MICROWAVE SPECTRUM AND CONFORMATION OF 1,3-DIFLUOROACETONE

$^{1}$ \footnote{G. A. Crowder and B. R. Cook, J. Mol. Spectrosc. 25, 133 (1968); and G. A. Crowder and P. Pruettiangkura, J. Mol. Struct. 18, 177 (1973).}Author Institution: Department of Chemistry, Harvard UniversityThe microwave spectrum of 1,3-dtfluoroacetonc, a molecule expected to show several conformations, has been studied in the region of 18-40 GHz using a commercial microwave spectrometer. The most Intense lines in the spectrum are a-type and R-branch transitions. The ground state species and the first excited state of each of several vibrational modes have been assigned. Rotational constants for the ground state species are A = 6024.84 MHz, B = 2454.41 MHz, and C = 1783.90 MHz. From the moments of Inertia a value of $\Delta$ = $I_{c}$ - $I_{a}$ - $I_{b}$ = - 6.48926 amu.A$^{2}$ has been calculated. This implies that the molecular conformation in the gas phase is one in which all heavy atoms lie in a plane (i.e., only the methyl hydrogens lie outside the plane defined by the other atoms). The rotational constants are consistent with a structure in which one fluorine is cis to the oxygen and the other trans. These results are In contrast with previously reported infrared $work.^{1}