The conformational analysis of push–pull enaminones using Fourier transform IR and NMR spectroscopy, and quantum chemical calculations. V. α-Methyl-, fluorine-β-N,N-dimethylaminovinyl trifluoromethyl ketones

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2014-10, Vol.131, p.94-101
• Main Authors: Vdovenko, Sergey I., Gerus, Igor I., Zhuk, Yuri I., Kukhar, Valery P., Röschenthaler, Gerd-Volker
• Format: Article
• Language: English
• Subjects: Conformational analysis; DFT calculations; Enaminoketones; NMR and IR-spectra
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2014.04.053

[Display omitted] •All studied enaminoketones are TRANS isomers which form s-cis and s—trans conformers.•s-Cis and s—trans conformers of DMTBN form ‘closed-ring’ hydrogen-bonded complex.•α-Substitution strongly influences on enaminoketone hydrogen-bond basicity.•Solvent influence on IR-spectra of studied enaminoketones strongly depends on α-substituent. IR Fourier spectra of two enaminoketones with general formula F3CCOCRCHN(CH3)2, R=F (DMTFBN); R=CH3, (DMTMBN) were studied in various pure solvents. For comparison results of earlier investigated enaminoketone R=H (DMTBN) was also presented. On the basis of NMR and IR spectra it was shown that enaminoketones DMTBN, DMTFBN and DMTMBN presented in solutions as equilibrium of two conformers, (E-s-Z)⇌(E-s-E) (for DMTFBN these conformers are denoted as (Z-s-Z) and (Z-s-E), respectively). DFT calculations were carried out to evaluate relative energy and dipole moment of each spatial form. It was shown that ‘closed-ring’ complex formation between (E-s-Z) and (E-s-E) conformers of DMTBN accounts for discrepancies between DFT calculations of conformer relative energies and experimentally evaluated enthalpies of (E-s-Z)⇌(E-s-E) equilibrium. In α-substituted DMTFBN and DMTMBN, where formation of ‘closed-ring’ complex was impossible we did not observe such discrepancies. For both (E-s-Z) and (E-s-E) conformers of the DMTBN and DMTMBN the main influence on the ν̃(CO) vibrations has the solvent’s hydrogen bond donor (HBD) acidity, whereas for the DMTFBN an influence of the solvent’s polarity/polarizability dominated.