Mesomorphism dependence on lateral substitution of functional groups and their position in series: 4(4'-n-alkoxy benzoyloxy)-3-chloro phenyl azo-2"-methoxy benzenes

Article abstract of DOI:10.1080/15421406.2015.1044156

Eleven homologues of the title series were synthesized. The methyl-to-pentyl derivatives are nonmesomorphic. The nematic mesophase commences from the sixth member of the series without any smectic phase. An odd-even effect in the nematic-isotropic transition curve is not observed. The nematic mesophase appeared as a threaded or a Schlieren-type texture as observed through a hot-stage polarizing microscope. The nematic-isotropic transition temperatures are between 89°C and 127°C with the mesomorphic range varying from 9°C to 44°C at the hexyl and tetradecyl derivative of the series, respectively. The nematic-isotropic transition curve initially rises and then falls in a normal manner as the series is ascended, but it abnormally rises beyond the 10th homologue. The series is enantiotropic nematic with a middle-ordered melting type. Analytical data support the structures of the molecules. The thermal stability and some other mesomorphic characteristics are compared with structurally similar homologous series. The average nematic-isotropic thermal stability is 105.4°C.

Full text of DOI:10.1080/15421406.2015.1044156

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphism dependence on lateral
substitution of functional groups and their
position in series: 4(4′-n-alkoxy benzoyloxy)-3-
chloro phenyl azo-2″-methoxy benzenes
D. H. Patel, H. R. Prajapati & A. V. Doshi
To cite this article: D. H. Patel, H. R. Prajapati & A. V. Doshi (2016) Mesomorphism dependence
on lateral substitution of functional groups and their position in series: 4(4′-n-alkoxy
benzoyloxy)-3-chloro phenyl azo-2″-methoxy benzenes, Molecular Crystals and Liquid Crystals,
624:1, 51-58, DOI: 10.1080/15421406.2015.1044156
To link to this article: http://dx.doi.org/10.1080/15421406.2015.1044156
Published online: 11 Feb 2016.
Submit your article to this journal
Article views: 10
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [Tulane University]
Date: 03 April 2016, At: 05:52

MOL. CRYST. LIQ. CRYST.
, VOL. , NO. , –
http://dx.doi.org/./..
Mesomorphism dependence on lateral substitution of
functional groups and their position in series: (ꢀ -n-alkoxy
benzoyloxy)--chloro phenyl azo-ꢀꢀ -methoxy benzenes
D. H. Patela, H. R. Prajapatib, and A. V. Doshic
aSheth P.T. Arts & Science College, Godhra, Gujarat, India; bC.U. Shah Science College, Ahmedabad, Gujarat, India;
cM. V. M. Science and Home Science College, Rajkot, Gujarat, India
ABSTRACT
KEYWORDS
Liquid crystal;
Eleven homologues of the title series were synthesized. The methyl-
to-pentyl derivatives are nonmesomorphic. The nematic mesophase
commences from the sixth member of the series without any smec-
tic phase. An odd–even effect in the nematic–isotropic transition curve
is not observed. The nematic mesophase appeared as a threaded
or a Schlieren-type texture as observed through a hot-stage polar-
izing microscope. The nematic–isotropic transition temperatures are
between 89°C and 127°C with the mesomorphic range varying from
9°C to 44°C at the hexyl and tetradecyl derivative of the series, respec-
tively. The nematic–isotropic transition curve initially rises and then falls
in a normal manner as the series is ascended, but it abnormally rises
beyond the 10th homologue. The series is enantiotropic nematic with a
middle-ordered melting type. Analytical data support the structures of
the molecules. The thermal stability and some other mesomorphic char-
acteristics are compared with structurally similar homologous series.
The average nematic–isotropic thermal stability is 105.4°C.
mesogenic; nematic;
polymesomorphism; smectic
Introduction
The increasing utility of liquid crystalline (LC) materials [1–6] inspired the synthesis and eval-
uation of a novel homologous series. Synthesis of novel LC materials requires the design of a
molecular structure that can alter the molecular rigidity and/or flexibility by substituting vary-
ing functional as end groups or lateral groups such as –Cl and –OCH3 at lateral positions of
=
rigid core, which consisted of three phenyl rings and central bridges –COO– and –N N–,
respectively. Thus, molecule is broadened through lateral –Cl and –OCH3 group to vary
molecular rigidity/flexibility [7–11], which may alter intermolecular distance and molecular
polarizability and the suitable magnitudes of the anisotropic forces of attractions. Thus, the
relation between LC properties and molecular structure can be understood and established
[12,13].
CONTACT D. H. Patel
drhrprajapati@yahoo.co.in
Sheth P.T. Arts & Science College, Godhra , Gujarat, India.
©  Taylor & Francis Group, LLC

52
D. H. PATEL ET AL.
Experimental
Synthesis
3-Chloro -4- hydroxy phenyl azo -2ꢀ- methoxy benzene (B) was synthesized by a known
method [14]. 4-Hydroxy benzoic acid was alkylated by the corresponding alkylating agents
(R-X) and converted to the acid chlorides (A) using SOCl2, by the method of Dave and Vora
[15].
4-(4ꢀ-n-Alkoxy benzoyloxy)-3-chloro phenyl azo-2ꢀꢀ -methoxy benzenes were prepared by
condensing (A) and (B) in dry cold pyridine [16]. The novel azoesters were purified in alco-
hol. The transition temperatures were determined by a hot-stage polarizing microscope. The
synthetic route to the series is mentioned in Scheme 1.
Scheme . Synthetic route to the series.

MOL. CRYST. LIQ. CRYST.
53
Table . Elemental analysis for ethoxy, hexyloxy, hexadecyloxy derivatives.
Elements % found (calculated %)
Sr. no.
Molecular formula
CHNOCl
C
H
N



. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
. (.)
C 
H NOCl
H NOCl
C
Characterization
Some selected members of the series were characterized by elemental analysis, Infrared spec-
tra (IR), and 1H NMR spectra. C, H, N composition were determined on Perkin-Elmer PE
1
2400. H NMR spectra were recorded on Bruker using CDCl3 as solvent. IR spectra were
recorded on Perkin-Elmer spectrum GX. Textures of the nematic phase were determined by
a miscibility method using polarizing microscopy. The data are recorded in Table 1.
Analytical data
IR spectra in cm−1 for C8 and C14 homologues
Octyl
2923.9, 2854.0, 1310.5 (alkyl group), 1732, 1164.9 (ester group), 1257.5, 1222.8 (ether group),
=
1431.1 (–N N–), 844.8 (p-sub. benzene), 752.2 (o-sub. benzene), 1060.8 (Ar–Cl linkage).
Tetradecyloxy
2916.2, 2850.6, 1396.4 (alkyl group), 1685.3, 1230.5, 1168.8 (ester group), 1257.5 (ether
=
group), 1431.1 (–N N–), 844 (p-sub. benzene), 756 (o-sub. benzene), 1072.3 (Ar–Cl link-
age).
1H NMR Spectra in CDCl3 in δ ppm for Octyloxy (C8) and Decyloxy (C10) Homologues
Octyloxy
0.897 (–CH3 of –C8 H17), 1.317 (–CH2 of –C8 H17), 1.829 (–CH2CH2O of –C8 H17), 3.654
(–OCH3), 4.037 (–OCH2CH2–), 6.970 and7.014, and 7.062 (o-sub. benzene), 7.085 and 7.127
(o-sub. benzene), 7.654 and 7.694 (p-sub. benzene), 7.897 and 7.940 (p-sub. benzene).
Decyl
0.888 (–CH3 of –C10H21), 1.795 (–COCH3), 4.041 (–OCH2CH2 of –C10H21), 6.905 and 6.971,
7.016 and 7.065 (p-sub. benzene), 7.654 and 7.694 (p-sub. benzene), 7.887 and 7.941 (p-sub.
benzene), 1.283 (–CH2–C10H21).
Textures by miscibility method
Nematic
Octyloxy homologue: Threaded texture
Tetradecyloxy homologue: Schlieren texture

54
D. H. PATEL ET AL.
Result and discussion
3-Chloro-4-hydroxy phenyl azo-2ꢀ-methoxy benzene is a nonliquid crystalline substance.
However, linking of phenyl ring through –COO– central bridge and para substituted n-alkoxy
left terminal group increases the length and aromaticity of the molecule. Increased length
and aromaticity increases polarity, polarizability, and length-to-breadth ratio, etc., as a conse-
quence of the net resulted molecular rigidity, and flexibility induces liquid crystallinity. Thus,
the added linking units with azo dye, though being nonliquid crystal, produces novel liq-
uid crystal substances except for the first five members and the hexadecyloxy member of the
series, which are nonmesomorphic. The mesomorphism exhibited is nematogenic in char-
acter and is enantiotropic. The transition temperatures as recorded in Table 1 were plotted
versus the number of carbon atoms in n-alkyl chain of the left n-alkoxy terminal end group,
and the phase diagram obtained is shown in Fig. 1.
Solid-isotropic or solid-mesomorphic transition curve follows a zigzag path of falling and
rising tendency in normal manner as series is ascended with overall descending tendency.
Solid-isotropic transition curve steeply falls from first to sixth member of the series and lev-
eled up rise takes place to the eighth. Then it again falls to the decyl derivative of the series.
Solid-isotropic or solid-mesomorphic transition curve again follows the rising path up to
tetradecyl member, followed by a fall in its value at hexadecyloxy member with maintenance
of a zigzag path. The nematic–isotropic transition curve shows initially rising tendency as
the series is ascended with fall at the decyloxy member and then abnormally rises to tetrade-
cyloxy derivative. Thus, methyl-to-pentyl derivatives of the series sharply transformed into
isotropic liquid at their melting point relatively at higher temperature because of their short
Figure . Phase behaviors of series.

MOL. CRYST. LIQ. CRYST.
55
Table . Transition temperatures of the homologous series: (ꢀ-n-alkoxy benzoyloxy) --chloro phenyl azo-
ꢀꢀ -methoxy benzenes.
Transition temperatures in °C
Compound no.
n-alkyl group CnHn+ (n)
Smectic (Sm)
Nematic (N)
Isotropic (I)











C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
chain length and higher magnitudes of intermolecular forces of attractions and thermal stabil-
ity. But in case of hexadecyloxy homologue, the longer n-alkyl chain causes the intermolecular
attractions to become poorer to resist exposed thermal vibrations. Hence, hexadecyl deriva-
tive sharply transformed into isotropic liquid without passing through LC state at relatively
lower temperature of melting. Thus, nonmesomorphic groups of methyl-to-pentyl and hex-
adecyl derivatives are unable to resist thermal vibrations exposed upon them for different
reasons and hence melted sharply at their melting point, without showing of LC state. Thus,
anti-mesogenic character suggests that neither the parallel orientations of molecules nor two-
dimensional sliding layered arrangement of molecules occur in floating condition, by C1 to
C5 and C16 homologue. Absence of odd–even effect in nematic–isotropic transition curve is
attributed to the longer n-alkyl chain of left n-alkoxy terminal end group, which may coil,
bend, flex, or couple to lie in major axis of the core, and odd members are absent from and
beyond C6 homologue. The variation of LC properties from homologue to homologue in same
series is attributed to the sequentially added methylene unit to the n-alkyl chain. Appearance
of nematogenic mesophase from hexyl to tetradecyloxy derivative of homologues is due to the
disalignment of molecules at an angle less than 90° resisting thermal vibrations exposed upon
them within definite range of temperature, during which molecules arrange themselves as
statistically parallel orientational two-dimensional order, while floating on the surface. Thus,
suitable magnitudes of anisotropic forces of intermolecular end-to-end attractions occur by
molecular rigidity and flexibility caused by combined effect of molecular polarity, polarizabil-
ity, aromaticity, inductive and steric effect, electron–electron interactions, etc.
The molecules from and beyond isotropic temperature are randomly oriented in all pos-
sible directions, i.e., high order of molecular disorder or high entropy (ꢀS = ꢀH/T) occurs,
which, on cooling the same below isotropic temperature, exhibit nematic phase formation in
reversible manner.
The nematogenic abnormal phase behavior of the nematic–isotropic transition curve is
attributed to the irregularity of the status of longer n-alkyl chain of left n-alkoxy terminal by
its coiling, bending, flexing, or coupling with major axis of core playing role.
The nematic phase appeared has threaded type of texture as determined by miscibility
method using hot-stage polarizing microscopy. The mesomorphic properties including aver-
age thermal stability (Table 3) and commencement of present homologous series 1 under
discussion whose mesomorphic property is compared with other structurally similar known
homologous series X [17] and series Y [18] is shown in Fig. 2.

56
D. H. PATEL ET AL.
Table . Relative thermal stabilities in °C.
Average thermal stabilities in °C
Series
Series 
Series X
Series Y
Smectic-isotropic
or
.
(C to C)
.
(C to C)
smectic-nematic
Commencement of smectic phase
Nematic-isotropic
or
C
C
.
(C to C)
.
.
(C to C)
(C to C)
isotropic-nematic
Commencement of nematic phase
C
C
C
The homologous series 1, X, and Y contain three phenyl rings, bridged through central
=
–COO– and –N N– groups and left n-alkoxy terminal for the same homologue as com-
mon identical features. Series 1 and X differ in their functional groups –OCH3 or –Cl on
third phenyl ring at different position of substitution with commonly substituted –Cl group
at middle phenyl ring. Series 1 and Y differ in the exchanged substitution –Cl and –OCH3, i.e.,
isomeric to each other, attached at middle or third phenyl ring irrespective of their position
of attachment.
Variations observed for mesogenic properties are directly related to the differing varying
features of series 1 from series X and Y. Therefore, degree of mesomorphism and the type or
types and the commencement of mesophase formation differ accordingly for the same homo-
logue from series to series under comparison. All the three series, 1, X, and Y, are laterally sub-
stituted by either –Cl and/or –OCH3 group. Therefore, molecular broadening due to increased
width causes variations in magnitudes of anisotropic forces of intermolecular attractions as
Figure . Structurally similar series.

MOL. CRYST. LIQ. CRYST.
57
a consequence of molecular rigidity and flexibility, including changing polarizability due to
positional difference of lateral group or groups. Molecular broadening causes two opposing
effects operating at a time for the same reason: (i) increased molecular width increases inter-
molecular distance, which reduces intermolecular cohesion; and (ii) broadening of a molecule
raises the molecular polarizability, which enhances intermolecular cohesion. The net result-
ing effect depends upon the predominating effect out of above two opposing effects. Series 1 is
only nematogenic, while series X and Y are nematogenic in addition to smectogenic in char-
acter, i.e., –Cl group present as right terminal end group increases length-to-breadth ratio,
which favorably induces lamellar packing of molecules in the crystal lattices of the molecules
of series X and Y due to predominance of (ii) effect related to molecular polarizability effect.
The only nematogenic character observed for present series 1 is attributed to the predomi-
nance of effect related to weakening of intermolecular adhesion by increased intermolecu-
lar distance. The lowest nematic–isotropic thermal stability of series 1 and the absence of its
smectic character can be linked to the predominancy of effects. The higher values of nematic–
isotropic and smectic–nematic thermal stabilities can be linked to the predominancy of the
effect (ii) as discussed above. Early commencement of nematic mesophase (from C3) by series
X and Y as compared to series 1 are also due to factors (i) and (ii), respectively, and the extent
of noncoplanarity caused by a respective molecule. Variation in mesogenic properties from
series to series for the same homologue is due to varying terminal end group or/and lateral
group of fixed polarity.
Conclusions
(1) Mesomorphism and the degree of mesomorphism are very sensitive and susceptible
to molecular structure.
(2) Group efficiency order for smectic and nematic derived on the basis of (i) thermal
stabilities and (ii) the early commencement of mesophase are as under.
(i)
Smectic group: para –Cl and > para-Cl and > meta –Cl and
efficiency order: meta –OCH3 meta –Cl meta –OCH3
i.e., (Series-Y) > (Series-X) > (Series-1)
Nematic Group: (Series-X) > (Series-Y) > (Series-1)
Smectic: (Series-Y) > (Series-X) > (Series-1)
(ii)
Nematic: (Series-X) = (Series-Y) > (Series-1)
(3) Molecular rigidity and flexibility depending upon molecular width and the polarity of
substituent operates the magnitudes of anisotropic forces of intermolecular attractions
as a result of dipole moment across the long molecular axis, dipole–dipole interactions,
dispersion forces, etc.
(4) End-to-end intermolecular attractions are more favored if substituent end group other
than –H preferred.
(5) Series is partly mesogenic (nematogenic) and partly nonmesogenic with relatively low
thermal stability and mesophase length 9°C to 44°C.
(6) Laterally substituted group may increase or decrease thermal stability and other meso-
genic characteristics of LC.
Acknowledgments
The authors are thankful to the Head, Applied Chemistry Department, Faculty of Technology and Engi-
neering, The M.S. University of Baroda, Vadodara, for his valuable cooperation in the microscopic work.
Authors are also thankful to the authorities and scientists of Central Salts & Marine Chemicals Research
Institute, Bhavnagar, for the analytical services of the samples.

58
D. H. PATEL ET AL.
References
[1] Reinitzer, F. (1888). Monatsch, 9, 421.
[2] Demus, D. (1988). Mol. Cryst. Liq. Cryst., 165, 45.
[3] Demus, D. (1989). Liq. Cryst., 5, 75.
[4] Naemura, S. (2001). Displays, 22, 1.
[5] Kim, W. S., Elston, S.J., & Raynes, F. P. (2008). Displays, 29, 458.
[6] (a) Doshi etal. (i) Suthar, D. M., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 575, 76. (ii) Chauhan,
H. N., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 570, 92. (iii) Chaudhari, R. P., Chauhan, M.
L., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 575, 88. (iv) Bhoya, U. C., Vyas, N. N., & Doshi,
A. V. (2012). Mol. Cryst, Liq. Cryst., 552, 104. (b) Gray, G. W., & Jones, B. (1954). J. Chem. Soc.,
2556.
[7] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Mc. Donnell, D. G. (1993). Liq. Cryst., 15, 123.
[8] Collings, P. J., & Hird, M. (1998). Introduction to Liquid Crystals: Chemistry and Physics, Taylor &
Francis: London.
[9] Marcos, M., Omenat, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Mater., 4, 285.
[10] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
[11] Imrie, C. T. (1999). Liq. Cryst. Dimers. Struct. Bond, 95, 149.
[12] Gray, G. W. (1974). In: Liquid Crystals and Plastic Crystals, Vol. 624, Gray, G. W. & Winsor, P. A.
(Eds.), pp. 103–153, Ellis Horwood: Chichester.
[13] Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals, Academic Press: Lon-
don.
[14] Furniss, B. S., Hannford, A. J., Smith, P. G. W., & Tatchelll, A. R. (Revisor) (1989). Vogel’s Text
Book of Practical Organic Chemistry, 4th ed., Longman: Singapore, pp. 563–649.
[15] Dave, J. S., & Vora, R. A. (1970). In: Liquid Crystal and Ordered Fluids, Johnson, J. F. & Porter, R.
S. (Eds.), p. 477, Plenum Press: New York.
[16] Suthar, D. M., Doshi, A. A., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 577, 51.
[17] Chauhan, B. C., & Doshi, A. V. (2011). Der Pharma Chemica, 3, 172.
[18] Chauhan, B. C., & Doshi, A. V. (2012). Der Pharma Chemica, 3, 110.