1. Butane and Isobutane: These two compounds are structural isomers of each other. They have the same molecular formula C4H10 but different structural arrangements. Butane has a straight-chain structure, while isobutane has a branched structure.2. Ethanol and Dimethyl Ether: These two compounds are functional isomers, specifically, they are examples of positional isomers. They have the same molecular formula C2H6O but different functional groups. Ethanol has an alcohol functional group -OH , while dimethyl ether has an ether functional group C-O-C .3. Acetic acid and Methyl Formate: These two compounds are also functional isomers, specifically, they are examples of functional group isomers. They have the same molecular formula C2H4O2 but different functional groups. Acetic acid has a carboxylic acid functional group -COOH , while methyl formate has an ester functional group COOCH3 .