ABSTRACT Spatial structure of nine dialkylaminoperfluoroalkyl ketones and two dialkylaminotrichloroalkyl ketones with common structure R1CO-CH=CH-NR2R3 (Figure 1) were investigated by 1H and 19F NMR, infrared spectroscopy, and DFT calculations. The findings of an earlier study of two simplest compounds, namely 3-(dimethylamino) acrylaldehyde (CH3)2N-CH=CH(COH) and 4-(dimethylamino)but-3-en-2-one (CH3)2N-CH=CH(COCH3), are also adduced for comparison. NMR spectra reveal that all of the enaminoketones studied are without exception (E)-isomers. Conformational behaviour of these enaminoketones is determined by the rotation around =C–N and =C–C=O single bonds. In fluorinated enaminoketones, (E-s-Z) conformer is more stable than (E-s-E) conformer, whereas for 3-(dimethylamino) acrylaldehyde, 4-(dimethylamino)but-3-en-2-one, and the chlorinated enaminoketones the stability of these conformers is opposite. This distinction was explained by the additional intra- and intermolecular C−H∙∙∙F interactions in fluorinated enaminoketones. The ratio [E-s-E]/[E-s-Z] = Keq in all the enaminoketones studied reveals a strong dependence on the total enaminoketone concentration. We evaluated the dependence of ln Keq on the total enaminoketone concentration quantitatively, and correlated the parameters of the equation obtained with enthalpies −∆H. In fluorinated enaminoketones the influence of the substituents R1, R2 and R3 on the stereoisomeric ratio is significantly different as a result of additional intramolecular Cβ−H∙∙∙F interaction in the (E-s-E) conformer whose strength varies with elongation of fluorinated R1 substituent in enaminoketones.
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