Structure-energy relationship inω-amino acids and related compounds

The potential energy surfaces of variousω-amino acids,ω-hydroxy acids, andω-amino alcohols have been investigated by ab-initio RHF calculations in the recent years. In order to find a common scheme for these molecules an energy function was developed, in which the energy is defined as a function of only those dihedral angles that are essential for the description of the nuclear framework. A least square fit procedure is performed to yield the parameters. Minimum geometries with unfavourable contributions are sorted out, as long as the correlation coefficient is below a predefined threshhold. The differences between the given (quantum chemical) and the estimated energies are small for minimum geometries which were used to fit the parameters, and larger for those which have been omitted in the fit. For conformers with intramolecular hydrogen bonding these energy differences turn out to be in the range of the interaction energy predicted for the H-bond contribution. The method can therefore be used as a semi-quantitative measure of the influence of additional interactions to the conformational energy.