Synthesis, single crystal X-ray structure and thermal analysis of a novel polycatenar liquid crystal: Theoretical and experimental approaches

Abstract

The title polycatenar liquid crystal benzene-1,4-diylbis(3,5-dibutoxybenzoate) (6) was synthesized efficiently. The 3,5-dihydroxy benzoic acid (1) was first converted into corresponding methyl ester (2) which upon alkylation with butyl bromide furnished compound (3). The hydrolysis of the ester (3) results in the formation of 3,5-dibutyloxy benzoic acid (4). The Steglich esterification of 3,5-dibutyloxy benzoic acid (4) with hydroquinone (5) in the presence of coupling agents DCC/DMAP gave the title polycatenar liquid crystal (6). The chemical structure of the title compound was ascertained by spectral data and single-crystals X-ray diffraction analysis. The single-crystal XRD analysis revealed that the space group of crystal as P1¯ with triclinic crystal system. FT-IR showed a prominent peak for carbonyl functionality of ester at 1731 cm−1. The signals in the 1H-NMR and 13C-NMR spectra were also in the acceptable region. The thermogravimetry analysis (TGA) of compound (6) showed that the decomposition was taken place in one step. A weight loss of 96% occurred between 300 and 412 °C. A single endothermic peak was found in differential scanning calorimetry (DSC) thermogram in the forward scan with an enthalpy of transition as −208.82 mJ. Computational investigations were performed at B3LYP/6-31G(d,p) level of theory to support experimental findings. Theoretically calculated infra-red (IR) spectra were in close agreement with the experimental one. EHOMO and ELUMOvalues for compound (6) were found to be −5.876eV and −1.589eV respectively whereas band gap (ΔE) was found to be −4.287 eV. Molecular electrostatic potential analysis showed thatnegativepotential is concentrated on oxygen (red), hence rendering nucleophilic character to oxygen atom. A positive potential is concentrated on C and H atoms revealing their electrophilic nature in a chemical reaction.