Diels-Alder reaction volumes in the solid state and solution

Abstract

The densities of anthracene, tetracyanoethylene, maleic anhydride, N-phenylmaleineimide, trans, trans-1,4-diphenylbuta-1,3-diene, and their Diels-Alder adducts were measured in the solid state and in solution at 25 °C. The reaction volumes in the solid state were calculated from the difference in molar volumes. They turned out to be low, close to each other (−4 to −11 cm3 mol−1), and slightly different from the reaction volumes (−8±1 cm3 mol−1) calculated from the van der Waals radii. The reaction volumes in solutions (−15 to −32 cm3 mol−1) were found from the difference in partial molar volumes of the reactants in dioxane, acetonitrile, and 1,2-dichloroethane, The experimental Diels-Alder reaction volumes in solution are determined not only by the formation of new bonds in an adduct: a considerably higher contribution (to 75%) is made by a change in the volume of intermolecular empty spaces in solution on going from reactants to adducts.