Study of the effect of molecular structure on mesomorphic properties through a novel homologous series α-3-[4′-n-alkoxy cinnamoyloxy] phenyl-β-4″-nitro benzoyl ethylenes

Article abstract of DOI:10.1080/15421406.2012.718228

Eleven members of a novel homologous series α-3-[4′-n-Alkoxy Cinnamoyloxy] phenyl-β-4″-nitro benzoyl ethylene are synthesized and evaluated for their mesomorphic properties. Seven members of the series are enantiotropically nematogenic without exhibition of smectogenic character, and the other four members are non-mesomorphic in character. Mesomorphic behavior from a phase diagram for solid to nematic and for nematic to isotropic transitions shows the normal behavior. The nematic to isotropic transition curve shows an odd-even effect. Analytical data support the structures of molecules. Nematogenic phase length ranges from 30°C to 62°C. Nematic-isotropic thermal stability is 175.7°C. The mesomorphic properties of the series are compared with the structurally similar isomeric series. Thus, the series is predominantly mesomorphic (nematogenic) and partly non-mesomorphic with middle-order melting points. Transition temperatures and other liquid crystal properties were determined by optical polarizing microscopy with a heating stage.

Full text of DOI:10.1080/15421406.2012.718228

This article was downloaded by: [Selcuk Universitesi]
On: 06 February 2015, At: 05:58
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Study of the Effect of Molecular
Structure on Mesomorphic Properties
Through a Novel Homologous Series α-3-
″
[
4′-n-Alkoxy cinnamoyloxy] Phenyl-β-4 -
nitro Benzoyl Ethylenes
a
b
D. M. Suthar & A. V. Doshi
a
Shri Jagdish Prasad Jhabarmal Tibrewala University, Jhunjhunu,
Rajasthan/Department of Chemistry, K. K. Shah Jarodwala
Maninagar Science College , Ahmedabad , Gujarat , India
b
Shri Jagdish Prasad Jhabarmal Tibrewala University , Jhunjhunu ,
Rajasthan , India
Published online: 22 Jan 2013.
To cite this article: D. M. Suthar & A. V. Doshi (2013) Study of the Effect of Molecular Structure
on Mesomorphic Properties Through a Novel Homologous Series α-3-[4′-n-Alkoxy cinnamoyloxy]
″
Phenyl-β-4 -nitro Benzoyl Ethylenes, Molecular Crystals and Liquid Crystals, 570:1, 76-83, DOI:
10.1080/15421406.2012.718228
To link to this article: http://dx.doi.org/10.1080/15421406.2012.718228
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 570: pp. 76–83, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.718228
Study of the Effect of Molecular Structure
on Mesomorphic Properties Through a Novel
ꢀ
Homologous Series α-3-[4 -n-Alkoxy cinnamoyloxy]
ꢀ
ꢀ
Phenyl-β-4 -nitro Benzoyl Ethylenes
1,∗
2
D. M. SUTHAR AND A. V. DOSHI
1Shri Jagdish Prasad Jhabarmal Tibrewala University, Jhunjhunu,
Rajasthan/Department of Chemistry, K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad, Gujarat, India
2
Shri Jagdish Prasad Jhabarmal Tibrewala University, Jhunjhunu, Rajasthan,
India
ꢀ
Eleven members of a novel homologous series α-3-[4 -n-Alkoxy Cinnamoyloxy] phenyl-
ꢀꢀ
β-4 -nitro benzoyl ethylene are synthesized and evaluated for their mesomorphic prop-
erties. Seven members of the series are enantiotropically nematogenic without exhibition
of smectogenic character, and the other four members are non-mesomorphic in charac-
ter. Mesomorphic behavior from a phase diagram for solid to nematic and for nematic
to isotropic transitions shows the normal behavior. The nematic to isotropic transition
curve shows an odd–even effect. Analytical data support the structures of molecules. Ne-
◦
◦
matogenic phase length ranges from 30 C to 62 C. Nematic-isotropic thermal stability
is 175.7 C. The mesomorphic properties of the series are compared with the structurally
◦
similar isomeric series. Thus, the series is predominantly mesomorphic (nematogenic)
and partly non-mesomorphic with middle-order melting points. Transition temperatures
and other liquid crystal properties were determined by optical polarizing microscopy
with a heating stage.
Keywords Enantiotropy; liquid crystal; mesomorphism; nematic; smectic
Introduction
Some compounds exhibit an intermediate state of matter between the crystalline solid
and the isotropic liquid, such phases of matter are called liquid crystals (LCs), and are
often termed as mesophases. This sort of physically distinct state of matter depends upon
suitable magnitudes of anisotropic intermolecular forces of attraction as a consequence of
favorable molecular rigidity and flexibility [1–3]. In present series, the molecular rigidity
is due to three phenyl rings linked through two central groups CH CH COO and
CH CH CO for all the members of the series, but flexible part of the molecule
(n-alkoxychain) varies in length. The effect of nonlinear broad shape molecular structure
∗
Address correspondence to D. M. Suthar, Department of Chemistry, K. K. Shah Jarodwala Man-
inagar Science College, 98, Madhav Park Society Part-4, Opp. Radhe Chamber, Vastral, Ahmedabad
82418, Gujarat, India. E-mail: dipakmsuthar@gmail.com
3
76

Novel Liquid Crystalline Nitro Benzoyl
77
on liquid crystallinity will be discussed in terms of molecular polarity, polarizability,
rigidity, and flexibility.
Experimental
Synthesis
4-Hydroxycinnamic acid and the 4-n-alkoxycinnamic acids, as well as the corresponding
acid chlorides (A), were prepared using the appropriate n-alkyl halides and subsequently us-
ꢀ
ing thionyl chloride by the modified method of Dave and Vora [4]. α-3-Hydroxy phenyl β-4 -
nitro benzoylethylene (B) was prepared by an established method [5c]. Components (A) and
(B) were condensed in dry cold pyridine to obtain final products. 4-hydroxybenzaldehyde,
3-hydroxybenzaldehyde, malonic acid, piperidine, pyridine, thionylchloride, alkyl halides,
methanol, KOH, ethanol, and 4-nitroacetophenpone required for synthesis were used as
received. The final products were all purified and crystallized from alcohol until they gave
constant transition temperatures. The synthetic route to the novel series is outlined in
Scheme 1.
Scheme 1. Synthetic route to the novel series.
Characterization
Some selected representative members of the series were characterized by Infrared (IR) and
1
Hydrogen-1 Nuclear Magnetic Resonance ( HNMR) spectra, and elemental analysis. The

78
D. M. Suthar and A. V. Doshi
Table 1. Elemental analysis (CHN) for ethyloxy, butyloxy, dodecyloxy, and andhexadecy-
loxy derivatives
Elements found % (calculated %)
No.
Molecular formula
C
H
N
1.
2.
3.
4.
C26H21NO6
C28H25NO6
C36H41NO6
C38H45NO6
70.38 (70.42)
71.29 (71.34)
74.12 (74.10)
74.69 (74.63)
4.79 (4.74)
5.35 (5.31)
7.10 (7.03)
7.29 (7.36)
3.10 (3.16)
2.94 (2.97)
2.36 (2.40)
2.34 (2.29)
1
IR spectra were recorded on a Perkin Elmer spectrum GX and the HNMR spectra were
recorded on a Bruker instrument using CDCl3 as solvent. Microanalysis was performed on
a Perkin Elmer PE 2400 CHN analyzer (Table 1). Transition temperatures and LC proper-
ties were investigated using optical polarizing microscopy equipped with a heating stage.
Thermodynamic quantities enthalpy (ꢀH) and entropy (ꢀS) are qualitatively discussed.
The texture of the nematic mesophase was determined by the miscibility method using
polarizing microscopy.
Analytical Data
Spectral Data
NMR in ppm for the octyloxy derivative.
0
.993 (−CH3 of OC8H17), 1.173(( CH2 )n of OC8H17), 3.718 ( OCH2 of OC8H17),
3.223 ( CH CH ), 6.611 ( CH CH CO ), 6.633 (p-substituted phenyl ring) 7.60
and 7.734 (m-substituted phenyl ring). NMR supports the structure.
NMR in ppm for the tetradecyloxy derivative.
0.872 ( CH3 of
OC14H29), 1.253(( CH2 )n of
OC14H29), 4.00 ( OCH2 of
OC14H29), 4.289&4.30 ( CH CH CO ), 6.88 and 7.931 (p-substituted phenyl ring),
.90 (m-substituted phenyl ring). NMR supports the structure.
6
−1
IR in cm for the hexyloxy derivative.
625 ( (CH2)n group of OC6H13), 760 (m-substituted phenyl ring), 1160 (>C O), 1230,
1600, and 1680( COO ), 1415 ( NO2 group), 930 ( CH CH ). IR supports the struc-
ture.
IR in cm for the decyloxy derivative.
25 ( (CH2)n group of OC10H21), 820 (p-substituted phenyl ring), 770 (m-substituted
−1
6
phenyl ring), 1160 (>C O), 1230, 1600, and 1680 ( COO ), 1415 and 1430 ( NO2),
30 ( CH CH ). IR confirms the structure.
9
Texture by miscibility method.
Pentyloxy homologueshows athreaded type texture and dodecyloxy shows a schlieren type
texture.

Novel Liquid Crystalline Nitro Benzoyl
79
ꢀ
Figure 1. Phase behavior of the novel series 1. Homologous series: α-3-[4 -n-alkoxy cinnamoyloxy]
ꢀꢀ
phenyl-β-4 -nitrobenzoyl ethylenes.
Results and Discussion
ꢀ
n-Alkoxycinnamic acids and α-3-hydroxyphenyl-β-4 -nitrobenzoyl ethylenes are non-
mesomorphics. However, mesomorphism is induced in seven final products of the novel
series. The other four members (methyl, ethyl, butyl, and hexadecyl derivatives) are non-
mesomorphics. The mesomorphic homologues exhibit enantiotropic nematogenic meso-
morphism only with absence of smectogenic character. A phase diagram (Fig. 1) shows
the phase behavior, and indicates that the solid to isotropic or solid to nematic transition
curve rises and falls in zigzag manner with an overall descending tendency. The nematic

80
D. M. Suthar and A. V. Doshi
◦
Table 2. Transition temperatures in C
Compound No.
R = 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
–
–
–
–
–
–
–
–
–
–
–
–
–
185.0
161.0
215.0
192.0
182.0
175.0
182.0
163.0
155.0
158.0
158.0
164.0
–
152.0
124.0
120.0
109.0
114.0
112.0
–
1
1
0
1
Sm = smectic; N = nematic.
to isotropic transition curve gradually falls as series is ascended with the exhibition of an
odd–even effect. The transition curves of the phase diagram show the number of carbon
atoms present in n-alkoxyterminal chain versus transition temperatures (Table 2) of ho-
◦
mologues. The mesomorphic phase length varies from a minimum of 30 C for the pentyl
◦
derivative to a maximum of 62 C for the octyl derivative of the series. The nematic to
isotropic transition curve is extrapolated [5c] for the non-mesomorphic homologues to
predict their probable latent transition temperatures (LTT) keeping in mind the trend of the
◦
actual transition curve. The predicted LTT for nematic to isotropic transition is 140 C, and
◦
◦
for butyl and hexadecyl derivatives, it is 158 C. The monotropic temperature of 140 C is
not realizable because before the nematic phase appears, crystallization occurs. The LTT
for nematic and solid to isotropic temperature coincided at 158 C. The nematic mesophase
◦
is induced in the novel series due to an increase in the number of phenyl rings from the two
non-mesomorphic components (A) and (B), which increases molecular aromaticity, polar-
ity, polarizability, and rigidity. Hence, the thermal vibrations give end-to-end intermolecular
anisotropic forces of attraction such that the molecules possess a statistically parallel ori-
entational order within definite range of temperature to form nematic mesophase [5, 6].
However, intermolecular forces of attraction are insufficient to cause lamellar packing of
molecules, and hence the smectic phase is not exhibited by any member of the novel se-
ries. The non-mesomorphic behavior of methyl, ethyl, butyl, and hexadecyl derivatives of
the series is attributed to their high crystallizing tendency arising from their shorter and
longest n-alkyl terminal chains, which causes unsuitable magnitudes of anisotropic forces
of intermolecular attractions. Hence, high degree of disorder, randomness, and entropy
(
ꢀS = ꢀH/T) generated and molecules are sharply transformed into the isotropic liquid
from crystalline solid state without passing through an intermediate LC state. Variations in
LC properties from homologue to homologue in the same series and the observed odd–even
effect are attributed to the sequentially added methylene unit in the n-alkoxy terminal chain.
The odd–even effect diminishes as the series is ascended because n-alkoxy chain of higher
homologues may coil, bend, flex, or couple to lie with major axis of the core. Thus, the
series is predominantly nematogenic and partly non-mesomorphic with middle order melt-
ing point and a moderate range of mesomorphism. The LC properties of the novel series
1, including average thermal stability (Table 3) and commencement of mesomorphism, are

Novel Liquid Crystalline Nitro Benzoyl
81
◦
Table 3. Relative average thermal stability in C
Series
1
–
S1
S2
Smectic to nematic or
smectic to isotropic
Commencement of
smectic phase
132.25 (C5–C10)
138.8 (C10–C14)
C5
C5
Nematic to isotropic
Commencement of
nematic phase
175.7 (C3–C14)
C3
171.5 (C5–C10)
C5
165.7 (C3–C14)
C3
compared with other structurally similar (Fig. 2) homologous series S1 and S2 as mentioned
below.
The three homologous series (Fig. 2) under comparison commonly contain three phenyl
rings bridged through CH CH COO and CH CH CO central groups, and an
n-alkoxy terminal chain. However, they differ in their geometrical shape, size, linearity of
molecules, and right terminal end group. Therefore, observed variations in their mesomor-
phic properties and degree of mesomorphism, including thermal stability, are attributed to
the differing magnitudes of molecular polarity, polarizability [7], molecular rigidity, and
flexibility [1–3] as well as intermolecular anisotropic forces of attraction. The relative av-
erage thermal stability and commencement of mesophase or phases of series 1, S1 [8], and
S2 [9] are mentioned in Table 3.
Table 3 indicates that the nematic to isotropic thermal stability shows a descending
order, i.e., series 1 > S1 > S2, and the smectic order of thermal stability is series S2 > S1 > 1.
Series 1 and S2 are nonlinear whereas series S1 is linear, i.e., series 1 and S2 are wider than
series S1. An increase of molecular width increases intermolecular distance, and hence
reduces intermolecular attractions and increases molecular polarizability. Thus, on one
hand intermolecular anisotropic forces of attraction are reduced due to increased molecular
width, while on the other hand, increased molecular polarizability enhances intermolecular
cohesive forces. Therefore, these two opposing effects are operating for series 1 and S2.
Figure 2. Structurally similar homologous series.

82
D. M. Suthar and A. V. Doshi
In such a case of molecular broadening or widening, the resultant net magnitudes of
intermolecular cohesion depend upon the predominating effect [7]. Series S1 being linear,
the intermolecular distance is smaller, and hence the intermolecular anisotropic forces
of attraction are relatively more than the isomeric series 1 of the present investigation,
which causes lamellar packing of molecules in their crystal lattices and causes sliding
layered arrangement of molecules in a floating condition under the influence of heat. The
absence of smectogenic character in series 1 indicates the absence of lamellar packing
due to intermolecular widening, which reduced intermolecular cohesive forces. The para-
substituted –NO2 and –OCH3 end groups of series 1 and series S2 are respectively bonded
with the phenyl ring in which nitrogen and oxygen atoms are directly linked with the
carbon atom of the phenyl ring. The electronegativity of oxygen atom is greater than the
¨
¨
nitrogen atom. Therefore, C O bond polarity will be greater than the C N bond polarity,
and hence the ratio of the molecular polarity to polarizability differs accordingly. Thus,
lamellar packing of molecules in case of series S2 is supported whereas it is not facilitated
in the novel series 1.
Conclusions
(
(
(
1) The novel series 1 is predominantly nematogenic without exhibition of smecto-
genic character.
2) Lamellar packing of molecules is facilitated more by –OCH3 terminal than –NO2
in equishaped molecules.
3) The group efficiency order derived for smectic and nematic on the basis of thermal
stability are as under.
Nematic: –NO2 > –NO2 > –OCH3
(
(
nonlinear) (linear)
S1) (S2)
Smectic: –OCH3 > –NO2 > –NO2
(
(
linear)(nonlinear)
S2) (S1) (1)
(
4) Molecular rigidity and flexibility depend upon the molecular shape, size, polarity
of terminal end group, and electron–electron interactions, and facilitates or hinders
the mesophase formation accordingly.
Acknowledgments
The authors give thanks to the Principal Dr. R. R. Shah and the head of chemistry de-
partment Dr. R. B. Patel to permit and cooperate for research work with the permission of
college management. Also, thanks are due to the Vaibhav Laboratory and head of chemistry
department of S. P. T. Science college, Godhra for their valuable cooperation to facilitate
analytical services and microscopic observations, respectively.
References
[
[
[
1] Marcos, M., Omenat, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Mater., 4, 285.
2] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
3] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & McDonnell, D. G. (1993). Liq. Cryst., 15,
123.

Novel Liquid Crystalline Nitro Benzoyl
83
[
4] (a) Dave, J. S., & Vora, R. A. (1970). Liquid Crystals and Ordered Fluids, Plenum Press: New
York, p. 477; (b) Vogel, A. I. (1989): Vogel’s Textbook of Practical Organic Chemistry, 4th ed.,
Longman Group Ltd.: Singapore.
[5] (a) Chauhan, M. L., Pandya, R. N., & Doshi, A. V. (2011). Mol. Cryst. Liq. Cryst., 548, 228–234;
(b) Doshi, A. V., & Makwana, N. G. (2011). Mol. Cryst. Liq. Cryst., 548, 220–227; (c) Patel,
R. B., Patel, V. R., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 3–9; (d) Doshi, A. V.,
Odedara, D. A., & Patel, R. B. (2012). Mol. Cryst. Liq. Cryst., 552, 97–103; (e) Bhoya, U. C.,
Vyas, N. N., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104–110.
6] (a) Patel, V. R., & Doshi, A. V. (2010). Derpharma Chemica, 2(6), 429–436; (b) Patel, R. B., &
Doshi, A. V. (2011). Derpharma Chemica, 3(2), 147–155.
[
[
7] Gray, G. W., & Windsor, P. A. (1974). Liquid Crystals and Plastic Crystals, Vol. 1., Chap. 4.
Ellis Horwood: Chichester, UK.
[
[
8] Suthar, D. M., & Doshi, A. V. (April 2012). Derpharma Chemica, 4(2), 813–818.
9] Chauhan, H. N., & Doshi, A. V. (2012). Synthesis of novel ethylene derivatives of liquid crys-
ꢀ
ꢀꢀ
tal properties in a homologous series α-3-[-4 -n–alkoxy cinnamoyloxy] phenyl β-4 -methoxy
benzoyl ethylenes. Mol. Cryst. Liq. Cryst. 569, 33–39.