Intramolecular Hydrogen Bonding in α-Keto and α-Alkoxy Carboxylic Acids. VIII. o-Methoxy-Substituted Phenoxyacetic and Phenylthioacetic Acids

Abstract The infrared spectra in the O–H stretching region of several ortho-substituted phenoxyacetic and phenylthioacetic acids were determined in dilute carbon tetrachloride solutions. The O–H stretching absorption of phenoxyacetic acids carrying o-methoxy-substituents shows three absorption maxima, all of these being attributed to the monomeric species, and they are assigned to the free O–H group, the O–H group hydrogen bonded with α-phenoxy oxygen atom and the O–H group hydrogen bonded with methoxyl oxygen atom in the order of decreasing frequency. The O–H stretching absorption at the lower frequency of o-methoxyphenylthioacetic acids is also assigned to the hydrogen bonded monomeric species in which the chelation occurs between the carboxylic O–H group and the methoxyl oxygen atom.