Which of the following best describes a molecule with a long chain carbon backbone?

• A. It is always a cyclic compound with a ring structure.
• B. It is always an aromatic compound with alternating double bonds.
• C. It must contain a $\mathrm{carboxyl}$ group at each end of the chain.
• D. It is typically an $\mathrm{alkane}$, consisting of only single bonds between carbon atoms.

Answer: (D)

Verified step by step guidance

1. Understand the term 'long chain carbon backbone': it refers to a molecule where carbon atoms are connected in a continuous, extended sequence, typically forming a straight or branched chain.
2. Evaluate the options given: a long chain carbon backbone is not necessarily cyclic, so it is not always a ring structure.
3. Consider aromatic compounds: these have alternating double bonds in a ring, but a long chain backbone does not imply aromaticity.
4. Check the presence of functional groups: a long chain does not require carboxyl groups at each end; such groups define specific molecules like dicarboxylic acids.
5. Recognize that a molecule with a long chain carbon backbone is typically an alkane, meaning it consists of only single bonds between carbon atoms, making it a saturated hydrocarbon.