Role of terminal heterocyclic ring on mesomorphic properties of homologous series

Article abstract of DOI:10.1080/15421400903290501

Two new homologous series of compounds with a heterocyclic ring having sulfur and oxygen as a hetero atom derived from p-hydroxy acetophenone and alkoxy aniline containing cinnamate-azomethine as central linkages have been synthesized. viz. 4(furalacryloxy) α-methyl benzylidine-4′-alkoxy aniline and 4(thianylacryloxy) α-methyl benzylidine-4′-alkoxy aniline. The compound of both the series have been characterized by elemental analysis, FT-IR, ¹H-NMR, and mass spectrometry method. Their liquid crystalline properties have been investigated by optical polarizing microscopy and differential scanning calorimetry (DSC) studies. All the derivatives are mesomorphic in nature showing the nemetic phase. The mesomorphic properties of the present two series are compared with other structurally related series to evaluate the effect of thiophene and furan on mesomorphism. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421400903290501

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Role of Terminal Heterocyclic Ring on
Mesomorphic Properties of Homologous
Series*
B. T. Thaker a , B. S. Patel a , D. B. Solanki a , Y. T. Dhimmer a & J. S.
Dave b
a Department of Chemistry, Veer Narmad South Gujarat University,
Surat, Gujarat, India
b Department of Applied Chemistry, Faculty of Technology and
Engineering, M. S. University of Baroda, Vadodara, Gujarat, India
Published online: 01 Mar 2010.
To cite this article: B. T. Thaker , B. S. Patel , D. B. Solanki , Y. T. Dhimmer & J. S. Dave (2010) Role
of Terminal Heterocyclic Ring on Mesomorphic Properties of Homologous Series*, Molecular Crystals
and Liquid Crystals, 517:1, 63-80, DOI: 10.1080/15421400903290501
To link to this article: http://dx.doi.org/10.1080/15421400903290501
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Mol. Cryst. Liq. Cryst., Vol. 517: pp. 63–80, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903290501
Role of Terminal Heterocyclic Ring on
Mesomorphic Properties of Homologous Seriesꢀ
B. T. THAKER,1 B. S. PATEL,1 D. B. SOLANKI,1
Y. T. DHIMMER,1 AND J. S. DAVE2
1Department of Chemistry, Veer Narmad South Gujarat University,
Surat, Gujarat, India
2Department of Applied Chemistry, Faculty of Technology and
Engineering, M. S. University of Baroda, Vadodara, Gujarat, India
Two new homologous series of compounds with a heterocyclic ring having sulfur and
oxygen as a hetero atom derived from p-hydroxy acetophenone and alkoxy aniline
containing cinnamate-azomethine as central linkages have been synthesized. viz.
4(furalacryloxy) a-methyl benzylidine-40-alkoxy aniline and 4(thianylacryloxy)
a-methyl benzylidine-40-alkoxy aniline. The compound of both the series have been
characterized by elemental analysis, FT-IR, 1H-NMR, and mass spectrometry
method. Their liquid crystalline properties have been investigated by optical polariz-
ing microscopy and differential scanning calorimetry (DSC) studies. All the deriva-
tives are mesomorphic in nature showing the nemetic phase. The mesomorphic
properties of the present two series are compared with other structurally related
series to evaluate the effect of thiophene and furan on mesomorphism.
Keywords Azomethine; central linkage; cinnamate; heterocyclic ring; homolo-
gous series; nematic mesophase
1. Introduction
The liquid crystalline properties of organic compounds are highly sensitive to
changes in chemical structure, and considerable effort has been devoted to the
systematic study of closely related compounds in order to establish empirical
relationships between structural and other parameters and the thermal stabilities
of the various types of mesophase which may be observed [1]. The design and syn-
thesis of liquid crystals containing heterocyclic units have been the subject of much
research in recent years [2–7]. Due to greater choices in the design of new mesogenic
molecules containing heterocyclic rings, the polarity and geometry of the molecules
may be varied by the introduction of heteroatoms [8,9]. There have been many
ꢀThis paper has been presented in ICFMAT, during 29–30th January, 2009 at Depart-
ment of Physics, Velammal Engineering College, Ambattur – Redhills Road, Chennai – 600
066, Tamil Nadu, India.
Address correspondence to B. T. Thaker, Department of Chemistry, Veer Narmad South
Gujarat University, Udhana-Magdalla Road, Surat 395007, India. E-mail: btthaker1@
yahoo.co.in
63

64
B. T. Thaker et al.
attempts made to introduce an oxygen and sulfur atom into the molecular rigid core
for liquid crystalline derivatives which are suitable for use as components of nemetic
liquid crystalline materials [10,11]. The 2,5-disubstituted thiophene ring is a poten-
tially useful element of the molecular structure of new nematic liquid crystals due
to a number of factors [12,13]. Liquid crystals derived from thiophene, a five member
heterocycle comprising sulfur, are interesting because they deviate from the classical
calamitic structure inducing looser packing and thus lowering the melting point.
The electronegative sulfur atom imparts a transverse dipole, and the ring itself is a
rich source of polarizable electrons, which may be useful for electro-optic applica-
tions [14–16]. Sulfur-containing heterocycles are important synthetic intermediates
and have a variety of applications in medicinal, agricultural, and materials chemistry
[17,18]. The heterocyclic mesogens reported so far mainly have nitrogen as a hetero-
atom [19,20] and mesomorphic compounds with oxygen as a heteroatom [21–23]
are rare.
The systematic study of the mesogenic properties of a thio and oxo heterocyclic
system would be interesting. Nguyen and Pham [24] have synthesized simple Schiff
bases with 2-substituted furan derivatives. Cinnamate esters have been well known
for over 30 years [25–27]. The ethylene linking group is a very useful structural unit
connecting one part of a rigid core with another in calamitic mesogen molecules. The
molecular structure of calamitic liquid crystals varies, and consequently, their meso-
morphic properties differ significantly [28]. The polarity and the size of heteroatom
affects the mesomorphic properties of a homologous series, and hence it was thought
useful to evaluate oxo and sulfur heteroatom liquid crystals. The present investi-
gation was undertaken with a view to study the effect of a-methyl group (azo-
methyne linkage) and heterocyclic moiety on the mesomorphic properties of such
molecules.
2. Experimental
2.1. Reagents and Technique
The solvents were used after purification, using the standard methods described in
the literature [29]. 4-Hydroxy acetanilide, p-hydroxy acetophenone were obtain from
Merck (Germany). Furan 2-aldehyde, thiophene 2-aldehyde, alkyl bromide, and
malonic acid were purchased from Fluka Chemie (Switzerland). Other auxiliary che-
micals were laboratory grade. Elemental analyses (C, H, N) performed at CDRI,
Lucknow. Infrared spectra were recorded with a Perkin-Elmer 2000 FT-IR spectro-
photometer in the frequency range 4000–400 cmꢁ1 with samples embedded in KBr
discs. 1H-NMR spectra of the compounds were recorded with a Jeol-GSX-400
instrument using CDCl3 as a solvent and TMS as an internal reference at SAIF,
Panjab University, Chandigarh. Mass spectra of the compounds were recorded at
SAIF, IIT Madras, Chennai. Thin-layer chromatography (TLC) analyses were per-
formed using aluminium-backed silica-gel plates (Merck60 F524) and examined
under shortwave UV light. The phase-transition temperatures were measured using
ShimadzuDSC-50 at heating and cooling rates of 10ꢂC minꢁ1, respectively. The
optical microscopy studies were carried out with a Carl Zeiss polarizing microscope
equipped with a MettlerFP52 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.

Role of Terminal Heterocyclic Ring
65
2.2. Synthesis
Series: I-Me
2.2.1. Synthesis of 4-n alkoxy anilines [30–32]
(I) [a] 4-n Alkoxy Acetanilides:
Paracetamol (0.1 mole), anhydrous potassium carbonate (0.15 mole),
respectively n-alkayl bromide (0.15 mole) and dry acetone (60 ml) were taken
in RBF provided with condenser and guard tube. The reaction mixture was
refluxed on water bath for (8–10 hrs). The whole mass was then added to
water and extracted with ether. The ether was evaporated, and the residual
solids were obtained as alkoxy acetanilides.
[b] 4-n Alkoxy Anilines:
A mixture of 4-n alkoxy acetanilide (0.146 mole), water (70 ml), and concen-
trated hydrochloric acid (45 ml) were stirred for 10 to 12 hrs at 90–95ꢂC and
then cooled to room temperature. The mixture was made alkaline with 50%
NaOH at 20ꢂC. The oily product (for the lower members C1 to C8) was
extracted with ether. The ether extract was dried and concentrated at reduced
pressure to give an oil which was purified by distillation. The higher members
(C10 to C18) separated as solid and were filtered directly without ether extrac-
tion. The boiling points and melting points of all the alkoxy anilines agree
well with the values reported in the literature [30–32].
(II) Synthesis of Furylacrylic Acid [33]
Redistilled furfural (0.1 mol, 8.3 ml) and malonic acid (0.15 mol, 15.6 gm)
were condensed in presence of dry pyridine (20–25 ml) by using few drops
of piperidine as a condensing agent. The reaction mixture was heated on
a steam-bath for 6 to 8 hrs. It was acidified with cold 1:1 hydrochloric acid,
the precipitated acid was filtered and washed with little cold hydrochloric
acid, followed by cold water. The acid was crystallized to fine white needles
using with dilute ethanol as solvent. Melting point 140ꢂC. The yield was
about 70%.
(III) Synthesis of Furylacryloyl Chloride [34]
Furylacrylic acid (0.01 mole, 1.4 gm) and freshly distilled thionyl chloride
(0.03 mole, 2.19 ml) were taken in around bottom flask attached with a reflux
condenser fitted with a calcium chloride guard tube. The mixture was refluxed
on water bath till evolution of hydrogen chloride gas ceased. Excess of thionyl
chloride was distilled off under reduced pressure using vacuum pump and the
furylacryloyl chloride left behind, directly treated for next reaction without
further purification.
(IV) Synthesis of 4(Furylacryloyloxy) Acetophenone
4-Hydroxy aetophenone (0.01 mole, 1.36 gm) was dissolved in dry pyridine
(10.0 ml) and was added drop wise with occasionally stirring into ice-cold fury-
lacryloyl chloride (0.01 mole, 1.71 gm) in a round bottom flask. Then mixture
was refluxed on hot water bath for two hours and was allowed to stand for over-
night. The mixture was acidified with cold 1:1 diluted hydrochloric acid to pre-
cipitate the product. The obtained solid was filtered, washed successively with
saturated NaHCO3 solution, dilute NaOH solution, and two to three times with
water. Thus crude solid was obtained which was crystallized from water until the
constant melting temperatures was obtained.

66
B. T. Thaker et al.
(V) Synthesis of 4(Furylacryloyloxy) a-Methyl Benzylidene-40-n-Alkoxyanilines
A mixture of 4(furylacryloyloxy) acetophenone (0.01 mole) and respective
alkoxy aniline (0.01 mole) and three drops of acetic acid in absolute ethanol
(10 ml) was refluxed for 4 hr. The reaction mixture was allowed to cool and
was stirred at room temperature overnight. The solid was collected, yield 75%.
All the compounds have been purified by column chromatography on silica
gel (80–120 mesh) using mixture of ethyl acetate=petroleum ether [7=3] followed
by repeated recrystallization from ethanol. Melting points and other thermal
properties of all the compounds (C1 to C8, C10 to C18) are recorded in Table 1.
Analytical Data for a Few Respective Compounds
Series: I-Me [A-10]Molecular formula: C32H39NO4 (501). Elemental analysis
calculated for C 76.70%, H 7.83%, N 2.85%; found C 76.54%, H 7.67%, and N
2.71%; FT-IR (KBr pellet): 3092 cmꢁ1 (-C-H Aromatic), 2970, 2881 cmꢁ1
(-CH3CH2 asymmetric nas and symmetric ns ꢁs1tretching, respectively), 1735 cmꢁ1
=
=
(C N stretching of Schiff base
(C O group of cinnamate linkage), 1640 cm
linkage), 1498 cmꢁ1 (C C stretching aromatic ring) 1H-NMR (CDCl3):
0.86–0.89 ppm (t, 3 H, CH3 of aliphatic chain), 1.25–1.76 ppm (m, (-CH2)n- of
alkoxy chain), 2.17 ppm (S, 3H, CH3 of acetophenone), 4.03–4.08 ppm (t, 2 H, -
=
=
OCH2 of alkoxy chain), 6.40 and 7.72 ppm (d, 2 H, -CH CH- of cinnamate),
6.62–6.78 ppm (m, Ar-H). FAB mass spectra: Molecular ion peak 501 (m=z, Mþ).
Series: II-Me
(I) Synthesis of 4-n-Alkoxy Anilines
4-n-Alkoxy anilines have been prepared as described in Series: I-Me (I).
(II) Synthesis of Thionylacrylic Acid
Thionylacrylic acid was prepared as per the procedure given in Series: I-Me
(II). Melting point 146ꢂC. The yield was 70%.
(III) Synthesis of Thionylacryloyl Chloride
Synthesis of thionylacryloyl chloride was carried out as per the procedure
given in Series: I-Me (III).
(IV) Synthesis of 4(Thionylacryloyloxy) Acetophenone
4-Hydroxy acetophenone (0.01 mole, 1.36 gm) was dissolved in dry pyridine
(10.0 ml) and was added drop wise with occasionally stirring into ice-cold thio-
nylacryloyl chloride (0.01 mole, 1.88 gm) in a round bottom flask. Then mix-
ture was refluxed on hot water bath for two hours and was allowed to stand
for overnight. The mixture was acidified with cold 1:1 diluted hydrochloric
acid to precipitate the product. The solid obtained was filtered, washed succes-
sively with saturated NaHCO3 solution, dilute NaOH solution, and two to
three times with water thus crude solid was obtained which was crystallized
from water until the constant melting temperatures was obtained.
(V) Synthesis of 4(Thionylacryloyloxy) a-Methyl Benzylidene-40-n-Alkoxyanilines
A mixture of 4-(thionylacryloyloxy) acetophenone (1 mole) and respective
alkoxy aniline (1 mole) and three drops of acetic acid in absolute ethanol
(10 ml) was refluxed for 4 hrs. The reaction mixture was allowed to cool
and was stirred at room temperature overnight. The solid was collected, yield
76%. All the compounds have been purified by column chromatography

67

68

Role of Terminal Heterocyclic Ring
69
on silica gel (80–120 mesh) using mixture of ethyl acetate=petroleum ether [7=3]
followed by repeated recrystallization from ethanol. Melting point and other
thermal properties of all the compounds (C1 to C8, C10 to C18) are given in
Table 2.
Analytical Data for a Few Respective Compounds
Series: II-Me [B-14]Molecular Formula: C36H47NO3S (573). Elemental analysis
for calculated for C 75.43%, H 8.24%, N 2.47%; found C 75.39%, H 8.20%, and
N 2.44%; FT-IR (KBr pellet): 3091 cmꢁ1 (-C-H Aromatic), 2973, 2880 cmꢁ1 (-CH3
CH2, asymmetric nas and symmetric ns stretching, respectively), 1731 cmꢁ1 (C O
=
group of cinnamate linkage), 1635 cmꢁ1 (C N stretching of Schiff base linkage),
=
1
1502 cmꢁ1 (C C stretching aromatic ring) H-NMR (CDCl3): 0.87–0.88 ppm (t, 3
=
H, CH3 of aliphatic chain), 1.25–1.78 ppm (m, (-CH2)n- of alkoxy chain),
2.17 ppm (s, 3H, -CH3 of acetophenone), 4.03–4.07 ppm (t, 2 H, -OCH2 of alkoxy
=
chain), 6.40 and 7.96 ppm (d, 2 H, -CH CH- of cinamate), FAB mass spectra:
Molecular ion peak ¼ 573(m=z ¼ Mþ).
3. Results and Discussion
Mesomorphic properties and thermal stability for the two new homologous Series:
I-Me and Series: II-Me were determined by hot stage polarizing microscopy and
Table 3. Transition temperature data of 4(furylacryloyloxy)
a-methyl benzylidene-40-n-alkoxyaniline (Series I-Me)
ꢂ
Transitiontemperature in C
Code no.
R ¼ n-alkyl
N
I
A1
A2
A3
A4
A5
A6
A7
A8
A10
A12
A14
A16
A18
Methyl
Ethyl
Propyl
Butyl
Pentyl
127
123
115
120
108
110
104
98
210
214
196
202
173
186
160
148
114
109
107
106
103
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
Octadecyl
79ꢀ
96
70
69
68
ꢀMonotropic phase

70
B. T. Thaker et al.
DSC and are given in Tables 3 and 4. The transition temperature data for the
analogues compound of both the series are included for comparison in Tables 5 to
8. Data for the analogous compounds of both series are included for comparison.
All the compounds show mesomorphic behavior.
In Series: I-Me, methoxy to octadecyloxy derivatives exhibit only nematic meso-
phase. No smectic mesophase is observed even in higher homologues. It is consistent
with the assignment of each mesophase type, using the classification systems reported
by Sackmann and Demus [35], Gray and Goodby [36]. The plot of transition tempera-
tures versus the number of carbon atoms in the alkoxy chain (Fig. 4) exhibits usual
odd–even effect and as the series is ascended the curve shows falling tendency.
In Series: II-Me, methoxy to octadecyloxy derivatives exhibit only nematic phase
as in Series: I-Me, no smectic mesophase is observed. The plot of transition tempera-
tures versus the number of carbon atoms in the alkoxy chain (Fig. 5) does not exhibit
old–even effect as that of in Series: I-Me.
Table 4. Transition temperature data of 4(thienylacryloyloxy)
a-methyl benzylidene-40-n-alkoxyaniline (Series II-Me)
ꢂ
Transition temperature in C
Code no.
R ¼ n-alkyl
N
I
B1
B2
B3
B4
B5
B6
B7
B8
B10
B12
B14
B16
B18
Methyl
Ethyl
Propyl
Butyl
Pentyl
137
141
133
135
130
129
127
126
131
103
80
181
184
180
178
174
170
162
156
148
129
112
110
108
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
Octadecyl
80
78

Role of Terminal Heterocyclic Ring
71
Table 5. Transition temperature data of 4(furylacryloyloxy)
benzylidene-40-n-alkoxyaniline (Series I-H) [38]
ꢂ
Transition temperature in C
Code no.
R ¼ n-alkyl
N
I
I1
I2
I3
I4
I5
I6
I7
I8
I10
I12
I14
I16
Methyl
Ethyl
Propyl
Butyl
Pentyl
138
128
117
122.5
110
117.5
94
103
98
98.5
98
220
226
205
207
191
196
180
177
171
162
153
145
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
95

72
B. T. Thaker et al.
Table 6. Transition temperature data of 3-(thiophine-2-yl)-acrylic
acid 4-(4-n-alkoxyphenylazo) phenyl ester (Series II) [39]
ꢂ
Transition temperature in C
Code no.
R ¼ n-alkyl
N
I
II1
II2
II3
II4
II5
II6
II7
II8
II9
II10
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Nonyl
Decyl
161.7
178.2
150.3
159.2
133.5
136
124.3
118.7
130.3
112.3
235.7
235.1
216.3
215.7
201.4
197.8
187.1
183.7
176.1
172.4
Table 7. Transition temperature data of 4(cinnamoyloyloxy)
benzylidene-40-n-alkoxyaniline (Series III-H) [38]
ꢂ
Transition temperature in C
Code no.
R ¼ n-alkyl
N
I
III1
III2
III3
III4
III5
III6
III7
III8
III10
III12
III14
III16
Methyl
Ethyl
Propyl
Butyl
Pentyl
131.5
155
130
128
118
114
108
107
106
109
109
103
226
234
219
216
207
201
198
192
179
178
166
160
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl

Role of Terminal Heterocyclic Ring
73
Table 8. Transition temperature data of 4-(4-n-alkoxyphenylazo)
phenyl cinnamates (Series IV) [39]
ꢂ
Transition temperature in C
Code no.
R ¼ n-alkyl
N
I
IV1
IV2
IV3
IV4
IV5
IV6
IV7
IV8
IV9
IV10
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Nonyl
Decyl
146.5
161.7
140.5
139.5
121.8
118.9
117.3
118.3
117.2
116.3
242.4
246.5
225.7
223.5
209.0
204.9
195.0
190.8
194.0
189.0
Table 9. Average nematic thermal stability
Series
I-Me
II-Me
I-H
II
III-H
IV
Nimatic thermal
stability
156.0
C1-C18
178
153.23
C1-C18
170
186.0
C1-C16
202.13
C1-C10
198.0
C1-C16
208
212
C1-C10
C1-C10
C1-C10
C1-C10
Table 10. Transition temperature and DSC data of the Series: I-Me and Series:
II-Me
Compound
code no.
Peak temp.
(microscopic temp.) C
DH (Jgꢁ1
)
DS (jg-1kꢁ1
)
ꢂ
Transition
A10
A14
B10
B14
Cr-N
N-I
Cr-N
N-I
Cr-N
N-I
Cr-N
N-I
78.52 (79)
114.70 (115)
70.57 (72)
107.49 (108)
131.34 (130)
149.11 (148)
80.24 (82)
32.97
109.61
27.16
0.419
0.955
0.388
0.733
0.769
0.804
0.307
2.031
78.81
101.06
120.42
24.68
112.48 (112)
55.37

74
B. T. Thaker et al.
Figure 1. Transition temperature curve of Series: I-Me.
Comparison of molecules of Series: I-Me and Series: II-Me shows that they
differ by terminal five membered heterocycle, which is oxo heterocycle in Series:
I-Me and thio heterocycle in Series: II-Me. The average nematic thermal satiability
of both the series is almost same. This indicates that a-methyl group which has
created steric hindrance and by that way increased the breadth of the molecules
over comes the negative effect created by the heterocyclic terminal linkage.
Molecules of Series: I-Me and Series: I-H differ only in an a-methyl group. On
the Schiff base linkage present in Series: I-Me, rest of the molecules are same. It is
known that a-methyl group increases the breadth of the molecules due to steric inter-
action and affects close packing of the molecules in nematic phase resulting into
decrees in nematic thermal satiability of the molecules. Due to this reason, the
average nematic thermal satiability of Series: I-Me is lower then those of Series:
I-H (Table 9).
The molecules of Series: II-Me and Series: II differ by Schiff base linkage having
a-methyl group and azolinkage in case of Series: II at that place. As discussed earlier
a-methyl group of Schiff base linkage increase breadth of the molecules due to steric
hindrance which reduces the nematic thermal satiability of Series: II-Me. This is the
case (Table 9) average nematic thermal satiability of Series: II-Me is quite lower
Figure 2. Transition temperature curve of Series: II-Me.

Role of Terminal Heterocyclic Ring
75
Figure 3. (a) DSC thermogram for compound A10 on heating (Series: I-Me). (b) DSC
thermogram for compound no A10 on cooling (Series: I-Me).
compared to Series: II. The DSC data of few representative compounds of Series-I-
MeA10 and A14 and Series-II-Me-B10 and B14 are given in Table 10 and their thermo-
gram are shown in Figures 3 to 5. The transition temperature data obtained from
OPM are almost agree with DSC thermogram peak data. Slightly vary in both tem-
perature because of rate of changes of temperature are different in both the processes.
Influence of altering the nature and position of left hand heterocyclic ring by phenyl
ring and a-methyl group on Schiff base linkage on mesomorphism: Molecules of
Series: I-Me have oxoheterocyclic ring where as molecules of Series: III-H have phe-
nyl ring at the end. Molecules of Series: I-Me have a-methyl Schiff base linkage as
one of the center linkage where as molecules of Series: III-H have azomethyne
linkage at that end.

76
B. T. Thaker et al.
Figure 4. DSC thermogram for compound A14 (Series: I-Me).
Comparison of C1-C10 member nematic thermal satiability of the Series: III-H is
higher than Series: I-Me. This indicates the presence of oxoheteroatom cannot com-
pensate the loss in molecular attractions created by a-methyl group in comparision
to Series: III-H having classical calamitic molecular architecture.
The nematic thermal satiability of Series IV are slightly higher then those of
Series: I-Me. This indicates that azolinkage of Series IV has played a batter role
due to their polarizability in this series.
The nematic thermal satiability of Series: III-H and Series IV is higher then
that of Series: II-Me. This may be related in the effect of linearity, polarizability,
and subsequent packing of the molecule in the heterocyclic compounds.
Oh [37] has reported that all the transition temperature of pyridine analogous
were lower compared with the benzene analogues.
Figure 5. (a) DSC thermogram for compound B10 (Series: II-Me). (b) DSC thermogram for
compound B14 (Series: II-Me).

Role of Terminal Heterocyclic Ring
77
In the present study, also the thiophene derivatives have lower transition tem-
perature. The heteroatom has high electronegativity and will, therefore, withdraw
electron from the other atoms of the ring system rendering the ring deactivated
related to benzene.
4. Conclusion
A host of new compounds have been synthesized where one of the terminus is
heterocyclic ring. a-Methyl group is introduced on one of the central Schiff base
linkage. The terminal heterocycle ring is furan and thiophene. The study has high-
lighted that small differences in the molecular structure have a marked effect on
mesophase thermal stabilities.
Acknowledgment
We are grateful to Prof. R. A. Vora retired Prof. and Head, Department of Applied
Chemistry, Faculty of Technology and Engineering, Kalabhavan, M. S. University
of Baroda, Vadodara for his valuable suggestion. We are also thankful to CDRI
Lucknow, I.I.T. Bombay, and SAIF Chandighar for providing facilities of elemental
1
analysis, FT-IR, H-NMR, mass spectral, and thermal analysis.
References
[1] Gray, G. W. (1962). Molecular Structure and the Properties of Liquid Crystals, Academic
Press: New York.
[2] Lin, H. C., Lai, L. L., Hsieh, W. P., & Huang, W. Y. (1997). Liq. Cryst., 22, 661.
[3] Semmler, K. J. K., Dingemans, T. J., & Samulski, E. T. (1998). Liq. Cryst., 24(6), 799.
[4] Tokuhisa, H., Era, M., & Tsutsui, T. (1998). Appl. Phys. Lett., 72, 2639.
[5] Tokuhisa, H., Era, M., & Tsutsui, T. (1998). Adv. Mater., 10, 404.
[6] Sato, M., Ohta, R., Handa, M., & Kasuga, K. (2002). Liq. Cryst., 29, 1441.
[7] Karamysheva, L. A., Torgova, S. I., & Agafonova, I. F. (2000). Liq. Cryst., 27, 393.
[8] Cai, R., & Samulski, E. T. (1991). Liq. Cryst., 9, 617.
[9] Parra, M., Alderete, J., Zuniga, C., Hidalgo, P., Vergara, J., & Fuentes, G. (2002). Liq.
Cryst., 29, 1375.
[10] Hsu, Y. Y. (1984). U.S. Patent 4 424 372.
[11] Schadt, M. (1993). Liq. Cryst., 14, 73.
[12] Demus, D. (2001). Mol. Cryst. Liq. Cryst., 364, 25.
[13] Gray, G. W., & Kelly, S. M. (1999). J. Mater. Chem., 9, 2037.
[14] Bretle, R., Dunmur, D. A., Marson, C. M., Pinol, M., & Toriyama, K. (1993). Liq.
Cryst., 13, 515.
[15] Bretle, R., Dunmur, D. A., Marson, C. M., Pinol, M., & Toriyama, K. (1992). Chem.
Lett., 21, 613.
[16] Seed, Alexander. (2007). Chem. Soc. Rev., 36, 2046–2069.
[17] Press, J. B. (1984). In: The Chemistry of Heterocyclic Derivatives. Thiophene and its
Derivatives; Gronowitz, S. (Ed.), Wiley: New York, Vol. 44 (Part-1), 353–456.
[18] Press, J. B. (1990). In: The Chemistry of Heterocyclic Derivatives. Thiophene and its
Derivatives; Gronowitz, S. (Ed.), Wiley: New York, Vol. 44 (Part-4), 397–502.
[19] Fishel, D. L., & Patel, P. R. (1972). Mol. Cryst. Liq. Cryst., 17, 139.
[20] Nash, J. A., & Gray, G. W. (1974). Mol. Cryst. Liq. Cryst., 25, 299.
[21] Pavluchenko, A. I., Smirnova, N. I., Titov, V. V., Kovshev, E. I., & Djumeev, K. M.
(1976). Mol. Cryst. Liq. Cryst., 37, 35.

78
B. T. Thaker et al.
[22] Dewar, M. J. S., & Riddle, R. M. (1975). J. Amer. Chem. Soc., 97, 6658.
[23] Thaker, N. N., & Trivedi, K. N. (1981). Indian J. Chem., 20A, 560.
[24] Nguyen, D. N., & Pham, T. C. (1976). Tap. Chi. Hoa. Hoc., 14, 13.
[25] Dave, J. S., & Lohar, J. M. (1981). Mol. Cryst. Liq. Cryst., 70, 279.
[26] Jones, F. Jr., & Ratto, J. (1973). J. Chem. Soc., Chem. Commun., 21, 841.
[27] Agrawal, Y. K., & Rajput, S. J. (1997). J. Indian Chem. Soc., 74, 689.
[28] Demus, D., Goodby, J., Gray, G. W., Spiess, H. W., & Vill, V. (Eds.). (1998). Handbook
of Liquid Crystals, VCH-Wiley: Weinheim.
[29] Saleh, A. A., Pleune, B., Fettinger, J. C., & Poli, R. (1997). Polyhedron, 16, 1391.
[30] Vyas, G. N., & Shah, N. M. (1963). Org. Syn. Coll., John Wiley and Sons Inc.: New York,
Vol. IV, 836.
[31] Criswell, T. R., Klanderman, B. H., & Batesky, B. C. (1973). Mol. Cryst. Liq. Cryst., 22,
211.
[32] Vora, R. A., & Dixit, N. (1979). Presented at Annual Convention of Chemists,
Kurukshetra, India.
[33] Vogel, A. I. (1972). In: Textbook of Practical Organic Chemistry, 3rd Edition, (E. L. B. S.
and Longman Group Ltd., London, 251.
[34] Dave, J. S., & Vora, R. A. (1970). Mesomorphic behavior of the cholestryl esters-1. Pera
normal alkoxy benzoates of cholesterol. In: Liquid Crystals and Ordered Fluid, Johnson,
J. F. & Porter, R. S., (Eds.), Plenum Press: New York, 1, 477.
[35] Sackmann, H., & Demus, D. (1966). Mol. Cryst. Liq. Cryst., 2, 81.
[36] Gray, G. W., & Goodby, J. (1984). Smectic Liquid Crystals: Textures and Structures.
Leonard Hill, Glasgow.
[37] Oh, C. S. (1972). Mol. Cryst. Liq. Cryst., 19, 95.
[38] Vora, R. A., & Gupta, Renu. (1983). Mol. Cryst. Liq. Cryst., 91, 45–52.
[39] Matharu, A. S., & Chambers-asman, D. (2007). Liq. Cryst., 34(11), 1317–1336.
Scheme 1 (Series: I-Me)
Synthesis of 4-n-alkoxy anilines
where CnH2nþ1 n ¼ 1 to 8, 10, 12, 14, 16, and 18.
Synthesis of furylacryoyl acid

Role of Terminal Heterocyclic Ring
Synthesis of furylacryoyloxy chloride
79
Synthesis of 4(furylacryloyloxy) acetophenone
Synthesis of 4(furylacryloyloxy) a-methyl benzylidene-40-n-alkoxyaniline
where CnH2nþ1 n ¼ 1 to 8, 10, 12, 14, 16, and 18.
Scheme 2 (Series: II-Me)
Synthesis of thionylacrylic acid

80
B. T. Thaker et al.
Synthesis of thionylacryloyl chloride
Synthesis of 4(thionylacryloyloxy) acetophenone
Synthesis of 4(thionylacryloyloxy) a-methyl benzylidene-40-n-alkoxyaniline
where CnH2nþ1 n ¼ 1 to 8, 10, 12, 14, 16, and 18.