Question about chemical substituent bonding on aromatic rings

[t_wrex]

I have been developing an amateur interest in chemistry lately. So far I'm mostly familiar with the basics of valency/orbital filling, covalent bonding where atoms share orbitals, and things like polarity (where one part of the molecule has atoms with a larger atomic number, and thus a higher attraction force for bonding).

If you have an aromatic ring and you want to, for example, add two separate methyl groups to it, what determines where exactly on the ring they are placed? I'm familiar with the "ortho-", "meta-", and "para-" denominations describing the locations of the substituents, but how (and why) do substituents end up in certain places? How would you ensure that a substituent you are adding in a reaction goes to a particular place?

Along the same lines, if your parent compound has 2 rings (or more), what dictates where the substiuents go?

Thanks, apologies if the question doesn't make sense, I've only just started relearning chemistry.

 

[TripSitterNZ]

recommend the claytons organic chemistry textbook edition 2 there are pdfs online for it which will explain and cover these topics alot better than i can https://www.amazon.com/Organic-Chem...BV8NNC6E0HK&psc=1&refRID=0J7ZF5W5CBV8NNC6E0HK find a pdf for this

 

[sekio]

If you have an aromatic ring and you want to, for example, add two separate methyl groups to it, what determines where exactly on the ring they are placed? [...] but how (and why) do substituents end up in certain places? How would you ensure that a substituent you are adding in a reaction goes to a particular place?

Generally speaking you have no direct control over where groups go. Read up on molecular orbital theory - basically the shape of the electron clouds around the ring will determine where substituents will go, so e.g. nitrobenzene will have different substitution patterns when brominated than chlorobenzene will.
Unfortunately we don't have reactions that allow arbitrary connections but we do know pretty well what connections we *can* make using the reactions we have. So people planning a synthesis will look for more feasible reactions that make their products in higher yield.

 

[t_wrex]

Generally speaking you have no direct control over where groups go. Read up on molecular orbital theory - basically the shape of the electron clouds around the ring will determine where substituents will go, so e.g. nitrobenzene will have different substitution patterns when brominated than chlorobenzene will.

Yes, I am having some difficulty wrapping my head around this. The book I’m reading now calls it orbital hybridization. I’m aware that each orbital has a specific shape, but can’t quite visualize how different ones interact in terms of placement, bond angle, etc.

More reading is necessary.