bluuebunny/crossref_metadata_2025 huggingface dataset:
A Review of Upper Atmospheric Photochemistry
Authors: Crutzen Paul
Published: May 2006

A review is given of the photochemical processes which determine the distribution of important minor constituents in the stratosphere and mesosphere. Although it is necessary to consider many reactions, it seems that for the first time satisfactory rate data are available for most of these processes. There is, however, a lack of knowledge about the detailed steps of the gas-phase oxidation of methane which affects theoretical results in the lower stratosphere. It is shown that rather fair agreement exists between the calculated and measured concentrations of several of the constituents. However, deviations exist concerning CH4, H2, and the NO profile which was obtained with the chemiluminescent technique.Nitrogen oxides catalyze destruction of ozone and reduce total ozone in the atmosphere considerably. The reduction of ozone by other reactions is also discussed. Some estimates are presented of the ozone reductions which could result from the operation of large fleets of supersonic aircraft due to exhaust injections of nitrogen oxides into the stratosphere.It is indicated that total ozone is rather insensitive to variations in the stratospheric water vapor content (there is a slight increase in total ozone, when the H2O content is increased). Total ozone is, however, much more sensitive to changes in the stratospheric NOx content. Variations in the stratospheric NOx content over long periods may explain those variations which have taken place in total ozone. It is essential to monitor variations in the solar output in the wavelength region 1750–2400 Å, as these may change the stratospheric NOx content and ozone production rates.The reintroduction of the ozone-destroying reaction HO2 + O3 → OH + 2O2 leads to an increase in calculated total ozone. The reason for this surprising result is given.A discussion is given of the possible role of vibrationally excited H2 and electronically excited O3 in the photochemistry of the mesosphere and thermosphere.
HOx, NOx, and ClOx: Their Role in Atmospheric Photochemistry
Authors: Wofsy Steven C. , McElroy Michael B.
Published: May 2006

Sources of atmospheric odd nitrogen and hydrogen are reviewed and their role m ozone photochemistry is discussed. A model, containing few adjustable parameters, gives good agreement with observed distributions of stratospheric and mesospheric ozone. Nitric oxide emitted by supersonic aircraft would lead to a significant reduction in the concentration of atmospheric ozone if the globally averaged source of NO should exceed 2 × 107 molecules cm−2 s−1. A traffic model projected by Broderick etal. for 1990 could lead to a reduction of about 2% in the column density of O3.Sources of atmospheric chlorine are discussed. It is argued that HCl should be the dominant form of atmospheric chlorine and that it is produced mainly from aerosols of marine origin. The atmospheric source strength is about 2 × 108 tons per year according to Chesselet etal. and HCl may be removed by gas phase reaction with NH3. The role of chlorine compounds as a catalyst for recombination of odd oxygen is discussed and shown to play no major role in the normal atmosphere. Reactions of OH and HO2 with O3 may provide an important sink for tropospheric odd oxygen such that O3 may not be a passive tracer for tropospheric motions.
Reduction of Stratospheric Ozone from High-flying Aircraft, Studied in a Two-dimensional Photochemical Model with Transport
Authors: Hesstvedt Eigil
Published: May 2006

A steady state two-dimensional model of the stratospheric ozone layer is presented. Chemical reactions involving oxygen, hydrogen, and nitrogen are considered along with the effect of a parameterized, two-dimensional transport, by mean motion and by eddies. The model is in reasonable agreement with observed ozone data. The reduction of ozone from emission of NOx from high flying aircraft is studied, assuming a fleet of 500 supersonic aircraft in transatlantic operation, flying at given altitudes. The effect is found to depend critically upon flight level. For mid-latitude, summer, the ozone column density is reduced by 0.3% for a flight level of 18 km. For flight levels of 23 and 28 km the reduction is 2 and 5%, respectively. Accordingly, the increase in u.v. radiation amounts to approximately 0.6, 4, and 10% for the same flight levels.
The Interaction of Ozone Photochemistry and Dynamics in the Stratosphere. A Three-dimensional Atmospheric Model
Authors: London Julius , Park Jae H.
Published: May 2006

In the stratosphere the relaxation times for transport and ozone photochemistry in an oxygen–hydrogen–nitrogen system are approximately comparable. Therefore, realistic models used to calculate ozone variations need to be based on the interaction of the photochemistry and dynamics in this region.The model used in the present study is the three-dimensional global circulation model developed at the National Center for Atmospheric Research. The photochemical calculations for ozone are carried out as time dependent in a three-dimensional O–H–N system.The dynamic model is started from an atmosphere initially at rest and then spun up to a steady state circulation corresponding to mid-January. An initial observed ozone distribution is added and the model is then run through 30 simulated days. Analysis of the time variation of the ozone distribution shows that photochemistry dominates the ozone changes in the sub-solar middle stratosphere, and transport processes redistribute the ozone poleward and downward into the troposphere. Although the general pattern of ozone changes seem to be correct, the model produces too much ozone in the Southern hemisphere subtropical stratosphere and transports too much ozone into the Northern subtropical troposphere. The computed lower boundary flux of about 5 × 1010 cm−2 s−1 corresponds quite well to estimates given in the literature.
Uncertainties in Stratospheric–Mesospheric Modeling
Authors: McConnell J. C.
Published: May 2006

Some of the problems and uncertainties of stratospheric–mesospheric modeling are discussed in terms of the variables which constitute the continuity equation. The status of one- and two-dimensional eddy coefficients, required in the evaluation of the flux equation, are briefly reviewed. The production and loss terms are discussed both generally and with respect to the particular uncertainties in the CH4, H2O–HOx, NOx, and O3 chemistries.
Kinetics of the Abstraction of H from Group IV Methyls by CF3 and CD3 Radicals
Authors: Bell T. N. , Slade P. , Sherwood A. G.
Published: May 2006

CD3 radicals from the photolysis of hexadeuteroacetone abstract H atoms from group IV methyls[Formula: see text]Through additional work on the Sn and Ge systems, a comparison of the data for CF3 or CD3 + (CH3)4M (where M = C, Si, Ge, Sn) leads to the reactivity ratio [Formula: see text] at 373 K. Arrhenius parameters for the abstraction processes are reported.
Ligand Abstraction in the Reaction of Aryldiazonium Ions with some Iron Complexes Containing Coordinated Cysteine, Maleonitriledithiol, or Triarylphosphine
Authors: Carroll James A. , Fisher David R. , Canham Geoffrey W. Rayner , Sutton Derek
Published: May 2006

The reactions of selected aryldiazonium tetrafluoroborates with Fe(CO)3(PR3)2, [Fe(mnt)2]−, [Fe(cystH)2]2+, and [Fe(CO)2(cyst)2] (mnt = S2C2(CN)2, cyst = SCH2CH(NH2)CO2H ) result in abstraction of the ligand to yield arenediazophosphonium ions, S-(arenediazo)cysteine or the dinitrogen extrusion product ArS(CN)C=C(CN)SAr. Arylazo complexes of iron were not obtained. The products have been characterized and compounds related to S-(arenediazo)cysteine, namely S-(arenediazo)triphenylmethyl mercaptan and S-(arenediazo)sulfones, have been synthesized for a detailed comparison of their Raman spectra. Assignments of ν(N=N) are made on the basis of 15N- and 2H-substitution experiments. The possible involvement of nucleophilic sulfur as a site for the activation and or reduction of complexed dinitrogen in biological nitrogen fixation is proposed.
Complexes of Tantalum and Antimony Pentafluorides with Dimethyl Ether and Trimethylamine
Authors: Brownstein S. , Farrall Marjorie Jean
Published: May 2006

Tantalum pentafluoride forms 1:1 and 1:2 complexes with dimethyl ether and trimethylamine. Antimony pentafluoride forms 2:1 and 1:1 complexes with dimethyl ether and trimethylamine. The rates of exchange of terminal and equatorial fluorines in the 1:1 TaF5 – dimethyl ether adduct have been measured.
Isotope Effects on Chemical Equilibria. Part II. Some Further Secondary Isotope Effects of the Second Kind
Authors: Barnes Douglas James , Golding Peter David , Scott John Marshall William
Published: May 2006

The ratio of the dissociation constants Ka(H)/Ka(D) has been measured conductimetrically for the isotopic pairs XCH2COOH/XCD2COOH where X = Cl, PhO, and PhS. Methods of calculating the ratio of the equilibrium constants are considered in some detail. Since the isotope effect varies with the nature of the X substituent it is concluded that the simple inductive description of these effects is not tenable.
Carbon-13 Nuclear Magnetic Resonance Spectra of 1,4-Oxathiane Derivatives
Authors: Szarek Walter A. , Vyas Dolatrai M. , Sepulchre Anne-Marie , Gero Stephan D. , Lukacs Gabor
Published: May 2006

The carbon-13 n.m.r. spectra of a series of 1,4-oxathianes, including the 4-oxide and 4,4-dioxide of 1,4-oxathiane, are reported. The results corroborated conclusions reached previously, on the basis of proton n.m.r. studies, concerning the conformational equilibria. The work also permitted a structural differentiation of the two nucleosides 6-chloro-9-(1,4-oxathian-2-yl)-9H-purine (1) and 6-chloro-9-(1,4-oxathian-3-yl)-9H-purine (2).
The Modular Structure of Lignin
Authors: Wayman M. , Obiaga T. I.
Published: May 2006

A kinetic investigation of the polymerization of lignin-like polymers of coniferyl alcohol (DHP) using horseradish peroxidase as the phenol oxidase revealed the product to have a bimodal distribution of molecular weight. A peak representing material of low molecular weight Mw 3000–4000 was first formed, followed by the formation of a second peak in the molecular weight range 80 000–100 000 whose growth appeared to proceed at the expense of the first.Alkaline degradation of lignins isolated from spruce and hemlock also gave products having a bimodal distribution of molecular weight, with peaks at the same values as found for the synthetic lignin. Lignin isolated during alkaline pulping of finely divided wood showed the presence of the same two components of high and low molecular weight.From these results, we have constructed models for the formation of lignin and for its degradation during an alkaline pulping of wood. The lignin macromolecule as it occurs in wood may well be material of narrow molecular weight distribution with d.p. about 500. It is proposed that this macromolecule is an assembly of subassemblies, or modules, each of d.p. about 20. Lignin formation is seen to proceed by enzyme dehydrogenation of the monomers first producing free radicals as described by Freudenberg, the free radicals reacting by a step condensation to form the modules, followed by intermodular addition polymerization to form the lignin macromolecules. Lignin degradation in pulping reactions involves first the nonrandom homolytic chain depolymerization of the macromolecule to yield free-radical carrying modules, which, after stabilization against recondensation by the pulping chemicals, break down to lower oligomers and monomers by a step depolymerization reaction.
Revision of the Shannon and Prewitt Effective Ionic Radii of Tetravalent Elements
Authors: Knop Osvald , Carlow John S.
Published: May 2006

A new empirical set of "effective ionic" radii for tetravalent atoms in 6-coordination has been constructed. It is based on V1/3vs. r plots for isostructural series of M4+ compounds of high symmetry. The radius values resulting from a non-linear least-squares refinement of all the data have been adjusted to coincide with the Shannon and Prewitt set of radii at Ti4+ and Sn4+. Evidence is presented for the existence of a cusp at Bk in the rvi(M4+) vs. atomic number curve for M4+ (5f).
Tricyclic Analogs of the Prodines
Authors: Ménard Marcel , Rivest Pierre , Morris Lee , Meunier Jacques , Perron Yvon G.
Published: May 2006

A search for an analgesic with the potency of β-prodine and with the quality of analgesia associated with the benzomorphans led to the preparation of the octahydrobenz[f] isoquinoline system, a system where β-prodine is bridged in a manner related to the benzomorphans. Three different syntheses of this system are described. They permit access to a variety of substitution patterns as well as to the possible stereoisomers. The hybrid β-prodine-benzomorphan system displayed interesting CNS activity.
Quaternary Bases from Hunteria eburnea Pichon
Authors: Burnell R. H. , Chapelle A. , Khalil M. F.
Published: May 2006

A re-examination of the quaternary alkaloids of Hunteria eburnea has shown the presence of antirhine β-methochloride 6, dihydroantirhine β-methochloride 7 (originally called H. alkaloid J), and pleiocarpamine methochloride 5 (H. alkaloid F). A novel structure (1) has been forwarded for hunteracine chloride (bromide).
The Total Synthesis of a Hexacyclic Relay for the Alkaloid Napelline
Authors: Wiesner Karel , Ho Pak-Tsun , Tsai Connie Shii Jeou (Pan)
Published: May 2006

The total synthesis of the racemic compound 12 and its identification with the corresponding optically active derivative prepared from lucidusculine is described.
Studies on N,N′-Diimidyl Systems by Nuclear Magnetic Resonance Spectroscopy
Authors: Verma Shiva Mohan , Sinha Kumar Om Prakash , Rao Chennupati Koteswara
Published: May 2006

A number of N,N′-diimidyl compounds, which possess asymmetry about the imidyl planes, have been synthesized and characterized by n.m.r. and i.r. spectroscopy. The n.m.r. spectra of the compounds were found to be temperature dependent and provide evidence for the hindered rotation about the N—N′ bond. This characteristic feature has been utilized to establish the proposed structures of the products. The asymmetric "cage moieties" have been found useful for the detection of noncoplanar ground states proposed for this system.
Photolysis of Di-tert-butyl Peroxide in Solution
Authors: Lissi Eduardo
Published: May 2006

Di-tert-butyl peroxide has been photolyzed at 3130 Å in carbon tetrachloride solution in the presence of cyclohexane. The quantum yield of free tert-butoxy radicals was 1.9 ± 0.1, independent of the hydrocarbon concentration. Unlike results obtained in the gas phase at 2537 Å, no evidence for the quenching of the excited peroxide molecule could be detected.
The Crystal Structure of Levoglucosan Triacetate
Authors: Leung F. , Marchessault R. H.
Published: May 2006

The crystal structure of the acetylated levoglucosan (1,6-anhydro-2,3,4-triacetylglucose) was determined by X-ray crystallography. The crystal data are: P212121, a = 10.916, b = 8.318, c = 15.612 Å. It was found that the pyranose ring of the molecule has the 1C(D) chair conformation with the acetate groups occupying the axial positions. The orientation of the acetate groups with respect to the pyranose ring was discussed in conjunction with other acetylated carbohydrate structures.
The Synthesis and Application of Anchored Catalysts in Hydrogen Isotope Exchange Systems. D2 – Protic Solvent Exchange
Authors: Strathdee Graeme , Given Russell
Published: May 2006

A number of polymer-attached, or anchored, catalysts of rhodium and ruthenium have been synthesized, and their activities for D2 exchange with ethanol have been measured. Among the rhodium anchored catalysts, three exhibited specific activity comparable to Wilkinson's catalyst, RhCl(PPh3)3. No polymer-attached ruthenium species had specific activities close to that of the active homogeneous catalyst RuCl2(PPh3)3. Conditions for the synthesis and optimum loading of complexing resins are discussed. Structural and kinetic comparisons are made between anchored catalysts and their homogeneous analogs.
Occurrence of Strontium–Iron Oxide SrFe12O19 in the Fe2O3–Na2O–SrSO4 System
Authors: Routil R. J. , Barham D.
Published: May 2006

The formation of SrFe12O19 in the Fe2O3–Na2CO3–SrSO4 system was found to proceed through three stages, first an endothermic reaction between Fe2O3 and Na2CO3 to form Na2Fe2O4 and CO2, second an exothermic reaction of Na2Fe2O4 with SrSO4 to produce Na2SO4, Sr7Fe10O22, and SrFe12O19, third an exothermic reaction between Sr7Fe10O22 and Fe2O3 towards more SrFe12O19. The yield of SrFe12O19 depended on the molar ratio of the reactants and on temperature. Below 700 °C the formation did not proceed beyond the second stage. Samples prefired at 900–1200 °C contained SrFe12O19 in all cases when the original relative molar concentrations xFe2O3,yNa2CO3, and zSrSO4 satisfied the condition (x − y + z)/z > 5/7 or x/y > 5/7 ≥ x/z. Substitution of Na2CO3 in the reaction mixtures with equivalent amounts of NaOH or other precursors of Na2O did not affect the second and the third stage of the reaction and the final yield of SrFe12O19. On the ternary diagram of the Fe2O3–Na2O–SrSO4 system the SrFe12O19 region was represented by the area of a quadrilateral with the corner points located at the composition points 98-1-1, 1-1-98, 26-36-38, and 50-49-1 mole percent. The highest yields were obtained from the mixtures represented by the molar ratio 6Fe2O3:1 Na2O:1SrSO4. The hexagonal lattice parameters of SrFe12O19 were determined as a0 = 5.885 Å and c0 = 23.047 Å. X-Ray diffraction reflections of SrFe12O19 were indexed and reassignment of several indices in ASTM 7-276 for BaFe12O19 was suggested.
On the Hydrogen Bond Breaking Ability of Fluorocarbons Containing Higher Halogens
Authors: Paolo Thérèse Di , Sandorfy C.
Published: May 2006

Infrared measurements show that fluorocarbons containing higher halogens are able to open O—H---O, N—H---N, S—H---S, N—H---O=C, type hydrogen bonds. This is probably due to a competitive mechanism of association consisting in the formation of donor–acceptor complexes. It is suggested that the breaking or perturbation of hydrogen bonds by this mechanism is of importance for the explanation of the anesthetic activity of these compounds.
The Detection of Alkoxy and Other Radicals in the Gamma Radiolysis of Alcohols by an Electron Spin Resonance and Spin Trapping Method
Authors: Sargent Frederick Peter , Gardy Edward Michael
Published: May 2006

The radicals produced during γ radiolysis of methanol, ethanol, 1-propanol, 2-propanol, and t-butanol have been trapped by reaction with 2-nitroso-2-methylpropane (t-nitrosobutane) to give nitroxides which are detected by e.s.r.[Formula: see text]All the alcohols gave alkoxy radicals and, with the exception of t-butanol, radicals derived by the loss of an H atom from the carbon atom adjacent to the OH group. Methyl radicals were detected in t-butanol.
Nucleic Acid Related Compounds. 14. 3′-O-Aminoacyl-2′-O-methyladenosines and 2′-O-Aminoacyl-3′-O-methyladenosines Related to Charged tRNA Termini
Authors: Robins Morris J. , MacCoss Malcolm , Ramani G.
Published: May 2006

Aminoacyl nucleosides derived from 2′-O-methyladenosine and 3′-O-methyladenosine have been isolated as pure solids and completely characterized for the first time. Coupling of 5′-O-(mono-p-methoxytrityl)-2′-O-methyl- (and 3′-O-methyl-) adenosines (1 and 6, respectively) with N-tert-butyloxycarbonyl(N-tBOC)-amino acid anhydrides (2a–c) (generated insitu from the corresponding N-tBOC-amino acids and N,N′-dicyclohexylcarbodiimide) in the presence of 4-N,N-dimethylaminopyridine gave the 3′-O-(N-tBOC-aminoacyl)-5′-O-(mono-p-methoxytrityl-2′-O-methyladenosines (3a–c) and 2′-O-(N-tBOC-aminoacyl)-5′-O-(mono-p-methoxytrityl-3′-O-methyladenosines (7a–c), respectively, in good yields. The L-leucine (a), L-phenylalanine (b), and L-methionine (c) compounds were prepared in each series. Complete deblocking was effected using 98% formic acid since usual procedures had disadvantages with these molecules. The 3′-O-(L-aminoacyl)-2′-O-methyladenosines (4a–c) and 2′-O-(L-aminoacyl)-3′-O-methyladenosines (8a–c) were obtained in high yields with no detectable hydrolysis of the aminoacyl or glycosidic bonds under these conditions.N-Formylmethionyl and N-acetylphenylalanyl derivatives were prepared in each series by acylation of the deblocked products with acetic formic anhydride and p-nitrophenyl acetate, respectively. Biochemical rationale for the use of these compounds in the study of protein biosynthesis and initiation processes are discussed. The puromycin-like activity of 3′-O-phenylalanyl-2′-O-methyl-adenosine (4b) was confirmed.
The Kinetics of the Isotopic Exchange of Oxygen-18 with the Oxygen of Copper(II) Molybdate
Authors: Klissurski D. G. , Ross R. A. , Griffith T. J.
Published: May 2006

The kinetics of the exchange of gas-phase oxygen-18 with the oxygen of copper(II) molybdate has been studied in an all-glass "static-circulation" apparatus using a quartz differential reactor. The activation energy of the exchange between 522 and 601 °C was 40 kcal mol−1 and the reaction order was 0.7 in the oxygen partial pressure range 5 to 30 Torr. The structure and physical properties of the molybdate were determined by X-ray, i.r., thermal and chemical analysis.It is shown that the exchange reactivity of the surface and bulk oxygen in copper(II) molybdate is closer to the reactivity of oxygen in MoO3 than it is to the oxygen in CuO. From current theories on the relationships between exchange rates and catalytic properties, it is deduced that copper(II) molybdate would be expected to exhibit properties similar to those of V2O5 in catalytic oxidation reactions.
The Reaction of O(3P) with C2Cl4
Authors: Sanhueza Eugenio , Heicklen Julian
Published: May 2006

The reaction of O(3P), prepared from Hg photosensitization of N2O with C2Cl4 was studied at 25 °C. The exclusive products of the reaction in the absence of O2 were CCl2O and polymer (as well as N2 from the N2O). The quantum yield of CCl2O production, Φ{CCl2O}, was 0.19 independent of the C2Cl4 pressure or the absorbed intensity, Ia. There was no evidence for CO, Cl2, c-C3Cl6, CCl3CCl(O), or [Formula: see text] production. The reaction mechanism is[Formula: see text]with k12a/k12 = 0.19. The CCl2 radical dimerizes and the energetic C2Cl4O* intermediate polymerizes. By competitive kinetics, the ratio k12/k13 was found to be 0.10, where k12 ≡ k12a + k12b and k13 is the rate coefficient of the O(3P) + C2F4 reaction.In the presence of O2, a chain process is involved in which CCl3CCl(O) and CCl2O are the major products. They are formed in a ratio of 2.0 independent of reaction conditions, but the chain length is proportional to [C2Cl4]/Ia1/2. Also produced is CO with a quantum yield of ∼0.18. The ratio Φ{CCl3CCl(O)}/Φ{CCl2O} = 2.0 is similar to that of 2.5 found in the Cl atom initiated oxidation. This result is interpreted to mean that chlorine atoms are involved in the chain. The reaction which initiates monoradicals in the system is[Formula: see text]
The Determination of the Preferred Stereochemistry and the Magnitude of the Hydrogen Isotope Effect for 1,3 Elimination in the Locked Norbornyl System Methyl exo-2-Bromo-1-norbornanecarboxylate-endo, endo-5,6-d2
Authors: Werstiuk Nick Henry
Published: May 2006

Methyl exo-2-bromo-1-norobornanecarboxylate-endo,endo-5,6-d2 (1b) has been prepared and solvolyzed at 112° in 80:20 EtOH-H2O buffered with NaOAc. The loss of 85–90% of the deuterium available on the front face of 1b in the formation of the tricyclic ester 6D coupled with a novel analysis established that the endo:exo preference for 1,3 elimination is at least 15:1 to 20:1. A comparison of the solvolytic kinetic isotope effect (1.18 ± 0.04) for 1b and the 1,3-elimination kinetic isotope effect (1.45–1.6) with data for 1,2 eliminations indicates that elimination occurs from the classical, perhaps 1,3 hyperconjugatively stabilized carbocation 20. The endo:exo preference established in this study is used to reinterpret 1,3-elimination data determined by Collins in the solvolysis of deuteriohydroxyphenyl norbornyl tosylates.
C -Nucleosides and Related Compounds. IV. The Synthesis and Chemistry of D,L-2,5-Anhydroallose Derivatives
Authors: Just George , Martel Alain , Grozinger Karl , Ramjeesingh Mohabir
Published: May 2006

Methyl β-nitroacrylate (1) reacted with furan to give the corresponding Diels–Alder adduct, which was converted to D,L-3,4-di-O-isopropylidene-2,5-anhydroallose (9) in a five-step sequence in 14% yield, based on 1. The conversion of 9 to its oxime, semicarbazone, and thiosemi-carbazone is described, as well as the synthesis of the free aldehyde 15, and of the Wittig reaction product 14.
Conformational Study of N-Alkyl 5,6-Dihydro-7h,12h-Dibenz[C,F]Azocines by Nuclear Magnetic Resonance Spectroscopy
Authors: Fraser Robert R. , Raza Mohammad A. , Renaud Roger N. , Layton Robert B.
Published: May 2006

The influence of substituents on the conformational properties of N-substituted 5,6-dihydro-7H,12H-dibenz[c,f]azocines and their conjugate acids was studied by n.m.r. spectroscopy. The position of the equilibrium between a rigid boat-chair and a flexible twist-boat conformation has been measured. The twist-boat conformation in deuterochloroform increased as the size of the substituent increased. However, the effect was opposite for the series of conjugate acids in trifluoroacetic acid.A number of inversion barriers for the [Formula: see text] and the [Formula: see text] equilibria in CDCl3 and TFA were determined. It was found that all barriers to interconversion were raised on protonation. The barrier to racemization for the twist-boat form of the quaternary methiodide of 1 was found to be >18 kcal/mol.
Complexes of Cobalt(II), Nickel(II), And Copper Acetates, Perchlorates, and Tetrafluoroborates with Heterocyclic Ligands Containing Va and Via Group Donor Atoms
Authors: Preti C. , Tosi G.
Published: May 2006

Cobalt(II), nickel(II), copper(II), and copper(I) acetate, perchlorate, and tetrafluoroborate complexes with thiazolidine-2-thione, thiomorpholin-3-one, and thiomorpholin-3-thione have been prepared. On the basis of infrared and far infrared spectra, electronic spectroscopy, magnetism, and molecular conductance, the stereochemistries of these complexes were identified. Assignments for the metal–ligand modes have also been made. By the use of infrared spectroscopy it has been possible to distinguish whether or not the polyanions present in the complexes are coordinated to the transition metal ion or are present as free ions. Spectroscopic parameters for the complexes have been calculated and compared with similar chromophores containing sulfur, oxygen, and nitrogen donor atoms.
A Raman Spectral Study of the Kinetics of Hydrolysis of Acetonitrile Catalyzed by Hg(II)
Authors: Sze Yu-Keung , Irish Donald E.
Published: May 2006

Raman spectroscopy has been employed to follow the relatively slow rate of hydrolysis of acetonitrile, catalyzed by mercury(II). Raman lines at 2275 and 2305 cm−1 are characteristic of CH3CN bound to Hg2+, and are distinct from lines of bulk solvent. The intensities of these new lines decrease with time. From the intensities, concentrations of bound acetonitrile, [CH3CN]B were calculated for a time span of 400 min. The data fit a second order rate law: Rate = k[CH3CN]B[H2O]. The specific rate constant, k, obtained from four sets of data for the system Hg(ClO4)2–CH3CN–H2O equals 1.05 ± 0.06 × 10−4 mol−1 1 min−1 at 25 °C. The energy of activation is 18.9 kcal mol−1. In the proposed mechanism water molecules attack acetonitrile molecules which are bound to Hg2+ and form a mercury(II)–acetamide complex. Raman lines characteristic of this species are observed. This species slowly converts to mercury(II) ammine complexes and acetic acid. Anions which coordinate with Hg2+ more strongly than CH3CN, such as nitrate or acetate, slow or prevent the hydrolysis reaction.
Electrochemical Oxidation of Trifluoroacetic Acid in an Organic Substrate. III. In the Presence of Substituted Malonic Acid Half Esters and Unsaturated Carboxylic Acid Esters
Authors: Renaud Roger N. , Champagne Philippe J.
Published: May 2006

The electrochemical oxidation of substituted malonic acid half-esters was studied in the presence of trifluoroacetic acid. Some 'crossed' Kolbe products were obtained together with some unsaturated carboalkoxy compounds, trifluoromethylated adducts to the double bond, and trifluoromethylated dimers.The electrolysis of trifluoroacetic acid in the presence of olefinic carboalkoxy compounds was also studied.
13C Nuclear Magnetic Resonance Studies. 45. The 13C Spectra of Some β,γ Unsaturated Polycyclic Ketones
Authors: Stothers J. B. , Swenson J. R. , Tan C. T.
Published: May 2006

The 13C spectra of several β,γ unsaturated polycyclic ketones have been recorded to examine the shielding differences for all carbons relative to those for their saturated analogs and the parent olefins. The variations of the sp2 carbon shieldings provide qualitative evidence for the existence of homoconjugative interactions between the olefinic and carbonyl groups in the ground state. Similar evidence of interaction between γ,δ double bonds and carbonyl groups was found from spectra for a few examples. A simple interpretation of the shielding trends entirely in terms of charge density variations arising from through space polarization is shown to be inadequate, thereby emphasizing the existence of other major shielding contributions.
The Structure of Isothiosemicarbazones
Authors: Yamazaki Chiji
Published: May 2006

Isothiosemicarbazones, except N2-substituted ones, were found to exist exclusively in the amino structure by means of i.r. and n.m.r. spectroscopy. The cis configuration (N1cis to N4 about the N2=C bond) with intramolecular hydrogen bonding was proposed as the predominant structure for N4-unsubstituted isothiosemicarbazones on the basis of the i.r. spectra from the partially deuterated compounds. The trans configuration (N1trans to N4 about the N2=C bond) was identified in all N4-monsubstituted and in a few N4-unsubstituted isothiosemicarbazones. The cis/trans ratios for the former varied depending on the solvent used.
Catalyzed Orientation Reversals in Diels–Alder Reactions
Authors: Stojanac Žarko , Dickinson Robert A. , Stojanac Nada , Woznow Ronald J. , Valenta Zdenek
Published: May 2006

Lewis acid catalysts cause an orientation reversal in the Diels–Alder additions of 2,6-di-methyl-1,4-quinone (1) and toluquinone (12) to 1-substituted 1,3-butadienes and to 1,2- and 1,3-dialkyl dienes. These results are explained by the preferential formation of one reactive quinone–Lewis acid salt.
Studies Related to Antitumor Antibiotics. Part III. Syntheses of 1,2,3,4,5,6-Hexahydro-2,3-benzazocin-5-ones as Possible Intermediates in the Biosynthesis of Mitomycins
Authors: Lown J. William , Itoh Tsuneo
Published: May 2006

The synthesis of 8-methoxy-9-methyl-N-p-toluenesulfonyl-1,2,3,4,5,6-hexahydro-2,3-benzazocin-5-one (23) and its conversion via transannular interaction to the 2,3-dihydro-lH-pyrrolo[1,2-a]indole ABC parent ring system of the antitumor antibiotic mitomycin C is described. The possible implication of this result in the biosynthesis of the mitosanes and the connection with the structurally and pharmacologically related pyrrolizidine alkaloids is discussed.
A Carbon-13 Nuclear Magnetic Resonance Study of Chlorinated and Polyol Analogs of Glucose and Related Oligomers
Authors: Colson Pierre , Slessor Keith N. , Jennings H. J. , Smith Ian C. P.
Published: May 2006

Complete assignments of the carbon-13 n.m.r. spectra of the following compounds in aqueous solution are presented: 6-chloro-6-deoxy-D-glucose, 6-O-methyl-D-glucose, ribitol, glucitol, 4-O-methyl-glucitol, maltose, maltitol, 6,6′-dichloro-6,6′-dideoxymaltose, 6′-chloro-6′-deoxy-maltose, isomaltose, isomaltitol, and 6′-chloro-6′-deoxyisomaltose. Some earlier assignments for maltose are reversed. Chlorination on the exocyclic carbon of the glucopyranose ring usually results in a substantial decrease in the chemical shift of the substituted carbon (−17 p.p.m.) and the next-nearest carbon (−1.2 p.p.m.); methylation leads to an increased chemical shift for the contiguous carbon (+10 p.p.m.) and only small changes for other carbons in the molecule. The response to 4-O-methylation in glucitol is opposite for C-3 (+0.7 p.p.m.) and C-5 (−0.8 p.p.m.) demonstrating that response of a particular carbon to substitution at a neighboring carbon depends upon the configuration of the particular carbon. Dissolution of these compounds in pyridine results in a bunching together of resonances which makes unambiguous assignments very difficult. The data for this series of compounds are useful in assigning the more complex spectra of microbial polysaccharides.
A Proton Magnetic Resonance Study of the Ultraviolet Photoproduct of d(TpT) in Aqueous Solution
Authors: Hruska Frank E. , Wood Donald J. , Ogilvie Kelvin K. , Charlton James L.
Published: May 2006

The p.m.r. data of d(TpT) and its predominant u.v. photoproduct d(T[p]T) in aqueous solution are compared. The data are consistent with the presence of a cis-syn cyclobutane ring in d(T[p]T). Consideration of the H1′ chemical shifts leads to the conclusion that changes in the sugar–base torsion angle of both nucleotide fragments of the parent molecule are required to bring the thymine bases into alignment for photodimerization. The coupling constants indicate that the conformation of the 5′-terminal fragment is only slightly affected by the cyclobutane ring formation. Photodimerization brings about a distortion of the sugar pucker in the 3′-terminal fragment. In this fragment both the gauche-gauche and gauche-trans conformers are significantly populated whereas the trans-gauche form is excluded.
Further Studies on the Assignment of Signals in 13C Magnetic Resonance Spectra of Aldoses and Derived Methyl Glycosides
Authors: Gorin Philip A. J. , Mazurek Mytosk
Published: May 2006

The 13C signals of most of the more common sugars and their methyl glycosides have been assigned, based on the α-carbon and β-carbon effects that occur on deuterium substitution. For pyranoses having the same hydroxyl configuration, replacement of the CH2OH substituent at C-5 with CH3, CO2H, CO2Me, or H is accompanied by displacement of the C-4, C-5, and when applicable C-6 signals. The magnitudes of the displacements in the glucopyranose and mannopyranose series are almost identical and were of aid in assigning signals in the 13C spectrum of methyl (methyl α-D-mannopyranuronosid)uronate. The displacements, however, differ from corresponding ones observed in the galactopyranose series. Some assignments are made for the 13C signals of structurally related methyl aldofuranosides.
Factor Analysis as a Complement to Band Resolution Techniques. III. Self Association in Trichloroacetic Acid
Authors: Bulmer J. T. , Shurvell H. F.
Published: May 2006

Digitized infrared spectra of nine solutions of trichloroacetic acid in CCl4 have been studied in the carbonyl stretching region. At all concentrations only two bands are visually apparent. However, factor analysis indicates the presence of four absorbing components. The contour resolution technique gives a monomer band at 1786 cm−1, a dimer band at 1749 cm−1, and a third band close to the dimer frequency at approximately 1735 cm−1. Examination of the changes in Cauchy–Gauss shape ratio of the monomer band with increasing concentration indicates the presence of an unresolved component. The band at 1735 cm−1 and the unresolved band near the monomer peak at 1786 cm−1 are assigned to absorption of carbonyl groups in linear polymers of trichloroaceticacid. The monomer–dimer equilibrium constant was calculated from the molar absorption coefficients and absorbances of monomer and dimer bands. The average value over the concentration range 0.305 × 10−3 to 0.1603 M was 287 l/mol at 33.9 ± 0.5 °C.
Thermodynamic Properties of Binary Liquid Acid–Base Mixtures
Authors: Sólimo Horacio N. , Riggio Roque , Davolio Franco , Katz Miguel
Published: May 2006

Viscosities, densities, refractive indices, and enthalpies at 25 °C were determined for the systems: propionic acid + aniline (PA + A ), propionic acid + N,N-dimethylaniline (PA + DMA ), and propionic acid + pyridine (PA + P). From the experimental results the excess volume, excess viscosity, excess molar free energy of activation, and excess enthalpy were calculated. The deviations from ideality for the excess thermodynamic functions are more important for the systems PA + A and PA + P than for PA + DMA. There is evidence for complex formation between propionic acid and aniline in the following molar relation: 2CH3CH2COOH·C6H5NH2.
Synthesis And Novel Stereochemical Results In The Lithium–Ammonia Reduction Of Some 4-Alkyl-Δ1(9)-2-octalones
Authors: Piers Edward , Phillips-Johnson Wynona M. , Berger Christian
Published: May 2006

The 4-alkyl-Δ1(9)-2-octalones 7–11, inclusive, prepared by conjugate addition of appropriate or ganocuprate reagents to the cross-conjugated dienones 13 and 14, were subjected to lithium–ammonia reduction. Interestingly, these reductions produced, in each case, a considerably higher proportion (13–35%) of the corresponding cis-fused 2-decalone (27–31, inclusive) as compared with that normally formed in the alkali metal – ammonia reduction of Δ1(9)-2-octalones. The results are qualitatively explained in terms of the proposals originally set forth by Robinson.
Substituent Effects of Phosphorus and Arsenic Containing Groups in Aromatic Substitution. IV. Nitration of Aromatic Phosphine Oxides
Authors: Malinski Edmund , Piekos Antonina , Modro Tomasz A.
Published: May 2006

The nitration of some tertiary phosphine oxides ArP(O)R2 in aqueous sulfuric acid has been investigated. All compounds studied react as conjugate acids. When the phosphinyl group is bonded directly to the benzene ring, high deactivation and meta-orientation is found, accompanied in most cases by some substitution at the ortho position. The substituent effects of the "quasiphosphonium" group P(OH)R2+are compared with those of structurally related systems and are discussed in terms of pπ–dπ, interactions of the oxygen and the phosphorus atom.
Agelasine: A Novel Quaternary 9-Methyladenine from the Sponge Agelasdispar
Authors: Cullen Ernest , Devlin John P.
Published: May 2006

The isolation of a novel quaternary 9-methyladenine from the sponge Agelasdispar is described. The constitution (1) is assigned on the basis of degradative and spectroscopic data.
Acid Catalyzed Rearrangements of Conjugated Cyclopropyl and Epoxy Ketones
Authors: Lee-Ruff E. , Khazanie P.
Published: May 2006

A series of spiro[n.2]alkan-2-ones and their 6 and 7 oxa derivatives were subjected to acid catalysis. In the former series, products arising from hydroxyl(cyclopropyl)carbinyl cations are observed, while in the latter series epoxide oxygen protonation appears to be the dominant reaction pathway. A novel oxavinylcyclopropane rearrangement is reported.
Entropy Production in Simple Chemical Reactions
Authors: Pritchard Huw O.
Published: May 2006

It is shown that entropy production appears to be a completely monotonic function of time for several chemical reactions or reaction sequences taking place in closed systems at constant temperature; however this monotonicity principle does not extend to autocatalytic or oscillatory processes. Where it occurs, the complete monotonicity of entropy production stems essentially from the completely monotonic behavior of the species number densities as functions of time in the evolution of the reaction.
Equilibria between Palladium(II) Acetate and Olefins in Acetic Acid containing Sodium Acetate
Authors: Pandey Raj N. , Henry Patrick M.
Published: May 2006

π-Complex equilibria between dimeric Pd(II) acetate and various olefins (ethylene, styrene, 3,3-dimethyl-1-butene, vinylic and allylic esters) in acetic acid solvent have been investigated by spectral means. The results indicate two π-complexes are formed. The first π-complex, which is formed rapidly, is a dimeric π-complex (ol = olefin ).[Formula: see text]The Benesi–Hildebrand plots for these complexes are linear for all olefins and thus values of Kπ22 can be readily evaluated. The values of the equilibrium coefficient, Kπ22, do not change with solution composition or [NaOAc]. The second π-complex is formed slowly. The data are consistent only with the equilibrium[Formula: see text]The data are inconsistent with the equilibrium[Formula: see text]which is analogous to that reported for the Na2Pd2Cl6 reaction with olefins in acetic acid. Furthermore, previous assumptions as to the equilibria between ethylene and Pd(II) in the all-acetate system have proved incorrect, and so the kinetics of oxidation of ethylene in this system must be reinterpreted in view of the present results.
The trans-Effect in Octahedral Complexes. VI. Base Hydrolysis of trans-Hydroxybromo and trans-Hydroxychlorobis(ethylenediamine)-rhodium(III) Complexes
Authors: Poë Anthony , Vuik Carol
Published: May 2006

The kinetics of base hydrolysis of the complexes trans-[Rh(en)2(OH)X]+ (X = Br or Cl) follow the pseudo first order rate equation kobs = k1 + k2[OH−]. The small contribution of the [OH−]-dependent term is due to lower values of ΔS2≠ − ΔS1≠ than are observed for the complexes cis-[Rh(en)2(OH)Cl]+ and [Rh(NH3)5X]2+ (X = Cl, Br, or I ). The values of ΔH1≠ are used to obtain new values of the intrinsickinetictrans-effect (i.k.t.e.) of hydroxide that agree with that determined from aquation of trans.-[Rh(en)2(OH)I]+ and place hydroxide in the i.k.t.e. series [Formula: see text] The new data also allow hydroxide to be placed in a thermodynamic trans-effect (t.t.e.) series I > OH > NH3 > Br > Cl > OH2, and the different position of hydroxide in the two series is discussed.
The 2- and 3-C-Methyl Derivatives of Methyl 2,3-Dideoxy-α-D-erythro-hex-2-enopyranosid-4-ulose
Authors: Hicks David Roy , Fraser-Reid Bert
Published: May 2006

The oxirane rings of carbohydrate 2,3-anhydro sugars are opened stereospecifically by lithium dimethyl cuprate. These reactions go in high yields, without the formation of abberant side products encountered with other organometallic reagents. The alcohols produced are converted via their xanthate esters to olefins in good overall yields. The latter on hydrolysis and oxidation give the title enones.
Conformations of Bridged Diphenyls. XIII. Crystal Structure of 2-(4′-Carbomethoxy-2′-nitrobenzoyl)-1,3,5-trimethylbenzene
Authors: van der Heijden Simon P. N. , Chandler W. David , Robertson Beverly E.
Published: May 2006

The structure of 2-(4′-carbomethoxy-2′-nitrobenzoyl)-1,3,5-trimethylbenzene, C18H17N05, has been determined by X-ray diffraction. The crystals are triclinic, a = 10.266(5), b = 7.672(5), c = 11.975(8) Å, α = 105.11(3), β = 100.08(3), γ = 111.50(3)°, [Formula: see text] with Z = 2. The integrated intensities of 3732 independent reflections were measured on a four circle diffractometer; 2784 of these reflections were used in the refinement to give a final least-squares weighted residual of 0.046 and a conventional R factor of 0.053.The molecule adopts the twist-nitro-proximal conformation similar to the conformation in the corresponding sulfoxide and sulfone. The angle subtended at the bridging carbon atom is 118.5(2)° and its bond lengths to phenyl carbon atoms are 1.502(2) and 1.503(2) Å.
The Use of the n-Propylammonium and n-Butylammonium Saltsof d-10-Camphorsulfonic Acid for the Calibration of Spectropolarimeters: Circular Dichrometer Calibration
Authors: Gillen Michael F. , Williams Ross E.
Published: May 2006

Two, easily prepared, nondeliquescent salts of d-10-camphorsulfonic acid have been used to improve the precision of the calibration of circular dichrometers.
Carbon-13 Nuclear Magnetic Resonance Studies of Compounds of the Vitamin B6 Group and Related Pyridine Derivatives
Authors: Lapper Roy D. , Mantsch Henry H. , Smith Ian C. P.
Published: May 2006

The I3C chemical shifts and 13C–31P spin–spin couplings (where applicable) are reported for pyridoxine, pyridoxamine, pyridoxal, pyridoxamine phosphate, and pyridoxal phosphate. Resonance assignments are made by consideration of substituent chemical shift effects, as tested on an analogous series of pyridine derivatives. Increased shielding of the C4′ and C5′ methylene groups of the vitamin B6 compounds and the methyl groups of 3,4-dimethylpyridine relative to the predicted values are attributed to steric compression. In aqueous solution pyridoxal exists as the hemiacetal form, although at high pH it is in rapid equilibrium with a significant amount of the aldehyde form. Pyridoxal phosphate exists as the aldehyde at high pH, as the hydrated aldehyde at low pH, and in a slow equilibrium between detectable amounts of both species at pH 4. The 13C–31P couplings through two bonds lie in the range 4.5 ± 0.5 Hz found for a variety of other organic phosphates. The couplings through three bonds indicate a preference for a trans arrangement of the phosphorus and ring carbon-5.
Theory of the Spin Hamiltonian Parameters for Low Spin Cobalt(II) Complexes
Authors: McGarvey B. R.
Published: May 2006

The theory for the spin Hamiltonian parameters of low spin cobalt(II), d7, complexes has been developed to third order in perturbation theory for all reasonable ground states. Two extensions beyond previous treatments have been made: (1) the spin–orbit mixing of excited quartet states into the doublet ground state has been considered and (2) configuration interaction involving mixing of [Formula: see text]orbitals in lower symmetry has been included. In the case of axial complexes a more complete calculation has been made to assess the errors incurred in only going to third order in perturbation theory. The theory has been applied to porphyrin and phthalocyanine complexes and is shown to adequately account for the observed data on these complexes. The excited quartet states are much higher in energy than the ground state for the four coordinate porphyrin complexes but become much lower in energy when basic adducts are complexed along the z axis. Further there is mixing of the 4s orbital with the [Formula: see text]orbital for the four coordinate complexes which is completely removed when basic adducts are complexed to the porphyrin system. Application of equations to lower symmetry complexes is considered and it is shown that is is difficult to make an unambiguous assignment of ground state on the basis of g and 59Co hyperfine splitting values alone, although the relative values of gy and gz do seem to provide some clue as to the correct ground state.
Kinetic Electron Spin Resonance Study of the Transfer of a Hydrogen Atom from α-Tetralin Hydroperoxide to a Tertiary Alkylperoxy Radical
Authors: Chenier J. H. B. , Howard J. A.
Published: May 2006

not available
Particle Motions in Sheared Suspensions. XXVIII. Configurations of Coiled Fibers in Shear Flow
Authors: Okagawa A. , Mason S. G.
Published: May 2006

The coiling of elastomer filaments in liquids undergoing shear flow was studied experimentally. In the steady state the rotating coils were stretched along the axes of flow and vorticity, compacted along the third orthogonal axis, and became progressively more entangled as the velocity gradient increased. Although the coils did not possess spherical symmetry, the distribution of end-to-end distances and maximum projected dimensions projected on a given axis or plane corresponded closely to random coiling statistics.
C Nuclear Magnetic Resonance Studies. Part 48. C Spectra of a Variety of Bicyclic Ketones
Authors: Grover S. H. , Marr D. H. , Stothers J. B. , Tan C. T.
Published: May 2006

not available