Synthesis and thermal behavior of new liquid crystals arylaldoxime esters

Abstract

Uma série de cristais líquidos derivados de ésteres arilaldoximas foi sintetizada e caracterizada via espectroscopia de 1 H, 13 C RMN, ATR/IV-FT e análise elementar. A estabilidade química e fotofísica desses compostos foram dependentes dos ciclos de aquecimento e resfriamento, com a decomposição sendo induzida pelo calor. As mudanças nas propriedades durante os ciclos de aquecimento foram acompanhadas através dos respectivos espectros de infravermelho. Todas as amostras se decompõem termicamente, gerando as respectivas nitrilas e ácidos carboxílicos como evidenciado pelos espectros de infravermelho e de 1 H NMR. As propriedades mesomórficas foram avaliadas apenas no primeiro ciclo de aquecimento, devido à decomposição térmica observada após a primeira transição para o estado isotrópico. Espectros de absorção em solventes orgânicos apresentam três bandas entre 230 e 340 nm, e uma banda de emissão, larga e sem estrutura, em 430 nm. Cálculos teóricos ab initio foram realizados para a obtenção de informações estruturais dos ésteres arilaldoximas. We report the synthesis of a series of liquid-crystalline materials based on arylaldoxime esters and the characterization of these materials by 1 H, 13 C NMR, ATR/FT-IR spectroscopy and elemental analysis. The chemical stability and liquid-crystalline as well as photophysical properties of the compounds are described being dependent on the heating/cooling cycles. The changes in chemical stability and the liquid crystals properties of arylaldoxime esters were observed during these thermal cycles by IR analysis. All samples underwent a thermal degradation yielding the corresponding nitriles and carboxylic acid as evidenced by IR and 1 H NMR spectra. Due to the decomposition process, information about the mesomorphic behaviour is lost. The UV-Vis absorption spectra in solution display three absorption bands between 230 and 340 nm. The fluorescence spectra exhibit a broad and structureless emission band located at 430 nm. Ab initio calculations were performed to obtain information on the molecular structure and properties of the title compounds.

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Preliminary ecotoxicity assessment of selected flavour and fragrance compounds using Microtox assay

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One-pot green synthesis of isoxazol-5(4H)-one derivatives by Dowex1-x8OH in water

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