In organic chemistry, what does the term stem refer to?

• A. The parent carbon chain
• B. The substituent group
• C. The functional group
• D. The side chain with the highest priority

Answer: (A)

In naming organic molecules, the stem is the parent carbon chain—the main backbone that determines the base name. You pick the longest continuous chain that contains the principal functional group; this chain becomes the stem. All substituents attach to this stem, and the functional group (if present) usually governs the suffix that attaches to the stem. So the stem being the parent chain makes sense because it provides the core structure from which the rest of the molecule is described. The other options describe features off that backbone: a substituent group is a branch off the stem, the functional group is the reactive unit that often dictates the suffix, and there isn’t a standard notion of a “highest priority” side chain in forming the stem.