What term refers to isomers that have the same molecular formula but a different structure?

• A. Structural isomer
• B. Geometric isomer
• C. Optical isomer
• D. Titration

Answer: (A)

Structural isomerism is when molecules have the same molecular formula but different bonding patterns between atoms. That means the atoms are connected in distinct ways, giving different carbon skeletons or functional group placements and, as a result, different properties. For example, two compounds with the formula C4H10 can differ because one has a straight-chain arrangement while the other branches in the middle. This concept contrasts with geometric isomerism, where the connectivity is the same but the spatial arrangement around a double bond or ring differs (cis/trans), and optical isomerism, where molecules are non-superimposable mirror images due to chirality. Titration is simply a lab technique and isn’t about how atoms are connected, so it isn’t an isomer type.