Question

which compound would you expect to have the highest melting point

Answer 1

In alkanes, the compound which has the longest chain has the highest melting point and highest boiling point. The longer the chain, the more it is subjected to Van der Waals forces, which strengthens the bond between the molecules and the more resistance from changing one state to the other (in the melting case, from solid to liquid). However, in ethers, amines, alcohols or alkyl halides, there can be another factor-polarity. The more polar the molecule is, the higher the melting point. The molecules align themselves wherein the positive end of one molecule is adjacent to the negative end of the other molecule. This kind of intermolecular force is called dipole-dipole interaction, which is stronger than the Van der Waals.