Equilibrium, Retrosynthesis, Arc & Block Arrows
Beyond straight, curved, and reaction arrows, Molkit includes paired equilibrium arrows, the open retrosynthesis arrow, circular arc arrows, and filled block arrow shapes. The first three live in the arrow tool flyout (A selects the arrow tool). Block arrows are shapes and live in the shape tool flyout.
Equilibrium and double harpoon arrows
Molkit has two paired arrow types. Equilibrium draws two parallel full-headed arrows pointing in opposite directions. Double Harpoon draws the standard equilibrium symbol: two half-headed harpoons, the top barb pointing right and the bottom barb pointing left. With the arrow tool active, press 7 for Equilibrium or 8 for Double Harpoon, or pick either from the flyout, then drag to draw.
When selected, both types show an endpoint handle at each end plus a rotation handle. Drag an endpoint to change length or angle; drag the body to move the pair as a unit.
Unequal-length variants are built from the same arrow in the Shape Properties panel:
- Top and Bottom length fields set each arrow’s length independently. A lock button links them so they change together while keeping their difference.
- When the lengths differ, a Shift slider (-100% to 100%) appears and slides the shorter arrow along the axis.
- Gap (1 to 20 px) sets the spacing between the two shafts.
The panel also offers separate stem and head colors for the top and bottom arrows.
Retrosynthesis arrows
The retrosynthesis arrow is an open double-shaft arrow: two parallel lines that converge into a hollow open head. Select it in the arrow flyout and drag to draw. It supports the same text zones above and below the shaft as reaction arrows.
Selected retrosynthesis arrows get endpoint handles and a rotation handle. The Shape Properties panel replaces the usual arrowhead style options with retro-specific controls:
- Gap sets the distance between the two shafts (default 6 px).
- Angle (15 to 60 degrees) sets the barb angle of the head.
- Curved head toggles concave head edges, with a curvature slider (5% to 45%).
- Stroke width uses finer 0.1 px steps, with a 1 px default.
Arc arrows
The arc arrow draws along part of a circle. Pick Arc Arrow from the arrow flyout, then drag: your drag becomes the diameter of a semicircle. The arrow is stored as a center, radius, and start and end angles rather than two endpoints.
When selected, an arc arrow shows a selection box plus two gold diamond handles at the arc ends. Drag either handle around the center to extend or shorten the sweep. The radius is set with the Radius slider (10 to 300) in the Arc section of the Shape Properties panel. Arrowhead style and size controls work as on other arrows.
Arc arrows do not snap or attach to atoms or bonds; they stay exactly where you draw them. A headless plain Arc is also available in the shape flyout (press 4 with the shape tool active).
Block arrows
Block arrows are filled shapes, not arrow annotations. The shape flyout includes Arrow Block, Double Arrow, Curved Arrow, U-Turn Arrow, and the related Chevron. Drag to size one like any shape: Shift constrains proportions, Alt draws from the center, and a plain click places a 60 by 60 default.
They resize with the standard corner and edge handles, rotate with the rotation handle, and take fill and stroke styling. Each variant adds gold diamond adjustment handles:
- Arrow Block and Double Arrow: shaft thickness and head length.
- Curved Arrow: shaft thickness, head length, curve depth, and head width.
- U-Turn Arrow: leg width, head length, and barb width.
- Chevron: notch depth.
Shadow and glow effects are not available on the Curved Arrow and U-Turn Arrow blocks.