Morphing the Internal Dynamics of Acetylacetone by CH3 → CF3 Substitutions. The Rotational Spectrum of Trifluoroacetylacetone

The rotational spectrum of trifluoroacetylacetone shows that the molecule exists in an enolic C-s form and displays the features of internal rotations of the CH3 and CF3 groups, whose barriers to internal rotation were determined to be V-3 = 379 and 30.8 cm(-1), respectively. Its internal dynamics appears to be intermediate between those of acetylacetone, where proton tunneling and low-barrier internal rotation of the two methyl groups make the spectrum quite complex, and hexafluoroacetylacetone, a perfectly "rigid" molecule on the time scale of microwave spectroscopy.