Here is a pretty good article about synthetics..
http://www.whatprice.co.uk/car/synthetic-oil.html
This is the way I understand it. I am not a chemist. I don't make oil, dino or synthetic for a living.
There is a major difference in 'dino' and 'synthetic'.
Dino oil is taken from the ground and 'cracked' essentially cooked and broken into smaller hydrocarbon chains then its sorted. Thus different types of things are made from crude oil.
Gas, motor oil, diesel fuel, etc.
Synthetic oil is engineered from the same types of materials. However, instead of being a major jumble of different sized hydrocarbon chains, synthetic hydrocarbon chains are made all the same. Thus making a lubricant that is made up of all the same sized hydrocarbon molecules. I imagine that the source of the hydrocarbons used to make synthetics varries quite a bit.