Examine the following pericyclic reactions. For each reaction, tell whether it is an electrocyclic reaction, a cycloaddition reaction, or a sigmatropic rearrangement. a. b. c. d.

Verified step by step guidance

1. Step 1: Understand the types of pericyclic reactions. Pericyclic reactions are a class of reactions that proceed via a concerted process and include electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements.
2. Step 2: Identify the characteristics of each type of pericyclic reaction. Electrocyclic reactions involve the opening or closing of a ring with a change in the number of π-bonds. Cycloaddition reactions involve the formation of a ring by the addition of two or more π-bonded molecules. Sigmatropic rearrangements involve the migration of a σ-bond across a π-system.
3. Step 3: Examine reaction (a) and determine if it involves the opening or closing of a ring (electrocyclic), the formation of a ring (cycloaddition), or the migration of a σ-bond (sigmatropic rearrangement).
4. Step 4: Repeat the analysis for reaction (b), looking for the same characteristics to classify it as an electrocyclic reaction, a cycloaddition reaction, or a sigmatropic rearrangement.
5. Step 5: Continue this process for reactions (c) and (d), using the same criteria to classify each reaction based on the changes in bonding and structure.

Key Concepts

Pericyclic Reactions

Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, involving a cyclic transition state. These reactions typically involve the rearrangement of electrons in a way that conserves orbital symmetry, allowing for the simultaneous breaking and forming of bonds. Common types include electrocyclic reactions, cycloadditions, and sigmatropic rearrangements.

Electrocyclic Reactions

Electrocyclic reactions are a type of pericyclic reaction where a conjugated system undergoes a ring closure or opening through the rotation of a sigma bond. The stereochemistry of the product depends on the thermal or photochemical conditions under which the reaction occurs, following the rules of orbital symmetry, specifically the Woodward-Hoffmann rules.

Cycloaddition Reactions

Cycloaddition reactions involve the formation of a cyclic compound by the addition of two or more unsaturated molecules. These reactions can be classified as [2+2] or [4+2] depending on the number of π bonds involved. Like electrocyclic reactions, cycloadditions also adhere to the principles of orbital symmetry, influencing the reaction pathway and product formation.