Chiral centers require a tetrahedral carbon with four different substituents

Steps:

• Identify tertiary carbons (bonded to three other carbons) in each hydrocarbon as potential chiral centers.
• List the four substituents on each tertiary carbon: H and the three carbon-based groups.
• Compare the groups to see if all four are unique in structure (e.g., methyl vs. ethyl).
• The pair with at least one hydrocarbon lacking such a carbon is the answer.

Why D is correct:

• In CH₃CH₂CH(CH₃)CH₃, the tertiary carbon bonds to H, -CH₃, -CH₃ (identical), and -CH₂CH₃, violating the four-different-substituents rule for chirality.

Why the others are wrong:

• A: Both have tertiary carbons with four different groups (e.g., first has methyl, H, ethyl, distinct branch).
• B: Both identical molecules have a tertiary carbon with four different groups.
• C: Both have tertiary carbons with four different groups (e.g., first has two methyls but propyl and branch differ).

Final answer: D