| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| Title
| - Intramolecular Hydrogen Bonding in Disubstituted Ethanes: General Considerations andMethodology in Quantum Mechanical Calculations of the Conformational Equilibria ofSuccinamate Monoanion
|
| has manifestation of work
| |
| related by
| |
| Author
| |
| Abstract
| - The importance of intramolecular hydrogen bonding between the carboxylate oxygen and amide proton ofsuccinamate anion has been investigated by quantum mechanical simulations as a function of solvent forcomparison with conformational equilibria estimated by NMR spectroscopy. The focus is on thosemethodological considerations of general interest to the conformational equilibrium problem, which are alsoparticularly relevant to the quantum calculations. The roughly planar symmetry of the amide and carboxylatesubstituents of succinamate anion and the possibility of intramolecular hydrogen-bond formation togethersuggest that the orientational degrees of freedom of the substituents could play an important role in theequilibrium of the CH2−CH2 torsion. To test this hypothesis, two-dimensional potential-energy surfaces (PESs)were mapped out from the quantum mechanical calculations, with coordinates corresponding to the CH2−CH2 torsional and amide group rotational degrees of freedom. The Boltzmann populations obtained fromtwo-dimensional PESs and those obtained from a one-dimensional adiabatic surface for the CH2−CH2 torsionwere compared with the experimental results. In these comparisons, the agreement of calculated gauche fractionswith corresponding experimental values was checked, as well as the agreement between predicted couplingconstants and those determined from experimental spectra. In polar protic and aprotic solvents, where highlypolar trans conformations can be stabilized by dipole−dipole and hydrogen-bonding interactions with thesolvent, the orientational degree of freedom of the amide substituent appears to play a sufficiently importantrole in the CH2−CH2 torsional equilibrium that it cannot be safely ignored in the simulations.
|
| article type
| |
| is part of this journal
| |
