Structural study of methyl and tert-butyl phenylacetate enolates in solution : spectroscopic determination of their E or Z configuration

The structures of Li and K methyl and tert-butyl phenylacetate enolates A,M and B,M have been examined by IR and 13 C NMR spectroscopy in different solvents and solvent mixtures. In the IR, coupling of aromatic ring mode with the v(C . - . O) stretching vibration allows assignment of the E (or Z) configuration to the corresponding enolate. The IR mode assignments are secured by specific deuteration of the phenyl or methyl moieties in methyl phenylacetate.