A series of highly chiral hetrocyclic esters have been studied. The effect that the choice of hetroatom has on the linearity of the molecules and hence the mesomophism of the materials has been investigated. Measurements of the spontaneous polarisation, tilt angle, current response time and rotational viscosities of the materials are reported. At 30 degrees C below the transition from the SmA phase all members of the series show a Ps of similar to 100nCcm(-2) and a high tilt angle of about 30 degrees. These physical measurements confirm the presence of a higher order antiferroelectric phase in the selenophene derivative in this series.