Definition
A reaction that disobeys conservation of orbital symmetry.
Explanation
Fontier orbitals, we find that the phases of the MOs do not overlap. This reaction is therefore said to be symmetry forbidden, and the reaction does not occur. A [2+2] cycloaddition. Can only be performed with photo chemical excitation. When one of the compounds is subjected to UV light, it can absorb the light to promote a p electron to the next higher energy level. In this excited state.