Ussing, Bryson Richard (2006-12). Systematic examination of dynamically driven organic reactions via kinetic isotope effects. Doctoral Dissertation. Thesis uri icon

abstract

  • Organic reactions are systematically examined experimentally and theoretically to determine the role dynamics plays in the outcome of the reaction. It is shown that trajectory studies are of vital importance in understanding reactions influenced by dynamical motion. This dissertation discusses how a combination of kinetic isotope effects, theoretical calculations, and quasiclassical dynamics trajectories aid in the understanding of the solvolysis of p-tolyldiazonium cation in water, the cycloadditions of cyclopentadiene with diphenylketene and dichloroketene, and the cycloaddition of 2- methyl-2-butene with dichloroketene. In the solvolysis of p-tolyldiazonium cation, significant 13C kinetic isotope effects are qualitatively consistent with a transition state leading to formation of an aryl cation, but on a quantitative basis, the isotope effects are not adequately accounted for by simple SN1 heterolysis to the aryl cation. The best predictions of the 13C isotope effects for the heterolytic process arise from transition structures solvated by clusters of water molecules. Dynamic trajectories starting from these transition structures afford products very slowly. The nucleophilic displacement process for aryldiazonium ions in water is determined to be at the boundary of the SN2Ar and SN1 mechanisms. The reaction of cyclopentadiene with diphenylketene affords both [4 + 2] and [2 + 2] cycloadducts directly. This is surprising. There is only one low-energy transition structure for adduct formation. Investigation of this reaction indicates that quasiclassical trajectories started from a single transition structure afford both [4 + 2] and [2 + 2] products. Overall, an understanding of the products, rates, selectivities, isotope effects, and mechanism in these reactions requires the explicit consideration of dynamic trajectories.
  • Organic reactions are systematically examined experimentally and theoretically to
    determine the role dynamics plays in the outcome of the reaction. It is shown that
    trajectory studies are of vital importance in understanding reactions influenced by
    dynamical motion. This dissertation discusses how a combination of kinetic isotope
    effects, theoretical calculations, and quasiclassical dynamics trajectories aid in the
    understanding of the solvolysis of p-tolyldiazonium cation in water, the cycloadditions
    of cyclopentadiene with diphenylketene and dichloroketene, and the cycloaddition of 2-
    methyl-2-butene with dichloroketene.
    In the solvolysis of p-tolyldiazonium cation, significant 13C kinetic isotope effects
    are qualitatively consistent with a transition state leading to formation of an aryl cation,
    but on a quantitative basis, the isotope effects are not adequately accounted for by simple
    SN1 heterolysis to the aryl cation. The best predictions of the 13C isotope effects for the
    heterolytic process arise from transition structures solvated by clusters of water
    molecules. Dynamic trajectories starting from these transition structures afford products very slowly. The nucleophilic displacement process for aryldiazonium ions in water is
    determined to be at the boundary of the SN2Ar and SN1 mechanisms.
    The reaction of cyclopentadiene with diphenylketene affords both [4 + 2] and [2 +
    2] cycloadducts directly. This is surprising. There is only one low-energy transition
    structure for adduct formation. Investigation of this reaction indicates that quasiclassical
    trajectories started from a single transition structure afford both [4 + 2] and [2 + 2]
    products. Overall, an understanding of the products, rates, selectivities, isotope effects,
    and mechanism in these reactions requires the explicit consideration of dynamic
    trajectories.

publication date

  • December 2006