The equilibrium geometries of a-, b- and g-picolinic acid mols. 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) basis sets. Theor. optimizations with both basis sets show that the equilibrium geometries of the three picolinic acid mols. are completely planar. The theor. predicted geometries, in which the bond lengths were determine according to the 4-21G optimized results together with some corresponding empirical corrections, are basically in agreement with the experiment results from X-ray crystallog. Deviations in some bond lengths and dihedral angle between planes of carboxyl group and pyridine have been discussed.

Key words: AB INITIO CALCULATION, PYRIDINECARBOXYLIC ACID