Thiosemicarbazides and thiosemicarbazones: non-linear quantitative structure–efficiency model of corrosion inhibition

The variation in the inhibition efficiency (η) of thiosemicarbazide and thiosemicarbazone derivatives was explained in terms of molecular parameters. The effect of concentration was taken into account by assuming that the adsorption of the corrosion inhibitors follows the Langmuir isotherm. The model used differs from that proposed earlier, because instead of the adsorption constant K, ln K was considered the dependent variable in the quantitative structure–efficiency relationships. This modification allowed treating the variation of η in terms of linear free-energy relationships. The numerical procedure used to obtain the regression coefficients was based on a non-linear regression technique.The results indicated that variation in η can be explained in terms of the energy of the highest occupied molecular orbital and the dipole moment, or alternatively, by the difference in the energy of the highest occupied and lowest unoccupied molecular orbitals.