# Is a Diels Alder reaction exothermic?

Feb 4, 2016

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 ($\text{D}$) to calculate an approximate value of $\text{ΔH}$ for this reaction.

Typical bond energies are: $\text{C-C}$ = 347 kJ/mol and $\text{C=C}$ = 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"

$= 2 {D}_{\text{C=C" color(white)(l)– 4D_"C-C" = "(2×614 -"color(white)(l)4×347) " kJ/mol" = "-160 kJ/mol}}$

This is only a rough value, but it shows that the formation of four new $\text{C-C}$ bonds makes the reaction quite exothermic.