Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці
Comparison of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones under exposure to UV-irradiation (λ = 275 nm (I), 290-300 nm, (II), 300-320 nm (III)) was studied by the FTIR spectroscopy and quantum chemical calculation (DFT...
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V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine
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Ukrainica Bioorganica Acta| _version_ | 1871193624501288960 |
|---|---|
| author | Vdovenko, Sergey I. Gerus, Igor I. Fedorenko, Olena A. |
| author_facet | Vdovenko, Sergey I. Gerus, Igor I. Fedorenko, Olena A. |
| author_institution_txt_mv | [
{
"author": "Sergey I. Vdovenko",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine"
},
{
"author": " Igor I. Gerus",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine"
},
{
"author": "Olena A. Fedorenko",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine"
}
] |
| author_sort | Vdovenko, Sergey I. |
| baseUrl_str | https://bioorganica.com.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-07-19T14:56:55Z |
| description | Comparison of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones under exposure to UV-irradiation (λ = 275 nm (I), 290-300 nm, (II), 300-320 nm (III)) was studied by the FTIR spectroscopy and quantum chemical calculation (DFT method). These are modeling drug compounds that contain vinyl trifluoromethyl ketone motif such as C2H5O–CH=C(R)–COCF3 (I-III) (I: R = H; II: R = F; III; R = CH3) in Ar-matrix. It was found that all conformational changes of enone (I) occur exclusively due to hindered rotation around CH2–O single bond. Contrary to enone (I), interconversion of conformers in enone (II) occurs predominantly due to synchronous rotation of the trifluoromethyl carbonyl group around O=C–C=C single bond and ethoxy group around EtO–C= single bond as a result of the mesomeric effect of the α-fluorine substituent. Introduction of methyl group as α-substituent reduces the ability of ethoxy group to hinder rotation around EtO–C= single bond. It was found that experimental kinetic parameters (k1 and k-1 rate constants) and calculated thermodynamic parameters (changes of zero-point corrected relative energies Δ(ΔE+ΔZPE)) of all studied processes form a single good correlation. Comparison with similar correlation for α-substituted β-diethylaminovinyl trifluoromethyl ketones reveals that conjugation in enaminoketone molecules is much weaker than that in appropriate α-substituted β-ethoxyvinyl trifluoromethyl ketones |
| doi_str_mv | 10.15407/bioorganica2025.01.032 |
| first_indexed | 2025-07-17T12:20:10Z |
| format | Article |
| fulltext |
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 1
UDC 543.632.52+547.221
DOI: https://doi.org/10.15407/bioorganica2025.01.032
32
Ukrainica Bioorganica Acta
www.bioorganica.org.ua
RESEARCH ARTICLE
Correlation of kinetic and thermodynamic parameters of conformational
transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones
under ultraviolet irradiation in an argon matrix
Sergiy I. Vdovenko*, Igor I. Gerus, Olena A. Fedorenko
V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine
Abstract: Comparison of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl
trifluoromethyl ketones under exposure to UV-irradiation (λ = 275 nm (I), 290-300 nm, (II), 300-320 nm (III)) was studied by the FTIR
spectroscopy and quantum chemical calculation (DFT method). These are modeling drug compounds that contain vinyl trifluoromethyl
ketone motif such as C2H5O–CH=C(R)–COCF3 (I-III) (I: R = H; II: R = F; III; R = CH3) in Ar-matrix. It was found that all
conformational changes of enone (I) occur exclusively due to hindered rotation around CH2–O single bond. Contrary to enone (I),
interconversion of conformers in enone (II) occurs predominantly due to synchronous rotation of the trifluoromethyl carbonyl group
around O=C–C=C single bond and ethoxy group around EtO–C= single bond as a result of the mesomeric effect of the α-fluorine
substituent. Introduction of methyl group as α-substituent reduces the ability of ethoxy group to hinder rotation around EtO–C= single
bond. It was found that experimental kinetic parameters (k1 and k-1 rate constants) and calculated thermodynamic parameters (changes of
zero-point corrected relative energies Δ(ΔE+ΔZPE)) of all studied processes form a single good correlation. Comparison with similar
correlation for α-substituted β-diethylaminovinyl trifluoromethyl ketones reveals that conjugation in enaminoketone molecules is much
weaker than that in appropriate α-substituted β-ethoxyvinyl trifluoromethyl ketones.
Keywords: conformers; interconversion; α-substituted β-ethoxyvinyl trifluoromethyl ketones; Ar-matrix.
Introduction
Isomerism of bioorganic molecules plays an extremely
important role in biochemistry [1, 2]. The knowledge of
possible conformations and their energy is especially
important for understanding the interactions between two
molecules, e.g. drug and receptor [3]. The structure of
numerous drugs contains α,β-unsaturated carbonyl systems
herefore enaminones have received a large attention as
potential prodrugs [4] and as potent allosteric modulators of
γ-aminobutyric acid A (GABA-A ) receptors [5]. Moreover,
enaminones are important organic intermediates used to
Received:
Revised:
Accepted:
Published online:
02.04.2025
28.04.2025
06.05.2025
30.06.2025
Corresponding author. Tel.: +380-44-573-2552;
e-mail: sergiuszvdovenko@gmail.com (S.I. Vdovenko)
ORCID: 0000-0002-0988-5250
synthesize various heterocyclic and biologically active
analogues. It is well known that fluorine atom or fluorine-
containing substituents play the outstanding role in drug
discovery. A vast majority of recently approved fluorinated
drugs contain CF3-group attached to benzene or other
(hetero)aromatic ring [6]. These substances can be easily
synthesized from readily available starting compounds
containing vinyl trifluoromethyl carbonyl motif, such as
β-(alkoxy-, dialkylamino)vinyl trifluoromethyl ketones [7].
Under the influence of external factors (temperature,
solvent polarity, ultraviolet irradiation), these trifluoroacetyl
vinyl compounds easily change their spatial structure and,
as a consequence, their reactivity. From this point of view it
is essential to investigate to quantitatively evaluate the
effect of ultraviolet irradiation on the isomerization of a
number of model compounds containing the fragment
C=C–C(O)CF3.
During last time very close attention has been given to
the development of methods to incorporate fluorine into
organic molecules. Many drugs or drug precursors now
feature fluorine for these reasons. For example Takagi et al
© Vdovenko S.I. et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited.
https://orcid.org/0000-0002-0988-5250
S.I. Vdovenko et al.
33
Figure 1. Experimental (a) and simulated spectra (b) in the region of double bond stretching vibrations of enones (I-III). (Numbers on
color marks correspond to spacial structures in Figure S8-S10).
[8-9] have reported the syntheses of several trifluorinated
analogues of daunomycin and and adriamycin which have
shown good antitumour activities. Nino Zanatta et al have
reported a three-step synthesis of a new series of 4-sub-
stituted 2-oxo-6-trihalomethyl-[1,3]oxazinane-3-carboxylic
acid ethyl esters, basing from -alkoxyvinyl trihalomethyl
ketones of general formula X3C–C(O)–CHC(R)–OR1,
where R = H, Me, Ph, and 4-Me-Ph; R1 = Me and Et; and X
= F and Cl. Some of the analyzed carbamates exhibited
significant in vitro antimicrobial activity [10]. Versatile
application of fluorinated organic compounds in many
different but interconnected research fields have been
described in detail in [11]. In particular, it was stated the
high sensitivity of 19F in nuclear magnetic resonance
(NMR) experiments makes this nucleus ideal for biological
studies, requiring the previous preparation of fluorine
containing amino acids and their further incorporation into
proteins [12].
Recently [13] it was shown that s-(tert-
butyl)trifluorothioacetate containing trifluoromethyl
carbonyl moiety has two feasible conformers, namely, syn-
and anti-form. The conformational preference and photo-
chemistry were studied by means of FTIR spectroscopy
(gas phase and Ar-matrix). Similarly, monomers of meta-
fluorophenol were trapped from gas phase into cryogenic
argon and nitrogen matrices, which were subjected to
irradiation with UV light and the phototransformations were
observed in these experiments [14]. The most suitable
synthons allowing to incorporate fluorine into various
bioorganic and organic molecules are β-alkoxyvinyl
trifluoromethyl ketones [10, 11, 13, 14]. We have been
concerned for a long time both with the synthetic use of
trifluoromethyl vinyl ketones [14, 15] and mechanistic
aspects [16-19] involved in the reaction of these compounds
with amines.
Earlier [17] we have shown alkoxyvinyl trifluoromethyl
ketones to form different conformers due to hindered
rotation around various bonds, namely C=C double bond,
=C−C single bond between vinyl and carbonyl group and
=C−O single bond between vinyl moiety and alkoxy group.
Distribution of electron density in enones strongly depends
on molecular spatial structure, i.e. on isomer/conformer
composition [18, 19].
Moreover, recently we have shown [18] that different
conformers of ethoxyvinyl trifluoromethyl ketones with
distinct structure exhibited different reactivity. In nonpolar
solvents and in neat liquids three -substituted -ethoxy-
vinyl trifluoromethyl ketones form various conformers. It is
worth to note that at room and moderately elevated
temperatures (20-80 ºC) these conformers are stable and not
prone to mutual transitions.
Earlier [20] we have quantitatively investigated
interconversion of different stereoisomeric forms of
α,β-unsaturated enaminoketones in Ar-matrix being
exposed to UV-irradiation. To our knowledge similar very
informative quantitative investigations of -substituted
-ethoxyvinyl trifluoromethyl ketones have not been carried
out yet. As it has been mentioned above it was essential to
fill the gap in experimental estimations of kinetic
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 1
34
parameters (direct k1 and reverse k-1 constants) and
calculated thermodynamic parameters (relative energies
(ΔE+ΔZPE) of products of interconversion processes) of
E ⇄ Z isomerization of possible isomers/conformers of
three model -substituted -ethoxyvinyl trifluoromethyl
ketones with general formula F3C–CO–CR=CH–OC2H5,
where R = H (I), R = F (II), and R = CH3, (III), in Ar
matrix under UV-irradiation.
Results and Discussion
Two-dimentional correlation spectroscopy
Although assignment of enone (I-III) initial conformers
have been done earlier [15] it was essential to carry out the
ν(C=O) and ν(C=C) band assignment of the interconversion
products of these conformers. For this purpose it was
conducted analysis of corresponding 2D IR correlation
spectra of enones (I-III) under UV-irradiation. To elucidate
sequence of spectroscopic intensity changes and succession
of changes of different stereoisomeric forms of enones
(I-III) in Ar matrix exposed to narrow-band UV-irradiation
we resorted to analyze the 2D IR correlation maps (see
Figure 1) [32-34]. A detailed description of the analysis of
the two-dimensional IR spectrum of enone (I) serves as an
illustration of the analytical technique applied to the
conformers of enones (I-III) in Ar matrices exposed to UV-
irradiation.
Analysis of 2D correlation spectrum of enone (I) in the
region of ν(C=O) and ν(C=C)
Region ν(C=O)
Figure 2 shows the synchronous 2D correlation spectrum
as contour map. The synchronous spectrum is symmetric
spectrum with respect to a diagonal line corresponding to
coordinates ν = 1707, 1727, and ν = 1749 cm-1. The peaks
located at diagonal position are referred to as autopeaks
having always positive magnitude. In Figure 2a autopeaks
have coordinates Φ(1707;1707), Φ(1727;1727) and
Φ(1749;1749). These autopeaks represent the overall
susceptibility of corresponding spectral region to change in
spectral intensity as an external perturbation (UV-
irradiation) is applied to the system [15]. Three cross peaks
located at the off-diagonal positions, namely, Φ(1707,1749),
Φ(1709,1727) and Φ(1727,1709) have negative sign and form
with corresponding autopeaks, at least, two correlation
squares [Φ(1707,1749) – Φ(1707,1707) – Φ(1749,1707) –
Φ(1749,1749)] and [Φ(1709,1727) – Φ(1709,1709) –
Φ(1727,1709) – Φ(1727,1727)]. It should be expected
existence the third correlation square therefore bearing in
mind the fact that ν(C=O) of two conformers of enone (I)
are very close one to another we created simulated model
data for spectral feature variation of two pares of bands
ν(C=O) = 1729, 1704 cm-1 and ν(C=O) = 1724, 1706 cm-1
changing in intencity in oposing directions with different
rates (see Figure 2c-f). Comparison of 2D correlation
spectrum with simulated model reveals that correlation
square [Φ(1709,1727) – Φ(1709,1709) – Φ(1727,1709) –
Φ(1727,1727)] coincides with square [Φ(1706,1729) –
Φ(1706,1706) – Φ(1729,1706) – Φ(1729,1729)]. Hence ν(C=O)
intensities of pairs of bands at 1727, 1704 cm-1; 1749,
1707 cm-1; and 1724, 1706 cm-1 change simultaneously in
opposite directions during UV-irradiation.
Asynchronous 2D correlation spectrum of enone (I)
conformers in region of ν(C=O) bands is shown in Figure
2b. It is known [15, 16] that intensity of an asynchronous
spectrum represents sequential or successive changes of
spectral intensities. The asynchronous spectrum has no
autopeaks, and consists exclusively of cross peaks located
at off-diagonal positions. The sign of an asynchronous cross
peaks becomes positive if intensity change at frequency ν1
occurs predominantly before that at frequency ν2. On the
other hand, the peak sign becomes negative if the change at
frequency ν1 occurs predominantly after that at frequency
ν2. By extending lines from the spectral coordinates to the
corresponding diagonal positions, we constructed correla-
tion squares. From Figure 1b we obtained three correlation
squares: Ψ(1704,1706) – Ψ(1704,1749) – Ψ(1749,1707);
Ψ(1704,1706) – Ψ(1704,1729 – Ψ(1729,1706) – Ψ(1707,1704);
Ψ(1729,1749) – Ψ(1749,1729). Some of the peaks have
negative sign whereas other have positive sign. Taking into
account the sign of the asynchronous peaks as well as the
signs of the synchronous correlation intensities at the same
coordinates we concluded that intensity changes ν(C=O) at
1729 cm-1 and 1704 cm-1 occur after the changes ν(C=O) at
1724 cm-1and 1706 cm-1. The same is true for intensity
changes ν(C=O) at 1749 and 1707 cm-1 which also change
after the changes ν(C=O) at 1724 and 1706 cm-1.
Region ν(C=C)
The synchronous 2D correlation spectrum of enone (I) in
region of ν(C=C) is presented in Figure 3a. Together with
three autopeaks, located at diagonal position cross peaks
form three correlation squares: Φ(1651,1651) – Φ(1651,1604)
– Φ(1604,1604) – (1651,1604); Φ(1639,1639) – Φ(1639,1621) –
Φ(1621,1639) – (1621,1624); Φ(1641,1641) – Φ(1641,1613) –
Φ(1613,1613) – (1613,1641). As a result ν(C=C) intensities of
pairs of bands at 1639, 1621 cm-1; 1613, 1641 cm-1; and
1604, 1651 cm-1 change simultaneously in opposite
directions during UV-irradiation.
At the same time from asynchronous 2D correlation
spectrum of conformers of enone (I) in region of ν(C=C)
bands (Figure 3b) we extracted three correlation squares,
namely, Ψ(1651,1621) – Ψ(1651,1604) – Ψ(1604,16211);
Ψ(1621,1651) – Ψ(1604,1621) – Ψ(1604,1651); Ψ(1651,1621) –
Ψ(1651,1604) – Ψ(1621,1604). According the sign rule [15]
and bearing in mind the peak sign of respective
synchronous peak with the same coordinates we revealed
that intensity changes ν(C=C) at 1651 and 1604 cm-1 occur
after the changes at 1639 and 1621 cm-1 and after the
changes at 1613 and 1641 cm-1 .
Thus, summing up the results of 2D correlation analysis
of synchronous and asynchronous spectra of conformers of
enone (I) in the region of (C=O) and (C=C) it can be stated
that each of the following interconversion processes occurs
synchronously while processes (1) and (2) occur before the
process (3):
S.I. Vdovenko et al.
35
(a)
(b)
(c)
(d)
(e)
(f)
Figure 2. 2D correlation IR-cpectrum of (I) under UV irradiation (λ = 275 nm) in the region ν(C=O) 1740-1717 cm-1: (a) synchronous
spectrum, (b) asynchronous spectrum. Simulated model data for spectral feature variation of two pares of bands ν(C=O) = 1729,
1704 cm-1 and ν(C=O) = 1724, 1706 cm-1 changing in intencity and oposit directions with different rate: synchronous spectra: (c) and (d);
asynchronous spectra: (e) and (f).
(a)
(b)
Figure 3. 2D correlation IR-cpectrum of (I) under UV irradiation (λ = 275 nm) in the region ν(C=C) 1680-1580 cm-1: (a) synchronous
spectrum, (b) asynchronous spectrum.
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 1
36
E-s-E-s-E-trans ⇄ E-s-E-s-E-cis (1)
E-s-Z-s-E-gosh ⇄ E-s-Z-s-E-cis (2)
E-s-Z-s-E-cis ⇄ E-s-E-s-E-gosh (3)
Analysis of 2D correlation spectrum of enone (II) in the
region of ν(C=O) and ν(C=C)
Region ν(C=O)
Synchronous 2D correlation spectrum of enone (II) in
region of ν(C=O) is presented in Figure S1A. As can be
seen the 2D synchronous spectrum consists of four
intensive autopeaks with coordinates Φ(1715,1715),
Φ(1719,1719), Φ(1721,1721), Φ(1738,1738). Besides these
autopeaks there are ten positive and six negative cross
peaks with different intensities. Together with autopeaks
they form five correlation squares: Φ(1715,1715) –
Φ(1715,1726) – Φ(1726,1726) – Φ(1715,1726); Φ(1719,1719) –
Φ(1719,1726) – Φ(1726,1726) – Φ(1726,1719); Φ(1721,1721) –
Φ(1721,1726) – Φ(1726,1726) – Φ(1726,1721); Φ(1715,1726) –
Φ(1726,1726) – Φ(1737,1726) – Φ(1737,1715); Φ(1721,1694) –
Φ(1721,1721) – Φ(1694,1721) – Φ(1694,1694). 2D correlation
analysis revealed that intensity changes (decrease) of
ν(C=O) at 1719, 1726, 1715 and 1721 cm-1 occur
synchronously with intensity changes (increase) at
1737, 1717, 1725 and 1694 cm-1 during conformer
interconversion of enone (II).
Asynchronous 2D correlation spectrum of conformers of
enone (II) in region of ν(C=O) bands (Figure S1B) contains
ten negative cross peaks and ten positive ones, grouped in
six clusters. The available cross-peaks allow us to construct
six correlation squares, namely: Ψ(1717,1715) – Ψ(1717,1725)
– Ψ(1717,1726); Ψ(1717,1725) – Ψ(1717,1721) – Ψ(1725,1717);
Ψ(1715,1725) – Ψ(1725,1726) – Ψ(1725,1715); Ψ(1725,1726) –
Ψ(1736,1726) – Ψ(1736,1715); Ψ(1694,1715) – Ψ(1717,1719) –
Ψ(1715,1694). Hence, 2D correlation analysis revealed that
intensity changes of ν(C=O) at 1726 and 1717 cm-1 occur
before ν(C=O) at 1719 and 1737 cm-1, ν(C=O) at 1715 and
1725 cm-1 and after ν(C=O) at 1721 and 1694 cm-1.
Region ν(C=C)
Synchronous 2D correlation spectrum of enone (II) in
region of ν(C=C) (Figure S2A) consists of six autopeaks:
Φ(1625,1625), Φ(1640,1640), Φ(1645,1645), Φ(1667,1667) and
Φ(1672,1672), which together with eight cross peaks form
four correlation squares, namely Φ(1625,1625) –
Φ(1625,1670) – Φ(1670,1670) – Φ(1670,1625); Φ(1645,1645) –
Φ(1645,1672) – Φ(1672,1672) – Φ(1672,1645); Φ(1640,1640) –
Φ(1640,1667) – Φ(1667,1667) – Φ(1667,1640); Φ(1644,1644) –
Φ(1644,1670) – Φ(1670,1670) – Φ(1644,1670). As a result we
obtained four pairs of peaks which intensities change
synchronously but in opposite directions during UV-
irradiation. In other words simultaneous interconversion of
the corresponding initial conformers is observed, viz. νC=C
(1645 → 1672), νC=C (1644 → 1664), νC=C (1640 → 1667)
and νC=C (1625 → 1670).
Asynchronous 2D correlation spectrum of conformers of
enone (II) in the region of ν(C=C) bands (Figure S2B) has
twenty cross peaks grouped into six clusters which form
seven correlation squares. Some of them are presented here:
Ψ(1625,1667) – (1667,1625); Ψ(1640,1670) – Ψ(1670,1640);
Ψ(1644,1664) – Ψ(1664,1644); Ψ(1645,1672) – Ψ(1672,1645).
From results obtained it is follows that intensity changes of
ν(C=C) at 1645 and 1672 cm-1, 1640 and 1667 cm-1, 1625
and 1670 cm-1 occur after ν(C=C) at 1644 and 1664 cm-1.
In conclusion it can be stated that each of the following
interconversion processes occurs synchronously while
processes (5) occur before the process (4), (6) and (7):
E-s-E-s-E-trans ⇄ E-s-Z-s-Z-cis (4)
E-s-E-s-Z-cis ⇄ E-s-Z-s-E-trans (5)
E-s-E-s-E-cis ⇄ E-s-Z-s-Z-cis (6)
E-s-E-s-E-gosh ⇄ E-s-E-s-Z-trans (7)
Analysis of 2D correlation spectrum of enone (III) in the
region of ν(C=O) and ν(C=C)
Region ν(C=O)
It is clear from Figure S3A that the synchronous 2D
correlation spectrum of enone (III) consists of three
autopeaks in the region ν(C=O) bands: Φ(1695,1695),
Φ(1699,1699), Φ(1702,1702), and twelve cross peaks which
form together with autopeaks four correlation squares, viz.
Φ(1695,1695) – Φ(1695,1699) – Φ(1699,1699) – Φ(1699,1695);
Φ(1695,1695) – Φ(16702,1702) – Φ(1702,1702) – Φ(1702,1695);
Φ(1702,1702) – Φ(1721,1702) – Φ(1721,1695) – Φ(1702,1695).
Obtained results reveal that intensities three pairs of
ν(C=O) bands, namely at 1699 and 1700 cm-1, 1702 and
1695 cm-1, 1695 and 1721 cm-1 simultaneously change in
opposite directions. It is worth to note that in second case
product of the reaction product is identical to the original
one. Asynchronous 2D correlation spectrum of conformers
of enone (II) in the region of ν(C=O) bands (Figure S3B)
comprises seven cross peaks which may be grouped in three
correlation squares: Ψ(1695,1699) – Ψ(1695,1702);
Ψ(1721,1695) – Ψ(1721,1695); Ψ(1699,1700) – Ψ(1700,1699).
According to these correlation squares change of intensity
of the band pair at 1702 and 1695 cm-1 occur before other
two pairs.
Region ν(C=C)
As in case of ν(C=O) region synchronous 2D correlation
spectrum of enone (III) in the region ν(C=C) bands (Figure
S4A) consists of three autopeaks: Φ(1695,1635),
Φ(1645,1645), Φ(1650,1650), and twelve cross peaks. We
managed to construct at least three correlation squares,
namely, Φ(1635,1635) – Φ(1645,1651) – Φ(1650,1650) –
Φ(1651,1645); Φ(1635,1635) – Φ(1635,1652) – Φ(1652,1635) –
Φ(1652,1645); Φ(1635,1635) – Φ(1645,1651) – Φ(1650,1650) –
Φ(1650,1645). Hence we observe simultaneous intensity
changes of three pairs of ν(C=C) bands at 1645 and
1651 cm-1, 1650 and 1652 cm-1, and 1635 and 1652 cm-1.
Bearing in mind the signs of correlation peaks the intensity
changes occur in opposite directions (the intensity of the
first peak decreases while the second one increases).
At the same time asynchronous 2D correlation spectrum
of conformers of enone (II) in the region of ν(C=O) bands
S.I. Vdovenko et al.
37
(Figure S4B) consists from two distinct cross peaks:
Ψ(1645,1651) and Ψ(1635,1652). In view of the fact that the
band at 1650 and 1635 cm-1 are almost coincide with bands
at 1650 and 1635 cm-1 it is very hard to discern appropriate
cross peaks. Nevertheless, from corresponding correlation
squares: Ψ(1645,1651) – Ψ(1651,1645); Ψ(1635,1652) –
Ψ(1652,1635) it follows that intensity changes in pairs of
ν(C=C) at 1645 and 1651 cm-1 and 1635 and 1652 cm-1
occur almost simultaneously.
We can conclude that during UV-irradiation conformers
of enone (III) undergo the following interconversions:
E-s-E-s-Z-trans ⇄ E-s-E-s-E-trans (8)
E-s-E-s-E-trans ⇄ E-s-Z-s-E-gosh (9)
E-s-Z-s-E-gosh ⇄ E-s-Z-s-E-trans (10)
All studied interconversion processes of enone (I-III)
conformers are listed in Table 1.
Infrared spectra of enones (I-III) during UV-irradiation
in Ar-matrix
It was shown [35] that UV photolysis of the α,β-un-
saturated aldehydes (acrolein, methacrolein and croton-
aldehyde) in argon matrices at λ > 300 nm occurs
predominantly through conformational isomerism of s-trans
form to the thermodynamically less stable s-cis conformer.
At shorter excitation wavelengths (λ > 230 nm) acrolein and
methacrolein isomerize to methylketene and dimethyl-
ketene, respectively. After 4h of continuous photolysis new
IR bands appear in the region 2060-2160 cm-1 (assigned to
methylketene, dimethylketene and CO) as a result of
1,3-hydrogen migration. Being exposed to UV-irradiation
(λ = 340 nm) in Ar matrices [15] effect of proton transfer
from the CH3N-H group to the oxygen of the carbonyl
group in β-N-methylaminovinyl trifluoromethyl ketone was
observed along with E ⇄ Z photoisomerization.
During relatively short UV-irradiation (30 min) of
enones (I-III) no extraneous bands were detected in the
region of 3500-3450 cm-1 and 2060-2160 cm-1 in all IR
spectra. Absence of C(H)=O and/or CH3N–H proton in
studied enones, narrow band UV-excitation (λ = 275, 300
and 320 nm) and relatively short UV exposure time prevent
the formation of identifiable dissociation products.
FTIR spectra of enone (I)
Earlier [13] we have shown that enone (I) in Ar matrix is
represented principally by three conformers, namely, E-s-E-
s-E-trans, E-s-Z-s-E-gosh, and E-s-Z-s-E-cis. During UV-
irradiation three new conformers E-s-E-s-E-cis, E-s-Z-s-E-
cis, and E-s-E-s-E-gosh appear as a result of
interconversions (see Table 1). These interconversion
processes occur parallel and independently of each other. It
should be noted that experimental constants (kexp) calculated
for initial conformers (Equation 2) and products of
interconversion (Equation 3) are very close and coincide
within the experimental error (see Table 3). From Table 1 it
is follows that interconversion of ethoxy moiety from trans-
to cis-form and gosh- into cis-form has similar rate
constants (kexp) whereas transition of cis-form into gosh-
form has twice higher constant kexp. Hence, interconversion
of all three conformers of enone (I) occurs exclusively due
to hindered rotation around O–CH2 single bond of ethoxy
group. Saying strictly for hindered rotation trans → gosh →
cis [Δ(ΔE+ΔZPE) = -5.19 kJ mol-1] it is needed sequential
energy adsorption, namely, (-1.72 mol-1, trans → gosh
transition) and (-3.47 kJ mol-1, gosh → cis transition). The
authors obtained a very close energy difference for
ethylbenzene s-cis and s-gosh conformers (ΔE+ΔZPE = –
4.45 kJ mol-1) [36].
Nevertheless, for these conformers of ethoxybenzene this
different is much higher, namely -24 kJ mol-1 [37].
Moreover, in s-ethyl fluorothioformate where, in contrast
with ethoxybenzene, the conjugation between S–CH2–CH3
group and F–C=O moiety is absent the energy difference
between s-cis and s-gosh conformer is significantly lower
(ΔE+ΔZPE = -0.37 kJ mol-1) [33]. At the same time values
of equilibrium constants (K) correspond to the values of
relative energies (ΔE+ΔZPE) of products of interconversion
processes (cf. (ΔE+ΔZPE) in Table 2 and (K) in Table 1).
Since conformers of enone (I) exhibit hindered rotation
exclusively around O–CH2 single bond, it becomes obvious
that the main contribution to the resonance structure is
made by structure (A) in Scheme 1. At the same time the
changes in entropy (ΔΔS) are quite significant and indicate
substantial changes in the ordering in the molecule due to
the hindered rotation around this single bond. While trans
→ cis transition [process (1) in Table 1] is accompanied by
significant net entropy increase (ΔΔS = -218.2 J mol-1 K-1),
corresponding transitions gosh → cis [process (2)] and
cis → gosh (process (3)] are characterized sharp increase of
positive entropy (namely, ΔΔS = +292.8 J mol-1 K-1 and
ΔΔS = +232.7 J mol-1 K-1), thus indicating on the disorder
increase in molecule.
To understand the processes of transformation of
conformers under of UV-irradiation may help the conside-
ration of electron density distribution (Mulliken charge on
the atoms of the conjugated system of the corresponding
enone). As it easily can be seen from Table 4 charges on
corresponding atoms of conjugated system of all initial
conformers are very close, thereby confirming dominance
of structure (A). Moreover, the charges on the atoms
forming an O–CH2 single bond are also very close in value,
which explains the relative ease of rotation around this
bond, namely, trans ⇄ gosh ⇄ cis.
FTIR spectra of enone (II)
Introduction of fluorine atom as α-substituent in enone
(II) results in appearance of four conformers, wiz. E-s-E-s-
E-trans, E-s-E-s-E-cis, E-s-E-s-E-gosh and E-s-E-s-Z-cis
(Table 5). In contrast with enone (I) where interconversion
occurs exclusively due to hindered rotation of ethyl group
around O–CH2 single bond, in conformers of enone (II) we
observe hindered rotation around both single bond between
carbonyl group and vinyl moiety (C=C–C=O) and between
ethoxy group and vinyl moiety (EtO–C=C) (see Table 1),
that is (s-E → s-Z) and (s-E-s-E → s-Z-s-Z) interconversion
processes [see (4) and (6) in Table 1]. Difference of
corrected relative energies [Δ(ΔE+ΔZPE) Table 2] of
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38
Table 1. Kinetic parameters (average experimental constants kav, equilibrium constants K, constants of direct k1 and reverse
k-1 reactions of conformers/isomers of enones (I-III) in Ar matrix under UV-irradiation (λ = 275 nm (I), 290-300 nm, (II),
300-320 nm (III)), T = 11 °K).
Table 2. Quantum chemical calculations: zero-point corrected relative energies (E+ΔZPE) (kJ mol-1), relative Gibbs free
energies ΔG (kJ mol-1), entropies S (J mol-1 K-1), and initial abundances (%) of enone conformers. (Numbers in parenthesis
correspond to enone spatial structures in Figure S4-S6).
Conformer E+ΔZPE ΔG S %
Enone (I)
E-s-E-s-E-trans (X 11) 0.00 0.85 77.3 31.99
E-s-Z-s-E-gosh (X 10) 2.06 0.00 -187.3 45.06
E-s-Z-s-E-cis (X 15) 3.68 2.56 -101.8 16.04
E-s-E-s-E-cis (X 12) 5.19 8.44 295.5 1.49
E-s-Z-s-E-cis (X 16) 6.53 7.69 105.5 2.02
E-s-E-s-E-gosh (X 14) 8.72 10.16 130.9 0.75
Enone (II)
E-s-E-s-E-trans (XF 10) 0.00 0.00 0.00 48.19
E-s-E-s-Z-cis (XF 9) 1.63 1.82 17.3 23.13
E-s-E-s-E-cis (XF 15) 2.03 4.68 240.9 14.90
E-s-E-s-E-gosh (XF 14) 3.74 4.65 422.7 7.38
E-s-Z-s-Z-cis (XF 12) 6.11 8.40 208.2 1.62
E-s-Z-s-E-trans (XF 11) 4.13 6.27 194.6 3.84
E-s-Z-s-Z-cis (XF16) 8.19 11.15 269.1 0.54
E-s-E-s-E-cis (XF17) 10.20 13.21 273.6 0.23
Enone (III)
E-s-E-s-E-trans (XC 9a) 0.00 0.00 0.00 66.65
E-s-Z-s-E-trans (XC 10) 6.77 4.90 -170.0 9.23
E-s-E-s-E-gosh (XC 14) 1.90 2.80 81.8 21.52
E-s-Z-s-E-gosh (XC 15) 8.62 8.06 -50.9 2.58
Process kav, s-1 K k1, s-1 k-1, s-1
Enone (I)
1 E-s-E-s-E-trans ⇄ E-s-E-s-E-cis (3.48±0.22)×10-3 6.25 (3.00±0.21)×10-3 (4.80±0.34)×10-4
2 E-s-Z-s-E-gosh ⇄ E-s-Z-s-E-cis (1.76±0.09)×10-3 5.26 (0.15±0.07)×10-3 (0.28±0.13)×10-3
3 E-s-E-s-E-cis ⇄ E-s-E-s-E-gosh (5.29±0.22)×10-3 1.22 (2.91±0.21)×10-3 (2.38±0.18)×10-3
Enone (II)
4 E-s-E-s-E-trans ⇄ E-s-Z-s-Z-cis (4.87±0.21)×10-3 3.86 (3.87±0.21)×10-3 (1.00±0.01)×10-3
5 E-s-E-s-Z-cis ⇄ E-s-Z-s-E-trans (1.22±0.11)×10-3 1.04 (0.62±0.13)×10-3 (0.59±0.13)×10-3
6 E-s-E-s-E-cis ⇄ E-s-Z-s-Z-cis (3.32±0.21)×10-3 1.36 (1.91±0.33)×10-3 (1.41±0.30)×10-3
7 E-s-E-s-E-gosh ⇄ E-s-E-s-Z-trans (0.92±0.20)×10-3 1.18 (0.50±0.30)×10-3 (0.42±0.30)×10-3
Enone (III)
8 E-s-E-s-Z-trans ⇄ E-s-E-s-E-trans (5.02±0.31)×10-3 2.50 (3.59±0.35)×10-3 (1.43±0.16)×10-3
9 E-s-E-s-E-trans ⇄ E-s-Z-s-E-gosh (4.51±0.21)×10-4 1.28 (2.53±0.18)×10-3 (1.98±0.16)×10-4
10 E-s-Z-s-E-gosh ⇄ E-s-Z-s-E-trans (3.79±0.12)×10-3 2.89 (2.82±0.28)×10-3 (9.74±0.60)×10-4
S.I. Vdovenko et al.
39
Table 3. Stretching ν(C=O) and ν(C=C) vibrations (cm-1), percentages of (%), and experimental constants (kexp) of
conformer interconversions of enone (I). (Numbers in parenthesis correspond to spatial structures in Table 2).
a) asymmetrical stretching vibration of (–C=C–C=O) moiety; b) symmetrical stretching vibration of (–C=C–C=O) moiety;
c) before UV-irradiation; d) after UV-irradiation.
C2H5O O
CF3
R
C2H5O O
CF3
R
C2H5O O
CF3
R
A B C
Scheme 1. Resonance structures of enones (I-III).
Table 4. Mulliken charges (with charges on hydrogen atoms summed into heavy atoms) on conjugated atoms of enone (I-
III) conformers. (Numbers in parenthesis correspond to spatial structures in Table 2).
Enone (I) F3C(10)–C(8)(=O(9))–C(5)=C(4)–O(14)–C(1)–C15
Conformer C(8) C(5) C(4) O(14) O(14) C(1)
E-s-E-s-E-trans (X11) -0.106929 0.655505 0.362471 -0.596889 -0.596889 0.381634
E-s-Z-s-E-gosh (X10) -0.156432 0.631799 0.338399 -0.571105 -0.571105 0.424737
E-s-Z-s-E-cis ( X15) -0.176986 0.680004 0.335490 -0.602432 -0.602432 0.445214
Enone (II) F3C(9)–C(7)(=O(8))–C(5)(–F(18))=C(4)–O(13)–C(1)–C14
Conformer C(7) C(5) C(4) O(13) O(13) C(1)
E-s-E-s-E-trans (XF 10) 0.027954 -0.149234 1.342708 -0.613028 -0.613028 0.461261
E-s-E-s-Z-cis (XF9) 0.223796 0.017757 0.964522 -0.630293 -0.630293 0.464758
E-s-E-s-E-cis (XF14) 0.292026 0.079327 0.739206 -0.586773 -0.586773 0.451397
E-s-E-s-E-gosh (XF15) 0.053896 0.041654 1.054206 -0.586067 -0.586067 0.479457
Enone (III) F3C(9)–C(7)(=O(8))–C(5)(–C(18))=C(4)–O(13)–C(1)–C14
Conformer C(7) C(5) C(4) O(13) O(13) C(1)
E-s-E-s-Z-trans (XC9a) -0.103231 0.560112 0.380617 -0.586711 -0.586711 0.480218
E-s-E-s-E-trans (XC10) -0.229656 0.652133 0.524211 -0.569596 -0.569596 0.436580
E-s-E-s-E-gosh (XC14) -0.241017 0.521252 0.445064 -0.557710 -0.557710 0.421123
EtOCH=CHCOCF3 enone (I)
E-s-E-s-E-trans (X11) E-s-Z-s-E-gosh (X10) E-s-Z-s-E-cis (X15)
ν(C=O) a) 1727 ν(C=O) a) 1749 ν(C=O) a) 1724
ν(C=C) b) 1639 ν(C=C) b) 1613 ν(C=C) b) 1604
kexp×103 2.07±0.20 kexp×103 1.68±0.08 kexp×103 5.68±0.39
% c) 31.09 % c) 16.04 % c) 45.06
E-s-E-s-E-cis (X12) E-s-Z-s-E-cis (X16) E-s-E-s-E-gosh (X14)
ν(C=O) a) 1704 ν(C=O) a) 1707 ν(C=O) a) 1706
ν(C=C) b) 1621 ν(C=C) b) 1641 ν(C=C) b) 1651
kexp×103 2.56±0.25 kexp×103 1.84±0.11 kexp×103 4.90±0.35
%d) 27.02 %d) 19.7 %d) 53.3
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40
Table 5. Stretching ν(C=O) and ν(C=C) vibrations (cm-1), percentages of (%), and experimental constants (kexp) of
transformations of conformers/isomers enone (II) conformers. (Numbers in parenthesis correspond to spatial structures in
Table 2).
Enone (II)
E-s-E-s-E-trans (XF10) E-s-E-s-Z-cis (XF 9) E-s-E-s-E-cis (XF 14) E-s-E-s-E-gosh (XF15)
ν(C=O)a) 1718 ν(C=O)a) 1770 ν(C=O)a) 1702 ν(C=O)a) 1735
ν(C=C)b) 1644 ν(C=C)b) 1645 ν(C=C)b) 1640 ν(C=C)b) 1625
kexp 4.90×10-3 kexp 1.47×10-3 kexp 3.19×10-3 kexp 0.91×10-3
%c) 39.03 %c) 42.27 %c) 5.21 %c) 18.17
E-s-Z-s-Z-cis (XF 12) E-s-Z-s-E-trans (XF 11) E-s-Z-s-Z-cis (XF 16) E-s-E-s-E-cis (XF 17)
ν(C=O)a) 1737 ν(C=O)a) 1768 ν(C=O)a) 1725 ν(C=O)a) 1742
ν(C=C)b) 1624 ν(C=C)b) 1629 ν(C=C)b) 1672 ν(C=C)b) 1629
kexp 4.83×10-3 kexp 0.96×10-3 kexp 3.45×10-3 kexp 0.93×10-3
%d) 20.30 %d) 56.40 %d) 4.47 %d) 18.83
a) asymmetrical stretching vibration of (–C=C–C=O) moiety;
b) symmetrical stretching vibration of (–C=C–C=O) moiety;
c) before UV-irradiation;
d) after UV-irradiation.
(s)
200 400 600 800 1000 1200 1400 1600 1800 2000
A
(C
=
C
)
(
=
1
6
4
6
c
m
-1
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
( E+ ZPE)
-9 -8 -7 -6 -5 -4 -3 -2 -1
k
e
x
p
*
1
0
3
,
s-
1
0
1
2
3
4
5
6
7
Figure 4. Variation of ν(C=C) integral intensity (A) of E-s-Z-s-
E-trans conformer during UV-irradiation (τ, s)
Figure 5. Plot of kinetic (kexp) vs. thermodynamic parameters
(changes of zero-point corrected relative energies Δ(ΔE+ΔZPE)).
S.I. Vdovenko et al.
41
Table 6. Stretching ν(C=O) and ν(C=C) vibrations (cm-1), percentages of (%), and experimental constants (kexp) of
transformations of conformers/isomers enone (III) conformers. (Numbers in parenthesis correspond to spatial structures in
Table 2).
EtOCH=C(CH3)COCF3 enone (III)
E-s-E-s-Z-trans XC9a E-s-E-s-E-trans XC10 E-s-Z-s-E-gosh XC15
ν(C=O)a) 1699 ν(C=O)a) 1702 ν(C=O)a) 1695
ν(C=C)b) 1645 ν(C=C)b) 1650 ν(C=C)b) 1635
%c) 66.65 %c) 9.23 %c) 21.52
kexp
5.03×10-3 kexp 4.61×10-4 kexp 5.17×10-3
E-s-E-s-E-trans XC10 E-s-Z-s-E-gosh XC15 E-s-Z-s-E-trans XC14
ν(C=O)a) 1700 νC=O)a) 1695 ν(C=O)a) 1721
ν(C=C)b) 1651 ν(C=C)b) 1635 ν(C=C)b) 1652
%d) 8.33 %d) 67.82 %d) 24.75
kexp 5.04×10-3 kexp 4.69×10-4 kexp 5.10×10-3
a) asymmetrical stretching vibration of (–C=C–C=O) moiety; b) symmetrical stretching vibration of (–C=C–C=O) moiety;
c) before UV-irradiation; d) after UV-irradiation.
appropriate conformers (-4.45 kJ mol-1) in interconversion
process (6) (Table 1) corresponds to (s-E-s-E → s-Z-s-Z)
transition (kav = 3.32×10-3 s-1) due to simultaneous hindered
rotation both trifluoromethyl carbonyl group (around C=C–
C=O single bond) and ethoxy group (around =C–OEt single
bond). At the same time this difference for similar process
(4), which also includes trans → cis rotation has
Δ(ΔE+ΔZPE) = -6.11 kJ mol-1 and kav = 4.90×10-3 s-1. As a
result pure trans → cis rotation demands additional 1.66 kJ
mol-1. At the same time increasing of net entropy in process
(4) (ΔΔS = -208.2 J mol-1 K-1) is less than in process (6)
(ΔΔS = -153.6 J mol-1 K-1) as a result of additional trans →
cis rotation in former one. Process (5) corresponds to
synchronous rotation of trifluoromethyl carbonyl group
(around O=C–C=C single bond), ethoxy group (around
EtO–C=C single bond), and ethyl group (around O–CH2
single bond), wiz. (s-E-s-Z-cis → s-Z-s-E-trans) with
Δ(ΔE+ΔZPE) = -2.50 kJ mol-1 and kav = 1.22×10-3 s-1.
Comparison ΔΔS in processes (4) (ΔΔS = -208.2 J mol-1 K-
1) and (5) (ΔΔS = -211.9 J mol-1 K-1) reveals that difference
ΔΔS of s-E-trans → s-Z-cis transition is almost the same as
for s-Z-cis → s-E-trans hindered rotation. At the same time
initial conformer E-s-E-s-E-gosh turns into corresponding
conformer E-s-E-s-Z-trans due to rotation s-E-gosh → s-Z-
trans [process (7)] with thermodynamic and kinetic
parameters [Δ(ΔE+ΔZPE) = -2.10 kJ mol-1 and kav =
0.95×10-3 s-1] being close to former one (see above). Hence,
due to mesomeric effect of α-fluor substituent, both
resonance structures (B) and (C) make a significant
contribution (Scheme 1) in enone (II), thus reducing the
double bonding of both formally single bonds (wiz. C=C–
C=O and EtO–C=C) and promoting simultaneous rotation
(s-E-s-Z-cis → s-Z-s-E-trans). In contrast to enone (I), the
charge distribution on the atoms of enone (II) is highly
diverse (see Table 4). However, it can be noted that the
values of the charges on the atoms forming a formally
single =C–O bond are close in value for all four
conformers, that is, in all four cases there is an easier
opportunity for s-E- ⇄ s-Z- rotation, indicating the
importance of structure (C) contribution. At the same time
charges on atoms forming =C–C= single bond for initial
conformers in processes (5) and (6) (Table 1) differ
significantly from the charge values on the corresponding
atoms of initial conformer in process (7). Particularly
noteworthy is the distribution of charges on the
corresponding atoms of the initial conformer in process (4).
Their low values indicate a low bond population and
therefore a predominant contribution of the canonical
structure (B). Summing up all of the above, we can
conclude that the charge distribution in the atoms of enone
(II) conformers contributes to hindered rotation E-s-E- ⇄
s-Z-s-Z- as a result of superposition of canonical structure
(B) and (C). As to charges on the atoms forming an O–CH2
single bond their values are the same in processes (4) and
(5) trans ⇄ cis, but somewhat less than in process gosh ⇄
trans.
FTIR spectra of enone (III)
α-CH3 substituted enone (III) consists of three
conformers, namely E-s-E-s-Z-trans, E-s-E-s-E-trans, and
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 1
42
E-s-Z-s-E-gosh (see Table 6). Special feature of
interconversion of conformers of enone (III) is involvement
of E-s-E-s-Z-trans conformer in interconversion processes
(Table 1) as initial (in process (9)) and reaction product (in
process (8)). As it is obvious from Figure 4 and Figure S11
where changes of integral intensities A(C=C) and A(C=O)
with time of UV-irradiation show that the content of this
conformer first increases over time to a maximum (reaction
(8)) and then decreases during reaction (9) to negligible
values. In the beginning we observe process of rotation
(s-Z → s-E) of ethoxy group around =C–OEt single bond
with kav = 5.02×10-3 s-1, Δ(ΔE+ΔZPE) = -6.77 kJ mol-1 and
ΔΔS = +170 J mol-1 K-1 (process (8)). The sharp entropy
increase during this transition is noteworthy. For compari-
son, different of corrected relative energies of E-s-E-s-trans
and E-s-Z-s-trans conformer of α-methyl-β-N-methylami-
novinyl trifluoromethyl ketone is very close, viz.
Δ(ΔE+ΔZPE = -7.01 kJ mol-1. Moreover, significant decre-
ase of net entropy also was observed for E-s-E-s-trans ⇄ E-
s-Z-s-trans process [20]. Accordingly, in initial E-s-E-s-Z-
trans conformer of enone (III) dominates canonical
structure (B) (Scheme 1) thus promoting this hindered
rotation. When the specified conversion (8) finished the
conformer E-s-E-s-E-trans turns into E-s-Z-s-E-gosh
[process (9)] due to simultaneous hindered rotations (s-E-s-
E → s-Z-s-E) and (trans → gosh) with kav = 0.45×10-3 s-1,
Δ(ΔE+ΔZPE) = -1.85 kJ mol-1 and ΔΔS = -119 J mol-1 K-1.
Thus, the conformer E-s-E-s-E-trans is characterized by the
predominant influence of the resonance structure (C).
Rotation (gosh → trans) occurs exclusively in process (10)
having kinetic (kav = 1.12×10-3 s-1) and thermodynamic
[Δ(ΔE+ΔZPE) = -6.72 kJ mol-1, ΔΔS = -132.7 J mol-1 K-1]
parameters. In contrast with enone (II) influence of
inductive methyl group as α-substituent in enone (III) leads
to the fact that resonance structure (B) dominates reducing
the double bonding of formally single bond O=C–C=C.
Considering the distribution of charges on respective
atoms, we came to the conclusion that in the case of process
(8), hindered rotation around the =C–O– bond is observed
(positive charge on carbon is the smallest among all initial
conformers), while for the process (9), where the positive
charges on the –C–C= atoms of the single bond are greatest,
and repulsion between them is large enough to promote
hindered rotation. As a result we observe s-E ⇄ s-Z rotation
around the =C–O bond (domination of structure (C) in
process (8)), whereas in process (9) s-E-s-E ⇄ s-Z-s-E
canonical structure (B) prevails. Practically identical values
of charges on the –O–CH2 atoms in processes (9) and (10)
indicate the identity of the hindered rotation trans ⇄ gosh
both clockwise and counterclockwise with similar
changes of enthalpies ΔΔS (respectively -119.1 and -132.7
J mol-1 K-1).
Summarizing results of investigation of interconversion
processes of conformers of enones (I-III) under UV-
irradiation, we obtained a good correlation (R2 = 0.982,
Figure 5) of kinetic (kexp) and thermodynamic parameters
(changes of zero-point corrected relative energies
Δ(ΔE+ΔZPE)) described by the Equation (11).
𝑘𝑒𝑥𝑝 × 103 , 𝑠−1 = −1.085 − 0.908 × [𝛥(∆𝐸 + ∆𝑍𝑃𝐸)] (11)
The same is true for direct (k1) and indirect (k-1)
processes (see Equation 12 and Equation 13):
𝑘1 × 103 , 𝑠−1 = −1.186 − 0.794 × [∆(∆𝐸 + ∆𝑍𝑃𝐸)] (12)
𝑘−1 × 103 , 𝑠−1 = −3.539 − 0.745 × [∆(∆𝐸 + ∆𝑍𝑃𝐸)] (13)
From the data earlier obtained for interconversion
process of E ⇄ Z isomerization of enaminoketone isomers
in Ar matrix under UV-irradiation [24] we obtained similar
correlations (14) (R2 = 0.998) and (15) (R2 = 0.997) for
direct (k1) and reverse (k-1) constants of transformation:
𝑘1 × 10−4 , 𝑠−1 = 3.386 − 2.343 × [𝛥(𝛥𝐸 + 𝛥𝑍𝑃𝐸)] (14)
𝑘−1 × 10−4 , 𝑠−1 = 1.786 − 1.677 × [𝛥(𝛥𝐸 + 𝛥𝑍𝑃𝐸)] (15)
As it easily can be seen in both cases we observe linear
regression of reaction constants with changes of zero-point
corrected relative energies Δ(ΔE+ΔZPE). Moreover slope
of this regression for α-substituted β-diethylaminovinyl
ketones is larger than the slope for respective α-substituted
β-N-methylaminovinyl trifluoromethyl ketones as a result of
higher conjugation between ethoxy- and trifluoromethyl
group in comparison with conjugation of diethylamino- and
trifluoromethyl group.
Earlier we have shown [22] that contribution of
resonance structure X+=CH–C(R)=C(CF3)–O- in enones
(X = EtO) is considerably higher then that in corresponding
enaminoketones (X = Et2N). Hence the hindered rotation
around X–CH and C–C(O)CF3 formally single bonds in
enones is much more hindered in comparison with that in
appropriate enaminoketones.
Conclusions
Upon ultraviolet irradiation of enone conformers in
Ar-matrix, the formation of various products (conformers)
is observed solely due to hindered rotation around O–CH2
single bond of ethoxy group, namely sequential (trans →
gosh → cis) rotation.
Introduction of fluorine as α-substituent in enone (II)
promotes appearance of new conformers as a result of
additional hindered rotations of both trifluoromethyl
carbonyl group and ethoxy group around single bonds.
Rotation of these groups occurs synchronously. In contrast
with enone (II) presence of a methyl group as α-substituent
in enone (III) has an inductive and steric effect on the
(CF3CO–C=C–OEt) conjugation skeleton of the confor-
mers. As a result new conformers appeared under UV-
irradiation due to separate rotations of trifluoromethyl
carbonyl or ethoxy group.
It was found that kinetic (k1 and k-1) and thermodynamic
Δ(ΔE+ΔZPE) parameters of all studied processes form
good correlations. Comparison of similar correlations for
α,β-enaminoketones reveals that conjugation between
ethoxy- and trifluoromethyl carbonyl group in α,β-enones is
higher than conjugation in respective α,β-enaminoketones.
S.I. Vdovenko et al.
43
Experimental section
Materials and methods
The starting compounds: (E)-4-ethoxy-1,1,1-trifluorobut-
3-en-2-one (I) [15], (Z)-4-ethoxy-1,1,1,3-tetrafluorobut-3-
en-2-one (II) [21], and (E)-1,1,1-trifluoro-4-ethoxypent-3-
en-2-one (III) [12] were prepared as published previously
[15, 17, 21]. All FTIR [13], UV-vis [16, 19], 1H, 13C, and
19F NMR [16, 17] spectra and results of chemical analysis
correspond to the chemical and spatial structure of studied
enones. Purity of enones (I-III) was ≥ 99%.
Matrix isolation studies
Neat liquid enones (I, II, and III) (purity > 99%) were
evaporated from a small bulb held at room temperature and
placed outside the cryostat chamber. Vapor thus obtained
was co-deposited with a large excess of argon onto a CsI
window kept at 15 °K. Cryogenic temperatures were
obtained by means of a closed cycle helium cryostat (ARS-
2HW) and were measured directly at the sample holder by a
silicon diode sensor working with a digital controller
(Scientific Instruments, model 9700). Infrared spectra
(4000-400 cm-1) were collected at 11 °K in transmission
mode with a resolution of 0.5 cm-1, using a Bruker IFS 66
spectrometer equipped with a liquid N2 cooled MCT
detector. After the infrared spectra of the initially deposited
samples were recorded, the matrices were subjected to the
tunable UV-irradiation provided by the frequency doubled
signal beam of a pulsed (duration 7 ns, repetition rate
10 Hz) optical parametric oscillator Vibrant (Opotec Inc.),
pumped with a Nd:YAG laser (Quantel).
Experimental matrix isolation infrared spectra and
simulated spectra of enones (I-III) in the region of double
bond stretching vibrations are presented in Figure 1 and
Figure S1-S3.
Conformers of enones (I-III) exposed to narrowband UV
light (λ = 275 nm (I), 290-300 nm, (II), 300-320 nm (III))
transform in Ar matrices into several stereoisomeric
structures according to schemes listed in Tables 1, 3-6.
These interconversions occur in parallel and independently
of each other therefore it is possible to evaluate kinetic
parameters of these processes. Calculations of the rate
constants of direct and reverse reactions (k1 + k-1) were
done with integrated intensities (A) of the
(C=O) and
(C=C) bands of appropriate stereoisomeric forms (after
deconvolution of respective spectral region, see Figure S1-
S3) assuming that specific integrated intensities (A) of
(C=O) or
(C=C) band (Equation 16) of different
stereoisomeric forms are similar
A= band
o/I)dνlog(I (16)
A detailed description of the method used for estimation
of the kinetic parameters is presented in [22-28]. The
obtained direct (k1) and reverse (k-1) constants of various
transformations of the conformers of enones (I-III) are
listed in Table 1. The experimental rate constants were
calculated using Equation (17):
𝐴0
𝐴𝑡
= 𝑒−𝑘𝑡 (17)
where 𝐴0 is initial integral intensity of
(C=O) or
(C=C) band of original conformer of enone (I-III), 𝐴𝑡 is
(C=O) or
(C=C) integral intensity of appropriate
conformer at time t. Simultaneously kexp were estimated for
final products of interconversions according to Equation
(18):
𝐴∞
𝐴∞−𝐴𝑡
= 𝑒−𝑘𝑡 (18)
where 𝐴∞ is terminal integral intensity of
(C=O) or
(C=C) band of product of interconversion of the conformer,
whereas 𝐴𝑡 is
(C=O) or
(C=C) integral intensity of
this product at time t. Equilibrium constant (K) for each
process was calculated with Equation (19):
𝑲 =
𝑨∞
𝒕𝒆𝒓𝒎
𝑨∞
𝒊𝒏 (19)
where 𝑨∞
𝒕𝒆𝒓𝒎 and 𝑨∞
𝒊𝒏 equilibrium integral intensity of
(C=O) or
(C=C) band, respectively, of origonal
conformer and product of interconversion.
Quantum chemical calculations
The method of quantum chemical calculations for
-substituted -unsaturated vinyl trifluoromethyl ketones
[24, 25] is the Gaussian 09 program package [20, 26].
Calculations of energies of formation for all possible
conformers of the investigated enones (I-III) 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 [24-
26]. 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, detailed results of
quantum chemical calculations of energies of formation for
all possible conformers of enones (I-III) (see Figure S4-S6)
are appended in Tables S1-S3. Zero-point corrected relative
energies (E+ΔZPE) (kJ mol-1), relative Gibbs free energies
ΔG (kJ mol-1), entropies S (kJ mol-1 K), and abundances
(%) of enone conformers are listed in Table 2. Fundamental
band assignments of enone (I-III) conformers have been
done earlier (see Figure 1) [15].
Calculations of 2D correlation IR spectra
Calculations of 2D correlation spectra of enones (I-III)
were carried out with program 2Dshige version 1.3 [32]
using averaged dynamic spectrum as a reference spectrum
[33]. Synchronous and asynchronous 2D correlation spectra
in the region of ν(C=O) and ν(C=C) vibration bands of
enones (I-III) are presented in Figure 1 and Figure S1-S4.
Notes
Acknowledgments and finances. The authors thank all
brave defenders of Ukraine who made this publication
possible. The authors declare no conflict of interest.
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 1
44
Supporting information
Relative Gibbs free energies ΔG, relative energies E
and zero-point corrected relative energies (E +ZPE) of
possible isomers of enones (I-III) (Table S1-S4); 2D
correlation IR-spectra for enones (I-III) (Figure S1-S4), and
other data.
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Кореляція кінетичних та термодинамічних параметрів конформаційних
перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією
ультрафіолетового опромінення в аргоновій матриці
С.І. Вдовенко*, І.І. Герус, О.А. Федоренко
Інститут біоорганічної хімії та нафтохімії ім. В.П. Кухаря НАН України, Київ, Україна
Резюме: За допомогою ІЧ-спектроскопії з перетворенням Фур'є та квантово-хімічного розрахунку (DFT-метод) досліджено кінетичні та
термодинамічні параметри конформаційних перетворень деяких α-заміщених β-етоксивінілтрифторметилкетонів, що моделюють препарати, що
містять вінілтрифторметилкетонний мотив, а саме C2H5O–CH=C(R)–COCF3 (I-III) (I: R = H; II: R = F; III: R = CH3) в Ar-матриці під впливом
УФ-випромінювання (λ = 275 нм (I), 290-300 нм, (II), 300-320 нм (III)). Було виявлено, що всі конформаційні зміни енону (I) відбуваються
виключно за рахунок утрудненого обертання навколо одинарного зв'язку CH2–O. На відміну від енону (I), взаємоперетворення конформерів
енону (II) відбувається переважно за рахунок синхронного обертання трифторметилкарбонільної групи навколо одинарного зв'язку O=C–C=C та
етоксигрупи навколо одинарного зв'язку EtO–C= в результаті мезомерного ефекту α-фторового замісника. Введення метильної групи як
α-замісника знижує здатність етоксигрупи до утрудненого обертання навколо цього одинарного зв'язку. Було виявлено, що експериментальні
кінетичні параметри (константа швидкості k1 та k-1) та розраховані термодинамічні параметри (зміни відносних енергій, скоригованих до
нульової точки Δ(ΔE+ΔZPE)) усіх досліджених процесів мають добру кореляцію. Порівняння з аналогічною кореляцією для α-заміщених
β-діетиламіновінілтрифторметилкетонів показує, що спряження в молекулах енамінокетонів є набагато слабкішим, ніж у відповідних
α-заміщених β-етоксивінілтрифторметилкетонів.
Ключові слова: конформери; інтерконверсія; α-заміщені β-етоксивінілтрифторметилкетони; Ar-матриця.
The starting compounds: (E)-4-ethoxy-1,1,1-trifluorobut-3-en-2-one (I) [15], (Z)-4-ethoxy-1,1,1,3-tetrafluorobut-3-en-2-one (II) [21], and (E)-1,1,1-trifluoro-4-ethoxypent-3-en-2-one (III) [12] were prepared as published previously [15, 17, 21]. All F...
Matrix isolation studies
Experimental matrix isolation infrared spectra and simulated spectra of enones (I-III) in the region of double bond stretching vibrations are presented in Figure 1 and Figure S1-S3.
𝑲=,,𝑨-∞-𝒕𝒆𝒓𝒎.-,𝑨-∞-𝒊𝒏.. (19)
where ,𝑨-∞-𝒕𝒆𝒓𝒎. and ,𝑨-∞-𝒊𝒏. equilibrium integral intensity of (C=O) or (C=C) band, respectively, of origonal conformer and product of interconversion.
Quantum chemical calculations
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| publisher | V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | bioorganicacomua/da/c50bb461a98a0b4d54d8278bc64e07da.pdf |
| spelling | oai:ojs2.bioorganica.com.ua:article-982026-07-19T14:56:55Z Correlation of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones under ultraviolet irradiation in an argon matrix Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці Vdovenko, Sergey I. Gerus, Igor I. Fedorenko, Olena A. conformers interconversion α-substituted β-ethoxyvinyl trifluoromethyl ketones Ar-matrix конформери інтерконверсія α-заміщені β-етоксивінілтрифторметилкетони Ar-матриця Comparison of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones under exposure to UV-irradiation (λ = 275 nm (I), 290-300 nm, (II), 300-320 nm (III)) was studied by the FTIR spectroscopy and quantum chemical calculation (DFT method). These are modeling drug compounds that contain vinyl trifluoromethyl ketone motif such as C2H5O–CH=C(R)–COCF3 (I-III) (I: R = H; II: R = F; III; R = CH3) in Ar-matrix. It was found that all conformational changes of enone (I) occur exclusively due to hindered rotation around CH2–O single bond. Contrary to enone (I), interconversion of conformers in enone (II) occurs predominantly due to synchronous rotation of the trifluoromethyl carbonyl group around O=C–C=C single bond and ethoxy group around EtO–C= single bond as a result of the mesomeric effect of the α-fluorine substituent. Introduction of methyl group as α-substituent reduces the ability of ethoxy group to hinder rotation around EtO–C= single bond. It was found that experimental kinetic parameters (k1 and k-1 rate constants) and calculated thermodynamic parameters (changes of zero-point corrected relative energies Δ(ΔE+ΔZPE)) of all studied processes form a single good correlation. Comparison with similar correlation for α-substituted β-diethylaminovinyl trifluoromethyl ketones reveals that conjugation in enaminoketone molecules is much weaker than that in appropriate α-substituted β-ethoxyvinyl trifluoromethyl ketones За допомогою ІЧ-спектроскопії з перетворенням Фур'є та квантово-хімічного розрахунку (DFT-метод) досліджено кінетичні та термодинамічні параметри конформаційних перетворень деяких α-заміщених β-етоксивінілтрифторметилкетонів, що моделюють препарати, що містять вінілтрифторметилкетонний мотив, а саме C2H5O–CH=C(R)–COCF3 (I-III) (I: R = H; II: R = F; III: R = CH3) в Ar-матриці під впливом УФ-випромінювання (λ = 275 нм (I), 290-300 нм, (II), 300-320 нм (III)). Було виявлено, що всі конформаційні зміни енону (I) відбуваються виключно за рахунок утрудненого обертання навколо одинарного зв'язку CH2–O. На відміну від енону (I), взаємоперетворення конформерів енону (II) відбувається переважно за рахунок синхронного обертання трифторметилкарбонільної групи навколо одинарного зв'язку O=C–C=C та етоксигрупи навколо одинарного зв'язку EtO–C= в результаті мезомерного ефекту α-фторового замісника. Введення метильної групи як α-замісника знижує здатність етоксигрупи до утрудненого обертання навколо цього одинарного зв'язку. Було виявлено, що експериментальні кінетичні параметри (константа швидкості k1 та k-1) та розраховані термодинамічні параметри (зміни відносних енергій, скоригованих до нульової точки Δ(ΔE+ΔZPE)) усіх досліджених процесів мають добру кореляцію. Порівняння з аналогічною кореляцією для α-заміщених β-діетиламіновінілтрифторметилкетонів показує, що спряження в молекулах енамінокетонів є набагато слабкішим, ніж у відповідних α-заміщених β-етоксивінілтрифторметилкетонів V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 2025-06-30 Article Article application/pdf application/pdf https://bioorganica.com.ua/index.php/journal/article/view/98 10.15407/bioorganica2025.01.032 Ukrainica Bioorganica Acta; Vol. 20 No. 1 (2025): Ukrainica Bioorganica Acta; 32-45 Ukrainica Bioorganica Acta; Том 20 № 1 (2025): Ukrainica Bioorganica Acta; 32-45 1814-9766 1814-9758 10.15407/bioorganica2025.01 en https://bioorganica.com.ua/index.php/journal/article/view/98/96 https://bioorganica.com.ua/index.php/journal/article/view/98/97 Copyright (c) 2025 Sergey I. Vdovenko, Igor I. Gerus, Olena A. Fedorenko https://creativecommons.org/licenses/by/4.0 |
| spellingShingle | конформери інтерконверсія α-заміщені β-етоксивінілтрифторметилкетони Ar-матриця Vdovenko, Sergey I. Gerus, Igor I. Fedorenko, Olena A. Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title | Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title_alt | Correlation of kinetic and thermodynamic parameters of conformational transformations of α-substituted β-ethoxyvinyl trifluoromethyl ketones under ultraviolet irradiation in an argon matrix |
| title_full | Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title_fullStr | Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title_full_unstemmed | Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title_short | Кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| title_sort | кореляція кінетичних та термодинамічних параметрів конформаційних перетворень α-заміщених β-етоксивінілтрифторметилкетонів під дією ультрафіолетового опромінення в аргоновій матриці |
| topic | конформери інтерконверсія α-заміщені β-етоксивінілтрифторметилкетони Ar-матриця |
| topic_facet | conformers interconversion α-substituted β-ethoxyvinyl trifluoromethyl ketones Ar-matrix конформери інтерконверсія α-заміщені β-етоксивінілтрифторметилкетони Ar-матриця |
| url | https://bioorganica.com.ua/index.php/journal/article/view/98 |
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