Automatic Plus Signs in Single step Reactions

    {warning} The Automatic Plus Signs in Single Step Reactions option in Preferences dialog is ON.

    This setting ensures that once a reaction arrow has been drawn, non-movable plus signs between reactants and product molecules are placed automatically.

    To place a reaction arrow

    • Choose the Arrow/Reaction/Atom Map button. You will see the reaction arrow on the tip of the cursor when you move the mouse into the canvas area.

    • Click the location of the tail of the arrow.

    • Drag the mouse and release at the location of the head.

    Reaction arrows snap every 7.5 degree. Pressing 'Shift' enables the free rotation of reaction arrows.

    You can place a reaction arrow on the canvas at any time, even on a blank canvas.

    The length and the direction of the arrow can be changed.

    {warning} If you draw a second reaction arrow, the + signs become movable and erasable, and the content of canvas is handled as graphical model.


    Once the reaction arrow has been placed on the canvas, MarvinSketch automatically puts plus signs between reactants and product molecules.

    To avoid plus signs between specific reactants and/or products, select the relevant fragments and use the Structure > Reaction > Merge Reactants (Products) menu option.

    To remove one or more molecules from such a merged item, select the relevant molecules and go to Structure > Reaction > Unmerge Reactants (Products).


    You can align and/or distribute the objects of the reaction scheme by selecting the relevant option in Edit > Object menu.

    Note that selected agent fragments and texts are moved together with the arrow while keeping the distance between them.


    Single step reaction will be automatically saved as a "reaction file" .

    In that case, only those file formats are available in the File<Save dialog which support reactions (MRV, CXSMILES, CXSMARTS, CSRXN, RXN, RDF, SMILES, SMARTS, CML, CDX, SKC ).

    In the exported file separate blocks are created for reactants, products and agents so that it can be used in reaction search.