Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: marsio95 on July 23, 2021, 10:27:34 AM
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Hello everyone,
I'm currently working on the synthesis of modified polysaccharides. I attempted to graft along some cellulose backbone a carboxylic acid through coupling reaction (CDI, DMAc). The question is now how do I work out the Degree of substitution ? Typically I do it by 1H NMR for modified polysaccharides. I normally use the anomeric proton as a reference (its integral actually accounts for 1 proton)and then select a specific signal of a side group of a known amount of protons and calculate their ratio.
However, in this case one of the signals of the carboxylic acid actually overlaps the anomeric proton thus making impossible to use the same procedure. I could use other techniques, elemental analysis for instance. Before going through that, is there a way I could extract the DS by analysing the proton spectrum ? Looking at the spectrum I have one clear isolated signal (corresponding to the methyl group of the acid) that accounts for 3 protons and then 2 overlapped signals around the anomeric region. The latter correspond to the anomeric proton (1 proton ) and the methylene of the acid (accounts for 2 protons). ??? ??? ???
Do you have any suggestion ?
Thank you everyone
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What about HRMS?
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I haven't tried it yet. I'd like to extract as many details as possible from the NMR spectrum I got, before moving on. But I'll keep it in mind, thanks.
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higher field NMR?
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The spectrum has already been recorded at 700 Mhz. I'll try to submit a picture as soon as I can.
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I just learned today that its possible to integrate 13C NMR signals with some fancy pulse sequence or whatever. Don't ask me how. Maybe that is worth a look?
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I think its a clever idea wildfyr.