# IUPAC Calculator

Free IUPAC calculator. Generate the systematic IUPAC name for simple organic compounds from chain length, functional group, and substituent positions.

## What this calculates

Generate the IUPAC systematic name for a simple organic compound by entering the parent chain length, the principal functional group, and any methyl or chloro substituents. The calculator applies the standard IUPAC nomenclature rules used in introductory and general organic chemistry courses.

## Inputs

- **Parent Chain Length (carbons)** — min 1, max 20 — Number of carbon atoms in the longest continuous chain. Accepts 1 (methane) through 20 (icosane).
- **Principal Functional Group** — options: Alkane (single bonds only), Alkene (one C=C double bond), Alkyne (one C≡C triple bond), Alcohol (-OH), Aldehyde (-CHO), Ketone (C=O in chain), Carboxylic acid (-COOH), Amine (-NH₂) — The highest-priority functional group sets the suffix in the IUPAC name.
- **Locant for Functional Group** — min 1, max 20 — Position number of the double bond, triple bond, -OH, =O, or -NH₂ on the chain. Ignored for alkanes, aldehydes, and carboxylic acids (which are always at carbon 1).
- **Methyl Substituents (-CH₃)** — min 0, max 6 — Number of methyl branches attached to the parent chain (0-6).
- **Methyl Positions** — options: Position 2, Position 3, Positions 2,2 (two on C2), Positions 2,3, Positions 3,3, Positions 2,2,3, Positions 2,3,3 — Comma-separated locants for the methyl groups. Use the lowest-locant numbering rule.
- **Chloro Substituents (-Cl)** — min 0, max 6 — Number of chlorine atoms attached to the parent chain.
- **Chloro Position** — min 1, max 20 — Locant for the first chloro substituent (used when one or more chloros are present).

## Outputs

- **IUPAC Name** — formatted as text — The generated systematic IUPAC name for the compound.
- **Parent Chain Stem** — formatted as text — The root name derived from the carbon count (meth-, eth-, prop-, but-, pent-, etc.).
- **Functional Group Suffix** — formatted as text — The suffix applied based on the principal functional group.
- **Molecular Formula** — formatted as text — Approximate molecular formula for the parent chain with the principal group applied (ignores branches).

## Details

The IUPAC calculator on this page builds systematic names from three pieces of information: the number of carbons in the longest continuous chain, the highest-priority functional group, and the locants and types of any substituents. It follows the 2013 IUPAC recommendations for preferred names of simple open-chain hydrocarbons and their common derivatives.

**How the IUPAC Calculator Works**

1. Pick the parent chain length from 1 (methane) to 20 (icosane). The stem is the root name, for example **prop-** for three carbons.
2. Select the principal functional group. The group with the highest priority controls the suffix: carboxylic acid beats aldehyde beats ketone beats alcohol beats amine beats alkyne beats alkene beats alkane.
3. Add the locant for the functional group where needed. The calculator numbers from the end that gives the lowest locant to the principal group.
4. Add methyl or chloro substituents. Prefixes are listed alphabetically (chloro before methyl), with di, tri, tetra multipliers for repeated groups.

**Parent Chain Stems (Carbons 1-20)**

| Carbons | Stem | Carbons | Stem |
|---------|------|---------|------|
| 1 | meth- | 11 | undec- |
| 2 | eth- | 12 | dodec- |
| 3 | prop- | 13 | tridec- |
| 4 | but- | 14 | tetradec- |
| 5 | pent- | 15 | pentadec- |
| 6 | hex- | 16 | hexadec- |
| 7 | hept- | 17 | heptadec- |
| 8 | oct- | 18 | octadec- |
| 9 | non- | 19 | nonadec- |
| 10 | dec- | 20 | icos- |

**Suffix by Functional Group**

- Alkane: -ane (propane)
- Alkene: -ene (prop-1-ene)
- Alkyne: -yne (prop-1-yne)
- Alcohol: -ol (propan-1-ol)
- Aldehyde: -al (propanal)
- Ketone: -one (propan-2-one, also known as acetone)
- Carboxylic acid: -oic acid (propanoic acid)
- Amine: -amine (propan-1-amine)

**Worked Example**

A five-carbon chain (pent-) with a methyl branch at position 2 and a ketone at position 3 becomes **2-methylpentan-3-one**. This is the IUPAC-preferred name for the compound commonly referenced in general chemistry textbooks.

**Limits of This Calculator**

This IUPAC calculator handles straight-chain parents up to 20 carbons, one principal functional group at a time, and methyl plus chloro substituents. It does not do rings, stereochemistry (R/S, E/Z), multiple different functional groups, aromatic ring naming, or IUPAC names from SMILES. For those cases, use a full structure-drawing IUPAC tool such as the ones provided by PubChem or ChemDraw.

## Frequently Asked Questions

**Q: What is an IUPAC calculator?**

A: An IUPAC calculator takes structural information about an organic compound and returns the systematic name set out by the International Union of Pure and Applied Chemistry. This one accepts a parent chain length, a principal functional group, and simple methyl or chloro substituents, then produces the preferred IUPAC name using the standard suffix and locant rules.

**Q: Which IUPAC nomenclature rules does this calculator follow?**

A: It follows the 2013 IUPAC recommendations for straight-chain parent names and single-suffix functional groups. Substituent prefixes are listed alphabetically, multiplying prefixes (di, tri, tetra) are applied for identical groups, and locants are placed directly before the part of the name they refer to. Hyphens separate numbers from letters.

**Q: Can this IUPAC calculator name complex molecules with rings or multiple functional groups?**

A: No. This calculator is built for teaching-level examples: open-chain parents up to 20 carbons with one principal functional group. For cyclic systems (cyclohexane, benzene derivatives), compounds with two or more different functional groups, or stereochemistry (R/S, E/Z, cis/trans), use a full structure-based IUPAC naming tool such as PubChem or commercial ChemDraw.

**Q: How does the calculator handle numbering and locants?**

A: The calculator assumes the user has already numbered the chain from the end that gives the principal group the lowest locant, per IUPAC rule. For alkenes and alkynes, the locant goes immediately before the -ene or -yne suffix (prop-1-ene, but-2-yne). For alcohols, ketones, and amines, the locant goes between the parent and the suffix (propan-2-ol, pentan-3-one).

**Q: Why does 2-methylpentan-3-one have the methyl before the ketone in the name?**

A: IUPAC lists substituent prefixes alphabetically before the parent name, then adds the suffix for the principal functional group. The methyl substituent is a prefix, while the ketone is the suffix. Locants go directly in front of the part of the name they describe: 2- for the methyl, 3- for the ketone carbonyl.

**Q: Are common names like acetone or acetic acid accepted by IUPAC?**

A: A small number of common names are retained in the 2013 IUPAC recommendations (acetic acid, formic acid, acetone, formaldehyde), but the preferred IUPAC names are the systematic ones: ethanoic acid, methanoic acid, propan-2-one, methanal. This calculator always returns the systematic form.

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Source: https://vastcalc.com/calculators/chemistry/iupac
Category: Chemistry
Last updated: 2026-04-08