bluuebunny/crossref_metadata_2025 huggingface dataset:
A 31P nmr spectroscopic study of complexation of tin(II) and lead(II) by some phosphines, phosphine oxides, and related ligands, with the 31P nuclear magnetic resonance spectra of two tetratertiary phosphine tetraoxides and the analogous tetra-sulfides and -selenides
Authors: Dean Philip A. W. , Phillips Donald D. , Polensek Lijana
Published: May 2006

31P nmr has been used to show that, in MeNO2, M(SbF6)2 (M = Sn or Pb) forms 1:1 complexes with Ph2P(CH2)2PPh2, PhP[(CH2)2PPh2]2, MeC(CH2PPh2)3, [Formula: see text][Formula: see text]P[(CH2)2PPh2]3, and Ph2P[(CH2)2PPh]2(CH2)2PPh2. The phosphonium ligands are formed in situ. Spectra characteristics of slow inter- and intramolecular exchange were obtained in all cases except, perhaps, those involving the last two ligands, which may be involved in rapid intramolecular exchange. For the first five ligands, the maximum denticity is achieved and unambiguous one-bond M(II)—31P (M = 117/119Sn or 207Pb) coupling constants are reported and discussed. In the presence of M(SbF6)2 (M = Sn or Pb). PPh3 is protonated in MeNO2, while in acetone Sn(SbF6)2 forms a 1:1 complex with PPh3 which appears to be solvent-inserted, [Sn—O—CMe2PPh3]2+.Reduced temperature 31P nmr spectroscopy has allowed the detection of 1:2 and 1:3 (M:L) complexes of OPPh3, and 1:1 complexes of Ph2P(O)(CH2)2P(O)Ph2, PhP(O)[(CH2)2P(O)Ph2]2, and (O)P[(CH2)2P(O)Ph2]3, with both tin(II) and lead(II). The 1:1 complexes with polydentate ligands are isolable; nmr shows that the maximum denticity occurs except with the last ligand which behaves in a tridentate manner. Several two-bond M—O—P coupling constants have been obtained. Also, the changes which complexation produces in the P—P couplings are compared with changes produced in the analogous phosphine complexes.The synthesis and characterization of Ph2P(E)[(CH2)2P(E)Ph]2(CH2)2P(E)Ph2 (E = S or Se) and (Se)P[(CH2)2P(Se)Ph2]3 are reported. The 31P nmr spectra of these compounds are compared with those of the parent tetraphosphines and other members of the corresponding tetraoxide–tetrachalcogenide series.
The fortuitous direct electrochemical synthesis of some copper(I) complexes
Authors: Said Farouq F. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of copper in the presence of RX (R = CH3, C6H5, C6H5CH2; X = Cl, Br, I, not all combinations) and either 2,2′-bipyridine or (C2H5)4NX gives rise to neutral or anionic copper(I) halide complexes. The current efficiency shows that CuX is produced at the anode; the subsequent solution chemistry influences the complex formation processes.
N,O- and S,O-bonded Hg(II) complexes with S-substituted amino acids: synthesis and crystal structures of bis(S-methyl-L-cysteinato)mercury(II) and bis(D,L-ethioninato)-mercury(II) diperchlorate
Authors: Book Langford , Carty Arthur J. , Chieh Chung
Published: May 2006

Complexes Hg[CH3SCH2CH(NH2)COO]2 and Hg[CH3CH2SCH2CH2CH(NH3COO]2(ClO4)2 obtained from reactions of yellow HgO with S-methyl-L-cysteine and ethionine respectively have been characterized by X-ray diffraction methods. The former is monoclinic, space group P21, with a = 13.790(4), b = 4.994(1), c = 9.898(2) Å, and β = 106.20(2)°. The R and Rw factors were 0.063 and 0.075 respectively for 980 independent reflections. The S-methyl-L-cysteine complex is N,O bonded with two Hg—N bond lengths of 2.16(3) and 2.13(3) Å and [Formula: see text]. There are eight [Formula: see text] distances within the range of 2.54–3.75 Å. The three shortest of these are distributed in an equatorial plane with respect to the N—Hg—N moiety. The Hg—O bond length of 2.54(2) Å is associated with the chelate ligand.The ethionine complex is triclinic, space group [Formula: see text] with a = 11.376(7), b = 12.009(8), c = 9.495(6) Å, α = 94.74(6), β = 108.01(5), and γ = 71.78(5)°. The R and Rw values for all 3526 reflections were 0.083 and 0.10 respectively but R became 0.058 for only observed reflections (I > 3 σ(I)). The Hg2+ is bonded to two sulfur, Hg—S = 2.436(5) and 2.537(4) Å, and two oxygen, Hg—O = 2.28(1) and 2.259(9) Å, atoms in a distorted tetrahedron. The Hg2+–carboxylate interactions are stronger in the S-bonded than the N-bonded complex probably indicating a preference for Hg–amine coordination. At low pH when the amino group is protonated, Hg–thioether coordination becomes important for S-substituted amino acids.
Nitroxide derivatives of acetylacetone as spin-labelled ligands
Authors: Plancherel D. , Eaton D. R.
Published: May 2006

Electron spin resonance spectra are reported from a number of radicals derived from 2,4-pentadione substituted at the 3 position with nitroxide-containing groups. If the substituent is t-butyl nitroxide no metal complexes are formed. This is attributed to steric factors which prevent the formation of the enol form of the β-diketone. If the substituent is trifluoromethyl nitroxide two types of metal complex have been observed. The esr spectra of the first type are very similar to that of the uncomplexed radical. Such complexes are formed with Co(III) and Al(III). The esr spectra of the second type show considerably increased 14N and 19F hyperfine coupling constants and in some cases large couplings to the metal nucleus. Complexes for the second type have been observed with Pd(II), Pt(II), and Rh(III). The possible structures of these radicals are discussed.
Synthesis of cis- and trans-platinum compounds with pyrimidine and crystal structures of trans-[Pt(pyrimidine)2X2] where X = Cl and Br
Authors: Rochon F. D. , Kong P. C. , Melanson R.
Published: May 2006

cis- and trans-[Pt(pm)2X2] where pm = pyrimidine and X = Cl, Br, have been synthesized. The cis-compounds were isolated from the reaction of K2PtCl4 and pm in water, while the trans-isomers were obtained by isomerization of cis-[Pt(pm2X2] in DMF in the presence of pm.The crystal structures of the two compounds trans-[Pt(pm)2X2] have been determined by X-ray diffraction. The two compounds (X = Br and Cl) are isostructural. The crystals belong to the monoclinic P21/c space group. The cell parameters are a = 4.787(3), b = 14.257(7), c = 8.503(3) Å and β = 99.33(4)° when X = Cl and a = 4.826(3), b = 14.822(5), c = 8.516(5) Å and β = 101.26(4)° when X = Br. The platinum atom is located on a centre of symmetry at the origin and Z = 2. The residual factors are R = 0.029 and Rw = 0.036 (X = Cl) and R = 0.036 and Rw = 0.035 (X = Br).
Crystal structures and conformations of 1-α-D-xylofuranosylcytosine and its protonated form (HCl salt)
Authors: Post Michael L. , Huber Carol P. , Birnbaum George I. , Shugar David
Published: May 2006

The structures of 1-α-D-xylofuranosylcytosine, C9H13N3O5 (1), and its hydrochloride salt, C9H13N3O5•HCl (1•HCl), have been determined by X-ray diffraction from diffractometer data, using direct method techniques. Both compounds crystallize in the orthorhombic system with Z = 4. Space group and cell parameters are, for 1: P21212, a = 18.706, b = 8.127, c = 7.007 Å; and for 1 HCl::P21212, a = 16.800, b = 8.045, c = 8.897 Å. Refinement by block-diagonal least-squares calculations gave a final R of 0.033 on 873 reflections and 0.034 on 914 reflections for 1 and 1 HCl, respectively. The glycosyl torsion angles are in the anti domain, χCN = −25.1° (1) and −28.6° (1•HC1), and the sugar puckers are nearly pure [Formula: see text] and 3E (1•HCl) forms. The C(4′)—C(5′) rotamer is trans–gauche in both cases. No intramolecular hydrogen bonding occurs in the xylofuranosyl rings. Lattice packing in the crystal structures occurs via intermolecular hydrogen bonding, with base stacking in pairs about one of the 2-fold axes for the neutral form, and with no base-stacking interactions for the protonated form. The biological implications of the structure and conformation of α-nucleosides are examined.
A total synthesis of the enantiomer of anhydromyriocin (anhydrothermozymocidin)
Authors: Payette Daniel R. , Just George
Published: May 2006

The optical antipode of anhydromyriocin, the γ-lactone derived from the antibiotic myriocin (thermozymocidin), was synthesized from L-arabinose, establishing the absolute configuration of myriocin as 47. In contrast to its natural enantiomer, it showed but little antifungal activity.
Applications of the ene reaction. Synthesis and properties of substituted α-methylene-γ-lactones
Authors: Hanson Alfred W. , McCulloch Archibald W. , McInnes A. Gavin
Published: May 2006

Substituted dimethyl 1,4-pentadiene-1,2-dicarboxylates (1 or 3) may be prepared by AlCl3-promoted or thermal ene reaction of olefins with dimethyl acetylenedicarboxylate. Lactonization of these adducts is catalyzed by acid. In the presence of 80% H2SO4 the predominant product (ca. 80%) is a (Z)-dihydro-3-carbomethoxymethylene-2(3H)-furanone (2 or 4). Cyclization with anhydrous HCl affords a mixture of products, the composition of which depends on the starting material; major products include the corresponding (E)- and δ-lactone isomers (6 and 7). Detailed 1H and 13C nmr data are reported for all compounds. The structures of the (E)-4,5,5-trimethyl-, (Z)-4,5,5-trimethyl-, and (Z)-4,4,5,5-tetramethyl furanone derivatives (6a, 2a, and 2b) have been established by X-ray crystallography. The properties of some of these lactones are discussed, as are possible methods of removal of the carbomethoxyl from 2.
The brex-5-yl system. A uniquely structured norbornyl homolog
Authors: Nickon Alex , Weglein Raymond C. , Mathew C. Thomas
Published: May 2006

The brexane skeleton functionalized at C-5 is perceived as potentially useful for various mechanistic studies. Our present objective was to prepare and characterize brex-5-yl derivatives and to seek spectroscopic evidence for geometric distortion in the skeleton. The structures synthesized include brex-4-ene, brexan-5-one, both of the epimeric brexan-5-ols, and various derivatives of these compounds. Spectroscopic data (ir, 1H nmr, and uv) are compared with those from relevant model compounds and are most simply interpreted on the basis of a twist in the brexyl skeleton. This distortion imparts more exo character to the C—H bonds at C-4 and more endo character to the C—H bonds at C-5. As an extension of the useful terms geminal and vicinal, we propose the word hominal to represent a 1,3-relationship between two groups.
Synthesis and conformations of α-aminoadipyl- and glycyl-α-aminoadipylthiazepine sulfoxides
Authors: Wolfe Saul , Bowers Raymond John , Hasan Syed Khaqan , Kazmaier Peter Michael
Published: May 2006

The title compounds, having the R-absolute configurations at sulfur, and labelled with 14C at carbons 5, 6, and 7 of the seven-membered ring, have been synthesized by condensation of isotopically labelled 3D-benzhydryloxycarbonyl-6L-amino-2,2-dimethyl-5-oxoperhydro-1,4-thiazepine with N-Boc- and α-benzhydryl-protected L-α-aminoadipic acid and glycyl-L-α-aminoadipic acid, followed by oxidation with m-chloroperoxybenzoic acid and complete deprotection with formic acid. The conformations of the sulfoxides, and related thiazepines and thiazepine sulfoxides, have been examined by 1Hmr spectroscopy. All thiazepines, and the two title sulfoxides, appear to exist in a twist boat conformation. Most other sulfoxides exist in a chair conformation, which is stabilized by an internal hydrogen bond between the sulfinyl oxygen and the amide proton at C6; when this hydrogen bond is not present, both chair and twist boat conformations may be observable. The title compounds are of interest as possible intermediates in penicillin biosynthesis from glycyl-δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (GACV) or ACV, according to a new theory, which deals, in particular, with the stereochemical course of the biosynthesis at the beta (β) carbon atom of valine.
Biosynthesis of elsinochromes C and D. Pattern of acetate incorporation determined by 13C and 2H nmr
Authors: Kurobane Itsuo , Vining Leo C. , McInnes A. Gavin , Smith Donald G. , Walter John A.
Published: May 2006

Elsinochromes C and D have been isotopically labelled by supplementing cultures of the producing fungus with sodium [1-13C]-, [2-13C]-, [1,2-13C]-, or [2-13C, 2-2H3]acetate and the distribution of isotope has been determined by 13C and 2H nuclear magnetic resonance spectroscopy. The pattern of 13C labelling is consistent with assembly of the elsinochrome carbon skeleton from two heptaketide chains with loss of the terminal carboxyl groups, and dimerization to generate the 1,2-dihydrobenzo (ghi)-perylene ring system. Elsinochrome D was converted to the more soluble triacetate to examine the fate of 2H presented to the culture as [2-13C, 2-2H3]acetate. Deuterium labelling was restricted to the C-14 and C-16 methyl groups, a result consistent with these belonging to the "starter" C2 units of polyketide intermediates. Carbon-13 enrichment data for elsinochromes labelled from [1,2-13C]acetate indicated that the polyketide chains were formed from a highly enriched precursor pool with subsequent dilution accounting for a much lower average incorporation. Presence of spin–spin coupling between linked carbons derived from separate polyketide precursors implies that dilution occurs after the dimerization step. From the combined evidence a plausible pathway for elsinochrome biosynthesis is deduced.
A relative extrusibility scale and its application to the thermal fragmentation patterns of 5-membered ring diazenes
Authors: Paine Anthony James , Warkentin John
Published: May 2006

Extrusion of a stable molecular fragment (like N2, CO2, SO2, CO, etc.) is a common chemical process. Using thermodynamic additivity concepts, group values, and heat of formation data, a Relative Extrusibility Scale (ΔHex0) has been defined for these fragmentations:[Formula: see text]Twenty-four such extrusions spanning 150 kcal mol−1 have been compiled. Typical values include N2 (−42.0), CO2 (−2.6), HCN (13.8), CO (15.4), H2CO (18.3), C2H4 (32.2), and 1CH2 (109). Among other theoretical and mechanistic applications, this list should be useful when designing synthetic routes involving extrusion reactions.In a particularly effective illustration of the usefulness of the scale, it rationalizes, for the first time, the variety of product types obtained from thermolyses of 14 different kinds of 5-membered ring diazenes. Heat of formation data on most of these compounds do not exist and they contain such sufficiently complicated functional group arrangements that most of the thermodynamic group equivalents are also unknown. This problem can be circumvented by thermodynamic cycles based on the Relative Extrusibility Scale, suitable models, and interfragment resonance corrections. Within an error framework of less than ± 5 kcal mol−1, enthalpy estimates are sufficiently accurate to give heats of reaction capable of predicting which of the potential fragmentation routes actually occur. Formation of a 3-membered ring must be exothermic by at least 30 kcal mol−1 to contribute to the products, but 3-piece fragmentation and 1,3-dipolar cycloreversion will contribute to the observed products when the process is either thermoneutral or exothermic. The unimportance of entropy is also discussed.
Kinetics and mechanism of the oxidation of cyclohexanone by a nickel(III) macrocyclic ligand complex in CH3CN
Authors: Welsh William A. , Otutakowski John , Henry Patrick M.
Published: May 2006

The oxidation of cyclohexanone by the Ni(III) complex of the macrocyclic ligand, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane(meso-[14]ane) in acetonitrile solution containing CF3CO2H obeyed the rate equation: −d[Ni(III)]/dt = k[Ni(III)][cyclohexanone]/[CF3CO2H]. Kinetic and spectral studies in the presence of CF3CO2Na indicate the inhibition term in CF3CO2H is not due to complexation of trifluoroacetate but is a real acid inhibition term. The isotope effect, kH/kD using 2,2,6,6-tetradeuterocyclohexanone as substrate, was 3.2. The main product found in greater than 100% yield based on Ni(III) was the non-oxidative product, 2(cyclohexen-1-yl)cyclohexanone, which must have been formed in a radical chain reaction. A mechanism involving deprotonation of one of the coordinated nitrogens followed by rearrangement to a Ni(II) ligand radical intermediate is proposed. The ligand radical extracts a hydrogen from cyclohexanone to give [Ni(II)meso-[14]ane] and a cyclohexanone radical which initiates a radical chain reaction to give the observed dimeric product. Support for the mechanism is provided by recent studies of the base catalyzed decomposition of Ni(III) complexes in aqueous and non-aqueous solvents.In the presence of CF3CO2Na, the Ni(III) complex decomposes rapidly even in the absence of cyclohexanone. This is believed to occur via trifiuoroacetoxy radicals, a mechanism which has analogy in other systems.
Analysis of generalized two-dimensional homonuclear nmr spectra
Authors: Bain Alex D. , Bornais Jacques , Brownstein Sydney
Published: May 2006

Analysis of the free induction decays from 90°–90° two-dimensional homonuclear pulse sequences gives complete spectral information from each transition in the f2 dimension. Theoretical intensities and frequencies are illustrated for the common cases AX, A2X, AMX, A2X2, AA′XX′, and A2X3 along with experimental examples of each. An analysis of intensities is given. From these examples it should be possible to determine chemical shift and spin-coupling values even when many lines in the f2 dimension are obscured by other spectral features.
Medium effect on acidity constants of some 2-styryl-4-phenylthiazole ethiodide derivatives
Authors: El-Kashef Hussein S. , Abdel-Hamide Refat , Mahmoud Mohamed R. , Hamed Maher M.
Published: May 2006

The pK values of some 2-styryl-4-phenylthiazole ethiodide derivatives in different organic solvent – water mixtures were determined. It is observed that as the amount of the organic solvent in the medium increases the pK of the dimethylamino derivative is decreased while that of the hydroxy derivatives is increased. It is concluded that the major important effects responsible for this behaviour are the difference in the stabilization of the base by dispersion forces in case of the amino derivative and by donor hydrogen bonds from solvent molecules in the case of the hydroxy derivatives. The effect of the molecular structure of the compound on pK is also discussed.
Spin trapping chemistry of 3,3,5,5-tetramethylpyrroline-N-oxide: an improved cyclic spin trap
Authors: Janzen Edward G. , Shetty Raghav V. , Kunanec Susan M.
Published: May 2006

The use of 3,3,5,5-tetramethylpyrroline-N-oxide as a spin trap has been investigated. Spin adducts are found to be more persistent than for 5,5-dimethylpyrroline-N-oxide (DMPO) although the esr spectra are quite similar.
N-Picrylethylenediamine – methoxide ion interactions: N-deprotonation and σ-complex formation reactions
Authors: Buncel Erwin , Hamaguchi Masashi , Norris Albert R.
Published: May 2006

The interactions of N-picrylethylenediamine as the HCl salt (PED) with methoxide ion in dimethyl sulfoxide – methanol (DMSO/MeOH) media and with 1,4-diazabicyclooctane in dimethyl sulfoxide have been investigated spectrophotometrically at 25.0 °C. Evidence is presented to show that, in solvent mixtures rich in dimethyl sulfoxide (e.g. 95/5, V/V, DMSO/MeOH), deprotonation reactions at the nitrogen centres on the ethylenediamine occur in preference to reactions in which σ-complexes are formed via addition of CH3O− to one or more ring carbon atoms. The initial 1:1 interaction of CH3O− and PED results in the rapid, reversible deprotonation of the NH centre while the 2:1 interaction is associated with rapid, reversible abstraction of H+ from the NH3+ centre. At mole ratios of CH3O− to PED > 3 a σ-complex is formed as a result of the addition of CH3O− ion to a C-3 ring carbon atom of the di-deprotonated PED. The uv–visible absorption properties of these various species are reported and compared to the properties of corresponding species formed in related systems.
Acylation du (cyclopropylméthyl)triméthylsilane. Une nouvelle voie d'accès aux énones non conjuguées
Authors: Grignon-Dubois M. , Dunoguès J. , Calas R.
Published: May 2006

Acylation of (cyclopropylmethyl)trimethylsilane using RCOCl/AlCl3 (R: saturated hydrocarbon group) constitutes a mild, convenient route to β,γ-unsaturated ketones free from the conjugated isomers. With α,β-unsaturated acyl chlorides a competitive reaction between the C—H and C—Si allylic cleavage is observed whereas chloroacetyl chloride affords the γ,δ-ethylenic corresponding ketone. A mechanism involving the catalytic role of HCl in the formation of β,γ-unsaturated and chloroketones is proposed.
Synthesis of 3′,7′-anhydrooctose nucleosides related to the ezomycins and the octosyl acids
Authors: Kim Kwan Soo , Szarek Walter A.
Published: May 2006

Several novel 3′,7′-anhydrooctose nucleosides, including a 3′,7′-anhydroocturonic acid nucleoside, namely l-(3,7-anhydro-5,6-dideoxy-β-D-allo-octofuranosyluronic acid)-3-methyluracil (40), have been synthesized. The synthetic sequence leading to 40 consists of three key steps: preparation of an octose nucleoside by a chain extension of an uridine derivative using a Wittig reaction, conversion of the octose nucleoside into a bicyclic-octose nucleoside by an intramolecular cyclization, and elaboration of a carboxylic acid function at the C-8′ position of the bicyclic-octose nucleoside. The structures of the 3′,7′-anhydrooctose nucleosides have been established by their uv, 1Hmr, 13Cmr, and mass spectral data.
Rotation optique et structure moléculaire. I. Cas des cyclitols et anhydro-1,6 sucres
Authors: Chastrette Maurice , Martin Jean-Claude
Published: May 2006

The relationships between molecular rotation and the structure of the rigid cyclitols and anhydro-1,6 sugars are studied as a function of the interactions between the carbon–oxygen bond dipoles and contributions from the ring or the hydrocarbon skeleton. The influence of long distance interactions (through 2 or 3 carbon atoms) is not negligible and a variety of parameters is suggested for each of the families of compounds studied. [Journal translation]
A125Te Mössbauer study of hexahalotellurates, pentahalotellurates, and tetrahaloaryltellurates
Authors: Dance Nigel S. , Dobud Pablo , Jones Colin H. W.
Published: May 2006

The 125Te Mössbauer spectra of a number of hexahalotellurates have been measured and no significant effects of the size or symmetry of the cation on the Mössbauer parameters were observed. The mixed hexahalotellurates, M2TeX4Y2 (X, Y = Cl, Br, or I), do not exhibit a quadrupole splitting, Δ, and the trends in δ with variation in X and Y are discussed. The pentahalotellurates MTeCl5, MTeBr5, and MTeBr4Cl also yield single line spectra and this is interpreted as evidence of intermolecular bridging. The tetrahaloaryltellurates MArTeX4 and MArTeX3Y (X, Y = Cl, Br, or I) have been studied and the trends in Δ with variation X and Y are consistent with an additive model. The trends in δ are more complex.
The iodination of azetidinone thio compounds. A convenient synthesis of 2-iodomethylpenams
Authors: Micetich Ronald G. , Fortier Robert A. , Wolfert Peter
Published: May 2006

A practical method for the synthesis of 2β-iodomethyl-2α-methylpenams is described. These compounds undergo facile isomerization to the 3β-iodo-3α-methylcephams. A preliminary kinetic study of these reactions is reported. The isomerization of the 2β-iodomethylpenams to the 3β-iodocephams can be prevented by oxidation to the sulfoxide.
Excess enthalpies of aqueous solutions of biuret at 25 °C. Interaction with urea
Authors: Barone Guido , Cacace Pasquale , Castronuovo Giuseppina , Elia Vittorio
Published: May 2006

The heats of dilution in water of biuret and the heats of mixing of biuret with urea have been determined by flow microcalorimetry at 25 °C. The excess enthalpies obtained from the experimental data can be expressed as virial expansions of the molalities.The value of the cross interaction coefficient hUB is compared to that calculated through the empirical relation hUB2 = (hUUhBB). The agreement between the two values outlines the strict analogy in the behaviour of these two solutes. The cited combining rule, verified up to now for pairs of solutes having both hii, hjj > 0, is here applied for the first time to a pair having hii, hjj < 0.
Theory of vibrational relaxation in mixtures of ortho- and para-hydrogen
Authors: Moise Avygdor , Pritchard Huw O.
Published: May 2006

A numerical study of the vibrational relaxation at 500 K of a mixture of ortho-H2 and para-H2 is described. The required state-to-state rate constants were calculated from the quantum results of Rabitz and co-workers, and missing pieces of data were estimated by interpolation.It is concluded that only one relaxation time will be observed in any mixture of ortho-H2 and para-H2 and that (except at very high dilutions in a third inert gas) the relaxation rate constant will be close to the mean of the individual rate constants for relaxation, weighted according to the respective mole fractions of ortho-H2 and para-H2 present in the mixture.We find that the relaxation process can be modelled very accurately as an electrical RC network, whose time constants can be written down quite easily as sums of the appropriate microscopic rate constants, and by using this model, it is a simple matter to explore the conditions required for a mixture of two gases to exhibit two distinct vibrational relaxation times.
Reactions of the methylmercury(II) ion with adenine and crystal structure of (adeninato-N9)methylmercury (II) monohydrate
Authors: Prizant Leonardo , Olivier Marc J. , Rivest Roland , Beauchamp André L.
Published: May 2006

Adenine (HAd) reacts with CH3HgX (X = NO3, ClO4) in basic aqueous solution to form a compound [CH3HgAd]•H2O, which crystallizes in the monoclinic space group C2/c, with a = 19.796, b = 7.119, c = 16.471 Å, β = 128.83°, and Z = 8. The CH3Hg+ group is linearly bonded to N(9) of deprotonated adenine and the molecules are held in pairs by two [Formula: see text] hydrogen bonds. With excess adenine, higher complexes of the formula [(CH3Hg)nAd]Xn−1(where n = 2, 3) are formed, in which positions N(9) (deprotonated), N(7), and N(3) are successively filled. Compounds [(CH3Hg)3(Ad-H)]X have been obtained at high pH by substitution of H(9) and an amino hydrogen, and with coordination of a third CH3Hg+ group probably to N(7). Complexation leads to significant changes in the infrared spectra and the 1750–1250 cm−1 regions are correlated with the substitution patterns. The structures are discussed in connection with the basicity of the donors in adenine and the basicity changes of the remaining donors when other atoms are already involved in coordination.
13C nuclear magnetic resonance spectra of 23-hydroxy spirostane sapogenins of Solanum hispidum
Authors: Chakravarty Ajit K. , Pakrashi Satyesh C. , Uzawa Jun
Published: May 2006

The 13C nmr spectra of some 23-hydroxy spirostane sapogenins from Solanum hispidum Pers., mostly as their acetates, have been studied. The effect of different orientations of the substituents at C-23 and C-25 as well as that due to change in the stereochemistry at C-22 have been discussed. The unexpected absence of the γg effect of the axial 23-OH on C-25 in hispigenin (5), a 22βO-spirostane derivative, presumably results from ring F deformation brought about by the steric interaction between 20-Me and 23-OH groups.
Synthesis of 3(2-haloethyl)aryltriazenes and study of their reactions in aqueous solution
Authors: Lown J. William , Singh Ranjit
Published: May 2006

Several 1-aryl-3-(2-haloethyl)triazenes have been synthesized and characterized spectroscopically as well as by their esterification of 3,5-dinitrobenzoic acid. Their rates of decomposition in aqueous media at pH7 were determined polarographically employing the electrochemically active triazene moiety. In two selected cases the rates of decomposition increase markedly with lowered pH in the range 9.3 to 4.65. The products of aqueous decomposition, both volatile and involatile, were identified and quantitated by gc and gc–ms. Discrimination between alternative decomposition pathways was possible by the preparation and use of selectively deuterated triazenes. The data are consistent with initial protonation of the triazene and generation therefrom of a 2-haloethyl cation (or its kinetic equivalent) which is subject to rearrangements detected by deuterium scrambling. A second competing pathway involves cyclization of the triazene to a 1-aryl-1,2,3-triazoline intermediate which is then subject to nucleophilic opening at two sites with attendant loss of nitrogen. The effects of structural changes in the triazenes on their modes of decomposition and generation of electrophiles should assist in the interpretation of their antitumor effects.
Charge distributions and chemical effects. XXIV. On the role of vibrational energies in determining molecular stabilities
Authors: Fliszár Sándor , Cantara J.-L.
Published: May 2006

A simple equation has been derived for calculating accurate ZPE + HT − H0 (zero-point and heat content) energies of saturated hydrocarbons from their enthalpies of formation and carbon-13 nuclear magnetic resonance spectra. Applications to conformational analysis indicate a near invariance of vibrational energies with respect to chair–boat conformational changes of the cyclohexane ring, the loss in molecular stability arising then from a weakening of the chemical binding due to a reorganization of the electronic charges. The origin of the destabilizing effect of butane gauche interactions is found, in the cyclohexane series, in a weakening of the chemical binding (∼1.85 kcal/mol) which is partially compensated by a lowering (∼0.85 kcal/mol) vibrational energy, thus offering an explanation for the loss in molecular stability of ∼1.00 kcal/mol for one gauche interaction without invoking Coulomb-type repulsions between non-bonded atoms. Calculated enthalpies of formation are presentd for a number of cycloalkanes.
A nuclear Overhauser effect difference study and a two-dimensional J proton magnetic resonance study of (6S)-prostaglandin I1
Authors: Kotovych George , Aarts Gerdy H. M. , Nakashima Tom T.
Published: May 2006

High-field nuclear Overhauser effect difference measurements allowed the assignment of the proton resonances for (6S)-prostaglandin I1 in phosphate buffer solutions. The two-dimensional J proton magnetic resonance experiments complemented these studies, as they also allowed the structure of several multiplets to be obtained when these multiplets are hidden by nearby resonances in a normal spectrum. The chemical shifts and coupling constants are compared with the data obtained previously for (6R)-prostaglandin I1.
Synthesis of N-acyl-1,3-oxathiol-2-imines
Authors: Kulka Marshall
Published: May 2006

A facile synthesis of N-acyl-1,3-oxathiol-2-imines, 7, is reported. It comprises the reaction of O-alkyl acylcarbamothioates, 4, with 2-chloroketones in the presence of alcoholic sodium alkoxide. The resulting O-alkyl-S-substituted-N-acylcarbonimidothiates, 6, undergo cyclization with elimination of alcohol, spontaneously, or upon heating in boiling toluene to form 7.
Rearrangement studies with 14C. XLV. The decomposition of cis- and trans-1,2-dianisyl-2-phenyl[2-14C]vinylphenyltriazenes in acetic acid
Authors: Lee Choi Chuck , Obafemi Craig A.
Published: May 2006

The decomposition of cis- or trans-1,2-dianisyl-2-phenyl[2-14C]vinylphenyltriazene (cis- or trans-1-NNNHPh-2-14C) in HOAc gave a 1:1 mixture of cis and trans products which showed about 3% scrambling of the label from C-2 to C-1 due to 1,2-phenyl shifts in the 1,2-dianisyl-2-phenylvinyl cation. The presence of the more nucleophilic acetate ion from the addition of different amounts of NaOAc was found to decrease or even completely suppress the extent of isotopic scrambling. Comparisons with earlier data such as those obtained from the decomposition of trianisyl[2-14C]vinylphenyltriazene (2-NNNHPh-2-14C) led to a calculated kr(An)/kr(Ph) of about 25 for the relative anisyl to phenyl migration ratio. A kOAc/kHOAc of about 1.5 × 103 for the product forming capture reactions in the 1,2-dianisyl-2-phenylvinyl cation from the decomposition of 1-NNNHPh-2-14C was also obtained.
Bridged-ring steroids. II. The synthesis of bridged steroids with a bicyclo[2.2.1]heptane ring A system
Authors: Yates Peter , Winnik Françoise M.
Published: May 2006

Bridged steroids with a bicyclo[2.2.1]heptane ring A system are formed on thermolysis of 5-vinyl 3-keto steroids. 5-Vinyl-5α-cholestan-3-one (26) on being heated at 350 °C in decalin gave 2α,5-(syn-methylmethano)-5α-cholestan-3-one (27). Similar treatment of 17β-hydroxy-5-vinyl-5β-estran-3-one (21) gave 17β-hydroxy-2β,5-(syn-methylmethano)-5β -estran-3-one (30), which was also obtained by reduction of 2β,5-(syn-methylmethano)-5β-estrane-3,17-dione (31) with sodium borohydride on alumina. Compound 31 was formed as the major product on thermolysis of 5-vinyl-5β-estrane-3,17-dione (24) at 350 °C, together with 5-(trans-propenyl)-A-nor-5β-estrane-3,17-dione (32). Compounds 27, 30, and 31 are considered to arise via intramolecular ene reactions of the Δ2-enols of compounds 26, 21, and 24, respectively. Compound 32 is postulated to be formed via an analogous reaction of the Δ3-enol of 24, followed by thermolysis of the resulting 3′-methyl-4β,5-dihydrocyclopropa[4,5]-5β-estrane-3,17-dione (36). Photolysis of 30 in methanol results in α-cleavage of the C2—C3 bond and the formation of a ketene-derived ester and two enal-derived oxetanes.
Orientations of the hydroxyl and isopropyl groups in the cis and trans conformers of 2-isopropylphenol and 2-isopropyl-6-methylphenol
Authors: Schaefer Ted , Addison Brenda M. , Sebastian Rudy , Wildman Timothy A.
Published: May 2006

Measurement of the long-range spin–spin coupling constants between methine or hydroxyl protons and the ring protons in 2-isopropylphenol shows that the trans conformer is favored by 2.5 ± 0.3 kJ/mol for a 2 mol% solution in CCl4, at 305 K. In this conformer the methine C—H bond of the isopropyl group points towards the hydroxyl group. In the cis conformer, the C—H bond points away from the hydroxyl group. In 2-isopropyl-6-methylphenol the conformation in which the O—H bond lies trans to the isopropyl group is preferred by 1.2 ± 0.3 kJ/mol in free energy at 305 K in CCl4 solution. This result agrees with an additive superposition of the conformational preferences of the hydroxyl groups in the monosubstituted phenol derivatives. Molecular orbital calculations do not agree with the existence of a cis conformer.
Methyl group inequivalence and rotational barrier heights from 1H nmr lineshapes: dimethylsulphoxide and trimethylsulphoxonium iodide
Authors: Ripmeester J. A.
Published: May 2006

The 1H nmr lineshapes obtained for a solid solution of DMSO-d3 in DMSO-d6 and for CH3(CD3)2SO+I− indicated the presence of inequivalent methyl groups in each solid. The effect of methyl group tunnelling on the lineshapes at low temperatures was used to derive barrier heights of 4.15 and 5.0 kcal/mol of a DMSO and 3.70 and 3.85 kcal/mol for CH3(CD3)2SO+I−. Using 1H nmr lineshapes, including temperature dependent effects, may well be one of the more sensitive techniques to detect inequivalent methyl groups.
Etude d'interactions moléculaires en solution par analyse de la relaxation quadripolaire du deutérium. II. Associations de l'albumine sérique de bœuf en solution aqueuse
Authors: Haverbeke Yves Van , Maquestiau André , Muller Robert , Elst Luce Vander
Published: May 2006

Deuterium longitudinal relaxation time is used for assessing the interaction between bovine serum albumin (BSA) and some drugs. The study of unenriched compounds by means of a reference equilibrium is successfully applied.The deuterium relaxation rate of pyridine versus the pH profile allows a better understanding of the nature of the interactions. Some experimental aspects are discussed.
Metal-catalyzed organic photoreactions. TiCl4-catalyzed photoreaction of 2-acetyl-1,3-dicarbonyl compounds in methanol
Authors: Saito Kimitoshi , Yuki Hidetaka , Shimada Tomoyuki , Sato Tadashi
Published: May 2006

When five- and six-membered cyclic β-dicarbonyl compounds having an acetyl group on the 2-position were irradiated in methanol in the presence of TiCl4, a coupling reaction between the acetyl carbonyl atom and the α-carbon atom of the methanol took place, giving γ-ketoaldehydes or dihydrofurans as the main product.
Configuration and conformation of alkoxyalkyl and hydroxyalkyl trifluoromethyl nitroxides. Anomeric effects and nitroxide conformations
Authors: Chatgilialoglu C. , Ingold K. U.
Published: May 2006

The epr spectral parameters for some [Formula: see text] radicals have been measured over a range of temperatures. These radicals are probably non-planar at nitrogen. Their OR groups are in the eclipsed position with respect to the N 2pz orbital, a conformational preference which is attributed to a combination of steric factors and the anomeric effect. For [Formula: see text] the H hyperfine splittings (hfs) are of unusually small magnitude. It is pointed out that all other known [Formula: see text] also have anomalously low H hfs. It is suggested that this is due to the anomeric effect which not only promotes the eclipsed conformation but also causes the OR group to bend towards the semioccupied orbital, thereby moving H and R2 towards the nodal plane of this orbital.
The role of the supporting electrolyte cation in the kinetics of outer-sphere electrochemical redox processes involving metal complexes
Authors: Weaver Michael J. , Liu H. Y. , Kim Yongjoo
Published: May 2006

The electroreduction rates of Cr(OH2)63+ and Cr(NH3)63+ at the mercury–aqueous interface were monitored as a function of electrode potential in electrolytes containing univalent, divalent, or trivalent cations with systematically varying atomic number in order to scrutinize the role of the supporting electrolyte cation in the kinetics of these simple one-electron outer-sphere electrode reactions. The comparison between the corresponding rate responses for Cr(OH2)63+ and Cr(NH3)63+ reduction brought about by changing the supporting electrolyte cation is expected to provide information on the influence of the cation upon the potential profile in the double layer; despite the close structural and mechanistic similarity of the reactants, the transition state for the latter reaction appears to lie significantly closer to the electrode than that for the former process. The virtues of comparing rate responses at a constant electrode charge density rather than at a constant electrode potential are pointed out. It was found that the variations in the effective average potential at constant charge [Formula: see text]ding changes in the electrode potential [Formula: see text] derived from thermodynamic double-layer measurements. These results, along with the observed variations in the transfer coefficients for the two reactions, are semiquantitatively consistent with a model involving changes in the position of the oHp as the supporting electrolyte cation is altered, but are inconsistent with a model attributing the rate variations to cation specific adsorption.
Tensiometric studies on wetting. I. Some effects of surface roughness (theoretical)
Authors: Bayramli Erdal , van de Ven Theodore G. M. , Mason Stanley G.
Published: May 2006

The effect of roughness on the wettability of an axisymmetric cylinder is investigated theoretically by making use of equilibrium meniscus shapes on solid surfaces analogously to previous studies for drops on horizontal surfaces. Employing circumferential sinusoidal and saw-toothed grooved structure, and using mechanistic arguments, one can explain wetting hysteresis, the formation of composite surfaces, and the presence of non-equilibrium jumps during contact line motion.On unidirectionally random surfaces the maximum surface slopes mainly determine the value of the advancing, and the minimum slopes of the receding contact angle. These effects of surface slopes diminish with decreasing roughness size. Diminishing roughness size also gives rise to numerous small non-equilibrium jumps imposed upon larger jumps during wetting. The contact angle hysteresis is found to show a nearly linear relationship with the spread in the distribution of solid surface slopes.
Ionic solution near an uncharged surface with image forces
Authors: Croxton T. , McQuarrie D. A. , Patey G. N. , Torrie G. M. , Valleau J. P.
Published: May 2006

We studied the ion density in a dilute electrolyte solution which is next to an uncharged surface at which there is a discontinuity in the dielectric constant. In particular, we treated the restricted primitive model of a 1–1 aqueous solution next to a pure phase of unit dielectric constant. This served as a primitive model of the interface between an electrolytic solution and the air. Monte Carlo data are presented: the image forces are included and treated exactly. The model was also treated using the Born–Green–Yvon (BGY) integral equation approach; a modification of BGY theory which ensures electroneutrality is in very good agreement with the Monte Carlo data. The use of a "screened self-image" approximation to the potential energy has been tested using Monte Carlo computation and is found to be inadequate for the present model. Hypernetted-chain equation results using this approximation are also reported.
The surface phase at the ideal polarized mercury electrode. IV. Determination of molar entropies of adsorption of specifically adsorbed halide ions
Authors: Charles M. H. , Mulenga M. , Jenard A. , Hurwitz H. D.
Published: May 2006

Differential capacitances are measured as a function of temperature at the ideal polarized Hg electrode in systems of mixed sodium halides at ionic strength J = 10−1 mol kg−1. A quasi-thermodynamic treatment is presented according to which excess entropies of adsorption in the inner layer are determined. The formation entropy of the inner layer and the water and ion molar entropies of adsorption are presented for a range of moderate and small ionic surface coverages.
Studies on the products resulting from the conversion of aspen poplar to an oil
Authors: Eager Richard L. , Mathews Joseph F. , Pepper James M. , Zohdi Hussein
Published: May 2006

Some observations are made on the nature of the reactions involved in the conversion of aspen poplar into a variety of chemical products as a result of its interaction with carbon monoxide and water in the presence of sodium carbonate at elevated temperatures and pressures. The original carbon content of the wood is distributed between an oil phase, a complex mixture of highly oxygenated water-soluble products many of which have been identified as low molecular weight aliphatic alcohols, ketones, and acids, and a gaseous phase consisting of mainly hydrogen and carbon dioxide. Using model substances (cellulose, cellobiose, D-glucose, D-fructose, D-xylose, D-sorbitol, glycerol, and an isolated lignin) information was obtained on the origin of the oil and of the water-soluble products. Studies at temperatures from 160° to 360 °C revealed a marked exothermic reaction occurring in the 200–240 °C range for wood and cellulose and which was reflected in the nature of the resulting product. With increasing temperature there is an increase in the yields of the water-soluble derivatives and also a change in their relative abundance.
Diastéréosélectivité de la réduction des alkyl-2 alkylidène-3 cyclopropyl alkyl cétones. Addition de RLi sur les aldéhydes α-cyclopropylidéniques
Authors: Audo Dominique , Vincens Maurice , Dumont Claude , Vidal Michel
Published: May 2006

The addition of RLi on trans 2-alkyl-3-methylene cyclopropane carboxaldehydes is not diastereoselective, while the reduction of trans (2-alkyl-3-alkylidene cyclopropyl) alkyl ketones shows for some compounds a high diastereoselectivity which may reach stereospecificity at low temperatures. This selectivity depends not only on the degree of substitution of the group fixed on the carbonyl but on the radical fixed in position 2 on the ring even though it shows a trans relation with the functional group.The relative configurations of secondary α-cyclopropylidene alcohols are determined from their ir and nmr data.
Complexes of methylmercury(II) with 1-methylcytosine and crystal structure of μ-(1-methylcytosinato-N3,N4)bis(methylmercury(II)) nitrate
Authors: Prizant Leonardo , Rivest Roland , Beauchamp André L.
Published: May 2006

Two types of solid complexes are isolated by reaction of CH3HgX (X = NO3 and ClO4) with 1-methylcytosine (MCy). The CH3Hg+ ion is probably bonded to N(3) in the [CH3Hg(MCy)]X compounds. Mercury binding to N(3) and the deprotonated amino group in [(CH3Hg)2(MCy—H)]X is confirmed by X-ray work on the nitrate salt. The crystals are orthorhombic, space group Pbca, with a = 12.014, b = 13.573, c = 16.353 Å, and Z = 8. The structure was refined on 962 independent reflections to an R factor of 0.038. The CH3Hg+ groups are arranged in a syn configuration and the angles around the mercury-bonded nitrogen atoms are severely distorted to prevent short Hg … Hg contacts. N(3)-coordination in the 1:1 complexes introduces minor changes in the infrared spectra, but the substitution of an amino proton in the 1:2 compounds produces important modifications. 1H nmr data in DMSO-d6 are reported for both types of compounds. This work emphasizes the important acidity enhancement experienced by the amino protons upon initial coordination to N(3), which facilitates further reaction of CH3Hg+ by proton displacement even in acidic media.
Capsidiol and 1-epicapsidiol: absolute configuration, nmr, and optical spectra of the dibenzoates
Authors: Stillman M. J. , Stothers J. B. , Stoess A.
Published: May 2006

Application of the exciton chirality method has confirmed that capsidiol, a unique eremophilane, has the absolute stereochemistry depicted in 1. The 1H and 13Cmr, circular dichroism, and magnetic circular dichroism spectra of capsidiol and 1-epicapsidiol dibenzoates are discussed.
Crystal and molecular structures of three transition metal complexes incorporating the anionic tridentate chelating ligands [Me2Ga(N2C5H7)OCH2CH2SR]− where R = Et or Ph
Authors: Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

X-ray crystallographic studies of three transition metal complexes incorporating the novel anionic tridentate chelating ligand [Me2Ga(N2C5H7)OCH2CH2SR]− (R = Et or Ph) show that the ligand is facially coordinated in each case. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thioethoxyethoxy)gallato(N(2), O,S)]nitrosylnickel(I) are monoclinic, a = 8.8313(4), b = 7.2402(2), c = 26.539(1) Å, β = 94.390(3)°, Z = 4, space group P21/c, R = 0.040 and Rw = 0.050 for 2489 reflections. The Ni atom is in a distorted tetrahedral environment with bond angles about Ni ranging from 87.90(7) to 127.9(1)°. The nitrosyl coordination is slightly non-linear with Ni—N—O = 170.1(4)°. Important bond lengths (corrected for libration) are: Ni—S, 2.326(1), Ni—O, 2.019(2), Ni—N(pyrazolyl), 1.980(3), Ni—N(O), 1.633(3) and N—O, 1.156(4) Å. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thiophenoxyethoxy)gallato(N(2),O,S)]tricarbonylmanganese(I) are triclinic, a = 9.4911(5), b = 10.4323(6), c = 11.7618(7) Å, α = 86.17(1), β = 69.547(5), γ = 81.402(4)°, Z = 2, space group [Formula: see text]R = 0.029 and Rw = 0.035 for 2496 reflections. The Mn atom is coordinated to the fac-tridentate gallate ligand and to three carbonyl ligands resulting in a slightly distorted octahedral geometry. Important corrected bond lengths are: Mn—S, 2.397(1), Mn—O, 2.055(2), Mn—N, 2.082(3), and Mn—C, 1.794(4), 1.807(4), and 1.807(4) Å. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thioethoxyethoxy)gallato(N(2),O,S)](η3-cycloheptatrienyl)dicarbonylmolybdenum are monoclinic, a = 17.030(3), b = 19.097(2), c = 15.908(3) Å, β = 115.99(1)°, Z = 8, space group P21/n R =0.036 and Rw = 0.043 for 4477 reflections. The two crystallographically independent molecules differ primarily in the orientation of the S-ethyl moiety and each contains an η3-C7H7 ligand which occupies one coordination site of a distorted octahedron as a %-donating ligand. Important corrected bond distances are: Mo—S, 2.527(2) and 2.541(2), Mo—O, 2.241(5) and 2.237(4), Mo—N, 2.277(5) and 2.254(5), Mo—C(O), 1.940(7)–1.960(7), and Mo—C(C7H7), 2.198(6)−2.391(7) Å.