REPLACING FLUORINES IN PERFLUOROCYCLOPENTENE WITH HYDROGENS CAUSES THE BARRIER TO RING PLANARITY TO INCREASE

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.4]{isms.eps} \end{wrapfigure} Previous work on 1H,2H-hexafluorocyclopentene and 1H-heptafluorocyclopentene\footnote{Ring puckering potentials of three fluorinated cyclopentenes: C5F8, C5HF7, and C5H2F6 E. A. Arsenault, B. E. Long, Wallace C. Pringle, Yoon Jeong Choi, S. A. Cooke, Esther J Ocola, Jaan Laane, Talk MG05, 70th International Symposium on Molecular Spectroscopy, 2015} has been improved upon and broadened. A test set of small pseudo-four membered rings with known experimental barriers to planarity has been used to explore suitable quantum mechanical approaches to this type of molecular problem. The best method has then been applied to 1H,2H-hexafluorocyclopentene and 1H-heptafluorocyclopentene. The existing data set on these fluorinated ring compounds has been extended by recording low resolution far infrared spectra which allowed an experimental determination of the barrier to planarity for these compounds. It is found that the barrier to planarity decreases in the order C$_5$H$_2$F$_6$ $>$ C$_5$HF$_7$ $>$ C$_5$F$_8$. Results will be presented together with an attempted rationale