CH?S hydrogen bonds as the organising force in 2,3-thienyl- and phenyl- or 2,3-dithienyl-substituted propenoic acid aggregates studied by the combination of FT-IR spectroscopy and computations

Article abstract of DOI:10.1016/j.molstruc.2010.09.033

Various propenoic acid stereoisomers 2,3-disubstituted with thienyl and/or phenyl groups were synthesised and their aggregation behaviour was studied both in solution and in the solid state by experimental (mid-range FT-IR spectroscopy) and computational

Full text of DOI:10.1016/j.molstruc.2010.09.033

Journal of Molecular Structure 993 (2011) 259–263
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
CAHꢀ ꢀ ꢀS hydrogen bonds as the organising force in 2,3-thienyl- and phenyl- or
2,3-dithienyl-substituted propenoic acid aggregates studied by the combination
of FT-IR spectroscopy and computations
a,
K. Csankó a, L. Illés a, K. Felföldi a, J.T. Kiss a, P. Sipos b, , I. Pálinkó
⇑
⇑
a Department of Organic Chemistry, University of Szeged, Dóm tér 8, Szeged H-6720, Hungary
b Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged H-6720, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 8 October 2010
Various propenoic acid stereoisomers 2,3-disubstituted with thienyl and/or phenyl groups were synthes-
ised and their aggregation behaviour was studied both in solution and in the solid state by experimental
(mid-range FT-IR spectroscopy) and computational (semiempirical and ab initio) methods. Experimental
approach embraced the identification of potential hydrogen bonding sites through finding the relevant IR
bands and monitoring their displacement upon increasing the acid concentration in solution and on going
from solution to the solid state. In solution OAHꢀ ꢀ ꢀO hydrogen bonds were only found providing short-
range ordering, while in the solid state CAHꢀ ꢀ ꢀS hydrogen bonds were identified. Hydrogen bonding sites
could be assigned and relevant aggregate models could be built. Molecular modelling allowed obtaining
good estimates for hydrogen bond lengths and angles and visualisation of the geometric arrangements.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Thienyl and/or phenyl 2,3-disubstituted
propenoic acids
Hydrogen bonded network
CAHꢀ ꢀ ꢀS hydrogen bonds
IR spectroscopy
Molecular modelling
1. Introduction
to explore all possible hydrogen bonding interactions in CCl4 or
CHCl3 solutions as well as and in the solid state. The syntheses
Some time ago it has been found that short-range ordering pre-
vails in -phenyl cinnamic acid (E- or Z-2,3-diphenyl propenoic
were performed in our laboratory applying a modified version of
the Perkin condensation [7,8].
a
acid) solutions (the organising force is strong OAHꢀ ꢀ ꢀO hydrogen
bonds) [1], while weak (aromatic)CAHꢀ ꢀ ꢀO hydrogen bonds are
responsible for long-range ordering in the solid state [2]. If substit-
uents are present in the molecules that are capable to act as hydro-
gen bond donors and acceptors (the oxygen of the methoxy group
on the aromatic rings [3] or the fluorine in the CF3 group in position
3 substituting the olefinic hydrogen [4] or on the aromatic rings [5]
or a furyl group in position 3 instead of the phenyl group [6]), they
take part in forming extended aggregates, but only in the solid state.
In this contribution the scope is further extended, experimental and
computational results concerning the aggregate-forming proper-
ties of a range of propenoic acid stereoisomers having thienyl
and phenyl or dithienyl groups in positions 2 and 3, in CCl4 or
CHCl3 solutions and in the solid state are communicated.
The general synthesis method is given as follows: benzaldehyde
or thiophene carbaldehyde was refluxed for an hour with phenyl-
acetic acid or thienylacetic acid in the presence of acetic anhydride
and triethyl amine. The workup procedure involved hydrolysis as
well as several crystallisations from dichloromethane. Isomeric
purity was checked with NMR spectroscopy and was found to be
over 99%.
2.2. IR spectra of the solutions and the solid acids
In the experimental part of the work, mid-range FT-IR spectros-
copy was the method of choice for structural investigations. For
studies in solution, CCl4 or CHCl3 were used as solvents and solu-
tions in the ꢁ10ꢂ2ꢂ10ꢂ4 mol/dm3 concentration range were inves-
tigated. The choice of solvent depended on the solubility of the
specific molecule ACCl4 was preferred since its IR spectrum does
not interfere with those of the acid molecules. For measurements
in the solid state the KBr technique was applied.
2. Experimental and computational methods
2.1. Materials
The FT-IR spectra were taken on a BIORAD FTS-65A/896 spec-
trometer equipped with a DTGS detector. The resolution was
2 cmꢂ1 and usually 256 scans were collected for a spectrum. Spec-
tra were evaluated by the WIN-IR software package. The spectra
were base-line corrected but were not transformed in any other
way.
Eight stereoisomer pairs of molecules (Fig. 1) have been syn-
thesised covering all possibilities of 2,3-substitution enabling us
⇑
Corresponding authors. Tel.: +36 62 544 288; fax: +36 62 544 200.
E-mail addresses: sipos@chem.u-szeged.hu (P. Sipos), palinko@chem.u-szeged.
hu (I. Pálinkó).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.09.033

260
K. Csankó et al. / Journal of Molecular Structure 993 (2011) 259–263
respectively. Optimisation was considered to be over when the
gradient became smaller than 0.1. Stationary points obtained were
checked with frequency calculations and were found to be minima.
COOH
S
S
C
C
C
C
H
COOH
H
3. Results and discussion
Z2P32'T ()
E2P32'T
3.1. General considerations
COOH
S
S
S
S
C
C
C
C
We experienced previously that in the solid state CAHꢀ ꢀ ꢀX
(where X was O [6,11] or N [11–13]) hydrogen bonds had crucial
role in the formation of extended aggregates within the heterocy-
cle-substituted propenoic acid and ester family of compounds even
if these interactions are considered to be weak [14]. The close con-
tacts were mainly identified with IR spectroscopy and in many
cases measurements were complemented with molecular model-
ling calculations. It was found that the carbon donor atom was al-
ways part of the aromatic ring.
Let us note here that for the acids, the dimers kept together by
two relatively strong OAHꢀ ꢀ ꢀO hydrogen bonds were considered to
be the basic structural units, since even in the gas phase they are
the predominant form of the molecule, and their proportion dimi-
nishes only in very dilute solutions.
H
COOH
H
Z22'T32'T
E22'T32'T
S
COOH
S
S
S
C
C
C
C
H
COOH
H
Z23'T32'T
S
E23'T32'T
S
COOH
S
S
C
C
C
C
H
COOH
H
Z22'T33'T
E22'T33'T
S
(A)
S
S
COOH
S
C
C
C
C
H
COOH
H
E23'T33'T
Z23'T33'T
S
S
COOH
C
C
C
H
C
H
COOH
Z2P33'T
E2P33'T
COOH
S
C
C
C
C
S
H
H
COOH
(B)
Z22'T3P
E22'T3P
S
COOH
S
C
C
C
C
H
H
COOH
Z23'T3P
E23'T3P
Fig. 1. The compounds investigated in the present study (E and Z correspond to
stereochemistry, T-thienyl, P-phenyl).
2.3. Computational methods
Molecular modelling was performed with semiempirical and
ab initio codes included in the Hyperchem package [9]. Preoptimisa-
tion was performed with the PM3 semiempirical method [10] and
H(artree)F(ock) ab initio calculations were done using the 6-31 Gꢃꢃ
and 6-31 Gꢃ basis sets for the dimers and the dimer of the dimers,
Fig. 2. The mid-range FT-IR spectra of E (A) and Z (B) stereoisomers of phenyl and
thienyl or dithienyl 2,3-disubstituted propenoic acids in the solid state (KBr
technique): (a) 2P320T, (b) 220T320T, (c) 230T320T, (d) 2P330T, (e) 220T330T,
(f) 230T330T, (g) 220T3P and (h) 230T3P.

K. Csankó et al. / Journal of Molecular Structure 993 (2011) 259–263
261
Table 1
Typical mid-IR band positions (cm–1) for the E isomers in the solid state (KBr) and in solution (10ꢂ2 M concentration).
Compound
E2P320T
Sample form
m
(OAH)mon
m
(OAH)assoc
m
(C@O)mon
m
(C@O)assoc
m
(C@C)
mar
m
(CAOH)
m(@CASAC@)
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
–
3400–2200
3400–2200
3200–2400
3200–2400
3300–2700
3200–2800
3200–2400
3200–2400
3100–2400
3100–2800
3400–2200
3400–2400
3400–2200
3400–2200
3400–2400
3400–2400
–
1663
1681
1667
1684
1708
1702
1670
1686
1667
1696
1674
1683
1663
1681
1675
1687
1602
1611
1611
1611
1609
1615
1611
1610
1606
1614
1611
1619
1609
1615
1611
1611
1594, 1415
1594, 1413
1601, 1413
1597, 1415
1595, 1413
1593, 1419
1492, 1425
1494, 1429
1528, 1437
1532, 1446
1561, 1435
1558, 1440
1594, 1413
1593, 1415
1596, 1412
1594, 1415
1274
1271
1273
1268
1250
1256
1272
1269
1273
1262
1257
1264
1274
1271
1269
1275
608
610
629
631
648
652
628
632
612
617
619
624
607
610
611
616
3536
–
3518
–
3514
–
–
–
3486
–
3508
–
–
–
–
1743
–
1745
–
1746
–
–
–
1741
–
1746
–
–
–
–
E2P330T
E220T3P
E230T3P
E220T320T
E220T330T
E230T320T
E230T330T
Solution
Table 2
Typical mid-IR band positions (cm–1) for the Z isomers in the solid state (KBr) and in solution (10ꢂ2 M concentration).
Compound
Z2P320T
Sample form
m
(OAH)mon
m
(OAH)assoc
m
(C@O)mon
m
(C@O)assoc
m
(C@C)
mar
m
(CAOH)
m
(@CASAC@)
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
Solution
Solid
–
3400–2800
3200–2800
3200–2600
3200–2600
3200–2400
3200–2400
3400–2400
3300–2800
3200–2400
3100–2800
3300–2600
3200–2400
3200–2400
3200–2400
3400–2500
3300–2800
–
1711
1693
1708
1702
1676
1688
1711
1699
1667
1696
1705
1698
1713
1696
1705
1698
1653
1661
1641
1641
1611
1618
1610
1611
1598
1604
1610
1618
1606
1606
1613
1614
1593, 1402
1591, 1411
1590, 1413
1592a, 1419
1500, 1411
1498, 1418
1500, 1422
1499, 1429
1528, 1437
1528, 1446
1585, 1410
1583, 1418
1501, 1420
1500, 1427
1535, 1413
1533, 1425
1190
1199
1221
1235
1275
1265
1244
1237
1273
1266
1262
1260
1206
1212
1231
1226
588
602
648
653
597
603
606
610
580
588
591
605
597
602
586
591
3521
–
3513
–
3541
–
3513
–
3489
–
3514
–
3503
–
3512
1745
–
1749
–
1728
–
1744
–
Z2P330T
Z220T3P
Z230T3P
Z220T320T
Z220T330T
Z230T320T
Z230T330T
1734
1751
–
1748
–
Solution
1738
a
At 10ꢂ3 M concentration.
3.2. IR spectroscopy of the solutions and the solid acids
However, there were shifts relevant to the @CASAC@ vibration
from going from the solid state to solutions (last columns in the ta-
bles). Together these two observations mean that long-range
ordering due to CAHꢀ ꢀ ꢀS hydrogen bonds ceased to exist even in
the most concentrated solutions. It is to be noted that at the same
time there were systematic changes in aromatic skeletal vibrations
(between 1450 cmꢂ1 and 1400 cmꢂ1) indicating that aromatic car-
bons were involved in the hydrogen bonding interactions.
The other possibility for long-range ordering would be the (ole-
finic)CAHꢀ ꢀ ꢀS hydrogen bond. The IR data collected reveal that this
is a viable possibility, but only if the sulphur atom is in position 20.
For these molecules, the bands assigned to the C@C double bonds
(ꢁ1650 cmꢂ1–1600 cmꢂ1 range) displayed red shift going from
solution to the solid sate. Such an interaction with sulphur at posi-
tion 30 is sterically hindered, for these compounds no or very slight
shifts in the C@C band positions were found, indeed. This type of
hydrogen bonding is rare among cinnamic acids [5], but relatively
frequent in their esters [17].
The short-range order largely remained in the solutions, the ba-
sic structural units were the dimers kept together with two
OAHꢀ ꢀ ꢀO hydrogen bonds (wide bands around 3000 cmꢂ1 and
the carbonyl bands for associated molecules near and below
1700 cmꢂ1). On dilution increasing proportion of the dimers disso-
ciate to form monomeric units. This is demonstrated by the
appearance of the band above 3500 cmꢂ1 (Tables 1 and 2) and
around 1740 cmꢂ1 typical for isolated OH and the non-associated
The infrared spectra of all the studied compounds taken by the
KBr technique are shown in Fig. 2.
It is to be seen that the spectra of the two stereoisomeric groups
differ, especially in the shape of the bands in the 3250–2250 cmꢂ1
wavenumber range, however, within one group they resemble
each other. This observation allows fast identification of the stereo-
chemistry of the compound irrespective to the number of thienyl
substituents and the position of the sulphur atom in the ring.
The comparison of the spectra of solutions with various concen-
trations of propenoic acid derivatives 2,3-disubstituted with various
aromatic rings to the relevant solid compounds and identifying con-
centration dependent bands have proved to be a fruitful method in
identifying hydrogen bonding interactions [1–6,15]. Accordingly,
this method was used here too.
Since the aim was to identify OAHꢀ ꢀ ꢀO, (aromatic)CAHꢀ ꢀ ꢀS and
(olefinic)CAHꢀ ꢀ ꢀS hydrogen bonds, whichever it exists here, the
possible shifts in the positions of
m(OH),
m
(C@O),
m
(C@C) m(aromatic)
,
and
m(@CASAC@) were monitored. The wavenumber data for the
two stereoisomers are collected in Tables 1 and 2.
The tables contain the positions or the range of positions of the
above-mentioned vibrations for the solid samples as well as for the
most concentrated solutions (10ꢂ2 M). In many instances more di-
luted solutions were also made, however, frequency data hardly
changed if at all, therefore they are not listed in the tables.

262
K. Csankó et al. / Journal of Molecular Structure 993 (2011) 259–263
carbonyl (Fig. 3a and b), respectively, at 10ꢂ2 M concentration for
the majority of the compounds, and the observation that their
intensities increased with the decreasing concentration.
(A)
O…O: 272 pm
o
−
3.3. Some results of molecular modelling
O H…O angle: 169
Molecular modelling is considered to be a good complementing
tool to experiments. It helps visualisation and has important value
in the rationalisation of experimental results. However, it has
many drawbacks. For instance, handling solutions, especially for
extended systems is difficult unless the solvent is apolar. Fortu-
nately, our solvents (CCl4 and CHCl3) are apolar or close to it. An-
other problem is the size of the system. If intermolecular
interactions are studied for these cinnamic acid derivatives, at least
four molecules should be considered (dimer of the dimers). Then,
the application of high-level theoretical methods becomes limited
due to constraints in computational power. Studying even more
extended systems does allow only semiempirical methods, even
with powerful computers. In our modelling work all possible
hydrogen bonding interactions were screened with the dimer of
the dimers for each molecule applying the PM3 semiempirical
method. In further optimisations HF ab initio calculations were per-
formed applying the 6-31 Gꢃꢃ basis set for the dimers and the 6-31
Gꢃ basis set for the dimers of the dimers. As an example, the opti-
mised geometry for the dimer of compound 2P320T and for the
long-range ordering force, (aromatic)CAHꢀ ꢀ ꢀS interaction that is,
C…S: 347 pm
S…H: 241 pm
(B)
o
−
C H…S angle: 177
C…S: 348 pm
S…H: 240 pm
C H…S angle: 177
o
−
Fig. 4. The geometric arrangement in (A) the dimer (6-31 Gꢃꢃ basis set) and (B) the
dimer of the dimers (6-31 Gꢃ basis set) of compound 2P320T after optimisation with
the HF ab initio method.
(A)
the obtained geometry for the dimer of the dimers for the same
compound, together with relevant distance values are displayed
in Fig. 4a and b.
For deciding if a close contact is a hydrogen bond or not, two
factors were taken into account [16]: the distance between the do-
nor and acceptor atoms of the possible hydrogen bonds should not
be larger than the sum of their van der Waals radii compiled by
Bondi [18], and the angle of this close contact should be larger than
90°. These limiting sums are 304 pm and 350 pm for the Oꢀ ꢀ ꢀO and
Cꢀ ꢀ ꢀS distances, respectively. As it is seen in the figures, both crite-
ria are met. The Oꢀ ꢀ ꢀO distances are identical, and they are signif-
icantly shorter than the limit indicating strong hydrogen bonding
(hydrogen bonding energy with BSSE correction is 60.9 kJ/mol).
The two (olefinic)Cꢀ ꢀ ꢀS distances are close to each other and they
are at the limit. Although it means weak hydrogen bonds (9.8 kJ/
mol after BSSE correction) and the (aromatic)CAHꢀ ꢀ ꢀS bonds are
just as weak (9.6 kJ/mol after BSSE correction), nevertheless they
have significant role in long-range ordering identified only in the
solid state.
(B)
4. Conclusions
The combination of experimental and computational approaches
proved to be powerful in exploring hydrogen bonding possibilities.
It was found that large aggregates were only formed in the
solid state. They were kept together by (olefinic)CAHꢀ ꢀ ꢀS and
(aromatic)CAHꢀ ꢀ ꢀS hydrogen bonds. Their combination allows
the formation of extended two-dimensional sheets typically found
for cinnamic acid derivatives [17]. The fundamental unit of the
network is the acid dimer which is kept together by strong
OAHꢀ ꢀ ꢀO hydrogen bonds. These units are found in solutions,
where long-range ordering was not found.
Fig. 3. (A) The IR spectra of the E2P330T compound; A: crystalline acid and
solutions with B: 10ꢂ2 M, and C: 10ꢂ3 M concentrations in the 1800–500 cmꢂ1
wavenumber region. (B) The IR spectra of the Z2P330T compound; A: crystalline
acid and solutions of B: 10ꢂ2 M, and C: 10ꢂ3 M and D: 10ꢂ4 M concentrations in the
1800–500 cmꢂ1 wavenumber region.
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