Knowledge Bank

The far infrared spectra of a number of five-membered ring compounds have been investigated. Twenty-three Q branches have been observed in the far infrared spectrum of $tetrahydrofuran.1$ The transitions which give rise to the Q branches belong to two series of pseudorotational levels with identical effective reduced masses. Possible explanations of these two series will be discussed with reference to microwave $evidence.2$ $Pyrrolidine,2$ N-deutero pyrrolidine, and tetrahydrothiophene have also been investigated. Preliminary results indicate that free pseudorotation exists in pyrrolidine as in tetrahydrofuran. Pseudorotation in tetrahydrothiophene is probably hindered.