Spectroscopic Evidence for Pseudorotation. II. The Far-Infrared Spectra of Tetrahydrofuran and 1,3-Dioxolane

Abstract

The absorption spectra of tetrahydrofuran and of 1,3‐dioxolane at about 0.3‐cm⁻¹ resolution are reported in the region of 20–370 cm⁻¹. It is found that dioxolane pseudorotates, and the earlier evidence for the pseudorotation of tetrahydrofuran is confirmed. Both compounds have barriers to pseudorotation of about 50 cm⁻¹. Pseudorotation constants in both the ground and in the first excited radial states are obtained. The spectra show the effects of a considerable number of complex rotation–vibration interactions, which can be understood qualitatively by comparison with the spectra of four‐membered‐ring compounds. The band shapes are explained semiquantitatively using a number of Coriolis terms in the effective Hamiltonian.