Instructions are reported at the bottom of the page

JME Editor courtesy of Peter Ertl, Novartis

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Useful commands in JSmol:

1) ALT + mouse --> rotate in the plan (x y)

2) CTRL+ ALT + mouse --> move to the screen plan (x y)

3) mouse wheel --> zoom in and out

4) left click and drag mouse --> rotate in the three dimensions

Background Colour

Choose the Alkene Carbons

Choose the Priorities

Choose the Configuration

Check Answer

Show all 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"

Configurations E / Z

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.