Sample is an MIP with Methacrylic acid as the monomer.
Solvent used: DMSO-d6
Hello Yasmin,
Do you observe a big peak at 3.3 ppm, which usually corresponds to water? In that case it may be your sample is too wet. DMSO is very hygroscopic so its very difficult to keep it dry.
If that is the problems then dry your sample longer, reduce the water content of your DMSO with some molecular sieves. To remove water traces I would recommend adding a few molecular sieves 3A. After this you may try running your sample yet again.
Hope that helps.
You don't get the OH peak of carboxylic acids because besides being taken up by the moisture it may simply not be present as -OH, rather -O(Na) [or with some other metals] might have formed while workup or due to any reaction conditions.
Otherwise, one should get the characteristic peak for a deshielded proton of carboxylic acid (actual delta value may vary for different deuterated solvent and its interaction with the molecule).
Confirm by 13C carbonyl peak, if you you have wet DMSO (it absorbs moisture even during transfer of sample in NMR tube, if environment is conducive)
As Vidhura Mahendra said, the COOH may have been converted to COOD giving an HOD peak at 3.3 ppm. I take it there is no peak corresponding to COOH between 10.5-12 ppm. The d6 DMSO should not exchange its Deuterium, however. Perhaps you could try d6 Acetone as a solvent, or a solvent without Deuterium.
As what the other fellow researchers have explained here, I also don't think that the COOH exists as COOH, which could have been converted into COOD (as Frank Stary said) or
Yes Vidhura Mahendra, there is a big peak.
Thank you so much for the replies, this helped me a lot.
Dear Yasmin,
I have a nmr spectra with carboxylic and amide group in the compound, however there is no broad peak observed at 3.3ppm...the structure been confirmed with 13C as well as mass spec which correspond to its molecular weight..however i didnt encountered the 3,3ppm peak in my spectra...may i know is there any possibilities that causes the missing of this peak..N-H and O-H peak?
Thanks in advance.
We cant say exact position of OH, NH, and SH groups chemical shift value in 1H NMR. Because its depends upon on the nature of the starting materials what we can use. And also one more think i suggest here most of my carboxyl containing compounds gives chemical shift values between 11-12 ppm in DMSO-d6. But in the same way if i took in D2O medium i couldn't see same region it will disappear and exchange into aliphatic region. So we can confirm by using 13C NMR spectrum it will show in the chemical shift value 168-175 ppm.
I had a similar phenomenon, where the COOH was missing in the proton nmr. However, I observed a broad peak at 3.459 as Vidhura and Frank mentioned. The carboxylic acid was confirmed by C13 and MS-TOF
Thank you for this helpful discussion.
I am wondering why Frank said maybe acetone-d6 would help.
I have a compound with a carboxyl group and mix it with acetone-d6. I have the same problem no peak due to COOH and a pig peak at 3.3 ppm.
I want to study the deprotonation of the carboxyl group in the target compound in an aqueous ionic solution.
Thanks,
Sara
Hi ! not answer but question?
I would wish to ask, can one see -COOH in solid state 1H-MAS?
Thanks!
In the 1H-NMR spectrum, the COOH protons appear downfield in the region 10.5-13 ppm and are in most cases very broad, being difficult to see above the baseline. It is very rare to see them upfield because of the low electron density from around the proton.
Due to exchange of proton from NMR solvent and it's converted to COOD which did not appear in NMR spectrum. Some time it appear in downfield but do not see clear due to below the baseline.
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