Special feature of kinetics of ZcE isomerization of ß-N-methylaminovinyl trifluoromethyl ketone in Ar matrix exposed to UV radiation and spontaneous E⇌Z isomerization of α-methyl-ß-N-methylaminovinyl trifluoromethyl ketone.

Although it is well known that reactivity of α,ß-unsaturated enaminoketones is closely associated with spatial and electronic structure but until now little attention was devoted to quantitative investigation of interconversion of different stereoisomeric forms of enaminoketones. In present work we studied peculiarities of kinetics of Z⇌E isomerization of enaminoketone 4-(N-methylamino)-1,1,1-trifluorobut-3-en-2-one F3C-COCHCHNH(CH3) (1) in Ar-matrix exposed to UV-radiation (λ=340nm) with IR Fourier and 2D correlation spectroscopy and we found that Z-s-Z-s-trans isomer transforms primarily into two E-isomers, E-s-E-s-trans and E-s-Z-s-trans which further turn into the E-s-E-s-cis and E-s-Z-s-cis conformers all interconversion rate constants being comparable in magnitude. Along with this process long-term exposure to the UV-radiation results in proton transfer from nitrogen of methylamino group to carbonyl oxygen with simultaneous isomerization of 'cyclic' iminoenol form into 'linear'one. In solution of enaminoketone 4-(N-methylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one F3C-CO-C(CH3)CH-NH(CH3) (2) we observed reversed process, namely, spontaneous interconversion of the E-s-E-s-trans and E-s-Z-s-trans conformers into the Z-s-Z-trans isomer. It was found that rate constants of the dimeric forms of the E-s-E-s-trans and E-s-Z-s-trans conformers are higher than those of the monomers and are independent on total enaminoketone concentration. Addition of highly polar HMPA promotes proton transfer from nitrogen to oxygen in the Z-s-Z-s-trans isomer of 2 with subsequent isomerization into the linear imino-enol product but the rate constant of this transformation is ten-fold smaller than that for 1 in the Ar matrix exposed to UV radiation.

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

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.

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.

IR Fourier spectra of two enaminoketones with general formula (CH(3))(2)NCR(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.

The conformational analysis of push-pull enaminoketones using Fourier transform IR and NMR spectroscopy, and quantum chemical calculations: II. Beta-dimethylaminoacrolein.

IR Fourier and (1)H NMR spectra of beta-dimethylaminoacrolein (DMAA) were investigated in various pure solvents. Quantum chemical calculations by the method AM1 also was carried out to evaluate relative energy and dipole moment of each conformer. On the basis of NMR and IR-spectra we showed that the (DMAA) presented in solutions as equilibrium of two conformers, (E-s-Z) <==> (E-s-E). Constant of this equilibrium, K(eq) = C(E-s-E)/C(E-s-Z), depended strongly on the total (DMAA) concentration: ln K(eq) = ln K(eq0) + a(1 - e(-bC) total). Besides, (E-s-Z) conformer of the (DMAA) was more polar and more stable than the (E-s-E) conformer. Correlation of the out-of-phase nu(C=O) and in-phase nu(C=C) vibrations with solvatochromic parameters of Kamlet, Abbot, and Taft (KAT) revealed that the main contribution to the shift of the out-of-phase nu(C=O) vibrations of the both conformers made solvent's hydrogen bond acceptor (HBA) (beta) term, whereas hydrogen bond donor (HBD) acidity (alpha) term influenced predominantly on the shift of the in-phase nu(C=C) vibrations of the conformers. Moreover, influence of these dominated terms was more pronounced for the (E-s-Z) conformer in comparison with the (E-s-E) conformer, hence the first conformer was more polarized than the last. Investigations of the enthalpies of the (E-s-Z) <==> (E-s-E) equilibrium in carbon tetrachloride, 1,4-dioxane and their mixtures showed that these enthalpies depended predominantly on the solvent's atomic and electronic polarization and dispersive interactions.

Solvent influence on the infrared spectra of beta-alkoxyvinyl methyl ketones II. Stretching vibrations and integrated intensities of carbonyl and vinyl bands of (3Z,E)-4-ethoxy-1,1,1-trifluoro-5,5-dimethylhex-3-en-2-one.

Infrared spectroscopy studies of beta-alkoxyvinyl trifluoromethyl ketone, with structure C(2)H(5)O-C(C(CH(3))(3))CH-COCF(3) (1), in twenty three different pure organic solvents were undertaken to investigate the solvent-solute interactions and to correlate solvent properties such as Reichard's parameter and solvatochromic parameters of Kamlet, Abbot, and Taft with carbonyl and vinyl stretching vibrations and their integrated intensities of existing spatial forms. It was shown that conjugation in CC-CO system of the (E-s-Z-o-Z) stereoisomer is higher than that in this system of the (Z-s-Z-o-Z) stereoisomer. From derived correlations of the v (CO) and v (CC) wavenumbers with solvatochromic parameters of Kamlet, Abbot, and Taft it is followed that the solvent polarity influences on the v (CO) and v (CC) wavenumbers more intense than the solvent HBD acidity, and, at the same time, the influence of these solvent properties is greater for the (E-s-Z-o-Z) stereoisomer. Analysis of derived KAT multiple regressions showed that the increase of the solvent polarity/polarizability (pi*) increased the conjugation in both stereoisomers, whereas the increase of the solvent HBD acidity (alpha) had opposite effect on conjugation in the (Z-s-Z-o-Z) and (E-s-Z-o-Z) stereoisomer. In the former case conjugation was weakened, whereas in the latter it was enhanced. These discrepancies were the consequence of different structure of H-bonded complexes between enone 1 and HBD solvents. The influence of the solvent HBA basicity (beta) also had peculiarity. The increase of the solvent HBA basicity disturbs the CC-CO conjugation in the (Z-s-Z-o-Z) stereoisomer due to carbonyl rotation, whereas in the (E-s-Z-o-Z) stereoisomer such increase enhanced this conjugation and, hence, increased the v (CO) and v (C==C) coupling.

Solvent effects on the infrared spectra of beta-alkoxyvinyl methyl ketones I. Carbonyl and vinyl stretching vibrations.

Infrared spectroscopy studies of six beta-alkoxyvinyl methyl ketones, with common structure R(1)O-CR(2)CH-COR(3), where R(1)=R(3)=CH(3), R(2)=H (1); R(1)=C(2)H(5), R(2)=H (2); R(3)=CF(3); R(1)=R(2)=CH(3), R(3)=CF(3) (3); R(1)=C(2)H(5), R(2)=C(6)H(5), R(3)=CF(3) (4); R(1)=C(2)H(5), R(2)=4-O(2)NC(6)H(4), R(3)=CF(3) (5); R(1)=C(2)H(5), R(2)=C(CH(3))(3), R(3)=CF(3) (6) in 11 pure organic solvents of different polarity were undertaken to investigate the solute-solvent interactions and to correlate solvent properties by means of linear solvation energy relationships (LSER) with the carbonyl and vinyl stretching vibrations of existing stereoisomeric forms. It was shown that contrary to simple carbonyl-containing compounds where solvent HBD acidity (alpha) has the largest influence on the nu (CO) band shift to lower wavenumbers, the dipolarity/polarizability (pi) term plays the main role in the interactions of conjugated enones with solvent molecules leading to the nu (CO) and nu (CC) bathochromic band shifts. The trifluoroacetyl group possesses a reduced ability to form hydrogen bonds with solvents. For the nu (CC) band of non-fluorinated enone 1 solvent HBD acidity (alpha) and solvent HBA basicity term (beta) play a perceptible role, whereas for 2 these terms are not significant. beta-Substituents in fluorinated enones such as R(2)=H, C(6)H(5), and C(CH(3))(3) assist in the intermolecular hydrogen bond formation of the carbonyl moiety with HBD solvents, while beta-substituents such as CH(3) and 4-NO(2)C(6)H(4) prevent the CO group to form the H-bonds with HBD solvents (the solvent HBD acidity term (alpha) is not significant). The comparison of four conformers of the enone 1 reveals that (EEE) form is the most polarizable conformer; the influences of the solvent dipolarity/polarizability (pi) and solvent HBD acidity (alpha) term on the bathochromic nu (CO) band shift are opposite to one another.