Experiment #1


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CH242 EXPERIMENT #1 A DIELS –ALDER REACTION (Synthesis of cis —1,2,3,6-tetrahydro-4,5-dimethylphthalic anhydride) Background The Diels-Alder reaction is an important, synthetically useful reaction in organic chemistry. It is named after Otto Diels and his student Kurt Alder who were awarded the Nobel Prize in chemistry in 1950 in recognition of the importance of their discovery. The Diels-Alder reaction is the cycloaddition of a 1,3- π system (a diene) with a π -bond that usually bears an electron-withdrawing group (a dienophile) to produce a six-membered ring. The reaction is concerted (bond breaking and forming occur simultaneously) and therefore results in high stereoselectivity (products with predictable stereochemistry). diene dienophile head-to-head overlap of p-orbitals to form two new sigma bonds In this experiment, you will perform a Diels-Alder reaction using 2,3-dimethyl- 1,3-butadiene as the diene and maleic anhydride as the dienophile. These substrates react to form the Diels-Alder product, cis —1,2,3,6-tetrahydro-4,5-dimethylphthalic anhydride. (The dark dots in the structure of the product, below, imply that the hydrogen atoms at these positions are both “up” as drawn and therefore are cis to each other.) After synthesizing your anhydride, you will need to purify it by recrystallization, and characterize it by obtaining a melting point (the literature value is 78-79 °C) and an IR spectrum. O
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