key term - Antarafacial

Definition

Antarafacial is a term used to describe the stereochemical relationship between the new bonds formed in a pericyclic reaction. It refers to the orientation of the newly formed bonds relative to the existing bonds in the reactant molecule, specifically when they are on opposite faces of the cyclic transition state.

5 Must Know Facts For Your Next Test

1. In an antarafacial pericyclic reaction, the new bonds are formed on the opposite face of the cyclic transition state relative to the existing bonds.
2. Antarafacial reactions are often observed in certain types of cycloadditions, such as the Diels-Alder reaction.
3. The antarafacial orientation of the new bonds is a result of the concerted nature of the pericyclic reaction and the preservation of orbital symmetry.
4. Antarafacial reactions are typically favored when the new bonds can be formed with minimal distortion of the existing bonds in the cyclic transition state.
5. The stereochemistry of the products in an antarafacial reaction is often opposite to that of the reactants, leading to the inversion of configuration.

Review Questions

• Explain the significance of the term 'antarafacial' in the context of pericyclic reactions.
  • The term 'antarafacial' refers to the stereochemical relationship between the new bonds formed in a pericyclic reaction and the existing bonds in the reactant molecule. In an antarafacial reaction, the new bonds are formed on the opposite face of the cyclic transition state relative to the existing bonds. This orientation is a result of the concerted nature of the pericyclic reaction and the preservation of orbital symmetry. The antarafacial stereochemistry of the products is often opposite to that of the reactants, leading to the inversion of configuration.
• Describe how the antarafacial orientation of new bonds affects the stereochemistry of the products in a cycloaddition reaction.
  • In a cycloaddition reaction, the antarafacial orientation of the new bonds formed in the cyclic transition state can have a significant impact on the stereochemistry of the products. When the new bonds are formed on the opposite face of the cyclic transition state relative to the existing bonds, the resulting products will have a stereochemistry that is inverted compared to the reactants. This inversion of configuration is a characteristic of antarafacial pericyclic reactions and is a consequence of the concerted nature of the reaction and the preservation of orbital symmetry.
• Analyze the role of the antarafacial relationship in determining the feasibility and selectivity of pericyclic reactions, particularly in the context of the Diels-Alder reaction.
  • The antarafacial relationship between the new bonds formed and the existing bonds in the reactants is a key factor in determining the feasibility and selectivity of pericyclic reactions. In the case of the Diels-Alder reaction, the antarafacial orientation of the new bonds is often favored, as it allows for the formation of the cyclic product with minimal distortion of the existing bonds in the cyclic transition state. This antarafacial relationship is a result of the concerted nature of the Diels-Alder reaction and the preservation of orbital symmetry. The selectivity of the Diels-Alder reaction is also influenced by the antarafacial orientation, as it can lead to the formation of specific stereoisomers of the cycloadduct.

Related terms

Pericyclic Reaction: A pericyclic reaction is a type of organic reaction that involves the concerted rearrangement of bonds in a cyclic transition state.

Suprafacial:

Suprafacial describes the stereochemical relationship where the new bonds are formed on the same face of the cyclic transition state as the existing bonds.

Cycloaddition:

A cycloaddition is a pericyclic reaction in which two or more unsaturated molecules or parts of the same molecule combine to form a cyclic product.