bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic and electrochemical studies on linkage isomerism in iron(II) complexes of benzotriazole, a corrosion inhibitor
Authors: Toma Henrique E. , Giesbrecht Ernesto , Espinoza Rojas Ramón L.
Published: May 2006

Benzotriazole reacts with the aquapentacyanoferrate(II) complex, at pH 4.5, producing a mixture of N-coordinated isomers. Characterization based on 1H and 13C nmr spectroscopy yielded an equilibrium constant K = 1.9 ± 0.3, favoring the less symmetric N1-isomer. Two reversible peaks of oxidation, corresponding to the N1 and N2 isomers, were observed in the cyclic voltammograms at high scan rates, with E1/2 = 0.43 and 0.53 V versus NHE, respectively. The cyclic voltammograms at intermediate scan rates were successfully analysed in terms of an isomerization reaction preceding reversible charge-transfer. The kinetic constants of isomerization, kf and kb, were 1.5 and 0.65 s−1, respectively. The limiting dissociative rates, k−L = 5.3 × 10−3 s−1, measured in the presence of dimethyl sulfoxide, support an intramolecular mechanism for the isomerization reaction.
Evans holes in the infrared spectra of some transition metal formate dihydrates
Authors: Tewari G. D. , Khandelwal D. P. , Bist H. D. , Tayal V. P.
Published: May 2006

Evans holes have been identified in OH(OD) stretching regions in the ir spectra of M(HCOO)2•2X2O (M = Mn, Co, Ni and Zn; X = H, D) and attributed to Fermi interaction between the stretching mode and an overtone of the bending mode of water.
The crystal and molecular structure of di-μ-phenylthiolatobis[trichloro(dimethyl sulfide) tungsten(IV) (W—W)]
Authors: Boorman P. Michael , Ball Joanne M. , Moynihan Kelly J. , Patel Vikram D. , Richardson John F.
Published: May 2006

The complex (Me2S)Cl3W(μ-SPh)2WCl3(SMe2), 1, has been isolated as one product of the 1:1 reaction between WCl4(Me2S)2 and SiMe3(SPh) in CH2Cl2 solution. A single crystal X-ray diffraction study shows that the molecule has the relatively unusual edge-shared bioctahedral structure, with a W—W bond length of 2.759(1) Å. The dimethyl sulfide ligands occupy positions trans to one another in the equatorial mean plane of the molecule, which has two-fold symmetry imposed on it. The structure was solved by the heavy atom method and refined to R = 0.044 and Rw = 0.058 for 2001 reflections. Crystals of 1 are monoclinic, space group C2/c, with a = 17.445(4), b = 12.594(2), c = 11.509(3) Å, β = 91.22(1)°, and Z = 4.
The synthesis of Nauclea indole-pyridine alkaloids. 3,4-Disubstituted and 3,4,5-trisubstituted pyridines as synthetic intermediates; a total synthesis of (±)-decarbomethoxy-3α- and -3β-nauclechine
Authors: Shariff Azim , McLean Stewart
Published: May 2006

Synthetic routes to a number of 3,4-disubstituted and 3,4,5-trisubstituted pyridines have been explored. These pyridines, designed to be used in the synthesis of Nauclea indole-pyridine alkaloids, are potentially useful intermediates in a number of syntheses. Particular attention has been paid to more highly substituted derivatives of 4-pyridineacetic acid, and the experimental limitations associated with their synthesis and use in subsequent reactions such as the Bischler–Napieralski cyclization have been described and explained. A synthesis of decarbomethoxynauclechine from 4-methylnicotinaldehyde avoiding these difficulties was then designed and executed. Both diastereoisomers, (±)-decarbomethoxy-3α-nauclechine and (±)-decarbomethoxy-3β-nauclechine, were obtained; the structure and stereochemistry of each was rigorously established, but it was not possible to demonstrate which corresponded to the natural alkaloid, decarbomethoxynauclechine, reported previously.
The intramolecular equilibrium in 2-tert-butylphenol and some derivatives. An anomalous indicating steric distortion
Authors: Schaefer Ted , Sebastian Rudy , Salman Salman R.
Published: May 2006

The 1H nmr spectral parameters in dilute carbon tetrachloride solution are reported for 2-tert-butylphenol, as obtained by decoupling of the sidechain protons. Long-range couplings between hydroxyl and ring protons are also reported for five derivatives of 2-tert-butylphenol. In the cis conformer of 2-tert-butylphenol an anomalous [Formula: see text] occurs, most likely as a consequence of a significant distortion of the COH geometry. Such an anomaly, which leads to an incorrect estimate of the cis–trans equilibrium constant, does not occur in other alkyl phenols, for example, in 2-tert-butyl-6-methylphenol. The coupling constant data provide no evidence for out-of-plane conformational preferences of the hydroxyl group in these compounds.
Synthesis of selectively modified cellulose derivatives via reductive amination of 2-oxy- and 3-oxy-cellulose intermediates
Authors: Yalpani Manssur , Hall Laurance D. , Defaye Jacques , Gadelle Andrée
Published: May 2006

Diamagnetic and paramagnetic amine derivatives of cellulose have been prepared from selectively oxidized cellulose precursors via the reductive amination method using sodium cyanoborohydride. 4-Amino-2,2,6,6-tetramethylpiperidine-1-oxyl was employed in the syntheses of nitroxide spin labelled cellulose derivatives 4 and 5 from 3-oxy-cellulose (1) and 6-O-triphenylmethyl-2-oxy-cellulose (2). Conversion of the linear polymer 1 into a highly branched, water soluble 3-deoxy-cellulose derivative 6 was accomplished by attachment of glucosamine side chains. 3-Amino-3-deoxy-cellulose 7 was obtained using ammonium acetate. A novel type of organometallic cellulose conjugate 8 was prepared by condensation of 2 and p-toluidine chromium tricarbonyl. Similarly, 1,10-diazo-18-crown-6 was added to 2 to form the crown ether derivative 9. The synthetic strategies involving either 6-O protected or unprotected oxy-cellulose intermediates are compared in terms of reaction yields and product properties.
Synthetic cardenolides and related products. IV. D-homo derivatives
Authors: Ferland J. M. , Lefebvre Y.
Published: May 2006

The synthesis of novel structures related to naturally occurring cardiotonic agents such as resibufogenin is described. These products retain the essential features of aglycones needed for biological activity. They are, however, thermodynamically stable and easily available from smilagenin. The methods of preparation, together with the proof of structures and configuration, are reported.
Dipole oscillator strength distributions and properties for methanol, ethanol, and n-propanol
Authors: Jhanwar B. L. , Meath William J.
Published: May 2006

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state methanol, ethanol, and n-propanol and used to evaluate integrated ("band") oscillator strengths and the dipole oscillator strength sums Sk and Lk (for a variety of k values) for these molecules. Each DOSD is constructed by using available experimental and theoretical photoabsorption cross sections and by constraining the resulting dipole oscillator strength data to satisfy the Thomas–Reiche–Kuhn sum rule and molar refractivity constraints. The discussion includes an analysis of the reliability of the results.
Hétérocycles à fonction quinone. V. Réaction anormale de la butanedione avec la diamino-1,2 anthraquinone; structure cristalline de la naphto [2,3-f] quinoxalinedione-7,12 obtenue
Authors: Baron Michel , Giorgi-Renault Sylviane , Renault Jean , Mailliet Patrick , Carré Daniel , Etienne Jean
Published: May 2006

Butanedione reacts on heating with 1,2-diaminoanthraquinone to give, not the expected 2,3-dimethyl-naphtho[2,3-f]quinoxaline-7,12-dione 3, but 2-(2-hydroxy-2-methyl-3-oxobutyl)-3-methylnaphtho[2,3-f]quinoxaline-7,12-dione 4a whose structure was established by X-ray diffraction. This compound crystallizes in the triclinic [Formula: see text] space group with unit cell dimensions of a = 9.091 (1), b = 16.966 (4), c = 12.375 (3) Å; α = 100.75 (2), β = 101.83 (2), γ = 100.29 (2)°, V = 1789 Å3, Z = 4. The structure was resolved by the direct method and refined to R = 0.039 for 3027 independent reflections. The overall conformation of the molecule is essentially planar. The principal characteristic is the presence of two cyclic arrangements caused by intramolecular hydrogen bonding. 2,3-Dimethylnaphtho[2,3-f]quinoxaline-7,12-dione is the intermediate in this reaction.
A 31P and 199Hg nuclear magnetic resonance and vibrational spectroscopic study of triarylphosphine complexes of HgCl2
Authors: Allman Tim , Goel Ram G.
Published: May 2006

Complexes of the type [HgCl2P(4-XC6H4)3]2 and HgCl2(P(4-XC6H4)3)2 (X = Me2N, MeO, Me, H, F, Cl) have been prepared. The tertiary phosphines have similar steric requirements but vary greatly in their basicities. The vibrational spectra of the complexes were measured and each complex was found to have the expected bridging dimeric (1:1) or pseudotetrahedral monomeric (1:2 Hg/P) structure. Their 31P and 199Hg nmr parameters were investigated and it was found that 1J(Hg—P) increases with increasing phosphine basicity, decreasing temperature, and decreasing sample concentration in dichloromethane solution. It is concluded that changes in the hybridisation on the P and Hg atoms may be largely responsible for the increases of 1J(Hg—P) with increasing phosphine basicity.
L-Glucose. A convenient synthesis from D-glucose
Authors: Szarek Walter A. , Hay George W. , Vyas Dolatrai M. , Ison Edward R. , Hronowski Lucjan J. J.
Published: May 2006

L-Glucose has been synthesized from D-glucose by a convenient method involving methyl 2,3-O-isopropylidene-β-D-gulo-furanosiduronic acid (6) as a key intermediate. Compound 6 was converted into L-glucono-1,5-lactone (8), which, by a selective reduction, afforded L-glucose (9).
Kinetics and isotope effects of the proton transfer reactions between 1-(4-nitrophenyl)-1-nitroethane to phenyltetramethylguanidine in dipolar aprotic solvents
Authors: Jarczewski Arnold , Pruszynski Przemyslaw , Kazi Mohammed , Leffek Kenneth T.
Published: May 2006

The carbon acid 1-(4-nitrophenyl)-1-nitroethane reacts with phenyltetramethylguanidine in the aprotic solvents acetonitrile, benzonitrile, and chlorobenzene in a bimolecular proton transfer reaction. The primary isotope effects, kH/kD, for these reactions at 25 °C are 8.5 ± 0.4, 6.1 ± 0.4, and 16 in acetonitrile, benzonitrile, and chlorobenzene respectively. The magnitude of the isotope effects on the enthalpy of activation [Formula: see text] are 2.3 ± 0.2, 1.6 ± 0.7, and 4.2 ± 0.6 kcal mol−1, which indicates a contribution from proton tunnelling to the reaction rate of the normal substrate.
The conformational properties of the gangliosides GM2 and GM1 based on 1H and,13C nuclear magnetic resonance studies
Authors: Sabesan Subramaniam , Bock Klaus , Lemieux Raymond U.
Published: May 2006

A comparison of the 1H and 13C nmr parameters for the disaccharide derivatives βDGal(1→ 4)βDGlcO(CH2)8COOCH3 (1), βDGalNAc(1 → 4)βDGalO(CH2)8COOCH3 (2), and βDGal(1 → 3)βDGalNAcO(CH2)2CH3 (3) allowed assignments of the signals observed for the asialo-GM2- and asialo-GM1-related synthetic haptens, βDGalNAc(1 → 4)βDGal(1→4)βDGlcO(CH2)8COOCH3 (4) and βDGal(1 → 3)βDGalNAc(1 → 4)βDGal(1 → 4)βDGlcO(CH2)8COOCH3 (5). 1H nuclear Overhauser enhancement studies confirmed the conformational preferences for 2 and 3 predicted by HSEA calculation. Comparison of the 1H and 13C spectra indicate that these preferences and that previously known for the lactoside (1) are closely maintained in the haptens 4 and 5. HSEA calculation indicates that the methyl group of methyl N-acetyl-α-D-neuraminic acid (10) prefers the orientation wherein the carboxyl group is near anti-periplanar to the methyl group. However, this orientation was not confirmed by saturation of the methyl group since no enhancement of either Ha-3 or He-3 was observed. On the other hand, saturation of Ha-3c of the αDNeuAc unit of the GM1-related pentasaccharide, βDGal(1 → 3)βDGalNAc(1 → 4)[αDNeuAc(2 → 3)]βDGal(1→4)α,βDGlc, caused strong enhancement of the signal for the aglyconic hydrogen, H-3bof the βDGal(1→4) unit. This observation, along with those of other nuclear Overhauser experiments, established that this pentasaccharide has the carboxyl group anti-periplanar to C-3b. Furthermore, the C-7c to C-9c chain of the αDNeuAc unit adopts nearly the same conformation for the compound in aqueous solution as exists for N-acetylneuraminic acid in the crystalline state. The HSEA calculation indicates important attractive interaction between this chain and the βDGalNAc unit of the aglycon. These conlcusions were extended to the GM2 and GM1 gangliosides by the comparison of chemical shift data. In these compounds, the carboxyl group projects over the hydrophobic α-side of the βDGalNAc unit and the polar OH-4c, NAc-5c, OH-7c groups project over the hydrophobic β-side of the lactose unit. Comments are made on the possible bearing of these topographical features on certain biological properties of gangliosides.
Oxidation of hydrocarbons. 12. Kinetics and mechanism of the oxidation of trans-cinnamic acid by ruthenate and perruthenate ions
Authors: Lee Donald G. , Helliwell Stuart
Published: May 2006

Recent theoretical calculations by Rappé and Goddard have pointed to the importance of spectator oxo groups in stabilizing intermediates produced during the reduction of high-valent transition metal oxides; intermediates which contain triply-bonded metal oxo groups are predicted to be unusually stable. In an attempt to test these conclusions experimentally, the rates of oxidation of cinnamate ion by ruthenate and perruthenate ions have been studied. Since the most likely intermediate formed from perruthenate ion (but not ruthenate ion) would contain a stabilizing, triply-bonded spectator oxo group, it would be expected to react faster if the calculations are correct. In agreement with these predictions, it was found that the activation energy (ΔG‡) for the ruthenate reaction was about 7 kcal/mol higher than for the corresponding perruthenate reaction.
The reaction of methyl radicals with neopentane in flow photolysis at 607–823 K
Authors: Furue Hiroshi , Manthorne Kim C. , Pacey Philip D.
Published: May 2006

Acetone was photolyzed in the presence of a large excess of neopentane in a flow system at total pressures between 7 and 150 Torr and at 607–823 K. For reactions[Formula: see text]and[Formula: see text]the quotient of rate coefficients, k12/k2, was calculated from CH4 and C2H6 yields and was extrapolated to the high pressure limit, k12/k2,x. Taking k2,x as 2.2 × 1010 L mol−1 s1, Arrhenius parameters for reaction [1] were found to be: log10A (L mol−1 s−1) = 10.0 ± 0.1, EA = 62( ± 2) kJ mol−1. In combination with data from the literature for the temperature range 365–953 K, the Arrhenius plot for k1/k2,x1/2 was strongly curved, with a heat capacity of activation of 71 ± 4 J K−1 mol−1.
The synthesis of derivatives of lactosamine and cellobiosamine to serve as probes in studies of the combining site of the monoclonal anti-I Ma antibody
Authors: Wong Ting C. , Lemieux Raymond U.
Published: May 2006

Syntheses are reported for a variety of structures used in a continuation of our studies of the combining site of the monoclonal anti-I Ma antibody. These structures include the N-acetyl, N-formyl, and N-pivalyl derivatives of methyl β-D-lactosaminide, the ethyl, propyl, isopropyl, and isobutyl β-glycosides of N-acetyllactosamine and the βDGal(1 → 4)βDGlcNAc(1 → 6)-, βDGal(1 → 4)βDGlcNH2(1 → 6)-, βDGal(1 → 4) βDGlcNCOCF3(1 → 6)-, and βDGlc(1 → 4)βDGlcNAc(1 → 6)-derivatives of 1,2;3,4-di-O-isopropylidene-α-D-galactopyranose. Also, preparations of 6-deoxy-βDGal(1 → 4)βDGlcNAc(1 → 6)α,βDGal and βDGlcNAc(1 → 6)βDGal(1 → 4) βDGlcNAcOCH3 are described.
Surface photochemistry: the effect of surface modification on the photophysics of naphthalene and pyrene adsorbed on silica gel
Authors: Bauer Richard K. , de Mayo Paul , Natarajan Lalgudi V. , Ware William R.
Published: May 2006

The influence of heat treatment and of added coadsorbates on the surface photophysics of pyrene and naphthalene adsorbed on silica gel is reported. When the silica gel surface is partially dehydroxylated, the distribution of pyrene or naphthalene is inhomogeneous, as indicated by multiexponential fluorescence decay and broad emission spectra. Addition of polar coadsorbates renders the surface more homogeneous with singlet lifetimes approaching solution values. The pretreatment and addition of coadsorbates, in the case of pyrene, also influence the relative importance of dynamic excimer formation vis-a-vis ground state association.
Interactions de l'ion Ag+ avec la glutarimide
Authors: Perron Johanne , Beauchamp André L.
Published: May 2006

The 1:1 complex formed between Ag+ ions and glutarimide was investigated by X-ray diffraction, infrared spectroscopy, and 1H and 13C nmr. The crystals are monoclinic, C2/c, a = 13.497(3) Å, b = 9.503(2) Å, c = 9.600(4) Å, β = 92.30(3)°, Z = 4 molecules per cell. The structure was refined on 1086 nonzero [Formula: see text] reflections to R = 0.027. One half of the Ag atoms are linearly coordinated to the N atoms of two deprotonated glutarimide ligands, whereas the other half are surrounded by an approximate tetrahedron of four carbonyl oxygens belonging to two adjacent [Glu–Ag–Glu]− units. The [Glu–Ag–Glu]− groups are joined by tetrahedrally coordinated Ag atoms into infinite chains along the c axis. Complexation introduces a number of changes in the infrared spectrum of glutarimide. They can be related to the disappearance of the N—H vibrator and the change of bond orders in the —C(O)—N—C(O)— portion of the ligand. The nmr spectra show that coordinated glutarimide retains a mirror plane when the Ag complex is dissolved in DMSO. This suggests that the O-bonded Ag atoms dissociate to a large extent in solution, leaving the linear [Glu–Ag–Glu]− ions as the major glutarimide complex species.
Synthetic approaches to β-lactam antibiotics: a stereocontrolled synthesis of trans 3-(S)-amino-4-(S)-ethyl-2-oxo-1-azetidine
Authors: Hanessian Stephen , Sahoo Soumya P.
Published: May 2006

A synthesis of the title compound, an immediate precursor of the biologically active 4-ethyl monobactam, from 2-amino-2-deoxy-D-glucose is described. The strategy allows for the synthesis of a variety of β-substituted α-amino acids, which are otherwise difficultly accessible.
The ultraviolet absorption spectrum of oxalic acid vapor
Authors: Back R. A.
Published: May 2006

The ultraviolet absorption spectrum of oxalic acid vapor has been studied for the first time. Low-resolution spectra show a moderately weak (εmax = 25 M−1 cm−1 at 277 nm) banded absorption system beginning at about 310 nm and extending to 250 nm where a stronger absorption begins. Medium-resolution spectra show a complex vibrational fine-structure at wavelengths above about 287 nm, with many sharp line-like R-branch heads, each corresponding to a different vibrational transition. A vibrational analysis was completed for 12C2O4H2, 12C2O4D2, and 13C2O4H2, and electronic origins were estimated to be at 31903.2, 31970.2, and 31949.4 cm−1, respectively (about 313 nm). Strong features were assigned to progressions in [Formula: see text] the C=O and C—O stretching vibrations, with prominent sequences in ν10, the C—C torsional vibration, running to the blue, implying that [Formula: see text].This absorption system has been assigned to the first excited singlet state, designated Ã, corresponding to a π* ← n+, 1Au ← 1Ag transition of planar trans-oxalic acid. High-resolution spectra of several bands show rotational fine-structure, and a partial analysis was carried out on the [Formula: see text], and [Formula: see text] bands of 12C2O4H2, based on apparently-simple diverging P-branches.
The retroaldol reaction of cinnamaldehyde
Authors: Guthrie J. Peter , Cooper Kevin J. , Cossar John , Dawson Brian A. , Taylor Kathleen F.
Published: May 2006

Rate and equilibrium constants have been measured for the hydration and retroaldol reactions of cinnamaldehyde. The equilibrium constant for the 1,4-addition of water to cinnamaldehyde is 4.42 × 10−3. The rate constants for hydroxide catalyzed reaction, extrapolated to zero hydroxide concentration (to correct for the addition of hydroxide to the aldol carbonyl), are: [Formula: see text];[Formula: see text]; and [Formula: see text]. The rate of the formation reaction was measured by adding small amounts of acetaldehyde to alkaline solutions of benzaldehyde: [Formula: see text] and Koverall = 1480 M−1. The course of the synthetically useful reaction of acetaldehyde with benzaldehyde is discussed in the light of these results.
ipso Nitration. XXIV. Nitration of 2-methylphenols. Formation and rearrangement of 6-methyl-6-nitrocyclohexa-2,4-dienones
Authors: Cross Gordon G. , Fischer Alfred , Henderson George N. , Smyth Trevor A.
Published: May 2006

Nitration of o-cresol and some mono-, di-, and trimethyl derivatives in acetic anhydride at −60 °C gives 6-methyl-6-nitrocyclohexa-2,4-dienones. The dienones are more labile than the isomeric 4-methyl-4-nitrocyclohexa-2,5-dienones and, if the 2-position of the dienone is not blocked, undergo regiospecific rearrangement to 6-nitro-o-cresols. 2,3,6-Trimethyl- and 2,3,5,6-tetramethylphenol also give a 2,5-dienone with nitro attached to a secondary carbon.
Skeletal isomerization of cyclohexene on Al2O3 and AlPO4–Al2O3 catalysts
Authors: Campelo J. M. , Garcia A. , Gutierrez J. M. , Luna D. , Marinas J. M.
Published: May 2006

Cyclohexene skeletal isomerization, in a microcatalytic pulse reactor, was investigated using Al2O3 and AlPO4–Al2O3 as catalysts. Apparent rate constants and apparent activation energies were calculated according to the kinetic model of Bassett–Habgood. Selectivity studies concluded that 1-MCP and 3-MCP were competitive products with a first-order kinetics. The rate constants as well as the selectivity at 1-MCP increase with an increase in the number and strength of stronger acid sites, measured by means of the irreversible adsorption of aniline in cyclohexane, at 298 K, using a spectrophotometric method. The parallel reaction pathway, proposed for AlPO4 catalysts, agrees with both the observed rates and selectivities using Al2O3 and AlPO4–Al2O3 catalysts.
Infrared absorption and resonance Raman scattering of photochromic triphenylformazans
Authors: Langbein Hubert , Grummt Ulrich-Walter
Published: May 2006

not available
Determination of CNDO/2 dipole moment derivatives from interpolating polynomials
Authors: Tarr Allan William , Henry Bryan Roger
Published: May 2006

A numerical differentiation technique is presented from which dipole moment derivatives are estimated from sets of CNDO/2 calculated dipole moment values. The dipole moment values are evaluated over a range of molecular geometries, which are obtained by distorting the molecule along CH-stretching local coordinates. The technique effectively fits the dipole moment values to an interpolating polynomial, but the utilization of difference tables and lozenge diagrams makes the explicit determination of the polynomial unnecessary.First, second, and third order pure derivatives, and second order mixed derivatives, are estimated for methane and ethane. Several testing procedures for the numerical technique are discussed. On this basis, the accuracy of these derivatives is judged to be very good.
Diterpenoids from the brown alga Dictyotabinghamiae
Authors: Pathirana Charles , Andersen Raymond J.
Published: May 2006

Extracts of the brown alga Dictyotabinghamiae contain three previously known and three new diterpenoids. The known compounds, pachydictyol A (1), dictyoxide (7), and the diacetal 16, were identified by comparison of their spectral data with published values. The structures of the new diterpenoids, dictyol G acetate (12), dictyoxide A (13), and dictyotriol A diacetate (15), were proposed on the basis of their spectral data and the structures of acetate 12 and ether 13 were confirmed by chemical interconversion.
Zinc(II) and cadmium(II) compounds with the 2-[(dimethylamino)methyl]phenyl ligand
Authors: Osman Akhtar , Steevensz Richard G. , Tuck Dennis G. , Meinema Harry A. , Noltes Jan G.
Published: May 2006

The compounds L2M (M = Zn, Cd; L = 2-[(dimethylamino)methyl]phenyl ligand) are obtained by reacting MCl2 with LiL. The organometallic halides have been prepared, either by a similar route (LZnCl), or by the direct electrochemical oxidation of cadmium metal in the presence of 1-bromo-2-[(dimethylamino)methyl]benzene (LCdBr). The latter can be converted to LCdMe or LCdPh. Proton nmr spectroscopy shows that both L2Zn and L2Cd undergo rapid intramolecular bond fission and formation at the M + NMe2 site. For L2Cd, studies of the Cd—C—C—H coupling show that the Cd—C6H5 bond undergoes rapid homo-exchange at room temperature.
The direct electrochemical synthesis of some thorium(IV) nitrate complexes
Authors: Kumar N. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of thorium in either nitric acid/tri-n-butyl phosphate (TBP) or dinitrogen tetroxide/ethyl acetate/acetonitrile media gives rise to non-aqueous solutions of thorium(IV) nitrate species. The only neutral adduct which could be obtained from HNO3/TBP solution was Th(NO3)4•8dmso (dmso = dimethylsulphoxide). Salts of [Th(NO3)6]2− with Et4N+, [(bpyH)3NO3]2+, and [(phenH)3NO3]2+ (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline) were also prepared by this route. Solutions in N2O4/EtOAc/CH3CN yield Th(NO3)4, and neutral adducts with dmso, bpy, phen, Ph3PO, and pyridine-N-oxide.
Limiting low-pressure rate constant for the stepladder model of a thermal unimolecular reaction
Authors: Pritchard H. O. , Vatsya S. R.
Published: May 2006

An explicit formula for the rate constant of a thermal unimolecular reaction with stepladder relaxation probabilities, together with the corresponding eigenvector, are derived; a comment is also made about the limiting behaviour of the incubation time for such a reaction.
Stereoselectivity of C(3)-methylation of camphor and derivatives
Authors: Hutchinson John H. , Money Thomas
Published: May 2006

Contrary to general expectations, kinetic methylation of camphor, 9-bromocamphor, or 9,10-dibromocamphor produces the 3-exo-methyl derivative as the major product.
Base catalysis as an alternative explanation for an apparent deuterium solvent isotope effect in the photochemical reactions of α,β-unsaturated esters
Authors: Weedon Alan C.
Published: May 2006

An apparent deuterium solvent isotope effect upon the photochemical reactions of the α,β-unsaturated esters ethyl 3,4,4-tri-methyl-2-pentenoate, 1, and ethyl 3,4-dimethyl-2-pentenoate, 4, is re-examined; it is concluded that the changes in reaction rate can be attributed to interception of the reaction intermediates (photochemically produced dienols) by basic impurities present in the solvent used. This conclusion is used to explain the apparently anomalous photochemistry of esters 1 and 5 in non-deuterated solvents. The results described also exemplify the use of a base to enhance the efficiency and to alter the direction of deconjugation in the photochemical conversion of α,β-unsaturated esters to their β,γ-unsaturated isomers.
Vinylogous nucleophilic catalysis. Tertiary amine promoted hydrolysis of 1-alkene-1-sulfonyl chlorides
Authors: King James Frederick , Hillhouse John Henry , Skonieczny Stanisław
Published: May 2006

We present evidence that the reactions of ethenesulfonyl chloride (1) and trans-1-propene-1-sulfonyl chloride (3) with water in the presence of pyridine, trimethylamine, and a number of other tertiary amines proceed primarily by way of an initial vinylogous substitution reaction to form the cationic sulfene, [Formula: see text], which subsequently reacts with water either by addition (and deprotonation) to form the betaine [Formula: see text], or by vinylogous substitution (and deprotonation) to give the alkenesulfonate anion, [Formula: see text] (R = H or CH3). Formation of the latter represents the first well-supported example of vinylogous nucleophilic catalysis. These conclusions are drawn from kinetic and product composition observations, including (a) α-monodeuteration in the betaine and lack of deuteration of the ethenesulfonate [Formula: see text] from the reaction in D2O, (b) rate lowerings of up to 2000-fold for 2- (and 6-) substituted pyridines from those expected from Brønsted-type relationships shown by "unhindered" pyridine bases, (c) lack of a kinetic solvent isotope effect in the reaction of 1 with 3-cyanopyridine, (d) a lower rate of reaction of 3 vs. 1 not directly correlated with product composition, and (e) formation of similar product mixtures from either 1 or Pyr+CH2CH2SO2Cl Cl− (18a) with aqueous pyridine. For the initial formation of the sulfene, [Formula: see text], the available evidence does not distinguish between a two-step mechanism via an intermediate zwitterion and a closely related concerted reaction, but for the further reaction of the sulfene a process involving a zwitterionic intermediate common to both products is favoured. For the reaction of 1 or 3 in the absence of tertiary amines evidence is presented for a direct displacement on sulfur mechanism leading to the alkenesulfonate anion, plus a small proportion (up to 15%) of formation of the 2-hydroxy-1-alkanesulfonate anion by way of the sulfene HOCHRCH=SO2 (R = H or CH3).
Reactions of 2,2-dibromocyclopropyl carboxylic acids with methyllithium
Authors: Sydnes Leiv K. , Skare Sølvi
Published: May 2006

For reactions of 2,2-dibromocyclopropyl carboxylic acids with methyllithium, the course of reaction depends mainly on the position of the carboxyl group. When the COOH group is directly attached to the gem-dibromocyclopropane ring MeLi generally attacks the gem-dibromo moiety and gives the corresponding monobromocyclopropane as the principal product. When the reaction is performed above −80 °C the monobromides are formed stereospecifically in the trans configuration. The highest yields, as high as 80–90%, are obtained at 0 °C. When the carboxyl group is not directly attached to the cyclopropane ring most of the MeLi is consumed in an acid–base reaction with the COOH group.
Studies of the initial steps in the polymerization of C2N2 induced by Xe+
Authors: Raksit Asit Baran , Bohme Diethard Kurt
Published: May 2006

A Selected-Ion Flow Tube (SIFT) apparatus has been used to produce Xe+ by electron impact and to study its reactions with C2N2. The 2P3/2 and 2P1/2 spin states of Xe+ were observed to react differently: by C2N2 addition to form Xe+•C2N2 and by charge transfer to form C2N2+, respectively. Further ion–molecule reactions with C2N2 were observed to establish polymeric ions of the type (C2N2)x+. The results indicate that the simple charge transfer model may be sufficient to account for the rate enhancement observed in the radiolytic polymerization of C2N2/Xe mixtures.
Propriétés nucléophiles des phosphoranures
Authors: Garrigues B. , Munoz A.
Published: May 2006

The reaction of various bases with P—H bond-containing phosphoranes bearing α-hydroxy acid, α-aminoacid, or iminodiacetic acid ligands leads to the formation of phosphoronates which react with electrophiles such as alkyl halides, phenyl azide, carbon disulfide, orthoquinones, or keto-acids. New phosphoranes and hexacoordinated phosphorus compounds could thus be prepared. [Journal translation]
Vibrational spectra of substituted toluenes – 4-amino-3-bromotoluene and 5-amino-2-bromotoluene
Authors: Sundar N. Syam
Published: May 2006

The infrared absorption and laser Raman spectra of 4-amino-3-bromotoluene and 5-amino-2-bromotoluene have been recorded. The vibrational analysis is presented assuming Cs symmetry for the molecules.
Mechanistic variation in the reactions of substituted acetamides in aqueous sulfuric acid
Authors: Druet Linda M. , Yates Keith
Published: May 2006

The acid-catalyzed reactions of acetamide 1, N-tert-butylacetamide 2, and several p-substituted N-benzylacetamides (3 = H, 4 = CH3, 5 = OCH3, 6 = Cl, 7 = NO2) have been studied as a function of acidity and temperature over a wide range of aqueous sulfuric acid solutions (0–91%). Analysis of the reaction products and rate–acidity profiles revealed that four different mechanisms are operative over different acidity regions depending on the structure of the substrate. These are: two A-2 hydrolysis mechanisms with N-acyl fission of the substrate (with participation of one or several water molecules in the rate-determining step); A-1 hydrolysis with N-alkyl fission; and sulfonation, followed by hydrolysis. These conclusions are supported by three complementary and detailed kinetic treatments based on the hydration parameter, transition state activity coefficient, and excess acidity approaches. The acidity domains of each mechanism have been established for each substrate. The mechanistic conclusions are fully supported by the different values of ΔH‡ and ΔS‡ obtained in different regions of acidity.
Dipolar cycloaddition reactions of diazoindene and the thermal behavior of the cycloadducts
Authors: Padwa Albert , Goldstein Steven I.
Published: May 2006

A study of the dipolar cycloaddition behavior of diazoindene toward electron-deficient acetylenic and olefinic dipolarophiles has been carried out. Reactions with alkynes afford transient 1,3-dipolar cycloadducts. Product formation can be attributed to a substituent-dependent partitioning between spiro 3H-pyrazole adducts and ring opened diazoalkenes. The initially formed cycloadducts lose nitrogen to give a spirocyclopropene derivative or undergo the van Alphen – Huttel rearrangement. When olefinic dipolarophiles are used, nitrogen deficient 1:1 adducts are isolated. The formation of the product involves the further loss of nitrogen from the initially formed spiropyrazoline adduct.
Structural effects on reactivity in intramolecular catalysis. The hydrolysis of N-alkylated monoamides derived from norbornene-2,3-dicarboxylic acid
Authors: Kluger Ronald , Brandl Michael
Published: May 2006

Monoamides of 2,3-endo-cis-5-norborene dicarboxylic acid (compounds 1–5) were prepared by addition of primary alkyl amines (n-propyl-, 2-methoxyethyl-, 2-fluoroethyl-, 2,2-difluoroethyl-, 2,2,2-trifluoroethyl-) to 2,3-endo-cis-5-norborene dicarboxylic anhydride. The rates of hydrolysis of each compound in solutions whose acid concentration ranged from 0.01 M to 9 M were determined. Rates increase with acidity above 0.1 M until a maximum rate is achieved in strong acid. The results are consistent with a mechanism involving intramolecular catalysis of the hydrolysis of the amide by the adjacent carboxylic acid. The dependence of rate on acidity can be interpreted in terms of a multistep mechanism involving formation of an intramolecular tetrahedral adduct, tautomerization of the adduct, and expulsion of the amine to give the anhydride. The identity of the rate-determining step is a function of the basicity of the substrate and the acidity of the medium. Analysis of the data in terms of the proposed mechanism suggests that the effective molarity of the groups involved in tautomerization of the tetrahedral internal addition intermediate is higher than in other rigid systems which lack the norbornene structure. It is proposed that ring strain and rotational entropy control cyclization and elimination steps. Interactions of the solvent with the entire substrate control reorganization of the intermediate. Conjugation of the interacting functional groups does not appear to have a significant effect upon their reactivity.
A general route to the synthesis of 3-alkylidene derivatives of 4-thiochromanone 1,1-dioxide
Authors: Still Ian W. J. , Ablenas Fred J.
Published: May 2006

The reactions of the trimethylsilyl enol ethers of both 4-thiochromanone and 4-thiochromanone 1,1-dioxide with various carbonyl compounds complexed with titanium tetrachloride give moderate yields of the previously unknown 3-alkylidene condensation products under mild conditions. Other Lewis acids, with the exception of boron trifluoride, were found to be ineffective in this transformation.
Spectroscopic studies of the compatibility of small molecules in polymers
Authors: Loutfy Rafik O. , Ong Beng S.
Published: May 2006

A spectroscopic technique has been developed to study the compatibility and stability of small molecules in polymers. The technique was applied to investigate the compatibility of an electron-acceptor molecule, n-butyl 9-dicyanomethylene fluorene-4-carboxylate (BDFC), 1, in six different polymers. The electronic absorption of the small molecule 1 in polymer films as a function of concentration and temperature was examined. The deviation in the absorption of 1 from the molecular absorption properties was taken to indicate the degree of incompatibility (phase separation). The small molecule 1 was found to be most compatible with halogenated and electron-donating polymers.In general, our results indicated the existence of very strong intermolecular interaction between the small molecules and weaker small molecule – polymer interaction, which lead to the small molecule aggregation, i.e., incompatibility. The extent of aggregation of 1 in various polymers varied with the concentration of 1, the speed of drying the film, and the post-casting heat treatment. Aggregation of 1 in polycarbonate was drastically suppressed by incorporating a donor molecule into the matrix.
Synthesis of dodecahedrane precursors. 3. Synthesis of alkylidene-1,3-cyclopentanediones and attempts to roof peristylanes
Authors: Eaton Philip E. , Bunnelle William H. , Engel Peter
Published: May 2006

Phenylsulfenylation of 2-alkyl-1,3-cyclopentanediones followed by oxidation and elimination is shown to give easy access to 2-alkylidene-1,3-cyclopentanediones, a heretofore rare class of highly reactive compounds with good synthetic potential as dienophiles, Michael acceptors, etc. The synthesis of 2-phenylthio-1,3-cyclopentanedione is given and its use as synthon for introduction of the 2-alkylidene-1,3-cyclopentadione group into other systems is described. The methodology is applied to the preparation of a substituted peristylane containing a complete complement of carbons, proper functionality, and correct stereochemistry for closure to a dodecahedrane. The X-ray structure analysis of an example of this ring system is given. Efforts to effect the closure are described.
Conformational features of acyclonucleosides: structure of acyclovir, an antiherpes agent
Authors: Birnbaum George I. , Cygler Miroslaw , Shugar David
Published: May 2006

Crystals of acyclovir belong to the space group P21/n, and the cell dimensions are a = 25.459(1), b = 11.282 (1), c = 10.768(1) Å, β = 95.16(1)°. Intensity data were measured on a diffractometer and the structure was determined by direct methods. The asymmetric unit was found to contain three independent molecules of acyclovir and two molecules of water. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.053 for 3970 observed reflections. In two of the molecules the side chain is partially folded, while in the third one it is fully extended. The glycosidic torsion angles are in the range 91.4–104.3°. The conformational features are compared with those in other known acyclonucleosides. They are also examined in relation to the behavior of acyclonucleosides and acyclonucleotides in various enzymatic systems, including those related to antiviral activities.
Linear oligopeptides. 118. Preferred conformations and modes of self-association of the fluoren-9-ylmethoxycarbonyl amino acid derivatives
Authors: Valle Giovanni , Bonora Gian Maria , Toniolo Claudio
Published: May 2006

An analysis of the preferred conformations and modes of self-association of the N-fluoren-9-methoxycarbonyl derivatives of L-alanine and α-aminoisobutyric acid was performed in solution and in the solid state using infrared absorption, 1H nuclear magnetic resonance, and X-ray diffraction. In a solvent of low polarity (deuterochloroform) non-associated and self-associated species (involving predominantly the hydroxyl and carbonyl groups of the carboxylic acid moiety) simultaneously occur. At high dilution, where self-association is absent, the amount of intramolecularly H-bonded forms, if any, should be extremely small. Z(trans) [Formula: see text]E(cis) isomerism about the amide bond of the secondary urethane moiety was observed only for the less bulky L-alanine derivative. In the solid state all H-bonding donors and acceptors of the L-alanine and α-aminoisobutyric acid derivatives take part to complex schemes of intermolecular H-bonds. In the L-alanine derivative, crystallized as monohydrate, most of the intermolecular H-bonds involve the water molecule. Intramolecular H-bonds are not observed in either compound. The conformation about the secondary urethane CO—NH bond is Z(trans) in both compounds. Both L-alanine and α-aminoisobutyric acid residues are partially folded. The observation of the long C(sp3)—O bond of the fluoren-9-yl-methoxycarbonyl moiety might contribute to explain the unexpected experimental result that this protecting group can be removed by catalytic hydrogenation.
The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm
Authors: Deslauriers Hélène , Collin Guy J.
Published: May 2006

The photofragmentation of 2,3-dimethylbutene and 3,3-dimethylbutene has been studied at 147 and 184.9 nm in the gas phase. The main primary decomposition process at both wavelengths involves the rupture of a β(C—C) bond. The quantum yield for this process is higher than 0.7 at 147 nm and is probably even higher at 184.9 nm. All dimethallyl radicals formed at 147 nm in this process decompose at low pressure, but some of them isomerize from the α,β- to the α,α- structure (and vice versa) — via a 1,4-H transfer — before decomposition. At 184.9 nm, the same primary process is used to get a rough value for the lifetime of the photoexcited molecule, compared with the one made with RRKM calculations by assuming that all the photon energy resides in the vibrational framework of the fundamental electronic state. These lifetimes are about one nanosecond or less.
Synthesis, molecular and electron transport properties of 2-alkyltrinitrofluoren-9-ones
Authors: Ong Beng S. , Keoshkerian Barkev , Martin Trevor I. , Hamer Gordon K.
Published: May 2006

2-Alkyltrinitrofluoren-9-ones 2 were conveniently synthesized by controlled nitration of 2-alkylfluoren-9-ones 5 with a mixture of red fuming HNO3 and concentrated H2SO4 at 0–25 °C. The precursors 5 were derived from the corresponding 2-acylfluorenes by appropriate reduction of the acyl function, followed by base-catalysed O2-oxidation at the C-9 position. The regiochemistry of nitration was interesting: with a sterically bulky substituent in 5, nitration occurred at C-4, -5, and -7 positions, affording 2-alkyl-4,5,7-trinitrofluoren-9-one in over 35% yield; on the other hand, 5 with a primary alkyl function underwent nitration predominantly at C-3, -5, and -7 positions. By virtue of its alkyl function, 2-alkyltrinitrofluoren-9-one 2 displayed better solubility and polymer compatibility characteristics than its non-alkylated analog, TNF. However, the charge transfer interactions of 2 with electron donors were weaker than those of TNF, despite the fact that they both have the same electron affinity. Both 2 and TNF exhibited good electron transport properties in poly(N-vinylcarbazole) matrices.
Styrene/butadiene block copolymer micelles in heptane
Authors: Bluhm T. L. , Whitmore M. D.
Published: May 2006

The radius of gyration of poly(styrene-b-butadiene) block copolymer micelles in n-heptane is measured by small angle X-ray scattering (SAXS). The results are compared with theoretical predictions, and good agreement is found, particularly for the appropriate scaling relations. It is argued that the radius of gyration of the micelles depends on both the molecular weight and the composition of the copolymers. The dominant factors which determine the micelle core and corona dimensions are identified.
Detailed copolymer characterization using ultraviolet spectroscopy
Authors: Garcia-Rubio L. H. , Ro N.
Published: May 2006

A method is demonstrated for the interpretation of the ultraviolet spectra of styrene-containing copolymers. This method is based on the use of model molecules to approximate the absorption behaviour of the known chromophores and on the statistical estimation of the average spectra of the unknown chromophores. The analysis yields directly the copolymer composition and an estimate of the background spectra which arise from the different arrangements of the styril units along the polymer chains. It is shown that reliable composition estimates are obtained for styrene – methyl methacrylate and styrene–acrylonitrile copolymers. The results from the interpretation of the spectra are discussed and compared with results obtained from the statistical copolymerization models.
The preparation and rearrangements of some 8,8-dimethylhomotropylium cations and their iron tricarbonyl complexes
Authors: Childs Ronald F. , Varadarajan Aravamuthan
Published: May 2006

The circumambulatory rearrangements of some 8,8-dimethylhomotropylium cations and their corresponding iron tricarbonyl complexes have been examined. 8,8-Dimethylhomotropylium cation, 4, has been prepared by protonation of 8,8-dimethyl-bicyclo[5.1.0]octa-3,5-dien-2-ol in FSO3H/SO2ClF. Evidence for homoaromatic delocalization in 4 was found in its characteristic 1H nmr spectrum, particularly when this was compared to that of the non-cyclically delocalized 8,8-dimethyl-bicyclo[5.1.0]octadienyliron tricarbonyl complex 7. Cation 4 was found to be stable at low temperatures but to isomerize to isopropyltropylium ion, 8, at −50 °C, [Formula: see text] The specifically deuterated cation 4D was prepared and a slow circumambulation of C8 around the basal 7-membered ring of this cation was found to occur at −90 °C. The free energy of activation for this circumambulation is 14.5 kcal/mol. Homotropylium cation 4 was also prepared by protonation of 8,8-dimethylbicyclo[3.2.1]octa-3,6-dien-2-ol, 14, at −120 °C. No evidence for the presence of the corresponding bicyclo[3.2.1]octadienyl ion 12 was obtained. The 2,8,8-trimethylhomotropylium cation, 17, was prepared and shown to undergo a circumambulatory rearrangement to give the 4,8,8-trimethyl substituted cation 20 as the major product. In this trimethyl series it also proved possible to generate the 2,8,8-trimethylbicyclo[3.2.1]octadienyl cation, 18, and observe its 1H nmr spectrum at very low temperatures (−116 °C). The proton chemical shifts of 18 suggest that the charge is predominantly located on the 3-carbon bridge. Cation 18 isomerized to 17, 20, and other products at temperatures above −100 °C. The 2,8,8-trimethylbicyclo[5.1.0]octadienyliron tricarbonyl complex 22 was also shown to undergo a circumambulatory rearrangement in which both C8 and the Fe(CO)3 grouping migrate.
Experimental and theoretical shakeup studies. VI. The fluoromethanes
Authors: Tse John S. , Pellach Emmanuel , Bancroft G. Michael
Published: May 2006

We report the observation of satellite structures associated with the core C 1s and F 1s levels in the photoelectron spectra of CH3F, CF3H, and CF4. These structures are attributed to monopole "shakeup" excitations. Qualitative assignments aided by theoretical Xα-SW calculations are presented. We found shakeup intensities in the C 1s spectrum of CF4 are enhanced by barrier created by the fluorine lone pair electrons. However, this effect is less apparent in the F 1s core hole photoelectron spectra.
Crystal and molecular structure of the binuclear Rh(I) complex (μ-Cl)(μ-pz) [Rh(CO)2]2 (pz = pyrazolyl, N2C3H3). An example of molecular stacking via weak intermolecular interactions
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis and physical properties of (μ-Cl)(μ-pz)[Rh(CO)2]2 are given. Crystals of (μ-chloro) (μ-pyrazolyl)-bis(dicarbonylrhodiumd(I)) are monoclinic, a = 7.0970(8), b = 20.5184(10), c = 15.808(2) Å, β = 94.695(6)°, Z = 8, space group P21/c. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.035 and Rw = 0.038 for 2949 reflections with I ≥ 3σ(I). The complex provides a rare example of molecular stacking in a binuclear transition metal complex with [Formula: see text] distances of 3.5107(8) and 3.6201(8) Å.