H-1 AND C-13 NMR-SPECTRA AND ISOMERISM OF 3-AMINOACROLEINS

A set of 3-alkylaminoacroleins ((RNHCH)-N-1=CHCH=O, R-1 = alkyl) were studied by C-13 and H-1 NMR spectroscopy in solutions of different sol vents and, for the simplest representative of the series, 3-methylamin oacrolein, at different temperatures. The equilibrium solutions of the se compounds consists of mixtures of the chelated ZZE form (Z geometry around the =C-C=O single bond and the C=C bond, and E geometry around the C-N bond) and the two E configurational isomers having the E disp osition around the -C-C=O single bond and differing in the disposition around the C-N bond (EEZ and EEE forms). The relative proportions of the three isomers depend on solvent polarity, concentration, bulk of s ubstituent R-1 and temperature. The EEZ isomer is the most abundant in polar solvents, while the concentration of the ZZE form increases in non-polar solvents and when increasing the bulk of R-1. A lineshape H- 1 NMR study for 3-methylaminoacrolein in CDCl3 gave a Delta G double d agger value of 66.0 kJ mol(-1) at 303 K for the EEZ --> EEE conversion . The presence of other tautomeric forms was not observed. (C) 1998 Jo hn Wiley & Sons, Ltd.