The halogen effects, specifically the replacement of chlorine with fluorine, on the shift in regioselectivity from 1,4- to 1,2-addition in the nucleophilic haloalkylation of α,β-enones have been investigated using density functional theory (DFT) calculations. Computational analysis revealed that the difluorocarbanion PhSO2CF2-, being a hard nucleophile with lower energy of the highest occupied molecular orbital (HOMO), selectively undergoes 1,2-addition of chalcone, primarily dominated by Coulombic interactions. In contrast, the nucleophilic 1,4-addition of chalcone by a soft dichlorocarbanion PhSO2CCl2- is controlled by frontier molecular orbital interactions. This work provides a deep understanding of the regioselective control in nucleophilic haloalkylation reactions.