The correct option for the IUPAC name of the compound HC≡CCH₃ is **B. Methyl acetylene**. Let's break down the reasoning step-by-step. ### Step-by-Step Explanation 1. **Understanding the Structure**: - The compound HC≡CCH₃ can be broken down into its components: - The first carbon (C) is connected to a hydrogen (H) and is part of a triple bond (≡) with the second carbon (C). - The second carbon (C) is then connected to a third carbon (C) which has three hydrogens (H₃) attached to it. - This structure can be visualized as: ``` H-C≡C-CH₃ ``` - The first carbon (C1) is part of a triple bond with the second carbon (C2), and the second carbon (C2) is connected to a third carbon (C3) which is a methyl group (CH₃). 2. **Identifying the Longest Carbon Chain**: - The longest continuous carbon chain in this compound consists of three carbon atoms (C1, C2, and C3). - The presence of a triple bond indicates that this compound is an alkyne. 3. **Naming the Compound**: - According to IUPAC nomenclature rules, the base name for a three-carbon alkyne is derived from "prop" (for three carbons) and the suffix "-yne" (indicating a triple bond). - However, since there is a methyl group (CH₃) attached to the terminal carbon (C3), we need to specify this in the name. - The correct name for this compound is "methyl acetylene" because: - "Acetylene" refers to the simplest alkyne (C₂H₂), which is ethyne (HC≡CH). - The methyl group (CH₃) is attached to the terminal carbon of the acetylene structure. ### Why Other Options Are Incorrect - **A. Acetylene**: - Acetylene refers specifically to the compound HC≡CH (ethyne), which has only two carbon atoms. Since our compound has three carbon atoms, this option is incorrect. - **C. Butanol**: - Butanol is an alcohol with the formula C₄H₉OH. It contains four carbon atoms and a hydroxyl (-OH) group. Our compound does not have a hydroxyl group and has only three carbon atoms, making this option incorrect. - **D. Decanoic acid**: - Decanoic acid is a fatty acid with the formula C₁₀H₂₀O₂. It contains ten carbon atoms and a carboxylic acid functional group (-COOH). Our compound does not fit this description, so this option is also incorrect. ### Summary of Key Points - The compound HC≡CCH₃ has three carbon atoms and a triple bond, classifying it as an alkyne. - The correct IUPAC name is "methyl acetylene," indicating the presence of a methyl group attached to the acetylene structure. - Other options are incorrect due to mismatches in the number of carbon atoms or functional groups. ### Revision Summary - The compound HC≡CCH₃ is named methyl acetylene. - It consists of three carbon atoms with a triple bond between the first two. - Acetylene (HC≡CH) has only two carbons, while butanol and decanoic acid have different structures and functional groups. - Always identify the longest carbon chain and any substituents when naming organic compounds.