Potential-function calculations, anomeric

V. The Anomeric and Exo-anomeric Effects in Potential-Function Calculations. .. 103... 

Radom et al. (234) seem to have been the first to interpret internal rotation in molecules exhibiting the anomeric effect by means of a Fourier expansion of the potential function. They performed ab initio SCF MO calculations for a wide variety of molecules but without geometry optimization. It was found that internal rotation in ethane, propane, fluoroethane, and methylamine is... 

Nevertheless, the theoreticians do calculate, for instance, anomeric equilibria and the proportions of a and B -sugars in anomeric mixtures. This is done with atom-atom potential functions and energy minimization but there is one very great weakness mainy of these potential functions have been derived from measurements made in aqueous solutions (Angyal, 1969), because that is how all the early measurements were made. 

A series of simplified force fields was created by Rasmussen et al. [56, 57]. The PEF400 [58] and PEF300 (potential energy function) and variants here of are used for the calculation of disaccharides and monosaccharides (cf. below). The parametri-sation of this force field program includes atomic charges which (in variant PEF422) differ for the anomeric carbon and the other carbon atoms. The parametrization is obtained from ab initio calculations. 

Fig. 4. Modelling of the torsion potential of the exo anomeric effect using the results of the ab initio calculation of dimethoxymethane. The difference between the non bonded terms and the ab initio calculation is fitted with the general function of torsion potentials to yield the equations for the oc-and the P-anomers discussed in Sect. 2.5.3 for the HSEA method...

---