Question

A reagent may attach itself to a conjugated diene to the carbons at the two ends of the conjugated system. Identify the reaction involved from the following:

• A. 1,2-addition
• B. 1,2-addition
• C. 1,3-addition
• D. 2,4-addition

Answer 1

The Correct Option is B

A conjugated diene is a molecule that contains two double bonds separated by a single bond, allowing for different types of addition reactions. The question involves identifying the correct addition pattern for a reagent attaching to a conjugated diene at the ends of the conjugated system.

In organic chemistry, the addition reactions of conjugated dienes can often be classified into different types based on the positioning of the added groups.

• 1,2-addition: This type of addition involves a reagent adding to the first and second carbon atoms of the diene system. It is a result of the kinetic control of the reaction. This option is stated as the correct answer.
• 1,3-addition: Also known as the 1,4-addition, in this type of addition, the reagent attaches to the first and third carbon atoms of the conjugated diene. This is under thermodynamic control and is not the option described in the question.
• 2,4-addition: This typically describes scenarios where certain transformations occur, such as in specific polymerization processes, but it is not relevant to the addition mode described in the question.

Correct Explanation: The question asks about a reagent attaching to the carbons at the two ends of the conjugated diene, which implies the addition across the initial double bond. Therefore, the correct addition pattern is 1,2-addition.

This addition mechanism occurs predominantly when the reaction is carried out at low temperatures, leading to the more kinetically controlled product.

Thus, the correct answer is 1,2-addition.