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Reaction of an acyl chloride with a dye.

Here's a dye, Lawsone:
http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/HNQ.svg/200px-HNQ.svg.png

It's first reacted with NaOH solution to give the R-O- ion(bonded with the carbon with the double bond) where R represents the rest of the molecule. It's then reacted with ethanoyl chloride to give , which is named B. A question then asks the structure of an isomer of B, which is also formed during the reaction of Lawsone with ethanoyl chloride, has the same functional groups as B, but with different arrangements.

My problem is that will the isomer be a cis-trans isomer, because there's no rotation allowed by the carbon-carbon double bond? And if it's cis-trans isomer, can it be shown by drawing the new "ester linkage" within the second ring?
(edited 11 years ago)

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It's not a geometric (cis-trans) isomer given the symmetry. Where did you get this question from, out of interest? :p:

I think it's probably wanting you to notice the keto-enol tautomerism :yes:
Reply 2
Original post by EierVonSatan
It's not a geometric (cis-trans) isomer given the symmetry. Where did you get this question from, out of interest? :p:

I think it's probably wanting you to notice the keto-enol tautomerism :yes:


It's from a past paper of A Level chemistry.

Never heard about "keto-enol tautomerism"!!:eek3: How could an A Level paper ask such a question then? :woo:
Original post by Zishi
It's from a past paper of A Level chemistry.

Never heard about "keto-enol tautomerism"!!:eek3: How could an A Level paper ask such a question then? :woo:


I don't know, that's why I'm asking where you got it from :mmm:

I'm not seeing what else it could be referring to, maybe someone else can.
Reply 4
Original post by EierVonSatan
I don't know, that's why I'm asking where you got it from :mmm:

I'm not seeing what else it could be referring to, maybe someone else can.


Ah, thanks for your help. :smile:

I hope someone else spots something related to A Level. :frown:
Original post by Zishi
Ah, thanks for your help. :smile:

I hope someone else spots something related to A Level. :frown:


I guess you're not being asked about how the isomer is formed, so could just not worry about the details and just drawn an isomer with the same groups but in different positions.
Reply 6
Original post by EierVonSatan
I guess you're not being asked about how the isomer is formed, so could just not worry about the details and just drawn an isomer with the same groups but in different positions.


Alright, so it means that I can attach CH3CO- group at one of the Oxygen atoms in the ketone in that dye?
Original post by Zishi
Alright, so it means that I can attach CH3CO- group at one of the Oxygen atoms in the ketone in that dye?


Yeah, try that.
Reply 8
Impossible! the question has it wrong. Surely the R-[O-] will form ion-dipole bonds with the Na+ from NaOH. So you get:

R - Na+O-.

And of course, water is eliminated.
Original post by Ilyas
Impossible! the question has it wrong. Surely the R-[O-] will form ion-dipole bonds with the Na+ from NaOH. So you get:

R - Na+O-.

And of course, water is eliminated.


But wouldn't the O-Na+ bond dissociate in solution as it's ionic?
Original post by EierVonSatan
I don't know, that's why I'm asking where you got it from :mmm:

I'm not seeing what else it could be referring to, maybe someone else can.


My thoughts were keto-enol tautomerisation as well.

Original post by thegodofgod
But wouldn't the O-Na+ bond dissociate in solution as it's ionic?

Indeed. He is wrong.

If you're interested, you can form the second product by pushing a few arrows around. If you take the C=C-O-, and push the negative charge down to form a C=O, push an arrow from the C=C down towards the cabonyl - double bond onto the next carbon, and then push the C=O electrons up onto the O you get a resonance form of the deprotonated structure (same idea as resonance structures in benzene). Then form the ester on this different O-.
(edited 11 years ago)
Original post by illusionz
My thoughts were keto-enol tautomerisation as well.


Indeed. He is wrong.

If you're interested, you can form the second product by pushing a few arrows around. If you take the C=C-O-, and push the negative charge down to form a C=O, push an arrow from the C=C down towards the C=O, and then push the C=O electrons up onto the O you get a resonance form of the deprotonated structure (same idea as resonance structures in benzene). Then form the ester on this different O-.


So are you suggesting: (attachment)
Original post by thegodofgod
So are you suggesting: (attachment)


Not quite. You will still have a enolate (C=C with an O- bound to one of the carbons).
You simply need to move the double bond 1 carbon round the ring and then push the arrows on the carbonyl up to the O so you don't get a pentavalent carbon.



Just re-read what I wrote and I can see how you got confused if you're not used to this sort of thing. When I said down towards the C=O i just meant down on the diagram, not actually onto the C=O, sorry!
(edited 11 years ago)
Original post by illusionz
Not quite. You will still have a enolate (C=C with an O- bound to one of the carbons).
You simply need to move the double bond 1 carbon round the ring and then push the arrows on the carbonyl up to the O so you don't get a pentavalent carbon.



Just re-read what I wrote and I can see how you got confused if you're not used to this sort of thing. When I said down towards the C=O i just meant down on the diagram, not actually onto the C=O, sorry!


See what you mean now :smile:
Original post by thegodofgod
See what you mean now :smile:


:yes:
Original post by illusionz
:yes:


Fun stuff!

Spoiler



Spoiler

Original post by thegodofgod
Fun stuff!

Spoiler



Spoiler



I found stuff like that much more interesting than most of the stuff you learn at A level. I honestly have no idea why some of the stuff at A level is even on the syllabus. Making people learn colour changes and chemical tests seems completely pointless and I've never come across a book/lecturer even mention chemical/flame tests apart from saying how crap they are.

Anyway, I should get to bed, should really do a few hours revision before brunch tomorrow. Finals and all :frown:
Original post by illusionz
I found stuff like that much more interesting than most of the stuff you learn at A level. I honestly have no idea why some of the stuff at A level is even on the syllabus. Making people learn colour changes and chemical tests seems completely pointless and I've never come across a book/lecturer even mention chemical/flame tests apart from saying how crap they are.

Anyway, I should get to bed, should really do a few hours revision before brunch tomorrow. Finals and all :frown:


Me too - it's almost 2! :eek:

Anyway, best of luck for your exams! :yy:
Reply 18
Oh, my goodness. I wish I knew about that. :cry2:
Original post by EierVonSatan
It's not a geometric (cis-trans) isomer given the symmetry. Where did you get this question from, out of interest? :p:

I think it's probably wanting you to notice the keto-enol tautomerism :yes:


So hold up, are you telling me that this would be one of the products :

IMG_0258.jpg

Because that's what I drew.

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