Arrange the following dienes in decreasing order of their reactivity towards 1-buten-3-one in a Diels-Alder reaction: (i) (ii) (iii)

Step-by-step solution

For a diene to undergo a Diels-Alder reaction, it must be able to adopt an s-cis conformation. The reactivity of the diene depends on how easily it can achieve this conformation. 1. Compound (ii) is cyclopentadiene. It is a cyclic diene permanently locked in the s-cis conformation. Because it is already in the ideal geometry for the transition state, it is highly reactive. 2. Compound (i) is 1,3-butadiene, an acyclic diene. At room temperature, it exists predominantly in the more stable s-trans conformation. To und