Himic Anhydride: A Retro Diels-Alder Reaction for the Organic Laboratory and an Accompanying NMR Study.

The thermal equilibration of himic anhydride [IUPAC (2- endo ,3- endo )-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride] to (2- exo ,3- exo )-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride and subsequent recrystallization of the exo -product can be performed as a standard undergraduate laboratory experiment requiring minimal equipment. The interpretation of the 1 H NMR spectra for these norbornene carboxylic anhydride molecules promotes an appreciation of constrained ring systems and factors that affect chemical shifts and coupling constants.