Skip to main content

Optical isomerism; tartaric acid; maleic/fumaric Z,E

Short answer

Optical isomerism arises from chirality, giving enantiomers that rotate plane-polarised light differently. Tartaric acid stereoisomers: active (2R,3R) and (2S,3S) pair, and inactive meso form. Maleic acid is Z (COOH groups on same side), fumaric acid is E (COOH groups opposite).

What is optical isomerism? Write the possible stereoisomers of tartaric acid. Specify Z and E configuration of maleic acid and fumaric acid.

Optical isomerism

Optical isomerism is stereoisomerism in which isomers have identical constitution but differ in their effect on plane-polarised light. It occurs when a molecule is chiral (non-superimposable on its mirror image), most commonly due to a carbon with four different groups. Optical isomers are called enantiomers.

Stereoisomers of tartaric acid

   COOH         COOH         COOH
H—C—OH       HO—C—H       H—C—OH
HO—C—H       H—C—OH       H—C—OH
   COOH         COOH         COOH
 (2R,3R)      (2S,3S)      meso (2R,3S)
 L-(+)        D-(−)        inactive
  • (2R,3R) and (2S,3S) are enantiomers (optically active, equal and opposite rotation).
  • The meso form has a plane of symmetry (internal mirror) between C2 and C3, so it is optically inactive by internal compensation. It is a diastereomer of both active forms.
  • An equimolar mixture of the (+) and (−) forms is the racemic (±) acid.

Maleic and fumaric acid

 HOOC   COOH            HOOC   H
    \  /                   \  /
     C=C                     C=C
    /  \                   /  \
   H    H                 H    COOH
 maleic acid           fumaric acid

On each carbon, COOH has higher priority than H. In maleic acid the COOH groups are on the same side, so it is Z. In fumaric acid they are on opposite sides, so it is E.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Engineering Chemistry chapter 9 questions →