The intramolecular torsional potential of ethylbenzene and ethoxybenzene has been calculated using the B3LYP density functional method with a triple-zeta polarized basis set. In its completely optimized geometry, ethylbenzene has the torsional angle at 90degrees, that is in correspondence of conformation with the plane containing C-CH2-CH3 perpendicular to the phenyl ring, while, in agreement with recent literature data, a very little pronounced energy maximum at similar or equal to20degrees and a shallow local minimum at 0degrees have been found. The ethoxybenzene molecule has its minimum geometry where both the ring and the ethyl group lie in the same plane, being in trans position with respect to the O-CH2 bond. The resulting data have then been fitted onto analytical functions, to be employed both in LXNMR spectroscopy and in computer simulations of realistic models of liquid crystals containing the alkyl-aryl and alkoxy-aryl linkages.