Why does isopentane have a lower melting point than n-pentane?
The structures of n-pentane and isopentane are:
As we can see that branching is present in isopentane. This decreases the surface area of molecule and makes it compact which results in decrease of intermolecular forces between different molecules. Lower the attractive intermolecular forces lower is the melting point. While in n-pentane, there is a 5 carbon long chain with higher surface area. More attractive forces between different molecules on n-pentane. Hence it has higher melting point than isopentane.
As we can see that branching is present in isopentane. This decreases the surface area of molecule and makes it compact which results in decrease of intermolecular forces between different molecules. Lower the attractive intermolecular forces lower is the melting point. While in n-pentane, there is a 5 carbon long chain with higher surface area. More attractive forces between different molecules on n-pentane. Hence it has higher melting point than isopentane.