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  • Organic Chemistry  (6)
  • Lunar and Planetary Exploration  (5)
  • 1995-1999  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810208
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  • 2
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    Electronic Resource
    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VIPart V: [1] Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro- Decacarbonyl{μ-[1,1-bis(methylthio-χS)ethane]}tetrairidium ([Ir4(CO)10-(μ2-(MeS)2CHMe)]), tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{ethylidenebis- [diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-(Ph2P)2CHMe)]), and tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{propane-1,3-diylbis[diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-Ph2P(CH2)3PPh2)]) (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 781-791 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The disubstituted clusters[Ir4(CO)10(μ2-L—L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L—L = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (L—L = (Ph2P)2CHMe, cluste 2; L—L =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1-3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810328
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  • 3
    Electronic Resource
    Electronic Resource
    The Diels-Alder Reactivity of 2,2′-Ethylidenebis[3,5-dimethylfuran] and Exploratory Chemistry of the Mono-adducts (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1415-1427 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of Me3Al, 1-cyanovinyl acetate added to 2,2′-ethylidenebis[3,5-dimethylfuran] (1) to give a 20:10:1:1 mixture of mono-adducts 4,5,6, and 7 resulting from the same regiocontrol (‘para’ orienting effect of the 5-methyl substituent in 1). The additions of a second equiv. of dienophile to 4-7 were very slow reactions. The major mono-adducts 4 (solid) and 5 (liquid) have 2-exo-carbonitrile groups. The molecular structure of 4(1RS,1′RS,2SR,4SR)-2-exo-cyano-4-[1-(3,5-dimethylfuran-2-yl)ethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate) was determined by X-ray single-crystal radiocrystallography. Mono-adducts 4 and 5 were saponified into the corresponding 7-oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1RS,1′SR,4RS,5RS,6RS)-4-[1-(3,5-dimethyl furan-2-yl)ethyl]-6-exo-methoxy-1,5-endo-dimethyl-7-oxabicyclo [2.2.1]heptan-2-one dimethyl acetal (12) and its (1′RS-stereoisomer 12a, respectively. Acetal hydrolysis of 12a followed by treatment with (t-Bu)Me2SiOSO2CF3 led to silylation and pinacol rearrangement with the formation of (1RS,1′RS,5RS,6RS)-4-[(tert-butyl)dimethy lsilyloxy]-1-(3,5-dimethylfuran-2-yl)ethyl]-5-methoxy-6-methyl-3-methylidene- 2-oxabicyclo[2.2.1]heptane (16). In the presence of Me3Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1RS,1′RS,2″RS,3″RS,4SR,4″RS,5 SR,6SR)-dimethyl 5-exo-hydroxy-4,6-endo-dimethyl-1-[1-(3-exo,5,5-trimeth oxy-2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-2-yl)ethyl]-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate (20). Acetylation of alcohol 20 followed by C=C bond cleavage afforded (1′RS,1″SR,2RS,2′″SR,3RS, 3″SR,4RS,4″SR,5RS)-dimethyl {3-acetoxy-2,3,4,5-tetrahydro-2,4-dimethyl-5-[1-(3-exo,5,5-trimethoxy -2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-1-yl)-ethyl]furan-2,5-diyl} bis[glyoxylate] (24).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790514
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  • 4
    Electronic Resource
    Electronic Resource
    Hetero-Diels-Alder Additions of α,β-Unsaturated-Acyl Cyanides. Part 3Part 1: [7], part 2: [8].. Syntheses of 3-bromo-2-ethoxy-3,4-dihydro-2H-pyran-6-carbonitriles, and about their transformation to 2-ethoxy-2H-pyrans (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 151-164 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of the α,β-unsaturated-acyl cyanides 1-3 with (Z)-or (E)-1-bromo-2-ethoxyethene (4) may be performed at moderate temperatures and provide in good yields the 3-bromo-2-ethoxy-3,4-dihydro-2H-pyran-6-carbonitriles 5-7, respectively (Scheme 1). Diastereoisomeric pairs of products result at room temperature merely from the ‘endo’- and ‘exo’-transition states; more complex mixtures appear above 60° as a consequence of (Z)/(E)-isomerization of 4. The relative stability of the anomers of 5 and 6 is explored by treatment with BF3·Et2O. Acid alcoholysis (MeOH or EtOH) of 5 leads to acetals 9a, b of 4-bromo-5-oxopentanoate. Alkyl (2Z,4E)-5-ethoxypenta-2,4-dienoates 12, 17, and 20, are formed in alcoholic alkoxide solutions from 5, 6, and 7, respectively, which is compatible with the intermediacy of 2-alkoxy-2H-pyrans and their valence tautomers, α,β-unsaturatedacyl cyanides. Methoxide addition to the CN group competes with dehydrobromination in case of 5; it leads to 3-bromo-3,4-dihydro-2H-pyran-6-carboximidate 13 (ca. 50% at -20°) which can be hydrolyzed to the methyl carboxylate 14. DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) in benzene converts 5 to 6-ethoxy-2-oxohexa-3,5-dienenitrile (11), the ring-opening product of an obviously unstable 2-ethoxy-2H-pyran; the same reagent dehydrobrominates 6 to 2-ethoxy-4-methyl-2H-pyran-6-carbonitrile (15). HBr Elimination from 7 takes place with great ease in presence of pyridine, or even during chromatography on alumina, and leads to the stable ethyl 6-cyano-2-ethoxy-2H-pyran-4-carboxylate (18); this dimerizes at room temperature to give a 1:3 mixture of tricyclic adducts ‘endo’-21 and ‘exo’-21. The structure of the latter is established by an X-ray crystallographic analysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780115
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  • 5
    Electronic Resource
    Electronic Resource
    NMR of Enaminones. Part 7Part 6: [l]. The general name enaminone is used for compounds containing the O=C—C=C—N moiety. 1H-, 13C-, and 17O-NMR and X-ray structure determinations of 1,2-disubstituted conjugated 3-[(tert-Butyl)amino]enones (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2137-2147 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-, 13C-, and 17O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)=CHNH(t-Bu) (1), EtC(O)C(Me)=CHNH(t-Bu) (2), PhC(O)C(Me)=CHNH(t-Bu) (3), and MeC(O)C(Me)=CHNH(t-Bu) (4) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,1,N-anti conformations A and B, respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the 17O-NMR spectrum by intramolecular H-bonding (ΔλHB) ranging from -28 to -41 ppm, depends on the substituents at C(l) and C(2). Crystals of 3 at 90 K are monoclinic. with a = 9.618(2) Å, b = 15.792(3) Å, c = 16.705(3) Å, and β = 94.44(3)°, and the space group is P21/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) Å, b = 8.637(6) Å, c = 11.024(7) Å, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800713
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  • 6
    Electronic Resource
    Electronic Resource
    Structure-odor correlation, XXIPart XX: P. Weyerstahl, K. Licha, H. Marschall, Liebigs Ann. Chem. 1994, 917-920.. Olfactory properties and convenient synthesis of furans and thiophenes related to rose furan and perillene and their isomersDedicated to Prof. Dr. Herbert Schumann on the occasion of his 60th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1849-1853 
    Details
    ISSN: 0947-3440
    Keywords: Rose furan ; Perillene ; Furans ; Thiophenes ; Structure-odor correlation ; Odoriferous substances ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from 3-bromofuran (1) or 3-bromothiophene (2) via alkylation in 2-position (→ 3-8) followed by the corresponding second alkylation in 3-position, we obtained rose furan (9), rose thiophene (10), and their analogs 11-16. From the α,β-unsaturated esters 17-20 by hydrogenation (→ 21-24), DIBAH reduction (→ 25-28), and Wittig reaction, perillene (29), thioperillene (30), and their analogs 29-36 were obtained. Olfactory evaluation showed that the difference between the furans and thiophene derivatives is remarkably small, particularly for perillene (29) compared with thioperillene (30), and their analogs. Also the influence of position and structure of the side chain is lower than expected within the compared compounds 9-36.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199510259
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  • 7
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    Volcanic Constructs on Ganymede and Enceladus: Topographic Evidence from Stereo Images and Photoclinometry (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-16
    Description: The morphology of volcanic features on Ganymede differs significantly from that on the terrestrial planets. Few if any major volcanic landforms, such as thick flows or shield volcanoes, have been identified to date. Using new stereo Voyager images, we have searched Ganymede for relief-generating volcanic constructs. We observed seven major types of volcanic structures, including several not previously recognized. The oldest are broad flat-topped domes partially filling many older craters in dark terrain. Similar domes occur on Enceladus. Together with smooth dark deposits, these domes indicate that the volcanic history of the dark terrain is complex. Bright terrain covers vast areas, although the style of emplacement remains unclear. Smooth bright materials embay and flood older terrains, and may have been emplaced as low- viscosity fluids. Associated with smooth bright material are a number of scalloped-shaped, semi- enclosed scarps that cut into preexisting terrain. In planform these structures resemble terrestrial calderas. The youngest volcanic materials identified are a series of small flows that may have flooded the floor of the multiring impact structure Gilgamesh, forming a broad dome, The identification of volcanic constructs up to I km thick is the first evidence for extrusion of moderate-to-high viscosity material on Ganymede. Viscosity and yield strength estimates for these materials span several orders of magnitude, indicating that volcanic materials on Ganymede have a range of compositions and/or were extruded under a wide range of conditions and/or eruptive styles.
    Keywords: Lunar and Planetary Exploration
    Type: NASA-CR-205163 , NAS 1.26:205163 , Paper-95JE01854 , LPI-Contrib-863 , Journal of Geophysical Research (ISSN 0148-0227); 100; E9; 19,009-19,022
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  • 8
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    The Geology of Callisto (1995)
    In:  CASI
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    Publication Date: 2019-08-15
    Description: The geology of Callisto is not boring. Although cratered terrain dominates Callisto (a key end-member of the Jovian satellite system), a number of more interesting features are apparent. Cratered terrain is broken into irregular map-able bright and dark subunits that vary in albedo by a factor of 2, and several relatively smooth units are depleted of small craters. Some of these areas may have been volcanically resurfaced. Lineaments, including parallel and radial sets, may be evidence for early global tectonism. Frost deposition occurs in cold traps, and impact scars have formed from tidally disrupted comets. Geologic evidence suggests that Callisto does have a chemically differentiated crust. Central pit and central dome craters and palimpsests are common. The preferred interpretation is that a relatively ice-rich material, at depths of 5 km or more, has been mobilized during impact and exposed as domes or palimpsests. The close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of Callisto may be as differentiated as on Ganymede. The geology of cratered terrain on Callisto is simpler than that of cratered terrain on Ganymede, however. Orbital evolution and tidal heating may provide the answer to the riddle of why Callisto and Ganymede are so different (Malhotra, 1991). We should expect a few surprises and begins to answer some fundamental questions when Callisto is observed by Galileo in late 1996.
    Keywords: Lunar and Planetary Exploration
    Type: NASA-CR-205300 , NAS 1.26:205300 , LPI-Contrib-864 , Paper-95JE01855 , Journal of Geophysical Research (ISSN 0148-0227); 100; E9; 19,023-19,040
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  • 9
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    Cometary Nuclei and Tidal Disruption: The Geologic Record of Crater Chains on Callisto and Ganymede (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: Prominent crater chains on Ganymede and Callisto are most likely the impact scars of comets tidally disrupted by Jupiter and are not secondary crater chains. We have examined the morphology of these chains in detail in order to place constraints on the properties of the comets that formed them and the disruption process. In these chains, intercrater spacing varies by no more than a factor of 2 and the craters within a given chain show almost no deviation from linearity (although the chains themselves are on gently curved small circles). All of these crater chains occur on or very near the Jupiter-facing hemisphere. For a given chain, the estimated masses of the fragments that formed each crater vary by no more than an order of magnitude. The mean fragment masses for all the chains vary by over four orders of magnitude (W. B. McKinnon and P. M. Schenk 1995, Geophys. Res. Lett. 13, 1829-1832), however. The mass of the parent comet for each crater chain is not correlated with the number of fragments produced during disruption but is correlated with the mean mass of the fragments produced in a given disruption event. Also, the larger fragments are located near the center of each chain. All of these characteristics are consistent with those predicted by disruption simulations based on the rubble pile cometary nucleus model (in which nuclei are composed on numerous small fragments weakly bound by self-gravity), and with those observed in Comet D/Shoemaker-Levy 9. Similar crater chains have not been found on the other icy satellites, but the impact record of disrupted comets on Callisto and Ganymede indicates that disruption events occur within the Jupiter system roughly once every 200 to 400 years.
    Keywords: Lunar and Planetary Exploration
    Type: NASA-CR-204594 , NAS 1.26:204594 , LPI-Contrib-886 , ICARUS: Article No. 0084 (ISSN 0019-1035); 121; 249-274
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  • 10
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    Topography of the South Polar Cap and Layered Deposits of Mars: Viking Stereo Grametry at Regional and Local Scales (1998)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: Layered deposits and residual polar caps on Mars may record the deposition of ice and sediment modulated by periodic climate change. Topographic information relating to layer thicknesses, erosional processes, and formation of dark spirals within these deposits has been sparce or unreliable until the arrival of MOLA in orbit in September 1997. To assist in evaluating these terrains prior to launch and to assess formation and erosion processes in the polar deposits, we have assembled Viking stereo mosaics of the region and have produced the first reliable DEM models of the south polar deposits using automated stereogrammetry tools. Here we report our preliminary topographic results, pending final image pointing updates. The maximum total thickness of the layered deposits in the south polar region is 2.5 km. The thick layered deposits consist of a series of megaterraces. Each terrace is several tens of kilometers wide and is flat or slopes very gently toward the pole. These terraces step downward from a central plateau near the south pole. Terraces are bounded by relatively steep scarps 100-500 meters high that face toward the equator. These scarps correspond to the pattern of dark spirals observed within the residual cap in southern summer, and are interpreted as ice or frost-free surfaces warmed by solar insolation. Several tongue-shaped troughs, with rounded cirquelike heads, are observed near the margins of the deposit. These troughs are 300-600 meters in deep and may be similar to troughs observed in the northern polar deposit.
    Keywords: Lunar and Planetary Exploration
    Type: The First International Conference on Mars Polar Science and Exploration; 32; LPI-Contrib-953
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