The conformational analysis of push-pull enaminones using Fourier transform IR and NMR spectroscopy, and quantum chemical calculations. IV. 4-(N,N-dimethylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one and 4-(N,N-dimethyl-amino)-1,1,1-trifluoropropen-3-en-2-one.

Abstract IR Fourier spectra of two enaminoketones with general formula (CH 3 ) 2 N CR 1 CR 2 C(O)CF 3 , R 1 H, R 2 CH 3 ( 2 ); R 1 CH 3 , R 2 H ( 3 ) were investigated in various pure solvents. For comparison results of earlier investigated enaminoketone R 1 H, R 2 H ( 1 ) were also presented. On the basis of NMR and IR spectra it was shown that enaminoketones 1 and 2 presented in solutions as an equilibrium of two conformers, ( E–s–Z ) ⇌ ( E–s–E ), whereas the enaminoketone 3 presented as equilibrium of two isomers, ( E–s–Z ) ⇌ ( Z–s–Z ). Quantum chemical calculations by the DFT methods were carried out to evaluate relative energy and dipole moment of each spatial form. For both ( E–s–Z ) and ( E–s–E ) conformer of the 1 and 2 the main influence on the ν ˜ ( C O ) vibrations has the solvent’s hydrogen bond donor (HBD) acidity whereas for the 3 influence of the solvent’s polarity/polarizability dominated. Both the solvent’s polarity/polarizability and solvent’s hydrogen bond donor (HBD) acidity influenced on the ν ˜ ( C C ) mode of the conformers of the 1 and 2 . Solvent influence on the ν ˜ ( C C ) vibrations of the 3 depended substantially whether the solvent is aprotic or an alcohol. In the former case the main contribution made the solvent’s hydrogen bond acceptor (HBA) basicity [( E–s–Z ) isomer] or the solvent’s polarity/polarizability with solvent’s hydrogen bond donor (HBD) acidity [( Z–s–Z ) isomer]. Alcohols influenced on the ν ˜ ( C C ) vibrations of both isomers predominantly due to the solvent’s polarity/polarizability. In aprotic solvents the greatest contribution in solvent influence on thermodynamic parameters of both ( E–s–Z ) ⇌ ( E–s–E ) and ( E–s–Z ) ⇌ ( Z–s–Z ) equilibrium made the solvent’s hydrogen bond acceptor (HBA) basicity. Rotation around double C C bond is characterized by higher sensitivity to the solvent’s hydrogen bond acceptor (HBA) basicity compared to the rotation around formally single C C O bond.