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Topic: NMR sample prep issue  (Read 3185 times)

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Offline Ingeniosuccinimide

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NMR sample prep issue
« on: February 24, 2014, 07:28:55 PM »
Hello, I have quite an unusual problem:

the (presumed) product of one reaction I'm investigating forms as a precipitate, and it is very easy to separate it. However, when I tried to take an NMR spectrum of that precipitate to see what it actually is, I remained shocked because none of the deuterated solvents I used is in grade to dissolve the precipitate!

 I tried dissolving it in following order (all deuterated): chloroform, DMSO, water, methanol, acetonitrile, acetone, benzene. None of these worked, and these are the only NMR solvents we have in our lab. What should I do in this rather confusing situation?


Offline TheUnassuming

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Re: NMR sample prep issue
« Reply #1 on: February 25, 2014, 09:43:22 AM »
That is unusual, though not unheard of.  I have a few hunches but first what reaction/conditions/substrates are you using?
When in doubt, avoid the Stille coupling.

Offline Ingeniosuccinimide

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Re: NMR sample prep issue
« Reply #2 on: February 26, 2014, 02:32:38 PM »
I know this definitely won't help me, but I can't draw any products here since the procedure is something completely new.

All what I can say is that the reaction is conducted at 0 °C in DCM and that the precipitate which forms can be very easily filtered and washed. However, when it comes to NMR, I really don't know how to dissolve that.

Only other thing I can say is that the reaction involves thiirane (or positively charged thiiranium cation) at some point.

There might be a chance that the product is some kind of oligomer. Does anyone know any polymers that can form from thiirane or similar high-strained heterocycles?

Offline TheUnassuming

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Re: NMR sample prep issue
« Reply #3 on: February 26, 2014, 03:10:28 PM »
Haha... well if you aren't able to even talk general structure/reaction conditions then it makes it rather hard/nearly impossible to trouble shoot. 
Polymerization is possible yes, it depends on the conditions and substrate functionalities, but generally possible yes.  A polymerization reaction could definitely make a precipitate that you can't dissolve in anything (especially DCM).  I spent three years making a polymer library and with a number of cases, solid state NMR was the only option for NMR.  In these cases I also found IR very useful.
When in doubt, avoid the Stille coupling.

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