Synthesis and mesomorphism of novel liquid-crystalline isobutyl-p-(p-n- Alkoxy Cinnamoyloxy) cinnamates

Article abstract of DOI:10.1080/15421406.2011.591659

A new homologous series viz. Isobutyl-p-(p-n-alkoxy cinnamoyloxy) cinnamates consisting of 11 homologs has been synthesized with an isobutyl cinnamate end group and a further cinnamate moiety as a linking group. The methyl to butyl homologs are nonmesomorphic, and the pentyl to hexadecyl derivatives are enantiotropic nematogens without exhibition of any smectic phases. The average thermal stability for the nematic phase is 138.1C with a middle ordered melting point. The structures of the novel materials were confirmed by spectroscopic techniques. The liquid crystal phase type was determined by optical polarizing microscopy and all textures are of the threaded type. The mesomorphic behavior of the series is compared with a structurally similar homologous series.

Full text of DOI:10.1080/15421406.2011.591659

Mol. Cryst. Liq. Cryst., Vol. 552: pp. 3–9, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.591659
Synthesis and Mesomorphism of Novel
Liquid-Crystalline Isobutyl-p-(pꢀ-n-Alkoxy
Cinnamoyloxy) Cinnamates
R. B. PATEL,1,∗ V. R. PATEL,2 AND A. V. DOSHI3
1K.K. Shah Jarodwala Maninagar Science College, Gujarat University,
Ahmedabad, Gujarat, India
2Sheth P.T., Arts and Science College, Godhra, India
3MVM Science and Home Science College, Rajkot, Gujarat, India
A new homologous series viz. Isobutyl-p-(pꢀ-n-alkoxy cinnamoyloxy) cinnamates con-
sisting of 11 homologs has been synthesized with an isobutyl cinnamate end group
and a further cinnamate moiety as a linking group. The methyl to butyl homologs are
nonmesomorphic, and the pentyl to hexadecyl derivatives are enantiotropic nematogens
without exhibition of any smectic phases. The average thermal stability for the nematic
phase is 138.1◦C with a middle ordered melting point. The structures of the novel
materials were confirmed by spectroscopic techniques. The liquid crystal phase type
was determined by optical polarizing microscopy and all textures are of the threaded
type. The mesomorphic behavior of the series is compared with a structurally similar
homologous series.
Keywords Liquid crystals; mesomorphic; nematic
Introduction
The number of liquid crystals compounds consisted of rigid part as two or three phenyl rings
bridged through central bridge or bridges and flexible part as varying left polar terminal,
alkyl or alkoxy [1–12] end group keeping right terminal end group intact of fix polarity with
or without lateral substitution [5,8]. In continuation of the same, presently a homologous
series with two phenyl rings bridged through vinyl carboxylate linkage and isobutyl vinyl
carboxylate fixed end group with n-alkoxy as left terminal end group, is synthesized to
investigate the effect of varying molecular structure by varying molecular rigidity and
flexibility on mesogenic property.
The present investigation is planned with a view to establish and to understand the
effect of molecular structure on liquid crystalline behavior of a substance.
∗Address correspondence to R. B. Patel, K. K. Shah Jarodwala Maninagar Science College,
Gujarat University, Ahmedabad 380008, Gujarat, India. E-mail: roshanpatel770@gmail.com
3

4
R. B. Patel et al.
Experimental
Characterization
Some homologs as representative members of the series were selected for characterization
1
of their structures by IR and HNMR techniques. IR spectra were recorded on Perkin
Elmer spectrum GX and NMR were recorded using CDCl3 as solvent. Microanalysis
was performed on Perkin Elmer PE 2400 CHN analyzer as shown in Table 1. Transition
and melting temperatures and liquid crystal properties were investigated by using optical
polarizing microscopy.
Synthesis
p-Hydroxy cinnamic acid was synthesized from p-hydroxy benzaldehyde and malonic acid,
and the hydroxy group is alkylated by suitable corresponding alkylating agent. Constituent
chemicals were used as received.
Scheme 1. Synthetic route to the series.
p-Hydroxy isobutyl cinnamate (A) was synthesized by an established method of es-
terification [6]. p-n-Alkoxy cinnamic acids and p-n-alkoxy cinnamoyl chlorides were syn-
thesized by a modified method of Dave and Vora [3]. The eleven esters of the series were
synthesized by condensing equimolar amounts of the p-n-alkoxy cinnamoyl chloride and
p-hydroxy isobutyl cinnamate (A) in pyridine. The esters were crystallized from alcohol
until constant transition temperatures were obtained.

Novel Liquid-Crystalline Cinnamoyloxy Cinnamates
5
Table 1. Elemental analysis for decyloxy and dodecyloxy derivatives
Elements% found (% calculated)
Molecular formula
C
H
C32H42O5
C34H46O5
76.02 (75.89)
76.69 (76.40)
8.30 (8.45)
8.87 (8.61)
Analytical Data
NMR: in ppm. Hexadecyl. 1.25 – CH3, 3.98 – O CH2, 4.01 – O CH2 of
O CH2 CH2 CH3, 4.44 and 4.02 – CH CH , 6.89, 6.92, 8.00, and 8.03 –p-sub.phenyl
two p-sub.benzene, 7.24 and 8.02 – p-subphenyl two p-subbenzene,
Octyl. 0.83 CH3, 1.21 CH2, 2.49 OCH2 CH2 , 3.5 O CH2 of COOC4H9,
3.31 – O CH2 of C8H17, 4.41 – CH CH , 6.80 and 6.83 two p-subphenyl ring, 7.75 and
7.78, two p-subphenyl ring.
1
IR in cm− . Tetradecyl. 2850 alkyl group, 1080,1150, and 1700 COO group, 660
cis CH CH group, 860 p-subphenyl ring, 3000 aromatic ring, 750 polymethylene of
C14H29
Hexyl. 2850.0 alkyl group, 1050,1150, and 1710 COO group, 660 cis CH CH
group, 850 p-subphenyl ring, 3000 aromatic ring, 750 polymethylene of C6H13,
Results and Discussion
The homologous series isobutyl p-(pꢀ-n-alkoxy cinnamoyloxy) cinnamates is presently
synthesized and studied for 11 homologs, which were evaluated for their mesomorphic
characteristics. The transition temperatures of the homologous series under discussion are
recorded in Table 2. The pentyl to hexadecyl members of the series showed a threaded
or Schlieren texture on heating the crystalline solid reversibly on heating and cooling
to isotropic liquid, while the methyl to butyl homologs are nonmesomorphic. Thus, the
Table 2. Transition temperatures of the series
Compound no.
R = CnH2n+1
Sm.
Nm.
I
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
8
10
12
14
16
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
132.0
97.0
110.0
105.0
115.0
110.0
105.0
200.0
210.0
144.0
125.0
165.0
136.0
125.0
130.0
142.0
143.0
129.0
10
11

6
R. B. Patel et al.
Figure 1. Structurally similar homogolous series.
pentyl to hexadecyl homologs are enantiotropically nematogenic without exhibition of any
smectogenic character.
Table 2 shows the dependence of transition temperatures on the number of carbon
atoms in the terminal chain.
The average thermal stability and other mesomorphic behavior of titled homologous
series 1 are compared with the structurally similar homologous series A and series B, as
shown in Fig. 1.
The solid-nematic or isotropic transition curve follows a zigzag path of rising and
falling tendency as the series is ascended. The plot of the phase diagram (Fig. 2) shows
the absence of the odd–even effect in the nematic-isotopic transition curve, and then it falls
up to the eighth homolog and then it rises up to the 14th homolog and finally falls off at
the hexadecyl homolog by 14o. Thus, the behavior of nematic-isotropic transition curve
of the present study suggests that, enthalpy change of the homolog from fifth to eighth
homolog decreases and then increases up to the 14th homolog and then finally decreases.
Hence, a low and a high value of enthalpy correspond to a low and a high amount of heat
energy requirement (low and high temperature) from surrounding to system. The opposing
effects to the molecular geometry of an isobutyl terminal group operates (1) an effect due to
widening of the molecule causing a reduction in the intermolecular adhesion by increasing
the intermolecular distance and on the other hand (2) increased molecular width, increases
molecular polarizability causing an increase in the intermolecular adhesion. Thus, closeness
of molecular packing depends upon the net resultant intermolecular forces of attractions,
which depend upon the predominating effect out of two opposing effects (1) and (1). In the
present study, the latter effect is a predominating effect. Table 3 summarizes the average
thermal stabilities and molecular structure of the present series and other structurally related
series A [6(i)] and series B [6(ii)] chosen for comparative study.
The molecular geometry of all the homologous series under comparison consists of
two phenyl rings linked through a carboxy or a vinyl carboxy ester central linkage with n-
alkoxy group at the left terminus and CH2 CH (CH3)2 and CH2 CH2 CH2 CH3
at the right terminus for series [(1) and (A)] and (B) respectively. The variation in the
mesomorphic characteristics can be attributed to the combined effect of the presence of

Novel Liquid-Crystalline Cinnamoyloxy Cinnamates
7
Table 3. Average thermal stabilities in ◦C
Series
(1)
(A)
(B)
Nematic isotropic
138.1 (C5–C16) 110.0 (C6–C14) 140.0 (C5–C16)
Commencement of nematic phase
Smectic isotropic
Commencement of smectic phase
C5
—
—
C6
—
—
C5
101.0 (C10–C12)
C10
Figure 2. Homologous series: Isobutyl-p- [pꢀ n-alkoxy cinnamoyloxy] cinnamates. Phase behavior
of series 1.

8
R. B. Patel et al.
central ester and different right terminal groups, which have different molecular rigidity and
flexibility related to molecular polarity and polarizibility for the formation of mesophase
[13,14].
On comparing the mesomorphic characteristics of series (1) with series A, it is ob-
served that, the homologs of both the series differing in respect of central bridge only
are enantiotropically nematogenic. Introduction of a polar isobutyl group at the terminal
position in series 1 enable considerable and significant anisotropic [1] forces of attraction
of suitable magnitude for pentyloxy to hexadecyloxy homologs, which serve to stabilize
statistically parallel orientational order of molecules by end-to-end attractions conducive to
the formation of a nematogenic mesophase. This effect persists even in the homologs with
long n-alkoxy groups. Comparison of series 1 with series B indicates that the series 1 has
an isobutyl group at the right terminal with a vinyl carboxy central group while series B has
n-butyl terminal group with a carboxy central group. The flexible straight chained n-butyl
group with COO central group in series B adds the formation of smectic mesophase
due to enhanced lateral attraction in addition to terminal attractions, which facilates lamel-
lar packing required for the formation of smectic mesophase (1). Thus, series B exhibits
smectogenic character in addition to nematogenic character. The nematic thermal stability
of series A being lower than series B is understandable because of the difference in terminal
attractions arising from the isobutyl and butyl groups.
Conclusion
The study suggests that a polar substituent at a terminal position in a homologous series
with present molecular geometry gives rise to the exhibition of a nematogenic mesophase.
Moreover, the presence of a vinyl carboxylate unit at a central and/or a terminal position
favorably induce a nematogenic mesophase.
Acknowledgment
The authors thank the head, chemistry department, Dr. N. N. Vyas and his colleague Dr.
M. L. Chauhan for their valuable co-operation in the work. The authors are also thankful to
the Authority of Uma laboratory, Vadodara, Vaibhav laboratory, Ahmedabad, and National
Salt and Marine Research institute, Bhavnagar for analysis of samples.
References
[1] (a) Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals, Acadmic Press:
London (b) Gray, G. W. and Winsor, P. A. (1974). Liquid Crystals and Plastic Crystals, Eillis
Harwood: Chichester.
[2] Collings, P. J. and Hird, M. (1997). Introduction to Liquid Crystals Chemistry and Physics,
Taylor and Francis: New York.
[3] Dave, J. S. and Vora, R. A. (1970). Liquid Crystals and Ordered Fluids, Plenum Press: New
York.
[4] Vogel, A. I. (1989). Textbook of Practical Organic Chemistry, Longmann: London.
[5] (a) Lohar, J. M. and Doshi, A. V. (1992). Acta Ciencia Indica, XVIII, 245 (b) Doshi, A. V. and
Makwana, N. G. (2008). J. Ind. Chem. Soc., 85, 263 (c) Doshi, A. V. and Prajapati, H. R. (2007).
J. Ind. Chem. Soc., 84, 258 (d) Doshi, A. V. and Prajapati, H. R. (2009). J. Ind. Chem. Soc., 86,
470 (e) Doshi, A. V. and Ganatra, K. (1999). J. Proc. Ind. Acad. Sci. (Chem. Soc.), 11, 563.
[6] (a) Chauhan, M. L. and Doshi, A. V. (2010). J. Inst. Chemists (India), 82, 1 (b) Chauhan, M. L.
and Doshi, A. V. (2008). Acta Ciencia Indica, XXXIV, 1.

Novel Liquid-Crystalline Cinnamoyloxy Cinnamates
[7] Imrie, C. T. and Taylor, L. (1989). Liquid Crystals, 6, 1.
9
[8] Berdage, P., Bayle, J. P., Ho, M. S., and Fung, B. M. (1993). Liquid Crystals, 14, 667.
[9] Lohar, J. M. and Dave Jayrang. (1983). Mol. Cryst. Liq. Cryst. (Eng.), 103(1–4), 181.
[10] Lohar, J. M. and Dave Jayrang. (1983). Mol. Cryst. Liq. Cryst. (Eng.), 103(1–4), 143.
[11] Baumeister, U., Kosterkiewiez, Z., Hartungs, H., Weissflos, W., and Demus, D. (1990). Liquid
Crystal, 7, 241.
[12] Chauhan, M. B., Bhoi, D. K., Machhar, M. T., Solanki, D. K., and Solanki, Dhaval. (2010). Der
Pharma Chemica, 2(4), 30–37.
[13] (a) Doshi, A. V. and Patel, V. R. (2010). Der Pharma Chemica, 2(6), 429–436 (b) Doshi, A. V.
and Patel, R. B. (2011). Der Pharma Chemica, 3(1), 72, 328, 538, 557.
[14] Doshi, A. V. and Chauhan, B. C. (2011). Der Pharma Chemica, 3(1), 172.