I am working on synthesis of heterocyclic compounds containg l-tryptophan. Most of the synthesized derivatives aren’t soluble in Dmso , I tried to use a mixture of TFA and Dmso-d6 , sample was soluble but the peaks wasn’t clear, Does the color of sample have any relation with clarity of the spectrum???
Dear Rana Diab thank you for asking this interesting technical question. Unfortunately it is not quite clear to me what you mean by "clarity" of the NMR spectrum? Either a compound is pure, then it will give a clean / clear spectrum in which all resonances can be assigned. When impurities are present, more signals are observed and the spectrum can get messy. If you add TFA, chances are that protonation reactions occur and you see the spectrum of a protonated species. In organic chemistry, a brown coloration normally indicates the presence of strongly colored impurities.
Frank T. Edelmann thank you for your helpful answer. I mean by clarity the absence of shimming and the visibility of all signals .
unfortunately, my compounds are brown colored so can you suggest the best solvent to crystallize them, they are N-acyl hydrazones but I have a few mgs of each so I was afraid to lose most of the product trying to dissolve and recrystallize .
There is no relation between the color of sample and the clarity of Hnmr spectrum. If the sample is pure its solution is perfectly clear.
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