[sharbeldam]

Hello guys!

I was trying to do a synthesis problem on a benzene (in theory not real life) and I ran across a question if you could help me with it, I had an aldehyde on a benzene and i protected it (with a diol, and now it's acetal/ketal), and I got confused if it would still be meta, some researcher told me it's meta and i get but is there a full list of deactivating groups, like the normal list dont contain ketal/acetal/C-OH/C-OR, i'd love a long list or a way to know simply if it's deactivating or activating so i can tell my students, that would help many!

thanks in advance

[rolnor]

No, its orto-para like a methyl group.

[sharbeldam]

Well i guess the researcher was wrong? so when you protect an aldehyde/ketone, it becomes o/p? despite having two oxygens that withdraw electrons?

[rolnor]

Oxygen is also electron donating. Also, there is no conjugation, you dont have a carbonyl double bond.

[sharbeldam]

as you say oxygen is electron donating, she says it's two oxygens that are electronegative and they are deactivating but less than carbonyls.

but ofcourse i always trust this site and you more, i appreciate the help.

[rolnor]

But they are on the methyl. Is dimetoxymethane acidic? Can you pick that proton on the CH2 with base? No. Acetals are very inert to base, not even BuLi will pick that proton.

[rolnor]

I should add, I am not sure how o,p-directing it is, maybe neutral, lika a hydrogen.

[OrganicH2O]

I am really curious about this and I don't think it's obvious. A carbon bonded to three chlorines is a deactivating meta director, because the chlorines can't donate by resonance and it just withdraws via induction. Oxygen is more electronegative than chlorine and so each oxygen should have a stronger inductive effect, assuming the alkyl groups connected to it have a minor effect. The solitary CH bond on the methine can donate via hyperconjugation. If it has a neutral effect like Rolnor is speculating, it would give a mixture of meta and para for steric reasons, I would think. And meta is favored due to random probability, if para and meta are both similar sterically.