Chemistry

Pericyclic reactions


Transition State Aromaticity: Summary

If one takes into account the extension of the concept of aromaticity to non-planar systems, s-orbitals and Möbius aromatics, the rules can be summarized in one sentence:

Selection rule for pericyclic reactions
Pericyclic reactions prefer to proceed through aromatic transition states.
  • No matter how the orbital phases are selected, Hückel systems have an even number (including zero) of phase changes in the cyclically delocalized system of the base orbitals. They are aromatic with 4n + 2 electrons.
  • No matter how the orbital phases are selected, Möbius systems have an odd number of phase changes in the cyclically delocalized system of the base orbitals. They are aromatic with 4n electrons.


Video: Pericyclic Reactions Part 1: Revisiting the Diels-Alder Reaction (December 2021).