Σg−).
The linear mixture formula in non-equilibrium chemical kinetics
Authors: Boyd Robert K.
Published: May 2006

The recent extensions of the 'eigenvalue approximation' of non-equilibrium kinetics proposed by Bartis and Widom to explain in a direct qualitative sense some general features of phenomenological chemical kinetics in ideal gas systems, have been used to investigate the problem of the 'linear mixture formula' applied to non-equilibrium kinetics of reactions proceeding in mixtures. For isomerization reactions in mixtures dilute in reactant, the model of Bartis and Widom, without further embellishment, has been shown to justify such an equation. Extrapolation of this result to account for recent empirical successes of a linear mixture formula in dissociation–recombination reactions of diatomic molecules X2 is not straightforward; the physical implications of the mathematical approximations employed are examined, and the non-linear recombination term is accounted for in the present purely qualitative context by an appropriate linearization. However, the appreciable contributions from X2–X2 collisions, under the conditions of the experiments cited, introduce inescapable non-linearities if vibration–vibration exchange, for example, is important. Problems associated with the role of the free atom X as a collision partner seem likely to be less important.
An acidity function based on thiocarbonyl indicators
Authors: Edward John T. , Lantos Ivan , Derdall Gary D. , Wong Sin Cheong
Published: May 2006

The ionization of 16 thiocarbonyl indicators of overlapping range has been used to establish an acidity function HT for 10–90% sulfuric acid. Agreement with an earlier HT scale of Tissier and Tissier using different thiocarbonyl indicators is good. Protonation constants pKTH+ derived by the classic Hammett–Deyrup approach are in good agreement with those derived by the Bunnett–Olsen relations, but in less satisfactory agreement with those derived by the Marziano–Cimino–Passerini relations.
The heat capacities, volumes, and expansibilities of tert-butyl alcohol – water mixtures from 6 to 65 °C
Authors: Visser Cees de , Perron Gerald , Desnoyers Jacques E.
Published: May 2006

The densities and specific heat capacities of mixtures of tert-butyl alcohol (TBA) and water (W) have been measured at 6, 10, 25, 40, 55, and 65 °C. From these data the apparent molal volumes[Formula: see text], heat capacities[Formula: see text], and expansibilities [Formula: see text] were evaluated. Generally, the temperature dependence of these quantities is rather characteristic of hydrophobic solutes in water. At high concentrations [Formula: see text]and [Formula: see text] resemble those of surfactants, suggesting the existence of some microphase separation. At low temperatures [Formula: see text] show a significant hump as a function of concentration, which is probably not due to the presence of the —OH group on the TBA molecule. A similar behaviour is observed for[Formula: see text]. The [Formula: see text] and [Formula: see text] of water in TBA have also been calculated; [Formula: see text] is in theTBA-rich region 2 to 2.5 cm3 mol−1 smaller than the molar volume of water, but [Formula: see text] is of the same order of magnitude as the molar heat capacity of water.
N-Methylamino acids in peptide synthesis. VI. A method for determining the enantiomeric purity of N-methylamino acids and their derivatives by ion-exchange chromatography as their C-terminal lysyl dipeptides
Authors: Cheung S. T. , Benoiton N. Leo
Published: May 2006

A method capable of detecting one part in one thousand of the other isomer is described for determining the enantiomeric purity of N-methylamino acids and their cleavable derivatives. The method consists in converting the N-methylamino acid to its N-benzyloxycarbonyl derivative, and/or coupling the derivative with benzyl Nε-εbenzyloxycarbonyl-L-lysinate using N,N′-dicyclohexylcarbodiimide, followed by removal of protecting groups by catalytic hydrogenation or other cleavage methods not affecting the chirality of the product. The resulting diastereomeric lysyl peptides are analyzed by ion-exchange chromatography on a 15 cm column of Aminex A-5 resin using an amino-acid analyzer. The method is applicable to samples contaminated by the corresponding unmethylated amino acid or derivative, and in effect, provides a new method for determining the enantiomeric purity of amino acids and their derivatives as well.Examples are given where, in some cases, optical purity verification or configurational assignment for N-methylamino acids can be achieved by inspection of the nmr spectra of related lysyl dipeptide derivatives.
Ring formation via β-keto ester dianions
Authors: Sum Phaik-Eng , Weiler Larry
Published: May 2006

The reaction of α,ω-dihalides with the dianion of methyl acetoacetate gives a mixture of mono- and bisalkylated products. The monoalkylated products can be cyclized via the monoanion to cyclic β-keto esters with a seven- or eight-membered ring. Alternatively these monoalkylated products can be cyclized via the dianion to γ-cyclopentyl- or γ-cyclohexyl-β-keto esters.
Total synthesis of ylango sesquiterpenoids: (+)-cis- and (+)-trans-sativenediol, (+)-helminthosporal, (+)-helminthosporol, prehelminthosporal, prehelminthosporal diethyl acetal, (+)-victoxinine, (+)-isosativenediol
Authors: Piers Edward , Isenring Hans-Peter
Published: May 2006

Oxidation of the previously prepared olefinic alcohol 26 with chromium trioxide – pyridine in dichloromethane containing trifluoroacetic acid gave the tricyclic ketone 29 as the major product. Hydroxylation of the latter, followed by reduction of the resulting α-hydroxy ketone 31, afforded a 1:1 mixture of (+)-cis- (22) and (+)-trans-sativenediol (23). In view of earlier synthetic transformations reported by a number of different researchers, the present work also constitutes formal total syntheses of the enantiomers of the following sesquiterpenoids: (−)-helminthosporal (1), (−)-helminthosporol (2), prehelminthosporal (3), prehelminthosporal diethyl acetal (4), (−)-victoxinine (8), and (−)-isosativenediol (19).
Studies in the usnic acid series. VI. The preparation of some ether derivatives of (+)-usnic acid
Authors: Kutney James P. , Sanchez Ignacio H.
Published: May 2006

Studies involving the selective O-alkylation of (+)-usnic acid (1) have provided high yielding methods for the preparation of mono- and diether derivatives of 1. With appropriate selection of conditions, either 7- or 9-O-alkyl derivatives can be prepared.
On the construction of the C,D ring system of chasmanine by the photochemical method
Authors: Wiesner K. , Sanchez I. H. , Atwal K. S. , Lee S. F.
Published: May 2006

Two highly stereoselective syntheses of the methoxy ketal 18, which had been previously transformed to the chasmanine model compound IV are described. Both these processes avoid the equilibration step [Formula: see text] which failed (with compounds [Formula: see text]) in the actual chasmanine synthesis. There is reason to believe that the second of these routes, remarkable by its brevity, will be applicable in the full chasmanine system.
X-Ray photoelectron spectroscopy of monosubstituted perfluorobenzenes
Authors: Trudell Barry C. , Price S. James W.
Published: May 2006

The gas phase X-ray photoelectron spectra, XPS, were observed for the series C6F5X (X = F, Cl, I, Br, H). Binding energies were determined from the spectra using the ESCAPLOT Program. Charge calculations were carried out using Equalization of Electronegativity, CNDO/2, and ACHARGE approaches on each molecule. The more sophisticated analysis leads to the following equation correlating the (C 1s) binding energies and the atomic charges qi[Formula: see text]
Viscosities of mixtures of SnR4 compounds and of some other large globular molecules. Effect of size difference
Authors: Jambon Claude , Delmas Geneviève
Published: May 2006

Solution viscosities have been measured at 25 °C on seven I systems of SnR4 compounds: SnBut4 with SnMe4, SnEt4, SnPr4, SnOct4, SnLaur4 and SnLaur4 with SnEt4 and SnPr4. The effect of shape difference on excess solution viscosities was investigated. The experimental value Δ ln ηexp = ln ηs − x1 ln η1 − x2 ln η2 was compared to Δ ln ηth.Δ ln ηth was obtained using ΔGM(mixing) in place of GM≠(activation) and free volume theories. Experimental heats of mixing have been measured and are used inΔ ln ηth. It was found that with the Van der Waals model for the energy, the difference Δ ln ηexp − Δ ln ηth, indicative of the agreement between the predicted and experimental value, is relatively small for mixtures of molecules not having a large size difference. However, for systems different in size, Δ ln ηexp − Δ ln ηth is positive and large and is shown to be an increasing function of the size difference. Δ ln ηth could be adjusted to Δ ln ηexp by adding a term ln ηΔV* = c(V1*1/2 − V2*1/2)2 where V* is the core volume. To confirm the validity of ln ηΔV*, the seven II systems chosen in order to present a large range (V1*1/2 − V2*1/2) were measured: SnBut4 + squalane, Si(OEt)4 + Si(OOct)4, n-C10 + Si(OOct)4, Si(OEt)4 + squalane, n-C12 + SnOct4, Si(OMe)4 + Si(OOct)4, n-C16 + benzene. A c value of 5.3 × 10−3 cm3 appears to be adequate for all the systems studied in this work. The 'condensation effect' of SnEt4 and SnPr4 observed by calorimetry is possibly seen here in the series SnLaur4 with SnEt4, SnPr4, SnBut4.
Anatoxin-a, a toxic alkaloid from Anabaena flos-aquae NRC-44h
Authors: Devlin J. P. , Edwards O. E. , Gorham P. R. , Hunter N. R. , Pike R. K. , Stavric B.
Published: May 2006

A toxic alkaloid, anatoxin-a, has been isolated from mass cultures of a unialgal clone, NRC-44h, of the freshwater blue-green algae Anabaena flos-aquae (Lyngb.) de Bréb., and its structure determined.
The ultraviolet absorption spectrum of methyl diimide vapor
Authors: Vidyarthi S.K. , Willis C. , Back R.A.
Published: May 2006

The vapor phase absorption spectra of CH3N=NH and CH3N=ND have been measured from 160–450 nm. There are three prominent features centered at 360 nm (ε = 6 M−1 cm−1), 208 nm (ε = 710 M−1 cm−1), and 170 nm (s = 2080 M−1 cm−1). The weak near-uv band is assigned to the valence shell transition π* ← n+ while the two far-uv bands are attributed to the 3s ← n+ and 3p ← n+ Rydberg transitions. The band at 208 nm has resolved vibrational structure on the long wavelength tail and a vibrational analysis shows the main progression excited is the ν10′ CNN deformation mode.
N-Ethylamino acid synthesis and N-acylamino acid cleavage using Meerwein's reagent
Authors: Chen Francis M.F. , Benoiton N. Leo
Published: May 2006

N-Ethylamino acids have been prepared by reaction of N-acetylamino acids with trimethyloxonium tetrafluoroborate (Meerwein's reagent) giving imino ether fluoroborates, followed by reduction with sodium borohydride. The use of Meerwein's reagent for the deacylation of N-acylamino and N-acyl, N-methylamino acid derivatives has been investigated.
A theoretical study of the Curtius rearrangement. The electronic structures and interconversions of the CHNO species
Authors: Rauk Arvi , Alewood Paul F.
Published: May 2006

The thermal and photochemical decomposition of formyl azide in the Curtius rearrangement has been studied by means of RHF–LCAO–MO–SCF calculations augmented by CI. The lower electronic states of carbonyl azides, carbonyl nitrenes, isocyanates, cyanates, oxazirenes, nitrile oxides (fulminates), and isofulminates are discussed on the basis of the results for formyl azide and the corresponding isomers of formula CHNO. The discovery of two nearly degenerate states of A′′ symmetry for formyl azide which may channel decomposition products directly to both isocyanates and carbonyl nitrenes explains some puzzling features of the photolytic Curtius rearrangement. The interconvertibility of the CHNO isomers (and the RCNO isomers) is discussed in terms of the energetics and intended correlations of the accessible electronic states of these species.
Determination of motional asymmetry of methyl rotators from 13C spin dynamics
Authors: Werbelow Lawrence G. , Grant David M.
Published: May 2006

Recent advances in the theory of dipolar relaxation in multispin systems are applied to studies of methyl rotators in isotropic fluids. A simple methodology is outlined which is very attractive for the investigation of anisotropic methyl group reorientation. It is demonstrated that this approach does not suffer from many of the inherent limitations of conventional applications of dipolar relaxation to such studies. Analogous extensions of the propounded method become temptingly obvious.
Hydroxymethylbenzimidazole carboxylic acid models of the Asp-His-Ser charge relay system of serine proteases
Authors: Jones J. Bryan , Taylor Keith E.
Published: May 2006

2-Hydroxymethyl- and 2-acetoxymethylbenzimidazole, and their C-4(7)-carboxy derivatives, have been synthesized and characterized for evaluation as chemical models of the Asp-His-Ser triad present at the active sites of several serine proteases. Preliminary studies of the 2-acetoxy compounds, which are analogues of the acyl enzymes, show that the rate of hydrolysis is augmented only 2.5 fold by the carboxylate group of the model charge relay system.