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International Letters of Chemistry, Physics and Astronomy
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Molecular Flexibility Operated Mesomorphism

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Abstract:

Novel homologous series: RO-C6H4-CH=CH-COO-CH2-C6H4-Br (p) synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal (LC) behavior of a series. Series consists of eleven homologues. C1 to C7 members of a novel series are non-liquid crystals. Mesomorphism commences from Octyloxy (C8) homologue and continued upto hexadecyloxy homologue (C16) as enantiotropic nematic without exhibition of smectic property. The textures of a nematic phase are threaded or Schlieren. Transition temperatures (table-2) and textures are determined by an optical polarizing microscopy equipped with a heating stage. Cr-N/I and N-I transition curve behaved in normal manner in phase diagram, showing their phase behavior (figure-1). Odd-even effect is absent for N-I transition curve. Analytical and spectral data confirmed the molecular structures of a series. The LC properties are compared with the structurally similar series. The transition temperatures are relatively lower than the corresponding n-alkoxy benzoic acid. Thus, present novel series is partly nematogenic with absence of smectic property whose mesogenic phase length is low and of low ordered melting type. Thermal stability for nematic is 93.0°C and the mesophaselength ranges from 8 to 21°C.

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Periodical:
International Letters of Chemistry, Physics and Astronomy (Volume 52)
Pages:
163-171
Citation:
R. B. Marathe et al., "Molecular Flexibility Operated Mesomorphism", International Letters of Chemistry, Physics and Astronomy, Vol. 52, pp. 163-171, 2015
Online since:
June 2015
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[2] . EXPERIMENTAL.

[4] -Hydroxy benzoic acid, Alkyl halides, Methanol, KOH, 4-bromo benzyl bromide or alcohol, N, N-Dimethyl Formamide, NaHCO3, HCl, Dry Pyridine, Thionyl chloride, EtOH etc required for the synthesis were used as received, except solvents which were dried and purified prior to synthesis.

[2] . 1 General method for the preparation of n-alkoxy benzoic acid and 4-Hydroxy-4-bromobenzyl cinnamate.

[4] -Hydroxy benzoic acid was alkylated by suitable alkylating agent R-X to form n-alkoxy benzoic acid by modified method of Dave and Vora [26] as main component of a series. 4-Hydroxy-4'-bromobenzyl cinnamate (m. p: 95-96°C) was prepared from 4-bromo benzyl bromide or alcohol and 4-Hydroxy Cinnamic acid by applying the method of European patent and the modified method of Doshi, Patel and Marathe [27].

DOI: https://doi.org/10.1002/0471264180.os078.13

[2] . 2 General method for the preparation of final esterified products. The n-alkoxy benzoic acid through their corresponding acid chlorides and 4-Hydroxy-4'-bromobenzyl cinnamate were condensed in dry cold Pyridine to form final products by usual established method [28]. Final esterified products were individually decomposed, filtered, washed, dried and purified till their constant transition temperatures obtained. Synthetic route to the series is mentioned below as scheme-1. Scheme-1: Synthetic route to the novel series.

[3] . CHARACTERIZATION The selected members of a novel homologues series were characterized and analyzed by elemental analysis and the structure elucidation by Infra-red spectra, 1HNMR spectra and mass spectra. Textures and Transition temperatures of homologues as well as of related materials were determined by an optical polarizing microscope, equipped with a heating stage. Elemental analysis was performed on Perkin-Elemer PE 2400 C, H, N analyzer. The percentage halide content is determined by usual analytical method. IR spectra were recorded on Shimadzu FTIR Model-IRAffinity-1S (MIRacle 10). 1HNMR spectra were determined on Bruker spectrometer using CDCl3 solvent and mass spectra were recorded on Shimadzu GC-MS Model No. QP-2010. Textures of nematic mesophase of some homologues were recognized either directly from the microscopic observations or by miscibility method.

DOI: https://doi.org/10.7554/elife.16673.022

[4] . ANALYTICAL DATA Table-1: Elemental analysis for (1) Ethoxy (2) Propyloxy and (3) Hexyloxy derivative Sr. No. Molecular formula % Elements calculated (Experimental %) C H Br.

[1] C25H21BrO5.

[62] . 37 (65. 22).

[4] . 36 (4. 80).

[16] . 63 (16. 48).

[2] C26H24BrO5.

[62] . 90 (63. 20).

[4] . 83 (4. 78).

[16] . 12 (16. 50).

[3] C29H29BrO5.

[64] . 80 (64. 80).

[5] . 50 (5. 40).

[14] . 78 (14. 89) Spectral Data.

[1] HNMR data for series.

[1] HNMR in ppm for the Methoxy Derivative: 1. 07-1. 19 (-CH3 groups), 2. 66 (–CH3), 5. 13-5. 27 (-CH=CH-), 6. 90-6. 92 (p-substituted phenyl ring), 7. 85-7. 91 (p-substituted benzene).

[1] HNMR in ppm for the Dodecyloxy Derivative: 0. 86-88 (-CH3 of C12H25), 1. 24-1. 77 (-CH2- of –C12H25), 3. 97-3. 99 (-O-CH2-), 5. 16-5. 30 (-CH=CH-), 6. 90-6. 93 (p-substituted phenyl ring), 7. 30-7. 40 (p-substituted benzene). NMR data confirm the structure. IR in cm-1 for Butyloxy Derivative.

[29] 54, 2870 (C-H str. ), 1465 (str. of (-CH2-) group of –OC4H9), 1675 (-COO- ester group), 1604 (C-H stretching of –CH=CH- ), 1512 (C=C str. of alkene), 1396 (C-H bending of alkene disubstituted), 1257 (C-O str. of ether linkage), 1165 (C-O str. of ester group), 1016 (Aromatic linkage of -Br), 848 (para substituted phenyl ring), 771 (Polymethylene group), 640-695 ( -CH2- Stretch). The IR data are consistent with the molecular structure. IR in cm-1 for Pentyloxy Derivative.

[29] 31, 2870 (C-H str. ), 1489 (str. of (-CH2-) group of –OC5H11), 1597 (-COO- ester group), 1712 (C-H stretching of –CH=CH-), 1512 (C=C str. of alkene), 1396 (C-H bending of alkene), 1257 (C-O str. of ether linkage), 1165 (C-O str. of ester group), 1010 (Aromatic linkage of -Br), 848 (para substituted phenyl ring), 756 (Polymethylene group), 648-689 (-CH2- Stretch). The IR data are consistent with the molecular structure. Mass spectra of Tetradecyloxy Derivative Theoratical Mass = 649. 0 Experimental Mass = 649. 80.

[1] (-Br) X (-OCH3) Y(-Cl) Nematic – Isotropic Or Smectic-Nematic Commencement of Smectic phase.

[92] . 78 (C1 - C16) C1 Nematic – Isotropic Commencement of Nematic phase.

[93] . 0 (C8 - C16) C8.

[21] 1. 54 (C1 – C16) C1.

[10] 0. 8 (C8 – C16) C8 Total Mesophaselength range in °C from Ti to Tj Ci Cj.

[8] . 0 to 21. 0 C14 C8 C16.

[17] . 0 to 72. 0 C14 C3.

[21] . 7-72. 2 C6 C8 Table-2 indicates that, · Homologous series-1 and X are only nematogenic whereas series-Y is smectogenic in addition to nematogenic. · Smectic mesophase commences from very first member of a series-Y, but it does not commence till the last member of the series-1 and X. · Nematic mesophase commences from very first member of a series-X, but it commences late from C8 membered homologue for series-1 and Y. · Nematic thermal stabilities are in increasing order from series-1 to series-Y to series-X. · Smectic thermal stability of series-Y is 92. 78 but smectogenic mesophase did not stabilize for series-1 and X. · Total mesophaselength ranges are varied in decreasing order from series-X to series-Y and series-1. Variations in the mesogenic behaviours of the series under comparison are attributed to the magnitudes of molecular flexibility arising from changing tail end groups –Br, -OCH3 and –Cl, whose individual group polarities group atomicity, inductive effect, effects due to molecular length to breadth ratio, ratio of the polarity to polarizability, permanent dipole moment across the long molecular axes, dipole-dipole and electronic interactions. C-Xi (where Xi= terminal tail group) bond polarity, dispersion forces, Vander Waals forces, the suitable magnitudes of anisotropic forces of intermolecular attractions as a consequence of varied molecular flexibility for the same homologue from series to series and from homologue to homologue in the same series etc; show variations in the mesogenic behaviours from series-1 to series-X to series-Y. Mono atomic –Cl tail end group of series-Y is more efficient and capable to build up lamellar packing of molecules in the crystal lattices as compared to –OCH3 and –Br terminal ends of greater size, which maintained sliding layered molecular arrangement for series-Y but fails to maintain the same for –OCH3 and –Br of series-1 and X to facilitate smectic mesophase formation. The formation of nematic mesophase of low thermal stability by –Br and –Cl terminal end groups is attributed to their low dipolarity of C-Xi bond but, -OCH3 terminal end group being highly polar and polarizable as compared to –Br and –Cl enhances nematic thermal stability more than halogen C-Xi substituent. Thus, resistivity towards exposed thermal vibrations being comparatively more for the series involving –OCH3 tail group stabilizes and facilitates nematic mesophase formation at the cost smectic phase with highest degree of mesomorphism.

DOI: https://doi.org/10.1007/978-3-662-03569-6_12

[6] . CONCLUSIONS · Presently investigated novel series is partly nematogenic without exhibition of smectogenic character of low melting and short degree of mesomorphism. · Group efficiency order derived for smectic and nematic on the basis of (i) thermal stability (ii) early commencement of mesophase (iii) the total mesophaselength. (i) Smectic Nematic (ii) Smectic Nematic (iii) (Sm+N) Total Mesophaselength · Present investigation may be useful for the study of binary system for LC devices workable between 57°C and 90°C. · Present novel compounds may be useful as fire resistance material. · Thus, present investigation supports the conclusions drawn earlier and raises the credibility to the existing literature on LC. Table-3: Transition temperatures in oC Compound No. n-alkyl chain CnH2n+1 (n) Sm N Isotropic.

DOI: https://doi.org/10.1016/j.fluid.2013.12.010

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[78] [86] Sm- Smectic; N- Nematic Figure-2: Phase Behavior of Series Acknowledgements Authors acknowledge thanks to the Green Circle Inc. Laboratory for providing research facilities services as and when needed. Authors acknowledge thanks to the Mr. Baldev Prajapati of Rajesh Pharma Ankleshwar, for providing the free sample of 4-Bromobenzyl bromide. Authors are also thankful to Dr. Vipul Patel and Dr. M.L. Chauhan, P.T. Arts and Science College, Godhara, for their valuable helping hand and microscopic facility. Also thanks are due to the Sophisticated Analytical Instrumentation Facility, Punjab University, (Chandigarh) for extending their help for analytical services. Reference.

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