Mesomorphism dependence on tail group

Article abstract of DOI:10.1080/15421406.2016.1146932

A chalconyl homologous novel series of thermotropic liquid crystals (LC) have been synthesized and studied with a view to understand and establish the effects of molecular structure on LC properties in thermotropic behaviors. Homologous series RO-C₆H₄-COO-C₆H₄-CO-CH=CH-C₆H₄-OC₁₄H₂₉ consists of 13 homologs (C₁–C₁₈), C₁–C₆ homologs are nonliquid crystals and the rest of the homologs are enantiotropically nematogenic without exhibition of smectic property. Transition temperatures and the textures of the nematic phase were determined by an optical polarizing microscopy, equipped with a heating stage. Texture of a nematic phase are threaded or schlieren. The Spectral and analytical data confirms the molecular structures of homologs. Thermal stability for nematic is 123.0°C and its mesogenicphaselength ranges between 13°C and 34°C. Cr-N/I and N-I transition curves behaved in normal manner except C₁₄ homolog which shows negligible abnormality for N-I transition temperature or curve with exhibition of odd-even effect. Some LC properties are compared with the structurally similar homologous series. Thus, present homologous series is nematogenic and middle ordered melting type.

Full text of DOI:10.1080/15421406.2016.1146932

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphism dependence on tail group
B. B. Jain & R. B. Patel
To cite this article: B. B. Jain & R. B. Patel (2016) Mesomorphism dependence on tail group,
Molecular Crystals and Liquid Crystals, 630:1, 121-129, DOI: 10.1080/15421406.2016.1146932
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Date: 21 July 2016, At: 23:19

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Mesomorphism dependence on tail group
B. B. Jain and R. B. Patel
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Liquid crystal; mesomorphic;
mesogenic; nematic; smectic
A chalconyl homologous novel series of thermotropic liquid crystals
(LC) have been synthesized and studied with a view to understand
and establish the effects of molecular structure on LC properties in
thermotropic behaviors. Homologous series RO-C6H4-COO-C6H4-CO-
CH=CH-C6H4-OC14H29 consists of 13 homologs (C1–C18), C1–C6 homologs
are nonliquid crystals and the rest of the homologs are enantiotropically
nematogenic without exhibition of smectic property. Transition tem-
peratures and the textures of the nematic phase were determined by
an optical polarizing microscopy, equipped with a heating stage. Tex-
ture of a nematic phase are threaded or schlieren. The Spectral and
analytical data confirms the molecular structures of homologs. Ther-
malstabilityfornematicis123.0°Canditsmesogenicphaselengthranges
between 13°C and 34°C. Cr-N/I and N-I transition curves behaved in nor-
malmannerexceptC14 homologwhichshowsnegligibleabnormalityfor
N-I transition temperature or curve with exhibition of odd-even effect.
Some LC properties are compared with the structurally similar homolo-
gous series. Thus, present homologous series is nematogenic and mid-
dle ordered melting type.
Introduction
The interest in the study of liquid crystalline (LC) [1] state of matter has attracted to scien-
tists and technologists because of its dual character as to flow like isotropic liquid and have
to behave as rigid crystals by thermotropic and lyotropic LC. Thermotropic or lyotropic LCs
has proved their ability in the interest of mankind. Some LCs like chalconyl esters derivatives
are thermotropically and biologically active materials which are useful for the manufacture
of LC devices or pharmaceutical preparation useful for curing of various physical disorder
of human or animal bodies [2–10]. Present investigation is planned to synthesize novel LC
material through homologous series with a view to understand and establish the effects of
molecular structure on thermotropic LC properties, with reference to changing the tail group
and its flexibility [11–14]. Thermotropic LC series of compounds of chalconyl ester deriva-
tives is selected for synthesis, which may be biologically active and the present investigation
is targeted to study their thermotropic behaviors through an optical polarizing microscopy
after their due characterization. Such thermotropic behaviors of novel LC compounds will
be compared with the structurally similar homologous series to derive group efficiency order,
CONTACT R. B. Patel
roshanpatel@gmail.com
lege, Gujarat University, Ahmedabad, Gujarat, India.
Chemistry Department, K.K. Shah Jarodwala Maninagar Science Col-
©  Taylor & Francis Group, LLC

122
B. B. JAIN AND R. B. PATEL ET AL.
Scheme . Synthetic route of series.
etc., and results will be interpreted in terms of molecular rigidity and flexibility [15–19]. Num-
ber of ester homologous series have been reported till the date [20–27].
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated using suitable alkylating agent (R-X) to convert it into
4-n-alkoxy benzoic acids by modified method of Dave and Vora [27]. α-4-hydroxyl ben-
zoyl β-4/-tetradecyloxy phenyl ethylene (B) was prepared by usual established method [28].
Acid chlorides component of each 4-n-alkoxy benzoic acid (A) were condensed with α-4/-
hydroxyl benzoyl β-4-tetradecyloxy phenyl ethylene (B) in dry cold pyridine by usual estab-
lished method [29] carefully. Thus, chalconyl ester homolog derivatives were finally decom-
posed, filtered, washed, dried, and purified till constant transition temperature obtained using
an optical polarizing microscope equipped with a heating stage.4-Hydroxy benzoic acid, alkyl
halides, thionyl chloride, MeOH, EtOH, KOH, acetone, pyridine, 4-hydroxy acetophenone,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
4-hydroxy benzaldehyde, tetradecyl halide, etc., required for synthesis were used as received
except solvents which were dried and distilled prior to use. The synthetic route to the series
is mentioned below as Scheme 1.
Characterization
Selected members of the novel homologous series were characterized by elemental analysis,
infrared spectroscopy, 1H NMR spectra (Table 1). IR spectra were recorded by Perkin-Elmer
spectrum GX, 1H NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanal-
ysis 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.
Analytical data
IR spectra in cm−1 for heptyloxy and tetradecyloxy derivatives
Heptyloxy: 686 Polymethylene (-CH2-)n of –OC7H15, 840(–C-H- def. m di-substituted-
para), 771 polymethylene (-CH2-) of –OC14H29, 948 (–C-H- def. hydrocarbon), 1056 and
1010 (-C-O-) Str, 1165,1249 and 1303 (-C-O str in –(CH2)n chain, 1427 and 1465 (-C-H- def.
in CH2),1512 (-C = C-)str, 1604,1681 and 1735 (-C = O group) and (-COO- ester group),
2854 and 2916 (-C-H str in CH3).
Tetradecyloxy: 717 polymethylene (-CH2-)n of –OC14H29, 840(–C-H- def. m di-substituted-
para), 771 polymethylene (-CH2-) of –OC14H29, 948 (–C-H- def. hydrocarbon), 1056 and
1018 (-C-O-) Str, 1396, 1303 and 1165, 1249 (-C-O str in –(CH2)n chain, 1427 and 1465 (-
C-H- def. in CH2),1512 (-C = C-)str, 1604,1681 and 1728 (-C = O group) and (-COO- ester
group), 2854 and 2924 (-C-H str in CH3).
1HNMR spectra in CDCl3 in δ ppm for decyloxy and hexadecyloxy derivative
Decyloxy: 0.82(t, -CH3 of –C10H21), 1.2–1.4(m, n-poly methylene groups of-OC10H21), 1.70
(m, n-poly methylene groups of -OC14H29),3.9(s,-OCH2-CH2-ofOC14H29), 6.9–7.2(s,-CO-
CH = CH), 8.0 (s, p-disubstituted phenyl ring).
Hexadecyloxy: 0.88 (t,-CH3 of –C16H33), 1.2–1.4(m, n-poly methylene groups of-OC16H33),
1.80 (m, n-poly methylene groups of -OC14H29), 3.5–3.6(s,-OCH2-CH2-ofOC16H33), 4.0(s,-
OCH2-CH2-of OC16H33), 6.9–7.3(s,-CO-CH = CH),8.1 (s, p-disubstituted phenyl ring).
Results and discussion
4-n-Alkoxy benzoic acids are dimeric and on linking them with nonmesogenic α - 4 –
hydroxy benzoyl β-4/-n-tetradecyloxy phenyl ethylene (m.p.−80°C), which added chalconyl
ester derivatives whose LC property as enantiotropicnematic commences from heptyloxy (C7)
homolog derivative and continued uptooctadecyloxy (C18) homolog with absence of smecto-
genic property. Transition temperatures (Table 3) as determined from an optical polarizing
microscopy, were plotted versus the number of carbon atoms present in n-alkyl chain of the
left n-alkoxy terminal end group. Transition curves Cr-N/I and N-I are obtained by link-
ing like or related points as depicted in a phase diagram (Fig. 1) showing the phase behav-
iors of a novel series. Cr-N/I transition curve adopts a zigzag path of rising and falling with

124
B. B. JAIN AND R. B. PATEL ET AL.
200
Cr-N/I
N-I
180
160
140
120
100
80
Isotropic (I)
N - I
Nematic (N)
Cr - N/ I
Solid (Cr)
60
40
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
No.of carbon atoms in n-alkyl chain-R
Figure . Phase behaviors of series.
overall falling tendency and behaves with normal manner. N-I transition curve is ascended
from C7 homolog, then it descended from C10 homolog to C16 homologs with negligible rise
of 1 or 2°C temperature of C14 and C18 derivatives, than normal expected path of propaga-
tion with exhibition of odd-even effect. Odd-even effect diminishes as series is ascended for
higher homologs from and beyond merging of N-I curves for odd and even members nearby
about C12 homolog. N-I transition curves for odd members occupy lower position than even
member’s curve. The N-I transition curve for even members is extrapolated to C6 homolog
to predict the N-I transition temperature and its exhibition of nematic mesophase forma-
tion. The changing trend in mesomorphic behaviors from homolog to homolog observed
for present novel series in usual manner. Thermal stability for nematic is 123.0°C, and the
total mesophase length ranges from 13.0°C to 34.0°C. Thus, present novel chalconyl ester
homologous series is middle ordered melting type whose melting transition temperatures vary
between 82°C and 137°C.
The lowering of transition temperatures of present chalconyl novel ester homologous as
compared to corresponding dimeric 4-n-alkoxy benzoic acids is attributed to breaking of
hydrogen bonding between two aromatic acid molecules by esterification process. Alter-
ations of transition or melting temperatures are due to odd and even number of carbon
atoms present in n-alkyl chain of the left n-alkoxy group. The nonmesomorphicity of C1–C6
homologs is attributed to their inability to resist exposed thermal vibrations which, abruptly
breaks the crystal lattices and sharply transform into isotropic liquid without exhibition of
smectic or nematic phase due to their high crystallization tendency. High crystallization
tendency of a substances (C1–C6) rises from unfavorable magnitudes of anisotropic forces
of intermolecular end to end and lateral attractions as a consequence of resultant rigidity
and flexibility due to low dipole-dipole interactions and the low magnitudes of dispersion

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
125
forces through interactions between instantaneous dipoles produced by the oscillation of
the electron clouds of the molecules. Thus, C1–C6 homolog molecules are randomly ori-
ented in all possible directions without any ordered molecular arrangement under floating
condition. Hence, they neither shows mesophase on heating nor they exhibit monotropic
mesophase formation on cooling the same. However, nematogenic mesophase formation
commences late from C7 homolog and continues up to last C18 homolog in enantiotropic
manners. The increasing length of n-alkyl chain by –CH2- unit, the corresponding per-
manent dipole moment across the long molecular axis and dispersion forces as a conse-
quences of favorable molecular rigidity and flexibility, causes occurrence of suitable magni-
tudes of anisotropic forces of intermolecular cohesion and closeness by end-to-end attrac-
tions only, which manages to float the molecules on the surface through statistically parallel
orientational order only from C7 to C18 homologs. Thus, only nematic mesophase forma-
tion induced for C7–C18. The absence of smectogenic character throughout the novel series
is due to the unsuitable magnitudes of lateral attractions which fails to induce lamellar pack-
ing of molecules in the crystal lattices from any stage of a novel series. Therefore, molec-
ular polarizability being less effective to form lamellar packing of molecules in their rigid
crystals which fails to adopt the sliding layered molecular arrangement in floating condi-
tion, to exhibit smectogenic property, under exposed thermal vibrations. The exhibition of
odd-even effect of N-I transition curve is attributed to sequentially added methylene unit
or units at the n-alkyl chain bonded to phenyl ring through oxygen atom. Diminishing of
odd-even effect from and beyond C12 homolog is due to coiling or bending or flexing or
coupling with major axes of a core structure of a molecule for longer n-alkyl chains. The
extrapolation [30–33] of N-I transition curve to nonmesogenic C6 homolog merges into its
isotropic temperature, which indicates that there is no temperature difference for appearance
of nematic phase above or below its isotropic temperature. The negligible abnormality in N-I
transition temperature of C14 homolog may be due to the bonding of –OC14H29 end groups
on both the terminals, whose vector sum of bond polarities contributed by –OC14H29 on
both ends of a molecule being equal in magnitudes and opposite in directions, which nul-
lifies the effects due to each other toward total molecular polarities and polarizability. Thus,
intermolecular dispersion forces of cohesion are disturbed and induce abnormality. Abnor-
mality observed for C18 homolog may be attributed to the uncertainty in the status of the
longest C18 n-alkyl chain of left n-alkoxy group. The variations in mesogenic behaviors from
homolog to homolog in the same series is due to the sequential addition of methylene unit
or units, which varies suitable or unsuitable magnitudes of molecular rigidity or/and flexibil-
ity responsible to induce mesophase formation. Some mesogenic properties of present novel
series 1 are compared with structurally similar series-X [34] and -Y [35] as shown below in
Fig. 2
Homologous series-1 of present investigation and the series-X and -Y chosen for compar-
ison are structurally identical with respect to three phenyl rings, central bridges –COO- and
–CO-CH=CH- and the left n-alkoxy terminal end group –OR for the same homolog from
series to series. However, they differ with respect to right-sided terminal tail end group viz.
–OC14H29, -Cl, -OC18H37, respectively, from series to series. Thus, the changing mesogenic
behaviors and the degree of mesomorphism depend upon the varying features of the com-
bined effects of molecular rigidity and flexibility, which induces, due to differing molecular
polarity and polarizability for the same homolog from series to series by changing right-sided
terminal end groups. Following Table 2 represents some mesogenic properties in comparative
manner for series-1, -X and -Y.

126
B. B. JAIN AND R. B. PATEL ET AL.
Figure . Structurally similar series.
Table . Elemental analysis for heptyloxy, decyloxy, tetradecyloxy, and hexadecyloxy derivatives.
Molecular
formula
Sr. no.
%Elements found
%Elements theoretical
C
.
.
.
.
H
C
H

C
HO
.
.
.
.
.
.
.
.
.
.
.
.



C
C
HO
HO
CHO
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. No.
Homolog
Texture

C
Threaded
Threaded
Threaded
Schlieren



C
C
C
α--(ꢀ-n-alkoxybenzoyloxy)benzoyl-β-ꢀꢀ-tetradecyloxyphenylethylenes
Table . Transition temperature of homologous series.
Transition temperatures in C
Nematic
Sr.no
R= n-alkyl group
Smectic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—





















MOLECULAR CRYSTALS AND LIQUID CRYSTALS
127
Table . Thermal stabilities in°C.
Series→
 (-OCH
__
)
X (-Cl)
__
Y (-OCH)
Smectic-isotropicorSmectic-
nematicCommencement of smectic
phase
__
Nematic-Isotropiccommencement
of nematic phase
Total mesophase length range in°C
.(C-
C)C
.(C–
C)C
–
CCC
.(C–
C)C
–CC
–
(Sm to N)
CCCC
From above Table 4, it is clear that,
r
homologous series-1, -X and -Y under comparative study are nematogenic with absence
of smectogenic property.
thermal stability for nematic is almost nearly equitable for series 1 and -Y, but it is less
than a series-X.
nematogenic mesophase commences from C5 homolog of series-X and –Y, but it com-
mences late from C7 homolog for series-1.
the total mesophaselength ranges from minimum to maximum in increasing order
from series-X to series-1 to series-Y. Coincidently the total mesophaselength ranges
from minimum to maximum by the homologs C7–C12 for all the series under
comparison.
r
r
r
Homologous series-1 and -Y are almost identical except the difference of four methylene
units at the tail end groups at right side of the molecules. Therefore, the molecular flexibility
differs to a very less extent affecting commencement of nematic phase and the intermolec-
ular end-to-end and cohesive or dispersion forces are nearly equivalent, which facilitate and
stabilize the exhibition of nematic property within definite range of temperature. Enthalpy
values (ꢀH) associated differs from homolog to homolog in the same series and for the same
homolog from series to series which plays role in the thermometric behavior of series to series
and the homolog to homolog. On comparing thermometric behaviors of series-1 and -X, the
dipolarity of a bond between third phenyl ring and tail end groups –OC14H29 and –Cl differs
because –Cl group is monoatomic and –OC14H29 is polyatomic which causes difference in the
intermolecular end to end and closeness as well as the extent of molecular noncoplanarity.
Thus, facilitation and stabilization of nematic mesophase is more favored in case of series-
X as compared to series-1 and -Y. Thus, commencement of nematic mesophase, mesophase
length range and the magnitudes of thermal stability show positive or negative variations in
mesogenic behaviors, from series to series for the same homolog and homolog to homolog in
the same series.
Conclusions
r
Present novel chalconyl ester series is predominantly nematogenic with absence of
smectic property and middle ordered melting type whose isotropic temperature varies
between 108°C and 137°C.
Group efficiency order derived for nematic on the basis of
r
(i) thermal stability
(ii) commencement of mesophase and

128
B. B. JAIN AND R. B. PATEL ET AL.
(iii) mesophaselength range are as under.
(i) Nematic
–Cl> –OC18H37 = –OC14H29
(ii) Nematic
–Cl = –OC18H37> –OC14H29
(iii) Nematic
–OC18H37>–Cl> –OC14H29
Molecular structure plays an important role in mesogenic behavior with reference to
changing tail end group.
Mesomorphism is very sensitive and susceptible to molecular structure.
Novel homolog of chalconyl ester derivatives may be useful in the study of their biological
activity lyotropically as antimalarial, anticancer, antibacterial …, etc.
Present study supported early views and raised reliability and credibility to the conclu-
sions drawn earlier.
r
r
r
r
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. Hemant Prajapati (C.U. Science College) and Dr.
A. V. Doshi, Ex-principal of M.V.M. Science College – Rajkot for their constant support, inspirations,
and help, as and when needed during the course of present investigation. Authors thank to NFDD
Centre for the analytical services and spectral services.
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