Disrotatory ring opening of cyclobutene
·
In the disrotatory case, a plane of symmetry is
conserved.
·
The HOMO of the reactant then correlates with a higher-lying
antibonding molecular orbital of the products.
·
Therefore the disrotatory ring opening reaction is symmetry
forbidden
To show this, we must analyse the symmetry of the orbitals with respect to the conserved mirror plane.
Molecular orbitals of the
reactant (cyclobutene)
