Previous density functional (DF) calculations of the structures of small hydrocarbon molecules (CH, CH2, C2H2, C2H4, C3H6, C3H8) have been extended to larger systems. The structure of a single chain of isotactic polypropylene (it-PP) has been optimized, and calculations have been performed for smaller molecules with closely related structures (propane C3H8, several conformers of isopentane C5H12, and 2,4,6-trimethyl heptane C10H22) using both local spin density (LSD) and non-local (gradient-corrected) energy functionals. The pronounced transferability of the local structural parameters between C5H12, C10H22 and it-PP suggests that the energy surfaces calculated for molecules with five carbon atoms should provide a very good representation of the local energy variations in much larger systems.