SummaryThe effect of the phenyl–alkyl connecting group on mesogenic properties of several series of isostructural compounds containing p-carborane (A and B), bicyclo[2.2.2]octane (C), and benzene (D) was investigated using thermal and optical methods. Results demonstrated that mesophase stability in the series containing A–D follows the order (Alk)CH2CH2– < (Alk)OOC– < (Alk)CH2O– < (Alk)COO–. Surprisingly, the connecting groups (Alk)CH2CH2– and (Alk)OOC– destabilize the mesophase significantly stronger for carboranes (A and B) than for carbocyclic derivatives (C and D). Analysis indicates that this effect may have quadrupolar and conformational origin.