What is the correct IUPAC name for a cyclohexane ring with a methyl group at carbon $1$ and an ethyl group at carbon $3$?

• A. $3$-methyl-$1$-ethylcyclohexane
• B. $3$-ethyl-$1$-methylcyclohexane
• C. $1$,$3$-dimethylcyclohexane
• D. $1$-ethyl-$3$-methylcyclohexane

Answer: (B)

Verified step by step guidance

1. Identify the substituents attached to the cyclohexane ring: a methyl group and an ethyl group.
2. Number the cyclohexane ring carbons to give the substituents the lowest possible numbers. Start numbering at the substituent that comes first alphabetically to assign carbon 1.
3. Compare the substituents alphabetically: 'ethyl' comes before 'methyl', so assign carbon 1 to the ethyl group and carbon 3 to the methyl group.
4. Write the name by listing the substituents in alphabetical order with their corresponding carbon numbers, followed by the parent name 'cyclohexane'.
5. Combine the parts to form the correct IUPAC name: \$3\(-methyl-\)1\(-ethylcyclohexane is incorrect because numbering should prioritize alphabetical order, so the correct name is \)1\(-ethyl-\)3$-methylcyclohexane.