organic chemistry question

[sarkywarky]

Hey guys. Can someone help me out with the problem below?

In part a, all of the compounds are non aromatic and I'm pretty sure the answer has to do with resonance. The question is asking for the compound with the lowest pka i.e. the most acidic compound which would mean the compound with the weakest conjugate base (most stable conjugate base) and therefore the one with the most resonance structures.

For part b, all of the compounds are aromatic and the question is asking for the strongest base, i.e. the most reactive/least stable base or the one with the least resonance structures.

I don't know if I'm drawing the resonance structures incorrectly or if there's some other way of figuring this out.
If someone would care to help me or even draw the resonance structures out, I'd really appreciate it!

Thanks!

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[Jordwin]

I can't see your upload, could just be because I'm on my phone idk.

 

[sarkywarky]

I can't see your upload, could just be because I'm on my phone idk.

huh weird. hang on let me try and attach it differently

 

[sarkywarky]

does this work?

 

[Jordwin]

Yep it works. I don't think I can adequately answer your question though. I need to work on my ochem a bit more :-/

 

[sskater]

Hey guys. Can someone help me out with the problem below?

In part a, all of the compounds are non aromatic and I'm pretty sure the answer has to do with resonance. The question is asking for the compound with the lowest pka i.e. the most acidic compound which would mean the compound with the weakest conjugate base (most stable conjugate base) and therefore the one with the most resonance structures.

For part b, all of the compounds are aromatic and the question is asking for the strongest base, i.e. the most reactive/least stable base or the one with the least resonance structures.

I don't know if I'm drawing the resonance structures incorrectly or if there's some other way of figuring this out.
If someone would care to help me or even draw the resonance structures out, I'd really appreciate it!

Thanks!

Hey so for
A)
The first structure with an anion on the top of it will be aromatic! Since there will be 6 pairs of pi/lp electrons in it, thus it's aromatic. Remembe 2, 6, 10,...AROMATIC. 4,8,12,16..ANTIAROMATIC
B)
We see here that the strongest base means the most unstable lonepair that isnt stabilzed by conjugation, aromaticity and what not.
For benzene it is obviously super stable, so we take that off our list. For the third choice, we see that the lone pair on the Nitrogen is able to push its electrons in the ring forming more resonance structures.

The middle choice is the only one where the LONE PAIR is not stabilized. The molecule itself is actually aromatic! Since the l.p doesn't count in aromaticity due to the area having pi bonds already.

Hope this helps you.

 

[sarkywarky]

Hey so for
A)
The first structure with an anion on the top of it will be aromatic! Since there will be 6 pairs of pi/lp electrons in it, thus it's aromatic. Remembe 2, 6, 10,...AROMATIC. 4,8,12,16..ANTIAROMATIC
B)
We see here that the strongest base means the most unstable lonepair that isnt stabilzed by conjugation, aromaticity and what not.
For benzene it is obviously super stable, so we take that off our list. For the third choice, we see that the lone pair on the Nitrogen is able to push its electrons in the ring forming more resonance structures.

The middle choice is the only one where the LONE PAIR is not stabilized. The molecule itself is actually aromatic! Since the l.p doesn't count in aromaticity due to the area having pi bonds already.

Hope this helps you.

I get your explanation for part b, but why is the first structure in part A aromatic? It doesn't have an anion. I thought compounds 1, 2 and 3 are non aromatic because they have sp3 carbons.

 

[Xo1991]

I get your explanation for part b, but why is the first structure in part A aromatic? It doesn't have an anion. I thought compounds 1, 2 and 3 are non aromatic because they have sp3 carbons.

when determining acidity, do so by looking at the conjugate base. so that first compound, when behaving as an acid, will lose a proton. the electrons will end up on the carbon, producing a carbanion with 2 electrons and a negative charge. 2+2+2=6, and following huckels rule, is an aromatic compound.

 

[sarkywarky]

when determining acidity, do so by looking at the conjugate base. so that first compound, when behaving as an acid, will lose a proton. the electrons will end up on the carbon, producing a carbanion with 2 electrons and a negative charge. 2+2+2=6, and following huckels rule, is an aromatic compound.

got it! 👍 thank you so much!