[kriggy]

Hi im digging through NMR determination of absolute configuration and have question about mosher´s acid method:
Lets say I have derivative with configuration X and then make the derivatives with configuration R-X and S-X. I compare the two spectra - some signals are downfield and some upfield so I can deduce the configuration. However, I never run the method until recently and found out that the derivatives compared to the parrent compound have the signals shifted the same way. Is that a common ? I mean, I thought I compare the spectra of derivatives to the spectra of parrent compound as well but then I cant get any information unless I compare ONLY derivatives. See the attached picture for more clear explanation -
 blue: non derivatized amine, green and red MTPA amides.