bluuebunny/crossref_metadata_2025 huggingface dataset:
Physico-chemical studies on areno-tropilidenes and tropones. I. The polarographic behaviour and electron affinities of thiophenotropone derivatives in buffer solutions of varying pH values and in DMF
Authors: Etaiw Safaa H. , Ismail Mohamed I. , El-Borai Mohamed
Published: May 2006

The polarographic behaviour of some thiophenotropone derivatives were studied in DMF and in Thiel buffer solutions of varying pH values and μ of 0.1 at 25 ± 0.1 °C. It was found that the carbonyl group is the active centre towards reduction. In strong acid media, the reduction proceeds via one reversible electron forming a free radical which dimerises to produce pinacol. In solutions of pH values from 4 to 9, the polarograms consist of two reduction waves of equal heights each corresponding to 1 F. In strong alkaline media, one wave is observed; in most cases, depending on the molecular structure, the wave corresponds to the uptake of two electrons. The first step involves the direct reduction of the basic form to the anion radical which undergoes a further reduction forming the corresponding thiophenotropolone. At pH values > 13, the height of the limiting current decreases until it attains the height corresponding to 1 F indicating that the anion radical is stable in such media. Also, the electron affinities of these compounds were calculated.
Sulfonyl radicals, sulfinic acid, and related species: an abinitio molecular orbital study
Authors: Boyd Russell J. , Gupta Abha , Langler Richard F. , Lownie Stephen P. , Pincock James A.
Published: May 2006

Extensive abinitio molecular orbital calculations on six sulfonyl radicals (XSO2 where X = H, CH3, NH2, OH, F, and Cl), the simplest sulfinic acid HSO2H3 and its isomeric sulfone H2SO2, the HSO2− anion of sulfinic acid, the isomeric anion SO2H−, and for completeness, the SO2H radical are presented. By use of the STO-3G* basis set, which includes d-type polarization functions on second-row atoms, all geometrical parameters are varied until the total energy is minimized, subject only to certain symmetry restrictions specified for each system. The inclusion of d orbitals on S is observed to affect the S—O bond lengths by as much as 0.45 Å. The calculations suggest that the radical site in sulfonyl radicals is significantly delocalized over the entire functional group and that the geometrical parameters of the SO2 functional group in sulfonyl radicals are nearly independent of the substituent (r(S—O) = 1.47 ± 0.01 Å, < OSO = 123 ± 2°). Estimates of the X—S bond energy in CH3SO2, NH2SO2, and OHSO2 are consistent with the chemistry of alkylsulfonyl and aminosulfonyl radicals and lead to an interesting prediction for alkoxylsulfonyl radicals. Furthermore the calculations yield lower total energies for HSO2H, HSO2−, and SO2H than for the respective isomeric forms H2SO2, SO2H−, and HSO2.
A systematic investigation of the reaction of SiF2 with ethylene and six methyl-substituted ethylenes. III. Structures and conformational behaviour of 1,2-disilacyclohexane products
Authors: Reynolds William F. , Thompson James C. , Wright A. P. Gerald
Published: May 2006

1,2-Disilacyclohexanes are generally formed as products in the reaction of SiF2 with alkenes. Unsymmetric methyl-substituted alkenes yield disilacyclohexanes with greater methyl substitution at C(2). Often two (or more isomeric) products are formed, and the reaction proceeds by a mechanism which allows isomerization of the methyl configurations. The disilacyclohexanes exist in distorted chair conformations and the chair-to-chair interconversion can be observed at low temperature in many cases. Consideration of the variable temperature 19F spectra and the effect of methyl groups on average and individual 19F chemical shifts allows assignment of configurations and preferred conformations of all disilacyclohexane derivatives.
Carbocyclization in natural products. III. Brominative cyclization of dehydrosaussurea lactone and costunolide
Authors: Jain Tikam C. , Banks Calvin M.
Published: May 2006

Treatment of dehydrosaussurea lactone 4 and costunolide 1 with N-bromosuccinimide (NBS) in aqueous acetone at room temperature furnished bromolactones 6, 7, and 8. Structural evidence for these bromolactones rests upon spectral data and transformation to the hydrogenated bromolactones 9, 10, and 11. The latter were found identical with the corresponding products obtained by the brominative cyclization of dihydrocostunolide 2.
Studies on allylic peroxides. II. Allyl-t-butyl peroxide
Authors: Hiatt R. , Nair V. G. K.
Published: May 2006

Allyl-tert-butyl peroxide decomposes thermally in toluene with kd = 1013.8 exp (−33200/θ) (s−1). Product studies show the reaction to be a mixture of homolysis and radical-induced decomposition, the latter involving both radical addition to C=C and allyl hydrogen abstraction by alkoxy radicals. Computer modelling of the system gives good agreement with the experimental results and suggests that the overall decomposition is about 50% homolysis.
The chemistry of aurodox and related antibiotics
Authors: Maehr Hubert , Leach Michael , Williams Thomas H. , Blount John F.
Published: May 2006

The studies which led to the complete structure elucidation of the antibiotic aurodox, including the chiralities of all eleven asymmetric centers and the cis–trans isomerism of all seven exocyclic double bonds, are summarized. Aurodox was correlated stereochemically with mocimycin. Thus, aurodox can be described as N-[7-[5(R)-[7-[1,2-dihydro-4-hydroxy-1-methyl-2-oxo-3-pyridinyl]-6-methyl-7-oxo-1(E),3(E),5(E)-heptatrienyl]tetrahydro-3(S),4(R)-dihydroxyfuran-2(S)-yl]-6(S)-methoxy-5,7(R)-dimethyl-2(E),4(E)-heptadienyl]-α(S)-ethyl-5,5-dimethyltetrahydro-2(R),3(R),4(R)-trihydroxy-6(S)-[1(E),3(Z)-pentadienyl]-2H-pyran-2-acetamide. Mocimycin, probably identical with kirromycin, is the corresponding N-desmethyl homolog.
Carbocyclic phenylaminephosphonate stereochemistry as probed via 13C nmr chemical shifts and nuclear spin couplings from 13C to 31P and 15N
Authors: Buchanan Gerald W. , Morin Frederick G.
Published: May 2006

13C nmr chemical shifts and 13C—31P couplings through one, two, and three bonds are reported for eleven carbocyclic phenylaminephosphonates with ring sizes from four to seven. On the basis of these data, inferences regarding preferred conformations are drawn. Low temperature spectra of the 4-methylcyclohexyl derivative show the existence of two conformers, populated in the ratio of approximately 2:1 at 183 K.
Organocation speciation. II. Methylene blue photosensitization as a model for speciation and toxicity of herbicides
Authors: Guy Robert D. , Narine Deoraj R.
Published: May 2006

A chemical model that employs the photosensitization properties of methylene blue to mimic herbicide toxicity is used to test size separation as a method of chemical speciation. A spectrophotometric study of the dye interactions with the humic colloid indicated that the dye – humic acid complex has a weaker absorption spectrum than the free dye. The absorption spectra suggested that the binding sites on the humic acid are sufficiently isolated to prevent dye–dye interactions on the colloid surface. The dye photosensitization of tryptophan degradation indicated that only the free methylene blue was active in the presence of humic acid, clay, and polystyrene sulphonic acid. The model suggests that if the pollutant must be in true solution to be biologically active then a size separation by dialysis would be a satisfactory speciation procedure.
Photochemical reactions of fluoro-substituted ketones with amines, tetraphenylborates, and organometals: an electron spin resonance study
Authors: Chen Kuang S. , Foster Terry , Wan Jeffrey K. S.
Published: May 2006

Ammonium ion-pairs, solvent-separated alkali-metal ion-pairs, and Group IVB organometallic adducts of fluoro-substituted ketones were generated photochemically. The structure and the controlling factors for the formation of contact ammonium ion-pair were deduced from the effects of solvent, amine, and fluorine substitution. The effect of fluorine on the formation of the alkali-metal ion-pairs and organometallic adducts was discussed.
Part II. Conformational analysis of 4- and 5-substituted thiazolidine-2-thiones
Authors: Chanon F. , Rajzmann M. , Chanon M. , Metzger J. , Pouzard G. , Drakenberg T.
Published: May 2006

Variation of the conformational properties in a series of 4-R-thiazolidine-2-thiones (4-R = Me, Et, iPr, tBu, OH) and 5-R-thiazolidine-2-thiones (5-R = Me, Et, iPr, tBu) is deduced from 1H nmr (Karplus 3J, chemical shifts, 2J44′, 2J55′) 13C nmr data and CNDO-2 calculations. In the absence of any transannular interaction, vicinal constraints and van der Waals requirements of the substituents control the conformational equilibrium. The pseudo-axial arrangement is favoured when 4-R = Me, while the substituent presents no preferential orientation when 5-R = Me. As the size of the 5-alkyl and the 4-alkyl substituent increases, its pseudo-equatorial orientation and the predominance of the C4C5 out-of-plane half-chair conformation are favoured. This does not lead to conformational exclusivity even when 4-R or 5-R is tBu. When 4-R is hydroxy, there is a definite pseudo-axial conformation (anomeric effect) and the ring preference is of the C4 out-of-plane type.
13C and 2H spin–lattice relaxation in solid adamantane
Authors: Wasylishen Roderick E. , Pettitt Brian A.
Published: May 2006

Spin–lattice relaxation times for the 13C nuclei of adamantane and the 2H nuclei of adamantane-d16 are reported for most of the temperature range of the solid I (plastic) phase, and for the solid II phase just below the transition point. Angular correlation times are shown to be in good agreement with those previously obtained from proton nmr data by Resing.
N1s core binding energies for 2-, 3-, and 4-substituted pyridines determined by X-ray photoelectron spectroscopy. Correlations with theoretical models, substituent parameters, and gas phase basicities
Authors: Brown R. S. , Tse A.
Published: May 2006

N1s binding energies for 36 pyridines substituted at the 2-, 3-, and 4-positions have been determined by X-ray photoelectron spectroscopy. The differences in BE relative to pyridine are analysed in terms of existing theoretical approaches (electrostatic, ground potential, and relaxation potential models) and compared with [Formula: see text] values calculated for analogous monosubstituted benzenes. One finds good correlations of [Formula: see text] with solution determined σ-substituent values although some substituent values deviate from the correlation probably due to solution effects which are not present in the gas phase. Correlations between [Formula: see text] and 14N nmr chemical shifts are poor, particularly for electron withdrawing substituents. The relationship between [Formula: see text] and gas phase basicity values (ΔG0) is good, and it appears as if the [Formula: see text] is more sensitive to the substituent than ΔG0. MINDO/3 calculations on the methoxypyridines and their conjugate acids employing full geometry optimizations are presented and analysed in order to determine the effect of geometric relaxation on the gas phase basicity.
Apparent molar heat capacities and volumes of unsaturated heterocyclic solutes in aqueous solution at 25 °C
Authors: Enea Octavian , Jolicoeur Carmel , Hepler Loren G.
Published: May 2006

Measurements at 25 °C with flow calorimeters and densimeters have led to heat capacities and densities of aqueous solutions of 15 unsaturated heterocyclic compounds containing nitrogen. From the results of these measurements we have obtained apparent molar heat capacities and volumes of the solutes. Extrapolations to infinite dilution have led to corresponding standard state apparent and partial molar heat capacities and volumes, which have been analyzed in terms of atomic and group additivity relationships.
The electronic spectra of coordinated nitrite ion: correlation between spectra and structure
Authors: Walker Ian M. , Lever A. B. P. , McCarthy Paul J.
Published: May 2006

The characteristic electronic spectrum of the nitrite ion survives when the ion is bonded to metal ions through the oxygen atoms. The vibrational fine structure associated with the n → π* electronic transition in the near uv region has been examined at 10 K in single crystals of K3[Hg(O2N)4](NO3) and in a series of nickel complexes with N-alkylated ethylenediamines. When either non-coordinated, monodentate oxygen coordinating, or bidentate chelating through oxygen, nitrite ion in the crystals shows vibronic features which depend on nitrite environment. It is suggested that the electronic spectra of the nitrite ion may constitute a useful tool in structure elucidation.
Complete and partial miscibility in ternary system: triethylamine–methylethylketone–water
Authors: Campbell Alan N.
Published: May 2006

The equilibrium diagram of the system triethylamine–methylethylketone–water has been investigated completely with respect to the occurrence of solid phases and of the lower and upper solution temperatures of the [Formula: see text] equilibria, where L1 and L2 are equilibrium liquid phases. The [Formula: see text] surface is not completely realizable because this surface is intersected by the [Formula: see text] surface. In this respect the system forms a contrast to the previously investigated system nicotine–methylethylketone–water, where the complete [Formula: see text] surface is realizable experimentally.
Photochemical reactions of charge-transfer complexes. The irradiation of the charge-transfer complexes between 1,4-, 1,5-, and 2,3-dimethoxynaphthalenes and 1,2-dicyanoethylenes
Authors: Wong P. C. , Arnold D. R.
Published: May 2006

The first part of this paper describes the experimental search for a donor which would complex preferentially one of the isomers of 1,2-dicyanoethylene. This involved measuring the association constants (KcDA) of the charge-transfer (ct) complexes of several dimethoxynaphthalenes (DMN) with maleonitrile (MN) and fumaronitrile (FN). From the measured KcDA, we found that MN complexes more strongly than FN with 1,4- and 1,5-DMN but that FN complexes more strongly with 2,3-DMN than does MN. These results are explained in terms of more than one favourable geometry for the ct complexes, since the donors are relatively large compared to the acceptors.Irradiation of the ct complexes between 1,4-, 1,5-, or 2,3-DMN and 1,2-dicyanoethylene led to isomerization of the olefins. The photostationary state depends on the absorption spectra of the ct complexes formed between the donor and the isomeric olefins. From spectroscopic and photo-CIDNP studies, we find evidence that the isomerization in polar solvents takes place via the triplet state of the olefin. The triplet is formed from the radical ion pair resulting after excitation of the ct complex.
The solution conformation of prostacyclin as determined by high field proton magnetic resonance techniques
Authors: Kotovych George , Aarts Gerdy H. M. , Nakashima Tom T. , Bigam Glen
Published: May 2006

The proton magnetic resonance (1H nmr) spectrum at 400 MHz of prostacyclin at pH 10.4 in glycine buffer has been completely analyzed utilizing homonuclear double resonance, inversion recovery, and difference nOe experiments. The spectral analysis shows that the two protons at C-4 are non-equivalent even though they are removed from the asymmetric centres at C-8 and C-9 by five bonds. The difference nOe measurements verify the configuration at C-5.Proton longitudinal relaxation times (T1) were measured at 400 and 200 MHz. From the T1 frequency dependence, effective rotational correlation times ranging from 2.3 × 10−10 to 3.0 × 10−10 s were calculated for H-5, H-9, H-11, and H-15. This indicates that the portion of the molecule encompassed by these protons has a longer correlation time than is observed for the C-2 and the C-17 to C-19 protons, for which the average correlation time is 1.2 × 10−10 s. Hence the aliphatic side chains have more segmental motion.
Electrophilic cleavage of cyclopropanes. The areneselenenylation of tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclene)1,2
Authors: Beaulieu Pierre L. , Morisset Veronique M. , Garratt Dennis G.
Published: May 2006

The reaction of benzeneselenenyl chloride with tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclene) yields, under conditions of kinetic control, adducts of both 1,3- and conjugative 1,6-addition, the latter being formed preferentially. Electrophilic cleavage of the cyclopropane ring occurs by both retention and inversion of configuration. In agreement with the known propensity for bond cleavage in this system only the C5—C6 and/or the C1—C7 bonds are broken. The rate of cyclopropane ring cleavage is found to follow second order kinetics, first order in quadricyclene and first order in selenenyl chloride; kobs = 1850 vs. 12 300 dm3 mol−1 s−1 for bicyclo[2.2.1]hepta-2,5- diene at 24.5 °C in methylene chloride solvent. The use of nucleophilic solvents such as HOAc, CH3OH, and CH3CN gives products of solvent-incorporation, preferentially via 1,3-addition.
Electrophilic cleavage of cyclopropanes. II. Concerning the effect of increasing electron demand upon the product-determining transition state in the reaction of 4-substituted-2-nitrobenzenesulphenyl chlorides and benzenesulphenyl chlorides with tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclene)
Authors: Beaulieu Pierre L. , Kabo Ann , Garratt Dennis G.
Published: May 2006

The effect of increasing electron demand upon the product-determining transition state in the reaction of arenesulphenyl chlorides with tetracyclo[3.2.0.02,7.04,6]heptane has been investigated. As the electron donating ability of the remote substituents on the phenyl ring of the sulphenyl chloride is varied from nitro to methoxy the relative proportion of adducts derived from edge-on attack is found to increase relative to that of adducts derived from corner attack. An ortho-nitro group was found to lead to a stabilizing interaction only in the case of 2,4-dinitrobenzenesulphenyl chloride. A mechanism involving the competition between the two conceptual modes of approach is suggested.
Electrochemical oxidation of carboxylic acid anions in the presence of some mono- and di-substituted olefins
Authors: Champagne Philippe J. , Renaud Roger N.
Published: May 2006

The anodic oxidation of the sodium salts of acetic, propionic, and isovaleric acids was performed in the presence of a series of ethylenic compounds bearing electron-withdrawing substituents. The results showed that under certain experimental conditions the electrogenerated radicals added to the ethylenic double bond to give mainly 1,2-dialkylated products.The stereoisomers obtained were separated and, whenever possible, identified. Their physical properties are reported.
The structure of an unusual disulfide, formed from reaction between a sulfene–amine zwitterion and thionyl chloride
Authors: Grossert J. Stuart , Bharadwaj Madan M. , Faught J. Brian , Terzis Aris
Published: May 2006

Thionyl chloride has been shown to react with the zwitterion from dimeric sulfene and triethylamine to give bis(methylsulfonyl dichloromethyl) disulfide, 3. The structure of 3 was determined from its spectral properties and was confirmed by an X-ray crystal structure analysis. Dechlorination of 3 gave bis(methylsulfonylmethyl) disulfide, 4. Raman spectra of 3 and 4, as well as of 5 and 6, two related sulfones derived from 2,4,6-trithiaheptane, are reported.
Electrophilic additions to allenes. IV. Concerning the nature of the ortho-nitro group effect in the reaction of arenesulphenyl chlorides with allenes
Authors: Garratt Dennis G. , Beaulieu Pierre L.
Published: May 2006

The reactions of twelve arenesulphenyl chlorides, five of which contained an ortho-nitro substituent, with ten 1,3-disubstituted allenes, using methylene chloride as solvent, are described. No evidence for a special ortho-nitro group effect involving a spirosulphurane type intermediate is observed. Variations in the chemoselectivity and configurational-selectivity of the additions are interpreted in terms of steric interactions in the product determining transition state.
Osmotic and activity coefficients in dilute potassium chloride solutions at 25 °C
Authors: Pan Chai-Fu
Published: May 2006

Osmotic and activity coefficients of dilute aqueous potassium chloride solutions are calculated from the simplified forms of the Stokes and Robinson equation. The hydration parameters in these equations are obtained from the vapor pressure data measured at higher concentration regions and the ion-size parameter is chosen as the sum of the crystallographic radii of the cation and anion of the electrolyte. The results are very satisfactory in comparison with existing data.
Complex fluoroanions in solution. XI. Complexes of silicon, germanium, and titanium tetrafluorides with simple anions
Authors: Brownstein S.
Published: May 2006

A fluorine-bridged silicon fluoroanion and many hexa-co-ordinate germanium and titanium fluoroanions have been identified in solution via fluorine magnetic resonance. A generalized shceme is used to correlate all fluorine chemical shift data for hexa-coordinate fluorine containing species.
Octahedral–tetrahedral equilibria in aqueous cobalt(II) solutions at high temperatures
Authors: Swaddle Thomas Wilson , Fabes Leonard
Published: May 2006

Evidence is presented to indicate that aqueous Co2+ exists as the hexaaquo-ion in equilibrium with minor amounts (upper limits 0.08% at 298 K, 7% at 625 K, at 16–25 MPa) of tetraaquocobalt(II), with ΔH ~ +17 kJ mol−1. The single visible absorption band of the supposed Co(H2O)42+ has maxima at 552 nm and 486 nm in the intensity ratio 2:1. Hydrogen sulfate ion (up to 0.5 M at least) does not complex Co2+(aq) detectably in acidic media, 290–625 K, and sulfuric acid therefore holds promise as a non-complexing strong monobasic acid for high-temperature aqueous studies. In water containing 2.0 M or more Cl−, the tetrahedral form of cobalt(II) is CoCl42−, ΔH for the octahedral → tetrahedral equilibrium being +62 kJ mol−1; forCoBr42−, the corresponding ΔH is +70 kJ mol−1, the greater endothermicity accounting entirely for the lower stability relative to CoCl42−.
Effect of t-butanol on the structural propensities of alkali halides in water
Authors: Murthy Neriyanuri Manohara , Subrahmanyam Saraswatula Venkata
Published: May 2006

The effect of NaCl, KCl, RbCl, KBr, and KI on the temperature corresponding to the sound velocity maximum (TSVM) of aqueous t-butanol has been studied. The structural contribution to the shift in the TSVM of aqueous t-butanol by the addition of alkali halides was found to be in the order NaCl > KCl > RbCl and KCl > KBr > KI, thereby indicating that Na+ > K+ > Rb+ and Cl− > Br− > I− in disrupting the hydrogen-bonded structure of water. The results also indicate an enhancement in the structure-breaking characteristic of both cations and anions in the presence of t-butanol. However, the order is the reverse of that found for pure water, i.e. Rb+ > K+ > Na+ and I− > Br− > Cl−. The results have been explained on the basis of hydrophobic–hydrophilic interactions prevalent in the ternary Systems.
A type II aqueous cholesteric lyomesophase
Authors: Acimis Mahmut , Reeves Leonard W.
Published: May 2006

The lyotropic liquid crystals formed by optically active detergents, water, and electrolyte have been investigated near and above the water-rich limit of the lamellar mesophase by using nuclear magnetic resonance, relative density observations, and polarized microscopy. The racemic mixture of α-alanine decyl ester forms a lamellar phase, a disc-micelle type II phase (which may co-exist in equilibrium), followed by an isotropic material as the water content increases. The resolved d or l detergent also forms a lamellar mesophase which may coexist with a type II disc-micelle system; however, as water content increases a transition occurs to a cholesteric lyotropic mesophase which itself passes over to an isotropic phase at the highest water contents studied. The range of existence, as a function of water content, for these intermediate type II DM and cholesteric phases is very narrow. The screw axis of the cholesteric mesophase aligns parallel to the magnetic field. A tentative structure of the cholesteric phase based on disc micelles distorted into a partial helix is suggested.
A high-field proton magnetic resonance and nuclear Overhauser effect study of prostaglandin E2
Authors: Kotovych George , Aarts Gerdy H. M. , Bigam Glen
Published: May 2006

The proton magnetic resonance (1H nmr) spectrum of prostaglandin E2 (PGE2) in CDCl3 at 400 MHz bas been completely analyzed utilizing homonuclear double resonance, inversion recovery, and nOe difference experiments. The nOe difference experiments are used to assign points of configuration, namely the H-10β and the H-10α proton resonances. A spectral analysis shows that the two protons at C-3 and the two protons at C-4 are nonequivalent, indicating a hindered rotation of the chain. This is possibly due to the hairpin conformation of PGE2 in solution.
Spin trapping azidyl (N3•), cyanatyl (OCN•), cyanyl (•CN) radicals, and chlorine atom (Cl•)
Authors: Janzen Edward G. , Stronks Henry J. , Nutter Jr. Dale E. , Davis Edward R. , Blount Henry N. , Poyer J. Lee , McCay Paul B.
Published: May 2006

Azidyl, cyanatyl, and cyanyl radicals and chlorine atoms have been detected by spin trapping using α-phenyl N-tert-butyl nitrone (PBN) in the monoelectronic electrooxidations of azide, cyanate, cyanide, and chloride. Azidyl and cyanatyl radicals were also detected with PBN in the persulfate oxidations of azide and cyanate. Azidyl radicals could be detected in the reaction of azide with hydroxyl radicals in the presence of PBN.
N-Methylpicramide–methoxide ion interactions: proton abstraction versus σ-complex formation
Authors: Buncel Erwin , Hamaguchi Masashi , Norris Albert R.
Published: May 2006

The interactions of N-methylpicramide (NMP) with methoxide ion in dimethylsulfoxide–methanol media and with 1,4-diazabicyclooctane in dimethylsulfoxide have been investigated spectrophotometrically at 25.0 °C. Dimethylsulfoxide has been found to stabilize the conjugate base of NMP, formed via loss of hydrogen ion from the methylamino group, with respect to the anionic σ-complex generated via addition of methoxide ion to a ring carbon position. As a result, methanol–dimethylsulfoxide solutions rich in dimethylsulfoxide (i.e., 95/5, v/v, DMSO/MeOH) contain the conjugate base of NMP as the sole product of the 1:1 interaction of NMP and methoxide ion. At mole ratios of methoxide ion to NMP > 1 a second interaction results, yielding a dianion formed via addition of methoxide ion to one of the H-bearing ring carbon atoms of the conjugate base. Values of absorption maxima and molar absorptivities at the absorption maxima for the conjugate base of NMP and the dianion are reported here for the first time.
The electrochemical synthesis of organometallic halides of titanium, zirconium, and hafnium
Authors: Said Farouq F. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of titanium, zirconium, or hafnium (= M) in a cell containing an organic halicie RX results in the formation of an organometallic halide of the metal concerned. These compounds are conveniently isolated as adducts of acetonitrile or 2,2′-bipyridine(bipy) also présent in the electrolyte phase. The products most commonly isolated are the [Formula: see text], but other species were obtained in certain cases. Possible reasons for these findings are discussed.
A 13Cmr study of 2′-deoxynucleotides in the syn and anti conformation
Authors: Niemczura Walter P. , Hruska Frank E.
Published: May 2006

not available
Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules
Authors: Chong Delano P.
Published: May 2006

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.
Solution properties of the molten hydrates of zinc nitrate
Authors: Jain Surendar Kumar , Tamamushi Reita
Published: May 2006

Density, conductivity, viscosity, refractive index, and surface tension of the molten Zn(NO3)2•xH2O(2 ≤ x ≤ 6) systems have been measured as a function of temperature. Both conductivity and fluidity exhibit a non-Arrhenius temperature dependence for all the compositions and have been described in terms of three parameter equations[Formula: see text]based on the free volume model. The parameters AY,AY′,BY′, BY′, T0,Y, and V0,Y are the constants characteristic of the medium. The composition dependence of these parameters has been discussed. The temperature dependence of the Walden's product could be satisfactorily described by the equation[Formula: see text]where p equals the ratio [Formula: see text]; EΛ and [Formula: see text] being the apparent activation energy for the conductance and the viscous flow respectively. The molar polarisations (PLL) computed using the Lorenz–Lorentz equation showed a slight temperature variation (< 0.2%) over the range 40–70 °C. Thermal expansivity (α) and the ratio α/αGD for the systems show a continuous fall with the decrease in the water content of the medium; the changes becoming more marked at x < 4. The surface tension – composition isotherms show a maximum near x = 4. The results are consistent with the change of configuration from octahedral to tetrahedral around Zn2+, the increased covalent character in the Zn2+—ONO2− bond and the water molecule acting as a bridging ligand in the melts containing less than 4 moles of water per mole of the salt.
Photo- and thermal isomerization of some 1-methoxyallyl cations
Authors: Childs Ronald F. , Hagar Mark E.
Published: May 2006

The 1-methoxy-, 1-methoxy-3-rnethyl-, and 1-methoxy-2,3-dimethylallyl cations, 2, 5, and 9, were prepared by treatment of the dimethyl acetals of acrolein, crotonaldehyde, and tiglaldehyde, respectively, with FSO3H. Each of these ions was capable of existing in various stereoisomeric forms. The thermodynamically preferred conformation of 2, 5, and 9 all had a C1—O, E configuration and 5 and 9 an E configuration about the C2—C3 bonds. Irradiation of FSO3H solutions of these ions at −70 °C using 254 nm light caused them to be converted to the other stereoisomers. Relatively efficient photoisomerism about both the C1—O and C2—C3 bonds was observed. The rates of the reverse thermal conversion of the photoproducts to 2, 5, and 9 were measured and on the basis of medium and substituent effects it was concluded that thermal isomerism about the C1—O bond takes place by an inversion process while stereomutation about the C2—C3 bond involves the addition of base to C3.
The crystal structure of ethyl-Z-3-amino-2-benzoyl-2-butenoate and measurement of the barrier to E,Z-isomerization
Authors: Fallon Gary D. , Gatehouse Bryan M. , Pring Allan , Rae Ian D. , Weigold Josephine A.
Published: May 2006

Ethyl-3-amino-2-benzoyl-2-butenoate crystallizes from pentane as either the E (mp 82–84 °C) or the Z-isomer (mp 95.5–96.5 °C). The E isomer is less stable, and changes spontaneously into the Z, which bas been identified by X-ray crystallography. The structure is characterised by an N–H/ester CO hydrogen bond and a very long C2—C3 bond (1.39 Å). Nuclear magnetic resonance methods have been used to measure the rate of [Formula: see text] isomerization at several temperatures, leading to the estimate that the free energy of activation at 268 K is 56 ± 8 kJ.
A stereospecific synthesis of napelline
Authors: Sethi Sat Paul , Atwal Karnail S. , Marini-Bettolo Rinaldo M. , Tsai Thomas Y. R. , Wiesner Karel
Published: May 2006

A simple and stereospecific synthesis of the triketolactam 15 is described. This compound has been previously converted to napelline 1. The key step of the synthesis is the rearrangement of the "denudatine" intermediate 11 to the napelline derivative 12. The denudatine skeleton was constructed by a stereospecific diene addition belween the o-quinone acetal 4 and benzyl vinyl ether. It is expected that this last process will be capable of general application in the synthesis of complex compounds.
C-Nucleosides and related compounds. XV. The synthesis of D,L-2′-epi-showdomycin and D,L-showdomycin
Authors: Just George , Liak T. J. , Lim Mu-Ill , Potvin Pierre , Tsantrizos Youla S.
Published: May 2006

The conversion of the Diels–Alder adduct of methyl β-nitroacrylate with furan to the title compounds and to D,L-2,5-anhydroglucose derivatives is described.
Spectral and photochromic properties of two long-chain spiropyranindoline monolayers at the air–solid interface
Authors: Morin Marcel , Leblanc Roger M. , Gruda Ilona
Published: May 2006

Some long-chain spiropyranindolines have been studied at the air–water and the air–solid interfaces. We have measured the surface pressure–area isotherms of these compounds and two of them are characterized by a solid film. We have also investigated the spectroscopic properties (uv–visible) of these spiropyranindolines in monolayer and in solution. The deposition of monolayers on quartz slides allowed the study of the photochromic properties of these compounds at the air–solid interface. The 3′,3′-dimethyl-1′-hexadecyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline), irradiated at 253.7 nm, showed the appearance of a new absorption band at 570 nm which varied in intensity when the number of monolayers and the time of irradiation were changed.
2-Epi- and 15-dihydro-2-epilubimin: new stress compounds from the potato
Authors: Stoessl A. , Stothers J. B.
Published: May 2006

The complement of sesquiterpenoidal stress compounds produced in the interaction of potato with the pathogenic fungus, Alternariasolani, includes representatives of a new stereochemical series, 2-epilubimin (1) and its reduction product, 15-dihydro-2-epilubimin (3). Their structures were deduced from 13C and 1H magnetic resonance data.
Vibrational spectroscopic studies of molecular associations by local anesthetics
Authors: Guérin M. , Dumas J.-M. , Sandorfy C.
Published: May 2006

Infrared spectroscopic studies have been performed on H-bonding for a number of local anesthetics: benzocaine, procaine, tetracaine, lidocaine, dibucaine, and three barbiturates: phenobarbital, pentobarbital, and thiopental. All these compounds have a marked tendency for self-association. When they are put into contact with systems containing H-bonds of the [Formula: see text], [Formula: see text], or [Formula: see text] types, however, the degree of self-association decreases and new H-bonds are formed at the expense of the former. The possible consequences of this for the chemical mechanism of anesthesia are briefly discussed.
Superoxide mediated autoxidation of hydrocarbons
Authors: Lee-Ruff Edward , Timms Neil
Published: May 2006

Potassium superoxide was found to initiale autoxidations of fluorene, diphenylmethane, and distyrylmethane. In each case the oxidation results in the formation of ketones as primary products. Kinetics of the fluorene and diphenylmethane oxidations showed typical sigmoidal autoxidation rate profiles. External hydroperoxides did not affect the rates of these reactions, however, these were efficiently transformed to ketones in the presence of [Formula: see text]. A mechanism for these autoxidations is proposed.
Effet d'engrenage. VIII. Extension à des dérivés fonctionnels de l'alanine
Authors: Blaive Bruno , Roussel Christian , Metzger Jacques , Sandström Jan
Published: May 2006

The gear effect has been discovered and studied for the first time on molecules where the interacting groups were alkyl substituents. In order to be closer to biochemical models, this effect has now been studied where one interacting group is asymmetric and functional. For this purpose eighteen new compounds derived from alanine have been prepared and studied by nmr and dynamic nmr. The gear effect is operating, and it appears to be a suitable means to modulate the interaction of two active functions.
Pyrochlores. XI. High-pressure studies of the antimonates A2Sb2O7 (A = Ca, Sr, Cd) and preparation of the weberite Sr2Bi2O7
Authors: Knop Osvald , Demazeau Gerard , Hagenmuller Paul
Published: May 2006

Reactive hot-pressing experiments at 60–70 kbar and 700–900 °C indicate that the relative stability of the pyrochlore and weberite phases of the A2Sb2O7 (A = Ca, Sr, Cd) antimonates depends primarily on the effective size of A2+ and the covalency of the A—O bond working in conjunction. The analogous bismuthate(V) Sr2Bi2O7, obtained by hot pressing of SrBiO3−x with an excess of KClO3, has been shown to have the weberite-type structure.
Muonium atoms observed in liquid hydrocarbons
Authors: Ito Yasuo , Ng Bill W. , Jean Yan-Ching , Walker David C.
Published: May 2006

Muonium atoms have been observed in n-hexane, c-hexane, and tetramethylsilane at 295 or 273 K by the MSR technique. The yield of muonium in these non-polar liquids is found to be quite comparable to that observed previously in water, methanol, and ethanol. This suggests that neither the dielectric constant of the medium nor the free-electron mobility has a major influence on the formation process. This in turn supports the view that muonium formation does not mainly result from intraspur reactions in the terminal spur of the muon's track.The chemical lifetime of muonium in these hydrocarbons is curtailed by spurious impurities so that high purity is required. In addition, however, there may be a chemical reaction between muonium and the hydrocarbon itself because the maximum lifetime found increases in the order of increasing bond energy. Reaction rate constants with added solutes have also been measured, and these observations open up the possibility of studying hydrophobic solutes and extending hydrogen-isotope studies to biologically-important media.
The reduction of aryl trifluoromethyl ketones by N-carbamoylmethyl-1,4-dihydronicotinamide
Authors: Stewart Ross , Teo K. C. , Ng L. K.
Published: May 2006

The reaction of 15 aryl trifluoromethyl ketones with N-carbamoylmethyl-1,4-dihydronicotinamide has been studied in aqueous sulfolane buffer. The unsubstituted ketone and those containing electron-withdrawing groups in the ring have the following reaction characteristics: (a) a high yield of alcohol is obtained, (b) the observed reaction rate is independent of ring substituent; however, when corrections are made for degree of hydration of the ketones the rate is correlated with Hammett σ values with a rho of +1.98, (c) a secondary isotope effect of approximately 1.08 and primary isotope effects of 1.45–1.62 are observed at 43.4 °C for the reaction of the dihydronicotinamide containing one or two atoms of deuterium at C-4, (d) ΔH≠ = 15.2 kcal mol−1, and ΔS≠ = −27.0 cal deg−1 mol−1 for the unsubstituted compound, uncorrected for ketone hydration; ΔS≠ for reaction of the unhydrated ketone and dihydronicotinamide is estimated to be −45 to −50 cal deg−1 mol−1. The mechanism for the reduction is consistent with hydride transfer from reductant to oxidant, very possibly accompanied by blind-alley formation of an adduct between ketone hydrate and dihydronicotinamide. Ketones containing electron-donating groups in the ring react with the dihydronicotinamide in some undetermined way, giving little or no alcohol as product.
Merostabilization in radical ions, triplets, and biradicals. 4. Substituent effects on the half-wave reduction potentials and n,π* triplet energies of aromatic ketones
Authors: Leigh William J. , Arnold Donald R. , Humphreys Robert W. R. , Wong Po Cheong
Published: May 2006

The half-wave reduction potentials, measured by cyclic voltammetry, and n,π* triplet energies, measured by phosphorescence spectroscopy, were determined for a series of eighteen symmetrically and unsymmetrically substituted benzophenones. Attempts are made to correlate the results with Hammett substituent constants. Better correlations are observed when the data are correlated with a two-parameter function consisting of Hammett substituent constants and a set of substituent parameters describing variations in free radical stability. Significant deviations from "normal" behaviour are observed for benzophenones substituted by both electron-donating and electron-withdrawing substituents. These deviations are attributed to merostabilization of the radical-like species, and an empirical approach designed to evaluate the importance of this effect is developed. Abinitio calculations of molecular orbital energies in meta- and para-substituted benzaldehydes are used to evaluate the substituent effects on E1/2red and ETn,π* in terms of the effect on the energies of the n- and π*-orbitals.
The rearrangement of isomeric linear decyn-1-ols by reaction with the sodium salt of 1,3-diaminopropane
Authors: Macaulay Suzanne R.
Published: May 2006

Isomerization of straight chain decyn-1-ols mediated by the sodium salt of 1,3-diaminopropane was studied as a function of time, temperature, and the initial position of the triple bond. At 50 °C 9-decyn-1-ol, the thermodynamically favoured isomer, was formed rapidly regardless of the initial position of the triple bond. At lower temperatures the appearance of intermediate isomers was observed. The homopropargylic isomer was found to be remarkably stable, and under suitable conditions, conversion of 2- to 3-decyn-l-ol was carried out in 68% isolated yield.
The nephritogenic glycopeptide from rat glomerular basement membrane: synthesis of α-D-glucopyranosylamine derivatives
Authors: Takeda Tadahiro , Sugiura Yoshihiro , Ogihara Yukio , Shibata Seiichi
Published: May 2006

N-(L-β-aspartyl)-α-D-glucopyranosylamine has been prepared, as a model of a corresponding derivative possibly present in glomerular basement membrane of rats, by the condensation of α-ethyl benzyloxycarbonyl-L-aspartate with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylamine in the presence of diethylphosphorocyanidate. This was followed by hydrogenolysis, de-O-acetylation, and deethoxylation of the resulting 2,3,4,6-tetra-O-acetyl-N-(α-ethyl benzyloxycarbonyl-L-β-aspartyl)-α-D-glucopyranosylamine to remove the protecting groups. The 13C nmr spectra of the corresponding glycosylamine derivatives are analyzed and discussed.
C-Nucleoside studies. Part XI. Cine-substitution in 1,4-dinitropyrazoles; application to the synthesis of formycin via nitropyrazole derivatives
Authors: Buchanan J. Grant , Stobie Alan , Wightman Richard H.
Published: May 2006

Reaction of 1,4-dinitro-3-methylpyrazole with a variety of nucleophiles led to the formation of 5-substituted 3-methyl-4-nitropyrazoles 11–15 by a process of cine-substitution. This reaction has been applied as the key step in a novel synthesis of formycin. Treatment of 1,4-dinitro-3-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole (17) with cyanide ion produced 3(5)-cyano-4-nitro-5(3)-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole (19) in 89% yield. Catalytic reduction to the 4-amino compound 20 (84%), and subsequent reaction with formamidine acetate yielded formycin triacetate 21 (79%). Methanolysis of 21 produced formycin (1) in 90% yield.
Effects of organic solvents on immobilized enzyme catalyses. Chymotrypsin immobilized on Sephadex
Authors: Pliura Diana H. , Jones J. Bryan
Published: May 2006

The esterolytic activities of native chymotrypsin (CT) and immobilized CT-Sephadex have been studied in the presence of up to 20% of the organic solvents methanol, ethanol, 2-propanol, tert-butyl alcohol, dioxane, or DMSO. The general cosolvent-induced inhibition of the native enzyme was attenuated for immobilized CT. Most noticeably, the apparent catalytic rate constants for the CT-Sephadex-catalyzed hydrolysis of N-acetyl-L-tyrosine ethyl ester were invariant over the 2–20% dioxane concentration range surveyed. In contrast, the activity of the native enzyme in 20% dioxane was only 3% the activity recorded in the absence of cosolvent. Increasing the hydrophobic character of the protic cosolvents destabilized the native enzyme but stabilized CT-Sephadex. Both native and immobilized CT displayed remarkable stability in 20% aqueous DMSO [Formula: see text]. At least part of the DMSO-induced inhibition of native CT and CT-Sephadex was offset by increasing the apparent pH of the reaction medium. The altered kinetic patterns for CT-Sephadex are best explained by the effects of diffusional limitations on the apparent enzyme activity. The best compromise solvent for preparative applications of CT-Sephadex was found to be tert-butyl alcohol.
The chemical synthesis of oligoribonucleotides. IX. A comparison of protecting groups in the dichloridite procedure
Authors: Ogilvie Kelvin K. , Theriault Nicole Y. , Seifert Jan-Marcus , Pon Richard T. , Nemer Mona J.
Published: May 2006

A series of phosphorodichloridites bas been prepared incorporating the most commonly used phosphate protecting groups in oligonucleotide synthesis. The groups include trichloroethyl, tribromoethyl, cyanoethyl, benzyl, methyl, p-chlorophenyl, and nitrophenethyl. The trichloroethyl and the nitrophenethyl appear to be the most stable groups while the cyanoethyl and methyl offer specific advantages. The benzyl and p-chlorophenyl groups are subject to limitations on their utility. Condensations can be carried out in a range of solvents including THF, pyridine, and DMF and at temperatures from −78 °C to 20 °C with a slight drop in yield with increasing temperature, at least for dinucleotide condensations.
The conformational free energy difference for the trideuteromethyl substituent in cyclohexane
Authors: Booth Harold , Everett Jeremy Ramsey
Published: May 2006

Studies at 169 K to 194 K of the 13C nmr spectrum of cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane show that the conformational enthalpy difference −ΔH°(C2H3) is 1.82 ± 0.07 kcal mol−1 and the conformational entropy difference ΔS°(C2H3) is −0.28 ± 0.4 cal K−1 mol−1, values which do not differ significantly from the values for CH3. However, analysis of the room temperature 13C nmr spectrum of a mixture of cis-1-ethyl-4-methylcyclohexane and cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane showed that −ΔG°(C2H3) at 298 K is 11.89 ± 1.46 cal mol−1less than that for CH3, i.e. C2H3 has a slightly greater preference than CH3 for the axial orientation. The 13C nmr spectrum of a mixture of trans-1-ethyl-4-methylcyclohexane and trans-1-ethyl-[4-Me-2H3]-4-methyl-cyclohexane indicates that deuterium-induced 13C nmr isotope shifts, all upfield, occur across 1,2, 3, and 5 bonds.
A new preparative ring expansion for bicyclic ketones. Homoketonization of cyclopropoxide analogs
Authors: Hoyano Yumiko , Patel Vijay , Stothers J. B.
Published: May 2006

Homoketonization of some readily prepared cyclopropoxides affords a new synthetic method for ring expansion of the [2.2.1] and [2.2.2] ring systems.
Electrophilic additions to allenes. VI. The role of steric versus electronic effects in the reactions of arenesulphenyl halides with allenes
Authors: Garrattz Dennis G. , Beaulieu Pierre L.
Published: May 2006

The role of steric and electronic effects during the rate and product determining steps for the addition of arenesulphenyl chlorides to 1,3-disubstituted allenes has been briefly examined. Both effects appear to be generally of minimal importance during the rate determining step. The available rate data indicate the presence of little, if any, build up of positive charge on sulphur. These results are interpreted in terms of an SN2 attack on bivalent sulphur leading to an alkylidenethiiranium ion intermediate. Steric effects are of greater importance in the product determining step, particularly when the sulphenyl chlorides possess two bulky ortho substituents, as in the case of 2,4,6-triisopropylbenzenesulphenyl chloride.