Chapter 11, Problem 54P

Interpretation Introduction

Interpretation:

The given cycloaddition reactions are allowed or forbidden according to the Woodward-Hoffmann rules is to be determined.

Concept introduction:

The orbitals directly involved in bond formation are called frontier orbitals. They are the HOMO of one reactant and LUMO of the other reactant.

Electron withdrawing groups attached to the dienophile increase its reactivity. Electrons flow from the diene to the dienophile.

In-phase overlap is necessary for the formation of a sigma bond. Such an overlap is termed as symmetry allowed, according to the Woodward-Hoffmann rules.

If the HOMO-LUMO lack symmetry and experience and antibonding interaction, then such an overlap is symmetry forbidden.