To determine the correct IUPAC name for a given compound, we need to follow the systematic rules set by the International Union of Pure and Applied Chemistry (IUPAC). Let's analyze the options provided and explain why option D, "3-methylbut-1-ene," is the correct answer. ### Step-by-Step Explanation 1. **Understanding the Structure**: - The name of an organic compound typically consists of a base name that indicates the longest carbon chain, along with prefixes and suffixes that indicate the presence of substituents (like methyl groups) and functional groups (like double bonds). - The base name "but" indicates that the longest carbon chain contains four carbon atoms. The suffix "ene" indicates that there is a double bond present in the structure. 2. **Identifying the Longest Carbon Chain**: - For all options, we need to identify the longest continuous chain of carbon atoms that includes the double bond. In this case, we are looking for a four-carbon chain (butane) with a double bond. 3. **Locating the Double Bond**: - The position of the double bond is crucial in naming. The double bond should be numbered from the end of the chain that gives it the lowest possible number. 4. **Analyzing Each Option**: - **Option A: 2-methylbut-3-ene** - This suggests a four-carbon chain (but) with a methyl group on the second carbon and a double bond starting at the third carbon. - If we draw this structure, we find that the double bond is indeed at the third position, but the methyl group is not in the correct position for this name. - **Option B: 2-methylbut-4-ene** - This indicates a four-carbon chain with a methyl group on the second carbon and a double bond starting at the fourth carbon. - However, this is incorrect because the double bond would be at the end of the chain, which is not the preferred position for naming. - **Option C: 3-methylbut-2-ene** - This suggests a four-carbon chain with a methyl group on the third carbon and a double bond starting at the second carbon. - This is a valid structure, but it does not represent the correct numbering for the lowest double bond position. - **Option D: 3-methylbut-1-ene** - This indicates a four-carbon chain with a methyl group on the third carbon and a double bond starting at the first carbon. - This is the correct structure because it gives the double bond the lowest possible number (1) and accurately describes the position of the methyl group. 5. **Conclusion**: - The correct IUPAC name is **3-methylbut-1-ene** (Option D) because it accurately reflects the structure of the compound with the longest chain, the correct position of the double bond, and the correct placement of the methyl substituent. ### Why Other Options Are Incorrect: - **Option A**: Incorrect placement of the double bond and methyl group. - **Option B**: The double bond is at the end of the chain, which is not preferred. - **Option C**: While it describes a valid structure, it does not provide the lowest number for the double bond. ### Revision Summary: - The IUPAC name reflects the longest carbon chain and the position of double bonds and substituents. - Always number the carbon chain to give the double bond the lowest possible number. - Methyl groups and other substituents should be placed according to their position on the carbon chain. - The correct answer for the given question is **3-methylbut-1-ene (Option D)**.