COMPUTATION OF O-C-F AND N-C-F SYSTEMS - ABINITIO CALCULATIONS AND A MM2 PARAMETERIZATION STUDY - THEORY VS EXPERIMENT

A parameterization scheme of Allinger's MM2 force field for the anomer ic effect in O-C-F and N-C-F systems is presented. The scarcity of exp erimental data, in particular for the N-C-F case, dictated the use of ab-initio calculations to account for the energetic and structural man ifestations of the effect. The resulting modified force field was test ed against available X-ray, microwave and NMR results leading to a ver y good agreement between calculations and experiment. In addition, ab- initio results were used to demonstrate the role of the anomeric effec t in lowering barriers to N-inversion and elevating barriers for rotat ion around single C-N bonds. The results for the fluoro compounds, whe n juxtaposed to other systems, provide a complete treatment of the ano meric effect for first row elements.