Question:
Rank the following compounds in ascending order of melting point (and explain your reasoning): CH3CH2CH2NH2, CH3CH2CH3, CH3CH2CH2OH
Answer:
CH3CH2CH3 , CH3CH2CH2NH2 , CH3CH2CH2OHThe only major intermolecular force that takes place in propane are the van deer waal forces made up by dipole to dipole interactions. The other two compounds have van der waal forces, but on top of that they engage in hydrogen bonding (thanks to the hydroxy and amine groups). This additional force strengthens the intermolecular forces and thus increases the melting point of the compound. Propanol has a higher MP than propylamine as oxygen has two lone pairs of electrons, whereas nitrogen has only one. This means that oxygen can form two hydrogen bonds whereas nitrogen can only form one. Propanol therefore has more hydrogen bonds and therefore has stronger intermolecular forces.
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