Compounds 6 and 7 are non-mesogenic due to the short spacer between the end group and the core unit. Unlike 4, which exhibits only a nematic phase, 8 and 9 both exhibit nematic and SmA phases. The enthalpy (and therefore entropy) associated with the N-SmAd transition is much larger for 9 than 8 and we will return to this point shortly. Compound 10 exhibits a direct Iso-SmA transition. All three phase transitions in Table display a strong odd-even effect; transition temperatures are notably higher for odd parity materials. The smectic layer spacing of 9 was determined by SAXS, and presented as a d/l ratio using calculated molecular lengths (B3LYP/6-31G(d) level, 21.2 Å) as a function of reduced temperature in Figure . We also measured the layer spacings of two comparator materials, these were selected as they have approximately the same molecular length as compound 9 -8OCB (L = 21.8 Å) and 2Si4OCB (L = 21.9 Å) -data are presented in Figure along with molecular structures (Figure , 3e) Typically the layer spacing of the SmAd phase is almost invariant with temperature, however some materials with an acyclic 'bulky' group display temperature dependent layer spacing in the SmAd phase. In the present study we observe the layer spacing of 9 to vary only slightly with temperature, however the d/l ratio is far larger than that of 8OCB (1.60 vs 1.43, respectively). The siloxane terminated material 2Si4OCB 30 exhibits a short range smectic A phase whose d/l ratio is intermediate between 9 and 8OCB. Study of compounds 8 and 10 by SAXS was complicated by crystallisation, however we were able to collect a single SAXS frame at a temperatures of 44 °C and 65 °C, respectively. For 8 and 10 we measure layer spacings of 31.7 Å and 35.4 Å, respectively; this corresponds to d/l ratios of 1.61 for both materials. Of the materials studied by SAXS (5, 8, 9, 10) we find the d/l ratios to be effectively identical.