[Cututu]

I did ester coupling between acid carboxylic containing bromo and alcohol. I purified and got pure product (TLC). But when I check H-NMR, the CH2 adjacent to bromide shows 2 triplet peaks with very different intensities ( the smaller one appears in the low field) . And next CH2 also shows similar phenomena ( the smaller appears in the high field). How can I explain it?

[Babcock_Hall]

What solvent did you use?

[Cututu]

What solvent did you use?

I used acetone-d6

[Babcock_Hall]

I meant to ask, "Which solvent did you use for the reaction, and have you checked the shift(s) associated with it versus you unexplained peaks."  BTW there is a useful list of NMR impurity peaks.  Fulmer et al. "NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist" 2010.  DOI: 10.1021/om100106e.

[clarkstill]

Any possibility of isomers or rotamers in the structure?

[Babcock_Hall]

Is it possible that the impurity will not be detected by TLC?  This might happen if one is using fluorescence quenching and the molecule does not absorb UV light, for example.  Or the impurity may be too low in concentration to detect on a TLC plate.

[Cututu]

I meant to ask, "Which solvent did you use for the reaction, and have you checked the shift(s) associated with it versus you unexplained peaks."  BTW there is a useful list of NMR impurity peaks.  Fulmer et al. "NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist" 2010.  DOI: 10.1021/om100106e.

Sorry for the mistake. I used DCM for reaction

[Cututu]

Is it possible that the impurity will not be detected by TLC?  This might happen if one is using fluorescence quenching and the molecule does not absorb UV light, for example.  Or the impurity may be too low in concentration to detect on a TLC plate.

At the first time I saw it, I also thought it was an impurity. so, I also tried to purify several times, and another person in my lab got the same NMR result too when he did this reaction. After that, I checked starting and it also has the same phenomenon.

[rolnor]

It would simplify if you draw the structure. If you have several conformations that are stable this might give double peaks like this