Dependence of thermotropic mesomorphism on lateral nitro group

Article abstract of DOI:10.1080/15421406.2016.1190136

A novel homologous series RO-C₆H₄-COO-C₆H₃-(NO₂)-CO-CH?CH-C₆H₄OC₁₈H₃₇(n) para of chalconyl ester derivatives have been synthesized and studied with view to understanding the effect of an ortho substituted nitro group on thermotropic liquid crystal (LC) behavior. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). The C₁ to C₄ homologues are nonliquid crystal (NLC) and the rest of the homologues (C₅ to C₁₈) homologues are enantiotropically nematogenic without exhibition of a smectic phase even in the monotropic condition. Transition temperatures were determined by an optical polarizing microscope (POM) equipped with a heating stage. Texture of nematic phase are threaded or Schlieren. Analytical, thermal and spectral data supported molecular structure of homologues. Thermal stability for nematic is 147.1°C whose mesophase lengths vary between 16.0 and 32.0°C the C₇ and C₁₈ homologues, respectively, and their mesogenic exhibition range between 96.0 and 166.0°C. Thus, the present novel series is middle ordered melting type, Group efficiency order is derived from comparative study of structurally similar series. The transition curves of a phase diagram behaved in normal manner except C₁₀ and C₁₆ homologues. Odd-even effect is observed for N-I transition curve. Group efficiency order derived is: -OC₁₂H₂₅ (n) > -OC₁₈H₃₇ (n) > -OC₁₈H₃₇ (n).

Full text of DOI:10.1080/15421406.2016.1190136

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Dependence of thermotropic mesomorphism on
lateral nitro group
Ravindra Solanki & R. B. Patel
To cite this article: Ravindra Solanki & R. B. Patel (2016) Dependence of thermotropic
mesomorphism on lateral nitro group, Molecular Crystals and Liquid Crystals, 634:1, 24-32,
DOI: 10.1080/15421406.2016.1190136
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1190136
Published online: 26 Sep 2016.
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Date: 28 September 2016, At: 02:22

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Dependence of thermotropic mesomorphism on lateral nitro
group
Ravindra Solanki and R. B. Patel
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Gujarat, India
ABSTRACT
KEYWORDS
Nematic; liquid Crystal;
smectic; enantiotropy;
mesogen
=
A novel homologous series RO-C6H4-COO-C6H3-(NO2)-CO-CH CH-
C6H4OC18H37(n) para of chalconyl ester derivatives have been synthe-
sized and studied with view to understanding the effect of an ortho sub-
stituted nitro group on thermotropic liquid crystal (LC) behavior. The
novel homologous series consists of thirteen homologues (C1 to C18).
The C1 to C4 homologues are nonliquid crystal (NLC) and the rest of
the homologues (C5 to C18) homologues are enantiotropically nemato-
genicwithoutexhibitionofasmecticphaseeveninthemonotropiccon-
dition. Transition temperatures were determined by an optical polar-
izing microscope (POM) equipped with a heating stage. Texture of
nematic phase are threaded or Schlieren. Analytical, thermal and spec-
tral data supported molecular structure of homologues. Thermal stabil-
ity for nematic is 147.1°C whose mesophase lengths vary between 16.0
and 32.0°C the C7 and C18 homologues, respectively, and their meso-
genic exhibition range between 96.0 and 166.0°C. Thus, the present
novel series is middle ordered melting type, Group efficiency order is
derived from comparative study of structurally similar series. The tran-
sition curves of a phase diagram behaved in normal manner except
C10 and C16 homologues. Odd-even effect is observed for N-I transition
curve. Group efficiency order derived is: -OC12H25 (n) > -OC18H37 (n) >
-OC18H37 (n).
Introduction
Mesogenic [1] materials have been exploited in the benefit of mankind and to the society as
a whole for electronic display devices and many other fields [2–4]. The present investigation
is planned with a view to understanding and establishing the effect of molecular structure on
liquid crystal (LC) properties [5–9]. A novel homologous series of chalconyl ester containing
three phenyl rings bonded through carboxy and chalconyl group is proposed to synthesize and
their thermotropic properties will be studied. Moreover, the chalconyl group being bioactive
group, which is antibacterial, antimalarial anticancer, antifungal, etc., which may be studied
by groups of biological scientists of pharmacy, medicine, etc. [10–14] in the benefit of society
as a whole. Thus, synthesis of novel compounds may be multi beneficiary to researchers of
scientific and technology community by synthesizing proposed novel compounds. Number
of homologous series of ester, azo-ester, chalconyl ester derivatives of monomers, dimer and
polymers have been reported till the date [15–26]. Group efficiency order will be derived with
CONTACT Ravindra Solanki
ravindrasolanki@gmail.com
Science College, Gujarat University, Ahmedabad-, Gujarat, India.
Chemistry Department, K. K. Shah Jarodwala Maninagar
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
25
reference to presence and absence of nitro group. The experimental data will be discussed and
interpreted on the basis of molecular rigidity and flexibility [27–30].
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated using suitable alkylating agent (R-X) to convert
it into 4-n-alkoxy benzoic acids (A) by modified method of Dave and Vora [31], α-3-
Nitro-4-Hydroxy benzoyl β-4ꢀ -n-Octadecyloxy phenyl ethylene (B) was prepared by usual
established method [32]. 4-n-Alkoxy benzoic acids and α-3-Nitro-4 Hydroxy benzoyl β-4ꢀ -
n-Octadecyloxy phenyl ethylene were condensed in 1,3-dicyclohexylcarbodiimide (DCC), 4-
dimethyl amino pyridine (DMAP) and CH2Cl2 [33] to obtain α-4-(4ꢀ-n-Alkoxy benzoyloxy)
3-nitro benzoyl-β-4ꢀ-n-Octadecyloxy phenyl ethylene. Final products were filtered, washed,
dried and purified till the constant transition temperatures obtained. The synthetic route to
the novel homologous series of ethylene derivatives is under mentioned in Scheme 1.
Characterization
Representative homologues of a series were characterized by elemental analysis, Infra red
spectroscopy, 1H NMR spectra. IR spectra were recorded on Perkin-Elmer spectrum GX, 1H
NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis was performed
on Perkin-Elmer PE 2400 CHN analyser (Table 1). Transition temperature and LC properties
(Textures) were determined using an optical polarising microscopy equipped with heating
stage. Textures of some homologues for the nematic phase determined by miscibility method
(Table 2).
Analytical data
IR spectra (KBr) in cm− for pentyloxy, decyloxy derivatives
Pentyloxy. 675, 725 (C-H alkane), 761 Poly methylene (-CH2-)n of -OC5H11, 835,(-C-H- def.
di-substituted-Para & Ortho aromatic ring), 894 Poly methylene (-CH2-) of -OC18H37, 1074
=
(-C-H- def. hydrocarbon), 1114 and 1172(-C-O-) Str, 1259 and 1303 and 1321(C O str in
=
(CH2)n Chain), 1384 (-N-O str Symmetric), 1512 (-N-O str Asymmetric),1581 (-C C-)str,
=
=
1606,1616 (-C O in CH CH- group), 1730 (-COO- ester group), 2927 and 3033 (-C-H str
in CH3).
Decyloxy. 667 (C-H- alkane), 725 Poly methylene (-CH2-)n of -OC10H21,829 and 894(-C-H-
def. m di-substituted-Para & Ortho aromatic ring), 975 (-C-H- def. hydrocarbon), 1022,1072,
1122, 1172,1215,1255(-C-O-) Str, of C18H37,1301 and 1336 (-C-O str in -(CH2)n chain,
1386 (-N-O str Symmetric)1421 (-C-H- def. in CH2),1512 (-N-O str Asymmetric) and 1548
=
=
=
(-C C-)str, 1608 (-C O in CH CH- group), 1722 (-COO- ester group), 2856 and 2923 and
3035,3064 (-C-H str in CH3).
H NMR spectra in CDCl in δ ppm for octyloxy & octadecyloxy derivative
Octyloxy. 0.90 (t, -CH3 of -C8H17), 1.32–1.80 (m, n-poly methylene groups of-OC8H17),
1.55–1.76 (m, n-poly methylene groups of -OC18H37), 4.10–4.20(s,-OCH2-CH2-ofOC18H37),

26
R. SOLANKI AND R. B. PATEL
Scheme . Synthetic route to the series.
=
4.0–4.2 (s,-OCH2-CH2-of OC8H17), 7.58 and 8.20(s,-CO-CH CH), 8.5–8.9 (s, p-di substi-
tuted phenyl ring).
Octadecyloxy. 0.88(t, -CH3 of -C18H37), 1.3–1.43(m, n-poly methylene groups of -OC18H37),
1.5–1.7(m, n-poly methylene groups of - OC18H37),4.1(s, -OCH2-CH2-of OC18H37),
4.1–4.4(s,-OCH2-CH2- of OC18H37), 6.94–7.15 (s, substituted benzene), 6.9–7.2(s, -CO-
=
CH CH), 7.6–7.8(s, p-substituted phenyl ring).
Results and discussion
The transition temperatures of novel chalconyl ester derivatives of lateral -NO2 group are rela-
tively higher than the other structurally similar series and the ten to twenty persent lower than
the corresponding n-alkoxy dimeric acids for the same homologue. The nematic mesophase

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
27
Table . Elemental analysis for butyloxy, heptyloxy, tetradecyloxy, hexadecyloxy derivatives.
Elements found %
H
Elements calculated %
H
Sr. No.
Molecular formula
C
N
C
N

C
C
C
C
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.



Table . Textures of Nematic phase by miscibility method for C, C, C, C.
Sr. No.
Homologue
Texture

C
C
C
C
Threaded
Threaded
Schlieren
Schlieren



Table . Transition Temperatures in°C for Homologous series:
Homologous series: α--(ꢀ-n-Alkoxy benzoyloxy) benzoyl-β-ꢀ-n-Octadecyloxy -nitro phenyl Phenyl
ethylenes
Transition temperatures in (˚C)
Compound no.
n-alkyl chain CnHn+
Smectic
Nematic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
formation commences from C5 homologue without exhibition of smectic property till the
last homologue (C18). Transition temperature (Table 3) as determined by POM were plotted
against the number of carbon atoms present in n-alkyl chain “R” of -OR group and then Cr-N
as well as N-I transition curves are obtained by linking like or related points as depicted in a
phase diagram (Fig. 1) as shown in Fig. 1.
The Cr-N/I transition curve follows a zigzag path of rising and falling with overall descend-
ing tendency and behaved in normal manner. N-I transition curve behaves in normal manner
except at C8 homologue for which N-I transition point deviates from expected place below the
ten to eleven degree Celsius temperature N-I transition curve for odd member lye below the
curve for even members showing odd-even effect unusual manner. The texture of nematic
phase are threaded or Schlieren as determined by miscibility method of some representative
members of a series and by direct observation of texture on the heating top of POM, for other

28
R. SOLANKI AND R. B. PATEL
Figure . Phase behavior of the series.
homologues of a series. Analytical, thermal, and spectral data conformed the molecular struc-
ture of homologues. The variation in mesogenic properties, behaviors and mesophase lengths,
etc. from homologue to homologue in present novel series is observed. Thus, present series is
only nematogenic without exhibition of smectogenic character and middle ordered melting
type whose transition temperatures vary between 96.0 and 196.0°C.
Dimerization of n- alkoxy acids disappears by esterification process by braking of hydrogen
bonding which may lower transition temperature but the increase of transition temperature is
attributed due to the polarizability induced by laterally substituted highly polar -NO2 group.
The exhibition of only nematogenic property is attributed to the position of -NO2 group in the
sequential order of its group efficiency as nematogenic functional group. Absence of smecto-
genic character indicates absence of lamellar packing of molecules. The nonmesomorphicity
–
of C1 C4 homologues and absence of smectogenic property is due to their high crystalliz-
–
ing tendency. The exhibition of nematic property (C5 C18) homologues is attributed to the
suitable magnitudes of anisotropic forces of intermolecular attraction and closeness as a con-
sequence of favorable molecular rigidity and flexibility caused by suitable magnitudes of dis-
persion force and dipole- dipole interaction which maintains the floating of homologue on
the surface under the influence of exposed thermal vibrations with statistically parallel orien-
tational order to facilitate formation of nematic mesophase for definite range of temperature.
The odd-even effect observed for N-I transition curve is due to the odd and even number of
carbon atom present in n-alkyl chain “R” of -OR group. The disappearance of odd-even effect
from C7 or C8 is attributed to the longer n-alkyl chain “‘R” of -OR and -C18H37 of -OC18H37
(n) which may coil or band or flex or couple to lye with principal axes of core structure of
molecule, modifying magnitudes of molecular rigidity and flexibility affecting possibility of
mesophase and the degree of mesomporphism. The appearance of deviation in transition tem-
perature for C8 homologue below expected transition temperature is attributed to the unex-
pected status of n-alkyl chain or chains. The variations in mesogenic properties behavior and
the degree of mesomorphism from homologue to homologue in the present novel homol-
ogous series is due to the sequentially and progressively added methylene unit or units in

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
29
Figure . Structurally Similar analogous Series.
n-alkyl chain “‘R” of -OR group. The changing mesogenic behavior of present novel series -1
are compared with structurally similar analogous series-X [34] and Y [35] as mention below
in Fig. 2.
From above Fig. 2, it is clear that, homologous series 1, X and Y are identical with respect
to three phenyl rings, two central bridge and left n- alkoxy terminal which contributes to
the total molecular rigidity and partly contributes to the molecular flexibility for the same
homologue from series to series, but, differs from homologue to homologue in the same series.
Homologous series-1 and X differs respect to presence and absence of lateral -NO2 group
which partly contributes to total molecular flexibility, molecular polarizability and polarity.
Homologous series 1 and Y are identical in all respect but, differs with respect to terminally
situated -OC18H37 (n) and -OC12H25 (n) group contributing to total molecular flexibility for
the same homologue from series to series. Thus, mesomorphic properties behavior and degree
of mesomorphism will depend upon differing features of series 1, X and Y under comparative
study, of analogous series. The thermotropically mesogenic some properties of homologous
series 1, X and Y are recorded in Table 4 as shown below for comparative study.
Table 3 represent comparative data of present investigated chalconyl ester homologous
series 1 and structurally similar analogous series X and Y selected for comparative study pur-
pose as under.
r
Homologous series 1, X, and Y are nematogenic only without exhibition of smectic prop-
erty.
r
Mesomorphism commence from C5 homologue in all the three series under comparison.
r
Thermal stability for nematic is in decreasing order from series Y to serie −1 to series-X.
r
Upper mesophase lengths are in increasing order from series-1 to series -X to series -Y
but the lower mesophase lengths are in decreasing order from series-Y to series- 1 to
series-X.
Table . Relative thermal stability in°C.
Series →
Series-
Series-X
Series-Y
Sm-I or Sm-N
Commencement of Smectic phase
—
—
—
N-I or I-N
Commencement of nematic phase
.
.
.
–
–
–
(C C)
(C C)
(C C)
C
C
C
Total
. to .
C C
. to .
C C
. to .
C C
Mesophase length from t to t°C

30
R. SOLANKI AND R. B. PATEL
From above comparative points it is clear that, the exhibition of only nematogenic character
and the commencement of nematic phase are identically same which suggests that the end to
end intermolecular cohesion and closeness are nearly equivant as a consequence of equivalent
molecular rigidity and flexibility induced by three phenyl rings, two similar central bridges
and terminally situated flexible n- alkoxy group. However, the difference in the magnitudes
of thermal stability among the series 1, X and Y can be attributed to the presence and absence
of laterally substituted flexible nitro group whose group polarizability and polarity factor pre-
dominates and contribute more to the intermolecular end to end cohesion and attractions,
Thus, energy stored (ꢀH) by the molecules of same homologue from series to series containg
lateral nitro group have (series- 1 and Y) higher resistivity toward exposed thermal vibration
leading to higher thermal stability for nematic as compared to the corresponding thermal
stability of series-X and order of lower mesophaselengths.
Conclusions
r
Homologous series-1 of present investigation is enantiotropically nematogenic whose
mesophaselengths minimum to maximum vary between 16.0 and 32.0°C and middle
ordered melting type.
The group efficiency order derived (i) on the basis of thermal stability, (ii) early
commencement of mesophase and (iii) upper mesophase lengths for nematic are as
under.
r
(i) Nematic
−OC12H25(n) > −OC18H37(n) > −OC18H37(n)
With − NO2 With − NO2 Without − NO2
(ii) Nematic
−OC18H37(n) = −OC18H37(n) = −OC12H25(n)
With − NO2 Without − NO2 With − NO2
(iii) (Nematic Smectic)
−OC12H25(n) > −OC18H37(n) > −OC18H37(n)
With − NO2 Without − NO2 With − NO2
r
Mesomorphism is very sensitive and susceptible to the molecular structure as a conse-
quence of
molecular rigidity and flexibility.
Study of binary system can be useful to manufacture electronic display devices. Chal-
conyl derivatives being bioactive molecules which may be applied or exploited in phar-
maceutical preparation and in agricultural production of healthy cropes to act as antibac-
terial as well as antifungal material which may reduce the consumption of insecticide and
pesticides.
r
r
r
Present investigation supports and raises credibility to the conclusion drawn earlier.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
31
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors are also thankful to Dr. A. V. Doshi, Ex-principal of M.V.M. Science &
Home Sci. College - Rajkot for his constant support, inspirations and valuable comments, suggestions
and help, as and when needed during the course of present investigation. Authors thank NFDD Centre
for the analytical and spectral services
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