RING-CHAIN TAUTOMERISM .8. SUBSTITUTED 2-(2-OXOPROPYL) AND 2(2-OXO-2-PHENYLETHYL)BENZOIC AND 2-(2-ACETYL AND 2-BENZOYLPHENYL)ACETIC ACIDS

The observed pK(a) values for 2-[2(substituted phenyl)-2-oxoethyl]benz oic, 2-[2-(substituted benzoyl)phenyl] acetic, 2(Z-oxopropyl) and 2-(1 ,1-dimethyl-2-oxopropyl)benzoic, 2-(2-acetylphenyl)acetic and 2-(2-ace tylphenyl)-2,2-dimethylacetic acids in 80% (m/m) 2-methoxyethanol-wate r have been measured, The occurrence of ring-chain tautomerism has bee n examined in these acids by IR and NMR spectroscopic methods. The sub stituted benzoyl acids are predominantly in the chain (normal) form an d the Hammett reaction constants have been used to study the transmiss ion of polar effects in these systems. The equilibrium constants for r ing-chain tautomerism for the acetyl acids have been determined direct ly by IR and NMR spectroscopy and indirectly from their observed pK(a) values. The results for ring-chain tautomerism in acyl carboxylic aci ds employing a comprehensive series of linking groups are discussed in terms of stereochemistry and steric 'bulk' interactions.