A considerable number of highly substituted acrylic acids or their lactols have been synthesized, and the Grignard reagent used to differentiate between the two possible structures. Acetyl chloride was found to be a satisfactory confirmatory agent, giving chlorides with the lactols, but not reacting with the open-chain acids. From the available evidence it is concluded that the differences may be attributed to cis-trans isomerism.Two other series of ketonic acids were investigated with both reagents; the Grignard reagent indicated mostly open-chain structures. The use of acetyl chloride led to a variety of products; by varying the procedure, dimers of undetermined structure, unsaturated lactones, enolic acetates, and methyl esters were obtained.Cyclohexanone gave cyclohexenyl acetate with acetyl chloride.The mechanism of the reactions is discussed, as well as the evidence for the possible structures of derivatives of levulinic acid. A mechanism is suggested to account for the formation of enolic esters and unsaturated lactones of enolized ketonic acids.