The basic structural differences between three thermotropic liquid crystals TB4A, TB7A and TB10A have been interpreted by analysing their Raman spectra. Three spectral regions, 925-1025, 1275-1475 and 1525-1650 cm-1, have been chosen in this context to incorporate their structural dissimilarity. The induced planarity of the backbone, as an effect of increasing chain length, has been studied by observing the changes in the respective Raman spectra of the three compounds. A tentative assignment of all the modes observed in the region 400-1700cm-1 is made in this context. The molecular conformations of the three compounds have been predicted in their solution states, and are compared with the molecular environment that exists in their liquid crystalline states. Structural disorder at the solid-SmG transition is discussed and the changes are incorporated systematically.