Orgo... double reinforcement??

[SmilezAllDay]

For this mini synthesis problem... the correct answer is A.

My initial answer is not even an option (4-bromo-2-nitrobenzoic acid). My question is, is this one of those instances where we opt for a double reinforcement, where COOH is meta to the nitro and ortho to the bromine ?

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[tyjacobs]

NVM

 

[SmilezAllDay]

??

 

[SmilezAllDay]

I don't know what you mean by a "double reinforcement." This is a multi-step synthesis EAS problem. For these types of problems, the key rule to remember is that when there are multiple substituents on a benzene ring, the strongest activating group determines regiochemistry.

Going through the problem step by step:

Step 1 is a bromination reaction. Because you have an alkyl substituent (ortho, para director) attached to the benzene ring already, the Bromine will add ortho or para to the methyl group.

View attachment 201940
Step 2 is a nitration reaction. Because there are 2 subtituents on the benzene ring at this point (the methyl group and the bromine), look for the strongest activating group and that group will determine regiochemistry. The methyl group is the strongest activating group; therefore, the NO2 group will add meta to the methyl group.
View attachment 201941
Step 3 is an oxidation reaction of an alkyl benzene. The requirement to this reaction is that there are allylic hydrogens on the alkyl group that is attached to the benzene ring (which there is in this case). Therefore, the methyl group will oxidize into a carboxylic acid.
View attachment 201943
Answer choice A represents one of the two products you can produce. All other answer choices are implausible. Therefore the answer is A

If you didn't know what all the reagents meant, check out my orgo notes. All of the reactions involved in this problem are included in my EAS chapter.

But in step 2, since methyl is the ring activator, wouldn't it direct the nitro group ortho or para? why would the activating group direct meta?

 

[tyjacobs]

But in step 2, since methyl is the ring activator, wouldn't it direct the nitro group ortho or para? why would the activating group direct meta?

now that I actually looked at the structure you thought was the right answer ur right

no2 should be added ortho or para to the ch3 group i dont know why this is the case. which testing software is this?

 

[DAT Destroyer]

View attachment 201922

For this mini synthesis problem... the correct answer is A.

My initial answer is not even an option (4-bromo-2-nitrobenzoic acid). My question is, is this one of those instances where we opt for a double reinforcement, where COOH is meta to the nitro and ortho to the bromine ?

You are overthinking a very poorly worded question. You are indeed correct, the major product would be 4-bromo-2-nitrobenzoic acid. No sane synthetic organic chemist would just install a bromine like this because there would be competition with the ortho isomer. In my 30 plus years experience of doing this, I would reckon that the ortho isomer would be as high as 40 %. Many times when a methyl group is on a ring, we get significant ortho isomer ratio.......For example if we nitrated toluene, we would get 55% ortho isomer bias. For the DAT, you will see clear cut questions, but I like the way you are thinking ! Do yourself a favor.....get a text written by a PhD in Organic chemistry to review the material. I suggest the David Klein text.

Hope this helps.

Dr. Jim Romano