MolDraw › Chemistry tools › Functional Group Identifier
Functional Group Identifier
In short: Draw a molecule or paste its SMILES. Every functional group is highlighted in colour and named, with its IUPAC priority, suffix and prefix.
Good for learning organic chemistry, checking drug structures and starting an IUPAC name: the highest-priority group gives the name its ending, and every other group becomes a prefix.
CC(=O)Oc1ccccc1C(=O)O, has a carboxylic acid, an ester and a benzene ring. The carboxylic acid is the principal group, so the name ends in -oic acid: 2-acetyloxybenzoic acid.Loading editor…
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How to use the functional group identifier
- Draw the molecule or paste its SMILES and press Enter.
- Each group is shaded in its own colour on the drawing.
- The table lists every group with its type (for example secondary alcohol or tertiary amine), its seniority for naming, and how it appears in an IUPAC name.
- The principal characteristic group gives the suffix of the name.
Functional group priority order for IUPAC naming
When a molecule has more than one group, the one highest in this list is the principal characteristic group. It is named as a suffix; the others become prefixes.
| Rank | Group | Example | Suffix | Prefix |
|---|---|---|---|---|
| 1 | Carboxylic acid | CH₃COOH | -oic acid | carboxy- |
| 2 | Sulfonic acid | C₆H₅SO₃H | -sulfonic acid | sulfo- |
| 3 | Acid anhydride | (CH₃CO)₂O | -oic anhydride | — |
| 4 | Ester | CH₃COOCH₃ | -oate | alkoxycarbonyl- |
| 5 | Acid halide (acyl halide) | CH₃COCl | -oyl halide | halocarbonyl- |
| 6 | Amide | CH₃CONH₂ | -amide | carbamoyl- |
| 7 | Nitrile (cyanide) | CH₃CN | -nitrile | cyano- |
| 8 | Aldehyde | CH₃CHO | -al | formyl- / oxo- |
| 9 | Ketone | CH₃COCH₃ | -one | oxo- |
| 10 | Alcohol | C₂H₅OH | -ol | hydroxy- |
| 10 | Phenol | C₆H₅OH | -ol | hydroxy- |
| 11 | Thiol | CH₃SH | -thiol | sulfanyl- |
| 12 | Amine | CH₃NH₂ | -amine | amino- |
| 13 | Imine | CH₃CH=NH | -imine | imino- |
Groups that are always prefixes (or part of the parent name)
| Group | Example | In the parent name | Prefix |
|---|---|---|---|
| Nitro | CH₃NO₂ | — | nitro- |
| Ether | CH₃OCH₃ | — | alkoxy- |
| Sulfide (thioether) | CH₃SCH₃ | — | alkylsulfanyl- |
| Halide | CH₃Cl | — | fluoro-, chloro-, bromo-, iodo- |
| Alkyne (C≡C) | HC≡CH | -yne | ynyl- |
| Alkene (C=C) | CH₂=CH₂ | -ene | enyl- |
| Aromatic ring (arene) | C₆H₆ | — | phenyl- / aryl- |
Short memory aid for exams: acid > anhydride > ester > acid halide > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne. (Alkene and alkyne are not suffix groups: they change -ane to -ene or -yne.)
Primary, secondary and tertiary
- Alcohols and alkyl halides are classified by the carbon carrying the OH or halogen: 1° if it is bonded to one other carbon, 2° for two, 3° for three.
- Amines and amides are classified by the nitrogen: 1° (NH₂), 2° (NH), 3° (no N–H).
- A halogen on a benzene ring is an aryl halide; on a C=C it is a vinyl halide. Both behave very differently from alkyl halides in SN1/SN2 reactions.
Worked examples
Paracetamol
Secondary amide, phenol and benzene ring. The amide outranks the phenol.
N-(4-hydroxyphenyl)acetamide
Ethyl acetoacetate
Ester and ketone. The ester is the principal group; the ketone becomes the prefix "oxo".
ethyl 3-oxobutanoate
Adrenaline
Two phenol OH groups, a secondary alcohol and a secondary amine. Alcohols and phenols outrank amines.
4-[1-hydroxy-2-(methylamino)ethyl]benzene-1,2-diol
Common mistakes
- Calling the O in an ester an ether. The C(=O)–O–C unit is one ester group.
- Calling an amide an amine plus a ketone. C(=O)–N is one amide group.
- Calling an OH on a benzene ring an alcohol. It is a phenol, which is far more acidic.
- Using the size of a group to choose the suffix. Only the priority list matters.
Draw it properly. Open the structure in the free MolDraw editor to add wedges, arrows and labels, then export a PNG or SVG for notes and slides.
Open full MolDraw editorFrequently asked questions
What is a functional group?
A specific group of atoms, such as –OH, –COOH or –NH₂, that gives a molecule its typical reactions and properties.
Which functional group has the highest priority?
Carboxylic acids, followed by sulfonic acids, anhydrides, esters, acid halides, amides, nitriles, aldehydes, ketones, alcohols and amines.
How do I find functional groups in a structure?
Draw the molecule or paste its SMILES into the tool. Each group is highlighted in colour and listed with its name and type.
Are alkenes and alkynes functional groups?
Yes, but in IUPAC names they are not suffix groups. They change the ending of the parent chain from -ane to -ene or -yne.
What is the difference between a phenol and an alcohol?
In a phenol the OH is attached directly to a benzene ring; in an alcohol it is on an sp³ carbon. Phenols are much more acidic (pKa about 10 versus about 16).
Is the functional group identifier free?
Yes. It runs in your browser with no sign-up.
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