LIQUID-CRYSTAL PROPERTIES OF SOME SUBSTITUTED PYRAZINES

A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition tempe ratures, together with examples of birefringence measurements, are rep orted. All the 2,5-disubstituted pyrazine systems are liquid crystalli ne showing high birefringence values for the biphenyl and terphenyl an alogues, whereas the 1,5-disubstituted systems are not liquid crystall ine. The pyrazine ethyne systems exhibit very high birefringence value s. X-ray diffraction has been used to identify the liquid crystal phas es of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine.