Chapter 28, Problem 33P

Interpretation Introduction

Interpretation:

The product of the reaction for given two reactants should be drawn.

Concept introduction:

In a sigmatropic reaction “ one new sigma-bond is formed as another breaks.”

Sigma tropic rearrangement reactions are designated with digits. For example a [1, 3] sigma tropic rearrangement describe a reaction in which the residue migrates from position 1 to position 3.

Woodward –Hoffmann rules are the set of rules used to vindicate or predict certain aspects of the stereo chemical outcome and activation energy of pericyclic reactions.

Woodward – Hoffmann rules for sigma tropic rearrangement reactions are listed below

$\begin{array}{ccc}\begin{array}{l}Sumofthenumberofbondsinthereacting\\ sytemsofbothreagents\end{array}& \text{Reaction}\text{conditions}& \text{Allowed}\text{mode}\text{of}\text{bond formation}\\ \text{Even}\text{number}& \text{Thermal}& \text{Antarafacial}\\ & \text{Photochemical}& \text{Suprafacial}\\ \text{Odd}\text{number}& \text{Thermal}& \text{Suprafacial}\\ & \text{Photochemical}& \text{Antarafacial}\end{array}$

Migration of carbon and hydrogen will occur in a sigmatropic rearrangement reaction. Migration of hydrogen in suprafacial and antarafacial rearrangement can be represented as follows,

Carbon migrating with one lobe of its p orbital interacting

Carbon migrating with both lobe of its p orbital interacting