β-Diketone interactions. Part 2. Pentane-2,4-dione and tertiary amines; infrared, nuclear magnetic resonance, and ab initio investigations

Abstract

The claim that pentane-2,4-dioine (PD) is the 100% enol tautomer in triethylamine (TEA) has been shown to be based on a misinterpretation of ¹H n.m.r. spectra. l.r. analysis shows the presence of 8.2% of the keto tautomer at infinite dilution in TEA. An alternative mode of interaction, other than the accepted hydrogen bonding one, is proposed and supported by ab initio calculations on propanedial (malondialdehyde, MDA) and NH₃. This interaction involves amine addition to the carbonyl group of PD.