CARBON ACIDITY .79. ACIDITY OF ENOLATE EQUIVALENT COMPOUNDS - OXIME ETHERS

A series of benzylic oxime ethers were synthesized (CH3ON = C(CH2Ar)2, Ar = phenyl (1), 4-biphenylyl (2), 1-naphthyl (3)), and the equilibrium ion pair acidities in THF were determined. The lithium ion pair acidity of 1 was found to be approximately 5 pK units lower than the corresponding cesium ion pair acidity. The oxime ethers are approximately 10 orders of magnitude less acidic than their corresponding ketones for cesium ion pairs. Thermodynamic parameters for the equilibrium acidities were measured and are consistent for contact ion pair monomers being the important species in solution. An aggregation study also indicates that these cesium oxime ether enolates exist mainly as ion pair monomers. The role of the gegenion in the stability of oxime ether anions is discussed.