Reaction Arrows

The reaction arrow is the horizontal arrow you place between reactants and products. Unlike a plain straight arrow, it carries two text zones, one above the shaft and one below, for reagents, catalysts, and conditions. The text zones travel with the arrow and stay centered as you move or resize it. Retrosynthesis arrows have the same text zones and behave the same way; see Special arrows.

Drawing a reaction arrow

Click the arrow button in the toolbar and pick Reaction Arrow from the flyout. Drag on the canvas from start to end; release to place the arrow. A short click without a drag places a default-length arrow instead.

Press A to activate the arrow tool from the keyboard, then press 6 to switch to the reaction arrow variant.

When you finish drawing, the text editor for the above zone opens automatically so you can type the reagents right away. Press Escape if you want to leave it empty.

Adding reagents and conditions

Double-click a text zone to edit it. Double-clicking anywhere else on the arrow also works and opens the above zone. While the editor is open:

Tab jumps to the other zone (if it is enabled)
Enter inserts a line break
Escape or Ctrl+Enter saves and closes

Only the above zone is on by default. To use the below zone, select the arrow and check Below in the Text Zones section of the Shape Properties panel.

Formatting

Zone text supports the same rich formatting as regular text annotations: Ctrl+B, Ctrl+I, and Ctrl+U toggle bold, italic, and underline, and the formatting toolbar gives you subscript, superscript, font, and color controls. See Text annotations for the full set.

Chemistry shortcuts

A few backslash codes expand to common symbols when the text is saved: \Delta or \heat becomes Δ, \hv becomes hν, \cat becomes cat., \rt becomes r.t., \eq becomes ⇌, and \arrow becomes →.

Resizing and moving

Use the Select tool to work with a placed arrow:

Move: drag the shaft. Both text zones move with it.
Resize: drag either white endpoint handle to lengthen, shorten, or re-angle the arrow. The text zones recenter on the new midpoint automatically.

The zones are anchored to the arrow itself, not to fixed canvas positions, so you never need to reposition text after adjusting the arrow.

Spacing and centering

The Text Zones section of the Shape Properties panel controls layout:

Gap sliders: set the distance between the shaft and each zone, 1 to 40 px, independently for above and below.
Center: choose whether text centers on the full arrow (endpoint midpoint) or on the shaft only, which excludes the arrowhead length. Shaft centering looks better on short arrows with large heads.

Cofactor arc

The Shape Properties Panel can add a cofactor arc to a reaction arrow: a small curved arrow that arcs over (or under) the shaft and touches it at the midpoint, the standard notation for coupled species such as NAD+/NADH in biochemical schemes. Select the arrow and check Enabled in the Cofactor Arc section, then choose Above or Below for which side the arc sits on. The Span slider (20 to 90%) sets how much of the shaft the arc covers. The same section also appears for straight and retrosynthesis arrows.