FMO Controlled Pericyclic Interactions
Diels-Alder cycloaddition can be considered as multicentre π-LUMO plus π-HOMO Lewis acid/base Complexation chemistry. However, it is sometimes difficult to decide which species is acting as the Lewis acid and which is the Lewis base.
In normal electron demand Diels-Alder cycloaddition chemistry the diene is electron rich, implying Lewis base character, and the alkene, the dieneophile, is electron deficient implying that the species is the Lewis acid:
In reverse electron demand cycloaddition, the diene acts as the electron deficient Lewis acid and the dieneophile is the electron rich Lewis base:
There are four general classes of pericyclic reaction process:
- Electrocyclic Reactions
- Sigmatropic Rearrangements
- Group Transfer Reactions
Pericyclic chemistry is discussed in detail elsewhere in this webbook.
Charge Transfer Complexes
π/π-Interactions can also lead to the formation of a charge-transfer complex, for example between the electron poor 1,3,5-trinitrobenzene and electron rich benzidine.
π/π-Interactions can also lead to the formation or conductive organic metals such as stacked TTF/TCNQ materials: