So.......a few findings and things maked clear from my hungarian friends.
So E85 it's actually approx 80%ethanol and the rest until 100% regular petrol.
Not quite - it's 85% ethanol (hence the name E85) and 15% petroleum spirits (or "other").
E85 chemical formula CH3-CH2-OH
Petrol chemical formula C8H18
Again, close; ethanol has the formular CH3-CH2(OH) or commonly Et.OH
iso-Octane (aka trimethylpentane) has the formular CH8H18 or (CH3)3-C-CH2-CH-(CH3)2 (CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3 would be 'plain' octane), but petrol isn't just iso-octane (in fact it probably contains very little of it).
There's a lot of toluene (C6H11-CH3) - I can't draw a benzene ring, but it's usually refered to as phenyl so: Ph-CH3 (~30%).
Maybe some benzene C6H12 (~5%), maybe some xylene Ph-(CH3)2
Maybe some polyaromatics like napthalene (~1%), maybe some shorter compounds like hexane, cyclohexane...
Anyway, it's a complex mixture of hydrocarbons that have boiling points (and molecular masses) within set parameters (this is where you can get different petroleum spirits, by picking the boiling point ranges).
The mixture changes from refininery to refinery, and from month to month because they change the mixture to help with cold starting in winter, and less ping in summer.
Petrol can contain something like 5% ethanol as a naturally occuring additive anyway (it can even be added to this level under EU spec EN 228); it's only when it gets above ~10% that it might be flagged as an ethanol containing fuel.
EDIT: I'm not not trying to criticise you - it's just that I'm a chemist, so I'm trying to be helpful.