SYNTHESIS AND INVESTIGATIONS OF 1,5 ANNULATED SEMIBULLVALENES (X-RAY CRYSTALLOGRAPHY).
Item
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Title
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SYNTHESIS AND INVESTIGATIONS OF 1,5 ANNULATED SEMIBULLVALENES (X-RAY CRYSTALLOGRAPHY).
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Identifier
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AAI8801722
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identifier
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8801722
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Creator
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IYENGAR, REVATHI.
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Contributor
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Klaus Grohmann
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Date
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1987
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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A new synthetic scheme was developed for annulating five-, six-, seven-, and eight membered rings at positions 1 and 5 of the 2,4,6,8-tetracarbomethoxy semibullvalene. The previously synthesized 1,5-dimethyl-2,4,6,8- tetrakis (carbomethoxy) semibullvalene rearranges at 5{dollar}\sp\circ{dollar}C (in solution) to the corresponding cyclooctatetraene. The activation energy for this process is 25 Kcal/mole, significantly lower than for the parent compound. None of the annulated semibullvalenes undergo the analogous rearrangement even on heating up to 200{dollar}\sp\circ{dollar}C. However, the 1,5 cyclopentano and the 1,5 cyclohexano compounds absorb oxygen in both the solid state and in solution yielding well defined endoperoxides. None of the other compounds show an analogous reaction with oxygen. The X-ray structure determination of the 1,5 cyclohexano compound shows bond elongation of C2-C8 to 1.83 A and a slight decrease in the non-bonded C4-C6 distance (2.19 A) indicating the approach towards the symmetric transition state. The X-ray structure of the 1,5 cyclooctano compound however exhibited a degree of symmetry in the semibullvalene part of the molecule, with C4-C6 = C2-C8 = 1.99 A, and C2-C3 = C3-C4 = C6-C7 = C7-C8 = 1.387 A. The free energy of activation for the Cope rearrangement in the 1,5 cyclohexano compound has been estimated to be 3.8 {dollar}\pm{dollar} 0.4 Kcal/mole at {dollar}-160\sp\circ{dollar}C. The room temperature CPMAS C-13 spectrum of the cyclooctano compound exhibited an averaged nmr spectrum for carbons 2,4,6, and 8. These results in combination with the X-ray data imply that the 1,5 cyclooctano compound is a neutral bishomoaromatic molecule. An alternative interpretation of dynamic behaviour in the solid state cannot be ruled out yet and further experiments such as low temperature solid state NMR studies need to be carried out.;A different approach was utilized towards the synthesis of 1,5-cyclopropa-2,6- dicyano semibullvalene starting from naphthalene. This route has so far led to bicyclo(3.3.0) deca-2,6-dicyano-2,6-diene, 37 (refer text). All attempts to generate the dianion of 37 have been unsuccessful. To assess the effect of an electron donor in positions 1 and 5 on the Cope rearrangement in semibullvalenes, MNDO studies have been carried out on the 1,5-dianion and 1,5allyl bridged (cation, anion, and radical) semibullvalenes.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Chemistry
