Self-Test 1.5B

[Justin Le 2I]

I am confused how the molecule of 2-methyl-1,3-butadiene was found. I was looking for two double bonds that fit the 1,3 sequence but I couldn't. The answer key added a double bond onto the 3. Why does it do this and why is it right?

[Chem_Mod]

This is a tricky question and it is related to a huge group of important molecules called "terpenes". Terpenes have a skeleton composed of units of 2-methyl-1,3-butadiene, aka "isoprene". However, to fuse these isoprene units together, electrons do have to shift to create bonds, and therefore the double bonds don't stay in the same place.

Refer to this figure: http://assets.decodedscience.com/wp-con ... action.jpg
to see how Limonene is made from 2 units of isoprene.