$Li^+$ ion complex of azacrown ether with restricted motion of freedom and pseudo-bilateral symmetry was studied by infrared spectroscopy, which has shown simplified and broadened vibrational features. The C=O and N-H stretching bands, in particular, shows anomalous broadening nearly ${sim}50;cm^{-1}$. The density functional calculation at the level of BP86/6-31+$G^{**}$ shows that $Li^+$ ion is trapped and rather free to move around inside the cavity, as much as about $0.70;{AA}$. Through the relocation of $Li^+$ ion inside the cavity, the conformational changes would occur rapidly in its symmetry $C_1;{ ightleftarrows};C_2;{ ightleftarrows};C_1$$. The potential barrier was obtained to be merely ~2.2 kJ/mol for $C_1;{ ightarrow};C_2$. During this conformational alteration, the amide backbone twists concurrently its dihedral angle side to side about up to ${pm}3$ degree. Selected vibrational modes were interpreted in terms of the force constant variations of local symmetry coordinates between conformations in the framework of $C_1;{ ightleftarrows};C_2;{ ightleftarrows};C_1$.