STEREOCHEMICAL REPRESENTATION
Stereochemistry is an important aspect of Organic Chemistry and you must be able to draw structures
which clearly indicate the stereochemical orientation of the various groups on a molecule. For any given
compound there will be a right way and many wrong ways to indicate stereochemistry. This handout
gives examples of the correct way to show stereochemistry for alkenes and for cyclic and acyclic
alkanes. Incorrect examples are also given to illustrate what is not acceptable.
ALKENES: Alkenes contain a carbon-carbon double bond. The carbons are sp2 hybridized, therefore
the geometry at those carbons is trigonal planar: all three substitutents attached to a carbon in a double
bond lie in the same plane and are approximately 120˚ apart from each other. Substituents are either cis
or Z (same side) or trans or E (opposite side) to each other. You cannot draw an alkene in a linear form
and say the groups are cis or trans---it must be drawn correctly.
Correct Incorrect
trans
E
cis
Z
H
H
CH3CHCHCH3---cis
all groups are in the same plane- you don't need
to use dashes and wedges on alkenes unless you are
making a special point about the faces of the alkene
top face
bottom face
CYCLIC ALKANES: Substituents on a cyclic alkane can be either cis or trans to each other. You
should draw the ring in the plane of the paper (solid lines) and use dashes and wedges to show whether
substitutents are above or below the plane of the ring.
Correct Incorrect
cis trans
On occassion you may wish to distinguish the faces of a cycloalkane.
top face
bottom face
a
b
a
b
bb
b
a a
a
