Dynamic NMR Study of Cyclopropylcarbonyl Fluoride. A Comparison of the Conjugating Abilities of the Cyclopropyl, Vinyl, and Phenyl Groups

Article abstract of DOI:10.1021/ja00387a010

Rotation about the bond between the COF group and C-1 of cyclopropylcarbonyl fluoride is slow on the NMR time scale at -163 deg C.The fluorine NMR spectrum at this temperature shows signals for two conformations, which have nearly identical free energies.A free energy barrier of 5.5 +/- 0.2 kcal/mol was calculated for interconversion of isomers at -134 deg C.Comparison of this barrier with the rotational barriers for acryloyl fluoride and benzoyl fluoride indicates that the ?-donating abilities of the vinyl and cyclopropyl groups are nearly equal and are lower than for phenyl, at least with the fluorocarbonyl group as the ? acceptor.