Chapter 30.9, Problem 10P

Interpretation Introduction

Interpretation:

The stereochemistry of the following pericyclic reactions,

a) The thermal cyclization of a conjugated tetraene.

Concept introduction:

a) A pericyclic reaction is a concerted reaction that proceeds through a cyclic transition state. Pericyclic reactions are completely stereospecific; that is, a single stereoisomer of the reactant forms a single stereoisomer of the product. Various kind of stereochemistry occurs in pericyclic reaction.

Interpretation Introduction

Interpretation:

The stereochemistry of the following pericyclic reactions,

b) The photochemical cyclization of a conjugated tetraene.

Concept introduction:

b) When like phases of the p orbitals are on the same side of the molecule, the two orbitals must rotate in opposite directions—one clockwise and one counterclockwise. Rotation in opposite directions is said to be disrotatory.

Interpretation Introduction

Interpretation:

The stereochemistry of the following pericyclic reactions,

c) A photochemical [4 1 4] cycloaddition.

Concept introduction:

c) When like phases of the p orbitals are on opposite sides of the molecule, the two orbitals must rotate in the same direction—both clockwise or both counterclockwise. Rotation in the same direction is said to be conrotatory.

Interpretation Introduction

Interpretation:

The stereochemistry of the following pericyclic reactions,

d) A thermal [2 1 6] cycloaddition.

Concept introduction:

d) A suprafacial stereochemistry occurs when like phases of the p orbitals of both reactants are on the same side of the pie system, so that two bonding interactions result.

Interpretation Introduction

Interpretation:

The stereochemistry of the following pericyclic reactions,

e) A photochemical [3, 5] sigmatropic rearrangement.

Concept introduction:

e) An antarafacial stereochemistry occurs when one pie system must twist to align like phases of the p orbitals of the terminal carbons of the reactants.