Why does neopentane have a higher melting point than n-pentane?
Many symmetrical molecules undergo a phase change before they melt.  This is usually interpreted as the ability to rotate without disrupting the lattice structure.  This has a much greater effect on the entropy of the solid than on its energy.  This reduces the entropy of fusion more than it reduces the enthalpy of fusion, thereby raising the melting point which equals delta-H/delta-S.  This is very dramatic in the comparison of melting points of octane, cyclo-octane, and bicyclo-octane.