Electronic Effects Upon the Barrier to Syn-Anti Isomerization in Substituted Acetone N-Phenylimines
McDevitt, William J.
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The kinetics of syn-anti isomerization about the carbon-nitrogen double bond of acetone N-phenylimine and its p-chloro, p-fluoro, p-methyl, and p-methoxy derivitives have been studied. The free energies of activation at the coalescence temperatures were found to be 20.5, 20.4, 21.4, 21.0, and 21.9 kcal/mol, respecitively. The rate constants at 25 degrees give a Hammett plot with a linear correlation coefficient of 0.86 when O+ substituent constants are used. A p-value of +1.10 is obtained indicating that these compounds do not undergo a rotation through a transition state with a negatively charged imino carbon atom as reported for their hexafluoro-acetone counterparts. The trifluoroacetone N-phenyliminides were found to exist as single isomers.A barrier of 19.0 kcal/mol was calculated for the isomerization in sym-tetrafluoroacetone N-phenylimine.