bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies in decarboxylation. XI. The gas phase pyrolysis of some arylacetic acids
Authors: Bigley David B. , Weatherhead Richard H.
Published: May 2006

The gas phase decarboxylations of 1-naphthyl-, 2-naphthyl-, and 9-phenanthrylacetic acids all proceed through a homolytic pathway. There is no evidence for the concerted 1,5-hydrogen shift usually encountered in the decarboxylation of β,γ-unsaturated acids.
The total synthesis of 4-deoxy-D,L-daunosamine
Authors: Hung Hing-Kwok , Lam Hing-Yat , Niemczura Walter , Wang Mei-Ching , Wong Chiu-Ming
Published: May 2006

The aminosugar 4-deoxy-D,L-daunosamine and its derivatives were synthesized starting with 2,4-pentanedione which was converted to the key intermediate oxazolino-α-pyrone (19) by enamine formation with morpholine, oxidation with benzoyl peroxide, condensation with ammonium acetate, bromination with N-bromosuccinimide, nitrile formation, acid hydrolysis, and cyclization with thionyl chloride. Hydrogenation of 19 gave the δ-lactone 22 which was converted to 4-deoxy-D,L-daunosamine derivatives by reducing the lactone ring to the corresponding hemiacetal 26.
The selective cleavage of glycopyranosiduronamide linkages in methylated polysaccharides
Authors: Aspinall Gerald Oliver , Rosell Karl-Gunnar
Published: May 2006

Hofmann degradation of glycosiduronamide linkages in methylated polysaccharides furnishes pentodialdose derivatives to which any sugar residues external to uronic acid residues remain attached together with degraded methylated polysaccharides carrying aglyconic hydroxyl groups. The selective degradation has been carried out on methylated derivatives of birch xylan, gum arabic, and the capsular polysaccharide from Klebsiella type 47. Procedures for the degradation of methylated polysaccharides in the vicinity of uronic acid residues are assessed.
Preparation of two acidic metabolites of timolol
Authors: Bélanger Patrice C.
Published: May 2006

The preparation of two acidic metabolites of timolol, 2-[4-(4-morpholinyl)-1,2,5-thiadiazol-3-yloxy]acetic acid and d,l-3-[4-(4-morpholinyi)-1,2,5-thiadiazol-3-yloxy]lactic acid is reported using 3-chloro-4-(4-morpholinyl)-1,2,5-thiadiazol as starting material.
Photolysis of diterpenoid quinones
Authors: Edwards Oliver E. , Ho Pak-Tsun
Published: May 2006

Photolysis of the diterpene quinone royleanone in benzene gave predominantly products resulting from both side-chain rearrangement and formation of an ether bridge to C-1. It is proposed that these arose by very specific transfer of two hydrogen atoms in a highly oriented complex between ground state royleanone and photo-excited royleanone. In contrast 7α-acetoxyroyleanone gave products of simple side chain rearrangement, with or without loss of acetic acid, probably via a spirocyclopropyl intermediate.Royleanone methyl ether gave mainly an oxetanol in benzene but a methylenedioxy com-pound and an acetoxymethoxy compound in acetic acid. It is suggested that these arise from diradical and zwitterionic intermediates.
Relationship between Taft and Kirkwood–Westheimer equations
Authors: Poh Bo-Long
Published: May 2006

The relationship between Taft and Kirkwood–Westheimer equations has been derived with the use of the modified MacInnes equation.
Sphere tensiometry: wall effects and correction factors
Authors: Bayramli E. , Huh C. , Mason S. G.
Published: May 2006

This paper is a supplement to an earlier one on the new absolute gravimetric method of measuring surface and interfacial tension which takes into account the effect of the wall in circular containers of finite radius which causes the liquid surface to dimple instead of remaining flat as in an unbounded system as assumed earlier.Using conventional capillarity theory, the basic principles for correcting force–displacement curves, called sphere-tensiograms, are derived. Numerical correction factors calculated from the theory for systems with perfect wetting (zero contact angle) for an experimentally realistic range of parameters, and corroborative experimental data are presented.
An investigation of discrepancies in the reported properties of tetraphenyl-p-dioxin
Authors: Yager Billy J. , Wootan Jr. Wilford L.
Published: May 2006

A compound prepared by refluxing methyl benzoate with boron sulfide (B2S3) and previously identified as tetraphenyl-p-dioxin has been identified in this investigation as tetraphenylthiophene.
The radiation chemistry of nitric oxide
Authors: Boyd A. W. , Miller O. A.
Published: May 2006

The yield of nitrogen from the radiolysis of nitric oxide is G(N2) = 4.5 ± 0.3 at doses from 0.1 to 1.0 × 1020 eV g−1 and at dose rates of 2.5 × 1016 and2 × 1027 eV g−1.s−1. The addition of SF6 to NO does not change this yield but in mixtures of NO with 90% Xe the addition of SF6 reduces G(N2) by an amount close to G(Xe+). These results are consistent with suppression of dissociative neutralisation in NO by clustering of the positive ion. Good agreement is obtained between the total energy absorbed and the amounts required for ionization, neutral dissociative excitation, and formation of subexcitation electrons. The neutral dissociative excitation yield is estimated to be G(NO → N + O) = 3.6 ± 0.3.
Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O3, NO2−, and CH2N2
Authors: Harcourt Richard D. , Roso Walter
Published: May 2006

Some ab-initio valence-bond wave-functions are reported for the π-electrons of the ground-states of O3, NO2−, and CH2N2. Examination of these wave-functions provides further support for the hypothesis that, for the ground-states of many electron-excess molecules, important valence-bond structures are those that are compatible with the electroneutrality principle, i.e. they carry either small or zero formal charges on each of the atoms. For O3 and CH2N2, the important valence-bond structures with zero atomic formal charges are [Formula: see text]Each of these structures has a 'long-bond' between non-adjacent atoms. The significance of 'long-bond' (or spin-paired diradical) structures for the electronic mechanism of 1,3-dipolar cycloaddition reactions is discussed and 'increased-valence' descriptions of the electronic structure of each molecule are presented. Some comments on the utility of 'increased-valence' structures are provided.
Aldol-type condensations of C(α)-dianions of azines
Authors: Davis Steven E. , Shealy Neal L. , Shealy Keith D. , Shaffer Lynn M. , Beam Charles F.
Published: May 2006

The C(α)-dianions of azines prepared from acetophenone or substituted acetophenones underwent dialdol condensations with ketones to give dihydroxyazines.
Photoinduced chlorination and bromination of haloadamantanes in tetrachloromethane and bromotrichloromethane
Authors: Perkins Robert R. , Pincock Richard E.
Published: May 2006

Irradiation of 1-fluoro-, 1-chloro-, and 1-bromoadamantanes in halogenated solvents leads to free radical halogenation of the adamantane skeleton without exchange of the 1-halo atom. Reactions in tetrachloromethane yield products substituted at both the secondary carbons (i.e., bridge carbons) and at tertiary bridgehead carbons. Bridgehead substituted bromo-products greatly predominate when bromotrichloromethane is used as a solvent. Using this difference in the type of products formed from CCl4 and BrCCl3 a variety of mixed-halo substituted adamantanes were prepared from 1-monohaloadamantanes. Irradiation of 1-iodoadamantane in either solvent proceeds initially only with halogen exchange rather than halogenation of the ring system.
Rates and activation energies of nitronium ion formation and reaction in the nitration of toluene in ∼78% sulphuric acid
Authors: Sheats George F. , Strachan Alec N.
Published: May 2006

A stopped-flow spectrometer has been used to investigate the mechanism of the nitration of toluene, and to determine kinetic parameters for the formation and reaction of nitronium ion, in 77.3 and 78.45 wt.% sulphuric acid. The protonation of nitric acid to form nitronium ion and water is found to occur at similar rates at both acid concentrations and to have an activation energy of 18.3 ± 4.0 kcal mol−1. The activation energy of the reverse reaction, the heat of the reaction, and the activation energy of encounter complex formation between nitronium ion and toluene are estimated to be respectively 10.5 ± 4.0, 7.8 ± 0.5, and 5.9 ± 0.1 kcal mol−1 in 77.3% H2SO4 and 12.0 ± 4.0, 6.3 ± 0.5, and 6.0 ± 0.1 kcal mol−1 in 78.45% H2SO4.
A consistent derivation of the Wilson–Decius s vectors, including new out-of-plane wag formulae
Authors: McIntosh D. F. , Michaelian K. H. , Peterson M. R.
Published: May 2006

A consistent derivation of the complete set of s vectors needed for vibrational analysis by the Wilson GF matrix method is presented. The vectors obtained for the out-of-plane wag are given by new formulae which are considerably simpler than those presently in use. The formulae for the linear bending coordinate are also derived.
SCF molecular orbitals and the photoelectron spectrum of 5,5-dimethyl-Δ3-1,3,4-oxadiazolin-2-one
Authors: Paine Anthony James , Werstiuk Nick Henry
Published: May 2006

CNDO/2 Frontier molecular orbital densities, ionization potentials (IP's), and electronic transition energies were calculated for the title compound (2b) and the 5,5-diprotio (2a), and 5,5-difluoro (2d) analogs. Bond lengths and angles were not optimized but rather taken from a crystal structure of the 2-imino System 3, with an assumed carbonyl bond length of Rco = 1.19 Å. This value is supported by a high infrared stretching frequency (1835 cm−1), X-ray crystal data of 3, and the effect of Rco variation on calculated IP's. The first three bands of the photoelectron spectrum of 2b were assigned as nN− (10.20 eV), π1 (11.52eV), and nco (13.26 eV) (vertical IP's). This unusually large nco IP is attributed to an inductive effect of the neighbouring strongly electron withdrawing azo group. The IP's obtained by CNDO/2 calculation (12.81, 13.37, and 15.15) are 1.5 to 2.5 eV higher than the experimental values, well within the predictive capability of the method, establishing that this theoretical treatment gives a good representation of the MO's of 2b.
Horseradish peroxidase. XXVIII. Formation and reactivity of the alkaline form. Evidence for an enzyme–substrate complex in compound 1 formation
Authors: Job Dominique , Dunford H. Brian
Published: May 2006

The rate of formation of 1 from horseradish peroxidase and hydrogen peroxide is investigated as a function of pH between pH9.5 and 11.5. For pH values smaller than 10, the rate depends linearly on hydrogen peroxide concentration, whereas between pH 10 and 11.5, the rate displays saturation kinetics. Evidence is presented for the formation of an intermediate complex before compound 1 formation. Two parameters were measured as a function of pH: kapp, the apparent rate constant for compound 1 formation, and kapp, the dissociation rate constant of the intermediate complex to 1. A third parameter, kapp, similar to a dissociation constant for the reaction was deduced from the two rate constants. The apparent rate constant kapp is pH independent for pH values < 9.5 and is directly affected by ionization of only one group on the native enzyme with a pK of 11. The pH dependances of kd and Kapp require a minimum of two ionizations. One corresponds to a group on the native enzyme which ionizes at a pH lower than that of the present study, the second corresponds to the ionizable group with pK of 11. For cyanide binding to horseradish peroxidase over the same pH interval, saturation kinetics were not observed, yet the pH profile for kapp exactly parallels that for formation of 1 (when corrected for the effect of the ionization of HCN) and shows an inflection at the same pH value.
Conformational studies on cyclohexa-1,4-diene derivatives. The crystal and molecular structures of 1,2,4,5-tetraphenyl-3,6-dicarbomethoxycyclohexa-1,4-diene and 1,2-dicarbomethoxy-4,5-dimethylcyclohexa-1,4-diene
Authors: Bennett M. J. , Purdham J. T.
Published: May 2006

1,2,4,5-Tetraphenyl-3,6-dicarbomethoxycyclohexa-1,4-diene crystallizes in the monoclinic space group I2/a (a non-standard setting of C2/c) with a = 20.052(2), b = 5.756(1), c = 22.782(2) Å, β = 95.73(1)°, and Z = 4. 1,2-Dicarbomethoxy-4,5-dimethylcyclohexa-1,4-diene crystallizes in the orthorhombic space group Pbca with a = 25.627(2), b = 11.240(1), c = 8.342(1) Å, and Z = 8. Both structures were solved by direct methods and refined by full matrix least-squares techniques to R = 0.040 and R = 0.036, respectively. Carbon–carbon double bond lengths are similar in the two compounds (1.326 and 1.333 Å, respectively), but the single bond lengths are significantly longer in l,2,4,5-tetraphenyl-3,6-dicarbomethoxycyclohexa-1,4-diene (1.518 Å) compared with the 1.493 Å average found in 1,2-dicarbomethoxy-4,5-dimethyl- cyclohexa-1,4-diene. This and the fact that there are also small deviations from planarity in the former compound are thought to be due to the presence of substituents on the methylenic carbon atoms.
The synthesis of hypecorinine and bicucullinine
Authors: Nalliah Bala C. , MacLean David B.
Published: May 2006

The total synthesis of two isoquinoline alkaloids of unusual structure, hypecorinine 2 and bicucullinine 3, from a common intermediate, dehydrobicuculline (1), is described.
A reformulation of the theory of unimolecular reactions
Authors: Yau Andrew W. , Pritchard Huw O.
Published: May 2006

The theory of unimolecular reactions is reformulated in a way which makes no reference to the concepts of a transition state, a reaction coordinate, or of an activated complex: the present theory is based, instead, on a simple master-equation approach using the estimated positions and lifetimes of the rotation–vibration energy levels of the molecule. The fundamental basis of this reformulation is that the unimolecular rate is derived from the perturbation of the normal modes of internal relaxation of the reactant molecule by the microscopic reaction processes. The thermal decompositions of cyclobutane, cyclopropane, ethyl isocyanide, ethyl chloride, and methyl isocyanide are examined in detail, and it is shown that not only is the present theory much easier to use than is conventional RRKM theory, but also that it gives better results.An Appendix provides a set of algorithms required for these calculations.
Complex fluoroanions in solution. VIII. Mixed anions containing fluoride and trifluoromethanesulfonate or fluorosulfate
Authors: Brownstein S. , Bornais J. , Latremouille G.
Published: May 2006

Binary fluorides of groups III, IV, V, and VI of the periodic table form fluoroanions with the trifluoromethanesulfonate and fluorosulfate ions. The complexes are weaker and there is less disproportionation than with the trifluoroacetate ion. Fluorine exchange reactions in these anions are generally slow on the nmr time scale at −70 °C.
Gas phase photolysis of 1-pentene and 1-pentene-d10 at 7.1 and 7.6 eV. Kinetic considerations
Authors: Więckowski Andrzej , Collin Guy J.
Published: May 2006

The gas phase photolysis of n-pentene was carried out in a static system using nitrogen resonance lines at [Formula: see text] and the bromine line at [Formula: see text] The mechanism for the photolysis was proposed and compared to what was concluded at 8.4 eV (147 nm, the xenon resonance line). The kinetics of the decomposition of the excited C3H5* radicals formed in the primary photochemical process and the C5H11* radicals formed by the addition of hydrogen atoms to the parent molecules were discussed. The investigations were extended to the n-C5D10 photolytic System. The observed decomposition rate constants of the excited pentyl radicals as well as the secondary non-equilibrium isotope effects agree with the data published earlier. It is concluded from these experiments that, at least at 7.6 eV, hot hydrogen atoms are produced.Only a small fraction of the C3H5* radicals décompose and yield aliène. At the same time the combined primary–secondary non-equilibrium isotope effects are much less than those calculated for the 'pure' primary isotope effects. To account for these observations, it is assumed that the C3H5* radicals are formed with a wide spread in the internal energies. Since the threshold of the decomposition of the excited C3H5* radical lies above its mean excess energy (calculated on the statistical basis), an analogy in the energy-distribution functions on the radicals activated photochemically and thermally may be suggested. If so, an inverse secondary isotope effect may contribute to the gross effect involved in the C3H5* radical decomposition.
Aminoglycoside antibiotics: Chemical conversion of neomycin B, paromomycin, and lividomycin B into bioactive pseudosaccharides
Authors: Hanessian Stephen , Takamoto Tetsuyoshi , Massé Robert , Patil Ghanshyam
Published: May 2006

Pseudosaccharides containing various natural combinations of rings present in aminoglycoside antibiotics were prepared from the parent antibiotics, neomycin B, paromomycin, and lividomycin B, by oxidation of available vicinal diols and β-elimination. Pseudotrisaccharides comprising rings A, B, and C of paromomycin and lividomycin B, a pseudotrisaccharide comprising rings B, C, and D of the three antibiotics, and a 'core' pseudotrisaccharide containing rings B and C were thus prepared. These are valuable biological probes and intermediates for semisynthetic work in this series.
Aminoglycoside antibiotics: Studies directed toward the selective modification of hydroxyl groups: Synthesis of 3′-epiparomamine and 3′-epineamine
Authors: Hanessian Stephen , Massé Robert , Nakagawa Toshio
Published: May 2006

Based on the knowledge that certain bacterial strains can produce enzymes that are capable of phosphorylating the 3′-hydroxyl group of a series of aminoglycoside antibiotics, the pseudodisaccharide 3′-epiparomamine was prepared through a series of high yieldingsteps, starting from paromamine. Application of selective halogenation and subsequent animation reactions allowed the efficient transformation of 3′-epiparomamine to 3′-epineamine. The two compounds were not substrates for the inactivating enzymes, however, they are also much weaker antibiotics compared to the parent compounds paromamine and neamine. Model synthetic studies in the 2-amino-2-deoxy-D-ghicose series are also reported.
The dissociation constant for potassium methylamide ion pairs in methylamine
Authors: Symons E. Allan , Bonnett J. Douglas
Published: May 2006

The limiting equivalent conductance (Λ0) and ion pair dissociation constant (Kd) have been obtained for potassium methylamide in methylamine from conductance data measured over the temperature range −55 to + 25° C. The value of Kd increases from 6.3 × 10−8 mol L−1 at the highest temperature to 9.4 × 10−7 mol L−1 at the lower limit. The results show good agreement with literature data for potassium amide in ammonia after corrections for differences in solvent viscosity and dielectric constant. The heat of dissociation is −26 kJ mol−1 above −15 °C, but decreases gradually at progressively lower temperatures as a shift occurs from tight to loose ion pair structures.
Reduction of cyclic anhydrides. II. Factors affecting regioselectivity of attack on the carbonyl group by metal hydrides
Authors: Kayser Margaret M. , Morand Peter
Published: May 2006

The reduction of unsymmetrically substituted cyclic anhydrides with metal hydrides often leads to the preferential formation of one of the two possible lactones. In the light of recent experimental findings and theories concerning metal hydride addition to the carbonyl function, the electronic and steric factors influencing regioselectivity of cyclic anhydride reductions are discussed and an explanation for the observed patterns is proffered. Similar considerations may be extended to predict the major lactonic products in the reductions of various other unsymmetrical cyclic anhydrides.
Indole N-alkylation of tryptamines via dianion and phthalimido intermediates. New potential indolealkylamine haptens
Authors: de Silva S. Osmund , Snieckus Victor
Published: May 2006

Tryptamine derivatives 3a–c and 4a, 4b, 4d have been converted into the indole N-p-carbomethoxybenzyl derivatives 1a, 1b, 1g, and 2a, 2b, 2c, respectively, using dianion and phase-transfer catalytic methodologies. Treatment of these compounds with lithium iodide and sodium cyanide in refluxing dimethylformamide gave the corresponding carboxylic acids 1d, 1e, 1h, and 2d, 2e, 2f. The serotonin analogue 1f was obtained by catalytic debenzylation of 1h. These products may be useful haptens for eliciting specific antibodies to indolealkylamines.
Observation de transitions de phase dans les dérivés dihalogénés du benzène par spectroscopie infrarouge lointain et diffusion Raman
Authors: Wyncke B. , Brehat F. , Hadni A. , Serrier J. , Baverez M.
Published: May 2006

Far infrared absorption and Raman spectra were recorded for ortho- and meta-disubstituted benzene ClC6H4Cl, ClC6H4Br, and BrC6H4Br from 15 to 250 cm−1 at different temperatures (80–300 K). From spectroscopic evidence, one phase transition is found for both the o- (200 K) and the m-dichlorobenzene (220 K), and two for the o-chlorobromobenzene (185 and 222 K).
Anesthesia and hydrogen bonding. A semi-quantitative infrared study at room temperature
Authors: Trudeau Ginette , Cole K. C. , Massuda Rachel , Sandorfy C.
Published: May 2006

It has been shown previously that certain anesthetics hinder the formation of hydrogen bonds of the [Formula: see text] types. An attempt bas now been made to correlate this hydrogen bond 'breaking' property with anesthetic potency. As a measure of the former, relative intensifies of infrared bands related to 'free' and hydrogen bonded species were used. The band which was chosen for this purpose is the OH or NH stretching + in-plane bending combination band. This made it possible to carry out the measurements at room temperature. A semi-quantitative relationship has been found. Its significance for the theories of anesthesia is discussed.
Ipso nitration. XX. Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride. Formation and rearomatization of adducts
Authors: Fischer Alfred , Teo Khay Chuan
Published: May 2006

Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride gives both diastereomers of the adduct 1-tert-butyl-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienyl acetate and one diastereomer of 1-tert-buty]-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienol, in 91% yield, together with 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene. Solvolysis of the dienyl acetate in acidified aqueous acetone and acidified methanol affords the diastereomers of the dienols and the dienyl methyl ethers, respectively. The dienyl methyl ethers are also formed from the dienyl acetate in neutral methanol and again on reaction with methanolic sodium methoxide. The dienols isomerize (epimerize) in acidified aqueous acetone. Reaction of the dienyl methyl ethers in aqueous methanol, or prolonged reaction in methanol, results in the formation of methyl-1,2,3-trimethylphenyl ether. Similar cleavage of the tert-butyl group is the main reaction on solvolysis of the dienyl acetate in aqueous acetic acid. Under more acidic conditions the dienyl acetate gives 5-tert-butyl-2,3-dimethylbenzyl nitrite and lesser amounts of 5-tert-butyl-2,3-dimethylphenylnitromethane and 5-tert-butyl-2,3-dimethylbenzyl acetate. In trifluoromethanesulfonic and fluorosulfonic acids 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene is the major product.
Chemistry and catalytic properties of oxidized rhodium chlorocarbonyl complexes, Rh4Cl4(CO)4(O2)2P2; P = tertiary phosphine ligands
Authors: Cullen William R. , James Brian R. , Stukul Giorgio
Published: May 2006

The reactions of the title complexes Rh4Cl4(CO)4(O2)2P2 (where P is a tertiary phosphine type ligand, in particular diphenylisobutylphosphinite) with both dihydrogen and carbon monoxide were studied in solution in the absence and presence of excess P. The reaction stoichiometries, particularly a measured carbon dioxide evolution, confirm the formulation of the reactant tetranuclear complexes. The complexes are effective for catalytic hydrogenation and hydroformylation of olefinic substrates, and the nature of the active catalysts is considered.
Cyclopropanation of steroidal A-ring 2-enol derivatives
Authors: Templeton John Freeland , Paslat Volker Gustav , Wie Chwi Wan
Published: May 2006

Cyclopropanation of 2-enol derivatives of 17β-acetoxy-5α- androstan-3-one has been studied. The preparation of A-ring cyclopropanol derivatives from the Simmons–Smith reagent or dibromocarbene is described. Long range shielding effects of the cyclopropane ring in the 1Hmr spectrum are discussed.
Carbon-13 enrichment in the room temperature multiphoton decomposition of CF3Br
Authors: Gauthier M. , Hackett P. A. , Drouin M. , Pilon R. , Willis C.
Published: May 2006

High isotopic selectivities have been observed in the multiphoton decomposition of CF3Br at room temperature. Photolysis of natural abundance CF3Br gives C2F6 enriched to 42% in carbon-13. This is higher than observed for CF3I even at very low temperatures.
Utilization of trimethylsilylpropyne as an acetonyl unit in the synthesis of cyclopentenones. Applications to the synthesis of jasmone and dihydrojasmone
Authors: Sum Phaik-Eng , Weiler Larry
Published: May 2006

The dianion of β-keto esters are alkylated at the γ-carbon with 3-bromo-1-trimethyIsilyl-1-propyne. The resulting alkynes are hydrated (H3O+, Hg2+) and cyclized (OH−) to the corresponding cyclopentenones, jasmone and dihydrojasmone. The failure to obtain cyclopentanones from the acid- and base-catalyzed cyclizations of 6-substituted 3-keto esters may be rationalized by Baldwin's rules for cyclization.
Heats and free energies of mixing of tridodecylamine with nine heptane isomers, two octanes, and one hexane. Disorder and steric hindrance contributions
Authors: Couchon Michèle , Hong Phuong Nguyen , Delmas Genevieve
Published: May 2006

Heats and free energies of mixing have been measured at 298 K for tridodecylamine in n-C7, and eight branched isomers, n-C8 and one branched isomer, and a branched hexane. Heats of mixing are such that these systems can be divided in three classes. Class A [Formula: see text] includes n-C7, and n-C8. Class B [Formula: see text] includes isomers which do not have two substituents on neighbouring carbon atoms, i.e. 2-MeC6 2,2-diMeC5, 2,4-diMeC5, 2,2,4-triMeC5. Class C which includes isomers having substituents on neighbouring carbon atoms; 2,3-diMeC5, 2,2,3-triMeC4, 3-MeC6, 3,3-diMeC5, 3-EtC5, has smaller values of heats of mixing [Formula: see text]. These results are interpreted as not showing an extensive destruction of the correlations of orientations of the dodecyl chains by the linear alkanes of class A. The larger heats of class B are indicative of more disorientations of the long chains by the globular isomers. The smaller values of the heats for class C are seen as the balance of a positive disordering contribution and a negative one. The negative contribution is associated with a sterically hindered character of the compounds having substituents on neighbouring atoms. Free energies of mixing do not separate in the same three classes. This is thought to be due to an enthalpy–entropy compensation in the disordering and steric hindrance contributions. The Xl2S1−l parameter of the Flory theory shows the same variation as HE.
The X-ray crystal structure of rapamycin, C51H79NO13
Authors: Swindells D. C. Neil , White Peter S. , Findlay John A.
Published: May 2006

The antifungal antibiotic Rapamycin crystallises in the orthorhombic space group P212121 with a = 34.85(2), b = 13.08(1), c = 12.25(1) Å. The molecular structure has been determined by X-ray crystallography to be a completely new type of macrolide antibiotic of formula C51H79NO13.
The preparation of platinum(II) complexes with an ortho-metallated carbene ligand: the X-ray and molecular structure of [Pt{C(NHC6H4CH3)(NHC6H3CH3)}{PPh2(CH2)2PPh2}]ClO4
Authors: Christian David F. , Clarke David A. , Clark Howard C. , Farrar David H. , Payne Nicholas C.
Published: May 2006

Treatment of PtCl(CNR)(acac) (R = p-tolyl; acac = acetylacetonate) with p-toluidine gives the carbene compound PtCl{C(NHR)2}(acac). Reaction of this complex with a silver salt, followed by treatment with a neutral ligand L, gave ortho-metallated species [Pt{C(NHC6H4CH3)(NHC6H3CH3)}L2]+ which have been isolated as crystalline salts. The molecular structure of the ClO4− salt with L2 = bisdiphenylphosphinoethane has been determined by X-ray diffraction. Crystals are monoclinic, space group P21/n, with four formula units in a cell of dimensions a = 20.370(3), b = 18.116(3), c = 10.770(2) Ǻ, and β = 99.47(6)°. Full matrix least-squares refinement on F using 3252 observations gave a conventional agreement factor R. = 0.047. While the formation of these ortho-metallated carbene complexes restricts the further extension of this chemistry, the ready reversal by acid treatment is unusual.
Thiosemicarbazide complexes of mercury (II) halides
Authors: Chieh Chung , Lee Laura P. C. , Chiu Cecilia
Published: May 2006

Dibromobis(thiosemicarbazide)mercury(II), HgBr2(tsc)2, is isostructural with dichlorobis-(thiosemicarbazide)mercury(II). The crystal is orthorhombic with a = 8.825(9), b = 8.587(11), c = 15.939(22) Å, Z = 4, space group Pbcn. Some bond lengths and angles are: Hg—Br = 2.860(4) Å, Hg—S = 2.45(1) Å, C—S = 1.76(4) Å and [Formula: see text]. In both HgCl2(tsc)2 and HgBr2(tsc)2, the configuration of the coordinated thiosemicarbazide (tsc) is the same as that of the free molecule. The ir and Raman (R) spectra for the complexes and tsc in the region 300–1600 cm−1 are very similar. The strong band at 800 (807 R) cm−1 in the tsc due to v(C—S) is shifted to 773 (796 R), 777 (796 R), and 660 (680 R) cm−1 for HgCl2−(tsc)2, HgBr2(tsc)2, and HgCl2(tsc) correspondingly. A strong band at 368 (R) cm−1 present uniquely for HgCl2(tsc) can be assigned to v(Hg—N), The halides in HgX2(tsc)2 are bonded to one mercury(II) ion and weakly bridged to a neighboring molecule with Hg … Cl = 3.250(3) Å and Hg…Br = 3.436(4) Å. As a result, two Raman bands due to Hg—X are expected. For HgCl2(tsc)2, the two Raman bands occur at 236 and 166 cm−1, whereas for HgBr2(tsc)2, one was observed at 190 cm−1 but the other was masked by lattice modes. In HgCl2(tsc), the two Hg—Cl bonds are different and bands at 220 and 190 cm−1 are assigned to v(Hg—Cl)t.
Base-catalyzed hydrogen isotope exchange of thiocamphor: α-thioenolization rate constants
Authors: Werstiuk Nick Henry , Andrews Paul
Published: May 2006

The rates of base-catalyzed protium–deuterium exchange (α-thioenolization) of the exo and endo protons of thiocamphor (1), in 2:1 dioxane-D2O at 25.0 ± 0.5 °C, have been determined by monitoring the uptake of deuterium mass spectrometrically. The exo and endo exchange rate constants, 2.20 × 10−2 and 5.60 × 10−4 M−1 s−1, respectively, are 23.2 and 12.3 times larger than the rate constants for exo and endo exchange in camphor (2). Factors which may determine the rate enhancements are discussed.
The nature of green alkaline iron sulfide solutions and the preparation of sodium iron(III) sulfide, NaFeS2
Authors: Taylor Peter , Shoesmith David W.
Published: May 2006

The intense emerald green solutions formed by the reaction of iron salts with alkali metal sulfides at pH 11–13 have been found to contain colloidal MFeS2, M = Li, Na, K. Solid KFeS2 and NaFeS2 have been recovered from these systems. X-ray powder diffraction studies confirmed the identity of KFeS2, and showed NaFeS2 to have a structure different from those of other MFeS2 compounds, and related to that of the mineral rasvumite, K3Fe9S14. Some aspects of the crystal structures and chemistry of different MFeS2 compounds are discussed. A mechanism for the formation of colloidal MFeS2 is proposed on the basis of kinetic data. It is likely that colloidal NaFeS2 is responsible for the colour of the "green liquor" of the pulp and paper industry.
Synthesis of azapolycyclic compounds by the aminium radical route: rearrangements of C-nitroso compounds and their stereoelectronic requirements
Authors: Lockhart Robert W. , Kitadani Masayuki , Einstein Frederick W. B. , Chow Yuan L.
Published: May 2006

The aminium radicals generated from the photolysis of N-nitroso-endo-2-methylamino-methylbicyclo[2.2.1]hept-5-en and N-nitroso-endo-2-methylaminomethylbicyclo[2.2.2]oct-5-ene cyclize at the C-6 position, since the relevant reacting centers can achieve excellent orbital overlap with minimum molecular motion in comparison to the alternative cyclization path at the C-5 position. The photolysis of the former compound gave a C-nitroso compound which underwent a series of unusual intramolecular cleavages, deoximations, and redox reactions during the work-up. Stereoelectronic requirements for these intramolecular reactions are discussed. Thermolysis of N-chloro-endo-2-methylaminomethylbicyclo[2.2.2]oct-5-en in methanol also gave the product with azaisotwistane skeleton.
Interaction of polymers in solution with porous solids. I. Penetration of porous glass by dextran
Authors: Day John C. , Alince Bohumil , Robertson A. Allen
Published: May 2006

Measurements of the penetration of porous substrates (porous glasses) by non-sorbing macromolecules (dextrans) have yielded penetration curves that relate the degree of penetration to molecular size. Combinations of well-characterized polymer fractions with a series of uniformly porous glasses have demonstrated that, in agreement with the theory, the penetration is dependent only on the relative size of the molecule and the pore. Several models differing in the methods of characterizing the sizes of the pores and solute molecules have been compared. The predictions of the shape of the penetration curves are similar for most models and are in similar agreement with the experimental data.
The {Li(NH3)n}+ and {Na(NH3)n}+ systems. A CNDO/2 study of the Li+ and Na+ ion solvation
Authors: Sieiro C. , Cañas P. , Martinez P.
Published: May 2006

We present the CNDO/2 calculations of Li+ and Na+ solvation in ammonia solvent. The results indicate a solvation number of n = 6 for Li+ and n ≥ 8 for Na+, at equilibrium distances of Li+…N = 2.3 Å and Na+…N = 2.9 Å. The charge transfer from ammonia to both ions is analyzed.
Substituent and steric effects in the oxidation of alkyl aryl sulfides by peroxydisulfate
Authors: Srinivasan C. , Kuthalingam P. , Arumugam N.
Published: May 2006

The kinetics of oxidation of a number of alkyl aryl sulfides with potassium peroxydisulfate in aqueous ethanol have been investigated. The effect of substituents on the oxidation has been studied by employing a number of p- and m-substituted phenyl methyl sulfides: the reaction is accelerated by electron-releasing and retarded by electron-withdrawing substituents, indicating a rate-determining electrophilic attack by the peroxydisulfate ion at the reaction site, sulfur. A good correlation is found to exist between the rate constants and the Hammett σ+/σ− constants, the ρ+ value for the reaction being −0.56 with a correlation coefficient of 0.979. The activation parameters have also been determined.Studies with different alkyl phenyl sulfides clearly indicate that the reaction is quite sensitive to steric congestion around the reaction site. The results obtained in this study are compared with those found for the oxidation of the same set of sulfides with different oxidants.
Absolute rate constants for hydrocarbon autoxidation. 25. Rate constants for hydrogen atom abstraction from alkanes by the tert-butylperoxy radical
Authors: Chenier J. H. B. , Tong S. B. , Howard J. A.
Published: May 2006

Rate constants for abstraction of secondary and tertiary hydrogens from structurally different alkanes by the tert-butylperoxy radical in solution at 30 °C have been determined by competitive experiments in the presence of tert-butyl hydroperoxide. Rate constants fall in the range 1 × 10−4to 9 × 10−4and 1 × 10−3–2 × 10−2 M−1 s−1 for secondary and tertiary aliphatic C—H bonds, respectively. The most reactive secondary hydrogen is, therefore, almost as reactive as the least reactive tertiary hydrogen. Differences in reactivity within a type of aliphatic C—H bond are governed by differences in steric hindrance to attack by the peroxy radical and by relief of steric strain upon removal of the labile hydrogen. Rate constants for reaction of perdeuterated methylcyclohexane and 3-methylpentane are much smaller than the values calculated from the maximum primary kinetic isotope effect for this reaction.
Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XV. Trimethyllead complexes of inorganic ligands
Authors: Millar Emiko K. , Evans Christopher A. , Rabenstein Dallas L.
Published: May 2006

The formation constants of the trimethyllead(IV) complexes of SO32−, SeO32−, S2O32−, SCN−, HPO42−, CO32−, Cl−, Br−, and I− have been determined in aqueous solution by 1H nuclear magnetic resonance spectroscopy. The formation constants are in general fairly small and the extent to which complexes form is strongly dependent on pH. At high pH (CH3)3PbOH forms while at low pH protonation of those ligands which are the conjugate bases of weak acids competes with complex formation. There is no indication of high selectivity in the binding of trimethyllead(IV) by a particular ligand type, and calculations indicate that trimethyllead(IV) is likely to be distributed among a variety of ligands in biological fluids, including chloride which forms uncharged and presumably lipid soluble (CH3)3PbCl.
Conformational dissymmetry. Circular dichroism of amino acid and peptide complexes
Authors: Sullivan E. A.
Published: May 2006

A number of Pd(II) and Pt(II) complexes of amino acids and dipeptides have been isolated and characterized. The solution and solid-state circular dichroism of the amino acid complexes show a fairly consistent pattern, which is opposite to that shown by the dipeptide complexes. Some of the problems associated with the interpretation of the spectra in terms of spectroscopic assignment and structural features are discussed.
ρ as a quantitative measure of transition state structure
Authors: Poh Bo-Long
Published: May 2006

The values of the Brønsted exponent for several examples of nucleophilic substitution reactions, aromatic electrophilic substitution reactions, and hydrogen atom abstraction from toluene by free radicals have been calculated from the ρ values of the corresponding reactions. The magnitude of the Brønsted exponent is shown to indicate the degree of charge developed in the transition state structure.
Dihydropyridines in synthesis and biosynthesis. I. Secodine and precursors of dehydrosecodine
Authors: Kutney James P. , Badger Rodney A. , Beck John F. , Bosshardt Herbert , Matough Fathy S. , Ridaura-Sanz Vicente E. , So Ying Hung , Sood Rattan S. , Worth Brian R.
Published: May 2006

A synthesis of 16,17-dihydrosecodin-17-ol and of secodine is described. Various indole derivatives were elaborated to a series of pyridinium salts, potential precursors for 1,2- and 1,6-dihydropyridine compounds exemplifying the proposed biointermediate 'dehydrosecodine.'
Structural changes at hydrophobic/hydrophilic interfaces induced by thermal changes and isotopic composition of the water
Authors: Fujiwara Fred Y. , Reeves Leonard W.
Published: May 2006

A lyomesophase prepared from decylammorium tetrafluoroborate, ammonium tetrafluoroborate, and water, which orients in a magnetic field perpendicular to the directors (type II), has been investigated with respect to the isotopic composition, H2O/D2O of the aqueous compartment at constant overall chemical composition. An effect of the isotopic composition of the water has been discovered, which influences the packing of the water and tetrafluoroborate ions at the interface. An interface structure transition occurs at ∼ 14 mol% D2O in H2O. The ammonium ions, which do not form part of the first bound layer at the interface, are affected to a much smaller degree and the sudden changes in the direction of variation of nmr parameters are not observed for this ion. The interface structure at > 14 mol% D2O evidently does include more remote participation of NH4+ ions.Recent low angle X-ray diffraction studies, available to us, indicate that the mesophases which orient in magnetic fields have two levels of structure, the packing of amphiphiles in discrete anisotropic micelles and the super-packing of the micelles themselves. These studies now enable us to reinterpret other similar thermally induced structural changes in the interface, from results previously encountered, in the decylammonium chloride system. It is possible to have changes in the packing of water, amphiphiles, and ions at the interface without changes in the superstructure. Such changes in interface packing might well go undetected in a measurement of bulk properties but are revealed by measurement of nmr parameters for the oriented mesophase of different species involved in the interface structure. The isotope effect on structural packing at the interface is absent in two other mesophases investigated.
Ipso chlorination of 4-alkylphenols. Formation of 4-alkyl-4-chlorocyclohexa-2,5-dienones
Authors: Fischer Alfred , Henderson George Narayanan
Published: May 2006

Chlorination of 4-methyl-, 4-ethyl-, 4-isopropyl-, and 4-tert-butylphenol, and of substituted 4-methylphenols, with chlorine in acetic anhydride gives 4-chloro-4-methyl-, 4-chloro-4-ethyl-, 4-chloro-4-isopropyl-, and 4-chloro-4-tert-butylcyclohexa-2,5-dien-1-one, and substituted 4-chloro-4-methylcyclohexa-2,5-dien-1-ones, respectively, in yields ranging from 19 to 100%.
Thermodynamic and physical behaviour of some water + polyethyleneglycol mixtures. II. Dielectric properties
Authors: Douhéret Gérard , Morénas Maurice
Published: May 2006

Dielectric constants of water + glycol (mono-, di-, tri-, and tetraethyleneglycol) mixtures have been measured at 298.15 K over the entire composition range. The mixtures involving monoethyleneglycol have also been studied at temperatures from 308.15 to 288.15 K. Calculated deviations from ideality are always positive and show one maximum. Related properties have been computed: polarizability volume and excess polarizability volume, correlation factor of mixtures, and dipole moments of both components using the Mecke–Reuter treatment. Results support conclusions previously deduced from excess and partial molar volumes; they suggest that the addition of glycol molecules gives rise to a slight enhancement of the water-lattice in the water-rich region, followed by a progressive destructuring; the ether functions do not seem to play a prominent role.
Mechanisms of bromination of uracil derivatives. 4. Formation of adducts in acidic aqueous solutions and their dehydration to 5-bromouracils
Authors: Tee Oswald S. , Banerjee Sujit
Published: May 2006

The reactions of bromine with uracil, 1-methyluracil, 3-methyluracil, and with 1,3-dimethyluracil in 0.125–2.0 M aqueous sulfuric acid have been examined. Under these conditions rapid attack by bromine upon the uracil leads to the formation of an observable intermediate, a 5-bromo-5,6-dihydro-6-hydroxyuracil, which subsequently undergoes slow acid-catalyzed dehydration to the appropriate 5-bromouracil. The intermediates derived from uracil and 3-methyluracil also show acid independent dehydration. The dehydration of the adduct derived from 6-methyluracil proceeds much more rapidly and so precludes observation of that adduct. The dehydrations show significant primary isotope effects for the rupture of C(5)—H bonds of the intermediates. The mechanistic implications of these results are discussed.
Nuclear magnetic resonance studies of the solvation of phosphorus(V) selenides, 1,2-bis(diphenylphosphino)ethane, and tris(dimethylamino)phosphine telluride by sulfur dioxide
Authors: Dean Philip A. W.
Published: May 2006

31P and 77Se nmr spectra have been measured for a range of phosphorus(V) selenides, diphosphorus(V) diselenides, and triphosphorus(V) triselenides in the inert solvent CH2Cl2 and in liquid SO2. Significant roughly-correlated reductions in |1J(PSe)| and deshielding of the 77Se resonance accompany change of solvent from CH2Cl2 to SO2. These changes are shown to arise from 1:1 phosphorus(V) selenide:SO2 donor:acceptor complex formation. Approximate thermodynamic constants for the formation of the complexes have been determined and possible structures for the 1:1 complexes with the diphosphorus(V) diselenides discussed. It is shown from 1H and 31P nmr spectral changes that Ph2P(CH2)2PPh2 forms a 1:1 complex with SO2, and approximate thermodynamic data for the SO2 complexation of the diphosphine have been established. Complexation is indicated by changes in both |1J(PTe)| and δP when (Me2N)3PTe is dissolved in SO2, but the chemical reactivity of this system precluded detailed study.
Chemistry of phenoxo complexes. VI. Reactions of phenoxocopper(I) complexes with carbon tetrachloride
Authors: Harrod John F. , Gheluwe Patrick Van
Published: May 2006

The reactions of several substituted cuprous phenoxides with CCl4 in acetonitrile were examined. Phenoxides without ortho-substituents usually gave high yields of tetraarylorthocarbonates. It is shown that the latter are also produced catalytically from sodium phenoxides and CCl4 in the presence of small amounts of cuprous chloride. Cuprous phenoxides with ortho-chloro substituents, in the absence of facile hydrogen transfer agents, gave stable mixed oxidation state complexes of approximate composition: Cu2ICuIICl2(OAr)2. In the presence of facile hydrogen atom transfer agents, such as free phenol or ascorbic acid, both the phenoxides without ortho-substituents and the ortho-chlorinated phenoxides gave moderate yields of triarylorthoformates. Some reactions of tritertbutylphenol and tritertbutylphenoxyl with copper complexes are described. The mechanisms of the various reactions are interpreted in terms of homo- and cross-coupling between phenoxyl and •CCl3 radicals.
Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 1. Composition and molecular weight distribution of extracted autohydrolysis lignin
Authors: Chua Miranda G. S. , Wayman Morris
Published: May 2006

Extractive-free aspen wood meal was subjected to autohydrolysis at 195 °C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was found to be higher in carbon but lower in hydrogen and oxygen content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences have been attributed to condensation and incorporation into the lignin of non-lignin components. A lignin extractability curve with a maximum delignification at autohydrolysis time of 30–40 min was found. From molecular weight distribution studies the ratio of high molecular weight to low molecular weight materials varied for the different extracted lignins and reached a maximum at autohydrolysis time of 40 min. A mechanism of depolymerization/repolymerization of the lignin via carbonium ions has been proposed. p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.
Oxidation products of N-substituted imines and ketone hydrazones in the presence of sodium in ether: new and convenient syntheses of diimines and substituted aryl diazomethanes
Authors: Giri B. P. , Prasad G. , Mehrotra K. N.
Published: May 2006

Several diimines have been synthesised from the reaction of substituted imines with sodium in dry ether followed by bubbling in oxygen and subsequent protonation. A probable mechanistic route for the formation of products through the dimerisation of initially formed anion radicals is presented and an alternative route, through the dimerisation of radicals formed by hydrogen abstraction from starting imine, has been excluded by substituent labelling experiments. Ketone hydrazones on treatment with sodium in ether and subsequent air oxidation gave substituted diazomethanes in excellent yields (88–95%).