IB Chemistry›Structure 3›3.2›3.2.7
HL

Stereoisomers

Same connectivity, different spatial arrangement.

A. Cis-Trans (Geometric) Isomerism

Occurs in alkenes or cyclic compounds.

Conditions

  • Restricted Rotation: Due to \(\pi\) bond or ring.
  • Distinct Groups: Each carbon must have two different groups.

Forms

  • Cis (Z): High priority groups on the same side.
  • Trans (E): High priority groups on opposite sides.

B. Optical Isomerism (Chirality)

The Chiral Center

A Carbon atom bonded to 4 different groups.

Key Properties

  • Enantiomers: Non-superimposable mirror images (like left and right hands).
  • Optical Activity: Rotate plane-polarized light in equal but opposite directions (+/−).
  • Racemic Mixture: 50:50 mix of both enantiomers. Optically inactive — rotations cancel.
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