Association of protons with oxygen-containing molecules in aqueous solution. Part 3.—The protonation of carbonyl compounds

Abstract

The spectrophotometric examination of p-nitroaniline in dilute solutions of ketones and carboxylic acids in water containing hydrochloric acid shows that p-nitroaniline competes for the protonated substrate-water complex and (H₂O)₄H⁺, as found for alcohols.¹ The proton association constants K_c for the carbonyl compounds are independent of acidity. K_c for acetone is independent of ionic strength and of [acetone]⩽10% v/v, increasing at [acetone]>10 %. The basicity of ketones and carboxylic acids is influenced by the electronegativity and steric effects of groups attached to the carbonyl group; this is compared with the basicity of alcohols.³