1H,13C and19FNMR studies on the structure of the intramolecularly hydrogen bondedcis-enols of 2-trifluoroacetylcycloalkanones

摘要

The1H,13C and19F NMR spectra of some 2-trifluoroacetylcycloalkanones comprising five-, six-, seven-, and eight-membered ring systems have been studied. These systems have been shown by19F NMR spectroscopy to be over 90 enolized. The effects of ring size on the1H,13C and19F chemical shifts and13C-19F coupling constants are discussed. The direction of enolization in these systems was investigated by1H,13C and19F NMR spectroscopy and evidences were presented in favour of a dominant exocyclic enol form in the five- and an endocyclic enol form in the six-, seven- and eight-membered ring systems.