Ring-Puckering Vibration of 2,3-Dihydrofuran

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Abstract
The far-infrared spectrum of 2,3-dihydrofuran vapor has been examined from 33 to 500 cm−1. Twelve sharp Q branches have been observed between 70 and 350 cm−1. These bands are assigned to transitions of the anharmonic ring-puckering vibration which is described by the following relation in reduced coordinates: V(cm−1) = 28.3(x4 − 3.44 x2). Such a potential predicts a puckered molecule in the ground and first excited states, a barrier to planarity of 83 cm−1, and a 0–1 transition of 20.5 cm−1. There is considerable disagreement between the previously predicted far-infrared spectrum and that observed.