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Carboxylic Acid to Thioamide Hydrogen Bonding
Suchitra Datta1, David A Lightner
1Department of Chemistry, University of Nevada, Reno, Nevada 89557.
Tetrahedron
|January 6, 2010
Summary
Dipyrrinones form strong amide-amide dimers, while thioamides form weaker ones. Introducing a carboxylic acid promotes intramolecular bonding in dipyrrinones but not in thioamides, which favor intermolecular thioamide dimers.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Hydrogen Bonding
Background:
- Dipyrrinones are known to form stable dimeric complexes through amide-amide hydrogen bonding in nonpolar solvents.
- Thioamides, derived from lactams, exhibit different hydrogen bonding characteristics compared to their oxygen counterparts.
Purpose of the Study:
- To investigate and compare the hydrogen bonding behavior of dipyrrinones and their corresponding dipyrrinthiones.
- To explore the influence of tethered carboxylic acid groups on the self-assembly of these molecules.
Main Methods:
- Synthesis of dipyrrinthiones using Lawesson's reagent.
- Spectroscopic analysis including NMR spectroscopy.
- Vapor pressure osmometry to determine association constants.
Main Results:
- Dipyrrinones form strong dimers (K(D) ~25,000 M(-1)) via amide-amide hydrogen bonds.
- Dipyrrinthiones form weaker dimers (K(D) ~200 M(-1)) through thioamide-thioamide hydrogen bonds.
- Tethering a carboxylic acid to dipyrrinone ([6]-semirubin) induces strong intramolecular hydrogen bonding, preventing dimer formation.
- The analogous [6]-thiosemirubin derivative favors intermolecular thioamide-thioamide dimer formation over intramolecular interactions.
Conclusions:
- The strength of hydrogen bonding in dipyrrinone derivatives is highly dependent on the presence of oxygen (lactam) versus sulfur (thioamide) in the amide group.
- Intramolecular hydrogen bonding can be favored in dipyrrinones by appropriate functionalization, altering self-assembly behavior.
- Dipyrrinthiones exhibit a propensity for intermolecular self-assembly, even in the presence of functional groups that would promote intramolecular interactions in their lactam analogs.
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