Question

Furan and maleimide undergo a Diels–Alder reaction at 25 °C to give the endo isomer of the product. When the reaction takes place at 70 °C, however, the major product is the exo isomer. Further study shows that the endo isomer of the product isomerizes to the exo isomer at 70 °C.

a)Using free energy diagram(s) explain why the endo isomer predominates when the reaction takes place at 25 °C and why the exo isomer predominates at 70 °C. Explain how the isomerization occurs.

Answer 1

Answer: According to the given question , The Diels-Alder reaction of maleimide with furan can produce two isomeric products. At room temperature, kinetic reaction control prevails and the less stable endo isomer2 is the main reaction product. At 70 °C and after long reaction times, the chemical equilibrium can assert itself and the thermodynamically more stable exo isomer 1 is formed. The exo product is more stable by virtue of a lower degree of steric congestion, while the endo product is favoured by orbital overlap in the transition state.

Hence it is all about the given question . Thank you :)