To name an organic compound using IUPAC nomenclature, follow these steps:
Step 1: Identify the structure. The compound is CH3C≡CCH(CH3)2. Writing it out carbon by carbon:
C-1: CH3
C-2: C (triple bond to C-3)
C-3: C (triple bond to C-2)
C-4: CH with two CH3 groups attached
Step 2: Find the longest carbon chain containing the triple bond. The four carbons above give a chain of 4. However, one of the methyl groups on C-4 can extend the chain to 5 carbons: C-1, C-2, C-3, C-4, C-5 (incorporating one methyl into the main chain). The remaining methyl group on C-4 becomes a branch.
Step 3: Number the chain to give the triple bond the lowest possible locants. Numbering from the CH3 end: the triple bond is at positions 2-3. This gives pent-2-yne.
Step 4: Name the substituent. The methyl branch is on C-4.