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Topic: Orgo mechanism....right or wrong?  (Read 3963 times)

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Offline noork85

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Orgo mechanism....right or wrong?
« on: May 01, 2013, 09:24:21 PM »
does this look right?

if not, please point out whats wrong with the mechanism.

https://www.dropbox.com/s/kn2is9cpl41hf96/2013-05-01%2021.11.02.jpg
« Last Edit: May 01, 2013, 09:43:08 PM by noork85 »

Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #1 on: May 01, 2013, 10:09:19 PM »
I don't think it's right, how come CH3OH becomes CH3O- ?
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Offline noork85

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Re: Orgo mechanism....right or wrong?
« Reply #2 on: May 01, 2013, 10:20:59 PM »
ok it adds as methanol and not methoxide, but it does lose the H when it bonds to the carbon, because oxygen forms a positive charge.

what else seems wrong???

Offline TwistedConf

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Re: Orgo mechanism....right or wrong?
« Reply #3 on: May 01, 2013, 10:27:15 PM »
It's not right at all-- and there are actually so many problems with what you wrote that it's not worth going through it.

Go back and review acid-catalyzed acetal formation reactions and then try it again.


Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #4 on: May 01, 2013, 10:27:39 PM »
Try taking 'hemiacetal route', react the alcohol with aldehyde group, it will form an hemiacetal, remove water, attack of carbocation on electron rich site(i.e. the carbon attached with OH), removal of proton, leads to the structure.

If you are not able to understand it properly, I will upload a picture for you..!
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Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #5 on: May 01, 2013, 10:30:10 PM »
ok it adds as methanol and not methoxide, but it does lose the H when it bonds to the carbon, because oxygen forms a positive charge.

what else seems wrong???

that H goes and stick with O- to form an hemiacetal..!

and after that the reaction proceeds..!
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Offline noork85

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Re: Orgo mechanism....right or wrong?
« Reply #6 on: May 01, 2013, 10:47:23 PM »
thanks.....i realize this is material we havent yet covered in my orgo class. i was doing a practice exam of my professors and she tends to recycle her exams, so thats where i got that from. and we havent covered hemiacetal formation yet

Offline noork85

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Re: Orgo mechanism....right or wrong?
« Reply #7 on: May 01, 2013, 10:49:22 PM »
Try taking 'hemiacetal route', react the alcohol with aldehyde group, it will form an hemiacetal, remove water, attack of carbocation on electron rich site(i.e. the carbon attached with OH), removal of proton, leads to the structure.

If you are not able to understand it properly, I will upload a picture for you..!

if isnt too much of a problem, can u please upload a picture. thank u

Offline Dan

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Re: Orgo mechanism....right or wrong?
« Reply #8 on: May 02, 2013, 02:53:22 AM »
It is standard acid-catalysed acetal formation, no funny business here.

Maybe look up linear vs cyclic forms of sugars, and look up glycosylation for inspiration.
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Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #9 on: May 02, 2013, 03:56:49 AM »
^^I think I already answered the question...isn't it ?

@noork85: No, not much of problem for me, will upload it in few hours.
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Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #10 on: May 02, 2013, 05:28:16 AM »
I think that you don't know the mechanism of formation of 'hemiacetal', so first I have shown the mechanism of formation of 'hemiacetal'.

In Step 2:  :resonance: represents resonating structures, and the one in which C bears the positive charge is more stable.
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Offline Dan

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Re: Orgo mechanism....right or wrong?
« Reply #11 on: May 02, 2013, 06:15:15 AM »
Right idea, but I think your steps are in the wrong order. Intramolecular reactions are faster than intermolecular reactions.

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Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #12 on: May 02, 2013, 09:04:22 AM »
^^^May I know which steps are in wrong order ?

He already had the answer, I gave him the mechanism. I gave him the hint, he was not able to understand it, it saves time. I gave him the mechanism how hemiacetal forms, which are available on other sites also.

Fine, it won't be repeated again.
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Offline Dan

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Re: Orgo mechanism....right or wrong?
« Reply #13 on: May 02, 2013, 09:41:38 AM »
^^^May I know which steps are in wrong order ?

I'd swap steps 2 and 6; I think this is an intermediate:

CC1CCC(O)O1
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Offline betterbesafehero

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Re: Orgo mechanism....right or wrong?
« Reply #14 on: May 02, 2013, 02:29:22 PM »
^^^Yes, I think you are right, but I wanted to show him how hemiacetal really forms. Well, thanks for your keen observation, I also learned something. There are many doubts in intramolecular substitution, you could have easily helped me. Some answers are still pending. I sometimes feel neglected here.

I am a very young student, I am yet to begin my undergraduate studies. I have read many books thoroughly, even multiple times extending it to 6 or 7 times. Whatever is there in the book, I understand it completely. Some topics are not covered in books, my teachers also skipped it.
“You never fail until you stop trying.”
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