1H NMR with Partial Transition Selectivity

Abstract

1H NMR has unique strengths, owing, for one, to 1H being the most sensitive NMR nucleus. However, the limited frequency range of 1H 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 1H 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 1H 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 1H to coupled 13C carbons at natural abundance and ending finally with 1H detection. The experiment may be termed CArbon Single transition EDited (CASED) 1H 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 1H NMR of a disaccharide is demonstrated as a first practical example