Microwave spectrum of 4-ethylcyclohexanone

The rotational spectrum of 4-ethylcyclohexanone in the ground vibrational state has been observed in the frequency region from 6.0 to 18.0 GHz. Transitions having a-, b-, and c-dipole selection rules were all seen. The rotational constants are A = 3660.3669(20), B = 931.6707(3) and C = 796.8889(3) MHz. The electric dipole moment was also measured to give ∣μa∣ = 3.111(2) D, ∣μb∣ = 0.481(6) D, ∣μc∣ = 1.059(2) D, ∣μtot∣ = 3.321(13) D. These rotational parameters are consistent with a chair conformation with the equatorial ethyl group and the terminal carbon staggering between the hydrogen and carbon.