Hadamard Homonuclear Broadband Decoupled TOCSY NMR: Improved Efficacy in Detecting Long-range Chemical Shift Correlations

The importance of Hadamard encoding pulses in one-dimensional pure shift yielded by the chirp excitation version of selective total correlation spectroscopy (1D PSYCHE-TOCSY) experiments is discussed for chemical-shift analysis of complex natural products at ultrahigh resolution. Herein, we adapted H-n Hadamard matrices to 1D PSYCHE-TOCSY and observed an overall circa square root of n-fold enhancement in the signal-to-noise (S/N) ratio when compared to conventional 1D PSYCHE-TOCSY recorded by refocusing only one spin at a time. This enhancement in S/N facilitates the observation of very weak long-range chemical-shift correlations from Hadamard-encoded PSYCHE-TOCSY (HE-PSYCHE-TOCSY). The proposed method will have a significant impact on structure determination of complex isolated/ synthetic natural products.