Abstract <p>The characteristic vibration frequencies of various prototropic forms of 5R-tetrazoles (R = H, Me, Ph, Cl, NO₂) were calculated using the DFT method in the B3LYP/6-311G+(d,p) approximation: 1<i>H</i>- and 2<i>H</i>-tautomeric forms of neutral tetrazoles, tetrazolate anions, and 1H,3H⁺-, 1H,4H⁺-, 2H,3H⁺-tetrazolium ions. The contributions of endocyclic bonds vibrations of the tetrazole ring to the resulting frequencies of the main absorption bands were analyzed. For all forms of 5R-tetrazoles, out-of-plane skeleton vibrations of the heteroring appear in the frequency range of 550–850 cm^–1 and stretching vibrations of endocyclic bonds and adjacent valence angles appear in the range of 950–1550 cm^–1. The signal intensity and characteristic frequencies in the IR spectra vary greatly depending on the prototropic form and the substituent in the heterocycle.</p>