Mosher's Acid
Mosher's acid, once converted to its corresponding acid chloride, reacts readily with alcohols and amines to give esters and amides, respectively. The lack of an alpha-proton on the acid prevents loss of stereochemical fidelity under the reaction conditions. Thus, using an enantiomerically pure Mosher's acid allows for determination of the configuration of simple chiral amines and alcohols.
Read more about this topic: Chiral Derivatizing Agent