THEORETICAL-STUDIES ON MOLECULAR EQUILIBR IUM GEOMETRIES OF PICOLINIC-ACID WITH AB-INITIO CALCULATIONS

The equilibrium geometries of alpha(-), beta(-) and gamma(-) picolinic acid molecules have been optimized by the ab initio gradient program TEXAS using the 4-21G and 4-21G (with d functions on N and O atoms) b asis sets. Theoretical optimizations with both basis sets show that th e equilibrium geometries of the three picolinic acid molecules are com pletely planar. The theoretical predicted geometries, in which the bon d lengths were determined according to the 4-21G optimized results tog ether with some corresponding empirical corrections, are basically in agreement with the experimental results from X-ray crystallogram. Devi ations in some bond lengths and dihedral angle between planes of carbo xyl group and pyridine have been discussed.