Suprafacial and Antarafacial
Suprafacial and antarafacial are terms used in organic chemistry to describe chemical reactions topologically . They describe the topology of the orbitals involved in bond formation , on or around a reaction center. Both σ and π orbitals as well as conjugated π systems can be meant here.
As suprafacial is called when it
- on the same orbital lobe of a p orbital
- on the same side of a conjugated π system
- on the same molecular orbital of a CC or CH σ- bond
a new bond formation or a change in the bond occurs.
Antarafacial describes the opposite case when it is:
- on both orbital lobes of a p orbital
- on the opposite side of a conjugated π system
- on both molecular orbitals of a CC or CH σ-bond
a new bond formation or a change in the bond occurs.
Classical suprafacial reactions include some cycloadditions (such as the Diels-Alder reaction ) and a number of sigmatropic rearrangements . The classic antarafacial reactions mainly include sigmatropic rearrangements.
Whether a reaction proceeds supra- or antarafacial depends on the orbital symmetries. The concept is used, for example, in the Woodward-Hoffmann rules .
source
- Entry to Antarafacial, Suprafacial . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.A00377 Version: 2.3.1.