Question

Following are three examples of Cope rearrangements of 1,5 -dienes. Show that each product can be formed in a single step by a mechanism involving redistribution of six electrons in a cyclic transition state.

Short answer

Question: Show that the products of three different Cope rearrangements can be formed in a single step by analyzing the electron redistribution in each example. Short Answer: The Cope rearrangement involves a pericyclic reaction mechanism that proceeds through a cyclic six-electron transition state in 1,5-dienes. By following this mechanism for each example, the bond formation and redistribution of electrons lead to the respective products in a single step. This demonstrates that various Cope rearrangement products can be formed in a single step through utilization of the same rearrangement mechanism.

Step-by-step solution

Example 1: 1,5-Diene rearrangement

1. Draw the given 1,5-diene reactant. 2. Based on the reaction mechanism, the two terminal carbons of the diene should form a bond, while the central double bond of the diene will break. 3. The bond between the 3rd and 4th carbons should form a double bond, and the original double bond between the 1st and 2nd carbons should become a single bond. 4. Verify that the product obtained matches the given product for the first example.

Example 2: 1,5-Diene rearrangement

1. Draw the given 1,5-diene reactant. 2. Based on the reaction mechanism, the two terminal carbons of the diene should form a bond, while the central double bond of the diene will break. 3. The bond between the 3rd and 4th carbons should form a double bond, and the original double bond between the 1st and 2nd carbons should become a single bond. 4. Verify that the product obtained matches the given product for the second example.

Example 3: 1,5-Diene rearrangement

1. Draw the given 1,5-diene reactant. 2. Based on the reaction mechanism, the two terminal carbons of the diene should form a bond, while the central double bond of the diene will break. 3. The bond between the 3rd and 4th carbons should form a double bond, and the original double bond between the 1st and 2nd carbons should become a single bond. 4. Verify that the product obtained matches the given product for the third example. By following the steps described for each example, the products obtained will match the given products for the three reactions, demonstrating that each Cope rearrangement can be formed in a single step using the described mechanism involving redistribution of six electrons in a cyclic transition state.