“…Although the extreme broadening of the shared proton stretch implied by this assignment is unprecedented, several recent reports have also found this motif to be unusually susceptible to strong anharmonic coupling. 19,20,22 Unfortunately, the expected anharmonic red shift would place the centroid of the shared deuteron stretch in the cluttered fingerprint region, thus frustrating the confirmation of this assignment using isotopic shifts. Nonetheless, we conclude that the structures with a strong intramolecular H-bond between -S À and -CO 2 H, best accommodates the spectroscopic data, and points to the need for further study to understand the strong anharmonicities that are associated with this motif.…”