Synthesis and mesomorphic properties of novel ethylene derivatives

Article abstract of DOI:10.1080/15421406.2013.782202

A novel homologous series, α-4-[-4′-n-alkoxy cinnamoyloxy] benzoyl-β-4″-methoxy phenyl ethylenes, has been synthesized, which consists of 12 homologues. The pentyl to tetradecyl homologues are enantiotropically mesomorphic, and the rest of the homologues are nonmesomorphic. The pentyl to octyl derivatives exhibit smectogenic character in addition to nematogenic character, but the decyl to tetradecyl homologues exhibit only nematogenic character without the exhibition of a smectic phase. A phase diagram of three transition curves shows a normal phase behavior. Analytical and spectral data confirm the molecular structure of the homologues. The optical microscopic textures are threaded or Schlieren for the nematic phase and the normal smectic A type, respectively. Liquid crystal properties and transition temperatures were determined using a hot stage polarizing microscope. The smectic and nematic thermal stabilities are 159.7°C and 174.1°C, respectively. Thus, the present novel series is predominantly nematogenic and partly smectogenic in nature and is compared with other structurally similar homologous series.

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Synthesis and Mesomorphic Properties of
Novel Ethylene Derivatives
R. P. Chaudhari a , R. B. Patel a & A. V. Doshi b
a Chemistry Department , K. K. Shah Jarodwala Maninagar Science
College , Ahmedabad , Gujarat , India
b Shri Jagdish Prasad Jhabarmal Tibrewala University (J.J.T. Uni.) ,
Jhunjhunu , Rajasthan , India
Published online: 09 Jul 2013.
To cite this article: R. P. Chaudhari , R. B. Patel & A. V. Doshi (2013) Synthesis and Mesomorphic
Properties of Novel Ethylene Derivatives, Molecular Crystals and Liquid Crystals, 577:1, 95-102, DOI:
10.1080/15421406.2013.782202
To link to this article: http://dx.doi.org/10.1080/15421406.2013.782202
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Mol. Cryst. Liq. Cryst., Vol. 577: pp. 95–102, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.782202
Synthesis and Mesomorphic Properties of Novel
Ethylene Derivatives
R. P. CHAUDHARI,1,∗ R. B. PATEL,1 AND A. V. DOSHI2
1Chemistry Department, K. K. Shah Jarodwala Maninagar Science College,
Ahmedabad, Gujarat, India
2Shri Jagdish Prasad Jhabarmal Tibrewala University (J.J.T. Uni.), Jhunjhunu,
Rajasthan, India
A novel homologous series, α-4-[-4ꢀ-n-alkoxy cinnamoyloxy] benzoyl-β-4ꢀꢀ-methoxy
phenyl ethylenes, has been synthesized, which consists of 12 homologues. The pentyl
to tetradecyl homologues are enantiotropically mesomorphic, and the rest of the ho-
mologues are nonmesomorphic. The pentyl to octyl derivatives exhibit smectogenic
character in addition to nematogenic character, but the decyl to tetradecyl homologues
exhibit only nematogenic character without the exhibition of a smectic phase. A phase
diagram of three transition curves shows a normal phase behavior. Analytical and spec-
tral data confirm the molecular structure of the homologues. The optical microscopic
textures are threaded or Schlieren for the nematic phase and the normal smectic A type,
respectively. Liquid crystal properties and transition temperatures were determined
using a hot stage polarizing microscope. The smectic and nematic thermal stabilities
are 159.7◦C and 174.1◦C, respectively. Thus, the present novel series is predominantly
nematogenic and partly smectogenic in nature and is compared with other structurally
similar homologous series.
Keywords Enantiotropy; ethylene derivatives; liquid crystal; nematic; smectic
Introduction
Molecular structure consists of different atoms making a variety of skeletons whose rigidity
and flexibility [1–3] vary from molecular skeleton to skeleton. Thus, suitable magnitudes
of anisotropic intermolecular forces of the end to end and lateral attractions also vary to
facilitate or to induce liquid crystal properties. Thus, the present study is planed with a
view to understand and establish the relationship between liquid crystal properties [4] and
the molecular structure by constructing a new skeleton of ethylene derivatives by linking
three phenyl rings through two central bridges CH CH COO and CO-CH CH
in which two terminal end groups of OR and OCH3 are attached at the pꢀ-pꢀꢀ positions
without any lateral substitution.
∗Address correspondence to R. P. Chaudhari, Chemistry Department, K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad 380008, Gujarat, India. E-mail: rpchaudhari@ymail.com
95

96
R. P. Chaudhari et al.
Scheme 1. Synthetic route to the series.
Experimental
Synthesis
4-n-Alkoxy cinnamic acids were prepared using suitable alkylating agents and 4-hydroxyl
cinnamic acid. cis-4-n-Alkoxy cinnamic acids were converted to the corresponding acid
chlorides (A) using thionyl chloride by the modified method of Dave and Vora [5]. α-4-
Hydroxy benzoyl β-4ꢀ-methoxy phenyl ethylene (B) was prepared by usual established
method [6]. Components (A) and (B) were condensed in dry cold pyridine [7]. Final
products were individually decomposed, filtered, washed, dried, and purified until constant
transition temperatures were obtained. 4-Hydroxy benzaldehyde, malonic acid, piperidine,
pyridine, alkyl halide, MeOH, KOH, EtOH, thionyl chloride were used as received, and
solvents were dried and purified prior to use. The synthetic route to the series is under
mentioned as Scheme 1.
Where R = CnH2n+1, n = 1,2,3,4,5,6,7,8,10,12,14,16.

Novel Ethylene Derivatives
97
Table 1. Elemental analysis for methoxy, ethoxy, butoxy, and pentyloxy derivatives
Elements % found (% Calculated)
Sr. no.
Molecular formula
C
H
1
2
3
4
C26H22O5
C27H24O5
C29H28O5
C30H30O5
75.41 (75.36)
75.80 (75.70)
76.64 (76.31)
75.75 (75.59)
5.38 (5.31)
5.78 (5.60)
6.37 (6.14)
6.49 (6.38)
Characterization
Selected members of the novel homologous series were characterized by elemental analysis
(Table 1), infrared (IR) spectroscopy, and 1HNMR spectroscopy techniques. Microanalysis
was performed on a Perkin-Elmer PE2400 CHN analyzer. IR spectra were recorded on a
1
Perkin-Elmer spectrum GX, and HNMR spectra were recorded on a Bruker instrument
using CDCl3 as the solvent. The mesogenic properties of the novel series were deter-
mined using polarizing microscopy. The textures of nematic and smectic mesophases were
determined by a miscibility method.
Texture Determination
Dodecyl–Threaded nematic
Octyl–Schilieren nematic
Hexyl–Smectic-A
Analytical Data
Spectral Data
NMR in ppm for the decyloxy derivative: 0.910 ( CH3 of OC10H21 group), 1.245
( (CH2)n polymethylene group of OC10H21), 3.670 (triplet) ( OCH2 CH2 of
OC10H21), 6.625 and 6.987 ( CH CH CO group), 7.277, 7.390, and 7.717 (p-
substituted phenyl ring). NMR supports the molecular structure.
NMR in ppm for the dodecyloxy derivative: 0.946 (−CH3 of OC12H25 group),
1.421 (CH2)n polymethylene group of OC12H25), 4.007 (triplet) ( OCH2 CH2
of OC12H25 group), 6.898 and 6.920 ( CH CH CO group), 7.899, 7.920, and 7.980
(p-substituted phenyl ring). NMR supports the molecular structure.
IR in cm−1 for the hexyloxy derivative: 740 polymethylene (CH2)n group of
OC6H13, 815 p-substituted phenyl ring, 1180 C O of OC6H13 group, 1220 and 1600
COO ester group, 930 CH CH group. IR supports the molecular structure.
IR in cm−1 for octyloxy derivative: 680 polymethylene (CH2)n group of OC8H17,
830 p-substituted phenyl ring, 1140 C O of OC8H17 group, 1250 and 1600 COO ester
group, 960 CH CH group. IR supports the molecular structure.
Results and Discussion
The novel homologous series consists of 12 homologues. The methyl to butyl and the
hexadecyl homologues are not liquid crystalline, the pentyl to octyl homologues are
enantiotropically smectogenic in addition to nematogenic, and the decyl to tetradecyl

98
R. P. Chaudhari et al.
Figure 1. Phase behavior of a series.
homologues are only enantiotropically nematogenic. Acid chlorides (A) and the ethylenic
component (B) forming the final homologue derivatives are nonmesomorphic. However,
the resulting final homologues from pentyl to tetradecyl derivatives are mesomorphic with
the exhibition of either the smectic and/or the nematic mesophase. A phase diagram (Fig. 1)
of the series is drawn for the number of carbon atoms present in the n-alkyl chain versus
the transition temperatures (Table 2) as determined from an optical polarizing microscope
equipped with a heating stage. The solid–mesomorphic or isotropic curve adopts a zigzag
path of rising and falling values with an overall falling tendency and behaves in a normal
manner. The smectic–nematic transition curve initially rises, passes through maxima, and
then descends with the exhibition of an odd–even effect and merges into the solid–nematic
transition temperature of decyloxy homologue, which indicates that, from and beyond, the

Novel Ethylene Derivatives
99
Table 2. Transition temperatures of series in ◦C
Transition temperatures in ◦C
Compound no.
n-Alkyl group -CnH2n+1 (n)
Sm
Nm
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
—
—
—
—
—
—
190.0
170.0
156.0
162.0
178.0
185.0
174.0
178.0
170.0
168.0
166.0
172.0
—
—
145.0
140.0
138.0
142.0
—
—
—
—
155.0
164.0
159.0
161.0
152.0
148.0
136.0
—
10
11
12
Sm, smectic; Nm, nematic.
decyloxy to tetradecyloxy homologues, the smectic mesophase formation ceases to appear
and only the nematogenic mesophase occurs. Thus, the smectic–nematic transition curve
behaves in the usual established manner. The nematic–isotropic transition curve follows a
descending tendency as the series is ascended with the exhibition of an odd–even effect and
merges into the isotropic point of the hexadecyloxy homologue showing that the nemato-
genic mesophase formation ceases to appear beyond the tetradecyloxy homologue, and
so the hexadecyloxy homologue is nonmesomorphic. Thus, nematic–isotropic transition
curve behaves in a normal manner. The smectogenic phase length varies from a minimum
of 10◦C at the pentyloxy homologue to maximum of 24◦C at the hexyloxy homologue.
The nematogenic mesophase length varies from a minimum of 15◦C at the heptyloxy ho-
mologue to maximum of 30◦C at the tetradecyloxy homologue. The smectic and nematic
thermal stabilities are 159.7◦C and 174.1◦C, respectively. Thus, the novel homologous se-
ries is predominantly nematogenic and partly smectogenic with a middle ordered melting
type. The mesomorphic properties vary from homologue to homologue in the same series.
The curves for the odd and the even homologues for smectic and nematic merge into each
other at the 9th and 11th homologues, respectively. Thus, the odd–even effect diminishes
as series is ascended for higher homologues, which is because the longer n-alkyl chain
may coil, bend, flex, or couple to lie on the major axis of the core [4,8]. The smectic and
nematic mesophase formation commences from the pentyloxy homologue. The members
of the novel homologous series are synthesized from two nonmesomorphic components (A)
and (B). The mesomorphic property induces from the pentyl to the tetradecyl homologues
because of suitable magnitudes of molecular rigidity and flexibility enables the molecules
to float in an ordered two-dimensional array causing formation of either smectic and/or ne-
matic mesophase. The molecules of the pentyl to octyl homologues show a lamellar packing
in their crystal lattices, which generates the smectic mesophase. However, on continued
heating the lamellar packing gives way to simply a statistically parallel orientational order
of the molecules, which generates the nematic mesophase. Thus, the smectic mesophase
and the nematic mesophase occur for the pentyl to octyl homologues. The octyl to tetradecyl

100
R. P. Chaudhari et al.
Figure 2. Structurally similar homologous series.
derivatives do not show a lamellar packing of the molecules, but the end to end intermolec-
ular attractions are sufficient to induce nematogenic character in these homologues. The
observed odd–even effect and variations in mesomorphic properties from homologue to
homologue in the same series is attributed to the sequentially added methylene unit [4, 8]
in the n-alkoxy terminal chain. The nonmesomorphic nature of the methyl to butyl and the
hexadecyl homologues is attributed to the high crystallizing tendency arising from unsuit-
able magnitudes of anisotropic intermolecular forces of attraction giving an unfavorable
combination of molecular rigidity and flexibility [1,2,3]. The mesomorphic properties of
the series (1) under discussion are compared with other homologous with similar molecular
structure, series X [9] and Y [10] as shown in Fig. 2.
Homologous series 1, X, and Y are identical in all respects with three phenyl rings,
two central groups CH CH COO and −CO CH CH and an n-alkoxy ( OR)
terminal chain. However, series 1, X, and Y differ with respect to terminal or lateral
units of OCH3, NO2, and Cl. Therefore, the observed differences in mesomorphic
properties and the degree of mesomorphism can be linked to these differing structural
features. Functional groups OCH3, NO2, and Cl have different polarities based upon
their positional substitution on the third phenyl ring. Therefore, the molecular polarities
and polarizability, length to breadth ratio based on linear (series 1 and Y) or nonlinear
(series X) shape, electronic interactions, suitable magnitudes of anisotropic intermolecular
forces of adhesion [4] cause the resultant molecular rigidity and flexibility to differ and
generate different melting points and mesomorphism. Table 3 shows the thermal stability
and the commencement of the mesophase.
Table 3. Average thermal stability in C◦
Series →
1
X
Y
Smectic–nematic or isotropic
159.7
(C5 C8)
C5
141.0
(C5 C10)
C5
132.6
(C8 C12)
C8
Commencement of the smectic phase
Nematic–isotropic
174.1
156.0
156.7
(C5 C14)
C5
(C5 C16)
C5
(C5 C16)
C5
Commencement of the nematic phase

Novel Ethylene Derivatives
101
Table 3 indicates that all the series (1, X, and Y) under comparison are capable enough
to induce smectic and nematic mesophases within definite range of temperature. However,
they differ in the extent of smectic and nematic thermal stability. The smectic thermal
stability decreases from series 1 to X to Y. Similarly, the nematic thermal stability of series 1
is the highest among the series under comparison. The thermal stability of series X and Y is
almost equivalent (56.0 ≈ 56.7). This suggests that the molecules of series 1 strongly resist
the exposed thermal vibrations due to the highest magnitudes of anisotropic intermolecular
forces of attractions facilitated by the highly polar OCH3 terminal end group of series 1.
A gradual weakening of the intermolecular attractions may be due the lower polarity and
polarizability of the Cl or NO2 terminal or lateral groups, respectively. The smectic
mesophase commences from fifth member of the series 1 and X, but it commences later
from the eighth member of series Y. The early or late commencement of a smectic phase
depends upon [11] the extent of noncoplanarity caused by a molecular flexibility [1,2,3]
because of the variation in the molecular structure arising from the OCH3, NO2, Cl
flexible molecular parts. Thus, the observed variations of mesomorphic properties for the
same homologue from series to series is attributed to the OCH3, NO2, and Cl group of
series 1, X, and Y. However, the commencement of the nematogenic mesophase formation
is unaffected by changing functional groups, which remains intact for each series. The group
efficiency order derived on the basis of (a) thermal stability and (b) early commencement
of smectic and nematic phases is mentioned below in the conclusions.
Conclusions
1. (a) Smectic group efficiency order: 4ꢀꢀ−OCH3 > 3ꢀꢀ NO2 > 4ꢀꢀ Cl
Nematic group efficiency order: 4ꢀꢀ−OCH3 > 4ꢀꢀ Cl ≈ 3ꢀꢀ NO2
(b) Smectic group efficiency order: 4ꢀꢀ−OCH3 ≈ 3ꢀꢀ NO2 > 4ꢀꢀ Cl
Nematic group efficiency order: 4ꢀꢀ−OCH3 3ꢀꢀ NO2 4ꢀꢀ Cl
2. The novel series is predominantly nematogenic and partly smectogenic with a
middle-ordered melting type and low mesomorphic range.
3. Favorable molecular rigidity and flexibility of suitable magnitudes can facilitate
mesophase formation.
4. Variations in mesomorphic properties from homologue to homologue in the same
series and from series to series for the same homologue are attributed to the pro-
gressively added methylene unit and unchanging terminal or lateral group of each
series, respectively.
Acknowledgments
The authors would like to thank K. K. Shah Jarodwala Maninagar Science College and
S.P.T Arts & Science College, Godhra, for their valuable cooperation in this work. They
would also like to thank Vaibhav Laboratory for their analytical services and Ankita Doshi,
Department of Biochemistry, M.S. University of Baroda, Vadodara, for valuable support in
the work.
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