Quantum mechanical calculations have been applied to a series of pyrazole derivatives used as corrosion inhibitors for zinc, copper and alpha-brass in order to assess quantum chemistry as a means of evaluating effectiveness of corrosion inhibitors. The corresponding structures have been optimized and the energies and coefficients of their molecular orbitals (HOMO and LUMO) have been computed using the semi-empirical method, MNDO. The theoretical results are then compared with experimental data.