Abstract
The microwave spectrum of the cis‐2‐butene molecule has been studied between 20 and 40 Gc/sec. Analysis of internal‐rotation splittings yields an effective threefold barrier of 0.73 kcal/mole, or 256 cm−1. The principal moments of inertia of the normal isotopic species are 31.479, 98.370, and 123.659 amu·Å2. The electric dipole moment is 0.257 D and lies along the b axis of the molecule.