The relation between mesomorphism and molecular structure of a novel azoester series involving laterally substituted chloro groups

Article abstract of DOI:10.1080/15421406.2014.939598

A novel azoester homologous series 4-(4'-n-alkoxy benzoyloxy) phenyl azo 2',6'-dichloro benzene is synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal behavior of a substance with reference to steric hindrance. The novel homologous series consists of twelve homologues. Mesomorphism commences from the heptyloxy homologue and continues up to the hexadecyloxy homologue as a monotropic nematic without the exhibition of any smectogenic characteristics. Transition temperatures were determined by an optical polarizing microscopy equipped with a heating stage. Transition curves of the phase diagram behave in a normal manner. The isotropic-nematic transition curve shows an odd-even effect in the very short range of temperature. The texture of nematic mesophase is threaded. Analytical and spectral data support the molecular structures of the homologues. Thermal stability is very low and the degree of mesomorphism is poor. Thus novel series is of low melting type and nematogenic only in a monotropic manner. Mesomorphic properties of the present, novel series are compared with structurally similar other known series.

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The Relation Between Mesomorphism
and Molecular Structure of a Novel
Azoester Series Involving Laterally
Substituted Chloro Groups
R. H. Mahetaa, G. N. Bholaa, D. L. Nameraa & U. C. Bhoyaa
a Department of Chemistry, Saurashtra University, Rajkot, Gujarat,
India
Published online: 26 Feb 2015.
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To cite this article: R. H. Maheta, G. N. Bhola, D. L. Namera & U. C. Bhoya (2015) The Relation
Between Mesomorphism and Molecular Structure of a Novel Azoester Series Involving Laterally
Substituted Chloro Groups, Molecular Crystals and Liquid Crystals, 607:1, 104-113, DOI:
10.1080/15421406.2014.939598
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Mol. Cryst. Liq. Cryst., Vol. 607: pp. 104–113, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.939598
The Relation Between Mesomorphism
and Molecular Structure of a Novel Azoester Series
Involving Laterally Substituted Chloro Groups
R. H. MAHETA,∗ G. N. BHOLA, D. L. NAMERA,
AND U. C. BHOYA
Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
A novel azoester homologous series 4-(4ꢀ-n-alkoxy benzoyloxy) phenyl azo 2ꢀꢀ,6ꢀꢀ-
dichloro benzene is synthesized and studied with a view to understand and establish the
effects of molecular structure on liquid crystal behavior of a substance with reference to
steric hindrance. The novel homologous series consists of twelve homologues. Mesomor-
phism commences from the heptyloxy homologue and continues up to the hexadecyloxy
homologue as a monotropic nematic without the exhibition of any smectogenic charac-
teristics. Transition temperatures were determined by an optical polarizing microscopy
equipped with a heating stage. Transition curves of the phase diagram behave in a
normal manner. The isotropic-nematic transition curve shows an odd-even effect in the
very short range of temperature. The texture of nematic mesophase is threaded. Ana-
lytical and spectral data support the molecular structures of the homologues. Thermal
stability is very low and the degree of mesomorphism is poor. Thus novel series is of low
melting type and nematogenic only in a monotropic manner. Mesomorphic properties
of the present, novel series are compared with structurally similar other known series.
Keywords Liquid crystal; mesomorphism; monotropy; nematic; sematic
Introduction
Benzoic and cinnamic acid derivatives are bioactive molecules [1] used for pharmaceutical
and medicinal [2, 3] preparations. Their derivatives of a liquid crystal nature are useful
in a variety of applications [4, 5]. Azoester types of mesomorphic substances are useful
to manufacture decorative articles which change their colors with frequencies of exposed
radiations and are sensitive to visible light [6]. The present investigation is planned with a
view to understanding and establishing the effects of molecular structure on liquid crystal
prosperities, [7–9] particularly in the isomeric homologous series of a mesogenic nature.
The presently proposed molecules of the azoester series consist of three phenyl rings bridged
through COO and N N groups, which will act as the rigid core of molecule, and an
OR terminal end group and two laterally substituted chloro groups closet to the N N
central group, which will act the flexible [10–12] part of molecule. Thus, the effects of
∗Address correspondence to R. H. Maheta, Department of Chemistry, Saurashtra University,
Rajkot-360005, Gujarat, India. E-mail: maheta rupali@yahoo.com
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
104

Relation Between Mesomorphism and Molecular Structure
105
molecular structure, and in particular the steric hindrance of two chloro groups, on liquid
crystal behavior can be studied.
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated by suitable alkylating agents by the modified method
of Dave and Vora [13]. n-Alkoxy benzoic acids were converted to the corresponding n-
alkoxy benzoyl chlorides (A) using thionyl chloride by an established method [14]. Azo
dye, 4-hydroxy phenyl azo-2ꢀ6ꢀ-dichlorobenzene (B) (M.P. = 76◦C) was prepared by a
diazotization method [14]. Components (A) and (B) were condensed in dry cold pyridine
by a known method [15]. The final azo-ester homologues of the novel series were decom-
posed, filtered, washed, dried, and purified until they gave constant transition temperatures.
Transition temperatures were determined on an optical polarizing microscope, equipped
with a heating stage. The chemicals required for the synthesis viz. 4-hydroxy benzoic
acid, alkylating agents R-X, 2,6-dichloro aniline, phenol, thionyl chloride, KOH, methanol,
ethanol, etc. were used as received except solvents which were purified prior to use.
Synthetic route to the series is outlined in scheme 1.
Characterization
Representative members of a novel series were characterized by elemental analysis
1
(Table 1), Infrared spectroscopy, HNMR spectroscopy, and mass spectroscopy. Micro-
analysis was performed on Perkin-Elmer PE 2400 CHN analyzer. IR spectra were recorded
1
on Shimadzu FTIR-8400, HNMR spectra were recorded on Bruker spectrometer using
DMSO-d6 as solvent and Mass spectra were recorded on Shimadzu GC-MS Model No.
QP-2010. The mesogenic behavior of the homologue derivatives were observed through
polarizing microscopy. The textures of nematogenic mesophase were determined by a
miscibility method.
Analytical Data
Spectral Data
1H NMR in ppm for Methyloxy Derivative
4.17 (s, 3H, OCH3), 7.15–7.17 (d, 2H, Ar H), 7.44–7.48 (t, 1H, Ar H), 7.57–7.59 (d,
2H, Ar H), 7.66–7.68 (q, 2H, Ar H), 8.04–8.06 (d, 2H, Ar H), and 8.06–8.13 (d, 2H,
Ar H).
1H NMR in ppm for Propyloxy Derivative
0.79–0.82 (t, 3H, CH3), 1.77–1.80 (m, 2H, CH2), 3.94–3.97 (t, 2H, OCH2), 6.91–6.94
(d, 2H, Ar H), 7.11–7.15 (t, 1H, Ar H), 7.33–7.36 (m, 4H, Ar H), 7.97–7.98 (d, 2H, A-
H), and 7.99–8.00 (d, 2H, Ar H).
1H NMR in ppm for Octayloxy Derivative
0.81–0.84 (t, 3H, CH3), 1.18–1.28 (m, 10H, 5 CH2), 2.10–2.25 (q, 2H –CH2),3.97–4.00
(t, 2H, OCH2), 6.91–6.93 (d, 2H, Ar H), 7.11–7.13 (t, 1H, Ar H), 7.33–7.36 (m, 4H,
Ar H), 7.98–8.00 (d, 2H, Ar H), and 8.09–8.11 (d, 2H, Ar H).

106
R. H. Maheta et al.
Scheme 1. Synthetic route to the novel series.
IR in cm−1 for Pentyloxy Derivative
2874, 2960 (C H Str. of ( CH2 )n group of OC5H11), 3080 (C H str. Of Ar. ring),
1726 (C O str. Of COO gp), 1606 ( N N str.), 1427, 1510 (C C str. Of Ar. ring),
1168 (C O str. of COO gp), 1143 (C O C str.), and 761 (C Cl Str. m-disub. Ar.
ring).

Relation Between Mesomorphism and Molecular Structure
107
Table 1. Elemental analysis for (1) butyloxy, (2) decyloxy, and (3) tetradecyloxy derivatives
Elements % found Elements % calculated
Sr. no.
Molecular formula
C
H
N
C
H
N
1
2
3
C23H20Cl2N2O3
C29H32Cl2N2O3
C33H40Cl2N2O3
62.20
65.98
67.84
4.48
6.06
6.71
6.28
5.16
4.72
62.31
66.03
67.92
4.55
6.11
6.91
6.32
5.31
4.80
IR in cm−1 for Dodecyloxy Derivative
2949 (C H str. Of Ar. ring), 2862, 2916 (C H str. Of ( CH2 )n gp of OC12H25), 1728
(C O str. Of COO gp), 1604 ( N N str.), 1425, 1506 (C C str. Of Ar. ring), 1166,
1199 (C O str. Of COO gp), 1072 (C O C str.), and 761 (C Cl Str. m-disub. Ar.
ring).
IR in cm−1 for Hexadecyloxy Derivative
3076 (C H str. Of Ar. ring), 2860, 2916 (C H str. Of ( CH2 )n gp of OC16H33), 1735
(C O str. Of COO gp), 1608 ( N N str.), 1427, 1506 (C C str. Of Ar. ring), 1166,
1197 (C O str. Of COO gp), 1145 (C O C str.), and 684 (C Cl Str. m-disub. Ar. ring).
Mass of Ethyloxy Derivative
m/z (rel.int%): 414 (M)+, 149, 121, 93, 65, and 44.
Mass of Hexyloxy Derivative
m/z (rel.int%): 470 (M)+, 205, 121, 93, 65, 44
Mass of Heptyloxy Derivative
m/z (rel.int%): 484 (M)+, 219, 121, 93, 57, 43
Texture by Miscibility Method
• Octyloxy derivative-nematic-threaded
• Tetradecyl derivative-nematic-Schlieren
Result and Discussion
Azo dye 4-hydroxy phenyl azo 2ꢀ, 6ꢀ-dichlorobenzene is a nonliquid crystal (NLC) com-
pound (m.p. 76◦C). The mesomorphic property is induced on linking it with 4-n-alkoxy
benzoic acid individually through their acid chlorides in pyridine at low temperature. The
azo ester derivatives formed exhibit mesomorphism as a monotropic nematic phase from
the heptyloxy homologue. A phase diagram showing phase behavior is shown (Fig. 1) for
the transition and melting temperatures (Table 2) as determined from a polarizing micro-
scope equipped with a heating stage, versus the number of carbon atoms present in n-alkyl

108
R. H. Maheta et al.
Figure 1. Phase behavior of series.
chain of the left n-alkoxy terminal end group. The phase diagram consists of two tran-
sition curves, a solid-isotropic transition curve and an isotropic-nematic transition curve.
The solid-isotropic transition curve follows a zigzag path of rising and falling values in
a normal manner. An isotropic-nematic transition curve rises from the heptyloxy to the
Table 2. Transition temperatures in ◦C
Transition temperature in ◦C
Compound no.
R = n-alkyl group CnH2n+1
Sm
N
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
95.8
123.9
100.0
90.8
89.6
84.2
69.7
84.1
69.0
86.9
88.1
66.1
—
(46.4)
(52.7)
(56.0)
(55.8)
(82.4)
(45.4)
10
11
12
() indicate monotropy.

Relation Between Mesomorphism and Molecular Structure
109
tetradecyloxy homologue and then descends as series is ascended until the hexadecyloxy
homologue, which reveals a very narrow and shorter odd-even effect. The curves for odd
and even homologues are extrapolated [16–18]. Keeping in view the trend of curvature of a
transition curve to magnify the odd-even effect and to predict the hypothetical monotropic
transition temperature for the butyloxy (42◦C), the pentyloxy (34◦C), and the hexyloxy
(48◦C) homologues, which are actually not liquid crystalline. Transition curves for odd
and even members of the series merge into each other at the nonyloxy homologue and
then a single curve prolongs for higher homologues and beyond the nonyloxy homologue.
Analytical and spectral data confirmed the structures of molecules. The textures of the
nematic mesophase are of the threaded type. The nematogenic phase length below the
isotropic temperature is relatively very short (1–2◦C) depending upon the rate of cooling.
Smectogenic character is totally absent. Thus the novel homologous series 4-(4ꢀ-n-alkoxy
benzoyloxy) phenylazo-2ꢀꢀ, 6ꢀꢀ-dichloro benzenes is nematogenic only with a low thermal
stability and transition temperatures as well as a late commencement of mesomorphism.
The mesomorphism of the series from homologue to homologue varies with changing
number of carbons in the n-alkyl chain. The odd-even effect diminishes as the series is as-
cended. The nonmesomorphic behavior of methoxy to hexyloxy homologues is attributed
to their inability to resist exposed thermal vibrations and their inner high crystalline ten-
dency, which depends upon the unsuitable magnitudes of anisotropic forces of attraction as
a consequence of unfavorable molecular rigidity and flexibility from the steric hindrance of
the laterally substituted two chloro groups. Thus, the methoxy to hexyloxy homologues of
the presently investigated novel homologous series undergo abrupt breaking of their crystal
lattices which sharply transforms into isotropic liquid without passing through anisotropic
liquid state or mesomorphic state. Exhibition of mesomorphic behavior from and beyond
the heptyloxy homologue is attributed to the disalignment of azoester molecules at an angle
less than 90◦ with the plane of a floating surface; under the influence of externally applied
heat, resisting exposed thermal vibrations. Thus, suitable magnitudes of anisotropic forces
of intermolecular end to end attractions as a consequence of favorable molecular rigidity
and flexibility, which leads to the molecular floating tendency on the surface irreversibly
below isotropic temperature with statistically parallel orientational order, depend upon the
combined effects of the polarizabiltiy and intermolecular closeness. Hence, nematogenic
mesophase formation occurs monotropically for very few degrees of temperature based on
the rate of cooling. The missing of smectogenic character is attributed to the absence of
lamellar packing molecules and unsuitable magnitudes of extent of molecular noncopla-
narity, which hinders the sliding layered arrangement of molecules on heating the sample
substance to induce smectogenic mesophase either reversibly or irreversibly. The variation
of mesogenic behavior from homolog to homologue in the same series is attributed to the
sequentially added methylene units to the left n-alkoxy terminal end group. Low thermal
stability of few degrees of nematogenic monotropic mesophase formation indicates that
steric hindrance caused by the two lateral chloro groups do not facilitate parallel orienta-
tional order of the molecules to prolong the appearance of nematogenic mesophase. The
diminishing of odd-even effect in isotropic-nematic transition curve for higher homologues
is attributed to coiling or bending or flexing or coupling of n-alkyl chain with the major
axis of core structure [19]. The mesomorphic properties of presently investigated novel
homologues series 1 are compared with the structurally similar other known homologues
series X [20] and series Y [21] as shown in Figure 2.
It is clear from Figure 2, that homologues series 1, X and Y are isomeric with respect
to their molecular structure. The molecular rigidity induced by three phenyl rings and two
central bridges viz. COO and N N is identical for all the homologues series 1, X

110
R. H. Maheta et al.
Figure 2. Structurally similar homologous series.
and Y. Moreover the flexibility contribution by OR flexible terminal end group for the
same homologue of present series and each series (X and Y) chosen for comparison is
also identical. However, the molecular flexibility contributed by same two chloro groups
present in molecules of each series differs due to their positions of substitution on same
(series 1 and X) phenyl ring or different (series Y) phenyl rings which bears variations.
Thus, the combined effects of molecular rigidity and flexibility, which governs a phenom-
ena of mesomorphism will differ from series to series for the same homologue for the
varied suitable magnitudes of anisotropic forces of intermolecular end to end terminal and
lateral attractions irrespective of unchanged polarity of chloro group. Hence, mesomorphic
properties and the degree of mesomorphism vary from series to series under comparison.
Table 3 represents some properties like thermal stability, commencement of mesophase or
mesophases, exhibition of type of mesophase, early or late occurrence of the mesophase,
mesophase length, etc. as shown below.
Table 3 indicates the following.
Table 3. Average thermal stability in ◦C
Series
1
X
Y
Smectic-nematic
or Smetic-isotrepic
106.0
(C6–C16)
75.75
(C10–C16)
—
—
commencement of
smectic phase
C6
C10
Nematic-isotropic or
Isotropic-nematic
Few degrees
1–2
156.25
(C1–C16)
149.4
(C3–C16)
(C7–C16)
commencement of
nematic phase
C7
C1
C3

Relation Between Mesomorphism and Molecular Structure
111
• Isomeric series X and Y exhibit smectogenic character, while the present series1
does not.
• Homologous series 1, X and Y all exhibit nematogenic property.
• The present novel series 1 is monotropic nematic while series X and Y are enan-
tiotropic nematic.
• Smectic mesophase commence from the sixth and tenth carbon of n-alkyl chain in
X and Y series respectively, while it does not occur at all in series 1.
• The nematogenic mesophase commences from the very first member of series X,
form third member of series Y and from seventh member of series 1 of present
investigation.
• Series X and Y are predominantly nematogenic and partly smectogenic, while,
present series is only nematogenic.
In homologues series X and Y one of the chloro groups occupies the position as a right
handed terminal end group. The group polarity and polarizibility of -Cl is more than -H.
Moreover two -Cl groups of series 1 as 2ꢀꢀ,6ꢀꢀ-dichloro restricts the molecular flexibility due
to the positional status on the third phenyl ring as the closet neighbor of the N N central
bridge, as compared to the positional status of two chloro groups in case of series X and Y.
Thus, the molecules of series X and Y strongly resist exposed thermal vibrations to float
on the surface with the sliding layered arrangement as well as with the statistically parallel
orientational, two-dimensional orders within definite range of temperature in enantiotropic
manner. Thus, molecules of series X and Y exert relatively stronger intermolecular end
to end attractions and facilitate lamellar packing of molecules in their crystal lattices.
However relatively weaker magnitudes of anisotropic forces of intermolecular end to end
and lateral attractions by steric hindrance induces only monotropic nematic mesophase
formation for very small range of temperature for series 1. Early or late commencement of
smectic or nematic depends upon the extend of noncoplanarity [22] caused by the molecule
due to a differing positional status of the two chloro groups, either on the same or different
phenyl ring or rings. Thus, the varying molecular rigidity and/or molecular flexibility causes
varying thermal stabilization energies and hence, thermal stability for smectic and nematic
mesophase acquires variations. The variations of mesomorphic behavior from series to
series for the same homologue arises by changing part of a molecule either in number of
phenyl rings, central group or groups linking phenyl ring, or terminal or lateral group or
groups or the positional status of substitution of same functional group or groups on either
of the phenyl ring.
Conclusions
• The group efficiency order for smectic and nematic on the basis of (i) thermal
stability and (ii) early commencement of mesophase are as under.
i. Smectic: 3ꢀꢀ, 4ꢀꢀ-dichloro > 3-chloro, 4ꢀꢀ-chloro > 2ꢀꢀ, 6ꢀꢀ-dichloro
Nematic: 3ꢀꢀ, 4ꢀꢀ-dichloro > 3-chloro, 4ꢀꢀ-chloro > 2ꢀꢀ, 6ꢀꢀ-dichloro
ii. Smectic: 3ꢀꢀ, 4ꢀꢀ-dichloro > 3-chloro, 4ꢀꢀ-chloro > 2ꢀꢀ, 6ꢀꢀ-dichloro
Nematic: 3ꢀꢀ, 4ꢀꢀ-dichloro > 3-chloro, 4ꢀꢀ-chloro > 2ꢀꢀ, 6ꢀꢀ-dichloro
• Suitable magnitudes of molecular rigidity and flexibility inducing favorable mag-
nitudes of molecular entropy (ꢀS = ꢀH ) or restricted molecular randomness can
T
induce thermotropic mesomorphism.
• Slight variation in the molecular structure can alter a great deal of mesomorphic
behavior.

112
R. H. Maheta et al.
• Phenomina of mesomorphism is very sensitive and susceptible to a molecular struc-
ture of substance.
• Present novel homologous series is monotropic nematic and low melting type. Such
homologues on mixing with other suitable component, forming binary system can
yield LC material, useful at desired low or room temperature for the manufacture of
LC devices.
Acknowledgments
We thank the Department of Chemistry (DST-FIST Funded & UGC-SAP Sponsored),
Saurashtra University, Rajkot, for research work. Special thanks to National Facility for
Drug Discovery through New Chemical Entities (NCEs) for sample analysis. We are also
thankful to Dr. A. V. Doshi Ex. Principal M.V.M. Science and Home Science College
Rajkot, for his valuable cooperation and suggestions during present investigation as and
when needed.
References
[1] Kazuki, I. et al. (2013). Review, Molecules. Appl. Biomat. Liq. Cryst., 18, 4703–4717.
[2] Darshan, R., et al. (2013). Derpharma Chemica, 5(3), pp. 305–317.
[3] Talwee, I., Shah, S., Ramteke, V., & Syed, I. (2012). Liquid crystals pharmaceutical application:
A review. IJPRAS Int. Pharma. Res. Appl. Sci., 1(2), pp. 06–11.
[4] Gray, G. W. & Winsor, P. A. (1974). Liquid Crystals and Plastic Crystals, Vol. 1, Chap. 4. Ellis
Horwood Ltd., Chichester Halsted Press. A division of John Wiley and Sons. Inc.: New York,
London.
[5] Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals. Academic Press:
London.
[6] (a) Patel, V. R. & Doshi, A. V. (2010). Derpharma Chemica, 2(6), 429. (b) Doshi, A. V. &
Makwana, N. G. (2011). Mol. Cryst. Liq. Cryst., 548, 220. (c) Chauhan, B. C. & Doshi, A. V.
(2011). Derpharma Chemica, 3(1), 172–180. (d) Imrie, C. T. & Taylor, L. (1989). Liq. Cryst.,
6, 1.
[7] (a) Gray, G. W. (1958). In Steric Effects in Conjugated Systems. Gray, G. W. (Ed.), Hull,
Chemical Society: London. (b) Gray, G. W. & Jones, B. (1954). Mesomorphism and Chemical
Constitution Part-3, the effect of halogen substitution on the 4-Alkoxy Benzoic Acids. J. Chem.
Soc., 2556–2562.
[8] Demus, D. (1988). 100 years of liquid crystal chemistry. Mol. Cryst. Liq. Cryst., 165, 45–84.
[9] Demus, D. (1989). Plenary lectures 100 years of liquid crystal chemistry; Thermotropic liquid
crystals with conventional and unconventional Molecular Structure. Liq. Cryst., 5, p. 75, 110.
[10] Marcos, M., Omenat, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Mater., 4, 285.
[11] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
[12] Hird. M., Toyne K. J., Gray G. W., Day, S. E., & McDonnell, D. G. (1993). Liq. Cryst., 15, 123.
[13] Dave, J. S. & Vora, R. A. (1970). Liquid Crystal and Ordered Fluids, Johnson, J. F., & Porter,
R. S. (Eds.), Plenum Press: New York, p. 477.
[14] (a) Furnish, B. S., Hannaford, A. J., Smith, P. W. G., & Tatchell, A. R. (1989). Vogel’s Textbook
of Practical Organic Chemistry, 4th ed., Longman: Singapore. (b) Vogel, A. I. (1989). Textbook
of Practical Organic Chemistry. 5th ed., ELBS, Longman: London, pp. 946.
[15] (a) Ganatra, K. J. & Doshi, A. V. (1999). Proc. Ind. Acad. Sci. (Chem. Sci.), 4(11), 562. (b) Bhoya,
U. C. & Doshi, A. V. (2000). J. Inst. Chem. (India), 72 (Part-I).
[16] Trevadi, J. J., Bhoya, U. C., & Doshi, A. V. (2012). Mol. Crystl. Liq. Crystl., 552, 10–15.
[17] Joshi, N. N. & Doshi, A. V. (1993). J. Ind. Chem. Soc., 70, 807–809.
[18] (a) Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol. Crystl. Liq. Crystl., 552, 104–110.
(b) Lohar, J. M. & Doshi, A. V. (1993). Proc. Ind. Acad. Sci. (Chem. Sci.)., 105, 209–214.

Relation Between Mesomorphism and Molecular Structure
113
[19] Collings, P. J. & Hird, M. (1997). Introduction to Liquid Crystal Chemistry and Physics, Taylor
and Francis: New York.
[20] Chauhan, B. C. & Doshi, A. V. (2003). Ph. D. Thesis (unpublished work), Saurashtra University:
Rajkot.
[21] Chauhan, B. C. & Doshi, A. V. (2011). Pharma. Chemica., 3(1), 172–180.
[22] Chauhan, H. N., Vyas, N. N., & Doshi, A. V., (2013). Mol. Cryst. Liq. Cryst., 575, 96–103.