Diels-Alder Reaction: Exo Transition State Structure
for the Reaction of E-1,3-Pentadiene and Maleic Anhydride

The transition state structures of the exo cycloaddition of E-1,3-pentadiene and maleic anhydride. This structure is only about 9.0 kcal/mol less stable than the precoordination complex. This activation barrier is very small and the Diels-Alder reaction can proceed quickly.

Figure. The MP2(full)/6-31G* optimized transition state structure of the exo cycloaddition of E-1,3-Pentadiene and Maleic Anhydride.