64 Unit 9: Dienes
In alkene^1 chemistry, we demonstrated that allylic carbon could maintain a cation charge
because the double bond could de-localize to support the charge. What of having two double
bonds separated by a single bond? What of having a compound that alternates between
double bond and single bond? In addition to other concepts, this chapter will explore what
a having a conjugated^2 system means in terms of stability and reaction.
Dienes are simply hydrocarbons which contain two double bonds. Dienes are intermediate
between alkene^3 s and polyenes.
Dienes can divided into three classes:
- Unconjugated dienes have the double bonds separated by two or more single bonds. These
are also known as isolated dienes. - Conjugated dienes have conjugated double bonds separated by one single bond
- Cumulated dienes (cumulenes^4 ) have the double bonds sharing a common atom as in a
group of compounds calledallenes.
1 Chapter 51 on page 191
2 Chapter 66 on page 237
3 Chapter 51 on page 191
4 https://en.wikipedia.org/wiki/cumulene