A PROOF OF DIELS-ALDER EXO ISOMER MECHANISTIC SURPRISE

Abstract

Critical analysis of published works shows that there is no evidence that any Diel- Alder reactions took place in a synchronous manner. The Diel-Alder reactions is a 4+2 cyclo addition of conjugated dienes and dinophiles which represents some mechanistic surprises of endo and exo products/isomers. Kinetically, endo product is more preffered to exo isomer because of its low activation energy. Therefore this experiment is carried out to support Diel-Alder exo-configuration product. The preparation of exo-cis-3,6- endoxotetrahydrophthalic anhydride (16.9g, 44.86%) with melting point 116.80c – 120.50c with IR 1781,1857 recorded on perkin elmer spectrum, Bx-FT IR system using KBr disk and 1Hr NMR(500MHz CDC13) using the Reichert Thermovar hot stage melting point apparatus by the reaction of furan(25g, 0.368mol) and maleic anhydride (22g, 0.224 mol) in diethylether. Preparation of bromolactonic acid and pseudo ester were also discussed. It was found out that the Diel-Alder product is exo-configuration as the literature of melting point of their exo-adduct is 1140c and for this experiment is 116.80c. Also, NMR spectrum of this experiment shows a signal for most proton and its absorption which is a proof. The IR spectrum shows that most functional groups behave as expected. It is then concluded that the product of this experiment is exo- isomer/product which is more thermodynamically stable as Diel- Alder exo-product indicated by the melting point and still remains significant and a major product.