Identify the type of pericyclic reaction shown below: $C_{6}H{6}_6$ undergoes a reaction with heat to form $C_{6}H{6}_6$ with a new six-membered ring. What is this reaction called?

• A. Diels-Alder reaction
• B. Electrocyclic reaction
• C. Sigmatropic rearrangement
• D. Ene reaction

Answer: (A)

Verified step by step guidance

1. Step 1: Recognize that the problem involves a reaction where a compound with formula C\_6H\_6 undergoes a transformation with heat to form a new six-membered ring, indicating a pericyclic reaction involving cyclic transition states.
2. Step 2: Recall the main types of pericyclic reactions: electrocyclic reactions (ring opening/closing), sigmatropic rearrangements (shifts of sigma bonds), cycloadditions (forming rings by joining two pi systems), and ene reactions (allylic hydrogen transfer with pi bond rearrangement).
3. Step 3: Note that the formation of a new six-membered ring from two components (one likely a diene and the other a dienophile) is characteristic of a [4+2] cycloaddition, which is the hallmark of the Diels-Alder reaction.
4. Step 4: Understand that the Diels-Alder reaction proceeds via a concerted mechanism involving the overlap of the diene's 4 pi electrons and the dienophile's 2 pi electrons, forming a new six-membered ring without intermediates.
5. Step 5: Conclude that since the problem describes the formation of a new six-membered ring from C\_6H\_6 components under heat, the reaction is best identified as a Diels-Alder reaction.