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Author: Subject: Is there a limit to what alcohols you can make with the grignard reaction? steric hinderance?
Cou
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[*] posted on 29-11-2020 at 23:49
Is there a limit to what alcohols you can make with the grignard reaction? steric hinderance?


i have yet to actually do it. i'm still collecting needed supplies, but the grignard reaction fascinates me greatly because it's so versatile and there are so many alcohols you can make with it.

is there a limit on what alcohols you can make, due to steric hinderance? what if you tried adding diethyl carbonate to tert-butyl magnesium bromide? or tritylmagnesium bromide? or converted the product tertiary alcohols to alkyl bromides and grignard reagents and did this AGAIN, thereby creating exponentially more massive alcohols? the final products would be very bulky and might not even be able to exist?

just an interesting thought, i can't find any literature on this issue.

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edit: the tri-tertbutyl carbinol compound does exist and has been characterized,

[Edited on 11-30-2020 by Cou]




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[*] posted on 30-11-2020 at 01:19


The short answer is stearic hinderance will prevent the formation of increasingly bulky alcohols.

The stearic hinderance is going to make this a hard synthesis with low yield regardless of method.
But instead of diethyl carbinol, you need hexamethyl acetone.
The ethyl ether groups in diethyl carbinol are not going to replace due to stearic hinderance.
You need a better leaving group. Or in the case of hexamethyl acetone, simply adding to a ketone.

Here is the literature reference of tri-tertbutyl carbinol.
And the structure corresponds to the second structure. The yield of tri-tert-butyl carbinol is 5%

https://pubs.acs.org/doi/pdfplus/10.1021/ja01217a049

The first structure would require hexaphenyl acetone using the same method which to my knowledge doesn't exist.
I am not certain if it can be made due to the stearic hinderance.

While the compounds may be interesting, I cannot think of a practical application.
This is of course science and practical applications are not the goal.
Commercial research labs generally have a goal.
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Cou
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[*] posted on 30-11-2020 at 02:37


That is nuts, you can't even make tri-t-butyl carbinol from t-butyl lithium and hexamethylacetone.



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Dr.Bob
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[*] posted on 30-11-2020 at 15:54


Even if you can make a super steric Grignard, it likely won't react. Some sterically hindered Grignards are used to deprotonate other compounds, much like butyl lithium, as they are just not very nucleophilic. I think isopropyl Grignard can even be hindered enough to do this. I'm sure there are some reactive ketones that it will react with, but with many compounds it just does little or nothing. I'm sure that people have already published some lists of what does and does not work, but it might be decades old.
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Cou
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[*] posted on 30-11-2020 at 22:10


I guess I have to get into organolithiums if I want to make diiisopropyl carbinol.
organic chemistry seems fun on paper, but often turns out to be disappointingly messy in reality.

[Edited on 12-1-2020 by Cou]




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[*] posted on 1-12-2020 at 09:04


Quote: Originally posted by Cou  
I guess I have to get into organolithiums if I want to make diiisopropyl carbinol.
organic chemistry seems fun on paper, but often turns out to be disappointingly messy in reality.
You’re finally getting it! Don’t be discouraged though. The challenges just make it more fun.



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