1H NMR with Partial Transition Selectivity

H-1 NMR has unique strengths, owing, for one, to H-1 being the most sensitive NMR nucleus. However, the limited frequency range of H-1 chemical shifts implies spectral crowding, leading to difficulties in assignment and interpretation of the spectra. Homonuclear broadband decoupling has been developed as a means of simplifying H-1 NMR spectra but clearly leads to the inevitable and complete loss of precious information on homonuclear scalar couplings in solution state. A novel experiment is introduced in this work, which leads to partial H-1 multiplet selectivity, thereby reducing spectral crowding, while at the same time permitting couplings to be inferred. The present one-dimensional (1D) experiment relies on two-way coherence transfer starting from H-1 to coupled C-13 carbons at natural abundance and ending finally with H-1 detection. The experiment may be termed CArbon Single transition EDited (CASED) H-1 NMR. The unusual spectral patterns that result are summarized, demonstrated, and rationalized for various molecular fragments. Artifacts in the present version of the CASED experiment are also described, and an application to the H-1 NMR of a disaccharide is demonstrated as a first practical example.

Automated summary

H-1 NMR has limitations due to the limited frequency range of H-1 chemical shifts, which leads to spectral crowding and difficulties in assignment and interpretation. The CASED experiment introduced in this work reduces spectral crowding while allowing for the inference of couplings. The experiment involves coherence transfer from H-1 to coupled C-13 carbons and ends with H-1 detection.