Antarafacial and suprafacial
Suprafacial and antarafacial are terms that are used in organic chemistry for the topological description of chemical reactions. They describe the topology of the orbitals involved in bond formation, at or around a reaction center. In this case both σ - and π - orbitals and π -conjugated systems can be meant.
As suprafacially referred to when it
- On the same lobes of a p- orbital
- On the same side of a conjugated π - system
- On the same molecular orbital of CC and CH σ - bond
Moves into a new bond formation, or to a change in binding.
Antarafacial describes the opposite case, if it so:
- On both lobes of a p- orbital
- On the opposite side of a conjugated π system,
- On both molecular orbitals of CC and CH σ - bond
Moves into a new bond formation, or to a change in binding.
The classic suprafacially running reactions include both some cycloaddition reactions ( such as the Diels -Alder reaction), as well as a number sigmatropic rearrangements. The classic antarafacial reactions which proceed mainly include sigmatropic rearrangements.
Whether a reaction is running supra - or antarafacial depending on orbital symmetries. The concept is used for example in the Woodward -Hoffmann rules.
Source
- Entry: antarafacial, suprafacially. In: IUPAC Compendium of Chemical Terminology (the " Gold Book "). doi: 10.1351/goldbook.A00377 ( Version: 2.3.1).
- Isomerism
- Reaction rule