Is a Diels Alder reaction exothermic?

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Answer 1 · 2016-02-04T02:18:48

Yes, a Diels-Alder reaction is exothermic.

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

Diels-Alder

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.