Chapter 17: Conjugated Pi Systems and Pericyclic Reactions

Question 1

Diene + Dienophile

Answer 1

• Diels Alder
• Forms 6-membered ring
• forms 2 sigma bonds from 2 pi bonds
• Cycloaddition: Lumo of dienophile binds with HOMO of diene
• diene must be in cis conformation
• Dienophile need EWG
• Concerted
• Endo preference: EWG likes to be in same place as forming pi bond
• this results in endo form of bicyclic compounds

Question 2

Conjugated pi system with heat/light

Answer 2

-Electrocyclic Reaction
-I pi turns to 1 sigma bond
-rotate bonds in terminal carbons of homo to form favourable overlap of lobes
-disrotary: opposite directions
Conrotary: same direction
-light will excite homo to lumo

Question 3

Sigmatropic Rearrangements

[1,5]

Answer 3

H moves to opposite terminal carbon

Question 4

Sigmatropic Rearrangements

Cope [3,3]

Answer 4

Favours formation of more subbed alkene

Question 5

Sigmatropic Rearrangements

Clasien Rearrangement

Answer 5

Favours formation of more subbed O=C