Determination of latent mesogenic behavior in nonmesogenic compounds by extrapolation method

Article abstract of DOI:10.1080/15421406.2011.604590

A homologous series of 8-(4-n-alkoxybenzoyloxy) quinolines were synthesized by established methods [5,6]. On evaluation by optical microscopy, none of the homologues were found to exhibit mesogenic behavior even in the monotropic condition. Then, each homologue (B) was mixed with a liquid crystal component (A) and binary systems were studied by optical microscopy. Solid-mesomorphic or isotropic-nematic transition temperatures of binary mixtures were determined and plotted to obtain the phase diagram for transition temperatures versus percentage composition of component (A). The nematic-isotropic transition curve was extrapolated to zero mole percentage of component (A) (100%B) to determine the latent transition temperature (LTT) of each nonmesomorphic homologue. The number of carbon atoms in the n-alkyl chain of each homologue versus LTT is plotted and a phase diagram is obtained. The isotropic-nematic transition curve behaves in a normal manner like a curve behaving for a typical nematogenic homologous series, including odd-even effects in its phase diagram. This method is useful to determine the probable temperature at which a nonmesogenic substance can show mesogenic behavior, provided a suitable condition is applied. Also, it is useful to correct the LTT of a homologue from the mesomorphic-isotropic transition curve.

Full text of DOI:10.1080/15421406.2011.604590

Mol. Cryst. Liq. Cryst., Vol. 552: pp. 104–110, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.604590
Determination of Latent Mesogenic Behavior
in Nonmesogenic Compounds by Extrapolation
Method
U. C. BHOYA,1 N. N. VYAS,2 AND A. V. DOSHI3,∗
1Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
2Sheth P.T. Arts and Science College, Godhra, Gujarat, India
3Matushri Virbaima Mahila Science and Home Science College, Rajkot,
Gujarat, India
A homologous series of 8-(4ꢀ-n-alkoxybenzoyloxy) quinolines were synthesized by es-
tablished methods [5,6]. On evaluation by optical microscopy, none of the homologues
were found to exhibit mesogenic behavior even in the monotropic condition. Then, each
homologue (B) was mixed with a liquid crystal component (A) and binary systems
were studied by optical microscopy. Solid–mesomorphic or isotropic–nematic transi-
tion temperatures of binary mixtures were determined and plotted to obtain the phase
diagram for transition temperatures versus percentage composition of component (A).
The nematic–isotropic transition curve was extrapolated to zero mole percentage of
component (A) (100%B) to determine the latent transition temperature (LTT) of each
nonmesomorphic homologue. The number of carbon atoms in the n-alkyl chain of each
homologueversus LTT is plotted andaphasediagram is obtained. Theisotropic–nematic
transition curve behaves in a normal manner like a curve behaving for a typical nemato-
genic homologous series, including odd–even effects in its phase diagram. This method
is useful to determine the probable temperature at which a nonmesogenic substance can
show mesogenic behavior, provided a suitable condition is applied. Also, it is useful to
correct the LTT of a homologue from the mesomorphic–isotropic transition curve.
Keywords Liquid crystal mixtures; mixed mesomorphism; monotropy; nematic;
smectic
Introduction
The liquid crystal or mesomorphic state of matter is a physically distinct state of matter,
intermediate to the crystalline solid and the isotropic liquid. Theoretically, all substances
should exhibit this unique intermediate state in addition to normal states of matter, viz., solid,
liquid, and gas. Sometimes, unexpectedly on synthesis of a new homologous series, all the
novel compounds are nonmesomorphic. In the present work, an attempt is made to search for
the latent ability of non-liquid crystal component (homologue), i.e., probable temperature
at which a non-liquid crystal substance can exhibit liquid crystal behavior [latent transition
temperature (LTT)] by extrapolation of mesomorphic–isotropic transition curve at 100 mole
percent of non-liquid crystal component of a binary system. The transition points might
∗Address correspondence to A. V. Doshi, Matushri Virbaima Mahila Science and Home Science
College, Kalawad Road, Rajkot 360007, Gujarat, India. E-mail: arvindbhaidoshi@yahoo.in
104

Latent Mesogenic Behavior in Nonmesogenic Compounds
105
lie below its melting point. Thus, a search for their virtual transition temperature is of
importance.
Experimental
Synthesis
Synthesis of 8[4ꢀ-n-Alkoxybenzoyloxy] Quinolines. p-n-Alkoxy benzoic acids were syn-
thesized by the modified method of Dave and Vora [2]. p-n-Alkoxy benzoic acids were
refluxed with freshly distilled excess of thionyl chloride till evolution of sulfur dioxide gas
ceases. Excess of thionyl chloride was distilled off. The p-n-alkoxy benzoyl chloride was
directly treated with an ice-cooled solution of 8-hydroxy quinoline in pyridine, dropwise.
The resulting reaction mixture was warmed through constant shaking for about half an
hour. Then, it was kept overnight. The next day, the product was decomposed and allowed
to settle with the formation of the ester. Final products were filtered, washed, dried, and
purified by alcohol crystallization [4–13].
Characterization
Products were characterized by hot stage polarizing optical microscopy to determine the
transition and melting temperatures as recorded in Table 1. Some representative samples
were selected for elemental analysis as recorded in Table 2.
Twelve binary systems consisting of various components, 12 homologues of non-
mesomorphic homologous series 8(4’-n-alkoxybenzoyloxy) quinolines, and a common
component (A) 4-n-octyloxy benzoic acid [Sm.101.0◦C, Nm.108.0◦C, and Iso.148.0◦C]
are thoroughly mixed by the method of [6,8,12,13] Dave and Lohar [7], Lohar and Doshi
[5], and Doshi and Ganatra [9]. 4-n-Octyloxy benzoic acid was prepared by the modified
method of Dave and Vora [2].
Table 1. Transition temperatures of 8[4ꢀ-n-alkoxybenzoyloxy] quinolines
Transition temperatures in ◦C
n-alkyl group-
Sr. No.
CnH2n+1
Smectic
Nematic
Isotropic
1
2
3
4
5
6
7
8
9
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
180.0
132.0
117.0
103.0
112.0
93.0
76.0
84.0
82.0
88.0
Decyl
10
11
12
Dodecyl
Tetradecyl
Hexadecyl
91.0
88.0

106
U. C. Bhoya et al.
Table 2. Combustion analysis data
% Theoretically
% Observation
H
Sr. No.
R = n-alkyl chain
C
H
N
C
N
1
2
3
C18H15O3N
C22H23O3N
C30H39O3N
73.72
75.64
78.09
5.12
6.59
8.45
4.78
4.01
3.03
73.62
75.55
78.01
5.16
6.50
8.38
4.84
4.04
3.10
Transition and melting temperatures of all the binary systems [A+B1,B2,–B12] and
pure components (Table 1) were observed through hot-stage polarizing optical microscopy.
Results and Discussion
The geometrical structure and shape of the ester homologous series 8[4ꢀ-n-
alkoxybenzoyloxy] quinolines determine that they have the potential to exhibit liquid
crystal mesophases. However, all homologues of the series under discussion were found to
be nonmesogenic.
The LTTs of all the homologues determined by extrapolation method are recorded in
Table 3. The phase diagrams of some selected binary systems are represented in Figs. 2
and 3. Transition temperatures derived from each phase diagram of the binary system
(B1–B12) are shown in Fig. 4.
The LTT of each homologue is plotted versus the number of carbon atoms in the
n-alkyl chain of left n-alkoxy terminal group. The phase diagram obtained is represented
in Fig. 1. Careful observation of the phase diagram of the series (Fig. 1) indicates that
the solid–isotropic transition curve shows descending tendency as the series is ascended.
The curve falls up to fourth homologue and then a rising and falling tendency is observed
in a zigzag manner. The isotropic–nematic transition curve falls, rises, and then falls in a
normal manner like a mesomorphic homologous series. The isotropic–nematic transition
Table 3. Latent transition temperatures
Sr. No.
Homologue
LTT in ◦C
1
2
3
4
5
6
7
8
9
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
126.5
128.0
80.0
44.0
56.0
52.0
55.0
68.0
79.0
83.0
83.0
60.0
10
11
12

Latent Mesogenic Behavior in Nonmesogenic Compounds
107
Figure 1.
curve shows odd–even effect like the mesomorphic series. The isotropic–nematic transition
curves for odd and even homologues merge into each other at the 10th homologue.
p-n-Alkoxy benzoic acids are mesomorphic (liquid crystal) in nature, because the
dimerised p-n-alkoxy benzoic acid has two phenyl rings bonded through hydrogen bond-
ing in its structure. On esterification, hydrogen bonding breaks and quinoline molecule
Figure 2.

108
U. C. Bhoya et al.
Figure 3.
is bridged through the COO group. Thus, liquid crystal property is expected to be
maintained like the p-n-alkoxy benzoic acids. However, liquid crystal property practically
disappears on esterification. Of course, the transition temperatures of non-liquid crystal es-
ter homologue under discussion are lowered, as compared to the corresponding p-n-alkoxy
benzoic acid, just like a liquid crystal homologous series. Thus, disappearance of liquid
crystal characteristics of p-n-alkoxy benzoic acids on linking with 8-hydroxy quinoline
Figure 4. Homologous Series: 8[4ꢀ-n-alkoxybenzoyloxy] quinoline.

Latent Mesogenic Behavior in Nonmesogenic Compounds
109
is attributed to the absence of intermolecular anisotropic forces of attraction of suitable
magnitude depending upon the molecular shape, size, polarity, polarizability, aromaticity,
effect due to lateral and terminal end groups, etc. The non-liquid crystal behavior of all
of the homologues is attributed to their either high crystallizing tendency due to stronger
intermolecular forces of attraction or weaker intermolecular forces of end-to-end and lat-
eral attraction than optimum intermolecular and isotropic forces of attraction of suitable
magnitude required for the formation of mesophase as a consequence of molecular rigidity,
flexibility, andmolecular bending. Theintermolecular forces of attractionare unable toresist
thermal vibrations imposed upon sample specimen homologues under discussion. There-
fore, molecules of all of the homologues under the influence of the exposed heat disalign on
the plane of the surface but do align at an angle less than 90◦C. Thus, disaligned molecules
of the sample homologues fail to maintain, or restrict to maintain, parallel orientational
order of molecules. Thus, molecules of the sample homologues are randomly oriented
without any regularity in floating condition. Under this situation, mesophase formation
does not appear to occur. Hence, the entire homologous series 8[4’-n-alkoxy benzoyloxy]
quinolines is nonmesomorphic in character. Therefore, all homologues of the series sharply
pass from solid to isotropic liquid without exhibition of any liquid crystal state.
Twelve binary systems of 12 nonmesomorphic homologues consisting of A+B1,
A+B2–A+B12 were studied under hot-stage polarizing optical microscopy. The extent
of composition range over which liquid crystal mesophase is observed depends upon the
degree of similarities of the molecules of components A and B, of a binary system in shape,
size, polarity, polarizability, etc. Solute molecules are structurally compatible and con-
ducive to liquid crystal mesophase formation. Therefore, mixed liquid crystals are formed
over a wider composition range either enantiotropically and/or monotropically in the re-
spective phase diagram of the binary system. The eutectic points in the phase diagrams
for binary systems meet melting point curves to the left of the respective eutectic points.
Therefore, eutectic points of the binary systems under discussion are in equilibrium with
the nematic liquid phase. In all of the binary systems, the isotropic liquid could be su-
percooled to the mesophase. The metastable monotropic mesophase formation observed is
within sufficient range of composition and temperature, leading to smooth extrapolation of
the melting/transition curve. Thus, reliable extrapolation of curve to zero mole percent of
component (A) (or 100 mole percent of B) of binary systems is easily achieved for all the
components (B) as shown in Table 3. Hence, the LTTs of all the homologues are reliable.
Reliable LTTs are plotted versus the number of carbon atoms in the n-alkyl chain of left
n-alkoxy terminal, which gives rise to a phase diagram for a non-liquid crystal homologous
series under discussion. This phase diagram of a non-liquid crystal homologous series very
well matches with a phase diagram of the mesogenic series. Thus, reliable extrapolation
and hence the extrapolation method is useful to test and correct the LTT of an individual
component of a binary system or a homologue of a non-liquid crystal homologous series.
Conclusion
The reliability of the LTT of a nonmesomorphic homologue of a homologous series or the
nonmesomorphic component of a binary system depends upon the similarity in molecular
structure of mixing components, homogeneity of a binary mixture, and melting point
difference of both components constituting the binary mixture with the condition that
mixing components should not mutually interact. The evidence obtained by the present
investigation places the extrapolation hypothesis on sound ground.

110
U. C. Bhoya et al.
Acknowledgments
The authors acknowledge the authority of the management, Shri Jalaram Uchcha Kelavani
Mandal-Rajkot for facilitating the research work. Thanks are due to the Head of the
Department of Applied Chemistry, M.S. University, Baroda, and CSMI, Bhavnagar, for
characterization of sample substances.
References
[1] Dewar, M. J. S., & Goldberg, R. S. (1970). J. Am. Chem. Soc., 92.
[2] Dave, J. S., & Vora, R. A. (1970). Liquid crystals and ordered fluids. In: J. F. Johnson & R. S.
Porter (Eds.), Plenum press: New York, p. 477.
[3] Vogel, A. I. (1989). Textbook of Practical Organic Chemistry, 5th ed., ELBS and Longman:
London, p. 946.
[4] Lohar, J. M., & Doshi, A. V. (1992). Acta Ciencia India, XVIII C (3), 245.
[5] Lohar, J. M., & Doshi, A. V. (1993). Proc. Ind. Acad. Sci. (Chem. Sci.), 105, 209–214.
[6] Walter, R. (1925). Ber. Dtsch. Chem. Ges., B58, 2303.
[7] Dave, J. S., & Lohar, J. M. (1959). Chem. Ind., 597.
[8] Joshi, N. N., & Doshi, A. V. (1993). J. Ind. Chem. Soc., 70, 807–809.
[9] Doshi, A. V., & Ganatra, K. J. J. (2000). Ind. Acad. Soc., 77, 61–64.
[10] Bhoya, U. C., & Doshi, A. V. (2002). J. Ind. Chem. Soc., 79 (March), 249–251.
[11] Lohar, J. M., & Dave, J. S., Jr. (1983). Mol. Cryst. Liq. Cryst., 103(1–4), 181–192 (Eng.).
[12] Lohar, J. M., & Dave, J. (1983). Mol. Cryst. Liq. Cryst., 103(1–4), 143–153 (Eng.).
[13] Makwana, N. G., & Doshi, A.V. (2008). J. Ind. Chem. Soc., 85(March), 257–262, 263–266.
[14] Patel, R. B., Chauhan, M. L., & Doshi, A. V. (2010). Der Pharma Chemica, 2(6), 57–164.
[15] Patel, V. R., & Doshi, A. V. (2010). Der Pharma Chemica, 2(6), 429–436.
[16] Doshi, A. V., & Prajapati, H. R. (2011). Der Pharma Chemica, 3(1).