Diels Alder

Topics: Benzene, Distillation, Thin layer chromatography Pages: 3 (787 words) Published: November 17, 2010
For the following experiment, a Diels-Alder reaction between maleic anhydride and anthracene was conducted. Reflux mechanism was used for the reaction to occur. To increase the speed of the reaction, xylene was used because of its high boiling point. After the reaction was complete, 1.08g of the off white product was obtained with a yield of 69.7%. It was not clear if a pure product had been formed because time constraints did not allow us to perform thin layer chromatography. Introduction

The Diels-Alder reaction is a commonly used reaction in Organic Chemistry. In this reaction, an electron rich diene reacts with an electron poor dienophile and produces a new six-member ring. There are not any ionic and radical intermediates present in this reaction. Instead, the reaction occurs through a concerted process in which bonds are broken and made simultaneously. The flow of electrons goes from a Higher Occupied Molecular Orbital (HOMO) to Lowest Unoccupied Molecular Orbital (LUMO). As the energy between HOMO and LUMO decreases, less energy is required to transfer electrons from the HOMO to the LUMO state, which allows the reaction to occur faster.

Benzene rings and related aromatic rings do not go through a Diels-Alder reaction. In the case of anthracene, the reaction takes place in the middle of the ring even though the kinetic barrier is relatively high. The pi-bond allows of anthracene rings allow for the reaction to take place, after which the aromaticity of the ring gets lost. There are two ways of accelerating such slow Diels-Alder reactions. One way is to simply reflux the solution in a solvent with a high boiling point and another method that can be used is adding a Lewis acid such as aluminum chloride into the reaction. Heat can also be used when refluxing by heating the reactants and using xylene, which is a high boiling point solvent to create a relatively slow Diels-Alder reaction. The figure below illustrates the reaction of an...
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