Mesomorphism and molecular structure: Novel homologous series 4-(4′-n-alkoxy cinnamoyloxy)-4″-methoxy benzyl benzoates

Article abstract of DOI:10.1080/15421406.2014.930220

A novel homologous series consists of 11 homologues, studied with a view to understand and establish the relations between mesomorphism and molecular structure of novel substances. All the novel members of a series except methoxy and pentyloxy homologue derivatives are liquid crystalline [LC] in nature. Mesomorphism commences from a second member of a series ethoxy, propyloxy, butyloxy, and hexyloxy to hexadecyloxy homologue derivatives are nematogenic while decyloxy, dodecyloxy, and tetradecyloxy homologue derivatives are smectogenic, in addition to nematogenic. All mesogenic homologues of a series are enantiotropic mesomorphic. Phase transition curve for Smectic-Nematic behave in normal manner without exhibition of odd-even effect, whereas nematic-isotropic transition curve adopts serpentile shape as rising and falling nature with exhibition of very minor odd-even effect. Textures of nematic phase are threaded or schlieren and that of a smectic mesophase is a focal conic fan shaped of the type smectic A or C. Analytical and spectral data supported molecular structures of homologues. The mesomorphic behaviors of present series are compared with a structurally similar other known series. Smectic and nematic thermal stabilities are 182.6 and 246.0°C, respectively. Present series is partly smectogenic and predominantly nematogenic with considerable degree of mesomorphism (maximum 100 °C) and high melting type.

Full text of DOI:10.1080/15421406.2014.930220

Mol. Cryst. Liq. Cryst., Vol. 607: pp. 78–86, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.930220
Mesomorphism and Molecular Structure:
Novel Homologous Series 4-(4ꢀ-n-alkoxy
cinnamoyloxy)-4ꢀꢀ-methoxy Benzyl Benzoates
BRIJESH H. PATEL1,∗ AND A. V. DOSHI2
1Huntsman, Baroda Textile Effects Pvt. Ltd, Vadodara, Gujarat, India
2Dr K. N. Modi University, Newai, Rajasthan, India
A novel homologous series consists of 11 homologues, studied with a view to under-
stand and establish the relations between mesomorphism and molecular structure of
novel substances. All the novel members of a series except methoxy and pentyloxy ho-
mologue derivatives are liquid crystalline [LC] in nature. Mesomorphism commences
from a second member of a series ethoxy, propyloxy, butyloxy, and hexyloxy to hex-
adecyloxy homologue derivatives are nematogenic while decyloxy, dodecyloxy, and
tetradecyloxy homologue derivatives are smectogenic, in addition to nematogenic. All
mesogenic homologues of a series are enantiotropic mesomorphic. Phase transition
curve for Smectic-Nematic behave in normal manner without exhibition of odd-even
effect, whereas nematic-isotropic transition curve adopts serpentile shape as rising and
falling nature with exhibition of very minor odd-even effect. Textures of nematic phase
are threaded or schlieren and that of a smectic mesophase is a focal conic fan shaped
of the type smectic A or C. Analytical and spectral data supported molecular struc-
tures of homologues. The mesomorphic behaviors of present series are compared with
a structurally similar other known series. Smectic and nematic thermal stabilities are
182.6 and 246.0◦C, respectively. Present series is partly smectogenic and predominantly
nematogenic with considerable degree of mesomorphism (maximum 100 ◦C) and high
melting type.
Keywords Enantiotropy; liquid crystals; mesomorphism; nematic; smectic
Introduction
The ester derivatives of alkoxy benzoic and cinnamic acids are bioactive [1] molecules,
which are useful for pharmaceuticals and medicinal preparations [2, 3]. Liquid crystal
properties can be induced by joining 4-hydroxy phenyl benzyl benzoate (or its substituted
benzyl benzoate) with an aromatic acid chloride by an appropriate synthetic method,
otherwise a diether forms instead of the ester derivative. Benzyl esters of aromatic hydroxy
carboxylic acids are useful as color developers for heat sensitive recording materials [4],
which on linking it with n-alkoxy aromatic carboxylic acid chloride can yield liquid crystal
bioactive materials [5, 6] containing three phenyl rings and two ester groups. Thus novel
substances may exhibit LC properties [7–9] and higher potency of biological activity. The
present study is restricted to synthesize novel double ester molecules and their evaluation
of mesogenic properties as a novel homologous series with characterization of homologues
∗Address correspondence to Brijesh H. Patel, A-21 Saket Bunglows Opp Yash Complex Gotri,
Baroda 390021, Gujarat, India. E-mail: brijpatel79@gmail.com
78

Mesomorphism and Molecular Structure
79
which consist of three phenyl rings bonded through CH CH COO and COO
central bridges as rigid core and two terminal groups, OCnH2n+1 and –OCH3 as left and
right end groups as flexible components of the molecule respectively, whose combined
effects of molecular rigidity and flexibility [10–12] operate the biometric and mesomorphic
behaviors [13–15] of the substance. Hence, the present investigation is planned with a
view to understand and establish the effects of molecular structure on mesomorphism
phenomenon [16].
Experimental
Synthesis
4-Hydroxy cinnamic acid was alkylated by suitable alkylating agents (CnH2n+1X) to form
n-alkoxy cinnamic acids by a modified method of Dave and Vora [17] as constituent com-
ponent (A) of a homologous series. Component (B) of (double) ester homologues was
prepared by reacting 4-hydroxy benzoic acid and 4-methoxy benzyl alcohol by the method
[18] of a European patent (m.p. 180◦C, yield is 33%). Final (double) ester homologues were
prepared by condensing components (A) individually through the acid chloride and (B) in
dry cold pyridine [19]. Final products of the novel homologous series were individually
decomposed filtered, washed, dried, and crystallized until they gave constant transition tem-
peratures. The chemicals, 4-methoxy cinnamic acid, 4-hydroxy benzoic acid, 4-methoxy
benzyl alcohol, dibutyltin oxide, pyridine, alkyl halides, MeOH, EtOH, thionyl chloride,
HCl, and KOH were used as received, except solvents, which were dried and distilled prior
to use. The synthetic route to the series is shown in scheme-1.
Characterization
Some selected members of a present novel series were characterized by elemental analy-
sis, infra red spectra, 1HNMR spectra and mass spectra. Micro analysis was performed by
Perkin-Elmer PE 2400 CHN analyzer, 1HNMR spectra were recorded on a Bruker spectrom-
eter using DMSO solvent. Infra red spectra were recorded on Perkin Elmer spectrum GX
instrument. Transition temperatures and the textures of smectic and nematic mesophases
as determined by a miscibility method, which were characterized by an optical polarizing
microscope equipped with a heating stage. Thermodynamic quantity enthalpy change (ꢀH)
and entropy change (ꢀS = ꢀH/T) are qualitatively discussed instead of DSC scane.
Analytical Data
Spectral Data
1HNMR in ppm for the Hexyloxy Derivative: 0.83–1.66 (H of C6H13), 2.45 ( O CH2 CH2
of –OC6H13), 3.67 ( OCH3), 3.92 ( OCH2 of –OC6H13), 4.98 (trans CH CH group),
6.53 (p-substituted phenyl ring), and 6.83–7.97 (presence of more benzene rings).
1HNMR in ppm for the Dodecyloxy Derivative: 1.1 (H of C12H25), 2.45
( O CH2 CH2 of –OC12H25), 3.64 ( O CH2 of –OC12H25), 3.41 ( OCH3), 3.92
( COO CH2 C6H4), 4.98 (trans CH CH group), 6.2–6.44 (p-substituted phenyl
ring), and 6.83–7.96 (presence of more benzene rings).
IR in cm−1 for Octyloxy Derivative: 825 para-substituted phenyl ring, 1123 ether link-
age of ( C8H17O C6H4), 1032, 1244, 1685( COO ester group), 960(trans CH CH
group), and 3447 (broad signal indicates –OH group).

80
B. H. Patel and A. V. Doshi
Scheme 1. Synthetic route to the series.
Series: 4-[4ꢀ-n-Alkoxy cinnamoyloxy]-4ꢀ-methoxy benzyl benzoates,
where R = CnH2n+1; n = 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16.
IR in cm−1 for Tetradecyloxy Derivative: 721 polymethylene of C14H29, 821 para-
substituted phenyl ring, 1018 ether linkage of ( C14H29O C6H4), 1173, 1217, 1650
( COO ester group), and 980 (trans CH CH group).
Mass Spectra
Mass Spectra for Decyloxy Derivative: Molecular formula C34H40O6 calculated molecular
weight 544. Practical mass observed by mass spectroscopy 544.
Texture of Nematic and Smectic Phase by Miscibility Method
Butyloxy derivative —————–→Threaded nematic
Octyloxy derivative —————–→Schlieren nematic
Dodecyloxy derivative ————→ Smectic A
Tetradecyloxy derivative———–→Smectic C

Mesomorphism and Molecular Structure
81
Table 1. Elemental analysis for methyloxy, ethyloxy, and propyloxy derivatives
Elements % found (% calculated)
S. no.
Molecular formula
C
H
1
2
3
C25H22O6
C26H24O6
C27H26O6
71.35 (71.77)
72.05 (72.22)
74.54 (72.64)
5.10 (5.26)
5.37 (5.55)
5.65 (5.82)
Results and Discussion
The constituent components forming homologues of the novel homologous series of cis-4-
n-alkoxy cinnamic acid and 4-hydroxy-4ꢀ-methoxy benzyl benzoate are nonliquid crystal
(NLC) components. However, on condensing two NLC components, yielded mesomor-
phism from the second member of the series. All the members of the novel series except the
first and the fifth members, exhibit either only nematogenic or smectogenic with the nemato-
genic mesophase in enantiotropic manner. The decyl, dodecyl, and tetradecyl homologues
are smectogenic in addition to nematogenic and the rest of the mesogenic homologues
including smectogenic homologues are nematogenic. Thus, the present series is predomi-
nantly nematogenic and partly smectogenic. Transition temperatures of the series (Table 2)
as determined by an optical polarizing microscopy are plotted versus the number of car-
bon atoms present in n-alkyl chain of left n-alkoxy terminal end group. Transition curves
viz. solid-isotropic/mesomorphic, smectic-nematic and nematic-isotropic are obtained by
joining like or related points, which formed a phase diagram (Fig. 1) of the series showing
the phase behavior of the series. The solid-isotropic/mesomorphic transition curve follows
a zigzag path of rising and falling values in the usual established manner. The smectic-
Nematic transition curve initially rises and then falls after passing through maxima, without
the exhibition of an odd-even effect and behaved in normal manner. The nematic-isotropic,
Table 2. Transition temperatures of series in ◦C
Transition temperature in ◦C
Compound no.
n-alkyl group ( CnH2n+1) (n)
Sm
Nm
Isotropic
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
8
10
12
14
16
—
—
—
—
—
—
—
186.0
182.0
180.0
—
—
198.0
243.0
228.0
226.0
202.0
254.0
266.0
242.0
262.0
217.0
276.0
195.0
209.0
208.0
—
154.0
188.0
215.0
222.0
188.0
182.0
10
11
Sm: Smectic Nm: Nematic.

82
B. H. Patel and A. V. Doshi
300
280
260
240
220
200
180
160
140
120
SMECTIC - NEMATIC
SOLID - ISOTROPIC
OR
NEMATIC - ISOTROPIC
MESOMORPHIC
ISOTROPIC
NEMATIC
SMECTIC
SOLID
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
No.of carbon atoms in n-alkyl chain-R
X-axis
Figure 1. Phase behavior of series.
transition curve deviates from normal behavior and adopted a path of rising and falling
values as the series is ascended for even members of the series with (i) exhibition of a
wave shaped appearance, and (ii) odd-even effect of about 5◦C. The nematic-isotropic
transition curves for the odd and the even members of the series merge into each other at
the butyloxy homologue and then curve for odd members from the pentyloxy homologue
and extrapolated [20–22] to first member of the series to magnify the odd-even effect for
nematic-isotropic transition curve. The textures of the nematic mesophase are threaded or
Schlieren as determined by a miscibility method, whereas, that of the smectic phase are
judged directly by observing mesophase through a polarizing microscope. The smectic
and nematic thermal stabilities of the series are 182.6 and 246◦C, whose mesophase length
varies between 18 and 100◦C at the fourth and sixth homologues, respectively. The isotropic

Mesomorphism and Molecular Structure
83
temperatures of the mesomorphic homologues vary between 276 and 217◦C. Thus, novel
homologous series is a high melting type with sufficient mesophase length. On condensing
two nonmesomorphic molecules, the molecular length, molecular polarity, and polarizabil-
ity and hence suitable magnitudes of anisotropic forces of intermolecular adhesion as a con-
sequence of favorable molecular rigidity and flexibility fitted in such a manner to facilitate
mesomorphism in the majority of members (nine) of the series, either only as nematogenic
or along with smectogenic behavior. Nonmesomorphic behavior of the odd members, viz.,
first and fifth member of a series is observed due to the n-alkyl chain of the left n-alkoxy
terminal end group, which hinders the suitable magnitudes of anisotropic forces of inter-
molecular attractions to induce mesomorphism, but induced high crystallizing tendency.
Hence, nonmesomorphic homologues are passing directly into isotropic liquid from solid
crystalline state, avoiding mesophase formation. Exhibition of mesomorphic behavior of a
substance is attributed to the respective sample substance against exposed thermal vibra-
tions arising from suitably favorable magnitudes of molecular rigidity and flexibility, which
maintain molecular disalignment at an angle of less than ninety degree for the definite range
of temperature, to float on the surface with a definite two-dimensional ordered arrangement.
The molecules of decyl, dodecyl, and tetratdecyl homologue derivatives possess lamellar
packing of molecules in their crystal lattices and maintained sliding layered arrangement of
molecules in floating condition between two temperatures with exhibition of enantiotropi-
cally smectogenic character. Then, the molecules of the same homologues floated with the
statistically parallel orientational order on the surface for a range of temperature facilitating
nematogenic character. Enantiotropic homologues display a mesogenic phase reversibly
at a temperature at which the mesophase disappears on cooling the melt. The rest of the
mesomorphic homologues show only nematogenic character by floating on the surface in a
manner as described above. Missing of odd-even effect for smectic-nematic transition curve
is due to the late commencement of smectic mesophase, and unfavorable extent of noncopla-
narity caused by the molecules. The odd-even effect for the nematic-isotropic transition
curve is observed from the third homologue and merges at the fourth homologue. Then
on extending it to an odd member, i.e., to fifth member, the curve separated from an even
membered curve and coincided with the solid-isotropic point of the pentyloxy homologue.
Such behavior of odd members indicates that the solid-nematic and nematic-isotropic point
of temperatures (202◦C) match with each other at the same point. The nematic-isotropic
transition curve is extrapolated [23] to the first member of the series for the purpose of
magnification of the odd-even effect keeping in mind, the trend of the nematic-isotropic
transition curve for odd members of the series. The smectic-nematic transition curve ex-
trapolated to the left toward the octyloxy homologue, which merges into the solid-nematic
transition point of temperature (188◦C) indicating that a smectic mesophase is absent prior
to nematic phase. Thus, the mesomorphic properties vary from homologue to homologue
for the presently investigated novel series due to sequential addition of methylene units.
The nematogenic and smectogenic phase lengths are vary from 18.0 to 100.0◦C and 8.0
to 40.0◦C, respectively. Thus, the present novel series is predominantly nematogenic and
partly smectogenic whose degree of mesomorphism is relatively wider and of a high melt-
ing type. Mesomorphic properties of present novel seires-1 are compared with structurally
similar known isomeric series X [24] and Y [25] chosen for comparison as shown above
in Fig. 2.
Homologous novel series-1 under discussion and isomeric homologous series X and
Y selected for comparison are structurally similar with respect to two terminal end groups
of –OR and –OCH3 inducing similar molecular flexibility. However, they differ with re-
spect to molecular rigidity due to the difference arising from the central linking group of

84
B. H. Patel and A. V. Doshi
Figure 2. Structurally similar homologous series.
COO CH2
,
CO CH CH , and CH CH CO for series-1, X and Y, respec-
tively. Three phenyl rings and one of the central group CH CH COO contribute to
molecular rigidity similarly, but the total molecular rigidity differs due to difference of the
other linking group. Therefore, the combined effect of molecular rigidity and flexibility re-
sponsible for inducing mesomorphic behavior and the degree of mesomorphism vary from
series to series, under comparison as shown in Fig. 2. Table-3 shows the thermal stabilities
for smectic and nematic phases, group efficiency order based on thermal stability and early
commencement of a mesophase.
The data in Table 3 shows the following.
• Homologous series-1 and X exhibit smectogenic character while homologous series
Y does not show smectogenic character.
• All the homologous series 1, X and Y under comparison are enantiotropically
nematogenic.
• Average thermal stabilities for smectic and nematic mesophases decreases from
series 1 to X to Y.
• The smectic and nematic mesophases for the presently investigated novel homol-
ogous series-1 commences from the decyloxy and ethoxy homologue derivatives,
respectively.
Table 3. Average thermal stability in ◦C
Series→
Smectic-nematic
Or
Smectic-isotropic
Commencement of
Smectic phase
Nematic-isotropic
Commencement of
nematic phase
Series 1
Series X
Series Y
—
182.6
(C10 – C14)
C10
159.7
(C5 – C8)
C5
242.0
(C2 – C16)
C2
174.1
(C5 – C14)
C5
166.6
(C5 – C14)
C5

Mesomorphism and Molecular Structure
85
• The smectic and nematic mesophase formation commences from the pentyloxy
homologue of series X and the nematic mesophase commences from the penty-
loxy homologue of a series Y but the smectogenic mesophase formation does not
commence until the last hexadecyloxy homologue of series Y.
Homologous series 1, X and Y are linear lath like, with differing overall magnitudes
of molecular rigidity and flexibility. Therefore, suitable magnitudes of anisotropic forces
of intermolecular attractions due to varying molecular length, double bond conjugation
( CH CH ) [26] molecular polarity and polarizability, position of CO group, lateral
and terminal attractions, vary from series to series. Moreover, the presence (series 1 and X)
or absence (series-Y) of lamellar packing of molecules in their crystal lattices and the extent
of noncoplanarity of the molecules depending upon magnitudes of intermolecular adhesion
vary from series to series, affecting the mesophase formation and stabilization as well as
degree of mesomorphism of the series under discussion. The variations in mesomorphic
properties for the same homologue form series to series are attributed to the differing part
of the molecules. The variations in mesomorphic properties from homologue to homologue
in the same series is attributed to the sequentially added methylene units, keeping rest of
the molecular structure unchanged.
Conclusions
• The group efficiency order derived for smectic and nematic on the basis of (i) thermal
stability and (ii) the early commencement of mesophase are as under.
(i) Smectic: COOCH2
Nematic: COOCH2
(ii) Smectic: CO CH CH
Nematic: COO CH2
>
>
CO CH CH
CO CH CH
>
>
CH CH CO
CH CH CO
CH CH CO
CH CH CO
>
COO CH2
>
>
CO CH CH
• Variations in mesomorphic properties from homologue to homologue in the same
series are due to the sequentially added methylene units.
• Variations in mesomorphic properties for the same homologue from series to series
is due to the changing molecular structure, such as the terminal end group or central
group or the number of phenyl rings, or the position of a group or changing polarity
or molecular linearity or nonlinearity.
• Suitable magnitudes of intermolecular attractions are a consequence of favorable
molecular rigidity and flexibility.
• Suitable magnitudes of molecular rigidity and flexibility are the main source of the
resulting mesomorphism phenomenon.
• Molecular rigidity and flexibility are very sensitive and susceptible to changes in
molecular structure.
Acknowledgment
Authors acknowledge thanks to the Green Circle Inc. Lab for research facilities services
as and when needed. Authors also thank Dr. N. N. Vyas, Dr. Vipul Patel, and Dr. M.
L. Chauhan for their valuable helping hand and microscopic facility. Thanks are due to
the Sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh for
analytical services.

86
B. H. Patel and A. V. Doshi
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