Ab initio quantum‐chemical calculations reveal that the interaction of isobutene with H3SO 4 + ions produced by self‐dissociation of sulfuric acid occurs virtually without an activation barrier, whereas the reactions involving neutral species of sulfuric acid are characterized by considerable activation barriers: 14.9 kcal/mol at the MP2(full)/6‐31+G*//6-31+G* level and 16.9 kcal/mol-1 at the MP2(full)/6‐31+G*//3‐21+G* level. It is also concluded that the species resulting from interaction of isobutane with H3SO 4 + ions of protonated tert‐butyl sulfuric acid are ion‐molecular complexes which should be considered as tert‐butyl carbenium ions weakly solvated by H2SO4 molecules. Although the concentration of these species in concentrated sulfuric acid is very low, presumably, they play a role of active intermediates in isobutene conversions catalyzed by sulfuric acid.