bluuebunny/crossref_metadata_2025 huggingface dataset:
Radical ions in photochemistry. 6. The photosensitized (electron transfer) ring opening of aryloxiranes
Authors: Albini Angelo , Arnold Donald R.
Published: May 2006

The photosensitized (electron transfer) irradiation of cis- and trans-2,3-diphenyloxirane (1 and 2) led to cleavage of the oxirane carbon–carbon bond and subsequent formation of the carbonyl ylide. The resulting carbonyl ylides have been trapped with the dipolarophiles, acrylonitrile, maleonitrile, and fumaronitrile. The resulting isomeric tetrahydrofuran derivatives have been characterized. Sensitizers (electron acceptors) which are effective include 1,4-dicyanonaphthalene, 1,4-dicyanobenzene, dimethyl terephthalate, and methyl 4-cyanobenzoate; 1-cyanonaphthalene was not effective. The proposed mechanism involves formation and cleavage of the oxirane radical cation followed by back electron transfer from the sensitizer radical anion to give the carbonyl ylide. Electrochemical and photophysical evidence which supports the proposed mechanism was obtained.
Branched-chain sugars. Reaction of furanoses with formaldehyde: A simple synthesis of D- and L-apiose
Authors: Ho Pak-Tsun
Published: May 2006

A simple synthesis of D- and L-apiose using the aldol condensation of furanose with formaldehyde under alkaline conditions as a key reaction is described.
Thermodynamics of chloroform and methanol mixtures
Authors: Singh Prem P. , Sharma Buta R. , Sidhu Kuljit S.
Published: May 2006

Heats of mixing and vapour pressures of chloroform (A)+ methanol (Bn) as a function of concentration have been determined at 303.15 K. The excess Gibbs free energy of mixing, GE values, have been obtained from the measured vapour pressure data. The heats of mixing values are negative for solutions rich in methanol but they become positive for solutions rich in chloroform. On the other hand, GE values are positive for all the methanol mole fractions and GE > HE. The results have been analysed in terms of Barker and ideal associated model theory of non-electrolyte solutions. The analysis has revealed that only the ideal associated model approach (which here assumes the presence of AmB (m = 1, 2), ABk (k = 2) and Bl (l = 1) molecular species) well describes the general behaviour of HE with xA over the entire chloroform concentration range for this mixture. The equilibrium constants for the various association reactions along with the enthalpy of formation of the various molecular species have also been calculated.
13C nuclear magnetic resonance spectral and conformational analysis of naturally occurring tetrahydrofuran lignans
Authors: Fonseca Sebastião F. , Barata Lauro E. S. , Rúveda Edmundo A. , Baker Paul M.
Published: May 2006

The 13C nmr spectra of the naturally occurring stereoisomers of the tetrahydrofuran lignans were recorded and the signals assigned. Based on these assignments, on the observed sensitivity of the benzylic carbon shifts to the orientation of the aryl groups, and on the comparison with previously reported 1H nmr data, the most probable conformations for the mentioned stereoisomers are suggested.
Tautomeric equilibria and pKa values for 'sulfurous acid' in aqueous solution: a thermodynamic analysis
Authors: Guthrie J. Peter
Published: May 2006

The free energy of formation of dimethyl sulfite in aqueous solution can be calculated as −91.45 ± 0.79 kcal/mol; this calculation required measurement of the solubility of dimethyl sulfite. From this value and the pKa of SO(OH)2, using previously reported methods, the free energy of formation of SO(OH)2 can be calculated to be −129.26 ± 0.89 kcal/mol. Comparison of this value with the value obtained from the free energy of formation of 'sulfurous acid' solutions, calculated from the free energy of formation of sulfite ion and the apparent pKa, values, permits evaluation of the free energy of covalent hydration of SO2 as 1.6 + 1.0 kcal/mol, in agreement with earlier qualitative spectroscopic observations. From the apparent pKa and the anticipated pKa values for the tautomers (SO(OH)2, pK1 = 2.3; HSO2(OH), pK1 = −2.6) it is possible to calculate the free energy change for tautomerization of SO(OH)2 to H—SO2(OH) as +4.5 ± 1.2 kcal/mol. All equilibrium constants required for Scheme 1, describing the species present in dilute aqueous solutions of SO2, have been calculated. In agreement with previous Raman studies the major tautomer of 'bisulfite ion' is calculated to be H—SO3−.
Band resolution of optical spectra of solvated electrons in water, alcohols, and tetrahydrofuran
Authors: Jou Fang-Yuan , Freeman Gordon R.
Published: May 2006

The optical absorption spectra of solvated electrons in water, alcohols, and tetrahydrofuran are empirically resolved into two Gaussian bands and a continuum tail. The first Gaussian band covers most of the low energy side of the spectrum. The second Gaussian band lies at an energy slightly above that of the absorption maximum of the total spectrum. With the exception of tert-butyl alcohol, in water and alcohols the following were observed: (a) the first Gaussian bands have the same half-width, but the oscillator strength in water is about double that in an alcohol;(b) the second Gaussian bands have similar half-widths and oscillator strengths; (c) the continuum tails have similar half-widths, yet that in water possesses only about one third as much oscillator strength as one in an alcohol. In tert-butyl alcohol and tetrahydrofuran the first Gaussian band and the continuum tail each carry nearly half of the total oscillator strength.
A stereoselective synthesis of sucrose. Part III. Spectroscopic analyses of key intermediates
Authors: Iley David Erle , Fraser-Reid Bert
Published: May 2006

Condensation of the diene 1 with the α,β-anomeric mixture of tetraacetyl fructofuranose and processing of the resulting product gives rise to a series of disaccharides, 5, 6, and 7, each of which is a mixture of two substances differing only in the anomeric configuration at the fructosyl centre, the linkage at the pyranosyl moiety being α in all cases. This conclusion is reached by careful comparison of the 1Hmr and 13Cmr spectra of these disaccharides with those of a number of fructofuranose derivatives. There are interesting correlations in configuration, conformation, and optical rotation.
Studies in membrane processes. VIII. A deuterium and sodium nuclear magnetic resonance investigation into the hexadecylpyridinium/hexadecyltrimethylammonium liquid crystalline system
Authors: Reeves Leonard W. , Tracey Alan S. , Tracey Marcelline M.
Published: May 2006

Novel lyotropic mesophases that spontaneously orient in magnetic fields have been prepared using hexadecylpyridinium chloride and hexadecyltrimethylammonium bromide as well as, in limited regions, mixtures of the two detergents. These mesophases of type II provide the opportunity to study the behaviour of oriented water (DOH) at the hydrophobic interface, sodium ions, and the effect on hydrocarbon chain motions of variations in composition of the constituent bilayers formed by the mixed detergent systems. The pyridinium head group is especially accessible to definitive studies using deuterium magnetic resonance spectra of specifically deuteriated ring and adjacent hydrocarbon chain segments. Such investigations reveal the lack of cylindrical symmetry of motion about the extended chain axis near the pyridinium head group.The deuterium resonance of the HOD species shows that both pyridinium and trimethylammonium head groups have a very small orienting effect on the adjacent water, which appears to be indifferent to the choice of these chemical identities. This is understandable in terms of the lack of hydrogen bonding to these moieties. Sodium ions also exhibit small quadrupole splittings in all systems studied here and thus probably play a passive role in the interface chemistry and structure.
Etude structurale des chlorure et sulfate de béryllium hydratés par spectrométrie infrarouge et Raman
Authors: Bertin François , Derouault Jean
Published: May 2006

The authors have investigated the nature of the compound which is formed by direct hydration of beryllium chloride. The compound is analysed by chemical means, by infrared and Raman spectroscopy, and by comparison with the spectra of tetrahydrated sulphate. The results are consistent with the formula [Be(OH)(H2O)2+Cl−]n.A cyclic trimeric compound is assumed and a simplified coordinate analysis is performed in order to support these assignments. [Journal translation]
Reactions of silicon fluorides with some non-metal hydrides
Authors: Thompson James Charlton , Wright Arthur Paul Gerald
Published: May 2006

The reactions of SiF4, Si2F6, and SiF2 with PH3, CH3PH2, (CH3)2PH, (CH3)4P2, HSCH3, and HSi(CH3)3 have been studied. Several new compounds resulting from insertion of Si—F containing units into P—H, S—H, or Si—H bonds have been identified.
Synthesis of a thioanalogue of neamine. The reaction of nitrosochloroadducts of glycals with thiols
Authors: Kavadias Gerry , Droghini Robert , Pépin Yvon , Ménard Marcel , Lapointe Philippe
Published: May 2006

The reaction of the dimeric 4-O-acetyl-6-azido-2,3,6-trideoxy-2-nitroso-α-D-ribo-hexopyranosyl chloride 2 with cyclohexanethiol and 2-propanethiol is stereospecific and produces the corresponding 2-hydroxyimino-1-thio-α-D-erythro-hexopyranosides 3a and 3c in high yields. Acetylation of the oxime 3a followed by reduction with borane, then by reduction with sodium borohydride and acetylation gave cyclohexyl 2,6-diacetamido-4-O-acetyl-2,3,6-trideoxy-l-thio-α-D-ribo-hexopyranoside (4b). By a similar sequence of reactions, the oxime 3c was converted to isopropyl 2,6-dibenzamido-4-O-benzoyl-2,3,6-trideoxy-l-thio-α-D-ribo-hexopyranoside (4c).Condensation of the nitrosochloro adduct 2 with (1S,2S,4R,5R)-2,4-diethoxycarbonylamino-5-hydroxycyclohexanethiol (5c) gave the α-D-thioglycoside 6c which, after acetylation followed by reduction and removal of the protective groups, yielded (1S,2S,4R,5R)-2,4-diamino-5-hydroxycyclohexyl 2,6-diamino-2,3,6-trideoxy-l-thio-α-D-ribo-hexopyranoside (7c), a thioanalogue of neamine.
Intramolecular alkylation of of α,β-unsaturated ketones: a study of the effect of substrate structure and experimental conditions on the site of alkylation
Authors: Piers Edward , Zbozny Michael , Wigfield Donald C.
Published: May 2006

The syntheses of 4a-(3-chloropropyl)- (22), 4a-(3-iodopropyl)- (23), and 4a-mesyloxymethyl-4,4a,5,6,7,8-hexahydro-2(3H)-naphthalenone (24) are described. The results obtained from the intramolecular alkylation of each of these compounds under a variety of experimental conditions are summarized in Tables 1 and 2. It was found that alkylative cyclization of compounds 22 and 23 gave varying amounts of two products, one (34) resulting from α′ alkylation and the other (35) being derived from α alkylation. In contrast, intramolecular alkylation of the enone 24 produced only the γ alkylation product 11, or afforded a mixture of 11 and the α alkylation product 41. The intramolecular alkylation results are discussed in terms of Scheme 5.
A study of 14N relaxation and nitrogen–proton spin coupling in Watson–Crick base pair models through Fourier transform measurements on NH proton spin–lattice relaxation in the rotating frame
Authors: Moseley Michael E. , Stilbs Peter
Published: May 2006

Indirect measurements of nitrogen-14 nuclear spin-lattice relaxation times and direct proton coupling constants are presented together with carbon-13 T1 data for a series of alkyl-substituted nucleic acid bases and mixtures thereof in DMSO-d6. With the exception of the guanine NH nitrogen, which possibly experiences a decrease in the electric field gradient upon complexation with cytosine, no indications of significant changes in the electronic environment around the nitrogen nuclei were found for any combination of bases. Forsen–Hoffman spin saturation transfer experiments on the NH and NH2 protons are also presented.
Absorption and magnetic circular dichroism spectra of metal-free phthalocyanine in ultraviolet-transparent solvents
Authors: Martin Katherine A. , Stillman Martin J.
Published: May 2006

Absorption and magnetic circular dichroism spectra of metal-free phthalocyanine (H2Pc) have been recorded over the range 270–800 nm. The use of solvents transparent in the 270–400 nm region allows the observation for the first time of the B band spectral envelope of H2Pc in solution. The mcd spectrum clearly indicates that the complex (NH4)2Pc is formed when ammonia is bubbled through a solution of H2Pc in dimethyl sulphoxide. The multi-transition nature of the B band region is identified as a property of the phthalocyanine π electron system rather than arising from charge transfer between the ring and a central metal cation.
On the interpretation of measured rotational and vibrational relaxation times. III. Failure of the mixture rule for non-dilute gases
Authors: Pritchard Huw O. , Labib Nabil I. , Lakshmi Arunachalam
Published: May 2006

The rotation–vibration relaxation of a mixture of a diatomic gas (approximately simulating hydrogen) with an inert gas is studied both by direct integration, and by an approximate linearised normal-mode method. It is shown that although the linearised normal-mode approximation is a powerful aid to understanding these processes, its numerical accuracy is limited to high dilutions (e.g. 1% of X2 in M) and to times shorter than the final relaxation time.Direct numerical integration of the relaxation equations for various mixture ratios shows that the plot of vibrational relaxation rate constant vs. mole fraction x is non-linear, and that the slope of this plot near x = 0 can be correlated with the rates of the R–R processes, not the V–V processes as is normally assumed. A brief discussion is presented of the conditions under which the linear mixture rule for relaxation is rigorously obeyed: as is the case for chemical reaction, these conditions are impossibly stringent.An appendix presents a comparison of the transition probabilities used in this series of papers with those recently obtained by Tarr and Rabitz for the relaxation of hydrogen in argon.
The enol content of simple carbonyl compounds: an approach based upon pKa estimation
Authors: Guthrie J. Peter
Published: May 2006

Rate constants for oxygen-base-catalyzed enolization of di- and tricarbonyl compounds can be correlated by a Marcus equation, with hydroxide requiring a slightly different curve from other oxyanions. Data for monocarbonyl compounds fall on a slightly different, but similar, set of curves. The equilibrium constants for enolization for a set of monocarbonyl compounds were derived from recent work in this laboratory. These correlations permit estimation of pKaKeto for a number of other monocarbonyl compounds from kinetics data in the literature. Elaboration of methods previously developed permits estimation of pKaEnol. From the values of pKaEnol and pKaKeto, pKEnol can be derived. It is pointed out that pKaKeto for acetone and acetophenone can be determined from the kinetics of the reaction with hypochlorite in base; the values so derived are in good agreement with those used in this work. pKEnol values are reported for: 1,3-dichloroacetone, 2.0; 1,1-dichloroacetone, 4.9; ethyl pyruvate, 4.2; bromoacetone, 3.5; chloroacetone, 3.7; l-phenyl-2-propanone, 4.5 (CH2); 7.2 (CH3); p-nitroacetophenone, 7.1; ethyl levulinate, 5.6; methoxyacetone, 6.9 (CH2); 7.6 (CH3); benzalacetone, 7.6; p-methoxyacetophenone, 7.8; 3-methyl-2-butanone, 8.0 (CH); 2,4-dimethyl-3-pentanone, 9.4.
The azidonitration of tri-O-acetyl-D-galactal
Authors: Lemieux R. U. , Ratcliffe R. M.
Published: May 2006

Reaction of 3,4,6-tri-O-acetyl-D-galactal with excess ceric ammonium nitrate and sodium azide in acetonitrile produced 2-azido-1-nitrate addition products (53% β-galacto, 22% α-galacto, and 8% α-talo) and N-acetyl-3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-galactopyranosylamine was formed, on hydrolysis, in 10% yield. The reaction product provides a convenient source of D-galactosamine and 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-galactopyranosylhalides. The crystalline β-chloride is also reported. The use of these glycosyl halides as reactants for the preparation of 2-azido-2-deoxy-α- and -β-D-galactopyranosides under conditions promoted by both mercuric cyanide and silver salts are reported.
The reactions of atomic oxygen with 1-propanol and 2-propanol
Authors: Ayub A. L. , Roscoe John M.
Published: May 2006

The reactions of O(3P) with n-propanol and isopropanol were studied as a function of temperature. The absolute rate constants for these reactions, in the units M−1 s−1, obey the following relations.[Formula: see text]The activation energies of these reactions are similar to those of the corresponding reactions of methanol and ethanol, although some dependence on the strength of the α-C—H bond is discernible. The nearly constant pre-exponential factors for the reactions of methanol, ethanol, n-propanol, and isopropanol suggest that no special steric effects are present in the reactions of these compounds with O(3P). Mechanisms are discussed for the reactions of n-propanol and isopropanol with O(3P).
Total synthesis of δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV), a biosynthetic precursor of penicillins and cephalosporins
Authors: Wolfe Saul , Jokinen Mark Gordon
Published: May 2006

The title compound has been synthesized as its disulfide by a classical route from the fully protected precursor N-BOC-S-trityl-δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine bisbenzhydryl ester. Deprotection has been achieved by oxidative removal of the trityl group with iodine, followed by removal of BOC and benzhydryl using trifluoroacetic acid. The final product is obtained in 23% overall yield from D-valine.
Benzocyclobutyl phenyl sulfone. An evaluation of its potential as a precursor to substituted benzocyclobutenes and ortho-quinodimethanes
Authors: Gowland Barbara D. , Durst Tony
Published: May 2006

Benzocyclobutyl phenyl sulfone has been converted to several 7-substituted benzocyclobutenes via reaction of its α-sulfonyl carbanion with typical electrophiles followed by desulfonylation with Na/Hg in methanol. Two benzocyclobutenes carrying remote terminal vinyl groups have been isomerized to tricyclic ring systems upon heating at 250 °C. The o-quinodimethane obtained from thermolysis of benzocyclobutyl phenyl sulfone in toluene at 250 °C is not trapped by maleic anhydride but by the solvent toluene in a Friedel–Crafts type alkylation.
Determination of ΔHf2980(C12F10,g) from studies of the combustion of decafluorobiphenyl in oxygen and calculation of D(C6F5—C6F5)
Authors: Price Stanley James W. , Sapiano Henry J.
Published: May 2006

The heat of formation of decafluorobiphenyl has been determined by the direct combustion method previously developed and used for hexafluorobenzene and related compounds. As in the hexafluorobenzene case the combustion of decafluorobiphenyl in oxygen yields CO2, CF4, and F2. With a ten-fold excess of oxygen the CO2 to CF4 ratio is 5.85 ± 0.08. A full material balance was obtained. The value of ΔHf2980(C12F10,g) = −1263.2 ± 5.1 kJ mol−1 may be combined with ΔHf2980(C6F5,g) = −387.4 ± 12.0 kJ mol−1 to give D(C6F5—C6F5) = 488.4 ± 24.5 kJ mol−1. Also with ΔHf2980(C6F6,g) = −945.6 ± 8.0 kJ mol−1 ΔH2980 for reaction [3][Formula: see text]is calculated to be −628.0 ± 16.8 kJ mol−1.
The formation and interconversion of oxazines and dioxazines from the reaction of nitrosocarbonyl compounds with cyclopentadienes
Authors: Dao Lê H. , Dust Julian M. , Mackay Donald , Watson Kenneth N.
Published: May 2006

The nitrosocarbonyl arenes or -alkanes, obtained by oxidation of hydroxamic acids, behave as dienophiles towards cyclopentadiene to give the bridged oxazines 1. In the case of pivalo-hydroxamic acid, however, the nitrosocarbonyl compound also reacts as a heterodiene, giving, as well as the oxazine 1d, the 1,4,2-dioxazine 2d; 1d is not converted into 2d under the conditions of the oxidation reaction.Extended heating of compounds 1 slowly converts them into 2 and other more complex reaction products. This contrasts with the rapid and quantitative isomerization of the analogous azodicarbonyl adducts, and probably reflects the lesser crowding of the reacting NCOR group by an adjacent oxygen than by an adjacent NCOR group.1,4-Dimethyl-2,3-diphenylcyclopentadiene traps the nitroso compounds to form the labile oxazines 8, which rapidly isomerize to the dioxazines 9 on brief heating or in polar solvents. In the case of the benzoyl compound 8a the isomerization to 9a is reversible in benzene at 80 °C, favouring the latter isomer by a factor of about 9:1.
The generation of C-glycosides through the enolate Claisen rearrangement
Authors: Ireland Robert E. , Wilcox Craig S. , Thaisrivongs Suvit , Vanier Noel R.
Published: May 2006

The [3,3]-sigmatropic rearrangements of silyl ketene acetals obtained from aliphatic esters of furanoid and pyranoid glycals is described. The heterocyclic γ,δ-unsaturated carboxylic acids II are produced in good yields. A new preparation of furanoid and pyranoid glycals is described.
Partial deconvolution of the absorption spectrum of trapped electrons in 15 M LiCl aqueous glasses at 77 K
Authors: Nguyen Tuan Quoc
Published: May 2006

Evidence is presented for the composite nature of the solvated (or trapped) electron absorption band in LiCl aqueous glass at 77 K. It is shown that the overall visible absorption spectrum can be deconvoluted into a homogeneously-bleachable 'green' band and a heterogeneously-bleachable 'red' band, whose relative magnitude and absorption band-maxima change with the concentration of electrolyte. From the combined results of time-resolved and steady-state photobleaching experiments, it is concluded that at least two unstable bands are formed during photobleaching (with smaller lifetimes for the band lying further towards the infrared) which then reconverted into the 'green' band with over 40% efficiency.
Infrared spectra of the ammonium ion in crystals. Part VI. Hydrogen bonding in simple and complex ammonium halides
Authors: Knop Osvald , Oxton Ian A. , Falk Michael
Published: May 2006

not available
The solvent extraction of Fe(III) from acidic chloride solutions by open cell polyurethane foam sponge (OCPUFS)
Authors: Oren J. J. , Gough K. M. , Gesser H. D.
Published: May 2006

The extraction of Fe(III) by open cell polyurethane foam sponge was studied as a function of acid, chloride, and iron concentration in the aqueous phase. The results indicate a mixed extraction of FeCl3 and HFeCl4. The results also show a dependence of the metal distribution coefficient on [Fe(III)]aq and indicate a dissociation (in the foam) of the extracted HFeCl4 species. The solid polyurethane is equated to a liquid extractant of a moderate dielectric constant.
A new synthesis of chasmanine and 13-desoxydelphonine: a preferred route to the aromatic intermediate
Authors: Tsai Thomas Y. R. , Nambiar Krishnan P. , Krikorian Dikran , Botta Maurizio , Marini-Bettolo Rinaldo , Wiesner Karel
Published: May 2006

An efficient synthesis (stereo- and regiospecific) of compound I (Scheme I) from o-cresol is described.
Intramolecular alkylation of α,β-unsaturated ketones: a total synthesis of (±)-isolongifolene and an approach to the synthesis of zizaane-type sesquiterpenoids
Authors: Piers Edward , Zbozny Michael
Published: May 2006

A total synthesis of (±)-isolongifolene 6, a C15 hydrocarbon derived from the acid-catalyzed rearrangement of the sesquiterpenoid longifolene, is described. The known carbomethoxyoctalone 10 was transformed via a 10-step sequence into the unsaturated keto tosylate 9. The key step of the overall synthesis involved the efficient intramolecular γ alkylation of 9 to produce the tricyclic α,β-unsaturated ketone 5. The latter compound was converted into the enone 33, which had previously served as a precursor for the synthesis of (±)-isolongifolene 6.
Synthesis of potential DNA bisintercalative agents of the phenanthridinium class
Authors: Lown J. William , Gunn Brian C. , Majumdar Krishna C. , McGoran E.
Published: May 2006

The syntheses are described of certain bis(5-alkyl-3,8-diamino-6-phenylphenanthridinium)dichlorides linked through the 8-amino group with diamide bridges, as well as bis(5-alkyl-3,8-diamino-6-alkylphenanthridinium)dichlorides linked through the 6-position by methylene bridges, as potential double intercalators into duplex nucleic acids. The work explores the syntheses of bisethidium compounds via permissible points of attachment of the chromophore consistent with optimal fluorescence enhancement upon intercalation.
Clionamide, a major metabolite of the sponge Clionacelata Grant
Authors: Andersen Raymond J. , Stonard Richard J.
Published: May 2006

Clionamide, the major metabolite of the burrowing sponge Cliona celata, has been isolated. The structure of clionamide (1) was shown to be (2S)-N-((1E)-5,6,7-trihydroxystyr-1-yl)-2-amino-3-(6-bromoindol-3-yl)propionamide by spectral analysis and by interconversion to its tetracetyl derivative 2. The structure of 2 was determined from spectral data and extensive chemical degradation and was confirmed by the synthesis of its ultimate hydrogenation product, N-(5,6,7-triacetoxypheneth-1-yl)-2-acetamido-3-(indol-3-yl)propionamide (11).
Transition state geometry in the scission and formation of cyclopentane and cyclohexane oxiranes. Use of the dilatometer in studying mixed reactions of different orders
Authors: Bovenkamp John W. , Langstaff Edward J. , Moir Robert Y. , Bannard Robert A. B.
Published: May 2006

Two methods, one more accurate, the other more convenient, were developed by which the dilatometer could be used with concurrent reactions of the second and third order. The more accurate method, employing a dilatometer of high specific surface area and equipped with a stable and responsive thermometer, was used in studying as many as six simultaneous oxirane scissions in acid solution. Interlocking double comparisons were made between cyclohexane and cyclopentane ring systems, between systems possessing or lacking a methoxyl substituent and between others having the substituent in varying orientations, between charged and uncharged nucleophiles, and between transition states of different degrees of protonation. Searching experimental checks were therefore possible in four main areas: (i) a quantitative dissection of the inductive effect from steric and conformational effects, and from dipole–ion or dipole–dipole interactions with the nucleophile, (ii) a quantitative demonstration of three main differences between transition states based on 5- and 6-membered rings, (iii) a proof that syn-1,3-effects in the transition states are very charge dependent, being large and positive with unfavourably arranged dipoles, and small or perhaps negative with favourable arrangements, and (iv) a rejection of certain proposed ion-pair alternatives to the A2 mechanism.
Active surface centres in vanadium pentoxide/alkali metal sulphate heterogeneous catalysts for 2-propanol decomposition
Authors: Fikis David Victor , Murphy William John , Ross Robert Anderson
Published: May 2006

Infrared spectra of the surfaces of vanadium pentoxide and vanadium pentoxide containing 9.09 mol% caesium and potassium, as sulphates, have been determined after exposure to 2-propanol for various times. Interpretation of the spectra leads to the proposal that the principal source of catalyst activity may be associated with surface hydrogen and hydroxyl groups on V5+ and V4+ sites. The "stability" of the catalysts towards reduction by the alcohol was consistent with the activity series derived from kinetic measurements: V2O5 (pure) < V2O5 (Cs) < V2O5 (K). The degree of sample reduction has also been assessed qualitatively by measurements of the ratio of surface area before to that after reaction and the same catalyst sequence was established. The trend in surface area ratios was similar to that shown by the surface "Tammann" temperatures of vanadium pentoxide and alkali metal sulphates which has been taken to imply that the ease and (or) extent with which the sulphates enter into inter-solid reactions with the oxide in the preparation stage may exert influence on the subsequent reducibility of the individual members of the catalyst series.
The thermal isomerisation of allyl isocyanide
Authors: Glionna Marsha T. J. , Pritchard Huw O.
Published: May 2006

The thermal isomerisation of allyl isocyanide to allyl cyanide has been studied in the gas phase over the temperature range 130–200 °C. The reaction is homogeneous and first order, and at high pressure (20 Torr) has an activation energy of 40.8 ± 0.6 (2sdm) kcal mol−1; the corresponding range of frequency factor is 1014.77±0.30 s−1.
Solution structures of dimeric methylpyrazolyl and indazolyl dimethyl-derivatives of boron, gallium, and indium from 1H nuclear magnetic resonance data
Authors: Peterson Louis K. , Thé Kwat I.
Published: May 2006

Trimethylboron and trimethylgallium react with 3-methylpyrazole to yield isomer pairs of dimeric products [Me2E(Mepz)]2 (E = B, Ga; Mepz = 3-methylpyrazolyl), in the approximate ratios 4:3 (E = B) and 9:1 (E = Ga), while trimethylindium gives a single species. Reactions of indazole with trimethylgallium and trimethylindium also yield a single structural isomer of the dimer [Me2Eind]2 (E = Ga, In; ind = indazolyl). Solution structures were interpreted on the basis of 1H nmr data.
A new method for the determination of the relative acidities of alcohols in alcoholic solutions. The nucleophilicities and competitive reactivities of alkoxides and phenoxides
Authors: Reeve Wilkins , Erikson Charles M. , Aluotto Patrick F.
Published: May 2006

A new semiquantitative method has been developed for measuring the relative acidities of methanol, ethanol, isopropyl alcohol, and tert-butyl alcohol in mixed hydroxylic solvents. A solution of the alkoxides of two alcohols in an excess of the two alcohols is allowed to react with n-butyl bromide to form a mixture of two ethers. The composition of the ether mixture is a measure of the "competitive reactivity" of thetwo alkoxides. This can be measured directly, and in theory can be factored into two components: the relative nucleophilicity and the relative basicity of the two alkoxides. Relative nucleophilicities are determined by using solutions in which phenol is one component. Knowing the competitive reactivities and nucleophilicities, the relative acidities of methanol, ethanol, isopropyl alcohol, and tert-butyl alcohol in alcoholic media are shown to be 4.4, 1.0, 0.24, and 0.21, respectively. The relative nucleophilicities of hydroxide, methoxide, ethoxide, isopropoxide, tert-butoxide, phenoxide, and m-cresoxide are 0.08, 0.82, 1.0, 0.4, 0.04, 0.46, and 0.57 respectively.
The thermal decomposition of 1-(2′-cyano-2′-propoxy)-4-oxo-2,2,6,6-tetramethylpiperidine
Authors: Grattan D. W. , Carlsson D. J. , Howard J. A. , Wiles D. M.
Published: May 2006

The thermal decomposition of 1-(2-cyano-2′-propoxy)-4-oxo-2,2,6,6-tetramethylpiperidine in solution has been studied as a function of solvent, temperature, and the presence of radical scavengers. In the absence of a scavenger, decomposition produces a hydroxylamine and methacrylonitrile, whereas in the presence of a scavenger such as oxygen, a nitroxide and 2-cyano-2-propyl radicals result. Decomposition in the presence of a scavenger is ∼50 times more rapid than decomposition in its absence. By using various free radical scavengers, scission of the NO—C bond is confirmed, that is the reverse of the normal nitroxide–alkyl radical reaction. Increasing solvent polarity causes a marked decrease in thermal stability, both in the presence or absence of radical traps. The importance of the thermal decomposition reactions in the interpretation of nitroxide scavenging of radicals is discussed.
Cinétique de la formation de la métalloporphyrine Cu(II)—dérivé tétra éthylènediamino de la protoporphyrine IX (ENP) en milieu aqueux
Authors: Paquette Guy , Zador Miklos
Published: May 2006

The kinetics of formation of the metalloporphyrin Cu(II)–ENP is dependent on the pH due to the protonation of the pyrrol nitrogen atoms and the protonation of the diamino groups of the side chains. The degree of protonation of these side chains also influences the degree of association of the prophyrin and the metalloporphyrin in solution. The order of reaction with respect to the porphyrin is not unity, a consequence of an inhibition by the reaction product; this inhibition operates via the formation of a new species, a mixed complex of porphyrin–metalloporphyrin of low reactivity.The order of reaction with respect to Cu(II) is also not unity, a consequence of the chelation of Cu(II) by the diamino groups of the side chains. The presence of Cu(II) ligands influence both the reaction kinetics and the nature of the final reaction product. [Journal translation]
The allyl and benzyl groups as hydrogen bond acceptors in derivatives of 2-allylphenol and 2-benzylphenol
Authors: Schaefer Ted , Sebastian Rudy , Wildman Timothy A.
Published: May 2006

The 1H nmr spectra of 2-allylphenol, 2-allyl-6-methylphenol, 2-allyl-6-chlorophenol, and 2-benzyl-4-chlorophenol are analyzed in some detail. It is shown that, relative to a methyl group, the allyl and benzyl moieties, respectively, favor a cis orientation by 1570 ± 250 J/mol and 900 ± 220 J/mol in free energy at 305 K in CCl4 solution. These numbers appear to be independent of the CCl4 solvent. Coupling parameters within the allyl group in these molecules and in propene and allylbenzene show some regularities but are probably not reliable indicators of the allyl conformational preference, at least in the absence of a model allowing for hindered rotor state populations.
Theoretical study of the X2B1, A2A1, 2B2 valence-shell and the first πu23s-type doublet and quartet Rydberg states of NH2
Authors: Peyerimhoff S. D. , Buenker R. J.
Published: May 2006

The angular potential energy curves of the X2B1, A2A1, B2B2 valence-shell and 4Σg−, 2Σg− (22B1), 2Δg (22A1, 32B1), and 2Σg+ Rydberg states arising from πu2 3s configurations are calculated by configuration interaction techniques. The data obtained reproduce very satisfactorily all X2B1 and A2A1 characteristics deduced from experiments; they support the previous theoretical prediction of a small-angle 2B2 state but find a very low |Re′e′′|2 value for the 2B2–A2A1 transition. The 4Σg− as well as three of the above four doublet Rydberg multiplets are found to prefer linear (or nearly linear) geometry and larger NH separations (in the symmetric structure) than NH2 in its ground state. A relatively large electronic transition moment for combination with both X2B1 and A2A1 is calculated for the lowest Rydberg multiplet which lies roughly 5.3 eV above the A2A1 state, while the intensity of transitions of the higher 3s states is found to be considerably smaller. Finally it is pointed out that the former Rydberg transition fits in well with recent emission experiments in this wavelength region recently reported by Herzberg.
Sulfides as precursors for sulfonyl chloride synthesis
Authors: Langler Richard Francis , Marini Zopito Alessio , Spalding Edward Sommers
Published: May 2006

Sulfides are advanced as sulfonyl chloride precursors. SN2 cleavage of the intermediate sulfonium ions is discussed in conjunction with both the sulfohaloform pathway and our previous hypothesis that asymmetric chlorosulfonium chloride salts undergo Pummerer rearrangements which exhibit regioselectivity that can be anticipated on the basis of substituent electronegativity difference (ΔXp). Thioglycolic acid is developed as a new sulfur transfer agent for sulfonyl chloride synthesis.
The biosynthesis of caerulomycin A in Streptomycescaeruleus. Incorporation of 14C- and 13C-labeled precursors and analyses of labeling patterns by 13C nmr
Authors: McInnes A. Gavin , Smith Donald G. , Walter John A. , Vining Leo C. , Wright Jeffrey L. C.
Published: May 2006

Carbon-13 nuclear magnetic resonance spectroscopy of caerulomycin A (1) produced by cultures of Streptomycescaeruleus has shown that [1-13C]acetate labels C-2, C-4, and C-4′, whilst [1,2-13C]acetate enriches these carbons plus C-2′, C-3, C-3′, C-5′, and C-6′. The results establish that acetate is incorporated with little dilution at C-3 and C-4 in the substituted ring of 1, whereas C-2, and C-2′ to C-6′ of the unsubstituted ring, are assembled from lysine via the symmetrical intermediate 2S,6S-diaminopimelic acid. The methoxyl carbon incorporates label from DL-[3-13C]serine, but this precursor does not enrich C-5, C-6, or C-7 of the substituted ring, and the origins of these carbons remain undetermined.
Synthèse et amination réductrice de phosphonopyruvates: préparation d'acides amino-2 carboxy-2 alkylphosphoniques (β-phosphonoalanine)
Authors: Varlet Jean-Marie , Collignon Noël , Savignac Philippe
Published: May 2006

The reaction of α-copper(I)alkanephosphonates with methyl and ethyl oxalyl chlorides gives methyl or ethyl dialkylphosphonopyruvates which, submitted to reductive amination in ethanol at pH 6–7 with sodium cyanohydridoborate (NaBH3CN) and ammonia, or primary amines, lead to phosphonic amino esters; hydrolysis with diluted HCl gives phosphonic amino acids. These three reactions constitute a general way to β-phosphonoalanine and β-alkyl β-phosphonoalanine.
Cshemistry of hexamethyldisilazane. Silylation of β-diketones and amination of β-triketones
Authors: Chu Daniel T. W. , Huckin Stuart N.
Published: May 2006

It is discovered that hexamethyldisilazane, a reagent generally used to silylate amino, hydroxyl, sulfhydryl, and carbonyl groups, reacts with β-diketones to form their trimethylsilyl enol ethers in high yield.An efficient and simple procedure for aminating β-triketones to their enaminodiketones by the use of hexamethyldisilazane is also described.
On the formation of cyclopentenium cations from all C6H10+• molecular ion structures
Authors: Wolkoffs Peder , Holmes John L. , Lossing F. P.
Published: May 2006

The structures of [C5H7]+ ions produced by methyl loss from thirty isomeric C6H10 molecular ions have been assessed from measurements of ionic heats of formation and the kinetic energy release associated with the fragmentation. It is proposed that the thermodynamically most stable [C5H7]+ ions [cyclopentenium]+ are formed at the dissociation threshold irrespective of the initial molecular ion structure. Mechanistic aspects of the fragmentations were studied by mean of deuterium labelling.Observations of metastable peak shapes for labelled compounds permitted the identification of reaction pathways having different energy requirements. The lowest energy routes involved little or no positional mixing of H and D prior to fragmentation. It is proposed that the molecular ions with sufficient energy to fragment on the μs time scale undergo successive (and reversible) isomerization by allylic 1,3-hydrogen shifts to their isomeric isolated diene molecular ions which, by an allylic 1,2-hydrogen shift, may isomerize to a methylcyclopentene molecular ion prior to loss of methyl. The sequence of isomerization of the molecular ions is alkyne → allene → conjugated diene → isolated diene. The de-conjugation step has an activation energy of ca. 10 kcal mol−1. We suggest, however, that allene molecular ions rearrange directly to isolated diene molecular ions.
Easily polarizable hydrogen bonds and solvate structure in aqueous solutions of acids with pKa < 1
Authors: Leuchs Martin , Zundel Georg
Published: May 2006

Aqueous solutions of 15 acids with pKa < 1 were studied by ir spectroscopy. The ir bands of the acid molecules demonstrate that the proton acceptor strength of the anions increases in the series CF3SO3−, HSO4−, ClO4−, HSeO4−, C6H5SO3−, NO3−. At very high concentrations (number of H2O/acid molecules, n < 1) easily polarizable[Formula: see text]hydrogen bonds are formed causing continuous absorption in the ir spectra. The deeper well of the double minimum energy surface of these hydrogen bonds at the beginning of the above series is present at the water molecule, and at the end of the series at the anion. The H3O+ character of the vibrations of the H+OH2 groups increases with increasing n. For n > 1 the weight of proton limiting structure II increases and more and more protons transfer from the acid–water into the water–water hydrogen bonds, i.e., they are present in H5O2+ groupings which are embedded in the whole hydrate structure network. H3O+ vibrations are no longer found. The easily polarizable hydrogen bond in these groupings causes continuous absorption and the water molecules of these groupings cause broad bands. Of all acids studied, this group is the only cause of continuum in the more diluted solutions. The absorbance of the continuum per H5O2+ group at n = 2 increases in the series HClO4, CF3SO3H, H2SO4, H2SeO4, C6H5SO3H. This is because of the increasing polarity of the environment of the H5O2+ in this series of acids. The position of the water bands in solutions with n = 6 can be used to characterize the hydrogen bond acceptor strength of the anions. The H2O scissor vibration shows that it increases in the series AuCl4−, PtBr62−, PtCl62−, ClO4−, BF4−, CF3SO3−, J−, HSO4−, HSeO4−, C6H5SO3−, C7H7SO3−, Cl−. Finally molecular quantities which determine the pKa values of the acids (proton acceptor strength, hydrogen bond acceptor strength, and special interaction properties of the anions) are discussed.
Constituents from Salmaliamalabaricum
Authors: Chauhan J. S. , Sultan M. , Srivastava S. K.
Published: May 2006

The phytochemical investigation of the root of Salmaliamalabaricum has resulted in the isolation and identification of n-triacontanol, β-sitosterol, and a new glycoside which was characterized as 5,7,3′,4′-tetrahydroxy-6-methoxyflavan-3-O-β-D-glucopyranosyl-α-D-xylopyranoside on the basis of spectral and degradative studies.
Photochemical rearrangements of 2-azido-4-thiochromanone 1-oxide and 1,1-dioxide: formation of 2H-benzo[f]-1,2-thiazepine derivatives
Authors: Still Ian W. J. , Leong Toong S.
Published: May 2006

Photolysis of 2-azido-4-thiochromanone 1,1-dioxide in benzene or dichloromethane leads to the formation of 2H-benzo[f]-1,2-thiazepin-5-one 1,1-dioxide, in very good yield. In contrast, the photolysis of the analogous sulfoxide was much more complex and no ring-expansion product could be isolated, although a small amount of a compound believed to be 2-aminothiochromone 1-oxide was formed. Several attempts to prepare the α-azidosulfide analogue, to compare its photochemical behavior, were unsuccessful and a rationale is proposed for the apparent instability of this member of the series.
Reaction of pyrylium salts with hydrazine and methylhydrazine. Concerning the scope of the 1,2(4H)-diazepine synthesis
Authors: Harris D. J. , Kan G.Y.-P. , Tschamber T. , Snieckus V.
Published: May 2006

The reaction of pyrylium salts 1a–e with methylhydrazine gives pyrazolines (2), pyrazoles (3), pyridines (4), 1,2-diazepine (5), and N-methylaminopyridinium salts (6). Product composition has been studied as a function of pyrylium salt counter anion, concentration of methylhydrazine, and conditions of the reaction (Table 1). Pyridines (4) and 1,2-diazepines (5) are minor components, the major products being the pyrazolines (2) and pyrazoles (3). The reactions of more unusual pyrylium salts (1f–i, 8a, 9a, 9c, and 11a) with hydrazine have been shown to provide 1,2(4H)-diazepines (10, 12–15) and N-aminopyridinium salts (8b, 9b) (Table 2), the nature of the product apparently depending on the absence or presence of 2-methyl substitution respectively in the starting pyrylium salts.
A comparison of the crystal structures of Sb2Tl7, Cu5Zn8 (γ-brass), and Ir3Ge7
Authors: Hellner Erwin , Koch Elke
Published: May 2006

The crystal structures of Sb2Tl7, Cu5Zn8, and Ir3Ge7 are discussed with the aid of shortest distances of Dirichlet domains and of voids in their frameworks. It will be pointed out that all three frameworks must be regarded as different though relations between the atomic parameters are obvious. The Sb2Tl7 structure represents a superstructure of an I lattice. The frameworks of Sb2Tl7 and of Cu5Zn8 contain tetrahedral voids only, while in Ir3Ge7 voids with a larger coordination number also exist.
Synthetic and oxidation studies of ruthenium(II) phthalocyanine complexes
Authors: Dolphin David , James Brian R. , Murray Alan J. , Thornback John R.
Published: May 2006

Ruthenium(II) phthalocyanine complexes of the type RuPcL2 (Pc = the phthalocyaninato dianion, L = various pyridines, imidazole, dimethylformamide, dimethylsulfoxide, and acetonitrile) may be prepared generally in solution by photolysis of RuPc(CO)L′ complexes in the presence of excess L (L′ may be the same as L or may be a different ligand), and in some cases as solids by extraction of crude RuPc with L. The solid RuPc(CO)L monocarbonyls can be formed from reaction of the RuPcL2 complexes with carbon monoxide, as well as via an extraction procedure using L with crude RuPc(CO) formed from Ru3(CO)12 and phthalocyanine.
Acylation of aromatic substrates with ketenes. An example of vinyl oxocation reactivity
Authors: Fountain K. R. , Heinze Pamela , Sherwood Mark , Maddex Dave , Gerhardt Greg
Published: May 2006

Acylations of aromatic substrates with ketenes involve the reactivity of species similar to vinyl cations. Resonance stabilization of ketene – aluminum chloride complexes seems to make these complexes less reactive than corresponding vinyl cations.The kinetic isotope effect of the reaction with dimethylketene and benzene is 1.06, compatible with vinylcation cases, but not with acylation with CH3COBF4 types of electrophiles.Substrate specificity was determined from k (toluene)/k (benzene) values. It was 47.2 for dimethylketene and 173.7 for diphenylketene. The diphenylketene – aluminum chloride complex could be isolated.
A proton magnetic resonance nuclear Overhauser enhancement study. Application to vitamin D derivatives D2 and D3
Authors: Kotovych George , Aarts Gerdy H. M. , Bock Klaus
Published: May 2006

Nuclear Overhauser effect difference experiments on vitamins D2 and D3 at 400 MHz allow an unambiguous assignment to be made for the HE and HZ protons bonded to the C-19 carbon. This assignment is especially important since the A ring, and hence the C-19 atom, undergoes a conformational interconversion. The results indicate the importance of proton nOe difference experiments in determining points of configuration and they indicate that the assignment of resonances based on allylic coupling constants in a molecule undergoing a conformational equilibrium can be incorrect.
Use of 13C in biosynthetic studies. The labeling pattern in dihydrofusarubin enriched from [13C]- and [13C, 2H]acetate in cultures of Fusarium solani
Authors: Kurobane Itsuo , Vining Leo C. , McInnes A. Gavin , Walter John A.
Published: May 2006

The pattern of 13C and 2H incorporation from [1-13C]-, [2-13C]-, [1-13C0;1;1,2-13C1;0;1]-, and [2-13C0;1,2-2H3;3]acetate into dihydrofusarubin 1, produced by cultures of Fusariumsolani, has been determined by 13C and 2H nmr of the derivatives anhydrofusarubin 3 and anhydrofusarubin diacetate 4. The results show that 1 is biosynthesized from seven uniformly-incorporated acetate units with C-3, C-11 originating from the "starter" unit. They strongly suggest that linear head-to-tail condensation of an acetate and six malonate units forms a single-chain heptaketide intermediate. The evidence also suggests that, during conversion of [13C, 2H]-labeled acetyl-CoA to malonyl-CoA, 2H is transferred to biotin carboxyl carrier protein where it does not exchange rapidly with the medium and is available for conversion of endogenous malonyl-CoA to [2H]-enriched acetyl-CoA.
The synthesis and reactions of 2,11-diselena[3,3]metacyclophanes. An investigation of the selenoxide elimination route to metacyclophane-1,8-dienes
Authors: Mitchell Reginald H.
Published: May 2006

2,11-Diselena[3,3]metacyclophane and its 9,18-dimethyl derivative are prepared in ca. 7% yield from Na2Se and xylylene bromide. Wittig rearrangement and benzyne induced Stevens rearrangement gave the ring contracted [2,2]metacyclophane derivative. Attempted selenoxide elimination to produce metacyclophane-diene failed. The 1Hmr spectra of the selenametacyclophane indicate that the syn-conformer is the more stable. A general synthesis of aryl-alkenes in an 80% yield starting from benzyl phenyl selenide, alkylation with an alkyl halide, and then selenoxide elimination is given.