Study of Liquid Crystal Behavior and Dependence on Additional Central Bridge of Ester Homologous Series

Article abstract of DOI:10.1080/15421406.2014.990249

A novel homologous series of esters was synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal (LC) properties. The series consists of 11 members, and all exhibit enantiotropically the smectogenic mesophase. The nematogenic mesophase is totally absent. The textures of smectic phases are of the type A or C. The Sm-I transition curve of the phase diagram behaves in abnormal manner. The average Sm-I thermal stability is 124.53°C with mesomorphic phase length between 6.5°C and 52.3°C and is of a middle-ordered melting type. LC properties of the novel series are compared with a structurally similar other known series. Analytical and spectral data of the homologous match the molecular structure.

Full text of DOI:10.1080/15421406.2014.990249

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Study of Liquid Crystal Behavior and Dependence
on Additional Central Bridge of Ester Homologous
Series
Rajesh B. Marathe & A. V. Doshi
To cite this article: Rajesh B. Marathe & A. V. Doshi (2015) Study of Liquid Crystal Behavior and
Dependence on Additional Central Bridge of Ester Homologous Series, Molecular Crystals and
Liquid Crystals, 616:1, 74-82, DOI: 10.1080/15421406.2014.990249
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Date: 16 February 2016, At: 19:42

Mol. Cryst. Liq. Cryst., Vol. 616: pp. 74–82, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.990249
Study of Liquid Crystal Behavior and Dependence
on Additional Central Bridge of Ester
Homologous Series
1,∗
2
RAJESH B. MARATHE AND A. V. DOSHI
1
Shree Ganesh Flats, Near Gayatri Water Tank, Gotri Baroda, Gujarat, India
Dr. K.N. Modi University, Newai Dist. Tonk, Rajasthan, India
2
A novel homologous series of esters was synthesized and studied with a view to un-
derstanding and establishing the effects of molecular structure on liquid crystal (LC)
properties. The series consists of 11 members, and all exhibit enantiotropically the
smectogenic mesophase. The nematogenic mesophase is totally absent. The textures of
smectic phases are of the type A or C. The Sm-I transition curve of the phase diagram
◦
behaves in abnormal manner. The average Sm-I thermal stability is 124.53 C with me-
◦
◦
somorphic phase length between 6.5 C and 52.3 C and is of a middle-ordered melting
type. LC properties of the novel series are compared with a structurally similar other
known series. Analytical and spectral data of the homologous match the molecular
structure.
Keywords Enantiotropic; liquid crystals; mesomorphism; nematic; smectic
Introduction
Since from the discovery in 1888 of a novel physical state of a matter [1] between a crys-
talline solid and a true isotropic liquid called the liquid-crystal (LC) state, various groups of
scientific and technological researchers have contributed enormously with different views,
aims, and objects or purposes [2–4]. Among the scientific groups, the chemists have played
an important basic role by designing and synthesizing novel LC materials useful to other
research groups [5–7]. LC materials are well known for their applications in pharmaceu-
ticals and medicinal preparations and importantly displays. The present investigation is
planned with a view to understanding and establishing the relation between LC properties
of substances and their molecular structure [8–10]. The proposed investigation consists of
ꢀ
the synthesis and characterization of novel ester derivatives of 4-hydroxy-4 -chloro benzyl
benzoate with n-alkoxy aromatic acids. Such derivatives are useful in the biological field
due to their bioactivity [11–13] and other fields of applications like heat-sensitive recording
material [14]. The LC behavior of the novel substances will be discussed and interpreted
in terms of molecular rigidity and flexibility with reference to the corresponding molecular
structures [15–18].
∗
Address correspondence to Rajesh B. Marathe, 306, Shree Ganesh Flats, Near Gayatri Water
Tank, Sevashi Road, Gotri Baroda 390021, Gujarat, India. E-mail: maratha raj@rediffmail.com
74

Ester Homologous Series
75
Experimental
Synthesis
4
-Hydroxy benzoic acid was alkylated by suitable alkylating agents R-X by the modi-
ꢀ
fied method of Dave and Vora [19]. 4-Hydroxy-4 -chlorobenzyl benzoate (m.p. −120 to
◦
−
130 C) was prepared from 4-chloro benzyl bromide and 4-hydroxy benzoic acid by the
method the modified method of Doshi and Patel [20,21]. n-Alkoxy benzoic acids and 4-
ꢀ
hydroxy-4 -chlorobenzyl benzoate were individually condensed in pyridine through their
corresponding acid chlorides by a usual established method [22,23]. Final esterified prod-
ucts were individually decomposed, filtered, washed, dried, and purified until constant
transition temperatures were obtained.
4-Hydroxy benzoic acid, alkyl halides, methanol, KOH, 4-chloro benzyl bromide,
N,N-DMF, NaHCO3, HCl, pyridine, thionyl chloride, EtOH, etc. required for the synthesis
were used as received, except for solvents which were dried and purified prior to synthesis.
Synthetic route to the series is shown in Scheme 1.
Scheme 1. Synthetic route to the series.
Characterization
Some selected members of the novel homologous were characterized by elemental analysis,
1
infrared spectra, HNMR spectra, and mass spectra. Textures and transition temperatures

76
R. B. Marathe and A. V. Doshi
of the homologous were determined by an optical polarizing microscope, equipped with
a heating stage. Elemental analysis was performed on Perkin-Elemer PE 2400 C,H,N
1
analyzer. IR spectra were recorded on Perkin-Elmer spectrum GX. HNMR spectra were
determined on Bruker spectrometer using CDCl3 solvent. Textures of smectic mesophase
of some homologous were recognized either directly from the microscopic observations or
by a miscibility method.
Analytical Data
Spectral data:
1HNMR in ppm for the Hexyloxy Derivative: 0.97 (CH3 of C6H13), 2.66 ( CH2
of –OC6H13), 3.93 ( OCH2 of –OC6H13), 5.25 ( O CH2- phenyl ring), 6.81–6.90 (p-
substituted phenyl ring), 7.84–7.94 (p-substituted benzene), 7.31–7.49 (p-substituted ben-
zene).
1HNMR in ppm for the Dodecyloxy Derivative: 0.969 (CH3 of C12H25), 2.261( CH2-
of –OC12H25), 3.75 ( O CH2 of –OC12H25), 4.98 ( OCH2- of phenyl ring), 6.53–6.64
(
p-substituted phenyl ring), 7.55–7.61 (p-substituted benzene), 7.06–7.19 (p-substituted
benzene).
NMR data confirm the structure.
−1
IR in cm for Decyloxy Derivative: 717 polymethylene of C10H21, 771 para Chloro
benzene, 845 para-substituted phenyl ring, 1167 ether linkage of (C10H21 O C6H4),
1105,1257,1672 ( COO ester group), 2560–2664 (presence of COOH groups), 3257
(
H bonding of OH).
−1
IR in cm for Pentyloxy Derivative: 772 para Chloro benzene, 843 para-substituted
benzene, 1166 ether linkage of (C5H11 O C6H4) polymethylene of C14H29, 821
para-substituted phenyl ring, 1018 ether linkage of ( C5H11O C6H4),1114, 1255,
1
672( COO-ester group), 2669, 2558 (presence of COOH groups), 3258 (H bond-
ing of OH).
IR data confirm the structure.
Mass Spectra
Mass Spectra for Butyloxy Derivative. Molecular weight: Calculated: 438.5. Molecular
formula: C25H23ClO5
Experimental: 439.
Texture of Smectic Phase by Miscibility Method
Butyloxy (C4) derivative −→ Smectic - A
Hexyloxy (C6) derivative −→ Smectic - A
Hexadecyloxy (C16) derivative −→ Smectic- C
Results and Discussion
The novel ester homologous series consisting of 11 members is entirely enantiotropically
smectogenic without exhibition of any nematogenic character. Transition temperatures
(Table 2) were plotted versus the number of carbon atoms present in the n-alkoxy terminal
end group. Like or related points were linked to draw solid-smectic and a smectic-isotropic
transition curves for the construction of a phase diagram (Fig. 1), showing the phase behavior

Ester Homologous Series
77
Table 1. Elemental analysis for methyloxy, ethyloxy, and propyloxy derivatives
%
Elements calculated (experimental%)
Sr. no.
Molecular formula
C
H
Cl
1
2
3
C22H17ClO5
C23H19ClO5
C24H21ClO5
66.49 (66.58)
61.28 (67.31)
67.50 (67.87)
4.05 (4.28)
4.50 (4.63)
4.89 (4.95)
8.88 (8.96)
8.33 (8.36)
7.88 (8.08)
of the novel series. The solid-smectic transition curve follows a zigzag path of rising and
falling values as the series is ascended in an overall descending manner. Thus, it behaves
in normal established manner. Smectic-isotropic transition curve initially shows a falling
tendency with the exhibition of an odd-even effect up to the butyloxy (C4) homologue
then it rises up to the hexyloxy homologue (C6) and then drastically falls to the octyloxy
(
C8) homologue and then adopts a rising tendency to the C16 homologue Thus, it behaves
exceptionally in an unusual manner. The odd-even effect for the Sm-I transition curve
disappears from and beyond the hexyloxy (C6) homologue Mesomorphic behavior and the
degree of mesomorphism vary from homologue to homologue in the present novel series.
◦
The average thermal stability for smectic is 124.53 C and the smectogenic mesophase
◦
◦
length varies between 6.5 C and 52.3 C. Thus novel series is entirely smectogenic without
exhibition of any nematic property and of a middle-ordered melting type.
Exhibition of only smectic property throughout the series is attributed to the misalign-
ment of molecules at an angle ninety degree with the plane of a floating surface under
the influence of heat. Therefore, a narrow rod like molecule with the dipole acting across
the long axis favors lamellar packing of molecules in their crystal lattices. The chloro
substituent with a weaker dipole, disfavors or excludes the nematic phase, but strongly
◦
Table 2. Transition temperatures of series in C
◦
n-alkyl group (-CnH2n+1)
(n)
Transition temperature in C
Compound no.
Sm
N
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
8
10
107.2
112.8
109.0
86.7
89.7
93.0
73.8
91.7
85.4
114.6
84.3
—
—
—
—
—
—
—
—
—
—
—
133.3
138.6
130.9
122.5
131.8
133.0
80.3
112.2
111.9
138.8
136.6
12
14
16
10
1
1
Sm: Smectic
N: Nematic

78
R. B. Marathe and A. V. Doshi
Figure 1. Phase behavior of series.
favors a layered crystal lattice. Consequently, the lateral intermolecular attractions of suit-
able magnitude of anisotropic forces retain the layered molecular arrangement to exhibit
the smectogenic mesophase only. The odd-even effect observed for the smectic-isotropic
transition curve is attributed to the sequentially added methylene unit at the n-alkoxy chain
bonded to the phenyl ring. The disappearance of the odd-even effect for higher homolo-
gous from and beyond the hexyloxy (C6) homologue is due to the coiling or bending or

Ester Homologous Series
79
Figure 2. Structurally similar series.
flexing or coupling of n-alkyl chain with the major axes of the core structure. Thus, un-
certainty in the status of longer n-alkyl chain affects considerably the suitable magnitudes
of molecular flexibility and molecular rigidity operating. However, the molecules of the
novel homologous series consist of three phenyl rings and two central ester bridges as well
as two flexible end groups (-OR and Cl) are narrow rod like with dipoles acting across
the long molecular axis, which induces suitable magnitudes of anisotropic forces of lateral
to terminal intermolecular attractions to favor strongly smectogenic property right from
the very first member to the last member (C16). Thus, the combined effects of molecular
rigidity and flexibility from homologue to homologue in the present series exerts variations
in the suitable magnitudes of the ratio of lateral to terminal attractions to favor layered and
sliding layered lattices with varying degree of smectogenic behavior without the exhibition
of nematic property. Thus, the novel series is entirely smectogenic whose mesophase ranges
◦
◦
from a minimum of 6.5 C at the octyloxy (C8) homologue to a maximum of 52 C at the
hexadecyloxy (C16) homologue The LC behaviors of present novel series-1 are compared
with the structurally similar other known series-X [24] as shown in Fig. 2.
Homologous series-1 and a series-X chosen for comparison are identical with respect
to their aromaticity, i.e., three phenyl rings, a left n-alkoxy ( OR) and a right terminal end
group ( Cl) for the same homologue from series to series, a central bridge of COO
linking first and middle phenyl ring. However, they differ with respect to the second
central bridge of COOCH2- and N N linking the middle and third phenyl rings.
Therefore, series-1 and series-X under comparison differ with respect to molecular rigidity
and the intermolecular forces involved, for the same homologue from series to series
and from homologue to homologue in the same series. Therefore, the LC properties and
the degree of mesomorphism vary for the same homologue from series to series and
from homologue to homologue in the same series. Table 3 represents the average thermal
stabilities, commencement of smectic and/or nematic phase, degree of mesomorphism, etc.
for the series under comparison.
From the Table 3, it is clear that
•
•
•
•
Series-1 is entirely smectogenic, while series-X is smectogenic in addition to ne-
matogenic.
Smectic thermal stability of series-1 is relatively lower than the series-X under
comparison.
Smecticmesophasecommencesfrom veryfirstmemberofseries-1, butitcommences
late from the sixth (C6) member of a series-X.
Nematic mesophase is absent for a series-1 but nematic mesophase is present from
very first to last member of a series-X.

80
R. B. Marathe and A. V. Doshi
◦
Table 3. Average thermal stability in C
Series→
1
X
Smectic-nematic
Or
124.53
(C1 C16)
C1
148.8
(C6 C16)
C6
Smectic-isotropic
Commencement of
Smectic phase
Nematic-isotropic
Commencement of
Nematic phase
217.6
(C1 C10)
C1
—
Sm 6.5–52.0
Nm
Total 6.5–52.0
Sm 18–66
Nm 25–121
Total 16–121
Mesophase length
Range
◦
◦
•
Smectogenic mesophase length ranges from 6.5 to 52 C for series-1, whereas it
◦
◦
ranges from 18 to 66 C for series-X, i.e., 52-6.5 = 45.5 C and 66-18 = 48 C.
Thus, series-1 is entirely smectogenic and series-X is predominantly nematogenic and
partly smectogenic.
In all other respects, there is close similarity, except the second central bridge which
is azo N N for series-X and COO CH2- in case of series-1. The oxygen atom of
the second central bridge bonded through CH2- unit of series-1 will undergo bumping
into the adjacent hydrogens of the aromatic ring which will cause considerable strains on
the molecules of series-1. Consequently, a twist around C O bond will occur forcing the
phenyl ring out of the plane of the molecule. Thus, the coplanarity of the molecule is reduced
to some extent making them broader. The central bridge N N certainly endows the
molecules with coplanarity in the trans position of series-X. On account of such differences,
the smectic-isotropic thermal stabilities of series-1 are lower than the corresponding smectic
thermal stability of series-X. Moreover, when a system consisting of three phenyl rings
are linked through one of the central group involving multiple bond ( N N series-X),
the LC transition temperatures are relatively higher because N N central group as
compared to COO CH2- extend the molecular rigidity and linearity associated with para
substituted phenyl rings. However, an additional central group like COOCH2- in which
conjugation is less extended in the mesogenic system which results into less thermally stable
LC than that central group ( N N ) of a kind, which permit conjugative interactions.
Thus, lowering of smectic thermal stability, transition temperatures, mesophase length,
range, and early commencement of smectic phase and absence of nematic phase of present
series-1, as compared to series-X are can be attributed to changing molecular rigidity and
flexibility.
Conclusions
•
The smectic and/or nematic group efficiency order derived on the basis of (i) thermal
stability and (ii) the early commencement of mesophase with respect to additional
or second central bridge are as under.

Ester Homologous Series
81
I) Smectic: N N > COO CH2-
Nematic: N N COO CH2-
>
II) Smectic: COO CH2> N N
Nematic: N N > COO CH2-
III) Smectic mesophase length range
COO CH2- ≈ N N
◦ ◦
45.5 C) (48.0 C)
(
Nematic mesophase length range
N N >>>>> COO CH2-
•
•
•
•
LC substances derived from the para-chloro-substituted benzyl alcohol are smecto-
genic.
LC property of substance is sensitive and susceptible to the suitable magnitudes of
molecular rigidity and flexibility.
Present novel series is entirely smectogenic without exhibition of nematogenic prop-
erty and it is of middle ordered melting type.
Central group of a molecule contributes to molecular rigidity, LC property, and
degree of mesomorphism.
•
•
LC property and its magnitudes or intensity depends on its molecular structures.
LC property of substance is a function of molecular structure.
Acknowledgments
Authors acknowledge thanks to the Principal, Head of chemistry department, Dr. N.N. Vyas
including Dr. V.R. Patel and Dr. M.L. Chauhan, P.T. Arts and Science College, Godhara,
for providing microscopic facility and other cooperation as and when needed. Authors also
thankful to the Green Circle Inc. laboratory, Vadodara, and our R and D lab for extending
their valuable support for services related to synthesis of novel products and moral support.
The authors are highly obliged to Punjab University, Chandigarh, for analytical services.
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