Abstract Sheet 2

Three types of dienes were discussed:
a. isolated
b. cumulated
c. conjugated
be able to define them and recognize them

Conjugated dienes are more stable because of resonance, i.e. delocalization of the π
electrons. This is supported by ∆H hydexperiments - understand how to utilize this data
to explain relative stabilities. The lower the∆H hydthe more stable the molecule being
hydrogenated.

Conjugated dienes undergo 1,2 and 1,4 addition of HX (or any electrophile)
These products are explained through the mechanism which involves delocalized
carbocation intermediates.

The following steps can be followed when drawing out the mechanism of the addition
reactionof HX to conjugated dienes to determine all the products that are formed.
1. Add H+to each double bond so that onlyallylic carbocations are formed.
2. Draw resonance structures of each intermediate allylic carbocation.
3. Add X-to allcarbons which have a positive(+) charge to give all the
products.