Synthesis and evaluation of liquid crystalline properties of a novel homologous series: α-3-[4′-n-alkoxy benzoyloxy] phenyl-β- 4″-nitro benzoyl ethylenes

Article abstract of DOI:10.1080/15421406.2012.762499

The titled homologous series consists of 11 members. The methyl and ethyl homologues are nonmesomorphic because of very high melting points, however, the propyl to hexadecyl derivatives are enantiotropic nematic with absence of smectogenic. The texture of nematic mesophase is threaded or Schlieren. The nematic-isotropic transition curve of the phase diagram behaves in a normal manner with the exhibition of an odd-even effect. The transition temperatures of the series and liquid crystal properties are observed through optical polarizing microscopy and a hot stage. The novel materials were characterized by elemental analysis, infrared, and ¹H NMR spectroscopy. Analytical data support the molecular structures. The liquid crystal properties of the novel series are compared with structurally similar homologous series. The novel series is entirely nematogenic with absence of smectic character and of a middle-ordered melting type. The nematic-isotropic thermal stability varies between around 120°C and 180°C.

Full text of DOI:10.1080/15421406.2012.762499

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Synthesis and Evaluation of Liquid
Crystalline Properties of a Novel
Homologous series: α-3-[4′-n-Alkoxy
Benzoyloxy] Phenyl-β-4″-Nitro Benzoyl
Ethylenes
D. M. Suthar a , Ankita A. Doshi b & A. V. Doshi c
a Chemistry Department , K. K. Shah Jarodwala Maninagar Science
College , Ahmedabad , Gujarat , India
b Department of Biochemistry , M.S. University of Baroda ,
Vadodara , India
c Shri Jagdish Prasad Jhabarmal Tibrewala University , Jhunjhunu ,
Rajasthan , India
Published online: 02 Apr 2013.
To cite this article: D. M. Suthar , Ankita A. Doshi & A. V. Doshi (2013) Synthesis and Evaluation
of Liquid Crystalline Properties of a Novel Homologous series: α-3-[4′-n-Alkoxy Benzoyloxy]
Phenyl-β-4″-Nitro Benzoyl Ethylenes, Molecular Crystals and Liquid Crystals, 574:1, 75-83, DOI:
10.1080/15421406.2012.762499
To link to this article: http://dx.doi.org/10.1080/15421406.2012.762499
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Mol. Cryst. Liq. Cryst., Vol. 574: pp. 75–83, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.762499
Synthesis and Evaluation of Liquid Crystalline
Properties of a Novel Homologous series:
α-3-[4ꢀ-n-Alkoxy Benzoyloxy] Phenyl-β-4ꢀꢀ-Nitro
Benzoyl Ethylenes
D. M. SUTHAR,1,∗ ANKITA A. DOSHI,2 AND A. V. DOSHI3
1Chemistry Department, K. K. Shah Jarodwala Maninagar Science College,
Ahmedabad, Gujarat, India
2Department of Biochemistry, M.S. University of Baroda, Vadodara, India
3Shri Jagdish Prasad Jhabarmal Tibrewala University, Jhunjhunu,
Rajasthan, India
The titled homologous series consists of 11 members. The methyl and ethyl homologues
are nonmesomorphic because of very high melting points, however, the propyl to hex-
adecyl derivatives are enantiotropic nematic with absence of smectogenic. The texture
of nematic mesophase is threaded or Schlieren. The nematic-isotropic transition curve
of the phase diagram behaves in a normal manner with the exhibition of an odd–even
effect. The transition temperatures of the series and liquid crystal properties are ob-
served through optical polarizing microscopy and a hot stage. The novel materials were
1
characterized by elemental analysis, infrared, and H NMR spectroscopy. Analytical
data support the molecular structures. The liquid crystal properties of the novel series
are compared with structurally similar homologous series. The novel series is entirely
nematogenic with absence of smectic character and of a middle-ordered melting type.
The nematic-isotropic thermal stability varies between around 120◦C and 180◦C.
Keywords Anisotropic; liquid crystal; mesomorphic; nematic; smectic
Introduction
The basic prime requirement to induce liquid crystalline properties in a substance is a
suitable compromise of molecular rigidity and flexibility [1–3]. Molecular rigidity and
flexibility occurs as a consequence of the molecular shape, size, and aromaticity types
of the central, terminal, and lateral groups, and their polarities, molecular polarity, and
polarizability, etc. Thus keeping these issues in view to synthesize novel liquid crystals
(LC) substances, the molecular structure of the novel series was designed with three phenyl
rings bridged through −COO− and −CH=CH−CO− central groups, and −OR, −NO2
as left and right terminal groups, respectively, without any lateral groups. The aim of the
present work is to further establish the relationship between liquid crystal properties and
molecular structure [4].
∗Address correspondence to D. M. Suthar, Chemistry Department, K. K. Shah Jarodwala Mani-
nagar Science College, Ahmedabad 380008, Gujarat, India. E-mail: dipakmsuthar@gmail.com
75

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76
D. M. Suthar et al.
Experimental
Synthesis
4-Hydroxybenzoic acid was alkylated by a suitable alkylating agent and the correspond-
ing 4-n-alkoxybenzoic acids were converted to the acid chlorides (A) using freshly
distilled thionyl chloride by the modified method of Dave and Vora [5]. α-3-[4ꢀ-n-
alkoxy benzoyloxy] phenyl-β-4ꢀꢀ-nitro benzoyl ethylene (B) was prepared by reacting
3-hydroxybenzaldehyde and 4-nitroacetophenone by an established method [6]. Compo-
nents (A) and (B) were condensed in dry cold pyridine with constant shaking of the reaction
mixture [7]. The final products were individually filtered, washed, dried, and purified until
constant transition temperatures were obtained. The synthetic route to the series is shown
in Scheme 1. 4-Hydroxybenzoic acid, n-alkyl halide, methanol, KOH, HCl, thionyl chlo-
ride, 4-nitroacetophenone, 3-hydroxybenzaldehyde, ethanol, etc., required for synthesis
were used as received, except for solvents that were used after purification, drying, and
distillation.
Scheme 1. Synthetic route to the series.
Characterization
Some of the homologues of the novel series were characterized by elemental analysis,
infrared (IR), and 1H NMR spectroscopy techniques. Microanalysis of the compounds was
performed on a Perkin-Elmer PE 2400 CHN analyzer (Sophisticated Analytical Instrumen-
tation facility (SAIF) Punjab University, Chandigarh) with results shown in Table 1. Nuclear
magnetic resonance (NMR) spectra were recorded using CDCl3 as solvent and IR spectra
were recorded using a Perkin-Elmer GX spectrometer (Vaibhav Laboratory, Ahmedabad).
The liquid crystal properties, transition temperatures, and melting temperatures were in-
vestigated by using optical polarizing microscopy. The texture of the nematic mesophase
was determined by the miscibility method. Thermodynamic quantities enthalpy (ꢀH) and
entropy (ꢀS) are discussed qualitatively instead of differential scanning calorimetry.