A free IUPAC nomenclature trainer

Meimay is a free, browser-based practice tool for learning how to name organic compounds using the IUPAC nomenclature of organic chemistry. It is aimed at undergraduate chemistry students, high-school students preparing for university entrance chemistry, and anyone who wants to get faster and more confident at turning a structure into a systematic name and back again.

Everything runs entirely in your browser. There is no account to create and no server that stores your work: your progress, streaks and review queue are kept locally on your own device using your browser's storage. You can close the tab and come back later, and your history is still there.

What you can practise

• Naming from structure — read a skeletal formula and give the correct systematic name.
• Drawing from a name — go the other way and identify the structure a name describes.
• Stereochemistry — assign R/S configuration at each stereocentre and E/Z across double bonds.
• Functional-group seniority — decide which group becomes the suffix and which become prefixes.

Where the chemistry comes from

The naming conventions follow the IUPAC Recommendations on the Nomenclature of Organic Chemistry (the 2013 recommendations and Preferred IUPAC Names). Individual compound names can be cross-checked against public chemical databases. Structures are rendered from SMILES strings using the open-source SmilesDrawer library (MIT licence).

Reference sources: the IUPAC Blue Book at iupac.org, the online edition edited by G. P. Moss at qmul.ac.uk, and PubChem (NIH) at pubchem.ncbi.nlm.nih.gov.

Who makes it

Meimay is developed and maintained by Shintaro Shimizu and Jumpei Toshimori, chemistry students building study tools they wished existed. It is an independent, non-commercial educational project and is not affiliated with IUPAC.

Contact

Questions, corrections or suggestions are welcome. If you spot a name you believe is wrong, please get in touch and include the compound so it can be checked.

Email: meimei440126@gmail.com

X (Twitter): @Meimaytipg

See the Privacy Policy and Disclaimer links in the footer for how data is handled and the limits of the tool.

Getting the most out of Meimay

Meimay is organised into a few practice modes, selectable from the tabs at the top. A good routine is to read the Learn material for a group, warm up with Flashcards, then test yourself with the Quiz. Here is what each mode does.

Learn

A reference and warm-up view. Pick a functional-group category to see its core rule, its suffix, and a few worked examples drawn as skeletal formulas. This is the place to check how a group behaves before you start being tested on it.

Flashcards

The core drill. You are shown a structure and asked for its name; reveal the answer to check yourself. Cards you find hard come back more often, so time spent here is weighted towards your weak spots. The header ring tracks how many compounds you have mastered, along with your current streak and accuracy.

Quiz

Assessment mode. It offers a Type variant, where you enter the English name yourself, and a Step-by-step variant, where the compound is named one decision at a time with hints — useful when a full name feels overwhelming and you want to see where your reasoning breaks down.

Draw

The reverse task: you are given a name and asked to identify the structure it describes. Naming and interpreting names use slightly different skills, and practising both directions makes each stronger.

Stereo R/S

Focused stereochemistry practice. For each stereocentre you read the bold wedge (bond coming toward you) and the hashed wedge (bond going away), rank the four groups by CIP priority, and assign R or S. See the Nomenclature guide for the priority rules themselves.

Options worth knowing

• Advanced — narrows practice to harder territory: poly-functional compounds, stereochemistry (R/S, E/Z), meso compounds and cis/trans.
• Old / new IUPAC — switches between older locant placement (for example 2-butanol) and the current style (butan-2-ol), so you can match whichever your course uses.
• Sound effects / BGM — toggle the sound effects and the background music independently from the footer buttons; turning effects off leaves the music playing.
• Reset progress — clears your saved history if you want a clean start.

Per-rule mastery is shown in the bar beneath the exercises, so you can see which rules still need work rather than just an overall score.

IUPAC organic nomenclature: a working guide

This is a practical primer on how a systematic name is built, written to be read alongside the exercises. It covers the decisions you actually make when naming a compound, in the order you make them. It is a summary, not a substitute for the full IUPAC recommendations.

1. The anatomy of a name

A systematic name is assembled from four parts that always appear in the same order: substituent prefixes, then a parent (the main chain or ring), then any unsaturation ending (-ene or -yne), then a principal-group suffix. Locants — the numbers that say where things are attached — are inserted next to the part they refer to. So 4-chloro-3-methylpent-2-en-1-ol reads as: two prefixes (chloro, methyl), the five-carbon parent (pent), a double bond (en), and the senior group as suffix (ol), each with its own locant.

2. Choosing the parent chain

The parent is the backbone the rest of the name hangs off. Selecting it is the first real decision, and getting it wrong cascades into every later step.

• Choose the chain that contains the principal characteristic group (see next section), even if a longer chain exists without it.
• Among candidates, prefer the chain with the most skeletal atoms.
• If chains tie on length, prefer the one with the greatest number of skeletal double and triple bonds.
• Still tied? Prefer the chain with the most substituents cited as prefixes, then the lowest locants.

The chain length gives the stem: 1–10 carbons are meth, eth, prop, but, pent, hex, hept, oct, non, dec.

3. The principal characteristic group and seniority

When a molecule has several functional groups, exactly one is chosen as the principal characteristic group and expressed as the suffix. Everything else is demoted to a prefix. Which group wins is fixed by a seniority order (highest to lowest):

Groups that lose out become prefixes, changing form as they do: a demoted C=O becomes oxo-, -OH becomes hydroxy-, -NH₂ becomes amino-, and -OR becomes alkoxy-. Two families never win at all: ethers and the halogens (fluoro, chloro, bromo, iodo) are always prefixes.

4. Numbering: the lowest-locant rule

Once the parent is fixed, number its atoms from one end so that the important features get the smallest numbers. Apply these tie-breakers in order:

1. Give the principal characteristic group the lowest possible locant.
2. If tied, give the set of double and triple bonds the lowest locants.
3. If still tied, give the set of all prefix substituents the lowest locants as a set.
4. If still tied, give the substituent that is first alphabetically the lower locant.

"Lowest as a set" compares the locants in ascending order at the first point of difference: {2,3,6} beats {2,4,5} because 3 < 4.

5. Substituent prefixes and their order

Substituents cited as prefixes are listed alphabetically, not by locant. Multiplying prefixes (di, tri, tetra) are added to say how many, but they are ignored when alphabetising: "dimethyl" files under m, not d. Complex substituents named with enclosing marks (such as dimethylamino) alphabetise by their first letter and use multipliers like bis, tris instead.

6. Double and triple bonds

Unsaturation is shown by changing the ending: -ane (saturated) becomes -ene for a C=C and -yne for a C≡C, with a locant for the first atom of the multiple bond. Where both are present, ene precedes yne, and if a choice of numbering remains, the double bond takes priority for the lower locant. The final -e of the parent is elided before a suffix beginning with a vowel (pentan-2-ol, not pentane-2-ol) but kept before a consonant (pentane-2,4-dione).

7. Rings and ring systems

A saturated ring takes the prefix cyclo-: cyclohexane, cyclopentanol. When a ring and a chain compete for the role of parent, the ring is chosen if it has the principal group or the greater number of skeletal atoms; otherwise the chain is parent and the ring is a substituent (cyclohexyl). Benzene-derived rings keep many retained names — toluene, phenol, aniline, benzoic acid — which serve as parents in their own right, with substituents numbered to give lowest locants.

8. Stereochemistry

E/Z across double bonds

On each carbon of a C=C, rank the two attached groups by CIP priority (higher atomic number wins; ties are broken by looking outward atom by atom). If the two higher-priority groups are on the same side, the bond is Z (zusammen, together); on opposite sides, E (entgegen, opposite).

R/S at a stereocentre

Rank the four groups on the stereocentre by CIP priority, 1 (highest) to 4 (lowest). Orient the molecule so the lowest-priority group points away from you, then trace 1→2→3: clockwise is R (rectus), anticlockwise is S (sinister). In a wedge drawing, a bold wedge comes toward you and a hashed wedge goes away; if the lowest group is already on a hashed wedge, you can read the sense directly.

Stereodescriptors are placed at the front of the name in italics and parentheses, for example (2R,3S). Meso compounds contain stereocentres but an internal mirror plane, so the molecule as a whole is achiral even though individual centres are labelled.

9. Old versus new locant style

Current IUPAC style places each locant immediately before the part it refers to: butan-2-ol, hex-3-ene, pentan-2-one. Older textbooks front-load the locant: 2-butanol, 3-hexene, 2-pentanone. Both point to the same structure; use whichever convention your course expects, and the toggle in the app will match it.

10. A quick checklist

1. Identify all functional groups; pick the senior one as suffix.
2. Find the longest chain (or the ring) that contains it — that is the parent.
3. Number to give the principal group the lowest locant, then bonds, then prefixes.
4. Name and alphabetise the remaining groups as prefixes with locants.
5. Add -ene/-yne endings and elide the final -e where needed.
6. Add stereodescriptors (E/Z, R/S) at the front.
7. Read it back: does every locant point where you meant?

Practise these decisions in the Flashcards and Quiz tabs; the Learn tab shows worked examples for each functional-group family.