Using ab initio methods, we calculated some properties such as the energies and compositions of frontier molecular orbitals and the atomic charges which are related to the reactive behavior of thionocarbamates containing different N-substituent groupings. The results of the calculations indicate that the efficiencies of N-substituent thionocarbamates depend on the investigated parameters, and the N-substituent groupings have significant effect on flotation performance of thionocarbamates as selective collectors for copper sulfide minerals. The order of electron-donating ability is O-isobutyl-N-ethyl-thionocarbamate (IBETC) > O-isobutyl-N-allyl-thionocarbamate (IBALTC) >> O-isobutyl-N-acetyl-thionocarbamate (IBACTC) > O-isobutyl-N-ethoxycarbonyl-thionocarbamate (IBECTC), and the order of feedback-electron-accepting ability is IBACrC approximate to IBECTC >> IBALTC > IBETC. This implies that IBECTC or IBACTC can react with copper atoms having (t(2g))(6)(e(g))(3)Cu(II) or t(6)e(4)Cu(I) configuration on the surfaces of copper sulfide minerals through normal covalent bond and back donation covalent bond, but the interaction of IBECTC or IBACrC with iron atoms having (t(2g))(6)(e(g))(0)Fe(II) or (t(2g)(a))(3)(e(g)(a))(2)Fe(III) configuration on the surface of iron sulfide minerals is very weak. IBECTC or IBACTC have excellent performance in these agents as flotation collectors with improved collecting power for copper sulfide minerals and selectivity against iron sulfide minerals. The theoretically obtained results are consistent with the experimental data reported in the literature. (C) 2008 Elsevier Ltd. All rights reserved.