Knowledge Bank

The microwave spectrum of the normal and two $C13$ isotopic species of methylenecyclopropene has been observed and analyzed. The unstable cross-conjugated hydrocarbon was prepared in a flow system by passing 2-bromomethylenecyclopropane through a heated column packed with potassium $t=butoxide.1$ Stark effect measurements led to a molecular electric dipole moment of $1.88\pm 0.01$ Debye, and the rotational constants yielded a heavy-atom structure as follows: $C1C2=1.323\pm 0.003,C1C3=1.441\pm 0.006$ and $C3C4=1.332\pm 0.006\backslash AA$. The structure is discussed and compared to that of cyclopropenone, which has been rederived from earlier $data.2$