The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ⁻ recognition because of the strong hydrogen bonds between the amide protons and F ⁻ , while the cavity expands upon Cl ⁻ binding because of the strong electron repulsion between the p electron of Cl ⁻ and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ⁻ coupling exists when Cl ⁻ is recognized. The strong anion binding energy with F ⁻ indicates that the polyamide cryptand prefers F ⁻ to Cl ⁻ .