Athanor by arbastro
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How to mark stereo groups (AND, OR, absolute)

Select the drawn stereocenters and choose Object › Stereo group: absolute, Stereo group: new AND (racemic) or Stereo group: new OR (one of two, unknown which). Stereo group: clear removes the mark.

Steps

  1. Draw the stereocenter with a wedge or hash first. A stereo group says what the drawn configuration means; on an undrawn center it does nothing, and Athanor says "None of the selected atoms is a stereocenter with a drawn configuration".
  2. Select the structure, or just its stereocenters.
  3. Choose one from Main menu › Object:
Command Means Label
Stereo group: absolute The configuration is exactly as drawn none
Stereo group: new AND Both configurations are present: a racemic mixture &1, &2 …
Stereo group: new OR One of the two, but it is not known which or1, or2 …
Stereo group: clear Removes the group

(S)-butan-2-ol marked as a racemic AND group, labeled &1.(S)-butan-2-ol marked as a racemic AND group, labeled &1.

Each new command starts another numbered group, so two centers can be racemic independently of each other.

Drawing basicsHow to draw wedge and hash bondsWith the Bond tool, press U for wedge, H for hash or Y for wavy, then click a bond to change it or click empty canvas to draw a new one. The narrow end sits on the stereocenter. View › Show stereochemistry labels each center R or S.Atoms, bonds and ringsHow to list every stereoisomer of a structureSelect the structure and choose Object › Chemistry › Stereoisomers. Every stereoisomer is listed with its own R/S and E/Z, meso forms counted once; press Place on one or Place all.

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Last updated Nov 12, 2026