Which of the following is NOT a pericyclic reaction?

• A.
• B.
• C.
• D.

Answer: (C)

Verified step by step guidance

1. Identify the characteristics of a pericyclic reaction. Pericyclic reactions are concerted processes that occur through a cyclic transition state and involve the redistribution of bonding electrons. Common types include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements.
2. Analyze the first reaction: the addition of OsO4 to a double bond. This is an example of a dihydroxylation reaction, which is not a pericyclic reaction. It involves the formation of a cyclic osmate ester intermediate, but it is not concerted in the sense of pericyclic reactions.
3. Examine the second reaction: the Diels-Alder reaction. This is a classic example of a pericyclic reaction, specifically a [4+2] cycloaddition, where a diene and a dienophile form a six-membered ring through a concerted mechanism.
4. Consider the third reaction: the addition of HCl to an alkene. This is an electrophilic addition reaction, not a pericyclic reaction. It involves the formation of a carbocation intermediate and is not concerted.
5. Review the fourth reaction: ozonolysis of an alkene. This reaction involves the formation of an ozonide intermediate and is not a pericyclic reaction. It is a stepwise process involving multiple steps, including the formation and cleavage of the ozonide.