HIGH-PRESSURE F-19 NMR-STUDY OF THE DEGENERATE ISOMERIZATION OF HEXAFLUOROACETONE ANILS - EVIDENCE FOR THE EXISTENCE OF 2 DIFFERENT INVERSION TRANSITION-STATES

Solvent, temperature, and pressure effects on the rate of the degenerate isomerization of hexafiuoroacetone anils were studied by 19F NMR. The results unequivocally demonstrated that the mechanism is not rotation about the carbon-nitrogen bond even in the presence of a strongly electron-donating substitutent in the para position of the phenyl group because the polarity of the reactant did not increase in the activation step. Combined with the substituent effects, the present results can be explained most reasonably by assuming two different conformations for the phenyl group in the inversion transition state, i.e., perpendicular and planar conformations for the electron-attracting and donating substituents, respectively. © 1990, American Chemical Society. All rights reserved.