K. Bowden et Jm. Byrne, RING-CHAIN TAUTOMERISM .8. SUBSTITUTED 2-(2-OXOPROPYL) AND 2(2-OXO-2-PHENYLETHYL)BENZOIC AND 2-(2-ACETYL AND 2-BENZOYLPHENYL)ACETIC ACIDS, Perkin transactions. 2, (9), 1996, pp. 1921-1924
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.