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2'-Hydroxybenzylideneanilines and 2-Hydroxyazobenzenes. The Role of Intramolecular O–HźźźN Resonance Assisted Hydrogen Bonds

Majewska P., Rospenk M., Sobczyk L.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

709-721

A short review on the effect of the OH groups in the ortho position on the liquid crystalline properties of benzylideneanilines and azobenzenes is presented. Numerous examples show that there are no general rules governing the behaviour of these compounds. How ever one finds most frequently a broadening of the existence range of mesophases both due to a decrease of freez ing temperature and an increase of the isotropisation temperature. In contrast, the presence of strongly polar groups such as –NO2 and –CN leads to a reverse be haviour that can be explained by as suming a strong pi-electron conjugation of these groups with the conjugate-chelatering formed by intramolecular O–HźźźN hydrogen bond. These rings are analyzed by us ing data related to the structure of molecules and infrared spectra in the region of the stretch ing ni(OH) and bend ing delta(OH) and gamma(OH) modes.

Liquid Crystalline Properties of Azobenzenes : I. 4-Methoxy-, 4-Ethoxy-, 4-Propoxy- and 4-Butoxy-4'-alkyloxyazobenzenes

Galewski Z., Hofmańska A., Zielińska K.

Polish Journal of Chemistry

1999

Vol. 73, nr 8

1357-1371

Liquid crystalline properties of four series of azobenzenes, 4-methoxy-4'-alkyloxy-azobenzenes (azo-1 n), 4-ethoxy-4'-alkyloxyazobenzenes (azo-2-n) were investigated. By polarizing microscopy nematic and smectic C mesophases were detected. By DSC and TOA thermo-optics the parameters of phase transitions were measured.