The molecular formula C3H8O has three stable isomers:

• 1-propanol: A primary alcohol with the structure CH3−CH2−CH2−OH
• 2-propanol: A secondary alcohol with the structure CH3−CH(OH)−CH3
• Ethyl methyl ether: An ether with the structure CH3−CH2−O−CH3 

Two of the isomers are alcohols, while the third is an ether. Ethers cannot be oxidized, so they do not react with potassium permanganate (KMnO4). However, alcohols can oxidize, and when they react with KMnO4, they produce carboxylic acid.