New liquid crystalline compounds involving ester-chalcone linkages having 1,3,5-trisubstituted pyrazole as a terminal group

Article abstract of DOI:10.1080/15421400903065549

Mesogens with chalcone central linkage are rare. It has been observed that-CO-CH=CH-linkage is less conducive to mesomorphism compared to-CH=N-(azomethine),-COO-(ester),-N=N-(azo) linkages due to the non linearity and angle strain arising from the keto group. But when-CO-CH=CH-linkage is present with other central linkages it becomes condusive to mesomorphism. In the present investigation two homologous series were synthesized having chalcone as a one of the central linkage. The homologous series have been derived from 1,3,5-trisubstituted pyrazole, p-hydroxy acetophenone, and alkoxy acid. Viz. 4(4′-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl-3-methyl-2- pyrazoline-5-one) [series-I] and 4 (4′-n-alkoxybenzoloxy) phenyl-propane-3-one (1-phenyl (4″-methyl)-3-methyl-2-pyrazoline-5-one) [series-II]. The compounds of the both series have been characterized by elemental analyses, FT-IR, ¹H-NMR, and Mass spectrometry methods. Their liquid crystalline properties have been investigated by optical polarizing microscopy and DSC studies. All the derivatives are mesomorphic in nature. C₁ to C₅ of both the series exhibit only nematic phase. C₆ to C₈ in series-I and C₇ & C₈ in series-II exhibit smectic as well as nematic phase. Whereas C ₁₀-C₁₆ in series-I and C₈-C₁₆ in series-II showing only smectic phase. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421400903065549

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New Liquid Crystalline
Compounds Involving Ester-
Chalcone Linkages Having
1,3,5-Trisubstituted Pyrazole
as a Terminal Group
B. T. Thaker a , D. M. Patel a & J. B. Kanojiya a
a Department of Chemistry, Veer Narmad South
Gujarat University, Surat, India
Published online: 05 Oct 2009.
To cite this article: B. T. Thaker , D. M. Patel & J. B. Kanojiya (2009) New Liquid
Crystalline Compounds Involving Ester-Chalcone Linkages Having 1,3,5-Trisubstituted
Pyrazole as a Terminal Group, Molecular Crystals and Liquid Crystals, 509:1, 145/
[887]-164/[906], DOI: 10.1080/15421400903065549
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Mol. Cryst. Liq. Cryst., Vol. 509, pp. 145=[887]–164=[906], 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903065549
New Liquid Crystalline Compounds Involving
Ester-Chalcone Linkages Having 1,3,5-Trisubstituted
Pyrazole as a Terminal Group
B. T. Thaker, D. M. Patel, and J. B. Kanojiya
Department of Chemistry, Veer Narmad South Gujarat University,
Surat, India
Mesogens with chalcone central linkage are rare. It has been observed that
=
=
–CO–CH CH– linkage is less conducive to mesomorphism compared to –CH N–
=
(azomethine), –COO– (ester), –N N–(azo) linkages due to the non linearity and
=
angle strain arising from the keto group. But when –CO–CH CH– linkage is
present with other central linkages it becomes condusive to mesomorphism. In
the present investigation two homologous series were synthesized having chalcone
as a one of the central linkage. The homologous series have been derived from
1,3,5-trisubstituted pyrazole, p-hydroxy acetophenone, and alkoxy acid. Viz.
4(40-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl-3-methyl-2-pyrazoline-5-
one) [series-I] and 4(40-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl(400-
methyl)-3-methyl-2-pyrazoline-5-one) [series-II]. The compounds of the both series
have been characterized by elemental analyses, FT-IR, 1H-NMR, and Mass spec-
trometry methods. Their liquid crystalline properties have been investigated by
optical polarizing microscopy and DSC studies. All the derivatives are meso-
morphic in nature. C1 to C5 of both the series exhibit only nematic phase. C6 to
C8 in series-I and C7 & C8 in series-II exhibit smectic as well as nematic phase.
Whereas C10–C16 in series-I and C8–C16 in series-II showing only smectic phase.
Keywords: chalcone; ester; mesomorphic; nematic phase; smectic phase; trisubstitude
pyrazole
We are thankful to I.I.T. Bombay, CDRI Lucknow and Garda chemicals Ltd.,
Ankleshwar (Gujarat) to providing an elemental analysis, FT-IR, 1H-NMR, 13C NMR,
Mass and Thermal studies and Department of Applied Chemistry, Faculty of Technology
and Engineering, M. S. University of Baroda, Vadodara for providing us Optical polariz-
ing microscope for mesophase study.
Address correspondence to B. T. Thaker, Department of Chemistry, Veer Narmad
South Gujarat University, Udhana-Magdalla Road, Surat, Surat-395007, India. E-mail:
btthaker1@yahoo.co.in
145=[887]

146=[888]
B. T. Thaker et al.
INTRODUCTION
The mesomorphic behaviour of an organic compound is basically
dependent on its molecular architecture in which a slight change in the
molecular geometry brings about considerable change in its
mesomorphic properties. A number of mesogenic homologous series
have been reported that have –COO–, –CH¼N–, –N¼N–, –CH¼CH–,
–CH¼CHCOO–, –C¼C–, –CꢀC– etc., groups as their central linkages.
Many mesogenic homologous series contain two central linkages, both
of which may either be ester [1–3] or azomethine groups [4,5] or one of
which may be ester and the other azomethine [6,7]. In the literature
there are few reports of mesogenic compounds having chalcone
linkages. However, many years ago Vora et al. [8] have reported
homologous series of polymer containing chalcone linkage. Soon after
that Chudghar et al. [9] reported homologous series containing
ester-chalcone linkages. Recently Yeap et al. [10] have also synthesized
mesomorphic compound containing ester-chalcone linkage. In our pre-
vious work we have reported the homologous series containing Schiff
base-chalcone linkage [11].
Chalcone is one of the important chemical compounds and is
being studied extensively because of its significant application in
various sectors. In the fields of biology and biochemistry, chalcone
has been claimed to be one of the compounds that plays a vital
role in antitumor [12,13], antiinflammatory [14,15] and antima-
laria [16] activities. It has also been documented that the chalcone
possesses a remarkable nonlinear optical (NLO) property, which is
an essential element for optical communications devices. The other
importance of this compound is its high photosensitivity and
thermal stability, which are used in developing various crystal-
line electro-optical devices [17–19] and also having fluorescent
properties [9].
However, heterocyclic compounds provide a great synthetic and
structural versatility due to presence of number of potential substitu-
tion positions. Furthermore heteroatoms offer the possibility of several
modes of co-ordination. In particular, pyrazoles derivatives allow
structural design to tune the molecular shape for the appearance of
mesomorphic properties. The mesogenic series with hetero atoms have
created wide interest in liquid crystal field. The introduction of
heteroatom causes considerable changes in chemical and physical
properties and influences the type of liquid crystal phase, also phase
transition temperatures and other properties of the mesogens [20].
Mesogenic heterocyclic homologous series containing nitrogen, oxygen
etc. as heteroatom are reported. Schubert et al. [21] have reported

New Liquid Crystalline Compounds
147/[889]
mesogenic pyron derivatives. Demus et al. [22,23] have reported
number of dioxygen derivatives exhibiting mesomorphic behaviour.
Pavluchenko et al. [24] have reported mesomorphic homologous series
containing benzoxazole and benzthiazoles hetero atoms. Nash and Gray
[25] have also reported some heterocyclic mesogens and have tried to
explain the mesogenic behaviors of these heterocyclic moieties. Indeed,
some 3, 5-disubstituted pyrazoles and 4-substituted pyrazoles have
demonstrated their ability to show liquid crystalline behavior [26–31].
In our previous work [32] we have synthesized two homologous series
containing ester-chalcone linkages having substituted benzene ring as a
terminal group. An attempt have been made to synthesized two new
homologous series containing same central linkages but different term-
inal heterocyclic moiety to study the influence of the terminal group on
mesomorphic and thermal stability of these compounds.
In this article, we report series of some newly analogues derived from
1,3,5-trisubstituted pyrazole as terminal groups and synthesized two
homologues series, Viz. 4(40-n-alkoxybenzoloxy) phenyl-propane-3-one
(1-phenyl-3-methyl-2-pyrazoline-5-one) [series-I] and 4(40-n-alkoxyben-
zoloxy) phenyl-propane-3-one(1-phenyl(400-methyl)-3-methyl-2-pyrazoline-
5-one) [series-II] in which the ester and chalcone are essential central
linkages.
All the compound of both the series has been characterized by ele-
1
mental analysis, FT-IR, H-NMR, 13C-NMR, and Mass spectrometry.
The liquid crystalline behaviors of these compounds were observed
by DSC study and polarizing microscope.
EXPERIMENTAL
Reagents and Technique
For the synthesis of compounds of the homologous series, following
materials were used. 4-Hydroxy benzoic acid, 4-hydroxy acetophe-
none, alkyl bromide (Lancaster, England). The solvents were
used after purification using the standard methods described in the
literature [33].
Elemental analyses (C, H, N) were performed at CDRI(Central
Drugs Research Institute), Lucknow. Infrared spectra were recorded
with a Perkin-Elmer2000 FT-IR spectrophotometer in the frequency
1
range 4000-400 cmꢁ1 with samples embedded in KBr discs. H-NMR
spectra of the compound were recorded with JEOL-GSX-400 using
CDCl3 as a solvent and TMS as an internal reference and Mass spectra
(EI) of the compounds at SAIF(Sofisticated Analytical Instrument
Facilities), IIT Madras, Chennai. 13C NMR spectra of the compound

148/[890]
B. T. Thaker et al.
were recorded with BRUKER AVANCE II 400 NMR Spectrometer,
SAIF, Chandigarh. Thin-layer chromatography analyses were
performed by using aluminium-backed silica-gel plates (Merck 60
F524) and examined under short-wave UV light.
The phase-transition temperatures were measured using a shi-
madzu DSC-50 at heating and cooling rates of 5ꢂC minꢁ1, respectively.
The DSC data are shown in Table 3. The optical microscopy studies
were carried out with a ‘‘Leitz Loborlux 12’’ POL(Wetzler,Gerrmany)
polarizing microscope equipped with a Mettler FP52 hot stage. The
textures of the compounds were observed using polarized light with
crossed polarizers with sample in thin film sandwiched between a
glass slide and coverslip.
Synthesis
Synthesis of 4-n-alkoxy benzoic acid
4-n-Alkoxy benzoic acid were prepared as reported by Dave and
Vora method [34]. The m.p. of these compounds were compared with
the reported one and they are almost similar to reported values.
Synthesis of 4-n-alkoxy benzoyl chlorides
4-n-alkoxy benzoyl chlorides were prepared by reported method
[34]. The m.p. of these compounds were compared with the reported
one and they are almost similar to reported values.
Synthesis of 4-(40-n-alkoxybenzoloxy)-acetophenone
4-hydroxy aetophenone (0.01 mole, 1.22 gm) was dissolved in dry
pyridine (10.0 ml) and was added drop wise with occasionally stirring
into ice-cold 4-n-alkoxy benzoyl chloride (0.01mole, 2.41 gm) in a round
bottom flask. Then mixture was refluxed on hot water bath for two
hours and was allowed standing overnight. The mixture was acidified

New Liquid Crystalline Compounds
149/[891]
with cold 1:1 dilute hydrochloric acid to precipitate the product. The
solid obtained was filtered, washed successive with saturated
NaHCO3 solution, dilute NaOH solution and two to three times with
water thus crude solid was obtained which has number of times
purified by hot water until the constant transition temperature were
obtained. The transition temperatures are in good accordance with
the literature [35].
Synthesis of Compound Series-I and Series-II [36–39]
Series-I Synthesis of 4(40-n-alkoxybenzoloxy) phenyl-propen-
3-one(1-phenyl-3-methyl-2-pyrazolin-5-one)
Take 4-(40-n-alkoxybenzoloxy) acetophenone (0.005 mole 1.6 gm)
and 1-phenyl-3-methyl-4-formyl-2-pyrazolin-5-one in flat bottom flask
containing 25 ml absolute alcohol and stirred it on a stirrer, till both
the reactants were dissolved completely. Then cold 10% aq. KOH solu-
tion added dropwise and continue the stirring further for four hours.
The reaction mixture was allowed to stand for overnight. The mixture
was neutralized by cold dilute HCl up to pH (6.5–7.0). Then solid
obtained was filtered, washed with water and dried. The crude pro-
ducts were purified by using column chromatography and crystallized
from methanol. The melting points and transition temperatures for
this homologous series are given in Table 1.

150/[892]
B. T. Thaker et al.
TABLE 1 Transition Temperature of Series-I
Transition temperature ꢂC
Compounds
R ¼ n alkoxy
Sm
N
I
C1
C2
C3
C4
C5
C6
C7
C8
C10
C12
C14
C16
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
–
–
–
–
–
63
87
78
89
55
64
51
126
116
131
110
146
104
101
93
–
–
–
–
223
220
231
212
197
192
174
140
125
113
107
121
Decyl
Dodecyl
Tetradecyl
Hexadecyl
Note: Sm: Smectic; N: Nematic; I: Isotropic.
Data
Series-I Compound-C12
Yield 70%. M.P.113ꢂC. Found: C, 75.05; H, 7.21; N, 4.63 Calc. for
C38H44O5N2; C, 75.01; H, 7.24; N, 4.61%. EI-MS m=z (rel.int %): 607
(M-1)þ IR (KBr): Vmax=cmꢁ1 2850–2935 cmꢁ1 (C–H aliphatic),
1776 cmꢁ1 (C¼O of ester), 1677 cmꢁ1 (C¼O of chalcone), 1606 cmꢁ1
(C¼C of vinyl gr. of chalcone), 1582 cmꢁ1 (C¼C of aromatic), 1255 cmꢁ1
1
(C–O–C), 1056 cmꢁ1 (C–O), H NMR (CDCl3): d 0.89–0.93 ppm (CH3),
1.28–1.82 ppm (CH2), 2.38 ppm (–CH3 of the pyrazolone ring) 4.01–
4.05 ppm (OCH2), 6.91–7.26 ppm (Ar–H), a ¼ 8.06 ppm, b ¼ 6.94 ppm
(R–CO–CaH¼CbH–R).
Series-II Synthesis of 4(40-n-alkoxybenzoloxy) phenyl-propen-
3-one(1-phenyl(400-methyl)-3-methyl-2-pyrazolin-5-one)
Take 4-(40-n-alkoxybenzoloxy) acetophenone (0.005 mole 1.6 gm)
and 1-phenyl(400-methyl)-3-methyl-4-formyl-2-pyrazolin-5-one in flat
bottom flask containing 25 ml absolute alcohol and stirred it on a
stirrer, till both the reactants were dissolved completely. Then cold
10% aq. KOH solution added dropwise and continues the stirring
further for four hours. The reaction mixture was allowed to stand for
overnight. The mixture was neutralized by cold dilute HCl up to pH
(6.5–7.0). Then solid obtained was filtered, washed with water and
dried. The crude products were purified by using column chromatogra-
phy and crystallized from methanol. The melting points and transition
temperatures for this homologous series are given in Table 2.

New Liquid Crystalline Compounds
151/[893]
Data
Series-II Compound-C12
Yield 86%. M.P.107ꢂC. Found: C, 75.21; H, 7.35; N, 4.47 Calc. for
C39H46O5N2; C, 75.24; H, 7.39; N, 4.50%. EI-MS m=z (rel.int %): 621
(M-1)þ IR (KBr): Vmax=cmꢁ1 2850–2953 cmꢁ1(C-H aliphatic),
1708 cmꢁ1 (C¼O of ester), 1642 cmꢁ1 (C¼O of chalcone), 1607 cmꢁ1
(C¼C of vinyl gr. of chalcone), 1580 cmꢁ1 (C¼C of aromatic),
1260 cmꢁ1 (C–O–C), 1063 cmꢁ1 (C–O), 1H NMR (CDCl3): d 1.01–
1.06 ppm (CH3), 1.41–1.87 ppm (CH2), 2.45 ppm (CH3 of the pyrazolone
TABLE 2 Transition Temperature of Series-II
Transition temperature ꢂC
Compounds
R ¼ n alkoxy
Sm
N
I
C1
C2
C3
C4
C5
C6
C7
C8
C10
C12
C14
C16
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
–
–
–
–
–
73
81
69
86
69
57
59
124
119
128
115
136
143
105
–
–
–
–
–
224
218
216
204
207
195
168
147
113
107
105
115
Decyl
Dodecyl
Tetradecyl
Hexadecyl
Note: Sm: Smectic; N: Nematic; I: Isotropic.

152/[894]
B. T. Thaker et al.
ring) 4.01–4.16 ppm (OCH2), 7.01–7.39 ppm (Ar–H), a ¼ 7.04 ppm,
b ¼ 8.19 ppm (R–CO–CaH¼CbH–R).
Results and Discussion
In our recent work, 12 homologous from each of the two series,
4(40-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl-3-methyl-2-
pyrazoline-5-one) [series-I] and 4(40-n-alkoxybenzoloxy) phenyl-propane-
3-one(1-phenyl(400-methyl)-3-methyl-2-pyrazoline-5-one) [series-II] have
been synthesized having ester-chalcone central linkages containing
terminal heterocyclic ring and their mesomorphic properties have
studied. The mesomorphic properties of all the synthesized compounds
have been characterized by differential scanning calorimetry
(DSC) and polarizing optical microscope (PMO) attached with Mettler
hot stage.
The transition temperature of both series are given in Tables 1 and 2.
In series-I the compounds (C1–C5) exhibit enatiotropic nematic
mesophase and (C6–C8) exhibit enantiotropic smectic and nematic
mesophases. While compound C10, C12, C14, and C16 exhibit only
FIGURE 1 (a) Texture of SmC phase of C7 of series-I at 87ꢂC, (b) Schlieren
texture of the Nematic phase of C3 of series-I at 130ꢂC on cooling, (c)
Schlieren texture of the Nematic phase of C5 of series-II at 136ꢂC on cooling,
and (d) Schlieren texture of the Nematic phase of C6 of series-II at 143ꢂC.

New Liquid Crystalline Compounds
153/[895]
FIGURE 2 Mesomorphic behaviour as a function of the number of carbon
atoms (n) in the terminal alkoxy chain for series-I.
enantiotropic smectic mesophase. In second homologous series-II, the
compound (C1 to C5) exhibit enatiotropic nematic mesophase C6 and
C7 exhibit enantiotropic smectic and nematic phases. While compound
C8, C10, C12, C14, and C16 exhibit only enantiotropic smectic mesophase.
The texture of the series I & II are given in Figure 1. On cooling the
isotropic liquid, small droplets appear, which coalesce to a classical
schlieren (threaded) texture characteristic of the nematic phase. It is
consistent with the assignment of each mesophase type using the clas-
sification systems reported by Gray and Goodby [40]. The plot of transi-
tion temperature against the number of carbon atom in the alkoxy
chain are shown in Figures 2 and 3. In which Cr-M transition tempera-
ture, a regular alternation of the temperature occurring between
homologous containing odd and even number carbon atoms in alkyl
chain. In the present work N-I transition temperature for the series I
and II of compounds do not behave in this way. This is because of the
terminal 1,3,5-trisubstituted pyrazole ring plays some role either in
FIGURE 3 Mesomorphic behaviour as a function of the number of carbon
atoms (n) in the terminal alkoxy chain for series-II.

154/[896]
B. T. Thaker et al.
packing of the molecule in crystal lattice or due to the stereochemistry
of the molecule is not symmetrically linear.
The series also exhibits smectic properties, the Sm-N transition tem-
perature fond to fall a number of carbon increase in alkyl chain. In
series-I and II only two or three compound exhibit smectic and nematic
both mesophases. Therefore, we could not give the trend for Sm-N curve.
In these both series Sm-I transition usually begins at about the
decyl, dodecyl, hexadecyl and octadecyl ethers together with the N-I
transition temperatures for the lower homologous contains an even
number of carbon atoms in alkyl chain, constitute one smoothly falling
mesorphic – isotropic transition temperatures. From the plot of transi-
tion temperatures against the number of carbon atoms (Figures 2
and 3), it can be noticed that Cr-M transition temperatures decreased
with increase in the length of terminal alkoxy chain. This is in agree-
ment with the observation reported for such homologous series [41].
Cr-M transition shows some what large transition temperature
changes for n ¼ 5 to n ¼ 6. This could be explained as, a common pat-
tern of behavior is that the lower homologues are nematic, the middle
members exhibit a smectic mesophase followed by nematic mesophase
and the long chain members, i.e., C10, C12, C14, C16 are purely smectic
as observed in Tables 2 and 3.
The Cr-M for n ¼ 5 in series-I is observed at 146ꢂC. The increment of
each methylene unit brings about regular changes in the transition
temperature of the series as reported by Gray [41]. For shorter chain
compounds C5, the separation of the aromatic nuclei is at a minimum
and terminal cohesive forces are strongest and predominant. As
nematic phase is highly disordered which required high energy to
overcome such forces, therefore, C5 compound exhibit nematic phase
at high temperature.
TABLE 3 DSC Data for Series-I and II Compounds
Peak temp.
(Microscopic temp.) ꢂC
Series
I
Compound
C6
Transition
DH Jgꢁ1
DS Jgꢁ1Kꢁ1
Cr-Sm
Sm-N
N-I
Cr-Sm
Sm-I
Cr-Sm
Sm-N
N-I
Cr-Sm
Sm-I
61.66 (63)
101.91 (104)
190.28 (192)
53.72 (55)
111.60 (113)
72.80 (73)
146.73 (143)
197.01 (195)
87.47 (86)
11.31
29.87
35.31
148.70
0.833
48.51
2.767
2.368
80.34
7.618
0.033
0.079
0.076
0.455
0.002
0.140
0.006
0.005
0.222
0.019
C12
C6
II
C10
112.35 (113)

New Liquid Crystalline Compounds
155/[897]
However, in the middle members e.g., n ¼ 6 (C6), the smectic proper-
ties appear, because the alkyl chain is increasing the lateral cohesive
forces and the molecules may maintain themselves in the layer
arrangement. The smectic phase is highly ordered–one compared to
nematic mesophase, which requires lower energy to observe smectic
behavior. Therefore, smectic mesophase observed in compound n ¼ 6
(C6), at 63ꢂC. Therefore, such large differences in Cr-N and Cr-Sm
temperature have been observed in present two series.
DSC is a valuable method for the detection of phase transition. It
yields quantitative results; therefore we may draw conclusions con-
cerning the nature of the phases that occur during the transition. In
the present study, enthalpies of two derivatives of series I and series
II were measured by DSC. Data are recorded in Table 3. Which helps
the further confirm the mesophase type. Table 3 shows the phase tran-
sition temperatures, associated enthalpy (DH) and molar entropy (DS)
for compound of series-I (C6, C12) and series-II (C6, C10). Enthalpy
values of the various transitions agree well with the existing related
literature values [42]. The DSC curves of representative compounds
are shown in Figures 4 to 7. Microscopic transition temperature values
are almost similar to DSC data.
Table 4 shows the comparison of Sm-N and N-I transition tempera-
ture of compound n ¼ 6, series I, and structurally related compounds
n ¼ 6, series II. The Sm-N mesophase range of compound n ¼ 6
(series-I) is lower by 29ꢂC, respectively, when compared with
FIGURE 4 DSC Curves of the compound C6 of series-I.

156/[898]
B. T. Thaker et al.
FIGURE 5 DSC Curves of the compound C12 of series-II.
compound n ¼ 6 (series-II). The N-I transition temperature of
compound, series-I, is higher by 36ꢂC, respectively, when compared
with compound 6 (series-II).
Although the mesomorphic phase stability is greater in series-II
compounds than that of series I, this is because of presence of –CH3
FIGURE 6 DSC Curves of the compound C6 of series-II.

New Liquid Crystalline Compounds
157/[899]
FIGURE 7 DSC Curves of the compound C10 of series-II.
group at pera- position on 1-phyenyl ring (which is attached to pyrazo-
line ring) produce a steric hindrance. The order of group efficiency
derived by Dave and Dewar [43,44] based on the magnitude of the
groups slope value. The decreasing order of the group efficiency is in
the decreasing order of group polarizability. The increase in N-I
transition temperature with increasing alkoxy chain in compounds
of series-I can be explained by increasing overall polarizability of the
molecule.
The FT-IR spectra of the mesomorphic ester-chalcone central link-
age exhibit different vibration modes corresponding to the stretching
and bending mode of different functional groups present in the mole-
cule. The FT-IR spectra of representative compound of homologous
series-I and Series-II are shown in Figures 8 and 9. IR spectra of
ester-chalcone central linkage show strong or medium bands around
1706 cmꢁ1and 1620 cmꢁ1, 1686 cmꢁ1 attributed to t(C¼O) of ester
TABLE 4 Different Transition Temperatures and Range of Mesophases
Observed in Series I and II
Sm-N mesophase
range (ꢂC)
N-I mesophase
range (ꢂC)
Series
Compound
SmC
N
I
I
II
n ¼ 6
n ¼ 6
63
73
104
143
192
195
41
70
88
52

158/[900]
B. T. Thaker et al.
FIGURE 8 IR Spectra of C12 of series-I.
group chalcone and pyrazoline ring respecting strong band appeared
at around 1606 cmꢁ1 is attributed to t(C¼C) vinyl group of chalcone.
In the present case all the spectra of mesomorphic compound show
two sharp bands at around 2919 cmꢁ1 and 2849 cmꢁ1 are due to
FIGURE 9 IR Spectra of C12 of series-II.

New Liquid Crystalline Compounds
159/[901]
aliphatic t(C–H) symmetrical and asymmetrical stretching vibration
of –CH3 and –CH2 groups of n-alkyl chain. Another two bands are also
observed 1465 cmꢁ1 and 1391 cmꢁ1 are due to aliphatic –CH3 and
–CH2 deformation vibrations. The sharp and medium band observed
at around 1578–1513 cmꢁ1 region due to aromatic n(C¼C) stretching.
The weak band observed at around 631–763 cmꢁ1 is due to rocking
vibration of –CH2 groups of alkyl chain. Out of plane deformation of
ring hydrogen band is establishing the position of substituent on
aromatic nuclei is well known. Although correlation can often be
useful in analysis of spectra of the mesomorphic compounds but their
performance is variable. Infrared spectra of the present class of the
compounds often show long wavelength regions crowded with a large
number of bands of similar intensities, and it is difficult to know which
bands belongs to this class. Further more compounds often contain
more than one aromatic nucleus and are often substituted with
strongly electronegative groups, such as alkoxy, which tend to upsets
the correlations.
1H-NMR spectra of representative compounds are shown in
Figures 10 and 11 and the chemical shifts (d, ppm) are noted. The
1H NMR spectra of ester-chalcone central linkage type of compounds
exhibited six signals present in spectra, indicating six type of different
enviroment proton present in these type of compound. The first signal
FIGURE 10 1H NMR spectra of C6 of series-I.

160/[902]
B. T. Thaker et al.
FIGURE 11 1H NMR spectra of C7 of series-II.
observed between d 0.91–0.95 ppm, which is sharp and triplet corre-
sponding terminal methyl proton of straight chain of n- alkoxy group.
The multiplate signals observed between d 1.28–1.82 ppm are due to
methylene (–CH2) proton of straight alkyl chain of n-alkoxy group
and d 2.38 ppm –CH3 proton of the pyrazolone ring. The triplet signal
observed between d 4.09–4.15 ppm is attributed to –OCH2 proton of
n-alkoxy group like to phenyl ring. The multiplate signal observed
between d 6.88–8.13 ppm are corresponding to substituted phenyl
rings. The ‘a’ and ‘b’ types of proton in the central linkage
[COCaH ¼ CbH] sharp singlet at
d 8.14 ppm and d 6.91 ppm
respectively.
The mass spectra of series-I and series-II are shown in Figures 12
and 13. The m=z ratios obtained from the spectra of each samples are
matched with route for mass fragmentation and abundances in the
mass spectrum. The molecular wt. obtained from the mass spectra
are almost equivalent to the calculated value of the compounds.
In series-I and II there are two linkages, one is ester and other is
chalcone. Mesogens with different central linkages are known [41].
However most of these central linkages have an even number of linking
groups. The chalcone linkage has an odd number of atoms. Moreover,
very few low molecular mesogens with the chalcone linkage are known.
–CH¼CH–CO– linkage is less conducive to mesomorphism compared
to –CH¼N–, –COO– linkages due to the non-linearity and angle strain
arising from the keto group [9]. Nguyen et al. [45] have reported that a

New Liquid Crystalline Compounds
161/[903]
FIGURE 12 Mass Spectra of C12 of Series-I.
ketonic group linking two phenyl rings (benzophonene derivatives) is
non-conducive to mesomorphism due to the angular shape of such
molecules resulting from the angle of keto group. But when molecule
having two linkage in which one is chalcone and other is –CH¼N or
–COO– it becomes conducive to the mesomorphism [9,11,32].
FIGURE 13 Mass Spectra of C12 of Series-II.

162/[904]
B. T. Thaker et al.
INFLUENCE OF THE TERMINAL GROUP
In this paper we have just presented compounds with the general
structure
Where R0 ¼ 1,3,5-trisubstituted pyrazole ring.
In our previous paper [32] we presented two homologous series A &
B as following structure,
In order to have better understanding we have synthesized the pre-
sent two new homologous series containing substituted pyrazolone
ring as a terminal group.
On comparision of the present pyrazole ring with previous benzene
ring we have observed that the transition temperature range of the
present homologous series containing pyrazole as a terminal group
becomes higher than the previous one and also mesophase stability
of these series becomes higher than simple benzene analogous due
to the introduction of pyrazole ring as a terminal group. Because pyr-
azole ring having highly delocalized system as a result of it shows very
high thermal stability compare to benzene analogous.
CONCLUSION
In this article we have presented the synthesis and characterization of
mesogenic two homologous series of 1,3,5-trisustituted pyrazole hav-
ing ester-chalcone linkage. All the compounds of the series exhibit
enantiotropic mesomorphism. The mesophase range of present series-I
is higher than those of structurally related compounds of series-II that
has been attributed to the high polarizability of the molecule because
the bulky group reduced the polarity of molecule and decreases the
mesophase stability of compound. Both series show nematic mesophase

New Liquid Crystalline Compounds
163/[905]
and higher homologues show smectic mesophase. The above studies on
a limited number of heterocyclic mesogens strongly suggests that
dominant effect of the hetero atom is to produce change in conjugative
interactions within the molecule which effect factors such as polariz-
ability and dipolarity. Intermolecular effects produced by the lone pair
of electrons are apparently, in certain case.
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