Read the Functional Group Priority Table Before Naming Anything
Every IUPAC name follows the same four-step recipe — find the principal chain (longest chain through the highest-priority functional group), name that group as a suffix, number to give it the lowest locant, then list substituents alphabetically as prefixes.
IUPAC Nomenclature is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
The principal chain must run through the senior functional group
The principal chain isn't simply 'the longest chain in the molecule' — it must be the longest chain that CONTAINS the highest-priority functional group. A molecule with a COOH group off a shorter branch of a longer alkyl chain still names the COOH-containing chain as principal, even if a longer all-carbon chain exists elsewhere in the structure; count carbons only after fixing which chain qualifies.
Functional group priority decides the suffix, not the prefix
When multiple functional groups are present, only the highest-priority one becomes the suffix (e.g. -oic acid, -amide, -al, -one, -ol); every other group is named as a substituent prefix instead (oxo-, hydroxy-, amino-). Acid derivatives (anhydrides, esters, amides, nitriles, acid halides) all outrank ketones and alcohols, which outrank amines — memorising this seniority order resolves most 'what's wrong with this name' questions.
Locants go to the principal characteristic group first, substituents second
Numbering starts from whichever end gives the LOWEST locant to the principal functional group's carbon — only when that's still ambiguous (e.g. a symmetric-looking chain) do substituent locants become the tiebreaker. Getting this order backward is the single most common nomenclature error tested.
Retained and common names still follow real rules
Names like vinyl acetate (not 'acryl acetate'), allyl (not 'neobutyl' for a tert-butyl-type group), and formyl/acetyl-type prefixes are retained IUPAC-accepted common names for specific, fixed structures — memorise these as exceptions rather than trying to derive them systematically, since misapplying a retained name to the wrong structure is a frequent trap.
OlympIQ exam lens
- ✓The principal chain must contain the highest-priority functional group, even if a longer chain exists elsewhere in the molecule.
- ✓Only the most senior functional group becomes the name's suffix; every other group is a prefix.
- ✓Number to give the LOWEST locant to the principal functional group first; substituent locants only break remaining ties.
- ✓Retained common names (vinyl, allyl, propargyl, formyl, acetyl) apply to specific fixed structures — don't extend them by analogy.
Don't pick the principal chain by carbon count alone — it must be the longest chain that actually contains the highest-priority functional group; a longer chain that misses that group is never the principal chain.
Ready to try the pattern?
100% coverage across the 32 linked questions.
Practise 32 linked questions