Orphan atoms

    When a map number appears only on one side of the reaction scheme , it marks an orphan atom.

    An orphan atom on the reactant side is removed, an orphan atom on the product side is added during the reaction.

    Take the reaction

    images/download/thumbnails/20417955/image2019-8-12_14-49-26.png

    Actual reaction according to the definition above

    images/download/thumbnails/20417955/image2019-8-12_14-50-6.png

    {primary} If a reaction includes substitution of a hydrogen on a carbon atom, the hydrogens should be expressed as explicit hydrogen atoms and marked as orphan atoms. Thus substitution only occurs on these explicit hydrogens.