Normal mode analysis of the vibrational spectrum of tropolone - A molecule with seven-membered ring

Infrared spectra of tropolone (2-hydroxy-2,4,6-cycloheptatriene-1-one) isolated in Ar and N₂ matrices are compared with the spectra theoretically calculated at the DFT (density functional theory) Becke, Lee, Yang, Paar (B3LYP)/6-31++G** and Møller-Plesset of the second order (MP2)/6-31+G* levels. The good agreement between experimental spectrum and DFT results allowed assignment of the bands observed in the IR spectrum to the theoretically predicted normal modes described in terms of potential energy distribution (PED). Internal coordinates describing in-plane and out-of-plane deformations of the seven-membered ring of D_7h symmetry (and for eight-membered ring of D_8h symmetry) were designed for the purpose of normal mode analysis.