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 (CH3)2NCR1CR2C(O)CF3, R1H, R2CH3 (2); R1CH3, R2H (3) were investigated in various pure solvents. For comparison results of earlier investigated enaminoketone R1H, R2H (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˜(CO) 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˜(CC) mode of the conformers of the 1 and 2. Solvent influence on the ν˜(CC) 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˜(CC) 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 CC bond is characterized by higher sensitivity to the solvent’s hydrogen bond acceptor (HBA) basicity compared to the rotation around formally single CCO bond.