A kinetic study of the suprafacial [1,5]-sigmatropic phenyl rearrangements of 3,4-bis- (para-substituted)-1,2,5-triphenyl-2,4- cyclopentadien-1-ols to 3,4-bis-(para-substituted)-2, 2,5-triphenyl-3-cyclopenten-1-ones, where the substituent were, t-butyl, methyl, hydrogen, chloro and bromo, has been performed at 180, 190, 200 and 210 ± 0.2° in tetraethylene glycol. The rearrangement was observed to be first order throughout the temperature range investigated, and the rate constants (k) at the temperatures used were found to be 8.057, 2.143, 2.930 and 6.456 x 10⁻⁴ sec⁻¹ for the t-butyl substituent; 4 7.700, 2.110, 3.434, and 6.581 x 10⁻⁴ sec⁻¹ for the methyl substituent; 0.909, 2.166, 3.678 and 6.448 x 10⁻⁴ sec⁻¹ for the unsubstituted alcohol; 1.469, 2.992, 5.989 and 11.12 x 10⁻⁴ sec⁻¹ for the chloro substituent; and 1.955, 3.215, 6.215 and 13.01 x 10⁻⁴ sec⁻¹ for the bromo substituent, respectively. . Calculations of the activation energy of this phenyl [1,5]-sigmatropic shift from the Arrhenius equation give values of 28.71, 30.31, 28.01, 29.38 and 27.49 kcal·mol⁻¹ for the above substituents respectively, while ΔH^‡ these phenyl migrations were 27.78, 29.39, 27.93, 28.45 and 26.56 kcal·mol⁻¹ respectively. ΔS^‡ values were also calculated to be -16.6, -13.1, -16.1, -14.0 and -17.8 eu, respectively for a mean temperature range of 453-483 ± 0.2°K. The isokinetic temperature was calculated to be 320°. Calculated rho (ρ) values for the sigmatropic migrations were -0.813, -0.400, -0.690 and -0.658 at 180, 190, 200 and 210 ± 0.2°C. These results are used to discuss both the mechanism of this rearrangement and the transition state for rearrangements in the pentaphenylcyclopentadienol system. Ina much broader sense these results and the results of previously documented sigmatropic rearrangements exhibiting electronic influences were used to formulate a general scheme to predict the outcome of those sigmatropic rearrangements that entail an electronic effect as seen in the rates of the above reactions. This scheme used as its basis the transition state approach invoking inductive and mesomeric arguments to rationalize the observed rates of the sigmatropic rearrangements of this dissertation, those of previously documented sigmatropic rearrangements and finally to predict a relative rate of rearrangements in general. Finally a mass spectral investigation of the fragmentation patterns of 1-para-phenylsubstituted 2,3,4,5-tetraphenyl-2,4-cyclopentadien-l-ols and 3,4-bis(para-substituted phenyl)-1,2,5-triphenyl-2,4- cyclopentadien-1-ols was undertaken. A continuum of two super imposable pathways with the choice of the major decomposition mode being determined by the electron donating or withdrawing ability of the substit- vent was established. Linear free energy relationships for mass spectral decomposition were presented as well as a justification for this behavior. / Ph. D.

This dissertation focuses on the development of cyclopentadienes as an emerging class of compounds for use in catalysis. Previous work in the Lambert group had established pentacarboxycyclopentadienes (PCCPs) as a promising class of Brønsted acids capable of being used as catalysts in acid-promoted reactions. The ease of their synthesis distinguished them from the comparable BINOL-derived phosphoric acids, and their unique mode of enantioinduction created opportunities for their use in enantioselective reactions. Initial efforts were focused on the synthesis of leading to the development of two complementary methods for their synthesis. Chapter 2 details the improvements made to the transesterification of penta(methoxycarbonyl)cyclopentadiene, which allowed for sterically encumbered alcohols to be used. Further, a new method for accessing the penta-acyl chloride intermediate was developed, leading to the ability for a wide array of electron-deficient PCCPs to be synthesized. The second half of the dissertation examines the use of electrophilic silicon reagents and their use as Lewis acids. Given our ability to access highly electron-deficient cyclopentadienes, the silyl cyclopentadienes were targeted as potential Lewis acids. Chapter 4 details the synthesis of these species, and their characterization. Having established a convenient route to silyl mono(carboxy)tetracyanocyclopentadienides, we examined their use as catalysts in halide abstraction reactions. Benzylic bromides could be activated and subsequently allylated, or arylated with a nucleophilic arene using allyltrimethylsilane as a sacrificial silyl source.

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Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

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Typescript (photocopy) / 199 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1982

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1982. / Typescript (photocopy).

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C-H bonds are easily the most common type of ordinary chemical bond and studying carbon acidity will help us understand and predict the reactivity of organic compounds. Carbon acidities are ranked using acidity scales. One of the most prominent is the Streitwieser Lithium Indicator (SLI) scale. The term "indicator scale" implies that acids have been measured against one another in sequential fashion. The SLI scale uses lithium ion as the conjugate-base counterion and THF as the solvent. Historically, the SLI scale has emphasized the characterization of weakly-acidic hydrocarbons. Prior to the work of our group, the strongest acid on the SLI scale has a pK value of about 10. Deck and Thornberry extended the scale to ca. pK = 0 by evaluating 23 perfluoroaryl-substituted cyclopentadiene and indene derivatives, using 19F NMR spectroscopy to determine the equilibrium constants of sequential acid-base reactions. This thesis describes the further extension of the SLI scale to ca. pK = −6. To achieve this result, a set of 11 tetrasubstituted cyclopentadienes were synthesized and their acidities evaluated sequentially with the goal of reaching a low pK value while minimizing the acidity ratio at each incremental step. The four ring substituents were combinations of pentafluorophenyl, perfluoro-4-tolyl, and perfluoro-4-pyridyl, electronegative groups listed in order of increasing electron-withdrawing power. The most acidic compound in the set was 1-pentafluorophenyl-2,3,4-tetrakis(tetrafluoro-4-pyridyl)cyclopentadiene, having pK = −5.99. Trends in the acidities of tetraarylcyclopentadienes are discussed including relative electron-withdrawing power of the three selected substituents, and conformational effects among pairs of regioisomeric cyclopentadiene derivatives. / Master of Science / Carbon acidity refers to the willingness of a carbon-hydrogen bond to release a hydrogen ion. C-H bonds are easily the most common type of ordinary chemical bond, so it makes sense that studying carbon acidity will help us understand and predict the reactivity of organic compounds. For the past several decades, emphasis in this area of research has focused on weak carbon acids, especially the simplest hydrocarbons like benzene and methane. This thesis aims in the opposite direction of synthesizing and measuring stronger and stronger carbon acids until we reach the theoretical limit for a given solvent. Because our research strategy is inherently incremental, compounds were synthesized and their acidities were measured, drawing close to the theoretical limit using tetrahydrofuran as the solvent.