The corrosion-inhibiting efficiencies of isoquinoline and its hydroxyl and carboxyl derivatives on Fe electrode in HCl solution have been determine with electrochem. method. Their structure parameters were obtained by means of HMO and CNDO/2 methods. It is found that the less the net charge and p charge of N atom has, the more the inhibition efficiency is. As the net charge sum of six atoms in pyridine ring increases, the efficiency increases. It is possible that the mols. of the inhibitors were adsorbed on the surface of Fe electrode in horizontal state.

Key words: CNDO APPROXIMATION, STRUCTURE AND PROPERTY CORRELATION, ELECTRONIC STRUCTURE, CHARGE DENSITY, EXTENDED HUCKEL MOLECULAR ORBITAL, ISOQUINOLINE