To determine which compound is an isomer of 2-methylprop-1-ene, we first need to understand what is meant by "isomer." Isomers are compounds that have the same molecular formula but different structural arrangements of atoms. ### Step 1: Identify the Molecular Formula of 2-methylprop-1-ene 2-methylprop-1-ene has the following structure: - The "prop" indicates a three-carbon chain (C3). - The "1-ene" indicates that there is a double bond between the first and second carbon atoms. - The "2-methyl" indicates that there is a methyl (CH3) group attached to the second carbon of the propene chain. The molecular formula for 2-methylprop-1-ene can be derived as follows: - The main chain has 3 carbons (C3). - There is one additional carbon from the methyl group (C1). - Therefore, the total number of carbons is 4 (C4). - The number of hydrogens can be calculated using the formula for alkenes, CnH2n, where n is the number of carbons. For 4 carbons, it would be H2(4) = H8. However, since there is a double bond, we subtract 2 hydrogens, giving us H6. Thus, the molecular formula for 2-methylprop-1-ene is C4H8. ### Step 2: Analyze the Options Now, let's analyze each option to see if they have the same molecular formula (C4H8) and if they are structural isomers of 2-methylprop-1-ene. **A. But-2-ene (C4H8)** - Structure: CH3-CH=CH-CH3 - This compound has the same molecular formula (C4H8) and is a structural isomer because it has a different arrangement of the double bond compared to 2-methylprop-1-ene. - **Conclusion**: This is a valid isomer. **B. Pent-1-ene (C5H10)** - Structure: CH2=CH-CH2-CH2-CH3 - This compound has a different molecular formula (C5H10) and therefore cannot be an isomer of 2-methylprop-1-ene. - **Conclusion**: This option is incorrect. **C. 2-methylbut-2-ene (C5H10)** - Structure: CH3-C(CH3)=CH-CH3 - This compound also has a different molecular formula (C5H10) and is not an isomer of 2-methylprop-1-ene. - **Conclusion**: This option is incorrect. **D. 2-methylbut-1-ene (C5H10)** - Structure: CH2=CH-CH(CH3)-CH3 - This compound has a different molecular formula (C5H10) and is not an isomer of 2-methylprop-1-ene. - **Conclusion**: This option is incorrect. ### Final Answer The correct option is **A. But-2-ene** because it is the only compound listed that has the same molecular formula (C4H8) and is a structural isomer of 2-methylprop-1-ene. ### Summary of Key Points - **Isomers**: Compounds with the same molecular formula but different structures. - **Molecular Formula of 2-methylprop-1-ene**: C4H8. - **Correct Isomer**: But-2-ene (C4H8) is a structural isomer of 2-methylprop-1-ene. - **Incorrect Options**: Pent-1-ene, 2-methylbut-2-ene, and 2-methylbut-1-ene all have different molecular formulas (C5H10) and cannot be isomers of 2-methylprop-1-ene.