CH$_3$C ≡ CHCH(CH$_3$)$_2$ The IUPAC nomenclature of the compound above is

To determine the IUPAC name of the compound CH$_3$C ≡ CCH(CH$_3$)$_2$, we must follow the standard IUPAC rules for naming alkynes.

1. Analyze the Structure

First, let's expand the condensed formula to see the carbon chain clearly:

• The structure is: CH$_3$ — C ≡ C — CH(CH$_3$)$_2$
• The group CH(CH$_3$)$_2$ is an isopropyl group attached to the main chain.

2. Identify the Longest Carbon Chain

We need to find the longest continuous carbon chain that contains the triple bond.

• Let's count the carbons: • CH$_3$ (1) — C (2) ≡ C (3) — CH (4) — CH$_3$ (5) • The branch (the other CH$_3$ group) is attached to carbon 4.
• The longest chain has 5 carbons, which corresponds to the parent alkane pentane. Since there is a triple bond, it becomes pentyne.

3. Number the Chain

Numbering must start from the end that gives the triple bond the lowest possible locant (position number):

• If we number from left to right: The triple bond starts at carbon 2.
• If we number from right to left: The triple bond starts at carbon 3.
• Therefore, we number from left to right. The parent name is pent-2-yne.

4. Identify and Locate Substituents

• With the chain numbered from left to right, the methyl group (–CH$_3$) is attached to carbon 4.
• Putting it all together: 4-methylpent-2-yne.

5. Conclusion

• Parent chain: Pent-2-yne
• Substituent: 4-methyl
• Full Name: 4-methylpent-2-yne

Comparing this to your options: A. 3-ethyl but-2-yne (Incorrect) B. 4-methylpent-2-yne (Correct) C. 2-ethyl but-2-yne (Incorrect) D. 2-methyl pent-2-yne (Incorrect)

Exam Tip: When naming hydrocarbons with multiple bonds, always prioritize the position of the functional group (the triple bond) over the position of the alkyl branches. Number the chain so the triple bond gets the smallest number possible, then name the branches alphabetically if there are multiple types.