IB Chemistry: Organic Nomenclature FAQ

Organic nomenclature is the IUPAC system for naming carbon compounds so any chemist can draw the structure from the name alone. Under the current DP Chemistry guide (first exams 2025), it sits in Structure 3.2 (Functional groups) and appears throughout Paper 1 and Paper 2, both SL and HL.

Find the longest continuous carbon chain containing the principal functional group, number it to give that group the lowest locant, name substituents alphabetically with their locants, and add the correct suffix (-ol, -one, -oic acid, and so on). Get the parent chain wrong and everything downstream is wrong too.

When a molecule has more than one functional group, the principal group is the one highest in the IB's seniority order — carboxylic acids rank above esters, amides, nitriles, aldehydes, ketones, alcohols, amines, then alkenes/alkynes and halides. The principal group gets the suffix; everything else becomes a prefix.

The biggest one: forgetting locants when there's only 'obviously' one position — the IB still wants them. Others include missing commas between multiple locants, wrong alphabetical order of substituents, and confusing 'di-/tri-' multiplying prefixes with the alphabetising of the substituent name itself.

E/Z naming applies to alkenes with restricted rotation: rank the two groups on each carbon by atomic number (CIP priority rules), and if the higher-priority groups sit on the same side it's Z, opposite sides it's E. R/S applies to chiral carbons using the same priority ranking viewed with the lowest priority group pointing away.

Yes. SL students name straight and branched chains, alcohols, aldehydes, ketones, carboxylic acids, esters and simple halogenoalkanes. HL adds structural isomer classification depth, E/Z geometric isomerism, and R/S optical isomerism — all still under the same Structure 3.2 sub-topic in the current guide.

There's no fixed 'nomenclature section' — it's usually worth 1-3 marks per question, but it recurs across nearly every organic-chemistry question on both papers, because you can't answer a mechanism or reaction question correctly if you can't name or draw the structure first.

Nomenclature questions usually use 'deduce' (work out the name/structure from given data), 'draw' (a full structural or skeletal formula) or 'state' (give the name directly). 'Deduce' commonly appears where you're given a molecular formula or spectral data and asked to identify the compound and name it.

Broadly comparable in content, but IB Chemistry HL pushes further into R/S optical isomerism and expects CIP-priority justification, not just a memorised name. A-level (AQA/Edexcel) covers similar functional groups but generally examines stereochemistry naming less rigorously at the equivalent level.

It's almost always a precision problem, not a comprehension one — missing a comma, numbering from the wrong end, or forgetting a stereodescriptor. These are mechanical errors that disappear with repeated, examiner-style practice rather than more conceptual teaching, which is why targeted worksheet drilling helps more than re-reading notes.

Drill little and often: name 10-15 structures a day from past paper Paper 1 and Paper 2 questions, then check every locant and hyphen against the mark scheme, not just whether the 'gist' is right. Nomenclature rewards precision over understanding, so repetition beats revisiting theory.

Yes — start with the IB Chemistry data booklet (free, and the exact reference students get in the exam) alongside topic-specific worksheets. RevisionPrep's Topical Worksheets and Revision Notes on organic chemistry give focused, examiner-style naming practice without the cost of a full course or private tuition.