The reaction of (Z)-butenedioic acid (fumaric acid) with 1,3-
cyclopentadiene gives only one product. Explain why.
The reaction of (Z)-butenedioic acid, also known as fumaric acid, with 1,3-cyclopentadiene gives only one product due to the nature of the reactants and the type of reaction that takes place.
Fumaric acid is a dicarboxylic acid with a double bond between the two carboxylic acid groups. On the other hand, 1,3-cyclopentadiene is a conjugated diene, meaning it has alternating double and single bonds in its carbon chain.
When these two reactants combine, they undergo a Diels-Alder reaction, which is a type of cycloaddition reaction. In this reaction, the diene (1,3-cyclopentadiene) acts as the dienophile, which is the species that accepts the electron-rich diene (fumaric acid).
The Diels-Alder reaction proceeds through a concerted mechanism, meaning that both the diene and the dienophile bonds break and form simultaneously in a single step. In this case, the reaction involves the formation of a new six-membered ring by the reaction between the diene and the dienophile.
The reactivity of (Z)-butenedioic acid and 1,3-cyclopentadiene is such that only one product is formed because there is only one way the reactants can come together to form a six-membered ring. The fumaric acid molecule must coordinate with the 1,3-cyclopentadiene molecule in a specific orientation to create the desired product. Other orientations would lead to strained or unreactive products.
Therefore, due to the specific geometry and reactivity of the reactants, the reaction between (Z)-butenedioic acid and 1,3-cyclopentadiene gives only one product.