Chapter 10: Conjugation in Alkadienes and Allylic Systems

Reactions of Dienes

In general terms, dienes undergo electrophilic addition reactions in a similar fashion to alkenes (review)

• Conjugated dienes undergo addition but the proximity of the conjugated C=C influences the reactions
• Isolated dienes react just like alkenes (chapter 6)
• Cumulated dienes react more like alkynes (after all, both have sp hybridised C atoms)

The π bonds are a region of high electron density (red). Therefore, conjugated dienes are typically nucleophiles. Hence, dienes react with electrophiles (e.g. H+, X+) Dienes can undergo addition reactions in which one or both of the π bonds are converted to new stronger σ bonds. Overall reaction :  Electrophilic addition

The reactions that will be considered in the following sections are:

• Addition of hydrogen halides
• Addition of halogens
• The Diels-Alder reaction

© Dr. Ian Hunt, Department of Chemistry