Given a molecule with the structure ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_3$ with an ethyl group attached to the third carbon, at which position does the IUPAC name indicate the ethyl group is located?

• A. Position $3$
• B. Position $1$
• C. Position $4$
• D. Position $2$

Answer: (A)

Verified step by step guidance

1. Identify the longest continuous carbon chain in the molecule. In this case, the chain has 6 carbons, which corresponds to hexane.
2. Number the carbon atoms in the main chain from the end nearest to the substituent to give the substituent the lowest possible number. This means starting from the end closest to the ethyl group.
3. Locate the position of the ethyl group on the main chain by counting the carbon atoms from the chosen end. The ethyl group is attached to the third carbon atom in the chain.
4. Confirm that the numbering chosen results in the substituent having the lowest possible number compared to numbering from the opposite end.
5. Conclude that the IUPAC name indicates the ethyl group is located at position 3 on the hexane chain.