Chloroaluminate ionic liquids (CIL) mixed with small amounts of aromatics are highly selective catalysts for the alkylation of isobutane and 2-butene. The effects of aromatics on the alkylation reaction were investigated by experimental methods and theoretical calculations. Through NMR, in situ IR, and Raman characterizations, it was found that the aromatics interacted with ions and formed aromatic–AlCl₄⁻, aromatic–Al₂Cl₇⁻, and [aromatic–H]⁺ species. These new species buffer the acidity at a lower level and modify the activity of CIL. Theoretical calculations show that only the aromatics enriched at the acid–hydrocarbon interface and with appropriate charge transfer can effectively affect the CIL alkylation. The aromatic–ion interaction inhibited the polymerization side reactions and promoted hydride transfer from isobutane to C₈⁺. These new insights have improved our understanding of the effects of ions on the CIL alkylation reaction.