MolDraw Learn

How to map atoms in a reaction

Beginner 4 min 2 steps

Short answer: Draw a simple reaction here, then number matching atoms with Automap in the full editor.

You will learn to: Draw a reaction with an arrow; Run Automap.

1 Watch demo2 Try in editor

Watch the demo

A reaction in about 15 seconds.

The steps in text

Step 1: Draw ethene to ethane

  1. Draw ethene: one bond, then make it double with Double from the bond menu.
  2. Pick the reaction arrow tool. Drag to the right of ethene.
  3. Draw a single bond right of the arrow.

Step 2: Run Automap

  1. Open the full editor in a new tab.
  2. Draw the same reaction.
  3. Open the Chemistry menu. Click Automap.
  4. Each atom now shows a number. The same number marks the same atom on both sides.
  5. Come back and click

Try it in the editor

The full MolDraw editor opens here. It loads when you open this tab.

Questions and answers

What is atom mapping?

It numbers each reactant atom and the product atom it becomes.

Why map atoms?

Maps help track bonds that form and break. Reaction databases use them.

For more detail, read the guide in the docs.