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 V3 = 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.