A natural product full 2D NMR spectrum shows nice sharp 13C peaks and sharp 1H peaks. However, few signals (CH2 and CH) are very broad and correlate in HSQC to carbons that are also very short and broad? what causes a part of the molecule to behave like this ? The only thing i can think of is rapid conformational change. In that case how do i fix this issue ? because solving the structure is not a possible with 5 signals being ambiguous. Thank you
P.S multiple crystallization attempts failed
at the begging, are you make chemical screening for sample? in other meaning, if yes, what class of compound you have. if no, try Drangndroff reagent to identify alkaloids.
I think, the broad peaks are due to the nitrogen group (amino) attach to CH2 or CH
Thank you for your response, although Nitrogen won't cause broadening to this extent (methine and methylene signal almost invisible in the C13). also based on my experience with alkaloids I didn't notice N to cause broadening of protons. Anyway the HRESIMS determined the formula to be C13H22O6.
Hello Amjad,
The broad signals may arise from dynamics in your molecule. You may wish to try and acquire some 1H 1D spectra at different temperatures in order to see if you can slow down the dynamics (going to lower temperature) or speed it up (higher temp). Upon cooling the broad signals may sharpen and split; one signal for each H of a given type per distinct molecule (.e.g, conformer). The high temperature route will yield a 'simpler' spectrum as you'll have just the time average of the two (or more) structures, but may be problematic for potential degradation.
Cheers,
Pedro
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