Question

Is a Diels Alder reaction exothermic?

Answer 1

Yes, a Diels-Alder reaction is exothermic.

Explanation:

A Diels-Alder involves the reaction of a diene with a dienophile to form a cyclohexene derivative.

We can use bond dissociation energies (`"D"`) to calculate an approximate value of `"ΔH"` for this reaction.

Typical bond energies are: `"C-C"` = 347 kJ/mol and `"C=C"` = 614 kJ/mol

`ΔH_"rxn" = SigmaD_"reactants"color(white)(l) – SigmaD_ "products" = 3D_"C=C" +D_"C-C"color(white)(l) – D_"C=C"color(white)(l) –5D_"C-C"`

`= 2D_"C=C" color(white)(l)– 4D_"C-C" = "(2×614 -"color(white)(l)4×347) " kJ/mol" = "-160 kJ/mol"`

This is only a rough value, but it shows that the formation of four new `"C-C"` bonds makes the reaction quite exothermic.