The Crystal Structure of the More-soluble Mosher’s Salt

Abstract

The crystal structure of salt 4 prepared from (S)-3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid [(S)-MTPA, (S)-1] and (R)-1-phenylethylamine [(R)-PEA, (R)-2] was determined using X-ray crystallography. The (S)-MTPA anion showed an unusual conformation. The closest ion-pair joined with a methoxy-group-assisted salt bridge and aromatic C–H⋯π interaction in a unique supR association. The aromatic C–H⋯π interactions between the 21 columns were not effective. These results clarified the mechanism of Mosher’s enantioresolution of (RS)-1 with (R)-2 in combination with the previously reported crystal structure of the diastereomeric salt 3 [(R)-1·(R)-2].