Study of the Effect of Lateral Substitution on Mesogenic Behavior with Reference to -CH=CH- Unit

Article abstract of DOI:10.1080/15421406.2015.1106281

A novel cinnamate ester homologous series has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal (LC) properties with a focus on the highly polar methoxy group as a lateral substituent. The series consists of twelve homologs; of which C₁-C₅ are nonmesogenic, and the rest of the homologs are enantiotropically smectogenic or and nematogenic. The texture of nematic phases is threaded or Schlieren and that of the smectic is either smectic A or C, as recognized and determined through an optical polarizing microscope equipped with a heating stage. The Sm-N I and N-I transition curves exhibit odd-even effects and behave in normalmanner. The Cr-IMbehaves in normalmanner. Analytical and spectral data confirm the molecular structures of homologs. The average thermal stabilities for smectic and nematic are 125.3 C and 129.8 C, respectively, whose total mesophase length varies from 13 C to 51 C. Some LC properties of present series are compared with the structurally similar known series.

Full text of DOI:10.1080/15421406.2015.1106281

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Study of the Effect of Lateral Substitution on
Mesogenic Behavior with Reference to -CH=CH-
Unit
J. J. Travadi, M. S. Vadodaria, K. D. Ladva & A. V. Doshi
To cite this article: J. J. Travadi, M. S. Vadodaria, K. D. Ladva & A. V. Doshi (2016) Study of
the Effect of Lateral Substitution on Mesogenic Behavior with Reference to -CH=CH- Unit,
Molecular Crystals and Liquid Crystals, 626:1, 90-99, DOI: 10.1080/15421406.2015.1106281
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Date: 30 April 2016, At: 21:20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Study of the Effect of Lateral Substitution on Mesogenic
Behavior with Reference to -CH=CH- Unit
J. J. Travadi , M. S. Vadodaria , K. D. Ladva , and A. V. Doshi
a
b
b
c
a
b
Chemistry Department, Kamani Sc. College and Prataprai Arts College, Amreli, Gujarat, India; Chemistry
c
Department, Shree M. & N. Virani Sc. College, Rajkot, Gujarat, India; Ex. Principal, Matushri Virbaima Mahila
Science and Home Science College, Rajkot, Gujarat, India
ABSTRACT
KEYWORDS
A novel cinnamate ester homologous series has been synthesized and
studied with a view to understanding and establishing the effects of
molecular structure on liquid crystal (LC) properties with a focus on the
highly polar methoxy group as a lateral substituent. The series consists
of twelve homologs; of which C –C are nonmesogenic, and the rest of
Liquid crystal; mesogenic;
smectic; nematic; Azoester
1
5
the homologs are enantiotropically smectogenic or and nematogenic.
The texture of nematic phases is threaded or Schlieren and that of the
smectic is either smectic A or C, as recognized and determined through
an optical polarizing microscope equipped with a heating stage. The
Sm-N I and N-I transition curves exhibit odd-even effects and behave
in normal manner. The Cr-I M behaves in normal manner. Analytical and
spectral data confirm the molecular structures of homologs. The aver-
age thermal stabilities for smectic and nematic are 125.3 C and 129.8 C,
respectively, whose total mesophase length varies from 13 C to 51 C.
Some LC properties of present series are compared with the structurally
similar known series.
Introduction
In continuation of our study on the liquid crystalline (LC) state [1] through an ester homolo-
gous series bearing lateral substitution of -OCH group, the present investigation consists of
3
two phenyl rings bonded through -COO- central bridge and n-alkoxy (-OR) as well as -CH
CH-COO-C H (n), both left and right terminal end groups including -OCH lateral group.
4
9
3
Thus, present investigation is planed with a view to understanding and establishing the effect
of molecular structure on LC properties by substituting n-C H chain as fixed unit at the tail
4
9
end for all homologs of a same series bonded to flexible -CH CH-COO- unit [2–5].
LC substances of thermotropic type are most useful for LC devices either directly or
through study of binary system [6–9], the interest is developed for synthesis of LC ester sub-
stances. Several LC substances have been reported to date [10–18] through ester homolo-
gous series. Hence, the novel substances will be synthesized, characterized by thermomet-
ric, spectral, and analytical data. Experimental data will be interpreted and discussed on the
basis of molecular rigidity and flexibility [19–22] and its LC behaviors will be compared and
interpreted with reference to structurally similar known series, to derive group efficiency
order for smectic and nematic.
CONTACT J. J. Travadi
College, Amreli, Gujarat , India.
 Taylor & Francis Group, LLC
j.travadi@gmail.com
Department of Chemistry, Kamani Science College and Prataprai Arts
©

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
91
Scheme . Synthetic route to the series. R –C H
where, n ,,,,,,,,,,,.
n
n+
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated by suitable alkylating agents (R-X) to convert it
into dimeric 4-n-alkoxy benzoic acids by the modified method of Dave and Vora [23]. 4-
Hydroxy-3-methoxy cinnamic acid (m.p. 64 C) was esterified by n-butenol by using conc.
H SO by usual established method [24]. The ester was very dense brown colored liq-
2
4
uid (yield 64.5%), which purified from n-hexane. Dimeric 4-n-alkoxy benzoic acids were
individually condensed with 4-hydroxy-3-methoxy n-butyl cinnamate in dry cold pyri-
dine through corresponding acid chlorides [25]. Final products were individually decom-
posed, filtered, washed, dried, and purified until constant transition temperatures were
obtained.
The synthetic route to the series is shown below in Scheme 1.
The chemicals required, 4-Hydroxy benzoic acid, MeOH, KOH, Alkyl halide (R-X),
Thionyl chloride, 4-hydroxy-3-methoxy cinnamic acid (Ferulic acid), n-Butenol, Conc.
H SO , Pyridine, 1:1 HCl, NaHCO , NaOH, anhydrous CaCl , Silicagel, Petrolium ether,
2
4
3
2
Methyl acetate, and n-Hexane were used as received, except solvents which were dried and
purified prior to use.

92
J. J. TRAVADI ET AL.
Table . Elemental analysis for propyloxy, pentyloxy, octyloxy, and dodecyloxy derivatives.
%
of C Experimental
(theoretical)
% of H Experimental
(theoretical)
Compound no.
Molecular formula
C H O
C
C
C
C
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)




C H O


C H O

 
CHO
Characterization
Representative homologs of the series were selected for characterization of structure by ele-
1
mental analysis (Table 1), IR spectra, mass spectra and H NMR spectroscopy. Microanalysis
was performed on Perkin Element PE 2400 CHN analyzer. IR spectra were recorded on Perkin
1
Elmer spectra GX. H NMR spectroscopy performed was recorded on Bruker using CDCl as
3
solvent.
Mesomorphic properties were investigated using hot stage polarizing microscope.
Analytical Data
1
IR spectra in cm for hexyloxy homolog derivative.
The IR spectrum of the compound showed
1
6
8
1
1
1
9
2
91.60 cm polymethylene of -C H group.
6
13
1
44.29 and 766.67 cm as para and ortho sub. benzene ring,
1
164.59 cm as -CO- of alkoxy group,
1
1
246.58, 1674.23 cm , and 1601.22 cm , conforms -COO- and -CO- of ester group,
1
423.45 and 1468.30 cm , confirms aromatic -C C-,
1
33.79 and 1020.03 cm , confirms trans -CH CH- group,
1
935.71 and 2861.18 cm , confirms alkyl group.
IR data support the molecular structures.
1
IR spectra in cm for octyloxy homolog derivative.
The IR spectrum of the compound showed,
1
6
8
2
1
1
1
9
43.93 cm , confirms polymethylene of -C H group,
8
17
1
1
45.69 cm and 761.67 cm , confirms para and ortho sub. benzene ring,
1
854.36 and 2929.43 cm , confirms alkyl group,
1
1
1
641.13 cm , 1606.20 cm , 1255.19 cm , confirms -COO- and -CO- group,
1
512.79 and 1419.84 cm , confirms aromatic -C C-,
1
156.31 and 1062.23 cm as -CO- of alkoxy group,
1
67.86 cm , confirms trans -CH CH- group,
IR data support the molecular structures.
1
H NMR spectra in ppm for pentyloxy and decyloxy derivatives.
Amyloxy.
1
H NMR data in δ ppm (n-pentyloxy derivative, 400 MHz, CDCl , standard TMS):-
3
0
.9677 (-CH of -C H ), 1.2697–1.4192 (-CH of -C H ), 1.6345–1.8558 (-OCH -CH
3
5
11
2
5
11
2
2
of -C H ), 3.8545 (-O-CH ), 4.0493 and 3.9740 (-O-CH - of -C H ), 6.4105–7.1766 (-O-
5
11
3
2
5
11
C H -CH CH-CO-), 7.5383 to 8.1700 (p-sub. benzene ring).
6
3
The data supports the molecular structure.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
93
Homolog
Theoretical
Experimental
C
C
.
.
.
.
1
Decyloxy. H NMR data in δ ppm (n-decyloxy derivative, 400 MHz, CDCl , standard TMS):-
3
0
.8936 (-CH of -C H ), 1.1847–1.3780 (-CH - of -C H ), 1.6185–1.7495 (-OCH -
3
10 21
2
10 21
2
CH - of -C H ), 3.7332 (-O-CH ), 3.9117–4.1366 (-O-CH - of -C H ), 6.7604–7.4537 (-
2
10 21
3
2
10 21
O-C H -CH CH-CO-), 7.5508–8.0565 (p-sub. benzene ring).
6
3
The data supports the molecular structure.
Texture determination by miscibility method.
•
•
•
•
Hexyloxy homolog ——→ Threaded nematic
Dodecyloxy homolog ——→ Schlieren nematic
Octyloxy homolog ——→ Smectic – A
Tetradecyloxy homolog ——→ Smectic – C
Results and discussion
ꢀ
The novel homologous series n-butyl-4(4 -n-alkoxy benzoyloxy)-3-methoxy cinnamates was
synthesized by condensing dimeric n-alkoxy benzoic acids and 4-hydroxy-3-methoxy-n-
butyl cinnamate (very dense brown liquid). The first five members of the series are nonmeso-
genic, C member is only nematogenic, C to C are smectogenic plus nematogenic and C to
6
7
12
14
C are only smectogenic. All LC homologs are enantiotropically smectogenic or and nemato-
16
genic. Transition temperatures (Table 2) of homologs are plotted versus the number of carbon
atoms present in n-alkyl chain of the left n-alkoxy terminal end group. Transition curves (Fig.
1
) are obtained on linking like or related points. Cr-I/M transition curve adopts a zigzag path
of rising and falling with overall descending tendency and behaves in normal manner. Sm-N
or Sm-I transition curve descended from C to C for even numbered homologs and rises
8
16
Table . Transition temperatures in C.
Compound no.
R -C H
Smectic
Nematic
Isotropic
n
n+

C
C
C
C
C
C
C
C
C
C
C
C
–
–
–
–
–
–
–
–
–
–
.
.
.
.
.
–
.
.
.
.
.
.
.
.
.
.
.











–
.
.
.
.
.
.



–
.

94
J. J. TRAVADI ET AL.
Figure . Phase behaviors of series.
from C to C and then descended to C through C homolog with exhibition of an odd-
7
14
16
12
even effect. N-I transition curves for odd and even members initially rises and then descends
up to the C homolog and ceases to exhibit nematic mesophase with exhibition of odd-even
12
effect. Transition curve of odd-members occupied lower position than a curve for even mem-
bers in case of Sm-I/N and N-I transition curves exhibiting odd-even effect. Transition curves
for odd and even members merge into C11 member of a series and then a single transition
curve for N-I and Sm-N/I progressed for higher homologs C , C , and C16 from and beyond
12
14
C homolog. Thus, transition curves of a phase diagram showing phase behaviors of a series
11
behaved in normal manner. N-I transition curve is extrapolated to nonmesogenic homolog
C to determine its latent transition temperature (LTT). Similarly Sm-I/N transition curve is
5
extrapolated to C to predict and interpret its nonsmectogenic behavior. The mesomorphism
6
commences from C homolog and the mesogenic properties like thermal stabilities for smec-
6
tic and nematic, and their mesophase length range etc. vary from homolog to homolog in the
same series. Thus, present novel series is partly smectogenic and partly nematogenic whose
degree of mesomorphism is low and is of middle ordered melting type.
Lowering of transition temperatures of novel homologs, corresponding to n-alkoxy ben-
zoic acid is attributed to breaking of hydrogen bonding between two molecules by esteri-
fication process. Alternation in transition temperature is due to the odd and even number
of carbon atom present in n-alkyl chain of -OR terminal. Exhibition of only smectogenic
or only nematogenic or smectic and subsequent nematic phase formation is attributed to
the disalignment of molecules at angle ninety or less than ninety degree with the plane of
surface with presence or absence of lamellar packing of molecules in crystal lattice of rigid
crystals. C –C16 homologs molecules bearing lamellar packing of molecules in their preoc-
7
cupied crystal lattices, which under exposed thermal vibrations arrange themselves in two-
dimensional network as sliding layers for definite range of temperature with appearance of
smectogenic character. The C –C homologs bearing residual intermolecular end-to-end
7
12

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
95
Figure . Structurally similar series.
anisotropic forces of suitable magnitudes arranges molecules to float with statistically par-
allel orientational order which induces nematogenic character beyond smectogenic charac-
ter. However, C homolog with absence of lamellar packing of molecules in its crystal lattices
6
fails to exhibit smectic phase but, exhibited only nematic phase. The converse of it, C and
14
C16 homologs bearing lamellar packing of molecules in their crystal lattices but, unsuitable
or insufficient magnitudes of residual intermolecular end-to-end attractions and closeness
fails to induce nematic phase beyond smectic phase and converted into isotropic state, at
which molecules are randomly oriented in all possible directions with high order of disor-
der or high entropy (ꢀS ꢀH T). The mesogenic homologs (C –C ) on cooling from their
6
16
isotropic state carefully, it resumes or reshows their mesogenic state (smectic or nematic) in
a reversible manner exactly at the same temperature at which it had appeared on heating.
Odd-even effect observed for N-I and Sm-I N transition curve is attributed to the sequen-
tially added methylene unit at the n-alkyl chain. Extrapolated [26–28] Sm-N transition curve
matches with the N-I transition point of C homolog, which indicates that Sm-N transition
6
temperature and N-I transition temperature coincided to each other at isotropic tempera-
ture 121.0 C, i.e., smectogenic phaselength is 121−121 00 zero. Means, there is no practi-
cal possibility for the occurrence of the smectogenic mesophase for C homolog. Similarly
6
extrapolation of N-I transition curve at C homolog to predict LTT 92 C, i.e., latent ability of
5
C homolog to exhibit LC property, which is not realizable due to its high crystallizing ten-
5
dency; at far below the isotropic temperature. Nonmesogenic property of C to C homologs is
1
5
attributed to their high crystallizing tendency arising from low dipole-dipole interactions and
the law magnitudes of dispersion forces by interactions between instantaneous dipoles pro-
duced by the spontaneous oscillations of electron clouds of the molecules as a consequence
of unfavorable molecular rigidity and flexibility. Hence the molecules of C –C are unable to
1
5
resist exposed thermal vibrations and abruptly breaking their crystal lattices and smoothly
and sharply transform into isotropic state without passing through LC state. Changing trend

96
J. J. TRAVADI ET AL.
in mesogenic properties from homolog to homolog in the same series is due to the changing
number of methylene unit or units at the left n-alkyl chain bonded to phenyl ring through
oxygen atom, keeping rest of the molecular part unchanged. The mesogenic properties of
present novel series are compared with the structurally similar known series as shown below in
Figure 2.
Homologous series-1 of present investigation and the structurally similar homologous
series-X [29] and -Y [30] selected for comparing some LC properties depending upon vari-
ation of molecular structure are as under. Homologous series-1 and -X are identical with
respect to two phenyl rings linked through -COO- central bridge and the left and right n-
alkoxy group (-OR) as well as tail group -CH CH-COO-C H , respectively, for the same
4
9
homolog from series-1 to series-X, but they differ with respect to presence and absence of
laterally substituted -OCH group. Therefore, the molecular rigidity of series-1 and -X is iden-
3
tical but differs with respect to molecular flexibility for the same homolog from series to series
and from homolog to homolog in the same series. Homologous series-1 and -Y are identical
with respect to molecular rigidity but they differ with molecular flexibility due to presence
and absence of laterally substituted -OCH group, respectively, and the replacement of a part
3
of tail end group, -CH CH-COO- by -COO-. Thus, variations in mesomorphic properties and
the degree of mesomorphism of series-1, -X, and -Y will depend upon changing features of
series under comparative study. Following Table 3 represent some mesogenic properties of
series-1, -X, and -Y as under.
Above Table 3 indicates that
•
•
•
Homologous series-1 and -X are smectogenic in addition to nematogenic, whereas
series-Y is only smectogenic without exhibition of nematic property.
Smectogenic mesophase formation commences from C , C , and C homolog for series-
7
10
5
1
, -X, and –Y, respectively.
Nematogenic mesophase commences from C to C homologs for series-1 and –X,
6
5
respectively, but it does not commence till C homolog for a series-Y.
16
•
•
Smectic thermal stability of series-1, -X, and -Y are in decreasing order.
Nematic thermal stability increases from series-1 to -X, but it destabilizes nematic phase
for series-Y.
Total mesophaselength is the highest for a series-X and the lowest for a series-Y, whereas
it is intermittent of present series-1.
•
Looking to the thermal stability for smectic, it decreases from series-1 to -X to -Y. Decreas-
ing order is attributed to the presence of highly polar lateral -OCH group which increases
3
molecular polarizability and the suitable magnitudes of intermolecular cohesion against the
decreasing intermolecular attraction by broadening of same molecule. Thus, predominancy
of the polarizability factor stabilizes and facilitates smectic mesophase formation of the
Table . Average thermal stability in C.
Series:→

X
Y
Smectic-isotropic or
smectic-nematic
Commencement of smectic
phase
Nematic-isotropic
Commencement of nematic
phase
. (C –C )
. (C –C )
. (C –C )


 


C
. (C –C )
C
C
. (C –C )
–
–




C
C
Total mesophaselength
range in C (Sm + N)
C to C
–
–
–
i
p
C C
C C

C C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
97
highest magnitudes (125.3) for presently investigated series-1. Moreover, series-X and -Y are
long linear lath like, whose suitable magnitudes of anisotropic forces of intermolecular cohe-
sion and closeness reduces due to absence of lateral group like -OCH . Homologous series-X
3
contain additional -CH CH- unit as similar to series-1 in a tail group -CH CH-COOC H (n),
4
9
but its thermal stability reduces by 125.3−101.0 24.3 units due to absence of lateral group.
However, a homologous series-Y contain -COOC H (n) flexible tail group, which differs from
4
9
flexible tail groups of series-1 and -X by -CH CH- unit which increases rigidity and flexibil-
ity. Thus, absence of -CH CH- unit at flexible tail group in addition to lateral group reduces
more reduction in thermal stability and lowering of transition temperatures. Thermal sta-
bility is related with thermodynamic quantity ꢀH and thermal resistivity towards exposed
thermal vibrations, which gradually decreases from series-1 to -X to -Y for maintaining smec-
tic mesophase. Therefore decreasing order of smectic thermal stability is observed. However
the residual end-to-end attractions and closeness beyond smectic mesophase are suitable to
induce nematic phase in case of series-1 and -X due to presence of -CH CH- unit in a same
flexible tail group -CH CH-COO-C H (n), but it fails the exhibition of nematic phase beyond
4
9
smectic phase due to absence of -CH CH- unit in -COO-C H (n) tail group. Thermal stabil-
4
9
ity for nematic for a series-X is more than a series-1, because, the reduction in smectic thermal
stability of series-X as compare to series-1 is compensated by increasing thermal stability for
nematic, i.e., nematic phase has stabilize at the cost of smectic phase. Nematogenic charac-
ter is totally lost at the cost of smectic phase in series-Y due to absence of -CH CH- unit at
the flexible tail -COO-C H (n). The commencement of smectic phase, i.e., early or late com-
4
9
mencement of smectic depends upon the extent of noncoplanarity of a molecule. The oxygen
atoms of -COO- group is bumping into the nonbonded sides of the adjacent hydrogen atoms
of the aromatic ring which causes considerable strain on the molecule, consequently a twist
around the C-O bond occurs forcing phenyl ring and n-butyl group out of the plane of the
molecule. Thus, the molecular coplanarity is reduced to some extent as compared to -CH
CH- unit containing series-1 and -X. On account of this difference the Sm-I thermal stability
of series-Y is the lowest and the smectic phase commences earliest from C and late from C7
5
and C for series-Y, -1 and –X, respectively. Total mesophase length range which is the high-
10
est for series-X is attributed to the higher phase length of its nematic mesophase length than
a series-1 and -Y, respectively, whose over all thermal resistivity (Sm + N) is relatively more.
Thus, the changing behaviors in LC properties and the degree of mesomorphism is attributed
to changing molecular rigidity and flexibility for the same homolog from series to series and
from homolog to homolog in the same series due to their changing molecular structure by
left n-alkoxy group in the same series and the changing right-handed tail group from series
to series for the same homolog.
Conclusions
•
•
•
Presently investigated ester homologous series is partly smectogenic and partly nemato-
genic whose mesophase length is considerably good and is of middle-ordered melting
type.
The group efficiency order derived on the basis of (i) thermal stability, (ii) early com-
mencement of mesophase, and (iii) total mesophaselength range for smectic and nematic
are as under.
The presence of -CH CH- unit in ester series is generally nematogenic and absence of
-
-
CH CH- unit is generally smectogenic or -CH CH-COO- group is nematogenic and
COO- group is smectogenic.

98
J. J. TRAVADI ET AL.
Smectic:-
-
CH CH-COOC H (n)
-CH CH-COOC H (n)
-COOC H (n)
 




With lateral -OCH group
Without lateral group
Nematic:-
Without lateral group

-
CH CH-COOC H (n)
-CH CH-COOC H (n)
-COOC H (n)




 
Without lateral group
With lateral -OCH group
Without lateral group

(
ii) Smectic:-
-
COOC H (n)
-CH CH-COOC H (n)
-CH CH-COOC H (n)




 
Without lateral group
With lateral -OCH group
Without lateral group

Nematic:-
-
CH CH-COOC H (n)
-CH CH-COOC H (n)
-COOC H (n)
Without lateral group




 
Without lateral group
With lateral -OCH group

(
iii) (Smectic + Nematic):-
-
CH H-COOC H (n)
-CH CH-COOC H (n)
-COOC H (n)




 
Without lateral group
With lateral -OCH group Without

lateral group
•
•
•
Molecular rigidity and flexibility corresponding to molecular structure are the main
operators of mesophase formation.
A mesomorphism phenomena is very sensitive and susceptible to the molecular
structure.
Presently investigated homologous series may be useful for the study of binary systems
and in agriculture field to grow quality fruits and flowers.
Acknowledgments
The authors are especially thankful to management, principal and HOD (chemistry Dept.) of Shree
M. & N. Virani Sc. College, Rajkot and Kamani Sc. College & Prataprai Arts College, Amreli, for their
valuable cooperation to facilitate present research work, and IR spectra. The authors are also thankful
to the authorities of Saurashtra University for analytical services.
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