August 13, 2020, 04:39:03 PM
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Topic: Need help with mechanism  (Read 585 times)

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Online Gameofketones

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Need help with mechanism
« on: August 02, 2020, 02:11:50 AM »
The correct option is (a). Is this Shapiro reaction? If so, can anyone help me out with the mechanism..I know the base abstracts the proton with Nitrogen but how does the ring reduce?

Offline AWK

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Re: Need help with mechanism
« Reply #1 on: August 02, 2020, 04:39:01 AM »
? May be this one.
CC(=C1CC1(C)C)C
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Offline Enthalpy

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Re: Need help with mechanism
« Reply #2 on: August 03, 2020, 04:59:50 AM »
For my personal information:
how reasonable is a prediction for such unstable compounds?

Offline AWK

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Re: Need help with mechanism
« Reply #3 on: August 03, 2020, 05:38:58 AM »
For my personal information:
how reasonable is a prediction for such unstable compounds?
There are many more unstable compounds that chemists work with. The derivative of the compound drawn by me (ring substituted propionate ester) is the pheromone of American cockroaches.
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Offline hollytara

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Re: Need help with mechanism
« Reply #4 on: August 04, 2020, 05:02:59 PM »
I think this is Bamford-Stevens not Shapiro. 

Shapiro uses 2 equivalents of BuLi while Bamford-Stevens uses "base" in general, so can be done in protic or aprotic solvents.  Both go through a Diazo intermediate, depending on conditions this may make a carbene (aprotic) or a carbocation (protic). 

So imagine a carbene or carbocation was formed where the N attaches to the ring.  How would that lead to what you find?

Offline wildfyr

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Re: Need help with mechanism
« Reply #5 on: August 05, 2020, 10:12:15 AM »
Totally unrelated, but how is =N-NH-Ts formed?

Offline AWK

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Re: Need help with mechanism
« Reply #6 on: August 05, 2020, 12:05:34 PM »
Totally unrelated, but how is =N-NH-Ts formed?
Very easy. Ketone and tosylhydrazine in methanol, a few drops of conc. HCl, RT overnight.
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Offline wildfyr

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Re: Need help with mechanism
« Reply #7 on: August 05, 2020, 07:51:49 PM »
Derp, thanks.

Offline Enthalpy

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Re: Need help with mechanism
« Reply #8 on: August 06, 2020, 03:22:07 PM »
For my personal information: how reasonable is a prediction for such unstable compounds?
There are many more unstable compounds that chemists work with [...]
Sure. I saw tentative rocket fuels with cyclopropenes and spirohex-1-ene
https://apps.dtic.mil/dtic/tr/fulltext/u2/a248465.pdf
But the authors easily recognized that they obtained 10 times the wrong compound and 1 time or 0 time the desired one, due to unpredictable rearrangements. That's why I wondered about predicting products.

Offline AWK

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Re: Need help with mechanism
« Reply #9 on: August 06, 2020, 06:29:23 PM »
For my personal information: how reasonable is a prediction for such unstable compounds?
There are many more unstable compounds that chemists work with [...]
Sure. I saw tentative rocket fuels with cyclopropenes and spirohex-1-ene
https://apps.dtic.mil/dtic/tr/fulltext/u2/a248465.pdf
But the authors easily recognized that they obtained 10 times the wrong compound and 1 time or 0 time the desired one, due to unpredictable rearrangements. That's why I wondered about predicting products.


In this particular case, the pyrolysis of tosyhydrazone sodium as a synthesis method rather excludes the most strained endocyclic cyclopropenes or cyclobutenes. The endocyclic double bond (isopropylidene or isopropenyl) is a much better explanation for thermal rearrangement. Therefore, I immediately indicated 1,1-dimethyl-2-isopropylidenecyclopropane.
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Offline AWK

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Re: Need help with mechanism
« Reply #10 on: August 07, 2020, 02:24:59 PM »
Correction:
Quote
The endocyclic double bond
It should be: The exocyclic double bond
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Online rolnor

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Re: Need help with mechanism
« Reply #11 on: August 07, 2020, 04:59:03 PM »
Gameoffketones give that the correct answer is a, he want the mechanism?

Offline AWK

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Re: Need help with mechanism
« Reply #12 on: August 07, 2020, 05:59:03 PM »
This is not the Shapiro reaction.
This is not the correct answer.
Hollytara gave the correct name of this reaction.
Gameofketones should show his work. I showed the most probable structure as a result of carbocation rearrangement (base -  MeONa in methanol).
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Online Gameofketones

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Re: Need help with mechanism
« Reply #13 on: August 10, 2020, 04:30:45 AM »
Is this correct?

Offline AWK

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Re: Need help with mechanism
« Reply #14 on: August 10, 2020, 05:36:57 AM »
The published synthesis I found (MeONa, 150°C) gave 1,1-dimethyl-2-isopropylidenecyclopropane and 1,1-dimethyl-2-isopropenylcyclopropane
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