Dependence of mesomorphism on geometrical shapes of isomeric and nonisomeric series of chalconyl esters

Article abstract of DOI:10.1080/15421406.2016.1264227

A meta substituted chalconyl ester homologous series: RO?C₆H₄?COO?C₆H₄(meta)?CO?CH?CH?C₆H₄?OC₁₂H_25(n)(para) is synthesized and studied with a view to understanding the effect of molecular substitution at meta position in a molecular structure on thermotropic liquid crystal properties. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). All the homologues except the nonliquid crystal homologues C₁, C₂, C₃ are enantiotropic nematic with the absence of smectic properties. The transition and melting temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren. Transition curves (Cr-N/I and N-I) behave in normal manner except homologues between C₁₀ and C₁₄ of N-I curve, which show negligible deviation from normal and a smooth descending tendency. The N-I transition curve exhibits an odd-even effect up to C₁₀ homologue and then the odd-even effect disappears for higher homologues. Analytical and the spectral data support the molecular structures. Thermal stability for nematic is 107.3°C and the mesophase lengths range between 13.0°C and 35.0°C at the C₁₈ and C₁₂ homologues respectively. Group efficiency order for nematic is derived on the basis of thermal stability as ?OC₁₂H_25(n) (linear) > ?OC₁₂H_25(n) (nonlinear) > ?OC₁₆H₃₃ (nonlinear).

Full text of DOI:10.1080/15421406.2016.1264227

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Dependence of mesomorphism on geometrical
shapes of isomeric and nonisomeric series of
chalconyl esters
Priya K. Patel & R. R. Shah
To cite this article: Priya K. Patel & R. R. Shah (2017) Dependence of mesomorphism on
geometrical shapes of isomeric and nonisomeric series of chalconyl esters, Molecular Crystals and
Liquid Crystals, 643:1, 168-177, DOI: 10.1080/15421406.2016.1264227
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1264227
Published online: 23 Feb 2017.
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Date: 23 February 2017, At: 21:41

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Dependence of mesomorphism on geometrical shapes
of isomeric and nonisomeric series of chalconyl esters
Priya K. Patel and R. R. Shah
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
A
meta substituted chalconyl ester homologous series:
Mesomorphism; liquid
crystal; nematic; smectic;
enantiotropic
RO–C H –COO–C H (meta)–CO–CH=CH–C H –OC H25(n)(para)
is
6
4
6
4
6
4
12
synthesized and studied with a view to understanding the effect of
molecular substitution at meta position in a molecular structure on
thermotropic liquid crystal properties. The novel homologous series
consists of thirteen homologues (C to C ). All the homologues except
1
18
the nonliquid crystal homologues C , C , C are enantiotropic nematic
1
2
3
with the absence of smectic properties. The transition and melting tem-
peratures were determined by an optical polarizing microscopy (POM)
equippedwithaheatingstage. Texturesofanematicphasearethreaded
or Schlieren. Transition curves (Cr-N/I and N-I) behave in normal manner
except homologues between C and C of N-I curve, which show negli-
1
0
14
gibledeviationfromnormalandasmoothdescendingtendency. TheN-I
transition curve exhibits an odd-even effect up to C10 homologue and
then the odd-even effect disappears for higher homologues. Analytical
and the spectral data support the molecular structures. Thermal sta-
bility for nematic is 107.3°C and the mesophase lengths range between
1
3.0°C and 35.0°C at the C18 and C12 homologues respectively. Group
efficiency order for nematic is derived on the basis of thermal stability
as –OC H (linear) > –OC H (nonlinear) > –OC H (nonlinear).
1
2
25(n)
12 25(n)
16 33
Introduction
Liquid crystalline (LC) [1] state of a matter has earned credit in the fields of electronic or in
general display device to be operated at room temperature or desired temperature and phar-
maceutical preparations of bioactive novel molecules [2–10]. Therefore present investigation
was planned to synthesize novel chalconyl ester derivatives with a view to understand and
establish the effect of molecular structure on thermotropic LC properties [11–17] with ref-
erence to geometrical shapes and size as linear and nonlinear in isomeric and nonisomeric
series. Therefore the present investigation will be restricted for thermotropic LC properties.
The novel substances will be synthesized, characterized and then evaluated thermometric data
which will be interprited and discussed in terms of molecular rigidity and flexibility [18–20].
Number of homologous series of esters, azoesters, chalconyl esters have been reported till the
date [21–29]. The novel chalconyl esters reported from present study may be useful to the
CONTACT R. R. Shah
lege, Gujarat University, Ahmedabad-, Gujarat, India.
 Taylor & Francis Group, LLC
ruteshshah@gmail.com
Chemistry Department, K. K. Shah Jarodwala Maninagar Science Col-
©

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
169
scientists and technologists working with the study for universal LC state with different aims,
objects and views at different angles to extend or to continue their research.
Experimental
Synthesis
4
-Hydroxybenzoic acid was alkylated by using suitable alkylating Agent (R-X) to convert it
into 4-n alkoxy benzoic acids by modified method of Dave and Vora [29].
ꢀ
α-3-Hydroxyl benzoyl β-4 -dodecyloxy phenyl ethylene (B) was prepared by usual estab-
lished method [30]. Acid chlorides component of each 4-n-alkoxy benzoic acid (A) were con-
densed with α-3-hydroxyl benzoyl β-4-dodecyloxy phenyl ethylene (B) in dry cold pyridine
by usual established method [31] carefully. Thus, chalconyl ester homologue derivatives were
finally decomposed, 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, 3-
Hydroxy acetophenone, 4- Hydroxy benzaldehyde, Dodecyl halide, etc., required for synthe-
sis were used as received except solvents which were dried and distilled prior to use. The
synthetic route to the series is shown below in Scheme 1.
Characterization
1
Some selected homologues of the series were characterized by infrared [IR], HNMR tech-
nique and elemental analysis. IR spectra were recorded on Perkin Elmer spectrum GX and
1
HNMR spectra were recorded using CDCl as solvent. Elemental analysis was performed
3
on Perkin Elmer PE 2400 CHN analyzer (Table 1). Liquid Crystal properties, i.e., transi-
tion and melting temperatures of homologues were investigated by an optical polarizing
microscopy with heating stage. Textures of the novel homologues were determined by a mis-
cibility method.
Analytical data
IR Spectra in cm  for butyloxy and hexadecyloxy derivatives
−
Butyloxy: 731 (polymethylene (–CH –)n of –OC H ), 786 (polymethylene (–CH –) of
2
4
9
2
–
OC H ), 839 (–OH def., m-disubstituted), 968 (–CH def. hydrocarbon), 1085 (–C–O-
18 37
stretching), 1328, 1309, 1244, 1230 & 1165 (–C–O– stretching in (–CH –)n chain), 1512 (–C
2
=
C- stretching), 1604 (–C = O group, –COO ester group), 2927 & 2850 (–CH stretching in
–
CH ).
3
Hexadecyloxy: 727 (polymethylene (–CH –)n of –OC H ), 781 & 761 (polymethylene
2
16 33
(
1
1
–CH –)n of –OC H ), 817 (–OH def. of m-disubstituted), 948 (–CH def. hydrocarbon),
2 18 37
060 (–C–O – stretching), 1390, 1309 & 1168 (–C–O stretching in (–CH )n chain), 1492 &
2
467 (–CH def. in –CH ), 1598 (–C = O group), 2848 & 2916 (–CH stretching in –CH ).
2
3

HNMR spectra in CDCl in δ ppm for hexyloxy and tetradecyloxy derivatives

Hexyloxy: 0.48–0.96 (t, –CH of C H ), 1.38–1.18 (m, n-polymethylene group of –OC H ),
3
6
13
6
13
2
5
.7–1.4 (m, n-polymethylene group of –OC H ), 3.2–2.8 (s, –OCH –CH of C H ),
18 37 2 2 18 37
.9–5.0 (s, –OCH –CH – OF –OC H ), 7.3–7.4 (s, –O–CH=CH–O), 10.0–8.0 (s, p-
2
2
18 37
disubstituted phenyl ring).

1
70
P. K. PATEL AND R. R. SHAH
Scheme . Synthetic route of the series-.
Tetradecyloxy: 0.79–0.43 (t, –CH of –OC H ), 1.2 - 1.0 (m, n-polyethylene group of
14 29 18 37 2 2
3
14 29
–
–
OC H ), 1.9–1.6 (m, n-polymethylene group of –OC H ), 3.5–3.0 (s, –OCH –CH – of
OC H ), 5.5–4.0 (s, –OCH –CH – of –OC H ), 7.0–6.3 (s, –O–CH=CH-), 10.0–8.0 (s,
18
37
2
2
14 29
p-disubstituted phenyl ring).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
171
ꢀ
ꢀꢀ
Homologous series: α-3 [4 -n-alkoxy benzyloxy] benzoyl β-4 -dodecyloxy phenyl
ꢀ
ꢀꢀ
ethylenes α-3 [4 -n-alkoxy benzyloxy] benzoyl β-4 -dodecyloxy phenyl ethylenes.
Results and discussion
ꢀ
α-3-Hydroxy benzoyl β-4 -dodecyloxy phenyl ethylene (m.p. –92°C, yield-68%) is a non-
mesomorphic component and on linking dimeric n-alkoxy benzoic acid, yielded mesomor-
phic novel chalconyl derivatives of lower transition temperatures than corresponding n-
alkoxy acids. Nematogenic mesomorphism commences from C homologue in enantiotropic
4
manner (C –C ) without exhibition of smectic property. A phase diagram showing phase
4
18
behaviours of series is obtained by linking like or related points from the plot of the transition
temperatures against number of carbon atoms present in n-alkyl chain ‘R’ of –OR, left termi-
nal end group. Cr-N/I transition curve adopted zigzag path of rising and falling with overall
descending tendency and behaved in normal expected manner. N-I transition curve exhibited
odd-even effect from C to C homologue. Transition curves for odd and even nematogenic
4
10
homologues are merging into each other at the C homologue; beyond which, N-I transition
10
curve adopted negligible deviation from normal descending tendency for higher homologues
C to C of longer n-alkyl chain ‘R’ of –OR and prolonged as a single transition curve. N-I
12
18
curve of even members occupied higher position as compared to an N-I curve for odd mem-
bers. The LC properties of mesogenic homologues undergo variations from homologue to
Table . Elemental analysis for butyloxy, pentyloxy, decyloxy, and dodecyloxy.
Element % found
Element % calculated
Molecular formula
C HO
C
H
C
H
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%


C H O
  
CHO
CHO
Table . Textures of nematic phase of C , C , C , C by miscibility method.




Sr. No.
Homologue
Texture

C
C
C
C
Threaded
Schlieren
Schlieren
Threaded




1
72
P. K. PATEL AND R. R. SHAH
homologue in the same series with changing molecular structure in length by added methy-
lene unit or units.
The lowering of transition temperatures of novel homologues as compared to the corre-
sponding n-alkoxy benzoic acids is attributed to the breaking of hydrogen bonding through
esterification process. The absence of LC properties of C –C homologues is due to the low
1
3
magnitudes of intermolecular dispersion forces and the low dipole-dipole interactions which
induces the inability in the nonmesogenic homologues to resist exposed thermal vibrations;
as a consequence of unsuitable magnitudes of molecular rigidity and flexibility, to cause
mesophase formation. Therefore, the molecules of such homologues (C –C ) sharply trans-
1
3
form into isotropic liquid from rigid crystalline state without passing through an intermediate
state of LC state prior to isotropic temperature, and then from and beyond isotropic tem-
perature, the molecules are randomly oriented in all possible directions with a high order
of disorder or high entropy (ꢀS = ꢀH/T). The isotropic mass of nonmesogenic homo-
logues on careful cooling below isotropic temperature do not exhibit monotropic meso-
morphism in irreversible manner but, undergo crystallization due to their high crystalliz-
ing tendency. The isotropic mass of nematogenic homologues (C –C ) on careful cooling
4
18
from and below isotropic temperature exhibited nematogenic mesophase formation which
reappeared in a reversible manner at a temperature at which nematogenic mesophase was
appeared on heating. Hence, such transitions are enantiotropic transition. The molecules of
nematogenic homologues on heating under exposed thermal vibrations disalign at an angle
less than ninety degree and resisted thermal vibrations for definite temperature range, called
as nematic mesophase length as a consequence of suitable magnitudes of anisotropic inter-
molecular forces of end to end attractions and closeness as well as due to favourable molecu-
lar rigidity and flexibility. Thus, nematogenic mesophase formation facilitated under floating
condition. However, the intermolecular forces of attractions are insufficient to build up layered
structure or subsequently sliding layered structure under floating condition, which eliminated
the possibility of facilitation of smectogenic mesophase formation prior to the nematogenic
mesophase formation. The exhibition of odd-even effect in N-I transition curve is due to the
subsequently and progressively added methylene unit to the n-alkyl chain ‘R’ of –OR of left
terminal end group. The disappearance of odd-even effect from and beyond C homologues
10
of longer n-alkyl chain of higher homologues is attributed to the coiling or bending or flexing
or coupling of longer n- alkyl chain with principal axis of the core structure of molecules. The
more or less or negligible deviations observed from normal descending tendency of N-I tran-
sition curve is attributed to the unusual and uncertainity in the status of longer n-alkyl chains
‘
R’ of –OR and −C H of –OC H terminally situated left and right end groups; from and
12
25
12 25
beyond C10 homologue. The changing trend in thermometric properties from homologue
to homologue in a same series is due to the changing molecular length by adding –CH2–
unit or units, altering molecular polarity and polarizability, molecular flexibility, permanent
dipole moment across the long molecular axis, magnitudes of dispersion forces, dipole-dipole
interactions, etc., keeping right sided tailed end group –OC H
unaltered. The mesogenic
12
25(n)
thermometric properties of present novel series-1 are compared with the structurally similar
analogous series-X [32] and Y [33] as under mentioned below in Figure 2.
Nonlinear homologous series-1 of present investigation and the homologous series-X (lin-
ear) and nonlinear series-Y chosen for comparative study are identical with respect to three
phenyl rings, two central bridges –COO− and −CO−CH=CH−, which contributes to the
molecular rigidity and left n-alkoxy (–OR) terminal end group contributing partly to the total
flexibility for the same homologue from series to series. However Series-1 and X, though
being identical with respect to tailed end groups –OC H25(n), but differ with respect to their
12

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
173
Figure . Phase behaviour of the series.
Figure . Structurally similar series.

1
74
P. K. PATEL AND R. R. SHAH
Table . Transition temperature in °C.
Compound
No.
Homologue
Transition temperatures in°C
(n-alkyl chain)
Smectic
Nematic
Isotropic

C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.












.
.
.
.
.
.
.
.
.
.




.
.
geometrical shapes as nonlinear and linear respectively. The homologous series-1 and Y are
though identical with respect to geometrical shapes as nonlinear, but differ with respect to
tailed end groups –OC H
and –OC H
respectively. Thus, variations in thermomet-
12
25(n)
16 33(n)
ric mesomorphic properties or behaviours will depend upon the differing features of series-1,
X and Y as a consequence of differing magnitudes of combined effect of molecular rigidity
and flexibility as depended upon molecular structure for the same homologue from series to
series and from homologue to homologue in the same series. Following table 4 represents
some thermometric properties of series-1, X and Y in comparative manner.
From Table 3, it is clear that
r
Homologous series-1, X and Y are nematogenic only with absence of smectic property.
r
Nematogenic mesophase commences earliest from C homologue of a nonlinear series-1
4
but it commences late from C homologue for series X and Y in equal manner.
6
r
Thermal stability of present series-1 is lower than a series-X and higher than series-Y for
nematic.
Nematogenic lower mesophase length of series-1 and X are equal and higher than a
series-X.
Nematogenic higher mesophase length for series Y is higher than a series-1, but it is
lower than a series-X.
r
r
The exhibition of only nematogenic character by all the series under comparison is
attributed to the suitable magnitudes of end to end intermolecular cohesion and closeness
as a consequence of favorable combined effect of molecular rigidity and flexibility, as varied
with geometrical shapes of core molecular structure. Thus, environmental and thermal con-
dition required to facilitate nematic mesophase formation for all the series establishes with
Table . Thermal stability in °C.
Series→
Series-
Series-X
Series-Y
Sm-I or Sm-N Commencement of smectic phase
N-I
Commencement of nematic phase
Total mesophase length (Sm + N) (upper and lower in°C)
−
.
−
−
.
.
(C —C ) C
(C —C ) C
(C —C ) C









. to . C C
. to . C C
. to . C C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
175
more or less degrees of mesomorphism for the same homologue from series to series. How-
ever the unsuitable magnitudes for more or less lateral attractions which is unable to facili-
tate sliding layered molecular arrangement in floating condition under the exposed thermal
vibrations. The early commencement of nematic phase is in decreasing order from series-1 to
series-X and Y which is attributed to the molecular planarity. The homologous series-1 and
Y are more nonco-planer series than linear series-X. But the presence of longer hexadecyl
chain may cause interruption in molecular polarity, polarizability and planarity of a molecule
which causes commencement of nematic phase later from series-1 by C homologue instead
6
of C . Thus, the polarity of end groups which are contributing to the flexibility can also affect
4
magnitudes of co-planarity for early or late commencement of mesophase. The lower values
of thermal stabilities of nonlinear series-1 and Y, as compared to a linear series-X is obviously
related to their shapes and the number of carbon atoms present in n-alkyl chain –C H and
16
33
–
C H of –OC H and –OC H tail ends for the same homologue from series to series,
12 25 16 33 12 25
which causes difference in the intermolecular cohesion and closeness, for linear and nonlin-
ear shaped homologous series. The highest upper mesophase length value of linear series-X
is due to the closer intermolecular distance which induces relatively higher intermolecular
attractions and higher thermal resistivity and stability as compared to nonlinear series-1 and
Y. Thus, higher or lower thermal resistivity against exposed thermal vibrations lengthens or
shortens the mesophase lengths or the degree of mesomorphism accordingly.
Conclusions
r
Homologous series nonlinear shaped novel chalconyl esters is nematogenic without
exhibition of smectic property whose thermal stability and upper mesophase length is
lower than the corresponding isomeric series of linear shape. It is a middle ordered melt-
ing type series.
The group efficiency order derived on the basis of (i) thermal stability (ii) early com-
mencement of mesophase (iii) upper and lower mesophase length for nematic is as
under.
r
(
i) Nematic
–
OC H
linear > –OC H
Nonlinear > –OC H
Nonlinear
Nonlinear
16 33(n)
1
2
25(n)
12 25(n)
16 33(n)
(ii) Nematic
–
OC H
Nonlinear > –OC H
linear = –OC H
1
2
25(n)
12 25(n)
(
iii) Total mesophase length (Sm ± N)
Upper
–
OC H
linear > –OC H
Nonlinear > –OC H
Nonlinear
Nonlinear > –OC H
linear
16 33(n) 12 25(n)
1
2
25(n)
16 33(n)
12 25(n)
Lower
OC H
–
Nonlinear = –OC H
1
2
25(n)
r
Transition temperatures, thermal stability, upper mesophase length of nonlinear homol-
ogous series are generally lower than linear isomeric series; whereas, lower mesophase
length increases from linear to nonlinear isomeric series.
r
Mesomorphism is very sensitive and susceptible to the molecular structural shapes and
size.
The study of binary system may help in the manufacture of LC devices to be operated at
room temperature or desired temperature. Chalconyl ester derivatives may be useful in
the pharmaceutical preparation due to their bioactive nature.
r
r
Present investigation supports and raises credibility to the early conclusions.

1
76
P. K. PATEL AND R. R. SHAH
Acknowledgments
The authors thank the management of the college and the Head of the Chemistry Department Dr. R. B.
Patel of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad for their valuable cooperation in
the work. The authors are also thankful to Dr. A. V. Doshi, Ex-Principal, M. V. M. Science and Home-
science College, Rajkot for his co-operation, valuable suggestions and help as and 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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