Microwave spectrum, ring conformation and electric dipole moment of cyclopent-2-enone

Abstract

The microwave rotational spectrum of cyclopent-2-enone has been observed and measured in the vibrational ground state and in several states having the ring bending mode excited. The planarity of the heavy atom skeleton of the molecule in the ground state is consistent with the ground state moments of inertia of the parent molecule and those of [¹⁸O]cyclopent-2-enone, and is conclusively established from the variation of the rotational constants with the vibrational quantum number associated with the ring bending mode. The ring conformation in cyclopent-2-enone is discussed in relation to those of related molecules. Measurements of the Stark effect in several transitions lead to a value of µ_a= 3.64 ± 0.01 D.