C. Zúñiga

New Schiff's bases containing 1,3,4-thiadiazole and 1,3,4-oxadiazole units: a study of the effect of the heterocyclic ring and the position of the lateral alkoxy group on liquid crystalline properties

The synthesis of novel Schiffs bases incorporating the five-membered 1,3,4-thiadiazole (series 7, 9) and 1,3,4-oxadiazole (series 8, 10) rings have been prepared and their liquid crystalline properties studied. All compounds of series 7 exhibit an enantiotropic smectic C phase. No liquid crystalline properties were observed for the compounds of series 8-10. A study of the structure/mesomorphic activity relationship is also described.

Synthesis and mesomorphic properties of esters derived from Schiff's bases containing 1,3,4-thiadiazole

Two homologous series of esters derived from Schiffs bases containing the 1,3,4-thiadiazole unit (series 3 and 5) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the position occupied by the carbonyl group, the smectic A phase was observed in series 3 and nematic phase in series 5.

Symmetric esters derived from 1,3,4-oxadiazole: synthesis, mesomorphic properties and structural study by semi-empirical calculations

Three homologous series of symmetric esters derived from 2-alkylthio-5-(p -hydroxy)phenyl-1,3,4-oxadiazole (series 3, 4 and 5) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the chain length, nematic and smectic C phases were observed in the series 3 ; smectic A and smectic C phases in series 4. None of the homologues of series 5 shows mesomorphic properties. These three series are compared with other previously reported oxadiazoles. A structural study of AM1 semi-empirical calculations is also described.

New chiral Schiff's bases with a 1,3,4‐thiadiazole ring in the mesogenic core: synthesis, mesomorphic and ferroelectric properties

Two new homologous series of chiral esters derived from Schiffs bases containing a 1,3,4‐thiadiazole unit (series 6 and 7) were synthesized and their liquid crystalline and ferroelectric properties investigated. All the compounds of series 6 exhibit SmC*–SmA dimorphism and the compounds of series 7 exhibit a SmC* phase. All the compounds of these series are ferroelectric liquid crystals.

Synthesis, mesomorphic properties and structural study by semi-empirical calculations of amides containing the 1,3,4-thiadiazole unit

The synthesis and liquid crystalline properties of a new series of amides (series 2a-f,3a-d and 4a-d) incorporating pyridine and 1,3,4-thiadiazole rings are reported. No homologues of the series 2 show mesomorphic properties. In the series 3 only the highest homologues (3d) displays an enantiotropic SmA mesophase; the compound 3c exhibits a monotropic SmA mesophase, and the homologues 3a,b display no liquid crystal properties. The amides 4b-d display an enantiotropic SmA phases and the first homologue (4a) exhibit only crystalisotropic transition. These series are compared with previously reported Schiffs bases and amide analogues. A structural study by AM1 semi-empirical calculation is also described.

Synthesis and mesomorphic properties of 6-n-decyloxy-2-[4′-N-alkoxyphenylimino)methyl]quinolines (IV)

Abstract The synthesis and mesomorphic properties of a new series of liquid crystals derived from quinoline with an imine central bond is described. All compounds exhibit mesophase ranges greater than 50°C. The lower homologues (n = 4–6) show trimorphism Sc-Sa-N (for n = 4, the Sc phase is monotropic). The higher homologues (n = 7–10) show nematic and smectic C phases. Compared to the styrylquinoline analogues the imine bond gives rise to similar liquid crystal phase ranges but lower melting points.

Esters derived from 7-decanoyloxychromone-3-carboxylic acid: Synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of a new series of calamitic liquid crystals containing 4-H-benzopyran-4-one (chromone) within the central core is reported. The first homologue in the series display SmA phase (8a), the homologues (8b–e) exhibit SmA and SmC mesophases and the homologues (8f–h) exhibit only a SmC mesophase.

Hydrogen-bonded complexes between mesogenic heterocyclic Schiff's bases and mesogenic 4- n -nonyloxybenzoic acid: mesomorphic behaviour, FTIR study and PM3 semi-empirical calculations

A new series of intermolecular hydrogen-bonded complexes has been obtained using mesogenic 4-n-nonyloxybenzoic acid and mesogenic 5-(4-pyridyl)-2-(4-n-alkoxy) benzylideneamino-1,3,4-thiadiazole moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Intermolecular hydrogen bonding was studied by FTIR spectroscopy, from crystalline to the isotropic state. A study by PM3 semi-empirical calculations is also described.

Synthesis and mesomorphic properties of 3‐(4‐n‐alkyloxyarylaminomethylene)chroman‐2,4‐diones

The synthesis, characterisation and mesomorphic properties of new liquid crystals are reported. The goal was to obtain amides starting from 7‐decanoyloxychromone‐3‐carboxylic acid and 4‐n‐alkoxyanilines. However, instead of the expected amides, in each case a mixture of two isomeric E/Z enaminones was isolated, with a ratio 3/1. The mesophase behaviour of the five mixtures was characterised and studied using differential scanning calorimetry and polarising optical microscopy. The transitions are enantiotropic, the peaks being sharp and the mesomorphic range wide. All the compounds exhibit a smectic C phase and the derivatives with shorter chains also exhibit a nematic phase.

SYNTHESIS AND TAUTOMERISM OF NEW 1-n-ALKYL-5-PYRAZOLONE DERIVATIVES

La alquilacion de la 3-fenil-5-pirazolona (1) ocurre selectivamente en la posicion 1 con un 40% de rendimiento. El compuesto alquilado (2) que se obtiene fue acilado (3) con 60% de rendimiento y nitrosado (4) con un 80% de rendimiento. De acuerdo con los datos espectroscopicos, se puede proponer una estructura N-H u O-H para el compuesto 1 en DMSO. El proton puede encontrarse en el N-2 o en el oxigeno unido al C-5. El compuesto alquilado 2 existe como 5-pirazolona en cloroformo y el C-4 es un CH2. En DMSO, 2 es un 5-hidroxipirazol. Para el compuesto 3 en cloroformo la estructura corresponde a 4-acil-5-hidroxipirazol. Para el compuesto 4 en cloroformo hay solo un tautomero con una estructura de 4-nitroso-5-hidroxipirazol mientras que en DMSO se encuentran dos tautomeros, 4-nitroso-5-hidroxipirazol (92%) y 4-nitroso-5-pirazolona (8%)