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Hydrogen bonding in Schiff bases--NMR, structural and experimental charge density studies
Anna Makal1, Wojciech Schilf, Bohdan Kamieński
1Department of Chemistry, University of Warsaw, Pasteura 1, 02-093, Warszawa, Poland.
Dalton Transactions (Cambridge, England : 2003)
|November 27, 2010
Summary
This study investigated Schiff bases, revealing how substituents and linker length influence hydrogen bonding. While OH tautomers dominate in solution, NH forms prevail in solid states, with specific exceptions noted for nitro and bromo derivatives.
Area of Science:
- Supramolecular Chemistry
- Organic Chemistry
- Computational Chemistry
Background:
- Schiff bases, derived from salicylaldehydes and aryl amines, are versatile molecules with potential for diverse applications.
- Hydrogen bonding plays a crucial role in molecular recognition and material properties.
- Understanding the factors influencing hydrogen bond formation is essential for designing novel functional materials.
Purpose of the Study:
- To investigate the impact of substituents and linker length on hydrogen bonding in Schiff bases.
- To elucidate the tautomeric preferences (OH vs. NH) in different phases (solution and solid-state).
- To characterize the nature and strength of intra- and intermolecular hydrogen bonds using experimental charge density analysis.
Main Methods:
- Synthesis and characterization of sixteen Schiff base derivatives.
- (15)N and (13)C Nuclear Magnetic Resonance (NMR) spectroscopy to study tautomerism.
- Experimental charge density investigations to analyze hydrogen bond properties.
Main Results:
- All studied Schiff bases formed six-membered chelate rings via traditional hydrogen bonds.
- OH tautomer is generally favored in solution, while NH tautomer dominates in the solid state, with exceptions for nitro and 5-Br derivatives.
- Experimental charge density analysis revealed significant differences in the strength and characteristics of intramolecular hydrogen bonds, with one being strong and the other weak.
Conclusions:
- The substituent and phase significantly influence the hydrogen bonding and tautomeric equilibrium in Schiff bases.
- The strength and nature of hydrogen bonds can be precisely characterized using charge density methods.
- This study provides valuable insights into the structure-property relationships of Schiff bases, aiding in the design of molecules with tailored hydrogen bonding characteristics.
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