Solvophobically-Driven Folding of Non-Biological Oligomers and the Solid Phase Synthesis of Phenylacetylene Oligomers
Nelson, James Curtis
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https://hdl.handle.net/2142/84387
Description
Title
Solvophobically-Driven Folding of Non-Biological Oligomers and the Solid Phase Synthesis of Phenylacetylene Oligomers
Author(s)
Nelson, James Curtis
Issue Date
1997
Doctoral Committee Chair(s)
Moore, Jeffrey S.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Polymer
Language
eng
Abstract
The ordered sequence of monomers in phenylacetylene oligomers can serve as a repeating motif to produce helical structures in solution which posses a tubular cavity. Calculations with modest size oligomers show stable helical conformations with as few as 8 monomer units. Oligomers with triglyme monomethyl ether benzoate functionalized monomers (R = -COO(CH$\rm\sb2CH\sb2O)\sb3CH\sb3)$ reveal dramatic chain-length-dependent aromatic chemical shifting in CD$\sb3$CN, indicative of aromatic stacking and helical structure. In addition. when chain length reaches 12 monomer units, oligomers begin to strongly aggregate which may be a result of helical oligomers associating like their corresponding macrocycles in a face-to-face parallel fashion. Chain length dependence of UV/Vis and $\sp1$H NMR spectra provide strong evidence of the ordering of monomers and intramolecular aromatic stacking which is consistent with the formation of helical structures. Using UV/Vis absorption at 303 nm as an indication of helical structure, reversible thermal helix-coil transitions were measured in 4/6, $\rm CH\sb3CN/CHCl\sb3.$ In agreement with the calculations, the octadecamer possesses the largest shift in $\rm\delta\sb{A},$ the best resolved $\sp1$H NMR spectra of the oligomers longer than 12 monomers, and the largest hypochromic shift at 303 nm which is attributed to intramolecular aromatic stacking.
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