Analysing the symmetry of the reactant molecular orbitals


                We now follow the same procedure for the basic Diels-Alder reaction as we did for the cycloaddition of 2 ethene molecules.


                We consider the MO diagram of the active MOs in the reactants and in the products and draw a correlation diagram -- with conservation of orbital symmetry.

Molecular orbitals of reactants


Lowest 3 MOs of reactants (butadiene +ethene):



Highest 3 MOs of the reactants