The Diels-Alder Reaction is a reaction used in organic chemistry that builds rings very efficiently (1), this cycloaddition process allows for the stereoselective formation of cyclohexene rings possessing as many as four contiguous stereogenic centers (3). This reaction occurs without intermediates, in a single step, which explains the stereospecificity due to substituents not being given the chance to “switch around”. (1)These six membered rings are synthesized by reacting a dienophile with a diene, forming two new carbon-carbon sigma bonds in the form of the ring. The dienophile used in this experiment was Maleic anhydride (a cyclic dienophile) and the diene used was cyclopentadiene (a cyclic diene). Due to the fact that more than one stereoisomer may form, it is important to know that the major product will be the one with the transition state for the endo stereochemistry while the minor product will be for the exo stereochemistry. The reason for this is because the reaction favors the product that involves the maximum overlap of pi electrons in its transition state, which in this case, is the endo isomer. To ease the concerns of orbital overlap between the HOMO (Highest Occupied Molecular Orbital) of cyclopentadiene with the LUMO (Lowest Unoccupied Molecular Orbital) maleic anhydride, reactants are used which possess electron withdrawing groups on the dienophile (maleic anhydride) and electron donating groups on the diene (cyclopentadiene). (2) Side reactions in this experiment include the reaction of cyclopentadiene with itself as it will dimerize to form dicyclopentadiene if kept at room temperature as well as the exo isomer of the product. Reaction Mechanism:
To begin this experiment, a fractional distillation was set up in order to distill dicyclopentadiene. A 10 mL conical vial was filled with 5 mL of dicyclopentadiene and then heated to a steady boiling point (40-42 C). Cyclopentadiene was then placed on ice while...
References: 1. Weldegirma, Solomon. "Diels-Alder Reaction: Synthesis of cis-Norbornene-5,6-endo-
dicarboxylic anhydride." Experimental Organic Chemistry. Print.
2. Myers, Kyle,. Roark, James. Diels-Alder Synthesis of Exo-Norbornene-cis-5,6-
Dicarboxylic Anhydride for Organic Chemistry Laboratory Instruction. Web.
3. Jacobsen, Pfaltz, Yamamato. Comprehensive Asymmetrical Catalysis I-III Ch. 33 Diels
Alder Reactions. Print.
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