Since you already know how
to name alkenes, this tutorial will focus more on the
concepts of dienes.
There are three types of conjugated dienes:
Isolated - these are double bonds that are isolated
Cumulative - these are double bonds that follow one another
Conjugated - these are double bonds that are separated by one single
As you will read later, conjugated dienes are very important.
Delocalization- existence of p electron
cloud extends over four carbons (in a conjugated diene), opposed to two in a normal -ene.
This is important because the delocalization means that the carbon has more electrons to
share amongst itself, which lowers energy and makes the molecule more stable.
Resonance theory - states whenever a molecule or ion can be
represented by two or more structures that differ only in the position of the electrons,
there are three implications: (I shamelessly stole these off of my organic chem book)
There are multiple structures to represent the same molecule
The actual structure is a mixture (hybrid) of the different possible structures
The molecule or ion is considerable more stable (that is, of lower energy) than would be
expected based on any single structure
This is a reaction where the bromine is removed from an alkene. The removal of bromine
creates a carbocation (since the bromine stole the electron pair that originally kept the
carbon neutral). A carbocation is a carbon with a positive charge. As the image above
demonstrates, the p bonds from the neighboring carbon can
"shift" over to the carbocation. However, this leaves the other carbon with a
positive charge. Eventually, you will add something to get rid of that charge. This is
resonance. Later on, in the aromatics chapter, you will see more examples of resonance.