Dependence of mesomorphism on molecular rigidity of nonlinear and linear isomeric and nonisomeric chalconyl esters

Article abstract of DOI:10.1080/15421406.2016.1177882

The novel thermotropic liquid crystalline (LC) materials have been synthesized and studied through chalconyl ester nonlinear (meta substituted) homologous series RO-C₆H₄?CH?CH?COO?C₆H₄-CO?CH?CH?C₆H₄-OC₁₄H₂₉(n) with a view to understand the effect of molecular structure on LC behavior with reference to determine the difference between linear and nonlinear shaped molecules. Novel series consisted of thirteen members, whose nematogenic enantiotropic mesomorphism commences from C₆ homologue and continued up to C₁₈ homologue with the absence of smectogenic character. C₁ to C₅ homologues are nonliquid crystals as determined through an optical polarising microscope (POM) equipped with a heating stage. Transition temperatures of LC homologues alternate and are lower than the corresponding n-alkoxy cinnamic acids. Cr-N/I and N-I transition curve behaved in normal manner. N-I transition curve exhibited odd-even effect in a phase diagram. Textures of nematic phase are threaded or Schlieren or determined by miscibility method and from observing mesophase on the top of the POM. Thermal stability for nematic is 92.5 and mesophase length minimum to maximum is 19.0 to 32.0°C at the C_10/18and C₆ homologue. Group efficiency order on the basis of thermal stability is (Formula presented.) Thus, novel series is nematogenic and low melting type. Analytical and spectral data confirmed the molecular structures of homologues.

Full text of DOI:10.1080/15421406.2016.1177882

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Dependence of mesomorphism on molecular
rigidity of nonlinear and linear isomeric and
nonisomeric chalconyl esters
B. B. Jain & R. B. Patel
To cite this article: B. B. Jain & R. B. Patel (2016) Dependence of mesomorphism on molecular
rigidity of nonlinear and linear isomeric and nonisomeric chalconyl esters, Molecular Crystals
and Liquid Crystals, 633:1, 54-62, DOI: 10.1080/15421406.2016.1177882
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1177882
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Date: 02 September 2016, At: 01:34

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Dependence of mesomorphism on molecular rigidity of
nonlinear and linear isomeric and nonisomeric chalconyl esters
B. B. Jain and R. B. Patel
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Nematic; smectic;
mesomorphism;
enantiotropy; liquid crystals
The novel thermotropic liquid crystalline (LC) materials have been
synthesized and studied through chalconyl ester nonlinear (meta
–
=
–
–
substituted) homologous series RO-C6H4 CH CH COO C6H4-
–
=
–
CO CH CH C6H4-OC14H29 (n) with a view to understand the effect of
molecular structure on LC behavior with reference to determine the
difference between linear and nonlinear shaped molecules. Novel series
consisted of thirteen members, whose nematogenic enantiotropic
mesomorphism commences from C6 homologue and continued up
to C18 homologue with the absence of smectogenic character. C1 to C5
homologues are nonliquid crystals as determined through an optical
polarising microscope (POM) equipped with a heating stage. Transition
temperatures of LC homologues alternate and are lower than the
corresponding n-alkoxy cinnamic acids. Cr-N/I and N-I transition curve
behaved in normal manner. N-I transition curve exhibited odd-even
effect in a phase diagram. Textures of nematic phase are threaded or
Schlieren or determined by miscibility method and from observing
mesophase on the top of the POM. Thermal stability for nematic is 92.5
and mesophase length minimum to maximum is 19.0 to 32.0°C at the
C10/18 and C6 homologue. Group efficiency order on the basis of thermal
−COO− > −CH=CH−COO− > −CH=CH−COO−
stability is
Thus, novel series
linear
linear
Nonlinear
is nematogenic and low melting type. Analytical and spectral data
confirmed the molecular structures of homologues.
Introduction
Increasing utility of LC materials [1] in the benefits of mankind [2–10] especially with
–
–
=
–
–
=
–
=
–
COO- or CH CH COO central bridges in combination with –N N-, -CO CH CH
–
–
–
–
or CH CH CO chalconyl groups because an ester group may improve the quality
of agricultural products and chalconyl group may reduce the consumption of insecti-
cides or pesticides including manufacture of LC devices. Therefore present investigation is
planned with a view to understand and establish the effects of molecular structure [11–
15] on LC properties with reference to central bridges CH CH COO in linear and
nonlinear isomeric vinyl carboxy central bridge with common chalconyl group as central
group. The novel investigation will include synthesis, Characterization by elemental analy-
sis, IR and H1NMR spectra, thermal study by hot stage polarizing microscopy, LC texture
–
=
–
–
CONTACT B. B. Jain
bijendrajain@gmail.com;R. B. Patel
K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad, Gujarat, India.
roshanpatel@gmail.com
Chemistry Department, K.
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
55
determination, mass spectra including qualitative approach to thermodynamic quantity
enthalpy and entropy instead of DSC scan or DSC scan. Then, evaluated thermometric data
will be compared with structurally similar analogous series. Evaluated thermal data will be
interpreted and discussed in terms of molecular rigidity and flexibility [16–19]. Number of
ester homologous series are reported till the date.[20–30].
Experimental
Synthesis
Trans 4-n-alkoxy cinnamic acids (A) were prepared by modified method [31,32]. α-3-
Hydroxy benzoyl β-4/tetradecyloxy ethylene (B) was prepared by usual established method
[33]. Esters were synthesized by a literature method [34]. Thus, the Chalconyl—ester homo-
logue derivatives were decomposed filtered, washed with solution of sodium bicarbonate
and sodium hydroxide followed by water dried and purified till constant transition tem-
peratures obtained using an optical polarising microscope equipped with a heating stage.
Alkyl halides, 4- hydroxybenzaldehyde, 3-hydroxy acetophenone, dicyclohexylcarbodimide,
Dimethyl amino pyridine, DCM, Ethanol, 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 below in Scheme 1.
Reaction scheme
Characterization
Selected members of the novel homologous series were characterized by Elemental Analy-
sis, infrared spectroscopy, 1H NMR spectra. IR spectra were recorded by Perkin-Elmer spec-
trum GX,1H NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis
was performed on a Perkin-Elmer PE2400 CHN analyzer. Transition temperature and LC
properties(Textures) were determined using an optical polarizing microscopy equipped with
a heating stage. Textures of nematic phase determined by miscibility method. Thermody-
namic quantity enthalpy (ꢀH) and entropy (ꢀH) are qualitatively discussed instead of DSC
scan.
Analytical Data
IR Spectra in cm−1 for Hexyloxy & Tetradecyloxy Derivatives:
=
–
Hexyloxy : 962 (Trans CH CH), 723 Polymethylene ( CH2-)n of –OC6H13, 835 (–C-H-
–
def. m di-substituted), 792 Polymethylene ( CH2-) of –OC14H29, 912 (–C-H- def. hydrocar-
– – – – – – – –
bon), 1112( C O ) Str, 1161,1246 and 1390 ( C O str in –(CH2)n chain), 1467 ( C H def.
– = – – =
–
–
in CH2), 1510 ( C C )str, 1604,1622 ( C O and group),1720, 1776 ( COO group) 2848
– –
and 2915 ( C H str in CH3).
Tetradecyloxy : 958(Trans CH CH), 723 Polymethylene ( CH2 )n of OC14H29, 833
– – – – – –
=
–
–
–
–
–
–
( C H def. m di-substituted), 792 Polymethylene ( CH2 ) of OC14H29, 910 ( C H def.
– – – – –
hydrocarbon), 1112 ( C O ) Str, 1161,1246 and 1388 ( C O str in –(CH2)n chain), 1465
– – –
– = –
–
–
–
( C H def. in CH2), 1510 ( C C )str, 1600,1662 ( C = O and group), 1777( COO group)
– –
2848 and 2918 ( C H str in CH3).

56
B. B. JAIN AND R. B. PATEL
Scheme . Synthetic route to the series.
1HNMR spectra in CDCl3 in δ ppm for Hexyloxy & Tetradecyloxy Derivative:
–
Hexyloxy: 0.85(t, CH3 of –C6H13), 1.1-1.5 (m, n-poly methylene groups of-OC6H13),
–
–
1.74 (m, n-poly methylene groups of OC14H29), 3.9(s,-OCH2 CH2-ofOC14H29),4.11
(s, OCH2 CH2-of OC6H13) 6.41 (d, CH CH ) 6.8-7.5 (s,-CO CH CH), 7.8 (s, p-
disubstituted phenyl ring).
Tetradecyloxy: 0.82 (t, CH3 of –C14H29), 1.2-1.5 (m, n-poly methylene groups of-
OC14H29),1.73 (m, n-poly methylene groups of -OC14H29),3.3-3.7 (s,-OCH2 CH2-of
OC14H29), 4.13 (s,-OCH2 CH2-of OC14H29), 6.5-6.8 (d, CH CH ) 7.1-7.5 (s,-CO
–
–
–
=
–
–
=
–
–
–
–
=
–
–
=
CH CH), 7.83 (s, p-disubstituted phenyl ring).
α-3-(4ꢀ-n-alkoxy cinnamoyloxy) benzoyl-β-4ꢀꢀ-tetradecyloxyphenyl ethylenes

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
57
Figure . Phase behaviors of series.
Results and discussion
Novel nonlinear series of chalconyl derivatives synthesized by condensation of trans 4-n-
alkoxy cinnamic acids and α-3-Hydroxy benzoyl β-4/ -n- tetradecyloxy phenyl ethylene (m.p.
: 72°C and yield : 66.54%). Series consist of thirteen (C1 to C18) homologues of which C1 to C5
homologues are nonliquidcrystals and C6 to C18 homologues are enantiotropically nemato-
genic without exhibition of smectic property. Transition and melting temperatures were deter-
mined through an optical polarising microscopy equipped with a heating stage and were
plotted versus the number of carbon atoms present in n-alkyl chain R of left –OR group.
Transition curves, Cr-N/I and N-I were drawn by linking like or related transition points
as depicted in a phase diagram (Figure 1) showing phase behavior of series. Cr-N/I tran-
sition curve follow zigzag path of rising and falling with overall descending tendency and
behaved in normal manner. N-I transition curve initially descended from C6 to C8 through
C7 homologue and then ascended to C12 homologue through C10 and finally descended up
to last C18 homologue with exhibition of odd-even effect. Thus, it behaves in normal manner.
Odd-even effect is observed between C6 to nearby C9 homologues and then it disappears from
and beyond C9 homologue for higher homologues of longer n-alkyl chain ‘R’ of –OR group.
N-I transition curve of odd members occupy lower position then even members. Textures
of nematic phase are threaded or Schlieren. Analytical, spectral and thermometric data sup-
ported the molecular structures of homologues. LC properties from homologue to homologue
in the same series varied keeping right terminal and geometrical shape unchanged through-
out the series, except number of changing number of methylene unit or units. The lowering
of transition temperatures of novel final chalconyl ester compounds as compared to corre-
sponding dimeric cinnamic acids is due to the breaking of hydrogen bonding between acid
molecules through esterification process. Alternation of transition temperatures is attributed
to the odd and even number of carbon atoms present in n-alkyl chain ‘R’ of –OR group. The

58
B. B. JAIN AND R. B. PATEL
exhibition of only nematic property by the present series is attributed the suitable magnitudes
(neither more nor less) of anisotropic forces of intermolecular end to end attractive cohe-
sion and closeness as a consequence of favorable molecular rigidity and flexibility to induce
a molecular arrangement in statistically parallel orientational order in floating condition
under the influence of exposed thermal vibrations. However combined effect of intermolec-
ular cohesion emerged from two opposing effects of decreasing and increasing intermolec-
ular attractions by molecular polarity and polarizability respectively for widening molecular
width which play an important role in facilitation and predomination of effective intermolec-
ular cohesion which is sufficient and suitable to induce nematic mesophase formation but
the magnitudes of the same is insufficient and unsuitable to induce smectogenic character as
depending upon magnitudes of dispersion forces and dipole-dipole interactions. The non-
mesomorphicity of C1 to C5 homologues is attributed to the low magnitudes of dispersion
forces and low magnitudes of dipole-dipole interaction as well as electronic interactions which
induces high crystallizing tendency and abruptly breaking crystal lattices which sharply trans-
form into isotropic liquid without passing through an intermediate physical state of existence
called as LC state. However on cooling the same from and below isotropic temperature neither
the nematic or smectic phase from nonmesomorphs (C1 to C5) nor the smectic phase from
enantiotropic nematogenic homologues observed in irreversible manner. Thus, monotropic
transitions either for nonmesomorphs (C1 to C5) or nematogenic homologues (C6 to C18) are
not observed for present novel series. The disappearance of odd-even effect from and beyond
nearby C9 homologues for N-I transition curve is attributed to the coiling or bending, or
flexing or coupling of longer n-alkyl chain of –OR and –OC14H29 (n) end groups with the
major axis of core structure of a molecule. N-I transition curve for odd and even homologues
are extrapolated [35,36,37,38] to C5 and C4 homologues respectively to highlight odd-even
effect and to predict their latent ability to exhibit mesophase formation at 61°C and 107°C
respectively, but, due to their high crystallizing tendency, it is not realizable in actual practice.
The changing behaviors of LC properties from homologue to homologue in the same series is
attributed to the changing number of methylene unit or units which causes variations in the
magnitudes of total molecular flexibility keeping molecular rigidity unaltered because rest
of the molecular part including tailed end remains unchanged throughout the novel present
series. Some LC properties evaluated from thermotropic data of presently investigated novel
series-1 and compared with other structurally similar analogous series X [39] and Y [40] as
mentioned below in following Figure 2.
Figure . Structurally similar analogous series.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
59
Table . Elmental Analysis for heptyloxy, decyloxy, dodecyloxy, and hexadecyloxy derivatives.
%Elements found
C
%ElementsTheoretical
Sr. No.
Molecular formula
H
C
H

CHO
CHO
HO
.
.
.
.
.
.
.
.
.
.
.
.
.



.
.
.
C
CHO
Table . Texture of Nematic Phase of C, C, C, C by miscibility method.
Sr. No.
Homologue
Texture

C
Threaded
Threaded
Schieren
Threaded



C
C
C
In the above Figure 2, the homologous series-1 of present investigation and a series-X,
selected for comparison are isomeric to each other but due to their linearity difference, their
magnitudes of combined effects of molecular rigidity and flexibility acquire difference by posi-
–
=
–
–
tional difference of bonding CH CH COO central group to middle phenyl ring. Homol-
ogous series 1 and X differs from series –Y with respect to a central bridges vinyl carboxy
and carboxy groups linking first and middle phenyl rings. Therefore magnitudes of molecu-
lar rigidity and flexibility differs from homologue to homologue in the same series and the
magnitudes of only rigidity undergo variations but molecular flexibility remains unaltered
for the same homologue from series to series. Thus, variations in mesomorphic properties
like thermal stability, commencement of mesophase, mesophase lengths etc will attend and
depend upon the magnitudes of changing features of homologous series 1,X and Y under
comparative study. Following table 4 represents some thermometric data for the series under
comparison.
From table 4,
r
Homologous series 1, X and Y are nematogenic only with absence of smectic property.
Thermal stability of series 1, X and Y are in increasing order.
The nematogenic mesophase commences in equal manner for isomeric series 1 and X
(C6) but it commences late by one more (C7) homologue in case of series-Y.
r
r
Table . Transition temperature of homologous series.
Transition temperatures in °C
Sr. no
R = n-alkyl group
Smectic
Nematic
Isotropic













C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
C
C
C
C
C
C
C
C

60
B. B. JAIN AND R. B. PATEL
Table . Thermal stability in °C.
Series- (nonlinear)
Series-X (Linear isomeric)
–
=
–
–
–
=
–
–
Series
CH CH COO
CH CH COO
Series-Y (Linear) -COO-
__
Sm-I or Sm-N
__
__
Commencement of Smectic
phase
N-I Commencement of
Nematic phase
. (C- C) C
. (C-C) C
. to . C C
. (C-C) C
Total mesophase lengths
. to . C/C C
. to . C C/C/C
from tc to tc
r
Total upper mesophase lengths are in increasing order of temperature but lower
mesophase lengths are in decreasing order from isomeric series to nonisomeic series.
The exhibition of only nematic property with absence of smectic property is obviously
related to the molecular arrangement in floating condition under exposed thermal vibrations
as required for emergence of nematic phase which facilitated in all the three series under
comparison. But, their thermal resistivity extremely against exposed thermal vibrations vary
from homologue to homologue in the same series and for the same homologue from series to
series due to changing magnitudes of thermodynamical quantity enthalpy (ꢀH), representing
energy stored in a molecule as a consequence of combined effect of molecular rigidity and flex-
ibility. The intermolecular cohesion and closeness are affected by intermolecular distance by
end to end attractions and molecular polarizablity which are operated more in nonlinear series
depending upon predominancy of the intermolecular forces of dispersion and magnitudes of
dipole-dipole interactions. The net effect of the suitable magnitudes of dispersive forces in
an isomeric linear series-X are stronger than nonlinear series-1 which lowers the transition
temperatures of series-1 as compared to linear analogous series-X. Therefore thermal stabil-
ity of series-1 calculated on the basis of N-I transition temperatures acquire magnitudes of
thermal stability. The highest thermal stability of linear series-Y, is due to presence of -COO-
–
=
–
–
central group in place of CH CH COO central bridge which more effectively contribute
–
=
–
to molecular rigidity and flexibility due to decrease in length by the absence of CH CH
unit and increased linearity as well as increase suitable magnitudes of intermolecular end to
end attractions and closeness. Thus, transition temperatures and hence the thermal stability
for nematic is the highest. Thus, increasing order of nematic thermal stability and the upper
mesophase lengths are maintained. The commencement of mesophase (nematic) is depended
upon the extent of molecular noncoplanarity. The data of commencement of mesophase for
isomeric series linear and nonlinear 1 and X suggests the equitable magnitudes (C6) of early
commencement of mesophase which depends on the shapes of molecules irrespective of linear
or nonlinear. However, the molecules of linear series-Y, commences its mesophase formation,
–
=
–
a little bit later from C7 homologue due to absence of CH CH unit as compared to series
–
=
–
1 and X. Thus, the presence or absence of CH CH unit disturb or facilitate suitable or
unsuitable magnitudes of the extent of molecular coplanarity, thermal stability, the degree of
mesomorphism etc.
Conclusions
r
A homologous chalconyl ester series of present investigation is nematogenic with
absence of smectic property and low degree of mesomorphism as well as of low ordered
melting type.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
61
r
r
Nonlinearity of a molecule lowers the transition temperature as compared to an isomeric
linear molecule.
–
–
=
–
The group efficiency order derived for nematic in combination with CO CH CH
central bridge .on the basis of (i) thermal stability (ii) early commencement of mesophase
and (iii) total upper and lower mesophase lengths are as under.
(i) Nematic
–
– – –
=
–
– –
=
–
COO > CH CH COO > CH CH COO
linear nonlinear
(ii) Nematic
–
=
–
=–
=
–
– – –
CH CH COO CH CH COO > COO
nonlinear linear linear
(iii) Total (nematic) Mesophase length
–
–=–
=
–
– –
=
–
–
upper : COO CH CH COO > CH CH COO
linear linear nonlinear
–
=
–
=–
=
–
– –
–
Lower : CH CH COO CH CH COO > COO
nonlinear linear linear
r
r
r
Mesomorphism phenomena is very sensitive and susceptible to molecular structure as a
consequence of molecular rigidity and/or molecular flexibility.
Chalconyl esters of low transition temperature may be useful for LC devices to be oper-
ated at room temperature or desired temperature.
Ester group of present novel investigation may be useful for the agricultural production
for the growth of quality and healthy fruits and flowers, potato and potato like material
as well as chalconyl group being biologically active and antibacterial and antifungal may
reduce the consumption of pesticides and insecticides.
r
Present investigation supports previous conclusions.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors also thank to Dr. A. V. Doshi, Ex-principal of M.V.M. Science and Home
Sci. College—Rajkot for his constant support, inspirations, suggestions and help, as and when needed
during the course of present investigation. Authors thank to NFDD Centre for the analytical and spec-
tral services.
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