Nomenclature | Poly functional Compounds | lec 06 | Dr. Rizwana

Polyfunctional compounds get their names by combining two ideas: (1) the functional group priority order that determines the parent suffix/prefix, and (2) a consistent numbering scheme that gives the lowest possible locants to substituents.

When multiple functional groups appear in the same molecule, the “highest-preference” group becomes part of the parent name (as a suffix or prefix), while the others are treated as substituents. The priority list given runs from carboxylic acid highest, followed by sulfonic acid, esters, acid halides, amines, nitriles, aldehydes, ketones, alcohols, amides (NH2/amide-type), alkenes, and finally alkynes. The key practical takeaway is that the preferred group’s name attaches to the parent chain, and the rest get incorporated as prefixes with their own locant numbers.

Naming also changes depending on whether a functional group is written as a suffix or as a prefix. For suffix-style functional groups, the naming uses the standard suffix pattern (for example, ketones use “-one” style forms). For prefix-style functional groups, the same carbonyl-type group is represented differently: ketones become “oxo-” in prefix form. The lecture stresses that this switch is not cosmetic—it changes the exact word used in the final IUPAC-style name.

Halogens and other common groups follow their own prefix conventions. Halogens are named as bromo-, chloro-, and iodo- when used as prefixes. Alkyl groups are treated as alkyl substituents (with examples like methyl-, ethyl-, and propyl- style naming). Alkoxy groups are handled as “alkoxy-” (illustrated with “methoxy-” when a methyl group is attached through oxygen). Hydroxy is written as “hydroxy-” in prefix form, and its position is indicated by a locant.

Several functional groups are translated into specific prefix words tied to their carbon position. Carbonyl-containing groups use “oxo-” for ketone-type prefix representation. Nitrogen-oxygen groups use “nitro-” and “nitroso-” as prefix forms. Nitrile is handled as “nitrile” in suffix form, but becomes “cyano-” when used as a prefix.

The lecture then applies these rules to polyfunctional examples. In a molecule containing both an alkene and an alkyne, the alkene takes priority, and numbering starts from the end that gives the alkene the lowest possible number. The parent chain name is built around the alkene position, while the alkyne position is included as a locant for the “-yne” part. Another example with an aldehyde uses aldehyde carbon as carbon-1, then continues numbering to assign double-bond locants and total chain length for the parent name.

A more complex case demonstrates how to choose numbering when a chain is “broken” by an ether oxygen (an O atom inside the chain). The functional group carbon(s) that define the parent get the lowest locants, and substituents are then listed alphabetically. The final naming sequence combines: parent selection from functional-group priority, correct prefix/suffix word choice (like oxo-, cyano-, nitro-, hydroxy-), locant assignment using least-number rules, and alphabetical ordering of substituent prefixes.