CHEM267 Chapter Notes - Chapter 17: Electrocyclic Reaction, Cyclopentadiene, Pericyclic Reaction

• School: University of Waterloo
• Department: Chemistry
• Course: CHEM267
• Professor: Monica Barra

Document Summary

3 major groups of pericyclic reactions: cycloaddition, electrocyclic, and sigmatrophic. Cycloaddition: +2 bonds, -2 bonds. Electrocyclic: +1 bonds, -1 bond. These are all concerted reactions (1 step); therefore, there are no intermediates! In this process, a ring is formed (therefore, it is a cycloaddition reaction) Called a [4+2] cycloaddition (2 different systems are involved: one with 4 atoms, one with 2) Note: the product of a diels-alder reaction is always a substituted cyclohexane! Moderate temperatures favour the formation of products in a diels-alder reaction. High temperatures (>200 c) favour the reverse diels-alder reaction: retro diels-alder reaction. Rule: cis alkene produces cis disubstituted ring; trans alkene produces trans disubstituted ring. Note: the diels-alder reaction only occurs when the diene is in an s-cis conformation: dienes that are in an s-trans conformation will result in no reaction. When cyclopentadiene is used as the starting diene, a bridged bicyclic compound is formed.