We have extended a recently introduced united atom model of n-alkanes to investigate the liquid-state dynamics of squalane, a molecule with six, symmetrically placed, methyl side groups. We compare our results with experimental measurements of diffusion in the same system and with experimental and simulation results on n-decane and n-tetracosane. The model reproduces the significantly different temperature dependence of diffusion in squalane and n-alkanes of similar mass. The results of a detailed comparative study of the intrachain local dynamics in the different molecules makes apparent its correlation with global single-chain relaxation processes. For linear alkanes, we also make a comparison between united atom and asymmetric united atom models.