[cuppajoe]

Hello, this is my first time in the forum. I had a question in regards to a problem I have from a worksheet and I seem to be confused by it. It refers to an acetylation of 4-nitroaniline (or p-nitroaniline) with excess acetic anhydride, but I am confused because I am not sure as to whether or not the acetylation takes place on the nitro group (which is the oxygenated group of the molecule and tends to be related to all of the answers on the worksheet from what I've been able to tell thus far as the oxygenated molecule for all of them is acetylated). I also think this is the case, because if I remember the rules of reacting benzyl compounds with other reagents, usually the nitro group blocks any reaction with other groups on the benzene ring (but I don't remember for sure). Let me know  and thanx in advance.   

[Archer]

Look up the resonance structures of R-NO₂.

Consider how reactive the oxygen atoms would be as neucleophiles.

Then look up aromatic amines as neucleophiles, you should be able to work out the answer.

[orgopete]

Although basicity and nucleophilicity are not proportional properties, they can give a hint about reactivity. For example, compare methyl amine and aniline in reactivity and basicity. Methyl amine is more reactive. Now compare aniline and nitromethane, oops, I don'tknow that you'll find the pKa of protonated nitromethane in many tables. Does that suggest anything?

[Archer]

I also think this is the case, because if I remember the rules of reacting benzyl compounds with other reagents, usually the nitro group blocks any reaction with other groups on the benzene ring (but I don't remember for sure). Let me know  and thanx in advance.   

You are thinking about the fact that the nitro group is strongly deactivating to the aromatic ring so affects electrophillic substitution. It doesn't block it though, how else could you get 3-nitro groups on phenol to make picric acid?

 

benzyl compounds
 

Take care with your nomenclature, nitroaniline in not a benzyl compound.