Mesogenic behavior of a novel homologous series: α-4-[4′-n- alkoxy benzoyloxy] benzoyl-β-4″-chloro phenyl ethylenes

Article abstract of DOI:10.1080/15421406.2013.768894

A novel homologous series entitled α-4-[4′-n-Alkoxy benzoyloxy] benzoyl β-4″-chloro phenyl ethylenes consists of 12 homologues. The pentyl to tetradecyl homologues are enatiotropically nematogenic and all of the other homologues (methyl to butyl and hexadecyl) are nonmesogenic. The textures of the nematogenic mesophase are threaded or Schlieren in nature. The transition temperatures were determined by an optical polarizing microscope with a heating stage. The phase diagram of the novel series shows a normal behavior with negligible abnormality in trend of the nematic-isotropic transition curve and exhibits an odd-even effect as expected. The nematic thermal stability is 149.4°C on average. The series is nematogenic without any smectogenic character. The mesogenic properties of the novel series are compared with known series that are structurally similar.

Full text of DOI:10.1080/15421406.2013.768894

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Mesogenic Behavior of a Novel
Homologous Series: α-4-[4′-n-Alkoxy
benzoyloxy] benzoyl-β-4″-chloro Phenyl
Ethylenes
H. N. Chauhan a , N. N. Vyas b & A. V. Doshi c
a Chemistry Department , K. K. Shah Jarodwala Maninagar Science
College , Ahmedabad , Gujarat , India
b Department of Chemistry , Sheth P.T. Arts and Science College ,
Godhara , Gujarat , India
c Department of Chemistry , Shri Jagdishprasad Jhabarmal Tibrewala
(J.J.T. Uni.) , Jhunjhunu , Rajasthan
Published online: 22 Apr 2013.
To cite this article: H. N. Chauhan , N. N. Vyas & A. V. Doshi (2013) Mesogenic Behavior of a Novel
Homologous Series: α-4-[4′-n-Alkoxy benzoyloxy] benzoyl-β-4″-chloro Phenyl Ethylenes, Molecular
Crystals and Liquid Crystals, 575:1, 96-103, DOI: 10.1080/15421406.2013.768894
To link to this article: http://dx.doi.org/10.1080/15421406.2013.768894
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Mol. Cryst. Liq. Cryst., Vol. 575: pp. 96–103, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.768894
Mesogenic Behavior of a Novel Homologous Series:
α-4-[4ꢀ-n-Alkoxy benzoyloxy] benzoyl-β-4ꢀꢀ-chloro
Phenyl Ethylenes
H. N. CHAUHAN,1 N. N. VYAS,2,∗ AND A.V. DOSHI3
1Chemistry Department, K. K. Shah Jarodwala Maninagar Science College,
Ahmedabad, Gujarat, India
2Department of Chemistry, Sheth P.T. Arts and Science College, Godhara,
Gujarat, India
3Department of Chemistry, Shri Jagdishprasad Jhabarmal Tibrewala (J.J.T. Uni.),
Jhunjhunu, Rajasthan
A novel homologous series entitled α-4-[4ꢀ-n-Alkoxy benzoyloxy] benzoyl β-4ꢀꢀ-chloro
phenyl ethylenes consists of 12 homologues. The pentyl to tetradecyl homologues are
enatiotropically nematogenic and all of the other homologues (methyl to butyl and
hexadecyl) are nonmesogenic. The textures of the nematogenic mesophase are threaded
or Schlieren in nature. The transition temperatures were determined by an optical
polarizing microscope with a heating stage. The phase diagram of the novel series
shows a normal behavior with negligible abnormality in trend of the nematic-isotropic
transition curve and exhibits an odd–even effect as expected. The nematic thermal
stability is 149.4◦C on average. The series is nematogenic without any smectogenic
character. The mesogenic properties of the novel series are compared with known series
that are structurally similar.
Keywords Liquid crystal; mesogen; mesomorphic; nematic; smectic
Introduction
The exhibition of mesogenic properties by any substance is a direct result of suitable
magnitudes of molecular rigidity and flexibility [1–3]. Intermolecular forces of attraction
of a suitable magnitude occur as a consequence of a net favorable molecular rigidity and
flexibility depending upon molecular shape, size, aromaticity, polarity, and polarizability,
the position of lateral and terminal end groups, and electronic–electronic interactions etc.
The present work was aimed at enhancing the understanding of and establishment of the
effects and relationship between molecular structure and mesogenic behavior of a substance
[4] by linking three phenyl rings to be bridged through two central groups COO and
CO CH CH as well as OR and Cl as the terminal end groups, without substituting
any lateral group at any phenyl ring in the lath-like linear molecule. The effect of varying
the central groups other than COO on mesogenic properties will be discussed, using
structurally similar homologous series selected for comparison.
∗Address correspondence to N. N. Vyas, Department of Chemistry, Sheth P.T. Arts and Science
College, Godhara, Gujarat, India. E-mail: nimeshvyas 23@yahoo.co.in
96

Mesogenic Behavior of a Novel Homologous Series
97
Experimental
Synthesis
4-Hydroxybenzoic acid was alkylated by suitable alkyl halides to form 4-n-alkoxybenzoic
acids by a modified method of Dave and Vora [5]. Dimeric n-alkoxy benzoic acids were con-
verted in to the corresponding n-alkoxybenzoyl chlorides [A] using freshly distilled thionyl
chloride under reflux conditions. Component [B] α-4-Hydroxy benzoyl –β-4ꢀ-chloro phenyl
ethylene was synthesized by reacting 4-chlorobenzaldehyde and 4-hydroxyacetophenone
by the usual established method [6a, b(i), b(ii), c]. Components A and B were condensed
in dry cold pyridine by an established method [7a, b, c, d, . . . .]. Final products were de-
composed, filtered, washed, dried, and purified until constant transition temperatures for
each individual homologue were obtained. The synthetic route to the series is mentioned
below in Scheme 1. 4-Hydroxybenzoic acid, alkyl halides, thionyl chloride, methanol,
KOH, HCl, 4-hydroxyacetophenone, 4-chloro enzaldehyde, and pyridine, required for
the synthesis were used as received except solvents which were dried and distilled prior
to use.
Scheme 1. Synthetic route to the series.
Characterization
Some of the selected homologues of the novel homologous series were characterized
1
for the determination of molecular structures by infra red [IR] and HNMR (Nuclear
magnetic resonance) techniques. Microanalysis was performed on a Perkin Elmer PE 2400
CHN analyzer. IR spectra were recorded on a Perkin–Elmer spectrum GX instrument,
and 1HNMR spectra was recorded on a Bruker instrument using CDCl3 as a solvent. The
mesogenic properties and transition temperatures of the series were investigated using an
optical polarizing microscope equipped with a heating stage. Thermodynamic quantity

98
H. N. Chauhan et al.
Enthalpy (ꢀH) and Entropy (ꢀS) are qualitatively discussed instead of using differential
scanning calorimeter scan. The textures of the smectic and the nematic mesophases were
determined by a miscibility method.
Analytical Data
Spectral Data:
NMR in ppm for the Propyloxy Derivative. 0.850 ( CH3 of OC3H7 group), 1.243
( CH2 of OC3H7), 4.001 ( OCH2 of OC3H7), 7.611 ( CO CH CH group),
6.9 to 8.04 (p-substituted phenyl ring). NMR supports the structure.
NMR in ppm for Octyloxy Derivative. 0.879 ( CH3 of OC8H17 group), 1.332 ( CH2
of OC8H17), 4.02 ( OCH2 of OC8H17), 6.9 ( CO CH CH group), 6.91 to 8.13
(p-substituted phenyl ring). NMR supports the structure.
IR in cm–1 for Pentyloxy Derivative. 700 polymethylene group of OC5H11, 760 Cl
group, 870 p-substituted phenyl ring, 1180 ( CO of OC5H11 group), 1240, 1440, 1605
COO ester group), 975 ( CH CH group). IR supports the structure.
IR in cm–1 for Tetradecyloxy Derivative. 680 polymethylene group of OC14H29), 750
Cl group, 860 (p-substituted phenyl ring), 1150 ( CO of OC14H29 group), 1200,
1280, 1600 ( COO ester group). IR supports the structure.
Texture by Miscibility Method
• Hexyl—Nematic—Threaded
• Decyl—Nematic—Schlieren
Results and Discussion
Hydrogen bonding of dimerized 4-n-alkoxybenzoic acids break on esterification. The ethy-
lene derivative [B] is nonmesomorphic, but on esterification with acid chlorides the enan-
tiotropic nematic phase appears in seven homologues. The transition temperatures of the
novel homologues were plotted against the number of carbon atoms in n-alkyl terminal
chain. The phase diagram (Fig. 1) consists of two transition curves. The solid-isotropic or
nematic transition curve adopts a zigzag path of rising and falling values as the series is
ascended with an overall descending tendency and behaves in a normal manner. The ne-
matogenic mesophase commences from the pentyl homologue derivative of the series. The
nematic-isotropic transition curve descends as the series is ascended with minor exceptional
behavior at the decyl homologue derivative with the exhibition of short ranged odd–even
effect. The nematic-isotropic transition temperatures varies between 168◦C and 138◦C with
a short range nematogenic mesophase length and a 149.4◦C thermal stability. Thus, the
novel series is entirely nematogenic with a middle ordered melting type. The texture of
nematic mesophase is of the threaded or Schlieren type. The smectogenic character of the
novel series is totally absent.
The methyl to butyl and the hexadecyl homologues are nonmesogenic and sharply
melt to the isotropic liquid phase without passing through an intermediate state of matter.
These five homologues are unable to resist the thermal vibrations exposed upon them. The

Mesogenic Behavior of a Novel Homologous Series
99
Figure 1. Phase behavior of series.
unfavorable molecular rigidity and flexibility without an ordered molecular arrangement in
floating condition means that the molecules are randomly oriented in all possible directions
and show a sharp melting point. The pentyl to tetradecyl homologoues are nematogenic
because the molecules resist thermal vibrations exposed upon them for a definite range
of temperatures. The molecules lie on the surface at an angle less than 90◦ withstanding
the exposed thermal vibrations and a statically parallel orientational order of molecules is
maintained between two temperatures enantiotropically (or monotropically) in a floating
condition. The statically parallel orientational order of the molecules in a floating condition
shows the formation of a nematogenic mesophase by suitable magnitudes of anisotropic
forces as a consequence of favorable molecular rigidity and flexibility [1–4]. Absence
of lamellar packing of the molecules in their crystal lattices precludes a sliding layered
arrangement of molecules in a floating condition. Hence, the smectogenic character is
absent. The nematogenic mesophase length varies from a minimum of 14◦C at the seventh
and eighth homologue to a maximum of 25◦C for the dodecyloxy homologue. Thus, it is a
series with narrow phase length. The appearance of an odd–even effect and a variation of
mesogenic properties from homologue to homologue in the same novel series is attributed
to the progressively and sequentially added methylene unit at the n-alkyl terminal chain.
The mesogenic properties of the present series 1 are compared with two other structurally
similar homologous series-X [8] and Y [9] as shown in the Fig. 2.

100
H. N. Chauhan et al.
Figure 2. Structurally similar homologous series.
Homologous series 1 and X under comparison are identical in all respects with three
phenyl rings, and left and right sided terminal end groups of OR and Cl respectively,
and a central group of COO linking the first and middle phenyl rings. However, both
series (1 and X) differ in respect of central group CO CH CH and N N linking
middle and third phenyl rings. Therefore, the observed difference of mesogenic properties
and degree of mesomorphism is attributed to the differing features between series 1 and
X. The effects due to three phenyl rings, that is, molecular aromaticity, central group
COO , and functional group polarity due to OR and Cl terminal end groups remains
the same; but the molecular length, length to breadth ratio, and other parameters relating
differing features of molecules, that is, magnitudes of anisotropic forces of intermolecular
lateral and terminal attraction as a consequence of resulted molecular rigidity and flexibility
[1–4] vary considerably, which causes variations in mesogenic properties and the degree of
mesomorphism. Homologous series 1 and Y are identical in all respects of COO central
group linking two phenyl rings, two terminal end groups OR and Cl, but they differ in
respect of molecular length due to the presence and absence of C6H4 CO CH CH
molecular moiety in series 1 and Y respectively. This differing feature of series 1 and Y
causes differences in magnitudes of mesogenic properties and the degree of mesomorphism
as a result of varying molecular rigidity and flexibility [1–4]. Table 3 represents thermal
stabilities and commencement of mesophase or mesophases etc. for the series 1, X, and Y
selected for a comparative study.
Table 3 indicates that homologous series 1 is entirely nematogenic while series Y is
entirely smectogenic. This observed difference can be attributed to the presence or absence
of the C6H4 CO CH CH molecular moiety of series 1 and Y respectively. The
presence of the C6H4 CO CH CH section of the molecules increases the molecular
length and restricts the lamellar arrangement of molecules in their crystal structure due
to the changing of molecular rigidity in such a manner that the end to end intermolecular
attractions increase to such an extent, that lamellar molecular arrangement does not occur
Table 1. Elemental analysis for butyloxy, heptyloxy, and dodecyloxy derivatives
Elements % calculated (% found)
Sr. no.
Molecular formula
C
H
1
2
3
C26H23O4Cl
C29H29O4Cl
C32H35O4Cl
71.81 (71.52)
73.03 (73.12)
74.06 (74.68)
5.29 (5.04)
6.10 (6.44)
6.75 (6.98)

Mesogenic Behavior of a Novel Homologous Series
101
Table 2. Transition temperatures of series in ◦C
Transition temperatures in ◦C
Compound no.
n-alkyl group (–CnH2n+1
)
Sm
Nm
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
10
12
14
16
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
182.0
189.0
177.0
198.0
168.0
157.0
148.0
144.0
148.0
143.0
138.0
140.0
—
145.0
138.0
134.0
130.0
126.0
118.0
116.0
—
10
11
12
Sm = smectic, Nm = nematic.
and only a statically parallel orientational order of the molecules is maintained in a floating
condition under the influence of heat. The absence of such a molecular section as mentioned
above in series Y allows a sliding layered arrangement of molecules in a floating condi-
tion under identical conditions of applied heat, which induces only smectogenic properties
in the series Y. Thus, the smectogenic character commences from the heptyl homologue
derivative of a series, but it does not commence until the hexadecyl homologue of series
1. On comparing the homologous series 1 and X, it is seen from Table 3 that series 1 is
entirely nematogenic, while series X is predominatly nematogenic and partly smectogenic.
Series 1 is a middle ordered melting type whose N-I thermal stability is 149.4◦C, while,
series X is high melting type whose smectic and nematic thermal stabilities are 148.8◦C and
217.6◦C. The smectic and nematic mesophase formation commences from the hexyl and
methyl homologues respectively (Series X). Though the end groups in both the series under
comparison are identical but, a central group linking the middle and third phenyl rings
which are CO CH CH and N N are different. This variation causes a difference
Table 3. Average thermal stabilities in ◦C
Average transition temperatures in ◦C
Series
Series (1)
Series (X)
Series (Y)
Smectic-nematic or
smectic-isotropic
Commencement of smectic
mesophase
Nematic-isotropic
Commencement of nematic
mesophase
148.8 (C6–C16) 104.7 (C12–C18)
—
C6
C7
—
149.4 (C5–C14) 217.6 (C1–C10)
C5 C1

102
H. N. Chauhan et al.
in molecular length, molecular polarity, and polarizabilty, magnitudes of anisotropic forces
of intermolecular attractions as a consequence of varying molecular rigidity of series 1 and
X. Thus, lamellar arrangement of molecules occurs in the crystal structure which enables
a sliding layered molecular arrangement in a floating condition under the influence of heat
in case of series X while it does not occur for series 1. Moreover, the stronger rigidity and
intermolecular end-to-end attractions of series X, resists the thermal vibrations above the
smectic-nematic transition temperature from the very first member of series X for a definite
temperature range. The molecules of a sample homologue from the methyl to the decyl
homologues of the series resist thermal vibrations due to stronger end-to-end attractions
up to the isotropic temperature forming a nematogenic mesophase in addition to a smec-
togenic mesophase in case of series X in comparison with series 1. The commencement
of the smectic phase does not occur until the last homologue of a series 1 while it occurs
from the sixth member of series X. This difference in the commencement of the smectic
phase depends upon the extent of the relative noncoplanarity [7] caused by the molecules
of series 1 and X. The central group N N maintains more linearity in the molecule
than a CO CH CH group. Hence, the molecules of series X are less noncoplanar
than the molecules series 1. As a result of this, lamellar packing of the molecules causes
a sliding layered molecular arrangement in floating condition. Thus, smectic and nematic
group efficiency order derived on the basis of thermal stability are under mentioned in the
conclusions. The odd–even effect diminishes as the series is ascended for higher homo-
logues from and beyond the seventh homologue because the longer n-alkyl terminal chain
may coil, bend, or flex or couple to lie [4] with major axis of the core.
Conclusions
(1) Group efficiency order for smectic as central group N N
CO CH CH (series X) (series Y) (series 1) Group efficiency order for
nematic as a central group N N CO CH CH CO CH CH
(2) (series X) (series 1) (series Y) Group efficiency of a central group with refer-
>
CO CH CH
>
>
>
ence to early commencement of smectic phase and nematic phase. N N
CO CH CH
>
(3) Central group CO CH CH is nematogenic.
(4) Central group N N increases molecular rigidity if molecular flexibility is
same.
(5) Central group CO CH CH restricts the lamellar packing of molecules in
their crystal lattices.
(6) Molecular rigidity and flexibility of a molecule are the deciding factors for
mesophase formation.
Acknowledgments
Authors acknowledge thanks to the principal, Dr. R.R. Shah and the head, Dr. R. B.
Patel, of chemistry of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad, for
their valuable cooperation and also Vaibhav Laboratory for analytical services. Authors
are thankful to head and staff of chemistry, S.P.T. Science College, Godhra, for providing
microscopic facility.

Mesogenic Behavior of a Novel Homologous Series
103
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.
[4] (a) Gray, G. W. (1962). Molecular Structure and the Properties of Liquid Crystal. Academic
Press: London and New York. (b) Gray, G.W., & Windsor, P. A. (1974). Liq. Cryst. and Plastic
Cryst. Vol. 1, Chapter 4, Ellis Horwood Ltd.: Chichester; Halsted Press: New York, London.
[5] Dave, J. S., & Vora, R. A. (1970). Liquid Crystals and Ordered Fluids. Plenum Press: New York,
477.
[6] (a) Vogel’s Textbook of Practical Organic Chemistry, 4th ed. publishers Pvt. Ltd.: Longman,
Singapore. (b) i. Chauhan, M. L., & Doshi, A. V. (August 2007). J. Indian Chem. Soc., 84, 774.
ii. Patel, R. B., & Doshi, A. V. (2011). Derpharma Chemica, 3(2), 147. iii. Chauhan, H. N., &
Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 569, 33. iv. Suthar, D. M., & Doshi, A. V. (2012).
Mol. Cryst. Liq. Cryst., 569, 64. (c) Ganatra, K. J., & Doshi, A. V. (1999). Proc. Ind. Acad.
Sci.(Chem. Sci.), 4(11), 562.
[7] (a) Patel, V. R., & Doshi, A. V. (2010). Derpharma Chemica, 2(6), 429. (b) Patel, R. B., & Doshi,
A. V. (2011). Derpharma Chemica, 3(2), 147. (c) Chauhan, M. L., Pandya, R. N., & Doshi, A.
V. (2011). Mol. Cryst. Liq. Cryst., 548, 228. (d) Doshi, A. V., & Makwana, N. G. (2011). Mol.
Cryst. Liq. Cryst., 548, 220. (e) Patel, R. B., Patel, V. R., & Doshi, A. V. (2012). Mol. Cryst. Liq.
Cryst., 552, 3–9. (f) Doshi, A. V., Odedara, D. A., & Patel, R. B. (2012). Mol. Cryst. Liq. Cryst.,
552, 97.
[8] Bhoya, U. C., & Doshi, A. V. (2000). J. Inst. Chem. (India) 72 (part-1), 15.
[9] Ph.D. thesis of Doshi, A. V., submitted to Saurashtra University-Rajkot [India] in July 1987 under
Dr. Lohar, J. M., entitled, “Study of mesomorphism and exploration of its characteristics.”