3D Molecule Builder Online, free molecule editor with OCL
Place atoms, draw bonds, and the molecular formula and molar mass sit right next to them. The name search knows 52 compounds with a stored structure, from water to cholesterol. Everything is computed in the browser, with no account and no install.
- 118
- elements to pick from, so the periodic table is complete.
- 52
- compounds the name search finds and places on the canvas ready-made.
- €0
- to build, rotate and export an image. You only need an account for flashcards.
The builder
The canvas opens from a window width of 1024 pixels. Below that you get a notice here, because the element picker, the bond tools and the 3D view sit side by side.
A molecule in three moves
- 1
Pick an element or type a name
The periodic table sits on the left, one click drops the atom onto the canvas. If you want to be faster, type a name into the search field, caffeine for example, and you get the stored structure.
- 2
Draw bonds and read along
Dragging from atom to atom sets a bond, another click makes it double, triple or aromatic. The molecular formula and the molar mass change with every move, so you see a mistake right away instead of in the marked exam.
- 3
Rotate, export, learn
In the 3D view you rotate the molecule with the mouse and see which groups really sit next to each other. The picture comes out as a PNG, and from a recognised compound Quanta builds two flashcards.
Three molecules to test the builder on
Type the name into the search or the SMILES line into the input field. Both routes lead to the same structure.
| Compound | SMILES | Formula | What tells you it is right |
|---|---|---|---|
| Caffeine | Cn1cnc2c1c(=O)n(C)c(=O)n2C | C₈H₁₀N₄O₂ | Two fused rings with four nitrogen atoms. This is where you see whether a program recognises an aromatic ring as such or draws it as a chain with double bonds. |
| Aspirin | CC(=O)Oc1ccccc1C(O)=O | C₉H₈O₄ | An ester group right next to a carboxylic acid on the same ring. Those two are the pair students mix up in exams, and in the 3D view they visibly sit apart. |
| Glucose | OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O | C₆H₁₂O₆ | Four fixed stereocentres, written as [C@H] and [C@@H] in the SMILES line, with the anomeric centre left open. Rotate the ring and you see which OH group points up. |
What OpenChemLib computes underneath
The chemistry under the builder comes from OpenChemLib, an open-source library under the BSD-3-Clause licence. It reads the SMILES line, generates two-dimensional coordinates from it, computes the three-dimensional ones for the rotating view and derives the molecular formula and molar mass from the structure rather than from a lookup table.
SMILES is a text notation for molecular structures, described by Weininger in 1988 in the Journal of Chemical Information and Computer Sciences. c1ccccc1 is benzene, CCO is ethanol, CC(=O)O is acetic acid. Lower-case letters mark aromatic atoms, the equals sign a double bond, the hash a triple bond.
After you draw, auto-clean rearranges the structure so bond angles and ring geometry match the usual depiction. That is why a six-membered ring thrown down by hand ends up looking like a six-membered ring.
Where the builder stops
Four points you are better off knowing beforehand than after ten minutes of searching.
- Below a window width of 1024 pixels the page shows a notice instead of the canvas. On a phone you read this text; you build on a computer.
- The flashcard button only appears for a compound the builder recognises from its own list. For a structure you drew yourself that it does not know, the button stays away, because the card would otherwise show a different notation than your picture.
- The builder does not compute reactions, equilibria or kinetics. It assembles structures and does not simulate chemistry.
- The structure stays in the browser and is not sent to a server. Only when you turn it into flashcards does it travel into your Quanta account.
From the molecule to a flashcard
With a recognised compound on the canvas, Quanta turns it into two flashcards: one shows the structure and asks for the name, the other shows the name and asks you to draw the structure. The back carries the molecular formula and the molar mass from the same computation you saw in the analysis panel a second earlier.
They are then studied with FSRS-6 (Ye et al. 2022, ACM SIGKDD). That route runs through signing up; the builder itself needs no account.
Frequently asked questions about the molecule builder
What is the Quanta 3D molecule builder?
Which molecules can I draw in the 3D molecule builder?
Is the 3D molecule builder free and usable without an account?
What is OCL / OpenChemLib?
Why does the builder not work on my phone?
The other two tools
Both also run in the browser and both also work without an account.
- Structural formula generator
SMILES to a 2D structural formula, with compound search and PNG export. Works on a phone too.
- LaTeX formula editor
Render formulas live, with quick insert for physics, chemistry and maths.
- Formula sheet
The collection behind the editor, every formula with its source and a worked example.