Build a reaction scheme

Put the reaction on the page

Draw or import the molecules. Put reactants on the left and products on the right.
Choose the arrow tool. Click to place a fixed-length arrow pointing right, or drag to set its length and direction.
Choose Text (T), click above or below the arrow and type the conditions.
Select related objects and use Properties to align them.

A complete esterification scheme with conditions above the reaction arrow.

Keep conditions on the arrow

Text you type or drop above or below a straight arrow attaches to it. Existing text beside an arrow attaches when you move it. The text stays centred on its side, and the arrow grows to fit the widest label with a little padding at each end.

Edit the text: an arrow fitted to the text grows or shrinks with it. An arrow you lengthened by hand keeps its length unless the text outgrows it.
Drag an end handle to lengthen the arrow. Shortening stops at the label width.
Move or rotate the arrow: its labels come along.
Drag the text across the arrow to switch sides, or away from it to detach it.
Copy, cut or delete the selected arrow: its conditions go with it. The eraser removes only what it touches.

Each side holds one label; press Enter in the text for more lines. Bending the arrow releases its labels. Only .rsk files keep the link; other formats keep the text where it is.

Bend an arrow

Click the arrow tool to reuse the current style. Hold it briefly or click its lower-right triangle to open the palette. Choose Curved / electron pair, Single electron, or Bent / elbow for electron flow and bent arrows. The palette also offers bold, dashed, hollow, and unequal equilibrium arrows.

The arrow palette includes bent, curved, equilibrium, and retrosynthesis arrows.

Select the arrow. Drag the diamond to bend it, or to move the corner of a bent arrow. A curved arrow also has a square handle on a line from each end. Drag a square to change how the arrow leaves or arrives; both ends stay where they are. Drag a round end handle to move that end. Properties provides Reverse, Flip bend, Straighten, and stroke settings. Expand Arrowhead & markers for head geometry, dipole crosses, and no-reaction markers.

With an arrow tool active, click an existing arrow to change its style. Repeated clicks with the same style cycle its variants: reverse the direction, change the side of a half-head, or switch the longer line of an unequal equilibrium arrow.

A selected curved arrow from a methoxide oxygen to a carbonyl carbon, with its diamond bend handle, two square direction handles and the arrow properties.

Point an arrow at atoms

Choose Curved / electron pair or Single electron. Attach ends to atoms and bonds in Properties is on by default.
Click where the arrow starts: an atom, a bond or a lone pair. ReShiki highlights it.
Click where the arrow ends. ReShiki adds the arrow in one Undo step.

The arrow follows its targets when they move. To draw a free arrow, Option/Alt-click, drag, or turn off Attach ends to atoms and bonds. Escape cancels a picked start. To release one end, select the arrow and choose Detach start or Detach end in Properties.

Only .rsk files keep the links between an arrow and its targets. Other formats keep the arrow’s shape.

Make the reaction exportable

The drawing can also carry explicit reactant, product, and reagent roles:

Select an arrow and open Properties → Reaction roles….
Select a molecule, then + Assign selected molecules under its role.
Repeat for the remaining molecules.

The reaction inspector assigns reactant, product, and reagent roles.

Use RXN or Reaction SMILES to export the chemical reaction. Captions and page layout belong in .rsk, SVG, PDF, or PNG instead.

Use Open for an RXN file. Use Import to paste RXN text or reaction SMILES. Reaction roles do not check reaction balance or predict products.

Map atoms between reactants and products

Atom maps number the atoms that correspond between reactants and products.

Assign reactants and products first. The Atom maps section below the roles then shows how many atoms are mapped.
To set one map, select one atom, type a number in Atom map and choose Set. You can also right-click an atom and choose Edit atom map….
To pair two atoms, select one reactant atom and one product atom, then choose Pair selected atoms.
To map the rest, choose Auto-map. Review atom maps lists each suggested pair; click a row to select that pair in the drawing.
Choose Apply maps to keep the suggestion, or Discard.
Choose Align mapped structures to turn and move each product so that its mapped atoms line up with the reactants.

Show maps shows or hides the map numbers. Move labels lets you drag the numbers; press Escape when you are done. Reset label positions returns them to automatic placement. Each edit is one Undo step.

Ethanol oxidized to acetaldehyde with map numbers 1, 2 and 3 on both sides, and the Atom maps section of Reaction roles showing six mapped atoms.

Auto-map compares structures only; it does not predict a reaction mechanism. It keeps the maps you set and does not map reagents. RXN and reaction SMILES keep the map numbers. Save a .rsk file to keep custom label positions too.

Let the assistant draft a scheme →

Open the esterification example.