# Diels-Alder Reaction: Step-by-Step Solution Let's solve a typical Diels-Alder reaction, which is a [4+2] cycloaddition between a diene and a dienophile. Suppose the reaction is: - **Diene:** 1,3-butadiene - **Dienophile:** ethene (ethylene) ## Step 1: Draw the Reactants - **1,3-Butadiene:** CH₂=CH–CH=CH₂ (a conjugated diene, four π electrons) - **Ethene:** CH₂=CH₂ (a simple alkene, two π electrons) ## Step 2: The Mechanism - The reaction involves the concerted movement of electrons: - The π electrons from the diene and the dienophile combine to form a new six-membered ring. ## Step 3: Draw the Product - The product is **cyclohexene**. - All new bonds form *syn*, so the stereochemistry is preserved (cis addition). ``` /\ / \ | | | | \ / || ``` Alternatively, using a condensed structural formula: ``` ____ / \ | | | | \____/ | H₂C—CH₂ ``` But for cyclohexene, the structure is:  *Alt text: Skeletal formula of cyclohexene, a six-membered ring with one double bond.* ## Step 4: Stereochemistry If the dienophile or diene has substituents, the stereochemistry is *cis* (if substituents are cis in the dienophile, they are cis in the product, and vice versa). In this case, both reactants are unsubstituted, so stereochemistry is not a concern. ## Final Answer **The product is cyclohexene.** - Six-membered ring - One double bond - No stereocenters in this specific example --- **If you need the product for a specific diene/dienophile pair with substituents, please specify them for a detailed drawing and stereochemistry!**