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JME Editor courtesy of Peter Ertl, Novartis

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Useful Commands in JSmol:

1) ALT + mouse drag --> rotate on the screen x y plane

2) CTRL+ ALT + drag mouse --> move horizontally / vertically on the screen x y plane

3) using mouse wheel --> increase / reduce zoom

4) mouse --> rotate in the three dimensions

Background Color

Choose the Alkene Carbons

Choose the Priority

Choose the Configuration

Check Answer

Show All the Configurations


1) to assign the priority, click on "Initialize".

2) click on the double bond carbons in JSMol and click on the "C1=C2" button

3) repeat the point 2 assigning the respective priority to the high priority on every carbon of the double bond

4) Assign the isomerism E or Z to both double bond carbons and click on Check Configuration

In the case there are more double bonds with E/Z isomerism:

5) repeat the points 2, 3 and 4 for all the alkene carbons

6) click on "Check all the Configurations"

  • E / Z Configurations

  • Sequence Rules

    Sequence Rules



    Assign the priority order to the susbtituents on the asymmetric carbon according to the Cahn-Ingold-Prelog rules.


    1. For every substituent, look at the first atom linked to the asymmetric carbon: the atom having the highest atomic number has the highest priority
    2. If it is not possible to define all the priorities in this way, look at the second atom away form the double bond carbon atom, and so on, until a point of difference can be found.
    3. The atoms having multiple bonds are equivalents to the same number of atoms linked by single bonds.


  • Configuration Assignment

    Configuration Assignment - 2


    Observe the two carbon of the double bond separately. Look at the substituents on each carbon atom. Si osservano i due carboni del gruppo alchenico e i loro sostituenti.

    Consider the relative priority between the two substituents on each double bond carbon atom, following the Cahn-Ingold-Prelog rules.

    If the groups having the highest priority for each double bond carbon atom are placed on the same side the configuration is Z (Zusammen, "together")

    If the groups having the highest priority for each double bond carbon atom are placed on opposite sides the configuration is E (Entgegen, "opposite")