MICROWAVE SPECTRUM, STRUCTURE AND DIPOLE MOMENT OF METHYLENECYCLOPROPENE

$^{1}$ S.W. Staley and T. D. Norden, J. Am. Chem. Soc. 106, 3699 (1984). $^{2}$ J. M. Pochan, J.E. Baldwin and W. H. Flygare, J. Am. Chem. Soc. 91, 1896 (1969). Address of Taylor and Hermony: Department of Chemistry, University of Kansas, Lawrence, KS 66045 Address of Norden and Staley: Department of Chemistry, University of Nebraska, Lincoln, NE 68588Author Institution:The microwave spectrum of the normal and two $C^{13}$ 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: $C_{1}C_{2} = 1.323 \pm 0.003, C_{1}C_{3} = 1.441 \pm 0.006$ and $C_{3}C_{4} = 1.332 \pm 0.006 {\AA}$. The structure is discussed and compared to that of cyclopropenone, which has been rederived from earlier $data.^{2}