In organic nomenclature, what information does the prefix provide?

• A. Substituents, branches, functional groups
• B. Stereochemistry and isotopes
• C. Reaction conditions
• D. Isomer counts

Answer: (A)

Prefixes in organic names flag what else is attached to the main carbon skeleton. They name substituents such as alkyl groups (methyl, ethyl), halogens (fluoro, chloro, bromo), nitro or cyano groups, and they can carry multiplicative prefixes like di- or tri to show how many of a given substituent there are. The numbers before the substituent names (locants) indicate where on the parent chain those groups are attached. The root describes the backbone and the suffix signals the main functional group, while the prefix reveals substituents, branches, and related groups not part of the main functional feature. Stereochemical descriptors or isotopic labels, reaction conditions, or isomer counts aren’t conveyed by the prefix in the same way.