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

Article abstract of DOI:10.1016/j.saa.2014.04.053

IR Fourier spectra of two enaminoketones with general formula F ₃CCOCRCHN(CH₃)₂, R = F (DMTFBN); R = CH ₃, (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 ν (CO) vibrations has the solvent's hydrogen bond donor (HBD) acidity, whereas for the DMTFBN an influence of the solvent's polarity/polarizability dominated.

Full text of DOI:10.1016/j.saa.2014.04.053

Accepted Manuscript
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
Sergey I. Vdovenko, Igor I. Gerus, Yuri I. Zhuk, Valery P. Kukhar, Gerd-Volker
Röschenthaler
PII:
S1386-1425(14)00626-X
http://dx.doi.org/10.1016/j.saa.2014.04.053
SAA 12017
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
Received Date:
Revised Date:
Accepted Date:
24 December 2013
7 March 2014
7 April 2014
Please cite this article as: S.I. Vdovenko, I.I. Gerus, Y.I. Zhuk, V.P. Kukhar, G-V. Röschenthaler, 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,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.
2014.04.053
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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
Sergey I. Vdovenko,*a Igor I. Gerus,a Yuri I. Zhuk,a Valery P. Kukhar,a Gerd-Volker
Röschenthalerb
a Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, ul. Murmanska
1, 02094, Kiev, Ukraine.
b Jacobs University Bremen gGmbH, School of Engineering and Science, Campus Ring 1, 28759 Bremen, Germany
ABSTRACT
IR Fourier spectra of two enaminoketones with general formula F3C-CO–CR=CH–N(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 (C=O) vibrations has the solvent’s hydrogen bond donor (HBD) acidity, whereas for the
ν
DMTFBN an influence of the solvent’s polarity/polarizability dominated.
Keywords: NMR and IR-spectra; Conformational analysis; Enaminoketones; DFT calculations.
1. INTRODUCTION
Earlier [1-5] we investigated various enaminones with general formula R1CO-CH=CH-
NR2R3 and showed that all studied enaminoketones presented in solutions as an equilibrium of
1

two conformers, (E-s-Z)
(E-s-E) where the ratio [(E-s-E)]/ [(E-s-Z)] depended not only on
R1, R2 and R3 substituents but also on solvent properties and total enaminone concentration.
Particularly, we showed that the enaminone with R1 = H existed, mainly, as the (E-s-E)
conformer (equilibrium constant at infinite dilution Keq(0) = 1.55 [5]), whereas in the
enaminoketone with R1 = CH3, the (E-s-Z) conformer prevailed and Keq(0) equaled 0.24 [6].
Further substitution of CH3-group by CCl3-group gave Keq(0) = 0.55 [4], whereas in the
enaminoketone with R1 = CF3 Keq(0) = 1.12. Hence, the nature of R1 substituent influenced not
only on electron distribution in molecule, but also determined prevailing stereoisomeric form of
the enaminoketone molecule. We also investigated the influence of the R2 and R3 substituents
and showed [4] that the influence of these substituents on the conformer ratio is, mainly, due to
steric interactions. From this point of view it was essential to investigate stereoisomeric
composition of the enaminoketones with general formula F3C-CO–CR=CH–N(CH3)2, where
substituents were R = H, F and CH3. Thus, in this work we examined the stereoisomeric forms of
the next three compounds: 4-(N,N-dimethylamino)-1,1,1-trifluorobut-3-en-2-one (CH3)2N-
CH=CH(COCF3) (DMTBN); 4-(N,N-dimethylamino)-1,1,1,3-tetrafluorobut-3-en-2-one F3C-
CO–CF=CH–N(CH3)2 (DMTFBN) and 4-(N,N-dimethylamino)-1,1,1-3-methylbut-3-en-2-one
F3C-CO–C(CH3)=CH–N(CH3)2 (DMTMBN).
2. Experimental
2.1. General
Solvents (obtained from Aldrich) were purified using standard techniques and were dried
over the appropriate drying agent before use. The enaminoketone DMTBN was obtained by the
method described earlier [6]; enaminoketones DMTFBN and DMTMBN were synthesized, as
was described in Experimental 2.2, distilled in vacuum, and stored under dry nitrogen at +4 °C.
2.2. Synthesis of studied enaminoketones DMTBN, DMTFBN, and DMTMBN.
1H, 13C, and 19F NMR spectra were recorded on a Bruker DRX-500 and Varian Unity
Plus-400 instruments. Chemical shifts (δ) are given in ppm relative to TMS (using residual
1
solvent signals at 7.27 ppm, H; 77.16 ppm, 13C) or CFCl3 (19F). Melting points were measured
in the open capillary; the values are uncorrected. The enaminoketones DMTBN [2], DMTFBN,
and DMTMBN have been obtained from the corresponding β-alkoxyvinyl ketones according to
the Scheme 1. The starting compounds: (E)-4-ethoxy-1,1,1-trifluorobut-3-en-2-one [1], and (E)-
4-ethoxy-1,1,1-trifluoro-3-methylbut-3-en-2-one [7] were prepared as published previously by
trifluoroacetylation of the corresponding alkyl vinyl ethers, and (Z)-1,1,1,3-tetrafluoro-4-
2

ethoxybut-3-en-2-one by the fluorination of α-unsubstituted (E)-4-ethoxy-1,1,1-trifluorobut-3-
en-2-one with xenon difluoride [8].
2.2.1. Typical procedure for the synthesis of enaminoketones DMTFBN, and DMTMBN.
Solution 0.454 g (4.0 mmol) of 40% Me2NH in the water was added to a solution of 0.5 g (2.7
mmol) of corresponding alkoxyenone in 3 ml of acetonitrile under stirring at 0 ºC and the
mixture was stirred for 2 h at 20 ºC. Then the solvents were evaporated in vacuum, the rest was
extracted by DCM (2 x 10 mL), organic phase was dried with MgSO4 and the solvent was
evaporated in vacuum. The rest was distilled in vacuum.
2.2.2. 4-(N,N-Dimethylamino)-1,1,1,3-tetrafluorobut-3-en-2-one (DMTFBN)
The yield of enaminone DMTFBN was 0.42 g (85%) as yellow oil, b.p. 70-71 ºC (1 mmHg).
1H NMR (500.1 MHz, CDCl3): δ = 3.22 (br. s, 6H), 6.88 (br. d, , J = 27.9 Hz, 0.47H), 7.11 (br. d,
J = 26.9 Hz, 0.53H). 13C NMR (125.8 MHz, CDCl3): δ = 38.8 (br. s), 39.2 (br. s), 46.6 (br. s),
47.2 (br. s), 117.1 (br. q, J = ~289.0 Hz), 136.0 (br. d, J = 228.9 Hz), 136.2 (br. d, J = 221.2 Hz),
136.5, 139.6, 168.0m, 169.7m. 19F NMR (376.3 MHz, CDCl3): δ = –68.68 (br. d, J ~ 6 Hz,
1.44F), –75.13 (br. d, J = 17.5 Hz, 1.56F), –170.41 (br. dm, J ~ 27.5 Hz, 0.47F), –77.3 (br. dq, J
~ 27.0 and 18.0 Hz, 0.53F).
Anal. Calcd for C6H7F4NO: C, 38.93, H, 3.81, N, 7.57. Found: C, 46.63, H, 5.58, N, 7.61.
2.2.3. 4-(N,N-Dimethylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one (DMTMBN)
The yield of enaminone DMTMBN was 0.38 g (%) as yellow oil, b.p. 120 ºC (12 mmHg).
1H NMR (500.1 MHz, CDCl3): δ = 2.04 (s, 3H), 3.20 (br. s, 6H), 7.34 (br. s, 1H). 13C NMR
(125.8 MHz, CDCl3): δ = 10.9, 43.8 (br. s), 100.1 (br. s), 118.4 (q, J = 292.5 Hz), 155.3, 178.1
(q, J = 30.5 Hz). 19F NMR (376.3 MHz, CDCl3): δ = –66.4 (br. s).
Anal. Calcd for C7H10F3NO: C, 46.41, H, 5.56, N, 7.73. Found: C, 46.37, H, 5.62, N, 7.61.
2.3. Infrared spectra
Infrared spectra were recorded on a Bruker Vertex 70 FTIR spectrometer with KBr
0
beamsplitter and RT-DLaTGS detector at ambient temperature (20 1 C). For all spectra 32
scans recorded at 2 cm-1 resolution were averaged. Solution spectra were measured in carbon
tetrachloride using standard NaCl cells with pathlengths 0.0103cm. Dilution measurements were
carried out in carbon tetrachloride using standard NaCl cells with pathlengths 0.0022, 0.0063
3

0.01028, 0.0212, 0.0521, and 0.102 cm. Temperature measurements were carried out in
thermostated ( 0.05 ºC) NaCl cell with pathlength 0.01223 cm. The solutions were scanned at
the same conditions as a background. The Bruker Opus software Version 6.0 was used for all
data manipulation.
2.4. Quantum chemical calculations
Quantum chemical calculations of energies of formation for all possible conformers of the
investigated enaminoketones DMTBN, DMTFBN, and DMTMBN were performed with a
program HyperChem (Hypercube Inc., release 8.0.3) by DFT method, the hybrid B3LYP
functional was combined with the 6-311G** basis set. The geometry of the conformers was
optimized without fixing any parameter with the Polak-Ribiere algorithm in vacuum at RMS
gradient 0.048 kJ mol−1. Results are listed in Table 1.
3. Results
3.1. NMR spectra.
The 1H, 19F, and 13C NMR spectra of studied enaminoketones are presented in Fig.S1 –
S10. Both 1H, 19F, and 13C NMR spectra reveal that DMTFBN exists as a mixture of two isomers
(Z-s-E) and (Z-s-Z) with about equal ratio (53 : 47, correspondingly) in CDCl3 solution at 293 °K
(see Fig.S1-S5) and this ratio remains the same even in more polar solvent, DMSO-d6. The Z-
configuration of the C=C double bond of DMTFBN is confirmed by the presence of two different
signals of both olefinic substituents: hydrogen and fluorine atoms with nearly equal coupling
constants 3JHF 26.9 and 27.9 Hz, which indicated a trans-orientation of the dimethylamino and
CF3CO groups – the common feature for push-pull acyclic enaminones. Doubled signals of both
olefinic protons in 1H NMR, and the olefinic fluorine atom and trifluoromethyl group in 19F
NMR spectrum are a result of slow rotation of trifluoroacetyl group around the single C=C–C=O
bond: two conformers (Z-s-E) and (Z-s-Z) of DMTFBN are detected by NMR spectrometry at
room temperature. We suggest that the coupling constants between olefinic fluorine atom and
trifluoromethyl group 4JFF 17.5 and ~6.0 Hz can be referred to (Z-s-E) and (Z-s-Z) conformers,
correspondingly. It is worth to mention that in 1H NMR spectra of DMTFBN Me2N group
demonstrates broadened signal in CDCl3 and two overlapped signals in DMSO-d6.
Consequently, we observe slightly hindered rotation around C–N single bond, similar to that we
have observed in NMR spectra of DMTMBN (Fig.S6) earlier. On the contrary, there are two
4

distinct separate signals of methyl groups in H1 NMR spectra of DMTBN (see Fig.S9). Results
of further NMR studies of DMTFBN and related compounds will be published elsewhere.
∼
3.2. Attribution of the absorption bands in the region of the (C=O) and (C=C) vibrations.
∼
ν
ν
In principle, push-pull β-dialkylamino vinyl trifluoromethyl carbonyl ketones are able to
generate various spatial forms due to rotational isomerism around C=C double bond and =C–C
single bond between vinyl and carbonyl group [1,9-14]. In general, eight stereoisomeric forms
are to be anticipated for studied enaminoketones (Scheme 2). In view of symmetric substitution
∼
∼
ν
ν
of dimethylamino group in studied compounds only four pairs of the (C=O) and (C=C)
bands should be expected in IR-spectrum. However, in all studied cases the number of bands was
less then four as a result of absence of some titled isomers or overlapping of some of their bands.
∼
∼
ν
ν
It is worth to note that (C=O) and (C=C) vibrations of the enaminoketones are strongly
coupled, possessing, in large measure, the character of out-of-phase and in-phase vibrational
modes, respectively [15-17]. Nevertheless, as previously [4-6], we shall continue to use the
∼
∼
(C=O) and (C=C) as a convenient form of shorthand.
ν
ν
In all IR-spectra of the DMTBN there were two pronounced ∼ (C=O) bands at 1686 and
ν
1672 cm−1 (in CCl4). Earlier [1,4,6] we ascribed ∼ (C=O) band with higher wavenumber to the
ν
(E-s-Z), and that with lower wavenumber to the (E-s-E) conformer, respectively. The profile of
−1
∼
the (C=C) band for the DMTBN was characterized by a major very strong band at 1591 cm
ν
with a shoulder at 1622 cm−1. In contrast to (C=O) stretching vibrations (C=C) is presented
as single band in IR-spectrum. Previously [6] we revealed that this apparent single band is
overall profile of two close highly overlapped bands: in the profile of this band for the deuterated
derivative DMTBN-d6 additional shoulder at 1562 cm−1 appeared. We used 2Dshige version 1.3
∼
∼
ν
ν
[18,19] for calculation of 2D correlation spectra of DMTBN in region of ∼ (C=C) stretching
ν
vibrations (see Fig.1) and simulated it in assumption that increase of total DMTBN concentration
changes intensities of two close bands in opposite directions (see Fig. S11). It is well known that
2D IR spectrum consists of much sharper and better resolved peaks than the corresponding 1D
spectrum [18]. The intensity changes, band shifts, and changes in band shapes are typical
spectral variations observed under dilution and temperature changes for fluorinated
enaminoketones [4-6, 20]. The effects of complex spectral feature variations, such as band shift
and line intensity changing, are best visualized with simulated model data emphasizing the
specific aspect of spectral changes. From Fig.1 it is clear that experimental and simulated spectra
2D spectra of DMTBN are very similar thus confirming our supposition. Minor discrepancies in
shape of experimental and simulated 2D spectra we account for small band drift (~1cm-1) to
lower wavenumbers when concentration increased. Hence, we fitted this profile with three
5

Lorentz bands. Basing on concentration and temperature investigations we attributed the bands at
1588 and 1593 cm−1 to the (E-s-Z) and (E-s-E) conformer, respectively [6].
In IR spectrum of DMTFBN we observed single broad band with relatively low intensity in
the region of ∼ (C=O) stretching vibrations and two very intensive bands in the region of
ν
∼ (C=C) stretching vibrations. In view of closeness of ∼ (C=O) and ∼ (C=C) bands we analyzed
ν
ν
ν
total profile of bands in region of double bond stretching vibrations. Similarly to DMTBN we
∼
assumed that (C=O) profile consists of two bands intensity of which changed in opposite
ν
∼
directions with increase of enaminoketone total concentration. As to (C=C) bands, we
ν
observed such opposite changes in intensity with concentration variations. The same trend in
band intensities we registered under temperature investigations. Using two pairs of ∼ (C=O) and
ν
-1
∼ (C=C) which intensity simultaneously changed (increasing for bands at 1704 and 1622 cm
ν
and decreasing for bands at 1694 and 1599 cm-1) under dilution (Fig.S12), we simulated profile
of DMTFBN spectrum at region of double bonds stretching vibrations. This simulation of
DMTFBN 2D correlation spectra (Fig.S13) revealed that our representation of DMTFBN
spectrum as a sum of two pairs of bands (namely, 1704 and 1622 cm-1, 1694 and 1599 cm-1) with
inverse changes of intensities corresponds to the facts. Quantum chemical calculations (PM3
method) showed that pair of bands at 1704 and 1622 cm-1 refers to (Z-s-E) conformer, whereas
the pair at 1694 and 1599 cm-1 regards to (Z-s-Z) conformer.
In case of DMTMBN situation is more complicated: IR-spectrum of this enaminoketone in
the region of double bond stretching vibrations has only one low-intensity broad band at 1672
cm-1 and one very intensive band at 1605 cm-1 with shoulder at lower frequency at 1564 cm-1. To
∼
elucidate whether there is only one isomer, or respective (C=O) and (C=C) bands are
∼
ν
ν
profiles of strongly overlapped bands of two or more isomers, we calculated 2D correlation
∼
∼
ν
ν
spectra of DMTMBN in the region of (C=O) (Fig.S14) and (C=C) vibrations (Fig.S15).
Fig.S14 shows results of simulation studies of the case, where position shift of two bands is
coupled with simultaneous intensity decrease of the band at 1692 cm-1 and intensity increase of
the band at 1660cm1 (similarly to those depicted in Fig.S16a ). The same simulation was made
∼
for (C=C) vibrations (using bands like those in Fig.S16b). It is apparent from the Fig.S14 and
ν
∼
S15 that both (C=O) and (C=C) band consists of two overlapped bands which position and
∼
ν
ν
∼
intensity varies during dilution, therefore we fitted the profile of (C=O) and
∼
ν
ν
(C=C)
vibrations with two Lorentz bands. In contrast to bands at 1672, 1660, and 1605 cm-1 the band at
1564 cm-1 did not change in intensity under temperature or concentration variation, therefore,
∼
similarly to the DMTBN, we ascribed this band to the [ (C
∼ (C=C)] vibration which is
ν
ν
−N) +
shifted to lover wavenumbers in view of mass increase of CH=C(CH3) moiety. Temperature rise
resulted in intensity increase of the pair of bands at 1660 and 1605 cm-1 with simultaneous
6

intensity decrease of the pair of bands at 1672 and 1598 cm-1 The opposite trend was observed
when passing from non polar carbon tetrachloride to polar acetonitrile: intensities of the bands at
1672 and 1598 cm-1 increased, whereas intensities of the bands at 1660 and 1605 cm-1 decreased
[20]. Earlier, basing on concentration and temperature investigations, we attributed the bands at
1672 and 1598 cm-1 to the ∼ (C=O) and ∼ (C=C) vibrations of the (E-s-Z) and the bands at 1660
ν
ν
and 1605 cm-1 to the ∼ (C=O) and ∼ (C=C) vibrations of the (E-s-E) conformer, respectively
[20]. It is worth to note that according to NMR data and results of quantum chemical calculations
there is possibility for existence of a (Z) conformer, namely, the (Z-s-Z), to which we attributed
the bands with very low intensity at 1698 cm-1 and 1628 cm-1 [20].
ν
ν
3.3. Results of DFT calculations
As it can be clearly seen from Table 1 the energy of the (E-s-E) conformer to be higher than the
energy of the (E-s-Z) conformer for DMBN, DMTBN and DMTFBN (for the last enaminoketone
hereinafter the (E-s-E) and (E-s-Z) conformers are denoted as (Z-s-E) and (Z-s-Z) , respectively,
see Scheme 2 and footnote (d) in Table 1) , whereas energies of the (E-s-Z) and (E-s-E)
conformer of DMTMBN are practically the same, although energy of the (E-s-E) conformer is
somewhat higher. Energy of the (E-s-Z) conformer of enaminoketones DMBN, DMTBN and (Z-
s-Z) conformer of DMTFBN is approximatly 13 kJ/mol lower than energy of the (E-s-E)
conformer. For all studied compounds relative energies of the (E-s-E) and (E-s-Z) isomer are
much lower than RE of the (Z-s-E) and (Z-s-Z) isomer. The (E-s-Z) and (E-s-E) conformers of
studied enaminoketones are practically planar, whereas the (Z-s-Z) and (Z-s-E) conformers are
considerably distorted, especially the conformers of DMTMBN. Particularly the (Z-s-E) isomer
of DMTMBN is significantly distorted (dihedral angle C=C-C=O is 139.3º).
According to experimental data for the enaminoketones DMBN, DMTBN and DMTFBN
(as it was mentioned for the last enaminoketone denomination conformers is (Z-s-E) and (Z-s-
E), respectively ) the (E-s-E) conformer is more stable in comparison with the (E-s-Z) conformer
(see enthalpies of Trans-s-cis
Trans-s-trans equilibrium in Table 1). In previous work [21]
we showed that this discrepancy between results of spectroscopic measurements and quantum
chemical calculations is a consequence of hydrogen bond formation between (E-s-Z) and (E-s-E)
conformer (see Scheme 3). More detailed discussion of this problem is done in Discussion part
of this work.
3.4. Solvent influence on IR spectra of the enaminoketones.
7

Solvent effects on the ∼ (C=O) and ∼ (C=C) bands were investigated in various solvents and
we correlated obtained wavenumbers with solvatochromic parameters of Kamlet, Abboud and
Taft [22] in accord with Eq. (1):
ν
ν
2
∼
∼
ν
ν
=
0 + (sπ* + dδ) + aα + bβ + h δH
(1)
∼
∼
ν
∼
ν
ν
where is the vibration wavenumber of solute [such as (C=O) and (C=C) vibration] in pure
solvent and 0 is the regression value of the ∼ (C=O) and ∼ (C=C) vibration in cyclohexane as a
reference solvent, π* is an index of solvent’s dipolarity/polarizability, δ is a discontinuous
polarizability correction term for poly-chlorine substituted aliphatic and aromatic solvents, α is a
measure of the solvent’s hydrogen bond donor acidity, β is a measure of the solvent hydrogen
bond acceptor basicity, and δH is the Hildebrand’s solubility parameter. In Table 2 we presented
the results of KAT correlations (Eqs.2-13) for all investigated enaminoketones.
∼
ν
ν
ν
3.5. Temperature investigations.
After band fitting the integrated intensity of each ∼ (C=O) and ∼ (C=C) band was calculated
ν
ν
according to Eq. (14).
A = (cs × d)−1 ×
log(Io /I)dν
(14)
∫
band
where A (l mol−1 cm−2) is integrated intensity of the ν(C=O) or ν(C=C) band, cs (mol/l) is the
concentration of the given conformer in solution, d (cm) stands for the cell pathlength. The main
problem was to evaluate the concentration of each stereoisomeric form cs. Since all
enaminoketones studied were presented as conformer equilibrium (E-s-Z)
(E-s-E) which
depended on total concentration of enaminoketone and temperature, we used the method
proposed earlier [6] for analysis of conformational equilibria assuming that the absorption
coefficients of corresponding bands were temperature independent. We plotted integrals of
∼ (C=O) (E-s-Z) vs. integrals of appropriate ∼ (C=O) (E-s-E) at various total concentrations of
ν
ν
the enaminoketone, ctotal, provided the product ctotal × pathlength was constant. Intercepts of this
∼
ν
plot with axes were integrals of
(C=O) bands of the (E-s-Z) and (E-s-E) conformer,
respectively, but for all that the concentration of the conformer equaled the total concentration of
enaminoketone, ctotal. Knowing the cell pathlength and ctotal, it was easy to calculate integrated
intensities of the ∼ (C=O) band of each conformer, and, hence, to evaluate from Eq. (14) the
ν
concentration of each stereoisomeric form, cs, at given temperature. From temperature
dependence of lnKeq = f(1/T), where Keq is an equilibrium constant, we calculated
8

thermodynamic parameters of the equilibrium (E-s-Z)
(E-s-E). The results are listed in
Table 1.
3.6. Evaluation of enaminoketone hydrogen-bond basicity.
Taft and co-workers [23] defined hydrogen-bond basicity pKHB as log Kf for the 1:1
complexation of bases with 4-fluorophenol (4FP) in carbon tetrachloride at 298 K, [Eqs. (15)-
(17)].
B + 4-FC6H4OH
4-FC6H4OH···B
(15)
(16)
(17)
Kf = [Hydrogen-bond complex]/[B][4-FC6H4OH]
pKHB = -log10 (dissociation constant of the complex) = log10 Kf
General equilibrium constant Kfav is defined by Eq. (18)
Kfav = Cc/CaCb = (Caº Ca)/[Ca(Cbº Caº + Ca)]
(18)
−
−
where Cc, Cb, Ca are the equilibrium concentrations of complex, base (enaminoketone) and acid
(4FP), respectively, and Caº and Cbº are initial concentrations determined by weight. Ca is
obtained from the IR absorbance of the free OH band of (4FP) at 3614 cm-1 (ε = 235 dm3 mol-1
cm-1 [24]). The equilibrium constants are taken as the mean of 9-10 values corresponding to 9-10
base concentrations. These concentrations are chosen such that the complex percentage is kept in
the range 20−80% of the initial acid concentration. All measurements are carried out at the (4FP)
concentration 7.4 × 10-3 mol dm-3 in order to avoid self-association. Kf is estimated to be
accurate to within 5-10% and consequently pKHB values are given to within 0.02÷0.05 pK units.
Kf evaluated thereby is average equilibrium constant which reflects general enaminoketone
basicity without sharing it between the (E-s-Z) and (E-s-E) stereoisomeric forms. Method of
estimation of equilibrium constants and enthalpies of hydrogen bond formation of individual
stereoisomeric forms is described in [25]. Results are listed in Table 3.
4. Discussion
4.1. Conformer stability according to DFT calculations and experimental data.
From Table 1 it is obvious that calculated relative energies (RE) of individual conformers
and enthalpies of equilibrium of these conformers are in good agreement with exception of
DMTBN, where according to DFT calculation (E-s-Z) conformer is more stable than (E-s-E)
one, whereas enthalpy of (E-s-Z)
(E-s-E) equilibrium testify to the effect that (E-s-E)
conformer is more stable. As it is follows from Fig.2 the dipole moment of the DMTBN
decreases with concentration increase although dielectric constant εr increases with increase of
9

total enaminone concentration. We interpreted this fact as evidence of H-complex formation
between molecules of the enaminoketone. Moreover, as we have shown in [4] the dependence of
band intensities on total DMTBN concentration was observed not only for ν(C=O) and ν(C=C)
but also for ν(C-H) and ν(C-F) stretching vibrations. Analyzing all these phenomena we reached
a conclusion that the (E-s-Z) and (E-s-E) conformers of DMTBN form ‘closed-ring’ hydrogen
bonded complex as it is shown on Scheme 3. We revealed that complex formation occurs in two
stages: at first, H-bond Cα− H···O=C arises with K = 214.4 M-1 and ∆H = 27.48 kJ M-1, and
-1
-1
−C
after that H-bond Cα− H···F F2 is formed with K = 16.4 M and ∆H = 6.71 kJ M . We assume
that just this complexation accounts for discrepancy between enthalpies (∆H) evaluated
experimentally for conformer equilibrium (E-s-Z)
(E-s-E) and calculated relative energies
(RE) of these conformers. Similar discrepancies were observed for many other β-alkylamino
vinyl perfluoroalkyl ketones [4]. On the other hand, we did not observe such discrepancies for
non-fluorinated DMBN and α-substituted enaminoketones DMTFBN and DMTMBN (see Table
1) where formation of ‘closed-ring’ hydrogen bonded complex is impossible.
4.2. Influence of α-substitution on hydrogen-bond basicity of enaminoketones.
α-Substitution changes sharply of electron density distribution in enaminoketone
conjugated system. This effect can be illustrated by comparison of hydrogen-bond basicity of
DMBN, DMTBN and its α-F and α-CH3 substituted derivatives (Table 3). It easy to notice that
fluorination of methyl group in DMTBN diminishes drastically hydrogen-bond basicity and
enthalpies of hydrogen bond formation (−∆H) of both conformers due to electron withdrawal
ability of CF3 group [25]. Introduction of fluorine atom as α-substituent in DMFTBN lowers
carbonyl hydrogen-bond basicity due to enhancement of electron withdrawal from carbonyl
oxygen. At the same time introduction of electron donating CH3 group into α-position strongly
increases carbonyl hydrogen-bond basicity and negative value of enthalpy of complexation
−∆H
(
) becomes even higher than the one for non-fluorinated DMBN.
4.3. Solvent influence on IR spectra of studied enaminoketones.
Influence of α-substitution on distribution of electron density in conjugated
enaminoketone system is more pronounced when spectra are compared in various solvents.
Generally speaking solvent influence on IR spectra depends on distribution of electron density in
solute molecule. The model equation of the linear solvation energy relationship (LSER) applied
in infrared spectroscopy is shown as Eq. (1). Besides the dielectric effects, reflected by solvent
polarity/polarizability term (π∗) of Eq. (1), solvent molecules interact directly with the C=O and
10

C=C group by two kinds of attractive forces. The first of these forces is that the solvent molecule
forms a hydrogen bond with oxygen of the carbonyl group (or with its π-system). The capability
of solvent to donate proton in solvent-to-solute (enaminoketone) hydrogen bond is described by
parameter α, solvent HBD acidity. The second is that the solvent molecule which has
electronegative atoms O, N or other can form hydrogen bonds with a solute as proton donor.
Parameter β describes the ability of a solvent to accept proton in solute-to-solvent hydrogen
bond, i.e. its hydrogen bond acceptor capability with respect to a reference hydrogen bond donor.
∼
We correlated the wavenumbers of the (C=O) and (C=C) bands with solvatochromic
∼
ν
ν
parameters of various solvents according to Eq. (1) and presented the results in Table 2 as
2
regression coefficients of parameters π*, δ, α, β, and δH denoting each set of obtained
coefficients as appropriate Eqs. (2) – (13) for stereoisomeric forms of studied enaminoketones.
Only terms at the 0.95 significance level or higher were retained. The quality of multiple linear
regressions is indicated by the standard error of the estimate (S.D., the smaller the better), the
Fisher index of reliability (F, the larger the better), and the correlation coefficient (R, variance =
R2, the closer to 1 the better) [22]. A correlation equation was considered as acceptable if the
product correlation coefficient, R, indicates that the equation accounts for more than 80% of the
variance (R2 ≥ 0.80). From Eqs. (2) – (13) it followed that even conformers of the same studied
enaminoketone differed notably in sensitivity to solvent influence, therefore it was reasonable to
examine these multiple correlations for studied enaminoketones separately and then to compare
the results obtained. Analysis of Table 2 revealed some general features: equations for all studied
enaminoketones were statistically significant (R2 ≥ 0.80) with exception of the Eq. (3) where R2
were much less then 0.8 (0.761), therefore we excluded this equation from consideration.
Another similarity was that almost in all equations coefficients d of parameter δ (a discontinuous
polarizability correction term) were insignificant, i.e. less then standard error of estimate (S.D.).
Negligible contribution of the discontinuous polarizability correction term δ in Eq. 1 we noted
∼
earlier for multiple correlations of the (C=O) and (C=C) bands of DMBN [6].
∼
ν
ν
4.1.1. Enaminoketone DMTBN
The detailed analysis of solvent influence on IR spectra of the DMTBN was done in our
previous works [6,20]. Here we adduce general conclusions according to which main
∼
∼
ν
ν
contribution to the (C=O) and (C=C) vibrations of both (E-s-Z) and (E-s-E) conformers
made the solvent’s hydrogen bond donor (HBD) acidity term (α) whereas solvent’s
polarity/polarizability (π∗) influenced in much less extent [see Table 2, Eqs (2)-(5)].
∼
Consequently, hydrogen bond formation determines the (C=O) and (C=C) bond shifts to
∼
ν
ν
lower wavenumbers. In case of (E-s-E) conformer contribution of the solvent’s
11

∼
polarity/polarizability term (π∗) to the (C=O) mode is greater than in the (E-s-Z) conformer
ν
due to the greater polarity/polarizability of carbonyl group in the (E-s-E) conformer. In so far as
vibrational coupling takes place, therefore, the out-of-phase component will go to increase the
∼
wavenumber and decrease the intensity of the upper [ (C=O)] vibration, whereas the in-phase
ν
∼
component will have the reverse effect on the (C=C) [11].
ν
4.1.2. Enaminoketone DMTFBN
∼
∼
In contrast to DMTBN the main influence on the (C=O) and (C=C) vibrations of
ν
ν
both (Z-s-Z) and (Z-s-E) conformers has solvent’s polarity/polarizability (π∗) term [Eqs (6)-(9)].
∼
∼
ν
ν
Hence, shift of the (C=O) and (C=C) bands to lower wavenumbers is principally defined by
dispersion interactions of this enaminoketone with solvent molecules. This fact confirms
conclusion of lowered hydrogen-bond basicity of carbonyl oxygen in DMTFBN in comparison
with DMTBN. Some exception has Eq.(7) where coefficients s and a are almost equal, that is
influence of the solvent’s polarity/polarizability (π∗) and solvent’s hydrogen bond donor (HBD)
∼
acidity term (α) on (C=C) vibrations enhance each other. It is worth to note that influence of
ν
∼
the solvent’s polarity/polarizability (π∗) term on (C=O) band of the (Z-s-Z) conformer [Eq.(6)]
ν
∼
is much higher than this influence on (C=C) band [Eq.(7)], whereas for the (Z-s-E) conformer
ν
these values are almost the same [cf. coefficient s in Eq.(8) and (9)]. From this comparison it is
follows that distribution of electron density in the (Z-s-Z) conformer is different than in the (Z-s-
E) conformer.
4.1.3. Enaminoketone DMTMBN.
∼
Solvent influence on the (C=O) and (C=C) vibrations of the (E-s-Z) and (E-s-E)
∼
ν
ν
conformers of the DMTMBN is very similar to that on corresponding conformers of the
DMTBN. It is easy to notice from Table 2 [Eqs (10) and (12)] that the main influence on the
∼
ν
(C=O) vibrations of both conformers has the solvent’s hydrogen bond donor (HBD) acidity
∼
term (α). The same is true for the (C=C) vibrations of the (E-s-Z) conformer, whereas for the
ν
(E-s-E) coefficient a is twice as large as coefficient s, that is the solvent influence on the
∼
ν
(C=C) vibrations of the (E-s-Z) conformer is realized predominantly through solvent’s
polarity/polarizability. It is worth to note that in both the (E-s-Z) and (E-s-Z) conformer the
solvent’s hydrogen bond acceptor (HBA) basicity term (β) makes significant contribution
12

∼
increasing the (C=C) wavenumbers as a result of disturbance of the (C=O) and (C=C)
∼
∼
ν
ν
ν
vibration coupling.
Comparing the enaminoketones DMTBN and DMTMBN it is obvious that in both cases
∼
∼
ν
ν
the solvent influence on the
(C=O) and
(C=C) vibrations is very similar and little
discrepancies are caused by the fact that both conformers of the enaminoketone DMTPN are
nonplanar (see Table 1).
5. Conclusions
1. All studied enaminoketones are TRANS isomers relatively to C=C double bond
independently to α-substituent and solvent polarity and form s-cis and s—trans conformers
relatively to C-C formally single bond.
2. s-Cis and s—trans conformers of DMTBN form ‘closed-ring’ hydrogen-bonded
complex in two stages.
3. ‘Closed-ring’ complex formation of DMTBN is a root of discrepancies between results
of DFT calculations of conformer stability and experimentally evaluated enthalpies of conformer
equilibrium.
4. α-Substitution strongly influences on enaminoketone hydrogen-bond basicity. Electron
withdrawing α-substitutuents lower hydrogen-bond basicity whereas electron-donating α-
substitutuents increase it significantly.
5. Solvent influence on IR-spectra of studied enaminoketones strongly depends on
electronic properties of α-substituent.
13

REFERENCES
[1] S.I. Vdovenko, I.I. Gerus, M.G. Gorbunova, J. Chem. Soc., Perkin Trans.2 (1993) 559.
[2] J. Wójcik, W. Domalewski, K. Kamieńska-Trela, L .Stefaniak, S.I. Vdovienko, I.I. Gerus,
M.G. Gorbunova, Magn Reson. Chem. 31 (1993) 808.
[3] I.I. Gerus, L.M.Kacharova, S.I. Vdovenko, Synthesis (2001) 431.
[4]. S. I. Vdovenko, I. I. Gerus, O.V. Balabon, V.P. Kukhar, Trends in organic chemistry 16
(2012) 93.
[5]. S.I. Vdovenko, I.I. Gerus, E.A. Fedorenko, Spectrochim. Acta Part A 74 (2009) 1010.
[6]. S.I. Vdovenko, I.I. Gerus, V.P. Kukhar, Vibrational Spectroscopy 52 (2010) 144.
[7]. I.S. Kondratov, V.G. Dolovanyuk, N.A. Tolmachova, I.I. Gerus, K. Bergander, R. Fröhlich, G.
Haufe, Org. Biomol. Chem. 10, (2012) 8778.
[8] I. I. Gerus, Y. I. Zhuk, L. M. Kacharova, G.-V. Röschenthaler, Book of Abstracts of 20th
International Symposium on Fluorine Chemistry, Kyoto, Japan, July 22-27, 2012, 234.
[9]. C.M. Kascheres, J. Braz. Chem. Soc. 14 (2003) 945.
[10]. J. Dąbrowski, K. Kamieńska-Trela, Spectrochim. Acta, 22 (1966) 211.
[11]. S.F. Tayyari, M. Fazli, F. Milani-nejad, J. Mol.Struct.(Theochem), 541 (2001) 11.
[12]. M.Bugaj and K. Kamieńska-Trela, Polish J.Chem., 80 (2006) 1217.
[13]. J. Wójcik, W. Domalewski, K. Kamieńska-Trela, L .Stefaniak, S.I. Vdovienko, I.I. Gerus,
M.G .Gorbunova, Magn. Reson. Chem., 31(1993) 808.
[14]. J. Wόjcik, K. Kamieńska-Trela, M. Pecul, E. Bartoszak-Adamska, S.I. Vdovenko, I.I. Gerus,
Chem. Phys. Phys. Chem., 5 (2004) 209.
[15]. P.J. Taylor, Spectrochim. Acta, Part A 32 (1976) 1471.
[16]. R.A. Nyquist, Interpreting Infrared, Raman, Nuclear Magnetic Resonance Spectra Vol.1,
Academic Press, 2001.
[17]. D. Smith and P.J. Taylor, Spectrochim. Acta, Part A 32 (1976) 1477.
[18]. S. Noda, Yu. Ozaki, Two-dimensional Correlation Spectroscopy – Applications in
Vibrational and Optical Spectroscopy, John Wiley & Sones, Ltd, 2004.
[19]. 2Dshige (c) Shigeaki Morita, Kwansei-Gakuin University, 2004-2005.
[20]. S.I.Vdovenko, I.I.Gerus, H.A.Fedorenko, Spectrochim. Acta, Part A 103 (2013) 368.
14

[21]. S.I.Vdovenko, I.I.Gerus, H.A.Fedorenko, V.P.Kukhar, ISRN Spectroscopy 2013, Article ID
640896, doi:20.5402/2012/640896.
[22]. M.H. Abraham, R.M. Doherty, M.J. Kamlet, J.M. Harris, R.W. Taft, J. Chem. Soc. Perkin
Trans.2 (1987) 913.
[23]. D. Gurka, R.W. Taft, J. Am. Chem. Soc. 91 (1969) 4794.
[24]. F. Besseau, M. Luçon, C. Laurence, M. Berthelot, J. Chem. Soc. Perkin Trans. 2 (1998) 101.
[25]. S.I.Vdovenko, I.i.Gerus, E.A.Fedorenko, V.P.Kukhar, J.Mol.Struct. 977 (2010) 237.
15

Captions for figures
Fig.1. Synchronous (A) and asynchronous (B) spectrum of DMTBN under dilution in the region
of ν(C=C) stretching vibrations;
Simulated synchronous (C) and asynchronous (D) spectrum of DMTBN in the region of
ν(C=C) stretching vibrations.
.
Fig. 2. Dependence of dipole moment (µ)vs. total concentration of DMTBN.
Scheme 1. Synthesis of studied enaminoketones.
Scheme 2. Possible stereoisomeric forms of the enaminoketones CF3CO-CR1=CH-NR2R3.
Scheme 3. Hydrogen bond cyclic complex formation between the (E-s-Z) and (E-s-E)
conformers.
16

(A)
(C)
(B)
(D)
Fig.1. Synchronous (A) and asynchronous (B) spectrum of DMTBN under dilution in the region of ν(C=C)
stretching vibrations;
Simulated synchronous (C) and asynchronous (D) spectrum of DMTBN in the region of ν(C=C) stretching
vibrations.
17

7.2
7.0
6.8
6.6
6.4
6.2
6.0
5.8
5.6
5.4
5.2
5.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
C, M
Fig. 2.
18

Scheme 1.
19

R2
H
R3
R2
H
R3
H
O
N
O
H
CF3
N
CF3
R2
R2
N
CF3
N
O
CF3
O
R3
R1
R1
R3
R1
R1
(R =H,Me)
1
(R1=H,Me)
E-s-E-n-E
E-s-Z-n-E
Z-s-Z-n-E (R1=H,Me)
E-s-E-n-E (R1=F)
(R =H,Me)
1
Z-s-E-n-E
Z-s-Z-n-E (R1=F)
E-s-E-n-E (R1=F)
Z-s-E-n-E (R1=F)
R3
H
R2
R3
H
R2
H
O
N
O
H
CF3
N
CF3
R3
R3
N
CF3
CF3
N
O
O
R2
R1
R2
R1
R1
R1
(R =H,Me)
1
Z-s-Z-n-Z (R1=H,Me)
(R =F)
E-s-E-n-Z (R1=H,Me)
Z-s-E-n-Z (R1=F)
E-s-Z-n-Z (R1=H,Me)
(R =F)
Z-s-E-n-Z
(R =F)
1
Z-s-Z-n-Z
E-s-E-n-Z
E-s-E-n-Z
1
1
Scheme 2.
20

Scheme 3.
21

Table 1. Calculated Total Energy, Relative Energya (RE), dipole moment (µ) and dihedral angle C=C–C=O (φ) of
studied enaminones by DFT method and thermodynamic parameters of Trans-s-cis
Trans-s-trans
equilibrium evaluated experimentally.
Thermodynamic parameters
of Trans-s-cis
s-trans equilibrium
Basis set 6-311G**
Trans-
Confor-
Enaminone
mer
Energy,
kJ dm3 mol-1
-953473.99
-953485.92
RE,
kJ dm3 mol-1
11.93
µ, D
φ, °
∆H,
∆S,
kJ mol-1
J mol-1 K-1
E-s-E
E-s-Z
5.75
4.66
179.3º
0.2º
DMBN[6]b
DMTBN[6]
9.72 1.89
-206.1 6.4
0
E-s-E
E-s-Z
Z-s-E
Z-s-Z
-1734386.52
-1734399.26
NEc
12.74
7.0
7.0
-
180.0
0.5
-
-10.64 0.27
-210.8 0.9
0
-
-1734367.96
31.30
6.2
7.6
E-s-E
E-s-Z
Z-s-E
Z-s-Z
-1994268.34
-1994302.11
-1994321.38
-1994333.74
64.66
31.63
12.36
0
6.5
6.3
6.4
6.3
156.7
4.1
DMTFBNc
179.9
0.8
11.76 1.06
12.13 1.55
-214 2.6
E-s-E
E-s-Z
Z-s-E
Z-s-Z
-1837019.56
-1837018.47
-1836989.31
-1837002.51
0
6.6
6.6
5.3
5.2
176.3
0.3
-204.0 5.4
1.09
30.25
17.05
DMTMBN[20]
139.3
21.2
aRelative Energy (RE) – the difference of energies of the conformers;
b 4-(dimethylamino)but-3-en-2-one
c NE – “not exists”: the conformer was transformed in ZZ-isomer under the geometry optimization;
d Denomination Z-s-E and Z-s-Z corresponds to Trans-s-cis and Trans-s-trans, respectively, for enaminoketone
DMTFBN in accord with IUPAC demands.
22

Table 2. The coefficients (s, d, a, b, and h), error of estimate (S.D.), Fisher index of reliability (F), and correlation coefficients (R2) of common
~
~
correlation equation Eq. (1) for  (C=O) and  (C=C) bands of studied enaminoketones F3C-CO–CR=CH–N(CH3)2. Solvatochromic parameters are
from [20].
Stereoisomeric
form
Independent
variable
Eq.
No.
Substituent R
Intercepta
1692
s
a
b
d
h
N
S.D.
0.87286 20.494
3.1461 13.590
0.73229 124.17
F
R2
~
–1.814
–4.766
5.483
–3.262
18
0.903
2
-10.207

(C=O)
E-s-Z
E-s-E
Z-s-Z
Z-s-E
E-s-Z
E-s-E
1598
1674
1597
7.056
–4.574
–3.335
–0.493 b
–0.748 b
–4.218
–1.650 b
0.090 b
1.860
–10.847
–0.417b
–0.692b
18
18
18
0.761
0.981
0.970
3
4
5
~
–11.051
–8.015
–8.242

(C=C)
1
2
3
H
~

(C=O)
~
1.0656
3.7652
76.969
29.524

(C=C)
1688
-10.726
-2.758b
-0.3610
8.961
21
0.908
6
~
-36.654

(C=O)
1608
1704
1631
-4.761
-1.183b
-3.306b
0.4800b
-0.2788b
-0.0895b
-2.403
3.281
-1.588
21
21
21
2.030
1.7109
1.4565
69.905
96.921
223.99
0.9589
0.970
0.987
7
8
9
~
-11.383
-22.787
-23.360
-12.899
-12.669
-14.533

(C=C)
F
~

(C=O)
~

(C=C)
1671
-7.906
2.769b
-1.117b
-0.730b
20
2.5017
24.612
0.905
10
~
-12.099

(C=O)
1598
1669
1603
-17.900
-4.988
6.500
-3.722
8.863
-0.2371b
-0.2055
-0.2679b
7.197
-8.689
8.831
20
20
20
2.3828
3.7545
2.4835
76.739
20.925
30.153
0.984
0.890
0.921
11
12
13
~
-24.678
-10.259
-12.724

(C=C)
CH3
~

(C=O)
~
-23.733

(C=C)
a Wavenumber, cm-1. b Not significant.

Table 3. Hydrogen bond basicity of the conformers (E-s-Z) and (E-s-E) ( for DMTFBN these conformers are
denoted as (Z-s-Z) and (Z-s-E)) of studied enaminoketones: frequency shifts ∆ν(OH), complex formation constants
−∆H).
Kf, pKHB values and enthalpies of hydrogen bond formation (
∆ν(OH), cm-1
Enaminoketone
DMBN[25]
conformer
E-s-Z
Kf
pKHB
2.363
2.801
−∆H,(kJ/M)
20.53 5.41
35.70 4.11
334
457
230.5
633.1
E-s-E
E-s-Z
E-s-E
212
325
35.8
42.5
1.554
1.628
15.84 1.47
29.58 2.18
DMTBN[25]
DMTFBN
Z-s-Z
Z-s-E
126
156
10.2
30.8
1.007
1.488
16.48 1.37
22.30 2.14
E-s-Z
E-s-E
206
253
690.76
553.35
2.839
2.743
31.84 1.50
40.82 2.11
DMTMBN
23

The conformational analysis of push-pull enaminones
using Fourier transform IR and NMR spectroscopy,
and quantum chemical calculations. V.  Methyl,
Fluorine–N,N−Dimethylaminovinyl trifluoromethyl
ketones
F3C
O
Keq
O
CF3
Represented equilibrium depends both on solvents
and temperature.
-Substitution strongly influences on
enaminoketone hydrogen-bond basicity.
H
H
R
(CH3)2N
(CH3)2N
R
Sergey I. Vdovenko, Igor I. Gerus, Yuri I. Zhuk,
Valery P. Kukhar, Gerd-Volker Röschenthaler
R = H (DMTBN); R = F, (DMTFBN); R =
CH3,(DMTMBN)

Highlights
1. All studied enaminoketones are TRANS isomers wich form s-cis and s—trans conformers.
2. s-Cis and s—trans conformers of DMTBN form ‘closed-ring’ hydrogen-bonded complex.
3. α-Substitution strongly influences on enaminoketone hydrogen-bond basicity.
4. Solvent influence on IR-spectra of studied enaminoketones strongly depends on α-substituent.
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