Spatial structure of β-substituted alkoxyvinyl trifluoromethyl ketones

Spatial structure of six β-substituted enones, with common structure R1O-CR2CH-COCF3, were R1 = C2H5, R2 = H (ETBO); R1 = R2 = CH3 (TMPO); R1 = C2H5, R2 = C6H5 (ETPO); R1 = C2H5, R2 = 4- O2NC6H4 (ETNO); R1 = C2H5, R2 = C(CH3)3 (ETDO) were investigated by 1H and 19F NMR, infrared spectroscopy and AM1 calculations. NMR spectra revealed that enones (MBO), (ETBO) and (TMPO) are exclusively (3E) isomers, whereas in (ETPO), (ETNO) and especially in (ETDO) the percentage of (3Z) isomers is significant and depends on the nature of solvents. Conformational behaviour of studied enones are determined by the rotation around of CC double bond, C-C and C-O single bonds (correspondingly trifluoroacetyl and alkoxy groups), and (EZZ) conformer being the most stable in all cases. IR spectra revealed that with the exception of (ETDO) (EZZ) conformer is most populated in all cases. Bulky substituents like phenyl or tert-butyl group at β-position of enone result in the equilibrium mainly between (EZZ) and (ZZZ) forms, whereas β-hydrogen and β-methyl substituents determine the equilibrium between (EZZ) and (EEZ) or (EZE) conformers.