Aromatic enaminones. Part 1. Ultraviolet absorption of N-aryl enaminones derived from dimedone

A series of enaminones derived from dimedone and various substituted anilines has been prepared. Their u.v. spectra are reported for acidic, neutral, and alkaline aqueous solution. For m-substituted derivatives the spectra show bathochromic shifts in comparison with aliphatic enaminones. These shifts are lower for o-substituted compounds because of steric interactions, and for p-substituted derivatives they vary with the properties of the substituent. Overall the aromatic ring is an electron donor to the enaminone system. Most of the compounds show hypsochromic shifts due to O-protonation; two (which have p-nitro-groups) show acidic properties in alkaline solution.