The invention relates to a method for isomerizing a saturated, branched, and cyclical hydrocarbon, wherein a tertiary C atom of the hydrocarbon is converted into a secondary C atom when isomerizing, in that the isomerization is performed in the presence of a super-acid ionic liquid, comprising an organic cation and an inorganic anion, wherein the anion is a super-acid aluminum trichloride Lewis base adduct, and a copper(II) compound.