Which of the following structures represents $4-\mathrm{ethyl}\mathrm{hex}-2-\mathrm{yne}$?

• A. A six-carbon chain with a triple bond between carbons $2$ and $3$, and an ethyl group attached to carbon $4$
• B. An eight-carbon chain with a triple bond between carbons $2$ and $3$
• C. A six-carbon chain with a triple bond between carbons $4$ and $5$, and an ethyl group attached to carbon $2$
• D. A six-carbon chain with a double bond between carbons $2$ and $3$, and an ethyl group attached to carbon $4$

Answer: (A)

Verified step by step guidance

1. Identify the parent chain length from the name: 'hex' indicates a six-carbon chain.
2. Locate the position of the triple bond from the suffix '2-yne', which means the triple bond starts at carbon 2 (between carbons 2 and 3).
3. Determine the position and identity of the substituent: '4-ethyl' means an ethyl group (–CH2CH3) is attached to carbon 4 of the main chain.
4. Draw the six-carbon chain with the triple bond between carbons 2 and 3, ensuring the numbering starts from the end nearest the triple bond to give it the lowest possible number.
5. Attach the ethyl substituent to carbon 4 on the main chain, confirming the structure matches the IUPAC name 4-ethylhex-2-yne.