The influence of lateral apolar substituents on the mesomorphic behaviour of tetracatenar liquid crystals

Article abstract of DOI:10.1134/S1070363210070194

Several series of new tetracatenar mesogens consisting of a five-ring aromatic core and bearing one or more apolar lateral substituents in the central benzene ring of the molecule have been synthesized and their mesomorphism is characterized by polarizati

Full text of DOI:10.1134/S1070363210070194

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 7, pp. 1331–1340. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.I. Smirnova, N.V. Zharnikova, B. Donnio, D.V. Brus, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 7,
pp. 1165–1174.
The Influence of Lateral Apolar Substituents
on the Mesomorphic Behaviour of Tetracatenar Liquid Crystals
A. I. Smirnovaa,b, N. V. Zharnikovab, B. Donnioc, and D. V. Brusa
a
Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
e-mail: db519@york.ac.uk
b
Nanomaterials Research Institute, Ivanovo State University,
ul. Ermaka 37/7, Ivanovo, 153025 Russia
e-mail: antonia_smirnova@mail.ru
c
CNRS-Université Louis Pasteur (UMR 7504), Institut de Physique et Chimie des Matériaux de Strasbourg,
23 rue du Loess BP 43, 67034 STRASBOURG Cedex 2, France
Received May 17, 2009
Abstract—Several series of new tetracatenar mesogens consisting of a five-ring aromatic core and bearing one
or more apolar lateral substituents in the central benzene ring of the molecule have been synthesized and their
mesomorphism is characterized by polarization microscopy, differential scanning calorimetry, and X-ray
diffraction methods. Introduction of one, two, or four methyl groups into these tetracatenar mesogens
destabilized columnar organization typical of the long-chain homologs, but did not suppress smectic C and
nematic phases. Introduction of larger substituents did, however, suppress lamellar organization (C15H31) or
mesomorphism (tert-butyl) totally.
DOI: 10.1134/S1070363210070194
Polycatenar liquid crystals are a class of thermo-
tropic mesogens composed of rigid elongated core and
at least three terminal flexible aliphatic chains (Fig. 1),
and they are generally classified as hexacatenar,
pentacatenar, tetracatenar, etc., depending on the total
number of alkyl chains attached [1]. Perhaps the most
remarkable thing about polycatenar mesogens is that at
one extreme (tricatenar mesogens) they show the
mesomorphism typical of calamitic materials, while at
the other (hexacatenar mesogens) they show columnar
mesophases, commonly found in discotic materials
[1, 2]. The appearance of certain phase depends on the
relative proportion of aliphatic and non-aliphatic
regions in the molecular structure, which is best
illustrated by certain tetracatenar mesogens that can
exhibit the whole range of mesomorphic organization
i.e nematic, smectic, cubic and columnar phases [3].
The reasons for columnar organization in these
materials are not apparent immediately, but models
exist explaining this behavior and showing that the
columns consist of groups of molecules [4, 5]. In
general then, the phase shown by a polycatenar
mesogen depends on the balance between the cross-
sectional area of the molecular core and the cross-sec-
tional area of the chains projected onto the core-chain
interface, which increases as the number or length of
the attached chains increases.
The mesomorphism of diskotic mesogens also
depends on the degree of coverage of the periphery by
flexible chains, and this idea was exploited by
Praefcke et al. [6] when they studied the lyotropic
liquid crystal properties of a series of giant disks
containing palladium and platinum. Here they used
organic solvents to modify the mesomorphism and
they introduced an idea of “internal” and “external”
solvent, where internal solvent represents the alkyl
Fig. 1. Schematic representation of a tetracatenar mesogen.
1331

1332
SMIRNOVA et al.
chains attached covalently to the discotic core, while
external solvent was the added hydrocarbon used to
induce lyotropic phases.
With these results in mind, we undertook a study of
the lyotropic liquid crystal behaviour of some poly-
catenar complexes of silver I.
OCnH2n+1
CnH2n+1
CnH2n+1
CnH2n+1
O
OCnH2n+1
O
N−Ag+−N
X−
OCnH2n+1
OCnH2n+1
O
CnH2n+1
O
I
It was the first study of lyomesomorphism in
polycatenar systems [7, 8]. It was shown in this study
that added polar solvents tended to associate with polar
core of the complexes I, while non-polar solvents
associated with non-polar periphery. For example, if
the material showed a cubic phase, then a columnar
phase could be induced by adding alkane solvent to the
system, as the alkane associates with the terminal
chains and not the core, effectively increasing the
volume of the former. Conversely, when a molecule
shows a columnar phase, the addition of polar solvents
causes an effective increase in the volume of the
central part of the molecule, which is equivalent to
reducing the volume of the periphery. As a con-
sequence, a cubic phase is induced. Moreover, we
discovered chromonic behaviour [9] using small polar
protic solvents (short-chain alcohols). In these systems
the solvent caused the complexes to form through
hydrogen bond the ribbon-like structures and so
nematic, tetragonal and lamellar phases were obtained
[7, 8].
However, complexes I differ from the more typical
polycatenar materials in a number of ways. For
example, they contain a metal, they have a charge in
the centre, they have a bulky anion associated with that
cation, and they are unique as materials that are
mesomorphic with six peripheral chains with only four
aromatic rings in the core. It was therefore of
considerable interest to prepare a series of more
conventional polycatenar mesogens and to examine
their behaviour as potential lyotropic mesogens.
The compounds studied have an aromatic core
composed of five benzene rings connected by ester
groups all of which are oriented towards the centre of
the molecule; the terminal chains are located in the
3,4-positions and provide more dense molecular
packing. Introduction of lateral, apolar substituents
into the middle part of the molecule allowed the
molecular structure to be varied with the aim of
decreasing both the melting and clearing points of the
mesogens.
Table 1. Mesomorphism of 3,4-dialkoxybenzoyloxybenzoic
acids
Compound
A-10
Phase transition
T, °C
Another aspect of lateral substitution (especially the
substitution with the long aliphatic chain like in
compound, VI) is that it is analogous to the
alkylsulfate anion of compounds I. Thus, in the case of
these polycatenar silver complexes, the long-chain
anion contributed partly to the terminal chain volume
at certain lengths when it was able to extend past the
end of the rigid core of the complex [10].
Cr–Cr'
Cr'–I
Cr–Cr'
Cr'–I
123.3
153.5
105.8
143.8
142.5
105.8
136.7
139.0
113.1
131.3
135.0
118.5
127.6
132.1
A-12
A-14
A-16
A-18
I–(N)
Cr–Cr'
Cr'–SmC
SmC–I
Cr–Cr'
Cr'–Col
Col–I
Cr–Cr'
Cr'–Col
Col–I
The compounds investigated in this work were
synthesized according to Scheme 1.
Thus, 3,4-dialkoxybenzoyloxybenzoic acids [11]
were esterified with the appropriate 1,4-hydroquinone
using DCC/DMAP in dichloromethane at room
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

THE INFLUENCE OF LATERAL APOLAR SUBSTITUENTS
1333
Scheme 1.
CnH2n+1
CnH2n+1
O
X2
X4
X1
X3
O
O
O
O
OH
+
HO
O−H
A-n
CnH2n+1
CnH2n+1
O
O
O
X2
X1
O
O
O
O
O
O
X4 O
X3
OCnH2n+1
OCnH2n+1
II-n−VII-n
temperature. Most of the hydroquinones were available
commercially, but those required for compounds V and
VI were prepared by published methods (see Experi-
with [11]), while the rest of the materials exhibit the
mesomorphism. Thus, for n = 12, we find a
monotropic nematic phase (Tuffin et al. [11] report the
same behaviour with almost identical temperatures for
the C14 homolog), while for A-14 we see an
enantiotropic SmC phase. For both A-16 and A-18, we
observed an enantiotropic columnar phase, although
we did not assign its symmetry. We note that in [11]
A-16 is reported as having both a monotropic nematic
and columnar hexagonal phase, while in A-18 [11]
reports a monotropic Colh phase. In both cases we
agree on the temperature of transition to isotropic.
However it is doubtful that a nematic phase appears in
a tetracatenar mesogen of this type with C16 chains
(Scheme 2).
1
mental). The H NMR spectra of the products showed
a typical AMX spin system for the ring bearing the
dialkoxy fragments and an AA'XX' system for the next
ring towards the centre. The splitting pattern for the
central ring depended on the hydroquinone used in the
reaction. Yields, NMR spectra, and analytical data are
collected in the Experimental.
Mesomorphism. Data on mesomorphic properties of
acids shown in Table 1 differ markedly from those
reported in [11]. Thus, the shortest-chain homologue
A-10 we obtained is non-mesomorphic (in agreement
Scheme 2.
CnH2n+1
O
O
O
X2
X1
O
O
CnH2n+1
O
O
O
O
X4 O
X3
OCnH2n+1
OCnH2n+1
II−VII
II-n, X1 = X2 = X3 = X4 = H; III-n, X1 = X3 = X4 = H, X2 = Me; IV-n, X1 = X2 = Me, X3 = X4 = H; V-n, X1 = X2 = X3 = X4 =
Me; VI-n, X1 = X3 = X4 = H, X2 = C15H31; VII-n, X1 = X3 = H, X2 = X4 = t-Bu.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

1334
SMIRNOVA et al.
Table 2. Differential scanning calorimetry data for com-
pounds II–VII
The polycatenar mesogens II to VII were studied
by polarization optical microscopy and DSC to
determine their mesomorphism. Results of these ex-
periments are compiled in Table 2.
Phase
Compound
T, °C
ΔH, kJ mol–1 ΔS, R
transition
Parent laterally unsubstituted compounds II-n
showed the expected and classical succession in
mesomorphism with the increasing chain length. Thus
for both n = 10 and 12 a SmC and a nematic phases
were seen which were identified readily from their
characteristic optical textures. As the chain length
increased to n = 14, the nematic phase disappeared and
a columnar phase was seen beneath the SmC phase;
the latter was now much reduced in range, appearing at
162.7°C and clearing at 164.3°C. As the chain length
increased further to n = 16, the lamellar phase
disappeared totally and the only phase observed was
the columnar phase. A noticeable feature of the
behaviour is the reducing stability of the clearing point
of the materials with the increasing chain length,
although the crystal phase stability does not follow the
same pattern. Interestingly, the mesomorphism of these
compounds is effectively the same as in the related
materials (VIII-n) reported by Nguyen et al. [12]
except for the mesomorphic ranges in homologues
with the longer chains VIII-12 and VIII-14 being a
little wider owing to a less stable crystal phase. The
explanation for this trend in mesomorphism with
increasing chain length is very well documented and
discussed elsewhere [4, 13] (Scheme 3).
II-10
Cr–SmC
SmC–N
N–I
153.6
174.4
183.3
162.5
170.2
171.9
154.0
162.7
164.3
145.8
158.9
127.7
148.1
162.0
127.5
133.6
143.9
151.5
130.7
142.2
144.7
130.4
137.2
126.3
132.5
134.8
163.0
176.4
133.0
157.1
163.4
133.5
155.7
157.2
102.9
107.7
125.1
120.4
120.0
69.2
9.7
162
22
2
1.1
II-12
II-14
Cr–SmC
SmC–N
N–I
73.7
4.7
169
11
2
0.7
Cr–Colr
Colr–SmC
SmC–I
Cr–Colr
Colr–I
72.2
0.6
169
1
8.2
19
170
21
24
205
3
II-16
71.2
9.0
III-10
Cr–SmC
SmC–N
N–I
9.6
86.2
1.2
III-12
III-14
Cr–Cr'
Cr'–SmC
SmC–N
N–I
16.4
68.4
9.4
41
168
23
3
1.3
Cr–SmC
SmC–N
N–I
111.2
7.1
275
17
1
0.6
III-16
III-18
IV-10
Cr–SmC
SmC–I
Cr–(SmC)
(SmC)–I
Cr–SmC
SmC–N
N–I
123.7
8.6
307
21
356
20
201
27
3
As suggested earlier, in considering undertaking
lyotropic studies of these polycatenar materials, there
142.3
7.9
T, °C
190
81.9
11.8
1.3
N
N
SmC
Cr
180
170
160
150
140
N
IV-12
IV-14
VI-12
Cr–SmC
SmC–N
N–I
99.3
10.6
1.2
245
25
3
SmC
SmC
SmC
Col
SmC
Cr
Cr–SmC
SmC–N
N–I
115.5
5.9
284
14
1
Col
Cr
Col
Cr
Cr
Cr
Cr
0.6
Cr–N
52.7
1.5
140
4
N–I
II-10 VIII-10 II-12 VIII-12 II-14 VIII-14 II-16
VII-10
VII-12
VII-14
Cr–I
99.8
107.0
124.7
251
272
317
Compound
Cr–I
Fig. 2. Comparison of the mesomorphism of compounds
II-n and VIII-n (no data available for VIII-16).
Cr–I
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

THE INFLUENCE OF LATERAL APOLAR SUBSTITUENTS
1335
Scheme 3.
CnH2n+1
O
O
O
O
CnH2n+1
O
O
O
O
O
O
OCnH2n+1
OCnH2n+1
VIII-n
was a concern that the transition temperatures may be
rather high and so the introduction of lateral sub-
stituents was considered as a profitable way in which
they might be modulated. The first series of materials
examined (III-n) possessed a lateral methyl group and
five homologs were prepared. Introduction of this
lateral methyl group was found to destabilize the
crystal phase on the average between 10 and 20°C and
to reduce clearing points by some 20°C. However,
there was also a profound effect on the mesomorphism
as the columnar phase was now totally suppressed. The
phase diagram (Fig. 3) shows a steady decrease in
clearing point with small variations in melting point,
but compared to compounds II-n, the nematic phase
persists to n = 14, while the SmC phase is seen across
all homologs prepared, although its stability falls off
rapidly at n = 18.
increased compared to those found for III-n, although
there was little effect on the melting point; this is
illustrated in Fig. 4. Thus, for IV-12 and IV-14, the
SmC range is much greater, almost double, while for
III-10 and IV-10 the range is about the same on
account of the lower stability of the crystal phase in the
former compound. Nematic ranges do not appear to
vary very much. One possible explanation for this is
that compounds IV-n have a higher symmetry than III-n
and it is well known that lower symmetry reduces
packing efficiency, and thus this may be the reason for
the decrease. Then, if compounds II-n and IV-n, are
compared, the latter possessing two methyl groups,
both with high molecular symmetry, then the steric
effect can be discerned by comparison between their
thermal behaviour; in compounds IV-n a considerable
destabilization of the crystal phase is observed and less
essential destabilization of the clearing points (Table 2).
In moving to compounds IV-n, a second methyl
group is added to the hydroquinone ring and,
curiously, the thermal stability of the mesophases
Only one homolog, V-12, was prepared using the
tetramethylhydroquinone core as it was found that the
T, °C
170
N
160
150
140
130
120
N
T, °C
165
N
N
160
N
155
N
SmC
SmC
SmC
Iso
150
SmC
N
SmC
Cr
SmC
145
140
SmC
135
130
125
Cr
Cr
Cr
Cr
Cr
III-10 IV-10 III-12 IV-12 III-14 IV-14
10
12
14
16
18
Compound
Chain length
Fig. 4. Comparison of the mesomorphism of compounds
III-n and IV-n.
Fig. 3. Mesomorphism of compounds III-n.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

1336
SMIRNOVA et al.
Intensity
Table 3. X-ray data of compounds II-14 and II-16
Experimental reflexes
Compound
T, °C
hkl
11
Cell parameters
hkl
Cell parameters
dexp,a Å
II-14
158
36.52
32.9
4.6
v.sb (sh)
s (sh)
a 65.8 Åc
b 43.9 Åc
S 1444 Å2
a 65.48 Å
b 43.82 Å
S 1435 Å2
d 36.52 Åd
A 64 Å2
20
11
a 73.04 Å
b 36.85 Å
S 1346 Å2
a 72.84 Å
b 36.65 Å
S 1335 Å2
20
v.s (w)
v.s (sh)
s (sh)
160
36.42
32.74
4.6
11
20
20
11
v.s (w)
v.s (sh)
v.s (w)
V.s (sh)
s (w)
166
150
36.52
4.6
001
II-16
38.13
34.08
4.6
11
20
a 68.16 Å
b 46.0 Å
S 1568 Å2
20
11
a 76.26 Å
b 38.1 Å
S 1453 Å2
a 75.5 Å
b 37.6 Å
S 1419 Å2
v.s (w)
v.s (sh)
s (sh)
155
37.75
33.65
4.6
11
20
a 67.3 Å
20
11
b 45.6 Å
S 1534 Å2
v.s (w
a
dexp are experimental reflexes, hkl are Miller indexes. b (v.s) very strong, (s) strong, (sh) sharpe, (w) wide. c a, b are cell parameters for
Colr phase, S is column square. d d is layer distantion for SmC phase, A is molecular square in SmC phase.
compound was subject to thermal decomposition as
soon as the isotropic state was reached. Thus, from one
heating cycle, the following transition sequence was
found: Cr·108–109·SmC·130.5·Iso.
lamellar, and a (001) reflection is observed cor-
responding to a layer spacing of 36.52 Å which, given
a molecular length (all trans conformation) of 68.4 Å
and assuming no interdigitation, would correspond to a
tilt angle of 58°. The expected reflection corres-
ponding to the flexible alkyl chains was also observed
at 4.6 Å. The X-ray data showed that the molecular
area in the SmC phase was about 64 Å2, i.e. 32 Å2 for a
single chain, which is reasonable for a SmC phase [16].
For compounds VI-n, again only one homolog was
prepared, namely VI-12. This compound was designed
as a covalent analog of the silver(I) stilbazole
complexes that we had studied earlier and which
possessed a lateral dodecylsulfate anion, whose chain
length equates to fifteen atoms when the O–S–O link
of the sulfate group is taken into account. Previously
we used a similar approach in preparing neutral
platinum(II) analogues of these silver complexes [15].
In this case, only a nematic phase was seen with a
rather narrow range and both the crystal state and the
mesophase had been significantly destabilized.
The columnar nature of the lower-temperature
phase was confirmed by X-ray analysis, and two
reflections corresponding to the fundamental
reflections of a rectangular lattice were observed. The
two reflections proved insufficient to identify the plane
group unequivocally and so it is not possible to assign
the plane group to one of the two most likely
possibilities, namely c2mm or p2gg. This also means
that unequivocal assignment of the two, lowest-angle
peaks as (11) and (20) is not possible and so Table 3
shows the lattice parameters calculated for both
possibilities. Homolog II-16 shows only a columnar
mesophase, which is also rectangular and again, the
plane group cannot be determined. The possibilities are
the same as for II-14 and the lattice parameters are
comparable when the increased terminal chain length
is taken into account.
Finally, three homolog of VII-n were prepared (n =
10, 12 and 14), but the steric effect of the tret-Bu
group was simply too great and none of the
compounds was mesomorphic, all melting close to
120°C.
X-ray investigation. Inasmuch as the symmetry of
columnar phases is notoriously difficult to determine
from optical textures alone, compounds II-14 and II-
16 were further investigated by X-ray diffraction
(Table 3). For II-14, the X-ray data are consistent with
the assignment of the higher-temperature phase as
Lyotropic mesomorphism. No solvent-induced
behaviour was observed for any of the above
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

THE INFLUENCE OF LATERAL APOLAR SUBSTITUENTS
1337
compounds in contact preparations with apolar
(alkanes of different length) or polar (DMSO, DMF)
solvents and the materials simply dissolved in the
solvents used at a given temperature. Given the results
obtained previously with inositols [17], palladium
discs [6] and polycatenar silver(I) complexes [7, 8],
this is perhaps surprising and the question will be
tested further with the preparation of additional
materials.
morphism in calamitic systems [19]. As stated earlier,
in polycatenar systems, the SmC is the only smectic
phase observed and the formation of the tilted phase is
driven by the mismatch in cross-sectional area of the
molecular core and cross-sectional area of the chains
projected onto the core-chain interface. To some extent
then, lateral groups are more shielded sterically and so
can be accommodated within the tilted phase with
disrupting it. If this is true, it is then a little more
difficult to rationalise the suppression of columnar
phases, when the columnar phase is still not evident
even when n = 18 (III-18: SmC) and when the lateral
bulk is doubled (IV-n) and the lamellar phase stability
increases. Nonetheless, the models discussed by us and
others do require that the SmC phase breaks up into
small separate columns that organize to form the
column and, superficially at least, it is unsurprising
that the lateral groups appear to inhibit this process.
However, the forgoing discussion emphasises the fact
that the explanation is not quite so straightforward.
The literature contains only few examples of
laterally substituted polycatenar mesogens, but two
examples are shown as IX and X along with their
mesomorphism [1, 2] (Scheme 4).
Thus, IX has a monotropic SmC phase while X
shows a monotropic N phase. It is well known in
calamitic systems that lateral alkyl groups suppress
lamellar phases in favor of the nematic phase [18], but
in III-n and IV-n, and in IX and X, it is the columnar
phase that is suppressed while the SmC phase persists.
Lateral substitution, therefore, has an effect that is
different in polycatenar systems when compared to
conventional calamitics. Thus, in calamitic materials,
the reason for the suppression of lamellar phases is
obvious as the lateral group prevents the molecules
associating into layers. However, it is important to note
that such arguments apply only to substituents with a
size from about methyl group and larger, for it is well
known that lateral fluorination is a productive strategy
for controlling both smectic and nematic meso-
EXPERIMENTAL
Polarization optical microscopy was performed on
microscope Leitz Laborlux 12 Pol fitted with Mettler
heating block FP90.
Differential scanning calorimetry was carried out at
a rate 10 K min–1 on Mettler DSC822e (running on the
Stare software which is equipped with an auto-
Scheme 4.
C14H29O
C14H29O
CH3
O
O
O
N
O
N
IX
OC14H29
OC14H29
CH3
Cr⋅133⋅(SmC⋅110)⋅Iso
C12H25O
C12H25O
O
O
Cl
N
N
O
Cl
OC12H25
OC12H25
X
O
Cr⋅140⋅(N⋅126)⋅Iso
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

1338
SMIRNOVA et al.
sampler). DSC data mentioned in this article are onset
temperatures.
temperature is controlled within ±0.05°C from 20 to
200°C; periodicities up to 60 Å can be measured. The
other set of diffraction patterns was registered on
Image Plate. Periodicities up to 90 Å can be measured,
and the sample temperature is controlled within ±0.3°C
from 20 to 350°C.
The X-ray patterns were obtained with two
different experimental setups, and in all cases, the
powdered sample was filled in Lindemann capillaries
of 1 mm diameter and 10 μm wall thickness. A linear
monochromatic CuKa beam (λ = 1.5405 Å) obtained
with a sealed-tube generator (900 W) and a bent quartz
monochromator were used (both generator and
monochromator were manufactured by Inel). One set
of diffraction patterns was registered with a curved
counter Inel CPS 120, for which the sample
Compounds were characterized by 1H NMR
spectroscopy using a Jeol JNM-EX 270 FT NMR
1
system at 270 MHz for H NMR and 68 MHz for 13C
NMR, while elemental analysis was carried out at the
University of Newcastle.
2-Pentadecyl-1,4-hydroquinone [20].
C15H31
OCH3
C15H31
OH
BuLi/THF
BBr3/CH2Cl2
H2O
H3CO
OCH3
H3CO
HO
C
15H31Br
n-Buthyl lithium (2.5 M, 34 ml, 86 mmol), was
added to a solution of 1,4-dimethoxybenzene (11.8 g,
85 mmol) in THF (20 ml) in a 500-ml two-neck round-
bottom flask at 0°C. The solution was stirred for 1 h
and then transferred dropwise into a solution of
bromopentadecane (29.9 g, 103 mmol) in THF (20 ml)
in another round-bottom flask. The resulting mixture
was stirred at room temperature for I h and then
poured into water (100 ml). The mixture was extracted
with diethyl ether (3×30 ml); the organic layers were
combined, washed with brine (30 ml), and dried over
magnesium sulfate. After removal of solvent, the crude
product was subjected to column chromatography on
silica gel (60 μm) with dichloromethane as eluent. The
resulting product is a colourless liquid. Yield: 14.1 g,
Table 4. Elemental analysis data for compounds II–VII
1
47% . H NMR (270 MHz, CDCl3): 6.72–6.67 m (3H,
Calculated (Found), %
Yield,
%
ArH), 3.75 s (3H, CH3O–), 3.74 s (3H, CH3O–), 2.57–
2.52 t (2H, –CH2–), 1.86–1.80 m (2H, –CH2–), 1.5–1.2
m (24H, –C12H24–), 0.88–0.83 t (3H, –CH3)
Compound
C
H
II-10
65
72
25
3
75.09 (75.29)
76.01 (76.32)
8.69 (9.07)
9.18 (9.20)
II-12
The compound so obtained (7.05 g) was dissolved
in dichloromethane (50 ml) and added slowly to a
solution of BBr3 (10.01 g, 0.041 mol) in dichloro-
methane (10 ml) at –78°C. After the addition was
complete, the solution was warmed up slowly to room
temperature and stirred for 24 h. The solution was then
added to an ice-water mixture with vigorous stirring
and the precipitated product was filtered off, washed
with water (25 ml), and dried. The product was
separated by column chromatography on silica gel
(60 μm) using hexane/ethyl acetate mixture (2:1) as the
II-14
76.77 (76.98)
77.43 (77.54)
75.22(75.22)
76.11 (76.26)
76.86 (77.02)
77.50 (77.24)
78.05 (77.42)
75.34 (75.19)
76.21 (76.18)
76.95 (76.70)
77.35 (77.31)
76.01 (76.34)
76.77 (76.74)
76.43 (77.16)
9.59 (9.56)
9.95 (9.94)
8.85 (8.80)
9.23 (9.40)
9.64 (9.80)
9.99 (10.40)
10.28 (11.48)
8.82 (8.87)
9.29 (9.31)
9.69 (9.78)
9.90 (9.91)
9.18 (9.20)
9.59 (9.97)
9.95 (10.43)
II-16
III-10
III-12
III-14
III-16
III-18
IV-10
IV-12
IV-14
VI-12
VII-10
VII-12
VII-14
45
30
16
6
3
36
43
28
85
44
61
65
1
eluent. Yield 3.4 g (53%). H NMR spectrum (270
MHz, CDCl3): 6.51–6.45 m (3H, ArH), 2.4–2.3 t (2H,
–CH2–), 1.42–1.39 m (2H, –CH2–), 1.15–1.11 m (24H,
–C12H24–), 0.75–0.71 t (3H, –CH3,)
Tetrametylhydroquinone was obtained by reduction
of the corresponding quinone with N,N-diethylhyd-
roxylamine following the procedure described in [21].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010

THE INFLUENCE OF LATERAL APOLAR SUBSTITUENTS
1339
2. Nguyen, H.-T., Destrade, C., and Malthête, J., Phasmids
and Polycatenar Mesogens. Handbook of Liquid
Crystals, Demus, D., Goodby, J.W., Gray, G.W.,
Spiess, H.W., and Vill, V., Eds., Weinheim: Wiley-VHC,
1998, vol. 2B, ch. XII, p. 865.
General procedure for the synthesis of tetracatenar
compounds II–VII. The appropriate 4-(3,4-dialkoxy-
benzoyloxy)benzoic acid (0.0015 mmol), the required
phenol (8×10–4 mmol), dicyclohexylcarbodimide
(DCC, 0.002 mmol), and 4-dimetylaminopyridine
(~40 mg) were stirred in dry dichloromethane (50 ml)
under a nitrogen atmosphere for 24 h. The resulting
mixtures were purified by flash column chromato-
graphy over silica gel (60 μm), using dichloromethane
as the eluent. For the synthesis of the longer-chain
homologs, up to five times more solvent was used than
for the lower homologs, and the reaction was allowed
to proceed at 36°C for 3 days. The elemental analysis
data of compounds obtained are given in Table 4.
3. Hoag, B.P. and Gin, D.L., Adv. Mater., 1998, vol. 10,
p. 1546; Isoda, K., Yasuda, T., and Kato, T., J. Mater.
Chem., 2008, vol. 18, p. 4522; Lincker, F., Bourgun, P.,
Masson, P., Didier, P., Gui-doni, L., Bigot, J.-Y.,
Nicoud, J.-F., Donnio, B., and Guillon, D., Org. Lett.,
2005, vol. 7, p. 1505; Eichhorn, S.H., Paraskos, A.J.,
Kishikawa, K., and Swager, T.M., J. Am. Chem. Soc.,
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Pociecha, D., Gorecka, E., Donnio, B., and Guillon, D.,
Chem. Eur. J., 2007, vol. 13, p. 3377; Rowe, K.E., and
Bruce, D.W., J. Mater. Chem., 1998, vol. 8, p. 331;
Cardinaels, T., Ramaekers, J., Nockemann, P., Driesen, K.,
Van Hecke, K., Van Meervelt, L., De Feyter, S., Wang, G.,
Fernandez Iglesias, E., Guillon, D., Donnio, B., Bin-
nemans, K., and Bruce, D.W., Soft Matter., 2008, vol. 4,
p. 2172.
4. Guillon, D., Heinrich, B., Ribeiro, A.C., Cruz, C., and
Nguyen, H.T., Mol. Cryst. Liq. Cryst., 1998, vol. 317,
p. 51.
5. Donnio, B., Heinrich, B., Allouchi, H., Kain, J., Diele, S.,
Guillon, D., and Bruce, D.W., J. Am. Chem. Soc., 2004,
vol. 126, p. 15258.
6. Praefcke, K., Holbrey, J.D., and Usol’tseva, N., Mol.
Cryst. Liq. Cryst., 1996, vol. 288, p. 189.
7. Smirnova, A.I. and Bruce, D.W., Chem. Commun.,
1
II-n: H NMR spectrum (270 MHz; CDCl3): 8.3 m
(4H); 7.8 d.d (2H); 7.7 d (2H); 7.37–7.34 m (4H); 7.3 s
(4H); 6.9 d (2H); 4.0 d.t (8H), 1.9 m (8H); 1.5–1.3 m
(56–104H); 0.8 m (12H)
1
III-n: H NMR spectrum (500 MHz; CDCl3): 8.3
d.d (4H); 7.8 d (2H); 7.7 s (2H); 7.4 d.d (4H); 7.2 d
(1H); 7.16 s (1H); 7.1 d (1H); 6.9 d (2H); 4.0 d.t (8H),
2.3 s (3H); 1.9 m (8H); 1.5–1.3 m (56–120H); 0.8 m
(12H).
IV-n: 1H NMR spectrum (400 MHz; CDCl3): 8.3 m
(4H); 7.8 d.d (2H); 7.7 d (2H); 7.3 m (4H); 7.1 s (2H);
6.9 d (2H); 4.0 d.t (8H), 2.2 s (6H); 1.9 m (8H); 1.5–
1.3 m (56–88H); 0.9 m (12H).
2002, vol. 2, p. 176.
V-12: No data were obtained as the compound was
8. Smirnova, A.I. and Bruce, D.W., J. Mater. Chem., 2006,
unstable in CDCl3 and CD2Cl2.
vol. 16, p. 4299.
1
9. Attwood, T.K., Lydon, J.E., Hall, C., and Tiddy, G.J.T.,
VI-12: H NMR spectrum (400 MHz; CDCl3): 8.3
Liq. Cryst., 1990, vol. 7, p. 657.
m (4H); 7.8 d.d (2H); 7.65 d (2H); 7.4 m (4H); 7.2–7.1
m (4H); 6.9 d (2H); 4.0 d.t (8H), 2.6 t (2H); 1.9 m
(8H); 1.5–1.3 m (100H); 0.9 m (12H).
10. Donnio, B. and Bruce, D.W., J. Mater. Chem., 1998,
vol. 8, p. 1993.
11. Tuffin, R.P., Toyne, K.J., and Goodby, J.W., J. Mater.
Chem., 1996, vol. 6. N 8, p. 1271.
1
VII-n: H NMR spectrum (270 MHz; CDCl3): 8.3
m (4H); 7.8 d.d (2H); 7.6 d (2H); 7.4 m (4H); 7.1 s
(2H); 6.9 d (2H); 4.0 d.t (8H), 1.9 m (8H); 1.5–1.2 m
(56–88H); 0.9 m (12H)
12. (a) Nguyen, H.T., Destrade, C., and Malthête, J., Liq.
Cryst., 1990, vol. 8, p. 797; (b) Malthête, J., Nguyen, H.T.,
and Destrade, C., Liq. Cryst., 1993, vol. 13. N 2, p. 171.
13. Fazio, D., Mongin, C., Donnio, B., Galerne, Y., Guillon, D.,
and Bruce, D.W., J. Mater. Chem., 2001, vol. 11,
p. 2852.
ACKNOWLEDGMENTS
We thank the EU Marie Curie programme for a
fellowship (AIS), the Royal Society for a Joint Project
Grant, and Professor Nadezhda Usol’tseva (Ivanovo,
Russia) for stimulating discussions.
14. Rourke, J.P., Fanizzi, F.P., Salt, N.J.S., Bruce, D.W.,
Dunmur, D.A., and Maitlis, P.M., J. Chem. Soc., Chem.
Commun., 1990, p. 229.
15. Mongin, C., Donnio, B., and Bruce, D.W., J. Am. Chem.
Soc., 2001, vol. 123, p. 8426.
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 7 2010