Conformations of 1-heptene secondary ozonide as studied by low temperature FT-IR spectroscopy

Article abstract of DOI:10.1016/j.molstruc.2007.04.041

Conformational diversity of the 1-heptene secondary ozonides (SOZ) in solid neat films as well as isolated in Ar or CO₂ matrices was studied by the means of FT-IR absorption spectroscopy. The ozonization reaction was performed at 77 K in the neat films of the reactants. The spectra of the ozonide were analyzed by combining the experimental data with the results of theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. It was found that the samples of 1-heptene secondary ozonide exist as a mixture of three dominating conformers. The most stable conformer is the one with O-O half-chair configuration of the five membered ring, the aliphatic radical attached to the ring in equatorial position and the aliphatic chain being in gauche (∠OCCC ≈ -60°) position. The other two stable conformers are equatorial with aliphatic chain in anti (∠OCCC ≈ 180°) and gauche (∠OCCC ≈ 60°) positions. It was found from Van't Hoff plots that ΔH of the equatorial anti conformer is equal to 0.24 ± 0.03 kJ/mol. The experimental value of ΔH is in reasonable accordance to the calculated one - 0.5 kJ/mol.

Full text of DOI:10.1016/j.molstruc.2007.04.041

Available online at www.sciencedirect.com
Journal of Molecular Structure 844–845 (2007) 186–192
www.elsevier.com/locate/molstruc
Conformations of 1-heptene secondary ozonide as studied
by low temperature FT-IR spectroscopy
*
R. Bariseviciute, J. Ceponkus, V. Sablinskas, L. Kimtys
Department of General Physics and Spectroscopy, Vilnius University, Universiteto str. 3, Vilnius 01513, Lithuania
Received 27 February 2007; received in revised form 24 April 2007; accepted 28 April 2007
Available online 13 May 2007
Abstract
Conformational diversity of the 1-heptene secondary ozonides (SOZ) in solid neat films as well as isolated in Ar or CO2 matrices was
studied by the means of FT-IR absorption spectroscopy. The ozonization reaction was performed at 77 K in the neat films of the reac-
tants. The spectra of the ozonide were analyzed by combining the experimental data with the results of theoretical calculations performed
at B3LYP 6-311++G (3df, 3pd) level. It was found that the samples of 1-heptene secondary ozonide exist as a mixture of three dom-
inating conformers. The most stable conformer is the one with O–O half-chair configuration of the five membered ring, the aliphatic
radical attached to the ring in equatorial position and the aliphatic chain being in gauche (\OCCC ꢀ ꢁ60ꢀ) position. The other two sta-
ble conformers are equatorial with aliphatic chain in anti (\OCCC ꢀ 180ꢀ) and gauche (\OCCC ꢀ 60ꢀ) positions. It was found from
Van’t Hoff plots that DH of the equatorial anti conformer is equal to 0.24 0.03 kJ/mol. The experimental value of DH is in reasonable
accordance to the calculated one – 0.5 kJ/mol.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: 1-Heptene secondary ozonide; Conformations; Matrix isolation; FT-IR spectroscopy
1. Introduction
bonyl compound (CC) and COX often known as Criegee
intermediate (CI) [5]. Further fate of the reaction depends
on the conditions in which the reaction proceeds [2]. Many
different reaction pathways are possible in the gas phase
such as dissociation or rearrangement of the CI followed
by the bimolecular reactions with CC or residual CI, which
leads to the rather complicated reaction sequence. The car-
bonyl compound and CI readily recombine to form sec-
ondary ozonide in the condensed phase. However, some
other competing processes may occur in the condensed
phase too. Suenram and Lovas have reported the detection
of dioxirane from ethene ozonolysis [5]. It is experimentally
observed that the SOZ is more stable than POZ [6]. At
room temperature it can remain from few hours up to a
few days. SOZ dissociates into formic acid and aldehide.
Stability of the SOZ depends on the size and configuration
of the radical. Unfortunately, it is not much known about
the spatial structures of the SOZs.
An ability of ozone to break double C@C bond in ole-
fins is known for more than five decades. Understanding
of those reactions is very important in atmospheric chemis-
try. Alkene ozonization reaction is believed to be pro-
ceeded under so-called Criegee three-step mechanism [1].
During different steps of the reaction the primary ozonide
(POZ), carbonyl oxide (COX) and the secondary ozonide
(SOZ) are formed. Fate of the reaction depends on many
parameters such as type of radical, conformation of alkene,
temperature of the reaction and environmental effects.
Despite of numerous studies of the reaction by different
spectroscopic techniques the precise mechanism of the
reaction is still unknown [2–5].
It is well established experimentally that POZ is highly
unstable intermediate, which rapidly dissociates into a car-
*
The variety of the possible conformations of 1-alkene
SOZs, are generally caused by three reasons. First, five
Corresponding author. Tel.: +370 52366086; fax: +370 526366003.
E-mail address: liudvikas.kimtys@ff.vu.lt (L. Kimtys).
0022-2860/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.04.041

R. Bariseviciute et al. / Journal of Molecular Structure 844–845 (2007) 186–192
187
membered ring of the SOZ can possess two different
structures – so-called C–O half-chair conformation and
O–O half-chair conformation [7]. According to Kuckow-
ski and Bauld-Bailey [8,9] the five member ring of SOZ
exists preferably in the O–O half-chair conformation.
Such configuration of the ring was confirmed experimen-
tally from the microwave spectroscopy experiments
[8,10–14].
belonging to the different conformers of the 1-heptene
SOZ, in the gas phase spectra were strongly overlapped
due to the broadness of the bands.
The aim of this study is to define the geometrical
structures and stability of the different conformers of
the 1-heptene secondary ozonide by combined analysis
of the low temperature experimental spectral data with
the results of Density Functional Theory (DFT)
calculations.
Second, an aliphatic chain of the 1-alkene ozonide
can be differently attached to the ring. In the case of
the 1-alkene SOZ an aliphatic chain can be attached
to the ring in either so-called axial or equatorial posi-
tions. In the axial conformer the chemical bond between
the ring carbon and the aliphatic carbon is perpendicu-
lar to the ring plane. This bond lies in the ring plane in
the equatorial conformer. It is notable, that the C–C
bond does not lie exactly parallel or perpendicular to
the plane of the ozonide five member ring but these
notations are still in use in the conformational analysis
of SOZs [8,15]. The structure of equatorial propene SOZ
conformer was determined by the microwave spectros-
copy [8]. Haas [16] used ab initio calculated vibrational
spectrum of the 1-hexene axial conformer for assign-
ment of the infrared spectral bands of the 1-hexene
ozonization reaction products isolated in the CO2
matrix. Samuni et al. [16] have not made any attempt
to consider the possible conformational diversity of the
ozonide.
Third, aliphatic chain by itself can have different con-
formations. It is very well established that the aliphatic
chain is usually planar in the most stable conformer of
any saturated aliphatic compound. However, rotation
around the closest to the ring C–C bond can cause for-
mation of so-called anti and gauche conformers in the
case of aliphatic chain attached to the five membered
ozonide ring (COCOO). It has been experimentally and
theoretically confirmed that energy difference between
anti and gauche conformers are of 3.4–3.8 kJ/mol
[17,18] for alkanes. This value can be different in the case
of the aliphatic chain attached to the COCOO ring of
the ozonide. This is due to the interactions between ring
and the aliphatic radical.
2. Experimental
Oxygen (99.999%) from AGA and 1-heptene (99%) from
Aldrich were used without an additional purification.
Ozone was prepared from oxygen by the electric discharge.
The ozonization reaction was performed in the con-
densed phase in the stainless steel reactor [19]. The inner
part of the reactor was cooled with liquid nitrogen. 1-Hep-
tene and ozone were consequently introduced in to the
reactor in the small portions (about 15 torr · l) thus form-
ing multi-layered film of the reactants on the walls of reac-
tor. When the reaction was finished the reactor was slowly
warmed up. Continuous pumping of the reactor during the
warm up allowed us to separate the SOZ from the other
reaction products. The products of the reaction started
actively evaporate only at temperatures close to their melt-
ing points. For instance, formaldehyde actively evaporates
starting from 140 to 160 K, hexanal – from 180 to 200 K.
Only the products, which evaporate from the walls of the
reactor at 275 K temperature were transferred to the vac-
uum system and used for preparation of amorphous film
of the secondary ozonide or the matrix sample.
Closed cycle Helium cryostat Leybold RW2 was used
for cooling the samples. Matrix mixture (ratio of 1-heptene
SOZ with Ar (or CO2) – 1:600) was deposited on CsI win-
dow of the cryostat cooled down to 20 K for Ar matrix or
65 K for CO2 matrix. The gaseous mixture was kept at
room temperature during the deposition. Photolysis exper-
iments of the matrix isolated samples were performed using
conventional high pressure Hg arc lamp, providing UV
radiation in the spectral range of 170–400 nm. The closed
cycle helium cryostat was used for the preparation of the
amorphous films of the 1-heptene SOZ. The gaseous SOZ
was deposited on the optical window cooled down to
60 K. Infrared absorption spectra were recorded on BRU-
KER Vertex 70 FT-IR spectrometer, using 0.5 cmꢁ1 spec-
tral resolution, glowbar source, KBr beamsplitter, and
MCT detector.
Our initial conformational studies of 1-alkene ozonides,
using gas phase FT-IR spectroscopy, are presented in [15].
It was concluded that at least two conformers of 1-heptene
were present in the gaseous samples. We were not able to
make more quantitative conclusions about the number
and stability of the conformers. Infrared absorption bands,
Table 1
DFT calculated (B3LYP\6-311++G(3df, 3pd)) relative potential energies DH (calculated taking in to account ZPE) of the four most stable conformers of
1-heptene SOZ
Conformer
DH, kJ/mol (sOCCC, sCCCC)
I
II
III
IV
O–O half-chair equatorial gauche
O–O half-chair equatorial anti
O–O half-chair axial anti
0 (sOCCC = ꢁ66.4ꢀ, sCCCC = ꢁ179.1ꢀ)
0.5 (sOCCC = ꢁ178.5ꢀ, sCCCC = 177.8ꢀ)
2.4 (sOCCC = ꢁ174.8ꢀ, sCCCC = ꢁ180ꢀ)
2.5 (sOCCC = 57.0ꢀ, sCCCC = ꢁ178.2ꢀ)
O–O half-chair equatorial gauche

Table 2
DFT calculated (B3LYP\6-311++G(3df, 3pd)) normal vibrations of four most stable 1-heptene SOZ conformers in the spectral region of the ring vibrations
Equatorial gauche (sOCCC = ꢁ66.4ꢀ)
Equatorial anti
Axial anti
Equatorial gauche (sOCCC = 57.0ꢀ)
Assignment
ꢁ1
ꢁ1
ꢁ1
mcalc*(cmꢁ1)
I (a.u.)
mcalc (cm
)
I (a.u.)
mcalc (cm
)
I (a.u.)
mcalc (cm
)
I (a.u.)
*
*
*
820
––
874
885
6.7
824
––
878
––
0.4
830
––
860
881
1.3
818
863
878
4.4
9
5.6
CH2 twist
O(1)–C(2)–C(3) def
O–O stretch
CH2 twist
6.8
8
4.9
11.1
1.5
––
896
––
––
931
––
––
986
990
––
1033
1045
––
1056
––
1062
––
13.5
16.6
889
903
––
3.9
4.4
892
––
––
5.2
895
––
908
––
––
957
––
6.5
9.7
CH3 rock
CH2 twist, CH3 rock
––
––
O–C–O asym. stretch, C(2)–O(3) stretch
O(1)–C(2), C(1)–O(2) stretch
O–C–O asym. stretch
CH2 twist, CH3 rock
C–C–C in plain def
CH2 twist, CH3 rock
C–C–C in plain def
C–C–C in plain def
C–C stretch
O–C–O sym. stretch
C–C–C in plain def
ring vibr
O–C–O sym. stretch
O–C–O sym. stretch
C–C–C in plain def
CH2 rock
946
962
––
12.4
47.6
949
958
––
10.6
57.2
33.2
14.5
10
––
––
––
1004
1014
––
1036
––
12.9
11.3
994
1014
––
1035
––
11.2
2
997
1013
––
1037
––
29.5
1.5
6.2
14.5
2.3
0.8
10
9.6
8.7
76.9
22.1
1054
––
11.6
1054
––
1054
––
1065
1105
1129
1140
1167
98.2
117.2
12.9
8.5
1061
1103
1121
1142
1155
37.2
216.3
12.8
9
1063
1121
1125
1137
1156
78.3
87.7
15.8
4.5
1105
1130
1139
1160
131.8
12.2
9
2.7
6.8
10.2
16.2
C–C–C out of plain def
*
The calculated wavenumbers are scaled by 0.99.

R. Bariseviciute et al. / Journal of Molecular Structure 844–845 (2007) 186–192
189
3. Results and discussion
from each other by 5–20 cmꢁ1 in this spectral region, while
they are completely or partly overlapped in the other regions.
Infrared absorption spectrum of the 1-heptene SOZ iso-
lated in Ar matrix is presented in Fig. 2a. The spectral
bands of the matrix isolated 1-heptene SOZ are surpris-
ingly broad and not suitable for the conformational analy-
sis. Broadness of the spectral bands of 1-heptene SOZ
isolated in Ar matrix can be explained by large number
3.1. Calculations
Theoretical calculations of the vibrational spectra and
the structure of the staggered conformers of the SOZ were
performed with Gaussian 03 program package, using the
DFT method B3LYP with 6-311++G (3df, 3pd) basis
set. The input parameters for the program were set in such
a way to look on the potential surface of the SOZ only for
equatorial and axial staggered conformers formed only due
to the rotation of the aliphatic radical around the C–C
bond nearest to the five membered ring. The conformers
formed due to the rotation around the other @C–C-bonds
are much less stable and therefore could be excluded from
the studies. Results of the calculations for the title ozonide
are presented in the Tables 1 and 2. The structures of the
four most stable 1-heptene SOZ conformers are presented
in Fig. 1.
of the trapping sites. The lattice constant of the Ar crystal
0
ꢀ
is 5.3 A [10] and the length of 1-heptene SOZ molecule – ca.
0
ꢀ
10 A. The SOZ molecule does not fit in to the cells of
the Ar crystal, and only various multi-substitutional trap-
ping sites are possible. Overlapping of the spectral bands
of the SOZs surrounded by slightly different environment
results their broadening.
The crystalline cage of the CO2 matrix is slightly larger
than that of Ar matrix. Even more, CO2 matrices obtained
by deposition of CO2 gas at temperatures as low as 20 K
are more amorphous than crystalline [16]. This makes the
environment more uniform and it results the narrower
spectral bands. Therefore the experiments with the SOZ
isolated in the CO2 matrix were carried out in this work.
FT-IR absorption spectrum of 1-heptene SOZ isolated in
CO2 matrix is presented Fig. 2b. As seen in the figure the
spectral bands of 1-heptene SOZ isolated in CO2 matrix
is narrower comparing to those of the ozonide isolated
in the Ar matrix. The theoretically calculated spectra of
four conformers of 1-heptene SOZ together with the
3.2. 1-Heptene SOZ in Ar and CO2 matrixes
Spectral region of the ozonide ring vibrations at
800–1200 cmꢁ1 was chosen for the conformational analysis
taking in to account the results of the theoretical calcula-
tions (Table 2). According to the calculations the spectral
bands belonging to the different conformers are separated
Fig. 1. Theoretically (B3LYP 6-311++G (3df, 3pd)) calculated structures of four the most stable 1-heptene SOZ conformers: (I) equatorial gauche
(\OCCC = ꢁ66.4); (II) equatorial (\OCCC = ꢁ178.5ꢀ); (III) axial anti (\OCCC = ꢁ174.8ꢀ); (IV) equatorial gauche (\OCCC = 57ꢀ).

190
R. Bariseviciute et al. / Journal of Molecular Structure 844–845 (2007) 186–192
window cooled to 90 K and following annealing at 160 K.
The annealing of the film at temperature higher than 160 K
leads to the crystallization of the film. The spectra of the
film annealed for 10 min. at 160 K and cooled down to
150, 120, and 70 K are presented in Fig. 4. The spectral
bands of amorphous 1-heptene SOZ are rather narrow,
what allows their assignment to the different conformers.
We were able to explain the main spectral features of amor-
phous 1-heptene SOZ taking in to account the results of
theoretical calculations (Table 2) and assuming that amor-
phous film of 1-heptene SOZ contains three conformers – I,
II, and IV. Surprisingly, the spectral bands of conformer
III which stability is expected to be nearly the same as con-
former IV were not found in the spectra. In order to use
amorphous film for determination of the stability of differ-
ent conformers one has to be sure that the film is fully
amorphous and crystallization was not yet started. Much
longer time up to 10 h was used for the annealing of the
amorphous film at 160 K, but the spectra look the same
as in the case of the annealing for 10 min. This experimen-
tal fact indicates that the 1-heptene SOZ film annealed at
temperature not exceeding 160 K remains fully amorphous
and the conformers in the film are in thermodynamical
equilibrium defined only by the temperature of the film.
This is not surprising, taking in to account the fact that
the melting point of the 1-heptene SOZ is at 203 K, e.g. –
much higher that the annealing temperature. Final prove
for the correct assignment of vibrational spectral bands
to different conformers in conformational analysis is crys-
tallization of amorphous solid [20]. Usually, only one type
conformers persist in the crystal cell after crystallization of
amorphous solid, containing different conformers. Con-
formers of two types can persist in the crystal cell when
two different conformers due to some sterical reasons can
be closely packed. The last is rare case and also can be used
as an argument for the correct assignment of vibrational
spectral bands to different conformers. The conformational
ratio is usually 1:1 in such crystals.
In order to crystallize the amorphous film temperature
of the film should be set slightly below the melting point.
The crystallization process depends on many experimental
parameters such as film deposition rate, annealing temper-
ature and annealing time, therefore relative intensity of the
bands belonging to different conformers in different exper-
iments were found to be different. The spectra of the film
annealed at 190 K for 20 and 120 min. together with the
spectrum of fully amorphous film at 160 K are presented
in Fig. 5 The film after annealing at 190 K for short time
becomes partly crystalline, containing mainly conformer
I. The spectral bands of conformer II completely disappear
from the spectrum. Prolonging the annealing time up to
120 min. leads to complete crystallization of the film. The
spectral bands assigned as a mixture of conformer I and
conformer IV, decrease dramatically during the prolonged
annealing of the film at 190 K. It is notable that the spectral
bands of conformer IV in the amorphous film nearly
completely overlap either with those of conformer I or
a
b
♦
*
*
*
800
850
900
950
1000
Wavenumber, cm-1
1050
1100
1150
1200
Fig. 2. IR absorption spectra of 1-heptene SOZ isolated in: (a) argon
matrix; (b) CO2 matrix. *, 1-heptene spectral bands, ꢀ, formic acid spectral
band.
experimental spectrum in 930–975 cmꢁ1 spectral regions
are presented in Fig. 3. The band at 936 cmꢁ1 can be
assigned to the equatorial gauche ( ꢀ ꢁ60ꢀ) conformer (I),
the bands at 947 and 965 cmꢁ1 – to equatorial anti con-
former (II) and the band at 956 cmꢁ1 – to equatorial gauche
( ꢀ 60ꢀ) conformer (Table 2). Separation of the spectral
bands of different conformers of 1-heptene SOZ isolated
in CO2 matrix is sufficient for the qualitative conforma-
tional analysis, but it is not enough for the quantitative
analysis – many spectral bands belonging to different con-
formers are still overlapped.
It is widely accepted in the conformational analysis, that
temperature evolution of the vibrational spectral bands of
fully amorphous solid can be also used for the quantitative
estimations of stability of the conformers. Therefore addi-
tional experiments with amorphous solid film of neat
1-heptene SOZ were carried out.
3.3. 1-Heptene SOZ in amorphous film
The amorphous film of the 1-heptene SOZe was formed
by deposition of the gaseous 1-heptene SOZ on the optical
I
II
III
IV
930
935
940
945
950
955
960
965
970
975
Wavenumber, cm-1
Fig. 3. IR absorption spectrum of 1-heptene SOZ isolated in CO2 matrix
(top). Theoretically calculated spectra of: (I) equatorial gauche
–
(s = ꢁ66.4ꢀ); (II) – equatorial anti; (III) – axial anti; (IV) – equatorial
gauche (s = 57ꢀ) conformers of 1-heptene SOZ.

R. Bariseviciute et al. / Journal of Molecular Structure 844–845 (2007) 186–192
191
I+II
0.6
0.24 0.03 kJ/mol
II+IV
II
I+IV
I+II+IV
I+IV
I+IV
I+II+IV
0.4
0.2
I+II+IV
II
II
I+IV
II
I
?
I
a
0.0
b
0.24 0.02 kJ/mol
c
-0.2
-0.4
800
850
900
950
1000
1050
1100
1150
1200
Wavenumber, cm-1
Fig. 4. IR absorption spectra of 1-heptene SOZ amorphous film at (a)
70 K; (b) 120 K; (c) 150 K temperature. Notation of the bands belonging
to the different conformers is the same as in the Table 1.
0.0008
0.0010
0.0012
0.0014
0.0016
0.0018
1/T×R, J×mol-1×K-1
Fig. 6. Van’t Hoff plots for the 1-heptene SOZ conformers in amorphous
film. Band pairs: d 923 (I) and 1016 cmꢁ1 (II); j 923 (I) and 944 cmꢁ1
(II).
I+II
II+IV
I+IV
I+IV
theoretical calculations, which predict existence of four
conformers. Nevertheless, this prediction we failed to
observe experimental evidences about existence of con-
former III (O–O half-chair equatorial gauche) in the low
temperature solid samples of the ozonide. It is notable that
the three conformers experimentally found in the amor-
phous film are equatorial, while this additional one, pre-
dicted by the theoretical calculations, is axial. The
theoretical calculations of the stability of a molecule con-
taining strained not planar five membered COCOO ring
is a challenging task and the results of the calculations
has to be treated with care. It might be, that the calcula-
tions underestimate strong interaction between the ring
and the closest to the ring CC bond in the axial conformer,
what finally gives DH = 2.4 kJ/mol. Perhaps, in reality this
value is much higher, what makes this axial conformer not
observable in the1-heptene SOZ amorphous film.
I+II+IV
II
I+II+IV
I+II+IV
II
I+IV
II
I
I+IV
I
II
↑
a
b
c
d
e
800
850
900
950
1000
1050
1100
1150
1200
Wavenumber, cm-1
Fig. 5. IR absorption spectrum of 1-heptene SOZ: (a) amorphous at 90 K;
partly crystalline after annealing of the amorphous film at 190 K: (b) for
20 min., (c) for 120 min; (d) and (e) theoretically calculated spectra of the
conformer I and conformer IV.
The temperature evolution of the spectral bands belong-
ing to the different conformers of 1-heptene SOZ fully
amorphous film can be used for the estimation of the stabil-
ity of the conformers. The Van’t Hoff plots for the two
pairs (923/944 and 923/1016) of the spectral band belong-
ing to conformer I and conformer II are presented in
Fig. 6. The DH values calculated from the both plots coin-
cide. The experimental value of DH equals to
0.24 0.03 kJ/mol is in reasonable accordance to the cal-
culated one – 0.5 kJ/mol. Unfortunately, the spectral bands
attributed to the conformer IV cannot be used to the delta
H estimation, due to the overlapping with the spectral
bands of other conformers.
conformer II (see Fig. 5a and b), what does not allow to
affirm for sure about presence of the conformer IV in the
sample. Nevertheless of this overlapping behavior of the
intensities of the overlapping spectral bands during the
annealing enables us to make conclusion about existence
of conformer IV in the film. Despite of much higher stabil-
ity of conformer II than conformer IV in amorphous film,
the conformer II is getting less abundant faster than con-
former IV during the crystallization. Perhaps, due to the
similarity of structure of the conformer I and the con-
former IV, the last one appears more stabilized during
the crystallization. Our experimental finding about pres-
ence of three conformers in the amorphous film of 1-hep-
tene SOZ is not in full accordance with results of the
4. Conclusions
The FT-IR spectra of 1-heptene SOZ isolated in Ar and
CO2 matrixes and its neat amorphous film were recorded.
Spectra were analyzed combining experimental results with

192
R. Bariseviciute et al. / Journal of Molecular Structure 844–845 (2007) 186–192
the theoretical calculations performed at B3LYP 6-
311++G (3df, 3pd) level. It was found that conventional
matrix media – Ar and CO2 in case of 1-heptene SOZ is
lacking the main matrix advantage – narrowing of the
vibrational spectral bands. This is due to the size of the
SOZ molecules, which excides the size of the matrix cage.
It was experimentally proved that the neat film of 1-hep-
tene SOZ at 90–160 K temperature range remains com-
pletely amorphous with the conformational mixture
defined by the temperature of the film. It was found that
the samples of amorphous 1-heptene secondary ozonide
exist as a mixture of three dominating conformers. The
most stable conformer is the one with O–O half-chair con-
figuration of the five membered ring, the aliphatic radical
attached to the ring in equatorial position and the aliphatic
chain being in gauche (\OCCC ꢀ ꢁ66.4ꢀ) position. The
other two stable conformers are equatorial with aliphatic
chain in anti (\OCCC ꢀ 180ꢀ) and gauche (\OCCC ꢀ 60ꢀ)
positions. The conformer III predicted by the theoretical
calculations was not observed in the amorphous film of
1-heptene SOZ. Perhaps, the calculations underestimate
interaction between the ring and the closest to the ring
CC bond in the axial conformer. This interaction is smaller
in the equatorial conformers due to orientation of the
closed to the ring CC bond in respect to the ring what
makes three staggered equatorial conformers (I, II, and
IV) more stable and abundant in the amorphous samples
of 1-heptene SOZ.
The ordered crystal of 1-heptene SOZ was obtained for
the first time. The crystal cage contains only one type of the
SOZ – conformer I. A closer look to the crystallization pro-
cess revealed that the conformer IV (DHcalc = 2.5 kJ/mol)
persists in the partly crystalline sample until very end of
completing of the crystallization while much more stable
conformer II (DHcalc = 0.5 kJ/mol) vanishes from the sam-
ple at the very beginning of the crystallization. This exper-
imental fact might be because of the similarity of the
structures of conformer I and conformer IV – both are
O–O half-chair equatorial gauche with only difference –
the torsional angle \OCCC being equal to ꢁ66.4ꢀ and
+57ꢀ, respectively.
obtained experimental value of DH equal to
0.24 0.03 kJ/mol is found to be in reasonable accordance
to the calculated one – 0.5 kJ/mol. Unfortunately, the spec-
tral bands attributed to the conformer IV cannot be used
for the DH estimation, due to their overlapping with the
spectral bands of the other conformers.
In order to overcome this difficulty a proper matrix
material has to be found. The matrix cage should be big
enough to fit large 1-heptene SOZ molecule in it. The nar-
rowing effect of the SOZ spectral bands can be expected in
such a matrix. Searching for a matrix material better suited
for the conformational studies of 1-heptene SOZ than Ar
and CO2 is underway.
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