UNUSUAL CONFORMATIONAL-DETERMINING INTERACTIONS IN OXYMETHYLPYRIDINES- AN AB-INITIO STUDY AND AN IMPROVED METHOD FOR REFINING MOLECULAR MECHANICS PARAMETERS

The conformational preferences of oxymethylpyridines have been investi gated by ab initio calculations and compared to similar calculations f or oxymethylbenzene. The C-O bond in the pyridine compounds was found to prefer eclipsing with a C-C bond in the ring, in agreement with pre vious observations but in disaccord with tentative MM2 calculations. T he effect was most pronounced in the 2-substituted pyridine. The benze ne compound, on the other hand, showed good agreement between the ener gies from MM2, MM3, and ab initio calculations. The conformational pre ferences are discussed in terms of stereoelectronic interactions. New MM2 and MM3 parameters were determined from ab initio calculations on nonstationary points on the energy hypersurface. The parameterization method is discussed. (C) 1995 by John Wiley and Sons, Inc.