Chapter 16, Problem 55PP

Interpretation Introduction

Interpretation:

For the given compound under thermal condition, the possible products and the formed product upon the conrotatory ring opening are needed to be determined and the reason for not formed product is to be explained.

Concept introduction:

• Electrocyclic reaction is a concerted cyclization reaction of conjugated polyenes (π-system), in which one π-bond is converted into an σ-bond and remaining π-bonds shift their positions. Thereby the newly formed σ-bond connects the two ends of π-system to form a ring.
• The mechanism for reverse of Electrocyclic reaction is drawn by using arrows representing the conversion of σ-bond to π-bond and the shifting of π-bonds in the π-system of a cyclic alkene.
• The mechanism for reverse of Electrocyclic reaction is drawn by using arrows representing the conversion of σ-bond to π-bond and the shifting of π-bonds in the π-system of a cyclic alkene.
• The reaction conditions (thermal or photochemical) controls the product in such a way that the rotation for end lobes (ring closure) of the HOMO of conjugated (π-system) polyene.
• According to Woodward-Hoffmann rule for thermal and photochemical Electrocyclic reactions,

π-systems	Thermal	Photochemical
4- π-electrons	Conrotatory	Disrotatory
6- π-electrons	Disrotatory	Conrotatory