NMR Analysis of Some Pentacycloundecanedione Derivatives
The completeNMRelucidation of four pentacycloundecanedione (PCUdione) derivatives is described. Major proton shifts occur when additions are performed on the carbonyl carbons. Some of the carbon signals are also transposed. Despite the fact that the signals of the methine protons on the cage skeleton experience major overlapping, complete assignment of all the protons is possible through 2D NMR experiments. Nuclear Overhauser Effect Spectroscopy (NOESY) interaction between the two nonequivalent bridge protons and protons on the cage skeleton proved to be a very convenient handle to elucidate the structures of the PCU compounds. A density functional theory (DFT) optimization [B3LYP/6-31+G(d)] of two possible ketal conformations was used to assist with the elucidation of the asymmetric ketal structure.
KEYWORDS: NMR elucidation, pentacycloundecane, 2D NMR.