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Let's split the difference: Nonchiral porphine macrocycles have been used as chemical shift agents for the determination of the enantiomeric excesses of chiral carboxylic acids. This method is based on the observation of the relative splitting induced in the 1H NMR resonances of the porphine protons. A mechanism for the recognition based on the fast exchange of the guest molecules has been proposed (see scheme).
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Labuta et al. (2011) studied this question.
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