Application of Deuterium Isotope Effects on NMR Parameters as a Method of Intramolecular Hydrogen Bond Characterization in Enolic Forms of 1,3-diketones in the Solid State

• Author / Creator

  Matlinska, Maria A.

• The application of deuterium isotope effects on 13C NMR chemical shifts to study the
  nature of intramolecular hydrogen bonding in the enolic forms of two 1,3-diketones,
  tetraacetylethane (TAE) and avobenzone, in the solid state is reported. Carbon-13 NMR spectra
  of natural abundance TAE and deuterium-labelled TAE (TAE-OD) obtained at room temperature
  show a deuterium shift of 1.0 ppm on one of the two enolic carbon nuclei. The deuterium isotope
  effect of 2.4 ppm at 163 K is reported. The position of the enolic hydrogen is determined as
  favoring one side on the molecule, confirming the asymmetric nature of the hydrogen bond. This
  finding is consistent with variable temperature neutron diffraction data, which is one of the most
  reliable methods of hydrogen position determination.
  In case of avobenzone, the apparent deuterium isotope effect on the enolic carbon on the
  tert-butyl side of the molecule is 1.3 ppm at room temperature and 2.0 ppm at 185 K. This is the
  largest deuterium isotope effect on carbon chemical shifts reported so far in the literature for
  enolic forms of 1,3-diketones. Moreover, variable temperature 13C spectra show temperaturedependent line shapes, indicating unusual intramolecular dynamics i.e., rapid flips of the
  methoxybenzene fragment of the molecule. This allowed to estimate the energy barrier of the
  methoxybenzene ring rotation that was found to be approximately 57 kJ mol-1
  .
  The experimental data supplemented by computational results indicates how a distinct
  behavior of the enol-bound carbon allows the determination of the position of the hydrogen in
  the keto-enol part of the molecule. The research presented in this thesis illustrates the application
  of deuterium isotope effects on 13C NMR parameters in the characterization of hydrogen bonding
  in the solid state. This thesis offers a distinctive insight into measuring NMR deuterium isotope
  effects on carbon-13 nuclei in the solid state, filling a substantial gap in the current literature.

• Subjects / Keywords

  • solid-state
  • NMR
  • Deuterium Isotope Effects
  • C-13 NMR
  • 1,3-diketones
  • hydrogen bonding in solids

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-fd8t-cj12

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.