---
title: Curved arrow mechanisms
url: https://www.moldraw.com/docs/reactions/how-to-draw-curved-arrow-mechanisms-and-fishhook-arrows/
section: Reactions and schemes
updated: 2026-10-20
publisher: LabCanvas
---

# Curved arrow mechanisms

> Pick the Reaction arrow tool, open the menu beside it and choose Electron flow (2e⁻) or Fishhook (1e⁻) under Mechanism. Drag from a lone pair, bond or atom to the atom or bond that receives the electrons. The arrow snaps to the structure and moves with it.

Curved arrows show where electrons go in a mechanism. MolDraw has two kinds. A **curved arrow** with a full head moves two electrons. A **fishhook** with a half head moves one electron, as in radical steps. For straight scheme arrows and reagent text, see [Reaction arrows](https://www.moldraw.com/docs/reactions/how-to-draw-reaction-arrows-with-reagents/).

1. Click the small menu beside **Reaction Arrow** in the left tool rail. Its name is **Reaction arrow style**.
2. Under **Mechanism**, pick **Electron flow (2e⁻)** or **Fishhook (1e⁻)**.
3. Point at the electron source. A highlight shows the lone pair, bond or atom the tail will sit on.
4. Drag to the target atom or bond and release. You can also click the start, then click the end.
5. To change the curve, click the arrow and drag its middle handle.

## Where the ends go

| End | Snaps to | Tip |
|---|---|---|
| Tail (start) | Lone pair, bond or atom | Point at O, N or a halide and the tail starts on its nearest lone pair. This works even when the pairs are not drawn. |
| Head (end) | Atom or bond | The head never lands on the tail's own atom or bond. On an atom, it sits on the side that faces the tail. |

A bond as the tail means the bonding pair moves. A bond to one of its own atoms, like C=O to O, gives a clear arc beside the bond. Away from any structure, an end stays where you release it.

> **Tip:** Hold `Alt` while you drag to place an end freely, without snapping.

## Adjust an arrow

- **Curve:** a new arrow bulges away from the structure. Click the arrow, then drag the middle handle to bend it more, less or to the other side.
- **Ends:** drag an end handle to move it. It snaps again to a new lone pair, bond or atom.
- **Follow the structure:** snapped ends stay attached. Drag the molecule and its arrows move with it.
- **Style:** pick the arrow tool with nothing selected to see the **Electron flow** panel. It sets **Head** (Filled, Open, Fishhook, None), **Tail** (None, Bar, Reverse, Circle) and **Head size**. For an arrow you already drew, select it and open **Color & style**.

## The snap setting

Open **Settings**, then **General**. In the **Canvas** group, **Snap curved arrows** is on by default. Turn it off to place every end freely. See the [settings reference](https://www.moldraw.com/docs/settings/moldraw-settings-reference/) for the other canvas options.

## Multistep mechanisms

1. Draw each species from left to right: starting material, intermediates, product.
2. Join the steps with a **Straight** arrow from the **Scheme** group of the same menu.
3. Add the curved arrows on the structures before the step they explain.
4. Turn on **Snap to grid** in **Settings**, **General**, **Canvas** to line the steps up.

Curved and fishhook arrows are display only. They do not split the drawing into reactants and products, so reaction SMILES, [Automap](https://www.moldraw.com/docs/reactions/how-to-map-atoms-in-a-reaction-with-automap/) and the [stoichiometry table](https://www.moldraw.com/docs/reactions/how-to-use-the-reaction-stoichiometry-table/) ignore them.

To start faster, place a ready mechanism from [mechanism templates](https://www.moldraw.com/docs/library/how-to-use-mechanism-and-reaction-setup-templates/), or write it as text in [MolScript](https://www.moldraw.com/docs/developers/molscript-language-for-reactions-and-mechanisms/). The [AI assistant](https://www.moldraw.com/docs/ai/how-to-use-the-ai-chemistry-assistant/) can also draw a mechanism from a request.

## Common problems

| Problem | Fix |
|---|---|
| The tail starts on the wrong pair | Move the pointer closer to the pair you want before you press. |
| The arrow will not attach | Check that **Snap curved arrows** is on, and that you are not holding `Alt`. |
| You drew a plain curved arrow | **Curved** in the **Scheme** group is a bent reaction arrow. Pick **Electron flow (2e⁻)** under **Mechanism** instead. |

For the rules of arrow pushing, read the [curly arrow guide](https://www.moldraw.com/blog/arrow-pushing-curly-arrows-guide.html). To practise, try the [arrow pushing practice tool](https://www.moldraw.com/tools/free-chem-tools/arrow-pushing-mechanism-practice.html).

## Questions and answers

**How do I draw a fishhook arrow in MolDraw?**
Open the menu beside the Reaction Arrow tool and pick Fishhook (1e⁻) under Mechanism. Drag from the bond or electron that moves to the atom that receives it.

**Do I need to draw lone pairs before a curved arrow?**
No. Point at a heteroatom and the tail starts on its nearest lone pair position. Draw the pairs if you want students to see the dots.

**How do I stop curved arrows snapping to atoms?**
Hold Alt while you drag to place one end freely. To turn snapping off for good, switch off Snap curved arrows in Settings, General, Canvas.

**Why do my curved arrows move when I move the molecule?**
Snapped ends are attached to the lone pair, bond or atom. This keeps the mechanism correct when you rearrange the drawing.

**Can I change a curved arrow into a fishhook later?**
Yes. Select the arrow, open Color & style and set Head to Fishhook.

## Practice it

- Interactive lesson: [How to draw curved arrow mechanisms](https://www.moldraw.com/learn/how-to-draw-curved-arrow-reaction-mechanisms/)

## Related pages

- [Reaction arrows](https://www.moldraw.com/docs/reactions/how-to-draw-reaction-arrows-with-reagents/)
- [Lone pairs, radicals and charges](https://www.moldraw.com/docs/drawing/how-to-add-lone-pairs-radicals-and-formal-charges/)
- [Templates panel](https://www.moldraw.com/docs/library/how-to-use-mechanism-and-reaction-setup-templates/)
- [MolScript](https://www.moldraw.com/docs/developers/molscript-language-for-reactions-and-mechanisms/)