ChemWriter Drawing Constraints
Last Updated on Friday, March 07, 2008.
Better-Looking Drawings… Faster
ChemWriter makes it easy to create attractive chemical structures with regular bond angles and lengths. A system of intelligent geometry constraints can assign correct bond angles in most cases. For the exceptional cases, ChemWriter lets you override these constraints to get exactly the result you need.
Plant and Pivot
If you click on the canvas area with the bond tool and then drag the mouse, you’ll notice that the placement of the second atom in the bond is constrained around a predefined set of coordinates. Although suitable for most chemical structures, some situations require less constrained atom placement. ChemWriter offers three levels of bond geometry constraint:
- Drag only. The bond length is fixed, but the bond angle can vary among pre-set values.
- Control-Drag. The bond length is not fixed, but the bond angle is.
- Shift-Drag. Both the bond length and bond angle are unconstrained.
New ring geometry can be determined analogously either through predefined angle constraints (Drag Only), or from the mouse (Shift-Drag).
Sprouting and Fusing Rings
New rings can be formed at an existing atom by clicking with a ring tool. Alternatively, the ‘a’ keyboard shortcut can be used to create a benzene ring. Depending on the valence of the atom being clicked, a new ring is either sprouted or fused:
- Sprouted Ring. The new ring is connected to the clicked atom, but doesn’t contain it.
- Fused Ring. The new ring inorporates the atom that was clicked.
For example, pressing the ‘a’ key while hovered over the oxygen atom of methanol creates anisole, while pressing the ‘a’ key while hovered over either carbon atom of ethane produces toluene.
Fuse to Skeleton
Sometimes the purpose of a bond is to connect two existing atoms. ChemWriter enables this type of bond by allowing a new bond to be fused to the existing structure skeleton.