Related Experiment Videos
Using Hydrogen Bonding to Control Carbamate C-N Rotamer Equilibria
Alexei L. Moraczewski1, Laura A. Banaszynski, Aaron M. From
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46656.
The Journal of Organic Chemistry
|October 24, 2001
Summary
Hydrogen bonding significantly influences molecular conformation. Specific interactions stabilize certain rotamers in carbamates, impacting their hydrogen bond accepting capabilities due to steric and electrostatic factors.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Computational Chemistry
Background:
- Carbamates exist as syn and anti rotamers, influencing their chemical properties.
- Hydrogen bonding interactions play a crucial role in stabilizing specific molecular conformations.
Purpose of the Study:
- To investigate the effect of different hydrogen bond donors on the syn/anti rotamer ratios of N-(2-pyridyl)carbamates and N-phenylcarbamates.
- To understand the factors governing hydrogen bond acceptor strength in different rotameric states.
Main Methods:
- Spectroscopic analysis (NMR) to determine syn/anti rotamer ratios in chloroform solution.
- Titration experiments to quantify hydrogen bonding interactions and determine binding constants (K(a)).
Main Results:
- Acetic acid moderately stabilized the syn rotamer of N-phenylcarbamates but not N-(2-pyridyl)carbamates.
- A 2,6-bis(octylamido)pyridine triad strongly stabilized the syn rotamer of N-(2-pyridyl)carbamates.
- The binding affinity (K(a)) for the syn rotamer of N-(2-pyridyl)carbamate with the pyridine triad was significantly higher (10^3-10^4 times) than for the anti rotamer.
Conclusions:
- The study highlights the differential impact of hydrogen bonding on carbamate rotamer stability.
- Steric and electrostatic factors dictate the hydrogen bond acceptor efficiency of alkoxy and carbonyl oxygens in different rotameric forms.