Vibrational spectra, structure, assignment, and ideal-gas thermodynamics of a three-ring molecule: dibenzofuran

Abstract

Gas, liquid and solid-phase vibrational spectra are recorded and assigned for the three-ring molecule dibenzofuran. The vapor-phase infrared and Raman spectra are consistent with a planar C 2v structure. The assignment of fundamentals is assisted and tested by scaling the AM1 force field of dibenzofuran using scale factors previously derived from both monocyclic and bicyclic sources. It is found that these monocyclic and bicyclic scale factors calculate the dibenzofuran fundamental wavenumbers to respective standard deviations of ≈ 17 and ≈ 13 cm −1, with most of the improvement for the bicyclic scale factor calculation attributable to the nonplanar blocks. The assignment of fundamentals supports the majority of fundamentals previously assigned, although several previous ambiguities are removed. From the assigned fundamentals, ideal-gas thermodynamics are derived using statistical mechanics. These values compare extremely well with those from calorimetry, the difference in entropy being generally less than 0.1% of the total ideal-gas entropy and well within the combined uncertainties of the two methods.