Modified MM2 scheme for computation of OCN‐containing systems

A modification of Allinger's MM2 force field for the anomeric effect in OCN systems is presented. For optimal consistency, it was parameterized by alternate use of ab initio (3‐21G level) and X‐ray results to account for the energetic and structural manifestations of the effect in the gas or condensed phase, respectively. The results obtained with the modified force field are in good agreement with those from both theoretical and experimental methods. The parameterization scheme explicitly treats all structural parameters of the COCNC moiety as well as CN bond lengths in tertiary amines contained within an anomeric unit. In addition, it includes directional H‐bond type interactions. A limited number of parameters is put forward, in accord with the general MM2 force‐field approach. © 1993 John Wiley & Sons, Inc.