Chapter 27, Problem 27.28P

Interpretation Introduction

(a)

Interpretation: The given reaction is to be classified as electrocyclic reaction, cycloaddition, or sigmatropic rearrangement. The stereochemistry whether the given reaction is conrotatory, disrotatory, suprafacial, or antarafacial is to be indicated.

Concept introduction: Electrocyclic reactions are pericyclic reactions which takes place by concerted mechanism. These reactions involve ring opening or ring closure in a conjugated polyene

Interpretation Introduction

(b)

Interpretation: The given reaction is to be classified as electrocyclic reaction, cycloaddition, or sigmatropic rearrangement. The stereochemistry whether the given reaction is conrotatory, disrotatory, suprafacial, or antarafacial is to be indicated.

Concept introduction: Sigmatropic rearrangements are pericyclic reactions which takes place by concerted mechanism. In these rearrangements migration of sigma bond takes place. According to Woodward-Hoffmann rules, the total number of electron pairs in sigma bond that is broken and the pi bonds that rearrange. The polyene containing even number of electron pairs in thermal conditions undergoes reaction in antrafacial fashion and polyene containing odd number of bonds undergo reaction in suprafacial fashion.

Interpretation Introduction

(c)

Interpretation: The given reaction is to be classified as electrocyclic reaction, cycloaddition, or sigmatropic rearrangement. The stereochemistry whether the given reaction is conrotatory, disrotatory, suprafacial, or antarafacial is to be indicated.

Concept introduction: Cycloaddition reactions are pericyclic reactions that take place in two compounds containing pi bonds to form a cyclic compound. These reactions are concerted and stereospecific in nature. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in photochemical conditions undergoes reaction in suprafacial fashion and polyene containing odd number of bonds undergo reaction in antrafacial fashion.