Using conceptual density functional theory to rationalize regioselectivity: A case study on the nucleophilic ring-opening of activated aziridines

► Regioselectivity of aziridine ring-opening was investigated through DFT. ► Regiochemistry is not governed by electrostatic or hard-hard interactions. ► FMO theory and the Fukui function were used successfully. ► Mulliken population analysis confirmed as inaccurate and strongly base-dependent.