Synthesis and characterization of liquid crystalline materials incorporating the novel 4-amino-1,2,4-triazole and isonicotinic acid hydrazide moiety

Article abstract of DOI:10.1080/15421400801915050

We report the synthesis and evaluation of thermal behavior of two new mesogenic homologous series of liquid crystalline compound containg 1,2,4-triazole and isonicotinic acid ring at the terminus of the molecule viz. 4-[(4H-1,2,4-triazol-4-ylimino) methyl] phenyl 4-alkoxybenzoate and 4-(2-isonicotinoylcarbonohydrazonoyl) phenyl 4-alkoxybenzoate. Both series have been characterized by elemental analysis, FT-IR, mass spectrometry, 1H-NMR, and 13C-NMR. Phase transition temperatures and the thermal parameters were obtained from differential scanning calorimetry (DSC). The texture observation was performed under polarizing optical microscopy (PMO) attached with Mettler hot stage. All the derivatives are mesomorphic in nature showing nematic phase and the higher member of both series shows smectic phase. The use of isonicotinic acid and triazole as a terminal group has a very dramatic effect on the melting and clearing points. The mesomorphic behavior has been analyzed in terms of structural property relationship.

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Synthesis and Characterization
of Liquid Crystalline Materials
Incorporating the Novel 4-
Amino-1,2,4-triazole and
Isonicotinic Acid Hydrazide
Moiety
B. T. Thaker a & Pranay Patel a
a Department of Chemistry , Veer Narmad South
Gujarat University , Surat, India
Published online: 22 Sep 2010.
To cite this article: B. T. Thaker & Pranay Patel (2008) Synthesis and Characterization
of Liquid Crystalline Materials Incorporating the Novel 4-Amino-1,2,4-triazole and
Isonicotinic Acid Hydrazide Moiety, Molecular Crystals and Liquid Crystals, 482:1, 3-20
To link to this article: http://dx.doi.org/10.1080/15421400801915050
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Mol. Cryst. Liq. Cryst., Vol. 482, pp. 3–20, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400801915050
Synthesis and Characterization of Liquid Crystalline
Materials Incorporating the Novel 4-Amino-1,2,4-triazole
and Isonicotinic Acid Hydrazide Moiety
B. T. Thaker and Pranay Patel
Department of Chemistry, Veer Narmad South Gujarat University,
Surat, India
We report the synthesis and evaluation of thermal behavior of two new mesogenic
homologous series of liquid crystalline compound containg 1,2,4-triazole and
isonicotinic acid ring at the terminus of the molecule viz. 4-[(4H-1,2,4-triazol-4-
ylimino) methyl] phenyl 4-alkoxybenzoate and 4-(2-isonicotinoylcarbonohydrazo-
noyl) phenyl 4-alkoxybenzoate. Both series have been characterized by elemental
analysis, FT-IR, mass spectrometry, 1H-NMR, and 13C-NMR. Phase transition tem-
peratures and the thermal parameters were obtained from differential scanning
calorimetry (DSC). The texture observation was performed under polarizing
optical microscopy (PMO) attached with Mettler hot stage. All the derivatives
are mesomorphic in nature showing nematic phase and the higher member of
both series shows smectic phase. The use of isonicotinic acid and triazole as a
terminal group has a very dramatic effect on the melting and clearing points.
The mesomorphic behavior has been analyzed in terms of structural property
relationship.
Keywords: ester; isonicotinic acid hydrazide; mesophase; nematic phase; smectic
phase; schiff base; triazole
INTRODUCTION
Liquid crystals containing heterocyclic units are of crucial importance
in the design and synthesis of novel advanced functional materials,
where liquid crystalline phases, polarity, geometry, luminescence, and
other properties of the molecule may be varied through the introduc-
tion of heteroatoms [1–3]. Furthermore, luminescent liquid crystals
Received June 21, 2007; accepted November 15, 2008.
Address correspondence to B. T. Thaker, Department of Chemistry, Veer Narmad
South Gujarat University, Surat 395007, India. E-mail: btthaker1@yahoo.co.in
3

4
B. T. Thaker and P. Patel
are of interest since their self-organizing properties can be exploited to
improve device performance and to achieve linearly polarized electro-
luminescence [4]. Several liquid crystalline compounds containing a
heterocyclic ring have been reported [4–10]. Mesogenic compounds
containing thiazole have recently been reported [11]. Usually, five-
or six-membered heterocycles are involved, and they form part of
the core in rod-shape (calamitic), bent-shape, or disc-shape (discotic)
molecules. However, few mesogenic five-membered and six-membered
heterocycles have been reported. In recent years, the great scientific
and practical interest in liquid crystals has generated an increasing
requirement for compounds with specific properties. Therefore,
chemists are still searching for new structural units and structural
variations in order to find compounds more capable to meet present
requirements since heterocyclic compounds can be extremely useful
in influencing the dielectric anisotropy, viscosity, birefringence,
Smectic C (SmC) ranges positively [12].
Recently we have focussed our attention on the extent to which
different heteroatoms incorporated in heterocyclic liquid crystal units
influence liquid crystalline properties. Hence, we have introduced
4-amino-1,2,4-triazole and isonicotinic acid hydrazide as terminal
groups and synthesized two homologues series, viz., 4-[(4H-1,2,4-triazol-
4-ylimino) methyl] phenyl 4-alkoxybenzoate (Series A) and 4-(2-isoni-
cotinoylcarbonohydrazonoyl) phenyl 4-alkoxybenzoate (Series B). The
presence of an additional amino group in the hydrazides causes
delocalization of electrons with subsequent changes in energy level
associated with the carbonyl oxygen which acts as an electron donor
in acid amides.
EXPERIMENTAL
Reagents and Technique
The solvents were used after purification by the standard methods,
described in the literature [13]. 4-Hydroxybenzoic acid, p-hydroxyben-
zaldehyde, and DMAP (4-dimethylaminopyridine) were obtained from
Merck (Germany). 4-Amino-1,2,4-triazole, isonicotinic acid hydrazide,
and dicyclohexylcarbodiimide (DCC) were purchased from Fluka
Chemie (Switzerland). Elemental analyses (C, H, N) were performed
at Central Drug Research Institute (CDRI), Lucknow. Infrared spectra
were recorded with a Perkin-Elmer 2000 FT-IR spectrophotometer in
the wave number range 4000–400 cmꢀ1 with samples embedded in

Liquid Crystalline Materials
5
1
KBr discs. HNMR spectra of the compounds were recorded with a
Jeol-GSX-400 instrument using CDCl3 as a solvent and TMS as an
internal reference at Sophisticated Analytical Instrumentation
Facility (SAIF), IIT Madras, Chennai. 13C NMR spectra of the com-
pound were recorded with Bruker Avance II 400 NMR spectrometer,
SAIF, Chandigarh. Mass spectra (GC-MS) of the compounds were
recorded at Department of Chemistry, Saurashtra University, Rajkot
(Gujarat). Thin-layer chromatography (TLC) analyses were performed
using aluminium-backed silica-gel plates (Merck 60 F524) and exam-
ined under shortwave UV light. The phase-transition temperatures
werꢁe measured using a Shimadzu DSC-50 at heating and cooling rates
of 5 C minꢀ1, respectively. The optical microscopy studies were carried
out with a Carl Zeiss polarizing microscope equipped with a Mettler
FP52 hot stage. The textures shown by the compounds were observed
using polarized light with crossed polarizers with the sample in a thin
film sandwiched between a glass slide and cover slip.
Synthesis
Synthesis of 4-n-Alkoxy Benzoic Acid [11]
This was prepared by the reported method.
Synthesis of 4-[(4-n-Alkoxy-benzyloxy) Benzaldehyde [11]
To a mixture of 4-n-alkoxybenzoic acid (1 mmol) and p-hydroxyben-
zaldehyde (1 mmol) in 150 ml of distilled dichloromethane, 0.1 mmol of
dimethyl aminopyridine (DMAP) was added under an argon atmos-
phere. The mixture was cooled in an ice-water bath, and after
10 min, 1 mmol of DCC was added under an argon atmosphere. The
mixture was stirred overnight at room temperature, the salts were
filtered off, and the solvent was evaporated. The crude product was
purified by flash chromatography using a mixture of hexanes=ethyl
acetate (7=1) as eluent.
Synthesis of Compound 3A and 3B
A. Synthesis of 4-[(4H-1,2,4-triazol-4-ylimino) methyl] Phenyl
4-alkoxybenzoate [14,15]. A mixture of 1 mmol of 4-[(4-n-alkoxyben-
zyloxy)benzaldehyde and 1 mmol of 4-amino-1,2,4-triazole, and three
drops of acetic acid in absolute ethanol were heated at reflux for 4 h.
The reaction mixture was allowed to cool and was stirred at room
temperature overnight. The solid was collected and recrystallized
from technical ethanol.

6
B. T. Thaker and P. Patel
Synthesis of 4-n-Alkoxybenzoic Acid
Synthesis of 4-Formylphenyl 4-Alkoxybenzoate
Synthesis of Compound 3A and 3B
Synthesis of 4-[(4H-1,2,4-Triazol-4-ylimino) methyl]Phenyl 4-
Alkoxybenzoate(3A)
Synthesis of 4-(2-Isonicotinoylcarbonohydrazonoyl) Phenyl 4-
Alkoxybenzoate(3B)

Liquid Crystalline Materials
7
Data
Compound A14:
Yield 77%. M.P.205ꢁC. Calc.for C30H40O3N4; C, 71.42; H, 7.93; N,
11.11%; found: C, 71.32; H, 7.83; N, 11.15. EI-MꢀS1 m=z (rel.int %):
504(2) (M)þ . IR (KBr): Vmax=cmꢀ1 2918, 2852 cm ꢀ(1CꢀH aliphatic),
ꢀ1
ꢀ1
=
=
=
1731 cm (C O of ester), 1650 cm (CH N), 1585 cm (C C aromatic),
1281 cmꢀ1(CꢀO), 1589, 1601 cmꢀ1(C N, triazole). 1H NMR (CDCl3):
=
d 0.88–0.89 ppm (s, CH3), 1.26–1.49 ppm (m, CH2), 4.03–4.06 ppm
=
(t, OCH2), 6.96–8.16 ppm (m, Ar-H), 8.79–8.90 ppm (s, CH N),
8.23 ppm (s, triazole-H). 13C NMR (CDCl3), 14.52 ppm (CH3), 22.95–
=
34.00 ppm (CH2), 108.00–162.20 ppm (Ar-C), 160.15 ppm (C N),
=
172.29 ppm (C O ester), 141.00–162.00 ppm (triazole-C).
B. Synthesis of 4-(2-Isonicotinoylcarbonohydrazonoyl) Phenyl 4-
alkoxybenzoate [14,15]. A mixture of 1 mmol of 4-[(4-n-alkoxybenzy-
loxy)benzaldehyde and 1 mmol of isonicotinic acid hydrazyde, and
three drops of acetic acid in absolute ethanol were refluxed for 4 h.
The reaction mixture was allowed to cool and was stirred at room tem-
perature overnight. The solid was collected and recrystallized from
technical ethanol.
Data
Compound B14:
Yield 76%. M.P.157ꢁC. Calc.for C34H43O4N3; C, 73.24; H, 7.71; N,
7.54%; found: C, 73.20; H, 7.69; N, 7.68. EI-MS m=z (rel.int %):
557(1) (ꢀM1)þ . IR (KBr): Vmax=cꢀm1ꢀ1 2918,2850 cmꢀꢀ11(C-H aliphatic),
=
=
=
1730 cm (C O of ester), 1652 cm (CH N), 1605 cm (C C aromatic),
1272 cmꢀ1 (CꢀO), 1665 cmꢀ1 (C O of hydrazone linkage), 3176–
=
3270 cmꢀ1 (NH) 1566,1570 cmꢀ1 (C N, pyridyl ring). H NMR (CDCl3):
1
=
d 0.86–0.89 ppm (s, CH3), 1.32–1.84 ppm (m, CH2), 4.04–4.07 ppm
=
(t, OCH2), 6.96–8.07 ppm (m, Ar-H), 8.49–8.77 ppm (s, CH N),
11.74 ppm (s, NH), 8.76–8.77 ppm (s, pyridyl-H). 13C NMR (CDCl3),
14.32 ppm (CH3), 23.00–34.70 ppm (CH2), 111.00–163.00 ppm (Ar-C),
=
=
159.00 ppm (C N), 172 ppm (C O ester), 154.00–167.00 ppm
=
(ꢀC OꢀNHꢀ), 150.00 ppm (pyridyl-C).
RESULTS AND DISCUSSION
The elemental analyses of series A and B compounds synthesized
above are shown in Tables 1 and 2. The observed values are in well
agreement with theoretical values indicating structure of respec-
tive compounds. The representative compounds are subjected for
1
1H-NMR study. The H-NMR data are given in Tables 3 and 4.

8

9

10
B. T. Thaker and P. Patel
TABLE 3 1H-NMR Spectral Data for the Series A
ꢀCH3
proton of
n-alkyl
chain
ꢀCH2
proton of
n-alkyl
chain
ꢀCH2O
proton
Sr.
Phenyl
=
No. Compound
of alkoxy
multiplate
CH N
Remarks
1
2
3
4
A4
A8
0.90 (t) 1.23–1.49 (m) 4.02–4.06 (t) 6.98–8.16 (m) 9.02 (s)
0.91 (t) 1.23–1.48 (m) 4.02–4.06 (t) 7.00–8.17 (m) 9.02 (s)
0.91 (t) 1.23–1.49 (m) 4.02–4.06 (t) 7.00–8.17 (m) 9.02 (s)
0.88 (t) 1.26–1.49 (m) 4.03–4.06 (t) 6.96–8.16 (m) 8.90 (s)
8.26
(Triazole-H)
8.25
(Triazole-H)
8.26
A12
A14
(Triazole-H)
8.23
(Triazole-H)
In continuation with our earlier work on heterocyclic liquid crystals
with unconventional molecular structures, two homologous series that
have 1,2,4-triazole and pyridyl heterocyclic ring as terminal group, such
as 4-[(4H-1,2,4-triazol-4-ylimino)methyl] phenyl 4-alkoxybenzoate
and 4-(2-isonicotinoylcarbonohydrazonoyl) phenyl 4-alkoxybenzoate,
have been synthesized. Conventional thermotropic liquid crystals
consist of anisotropic molecules (mesogens) that are either rod-
shaped (calamitic) or disc-shaped (discotic). The thermal behavior
of these two types of liquid crystals is generally well understood
and therefore they have been recognized as materials for many prac-
tical applications, especially in liquid crystal display devices. The
common structural features of the compounds are that they consist
TABLE 4 1H-NMR Spectral Data for the Series B
ꢀCH3
ꢀCH2
proton of proton of ꢀCH2O
Sr.
n-alkyl
n-alkyl
proton of
alkoxy
Phenyl
multiplate CH N ꢀNHꢀ Remarks
=
No. Compound
chain
chain
1
2
3
4
5
B4
B5
0.86 (t) 1.32–1.84 4.03–4.07 7.00–8.13 8.49 (s) 11.70
(m) (t) (m)
0.86 (t) 1.33–1.83 4.03–4.07 7.00–8.13 8.49 (s) 11.73
(m) (t) (m)
0.87 (t) 1.33–1.84 4.03–4.07 6.99–8.13 8.49 (s) 11.76
(m) (t) (m)
0.87 (t) 1.31–1.83 4.03–4.07 6.96–8.10 8.49 (s) 11.70
(m) (t) (m)
0.86 (t) 1.32–1.84 4.04–4.07 6.96–8.07 8.49 (s) 11.74
(m) (t) (m)
8.76–8.77
(pyridyl-H)
8.76–8.77
(pyridyl-H)
8.70–8.75
(pyridyl-H)
8.76–8.77
(pyridyl-H)
8.76–8.77
(pyridyl-H)
B10
B12
B14

Liquid Crystalline Materials
11
of two phenyl rings with different terminal groups at one end. The
mesomorphic properties of all the synthesized compounds have been
characterized by differential scanning calorimetry (DSC) and polariz-
ing optical microscope (PMO) attached with Mettler hot stage. Table 5
shows the phase transition temperatures and associated enthalpy (DH)
for compound of series A (A14, A16) and series B (B10, B14). Enthalpy
values of the various transitions agree well with the existing related
literature values [16].
All the compounds of series A and B (except B1, B2, and B3) exhibit
enantiotropic mesomorphism, on ordinary slides. The melting peaks
are sharp. In series A, the lower members show nematic phase
whereas the higher member of the series shows SmC phase along with
nematic phase. Only A16 shows SmC mesophase at very low tempera-
ture. On cooling the isotropic liquid, small droplets appear which
coalesce to a classical schlieren texture characteristic of the nematic
phase. It is consistent with the assignment of each mesophase type
using the classification systems reported by Gray and Goodby [17].
The textures of the SmC phase for compounds of series A is shown
in Figure 1. Transition temperatures are recorded in Table 6 and plot
of transition temperatures against the number of carbon atom in the
alkoxy chain (Fig. 2) shows steady fall in N-I and Sm-N transitions.
In series B, n-methyloxy to n-propyloxy does not show mesomorphism.
First, three compounds in series B have sharp melting point due to
short alkoxy chain. B4 to B16 exhibit an enantiotropic nematic meso-
phase. A smectic mesophase appears from the n-dodecyloxy derivative,
TABLE 5 DSC Data for Series A and B Compounds
Peak temp.
(Microscopic temp.) C
ꢁ
Series
A
Compound
A14
Transition
DH Jgꢀ1
Cr-SmC
SmC-N
N-I
62.82 (63)
142 (143)
205 (205)
52.34
59.00
54.50
A16
B10
B14
Cr-SmC
SmC-N
N-I
30 (32)
128 (129)
191 (192)
48.27
50.83
51.37
B
Cr-SmC
SmC -N
N-I
129 (131)
159 (159)
167 (166)
49.65
39.00
33.54
Cr-SmC
SmC-N
N-I
100.81 (101)
143.84 (144)
157.06 (157)
46.30
37.82
32.52

12
B. T. Thaker and P. Patel
FIGURE 1 (a) Fan texture of the SmC phase of A16 at 30ꢁC; (b) optical photo-
micrograph of compound B14 exhibiting Nematic Phase; (c) SmC Phase of C10
at 131ꢁC.
as enantiotropic behavior and remains up to the n-hexadecyloxy
derivative. The texture of the nematic phase for compounds of series
B is shown in Figure 1. The transition temperatures are recorded in
Table 7. The plot of transition temperature against the number of
carbon atom in the alkoxy chain (Fig. 3) shows a smooth falling tendency
for nematic-isotropic transition temperatures throughout the series.
Series B also exhibit falling tendency of Sm-N transition temperatures
for the higher homologous. From the plot of transition temperatures
against the number of carbon atoms (Figs. 2 and 3), it can be noticed

Liquid Crystalline Materials
13
I
TABLE 6 Transition Temperature of Series A
Compound
R ¼ n-alkoxy
Cr
SmC
N
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
.
.
.
.
.
.
.
.
.
.
.
.
–
–
–
–
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
226
213
209
204
196
189
177
162
164
166
142
128
.
.
.
.
.
.
.
.
.
.
.
.
243
239
238
232
229
226
219
215
208
207
205
191
.
.
.
.
.
.
.
.
.
.
.
.
10
11
12
76
63
30
Note: SmC - Smectic C; N - nematic; I - isotropic.
that Cr-M transition temperature decreases with increase in the
length of terminal alkoxy chain. However, the odd-even effect of this
series is not so pronounced. This is in agreement with the data
reported earlier for such homologous series [18].
FIGURE 2 Mesomorphic behavior as a function of the number of carbon
atoms (n) in the terminal alkoxy chain for series A.

14
B. T. Thaker and P. Patel
TABLE 7 Transition Temperature of Series B
Compound
R ¼ n-alkoxy
Cr
SmC
N
I
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
.
.
.
.
.
.
.
.
.
.
.
.
–
–
–
–
–
–
–
–
129
113
101
87
.
.
.
.
.
.
.
.
.
.
.
.
–
–
–
82
.
.
.
.
.
.
.
.
.
.
.
.
201
195
192
190
184
177
176
169
167
161
157
152
.
.
.
.
.
.
.
.
.
.
.
.
98
121
129
142
159
132
144
139
10
11
12
Note: SmC - Smectic; N - nematic; I - isotropic.
DSC is a valuable method for the detection of phase transition.
It yields quantitative results; therefore, we may draw conclusions
concerning the nature of the phases that occur during the transition.
In the present study, enthalpies of two derivatives of series A and
FIGURE 3 Mesomorphic behavior as a function of the number of carbon
atoms (n) in the terminal alkoxy chain for series B.

Liquid Crystalline Materials
15
series B were measured by DSC. Enthalpy values of the various
transitions agree well with the existing related literature values [19]
which helps to further confirm the mesophase type. There have been
a variety of compounds reported with liquid crystalline properties,
but heterocyclic moieties [20, 21] are less explored, compared to homo-
cyclic moieties. 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 [22]. In our present study we introduced
two new heterocyclic moieties, one is 1,2,4-triazole and the second is
isonocotinic acid hydrazide. Isotropic temperature of compound in ser-
ies A is higher than the compound of series B which is due to hydrozone
linkage. Hydrazone linkage is less stable than azomethine linkage.
Conjugation in compound of series A has also affected the transition
temperature. In the past, many compounds contain ester-Schiff’s base
central linkage shows mesomorphism [11,23]. Table 8 shows the com-
parison of Sm–N and N-I transition temperature of compound n ¼ 14,
series A, and structurally related compounds n ¼ 14, series B. The
SmC–N mesophase range of compound n ¼ 14 (series A) is higher by
36ꢁC, when compared with compound n ¼ 14 (series B). The N-I tran-
sition temperature of compound of, series B, is lower by 50ꢁC, when
compared with compound 14 (n ¼ 14, series B). The two series differ
by terminal heterocyclic ring (series A contains 1,2,4-triazole and ser-
ies B contains pyridyl ring) as well as linking group. Ester linkage is
common in both the series but another linkage is different (series A
contains Schiff base linkage and series B contains hydrazone linkage).
Thermal Study
Thermal properties of both series were investigated by POM and
DSC. The polarized microphotographs and the typical DSC thermo-
gram for the compounds under study are shown in chart Figures 1,
4, and 5, respectively. In order to aid an analysis of their mesomorphic
TABLE 8 Different Transition Temperatures and Range Mesophases
Observed in Series A and B
Sm-N mesophase
range (ꢁC)
N-I mesophase
range (ꢁC)
Series
Compound
SmC
N
I
A
B
N ¼ 14
N ¼ 14
63
101
142
144
205
157
79
43
63
13
Note: SmC - Smectic C; N - nematic; I - isotropic.

16
B. T. Thaker and P. Patel
behavior, the target compounds were grouped into two sets, series A
and B; for compounds where the [1,2,4]-triazole heterocycle was placed
at the end of the rigid core (series A). The DSC thermograms for this
compound (A14) are shown in Figure 4. On heating, the compound
melts to the SmC phase at 62.82ꢁC and goes to the nematic phase at
142ꢁC just below the clearing point at 205ꢁC, at a rate of 10ꢁC=min.
The enthalpy value of A14 is mentioned in Table 5. A typical thermo-
gram obtained for compound B14 by DSC analysis is presented in
Figure 5. On heating, the compound melts at 100.81ꢁC to the SmC
phase and goes to nematic phase at 143.84ꢁC and at the last an
isotropic liquid at 157.06ꢁC. The same pattern is observed on cooling
in both cases. Compounds of both series are enantiotropic in nature.
DSC studies further reported the appearance of an enantiotropic
nematic phase in all the compounds studied.
The present series A and B are compared with other structurally
related compounds to evaluate the effect of terminally situated cyclo-
hexyl ring and nephthalene ring.
The present homologues series A and B are compared with structur-
ally related series.

Liquid Crystalline Materials
17
FIGURE 4 DSC thermogram for the compounds A14
.
FIGURE 5 DSC thermogram for the compounds B14
.

18
B. T. Thaker and P. Patel
TABLE 9 Melting Points of Series C
n-alkoxy
M.P.
Butyl
Hexyl
Heptyl
Octyl
Decyl
140
140
142
136
133
127
115
Tetradecyl
Hexadecyl
Comparison of series A and series B with series C, respectively,
give insight on the role played by the terminal ring. The structural
difference between the series is one of the terminal rings. The com-
pounds of series A and series B are mesogenic (Tables 6 and 3)
whereas series C is nonmesogenic (Table 9) in nature [24]. This is
because of cyclohexane moieties nonconducive for mesomoephism
and saturated nonheterocyclic ring. Series A and series B are com-
pared with related series D. All the members of series D exhibit an
enantiotropic nematic phase. The SmC mesophase commences from
the n-heptyloxy and n-octyloxy derivative as a monotropic phase.
n-Decyloxy to n-hexadecyloxy members exhibit an enantiotropic
SmC phase [25], whereas in series A n-dodecyloxy to n-hexadecyloxy
exhibit SmC phase along with enantiotropic nematic phase. Thermal
stabilities of the compounds of series D is greater than compounds of
TABLE 10 Transition Temperature of Series D
Compounds
R ¼ n-alkoxy
Cr
SmC
N
I
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
.
.
.
.
.
.
.
.
.
.
.
.
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
142
137
129
133
128
116
120
115
141
157
162
155
.
.
.
.
.
.
.
.
.
.
.
.
270
167
254
249
239
235
225
220
209
198
194
187
.
.
.
.
.
.
.
.
.
.
.
.
–
(85)
(94)
109
106
101
95
10
11
12
Note: Values in parantheses indicate monotropy.

Liquid Crystalline Materials
19
series A and B; this is because the naphtha ring is more conducive for
mesomorphism and highly resonating in nature (Table 10).
CONCLUSION
We have described the synthesis of new heterocyclic ring based liquid
crystalline compounds which exhibit enantiotropic mesomorphism.
We have noticed that the molecules generated as highly ordered
molecular aggregations by introduction of the terminal heterocyclic
ring. The comparision of both our series with nonheterocyclic ring,
the heterocyclic ring propose mesomorphism that of nonheterocyclic
ring which does not have any conjugation. Thermal stabilities of series
A is also high compared with series B due to triazole ring.
ACKNOWLEDGMENT
We are thankful to I.I.T. Bombay, CDRI Lucknow, and Garda Chemi-
cals Ltd., Ankleshwar (Gujarat) for providing an elemental analysis,
1
FT-IR, H-NMR, 13C NMR mass and thermal studies.
REFERENCES
[1] Sung, H. H. & Lin, H. C. (2004). Liq. Cryst., 31, 831.
[2] Vasconcelos, U. V., Dalmolin, E., & Merlo, A. A. (2005). Org. Lett., 7, 1027.
[3] Cristiano, R., Santos, D. M. P. O., & Gallardo, H. (2005). Liq. Cryst., 32, 7.
[4] Aldred, M. P., Eastwood, A. J., Kelly, S. M., & Vlachos, P. (2004). Chem. Mater., 16,
4928.
[5] Young, W. R., Haller, I., & Williams, L. (1970). Liq. Cryst. Ord. Fluids, 383.
[6] Arora, S. L. & Fergason, J. L. (1971). Symp. Faraday Soc. No. 5, 97–106.
[7] Oh, C. S. (1972). Mol. Cryst. Liq. Cryst., 19, 95.
[8] Nash, J. A. & Gray, G. W. (1974). Mol. Cryst. Liq. Cryst., 25, 299.
[9] Boller, A., Cereghetti, M., Schadt, M., & Scherrer, H. (1977). Mol. Cryst. Liq. Cryst.,
42, 215.
[10] Karamysheva, L. A., Kovshev, E. I., Pavluchenko, A. L., Roitman, K. V., Titov, V. V.,
Torgova, S. I., & Grebenkin, M. F. (1981). Mol. Cryst. Liq. Cryst., 67, 241.
[11] Thaker, B. T., Patel, Pranay., Vansadia, A. D., & Patel, H. G., (2007). Mol. Cryst.
Liq. Cryst., 466, 13.
[12] Zaschkhe, H. (1980). Advances in Liquid Crystal Research and Applications, edited
by L. Bata: Pergamon Press, London, 1059.
[13] Saleh, A. A., Pleune, B., Fettinger, J. C., & Poli, R. (1997). Polyhedron, 16, 1391.
[14] Pinol, R., Ros, M. B., Serrano, J. L. & Sierra, T. (2004). Liquid Crystals, 31(9), 1293.
[15] Dec, M., Pina, C., & Serrano, J. L. (2003). Liquid Crystals, 30(6), 651.
[16] Marzotko, D. & Demus, D. (1975). Pramana, 1, 189.
[17] Gray, G. W. & Goodby, J. W. (1984). Smectic Liquid Crystals: Texture and
Structures, Heyden: Philadelphia.
[18] Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals,
Academic Press, Inc.: New York.

20
B. T. Thaker and P. Patel
[19] Marzotko, D. & Demas, D. (1975). Pramana, 1, 189.
[20] Nash, J. A. & Gray, G. W. (1974). Mol. Cryst. Liq. Cryst., 25, 299.
[21] Brown, J. W., Hurst, D. T., & Donovan, J. P. (1994). Liq. Cryst., 17, 689.
[22] Karamysheva, L. A., Kovshe, E. I., Pavluchenko, A. I., Roltman, K. V., Titov, V. V.,
Torgova, S. I., & Grebenkin, M. F. (1981). Mol. Cryst. Liq. Cryst., 67, 241.
[23] Yeop, Guan-Yeow., Ha, Sie-Tiong., Lim, Phaik-Leng., & Boeg, Peng-Lim. (2006).
Mol. Cryst. Liq. Cryst., 452, 63.
[24] Vora, R. A., Mahajan, R., & Nandedkar, H. (1997). Liq. Cryst., 304, 495.
[25] Vora, R. A. & Prajapati, A. K. (1998). Liq. Cryst., 25, 567.