Dependence of mesomorphism on tail group in combination with a lateral methoxy group

Article abstract of DOI:10.1080/15421406.2015.1068996

A novel homologous series of esters with a lateral methoxy group and terminal n-heptyl cinnamate group was synthesized and studied to investigate mesomorphic behavior in relation to structure. The twelve membered series consists of methoxy to pentyloxy derivatives that are nonmesomorphic and the rest of the homologs as smectegenically mesomorphic, including C₆ and C₇ monotropic smectic and C₈ to C₁₆ enantiotropic smectic without exhibition of any nematic property. The textures of smectogenic mesophases are focal conic fan shaped or batonates of the type smectic-A or Schlieren-C. An odd-even effect is exhibited by the Sm-I transition curve in the phase diagram. The Cr-Sm and Sm-I transition curves behave in a normal manner. Transition temperatures and textures were determined on an optical polarizing microscope, equipped with a heating stage. Some representative members were characterized by IR, H¹NMR, mass spectra, and elemental analysis. Analytical data support the molecular structures of the homologs. Mesomorphic properties of the present novel series are compared with the structurally similar known series. The present series is smectogenic only, whose thermal average stability is 89.8°C and of a middle-ordered melting type.

Full text of DOI:10.1080/15421406.2015.1068996

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Dependence of mesomorphism on tail group in
combination with a lateral methoxy group
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) Dependence of
mesomorphism on tail group in combination with a lateral methoxy group, Molecular Crystals
and Liquid Crystals, 625:1, 63-71, DOI: 10.1080/15421406.2015.1068996
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Date: 05 March 2016, At: 22:27

MOL. CRYST. LIQ. CRYST.
, VOL. , –

http://dx.doi.org/./..
Dependence of mesomorphism on tail group in combination
with a lateral methoxy group
a
b
b
c
J. J. Travadi , M. S. Vadodaria , K. D. Ladva , and A. V. Doshi
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 homologous series of esters with a lateral methoxy group and
terminal n-heptyl cinnamate group was synthesized and studied to
investigate mesomorphic behavior in relation to structure. The twelve
membered series consists of methoxy to pentyloxy derivatives that are
nonmesomorphic and the rest of the homologs as smectegenically
mesomorphic, including C and C monotropic smectic and C to C
Liquid crystal; mesogenic
ester; mesomorphism;
nematic; smectic
6
7
8
16
enantiotropic smectic without exhibition of any nematic property. The
textures of smectogenic mesophases are focal conic fan shaped or bato-
nates of the type smectic-A or Schlieren-C. An odd-even effect is exhib-
ited by the Sm–I transition curve in the phase diagram. The Cr–Sm and
Sm-I transition curves behave in a normal manner. Transition temper-
atures and textures were determined on an optical polarizing micro-
scope, equipped with a heating stage. Some representative members
1
were characterized by IR, H NMR, mass spectra, and elemental analy-
sis. Analytical data support the molecular structures of the homologs.
Mesomorphic properties of the present novel series are compared with
the structurally similar known series. The present series is smectogenic
°
only, whose thermal average stability is 89.8 C and of a middle-ordered
melting type.
Introduction
The liquid crystal state has flow properties like a liquid and optical properties like crystals,
hence it is termed a liquid crystal (LC) state or an anisotropic liquid state or a mesomorphic
state [1]. The dual character of flow and anisotropy brings a usefulness in various fields of
applications [2–5]. The present study is planned with a view to synthesize novel LC substances
through homologous series by varying molecular structures by changing number of phenyl
rings or central groups linking phenyl rings or terminal end group or groups of different polar-
ity or by changing position (o, m, p) or positions of same polar group in isomeric series, etc.
to understand and establish the relations between LC property and the molecular structures
[
6–8]. Thus, novel substances can be useful to physics, biology, pharmacy, agriculture, engi-
neering, and technology including chemistry, because LC materials either of the thermotropic
type or Lyotropic type are useful to mankind [9–12]. A literature survey on thermotropic LCs
CONTACT J. J. Travadi
Amreli, Gujarat, India, .
 Taylor and Francis Group, LLC
j.travadi@gmail.com
Chemistry Department, Kamani Sc. College and Prataprai Arts College,
©

6
4
J. J. TRAVADI ET AL.
[
13–16] prompted the proposed investigation of the synthesis of ester homologs with a lat-
eral –OCH group at the ortho position to central –COO– group and varying right handed
3
terminal end groups of –CH=CH-COOC H (n) in combination with left –OC H
end
7
15
n
2n+1
group. Then the novel data are interpreted on the basis of molecular rigidity and flexibility
17–20] of the molecular structure after characterization of novel substances.
[
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 [21]. 4-Hydroxy
-methoxy cinnamic acid (m.p. 64°C yield 67%) was esterified by n-heptanol by using conc.
H SO by a usual established method [22]. The ester was a very viscous and dense brown
3
2
4
liquid, which was purified from distilled n-hexane. The yield was 62.5%. Dimeric 4-n-alkoxy
benzoic acids were individually condensed with 4-hydroxy, 3-methoxy n-heptyl cinnamate in
dry cold pyridine through corresponding acid chlorides [23]. Final products were individually
decomposed, 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 halides (R-X), thionyl chloride, 4-hydroxy, 3-
methoxy, cinnamic acid (Ferulic acid), n-heptanol, Conc. H SO , pyridine, 1:1 HCl, NaHCO ,
2
4
3
NaOH, anhydrous CaCl , silica gel, petroleum ether, methyl acetate, and n-hexane were used
2
as received, except solvents which were dried and purified prior to use.
Scheme . Synthetic route to the series

MOL. CRYST. LIQ. CRYST.
65
Table . Elemental analysis for ethyloxy, butyloxy, octyloxy and dodecyloxy derivatives.
Compound no.
Molecular formula
C H O
Mol.% of C Experimental (Theoretical)
Mol.% of H Experimental (Theoretical)
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 Elmer PE 2400 CHN analyzer. IR spectra were recorded on Perkin
1
Elmer spectra GX. H NMR spectroscopy performed were recorded on Bruker instrument
using CDCl as solvent.
3
Mesomorphic properties were investigated using hot stage polarizing microscope.
Analytical data
Elemental analysis for ethyloxy, butyloxy, octyloxy, and dodecyloxy derivatives:
-
IR spectra in cm for methyloxy and ethyloxy homologue derivatives
Methyloxy: The IR spectrum of the compound showed,
-
1
-1
8
6
2
1
1
1
1
41.66 cm and 758.39 cm confirms p-sub. benzene ring,
-1
88.72 cm confirms polymethylene of –C7H15 group,
-
1
-1
-1
956.00 cm and 2917.90 cm & 2854.00 cm confirms alkyl group,
-
1
-1
-1
249.92 cm , 1604.08 cm and 1709.64 cm , confirms –COO– & –CO– group,
-
1
511.33 & 1459.05 cm confirms aromatic –C=C–,
-
1
164.49 cm as .CO- of alkoxy group,
-
1
-1
026.20 cm and 980.78 cm confirms trans –CH=CH– group,
IR data supports the structure.
−1
IR Spectra in cm for ethyloxy homolog derivatives
Ethyloxy:- The IR spectrum of the compound showed,
-
1
8
6
2
1
1
1
1
45.19 and 769.25 cm confirms p-sub. benzene ring,
-1
-1
47.18 cm and 695.28 cm confirms polymethylene of –C H group,
7
15
-
1
931.19 and 2860.06 cm confirms alkyl group,
-
1
-1
248.21, 1605.48 cm and 1711.3 cm confirms –COO– & –CO of ester group,
-1
510.78 cm confirms aromatic –C=C–,
-1
165.83 cm as –CO– of alkoxy group,
-
1
042.36 and 1099.61 cm confirms trans –CH=CH– group.
IR data supports the molecular structure.

6
6
J. J. TRAVADI ET AL.
1H NMR spectra in ppm for heptyloxy and decyloxy derivatives heptyloxy
1
H NMR Data in δ ppm (n-hexyloxy derivative, 400 MHz, CDCl , Standard TMS)
3
0
.808 (–CH3 of –C H ), 1.2376 (–CH of —–C H ), 1.7629 (–OCH –CH of
7
15
2
7
15
2
2
–
C H ), 3.7696 (–O–CH ), 3.947 (–O–CH – of –C H ), 7.0883 and 7.0723
7
15
3
2
7
15
(
–O–C H –CH=CH–CO–), 8.059 and 8.0812 (p-sub. Benzene ring).
6
3
The data support the molecular structure.
Decyloxy

H NMR data in δ ppm (n-Decyloxy Derivative,  MHz CDCl , Standard TMS)

0
.8128 (–CH of –C H ), 1.2229 (–CH of –C H ), 1.7308 and 1.7481 (–OCH –CH of
3
10 21
2
10 21
2
2
–
C H ), 3.7547 (–O–CH ), 3.9458 (–O–CH – of –C H ), 7.0764 and 7.0616
10
21
3
2
10 21
(
–O–C H –CH=CH–CO–), 8.0493 and 8.0714 (p-sub. Benzene ring).
6
3
The data supports the molecular structure.
Texture determination by miscibility method
r
Octyloxy homolog
Decyloxy homolog
——→ Smectic – A
——→ Smectic – A
r
r
Tetradecyloxy homolog ——→ Smectic –C
Mass spectra
Homolog: Theoretical Experimental
C2
C4
440.53
568.58
440.0
568.25
Results and discussion
Homologous series 4-(4’-n-alkoxy benzoyloxy)-3-methoxy-n-heptyl cinnamates was synthe-
sized from dimeric 4-n-akoxy benzoic acid through their corresponding acid chlorides and
a nonmesomophic component 3-methoxy–4-hydroxy-n-heptyl cinnamate (very viscous and
dense brown liquid, yield 62.5%). The C to C homologs are nonmesomorphic, but meso-
1
5
morphism commences from the C homolog in a monotropic manner as a smectic type and
6
continues until the last C16 member of the series as an enantiotropic smectic phase; how-
ever, the C homolog behaves in monotropic (Sm) manner. Nematic mesophase exhibition is
7
missing for the homologs of entire series of the present investigation. Transition temperatures
(
Table 2) of the homologs are plotted versus the number of carbon atoms present in n-alkyl
(
-C H
) chain. Transition curves (Cr-I or Sm and Sm-I or I-Sm) are formed showing phase
n
2n+1
behaviors of a series in a phase diagram (Fig. 1). Cr-I or Sm transition curve adopt a zigzag
path of rising and falling values with overall descending tendency as series is ascended. Sm-I
(
or I-Sm) transition curve initially rises for odd members and falls for even members up to
the decyloxy (C ) homolog. Both transition curves for odd and even members are merge into
10
each other between C and C homologs and then from and beyond, (Sm-I) transition curve
rises to maxima at dodecyloxy (C ) homolog and descended as series is ascended in usual
9
10
12

MOL. CRYST. LIQ. CRYST.
67
Figure . Phase behaviors of series.
established manner. Thus, odd-even effect is exhibited by Sm-I transition curve and both tran-
sition curves i.e. Cr-Sm or Cr-I and Sm-I transition curves behaved in normal manner. The
Sm-I transition curve for odd members is extrapolated to pentyloxy (C homolog to predict
5)
and determine its latent transition temperature (L.T.T.). Sm-I transition curve follows as sin-
gle curve from and beyond decyloxy (C ) homolog, i.e., odd-even effect disappears from and
10
beyond C homolog for higher homologs of longer n-alkyl chain. The average thermal stabil-
10
ity for smectic is 89.8°C and the mesomorphic (Sm) phase length is varied between 11°C and
3
5°C. The mesomorphic properties from homolog to homolog are changing with molecular
length. Thus, presently investigated ester series with lateral substitution by –OCH group is
3
smectogenic without exhibition of smectic property.
The ester homologs from C to C do not exhibit any type of mesomorphism, because
1
5
the magnitudes of anisotropic forces of intermolecular end to end and/or lateral attractions
occurred as a consequence of unsuitable molecular rigidity and flexibility which induces
inability to resist exposed thermal vibrations to cause mesomorphism, and hence have a high
crystallizing tendency. The molecules of homolog derivatives C to C16 generate a lamel-
6
lar packing of molecules with layered structure. Thus, smectogenic mesophase formation is
observed within a definite temperature range. The same sample on cooling from isotropic state
by proper rate of cooling, the smectogenic mesophase formation reappears from and below
Table . Transition temperatures in °C.
Compound No.
n-Alkyl group R=-C H
Sm
N
Isotropic
n
n+
C
C
C
C
C
C
C
C
C
C
C
C
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.






(.)
(.)
.
.
.
.
.








(
) indicates monotropy.

6
8
J. J. TRAVADI ET AL.
Figure . Structurally similar series.
isotropic temperature till solid crystalline state. Thus, enantiotropic smectic mesophase for-
mation without exhibition of nematic phase observed for C to C homologs of the present
6
16
novel series. The exhibition of an odd-even effect and alternation of transition temperatures
of ester derivatives are due to the changing number of methylene unit at the n-alkyl chain of
left n-alkoxy (-OR) terminal end group. Disappearance of odd-even effect from and beyond
C homologs for higher homologs of longer n-alkyl chain is attributed to the coiling, bend-
10
ing, flexing, or coupling of n-alky chain with major axis of the core structure of molecules.
The extrapolation [24–27] of the Sm-I transition curve for C nonmesomorphic homolog to
5
determine its probable L.T.T. which is at 74° C. Mesomorphic properties vary from homolog
to homolog in present series is attributed to the changing number of methylene units which
changes molecular length, polarity and polarizability, length to breadth ratio, etc. which causes
variations in molecular rigidity and flexibility for emerging suitable or unsuitable magnitudes
of anisotropic forces of intermolecular attractions to induce mesomorphism. The mesomor-
phic properties of present series-1 are compared with the structurally similar homologous
series-X [28] as shown below in Fig. 2.
The homologous series of the present investigation (series-1) and a known homologous
series-X chosen for comparison are identical with respect to two phenyl rings, central bridge
–
COO–, left n-alkoxy (–OC H
) terminal end group for the same homolog from series
n
2n+1
to series and the part of terminal end group of series-1 and a central group of series-X, i.e.,
–
CH=CH–COO–. The differences between the structures of the two series (1 and X) are
clearly seen in Fig. 2. Table 3 represents some mesomorphic properties like average ther-
mal stability, commencement of mesophase, number of homologs and their type, mesophase
length range, odd even effect, etc. under comparison.
Table 3 indicates that
r
homologous series-1 of present investigation is only smectogenic, whereas a series-X
chosen for comparison is smectogenic in addition to nematoganic.
r
Smectic mesophase commences from C homolog in series-1 and X, i.e., both series are
equi-smectogenic.
6
Table . Average thermal stability in °C.
Series:→

X
Smectic-Isotropic or Smectic-nematic
Commencement of Smectic phase
Nematic- Isotropic
Commencement of nematic phase
Total mesophase length range in °C (Sm + N)
. (C -C )
. (C -C )




C
–
–
C
. (C -C )


C
. to . (C ) (C )
. to . (C ) (C )


 

MOL. CRYST. LIQ. CRYST.
69
r
r
Nematic mesophase commences from C member of a series-X, but it does not com-
5
mence till the last C homolog member of a present series-1.
16
The mesophase length range difference between minimum and maximum in °C are (35
–
11 = 24) twenty four for series-1 and (59 – 33 = 25) twenty five for a series-X, i.e.,
series-1 and X are equally resistive and efficient against exposed thermal vibrations to
cause mesophase stabilization, but the mesophase stabilization temperatures of series-X
are higher for the same homolog from series to series.
r
Thermal stability in average of present series-1 for mesophase (Sm and N) is relatively
lower than a series-X under comparison.
Homologous series-1 is laterally substituted by highly polar methoxy group, which
increases molecular width and reduces intermolecular attractions and at the same time, inter-
molecular attractions are enhanced by increased molecular polarizability through increase in
molecular width. Thus, two opposing effects of intermolecular attractions or molecular cohe-
sion occur for the same reason. Therefore, net effect of intermolecular attractions depends
upon the dominance of the two opposing effects operated at a time for the same reason. More-
over, series-1, consisted of two phenyl rings whereas series-X under comparison consists of
three phenyl rings. Therefore, aromaticity, and the molecular rigidity of series-X is more than
a series-1. The left n-alkoxy terminal end group of series-1 and X are identical for the same
homolog from series to series, but the right terminal end group though, consisted of seven
carbon for both the series, they differ in length, type of hybridization and aromaticity, i.e.,
right-handed terminal end group bonded to -COO- group in series-1 is an aliphatic open
3
hydrocarbon chain in which sp hybridized carbons are involved, whereas in case of series-X,
2
the six carbons are aromatic hydrocarbons bearing cyclic ring in which sp hybridized carbons
are bonded with -COO- group through -CH - methylene unit. Thus, molecules of series-1
2
bears more flexible open n-alkyl chain of unexpected status of flexibility, than, a series-X, in
2
which six sp carbons occupy their restricted position in an aromatic phenyl ring and increases
molecular rigidity. Thus, the same homolog molecules from series to series are under com-
petition of the extent of molecular rigidity and flexibility; and the combine effect of which
in suitable magnitudes operates induction of mesophase formation, the degree of mesomor-
phism and the type or types of mesomorphism. The lowering of smectic thermal stability of
present novel series-1 is attributed to the broadening of molecular width effect, which pre-
dominated between two opposing effects, resulted from laterally substituted –OCH group.
3
Thus, transition temperatures (Cr-Sm and Sm-I) and consequently, thermal stabilities are low-
ered for series-1 as compared to series-X with (equal) commencement of smectic phase from
the same C homolog. However, nematic mesophase in present novel series-1 is observed to be
6
missed, while it appeared in case of series-X above its smectic transition temperature (Sm-N),
i.e., aromatic ring system being relatively more stable and rigid, bears stronger intermolecu-
lar end to end attractions, facilitated, statistically parallel orientational molecular order from
and beyond Sm-N, transition temperature to induce nematic mesophase formation from C5
in series-X as observed against flexibility effect caused by n-C H alkyl chain which hinders
7
15
nematic mesophase formation till the last C homolog of a series-1 of present investigation.
16
Thus, mesomorphic properties of a substance depend upon the molecular rigidity and flexi-
bility as emerged from the molecular structure of a substance.
Conclusions
r
Homologous series of present investigation with two phenyl rings, –OCH lateral
3
group and –CH=CH–COO–C H (n) end group is smectogenic without exhibition
7
15

7
0
J. J. TRAVADI ET AL.
of nematic property whose, smectic property commences from C homolog and inter-
6
molecular cohesive forces are more conducive to molecular width instead of molecular
polarizability.
r
Group efficiency order derived for smectic and nematic on the basis of (i) thermal sta-
bility, (ii) commencement of mesophase, and (iii) total mesophaselength range are as
under.
(
i) Smectic
–
CH=CH–COO–CH
> –CH=CH–COO–CH –C H (n)
2
2
6
13
with –OCH lateral group
3
Nematic
–
CH=CH–COO–CH
> –CH=CH–COO–CH –C H (n)
2
2
6
13
with –OCH lateral group
3
(ii) Smectic
–
CH=CH–COO–CH –C H (n) = –CH=CH–COO–CH
2
6
13
2
with –OCH lateral group
3
Nematic
–
CH=CH–COO–CH2
> –CH=CH–COO–CH –C H (n)
2
6
13
(
–
iii) (Sm + N)
CH=CH–COO–CH -C H (n) ࣈ –CH=CH–COO–CH
2
6
13
2
r
Molecular rigidity and flexibility depending on molecular structure are operating the
mesomorphic behaviors of a substance.
r
r
r
r
The mesomorphic properties from homolog to homolog in the same series depends
upon the sequentially added methylene unit at the left n-alkoxy terminal end group.
The mesomorphic properties for the same homolog from series to series depends upon
the changing part (lateral or terminal or o, m, p position) of the series under comparison.
Mesomorphism and degree of mesomorphism are sensitive and susceptible to molecular
structure.
Present investigation may be useful for the study of mixed mesomorphism to operate
LC devices at desired temperature. Biological activity of the novel compounds may be
useful in pharmaceutical, agricultural and medicinal preparations.
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 valu-
able cooperation to facilitate for present research work, and IR spectra. The authors are also thankful
to the authorities of Saurashtra University for analytical services.
References
[
[
[
[
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6] Gray, G. W. (1974). In: Liquid. Crystals and Plastic Crystals, Gray, G. W., & Windsor, P. A. (Eds.),
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