Molecular Arrangement in Mesogenic Compounds with a Terminal Cyano Group

The crystal structures of three mesogenic, compounds with a terminal cyano group but with a different polyaromatic central core, showing a nematic and for one of them a cholesteric mesophase, have been solved. The molecular arrangement of two of them is typically nematic while the third one is smectic C-like. All of them involve strong dipolar interactions between their terminal cyano groups with a binding energy ranging -2.7 and -3.8 kcal.mole(-1) and a dipole moment mu around 3.5 Debye. For the compound with the smectic, C-like arrangement the binding energy within the sheet is -17.5 kcal.mole(-1) while the intersheet energy is as large as -3.9 kcal.mole(-1), which is much more than what is observed in mesogenic compounds with a terminal alkyl group.