Synthesis and liquid crystal properties of novel ethylene derivatives: α-3-[-4′-n-alkoxy cinnamoyloxy] phenyl β-4″-methoxy benzoyl ethylenes

Article abstract of DOI:10.1080/15421406.2012.694754

Eleven members of a novel homologous series of α-3-[-4′-n- alkoxy cinnamoyloxy] phenyl β-4″-methoxy benzoyl ethylenes were synthesized. The methyloxy, ethyloxy, butyloxy, and hexadecyloxy homologues are nonmesomorphic, while all the other homologues are mesomorphic. The mesomorphic homologues are enantiotropically smectogenic in combination with nematogenic character, except for the propyloxy homologue, which shows only nematogenic character. A phase diagram of the series shows the expected mesomorphic behavior. Transition temperatures of this series are observed through an optical polarizing microscope equipped with a heating stage. An odd-even effect is observed for nematic-isotropic transition curve. Analytical data supports the structures of the molecules. Mesomorphic temperature range varies from 23°C to 51°C. Liquid crystal properties of this series are compared with a structurally similar homologous series. The smectic and nematic thermal stability of the series are 138.8°C and 165.7°C, respectively. The nematic phase shows a threaded or schlieren texture, and the smectic phase is a smectic A phase. Copyright Taylor & Francis Group, LLC.

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Synthesis and Liquid Crystal Properties
of Novel Ethylene Derivatives: α-3-[-4′-
n-Alkoxy Cinnamoyloxy] phenyl β-4′′-
methoxy Benzoyl Ethylenes
a b
a
H. N. Chauhan
& A. V. Doshi
a
Shri Jagdishprasad Jhabarmal Tibrewala University, Jhunjhunu,
Rajasthan, India
b
Chemistry Department, K.K. Shah Jarodwala Maninagar Science
College, Gujarat University, Ahmedabad, Gujarat, Indiaq
Published online: 16 Nov 2012.
To cite this article: H. N. Chauhan & A. V. Doshi (2012) Synthesis and Liquid Crystal Properties
of Novel Ethylene Derivatives: α-3-[-4′-n-Alkoxy Cinnamoyloxy] phenyl β-4′′-methoxy Benzoyl
Ethylenes, Molecular Crystals and Liquid Crystals, 569:1, 33-39, DOI: 10.1080/15421406.2012.694754
To link to this article: http://dx.doi.org/10.1080/15421406.2012.694754
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Mol. Cryst. Liq. Cryst., Vol. 569: pp. 33–39, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.694754
Synthesis and Liquid Crystal Properties of Novel
ꢀ
Ethylene Derivatives: α-3-[-4 -n-Alkoxy
ꢀ
ꢀ
Cinnamoyloxy] phenyl β-4 -methoxy Benzoyl
Ethylenes
H. N. CHAUHAN1 AND A. V. DOSHI
,2,∗
1,∗
1
Shri Jagdishprasad Jhabarmal Tibrewala University, Jhunjhunu, Rajasthan, India
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College,
2
Gujarat University, Ahmedabad, Gujarat, Indiaq
ꢀ
Eleven members of a novel homologous series of α-3-[-4 -n-alkoxy cinnamoyloxy]
ꢀ
ꢀ
phenyl β-4 -methoxy benzoyl ethylenes were synthesized. The methyloxy, ethyloxy,
butyloxy, and hexadecyloxy homologues are nonmesomorphic, while all the other homo-
logues are mesomorphic. The mesomorphic homologues are enantiotropically smecto-
genic in combination with nematogenic character, except for the propyloxy homologue,
which shows only nematogenic character. A phase diagram of the series shows the
expected mesomorphic behavior. Transition temperatures of this series are observed
through an optical polarizing microscope equipped with a heating stage. An odd–even
effect is observed for nematic–isotropic transition curve. Analytical data supports the
◦
◦
structures of the molecules. Mesomorphic temperature range varies from 23 C to 51 C.
Liquid crystal properties of this series are compared with a structurally similar homol-
ogous series. The smectic and nematic thermal stability of the series are 138.8 C and
◦
◦
1
65.7 C, respectively. The nematic phase shows a threaded or schlieren texture, and the
smectic phase is a smectic A phase.
Keywords Liquid crystal; mesophase; monotropy; nematic; smectic
Introduction
Suitable magnitudes of anisotropic forces of intermolecular attractions as a consequence
of molecular rigidity and flexibility can favorably induce a physically distinct state of a
substance between the crystalline solid and the isotropic liquid states, called the liquid
crystal state. Many homologous series with varying molecular rigidity and flexibility have
been reported [1–3]. Normally structures consist of two or more rings (aromatic, alicyclic,
or heterocyclic) and central linking groups comprise the rigidity and lateral or/and terminal
groups act as the flexible part of the molecule. The present series involves three phenyl
rings bridged through a cinnamoyoxy group (–CH=CH–COO–) and a cinnamoyl group
(–CH=CH–CO–) to give the rigid section, and terminal n-alkoxy (–OR) groups as the
∗
Address correspondence to A.V. Doshi, A/365 , Vrajdham society, Jambuva jakat naka, Maneja
post office, Makarpura road, BARODA 390013 Gujarat, India. E-mail: shreeyashailee@yahoo.in and
H.N. Chauhan, 8, Shyamal apts., 17, Devang society, Near Vallabhvadi bus stop, Bhairavnath road,
Maninagar, Ahmedabad 380008 Gujarat, India. E-mail: arvindbhaidoshi@yahoo.in
33

34
H. N. Chauhan and A. V. Doshi
Table 1. Elemental analysis for ethoxy, butyloxy, and hexadecyloxy derivatives
Elements % found (compared with%
calculated)
Molecular formula
C
H
1
2
3
C27H24O5
C29H28O5
C41H52O5
75.70 (75.67)
76.32 (76.34)
78.85 (78.86)
5.61 (5.59)
6.14 (6.17)
8.33 (8.35)
flexible parts of the molecule. The resultant magnitudes of molecular rigidity and flexibility
induce the liquid crystal in seven homologues of the eleven investigated.
Experimental
Characterization
1
The materials were characterized for the molecular structure by IR (infra red) and H NMR
(proton nuclear magnetic resonance) techniques. Microanalysis was performed using a
Perkin Elmer PE 2400 CHN analyzer. IR spectra were recorded on a Perkin-Elmer spectrum
1
GX, and H NMR spectra were recorded on a Bruker instrument using CDCl3 as a solvent.
The mesogenic properties and transition temperatures of the series were investigated using
an optical polarizing microscope equipped with heating stage.
Synthesis
4-Methoxyacetophenone, 3-hydroxybenzaldehyde, ethanol, potassium hydroxide, pyridine,
thionyl chloride, malonic acid, piperidine, and n-alkyl halides were used as received.
Thionyl chloride was freshly distilled. 4-n-Alkoxycinnamic acids and 4-n-alkoxycinnamoyl
chlorides (A) were synthesized by the modified method of Dave and Vora [4]. α-3-Hydroxy
ꢀ
phenyl β-4 -methoxy benzoyl ethylene (B) was prepared by the known method [4,5].
ꢀ
ꢀ
α-3-[4 -n-alkoxy cinnamoyloxy] phenyl β-4 -methoxy benzoyl ethylenes were synthesized
by condensing 4-n-alkoxy cinnamoyl chloride (A) with α-3-hydroxy phenyl β-4 -methoxy
ꢀ
benzoyl ethylene (B) in dry cold pyridine [6]. Final products of the series were decomposed,
filtered, washed, dried, and crystallized from alcohol until constant transition temperatures
were obtained. Analytical data were found satisfactory as shown in Table 1. The synthetic
route to the series is outlined as shown in Scheme 1.
Analytical Data for Series 1
Analytical data for series 1 is given in Table 1.
Spectral Data for Series 1
NMR in PPM (parts per million) for the hexyloxy derivative: 0.868 (–CH3 of –OC6H13),
1.245 (–CH2– of –OC6H13), 4.07 (triplet) (–OCH2–CH2 of –OC6H13), 6.98 (broad)
–
CH=CH, 7.15 and 7.27 (–CH=CH–CO–), 6.9–8.6 (phenyl ring) NMR confirms the
structure.
NMR in PPM for the octyloxy derivative: 0.88 (–CH3 of –OC8H17), 1.308 and 1.77
(triplet) (–CH2– of –OC8H17), 4.02 (triplet) (–OCH2–CH2) of –OC8H17), 7.00 (broad)
CH=CH, 6.9–8.6 (phenyl ring) NMR confirms the structure.

LC Properties of Novel Ethylene Derivatives
35
Scheme 1. Synthetic route to the series.
−1
IR in cm for pentyloxy derivative: 700 (polymethylene of –OC5H11), 840 (phenyl ring),
9
40 (–CH=CH–), 1170 of –OC5H11 , 1250, 1600, and 1680 , (–COO group), 650 and
770 (phenyl ring), IR supports the structure.
−1
IR in cm for dodecyloxy derivative: 680 polymethylene of OC12H25, 720 and 770 (phenyl
ring), 840 (phenyl ring). 1160 (C–O of –OC12H25), 1220, 1260, and 1605 (–COO
group), IR supports the structure.
Miscibility Method
Derivative
Texture
•
•
•
•
Propyloxy derivative
Octyloxy derivative
Pentyloxy derivative
Decyloxy derivative
Nematic threaded type
Nematic schlieren type
Smectic A type
Smectic A type
Results and Discussion
4
-n-Alkoxycinnamic acids and the corresponding acid chlorides and α-3-hydroxy phenyl
ꢀ
β-4 -methoxy benzoyl ethylene are all nonmesomorphic. However, on condensing, both of
them can turn to liquid crystalline materials, and in this study, seven members of the titled
series of eleven members thus found to have liquid crystalline characteristic. The propyloxy

36
H. N. Chauhan and A. V. Doshi
Figure 1. Phase behavior of the series.
homologue exhibits only nematogenic character, while the pentyloxy to tetradecyloxy ho-
mologues exhibit enantiotropic nematogenic character in addition to smectogenic character.
The methyloxy, ethyloxy, butyloxy, and hexadecyloxy homologues are nonmesomorphic.
A phase diagram (see Fig. 1) is plotted for the transition temperature of homologues as
recorded in Table 2 versus the number of carbon atoms present in n-alkyl chain of left
n-alkoxy terminal end group. A solid mesomorphic transition curve follows a zigzag path
of rising and falling values, as the series is ascended with an overall falling tendency,
except for the hexadecyloxy homologue. The smectic–nematic transition curve initially
rises, passes through maxima, and smoothly adopts a descending tendency as the series
is ascended and behaves in an expected manner, without showing an odd–even effect. The
nematic–isotropic transition curve adopts a descending tendency as the series is ascended
with an odd–even effect and behaves in the usual expected manner. The nematic–isotropic

LC Properties of Novel Ethylene Derivatives
37
◦
Table 2. Transition temperatures of the series in C
◦
Transition temperatures in C
Compound no.
n-alkyl group,CnH2n+1 (n)
Sm
N
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
8
10
12
14
16
–
–
–
–
–
–
178.0
161.0
173.0
190.0
175.0
180.0
170.0
161.0
154.0
148.0
160.0
150.0
–
124.0
130.0
119.0
120.0
116.0
113.0
–
138.0
144.0
148.0
141.0
134.0
128.0
–
1
1
0
1
Note: Sm: Smectic; N: Nematic.
transition curve is extrapolated to the solid-isotropic transition temperature of the
nonmesomorphic butyloxy homologue, following the trends of the nematic–isotropic
transition curve, and clearly coincides with the nematic–isotropic transition temperature.
Thus the predicted latent transition temperature (LTT) for the nematic–isotropic transi-
◦
◦
tion for the butyloxy homologue is 190 C, but the melting point is 190 C, so no mesophase
exists. Similarly, the nematic–isotropic and smectic–nematic transition curves are extrapo-
lated for the nonmesomorphic hexadecyloxy homologue following the trend of the respec-
tive curves. This suggests that the probable predicted LTT for nematic and smectic phases
◦
◦
should be 142 C and 125 C, respectively. Mesophase temperature ranges vary between a
◦
◦
minimum of 23 C and a maximum 51 C. The odd–even effect diminishes from the hep-
tyloxy homologue by merging both curves because the longer n-alkyl chain may coil or
couple to lie in the line with the major axis of core and bend in such a manner that end-to-end
contact would then be the same for odd and even homologues. Thus, higher homologues
do not show an odd–even effect. The nonmesomorphic behavior of the methoxy, ethoxy,
butyloxy, and hexadecyloxy homologues is due to their high crystallizing tendency arising
from unsuitable magnitudes of anisotropic intermolecular forces of attractions related to
molecular rigidity and flexibility [1–3]. Thus molecules of nonmesomorphic homologues
are unable to resist thermal vibrations exposed upon them and melt sharply at their melting
point from the crystalline state to the isotropic liquid state without passing through an in-
termediate liquid crystal or mesogenic state. The exhibition of a mesomorphic state by the
seven homologues of the series either smectic and/or nematic is attributed to their molecular
◦
disalignment at an angle less than 90 C with the plane of the surface under the influence
of exposed heat energy to a thermodynamic system (homologue) from surroundings. The
molecules showing smectic or/and nematic mesophase or mesophases are capable of resist-
ing exposed thermal vibrations and arrange themselves either (i) statistically parallel or/and
(ii) in a sliding layered molecular order due to lamellar packing in their crystal lattices, as a
consequence of molecular rigidity and flexibility [1–3], which causes suitable magnitudes
of intermolecular anisotropic forces of attractions. An odd–even effect observed for the

38
H. N. Chauhan and A. V. Doshi
◦
Table 3. Average thermal stabilities in C
Average transition temperatures
◦
in C
Series
Series 1
138.8
Series Y
Smectic–nematic or isotropic
(
C5–C14)
C5
—
Commencement of smectic phase
Nematic–isotropic
165.7
C3–C14)
C3
144.5
(C6–C16)
C6
(
Commencement of nematic mesophase
nematic–isotropic transition curve and the variation in mesogenic character from homo-
logue to homologue in the same series are attributed to the sequentially and progressively
added methylene unit [7]. Thermal stabilities (see Table 3) and other liquid crystal prop-
erties of the present series 1 are compared with another structurally similar homologous
series Y [5] as shown in Fig. 2.
Homologous series 1 and series Y are structurally similar with respect to three phenyl
rings bridged through –CH=CH–COO– and –CH=CH–CO– central linking groups as the
rigid section and the n-alkoxy end group as a common flexible part of the molecules. There-
fore both series 1 and series Y are identical with respect to molecular rigidity, aromaticity,
size, etc., but they differ in the flexible end groups –OCH3 and –H, length-to-breadth ratio,
molecular polarity and polarizability due to the –OCH3 end group [7], end-to-end attrac-
tions, intermolecular distance, molecular planarity or extent of noncoplanarity, etc. There-
fore observed variations in mesomorphic properties and thermal stabilities of mesophases
are attributed to the structural differences mentioned above causing difference in the in-
termolecular forces of attractions between series 1 and series Y. Average thermal stability
for smectic and nematic mesophases and commencement of mesophases are mentioned in
Table 3.
From Table 3, it is clear that the average thermal stability for the smectic and nematic
mesophases of series 1 is relatively higher than those of series Y. The higher values
of thermal stabilities for series 1 suggest that heat content or enthalpy (ꢀH) values of
homologues of series 1 are relatively more than series Y. As temperature is raised for the
homologue under observation, the quantum of heat required for the transition corresponds
to the quantum of energy stored (ꢀH value) by a molecule to stabilize at room temperature.
Initially heat supplied to the system (homologue) with lamellar packing gives rise to the
sliding layered arrangement of molecule under floating conditions at the solid-smectic
Figure 2. Structurally similar series.

LC Properties of Novel Ethylene Derivatives
39
temperature and then converted to maintain a statistically parallel orientational order of the
molecules under floating conditions relatively at higher temperature to cause smectic and/or
nematic mesophases, respectively. The difference of two temperatures for any mesophase is
called a mesophase length and the ratio of enthalpy value to the corresponding temperature,
that is, ꢀH/T is called entropy (ꢀS) value of a sample at a given temperature. The molecular
widthof series 1 is more thanseries Y. Hencemolecular polarizability andmolecular polarity
[7] due to molecular breadth including the presence of the highly polar –OCH3 end group
is relatively more than –H, which raises intermolecular attractions for series 1 and results in
higher values of thermal stability and phase length as compared with series Y. Early or late
commencement of a smectic mesophase is related to the extent of noncoplanarity caused by a
molecule [6,8]. Molecules of series 1 are less coplaner than the molecules of series Y, which
results in early commencement of the smectic and nematic mesophases. The difference of
mesomorphic properties for the same homologue from series to series is attributed to the
varying end groups of fixed polarity (i.e., the polarity order is –OCH3 > H).
Conclusions
1
2
3
The group efficiency order derived on the basis of thermal stability for the smectic
and nematic mesophases are OCH3 > H.
The molecular flexibility and rigidity are important parameters to cause mesophase
formation and mesophase length.
The results of the presently investigated series support the conclusions drawn and
enhance the understanding of structure–property relationships in liquid crystals.
Acknowledgment
The authors thank the principal Dr. R. R. Shah and Dr. R. B. Patel, Head of the Chemistry
Department at K. K. Shah Jarodwala Maninagar Science College, Ahmedabad, for their
valuable cooperation and also Vaibhav laboratory for analytical services.
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