Chemistry (Year 12) - Organic Chemistry
Structure of Alcohols
Alcohols have the general formula of R - OH. This alcohol group is present when a functional C atom forms a single bond to an O atom bonded to an H atom.
We can classify alcohols as primary, secondary or tertiary. This classification depends on the number of C atoms bonded to the C atom bearing the - OH group.
Intermolecular Forces Present
Alcohols exhibit dispersion forces, dipole-dipole forces and hydrogen bonding between their molecules and with water.
The Boiling Point of Alcohols
Due to the strong presence of hydrogen bonding between alcohol molecules, alcohols have significantly higher boiling points than alkanes/alkenes of similar molecular weight.
As the carbon chain length increases, the sum of dispersion forces between alcohol molecules becomes stronger than the hydrogen bonding between alcohol-water molecules.
This means that alcohols with very high molecular weights will have similar boiling points with alkanes/alkenes of similar molecular weights.
Solubility of Alcohols in Water
As alcohols have similar intermolecular forces with water and can form strong hydrogen bonds, alcohols with short to medium carbon chains have a very high solubility in water.
The solubility of alcohols in water diminishes as the carbon chain length increases due to dispersion forces becoming the predominant intermolecular force.