What is the Difference Between Suprafacial and Antarafacial?
🆚 Go to Comparative Table 🆚The terms suprafacial and antarafacial are used in organic chemistry to describe the relationship between chemical bond making and/or bond breaking processes at a reaction center, such as a conjugated/pi system, a p orbital, or an sp orbital. The key difference between the two lies in the orientation of the processes:
- Suprafacial: If a component undergoes addition (forms a bond) on the same face of the reaction center, it is called a suprafacial component. For example, in a suprafacial [1,3]-hydride shift, the interacting frontier orbitals are the allyl free radical and the hydrogen 1s orbitals.
- Antarafacial: If a component undergoes addition on opposite faces of the reaction center, it is called an antarafacial component. In an antarafacial transition, orbital contributions to the reaction that involve bond-breaking and bond-making processes occur on opposite faces of a conjugated/pi system or an isolated orbital.
These topological concepts can be applied to various reactions, including pericyclic reactions, sigmatropic rearrangements, and cycloadditions. The classification of these components as either suprafacial or antarafacial determines the stereochemistry of the reaction.
Comparative Table: Suprafacial vs Antarafacial
The terms suprafacial and antarafacial describe the topographical relationships between the simultaneous processes of bond breaking and/or bond formation in organic chemistry, particularly in pericyclic reactions. Here is a table comparing the differences between suprafacial and antarafacial:
| Feature | Suprafacial | Antarafacial |
|---|---|---|
| Definition | If a component undergoes addition (forms bond) on the same face, it is called a suprafacial component. | If a component undergoes addition on opposite faces, it is called an antarafacial component. |
| Bonding | Bonding interactions occur between lobes on the same face of one reactant and lobes on the same face of another reactant. | Bonding interactions occur between lobes on opposite faces of the π system or isolated orbital. |
| Stereochemistry | Suprafacial topology corresponds to retention of configuration for the carbon atom of a [1,n]-sigmatropic rearrangement and disrotation for cycloadditions. | Antarafacial topology corresponds to inversion of configuration for the carbon atom of a [1,n]-sigmatropic rearrangement and conrotation for cycloadditions. |
| Geometric Constraints | Suprafacial cycloadditions are more common for small π systems due to fewer geometric constraints. | Antarafacial reactions can be more difficult due to the twisting of the π orbital system in one of the reactants. |
Both suprafacial and antarafacial cycloadditions are symmetry-allowed, but geometric constraints often make antarafacial reactions more challenging.
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