Knowledge Bank

The microwave spectra of thietanone-3 (I) and 1, 2 Dimethylene-cyclobutane (II) have been studied in the range 26.5 - 40.0 GHz. The rotational constants of (I) have been derived [FIGURE] by fitting a-type low-J R-branch transitions in the ground vibrational state (in MHz: A = 10 205.00; B = 3266.63; C = 2559.70) and 10 excited states of the ring-puckering mode. Analysis of these yields a single minimum potential function which implies a planar ring skeleton in agreement with a previous far-infrared $study.1$ Analysis of the Stark effect yielded the dipole moment in the ground state ($\mu a=0.999\pm 0.003D)$ and 5 vibrationally excited states. The rotational constants of (II) in the ground state (in MHz: A = 4925.21; B = 4089.88; C = 2301.67) and 4 excited states of the ring-puckering vibration have been derived from fitting b-type low-J R-branch transitions. Stark effect measurements yield $\mu +b=0.457\pm 0.002D$. The data are not sufficient to determine the value of the potential constants for the ring-puckering vibration, but the value of $Ic-Ia-Ib$ in the ground state and the smooth variation of rotational constants with vibrational state are sufficient to rule out the possibility of a non-planar ring $skeleton.2$