Vibrational assignment and analysis for 2,3-dihydrofuran and 2,5-dihydrofuran

The vibrational spectra of 2,3-dihydrofuran and 2,5-dihydrofuran have been recorded using IR and Raman spectroscopy for the gas, liquid and solid states. A vibrational assignment consisting of a nearly complete set of vapor phase wavenumbers is proposed for both molecules based on the observed spectra and normal coordinate analyses. The normal coordinate analyses have been made by scaling the AM1 force field for each molecule with scale factors transferred from an analysis of the cyclopentene fundamental vibrations. The predicted a priori vibrational frequencies justify one reassignment of the fundamentals for 2,5-dihydrofuran from that previously reported. The vibrational assignment for 2,3-dihydrofuran is reported for the first time. Thermodynamic functions are computed for each molecule using the experimentally determined vibrational frequencies.