Internal Rotation of Cis 2,3-Epoxybutane from the Microwave Spectrum

Abstract

The microwave spectrum of cis 2,3‐epoxybutane was investigated in the region from 8000 to 29 000 Mc. The spectrum consists of singlets and triplets. The ground torsional state shows a pseudo rigid‐rotor spectrum with rotational constants 8057.71, 4461.36, and 3468.60 Mc. The triplets yield a barrier to internal rotation of 1607±150 cal/mole independent of a range of assumptions concerning the coupling of the two methyl groups. The dipole moment was found to be 2.03±0.02D with 2.01±0.02D in the plane of the ring. A group theoretical discussion of double rotors with one rotor on each side of a plane of symmetry is given.