This article Stereospecific Reactions mentions properties and their types based on mechanism and starting material stereochemistry.

What are the properties of Stereospecific reactions?

  1. Reactions in which the stereochemistry of the product is determined by the stereochemistry of the starting material are called stereospecific
  2. Stereospecific reactions lead to the production of a single isomer.
  3. It depends upon the mechanism of the reaction and the stereochemistry of the starting material.
  4. There is no choice in the reaction pathway.
  5. The reaction gives a different diastereoisomer of the product from each stereoisomer of the starting material

Different types of Stereospecific reactions?

E2 eliminations from cyclohexanes

EXAMPLE 1

  1. Reactant stereochemistry: equatorial substituted cyclohexane
  2. Mechanism: anti-periplanar transition state
  3. Product stereochemistry: No product
  4. Reason: equatorial C-X anti-periplanar to two equatorial C-C bonds hence can not E2 eliminated

EXAMPLE 2

  1. Reactant stereochemistry: axial substituted cyclohexane
  2. Mechanism: anti-periplanar transition state
  3. Product stereochemistry: Cyclohexene
  4. Reason: though axial substituted cyclohexane unstable, ring flipping possible E2 elimination easily, as axial C-X anti-periplanar to two axial C-H

Epoxidation of alkene’s

EXAMPLE 1

  1. Reactant stereochemistry:cis-alkene
  2. Mechanism: new C–O bonds are formed on the same face of the alkene’s π bond,
  3. Product stereochemistry: cis-epoxide
  4. Reason: the geometry of the alkene is reflected in the stereochemistry of the epoxide

EXAMPLE 2

  1. Reactant stereochemistry: trans-alkene.
  2. Mechanism: SN2 reaction has no choice but to go with inversion,
  3. Product stereochemistry: trans epoxide.
  4. Reason: the geometry of the alkene is reflected in the stereochemistry of the epoxide

Epoxide ring opening

EXAMPLE 1

  1. Reactant stereochemistry EPOXIDE top face of the ring
  2. Mechanism: SN2 reaction has no choice but to go with an inversion
  3. Product stereochemistry: anti diastereoisomer, but each gives an opposite enantiomers
  4. Reason: Me2NH will attack the two identical ends of the epoxide with precisely equal probability
Giving different enantiomers

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