Study of mesomorphism and laterally substituted nitro group

Article abstract of DOI:10.1080/15421406.2016.1190143

A novel thermotropically mesomorphic, meta-substituted nitro group of chalconyl ester series, RO-C₆H₄-COO-C₆H₃-(NO₂)-CO-CH=CH-C₆H₄OC₁₂H₂₅(n) (para) is synthesized and studied with an aim to establish the relation between molecular structure and the mesomorphism with reference to changing molecular flexibility in presence of nitro lateral group. Novel homologous series consist of thirteen homologs (C₁–C₁₈) whose mesomorphism commences from C₅ homolog as enantiotropic nematogenic with absence of smectic property, even in the monotropic condition. Transition temperatures of novel substances were determined by an optical polarizing microscope, equipped with a heating stage (POM). Textures of a nematic phase are threaded or Schlieren. N-I transition curve exhibited narrow, sharp and short odd-even effect; with deviating trend in a phase diagram. Analytical, spectral and thermal data confirmed the molecular structures of homologs. Thermal stability for nematic is 182.89°C, whose mesophase lengths minimum to maximum ranges from 17°C to 45°C and it is an upper middle ordered melting type series. Group efficiency order for nematic is series 1 > series Y > series X, as derived from comparative study of structurally similar analogous series.

Full text of DOI:10.1080/15421406.2016.1190143

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Study of mesomorphism and laterally substituted
nitro group
Priya K. Patel & R. R. Shah
To cite this article: Priya K. Patel & R. R. Shah (2016) Study of mesomorphism and
laterally substituted nitro group, Molecular Crystals and Liquid Crystals, 634:1, 41-49, DOI:
10.1080/15421406.2016.1190143
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1190143
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Date: 27 September 2016, At: 00:59

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Study of mesomorphism and laterally substituted nitro group
Priya K. Patel and R. R. Shah
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
A novel thermotropically mesomorphic, meta-substituted nitro group
of chalconyl ester series, RO-C H -COO-C H -(NO )-CO-CH=CH-
Nematic; smectic;
enantiotropy; liquid crystal;
mesogen
6
4
6
3
2
C H OC H (n) (para) is synthesized and studied with an aim to
6
4
12 25
establish the relation between molecular structure and the mesomor-
phism with reference to changing molecular flexibility in presence
of nitro lateral group. Novel homologous series consist of thirteen
homologs (C –C ) whose mesomorphism commences from C
1
18
5
homolog as enantiotropic nematogenic with absence of smectic
property, even in the monotropic condition. Transition tempera-
tures of novel substances were determined by an optical polarizing
microscope, equipped with a heating stage (POM). Textures of a
nematic phase are threaded or Schlieren. N-I transition curve exhibited
narrow, sharp and short odd-even effect; with deviating trend in a
phase diagram. Analytical, spectral and thermal data confirmed the
molecular structures of homologs. Thermal stability for nematic is
182.89°C, whose mesophase lengths minimum to maximum ranges
from 17°C to 45°C and it is an upper middle ordered melting type series.
Group efficiency order for nematic is series 1 > series Y > series X,
as derived from comparative study of structurally similar analogous
series.
Introduction
Liquid crystalline [25] substances have established their applicability and utility in the manu-
facture of LC devices related to thermography, display devices, etc. in the benefit of mankind
[
14,22,20]. Moreover the Liquid crystal (LC) chalconyl ester derivatives being bioactive,
may be applied as antibacterial, antifungal, antimalarial, anticancer, anti-inflammatory, etc.
1,9,12,19,23,28] which may be applicable in the benefit of mankind in the pharmaceuti-
[
cal field and agricultural production to reduce the utilization of pesticides and insecticides.
Therefore, present investigation is planned with a view to understand the effect of molecular
structure on LC properties of chalconyl ester derivatives [10,11,13,17] through synthesis of
homologous series of dual applicability and utility for mankind. Proposed investigation will
consist of novel substances involving three phenyl rings, two central bridges –COO– and –
CO–CH=CH–, two terminal end groups –OR and –OC H (n) as well as meta substituted
12
25
nitro lateral group at the middle phenyl ring. The evaluated thermometric data will be inter-
preted and discussed in terms of molecular rigidity and flexibility [3,15,16,21]. Several ester
CONTACT Priya K. Patel
Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad, Gujarat, India.
 Taylor & Francis Group, LLC
pp@gmail.com; R. R. Shah
ruteshshah@gmail.com
Chemistry Department, K. K.
©

4
2
P. K. PATEL AND R. R. SHAH
homologous series are reported to date [5–8,18,24,26]. The effect of laterally substituted nitro
group efficiency order will be derived for smectic and nematic from comparative study of
structurally analogous series.
Experimental
Synthesis
4
4
-Hydroxy benzoic acid was alkylated using suitable alkylating Agent (R-X) to convert it into
-n alkoxy benzoic acids by a modified method of Dave and Vora [4].
Scheme . Synthetic route to the series .

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
ꢀ
α-3-Nitro-4-hydroxy benzoyl β-4 -dodecyloxy phenyl ethylene (B) was prepared by
usual established method [30]. Chalconyl esters were synthesized by a literature method
[
29]. Thus, the Chalconyl-ester homolog derivatives were filtered, washed with sodium
bicarbonate solution followed by distilled water, dried, and purified till constant tran-
sition temperatures obtained using an optical polarizing microscope equipped with a
heating stage (POM). 4-Hydroxy benzoic acid, alkyl halides, 4-hydroxy benzaldehyde,
3
-nitro 4-hydroxy acetophenone, dicyclohexyl carbodimide, dimethyl amino pyridine,
DCM, MeOH, acetone required for synthesis were used as received except solvents which
were dried and distilled prior to use. The synthetic route to a series is mentioned in
Scheme 1.
Characterization
Some selected representative homologs of the series were characterized by infrared [IR],
1
HNMR technique and elemental analysis. IR spectra were recorded on Perkin Elmer spec-
1
trum GX. HNMR spectra were recorded using CDCl as solvent. Elemental analysis was
3
performed on Perkin Elmer PE 2400 CHN analyzer (Table 1). Liquid Crystal properties, i.e.,
transition and melting temperatures of homologs were investigated by an optical polarizing
microscope with heating stage. Textures of the novel homologs were determined by miscibility
method.
Analytical data
Table . Elemental Analysis for heptyloxy, octyloxy, decyloxy, and tetradecyloxy.
Element % found
H
Element % calculated
H
Molecular formula
C H O N
C
N
C
N
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%

  
C H O N

  
CH O N


CH O N


−1
IR Spectra in cm for pentyloxy and dodecyloxy derivatives:
Pentyloxy: 648.08 & 690.52(m-substituted phenyl ring), 786.96(polymethylenes (-CH ) of
2
–
OC H ), 833.25(-OH deferences in m-disubstituted para), 968(-CH deferences hydrocar-
5
11
bon), 1163.08(C-O of alkoxy –OC H ), 1244 & 1309.67(C-O stretching in(-CH2) chain),
5
11
n
1
&
344.28(-NO group), 1467.83(-C-H deferences in –CH ), 1606.70(-C = O group), 2850.79
2
2
2922.16(-CH stretching in –CH ). IR supports the structure.
3
Dodecyloxy: 646.15(m-substituted phenyl ring), 717.52(polymethylene (-CH2) of –
n
OC H ), 921(-CH deferences hydrocarbon), 1060(-CO stretching), 1150 & 1241.48(-CO
12
25
deferences in –CH ), 1276.88(-COO group), 1465.90(-CH deferences in –CH ), 1537.27(-
2
2
NO group), 1606.70(-C = O group), 2852.72 & 2922.16(-CH stretching in –CH ). IR sup-
2
3
ports the structure.
1
HNMR Spectra in CDCl in δ ppm for hexyloxy and hexadecyloxy derivatives:
3
Hexyloxy: 1.19(-CH of –OC H ), 2.00 to 2.19(m, n-polymethylene group of –OC H ),
2
6
13
6
13
2
.90 to 3.09(s, -OCH -CH of –OC H ), 4.20 to 4.99(t, -OCH -CH of –OC H ), 6.1(s, -
2 2 6 13 2 2 6 13
CO-CH = CH), 7.1(s, p-disubstituted phenyl ring). NMR supports the structure.

4
4
P. K. PATEL AND R. R. SHAH
Hexadecyloxy: 1.14 to 1.26(-CH of –OC H ), 1.98 to 2.70(m, n-polymethylene group
2
16 33
of -OC H ), 3 to 3.9(s, -OCH -CH of –OC H ), 6.3(s, -CO-CH = CH). NMR supports
16
33
2
2
16 33
the structure.
Table . Texture of nematic phase of C, C, C, and C by miscibility method.
Sr. No.
Homolog
Texture

C
C
C
C
Threaded
Threaded
Threaded
Schlieren



ꢀ
ꢀꢀ
Homologous series: α-4 [4 -n-alkoxy benzyloxy] 3-nitro benzoyl β-4 dodecyloxy phenyl
ethylenes
Table . Transition temperature in°C.
Transition temperatures in°C
Compound No.
Homolog (n-alkyl chain)
Smectic
Nematic
Isotropic

C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
















ꢀ
ꢀꢀ
Homologous series: α-4 [4 -n-alkoxy benzyloxy] 3-nitro benzoyl β-4 dodecyloxy phenyl
ethylenes

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
45
Figure . Phase behavior of series.
Results and discussion
Though the dimerization of 4-n-alkoxy benzoic acids disappears by the process of esterifica-
tion, the transition temperatures of novel chalconyl ester derivatives are not lowered to the
expected extent. The C –C homologs of a present series are enantiotropically nematogenic
5
18
with absence of smectogenic character. C –C homologs are nonliquid crystals. Transition
1
5
temperatures (Table 2) as determined by an optical polarizing microscopy (POM) equipped
with a heating stage were plotted versus the number of carbon atoms present in n-alkyl chain
‘
R’ of –OR flexible group and the Cr-N and N-I transition curves were plotted by linking like
or related points as depicted in a phase diagram (Figure 1), showing phase behaviors of a
novel series. Cr-N/I transition curve rises and falls in zigzag manner with overall descending
tendency and behaved in normal manner. N-I transition curve deviated from normal behav-
ior from C –C homolog with exhibition of odd-even effect. Thermal stability for nematic
8
18
is 182.89°C and the mesophase length ranges minimum to maximum which is 17°C–45°C
at the C and C homologs, respectively. The odd-even effect diminishes from and beyond
14
5
C homolog for higher homologs of longer n-alkyl chain. The textures of nematic phase are
8
threaded or schlieren. The evaluated analytical, spectral, and thermal data confirm the molec-
ular structure of homologs. The mesogenic properties from homolog to homolog in present
series undergo variations. The mesomorphic transition temperatures varied between 136.0°C
and 196.0°C.
The exhibition of nonmesomorphic behavior of C –C homologs is attributed to the low
1
4
magnitudes of dispersion forces and low magnitudes of dipole-dipole interactions, which
induces high crystallizing tendency in a substances and inability to resist exposed thermal
vibrations. Hence, the facilitation of mesophase formation is hindered and abruptly breaks
the crystal lattices to melt sharply and directly transformation to isotropic state or from
isotropic state to crystalline state with high crystallizing tendency on cooling the same.
The molecules of C –C homologs resists exposed thermal vibrations and dis-aligned at
5
18
an angle less than ninety degree and maintain floating of the molecules on the surface

4
6
P. K. PATEL AND R. R. SHAH
with only statistically parallel orientational order for definite temperature gradient to induce
nematic phase and then continued excessive, heating results into random orientation of
molecules with high order of disorder from and beyond isotropic temperature. However on
cooling the same from and below isotropic temperature, the same energized randomly ori-
ented molecules de-energies by loosing energy and exhibit to reappear nematic mesophase
formation in reversible manner at a same temperature at which nematic mesophase was
appeared on heating. Thus, mesophase appearance in reversible manner for the same sam-
ple is termed as enantiotropic transition. The odd-even effect observed for the N-I tran-
sition temperature is due to sequential addition of methylene unit at the n-alkyl chain ‘R’
of −OR group. The lowering of transition temperatures by esterification process of present
novel homologs is not as low as it is expected, because the highly polar meta substituted lat-
eral nitro group increases molecular width but induces molecular polarizability to such an
extent that, suitable magnitudes of anisotropic forces of intermolecular end to end attractions
raised to increase mesophase lengths and transition temperatures above 200°C. The disap-
pearance of odd-even effect from and beyond C homolog for higher homologs of longer
8
n-alkyl chain ‘R’ of −OR and −C H of –OC H group is attributed to the coiling or
12
25
12 25
bending or flexing or coupling of n-alkyl chains with principal axes of core structure of
molecules. Therefore, uncertainty and its magnitudes in the status of n-alkyl chain may vary
from homolog to homolog which may modify the morphological appearance of molecule
and the magnitudes of molecular rigidity and/or flexibility as depended upon magnitudes of
uncertainty and its type which induces deviation in the mesogenic behaviors in the transition
curve or curves; of a phase diagram. The variations of mesomorphic properties, behaviors,
and the degree of mesomorphism from homolog to homolog in the same series is attributed
to the net intermolecular end-to-end cohesion and closeness as a result of changing molecular
length, permanent dipole moment across the long molecular axes, dispersion forces, effective
and favorable molecular rigidity and flexibility, etc., which vary with the number of carbon
atoms present in n-alkyl chain ‘R’ of −OR group, keeping rest of the molecular part intact.
The changing trends in mesomorphic properties of presently investigated novel series-1 and
the structurally similar analogous series X [27] and Y [2] chosen for comparative study are
mentioned below in Figure 2.
Above homologous series involving three phenyl rings and two central bridges contribut-
ing to total molecular rigidity are identically same and −OR flexible group at the left end
are also identically same contributing partly to the total molecular flexibility for the same
homolog from series to series. The ortho- or meta-substituted nitro group with respect to
−
CO–CH = CH- central group at the middle or last phenyl rings differs partly to the total
flexibility irrespective of same highly polar and polarizable nitro group due to their varied
positional difference and their substitution at different phenyl rings for the same homolog

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
47
from series to series. Moreover they differ with respect to different terminal end groups –
OC H (n), -H and –H which alters the magnitudes of total molecular flexibility. Thus, vari-
12
25
ations in mesomorphic properties, behaviors and the degrees of mesomorphism for the same
homolog from series to series can be linked to the differing features of series 1, X, and Y,
respectively, under comparative study. Following Table 3 represents some thermotropic prop-
erties and evaluated data in comparative manner are as under.
Table . Relative thermal stability in °C.
Series→
NO middle ring)
Series  (meta
-
Series X (meta-NO)
Series Y (ortho-NO)

Sm-N or Sm-I
Commencement of smectic phase
–
.
.
(
C -C )
 
C
(
C -C )


C
N-I
Commencement of nematic phase
.
.
.
(
C –C )


C
(
C –C )


C
(
C –C )


C
Total mesophase lengths in°C
.–.
.–.
.–.
C C
C C
C C
From above table it is clear that,
•
Homologous series 1 is only nematogenic but the series X and Y selected for comparison
are smectogenic plus nematogenic.
•
Mesomorphism commences from C homolog of series 1 but it commences from C and
5
6
C homolog for series-X and Y respectively.
Thermal stabilities for smectic adopt increasing order from series 1 to X to Y.
Thermal stabilities for nematic is in decreasing order from series 1 to series Y to series
X.
3
•
•
•
Lower mesophase length of series 1 is higher than series Y and X but upper mesophase
length is in decreasing order from series X to series Y to series Y to series 1.
In exhibition of smectogenic character by homologous series 1 of present investigation
as compared to analogous series-X and Y is attributed to the magnitudes of flexibility con-
tributed by right-ended tail group –OC H (n) as compared to tailed end –H of series X
12
25
and Y whose group polarity, polarizability, and permanent dipole moment across the long
molecular axis affects the extent of molecular noncoplanarity as well as hinders the forma-
tion of lamellar packing of molecules in their preoccupied crystal lattices and then conse-
quently sliding layered molecular arrangement in floating condition on the surface which
fails to occur. Thus, smectogenic property disappears in case of series 1 and positive possi-
bility of lamellar packing of molecules in case of series X and Y in absence of bulky group
like –OC H (n) which does not hinder the formation of smectogenic mesophase or facili-
12
25
tate smectic phase formation. The presence of bulky tailed group −OC H (n) in presence
12
25
of ortho- or meta-substituted lateral –NO group at middle or third phenyl ring favorably
2
increases intermolecular end-to-end attractions and closeness due to which energy stored in

4
8
P. K. PATEL AND R. R. SHAH
the molecules (ꢀH) of series 1 resists exposed thermal vibrations to considerable extent and
raises thermal stability for nematic as compared to series X and Y. The early or late commence-
ment of mesophase or mesophases depends upon the extent of molecular non co-planarity as
a consequence of changing molecular rigidity and flexibility together, which induces suitable
or unsuitable magnitudes of anisotropic forces of intermolecular attractions and resistivity
against exposed thermal vibration under floating condition on the surface. Thus, variations
in mesogenic properties for the same homolog from series to series and homolog to homolog
in the same series depend upon the difference of group polarity of terminal end groups as well
as polarizability and polarity of lateral group.
Conclusions
•
•
Homologous series of present investigation is nematogenic with absence of smectic prop-
erty whose mesophase length is moderately good enough and it is a middle-ordered
melting type series.
The group efficiency order derived for smectic and nematic on the basis of (a) thermal
stabilities (b) early commencement of mesophases, and (c) total mesophase lengths with
respect to lateral nitro group is as under.
a) Smectic
Series Y > Series X > Series 1
Nematic
Series 1 > Series Y > Series X
b) Smectic
Series Y > Series X > Series 1
Nematic
Series Y > Series 1 > Series X
c) Total mesophase lengths (Sm± N)
Upper: Series X > Series Y > Series 1
Lower: Series 1 > Series Y > Series X
•
•
Molecular structure of a molecule is very sensitive and susceptible to a phenomenon of
mesomorphism as a consequence of effective molecular rigidity and flexibility.
Lateral Nitro group on middle phenyl ring eliminates smectic mesophase formation
whereas its presence on tailed phenyl ring favors formation of smectic mesophase at
ortho or meta position.
•
•
•
Study of binary systems of present investigation may be useful for the electronic display
devices to be operated between 120°C and 196°C.
Biological activity of present novel substances may be useful for the preparations of phar-
maceutical products.
Present investigation supports and raises the credibility to the conclusions drawn earlier.
Acknowledgments
Authors acknowledge thanks to the management of the college and the Head of the Chemistry Depart-
ment Dr. R. B. Patel of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad for their valuable
cooperation in the work. Authors are also thankful to Dr. A. V. Doshi, Ex-Principal, M. V. M. Science
and Homescience College, Rajkot for his co-operation, valuable suggestions, comments, and help as and

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
49
when needed during the course of present investigation. Thanks are due to NFDD Centre, Saurashtra
University, Rajkot for analytical and spectral services.
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