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Concentration dependent ¹H-NMR chemical shifts of quinoline derivatives

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Adam Beck (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Paulo Almeida

Abstract: Quinolines are an important group of heterocyclic compounds that are found in many biologically active natural products and synthetic molecules. The non-exchangeable hydrogens of quinolines have been shown to have unusual concentration dependent chemical shift changes in 1H-NMR studies. It is proposed that these changes are due to dipole-dipole and p-p interactions between two or more quinolines. The approach used to investigate the inter- and intramolecular p-p interactions of the quinoline protons in solution was to synthesize quinoline monomers and dimers substituted at the 6 and 8 positions and compare their concentration dependent chemical shifts of their aromatic protons. The quinoline dimers with C3, C6 and C10 tethers were evaluated with respect to the substitution location, length of tether and functional group attaching the tether and the quinoline ring. The concentration dependent chemical shifts (?d/?C) of the quinoline protons on the 6-substituted diquinoline diesters were smaller than those of the equivalent 6-monoesters. However, the 8-substituted diquinoline diesters had similar chemical shifts compared to the 8-monoesters. This data is consistent with the 6-substituted dimers being able to stack intramolecularly in an anti-parallel conformation. The ?d/?C of the 6-substituted diethers and the 8-substituted diethers were similar to their respective 6 and 8-substituted monoethers. This shows that while the position of the substituent contributes to interand intramolecular interactions, it is not the only determining factor. The 6-substituted monoethers supported p – p stacking in an anti-parallel conformation with longer ether linkages creating more steric interference. The 8-substituted monoethers also supported p – p stacking in an anti-parallel conformation with longer ether linkages hindering intermolecular lateral movement between rings.

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Heterocyclic compounds, Quinoline
Heterocyclic compounds