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

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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.
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