Repository navigation
Rings and Chains
This page explains straight and flexible chains, ring templates, fusion, and the valence checks that protect existing structures.
The Main Toolbar includes a Chain Tool, Flexible Chain Tool, and templates for cyclopentane, cyclohexane, benzene, and two chair cyclohexane orientations. The Chain Tool has shortcut C; cyclopentane has R. Choose a template and click blank space for a separate ring, or click an atom to attach it.
Press and drag with the Chain Tool on the canvas or an atom. The drag length determines the carbon count. Its first bond follows the standard 15° angle snap; hold Option on macOS or Alt on Windows for free-angle aiming. When dragging from an atom, normal bond length is retained until the custom-length breakaway, after which the aimed length is retained.
The Flexible Chain Tool is intentionally different. Drag its path as you want the zig-zag to run; it bends to follow the pointer rather than snapping to the angle grid. Both modes create native molecular atoms and bonds, so they are subject to the same valence checks as a hand-drawn bond.
Click an atom to attach a ring sharing that atom; click a bond to attempt a fused placement. A normal click selects and places a ring, while a long press on the toolbar item opens the ring flyout. The preview is significant: it uses the same placement plan as the final action.
If a ring cannot attach safely, ChemDraft places it separately and reports the reason instead of changing the existing molecule. Reasons can include no free valence at an atom, no free valence at a bond endpoint, a ring closure onto an atom with no free valence, or double-bond re-pairing that would overfill a neighboring atom. The same protection applies to ring hover hotkeys and to a cyclic-bond closure.
This matters for realistic edge cases. A one-bond OMe label is already full at its attachment point; a fusion there is refused. A spiro placement is not rejected merely because it is spiro: it is tested against the actual element, charge, label reading, bond-order use, and radicals.
Ring templates and fused systems remain editable molecular objects.
When the pointer is over a native atom, the numeric drawing keys are context actions: 0 cyclic bond, 1 single bond, 2 carbonyl, 3 benzene, 4 wedge bond, 5 hashed wedge bond, 6 cyclohexane, 7 cyclopentane, 8 methylidene, and 9 gem-dimethyl. Hovering a bond uses a related context set for bond order and ring fusion. These keys are not replacements for a ring template on the toolbar; they are faster operations on an identified atom or bond. A refusal leaves the document unchanged.
Use Structure > Clean up Structure 2D for the registered 2D cleanup command. It is separate from drawing a ring and should not be used as a way to repair an overfilled structure: ChemDraft prevents that error at placement time. For group-label attachment behavior, see Atoms and Labels. For molecules arranged as a figure, see Compound Layouts.