Vibrational analysis of the imidazolate ring

Abstract IR and Raman spectra have been investigated for imidazolate and 4-methylimidazolate including five and three deuterated analogs, respectively. Assignment of the observed IR and Raman bands has been made on the basis of isotopic frequency shifts, Raman polarization properties, and normal coordinate calculations. The calculated normal frequencies are in good agreement with experimental ones: the average error below 1600 cm −1 is 4.5 cm −1 for 104 in-plane vibrations and 3.8 cm −1 for 43 out-of-plane vibrations. The calculated vibrational modes are useful in analyzing the Raman bands of histidine residues in proteins.