How does a double bond affect chirality?

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Cis / trans-Isomerism

Cis / trans-Isomerism
When atoms or groups are arranged around a bond that has limited or no rotatability, this is called cis / trans-Isomerism or geometric isomerism.

She occurs at:

  • Double bonds
  • Monocyclic or fused ring systems

Since the cis / trans-Nomenclature is only applicable to a limited extent, is often also the E / Z-Nomenclature used.

Cis / trans-Isomerism of double bonds

Double bonds have a planar structure. The reference plane runs perpendicular to the plane of the paper through the double bond. The substituents are then below and above the reference plane.

Cis / trans-Isomerism of ring systems

In simple cyclic systems, the reference plane lies in the plane of the ring. The substituents are then either on the same or on opposite sides of the plane.

In saturated systems, however, the tetrahedral arrangement of the substituents around the carbon atom causes the ring to bend into a chair or boat conformation. So can cis / trans-Isomers take on both the axial and equatorial positions.