Mesomorphism in chloro substituted isomeric series including chalconyl central bridge

Article abstract of DOI:10.1080/15421406.2016.1272801

A novel homologous series of thermotropic liquid crystals α-4-(4′-n-alkoxy benzoyloxy phenyl) β-2″-chloro benzoyl ethylenes have been synthesized and studied with a view to understand and establish the effect of molecular structure on liquid crystal (LC) properties with reference to molecular flexibility in isomeric series with differing positional status of same functional group. Novel homologues series consist of 12 homologues C₁ to C_16. C₁, C₂, and C₃ homologues are nonliquid crystals (NLC) and rest of the homologues are liquid crystals. C₁₀ to C₁₆ homologues are enantiotropically smectogenic plus nematogenic and C₄ to C₈ homologues are enantiotropic nematic. The texture of nematogenic derivatives is threaded or schlieren and that of the smectic mesophase are focal conic of the type smectic A or C. Analytical, thermal and spectral data supported molecular structures of novel homologues. Transition temperatures as determine by a hot stage polarizing optical microscopy (POM) were plotted against number of carbon atom present in n-alkyl chain ‘R’ of left n-alkoxy (-OR) group and the phase transition curves Cr–I/M, Sm–N, N–I were obtained on linking like or related points. The odd–even effect is observed for the N–I transition curve and thus transition curves behaved in normal manner. The even-membered nematic transition curve occupied higher position than the odd-membered transition curve. Present series is predominantly nematogenic and partly smectogenic with middle-ordered melting type.

Full text of DOI:10.1080/15421406.2016.1272801

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphism in chloro substituted isomeric
series including chalconyl central bridge
Dipti L. Namera, Avani R. Ranchchh & U. C. Bhoya
To cite this article: Dipti L. Namera, Avani R. Ranchchh & U. C. Bhoya (2017) Mesomorphism in
chloro substituted isomeric series including chalconyl central bridge, Molecular Crystals and Liquid
Crystals, 643:1, 233-240, DOI: 10.1080/15421406.2016.1272801
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1272801
Published online: 23 Feb 2017.
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Date: 27 February 2017, At: 02:55

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Mesomorphism in chloro substituted isomeric series including
chalconyl central bridge
Dipti L. Namera, Avani R. Ranchchh, and U. C. Bhoya
Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
ABSTRACT
KEYWORDS
A novel homologous series of thermotropic liquid crystals α-4-(4ꢀ-n-
alkoxy benzoyloxy phenyl) β-2ꢀꢀ-chloro benzoyl ethylenes have been
synthesized and studied with a view to understand and establish the
effect of molecular structure on liquid crystal (LC) properties with refer-
ence to molecular flexibility in isomeric series with differing positional
status of same functional group. Novel homologues series consist of 12
homologues C1 to C16. C1, C2, and C3 homologues are nonliquid crystals
(NLC) and rest of the homologues are liquid crystals. C10 to C16 homo-
logues are enantiotropically smectogenic plus nematogenic and C4 to
C8 homologues are enantiotropic nematic. The texture of nematogenic
derivatives is threaded or schlieren and that of the smectic mesophase
arefocalconicofthetypesmecticAorC. Analytical, thermalandspectral
data supported molecular structures of novel homologues. Transition
temperatures as determine by a hot stage polarizing optical microscopy
(POM) were plotted against number of carbon atom present in n-alkyl
chain ‘R’of left n-alkoxy (-OR) group and the phase transition curves Cr–
I/M, Sm–N, N–I were obtained on linking like or related points. The odd–
even effect is observed for the N–I transition curve and thus transition
curves behaved in normal manner. The even-membered nematic transi-
tion curve occupied higher position than the odd-membered transition
curve. Present series is predominantly nematogenic and partly smecto-
genic with middle-ordered melting type.
Enantiotropy; liquid crystals;
smectic; nematic;
mesomorphism
Introduction
The study of a unique physical state Liquid Crystal (LC) is important [1] from the application
point of view in the field of thermography, electronic display devices, and pharmacology
[2–6]. A chemist synthesized novel LC materials by changing the molecular structure through
the change of geometrical shapes, size, terminal–central–lateral groups or by changing posi-
tional status of same group in an isomeric series or different groups in nonisomeric series,
change of central bridges and number of phenyl or heterocyclic or other ring or rings. Thus,
by changing molecular rigidity and/or flexibility causes variations in LC properties and the
degree of mesomorphism [7–10]. Hence, the present study involves only the synthesis and
characterization of novel LC, materials but, the present study does not include applications
CONTACT U. C. Bhoya
India.
drucbhoya@gmail.com
Department of Chemistry, Saurashtra University, Rajkot , Gujarat,
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

234
D. L. NAMERA ET AL.
of novel material. However, the present study includes and derives the relation between
thermotropic liquid crystal properties and the molecular structure [11–15].
Synthesis
n-Alkoxy benzoic acids were prepared from 4-hydroxy benzoic acid, by suitable alkylating
agents by the modified method of Dave and Vora [16]. α-4-hydroxy phenyl β-2ꢀchloro ben-
zoyl ethylene (B) was prepared by an established method [17]. The coupling of compound A
and compound B is done by the steglich esterification to yield α-4-(4ꢀ-n-alkoxy benzoyloxy
phenyl) β-2ꢀꢀ-chlorobenzoyl ethylenes [18].
The synthetic route to the novel homologous series is under mentioned in Scheme 1.
Scheme . Synthetic route to the novel series.
Characterization
Some of members of a novel series as the representative member of a series were char-
1
acterized by elemental analysis (Table 1), infrared spectroscopy, H NMR spectra, and
mass spectroscopy. Microanalysis was performed on EuroEA Elemental Analyzer. IR spectra
were recorded on Shimadzu FTIR Model-IRAffinity-1S (MIRacle 10), 1HNMR spectra were
recorded on Bruker spectrometer using CDCl3 as a solvent and mass spectra were recorded
on Shimadzu GC-MS Model No.QP-2010.
Table . Elemental analysis for () Pentyloxy, () Octyloxy, and () Tetradecyloxy derivatives.
Elements %Found
H
Elements %Calculated
H
S. No.
Molecular formula
C
O
C
O



CHClO
CHClO
HClO
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
235
Spectral data
1
–
–
HNMR in ppm for decyloxy derivative (D-08). 0.97–1.0 (t, 3H, CH3 of OC10H21 group),
–
–
– –
–
1.28–1.38 (m, 10H, CH2-(CH2-)3 CH2 O ), 1.71–1.76(m, 2H, OCH2CH2) 3.99–4.1 (t,
2H, CH2 O ), 7.05–7.06 (d, 2H, pheny ring proton ortho to alkyloxy group), 7.27–7.28
–
– –
(pheny ring proton ortho to ester group) 7.32–7.68 (m, 11H, substituted phenyl ring), 8.08–
–
–
=
8.10 (d, 2H, in phenyl ring ortho to COO ) 8.21–8.24 (d, 1H, CH CH group proton nearest
to carbonyl group). The NMR data are reliable with the molecular structure.
HNMR in ppm for dodecyloxy derivative (D-10). 0.97–0.99 (t, 3H, CH3 of OC10H21
group), 1.27–1.36 (m, 18H, CH2 (CH2 )7 CH2 O ), 3.98–4.0 (t, 2H, CH2 O ), 7.06–7.07
1
–
–
–
–
– –
– –
–
– –
(d, 2H, pheny ring proton ortho to alkyloxy group), 7.24–7.26 (pheny ring proton ortho to
=
ester group) 7.32–7.62 (m, 6H, substituted phenyl ring), 7.67–7.69 (d, 1H, CH CH group
proton nearest to phenyl ring), 8.08–8.10 (d, 2H, in phenyl ring ortho to COO ) 8.19–8.22
–
–
=
(d, 1H, CH CH group proton nearest to carbonyl group). The NMR data are reliable with
the molecular structure.
IR in cm−1for heptyloxy derivative (D-07). 2966 (C H Str. of ( CH2 )n group of
–
–
–
–
–
OC7H15), 1423, 1589 (aromatic C C Str.), 3269, 3068 (C H Str. of aromatic ring), 1022, 1280
–
–
–
–
–
– – –
(C O Str. of COO group), 1722 (C O, Str. of COO group), 1163 (C O C ), 669 (C–Cl
Str.), 788, 862 (para- and ortho-substituted phenyl ring), The IR data are consistent with the
molecular structure.
IR in cm−1 for decyloxy derivative (D-10). 2928 (C H Str. of ( CH2 )n group of
–
–
–
–
–
–
OC10H21), 1448, 1512, 1583 (aromatic C C Str.), 3277, 3072 (C H Str. of aromatic ring),
–
–
–
–
– – –
1022, 1280 (C O Str. of COO group), 1724 (C O, Str. of COO group), 1136 (C O C ),
682 (C–Cl Str.), 794, 891 (para- and ortho-substituted phenyl ring), The IR data are consistent
with the molecular structure
Mass Spectra of Ethyloxy derivatives (D-02). M+ = 406.
Mass Spectra of Propyloxy derivatives (D-03). M+ = 420.
Results and discussion
A homologous series of novel chalconyl ester derivatives is thermotropically liquid crystalline
in nature, it consists of 12 members of series C1 to C16. Mesomorphism commences from
C4 homologue. C4 to C8 homologous are enantiotropically only nematogenic and C10 to C16
homologues are enantiotropically smectogenic in addition to the nematogenic. The rest of the
homologues C1 to C3 are nonmesomorphic. Transition temperatures (Table 2) of homologues
were plotted for the number of carbon atoms present in n-alkyl chain ‘R’ of -OR terminal end
group. Transition curves Cr–I/M, Sm–N, and N–I are obtained by linking like or related points
of phase diagram (Figure 1). Cr–M/I transition curve follows a zigzag path of rising and falling
with overall descending tendency and behaved in a normal manner. A, Sm–N transition curve
commenced from C10 homologue and behave in a normal established manner, A, N–I transi-
tion curve initially rises and then descended as series is ascended from C4 to C16 and behaved
in a normal manner. The odd–even effect is observed for the N–I transition curve. Curves
(N–I) for odd and even members are matching into each other at C10 member of a series and
then curve prolong as a single transition curve for higher homologues of longer n-alkyl chain.
The Sm–N transition curve is extrapolated [19, 20, 21, 22] to nonsmectogenic C8 homologue
derivative to predict its latent transition temperature (LTT). Analytical, thermal, and spec-
tral data confirm the molecular structure of novel homologues. Textures of homologues as
threaded or schlieren/smectic A or C were confirmed by the miscibility method.

236
D. L. NAMERA ET AL.
Table . Transition temperatures.
Transition temperatures (°C)
S. No.
R = n-alkyl group
Smectic
Nematic
Isotropic
.
.
.
.
.
.
.
.
.
.
.
.
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
—
—
—
—
—
—
—
—
.
.
.
.
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Decyl
Dodecayl
Tetradecayl
Hexadecayl
The tendency of the mesomorphism exhibition from C4 to C16 is attributed to the disalign
the molecules under the exposed thermal vibrations corresponding to their disalignment at
an angle ninety degree less than ninety degree with the plane of the floating surface. The
nonmesomorphicity of C1, C2, C3 homologues is attributed to their low magnitude of disper-
sion forces and low magnitudes of the dipole–dipole interaction which hinders the floating
of victim homologue molecules in two-dimensional arrays under floating condition. Thus,
exhibition of any sort of mesomorphism is missing and molecule of C1, C2, C3 passes directly
into the isotropic liquid state with high order of molecular disorder which randomly ori-
ent in all possible direction without passing through the LC state from the solid crystalline
state due to unsuitable magnitudes of their molecular flexibility, including approximately or
nearly equivalent rigidity, causing to induce high crystallizing tendency. However on increas-
ing the molecular length through n-alkyl chain R of -OR from and beyond the C4 homologue,
the molecules of C4, C5, C6, C7, and C8 disalign only at an angle less then ninety degree due
to favorable and suitable magnitudes of changing molecular flexibility and approximately or
Figure . Phase behavior of series.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
237
nearly equivalent fixed molecular rigidity which allow the molecule to float only with statis-
tically parallel orientational two-dimensional order, causing to induce or to appear nemetic
mesophase between two temperature of difference range of mesophase length of their suitabil-
ity of accepting exposed thermal vibrations. However, the molecules of C10, C12, C14, and C16
homologue are disaligned at an angle perpendicular to the plane of a floating surface which
initially acquire the focal conic smectic mesophase of the type A or C by sliding out layers
of molecular terraces and then residual finding forces maintain the statistically parallel ori-
entational order of molecules of different higher nematogenic mesophase length range, other
than lower smectogenic mesophase length range under the exposed thermal vibrations of
suitable molecular flexibility in addition to rigidity of nearly equivalent magnitudes. Thus,
a novel series become predominately nematogenic and partly smectogenic of the middle-
ordered melting type. The exhibition of the odd–even effect is attributed to even and odd
numbers of methylene units presents in n-alkyl chain ‘R’ of -OR group related to changing
molecular flexibility. The odd–even effect for nematic appears approximately up to C10 homo-
logue; beyond which it disappears for higher homologues of longer n-alkyl chain, because the
longer n-alkyl chain may coil, band, flax, or couple to lie with the principle axis of a core
structure of a molecule. Therefore, uncertainty in the status of n-alkyl chain ‘R’ of -OR group
affects the length of a molecule or to the molecular flexibility or the magnitudes of disper-
sion forces or the dipole moments across the long molecular axis which affects behavioral
status of rising or falling tendencies of transition curves of a phase diagram. Of course, the
phase behaviors of transition curves in the case of present novel series are normal without any
exceptional behavior. The minor lowering of the transition temperature of novel homologues
as compared to corresponding n-alkoxy benzoic acids is due to their breaking of the hydrogen
bonding by the esterification process. The mesogenic behaviors of present novel homologues
series-1 are compared with structurally similar analogs isomeric series -X [23] as under in
following Figure 2.
Homologous series-1 of the present investigation is isomeric with a homologous series-
X chosen for comparison. However, they differ with respect to an arrangement of atoms
in space of -Cl on tail ended phenyl ring occupy ortho or para position which causes dif-
ference in the molecular flexibility, shape, size, permanent dipole moment across the long
molecular axis and the magnitudes of anisotropic forces of intermolecular cohesions for
the same homolog from series to series. Moreover, the configuration of the central bridge
–
=
–
–
linking middle and third or tailed phenyl ring is CH CH CO for present series-1 and
–
–
=
–
CO CH CH under identical condition between middle and third phenyl ring for the
series-X chosen for comparison purpose. Therefore, the direct bonding of CO group with
middle phenyl ring of series-1 an the direct bonding of CO group with third phenyl ring of
series-X causes the difference in total molecular rigidity for the same homologue from series
to series. Thus, the combined effect of related cohesive intermolecular forces with respect
–
–
–
–
Figure . Structurally similar series.

238
D. L. NAMERA ET AL.
to molecular polarity and polarizability and properties for the same homologue from series
to series or from homologue to homologue in the same series causes magnitudes of vari-
ations in the ordered or disordered arrangement of molecules in the floating condition on
the surface, under the influence of exposed thermal vibrations or emergence of liquid crys-
talline state of definite degree of mesomorphism between varying degrees of temperature
difference.
Following Table 3 shows the value of some thermal data for the present series-1 and iso-
meric series-X chosen for comparative purpose as under.
From above data tabulated, it is clear that
r
Homologous series-1 is enantiotropically smectogenic plus nematogenic.
Thermal stability for smectic for series-1of the present investigation is higher by
145 times more than a series-X [zero].
Mesomorphism commences from C4 homologue of series-1, but it commences late from
C5 homologue of series-X.
Lower total mesophase lengths are the same for the series under comparison but almost
more than double for a series-1 as compared to series-X.
The odd–even effect is observed for series under comparative study.
r
r
r
r
The exhibition of smectic plus nematic mesophase by the isomeric series-1 is attributed
to the length to breath ratio and the polarizability induced by ortho substituted flexible
–
–
monoatomic -Cl group and the favorable rigidity induced by CO group which directly
linked to tailed phenyl ring of series-1 due to which it causes the disalignment of molecules
at an angle ninety or less than ninety degree to resist exposed thermal vibrations and make
it possible the lamellar packing of molecules in their crystal lattice with ordered sliding
layered arrangement to induce the smectic phase. Then, the residual intermolecular forces
of attraction adopt statistically parallel orientational order of molecules causing formation
of nematogenic mesophase commencing from C10 homologues well as only nematogenic
mesophase from C4–C16 homologue derivatives. The para substituted -Cl derivatives of
series-X under identical condition do not have sufficient polarity and polarizability through
their molecular rigidity and flexibility to manage or build up lamellar packing of molecules
but maintain only statically parallel orientational order of molecules under the floating
condition with the appearance of only the nematogenic mesophase commencing from C5
homologue. The extent of molecular noncoplanarity of ortho-substituted Chloro group
of series-1 is more than isomeric para substituted -chloro group of series which favorably
induce smectogenic character whose resistivity towards exposed thermal vibrations which
leads to early commencement of mesophases, higher thermal stabilities, higher degree of
Table . Relative thermal stabilities in °C.
Series- Ortho chloro with
Series-X Para chloro With
–
–
–
–
–
–
Series →
CH=CH CO
CO CH=CH
Smectic–Nematic
or
.
(C–C)
—
Smectic–Isotropic
Commencement of
Smectic mesophase
Nematic–Isotropic
C
—
.
(C–C)
.
(C–C)
Commencement of
nematic phase
Total Mesophase length
in centigrade
C
C
.–.
C C
.–.
C/ C C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
239
mesomorphism for smectic and nemetic as compared to same homologues of isomeric
series-X under comparative study. Thus, series-1 of the present investigation is predomi-
nately nematogenic and partly smectogenic with middle-ordered melting type; whereas an
isomeric series-X is nematogenic only with low degree of mesomorphism and low thermal
stabilities.
Conclusions
r
Presently investigated ortho-substituted chalconyl ester derivatives exhibited rich
mesomorphism.
A phenomena of mesomorphism is drastically sensitive and susceptible to the positional
status (ortho, meta, para) of substitution of same functional group and inverted config-
uration of a central bridge.
r
r
Group efficiency order derived for smectic and nematic in the case of halogen substituted
isomeric series are as under with respect to (i) thermal stabilities (ii) early commence-
ment mesophase and mesophase lengths are as under
(i) Smectic
–
–
=
–
Ortho-Cl > para-Cl with CO CH CH central bridge
Nematic
–
–
=
–
Ortho-Cl > para-Cl with CO CH CH central bridge
(ii) Smectic and Nematic
–
–
=
–
Ortho-Cl > para-Cl with CO CH CH central bridge
(iii) Smectic and Nematic
–
–
=
–
Upper: Ortho-Cl > para-Cl with CO CH CH central bridge
=
Lower: Ortho-Cl para-Cl
r
r
Present investigation supported and raised the credibility to the conclusions drawn
earlier.
Present moiety of the novel molecule are bioactive, may be studied by biologist further.
Acknowledgments
The authors acknowledge thanks to the Department of Chemistry (DST-FIST Funded & UGC-SAP
Sponsored), Saurashtra University, Rajkot, for research work. The authors are also thankful to Dr. A.V.
Doshi, Ex. Principal M.V.M. Science and Home Science College Rajkot, for his valuable co-operation
during present investigation as and when needed. Also, thanks to the National Facility for Drug Dis-
covery through New Chemical Entities (NCE’s) for analysis of samples.
References
[1] Renizer, F. (1888). Monatsh, 9, 421.
[2] Naemura, S. (2001). Disp., 22(1), 1.
[3] Kim, W. S., Elston, S. J., & Raynes, F. P. (2008). Displays, 29, 458–463.
[4] Gray, G.W., & Windsor, P. A. (1974). Liq. Cryst. Plastic Cryst., 1, 308–326.
[5] Calliste, C. A., Bail, J. C., Trouilas, P., Pouget, C., Chulia, A. J., & Duroux, L. J. (2001). Anticancer
Res., 21, 3949–3956.
[6] Jain, U. K., Bhatiya, R. K., Rao, A. R., Singh, R., Saxena, A. K. & Seha, I., (2014), Trop. J. Pharma.
Res., 13(1), 73–80.
[7] (a) Suthar, D. M., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 575, 76–83. (b) Chuhan, H. N.,
& Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 570, 92–100. (c) Chudhari, R. P., Chuhan, M. L., &
Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 575, 88–95.

240
D. L. NAMERA ET AL.
[8] (a) Suthar, D. M., Doshi, A. A., & Doshi, A.V., (2013). Mol. Cryst. Liq. Cryst., 582, 79–87. (b)
Marathe, R. B., Vyas, N. N. & Doshi, A. V. (2015). ILCPA, Scipress Ltd., 52, 163–171.
[9] (a) Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Mc Donnell, D. G. (1993). Liq Cryst., 15, 123.
(b) Hird, M., Toyne, K. J., Gray, G. W., & Day, S. E. (1993). Liq. Cryst., 14, 741.
[10] (a) Collings, P. J., & Hird, M. (1997). Introduction to Liquid Crystals Chemistry and Physics, Taylor
and Fransis Ltd.: UK (b) Marcos, M., Omenat, A., Serrano, J. L. & Ezcurra, A. (1992). Adv. Matter.,
4, 285.
[11] Imrie, C. T. (1999). Struct. Bond, 95, 149–192.
[12] Gray, G. W., & Windsor, P. A. (1974). Liq. Cryst. Plastic Cryst., Ellis Horwood: Chichester, U.K.,
1(4), 103–153.
[13] Gray, G. W (1962). Molecular Structure and the Properties of Liquid Crystal, Academic Press:
London.
[14] Gray, G. W., & Jones, B. (1954). J. Chem. Soc., 2556–2562.
[15] Henderson, P. A., Niemeyer, Os., & Imrie, C. T. (2001). Liq. Cryst., 28, 463–472.
[16] Dave, J. S., & Vora, R. A. (1970).In: Liquid Crystal and Ordered Fluids, Johonson, J. F. & Porter, R.
S. (Eds.), Plenum Press: New York, 477.
[17] Patel, R. B., Patel, V. R., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 3–9.
[18] (a) Greene, T. W., & Wuts, P. G. M. (1991). Protective Groups in Organic Synthesis, 2nd ed.; John
Wiley and Sons: New York. (b) Kocienski, P. J. Protecting Groups; Georg Thieme: Stuttgart (1994).
[19] Doshi, A. V., & Lohar, J. M. (1993), Ind. Acad. Sci. Chem. Sci., 105(3), 209–214.
[20] Ganatra K. J., & Doshi, A. V. (2000). J. Indian Chem. Soc., 77, 322–325.
[21] Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104–110
[22] Travadi, J. J., Bhoya, U. C., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 10–15.
[23] Chauhan, H. N., Vyas, N. N., & Doshi A. V. (2013). Mol. Cryst. Liq. Cryst., 557, 96–103.